Improved tests of extra-dimensional physics and thermal quantum field theory from new Casimir force measurements

We report new constraints on extra-dimensional models and other physics beyond the Standard Model based on measurements of the Casimir force between two dissimilar metals for separations in the range 0.2--1.2 $\mu$m. The Casimir force between an Au-coated sphere and a Cu-coated plate of a microelectromechanical torsional oscillator was measured statically with an absolute error of 0.3 pN. In addition, the Casimir pressure between two parallel plates was determined dynamically with an absolute error of $\approx 0.6$ mPa. Within the limits of experimental and theoretical errors, the results are in agreement with a theory that takes into account the finite conductivity and roughness of the two metals. The level of agreement between experiment and theory was then used to set limits on the predictions of extra-dimensional physics and thermal quantum field theory. It is shown that two theoretical approaches to the thermal Casimir force which predict effects linear in temperture are ruled out by these experiments. Finally, constraints on Yukawa corrections to Newton's law of gravity are strengthened by more than an order of magnitude in the range 56 nm to 330 nm.Comment: Revtex 4, 35 pages, 14 figures in .gif format, accepted for publication in Phys. Rev.

Measuring efficiency and productivity in professional football teams: Evidence from the English Premier League

Professional football clubs are unusual businesses, their performance judged on and off the field of play. This study is concerned with measuring the efficiency of clubs in the English Premier League. Information from clubs’ financial statements is used as a measure of corporate performance. To measure changes in efficiency and productivity the Malmquist non-parametric technique has been used. This is derived from the Data Envelopment Analysis (DEA) linear programming approach, with Canonical Correlation Analysis (CCA) being used to ensure the cohesion of the input-output variables. The study concludes that while clubs operate close to efficient levels for the assessed models, there is limited technological advance in their performance in terms of the displacement of the technological frontier

CO2 evaporation in microchannels: numerical simulations and microfabrication of cooling chips

International audienc

Evaporation of CO2 in microchannels : CFD simulations with Fluent and microfabrication process

International audienceThanks to its good thermo-physical properties, in particular its high latent heat, CO2 is considered as a good choice for two-phase cooling devices [1]. The next generation of tracking detectors at LHC (CERN) will be cooled at temperatures between 10°C and -40°C, by evaporating the liquid CO2 flow circulating in titanium mini-channels attached to the pixel silicon sensors of 4 cm². For the next eneration of pixel detectors installed on the Future Circular Collider ( 2045) , a new option, studied by the LEGI-LAPP team (Laboratoire d'Ecoulements Géophysiques et Industriels & Laboratoire d'Annecy de Physique des Particules) is to circulate the CO2 within micro-channels integrated in the silicon covering the whole surface of the sensors. Within the current decade, their thermal performances will have to be evaluated to validate this option. For this deadline, the numerical simulation of two-phase flows should help us to predict the cooling performances of CO2 in microchannels over a wide range of operating conditions (saturation temperature, cooling power, hydraulic diameter and materials of the channels, mass flow rates, etc. . . ). Until now, 2D simulations have been carried out on ANSYS Fluent 2020 for an isolated static bubble, with the Volume Of Fluid (VOF) method. This work has two main objectives which are discussed here: 1/ control and reduce the spurious currents induced by the low viscosity of CO2 caused by the modeling of the surface tension force, 2/ set up a boiling model able to guess the correct bubble’s growth rate for a given temperature field in the frame of VOF and VOF/Level Set approaches. With this work, we intend to simulate a CO2 two-phase flow in a microchannel. In parallel, the fabrication in a clean room of silicon microchannels, sealed with pyrex, has begun. The primary objective is to measure the pressure resistance of prototypes of different dimensions, and to compare the results with the measurements done at CERN in 2020 [2]. Several challenges have to be overcome, in particular regarding the robustness of the connectors. The ultimate goal is to manufacture prototypes of single and multi-microchannels, in order to measure the dynamic and thermal behavior of CO2 convective boiling on a test bench in the LAPP laboratory (Annecy, France), and to compare experimental results with the numerical simulations

Evaporation of CO2 in microchannels : CFD simulations with Fluent and microfabrication process

International audienceThanks to its good thermo-physical properties, in particular its high latent heat, CO2 is considered as a good choice for two-phase cooling devices [1]. The next generation of tracking detectors at LHC (CERN) will be cooled at temperatures between 10°C and -40°C, by evaporating the liquid CO2 flow circulating in titanium mini-channels attached to the pixel silicon sensors of 4 cm². For the next eneration of pixel detectors installed on the Future Circular Collider ( 2045) , a new option, studied by the LEGI-LAPP team (Laboratoire d'Ecoulements Géophysiques et Industriels & Laboratoire d'Annecy de Physique des Particules) is to circulate the CO2 within micro-channels integrated in the silicon covering the whole surface of the sensors. Within the current decade, their thermal performances will have to be evaluated to validate this option. For this deadline, the numerical simulation of two-phase flows should help us to predict the cooling performances of CO2 in microchannels over a wide range of operating conditions (saturation temperature, cooling power, hydraulic diameter and materials of the channels, mass flow rates, etc. . . ). Until now, 2D simulations have been carried out on ANSYS Fluent 2020 for an isolated static bubble, with the Volume Of Fluid (VOF) method. This work has two main objectives which are discussed here: 1/ control and reduce the spurious currents induced by the low viscosity of CO2 caused by the modeling of the surface tension force, 2/ set up a boiling model able to guess the correct bubble’s growth rate for a given temperature field in the frame of VOF and VOF/Level Set approaches. With this work, we intend to simulate a CO2 two-phase flow in a microchannel. In parallel, the fabrication in a clean room of silicon microchannels, sealed with pyrex, has begun. The primary objective is to measure the pressure resistance of prototypes of different dimensions, and to compare the results with the measurements done at CERN in 2020 [2]. Several challenges have to be overcome, in particular regarding the robustness of the connectors. The ultimate goal is to manufacture prototypes of single and multi-microchannels, in order to measure the dynamic and thermal behavior of CO2 convective boiling on a test bench in the LAPP laboratory (Annecy, France), and to compare experimental results with the numerical simulations

CO2 evaporation in microchannels: numerical simulations and microfabrication of cooling chips

International audienc