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We report the direct observation of a novel type of rainbow caustic. In contrast to known examples, this caustic originates from a dissipative, stochastic process. We have observed this using cold ^{87}Rb atoms bouncing inelastically on an evanescent-wave atom mirror. The caustic appears as a sharp peak at the lower edge of the asymmetric velocity distribution of the bouncing atoms. The stochastic process is a spontaneous Raman transition due to photon scattering during the bounce. The results are in good agreement with a classical calculation.
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arxiv:physics/0101088
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General phenomenological theory of hydrodynamic waves in regions with smooth loss of convexity of isentropes is developed based on the fact that for most media these regions in p-V plane are anomalously small. Accordingly the waves are usually weak and can be described in the manner analogous to that for weak shock waves of compression. The corresponding generalized Burgers equation is derived and analyzed. The exact solution of the equation for steady shock waves of rarefaction is obtained and discusses.
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arxiv:physics/0101103
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The delta function gauge of the electromagnetic potential allows semiclassical formulas to be obtained for the probability of exciting a single electron out of the ground state in an ultrarelativistic heavy ion reaction. Exact formulas have been obtained in the limits of zero impact parameter and large, perturbative, impact parameter. The perturbative impact parameter result can be exploited to obtain a semi-empirical cross section formula of the form, sigma = A ln(gamma) + B, for single electron ionization. A and B can be evaluated for any combination of target and projectile, and the resulting simple formula is good at all ultrarelativistic energies. The analytical form of A and B elucidates a result previously found in numerical calculations: scaled ionization cross sections decrease with increasing charge of the nucleus being ionized. The cross section values obtained from the present formula are in good agreement with recent CERN SPS data from a Pb beam on various nuclear targets.
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arxiv:physics/0102045
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Reduction of costs in biological signalling seems an evolutionary advantage, but recent experiments have shown signalling codes shifted to signals of high cost with a underutilisation of low cost signals. Here I show that errors in the efficient translation of biological states into signals shift codes to higher costs, effectively performing a quality control. The statistical structure of signal usage is predicted to be of a generalised Boltzmann form that penalises signals that are costly and sensitive to errors. This predicted distribution of signal usage against signal cost has two main features: an exponential tail required for cost efficiency and an underutilisation of the low cost signals required to protect the signalling quality from the errors. These predictions are shown to correspond quantitatively to the experiments in which gathering signal statistics is feasible as in visual cortex neurons.
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arxiv:physics/0102076
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Interaction of an intense electromagnetic (EM) beam with hot relativistic plasma is investigated. It is shown that the thermal pressure brings about a fundamental change in the dynamics - localized, high amplitude, EM field structures, not accessible to a cold (but relativisic) plasma, can now be formed under well- defined conditions. Examples of the trapping of EM beams in self-guiding regimes to form stable 2D solitonic structures in a pure e-p plasma are worked out.
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arxiv:physics/0102077
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Multipath propagation of radio waves in indoor/outdoor environments shows a highly irregular behavior as a function of time. Typical modeling of this phenomenon assumes the received signal is a stochastic process composed of the superposition of various altered replicas of the transmitted one, their amplitudes and phases being drawn from specific probability densities. We set out to explore the hypothesis of the presence of deterministic chaos in signals propagating inside various buildings at the University of Calgary. The correlation dimension versus embedding dimension saturates to a value between 3 and 4 for various antenna polarizations. The full Liapunov spectrum calculated contains two positive exponents and yields through the Kaplan-Yorke conjecture the same dimension obtained from the correlation sum. The presence of strange attractors in multipath propagation hints to better ways to predict the behaviour of the signal and better methods to counter the effects of interference. The use of Neural Networks in non linear prediction will be illustrated in an example and potential applications of same will be highlighted.
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arxiv:physics/0103048
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We report the development of a new ray-tracing simulation tool having the potential of the full characterization of a radio link through the accurate study of the propagation path of the signal from the transmitting to the receiving antennas across a perturbed atmosphere. The ray-tracing equations are solved, with controlled accuracy, in three dimensions (3D) and the propagation characteristics are obtained using various refractive index models. The launching of the rays, the atmospheric medium and its disturbances are characterized in 3D. The novelty in the approach stems from the use of special numerical techniques dealing with so called stiff differential equations without which no solution of the ray-tracing equations is possible. Starting with a given launching angle, the solution consists of the ray trajectory, the propagation time information at each point of the path, the beam spreading, the transmitted (resp. received) power taking account of the radiation pattern and orientation of the antennas and finally, the polarization state of the beam. Some previously known results are presented for comparative purposes and new results are presented as well as some of the capabilities of the software.
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arxiv:physics/0104004
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Microarray data consists of mRNA expression levels of thousands of genes under certain conditions. A difference in the expression level of a gene at two different conditions/phenotypes, such as cancerous versus non-cancerous, one subtype of cancer versus another, before versus after a drug treatment, is indicative of the relevance of that gene to the difference of the high-level phenotype. Each gene can be ranked by its ability to distinguish the two conditions. We study how the single-gene classification ability decreases with its rank (a Zipf's plot). Power-law function in the Zipf's plot is observed for the four microarray datasets obtained from various cancer studies. This power-law behavior in the Zipf's plot is reminiscent of similar power-law curves in other natural and social phenomena (Zipf's law). However, due to our choice of the measure of importance in classification ability, i.e., the maximized likelihood in a logistic regression, the exponent of the power-law function is a function of the sample size, instead of a fixed value close to 1 for a typical example of Zipf's law. The presence of this power-law behavior is important for deciding the number of genes to be used for a discriminant microarray data analysis.
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arxiv:physics/0104028
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Scattering of ortho positronium (Ps) by cesium and rubidium atoms has been investigated employing a three-Ps-state coupled-channel model with Ps(1s,2s,2p) states using a time-reversal-symmetric regularized electron-exchange model potential. We find a narrow S-wave singlet resonance at 5.057 eV of width 0.003 eV in the Ps-Rb system and at 5.067 eV of width 0.003 eV in the Ps-Cs system. Singlet P-wave resonances in both systems are found at 5.3 eV of width 0.4 eV. Singlet D-wave structures are found at 5.4 eV in both systems. The pronounced P- and D-wave resonances in these systems lead to easily detectable local minima in the low-energy elastic cross sections. We also report results for elastic and Ps-excitation cross sections for Ps scattering by Rb and Cs.
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arxiv:physics/0104037
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In the frame of multifractal theory of time and space (in this model our universe is consisting of real time and space fields and is the multifractal universe) in the works [1]-[16] some problems were analyzed: how the fractional dimensions of real fields of time and space influence on behavior of different physical phenomena. In this paper it is shown that in the multifractal theory of time and space the corrections of general relativity to Newton gravitational forces are explaining very simple in Newton approach. It is shown also that there is dependence (though very small) of bodies gravitational acceleration from their masses, so the principle of equivalence in multifractal universe is not absolute and it is only a very good approach. For perihelion of Mercury rotation the correction to known results of Einstein relativity is consi- dered. CONTENTS: 1. Introduction; 2. Newton Equations in the Multifractal Universe; 3. Is Gravitational Acceleration Depends of the Mass of the Accelerated Body? 4. Experimental Checking; 5. Conclusions
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arxiv:physics/0104039
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We reelaborate on the basic properties of lossless multilayers. We show that the transfer matrices for these multilayers have essentially the same algebraic properties as the Lorentz group SO(2,1) in a (2+1)-dimensional spacetime, as well as the group SL(2,R) underlying the structure of the ABCD law in geometrical optics. By resorting to the Iwasawa decomposition, we represent the action of any multilayer as the product of three matrices of simple interpretation. This group-theoretical structure allows us to introduce bilinear transformations in the complex plane. The concept of multilayer transfer function naturally emerges and its corresponding properties in the unit disc are studied. We show that the Iwasawa decomposition reflects at this geometrical level in three simple actions that can be considered the basic pieces for a deeper undestanding of the multilayer behavior. We use the method to analyze in detail a simple practical example.
