Transmission Electron Microscopy-Based Analysis of Electrically Conductive Surface Defects in Large Area GaSb Homoepitaxial Diodes Grown Using Molecular Beam Epitaxy

We investigate a mechanism causing shorting of large area GaSb diodes grown on GaSb substrates using molecular beam epitaxy (MBE). The source of these shorts is determined to be large crystallographic defects on the surface of the diodes that are formed around droplets of gallium ejected from the gallium Knudsen cells during MBE. The gallium droplets cause defects in the crystal structure, and, as the epitaxy continues, the gallium is incorporated into the surrounding material. The shape of the defects is pyramidal with a central void extending from the epi-surface to the gallium core. Processing a GaSb diode with these surface defects results in the top-side contact metal migrating into the defect and shorting the diode. This prevents realization of large area diodes that are critical to applications such as photovoltaics and detectors. The diodes in this study are electrically characterized and the defect formation mechanism is investigated using cross-section transmission electron microscopy and electron dispersive spectroscopy.     

A method for improving global pyranometer measurements by modeling responsivity functions

Accurate global solar radiation measurements are crucial to climate change research and the development of solar energy technologies. Pyranometers produce an electrical signal proportional to global irradiance. The signal-to-irradiance ratio is the responsivity (RS) of the instrument (RS = signal/irradiance = microvolts/(W/m²)). Most engineering measurements are made using a constant RS. It is known that RS varies with day of year, zenith angle, and net infrared radiation. This study proposes a method to find an RS function to model a pyranometer’s changing RS. Using a reference irradiance calculated from direct and diffuse instruments, we found instantaneous RS for two global pyranometers over 31 sunny days in a two-year period. We performed successive independent regressions of the error between the constant and instantaneous RS with respect to zenith angle, day of year, and net infrared to obtain an RS function. An alternative method replaced the infrared regression with an independently developed technique to account for thermal offset. Results show improved uncertainties with the function method than with the single-calibration value. Lower uncertainties also occur using a black-and-white (8-48), rather than all-black (PSP), shaded pyranometer as the diffuse reference instrument. We conclude that the function method is extremely effective in reducing uncertainty in the irradiance measurements for global PSP pyranometers if they are calibrated at the deployment site. Furthermore, it was found that the function method accounts for the pyranometer’s thermal offset, rendering further corrections unnecessary. The improvements in irradiance data achieved in this study will serve to increase the accuracy of solar energy assessments and atmospheric research.     

X-ray diffraction from intact tau aggregates in human brain tissue

We describe an instrument to record x-ray diffraction patterns from diseased regions of human brain tissue by combining an in-line visible light fluorescence microscope with an x-ray diffraction microprobe. We use thiazine red fluorescence to specifically label and detect the filamentous tau protein pathology associated with Pick's disease, as several labs have done previously. We demonstrate that thiazine red-enhanced regions within the tissue show periodic structure in x-ray diffraction that is not observed in healthy tissue. One observed periodicity (4.2 ?) is characteristic of cross-beta sheet structure, consistent with previous results from powder diffraction studies performed on purified, dried tau protein.     

Evaluation of alpine skiing and snowboarding injury in a northeastern state

BACKGROUND: To demonstrate the injury patterns of Alpine skiing and snowboarding in a northeastern state and evaluate potential risk factors. METHODS: The medical records of a single pediatric and adult Level I trauma center were evaluated from January 1, 1990, through December 31, 1995. All admissions with injuries caused by Alpine skiing or snowboarding were reviewed. Those patients arriving from two local ski resorts, all of whose injuries are referred to the institution for care, were separated out for consideration. Age, sex, type of injury, date of injury, Injury Severity Score, operations performed, and outcome (including mortality) were evaluated. In addition, resort utilization for the study period was obtained from the two resorts included in the evaluation. Mortality data was obtained from the Vermont office of the Chief Medical Examiner for the same time period. RESULTS: For the 6-year period of the study approximately 2,978,000 skier and snowboarder days were recorded at the study sites. Approximately 447,000 of those days were attributed to snowboarders (15%). In all, 279 patients were admitted for injuries (0.01%), 238 were related to Alpine skiing (incidence 0.01%) and 40 to snowboarding (incidence 0.01%). Snowboarders were statistically younger (20 years; range, 4-44 years) than skiers (29 years; range, 6-70 years) (p < 0.001) and had a significantly lower Injury Severity Score (15 in snowboarders vs. 27 in skiers, p < 0.03). Two female patients were injured snowboarding and 68 female patients were injured skiing. Eight percent of injured snowboarders and 16% of injured skiers sustained multiple injuries (p < 0.01). Injury patterns were significantly different. Upper extremity injuries were almost exclusively found in snowboarders (24% vs. 7%, p < 0.003), whereas cruciate ligament injuries occurred far more commonly in skiers (45% vs. 4%, p < 0.001 Lower extremity injuries in general were more common in skiers (78% vs. 38%, p < 0.001). Central nervous system injuries, including head and spine, were evenly distributed over the two groups, although the snowboarders with central nervous system injuries were younger. In addition, splenic injuries were more common in snowboarders (13% vs. 2%, p < 0.01). Snowboarding accidents were far more common in December, March, and April than other months. Fifty-one patients sustained abdominal or chest injuries and only two of these required operative intervention (two splenectomies). Other operative interventions were limited to extremity injuries, injuries of the spine, or placement of an intracranial pressure monitor. There were no fatalities recorded in this population, although over the 6.5 years, there were 25 deaths related to alpine skiing and one to snowboarding in the State (incidence 0.0000009 skier days). Victims tended to be male: 96% of the skiers and the one snowboarder. The predominant cause of death was blunt head trauma followed by blunt chest trauma. Helmets were not worn by those sustaining head injuries or fatalities. Spine injuries were recorded only in extremely young snowboarders and skiers out of control. CONCLUSION: Snowboarders and Alpine skiers are equally prone to injury. Snowboarding accidents are typically less severe and show significantly different injury patterns than skiing accidents. Abdominal and chest injuries in this population are generally amenable to nonoperative management. Prevention programs are best targeted at safe skiing and snowboarding practices, not skiing or snowboarding in poor conditions, use of helmets for skiers, and restraint of snowboard use in very young children.     

