Interplay of spin and lattice degrees of freedom in the frustrated antiferromagnet CdCr2O4: High-field and temperature-induced anomalies of the elastic constants

Temperature and magnetic field studies of the elastic constants of the chromium spinel CdCr2O4 show pronounced anomalies related to strong spin-phonon coupling in this frustrated antiferromagnet. A detailed comparison of the longitudinal acoustic mode propagating along the 111] direction with a theory based on an exchange-striction mechanism leads to an estimate of the strength of the magnetoelastic interaction. The derived spin-phonon coupling constant is in good agreement with previous determinations based on infrared absorption. Further insight is gained from intermediate and high magnetic field experiments in the field regime of the magnetization plateau. The role of the antisymmetric Dzyaloshinskii-Moriya interaction is discussed.

Vapor pressure and dissociation energy of (In2O)

The vapor pressure of pure liquid indium, and the sum of pressures of (In) and (In2O) species over the condensed phase mixture {In} + , contained in a silica vessel, have been measured by Knudsen effusion and Langmuir free vaporization methods in the temperatue range 600 to 950°C. Mass spectrometric studies reported in the literature show that (In) and (In2O) are the important species in the vapor phase over the {In} + ; mixture. The vapor pressure of (In2O) corresponding to the reaction, deduced from the present measurements is given by the equation, The “apparent evaporation coefficient” for the condensed phase mixture is approximately 0.8. The energy for the dissociation (In2O) molecule into atoms calculated from the above equation is D°0 = 180.0 (± 1.0) kcal mol−1.

Formulas for algorithmic computation of impedance matrix using general circuit constants

A set of formulas is derived from general circuit constants which facilitates formation of the impedance matrix of a power system by the bus-impedance method. The errors associated with the lumpedparameter representation of a transmission line are thereby eliminated. The formulas are valid for short lines also, if the relevant general circuit constants are employed. The mutual impedance between the added line and the existing system is not considered, but the approach suggested can well be extended to it.

Combined Electron Transfer Dissociation-Collision-Induced Dissociation Fragmentation in the Mass Spectrometric Distinction of Leucine, Isoleucine, and Hydroxyproline Residues in Peptide Natural Products

Distinctions between isobaric residues have been a major challenge in mass spectrometric peptide sequencing. Here, we propose a methodology for distinction among isobaric leucine, isoleucine, and hydroxyproline, a commonly found post-translationally modified amino acid with a nominal mass of 113 Da, through a combined electron transfer dissociation-collision-induced dissociation approach. While the absence of c and z(center dot) ions, corresponding to the Yyy-Xxx (Xxx = Leu, Ile, or Hyp) segment, is indicative of the presence of hydroxyproline, loss of isopropyl (Delta m = 43 Da) or ethyl radicals (Delta m = 29 Da), through collisional activation of z(center dot) radical ions, are characteristic of leucine or isoleucine, respectively. Radical migration processes permit distinctions even in cases where the specific e ions, corresponding to the Yyy-Leu or -Ile segments, are absent or of low intensity. This tandem mass spectrometric (MSn) method has been successfully implemented in a liquid chromatography MSn platform to determine the identity of 23 different isobaric residues from a mixture of five different peptides. The approach is convenient for distinction of isobaric residues from any crude peptide mixture, typically encountered in natural peptide libraries or proteomic analysis.

Synthesis of beta-arabinofuranoside glycolipids, studies of their binding to surfactant protein-A and effect on sliding motilities of M. smegmatis