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arxiv:physics/0104050
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The present contribution documents the harmony of postulates and conclusions of Wheeler-Feynman absorber theory and the model of Expansive Nondecelerative Universe. A relationship connecting advanced electromagnetic waves and gravitational field quanta is rationalized.
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arxiv:physics/0104066
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The hyperspherical harmonics (HH) provide a complete basis for the expansion of atomic wave functions, but even for two particles the number of harmonics for a given order is not trivial and, as the number of electrons increases, this degeneracy becomes absolutely prohibitive. We modify the method by selecting a subset of the basis that, we feel, will yield the physically most important part of the wave function, and test the idea on simple systems. In a previous work (with M. Haftel) of the singlet ground and first excited states of the helium atom we found that the error in the binding energy of the ground state was of the order of 1 part in 10,000 and that it decreased for the first excited state. We now have applied our method to the equivalent triplet states. We report on this work, and our results, and hope to draw attention to the interesting accuracy that we obtain with the relatively simple wave functions of our formulation.
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arxiv:physics/0105076
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The performance of a large (3x3 $cm^2$) streamer tube cell in drift mode is shown. The detector space resolution has been studied using cosmic muons crossing an high precision silicon telescope. The experimental results are compared with a GARFIELD simulation.
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arxiv:physics/0105099
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The thermodynamic properties for three different types of off-lattice four-strand beta-sheet protein models interacting via a hybrid Go-type potential have been investigated. Discontinuous molecular dynamic simulations have been performed for different sizes of the bias gap g, an artificial measure of a model protein's preference for its native state. The thermodynamic transition temperatures are obtained by calculating the squared radius of gyration, the root-mean-squared pair separation fluctuation, the specific heat, the internal energy of the system, and the Lindemann disorder parameter. In spite of the simplicity, the protein-like heteropolymers have shown a complex set of protein transitions as observed in experimental studies. Starting from high temperature, these transitions include a collapse transition, a disordered-to-ordered globule transition, a folding transition, and a liquid-to-solid transition. These transitions strongly depend on the native-state geometry of the model proteins and the size of the bias gap. A strong transition from the disordered globule state to the ordered globule state with large energy change and a weak transition from the ordered globule state to the native state with small energy change were observed for the large gap models. For the small gap models no native structures were observed at any temperature, all three beta-sheet proteins fold into a partially-ordered globule state which is geometrically different from the native state. For small bias gaps at even lower temperatures, all protein motions are frozen indicating an inactive solid-like phase.
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arxiv:physics/0106019
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The celebrated Franck-Hertz experiment is reinterpreted by analogy with the Glimmentladung experiment, formerly performed by Heinrich Hertz.
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arxiv:physics/0106029
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We show that a dense spectrum of chaotic multiply-excited eigenstates can play a major role in collision processes involving many-electron multicharged ions. A statistical theory based on chaotic properties of the eigenstates enables one to obtain relevant energy-averaged cross sections in terms of sums over single-electron orbitals. Our calculation of the low-energy electron recombination of Au$^{25+}$ shows that the resonant process is 200 times more intense than direct radiative recombination, which explains the recent experimental results of Hoffknecht {\em et al.} [J. Phys. B {\bf 31}, 2415 (1998)].
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arxiv:physics/0106035
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We discuss on the potential of suspensions of gold nanoparticles with variable refractive index for the possible physical realization of in-relief virtual dynamic display of plane images. A reasoning approach for a vision system to display in real-time volumetric moving images is proposed based on well-known properties of optical media, namely the anomalous dispersion of light on certain transparent media and the virtual image formed by a refracting transparent surface. The system relies on creating mechanisms to modify the refractive index of in-relief virtual dynamical display (iVDD) bulbs that ideally would contain a suspension of gold nanoparticles each and that might be ordered in an array filling up a whole screen.
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arxiv:physics/0106050
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Reversing the flow of time between Casimir plates raises the question of whether or not a recently deceased, intact organism could be brought back to life. The odds are not good.
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arxiv:physics/0106056
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Properties of the disrupted NLC beam at the Interaction Point (IP) and particle loss in the extraction line are analyzed as a function of beam-to-beam position and angular offset at IP. The simulations show that disruption and beam loss maximize when the vertical beam separation at IP is about 20 times the rms vertical beam size. The horizontal offset does not increase the disruption and the beam loss. The angular offsets cause particle loss in the extraction line mainly because of the beam orbit oscillations.
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arxiv:physics/0106061
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The two main functions of the NLC extraction line include: 1) transmission of the outgoing disrupted beam and secondary particles to the dump with minimal losses; and 2) beam diagnostics and control. In this report, we describe the extraction line optics, present the results of tracking studies, and discuss the extraction line instrumentation.
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arxiv:physics/0106062
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We perform an extrapolative analysis of "fast-growth" free-energy-difference (DF) estimates of a computer-modeled, fully-solvated ethane<->methanol transformation. The results suggest that extrapolation can greatly reduce the systematic error in DF estimated from a small number of very fast switches. Our extrapolation procedure uses block-averages of finite-data estimates, and appears to be particularly useful for broad, non-Gaussian distributions of data which produce substantial systematic errors with insufficient data. In every tested case, the extrapolative results were better than direct estimates.
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arxiv:physics/0107066
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A simple experiment is presented that enables qualitative and quantitative measurement of the extraordinary refractive index direction dependency in an uniaxial nematic liquid crystal. Three liquid crystaline cells were designed in which elongated molecules of nematic liquid crystal align in directions which enable to observe the variation of extraordinary refractive index as a function of the direction of light.
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arxiv:physics/0108013
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The idea and principles of volume free electron lasers were proposed in [1-4]. It was shown there that volume distributed feedback (VDFB) can essentially reduce the threshold current of generation and provide the possibility of smooth frequency tuning. The present work considers an undulator VFEL with multiwave VDFB. It is shown that dependence of threshold current on the interaction length changes in the point of roots degeneration. This leads to the sharp decrease of start current if condition of dynamical diffraction is fulfilled. The dependence of amplification coefficient changes, too. So the interaction length for generation appears shorter. The proposed scheme can be used for generation in wide spectral range from microwaves to X-rays. The operating features of undulator VFEL is considered.
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arxiv:physics/0108020
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A new conceptual approach for examining the origin of cosmic rays is developed by considering the characteristics of particle trajectory distributions in four-dimensional Euclidean space-time. Transformation of an isotropic distribution into a velocity distribution in ordinary three-dimensional space results in a spatially isotropic flux of highly relativistic particles. This particle flux exhibits a power-law energy spectrum that decreases with increasing energy approximately inversely as the square of the energy and peaks at much lower energies. This model also provides additional results resembling the observed characteristics of cosmic radiation.
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arxiv:physics/0108049
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We present a theoretical derivation of the homogenous Maxwell equations, based on Stokes theorem for Minkowski space tensors.
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arxiv:physics/0108069
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Electron injection from an adsorbed molecule to the substrate (heterogeneous electron transfer) is studied. One reaction coordinate is used to model this process. The surface phonons and/or the electron-hole pairs together with the internal degrees of freedom of the adsorbed molecule as well as possibly a liquid surrounding the molecule provide a dissipative environment, which may lead to dephasing, relaxation, and sometimes excitation of the relevant system. In the process studied the adsorbed molecule is excited by a light pulse. This is followed by an electron transfer from the excited donor state to the quasi-continuum of the substrate. It is assumed that the substrate is a semiconductor. The effects of dissipation on electron injection are investigated.
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arxiv:physics/0109012
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The gravitational inverse square law is microscopic approximation. I suggest that it should be modified for elementary particles to use the surface-to-surface separation of the particles rather than the center-to-center separations. For small particles at macroscopic separations, the ratio between the center-to-center distance D and the surface-to-surface distance d, D/d, approaches unity. At microscopic separations, this ratio grows very large. Here I apply this ratio to several microscopic situations and derive the nuclear coupling constants. I will then present a model of a gluon/graviton transformation to justify my surface originating modification.
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arxiv:physics/0110001
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A Hamiltonian approach to the solution of the Vlasov-Poisson equations has been developed. Based on a nonlinear canonical transformation, the rapidly oscillating terms in the original Hamiltonian are transformed away, yielding a new Hamiltonian that contains slowly varying terms only. The formalism has been applied to the dynamics of an intense beam propagating through a periodic focusing lattice, and to the coherent beam-beam interaction. A stationary solution to the transformed Vlasov equation has been obtained.
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arxiv:physics/0110014
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Modification of three ideas underlying Newton's original world view, with only minor changes in context, might offer two advantages to introductory physics students. First, the students will experience less cognitive dissonance when they encounter relativistic effects. Secondly, the map-based Newtonian tools that they spend so much time learning about can be extended to high speeds, non-inertial frames, and even (locally, of course) to curved-spacetime.
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arxiv:physics/0110020
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A scheme of laser wakefield acceleration, when a relatively rare and long bunch of non-relativistic or weakly-relativistic electrons is initially in front of the laser pulse, is suggested and considered. The motion of test electrons is studied both in the one-dimensional case (1D wakefield) and in the three-dimensional laser wakefield excited in a plasma channel. It is shown that the bunch is trapped, effectively compressed both in longitudinal and transverse directions and accelerated to ultra-relativistic energies in the region of first accelerating maximum of the wakefield. The accelerated bunch has sizes much less than the plasma wavelength and relatively small energy spread.
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arxiv:physics/0110030
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An analysis of the collapse of the Twin Towers is carried on with the aid of simple mechanical laws. The motion of the collapse front is calculated in terms of geometric and energetic quantities.
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arxiv:physics/0110043
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It is shown that the distribution of low variability periods in the activity of human heart rate typically follows a multi-scaling Zipf's law. The presence or failure of a power law, as well as the values of the scaling exponents, are personal characteristics depending on the daily habits of the subjects. Meanwhile, the distribution function of the low-variability periods as a whole discriminates efficiently between various heart pathologies. This new technique is also applicable to other non-linear time-series and reflects these aspects of the underlying intermittent dynamics, which are not covered by other methods of linear- and nonlinear analysis.
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arxiv:physics/0110075
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Most of the devices in the SLAC control system are accessed via interface modules in ~450 CAMAC crates. Low-cost controllers in these crates communicate via a SLAC-proprietary bit-serial protocol with 77 satellite control computers ("micros") within the accelerator complex. A proposed upgrade replaces the existing Multibus-I implementation of the micro hardware with commercial-off-the-shelf ("COTS") personal computers. For increased reliability and ease of maintenance, these micros will move from their current electrically noisy and environmentally challenging sites to the control center's computer room, with only a stand-alone portion of each micro's CAMAC interface remaining in the micro's original location. This paper describes the hardware/software architecture of that intelligent front-end CAMAC controller and the accompanying fiber optic link board that connects it to the PC-based micro's PCI bus. Emphasis is placed on the hardware/software techniques employed to minimize real-time latency for pulse-to-pulse operations that control accelerator timing, acquire data for fast feedback loops, and change device settings to close those loops. The controller provides the sole interface between the COTS computing/networking environment and the existing CAMAC plant. It also supports higher bandwidth commercial byte-serial crate controllers and legacy BITBUS hardware.
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arxiv:physics/0111032
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The equipment control (EC) software of the GSI accelerators has been written entirely in Pascal. Modern software development is based on C++ or Java. To be prepared for the future, we decided to convert the EC software from Pascal to C in a first step. Considering the large amount of software, this is done automatically as far as possible. The paper describes our experiences gained using a Pascal to C translator, Perl scripts, and, of course, some manual interaction.
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arxiv:physics/0111056
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In the past, the features of a user interface were limited by those available in the existing graphical widgets it used. Now, improvements in processor speed have fostered the emergence of interpreted languages, in which the appropriate method to render a given data object can be loaded at runtime. XML can be used to precisely describe the association of data types with their graphical handling (beans), and Java provides an especially rich environment for programming the graphics. We present a graphical user interface builder based on Java Beans and XML, in which the graphical screens are described textually (in files or a database) in terms of their screen components. Each component may be a simple text read back, or a complex plot. The programming model provides for dynamic data pertaining to a component to be forwarded synchronously or asynchronously, to the appropriate handler, which may be a built-in method, or a complex applet. This work was initially motivated by the need to move the legacy VMS display interface of the SLAC Control Program to another platform while preserving all of its existing functionality. However the model allows us a powerful and generic system for adding new kinds of graphics, such as Matlab, data sources, such as EPICS, middleware, such as AIDA[1], and transport, such as XML and SOAP. The system will also include a management console, which will be able to report on the present usage of the system, for instance who is running it where and connected to which channels.
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arxiv:physics/0111057
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Accelerator control at DESY has in the past been hampered by the 'many-control-systems' syndrome, where different subsystems were controlled by completely different means offering no possibility of intercommunication. Today, practically all subsystems of HERA are controlled by TINE. Important exceptions include the Proton Vacuum(DOOCS), cryogenics control(D3), and the super-conducting electron RF cavities and the power and cooling subsystems, the latter two of which are controlled by EPICS IOCs. A step toward integrating the EPICS IOCs into the HERA mainstream has been taken in that an EPICS to TINE translator process has been written, which runs directly on the EPICS IOC and offers a TINE view of the hardware control to the rest of the control system. This in effect renders the EPICS IOC into a bi-lingual server, and highlights the principal difference between a 'translator' and a 'gateway'. Details of this translator are presented in this paper.
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arxiv:physics/0111064
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A beam physics model server (Art++) has been developed for the Jefferson Lab accelerator. This online model server is a redesign of the ARTEMIS model server. The need arose from an impedance mismatch between the current requirements and ARTEMIS capabilities. The purpose of the model server is to grant access to both static (machine lattice parameters) and dynamic (actual machine settings) data using a single programming interface. A set of useful optics calculations (R-matrix, orbit fit, etc.) has also been implemented and can be invoked by clients via the model interface. Clients may also register their own dynamic models in the server. The server interacts with clients using the CDEV protocol and data integrity is guaranteed by a relational database (Oracle8i) accessed through a persistence layer. By providing a centralized repository for both data and optics calculations, the following benefits were achieved: optimal use of network consumption, software reuse, and ease of maintenance.
