Search

The broad-band reflection spectra of YB6 and YbB6 hexaborides with Jahn–Teller instability of the boron cage have been measured at room temperature. An optical conductivity analysis has revealed, along with the Drude electronic components, heavily overdamped collective modes, which are notable in YB6 for high dielectric contributions, Δε = 2000–5700. The fraction of nonequilibrium charge carriers in YB6, which is at the boundary of structural instability in the hexaboride family, reaches 85–90%, whereas this fraction in doped YbB6 semiconductor is not higher than 25%. It has been shown that unlike the predictions of the topological Kondo insulator model, the surface "metallization" in Yb2+B6 crystals can be explained by additional doping of a surface layer with Yb3+ ions. [ABSTRACT FROM AUTHOR]

This article is devoted to the Monte Carlo simulation of the colloidal crystallization kinetics of cadmium selenide (CdSe) nanoparticles (NPs), i.e., the growth of nanoparticles from individual CdSe molecules. The model of CdSe NP crystallization is modified taking into account available experimental data. This model comprises the rate constants of crystallization in a colloidal solution. It is assumed that the control over the sizes, size distribution, and yield of NPs plays the key role in improving the properties of NPs. The model constants of particle nucleation, growth, and subsequent crystallization are determined under the dynamic equilibrium approximation. The frequencies of attachment and detachment transitions of monomer–NP complexes as depending on the sizes and concentration of NPs are the key parameters of NP formation process. The processes of predecessor particle transformation into a monomer, the formation of an effective monomer, and the nucleation pass to the stage of CdSe NP growth. The Monte Carlo method is used to approximate the kinetic model of the nucleation and growth of CdSe NPs with allowance for individual contributions (concentrations of formed monomers and their diffusion coefficients) to the rate constants of NP formation. The kinetic dependences of the average radius and concentration of CdSe NPs, as well as the NP size distributions, are simulated at different kinetic constants of the colloidal crystallization process. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effect of magnetic activation on the surface characteristics of clinoptilolite, such as particle size, surface area, pore size, and distribution, were determined. Magnetic activation was performed in an ultrahigh frequency electromagnetic field (UHF EMF) and a weak pulsed magnetic field (WPMF). A significant effect of magnetic activation was detected: particle aggregation during treatment of clinoptilolite with UHF EMF and dispersing the particles when exposed to WPMF. The average particle size of the zeolite was increased by 134 nm when treated with UHF EMF and significantly decreased by 560 nm when exposed to WPMF. An increase in modality under the influence of EMF was found. The specific adsorption capacity was increased by 1.3 and 7 times when treated in WPMF in comparison with the UHF EMF-activated sample and natural clinoptilolite, respectively. The Gaussian distribution of clinoptilolite particles as a result of the WPMF aftereffect was found. Magnetic activation practically did not affect the specific surface area of clinoptilolite. The pore volume and the relative value of dV/dlog(D) were increased to a greater extent under the influence of WPMF compared to the data obtained when the sample was treated with UHF EMF and on natural clinoptilolite. [ABSTRACT FROM AUTHOR]

The temperature dependence of the conductivity of the topological Kondo-insulator (TKI) Sm1 –xYbxB6 is investigated in the temperature range 2 < T < 300 K for compositions with x ≤ 0.024. It is found that the ytterbium impurity most strongly affects the low-temperature (T < 20 K) electrical conductivity: when changing from x = 0 to x = 0.024, the activation energy of bulk conductivity decreases by 1.8 times from 4 to 2.2 meV, and the 2D surface conductivity increases by six times. The separation made for the contributions to the conductivity enables us to establish that the one-parameter scaling model can be used for describing the conductivity of 2D surface states in the Sm1 –xYbxB6 TKI in which both the interaction with phonons and the electron–electron scattering effects are taken into account. [ABSTRACT FROM AUTHOR]

Critical fluctuations are known to induce a collapse of polymer chains in a mixed solvent upon approaching its liquid–liquid critical point, as originally predicted by Brochard and de Gennes. Recently, we have found that closer to the critical point this collapse is followed by a reswelling of the polymer coils well beyond the original dimensions, a phenomenon not predicted by the theory of Brochard and de Gennes. We submit that upon approaching the critical temperature more closely, the correlation length of the critical fluctuations inside the polymer coils can no longer further increase due to the finite size of the coils, resulting in the appearance of large critical Casimir forces that cause a significant expansion of the polymer coils. Eventually, micro-phase separation inside the coils will appear and the coils will reshrink. This entire process takes place while the bulk solution is still in the one-phase region. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. Cerdeiriña 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. [ABSTRACT FROM AUTHOR]

