Pseudo-Riemannian Jacobi-Videv Manifolds

2007-08-08

We exhibit several families of Jacobi-Videv pseudo-Riemannian manifolds which are not Einstein. We also exhibit Jacobi-Videv algebraic curvature tensors where the Ricci operator defines an almost complex structure.

Author(s): P. Gilkey S. Nikcevic

Totalistic two-dimensional cellular automata exhibiting global periodic behavior

1999-03-29

We have determined families of two-dimensional deterministic totalistic cellular automaton rules whose stationary density of active sites exhibits a period two in time. Each family of deterministic rules is characterized by an ``average probabilistic totalistic rule'' exhibiting the same periodic behavior.

Author(s): Nino Boccara Michel Roger

Localization and Capacitance Fluctuations in Disordered Au Nano-junctions

2004-02-02

Nano-junctions, containing atomic-scale gold contacts between strongly disordered leads, exhibit different transport properties at room temperature and at low temperature. At room temperature, the nano-junctions exhibit conductance quantization effects. At low temperatures, the contacts exhibit Coulomb-Blockade. We show that the differences between the room-temperature and low temperature properties arise from the localization of electronic states in the leads. The charging energy and capacitance of the nano-junctions exhibit strong fluctuations with applied magnetic field at low temperature, as predicted theoretically.

Author(s): M. Bowman A. Anaya A. L. Korotkov D. Davidovic

Higgs Boson in Superconductors

2001-09-21

Superfluid helium, describable by a two-component order parameter, exhibits only the Bogolubov mode with energy $\to 0$ at long wavelengths, while a Lorentz-invariant theory with a two-component order parameter exhibits a finite energy mode at long wavelengths (the Higgs Boson), besides the above mass-less mode. The mass-less mode moves to high energies if it couples to electromagnetic fields (the Anderson-Higgs mechanism). Superconductors, on the other hand have been theoretically and experimentally shown to exhibit both modes. This occurs because the excitations in superconductors have an (approximate) particle-hole symmetry and therefore show a similarity to Lorentz-invariant theories.

Author(s): C. M. Varma

Interplay of frequency-synchronization with noise: current resonances, giant diffusion and diffusion-crests

2001-12-17

We elucidate how the presence of noise may significantly interact with the synchronization mechanism of systems exhibiting frequency-locking. The response of these systems exhibits a rich variety of behaviors, such as resonances and anti-resonances which can be controlled by the intensity of noise. The transition between different locked regimes provokes the development of a multiple enhancement of the effective diffusion. This diffusion behavior is accompanied by a crest-like peak-splitting cascade when the distribution of the lockings is self-similar, as it occurs in periodic systems that are able to exhibit a Devil's staircase sequence of frequency-lockings.

Author(s): D. Reguera P. Reimann P. Hänggi J. M. Rubí

Tunneling effect of the spin-2 Bose condensate driven by external magnetic fields

2003-11-15

In this paper, we have studied tunneling effect of the spin-2 Bose condensate driven by external magnetic field. We find that the population transfers among spin-0 and spin-$\pm1$, spin-0 and spin-$\pm2$ exhibit the step structure under the external cosinusoidal magnetic field respectively, but there do not exist step structure among spin-$\pm1$ and spin-$\pm2$. The tunneling current among spin-$\pm1$ and spin-$\pm2$ may exhibit periodically oscillation behavior, but among spin-0 and spin-$\pm1$, spin-0 and spin-$\pm2$, the tunneling currents exhibit irregular oscillation behavior.

Author(s): Zhao-xian Yu Zhi-yong Jiao

Physical realization of the four color problem in quantum systems

2005-10-07

A multi-component electron model on a lattice is constructed whose ground state exhibits a spontaneous ordering which follows the rule of map-coloring used in the solution of the four color problem. The number of components is determined by the Euler characteristics of a certain surface into which the lattice is embedded. Combining the concept of chromatic polynomials with the Heawood-Ringel-Youngs theorem, we derive an index theorem relating the degeneracy of the ground state with a hidden topology of the lattice. The system exhibits coloring transition and hidden-topological structure transition. The coloring phase exhibits a topological order.

