21,551 research outputs found
Many-polaron states in the Holstein-Hubbard model
A variational approach is proposed to determine some properties of the
adiabatic Holstein-Hubbard model which describes the interactions between a
static atomic lattice and an assembly of fermionic charge carriers. The sum of
the electronic energy and the lattice elastic energy is proved to have minima
with a polaron structure in a certain domain of the phase diagram. Our
analytical work consists in the expansion of these energy minima from the zero
electronic transfer limit which remarkably holds for a finite amplitude of the
onsite Hubbard repulsion and for an unbounded lattice size.Comment: submitted to Journal of Statistical Physic
Visual motion processing and human tracking behavior
The accurate visual tracking of a moving object is a human fundamental skill
that allows to reduce the relative slip and instability of the object's image
on the retina, thus granting a stable, high-quality vision. In order to
optimize tracking performance across time, a quick estimate of the object's
global motion properties needs to be fed to the oculomotor system and
dynamically updated. Concurrently, performance can be greatly improved in terms
of latency and accuracy by taking into account predictive cues, especially
under variable conditions of visibility and in presence of ambiguous retinal
information. Here, we review several recent studies focusing on the integration
of retinal and extra-retinal information for the control of human smooth
pursuit.By dynamically probing the tracking performance with well established
paradigms in the visual perception and oculomotor literature we provide the
basis to test theoretical hypotheses within the framework of dynamic
probabilistic inference. We will in particular present the applications of
these results in light of state-of-the-art computer vision algorithms
Multi-dimensional metric approximation by primitive points
We refine metrical statements in the style of the Khintchine-Groshev Theorem
by requiring certain coprimality constraints on the coordinates of the integer
solutions
Liquid bridging of cylindrical colloids in near-critical solvents
Within mean field theory, we investigate the bridging transition between a
pair of parallel cylindrical colloids immersed in a binary liquid mixture as a
solvent which is close to its critical consolute point . We determine the
universal scaling functions of the effective potential and of the force between
the colloids. For a solvent which is at the critical concentration and close to
, we find that the critical Casimir force is the dominant interaction at
close separations. This agrees very well with the corresponding Derjaguin
approximation for the effective interaction between the two cylinders, while
capillary forces originating from the extension of the liquid bridge turn out
to be more important at large separations. In addition, we are able to infer
from the wetting characteristics of the individual colloids the first-order
transition of the liquid bridge connecting two colloidal particles to the
ruptured state. While specific to cylindrical colloids, the results presented
here provide also an outline for identifying critical Casimir forces acting on
bridged colloidal particles as such, and for analyzing the bridging transition
between them.Comment: 23 pages, 12 figure
Recent X-ray observations of intermediate BL Lac objects
We present recent ROSAT, ASCA and SAX observations of intermediate BL Lac
objects (IBLs), i.e. BL Lacs which are located between high-energy and
low-energy peaked BL Lac objects with respect to alpha_rx. Both the statistical
properties of IBLs from the RGB sample and a detailed broad band X-ray spectral
analysis of two objects (1424+2401, 1055+5644) point towards a continuous
distribution of synchrotron emission peak frequencies among BL Lac objects.Comment: 4 pages, 4 figures; to appear in the proceedings of the conference
"BL Lac Phenomenon" held in Turku, Finland, June 22-26, 199
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