Light-induced effects-impacts to module performance measurements and reliability testing: An overview

The stability of solar cells is a key factor in determining the reliability of photovoltaic modules and is of great interest in the case of solar cells having a new technology which has not yet been fully developed. In particular this question arises with hydrogenated amorphous silicon (a-Si) solar cells because a-Si exhibits reversible light induced changes in its electronic properties, commonly referred to as the Staebler-Wronski effect (SWE). Continuous progress is being made in the peak conversion efficiencies of a-Si solar cells and efficiencies in excess of 11% have been achieved. However, stability is still a problem. ARCO Solar reports results on solar cells which, after over a year's exposure to sunlight, under open circuit conditions, still have about 7% conversion efficiency. Other results show a region of fast degradation for about a month, after which the degradation diminishes rapidly

Microstructure and mechanical properties of sintered (2-4)Mn-(0¿6.-0¿8)C steels

YesMechanical properties of 2¿4% manganese PM steels were determined in tension and in bending following laboratory sintering in dry, hydrogen rich atmospheres. Young's modulus determined by an extensometric technique was about 115 GPa; when measured by an ultrasonic method it was about 153 GPa, in accordance with the`law of mixtures¿. The microstructures, significantly devoid of oxide networks, were predominantly pearlitic, but frequently with variability for specimens similarly processed, resulting in appreciable variations in the stresses for macroscopic yielding and fracture. The majority of the experiments were conducted on 3 and 4Mn¿0·6C alloys and for these R0·1 was in the range 275¿500 MPa, tensile strength (TS) 300¿600 MPa, and (apparent) transverse rupture strength (TRS) 640¿1260 MPa. Statistical techniques were employed to analyse the data. When careful control of processing was maintained, the Weibull modulus was highest, at about 17, for TS of furnace cooled specimens, and lowest, about 6, for TRS of the rapidly cooled specimens. In order to interpret the significant differences between the TRS and the TS values, both apparently measuring the critical stress for cracking after strains of up to 7%, a two stage normalising technique for TRS was adopted. By taking account of the plastic strains preceding failure, the elastic`strength of materials¿ formula was modified to allow true fracture stresses to be calculated. It was also postulated that failure was initiated from a population of flaws of variable size and then the `normalised¿ bend strengths, smaller than TRSs, were shown to correspond well with TSs. It is suggested that this combined plasticity correction and Weibull analysis approach, which has a sound scientific basis, should be employed to interpret bend test data in preference to empirical correlations between TS and TRS

Sintering microstructure and mechanical properties of PM manganese-molybdenum steels

YesThe effects of 0·5 wt-%Mo addition on the processing, microstructure, and strength of PM Fe¿3·5Mn¿0·7C steel are described. Water atomised and sponge irons, Astaloy 1·5Mo, milled ferromanganese, and graphite were the starting powders. During sintering in 75H2 /25N2 or pure hydrogen the dewpoint was controlled and monitored; in particular the effects of improving it from -35 to -60°C were investigated. Faster heating rates (20 K min-1), sufficient gas flowrates, milling the ferro alloy under nitrogen, a low dewpoint (<-60°C), and a getter powder can all contribute to the reduction or prevention of oxidation of the manganese, in particular formation of oxide networks in the sintered steels. For 600 MPa compaction pressure densities up to 7·1 g cm-3 were obtained; these were not significantly affected by sintering at temperatures up to 1180°C. The sintered microstructures were sensitively dependent on the cooling rate. Irrespective of the presence of Mo, slow furnace cooling at 4 K min-1 resulted in mainly pearlitic structures with some ferrite and coarse bainite, whereas fast cooling at 40 K min-1 produced martensite and some retained austenite, very fine pearlite, bainite, and some ferrite. Young's modulus, determined by tensile and ultrasonic tests, was in the range 110¿155 GPa. Sintering with -60°C dewpoint resulted in tensile and transverse rupture strengths of420 and 860 MPa for the Mn steel, rising to 530 and1130 MPa as a result of the Mo addition. This contrasts with strength decreases observed when processing included use of high oxygen containing ferromanganese and sintering with -35°C dewpoint

Role of Corticosteroids in Bone Loss During Space Flight

The primary objective of this research project is to test the hypothesis that corticosteroids contribute to the adverse skeletal effects of space flight. To achieve this objective, serum corticosteroids, which are known to increase during space flight, must be maintained at normal physiologic levels in flight rats by a combination of adrenalectomy and corticosteroid supplementation via implanted hormone pellets. Bone analyses in these animals will then be compared to those of intact flight rats that, based on past experience, will undergo corticosteroid excess and bone loss during space flight. The results will reveal whether maintaining serum corticosteroids at physiologic levels in flight rats affects the skeletal abnormalities that normally develop during space flight. A positive response to this question would indicate that the bone loss and decreased bone formation associated with space flight are mediated, at least in part, by corticosteroid excess

