Transport coefficients for inelastic Maxwell mixtures

The Boltzmann equation for inelastic Maxwell models is used to determine the Navier-Stokes transport coefficients of a granular binary mixture in $d$ dimensions. The Chapman-Enskog method is applied to solve the Boltzmann equation for states near the (local) homogeneous cooling state. The mass, heat, and momentum fluxes are obtained to first order in the spatial gradients of the hydrodynamic fields, and the corresponding transport coefficients are identified. There are seven relevant transport coefficients: the mutual diffusion, the pressure diffusion, the thermal diffusion, the shear viscosity, the Dufour coefficient, the pressure energy coefficient, and the thermal conductivity. All these coefficients are {\em exactly} obtained in terms of the coefficients of restitution and the ratios of mass, concentration, and particle sizes. The results are compared with known transport coefficients of inelastic hard spheres obtained analytically in the leading Sonine approximation and by means of Monte Carlo simulations. The comparison shows a reasonably good agreement between both interaction models for not too strong dissipation, especially in the case of the transport coefficients associated with the mass flux.Comment: 9 figures, to be published in J. Stat. Phy

Animaci?n a la lectura mediante estrategias virtuales para favorecer la interacci?n literaria en los estudiantes del Ciclo 1, del colegio San Bernardino I.E.D.

119 P?ginasRecurso Electr?nicoEl presente informe tiene como principal objetivo esquematizar los resultados del proyecto de investigaci?n formativa; la indagaci?n gir? en torno a la pregunta ?De qu? manera la animaci?n a la lectura y el uso de estrategias virtuales permiten favorecer la interacci?n literaria en los estudiantes de ciclo uno, del Colegio San Bernardino I.E.D? En este sentido, el proceso de intervenci?n tom? varios enfoques metodol?gicos; uno de ellos fue el m?todo de animaci?n a la lectura de Montserrat Sarto (1998) que usa las estrategias en forma de juego creativo para contribuir al desarrollo de la capacidad lectora que tiene el ni?o, cultivar su inteligencia y buscar el placer literario. Del mismo modo, se tom? como referencia los aportes de Carmen Gil para desarrollar m?ltiples actividades de animaci?n a la lectura que intentan convencer por encantamiento el gusto por la literatura. Los aportes metodol?gicos se articularon con la creaci?n de un ambiente virtual, que permiti? favorecer, motivar y cautivar a los estudiantes, a trav?s de nuevos lenguajes incorporados por las tics, de acuerdo a los postulados de Jes?s Mart?n Barbero y Manuel Castells. Las actividades propuestas se distribuyeron en tres talleres educativos: el primer taller se denomin? ?La magia de la lectura?; el segundo se denomin? ?leyendo aprendo? y el tercer taller ?la tecnolog?a: puerta a la lectura y a la fantas?a?, fase que permiti? plasmar en un blog la producci?n de los procesos lectores alcanzados por los ni?os.ABSTRACT. The following report is aimed to show the results got from the research project Inquiring was focused on the question: How can the using of the on-line strategies encourage students from elementary grades, cycle 1 at San Bernardino School, to read literature? Thus, the intervention process had some methodological approaches; one of them was motivation to reading from Montserrat Sarto (1998) who stated ?use the strategies in terms of creative game? to contribute to children?s reading capacity development , grow their intelligence and search the perfection in reading? similarly, it was taken as reference, Carmen Gil?s contributions, besides she is developing multiple encouraging activities toward reading that intend to convince people by charming the enjoyment of reading. The methodological contributions above were linked with the creation of an on-line environment that allowed upholding, motivating and captivating the students through ?the new languages inserted by the educational technology? according to Jesus Martin Barbero?s postulates and Manuel Castells. The activities proposed were organized in three educational workshops: The first one was labeled ?the magic of reading?; the second was called ?by reading I can learn? and the third workshop ?technology: the door toward reading and fantasy?; stage that allowed capture in a blog reader production process reached by children.INTRODUCCI?N 15 1. PLANTEAMIENTO DEL PROBLEMA 17 1.1 DESCRIPCI?N Y FORMULACI?N DEL PROBLEMA 17 2. MARCO TE?RICO 19 2.1. MARCO LEGAL 19 2.2. MARCO EPISTEMOL?GICO 23 2.3. MARCO PEDAG?GICO 25 2.4. MARCO PSICOL?GICO 30 2.5. ANTECEDENTES 33 3. JUSTIFICACI?N 36 4. OBJETIVOS 37 4.1 OBJETIVO GENERAL 37 4.2 OBJETIVOS ESPEC?FICOS 37 5. DISE?O METODOL?GICO 38 5.1 TIPO DE INVESTIGACI?N 38 5.2 HIP?TESIS EXPLICATIVA 38 5.3 PAR?METROS DE LA INVESTIGACI?N 39 5.3.1 Poblaci?n 40 5.3.2 Muestra 40 5.4 FORMA DE RECOLECCI?N DE LA INFORMACI?N 42 5.4.1 Observaci?n 42 5.4.2 Diario de campo 42 5.4.3 Estudio de caso 43 5.4.4 Entrevista 43 5.4.5 Grupo focal 43 5.4.6 Cuadro resumen 43 6. INSTRUMENTOS Y METODOLOG?A UTILIZADOS EN EL PROCESO DE INTERVENCI?N PEDAG?GICA 44 7. T?CNICAS QUE SE UTILIZARON PARA REALIZAR El AN?LISIS DE RESULTADOS 45 8. AN?LISIS DE LOS RESULTADOS 47 8.1 PERFIL DEL ESTUDIANTE 47 8.1.1 Desde la edad 48 8.1.2 Desde el contexto socio-econ?mico 48 9. DESARROLLO DE LAS ACTIVIDADES Y RESULTADOS 50 9.1 TALLER DE AMBIENTACI?N: LA MAGIA DE LA LECTURA 50 9.1.1 Tabla 6. Taller de ambientaci?n: la magia de la lectura 50 9.2 TALLER DE DESARROLLO: LEYENDO APRENDO 58 9.2.1 Tabla 7. Taller de desarrollo: leyendo aprendo 58 9.3 Taller de producci?n: La tecnolog?a, puerta a la lectura y a la fantas?a 63 9.3.1 Tabla 8. Taller de producci?n: la tecnolog?a, puerta a la lectura y a la fantas?a 64 10. AN?LISIS COMPARATIVO: TALLER DE AMBIENTACI?N Y DE PRODUCCI?N 71 10.1 An?lisis del taller de ambientaci?n: la magia de la lectura 71 10.2 An?lisis del taller de producci?n: la tecnolog?a, puerta a la fantas?a 75 11. CONCLUSIONES 80 RECOMENDACIONES 82 REFERENCIAS 8

Statistical equilibrium of silicon in the solar atmosphere

The statistical equilibrium of neutral and ionised silicon in the solar photosphere is investigated. Line formation is discussed and the solar silicon abundance determined. High-resolution solar spectra were used to determine solar $\log gf\epsilon_{\rm Si}$ values by comparison with Si line synthesis based on LTE and NLTE level populations. The results will be used in a forthcoming paper for differential abundance analyses of metal-poor stars. A detailed analysis of silicon line spectra leads to setting up realistic model atoms, which are exposed to interactions in plane-parallel solar atmospheric models. The resulting departure coefficients are entered into a line-by-line analysis of the visible and near-infrared solar silicon spectrum. The statistical equilibrium of \ion{Si}{i} turns out to depend marginally on bound-free interaction processes, both radiative and collisional. Bound-bound interaction processes do not play a significant role either, except for hydrogen collisions, which have to be chosen adequately for fitting the cores of the near-infrared lines. Except for some near-infrared lines, the NLTE influence on the abundances is weak. Taking the deviations from LTE in silicon into account, it is possible to calculate the ionisation equilibrium from neutral and ionised lines. The solar abundance based on the experimental $f$-values of Garz corrected for the Becker et al.'s measurement is $7.52 \pm 0.05$. Combined with an extended line sample with selected NIST $f$-values, the solar abundance is $7.52 \pm 0.06$, with a nearly perfect ionisation equilibrium of \Delta\log\epsilon_\odot(\ion{Si}{ii}/\ion{Si}{i}) = -0.01.Comment: 13pages 10 figures. A&A acceptte

Abundances and Kinematics of Field Halo and Disk Stars I: Observational Data and Abundance Analysis

We describe observations and abundance analysis of a high-resolution, high-S/N survey of 168 stars, most of which are metal-poor dwarfs. We follow a self-consistent LTE analysis technique to determine the stellar parameters and abundances, and estimate the effects of random and systematic uncertainties on the resulting abundances. Element-to-iron ratios are derived for key alpha, odd, Fe-peak, r- and s-process elements. Effects of Non-LTE on the analysis of Fe I lines are shown to be very small on the average. Spectroscopically determined surface gravities are derived that are generally close to those obtained from Hipparcos parallaxes.Comment: 41 pages, 7 Postscript figures. Accepted for publication in the A

Peripheral Nerve Ultrasound for the Differentiation between ALS, Inflammatory, and Hereditary Polyneuropathies

