EQCM Investigation of the Electrodeposition of MnO2 and Its Capacitance Behavior

Electro-oxidation of Mn2+ to MnO2 by cyclic voltammetry on gold in acidic (0.1 M H2SO4) and neutral (0.1 M Na2SO4) media was studied using electrochemical quartz-crystal microbalance (EQCM). The cyclic voltammetric behavior of Au is different in these electrolytes. From EQCM data of mass variation during cycling, the rate of electrodeposition of MnO2 is higher in the neutral medium than in the acidic medium. Specific capacitance of MnO2 deposited from the neutral medium is higher than that deposited from the acidic medium owing to different crystallographic structures.

Behavior Of High-Voltage Machine Insulation System In The Presence Of Thermal And Electrical Stresses

This paper presents the results on a resin-rich machine insulation system subjected to varying stresses such as electrical (2.6 to 13.3 MV/m) and thermal (40 to 155° C) acting together. Accelerated electro-thermal aging experiments subsequently have been performed to understand the insulation degradation The interpretations are based on several measured properties like capacitance, loss tangent, ac resistance, leakage current, and partial discharge quantities. The results indicate that the changes in properties are not significant below a certain temperature for any applied stress, Beyond this temperature large variations are observed even for low electrical stresses. Electrothermal aging studies reveal that the acceleration of the insulation degradation and the ultimate time to failure depends on the relative values of temperature and voltage stresses. At lower temperatures, below critical, material characteristics of the system predominate whereas beyond this temperature, other phenomena come into play causing insulation deterioration. During aging under combined stresses, it appears that the prevailing temperature of the system has a significant role in the insulation degradation and ultimate failure.

Fracture Behavior of Ferrocement Beams

An attempt is made to study the fracture behavior of ferrocement beams using J-integral and critical crack opening displacement approaches. Ferrocement beams with three different relative notch depths and different percentages of mesh reinforcement were tested in four-point bending (third-point loading). The experimental results were used to evaluate the apparent J-integral and CODc values. Results show that the apparent J-integral does not seem to follow any particular trend in variation with notch depth, but is sensitive to the increase of mesh reinforcement. Hence, the apparent J-integral appears to be a useful fracture criterion for ferrocement. The computed values of CODt are found to be dependent on the depth of notch and, thus, cannot possibly be considered as a suitable fracture criterion for ferrocement.

A composition dependent thermal behavior of GexSe35-xTe65 glasses

Alternating differential scanning calorimetric (ADSC) studies have been performed to understand the thermal behavior of bulk GexSe35-xTe65 glasses (17 <= x <= 25); it is found that the glasses with x <= 20 exhibit two crystallization exotherms (T-c1 & T-c2). On the other hand, those with x >= 20.5, show a single crystallization reaction upon heating. The exothermic reaction at T-c1 has been found to correspond to the partial crystallization of the glass into hexagonal Te and the reaction at T-c2 is associated with the additional crystallization of rhombohedral Ge-Te phase. The glass transition temperature of GexSe35-xTe65 glasses is found to show a linear but not-steep increase, indicating a progressive, but a gradual increase in network connectivity with Ge addition. It is also found that T-c1 of GexSe35-xTe65 glasses with x <= 20, increases progressively with Ge content and eventually merges with T-c2 at x approximate to 20.5 (< r > = 2.41); this behavior has been understood on the basis of the reduction in Te-Te bonds of lower energy and increase in Ge-Te bonds of higher energy, with increasing Ge content. Apart from the interesting composition dependent crystallization, an anomalous melting behavior is also exhibited by the GexSe35-xTe65 glasses.

Differences in the Behavior of Luteinizing Hormones of Various Species at the Rat Gonadal Cell Receptor Site

