Study of electron states of solids by techniques of electron spectroscopy

Studies of valence bands and core levels of solids by photoelectron spectroscopy are described at length. Satellite phenomena in the core level spectra have been discussed in some detail and it has been pointed out that the intensity of satellites appearing next to metal and ligand core levels critically depends on the metal-ligand overlap. Use of photoelectron spectroscopy in investigating metal-insulator transitions and spin-state transitions in solids is examined. It is shown that relative intensities of metal Auger lines in transition metal oxides and other systems provide valuable information on the valence bands. Occurrence of interatomic Auger transitions in competition with intraatomic transitions is discussed. Applications of electron energy loss spectroscopy and other techniques of electron spectroscopy in the study of gas-solid interactions are briefly presented.

Flow through a plateau border of cellular foam

Experimentally measured average velocities through plateau borders of stationary cellular foam, when compared with those calculated with the assumption of rigid Plateau Border walls, show that the assumption of rigid walls severely underestimates the velocities. An analysis of the situation wherein plateau border walls have velocities, as decided by the surface viscosity of the system, is presented here. The plateau border is idealized as a pipe of equilateral triangular cross-section with vertices of the triangle having zero velocity. The pertinent form of Navier-Stoke's equations with inhomogeneous boundary conditions and its solution through a procedure of successive approximations is presented in dimensionless form. The solution reduces to the known solution of slow steady flow through a triangular pipe, when surface viscosity is infinite. Results indicate that the assumption of rigid plateau border walls is valid only when value of the inverse of dimensionless surface viscosity is less than 0.044. Beyond that the assumption severely underestimates the flow and the effect of nonrigidity of the wall must be considered.

Application of various viscosity theories to the viscosity data of methyl methacrylate-acrylonitrile random copolymersstar

Values of Ko, Flory constant related to unperturbed dimensions, are evaluated for methyl methacrylate-acrylonitrile random copolymers using Flory-Fox, Kurata-Stockmayer and Inagaki-Ptitsyn methods and compared with the Ko values obtained by Stockmayer-Fixman method. Ko values are seen to be less in solvents which have large a (Mark-Houwink exponent) values. A correlation between Ko and a is developed to arrive at a more reliable estimate of Ko for this copolymer system.

Theoretical studies on penicillins, penicillin sulphones and their 1-oxa-1-dethia and 1-carba-1-dethia analogues: binding specificities of transeptidases and penicillinases

Empirical potential energy calculations have been carried out to determine the preferred conformations of penicillins and penicillin sulphones and their 1-oxa-1-dethia and 1-carba-1-dethia analogues. With the exception of 1-oxa-1-dethia penicillins, all the other compounds favour C2 and the C3 puckered conformations of their five-membered rings. Replacement of C2 methyl groups by hydrogen atoms as in bisnorpenicillin V or oxidation of sulphur in position 1 as in sulphones, makes the C3 puckered form much less favourable. Addition of an amino-acyl group at the C6 atom, however, makes the C3 puckered form more favoured in penicillin G or V and in 1-carba-1-dethia penicillins. Through the replacement of the sulphur atom at position 1 by an oxygen atom or by a -CH2 group increases the non-planarity of the lactam peptide bond, it significantly affects the relative disposition of the C3 carboxyl group with respect to the β-lactam ring. These conformational differences have been correlated with the biological activities of these compounds. The present study suggests that the conformation of the bicyclic ring system may be more important for initial binding with the crosslinking enzyme(s) involved in the biosynthesis of bacterial cell-wall peptidoglycan and that the mode of binding is influenced by the nature of the side-group at the C6 atom. These studies predict, in agreement with experimental results, that the 1-oxa-1-dethia penicillin nulceus is an inhibitor of penicillianses. The study also suggests that the stereospecificities of the crosslinking enzyme(s) and penicillinases are very similar with regard to the nature of the side-group at the 6 atom and the confirmation of the bicyclic ring system. However, the confirmational requirement for the bicyclic ring system appears to be more specific in the former enzyme than in the latter.

