1,383 research outputs found
Two regimes for effects of surface disorder on the zero-bias conductance peak of tunnel junctions involving d-wave superconductors
Impurity-induced quasiparticle bound states on a pair-breaking surface of a
d-wave superconductor are theoretically described, taking into account
hybridization of impurity- and surface-induced Andreev states. Further a theory
for effects of surface disorder (of thin impurity surface layer) on the
low-bias conductance of tunnel junctions is developed. We find a threshold
for surface impurity concentration , which separates the two regimes
for surface impurity effects on the zero-bias conductance peak (ZBCP). Below
the threshold, surface impurities do not broaden the ZBCP, but effectively
reduce its weight and generate impurity bands. For low impurity bands can
be, in principle, resolved experimentally, being centered at energies of bound
states induced by an isolated impurity on the surface. For larger
impurity bands are distorted, move to lower energies and, beginning with the
threshold concentration , become centered at zero energy. With
increasing above the threshold, the ZBCP is quickly destroyed in the case
of strong scatterers, while it is gradually suppressed and broaden in the
presence of weak impurity potentials. More realistic cases, taking into account
additional broadening, not related to the surface disorder, are also
considered.Comment: 9 pages, 7 figure
MED12 regulates a transcriptional network of calcium-handling genes in the heart
The Mediator complex regulates gene transcription by linking basal transcriptional machinery with DNA-bound transcription factors. The activity of the Mediator complex is mainly controlled by a kinase submodule that is composed of 4 proteins, including MED12. Although ubiquitously expressed, Mediator subunits can differentially regulate gene expression in a tissue-specific manner. Here, we report that MED12 is required for normal cardiac function, such that mice with conditional cardiac-specific deletion of MED12 display progressive dilated cardiomyopathy. Loss of MED12 perturbs expression of calcium-handling genes in the heart, consequently altering calcium cycling in cardiomyocytes and disrupting cardiac electrical activity. We identified transcription factors that regulate expression of calcium-handling genes that are downregulated in the heart in the absence of MED12, and we found that MED12 localizes to transcription factor consensus sequences within calcium-handling genes. We showed that MED12 interacts with one such transcription factor, MEF2, in cardiomyocytes and that MED12 and MEF2 co-occupy promoters of calcium-handling genes. Furthermore, we demonstrated that MED12 enhances MEF2 transcriptional activity and that overexpression of both increases expression of calcium-handling genes in cardiomyocytes. Our data support a role for MED12 as a coordinator of transcription through MEF2 and other transcription factors. We conclude that MED12 is a regulator of a network of calcium-handling genes, consequently mediating contractility in the mammalian heart
Excitonic effects on the two-color coherent control of interband transitions in bulk semiconductors
Quantum interference between one- and two-photon absorption pathways allows
coherent control of interband transitions in unbiased bulk semiconductors;
carrier population, carrier spin polarization, photocurrent injection, and spin
current injection may all be controlled. We extend the theory of these
processes to include the electron-hole interaction. Our focus is on photon
energies that excite carriers above the band edge, but close enough to it so
that transition amplitudes based on low order expansions in are
applicable; both allowed-allowed and allowed-forbidden two-photon transition
amplitudes are included. Analytic solutions are obtained using the effective
mass theory of Wannier excitons; degenerate bands are accounted for, but
envelope-hole coupling is neglected. We find a Coulomb enhancement of two-color
coherent control process, and relate it to the Coulomb enhancements of one- and
two-photon absorption. In addition, we find a frequency dependent phase shift
in the dependence of photocurrent and spin current on the optical phases. The
phase shift decreases monotonically from at the band edge to 0 over an
energy range governed by the exciton binding energy. It is the difference
between the partial wave phase shifts of the electron-hole envelope function
reached by one- and two-photon pathways.Comment: 31 pages, 4 figures, to be published in Phys. Rev.