Background and Objectives: Ultrasound (US) is a non-invasive tool for the in vivo detection of peripheral nerve alterations. Materials and Methods: In this study, we applied nerve US to assist the discrimination between the spectrum of amyotrophic lateral sclerosis (ALS, n = 11), chronic inflammatory demyelinating polyradiculoneuropathy (CIDP, n = 5), and genetically confirmed Charcot–Marie–Tooth disease (CMT, n = 5). All participants and n = 15 controls without neurological diseases underwent high-resolution US of the bilateral tibial nerve. The nerve cross-sectional area (CSA) and nerve microvascular blood flow were compared between the groups and related to cerebrospinal fluid (CSF) measures, clinical symptoms, and nerve conduction studies. The analyses are part of a larger multimodal study on the comparison between US and 7 Tesla (7T) magnetic resonance neurography (MRN). Results: The patients and controls were matched with respect to their demographical data. CMT had the longest disease duration, followed by CIDP and ALS. CSA was related to age, weight, and disease duration. CSA was larger in CMT and CIDP compared to ALS and controls. The blood flow was greatest in CIDP, and higher than in CMT, ALS, and controls. In ALS, greater CSA was correlated with greater CSF total protein and higher albumin quotient. The US measures did not correlate with clinical scores or nerve conduction studies in any of the subgroups. Conclusion: Our results point towards the feasibility of CSA and blood flow to discriminate between ALS, CIDP, and CMT, even in groups of small sample size. In ALS, larger CSA could indicate an inflammatory disease subtype characterized by reduced blood–nerve barrier integrity. Our upcoming analysis will focus on the additive value of 7T MRN in combination with US to disentangle the spectrum between more inflammatory or more degenerative disease variants among the disease groups

Abundances In Very Metal Poor Dwarf Stars

We discuss the detailed composition of 28 extremely metal-poor dwarfs, 22 of which are from the Hamburg/ESO Survey, based on Keck Echelle spectra. Our sample has a median [Fe/H] of -2.7 dex, extends to -3.5 dex, and is somewhat less metal-poor than was expected from [Fe/H](HK,HES) determined from low resolution spectra. Our analysis supports the existence of a sharp decline in the distribution of halo stars with metallicity below [Fe/H] = -3.0 dex. So far no additional turnoff stars with [Fe/H]}<-3.5 have been identified in our follow up efforts. For the best observed elements between Mg and Ni, we find that the abundance ratios appear to have reached a plateau, i.e. [X/Fe] is approximately constant as a function of [Fe/H], except for Cr, Mn and Co, which show trends of abundance ratios varying with [Fe/H]. These abundance ratios at low metallicity correspond approximately to the yield expected from Type II SN with a narrow range in mass and explosion parameters; high mass Type II SN progenitors are required. The dispersion of [X/Fe] about this plateau level is surprisingly small, and is still dominated by measurement errors rather than intrinsic scatter. The dispersion in neutron-capture elements, and the abundance trends for Cr, Mn and Co are consistent with previous studies of evolved EMP stars. Two dwarfs in the sample are carbon stars, while two others have significant C enhancements, all with C12/C13 ~ 7 and with C/N between 10 and 150. Three of these C-rich stars have large enhancements of the heavy neutron capture elements, including lead, which implies a strong s-process contribution, presumably from binary mass transfer; the fourth shows no excess of Sr or Ba.Comment: Accepted for publication in the Ap

Oxygen Abundances in Two Metal-Poor Subgiants from the Analysis of the 6300 A Forbidden O I Line

Recent LTE analyses (Israelian et al. 1998 and Bosegaard et al. 1999) of the OH bands in the optical-ultraviolet spectra of nearby metal-poor subdwarfs indicate that oxygen abundances are generally higher than those previously determined. The difference increases with decreasing metallicity and reaches delta([O/Fe]) ~ +0.6 dex as [Fe/H] approaches -3.0. Employing high resolution (R = 50000), high S/N (~ 250) echelle spectra of the two stars found by Israelian et al. (1998) to have the highest [O/Fe]-ratios, viz, BD +23 3130 and BD +37 1458, we conducted abundance analyses based on about 60 Fe I and 7-9 Fe II lines. We determined from Kurucz LTE models the values of the stellar parameters, as well as abundances of Na, Ni, and the traditional alpha-elements, independent of the calibration of color vs $T_{eff}$ scales. We determined oxygen abundances from spectral synthesis of the stronger line (6300 A) of the [O I] doublet. The syntheses of the [O I] line lead to smaller values of [O/Fe], consistent with those found earlier among halo field and globular cluster giants. We obtain [O/Fe] = +0.35 +/- 0.2 for BD +23 3130 and +0.50 +/- 0.2 for BD +37 1458. In the former, the [O I] line is very weak (~ 1 mA), so that the quoted [O/Fe] value may in reality be an upper limit. Therefore in these two stars a discrepancy exists between the [O/Fe]- ratios derived from [O I] and the OH feature, and the origin of this difference remains unclear. Until the matter is clarified, we suggest it is premature to conclude that the ab initio oxygen abundances of old, metal-poor stars need to be revised drastically upward.Comment: 38 pages, 5 tables, 14 figures To appear in July 1999 AJ Updated April 16, 1999. Fixed typo

