Search

Evaluation of the photoresponse in wurtzite GaN photoconductive switches is presented based on kinetic Monte Carlo simulations. The focus is on electron transport physics and assessment of high frequency operation. The roles of GaN band structure, Pauli exclusion, and treatment of internal fields based on the fast multipole method are all comprehensively included. The implementation was validated through comparisons of velocity-field characteristics for GaN with computational results in the literature. Photocurrent widths of less than ∼7 ps for the 1 μm device can be expected, which translates into a 100 GHz upper bound. Photocurrent pulse compression below the laser full width at half maxima at high applied fields are predicted based on the interplay of space-charge effects and the negative differential velocity characteristics of GaN. [ABSTRACT FROM AUTHOR]

Argues for development of a code of ethics for college faculty by answering common objectives to such codes; proposing ethical theories, principles, and rules to guide the formulation of a impartial, well-crafted code; and identifying benefits, including providing guidelines for resolving moral dilemmas, of such codes. (DB)

The magnetic sensitivity of Hall-effect sensors made of InAlN/GaN and AlGaN/GaN heterostructures was measured between room temperature and 576 °C. Both devices showed decreasing voltage-scaled magnetic sensitivity at high temperatures, declining from 53 mV/V/T to 8.3 mV/V/T for the InAlN/GaN sample and from 89 mV/V/T to 8.5 mV/V/T for the AlGaN/GaN sample, corresponding to the decreasing electron mobility due to scattering effects at elevated temperatures. Alternatively, current-scaled sensitivities remained stable over the temperature range, only varying by 13.1% from the mean of 26.3 V/A/T and 10.5% from the mean of 60.2 V/A/T for the InAlN/GaN and AlGaN/GaN samples, respectively. This is due to the minimal temperature dependence of the electron sheet density on the 2-dimensional electron gas (2DEG). Both devices showed consistency in their voltage- and current-scaled sensitivity over multiple temperature cycles as well as nearly full recovery when returned to room temperature after thermal cycling. Additionally, an AlGaN/GaN sample held at 576 °C for 12 h also showed nearly full recovery at room temperature, further suggesting that GaN-based Hall-effect sensors are a good candidate for use in high temperature applications. [ABSTRACT FROM AUTHOR]

A sharp decrease to <50% in the numbers of mucus cells mm−2 of epidermis was observed in the skin of Atlantic salmon Salmo salar at the beginning of the smoltification period in 1997 and 1999. Average numbers decreased in 1997 from 662 mm−2 on 6 March to 275 mm−2 on 20 March and in 1999 from 828 mm−2 on 3 March to 388 mm2 on 24 March. A second smaller decrease was observed towards the end of smoltification in both years. [ABSTRACT FROM AUTHOR]

This article describes a wide-field time-domain fluorescence lifetime imaging (FLIM) microscope with optical sectioning. The FLIM system utilizes a wide-field time-gated optical image intensifier, with a minimum gate width of 85 ps, to achieve high temporal resolution of fluorescence decays induced by ultrashort laser pulses. Different configurations, using excitation pulses of picojoule energy at 80 MHz repetition rate and of nanojoule energy at 10 kHz, are compared. The instrument has a temporal dynamic range spanning from 100 ps to tens of µs and is shown to have a temporal discrimination better than 10 ps. When applied to laser dye samples, it has produced FLIM maps demonstrating sensitivity to variations in both chemical species and local environment, e.g., viscosity. Wide-field optical sectioning is achieved using the technique of structured illumination, which is applied to remove out-of-focus light that can result in lifetime artifacts. The sectioning strength, which may be adjusted by choosing an appropriate spatial modulation frequency, is characterized and shown to be comparable to that of a confocal microscope. Practical considerations concerned with improving the quality of sectioned fluorescence lifetime maps, including using a large bit depth camera, are discussed. [ABSTRACT FROM AUTHOR]

We report the development of a whole-field fluorescence lifetime imaging (FLIM) system with high temporal resolution based on a time-gated image intensifier. The optimized temporal gate width is <100ps, and changes in the environment of a fluorescent phantom, causing lifetime differences less than 10ps, have been imaged. The versatility of this FLIM system has been demonstrated by measuring both the temporal and spectral profiles of multiple fluorescent samples in a single acquisition. Initial fluorescence lifetime images suggest that this technique can provide a means of distinguishing between different tissue constituents. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the role of metallic stents in treating stenoses involving prosthetic arterial bypass grafts.Methods: Patients undergoing stent placement within a failing prosthetic bypass graft, during a 41-month period, were reviewed for treatment outcome and complications. The indications for stent placement in 15 patients included severe claudication (n = 3), rest pain (n = 9), and minor or major tissue loss (n = 3). Lesions were at the proximal anastomosis (n = 6), the distal anastomosis (n = 3), or within the graft (n = 6).Results: Treatment with metallic stents was successful in all patients. There was one acute stent thrombosis, successfully treated with thrombolytic therapy. Follow-up data are available for a mean duration of 12.3 months. The mean duration of primary patency was 9.4 months with 6- and 12-month primary patency rates of 51.9% and 37.0%, respectively. The mean duration of secondary patency was 12.1 months with 6- and 12-month secondary patency rates of 80.0% and 72.7%, respectively. Two patients with discontinuous runoff and preexisting gangrene required a below-knee amputation. Six patients were revised surgically after stent placement (at a mean of 10.8 months). Three late deaths occurred during follow-up.Conclusion: Given the mortality risks of surgical revision and the reduced life expectancy of this patient population, metallic stent placement represents a viable, short-term treatment option for stenoses within or at the anastomoses of prosthetic grafts. Further evaluation is warranted to compare intragraft stent placement with surgical graft revision. [ABSTRACT FROM AUTHOR]

PURPOSE: To evaluate the safety and efficacy of the recombinant tissue plasminogen activator alteplase in the clearance of poorly functioning tunneled hemodialysis catheters. METHODS: We retrospectively reviewed the outcomes of 25 patients who presented with poorly functioning hemodialysis catheters and were treated with alteplase. After confirming fluoroscopically the need for thrombolytic therapy, alteplase was administered over 2 hours as a 2.5-mg/hour/catheter lumen infusion (total 10 mg). Treatment was considered a clinical success if a flow rate of 250 mL or more per minute was established. RESULTS: Clinical success was achieved in each of 25 patients (100%). There were no thrombolytic-related complications. Catheter survival was extended 30 days in 54% of patients and 45 days in 33% of patients. CONCLUSION: Alteplase is a safe and effective means of producing clearance of blocked tunneled catheters. [ABSTRACT FROM AUTHOR]