Influence of temperature and strain rate on the flow stress of an FeAl alloy

The deformation behavior of an FeAl alloy processed by hot extrusion of water atomized powder has been investigated. Compression tests are performed in the temperature range 1073–1423 K and in the strain rate range 0.001–100 s−1 up to a true plastic strain of 0.5. The flow stress has been found to be strongly dependent on temperature as well as strain rate. The stress exponent in the power law rate equation is estimated to be in the range 7.0–4.0, decreasing with temperature. The activation energy for plastic flow in the range 1073–1373 K varies from 430 kJ mol−1 at low stresses to 340 kJ mol−1 at high stresses. However, it is fairly independent of strain rate and strain. The activation area has similarly shown a stress dependence and lies in the range 160–45b2. At 1423 K and at strain rates lower than 0.1 s−1 a strain rate sensitivity of 0.3 is observed with an associated activation energy of 375 kJ mol−1. The plastic flow in the entire range of temperature and strain rate investigated appears to be controlled by a diffusion mechanism. The results have revealed that it is possible to process the alloy by superplastic forming in the range 1373–1423 K at strain rates lower than 0.1 s−1.

Axially homogeneous, zero mean flow buoyancy-driven turbulence in a vertical pipe

We report an experimental study of a new type of turbulent flow that is driven purely by buoyancy. The flow is due to an unstable density difference, created using brine and water, across the ends of a long (length/diameter=9) vertical pipe. The Schmidt number Sc is 670, and the Rayleigh number (Ra) based on the density gradient and diameter is about 108. Under these conditions the convection is turbulent, and the time-averaged velocity at any point is ‘zero’. The Reynolds number based on the Taylor microscale, Reλ, is about 65. The pipe is long enough for there to be an axially homogeneous region, with a linear density gradient, about 6–7 diameters long in the midlength of the pipe. In the absence of a mean flow and, therefore, mean shear, turbulence is sustained just by buoyancy. The flow can be thus considered to be an axially homogeneous turbulent natural convection driven by a constant (unstable) density gradient. We characterize the flow using flow visualization and particle image velocimetry (PIV). Measurements show that the mean velocities and the Reynolds shear stresses are zero across the cross-section; the root mean squared (r.m.s.) of the vertical velocity is larger than those of the lateral velocities (by about one and half times at the pipe axis). We identify some features of the turbulent flow using velocity correlation maps and the probability density functions of velocities and velocity differences. The flow away from the wall, affected mainly by buoyancy, consists of vertically moving fluid masses continually colliding and interacting, while the flow near the wall appears similar to that in wall-bound shear-free turbulence. The turbulence is anisotropic, with the anisotropy increasing to large values as the wall is approached. A mixing length model with the diameter of the pipe as the length scale predicts well the scalings for velocity fluctuations and the flux. This model implies that the Nusselt number would scale as Ra1/2Sc1/2, and the Reynolds number would scale as Ra1/2Sc−1/2. The velocity and the flux measurements appear to be consistent with the Ra1/2 scaling, although it must be pointed out that the Rayleigh number range was less than 10. The Schmidt number was not varied to check the Sc scaling. The fluxes and the Reynolds numbers obtained in the present configuration are much higher compared to what would be obtained in Rayleigh–Bénard (R–B) convection for similar density differences.

Novel double insertion of carbon disulfide into two Ru-H bonds of [(dppm)(2)Ru(H)(2)] (dppm = Ph2PCH2PPh2): Synthesis and crystal structure of a methanedithiolate complex

Addition of excess carbon disulfide to cis/trans-[(dPPM)(2)Ru(H)(2)] results in the methanedithiolate complex [(dppm)(2)Ru(eta(2)-S2CH2)] 4 via the intermediacy of cis-[(dppm)(2)Ru(H)(SC(S)H)] 2. The X-ray crystal structure of this species has been determined.

