Free overall in circular channels with flat base: a method of open channel flow measurement

A free overfall at the end of an open channel offers a simple means of measuring flow discharge. In this paper, two methods are presented for the computation of end-depth and discharge of a free overfall from smooth circular channels with flat base. Firstly, applying the momentum equation based on the Boussinesq approximation, the flow upstream of a free overfall is theoretically analyzed to calculate the end-depth-ratio (EDR). This approach eliminates the need of an experimentally determined pressure coefficient. In subcritical flows, the EDR is related to the critical-depth that occurs far upstream. In supercritical flows, the Manning equation is used to express the end-depth as a function of streamwise slope of the channel. Methods to estimate discharge from the end-depth in subcritical and supercritical flows are presented. The upstream flow profiles of a free overfall are computed using the streamline curvature at free surface. Secondly, an alternate method for analyzing free overfall from circular channels with flat base is also presented, where a free overfall in a circular channel with flat base is simulated by the flow over a sharp-crested weir to calculate the EDR. The comparisons of the computed results with the experimental data are satisfactory for subcritical flow and acceptable for supercritical flow.     

Trypanothione overproduction and resistance to antimonials and arsenicals in Leishmania

Leishmania resistant to arsenicals and antimonials extrude arsenite. Previous results of arsenite uptake into plasma membrane-enriched vesicles suggested that the transported species is a thiol adduct of arsenite. In this paper, we demonstrate that promastigotes of arsenite-resistant Leishmania tarentolae have increased levels of intracellular thiols. High-pressure liquid chromatography of the total thiols showed that a single peak of material was elevated almost 40-fold. The major species in this peak was identified by matrix-assisted laser desorption/ionization mass spectrometry as N1,N8-bis-(glutathionyl)spermidine (trypanothione). The trypanothione adduct of arsenite was effectively transported by the As-thiol pump. No difference in pump activity was observed in wild type and mutants. A model for drug resistance is proposed in which Sb(V)/As(V)-containing compounds, including the antileishmanial drug Pentostam, are reduced intracellularly to Sb(III)/As(III), conjugated to trypanothione, and extruded by the As-thiol pump. The rate-limiting step in resistance is proposed to be formation of the metalloid-thiol pump substrates, so that increased synthesis of trypanothione produces resistance. Increased synthesis of the substrate rather than an increase in the number of pump molecules is a novel mechanism for drug resistance.     

A novel esterase from Saccharomyces carlsbergensis, a possible function for the yeast TIP1 gene

An extracellular esterase was isolated from the brewer's yeast, Saccharomyces carlsbergensis. Inhibition by diisopropyl fluorophosphate shows that the enzyme has a serine active site. By mass spectrometry, the molecular weight of the enzyme was 16.9 kDa. The optimal pH for activity was in the range of four to five. Esterase activity was found in beer before pasteurization, and a low level of activity was still present after pasteurization. Caprylic acid, which is present in beer, competitively inhibited the esterase. The substrate preference towards esters of p-nitrophenol indicated that the enzyme prefers esters of fatty acids from four to 16 carbon atoms. The esterase has lipolytical activity; olive oil (C-18:1), which is a classical substrate for lipase, was hydrolysed. N-terminal sequence analysis of the esterase yielded a sequence which was identical to the deduced amino acid sequence of the S. cerevisiae TIP1 gene. The esterase preparation did not appear to contain significant amounts of other proteins than Tip1p, indicating that the TIP1 gene is the structural gene for the esterase.     

Microstructural evolution in Zr3Al-based alloys during various long-time annealing treatments

The Zr₃Al-based intermetallics have been considered as candidate materials for structural components in pressurized heavy water nuclear reactors due to their attractive properties. However, these alloys could not be used for structural application in the reactors because of their poor room-temperature ductility and irradiation-induced amorphization. Our recent studies of ternary addition of niobium in Zr₃Al have shown some promising results. The present article reports the microstructural evolution in these alloys upon long-time annealing treatments. The formation of various phases, temperature regime of their stability, chemical composition, and volume fraction of these phases during prolonged annealing have also been studied. A pseudobinary phase diagram with varying niobium concentration has also been developed. The morphology and distribution of the Zr₃Al phase have been explained on the basis long-range diffusion as the rate-controlling step. This article is based on a presentation made in the symposium entitled “Processing and Properties of Structural Materials,” which occurred during the Fall TMS meeting in Chicago, Illinois, November 9–12, 2003, under the auspices of the Structural Materials Committee.     

