10,280 research outputs found
The t-J model on a semi-infinite lattice
The hole spectral function of the t-J model on a two-dimensional
semi-infinite lattice is calculated using the spin-wave and noncrossing
approximations. In the case of small hole concentration and strong
correlations, , several near-boundary site rows appear to be depleted
of holes. The reason for this depletion is a deformation of the magnon cloud,
which surrounds the hole, near the boundary. The hole depletion in the boundary
region leads to a more complicated spectral function in the boundary row in
comparison with its bulk shape.Comment: 8 pages, 5 figure
Coherent Excitation of the 6S1/2 to 5D3/2 Electric Quadrupole Transition in 138Ba+
The electric dipole-forbidden, quadrupole 6S1/2 5D3/2 transition in Ba+
near 2051 nm, with a natural linewidth of 13 mHz, is attractive for potential
observation of parity non-conservation, and also as a clock transition for a
barium ion optical frequency standard. This transition also offers a direct
means of populating the metastable 5D3/2 state to measure the nuclear magnetic
octupole moment in the odd barium isotopes. Light from a diode-pumped, solid
state Tm,Ho:YLF laser operating at 2051 nm is used to coherently drive this
transition between resolved Zeeman levels in a single trapped 138Ba+ ion. The
frequency of the laser is stabilized to a high finesse Fabry Perot cavity at
1025 nm after being frequency doubled. Rabi oscillations on this transition
indicate a laser-ion coherence time of 3 ms, most likely limited by ambient
magnetic field fluctuations.Comment: 5 pages, 5 figure
Chromatic Ramsey number of acyclic hypergraphs
Suppose that is an acyclic -uniform hypergraph, with . We
define the (-color) chromatic Ramsey number as the smallest
with the following property: if the edges of any -chromatic -uniform
hypergraph are colored with colors in any manner, there is a monochromatic
copy of . We observe that is well defined and where
is the -color Ramsey number of . We give linear upper bounds
for when T is a matching or star, proving that for , and where
and are, respectively, the -uniform matching and star with
edges.
The general bounds are improved for -uniform hypergraphs. We prove that
, extending a special case of Alon-Frankl-Lov\'asz' theorem.
We also prove that , which is sharp for . This is
a corollary of a more general result. We define as the 1-intersection
graph of , whose vertices represent hyperedges and whose edges represent
intersections of hyperedges in exactly one vertex. We prove that for any -uniform hypergraph (assuming ). The proof uses the list coloring version of Brooks' theorem.Comment: 10 page
Human Perception and the Color of Flavor
Human taste perception can be analyzed in different areas of study. Physiology and psychology work together to construct the way we taste, and our sense of taste is not obtained merely from the tongue. The process of tasting involves olfaction, vision, and texture reception to form our overall perception of taste. The present study involved 25 participants who tasted and rated multiple samples of flavored gelatin. Half of the gelatin samples were unlikely color/flavor combinations, and half were unlikely flavor/scent combinations. Responses to the flavors as perceived were collected and used to gain insight into the interactions among sight, smell, and taste perception
Resonance peak in underdoped cuprates
The magnetic susceptibility measured in neutron scattering experiments in
underdoped YBaCuO is interpreted based on the self-consistent
solution of the t-J model of a Cu-O plane. The calculations reproduce correctly
the frequency and momentum dependencies of the susceptibility and its variation
with doping and temperature in the normal and superconducting states. This
allows us to interpret the maximum in the frequency dependence -- the resonance
peak -- as a manifestation of the excitation branch of localized Cu spins and
to relate the frequency of the maximum to the size of the spin gap. The
low-frequency shoulder well resolved in the susceptibility of superconducting
crystals is connected with a pronounced maximum in the damping of the spin
excitations. This maximum is caused by intense quasiparticle peaks in the hole
spectral function for momenta near the Fermi surface and by the nesting.Comment: 9 pages, 6 figure
Optical properties, electron-phonon coupling, and Raman scattering of vanadium ladder compounds
The electronic structure of two V-based ladder compounds, the quarter-filled
NaVO in the symmetric phase and the iso-structural half-filled
CaVO is investigated by ab initio calculations. Based on the
bandstructure we determine the dielectric tensor of these
systems in a wide energy range. The frequencies and eigenvectors of the fully
symmetric A phonon modes and the corresponding electron-phonon and
spin-phonon coupling parameters are also calculated from first-principles. We
determine the Raman scattering intensities of the A phonon modes as a
function of polarization and frequency of the exciting light.
All results, i.e. shape and magnitude of the dielectric function, phonon
frequencies and Raman intensities show very good agreement with available
experimental data.Comment: 11 pages, 10 figure
Relativistic diffusion
We discuss a relativistic diffusion in the proper time in an approach of
Schay and Dudley. We derive (Langevin) stochastic differential equations in
various coordinates.We show that in some coordinates the stochastic
differential equations become linear. We obtain momentum probability
distribution in an explicit form.We discuss a relativistic particle diffusing
in an external electromagnetic field. We solve the Langevin equations in the
case of parallel electric and magnetic fields. We derive a kinetic equation for
the evolution of the probability distribution.We discuss drag terms leading to
an equilibrium distribution.The relativistic analog of the Ornstein-Uhlenbeck
process is not unique. We show that if the drag comes from a diffusion
approximation to the master equation then its form is strongly restricted. The
drag leading to the Tsallis equilibrium distribution satisfies this restriction
whereas the one of the Juettner distribution does not. We show that any
function of the relativistic energy can be the equilibrium distribution for a
particle in a static electric field. A preliminary study of the time evolution
with friction is presented. It is shown that the problem is equivalent to
quantum mechanics of a particle moving on a hyperboloid with a potential
determined by the drag. A relation to diffusions appearing in heavy ion
collisions is briefly discussed.Comment: 9 pages,some numerical factors correcte
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