3,480 research outputs found
Progressor: Social navigation support through open social student modeling
The increased volumes of online learning content have produced two problems: how to help students to find the most appropriate resources and how to engage them in using these resources. Personalized and social learning have been suggested as potential ways to address these problems. Our work presented in this paper combines the ideas of personalized and social learning in the context of educational hypermedia. We introduce Progressor, an innovative Web-based tool based on the concepts of social navigation and open student modeling that helps students to find the most relevant resources in a large collection of parameterized self-assessment questions on Java programming. We have evaluated Progressor in a semester-long classroom study, the results of which are presented in this paper. The study confirmed the impact of personalized social navigation support provided by the system in the target context. The interface encouraged students to explore more topics attempting more questions and achieving higher success rates in answering them. A deeper analysis of the social navigation support mechanism revealed that the top students successfully led the way to discovering most relevant resources by creating clear pathways for weaker students. © 2013 Taylor and Francis Group, LLC
The Gaseous Extent of Galaxies and the Origin of \lya Absorption Systems. III. Hubble Space Telescope Imaging of \lya-Absorbing Galaxies at z < 1
We present initial results of a program to obtain and analyze HST WFPC2
images of galaxies identified in an imaging and spectroscopic survey of faint
galaxies in fields of HST spectroscopic target QSOs. We measure properties of
87 galaxies, of which 33 are associated with corresponding \lya absorption
systems and 24 do not produce corresponding \lya absorption lines to within
sensitive upper limits. Considering only galaxy and absorber pairs that are
likely to be physically associated and excluding galaxy and absorber pairs
within 3000 \kms of the background QSOs leaves 26 galaxy and absorber pairs and
seven galaxies that do not produce corresponding \lya absorption lines to
within sensitive upper limits. Redshifts of the galaxy and absorber pairs range
from 0.0750 to 0.8912 with a median of 0.3718, and impact parameter separations
of the galaxy and absorber pairs range from 12.4 to kpc with a
median of kpc. The primary result of the analysis is that the
amount of gas encountered along the line of sight depends on the galaxy impact
parameter and B-band luminosity but does not depend strongly on the galaxy
average surface brightness, disk-to-bulge ratio, or redshift. This result
confirms and improves upon the anti-correlation between \lya absorption
equivalent width and galaxy impact parameter found previously by Lanzetta et
al. (1995). There is no evidence that galaxy interactions play an important
role in distributing tenuous gas around galaxies in most cases. Galaxies might
account for all \lya absorption systems with \AA, but this depends on
the unknown luminosity function and gaseous cross sections of low-luminosity
galaxies as well as on the uncertainties of the observed number density of \lya
absorption systems.Comment: Minor changes. Figure 1 stays intact and is available at
ftp://ftp.ess.sunysb.edu/pub/lanzetta/wfpc
QuizMap: Open social student modeling and adaptive navigation support with TreeMaps
In this paper, we present a novel approach to integrate social adaptive navigation support for self-assessment questions with an open student model using QuizMap, a TreeMap-based interface. By exposing student model in contrast to student peers and the whole class, QuizMap attempts to provide social guidance and increase student performance. The paper explains the nature of the QuizMap approach and its implementation in the context of self-assessment questions for Java programming. It also presents the design of a semester-long classroom study that we ran to evaluate QuizMap and reports the evaluation results. © 2011 Springer-Verlag Berlin Heidelberg
Phosphorylation drives a dynamic switch in serine/arginine-rich proteins.
