Ultrasonic edge shadowing around cylindrical cavities with and without walls

In B-mode ultrasound images, the speckle distal to the edges of cavities of contrasting speed of sound (SOS) can be imprinted with a pattern characteristic of the cavity. This pattern, termed edge shadowing, is likely to involve alteration of both the speckle amplitude and its correlation length. Using the acoustic field calculated from the exact solution to the wave equation, we have simulated the ensemble-averaged speckle amplitude in B-mode images of cylindrical cavities both with and without walls, and compared the results to a simpler ray-based model. The simulations show that edge shadowing is caused predominantly by contrasts of the SOS, rather than of the density. The shadows on both walled and wall-less cylinders, for a focused incident beam, grow darker as the magnitude of the SOS contrast increases over a range up to +/- 10%. Extra shadows, caused by the inner wall boundary, appear on images of walled cylinders. The ray-based model agrees well with the wave model except in the shadow regions, within which the complexity of the phenomena seems to require the wave model.     

Synergistic effects of multiple carbon fillers on the rheology of liquid crystal polymer based resins

Adding conductive carbon fillers to insulating thermoplastic resin increases composite electrical and thermal conductivity. Often, as much of a single type of carbon filler is added to achieve the desired conductivity, while still allowing the material to be molded into a bipolar plate for a fuel cell. In this study, varying amounts of three different carbons (carbon black, synthetic graphite particles, and carbon fiber) were added to Vectra A950RX liquid crystal polymer. The rheology of resulting single filler composites was tested. In addition, the rheological properties of composites containing combinations of two different carbon fillers were studied via a factorial design. In all cases, viscosity increased with increasing filler volume fraction for all shear rates. Over the range of shear rates studied, the viscosity followed a shear‐thinning power law model. The factorial design results indicated that each of the single fillers and all of the two filler combinations caused a statistically significant increase in composite viscosity at a shear rate of 1,000 s⁻¹. The composites containing carbon black and synthetic graphite caused the largest increase in viscosity. It is possible that the highly branched, high surface area structure of carbon black ‘links’ with the synthetic graphite particles, which results in increased composite viscosity. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.     

Gas phase electrodeposition: a programmable multimaterial deposition method for combinatorial nanostructured device discovery

This article reports and applies a recently discovered programmable multimaterial deposition process to the formation and combinatorial improvement of 3D nanostructured devices. The gas-phase deposition process produces charged <5 nm particles of silver, tungsten, and platinum and uses externally biased electrodes to control the material flux and to turn deposition ON/OFF in selected domains. Domains host nanostructured dielectrics to define arrays of electrodynamic 10 × nanolenses to further control the flux to form <100 nm resolution deposits. The unique feature of the process is that material type, amount, and sequence can be altered from one domain to the next leading to different types of nanostructures including multimaterial bridges, interconnects, or nanowire arrays with 20 nm positional accuracy. These features enable combinatorial nanostructured materials and device discovery. As a first demonstration, we produce and identify in a combinatorial way 3D nanostructured electrode designs that improve light scattering, absorption, and minority carrier extraction of bulk heterojunction photovoltaic cells. Photovoltaic cells from domains with long and dense nanowire arrays improve the relative power conversion efficiency by 47% when compared to flat domains on the same substrate.     

Language and spatial reorientation: Evidence from severe aphasia.

Investigating spatial cognition in individuals with acquired language impairments can inform our understanding of how components of language are involved in spatial representation. Using the reorientation paradigm of Hermer-Vazquez, Spelke, and Katsnelson (1999), we examined spatial cue integration (landmark–geometry conjunctions) in individuals with severe agrammatic or global aphasia and in a group of healthy older adults. Participants with aphasia performed similarly to healthy controls in the reorientation task, demonstrating the ability to integrate landmark and geometric cues, even during a concurrent verbal task designed to block access to any residual lexical resources. These results extend previous findings with healthy adults by suggesting that neither syntax nor lexicon is essential for spatial cue representation in a mature cognitive system, and provide further evidence that language deficits in aphasia can be independent from other domains of reasoning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new derivation of a closed form expression for Chebyshev polynomials of any order

The author presents a new derivation of a closed-form expression for the Chebyshev polynomial C/sub n/( omega ) based on the method of the Z-transform. The result permits the rapid determination of C/sub n/( omega ) for any order n without the need to evaluate C/sub n/( omega ) for all lower values of n.<>     

Psychopathology of adolescent suicide: Hopelessness, coping beliefs, and depression.

