181 research outputs found
On eigenfunction approximations for typical non-self-adjoint Schroedinger operators
We construct efficient approximations for the eigenfunctions of
non-self-adjoint Schroedinger operators in one dimension. The same ideas also
apply to the study of resonances of self-adjoint Schroedinger operators which
have dilation analytic potentials. In spite of the fact that such
eigenfunctions can have surprisingly complicated structures with multiple local
maxima, we show that a suitable adaptation of the JWKB method is able to
provide accurate lobal approximations to them.Comment: 17 pages, 11 figure
La tuberculose extra-ganglionnaire de la sphere O.R.L.
La tuberculose extra ganglionnaire est une pathologie rare en ORL. Elle pourrait poser des problÚmes diagnostiques surtout avec la pathologie tumorale. Nous rapportons 10 cas de localisations extra-ganglionnaires, colligés au service ORL de l\'hÎpital Tahar Sfar de Mahdia entre 1988 et 2004. Il s\'agissait de 7 femmes et 3 hommes, ùgés entre 19 et 77 ans (moyenne : 39 ans). La maladie a touché le cavum dans 3 cas, les glandes salivaires dans 3 cas, les amygdales palatines dans 2 cas et le larynx chez 2 patients. Le diagnostic était dans tous les cas histo-pathologique. Tous nos patients ont reçu un traitement anti-tuberculeux. L\'évolution était favorable avec un recul moyen de 11 mois. Conclusion : La tuberculose extra-ganglionnaire en ORL pose surtout des problÚmes diagnostiques. Son diagnostic est le plus souvent histo-pathologique. Son traitement repose sur la himiothérapie anti-tuberculeuse. Extra-nodal tuberculosis is a rare in ENT practice. We report 10 cases of extra-ganglionic localizations of tuberculosis, treated in ENT department of the Tahar Sfar hospital of Mahdia between 1988 and 2004. They were 7 women and 3 men, aged between 19 and 77 years (average: 39 years) . The disease has touched the nasopharynx in 3 cases, the salivary glands in 3 cases, the tonsils in 2 cases and the larynx in 2 cases. The diagnosis was in all cases histo-pathological. All our patients received an anti-tubercular treatment. The evolution was favorable with 11 months average outcome. Conclusion: Extra-nodal tuberculosis in ENT poses especially diagnostic problems. Its treatment is based on anti-tubercular chemotherapy. Journal Tunisien d\'ORL et de chirurgie cervico-faciale Vol. 16 2006: pp. 36-3
On the Born-Oppenheimer approximation of diatomic molecular resonances
We give a new reduction of a general diatomic molecular Hamiltonian, without
modifying it near the collision set of nuclei. The resulting effective
Hamiltonian is the sum of a smooth semiclassical pseudodifferential operator
(the semiclassical parameter being the inverse of the square-root of the
nuclear mass), and a semibounded operator localised in the elliptic region
corresponding to the nuclear collision set. We also study its behaviour on
exponential weights, and give several applications where molecular resonances
appear and can be well located.Comment: 22 page
Histiocytose langerhansienne multiviscerale avec atteinte auriculaire bilaterale a propos dâune observation
Lâhistiocytose langerhansienne multi-viscĂ©rale est une prolifĂ©ration clonale des cellules de Langerhans, touchant plusieurs organes. Cette entitĂ© se voit surtout chez lâenfant. Dans ce travail, nous rappelons les aspects cliniques avec la frĂ©quence dâatteinte oto-rhino-laryngologique, ainsi que les moyens de diagnostic et le traitement de cette affection rare. Nous prĂ©sentons le cas dâun enfant ĂągĂ© de 2 ans qui a Ă©tĂ© hospitalisĂ© pour une pneumopathie interstitielle, associĂ©e Ă une otorrhĂ©e bilatĂ©rale. Lâexamen a montrĂ© un comblement des 2 conduits auditifs externes et des lĂ©sions cutanĂ©es squameuses. La biopsie a conclu Ă une histiocytose langerhansienne. MalgrĂ© la chimiothĂ©rapie, lâenfant est dĂ©cĂ©dĂ© aprĂšs 11 mois.Mots-clĂ©s : Histiocytose langerhansienne, atteinte auriculaire
Electrocaloric effect in Ba(0.2)Ca(0.8)Ti(0.95)Ge(0.05)O(3) determined by a new pyroelectric method
The present letter explores the electrocaloric effect (ECE) in the lead free
oxide Ba0.8Ca0.2Ti0.95Ge0.05O3 ceramics (BCTG). The electrocaloric responsivity
(dT/dE) was determined by two different methods using the Maxwell relationship
(dT/dE)~(dP/dT)_E. In a first well-known indirect method, P-E hysteresis loops
were measured in a wide temperature range from which the pyroelectric
coefficient p_E=(dP/dT)_E and thus (dT/dE) were determined by derivation of
P(T,E) data. In the second novel method the pyroelectric coefficient p_E and
consequently the electrocaloric responsivity was determined by direct
