Graphene Analogues of BN: Novel Synthesis and Properties

Enthused by the fascinating properties of graphene, we have prepared graphene analogues of BN by a chemical method with a control on the number of layers. The method involves the reaction of boric acid with urea, wherein the relative proportions of the two have been varied over a wide range. Synthesis with a high proportion of urea yields a product with a majority of 1-4 layers. The surface area of BN increases progressively with the decreasing number of layers, and the high surface area BN exhibits high CO, adsorption, but negligible H, adsorption. Few-layer BN has been solubilized by interaction with Lewis bases. We have used first-principles simulations to determine structure, phonon dispersion, and elastic properties of BN with planar honeycomb lattice-based n-layer forms. We find that the mechanical stability of BN with respect to out-of-plane deformation is quite different from that of graphene, as evident in the dispersion of their flexural modes. BN is softer than graphene and exhibits signatures of long-range ionic interactions in its optical phonons. Finally, structures with different stacking sequences of BN have comparable energies, suggesting relative abundance of slip faults, stacking faults, and structural inhomogeneities in multilayer BN.

Micro-treatment options for components of organic fraction of MSW in residential areas

There is a growing interest in management of MSW through micro-treatment of organic fraction of municipal solid wastes (OFMSW) in many cities of India. The OFMSW fraction is high (> 80%) in many pockets within South Indian cities like Bangalore, Chikkamagalur, etc. and is largely represented by vegetable, fruit, packing and garden wastes. Among these, the last three have shown problems for easy decomposition. Fruit wastes are characterized by a large pectin supported fraction that decomposes quickly to organic acids (becomes pulpy) that eventually slow down anaerobic and aerobic decomposition processes. Paper fraction (newsprint and photocopying paper) as well as paddy straw (packing), bagasse (from cane juice stalls) and tree leaf litter (typical garden waste and street sweepings) are found in reasonably large proportions in MSW. These decompose slowly due to poor nutrients or physical state. We have examined the suitability of these substrates for micro-composting in plastic bins by tracking decomposition pattern and physical changes. It was found that fruit wastes decompose rapidly to produce organic acids and large leachate fraction such that it may need to be mixed with leachate absorbing materials (dry wastes) for good composting. Leaf litter, paddy straw and bagasse decompose to the tune of 90, 68 and 60% VS and are suitable for composting micro-treatment. Paper fractions even when augmented with 10% leaf compost failed to show appreciable decomposition in 50 days. All these feedstocks were found to have good biological methane potential (BMP) and showed promise for conversion to biogas under a mixed feed operation. Suitability of this approach was verified by operating a plug-flow type anaerobic digester where only leaf litter gathered nearby (as street sweepings) was used as feedstock. Here only a third of the BMP was realized at this scale (0.18 m(3) biogas/kg VS 0.55 m(3)/kg in BMP). We conclude that anaerobic digestion in plug-flow like digesters appear a more suitable micro-treatment option (2-10 kg VS/day) because in addition to compost it also produces biogas for domestic use nearby.

Studies on phosphorus oxychloride and aluminium chloride complex

1. Anhydrous aluminium chloride reacts with phosphorus oxychloride to give a complex with a composition AlCl3.2 POCl3 which can be prepared in the form of a free flowing powder. 2. The phosphorus oxychloride-aluminium chloride complex in nitrobenzene dissociates into AlCl3.POCl3 and POCl3 as indicated by the cryoscopic measurements. 3. The solution of the complex in nitrobenzene has a higher specific conductivity than the corresponding electrical conductivities of individual components. Similar higher electrical conductance is observed when the two components are mixed in nitrobenzene in different proportions. 4.When a solution of anhydrous aluminium chloride in nitrobenzene is titrated conductometrically against a solution of phosphorus oxychloride in nitrobenzene, a limiting value in the conductivity is reached at point corresponding to the molecular composition, the components in the ratio of 1:2 AlCl3: POCl3 in solution. 5. The absorption maxima of the complex in nitrobenzene solution differ from the absorption maximum of the individual components.

