Tensorial depolarization of alkali atoms by isotropic collisions with neutral hydrogen

Results. We consider the problem of isotropic collisions between an alkali atom and neutral hydrogen. We calculate the collisional tensorial components of general p and s-states, characterized by their effective principal quantum number $n^{*}$. It is found that the behaviour of the tensorial components obey simple power laws allowing quick calculations of the depolarizing collisional rates. As application, our results should allow a rigorous treatment of the atomic polarization profiles of the D1 -D2 lines of alkali atoms. Conclusions. Close coupling treatments of atomic collisions are needed to decipher the information encoded in the polarized radiation from the Sun. Important problems remain unresolved like the role of collisions in the Paschen-Back conditions.Comment: Accepted for publication in A&

Peptide Bonds in the Interstellar Medium: Facile Autocatalytic Formation from Nitriles on Water-Ice Grains

A recent suggestion that acetamide, \ce{CH3C(O)NH2}, could be readily formed on water-ice grains by the acid induced addition of water across the \ce{CN} bond is now shown to be valid. Computational modelling of the reaction between \ce{R-CN} (R = H, \ce{CH3}) and a cluster of 32 molecules of water and one \ce{H3O+} proceeds auto-catalytically to form firstly a hydroxy imine \ce{R-C(OH)=NH} and secondly an amide \ce{R-C(O)NH2}. Quantum mechanical tunnelling, computed from small-curvature estimates, plays a key role in the rates of these reactions. This work represents the first credible effort to show how amides can be formed from abundant substrates, namely nitriles and water, reacting on a water-ice cluster containing catalytic amounts of hydrons in the interstellar medium with consequential implications towards the origins of life.Comment: 19 pages, 8 Figure

Polarized line formation with J-state interference in the presence of magnetic fields: A heuristic treatment of collisional frequency redistribution

An expression for the partial frequency redistribution (PRD) matrix for line scattering in a two-term atom, which includes the J-state interference between its fine structure line components is derived. The influence of collisions (both elastic and inelastic) and an external magnetic field on the scattering process is taken into account. The lower term is assumed to be unpolarized and infinitely sharp. The linear Zeeman regime in which the Zeeman splitting is much smaller than the fine structure splitting is considered. The inelastic collision rates between the different levels are included in our treatment. We account for the depolarization caused by the collisions coupling the fine structure states of the upper term, but neglect the polarization transfer between the fine structure states. When the fine structure splitting goes to zero, we recover the redistribution matrix that represents the scattering on a two-level atom (which exhibits only m-state interference --- namely the Hanle effect). The way in which the multipolar index of the scattering atom enters into the expression for the redistribution matrix through the collisional branching ratios is discussed. The properties of the redistribution matrix are explored for a single scattering process for an L=0 to 1 to 0 scattering transition with S=1/2 (a hypothetical doublet centered at 5000 A and 5001 A). Further, a method for solving the Hanle radiative transfer equation for a two-term atom in the presence of collisions, PRD, and J-state interference is developed. The Stokes profiles emerging from an isothermal constant property medium are computed.Comment: Accepted for publication in Journal of Quantitative Spectroscopy and Radiative Transfer (JQSRT

Développement d'un traitement acoustique basses-fréquences pour application aérospatiale

