Roton excitations in Bose–Einstein condensates and a fluid–solid transition

Several authors have recently discussed the existence of roton excitations in Bose–Einstein condensates (BECs) and considered how a roton dip in the dispersion curve of elementary excitations may be related to the formation of a spatially modulated ground state. Here attention is drawn to a theoretical study of Minguzzi et al. on interatomic correlations in a BEC from dipole–dipole interactions induced by laser light of increasing intensity. Attractive interactions in superfluid ⁴He and repulsive interactions in ‘untuned’ BECs are then compared and contrasted, the experiments of Woods and Cowley and of Greiner et al. providing the focus respectively. It is stressed that, contrary to a very recent assertion by Nazario and Santiago, ⁴He is crucially different from BECs at the lowest temperatures.     

Anatase–silica composite aerogels: a nanoparticle-based approach

Herein we present the synthesis of anatase–silica aerogels based on the controlled gelation of preformed nanoparticle mixtures. The monolithic aerogels with macroscopic dimensions show large specific surface areas, and high and uniform porosities. The major advantage of such a particle-based approach is the great flexibility in pre-defining the compositional and structural features of the final aerogels before the gelation process by fine-tuning the properties of the titania and silica building blocks (e.g., size, composition and crystallinity) and their relative ratio in the dispersion. Specific surface functionalization enables control over the interaction between the nanoparticles and thus over their distribution in the aerogel. Positively charged titania nanoparticles are co-assembled with negatively charged Stoeber particles, resulting in a binary aerogel with a crystalline anatase and amorphous silica framework directly after supercritical drying without any calcination step. Titania–silica aerogels combine the photocatalytic activity of the anatase nanoparticles with the extensive silica chemistry available for silica surface functionalization.     

Recombination in complex systems – an analytical approach

A new analytical model is proposed to describe the kinetics of trapping and recombination of charge carriers in complex systems with an arbitrary spatial distribution of traps and recombination centres. The structural properties of a material are described by two functions Γ_m and Γ_n irrespective of the thermal history of the sample. A simple method is proposed to determine the function Γ_m from simultaneous thermoluminescence (TL) and thermally stimulated conductivity (TSC) measurements.     

UNIQUAC correlation of liquid–liquid equilibrium in systems involving ionic liquids: The DFT–PCM approach. Part II

In this work, new UNIQUAC structural parameters r and q for the ionic liquids were determined by quantum chemistry calculations performed with the Gaussian 03 and GAMESS 7.1 packages, including the density functional theory (DFT) for the optimization of the structures and the polarizable continuum method (PCM) for the calculation of molecular areas and volumes. Data liquid–liquid equilibrium (LLE) of 41 ternary systems involving 15 different ionic liquids, comprising 379 experimental tie-lines, was correlated by the UNIQUAC model for the activity coefficient. The results, expressed by deviations between experimental and calculated compositions, are very satisfactory, with deviation values about 1.93%.     

Range,strength and anisotropy of intermolecular forces in atom–molecule systems: an atom–bond pairwise additivity approach

A new method is proposed to calculate bond energies and equilibrium distances in atom–molecule van der Waals complexes which arises from a balancing between long-range attraction and asymptotic tail of the repulsion. The method, based on correlation formulas between the polarizability of the interacting partners and the main interaction parameters, is an extension of an approach originally developed for atom–atom cases. The basic idea exploits the concept of bond polarizability additivity to represent both the molecular repulsion, in terms of a size which is mainly ascribed to the molecular bonds nearest to the probe atom, and the molecular attraction as due to multi-dispersion centers delocalized on the molecular frame. The method, mainly tested on hydrocarbon–rare gas complexes, can be considered as the starting point for the study of systems of higher complexity.     

Analysis of homogeneous–heterogeneous reactions in a micropolar nanofluid past a nonlinear stretching surface: semi-analytical approach

In the present scenario, the application of reactive agents in industries plays a vital role in the production processes of various materials such as paper production, drawing of wires, etc. Keeping in mind it is necessary to discuss the application of heterogeneous and homogeneous chemical reactions in a micropolar nanofluid flow over a stretching surface where the sheet is considered to be nonlinear. In addition to that, the inclusion of heat generation/absorption in the energy equation of an electrically conducting fluid also affects the fluid flow phenomena. In the present analysis, the Maxwell model thermal conductive is considered with Fe₃O₄, CuO nanoparticles, and water is treated as base fluid. It is very much transparent that the nonlinear dimensional form of the PDEs gets transformed into ODEs and a semi-analytical approach is employed, i.e., Adomian decomposition method (ADM) for those transformed ODEs. The computation for several characterizing parameters is obtained using the mathematical package MAPLE and these are displayed via graphs and tables. An excellent concurrence with the earlier established result is found which validates the result with the current methodology.

