6,002 research outputs found
Heat conductivity in the presence of a quantized degree of freedom
We propose a model with a quantized degree of freedom to study the heat
transport in quasi-one dimensional system. Our simulations reveal three
distinct temperature regimes. In particular, the intermediate regime is
characterized by heat conductivity with a temperature exponent much
greater than 1/2 that was generally found in systems with point-like particles.
A dynamical investigation indicates the occurrence of non-equipartition
behavior in this regime. Moreover, the corresponding Poincar\'e section also
shows remarkably characteristic patterns, completely different from the cases
of point-like particles.Comment: 7 pages, 4 figure
Constraints on Holographic Dark Energy from Latest Supernovae, Galaxy Clustering, and Cosmic Microwave Background Anisotropy Observations
The holographic dark energy model is proposed by Li as an attempt for probing
the nature of dark energy within the framework of quantum gravity. The main
characteristic of holographic dark energy is governed by a numerical parameter
in the model. The parameter can only be determined by observations.
Thus, in order to characterize the evolving feature of dark energy and to
predict the fate of the universe, it is of extraordinary importance to
constrain the parameter by using the currently available observational
data. In this paper, we derive constraints on the holographic dark energy model
from the latest observational data including the gold sample of 182 Type Ia
supernovae (SNIa), the shift parameter of the cosmic microwave background (CMB)
given by the three-year {\it Wilkinson Microwave Anisotropy Probe} ({\it WMAP})
observations, and the baryon acoustic oscillation (BAO) measurement from the
Sloan Digital Sky Survey (SDSS). The joint analysis gives the fit results in
1-: and . That
is to say, though the possibility of is more favored, the possibility of
can not be excluded in one-sigma error range, which is somewhat different
from the result derived from previous investigations using earlier data. So,
according to the new data, the evidence for the quintom feature in the
holographic dark energy model is not as strong as before.Comment: 22 pages, 8 figures; accepted for publication in Phys. Rev.
Abelian and Non-Abelian Quantum Geometric Tensor
We propose a generalized quantum geometric tenor to understand topological
quantum phase transitions, which can be defined on the parameter space with the
adiabatic evolution of a quantum many-body system. The generalized quantum
geometric tenor contains two different local measurements, the non-Abelian
Riemannian metric and the non-Abelian Berry curvature, which are recognized as
two natural geometric characterizations for the change of the ground-state
properties when the parameter of the Hamiltonian varies. Our results show the
symmetry-breaking and topological quantum phase transitions can be understood
as the singular behavior of the local and topological properties of the quantum
geometric tenor in the thermodynamic limit.Comment: 5 pages, 2 figure
The Euler Number of Bloch States Manifold and the Quantum Phases in Gapped Fermionic Systems
We propose a topological Euler number to characterize nontrivial topological
phases of gapped fermionic systems, which originates from the Gauss-Bonnet
theorem on the Riemannian structure of Bloch states established by the real
part of the quantum geometric tensor in momentum space. Meanwhile, the
imaginary part of the geometric tensor corresponds to the Berry curvature which
leads to the Chern number characterization. We discuss the topological numbers
induced by the geometric tensor analytically in a general two-band model. As an
example, we show that the zero-temperature phase diagram of a transverse field
XY spin chain can be distinguished by the Euler characteristic number of the
Bloch states manifold in a (1+1)-dimensional Bloch momentum space
Finite-Temperature Scaling of Magnetic Susceptibility and Geometric Phase in the XY Spin Chain
We study the magnetic susceptibility of 1D quantum XY model, and show that
when the temperature approaches zero, the magnetic susceptibility exhibits the
finite-temperature scaling behavior. This scaling behavior of the magnetic
susceptibility in 1D quantum XY model, due to the quantum-classical mapping,
can be easily experimentally tested. Furthermore, the universality in the
critical properties of the magnetic susceptibility in quantum XY model is
verified. Our study also reveals the close relation between the magnetic
susceptibility and the geometric phase in some spin systems, where the quantum
phase transitions are driven by an external magnetic field.Comment: 6 pages, 4 figures, get accepted for publication by J. Phys. A: Math.