X-ray studies on crystalline complexes involving amino acids and peptides XIX. Effects of change in chirality in the complexes of succinic acid with dl- and l-arginine

Crystals of dl-arginine hemisuccinate dihydrate (I)(monoclinic; P21/c; a = 5.292, b = 16.296, c = 15.203 Å; α= 92.89°; Z = 4) and l-arginine hemisuccinate hemisuccinic acid monohydrate (II) (triclinic; P1; a = 5.099; b = 10.222, c = 14.626 Å; α= 77.31, β= 89.46, γ= 78.42°; Z = 2) were grown under identical conditions from aqueous solutions of the components in molar proportions. The structures were solved by direct methods and refined to R = 0.068 for 2585 observed reflections in the case of (I) and R = 0.036 for 2154 observed reflections in the case of (11). Two of the three crystallographically independent arginine molecules in the complexes have conformations different from those observed so far in the crystal structures containing arginine. The succinic acid molecules and the succinate ions in the structures are centrosymmetric and planar. The crystal structure of (II) is highly pseudosymmetric. Arginine-succinate interactions in both the complexes involve specific guanidyl-carboxylate interactions. The basic elements of aggregation in both the structures are ribbons made up of alternating arginine dimers and succinate ions. However, the ribbons pack in different ways in the two structures. (II) presents an interesting case in which two ionisation states of the same molecule coexist in a crystal. The two complexes provide a good example of the effect of change in chirality on stoichiometry, conformation, aggregation, and ionisation state in the solid state.

Purification and functional characteristics of an endocellulase from Chaetomium thermophile var. coprophile

An endocellulase (1→4)-β-d-glucan 4-glucanohydrolase was isolated from the culture filtrates of Chaetomium thermophile. The enzyme was homogeneous by PAGE and SDS-PAGE. The molecular weight was 36 000 by SDS-PAGE and 38 000 by gel filtration. It was a glycoprotein. From the amino acid composition, it was found to be rich in glycine, threonine, and aspartic and glutamic acids, but contained only low proportions of histidine and sulfur-containing amino acids. It was optimally active at pH 6 and at 60°. The enzyme did not hydrolyze cellobiose and cellotriose, but hydrolyzed cello-tetraose, -pentaose, and -hexaose at comparable rates. It was specific for molecules containing β-(1→4) linkages. It showed high activity towards amorphous cellulose, and the reaction products contained cellobiose to cellopentaose, showing that it effects random cleavage of cellulose.

Integral method for the calculation of incompressible two-dimensional transitional boundary layers

The method proposed here considers the mean flow in the transition zone as a linear combination of the laminar and turbulent boundary layer in proportions determined by the transitional intermittency, the component flows being calculated by approximate integral methods. The intermittency distribution adopted takes into account the possibility of subtransitions within the zone in the presence of strong pressure gradients. A new nondimensional spot formation rate, whose value depends on the pressure gradient, is utilized to estimate the extent of the transition zone. Onset location is determined by a correlation that takes into account freestream turbulence and facility-specific residual disturbances in test data. Extensive comparisons with available experimental results in strong pressure gradients show that the proposed method performs at least as well as differential models, in many cases better, and is always faster.

An Investigation Of Alkali Aluminosilicate Glasses By Si-29 And Al-27 Magic-Angle-Spinning Nmr-Spectroscopy

Alkali aluminosilicate glasses prepared by the gel and the melt routes have been investigated by Si-29 and Al-27 MAS NMR spectroscopy. It is found that Al has a tetrahedral coordination in the gel glasses modified with equivalent proportions of alkalis unlike in a pure aluminosilicate glass where Al has both four and six coordinations. Silicon is present as Q4 units in all the 5M2O 5Al2O3 9OSiO2 ( M = Li, Na and K) gel glasses studied whereas it is present in Q2 or Q3 species in the lithium aluminosilicate glasses of compositions 40Li2O x Al2O3 (1-x)SiO2 (1 less-than-or-equal-to x less-than-or-equal-to 15) and xLi2O 10Al2O3 (1-x)SiO2 (20 less-than-or-equal-to x less-than-or-equal-to 40). The combination of Q2 and Q3 is also found in certain sodium aluminosilicate glasses, but they change to Q2 and Q1 as the concentration of SiO2 decreases.