Author(s): Masanori Yamanaka Akinori Tanaka

Programs with Stringent Performance Objectives Will Often Exhibit Chaotic Behavior

1999-05-27

Software for the resolution of certain kind of problems, those that rate high in the Stringent Performance Objectives adjustment factor (IFPUG scheme), can be described using a combination of game theory and autonomous systems. From this description it can be shown that some of those problems exhibit chaotic behavior, an important fact in understanding the functioning of the related software. As a relatively simple example, it is shown that chess exhibits chaotic behavior in its configuration space. This implies that static evaluators in chess programs have intrinsic limitations.

Author(s): M. Chaves

Can Small Free Methane Clusters Exhibit Phase-like Transitions?

2003-12-16

Low-temperature (below 60K) phase changes of free clusters containing 50, 137, and 229 methane molecules have been observed in isoenergetic Molecular Dynamics computations. Bulk solid methane exhibits structural phase transformation at 20.4 K. However, clusters of 50 molecules already melt at about 25 K, which makes the observation of solid-solid transformations rather challenging. Molecular Dynamics calculations of isoenergetic free methane clusters show that they exhibit transformations from an orientationally-ordered (~ 10K) and a disordered phase (above 20K). There is no hysteresis in the cooling-heating regime - a signal for continuous transition.

Author(s): E. Daykova Ana Proykova

Stochastic Resonance with a Single Metastable State

2007-05-29

We study thermal instability in NbN superconducting stripline resonators. The system exhibits extreme nonlinearity near a bifurcation, which separates a monostable zone and an astable one. The lifetime of the metastable state, which is locally stable in the monostable zone, is measure near the bifurcation and the results are compared with a theory. Near bifurcation, where the lifetime becomes relatively short, the system exhibits strong amplification of a weak input modulation signal. We find that the frequency bandwidth of this amplification mechanism is limited by the rate of thermal relaxation. When the frequency of the input modulation signal becomes comparable or larger than this rate the response of the system exhibits sub-harmonics of various orders.

Author(s): Eran Segev Baleegh Abdo Oleg Shtempluck Eyal Buks

Crosslinked networks of stiff filaments exhibit negative normal stress

2008-07-11

Motivated by recent experiments showing that stiff biopolymer gels exhibit highly unusual negative normal elastic stresses, we develop a computational model for stiff polymer networks subject to large strains. In all cases, we find that such networks develop normal stresses that are both negative and of magnitude comparable to the corresponding shear stress. We find that these normal stresses coincide with other nonlinearities in our networks, and specifically with compressive bucking of the individual filaments. Our results suggest that negative normal stresses are a characteristic feature of stiff (bio)polymer gels that have been shown to exhibit strong nonlinear elastic properties.

Author(s): Enrico Conti F. C. MacKintosh

Nonuniform hyperbolicity for C^1-generic diffeomorphisms

2008-09-19

We study the ergodic theory of non-conservative C^1-generic diffeomorphisms. First, we show that homoclinic classes of arbitrary diffeomorphisms exhibit ergodic measures whose supports coincide with the homoclinic class. Second, we show that generic (for the weak topology) ergodic measures of C^1-generic diffeomorphisms are nonuniformly hyperbolic: they exhibit no zero Lyapunov exponents. Third, we extend a theorem by Sigmund on hyperbolic basic sets: every isolated transitive set L of any C^1-generic diffeomorphism f exhibits many ergodic hyperbolic measures whose supports coincide with the whole set L. In addition, confirming a claim made by R. Man\'e in 1982, we show that hyperbolic measures whose Oseledets splittings are dominated satisfy Pesin's Stable Manifold Theorem, even if the diffeomorphism is only C^1.

Author(s): Flavio Abdenur Christian Bonatti Sylvain Crovisier

Spectral evolution in an insulator exhibiting linear specific heat

2009-10-26

We investigate the spectral evolution of an antiferromagnetic insulator, La$_{0.2}$Sr$_{0.8}$MnO$_3$ exhibiting linear specific heat using state-of-the-art high resolution photoemission spectroscopy. Experimental spectral functions exhibit Fermi liquid like energy dependence at all the temperatures studied. Room temperature spectrum possess finite density of states at the Fermi level that vanishes generating a soft gap at about 260 K (the magnetic transition temperature). High resolution spectra reveal a hard gap in the magnetically ordered phase (C-type antiferromagnet). These results indicate signature of an amorphous phase coexisting with the long range ordered phase in these materials.

