On the development of a three-dimensional transient thermal model to predict ingot cooling behavior during the start-up phase of the direct chill-casting process for an AA5182 aluminum alloy ingot

The control of the heat transfer during the start-up phase of the direct-chill (DC) casting process for aluminum sheet ingots is critical from the standpoint of defect formation. Process control is difficult because of the various inter-related phenomena occurring during the cast start-up. First, the transport of heat to the mold is altered as the ingot base deforms and the sides are pulled inward during the start-up phase. Second, the range of temperatures and water flow conditions occurring on the ingot surface as it emerges from the mold results in the full range of boiling-water heat-transfer conditions—e.g., film boiling, transition boiling, nucleate boiling, and convection—making the rate of transport highly variable. For example, points on the ingot surface below the point of water impingement can experience film boiling, resulting in the water being ejected from the surface, causing a dramatic decrease in heat transfer below the point of ejection. Finally, the water flowing down the ingot sides may enter the gap formed between the ingot base and the bottom block due to butt curl. This process alters the heat transfer from the base of the ingot and, in turn, affects the surface temperature on the ingot faces, due to the transport of heat within the ingot in the vertical direction. A comprehensive mathematical model has been developed to describe heat transfer during the start-up phase of the DC casting process. The model, based on the commercial finite-element package ABAQUS, includes primary cooling via the mold, secondary cooling via the chill water, and ingot-base cooling. The algorithm used to account for secondary cooling to the water includes boiling curves that are a function of ingot-surface temperature, water flow rate, impingement-point temperature, and position relative to the point of water impingement. In addition, a secondary cooling algorithm accounts for water ejection, which can occur at low water flow rates (low heat-extraction rates). The algorithm used to describe ingot-base cooling includes both the drop in contact heat transfer due to gap formation between the ingot base and bottom block (arising from butt curl) as well as the increase in heat transfer due to water incursion within the gap. The model has been validated against temperature measurements obtained from two 711×1680 mm AA5182 ingots, cast under different start-up conditions (nontypical “cold” practice and nontypical “hot” practice). Temperature measurements were taken at various locations on the ingot rolling and narrow faces, ingot base, and top surface of the bottom block. Ingot-based deflection data were also obtained for the two test conditions. Comparison of the model predictions with the data collected from the cast/embedded thermocouples indicates that the model accounts for the processes of water ejection and water incursion and is capable of describing the flow of heat in the early stages of the casting process satisfactorily.     

Comparison of key informant and survey methods for ascertainment of childhood epilepsy in West Bengal, India

BACKGROUND: This study aimed to compare efficacy and cost of key informants and survey for ascertainment of childhood epilepsy within a treatment context in rural India. METHODS: The study was set in a non-governmental, community programme for the functional and socioeconomic rehabilitation of children with disabilities in rural West Bengal, India. Ascertainment was by two methods: house-to-house survey of 15000 households and also by 430 key informants including village leaders, health workers and 670 schoolchildren. Methods were compared for positive predictive value, and sensitivity by capture-recapture technique. Ninety four children were enrolled into treatment. Predictors of treatment success were determined by multiple logistic regression analysis, giving adjusted odds ratios for remission. The costs of identifying one case and one treatment success were measured by costing personnel, materials and overheads. RESULTS: The survey was four times as sensitive as key informants although the positive predictive values were similar (36%, 40%). The survey had an absolute sensitivity of only 59%. Identification by key informants strongly predicted successful treatment outcome (odds ratio [OR] = 4.74, 95% confidence interval [CI] : 1.19-18.85). The cost of finding one case was US$11 and US$14, and of finding one successful treatment outcome US$35 and US$67 for informants and survey respectively. Key informants were essential in attaining longer term programme objectives. CONCLUSIONS: In the context of a treatment programme, key informants were the more cost-effective method, but community involvement was traded against low sensitivity in the short term. Overall ascertainment costs were significant in the context of primary health care in India.     