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arxiv:physics/0111074
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The LIGO Control and Data system (CDS) features a tightly coupled and highly integrated control and data acquisition system. Control of the interferometers requires many Multiple Input Multiple Output (MIMO) control loops closed both locally and across the 4-kilometer interferometer arm lengths. In addition to providing the closed loop control, the control systems front end processors act as Data Collection Units (DCU) for the data acquisition system. Data collected by these front ends and the data acquisition system must be collected and time stamped to an accuracy of 1 microsecond and made available to on-line analysis tools such as the Global Diagnostics System (GDS)[1]. Data is also sent to the LIGO Data Analysis System (LDAS)[2] for long-term storage and off-line analysis. Data rates exceed 5 Mbytes per second per interferometer continuous. Connection between the various front end processors and the data acquisition system is achieved using fiber optic reflective memory networks. Both controls and data acquisition systems use VME hardware and VxWorks operating systems. This paper will present an overview of the LIGO CDS and discuss key aspects of its design.
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arxiv:physics/0111077
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Experience using hardware knobs as an operator interface for controlling equipment has varied considerably at different facilities. Reactions have ranged from "indispensable" at some facilities, to "virtually useless" at others. In this paper, we will attempt to outline some basic principles for successful knob implementation. These principles derive from our own experience with control knobs at the LANSCE Accelerator Complex and our recent effort to adapt our control knobs to EPICS. Topics to be covered include what the operator needs the knob to do, what the knob needs to know about the device it is controlling, and knob scaling issues. Advanced topics such as closed-loop, PID, and aggregate knobs are left as topics for future papers.
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arxiv:physics/0111082
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We propose a model that, accounting for the intrinsic non-linearity of the electronic system, is able to rationalize steady-state electronic and vibrational spectra of polar chromophores in solution, as well as time-resolved experiments.
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arxiv:physics/0111086
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The Bayesian approach has proved to be a coherent approach to handle ill posed Inverse problems. However, the Bayesian calculations need either an optimization or an integral calculation. The maximum a posteriori (MAP) estimation requires the minimization of a compound criterion which, in general, has two parts: a data fitting part and a prior part. In many situations the criterion to be minimized becomes multimodal. The cost of the Simulated Annealing (SA) based techniques is in general huge for inverse problems. Recently a deterministic optimization technique, based on Graduated Non Convexity (GNC), have been proposed to overcome this difficulty. The objective of this paper is to show two specific implementations of this technique for the following situations: -- Linear inverse problems where the solution is modeled as a piecewise continuous function. The non convexity of the criterion is then due to the special choice of the prior; -- A nonlinear inverse problem which arises in inverse scattering where the non convexity of the criterion is due to the likelihood part. Keywords: Inverse problems, Regularization, Bayesian calculation, Global optimization, Graduated Non Convexity.
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arxiv:physics/0111121
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In this paper we propose a new Bayesian estimation method to solve linear inverse problems in signal and image restoration and reconstruction problems which has the property to be scale invariant. In general, Bayesian estimators are {\em nonlinear} functions of the observed data. The only exception is the Gaussian case. When dealing with linear inverse problems the linearity is sometimes a too strong property, while {\em scale invariance} often remains a desirable property. As everybody knows one of the main difficulties with using the Bayesian approach in real applications is the assignment of the direct (prior) probability laws before applying the Bayes' rule. We discuss here how to choose prior laws to obtain scale invariant Bayesian estimators. In this paper we discuss and propose a familly of generalized exponential probability distributions functions for the direct probabilities (the prior $p(\xb)$ and the likelihood $p(\yb|\xb)$), for which the posterior $p(\xb|\yb)$, and, consequently, the main posterior estimators are scale invariant. Among many properties, generalized exponential can be considered as the maximum entropy probability distributions subject to the knowledge of a finite set of expectation values of some knwon functions.
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arxiv:physics/0111125
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DIAMOND is a new synchrotron light source currently being designed in the UK. The control system for DIAMOND will be a site wide monitoring and control system for the accelerators, beamlines and conventional facilities. Initial work on the control system has selected EPICS as the basis for the control system design. The requirements of the control system are presented. The technical solutions being considered to interface EPICS to the equipment being controlled are discussed together with the requirements for configuration and management of a large EPICS installation. Options being considered for the procurement, installation and commissioning of the control system are also presented.
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arxiv:physics/0111150
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We propose a simple cluster-based method with application to calculations of Compton profile anisotropies of ice. The convergence of the method is checked with respect to Crystal95 results. Increasing both basis-set quality and cluster sizes results in a decrease of the magnitude of theoretical Compton anisotropies. The agreement with experimental data is therefore improved towards previously calculated anisotropies. Moreover, analyzing directional autocorrelation functions shows an evidence for both anti-bonding and polarization effects.
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arxiv:physics/0111157
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We describe the software requirements and development methodology developed for the NLC control system. Given the longevity of that project, and the likely geographical distribution of the collaborating engineers, the planned requirements management process is somewhat more formal than the norm in high energy physics projects. The short term goals of the requirements process are to accurately estimate costs, to decompose the problem, and to determine likely technologies. The long term goal is to enable a smooth transition from high level functional requirements to specific subsystem and component requirements for individual programmers, and to support distributed development. The methodology covers both ends of that life cycle. It covers both the analytical and documentary tools for software engineering, and project management support.
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arxiv:physics/0111161
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In the last three years, the architecture of Frascati Tokamak Upgrade (FTU) experimental database has undergone meaningful modifications, data and codes have been moved from mainframe to UNIX platforms and AFS (Andrew File System) has been adopted as distributed file system. Further improvement we have added regards data storage system; the choice of SAN (Storage Area Network) over Fiber Channel, combined with power and flexibility of AFS, has made data management over FTU very reliable. Performance tests have been done, showing better transfer rate than previous system, based on JBOD modules with SCSI connection.
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arxiv:physics/0111164
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The tunneling time is here investigated by means of an electromagnetic model, for a system where a gap, between two parallel planes, acts as a classically-forbidden region for an impinging pulse with incidence angle larger than the critical angle. In all cases of frustrated total reflection we obtain a superluminal behavior both for phase and group delays.
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arxiv:physics/0111192
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We introduce a probabilistic model for protein sliding motion along DNA during the search of a target sequence. The model accounts for possible effects due to sequence-dependent interaction between the nonspecific DNA and the protein. As an example, we focus on T7 RNA-polymerase and exploit the available information about its interaction at the promoter site in order to investigate the influence of bacteriophage T7 DNA sequence on the dynamics of the sliding process. Hydrogen bonds in the major groove are used as the main sequence-dependent interaction between RNA-polymerase and DNA. The resulting dynamical properties and the possibility of an experimental verification are discussed in details. We show that, while at large times the process reaches a pure diffusive regime, it initially displays a sub-diffusive behavior. The subdiffusive regime can lasts sufficiently long to be of biological interest.
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arxiv:physics/0112007
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We have investigated structure and properties of small metal clusters using all-electron ab initio theoretical methods based on the Hartree-Fock approximation and density functional theory, perturbation theory and compared results of our calculations with the available experimental data and the results of other theoretical works. We have systematically calculated the optimized geometries of neutral and singly charged sodium clusters having up to 20 atoms, their multipole moments (dipole and quadrupole), static polarizabilities, binding energies per atom, ionization potentials and frequencies of normal vibration modes. Our calculations demonstrate the great role of many-electron correlations in the formation of electronic and ionic structure of small metal clusters and form a good basis for further detailed study of their dynamic properties, as well as structure and properties of other atomic cluster systems.
