7,868 research outputs found

### Very Fast Chip-level Thermal Analysis

We present a new technique of VLSI chip-level thermal analysis. We extend a
newly developed method of solving two dimensional Laplace equations to thermal
analysis of four adjacent materials on a mother board. We implement our
technique in C and compare its performance to that of a commercial CAD tool.
Our experimental results show that our program runs 5.8 and 8.9 times faster
while keeping smaller residuals by 5 and 1 order of magnitude, respectively.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions

### Position measurements of rapidly fluctuating microwave bursts

It was investigated whether microwave source positions change while the total fluxes of hard X-rays and microwaves show remarkable rapid fluctuations of the order of seconds. The position measurements were made in one dimension (east-west direction) with the 17 GHz interferometer at Nobeyama. Position changes greater than a few arc seconds can be detected. The result shows that significant position changes are found for five of seven bursts but that no position changes greater than 3 arc seconds are found for the remaining two bursts

### Thermodynamic Construction of an One-Step Replica-Symmetry-Breaking Solution in Finite Connectivity Spin Glasses

An one-step replica-symmetry-breaking solution for finite connectivity
spin-glass models with K body interaction is constructed at finite temperature
using the replica method and thermodynamic constraints. In the absence of
external fields, this construction provides a general extension of replica
symmetric solution at finite replica number to one-step
replica-symmetry-breaking solution. It is found that this result is formally
equivalent to that of the one-step replica-symmetry-breaking cavity method. To
confirm the validity of the obtained solution, Monte Carlo simulations are
performed for K = 2 and 3. The thermodynamic quantities of the Monte Carlo
results extrapolated to a large-size limit are consistent with those estimated
by our solution for K = 2 at all simulated temperatures and for K = 3 except
near the transition temperature.Comment: 11pages, 19 figures. Added content and references. Accepted to Phys.
Rev.

### A Systematic Study of X-Ray Flares from Low-Mass Young Stellar Objects in the Rho Ophiuchi Star-Forming Region with Chandra

We report on the results of a systematic study of X-ray flares from low-mass
young stellar objects, using Chandra observations of the main region of the Rho
Oph. From 195 X-ray sources, including class I-III sources and some young brown
dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the
typical profile of solar and stellar flares, fast rise and slow decay. We
derived the time-averaged temperature (kT), luminosity (L_X), rise and decay
timescales (tau_r and tau_d) of the flares, finding that (1) class I-II sources
tend to have a high kT, (2) the distribution of L_X during flares is nearly the
same for all classes, and (3) positive and negative log-linear correlations are
found between tau_r and tau_d, and kT and tau_r. In order to explain these
relations, we used the framework of magnetic reconnection model to formulate
the observational parameters as a function of the half-length of the
reconnected magnetic loop (L) and magnetic field strength (B). The estimated L
is comparable to the typical stellar radius of these objects (10^{10-11} cm),
which indicates that the observed flares are triggered by solar-type loops,
rather than larger ones (10^{12} cm) connecting the star with its inner
accretion disk. The higher kT observed for class I sources may be explained by
a higher magnetic field strength (about 500 G) than for class II-III sources
(200-300 G).Comment: 33 pages, 7 figures, accepted for publication in PASJ, the complete
version of tables are available at
ftp://ftp-cr.scphys.kyoto-u.ac.jp/pub/crmember/kensuke/PASJ_RhoOph/KI_all.tar
.g

### High-Energy Spin Dynamics in La$_{1.69}$Sr$_{0.31}$NiO$_4$

We have mapped out the spin dynamics in a stripe-ordered nickelate,
La$_{2-x}$Sr$_{x}$NiO$_{4}$ with $x \simeq 0.31$, using inelastic neutron
scattering. We observe spin-wave excitations up to 80 meV emerging from the
incommensurate magnetic peaks with an almost isotropic spin-velocity: $\hbar
c_s\sim 0.32$ eV \AA, very similar to the velocity in the undoped, insulating
parent compound, La$_{2}$NiO$_{4}$. We also discuss the similarities and
differences of the inferred spin-excitation spectrum with those reported in
superconducting high-$T_c$ cuprates.Comment: 4 figure

### An Approach to ${\cal N}=4$ ADE Gauge Theory on K3

We propose a recipe for determination of the partition function of ${\cal
N}=4$ $ADE$ gauge theory on $K3$ by generalizing our previous results of the
SU(N) case. The resulting partition function satisfies Montonen-Olive duality
for $ADE$ gauge group.Comment: 28 pages, Latex, enlarged published versio

### Development of spin correlations in the geometrically frustrated triangular-lattice Heisenberg antiferromagnet CuCrO2

Magnetic excitations in the triangular-lattice Heisenberg antiferromagnet
(TLHA) CuCrO2 were studied using single-crystal inelastic neutron scattering. A
diffusive quasielastic component that persisted without developing a
correlation length over a wide temperature range both below and above the
ordering temperature was observed. Furthermore, characteristic momentum
dependence was observed that was reproduced using minimum spin clusters. The
robust spin clusters contrast with conventional magnetic ordering and may be
universal in TLHAs.Comment: 5 pages, 3 figure

### Inelastic neutron scattering study of phonon anomalies in La1.5Sr0.5NiO4

The high-energy phonons in La1.5Sr0.5NiO4, in which the checkerboard charge
ordering is formed, was investigated by the inelastic neutron scattering. We
found that the longitudinal modes show strong anomalies compared with La2NiO4.
We argue the similarity and difference in the phonon anomalies between the
present sample and the preceding works of different compositions.Comment: 5 pages, 2 figures, to be published in J. Phys.: Conf. Se

### Giant Nernst effect in a Kondo lattice close to a quantum critical point

We present a study of Nernst and Seebeck coefficients of the heavy-fermion
superconductor CeCoIn$_{5}$. Below 18 K, concomitant with a field-dependent
Seebeck coefficient, a large sub-linear Nernst signal emerges with a magnitude
drastically exceeding what is expected for a multi-band Fermi-liquid metal. In
the mixed state, in contrast with all other superconductors studied before,
this signal overwhelms the one associated with the motion of superconducting
vortices. The results point to a hitherto unknown source of transverse
thermoelectricity in strongly interacting electrons.Comment: 5 pages including 3 figure

### Electric Polarization Induced by a Proper Helical Magnetic Ordering in a Delafossite Multiferroic CuFe1-xAlxO2

Multiferroic CuFe1-xAlxO2 (x=0.02) exhibits a ferroelectric ordering
accompanied by a proper helical magnetic ordering below T=7K under zero
magnetic field. By polarized neutron diffraction and pyroelectric measurements,
we have revealed a one-to-one correspondence between the spin helicity and the
direction of the spontaneous electric polarization. This result indicates that
the spin helicity of the proper helical magnetic ordering is essential for the
ferroelectricity in CuFe1-xAlxO2. The induction of the electric polarization by
the proper helical magnetic ordering is, however, cannot be explained by the
Katsura-Nagaosa-Balatsky model, which successfully explains the
ferroelectricity in the recently explored ferroelectric helimagnets, such as
TbMnO3. We thus conclude that CuFe1-xAlxO2 is a new class of magnetic
ferroelectrics.Comment: 4 pages, 4 figure

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