Semiclassical interferences and catastrophes in the ionization of Rydberg atoms by half-cycle pulses

A multi-dimensional semiclassical description of excitation of a Rydberg electron by half-cycle pulses is developed and applied to the study of energy- and angle-resolved ionization spectra. Characteristic novel phenomena observable in these spectra such as interference oscillations and semiclassical glory and rainbow scattering are discussed and related to the underlying classical dynamics of the Rydberg electron. Modifications to the predictions of the impulse approximation are examined that arise due to finite pulse durations

Chaste: an open source C++ library for computational physiology and biology

Chaste - Cancer, Heart And Soft Tissue Environment - is an open source C++ library for the computational simulation of mathematical models developed for physiology and biology. Code development has been driven by two initial applications: cardiac electrophysiology and cancer development. A large number of cardiac electrophysiology studies have been enabled and performed, including high performance computational investigations of defibrillation on realistic human cardiac geometries. New models for the initiation and growth of tumours have been developed. In particular, cell-based simulations have provided novel insight into the role of stem cells in the colorectal crypt. Chaste is constantly evolving and is now being applied to a far wider range of problems. The code provides modules for handling common scientific computing components, such as meshes and solvers for ordinary and partial differential equations (ODEs/PDEs). Re-use of these components avoids the need for researchers to "re-invent the wheel" with each new project, accelerating the rate of progress in new applications. Chaste is developed using industrially-derived techniques, in particular test-driven development, to ensure code quality, re-use and reliability. In this article we provide examples that illustrate the types of problems Chaste can be used to solve, which can be run on a desktop computer. We highlight some scientific studies that have used or are using Chaste, and the insights they have provided. The source code, both for specific releases and the development version, is available to download under an open source Berkeley Software Distribution (BSD) licence at http://www.cs.ox.ac.uk/chaste, together with details of a mailing list and links to documentation and tutorials

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

MQDT operatorial formalism analysis of molecular Rydberg states in weak electric fields : application to Na2_2

We present the Multichannel Quantum Defect Theory in its operatorial form and its application to the problem of Rydberg states of a diatomic molecule in external electric fields. The theoretical analysis consists in the description of the close connection between the resolvent operator and the Density-Of-State matrix which defines the whole spectrum. In the particular case of the discrete spectrum in weak electric fields, bound states are deduced from the poles of this matrix. We give an example of the use of this theory in the case of Na$_2$ but it could be applied to any other non hydrogenic system as well. Calculated spectra of Rydberg states of Na$_2$ in weak fields are compared to experimental data. The presence of extra-lines and the emergence of hydrogenic multiplets is emphasized. We also show the influence of the penetrating $n{\rm f}\Lambda$ series on the shape of the multiplets and estimate orders of magnitude for their quantum defects.Nous présentons la théorie du défaut quantique à plusieurs voies dans son formalisme opératoriel ainsi que son application au problème des états de Rydberg d'une molécule diatomique en champ électrique. L'analyse théorique consiste principalement à décrire le rapport étroit qui existe entre l'opérateur résolvante et la matrice densité d'états qui définit entièrement les propriétés du spectre. Dans le cas particulier du spectre discret en champ électrique faible, les propriétés des états liés sont déduites des pôles de cette matrice. Nous donnons un exemple de l'utilisation de cette théorie dans le cas de Na$_2$ mais elle pourrait être appliquée aussi bien à tout autre système non hydrogénoïde. Des spectres calculés d'états de Rydberg de Na$_2$ en champs faibles sont comparés aux données expérimentales. La présence d'extra-raies et l'apparition des multiplets hydrogénoïdes sont discutées. Nous démontrons l'influence des séries $n{\rm f}\Lambda$ pénétrantes sur la forme des multiplets et en déduisons l'ordre de grandeur de leurs défauts quantiques

Multichannel quantum defect theory analysis of the Rydberg spectrum of Na2

The ns and nd Na2 Rydberg states have been excited by Optical-Optical Double Resonance for 15 < n < 80 and 4 < J < 45. The observed spectra are analysed in terms of the Multi-Channel Quantum Defect Theory. The intensities and the energies of all the measured lines are theoretically calculated using as parameters the quantum defects of the various series and the molecular constants of the Na2+ ion. The agreement between experimental and theoretical lines is remarkable and the main effects observed in the spectra are interpreted by a simple physical picture (stroboscopic effect). The possibility of s-d mixing is also investigated and we show that it can be neglected within the accuracy of our measurement.Les séries de Rydberg ns et nd de la molécule Na2 ont été excitées par double résonance optique pour 15 < n < 80 et 4 < J < 45. Les spectres observés sont analysés par la théorie du défaut quantique à plusieurs voies. Les énergies et les intensités de toutes les raies mesurées expérimentalement sont calculées théoriquement en utilisant comme paramètres les défauts quantiques des différentes raies et les constantes moléculaires de l'ion. L'accord entre les raies théoriques et expérimentales est remarquable et les principaux effets observés dans les spectres sont interprétés par une image physique simple (effet stroboscopique). L'éventualité d'un mélange s-d est également envisagée et on montre qu'il est négligeable à la précision de nos mesures. Finalement des quasi-profils de Fano sont observés pour les très grandes valeurs de J

Microscopie de photoïonisation

Nous présentons les premiers résultats expérimentaux obtenus en microscopie de photolonisation. Les électrons issus d'un processus d'ionisation du xénon au seuil en champ électrique sont détectés par imagerie. Les interférences entre les différentes trajectoires conduisant l'électron de la source jusqu'au point d'impact sur le détecteur sont observées grâce à l'amélioration de notre spectromètre qui inclut une lentille électrostatique de grandissement. L'interférogramme observé représente la composante transverse de la fonction d'onde électronique. La structure d'interférences évolue régulièrement avec l'énergie ce qui indique que la contribution dominante est celle du continuum, les résonances Stark contribuant seulement à une modulation de cette structure