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arxiv:physics/0112038
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The motion of a pendulum is described as Simple Harmonic Motion (SHM) in case the initial displacement given is small. If we relax this condition then we observe the deviation from the SHM. The equation of motion is non-linear and thus difficult to explain to under-graduate students. This manuscript tries to simplify things.
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arxiv:physics/0112056
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A generalized formalism of the so-called non-adiabatic quantum molecular dynamics is presented, which applies for atomic many-body systems in external laser fields. The theory treats the nuclear dynamics and electronic transitions simultaneously in a mixed classical-quantum approach. Exact, self-consistent equations of motion are derived from the action principle by combining time-dependent density functional theory in basis expansion with classical molecular dynamics. Structure and properties of the resulting equations of motion as well as the energy and momentum balance equations are discussed in detail. Future applications of the formalism are briefly outlined.
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arxiv:physics/0112064
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In this paper, we introduce an estimate of the "commercial efficiency" of Santilli's hadronic reactors of molecular type (Patented and International Patents Pending) which convert a liquid feedstock (such as automotive antifreeze and oil waste, city or farm liquid waste, crude oil, etc.) into the clean burning magnegas plus heat acquired by the liquid feedstock. The "commercial efficiency" is defined as the ratio between the total energy output (energy in magnegas plus heat) and the electric energy used for its production, while the "scientific efficiency" is the usual ratio between the total energy output and the total energy input (the sum of the electric energy plus the energy in the liquid feedstock as well as that in the carbon electrodes). A primary purpose of this paper is to show that conventional thermochemistry does indeed predict a commercial efficiency bigger than one, although their values is considerably smaller than the actual efficiency measured in the reactors, thus indicating the applicability of the covering hadronic chemistry from which the reactors have received their name. We reach an upper limit of the commercial efficiency of 3.11 for the use of pure water as feedstock, and of 3.11 to 7.5 for a mixture of ethyleneglicole and water. The study of the heat produced by the reactions leads to large divergencies between the thermochemical predictions and experimental data of at least a factor of three. Such divergencies can only be explained with deviations from quantum chemistry in favor of the covering hadronic chemistry. In particular, the indicated large divergencies can only be explained with the assumption that the produced combustible gas has the new non-valence chemical structure of Santilli magnecules.
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arxiv:physics/0112067
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We have measured the 6s - 7p_{1/2,3/2} transition probabilities in atomic cesium using a direct absorption technique. We use our result plus other previously measured transition rates to derive an accurate value of the vector transition polarizability \beta and, consequently, re-evaluate the weak charge Q_W. Our derived value Q_W=-72.65(49) agrees with the prediction of the standard model to within one standard deviation.
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arxiv:physics/0112071
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Doing research is fighting, what any other thing the human being could do? Fight against powers or to get powers, that depends on us. Science can be a revolution or deadlocked idleness. Still waters, without hitting the stones along their history, trend to form bogs.
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arxiv:physics/0201012
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We introduce a novel heuristic global optimization method, energy landscape paving (ELP), which combines core ideas from energy surface deformation and tabu search. In appropriate limits, ELP reduces to existing techniques. The approach is very general and flexible and is illustrated here on two protein folding problems. For these examples, the technique gives faster convergence to the global minimum than previous approaches.
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arxiv:physics/0201054
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Influence of associative delusions (AD) onto development of physics and mathematics is investigated. The associative delusion (AD) means a mistake, appearing from incorrect associations, when a property of one object is attributed to another one. Examples of most ancient delusions are: (1) connection of the gravitation field direction with a preferred direction in space (instead of the direction towards the Earth centre), that had lead to the antipode paradox, (2) statement that the Earth (not the Sun) is the centre of the planetary system, that had lead to the Ptolemaic doctrine. Now these ADs have been overcame. In the paper one considers four modern and not yet got over ADs, whose corollaries are false space-time geometry in the micro world and most of problems and difficulties of the quantum field theory (QFT). One shows that ADs have a series of interesting properties: (1) ADs appear to be long-living delusions, because they are compensated partly by means of introduction of compensating (Ptolemaic) conceptions, (2) ADs influence on scientific investigations, generating a special pragmatic style (P-style) of investigations resembling experimental trial and error method, (3) acting on investigations directly and via P-style, ADs direct the science development into a blind alley. One considers concrete properties of modern ADs and the methods of their overcoming. From viewpoint of application the paper is an analysis of mistakes, made in the quantum theory development. One analyses reasons of these mistakes and suggests methods of their correction.
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arxiv:physics/0201065
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In the Hartree-Fock approximation the Pauli exclusion principle leads to a Schroedinger Eq. of an integro-differential form. We describe a new spectral noniterative method (S-IEM), previously developed for solving the Lippman-Schwinger integral equation with local potentials, which has now been extended so as to include the exchange nonlocality. We apply it to the restricted case of electron-Hydrogen scattering in which the bound electron remains in the ground state and the incident electron has zero angular momentum, and we compare the acuracy and economy of the new method to three other methods. One is a non-iterative solution (NIEM) of the integral equation as described by Sams and Kouri in 1969. Another is an iterative method introduced by Kim and Udagawa in 1990 for nuclear physics applications, which makes an expansion of the solution into an especially favorable basis obtained by a method of moments. The third one is based on the Singular Value Decomposition of the exchange term followed by iterations over the remainder. The S-IEM method turns out to be more accurate by many orders of magnitude than any of the other three methods described above for the same number of mesh points.
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arxiv:physics/0201066
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The connection between the quantum frequency of radiation by the transition of the electron from orbit n to orbit k and frequencies of circling of electron in these orbits for the atom of hydrogen is determined.
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arxiv:physics/0202005
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Using the geomagnetic storm of July 15, 2000 as an example, we investigated the dependence of GPS navigation system performance on the nightside at mid-latitudes on the level of geomagnetic disturbance. The investigation was based on the data from the global GPS system available through the Internet. It was shown that the number of GPS phase slips increases with the increasing level of disturbance and that there is a good correlation between the rate of Dst-variation and the frequency of slips. It was further shown that the relative frequency of slips has also a clearly pronounced aspect dependence. Phase slips of the GPS signal can be caused by the scattering from small-scale irregularities of the ionospheric E-layer. Phase slip characteristics are indicative of Farley-Buneman instabilities as a plausible physical mechanism that is responsible for the formation of geomagnetic field-aligned irregularities. Using simultaneous measurements of backscatter signal characteristics from the Irkutsk incoherent scatter radar and existing models for such irregularities, we estimated the order of magnitude of the expected phase fluctuations of the GPS signal at a few degrees.
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arxiv:physics/0202052
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A long cylindrical body of circular cross-section and homogeneous density may float in all orientations around the cylinder axis. It is shown that there are also bodies of non-circular cross-sections which may float in any direction. Apart from those found by Auerbach for rho=1/2 there are one-parameter families of cross-sections for rho not= 1/2 which have a p-fold rotation axis. For given p they exist for p-2 densities rho. There are strong indications, that for all p-2 densities one has the same family of cross-sections. (Proven in physics/0205059)
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arxiv:physics/0203061
|
The temporal dynamics of a storage-ring Free Electron Laser is here investigated with particular attention to the case in which an external modulation is applied to the laser-electron beam detuning. The system is shown to produce bifurcations, multi-furcations as well as chaotic regimes. The peculiarities of this phenomenon with respect to the analogous behavior displayed by conventional laser sources are pointed out. Theoretical results, obtained by means of a phenomenological model reproducing the evolution of the main statistical parameters of the system, are shown to be in a good agreement with experiments carried out on the Super-ACO Free Electron Laser.
