16,633 research outputs found
Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. III: Role of particle-number projection
Starting from HFB-6, we have constructed a new mass table, referred to as
HFB-8, including all the 9200 nuclei lying between the two drip lines over the
range of Z and N > 6 and Z < 122. It differs from HFB-6 in that the wave
function is projected on the exact particle number. Like HFB-6, the isoscalar
effective mass is constrained to the value 0.80 M and the pairing is density
independent. The rms errors of the mass-data fit is 0.635 MeV, i.e. better than
almost all our previous HFB mass formulas. The extrapolations of this new mass
formula out to the drip lines do not differ significantly from the previous
HFB-6 mass formula.Comment: 9 pages, 7 figures, accepted for publication in Phys. Rev.
An Empirically Based Calculation of the Extragalactic Infrared Background
Using the excellent observed correlations among various infrared wavebands
with 12 and 60 micron luminosities, we calculate the 2-300 micron spectra of
galaxies as a function of luminosity. We then use 12 micron and 60 micron
galaxy luminosity functions derived from IRAS data, together with recent data
on the redshift evolution of galaxy emissivity, to derive a new, empirically
based IR background spectrum from stellar and dust emission in galaxies. Our
best estimate for the IR background is of order 2-3 nW/m^2/sr with a peak
around 200 microns reaching 6-8 nW/m^2/sr. Our empirically derived background
spectrum is fairly flat in the mid-IR, as opposed to spectra based on modeling
with discrete temperatures which exhibit a "valley" in the mid-IR. We also
derive a conservative lower limit to the IR background which is more than a
factor of 2 lower than our derived flux.Comment: 14 pages AASTeX, 2 .ps figures, the Astrophysical Journal, in pres
Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. II: Role of the effective mass
We have constructed four new complete mass tables, referred to as HFB-4 to
HFB-7, each one including all the 9200 nuclei lying between the two drip lines
over the range of Z and N>8 and Z<120. HFB-4 and HFB-5 have the isoscalar
effective mass M*_s$ constrained to the value 0.92 M, with the former having a
density-independent pairing, and the latter a density-dependent pairing. HFB-6
and HFB-7 are similar, except that M*_s is constrained to 0.8 M. The rms errors
of the mass-data fits are 0.680, 0.675, 0.686, and 0.676 MeV, respectively,
almost as good as for the HFB-2 mass formula, for which M*_s was unconstrained.
However, as usual, the single-particle spectra depend significantly on M*_s.
This decoupling of the mass fits from the fits to the single-particle spectra
has been achieved only by making the cutoff parameter of the delta-function
pairing force a free parameter. An improved treatment of the center-of-mass
correction was adopted, but although this makes a difference to individual
nuclei it does not reduce the overall rms error of the fit. The extrapolations
of all four new mass formulas out to the drip lines are essentially the same as
for the original HFB-2 mass formula.Comment: 12 pages revtex, 9 eps figures, accepted for publication in Phys.
Rev.
Quantifying spin Hall angles from spin pumping: Experiments and Theory
Spin Hall effects intermix spin and charge currents even in nonmagnetic
materials and, therefore, ultimately may allow the use of spin transport
without the need for ferromagnets. We show how spin Hall effects can be
quantified by integrating permalloy/normal metal (N) bilayers into a coplanar
waveguide. A dc spin current in N can be generated by spin pumping in a
controllable way by ferromagnetic resonance. The transverse dc voltage detected
along the permalloy/N has contributions from both the anisotropic
magnetoresistance (AMR) and the spin Hall effect, which can be distinguished by
their symmetries. We developed a theory that accounts for both. In this way, we
determine the spin Hall angle quantitatively for Pt, Au and Mo. This approach
can readily be adapted to any conducting material with even very small spin
Hall angles.Comment: 4 pages, 4 figure
Semi-classical equation of state and specific heats for neutron-star inner crust with proton shell corrections
An approach to the equation of state for the inner crust of neutron stars
based on Skyrme-type forces is presented. Working within the Wigner-Seitz
picture, the energy is calculated by the TETF (temperature-dependent extended
Thomas-Fermi) method, with proton shell corrections added self-consistently by
the Strutinsky-integral method. Using a Skyrme force that has been fitted to
both neutron matter and to essentially all the nuclear mass data, we find
strong proton shell effects: proton numbers = 50, 40 and 20 are the only
values possible in the inner crust, assuming that nuclear equilibrium is
maintained in the cooling neutron star right down to the ambient temperature.
