5,930 research outputs found
Fluctuation Study of the Specific Heat of MgB2
The specific heat of polycrystalline MgB has been measured with
high resolution ac calorimetry from 5 to 45 K at constant magnetic fields. The
excess specific heat above T is discussed in terms of Gaussian
fluctuations and suggests that MgB is a bulk superconductor with
Ginzburg-Landau coherence length \AA . The transition-width
broadening in field is treated in terms of lowest-Landau-level (LLL)
fluctuations. That analysis requires that \AA . The underestimate
of the coherence length in field, along with deviations from 3D LLL
predictions, suggest that there is an influence from the anisotropy of B
between the c-axis and the a-b plane.Comment: Phys. Rev. B 66, 134515 (2002
Improving Phase Change Memory Performance with Data Content Aware Access
A prominent characteristic of write operation in Phase-Change Memory (PCM) is
that its latency and energy are sensitive to the data to be written as well as
the content that is overwritten. We observe that overwriting unknown memory
content can incur significantly higher latency and energy compared to
overwriting known all-zeros or all-ones content. This is because all-zeros or
all-ones content is overwritten by programming the PCM cells only in one
direction, i.e., using either SET or RESET operations, not both. In this paper,
we propose data content aware PCM writes (DATACON), a new mechanism that
reduces the latency and energy of PCM writes by redirecting these requests to
overwrite memory locations containing all-zeros or all-ones. DATACON operates
in three steps. First, it estimates how much a PCM write access would benefit
from overwriting known content (e.g., all-zeros, or all-ones) by
comprehensively considering the number of set bits in the data to be written,
and the energy-latency trade-offs for SET and RESET operations in PCM. Second,
it translates the write address to a physical address within memory that
contains the best type of content to overwrite, and records this translation in
a table for future accesses. We exploit data access locality in workloads to
minimize the address translation overhead. Third, it re-initializes unused
memory locations with known all-zeros or all-ones content in a manner that does
not interfere with regular read and write accesses. DATACON overwrites unknown
content only when it is absolutely necessary to do so. We evaluate DATACON with
workloads from state-of-the-art machine learning applications, SPEC CPU2017,
and NAS Parallel Benchmarks. Results demonstrate that DATACON significantly
improves system performance and memory system energy consumption compared to
the best of performance-oriented state-of-the-art techniques.Comment: 18 pages, 21 figures, accepted at ACM SIGPLAN International Symposium
on Memory Management (ISMM
Magnetic-Field Variations of the Pair-Breaking Effects of Superconductivity in (TMTSF)2ClO4
We have studied the onset temperature of the superconductivity Tc_onset of
the organic superconductor (TMTSF)2ClO4, by precisely controlling the direction
of the magnetic field H. We compare the results of two samples with nearly the
same onset temperature but with different scattering relaxation time tau. We
revealed a complicated interplay of a variety of pair-breaking effects and
mechanisms that overcome these pair-breaking effects. In low fields, the linear
temperature dependences of the onset curves in the H-T phase diagrams are
governed by the orbital pair-breaking effect. The dips in the in-plane
field-angle phi dependence of Tc_onset, which were only observed in the
long-tau sample, provides definitive evidence that the field-induced
dimensional crossover enhances the superconductivity if the field direction is
more than about 19-degrees away from the a axis. In the high-field regime for
H//a, the upturn of the onset curve for the long-tau sample indicates a new
superconducting state that overcomes the Pauli pair-breaking effect but is
easily suppressed by impurity scatterings. The Pauli effect is also overcome
for H//b' by a realization of another state for which the maximum of
Tc_onset(phi) occurs in a direction different from the crystalline axes. The
