Positional control of catalyst nanoparticles for the synthesis of high density carbon nanofiber arrays

Precise arrangement of nanoscale elements within larger systems, is essential to controlling higher order functionality and tailoring nanophase material properties. Here, we present findings on growth conditions for vertically aligned carbon nanofibers that enable synthesis of high density arrays and individual rows of nanofibers, which could be used to form barriers for restricting molecular transport, that have regular spacings and few defects. Growth through plasma-enhanced chemical vapor deposition was initiated from precisely formed nickel catalyst dots of varying diameter and spacing that were patterned through electron beam lithography. Nanofiber growth conditions, including power, precursor gas ratio, growth temperature and pressure were varied to optimize fiber uniformity and minimize defects that result from formation and migration of catalyst particles prior to growth. It was determined that both catalyst dot diameter and initial plasma power have a considerable influence on the number and severity of defects, while growth temperature, gas ratio (C₂H₂:NH₃) and pressure can be varied within a considerable range to fine-tune nanofiber morphology.     

Thermally stimulated current spectroscopy of high-purity semi-insulating 4H-SiC substrates

High-purity semi-insulating (HPSI) 4H-SiC has been widely used as a substrate material for AlGaN/GaN high electron-mobility transistors because of its fairly good lattice match with GaN and its high thermal conductivity. To control material quality, it is important to understand the nature of the deep traps. For this purpose, we have successfully applied thermally stimulated current (TSC) spectroscopy to investigate deep traps in two HPSI 4H-SiC samples grown by physical vapor transport (PVT) and high-temperature chemical vapor deposition (HTCVD), respectively. Fundamentals of TSC spectroscopy, typical TSC spectra obtained on the two samples, and theoretical fittings of a boron-related trap (peaked at ∼ 150 K) will be presented. Based on literature data for deep traps in conductive 4H-SiC, the impurity and point-defect nature of several commonly observed TSC traps, peaked at ∼105 K (0.22 eV), ∼150 K (0.29 eV), ∼175 K (∼0.33 eV), ∼260 K (∼0.53 eV), ∼305 K (∼0.63 eV), and ∼360 K (0.91 eV), in the HPSI 4H-SiC will be discussed.     

A clinical pathway for ostomy care in the home: process and development

Infusion of insulin directly into thyroid arterial blood perfusing the surgically isolated in situ pig thyroid gland produced an increase in the secretion rate of calcitonin (CT) measured by immunoassay in thyroid venous effluent blood. Insulin in concentrations ranging from approximately 1 to 400 ng/ml produced a maximal stimulation of 4-5 fold. The stimulatory effect of insulin on CT could not be duplicated by infusion of either IGF-I or amylin. Specific binding of radiolabeled insulin was demonstrated using isolated pig thyroid plasma membranes and both rat (6-23) and human (TT) medullary thyroid carcinoma C-cells. Increased CT release was observed from C-cells exposed to a high concentration of insulin. The administration of glucose iv to pigs in order to stimulate secretion of endogenous insulin produced an increase in circulating insulin, which was accompanied by an increase in the secretion of CT. The results show that insulin, delivered directly to the pig thyroid gland, can stimulate CT release. The in vitro binding and secretion studies indicate that C-cells can bind insulin and respond with an increase in CT secretion, and the iv glucose experiments suggest that endogenous insulin is capable of stimulating CT secretion. The findings imply that insulin is capable of acting as a CT secretagogue and suggest that changes in CT secretion may accompany altered states of insulin production such as diabetes or insulin-secreting tumors.     

Transport coefficients of AlGaN/GaN heterostructures

We have experimentally determined the effective mass (m*) of GaN, the classical (τ _c), and quantum (τ _q) scattering times for a two-dimensional electron gas residing at the interface of an AlGaN/GaN heterostructure, using the Shubnikovde Haas effect. The ratio of the two scattering times, τ _c/τ _q, suggests that, at low temperatures, the scattering mechanism limiting the mobility is due to remote ionized impurities located in AlGaN. This study should provide sample growers with information useful for improving the quality of the nitride heterostuctures.     

Hybrid valve structure for high-throughput, low-volume liquid-handling applications

A hybrid valve that integrates precision microfluidics for fluid routing, high-speed valving for fluid switching, and reagent-jetting devices for metering the fluid dispenses is described. The hybrid valve enables parallel switching between aspiration and dispense modes for multiple sample streams. This unique valve structure addresses many of the concerns with handling microscale volumes, including efficient use of samples, degradation of ink jet valves and speed of operation. A broad range of volumes can be manipulated with excellent reproducibility. The hybrid valve can be configured for a variety of applications. Pick-and-place aspiration and dispensing of unique reagents and rapid dispensing of a common reagent are possible. Together these features lead to higher-speed transfer of smaller volumes of reagent.     

Assessment center validity: A longitudinal study.

Data on 254 managers attending an assessment center were examined for changes in validities over time. 24 predictors were correlated with a criterion of salary growth measured 1, 3, and 5 yrs after Ss were assessed. Before conducting the analyses, Ss were grouped into 3 generations based on the year they were assessed. Peer and assessor ratings, along with linear combinations, were significantly correlated with the criterion. The multiple correlations generalized well across time and generations. A general increasing trend in the validity coefficients was noted over time. Comparison of overall assessor rating with multiple correlation did not indicate any marked superiority for actuarial prediction. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A heuristic technique for CTIS image reconstruction

An iterative method is presented for computed tomography imaging spectrometer (CTIS) image reconstruction in the presence of both photon noise in the image and postdetection Gaussian system noise. The new algorithm, which assumes the transfer matrix of the system has a particular structure, is evaluated experimentally with the result that it is significantly better, for larger problems, than both the multiplicative algebraic reconstruction technique (MART) and the mixed-expectation image-reconstruction technique (MERT) with respect to accuracy and computation time.