12,625 research outputs found
Superconductivity Near a Quantum Critical Point in Ba(Fe,Co)2As2
We will examine the possible link between spin fluctuations and the
superconducting mechanism in the iron-based high temperature superconductor
Ba(Fe,Co)2As2 based on NMR and high pressure transport measurements.Comment: Invited paper to m2s-IX (2009
Systematics of fusion probability in "hot" fusion reactions
The fusion probability in "hot" fusion reactions leading to the synthesis of
super-heavy nuclei is investigated systematically. The quasi-fission barrier
influences the formation of the super-heavy nucleus around the "island of
stability" in addition to the shell correction. Based on the quasi-fission
barrier height obtained with the Skyrme energy-density functional, we propose
an analytical expression for the description of the fusion probability, with
which the measured evaporation residual cross sections can be reproduced
acceptably well. Simultaneously, some special fusion reactions for synthesizing
new elements 119 and 120 are studied. The predicted evaporation residual cross
sections for 50Ti+249Bk are about 10-150fb at energies around the
entrance-channel Coulomb barrier. For the fusion reactions synthesizing element
120 with projectiles 54Cr and 58Fe, the cross sections fall to a few femtobarns
which seems beyond the limit of the available facilities.Comment: 5 figures, 1 tabl
Extremal Isolated Horizon/CFT Correspondence
The near-horizon limit of the extremal (weakly) isolated horizon is obtained
under the Bondi-like coordinates. For the vacuum case, explicit coordinate
transformation relating the near-horizon metric under the Bondi-like
coordinates and the standard Poincar\'e-type or global near-horizon metric of
the extremal Kerr black hole is found, which shows that the two geometries are
the same. Combined with the known thermodynamics of the (weakly) isolated
horizon, it is argued that the Kerr/CFT correspondence can be generalized to
the case of a large class of non-stationary extremal black holes.Comment: 13 pages, no figure, revtex4; v2: abstract revised, minor
corrections, references added; v3: minor corrections, version to appear in
PR
Adjusted Empirical Likelihood for Long-memory Time Series Models
Empirical likelihood method has been applied to short-memory time series
models by Monti (1997) through the Whittle's estimation method. Yau (2012)
extended this idea to long-memory time series models. Asymptotic distributions
of the empirical likelihood ratio statistic for short and long-memory time
series have been derived to construct confidence regions for the corresponding
model parameters. However, computing profile empirical likelihood function
involving constrained maximization does not always have a solution which leads
to several drawbacks. In this paper, we propose an adjusted empirical
likelihood procedure to modify the one proposed by Yau (2012) for
autoregressive fractionally integrated moving average (ARFIMA) model. It
guarantees the existence of a solution to the required maximization problem as
well as maintains same asymptotic properties obtained by Yau (2012).
Simulations have been carried out to illustrate that the adjusted empirical
likelihood method for different long-time series models provides better
confidence regions and coverage probabilities than the unadjusted ones,
especially for small sample sizes
Inverted spin polarization of Heusler alloys for new spintronic devices
A new magnetic logic overcomes the major limitations of field programmable
gate arrays while having a 50% smaller unit cell than conventional designs
utilizing magnetic tunnel junctions with one Heusler alloy electrode. These
show positive and negative TMR values at different bias voltages at room
temperature which generally adds an additional degree of freedom to all
spintronic devices
Explanation of the RHIC HBT Puzzle by a Granular Source of Quark-Gluon Plasma Droplets
We present a review on the explanation of the RHIC HBT puzzle by a granular
pion-emitting source of quark-gluon plasma droplets. The evolution of the
droplet is described by relativistic hydrodynamics with an equation of state
suggested by lattice gauge results. The granular source evolution is obtained
by superposing all of the evolutions of individual droplets. Pions are assumed
to be emitted thermally from the droplets at the freeze-out configuration
characterized by a freeze-out temperature . We find that the average
particle emission time scales with the initial radius of the droplet. Pions
will be emitted earlier if the droplet radius is smaller. An earlier emission
time will lead to a smaller extracted HBT radius , while the
extracted HBT radius is determined by the scale of the
distribution of the droplet centers. However, a collective expansion of the
droplets can further decrease . As a result, the value of can be close to, or even less than 1 for theComment: 8 pages, 4 figures, invited talk presented at the XI International
Workshop on Correlation and Fluctuation in Multiparticle Production, Nov.
21-24, 2006, Hangzhou, Chin
Non-damping oscillations at flaring loops
Context. QPPs are usually detected as spatial displacements of coronal loops
in imaging observations or as periodic shifts of line properties in
spectroscopic observations. They are often applied for remote diagnostics of
magnetic fields and plasma properties on the Sun. Aims. We combine imaging and
spectroscopic measurements of available space missions, and investigate the
properties of non-damping oscillations at flaring loops. Methods. We used the
IRIS to measure the spectrum over a narrow slit. The double-component Gaussian
fitting method was used to extract the line profile of Fe XXI 1354.08 A at "O
I" window. The quasi-periodicity of loop oscillations were identified in the
Fourier and wavelet spectra. Results. A periodicity at about 40 s is detected
in the line properties of Fe XXI, HXR emissions in GOES 1-8 A derivative, and
Fermi 26-50 keV. The Doppler velocity and line width oscillate in phase, while
a phase shift of about Pi/2 is detected between the Doppler velocity and peak
intensity. The amplitudes of Doppler velocity and line width oscillation are
about 2.2 km/s and 1.9 km/s, respectively, while peak intensity oscillate with
amplitude at about 3.6% of the background emission. Meanwhile, a quasi-period
of about 155 s is identified in the Doppler velocity and peak intensity of Fe
XXI, and AIA 131 A intensity. Conclusions. The oscillations at about 40 s are
not damped significantly during the observation, it might be linked to the
global kink modes of flaring loops. The periodicity at about 155 s is most
likely a signature of recurring downflows after chromospheric evaporation along
flaring loops. The magnetic field strengths of the flaring loops are estimated
to be about 120-170 G using the MHD seismology diagnostics, which are
consistent with the magnetic field modeling results using the flux rope
insertion method.Comment: 9 pages, 9 figures, 1 table, accepted by A&
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