Influence of the electric field on a particle in a space with a disclination

We consider a quantum particle in a space with a linear topological defect, i.e., disclination. The effect of the uniform electric field in this space, on the particle, is shown to cause a translation of the wave function. In addition, the electric field is not found to be affected by the defect. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

On the hydrodynamics of a superfluid with a three-particle “condensate”

Abstract

Since 1974 there have been serious experimental and also theoretical pointers to the possibility that no Bose condensation occurs in superfluid He⁴. Evans presented a theoretical argument against a condesate, suggesting a “pairing” model of superfluid helium. As yet, experiment connot decide if the concept of a one-particle condensate can be replaced by the idea of a two-particle condensate. March and Galasiewicz have argued that, if there is no one-particle condensate in He⁴, a ground state wave function cannot be built from a product of pairs but must fundamentally include three-particle correlations at least. So the idea of a three (not two) particle condensate seems worth some attention. It is demonstrated here that assuming a three-particle condensate we can regain from microscopic theory the Landau hydrodynamic equation for the superfluid velocity.     

On the use of a focusing spectrometer with a Cambridge Electron Probe

Summary A focusing X-ray spectrometer has been installed on a Cambridge Electron Probe. Significant improvements in peak intensities, peak to background ratios and resolution were obtained and the quantitative capabilities of the instrument correspondingly enhanced. The difficulties encountered due to increased focusing sensitivity are discussed.

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Zusammenfassung Ein fokussierendes Röntgenstrahlenspektrometer wurde in einem Cambridge-Elektronenstrahlmikroanalysator eingebaut. Damit ergaben sich signifikante Verbesserungen der Peak-Höhen, der Peak-Hintergrundverhältnisse und der Auflösung. Die quantitative Leistung des Instruments wurde damit entsprechend vergrößert. Die sich aus der erhöhten Empfindlichkeit ergebenden Schwierigkeiten wurden diskutiert.

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Résumé On a fixé un spectromètre à rayons X à focalisation une microsonde electronic Cambridge. Des progrès significatifs ont été obtenus en matière de maximums d'intensité, de rapports de pointes à fond et de résolution; les possibilités quantitatives de l'instrument s'en trouvent accrues en conséquence. Les difficultés qui découlent de la délicatesse de focalisation du spectromètre lors de son emploi avec des cristaux de haute résolution sont passées en revue.

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Presented in part at the Second National Conference on Electron Microprobe Analysis, Boston, Mass., June 14–16, 1967.     

A disilapentalene and a stable diradical from the reaction of a dilithiosilole with a dichlorocyclopropene

The reaction of 1,1-dilithio-2,3,4,5-tetraphenylsilole (1) with 1,1-dichloro-2,3-diphenylcyclopropene (2) leads to the novel 1,4-disila-1,4-dihydropentalene (4), as well as an exceptionally stable diradical for which the structure 3 is suggested. The diradical is unreactive toward water, methanol, and chloroform; upon heating it transforms into 4. Structure 3 for the paramagnetic species is proposed on the basis of EPR data and theoretical calculations. The trans-trans isomer of diradical 3 was calculated to be more stable than its cis-cis isomer. The strong and stable EPR signal in the reaction mixture is probably due to the trans-trans isomer of diradical 3 in the triplet state. A reaction scheme describing the formation of 3 and 4 is presented.     

Luminophores of the azlactone series with a difluoromethylsulfonyl group

Organic luminophores of the azlactone series that contain a strong electronacceptor substituent, viz., a difluoromethylsulfonyl group, were synthesized. The significant effect of the electronic nature of the substituents on the frequencies of the stretching vibrations of the CO and C=N groups was demonstrated, and the trans configuration of the investigated compounds was confirmed. The introduction of a difluoromethylsulfonyl group in the azlactone molecule promotes the development of intense fluorescence in solutions at room temperature. The character of the substituents and their mutual orientation have a substantial effect on the optical characteristics.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1600–1603, December, 1981.     

