A rotorcraft is a class of aircraft that uses large-diameter rotating wings to accomplish efficient vertical take-off and landing. The class encompasses helicopters of numerous configurations (single ...main rotor and tail rotor, tandem rotors, coaxial rotors), tilting proprotor aircraft, compound helicopters, and many other innovative configuration concepts. Aeromechanics covers much of what the rotorcraft engineer needs: performance, loads, vibration, stability, flight dynamics, and noise. These topics include many of the key performance attributes and the often-encountered problems in rotorcraft designs. This comprehensive book presents, in depth, what engineers need to know about modelling rotorcraft aeromechanics. The focus is on analysis, and calculated results are presented to illustrate analysis characteristics and rotor behaviour. The first third of the book is an introduction to rotorcraft aerodynamics, blade motion, and performance. The remainder of the book covers advanced topics in rotary wing aerodynamics and dynamics.
Low-temperature Ag sintering provides a lead-free die attachment method that is compatible with high-temperature (300 °C) power electronics applications. The reliability of sintered Ag die attach for ...Si and SiC die has been studied on both thick film substrates for lower current power applications and direct bond copper (DBC) substrates for higher current power applications. Pressureless and low-pressure sintering were evaluated. Sintering with low pressure yielded lower porosity (15-17%) versus pressureless sintering (~30%). Reliability was evaluated with thermal aging (300 °C) and thermal cycling (-55 °C to + 300 °C) tests. Reliable Ag sintered die attach was achieved with assemblies having Ag-bearing surface finishes on both the die and the substrate. In contrast, the shear strength after 300 °C aging was greatly reduced when Au metallization was used either on the die or on substrate surface. In some cases, low-pressure sintering delayed the failure of the sintered Ag die attach to Au surfaces when aged at 300 °C compared to the pressureless sintering. The reliability with Pd-containing substrate metallizations was intermediate between Ag and Au metallizations. The thermal cycle reliability on DBC substrates was limited by failure at the Cu-to-alumina interface over the wide temperature range, while on the thick film substrates high adhesion was maintained after 1000 thermal cycles.
Obesity is a growing global health concern. The increased body mass and altered mass distribution associated with obesity may be related to increases in plantar shear that putatively leads to ...physical functional deficits. Therefore, measurement of plantar shear may provide unique insights on the effects of body mass and body distribution on physical function or performance.
1) To investigate the effects of body mass and distribution on plantar shear. 2) To examine how altered plantar shear influences postural control and gait kinetics.
1) a weighted vest forward distributed (FV) would shift the center of pressure (CoP) location forward during standing compared with a weighted vest evenly distributed (EV), 2) FV would increase plantar shear spreading forces more than EV during standing, 3) FV would increase postural sway during standing while EV would not, and 4) FV would elicit greater compensatory changes during walking than EV.
Twenty healthy young males participated in four different tests: 1) static test (for measuring plantar shear and CoP location without acceleration, 2) bilateral-foot standing postural control test, 3) single-foot standing postural test, and 4) walking test. All tests were executed in three different weight conditions: 1) unweighted (NV), 2) EV with 20% added body mass, and 3) FV, also with 20% added body mass. Plantar shear stresses were measured using a pressure/shear device, and several shear and postural control metrics were extracted. Repeated measures ANOVAs with Holms post hoc test were used to compare each metric among the three conditions (α = 0.05).
FV and EV increased both AP and ML plantar shear forces compared to NV. FV shifted CoP forward in single-foot trials. FV and EV showed decreased CoP range and velocity and increased Time-to-Boundary (TTB) during postural control compared to NV. EV and FV showed increased breaking impulse and propulsive impulse compared to NV. In addition, EV showed even greater impulses than FV. While EV increased ML plantar shear spreading force, FV increased AP plantar shear spreading force during walking.
Added body mass increases plantar shear spreading forces. Body mass distribution had greater effects during dynamic tasks. In addition, healthy young individuals seem to quickly adapt to external stimuli to control postural stability. However, as this is a first step study, follow-up studies are necessary to further support the clinical role of plantar shear in other populations such as elderly and individuals with obesity or diabetes.
As HIV infection continues unabated, there is a need for effective interventions targeting at-risk men who have sex with men (MSM). Engaging MSM online where they meet sexual partners is critical for ...HIV prevention efforts.
A randomized controlled trial (RCT) conducted online among U.S. MSM recruited from several gay sexual networking websites assessed the impact of 2 HIV prevention videos and an HIV prevention webpage compared to a control condition for the study outcomes HIV testing, serostatus disclosure, and unprotected anal intercourse (UAI) at 60-day follow-up. Video conditions were pooled due to reduced power from low retention (53%, n = 1,631). No participant incentives were provided.
Follow-up was completed by 1,631 (53%) of 3,092 eligible men. In the 60 days after the intervention, men in the pooled video condition were significantly more likely than men in the control to report full serostatus disclosure ('asked and told') with their last sexual partner (OR 1.32, 95% CI 1.01-1.74). Comparing baseline to follow-up, HIV-negative men in the pooled video (OR 0.70, 95% CI 0.54-0.91) and webpage condition (OR 0.43, 95% CI 0.25-0.72) significantly reduced UAI at follow-up. HIV-positive men in the pooled video condition significantly reduced UAI (OR 0.38, 95% CI 0.20-0.67) and serodiscordant UAI (OR 0.53, 95% CI 0.28-0.96) at follow-up.
