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Randomness and frustration are believed to be two crucial criteria for the formation of spin glass state. However, the spin freezing occurs in some well-ordered crystals below the related temperature T f due to the instability of each spin state, which induces the variation of either magnetic moment value or exchange energy. Here we explore the new mechanism of the in-site originated disorder in antiferromagnets Gd 0.73 La 0.27 B 6 and GdB 6 , which is caused by the random mutual shifts of Gd 3+ spins from the centrally symmetrical positions in the regular cubic lattice. The universal scaling of ESR linewidth temperature dependencies to the power law ΔH(T) ~ ((T - T D )/T D ) α with α = - 1.1 ± 0.05 in the paramagnetic phase of both compounds demonstrates the identity of the origin of magnetic randomness. In Gd 0.73 La 0.27 B 6 the resulting random spin configurations freeze at T f  ≈ 10.5 K where the maximum of magnetization is observed. Below T f the splitting of ZFC and FC magnetization curves takes place as well as the magnetic state depends on the antecedent sample history. In the case of GdB 6 the coherent displacement of Gd ions compete with these random shifts forming an antiferromagnetic (AFM) phase at T N  = 15.5 K, which prevails over the spin freezing at T f  ≈ 13 K, expected from the ESR data. The observation of the hysteresis of the ESR spectrum in the AFM phase suggests that its properties may be determined by the competition of two types of AFM orders, which results in formation of stable magnetic domains with nonequivalent positions of AFM Gd pairs at T < 10 K.

Seebeck effect in the crystalline samples of Eu x Yb 1-x B 6 ( x = 0, 0.082, 0.127, 0.9, 1) was investigated at temperatures 2-300 K. For all the compounds thermopower is shown to be well described by the sum of diffusion ( S d = AT ) and phonon drag components. The latter contribution is induced by quasilocal (Einstein) modes of ytterbium and europium ions with characteristic temperatures Θ E (YbB 6 ) ≈ 91 K and Θ E (EuB 6 ) ≈ 122 K. The estimation of effective mass m * of the charge carriers proves that increasing of Eu content induces crossover from 'heavy' holes with m h * ( x ⩽ 0.127) ≈ 0.3-0.36 m 0 to 'light' electrons with m e * ( x ⩾ 0.9) ≈ 0.12-0.13 m 0 ( m 0 -free electron mass). For the Eu-rich compounds we propose the existence of additional point on the phase diagram, which corresponds to short-range magnetic order with enhanced spin fluctuations preceding the stabilization of magnetic polarons., (© 2020 IOP Publishing Ltd.)

We report the results of a computer simulation study of the thermodynamic properties and the thermal conductivity of supercooled water as a function of pressure and temperature using the TIP4P-2005 water model. The thermodynamic properties can be represented by a two-structure equation of state consistent with the presence of a liquid-liquid critical point in the supercooled region. Our simulations confirm the presence of a minimum in the thermal conductivity, not only at atmospheric pressure, as previously found for the TIP5P water model, but also at elevated pressures. This anomalous behavior of the thermal conductivity of supercooled water appears to be related to the maximum of the isothermal compressibility or the minimum of the speed of sound. However, the magnitudes of the simulated thermal conductivities are sensitive to the water model adopted and appear to be significantly larger than the experimental thermal conductivities of real water at low temperatures.

We review the available experimental information on the thermodynamic properties of supercooled water and demonstrate the possibility of modeling these thermodynamic properties on a theoretical basis. We show that by assuming the existence of a liquid-liquid critical point in supercooled water, the theory of critical phenomena can give an accurate account of the experimental thermodynamic-property data up to a pressure of 150 MPa. In addition, we show that a phenomenological extension of the theoretical model can account for all currently available experimental data in the supercooled region, up to 400 MPa. The stability limit of the liquid state and possible coupling between crystallization and liquid-liquid separation are also discussed. It is concluded that critical-point thermodynamics describes the available thermodynamic data for supercooled water within experimental accuracy, thus establishing a benchmark for further developments in this area., (© 2012 American Institute of Physics)

We investigate the connection between the theory of complete scaling and a field-theoretic (FT) treatment of asymmetric fluid criticality. To facilitate the comparison, we develop an equation of state from a simplified form of the complete scaling transformations and systematically compare this equation of state with the equation of state generated by a FT treatment of an asymmetric Landau-Ginzburg-Wilson Hamiltonian. We find, with care in interpretation, that these two approaches may be read as equivalent up to terms involving an independent higher-order asymmetric correction-to-scaling exponent.

