Ultrafast carrier relaxation in GaN, In_(0.05)Ga_(0.95)N and an In_(0.05)Ga_(0.95)/In_(0.15)Ga_(0.85)N Multiple Quantum Well

Room temperature, wavelength non-degenerate ultrafast pump/probe measurements were performed on GaN and InGaN epilayers and an InGaN multiple quantum well structure. Carrier relaxation dynamics were investigated as a function of excitation wavelength and intensity. Spectrally-resolved sub-picosecond relaxation due to carrier redistribution and QW capture was found to depend sensitively on the wavelength of pump excitation. Moreover, for pump intensities above a threshold of 100 microJ/cm2, all samples demonstrated an additional emission feature arising from stimulated emission (SE). SE is evidenced as accelerated relaxation (< 10 ps) in the pump-probe data, fundamentally altering the re-distribution of carriers. Once SE and carrier redistribution is completed, a slower relaxation of up to 1 ns for GaN and InGaN epilayers, and 660 ps for the MQW sample, indicates carrier recombination through spontaneous emission.Comment: submitted to Phys. Rev.

COVID-19 and immunosuppression: a review of current clinical experiences and implications for ophthalmology patients taking immunosuppressive drugs

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in December 2019 in Wuhan city, Hubei province, China. This is the third and largest coronavirus outbreak since the new millennium after SARS in 2002 and Middle East respiratory syndrome (MERS) in 2012. Over 3 million people have been infected and the COVID-19 has caused more than 217 000 deaths. A concern exists regarding the vulnerability of patients who have been treated with immunosuppressive drugs prior or during this pandemic. Would they be more susceptible to infection by the SARS-CoV-2 and how would their clinical course be altered by their immunosuppressed state? This is a question the wider medical fraternity-including ophthalmologists, rheumatologists, gastroenterologist and transplant physicians among others-must answer. The evidence from the SARS and MERS outbreak offer some degree of confidence that immunosuppression is largely safe in the current COVID-19 pandemic. Preliminary clinical experiences based on case reports, small series and observational studies show the morbidity and mortality rates in immunosuppressed patients may not differ largely from the general population. Overwhelmingly, current best practice guidelines worldwide recommended the continuation of immunosuppression treatment in patients who require them except for perhaps high-dose corticosteroid therapy and in patients with associated risk factors for severe COVID-19 disease.Ophthalmic researc

Evolving consensus for immunomodulatory therapy in non-infectious uveitis during the COVID-19 pandemic

Background Immunomodulatory therapy (IMT) is often considered for systemic treatment of non-infectious uveitis (NIU). During the evolving coronavirus disease-2019 (COVID-19) pandemic, given the concerns related to IMT and the increased risk of infections, an urgent need for guidance on the management of IMT in patients with uveitis has emerged. Methods A cross-sectional survey of international uveitis experts was conducted. An expert steering committee identified clinical questions on the use of IMT in patients with NIU during the COVID-19 pandemic. Using an interactive online questionnaire, guided by background experience and knowledge, 139 global uveitis experts generated consensus statements for IMT. In total, 216 statements were developed around when to initiate, continue, decrease and stop systemic and local corticosteroids, conventional immunosuppressive agents and biologics in patients with NIU. Thirty-one additional questions were added, related to general recommendations, including the use of non-steroidal anti-inflammatory drugs (NSAIDs) and hydroxychloroquine. Results Highest consensus was achieved for not initiating IMT in patients who have suspected or confirmed COVID-19, and for using local over systemic corticosteroid therapy in patients who are at high-risk and very high-risk for severe or fatal COVID-19. While there was a consensus in starting or initiating NSAIDs for the treatment of scleritis in healthy patients, there was no consensus in starting hydroxychloroquine in any risk groups. Conclusion Consensus guidelines were proposed based on global expert opinion and practical experience to bridge the gap between clinical needs and the absence of medical evidence, to guide the treatment of patients with NIU during the COVID-19 pandemic.Ophthalmic researc

Long-Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE) Conceptual Design Report Volume 2: The Physics Program for DUNE at LBNF

The Physics Program for the Deep Underground Neutrino Experiment (DUNE) at the Fermilab Long-Baseline Neutrino Facility (LBNF) is described

Highly-parallelized simulation of a pixelated LArTPC on a GPU

The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 10^3 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype

Pressure dependence of donor excitation spectra in AlSb

We have investigated the behavior of ground to bound excited-state electronic transitions of Se and Te donors in AlSb as a function of hydrostatic pressure. Using broadband far-infrared Fourier transform spectroscopy, we observe qualitatively different behaviors of the electronic transition energies of the two donors. While the pressure derivative of the Te transition energy is small and constant, as might be expected for a shallow donor, the pressure derivatives of the Se transition energies are quadratic and large at low pressures, indicating that Se is actually a deep donor. In addition, at pressures between 30 and 50 kbar, we observe evidence of an anti-crossing between one of the selenium electronic transitions and a two-phonon mode

Hydrogen in semiconductors symposium held April 13 14, 2004, San Francisco, California, U.S.A. ; Symposium H, held at the 2004 MRS spring meeting

Hydrogen in Semiconductor

Generation and characterization of point defects in SrTiO3 and Y3Al5O12

Positron annihilation lifetime spectroscopy (PALS) was applied to characterize point defects in single crystals of Y3Al5O12 and SrTiO3 after populating different types of defects by relevant thermal treatments. In SrTiO3, PALS measurements identified Sr vacancy, Ti vacancy, vacancy complexes of Ti–O (vacancy) and hydrogen complex defects. In Y3Al5O12 single crystals the measurements showed the presence of Al-vacancy, (Al–O) vacancy and Al-vacancy passivated by hydrogen. These defects are shown to play the major role in defining the electronic and optical properties of these complex oxides