Theo
Light Rays at Optical Black Holes in Moving Media
Light experiences a non-uniformly moving medium as an effective gravitational
field, endowed with an effective metric tensor , being the refractive index and the
four-velocity of the medium. Leonhardt and Piwnicki [Phys. Rev. A {\bf 60},
4301 (1999)] argued that a flowing dielectric fluid of this kind can be used to
generate an 'optical black hole'. In the Leonhardt-Piwnicki model, only a
vortex flow was considered. It was later pointed out by Visser [Phys. Rev.
Lett. {\bf 85}, 5252 (2000)] that in order to form a proper optical black hole
containing an event horizon, it becomes necessary to add an inward radial
velocity component to the vortex flow. In the present paper we undertake this
task: we consider a full spiral flow, consisting of a vortex component plus a
radially infalling component. Light propagates in such a dielectric medium in a
way similar to that occurring around a rotating black hole. We calculate, and
show graphically, the effective potential versus the radial distance from the
vortex singularity, and show that the spiral flow can always capture light in
both a positive, and a negative, inverse impact parameter interval. The
existence of a genuine event horizon is found to depend on the strength of the
radial flow, relative to the strength of the azimuthal flow. A limitation of
our fluid model is that it is nondispersive.Comment: 30 pages, LaTeX, 4 ps figures. Expanded discussion especially in
section 6; 5 new references. Version to appear in Phys. Rev.
Entanglement and quantum phase transition in the extended Hubbard model
We study quantum entanglement in one-dimensional correlated fermionic system.
Our results show, for the first time, that entanglement can be used to identify
quantum phase transitions in fermionic systems.Comment: 5 pages, 4 figure
Dysregulation of Glucagon Secretion by Hyperglycemia-Induced Sodium-Dependent Reduction of ATP Production
© 2018 The Author(s). Published by Elsevier Inc.Diabetes is a bihormonal disorder resulting from combined insulin and glucagon secretion defects. Mice lacking fumarase (Fh1) in their β cells (Fh1βKO mice) develop progressive hyperglycemia and dysregulated glucagon secretion similar to that seen in diabetic patients (too much at high glucose and too little at low glucose). The glucagon secretion defects are corrected by low concentrations of tolbutamide and prevented by the sodium-glucose transport (SGLT) inhibitor phlorizin. These data link hyperglycemia, intracellular Na+ accumulation, and acidification to impaired mitochondrial metabolism, reduced ATP production, and dysregulated glucagon secretion. Protein succination, reflecting reduced activity of fumarase, is observed in α cells from hyperglycemic Fh1βKO and β-V59M gain-of-function KATP channel mice, diabetic Goto-Kakizaki rats, and patients with type 2 diabetes. Succination is also observed in renal tubular cells and cardiomyocytes from hyperglycemic Fh1βKO mice, suggesting that the model can be extended to other SGLT-expressing cells and may explain part of the spectrum of diabetic complications.Peer reviewe
Cervical Cancer Prevention Through HPV Vaccination in Low- and Middle-Income Countries in Asia
Cervical cancer is ranked the first or second most common cancer in women of low- and middle-income countries
(LMICs) in Asia. Cervical cancer is almost exclusively caused by human papillomavirus (HPV), and majority of the
cases can be prevented with the use of HPV vaccines. The HPV vaccines have demonstrated high vaccine efficacies
against HPV infection and cervical cancer precursors in clinical and post-marketing studies, and are in use in most
high-income countries. However, their use in LMICs are limited mainly due to the high costs and logistics in delivering
multiple doses of the vaccine. Other issues such as the safety of the vaccines, social and cultural factors, as well as
poor knowledge and awareness of the virus have also contributed to the low uptake of the vaccine. This mini-review
focuses on the need for HPV vaccine implementation in Asia given the substantial disease burden and underuse of HPV
vaccines in LMICs in this region. In addition, the progress towards HPV vaccine introduction, and barriers preventing
further rollout of these essential, life-saving vaccines are also discussed in this article
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