Upper limits on a stochastic background of gravitational waves

The Laser Interferometer Gravitational-Wave Observatory has performed a third science run with much improved sensitivities of all three interferometers. We present an analysis of approximately 200 hours of data acquired during this run, used to search for a stochastic background of gravitational radiation. We place upper bounds on the energy density stored as gravitational radiation for three different spectral power laws. For the flat spectrum, our limit of omega0 < 8.4 x 10(-4) in the 69-156 Hz band is approximately 10(5) times lower than the previous result in this frequency range.

Colloidal Jamming at Interfaces: A Route to Fluid-Bicontinuous Gels

Colloidal particles or nanoparticles, with equal affinity for two fluids, are known to adsorb irreversibly to the fluid-fluid interface. We present large-scale computer simulations of the demixing of a binary solvent containing such particles. The newly formed interface sequesters the colloidal particles; as the interface coarsens, the particles are forced into close contact by interfacial tension. Coarsening is markedly curtailed, and the jammed colloidal layer seemingly enters a glassy state, creating a multiply connected, solidlike film in three dimensions. The resulting gel contains percolating domains of both fluids, with possible uses as, for example, a microreaction medium.

Physical and computational scaling issues in lattice Boltzmann simulations of binary fluid mixtures

We describe some scaling issues that arise when using lattice Boltzmann (LB) methods to simulate binary fluid mixtures--both in the presence and absence of colloidal particles. Two types of scaling problem arise: physical and computational. Physical scaling concerns how to relate simulation parameters to those of the real world. To do this effectively requires careful physics, because (in common with other methods) LB cannot fully resolve the hierarchy of length, energy and time-scales that arise in typical flows of complex fluids. Care is needed in deciding what physics to resolve and what to leave unresolved, particularly when colloidal particles are present in one or both of two fluid phases. This influences steering of simulation parameters such as fluid viscosity and interfacial tension. When the physics is anisotropic (for example, in systems under shear) careful adaptation of the geometry of the simulation box may be needed; an example of this, relating to our study of the effect of colloidal particles on the Rayleigh-Plateau instability of a fluid cylinder, is described. The second and closely related set of scaling issues are computational in nature: how do you scale-up simulations to very large lattice sizes? The problem is acute for systems undergoing shear flow. Here one requires a set of blockwise co-moving frames to the fluid, each connected to the next by a Lees-Edwards like boundary condition. These matching planes lead to small numerical errors whose cumulative effects can become severe; strategies for minimizing such effects are discussed.

Limits on gravitational-wave emission from selected pulsars using LIGO data

We place direct upper limits on the amplitude of gravitational waves from 28 isolated radio pulsars by a coherent multidetector analysis of the data collected during the second science run of the LIGO interferometric detectors. These are the first direct upper limits for 26 of the 28 pulsars. We use coordinated radio observations for the first time to build radio-guided phase templates for the expected gravitational-wave signals. The unprecedented sensitivity of the detectors allows us to set strain upper limits as low as a few times 10(-24). These strain limits translate into limits on the equatorial ellipticities of the pulsars, which are smaller than 10(-5) for the four closest pulsars.

HAIR- AN Syndrome

Abstract

Biodegradable synthetic polymers for tissue engineering

This paper reviews biodegradable synthetic polymers focusing on their potential in tissue engineering applications. The major classes of polymers are briefly discussed with regard to synthesis, properties and biodegradability, and known degradation modes and products are indicated based on studies reported in the literature. A vast majority of biodegradable polymers studied belongs to the polyester family, which includes polyglycolides and polylactides. Some disadvantages of these polymers in tissue engineering applications are their poor biocompatibility, release of acidic degradation products, poor processability and loss of mechanical properties very early during degradation. Other degradable polymers such as polyorthoesters, polyanhydrides, polyphosphazenes, and polyurethanes are also discussed and their advantages and disadvantages summarised. With advancements in tissue engineering it has become necessary to develop polymers that meet more demanding requirements. Recent work has focused on developing injectable polymer compositions based on poly (propylene fumarate) and poly (anhydrides) to meet these requirements in orthopaedic tissue engineering. Polyurethanes have received recent attention for development of degradable polymers because of their great potential in tailoring polymer structure to achieve mechanical properties and biodegradability to suit a variety of applications.

Interactions and correlations of particulate inclusions in a columnar phase

We calculate the elastic-field-mediated interaction between macroscopic particles in a columnar hexagonal phase. The interaction is found to be long-ranged and non-central, with both attractive and repulsive parts. We show how the interaction modifies the particle correlations and the column fluctuations. We also calculate the interaction of particles with the topological defects of the columnar phase. The particle-defect interaction reduces the mobility of the defects.

Selective Protection Strategies in the Synthesis of TRIS-Fatty Ester Derivatives

A methodology for the selective synthesis of lipophilic acyl derivatives of the glycinamido triol (1) with either one, two, or three fatty ester groups has been established. Peracylation of (1), with palmitoyl chloride gave the triacylated derivative. Conversion of (1) into the acetonide, followed by acylation with either palmitoyl chloride or lauroyl chloride, and acetal hydrolysis provided the monoacylated derivatives. Treatment of (1) with trimethyl orthoacetate gave the orthoacetate derivative. Mild hydrolysis provided the monoacetate/diol. Acylation of the two hydroxyl groups with palmitoyl chloride gave the dipalmitate/acetate. Selective cleavage of the acetate group afforded the dipalmitate of (1). Analogous chemistry with trimethyl orthoformate provided the same dipalmitate via the orthoformate, monoformate/diol, and dipalmitate/formate. A more robust synthesis of the dipalmitate was achieved by converting the hydroxyl group of the acetonide of (1) into a tert-butyldiphenylsilyl ether, followed by acetal hydrolysis, palmitoylation of the liberated hydroxyl groups, and desilylation.

Determination and optimization of mode matching into optical cavities by heterodyne detection

We report on a novel high-sensitivity method to characterize and improve mode matching into optical cavities. This method is based on heterodyne detection of cylindrical transverse cavity modes. A specially designed annular-segmented photodiode is used to measure the amplitude of nonresonant modes reflected by the cavity. Our measurements allow us to optimize cavity mode matching to nearly 99.98% and will play an important diagnostic role in gravitational-wave detectors.

A polymorphic L1 retroposon insertion in the centromere of the human Y chromosome

We have identified a novel polymorphic L1 retroposon insertion, designated LY1, in the centromeric alphoid array of the human Y chromosome. The element belongs to the transpositionally active Ta subset and its presence is compatible with normal centromere function. It was found at highest frequency in China, where it accounts for 23% of the Han sample, and was present at low frequencies in the surrounding areas, but was not found at all outside Asia. Chromosomes carrying LY1 show considerable microsatellite diversity, suggesting an ancient origin for the lineage at approximately 10 000 years ago (with wide confidence limits), but only limited subsequent migration.