Analysis of shear flow alignment of nematic liquid crystals at low shear stress based on catastrophe theory

The low stress shear flow alignment of a nematic liquid crystal in the presence of strong anchoring at the boundaries is analysed. Layers with pretilted director orientation are taken into account. Two kinds of symmetric deformations are assumed. They differ in the director distribution in the vicinity of the boundaries. The analysis is carried out using an expansion of the free energy of the layer in powers of the maximum deformation angle. The results have qualitative character. The condition for the threshold behaviour and the stability of the solutions are discussed. The deformation may develop continuously or discontinuously. The transition between two kinds of deformation is predicted. The facts already known are confirmed and supplemented.     

Practical limitations of capillary gas chromatography

Glass capillary gas chromatography is a high resolution separation method which allows the qualitative and quantitative analysis of even complex mixtures, which may contain many components–also isomeric–in a wide range of volatilities, polarities and concentrations. The principal limitation of gas chromatographic application is given by an insufficient volatility of the species to be separated. Elevated temperatures have to be applied if the application range is to be extended and to achieve steep peak profiles, i.e. low detection limits at high resolution. The use of elevated temperatures is limited, of course, by the temperature stability of both the solvent (stationary liquid and support) and the solutes. The problems of trace analysis for low volatility compounds at high resolution and its limitational parameters regarding sampling, separation and detection are discussed. The applicability of glass capillary columns in this field is influenced by the following parameters: tailing behaviour; irreversible adsorption of polar and decomposition of unstable solutes; thermal stability of stationary liquid (including the support deactivation); separation efficiency and sample capacity (film thickness). Multidimensional gas chromatography using capillary columns coupled either with a packed or another capilllary column for preseparations may be applied with advantage in the analysis of complex mixtures.     

阿胶、龟甲胶中脂溶性成分的高效液相色谱指纹图谱

采用高效液相色谱法研究并建立东阿阿胶、龟甲胶脂溶性成分的指纹图谱,为药用动物胶的质量控制提供了有效的方法。采用液-液-液三相静态萃取方法制备样品,以水-乙腈为流动相进行二元梯度洗脱,检测波长为205 nm,柱温25 ℃,分析时间为60 min。采集20批样品的色谱图并对其进行相似度和聚类分析。分别标定了阿胶、龟甲胶的共有峰,其相似度分析及聚类分析结果显示两种胶间存在着明显的差异。该方法稳定可靠,可以有效地区别不同种属的药用动物胶,为动物胶剂的鉴别及质量控制提供了依据。     

Design parameters for a robust superhydrophobic electrospun nonwoven mat

Electrospun nonwoven mats exhibiting extreme hydrophobicity have recently attracted much attention for their use in a wide range of applications. These materials are highly heterogeneous and irregular in structure, and accordingly, the design parameters of such materials need to be carefully chosen for obtaining higher apparent contact angles along with the robust composite solid-liquid-vapor interface. Here, we present two dimensionless design parameters, namely, the spacing ratio and pressure difference across the liquid-vapor interface, for enhancing the stability of the Cassie regime. These design parameters are essentially dependent upon the structural characteristics of the electrospun mat and equilibrium contact angle of the liquid. Interestingly, the stability of the composite interface is a trade-off between these dimensionless parameters. Moreover, the pressure difference across the interface can significantly increase by reducing the fiber diameter to nanoscale. The stability of the Cassie state in an electrospun nonwoven mat consisting of lower fiber volume fractions at the nanostructural scale can restore superhydrophobicity even after the impact of a rainfall.     

Prediction of number and position of domain boundaries in multi-domain proteins by use of amino acid sequence alone

Prediction of protein domain boundaries is an important step for the prediction of three-dimensional structure. The simple method PDP has been elaborated for prediction of the number and position of domain boundaries in multi-domain proteins by use of amino acid sequence alone. The method uses an optimized scale based on the statistics of appearance of amino acid residues at domain boundaries. Our method demonstrates promising results in comparison to other methods that do not use homologous sequences. From the database of proteins that are targets from CASP6 (Critical Assessment of Techniques for Protein Structure Prediction) our program correctly assigned the number of domains for approximately 80% of one domain proteins and approximately 50% for two-domain proteins. Our method offers three main advantages: it is very simple, it is fast, and it uses a minimal number of parameters in comparison with other methods.     

Freedericksz transitions in smectic liquid crystals in annular geometries

This paper investigates the stability of simple static orientation patterns in a sample of smectic liquid crystal confined to a cylindrical annulus, when a magnetic field is applied. Four different arrangements are considered, covering cases where the layer normal is everywhere either radial or axial, and the (orthogonal) magnetic field is either radial, azimuthal or axial. A classification is given of the threshold radii for mechanical instabilities, and of the threshold magnetic fields for Freedericksz transitions for these cases, with strong anchoring at the boundaries.     