Tensile properties of Fe-3Mn-0¿6/0¿7C steels sintered in semiclosed containers in dry hydrogen, nitrogen and mixtures thereof

Ye

A Tale of Two Democrats: How Authoritarianism Divides the Democratic Party

Authoritarianism has been predominantly used in American politics as a predictor of Republican identification and conservative policy preferences. We argue that this approach has neglected the role authoritarianism plays among Democrats and how it can operate within political parties regardless of their ideological orientation. Drawing from three distinct sets of data, we demonstrate the impact of authoritarianism in the 2016 Democratic Party’s primaries. Authoritarianism consistently predicts differences in primary voting among Democrats, particularly support for Hillary Clinton over Bernie Sanders. This effect is robust across various model specifications including controls for ideology, partisan strength, and other predispositions. These results highlight the potential of authoritarianism to shape leadership preferences within the Democratic Party. We advocate for a reconsideration of authoritarianism as a disposition with meaningful consequences for intraparty dynamics and conclude with practical implications regarding the future of the Democratic Party

The 'Fast' and 'Slow' Light Induced Defects in Diluted and Undiluted Hydrogenated Amorphous Silicon Solar Cells and Materials

International audienceStudies have been carried out on a-Si:H p-in solar cells and corresponding i-layer films fabricated with and without hydrogen dilution for kinetics with high intensity and 1 sun illuminations. The results show a striking similarity between the kinetics in the fill factors (FF) of the p-in solar cells and the mobility lifetime (µτ) products of the corresponding i layer films. New results are presented on thermal annealing after 10 sun degradation which further substantiate the presence of fast and slow defects in the light induced changes of a-Si:H materials, as do the degradation kinetics of both cells and films under 1 sun illumination to their degraded steady states (DSS). Initial (fast) and subsequent (slow) regimes approaching DSS are present at temperatures between 25°C and 100°C, with the two regimes having distinctly different dependences on temperature. The DSS in the films and cells improve monotonically with temperature whereas the initial regimes show a clear reversal in their temperature dependence between 40°C and 50°C. The inability to express these results of 1 sun kinetics with rate equations containing only single time constants for creation and annealing provides further evidence that more than one defect is responsible for light induced degradation in a-Si:H materials and solar cells

Why Acute Ischemic Stroke Patients in the United States Use or Do Not Use Emergency Medical Services Transport? Findings of an Inpatient Survey

Background Patients with acute ischemic stroke (AIS) who use emergency medical services (EMS) receive quicker reperfusion treatment which, in turn, mitigates post-stroke disability. However, nationally only 59% use EMS. We examined why AIS patients use or do not use EMS. Methods During 2016–2018, a convenience sample of AIS patients admitted to a primary stroke center in South Carolina were surveyed during hospitalization if they were medically fit, available for survey when contacted, and consented to participate. The survey was programed into EpiInfo with skip patterns to minimize survey burden and self-administered on a touchscreen computer. Survey questions covered symptom characteristics, knowledge of stroke and EMS importance, subjective reactions, role of bystanders and financial factors. Descriptive and multiple regression analyses were performed. Results Of 108 inpatients surveyed (out of 1179 AIS admissions), 49% were male, 44% African American, mean age 63.5 years, 59% mild strokes, 75 (69%) arrived by EMS, 33% were unaware of any stroke symptom prior to stroke, and 75% were unaware of the importance of EMS use for good outcome. Significant factors that influenced EMS use decisions (identified by regression analysis adjusting for stroke severity) were: prior familiarity with stroke (self or family/friend with stroke) adjusted odds ratio, 5.0 (95% confidence interval, 1.6, 15.1), perceiving symptoms as relevant for self and indicating possible stroke, 26.3 (7.6, 91.1), and bystander discouragement to call 911, 0.1 (0.01,0.7). Further, all 27 patients who knew the importance of EMS had used EMS. All patients whose physician office advised actions other than calling EMS at symptom onset, did not use EMS. Conclusion Systematic stroke education of patients with stroke-relevant comorbidities and life-style risk factors, and public health educational programs may increase EMS use and mitigate post-stroke disability

Hole Drift-Mobility Measurements in Contemporary Amorphous Silicon

We present hole drift-mobility measurements on hydrogenated amorphous silicon from several laboratories. These temperature-dependent measurements show significant variations of the hole mobility for the differing samples. Under standard conditions (displacement/field ratio of 2×10-9 cm2/V), hole mobilities reach values as large as 0.01 cm2/Vs at room-temperature; these values are improved about tenfold over drift-mobilities of materials made a decade or so ago. The improvement is due partly to narrowing of the exponential bandtail of the valence band, but there is presently little other insight into how deposition procedures affect the hole drift-mobility