26,840 research outputs found
Evidence for the Collective Nature of the Reentrant Integer Quantum Hall States of the Second Landau Level
We report an unexpected sharp peak in the temperature dependence of the
magnetoresistance of the reentrant integer quantum Hall states in the second
Landau level. This peak defines the onset temperature of these states. We find
that in different spin branches the onset temperatures of the reentrant states
scale with the Coulomb energy. This scaling provides direct evidence that
Coulomb interactions play an important role in the formation of these reentrant
states evincing their collective nature
Cardiac-specific Conditional Knockout of the 18-kDa Mitochondrial Translocator Protein Protects from Pressure Overload Induced Heart Failure.
Heart failure (HF) is characterized by abnormal mitochondrial calcium (Ca2+) handling, energy failure and impaired mitophagy resulting in contractile dysfunction and myocyte death. We have previously shown that the 18-kDa mitochondrial translocator protein of the outer mitochondrial membrane (TSPO) can modulate mitochondrial Ca2+ uptake. Experiments were designed to test the role of the TSPO in a murine pressure-overload model of HF induced by transverse aortic constriction (TAC). Conditional, cardiac-specific TSPO knockout (KO) mice were generated using the Cre-loxP system. TSPO-KO and wild-type (WT) mice underwent TAC for 8 weeks. TAC-induced HF significantly increased TSPO expression in WT mice, associated with a marked reduction in systolic function, mitochondrial Ca2+ uptake, complex I activity and energetics. In contrast, TSPO-KO mice undergoing TAC had preserved ejection fraction, and exhibited fewer clinical signs of HF and fibrosis. Mitochondrial Ca2+ uptake and energetics were restored in TSPO KO mice, associated with decreased ROS, improved complex I activity and preserved mitophagy. Thus, HF increases TSPO expression, while preventing this increase limits the progression of HF, preserves ATP production and decreases oxidative stress, thereby preventing metabolic failure. These findings suggest that pharmacological interventions directed at TSPO may provide novel therapeutics to prevent or treat HF
Growth rate analysis of scalar gradients in generalized surface quasigeostrophic equations of ideal fluids
The growth rates of scalar gradients are studied numerically and analytically in a family of two-dimensional (2D) incompressible fluid equations related to the surface quasigeostrophic (SQG) equation. The active scalar is related to the stream function ψ by θ=(−△)α/2ψ (0⩽α⩽2). A notable difference is observed in a comparison of the instantaneous growth rates in Lp and in L∞ norms, depending on the stage of the time evolution. The crux is the phase-shift effect of singular integral operators, which displaces the peak location of the scalar gradient from that of the strain rate. On this basis, a method of detecting such a dislocation is proposed in view of the importance of their coalescence needed for a possible blow-up. Moreover, it is found in the long-time evolution that a solution of the SQG equation (whose regularity is not known) is less singular than that of the 2D Euler equations (known to be regular) on the time interval covered by this computation. This consistently expands an earlier observation by Majda and Tabak [Physica D 98, 515 (1996).] in some detail. A 1D model problem is discussed to illustrate the present method, and extensions to the 3D case are also are briefly discussed
Electronic Structure and Lattice dynamics of NaFeAs
The similarity of the electronic structures of NaFeAs and other Fe pnictides
has been demonstrated on the basis of first-principle calculations. The global
double-degeneracy of electronic bands along X-M and R-A direction indicates the
instability of Fe pnictides and is explained on the basis of a tight-binding
model. The de Haas-van Alphen parameters for the Fermi surface (FS) of NaFeAs
have been calculated. A spin density wave (SDW)
instead of a charge density wave (CDW) ground state is predicted based on the
calculated generalized susceptibility and a criterion
derived from a restricted Hatree-Fock model. The strongest electron-phonon
(e-p) coupling has been found to involve only As, Na z-direction vibration with
linear-response calculations. A possible enhancement mechanism for e-p coupling
due to correlation is suggested
Extended crossover from Fermi liquid to quasi-antiferromagnet in the half-filled 2D Hubbard model
The ground state of the Hubbard model with nearest-neighbor hopping on the
square lattice at half filling is known to be that of an antiferromagnetic
(AFM) band insulator for any on-site repulsion. At finite temperature, the
absence of long-range order makes the question of how the interaction-driven
insulator is realized nontrivial. We address this problem with controlled
accuracy in the thermodynamic limit using self-energy diagrammatic determinant
Monte Carlo and dynamical cluster approximation methods and show that
development of long-range AFM correlations drives an extended crossover from
Fermi liquid to insulating behavior in the parameter regime that precludes a
metal-to-insulator transition. The intermediate crossover state is best
described as a non-Fermi liquid with a partially gapped Fermi surface.Comment: 6 pages, 4 figures, with supplemental material: 2 pages, 3 figure
Crossing bonds in the random-cluster model
We derive the scaling dimension associated with crossing bonds in the
random-cluster representation of the two-dimensional Potts model, by means of a
mapping on the Coulomb gas. The scaling field associated with crossing bonds
appears to be irrelevant, on the critical as well as on the tricritical branch.