NUPARM and NUCGEN: software for analysis and generation of sequence dependent nucleic acid structures

Software packages NUPARM and NUCGEN, are described, which can be used to understand sequence directed structural variations in nucleic acids, by analysis and generation of non-uniform structures. A set of local inter basepair parameters (viz. tilt, roll, twist, shift, slide and rise) have been defined, which use geometry and coordinates of two successive basepairs only and can be used to generate polymeric structures with varying geometries for each of the 16 possible dinucleotide steps. Intra basepair parameters, propeller, buckle, opening and the C6...C8 distance can also be varied, if required, while the sugar phosphate backbone atoms are fixed in some standard conformation ill each of the nucleotides. NUPARM can be used to analyse both DNA and RNA structures, with single as well as double stranded helices. The NUCGEN software generates double helical models with the backbone fixed in B-form DNA, but with appropriate modifications in the input data, it can also generate A-form DNA ar rd RNA duplex structures.

Investigations of a two-stage pulse tube cryocooler operating down to 2.5K

A two-stage pulse tube cryocooler (PTC) which produces a no-load temperature of similar to 2.5 K in its second stage at an operating frequency of 1.6 Hz has been designed and fabricated. The second stage of the system provides a refrigeration power of similar to 250 mW at 5.0 K. The system uses stainless steel meshes (mesh size 200) along with lead (Pb) granules and combinations of Pb, Er3Ni, and HoCu2 as the first and second stage regenerator materials, respectively. Experimental studies have been carried out on different pulse tube configurations by varying the dimensions of the pulse tubes and regenerators to arrive at the best one, which leads to the lowest no-load second stage cold head temperature. Using this configuration, detailed experimental studies have been conducted by varying the volume percentage ratios of the second stage regenerator materials such as HoCu2, Er3Ni, and Pb (with an average grain size of similar to 250 mu m). This article presents the results of our experimental studies on cryocoolers with the regenerator material arranged in layered structures. Comparative studies have also been presented for specific cases where the regenerator materials are arranged as a homogeneous mixture in the second stage. The experimental results clearly indicate that the design of PTCs should use only layered structures of regenerator materials and not homogenous mixtures.

Anomalin. A Dihydropyranocoumarin Derivative from the Plant Lingusticum elatum

The title compound, 9,10-dihydro-8,8-dimethyl-2-oxo-2H,8H-benzo[1,2-b:3,4-b']dipyran-9,10-diyl 2-methyl-2-butenoate, C24H26O7, contains a highly planar coumarin nucleus and a substituted dihydropyran ring (C), which has a distorted half-chair conformation, with an 8 alpha,9 beta orientation. The conformation of ring C is further supported by the two angelyloxy (2-methyl-2-butenoyloxy) substituents at positions C9 and C10, which are cis oriented and thus cannot both occupy equatorial positions with respect to the plane of ring C. The conformations of the two angelyloxy substituents are different, as indicated by their endocyclic torsion angles. The most striking of these angles are O1'-C2'-C4'=C6' and O1'-C2'-C4'-C5' [-137.7 (5) and 43.7 (5)degrees, respectively, in the chain at C10 and 155.8 (5) and -24.7 (9)degrees, respectively in the chain at C9]. These variations are due to two intramolecular hydrogen bonds, namely, C16-H161 ... O1' [C16 ... O1' 3.056 (7) Angstrom] and C7''-H7Y ... O3'' [C7'' ... O3'' 2.955 (12) Angstrom]. The methyl substituents, C15 and C16, at position C8 are alpha and beta oriented, respectively. The crystal structure is stabilized by a weak C4-H41 ... O3' hydrogen bond [C4 ... O3' 3.297 (6) Angstrom] between the screw-related molecules.

Hydrography and circulation in the western Bay of Bengal during the northeast monsoon

The Bay of Bengal, a semienclosed tropical basin that comes under the influence of monsoonal wind and freshwater influx, is distinguished by a strongly stratified surface layer and a seasonally reversing circulation. We discuss characteristics of these features in the western Bay during the northeast monsoon, when the East India Coastal Current (EICC) flows southward, using hydrographic data collected during December 1991. Vertical profiles show uniform temperature and salinity in a homogeneous surface layer, on average, 25 m deep but shallower northward and coastward. The halocline, immediately below, is approximately 50 m thick; salinity changes by approximately 3 parts per thousand. About two thirds of the profiles show temperature inversions in this layer. Salinity below the halocline hardly changes, and stratification is predominantly due to temperature variation, The halocline is noticeably better developed and the surface homogeneous layer is thinner in a low-salinity plume that hugs the coastline along the entire east coast of India, The plume is, on average, 50 km wide, with isohalines sloping down toward the coast. Most prominent in the geostrophic velocity field is the equatorward EICC. Its transport north of about 13 degrees N, computed with 1000 dbar as the level of reference, varies between 2.6 and 7.1 x 10(6) m(3) s(-1); just south of this latitude, a northwestward flow from offshore recurves and merges with the coastal current. At the southern end of the region surveyed, the transport is 7.7 x 10(6) m(3) s(-1). Recent model studies lead us to conclude that the EICC during the northeast monsoon is driven by winds along the east coast of India and Ekman pumping in the interior bay. In the south, Ekman pumping over the southwestern bay is responsible for the northwestward flow that merges with the EICC.