Findings from this online RCT of MSM recruited from sexual networking websites suggest that a low cost, brief digital media intervention designed to engage critical thinking can increase HIV disclosure to sexual partners and decrease sexual risk. Effective, brief HIV prevention interventions featuring digital media that are made widely available may serve as a complementary part of an overall behavioral and biomedical strategy for reducing sexual risk by addressing the specific needs and circumstances of the target population, and by changing individual knowledge, motivations, and community norms.
ClinicalTrials.gov NCT00649701.
Orthopaedic surgery is among the least diverse fields in all of medicine. To promote the recruitment of minorities, a commonly proposed strategy is to increase the exposure of minority medical ...students to orthopaedic surgeons and residents who are minorities themselves. This study examines the degree to which the racial/ethnic diversity of the orthopaedic faculty and residency program influences underrepresented in medicine (URM) medical students at that institution to pursue a career in orthopaedics.
Using data provided by the Association of American Medical Colleges, we identified all US medical schools that were affiliated with an orthopaedic department and an orthopaedic residency program (n = 110). For each institution, data were collected on URM representation among the orthopaedic faculty and residents (2013 to 2017), as well as the proportion of URM medical students who applied to an orthopaedic residency program (2014 to 2018). The association between institutional factors and the URM medical student orthopaedic application rate was then assessed.
Of 11,887 URM students who graduated from medical school during the 5-year study period, 647 applied to an orthopaedic residency program (5.4%). URM students who attended medical school at institutions with high URM representation on the orthopaedic faculty were more likely to apply in orthopaedics (odds ratio 1.27, 95% confidence interval 1.04 to 1.55, P = 0.020), as were URM students at institutions with high URM representation in the residency program (odds ratio 1.45, 95% confidence interval 1.17 to 1.79, P < 0.001).
The benefits of a diverse orthopaedic workforce are widely acknowledged. In this study, we found that increased URM representation among the orthopaedic faculty and residents was associated with a greater likelihood that URM medical students at that institution would apply in orthopaedics. We also suggest a set of strategies to break the cycle and promote the recruitment of minorities into the field of orthopaedic surgery.
Pre-exposure prophylaxis (PrEP) use among populations most vulnerable to HIV as identified in the national HIV prevention goals is not fully known. This systematic review assessed trends of lifetime ...self-reported PrEP use and disparities among key populations.
We used the CDC HIV/AIDS Prevention Research Synthesis cumulative database of electronic and manual searches in MEDLINE, CINAHL, EMBASE, and PsycINFO from 2000 to 2019 to identify English-language primary studies reporting PrEP use. Two reviewers independently screened citations, extracted data, and assessed the risk of bias with the modified Newcastle-Ottawa Scale. We estimated pooled proportions and crude/adjusted odds ratio.
We identified 95 eligible studies including 95,854 US-based survey respondents. A few studies (6.3%) focused on persons who inject drugs. In 2015-2017, men who have sex with men (MSM) had highest proportion of individuals who used PrEP over their lifetime 13.9% (95% confidence interval: 8.8 to 21.1), k (number of surveys) = 49 followed by Hispanic/Latinos 11.5 (7.1 to 18.1), 12, transgender women 11.2 (5.8 to 20.6), 5, and blacks 9.9 (8.3 to 11.8), 18. Odds of PrEP use increased by 34%/year odds ratio = 1.34/year (95% confidence interval: 1.09 to 1.64) and significantly increased over time among MSM 1.53/year (1.21-1.93) and blacks 1.44 (1.13-1.83). People in the Southern United States 9.9 (4.7-19.7), 8 and youth 7.3 (4.7-11.2), 8 had lower rates and did not demonstrate growth 0.94 (0.29-3.18); 0.82 (0.43-1.55). Odds of reporting lifetime PrEP use was twice 2.07 (1.27-3.38) as great among MSM than non-MSM.
Proportions of PrEP use in published surveys have been growing, but remain low for people in the Southern United States and youth, and understudied in persons who inject drugs. Limitations include few studies in certain years, whereas strengths include a large number of respondents. Culturally tailored approaches targeting vulnerable populations are essential in increasing PrEP use to reduce disparities in HIV acquisition.
In this letter, we present AlGaN/GaN lateral Schottky barrier diodes on silicon with recessed anodes and dual field plates. A low specific ON-resistance R ON,SP (5.12 mQ · cm 2 ), a low turn-ON ...voltage (<; 0.7 V), and a high reverse breakdown voltage (BV) (>1.9 kV) were simultaneously achieved in devices with a 25-μm anode/cathode distance, resulting in a power figure-of-merit BV 2 /R ON,SP of 727 MW · cm -2 . The record high BV of 1.9 kV is attributed to the dual field-plate structure.
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