1,566 research outputs found
Studies on residual stress developed in laser surface irradiated 0.6% carbon steel
Laser surface hardening is a process of microstructural modification of the near surface region of iron-based component by inducing martensitic transformation with a high power laser beam as a source of heat. The process is aimed at introducing a hard and wear-resistant layer on the surface, thereby increasing the service life of the component. Due to a rapid rate of heating and cooling and a large thermal gradient associated with the process, a measurable amount of residual stress is developed in the laser irradiated region. In the present investigation, an attempt has been made to surface harden medium carbon steel (0.6% Carbon) using 2.5 kW continuous wave CO2 laser as a source of heat using Ar as shrouding gas. The microstructure and phase analysis of the irradiated region have been carried out in details. Residual stress developed in the laser-irradiated region has been carefully measured. Effect of laser parameters on microhardness and wear resistance has been studied. Finally, the processing zone for the surface hardening has been derived following a detailed structure-property correlation
Probing Pseudo-Dirac Neutrino through Detection of Neutrino Induced Muons from GRB Neutrinos
The possibility to verify the pseudo-Dirac nature of neutrinos is
investigated here via the detection of ultra high energy neutrinos from distant
cosmological objects like GRBs. The very long baseline and the energy range
from TeV to EeV for such neutrinos invokes the likelihood to
probe very small pseude-Dirac splittings. The expected secondary muons from
such neutrinos that can be detected by a kilometer scale detector such as
ICECUBE is calculated. The pseudo-Dirac nature, if exists, will show a
considerable departure from flavour oscillation scenario in the total yield of
the secondary muons induced by such neutrinos.Comment: 11 pages, 3figure
Laser surface treatment of Ti-6Al-4V for bio-implant application
The present study aims at enhancing the wear resistance of Ti-6Al-4V by laser surface melting and nitriding and subsequently, studying the influence of laser surface treatment on the corrosion resistance in a simulated body fluid and also the bio-compatibility. The laser surface treatment is carried out using a high power continuous wave diode laser with argon and nitrogen as shrouding gas. Laser surface melting leads to an increased volume fraction of acicular martensite and a decreased volume fraction of the β phase in the microstructure. Laser surface nitriding leads to the formation of titanium nitride dendrites. The micro-hardness could be improved up to a maximum of 450 Hv in laser surface melting and 900-950 Hv in the case of laser surface nitriding as compared to 260 Hv of the as-received substrate. Surface melting increases the corrosion potential (Ecorr) and primary potential for pit formation (Epp1) significantly as compared to the as-received Ti-6Al-4V. However, when processed under similar conditions, surface nitriding shifts Ecorr marginally in the more noble direction, and increased Epp1 as compared to Ti-6Al-4V. The biocompatibility behaviour shows a superior cell viability on surface nitriding and an inferior cell viability on surface melting as compared to the as-received Ti-6Al-4V
Exchange bias effect in alloys and compounds
The phenomenology of exchange bias effects observed in structurally
single-phase alloys and compounds but composed of a variety of coexisting
magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic,
spin-glass, cluster-glass and disordered magnetic states are reviewed. The
investigations on exchange bias effects are discussed in diverse types of
alloys and compounds where qualitative and quantitative aspects of magnetism
are focused based on macroscopic experimental tools such as magnetization and
magnetoresistance measurements. Here, we focus on improvement of fundamental
issues of the exchange bias effects rather than on their technological
importance
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Systematics of Inclusive Photon Production in 158 AGeV Pb Induced Reactions on Ni, Nb, and Pb Targets
The multiplicity of inclusive photons has been measured on an event-by-event
basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The
systematics of the pseudorapidity densities at midrapidity (rho_max) and the
width of the pseudorapidity distributions have been studied for varying
centralities for these collisions. A power law fit to the photon yield as a
function of the number of participating nucleons gives a value of 1.13+-0.03
for the exponent. The mean transverse momentum, , of photons determined
from the ratio of the measured electromagnetic transverse energy and photon
multiplicity, remains almost constant with increasing rho_max. Results are
compared with model predictions.Comment: 16 pages including 4 figure
Identifying the neutrino mass spectrum from a supernova neutrino burst
We study the role that the future detection of the neutrino burst from a
galactic supernova can play in the reconstruction of the neutrino mass
spectrum. We consider all possible 3 mass and flavor spectra which
describe the solar and atmospheric neutrino data. For each of these spectra we
find the observable effects of the supernova neutrino conversions both in the
matter of the star and the earth. We show that studies of the electron neutrino
and anineutrino spectra as well as observations of the neutral current effects
from supernova will allow us (i) to identify the solar neutrino solution, (ii)
to determine the type of mass hierarchy (normal or inverted) and (iii) to probe
the mixing to values as low as .Comment: 53 pages, 13eps figures. Substantial changes made, new results,
figures and tables adde
Constraints on Astro-unparticle Physics from SN 1987A
SN 1987A observations have been used to place constraints on the interactions
between standard model particles and unparticles. In this study we calculate
the energy loss from the supernovae core through scalar, pseudo scalar, vector,
pseudo vector unparticle emission from nuclear bremsstrahlung for degenerate
nuclear matter interacting through one pion exchange. In order to examine the
constraints on we considered the emission of scalar, pseudo
scalar, vector, pseudo vector and tensor through the pair annihilation process
. In addition we have re-examined other pair
annihilation processes. The most stringent bounds on the dimensionless coupling
constants for and are obtained from
nuclear bremsstrahlung process for the pseudo scalar and pseudo-vector
couplings and for
tensor interaction, the best limit on dimensionless coupling is obtained from
and we get .Comment: 12 pages, 2 postscript figure
Scaling of Particle and Transverse Energy Production in 208Pb+208Pb collisions at 158 A GeV
Transverse energy, charged particle pseudorapidity distributions and photon
transverse momentum spectra have been studied as a function of the number of
participants (N_{part}) and the number of binary nucleon-nucleon collisions
(N_{coll}) in 158 A GeV Pb+Pb collisions over a wide impact parameter range. A
scaling of the transverse energy pseudorapidity density at midrapidity as
N_{part}^{1.08 \pm 0.06} and N_{coll}^{0.83 \pm 0.05} is observed. For the
charged particle pseudorapidity density at midrapidity we find a scaling as
N_{part}^{1.07 \pm 0.04} and N_{coll}^{0.82 \pm 0.03}. This faster than linear
scaling with N_{part} indicates a violation of the naive Wounded Nucleon Model.Comment: 13 pages, 16 figures, submitted to European Physical Journal C
(revised results for scaling exponents
Centrality Dependence of Neutral Pion Production in 158 A GeV Pb + Pb Collisions
The production of neutral pions in 158AGeV Pb+Pb collisions has been studied
in the WA98 experiment at the CERN SPS. Transverse momentum spectra are studied
for the range 0.3 GeV/c < mT-m0 < 4.0 GeV/c. The results for central collisions
are compared to various models. The centrality dependence of the neutral pion
spectral shape and yield is investigated. An invariance of the spectral shape
and a simple scaling of the yield with the number of participating nucleons is
observed for centralities with greater than about 30 participating nucleons
which is most naturally explained by assuming an equilibrated system.Comment: 5 pages, Latex, including 3 eps figures, submitted to Phys.Rev.Lett;
updated pQCD comparison due to new input from the author, updated references,
corrected plotting error in figure
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