Résumé : Tout comme l’aéronautique, l’industrie aérospatiale s’est tournée progressivement vers l’emploi des coques à base des matériaux composites. Cette transition a permis d’alléger considérablement les structures aéronautiques et aérospatiales, et par conséquent, a réduit la consommation de carburants ainsi que l’impact écologique des aéronefs et des lanceurs. Toutefois, la loi de masse stipule que cela ne peut être sans conséquence sur la perte par transmission acoustique des panneaux, surtout sur les basses fréquences. Que ce soit pour la conformité aux exigences des normes aéronautiques en terme de niveau de pression acoustique à l’intérieur des cabines ou la protection des charges utiles dans les coiffes des lanceurs, les traitements acoustiques ciblant les basses fréquences s’avèrent un défi d’envergure. En effet, avec des contraintes très strictes de minimum de masse et de volume ajoutés, il est difficile de traiter les problèmes d’absorption acoustique basses-fréquences, avec les traitements phoniques classiques. Afin de tirer avantage des effets résonants pour améliorer l’absorption sur les basses fréquences, ce projet se propose d’étudier l’intégration d’écrans résistifs à très faibles épaisseurs dans les revêtements acoustiques, tout en minimisant le poids. Il a été proposé dans le cadre de la chaire industrielle de recherche en aéroacoustique dont les principaux bailleurs de fonds sont Bombardier aerospace, Pratt & whitney et Bell helicopter. Aussi, des travaux de recherche connexes se sont déroulés en partenariat avec ULA (United Launch Alliance). Ce travail de maîtrise comporte une partie bibliographique qui présente une étude exhaustive des traitements basses-fréquences existants, tout en y portant un regard critique. La partie théorique met particulièrement l’emphase sur les différents modèles de propagation d’onde et les phénomènes de dissipations dans les milieux poreux. Dans cette partie, on dénombre également les différents types d’écrans ainsi que les modèles de propagation correspondants. Des critères permettant une étude comparative objective du point de vue masse/performance ont été proposés. En plus des paramètres non acoustiques, les conditions de montage et d’agencement des couches ont été étudiées avec des simulations numériques appuyées par des mesures expérimentales. Dans l’avant dernier chapitre, un modèle SEA (Statical Energy Analysis) d’une coiffe de lanceur a été construit avec tous ses détails à partir d’un exemple concret. Les simulations se sont terminées avec une étude comparative de la réduction de niveau de pression acoustique dans la coiffe. Le dernier chapitre résume les principaux résultats et conclusions de cette étude.Abstract : Over the last few decades, the aerospace industry has witnessed a significant emergence of the use of composite shells. The latter are continuously replacing the metallic ones. This transition allowed a significant weight reduction of flying structures. Consequently, it substantially lessened the fuel consumption and mitigated the environmental footprint of aircrafts and space launch vehicles. However, evoking the mass law, this transition clearly cannot be without consequences on the acoustic transmission loss of fuselage panels. Neither can it be on payload fairings, especially over the low frequencies. Whether to meet with the standards and regulations in terms of acoustic pressure levels inside the pressurized cabins or to protect the payloads inside the launchers fairings, acoustic treatments design targeting the low frequencies seems to be a challenging issue. Indeed, with very stringent constraints in terms of added weight and volume, it is difficult to deal with the low frequencies noise and vibration, using passive monolayers. In order to take advantage of the resonant effects in enhancing low frequencies absorption, this work intends to investigate the integration of heavy treatments of very low thicknesses in acoustic coatings while minimizing weight. It was conducted within the frame work of the industrial research chair in aeroacoustics, whose main funders are : Bombardier Aerospace, Pratt & Whitney and Bell Helicopter. Also, other related researches were jointly carried out in partnership with ULA (United Launch Alliance). This master thesis includes a bibliographical section which consists of an overview of the existing low-frequencies solutions while keeping a critical eye on most of them. The following theoretical part focuses on the different models describing wave s’ propagation and dissipation phenomena in porous media. In the same section, we also list the different types of screens and the corresponding propagation models. Criteria for an objective comparative study in terms of weight versus performance were suggested. In addition to non-acoustic parameters, the layout and the mounting conditions of the acoustic packages were also investigated by means of numerical simulations, seconded by experimental measurements. In the penultimate chapter, an SEA detailed model of a launcher fairing was built based on data taken from a concrete example. The simulations ended with a comparative study of the sound pressure level reduction in the inner fairing cavity. The final chapter summarizes the main findings, conclusions and perspectives of this study

Conception d'un outil informatique basé sur un réseau de neurones artificiels pour la classification automatique des stades du sommeil

L’objectif de notre travail est de développer un outil d’analyse automatique des stades du sommeil basé sur les réseaux de neurones artificiels (RNA). Dans ce papier nous présentons notre démarche pour la conception de cet outil. La première difficulté consiste dans le choix de la représentation des signaux physiologiques et en particulier de l’électroencéphalogramme (EEG). Une fois la représentation adoptée, l’étape suivante est la conception du réseau de neurones optimal déterminé par un processus d’apprentissage et de validation sur les données issues d’un ensemble d'enregistrements de nuits de sommeil. Le résultat obtenu avec un taux de 63% de bonne classification pour six stades, nous incite à approfondir l’étude de cette problématique aux niveaux représentation et conception pour améliorer les performances de notre outil

The broadening of Fe II lines by neutral hydrogen collisions

Data for the broadening of 24188 Fe II lines by collisions with neutral hydrogen atoms have been computed using the theory of Anstee & O'Mara as extended to singly ionised species and higher orbital angular momentum states by Barklem & O'Mara. Data have been computed for all Fe II lines between observed energy levels in the line lists of Kurucz with log gf > -5 for which the theory is applicable. The variable energy debt parameter Ep used in computing the second order perturbation theory potential is chosen to be consistent with the long range dispersion interaction constant C6 computed using the f-values from Kurucz.Comment: Accepted for A&A. 5 pages, 5 figures, 2 electronic tables. Tables will be available via CDS; presently also at http://www.astro.uu.se/~barklem/papers/fe2_data.tar.g

Pharmacological and Behavioral Strategies to Improve Vision in Acquired Pendular Nystagmus.

