-
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
-
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
-
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
-
2010-05-30
We consider the behavior of open strings on AdS wormholes in Gauss-Bonnet
theory, which are the Gauss-Bonnet gravity duals of a pair of field theories. A
string with both endpoints on the same side of the wormhole describes two
charges within the same field theory, which exhibit Coulomb interaction for
small separation. On the other hand, a string extending through the wormhole
describes two charges which live in different field theories, and they exhibit
a spring-like confining potential. A transition occurs when there is a pair of
charges present within each field theory: for small separation each pair of
charges exhibits Coulomb interaction, while for large separation the charges in
the different field theories pair up and exhibit confinement. If two charges
move faster than a critical speed, then they exhibit a separation gap and
energy is transferred from the leading charge to the lagging one.
Author(s):
Mir Ali
Frenny Ruiz
Carlos Saint-Victor
Justin F. Vazquez-Poritz
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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