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 2×105 up to 11.4×106. 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. [ABSTRACT FROM AUTHOR]

In this paper we show that the virial expansion up to third order for the osmotic pressure of a dilute polymer solution, including first-order perturbative corrections to the virial coefficients, allows for a scaling description of phase-separation data for polymer solutions in reduced variables. This scaling description provides a method to estimate the Θ-temperature, where demixing occurs in the limit of vanishing polymer volume fraction φ and infinite chain length N, without explicit assumptions concerning the chain-length dependence of the critical parameters T[sub c] and φ[sub c]. The scaling incorporates three limiting regimes: The Ising limit asymptotically close to the critical point of phase separation, the pure-solvent limit, and the tricritical limit for the polymer-rich phase asymptotically close to the theta point. We incorporate the effects of critical and tricritical fluctuations on the coexistence-curve scaling by using renormalization-group methods. We present a detailed comparison with experimental and simulation data for coexistence curves and compare our estimates for the Θ-temperatures of several systems with those obtained from different extrapolation schemes. [ABSTRACT FROM AUTHOR]

An accurate equation of state is presented for the thermodynamic properties of mixtures of H[sub 2]O and D[sub 2]O in the critical region. The equation incorporates a crossover from fluctuation-induced singular behavior near the locus of vapor–liquid critical points to regular behavior outside the critical region. It is a generalization of a crossover equation-of-state previously developed for pure H[sub 2]O and pure D[sub 2]O extended to the mixtures on the basis of the principle of isomorphism of critical behavior. The equation represents the thermodynamic properties of mixtures of H[sub 2]O and D[sub 2]O in the same range of temperatures and densities as for the pure components. A comparison is made with available experimental data for the pressure, for the isochoric heat capacity, for the enthalpy of mixing, and for the isotope fraction ratio of mixtures of H[sub 2]O and D[sub 2]O. An analysis is presented of the near-critical behavior of various thermodynamic properties, such as the isobaric heat capacity, the partial molar volumes, Henry’s constant, and the vapor–liquid distribution ratio (K factor). © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It has been generally assumed that the asymptotic critical behavior of real fluids can be characterized in terms of the same physical variables as that of the lattice gas. This assumption implies that, below T[sub c], the second derivative of the pressure with respect to temperature should asymptotically diverge like the isochoric heat capacity C[sub V], while the second derivative of the chemical potential with respect to the temperature should remain finite at the critical point. The validity of this assumption has recently been questioned on the basis of an analysis of experimental two-phase C[sub V] data in terms of the so-called Yang–Yang relation. In this paper we show how such an analysis may be affected by the presence of a small amount of impurity as well as by other nonasymptotic deviations from lattice-gas symmetry. When corrections for a small amount of impurity are applied and allowance is made for the leading asymmetric Wegner correction, the experimental C[sub V] data are not inconsistent with previous treatments in which the second derivative of the chemical potential exhibits a cusplike singularity with a finite limiting value at the critical temperature. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Marine organisms are a rich resource of pharmaceutical active compounds which have a wide range of biological activity, including anticoagulant action, immunomodulating action, anti-tumor activity, antibacterial, antifungal and antiviral, antiinflammatory, antioxidant, lipid-corrective activity etc. Antivir, Laminaran and Fucoidan derived from Laminaria cichorioides were tested in field conditions, as stimulants of growth and development of barley (Hordeum vulgare L.), wheat (Triticum aestivum L.) and buckwheat (Fagopyrum esculentum Moench). Research shows that stimulating effect depends on chemical structure of polysaccharides and on plant species. Antivir, Laminaran and Fucoidan at different concentrations stimulate growth, productivity and morphological traits (plant height, ear length, productive bushiness and others) of barley, wheat and buckwheat. Carbohydrate containing biopolymers derived from the sea algae effect differently upon rutin content in seeds and stems of buckwheat. [ABSTRACT FROM AUTHOR]