The ability of different LH-like hormones, such as hCG, PMSG/equine (e) CG, ovine (o) LH, eLH, and rat (r) LH, to bind to and stimulate steroidogenesis in two types of rat gonadal cells was studied under the same experimental conditions. In both Leydig and granulosa cells, the maximal steroidogenic responses elicited by optimal doses of different LHs present during a 2-h incubation were comparable. However, if the cells were exposed to the different LHs for a brief period and then subjected to interference with hormone action by removing the unbound hormone from the medium by washing or adding specific antisera, differences were observed in the amount of steroid produced during subsequent incubation in hormone-free medium. Thus, in the case of hCG, either of these procedures carried out at 15 or 30 min of incubation had little inhibitory effect on the amount of steroid produced at 2 h, the latter being similar to that produced by cells incubated in the continued presence of hCG for 2 h. With eCG and rLH, the effect was dramatic, in that there was a total inhibition of subsequent steroidogenic response. In cells exposed to eLH and oLH, inhibition of subsequent steroidogenesis due to either removal of the free-hormone or addition of specific antisera at 15 or 30 min was only partial. Although all of the antisera used were equally effective in inhibiting the steroidogenic response to respective gonadotropins when added along with hormones at the beginning of incubation, differences were observed in the degree of inhibition of this response when the same antisera were added at later times of incubation. Thus, when antisera were added 60 min after the hormone, the inhibition of steroidogenesis was total (100%) for eCG, partial (10–40%) for eLH and oLH, and totally lacking in cells treated with hCG. From this, it appears that hCG bound to the receptor probably becomes unavailable for binding to its antibody with time, while in the case of eCG and other LHs used, the antibody can still inhibit the biological activity of the hormone. Studies with 125I-labeled hormones further supported the conclusion that hCG differs from all other LHs in being most tightly bound and, hence, least dissociable, while eCG and rLH dissociate most readily; oLH and eLH can be placed in between these hormones in the extent of their dissociability. (Endocrinology 116: 597–603,1985)

Stochastic Modeling of an Aircraft Traversing a Runway Using Time Series Analysis

Time series, from a narrow point of view, is a sequence of observations on a stochastic process made at discrete and equally spaced time intervals. Its future behavior can be predicted by identifying, fitting, and confirming a mathematical model. In this paper, time series analysis is applied to problems concerning runwayinduced vibrations of an aircraft. A simple mathematical model based on this technique is fitted to obtain the impulse response coefficients of an aircraft system considered as a whole for a particular type of operation. Using this model, the output which is the aircraft response can be obtained with lesser computation time for any runway profile as the input.

Influence of heat-treatment on the strength and fracture-behavior of fe-12cr-6al ferritic stainless-steel

The changes in the tensile properties and fracture mode brought about by heat treatment of Fe-12Cr-6Al ferritic stainless steel have been studied. A favourable combination of high strength and good ductility is obtained by heating the material at 1370 K for 2 h followed by a water quench. The high-temperature treatment results in carbide dissolution as well as an increase in the grain size. The mechanism of strengthening has been evaluated from the apparent activation energy (28 kJ mol–1) and is identified to be the unpinning of dislocations from the atmosphere of carbon atoms. As the heat-treatment temperature is increased, the fracture behaviour changes from ductile to brittle mode and this is related to the changes in grain size and friction stress.

Behavior of the indian social wasp ropalidia-cyathiformis on a nest of separate combs (hymenoptera, vespidae)

Observations were made on a nest of Ropalidia cyathiformis consisting of three combs. The number of eggs, larvae, pupae and adults were monitored at about 3-day intervals for a 2-month period. The behaviour of the adults was observed with special reference to the proportion of time spent on each of the three combs, the proportion of time spent away from the nest site and the frequencies of dominance interactions and egg laying. The adults moved freely between the three combs suggesting that all of them and all the three combs belonged to one nest. However, most of the adults preferred combs 2 and 3 over comb 1. Of the 10 animals chosen for a detailed analysis of behaviour, seven spent varying periods of time away from the nest site and oRen brought back food or building material. Five of the 10 animals laid at least one egg each but two adults monopolized most of the egg-laying. The animals showed a variety of dominance interactions on the basis of which they have been arranged in a dominance hierarchy. The dominant individuals laid most of the eggs and spent little or no time foraging, while the subordinate individuals spent more time foraging and laid few eggs or none. It is argued that R. cyathiformis is different from R. marginata, the only other Indian social wasp whose behaviour has been studied, in being at a more primitive stage of social organization.

Stochastic kinetics of ribosomes: Single motor properties and collective behavior

Syntheses of protein molecules in a cell are carried out by ribosomes.A ribosome can be regarded as a molecular motor which utilizes the input chemical energy to move on a messenger RNA (mRNA) track that also serves as a template for the polymerization of the corresponding protein. The forward movement, however, is characterized by an alternating sequence of translocation and pause. Using a quantitative model, which captures the mechanochemical cycle of an individual ribosome, we derive an exact analytical expression for the distribution of its dwell times at the successive positions on the mRNA track. Inverse of the average dwell time satisfies a Michaelis-Menten-type'' equation and is consistent with the general formula for the average velocity of a molecular motor with an unbranched mechanochemical cycle. Extending this formula appropriately, we also derive the exact force-velocity relation for a ribosome. Often many ribosomes each synthesizes a copy of the same protein. We extend the model of a single ribosome by incorporating steric exclusion of different individuals on the same track. We draw the phase diagram of this model of ribosome traffic in three-dimensional spaces spanned by experimentally controllable parameters. We suggest new experimental tests of our theoretical predictions.