measurements of the pyroelectric currents under different applied electric
fields. Within the experimental error good agreement was obtained between two
methods with an electrocaloric responsivity equal to 0.18 +/- 0.05 10-6 K.m.V-1
was obtained at about 410 KComment: 5 pages, 4 figure
Addressing the âwhysâ of UK childrenâs YouTube use: a purposes approach
Despite the widespread use of YouTube by children, there has been limited research undertaken on the âwhyâ questions of their use. Past theoretical approaches have framed these questions in terms of broader individual needs and their relation to media use, though this work has mainly focused on adults and adolescents. This article presents relevant findings from a mixed methods study of childrenâs (aged 0â16) uses of social media in the United Kingdom to consider instead the âpurposesâ of childrenâs YouTube use, drawing on: (1) an online family survey; (2) family case studies; (3) child focus groups; and (4) child telephone interviews. âPurposeâ is theorized in the article in relation to the ways children themselves make sense of and articulate the reasons they use YouTube or, in the case of parents and carers, for allowing, facilitating, or encouraging their children to use YouTube. Parents tended to frame the purposes of childrenâs YouTube use more instrumentally, focusing on perceived educational benefits and their own convenience needs. While sharing a focus on instrumental purposes, children sometimes emphasized broader dimensions of purpose, with an increased focus on humor, sensory, and hedonic dimensions. Childrenâs responses also emphasized the autotelic nature of play. The study foregrounded the extent to which the purposes of others (such as commercial entities) are served by childrenâs YouTube use. Seven child-centered, parent-centered, and âotherâ purposes for childrenâs YouTube use are discussed: cognitive, corporeal, cultural, collaborative, creative, commercial, and convenience
Wigner's Dynamical Transition State Theory in Phase Space: Classical and Quantum
A quantum version of transition state theory based on a quantum normal form
(QNF) expansion about a saddle-centre-...-centre equilibrium point is
presented. A general algorithm is provided which allows one to explictly
compute QNF to any desired order. This leads to an efficient procedure to
compute quantum reaction rates and the associated Gamov-Siegert resonances. In
the classical limit the QNF reduces to the classical normal form which leads to
the recently developed phase space realisation of Wigner's transition state
theory. It is shown that the phase space structures that govern the classical
reaction d ynamicsform a skeleton for the quantum scattering and resonance
wavefunctions which can also be computed from the QNF. Several examples are
worked out explicitly to illustrate the efficiency of the procedure presented.Comment: 132 pages, 31 figures, corrected version, Nonlinearity, 21 (2008)
R1-R11
Structure and dynamics of ring polymers: entanglement effects because of solution density and ring topology
The effects of entanglement in solutions and melts of unknotted ring polymers
have been addressed by several theoretical and numerical studies. The system
properties have been typically profiled as a function of ring contour length at
fixed solution density. Here, we use a different approach to investigate
numerically the equilibrium and kinetic properties of solutions of model ring
polymers. Specifically, the ring contour length is maintained fixed, while the
interplay of inter- and intra-chain entanglement is modulated by varying both
solution density (from infinite dilution up to \approx 40 % volume occupancy)
and ring topology (by considering unknotted and trefoil-knotted chains). The
equilibrium metric properties of rings with either topology are found to be
only weakly affected by the increase of solution density. Even at the highest
density, the average ring size, shape anisotropy and length of the knotted
region differ at most by 40% from those of isolated rings. Conversely, kinetics
are strongly affected by the degree of inter-chain entanglement: for both
unknots and trefoils the characteristic times of ring size relaxation,
reorientation and diffusion change by one order of magnitude across the
considered range of concentrations. Yet, significant topology-dependent
differences in kinetics are observed only for very dilute solutions (much below
the ring overlap threshold). For knotted rings, the slowest kinetic process is
found to correspond to the diffusion of the knotted region along the ring
backbone.Comment: 17 pages, 11 figure
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