High pressure electrical measurements on Ge-Te-Se glasses

Electrical resistivity measurements have been carried out on bulk Ge-Te-Se glasses in a Bridgman anvil System. The resistivity of the Ge-Te-Se samples is found to decrease continuously with increasing pressure, with the metallization occurring around 8 GPa. Ge20TexSe80-x glasses (10 less than or equal to x less than or equal to 50) with the mean co-ordination number Z(av) = 2.4 exhibit a plateau in resistivity up to about 4 GPa pressure, followed by a continuous decrease to metallic values. On the other hand, Ge10TexSe90-x glasses (10 less than or equal to x less than or equal to 40) having Z(av) = 2.2, exhibit a smaller plateau (only up to 1 GPa), followed by a decrease in resistivity with pressure. This subtle difference in the high pressure resistivity of Ge-Te-Se glasses with Z(av) < 2.4 and Z(av) greater than or equal to 2.4 can be associated with the changes in the local structure of the chalcogenide glasses with composition.

Injection cooling of blunt bodies flying at high Mach numbers

A study of transpiration cooling of blunt bodies such as a hemicylinder is made by solving Navier-Stokes equations. An upwind, implicit time-marching code is developed for this purpose. The study is conducted for both perfect-gas and real-gas (chemical equilibrium) flows. Investigations are carried out for a special wall condition that is referred to as no heat flow into the wall condition. The effects of air injection on wall temperature are analyzed. Analyses are carried out for Mach numbers ranging between 6-10 and Reynolds numbers ranging between 10(6)-10(7). Studies are made for spatially constant as well as spatially varying mass injection rate distributions, White cold air injection reduces the wall temperature substantially, transpiration cooling is relatively less effective when the gas is in chemical equilibrium.

Chordal Bipartite Graphs with High Boxicity

The boxicity of a graph G is defined as the minimum integer k such that G is an intersection graph of axis-parallel k-dimensional boxes. Chordal bipartite graphs are bipartite graphs that do not contain an induced cycle of length greater than 4. It was conjectured by Otachi, Okamoto and Yamazaki that chordal bipartite graphs have boxicity at most 2. We disprove this conjecture by exhibiting an infinite family of chordal bipartite graphs that have unbounded boxicity.

Electron-Beam-Induced Modifications in High-Density Polyethylene

Post-irradiation studies have been carried out to elucidate the effects of electron beam irradiation on the structural, optical, dielectric, and thermal properties of high-density polyethylene (HDPE) films. The experimental results showed that both the optical band gap and activation energy of HDPE films decreases with an increase in the doses of electron radiation. The electrical measurements showed that dielectric constant and the ac conductivity of HDPE increases with an increase in the dose of electron radiation. The thermal analysis carried out using DSC and TGA revealed that the melting temperature, degree of crystallinity, and thermal stability of the HDPE films increased, obviously, due to the predominant cross-linking reaction following high doses of electron irradiation.

The effect of grain size on the high-strain, high-strain-rate behavior of copper

Copper with four widely differing grain sizes was subjected to high-strain-rate plastic deformation in a special experimental arrangement in which high shear strains of approximately 2 to 7 were generated. The adiabatic plastic deformation produced temperature rises in excess of 300 K, creating conditions favorable for dynamic recrystallization, with an attendant change in the mechanical response. Preshocking of the specimens to an amplitude of 50 GPa generated a high dislocation density; twinning was highly dependent on grain size, being profuse for the 117- and 315-mu m grain-size specimens and virtually absent for the 9.5-mu m grain-size specimens. This has a profound effect on the subsequent mechanical response of the specimens, with the smaller grain-size material undergoing considerably more hardening than the larger grain-size material. A rationale is proposed which leads to a prediction of the shock threshold stress for twinning as a function of grain size. The strain required for localization of plastic deformation was dependent on the combined grain size/shock-induced microstructure, with the large grain-size specimens localizing more readily. The experimental results obtained are rationalized in terms of dynamic recrystallization, and a constitutive equation is applied to the experimental results; it correctly predicts the earlier onset of localization for the large grain-size specimens. It is suggested that the grain-size dependence of shock response can significantly affect the performance of shaped charges.

