Puissance (physique) | EPFL Graph Search

En physique, la puissance est la quantité d'énergie par unité de temps fournie par un système à un autre. C'est donc une grandeur scalaire. La puissance correspond à un débit d'énergie : si deux systèmes de puissances différentes fournissent le même travail, le plus puissant des deux est celui qui le fournit le plus rapidement. Définition D'une façon générale, l'intégrale de la puissance P fournie pendant une durée τ représente l'énergie totale fournie : :W = \int_{0}^{\tau} \mathcal{P}(t) , \mathrm{d}t. Lorsque la puissance P est constante, la capacité d'un système à fournir un travail W au cours d'une durée Δt s'exprime alors par le rapport : :\mathcal{P}=\frac{W}{\Delta t}. Dans le système international d'unités, une puissance s'exprime en watts, qui correspondent à des joules par seconde, ou de façon équivalente à des . Ainsi, = = . Une unité ancienne était le cheval-vapeur, par lequel la capacité de traction d'une machine à vapeur étai

The Agora High-Resolution Galaxy Simulations Comparison Project. Ii. Isolated Disk Test

Hongyu Li, Alessandro Lupi, Yves Revaz

Using an isolated Milky Way-mass galaxy simulation, we compare results from nine state-of-the-art gravitohydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e. g., radiative cooling and UV background by the standardized package GRACKLE) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, we find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt-Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly formed stellar clump mass functions show more significant variation (difference by up to a factor of similar to 3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low-density region, and between more diffusive and less diffusive schemes in the high-density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes.

Iop Publishing Ltd2016

Design of the third-generation lead-based neutron spallation target for the neutron time-of-flight facility at CERN

Nicola Colonna, Raffaele Esposito, Roland Logé

The neutron time-of-flight (n_TOF) facility at the European Laboratory for Particle Physics (CERN) is a pulsed white-spectrum neutron spallation source producing neutrons for two experimental areas: the Experimental Area 1 (EAR1), located 185 m horizontally from the target, and the Experimental Area 2 (EAR2), located 20 m above the target. The target, based on pure lead, is impacted by a high-intensity 20-GeV/c pulsed proton beam. The facility was conceived to study neutron-nucleus interactions for neutron kinetic energies between a few meV to several GeV, with applications of interest for nuclear astrophysics, nuclear technology, and medical research. After the second-generation target reached the end of its lifetime, the facility underwent a major upgrade during CERN's Long Shutdown 2 (LS2, 2019-2021), which included the installation of the new third-generation neutron target. The first- and second-generation targets were based on water-cooled massive lead blocks and were designed focusing on EAR1, since EAR2 was built later. The new target is cooled by nitrogen gas to avoid erosion-corrosion and contamination of cooling water with radioactive lead spallation products. Moreover, the new design is optimized also for the vertical flight path and EAR2. This paper presents an overview of the target design focused on both physics and thermomechanical performance, and includes a description of the nitrogen cooling circuit and radiation protection studies.

AMER PHYSICAL SOC2021

The Agora High-Resolution Galaxy Simulations Comparison Project. Ii. Isolated Disk Test

Hongyu Li, Alessandro Lupi, Yves Revaz

Iop Publishing Ltd2016