315 research outputs found

    Entrainment, motion and deposition of coarse particles transported by water over a sloping mobile bed

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    In gravel-bed rivers, bedload transport exhibits considerable variability in time and space. Recently, stochastic bedload transport theories have been developed to address the mechanisms and effects of bedload transport fluctuations. Stochastic models involve parameters such as particle diffusivity, entrainment and deposition rates. The lack of hard information on how these parameters vary with flow conditions is a clear impediment to their application to real-world scenarios. In this paper, we determined the closure equations for the above parameters from laboratory experiments. We focused on shallow supercritical flow on a sloping mobile bed in straight channels, a setting that was representative of flow conditions in mountain rivers. Experiments were run at low sediment transport rates under steady nonuniform flow conditions (i.e., the water discharge was kept constant, but bedforms developed and migrated upstream, making flow nonuniform). Using image processing, we reconstructed particle paths to deduce the particle velocity and its probability distribution, particle diffusivity, and rates of deposition and entrainment. We found that on average, particle acceleration, velocity and deposition rate were responsive to local flow conditions, whereas entrainment rate depended strongly on local bed activity. Particle diffusivity varied linearly with the depth-averaged flow velocity. The empirical probability distribution of particle velocity was well approximated by a Gaussian distribution when all particle positions were considered together. In contrast, the particles located in close vicinity to the bed had exponentially distributed velocities. Our experimental results provide closure equations for stochastic or deterministic bedload transport models.Comment: Submitted to Journal of Geophysical Researc

    Screening for amblyopia in childhood.

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    BACKGROUND: Amblyopia is a reversible deficit of vision that has to be treated within the sensitive period for visual development. Screening programmes have been set up to detect this largely asymptomatic condition and refer children for treatment while an improvement in vision is still possible. The value of such programmes and the optimum protocol for administering them remain controversial. OBJECTIVES: The objective of this review was to evaluate the effectiveness of vision screening in reducing the prevalence of amblyopia. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL), which contains the Cochrane Eyes and Vision Group Trials Register, on The Cochrane Library Issue 2, 2005, MEDLINE (1966 to May 2005 week 1) and EMBASE (1980 to 2005 week 19). No language restrictions were placed on these searches. No handsearching was done. SELECTION CRITERIA: We planned to analyse data from randomised controlled trials and cluster-randomised trials comparing the prevalence of amblyopia in screened versus unscreened populations. DATA COLLECTION AND ANALYSIS: Two authors independently assessed study abstracts identified by the electronic searches. Full text copies of appropriate studies were obtained and, where necessary, authors were contacted. No data were available for analysis and no meta-analysis was performed. MAIN RESULTS: Despite the large amount of literature available regarding vision screening no trials designed to compare the prevalence of amblyopia in screened versus unscreened populations were found. Data currently under preparation may be available for updates to the review. AUTHORS' CONCLUSIONS: The lack of data from randomised controlled trials makes it difficult to analyse the impact of existing screening programmes on the prevalence of amblyopia. The absence of such evidence cannot be taken to mean that vision screening is not beneficial; simply that this intervention has not yet been tested in robust trials. To facilitate such trials normative data on age-appropriate vision tests need to be available and a consensus reached regarding the definition of amblyopia. In addition, the consequences of living with untreated amblyopia have yet to be quantified and a cost-benefit analysis carried out

    Prioritisation of indicators in SDG 4:Voluntary national reviews as a tool of soft governance

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    Voluntary national reviews (VNRs) are an important component of the follow-up and review process for the Sustainable Development Goals (SDGs). Presented by countries at the annual United Nations High-Level Political Forum on Sustainable Development (HLPF), VNRs detail a country’s self-reported progress to peers. This voluntary process has been criticised for its weak accountability. Global governance literature, however, points to an increase in these “soft” governance mechanisms as well as the potential strategic benefits of this approach. Using a mix of logistic regression and document analysis, this study examined VNRs as a soft governance tool and a reflection of the governance mechanism of the SDGs. The authors examined the scope and content of VNR submissions from 2016 to 2022, with a deeper review of 2022, which focused on the global goal for education (SDG 4). Three types of soft governance – governing by goal-setting, by numbers and by morality – were used as lenses to make sense of the results. The authors’ findings demonstrate the ability of soft governance tools to bring together diverse actors around a broad set of goals, and how the power of numbers can influence which indicators countries report on in their VNR.</p

