Compositional and structural evolution of sputtered Ti-Al-N

The compositional and structural evolution of Ti-Al-N thin films as a function of the total working gas pressure (p_T), the N₂-to-total pressure ratio (p_N2/p_T), the substrate-to-target distance (ST), the substrate position, the magnetron power current (I_m), the externally applied magnetic field, and the energy and the ion-to-metal flux ratio of the ion bombardment during reactive sputtering of a Ti_0.5Al_0.5 target is investigated in detail. Based on this variation we propose that the different poisoning states of the Ti and Al particles of the powder-metallurgically prepared Ti_0.5Al_0.5 target in addition to scattering and angular losses of the sputter flux cause a significant modification in the Al/Ti ratio of the deposited thin films ranging from ~ 1.05 to 2.15.The compositional variation induces a corresponding structural modification between single-phase cubic, mixed cubic-hexagonal and single-phase hexagonal. However, the maximum Al content for single-phase cubic Ti_1−xAl_xN strongly depends on the deposition conditions and was obtained with x = 0.66, for the coating deposited at 500 °C, p_T = 0.4 Pa, ST = 85 mm, and p_N2/p_T = 17%. Our results show, that in particular, the N₂-to-total pressure ratio in combination with the sputtering power density of the Ti_0.5Al_0.5 compound target has a pronounced effect on the Al/Ti ratio and the structure development of the coatings prepared.     

A thermal model of the immobilization of low-level radioactive waste as grout in concrete vaults

Salt solution, from radioactive waste generated by the production of plutonium and tritium in nuclear reactors at the Savannah River Site, will be mixed with cement and flyash/slag to form a grout which will be poured into above ground concrete vaults. The curing process is exothermic, and a transient thermal model of the pouring and curing process is herein described. A peak temperature limit of 85 °C for the curing grout restricts the rate at which it can be poured into a vault. The model is used to optimize the pouring.     

Design and Fabrication of a Movable Langmuir Probe for Plasma Edge Parameters Measurement in the IR-T1 Tokamak

For the edge plasma parameters measurement, a movable Langmuir probe is fabricated and installed on the IR-T1 tokamak. The set-up consists of two sets of single Langmuir probes with tungsten tip movable in the radial direction. Edge plasma parameters including electron temperature, Ion density, floating potential and the corresponding radial changes are measured. Using two-point correlation technique clearly reveal that in the SOL region the poloidal propagation of floating potential fluctuation is in the direction of ion diamagnetic drift and in the edge it propagates in the electron diamagnetic drift direction.     

New measurement and evaluation of the excitation function of Ni(p,n) reaction for the production of Cu

One of the radioisotopes for which a growing interest exists in nuclear medicine is ⁶⁴Cu. Its branched decay makes it suitable for both diagnostic and therapeutic purposes. Activation cross sections of the proton induced reaction on enriched ⁶⁴Ni have been studied using the stacked foil technique up to 24 MeV. The experimental cross sections are compared with values available from literature. Thick target yields, based on the discrete measured values of the cross sections are calculated and allow a better estimation of the optimum production parameters.     

Ultrasonic technique as tool for determining physical and mechanical properties of frozen soils

Ultrasonic velocities of compressional and shear waves in frozen sand, silty-sand and silt were measured at subfreezing temperature and the relationship between acoustic and physical-mechanical properties examined. Ultrasonic measurements revealed that the influence of temperature on ultrasonic velocities is due to the phase transition from water to ice. Different methods were proposed to determine the amount of unfrozen water in frozen soils. The unfrozen water content was measured directly by time domain reflectometry and compared to predicted values using different theoretical approaches. The prediction models showed good agreements with measured values at low temperatures. However, the shape of the curves obtained did not completely satisfying as the estimated unfrozen water fraction near 0 °C was significantly greater than the measured values. Finally, based on the elastic wave theory and measured acoustic velocities the elastic constants of the frozen soils were calculated. The changes in elastic constants were found to be related to the increase in ice content, ice stiffness by ice cementation and a decrease in unfrozen water content.     

Fabrication of switchable liquid crystal devices using surface relief gratings in photopolymer

Holographically recorded surface relief gratings in dry, self-developing acrylamide based photopolymer were used to fabricate two types of switchable liquid crystal (LC) device. One is an electrically switchable LC diffraction grating and the other is an electrically switchable polarization rotator. The electrically switchable diffraction grating was characterized by measuring the dependence of the intensity in the first diffracted order on the applied electric field. The polarization rotator was characterized by studying the influence of the applied electric field on the twist angle and the variation of intensity in the zero and the first orders of diffraction.     

Predicting compliance of children with and without developmental delay.

Noncompliance is a common problem exhibited by children with developmental delay (DD; Walker, 1993). The authors evaluated whether performance on the Assessment of Basic Learning Abilities (ABLA) test would predict compliance of children with and without DD to instructions alone (IA) versus instructions with modelling and/or gestures (IMG) administered by their caregivers. The ABLA test uses standard prompting and reinforcement procedures to assess the ease or difficulty with which a testee is able to learn a simple imitation and five two-choice discriminations. Twenty-one children without DD and 16 children with DD were presented with five age-appropriate educational tasks by their respective caregivers in a structured teaching session that included IA on some trials and IMG on others. The ABLA test performance reliably predicted the compliance of the children in the two conditions, and the results were consistent across both groups. The results are important for providing information to caregivers on how best to instruct their children in an effort to increase compliance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)