120 research outputs found
Spectral properties of Andreev reflection from quantum turbulence in 3He-B: What do they tell about turbulent fluctuations?
No full textOne of the experimental techniques developed to measure quantum turbulence at low temperatures in 3He-B utilizes the Andreev reflection of thermal quasiparticle excitations from quantized vortices and vortex structures. We present the results of theoretical, numerical, and experimental study of Andreev scattering from quantum turbulence in 3He-B. We analyze the spectral properties of the Andreev reflection and compare these with the spectral properties of superfluid turbulence, and discuss the physical mechanisms responsible for the scaling of spectral densities. Finally, we discuss the relation between our findings and related observables in ordinary turbulence
HIV transmission risk through anal intercourse: systematic review, meta-analysis and implications for HIV prevention.
No full textBACKGROUND: The human immunodeficiency virus (HIV) infectiousness of anal intercourse (AI) has not been systematically reviewed, despite its role driving HIV epidemics among men who have sex with men (MSM) and its potential contribution to heterosexual spread. We assessed the per-act and per-partner HIV transmission risk from AI exposure for heterosexuals and MSM and its implications for HIV prevention. METHODS: Systematic review and meta-analysis of the literature on HIV-1 infectiousness through AI was conducted. PubMed was searched to September 2008. A binomial model explored the individual risk of HIV infection with and without highly active antiretroviral therapy (HAART). RESULTS: A total of 62,643 titles were searched; four publications reporting per-act and 12 reporting per-partner transmission estimates were included. Overall, random effects model summary estimates were 1.4% [95% confidence interval (CI) 0.2-2.5)] and 40.4% (95% CI 6.0-74.9) for per-act and per-partner unprotected receptive AI (URAI), respectively. There was no significant difference between per-act risks of URAI for heterosexuals and MSM. Per-partner unprotected insertive AI (UIAI) and combined URAI-UIAI risk were 21.7% (95% CI 0.2-43.3) and 39.9% (95% CI 22.5-57.4), respectively, with no available per-act estimates. Per-partner combined URAI-UIAI summary estimates, which adjusted for additional exposures other than AI with a 'main' partner [7.9% (95% CI 1.2-14.5)], were lower than crude (unadjusted) estimates [48.1% (95% CI 35.3-60.8)]. Our modelling demonstrated that it would require unreasonably low numbers of AI HIV exposures per partnership to reconcile the summary per-act and per-partner estimates, suggesting considerable variability in AI infectiousness between and within partnerships over time. AI may substantially increase HIV transmission risk even if the infected partner is receiving HAART; however, predictions are highly sensitive to infectiousness assumptions based on viral load. CONCLUSIONS: Unprotected AI is a high-risk practice for HIV transmission, probably with substantial variation in infectiousness. The significant heterogeneity between infectiousness estimates means that pooled AI HIV transmission probabilities should be used with caution. Recent reported rises in AI among heterosexuals suggest a greater understanding of the role AI plays in heterosexual sex lives may be increasingly important for HIV prevention
Sensitivity of Internal Tibial Forces and Moments to Static Optimization Moment Constraints at the Subtalar and Ankle Joints
No full textWe examined the sensitivity of internal tibial forces and moments during running to different subtalar/ankle moment constraints in a static optimization routine. Seventeen participants ran at 2.20, 3.33, and 4.17 ms−1 while force and motion data were collected. Ankle joint contact force was estimated using inverse-dynamics-based static optimization. Three sets of joint moment constraints were tested. All sets included the flexion–extension and abduction–adduction moments at the hip and the flexion–extension moment at the knee but differed in the constraints used at the subtalar/ankle: (1) flexion–extension at the ankle (Sag), (2) flexion–extension and inversion–eversion at ankle (Sag + Front), and (3) flexion–extension at the ankle and supination–pronation at the subtalar (Sag + SubT). Internal tibial forces and moments were quantified at the distal one-third of the tibia, by ensuring static equilibrium with applied forces and moments. No interaction was observed between running speed and constraint for internal tibial forces or moments. Sag + SubT resulted in larger internal mediolateral force (+41%), frontal (+79%), and transverse (+29%) plane moments, compared to Sag and Sag + Front. Internal axial force was greatest in Sag + Front, compared to Sag and Sag + SubT (+37%). Faster running speeds resulted in greater internal tibial forces and moments in all directions (≥+6%). Internal tibial forces and moments at the distal one-third of the tibia were sensitive to the subtalar and ankle joint moment constraints used in the static optimization routine, independent of running speed.This accepted article is published as Baggaley M, Derrick TR, Brent Edwards W. Sensitivity of Internal Tibial Forces and Moments to Static Optimization Moment Constraints at the Subtalar and Ankle Joints. J Biomech Eng. 2023 Jan 1;145(1):011008. doi: 10.1115/1.4055036. Posted with permission. Copyright 2023 by ASME<br
Aboriginal artefacts on the continental shelf reveal ancient drowned cultural landscapes in northwest Australia
