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We show that the isotropic 3-wave kinetic equation is equivalent to the mean field rate equations for an aggregation-fragmentation problem with an unusual fragmentation mechanism. This analogy is used to write the theory of 3-wave turbulence almost entirely in terms of a single scaling parameter. A new numerical method for solving the kinetic equation over a large range of frequencies is developed by extending Lee's method for solving aggregation equations. The new algorithm is validated against some analytic calculations of the Kolmogorov-Zakharov constant for some families of model interaction coefficients. The algorithm is then applied to study some wave turbulence problems in which the finiteness of the dissipation scale is an essential feature. Firstly, it is shown that for finite capacity cascades, the dissipation of energy becomes independent of the cut-off frequency as this cut-off is taken to infinity. This is an explicit indication of the presence of a dissipative anomaly. Secondly, a preliminary numerical study is presented of the so-called bottleneck effect in a wave turbulence context. It is found that the structure of the bottleneck depends non-trivially on the interaction coefficient. Finally some results are presented on the complementary phenomenon of thermalisation in closed wave systems which demonstrates explicitly for the first time the existence of so-called mixed solutions of the kinetic equation which exhibit aspects of both Kolmogorov-Zakharov and equilibrium equipartition spectra.
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arxiv:0905.1589
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It is quite possible that the reheat temperature of the universe is extremely low close to the scale of Big Bang nucleosynthesis, i.e. $T_{R}\sim 1-10$ MeV. At such low reheat temperatures generating matter anti-matter asymmetry and synthesizing dark matter particles are challenging issues which need to be addressed within a framework of beyond the Standard Model physics. In this paper we point out that a successful cosmology can emerge naturally provided the R-parity violating interactions are responsible for the excess in baryons over anti-baryons and at the same time they can explain the longevity of dark matter with the right abundance.
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arxiv:0905.1625
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According to general relativity a perturbed black hole will settle to a stationary configuration by the emission of gravitational radiation. Such a perturbation will occur, for example, in the coalescence of a black hole binary, following their inspiral and subsequent merger. At late times the waveform is a superposition of quasi-normal modes, which we refer to as the ringdown. The dominant mode is expected to be the fundamental mode, l=m=2. Since this is a well-known waveform, matched filtering can be implemented to search for this signal using LIGO data. We present a search for gravitational waves from black hole ringdowns in the fourth LIGO science run S4, during which LIGO was sensitive to the dominant mode of perturbed black holes with masses in the range of 10 Msun to 500 Msun, the regime of intermediate-mass black holes, to distances up to 300 Mpc. We present a search for gravitational waves from black hole ringdowns using data from S4. No gravitational wave candidates were found; we place a 90%-confidence upper limit on the rate of ringdowns from black holes with mass between 85 Msun and 390 Msun in the local universe, assuming a uniform distribution of sources, of 3.2 x 10^{-5} yr^{-1} Mpc^{-3} = 1.6 x 10^{-3}yr^{-1} L_{10}^{-1}, where L_{10} is 10^{10} times the solar blue-light luminosity.
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arxiv:0905.1654
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In a recent paper, Trent and Wick establish a strong relation between the corona problem and the Toeplitz corona problem for a family of spaces over the ball and the polydisk. Their work is based on earlier work of Amar. In this note, several of their lemmas are reinterpreted in the language of Hilbert modules, revealing some interesting facts and raising some questions about quasi-free Hilbert modules. Moreover, a modest generalization of their result is obtained.
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arxiv:0905.1659
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In this paper we investigate the use of quantum information to share classical secrets. While every quantum secret sharing scheme is a quantum error correcting code, the converse is not true. Motivated by this we sought to find quantum codes which can be converted to secret sharing schemes. If we are interested in sharing classical secrets using quantum information, then we show that a class of pure $[[n,1,d]]_q$ CSS codes can be converted to perfect secret sharing schemes. These secret sharing schemes are perfect in the sense the unauthorized parties do not learn anything about the secret. Gottesman had given conditions to test whether a given subset is an authorized or unauthorized set; they enable us to determine the access structure of quantum secret sharing schemes. For the secret sharing schemes proposed in this paper the access structure can be characterized in terms of minimal codewords of the classical code underlying the CSS code. This characterization of the access structure for quantum secret sharing schemes is thought to be new.
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arxiv:0905.1661
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We show how the excursion set moving barrier model for halo abundances may be generalized to the local non-Gaussian f_{nl} model. Our estimate assumes that the distribution of step sizes depends on f_{nl}, but that they are otherwise uncorrelated. Our analysis is consistent with previous results for the case of a constant barrier, and highlights some implicit assumptions. It also clarifies the basis of an approximate analytic solution to the moving barrier problem in the Gaussian case, and shows how it might be improved.
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arxiv:0905.1702
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Graphene has been attracting great interest because of its distinctive band structure and physical properties. Today, graphene is limited to small sizes because it is produced mostly by exfoliating graphite. We grew large-area graphene films of the order of centimeters on copper substrates by chemical vapor deposition using methane. The films are predominantly single layer graphene with a small percentage (less than 5%) of the area having few layers, and are continuous across copper surface steps and grain boundaries. The low solubility of carbon in copper appears to help make this growth process self-limiting. We also developed graphene film transfer processes to arbitrary substrates, and dual-gated field-effect transistors fabricated on Si/SiO2 substrates showed electron mobilities as high as 4050 cm2V-1s-1 at room temperature.
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arxiv:0905.1712
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Motivated by recent interest in redshifted 21 cm emission of intergalactic hydrogen, we investigate the 8.7 GHz ^2S_{1/2} F=0-1 hyperfine transition of ^3He^+. While the primordial abundance of 3He relative to hydrogen is 10^-5, the hyperfine spontaneous decay rate is 680 times larger. Furthermore, the antenna temperature is much lower at the frequencies relevant for the ^3He^+ transition compared to that of z>6 21 cm emission. We find that the spin temperature of this 8.7 GHz line in the intergalactic medium is approximately the cosmic microwave background temperature, such that this transition is best observed in absorption against high-redshift, radio-bright quasars. We show that intergalactic 8.7 GHz absorption is a promising, unsaturated observable of the ionization history of intergalactic helium (for which HeII->HeIII reionization is believed to be complete at z~3) and of the primordial 3He abundance. Instruments must reach ~1 \mu Jy RMS noise in bands of 1 MHz on a 1 Jy source to directly resolve this absorption. However, in combination with HI Ly\alpha forest measurements, an instrument can statistically detect this absorption from z > 3 with 30 \mu Jy RMS noise in 0.1 MHz spectral bands over 100 MHz, which may be within the reach of present instruments.
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arxiv:0905.1715
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Quantum phase slippage (QPS) in a superconducting nanowire is a new candidate for developing a quantum bit. It has also been theoretically predicted that the occurrence of QPS significantly changes the current-phase relationship (CPR) of the wire due to the tunneling between topologically different metastable states. We present studies on the microwave response of the superconducting nanowires to reveal their CPRs. First, we demonstrate a simple nanowire fabrication technique, based on commercially available adhesive tapes, which allows making thin superconducting wire from different metals. We compare the resistance vs. temperature curves of Mo$_{76}$Ge$_{24}$ and Al nanowires to the classical and quantum models of phase slips. In order to describe the experimentally observed microwave responses of these nanowires, we use the McCumber-Stewart model, which is generalized to include either classical or quantum CPR.
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arxiv:0905.1726
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We derive the phase diagram of a paradigmatic model of Coulomb frustrated phase separation in two-dimensional systems with negative short-range electronic compressibility. We consider the system subject either to the truly three-dimensional long-range Coulomb interaction (LRC) and to a two-dimensional LRC with logarithmic-like behavior. In both cases we find that the transition from the homogeneous phase to the inhomogeneous phase is generically first-order except for a critical point. Close to the critical point, inhomogeneities arrange in a triangular lattice with a subsequent first-order topological transition to stripe-like objects by lowering the Coulomb frustration. A proliferation of inhomogeneities which have inside smaller inhomogeneities is expected near all the transition lines in systems embedded in the three-dimensional LRC alone.
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arxiv:0905.1739
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HH 211 is a nearby young protostellar system with a highly collimated jet. We have mapped it in 352 GHz continuum, SiO (J=8-7), and HCO+ (J=4-3) emission at up to ~ 0.2" resolution with the Submillimeter Array (SMA). The continuum source is now resolved into two sources, SMM1 and SMM2, with a separation of ~ 84 AU. SMM1 is seen at the center of the jet, probably tracing a (inner) dusty disk around the protostar driving the jet. SMM2 is seen to the southwest of SMM1 and may trace an envelope-disk around a small binary companion. A flattened envelope-disk is seen in HCO+ around SMM1 with a radius of ~ 80 AU perpendicular to the jet axis. Its velocity structure is consistent with a rotation motion and can be fitted with a Keplerian law that yields a mass of ~ 50+-15 Jupiter mass (a mass of a brown dwarf) for the protostar. Thus, the protostar could be the lowest mass source known to have a collimated jet and a rotating flattened envelope-disk. A small-scale (~ 200 AU) low-speed (~ 2 km/s) outflow is seen in HCOP+ around the jet axis extending from the envelope-disk. It seems to rotate in the same direction as the envelope-disk and may carry away part of the angular momentum from the envelope-disk. The jet is seen in SiO close to ~ 100 AU from SMM1. It is seen with a "C-shaped" bending. It has a transverse width of <~ 40 AU and a velocity of ~ 170+-60 km/s. A possible velocity gradient is seen consistently across its innermost pair of knots, with ~ 0.5 km/s at ~ 10 AU, consistent with the sense of rotation of the envelope-disk. If this gradient is an upper limit of the true rotational gradient of the jet, then the jet carries away a very small amount of angular momentum of ~ 5 AU km/s and thus must be launched from the very inner edge of the disk near the corotation radius.
