Coherent Control of Isotope Separation in HD+ Photodissociation by Strong Fields

The photodissociation of the HD+ molecular ion in intense short- pulsed linearly polarized laser fields is studied using a time- dependent wave-packet approach where molecular rotation is fully included. We show that applying a coherent superposition of the fundamental radiation with its second harmonic can lead to asymmetries in the fragment angular distributions, with significant differences between the hydrogen and deuterium distributions in the long wavelength domain where the permanent dipole is most efficient. This effect is used to induce an appreciable isotope separation.Comment: Physical Review Letters, 1995 (in press). 4 pages in revtex format, 3 uuencoded figures. Full postcript version available at: http://chemphys.weizmann.ac.il/~charron/prl.ps or ftp://scipion.ppm.u-psud.fr/coherent.control/prl.p

Shared Memory Pipelined Parareal

For the parallel-in-time integration method Parareal, pipelining can be used to hide some of the cost of the serial correction step and improve its efficiency. The paper introduces an OpenMP implementation of pipelined Parareal and compares it to a standard MPI-based variant. Both versions yield almost identical runtimes, but, depending on the compiler, the OpenMP variant consumes about 7% less energy and has a significantly smaller memory footprint. However, its higher implementation complexity might make it difficult to use in legacy codes and in combination with spatial parallelisation

A quantitative theory-versus-experiment comparison for the intense laser dissociation of H2+

A detailed theory-versus-experiment comparison is worked out for H$_2^+$ intense laser dissociation, based on angularly resolved photodissociation spectra recently recorded in H.Figger's group. As opposite to other experimental setups, it is an electric discharge (and not an optical excitation) that prepares the molecular ion, with the advantage for the theoretical approach, to neglect without lost of accuracy, the otherwise important ionization-dissociation competition. Abel transformation relates the dissociation probability starting from a single ro-vibrational state, to the probability of observing a hydrogen atom at a given pixel of the detector plate. Some statistics on initial ro-vibrational distributions, together with a spatial averaging over laser focus area, lead to photofragments kinetic spectra, with well separated peaks attributed to single vibrational levels. An excellent theory-versus-experiment agreement is reached not only for the kinetic spectra, but also for the angular distributions of fragments originating from two different vibrational levels resulting into more or less alignment. Some characteristic features can be interpreted in terms of basic mechanisms such as bond softening or vibrational trapping.Comment: submitted to PRA on 21.05.200

The listening talker: A review of human and algorithmic context-induced modifications of speech

International audienceSpeech output technology is finding widespread application, including in scenarios where intelligibility might be compromised - at least for some listeners - by adverse conditions. Unlike most current algorithms, talkers continually adapt their speech patterns as a response to the immediate context of spoken communication, where the type of interlocutor and the environment are the dominant situational factors influencing speech production. Observations of talker behaviour can motivate the design of more robust speech output algorithms. Starting with a listener-oriented categorisation of possible goals for speech modification, this review article summarises the extensive set of behavioural findings related to human speech modification, identifies which factors appear to be beneficial, and goes on to examine previous computational attempts to improve intelligibility in noise. The review concludes by tabulating 46 speech modifications, many of which have yet to be perceptually or algorithmically evaluated. Consequently, the review provides a roadmap for future work in improving the robustness of speech output

Semiclassical ionization dynamics of the hydrogen molecular ion in an electric field of arbitrary orientation

Quasi-static models of barrier suppression have played a major role in our understanding of the ionization of atoms and molecules in strong laser fields. Despite their success, in the case of diatomic molecules these studies have so far been restricted to fields aligned with the molecular axis. In this paper we investigate the locations and heights of the potential barriers in the hydrogen molecular ion in an electric field of arbitrary orientation. We find that the barriers undergo bifurcations as the external field strength and direction are varied. This phenomenon represents an unexpected level of intricacy even on this most elementary level of the dynamics. We describe the dynamics of tunnelling ionization through the barriers semiclassically and use our results to shed new light on the success of a recent theory of molecular tunnelling ionization as well as earlier theories that restrict the electric field to be aligned with the molecular axis