Reliability bounds and other inequalities for discrete life distributions

In this paper we give sharp bounds on the reliability of discrete IFR, IFRA, NBU, DFR, DFRA and NWU classes, based on one known moment. Subsequently the discrete analogues of several continuous-time results related to maintained systems are also presented.     

Exact piezothermoelastic axisymmetric solution of a finite transversely isotropic cylindrical shell

This work presents an exact piezothermoelastic solution of a finite transversely isotropic piezoelectric cylindrical shell under axisymmetric thermal, pressure and electrostatic excitation. The general solution of the governing equations is obtained in terms of potential functions which satisfy the boundary conditions at the ends. The axisymmetric loadings are expanded as a Fourier series in the axial coordinate. The coefficients in the infinite set of potential functions are obtained by solving sets of six algebraic equations resulting from the satisfaction of boundary conditions at the inner and outer surfaces of the shell for each Fourier component. The inverse problem of inferring the applied temperature and pressure fields from the given measured distribution of electrical potential difference between the inner and outer surfaces of the shell has also been solved. Numerical results are presented for typical pressure, thermal and electrostatic loadings.     

Magneto-thermo-visco-elastic waves in an initially stressed conducting layer

The aim of this paper is to investigate magneto-thermo-viscoelastic surface waves in electrically and thermally conducting layers involving time rates of strain and stress of ordern, the media being under an initial stress in the nature of hydrostatic tension or compression. The theory of magneto-thermo-visco-elastic surface waves in the conducting medium involving strain rate and stress rate ofnth order is derived under initial stress. This theory is then employed to obtain wave velocity equations in specific cases. Results obtained in the above cases reduce to well-known classical results when additional fields are absent.     

Delay analysis of a packet voice multiplexer by the ΣDi/D/1 queue

The performance of a statistical multiplexer whose inputs consist of a superposition of voice packet streams is studied. The delay for such a system is analyzed by solving the ΣD_i/ D/1 queue. The analytic method can be used to find the approximate mean delay for an arbitrarily large number of trunks and the approximate delay distribution when the number of trunks is less than 100. An efficient hybrid simulation of the packet voice multiplexer which can be used to find the delay distribution for a large number of trunks is presented. In addition, easily computable error bounds for the present approximation are provided, and the accuracy of the M/ D/1 approximation is investigated     

Activity measurements in aqueous mixed electrolyte solutions—III. HClCaCl2 mixtures of constant total ionic strength

Emf measurements have been made in cells without liquid junction of the type H₂/HX (m₁), MX_n(m₂)/AgCl, Ag . . (I) containing mixtures of HCl and CaCl₂ in different proportions, but at constant total ionic strength (I = 2, 1, 0.5). The measurements have been carried out at 5°C intervals over the temperature range 5–35°C. AgAgCl electrodes prepared by two different methods (thermal and thermoelectrolytic) were used of which the thermoelectrolytic electrodes were found to give more consistent results. The results when extrapolated properly lead to E° values at the different temperatures which agree well with those reported in literature. The application of the Pitzer method leads to the calculation of the ionic interaction coefficients α₁₂ and α₂₁, at the different constant ionic strengths. The nature of variation of these α's with the total mixture ionic strength at different temperatures has been considered.     

Triglyceride composition of tea seed oil

Fatty acid and triglyceride compositions of the seed oil of Thea sinensis (tea seed oil) of Indian origin have been determined by combination of techniques of low temperature crystallisation, spectrophotometry, pancreatic lipase hydrolysis, thin-layer chromatography, gas–liquid chromatography and densitometry. Percentages of individual fatty acids were found to be: palmitic, 17.8; stearic, 3.0; oleic, 59.9; linoleic, 18.0. Triglyceride composition was calculated from the fatty acid compositions of the native oil and of the monoglycerides produced from it by pancreatic lipase hydrolysis. The oil is composed of 0.7, 11.1, 41.9 and 46.3% GS₃, GS₂U, GSU₂ and GU₃ respectively. Prominent features of the oil is its content of 11.6, 21.4 and 22.0% dioleolinolein, triolein and dioleopalmitin respectively.