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arxiv:physics/0203083
|
In many applications, such as those arising from the field of cellular networks, it is often desired to determine the interaction (graph) structure of a set of differential equations, using as data measured sensitivities. This note proposes an approach to this problem.
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arxiv:physics/0205003
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It is argued that electron can be treated as an anyon which carries a charge (-e) and a magnetic flux $\pm \frac{\Phi_{0}}{2}$ in the presence and absence of a uniform external magnetic field. This flux is shown to arise due to the spin of the electron. The flux associated with the electron spin is calculated using a semi-classical model which is based on the magnetic top model. In accordance with spherical top model it is assumed that the spin angular momentum of the electron is produced by the fictitious point charge (-e) rotating in a circular orbit. It is shown that the flux through the circular orbit is independent of the radius and $\frac{\Phi_{0}}{2}$ for a spin down electron and -$\frac{\Phi_{0}}{2}$ for a spin up one. Where $\Phi_{0}=\frac{hc}{e}$ is the flux quantum.
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arxiv:physics/0205038
|
Sir Joseph LARMOR showed in 1897 that an oscillating electric charge emits radiation energy proportional to (acceleration)$^2$. At first sight,the result appears to be valid for arbitrary accelerations. But, perpetual uniform acceleration has been a case of nagging doubts, as radiation reaction vanishes and the equivalence principle, as also conformal symmetry of Maxwell equations each require nil energy loss. Special hypotheses are devised by some to justify the assumption of radiation loss for both perpetual and non-perpetual (uniform) accelerations which, as in the case of (uniform) velocities, are really different. The problem is here simply resolved by an explicit computation to show absence of radiation for the perpetual case and by illustrating that Larmor formula makes sense {\it only if} there is {\it change} in acceleration, just as kinetic energy has nontrivial quantitative sense, only when there is change in velocity.
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arxiv:physics/0205046
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This paper describes the optimization of a variable energy degrader design for the Midwest Proton Radiotherapy Institute (MPRI) [1]. To optimize the energy degrader design we investigate the choice of an optimal material for the degrader, the beam emittance growth in the degrader, and the matching of the degraded beam with the acceptance of a medical beam line.
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arxiv:physics/0205061
|
This paper is a study of continuous time Singular Spectrum Analysis (SSA). We show that the principal eigenfunctions are solutions to a set of linear ODEs with constant coefficients. We also introduce a natural generalization of SSA, constructed using local (Lie-) transformation groups. The time translations used in standard SSA is a special case. The eigenfunctions then satisfy a simple type of linear ODE with time dependent coefficient, determined by the infinitesimal generator of the transformation group. Finally, more general one parameter mappings are considered.
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arxiv:physics/0205094
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Textual analysis of typical microbial genomes reveals that they have the statistical characteristics of a DNA sequence of a much shorter length. This peculiar property supports an evolutionary model in which a genome evolves by random mutation but primarily grows by random segmental self-copying. That genomes grew mostly by self-copying is consistent with the observation that repeat sequences in all genomes are widespread and intragenomic and intergenomic homologous genes are preponderance across all life forms. The model predicates the coexistence of the two competing modes of evolution: the gradual changes of classical Darwinism and the stochastic spurts envisioned in ``punctuated equilibrium''.
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arxiv:physics/0206024
|
The maximum bit-rate of a slab waveguide is ultimately determined by the waveguide dispersion. We show that while the maximum bit rate in a waveguide is inversely proportional to the waveguide's width, bit rate per unit width (i.e., spatial capacity) decreases, and in the limit of a zero-width waveguide it converges to a value, which is independent of the waveguide's refractive indices. This value is qualitatively equivalent to the transmission rate per unit of width in free space. We also show that in a 3D waveguide (e.g., fibers), unlike free space, the spatial capacity vanishes in the same limit.
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arxiv:physics/0206035
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A new state of the H$_2^+$ molecular ion with binding energy of 1.09$\times10^{-9}$ a.u. below the first dissociation limit is predicted, using highly accurate numerical nonrelativistic quantum calculations. It is the first L=0 excited state, antisymmetric with respect to the exchange of the two protons. It manifests itself as a huge p-H scattering length of $a=750\pm 5$ Bohr radii.
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arxiv:physics/0207007
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This article describes some collaborative activities of the authors, aimed at improving science education in elementary schools. These include curriculum enhancement, development of new apparatus (a wind tunnel), science-education web site contributions and production of a film about the physics of flight. The output of these projects is intended to be generally accessible or reproducible.
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arxiv:physics/0207051
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We introduce notions of free energy and loss in linear, absorbing dielectric media which are relevant to the regime in which the macroscopic Maxwell equations are themselves relevant. As such we solve a problem eluded to by Landau and Lifshitz in 1958, and later considered explicitly by Barash and Ginzburg, and Oughtsun and Sherman. As such we provide physically-relevant real-time notions of "energy" and "loss" in all analogous linear dissipative systems.
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arxiv:physics/0207117
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Proceeding from the concept of rational expectations, a new dynamic model of supply and demand in a single market with one supplier, one buyer, and one kind of commodity is developed. Unlike the cob-web dynamic theories with adaptive expectations that are made up of deterministic difference equations, the new model is cast in the form of stochastic differential equations. The stochasticity is due to random disturbances ("input") to endogenous variables. The disturbances are assumed to be stationary to the second order with zero means and given covariance functions. Two particular versions of the model with different endogenous variables are considered. The first version involves supply, demand, and price. In the second version the stock of commodity is added. Covariance functions and variances of the endogenous variables ("output") are obtained in terms of the spectral theory of stochastic stationary processes. The impact of both deterministic parameters of the model and the random input on the stochastic output is analyzed and new conditions of chaotic instability are found. If these conditions are met, the endogenous variables undergo unbounded chaotic oscillations. As a result, the market that would be stable if undisturbed loses stability and collapses. This phenomenon cannot be discovered even in principle in terms of any cobweb deterministic model.
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arxiv:physics/0207118
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The primary relaxation in glass forming supercooled liquids (SCLs) above the glass transformation temperature T_g is discussed in terms of the first-order (steepness) and the second-order (curvature) temperature derivatives of the observed primary relaxation timescale. We report new insights into the problem of the domain of the Vogel-Fulcher-Tamman (VFT) equation, raised by Stickel et al. (J. Chem. Phys.,1995, 1996) and discussed by Richert and Angell (ibid., 1998). A new ergodic-cluster Gaussian statistical approach to the problem is given based on Onsager's thermodynamic principle. The primary relaxation is described by the VFT equation below the crossover temperature T_c (known from mode coupling theory (MCT)), and above T_c by an extended (VFTE) equation obtained after accounting for cluster-size fluctuations. The timescale is parametrized by a finite number of observable parameters such as the steepness function m_T, the MCT slowing-down exponent gamma_c, and the VFT and VFTE strength indices D_g and D_c. The latter are defined at T_g and T_c, respectively, for the strongly and moderately SCL states, which show absolute thermodynamic instability at the same VFT temperature T_0, associated with the Kauzmann temperature. For both states the limiting cluster-size characteristics are derived from experiment. A thermodynamic-dynamic correspondence is established between the dynamic VFT equation and the thermodynamic Adam and Gibbs model. The problem of the irregular SCLs, which are not consistent with the standard VFT equation, such as salol, ortho-terphenyl, and bis-methoxy-enyl-cyclohexane, is also discussed.