Twenty years ago Poole et al. suggested that the anomalous properties of supercooled water may be caused by a critical point that terminates a line of liquid-liquid separation of lower-density and higher-density water. Here we present a thermodynamic model based on this hypothesis, which describes all available experimental data for supercooled water with better quality and fewer adjustable parameters than any other model. Liquid water at low temperatures is viewed as an 'athermal solution' of two molecular structures with different entropies and densities. Alternatively to popular models for water, in which liquid-liquid separation is driven by energy, the phase separation in the athermal two-state water is driven by entropy upon increasing the pressure, while the critical temperature is defined by the 'reaction' equilibrium constant. The model predicts the location of density maxima at the locus of a near-constant fraction of the lower-density structure.

On the basis of the principle of critical-point universality, we examine the peculiar thermodynamics of the liquid-liquid critical point in supercooled water. We show that the liquid-liquid criticality in water represents a special kind of critical behavior in fluids, intermediate between two limiting cases: the lattice gas, commonly used to model liquid-vapor transitions, and the lattice liquid, a weakly compressible liquid with an entropy-driven phase separation. While the ordering field in the lattice gas is associated with the chemical potential and the order parameter with the density, in the lattice liquid the ordering field is the temperature and the order parameter is the entropy. The behavior of supercooled water is much closer to lattice-liquid behavior than to lattice-gas behavior. Using new experimental data recently obtained by Mishima [J. Chem. Phys. 2010, 133, 144503], we have revised the parametric scaled equation of state, previously suggested by Fuentevilla and Anisimov [Phys. Rev. Lett. 2006, 97, 195702], and obtain a consistent description of the thermodynamic anomalies of supercooled water by adjusting linear backgrounds, one critical amplitude, and the critical pressure. We also show how the lattice-liquid description affects the finite-size scaling description of supercooled water in confined media., (© 2011 American Chemical Society)

By applying a thermodynamic theory that incorporates the concept of complete scaling, we derive the asymptotic temperature dependence of the critical behavior of the dielectric constant above the critical temperature along the critical isochore and below the critical temperature along the coexistence curve. The amplitudes of the singular terms in the temperature expansions are related to the changes of the critical temperature and the critical chemical potential upon the introduction of an electric field. The results of the thermodynamic theory are then compared with the critical behavior implied by the classical Clausius-Mossotti approximation. The Clausius-Mossotti approximation fails to account for any singular temperature dependence of the dielectric constant above the critical temperature. Below the critical temperature it produces an apparent asymmetric critical behavior with singular terms similar to those implied by the thermodynamic theory, but with significantly different coefficients. We conclude that the Clausius-Mossotti approximation only can account for the observed asymptotic critical behavior of the dielectric constant when the dependence of the critical temperature on the electric field is negligibly small., (© 2011 American Chemical Society)

Intranasal administration of dopamine (0.3; 3 and 30 microg/kg) on anxious behaviour of mice was studied using elevated plus-maze and open fields tests and the pinch-induced catalepsy on parallel bars test. Dopamine was introduced as nose drops or inhalation of nanoparticles of the compound solution in C57B1/6J and CBA/Lac mice with differences of dopaminergic function features. In our experiment, dopamine had anxiolytic and elevated motor activity effects in C57B1/6J, but not in the CBA/Lac mice. Nose drops were more effective than inhalation; perhaps, it was a more stressful manipulation. Apparently dopamine increased the number of CBA/Lac mice who demonstrated catalepsy and the reflex duration. Indeed, the neurotransmitter is active in different psycho-emotional phenomena.

