Dynamics of orientational fluctuations in a homeotropic Fréedericksz transition under a rotating magnetic field

We study the problem of the Fréedericksz transition under a rotating magnetic field by using a dynamical model which incorporates thermal fluctuations into the whole set of nematodynamic equations. In contrast to other geometries, nonuniform textures in the plane of the sample do not appear favored. The proper consideration of thermal noise enables us to describe the dynamics of orientational fluctuations both below and above the shifted instability.

Ground- and excited-state properties of M-center oxygen vacancy aggregates in the bulk and the surface of MgO

Aggregates of oxygen vacancies (F centers) represent a particular form of point defects in ionic crystals. In this study we have considered the combination of two oxygen vacancies, the M center, in the bulk and on the surface of MgO by means of cluster model calculations. Both neutral and charged forms of the defect M and M+ have been taken into account. The ground state of the M center is characterized by the presence of two doubly occupied impurity levels in the gap of the material; in M+ centers the highest level is singly occupied. For the ground-state properties we used a gradient corrected density functional theory approach. The dipole-allowed singlet-to-singlet and doublet-to-doublet electronic transitions have been determined by means of explicitly correlated multireference second-order perturbation theory calculations. These have been compared with optical transitions determined with the time-dependent density functional theory formalism. The results show that bulk M and M+ centers give rise to intense absorptions at about 4.4 and 4.0 eV, respectively. Another less intense transition at 1.3 eV has also been found for the M+ center. On the surface the transitions occur at 1.6 eV (M+) and 2 eV (M). The results are compared with recently reported electron energy loss spectroscopy spectra on MgO thin films.

Transient dynamics of orientational fluctuations in the Fréedericksz transition

Transient dynamics of spatial fluctuations of the director field in the pure twist Fréedericksz transition is studied. A nonlinear calculation is presented. Anomalous transient fluctuations are shown. Different stages of evolution and the domain of validity of linear theories are discussed.

Alignment of hexatic langmuir monolayers under shear

We have studied the structural changes that fatty acid monolayers in the Ov phase undergo when a simple shear flow is imposed. A strong coupling is revealed by the changes in domain structure that are observable using Brewster angle microscopy, suggesting the possibility of shear alignment. The dependence of the alignment on the molecular polar tilt proves that the mechanism is different than in nematic liquid crystals. We argue that the degenerate lattice symmetry lines of the underlying pseudohexagonal lattice align in the flow direction, and we explain the observed alignment angle using geometrical arguments.

A first-principles analysis of the magnetism of CuII polynuclear coordination complexes: the case of [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4·2.5H2O

The magnetic structure of the [Cu4(bpy)4(aspartate)2(H2O)3](ClO4)4·2.5 H2Ocrystal - using fractional coordinates determined at room-temperature ¿ has beenanalysed in detail. This analysis has been carried out by extending our first principlesbottom-up theoretical approach, which was initially designed to study through-spacemagnetic interactions, to handle through-bond magnetic interactions. The only input datarequired by this approach are the values of the computed JAB exchange parameters for allthe unique pairs of spin-containing centres. The results allow the magnetic structure ofthe crystal, which presents two types of isolated tetranuclear CuII clusters, to be definedin quantitative terms. Each of these clusters presents ferro and antiferromagneticinteractions, the former being stronger, although outnumbered by the latter. Thecomputed magnetic susceptibility curve shows the same qualitative features as theexperimental data. However, there are small differences that are presumed to beassociated with the use of room-temperature crystal coordinates.