Critical Reappraisal of Colloidal Activity of Clays

Soil properties and their behavior, apart from stress history, are influenced markedly by physicochemical characteristics of the constituent clay and nonclay minerals and their relative proportions. Atterberg limits and Skempton’s colloidal activity, which are simple quantitative parameters, reflect the composite effects of the soil constituents and their interactions with pore fluid. Micromechanistic interpretations of these parameters have been provided in this paper. It has been shown that, in general, the liquid limit of fine-grained soils reflects the physicochemical potential and that each of the factors of Skempton’s colloidal activity are interdependent. It has been illustrated that property correlations with colloidal activity, as well as with Atterberg limits, result in involved interrelationships due to the interdependence of the parameters.

Critical Reappraisal of Colloidal Activity of Clays

Soil properties and their behavior, apart from stress history, are influence markedly by physicochemical characteristics of the constituent clay and nonclay minerals and their relative proportions. Atterberg limits and Skempton's colloidal activity, which are simple quantitative parameters, reflect the composite effects of the soil constituents and their interactions with pore fluid. Micromechanistic interpretations of these parameters have been provided in this paper. It has been shown that, in general, the liquid limit of fine-grained soils reflects the physicochemical potential and that each of the factors of Skempton's colloidal activity are interdependent. It has been illustrated that property correlations with colloidal activity, as well as with Atterberg limits, result in involved interrelationships due to the interdependence of the parameters.

Proportioning of fly-ash cement concrete mixes

The accumulation of fly ash throughout the world is several million tons per day. The main problem with the usage of fly ash is the slow rate of strength gain, primarily due to slow pozzolanic reactions. Existing methods of proportioning fly ash concrete are lacking. These methods are involved and do not directly take into account the properties of the constituent materials. The Generalized Approach for Mix Proportioning developed at the Indian Institute of Science, Bangalore, is the basis for the development of the proposed method, which takes into account the characteristics of cement, fly ash, and aggregates. Based on the basic trial mix data obtained by using the American Concrete Institute (ACI 211.1-81) method, the proportions of fly-ash concrete mixes were arrived at using the Generalized Approach for Mix Proportioning. The method proposed was applied to and found applicable for fly-ash concretes using fly ashes from two different sources.

Coadsorption of Dioxygen and Water on the Ni(110) Surface: Role of O1--Type Species in the Dissociation of Water

While the adsorption of dioxygen at a clean Ni(110) surface gives rise to two O(1s) features at 531 and 530 eV assigned to O-(a) and O2-(a) type species respectively, coadsorption of dioxygen and water mixtures result in the additional formation of hydroxyl species characterized by an O(1s) peak at 532.3 eV. The latter is attributed to the oxygen induced dissociation of water via a low energy pathway involving the O-(a)-type species. The proportions of the O-(a) and the hydroxyl species are greater for small O-2/H2O ratios and lower temperatures (120 K). With increase in temperature, the relative surface concentrations of the O-(a) and the hydroxyl species decrease while there is an increase in the concentration of the oxidic O2-(a) species. Thus, the surface concentrations of both the hydroxyl and the O2-(a) species depend critically on the presence of O- type species. Above 300K the surface chemistry in the main involves the conversion of O- to O2- species via the hydroxyl species.

Microstructure control and wear of Al2O3-SiC-(Al,Si) composites made by melt oxidation

Ceramic matrix composites of Al2O3-SiC-(Al,Si) have been fabricated by directed melt oxidation of aluminum alloys into SiC particulate preforms. The proportions of Al2O3, alloy, and porosity in the composite can be controlled by proper selection of SLC particle size and the processing temperature. The wear resistance of composites was evaluated in pin-on-disk experiments against a hard steel substrate. Minimum wear rate comparable to conventional ceramics such as ZTA is recorded for the composition containing the highest fraction of alloy, owing to the development of a thin and adherent tribofilm with a low coefficient of friction.

