Balance (instrument)

Résumé

Une balance, du latin bis (deux fois) et lanx (plateau), est un instrument de mesure qui sert à évaluer des masses par comparaison avec des « poids », dans le langage courant, ou « masses marquées » dont les masses sont connues. Les balances existent depuis l'Antiquité. La balance nécessitant l'utilisation de poids, elle obligea à réglementer le pesage avec le plus grand soin. Les balances ne sont devenues de véritables instruments de précision qu'au . Au , l'invention de Roberval révolutionne le pesage avec l'idée de poser les plateaux au-dessus du fléau (pièce oblongue pivotant autour d'un axe horizontal) et non plus en dessous. Au , les observations et les gains de sensibilité dus à Lavoisier sont propices à un usage performant dans les laboratoires. La balance Roberval est perfectionnée par Béranger qui réduit les forces latérales et les frottements en remplaçant les tiges de force par de petits fléaux secondaires. Au , les balances « Roberval » et « Béranger » sont sur tous les

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, ,

Using a set of cosmological hydro-dynamical simulations, we constrained the properties of primordial magnetic fields by studying their impact on the formation and evolution of dwarf galaxies. We performed a large set of simulations (8 dark matter only and 72 chemo-hydrodynamical) including primordial magnetic fields through the extra density fluctuations they induce at small length scales (k >= 10 h Mpc(-1)) in the matter power spectrum. Our sample of dwarfs includes nine systems selected out of the initial (3.4 Mpc h(-1))(3) parent box, resimulated from z=200 to z=0 using a zoom-in technique and including the physics of baryons. We explored a wide variety of primordial magnetic fields with strength B-lambda ranging from 0.05 to 0.50 nG and magnetic energy spectrum slopes n(B) from -2.9 to -2.1. Strong magnetic fields characterized by a high amplitude (B-lambda=0.50, 0.20 nG with n(B)=-2.9) or by a steep initial power spectrum slope (n(B)=-2.1, -2.4, with B-lambda=0.05 nG) induce perturbations on mass scales from 10(7) to 10(9) M-circle dot. In this context emerging galaxies see their star formation rates strongly boosted. They become more luminous and metal rich than their counterparts without primordial magnetic fields. Such strong fields are ruled out by their inability to reproduce the observed scaling relations of dwarf galaxies. They predict that dwarf galaxies are at the origin of an unrealistically early reionization of the Universe and that they also overproduce luminous satellites in the Local Group. Weaker magnetic fields impacting the primordial density field at corresponding masses less than or similar to 10(6) M-circle dot, produce a large number of mini dark matter halos orbiting the dwarfs, however out of reach for current lensing observations. This study allows us, for the first time, to constrain the properties of primordial magnetic fields based on realistic cosmological simulations of dwarf galaxies.

EDP SCIENCES S A2020

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Scale invariance, unimodular gravity and dark energy

Daniel Zenhäusern

We demonstrate that the combination of the ideas of unimodular gravity, scale invariance, and the existence of an exactly massless dilaton leads to the evolution of the universe supported by present observations: inflation in the past, followed by the radiation and matter dominated stages and accelerated expansion at present. All mass scales in this type of theories come from one and the same source. © 2008 Elsevier B.V. All rights reserved.

2009

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Nanowatt Acoustic Inference Sensing Exploiting Nonlinear Analog Feature Extraction

Christian Enz, Minhao Yang, Jun Zhang

Ultralow-power sensing with inference functionality embedded in sensor nodes is essential for enabling the emerging pervasive intelligence. For acoustic inference sensing, the feature extraction can take advantage of power-efficient analog circuits. However, the existing solutions have been mostly constrained to linear analog signal processing, which largely limits the achievable power efficiency. In this article, we show that tasks like voice activity detection and keyword spotting can well accommodate analog feature extractor's high nonlinearity, which arises from electronic device physics and circuit design constraints. Applying this principle to a 65-nm CMOS chip implementation, we demonstrate high classification accuracy with nonlinear analog feature extraction consuming only 50 nW. At the end of digital scaling, this study may shed light on the possibility of exploiting the largely relaxed degree of freedom, i.e., linearity, in analog circuit design in the pursuit of extreme power efficiency for designing future inference sensing systems.

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC2021

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