Strength differential in Al---Li alloy 8090

Cyclic strength differential (SD) data have been derived from the variation of the tensile and the compressive stress amplitude with elapsed cycles during low cycle fatigue (LCF) for the quaternary Al---Li alloy 8090 in the T8E51 condition. LCF test specimens were machined out of the rolled plate such that the direction of stressing was along the longitudinal (L), L+45° and long transverse (LT) directions. The analysis of cyclic stress amplitude data corresponding to the half-life revealed an SD effect at all strain levels in the L+45° and LT directions. In the case of the L direction, at strain levels below 8.5 × 10⁻³, the SD is more than compensated by the Bauschinger effect resulting from the prestretch. The alloy exhibits a similar SD behaviour under monotonic loading conditions. The magnitude of cyclic SD at intermediate strain amplitudes in all the three test directions decreases upon cycling, which behaviour can be attributed to the relaxation of prestretch-related residual stresses leading to a decrease in σ_T only in the L direction and σ_C only in the L+45° and LT directions. As microstructural features vary in the differently heat-treated conditions, a comparison has been made of the monotonic SD data in the stretched and aged (T8E51) condition with those in the solution-treated, in the peak-aged (T6) and in the overaged (T7) conditions.     

Scanned electron beam irradiation of Ti Schottky contacts to n-GaAs

Ti Schottky contacts were formed on n-GaAs surfaces and irradiated using a low energy scanned electron beam at various fluence levels from 10¹⁵ to 10¹⁸ cm^–2. For fluence levels up to 10¹⁷ cm^–2, the Schottky contacts were found to exhibit a reduction in their leakage currents and increased barrier voltages. For fluence levels in excess of 10¹⁷ cm^–2, the Schottky diodes were found to exhibit significantly increased leakage currents and barrier voltages. The changes in leakage currents were consistent with the changes in their respective interface state density (D _it) values. However, the electron beam irradiation had little or no effect on the diode ideality factorn.     

Weld microstructure refinement in a 1441 grade aluminium-lithium alloy

Clad 2 mm thick sheets of Russian 1441 grade Al-Li alloys were welded using a gas tungsten arc welding process (GTAW). Comparisons were made between the weld beads obtained under (i) continuous current (CC), (ii) pulsed current (PC), and (iii) arc oscillation (AO) conditions for their macro- and microstructural details. In the case of CC GTAW, sound welds could be produced only under a narrow range of welding parameters. Centre line cracks, which occurred in CC GTAW welds under certain conditions, were halted by switching to PC or AO conditions while the welding was in progress. Microstructural refinement was significant in the case of PC and AO GTA welding. This revised version was published online in November 2006 with corrections to the Cover Date.     

Endohedral Formation from Neutron Activation of Interstitial Rare Cas C60 Fullerides

Rare gas interstitial fullerenes, produced by hot isostatic pressing solid C₆₀ in the presence of Ar, Kr or Xe, have been neutron irradiated and their behaviour investigated. The activity of the generated radionuclides was found to be in agreement with calculations and this combined with X-ray powder diffraction showed that both the activated radionuclides and the unactivated rare gas remained trapped in the solid after they have been subjected to the harsh conditions encountered in a nuclear reactor. Gamma spectroscopy of the irradiated solids and solutions of them in toluene provided strong evidence for endohedral compound formation. We estimate 1-2% of the activated rare gas atoms, which recoil as a result of prompt gamma emission, end up in the centre of what is most likely too be the C₆₀ molecule or some other fullerene derivative. On this basis, we postulate the formation of RN@C_6o where the radionuclide (RN)is ^125gXe, ^133gXe, ^I35gXe, ⁴¹Ar or^85mKr.     