Recovery of copper from vanadiferrous magnetite ore of Masanikere area, Shimoga district

Studies have been carried out to recover copper from vanadiferrous magnetite ores by a novel reaction with lime in the presence of water vapour. The ore, mixed with different proportions of lime, has been roasted in the presence of steam. The roasted product is either directly leached with dilute mineral acids or subjected to magnetic separation and then leached. The effect of various parameters such as amount of lime added, temperature and duration of roasting and time of leaching on the recovery of copper has been investigated. The results indicate that over 90% copper could be recovered under optimum conditions of roasting and leaching.

Quantitation of spermatogenesis by DNA flow cytometry: Comparative study among six species of mammals

Suspensions of testicular germ cells from six species of mammals were prepared and stained for the DNA content with a fluorochrome (ethidium bromide) adopting a common technique and subjected to DNA flow cytometry. While uniform staining of the germ cells of the mouse, hamster, rat and monkey could be obtained by treating with 0.5% pepsin for 60 min followed by staining with ethidium bromide for 30 min, that of the guinea pig and rabbit required for optimal staining pepsinization for 90 min and treatment with ethidium bromide for 60 min. The procedure adopted here provided a uniform recovery of over 80% of germ cells with each one of the species tested and the cell population distributed itself according to the DNA content (expressed as C values) into 5 major classes-spermatogonia (2C), cells in S-phase, primary spermatocytes (4C), round spermatids (1C), and elongating/elongated spermatids (HC). Comparison of the DNA distribution pattern of the germ cell populations between species revealed little variation in the relative quantities of cells with 2C (8-11%), S-phase (6-9%), and 4C (6-9%) amount of DNA. Though the spermatid cell populations exhibited variations (1C:31-46%, HCI:7-20% and and HC2:11-25%) they represented the bulk of germ cells (70-80%). The overall conversion of 2C to 1C (1C:2C ratio) and meiotic transformation of 4C cells to IC (1C:4C ratio) kinetics were relatively constant between the species studied. The present study clearly demonstrates that DNA flow cytometry can be adopted with ease and assurance to quantify germ cell transformation and as such spermatogenesis by analysing a large number of samples with consistency both within and across the species barrier. Any variation from the norms in germ cell proportions observed following treatment, for e.g. hormonal stimulation or deprivation can then be ascribed due to a specific effect of the hormone/drug on single/multiple steps in germ cell transformation

The precision of regulation in Dictyostelium discoideum: implications for cell-type proportioning in the absence of spatial pattern

We have made careful counts of the exact number of spore, stalk and basal disc cells in small fruiting bodies of Dictyostelium discoideum (undifferentiated amoebae are found only rarely and on average their fraction is 4.96 x 10(-4)). (i) Within aggregates of a given size, the relative apportioning of amoebae to the main cell types occurs with a remarkable degree of precision. In most cases the coefficient of variation (c.v.) in the mean fraction of cells that form spores is within 4.86%. The contribution of stalk and basal disc cells is highly variable when considered separately (c.v.'s upto 25% and 100%, respectively), but markedly less so when considered together. Calculations based on theoretical models indicate that purely cell-autonomous specification of cell, fate cannot account for die observed accuracy of proportioning. Cell-autonomous determination to a prestalk or prespore condition followed by cell type interconversion, and stabilised by feedbacks, suffices to explain the measured accuracy. (ii) The fraction of amoebae that differentiates into spores increases monotonically with the total number of cells. This fraction rises from an average of 73.6% for total cell numbers below 30 and reaches 86.0% for cell numbers between 170 and 200 (it remains steady thereafter at around 86%). Correspondingly, the fraction of amoebae differentiating into stalk or basal disc decreases viith total size. These trends are in accordance with evolutionary expectations and imply that a mechanism for sensing the overall size of the aggregate also plays an essential role in the determination of cell-type proportions.