Mineral inventory of continuously erupting basaltic andesites at Arenal volcano, Costa Rica: implications for interpreting monotonous, crystal-rich, mafic arc stratigraphies

Except for the first 2 years since July 29, 1968, Arenal volcano has continuously erupted compositionally monotonous and phenocryst-rich (similar to35%) basaltic andesites composed of plagioclase (plag), orthopyroxene (opx), clinopyroxene (cpx), spinel olivine. Detailed textural and compositional analyses of phenocrysts, mineral inclusions, and microlites reveal comparable complexities in any given sample and identify mineral components that require a minimum of four crystallization environments. We suggest three distinct crystallization environments crystallized low Mg# (<78) silicate phases from andesitic magma but at different physical conditions, such as variable pressure of crystallization and water conditions. The dominant environment, i.e., the one which accounts for the majority of minerals and overprinted all other assemblages near rims of phenocrysts, cocrystallized clinopyroxene (Mg# similar to71-78), orthopyroxene (Mg# similar to71-78), titanomagnetite and plagioclase (An(60) to An(85)). The second environment cocrystallized clinopyroxene (Mg# 71-78), olivine (<Fo(78)), titanomagnetite, and very high An (similar to90) plagioclase, while the third cocrystallized clinopyroxene (Mg# 71-78) with high (>7) Al/Ti and high (>4 wt.%) Al2O3, titanomagnetite with considerable Al2O3 (10-18 wt.%) and possibly olivine but appears to lack plagioclase. A fourth crystallization environment is characterized by clinopyroxene (e.g., Mg#=similar to78-85; Cr2O3=0.15-0.7 wt.%), Al-, Cr-rich spinel olivine (similar toFo(80)), and in some circumstances high-An (>80) plagioclase. This assemblage seems to record mafic inputs into the Arenal system and crystallization at high to low pressures. Single crystals cannot be completely classified as xenocrysts, antecrysts (cognate crystals), or phenocrysts, because they often contain different parts each representing a different crystallization environment and thus belong to different categories. Bulk compositions are mostly too mafic to have crystallized the bulk of ferromagnesian minerals and thus likely do not represent liquid compositions. On the other hand, they are the cumulative products of multiple mixing events assembling melts and minerals from a variety of sources. The driving force for this multistage mixing evolution to generate erupting basaltic andesites is thought to be the ascent of mafic magma from lower crustal levels to subvolcanic depths which at the same time may also go through compositional modification by fractionation and assimilation of country rocks. Thus, mafic magmas become basaltic andesite through mixing, fractionation and assimilation by the time they arrive at subvolcanic depths. We infer new increments of basaltic andesite are supplied nearly continuously to the subvolcanic reservoir concurrently to the current eruption and that these new increments are blended into the residing, subvolcanic magma. Thus, the compositional monotony is mostly the product of repetitious production of very similar basaltic andesite. Furthermore, we propose that this quasi-constant supply of small increments of magma is the fundamental cause for small-scale, decade-long continuous volcanic activity; that is, the current eruption of Arenal is flux-controlled by inputs of mantle magmas. (C) 2004 Elsevier B.V. All rights reserved.

Myeloid-related proteins 8 and 14 contribute to monosodium urate monohydrate crystal-induced inflammation in gout.

OBJECTIVE: Monosodium urate monohydrate (MSU) crystal-induced interleukin-1β (IL-1β) secretion is a critical factor in the pathogenesis of gout. However, without costimulation by a proIL-1β-inducing factor, MSU crystals alone are insufficient to induce IL-1β secretion. The responsible costimulatory factors that act as a priming endogenous signal in vivo are not yet known. We undertook this study to analyze the costimulatory properties of myeloid-related protein 8 (MRP-8) and MRP-14 (endogenous Toll-like receptor 4 [TLR-4] agonists) in MSU crystal-induced IL-1β secretion and their relevance in gout. METHODS: MRP-8/MRP-14 was measured in paired serum and synovial fluid samples by enzyme-linked immunosorbent assay (ELISA) and localized in synovial tissue from gout patients by immunohistochemistry. Serum levels were correlated with disease activity, and MSU crystal-induced release of MRPs from human phagocytes was measured. Costimulatory effects of MRP-8 and MRP-14 on MSU crystal-induced IL-1β secretion from phagocytes were analyzed in vitro by ELISA, Western blotting, and polymerase chain reaction. The impact of MRP was tested in vivo in a murine MSU crystal-induced peritonitis model. RESULTS: MRP-8/MRP-14 levels were elevated in the synovium, tophi, and serum of patients with gout and correlated with disease activity. MRP-8/MRP-14 was released by MSU crystal-activated phagocytes and increased MSU crystal-induced IL-1β secretion in a TLR-4-dependent manner. Targeted deletion of MRP-14 in mice led to a moderately reduced response of MSU crystal-induced inflammation in vivo. CONCLUSION: MRP-8 and MRP-14, which are highly expressed in gout, are enhancers of MSU crystal-induced IL-1β secretion in vitro and in vivo. These endogenous TLR-4 ligands released by activated phagocytes contribute to the maintenance of inflammation in gout.