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arxiv:0905.1747
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We provide a rigorous treatment of the inverse scattering transform for the entire Toda hierarchy for solutions which are asymptotically close to (in general) different finite-gap solutions as $n\to\pm\infty$.
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arxiv:0905.1800
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I report on recent measurements from the Belle and BaBar collaborations on the decay of the B-meson to hadronic final states without a charm quark.
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arxiv:0905.1830
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In [BGLM] and [GLNP] it was conjectured that if $H$ is a simple Lie group of real rank at least 2, then the number of conjugacy classes of (arithmetic) lattices in $H$ of covolume at most $x$ is $x^{(\gamma(H)+o(1))\log x/\log\log x}$ where $\gamma(H)$ is an explicit constant computable from the (absolute) root system of $H$. In this paper we prove that this conjecture is false. In fact, we show that the growth is at rate $x^{c\log x}$. A crucial ingredient of the proof is the existence of towers of field extensions with bounded root discriminant which follows from the seminal work of Golod and Shafarevich on class field towers.
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arxiv:0905.1841
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We consider geometric variational problems for a functional defined on a curve in three-dimensional space. The functional is assumed to be written in a form invariant under the group of Euclidean motions. We present the Euler-Lagrange equations as equilibrium equations for the internal force and moment. Classical as well as new examples are discussed to illustrate our approach. This new form of the equations particularly serves to promote the study of bio- and nanofilaments.
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arxiv:0905.1880
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We investigate distributed source coding of two correlated sources X and Y where messages are passed to a decoder in a cascade fashion. The encoder of X sends a message at rate R_1 to the encoder of Y. The encoder of Y then sends a message to the decoder at rate R_2 based both on Y and on the message it received about X. The decoder's task is to estimate a function of X and Y. For example, we consider the minimum mean squared-error distortion when encoding the sum of jointly Gaussian random variables under these constraints. We also characterize the rates needed to reconstruct a function of X and Y losslessly. Our general contribution toward understanding the limits of the cascade multiterminal source coding network is in the form of inner and outer bounds on the achievable rate region for satisfying a distortion constraint for an arbitrary distortion function d(x,y,z). The inner bound makes use of a balance between two encoding tactics--relaying the information about X and recompressing the information about X jointly with Y. In the Gaussian case, a threshold is discovered for identifying which of the two extreme strategies optimizes the inner bound. Relaying outperforms recompressing the sum at the relay for some rate pairs if the variance of X is greater than the variance of Y.
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arxiv:0905.1883
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Pre-main sequence (PMS) binaries and multiples enable critical tests of stellar models if masses, metallicities, and luminosities of the component stars are known. We have analyzed high-resolution, high signal-to-noise echelle spectra of the quadruple-star system HD 98800 and using spectrum synthesis, computed fits to the composite spectrum for a full range of plausible stellar parameters for the components. We consistently find that sub-solar metallicity yields fits with lower $\chi^2$ values, with an overall best-fit of $[M/H] = -0.20\pm0.10$. This metallicity appears to be consistent with PMS evolutionary tracks for the measured masses and luminosities of the components of HD 98800 but additional constraints on the system and modelling are needed.
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arxiv:0905.1907
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Using q-theory, we show that the electroweak crossover can generate a remnant vacuum energy density \Lambda \sim E_{ew}^8 / E_{planck}^4, with effective electroweak energy scale E_{ew} \sim 10^{3} GeV and reduced Planck-energy scale E_{planck} \sim 10^{18} GeV. The obtained expression for the effective cosmological constant \Lambda may be a crucial input for the suggested solution by Arkani-Hamed et al. of the triple cosmic coincidence puzzle (why the orders of magnitude of the energy densities of vacuum, matter, and radiation are approximately the same in the present Universe).
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arxiv:0905.1919
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We study structural properties of trees grown by preferential attachment. In this mechanism, nodes are added sequentially and attached to existing nodes at a rate that is strictly proportional to the degree. We classify nodes by their depth n, defined as the distance from the root of the tree, and find that the network is strongly stratified. Most notably, the distribution f_k^(n) of nodes with degree k at depth n has a power-law tail, f_k^(n) ~ k^{-\gamma(n)}. The exponent grows linearly with depth, gamma(n)=2+(n-1)/<n-1>, where the brackets denote an average over all nodes. Therefore, nodes that are closer to the root are better connected, and moreover, the degree distribution strongly varies with depth. Similarly, the in-component size distribution has a power-law tail and the characteristic exponent grows linearly with depth. Qualitatively, these behaviors extend to a class of networks that grow by a redirection mechanism.
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arxiv:0905.1920
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We report a highly significant Submillimeter Array (SMA) detection of the prototypical submillimeter source HDF 850.1, which is the brightest submillimeter source in the Hubble Deep Field-North proper. The detection yields an extremely precise position of RA(2000)=12:36:51.99 and Dec(2000)=+62:12:25.83 with a 1-sigma positional uncertainty of 0.17 arcsec. The position is consistent with the location of a millimeter wavelength interferometric detection and with the locations of weak VLA detections at 1.4 and 8.4 GHz, but it is not consistent with any previous optical/near-infrared identifications. The source appears pointlike at the 2 arcsec resolution of the SMA, and the detected flux of 7.8+/-1.0 mJy is consistent with the measured SCUBA fluxes. We tabulate fluxes and limits on HDF 850.1 at other wavelengths. Our redshift estimate for HDF 850.1 based on the radio through mid-infrared measurements is z=4.1. The faintness of the source at optical/near-infrared wavelengths and the high estimated redshift suggest that HDF 850.1 may be an analog of the brighter submillimeter source GOODS 850-5, which is also thought to be at z>4. The fact that a source like HDF 850.1 should have appeared in one of the very first blank-field SCUBA observations ever made suggests that such high-redshift sources are quite common. Thus, we are led to conclude that high-redshift star formation is dominated by giant dusty star-forming galaxies, just as it is at lower redshifts.
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arxiv:0905.1946
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We present simple stellar population (SSP) models with scaled-solar and alpha-element enhanced abundances. The SSP models are based on the Dartmouth Stellar Evolution Database, our library of synthetic stellar spectra, and a detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity. In order to test the relative importance of a variety of SSP model ingredients, we compare our SSP models with integrated spectra of 41 Milky Way Globular Clusters (MWGCs) from Schiavon et al. (2005). Using the Mg b and Ca4227 indices, we confirm that Mg and Ca are enhanced by about +0.4 and +0.2 dex, respectively, in agreement with results from high resolution spectra of individual stars in MWGCs. Balmer lines, particularly Hgamma and Hdelta, of MWGCs are reproduced by our alpha-enhanced SSP models not only because of the combination of isochrone and spectral effects but also because of our reasonable HB treatment. Moreover, it is shown that the Mg abundance significantly influences Balmer and iron line indices. Finally, the investigation of power-law initial mass function (IMF) variations suggests that an IMF much shallower than Salpeter is unrealistic because the Balmer lines are too strong on the metal-poor side to be compatible with observations.
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arxiv:0905.1947
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Techniques are developed for exploring the complete space of intersecting brane models on an orientifold. The classification of all solutions for the widely-studied T^6/Z_2 x Z_2 orientifold is made possible by computing all combinations of branes with negative tadpole contributions. This provides the necessary information to systematically and efficiently identify all models in this class with specific characteristics. In particular, all ways in which a desired group G can be realized by a system of intersecting branes can be enumerated in polynomial time. We identify all distinct brane realizations of the gauge groups SU(3) x SU(2) and SU(3) x SU(2) x U(1) which can be embedded in any model which is compatible with the tadpole and SUSY constraints. We compute the distribution of the number of generations of "quarks" and find that 3 is neither suppressed nor particularly enhanced compared to other odd generation numbers. The overall distribution of models is found to have a long tail. Despite disproportionate suppression of models in the tail by K-theory constraints, the tail in the distribution contains much of the diversity of low-energy physics structure.
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arxiv:0905.1951
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We obtain explicit solutions for the density $\varphi_T$ of the first-time $T$ that a one-dimensional Brownian process $B$ reaches the twice, continuously differentiable moving boundary $f$ and such that $f''(t)\geq 0$ for all $t\in \mathbb{R}^+$. We do so by finding the expected value of some functionals of a 3-dimensional Bessel bridge $\tilde{X}$ and exploiting its relationship with first-passage time problems as pointed out by Kardaras (2007). It turns out that this problem is related to Schr\"odinger's equation with time-dependent linear potential, see Feng (2001).
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arxiv:0905.1971
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This paper studies the question of how well a signal can be reprsented by a sparse linear combination of reference signals from an overcomplete dictionary. When the dictionary size is exponential in the dimension of signal, then the exact characterization of the optimal distortion is given as a function of the dictionary size exponent and the number of reference signals for the linear representation. Roughly speaking, every signal is sparse if the dictionary size is exponentially large, no matter how small the exponent is. Furthermore, an iterative method similar to matching pursuit that successively finds the best reference signal at each stage gives asymptotically optimal representations. This method is essentially equivalent to successive refinement for multiple descriptions and provides a simple alternative proof of the successive refinability of white Gaussian sources.
