499 research outputs found
The use of a combination frequency technique to measure the surf zone bubble population
There are great benefits to sizing bubbles using a two frequency technique, which examines the appearance of sum-and-difference signals generated by the interaction between a resonant bubble pulsation and a much higher frequency imaging beam. This paper presents the results from using the technique to size bubbles in the ocean surf zone, and details the pulsation model used to calibrate the returned data such that the height of the bubble scattered signal can be related to the number of resonant bubbles of that size. It also shows how ambiguities and inaccuracies (brought on through turbulence and the substantial off-resonance nature of the signal) which affected earlier oceanic tests using the same method can be identified in the returned signal or removed from the estimate during the data processin
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Spatial and temporal variability of the concentration field from localized releases in a regular building array
Spatial and temporal fluctuations in the concentration field from an ensemble of continuous point-source releases in a regular building array are analyzed from data generated by direct numerical simulations. The release is of a passive scalar under conditions of neutral stability. Results are related to the underlying flow structure by contrasting data for an imposed wind direction of 0 deg and 45 deg relative to the buildings. Furthermore, the effects of distance from the source and vicinity to the plume centreline on the spatial and temporal variability are documented. The general picture that emerges is that this particular geometry splits the flow domain into segments (e.g. “streets” and “intersections”) in each of which the air is, to a first approximation, well mixed. Notable exceptions to this general rule include regions close to the source, near the plume edge, and in unobstructed channels when the flow is aligned. In the oblique (45 deg) case the strongly three-dimensional nature of the flow enhances mixing of a scalar within the canopy leading to reduced temporal and spatial concentration fluctuations within the plume core. These fluctuations are in general larger for the parallel flow (0 deg) case, especially so in the long unobstructed channels. Due to the more complex flow structure in the canyon-type streets behind buildings, fluctuations are lower than in the open channels, though still substantially larger than for oblique flow. These results are relevant to the formulation of simple models for dispersion in urban areas and to the quantification of the uncertainties in their predictions
Kinetic Turbulence
The weak collisionality typical of turbulence in many diffuse astrophysical
plasmas invalidates an MHD description of the turbulent dynamics, motivating
the development of a more comprehensive theory of kinetic turbulence. In
particular, a kinetic approach is essential for the investigation of the
physical mechanisms responsible for the dissipation of astrophysical turbulence
and the resulting heating of the plasma. This chapter reviews the limitations
of MHD turbulence theory and explains how kinetic considerations may be
incorporated to obtain a kinetic theory for astrophysical plasma turbulence.
Key questions about the nature of kinetic turbulence that drive current
research efforts are identified. A comprehensive model of the kinetic turbulent
cascade is presented, with a detailed discussion of each component of the model
and a review of supporting and conflicting theoretical, numerical, and
observational evidence.Comment: 31 pages, 3 figures, 99 references, Chapter 6 in A. Lazarian et al.
(eds.), Magnetic Fields in Diffuse Media, Astrophysics and Space Science
Library 407, Springer-Verlag Berlin Heidelberg (2015
The Effects of Alfven Waves and Radiation Pressure in Dust Winds of Late-type Stars
In the present study, we analyze the effects of a flux of Alfven waves acting
together with radiation pressure on grains as an acceleration mechanism of the
wind of late-type stars. In the wind model we simulate the presence of grains
through a strong damping of the waves, we used a non-isothermal profile for
temperature, coherent with grain formation theories. We examine the changes in
the velocity profile of the wind and we show that if the grains are created in
the region 1.1 < r/r_0 < 2.0 their presence will affect the mass loss and
terminal velocity. The model is applied to a K5 supergiant star and for
Betelgeuse (alpha Ori).Comment: 6 pages, 3 figures, accepted in ApJ (Sep, 2002
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Harm reduction behaviors are associated with carrying naloxone among patients on methadone treatment
