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.

Molecular insights into the mechanism of phenotypic tolerance to rifampicin conferred on mycobacterial RNA polymerase by MsRbpA

The protein MsRbpA from Mycobacterium smegmatis rescues RNA polymerase (RNAP) from the inhibitory effect of rifampicin (Rif). We have reported previously that MsRbpA interacts with the beta-subunit of RNAP and that the effect of MsRbpA on Rif-resistant (Rif(R)) RNAP is minimal. Here we attempted to gain molecular insights into the mechanism of action of this protein with respect to its role in rescuing RNAP from Rif-mediated transcription inhibition. Our experimental approach comprised multiple-round transcription assays, fluorescence spectroscopy, MS and surface plasmon resonance in order to meet the above objective. Based on our molecular studies we propose here that Rif is released from its binding site in the RNAP-Rif complex in the presence of MsRbpA. Biophysical studies reveal that the location of MsRbpA on RNAP is at the junction of the beta- and beta'-subunits, close to the Rif-binding site and the (i + 1) site on RNAP.

Mapping of large scale 158 mu m [CII] line emission: Orion A

We present the first results of an observational programme undertaken to map the fine structure line emission of singly ionized carbon ([ CII] 157 : 7409 mum) over extended regions using a Fabry Perot spectrometer newly installed at the focal plane of a 100 cm balloon- borne far- infrared telescope. This new combination of instruments has a velocity resolution of similar to 200 km s(-1) and an angular resolution of 1.'5. During the first flight, an area of 30' x 15' in Orion A was mapped. These observations extend over a larger area than previous observations, the map is fully sampled and the spectral scanning method used enables reliable estimation of the continuum emission at frequencies adjacent to the [ CII] line. The total [ CII] line luminosity, calculated by considering up to 20% of the maximum line intensity is 0.04% of the luminosity of the far- infrared continuum. We have compared the [ CII] intensity distribution with the velocity- integrated intensity distributions of (CO)-C-13(1- 0), CI(1- 0) and CO( 3- 2) from the literature. Comparison of the [ CII], [ CI] and the radio continuum intensity distributions indicates that the largescale [ CII] emission originates mainly from the neutral gas, except at the position of M 43, where no [ CI] emission corresponding to the [ CII] emission is seen. Substantial part of the [ CII] emission from here originates from the ionized gas. The observed line intensities and ratios have been analyzed using the PDR models by Kaufman et al. ( 1999) to derive the incident UV flux and volume density at a few selected positions. The models reproduce the observations reasonably well at most positions excepting the [ CII] peak ( which coincides with the position of theta(1) Ori C). Possible reason for the failure could be the simplifying assumption of a homogeneous plane parallel slab in place of a more complicated geometry.

High temperature seebeck measurements on YBa2Cu3O7-δ

The Seebeck coefficient (S) of YBa2Cu3O7-δ was measured in the temperature range 450 – 1200 K in air and in pure oxygen in order to derive information on charge carrier concentration. The orthorhombic to tetragonal phase transition manifests as maxima in the variation of (dS/dT) with temperature. Seebeck coefficient in air decreases beyond ∼ 1130K corresponding to a value of δ = 0.73.

La-Doped Ba2In2O5 Electrolyte: Pechini Synthesis, Microstructure, Electrical Conductivity, and Application for CO Gas Sensing

Dense (Ba1―xLax)2In2O5+x (BLIO) electrolytes with different compositions (x = 0.4, 0.5, 0.6) were fabricated using powders obtained by the Pechini method. The formation of BLIO powders was investigated by using X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The calcination temperature and time were optimized. The sintered (Ba1―xLax)2In2O5+x electrolytes showed a relative density greater than ∼97%, and the major phase of three electrolyte compositions was indexed as a cubic perovskite. The electrical conductivity of BLIO ceramics at elevated temperatures in air was measured by ac-impedance spectroscopy. The activation energies for conduction in BLIO were 102 kJ mol―1 between 473 and 666 K and 118 kJ mol―1 between 769 and 873 K, which are comparable to that for 8 mol % yttria-stabilized cubic zirconia. Mixed-potential gas sensors utilizing BLIO-based electrolytes exhibited good sensitivity to different CO concentrations from ∼100 to ∼500 ppm and excellent selectivity to methane at around 873 K.