Author(s): R. Bindu Ganesh Adhikary Sudhir K. Pandey Kalobaran Maiti

Fractal space-time fluctuations: A signature of quantumlike chaos in dynamical systems

2004-08-19

Dynamical systems in nature such as fluid flows, heart beat patterns, rainfall variability, stock market price fluctuations, etc. exhibit selfsimilar fractal fluctuations on all scales in space and time. Power spectral analyses of fractal fluctuations exhibit inverse power law form indicating long-range space-time correlations, identified as self-organized criticality. The author has proposed a general systems theory, which predicts the observed self-organized criticality as signatures of quantumlike chaos. The model shows that (1) the fractal fluctuations result from an overall logarithmic spiral trajectory with the quasiperiodic Penrose tiling pattern for the internal structure. Conventional power spectral analysis of such a logarithmic spiral trajectory will show a continuum of eddies with progressive increase in phase. (2) Power spectral analyses of fractal fluctuations of dynamical systems exhibit the universal inverse power law form of the statistical normal distribution. Such a result indicates that the additive amplitudes of eddies, when squared (namely the variance) represent the probabilities, a characteristic exhibited by the subatomic dynamics of quantum systems such as the electron or photon. Further, long-range space-time correlations or non-local connections such as that exhibited by macroscale dynamical systems characterize quantum systems also. Therefore selfsimilar fractal fluctuations generic to dynamical systems of all scales in nature is a signature of quantumlike chaos. The model concepts are applied to show that the frequency distribution of bases A, C, G, T in Human Chromosome Y DNA exhibit long-range spatial correlations.

Author(s): A. M. Selvam

Did SN 1989B Exhibit a Light Echo?

2002-10-10

The late light curves of SN 1989B exhibited an emission excess relative to other type Ia supernovae. We investigate whether this emission excess suggests light echo emission from this supernova, or rather intense background galaxy contamination at the location of the supernova. We conclude that stellar emission can better explain the late spectra, and that the emission excess is likely due to background contamination.

Author(s): P. A. Milne L. A. Wells

Bose-Einstein condensation and superfluidity in trapped atomic gases

2001-01-19

Bose-Einstein condensates confined in traps exhibit unique features which have been the object of extensive experimental and theoretical studies in the last few years. In this paper I will discuss some issues concerning the behaviour of the order parameter and the dynamic and superfluid effects exhibited by such systems.

Author(s): Sandro Stringari

Origin of room-temperature ferromagnetism in Mn doped semiconducting CdGeP2

2001-11-29

CdGeP2 chalcopyrites doped with Mn have been recently found to exhibit room temperature ferromagnetism. Isovalent substitution of the Cd site is expected, however, to create antiferromagnetism, in analogy with the well-known CdTe:Mn (d^5) case. However, chalcopyrite semiconductors exhibit low-energy intrinsic defects. We show theoretically how ferromagnetism results from the interaction of Mn with hole-producing intrinsic defects.

Author(s): Priya Mahadevan Alex Zunger

Spatial Patterns Induced Purely by Dichotomous Disorder

2003-03-18

We study conditions under which spatially extended systems with coupling a la Swift-Hohenberg exhibit spatial patterns induced purely by the presence of quenched dichotomous disorder. Complementing the theoretical results based on a generalized mean-field approximation, we also present numerical simulations of particular dynamical systems that exhibit the proposed phenomenology.

Author(s): J. Buceta Katja Lindenberg

A lattice model exhibiting radiation-induced anomalous conductivity

2003-06-10

A lattice-based model exhibits an unusual conductivity when it is subjected to both a static magnetic field and electromagnetic radiation. This conductivity anomaly may explain some aspects of the recently observed "zero-resistance states". PACS: 72.40+w, 73.40-c, 73.63 Keywords: Zero-resistance states, negative conductivity, lattice model

Author(s): J. C. Kimball Keeyung Lee

Klein spin model ground states on general lattices

2006-06-05

We prove that in short range Klein spin models on general lattices, all ground states are of the dimer type- each fundamental plaquette must host at least one singlet. These ground states are known to rigorously exhibit high dimensional fractionalization. When combined with a recent theorem, this establishes that Klein spin models exhibit topological order on the pyrochlore and checkerboard lattices.

Author(s): Zohar Nussinov