Thermal stress cycling of GaAs solar cells

A thermal cycling experiment was performed on GaAs solar cells to establish the electrical and structural integrity of these cells under the temperature conditions of a simulated low-Earth orbit of 3-year duration. Thirty single junction GaAs cells were obtained and tests were performed to establish the beginning-of-life characteristics of these cells. The tests consisted of cell I-V power output curves, from which were obtained short-circuit current, open circuit voltage, fill factor, and cell efficiency, and optical micrographs, spectral response, and ion microprobe mass analysis (IMMA) depth profiles on both the front surfaces and the front metallic contacts of the cells. Following 5,000 thermal cycles, the performance of the cells was reexamined in addition to any factors which might contribute to performance degradation. It is established that, after 5,000 thermal cycles, the cells retain their power output with no loss of structural integrity or change in physical appearance

Coherent Destruction of Coulomb Blockade Peaks in Molecular Junctions

Coherent electronic transport in single-molecule junctions is investigated in the Coulomb blockade regime. Both the transmission phase and probability are calculated for junctions with various contact symmetries. A dramatic suppression of the Coulomb blockade peaks is predicted for junctions where multiple atomic orbitals of the molecule couple to a single electrode although the charging steps are unaffected.Comment: 6 pages, 4 figure

The Effects of Beetle-Induced Tree Death on Forest Bird Diversity in Western Montana

In forest ecosystems, climate change can hinder management success by increasing the frequency and intensity of fire and insect outbreaks that cause massive tree die-offs and abrupt habitat change. Resource managers often use ecological indicators to gain insight into the health and status of ecosystems due to the challenge of monitoring all aspects of any ecosystem. Birds are increasingly identified as appropriate taxa for predicting changes in biodiversity and ecological integrity around the globe. We assessed the effects of bark beetle induced forest die-off on patterns of avian diversity in western Montana. We used songbirds, which are ubiquitous and possess attributes capturing the complexity of forests as ecological indicators. In addition to assessing the effects of bark beetle forest die-off on bird diversity we also sought to examine the relative importance of the “conspecific neighborhood” in influencing species-level occurrence rates at a given survey location. This approach is motivated by the idea that individuals of a species aggregate around resources. It follows, that a species is more likely to occur in a patch surrounded by other occupied patches (the conspecific neighborhood). Incorporating measures of spatial autocorrelation in ecological studies is not new. However, this topic is only just beginning to be applied in the context of more recent analytical advances such as Bayesian multi-species hierarchal models used to estimate species abundance and occurrence rates

Effect of statins on venous thromboembolic events: a meta-analysis of published and unpublished evidence from randomised controlled trials

Background - It has been suggested that statins substantially reduce the risk of venous thromboembolic events. We sought to test this hypothesis by performing a meta-analysis of both published and unpublished results from randomised trials of statins. Methods and Findings - We searched MEDLINE, EMBASE, and Cochrane CENTRAL up to March 2012 for randomised controlled trials comparing statin with no statin, or comparing high dose versus standard dose statin, with 100 or more randomised participants and at least 6 months' follow-up. Investigators were contacted for unpublished information about venous thromboembolic events during follow-up. Twenty-two trials of statin versus control (105,759 participants) and seven trials of an intensive versus a standard dose statin regimen (40,594 participants) were included. In trials of statin versus control, allocation to statin therapy did not significantly reduce the risk of venous thromboembolic events (465 [0.9%] statin versus 521 [1.0%] control, odds ratio [OR] = 0.89, 95% CI 0.78–1.01, p = 0.08) with no evidence of heterogeneity between effects on deep vein thrombosis (266 versus 311, OR 0.85, 95% CI 0.72–1.01) and effects on pulmonary embolism (205 versus 222, OR 0.92, 95% CI 0.76–1.12). Exclusion of the trial result that provided the motivation for our meta-analysis (JUPITER) had little impact on the findings for venous thromboembolic events (431 [0.9%] versus 461 [1.0%], OR = 0.93 [95% CI 0.82–1.07], p = 0.32 among the other 21 trials). There was no evidence that higher dose statin therapy reduced the risk of venous thromboembolic events compared with standard dose statin therapy (198 [1.0%] versus 202 [1.0%], OR = 0.98, 95% CI 0.80–1.20, p = 0.87). Risk of bias overall was small but a certain degree of effect underestimation due to random error cannot be ruled out. Please see later in the article for the Editors' Summary. Conclusions - The findings from this meta-analysis do not support the previous suggestion of a large protective effect of statins (or higher dose statins) on venous thromboembolic events. However, a more moderate reduction in risk up to about one-fifth cannot be ruled out

