2,122 research outputs found
Crystal structure of LaTiO_3.41 under pressure
The crystal structure of the layered, perovskite-related LaTiO_3.41
(La_5Ti_5O_{17+\delta}) has been studied by synchrotron powder x-ray
diffraction under hydrostatic pressure up to 27 GPa (T = 295 K). The
ambient-pressure phase was found to remain stable up to 18 GPa. A sluggish, but
reversible phase transition occurs in the range 18--24 GPa. The structural
changes of the low-pressure phase are characterized by a pronounced anisotropy
in the axis compressibilities, which are at a ratio of approximately 1:2:3 for
the a, b, and c axes. Possible effects of pressure on the electronic properties
of LaTiO_3.41 are discussed.Comment: 5 pages, 6 figure
When can Fokker-Planck Equation describe anomalous or chaotic transport?
The Fokker-Planck Equation, applied to transport processes in fusion plasmas,
can model several anomalous features, including uphill transport, scaling of
confinement time with system size, and convective propagation of externally
induced perturbations. It can be justified for generic particle transport
provided that there is enough randomness in the Hamiltonian describing the
dynamics. Then, except for 1 degree-of-freedom, the two transport coefficients
are largely independent. Depending on the statistics of interest, the same
dynamical system may be found diffusive or dominated by its L\'{e}vy flights.Comment: 4 pages. Accepted in Physical Review Letters. V2: only some minor
change
Spin of ground state baryons
We calculate the quark spin contribution to the total angular momentum of
flavor octet and flavor decuplet ground state baryons using a spin-flavor
symmetry based parametrization method of quantum chromodynamics. We find that
third order SU(6) symmetry breaking three-quark operators are necessary to
explain the experimental result Sigma_1=0.32(10). For spin 3/2 decuplet baryons
we predict that the quark spin contribution is Sigma_3=3.93(22), i.e.
considerably larger than their total angular momentum.Comment: 8 page
A classical scaling theory of quantum resonances
The quantum resonances occurring with delta-kicked particles are studied with
the help of a fictitious classical limit, establishing a direct correspondence
between the nearly resonant quantum motion and the classical resonances of a
related system. A scaling law which characterizes the structure of the resonant
peaks is derived and numerically demonstrated.Comment: 4 pages, 2 Fig
Tracking quasi-classical chaos in ultracold boson gases
We study the dynamics of a ultra-cold boson gas in a lattice submitted to a
constant force. We track the route of the system towards chaos created by the
many-body-induced nonlinearity and show that relevant information can be
extracted from an experimentally accessible quantity, the gas mean position.
The threshold nonlinearity for the appearance of chaotic behavior is deduced
from KAM arguments and agrees with the value obtained by calculating the
associated Lyapunov exponent.Comment: 4 pages, revtex4, submitted to PR
Extremely Small Energy Gap in the Quasi-One-Dimensional Conducting Chain Compound SrNbO
Resistivity, optical, and angle-resolved photoemission experiments reveal
unusual one-dimensional electronic properties of highly anisotropic
SrNbO. Along the conducting chain direction we find an extremely small
energy gap of only a few meV at the Fermi level. A discussion in terms of
typical 1D instabilities (Peierls, Mott-Hubbard) shows that neither seems to
provide a satisfactory explanation for the unique properties of SrNbO.Comment: 4 pages, 3 figure
Position and velocity space diffusion of test particles in stochastic electromagnetic fields
The two--dimensional diffusive dynamics of test particles in a random
electromagnetic field is studied. The synthetic electromagnetic fluctuations
are generated through randomly placed magnetised ``clouds'' oscillating with a
frequency . We investigate the mean square displacements of particles
in both position and velocity spaces. As increases the particles
undergo standard (Brownian--like) motion, anomalous diffusion and ballistic
motion in position space. Although in general the diffusion properties in
velocity space are not trivially related to those in position space, we find
that energization is present only when particles display anomalous diffusion in
position space. The anomalous character of the diffusion is only in the
non--standard values of the scaling exponents while the process is Gaussian.Comment: 10 pages, 4 figure
Pseudo-classical theory for fidelity of nearly resonant quantum rotors
Using a semiclassical ansatz we analytically predict for the fidelity of
delta-kicked rotors the occurrence of revivals and the disappearance of
intermediate revival peaks arising from the breaking of a symmetry in the
initial conditions. A numerical verification of the predicted effects is given
and experimental ramifications are discussed.Comment: Shortened and improved versio
Coherent acceleration of material wavepackets in modulated optical fields
We study the quantum dynamics of a material wavepacket bouncing off a
modulated atomic mirror in the presence of a gravitational field. We find the
occurrence of coherent accelerated dynamics for atoms beyond the familiar
regime of dynamical localization. The acceleration takes place for certain
initial phase space data and within specific windows of modulation strengths.
The realization of the proposed acceleration scheme is within the range of
present day experimental possibilities
Degeneracy Between the Regge Slope of Mesons and Baryons from Supersymmetry
We consider the degeneracy between the Regge slope of mesons and baryons in
QCD. We argue that within the "orientifold large-N approximation"
asymptotically massive mesons and baryons become supersymmetric partners and
hence degenerate. To this end, we generalize QCD by a SU(N) theory with a quark
in the two-index antisymmetric representation. We show that in this framework
the meson is represented by an oriented bosonic QCD-string and the baryon is
represented by an un-oriented fermionic QCD-string. At large-N, due to an
equivalence with super Yang-Mills, the tensions of the bosonic and the
fermionic strings coincide. Our description of mesons and baryons as oriented
and un-oriented bosonic and fermionic QCD-strings is in full agreement with the
spectra of open strings in the dual type 0' string theory.Comment: v2: extended version. Appendices and references adde
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