Mott insulator high T-c bipolaronic superconductor transition in cuprates - Discussion

All ‘undoped’ cuprates are antiferromagnetic Mott insulators. We argue that with doping they remain to be insulators including the ‘overdoped’ samples. Hence, there is no clear dividing line between non–metallic cuprates and high–temperature superconductors. Based on the generic Hamiltonian including the electron–phonon interaction and the direct Coulomb repulsion the ground state of doped cuprates is shown to be a charged 2e Bose liquid of small bipolarons. A theory of the normal state transport of copper oxides is developed. The temperature dependence of the resistivity and of the Hall effect agrees remarkably well with the experimental data in La2–xSrxCuO4 for the entire temperature regime including unusual ‘logarithmic’ low–temperature region. The violation of Kohler's rule in magnetoresistivity is explained. The resistive and thermodynamic superconducting transitions in a magnetic field are quantitatively described.

Metamorphic-metasomatic fluids and Al, Si order/disorder of K-rich alkali feldspars from southern Indian high grade terrain

The structural state of K-feldspars in the quartzofeldspathic gneisses, charnockites, metapelites and pegmatites from the southern Kamataka, northern Tamil Nadu and southern Kerala high-grade regions of southern India has been characterized using petrographic and powder X-ray diffraction methods. The observed distribution pattern of structural state with a preponderance of disordered K-feldspar polymorphs in granulites compared to the ordered microclines in the amphibolite facies rocks is interpreted to reflect principally the varying H2O contents in the metamorphic-metasomatic fluids across metamorphic grade. The K-feldspars in the pegmatites of granitic derivation and in a pegmatite of inferred metamorphic origin also point to the important role of aqueous fluids in their structural state.

Suboptimal Midcourse Guidance of Interceptors for High-Speed Targets with Alignment Angle Constraint

Using the recently developed computationally efficient model predictive static programming and a closely related model predictive spread control concept, two nonlinear suboptimal midcourse guidance laws are presented in this paper for interceptors engaging against incoming high-speed ballistic missiles. The guidance laws are primarily based on nonlinear optimal control theory, and hence imbed effective trajectory optimization concepts into the guidance laws. Apart from being energy efficient by minimizing the control usage throughout the trajectory (minimum control usage leads to minimum turning, and hence leads to minimum induced drag), both of these laws enforce desired alignment constraints in both elevation and azimuth in a hard-constraint sense. This good alignment during midcourse is expected to enhance the effectiveness of the terminal guidance substantially. Both point mass as well as six-degree-of-freedom simulation results (with a realistic inner-loop autopilot based on dynamic inversion) are presented in this paper, which clearly shows the effectiveness of the proposed guidance laws. It has also been observed that, even with different perturbations of missile parameters, the performance of guidance is satisfactory. A comparison study, with the vector explicit guidance scheme proposed earlier in the literature, also shows that the newly proposed model-predictive-static-programming-based and model-predictive-spread-control-based guidance schemes lead to lesser lateral acceleration demand and lesser velocity loss during engagement.

Theory of combined AM and high-harmonic FM mode locked laser

Closed form solutions for a simultaneously AM and high-harmonic FM mode locked laser system is presented. Analytical expressions for the pulsewidth and pulsewidth-bandwidth products are derived in terms of the system parameters. The analysis predicts production of 17 ps duration pulses in a Nd:YAG laser mode locked with AM and FM modulators driven at 80 MHz and 1.76 GHz for 1 W modulator input power. The predicted values of the pulsewidth-bandwidth product lie between the values corresponding to the pure AM and FM mode locking values.

A high performance scheme for EEG compression using a multichannel model

The amount of data contained in electroencephalogram (EEG) recordings is quite massive and this places constraints on bandwidth and storage. The requirement of online transmission of data needs a scheme that allows higher performance with lower computation. Single channel algorithms, when applied on multichannel EEG data fail to meet this requirement. While there have been many methods proposed for multichannel ECG compression, not much work appears to have been done in the area of multichannel EEG. compression. In this paper, we present an EEG compression algorithm based on a multichannel model, which gives higher performance compared to other algorithms. Simulations have been performed on both normal and pathological EEG data and it is observed that a high compression ratio with very large SNR is obtained in both cases. The reconstructed signals are found to match the original signals very closely, thus confirming that diagnostic information is being preserved during transmission.

