Vortex Lattice in Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} Well Above the First-Order Phase-Transition Boundary

Measurements of non-local in-plane resistance originating from transverse vortex-vortex correlations have been performed on a Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} high-T_c superconductor in a magnetic field up to 9 T applied along the crystal c-axis. Our results demonstrate that a rigid vortex lattice does exist over a broad portion of the magnetic field -- temperature (H-T) phase diagram, well above the first-order transition boundary H_{FOT}(T). The results also provide evidence for the vortex lattice melting and vortex liquid decoupling phase transitions, occurring above the H_{FOT}(T).Comment: 14 pages, 10 figure

Asymmetric vortex merger: mechanism and criterion

The merging of two unequal co-rotating vortices in a viscous fluid is investigated. Two-dimensional numerical simulations of initially equal sized Lamb-Oseen vortices with differing relative strengths are performed. Results show how the disparity in deformation rates between the vortices alters the interaction. Key physical mechanisms associated with vortex merging are identified. A merging criterion is formulated in terms of the relative timing of core detrainment and destruction. A critical strain parameter is defined to characterize the establishment of core detrainment. This parameter is shown to be directly related to the critical aspect ratio in the case of symmetric merger

X-ray Reflection By Photoionized Accretion Discs

We present the results of reflection calculations that treat the relevant physics with a minimum of assumptions. The temperature and ionization structure of the top five Thomson depths of an illuminated disc are calculated while also demanding that the atmosphere is in hydrostatic equilibrium. In agreement with Nayakshin, Kazanas & Kallman, we find that there is a rapid transition from hot to cold material in the illuminated layer. However, the transition is usually not sharp so that often we find a small but finite region in Thomson depth where there is a stable temperature zone at T \sim 2 x 10^{6} K due to photoelectric heating from recombining ions. As a result, the reflection spectra often exhibit strong features from partially-ionized material, including helium-like Fe K lines and edges. We find that due to the highly ionized features in the spectra these models have difficulty correctly parameterizing the new reflection spectra. There is evidence for a spurious $R-\Gamma$ correlation in the ASCA energy range, where $R$ is the reflection fraction for a power-law continuum of index $\Gamma$, confirming the suggestion of Done & Nayakshin that at least part of the R-Gamma correlation reported by Zdziarski, Lubinski & Smith for Seyfert galaxies and X-ray binaries might be due to ionization effects. Although many of the reflection spectra show strong ionized features, these are not typically observed in most Seyfert and quasar X-ray spectra.Comment: 16 pages, accepted by MNRAS, Fig. 8 is in colour Figures and tables changed by a code update. Conclusions unchange

Star Models with Dark Energy

We have constructed star models consisting of four parts: (i) a homogeneous inner core with anisotropic pressure (ii) an infinitesimal thin shell separating the core and the envelope; (iii) an envelope of inhomogeneous density and isotropic pressure; (iv) an infinitesimal thin shell matching the envelope boundary and the exterior Schwarzschild spacetime. We have analyzed all the energy conditions for the core, envelope and the two thin shells. We have found that, in order to have static solutions, at least one of the regions must be constituted by dark energy. The results show that there is no physical reason to have a superior limit for the mass of these objects but for the ratio of mass and radius.Comment: 20 pages, 1 figure, references and some comments added, typos corrected, in press GR

