18,990 research outputs found
Ferromagnetic resonance with a magnetic Josephson junction
We show experimentally and theoretically that there is a coupling via the
Aharonov-Bohm phase between the order parameter of a ferromagnet and a singlet,
s-wave, Josephson supercurrent. We have investigated the possibility of
measuring the dispersion of such spin waves by varying the magnetic field
applied in the plane of the junction and demonstrated the electromagnetic
nature of the coupling by the observation of magnetic resonance side-bands to
microwave induced Shapiro steps.Comment: 6 pages, 5 figure
On a q-analogue of the multiple gamma functions
A -analogue of the multiple gamma functions is introduced, and is shown to
satisfy the generalized Bohr-Morellup theorem. Furthermore we give some
expressions of these function.Comment: 8 pages, AMS-Late
A three-loop check of the 'a - maximization' in SQCD with adjoint(s)
The 'a - maximization' was introduced by K. Inrtiligator and B. Wecht for
finding anomalous dimensions of chiral superfields at the IR fixed points of
the RG flow. Using known explicit calculations of anomalous dimensions in the
perturbation theory of SQCD (with one or two additional adjoint fields), it is
checked here at the three-loop level.Comment: 5 pages; the title changed, the text improved and expande
Statistics of anomalously localized states at the center of band E=0 in the one-dimensional Anderson localization model
We consider the distribution function of the eigenfunction
amplitude at the center-of-band (E=0) anomaly in the one-dimensional
tight-binding chain with weak uncorrelated on-site disorder (the
one-dimensional Anderson model). The special emphasis is on the probability of
the anomalously localized states (ALS) with much larger than the
inverse typical localization length . Using the solution to the
generating function found recently in our works we find the
ALS probability distribution at . As
an auxiliary preliminary step we found the asymptotic form of the generating
function at which can be used to compute other
statistical properties at the center-of-band anomaly. We show that at
moderately large values of , the probability of ALS at E=0
is smaller than at energies away from the anomaly. However, at very large
values of , the tendency is inverted: it is exponentially
easier to create a very strongly localized state at E=0 than at energies away
from the anomaly. We also found the leading term in the behavior of
at small and show that it is
consistent with the exponential localization corresponding to the Lyapunov
exponent found earlier by Kappus and Wegner and Derrida and Gardner.Comment: 25 pages, 9 figure
Bi-layer splitting in overdoped high cuprates
Recent angle-resolved photoemission data for overdoped Bi2212 are explained.
Of the peak-dip-hump structure, the peak corresponds the component
of a hole condensate which appears at . The fluctuating part of this same
condensate produces the hump. The bilayer splitting is large enough to produce
a bonding hole and an electron antibonding quasiparticle Fermi surface. Smaller
bilayer splittings observed in some experiments reflect the interaction of the
peak structure with quasiparticle states near, but not at, the Fermi surface.Comment: 4 pages with 2 figures - published versio
Turbulent transport in tokamak plasmas with rotational shear
Nonlinear gyrokinetic simulations have been conducted to investigate
turbulent transport in tokamak plasmas with rotational shear. At sufficiently
large flow shears, linear instabilities are suppressed, but transiently growing
modes drive subcritical turbulence whose amplitude increases with flow shear.
This leads to a local minimum in the heat flux, indicating an optimal E x B
shear value for plasma confinement. Local maxima in the momentum fluxes are
also observed, allowing for the possibility of bifurcations in the E x B shear.
