6,891 research outputs found
Detection of Minimum-Ionizing Particles and Nuclear Counter Effect with Pure BGO and BSO Crystals with Photodiode Read-out
Long BGO (Bismuth Germanate) and BSO (Bismuth Silicate) crystals coupled with
silicon photodiodes have been used to detect minimum-ionizing particles(MIP).
With a low noise amplifier customized for this purpose, the crystals can detect
MIPs with an excellent signal-to-noise ratio. The NCE(Nuclear Counter Effect}
is also clearly observed and measured. Effect of full and partial wrapping of a
reflector around the crystal on light collection is also studied.Comment: 18 pages, including 5 figures; LaTeX and EP
Warm Asymmetric Nuclear Matter and Proto-Neutron Star
Asymmetric nuclear matter equation of state at finite temperature is studied
in SU(2) chiral sigma model using mean field approximation. The effect of
temperature on effective mass, entropy, and binding energy is discussed.
Treating the system as one with two conserved charges the liquid-gas phase
transition is investigated. We have also discussed the effect of proton
fraction on critical temperature with and without -meson contribution. We
have extended our work to study the structure of proto-neutron star with
neutron free charge-neutral matter in beta-equilibrium. We found that the mass
and radius of the star decreases as it cools from the entropy per baryon S = 2
to S = 0 and the maximum temperature of the core of the star is about 62 MeV
for S = 2.Comment: 25 pages, 16 figure
Cluster expansion Monte Carlo study of phase stability of vanadium nitrides
Phase stability of stable and metastable vanadium nitrides is studied using density functional theory (DFT) based total-energy calculations combined with cluster expansion Monte Carlo simulation and supercell methods. We have computed the formation enthalpy of the various stable and metastable vanadium nitride phases considering the available structural models and found that the formation enthalpies of the different phases decrease in the same order as they appear in the experimental aging sequence. DFT calculations are known to show stoichiometric V2N to be polymorphic in ϵ-Fe_2N and ζ-Fe2_N structures within a few meV and VN to be more stable in WC(B_h) phase than in the experimentally observed NaCl(B1) structure. As these nitrides are known to be generally nonstoichiometric due to presence of nitrogen vacancies, we used cluster expansion and supercell methods for examining the effect of nitrogen vacancies on the phase stability. It is found that nitrogen vacancies, represented by ◻, stabilize ϵ-Fe_2N phase of V_2N_(1−x◻x) and NaCl(B1) phase of VN_(1−x◻x) compared to ζ-Fe_2N and WC(B_h) phases respectively, rendering the computed phase stability scenario to be in agreement with experiments. Analysis of supercell calculated electronic density of states (DOS) of VN_(1−x◻x) with varying x, shows that the nitrogen vacancies increase the DOS at Fermi level in WC phase, whereas they decrease the DOS in NaCl phase. And this serves as the mechanism of enhancement of the stability of the NaCl phase. Monte Carlo simulations were used for computing the finite temperature formation enthalpies of these phases as a function of nitrogen-vacancy concentration and found close agreement for NaCl(B1) phase of VN_(1−x◻x) for which measured values are available
Ab Initio Theory of Gate Induced Gaps in Graphene Bilayers
We study the gate voltage induced gap that occurs in graphene bilayers using
\textit{ab initio} density functional theory. Our calculations confirm the
qualitative picture suggested by phenomenological tight-binding and continuum
models. We discuss enhanced screening of the external interlayer potential at
small gate voltages, which is more pronounced in the \textit{ab initio}
calculations, and quantify the role of crystalline inhomogeneity using a
tight-binding model self-consistent Hartree calculation.Comment: 7 pages, 7 figures; the effect of r3 coupling included; typo
correcte
Case analysis of complete uterine rupture in a tertiary health care center
Background: To determine the incidence, etiology, risk factors, complications, treatment strategies, maternal and fetal outcome associated with complete rupture uterus.Methods: This observational study was carried out in the Department of Obstetrics and Gynecology of Shriram Chandra Bhanj Medical College and Hospital, Cuttack, Odisha. The details of retrospective analysis of 52 cases of complete uterine rupture managed between July 2014 to April 2016 were reviewed.Results: The incidence of uterine rupture was 1 in 353 deliveries (0.28%). Most of the patients (61.5%) presented belonged to age group of 26-30 years. The most common cause of rupture uterus was rupture of previous caesarean scar in 30 cases (57.64%), whereas cepahalopelvic disproportion was predisposing factor in 18 cases (34.61%) and malpresentation in 4 cases. In majority 80.76 % of lower uterine segment was involved. Bladder injury was seen in 4 cases (7.69%) A most common form of management was rent repair in 53.84% cases. There were 2 maternal deaths with perinatal mortality rate being 100% associated with complete uterine rupture.Conclusions: Rupture of uterus is a dire emergency with high incidence of maternal and fetal mortality and morbidity. Most cases of rupture uterus are preventable with good antenatal and intrapartum care, and proper identification of high risk factors. Early diagnosis and active surgical management will go a long way in reducing the maternal and fetal mortality and morbidity.
475°C Embrittlement and Room Temperature Fatigue of Duplex Stainless Steel
Duplex stainless steels (DSSs) are two-phase materials consisting of both the ferritic and the
austenitic phase. The alloys are prone to embrittlement particularly in the temperature range
between 280°C and 512°C. This so-called 475°C embrittlement is caused by a
decomposition of the ferritic phase into a chromium-rich α' and an iron-rich α phase. The
objective of this study is to develop a better understanding of the embrittling process of DSS
of type SAF 2205. Embrittled and non-embrittled DSS was fatigue tested in stress-controlled
tests at 475°C and in strain-controlled tests at room temperature. The high temperature
fatigue tests were stopped at different cycle numbers in order to characterize the changing
material conditions by means of room-temperature tensile tests and scanning electron
microscopy pictures of the fracture surfaces
The {\alpha}-Decay Chains of the Isotopes using Relativistic Mean Field Theory
We study the binding energy, root-mean-square radius and quadrupole
deformation parameter for the synthesized superheavy element Z = 115, within
the formalism of relativistic mean field theory. The calculation is dones for
various isotopes of Z = 115 element, starting from A = 272 to A = 292. A
systematic comparison between the binding energies and experimental data is
made.The calculated binding energies are in good agreement with experimental
result. The results show the prolate deformation for the ground state of these
nuclei. The most stable isotope is found to be 282115 nucleus (N = 167) in the
isotopic chain. We have also studied Q{\alpha} and T{\alpha} for the
{\alpha}-decay chains of 115.Comment: 12 Pages 6 Figures 3 Table
Nuclear equation of state at high density and the properties of neutron stars
We discuss the relativistic nuclear equation of state (EOS) using a
relativistic transport model in heavy-ion collisions. From the baryon flow for
systems at SIS to AGS energies and above we find that the strength of
the vector potential has to be reduced moderately at high density or at high
relative momenta to describe the flow data at 1-10 A GeV. We use the same
dynamical model to calculate the nuclear EOS and then employ this to calculate
the gross structure of the neutron star considering the core to be composed of
neutrons with an admixture of protons, electrons, muons, sigmas and lambdas at
zero temperature. We then discuss these gross properties of neutron stars such
as maximum mass and radius in contrast to the observational values.Comment: 17 pages, 5 figures, to be published in Phy. Rev.
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