Serine/arginine-rich (SR) proteins are important players in RNA metabolism and are extensively phosphorylated at serine residues in RS repeats. Here, we show that phosphorylation switches the RS domain of the serine/arginine-rich splicing factor 1 from a fully disordered state to a partially rigidified arch-like structure. Nuclear magnetic resonance spectroscopy in combination with molecular dynamics simulations revealed that the conformational switch is restricted to RS repeats, critically depends on the phosphate charge state and strongly decreases the conformational entropy of RS domains. The dynamic switch also occurs in the 100kDa SR-related protein hPrp28, for which phosphorylation at the RS repeat isrequired for spliceosome assembly. Thus, a phosphorylation-induced dynamic switch is common tothe class of serine/arginine-rich proteins and provides a molecular basis for the functional redundancy of serine/arginine-rich proteins and the profound influence of RS domain phosphorylation on protein-protein and protein-RNA interactions
Comprehensive Observations of the Bright and Energetic Type Iax SN 2012Z: Interpretation as a Chandrasekhar Mass White Dwarf Explosion
We present UV through NIR broad-band photometry, and optical and NIR
spectroscopy of Type Iax supernova 2012Z. The data set consists of both early
and late-time observations, including the first late phase NIR spectrum
obtained for a spectroscopically classified SN Iax. Simple model calculations
of its bolometric light curve suggest SN 2012Z produced ~0.3 M_sun of (56)Ni,
ejected about a Chandrasekhar mass of material, and had an explosion energy of
~10^51 erg, making it one of the brightest and most energetic SN Iax yet
observed. The late phase NIR spectrum of SN 2012Z is found to broadly resemble
similar epoch spectra of normal SNe Ia; however, like other SNe Iax,
corresponding visual-wavelength spectra differ substantially compared to all
supernova types. Constraints from the distribution of IMEs, e.g. silicon and
magnesium, indicate that the outer ejecta did not experience significant mixing
during or after burning, and the late phase NIR line profiles suggests most of
the (56)Ni is produced during high density burning. The various observational
properties of SN 2012Z are found to be consistent with the theoretical
expectations of a Chandrasekhar mass white dwarf progenitor that experiences a
pulsational delayed detonation, which produced several tenths of a solar mass
of (56)Ni during the deflagration burning phase and little (or no) (56)Ni
during the detonation phase. Within this scenario only a moderate amount of
Rayleigh-Taylor mixing occurs both during the deflagration and fallback phase
of the pulsation, and the layered structure of the IMEs is a product of the
subsequent denotation phase. The fact that the SNe Iax population does not
follow a tight brightness-decline relation similar to SNe Ia can then be
understood in the framework of variable amounts of mixing during pulsational
rebound and variable amounts of (56)Ni production during the early subsonic
phase of expansion.Comment: Submitted to A&A, manuscript includes response to referee's comments.
39 pages, including 16 figures, 9 table
A New Constraint on the Escape Fraction in Distant Galaxies Using Gamma-ray Burst Afterglow Spectroscopy
We describe a new method to measure the escape fraction fesc of ionizing
radiation from distant star-forming galaxies using the afterglow spectra of
long-duration gamma-ray bursts (GRBs). Optical spectra of GRB afterglows allow
us to evaluate the optical depth of the host ISM, according to the neutral
hydrogen column density N(HI) observed along the sightlines toward the
star-forming regions where the GRBs are found. Different from previous effort
in searching for faint, transmitted Lyman continuum photons, our method is not
subject to background subtraction uncertainties and does not require prior
knowledge of either the spectral shape of the host galaxy population or the IGM
Lya forest absorption along these GRB sightlines. Because most GRBs occur in
sub-L_* galaxies, our study also offers the first constraint on fesc for
distant low-mass galaxies that dominate the cosmic luminosity density. We have
compiled a sample of 27 GRBs at redshift z>2 for which the underlying N(HI) in
the host ISM are known. These GRBs together offer a statistical sampling of the
integrated optical depth to ionizing photons along random sightlines from
star-forming regions in the host galaxies, and allow us to estimate the mean
escape fraction averaged over different viewing angles. We find
=0.02\pm 0.02 and place a 95% c.l. upper limit <= 0.075 for these
hosts. We discuss possible biases of our approach and implications of the
result. Finally, we propose to extend this technique for measuring at
z~0.2 using spectra of core-collapse supernovae.Comment: Five journal pages, including one figure; ApJL in pres
Counterion adsorption on flexible polyelectrolytes: comparison of theories
Counterion adsorption on a flexible polyelectrolyte chain in a spherical
cavity is considered by taking a "permuted" charge distribution on the chain so
that the "adsorbed" counterions are allowed to move along the backbone. We
compute the degree of ionization by using self-consistent field theory (SCFT)
and compare with the previously developed variational theory. Analysis of
various contributions to the free energy in both theories reveals that the
equilibrium degree of ionization is attained mainly as an interplay of the
adsorption energy of counterions on the backbone, the translational entropy of
the small ions, and their correlated density fluctuations. Degree of ionization
computed from SCFT is significantly lower than that from the variational
formalism. The difference is entirely due to the density fluctuations of the
small ions in the system, which are accounted for in the variational procedure.