The sensitive dependence of heat flux on temperature gradient is relaxed for
large flow shear values, with the critical temperature gradient increasing at
lower flow shear values. The turbulent Prandtl number is found to be largely
independent of temperature and flow gradients, with a value close to unity.Comment: 4 pages, 5 figures, submitted to PR
PEPSI deep spectra. III. A chemical analysis of the ancient planet-host star Kepler-444
We obtained an LBT/PEPSI spectrum with very high resolution and high
signal-to-noise ratio (S/N) of the K0V host Kepler-444, which is known to host
5 sub-Earth size rocky planets. The spectrum has a resolution of R=250,000, a
continuous wavelength coverage from 4230 to 9120A, and S/N between 150 and
550:1 (blue to red). We performed a detailed chemical analysis to determine the
photospheric abundances of 18 chemical elements, in order to use the abundances
to place constraints on the bulk composition of the five rocky planets. Our
spectral analysis employs the equivalent width method for most of our spectral
lines, but we used spectral synthesis to fit a small number of lines that
require special care. In both cases, we derived our abundances using the MOOG
spectral analysis package and Kurucz model atmospheres. We find no correlation
between elemental abundance and condensation temperature among the refractory
elements. In addition, using our spectroscopic stellar parameters and isochrone
fitting, we find an age of 10+/-1.5 Gyr, which is consistent with the
asteroseismic age of 11+/-1 Gyr. Finally, from the photospheric abundances of
Mg, Si, and Fe, we estimate that the typical Fe-core mass fraction for the
rocky planets in the Kepler-444 system is approximately 24 per cent. If our
estimate of the Fe-core mass fraction is confirmed by more detailed modeling of
the disk chemistry and simulations of planet formation and evolution in the
Kepler-444 system, then this would suggest that rocky planets in more
metal-poor and alpha-enhanced systems may tend to be less dense than their
counterparts of comparable size in more metal-rich systems.Comment: in press, 11 pages, 3 figures, data available from pepsi.aip.d
Multiscale Gyrokinetics for Rotating Tokamak Plasmas: Fluctuations, Transport and Energy Flows
This paper presents a complete theoretical framework for plasma turbulence
and transport in tokamak plasmas. The fundamental scale separations present in
plasma turbulence are codified as an asymptotic expansion in the ratio of the
gyroradius to the equilibrium scale length. Proceeding order-by-order in this
expansion, a framework for plasma turbulence is developed. It comprises an
instantaneous equilibrium, the fluctuations driven by gradients in the
equilibrium quantities, and the transport-timescale evolution of mean profiles
of these quantities driven by the fluctuations. The equilibrium distribution
functions are local Maxwellians with each flux surface rotating toroidally as a
rigid body. The magnetic equillibrium is obtained from the Grad-Shafranov
equation for a rotating plasma and the slow (resistive) evolution of the
magnetic field is given by an evolution equation for the safety factor q.
Large-scale deviations of the distribution function from a Maxwellian are given
by neoclassical theory. The fluctuations are determined by the high-flow
gyrokinetic equation, from which we derive the governing principle for
gyrokinetic turbulence in tokamaks: the conservation and local cascade of free
energy. Transport equations for the evolution of the mean density, temperature
and flow velocity profiles are derived. These transport equations show how the
neoclassical corrections and the fluctuations act back upon the mean profiles
through fluxes and heating. The energy and entropy conservation laws for the
mean profiles are derived. Total energy is conserved and there is no net
turbulent heating. Entropy is produced by the action of fluxes flattening
gradients, Ohmic heating, and the equilibration of mean temperatures. Finally,
this framework is condensed, in the low-Mach-number limit, to a concise set of
equations suitable for numerical implementation.Comment: 113 pages, 3 figure
Zero-Turbulence Manifold in a Toroidal Plasma
Sheared toroidal flows can cause bifurcations to zero-turbulent-transport
states in tokamak plasmas. The maximum temperature gradients that can be
reached are limited by subcritical turbulence driven by the parallel velocity
gradient. Here it is shown that q/\epsilon (magnetic field pitch/inverse aspect
ratio) is a critical control parameter for sheared tokamak turbulence. By
reducing q/\epsilon, far higher temperature gradients can be achieved without
triggering turbulence, in some instances comparable to those found
experimentally in transport barriers. The zero-turbulence manifold is mapped
out, in the zero-magnetic-shear limit, over the parameter space (\gamma_E,
q/\epsilon, R/L_T), where \gamma_E is the perpendicular flow shear and R/L_T is
the normalised inverse temperature gradient scale. The extent to which it can
be constructed from linear theory is discussed.Comment: 5 Pages, 4 Figures, Submitted to PR
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