1,323 research outputs found
Literacy practices of primary education children in Andalusia (Spain): a family-based perspective
Primary school children develop literacy practices in various domains and situations in everyday life.
This study focused on the analysis of literacy practices of children aged 8–12 years from the perspec-
tive of their families. 1,843 families participated in the non-experimental explanatory study. The
children in these families speak Spanish as a first language and are schooled in this language. The
instrument used was a self-report questionnaire about children’s home-literacy practices. The data
obtained were analysed using categorical principal components analysis (CATPCA) and analysis of
variance (ANOVA). The results show the complex relationship between literacy practices developed
by children in the domains of home and school and the limited development of a literacy-promoting
‘third space’. In conclusion, the families in our study had limited awareness of their role as literacy-
promoting agents and thought of literacy learning as restricted to formal or academic spaces
The Boltzmann factor, DNA melting, and Brownian ratchets: Topics in an introductory physics sequence for biology and premedical students
Three, interrelated biologically-relevant examples of biased random walks are
presented: (1) A model for DNA melting, modelled as DNA unzipping, which
provides a way to illustrate the role of the Boltzmann factor in a venue
well-known to biology and pre-medical students; (2) the activity of helicase
motor proteins in unzipping double-stranded DNA, for example, at the
replication fork, which is an example of a Brownian ratchet; (3) force
generation by actin polymerization, which is another Brownian ratchet, and for
which the force and actin-concentration dependence of the velocity of actin
polymerization is determined
Quantitative phase-field modeling of solidification at high Lewis number
A phase-field model of nonisothermal solidification in dilute binary alloys is used to study the variation of growth velocity, dendrite tip radius, and radius selection parameter as a function of Lewis number at fixed undercooling. By the application of advanced numerical techniques, we have been able to extend the analysis to Lewis numbers of order 10 000, which are realistic for metals. A large variation in the radius selection parameter is found as the Lewis number is increased from 1 to 10 000
Phase field analysis of eutectic breakdown.
In this paper an isotropic multi-phase-field model is extended to include the effects of anisotropy and the spontaneous nucleation of an absent phase. This model is derived and compared against a published single phase model. Results from this model are compared against results from other multi-phase models, additionally this model is used to examine the break down of a regular two dimensional eutectic into a single phase dendritic front
Hubble Space Telescope Weak-lensing Study of the Galaxy Cluster XMMU J2235.3-2557 at z=1.4: A Surprisingly Massive Galaxy Cluster when the Universe is One-third of its Current Age
We present a weak-lensing analysis of the z=1.4 galaxy cluster XMMU
J2235.3-2557, based on deep Advanced Camera for Surveys images. Despite the
observational challenge set by the high redshift of the lens, we detect a
substantial lensing signal at the >~ 8 sigma level. This clear detection is
enabled in part by the high mass of the cluster, which is verified by our both
parametric and non-parametric estimation of the cluster mass. Assuming that the
cluster follows a Navarro-Frenk-White mass profile, we estimate that the
projected mass of the cluster within r=1 Mpc is (8.5+-1.7) x 10^14 solar mass,
where the error bar includes the statistical uncertainty of the shear profile,
the effect of possible interloping background structures, the scatter in
concentration parameter, and the error in our estimation of the mean redshift
of the background galaxies. The high X-ray temperature 8.6_{-1.2}^{+1.3} keV of
the cluster recently measured with Chandra is consistent with this high lensing
mass. When we adopt the 1-sigma lower limit as a mass threshold and use the
cosmological parameters favored by the Wilkinson Microwave Anisotropy Probe
5-year (WMAP5) result, the expected number of similarly massive clusters at z
>~ 1.4 in the 11 square degree survey is N ~ 0.005. Therefore, the discovery of
the cluster within the survey volume is a rare event with a probability < 1%,
and may open new scenarios in our current understanding of cluster formation