Antimicrobial and hemolytic activity of ethanol extract of brown seaweed Laminaria cichorioides Miyabe, its lipophilic fractions, various classes of substances of lipophilic fraction, such as chlorophylls, fucoxanthin, monogalactosyldiacylglycerols, digalactosyldiacylglycerols, sulfoquinovosyldiacylglycerols, and fatty acids were investigated. The antimicrobial activity was studied by means of yeast cells Safale S-04 and Candida albicans CMM 455, fungi Aspergillus niger CMM 4634 and Fusarium oxysporum CMM 4639, bacteria Staphylococcus aureus ATCC 21027 (gram-positive) and Escherichia coli ATCC 15034 (gram-negative) which demonstrated selective sensitivity to the studied substances. Hemolytic activity was investigated at concentrations of substances in the range of 0.2-2000 microg/ml at different pH of erythrocyte suspension. All investigated substances caused hemolysis. The dependence of hemolytic activity of substances on pH of media was determined.

"Complete scaling," which maps asymmetric fluid criticality onto the symmetric Ising model, is extended to spatially inhomogeneous fluids. This extension enables us to obtain a fluctuation-modified asymmetric interfacial density profile, which incorporates leading effects from the asymmetry of fluid phase coexistence and the asymmetry of the correlation length. The derived asymmetric interfacial profile is used to calculate Tolman's length, the diverging coefficient of the curvature correction to the surface tension. The amplitude of the divergent Tolman length is found to depend on the asymmetry of the correlation length.

The thermodynamics of asymmetric liquid-liquid criticality is updated by incorporating pressure effects into the complete-scaling formulation earlier developed for incompressible liquid mixtures [C. A. Cerdeirina et al., Chem. Phys. Lett. 424, 414 (2006); J. T. Wang et al., Phys. Rev. E 77, 031127 (2008)]. Specifically, we show that pressure mixing enters into weakly compressible liquid mixtures as a consequence of the pressure dependence of the critical parameters. The theory is used to analyze experimental coexistence-curve data in the mole fraction-temperature, density-temperature, and partial density-temperature planes for a large number of binary liquid mixtures. It is shown how the asymmetry coefficients in the scaling fields are related to the difference in molecular volumes of the two liquid components. The work resolves the question of the so-called "best order parameter" discussed in the literature during the past decades.

In this study we investigated the hemolytic, antimicrobial, and phytoregulatory activity of various classes of lipids (triacylglycerols, free fatty acids (FFA), the glyceroglycolipids monogalactosyl diacylglycerol (MGDG), sulfoquinovosyl diacylglycerol (SQDG)), sterols, all of them were obtained from the medical herb Kalanchoe diagremontiana, and also pigments, phenolic compounds (FC), polysaccharides, and ethanol extract (EE) of the herbal. It was established that EE, FC, FFA, and sterols display pH-dependent membranothropic activity. FFA showed antimicrobial activity and stimulated growth of buckwheat stalk sprouts. K. diagremontiana glyceroglycolopids did not display expressed biological activity. Caroteniods displayed pH-independent membranothopic action and antibacterial activity. Chlorophylls displayed antimicrobial action, but did not influence erythrocytes and buckwheat sprouts. Polysaccharides acted against the microorganisms Safale S-04, Candida albicans, Fusarium oxysperum and buckwheat sprouts.

Using an improved static and dynamic light-scattering technique, we have observed multiscale relaxation of the pretransitional fluctuations in the isotropic phase of a cromolyn aqueous solution, a lyotropic liquid crystal where rods are formed by aggregates of disklike molecules. We have detected the onset of cromolyn aggregation about 12 degrees C above the transition temperature. The onset is manifested by the emergence of strong scattering due to the fluctuations of local anisotropy and by the split of the diffusion dynamics into two distinctly different modes, one associated with the relatively fast diffusion of monomer-size particles and the other one with the much slower diffusion of the cromolyn aggregates. A third observed dynamic mode is associated with the pretransitional slowing down of fluctuations of the local anisotropy. This mode behaves differently in polarized and depolarized light scattering, due to a coupling between fluctuations of the local-anisotropy and velocity fluctuations.

