Changed lyotropic liquid crystalline structure due to polymerization of the amphiphilic component

Optical patterns in polarized light and x-ray reflections in the low-angle region were used to detect a shift from one liquid crystalline structure to another during polymerization. The polymerization took place in a Iotropic liquid crystal of water and sodium undecenoate, with a structure consisting of cylinders in a two-dimensional hexagonal close packing. After polymerization, a lamellar liquid crystalline structure was obtained.     

Surface crystallization in a liquid AuSi alloy

X-ray measurements reveal a crystalline monolayer at the surface of the eutectic liquid Au82Si18, at temperatures above the alloy's melting point. Surface-induced atomic layering, the hallmark of liquid metals, is also found below the crystalline monolayer. The layering depth, however, is threefold greater than that of all liquid metals studied to date. The crystallinity of the surface monolayer is notable, considering that AuSi does not form stable bulk crystalline phases at any concentration and temperature and that no crystalline surface phase has been detected thus far in any pure liquid metal or nondilute alloy. These results are discussed in relation to recently suggested models of amorphous alloys.     

LIQUID CRYSTALS: New Banana Phases

Liquid crystals-materials that flow like a fluid but are optically anisotropic like a crystal-exhibit large responses to modest external disturbances. In his Perspective, Lubensky discusses the advances reported in two papers in this issue, both of which involve liquid crystals made from V-shaped or bent-core molecules. Walba et al. report a synthetic strategy for producing a ferroelectric phase from achiral bent-core molecules. Pratibha et al. show that new liquid crystalline phases form when bent-core molecules are mixed with a particular class of rodlike molecules. These papers introduce new molecular designs that yield new liquid crystalline phases with controlled structure and properties.     

An orientational transition of bent-core molecules in an anisotropic matrix

We report the discovery of an orientational transition of bent-core molecules in a background anisotropic medium, in this case a smectic liquid crystal made of rod-like molecules. The resulting director is apolar in nature, and the medium can be described as an orthogonal biaxial smectic. The detailed phase diagram of mixtures of the two types of compounds revealed the induction of two liquid crystalline phases that are specific to compounds with bent-core molecules. The chemical nature of the bounding surface had a marked influence on the observed textures.     

Structure of membrane surfactant and liquid crystalline smectic lamellar phases under flow

Synchrotron x-ray scattering studies were performed to probe the nonequilibrium structures of two layered systems at high shear rates: the smectic-A phase of the thermotropic liquid crystal 4-cyano-4'-octylbiphenyl (8CB) and the lamellar L(alpha) phases of surfactant membranes composed of sodium dodecyl sulfate and pentanol. Whereas the lamellar surfactant phases oriented primarily with their layers parallel to the shearing plates, as expected intuitively, in the corresponding high shear regime, the smectic-A liquid crystalline material oriented with the layers perpendicular to the shearing plates. A careful numerical study revealed that this surprising layer orientation results from nonlinear dynamics of the liquid crystal director and is caused by the flow distortion of thermal fluctuations.     

Structural diversity of sodium

Sodium exhibits a pronounced minimum of the melting temperature at approximately 118 gigapascals and 300 kelvin. Using single-crystal high-pressure diffraction techniques, we found that the minimum of the sodium melting curve is associated with a concentration of seven different crystalline phases. Slight changes in pressure and/or temperature induce transitions between numerous structural modifications, several of which are highly complex. The complexity of the phase behavior above 100 gigapascals suggests extraordinary liquid and solid states of sodium at extreme conditions and has implications for other seemingly simple metals.     

空气罐控制管道水击实验研究

在实验室的简单管路水力系统中，加设一种气囊式空气罐，进行简单管路的水击实验，可以有效地控制水击危害，并模拟出生产管道的水击动态特性，这种空气罐具有气密性、可梗换节流孔口、计算机能够模拟罐的容积的结构特点，用以达到控制管路系统中因阀门瞬时关闭产生的水击增压速率，并防止液柱分离，在瞬变分析忽略阀门和罐间摩阻、三通连接的局部摩阻、罐和管路间的摩阻、液流惯性和罐内液面变化的前提下，建立了阀门、窑罐的复合边     

Spontaneous vesicles formed from hydroxide surfactants: evidence from electron microscopy

Dialkyldimethylammonium hydroxide surfactants are highly soluble in water and form spontaneous stable vesicles. These vesicles can be grown to size with added acid, and appear to provide an ideal membrane mimetic system for the study of fusion and ion transport. These phenomena are a consequence of strong hydration forces that are not necessarily limited to the hydroxide ions. The forces can be used to design a variety of model systems whose behavior differs from that of systems in which double-chained surfactants form insoluble liquid crystalline phases in water and unstable vesicle suspensions on prolonged sonication.     

