kHz dye laser for use with ultrafast laser systems

We have constructed a cavity-dumped dye laser optimized for use with kHz repetition rate ultrafast lasers for performing experiments on atomic and molecular systems. The dye laser is inexpensive, robust, and requires little pump energy, making it ideal for experiments requiring multiple excitations for state preparation.     

Novel flame retardant polyarylethers: synthesis and testing

Three new polyarylethers A-C based on bisphenol C and its derivatives have been synthesized and tested. These new polymers all show a glass transition temperature and are inherently flame resistant and do not require the use of any flame retardant synergist. The new polyarylethers can all be made in 2-3 steps from available raw materials, keeping cost to a minimum. The thermal and flame retardant properties, such as DSC and UL-94 rating, are examined.     

"Health information on the Internet and people living with HIV/AIDS: Information evaluation and coping styles": Response.

Comments on the article by S. C. Kalichman et al. (see record 2006-03515-009) about Internet use and coping among those with HIV/AIDS in a mostly African American sample. Using correlation, Kalichman et al. concluded that African Americans correlated with less general and health-information Internet use than did Whites. Using regression, they concluded that African Americans, as compared with Whites, were more likely to consider as credible both scientifically and nonscientifically based website information. The current author contends that the employed analytic approach may not truly determine these results. It may be very useful to conduct and report these analyses using the nominal-level approach to determine if these results are true for African Americans. In addition, there may be a typographical error for the gender correlation results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling of curvature in multilayered epitaxially grown films

A model was developed to calculate the radius of curvature produced by stresses in lattice-mismatched multilayers grown epitaxially on a planar substrate. The analysis was done for any number (N) of layers using beam bending theory and strain partitioning theory introduced by our group earlier. This model is reduced to a limiting case of a two-layer structure (film-substrate). The variation of the radius of curvature with the relative thicknesses and other material properties of the layers was determined and compared to finite element calculations. The analytical model was further verified by applying it to a symmetric tri-laminate structure.     

Single-molecule spectroscopy using nanoporous membranes

We describe a novel approach for optically detecting DNA translocation events through an array of solid-state nanopores that potentially allows for ultra high-throughput, parallel detection at the single-molecule level. The approach functions by electrokinetically driving DNA strands through sub micrometer-sized holes on an aluminum/silicon nitride membrane. During the translocation process, the molecules are confined to the walls of the nanofluidic channels, allowing 100% detection efficiency. Importantly, the opaque aluminum layer acts as an optical barrier between the illuminated region and the analyte reservoir. In these conditions, high-contrast imaging of single-molecule events can be performed. To demonstrate the efficiency of the approach, a 10 pM fluorescently labeled lambda-DNA solution was used as a model system to detect simultaneous translocation events using electron multiplying CCD imaging. Single-pore translocation events are also successfully detected using single-point confocal spectroscopy.     

EBSD-Based Microscopy: Resolution of Dislocation Density

Consideration is given to the resolution of dislocation density afforded by EBSD-based scanning electron microscopy. Comparison between the conventional Hough- and the emerging high-resolution cross-correlation-based approaches is made. It is illustrated that considerable care must be exercised in selecting a step size (Burger's circuit size) for experimental measurements. Important variables affecting this selection include the dislocation density and the physical size and density of dislocation dipole and multi-pole components of the structure. It is also illustrated that simulations can be useful to the interpretation of experimental recoveries.     

Sodium borohydride hydrolysis kinetics comparison for nickel,cobalt, and ruthenium boride catalysts

Hydrolysis tests have been performed at a constant temperature of 60 °C over a range of sodium borohydride (2.5–30 wt%) and sodium hydroxide (2.5–30 wt%) concentrations. Catalysts used to initiate the hydrolysis reaction were developed through the metal salt reduction method with sodium borohydride. These catalysts were identified as nickel boride, cobalt boride, and ruthenium with each catalyst having similar morphology. Catalysts were tested in loose, powder form free of binders or substrates. Hydrolysis rate comparisons show that reaction rates decrease linearly with increasing NaBH₄ concentrations due to mass transfer limitations. Increasing NaOH concentration has been shown to drive a non-catalyzed intermediate reaction with the rate of the overall reaction hindered by the catalysts’ ability to bind hydrogen to active sites. Maximum hydrogen production rates for the Ni₃B, Co₃B, and Ru catalysts were found to be 1.3, 6.0, and 18.6 L min⁻¹ g_cat⁻¹, respectively.     

