642 research outputs found
Ultrasonic Attenuation in Clean d-Wave Superconductors
We calculate the low temperature longitudinal ultrasonic attenuation rate
in clean d-wave superconductors. We consider the contribution of
previously ignored processes involving the excitation of a pair of quasi-holes
or quasi-particles. These processes, which are forbidden by energy conservation
in conventional s-wave superconductors, have a finite phase space in d-wave
superconductors due to the presence of nodes in the gap which give rise to soft
low-energy electronic excitations. We find the contribution to from
these processes to be proportional to in the regime ,(ultra-low temperature regime) and to be proportional to 1/T in
the region , (low temperature regime) where is the ultrasound wave-vector and is the maximum gap amplitude.
We explicitly evaluate these terms, for parameters appropriate to the cuprates,
for along the nodal and the antinodal directions and compare it with
the contribution from processes considered earlier(I.Vekhter et al {\it Phys.
Rev.}{\bf B59}, 7123(1999)). In the ultra-low temperature regime, the processes
considered by us make a contribution which is smaller by about a factor of 10
for along the nodal direction, while along the antinodal direction it
is larger by a factor of 100 or so. In the low temperature regime on the other
hand the contribution made by these terms is small. However taken together with
the original terms we describe a possible way to evaluate the parameter
.Comment: 9 pages, RevTex, accepted for publication in Physica
R-parity violation effect on the top-quark pair production at linear colliders
We investigate in detail the effects of the R-parity lepton number violation
in the minimal supersymmetric standard model (MSSM) on the top-quark pair
production via both and collision modes at the linear
colliders. We find that with the present experimental constrained
parameters, the effect from interactions on the processes
and could be
significant and may reach -30% and several percent, respectively. Our results
show that the effects are sensitive to the c.m.s. energy and the
relevant parameters. However, they are not sensitive to squark and
slepton masses when (or ) and are almost independent on the Comment: Accepted by Phys.Rev.
Quasi-spin Model for Macroscopic Quantum Tunnelling between Two Coupled Bose-Einstein Condensates
The macroscopic quantum tunneling between two coupled Bose-Einstein
condensates (BEC) (radio-frequency coupled two-component BECs or two BECs
confined in a double-well potential) is mapped onto the tunneling of an
uniaxial spin with an applied magnetic field. The tunneling exponent is
calculated with an imaginary-time path-integral method. In the limit of low
barrier, the dependence of tunneling exponent on the system parameters is
obtained, and the crossover temperature from thermal regime to quantum regime
is estimated. The detailed information about the tunnelling will give help to
control population conversion between coupled BECs and realize quantum
computation with coupled BECs.Comment: 20 pages, 4 figures, accepted by Phys.Rev.
Microscopic View on Short-Range Wetting at the Free Surface of the Binary Metallic Liquid Gallium-Bismuth: An X-ray Reflectivity and Square Gradient Theory Study
We present an x-ray reflectivity study of wetting at the free surface of the
binary liquid metal gallium-bismuth (Ga-Bi) in the region where the bulk phase
separates into Bi-rich and Ga-rich liquid phases. The measurements reveal the
evolution of the microscopic structure of wetting films of the Bi-rich,
low-surface-tension phase along different paths in the bulk phase diagram. A
balance between the surface potential preferring the Bi-rich phase and the
gravitational potential which favors the Ga-rich phase at the surface pins the
interface of the two demixed liquid metallic phases close to the free surface.
This enables us to resolve it on an Angstrom level and to apply a mean-field,
square gradient model extended by thermally activated capillary waves as
dominant thermal fluctuations. The sole free parameter of the gradient model,
i.e. the so-called influence parameter, , is determined from our
measurements. Relying on a calculation of the liquid/liquid interfacial tension
that makes it possible to distinguish between intrinsic and capillary wave
contributions to the interfacial structure we estimate that fluctuations affect
the observed short-range, complete wetting phenomena only marginally. A
critical wetting transition that should be sensitive to thermal fluctuations
seems to be absent in this binary metallic alloy.Comment: RevTex4, twocolumn, 15 pages, 10 figure
Tea drinking and cognitive function in oldest-old Chinese
10.1007/s12603-012-0077-1The Journal of Nutrition, Health & Aging169754-75
Partial Wave Analysis of
BES data on are presented. The
contribution peaks strongly near threshold. It is fitted with a
broad resonance with mass MeV, width MeV. A broad resonance peaking at 2020 MeV is also required
with width MeV. There is further evidence for a component
peaking at 2.55 GeV. The non- contribution is close to phase
space; it peaks at 2.6 GeV and is very different from .Comment: 15 pages, 6 figures, 1 table, Submitted to PL
Management of children visiting the emergency department during out-of-office hours: An observational study
Background The aim was to study the characteristics
and management of children visiting the emergency
department (ED) during out-of-office hours.
Methods We analysed electronic health record data from
119 204 children visiting one of five EDs in four European
countries. Patient characteristics and management
(diagnostic tests, treatment, hospital admission and
paediatric intensive care unit admission) were compared
between children visiting during office hours and evening
shifts, night shifts and weekend day shifts. Analyses were
corrected for age, gender, Manchester Triage System
urgency, abnormal vital signs, presenting problems and
hospital.
Results Patients presenting at night were younger
(median (IQR) age: 3.7 (1.4–8.2) years vs 4.8 (1.8–9.9)),
more often classified as high urgent (16.3% vs 9.9%) and
more often had ≥2 abnormal vital signs (22.8% vs 18.1%)
compared with office hours. After correcting for disease
severity, laboratory and radiological tests were less likely
to be requested (adjusted OR (aOR): 0.82, 95% CI 0.78–
0.86 and aOR: 0.64, 95% CI 0.60–0.67, respectively);
treatment
X-Ray Polarization of Solar Flares Measured with Rhessi
The degree of linear polarization in solar flares has not yet been precisely
determined despite multiple attempts to measure it with different missions. The
high energy range in particular has very rarely been explored, due to its
greater instrumental difficulties. We approached the subject using the Reuven
Ramaty High Energy Spectroscopic Imager (RHESSI) satellite to study 6 X-class
and 1 M-class flares in the energy range between 100 keV and 350 keV. Using
RHESSI as a polarimeter requires the application of strict cuts to the event
list in order to extract those photons that are Compton scattered between two
detectors. Our measurements show polarization values between 2% and 54%, with
errors ranging from 10% to 26% in 1 sigma level. In view of the large
uncertainties in both the magnitude and direction of the polarization vector,
the results can only reject source models with extreme properties.Comment: 26 pages, 11 figures, accepted for publication by Solar Physic
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS
The chi_b(nP) quarkonium states are produced in proton-proton collisions at
the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS
detector. Using a data sample corresponding to an integrated luminosity of 4.4
fb^-1, these states are reconstructed through their radiative decays to
Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks
corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new
structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is
also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes.
This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table,
corrected author list, matches final version in Physical Review Letter
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