Infrared,Raman, electrical and thermal analysis of lithium sulphate monohydrate single crystals

In this work, single crystals of lithium sulphate monohydrate were grown by slow evaporation technique. Structural studies of the grown crystals were carried out by powder X-ray diffraction technique showing a monoclinic structure. Effect of temperature on the vibrational modes of different groups was observed and analyzed by Fourier transform infrared and Raman spectroscopy. The temperature dependent dielectric behaviour and ac conductivity of the grown crystals were also studied. The effect of temperature on the vibrational spectra as observed by Fourier transform infrared and Raman spectroscopy were correlated with the electrical behavior of the crystals. The relaxation studies were also undertaken using the complex-modulus M^* formalism which showed a thermally activated relaxation caused by the hopping motion of H⁺ ions in the crystal. All the observed characteristics were found to be closely related with water loss in the crystal structure. Thermal analysis of the grown crystal was carried out by using differential scanning calorimetric technique yielding various thermodynamic parameters such as ΔH, ΔS and ΔC_p. The activation energy for the dehydration step of lithium sulphate monohydrate was also evaluated by using Coats-Redfern integral method.     

Effect of heat treatment on tensile behaviour of Ti-6Al-5Zr-0.5Mo-0.25Si alloy

Tensile behaviour of the near a titanium alloy, Ti-6Al-5Zr-0.5Mo-0.25Si (LT26A), was investigated in (α + β) as well as β treated condition, over a wide range of temperature from RT to 823 K. It was observed that there were distinct serrations on the load-elongation curves of the a + β treated material at intermediate temperatures from 623 to 723 K. Tensile tests at 673 K over a wide range of strain rate from 0052 to 5.60 (× 10^-2) s^-1 showed negative strain rate sensitivity. Thus, occurrence of DSA was confirmed. It was established from the measured activation energy for DSA that it was essentially controlled by diffusion of the solid solution strengthener silicon in the matrix.     

Indirect influence on modality on direct memory for words and their modality: Closed-head-injured and control participants.

Twenty closed-head-injured (CHI) patients and 28 control participants were tested on recall and recognition of words. In addition, memory for modality (i.e., visual vs. auditory) of word presentation was measured directly (i.e., recognition) and indirectly (i.e., by its influence on word and modality recognition). As predicted, the CHI patients were impaired relative to controls on all of the direct memory tasks; that is, word recall, word recognition, and modality judgment. However, the CHI and control groups did not differ significantly on the magnitude of the modality effect (i.e., facilitation due to correspondence of modality in learning and test). The findings are interpreted in the theoretical framework that distinguishes between item (i.e., words) and source (i.e., modality) memory and between direct and indirect measures of memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

CFAR detection for multistatic radar

In this paper a multistatic radar system with n transmitters and one receiver is considered and several constant false alarm rate (CFAR) algorithms for detection are introduced. The decision statistics of the proposed detectors are the sum of the n largest returning signals in an array of N+n range cells. It is shown that the proposed decision statistic satisfies the CFAR condition and it is justified that the sum of the largest returning signals is the optimal statistic. The proposed CFAR detectors are simulated both in homogenous and non-homogenous backgrounds and their performances are compared with the performance of a monostatic radar of higher power. It is shown that a multistatic radar outperforms a monostatic radar under equal transmit power condition.     

Problems and prospects of housing CBOs: An analysis of 30 case studies from Africa and Latin America, 1964–1994

There is little research literature that sheds light on how community-based organizations (CBOs) in the shelter sector contribute to development. This paper describes the results of an analysis of information contained in 30 case studies of housing CBOs, representing 16 countries and covering the period 1964 to 1994. A framework is employed for the analysis that incorporates both internal characteristics and the external environment of the organizations. Implications of the research for housing policy are discussed and include: CBO size and membership criteria, gender, financing, the viability of self-help labour, interference of politicians and political parties, and appropriate roles for central and local governments, non-government organizations and other external actors. The paper concludes that the diversity of housing CBOs should be recognized, and that these organizations need greater autonomy and a stronger support system.     

Field probe for measuring both amplitude and phase of antenna radiation patterns

Small probe antennas are often used for measuring the amplitude and phase of antenna radiation patterns. Phase measurements are complicated by the need for an accurate r.f. phase reference to be conveyed to or from the mobile probe. The letter describes a scheme for simplifying such measurements by the use of a probe unit which backscatters incident energy after subjecting it to a single sideband frequency translation. The scheme has application to both compact ranges and to the measurement of profile errors in reflector antennas by phase measurements within the aperture plane.     

Effects of prior cold working on low cycle fatigue behavior of stainless steels, titanium alloy timetal 834 and superalloy IN 718: A review

This paper gives a brief review of the efforts made to study the effects of cold rolling on low cycle fatigue (LCF) behavior of stainless steels, titanium alloy Timetal 834 and Ni-Fe based Super alloy IN 718 at different temperatures and different strain amplitudes. Low Cycle Fatigue tests on cold worked 316L stainless steel at various temperatures from room temperature to 923K have been reported. In all tests the effect of 20% prior cold work(PCW) on LCF behavior of type 316L (N) stainless steel had been studied at 873K under total axial strain controlled mode in air at strain amplitudes from ±0.25% to ±1.0%. Fatigue life in the solution annealed condition was similar to that of the PCW material at higher strain amplitudes (≥0.5%) while at lower strain amplitudes the PCW material exhibited longer life. The influence of PCW on LCF behavior of type 304 and AISI 304LN stainless steel was studied at various temperatures and it was observed that the fatigue life was strongly dependent on prior cold work, temperature, and strain amplitude employed. Cold rolling of the titanium alloy Timetal 834 and age hardenable Ni-Fe-based superalloy IN 718 has been found to cause marked enhancement in LCF life at low strain amplitude and eliminate the bilinearity from the Coffin-Manson(C-M) relationship. Work carried on this aspect, however is very limited particularly in the case of Titanium alloys and Ni-Fe based Superalloy IN 718     

Two-dimensional side-by-side circular cylinders at moderate Reynolds numbers

In a companion article [1], we described computer simulations of the flow around 2 two-dimensional, tandem circular cylinders in a flow for 1?Re?20. In this article we adopt a similar approach to characterize the flow around side-by-side cylinders with surface-to-surface separation/diameter in the range 0.1 < s/D < 30. The results revealed some distinct and interesting features of the flow, which are completely different than those observed at higher Reynolds numbers.At low Reynolds numbers, 1?Re?5, for all gap spacings, the flow contains no regions of flow separation. At higher Re, four distinct flow behaviors were observed. For very small gap spacings, e.g. 0.1 < s/D < 0.6 at Re = 20, two elongated “detached vortices” form downstream of the cylinders. The drag coefficient increases sharply with the gap spacing. For gap spacings 0.6 < s/D < 0.7 at Re = 20, no vortices form anywhere in the flow. For gap spacings around s/D ≈ 1 separation regions form only on the inside portions of the cylinders. For larger gap spacings s/D > 1 the flow reverts to something similar to that around an isolated cylinder in the flow, i.e. two attached vortices on the rear side of each cylinder. In general, the drag coefficient increases as the gap spacing increases. At higher Reynolds number it is known that the cylinder lift coefficients decrease monotonically with gap spacing. In contrast, at these lower Reynolds number the lift coefficient curves rise to a maximum for 0.3 < s/D < 3 and then decrease monotonically for larger s/D.