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arxiv:0905.1990
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We report our observational results of 870 $\mu$m continuum emission and its linear polarization in the massive star formation site W51 e2/e8. Inferred from the linear polarization maps, the magnetic field in the plane of sky (B$_{\bot}$) is traced with an angular resolution of 0$\farcs$7 with the Submillimeter Array (SMA). Whereas previous BIMA observations with an angular resolution of 3$\arcsec$ (0.1 pc) showed a uniform B field, our revealed B$_{\bot}$ morphology is hourglass-like in the collapsing core near the Ultracompact H II region e2 and also possibly in e8. The decrease in polarization near the continuum peak seen at lower angular resolution is apparently due to the more complex structures at smaller scales. In e2, the pinched direction of the hourglass-like B field morphology is parallel to the plane of the ionized accretion flow traced by H53$\alpha$, suggesting that the massive stars are formed via processes similar to the low mass stars, i.e. accretion through a disk, except that the mass involved is much larger. Furthermore, our finding that the resolved collapsing cores in e2 and e8 lie within one subcritical 0.5 pc envelope supports the scenario of \textit{magnetic fragmentation} via ambipolar diffusion. We therefore suggest that magnetic fields control the dynamical evolution of the envelope and cores in W51 e2 and e8.
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arxiv:0905.1996
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The authors report on the crystallographic orientation dependence of the Schottky properties for heterojunctions between a half-metallic ferromagnet La$_0.6$Sr$_0.4$MnO$_3$ (LSMO) and Nb-doped SrTiO3 semiconductor. The Schottky barrier height determined by in situ photoemission measurements is independent for the substrate orientations (001) and (110), while the magnetic properties of LSMO (110) films are more enhanced than for (001) films. These results suggest that the performance of magnetic devices based on ferromagnetic manganite is improved by using (110)-oriented substrates.
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arxiv:0905.2018
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We report on a comparative study of the crystal structure and the magnetic properties of FeSe1-x (x= 0.00 - 0.15) superconducting samples by neutron powder diffraction and magnetization measurements. The samples were synthesized by two different methods: a 'low-temperature' one using powders as a starting material at T =700 C and a "high-temperature' method using solid pieces of Fe and Se at T= 1070 C. The effect of a starting (nominal) stoichiometry on the phase purity of the obtained samples, the superconducting transition temperature Tc, as well as the chemical instability of FeSe1-x at ambient conditions were investigated. It was found that in the Fe-Se system a stable phase exhibiting superconductivity at Tc~8K exists in a narrow range of selenium concentration (FeSe0.974(2)).
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arxiv:0905.2115
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The next generation of radioactive ion beam facilities, which will give experimental access to many exotic nuclei, are presently being developed. These facilities will make it possible to study very short lived exotic nuclei with extreme values of isospin far from the line of beta stability. Such nuclei will be produced with very low cross sections and to study them, new detector arrays are being developed. At the SPIRAL facility in GANIL a neutron detector array, the Neutron Wall, is located. In this work the Neutron Wall has been characterized regarding neutron detection efficiency and discrimination between neutrons and gamma rays. The possibility to increase the efficiency by increasing the high voltage of the photomultiplier tubes has also been studied. For SPIRAL2 a neutron detector array, NEDA, is being developed. NEDA will operate in a high gamma-ray background environment which puts a high demand on the quality of discrimination between neutrons and gamma rays. To increase the quality of the discrimination methods pulse-shape discrimination techniques utilizing digital electronics have been developed and evaluated regarding bit resolution and sampling frequency of the ADC. The conclusion is that an ADC with a bit resolution of 12 bits and a sampling frequency of 100 MS/s is adequate for pulse-shape discrimination of neutrons and gamma rays for a neutron energy range of 0.3-12 MeV.
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arxiv:0905.2132
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We present a new boosting algorithm, motivated by the large margins theory for boosting. We give experimental evidence that the new algorithm is significantly more robust against label noise than existing boosting algorithm.
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arxiv:0905.2138
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Dans cette note nous pr\'esentons les principaux r\'esultats du r\'ecent travail hal-00376547/arXiv:0904.2760, o\`u le ph\'enom\`ene d'amortissement Landau est pour la premi\`ere fois \'etabli dans un contexte non lin\'eaire. ----- In this note we present the main results from the recent work hal-00376547 / arXiv:0904.2760, which for the first time establish Landau damping in a nonlinear context.
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arxiv:0905.2168
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Given a smooth family F/Y of geometrically irreducible surfaces, we study sequences of arbitrarily near T-points of F/Y; they generalize the traditional sequences of infinitely near points of a single smooth surface. We distinguish a special sort of these new sequences, the strict sequences. To each strict sequence, we associate an ordered unweighted Enriques diagram. We prove that the various sequences with a fixed diagram form a functor, and we represent it by a smooth Y-scheme. We equip this Y-scheme with a free action of the automorphism group of the diagram. We equip the diagram with weights, take the subgroup of those automorphisms preserving the weights, and form the corresponding quotient scheme. Our main theorem constructs a canonical universally injective map \Psi from this quotient scheme to the Hilbert scheme of F/Y; further, this map is an embedding in characteristic 0. However, in every positive characteristic, we give an example, in Appendix B, where the map is purely inseparable.
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arxiv:0905.2169
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In the case of one extra dimension, well known Newton's potential $\phi (r_3)=-G_N m/r_3$ is generalized to compact and elegant formula $\phi(r_3,\xi)=-(G_N m/r_3)\sinh(2\pi r_3/a)[\cosh(2\pi r_3/a)-\cos(2\pi\xi/a)]^{-1}$ if four-dimensional space has topology $\mathbb{R}^3\times T$. Here, $r_3$ is magnitude of three-dimensional radius vector, $\xi$ is extra dimension and $a$ is a period of a torus $T$. This formula is valid for full range of variables $r_3 \in [0,+\infty)$ and $\xi\in [0,a]$ and has known asymptotic behavior: $\phi \sim 1/r_3$ for $r_3>>a$ and $\phi \sim 1/r_4^2$ for $r_4=\sqrt{r_3^2+\xi^2}<<a$. Obtained formula is applied to an infinitesimally thin shell, a shell, a sphere and two spheres to show deviations from the newtonian expressions. Usually, these corrections are very small to observe at experiments. Nevertheless, in the case of spatial topology $\mathbb{R}^3\times T^{d}$, experimental data can provide us with a limitation on maximal number of extra dimensions.
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arxiv:0905.2222
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We study intersection theory on the relative Hilbert scheme of a family of nodal-or-smooth curves, over a base of arbitrary dimension. We introduce an additive group called 'discriminant module', generated by diagonal loci, node scrolls, and twists thereof, and determine the action of the discriminant or big diagonal divisor on this group by intersection. We show that this suffices to determine arbitrary polynomials in Chern classes, in particular Chern numbers, for the tautological vector bundles on the Hilbert schemes, which are closely related to enumerative geometry. The latest version includes some new explicit computations and reference to a computer program due to G. Liu implementing our intersection calculus.
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arxiv:0905.2229
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This paper constructs perfectly matched layers (PML) for a system of 2D Coupled Nonlinear Schr\"odinger equations with mixed derivatives which arises in the modeling of gap solitons in nonlinear periodic structures with a non-separable linear part. The PML construction is performed in Laplace Fourier space via a modal analysis and can be viewed as a complex change of variables. The mixed derivatives cause the presence of waves with opposite phase and group velocities, which has previously been shown to cause instability of layer equations in certain types of hyperbolic problems. Nevertheless, here the PML is stable if the absorption function $\sigma$ lies below a specified threshold. The PML construction and analysis are carried out for the linear part of the system. Numerical tests are then performed in both the linear and nonlinear regimes checking convergence of the error with respect to the layer width and showing that the PML performs well even in many nonlinear simulations.
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arxiv:0905.2321
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In this paper, we demonstrate the LHC discovery potential of new charged vector boson $W_1^{\pm}$ predicted by the Minimal Higgsless model in the process $pp\to W_1^{\pm}qq^{\prime}\to W^{\pm}Z^0qq^\prime\to \ell^{\pm}\ell^+\ell^-\nu qq^{\prime}(\ell=e,\mu)$ by analyzing the generator level events of the signal and backgrounds. The generator for the signal $pp \to {W_1}^{\pm}qq^\prime\to W^{\pm}Z^0qq^\prime$ at tree level is developed with the Minimal Higgsless model and then interfaced with PYTHIA for the parton showers and hadronization. The backgrounds are produced with PYTHIA and ACERMC. We give integrated luminosities required to discover 5$\sigma$ signal as a function of $W_1^{\pm}$ mass.
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arxiv:0905.2336
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We give a short introduction to the Analytic Perturbation Theory (APT) and its generalization to Fractional powers -- FAPT. We describe how to treat heavy-quark thresholds in FAPT and then show how to resum perturbative series in both the one-loop APT and FAPT. As an application we consider FAPT description of the Higgs boson decay $H^0\to b\bar{b}$.