Germination of buckwheat seeds in solutions of synthetic mono- and tricyclic cyclopentane-containing beta,beta'-triketones of various concentrations was accompanied by inhibition of seedling root growth and changes in the contents of glutamate, gamma-aminobutyric acid, proline, glutamine, and alanine. The monocyclic triketone also affected the amount of isoleucine. It is likely that the increase in proline content is a nonspecific response significant for enhancing stress tolerance in seedlings.

The influence of cyclopentane beta,beta'-triketones on the ultrastructure of root cap meristematic cells of Cucumis sativus L. under inhibition of root growth by these compounds was studied. It was shown that treatment of the seedlings by these substances at the concentration of 100 microg/ml caused, on the one hand, stimulation of protein-synthesizing apparatus (increase in the nucleolus size and in the number of mitochondria and rough endoplasmic reticulum membranes) and, on the other hand, stimulation of lytic processes. The fact that the used compounds, causing inhibition of the seedling growth, do not suppress but stimulate protein-synthesizing activity of the cells, according to existing concept, testifies to the compound-mediated induction of the cell resistance to unfavourable factors. Consequently, these compounds, in contrast with growth inhibitors suppressing cell metabolism completely, possess properties peculiar to retardants, growth inhibitors valuable for crop production.

Using dynamic light scattering we have investigated the time dependence of fluctuations near the critical point of phase separation in solutions of polystyrene in cyclohexane with polymer molecular weights ranging from 196,000 to 11.4 x 10(6) g mol(-1). At the lowest polymer molecular weight the dynamic correlation function follows a single-exponential decay with a decay rate that can be represented by the mode-coupling theory of critical dynamics but with a mesoscopic viscosity that characterizes the hydrodynamic environment of the polymers in the solution. At all higher polymer molecular weights two distinct dynamic modes are observed, a slow and a fast mode, that originate from a coupling of the critical concentration fluctuations with viscoelastic relaxation of the polymer chain in solutions. This coupling causes an additional slowing down of the fluctuations on top of the well-known critical slowing down expected in the absence of a coupling between the two modes. From an analysis of the time dependence of the experimental dynamic correlation functions in terms of a theory of coupling of dynamic modes we are able to determine the viscoelastic properties of the polymers in the solution. These viscoelastic properties diverge in the theta-point limit of infinite polymer molecular weight.

The application of "complete scaling" [Kim et al., Phys. Rev. E 67, 061506 (2003); Anisimov and Wang, Phys. Rev. Lett. 97, 025703 (2006)] to the interfacial behavior of fluids shows that Tolman's length, a curvature correction to the surface tension, diverges at the critical point of fluids much more strongly than is commonly believed. The amplitude of the divergence depends on the degree of asymmetry in fluid phase coexistence. In highly asymmetric fluids and fluid mixtures the Tolman length may become large enough to significantly affect the interfacial behavior.

We have developed a scaled parametric equation of state to describe and predict thermodynamic properties of supercooled water. The equation of state, built on the growing evidence that the critical point of supercooled liquid-liquid water separation exists, is universal in terms of theoretical scaling fields and is shown to belong to the Ising-model class of universality. The theoretical scaling fields are postulated to be analytical combinations of the physical fields, pressure, and temperature. The equation of state enables us to accurately locate the "Widom line" (the locus of stability minima) and determine that the critical pressure is considerably lower than predicted by computer simulations.

The approach to asymptotic critical behavior in polymer solutions is governed by a competition between the correlation length of critical fluctuations diverging at the critical point of phase separation and an additional mesoscopic length scale, the radius of gyration. In this paper we present a theory for crossover between two universal regimes: a regime with Ising (fluctuation-induced) asymptotic critical behavior, where the correlation length prevails, and a mean-field tricritical regime with theta-point behavior controlled by the mesoscopic polymer chain. The theory yields a universal scaled description of existing experimental phase-equilibria data and is in excellent agreement with our light-scattering experiments on polystyrene solutions in cyclohexane with polymer molecular weights ranging from 2 x 10(5) up to 11.4 x 10(6). The experiments demonstrate unambiguously that crossover to theta-point tricriticality is controlled by a competition of the two mesoscales. The critical amplitudes deduced from our experiments depend on the polymer molecular weight as predicted by de Gennes [Phys. Lett. 26A, 313 (1968)]. Experimental evidence for the presence of logarithmic corrections to mean-field tricritical theta-point behavior in the molecular-weight dependence of the critical parameters is also presented.

