A critical re-examination and a revised phase diagram of La1-xSrxCoO3

We report the results of a comprehensive study on dc magnetization, ac susceptibility, and the magnetotransport properties of the La1-xSrxCoO3(0 <= x <= 0.5) system. At higher Sr doping (x >= 0.18), the system exhibits Brillouin-like field cooled magnetization (M-FC). However, for x < 0.18, the system exhibits a kink in the M-FC, a peak at the intermediate field in the thermoremnant magnetization and a non-saturating tendency in the M-H plot that all point towards the characteristic of spin glass behavior. More interestingly, dc magnetization studies for x < 0.18 do not suggest the existence of ferromagnetic correlation that can give rise to an irreversible line in the spin glass regime. The ac susceptibility study for x > 0.2 exhibits apparently no frequency dependent peak shift around the ferromagnetic transition region. However, a feeble signature of glassiness is verified by studying the frequency dependent shoulder position in chi `' (T) and the memory effect below the Curie temperature. But, for x < 0.18, the ac susceptibility study exhibits a considerable frequency dependent peak shift, time dependent memory effect, and the characteristic spin relaxation time scale tau(0) similar to 10(-13) s. The reciprocal susceptibility versus temperature plot adheres to Curie-Weiss behavior and does not provide any signature of preformed ferromagnetic clusters well above the Curie temperature. The magnetotransport study reveals a cross over from metallic to semiconducting-like behavior for x <= 0.18. On the semiconducting side, the system exhibits a large value of magnetoresistance (upto 75%) towards low temperature and it is strongly connected to the spin dependent part of the random potential distribution in the spin glass phase. Based on the above observations, we have reconstructed a new magnetic phase diagram and characterized each phase with associated properties.

A High Pressure Study of the Phase Diagram and the Critical Exponent β of Binary Liquid Systems

The pressure dependence of critical parameters xc, Tc, and β have been analysed in four systems namely cyclohexane + acetic anhydride, n-heptane + acetic anhydride, methanol + n-heptane, and carbon disulphide + acetonitrile. The separation temperature was found to increase linearly with pressure the value of dTc/dP being 28 mK, 11 mK, 22 mK, and 25 mK respectively. These are in fair agreement with earlier measurements available for two systems. For the methanol + n-heptane system dTc/dP is apparently not consistent with the value predicted from the specific heat and thermal expansion data.Die Druckabhängigkeit der kritischen Parameter xc, Tc und β ist in den vier Systemen Cyclohexan + Essigsäureanhydrid, n-Heptan + Essigsäureanhydrid, Methanol + n-Heptan und Schwefelkohlenstoff + Acetonitril analysiert worden. Es wurde gefunden, daß die kritische Temperatur linear mit dem Druck ansteigt. Die Werte für dTc/dP betragen 28 mK, 11 mK, 22 mK und 25 mK. Sie sind in guter überein-stimmung mit früheren Messungen an zweien dieser Systeme. Für Methanol + n-Heptan stimmt der Wert für dT/dP offensichtlich nicht mit Werten, die mit Hilfe von Daten für die spezifische Wärme und die thermische Ausdehnung vorhergesagt wurden, überein.

Influence of Die Surface Textures during Metal Forming-A Study Using Experiments and Simulation

Friction plays an important role in metal forming processes, and the surface texture of the die is a major factor that influences friction. In the present investigation, experiments were conducted to understand the role of surface texture of the harder die surface and load on coefficient of friction. The data analysis showed that the coefficient of friction is highly dependent on the surface texture of the die surface. Assigning different magnitude of coefficients of friction, obtained in the experiments, at different regions between the die and the workpiece, Finite element (FE) simulation of a compression test was carried out to understand the effect of friction on deformation and stress/strain-rate distribution. Simulation results revealed that, owing to the difference in coefficient of friction, there is a change in metal flow pattern. Both experimental and simulation results confirmed that the surface texture of the die surface and thus coefficient of friction directly affects the strain rate and flow pattern of the workpiece.

