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Reliability Prediction of PV Inverters Based on MIL-HDBK-217F N2
No full textThis paper initially discusses the reliability of a 250W Photovoltaic (PV) micro inverter. Using the bill of materials the reliabilities of the main, gate drive, power supply, current and voltage sensing and microprocessor circuits were investigated, and the failure rate and Mean Time Between Failure (MTBF) calculated. The sum of component failure rates equals the complete PV micro inverter failure rate. To account for temperature effects the component failure rate was calculated for each inverter operating temperature, and multiplied by the percentage occurrence of this operating temperature to obtain a weighted failure rate. A similar procedure was used to calculate the failure rate for the main circuits of a 4.6kW & a 4.5kW multi-string inverter. All calculations are based on MIL-17F N2 method
LES of density ratio effects on film cooling under rotating frame
No full textA numerical study was conducted to investigate the performance of film cooling injection from a row of multiple square holes spaced laterally across a flat plate. LES with the standard Smagorinsky-Lilly model was used to investigate the dynamic mixing process between the coolant jet stream and the mainstream flows. The finite volume method and the unsteady PISO algorithm on a non-uniform staggered grid were applied. The values of rotation number (Ro) examined were 0.0, 0.03021, 0.06042, and 0.12084, jet spacing to jet width ratio (P/D) was 3.0, and a jet Reynolds number (Re) of 4700, which based on the hole width and the jet exit velocity. The effects of the coolant to mainstream density ratio (DR) on the film cooling effectiveness were investigated by injecting either Nitrogen (DR = 0.98) or Carbon dioxide (DR = 1.55) as the coolant streams. The effect of density ratio on the film-cooling effectiveness is coupled with varying velocity ratio (VR=0.5 and 1.0). The coolant gas was injected at 90o to the mainstream flow. The flow fields of the present study were compared with experimental data in order to validate the reliability of the LES technique. It was shown that rotation has a strong impact on the jet trajectory behaviour and the film cooling effectiveness. In all cases, as the rotation number increases, the film effectiveness increases; this effect is increased as the velocity ratio increases. The results also showed the strong influence of velocity ratio on the flow field behaviour and the film cooling where the jet penetrates further into the cross flow as VR increases and the wake region increases with increasing VR. Furthermore, It was concluded that density ratio has only a minor effect on flow field and heat transfer at a constant velocity ratio
Ice nucleation by combustion ash particles at conditions relevant to mixed-phase clouds
No full textIce-nucleating particles can modify cloud properties with implications for climate and the hydrological cycle; hence, it is important to understand which aerosol particle types nucleate ice and how efficiently they do so. It has been shown that aerosol particles such as natural dusts, volcanic ash, bacteria and pollen can act as ice-nucleating particles, but the ice-nucleating ability of combustion ashes has not been studied. Combustion ashes are major by-products released during the combustion of solid fuels and a significant amount of these ashes are emitted into the atmosphere either during combustion or via aerosolization of bottom ashes. Here, we show that combustion ashes (coal fly ash, wood bottom ash, domestic bottom ash, and coal bottom ash) nucleate ice in the immersion mode at conditions relevant to mixed-phase clouds. Hence, combustion ashes could play an important role in primary ice formation in mixed-phase clouds, especially in clouds that are formed near the emission source of these aerosol particles. In order to quantitatively assess the impact of combustion ashes on mixed-phase clouds, we propose that the atmospheric abundance of combustion ashes should be quantified since up to now they have mostly been classified together with mineral dust particles. Also, in reporting ice residue compositions, a distinction should be made between natural mineral dusts and combustion ashes in order to quantify the contribution of combustion ashes to atmospheric ice nucleation
Simple measures of climate, soil properties and plant traits predict national scale grassland soil carbon stocks
No full textSoil carbon (C) storage is a key ecosystem service. Soil C stocks play a vital role in soil fertility and climate regulation, but the factors that control these stocks at regional and national scales are unknown, particularly when their composition and stability are considered. As a result, their mapping relies on either unreliable proxy measures or laborious direct measurements. Using data from an extensive national survey of English grasslands, we show that surface soil (0–7 cm) C stocks in size fractions of varying stability can be predicted at both regional and national scales from plant traits and simple measures of soil and climatic conditions. Soil C stocks in the largest pool, of intermediate particle size (50–250 μm), were best explained by mean annual temperature (MAT), soil pH and soil moisture content. The second largest C pool, highly stable physically and biochemically protected particles (0·45–50 μm), was explained by soil pH and the community abundance-weighted mean (CWM) leaf nitrogen (N) content, with the highest soil C stocks under N-rich vegetation. The C stock in the small active fraction (250–4000 μm) was explained by a wide range of variables: MAT, mean annual precipitation, mean growing season length, soil pH and CWM specific leaf area; stocks were higher under vegetation with thick and/or dense leaves. Testing the models describing these fractions against data from an independent English region indicated moderately strong correlation between predicted and actual values and no systematic bias, with the exception of the active fraction, for which predictions were inaccurate. Synthesis and applications. Validation indicates that readily available climate, soils and plant survey data can be effective in making local- to landscape-scale (1–100 000 km2) soil C stock predictions. Such predictions are a crucial component of effective management strategies to protect C stocks and enhance soil C sequestration