During the last half of century, Classical Nucleation Theory (CNT) has been developed and there have been advances in the molecular theory of nucleation. Most of these efforts have been directed towards small molecule system modeling using intermolecular potentials. Summarizing the nucleation theory, it can be concluded that the current theory is far from complete. Agreement is generally not obtained between experimental and theoretical results. In practical applications, parametric theories can be used for the systems of interest. However, experimental measurements are still the best source of information on nucleation. Experiments are labor intensive and costly, and thus, it is useful to extend the value of limited experimental measurements to a broader range of nucleation conditions. The available nucleation parameters represent only small regions of possible nucleation conditions over the range from the critical temperature to absolute zero. Thus, it is useful to develop better tools to use the data to estimate semi-empirical nucleation rate surfaces. Following our published approach, the nucleation rate surface for any system can be constructed over its phase diagram. This concept involves using the phase equilibrium diagram to establish lines of zero nucleation rates. Nucleation rate surfaces arise from equilibrium lines and their extensions that are representing unstable equilibria. Only limited experimental data is available for use in normalizing the slopes of the linearized nucleation rate surfaces. The nucleation rate surface is described in terms of steady-state nucleation rates. To design the surfaces of nucleation rates, several assumptions are presented. In the present study, an algorithm for the semi-empirical design of nucleation rate surfaces is introduced. The topology of the nucleation rate surface for a unary system using the example of water vapor nucleation is created semi-empirically. The nucleation of two concurrent (stable and unstable) phase states of critical embryos is considered in the context of multi-surface nucleation rates. Only one phase transition (melting) in the condensed state of water is considered for simplicity. The nucleation rate surface is constructed numerically using the available experimental results for vapor nucleation and phase diagram for water. The nucleation rate for water vapor is developed for the full temperature interval, i.e. from critical point to absolute zero. The results help to suggest a new direction for experimental nucleation research.

We have studied isotropic-to-nematic pretransitional fluctuations in an aqueous solution of disodium cromoglycate (cromolyn) by static and dynamic light scattering. Cromolyn is a representative of lyotropic chromonic liquid crystals with building units being elongated rods formed by aggregates of disk-like molecules. By combining light-scattering and viscosity measurements we have determined the correlation length and relaxation time of the orientational order-parameter fluctuations and estimated the size of the cromolyn aggregates. The pretransitional behavior of light scattering does not completely follow the classic Landau-de Gennes model. This feature is most probably associated with the variable length of cromolyn aggregates. We have observed a dramatic increase of the shear viscosity near the transition to the nematic phase, the fact which correlates with the idea of growing supramolecular aggregates. The steep temperature dependence of the viscosity is accompanied by a practically temperature-independent translational diffusion coefficient.

We address a controversial issue regarding the nature of critical behavior in ternary electrolyte solutions of water, 3-methylpyridine, and sodium bromide. Earlier light-scattering studies showed an anomalous critical behavior in this system that was attributed to the formation of a microheterogeneous phase associated with ion-molecule clustering [M.A. Anisimov, J. Jacob, A. Kumar, V.A. Agayan, and J. V. Sengers, Phys. Rev. Lett. 85, 2336 (2000)]], while some other investigators subsequently found this system to exhibit ordinary Ising-like critical behavior. This contradiction forced us to revisit the problem and perform an accurate and comprehensive study of light scattering in this system paying attention to the achievement of thermodynamic equilibrium, hysteresis effects, aging, and prehistory of the samples, and a possible role of impurities. We show that properly aged, equilibrium samples of aqueous solutions of 3-methylpyridine with NaBr exhibit universal Ising-like critical behavior, typical for other aqueous solutions. No evidence for an equilibrium microheterogeneous phase was found. We have been able to reproduce anomalous behavior (similar to that reported initially) in a fast run on a freshly prepared sample. We attribute the observed anomalies to mesoscopic nonequilibrium aggregates, possibly associated with supramolecular restructuring in aqueous solutions. To support this conclusion we performed a study of aqueous solutions of 3-methylpyridine without NaBr and have found long-living nonequilibrium states in aqueous solutions of 3-methylpyridine.

