Constraints on light dark matter from core-collapse supernovae

We show that light (approximately or = 1-30 MeV) dark matter particles can play a significant role in core-collapse supernovae, if they have relatively large annihilation and scattering cross sections, as compared to neutrinos. We find that if such particles are lighter than approximately or = 10 MeV and reproduce the observed dark matter relic density, supernovae would cool on a much longer time scale and would emit neutrinos with significantly smaller energies than in the standard scenario, in disagreement with observations. This constraint may be avoided, however, in certain situations for which the neutrino-dark-matter scattering cross sections remain comparatively small.     

Dynamic compressibility and aging in Wigner crystals and quantum glasses

We study the nonequilibrium linear response of quantum elastic systems pinned by quenched disorder with Schwinger-Keldysh real-time techniques complemented by a mean-field variational approach. We find (i) a quasiequilibrium regime in which the analytic continuation from the imaginary-time replica results holds provided the marginality condition is enforced, and (ii) an aging regime. The conductivity and compressibility are computed. The latter is found to cross over from its dynamic to static value on a scale set by the waiting time after a quench, an effect which can be probed in experiments in, e.g., Wigner glasses.     

Malmquist indexes with quasi-fixed inputs: an application to school districts in Québec

We present a space and time allocation problem that arises in assembly halls producing large building blocks (namely, a shipyard which assembles prefabricated keel elements). The building blocks are very large, and, once a block is placed in the hall, it cannot be moved until all assembly operations on this block are complete. Each block must be processed during a predetermined time window. The objective is to maximize the number of building blocks produced in the hall.     

Reversible and Non Reversible Oxidation of Polyacetylene In Aqueous and Non Aqueous Media : An Electrochemical Study

Cyclic voltammetry has been applied to study the reversibility of the oxidation of polyacetylene in sulfuric acid solutions and in lithium salts - nitromethane solutions. The intensity-potential curves indicate generally two steps of oxidation : the first one, corresponding to the doping, is reversible and is characterized by a dramatic increase of the electrical conductivity; the second one, called overoxidation, is due to the irreversible destruction of the carbon-carbon double bonds by formation of sp3 carbon atoms and is evidenced by the lowering of the conductivity.     

A short walk through quantum optomechanics

This paper gives a brief review of the basic physics of quantum optomechanics and provides an overview of some of its recent developments and current areas of focus. It first outlines the basic theory of cavity optomechanical cooling and gives a brief status report of the experimental state‐of‐the‐art. It then turns to the deep quantum regime of operation of optomechanical oscillators and covers selected aspects of quantum state preparation, control and characterization, including mechanical squeezing and pulsed optomechanics. This is followed by a discussion of the “bottom‐up” approach that exploits ultracold atomic samples instead of nanoscale systems. It concludes with an outlook that concentrates largely on the functionalization of quantum optomechanical systems and their promise in metrology applications.     

Classroom note: Using Platonic bodies to generate a random sample from a population having two characteristics linked with a predetermined coefficient of correlation

This note describes a simple method of generating a random sample of N pairs (U _i ,?W _i ) from a population whose elements have two characteristics U  and W associated with a known coefficient of correlation. Although the method described is extremely advantageous when Platonic bodies are used, it can be generalized to include any discrete uniform distribution.