2,233 research outputs found
Impact of Many-Body Effects on Landau Levels in Graphene
We present magneto-Raman spectroscopy measurements on suspended graphene to
investigate the charge carrier density-dependent electron-electron interaction
in the presence of Landau levels. Utilizing gate-tunable magneto-phonon
resonances, we extract the charge carrier density dependence of the Landau
level transition energies and the associated effective Fermi velocity
. In contrast to the logarithmic divergence of at
zero magnetic field, we find a piecewise linear scaling of as a
function of charge carrier density, due to a magnetic field-induced suppression
of the long-range Coulomb interaction. We quantitatively confirm our
experimental findings by performing tight-binding calculations on the level of
the Hartree-Fock approximation, which also allow us to estimate an excitonic
binding energy of 6 meV contained in the experimentally extracted
Landau level transitions energies.Comment: 10 pages, 6 figure
Where is Population II?
The use of roman numerals for stellar populations represents a classification
approach to galaxy formation which is now well behind us. Nevertheless, the
concept of a pristine generation of stars, followed by a protogalactic era, and
finally the mainstream stellar population is a plausible starting point for
testing our physical understanding of early star formation. This will be
observationally driven as never before in the coming decade. In this paper, we
search out observational tests of an idealized coeval and homogeneous
distribution of population II stars. We examine the spatial distribution of
quasars, globular clusters, and the integrated free electron density of the
intergalactic medium, in order to test the assumption of homogeneity. Any
inhomogeneity implies a population II that is not coeval.Comment: for publication in PAS
Where is Population II?
The use of roman numerals for stellar populations represents a classification
approach to galaxy formation which is now well behind us. Nevertheless, the
concept of a pristine generation of stars, followed by a protogalactic era, and
finally the mainstream stellar population is a plausible starting point for
testing our physical understanding of early star formation. This will be
observationally driven as never before in the coming decade. In this paper, we
search out observational tests of an idealized coeval and homogeneous
distribution of population II stars. We examine the spatial distribution of
quasars, globular clusters, and the integrated free electron density of the
intergalactic medium, in order to test the assumption of homogeneity. Any
inhomogeneity implies a population II that is not coeval.Comment: for publication in PAS
Native myocardial T1 time can predict development of subsequent anthracycline-induced cardiomyopathy
Aims: This study aims to assess subclinical changes in functional and morphological myocardial magnetic resonance parameters very early into an anthracycline treatment, which may predict subsequent development of anthracycline-induced cardiomyopathy (aCMP). Methods and results: Thirty sarcoma patients with planned anthracycline-based chemotherapy (360-400 mg/m doxorubicin-equivalent) were recruited. Median treatment time was 19.1 ± 2.1 weeks. Enrolled individuals received three cardiovascular magnetic resonance studies (before treatment, 48 h after first anthracycline treatment, and upon completion of treatment). Native T1 mapping (modified Look-Locker inversion recovery 5s(3s)3s), T2 mapping, and extracellular volume maps were acquired in addition to a conventional cardiovascular magnetic resonance with steady-state free precession cine imaging at 1.5 T. Patients were given 0.2 mmol/kg gadoteridol for extracellular volume quantification and late gadolinium enhancement imaging. Development of relevant aCMP was defined as drop of left ventricular ejection fraction (LVEF) by >10%. For analysis, 23 complete data sets were available. Nine patients developed aCMP with LVEF reduction >10% until end of chemotherapy. Baseline LVEF was not different between patients with and without subsequent aCMP. When assessed 48 h after first dose of antracyclines, patients with subsequent aCMP had significantly lower native myocardial T1 times compared with before therapy (1002.0 ± 37.9 vs. 956.5 ± 29.2 ms, P  0.05). Patients with aCMP had decreased left ventricular mass upon completion of therapy (86.9 ± 24.5 vs. 81.1 ± 22.3 g; P = 0.02), while patients without aCMP did not show a change in left ventricular mass (81.8 ± 21.0 vs. 79.2 ± 18.1 g; P > 0.05). No patient developed new myocardial scars or compact myocardial fibrosis under chemotherapy. Conclusions: Early decrease of T1 times 48 h after first treatment with anthracyclines can predict the development of subsequent aCMP after completion of chemotherapy
Single-qubit unitary gates by graph scattering
We consider the effects of plane-wave states scattering off finite graphs, as
an approach to implementing single-qubit unitary operations within the
continuous-time quantum walk framework of universal quantum computation. Four
semi-infinite tails are attached at arbitrary points of a given graph,
representing the input and output registers of a single qubit. For a range of
momentum eigenstates, we enumerate all of the graphs with up to vertices
for which the scattering implements a single-qubit gate. As increases, the
number of new unitary operations increases exponentially, and for the
majority correspond to rotations about axes distributed roughly uniformly
across the Bloch sphere. Rotations by both rational and irrational multiples of
are found.Comment: 8 pages, 7 figure
Applied Remote Sensing Program (ARSP)
There are no author-identified significant results in this report
Entangling flux qubits with a bipolar dynamic inductance
We propose a scheme to implement variable coupling between two flux qubits
using the screening current response of a dc Superconducting QUantum
Interference Device (SQUID). The coupling strength is adjusted by the current
bias applied to the SQUID and can be varied continuously from positive to
negative values, allowing cancellation of the direct mutual inductance between
the qubits. We show that this variable coupling scheme permits efficient
realization of universal quantum logic. The same SQUID can be used to determine
the flux states of the qubits.Comment: 4 pages, 4 figure
Electron-phonon coupling in the conventional superconductor YNiBC at high phonon energies studied by time-of-flight neutron spectroscopy
We report an inelastic neutron scattering investigation of phonons with
energies up to 159 meV in the conventional superconductor YNiBC. Using
the SWEEP mode, a newly developed time-of-flight technique involving the
continuous rotation of a single crystal specimen, allowed us to measure a four
dimensional volume in (Q,E) space and, thus, determine the dispersion surface
and linewidths of the (~ 102 meV) and (~ 159 meV) type phonon
modes for the whole Brillouin zone. Despite of having linewidths of , modes do not strongly contribute to the total electron-phonon
coupling constant . However, experimental linewidths show a remarkable
agreement with ab-initio calculations over the complete phonon energy range
demonstrating the accuracy of such calculations in a rare comparison to a
comprehensive experimental data set.Comment: accepted for publication in PR
Turbulent states in plane Couette flow with rotation
Shearing and rotational forces in fluids can significantly alter the
transport of momentum.A numerical investigation was undertaken to study the
role of these forces using plane Couette flow subject to rotation about an axis
perpendicular to both wall-normal and streamwise directions. Using a set of
progressively higher Reynolds numbers up to Re = 5200, we find that the torque
for a given Re is a non-monotonic function of rotation number, Ro. For
low-to-moderate turbulent Reynolds numbers we find a maximum that is associated
with flow fields that are dominated by downstream vortices and calculations of
2-d vortices capture the maximum also quantitatively. For higher shear Reynolds
numbers a second stronger maximum emerges at smaller rotation numbers, closer
to non-rotating plane Couette flow. It is carried by flows with a markedly 3-d
structure and cannot be captured by 2-d vortex studies. As the Reynolds number
increases, this maximum becomes stronger and eventually overtakes the one
associated with the 2-d flow state.Comment: 15 pages, 10 figure
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