within the standard cosmological model.Comment: Accepted to ApJ for publication. 40 pages and 14 figure
Simulations of three-dimensional dendritic growth using a coupled thermo-solutal phase-field model
Using a phase field model, which fully couples the thermal and solute concentration field, we present simulation results in three dimensions of the rapid dendritic solidification of a class of dilute alloys at the meso scale. The key results are the prediction of steady state tip velocity and radius at varying undercooling and thermal diffusivities. Less computationally demanding 2-dimensional results are directly compared with the corresponding 3-dimensional results, where significant quantitative differences emerge. The simulations provide quantitative predictions for the range of thermal and solutal diffusivities considered and show the effectiveness and potential of the computational techniques employed. These results thus provide benchmark 3-dimensional computations, allow direct comparison with underlying analytical theory, and pave the way for further quantitative results
Multi-wavelength study of XMMU J2235.3-2557: the most massive galaxy cluster at z > 1
[Abridged] XMMU J2235.3-2557 is one of the most distant X-ray selected
clusters, spectroscopically confirmed at z=1.39. We characterize the galaxy
populations of passive members, the thermodynamical properties of the hot gas,
its metal abundance and the total mass of the system using imaging data with
HST/ACS (i775 and z850 bands) and VLT/ISAAC (J and K_s bands), extensive
spectroscopic data obtained with VLT/FORS2, and deep Chandra observations. Out
of a total sample of 34 spectroscopically confirmed cluster members, we
selected 16 passive galaxies within the central 2' (or 1 Mpc) with ACS
coverage, and inferred star formation histories for a sub-sample of galaxies
inside and outside the core by modeling their spectro-photometric data with
spectral synthesis models, finding a strong mean age radial gradient. Chandra
data show a regular elongated morphology, closely resembling the distribution
of core galaxies, with a significant cool core. We measure a global X-ray
temperature of kT=8.6(-1.2,+1.3) keV (68% c.l.). By detecting the rest-frame
6.7 keV Iron K line, we measure a metallicty Z= 0.26(+0.20,-0.16) Zsun. In the
likely hypothesis of hydrostatic equilibrium, we obtain a total mass of Mtot(<1
Mpc)=(5.9+-1.3)10^14 Msun. Overall, our analysis implies that XMM2235 is the
hottest and most massive bona-fide cluster discovered to date at z>1, with a
baryonic content, both its galaxy population and intra-cluster gas, in a
significantly advanced evolutionary stage at 1/3 of the current age of the
Universe.Comment: 9 pages, 8 figures, accepted for publication in A&A (v2:
typos/language style corrections, updated references
Witnessing the formation of a brightest cluster galaxy at z>2
We present deep observations taken with the HST Advanced Camera for Surveys
of the central massive galaxy in a forming cluster at z=2.2. The galaxy hosting
the powerful radio source MRC 1138-262 is associated with one of the most
extensive merger systems known in the early universe. Our HST/ACS image shows
many star-forming galaxies merging within a ~200 kpc region that emits both
diffuse line emission and continuum in the rest-frame UV. Because this galaxy
lives in an overdense environment, it represents a rare view of a brightest
cluster galaxy in formation at z>2 which may serve as a testbed for predictions
of massive cluster galaxy formation.Comment: Contribution to the proceedings of "The Fate of Gas in Galaxies",
Dwingeloo, July 2006, with 2 colour figures. To appear in New Astronomy
Reviews, Vol. 51 (2007), eds. Morganti, Oosterloo, Villar-Martin & van Gorko
Bubble dynamics in DNA
The formation of local denaturation zones (bubbles) in double-stranded DNA is
an important example for conformational changes of biological macromolecules.
We study the dynamics of bubble formation in terms of a Fokker-Planck equation
for the probability density to find a bubble of size n base pairs at time t, on
the basis of the free energy in the Poland-Scheraga model. Characteristic
bubble closing and opening times can be determined from the corresponding first
passage time problem, and are sensitive to the specific parameters entering the
model. A multistate unzipping model with constant rates recently applied to DNA
breathing dynamics [G. Altan-Bonnet et al, Phys. Rev. Lett. 90, 138101 (2003)]
emerges as a limiting case.Comment: 9 pages, 2 figure
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