effect on Tc_onset of tilting the applied field out of the conductive plane
suggests that the Pauli effect plays a significant role in determining
Tc_onset. The most plausible explanation of these results is that (TMTSF)2ClO4
is a singlet superconductor and exhibits Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) states in high fields.Comment: 12 pages, 10 figures. To be published in J. Phys. Soc. Jpn. (vol.77,
2008
Transport properties and microstructure of La0.7Sr0.3MnO3 nanocrystalline thin films grown by polymer-assisted chemical solution deposition
Study of time-dependent CP violation in B0 -> J/Psi pi0 decays
We report a measurement of CP asymmetry parameters in the decay B0(B0bar) ->
J/Psi pi0, which is governed by the b->c cbar d transition. The analysis is
based on a 140/fb data sample accumulated at the Upsilon(4S) resonance by the
belle detector at the KEKB asymmetric-energy e+e- collider. We fully
reconstruct one neutral B meson in the J/Psi pi0 final state. The accompanying
B meson flavor is identified by its decay products. From the distribution of
proper time intervals between the two B decays, we obtain the following
CP-violating parameters: S_{J/Psi pi0}=-0.72+-0.42+-0.09 and A_{J/Psi
pi0}=-0.01 +-0.29+-0.03.Comment: 5 pages, 2 figures, submitted to PR
Search for the b --> d gamma process
We report the results of a search for the flavor-changing neutral current
process b --> d gamma using a sample of 275 million B meson pairs accumulated
by the Belle detector at KEKB. We find no significant signal for the exclusive
decays B- --> rho- gamma, B0B --> rho0 gamma, or B0B --> omega gamma. Assuming
an isospin relation between the three modes, we set an upper limit for the
combined branching fraction Br(B --> (rho,omega) gamma) < 1.4 x 10-6 at the 90%
confidence level. This limit can be used to constrain the ratio of CKM matrix
elements |Vtd/Vts|.Comment: 6 pages, 2 figures, submitted to Phys. Rev. D (RC
Observation of a near-threshold omega-J/psi mass enhancement in exclusive B-->K omega J/psi decays
We report the observation of a near-threshold enhancement in the omega-J/psi
invariant mass distribution for exclusive B-->K omega J/psi decays. The results
are obtained from a 253 fb-1 data sample that contains 275 million BB-bar meson
pairs that were collected near the Upsilon(4S) resonance with the Belle
detector at the KEKB asymmetric energy e+e- collider. The statistical
significance of the omega-J/psi mass enhancement is estimated to be greater
than 8 sigma.Comment: 12 pages, 4 figures, submitted to Physical Review Letter
Search for the Lepton-Flavor-Violating Decay at Belle
We have searched for the Lepton Flavor Violating decay using a data sample of 84.3 fb accumulated with the Belle detector
at KEK. The -meson was detected through the decay modes: and . No signal candidates are found, and we
obtain an upper limit for the branching fraction at the 90% confidence level.Comment: Submitted to Phys.Rev.Let
Evidence of B0 --> rho0 pi0
We present the first evidence of the decay B0 --> rho0 pi0, using 140fb^-1 of
data collected at the Upsilon(4S) resonance with the Belle detector at the KEKB
asymmetric e+e- collider. We detect a signal with a significance of 3.5
standard deviations, and measure the branching fraction to be Br(B0 ->- rho0
pi0) = (5.1 +/- 1.6(stat) +/- 0.9(syst))*10^-6.Comment: RevTex4, 5 pages, 4 figures, submitted to Phys.Rev.Let
An inclusive measurement of the photon energy spectrum in b->s gamma decays
We report a fully inclusive measurement of the flavour changing neutral
current decay b->s gamma in the energy range 1.8 GeV < E* < 2.8 GeV, covering
95% of the total spectrum. Using 140 fb^-1 we obtain BF(b->s gamma)= 3.55 +/-
0.32 +0.30-0.31 +0.11-0.07, where the errors are statistical, systematic and
from theory corrections. We also measure the first and second moments of the
photon energy spectrum above 1.8 GeV and obtain = 2.292 +/- 0.026 +/- 0.034
GeV and -^2 = 0.0305 +/- 0.0074 +/- 0.0063 GeV^2, where the errors are
statistical and systematic.Comment: RevTex4, 6 pages, Submitted to Phys.Rev.Lett. Replaced: added table
of systematic errors. New results take into account radiative J/Psi decay
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