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arxiv:physics/0208064
|
We confront, quantitatively, the theoretical description of the reaction-diffusion of a second order reaction to experiment. The reaction at work is \ca/CaGreen, and the reactor is a T-shaped microchannel, 10 $\mu$m deep, 200 $\mu$m wide, and 2 cm long. The experimental measurements are compared with the two-dimensional numerical simulation of the reaction-diffusion equations. We find good agreement between theory and experiment. From this study, one may propose a method of measurement of various quantities, such as the kinetic rate of the reaction, in conditions yet inaccessible to conventional methods.
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arxiv:physics/0208091
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The spectrum of the (L_i^3 + p-bar + 2e) four-body system was calculated in an adiabatic approach. The two-electron energies were approximated by a sum of two single-electron effective charge two-center energies as suggested in [6]. While the structure of the spectrum does not exclude the existence of long-lived states, their experimental observability is still to be clarified.
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arxiv:physics/0208102
|
Normal human heart rate shows complex fluctuations in time, which is natural, since heart rate is controlled by a large number of different feedback control loops. These unpredictable fluctuations have been shown to display fractal dynamics, long-term correlations, and 1/f noise. These characterizations are statistical and they have been widely studied and used, but much less is known about the detailed time evolution (dynamics) of the heart rate control mechanism. Here we show that a simple one-dimensional Langevin-type stochastic difference equation can accurately model the heart rate fluctuations in a time scale from minutes to hours. The model consists of a deterministic nonlinear part and a stochastic part typical to Gaussian noise, and both parts can be directly determined from the measured heart rate data. Studies of 27 healthy subjects reveal that in most cases the deterministic part has a form typically seen in bistable systems: there are two stable fixed points and one unstable one.
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arxiv:physics/0208103
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We discuss the origin of two classes of germinal centers that have been observed during humoral immune responses: Some germinal centers develop very well and give rise to a large number of high affinity antibody producing plasma cells. Other germinal center reaction are very weak and the output production is practically absent. We propose an explanation for this nearly all-or-none behavior of germinal center reactions: The affinity of the seeder B-cells to the antigen is the critical parameter that determines the fate of the germinal center reaction. This hypothesis is verified in the framework of a space-time simulation of germinal center reactions.
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arxiv:physics/0209009
|
This paper analyzes the suitability of a beamed propulsion concept having properties consistent with the impulse gravity generator described by Podkletnov et al. [physics/0108005]. The use of this propulsion concept for orbital maneuver, Earth-to-orbit, interplanetary, and interstellar applications based on presently available experimental results and theory is considered, and areas for future research needed to better characterize this phenomenon are discussed. A beam of radiation or particles with the properties described for the impulse gravity generator would appear to be an excellent candidate for use in beamed spacecraft propulsion. Besides the usual benefits of beamed propulsion, it would not need sails or other special spacecraft components to function, could safely provide high accelerations to delicate components, and might operate at higher efficiencies than other beamed propulsion concepts.
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arxiv:physics/0209023
|
Length scales are determined that govern the behavior at small separations of the correlations of fluid-particle acceleration, viscous force, and pressure gradient. The length scales and an associated universal constant are quantified on the basis of published data. The length scale governing pressure spectra at high wave numbers is discussed. Fluid-particle acceleration correlation is governed by two length scales; one arises from the pressure gradient, the other from the viscous force.
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arxiv:physics/0209029
|
We present a genetic algorithm developed (GA) to optimize molecular AF_6 cluster configurations with respect to their energy. The method is based on the Darvin's evolutionary theory: structures with lowest energies survive in a system of fixed number of clusters. Two existing structures from a given population are combined in a special way to produce a new structure (child) which is kept if its energy is lower than the highest energy in the ensemble. To keep the population constant we reject the structure with the highest energy. This algorithm gives a better result than the optimization techniques used previously. Using the GA we have found a new structure corresponding to the (seemingly) global minimum. The most important result is that the new structure is detected only if the molecular cluster contains more than a critical number of molecules.
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arxiv:physics/0209055
|
Artificial Life provides the opportunity to study the emergence and evolution of simple ecosystems in real time. We give an overview of the advantages and limitations of such an approach, as well as its relation to individual-based modeling techniques. The Digital Life system Avida is introduced and prospects for experiments with ab initio evolution (evolution "from scratch"), maintenance, as well as stability of ecosystems are discussed.
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arxiv:physics/0209081
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Lochlainn O'Raifeartaigh and his work are recalled; the connection between fluid mechanics -- his last research topic -- and noncommuting gauge fields is explained.
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arxiv:physics/0209108
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Nowadays, commonly used Resistive Plate Chambers (RPCs) have counting rate capabilities of ~10E4Hz/cm2 and position resolutions of ~1cm. We have developed small prototypes of RPCs (5x5 and 10x10cm2) having rate capabilities of up to 10E7Hz/cm2 and position resolutions of 50 micron("on line" without application of any treatment method like "center of gravity"). The breakthrough in achieving extraordinary rate and position resolutions was only possible after solving several serious problems: RPC cleaning and assembling technology, aging, spurious pulses and afterpulses, discharges in the amplification gap and along the spacers. High-rate, high-position resolution RPCs can find a wide range of applications in many different fields, for example in medical imaging. RPCs with the cathodes coated by CsI photosensitive layer can detect ultraviolet photons with a position resolution that is better than ~30 micron. Such detectors can also be used in many applications, for example in the focal plane of high resolution vacuum spectrographs or as image scanners.
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arxiv:physics/0210006
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We investigate the work dissipated during the irreversible unfolding of single molecules by mechanical force, using the simplest model necessary to represent experimental data. The model consists of two levels (folded and unfolded states) separated by an intermediate barrier. We compute the probability distribution for the dissipated work and give analytical expressions for the average and variance of the distribution. To first order, the amount of dissipated work is directly proportional to the rate of application of force (the loading rate), and to the relaxation time of the molecule. The model yields estimates for parameters that characterize the unfolding kinetics under force in agreement with those obtained in recent experimental results (Liphardt, J., et al. (2002) {\em Science}, {\bf 296} 1832-1835). We obtain a general equation for the minimum number of repeated experiments needed to obtain an equilibrium free energy, to within $k_BT$, from non-equilibrium experiments using the Jarzynski formula. The number of irreversible experiments grows exponentially with the ratio of the average dissipated work, $\bar{\Wdis}$, to $k_BT$.}
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arxiv:physics/0210063
|
The use of covariant projection finite elements in the efficient 3-D vector finite element analysis of wave guide is presented.
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arxiv:physics/0210079
|
We study experimentally and theoretically the polarization alternation during the switch-on transient of a quasi-isotropic CO$_2$ laser emitting on the fundamental mode. The observed transient dynamics is well reproduced by means of a model which provides a quantitative discrimination between the intrinsic asymmetry due to the kinetic coupling of molecules with different angular momenta, and the extrinsic anisotropies, due to a tilted intracavity window. Furthermore, the experiment provides a numerical assignment for the decay rate of the coherence term for a CO$_2$ laser.
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arxiv:physics/0210086
|
We study the three-dimensional static configurations of nonhomogeneous Kirchhoff filaments with periodically varying Young's modulus. This type of variation may occur in long tandemly repeated sequences of DNA. We analyse the effects of the Young's modulus frequence and amplitude of oscillation in the stroboscopic maps, and in the regular (non chaotic) spatial configurations of the filaments. Our analysis shows that the tridimensional conformations of long filaments may depend critically on the Young's modulus frequence in case of resonance with other natural frequencies of the filament. As expected, far from resonance the shape of the solutions remain very close to that of the homogeneous case. In the case of biomolecules, it is well known that various other elements, besides sequence-dependent effects, combine to determine their conformation, like self-contact, salt concentration, thermal fluctuations, anisotropy and interaction with proteins. Our results show that sequence-dependent effects alone may have a significant influence on the shape of these molecules, including DNA. This could, therefore, be a possible mechanical function of the ``junk'' sequences.