Convergence problems with the TETF expansion for the entropy, and our way of
handling them, are discussed. Full TETF expressions for the specific heat of
inhomogeneous nuclear matter are presented. Our treatment of the electron gas,
including its specific heat, is essentially exact, and is described in detail.Comment: 41 pages, 6 figure
Evaluating elbow osteoarthritis within the prehistoric Tiwanaku state using generalized estimating equations (GEE).
OBJECTIVES:Studies of osteoarthritis (OA) in human skeletal remains can come with scalar problems. If OA measurement is noted as present or absent in one joint, like the elbow, results may not identify specific articular pathology data and the sample size may be insufficient to address research questions. If calculated on a per data point basis (i.e., each articular surface within a joint), results may prove too data heavy to comprehensively understand arthritic changes, or one individual with multiple positive scores may skew results and violate the data independence required for statistical tests. The objective of this article is to show that the statistical methodology Generalized Estimating Equations (GEE) can solve scalar issues in bioarchaeological studies. MATERIALS AND METHODS:Using GEE, a population-averaged statistical model, 1,195 adults from the core and one colony of the prehistoric Tiwanaku state (AD 500-1,100) were evaluated bilaterally for OA on the seven articular surfaces of the elbow joint. RESULTS:GEE linked the articular surfaces within each individual specimen, permitting the largest possible unbiased dataset, and showed significant differences between core and colony Tiwanaku peoples in the overall elbow joint, while also pinpointing specific articular surfaces with OA. Data groupings by sex and age at death also demonstrated significant variation. A pattern of elbow rotation noted for core Tiwanaku people may indicate a specific pattern of movement. DISCUSSION:GEE is effective and should be encouraged in bioarchaeological studies as a way to address scalar issues and to retain all pathology information
Recurrence interval analysis of high-frequency financial returns and its application to risk estimation
We investigate the probability distributions of the recurrence intervals
between consecutive 1-min returns above a positive threshold or
below a negative threshold of two indices and 20 individual stocks in
China's stock market. The distributions of recurrence intervals for positive
and negative thresholds are symmetric, and display power-law tails tested by
three goodness-of-fit measures including the Kolmogorov-Smirnov (KS) statistic,
the weighted KS statistic and the Cram\'er-von Mises criterion. Both long-term
and shot-term memory effects are observed in the recurrence intervals for
positive and negative thresholds . We further apply the recurrence interval
analysis to the risk estimation for the Chinese stock markets based on the
probability , Value-at-Risk (VaR) analysis and VaR analysis
conditioned on preceding recurrence intervals.Comment: 17 pages, 10 figures, 1 tabl
Limits on Arcminute Scale Cosmic Microwave Background Anisotropy with the BIMA Array
We have used the Berkeley-Illinois-Maryland-Association (BIMA) millimeter
array outfitted with sensitive cm-wave receivers to search for Cosmic Microwave
Background (CMB) anisotropies on arcminute scales. The interferometer was
placed in a compact configuration which produces high brightness sensitivity,
while providing discrimination against point sources. Operating at a frequency
of 28.5 GHz, the FWHM primary beam of the instrument is 6.6 arcminutes. We have
made sensitive images of seven fields, five of which where chosen specifically
to have low IR dust contrast and be free of bright radio sources. Additional
observations with the Owens Valley Radio Observatory (OVRO) millimeter array
were used to assist in the location and removal of radio point sources.
Applying a Bayesian analysis to the raw visibility data, we place limits on CMB
anisotropy flat-band power Q_flat = 5.6 (+3.0 -5.6) uK and Q_flat < 14.1 uK at
68% and 95% confidence. The sensitivity of this experiment to flat band power
peaks at a multipole of l = 5470, which corresponds to an angular scale of
approximately 2 arcminutes. The most likely value of Q_flat is similar to the
level of the expected secondary anisotropies.Comment: 15 pages, 5 figures, LaTex, aas2pp4.sty, ApJ submitte
Voltage-Controlled Superconducting Quantum Bus
We demonstrate the ability of an epitaxial semiconductor-superconductor
nanowire to serve as a field-effect switch to tune a superconducting cavity.
Two superconducting gatemon qubits are coupled to the cavity, which acts as a
quantum bus. Using a gate voltage to control the superconducting switch yields
up to a factor of 8 change in qubit-qubit coupling between the on and off
states without detrimental effect on qubit coherence. High-bandwidth operation
of the coupling switch on nanosecond timescales degrades qubit coherence
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