Modelo de distribución de agua en suelo regado por goteo

[ES] Se desarrolla un modelo de simulación de la dinámica del agua en el suelo en riego localizado, denominado SIMDAS. Para el desarrollo del procedimiento numérico, se utiliza la teoría de flujo de agua en condiciones de no saturación, sin efecto histerético, resolviendo la ecuación de flujo axisimétrico sin y con extracción de agua por la planta a partir de un método en diferencias finitas, con la consideración de los distintos horizontes del suelo. Verificado el modelo en campo, los resultados que presenta son satisfactorios cuando no se contempla la presencia de cultivo, pero no lo son cuando interviene la extracción de agua por la planta. Por consiguiente, el grado de aceptabilidad es suficiente para fines de diseño agronómico de sistemas de riego localizado, pero no lo es para aquellos casos en que la extracción de agua por la planta interviene de manera destacada, como en el manejo y la programación de riegos.Ramírez De Cartagena Bisbe, F.; Sáinz Sánchez, MA. (1997). Modelo de distribución de agua en suelo regado por goteo. Ingeniería del Agua. 4(1):57-70. https://doi.org/10.4995/ia.1997.2716SWORD577041Armstrong C.F., Wilson T.V. (1983) Computer model for moisture distribution in stratified soils under a trickle source. Transactions of the American Society of Agricultural Engineers: 1704-1709.Belmans C., Wesswling J.G., Feddes R.A. (1983) Simulation model of the water balance of a cropped soil: SWATRE. Journal of Hidrology. 63 & 21: 271-286.Ben-Asher J., Charach CH., Zemel A. (1986) Infiltration and water extraction from trickle irrigation source: The effective hemisphere model. Soil Science Society of America Journal. 50: 882-887.Brandt A., BreslerE., Diner N., Ben-Asher J., Heller J., Goldberg. (1971) Infiltration from a trickle source: I. Mathematical models. Soil Science Society of America Proceedings, 35: 675-682.Bresler R E. (1975) Two-dimensional transport of solutes during nonsteady infiltration from a trickle source. Soil Science Society of America Proceedings, 39: 604-613.Feddes R.A., Kowalik P.J., Zaradny H. (1978) Simulation of field water use and crop yield. PUDOC, Wageningen. 189pp.Ghali S.G. (1986) Mathematical modelling of soil moisture dynamics in trickle irrigated fields. Thesis, University of Southampton (UK).Gupta S.C., Larson W.E. (1979) Estimating soil wáter retention characteristics from particle size distribution, organic matter percent, and bulk density. Water Resources Research, 15(6): 1633-1635.Hillel D. (1977) Computer simulation of soil-waters dynamics. A compendium of recent work. IDRC, Ottawa, Canada. 214 pp.Jackson R.D. (1972) On the calculation of hydraulic conductivity. Soil Science Society of America Proceedings. 36: 380-382.Keller J. (1978) Trickle irrigation. In Irrigation (Ch. 7). National Engineering Handbook USDA-SCS.Keller J., Karmelid. (1975) Trickle irrigation design. Rain Bird Corp. Glendora, California USA. 133 pp.Khatri K.C. (1984) Simulation of soil moisture migration from a point source. Thesis, McGill University, Quebec, Canada.Kunze R.J., Uehara G., Graham K. (1968) Factors important in the calculation of hydraulic conductivity. Soil Science Soc. Amer. Proc., 32: 760-765.Lafolie F., Guenelon R., Van Genuchten M.TH. (1989a.) Analysis of water flow under trickle irrigation: I. Theory and numerical solution. Soil Science Society of America Journal, 53: 1310-1318.Lafolie P., Guenelon R., Van Genuchten M.TH. (1989b.) Analysis of water flow under trickle irrigation: II. Experimental evaluation. Soil Science Society of America Journal. 53: 1318-1323.Marino M.A., Tracy J.C. (1988) Flow of water through root-soil environment. Journal of Irrigation and Drainage Engineering, 114 (4): 588-604.Marshall T.J. (1958) A relation between permeability and size distribution of pores. Journal of Soil Science, 9 (8): 1-8.Millington R.J., Quirk J.P. (1959) Permeability of porous media Nature, 183: 378-388.Molz F.J., Remson I. (1970) Extraction term models of soil moisture use by transpiring plants. Water Resources Research, 6 (5): 1346-1356.Philip J.R. (1971) General theorem on steady infiltration from surface sources, with application to point and line sources. Soil Science Society of America Proceedings, 35: 867-871.Pradad R. (1988) A linear root water uptake model Journal of Hidrology, 99: 297-306.Raats P.A.C. (1977) Laterally confined, steady flows of water from sources and to sinks in unsaturated soils. Soil Science Society of America Journal, 41:294-304.Ramírez De Cartagena F. (1994) Simulación numerica de la dinámica del agua en el suelo. Aplicacion al diseño de sistemas de riego LAF. Tesis Doctoral. ETSEA. Universidad de Lleida.Rawls W.J., Brakensiek D.L. (1982) Estimating soil water retention from soil properties. Journal of the Irrigation and Drainage Division, Proc. of the ASCE, 108, IR2: 166-171.Saxton K.E., Rawls W.J., Romberger J.S., Papendick R.I. (1986) Estimating generalized soil-water characteristics from texture. Soil Science Society of America Journal, 50: 1031-1036.Taghavi S.A., Mariño M.A., Rolston D.E. (1985) Infiltration from a trickle source in a heterogeneous soil medium. Journal of Hidrology, 78: 107-121.Van Der Ploeg R.R., Benecke P. (1974) Unsteady, unsaturated, n-dimensional moisture flow in soil: A computer simulation program. Soil Science Society of America Proceedings, 38: 881-885Vermeiren L., Jobling G.A. (1986) Riego localizado. Estudios FAO Riego y Drenaje, n°36. FAO. Roma. 203 pp.Warrick A.W., Lomen D.O., Amoozegarfard A. (1980) Linearized moisture flow with root extraction for three dimensional, steady conditions. Soil Science Society of America Journal, 44: 911-914