Surfactant protein A (SP-A), which is a lung innate immune system component, is known to bind glycolipids present at the cell surface of a mycobacterial pathogen. Lipoarabinomannan (LAM), a component of mycobacterial thick, waxy cell wall, is one of the glycolipid ligands for SP-A. In order to assess binding of synthetic glycolipids with SP-A and the glycosidic linkage preferences for the interaction, beta-arabinofuranoside trisaccharide glycolipids constituted with beta-(1 -> 2), beta-(1 -> 3) and beta-(1 -> 2), beta-(1 -> 5) linkages relevant to LAM were synthesized through chemical glycosylations. The efficacies of synthetic glycolipids to interact with SP-A were assessed by using the surface plasmon resonance (SPR) technique, from which association-dissociation rate constants and equilibrium binding constants were derived. The equilibrium binding constants of the interaction of two constitutionally varying beta-arabinofuranoside glycolipids with SP-A were found to be in the millimolar range. A comparison of the results with few alpha-anomeric arabinofuranoside glycolipids showed that glycolipids with beta-anomeric linkages were having relatively lower equilibrium binding constants than those with alpha-anomeric linkages in binding to the protein, whereas oligosaccharides alone, without lipidic chains, exhibited higher equilibrium binding constants. Further, the synthetic compounds inhibited the growth of mycobacteria and affected sliding motilities of the bacteria, although to an extent relatively lesser than that of synthetic compounds constituted with alpha-anomeric linkages.

Structure constants of beta deformed super Yang-Mills

We study the structure constants of the N = 1 beta deformed theory perturbatively and at strong coupling. We show that the planar one loop corrections to the structure constants of single trace gauge invariant operators in the scalar sector is determined by the anomalous dimension Hamiltonian. This result implies that 3 point functions of the chiral primaries of the theory do not receive corrections at one loop. We then study the structure constants at strong coupling using the Lunin-Maldacena geometry. We explicitly construct the supergravity mode dual to the chiral primary with three equal U(1) R-charges in the Lunin-Maldacena geometry. We show that the 3 point function of this supergravity mode with semi-classical states representing two other similar chiral primary states but with large U(1) charges to be independent of the beta deformation and identical to that found in the AdS(5) x S-5 geometry. This together with the one-loop result indicate that these structure constants are protected by a non-renormalization theorem. We also show that three point function of U(1) R-currents with classical massive strings is proportional to the R-charge carried by the string solution. This is in accordance with the prediction of the R-symmetry Ward identity.

Thermal Decomposition of Propargyl Alcohol: Single Pulse Shock Tube Experimental and ab Initio Theoretical Study

Thermal decomposition of propargyl alcohol (C3H3OH), a molecule of interest in interstellar chemistry and combustion, was investigated using a single pulse shock tube in the temperature ranging from 953 to 1262 K. The products identified include acetylene, propyne, vinylacetylene, propynal, propenal, and benzene. The experimentally observed overall rate constant for thermal decomposition of propargyl alcohol was found to be k = 10((10.17 +/- 0.36)) exp(-39.70 +/- 1.83)/RT) s(-1) Ab initio theoretical calculations were carried out to understand the potential energy surfaces involved in the primary and secondary steps of propargyl alcohol thermal decomposition. Transition state theory was used to predict the rate constants, which were then used and refined in a kinetic simulation of the product profile. The first step in the decomposition is C-O bond dissociation, leading to the formation of two important radicals in combustion, OH and propargyl. This has been used to study the reverse OH propargyl radical reaction, about which there appears to be no prior work. Depending on the site of attack, this reaction leads to propargyl alcohol or propenal, one of the major products at temperatures below 1200 K. A detailed mechanism has been derived to explain all the observed products.

Reduced graphene oxide-titania based platform for label-free biosensor

A label-free biosensor has been fabricated using a reduced graphene oxide (RGO) and anatase titania (ant-TiO2) nanocomposite, electrophoretically deposited onto an indium tin oxide coated glass substrate. The RGO-ant-TiO2 nanocomposite has been functionalized with protein (horseradish peroxidase) conjugated antibodies for the specific recognition and detection of Vibrio cholerae. The presence of Ab-Vc on the RGO-ant-TiO2 nanocomposite has been confirmed using electron microscopy, Fourier transform infrared spectroscopy and electrochemical techniques. Electrochemical studies relating to the fabricated Ab-Vc/RGO-ant-TiO2/ITO immunoelectrode have been conducted to investigate the binding kinetics. This immunosensor exhibits improved biosensing properties in the detection of Vibrio cholerae, with a sensitivity of 18.17 x 10(6) F mol(-1) L-1 m(-2) in the detection range of 0.12-5.4 nmol L-1, and a low detection limit of 0.12 nmol L-1. The association (k(a)), dissociation (k(d)) and equilibrium rate constants have been estimated to be 0.07 nM, 0.002 nM and 0.41 nM, respectively. This Ab-Vc/RGO-ant-TiO2/ITO immunoelectrode could be a suitable platform for the development of compact diagnostic devices.