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arxiv:0905.2356
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Several multi-frequency polarization studies have shown the presence of systematic Faraday Rotation gradients across the parsec-scale jets of Active Galactic Nuclei (AGN), taken to be due to the systematic variation of the line-of-sight component of a helical magnetic (B) field across the jet. Other studies have confirmed the presence and sense of these gradients in several sources, thus providing evidence that these gradients persist over time and over large distances from the core. However, we find surprising new evidence for a reversal in the direction of the Faraday Rotation gradient across the jet of B1803+784, for which multi-frequency polarization observations are available at four epochs. At our three epochs and the epoch of Zavala & Taylor (2003), we observe transverse Rotation Measure (RM) gradients across the jet, consistent with the presence of a helical magnetic field wrapped around the jet. However, we also observe a "flip" in the direction of the gradient between June 2000 and August 2002. Although the origins of this phenomena are not entirely clear, possibly explanations include (i) the sense of rotation of the central supermassive black hole and accretion disc has remained the same, but the dominant magnetic pole facing the Earth has changed from North to South; (ii) a change in the direction of the azimuthal B field component as a result of torsional oscillations of the jet; and (iii) a change in the relative contributions to the observed rotation measures of the "inner" and "outer" helical fields in a magnetic-tower model. Although we cannot entirely rule out the possibility that the observed changes in the RM distribution are associated instead with changes in the thermal-electron distribution in the vicinity of the jet, we argue that this explanation is unlikely.
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arxiv:0905.2368
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We formulate a time-optimal approach to adiabatic quantum computation (AQC). A corresponding natural Riemannian metric is also derived, through which AQC can be understood as the problem of finding a geodesic on the manifold of control parameters. This geometrization of AQC is demonstrated through two examples, where we show that it leads to improved performance of AQC, and sheds light on the roles of entanglement and curvature of the control manifold in algorithmic performance.
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arxiv:0905.2376
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We investigate the impact of nonlinear evolution of the gravitational potentials in the LCDM model on the Integrated Sachs-Wolfe (ISW) contribution to the CMB temperature power spectrum, and on the cross-power spectrum of the CMB and a set of biased tracers of the mass. We use an ensemble of N-body simulations to directly follow the potentials and compare results to perturbation theory (PT). The predictions from PT match the results to high precision for k<0.2 h/Mpc. We compute the nonlinear corrections to the angular power spectrum and find them to be <10% of linear theory for l<100. These corrections are swamped by cosmic variance. On scales l>100 the departures are more significant, however the CMB signal is more than a factor 10^3 larger at this scale. Nonlinear ISW effects therefore play no role in shaping the CMB power spectrum for l<1500. We analyze the CMB--density tracer cross-spectrum using simulations and renormalized bias PT, and find good agreement. The usual assumption is that nonlinear evolution enhances the growth of structure and counteracts linear ISW on small scales, leading to a change in sign of the CMB-LSS cross-spectrum at small scales. However, PT analysis suggests that this trend reverses at late times when the logarithmic growth rate f(a)=dlnD/dlna<0.5 or om_m(a)<0.3. Numerical results confirm these expectations and we find no sign change in ISW-LSS cross-power for low redshifts. Corrections due to nonlinearity and scale dependence of the bias are found to be <10% for l<100, therefore below the S/N of the current and future measurements. Finally, we estimate the CMB--halo cross-correlation coefficient and show that it can be made to match that for CMB--dark matter to within 5% for thin redshift shells, mitigating the need to model bias evolution.
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arxiv:0905.2408
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We have studied the frequency and voltage dependence of voltage-induced torsional strains in orthorhombic TaS3 [V. Ya. Pokrovskii, et al, Phys. Rev. Lett. 98, 206404 (2007)] by measuring the modulation of the resonant frequency of an RF cavity containing the sample. The strain has an onset voltage below the charge-density-wave (CDW) threshold voltages associated with changes in shear compliance and resistance, suggesting that the strain is associated with polarization of the CDW rather than CDW current. Measurements with square-wave voltages show that the strain is very sluggish, not even reaching its dc value at a frequency of 0.1 Hz, but the dynamics appear to be very sample dependent. By applying oscillating torque while biasing the sample with a dc current, we have also looked for strain induced voltage in the sample; none is observed at the low biases where the voltage-induced strains first occur, but an induced voltage is observed at higher biases, probably associated with strain-dependent CDW conductance.
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arxiv:0905.2426
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In this work we generalize the plain MS trackers and attempt to overcome standard mean shift trackers' two limitations. It is well known that modeling and maintaining a representation of a target object is an important component of a successful visual tracker. However, little work has been done on building a robust template model for kernel-based MS tracking. In contrast to building a template from a single frame, we train a robust object representation model from a large amount of data. Tracking is viewed as a binary classification problem, and a discriminative classification rule is learned to distinguish between the object and background. We adopt a support vector machine (SVM) for training. The tracker is then implemented by maximizing the classification score. An iterative optimization scheme very similar to MS is derived for this purpose.
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arxiv:0905.2463
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We calculate pion vector and scalar form factors in two-flavor lattice QCD and study the chiral behavior of the vector and scalar radii <r^2>_{V,S}. Numerical simulations are carried out on a 16^3 x 32 lattice at a lattice spacing of 0.12 fm with quark masses down to \sim m_s/6, where m_s is the physical strange quark mass. Chiral symmetry, which is essential for a direct comparison with chiral perturbation theory (ChPT), is exactly preserved in our calculation at finite lattice spacing by employing the overlap quark action. We utilize the so-called all-to-all quark propagator in order to calculate the scalar form factor including the contributions of disconnected diagrams and to improve statistical accuracy of the form factors. A detailed comparison with ChPT reveals that the next-to-next-to-leading-order contributions to the radii are essential to describe their chiral behavior in the region of quark mass from m_s/6 to m_s/2. Chiral extrapolation based on two-loop ChPT yields <r^2>_V=0.409(23)(37)fm and <r^2>_S=0.617(79)(66)fm, which are consistent with phenomenological analysis. We also present our estimates of relevant low-energy constants.
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arxiv:0905.2465
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We recently reported that the simple genetic algorithm (SGA) is capable of performing a remarkable form of sublinear computation which has a straightforward connection with the general problem of interacting attributes in data-mining. In this paper we explain how the SGA can leverage this computational proficiency to perform efficient adaptation on a broad class of fitness functions. Based on the relative ease with which a practical fitness function might belong to this broad class, we submit a new hypothesis about the workings of genetic algorithms. We explain why our hypothesis is superior to the building block hypothesis, and, by way of empirical validation, we present the results of an experiment in which the use of a simple mechanism called clamping dramatically improved the performance of an SGA with uniform crossover on large, randomly generated instances of the MAX 3-SAT problem.
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arxiv:0905.2473
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In high energy collisions saturation and multiple collisions are most easily accounted for in transverse coordinate space, while analyses in momentum space have been more suitable for calculating properties of exclusive final states. In this talk I describe an extension of Mueller's dipole cascade model, which attempts to combine the good features of both these descriptions. Besides saturation it also includes effects of correlations and fluctuations, which have been difficult to account for in previous approaches. The model reproduces successfully total, elastic, and diffractive cross sections in pp collisions and DIS, and a description of final states will be ready soon.
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arxiv:0905.2492
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We will present a review of the most interesting results on rare B decays from the B Factories, based on the data collected by the BaBar and Belle detectors at asymmetric $e^+ e^-$ colliders at the center of mass energy of the $\Upsilon(4S)$ resonance.
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arxiv:0905.2503
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We consider a finite quantum system S coupled to two environments of different nature. One is a heat reservoir R (continuous interaction) and the other one is a chain C of independent quantum systems E (repeated interaction). The interactions of S with R and C lead to two simultaneous dynamical processes. We show that for generic such systems, any initial state approaches an asymptotic state in the limit of large times. We express the latter in terms of the resonance data of a reduced propagator of S+R and show that it satisfies a second law of thermodynamics. We analyze a model where both S and E are two-level systems and obtain the asymptotic state explicitly (lowest order in the interaction strength). Even though R and C are not direcly coupled, we show that they exchange energy, and we find the dependence of this exchange in terms of the thermodynamic parameters. We formulate the problem in the framework of W*-dynamical systems and base the analysis on a combination of spectral deformation methods and repeated interaction model techniques. We do not use master equation approximations.
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arxiv:0905.2558
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In this work, we consider achievable secrecy rates for symmetric $K$-user ($K \ge 3$) interference channels with confidential messages. We find that nested lattice codes and layered coding are useful in providing secrecy for these channels. Achievable secrecy rates are derived for very strong interference. In addition, we derive the secure degrees of freedom for a range of channel parameters. As a by-product of our approach, we also demonstrate that nested lattice codes are useful for K-user symmetric interference channels without secrecy constraints in that they yield higher degrees of freedom than previous results.
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arxiv:0905.2643
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Pion exchange in S-wave between hadrons that are themselves in a relative S-wave can shift energies by hundreds of MeV. In the case of charmed mesons $D,D^*,D_0,D_1$ a spectroscopy of quasi-molecular states may arise consistent with enigmatic charmonium states observed above 4 GeV in $e^+e^-$ annihilation. A possible explanation of $Y(4260)\to \psi\pi\pi$ and $Y(4360) \to \psi'\pi\pi$ is found. Searches in $D\bar{D}3\pi$ channels as well as B decays are recommended to test this hypothesis.
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arxiv:0905.2687
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Given a group with at least two more generators than relations, we give an effective estimate on the minimal index of a subgroup with a nonabelian free quotient. We show that the index is bounded by a polynomial in the length of the relator word. We also provide a lower bound on the index.
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arxiv:0905.2713
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While heating of a current carrying Ohmic conductors is an obvious consequence of the diffusive nature of the conduction in such systems, current induced cooling has been recently reported in some molecular conduction junctions. In this paper we demonstrate by simple models the possibility of cooling molecular junctions under applied bias, and discuss several mechanisms for such an effect. Our model is characterized by single electron tunneling between electrodes represented by free electron reservoirs through a system characterized by it electron levels, nuclear vibrations and their structures. We consider cooling mechasims resulting from (a) cooling of one electrode surface by tunneling induced depletion of high energy electrons; (b) cooling by coherent sub resonance electronic transport analogous to atomic laser nduced cooling and (c) the incoherent analog of process (b) - cooling by driven activated transport. The non-equilibrium Green function formulation of junction transport is used in the first two cases, while a master equation approach is applied in the analysis of the third.
