130 research outputs found

    Spray forming, droplet microstructure and impingement behavior

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    Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996.Vita.Includes bibliographical references (leaves 89-91).by Matthier Rolland.M.S

    Packing fixed bed reactors with cylinders: influence of particle length distribution

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    In this work, we are interested in a better understanding of the local packing structure of fixed bed reactors made of cylindrical pellets packed in cylindrical tubes. Packing of cylindrical particles is simulated using Grains3D DEM code and results are analyzed in terms of void fraction using 3D analysis tools. With tube diameter as a secondary parameter, we investigate the porous structure depending on the pellet length distribution: average porosity, radial porosity, orientation of the pellets and variability of those indicators when repeating the numerical experiments

    DIRAC framework evaluation for the Fermi\boldsymbol{Fermi}-LAT and CTA experiments

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    DIRAC (Distributed Infrastructure with Remote Agent Control) is a general framework for the management of tasks over distributed heterogeneous computing environments. It has been originally developed to support the production activities of the LHCb (Large Hadron Collider Beauty) experiment and today is extensively used by several particle physics and biology communities. Current (FermiFermi Large Area Telescope -- LAT) and planned (Cherenkov Telescope Array -- CTA) new generation astrophysical/cosmological experiments, with very large processing and storage needs, are currently investigating the usability of DIRAC in this context. Each of these use cases has some peculiarities: FermiFermi-LAT will interface DIRAC to its own workflow system to allow the access to the grid resources, while CTA is using DIRAC as workflow management system for Monte Carlo production and analysis on the grid. We describe the prototype effort that we lead toward deploying a DIRAC solution for some aspects of FermiFermi-LAT and CTA needs.Comment: proceedings to CHEP 2013 conference : http://www.chep2013.org

    Modeling crowd dynamics through coarse-grained data analysis

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    Understanding and predicting the collective behaviour of crowds is essential to improve the efficiency of pedestrian flows in urban areas and minimize the risks of accidents at mass events. We advocate for the development of crowd traffic management systems, whereby observations of crowds can be coupled to fast and reliable models to produce rapid predictions of the crowd movement and eventually help crowd managers choose between tailored optimization strategies. Here, we propose a Bi-directional Macroscopic (BM) model as the core of such a system. Its key input is the fundamental diagram for bi-directional flows, i.e. the relation between the pedestrian fluxes and densities. We design and run a laboratory experiments involving a total of 119 participants walking in opposite directions in a circular corridor and show that the model is able to accurately capture the experimental data in a typical crowd forecasting situation. Finally, we propose a simple segregation strategy for enhancing the traffic efficiency, and use the BM model to determine the conditions under which this strategy would be beneficial. The BM model, therefore, could serve as a building block to develop on the fly prediction of crowd movements and help deploying real-time crowd optimization strategies

    The Mini Nutritional Assessment-Short Form and mortality in nursing home residents — Results from the INCUR study

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    **Objectives** To examine whether the Mini Nutritional Assessment-Short Form (MNA-SF) score and its individual items are predictors of mortality in a nursing home population. **Design** Prospective, secondary analysis from the Incidence of pNeumonia and related ConseqUences in nursing home Residents (INCUR) study with 1-year follow-up. **Participants** A total of 773 older persons (women 74.4%) living in 13 French nursing homes. **Measurements** At baseline, nutritional status was assessed with the MNA-SF. Overall mortality rate was measured over a 12-month follow-up period after the baseline assessment visit. Cox proportional hazard models were performed to test the predictive capacity of the MNA-SF score and its single components for mortality. **Results** Mean age of participants was 86.2 (standard deviation, SD 7.5) years. Mean MNA-SF score was 9.8 (SD 2.4). Among participants, 198 (25.6%) presented a normal nutritional status (12–14 points), 454 (58.7%) were at risk of malnutrition (8–11 points), and 121 (15.7%) were malnourished. After one year of follow-up, 135 (17.5%) participants had died. Age, female gender, baseline weight, BMI and MNA-SF were significant predictors of mortality whereas no specific chronic disease was. The total MNA-SF score was a significant predictor of mortality (Hazard Ratio=0.83; 95% CI 0.75–0.91; p<0.001), even after adjustment for potential confounders. Four individual items: weight loss, decrease in food intake, recent stress and BMI were independent predictors of mortality. **Conclusion** The MNA-SF appears to be an accurate predictor of one-year mortality in nursing home residents. Thus, this tool may be regarded not only as a nutritional screening tool, but also as an instrument for identifying the most-at-risk individuals in this population

    Seismic constraints from a Mars impact experiment using InSight and Perseverance

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    NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed1,2 and uncrewed3,4 spacecraft, and on the Moon during the Apollo era5, but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance’s entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance–amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy)

    Seismic constraints from a Mars impact experiment using InSight and Perseverance

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    NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed1,2 and uncrewed3,4 spacecraft, and on the Moon during the Apollo era5, but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance’s entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance–amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy)

    Contribution of Maternal Antiretroviral Therapy and Breastfeeding to 24-Month Survival in Human Immunodeficiency Virus-Exposed Uninfected Children: An Individual Pooled Analysis of African and Asian Studies

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    Background: Increasing numbers of HIV-infected pregnant women receive antiretroviral therapy (ART) to prevent mother-to-child transmission (PMTCT). Studies suggested that HIV-exposed uninfected (HEU) children face higher mortality than HIV-unexposed children, but evidence mostly relates to the pre-ART era, breastfeeding of limited duration and considerable maternal mortality. Maternal ART and prolonged breastfeeding under cover of ART may improve survival, although this has not been reliably quantified. Methods: Individual data on 19,219 HEU children from 21 PMTCT trials/cohorts undertaken 1995-2015 in Africa and Asia were pooled and the association between 24-month mortality and maternal/infant factors quantified using random-effects Cox proportional hazards models accounting for between-study heterogeneity. Adjusted attributable fractions of risks computed using the predict function in the R package "frailtypack" estimate the relative contribution of risk factors to overall mortality in HEU children. Results: Cumulative incidence of death was 5.5% (95%CI: 5.1-5.9) by age 24 months. Low birth weight (LBW&lt;2500g, adjusted Hazard Ratio (aHR: 2.9), no breastfeeding (aHR: 2.5) and maternal death (aHR: 11.1) were significantly associated with increased mortality. Maternal ART (aHR: 0.5) was significantly associated with lower mortality. At population level, LBW accounted for 16.2% of child deaths by 24 months, never breastfeeding for 10.8%, mother not receiving ART for 45.6%, and maternal death for 4.3%; these factors combined explained 63.6% of deaths by age 24 months. Conclusion: Survival of HEU children could be substantially improved if public health strategies provided all mothers living with HIV with ART and supported optimal infant feeding and care for LBW neonates
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