310 research outputs found
Fock space localization, return probability, and conductance of disordered interacting electrons
We numerically simulate the low-energy properties of interacting electrons in
a random potential using the Hartree-Fock based exact diagonalization method.
In particular, we investigate how the transport properties are influenced by
the combined effects of disorder and correlations in the presence of the
electron spin. To this end we calculate the participation number of
many-particle states in Fock space, the return probability of single-particle
excitations, and the Kubo-Greenwood conductance. It turns out that in the
strongly localized regime interactions increase the conductance whereas for
weak disorder interactions decrease the conductance. In contrast,
single-particle excitations in general experience a localizing influence of the
interactions.Comment: 4 pages, 4 eps figures, Proc. of the Symposium on Wave Propagation
and Electronic Structure in Disordered Systems, FORTH, Heraklion, Crete,
Greece (June 2000
Dihydrochalcone glycosides from Oxytropis myriophylla
Chemical investigations of the 70% alcohol extract of Oxytropis myriophylla (Pall.) DC. (Leguminosae) have afforded the new natural product neohesperidin dihydrochalcone (1) and the known phloretin-4'-O-β-D-glucopyranoside (2), which was the first reported from the genus Oxytropis. This paper reports the isolation and full spectroscopic characterization of compounds 1 and 2 by NMR, UV, IR and MS data
A Fermi liquid model for the overdoped and optimally doped cuprate superconductors: scattering rate, susceptibility, spin resonance peak and superconducting transition
This paper treats a number of issues of the cuprates, ranging from the spin
resonance peak and the linear one-particle scattering rate to the
superconducting transition, in the frame of a Fermi liquid model. Recent ARPES
expts. by Valla et al., Science vol. 285, 2110 (1999), and e-print
cond-mat/0003407, directly support the linearity of the one-particle scattering
rate everywhere in the Brillouin zone we obtained here. We show that the origin
of this linearity is the strong linear in energy term of the imaginary part of
the carrier susceptibility. This result yields directly a linear in temperature
resistivity and linear in 1/energy optical conductivity. We show that the low
energy dependence of the susceptibility can have a purely fermionic origin. We
introduce an antiferromagnetic ansatz for the susceptibility of the
carriers.Inter alia, this ansatz may explain the appearance of the spin
resonance peak (observed in neutron scattering) in the normal state of the
cuprates. Further, we obtain particularly high transition temperatures
from our Eliashberg scheme by using this ansatz: we have a gap
with K for nearest neighbour hopping .Comment: This version corrects a few misprints of the printed versio
Magnetic order in orbital models of the iron pnictides
We examine the appearance of the experimentally-observed stripe
spin-density-wave magnetic order in five different orbital models of the iron
pnictide parent compounds. A restricted mean-field ansatz is used to determine
the magnetic phase diagram of each model. Using the random phase approximation,
we then check this phase diagram by evaluating the static spin susceptibility
in the paramagnetic state close to the mean-field phase boundaries. The momenta
for which the susceptibility is peaked indicate in an unbiased way the actual
ordering vector of the nearby mean-field state. The dominant orbitally resolved
contributions to the spin susceptibility are also examined to determine the
origin of the magnetic instability. We find that the observed stripe magnetic
order is possible in four of the models, but it is extremely sensitive to the
degree of the nesting between the electron and hole Fermi pockets. In the more
realistic five-orbital models, this order competes with a strong-coupling
incommensurate state which appears to be controlled by details of the
electronic structure below the Fermi energy. We conclude by discussing the
implications of our work for the origin of the magnetic order in the pnictides.Comment: 19 pages, 19 figures; published version, typos corrected, references
adde
Dance Type and Flight Parameters Are Associated with Different Mushroom Body Neural Activities in Worker Honeybee Brains
Background: Honeybee foragers can transmit the information concerning the location of food sources to their nestmates using dance communication. We previously used a novel immediate early gene, termed kakusei, to demonstrate that the neural activity of a specific mushroom body (MB) neuron subtype is preferentially enhanced in the forager brain. The sensory information related to this MB neuron activity, however, remained unclear. Methodology/Principal Findings: Here, we used kakusei to analyze the relationship between MB neuron activity and types of foraging behavior. The number of kakusei-positive MB neurons was higher in the round dancers that had flown a short distance than in the waggle dancers that had flown a long distance. Furthermore, the amount of kakusei transcript in the MBs inversely related to the waggle-phase duration of the waggle dance, which correlates with the flight distance. Using a narrow tunnel whose inside was vertically or axially lined, we manipulated the pattern of visual input, which is received by the foragers during flight, and analysed kakusei expression. The amount of kakusei transcript in the MBs was related to the foraging frequency but not to the tunnel pattern. In contrast, the number of kakusei-positive MB neurons was affected by the tunnel patterns, but not related to foraging frequency. Conclusions/Significance: These results suggest that the MB neuron activity depends on the foraging frequency, whereas the number of active MB neurons is related to the pattern of visual input received during foraging flight. Our results sugges
Magnetism and its microscopic origin in iron-based high-temperature superconductors
High-temperature superconductivity in the iron-based materials emerges from,
or sometimes coexists with, their metallic or insulating parent compound
states. This is surprising since these undoped states display dramatically
different antiferromagnetic (AF) spin arrangements and Nel
temperatures. Although there is general consensus that magnetic interactions
are important for superconductivity, much is still unknown concerning the
microscopic origin of the magnetic states. In this review, progress in this
