Bistable nonlinear damper based on a buckled beam configuration

International audienceThis article addresses a particular realization of a compact bistable nonlinear absorber based on the concept of Nonlinear Energy Sink. The article presents both a detailed description of the absorber mechanics and an illustration of the targeted energy transfer between the absorber and a linear system. The experimental results are accompanied with the numerical simulations. Beside practical improvements linked to the features of absorber design, the obtained results stay in line with those found for simpler realizations of a bistable Nonlinear Energy Sinks

The HPS electromagnetic calorimeter

The Heavy Photon Search experiment (HPS) is searching for a new gauge boson, the so-called “heavy photon.” Through its kinetic mixing with the Standard Model photon, this particle could decay into an electron-positron pair. It would then be detectable as a narrow peak in the invariant mass spectrum of such pairs, or, depending on its lifetime, by a decay downstream of the production target. The HPS experiment is installed in Hall-B of Jefferson Lab. This article presents the design and performance of one of the two detectors of the experiment, the electromagnetic calorimeter, during the runs performed in 2015–2016. The calorimeter's main purpose is to provide a fast trigger and reduce the copious background from electromagnetic processes through matching with a tracking detector. The detector is a homogeneous calorimeter, made of 442 lead-tungstate (PbWO4) scintillating crystals, each read out by an avalanche photodiode coupled to a custom trans-impedance amplifier

Translationally invariant calculations of form factors, nucleon densities and momentum distributions for finite nuclei with short-range correlations included

Relying upon our previous treatment of the density matrices for nuclei (in general, nonrelativistic self-bound finite systems) we are studying a combined effect of center-of-mass motion and short-range nucleon-nucleon correlations on the nucleon density and momentum distributions in light nuclei ($^{4}He$ and $^{16}O$). Their intrinsic ground-state wave functions are constructed in the so-called fixed center-of-mass approximation, starting with mean-field Slater determinants modified by some correlator (e.g., after Jastrow or Villars). We develop the formalism based upon the Cartesian or boson representation, in which the coordinate and momentum operators are linear combinations of the creation and annihilation operators for oscillatory quanta in the three different space directions, and get the own "Tassie-Barker" factors for each distribution and point out other model-independent results. After this separation of the center-of-mass motion effects we propose additional analytic means in order to simplify the subsequent calculations (e.g., within the Jastrow approach or the unitary correlation operator method). The charge form factors, densities and momentum distributions of $^{4}He$ and $^{16}O$ evaluated by using the well known cluster expansions are compared with data, our exact (numerical) results and microscopic calculations.Comment: 19 pages, 6 figure

Le pompage énergétique par absorbeur non-linéaire bi-stable

National audienceL’absorbeur dynamique non-linéaire offre une meilleure robustesse en fréquence par rapport aux dispositifs existants actuellement. Ce système à raideur non-linéaire ne possède pas de fréquence propre et peut osciller librement à n’importe quelle fréquence. Une fois accroché sur un système vibrant, on peut obtenir (sous certaines conditions) des régimes de fonctionnement très particuliers où les échanges d’énergie se font dans un seul sens : du système vibrant vers l‘étouffeur non linéaire. On parle alors de « pompage d’énergie ».Les études menées au LMA depuis une demi-douzaine d’années sur le pompage énergétique en Acoustique ont amené au développement d’une nouvelle méthode de réduction du niveau sonore en utilisant une membrane viscoélastique faiblement tendue.Plus récemment, nous avons cherché à étendre ce principe au domaine de le Vibroacoustique. Nous développons un nouveau type d’absorbeur dynamique non linéaire basé sur des lames minces bistables légères. Les résultats, tant expérimentaux que numériques, montrent qu’une réduction de plus de 10 dB du niveau vibratoire de poutres et de plaques peut être obtenue sur une large gamme de configurations