Full day simulations of anti-reflection coatings for flat plate silicon photovoltaics

This paper presents an investigation into the use of thin films of silicon oxide and silicon nitride as anti-reflection coatings to minimise the reflection losses of incident solar insolation on silicon photovoltaic cells. The total theoretical reflectance under two insolation cases is investigated. Firstly, with AM 1.5 direct beam radiation at normal incidence, as is usually simulated, and secondly, with the direct beam simulated over a full day. Ensuring that a minimum silicon oxide layer of 20 nm is deposited on the silicon wafer for surface passivation, variations in optimised film thicknesses between both simulations were approximately 4%. The theoretical results also showed a strong correlation to experimental results for the normal incident case. The results demonstrate that surfaces optimised for normally incident radiation are adequate for non-tracking photovoltaic cells under real conditions. The seasonal variations of an optimised surface showed variations in a performance of less than 0.1%. We have also demonstrated that the excellent surface passivation obtained with a thin thermal oxide is maintained after depositing a silicon nitride layer using low-pressure chemical vapour deposition.     

Affine invariant extended cyclic codes over Galois rings

Recently, Blackford and Ray-Chaudhuri used transform domain techniques to permutation groups of cyclic codes over Galois rings. They used the same technique to find a set of necessary and sufficient conditions for extended cyclic codes of length 2/sup m/ over any subring of GR(4,m) to be affine invariant. Here, we use the same technique to find a set of necessary and sufficient conditions for extended cyclic codes of length p/sup m/ over any subring of GR(p/sup e/,m) to be affine invariant, for e=2 with arbitrary p and for p=2 with arbitrary e. These are used to find two new classes of affine invariant Bose-Chaudhuri-Hocquenghem (BCH) and generalized Reed-Muller (GRM) codes over Z/sub 2//sup e/ for arbitrary e and a class of affine invariant BCH codes over Z/sub p//sup 2/ for arbitrary prime p.     

Heat transfer aspects of an elevated linear absorber

This paper describes aspects of the design methodology and heat transfer calculations for an elevated north–south oriented linear absorber. The absorber is part of a direct steam generation solar thermal concentrating system based on the Australian compact linear Fresnel reflector (CLFR) concept. The basic absorber design is an inverted air cavity with a glass cover enclosing a selective surface. This arrangement has been shown previously to offer good optical and thermal performance from measurements on a 4 kW_thermal outdoor test apparatus. Two main design aims are discussed here: Firstly to maximise the heat transfer between the absorbing surface and the steam pipes, and secondly, to ensure that the absorber surface temperature is sufficiently uniform so as not to cause thermal degradation of the selective surface. Results are given of the absorber temperature distribution obtained from finite element analysis. Sufficiently low temperature differences between the fluid surface and the absorbing surface (<20 K) can be achieved with satisfactory pipe separations and sizes, and with practical absorber plate thicknesses.     

Mechanism of instability of Falkner-Skan flows

Summary. It is shown that the mechanism of linear instability of boundary-layer flows driven by favorable and adverse pressure gradients can be understood as a kinematic resonant interaction between inviscid and viscous partial modes. This kind of interaction has been proposed by Baines, Majumdar and Mitsudera [4] for the Blasius boundary layer. Here, this proposal has been examined for more general flows and quantitative confirmation has been obtained. Piecewise linear approximations of Falkner-Skan velocity profiles are taken as the mean flows. To understand the mechanism, it proves sufficient to examine eigensolutions of the viscous part obtained by enforcing no-slip. This leads to the prediction of the parameters for maximum growth in the space of Reynolds number and wave number. In the case of adverse pressure gradient the inviscid flow itself is unstable due to the presence of an inflexion point. We show that the instability mechanism stated above has a role in the flows of this kind, too.     

Vacuum glazing—A new component for insulating windows

The substantial progress in the science and technology of vacuum glazing that has occurred over the past few years is reviewed. Vacuum glazing up to 1 m × 1 m in size has been produced with an air-to-air, mid-device thermal conductance as low as 0.90 W m⁻² K⁻¹, compared with 1.3 W m⁻² K⁻¹ for high performance double glazing. The mechanical tensile stresses in vacuum glazing due to pressure and temperature differentials are well understood, and appear to be tolerably small. The internal vacuum is high, and extremely stable over long times at moderate temperatures. The likely cost of volume production of vacuum glazing should be only slightly greater than for high performance double glazing.     

Precipitation hardening in 350 grade maraging steel

Evolution of microstructure in a 350 grade commercial maraging steel has been examined. In the earlier stages of aging, the strengthening phases are formed by the heterogeneous precipitation, and these phases have been identified as intermetallic compounds of the Ni₃ (Ti, Mo) and Fe₂Mo types. The kinetics of precipitation are studied in terms of the activation energy by carrying out isothermal hardness measurements of aged material. The mechanical properties in the peak-aged and overaged conditions were evaluated and the flow behavior examined. The overaging behavior of the steel has been studied and the formation of austenite of different morphologies identified. The crystallography of the austenite has been examined in detail. From the microstructural examination of peak-aged and deformed samples, it could be inferred that the dislocation-precipitate interaction is by precipitate shearing. Increased work hardening of the material in the overaged condition was suggestive of looping of precipitates by dislocations.