When these fluctuations are deliberately suppressed in the truncated
variational procedure, there emerges a remarkable quantitative agreement in the
various contributing factors to the equilibrium degree of ionization, in spite
of the fundamental differences in the approximations and computational
procedures used in these two schemes. Nevertheless, since the significant
effects from density fluctuations of small ions are not captured by the SCFT,
and due to the close agreement between SCFT and the other contributing factors
in the more transparent variational procedure, the latter is a better
computational tool for obtaining the degree of ionization
Motivational Social Visualizations for Personalized E-Learning
A large number of educational resources is now available on the Web to support both regular classroom learning and online learning. However, the abundance of available content produces at least two problems: how to help students find the most appropriate resources, and how to engage them into using these resources and benefiting from them. Personalized and social learning have been suggested as potential methods for addressing these problems. Our work presented in this paper attempts to combine the ideas of personalized and social learning. We introduce Progressorâ+â, an innovative Web-based interface that helps students find the most relevant resources in a large collection of self-assessment questions and programming examples. We also present the results of a classroom study of the Progressorâ+â in an undergraduate class. The data revealed the motivational impact of the personalized social guidance provided by the system in the target context. The interface encouraged students to explore more educational resources and motivated them to do some work ahead of the course schedule. The increase in diversity of explored content resulted in improving studentsâ problem solving success. A deeper analysis of the social guidance mechanism revealed that it is based on the leading behavior of the strong students, who discovered the most relevant resources and created trails for weaker students to follow. The study results also demonstrate that students were more engaged with the system: they spent more time in working with self-assessment questions and annotated examples, attempted more questions, and achieved higher success rates in answering them
The Supernova Legacy Survey 3-year sample: Type Ia Supernovae photometric distances and cosmological constraints
We present photometric properties and distance measurements of 252 high
redshift Type Ia supernovae (0.15 < z < 1.1) discovered during the first three
years of the Supernova Legacy Survey (SNLS). These events were detected and
their multi-colour light curves measured using the MegaPrime/MegaCam instrument
at the Canada-France-Hawaii Telescope (CFHT), by repeatedly imaging four
one-square degree fields in four bands. Follow-up spectroscopy was performed at
the VLT, Gemini and Keck telescopes to confirm the nature of the supernovae and
to measure their redshifts. Systematic uncertainties arising from light curve
modeling are studied, making use of two techniques to derive the peak
magnitude, shape and colour of the supernovae, and taking advantage of a
precise calibration of the SNLS fields. A flat LambdaCDM cosmological fit to
231 SNLS high redshift Type Ia supernovae alone gives Omega_M = 0.211 +/-
0.034(stat) +/- 0.069(sys). The dominant systematic uncertainty comes from
uncertainties in the photometric calibration. Systematic uncertainties from
light curve fitters come next with a total contribution of +/- 0.026 on
Omega_M. No clear evidence is found for a possible evolution of the slope
(beta) of the colour-luminosity relation with redshift.Comment: (The SNLS Collaboration) 40 pages, 32 figures, Accepted in A&
Optimizing end-labeled free-solution electrophoresis by increasing the hydrodynamic friction of the drag-tag
We study the electrophoretic separation of polyelectrolytes of varying
lengths by means of end-labeled free-solution electrophoresis (ELFSE). A
coarse-grained molecular dynamics simulation model, using full electrostatic
interactions and a mesoscopic Lattice Boltzmann fluid to account for
hydrodynamic interactions, is used to characterize the drag coefficients of
different label types: linear and branched polymeric labels, as well as
transiently bound micelles.
It is specifically shown that the label's drag coefficient is determined by
its hydrodynamic size, and that the drag per label monomer is largest for
linear labels. However, the addition of side chains to a linear label offers
the possibility to increase the hydrodynamic size, and therefore the label
efficiency, without having to increase the linear length of the label, thereby
simplifying synthesis. The third class of labels investigated, transiently
bound micelles, seems very promising for the usage in ELFSE, as they provide a
significant higher hydrodynamic drag than the other label types.
The results are compared to theoretical predictions, and we investigate how
the efficiency of the ELFSE method can be improved by using smartly designed
drag-tags.Comment: 32 pages, 11 figures, submitted to Macromolecule
- âŠ