Optimisation of different physical parameters for bioleaching of phosphate by Aspergillus niger from Indian rock phosphate

A mutant strain of Aspergillus niger AB100 was incubated with samples of rock phosphate. Mutation resulted in a greater amount of solubilisation (30 to 35%) as against the parent strain (10 to 15%). The influence of leaching parameters such as ore concentration (pulp density), particle size, initial pH of the medium, temperature, volume of the medium in 250 ml flasks, inoculum concentration and age of inoculum was studied. When low quantity of rock phosphate is applied (0.1%) the solubilisation of phosphorus was optimal (40.5%). Optimum particle size was--200 to 240 mesh, initial pH of the medium 4.0, optimum volume of the fermentation medium 160 ml, time period of incubation was 8 days, inoculum volume was 7.5 ml, and age of inoculum 7 days. The maximum leaching of phosphorus by using these optimum physical parameters is 45 to 50%.     

Neutron diffraction structural study of 1201 superconductor (Hg0.7Cr0.3)Sr2CuOδ

Rietveld analysis of powder neutron diffraction pattern recorded on Sr-based 1201-phase superconductor (T _c =53 K), (Hg_0.7Cr_0.3)Sr₂CuO_4+δ shows that the oxygen atoms at O(3) site are disordered atx=y=0.3712. This fourfold split site has a total combined occupancy of ～80% and is the only occupied site in the (Hg, Cr)O plane.     

The island posterior calf fasciocutaneous flap: an alternative to the gastrocnemius muscle for cover of knee and tibial defects

By repeatedly presenting an alien scent to territory-owning beavers, Castor canadensis, we tested two competing hypotheses about the function of scent marking: scent fence and scent matching. The scent-fence hypothesis predicts that territory owners should respond increasingly strongly over time towards a recurrent alien scent because of the ineffectiveness of previous responses. The scent-matching hypothesis predicts that the intensity of response should be the same or decrease because, without the presence of the intruding signaller coupled with the chemical signal, the presence of the scent itself does not advertise the ownership of a territory. The response level of resident beaver families was stable to strangers' anal gland secretions (AGSs) and decreased to strangers' castoreum during a period of 6 days. These results support the scent-matching hypothesis but not the scent-fence hypothesis. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.     

Structure and mechanism of action and inhibition of steroid dehydrogenase enzymes involved in hypertension

Members of the NADPH-dependent short chain dehydrogenase/reductase (SDR) family control blood pressure, fertility, and natural and neoplastic growth. Despite the fact that only one amino acid residue is strictly conserved in the 100 known members of the family, all appear to have a dinucleotide-binding Rossmann fold and homologous catalytic residues including the conserved tyrosine. Variation in the binding pocket creates specificity for steroids, prostaglandins, sugars and alcohols. The critically important tyrosine appears to maintain a fixed position relative to the scaffolding of the Rossmann fold and the cofactor position, while the substrate-binding pocket alters in such a way that the dehydrogenation/reduction reaction site is brought into bonding distance of the tyrosine hydroxyl group. Licorice induces high blood pressure by inhibiting an SDR in the kidney. The crystal structure of the complex of 3alpha,20beta-hydroxysteroid dehydrogenase and carbenoxolone reveals the mechanism of enzyme inhibition by licorice. The most potent dehydrogenase enzyme inhibitors are those that displace substrate and cofactor and form strong hydrogen bonds to one or more amino acid residues involved in catalysis.     

Influences of material parameters and microstructure on superplastic forming

The strain rate sensitivity of flow stress has long been recognized as an important factor in determining superplastic ductility, and its relationship to high tensile elongations is well understood from the mechanics point of view. However, the measurements of this parameter and other properties of superplastic materials are challenging, and quite varied results are observed from different test procedures used. In this paper a discussion of the various characterization methods is presented, and the relationship between the superplastic characteristics and the microstructure is brought forth. The applicability of the uniaxial superplastic properties on the biaxial deformation behavior as in the superplastic forming process is addressed, including a relationship of such properties to the selection of forming parameters. This paper is based on a presentation made at the symposium “On the Mechanical, Microstructural and Fracture Processes in Superplasticity” held at the annual meeting of the AIME in Pittsburgh, PA on October 7, 1980 under the sponsorship of the Flow and Fracture Activity of the Materials Science Division of ASM.     

Development of forming limits for superplastic formed fine grain 7475 AI

Forming limits in conventional sheet metal forming are given by strain levels obtainable prior to the onset of a localized neck or tear in the sheet. While the external appearance of such a neck is not observed in superplastic metals until strains become quite large, the formation of internal cavities could dictate the tolerable levels of strain in formed components. In this paper, these useful strain limits for a superplastic 7475 Al alloy have been explored. The approach used was to establish the influence of strain state (uniaxial, plane strain, and balanced biaxial) on the inception and growth characteristics of cavities and to correlate the extent of cavitation with material properties. Based on these data, it was then possible to establish strain states for which little or no loss in properties was observed, and thereby to define forming limits for superplastic forming this material. These results, coupled with comparisons against strains developed in actual parts as well as analytically predicted strains, show that a wide range of structural parts can be superplastically formed within the constraints of the recommended forming limits.     

Studies on glass-reinforced epoxy resin using either Vulkadur A or a mixture of Vulkadur A and triethanolamine as crosslinking agent

Epoxy resin can be reinforced with glass (fabric form) using Vulkadur A (a phenol formaldehyde resin containing an hardening agent) as a crosslinking agent. Overall enhancement in mechanical properties has been observed with stocks cured with a mixture of Vulkadur A and triethanolamine.     

Strain hardening and instability in biaxially streched sheets

This work is concerned with the origins of the two different patterns of failure limits in biaxially stretched sheets which were recently described in Ref. 1: the brass-type in which the limit strain is insensitive to strain state, and that of ferritic steel in which the limit strain increases as the imposed strain-ratio, ρ = ε₂/ε₁, changes from zero (plane-strain tension) toward unity (balanced biaxial tension). An earlier proposal that different slip modes,i.e. wavy in ferrite vs planar in brass, might have contributed to these failurelimit differences was found not to be valid. There were two parts to the main experimental program: the prestraining of small sheets by proportional loading on different paths betweenρ = 0 andρ = 1, followed by tension testing, and a more direct measurement of strain hardening and instability between ρ ≅ — 1/2 (uniaxial tension) andρ = 0. The principal finding was that the overall hardening rate, essentially as it appeared in the material’s effective stress-strain curve, changed with the loading path. Inα brass it decayed as p was increased from ∼—1/2 to 1; in ferritic steel it increased; and in aluminum it was affected very little. Such changes in hardening rate cause similar changes in the material’s capacity for stable flow. The stable flow, in turn, is the base to which a quasistable-flow increment (whenρ is >0) is added in reaching the observed failure limit. Thus a base ofρ-dependent height can account for the failure-limit patterns. There is still no explanation for the ρ dependence of the hardening rate. AMIT K. GHOSH, formerly Graduate Student, Massachusetts Institute of Technology, Cambridge, Mass. 02139, This paper is based upon a thesis submitted by AMIT K. GHOSH in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology.