Aqueous lateral epitaxy overgrowth of ZnO on (0001) GaN at 90 °C: Part I. Increasing the critical thickness

Thick, epitaxial ZnO thin films have been grown on (0001) GaN buffered Al₂O₃ substrates using an aqueous solution at 90 °C. Films with improved structural, optical and electrical characteristics, were grown using a lateral epitaxial overgrowth (LEO) method. Different photoresist masks were used to enable LEO. The masks included linear windows and two different hexagonal arrays of circular windows. Films that exceeded a critical thickness mechanically failed through buckling, consistent with the large compressive stresses expected due to the mismatch of the ZnO lattice with the underlying GaN substrate. It was shown that improved mechanical stability could be achieved using the LEO method. Without LEO, a film thickness no greater than 4 µm could be grown without buckling. The critical thickness could be increased to 10 µm using linear windows, whereas a critical thickness of 50 μm was achieved with one array of circular windows, and 80 µm for a second array. The two different arrays of circular windows differed relative to their orientation on the substrate. It was also shown that the critical thickness increased with increasing distance between the growth windows. Optical transmission, micro-photoluminescence and Hall Effect measurements showed that the LEO method also results in improved optoelectronic properties.     

National structural change and metropolitan specialization in the United States

The national economy is split into four broad sectors. The observed variation in long-term growth among sectors leads to a shift in the composition of aggregate demand. I test Henderson's propositions, namely that secular shifts in the composition of national demand lead to changes in the numbers and sizes of different types of urban places. The numbers and sizes of places specialized in the information sector has increased while the numbers and sizes of places specialized in manufacturing has decreased or has not changed. Metropolitan population growth and per capita earnings growth are enhanced by specialization in the information sector. Received: 29 January 1998 / Accepted: 9 March 1999     

Bridging the acculturation gap: Parent-child relationship quality as a moderator in Mexican American families.

The authors examined the degree to which disparities in parent and child acculturation are linked to both family and child adjustment. With a sample of 1st- and 2nd-generation Mexican American children, acculturation and parent-child relationship quality at 5th grade, and parent-child conflict, child internalizing, and child externalizing at 7th grade were measured. Acculturation gaps with fathers were found to be related to later father-child conflict as well as internalizing and externalizing outcomes. Many of the associations between father-child acculturation gaps and outcomes were moderated by the child's report of the relationship quality between the child and his or her father. Father-child acculturation gaps were associated with negative outcomes only when children reported a poor relationship with their fathers. Mother-child acculturation gaps were not associated with mother-child conflict or adjustment indices. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feasibility of using PtFe alloys as cathodes in direct methanol fuel cells

Carbon-supported platinum–iron catalysts were fabricated and characterised by means of scanning electron microscopy, energy-dispersive X-ray system and X-ray diffraction. The catalysts were tested in electrochemical half cells for oxygen reduction using voltammetry and steady-state polarisation measurements and in direct methanol fuel cells. Use of PtFe/C cathodes, instead of a Pt/C cathode, partially suppressed methanol oxidation and led to higher net oxygen reduction currents in the presence of methanol. Consequently, an increase in power density up to 30% was achieved in direct methanol fuel cells with PtFe/C cathodes, compared to that with Pt/C cathode. The influence of alloy composition and operation conditions on the cell performance has been investigated.     

H∞ control for discrete‐time nonlinear switching systems

This paper formulates and solves the robust H^∞ control problem for discrete‐time nonlinear switching systems. The H^∞ control problem is interpreted as the l₂ finite gain control problem and is studied using a dissipative systems theory for switched systems. Both state and measurement feedback control problems are formulated as dynamic games and solved using dynamic programming. The partially observed dynamic game corresponding to the measurement feedback control problem is solved by transforming into a completely observed, full state infinite‐dimensional game problem using information states. Our results are illustrated with an example. Copyright © 2007 John Wiley & Sons, Ltd.     

Impact of Posttraumatic Stress Disorder on early smoking lapse and relapse during a self-guided quit attempt among community-recruited daily smokers

The present investigation examined whether daily smokers with posttraumatic stress disorder (PTSD), as compared to daily smokers with either anxiety psychopathology or no current Axis I psychopathology, have decreased success in the early phases of a self-guided smoking quit attempt. Participants were 140 daily smokers (81 women; M (age) = 29.5; SD = 11.9; range = 18-65 years); approximately one-third of the sample met criteria for current PTSD (n = 47), one-third met criteria for other current anxiety disorders (without PTSD; n = 33), and one-third did not meet criteria for any current Axis I disorder (n = 60). Consistent with prediction, membership in the PTSD group, compared to membership in the other anxiety disorders group and the group with no current Axis I psychopathology, was associated with increased risk of lapse during the first week following quit day. Additionally, daily smokers with PTSD and other anxiety disorders were at significantly increased risk of relapse during the first week post-cessation compared to persons without Axis I psychopathology. However, the PTSD group and the other anxiety disorders group did not differ from one another in terms of relapse. Results suggest that PTSD is associated with increased risk of smoking lapse and relapse compared to smokers with no current Axis I psychiatric problems, and increased risk of early smoking lapse but not relapse, as compared to those with other anxiety disorders. Findings provide novel evidence that PTSD, and perhaps anxiety disorders more generally, may be important factors in reducing the odds of successful unaided quit attempts in the early phases of cessation.     

Cold fusion experiments using Maxwellian plasmas and sub-atmospheric deuterium gas

Experiments are being performed to initiate the cold fusion process in Maxwellian plasmas and sub-atmospheric deuterium gas. Thus far, apparent neutron counts have been observed using a BF₃ probe and Ludlum model 2200 digital counter, and a broad 8.1 MeV peak has been observed using a 3-inch sodium iodide crystal and a Nucleus PCA II multichannel analyzer. The results appear to be dependent upon the temperature of the palladium sample, deuterium pressure, and the type of palladium sample used. The results are interesting but not sufficient for any conclusions at this point.     

Investigation of Die Stress Profiles During Powder Compaction Using Instrumented Die

The die stress profiles during compaction of commercially pure titanium (Ti) and commercial lubricated iron (Fe) powders were experimentally investigated using an instrumented die. The die was designed to simulate double-action pressing, and a detailed stress profile was measured along the height of the die using multiple custom-made strain gage pins. The stress history shows that residual stress remained in the die in the radial direction after the axial compaction stress was removed from the powder. Also, the stress profile at the maximum axial stress and the residual stress profile were observed to be symmetric across the height of the compact for both powders, but both have a unique shape for each powder. For both the stress profile at the maximum axial stress and the residual stress profile, the unlubricated Ti powder produced a much higher radial stress at the center of the compact with a steep pressure gradient on both top and bottom of the compact, while the lubricated Fe powder produced a rather uniform radial stress distribution along the height of the compact. This article was presented at Materials Science & Technology 2007, Automotive and Ground Vehicles symposium held September 16–20, 2007, in Detroit, MI.