El arte del ruido / el futuro del sonido

Un tópico muy difundido (sobre todo entre aquéllos que invirtieron la vida dominando un instrumento) considera que la música sólo existe como pretexto para que el instrumentista manifieste su virtuosismo. Este sofisma amplifica su error cuando se confunde la maestría de un intérprete con su velocidad (lo cual implicaría reducir el oficio del Arte a mero récord Guiness). Si se aplicara la definición de cierto novelista irlandés que considera al arte como «la disposición voluntaria de la materia sensible con un fin estético»,1 se deduciría que ni las notas musicales, ni los dedos del violinista, ni las cuerdas vocales del cantante, constituyen la «materia sensible» de la música, la cual está conformada, en unsentido más amplio, por todas las posibilidades del sonido (entendido como una sumatoria de la frecuencia, la intensidad, la duración y el timbre) cuando se somete a una estructura temporal (rítmica, melódica y armónica) elegida por el artista para producir un resultado estético, e inducir en el escucha una determinada emoción, una cierta parálisis

Les concessions à charge de remblais en Polynésie française ou les politiques face à la privatisation

Les concessions dites « à charge de remblais » autorisées par les pouvoirs publics permettent aux collectivités et aux particuliers d’utiliser l’espace maritime littoral en le remblayant. Les réglementations d’attribution de ces concessions sont traitées depuis les premiers textes et il n’y a plus actuellement que des dérogations. Les remblais sauvages et donc illicite au regard de la loi peuvent néanmoins être régularisés. Malgré des progrès en vue de mieux gérer ce problème de la privatisation du littoral, il est clair que les faits démontrent l’absence de volonté politique pour faire respecter l’inaliénabilité du domaine maritime. Les concessions bien que temporaires sont en fait définitives et le droit de passage de trois mètres de largeur sur la plage n’est jamais exigé. Les conséquences de ces remblais sont traitées dans le texte. Entre électoralisme et intérêt public, le pouvoir politique n’a pas encore eu le courage de faire appliquer la loi.Concessions, called ‘backfill load’, that are authorized by the authorities allow communities and individuals to use backfilled maritime areas for the public interest, or for the interests of riparian owners of the lagoon in order to enlarge their land. These concessions are issued according to regulations that have evolved in recent decades. There are currently no more concessions permitted except under special exemptions. Wild embankments that are therefore illegal in view of the law may nevertheless be regularized. Despite progress towards better management of the coastal privatization problem, there is clear evidence demonstrating a lack of political will to respect the inalienability of the maritime domain. The temporary concessions that are effectively final have never ensured the right of passage - three meters large - to the beach. Between electioneering schedules and public interest, political powers have lacked the courage to enforce these laws in spite of consequences of these embankments

Numerical simulation of skin transport using Parareal

In silico investigation of skin permeation is an important but also computationally demanding problem. To resolve all scales involved in full detail will not only require exascale computing capacities but also suitable parallel algorithms. This article investigates the applicability of the time-parallel Parareal algorithm to a brick and mortar setup, a precursory problem to skin permeation. The C++ library Lib4PrM implementing Parareal is combined with the UG4 simulation framework, which provides the spatial discretization and parallelization. The combination’s performance is studied with respect to convergence and speedup. It is confirmed that anisotropies in the domain and jumps in diffusion coefficients only have a minor impact on Parareal’s convergence. The influence of load imbalances in time due to differences in number of iterations required by the spatial solver as well as spatio-temporal weak scaling is discussed

Asynchronous decentralized accelerated stochastic gradient descent

In this work, we introduce an asynchronous decentralized accelerated stochastic gradient descent type of method for decentralized stochastic optimization, considering communication and synchronization are the major bottlenecks. We establish $\mathcal{O}(1/\epsilon)$ (resp., $\mathcal{O}(1/\sqrt{\epsilon})$) communication complexity and $\mathcal{O}(1/\epsilon^2)$ (resp., $\mathcal{O}(1/\epsilon)$) sampling complexity for solving general convex (resp., strongly convex) problems

Covalent enzyme coupling on cellulose acetate membranes for glucose sensor development

International audienceMethods for immobilizing glucose oxidase (GOx) on cellulose acetate (CA) membranes are compared. The optimal method involves covalent coupling of bovine serum albumin (BSA) to CA membrane and a subsequent reaction of the membrane with GOx, which has previously been activated with an excess of p-benzoquinone. This coupling procedure is fairly reproducible and allows the preparation of thin membranes (5-20 µm) showing high surface activities (1-3 U/cm2) which are stable over a period of 1-3 months. Electrochemical and radiolabeling experiments show that enzyme inactivation as a result of immobilization is negligible. A good correlation between surface activity of membranes and their GOx load is observed