Experimental Facilities to Monitor Various Types of Atmospheric Parameters in the Radio and Atmospheric Sciences Division (RASD) of CSIR-National Physical Laboratory

The Indian subcontinent with Himalayan Mountains on northern side, Bay of Bengal on eastern side, Arabian Sea on the western side and Indian Ocean on the southern side presents a unique natural setting with highly variable climatic features. The seasonal variation in North India is highly pronounced whereas in southern India it is moderate, the coastal areas are influenced by cyclones, north western India dominated by western disturbances and desert conditions. Added to these natural influences the rapid urbanization of regions resulted in changing atmospheric conditions leading to sudden occurrence of natural calamities. Prediction of these events requires very reliable climatic models which is a gigantic task. To develop climatic models suitable to our country, huge reliable data base of atmospheric parameters is required. Keeping this objective in view the Radio and Atmospheric Sciences Division of National Physical Laboratory has been engaged in monitoring the atmospheric parameters using various facilities with focus on northern plains. The present paper describes the latest research activities using the existing facilities and future activities and facilities planned in this division.     

Characterization of adsorbed silane on fillers used in dental composite restoratives and its effect on composite properties

The purpose was to study the effect of silane treatment of fillers on viscosity, flexural strength, and hydrolytic degradation of experimental dental composite resins fabricated with these fillers. The fillers consisted of a mixture of barium glass and amorphous silica. The resin was mainly based on ethoxylated bisphenol A dimethacrylate and polycarbonate dimethacrylate. The adsorption of silane on the filler surface was characterized by FTIR. There was significant correlation between the adsorbed silane on filler surface and the silane concentration in silane/methanol solution used for filler treatment. The silane concentration varied from 0.75 to 14% by weight. An increase in silane concentration led to a decrease in viscosities of the corresponding composite resins. The flexural strengths of composites with silanated fillers were greater than that of composites with unsilanated fillers: however, no significant difference was found between the flexural strengths of various silanated groups. The resistance to hydrolytic degradation of different composites increased when the fillers were treated with silane and was the highest at 1.1% silane.     

Studies on electrodeposition and corrosion behaviour of a Ni–W–Co amorphous alloy

A ternary alloy Ni–W–Co was electrodeposited and operational parameters in relation to its corrosion resistance and deposition efficiency were optimized. A 2² full factorial design was successfully employed for experimental design analysis of the results. By means of response surface analysis, the statistical model identified the following operating conditions for obtaining corrosion resistant alloy: 60 mA/cm² current density, 70 °C temperature, 20 rpm cathode rotation and 8.0 pH. The alloy was deposited at 36% current efficiency, with an average composition of 70% Ni, 8% Co, 22% W and traces of boron and with E _corr −0.508 V and R _p 4.56 × 10⁴ Ohm. The deposit obtained under these conditions had an amorphous character and showed good adherence, high corrosion resistance and presence of nodules on its surface. Electrochemical corrosion tests verified that the Ni–W–Co alloy had better corrosion resistance than similarly electrodeposited Co–W amorphous alloy.     

An impact-citations-exergy (<Emphasis Type="Italic">iCX</Emphasis>) trajectory analysis of leading research institutions in India

A thermodynamic analogy allows bibliometric research assessment of information production processes to be based on a scalar indicator which is an energy-like term called exergy. Derived from standard indicators like impact, citations and number of papers, the exergy indicator X is a multiplicative product of quality and quantity of a scientist’s or group’s performance using available bibliometric information. Thus, given the bibliometric sequences of leading research agencies and institutions, research performance can be displayed as trajectories on a two-dimensional map as time progresses. In this paper, we track the performance of several of the leading players contributing to academic scientific research in India.     

Three dimensional boundary formulations for nonlinear thermal shape sensitivities

Implicit differentiation of the discretized boundary integral equations governing the conduction of heat in three dimensional (3D) solid objects, subjected to nonlinear boundary conditions, and with temperature dependent material properties, is shown to generate an accurate and economical approach for the computation of shape sensitivities. The theoretical formulation for primary response (surface temperature and normal heat flux) sensitivities and secondary response (surface tangential heat flux components and internal temperature and heat flux components) sensitivities is given. Iterative strategies are described for the solution of the resulting sets of nonlinear equations and computational performances examined. Multi-zone analysis and zone condensation strategies are demonstrated to provide substantial computational economies in this process for models with either localized nonlinear boundary conditions or regions of geometric insensitivity to design variables. A series of nonlinear sensitivity example problems are presented that have closed form solutions. Sensitivities computed using the boundary formulation are shown to be in excellent agreement with these exact expressions.