Matched thermochemical diagram for vacuum decarburization of ferroalloys

The carbon content of high carbon ferroalloy melts can be reduced by a vacuum treatment. Carbon and oxygen dissolved in the melt react to form CO. Although this process has been suggested in the literature, no comprehensive analysis of the equilibrium partial pressure of CO over an alloy melt with a given carbon and oxygen content has been reported. In this paper, a new type of matched thermochemical diagram is introduced, from which the feasibility of decarburization at reduced CO pressure and the minimum achievable carbon level can be graphically evaluated for any alloy composition and temperature. Carbon and oxygen potentials of different alloys are plotted as functions of temperature on two terminal diagrams. By projecting information from these plots onto a central diagram, containing data on the Gibbs' energy of mixing for the C-O system, equilibrium partial pressures of CO and CO2 are obtained. Nomograms on the central diagram give a direct indication of the equilibrium partial pressures at any given temperature. The carbon and oxygen activities in ferrochromium alloys have been assessed and the results are presented to illustrate the construction and use of the matched thermochemical diagrams.

Microbial identification by detection of ligation probes on DNA microarray

Microbes in natural and artificial environments as well as in the human body are a key part of the functional properties of these complex systems. The presence or absence of certain microbial taxa is a correlate of functional status like risk of disease or course of metabolic processes of a microbial community. As microbes are highly diverse and mostly notcultivable, molecular markers like gene sequences are a potential basis for detection and identification of key types. The goal of this thesis was to study molecular methods for identification of microbial DNA in order to develop a tool for analysis of environmental and clinical DNA samples. Particular emphasis was placed on specificity of detection which is a major challenge when analyzing complex microbial communities. The approach taken in this study was the application and optimization of enzymatic ligation of DNA probes coupled with microarray read-out for high-throughput microbial profiling. The results show that fungal phylotypes and human papillomavirus genotypes could be accurately identified from pools of PCR amplicons generated from purified sample DNA. Approximately 1 ng/μl of sample DNA was needed for representative PCR amplification as measured by comparisons between clone sequencing and microarray. A minimum of 0,25 amol/μl of PCR amplicons was detectable from amongst 5 ng/μl of background DNA, suggesting that the detection limit of the test comprising of ligation reaction followed by microarray read-out was approximately 0,04%. Detection from sample DNA directly was shown to be feasible with probes forming a circular molecule upon ligation followed by PCR amplification of the probe. In this approach, the minimum detectable relative amount of target genome was found to be 1% of all genomes in the sample as estimated from 454 deep sequencing results. Signal-to-noise of contact printed microarrays could be improved by using an internal microarray hybridization control oligonucleotide probe together with a computational algorithm. The algorithm was based on identification of a bias in the microarray data and correction of the bias as shown by simulated and real data. The results further suggest semiquantitative detection to be possible by ligation detection, allowing estimation of target abundance in a sample. However, in practise, comprehensive sequence information of full length rRNA genes is needed to support probe design with complex samples. This study shows that DNA microarray has the potential for an accurate microbial diagnostic platform to take advantage of increasing sequence data and to replace traditional, less efficient methods that still dominate routine testing in laboratories. The data suggests that ligation reaction based microarray assay can be optimized to a degree that allows good signal-tonoise and semiquantitative detection.

Phase diagram of the two-dimensional disordered Hubbard model in the Hartree-Fock approximation

Ground-state properties of the two-dimensional Hubbard model with point-defect disorder are investigated numerically in the Hartree-Fock approximation. The phase diagram in the p(point defect concentration)-delta(deviation from half filling) plane exhibits antiferromagnetic, spin-density-wave, paramagnetic, and spin-glass-like phases. The disorder stabilizes the antiferromagnetic phase relative to the spin-density-wave phase. The presence of U strongly enhances the localization in the antiferromagnetic phase. The spin-density-wave and spin-glass-like phases are weakly localized.

