Mechanism of enhanced positronium formation in low-temperature polymers

An enhanced positronium (Ps) formation in low-temperature polymers has been widely observed. The additional positronium formation is due to shallow trapped electrons in them. Positron annihilation lifetime spectroscopy was applied to investigate the Ps formation in a series of polymers, such as low-density polyethylene, ethylene-methyl methacrylate copolymers with various methyl methacrylate contents, and pure poly(methyl methacrylate) at low temperature. An analysis of the experimental data based on simple kinetic equations enables one to understand the Ps formation mechanism in polymers during low-temperature positron annihilation experiments as functions of the temperature and elapsed time. Good fittings of the experimental data were obtained. The fitting parameters seemed to show clear physical meanings.     

Density,viscosity, and excess properties of aqueous solution of diethylenetriamine (DETA)

Densities and viscosities of aqueous DETA solutions were measured for the entire concentration range and for the temperature range between (293.15 and 363.15) K. The excess molar volume was determined from the experimental density data whereas the excess Gibbs free energy and the excess entropy of flow were determined from the experimental viscosity data by implementing the theory of rate processes of Eyring. A Redlich–Kister equation was applied to correlate the excess properties such as: the excess molar volume and the excess Gibbs free energy of flow as functions of the DETA mole fraction and temperature. The results showed that the model agree very well with the experimental data. In comparison with AEEA and DEA, the excess properties of DETA are higher than these amines.     

The Kirkwood-Buff integrals for one-component liquids

The Kirkwood-Buff integrals (KBIs) for one-component systems are calculated from either the pair correlation functions or from experimental macroscopic quantities. As in the case of mixtures, the KBIs provide important information on the local densities around a molecule. In the low density limit (rho-->0) one can extract from the KBI some information on the strength of the intermolecular forces. No such information may be extracted from the KBIs at higher densities. We used experimental data on densities and isothermal compressibilities to calculate the KBIs for various liquids ranging from inert molecules, to hydrocarbons, alcohols, and liquid water.     

Radial distribution functions of sub- and supercritical water according to the nonempirical molecular dynamics data

The Car-Parrinello nonempirical molecular dynamics method was used to obtain radial distribution functions of water at the critical point and in six sub- and supercritical states. The influence of changes in state parameters on radial distribution functions was found to be much stronger close to the saturation curve than in the region of high pressures. The reproduction of radial distribution functions by classical and quantum molecular dynamics methods was analyzed. The positions of radial distribution peaks and the ratios between their heights were found to be almost identical and to correspond to the experimental data, but, as concerns quantitative estimates of peak heights, the same contradictions are observed as between the data of various experimental studies.     

Extraction of site–site bridge functions and effective pair potentials from simulations of polar molecular liquids

We develop an efficient method to extract site–site bridge functions from molecular simulations. The method is based on the inverse solution of the reference site interaction model. Using the exact long‐range asymptotics of site–site direct correlation functions defined by the site–site Ornstein–Zernike equations, we regularize the ill‐posed inverse problem, and then calculate site–site bridge functions and effective pair potentials for ambient water, methanol, and ethanol. We have tested the proposed algorithm and checked its performance. Our study has revealed various peculiarities of the site–site bridge functions, such as long‐range behavior, strong dependence on the electrostatic interactions. Using the obtained data, we have calculated thermodynamic properties of the solvents, namely, isothermal compressibility, internal energy, and Kirkwood‐Buff integrals. The obtained values are in excellent agreement not only with molecular simulations but also with available experimental data. Further extensions of the method are discussed. © 2014 Wiley Periodicals, Inc.     

Numerical methods for inverse problems in electrooptics of polydisperse colloids

In this paper we propose a new method for the determination of the distribution of electrical and geometrical particle parameters based on electrooptical experimental data. The electrooptical method leads to the solution of inverse ill-posed problems. The main equations for the determination of the distribution of particles on these parameters are presented. To find out the distribution functions from the electrooptical experimental data one has to solve the first-kind Fredholm integral equation corresponding to the problem under study. The proposed method of its solution is based on the penalty functions method. The results of modelling that let us compare the various numerical methods are presented.     

Biosorption of As3+ Ions Using Ternary Microspheres of Chitosan,Yeast, and Gelatin: A Dynamic and Equilibrium Investigation

Ternary biopolymeric microspheres of chitosan, yeast and gelatin were prepared and characterized by FTIR spectral analysis, particle size measurements, and scanning electron micrograph techniques. The prepared microspheres were investigated for static and dynamic studies of adsorption of As⁺³ ions onto the microspheres surfaces at fixed pH and ionic strength of the aqueous solution.The adsorption data were applied to Langmuir and Freundlich isotherm equations and various static parameters were calculated. The dynamic nature of adsorption was quantified in terms of several kinetic constants such as rate constants for adsorption, Lagergreen rate constant, inter particle diffusion rate constant and pore diffusion coefficient. The influence of various experimental parameters such as solid to liquid ratio, pH, temperature, and chemical composition of biopolymeric microspheres were investigated on the adsorption of arsenic ion and various thermodynamic parameter were also calculated.     

