Conductivity and superlattice ordering in an icosahedral Al-Pd-Mn phase

9 págs.; 6 figs.; PACS number(s): 61.44.Br, 61.10.Nz, 71.30.1h>In situ> conductivity measurements on Al-Pd-Mn quasicrystals have been combined with synchrotron x-ray-diffraction experiments for studying its behavior during phase transformations. In order to confidently reduce the possible contribution to the conductivity of defects and grain boundaries, single-crystal samples have been annealed in situ under UHV conditions. This combined experiment allows us to affirm unambiguously that the structural state of the i-Al-Pd-Mn single crystal influences the electrical conductivity. ©2003 American Physical SocietyThe authors thank Y. Calvayrac and A. Kvick for providing the sample, the ESRF for the beamtime allocation, and J. J. de Miguel for careful reading.Peer Reviewe

Use of W-Boson Longitudinal-Transverse Interference in Top Quark Spin-Correlation Functions: II

This continuation of the derivation of general beam-referenced stage-two spin-correlation functions is for the analysis of top-antitop pair-production at the Tevatron and at the Large Hadron Collider. Both the gluon-production and the quark-production contributions are included for the charged-lepton-plus-jets reaction p p or p bar{p} --> t bar{t} --> (W^+ b)(W^- bar{b}) --> (l^{+} nu b)(W^- bar{b}). There is a simple 4-angle beam-referenced spin-correlation function for determination of the relative sign of, or for measurement of a possible non-trivial phase between the two dominant helicity amplitudes for t --> W^{+} b decay. There is an analogous function and tests for bar{t} --> W^{-} bar{b} decay. This signature requires use of the (t bar{t}) c.m.-energy of the hadronically decaying W-boson, or the kinematically equivalent cosine of the polar-angle of W-boson emission in the anti-top (top) decay frame. Spinors and their outer-products are constructed so that the helicity-amplitude phase convention of Jacob & Wick can be used throughout for the fixing of the signs associated with this large W-boson longitudinal-transverse interference effect.Comment: Continuation of hep-ph/0506240 to include gluon-production contribution; 3 "postscript" figures. Equation numbers as in published-on-line EPJ

Health beliefs and compliance with inhaled corticosteroids by asthmatic patients in primary care practices

AbstractThe aim of this study was to determine factors associated with regular use of inhaled corticosteroids (ICS) by asthmatic patients in primary care practices. A cross-sectional survey was carried out over 12 family practices in the Philadelphia greater Metropolitan area. A total of 394 patients aged 18–49 years, who received medical care for asthma from their primary care physician and had been prescribed ICS between 1 January 1995 and 31 December 1996, were included.The study measured self-reported demographics, experience with asthma, use of and attitudes about ICS, and health beliefs in six domains.Only 38% of patients reported using ICS at least twice a day almost every day. The most frequently cited reasons for inconsistent or non-use of ICS were related to a belief that ICS were unnecessary during asymptomatic periods and to a general concern about side-effects. By logistic regression, factors associated with regular use of ICS were two patient health beliefs, namely the health belief of ‘Active’ participation in clinical decision-making with their physician (OR=4·6, 95% CI 2·8, 7·5), and the health belief that asthma was a ‘Serious’ health problem (OR=2·3, 95% CI 1·4, 3·7), and hospitalization for asthma within the previous 12 months (OR=2·3, 95% CI 1·6, 4·6).Patients were more likely to report regular use of ICS if they saw themselves as active participants in their treatment planning and conceptualized asthma as a potentially serious illness. These results support the themes of patient education and shared decision-making between patients and physicians that are promoted by the Asthma Guidelines from the National Heart, Lung and Blood Institute (NHLBI)

Dependence of the vortex configuration on the geometry of mesoscopic flat samples

The influence of the geometry of a thin superconducting sample on the penetration of the magnetic field lines and the arrangement of vortices are investigated theoretically. We compare superconducting disks, squares and triangles with the same surface area having nonzero thickness. The coupled nonlinear Ginzburg-Landau equations are solved self-consistently and the important demagnetization effects are taken into account. We calculate and compare quantities like the free energy, the magnetization, the Cooper-pair density, the magnetic field distribution and the superconducting current density for the three geometries. For given vorticity the vortex lattice is different for the three geometries, i.e. it tries to adapt to the geometry of the sample. This also influences the stability range of the different vortex states. For certain magnetic field ranges we found a coexistence of a giant vortex placed in the center and single vortices toward the corners of the sample. Also the H-T phase diagram is obtained.Comment: 9 pages, 17 figures (submitted to Phys. Rev. B

Structure, productivité et régime hydrique de phytocénoses halophiles sous climat méditerranéen