area is summarized, focusing on recent experimental and theoretical results and
discussing their microscopic implications. It is concluded that the parent
compounds are in a state that is more complex than implied by a simple Fermi
surface nesting scenario, and a dual description including both itinerant and
localized degrees of freedom is needed to properly describe these fascinating
materials.Comment: 14 pages, 4 figures, Review article, accepted for publication in
Nature Physic
High efficient differentiation of functional hepatocytes from porcine induced pluripotent stem cells
Hepatocyte transplantation is considered to be a promising therapy for patients with liver diseases. Induced pluripotent stem cells (iPSCs) provide an unlimited source for the generation of functional hepatocytes. In this study, we generated iPSCs from porcine ear fibroblasts (PEFs) by overexpressing Sox2, Klf4, Oct4, and c-Myc (SKOM), and developed a novel strategy for the efficient differentiation of hepatocyte-like cells from porcine iPSCs by following the processes of early liver development. The differentiated cells displayed the phenotypes of hepatocytes, exhibited classic hepatocyte-associated bio-functions, such as LDL uptake, glycogen storage and urea secretion, as well as possessed the metabolic activities of cytochrome P-450 (CYP) 3A and 2C. Furthermore, we compared the hepatocyte differentiation efficacy of our protocol with another published method, and the results demonstrated that our differentiation strategy could significantly improve the generation of morphological and functional hepatocyte-like cells from porcine iPSCs. In conclusion, this study establishes an efficient method for in vitro generation of functional hepatocytes from porcine iPSCs, which could represent a promising cell source for preclinical testing of cell-based therapeutics for liver failure and for pharmacological applications. © 2014 Ao et al
The Hubbard model within the equations of motion approach
The Hubbard model has a special role in Condensed Matter Theory as it is
considered as the simplest Hamiltonian model one can write in order to describe
anomalous physical properties of some class of real materials. Unfortunately,
this model is not exactly solved except for some limits and therefore one
should resort to analytical methods, like the Equations of Motion Approach, or
to numerical techniques in order to attain a description of its relevant
features in the whole range of physical parameters (interaction, filling and
temperature). In this manuscript, the Composite Operator Method, which exploits
the above mentioned analytical technique, is presented and systematically
applied in order to get information about the behavior of all relevant
properties of the model (local, thermodynamic, single- and two- particle ones)
in comparison with many other analytical techniques, the above cited known
limits and numerical simulations. Within this approach, the Hubbard model is
shown to be also capable to describe some anomalous behaviors of the cuprate
superconductors.Comment: 232 pages, more than 300 figures, more than 500 reference
The relationship between lung function impairment and quantitative computed tomography in chronic obstructive pulmonary disease
Contains fulltext :
109919.pdf (Publisher’s version ) (Open Access)OBJECTIVES: To determine the relationship between lung function impairment and quantitative computed tomography (CT) measurements of air trapping and emphysema in a population of current and former heavy smokers with and without airflow limitation. METHODS: In 248 subjects (50 normal smokers; 50 mild obstruction; 50 moderate obstruction; 50 severe obstruction; 48 very severe obstruction) CT emphysema and CT air trapping were quantified on paired inspiratory and end-expiratory CT examinations using several available quantification methods. CT measurements were related to lung function (FEV(1), FEV(1)/FVC, RV/TLC, Kco) by univariate and multivariate linear regression analysis. RESULTS: Quantitative CT measurements of emphysema and air trapping were strongly correlated to airflow limitation (univariate r-squared up to 0.72, p < 0.001). In multivariate analysis, the combination of CT emphysema and CT air trapping explained 68-83% of the variability in airflow limitation in subjects covering the total range of airflow limitation (p < 0.001). CONCLUSIONS: The combination of quantitative CT air trapping and emphysema measurements is strongly associated with lung function impairment in current and former heavy smokers with a wide range of airflow limitation.01 januari 201
Spin Fluctuation Theory for Quantum Tricritical Point Arising in Proximity to First-Order Phase Transitions: Applications to Heavy-Fermion Systems, YbRh2Si2, CeRu2Si2, and beta-YbAlB4
We propose a phenomenological spin fluctuation theory for antiferromagnetic
quantum tricritical point (QTCP), where the first-order phase transition
changes into the continuous one at zero temperature. Under magnetic fields,
ferromagnetic quantum critical fluctuations develop around the
antiferromagnetic QTCP in addition to antiferromagnetic ones, which is in sharp
contrast with the conventional antiferromagnetic quantum critical point. For
itinerant electron systems,} we show that the temperature dependence of
critical magnetic fluctuations around the QTCP are given as chiQ \propto
T^{-3/2} (chi0\propto T^{-3/4}) at the antiferromagnetic ordering
(ferromagnetic) wave number q=Q (q=0). The convex temperature dependence of
chi0^{-1} is the characteristic feature of the QTCP, which is never seen in the
conventional spin fluctuation theory. We propose that the general theory of
quantum tricriticality that has nothing to do with the specific Kondo physics
itself, solves puzzles of quantum criticalities widely observed in
heavy-fermion systems such as YbRh2Si2, CeRu2Si2, and beta-YbAlB4. For
YbRh2Si2, our theory successfully reproduces quantitative behaviors of the
experimental ferromagnetic susceptibility and the magnetization curve by
choosing the phenomenological parameters properly. The quantum tricriticality
is also consistent with singularities of other physical properties such as
specific heat, nuclear magnetic relaxation time 1/T_1T, and Hall coefficient.
For CeRu2Si2 and beta-YbAlB4, we point out that the quantum tricriticality is a
possible origin of the anomalous diverging enhancement of the uniform
susceptibility observed in these materials.Comment: 17 pages, 10 fugures, to appear in Journal of the Physical Society of
Japan Vol.78 No.
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