Examining Changes in Central and Peripheral Pain as Mediates of Fatigue Improvement: Results From the British Society for Rheumatology Biologics Register for Rheumatoid Arthritis
No full textObjective: Following anti-TNF therapy, improvements in rheumatoid Arthritis (RA) fatigue are driven by reductions in pain. However, therapies may modify central and peripheral pain. This study sought to examine the hypothesis that reductions in fatigue after anti-TNF therapy reflect changes in central, not peripheral, pain mechanisms. Methods: Data of patients with severe baseline fatigue (SF36 Vitality ≤12.5; n=2652), recruited to the British Society for Rheumatology Biologics Register for RA for commencing anti-TNF therapies between October 2000 and November 2008, were used. Data of interest comprised change over 6-months in fatigue, pain (SF36 Bodily Pain) and disease activity constituents (DAS28; ESR, global health, swollen and tender joints). Principal components factor analysis with varimax rotation determined latent variables of symptom change; variables were accepted provided they had eigenvalues≥1. Results: Six factors were identified, of which two met acceptance criteria (eigenvalues 2.39 and 1.14, respectively). Following rotation, loadings indicated that factor 1 comprised markers of peripheral inflammation; change in ESR, swollen and tender joints, and global health. This distinct loading led to factor 1 being labelled ‘peripheral inflammation’. Conversely, factor 2 comprised change in pain, fatigue and global health and an absence of peripheral inflammation markers, and was therefore labelled as ‘central inflammation’. Conclusions: Following anti-TNF therapies, reductions in fatigue and pain appear to reflect improvements in central, rather than peripheral, inflammation. Therefore, for those seeking to treat fatigue via pain mechanisms, improvements may be maximised by the application of treatment modalities which effectively target central mechanisms
Cohort effects on the need for health care and implications for health care planning in Canada.
No full textThe sustainability of publicly funded health care systems is an issue for governments around the world. The economic climate limits governments' fiscal capacity to continue to devote an increasing share of public funds to health care. Meanwhile the demands for health care within populations continue to increase. Planning the future requirements for health care is typically based on applying current levels of health service use by age to demographic projections of the population. But changes in age-specific levels of health over time would undermine this 'constant use by age' assumption. We use representative Canadian survey data (Canadian Community Health Survey) covering the period 2001-2012, to identify the separate trends in demography (population ageing) and epidemiology (population health) on self-reported health. We propose an approach to estimating future health care requirements that incorporates cohort trends in health. Overall health care requirements for the population increase as the size and mean age of the population increase, but these effects are mitigated by cohort trends in health-we find the estimated need for health care is lower when models account for cohort effects in addition to age effects
Managing inadequate antidepressant response in depressive illness.
No full textINTRODUCTION OR BACKGROUND: Depression frequently fails to respond to initial treatment. SOURCES OF DATA: Predominantly meta-analyses and RCTs but supplemented where necessary by additional data and the authors' clinical experience. AREAS OF AGREEMENT: A systematic assessment to identify remedial causes of poor response should be followed by planned sequential treatment trials. Joint decision making by the patient and clinician is essential. Strategies with the strongest support are antidepressant augmentation with lithium or second generation antipsychotics and adding cognitive behavioural treatment. Electroconvulsive therapy is highly effective in resistant depression but there is a high relapse rate when treatment ends. AREAS OF CONTROVERSY: Some pharmacological strategies have inconsistent data (e.g. antidepressant combinations, T3 augmentation) or limited preliminary data (e.g. ketamine, antidepressant augmentation with pramipexole). The efficacy of vagus nerve stimulation, deep brain stimulation and repetitive transcranial magnetic stimulation is unclear. GROWING POINTS: A greater understanding of the causes of depression may assist the development of more effective treatments. AREAS TIMELY FOR DEVELOPING RESEARCH: Role of glutamate antagonists and psychological treatments, other than cognitive behavioural therapy, as adjunctive treatments.Copyright © The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: [email protected]