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arxiv:0905.2748
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We extend the model of a 2$d$ solid to include a line of defects. Neighboring atoms on the defect line are connected by ?springs? of different strength and different cohesive energy with respect to the rest of the system. Using the Migdal-Kadanoff renormalization group we show that the elastic energy is an irrelevant field at the bulk critical point. For zero elastic energy this model reduces to the Potts model. By using Monte Carlo simulations of the 3- and 4-state Potts model on a square lattice with a line of defects, we confirm the renormalization-group prediction that for a defect interaction larger than the bulk interaction the order parameter of the defect line changes discontinuously while the defect energy varies continuously as a function of temperature at the bulk critical temperature.
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arxiv:0905.2756
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In the article, the complete elliptic integrals of the first and second kinds are bounded by using the power series expansions of some functions, the celebrated Wallis' inequality, and an integral inequality due to R. P. Agarwal, P. Cerone, S. S. Dragomir and F. Qi.
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arxiv:0905.2787
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We investigate the finite temperature momentum distribution of bosonic noncondensate particles inside a 3D optical lattice near the superfluid to Mott insulator transition point, treating the quantum fluctuation and thermal fluctuation effects on equal footing. We explicitly address the different momentum ($q$) dependence of quasi-particles excitations resulted from thermal and quantum origin: the former scales as $|\bfq|^{-2}$ and hence is dominant in the small momentum region, while the later scales as $|\bfq|^{-1}$ and hence dominant in the large momentum limit. Analytic and semi-analytic results are derived, providing a unique method to determine the temperature, condensate density, coherent length and/or single particle gap etc. inside the optical lattice. Our results also agree with the scaling theory of a quantum $XY$ model near the transition point. Experimental implication of the TOF measurement is also discussed.
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arxiv:0905.2837
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In this paper, the author proposes a numerical method to solve a parabolic system of two quasilinear equations of nonlinear heat conduction with sources. The solution of this system may blow up in finite time. It is proved that the numerical solution also may blow up in finite time and an estimate of this time is obtained. The convergence of the scheme is obtained for particular values of the parameters.
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arxiv:0905.2862
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This paper deals with the location of the complex zeros of the Tutte polynomial for a class of self-dual graphs. For this class of graphs, as the form of the eigenvalues is known, the regions of the complex plane can be focused on the sets where there is only one dominant eigenvalue in particular containing the positive half plane. Thus, in these regions, the analyticity of the pressure can be derived easily. Next, some examples of graphs with their Tutte polynomial having a few number of eigenvalues are given. The cases of the strip of triangles with a double edge, the wheel and the cycle with an edge having a high order of multiplicity are presented. In particular, for this last example, we remark that the well known conjecture of Chen et al. is false in the finite case.
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arxiv:0905.2863
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According to recent works [Tsui PSS \textbf{55}, 237-242 (2007), \textbf{55}, 2042-2044 (2007)], the Neptune Adams ring main arc Fraternite is regarded as captured by the corotation elliptic resonance (CER) potential of Galatea. The minor arcs Egalite(2,1), Liberte, and Courage are located at positions where the time averaged forces, due to the 42-43 corotation-Lindblad resonances under the central field of Neptune, vanish. With adequately chosen Fraternite mass and Galatea eccentricity, this model gives minor arc locations compatible to observed positions, and allows a dynamic transport of materials among arcs. To complement this model, the effect of self-gravity of Fraternite, with a distributed mass, is evaluated together with the CER potential to account for its $10^{0}$ longitudinal span. Although self-gravity is the collective action of all the particles in the arc, each individual particle will see the self-potential with a central maximum as an external potential generated by other particles.
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arxiv:0905.2888
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Motivated by questions in property testing, we search for linear error-correcting codes that have the "single local orbit" property: i.e., they are specified by a single local constraint and its translations under the symmetry group of the code. We show that the dual of every "sparse" binary code whose coordinates are indexed by elements of F_{2^n} for prime n, and whose symmetry group includes the group of non-singular affine transformations of F_{2^n} has the single local orbit property. (A code is said to be "sparse" if it contains polynomially many codewords in its block length.) In particular this class includes the dual-BCH codes for whose duals (i.e., for BCH codes) simple bases were not known. Our result gives the first short (O(n)-bit, as opposed to the natural exp(n)-bit) description of a low-weight basis for BCH codes. The interest in the "single local orbit" property comes from the recent result of Kaufman and Sudan (STOC 2008) that shows that the duals of codes that have the single local orbit property under the affine symmetry group are locally testable. When combined with our main result, this shows that all sparse affine-invariant codes over the coordinates F_{2^n} for prime n are locally testable. If, in addition to n being prime, if 2^n-1 is also prime (i.e., 2^n-1 is a Mersenne prime), then we get that every sparse cyclic code also has the single local orbit. In particular this implies that BCH codes of Mersenne prime length are generated by a single low-weight codeword and its cyclic shifts.
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arxiv:0905.2919
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Theories that attempt to explain the observed cosmic acceleration by modifying general relativity all introduce a new scalar degree of freedom that is active on large scales, but is screened on small scales to match experiments. We show that if such screening occurrs via the chameleon mechanism such as in f(R), it is possible to have order one violation of the equivalence principle, despite the absence of explicit violation in the microscopic action. Namely, extended objects such as galaxies or constituents thereof do not all fall at the same rate. The chameleon mechanism can screen the scalar charge for large objects but not for small ones (large/small is defined by the gravitational potential and controlled by the scalar coupling). This leads to order one fluctuations in the inertial to gravitational mass ratio. In Jordan frame, it is no longer true that all objects move on geodesics. In contrast, if the scalar screening occurrs via strong coupling, such as in the DGP braneworld model, equivalence principle violation occurrs at a much reduced level. We propose several observational tests of the chameleon mechanism: 1. small galaxies should fall faster than large galaxies, even when dynamical friction is negligible; 2. voids defined by small galaxies would be larger compared to standard expectations; 3. stars and diffuse gas in small galaxies should have different velocities, even on the same orbits; 4. lensing and dynamical mass estimates should agree for large galaxies but disagree for small ones. We discuss possible pitfalls in some of these tests. The cleanest is the third one where mass estimate from HI rotational velocity could exceed that from stars by 30 % or more. To avoid blanket screening of all objects, the most promising place to look is in voids.
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arxiv:0905.2966
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We investigate the spectrum and eigenstates of ultracold fermionic atoms in the bilayer honeycomb optical lattice. In the low energy approximation, the dispersion relation has parabolic form and the quasiparticles are chiral. In the presence of the effective magnetic field, which is created for the system with optical means, the energy spectrum shows an unconventional Landau level structure. Furthermore, the experimental detection of the spectrum is proposed with the Bragg scattering techniques.
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arxiv:0905.3035
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LDA+DMFT (Local Density Approximation combined with Dynamical Mean-Field Theory) computation scheme has been used to calculate spectral properties of LaFeAsO -- the parent compound of the new high-T_c iron oxypnictides. The average Coulomb repulsion U=3-4 eV and Hund's exchange J=0.8 eV parameters for iron 3d electrons were calculated using the first principles constrained density functional theory scheme in the Wannier functions formalism. DMFT calculations using these parameters result in moderately correlated electronic structure with effective electron mass enhancement m^*~2 that is in agreement with the experimental X-ray and photoemission spectra. Conclusion of moderate correlations strength is confirmed by the observation that pnictides experimental spectra agree well with corresponding spectra for metallic iron while being very different with Mott insulator FeO spectra.
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arxiv:0905.3038
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We describe two algorithms for finding representatives of the nilpotent orbits of a theta-group. The algorithms have been implemented in the computer algebra system GAP (inside the package SLA). We comment on their performance. We apply the algorithms to study the nilpotent orbits of theta-groups, where theta is an N-regular automorphism of a simple Lie algebra of exceptional type.
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arxiv:0905.3149
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The knowledge of accurate stellar parameters is a key stone in several fields of stellar astrophysics, such as asteroseismology and stellar evolution. Although the parameters can be derived both via spectroscopy and multicolor photometry, the obtained results are sometimes affected by systematic uncertainties. In this paper we present a self-consistent spectral analysis of the solar-type star HD49933, which is a primary target for the CoRoT satellite. We used high-resolution and high signal-to-noise ratio spectra to carry out a consistent parameter estimation and abundance analysis of HD49933. The LLmodels code was employed for model atmosphere calculations, while Synth3 and Width9 codes were used for line profile calculation and LTE abundance analysis. In this paper we provide a detailed description of the methodology adopted to derive the fundamental parameters and the abundances. Although the obtained parameters differ from the ones previously derived by other authors, we show that only the set obtained in this work is able to fit the observed spectrum accurately. In particular, the surface gravity was adjusted to fit pressure-sensitive spectral features. We confirm the importance of a consistent analysis of relevant spectroscopic features, application of advanced model atmospheres, and the use of up-to-date atomic line data for the determination of stellar parameters. These results are crucial for further studies, e.g. detailed theoretical modelling of the observed pulsation frequencies.