The synthesis, characterization and biocompatibility of poly(ester urethane)/polyhedral oligomeric silesquioxane nanocomposites

The primary goal of this study is to develop a facile and inexpensive synthesis method for a new biodegradable and biocompatible poly(ester urethane) (PEU)/polyhedral oligomeric silesquioxanes (POSS) nanocomposite via in situ homogeneous solution polymerization reaction into prescribed macromolecular structure and properties including improved biocompatibility, thermal and hydrolytic stability, and stiffness and strength. Cell culture studies, nuclear magnetic resonance spectroscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetry, and dynamic mechanical analysis measurements were used to confirm the structure and property improvements. The results show that the targeted PEU/POSS nanocomposites (which are remarkably different from conventional polymers, polymer nanocomposites and microcomposites) have significant improvements in mechanical properties and degradation resistance at small POSS concentrations (≤6 wt%). The nanocomposites exhibited excellent support for cell growth without any toxicity. POSS concentration did not affect cell adhesion or cell growth, but it significantly changed the surface structure of the PEU into a 3-dimensional matrix with regular pores that may allow cells to better access the growth factors/nutrients, waste exchange, and tissue remodeling. The PEU/POSS nanocomposites were resistant to degradation over a period of six months when exposed to a buffer solution. These desirable characteristics suggest that the nanocomposites may hold great promise for future high-end uses such as in biomedical devices, especially at cardiovascular interfaces.     

Supported Lipid Bilayer Platform for Characterizing the Membrane-Disruptive Behaviors of Triton X-100 and Potential Detergent Replacements

Triton X-100 (TX-100) is a widely used detergent to prevent viral contamination of manufactured biologicals and biopharmaceuticals, and acts by disrupting membrane-enveloped virus particles. However, environmental concerns about ecotoxic byproducts are leading to TX-100 phase out and there is an outstanding need to identify functionally equivalent detergents that can potentially replace TX-100. To date, a few detergent candidates have been identified based on viral inactivation studies, while direct mechanistic comparison of TX-100 and potential replacements from a biophysical interaction perspective is warranted. Herein, we employed a supported lipid bilayer (SLB) platform to comparatively evaluate the membrane-disruptive properties of TX-100 and a potential replacement, Simulsol SL 11W (SL-11W), and identified key mechanistic differences in terms of how the two detergents interact with phospholipid membranes. Quartz crystal microbalance-dissipation (QCM-D) measurements revealed that TX-100 was more potent and induced rapid, irreversible, and complete membrane solubilization, whereas SL-11W caused more gradual, reversible membrane budding and did not induce extensive membrane solubilization. The results further demonstrated that TX-100 and SL-11W both exhibit concentration-dependent interaction behaviors and were only active at or above their respective critical micelle concentration (CMC) values. Collectively, our findings demonstrate that TX-100 and SL-11W have distinct membrane-disruptive effects in terms of potency, mechanism of action, and interaction kinetics, and the SLB platform approach can support the development of biophysical assays to efficiently test potential TX-100 replacements.     

Stress-based design of thermal structures via topology optimization

The design of thermal structures in the aerospace industry, including exhaust structures on embedded engine aircraft and hypersonic thermal protection systems, poses a number of complex design challenges. These challenges are particularly well addressed by the material layout capabilities of structural topology optimization; however, no topology optimization methods are readily available with the necessary thermoelastic considerations for these problems. This is due in large part to the emphasis on cases of maximum stiffness design for structures subjected to externally applied mechanical loads in the majority of topology optimization applications. In addition, while limited work in the literature has investigated thermoelastic topology optimization, a direct treatment of thermal stresses is not well documented. Such a treatment is critical in the design of thermal structures where excessive thermal stresses are a primary failure mode. In this paper, we present a method for the topology optimization of structures with combined mechanical and thermoelastic (temperature) loads that are subject to stress constraints. We present the necessary steps needed to address both the design-dependent thermal loads and accommodate the challenges of stress-based design criteria. A relaxation technique is utilized to remove the singularity phenomenon in stresses and the large number of stress constraints is handled using a scaled aggregation technique that has been shown previously to satisfy prescribed stress limits in mechanical problems. Finally, the stress-based thermoelastic formulation is applied to two numerical example problems to demonstrate its effectiveness.