Canine atopic disease: the prevalence of positive intradermal skin tests at two sites in the north and south of Great Britain

Results of intradermal skin test responses to the same panel of 53 allergens were compared in 118 dogs with atopic disease presented at two geographical centres, Edinburgh (87 cases) and London (31 cases). The allergens most commonly positive at both centres were human dander and Dermatophagoides farinae, but positive tests to all of the allergens used occurred in at least one case. The mean number of allergens to which positive tests resulted in atopic dogs was 5.126 (Edinburgh) and 5.129 (London). The majority of animals were sensitive to allergens from more than one group. A significantly higher number of positive reactors to house dust allergen was observed at London than at Edinburgh (P < 0.05), while a significantly higher number of positive reactions to grass pollens was detected at Edinburgh than in London (P < 0.05). Sensitivity to Dermatophagoides pteronyssinus, in the absence of sensitivity to D. farinae, was uncommon and therefore both of these mite allergens should be incorporated in intradermal skin testing panels in Great Britain.     

Immortalization of neuroendocrine pinealocytes from transgenic mice by targeted tumorigenesis using the tryptophan hydroxylase promoter

Tryptophan hydroxylase (TPH) is the first enzyme in both serotonin and melatonin biosynthesis in neuroendocrine cells of the pineal gland. The lack of immortalized neuroendocrine pineal cell lines has been a major obstacle to the study of the tissue-specific and circadian regulation of TPH gene expression in the pineal gland. Previously, we demonstrated that a 6.1 kb 5' upstream region of the mouse TPH gene directs the restricted expression of a lacZ reporter gene to the pineal gland and the raphe nuclei of transgenic mice. Therefore, to develop TPH-expressing pineal cell lines we first established transgenic mice carrying a construct consisting of 6.1 kb of 5' flanking region fused to the SV40 T-antigen. These animals developed highly invasive pineal tumors and died at 12-15 weeks of age. The pineal tumors obtained from the transgenic mice were utilized to establish the immortalized pinealocyte-derived cell lines. These cells express two marker enzymes, TPH and serotonin N-acetyltransferase (NAT). In pineal gland TPH and NAT expressions have been known to be regulated during circadian cycle. The two established cell lines therefore promise to be a valuable in vitro model system for the study of the rhythmic nature of the pineal function at molecular level in mammal.     

Comparison of 5-fluorouracil pharmacokinetics in patients receiving continuous 5-fluorouracil infusion and oral uracil plus N1-(2''-tetrahydrofuryl)-5-fluorouracil

In order to examine the relationship between long-term potentiation (LTP) and phosphoinositide (PI) turnover, we evaluated these throughout anesthetized rat brain using carbon-11-labeled diacylglycerol (11C-DAG). High-frequency tetanic stimulation (400 pulses at 400 Hz) to the perforant pathway induced LTP in rat dentate gyrus. In autoradiograms of rat brains, LTP was associated with the occurrence of multiple highly radioactive spots in many regions distant from the stimulated site. Following i.v. administration of an NMDA receptor antagonist prior to stimulation, however, no high-density spots were found. These findings directly demonstrate that potentiation of phosphoinositide-derived signaling was induced during LTP, and the finding of multiple location suggests the occurrence of polysynaptic neurotransmission through neural networks pertaining to learning and memory.