The hemolytic activity of the epoxydammarane triterpenoids isolated from the Far-East species of the genus Betula and their semi-synthetic derivatives was investigated. Comparative studies of epoxydammarane triterpenoid activities at pH 5.5 and 5.0 and at 37 and 42 degrees C showed that 3-oxo, 3,11-dioxo, 3- and 11-acetoxy, as well as 3,11-diacetoxy derivatives had hemolytic potencies lower than the corresponding polyols; triterpenoids with a 3alpha-OH group were stronger than their analogues with a 3beta-OH group; epoxydammaranetriols were somewhat more potent than epoxydammaranediols. Triterpenoids esterified with malonic acid at C-3 possessed the strongest hemolytic activity among the tested compounds.

A newly discovered Paleolithic site on the Yana River, Siberia, at 71 degrees N, lies well above the Arctic circle and dates to 27,000 radiocarbon years before present, during glacial times. This age is twice that of other known human occupations in any Arctic region. Artifacts at the site include a rare rhinoceros foreshaft, other mammoth foreshafts, and a wide variety of tools and flakes. This site shows that people adapted to this harsh, high-latitude, Late Pleistocene environment much earlier than previously thought.

A study was made of the ultrastructure of root cap meristematic cells in the seedlings of Cucumis sativus L., whose growth was inhibited by the action of 2-acetyl-4-metylcyclopent-4-en-1,3-dione (AMCD). It is shown that the treatment of seeds by this substance at a concentration of 100 microg/ml leads to the main root inhibition by 73% and, as compared to the control, causes the highest changes in mitochondria that do not reach normal dimensions and undergo degeneration. AMCD caused significant changes in the cell walls that in test samples unusually became electron-dense. Deposits of osmiophylic substance, presumably consisting of terpenoid-like compounds, were often found in the cytoplasm of treated cells as well as in the extracellular space. In many cells, plasmalemma and amiloplast membranes underwent destructive changes. We discuss a possible relation between inhibitory effect of AMCD on the root growth, and its influence on the ultrastructure in investigated cells.

We studied the effect of extractive substances (ES) and total glycoside fraction (TGF) from Panax ginseng on plant cell growth. The seeds of cucumber Cucumis sativus L., KIT variety, were used for the biological assay. The tested substances inhibited the primary root growth in Cucumis sativus seedlings. Actively growing seedlings were most sensitive to this effect.

Cytotoxic activity of dammarane triterpenoids isolated from beach leaves was studied. These substances differ from the native ginseng genin (20(S)-protopanaxadiol) by the number, location, or configuration of OH-groups. Using fertilized egg cells of sea urchin Stronglyocentrotus intermedius we demonstrate that the orientation of C-3 OH-group has no effect on cytotoxic activity of triterpenoids as well as a higher activity of a triterpenoid with 3 alpha,12 beta-OH as compared to a C-3 ketone but lower activity as compared to a triterpenoid with 3 alpha,17 alpha-OH. Depending on the number of OH-groups the cytotoxic activity of triterpenoids decreases in the row: tetraol > pentaol > triol. Dammar-24-ene-3 alpha 2 beta,17 alpha,20(S)-tetraol (compound IV) is cytotoxic for the Ehrlich ascite carcinoma cells and this effect is additive to cytotoxic activity of anthracycline antibiotic carminomycin in vitro. Compound IV changes the permeability and microviscosity of the tumor cell membranes.