     

Regulation of a phase structure at the interface in epoxy–polysulfone systems

Russian Chemical Bulletin - The influence of technological parameters on the formation of an interfacial diffusion region and a gradient heterogeneous structure during a curing reaction of...     

Phase equilibria in polymer–solvent systems: Progress in the field of fibers

The progress in phase equilibria of polymer-solvent systems is briefly reviewed. The features of phase diagrams intended for production of fibers with high strength, deformation, and thermal properties are considered. Some attention is given to the fundamental role of S.P. Papkov in the creation and development of scientific concepts on phase equilibria in fiber-forming polymers involving solvents.     

A Pressure-Induced Inverse Order–Disorder Transition in Double Perovskites

Given the consensus that pressure improves cation ordering in most of known materials, a discovery of pressure-induced disordering could require recognition of an order–disorder transition in solid-state physics/chemistry and geophysics. Double perovskites Y₂CoIrO₆ and Y₂CoRuO₆ polymorphs synthesized at 0, 6, and 15 GPa show B-site ordering, partial ordering, and disordering, respectively, accompanied by lattice compression and crystal structure alteration from monoclinic to orthorhombic symmetry. Correspondingly, the long-range ferrimagnetic ordering in the B-site ordered samples are gradually overwhelmed by B-site disorder. Theoretical calculations suggest that unusual unit-cell compressions under external pressures unexpectedly stabilize the disordered phases of Y₂CoIrO₆ and Y₂CoRuO₆.     

Electric Double Layer on a Renewable Liquid (Cd–Ga) Electrode in Acetonitrile Solutions

Russian Journal of Electrochemistry - Parameters that characterize the electric double layer structure on a renewable liquid (Cd–Ga) (0.3 at % Cd) electrode in solutions of surface-inactive...     

Enantiopure 2-sulfinylbuta-1,3-dienes in Diels–Alder cycloadditions: a stereoselective approach to an azasteroidal skeleton

The synthesis of enantiopure 4-[1-(alkylsulfinyl)vinyl]-1,2-dihydronaphthalenes and their Diels–Alder reactions are described. Cycloadditions with N-phenylmaleimide occur under thermal conditions, very slowly but with notable stereoselection, giving in each case just one of the two endo adducts in high yield. The obtained 16-azasteroid derivatives undergo chiral auxiliary removal in the presence of TMSI.     

Electrical Double Layer Structure in Surface-Inactive Electrolytes on a Liquid Cd–Ga Electrode in Methanol and Propylene Carbonate

Differential capacitance curves and potentials of zero charge are obtained for liquid Cd–Ga electrodes in methanol and propylene carbonate solutions of a surface-inactive electrolyte. It is found that double-layer characteristics of the Cd–Ga electrode differ from those of a Ga electrode both in nonaqueous solutions and in water. The lyophilic nature of the Cd–Ga electrode, relative to methanol and propylene carbonate, is shown to approach that of the In–Ga electrode. In the absence of a metal–solvent chemisorption interaction, the difference between reciprocal metallic capacitances for Cd–Ga and Hg electrodes is independent of the solvent nature. The chemisorption interaction between the solvents and Cd–Ga, Ga, and In–Ga electrodes increases with the solvents' donor number.     

Use of D–T-produced fast neutrons for in vivo body composition analysis: a reference method for nutritional assessment in the elderly

Body composition has become the main outcome of many nutritional intervention studies including osteoporosis, malnutrition, obesity, AIDS, and aging. Traditional indirect body composition methods developed with healthy young adults do not apply to the elderly or diseased. Fast neutron activation (for N and P) and neutron inelastic scattering (for C and O) are used to assess in vivo elements characteristic of specific body compartments. Non-bone phosphorus for muscle is measured by the ³¹P(n,)²⁸Al reaction, and nitrogen for protein via the ¹⁴N(n,2n)¹³N fast neutron reaction. Inelastic neutron scattering is used to measure total body carbon and oxygen. Body fat is derived from carbon after correcting for contributions from protein, bone, and glycogen. Carbon-to-oxygen ratio (C/O) is used to measure the distribution of fat and lean tissue in the body and to monitor small changes of lean mass. A sealed, D–T neutron generator is used for the production of fast neutrons. Carbon and oxygen mass and their ratio are measured in vivo at a radiation exposure of less than 0.06 mSv. Gamma-ray spectra are collected using large BGO detectors and analyzed for the 4.43 MeV state of carbon and 6.13 MeV state of oxygen, simultaneously with the irradiation. P and N analysis by delayed fast neutron activation is performed by transferring the patient to a shielded room equipped with an array of NaI(Tl) detectors. A combination of measurements makes possible the assessment of the quality of fat-free mass. The neutron generator system is used to evaluate the efficacy of new treatments, to study mechanisms of lean tissue depletion with aging, and to investigate methods for preserving function and quality of life in the elderly. It is also used as a reference method for the validation of portable instruments of nutritional assessment.