Estimating successive pK(a) values of polyprotic acids from ab initio molecular dynamics using metadynamics: the dissociation of phthalic acid and its isomers

Estimation of the dissociation constant, or pK(a), of weak acids continues to be a central goal in theoretical chemistry. Here we show that ab initio Car-Parrinello molecular dynamics simulations in conjunction with metadynamics calculations of the free energy profile of the dissociation reaction can provide reasonable estimates of the successive pK(a) values of polyprotic acids. We use the distance-dependent coordination number of the protons bound to the hydroxyl oxygen of the carboxylic group as the collective variable to explore the free energy profile of the dissociation process. Water molecules, sufficient to complete three hydration shells surrounding the acid molecule, were included explicitly in the computation procedure. Two distinct minima corresponding to the dissociated and un-dissociated states of the acid are observed and the difference in their free energy values provides the estimate for pK(a), the acid dissociation constant. We show that the method predicts the pK(a) value of benzoic acid in good agreement with experiment and then show using phthalic acid (benzene dicarboxylic acid) as a test system that both the first and second pK(a) values as well, as the subtle difference in their values for different isomers can be predicted in reasonable agreement with experimental data.

Exact N-wave solutions of generalized Burgers equations

Exact N-wave solutions for the generalized Burgers equation u(t) + u(n)u(x) + (j/2t + alpha) u + (beta + gamma/x) u(n+1) = delta/2u(xx),where j, alpha, beta, and gamma are nonnegative constants and n is a positive integer, are obtained. These solutions are asymptotic to the (linear) old-age solution for large time and extend the validity of the latter so as to cover the entire time regime starting where the originally sharp shock has become sufficiently thick and the viscous effects are felt in the entire N wave.

Nonlinear Enzyme Kinetics Can Lead to High Metabolic Flux Control Coefficients: Implications for the Evolution of Dominance

In a classic study, Kacser & Burns (1981, Genetics 97, 639-666) demonstrated that given certain plausible assumptions, the flux in a metabolic pathway was more or less indifferent to the activity of any of the enzymes in the pathway taken singly. It was inferred from this that the observed dominance of most wild-type alleles with respect to loss-of-function mutations did not require an adaptive, meaning selectionist, explanation. Cornish-Bowden (1987, J. theor. Biol. 125, 333-338) showed that the Kacser-Burns inference was not valid when substrate concentrations were large relative to the relevant Michaelis constants. We find that in a randomly constructed functional pathway, even when substrate levels are small, one can expect high values of control coefficients for metabolic flux in the presence of significant nonlinearities as exemplified by enzymes with Hill coefficients ranging from two to six, or by the existence of oscillatory loops. Under these conditions the flux can be quite sensitive to changes in enzyme activity as might be caused by inactivating one of the two alleles in a diploid. Therefore, the phenomenon of dominance cannot be a trivial ''default'' consequence of physiology but must be intimately linked to the manner in which metabolic networks have been moulded by natural selection.

Synthesis of some copper(II)-chelating (dialkylamino)pyridine amphiphiles and evaluation of their esterolytic capacities in cationic micellar media