Sustainable biomass production for energy in selected Asian countries

This paper presents a synthesis of assessment of sustainable biomass production potential in six Asian countries-China, India, Malaysia, Philippines, Sri Lanka and Thailand, and is based on the detailed studies carried out in these countries under the Asian Regional Research Programme in Energy, Environment and Climate (ARRPEEC). National level studies were undertaken to estimate land availability for biomass production, identify and evaluate the biomass production options in terms of yield per hectare and financial viability, estimate sustainable biomass production for energy, and estimate the energy potential of biomass production in the six Asian countries. Sustainable biomass production from plantation is estimated to be in the range of 182.5-210.5, 62-310, 0.4-1.7, 3.7-20.4, 2.0-9.9 and 11.6-106.6 Mt yr(-1) for China, India, Malaysia, Philippines, Sri Lanka and Thailand, respectively. The maximum annual electricity generation potential, using advanced technologies, from the sustainable biomass production is estimated to be about 27, 114, 4.5, 79, 254 and 195 percentage of the total electricity generation in year 2000 in China, India, Malaysia, Philippines, Sri Lanka and Thailand, respectively. Investment cost for bioenergy production varies from US$381 to 1842 ha(-1) in the countries considered in this study; investment cost for production of biomass varies from US$5.1 to 23 t(-1). (C) 2003 Elsevier Ltd. All rights reserved.

Thermodynamic properties of SmFeO3(S) and SM3R5O12(S)

The enthalpy increments and the standard molar Gibbs energy (G) of formation of SmFeO3(S) and SM3Fe5O12(s) have been measured using a Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. A X-type transition, related to magnetic order-disorder transformation (antiferromagnetic to paramagnetic), is apparent from the heat capacity data at similar to673 K for SmFeO3(s) and at similar to560 K for Sm3Fe5O12(S). Enthalpy increment data for SmFeO3(s) and SM3Fe5O12(s), except in the vicinity of X-transition, can be represented by the following polynomial expressions: {H-m(0)(T) - H-m(0)(298.15 K){/J mol-(1)(+/-1.2%) = -54 532.8 + 147.4 . (T/K) + 1.2 . 10(-4) . (T/K)(2) +3.154 . 10(6) . (T/K)(-1); (298.15 less than or equal to T/K less than or equal to 1000) for SmFeO3(s), and {H-m(0)(T) - H-m(0)(298.15 K)}/J mol(-1) (+/-1.4%) = -192 763 + 554.7 . (T/K) + 2.0 . 10(-6) . (T/K)(2) + 8.161 . 10(6) - (T/K)(-1); (298.15 less than or equal to T/K less than or equal to 1000) for Sm3Fe5O12(s). The reversible emf of the solid-state electrochemical cells, (-)Pt/{SmFeO3(s) + Sm2O3(S) + Fe(s)) // YDT / CSZ // {Fe(s) + Fe0.95O(s)} / Pt(+) and (-)Pt/{Fe(s) + Fe0.95O(S)} // CSZ // {SmFeO3(s) + Sm3Fe5O12(s) + Fe3O4(s) / Pt(+), were measured in the temperature ranges of 1005-1259 K and 1030-1252 K, respectively. The standard molar G of formation of solid SmFeO3 and Sm3Fe5O12 calculated by the least squares regression analysis of the data obtained in the current study, and data for Fe0.95O and Sm2O3 from the literature, are given by: Delta(f)G(m)(0)(SmFeO3, s)/kj . mol(-1)(+/-2.0) = -1355.2 + 0.2643 . ; (1005 less than or equal to T/K less than or equal to 1570) and Delta(f)G(m)(0)(Sm3Fe5O12, s)/kj . mol(-1) (+/- 3.1) = -4891.0 + 1.0312 . (T/K); (1030 less than or equal to T/K less than or equal to 1252) The uncertainty estimates for Delta(f)G(m)(0) include the standard deviation in the emf and uncertainty in the data taken from the literature. Based on these thermodynamic data, the oxygen potential diagram for the system Sm-Fe-O was constructed at 1250 K.