BACKGROUND Acquired pendular nystagmus (APN) is a back and forth, oscillatory eye movement in which the 2 oppositely directed slow phases have similar waveforms. APN occurs commonly in multiple sclerosis and causes a disabling oscillopsia that impairs vision. Previous studies have proven that symptomatic therapy with gabapentin or memantine can reduce the nystagmus amplitude or frequency. However, the effect of these medications on visual acuity (VA) is less known and to our knowledge the impact of non-pharmacological strategies such as blinking on VA has not been reported. This is a single observational study without controls (Class IV) and is meant to suggest a future strategy for study of vision in patients with disabling nystagmus and impaired vision. CASE REPORT A 49-year-old woman with primary progressive multiple sclerosis with spastic paraparesis and a history of optic atrophy presented with asymmetrical binocular APN and bothersome oscillopsia. We found that in the eye with greater APN her visual acuity improved by 1 line (from 0.063 to 0.08 decimals) immediately after blinking. During treatment with memantine, her VA without blinking increased by 2 lines, from 0.063 to 0.12, but improved even more (from 0.12 to 0.16) after blinking. In the contralateral eye with a barely visible nystagmus, VA was reduced by 1 line briefly (~500 ms) after blinking. CONCLUSIONS In a patient with APN, blinking transiently improved vision. The combination of pharmacological treatment with memantine and the blinking strategy may induce better VA and less oscillopsia than either alone

Bound Electron Enhanced Radiosensitisation of Nimorazole upon Charge Transfer

This novel work reports nimorazole (NIMO) radiosensitizer reduction upon electron transfer in collisions with neutral potassium (K) atoms in the lab frame energy range of 10-400 eV. The negative ions formed in this energy range were time-of-flight mass analyzed and branching ratios were obtained. Assignment of different anions showed that more than 80% was due to the formation of the non-dissociated parent anion NIMO#~ at 226 u and nitrogen dioxide anion NC2- at 46 u. The rich fragmentation pattern revealed that significant collision induced the decomposition of the 4-nitroimidazole ring, as well as other complex internal reactions within the temporary negative ion formed after electron transfer to neutral NIMO. Other fragment anions were only responsible for less than 20% of the total ion yield. Additional information on the electronic state spectroscopy of nimorazole was obtained by recording a K+ energy loss spectrum in the forward scattering direction (9 « 0°), allowing us to determine the most accessible electronic states within the temporary negative ion. Quantum chemical calculations on the electronic structure of NIMO in the presence of a potassium atom were performed to help assign the most significant lowest unoccupied molecular orbitals participating in the collision process. Electron transfer was shown to be a relevant process for nimorazole radiosensitisation through efficient and prevalent non-dissociated parent anion formation.publishersversionpublishe

Periodic hypokalemic paralysis disclosing thyrotoxicosis

BACKGROUND: Hypokaliemic periodic paralysis is an uncommon complication of hyperthyroidism occurring sporadically almost exclusively in young Asian men. The clinical presentation is the same as in familial hypokaliemic periodic paralysis. Treatment consists of conventional management for thyrotoxicosis. CASE REPORT: A Laotian man aged 42 years had suffered episodes of pain and fatigue in the lower limbs lasting 2 to 7 days over the last few months. The patient was hospitalized with severe limb pain. Clinical examination found severe motor deficit involving all four limbs. Laboratory findings induced hypokaliemia (1.8 mmol/l) and hyperthyroidism (free thyroxin 36 pmol/l, TSH < 0.005 mlU/l). Thyroid echography revealed multinodular goitre with two heterogeneous nodules. Strong uptake was seen on the scintigram. The motor deficit regressed within 8 hours and the kaliemia was restored with 1.50 g KCl. The patient was discharged with carbimazole (30 mg/d). Three months later he was euthyroid and symptom free. Total thyroidectomy was performed and L-thyroxin prescribed. The patient remains symptom-free at the last follow-up, 5 months after thyroidectomy. DISCUSSION: The pathogenesis of hypokaliemic periodic paralysis involves the ATPase-dependent sodium-potassium pump whose activity is stimulated by thyroid hormones. The reasons for the ethnic and male predominance are poorly elucidated