Study of protein stability in solutions is important for better understanding the pathogenesis of diseases caused by abnormal protein folding and aggregation. Lysozyme is known to form mesoscopic aggregates (30–100 nm radius) in concentrated solutions (>30 mg/mL), however the origin and thermodynamic status of these aggregates remain unclear. In this work we have investigated the effects of concentration, filtration, and temperature on the sizes and relative amount of mesoscale aggregates in solutions of lysozyme. We have used dynamic light scattering, small-angle X-ray scattering, and size exclusion chromatography (SEC). Mesoscopic protein aggregates were commonly thought to be in equilibrium with protein monomers in solution, resulting from a reversible self-assembly of the monomers. We instead show that systematic filtration through 20 nm pore size filters completely removes the aggregates from solution. The aggregates do not reemerge. Without filtering, the relative number of monomers decreases with increasing solution temperature, indicating formation of more aggregates. SEC was used to search for the presence of lysozyme dimers, which have been previously hypothesized to be related to the formation of mesoscopic aggregates. SEC did not detect dimers in solutions of filtered or unfiltered lysozyme. Taken together, our results strongly suggest that the mesoscopic aggregates in lysozyme are not caused by reversible self-assembly of lysozyme monomers and are not an intrinsic property of lysozyme monomers in their native state. We hypothesize that the lysozyme aggregation is likely due to some impurities in lysozyme introduced during purification or lyophilization and/or to traces of misfolded lysozyme. [ABSTRACT FROM AUTHOR]

This paper presents the first results of geological and geoarchaeological multi-proxy studies conducted from 2012 to 2017 in the northern part of Narva-Luga Klint Bay (between the Kurgalov and Kurovitski Plateaus). A detailed geological study using ground-penetrating radar (GPR), drilling, outcrops description and sampling revealed a previously unknown accumulative landform (the Kuzemkino "palaeospit"). The GPR data set indicates that the accretion form is a polygenic, steeply inclined glaciofluvial delta foreset, which was formed during the Pandivere stage of deglaciation as a result of consistent discharges of huge amounts of sediment materials from the melting ice-sheet and arriving from the south, west, north-west and south-west. The foreset was formed within a relatively shallow (approximately 20 m) ice-dammed lake, which did not have an outlet in the south-western direction during that time period. In the Holocene, the foreset became a source of sediment for the development of the largest accretion form of Narva-Luga Klint Bay – the Kudruküla Spit. During the maximal level of the Littorina transgression, the Kuzemkino landform was a peninsula or an island. A relatively long-term stabilization of the sea level apparently occurred at 8.5 m a.s.l. The beach and submarine sand ridges formed during this time interval were subsequently unaffected by marine transgressions and were preserved as relict forms in the relief. The Kuzemkino landform was settled by ancient peoples after the Littorina maximum. There is evidence that the settlers' long-term subsistence strategy was based on the combined exploitation of coastal and forest resources. [ABSTRACT FROM AUTHOR]

We have tested the conduction band electrons of lanthanum hexaboride that is among the most effective electron-beam sources with one of the highest brightness of thermionic emission. We performed infrared spectroscopic, DC (direct current) resistivity and Hall-effect studies of LaB6 single crystals with various 10B and 11B isotope contents. We find that only a small amount of conduction electrons behave as Drude-type charge carriers while about 70% of the electrons are involved in collective oscillations of electron density coupled to vibrations of both the Jahn-Teller unstable rigid boron cage and rattling modes of La-ions loosely bound to the lattice. We suggest that exactly these non-equilibrium conduction electrons determine the extraordinary low work function of thermoemission in LaB6. [ABSTRACT FROM AUTHOR]

A study of the charge transport, magnetization, and high frequency (ω/2π=60 GHz) electron spin resonance (ESR) has been carried out on La1-xCaxMnO3 single crystals corresponding to the dielectric side of the concentration driven metal-insulator transition (x≤xMIT∼0.22). For x=0.22 the onset of ferromagnetism below the Curie temperature TC≈183 K was found to induce crossover from holelike (T>TC) to electronlike (TC) conductivity. The activation behavior of resistivity and Seebeck coefficients with the respective activation energies Eaρ∼123 meV and EaS∼32 meV was detected in the paramagnetic state of x=0.22 compound for T>TC. A large enhancement of the Hall effect, which is accompanied by the increase in Hall mobility to the values of μH∼-20 cm2/V s, was observed at intermediate temperatures 150 KC. Besides, a single ESR line with g factor g≈2 observed for x=0.2 at T>TC was shown to evolve into an intricate two-mode ESR spectrum with irregular fine structure characterizing the ferromagnetic insulating (FI) state formed below TC. The anomalies of charge transport and magnetic properties found in FI state seem to be associated with the peculiarities of strongly disordered state with phase separation (ferromagnetic metallic domains embedded in the insulating matrix of La1-xCaxMnO3). [ABSTRACT FROM AUTHOR]