The latter result stands in a remarkable contrast with the existing result for
the tricritical O(n) model that crossing bonds are relevant. In order to obtain
independent confirmation of the Coulomb gas result for the crossing-bond
exponent, we perform a finite-size-scaling analysis based on numerical
transfer-matrix calculations.Comment: 2 figure
Nanosecond electric pulses penetrate the nucleus and enhance speckle formation
Nanosecond electric pulses generate nanopores in the interior membranes of cells and modulate cellular functions. Here, we used confocal microscopy and flow cytometry to observe Smith antigen antibody (Y12) binding to nuclear speckles, known as small nuclear ribonucleoprotein particles (snRNPs) or intrachromatin granule clusters (IGCs), in Jurkat cells following one or five 10 ns, 150 kV/cm pulses. Using confocal microscopy and flow cytometry, we observed changes in nuclear speckle labeling that suggested a disruption of pre-messenger RNA splicing mechanisms. Pulse exposure increased the nuclear speckled substructures by 2.5-fold above basal levels while the propidium iodide (PI) uptake in pulsed cells was unchanged. The resulting nuclear speckle changes were also cell cycle dependent. These findings suggest that 10 ns pulses directly influenced nuclear processes, such as the changes in the nuclear RNA–protein complexes
Seismic Stability Analysis of a High Earth and Rockfill Dam
Accumulation of knowledge on earthquake activity in California has lead to stronger ground motions being postulated for the evaluation of the seismic stability of dams. A recent regional seismicity study for a 555 ft high earth and rockfill dam in central California lead to a ground motion with peak ground acceleration (PGA) of 0.50g originating in a local fault system 3 miles from the dam site. This PGA is more than 6 times higher than the PGA=0.08g value originally adopted when the Dam was analyzed for seismic stability 20 years ago. Thus, as part of FERC Part 12 evaluation requirements, the seismic stability of the Dam was re-evaluated using the updated ground motion and state-of-the-practice technology. This paper presents the analysis procedures and the results
On the Light Curve and Spectrum of SN 2003dh Separated from the Optical Afterglow of GRB 030329
The net optical light curves and spectra of the supernova (SN) 2003dh are
obtained from the published spectra of GRB 030329, covering about 6 days before
SN maximum to about 60 days after. The bulk of the U-band flux is subtracted
from the observed spectra using early-time afterglow templates, because strong
line blanketing greatly depresses the UV and U-band SN flux in a metal-rich,
fast-moving SN atmosphere. The blue-end spectra of the gamma-ray burst
(GRB)connected hypernova SN 1998bw is used to determine the amount of
subtraction. The subtraction of a host galaxy template affects the late-time
results. The derived SN 2003dh light curves are narrower than those of SN
1998bw, rising as fast before maximum, reaching a possibly fainter maximum, and
then declining ~ 1.2-1.4 times faster. We then build UVOIR bolometric SN light
curve. Allowing for uncertainties, it can be reproduced with a spherical ejecta
model of Mej ~ 7+/-3 Msun, KE ~ (3.5+/-1.5)E52 ergs, with KE/Mej ~ 5 following
previous spectrum modelling, and M(Ni56) ~ (0.4 +0.15/-0.1) Msun. This suggests
a progenitor main-sequence mass of about 25-40 Msun, lower than SN 1998bw but
significantly higher than normal Type Ic SNe and the GRB-unrelated hypernova SN
2002ap.Comment: 18 pages, 7 figures, published by Ap
SN 2006aj Associated with XRF 060218 At Late Phases: Nucleosynthesis-Signature of A Neutron Star-Driven Explosion
Optical spectroscopy and photometry of SN 2006aj have been performed with the
Subaru telescope at t > 200 days after GRB060218, the X-ray Flash with which it
was associated. Strong nebular emission-lines with an expansion velocity of v ~
7,300 km/s were detected. The peaked but relatively broad [OI]6300,6363
suggests the existence of ~ 2 Msun of materials in which ~1.3 Msun is oxygen.
The core might be produced by a mildly asymmetric explosion. The spectra are
unique among SNe Ic in (1) the absence of [CaII]7291,7324 emission, and (2) a
strong emission feature at ~ 7400A, which requires ~ 0.05 Msun of
newly-synthesized 58Ni. Such a large amount of stable neutron-rich Ni strongly
indicates the formation of a neutron star. The progenitor and the explosion
energy are constrained to 18 Msun < Mms < 22 Msun and E ~ (1 - 3) 10^{51} erg,
respectively.Comment: Accepted for Publication in the Astrophysical Journal Letters (2007,
ApJ, 658, L5). 8 pages, including 1 table and 3 figures. Typos correcte
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