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arxiv:0905.3153
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We present a comparison of CN bandstrength variations in the high-metallicity globular clusters NGC 6356 and NGC 6528 with those measured in the old open clusters NGC 188, NCG 2158 and NGC 7789. Star-to-star abundance variations, of which CN differences are a readily observable sign, are commonplace in moderate-metallicity halo globular clusters but are unseen in the field or in open clusters. We find that the open clusters have narrow, unimodal distributions of CN bandstrength, as expected from the literature, while the globular clusters have broad, bimodal distributions of CN bandstrength, similar to moderate-metallicity halo globular clusters. This result has interesting implications for the various mechanisms proposed to explain the origin of globular cluster abundance inhomogeneities, and suggests that the local environment at the epoch of cluster formation plays a vital role in regulating intracluster enrichment processes.
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arxiv:0905.3175
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In this paper we demonstrate the possibility of dissipationless spin transport in the chiral d-density wave state, by the sole application of a uniform Zeeman field gradient. The occurrence of these spontaneous spin currents is attributed to the parity (${\cal P}$) and time-reversal (${\cal T}$) violation induced by the $d_{xy}+id_{x^2-y^2}$ density wave order parameter. We calculate the spin Hall conductance and reveal its intimate relation to the Berry phase which is generated when the Zeeman field is applied adiabatically. Finally, we demonstrate that in the zero temperature and doping case, the spin Hall conductance is quantized as it becomes a topological invariant.
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arxiv:0905.3228
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We develop a unified, information theoretic interpretation of the number-phase complementarity that is applicable both to finite-dimensional (atomic) and infinite-dimensional (oscillator) systems, with number treated as a discrete Hermitian observable and phase as a continuous positive operator valued measure (POVM). The relevant uncertainty principle is obtained as a lower bound on {\it entropy excess}, $X$, the difference between the entropy of one variable, typically the number, and the knowledge of its complementary variable, typically the phase, where knowledge of a variable is defined as its relative entropy with respect to the uniform distribution. In the case of finite dimensional systems, a weighting of phase knowledge by a factor $\mu$ ($> 1$) is necessary in order to make the bound tight, essentially on account of the POVM nature of phase as defined here. Numerical and analytical evidence suggests that $\mu$ tends to 1 as system dimension becomes infinite. We study the effect of non-dissipative and dissipative noise on these complementary variables for oscillator as well as atomic systems.
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arxiv:0905.3269
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The concept of "dyadotorus" was recently introduced to identify in the Kerr-Newman geometry the region where vacuum polarization processes may occur, leading to the creation of $e^--e^+$ pairs. This concept generalizes the original concept of "dyadosphere" initially introduced for Reissner-Nordstr\"{o}m geometries. The topology of the axially symmetric dyadotorus is studied for selected values of the electric field and its electromagnetic energy is estimated by using three different methods all giving the same result. It is shown by a specific example the difference between a dyadotorus and a dyadosphere. The comparison is made for a Kerr-Newman black hole with the same total mass energy and the same charge to mass ratio of a Reissner-Nordstr\"{o}m black hole. It turns out that the Kerr-Newman black hole leads to larger values of the electromagnetic field and energy when compared to the electric field and energy of the Reissner-Nordstr\"{o}m one. The significance of these theoretical results for the realistic description of the process of gravitational collapse leading to black hole formation as well as the energy source of gamma ray bursts are also discussed.
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arxiv:0905.3274
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The plant microtubule cortical array is a striking feature of all growing plant cells. It consists of a more or less homogeneously distributed array of highly aligned microtubules connected to the inner side of the plasma membrane and oriented transversely to the cell growth axis. Here we formulate a continuum model to describe the origin of orientational order in such confined arrays of dynamical microtubules. The model is based on recent experimental observations that show that a growing cortical microtubule can interact through angle dependent collisions with pre-existing microtubules that can lead either to co-alignment of the growth, retraction through catastrophe induction or crossing over the encountered microtubule. We identify a single control parameter, which is fully determined by the nucleation rate and intrinsic dynamics of individual microtubules. We solve the model analytically in the stationary isotropic phase, discuss the limits of stability of this isotropic phase, and explicitly solve for the ordered stationary states in a simplified version of the model.
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arxiv:0905.3288
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Selection in a time-periodic environment is modeled via the two-player replicator dynamics. For sufficiently fast environmental changes, this is reduced to a multi-player replicator dynamics in a constant environment. The two-player terms correspond to the time-averaged payoffs, while the three and four-player terms arise from the adaptation of the morphs to their varying environment. Such multi-player (adaptive) terms can induce a stable polymorphism. The establishment of the polymorphism in partnership games [genetic selection] is accompanied by decreasing mean fitness of the population.
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arxiv:0905.3297
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Here we propose and demonstrate an all-optical wavelength-routing approach which uses a tuning mechanism based upon the optical gradient force in a specially-designed nano-optomechanical system. The resulting mechanically-compliant "spiderweb" resonantor realizes seamless wavelength routing over a range of 3000 times the intrinsic channel width, with a tuning efficiency of 309-GHz/mW, a switching time of less than 200-ns, and 100% channel-quality preservation over the entire tuning range. These results indicate the potential for radiation pressure actuated devices to be used in a variety of photonics applications, such as channel routing/switching, buffering, dispersion compensation, pulse trapping/release, and widely tunable lasers.
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arxiv:0905.3336
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We map narrow-line regions (NLRs) of 11 nearby Seyfert 2 galaxies with the optical integral-field spectrograph OASIS mounted at CFHT. We model emission-line profiles of 5 forbidden-line doublets and 2 Balmer lines, correcting for the underlying stellar absorption by reconstructing stellar spectra with synthetic evolutionary stellar population models. For each of the 11 targets, we present 2D maps of surface brightness in the observed emission lines, diagnostic line intensity ratios, gas kinematics (mean line-of-sight velocity and velocity dispersion), electron density, and interstellar reddening, and we plot spatially resolved spectral-diagnostic diagrams. The stellar data are represented by maps of mean line-of-sight (LOS) velocities and of the relative mass fractions of the young stellar populations. The gas velocity fields in 80% of the sample exhibit twisted S-shaped isovelocity contours, which are signatures of non-circular orbits and indicate non-axisymmetric gravitational potentials, gas motions out of the galactic plane, or possible outflows and inflows. Based on the kinematic measurements, we identified a possible nuclear ring or radial gas flow in NGC 262 (Mrk 348), not reported before. Eight of the eleven observed objects exhibit strongly asymmetric or multi-component emission-line profiles, in most cases confined to an elongated region passing through the galactic centre, perpendicular to the major axis of emission.
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arxiv:0905.3349
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It is shown that observers in the standard ADM 3+1 treatment of matter are the same as the observers used in the matter treatment of Bondi: they are comoving and local Minkowskian. Bondi's observers are the basis of the post--quasitatic approximation (PQSA) to study a contracting distribution of matter. This correspondence suggests the possibility of using the PQSA as a test bed for Numerical Relativity. The treatment of matter by the PQSA and its connection with the ADM 3+1 treatment are presented, for its practical use as a calibration tool and as a test bed for numerical relativistic hydrodynamic codes.
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arxiv:0905.3362
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We calculate the dissipative dynamics of two-qubit quantum discord under Markovian environments. We analyze various dissipative channels such as dephasing, depolarizing, and generalized amplitude damping, assuming independent perturbation, in which each qubit is coupled to its own channel. Choosing initial conditions that manifest the so-called sudden death of entanglement, we compare the dynamics of entanglement with that of quantum discord. We show that in all cases where entanglement suddenly disappears, quantum discord vanishes only in the asymptotic limit, behaving similarly to individual decoherence of the qubits, even at finite temperatures. Hence, quantum discord is more robust than the entanglement against to decoherence so that quantum algorithms based only on quantum discord correlations may be more robust than those based on entanglement.
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arxiv:0905.3376
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Pumping characteristics were studied of the hybrid normal-metal/superconductor single-electron transistor embedded in a high-ohmic environment. Two 3 micrometer-long microstrip resistors of CrOx with a sum resistance R=80kOhm were placed adjacent to this hybrid device. Substantial improvement of pumping and reduction of the subgap leakage were observed in the low-MHz range. At higher frequencies 0.1-1GHz, a slowdown of tunneling due to the enhanced damping and electron heating negatively affected the pumping, as compared to the reference bare devices.
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arxiv:0905.3402
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We discuss the properties of 137 cataclysmic variables (CVs) which are included in the Sloan Digital Sky Survey (SDSS) spectroscopic data base, and for which accurate orbital periods have been measured. 92 of these systems are new discoveries from SDSS and were followed-up in more detail over the past few years. 45 systems were previously identified as CVs because of the detection of optical outbursts and/or X-ray emission, and subsequently re-identified from the SDSS spectroscopy. The period distribution of the SDSS CVs differs dramatically from that of all the previously known CVs, in particular it contains a significant accumulation of systems in the orbital period range 80--86 min. We identify this feature as the elusive "period minimum spike" predicted by CV population models, which resolves a long-standing discrepancy between compact binary evolution theory and observations. We show that this spike is almost entirely due to the large number of CVs with very low accretion activity identified by SDSS. The optical spectra of these systems are dominated by emission from the white dwarf photosphere, and display little or no spectroscopic signature from the donor stars, suggesting very low-mass companion stars. We determine the average absolute magnitude of these low-luminosity CVs at the period minimum to be <M_g>=11.6+-0.7. Comparison of the SDSS CV sample to the CVs found in the Hamburg Quasar Survey and the Palomar Green Survey suggests that the depth of SDSS is the key ingredient resulting in the discovery of a large number of intrinsically faint short-period systems.