We have performed accurate dynamic light-scattering measurements near critical demixing points of solutions of polystyrene in cyclohexane with polymer molecular weight ranging from 200 000 to 11.4 x 10(6). Two dynamic modes have been observed, "slow" and "fast," which result from a coupling between diffusive relaxation of critical fluctuations of the concentration and viscoelastic relaxation associated with the entanglement network of the polymer chains. The coupling with the viscoelastic mode causes an additional slowdown of the critical mode on top of the uncoupled diffusion mode. By implementing crossover from the critical to the theta-point tricritical behavior for both static and dynamic properties, we are able to present a quantitative description of the phenomenon and obtain a scaling of the viscoelastic parameters as a function of the molecular weight.

We show that the approach to asymptotic fluctuation-induced critical behavior in polymer solutions is governed by a competition between a correlation length diverging at the critical point and an additional mesoscopic length-scale, the radius of gyration. Accurate light scattering experiments on polystyrene solutions in cyclohexane with polymer molecular weights ranging from 200 000 up to 11.4x10(6) clearly demonstrate a crossover between two universal regimes: a regime with Ising asymptotic critical behavior, where the correlation length prevails, and a regime with tricritical theta-point behavior determined by a mesoscopic polymer-chain length.

An accurate photon-correlation spectrometer capable of measuring scattered light at two fixed scattering angles simultaneously in the temperature range from 10 to 120 degrees C is described. For the detection of the correlation function of the scattered light both an original correlator (PhotoCor-SP) with a linear-time-scale channel spacing and an ALV GmbH correlator (Model ALV-5000) with a logarithmic-time-scale channel spacing are used. High-resolution static and dynamic light-scattering measurements near the critical point of a polystyrene solution were performed with this instrument. The static-intensity measurements reveal that the crossover from mean-field to Ising behavior occurs at a temperature at which the correlation length of the critical fluctuations becomes equal to the radius of gyration of the polymer molecule. We found that the wave-number dependence and the temperature dependence of the diffusion coefficient of the concentration fluctuations are not consistent with existing theory for critical dynamics in low-molecular-weight liquid mixtures.

Dynamic light scattering with an original optical scheme has been used for the investigation of opaque (strongly light-absorbing) asphaltene colloids in crude oils and hydrocarbon mixtures. Diffusion-limited aggregation and reaction-limited aggregation as well as a crossover between these two regimes have been observed. A simple interpolation for the crossover kinetics is proposed. Asphaltene colloidal structures, originally persisting in crude oils, have been detected. Addition of a precipitant above a threshold induces asphaltene aggregation. Depending on the nature of the precipitant, different crude oils respond differently on its addition: (a) exponential-in-time growth of aggregates to huge flocks or (b) fast formation of stable-in-size particles.

We present a parametric equation for the thermodynamic properties in the critical region of three-dimensional Ising-like systems which include fluids and fluid mixtures. The equation of state incorporates a crossover from singular Ising behavior asymptotically close to the critical point to classical (mean-field) behavior further away from the critical point, characterized by two physical crossover parameters: a coupling constant related to the strength and range of molecular interactions and a "cutoff" wave number for the critical fluctuations. In the asymptotic Ising limit, the crossover equation reproduces the most recent theoretical estimates for the universal ratios of the leading and correction-to-scaling critical amplitudes. The equation has been tested by comparing it with recent experimental thermodynamic-property data for 3He near its vapor-liquid critical point.

We studied membranotropic effect of dammarane-type triterpenes (isolated from birch leaves) with a variable side chain structure, as well as the number and configuration of OH groups as a function of temperature and pH. Polyols with an acyclic side chain and four OH groups proved to have a higher hemolytic activity as compared to polyols with three or five hydroxyl groups. The triterpenes, with tetrahydrofurane cycle as the side chain, exert a hemolytic effect at a more acidic pH (5.0) and higher temperature (45 degrees C), as compared to the polyols with acyclic side chain. Irrespective of the side chain structure, the compounds with a 24(S) configuration lysed the erythrocytes at lower rate, as compared to the compounds with a 24(R) configuration.