Growth inhibitory, apoptotic and anti-inflammatory activities displayed by a novel modified triterpenoid, cyano enone of methyl boswellates

Triterpenoids are pentacyclic secondary metabolites present in many terrestrial plants. Natural triterpenoids have been reported to exhibit anti-inflammatory and anti-carcinogenic activities. Here, we show that modifications of ring A of boswellic acid (2 cyano, 3 enone) resulted in a highly active growth inhibitory, anti-inflammatory, pro-differentiative and anti-tumour triterpenoid compound called cyano enone of methyl boswellates (CEMB). This compound showed cytotoxic activity on a number of cancer cell lines with IC50 ranging from 0.2 to 0.6 mu M. CEMB inhibits DNA synthesis and induces apoptosis in A549 cell line at 0.25 mu M and 1 mu M concentrations, respectively. CEMB induces adipogenic differentiation in 3T3-L1 cells at a concentration of 0.1 mu M. Finally, administration of CEMB intra-tumourally significantly inhibited the growth of C6 glioma tumour xenograft in immuno-compromised mice. Collectively, these results suggest that CEMB is a very potent anti-tumour compound.

Adaptation of small capacity natural gas engine for producer gas operation

This article addresses the adaptation of a low-power natural gas engine for using producer gas as a fuel. The 5.9 L natural gas engine with a compression ratio of 10.5:1, rated at 55 kW shaft power, delivered 30 kW using producer gas as fuel in the naturally aspirated mode. Optimal ignition timing for peak power was found to be 20 degrees before top dead centre. Air-to-fuel ratio (A/F) was found to be 1.2 +/- 0.1 over a range of loads. Critical evaluation of the energy flows in the engine resulted in identifying losses and optimizing the engine cooling. The specific fuel consumption was found to be 1.2 +/- 0.1 kg of biomass per kilowatt hour. A reduction of 40 per cent in brake mean effective pressure was observed compared with natural gas operation. Governor response to load variations has been studied with respect to frequency recovery time. The study also attempts to adopt a turbocharger for higher power output. Preliminary results suggest a possibility of about 30 per cent increase in the output.

Investigations into enhanced wax production with combustion synthesized Fischer-Tropsch catalysts

Combustion synthesized (CS) cobalt catalysts deposited over two supports, alumina and silica doped alumina (SDA), were characterized and tested for its Fischer-Tropsch (FT) activity. The properties of CS catalysts were compared to catalysts synthesized by conventional impregnation method (IWI). The CS catalysts resulted in 40-70% increase in the yield of C6+ hydrocarbons compared to MI catalysts. The FT activity for CS catalysts showed formation of long chain hydrocarbon waxes (C24+) compared to the formation of middle distillates (C-10-C-20) for IWI synthesized catalysts, indicating higher hydrocarbon chain growth probability for CS catalysts. This is ascribed to the smaller crystallite sizes, increased degree of cobalt reduction and consequentially, a higher number of active metal sites, exposed over the catalyst surface. Additionally, 12-13% increase in the overall C6+ hydrocarbon yield is realized for SDA-CS catalysts, compared to Al2O3-CS catalysts. The improved performance of CS-SDA catalysts is attributed to 48% increase in cobalt dispersion compared to Al2O3 supported CS catalysts, which is again caused by the decrease in the cobalt -support interaction for SDA supports. The metal support interactions were analyzed using XPS and H-2 TPR-TPD experiments. Combustion method produced catalysts with smaller crystallite size (17-18 nm), higher degree of reduction (similar to 92%) and higher metal dispersion (16.1%) compared to the IWI method. Despite its enhanced properties, the CS catalysts require prominently higher reduction temperatures (similar to 1100-1200 K). The hydrocarbon product analysis for Al2O3 supported catalyst showed higher paraffin wax concentrations compared to SDA supported catalysts, due to the lower surface basicity of Al2O3. This work reveals the impact of the CS catalysts and the nature of support on FT activity and hydrocarbon product spectrum. (C) 2016 Elsevier Ltd. All rights reserved.