Eleven polyketides that have been tested in laboratory and field conditions as growth stimulants of the spring barley (Hordeum vulgare L.) were educed from marine fungus Penicillium thomii Maire KMM 4675, which was obtained from mycobiota of the brown seaweed Sargassum pallidum (Novik Bay, Russky Island, Sea of Japan). Depending on the chemical structure, polyketides have different effects on the growth of barley sprouts. It is shown that the compounds pallidopenilline A, 1-acetoxy-pallidopenilline A, 1-deacetyl- pallidopenilline B, pallidopenilline E, pallidopenilline F, and pallidopenilline H have a stimulating effect on the growth of sprout roots (from 2 to 24%) and the compounds pallidopenilline A and 1-acetoxy-pallidopenilline A stimulate the productivity of the spring barley at concentrations of 1.0 μg/mL (17.1%) and 10.0 μg/mL (19.5%), respectively. Pallidopenilline A and its acetylized derivative 1-acetoxy-pallidopenilline A showed the maximum stimulatory effect (24 and 10%, respectively) on the growth of barley sprouts at a concentration of 0.01 μg/mL. Pallidopenilline A is recommended for wider use in the field conditions as a growth stimulant. [ABSTRACT FROM AUTHOR]

In the conditions of Primorye krai, the Fagopyrum esculentum Moench cultivars of different ecological and geographical origin were studied in terms of their productivity and fruit biochemical composition. The cultivar Bashkirskaya krasnostebelnaya was found to be of interest for the purposes of breeding buckwheat for higher content of flavonoids: it exceeds the reference cultivar Izumrud by 7.5 mg/100 g. The cultivar Demetra is richer in essential amino acid content (arginine, lysine, phenylalanine, leucine, isoleucine, valine, and tryptophane) in its fruits. The studied cultivars had more potassium (1.41-1.49) than phosphorus (0.54-0.55) in their fruits. As a result, the promising cultivars were selected as follows: the indeterminate ones—Zemlyachka, Inzerskaya, and Bashkirskaya krasnostebelnaya; the determinant ones—Demetra and Dikul with a high content of flavonoids, protein, fat, and essential amino acids in their fruits. Using the adaptability parameters, we identified the determinant cultivars Dikul and Dialogue as highly adaptable and stable; their average productivity reached 1.5 t ha-1 and exceeded the reference cultivar by 5-18%. [ABSTRACT FROM AUTHOR]

The effect of electromagnetic fields on the adsorption-desorption properties of natural zeolites is a new direction in the theory of physical and chemical processes associated with the surface characteristics of aluminosilicates. The influence of two types of fields, an ultrahigh-frequency electromagnetic field (UHF EMF) and a weak pulsed magnetic field (WPMF) is considered. Modes for treatment of natural zeolite (clinoptilolite) and its activated forms for the most effective sorption of formaldehyde, water, and a mixture thereof were found. It was shown that the preadsorption activation of zeolite in a UHF EMF enhances the selectivity of water vapor sorption, whereas treatment of the sorbent in a WPMF largely affects the selectivity of the absorption of formaldehyde vapors. The decreased desorption of formaldehyde as a result of activation of the mineral in a UHF EMF, as well as complete absence of formaldehyde desorption when a WPMF was used as an activator, was detected. [ABSTRACT FROM AUTHOR]

High-precision measurements of the Hall effect and Raman scattering have been performed for single crystals of ZrB superconductor in the wide temperature range of 5-300 K. For ZrB, the boson peak with ω ~ 100 cm has been observed for the first time within the low-frequency range of the Raman spectrum I(ω). The sizes of vibrational clusters with the correlation length ranging from 25 to 35 Å are estimated. The relation between the renormalization of the low-frequency density of vibrational states accompanying the transition to the cage-glass phase ( T* ~ 90 K) and the enhancement of superconductivity in ZrB is discussed. [ABSTRACT FROM AUTHOR]

