Response of tantalum capacitors to fast transient overvoltages

Report describes tests used to determine minimum time for capacitors to fail due to overvoltage and maximum amount of overvoltage that capacitors could sustain without permanent damage

Tantalum capacitor behavior under fast transient overvoltages

Tantalum capacitors were tested to determine failure time when subjected to short-duration, high-voltage surges caused by lightning strikes. Lightning is of concern to NASA because of possible damage to critical spacecraft circuits. The test was designed to determine the minimum time for tantalum capacitor failure and the amount of overvoltage a capacitor could survive, without permanent damage, in 100 microseconds. All tested exhibited good recovery from the transient one-shot pulses with no failure at any voltage, forward or reverse, in less than 25 microseconds

Analysis of Fluvial Suspended Sediment Load Contribution through Anthropocene History to the South Atlantic Bight Coastal Zone, U.S.A.

Discerning the effects of anthropogenic activities (i.e., reservoir construction, land use change), as opposed to those of natural processes (i.e., climate variability), on suspended sediment flux has become an increasingly difficult challenge. This contribution presents water and suspended sediment flux from five major watersheds that discharge into the southeastern U.S. Atlantic, a region that is currently considered sediment starved. Three periods of Anthropocenetime were defined and evaluated: (1) “pre-European conditions” (1680–1700), (2) “pre-dam conditions (1905-1925), and (3) post-dam conditions (1985-2005). Physical and hydrologic watershed data were used to run a climate-driven hydrological transport numerical model (HydroTrend) to estimate suspended sediment flux for each period. Results indicate that the suspended sediment contribution to the South Atlantic Bight coastal zone increased by up to 145% as a result of accelerated soil erosion conditions caused by the arrival of European settlers and has since declined by approximately 55%, primarily because of the construction of large resevoirs. This trend suggests a return to pre-European sediment yields, approximately 100 years after historic peak of soil erosion in the southeastern Piedmont. Our results indicate that variations in sediment yield between time periods are primarily caused by direct anthropogenic forcings, while climate changes over the periods considered have played an insignificant role

Development and Experimental Evaluation of Passive Fuel Cell Thermal Control

To provide uniform cooling for a fuel cell stack, a cooling plate concept was evaluated. This concept utilized thin cooling plates to extract heat from the interior of a fuel cell stack and move this heat to a cooling manifold where it can be transferred to an external cooling fluid. The advantages of this cooling approach include a reduced number of ancillary components and the ability to directly utilize an external cooling fluid loop for cooling the fuel cell stack. A number of different types of cooling plates and manifolds were developed. The cooling plates consisted of two main types; a plate based on thermopyrolytic graphite (TPG) and a planar (or flat plate) heat pipe. The plates, along with solid metal control samples, were tested for both thermal and electrical conductivity. To transfer heat from the cooling plates to the cooling fluid, a number of manifold designs utilizing various materials were devised, constructed, and tested. A key aspect of the manifold was that it had to be electrically nonconductive so it would not short out the fuel cell stack during operation. Different manifold and cooling plate configurations were tested in a vacuum chamber to minimize convective heat losses. Cooling plates were placed in the grooves within the manifolds and heated with surface-mounted electric pad heaters. The plate temperature and its thermal distribution were recorded for all tested combinations of manifold cooling flow rates and heater power loads. This testing simulated the performance of the cooling plates and manifold within an operational fuel cell stack. Different types of control valves and control schemes were tested and evaluated based on their ability to maintain a constant temperature of the cooling plates. The control valves regulated the cooling fluid flow through the manifold, thereby controlling the heat flow to the cooling fluid. Through this work, a cooling plate and manifold system was developed that could maintain the cooling plates within a minimal temperature band with negligible thermal gradients over power profiles that would be experienced within an operating fuel cell stack

Effect of implanted metal impurities on superconducting tungsten films

The superconducting transition temperature of more than 30 thin-film tungsten samples was measured using a dilution refrigerator. The samples were fabricated using a 99.999% pure tungsten target and a dc magnetron sputtering system. Individual films were then doped with metal impurity ions using an accurate ion implantation technique. The effect of the metal–ion doping on the superconducting transition temperature was measured for samples with superconducting transitions in the range of 40–150 mK. Magnetic dopant species including Ni, Co, and Fe resulted in suppressed values of the tungsten Tc. The suppression was linear with increasing dopant concentration, for concentrations up to tens of ppm. For higher concentrations of magnetic atoms, the data are consistent with the Abrikosov–Gor\u27kov theory [Soviet Physics JETP 12, 1243 (1961)] modified by antiferromagnetic impurity–impurity interactions. By contrast, tungsten films implanted with Mg or Cr showed little change in Tc after doping. In this article, we present data from cryogenic experiments on these films. We also present x-ray diffraction (XRD) spectra for a subset of the films. Our XRD data confirm that the observed suppression in Tc for the magnetically doped samples is not due to any structural changes (e.g., lattice distortion or damage) induced by the implantation process

Estimating expansion of the range of oak processionary moth (Thaumetopoea processionea) in the UK from 2006 to 2019

1. The expansion of oak processionary moth (OPM) in South-East England continues despite ongoing efforts to control the pest since its introduction in 2006. 2. Using locations of OPM larval nests, supplied by the Forestry Commission and recorded as part of ongoing surveillance and control measures from 2006 onwards, we show that the expansion of the range of OPM in South-East England up to 2019 was biphasic with a higher rate of expansion from 2015 onwards. 3. The maximum rate of OPM range expansion in the United Kingdom from 2006 to 2014 was estimated as 1.66 km/year (95% CI = [1.22, 2.09]), whereas the 2015–2019 expansion rate was estimated as 6.17 km/year (95% CI = [5.49, 6.84]). This corresponds to an estimated species range distribution area of 7077 km2 in 2019. 4. To explain the faster expansion of OPM range from 2015 onwards, we discuss potential reasons that include: natural capability of species of both short- and long-distance dispersal; external factors such as environmental heterogeneity; a reduction of active control

A qualitative investigation of obese men\u27s experiences with their weight

Objectives: To investigate obese men\u27s health behaviors and strategies for change. Methods: Qualitative interviews with 36 men (BMI 30 and over). Results: All men felt personally responsible for their weight gain. Sedentary lifestyles, stress, lack of worklife balance and weight-based stigma were all significant causes of weight gain and barriers to weight loss. These factors also contributed to men\u27s unwillingness to seek help for their overweight. Conclusion: Addressing the self-blame and stigma associated with obesity is important in developing strategies to improve the health and well-being of obese men