UHE neutrino damping in a thermal gas of relic neutrinos

We present a calculation of the damping of an ultra-energetic (UHE) cosmic neutrino travelling through the thermal gas of relic neutrinos, using the formalism of finite-temperature field theory. From the self-energy diagram due to Z exchange, we obtain the annihilation cross section for an UHE neutrino interacting with an antineutrino from the background. This method allows us to derive the full expressions for the UHE neutrino transmission probability, taking into account the momentum of relic neutrinos. We compare our results with the approximations in use in the literature. We discuss the effect of thermal motion on the shape of the absorption dips for different UHE neutrino fluxes as well as in the context of relic neutrino clustering. We find that for ratios of the neutrino mass to the relic background temperature $10^2$ or smaller, the thermal broadening of the absorption lines could significantly affect the determination of the neutrino mass and of the characteristics of the population of UHE sources.Comment: 18 pages, 6 figures. Typos corrected. More accurate treatment of the interaction with relic neutrino clusters. Accepted for publication in Astroparticle Physic

Depressed clad hollow optical fiber with fundamental LP01 mode cut-off

We propose a depressed clad hollow optical fiber with fundamental (LP01) mode cut-off suitable for high power short-wavelength, especially three-level, fiber laser operation by introducing highly wavelength dependent losses at longer wavelengths. The cut-off characteristic of such fiber structure was investigated. A Yb-doped depressed clad hollow optical fiber laser generating 59.1W of output power at 1046nm with 86% of slope efficiency with respect to the absorbed pump power was realised by placing the LP01 mode cut-off at ~1100nm

Effect of 475oC embrittlement on the fatigue behaviour of a duplex stainless steel

The low cycle fatigue behaviour of a duplex stainless steel was studied in standard heat treated and embrittled (by aging at 475°C for 100 hours) condition by mechanical testing, scanning and transmission electron microscopy. The fatigue crack initiation behaviour was studied in the embrittled condition by interrupting stress-controlled fatigue tests, identifying the crack initiation sites and relating them to the crystallographic parameters obtained from EBSD-OIM scans. The aging treatment at 475°C resulted in the precipitation of a' in the ferritic phase. Impact energy drops from 260 Joules in the annealed condition to 8 Joules in the aged condition. The drop in impact energy was caused by the inability of the ferritic phase to form deformation twins in the embrittled condition, which was confirmed by TEM examination. From the low cycle fatigue experiments conducted at A C/2 = 4. Ox 10-', 6. Ox 10-', 8.Oxl0-3 and 1.Ox10"2, it was established that the deformation curves in the annealed condition has three discernible stages: (i) cyclic hardening, (ii) cyclic softening and (iii) cyclic saturation and in the aged condition has two discernible stages: (i) cyclic hardening, and (ii) cyclic softening till final failure for all values of strain amplitude. A change in slope is observed in the cyclic stress-strain curve in the aged condition as compared to the standard heat treated condition. In the range of strain amplitude employed, in the aged condition, fatigue life is longer at lower plastic strain amplitude, decreases and becomes similar at intermediate plastic strain amplitude and becomes shorter at higher plastic strain amplitude in comparison to the standard heat treated condition. The gradual decrease in fatigue life with increase in plastic strain amplitude in the aged condition was attributed to the rapid cyclic softening caused by disappearance of the a' precipitates. From the fatigue crack initiation studies conducted at Ao12 = 400 MPa and 500 MPa, it was established that the crack initiation sites are the slip markings corresponding to { 111 } plane traces in the austenitic grains at Dof2 = 400 MPa and more cracks were observed to initiate at E3 CSL boundaries in the austenitic grain at Do12 = 500 MPa in the aged condition. The major resistance to crack growth came from the ay phase boundary

New technology may help scale up memory storage capacity

Silicon-based memory devices such as hard drives and flash drives are in high demand for gadgets that require storage. Conventional semiconductor material-based memory devices have limited scale-up ability to increase their storage capacity. Hence, there is a quest in developing new memory technologies with superior characteristics. In this direction, a group of Indian researchers has developed a new type of resistive random access memory (RRAM) device that can be controlled with magnetic fields

UV Interstellar Absorption Lines towards the Starburst Dwarf Galaxy NGC 1705

Archival Goddard High Resolution Spectrograph low-resolution spectra of NGC 1705, with wavelength ranges 1170.3 to 1461.7 A and 1453.5 to 1740.1 A and a velocity resolution of about 100 km\s, have been used to derive the velocity structure and equivalent widths of the absorption lines of Si II 1190.42, 1260.42, 1304.37 and 1526.71 A, S II 1253 , Al II 1670.79 Aand Fe II 1608.45 A in this sightline. Three relatively narrow absorption components are seen at LSR velocities --20 km/s, 260 km/sand 540 km/s. Arguments are presented to show these absorption features are interstellar rather than stellar in origin based on a comparison with the C III 1175.7 A absorption feature. We identify the --20 km/s component with Milky Way disk/halo gas and the 260 km/s component with an isolated high-velocity cloud HVC 487. This small HVC is located about 10 degrees from the H I gas which envelops the Magellanic Clouds and the Magellanic Stream (MS). The (Si/H) ratio for this HVC is > 0.6 (Si/H)solar which together with velocity agreement, suggests association with the Magellanic Cloud and MS gas. H-alpha emission line kinematics of NGC 1705 show the presence of a kpc-scale expanding supershell of ionized gas centered on the central nucleus with a blue-shifted emission component at 540 km/s (Meurer et al. 1992). We identify the 540 km/s absorption component seen in the GHRS spectra with the front side of this expanding, ionized supershell. The most striking feature of this component is strong Si II and Al II absorption but weak Fe II 1608 A absorption. The low Fe II column density derived is most likely intrinsic since it cannot be accounted for by ionization corrections or dust depletion. Due to their shallow gravitational potential wells, dwarf galaxies have small gravitational binding energies and are vulnerable to largeComment: 15 pages, LaTEX, 1 figure. Accepted for publication in Astrophysical Journal Letter

Thermal effects on the absorption of ultra-high energy neutrinos by the cosmic neutrino background

We use the formalism of finite-temperature field theory to study the interactions of ultra-high energy (UHE) cosmic neutrinos with the background of relic neutrinos and to derive general expressions for the UHE neutrino transmission probability. This approach allows us to take into account the thermal effects introduced by the momentum distribution of the relic neutrinos. We compare our results with the approximate expressions existing in the literature and discuss the influence of thermal effects on the absorption dips in the context of favoured neutrino mass schemes, as well as in the case of clustered relic neutrinos.Comment: 3 pages, 2 figures. Prepared for the Proceedings of the 9th International Conference on Topics in Astroparticle and Underground Physics (TAUP 2005), Zaragoza (Spain), September 10-14, 200

Raman amplification and pulsed lasing in cladding-pumped germanosilicate fiber

We report for the first time Raman amplification in a cladding-pumped fiber. The double-clad germanosilicate fiber was pumped by a Q-switched Er-Yb co-doped fiber laser at 1570 nm. The power conversion efficiency was up to 36%, with a slope of 64%