260 research outputs found
Some exact results for the multicomponent t-J model
We present a generalization of the Sutherland's multicomponent model. Our
extension includes both the ferromagnetic and the antiferromagnetic t-J model
for any value of the exchange coupling J and the hopping parameter t. We prove
rigorously that for one dimensional chains the ground-state of the generalized
model is non-degenerate. As a consequence, the ordering of energy levels of the
antiferromagnetic t-J model is determined. Our result rigorously proves and
extends the analysis carried out by Sutherland in establishing the phase
diagram of the model as a function of the number of components.Comment: 11 pages, RevTeX 3.0, no figure
Perception of Nuclear Energy and Coal in France and the Netherlands
This study focuses on the perception of large scale application of nuclear energy and coal in the Netherlands and France. The application of these energy-sources and the risks and benefits are judged differently by various group in society. In Europe, France has the highest density of nuclear power plants and the Netherlands has one of the lowest. In both countries scientists and social scientists completed a questionnaire assessing the perception of the large scale application of both energy sources. Furthermore, a number of variables relating to the socio cultural and political circumstances were measured. The results indicate that the French had a higher risk perception and a more negative attitude toward nuclear power than the Dutch. But they also assess the benefits of the use of nuclear power to be higher. Explanations for these differences are discussed
Oxygen transport and consumption in germinating seeds
Three mathematical models were formulated to describe the oxygen con-sumption of seeds during germination. These models were fitted to measure-ment data of oxygen consumption curves for individual germinating seeds of Savoy cabbage, barley and sugar beet provided by Fytagoras. The first model builds on a logistic growth model for the increasing population of mitochondria in the embryo during growth. The other two take the anatomy and physiologi-cal properties of the seed into account. One describes the oxygen uptake during the germination phase only. An extension of this model is capable of fitting the complete oxygen consumption curve, including the initial ‘repair’ phase in which the embryonic cells recover from their dormant state before extensive cell division and growth commences. Keywords: Modelling, seed germination, cellular respiration, oxygen transpor
Kondo screening cloud and the charge staircase in one-dimensional mesoscopic devices
We propose that the finite size of the Kondo screening cloud, xi_K, can be
probed by measuring the charge quantization in a one-dimensional system coupled
to a small quantum dot. When the chemical potential, mu in the system is varied
at zero temperature, one should observe charge steps whose locations are at
values of mu that are controlled by the Kondo effect when the system size L is
comparable to xi_K. We show that, if the standard Kondo model is used, the
ratio between the widths of the Coulomb blockade valleys with odd or even
number of electrons is a universal scaling function of xi_K/L. If we take into
account electron-electron interactions in a single-channel wire, this ratio
also depends on the parameters of the effective Luttinger model; in addition,
the scaling is weakly violated by a marginal bulk interaction. For the geometry
of a quantum dot embedded in a ring, we show that the dependence of the charge
steps on a magnetic flux through the ring is controlled by the size of the
Kondo screening cloud.Comment: This is an extended version of cond-mat/0612635 with an analysis of
bulk Luttinger liquid interactions added as well as a discussion of
experimental possibilitie
Coverage-dependent adsorption and desorption of oxygen on Pd(100)
Catalysis and Surface Chemistr
Critical Nature of Non-Fermi Liquid in Spin 3/2 Multipolar Kondo Model
A multipolar Kondo model of an impurity spin S_I=3/2 interacting with
conduction electrons with spin s_c=3/2 is investigated using boundary conformal
field theory. A two-channel Kondo (2CK) -like non-Fermi liquid (NFL) under the
particle-hole symmetry is derived explicitly using a ``superspin absorption''
in the sector of a hidden symmetry, SO(5). We discuss the difference between
the usual spin-1/2 2CK NFL fixed point and the present one. In particular, we
find that, unlike the usual 2CK model, the low temperature impurity specific
heat is proportional to temperature.Comment: 4 pages, 2 figure