Despite the widespread availability of naloxone, US opioid overdose rates continue to rise. The “Cascade of Care” (CoC) is a public health approach that identifies steps in achieving specific outcomes and has been used to identify gaps in naloxone carriage among individuals with opioid use disorder (OUD). We sought to apply this framework to a treatment-seeking population with OUD that may be more inclined to engage in harm reduction behaviors. Patients were recruited from an urban methadone program to complete a survey. We assessed naloxone familiarity, availability, obtainability, training, and possession, as well as naloxone carriage rates, demographics, and harm reduction behaviors. A multivariable logistic regression examined associations between naloxone carriage and individual-level factors. Participants (n = 97) were majority male (59%), with a mean age of 48 (SD = 12), 27% had college education or higher, 64% indicated injection drug use, and 84% reported past naloxone training. All participants endorsed familiarity with naloxone, but only 42% regularly carried naloxone. The following variables were associated with carrying naloxone: White race (aOR = 2.94, 95% CI 1.02–8.52), college education (aOR = 8.11, 95% CI 1.76–37.47), and total number of self-reported harm reduction behaviors (aOR = 1.45, 95% CI 1.00–2.11). We found low rates of naloxone carriage among methadone-treated patients. Methadone programs provide opportunities for naloxone interventions and should target racial/ethnic minorities and individuals with lower education. The spectrum of harm reduction behaviors should be encouraged among these populations to enhance naloxone carriage.https://doi.org/10.1186/s12954-023-00745-
Biological and geophysical feedbacks with fire in the Earth system
Roughly 3% of the Earth’s land surface burns annually, representing a critical exchange of energy and
matter between the land and atmosphere via combustion. Fires range from slow smouldering peat
fires, to low-intensity surface fires, to intense crown fires, depending on vegetation structure, fuel
moisture, prevailing climate, and weather conditions. While the links between biogeochemistry,
climate and fire are widely studied within Earth system science, these relationships are also mediated
by fuels—namely plants and their litter—that are the product of evolutionary and ecological
processes. Fire is a powerful selective force and, over their evolutionary history, plants have evolved
traits that both tolerate and promote fire numerous times and across diverse clades. Here we outline a
conceptual framework of how plant traits determine the flammability of ecosystems and interact with
climate and weather to influence fire regimes. We explore how these evolutionary and ecological
processes scale to impact biogeochemical and Earth system processes. Finally, we outline several
research challenges that, when resolved, will improve our understanding of the role of plant evolution
in mediating the fire feedbacks driving Earth system processes. Understanding current patterns of fire
and vegetation, as well as patterns of fire over geological time, requires research that incorporates
evolutionary biology, ecology, biogeography, and the biogeosciences
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Evaluation of fast atmospheric dispersion models in a regular street network
The need to balance computational speed and simulation accuracy is a key challenge in designing atmospheric dispersion models that can be used in scenarios where near real-time hazard predictions are needed. This challenge is aggravated in cities, where models need to have some degree of building-awareness, alongside the ability to capture effects of dominant urban flow processes. We use a combination of high-resolution large-eddy simulation (LES) and wind-tunnel data of flow and dispersion in an idealised, equal-height urban canopy to highlight important dispersion processes and evaluate how these are reproduced by representatives of the most prevalent modelling approaches: (i) a Gaussian plume model, (ii) a Lagrangian stochastic model and (iii) street-network dispersion models. Concentration data from the LES, validated against the wind-tunnel data, were averaged over the volumes of streets in order to provide a high-fidelity reference suitable for evaluating the different models on the same footing. For the particular combination of forcing wind direction and source location studied here, the strongest deviations from the LES reference were associated with mean over-predictions of concentrations by approximately a factor of 2 and with a relative scatter larger than a factor of 4 of the mean, corresponding to cases where the mean plume centreline also deviated significantly from the LES. This was linked to low accuracy of the underlying flow models/parameters that resulted in a misrepresentation of pollutant channelling along streets and of the uneven plume branching observed in intersections. The agreement of model predictions with the LES (which explicitly resolves the turbulent flow and dispersion processes) greatly improved by increasing the accuracy of building-induced modifications of the driving flow field. When provided with a limited set of representative velocity parameters, the comparatively simple street-network models performed equally well or better compared to the Lagrangian model run on full 3D wind fields. The study showed that street-network models capture the dominant building-induced dispersion processes in the canopy layer through parametrisations of horizontal advection and vertical exchange processes at scales of practical interest. At the same time, computational costs and computing times associated with the network approach are ideally suited for emergency-response applications