Resonant scattering in a strong magnetic field: exact density of states
We study the structure of 2D electronic states in a strong magnetic field in
the presence of a large number of resonant scatterers. For an electron in the
lowest Landau level, we derive the exact density of states by mapping the
problem onto a zero-dimensional field-theoretical model. We demonstrate that
the interplay between resonant and non-resonant scattering leads to a
non-analytic energy dependence of the electron Green function. In particular,
for strong resonant scattering the density of states develops a gap in a finite
energy interval. The shape of the Landau level is shown to be very sensitive to
the distribution of resonant scatterers.Comment: 12 pages + 3 fig
Free particle scattering off two oscillating disks
We investigate the two-dimensional classical dynamics of the scattering of
point particles by two periodically oscillating disks. The dynamics exhibits
regular and chaotic scattering properties, as a function of the initial
conditions and parameter values of the system. The energy is not conserved
since the particles can gain and loose energy from the collisions with the
disks. We find that for incident particles whose velocity is on the order of
the oscillating disk velocity, the energy of the exiting particles displays
non-monotonic gaps of allowed energies, and the distribution of exiting
particle velocities shows significant fluctuations in the low energy regime. We
also considered the case when the initial velocity distribution is Gaussian,
and found that for high energies the exit velocity distribution is Gaussian
with the same mean and variance. When the initial particle velocities are in
the irregular regime the exit velocity distribution is Gaussian but with a
smaller mean and variance. The latter result can be understood as an example of
stochastic cooling. In the intermediate regime the exit velocity distribution
differs significantly from Gaussian. A comparison of the results presented in
this paper to previous chaotic static scattering problems is also discussed.Comment: 9 doble sided pages 13 Postscript figures, REVTEX style. To appear in
Phys. Rev.
Quantum point contact on graphite surface
The conductance through a quantum point contact created by a sharp and hard
metal tip on the graphite surface has features which to our knowledge have not
been encountered so far in metal contacts or in nanowires. In this paper we
first investigate these features which emerge from the strongly directional
bonding and electronic structure of graphite, and provide a theoretical
understanding for the electronic conduction through quantum point contacts. Our
study involves the molecular-dynamics simulations to reveal the variation of
interlayer distances and atomic structure at the proximity of the contact that
evolves by the tip pressing toward the surface. The effects of the elastic
deformation on the electronic structure, state density at the Fermi level, and
crystal potential are analyzed by performing self-consistent-field
pseudopotential calculations within the local-density approximation. It is
found that the metallicity of graphite increases under the uniaxial compressive
strain perpendicular to the basal plane. The quantum point contact is modeled
by a constriction with a realistic potential. The conductance is calculated by
representing the current transporting states in Laue representation, and the
variation of conductance with the evolution of contact is explained by taking
the characteristic features of graphite into account. It is shown that the
sequential puncturing of the layers characterizes the conductance.Comment: LaTeX, 11 pages, 9 figures (included), to be published in Phys. Rev.
B, tentatively scheduled for 15 September 1998 (Volume 58, Number 12
Electron-electron interaction at decreasing
The contribution of the electron-electron interaction to conductivity is
analyzed step by step in gated GaAs/InGaAs/GaAs heterostructures with different
starting disorder. We demonstrate that the diffusion theory works down to , where is the Fermi quasimomentum, is the mean free
paths. It is shown that the e-e interaction gives smaller contribution to the
conductivity than the interference independent of the starting disorder and its
role rapidly decreases with decrease.Comment: 5 pages, 6 figure
Numerical atomic orbitals for linear scaling
The performance of basis sets made of numerical atomic orbitals is explored
in density-functional calculations of solids and molecules. With the aim of
optimizing basis quality while maintaining strict localization of the orbitals,
as needed for linear-scaling calculations, several schemes have been tried. The
best performance is obtained for the basis sets generated according to a new
scheme presented here, a flexibilization of previous proposals. The basis sets
are tested versus converged plane-wave calculations on a significant variety of
systems, including covalent, ionic and metallic. Satisfactory convergence
(deviations significantly smaller than the accuracy of the underlying theory)
is obtained for reasonably small basis sizes, with a clear improvement over
previous schemes. The transferability of the obtained basis sets is tested in
several cases and it is found to be satisfactory as well.Comment: 9 pages with 2 encapsulated postscript figures, submitted to Phys.