Identification and characterization of cysteine proteinases of Trypanosoma evansi

Trypanosoma evansi is a causative agent of `surra', a common haemoprotozoan disease of livestock in India causing high morbidity and mortality in disease endemic areas. The proteinases released by live and dead trypanosomes entail immunosuppression in the infected host, which immensely contribute in disease pathogenesis. Cysteine proteinases are identified in the infectious cycle of trypanosomes such as cruzain from Trypanosoma cruzi, rhodesain or brucipain from Trypanosoma brucei rhodesiense and congopain from Trypanosoma congelense. These enzymes localised in lysosome-like organelles, flagellar pocket and on cell surface, which play a critical role in the life cycle of protozoan parasites, viz. in host invasion, nutrition and alteration of the host immune response. The paper describes the identification of cysteine proteinases of T. evansi lysate, activity profile at different pH optima and inhibition pattern using a specific inhibitor, besides the polypeptide profile of an antigen. Eight proteinases of T. evansi were identified in the molecular weight (MW) ranges of 28-170 kDa using gelatin substrate-polyacrylamide gel electrophoresis (GS-PAGE), and of these proteinases, six were cysteine proteinases, as they were inhibited by L-3-carboxy-2,3-transepoxypropionyl-lecuylamido (4-guanidino)-butane (E-64), a specific inhibitor. These proteolytic enzymes were most reactive in acidic pH between 3.0 and 5.5 in the presence of dithiothreitol and completely inactive at alkaline pH 10.0. Similarly, the GS-PAGE profile of the serum samples of rats infected with T. evansi revealed strong proteolytic activity only at the 28-kDa zone at pH 5.5, while no proteolytic activity was observed in serum samples of uninfected rats. Further, the other zones of clearance, which were evident in T. evansi antigen zymogram, could not be observed in the serum samples of rats infected with T. evansi. The polypeptide pattern of the whole cell lysate antigen revealed 12-15 polypeptide bands ranging from 28 to 81 kDa along with five predominant polypeptides bands (MW of 81, 66, 62, 55 and 45 kDa), which were immunoreactive with hyperimmune serum (HIS) and serum of experimentally infected rabbits with T. evansi infection. The immunoblot recognised antibodies in experimentally infected rabbits and against HIS as well, corresponding to the zone of clearances at lower MW ranges (28-41 kDa), which may be attributed to the potential of these proteinases in the diagnosis of T. evansi infection. Since these thiol-dependent enzymes are most active in acidic pH and considering their inhibition characteristics, these data suggest that they resemble to the mammalian lysosomal cathepsin B and L.

Spatial Variation of Physico-Chemical and hydrological Parameters with land-use in Venkatapura Catchment,Karnataka

Social, economic and political development of a region is dependent on the health and quantity of the natural resources. Integrated approaches in the management of natural resources would ensure sustainability, which demands inventorying, mapping and monitoring of resources considering all components of an ecosystem. The monitoring of hydrological and catchment landscape of river resources have a vital role in the conservation and management of aquatic resources. This paper presents a case study Venkatapura river basin in Uttara Kannada district of Karnataka State, India based on stream hydrology and landuse analyses. The results revealed variations in dissolved oxygen and free carbon dioxide according to the flow nature of the water, and increased amount of phosphates and coliform contamination in streams closer to anthropogenic activities.

Intruder detection over sensor placement in a hexagonal lattice

The problem of intrusion detection and location identification in the presence of clutter is considered for a hexagonal sensor-node geometry. It is noted that in any practical application,for a given fixed intruder or clutter location, only a small number of neighboring sensor nodes will register a significant reading. Thus sensing may be regarded as a local phenomenon and performance is strongly dependent on the local geometry of the sensor nodes. We focus on the case when the sensor nodes form a hexagonal lattice. The optimality of the hexagonal lattice with respect to density of packing and covering and largeness of the kissing number suggest that this is the best possible arrangement from a sensor network viewpoint. The results presented here are clearly relevant when the particular sensing application permits a deterministic placement of sensors. The results also serve as a performance benchmark for the case of a random deployment of sensors. A novel feature of our analysis of the hexagonal sensor grid is a signal-space viewpoint which sheds light on achievable performance.Under this viewpoint, the problem of intruder detection is reduced to one of determining in a distributed manner, the optimal decision boundary that separates the signal spaces SI and SC associated to intruder and clutter respectively. Given the difficulty of implementing the optimal detector, we present a low-complexity distributive algorithm under which the surfaces SI and SC are separated by a wellchosen hyperplane. The algorithm is designed to be efficient in terms of communication cost by minimizing the expected number of bits transmitted by a sensor.