On the reaction of glycidol with a secondary amine

The attempt was made to prepare an ionene like base by reacting diethylamine (DEA) with glycidol (Gly). It turned out that the reaction proceeds via two steps witch differ significantly. When the rate of added DEA to Gly in bulk becomes 1 : 13 the temperature jumps up suddenly. The product proved to be a water soluble oligomer having a molecular weight of M_n > 465 g/mol, a nitrogen content of 1.06%, and pH 9.5. Based on the ¹³C NMR and IR spectra, schemes of polyreactions were proposed according to which amine groups containing moieties of low molecular weight are formed. These subsequently function as initiators of Gly homopolymerization according to a chain mechanism.     

The strength with which a peptide group can form a hydrogen bond varies with the internal conformation of the polypeptide chain

The strength of the H-bond formed between a dipeptide and a proton acceptor molecule is assessed by correlated ab initio quantum calculations for a broad range of different conformations of the dipeptide. The H-bond energy is very sensitive to the internal (phi,psi) angles, even when the geometry of the H-bond does not vary significantly from one conformation to another. This result indicates that the peptide NH is a much less potent proton donor in certain conformations than in others. In particular, extended conformations of a polypeptide are capable of only weak H-bonds. Thus, the interstrand NH...O H-bonds in parallel and antiparallel beta-sheets are expected to be significantly weaker than those found in other conformations, such as helices, ribbons, and beta-bends, even if the H-bond geometries are similar.     

Calculation procedure for the kinetic analysis of a reaction with a thermal effect

A calculation procedure for the numerical analysis of a non-isothermal reaction taking place at constant pressure is described. The procedure is used to calculate the temperature dependence of the ignition delay of H₂ oxidation using a 44-reaction mechanism.

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Описывается алгоритм численного решения прямой кинетической задачи с учетом теплового эффекто реакции, протекающей при постоянном давлении. Применение метода иллюстрируется расчетом температурной зависимости задержки воспламенения водорода для кинетической схемы, включающей 44 элементарные стадии.

     

Properties of a liquid crystalline polyester with a mesogen containing the bicyclooctylene ring

A liquid crystalline polyester with a decamethyene flexible spacer and a mesogenic unit containing a central 1,4-bicyclo(2,2,2)octylene ring was prepared for comparison with the equivalent polymer containing a central p-phenylene ring in the mesogen. Both polymers formed a nematic phase on melting, and as expected, the former had a much lower isotropization temperature than the latter. The polymer containing the bicyclooctylene ring, however, showed a batonnet texture, indicative of a smectic phase, at a temperature above that of the nematic state, especially on cooling from the isotropic melt.     

Solution of the kinetic equation for a semiconductor with a narrow conduction band

Kinetic coefficients are calculated for a rectangular lattice and for a planar face-centered one. Analytic expressions are derived for the kinetic transport coefficients, which become the usual expressions from the ordinary theory of semiconductors if the bands are broad. The effects of narrow bands are considered.     

Spectroscopic characterization of a molecule with a weak bond: the BrOO radical

Pure rotational spectra of the BrOO radical for the 79Br and 81Br isotopomers have been observed using a Fourier transform microwave spectrometer. The radical was produced in a supersonic jet by discharging a mixture gas containing bromine and oxygen diluted in argon. A-type rotational transitions are observed for N" = 1-5, K(a) = 0 with spin doublings and hyperfine splittings due to the nuclear spin of the bromine atom. High-level ab initio calculations by RCCSD(T) and MRCI have also been performed, and results are compared with the experimental data. Molecular structure of BrOO has been discussed based on the present experimental data, supplemented by the tendency among the halogen peroxide series and the results of the ab initio calculations; the Br-O bond is found to be anomalously long and weak. Systematic comparisons with other halogen peroxides have revealed anomalous nature of the X-O (X = halogen atom) bonds for this series of radicals.     

Investigation of the surface of a polymeric adsorbent with pyrene as a fluorescence probe

Pyrene was used as a fluorescence probe to study the surface and pyrene/surface interactions which occur on a polypropylene adsorbent. The surface interaction between this adsorbent and pyrene was found to be very similar to that found for pyrene in hydrocarbon solvents. In contrast to the surfaces of other types of adsorbents, the polypropylene surface presents an energetically homogeneous surface to adsorbing molecules. Consequently, adsorption takes place essentially randomly as opposed to being associated with activated sites.     