Melt variability in percolated peridotite: an experimental study applied to reactive migration of tholeiitic basalt in the upper mantle

Melt-rock reaction in the upper mantle is recorded in a variety of ultramafic rocks and is an important process in modifying melt composition on its way from the source region towards the surface. This experimental study evaluates the compositional variability of tholeiitic basalts upon reaction with depleted peridotite at uppermost-mantle conditions. Infiltration-reaction processes are simulated by employing a three-layered set-up: primitive basaltic powder ('melt layer') is overlain by a 'peridotite layer' and a layer of vitreous carbon spheres ('melt trap'). Melt from the melt layer is forced to move through the peridotite layer into the melt trap. Experiments were conducted at 0.65 and 0.8 GPa in the temperature range 1,170-1,290 degrees C. In this P-T range, representing conditions encountered in the transition zone (thermal boundary layer) between the asthenosphere and the lithosphere underneath oceanic spreading centres, the melt is subjected to fractionation, and the peridotite is partially melting (T (s) similar to 1,260 degrees C). The effect of reaction between melt and peridotite on the melt composition was investigated across each experimental charge. Quenched melts in the peridotite layers display larger compositional variations than melt layer glasses. A difference between glasses in the melt and peridotite layer becomes more important at decreasing temperature through a combination of enrichment in incompatible elements in the melt layer and less efficient diffusive equilibration in the melt phase. At 1,290A degrees C, preferential dissolution of pyroxenes enriches the melt in silica and dilutes it in incompatible elements. Moreover, liquids become increasingly enriched in Cr(2)O(3) at higher temperatures due to the dissolution of spinel. Silica contents of liquids decrease at 1,260 degrees C, whereas incompatible elements start to concentrate in the melt due to increasing levels of crystallization. At the lowest temperatures investigated, increasing alkali contents cause silica to increase as a consequence of reactive fractionation. Pervasive percolation of tholeiitic basalt through an upper-mantle thermal boundary layer can thus impose a high-Si 'low-pressure' signature on MORB. This could explain opx + plag enrichment in shallow plagioclase peridotites and prolonged formation of olivine gabbros.

Deicer Scaling Resistance of Concrete Mixtures Containing Slag Cement Phase 2: Evaluation of Different Laboratory Scaling Test Methods, TPF-5(100), 2012

With the use of supplementary cementing materials (SCMs) in concrete mixtures, salt scaling tests such as ASTM C672 have been found to be overly aggressive and do correlate well with field scaling performance. The reasons for this are thought to be because at high replacement levels, SCM mixtures can take longer to set and to develop their properties: neither of these factors is taken into account in the standard laboratory finishing and curing procedures. As a result, these variables were studied as well as a modified scaling test, based on the Quebec BNQ scaling test that had shown promise in other research. The experimental research focused on the evaluation of three scaling resistance tests, including the ASTM C672 test with normal curing as well as an accelerated curing regime used by VDOT for ASTM C1202 rapid chloride permeability tests and now included as an option in ASTM C1202. As well, several variations on the proposed draft ASTM WK9367 deicer scaling resistance test, based on the Quebec Ministry of Transportation BNQ test method, were evaluated for concretes containing varying amounts of slag cement. A total of 16 concrete mixtures were studied using both high alkali cement and low alkali cement, Grade 100 slag and Grade 120 slag with 0, 20, 35 and 50 percent slag replacement by mass of total cementing materials. Vinsol resin was used as the primary air entrainer and Micro Air® was used in two replicate mixes for comparison. Based on the results of this study, a draft alternative test method to ASTM C762 is proposed.