Relation of coordination number to memory and threshold switching in chalcogenides

The paper reports a structural study of some memory and threshold chalcogenides in terms of coordination numberC, defined byC=8−N, and is the average coordination number for covalently bonded materials. The average number of nearest neighbours surrounding a central atom, obtained for As-Ge-Te (memory) and Se-Ge-Te (threshold) systems have been used to estimate the cohesive energies, assuming simple additivity of bond energies. The bonding pattern so obtained, explains certain properties of these glasses.     

Protonation constant of some sulpha-drugs in dioxan water medium

The dissociation constants of some sulpha-drugs have been determined potentiometrically in 10–50% (v/v) dioxan—water media at 25° at ionic strength O.1M (NaClO₄). Correlation of mole fraction of dioxan and pK gives a straight line. The pK values do not vary linearly with reciprocal of the dielectric constant of the medium at high percentage of dioxan.     

Electro-kinetic transport of acetone,water and their binary mixtures

Summary Electroosmosis of acetone, water and their binary mixtures through thorium oxide (ThO₂) plug membrane has been studied and the data analysed using non-equilibrium thermodynamics. The phenomenological coefficients,L ₁₁ andL ₁₂ have been found to vary nonlinearly with composition. Excess phenomenological coefficients have therefore been evaluated and the results explained in terms of the membrane permeant and permeant-permeant interactions. The results on the measurement of electrophoretic velocity of ThO₂ particles dispersed in acetone-water mixtures also lead to the conclusion that the components of the mixture interact appreciably.

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Zusammenfassung Die Elektroosmose von Aceton, Wasser and deren binären Gemische durch eine ThO₂-Pflock-Membran wurde untersucht; die Daten wurden mit Hilfe der Nichtgleich-gewichts-Thermodynamik analysiert. Die phänomenologischen KoeffizientenL ₁₁ undL ₁₂ ändern sich hiernach nichtlinear mit der Zusammensetzung. Es wurden daher Exzess-L ₁₁-und -L ₁₂-Werte berechnet; die Ergebnisse wurden auf Grund der Membran-Permeant- und Permeant-Permeant-Wechselwirkungen diskutiert. Aus der Messung der elektrophoretischen Geschwindigkeit von ThO₂-Teilchen, die in Aceton-Wasser-Gemischen dispergiert sind, folgt, daß eine merkliche Wechselwirkung zwischen den Komponenten der Mischung vorliegt.

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With 8 figures and 1 table     

Homoclinic points and isomorphism rigidity of algebraic ℤ<Superscript><Emphasis Type="Italic">d</Emphasis></Superscript>-actions on zero-dimensional compact abelian groups

Letd>1, and letα andβ be mixing ? ^d -actions by automorphisms of zero-dimensional compact abelian groupsX andY, respectively. By analyzing the homoclinic groups of certain sub-actions ofα andβ we prove that, if the restriction ofα to some subgroup Γ ? ? ^d of infinite index is expansive and has completely positive entropy, then every measurable factor mapφ: (X, α)→(Y, β) is almost everywhere equal to an affine map. The hypotheses of this result are automatically satisfied if the actionα contains an expansive automorphismα ⁿ ,n ∈ ? ^d , or ifα arises from a nonzero prime ideal in the ring of Laurent polynomials ind variables with coefficients in a finite prime field. Both these corollaries generalize the main theorem in [9]. In several examples we show that this kind of isomorphism rigidity breaks down if our hypotheses are weakened.     

Olefin polymerization with Me4Cp–Amido complexes with electron‐withdrawing groups

A series of Me₄Cp–amido complexes {[η⁵:η¹‐(Me₄C₅)SiMe₂NR]TiCl₂; R = t‐Bu, 1 ; C₆H₅, 2 ; C₆F₅, 3 ; SO₂Ph, 4 ; or SO₂Me, 5 } were prepared and investigated for olefin polymerization in the presence of methylaluminoxane (MAO). X‐ray crystallography of complexes 3 and 4 revealed very long Ti N bonds relative to the bonds of 1 . These complexes were employed for ethylene–styrene copolymerizations, styrene homopolymerizations, and propylene homopolymerizations in the presence of MAO. The productivities of the catalysts derived from 3 – 5 were much lower than the productivity of the catalyst derived from 1 for the propylene polymerizations and ethylene–styrene copolymerizations, whereas the styrene polymerization activities were much higher for the catalysts derived from 3 – 5 than for the catalyst derived from 1 . The polymerization behavior of the catalysts derived from the metallocenes 3 – 5 were more reminiscent of monocyclopentadienyl titanocene Cp′TiX₃/MAO catalysts than of CpATiX₂/MAO catalysts such as 1 containing alkylamido ligands. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4649–4660, 2000     

Simultaneous quantification of centchroman and its 7-demethylated metabolite in rat dried blood spot samples using LC-MS/MS

An approach has been developed for the quantitative determination of concentrations of centchroman ( I), a nonsteroidal once‐a‐week oral contraceptive, and its major metabolite (7‐desmethyl centchroman, II) using dried blood spots (DBS) on paper, rather than conventional plasma samples. The assay employed simple solvent extraction of the DBS sample circle (6 mm) requiring small blood volumes (30 μL) followed by reversed‐phase HPLC separation, combined with multiple reaction monitoring mass spectrometric detection. The calibration plot in matrix using d ‐trans‐hydroxy chroman as internal standard (IS) was linear (r² = 0.998) over ranges of 1.5–240 and 4.5–720 ng/mL for I and II, respectively. The recoveries of both I and II were always >60% with quantification limits (signal‐to‐noise ratio = 10) of 1.5 and 4.5 ng/mL for I and II, respectively. The intra‐day and inter‐day precision (%RSD) and accuracy (%bias) variations in blood spots for both I and II were better than 13%. Moreover, both I and II were stable in DBS for at least 3 months when stored at room temperature. The developed method was successfully applied to the pharmacokinetic interaction study after oral administration of centchroman with and without co‐administration of carbamazepine in female Sprague–Dawley rats using serial sampling and results were comparable with the plasma concentrations reported earlier. Copyright © 2011 John Wiley & Sons, Ltd.     