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arxiv:0905.3476
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We prove that the NS cubic superstring field theories are classically equivalent, regardless of the choice of Y_{-2} in their definition, and illustrate it by an explicit evaluation of the action of Erler's solution. We then turn to examine this solution. First, we explain that its cohomology is trivial also in the Ramond sector. Then, we show that the boundary state corresponding to it is identically zero. We conclude that this solution is indeed a closed string vacuum solution despite the absence of a tachyon field on the BPS D-brane.
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arxiv:0905.3501
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The study of biochemical pathways usually focuses on a small section of a protein interactions network. Two distinct sources contribute to the noise in such a system: intrinsic noise, inherent in the studied reactions, and extrinsic noise generated in other parts of the network or in the environment. We study the effect of extrinsic noise entering the system through a nonlinear uptake reaction which acts as a nonlinear filter. Varying input noise intensity varies the mean of the noise after the passage through the filter, which changes the stability properties of the system. The steady-state displacement due to small noise is independent on the kinetics of the system but it only depends on the nonlinearity of the input function. For monotonically increasing and concave input functions such as the Michaelis-Menten uptake rate, we give a simple argument based on the small-noise expansion, which enables qualitative predictions of the steady-state displacement only by inspection of experimental data: when weak and rapid noise enters the system through a Michaelis-Menten reaction, then the graph of the system's steady states vs. the mean of the input signal always shifts to the right as noise intensity increases. We test the predictions on two models of lac operon, where TMG/lactose uptake is driven by a Michaelis-Menten enzymatic process. We show that as a consequence of the steady state displacement due to fluctuations in extracellular TMG/lactose concentration the lac switch responds in an asymmetric manner: as noise intensity increases, switching off lactose metabolism becomes easier and switching it on becomes more difficult.
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arxiv:0905.3502
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Let K and L be compact convex sets in R^n. The following two statements are shown to be equivalent: (i) For every polytope Q inside K having at most n+1 vertices, L contains a translate of Q. (ii) L contains a translate of K. Let 1 <= d <= n-1. It is also shown that the following two statements are equivalent: (i) For every polytope Q inside K having at most d+1 vertices, L contains a translate of Q. (ii) For every d-dimensional subspace W, the orthogonal projection of the set L onto W contains a translate of the corresponding projection of the set K onto W. It is then shown that, if K is a compact convex set in R^n having at least d+2 exposed points, then there exists a compact convex set L such that every d-dimensional orthogonal projection of L contains a translate of the corresponding projection of K, while L does not contain a translate of K. In particular, such a convex body L exists whenever dim(K) > d.
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arxiv:0905.3514
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We find a link between oriented matroid theory and 2d gravity with torsion. Our considerations may be useful in the context of noncommutative phase space in a target spacetime of signature (2+2) and in a possible theory of gravity ramification.
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arxiv:0905.3543
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In the non-relativistic theory of gravitation recently proposed by Horava, the Hamiltonian constraint is not a local equation satisfied at each spatial point but an equation integrated over a whole space. The global Hamiltonian constraint is less restrictive than its local version, and allows a richer set of solutions than in general relativity. We show that a component which behaves like pressureless dust emerges as an "integration constant" of dynamical equations and momentum constraint equations. Consequently, classical solutions to the infrared limit of Horava-Lifshitz gravity can mimic general relativity plus cold dark matter.
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arxiv:0905.3563
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We introduce the notion of symplectic microfolds and symplectic micromorphisms between them. They form a monoidal category, which is a version of the "category" of symplectic manifolds and canonical relations obtained by localizing them around lagrangian submanifolds in the spirit of Milnor's microbundles.
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arxiv:0905.3574
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We have developed a set of seven observational equations that include all of the physics necessary to relate the most important of the fundamental constants to the definitions of the SI kilogram and ampere. We have used these to determine the influence of alternative definitions being considered for the SI kilogram and ampere on the uncertainty of three of the fundamental constants (h, e and mu). We have also reviewed the experimental evidence for the exactness of the quantum metrology triangle resulting from experiments combining the quantum Hall effect, the Josephson effects and single-electron tunnelling.
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arxiv:0905.3635
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The use of the equations of motion and meson field redefinitions allows the development of a simplified resonance chiral theory lagrangian: terms including resonance fields and a large number of derivatives can be reduced into corresponding O(p2) resonance operators, containing the lowest possible number of derivatives. This is shown by means of the explicit computation of the pion vector form-factor up to next-to-leading order in 1/Nc. The study of the renormalization group equations for the corresponding couplings demonstrates the existence of an infrared fixed point in the resonance theory. The possibility of developing a perturbative 1/Nc expansion in the slow running region around the fixed point is shown here.
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arxiv:0905.3676
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We study the optimal use of third order statistics in the analysis of weak lensing by large-scale structure. These higher order statistics have long been advocated as a powerful tool to break measured degeneracies between cosmological parameters. Using ray-tracing simulations, incorporating important survey features such as a realistic depth-dependent redshift distribution, we find that a joint two- and three-point correlation function analysis is a much stronger probe of cosmology than the skewness statistic. We compare different observing strategies, showing that for a limited survey time there is an optimal depth for the measurement of third-order statistics, which balances statistical noise and cosmic variance against signal amplitude. We find that the chosen CFHTLS observing strategy was optimal and forecast that a joint two- and three-point analysis of the completed CFHTLS-Wide will constrain the amplitude of the matter power spectrum $\sigma_8$ to 10% and the matter density parameter $\Omega_m$ to 17%, a factor of ~2.5 improvement on the two-point analysis alone. Our error analysis includes all non-Gaussian terms, finding that the coupling between cosmic variance and shot noise is a non-negligible contribution which should be included in any future analytical error calculations.
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arxiv:0905.3726
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We report on recent results in the study of extremal black hole attractors in N=2, d=4 ungauged Maxwell-Einstein supergravities. For homogeneous symmetric scalar manifolds, the three general classes of attractor solutions with non-vanishing Bekenstein-Hawking entropy are discussed. They correspond to three (inequivalent) classes of orbits of the charge vector, which sits in the relevant symplectic representation R_{V} of the U-duality group. Other than the 1/2-BPS one, there are two other distinct non-BPS classes of charge orbits, one of which has vanishing central charge. The complete classification of the U-duality orbits, as well as of the moduli spaces of non-BPS attractors (spanned by the scalars which are not stabilized at the black hole event horizon), is also reviewed. Finally, we consider the analogous classification for N>2-extended, d=4 ungauged supergravities, in which also the 1/N-BPS attractors yield a related moduli space.
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arxiv:0905.3739
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We present a study of the properties of network of political discussions on one of the most popular Polish Internet forums. This provides the opportunity to study the computer mediated human interactions in strongly bipolar environment. The comments of the participants are found to be mostly disagreements, with strong percentage of invective and provocative ones. Binary exchanges (quarrels) play significant role in the network growth and topology. Statistical analysis shows that the growth of the discussions depends on the degree of controversy of the subject and the intensity of personal conflict between the participants. This is in contrast to most previously studied social networks, for example networks of scientific citations, where the nature of the links is much more positive and based on similarity and collaboration rather than opposition and abuse. The work discusses also the implications of the findings for more general studies of consensus formation, where our observations of increased conflict contradict the usual assumptions that interactions between people lead to averaging of opinions and agreement.
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arxiv:0905.3751
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Axion-Like Particles (ALPs) are the focus of intense current research. We analyze photon-ALP conversion in the context of relativistic jet models of Active Galactic Nuclei (AGN) for more than 100 sources. Contrary to previous claims, we find that this process cannot occur above 100 GeV regardless of the actual AGN model and the values of ALP parameters. This result rules out a proposed strategy to bypass the cosmic opacity above 100 GeV, as apparently required by observations. We also show that for some AGN an observable effect can show up in the X and soft gamma-ray bands.
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arxiv:0905.3752
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We devise an ab initio formalism for the quantum dynamics of Auger decay by laser-dressed atoms which are inner-shell ionized by extreme ultraviolet (XUV) light. The optical dressing laser is assumed to be sufficiently weak such that ground-state electrons are neither excited nor ionized by it. However, the laser has a strong effect on continuum electrons which we describe in strong-field approximation with Volkov waves. The XUV light pulse has a low peak intensity and its interaction is treated as a one-photon process. The quantum dynamics of the inner-shell hole creation with subsequent Auger decay is given by equations of motion (EOMs). For this paper, the EOMs are simplified in terms of an essential-states model which is solved analytically and averaged over magnetic subshells. We apply our theory to the M_4,5 N_1 N_2,3 Auger decay of a 3d hole in a krypton atom. The orbitals are approximated by scaled hydrogenic wave functions. A single attosecond pulse produces 3d vacancies which Auger decay in the presence of an 800nm laser with an intensity of 10^13 W / cm^2. We compute the Auger electron spectrum and assess the convergence of the various quantities involved.