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arxiv:physics/0210118
|
We analyse a RLC circuit taking the Second Law of Thermodynamics into consideration.
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arxiv:physics/0210124
|
In order to achieve a high quality, i. e. monoergetic, intense ion beam, we propose the use of a double layer target. The first layer, at the target front, consists of high-Z atoms, while the second (rear) layer is a thin coating of low-Z atoms. The high quality proton beams from the double layer target, irradiated by an ultra-intense laser pulse, are demonstrated with three dimensional Particle-in-Cell simulations.
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arxiv:physics/0211104
|
The structure and dynamics of aqueous solvation of ethanol and ethylene are studied by DFT-based Car-Parrinello molecular dynamics. We did not find an enhancement of the structure of the hydrogen bonded network of hydrating water molecules. Both ethanol and ethylene can easily be accommodated in the hydrogen-bonded network of water molecules without altering its structure. This is supports the conclusion from recent neutron diffraction experiments that there is no hydrophobic hydration around small hydrophobic groups. Analysis of the electronic charge distribution using Wannier functions shows that the dipole moment of ethanol increases from 1.8 D to 3.1 D upon solvation, while the apolar ethylene molecule attains an average dipole moment of 0.5 D. For ethylene, we identified configurations with $\pi$-H bonded water molecules, that have rare four-fold hydrogen-bonded water coordination, yielding instantaneous dipole moments of ethylene of up to 1 D. The results provide valuable information for the improvement of empirical force fields, and point out that for an accurate description of the aqueous solvation of ethanol, and even of the apolar ethylene, polarizable force fields are required.
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arxiv:physics/0212007
|
On the basis of the data given in the works of different authors a criterion of phase-photometric method of measurement of energy angle of divergence has been formulated. Validity of application of the obtained relations for a ray beam with an arbitrary diameter and an arbitrary shape of the wave front has been proved. Advantages of the proposed phase-photometric method in comparison with the focal-spot method have been confirmed. Necessity and possibility of building a standard solid angle has been proved.
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arxiv:physics/0212012
|
A population of neurons typically exhibits a broad diversity of responses to sensory inputs. The intuitive notion of functional classification is that cells can be clustered so that most of the diversity is captured in the identity of the clusters rather than by individuals within clusters. We show how this intuition can be made precise using information theory, without any need to introduce a metric on the space of stimuli or responses. Applied to the retinal ganglion cells of the salamander, this approach recovers classical results, but also provides clear evidence for subclasses beyond those identified previously. Further, we find that each of the ganglion cells is functionally unique, and that even within the same subclass only a few spikes are needed to reliably distinguish between cells.
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arxiv:physics/0212114
|
The interaction energies between the different types of bases of a single strand of DNA molecule have been calculated. Using these original values of energies the harmonic behavior of a number of base patterns of DNA has been studied. In view of the great interest aroused by the discovery of the role of the telomere segment of the DNA in the replication process and its possible link with the aging process, we have investigated, with simple models, the harmonic behavior of the telomeric pattern of bases as well as the thermodynamic response in the biological system. With these results a conclusion on the probable role of the telomeric pattern on aging has also been drawn. Here the calculated values of harmonic frequencies of the telomeric pattern of bases and of other possible patterns show that the telomeric pattern is associated with the highest vibrational frequency among all patterns of base combinations at the replication end of DNA. This seems to suggest that due to the existing telomeric pattern being closest to the frequencies of the electromagnetic radiation coming from sunlight, resonance of the telomeric frequency with such radiation may be responsible for damage to the reproductive ability of the cells and consequent aging and other problems. On the other hand in the last part of this work we have calculated the thermal vibrational amplitudes of the telomeric pattern and other possible patterns which show that the amplitude for the telomeric pattern is the least, and this suggests that the telomeric pattern is more mechanically and thermally stable than other possible patterns in the biological environment against damage from ordinary heat and mechanical effects.
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arxiv:physics/0301031
|
We present a theorical investigation of the optical transmission of a dielectric grating carved in a tungsten layer. For appropriate wavelengths tungsten shows indeed a dielectric behaviour. Our numerical simulations leads to theoretical results similar to those found with metallic systems studied in earlier works. The interpretation of our results rests on the idea that the transmission is correlated with the resonant response of eigenmodes coupled to evanescent diffraction orders.
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arxiv:physics/0301068
|
Newton's law of motion relative to an inertial frame ("the laboratory") for a particle subject to a force acting at a certain time may be interpreted in either of two ways: (1) The force acting on the particle during an infinitesimal time imparts to the laboratory a boost (impulse divided by the mass) while the particle maintains the original velocity relative to the new frame and (2) The force acting on the particle during an infinitesimal time imparts to the particle the same boost relative to the proper frame of the particle which moves with the original velocity with respect to the laboratory. We show that the relativistic law of motion admits both interpretations, the first of which is in fact equivalent to the law of motion. As a consequence, we show that the relativistic law of motion may also be reformulated as "force equals mass times acceleration" in analogy with Newton's law, but with a relativistic mass and a relativistic acceleration defined in terms of the relativistic addition law of velocities, rather than ordinary mass and ordinary vectorial addition of velocities that lead to the classical acceleration and to Newton's law.
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arxiv:physics/0302065
|
We study the class of endlessly single-mode all-silica photonic crystal fibers with a triangular air-hole cladding. We consider the sensibility to longitudinal nonuniformities and the consequences and limitations for realizing low-loss large-mode area photonic crystal fibers. We also discuss the dominating scattering mechanism and experimentally we confirm that both macro and micro-bending can be the limiting factor.
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arxiv:physics/0302072
|
It is generally believed that quarks being confined inside nucleons should make their presence felt explictly in nuclei only at higher energies. However it is shown here that the hole in the centre of $ ^{3}H $, $ ^{3}He $ and $ ^{4}He $, the neutron halos in nuclei, the $ \alpha - $ and other clustering effects in nuclei and the nuclear molecules all basically arise due to the same underlying quark effects. Also the role of triton clustering in very neutron rich nuclei is emphasized. These require the concept of hidden colour states which arise from the confinement ideas of QCD for the multi-quark systems.
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arxiv:physics/0303019
|
In this essay the ontological structure of reality is explored. The question of reducibility of biology to physics is considered in the context of their ultimate principles. It is shown that biology is an ontologically autonomous science and is based on its own, independent ultimate principle that is independent from that of physics. In the next step it is shown that self-consciousness represents a separate realm with its own, ontologically autonomous, ultimate principle. Understanding that reality is based on ultimate principles, a new possibility arises to interpret the origin of physical laws.
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arxiv:physics/0303025
|
We investigate a map-based model of paced cardiac muscle in the presence of closed-loop feedback control. The model relates the duration of an action potential to the preceding diastolic interval as well as the preceding action potential duration and thus has some amount of `memory.' We find that the domain of control depends on this memory, independently of the specific functional form of the map. The memory-dependent domain of control can encompass large feedback gains, thus providing the first possible explanation of the recent experimental results of Hall et al. [Phys. Rev. Lett, 88, 198102 (2002)] on controlling alternans in small pieces of rapidly-paced cardiac muscle.
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arxiv:physics/0303099
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