No full textThis article reports Australia’s first confirmed ancient underwater archaeological sites from the continental shelf, located off the Murujuga coastline in north-western Australia. Details on two underwater sites are reported: Cape Bruguieres, comprising > 260 recorded lithic artefacts at depths down to −2.4 m below sea level, and Flying Foam Passage where the find spot is associated with a submerged freshwater spring at −14 m. The sites were discovered through a purposeful research strategy designed to identify underwater targets, using an iterative process incorporating a variety of aerial and underwater remote sensing techniques and diver investigation within a predictive framework to map the submerged landscape within a depth range of 0–20 m. The condition and context of the lithic artefacts are analysed in order to unravel their depositional and taphonomic history and to corroborate their in situ position on a pre-inundation land surface, taking account of known geomorphological and climatic processes including cyclone activity that could have caused displacement and transportation from adjacent coasts. Geomorphological data and radiometric dates establish the chronological limits of the sites and demonstrate that they cannot be later than 7000 cal BP and 8500 cal BP respectively, based on the dates when they were finally submerged by sea-level rise. Comparison of underwater and onshore lithic assemblages shows differences that are consistent with this chronological interpretation. This article sets a foundation for the research strategies and technologies needed to identify archaeological targets at greater depth on the Australian continental shelf and elsewhere, building on the results presented. Emphasis is also placed on the need for legislation to better protect and manage underwater cultural heritage on the 2 million square kilometres of drowned landscapes that were once available for occupation in Australia, and where a major part of its human history must lie waiting to be discovered
Biomechanics of Graded Running: Part I - Stride Parameters, External Forces, Muscle Activations
No full textBiomechanical alterations with graded running have only been partially quantified, and the potential interactions with running speed remain unclear. We measured spatiotemporal parameters, ground reaction forces and leg muscle activations (EMG) in nineteen adults (10F/9M) running on an instrumented treadmills at 2.50, 3.33 and 4.17 m·s-1 and 0, ±5o, and ±10o. Step frequency illustrated a significant speed × grade interaction (P < 0.001) and was highest (+3%) at the steepest grade (+10o) and fastest speed (4.17 m·s-1) when compared to level running (LR) at the same speed. Significant interaction was also observed for ground reaction forces (all P ≤ 0.047). Peak ground reaction forces in the normal direction increased with running speed during downhill running (DR) only (+9% at -10o and 4.17 m·s-1). Impulse in the normal direction decreased at fastest speed and steepest DR (-9%) and uphill running (UR) (-17%) grades. Average normal loading rate increased and decreased at fastest speed and steepest DR (+52%) and UR (- 28%) grades, respectively. Negative parallel impulse increased and decreased at fastest speed and steepest DR (+166%) and UR (-90%), respectively. Positive parallel impulse decreased and increased at fastest speed and steepest DR (-75%) and UR (+111%), respectively. EMG showed comparable u-shaped curves across the grades investigated, although only a change in vastus lateralis and tibilias anterior activity was detectable at the steepest grades and fastest speed. Overall, running grade and speed significantly influences spatiotemporal parameters, ground reaction forces, and muscle activations
Countercultural and opposing values at a two-year college
No full textIn an attempt to replicate findings using demographically different populations, the author compared results of principal components analyses on a chart of 456 "fundamental world perspectives." In addition, the Comrey Personality Scale and a "social concepts" questionnaire by Kerlinger were administered to the second group of subjects. Principal components analysis of the second group's data was performed yielding comparable results across the different samples
Commentary on: “Speed and surface steepness affect internal tibial loading during running”
No full textIs There A Relationship Between Hip Structure, Hip Muscle Strength, and Lower Extremity Frontal Plane Kinematics During Treadmill Running?
No full textINTRODUCTION: Excessive hip adduction (HADD) has been associated with a number of lower extremity overuse injuries, and it has been suggested that it may be the result of reduced strength of the hip abduction musculature. Hip structure has been postulated to influence both hip abduction (HABD) strength and HADD. The purpose of this study was to investigate the relationship between hip structure, HABD strength, and frontal plane kinematics during running. METHODS: Peak isometric HABD strength, lower extremity kinematics, femoral neck-shaft angle (NSA), and pelvis width-femur length (pw-fl) ratio were recorded for 25 female subjects. Pearson correlations (P \u3c .05) were performed between variables. RESULTS: A fair relationship was observed between femoral NSA and HABD strength (r = -.472 P = .017) where an increased NSA was associated with reduced HABD strength. No relationship was observed between HABD strength and frontal plane kinematics or between NSA/pw-fl and frontal plane kinematics. CONCLUSION: Alterations in the femoral NSA have the ability to influence peak isometric hip abduction strength. However, alterations in strength did not result in changes in lower extremity kinematics. Structural deviations at the hip do not appear to influence hip kinematics during running
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