Interference in Multiprocessor Systems with Localized Memory Access Probabilities

Past studies of memory interference in multiprocessor systems have generally assumed that the references of each processor are uniformly distributed among the memory modules. In this paper we develop a model with local referencing, which reflects more closely the behavior of real-life programs. This model is analyzed using Markov chain techniques and expressions are derived for the multiprocessor performance. New expressions are also obtained for the performance in the traditional uniform reference model and are compared with other expressions-available in the literature. Results of a simulation study are given to show the accuracy of the expressions for both models.

Relaxor characteristics of layered Ba1-(3/2)xLaxBi2Nb2O9 ceramics

Barium lanthanum bismuth niobate Ba1−(3/2)xLaxBi2Nb2O9 (x = 0, 0.05, 0.1, and 0.15) powders have been prepared via solid state reaction route. The monophasic layered perovskite nature of each composition of these was confirmed by x-ray diffraction studies. A continuous decrease in the lattice parameter c of parent BaBi2Nb2O9 with increase in La3+ doping level was noteworthy. A decrease in dielectric constant maximum (εm), a shift in dielectric anomaly to lower temperatures (from 488 to 382 K), and an increase in the diffuseness (γ) (from 1.58 to 1.84) of dielectric anomaly were encountered on increasing x from 0 to 0.15. Vogel-Fulcher analyses showed a decrease in freezing temperature (Tf) (from 157 to 40 K) and an increase in the activation energy (0.53 to 1.12 eV) for frequency dispersion with increase in La3+ content. A downward shift in the peak position of the pyroelectric coefficient with increasing La3+ doping level was observed. The observed changes in the above physical properties were attributed to the increase in A-site chemical heterogeneity as a result of aliovalent La3+ doping on Ba2+ sites and associated A-site vacancy formation.

A Method of Evaluating Electrical Response of Solion Diodes

A method of evaluating the transient electrical response of a solion diode when excited by different current stimuli is given. This method is extended to obtain the transient response of the solion when connected in a circuit. To illustrate the utility of this method a circuit incorporating a solion diode has been analyzed.

Catabolite repression of phosphoenolpyruvate carboxykinase by a zinc finger protein under biotin- and pyruvate carboxylase-deficient conditions in Pichia pastoris

We have identified a methanol- and biotin-starvation-inducible zinc finger protein named ROP [repressor of phosphoenolpyruvate carboxykinase (PEPCK)] in the methylotrophic yeast Pichia pastoris. When P. pastoris strain GS115 (wild-type, WT) is cultured in biotin-deficient, glucose-ammonium (Bio(-)) medium, growth is suppressed due to the inhibition of anaplerotic synthesis of oxaloacetate, catalysed by the biotin-dependent enzyme pyruvate carboxylase (PC). Deletion of ROP results in a strain (Delta ROP) that can grow under biotin-deficient conditions due to derepression of a biotin- and PC-independent pathway of anaplerotic synthesis of oxaloacetate. Northern analysis as well as microarray expression profiling of RNA isolated from WT and Delta ROP strains cultured in Bio(-) medium indicate that expression of the phosphoenolpyruvate carboxykinase gene (PEPCK) is induced in Delta ROP during biotin- or PC-deficiency even under glucose-abundant conditions. There is an excellent correlation between PEPCK expression and growth of Delta ROP in Bio(-) medium, suggesting that ROP-mediated regulation of PEPCK may have a crucial role in the biotin- and PC-independent growth of the Delta ROP strain. To our knowledge, ROP is the first example of a zinc finger transcription factor involved in the catabolite repression of PEPCK in yeast cells cultured under biotin- or PC-deficient and glucose-abundant conditions.

