Hysteresis and ribbons in Taylor-Couette flow of a semidilute non-colloidal suspension

In this study, we numerically investigate hysteretic behaviors of secondary bifurcations in the Taylor-Couette flow of a semidilute, neutrally buoyant, and noncolloidal suspension. We consider a suspension with a bulk particle volume fraction of 0.1, a radius ratio of 0.877, and a particle size of 60. The suspension balance model (SBM) is introduced for numerical simulations to model the dynamics of particles undergoing shear-induced particle migration with rheological constitutive laws. The suspension flow transitions from circular Couette flow (CCF) via ribbons (RIB), spiral vortex flow (SVF), and wavy spiral vortex flow (WSVF) to wavy vortex flow (WVF) with the increase of suspension Reynolds number. The primary transition arises very slowly with an oscillatory critical mode and appears through a supercritical (or non-hysteretic) bifurcation. However, we find hysteretic behaviors in subsequent bifurcations (spiral vortex flow (SVF) to wavy spiral vortex flow (WSVF) and WSVF to wavy vortex flow (WVF)) during increasing-Re and decreasing-Re procedures with a rapid-step change near the transition boundaries. The WSVF and WVF states are more sustained below the transition boundaries when the Reynolds number is rapidly decreased in stages. However, the SVF and WSVF become WSVF and WVF more sharply with increasing Re, respectively. To conclude this study, we also examine in detail, a standing wave of weak counter-rotating vortices that occurs as the primary instability and analyze the wave that oscillates in time but is stationary in space in the RIB state

Pressure Drop in a Pebble Bed Reactor

Pressure drops over a packed bed of pebble bed reactor type are investigated. Measurement of porosity and pressure drop over the bed were carried out in a cylindrical packed bed facility. Air and water were used for working fluids. There are several parameters of the pressure drop in packed beds. One of the most important factors is wall effect. The inhomogeneous porosity distribution in the bed and the additional wetted surface introduced by the wall cause the variation of pressure drop. The importance of the wall effects and porosity can be explained by using different bed-to-particle diameter ratios. Four different bed-to-particle ratios were used in these experiments (D/dp = 19, 9.5, 6.33 and 3.65). A comparison is made between the predictions by a number of empirical correlations including the Ergun equation (1952) and KTA (by the Nuclear Safety Commission of Germany) (1981) in the literature. Analysis of the data indicated the importance of the bed-to-particle size ratios on the pressure drop. The comparison between the present and the existing correlations showed that the pressure drop of large bed-to-particle diameter ratios (D/dp = 19, 9.5and 6.33) matched very well with the original KTA correlation. However the published correlations cannot be expected to predict accurate pressure drop for certain conditions, especially for pebble bed with D/dp (bed-to-particle diameter ratio) </= 5. An improved correlation was obtained for a small bed-to-particle diameter ratio by fitting the coefficients of that equation to experimental database

ContactGen: Contact-Guided Interactive 3D Human Generation for Partners

Among various interactions between humans, such as eye contact and gestures, physical interactions by contact can act as an essential moment in understanding human behaviors. Inspired by this fact, given a 3D partner human with the desired interaction label, we introduce a new task of 3D human generation in terms of physical contact. Unlike previous works of interacting with static objects or scenes, a given partner human can have diverse poses and different contact regions according to the type of interaction. To handle this challenge, we propose a novel method of generating interactive 3D humans for a given partner human based on a guided diffusion framework. Specifically, we newly present a contact prediction module that adaptively estimates potential contact regions between two input humans according to the interaction label. Using the estimated potential contact regions as complementary guidances, we dynamically enforce ContactGen to generate interactive 3D humans for a given partner human within a guided diffusion model. We demonstrate ContactGen on the CHI3D dataset, where our method generates physically plausible and diverse poses compared to comparison methods.Comment: Accepted by AAAI 202

Convection thermique d'un fluide diélectrique confiné dans un anneau cylindrique en rotation auquel sont appliqué un gradient de température et une tension électrique alternative