Formation of a regular cellular structure on the surface of Zr<Subscript>67</Subscript>Ni<Subscript>30</Subscript>Si<Subscript>3</Subscript> alloy at electrochemical polishing in ionic liquids

The surfaces of the alloy based on Zr₂Ni doped by silicon (3 at.%) in the amorphous and crystalline states and of the Zr and Ni foils were electrochemically modified for the first time. The modification was carried out in the ionic liquid in the galvanostatic regime. The much more uniform distribution of the nanosized fragments can be obtained and stability of their geometric shapes can be retained in the absence of intergrain boundaries and texture in the amorphous materials.     

Ion-transfer- and photo-electrochemistry at liquid|liquid|solid electrode triple phase boundary junctions: perspectives

Ion transfer at liquid|liquid junctions is one of the most fundamental processes in nature. It occurs coupled to simultaneous electron transfer at the line junction (or triple phase boundary) formed by the two liquids in contact to an electrode surface. The triple phase boundary can be assembled from a redox active microdroplet deposit of a water-immiscible liquid on a suitable electrode surface immersed into aqueous electrolyte. Ion transfer voltammetry measurements at this type of electrode allow both thermodynamic and kinetic parameters for coupled ion and electron transfer processes to be obtained. This overview summarises some recent advances in understanding and application of triple phase boundary redox processes at organic liquid|aqueous electrolyte|working electrode junctions. The design of novel types of electrodes is considered based on (i) extended triple phase boundaries, (ii) porous membrane processes, (iii) hydrodynamic effects, and (iv) generator-collector triple phase boundary systems. Novel facilitated ion transfer processes and photo-electrochemical processes at triple phase boundary electrodes are proposed. Potential future applications of triple phase boundary redox systems in electrosynthesis, sensing, and light energy harvesting are indicated.     

Formation of ring calcium oxalate patterns induced by domains in DPPC Langmuir-Blodgett films

The ring patterns of calcium oxalate crystals were induced by domains in Langmuir-Blodgett （LB） films of dipalmitoylpho- sphatidylcboline （DPPC）. The result was explained by the defects at the ring boundaries of liquid condensed （LC） and liquid expanded （LE） phases of LB film. These boundaries could provide less free energy and much more nucleating sites for COM crystals.     

A new similarity found from the correspondence of the critical and Zeno-line parameters

We find a new similarity based on the relation between the critical and unit compressibility line (Zeno-line) parameters. Our study relies on the fact that the Zeno-line must be tangential to the extension of the binodal liquid branch at the zero temperature domain. We show that this similarity faithfully describes both the numerical simulation data and experimental data for a wide class of real materials (17 gases, water, and 5 metals). Finally we make some predictions for metals which have critical parameters in the phase diagram domain still inaccessible for experiment.     

Phase equilibrium calculations for unprocessed well streams containing hydrate inhibitors

It is shown that the phase distribution of methanol and water between a hydrocarbon gas phase, a hydrocarbon liquid phase and an aqueous phase can be represented using the Soave-Redlich-Kwong equation with a non-conventional mixing rule for the a-parameter suggested by Huron and Vidal. Model parameters are estimated from data for binaries of the type methanolhydrocarbon and waterhydrocarbon. New experimental data are presented for two reservoir fluids and for one model system. The paper further presents a phase equilibrium algorithm for calculating the phase boundaries and the equilibrium compositions at the phase boundary for a system consisting of a gas, a liquid and a mixed aqueous phase.     

Molecular dynamics simulation of the equilibrium liquid–vapor interphase with solidification

The equilibrium structure of the finite, interphase interfacial region that exists between a liquid film and a bulk vapor is resolved by molecular dynamics simulation. Argon systems are considered for a temperature range that extends below the melting point. Physically consistent procedures are developed to define the boundaries between the interphase and the liquid and vapor phases. The procedures involve counting of neighboring molecules and comparing the results with boundary criteria that permit the boundaries to be precisely established. Two-dimensional radial distribution functions at the liquid and vapor boundaries and within the interphase region demonstrate the physical consistency of the boundary criteria and the state of transition within the region. The method developed for interphase boundary definitions can be extended to nonequilibrium systems. Spatial profiles of macroscopic properties across the interphase region are presented. A number of interfacial thermodynamic properties and profile curve-fit parameters are tabulated, including evaporation/condensation coefficients determined from molecular flux statistics. The evaporation/condensation coefficients away from the melting point compare more favorably with transition state theory than those of previous simulations. Near the melting point, transition theory approximations are less valid and the present results differ from the theory. The effects of film substrate wetting on evaporation/condensation coefficients are also presented.     

Solute-Solvent Interactions in the Nematic and Smectic A Phases of 4 4-di-n-Heptylazoxybenzene Studied by Deuteron NMR

The orientational order parameters have been measured by deuteron N.M.R. of both solute (at low dilution) and solvent in various binary mixtures involving the liquid crystal 4,4'-di-n-heptylazoxybenzene (HAB). The solutes studied were azoxybenzene-d₁₀ and n-heptylbenzene-d₇ which are fragments of HAB, azobenzene-d₁₀ because of its similarity to azoxybenzene, and anthracene-d₁₀ because of its known structure and symmetric shape. The major and biaxial order parameters of the solutes are analysed in terms of a molecular field model for the potential of mean torque for biaxial particles. The behaviour of the solute order parameters on approaching and entering the smectic A phase is interpreted in terms of a temperature and phase dependent partitioning of the solute between aromatic and aliphatic regions of the solvent.     