Structure of a Langmuir film on a liquid metal surface

The structure of organic monolayers on liquid surfaces depends sensitively on the details of the molecular interactions. The structure of a stearic acid film on a mercury surface was measured as a function of coverage with angstrom resolution. Unlike monolayers on water, the molecules were found here to undergo a transition from surface-parallel to surface-normal orientation with increasing coverage. At high coverage, two condensed hexatic phases of standing-up molecules were found. At low coverage, a two-dimensional (2D) gas phase and condensed single- and double-layered phases of flat-lying molecular dimers were revealed, exhibiting a 1D longitudinal positional order. This system should provide a broader tunability range for nanostructure construction than solid-supported self-assembled monolayers.     

Mechanisms of trace metal transport in rivers

Trace metals transported by the Amazon (and Yukon rivers were analytically partitioned among the transport phases: in solutions, ion exchange, organic materials, metallic coatings, and crystalline solids. The distribution for both rivers is similarly proportioned, with copper and chromium transported mainly in the crystalline solids, manganese in coatings, and iron, nickel, and cobalt distributed equally between precipitated metallic coatings and crystalline solids.     

Giant supramolecular liquid crystal lattice

Self-organized supramolecular organic nanostructures have potential applications that include molecular electronics, photonics, and precursors for nanoporous catalysts. Accordingly, understanding how self-assembly is controlled by molecular architecture will enable the design of increasingly complex structures. We report a liquid crystal (LC) phase with a tetragonal three-dimensional unit cell containing 30 globular supramolecular dendrimers, each of which is self-assembled from 12 dendron (tree-like) molecules, for the compounds described here. The present structure is one of the most complex LC phases yet discovered. A model explaining how spatial arrangement of self-assembled dendritic aggregates depends on molecular architecture and temperature is proposed.     

生长育肥猪胃肠道正常厌氧菌群的数量和分区

采用厌氧微生物学方法,对2头育肥猪的胃、小肠、盲肠、结肠和直肠的固相、液相和粘膜中的总厌氧菌、淀粉分解菌,纤维分解菌和蛋白分解菌的数量分布和比例进行了研究,结果表明,上述总厌摒力和3种功能菌群的数量在胃和小肠区段固相内容物中占绝对优势,而在盲肠、结肠和直肠内容物中以液相菌群占绝对优势,在胃和小肠区段,固相,液相内容物中3种功能菌群的数量间无明显差异,但在盲肠、结肠和直肠段,固相、液相内容物中淀粉分解菌和蛋白分解菌为优势菌群,在各区段胃肠道粘膜中,胃和小肠的3种菌群的数量相对较低,盲肠粘膜中主要菌群数量分布为蛋白分解菌＞淀粉分解菌＞纤维分解菌（P＜0．01）;而结肠和直肠粘膜中以淀粉分解菌占绝对优势。     

Structure and Properties of Crystalline Polymers: Supramolecular structure is complex, can be controlled, and influences mechanical properties

Through control of the crystallization process many polymers can be made to exhibit a broad spectrum of structural possibilities, ranging from a state of high disorder to one of high order. Emphasis has been placed on bulk-crystallized polymers which normally fall near the center of this spectrum. This was done in part because polymers are most commonly fabricated in this manner, and also because the amount of attention given in recent years to crystals grown from dilute solution has tended to obscure important aspects of the structure of bulk-crystallized polymers. Differences in the structure of the interlamellar regions account most reasonably for many of the variations in mechanical properties that crystalline polymers can be made to display. The interlamellar amorphous model, proposed here as a structural model for bulk-crystallized polymers, largely neglects the lamellae themselves, because so little is known about the structure of the lamellae of bulk-crystallized polymers and how variations in lamellar structure can affect properties. This model is intended, therefore, as both a working hypothesis to aid further investigation and as an outline to be filled in as more is learned about the supramolecular structure of crystalline polymers (31).     

Electron microprobe analysis of lunar samples

Plagioclase feldspar, clinopyroxene, and ilmenite in a polished thin section of a type A crystalline rock were analyzed. The clinopyroxene grains are compositionally variable, and both high Ca and low Ca phases are present. The plagioclase is compositionally homogeneous. The ilmenite is chemically homogeneous except for occasional, small areas of high local chromium concentration. Accessory minerals are: apatite (containing Cl, F, Y, and Ce), troilite, and metallic iron. Glassy spherules from the lunar soil are for the most part similar in composition to the crystalline rocks; however, some appear to have been monomineralic. The crystalline rock has apparently formed by relatively rapid cooling of a silicate melt under conditions of low oxygen partial pressure. Many components of the soil appear to have formed by meteoritic impact.     