Synthesis, Reactivity Studies, Structural Aspects, and Solution Behavior of Half Sandwich Ruthenium(II) N,N `,N `'-Triarylguanidinate Complexes

[(eta(6)-C(10)H(14))RuCl(mu-Cl)](2) (eta(6)-C(10)H(14) = eta(6)-p-cymene) was subjected to a bridge-splitting reaction with N,N',N `'-triarylguanidines, (ArNH)(2)C=NAr, in toluene at ambient temperature to afford [(eta(6)-C(10)H(14))RuCl{kappa(2)(N,N')((ArN)(2)C-N(H)Ar)}] (Ar = C(6)H(4)Me-4 (1), C(6)H(4)(OMe)-2 (2), C(6)H(4)Me-2 (3), and C(6)H(3)Me(2)-2,4 (4)) in high yield with a view aimed at understanding the influence of substituent(s) on the aryl rings of the guanidine upon the solid-state structure, solution behavior, and reactivity pattern of the products. Complexes 1-3 upon reaction with NaN(3) in ethanol at ambient temperature afforded [(eta(6)-C(10)H(14))RuN(3){kappa(2)(N,N')((ArN)(2)C-N(H)Ar)}] (Ar = C(6)H(4)Me-4 (5), C(6)H(4)(OMe)-2 (6), and C(6)H(4)Me-2 (7)) in high yield. [3 + 2] cycloaddition reaction of 5-7 with RO(O)C-C C-C(O)OR (R = Et (DEAD) and Me (DMAD)) (diethylacetylenedicarboxylate, DEAD; dimethylacetylenedicarboxylate, DMAD) in CH(2)Cl(2) at ambient temperature afforded [(eta(6)-C(10)H(14))Ru{N(3)C(2)(C(O)OR)(2)}{kappa(2)(N,N')((ArN)(2) C-N(H)Ar)}center dot xH(2)O (x = 1, R = Et, Ar = C(6)H(4)Me-4 (8 center dot H(2)O); x = 0, R = Me, Ar = C(6)H(4)(OMe)-2 (9), and C(6)H(4)Me-2 (10)) in moderate yield. The molecular structures of 1-6, 8 center dot H(2)O, and 10 were determined by single crystal X-ray diffraction data. The ruthenium atom in the aforementioned complexes revealed pseudo octahedral ``three legged piano stool'' geometry. The guanidinate ligand in 2, 3, and 6 revealed syn-syn conformation and that in 4, and 10 revealed syn-anti conformation, and the conformational difference was rationalized on the basis of subtle differences in the stereochemistry of the coordinated nitrogen atoms caused by the aryl moiety in 3 and 4 or steric overload caused by the substituents around the ruthenium atom in 10. The bonding pattern of the CN(3) unit of the guanidinate ligand in the new complexes was explained by invoking n-pi conjugation involving the interaction of the NHAr/N(coord)Ar lone pair with C=N pi* orbital of the imine unit. Complexes 1, 2, 5, 6, 8 center dot H(2)O, and 9 were shown to exist as a single isomer in solution as revealed by NMR data, and this was ascribed to a fast C-N(H)Ar bond rotation caused by a less bulky aryl moiety in these complexes. In contrast, 3 and 10 were shown to exist as a mixture of three and five isomers in about 1:1:1 and 1.0:1.2:2:7:3.5:6.9 ratios, respectively in solution as revealed by a VT (1)H NMR, (1)H-(1)H COSY in conjunction with DEPT-90 (13)C NMR data measured at 233 K in the case of 3. The multiple number of isomers in solution was ascribed to the restricted C-N(H)(o-tolyl) bond rotation caused by the bulky o-tolyl substituent in 3 or the aforementioned restricted C-NH(o-tolyl) bond rotation as well as the restricted ruthenium-arene(centroid) bond rotation caused by the substituents around the ruthenium atom in 10.

Network pricing for QoS: A 'Regulation' approach

V. S. Borkar’s work was supported in part by grant number III.5(157)/99-ET from the Department of Science and Technology, Government of India. D. Manjunath’s work was supported in part by grant number 1(1)/2004-E-Infra from the Ministry of Information Technology, Government of India.

Interactions between oppositely-charged vs. those between like-charged species in crystal of aminoacetonitrile picrate: a charge density investigation

Energy and charge aspects of two types of ion association - between oppositely-charged and between like-charged species - were quantified using the topological analysis of the electron density function derived from the low-temperature X-ray diffraction experiment for a crystal of aminoacetonitrile picrate (sp. gr. Cmca, Z = 8, R = 0.0187), providing an experimental evidence of their ``equal rights'' in crystal packing formation.