A novel current injected strained quantum well laser grown by MOVPE

Conventional long wavelength (1.3 and 1.55 μm emitting) GalnAsP alloy lasers suffer from two disadvantages. Firstly, carriers in the highest lying valence band have a heavy effective mass relative to carriers in the conduction band. This asymmetry leads to an increase in the carrier density required for lasing action to occur. Secondly, non-radia-tive recombination processes, such as Auger Recombination (AR) and Inter Valence Band Absorption (IVBA), which involve occupancy of the heavy-hole (HH) states, are thought to be significant in these materials. These again lead to higher thresholds and lower values ofT ₀than might otherwise be the case. Recently, there has been considerable interest in the prospect of “engineering” the band structure of a 1.5 μm emitting device so as to overcome these problems. It has been reported that for a quantum well under biaxial compression, the light-hole/heavy-hole (LH/HH) degeneracy at the gamma point will be lifted such that the highest lying valence band will be LH-like in the in-plane direction. This should reduce both the effective mass asymmetry and the thermal occupancy of the HH states, lowering the threshold carrier density and reducing the AR and IVBA rates. This paper describes MOVPE growth and characterisation of the first 1.55 μm emitting current injected strained layer laser structure. The active region contains 3.5 nm thick strained quantum wells of Ga_o.3In_o.7As situated in the central region of a quaternary waveguide and grown on InP. TEM micrographs and x-ray data demonstrate that the lattice mismatch (approximately 1%) has been accommodated elastically, without the formation of misfit dislocations. Broad area lasers have been fabricated with lengths of 200–1200 μm and threshold current densities as low as 930 Acm^-2 have been measured from the longer devices. Similar 1.55 μm emitting structures containing unstrained 7.5 nm thick Ga_o.47In_o.53As wells have also been grown and characterised for comparison. As yet, no significant improvement in either threshold current orT ₀has been observed for strained lasers over unstrained devices.     

Contact problems for the elastic beam

The paper describes numerical experience on the use of variational inequalities and finite elements to obtain approximate solutions to bending problems for elastic beams in the presence of a rigid barrier. The methods are applicable to plate problems but in order that comparisons could be made with exact solutions, only one dimensional beam problems have been considered in this paper. Even these problems display a variety of contact situations and in all cases the numerical solution represented the exact solution well.Convergence rates were examined and the effect of a free boundary adjustment routine which allowed a more accurate location of the contact region was assessed.     

Tunable PDL of twisted-tilted fiber gratings

We fabricated highly tilted fiber gratings and demonstrated that the broad-band polarization-dependent loss (PDL) of the gratings may be tuned by twisting the fiber along the length of the grating. We show that the PDL for a given twist angle can be determined from a simple Jones matrix calculation which can also take into account birefringence on the PDL axis. We combine the twisted-tilted grating with a polarization controller to form a PDL compensator and use it to minimize the polarization-dependent responsivity of a nonlinear silicon avalanche photodiode.     

High scales on the Strong Vocational Interest Blank and the Kuder Occupational Interest Survey using Holland's occupational codes.

Compared the arrays of high-interest occupations produced by the Strong Vocational Interest Blank, T-399, and the Kuder Occupational Interest Survey (Form DD) when the instruments were administered to the same Ss (60 male college students). Holland-type summary codes were devised from the arrays of occupations and were analyzed by correlated t tests and Pearson r correlations. A frequency percentage count showed 85% of the pairs of summary codes had 2 identical characteristics, and some support was found for J. L. Holland's hexagon. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recent NASA contributions to biomedical telemetry.

Reviews technological progress that has been made by the National Aeronautics and Space Administration (NASA) in the field of biotelemetry over the past 5 yrs. Emphasis is placed on those developments that have direct applications for human or animal use on earth. Examples of biobelt personal telemetry systems, swallowable telemetry capsules, cardiovascular multichannel implantable telemetry units, and long-range radiotelemetry of biologic data are presented. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceived problem areas by Black and White students and hints about comparative counseling needs.

The Student Problem Areas Survey was administered to 108 Black and 184 White students attending a predominantly White university and to 55 Black students attending a predominantly Black university. Data from a 2-way randomized block design were analyzed by way of the multivariate ANOVA and a series of ANOVAs. The pattern of results shows several significant differences on specific problem areas but none between Blacks attending universities with different racial make-ups nor between the groups on variables that typically suggest counseling needs. There was one Group?×?Class interaction; the ranking of the problem areas was the same for the 3 groups. Results are discussed in terms of their implications for counseling needs of Black students in university settings. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

In a resource-poor country, mutation identification has the potential to reduce the cost of family management for hereditary nonpolyposis colorectal cancer

PURPOSE: Colonoscopic surveillance of family members at risk of hereditary nonpolyposis colorectal cancer is difficult in a resource-poor country because of its expense. For family members who live in remote areas, poor communication and limited access to sophisticated medical care make surveillance even more difficult. The identification of the mutation causing the disease will simplify surveillance. Our aim was to assess the impact of mutation analysis on the management of a South African family with more than 150 members at risk for hereditary nonpolyposis colorectal cancer. METHODS: We studied a family that met the Amsterdam criteria for hereditary nonpolyposis colorectal cancer. Colorectal cancer affected 27 members in three generations (evidence from histology in 12, barium enema in 1, and family statements in 14 family members). Leukocyte DNA from family members was tested for linkage to candidate loci for colorectal cancer, and DNA from formalin-fixed cancers from six family members was studied for microsatellite instability. DNA from all available family members was then screened for mutations in the hMLH1 gene. The number of individuals at 50 percent risk was calculated by family pedigree and compared with the number who have the mutation. RESULTS: A disease-causing mutation in exon 13 of hMLH1 segregated with the disorder in members of this kindred. Test results of 100 chromosomes from population-matched controls were negative. Sixty family members between the ages of 16 and 50 years are at 50 percent risk for colon cancer by pedigree analysis, but of these, only 26 (43 percent) have the mutation. CONCLUSION: A mutation in the DNA repair gene hMLH1 was found in family members with hereditary nonpolyposis colorectal cancer and in some unaffected relatives previously at 50 percent risk, but not in unrelated subjects. The blood test for the mutation will simplify management, counseling, and surveillance and help to establish prophylactic colectomy.