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arxiv:0905.3756
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We present an analysis of several high-resolution Chandra grating observations of the X-ray binary pulsar Her X-1. With a total exposure of 170 ks, the observations are separated by years and cover three combinations of orbital and super-orbital phases. Our goal is to determine distinct properties of the photoionized emission and its dependence on phase-dependent variations of the continuum. We find that the continua can be described by a partial covering model which above 2 keV is consistent with recent results from \rxte studies and at low energies is consistent with recent \xmm and \sax studies. Besides a powerlaw with fixed index, an additional thermal blackbody of 114 eV is required to fit wavelengths above 12 \AA ($\sim$ 1 keV). We find that likely all the variability is caused by highly variable absorption columns in the range (1 -- 3)$\times 10^{23}$ cm$^{-2}$. Strong Fe K line fluorescence in almost all observations reveals that dense, cool material is present not only in the outer regions of the disk but interspersed throughout the disk. Most spectra show strong line emission stemming from a photoionized accretion disk corona. We model the line emission with generic thermal plasma models as well as with the photoionization code XSTAR and investigate changes of the ionization balance with orbital and superorbital phases. Most accretion disk coronal properties such as disk radii, temperatures, and plasma densities are consistent with previous findings for the low state. We find that these properties change negligibly with respect to orbital and super-orbital phases. A couple of the higher energy lines exhibit emissivities that are significantly in excess of expectations from a static accretion disk corona.
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arxiv:0905.3773
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The configuration-fixed constrained triaxial relativistic mean-field approach is extended by including time-odd fields and applied to study the candidate multiple chiral doublets (MKiD) nucleus 106Rh. The energy contribution from time-odd fields and microscopical evaluation of center-of-mass correction as well as the modification of triaxial deformation parameters beta, gamma due to the time-odd fields are investigated. The contributions of the time-odd fields to the total energy are 0.1-0.3 MeV and they modify slightly the gamma values. However, the previously predicted multiple chiral doublets still exist.
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arxiv:0905.3785
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We analyze, without resort to any model field-mixing scheme, the leading temperature-dependent term in the "diameter" of the coexistence curve asymptotically close to the vapor-liquid critical point. For this purpose, we use a simple non-parametric equation of state which we develop by meeting several general requirements. Namely, we require that the desired equation (1) lead to correct asymptotic behavior for a limited number of the fluid's parameters along selected thermodynamic paths, (2) reveal a Van der Waals loop below the critical point, and (3) be consistent with a rigorous definition of the isothermal compressibility in the critical region. For the temperature interval in question, the proposed equation approximates experimental data with an accuracy comparable to those given by Schofield's parametric equation and by other authors' equations. The desired term is obtained by applying the Maxwell rule to the equation and can be represented as D_{2 \beta} | \tau |^{2 \beta}, where | \tau | = | T - T_{c} | / T_{c}, and \beta is the critical exponent for the order parameter. The amplitude D_{2 \beta} is determined explicitly for the volume-temperature and entropy-temperature planes.
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arxiv:0905.3793
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We present a transport study of semi-metallic bismuth in presence of a magnetic field applied along the trigonal axis extended to 55 T for electric conductivity and to 45 T for thermoelectric response. The results uncover a new field scale at about 40 T in addition to the previously detected ones. Large anomalies in all transport properties point to an intriguing electronic instability deep in the ultraquantum regime. Unexpectedly, both the sheer magnitude of conductivity and its metallic temperature dependence are enhanced by this instability.
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arxiv:0905.3835
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We analyze the effect of plasma screening on nuclear reaction rates in dense matter composed of atomic nuclei of one or two types. We perform semiclassical calculations of the Coulomb barrier penetrability taking into account a radial mean field potential of plasma ions. The mean field potential is extracted from the results of extensive Monte Carlo calculations of radial pair distribution functions of ions in binary ionic mixtures. We calculate the reaction rates in a wide range of plasma parameters and approximate these rates by an analytical expression that is expected to be applicable for multicomponent ions mixtures. Also, we analyze Gamow-peak energies of reacting ions in various nuclear burning regimes. For illustration, we study nuclear burning in C-O mixtures.
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arxiv:0905.3844
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The Sloan Digital Sky Survey (SDSS) source J102347.6+003841 was recently revealed to be a binary 1.69 millisecond radio pulsar with a 4.75 hr orbital period and a ~0.2 M_sun companion. Here we analyze the SDSS spectrum of the source in detail. The spectrum was taken on 2001 February 1, when the source was in a bright state and showed broad, double-peaked hydrogen and helium lines -- dramatically different from the G-type absorption spectrum seen from 2003 onward. The lines are consistent with emission from a disk around the compact primary. We derive properties of the disk by fitting the SDSS continuum with a simple disk model, and find a temperature range of 2000--34000 K from the outer to inner edge of the disk. The disk inner and outer radii were approximately 10^9 and 5.7x10^10 cm, respectively. These results further emphasize the unique feature of the source: it is likely a system at the end of its transition from an X-ray binary to a recycled radio pulsar. The disk mass is estimated to have been ~10^23 g, most of which would have been lost due to pulsar wind ablation (or due to the propeller effect if the disk had extended inside the light cylinder of the pulsar) before the final disk disruption event. The system could undergo repeated episodes of disk formation. Close monitoring of the source is needed to catch the system in its bright state again, so that this unusual example of a pulsar-disk interaction can be studied in much finer detail
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arxiv:0905.3899
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We present results on the mass and spin of the final black hole from mergers of equal mass, spinning black holes. The study extends over a broad range of initial orbital configurations, from direct plunges to quasi-circular inspirals to more energetic orbits (generalizations of Newtonian elliptical orbits). It provides a comprehensive search of those configurations that maximize the final spin of the remnant black hole. We estimate that the final spin can reach a maximum spin $a/M_h \approx 0.99\pm 0.01$ for extremal black hole mergers. In addition, we find that, as one increases the orbital angular momentum from small values, the mergers produce black holes with mass and spin parameters $\lbrace M_h/M, a/M_h \rbrace$ ~spiraling around the values $\lbrace \hat M_h/M, \hat a/M_h \rbrace$ of a {\it golden} black hole. Specifically, $(M_h-\hat M_h)/M \propto e^{\pm B\,\phi}\cos{\phi}$ and $(a-\hat a)/M_h \propto e^{\pm C\,\phi}\sin{\phi}$, with $\phi$ a monotonically growing function of the initial orbital angular momentum. We find that the values of the parameters for the \emph{golden} black hole are those of the final black hole obtained from the merger of a binary with the corresponding spinning black holes in a quasi-circular inspiral.
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arxiv:0905.3914
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We are concerned with the behavior of the polynomial maps $F=(P,Q)$ of $\mathbb{C}^2$ with finite fibres and satisfying the condition that all of the curves $aP+bQ=0$, $(a:b)\in \mathbb{P}^1$, are irreducible rational curves. The obtained result shows that such polynomial maps $F$ is invertible if $(0,0)$ is a regular value of $F$ or if the Jacobian condition holds.
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arxiv:0905.3939
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The most general SU(3)-singlet space of gauged N=8 supergravity in four-dimensions is studied recently. The SU(3)-invariant six scalar fields are realized by six real four-forms. A family of holographic N=1 supersymmetric RG flows on M2-branes in three-dimensions is described. This family of flows is driven by three independent mass parameters from the N=8 SO(8) theory and is controlled by two IR fixed points, N=1 G_2-invariant one and N=2 SU(3) x U(1)-invariant one. The generic flow with arbitrary mass parameters is N=1 supersymmetric and reaches to the N=2 SU(3) x U(1) fixed point where the three masses become identical. A particular N=1 supersymmetric SU(3)-preserving RG flow from the N=1 G_2-invariant fixed point to the N=2 SU(3) x U(1)-invariant fixed point is also discussed.
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arxiv:0905.3943
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The purpose of this reanalysis of the WMAP uncalibrated time ordered data (TOD) was two fold. The first was to reassess the reliability of the detection of the anisotropies in the official WMAP sky maps of the cosmic microwave background (CMB). The second was to assess the performance of a proposed criterion in avoiding systematic error in detecting a signal of interest. The criterion was implemented by testing the null hypothesis that the uncalibrated TOD was consistent with no anisotropies when WMAP's hourly calibration parameters were allowed to vary. It was shown independently for all 20 WMAP channels that sky maps with no anisotropies were a better fit to the TOD than those from the official analysis. The recently launched Planck satellite should help sort out this perplexing result.
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arxiv:0905.3971
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We present a unified description of heat flow in two-terminal hybrid quantum systems. Using simple models, we analytically study nonlinear aspects of heat transfer between various reservoirs: metals, solids, and spin baths, mediated by the excitation/relaxation of a central (subsystem) mode. We demonstrate rich nonlinear current-temperature characteristics, originating from either the molecular anharmonicity, or the reservoirs (complex) energy spectra. In particular, we establish sufficient conditions for thermal rectification in two-terminal junctions. We identify two classes of rectifiers. In type-A rectifiers the density of states of the reservoirs are dissimilar. In type-B rectifiers the baths are identical, but include particles whose statistics differ from that of the subsystem, to which they asymmetrically couple. Nonlinear heat flow, and specifically thermal rectification, are thus ubiquitous effects that could be observed in a variety of systems, phononic, electronic, and photonic.
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arxiv:0905.4015
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Supersymmetric (SUSY) standard models in which the lightest SUSY particle (LSP) is an ultralight gravitino (m_{3/2}=O(1) eV) are very attractive, since they are free from the cosmological gravitino problems. If the neutralino is the next lightest SUSY particle (NLSP), it decays into a photon and the gravitino in collider experiments. We propose a simple test for the lightness of gravitino at the LHC.
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arxiv:0905.4034
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In this paper we prove genus bounds for closed embedded minimal surfaces in a closed 3-dimensional manifold constructed via min-max arguments. A stronger estimate was announced by Pitts and Rubistein but to our knowledge its proof has never been published. Our proof follows ideas of Simon and uses an extension of a famous result of Meeks, Simon and Yau on the convergence of minimizing sequences of isotopic surfaces. This result is proved in the second part of the paper.
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arxiv:0905.4035
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