Three new (dialkylamino)pyridine (DAAP)-based ligand amphiphiles 3-5 have been synthesized. All of the compounds possess a metal ion binding subunit in the form of a 2,6-disubstituted DAAP moiety. In addition, at least one ortho-CH2OH substituent is present in all the ligands. Complex formation by these ligands with various metal ions were examined under micellar conditions, but only complexes with Cu(II) ions showed kinetically potent esterolytic capacities under micellar conditions. Complexes with Cu(II) were prepared in host comicellar cetyltrimethylammonium bromide (CTABr) media at pH 7.6. Individual complexes were characterized by UV-visible absorption spectroscopy and electron paramagnetic resonance spectroscopy. These metallomicelles speed the cleavage of the substrates p-nitrophenyl hexanoate or p-nitrophenyl diphenyl phosphate. To ascertain the nature of the active esterolytic species, the stoichiometries of the respective Cu(II) complexes were determined from the kinetic version of Job's plot. In all the instances, 2:1 complex ligand/Cu(II) ion are the most kinetically competent species. The apparent pK(a) values of the Cu(II)-coordinated hydroxyl groups of the ligands 3, 4, and 5, in the comicellar aggregate, are 7.8, 8.0, and 8.0, respectively, as estimated from the rate constant vs pH: profiles of the ester cleavage reactions. The nucleophilic metallomicellar reagents and the second-order "catalytic" rate constants toward esterolysis of the substrate p-nitrophenyl hexanoate (at 25 degrees C, pH 7.6) are 37.5 for 3, 11.4 for 4, and 13.8 for 5. All catalytic systems comprising the coaggregates of 3, 4, or 5 and CTABr demonstrate turnover behavior in the presence of excess substrate.

The high temperature mechanical characteristics of superplastic 3 mol% yttria stabilized zirconia

A detailed study was undertaken to characterize the deformation behavior of a superplastic 3 mol% yttria-stabilized tetragonal zirconia (3YTZ) over a wide range of strain rates, temperatures and grain sizes. The experimental data were analyzed in terms of the following equation for high temperature deformation: Image Full-size image ∞ σn d−pexp(−Q/RT), where Image Full-size image is the strain rate, σ is the flow stress, d is the grain size, Q is the activation energy, R is the gas constant, T is the absolute temperature, and n and p are constants termed the stress exponent and the inverse grain size exponent, respectively. The experimental data over a wide range of stresses revealed a transition in stress exponent. Deformation in the low and high stress regions was associated with n not, vert, similar 3 and p not, vert, similar 1, and n not, vert, similar 2 and p not, vert, similar 3, respectively. The transition stress between the two regions decreased with increasing grain size. The activation energy was similar for both regions with a value of not, vert, similar 550 kJ mol−1. Microstructural measurements revealed that grains remained essentially equiaxed after the accumulation of large strains, and very limited concurrent grain growths occurred in most experiments. Assessment of possible rate controlling creep mechanisms and comparison with previous studied indicate that in the n not, vert, similar 2 region, deformation occurs by a grain boundary sliding process whose rate is independent of impurity content. Deformation in the n not, vert, similar 3 region is controlled by an interface reaction that is highly sensitive to impurity content. It is concluded that an increase in impurity content increases yttrium segregation to grain boundaries, which enhances the rate of the interface reaction, thereby decreasing the apparent transition stress between the n not, vert, similar 2 and n not, vert, similar 3 regions. This unified approach incorporating two sequential mechanisms can rationalize many of the apparently dissimilar results that have been reported previously for deformation of 3YTZ.

Colossal dielectric behavior of semiconducting Sr2TiMnO6 ceramics

Manganitelike double perovskite Sr2TiMnO6 (STMO) ceramics fabricated from the powders synthesized via the solid-state reaction route, exhibited dielectric constants as high as similar to 10(5) in the low frequency range (100 Hz-10 kHz) at room temperature. The Maxwell-Wagner type of relaxation mechanism was found to be more appropriate to rationalize such high dielectric constant values akin to that observed in materials such as KxTiyNi(1-x-y)O and CaCu3Ti4O12. The dielectric measurements carried out on the samples with different thicknesses and electrode materials reflected the influence of extrinsic effects. The impedance studies (100 Hz-10 MHz) in the 180-300 K temperature range revealed the presence of two dielectric relaxations corresponding to the grain boundary and the electrode. The dielectric response of the grain boundary was found to be weakly dependent on the dc bias field (up to 11 V/cm). However, owing to the electrode polarization, the applied ac/dc field had significant effect on the low frequency dielectric response. At low temperatures (100-180 K), the dc conductivity of STMO followed a variable range hopping behavior. Above 180 K, it followed the Arrhenius behavior because of the thermally activated conduction process. The bulk conductivity relaxation owing to the localized hopping of charge carriers obeyed the typical universal dielectric response.