Inverse Monte Carlo procedure for conformation determination of macromolecules

A novel numerical method for determining the conformational structure of macromolecules is applied to idealized biomacromolecules in solution. The method computes effective inter-residue interaction potentials solely from the corresponding radial distribution functions, such as would be obtained from experimental data. The interaction potentials generate conformational ensembles that reproduce thermodynamic properties of the macromolecule (mean energy and heat capacity) in addition to the target radial distribution functions. As an evaluation of its utility in structure determination, we apply the method to a homopolymer and a heteropolymer model of a three-helix bundle protein [Zhou, Y.; Karplus, M. Proc Natl Acad Sci USA 1997, 94, 14429; Zhou, Y. et al. J Chem Phys 1997, 107, 10691] at various thermodynamic state points, including the ordered globule, disordered globule, and random coil states.     

Modeling adsorption of colloids and proteins

Recent developments in the modeling of particle and protein adsorption kinetics on solid surfaces are discussed. Emphasis is focused on the coarse-grained methods, where protein molecules are treated as particles having a regular shape (spheres, spheroids) or a system of spherical beads of various sizes. Using such approaches hydrodynamic radii and diffusion coefficients of protein molecules are calculated in an exact way using the linear Stokes equation. Additionally, the surface blocking functions and jamming coverages for such molecule shapes are determined using the random sequential adsorption simulations. Theoretical results obtained in this way for various molecule shapes, including the bead models of fibrinogen are discussed. Knowing the jamming coverage and blocking functions one can formulate boundary conditions for bulk transport equations. Solutions of these equations for the convection and diffusion-controlled transport are presented. These theoretical predictions proved adequate for interpreting experimental data obtained for fibrinogen using AFM, ellipsometry and fluorescence methods. It is, therefore, concluded that these coarse grained approaches combined with solutions of the continuity equation can be efficiently used for quantitatively predicting protein adsorption kinetics for the time scale met under practical situations.     

Chain scission of butyl rubber by nitrogen dioxide. II. Photo-oxidation as function of nitrogen dioxide,oxygen pressure,and temperature

Studies of chain scission of butyl rubber (1.75% by weight of isoprene) have been extended. Experiments showing chain scission as function of various oxygen and nitrogen pressures, temperatures, and near-ultraviolet light intensity are presented. The experimental data agree with the mechanisms assumed in previous work or with elaborations of such mechanisms to include additional factors (ultraviolet radiation etc.). NO₂ retards chain scission in presence of near-ultraviolet light. Photo-oxidation in presence of relatively high and low nitrogen dioxide pressures, respectively, show experimental curves of opposite curvature; these data have also been evaluated in terms of méchanism. Arrhenius equations are presented for experiments related to the different reaction mechanisms.     

Ab initio calculation of some low-lying electronic excited states of methane

The energies of some low-lying electronic excited states of methane are calculated by using wave functions built up in terms of plane waves modulated by multicenter Gaussian factors. The wave functions of the various states are evaluated by a two steps iterative process. In the first step, each excited orbital is determined while keeping all other rigid; in the second, rearrangement effects are introduced. Final results are in good agreement with experimental data and allow to enhance an assignement hypothesis for the first electronic transitions.     

Der einfluβ der molmassenverteilung und der kettenabstandsverteilung auf die streufunktion von polymeren in lösung

Universal expressions of the scattering function for coils with uniform and non-uniform expansion, gaussian and non-gaussian chain segment distribution functions and various types of molar mass distributions are given. Facilities to determine the parameters of the functions are discussed. Comparison of the calculated scattering functions with experimental data, for vinyl-polymers in good and poor solvents and for cellulose derivatives in solution, lead to the following statements: (1) Up to now light scattering measurements do not have the precision necessary to predict the form of the chain segment distribution function. Nevertheless measurements on vinyl-polymers in good solvents indicate non-gaussian chain segment distribution functions. (2) The experimental determined scattering function for vinyl-polymers in poor solvents and cellulose derivatives in solution correspond to the calculated scattering function for coils with uniform expansion and gaussian chain segment distribution function within experimental error.     