Synthesis of a new bluish pigment from the reaction of a methylpyranoanthocyanin with sinapaldehyde

The synthesis of a new pigment with a bluish color was obtained from the reaction of methylpyranomalvidin-3-glucoside with sinapaldehyde and its formation mechanism seems to involve a charge-transfer reaction pathway. The structure of this compound was fully characterized by LC/DAD-MS and NMR. Its equilibrium forms present in water at different pH values and the respective ionization constants were determined by UV-visible spectroscopy. The results revealed the presence of three equilibria involving only deprotonation reactions at the 7-OH and 4′-OH positions of the pyranoanthocyanin moiety and at the 4′″-OH of the syringol moiety (pK_a1 = 3.64 ± 0.01; pK_a2 = 8.02 ± 0.01; pK_a3 = 11.19 ± 0.01).     

Determination of the surface anchoring potential of a nematic in contact with a substrate

We have developed a method for determining the surface anchoring potential for nematics in contact with a substrate that provides director alignment. Our main result is that the surface torque and hence the anchoring potential may be determined from either dielectric or optical phase response of a nematic undergoing a Freedericksz transition. The method is based on the Frank-Oseen continuum theory, and makes no assumptions about the functional form of the potential. We have measured the surface anchoring potential of two types of substrate in contact with the nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl. The surfaces were ITO-coated float glass, coated either with obliquely evaporated SiO or a buffed polymer film. Comparison of the results obtained from capacitance and optical measurements provides an estimate of the goodness of the method.     

Study of the aggregation behavior of a π-conjugated dendrimer with a twisted core

A dendrimer having phenylene vinylene and phenylene ethynylene moieties, a twisted core, and eighteen chiral centers on the periphery has been prepared in high yield by using Sonogashira and Horner–Wadsworth–Emmons reactions. UV–visible and fluorescence spectra and circular dichroism measurements have been envisaged to study the aggregation behavior.     

Effect of Pulsed Ultrasonic Field on the Filling of a Capillary with a Liquid

The filling of capillaries with liquids of various viscosity in the ultrasonic field is experimentally investigated. It is shown that the breakage of the meniscus and the fast intense dissolution of the gas that filled the capillary occur at the threshold switching-on of the ultrasonic field in low-viscosity liquids. This causes the residual (after switching-off of the ultrasound) filling of the capillaries with a low-viscosity liquid. It is established that the residual filling of capillaries is observed only with the pressure amplitudes P _m exceeding some critical value; the residual filling increases with P _m and disappears as cavitation is induced below the capillary end. It is shown that pulsed regime is optimal for the ultrasonication.     

Evaluation of the adsorption trends of a low molecular-weight polyelectrolyte with a site-binding model

The site-binding model is very useful for describing the adsorption of ions and small ionized molecules. It has been slightly modified to include multi-site adsorption of larger molecules such as oligomers and low molecular weight polyelectrolytes. We describe alterations of the classical model and the results of calculations for adsorption of polyacrylic acid onto titanium dioxide as an example. The triple layer model is used to relate charge densities to interfacial potential profiles. Comparison between adsorption trends and the surface layer composition as a function of pH and ionic strength demonstrates the prominent influence of ions binding in the adsorption process. The site-binding model makes it easy to simulate the ions displacement associated with polyelectrolyte adsorption. Strongly bound electrolyte anions prevent polyacrylic acid from adsorbing, and, in contrast, electrostatic screening due to cation condensation makes it easier. Calculations of the pH change in the solution, due to adsorption, are also made by comparing ionization ratios of both the surface and polymer units in the adsorbed layer and before adsorption. Trends in electrokinetic potentials as a function of the solution's parameters are evaluated assuming the identity of the shearing surface and the inner boundary of the diffuse layer. All data compare well with experimental values. The very good agreement betwen the experiment and model calculations supports the fact that (small) polyelectrolyte molecules adsorb essentially flat on the surface.