An investigation of the ordered DO19 phase formation in the Ti-Al system

For the Ti-rich, Ti-AI system, the- and- ₂ phase boundaries have been obtained through differential thermal analysis for alloy compositions ranging from 10.2 to 25.2 at% Al (6 to 16 wt% Al). It has been shown that in the above mentioned composition range, a metastable disordered-phase can be quenched in. This metastable then transforms to the ordered ₂(DO)₁₉ phase upon heating and/or isothermal ageing. It has also been observed that the kinetics of this ordering phenomenon is composition dependent.     

The inhibitive effect of extraneous ion addition on stress corrosion cracking of alpha-brass

The addition of ammonium chloride, cobalt sulphate, cesium sulphate and ethylene diamine to a Mattsson solution and the addition of ammonium sulphate to the Pugh solution have been found to produce an inhibitive effect on the stress corrosion cracking of alpha-brass in these solutions. Ammonium chloride and ammonium sulphate additions affect the tarnish formation on the specimen as well as the cracking pattern. Electrochemical polarization studies have also been carried out with these two additives. The observations have been explained in the light of adsorption of these ionic species at selected sites on the metal surface and their possible interference with the cathodic reactions.     

Electrothermal study of carbon loaded ethylene-vinylacetate copolymer

Temperature dependence of resistance of carbon black loaded ethylene-vinylacetate (EVA) copolymer was studied from ?100 to 250°C in a modified differential scanning calorimeter (DSC) apparatus. Both room temperature resistivity and positive temperature coefficient of resistance (PTC) effects can be correlated with carbon black parameters (structure, surface area, porosity). Room temperature resistivity and the degree of increase of resistivity, (ratio of maximum to minimum) progressively decrease with carbon black structure if occlusion of polymer by carbon black is considered in calculating the volume fraction. An integrated surface areastructure-porosity equivalence of the carbon black is derived by introducing factors proportional to the volume and porosity of the black used. Any black parameter that increases conductivity (loading, surface area, structure, porosity) decreases the PTC effect. A cable compounder can therefore minimize the undesirable impact of PTC by suitable choice of black-parameters. The necessary considerations for other uses, where PTC effect is used for microswitches, heaters, etc., will be just the opposite. The modified DSC method provides a quick scanning tool for determining the suitability of semicrystalline polymer recipes, either for cable or for any other material using the PTC effect.     

Time delays and angles of arrival estimation using known signals

Channel estimation in a multipath mobile communication system is addressed in this paper, and a novel approach based on the linear prediction in frequency domain and the singular value decomposition technique is presented for joint estimation of the angles of arrival and the time delays of multiple reflections of a known signal. Simulation results illustrating the performance of the proposed algorithm are included, and the results show that the proposed method is close in accuracy when compared to the iterative maximum-likelihood method. However, when the two methods are compared in computational complexity, it is demonstrated that the proposed method reduces the complexity to nearly half of that of the maximum-likelihood method. The Cramer–Rao bounds are computed for comparison.     

Influence of zeolite on electrochemical and physicochemical properties of polyethylene oxide solid electrolyte

A composite polymer electrolyte of polyethyleneoxide-LiBF₄ containing fine particles of zeolite was studied using electrochemical impedance spectroscopy, cyclic voltammetry, differential scanning calorimetry, infrared spectroscopy and scanning electron microscopy. When compared with the polymer electrolyte without zeolite, the specific conductivity of the composite electrolyte film is higher by about two orders of magnitude at room temperature. The increase in specific conductivity is explained as due to increased amorphocity which is reflected in the thermal studies. The nature of the cyclic voltammograms and infrared spectra is discussed.Part of this work was presented at the Electrochemical Society Meeting, Honolulu, Hawai (May 1993).     

On the measurement of sorption kinetics by differential test: Effect of the heat of sorption

It is shown by a simplified theoretical analysis of the heat dissipation from the adsorbent particles during the measurement of sorption kinetics that even a small change in the adsorbent temperature can cause significant error in the calculation of the sorption diffusivity by the assumption of isothermal behavior. Thus, the use of a differential step change in the adsorbate loading during the kinetic measurements, which produces a small change in the adsorbent temperature, may not assure correct interpretation of the data by the isothermal models.     

Estimation of hole conductivity of AgI through tarnishing studies of silver in iodine vapour at about room temperature

This work reports the hole conductivity data of growing AgI film on silver both for the thicker (5500 to 30 000 Å) and thinner (<6000 Å) ranges at about room temperature. Hole conductivity has been estimated through tarnishing studies of silver in iodine atmosphere and estimation has been based on the fundamental equation of Wagner relating the rate constant and the conductivity of the film. It is revealed that the thinner films show a higher hole conductivity than that of the thicker films under similar temperature and iodine pressure.     

Evaluation of the suitability of data base management systems: a case study at the US Forest Service

A methodology for assessing the feasibility of a data base management system is described, and its use demonstrated in a specific situation: the U.S. Forest service. A series of questions to be answered at the test organization is formulated, aimed at quantifying the benefits of a DBMS. Results of attempting to answer these questions at two test sites are provided. Implications of these results are given for both forest and higher level management.