Magnetoresistance (H,T) of several heavy-fermion compounds, CeAl2, CeAl3 and CeCu6, substitutional solid solutions with quantum critical behavior CeCu6-xAux (x = 0.1, 0.2) and alloys with magnetic ground state Ce(Al1-xMx)2 (M = Co, Ni,x = 0.8) was studied in a wide range of temperatures (1.8-40 K) in magnetic fields up to 80 kOe. It was shown that a consistent interpretation of the field dependences of the resistance for both non-magnetic and magnetically ordered cerium-based intermetallic compounds with strong electron correlations can be achieved within the framework of an approach that accounts for scattering of charge carriers by localized magnetic moments in a metal matrix. Within this approach, three different components of the magnetoresistance of ceriumintermetallic compounds were identified: the negative Brillouin contribution proportional to the local magnetization (-/~M2loc-/~Mloc2), the alternating linear contribution (/~H/~H) and the magnetic component, saturating in magnetic fields below 15 kOe. In the framework of the Yosida model for the cerium alloys under study, estimates of the local magnetic susceptibility loc(H, T0) were obtained from the magnetoresistance data. Numerical differentiation of the magnetoresistance with respect to the magnetic field and analysis of the obtained d/dH=f(H,T)d/dH=f(H,T) dependences allowed us to reconstruct the H-T magnetic phase diagrams of the strongly correlated electron systems under study as well as to examine the effects of spin polarization and renormalization of the electronic states on charge transport both in the regime of quantum critical behavior and in the magnetically ordered state. [ABSTRACT FROM AUTHOR]

A growth-regulating effect of triterpene glycosides of hederagenin (caulosides A, C, D, and G which were isolated from Caulophyllum robustum Maxim.) on a growth of roots of Cucumis sativus L. seedlings was studied. The efficacy of the growth-regulating action of the studied compounds was shown to depend on their chemical structure. Caulosides A and C had one carbohydrate chain. They inhibited the growth of roots of the Cucumis sativus L. seedlings in concentrations of 500 and 100 μg/mL by 10.3 and 20.4%, respectively. Caulosides D and G had two carbohydrate chains. These compounds did not inhibit the root growth in concentrations up to 500 μg/mL, but exhibited a slight stimulating effect (9.1 and 10.4%, respectively) in their concentrations of 100 and 250 μg/mL. The inhibiting effect of cauloside C was directed, for the first time, to the seedlings with an intensively growing main root. [ABSTRACT FROM AUTHOR]

It has been established experimentally that the thermodynamic properties of fluids satisfy scaling laws with universal critical exponents asymptotically close to a single critical point of the vapor-liquid phase transition. In contrast to the conjecture of Woodcock, there is no reliable experimental evidence to doubt the existence of such a single critical point in the thermodynamic limit and of the validity of the scaling theory for critical thermodynamic behavior. [ABSTRACT FROM AUTHOR]

Estimation of flavonoids content in leaves and stems of 56 varieties of winter wheat is calculated. The association between anthocyanin pigmentation of the plant stem with high flavonoids content is defined. This proves the possibility of using the coloration as a diagnostic trait in selection practice. The role of phenol compounds in the increase of resistance of some winter wheat varieties to abiotic and biotic factors is shown. [ABSTRACT FROM AUTHOR]

The behavior of the electrical resistivity and magnetoresistance of lanthanum hexaboride with isolated (∼1%) Ce or Ho magnetic impurities has been studied. It has been shown that the low-temperature growth of the resistivity is characteristic of the weak localization regime for charge carriers rather than of the Kondo effect. The negative magnetoresistance observed in CeLaB and HoLaB at liquid helium temperatures also cannot be interpreted in terms of the Kondo model and corresponds to the formation of many-body states of a spin-polaron type near magnetic rare-earth ions in LaB. [ABSTRACT FROM AUTHOR]

The features of the formation of the magnetic moments of Tm and Yb ions in a metallic matrix of LuB cage glass have been studied in measurements of the magnetization and specific heat in the temperature range of 1.9-300 K in magnetic fields up to 90 kOe. It has been shown that a paramagnetic response from the localized moments of isolated ions Tm (7.6μ) and Yb (4.5μ) is observed at temperatures of 150-300 K. A transition to the cage glass phase at low temperatures ( T ≪ T* ∼ 60 K) is accompanied by disordering in the system of rare-earth ions and by formation of many-body states near Tm and Yb ions. At low temperatures near T in low magnetic fields, the appearance of an additional spin polarization, which is suppressed with an increase in the field, has been observed. The effective moments and g-factors of Tm and Yb obtained in high fields imply both the binding of a small fraction of magnetic ions to antiferromagnetic dimers and the Γ ground state of the F multiplet of the ytterbium ion. A scenario alternative to the Kondo-type behavior has been proposed to explain the nature of many-body states and the appearance of the spin polarization in rare-earth dodecaborides. [ABSTRACT FROM AUTHOR]