High Resolution Optical Spectroscopy of the F Supergiant Proto-Planetary Nebula V887 Her=IRAS 18095+2704

An abundance analysis is presented for IRAS 18095+2704 (V887 Her), a post-AGB star and proto-planetary nebula. The analysis is based on high-resolution optical spectra from the McDonald Observatory and the Special Astrophysical Observatory. Standard analysis using a classical Kurucz model atmosphere and the line analysis program MOOG provides the atmospheric parameters: Teff = 6500 K, log g = +0.5, and a microturbulent velocity Vt = 4.7 km/s and [Fe/H] = -0.9. Extraction of these parameters is based on excitation of FeI lines, ionization equilibrium between neutral and ions of Mg, Ca, Ti, Cr, and Fe, and the wings of hydrogen Paschen lines. Elemental abundances are obtained for 22 elements and upper limits for an additional four elements. These results show that the star's atmosphere has not experienced a significant number of C- and s-process enriching thermal pulses. Abundance anomalies as judged relative to the compositions of unevolved and less-evolved normal stars of a similar metallicity include Al, Y, and Zr deficiencies with respect to Fe of about 0.5 dex. Judged by composition, the star resembles a RV Tauri variable that has been mildly affected by dust-gas separation reducing the abundances of the elements of highest condensation temperature. This separation may occur in the stellar wind. There are indications that the standard 1D LTE analysis is not entirely appropriate for IRAS 18095+2704. These include a supersonic macroturbulent velocity of 23 km/s, emission in H-alpha and the failure of predicted profiles to fit observed profiles of H-beta and H-gamma.Comment: Accepted for publication in MNRA

The Hamburg/ESO R-process Enhanced Star survey (HERES) VI. The Galactic Chemical Evolution of Silicon

We determined the silicon abundances of 253 metal-poor stars in the metallicity range $-4<\mathrm{[Fe/H]} <-1.5$, based on non-local thermodynamic equilibrium (NLTE) line formation calculations of neutral silicon and high-resolution spectra obtained with VLT-UT2/UVES. The $T_{\mathrm{eff}}$ dependence of [Si/Fe] noticed in previous investigation is diminished in our abundance analysis due to the inclusion of NLTE effects. An increasing slope of [Si/Fe] towards decreasing metallicity is present in our results, in agreement with Galactic chemical evolution models. The small intrinsic scatter of [Si/Fe] in our sample may imply that these stars formed in a region where the yields of type II supernovae were mixed into a large volume, or that the formation of these stars was strongly clustered, even if the ISM was enriched by single SNa II in a small mixing volume. We identified two dwarfs with $\mathrm{[Si/Fe]}\sim +1.0$: HE 0131$-$3953, and HE 1430$-$1123. These main-sequence turnoff stars are also carbon-enhanced. They might have been pre-enriched by sub-luminous supernovae.Comment: 12 pages, 9 figures, 1 electronical table. Accepted by A &

Chemical Abundances Of Three Metal-Poor Globular Clusters (NGC 6287, NGC 6293, And NGC 6541) In The Inner Halo

We present a chemical abundance study of three inner old halo clusters NGC 6287, NGC 6293, and NGC 6541, finding [Fe/H] = -2.01 +/- 0.05, -1.99 +/- 0.02, and -1.76 +/- 0.02, respectively, and our metallicity measurements are in good agreement with previous estimates. The mean alpha-element abundances of our program clusters are in good agreement with other globular clusters, confirming previous results. However, the individual alpha-elements appear to follow different trends. The silicon abundances of the inner halo clusters appear to be enhanced and the titanium abundances appear to be depleted compared to the intermediate halo clusters. Our results also appear to oppose to those of metal-rich bulge giants studied by McWilliam and Rich, who found that bulge giants are titanium enhanced and silicon deficient. In particular, [Si/Ti] ratios appear to be related to Galactocentric distances,in the sense that [Si/Ti] ratios decrease with Galactocentric distance. We propose that contributions from different masses of the SNe II progenitors that enriched proto-globular cluster clouds' elemental abundances and the different initial physical environments surrounding the proto-globular clusters clouds are responsible for this gradient in [Si/Ti] ratios versus Galactocentric distances of the "old halo" globular clusters. On the other hand, our program clusters' enhanced s-process elemental abundances suggest that the formation timescale of our program clusters might be as short as a few times 10^8 yr after the star formation is initiated in the Galaxy's central regions, if the s-process site is intermediate mass AGB stars.Comment: Accepted for publication in AJ (Sept. 2002