Observation of reentrant spin glass behavior in LaCo0.5Ni0.5O3

The magnetic and transport properties of LaCo0.5Ni0.5O3 have been studied. The dc magnetization and the ac susceptibility studies suggest the presence of a magnetic-phase transition from a ferromagnetic (FM) to a spin glass phase at a low temperature. This type of reentrant spin-glass (RSG) behavior attached to a long-range ordered ferromagnet is observed in this system. A magnetoresistance of ~10% is observed at 5 K which is unsaturated up to 11 Tesla suggests the presence of antiferromagnetic (AFM) interactions. It is likely that the competition between such AFM interactions with FM interactions yield an RSG phase.

Improving Flow-Insensitive Solutions for Non-Separable Dataflow Problems

Flow-insensitive solutions to dataflow problems have been known to be highly scalable; however also hugely imprecise. For non-separable dataflow problems this solution is further degraded due to spurious facts generated as a result of dependence among the dataflow facts. We propose an improvement to the standard flow-insensitive analysis by creating a generalized version of the dominator relation that reduces the number of spurious facts generated. In addition, the solution obtained contains extra information to facilitate the extraction of a better solution at any program point, very close to the flow-sensitive solution. To improve the solution further, we propose the use of an intra-block variable renaming scheme. We illustrate these concepts using two classic non-separable dataflow problems --- points-to analysis and constant propagation.

Photoelastic studies on progress of separation in interference fits

Interference fits are used extensively in aircraft structural joints because of their improved fatigue performance. Recent advances in analysis of these joints have increased understanding of the nonlinear load-contact and load-interfacial slip variations in these joints. Experimental work in these problems is lacking due to difficulties in determining partial contact and partial slip along the pin-hole interface. In this paper, an experimental procedure is enumerated for determining load-contact relations in interference/clearance fits, using photoelastic models and applying a technique for detecting progress of separation/contact up to predetermined locations. The study incorporates a detailed procedure for model making, controlling interference, locating break of contact up to known locations around the interface, estimating optically the degree of interference, determining interfacial friction and evaluating stresses in the sheet. Experiments, simulating joints in large sheets, were carried out under both pin and plate loads. The present studies provide load-separation behavior in interference joint with finite interfacial friction.

Application of partition method to vibration problems of plates

The “partition method” or “sub-domain method” consists of expressing the solution of a governing differential equation, partial or ordinary, in terms of functions which satisfy the boundary conditions and setting to zero the error in the differential equation integrated over each of the sub-domains into which the given domain is partitioned. In this paper, the use of this method in eigenvalue problems with particular reference to vibration of plates is investigated. The deflection of the plate is expressed in terms of polynomials satisfying the boundary conditions completely. Setting the integrated error in each of the subdomains to zero results in a set of simultaneous, linear, homogeneous, algebraic equations in the undetermined coefficients of the deflection series. The algebraic eigenvalue problem is then solved for eigenvalues and eigenvectors. Convergence is examined in a few typical cases and is found to be satisfactory. The results obtained are compared with existing results based on other methods and are found to be in very good agreement.

On quasi-degeneracies in plate vibration problems

In plotting the variation of frequencies with geometric parameters such as side ratio, skew angle, thickness taper, etc. in detailed studies of the vibration characteristics of plates, situations are encountered such as crossing of the frequency curves or the tendency of these curves to come close together and veer away from each other. These have been generally referred to as “frequency crossings” and “transitions” respectively. The latter may preferably be referred to as “quasi-degeneracies”. In the literature there appears to be some ambiguity in the analysis and interpretation of these features. In this paper, a clarification of some of these questions as regards rectangular and skew plates is presented by making use of concepts from physics dealing with molecular vibrations.

A Method of Characteristics for Solving Two-dimensional Unsteady Flow Problems

The aim of this investigation is to evolve a method of solving two-dimensional unsteady flow problems by the method of characteristics. This involves the reduction of the given system of equations to an equivalent system where only interior derivatives occur on a characteristic surface. From this system, four special bicharacteristic directional derivatives are chosen. A finite difference scheme is prescribed for solving the equations. General rectangular lattices are also considered. As an example, we investigate the propagation of an initial pressure distribution in a medium at rest.