Studies on laser surface melting of Al-11% Si alloy

In the present investigation the effect of laser surface melting on wear and corrosion resistance of Al-11 wt.% Si alloy has been investigated. Laser surface melting has been carried out using a 2 kW continuous wave CO2 laser at an applied power of 2.3 kW and scan speed ranging from 6 to 12 mm/min. Following the laser surface melting, a detailed investigation of the melted zone in terms of microstructure, composition and phases were undertaken. Mechanical properties of the melted zone were evaluated so far as the microhardness and wear resistance were concerned. The corro-sion behaviour of the as-received and the laser surface melted surface was evaluated in 1(M) H2SO4, 1(M) HNO3 and 3.56 wt.% NaCl solutions. The microstructure of the melt zone consists of grain refinedAl andAl-Si eutec-tic colonies which results in an improved microhardness from 87 VHN as compared to 55 VHN of the as-received Al-Si alloy. The wear resistance of the melt surface was improved significantly as compared to the as-received Al-Si alloy. A detailed corrosion study in various environments showed that corrosion resistance was marginally less in the 3.56 wt.% NaCl and 1 M H2SO4 solutions, but was better in the 1 M HNO3 solution

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

ANCA-negative limited Wegener's granulomatosis

A 26-year-old man presented with epistaxis, nasal obstruction and a subcutaneous swelling over the left malar region with radiological evidence of a mass in the right nasal cavity. Histology of the lesions showed necrotizing granuloma with evidence of vasculitis. There was no other systemic involvement and the patient was ANCA-negative. Excellent response to systemic steroid and cyclophosphamide therapy was noted

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 $\sim$ TeV to $\sim$ 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

The STAR Photon Multiplicity Detector

Details concerning the design, fabrication and performance of STAR Photon Multiplicity Detector (PMD) are presented. The PMD will cover the forward region, within the pseudorapidity range 2.3--3.5, behind the forward time projection chamber. It will measure the spatial distribution of photons in order to study collective flow, fluctuation and chiral symmetry restoration.Comment: 15 pages, including 11 figures; to appear in a special NIM volume dedicated to the accelerator and detectors at RHI

Persistence Exponents and Scaling In Two Dimensional XY model and A Nematic Model

The persistence exponents associated with the T=0 quenching dynamics of the two dimensional XY model and a two dimensional uniaxial spin nematic model have been evaluated using a numerical simulation. The site persistence or the probability that the sign of a local spin component does not change starting from initial time t=0 up to certain time t, is found to decay as L(t)^-theta, (L(t) is the linear domain length scale), with theta =0.305 for the two dimensional XY model and 0.199 for the two dimensional uniaxial spin nematic model. We have also investigated the scaling (at the late time of phase ordering) associated with the correlated persistent sites in both models. The persistence correlation length was found to grow in same way as L(t).Comment: 8 figures, only three new references are included in this version. (ref. 18 and ref. 32

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$\nu$ 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 $|U_{e3}|^2$ to values as low as $10^{-4} - 10^{-3}$.Comment: 53 pages, 13eps figures. Substantial changes made, new results, figures and tables adde