Two studies of adolescents examined the relation of several cognitive variables and depression to suicide-related behaviors. Study 1 compared hopelessness and depression in 281 high school students. Unlike research with adults, depression was significantly related to suicidal behaviors, even after hopelessness was statistically controlled. When depression was controlled, hopelessness was unrelated to suicidal behaviors for boys and only modestly related for girls. Study 2 examined depression, hopelessness, survival–coping beliefs, fear of social disapproval, and social desirability in relation to suicidal behaviors in 53 male juvenile delinquents. Again, hopelessness did not account for a significant proportion of the variance in suicide. Depression was uniquely related to past suicide attempts. Survival–coping beliefs were associated with self-predicted future suicide and other suicidal behaviors. Survival–coping beliefs are discussed as a cognitive buffer to suicidal ideation in adolescence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Yeast heat shock mRNAs are exported through a distinct pathway defined by Rip1p

We reported previously that heat or ethanol shock in Saccharomyces cerevisiae leads to nuclear retention of most poly(A)+ RNA but heat shock mRNAs (encoding Hsp70 proteins Ssa1p and Ssa4p) are efficiently exported in a process that is independent of the small GTPase Ran/Gsp1p, which is essential for most nucleocytoplasmic transport. To gain further insights into proteins essential or nonessential for export of heat shock mRNAs, in situ hybridization analyses to detect mRNA and pulse-labeling of proteins were used to examine several yeast mutant strains for their ability to export heat shock mRNAs following stress. Rip1p is a 42-kD protein associated with nuclear pore complexes and contains nucleoporin-like repeat sequences. It is dispensable for growth of yeast cells under normal conditions, but we report that it is essential for the export of heat shock mRNAs following stress. When SSA4 mRNA was induced from a GAL promoter in the absence of stress, it was efficiently exported in a strain lacking RIP1, indicating that Rip1p is required for export of heat shock mRNAs only following stress. Npl3p, a key mediator of export of poly(A)+ RNA, was not required for heat shock mRNA export, whereas Rss1p/Gle1p, a NES-containing factor essential for poly(A)+ RNA export, was also required for export of heat shock mRNAs after stress. High-level expression of the HIV-1 Rev protein, but not of Rev mutants, led to a partial block in export of heat shock mRNAs following stress. The data suggest a model wherein the requirement for Npl3p defines the mRNA export pathway, the requirement for Rip1p defines a pathway used for export of heat shock mRNAs after stress, and additional factors, including Rss1p/Gle1p and several nucleoporins (Rat7p/Nup159p, Rat2p/Nup120p, and Nup145p/Rat10p), are required in both pathways.     

Monolithic two-dimensional arrays of micromachined microstructuresfor infrared applications

Small micromachined structures (typically 10^-5 cm² ) have been fabricated that have very small thermal mass (c, about 10^-9 J/K) and that are suspended from the underlying silicon substrate by supports of such delicacy that the structures are extremely well thermally isolated from the substrate (thermal conductance to the substrate g of 10^-7 W/K). This thermal conductance is close to the smallest value possible (about 10^-8 W/K) due to radiative energy exchange. This high thermal isolation allows the microstructure temperature to be readily controlled by very small heating currents, or very small amount of infrared (IR) incident IR flux. Large arrays of such microstructures have been fabricated on silicon wafers, complete with complex integrated electronic circuits, and operated as (1) sensitive room-temperature IR sensors (“microbolometers”) for night-vision IR imaging and (2) large arrays of individually controllable IR microemitters. The latter provide dynamic infrared “scene generators” that allow realistic simulations of IR scenes, an important tool for the development of IR cameras and IR missile seekers