A macro-micromechanics analysis of a notched metal matrix composite

A macro-micromechanics analysis was formulated to determine the matrix and fiber behavior near the notch tip in a center-notched metal matrix composite. Results are presented for a boron/aluminum monolayer. The macro-level analysis models the entire notched specimen using a three dimensional finite element program which uses the vanishing-fiber-diameter model to model the elastic-plastic behavior of the matrix and the elastic behavior of the fiber. The micro-behavior is analyzed using a Discrete Fiber-Matrix (DFM) model containing one fabric and the surrounding matrix. The dimensions of the DFM model were determined by the ply thickness and the fiber volume fraction and corresponded to the size of the notch-tip element in the macro-level analysis. The boundary conditions applied to the DFM model were determined from the macro-level analysis. Stress components within the DFM model were calculated and stress distributions are presented along selected planes and surfaces within the DFM model, including the fiber-matrix interface. Yielding in the matrix was examined at the notch tip in both the macro- and micro-level analyses. The DFM model predicted higher stresses (24 percent) in the fiber compared to the global analysis. In the notch-tip element, the interface stresses indicated that a multi-axial criterion may be required to predict interfacial failure. The DFM analysis predicted yielding to initiate in the notch-tip element at a stress level 28 percent lower than predicted by the global analysis

X-ray properties of the microquasar GRS 1915+105 during a variability class transition

We present a detailed X-ray study of the microquasar GRS 1915+105 during a variability class transition observed in 2000 June with the PPCs of the Indian X-ray Astronomy Experiment. We supplement this observation with data from the RXTE archives. The source made a transition from a steady low-hard state to a regular oscillatory behaviour in the light curve known as bursts or class `rho' (Belloni et al. 2000) between 2000 May 11 and 17 and reverted back to the low-hard state on 2000 June 27. A gradual change in the burst recurrence time from about 75 s to about 40 s was observed which then increased to about 120 s during the ~ 40 days of class `rho'. The regular bursts disappeared from the X-ray light curves and the class transition was observed to occur within 1.5 hours on 2000 June 27 with the PPCs. A correlation is found between the observed QPO frequency at 5-8 Hz in the quiescent phase and the average X-ray intensity of the source during the class `rho'. We notice a strong similarity between the properties of the source during the class `rho' and those during the oscillatory phase of the observations of class `alpha'. From the timing and spectral analysis, it is found that the observed properties of the source over tens of days during the class `rho' are identical to those over a time scale of a few hundreds of seconds in the class `alpha'. Examining the light curves from the beginning of the RXTE/PCA and RXTE/ASM observations, it is found that the change of state from radio-quiet low-hard state to high state occurs through the X-ray classes `rho' and `alpha' which appear together during the state transition. It is further inferred that the source switches from low-hard state to the class `rho' through the intermediate class `alpha'.Comment: 10 pages with 9 figures, LaTex. To be appeared in MNRA

Differences in peripheral noradrenergic function among actively drinking and abstinent alcohol-dependent individuals.

We examined whether excessive alcohol consumption was related to changes in plasma levels of noradrenaline (NA) and whether these changes recover following abstinence. We also explored whether there were differences in NA levels between Type I and Type II alcoholics and controls during active drinking and abstinence. Plasma concentrations of NA were determined in (1) 27 Caucasian men with alcohol dependence who were regularly drinking (active drinkers) within 24 hours of hospitalization, (2) 29 Caucasian alcohol-dependent men who were in remission (abstinent for a minimum of three months), and (3) 28 race- and gender-matched healthy controls. NA concentrations were significantly higher in actively drinking alcohol-dependent subjects compared to those in remission and controls. While Type I and Type II alcoholic individuals differed across clinical measures, NA levels were similar in the two subtypes. Both subtypes showed an elevation in NA levels during active drinking compared to controls, but NA levels did not differ between the two subtypes and controls during remission. The findings indicate that chronic exposure to alcohol may lead to disturbances in NA activity that may manifest in early abstinence. However, the changes in NA activity appears to normalize after a longer period of abstinence. Alterations in NA activity do not seem to be specific for Type I or Type II subtypes of alcoholism

Noise thermometry and electron thermometry of a sample-on-cantilever system below 1 Kelvin

We have used two types of thermometry to study thermal fluctuations in a microcantilever-based system below 1 K. We measured the temperature of a cantilever's macroscopic degree-of-freedom (via the Brownian motion of its lowest flexural mode) and its microscopic degrees-of-freedom (via the electron temperature of a metal sample mounted on the cantilever). We also measured both temperatures' response to a localized heat source. We find it possible to maintain thermal equilibrium between these two temperatures and a refrigerator down to at least 300 mK. These results are promising for ongoing experiments to probe quantum effects using micromechanical devices

On the origin of the various types of radio emission in GRS 1915+105

We investigate the association between the radio ``plateau'' states and the large superluminal flares in GRS 1915+105 and propose a qualitative scenario to explain this association. We identify several candidate superluminal flare events from available monitoring data on this source and analyze the contemporaneous RXTE pointed observations. We detect a strong correlation between the average X-ray flux during the ``plateau'' state and the total energy emitted in radio during the subsequent radio flare. We find that the sequence of events is similar for all large radio flares with a fast rise and exponential decay morphology. Based on these results, we propose a qualitative scenario in which the separating ejecta during the superluminal flares are observed due to the interaction of the matter blob ejected during the X-ray soft dips, with the steady jet already established during the ``plateau'' state. This picture can explain all types of radio emission observed from this source in terms of its X-ray emission characteristics.Comment: Corrected typo in the author names, contents unchanged, accepted in Ap

Hydrodynamic changes due to large seabed installations in coastal waters off west coast of India

Offshore marine environment can very well be utilized for mass storage of liquids which are not harmful to that environment. Improper placement of large tanks on the seabed, to store large quantities of liquids, would adversely affect the hydrodynamics of adjoining environment. Thorough understanding on the hydrodynamics of the adjoining environment is thus required before and after placing such tanks so as to properly plan the placement of these large tanks. A two dimensional numerical hydrodynamic model is used to study influence of placing large number of tanks in a dynamic marine environment. Cylindrical tanks (5 m dia.) are arranged in three rows with 50 tanks placed in each row with their length (100 m) aligned perpendicular to the coast. These tanks cover an area of about 36000 m2 and are placed on seabed in water depths about 15 m. Hydrodynamic simulations carried out with tidal forcing for cases of (a) before and (b) after placement of tanks showed that current speeds increase up to 65% in the region where the tanks are placed compared to currents without placement of tanks. However, up to 85% increase in current speeds is observed in regions beyond the tanks. In this manuscript results of the effects on the hydrodynamics of a region due to placing large number of tanks in shallow waters are presented

Secure quantum channels with correlated twin laser beams

This work is the development and analysis of the recently proposed quantum cryptographic protocol, based on the use of the two-mode coherently correlated states. The protocol is supplied with the cryptographic control procedures. The quantum noise influence on the channel error properties is examined. State detection features are proposed