Mass analysis in islands of stability with linear quadrupoles with added octopole fields

Mass analysis with linear quadrupole mass filters is possible by forming "islands" in the stability diagram with auxiliary quadrupole excitation. In this work, computer simulations are used to calculate stability boundaries, island positions, and peak shapes and ion transmission for mass analysis with linear quadrupole mass filters that have added octopole fields of about 2 to 4%. Rod sets with exact geometries that have quadrupole and octopole fields only in the potential, and round rod sets, with multipoles up to N = 10 (the twenty pole term) included in the calculations, show the same stability boundaries, island positions, and peak shapes. With the DC voltage applied to the rods so that the Mathieu parameter a < 0, conventional mass analysis is possible without the use of an island. With the DC polarity reversed so that a > 0, the resolution and transmission are poor preventing conventional mass analysis. In principle, mass analysis in an island is possible with operation at either of two tips. Provided the correct island tip is chosen for mass analysis, peak shapes comparable to those with a > 0 and no excitation are possible, both with a > 0 and with a < 0. In the latter case, the use of an island of stability allows mass analysis when the added octopole otherwise prevents conventional mass analysis.     

Mechanistic comparison of ruthenium olefin metathesis catalysts: DFT insight into relative reactivity and decomposition behavior

The reaction mechanism and substrate-induced decomposition behavior of three ruthenium olefin metathesis catalysts, viz. first- and second-generation catalysts and the recently developed Phoban catalyst (“Phobcat”) are compared by constructing ΔG surfaces at 298.15 K and 1 atm for the complete ligand systems. From these calculations fundamental insight is gained into the reactivity and stability observed experimentally for the three catalysts. In particular, the higher conversions obtained for the first-generation derived Phobcat catalyst, compared to conventional first-generation catalysts, is attributed to its similarity to the second-generation catalysts instead of first-generation catalyst. Important differences between the calculated ΔG surfaces and previously reported total electronic energy (ΔE) surfaces for the metathesis mechanism with complete ligand complexes are discussed.     

Colloid–chemical regression model in analyzing the relationship between dynamic surface tension and the content of total protein and albumins in blood

Mathematical statistics methods in chemistry and biology make it possible to apply certain analytical methods, e.g., interphase tensiometry, in diagnosing physiological states of humans and animals. This study is the first to use the regression method for modeling the relationship between the biochemical parameters of blood serum and dynamic surface tension (DST). We also demonstrate how the regression model can be used to determine the contents of total protein and albumins in blood serum from the known DST values at the liquid/air interface. As a result of constructing the regression model, we propose the regression equations characterizing the relationship between the DST values and the content of protein components in blood serum of animals.     

Elution power of a solvent as a criterion of relative lipid polarity

New parameters are proposed that allow reliable calculation of fixed hydrophilicity values for different classes of lipids over the widest possible range, based on the elution power of solvents and using two compounds at the boundaries of the range as standards. The values of relative hydrophilicity are calculated from the values of relative chromatographic mobility of these types of compounds. It is established that the levels of hydrophilicity of different classes of lipids relative to the selected hexadecane–glycerol pair do not depend on the composition of the different mobile phases used in either planar or column types of liquid chromatography for the separation of complex lipid mixtures.     

Three-dimensional lattice Monte Carlo simulations of model proteins. IV. Proteins at an oil-water interface

Lattice Monte Carlo simulations describe the adsorption of protein-like heteropolymer chains at an oil/water interface. The heteropolymers are designed sequences of 27 and 64 amino acid-type lattice sites taken from a 20-letter alphabet. We use our recently suggested energy scale to model oil and water. We investigate the effect of the oil parameters on adsorption properties of a single chain and on the aggregation of adsorbed chains while keeping the water parameters fixed to their optimum values found previously. By varying the oil parameters, we can cause a large range of adsorption behavior: from no adsorption to reversible adsorption to irreversible adsorption. We compare adsorption at a liquid/solid interface to that at a liquid/liquid interface. A liquid interface leads to stronger adsorption and denaturation than a solid interface with the same water and oil interaction parameters. We propose "optimal" oil parameters and use them to study multichain adsorption at a liquid interface.     

Rheological properties of interphase adsorption layers of gossypin at a liquid-liquid phase separation boundary. III. Influence of chemical modification

The rheological properties of interphase absorption layers of gossypin derivatives at liquid phase separation boundaries and the stability of benzene emulsions have been investigated. It has been shown that the acylation of gossypin with acetic and succinic anhydrides lowers the strength properties of the adsorption layers of protein, leading to a change in the stability of benzene emulsions stabilized by gossypin. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, FAX (3712) 89-14-75. M. V. Lomonosov Moscow State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 528–533, July–August, 1994.