Bearing capacity factors of circular foundations for a general c-phi soil using lower bound finite elements limit analysis

By using the lower bound limit analysis in conjunction with finite elements and linear programming, the bearing capacity factors due to cohesion, surcharge and unit weight, respectively, have been computed for a circular footing with different values of phi. The recent axisymmetric formulation proposed by the authors under phi = 0 condition, which is based on the concept that the magnitude of the hoop stress (sigma(theta)) remains closer to the least compressive normal stress (sigma(3)), is extended for a general c-phi soil. The computational results are found to compare quite well with the available numerical results from literature. It is expected that the study will be useful for solving various axisymmetric geotechnical stability problems. Copyright (C) 2010 John Wiley & Sons, Ltd.

Construction of energy-level diagram of oriented benzene using connectivity information obtained by modified z-cosy experiment

Experiments involving selective perturbation of a transition yield information about the directly connected transitions, which in turn yield information for deriving the parameters of the spin Hamiltonian of oriented molecules. Problems involved with selective perturbation are removed by the use of a two-dimensional experiment, namely, the modified Z-COSY-experiment, The use of this experiment is demonstrated for obtaining the connectivity information and for determining the parameters of the spin Hamiltonian of oriented benzene, a strongly coupled six-spin system

Central Limit Theorem for truncated heavy tailed Banach valued random vectors

In this paper the question of the extent to which truncated heavy tailed random vectors, taking values in a Banach space, retain the characteristic features of heavy tailed random vectors, is answered from the point of view of the central limit theorem.

Evidence for supramolecular organization of alkane and surfactant molecules in the process of forming mesoporous silica

Investigations of the pore expansion in mesoporous silica in the presence of n-alkanes suggest a cooperative organization of the surfactant and alkane molecules, involving additivity of chain lengths.

Solubilization of n-decane into n-decyl-polyoxyethylene surfactants: A cavity forming free energy based model

The present paper reports the results of a theoretical study of the forces and factors driving the solubilization of n-alkane solubilizates into the micellar core of some non-ionic surfactants, based on a micellar model which includes the cavity forming free energy as a component of micellization. The solubilizate is n-decane and the non-ionic surfactants considered are n-decyl-polyoxyethylene surfactants. The extent of solubilization, i.e. the mole fraction of the solubilizate within the core has been calculated. The results indicate that the incorporated solubilizate has more translational and rotational degrees of freedom as compared to those of the tail parts of the surfactants present in the core. This drives the total free energy of aggregation after solubilization into a more favourable direction. The results are in fair agreement with the experimental results.

Differences in the glass-forming ability of rapidly solidified and mechanically alloyed Ti-Ni-Cu alloys

Melt spinning of Ti50Ni50 ? xCux (x = 10, 25, 40) alloys showed that the glass-forming ability is good for Cu-rich compositions and poor for Ni-rich compositions. The results of mechanical alloying experiments in the same system showed a reverse trend as far as the glass-forming ability is concerned. These contradictory results are explained in the light of thermodynamic and kinetic considerations. Crystallization results of the melt spun alloys are also presented.

Relationship between nonlinear resistivity and the varistor forming mechanism in ZnO ceramics

The use of a number of perovskite phases M� M�O3-x, as the only forming additive in ZnO ceramics, produces a high nonlinearity index, ?(up to 45), where M� is a multivalent transition?metal ion and M� is an alkaline earth or a rare?earth ion. From this study, the formation parameters crucial to high nonlinearity, such as nonstoichiometry in the as?received ZnO powder, low x values of the additives and fast cooling rate after the sintering, are explainable on the basis of a depletion layer formation at the presintering stage. This is because of the surface states arising out of the chemisorbed oxygen. The depletion layer is retained during sintering as a result of the higher valence state of M� ions, preferentially present at the grain?boundary regions. The fast cooling freezes in the high?temperature concentration of donor?type defects, thereby decreasing the depletion layer width.