Des recherches sur le régime hydrique de la couverture végé tale (potentiel hydrique et transpiration), les variations de la bio masse végétale (matière sèche, composition chimique et valeur énergétique) et la production primaire ont été effectuées parallè lement à une étude de la composition floristique, de la salinité et de la profondeur de la nappe phréatique le long d’un transect implanté dans une végétation halophile dominée par Salicornia fruticosa et Arthrocnemum glaucum. Les biomasses végétales se sont avérées relativement élevées dans le Salicornietum fruticosae : de l’ordre de 3 kg de matière sèche par m2, alors qu’elles n’atteignent que 0,4 kg m-2 dans Y Arthrocnemetum. L’analyse des variations saisonnières de cette biomasse a permis de situer la production primaire annuelle du Salicornietum fruticosae entre 0,5 et 1 kg de matière sèche par m2, correspondant à un équivalent énergétique de 8-16 MJ m— 2, pour un rayonnement global incident de l’ordre de 6000 MJ par an. Sans atteindre les valeurs élevées qui caractérisent les marais d’eau douce ou les cultures, elle est du même ordre de grandeur que celle d’un peuplement de Quercus ilex étudié sous le même climat. La zone étudiée est caractérisée par la présence d’une nappe phréatique salée (10-45 g 1— 1) présentant des oscillations saison nières de niveau. A une période de submersion hivernale, au cours de laquelle il y a des risques d’asphyxie des racines, succède un assèchement, puis un abaissement de la nappe qui descend jus qu’à environ 70 cm dans le courant de l’été. Cet abaissement se manifeste par une chute du potentiel hydrique dans la vasculari sation et par une régulation de la transpiration ; parallèlement on observe un ralentissement très net de la croissance, qui fait que la production primaire est réalisée, pour l’essentiel, en trois mois (mai à juillet). La comparaison de deux zones se distinguant par la salinité de la nappe et le mode d’enracinement a montré la complexité et la nature de certaines relations entre les fluctuations de salinité et de profondeur de la nappe, l’évolution du régime hydrique de la plante et les variations de la biomasse. La répartition des raci nes en plusieurs strates joue un rôle important dans le maintien du potentiel hydrique de la plante. La présence d’une strate pro fonde lui permet, en été, de s’affranchir des horizons superficiels, où viennent s’accumuler les sels, et de garder le contact avec la frange capillaire. La présence d’une strate superficielle lui permet, au début de son cycle végétatif, d’éviter l’asphyxie lorsque la nappe est encore proche de la surface.Research on the water relations of the vegetation (water potential and transpiration), on seasonal changes in plant biomass (dry matter, chemical composition and caloric value), and on primary production have been carried out concurrently with records of species distribution, and depth and salinity of the water table along a transect in a halophytic vegetation dominated by Salicornia fruticosa and Arthrocnemum glaucum. Values of above-ground plant biomass are rather high in Salicornia fruticosa stands : about 3 kg m— 2 (dry matter), compa red to only 0,4 kg m— 2 in Arthrocnemum stands. Shoot net pro ductivity of Salicornia fruticosa stands was estimated to be between 0.5 and 1.0 kg m— 2 yr—1, which is equivalent to a caloric content of 8-16 MJ m— 2, for an incident global radiation of about 6000 MJ m— 2 yr- 1. This value is lower than those recorded for freshwater marshes or cultivated land, but of the same order of magnitude as in a Quercus ilex stand under the same climatic conditions. The area studied is characterized by the presence of saline underground water (10-45 g 1— 1), presenting seasonal variations in level. After a period of winter submersion, with risks of root asphyxia, there is a period of drying up and a lowering of the water table to a level of about — 70 cm in midsummer. This lowering is reflected by a drop of the water potential in the vas cularization and by a stomatal regulation leading to a decrease in transpiration ; concurrently a sharp reduction in growth is observed, with the result that most of the primary production is carried out in three months (May to July). Comparison between two areas differing in salinity of ground water and in root distribution showed the complexity and the nature of certain relationships between fluctuations of the water level and salinity of the ground water on the one hand, and evo lution of the water regime of the plant and biomass changes on the other hand. Distribution of roots in several layers plays an important role in the maintenance of the plant water potential. The presence of a deep root layer is useful to the plants in sum mer : it allows them to become independent from the upper horizons, in which salts accumulate, and to remain in contact with the capillary fringe. The presence of a superficial layer enables the plant to avoid asphyxia at the beginning of the gro wing season, when the water is still near the surface

Squark Mixing in Electron-Positron Reactions

Squark mixing plays a large role in the phenomenology of the minimal supersymmetric standard model, determining the mass of the lightest Higgs boson and the electroweak interactions of the squarks themselves. We examine how mixing may be investigated in high energy $e^+ e^-$ reactions, both at LEP-II and the proposed linear collider. In particular, off-diagonal production of one lighter and one heavier squark allows one to measure the squark mixing angle, and would allow one to test the mass relations for the light Higgs boson. In some cases off-diagonal production may provide the best prospects to discover supersymmetry. In the context of the light bottom squark scenario, we show that existing data from LEP-II should show definitive evidence for the heavier bottom squark provided that its mass $m_{\tilde{b}_2} \le 120$ GeV.Comment: 22 pages, latex, 6 figure

Vortex states in superconducting rings

The superconducting state of a thin superconducting disk with a hole is studied within the non-linear Ginzburg-Landau theory in which the demagnetization effect is accurately taken into account. We find that the flux through the hole is not quantized, the superconducting state is stabilized with increasing size of the hole for fixed radius of the disk, and a transition to a multi-vortex state is found if the disk is sufficiently large. Breaking the circular summetry through a non central location of the hole in the disk enhances the multi-vortex state.Comment: 11 pages, 23 figures (postscript). To appear in Physical Review B, Vol. 61 (2000

Diffractive Meson Production and the Quark-Pomeron Coupling

Diffractive meson production at HERA offers interesting possibilities to investigate diffractive processes and thus to learn something about the properties of the pomeron. The most succesful phenomenological description of the pomeron so far assumes it to couple like a $C = +1$ isoscalar photon to single quarks. This coupling leads, however, to problems for exclusive diffractive reactions. We propose a new phenomenological pomeron vertex, which leads to very good fits to the known data, but avoids the problems of the old vertex.Comment: 20 pages, latex with uuencoded postscript, revised versio

Properties of mesoscopic superconducting thin-film rings. London approach

Superconducting thin-film rings smaller than the film penetration depth (the Pearl length) are considered. The current distribution, magnetic moment, and thermodynamic potential ${\cal F}(H,N,v)$ for a flat, washer-shaped annular ring in a uniform applied field $H$ perpendicular to the film are solved analytically within the London approach for a state with winding number $N$ and a vortex at radius $v$ between the inner and outer radii.Comment: Submitted to Phys. Rev.