Comparative study on flexural response of full and partial depth fiber-reinforced high-strength concrete

This study presents the results of an experimental and analytical comparison of the flexural behavior of a high-strength concrete specimen (no conventional reinforcement) with an average plain concrete cube strength of nearly 65 MPa and containing trough shape steel fibers. Trough shape steel fibers with a volume fraction ranging from 0 to 1.5% and having a constant aspect ratio of 80 have been used in this study. Increased toughness and a more ductile stress-strain response were observed with an increase in fiber content, when the fibers were distributed over the full/partial depth of the beam cross section. Based on the tests, a robust analytical procedure has been proposed to establish the required partial depth to contain fiber-reinforced concrete (FRC) so as to obtain the flexural capacity of a member with FRC over the full depth. It is expected that this procedure will help designers in properly estimating the required partial depth of fibers in composite sections for specific structural applications. Empirical and mechanistic relations have also been proposed in this study to establish the load-deflection behavior of high-strength FRC.

High temperature phase chemistry of system Eu-Pd-O

An isothermal section of the phase diagram for the system Eu - Pd - O at 1223 K has been established by equilibration of samples representing 20 different compositions, and phase identification after quenching by optical and scanning electron microscopy, X-ray powder diffraction, and energy dispersive spectroscopy. Three ternary oxides, Eu4PdO7, Eu2PdO4, and Eu2Pd2O5, were identified. Liquid alloys and the intermetallic compounds EuPd2 and EuPd3 were found to be in equilibrium with EuO. The compound EuPd3 was also found to coexist separately with Eu3O4 and Eu2O3. The oxide phase in equilibrium with EuPd5 and Pd rich solid solution was Eu2O3. Based on the phase relations, four solid state cells were designed to measure the Gibbs energies of formation of the three ternary oxides in the temperature range from 925 to 1350 K. Although three cells are sufficient to obtain the properties of the three compounds, the fourth cell was deployed to crosscheck the data. An advanced version of the solid state cell incorporating a buffer electrode with yttria stabilised zirconia solid electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode was used for high temperature thermodynamic measurements. Equations for the standard Gibbs energy of formation of the interoxide compounds from their component binary oxides Eu2O3 with C type structure and PdO have been established. Based on the thermodynamic information, isothermal chemical potential diagrams and isobaric phase diagrams for the system Eu - Pd - O have been developed.

Insulator-metal transition and magnetoresistance of La0.5Ca0.5MnOy induced by tuning the oxygen content

The oxygen content of La0.5Ca0.5MnOy was tuned by annealing the samples at high temperatures in flowing nitrogen with graphite powder nearby. The reduction of oxygen content has dramatic effect on the electrical transport and magnetic properties. The samples with y=2.983, 2.83, and 2.803 show an insulator-metal transition, and an unusual temperature and magnetic-field dependence of the magnetoresistance. The paramagnetic-ferromagnetic transition also shifts to lower temperatures and the antiferromagnetic transition at lower temperature is suppressed. The results are discussed in terms of the effect of oxygen vacancies on the various properties of La0.5Ca0.5MnOy. (C) 2002 American Institute of Physics.

Dynamic subspace clustering for very large high-dimensional databases

Emerging high-dimensional data mining applications needs to find interesting clusters embeded in arbitrarily aligned subspaces of lower dimensionality. It is difficult to cluster high-dimensional data objects, when they are sparse and skewed. Updations are quite common in dynamic databases and they are usually processed in batch mode. In very large dynamic databases, it is necessary to perform incremental cluster analysis only to the updations. We present a incremental clustering algorithm for subspace clustering in very high dimensions, which handles both insertion and deletions of datapoints to the backend databases.

Effect of spinel second phase on high temperature deformation in alumina

Constant stress compression creep experiments were carried out on high purity alumina composites with spinel contents of 8 and 30%, corresponding to a situation with isolated and interconnected second phases. The creep experiments were conducted over a stress and temperature range of 10 to 150 MPa and 1623 to 1723 K, respectively. Analysis of the experimental data indicated that the variation in spinel content did not have any influence on high temperature deformation in the composite. The spinel phase retards grain growth, and this may enhance superplasticity in alumina-spinel composites.