Sex differences in brain atrophy in multiple sclerosis

BACKGROUND: Women are more susceptible to multiple sclerosis (MS) than men by a ratio of approximately 3:1. However, being male is a risk factor for worse disability progression. Inflammatory genes have been linked to susceptibility, while neurodegeneration underlies disability progression. Thus, there appears to be a differential effect of sex on inflammation versus neurodegeneration. Further, gray matter (GM) atrophy is not uniform across the brain in MS, but instead shows regional variation. Here, we study sex differences in neurodegeneration by comparing regional GM atrophy in a cohort of men and women with MS versus their respective age- and sex-matched healthy controls. METHODS: Voxel-based morphometry (VBM), deep GM substructure volumetry, and cortical thinning were used to examine regional GM atrophy. RESULTS: VBM analysis showed deep GM atrophy in the thalamic area in both men and women with MS, whereas men had additional atrophy in the putamen as well as in localized cortical regions. Volumetry confirmed deep GM loss, while localized cortical thinning confirmed GM loss in the cerebral cortex. Further, MS males exhibited worse performance on the 9-hole peg test (9HPT) than MS females. We observed a strong correlation between thalamic volume and 9HPT performance in MS males, but not in MS females. CONCLUSION: More regional GM atrophy was observed in men with MS than women with MS, consistent with previous observations that male sex is a risk factor for worse disease progression

Dynamical Renormalization Group Approach to Quantum Kinetics in Scalar and Gauge Theories

We derive quantum kinetic equations from a quantum field theory implementing a diagrammatic perturbative expansion improved by a resummation via the dynamical renormalization group. The method begins by obtaining the equation of motion of the distribution function in perturbation theory. The solution of this equation of motion reveals secular terms that grow in time, the dynamical renormalization group resums these secular terms in real time and leads directly to the quantum kinetic equation. We used this method to study the relaxation in a cool gas of pions and sigma mesons in the O(4) chiral linear sigma model. We obtain in relaxation time approximation the pion and sigma meson relaxation rates. We also find that in large momentum limit emission and absorption of massless pions result in threshold infrared divergence in sigma meson relaxation rate and lead to a crossover behavior in relaxation. We then study the relaxation of charged quasiparticles in scalar electrodynamics (SQED). While longitudinal, Debye screened photons lead to purely exponential relaxation, transverse photons, only dynamically screened by Landau damping lead to anomalous relaxation, thus leading to a crossover between two different relaxational regimes. We emphasize that infrared divergent damping rates are indicative of non-exponential relaxation and the dynamical renormalization group reveals the correct relaxation directly in real time. Finally we also show that this method provides a natural framework to interpret and resolve the issue of pinch singularities out of equilibrium and establish a direct correspondence between pinch singularities and secular terms. We argue that this method is particularly well suited to study quantum kinetics and transport in gauge theories.Comment: RevTeX, 40 pages, 4 eps figures, published versio

Measurement of the Charged Multiplicities in b, c and Light Quark Events from Z0 Decays

Average charged multiplicities have been measured separately in $b$, $c$ and light quark ($u,d,s$) events from $Z^0$ decays measured in the SLD experiment. Impact parameters of charged tracks were used to select enriched samples of $b$ and light quark events, and reconstructed charmed mesons were used to select $c$ quark events. We measured the charged multiplicities: $\bar{n}_{uds} = 20.21 \pm 0.10 (\rm{stat.})\pm 0.22(\rm{syst.})$, $\bar{n}_{c} = 21.28 \pm 0.46(\rm{stat.}) ^{+0.41}_{-0.36}(\rm{syst.})$ $\bar{n}_{b} = 23.14 \pm 0.10(\rm{stat.}) ^{+0.38}_{-0.37}(\rm{syst.})$, from which we derived the differences between the total average charged multiplicities of $c$ or $b$ quark events and light quark events: $\Delta \bar{n}_c = 1.07 \pm 0.47(\rm{stat.})^{+0.36}_{-0.30}(\rm{syst.})$ and $\Delta \bar{n}_b = 2.93 \pm 0.14(\rm{stat.})^{+0.30}_{-0.29}(\rm{syst.})$. We compared these measurements with those at lower center-of-mass energies and with perturbative QCD predictions. These combined results are in agreement with the QCD expectations and disfavor the hypothesis of flavor-independent fragmentation.Comment: 19 pages LaTex, 4 EPS figures, to appear in Physics Letters

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the $\gamma p$ centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil

Determination of alphaS from Hadronic Event Shapes in e+e- Annihilation at 192 < sqrt(s) < 208 GeV

Results are presented from a study of the structure of high energy hadronic events recorded by the L3 detector at sqrt(s)>192 GeV. The distributions of several event shape variables are compared to resummed O(alphaS^2) QCD calculations. We determine the strong coupling constant at three average centre-of-mass energies: 194.4, 200.2 and 206.2 GeV. These measurements, combined with previous L3 measurements at lower energies, demonstrate the running of alphaS as expected in QCD and yield alphaS(mZ) = 0.1227 +- 0.0012 +- 0.0058, where the first uncertainty is experimental and the second is theoretical