145 research outputs found
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
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 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
-values of Garz corrected for the Becker et al.'s measurement is . Combined with an extended line sample with selected NIST -values, the
solar abundance is , 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 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 , based on non-local thermodynamic
equilibrium (NLTE) line formation calculations of neutral silicon and
high-resolution spectra obtained with VLT-UT2/UVES. The
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
: HE 01313953, and HE 14301123. 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
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