We present results of precision measurements of magnetoresistance of isotopically pure Ho11B12 at low temperatures 2 10 K in magnetic field up to 80 kOe of different orientation to the crystal axes. The data obtained revealed strong anisotropy of magnetoresistance and allowed us to reconstruct magnetic H-T phase diagrams for main crystallographic directions H k [001], [110], and [111]. Analysis of magnetoresistance derivatives allowed to conclude in favor of two main magnetoresistance contributions. Among of them the negative quadratic component is attributed to charge carriers scattering on a magnetic clusters of Ho3+ ions (4f component) and positive linear one may be explained in terms of scattering on a spin density waves (5d component). [ABSTRACT FROM AUTHOR]

Transport and magnetic properties of polycrystalline Tm0.03Yb0.97B12 samples were investigated at temperatures 1.8-300 K in magnetic fields up to 9 T. The activated behavior of resistivity, the Hall coefficient and thermopower is described in terms of a narrow gap εg≈ 16:6 meV, which controls the charge transport in Tm0.03Yb0.97B12 at T > 40 K. The maximum of magnetic susceptibility found at 50 K is shown to be induced by a spin gap Δ ≈ 4:7 meV being close to the half of the spin fluctuation energy in YbB12. Large diffusive thermopower S = AT, A = -29.1 μV/K2 and the Pauli susceptibility χ0 ≈ 7.2×10-3 emu/mol found below 20 K seem to be associated with the many-body resonance, which corresponds to states with an enhanced effective mass m* ≈ 250m0 (m0 - free electron mass). The effective parameters of magnetic centers and the analysis of anomalies favor the nonequivalent states of substitute Tm ions. [ABSTRACT FROM AUTHOR]

The anisotropy of charge transport was investigated in the antiferromagnetic II state of GdB6 from precise measurements of transverse magnetoresistance. Based on the data obtained we detected a complicated behavior of magnetoresistance curves which are characterized by the appearance of considerable hysteresis on the field and angular dependences below TN2. Moreover it was shown that the system GdB6 is sensitive to cooling- warming prehistory. The data analysis allowed to reconstruct magnetic H-T phase diagram of GdB6 along main crystallographic directions (H ‖ <001>, <110> <111> and to propose additional phase transition inside AF II phase at H1 ≈ 0:5 T. [ABSTRACT FROM AUTHOR]

The article presents a study on global atmospheric oscillation (GAO) and its effect on the North Atlantic Ocean's hydrophysical regime. It mentions its impact on ocean temperature, salinity level and velocity of currents as well as manifestation as structural deformations of atmospheric pressure fields. An overview of its mediated effects with El Niño and La Niña currents is also provided.

Biological (antimicrobial, cytotoxic, embryotoxic, and hemolytic) activity of total lipids, individual fractions and classes of lipids, and photosynthetic pigments of Saccharina cichorioides (Miyabe) were studied, together with the effect of season of the alga harvesting and changes in fatty acid composition of lipids on their activity. Antimicrobial activity was more pronounced in total lipids, individual fractions of lipids, and photosynthetic pigments of S. cichorioides collected in March. High antimicrobial activity was also demonstrated by total lipids of alga samples collected in September and November and hemolytic activity, in those collected in March and November. Pronounced hemolytic activity was demonstrated by some classes of glyceroglycolipids of laminaria samples collected in November. Cytotoxic activity toward mouse splenocytes was demonstrated only by total lipids of alga collected in March. Toxic effects toward embryos of sea urchin were demonstrated by lipids of S. cichorioides collected in June and September. None of the lipids or pigments was active against Ehrlich ascites carcinoma. [ABSTRACT FROM AUTHOR]

The new highly oxidized chromene oxirapentyn E was isolated from marine isolate of the fungus Isaria felina (DC.) Fr. Its structure was established based on NMR spectroscopy, high-resolution mass spectrometry, and convergent synthesis. Oxirapentyn E at low and ultralow (10 –5–10 –17 M) doses exhibited stimulating activity on the growth of corn ( Zea mays L.) and barley ( Hordeum vulgare L.) rootlets. The dose–effect curves were bimodal in nature. [ABSTRACT FROM AUTHOR]