The effect of plant carboxyl-containing glycoside cauloside C upon eucaryotic cells has been studied. The glycoside interacts with cells as a pH-dependent cytotoxin and increases K+ leakage and Ca2+ uptake with strong action in acidic media Cell viability after glycoside action at acidic pH may be recovered by the shift of medium pH from 5.6 to 7.4. Directed transport of low molecular weight effectors such as cAMP and Ca2+ to human embryo fibroblasts under the action of cauloside C has been demonstrated. Calcium uptake is accompanied by about a twofold stimulation of fibroblast proliferation in serum-free medium. The manifestation of the effect depends on the strictly determined time of the 'open' state of the membrane permeability (2 min) and upon concentration of glycoside in the medium (1 ng/ml) Cauloside C-stimulated Ca-transport is not blocked by Ca-channel blockers such as verapamil, diltiasem, and nitrendipine (all at a concentration of 1 x 10(-6) M) but these blockers inhibit cauloside C-stimulated proliferation of fibroblasts. We conclude that stimulation of fibroblast proliferation is caused by activation of membrane associated Ca-channels at the expense of calcium, incorporated into cells with cauloside C. The use of cauloside C as a new biochemical tool for cell permeabilisation is suggested.

This feature issue of Applied Optics contains 25 research papers on photon correlation and scattering. Many of the papers in this volume were presented at an OSA Topical Meeting that was held 21-24 August 1996 in Capri, Italy. The focus of these papers is research in dynamic light scattering, surface light scattering, photon correlation, laser velocimetry, and their applications to biological, chemical, and physical processes.

The authors analysed 373 patients with acute pancreatitis which developed after operations on the organs of the pancreatoduodenal zone. Acute postoperative pancreatitis developed in 17.15% of cases after operations on the biliary tract, in 26.8% after resection of the stomach for ulcer, and in 51.47% of cases after resection of the stomach for carcinoma. A comparative evaluation of various methods for the prevention and treatment of acute postoperative pancreatitis (APP) is given, with appraisal of the traditional therapy (154 patients) without the use of protease inhibitors, and various methods of administration of protease inhibitors (135 patients) and cytostatics (84 patients). The mortality rate in progressive forms of APP was 25.2%, mortality being highest (30.4%) in treatment by the traditional methods including protease inhibitors and lowest in inclusion of cytostatics in the complex of therapeutic measures (7.1%).

The effect of the medium pH on accumulation of [3H]-cauloside C by tumor cells, its intracellular localization, and interaction of the glicoside with membranes of tumor cells and liposomes has been studied. The shift towards weakly acids pH leads to the increase in the amount of cauloside C accumulated by tumor cells and changes the pattern of interaction of cauloside C with the membranes.

The sum of triterpene glycosides of the Far Eastern holothurian Stichopus japonicus Selenka (holotoxins A1 and B1) possesses the contraceptive activity. Glycoside holoturin A of the tropical holothurian Holoturia atra lacks these properties. The action of the sum of holotoxins is based on the estrogenic activity which was demonstrated both in the uterotropic and vaginotropic tests. The drug under study suppresses ovulation and stimulates the contractile activity of the uterus.

The effect of triterpene glycosides (cauloside C from Caulophyllum robustum, theasaponine from Thea sinensis, cucumarioside G from Cucumaria fraudatrix stichoposide A from Stichopus japonicus S., holothurines A and B from Holothuria mexicana, holothurine C from Bohadschia sp.) on the membrane permeability for K+ ions and UV-absorbing substances was compared with that of polyene antibiotics, viz., amphotericine B and nystatine. As a biological model fertilized eggs of sea urchin Strongylocentrotus nudus and yeast Saccharomyces carlsbergensis were used. In the sea urchin study most triterpene glycosides in low concentrations induced the outflux of K+ and in hgih concentrations that of both K+ and UV-absorbing agents. In the yeast study triterpene glycosides at identical doses induced the outflux of both K+ and UV-absorbing agents. The membranotropic effect of triterpene glycosides depended on the medium temperature and the biological system used.

The absorption spectrum of stichoposid A with sulfuric acid, vanillin and alkaline was studied for the purpose of possibly using the reactions with these substances for quantitative determination of stichoposid A in biological materials. The reaction with 1 N NaOH was shown to be the most useful since it is highly specific with respect to the glycoside aglycone and makes it possible to investigate stichoposid A interaction with the cells of the yeast microflora.