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.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
In this study, we measured translational water diffusion selectively along symplast pathway through plasmodesmata in maize roots, and the effective plasmodesmata permeability coefficient (P) was ...determined using a nuclear magnetic resonance (NMR) spin echo method. Measuring of water transport selectively along the plant root plasmodesmata was achieved with paramagnetic complexes (PCs) of high relaxation efficiency. PCs penetrate into the intercellular space of root tissue, but not into cells, and accelerate the magnetic relaxation processes of intercellular water, thereby excluding the contribution of intercellular water to the registered NMR diffusion echo attenuation. In result, NMR control of translational diffusion can be applied to the signal of the water moving along the symplast pathway through plasmodesmata, where the PCs do not penetrate. Diethylenetriaminepentaacetic acid (GdDTPA), Mn2+-trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (MnDCTA), and GdCl3 were used as PCs. An increase in the PCs concentration led to a side effect in the form of a varying decrease in diffusive water transport in the roots. The P was determined by extrapolating the concentration dependence to zero concentration of PCs. Among the PCs studied, MnDCTA had the least side effects on the water transport when the concentration dependence was linear. When MnDCTA was used, the P accounted for 30–35% of the total cell water permeability (by transmembrane and symplast pathways). The rate of water flow along the plasmodesmata in the approximation of the piston mode of flow along the linear cell chain was estimated to range from 4.5 × 10−7 to 8.8 × 10−7 m/s.
•Water transport along plant root plasmodesmata by NMR and paramagnetics was studied.•Paramagnetic complexes can reduce cell-to-cell water transport in plant roots.•The rate of water flow through plasmodesmata was calculated.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The first example of a gram-scale synthesis of methylmethoxysilanes using the direct reaction of silicon with dimethyl ether (DME) is presented. The direct synthesis (DS) of methylmethoxysilanes was ...carried out in a high-pressure mechanochemical reactor (HPMR) at 250 °C using CuCl as a catalyst and Sn and Zn as promoters. The mechanochemical approach allows the use of large-grain inactivated technical grade silicon without preliminary stages of contact mass (CM) preparation usually required in such works. Under these conditions, the direct synthesis of organoalkoxysilanes proceeds with almost complete silicon conversion and high selectivity (81.6%) for dimethyldimethoxysilane and dimethylsilyl siloxanes. Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) studies of the CM confirmed that the reaction proceeds with very high (90-100%) silicon conversions when the products are produced in gram quantities.
First gram-scale synthesis of methylmethoxysilanes
via
mechanochemical direct reaction of Si with dimethyl ether, achieving nearly 100% silicon conversion and high selectivity for dimethylsilyl-containing products.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A newly discovered Paleolithic site on the Yana River, Siberia, at 71°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.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
In the long term, the innovative development strategy efficiency is considered as the most crucial condition for assurance of economic system competitiveness in market conditions. It determines the ...problem relevance of such justification strategies with regard to specific systems features and conditions of their operation. The problem solution for industrial enterprises can be based on mathematical models of supporting the decision-making on the elements of the innovative manufacturing program. An optimization model and the planning method of innovative products volume and variety are suggested. The feature of the suggested model lies in the nonlinear nature of the objective function. It allows taking into consideration the law of diminishing marginal utility. The suggested method of optimization takes into account the system features and enables the effective implementation of manufacturing capabilities in modern conditions of production organization and sales in terms of market saturation.
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.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
The synthesis of novel stereoregular carborane-containing phenylcyclosiloxanes (4, 5, 6, 8, and 12 -SiO- units in the ring) has been developed. The structures of all compounds were confirmed by a ...series of physicochemical methods. Tris-
cis
-tris-
trans
-dodecaphenyl(1(3-(9-
m
-carboranyl)propyl)dimethylsiloxy)cyclododecasiloxane has been studied by NMR spectroscopy and it was found that such a configuration of the ring makes two methyl groups diastereotopic, resulting in magnetic non-equivalence of the protons of these groups. The results of thermal studies of the obtained compounds are also described.
The synthesis of novel stereoregular carborane-containing phenylcyclosiloxanes (4, 5, 6, 8, and 12 -SiO- units in the ring) has been developed.
Fluid polyamorphism is the existence of different condensed amorphous states in a single-component fluid. It is either found or predicted, usually at extreme conditions, for a broad group of very ...different substances, including helium, carbon, silicon, phosphorous, sulfur, tellurium, cerium, hydrogen, and tin tetraiodide. This phenomenon is also hypothesized for metastable and deeply supercooled water, presumably located a few degrees below the experimental limit of homogeneous ice formation. We present a generic phenomenological approach to describe polyamorphism in a single-component fluid, which is completely independent of the molecular origin of the phenomenon. We show that fluid polyamorphism may occur either in the presence or in the absence of fluid phase separation depending on the symmetry of the order parameter. In the latter case, it is associated with a second-order transition, such as in liquid helium or liquid sulfur. To specify the phenomenology, we consider a fluid with thermodynamic equilibrium between two distinct interconvertible states or molecular structures. A fundamental signature of this concept is the identification of the equilibrium fraction of molecules involved in each of these alternative states. However, the existence of the alternative structures may result in polyamorphic fluid phase separation only if mixing of these structures is not ideal. The two-state thermodynamics unifies all the debated scenarios of fluid polyamorphism in different areas of condensed-matter physics, with or without phase separation, and even goes beyond the phenomenon of polyamorphism by generically describing the anomalous properties of fluids exhibiting interconversion of alternative molecular states.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM, UPUK
A series of mono- and polyfunctional carborane organosilicon derivatives were prepared with good yields based on the hydrosilylation reactions of allylcarboranes with hydride-containing organosilicon ...compounds such as tetramethyldisiloxane, decamethylpentasiloxane and triethoxysilane in the presence of Karstedt's catalyst. The functionalization of the double bonds in the allylcarboranes proceeded regioselectively in accordance with the Farmer's rule, providing efficient access to carborane silicon compounds. It was found for 9-
o
- and 9-
m
-allylcarboranes that an excess of Karstedt's catalyst could promote the migration of a double bond in allylcarboranes to form boron-substituted propenyl derivatives; the structure of the ortho-isomer was supported by X-ray diffraction analysis.
A series of mono- and polyfunctional carborane organosilicon derivatives were prepared with good yields based on the hydrosilylation reactions of allylcarboranes with hydride-containing organosilicon compounds such as tetramethyldisiloxane, decamethylpentasiloxane and triethoxysilane in the presence of Karstedt's catalyst.
PDF