Rev.
Graphite and Hexagonal Boron-Nitride Possess the Same Interlayer Distance. Why?
Graphite and hexagonal boron nitride (h-BN) are two prominent members of the
family of layered materials possessing a hexagonal lattice. While graphite has
non-polar homo-nuclear C-C intra-layer bonds, h-BN presents highly polar B-N
bonds resulting in different optimal stacking modes of the two materials in
bulk form. Furthermore, the static polarizabilities of the constituent atoms
considerably differ from each other suggesting large differences in the
dispersive component of the interlayer bonding. Despite these major differences
both materials present practically identical interlayer distances. To
understand this finding, a comparative study of the nature of the interlayer
bonding in both materials is presented. A full lattice sum of the interactions
between the partially charged atomic centers in h-BN results in vanishingly
small monopolar electrostatic contributions to the interlayer binding energy.
Higher order electrostatic multipoles, exchange, and short-range correlation
contributions are found to be very similar in both materials and to almost
completely cancel out by the Pauli repulsions at physically relevant interlayer
distances resulting in a marginal effective contribution to the interlayer
binding. Further analysis of the dispersive energy term reveals that despite
the large differences in the individual atomic polarizabilities the
hetero-atomic B-N C6 coefficient is very similar to the homo-atomic C-C
coefficient in the hexagonal bulk form resulting in very similar dispersive
contribution to the interlayer binding. The overall binding energy curves of
both materials are thus very similar predicting practically the same interlayer
distance and very similar binding energies.Comment: 18 pages, 5 figures, 2 table
Phase 1 study of seviteronel, a selective CYP17 lyase and androgen receptor inhibitor, in women with estrogen receptor-positive or triple-negative breast cancer
Purpose: Seviteronel (INO-464) is an oral, selective cytochrome P450c17a (CYP17) 17,20-lyase (lyase) and androgen receptor inhibitor with in vitro and in vivo anti-tumor activity. This open-label phase 1 clinical study evaluated safety, tolerability, pharmacokinetics (PK), and activity of once-daily (QD) seviteronel in women with locally advanced or metastatic TNBC or ER+ breast cancer. Methods: Seviteronel was administered in de-escalating 750, 600, and 450 mg QD 6-subject cohorts. The 750 mg QD start dose was a phase 2 dose determined for men with castration-resistant prostate cancer in (Shore et al. J Clin Oncol 34, 2016). Enrollment at lower doses was initiated in the presence of dose-limiting toxicities (DLTs). The primary objective of this study was to determine seviteronel safety, tolerability, and MTD. The secondary objectives included description of its PK in women and its initial activity, including clinical benefit rate at 4 (CBR16) and 6 months (CBR24). Results: Nineteen women were enrolled. A majority of adverse events (AEs) were Grade (Gr) 1/2, independent of relationship; the most common were tremor (42%), nausea (42%), vomiting (37%), and fatigue (37%). Four Gr 3/4 AEs (anemia, delirium, mental status change, and confusional state) deemed possibly related to seviteronel occurred in four subjects. DLTs were observed at 750 mg (Gr 3 confusional state with paranoia) and 600 mg (Gr 3 mental status change and Gr 3 delirium) QD, with none at 450 mg QD. The recommended phase 2 dose (RP2D) was 450 mg QD, and at the RP2D, 4 of 7 subjects reached at least CBR16 (2 TNBC subjects and 2 ER+ subjects achieved CBR16 and CBR24, respectively); no objective tumor responses were reported. Conclusions: Once-daily seviteronel was generally well tolerated in women with and 450 mg QD was chosen as the RP2D
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