NRG approach to the transport through a finite Hubbard chain connected to reservoirs
We study the low-energy properties of a Hubbard chain of finite size N_C
connected to two noninteracting leads using the numerical renormalization group
(NRG) method. The results obtained for N_C = 3 and 4 show that the low-lying
eigenstates have one-to-one correspondence with the free quasi-particle
excitations of a local Fermi liquid. It enables us to determine the transport
coefficients from the fixed-point Hamiltonian. At half-filling, the conductance
for even N_C decreases exponentially with increasing U showing a tendency
towards the development of a Mott-Hubbard gap. In contrast, for odd N_C, the
Fermi-liquid nature of the low-energy states assures perfect transmission
through the Kondo resonance. Our formulation to deduce the conductance from the
fixed-point energy levels can be applied to various types of interacting
systems.Comment: One typo found in Eq.(3) in previous version has been correcte
Fermi liquid theory for the nonequilibrium Kondo effect at low bias voltages
In this report, we describe a recent development in a Fermi liquid theory for
the Kondo effect in quantum dots under a finite bias voltage . Applying the
microscopic theory of Yamada and Yosida to a nonequilibrium steady state, we
derive the Ward identities for the Keldysh Green's function, and determine the
low-energy behavior of the differential conductance exactly up to terms
of order for the symmetric Anderson model. These results are deduced
from the fact that the Green's function at the impurity site is a functional of
a nonequilibrium distribution , which at
coincides with the Fermi function. Furthermore, we provide an alternative
description of the low-energy properties using a renormalized perturbation
theory (RPT). In the nonequilibrium state the unperturbed part of the RPT is
determined by the renormalized free quasiparticles, the distribution function
of which is given by . The residual interaction between
the quasiparticles , which is defined by the full vertex part at
zero frequencies, is taken into account by an expansion in the power series of
. We also discuss the application of the RPT to a high-bias
region beyond the Fermi-liquid regime.Comment: 8 pages, to appear in a special edition of JPSJ "Kondo Effect -- 40
Years after the Discovery", typos are correcte
Experimental techniques for aberration retrieval with through-focus intensity images
Measurement techniques to determine the aberration of an optical system, by obtaining through-focus intensity images that are produced when the object is a point source at infinity, are shown. The analysis of the aberrations is made using the extended version of the Nijboer-Zernike diffraction theory. This theory provides a semi analytical solution of the Debye diffraction integral and thus a direct relation between the intensity distribution of the field at the focal region and the exit pupil of the optical syste
Pathophysiological regulation of lung function by the free fatty acid receptor FFA4.
Increased prevalence of inflammatory airway diseases including asthma and chronic obstructive pulmonary disease (COPD) together with inadequate disease control by current frontline treatments means that there is a need to define therapeutic targets for these conditions. Here, we investigate a member of the G protein-coupled receptor family, FFA4, that responds to free circulating fatty acids including dietary omega-3 fatty acids found in fish oils. We show that FFA4, although usually associated with metabolic responses linked with food intake, is expressed in the lung where it is coupled to Gq/11 signaling. Activation of FFA4 by drug-like agonists produced relaxation of murine airway smooth muscle mediated at least in part by the release of the prostaglandin E2 (PGE2) that subsequently acts on EP2 prostanoid receptors. In normal mice, activation of FFA4 resulted in a decrease in lung resistance. In acute and chronic ozone models of pollution-mediated inflammation and house dust mite and cigarette smoke-induced inflammatory disease, FFA4 agonists acted to reduce airway resistance, a response that was absent in mice lacking expression of FFA4. The expression profile of FFA4 in human lung was similar to that observed in mice, and the response to FFA4/FFA1 agonists similarly mediated human airway smooth muscle relaxation ex vivo. Our study provides evidence that pharmacological targeting of lung FFA4, and possibly combined activation of FFA4 and FFA1, has in vivo efficacy and might have therapeutic value in the treatment of bronchoconstriction associated with inflammatory airway diseases such as asthma and COPD
- …