Le champ électrique couplé à un gradient de température sur un fluide diélectrique est un outil de génération de la convection thermique, en particulier dans des conditions de microgravité où la poussée d'Archimède devient négligeable [1]. On considère un fluide diélectrique incompressible dans un anneau cylindrique tournant autour de son axe en condition d'apesanteur. Les surfaces cylindriques sont des électrodes maintenues à des températures différentes et auxquelles est appliquée une tension électrique alternative de haute fréquence. Le champ électrique radial agit sur la stratification de permittivité électrique pour donner lieu à la force diélectrophorétique (DEP). Dans ce cas, deux poussées thermiques sont effectives : la poussée liée à l'action de l'accélération centrifuge sur la stratification de masse volumique, et la force DEP qui s'apparente à l'action d'une gravité centripète de nature électrique (gravité électrique) sur la stratification de masse volumique [2]. A l'aide de l'analyse de stabilité linéaire, l'instabilité pilotée par ces deux poussées thermiques protagonistes est caractérisée par le nombre de Rayleigh associé à chacune d'entre elles. Les cellules de convections sont sous formes de vortex contrarotatifs hélicoïdaux pour les faibles taux de rotation, et prennent la forme de colonnes alignées à l'axe de l'anneau lorsque le taux de rotation est suffisamment important [3]. La gravité électrique et l'accélération centrifuge étant de directions opposées, le sens du gradient de température a un fort impact sur les mécanismes de l'instabilité. Une attention particulière est portée sur la nature instationnaire des modes critiques.   [1] B. Futterer, A. Krebs, A.C. Plesa, F. Zaussinger, R. Hollerbach, D. Breuer, C. Egbers, Sheet-like and plume-like thermal flow in a spherical convection experiment performed under microgravity, J. Fluid Mech. 735, 647 (2013). [2] H.N. Yoshikawa, O. Crumeyrolle & I. Mutabazi, Dielectrophoretic force-driven thermal convection in annular geometry, Phys. Fluids 25, 024106 (2013). [3] A. Meyer, M. Jongmans, M. Meier, C. Egbers & I. Mutabazi, Thermal convection in a cylindrical annulus under a combined effect of the radial and vertical gravity, C.R. Mecanique 2016 (http://dx.doi.org/10.1016/j.crme.2016.10.003)

A scalable two-stage Bayesian approach accounting for exposure measurement error in environmental epidemiology

Accounting for exposure measurement errors has been recognized as a crucial problem in environmental epidemiology for over two decades. Bayesian hierarchical models offer a coherent probabilistic framework for evaluating associations between environmental exposures and health effects, which take into account exposure measurement errors introduced by uncertainty in the estimated exposure as well as spatial misalignment between the exposure and health outcome data. While two-stage Bayesian analyses are often regarded as a good alternative to fully Bayesian analyses when joint estimation is not feasible, there has been minimal research on how to properly propagate uncertainty from the first-stage exposure model to the second-stage health model, especially in the case of a large number of participant locations along with spatially correlated exposures. We propose a scalable two-stage Bayesian approach, called a sparse multivariate normal (sparse MVN) prior approach, based on the Vecchia approximation for assessing associations between exposure and health outcomes in environmental epidemiology. We compare its performance with existing approaches through simulation. Our sparse MVN prior approach shows comparable performance with the fully Bayesian approach, which is a gold standard but is impossible to implement in some cases. We investigate the association between source-specific exposures and pollutant (nitrogen dioxide (NO$_2$))-specific exposures and birth outcomes for 2012 in Harris County, Texas, using several approaches, including the newly developed method.Comment: 34 pages, 8 figure

Thermoelectric convection in a planar capacitor: theoretical studies and experiments in parabolic flights

International audienceNous avons étudié la convection thermoélectrique dans un condensateur plan placé dans un environnement de microgravité et dans des conditions terrestres avec une stratification thermique instable ou stable. L’analyse énergétique montre que dans le cas de stratification stable, la convection thermoélectrique est retardée alors que dans le cas de stratification thermique instable, elle est amplifiée par la poussée d’Archimède avant que cette dernière ne prenne le dessus et pilote la convection thermique naturelle. Une expérience réalisée lors des vols paraboliques illustre la formation de la convection thermoélectrique à la fin de la phase de microgravité

Comparison of acute phase reactant levels of Kawasaki disease patients who visited with less than 5 days duration of fever and with 5 days or longer

Purpose Kawasaki disease (KD) is a common, acute systemic vasculitis in children. Acute phase reactants (APRs) have been used to assist diagnosis, and to predict outcome in children with KD. However, it remains unknown on levels of APRs depending on duration of fever. We aimed to compare APR levels of children with KD who visited with < 5 days duration of fever and with ≥ 5 days. Methods Children (≤ 15 years) with complete KD who visited the emergency department were enrolled from March 2012 through February 2018. The children were divided into the early (fever < 5 days) and late (fever ≥ 5 days) presenters. The baseline characteristics, APR levels, such as platelet count, and outcomes were compared between the 2 groups. Results A total of 145 children with complete KD were enrolled. Median age was 27.0 (interquartile range [IQR], 12.0-46.5) months, and boys accounted for 60.0%. The early presenters (63 [43.4%]) had a younger age (17.0 [IQR, 7.0-45.0] vs. 32.5 [IQR, 14.0-48.0] months; P = 0.006), shorter duration of fever (3.0 [IQR, 2.0-4.0] days vs. 6.0 [IQR, 5.0-7.0] days; P < 0.001), and a lower platelet count (336.7 ± 105.2 [× 103/μL] vs. 381.6 ± 121.8 [× 103/μL], P = 0.02) than the late presenters. The other APR levels, and frequency of resistance to intravenous immunoglobulin and coronary artery abnormalities showed no differences between the 2 groups. Conclusion Children with KD who visited with < 5 days duration of fever had a lower platelet count compared to those with ≥ 5 days. No differences were found in the other APR levels and the outcomes. It may be necessary to consider the differences in APR levels depending on duration of fever when treating children with KD