Photoacoustic "signatures" of particulate matter: optical production of acoustic monopole radiation

Absorption of pulsed laser radiation by a single particle generates a photoacoustic wave whose time profile can be measured with a wideband pressure transducer. Solution of the wave equation for pressure in one, two, and three dimensions shows that the photoacoustic wave is determined by the geometry and dimensions of the particle, and by its sound speed and density relative to the fluid that surrounds it. Photoacoustic waves, referred to here as signatures, are reported in experiments in which fluid droplets, cylinders, and layers are irradiated with 10-nanosecond laser pulses.     

Spin-liquid ground state of the S = 1/2 kagome Heisenberg antiferromagnet

We use the density matrix renormalization group to perform accurate calculations of the ground state of the nearest-neighbor quantum spin S = 1/2 Heisenberg antiferromagnet on the kagome lattice. We study this model on numerous long cylinders with circumferences up to 12 lattice spacings. Through a combination of very-low-energy and small finite-size effects, our results provide strong evidence that, for the infinite two-dimensional system, the ground state of this model is a fully gapped spin liquid.     

High-Temperature XAS Study of Fe2SiO4 Liquid: Reduced Coordination of Ferrous Iron

X-ray absorption spectroscopy (XAS) of Fe(2+) in Fe(2)SiO(4) liquid at 1575 kelvin and 10(-4) gigapascal (1 bar) shows that the Fe(2+) -O bond length is 1.98 +/- 0.02 angstroms compared with approximately 2.22 angstroms in crystalline Fe(2)SiO(4) (fayalite) at the melting point (1478 kelvin), which indicates a decrease in average Fe(2+) coordination number from six in fayalite to four in the liquid. Anharmonicity in the liquid was accounted for using a data analysis procedure. This reduction in coordination number is similar to that observed on the melting of certain ionic salts. These results are used to develop a model of the medium-range structural environment of Fe(2+) in olivine-composition melts, which helps explain some of the properties of Fe(2)SiO(4) liquid, including density, viscosity, and the partitioning of iron and nickel between silicate melts and crystalline olivines. Some of the implications of this model for silicate melts in the Earth's crust and mantle are discussed.     

Long-lived giant number fluctuations in a swarming granular nematic

Coherently moving flocks of birds, beasts, or bacteria are examples of living matter with spontaneous orientational order. How do these systems differ from thermal equilibrium systems with such liquid crystalline order? Working with a fluidized monolayer of macroscopic rods in the nematic liquid crystalline phase, we find giant number fluctuations consistent with a standard deviation growing linearly with the mean, in contrast to any situation where the central limit theorem applies. These fluctuations are long-lived, decaying only as a logarithmic function of time. This shows that flocking, coherent motion, and large-scale inhomogeneity can appear in a system in which particles do not communicate except by contact.     

End-to-end stacking and liquid crystal condensation of 6 to 20 base pair DNA duplexes

Short complementary B-form DNA oligomers, 6 to 20 base pairs in length, are found to exhibit nematic and columnar liquid crystal phases, even though such duplexes lack the shape anisotropy required for liquid crystal ordering. Structural study shows that these phases are produced by the end-to-end adhesion and consequent stacking of the duplex oligomers into polydisperse anisotropic rod-shaped aggregates, which can order into liquid crystals. Upon cooling mixed solutions of short DNA oligomers, in which only a small fraction of the DNA present is complementary, the duplex-forming oligomers phase-separate into liquid crystal droplets, leaving the unpaired single strands in isotropic solution. In a chemical environment where oligomer ligation is possible, such ordering and condensation would provide an autocatalytic link whereby complementarity promotes the extended polymerization of complementary oligomers.     

Precipitate formation in the strontium-phosphate system

Study of the precipitation process in the aqueous Sr(OH)(2)-H(3)PO(4) system, in order to elucidate the phase transformations and the nature of the final solid phases, shows that over much of the range of compositions studied the initial precipitate is poorly crystalline; the x-ray pattern resembles that of strontium hydroxyapatite but has a strontium: phosphorus molar ratio close to 1.3. Within 1 hour the initial precipitate changes to a stable crystalline phase (or phases), with corresponding change, either up or down, in the strontium: phosphorus ratio. At high ratios of Sr(OH)(2) to H(2)PO(4) the initial precipitate is Sr(3)(PO(4))(2)-4H(2)O, which then converts to a phase having the x-ray diffraction pattern of strontium hydroxyapatite, but having a strontium: phosphorus ratio that depends somewhat on the initial ratio of Sr(OH)(2) to H(3)PO(4) used in the precipitation.