Structure and dynamics of solutions of a polystyrene–polybutadiene pentablock copolymer in a styrene‐selective solvent

We have examined solutions of a polystyrene–polybutadiene pentablock copolymer in 1,4‐dioxane, a slightly selective solvent for polystyrene and a θ solvent for polybutadiene, with static light scattering (SLS), dynamic light scattering (DLS), and small‐angle neutron scattering (SANS). The SANS data have been analyzed with the Percus–Yevick model to represent the scattering from interacting cores, approximated as hard spheres, and with a Lorentzian function to represent the scattering from unassociated and associated polymer chains. The SANS data at 25 °C clearly reveal interacting domains, approximately 6 nm in radius, formed by the association of the insoluble polybutadiene block in the 20% sample. The 4% sample does not show such domains, whereas the 7% sample represents an intermediate situation, with both unassociated polymer and associated polymer. At higher temperatures, the domains dissolve. The DLS data for samples with concentrations of 2–22% show two diffusive modes: a fast mode corresponding to the cooperative dynamics of concentration fluctuations and a slow mode corresponding to the diffusion of clusters. The large length‐scale heterogeneities, indicated by the strong angular dependence of SLS, implies that the small microdomains of about 10–15 polybutadiene blocks are bridged by the polystyrene chains, forming large aggregates with randomly distributed crosslinks on length scales much larger than the domain size. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2807–2816, 2002     

Regulation of vincamine biosynthesis and associated growth promoting effects through abiotic elicitation,cyclooxygenase inhibition,and precursor feeding of bioreactor grown Vinca minor hairy roots

Hydroxylase/acetyltransferase elicitors and cyclooxygenase inhibitor along with various precursors from primary shikimate and secoiridoid pools have been fortified to vincamine less hairy root clone of Vinca minor to determine the regulatory factors associated with vincamine biosynthesis. Growth kinetic studies revealed that acetyltransferase elicitor acetic anhydride and terpenoid precursor loganin significantly reduce the growth either supplemented alone or in combination (GI?=?140.6?±?18.5 to 246.7?±?24.3), while shikimate and tryptophan trigger biomass accumulation (GI?=?440.2?±?31.5 to 540.5?±?40.3). Loganin also downregulates total alkaloid biosynthesis. Maximum flux towards vincamine production (0.017?±?0.001 % dry wt.) was obtained when 20-day-old hairy roots were fortified with secologanin (10 mg/l) along with tryptophan (100 mg/l), naproxen (8.4 mg/l), hydrogen peroxide (20 μg/l), and acetic anhydride (32.4 mg/l). This was supported by RT PCR (qPCR) analysis where 2- and 3-fold increase in tryptophan decarboxylase (TDC; RQ?=?2.0?±?0.09) and strictosidine synthase (STR; RQ?=?3.3?±?0.36) activity, respectively, was recorded. The analysis of variance (ANOVA) for growth kinetics, total alkaloid content, and gene expression studies favored highly significant data (P?<?0.05–0.01). Above treated hairy roots were also up-scaled in a 5-l stirred-tank bioreactor where a 40-day cycle yielded 8-fold increase in fresh root mass.     

Recent applications of sample preparation techniques in food analysis

Even with the emergence of advanced techniques of separation and identification, it is rarely possible to analyse food without manipulation. The traditional techniques for sample preparation are time consuming and require large amount of reagents, which are expensive, generate considerable waste, contaminate the sample and can enrich it for analytes. The more analytical techniques have become highly developed, the more has sample clean-up become important in order to fully take advantage of them. Due to the multiplicity of food matrices, it is not possible to use one sample preparation technique, so many methods have been proposed for meeting all the requirements. The newest variations of wet digestion, solvent and sorbent extraction and membrane separation are summarised and their most recent applications to food analysis are provided.     

Bioleaching of Nickel and Cobalt from Lateritic Chromite Overburden Using the Culture Filtrate of Aspergillus niger

Extraction of metals (Ni, Co) from chromite overburden of Sukinda mines of Orissa, India, with the culture filtrate of Aspergillus niger was studied. Results showed that the amounts of metals leached varied directly with reaction temperature and period of fermentation. The culture filtrate was analyzed for citric and oxalic acids, and contained only oxalic acid—the concentration of which increased with time. Although this acid played the major role in leaching of metals, other unidentified metabolites present in the culture filtrate influenced the dissolution of the metals significantly. Maximum recovery of metals from raw and roasted ore samples was achieved at 80 °C with the 21-day culture filtrate containing the highest amount of oxalic acid. Under identical experimental conditions, much higher amounts of the metals were leached from roasted ore. Microstructures of the ore particles were studied by scanning electron microscopy and transmission electron microscopy; the bonding behaviors of metal compounds were identified by Fourier transform infrared spectroscopy which showed that the metals were leached after chelation with oxalic acid.