    Reducing Rydberg state dc polarizability by microwave dressing

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    We demonstrate reduction of the dc polarizability of Cesium atom Rydberg states in a 77 K environment utilizing microwave field dressing. In particular we reduce the polarizability of 52P3/252P_{3/2} states which have resonances at 5.35 GHz to 51D5/251D_{5/2}, suitable for interfacing Rydberg atoms to superconducting resonators in a cryogenic environment. We measure the polarizability of the Rydberg states using Magneto-Optical-Trap (MOT) loss spectroscopy. Using an off-resonant radio-frequency (RF) dressing field coupling 52P3/252P_{3/2} and 51D5/251D_{5/2} we demonstrate a reduction in dc polarizability of the 52P3/2 52P_{3/2} states over 80%\%. Experimental findings are in good agreement with a numerical model of the atom-dressing field system developed using the Shirley-Floquet formalism. We also demonstrate that the dc polarizability reduction is highly anisotropic, with near total nulling possible when the dc and dressing fields are aligned, but only a factor of two reduction in polarizability when the fields are orthogonal. These results may aid in stabilizing Rydberg resonances against varying dc fields present near surfaces, enabling advancement in the development of hybrid Rydberg atom - superconducting resonator quantum gates

    Robotic-assisted laparoscopic donor nephrectomy: Decreasing length of stay

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    Background: The number of robotic operations performed with the da Vinci Surgical System has increased during the past decade. This system allows for greater maneuverability and control than hand-assisted laparoscopic procedures, resulting in less tissue manipulation and irritation

    A Universal Model of Global Civil Unrest

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    Civil unrest is a powerful form of collective human dynamics, which has led to major transitions of societies in modern history. The study of collective human dynamics, including collective aggression, has been the focus of much discussion in the context of modeling and identification of universal patterns of behavior. In contrast, the possibility that civil unrest activities, across countries and over long time periods, are governed by universal mechanisms has not been explored. Here, we analyze records of civil unrest of 170 countries during the period 1919-2008. We demonstrate that the distributions of the number of unrest events per year are robustly reproduced by a nonlinear, spatially extended dynamical model, which reflects the spread of civil disorder between geographic regions connected through social and communication networks. The results also expose the similarity between global social instability and the dynamics of natural hazards and epidemics.Comment: 8 pages, 3 figure

    Role of special coagulation studies for preoperative screening of thrombotic complications in simultaneous pancreas-kidney transplantation

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    Background: Vascular thrombosis is a well-known complication after simultaneous pancreas-kidney (SPK) transplantation procedures. The role of preoperative special coagulation studies to screen patients at high risk for vascular thrombosis is unclear and not well studied

    Factibilidad técnica y de salud pública de la recolección de aguas nieblas: estudio de caso

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    Objetivos Evaluación para consumo humano de la captación de aguas nieblas en el municipio de San Antonio (Cundinamarca).Método Se recolectó agua niebla mediante un prototipo de captador de 6 m2, que se instaló en el área durante 53 días consecutivos y se analizó el agua recolectada para evaluar su viabilidad para consumo humano.Resultados El volumen promedio diario de captación en la zona fue de 43,26 L/día y los parámetros de potabilidad evaluados cumplen con los valores mínimos establecidos en el Reglamento de Agua Potable y Saneamiento Básico RAS 2000, con excepción del pH.Conclusión Esta alternativa para captación y uso de agua plantea opciones alternativas y puede escalarse para producir las cantidades necesarias en comunidades asentadas en zonas de baja precipitación, adicionalmente, la calidad del agua recolectada en esta zona es adecuada para consumo humano, por lo que mejora las condiciones de salud de la población. Se sugiere realizar una evaluación de factibilidad económica para su aplicación y sostenibilidad
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