15,437 research outputs found
Direct measurements of the magnetocaloric effect in pulsed magnetic fields: The example of the Heusler alloy NiMnIn
We have studied the magnetocaloric effect (MCE) in the shape-memory Heusler
alloy NiMnIn by direct measurements in pulsed magnetic
fields up to 6 and 20 T. The results in 6 T are compared with data obtained
from heat-capacity experiments. We find a saturation of the inverse MCE,
related to the first-order martensitic transition, with a maximum adiabatic
temperature change of K at 250 K and a conventional
field-dependent MCE near the second-order ferromagnetic transition in the
austenitic phase. The pulsed magnetic field data allow for an analysis of the
temperature response of the sample to the magnetic field on a time scale of
to 100 ms which is on the order of typical operation frequencies (10
to 100 Hz) of magnetocaloric cooling devices. Our results disclose that in
shape-memory alloys the different contributions to the MCE and hysteresis
effects around the martensitic transition have to be carefully considered for
future cooling applications.Comment: 5 pages, 4 figure
Large zero-field cooled exchange-bias in bulk Mn2PtGa
We report a large exchange-bias (EB) effect after zero-field cooling the new
tetragonal Heusler compound Mn2PtGa from the paramagnetic state. The
first-principle calculation and the magnetic measurements reveal that Mn2PtGa
orders ferrimagnetically with some ferromagnetic (FM) inclusions. We show that
ferrimagnetic (FI) ordering is essential to isothermally induce the exchange
anisotropy needed for the zero-field cooled (ZFC) EB during the virgin
magnetization process. The complex magnetic behavior at low temperatures is
characterized by the coexistence of a field induced irreversible magnetic
behavior and a spin-glass-like phase. The field induced irreversibility
originates from an unusual first-order FI to antiferromagnetic transition,
whereas, the spin-glass like state forms due to the existence of anti-site
disorder intrinsic to the material.Comment: 5 pages, 4 figures, supplementary material included in a separate
file; accepted for publication in PR
Fractional statistic
We improve Haldane's formula which gives the number of configurations for
particles on states in a fractional statistic defined by the coupling
. Although nothing is changed in the thermodynamic limit, the new
formula makes sense for finite with integer and A
geometrical interpretation of fractional statistic is given in terms of
''composite particles''.Comment: flatex hald.tex, 3 files Submitted to: Phys. Rev.
Color Octet Contribution to High p_T J/\Psi Production in pp Collisions at \sqrt s = 500 and 200 GeV at RHIC
We compute \frac{d\sigma}{dp_T} of the J/\psi production in pp collisions at
RHIC at \sqrt s = 500 and 200 GeV by using both the color octet and singlet
models in the framework of non-relativistic QCD. The J/\psi we compute here
includes the direct J/\psi from the partonic fusion processes and the J/\psi
coming from the radiative decays of \chi_J's both in the color octet and
singlet channel. The high p_T J/\psi production cross section is computed
within the PHENIX detector acceptance ranges: -0.35 < \eta < 0.35 and 1.2 <
\|\eta| < 2.4, the central electron and forward muon arms. It is found that the
color octet contribution to J/\psi production is dominant at RHIC energy in
comparison to the color singlet contributions. We compare our results with the
recent preliminary data obtained by PHENIX detector for the high p_T J/\psi
measurements. While the color singlet model fails to explain the data
completely the color octet model is in agreement with the single data point
above 2 GeV transverse momentum. A measurement of J/\psi production at RHIC in
the next run with better statistics will allow us to determine the validity of
the color octet model of J/\psi production at RHIC energies. This is very
important because it is necessary to know the exact mechanism for J/\psi
production in pp collisions at RHIC if one is to make predictions of J/\psi
suppression as a signature of quark-gluon plasma. These mechanisms also play an
important role in determining the polarized spin structure function of the
proton at RHIC.Comment: 16 pages latex, 6 figure
A study of complications in cases of placenta previa
Background: Haemorrhage in obstetrics is almost life-threatening emergency especially in the last trimester. Placenta previa contributes to 1/5th of the cases of antepartum haemorrhage. This catastrophic complication not only poses a risk to the fetus but also endangers the mother’s life. The aims of this study were to estimate the incidence of placenta previa and to study the various complications and its impact on maternal and neonatal morbidity and mortality. Methods: An observational prospective clinical study was carried out in Department of OBG-GYN on total 30 cases-admitted patients coming from both rural and urban areas, presented with placenta previa after 28 weeks of pregnancy in duration of January 2012 to August 2013.Results: In the present study, the incidence of placenta previa contributed to 0.23% cases. The general perinatal mortality was 18 per 1000 live births and that due to placenta previa was 6.6 per 1000 live births. The maternal mortality rate due to placenta previa in this study was nil.Conclusions: A marked reduction in maternal mortality rate from placenta previa was achieved during the last half of the 20th century but still placenta previa is an important cause of perinatal morbidity and mortality. A good antenatal care, early detection of placenta previa by ultrasound and the conservative management may definitely contribute to the dramatic reduction in the perinatal mortality in placenta previa.
Production and Equilibration of the Quark-Gluon Plasma with Chromoelectric Field and Minijets
Production and equilibration of quark-gluon plasma are studied within the
color flux-tube model, at the RHIC and LHC energies. Non-Abelian relativistic
transport equations for quarks, antiquarks and gluons, are solved in the
extended phase space which includes coordinates, momenta and color. Before the
chromoelectric field is formed, hard and semihard partons are produced via
minijets which provide the initial conditions necessary to solve the transport
equations. The model predicts that in spite of the vast difference between the
RHIC and LHC incident energies, once the local equilibrium is reached, the
energy densities, the number densities and the temperatures at the two machines
may not be very different from each other. The minijet input significantly
alters the evolution of the deconfined matter, unless the color field is too
strong. For the input parameters used here the equilibration time is estimated
to be fm at RHIC and fm at LHC, measured from the instant
when the two colliding nuclei have just passed through each other. The
temperature at equilibration is found to be MeV at RHIC and MeV at LHC.Comment: version to appear in Phys. Rev. C; discussion enlarged to include
comparison with other models; conclusions unchanged; 14 single-spaced pages +
8 ps figure
Gauge Fixing Identity in the Background Field Method of QCD in Pure Gauge
In this paper we derive a gauge fixing identity by varying the covariant
gauge fixing term in in the background field method
of QCD in pure gauge. Using this gauge fixing identity we establish a relation
between in QCD and in
background field method of QCD in pure gauge. We show the validity of this
gauge fixing identity in general non-covariant and general Coulomb gauge
fixings respectively. This gauge fixing identity is used to prove factorization
theorem in QCD at high energy colliders and in non-equilibrium QCD at high
energy heavy-ion colliders.Comment: 14 pages latex, Non-covariant gauge fixing added, (Accepted for
Publication in IJMPA
Black Holes in Non-flat Backgrounds: the Schwarzschild Black Hole in the Einstein Universe
As an example of a black hole in a non-flat background a composite static
spacetime is constructed. It comprises a vacuum Schwarzschild spacetime for the
interior of the black hole across whose horizon it is matched on to the
spacetime of Vaidya representing a black hole in the background of the Einstein
universe. The scale length of the exterior sets a maximum to the black hole
mass. To obtain a non-singular exterior, the Vaidya metric is matched to an
Einstein universe. The behaviour of scalar waves is studied in this composite
model.Comment: 8 pages, 3 postscript figures, minor corrections Journal Ref:
accepted for Physical Review
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