Establishment of peripheral intravenous catheter for pediatric patients in the emergency department: who and how?

Purpose Peripheral intravenous cannulation (PIC) for children is technically difficult. We aimed to investigate factors associated with the primary success of PIC for children in the emergency department (ED). Methods This prospective observational study was conducted on children younger than 3 years who visited the ED from September 2014 to August 2015. The children undergoing primary success, defined as success at the first attempt, comprised the success group. Using a case report form, information about the children (age, sex, and weight), practitioners’ occupation (doctors, nurses, emergency medical technicians [EMTs]), treatment venue, insertion site of PIC, presence of guardians, and use of auxiliary devices were collected and compared between the success and failure groups. Multivariable logistic regression models were constructed to identify factors associated with the primary success. Results Of 439 children, 271 underwent the primary success (61.7%). The success group showed older age, heavier weight, and higher proportion of EMT. No differences were found in treatment venue, insertion site, and presence of the guardian. We found that patients’ age (odds ratio [OR], 1.03; 95% confidence interval [CI], 1.003-1.1), and practitioners’ occupation (EMT; OR, 3.0; 95% CI, 1.9-4.7, compared with doctors) were the factors associated with the primary success. Conclusion Practitioners’ occupation (EMT) and children’s age (older) may be associated with the primary success of PIC. It may be helpful to have specialized personnel when performing PIC on children in the ED

Single atom and defect engineering of CuO for efficient electrochemical reduction of CO 2 to C 2 H 4

Electrochemical CO2 transformation to high‐value ethylene (C2H4) at high currents and efficiencies is desired and yet remains a grand challenge. We show for the first time that coupling single Sb atoms and oxygen vacancies of CuO enable synergistic electrocatalytic reduction of CO2 to C2H4 at low overpotentials. Highly dispersed Sb atoms occupying metal substitutional sites of CuO are synthesized under mild conditions. The overall CO2 reduction faradaic efficiency (FE) reaches 89.3 ± 1.1% with an FE toward C2H4 exceeding 58.4% at a high‐current density of 500 mA/cm2. Addition of the p‐block metal is found to induce transformation of CuO from flakes to nanoribbons rich in nanoholes and oxygen vacancies, greatly enhancing CO2 adsorption and activation while suppressing hydrogen evolution. Further density functional theory calculations with in situ X‐ray diffraction reveal that combining Sb sites and oxygen vacancies prominently lessen the dimerization energy of adsorbed CO intermediate, thus boosting the conversion of CO2 to produce C2H4. This study provides a new perspective for promoting selective C–C coupling for electrochemical CO2 reduction

Therapeutic effect of ascorbic acid on dapsone-induced methemoglobinemia in rats

Objective Dapsone (diaminodiphenyl sulfone, DDS) is currently used to treat leprosy, malaria, dermatitis herpetiformis, and other diseases. It is also used to treat pneumocystis pneumonia and Toxoplasma gondii infection in HIV-positive patients. The most common adverse effect of DDS is methemoglobinemia from oxidative stress. Ascorbic acid is an antioxidant and reducing agent that scavenges the free radicals produced by oxidative stress. The present study aimed to investigate the effect of ascorbic acid in the treatment of DDS induced methemoglobinemia. Methods Male Sprague-Dawley rats were divided into three groups: an ascorbic acid group, a methylene blue (MB) group, and a control group. After DDS (40 mg/kg) treatment via oral gavage, ascorbic acid (15 mg/kg), MB (1 mg/kg), or normal saline were administered via tail vein injection. Depending on the duration of the DDS treatment, blood methemoglobin levels, as well as the nitric oxide levels and catalase activity, were measured at 60, 120, or 180 minutes after DDS administration. Results Methemoglobin concentrations in the ascorbic acid and MB groups were significantly lower compared to those in the control group across multiple time points. The plasma nitric oxide levels and catalase activity were not different among the groups or time points. Conclusion Intravenous ascorbic acid administration is effective in treating DDS-induced methemoglobinemia in a murine model