The Skeletal Organic Matrix from Mediterranean Coral Balanophyllia europaea Influences Calcium Carbonate Precipitation
Scleractinian coral skeletons are made mainly of calcium carbonate in the form of aragonite. The mineral deposition occurs in a biological confined environment, but it is still a theme of discussion to what extent the calcification occurs under biological or environmental control. Hence, the shape, size and organization of skeletal crystals from the cellular level through the colony architecture, were attributed to factors as diverse as mineral supersaturation levels and organic mediation of crystal growth. The skeleton contains an intra-skeletal organic matrix (OM) of which only the water soluble component was chemically and physically characterized. In this work that OM from the skeleton of the Balanophyllia europaea, a solitary scleractinian coral endemic to the Mediterranean Sea, is studied in vitro with the aim of understanding its role in the mineralization of calcium carbonate. Mineralization of calcium carbonate was conducted by overgrowth experiments on coral skeleton and in calcium chloride solutions containing different ratios of water soluble and/or insoluble OM and of magnesium ions. The precipitates were characterized by diffractometric, spectroscopic and microscopic techniques. The results showed that both soluble and insoluble OM components influence calcium carbonate precipitation and that the effect is enhanced by their co-presence. The role of magnesium ions is also affected by the presence of the OM components. Thus, in vitro, OM influences calcium carbonate crystal morphology, aggregation and polymorphism as a function of its composition and of the content of magnesium ions in the precipitation media. This research, although does not resolve the controversy between environmental or biological control on the deposition of calcium carbonate in corals, sheds a light on the role of OM, which appears mediated by the presence of magnesium ions
Rationale, design and methodology of a double-blind, randomized, placebo-controlled study of escitalopram in prevention of Depression in Acute Coronary Syndrome (DECARD)
<p>Abstract</p> <p>Background</p> <p>The prevalence of depression in patients with acute coronary syndrome, i.e. myocardial infarction and unstable angina, is higher than in the general population. The prevalence of anxiety is higher as well. Both depression and anxiety are associated with poor cardiac outcomes and higher mortality. Comorbid depression in patients with acute coronary syndrome often goes undiagnosed, and it is therefore a challenging task to prevent this risk factor. The study of DEpression in Coronary ARtery Disease (DECARD) is designed to examine if it is possible to prevent depression in patients with acute coronary syndrome.</p> <p>Methods</p> <p>Two hundred forty non-depressed patients with acute coronary syndrome are randomized to treatment with either escitalopram or placebo for 1 year. Psychiatric and cardiac assessment of patients is performed to evaluate the possibility of preventing depression. Diagnosis of depression and Hamilton Depression Scale are the primary outcome measures.</p> <p>Discussion</p> <p>This is the first study of prevention of depression in patients after acute coronary syndrome with a selective serotonin reuptake inhibitor.</p> <p>Trial Registration</p> <p><url>http://www.ClinicalTrials.gov.</url> Identifier: NCT00140257</p
Effectiveness of joint mobilisation after cast immobilisation for ankle fracture: a protocol for a randomised controlled trial [ACTRN012605000143628]
BACKGROUND: Passive joint mobilisation is a technique frequently used by physiotherapists to reduce pain, improve joint movement and facilitate a return to activities after injury, but its use after ankle fracture is currently based on limited evidence. The primary aim of this trial is to determine if adding joint mobilisation to a standard exercise programme is effective and cost-effective after cast immobilisation for ankle fracture in adults. METHODS/DESIGN: Ninety participants will be recruited from the physiotherapy departments of three teaching hospitals and randomly allocated to treatment or control groups using a concealed procedure. All participants will perform an exercise programme. Participants in the treatment group will also receive joint mobilisation twice a week for four weeks. Blinded follow-up assessments will be conducted four, 12 and 24 weeks after randomisation. The primary outcome measures will be the Lower Extremity Functional Scale and the Assessment of Quality of Life. Secondary outcomes will include measures of impairments, activity limitation and participation. Data on the use of physiotherapy services and participants' out-of-pocket costs will be collected for the cost-effective and cost-utility analyses. To test the effects of treatment, between-group differences will be examined with analysis of covariance using a regression approach. The primary conclusions will be based on the four-week follow-up data. DISCUSSION: This trial incorporates features known to minimise bias. It uses a pragmatic design to reflect clinical practice and maximise generalisability. Results from this trial will contribute to an evidence-based approach for rehabilitation after ankle fracture
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