Chemical, structural, and thermal properties of Zn(II)-Cr(III) layered double hydroxides intercalated with sulfated and sulfonated surfactants

Zn(II)-Cr(III)-LDHs (layered double hydroxides) containing sulfated or sulfonated surfactants as the interlamellar anion were synthesized by the coprecipitation method. The syntheses were conducted under various different experimental conditions, such as the Zn : Cr ratio, pH, and aging time. In each of the prepared materials, unlike previously reported data, the interlayer anion arrangement did not change, being consistent with a perpendicular monolayer. The thermal decomposition process of the prepared materials was studied by a set of analysis methods, such as TG/DTA, TG/MS, PXRD, and FT-IR. From the results obtained it was possible to conclude that, in an air atmosphere, the anions decomposed by a partial combustion, leading to the formation of sulfide. The results also showed that sulfonated surfactants containing LDHs are much more stable than those containing sulfated surfactants. A mechanism was proposed for the thermal decomposition of such LDHs based on the experimental results.     

Topological data analysis: A promising big data exploration tool in biology,analytical chemistry and physical chemistry

An important feature of experimental science is that data of various kinds is being produced at an unprecedented rate. This is mainly due to the development of new instrumental concepts and experimental methodologies. It is also clear that the nature of acquired data is significantly different. Indeed in every areas of science, data take the form of always bigger tables, where all but a few of the columns (i.e. variables) turn out to be irrelevant to the questions of interest, and further that we do not necessary know which coordinates are the interesting ones. Big data in our lab of biology, analytical chemistry or physical chemistry is a future that might be closer than any of us suppose. It is in this sense that new tools have to be developed in order to explore and valorize such data sets. Topological data analysis (TDA) is one of these. It was developed recently by topologists who discovered that topological concept could be useful for data analysis. The main objective of this paper is to answer the question why topology is well suited for the analysis of big data set in many areas and even more efficient than conventional data analysis methods. Raman analysis of single bacteria should be providing a good opportunity to demonstrate the potential of TDA for the exploration of various spectroscopic data sets considering different experimental conditions (with high noise level, with/without spectral preprocessing, with wavelength shift, with different spectral resolution, with missing data).     

Theoretical Calculations of Dipole Moments,Polarizabilities, and Hyperpolarizabilities of HF,OCS, O3, CH3F,and CH3Cl by Local Density Approximation

The dipole moments, polarizabilities, and hyperpolarizabilities of five molecules (HF, OCS, O₃, CH₃F, and CH₃Cl) have been computed at their experimental equilibrium geometries using the deMon density functional program. For molecules of such sizes, we augmented the basis set of valence double-zeta plus polarization functions with field-induced polarization functions. Contamination of least-squares fitted parameters by higher-order hyperpolarizabilities have been greatly reduced by fitting the field-dependent dipole moments to eighth order polynomials using as many as 37 points per molecule. The results compare well with experiment.     

Theoretical study of isoelectronic systems: Diazomethane,ketene and allene

All-electron SCF –LCAO –MO computations for diazomethane, ketene and allene are presented. The basis functions are contracted Gaussian orbitals. Theoretical results are discussed and related to available experimental data.     

Test of the consistency of various linearized semiclassical initial value time correlation functions in application to inelastic neutron scattering from liquid para-hydrogen

The linearized approximation to the semiclassical initial value representation (LSC-IVR) is used to calculate time correlation functions relevant to the incoherent dynamic structure factor for inelastic neutron scattering from liquid para-hydrogen at 14 K. Various time correlations functions were used which, if evaluated exactly, would give identical results, but they do not because the LSC-IVR is approximate. Some of the correlation functions involve only linear operators, and others involve nonlinear operators. The consistency of the results obtained with the various time correlation functions thus provides a useful test of the accuracy of the LSC-IVR approximation and its ability to treat correlation functions involving both linear and nonlinear operators in realistic anharmonic systems. The good agreement of the results obtained from different correlation functions, their excellent behavior in the spectral moment tests based on the exact moment constraints, and their semiquantitative agreement with the inelastic neutron scattering experimental data all suggest that the LSC-IVR is indeed a good short-time approximation for quantum mechanical correlation functions.     

Transport Properties of Compact Clays: I. Conductivity and Permeability

Conductivity and permeability of model and natural clays have been studied experimentally. Local properties such as porosity and zeta potentials were measured as functions of the electrolyte solutions. Whenever possible, experimental data were compared to numerical data obtained for random packings of grains of arbitrary shape, and a good agreement was found between them.     

Potential functions of inversion of R2CO (R=H, F, Cl) molecules in the lowest excited electronic states

The inversion potentials of R₂CO (R=H, F, Cl) molecules in the lowest excited electronic states were determined from experimental data using various model potential functions and approximations for the kinetic energy operator of inversion motion. The estimates of the heights of the barriers to inversion and the equilibrium values of the inversion coordinate for the H₂CO molecule in the S₁ and T₁ states are fairly stable. The results for the F₂CO and Cl₂CO molecules are strongly dependent on the approximation used; for these molecules, the most reliable parameters of the potential functions were chosen. The problem of qualitative characteristics of the shape of inversion potentials is discussed using the results ofab initio quantum-chemical calculations of the molecules under study. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 645–651, April, 1999.