Система обнаружения с беспроводной зарядкой на основе катушки с крестовидной перемычкой и активной системой управления аккумулятором

The article presents a detection system with spider web coil-based wireless charging. Commonly available metal detectors are sold as handheld systems, which enable only progressive, lengthy, time-consuming search. Importantly, a part of the investigated area can thus be easily missed, and the probability that a metal object will not be found increases substantially. This problem, however, is eliminable via the automatic position tracking mode embedded in the solution obtained through our research. The proposed system facilitates using the spider web coil simultaneously for wireless charging and metal detection by pulse induction. The topology of the detector can emit variable pulse lengths, thus allowing the device to detect more types of metal and to adapt itself to the permeability of the soil. The coil has a branch in a relevant part of the winding to reduce undesirable electromagnetic interference during the charging. On the transmitting side of the topology, impedance matching is included to maintain the maximum spatial gap variability. By changing the position of the receiving side, the output voltage changes; therefore, a high efficiency DC/DC converter is employed. The individual battery cells demonstrate different internal resistances, requiring us to apply a new method to balance the cells voltage. The system can be utilized on self-guided vehicles or drones; advantageously, a GPS resending the coordinates to a mesh radio allows for accurate positioning. With the mesh topology, potential cooperation between the multiple systems is possible. The setup utilizes the same coil for wireless power transfer and detection.В статье представлена система обнаружения с беспроводной зарядкой на основе катушки с крестообразной перемычкой. Обычно доступные металлоискатели продаются в виде переносных систем, которые позволяют осуществлять только постепенный, длительный и трудоемкий поиск. Важно отметить, что часть исследуемой зоны, таким образом, может быть легко пропущена, и вероятность того, что металлический объект не будет найден, существенно возрастает. Эта проблема устраняется с помощью автоматического режима отслеживания местоположения, встроенного в решение, полученное в результате наших исследований. Предлагаемая система облегчает одновременное использование катушки с крестообразной перемычкой для беспроводной зарядки и обнаружения металла с помощью импульсной индукции. Топология детектора может излучать переменную длину импульсов, что позволяет устройству обнаруживать больше типов металлов и адаптироваться к проницаемости почвы. Катушка имеет ответвление в соответствующей части обмотки, чтобы уменьшить нежелательные электромагнитные помехи во время зарядки. На передающей стороне топологии включено согласование импеданса для поддержания максимальной изменчивости пространственного зазора. При изменении положения приемной стороны изменяется выходное напряжение, поэтому используется высокоэффективный преобразователь постоянного тока в постоянный. Отдельные элементы батареи демонстрируют различные внутренние сопротивления, что требует применения нового метода для балансировки напряжения элементов. Система может быть использована на самонаводящихся транспортных средствах или беспилотных летательных аппаратах; GPS, успешно отправляющие координаты на многоканальное радио, обеспечивают точное позиционирование. При наличии многоканальной топологии возможно потенциальное сотрудничество между разнообразными системами. В установке используется одна и та же катушка для беспроводной передачи и обнаружения энергии

Single-phonon addition and subtraction to a mechanical thermal state

Adding or subtracting a single quantum of excitation to a thermal state of a bosonic system has the counter-intuitive effect of approximately doubling its mean thermal occupation. We perform the first experimental demonstration of this effect outside optics by implementing single-phonon addition and subtraction to a thermal state of a mechanical oscillator via Brillouin optomechanics in an optical whispering-gallery microresonator. Using a detection scheme that combines single-photon counting and optical heterodyne detection, we observe this doubling of the mechanical thermal fluctuations to a high precision. The capabilities of this joint click-dyne detection scheme adds a significant new dimension for optomechanical quantum science and applications