295 research outputs found
Language Policy and the Preparedness of Mainstream Teachers for Serving ELs in K-12 Classrooms
English language learners (ELs) numbers are increasing steadily in classrooms across the United States. Some southeastern states have seen more than a 200% EL student increase in recent years (Migration Policy Institute, 2010). Since the inception of No Child Left Behind (NCLB) and especially since Title I “flexibility” revisions, responsibility for educating ELs has shifted from ESOL and bilingual teachers to primarily mainstream teachers. States that have opted out of NCLB under flexibility revisions are no longer as accountable to the U. S. Department of Education for the education of ELs. States and school districts are no longer required to include some EL test scores in accountability measures. Mainstream classroom teachers may no longer receive quality support from ESOL professionals in educating mainstreamed ELs. Are mainstream teachers prepared to educate ELs? This study examines the perceptions that mainstream classroom teachers have regarding their preparedness in serving the ELs in their classrooms. Findings indicated four emergent categories of mainstream teachers: 1) teachers who knew virtually nothing about serving ELs, 2) teachers who presumed they would send ELs out of their classroom for instruction and assessment, 3) teachers who sought instructional and assessment assistance, and 4) teachers who were familiar with best practices for teaching ELs. Mainstream teachers in this study who were being held accountable for EL student achievement overall lacked knowledge or had misconceptions about the strategies used to teach and assess ELs. Current policy shaping the education of ELs is unlikely to assure they receive an adequate education
Systematic variation of central mass density slope in early-type galaxies
We study the total density distribution in the central regions (
effective radius, ) of early-type galaxies (ETGs), using data from
the SPIDER survey. We model each galaxy with two components (dark matter halo +
stars), exploring different assumptions for the dark matter (DM) halo profile,
and leaving stellar mass-to-light () ratios as free fitting
parameters to the data. For a Navarro et al. (1996) profile, the slope of the
total mass profile is non-universal. For the most massive and largest ETGs, the
profile is isothermal in the central regions (), while for
the low-mass and smallest systems, the profile is steeper than isothermal, with
slopes similar to those for a constant-M/L profile. For a concentration-mass
relation steeper than that expected from simulations, the correlation of
density slope with mass tends to flatten. Our results clearly point to a
"non-homology" in the total mass distribution of ETGs, which simulations of
galaxy formation suggest may be related to a varying role of dissipation with
galaxy mass.Comment: 3 pages, 1 figure, to appear on the refereed Proceeding of the "The
Universe of Digital Sky Surveys" conference held at the INAF--OAC, Naples, on
25th-28th november 2014, to be published on Astrophysics and Space Science
Proceedings, edited by Longo, Napolitano, Marconi, Paolillo, Iodic
Plasma lensing of a laser wakefield accelerated electron bunch
We report on the first all-optical demonstration of
plasma lensing using laser wakefield accelerated
elec-trons in a two-stage setup. The LWFA electron
bunch was focused by a second plasma stage without
any ex-ternal fields applied..
Demonstration of passive plasma lensing of a laser wakefield accelerated electron bunch
We report on the first demonstration of passive all-optical plasma lensing using a two-stage setup. An intense femtosecond laser accelerates electrons in a laser wakefield accelerator (LWFA) to 100 MeV over millimeter length scales. By adding a second gas target behind the initial LWFA stage we introduce a robust and independently tunable plasma lens. We observe a density dependent reduction of the LWFA electron beam divergence from an initial value of 2.3 mrad, down to 1.4 mrad (rms), when the plasma lens is in operation. Such a plasma lens provides a simple and compact approach for divergence reduction well matched to the mm-scale length of the LWFA accelerator. The focusing forces are provided solely by the plasma and driven by the bunch itself only, making this a highly useful and conceptually new approach to electron beam focusing. Possible applications of this lens are not limited to laser plasma accelerators. Since no active driver is needed the passive plasma lens is also suited for high repetition rate focusing of electron bunches. Its understanding is also required for modeling the evolution of the driving particle bunch in particle driven wake field acceleration
Probability distributed time delays: integrating spatial effects into temporal models
Background: In order to provide insights into the complex biochemical processes inside a cell, modelling approaches must find a balance between achieving an adequate representation of the physical phenomena and keeping the associated computational cost within reasonable limits. This issue is particularly stressed when spatial inhomogeneities have a significant effect on system's behaviour. In such cases, a spatially-resolved stochastic method can better portray the biological reality, but the corresponding computer simulations can in turn be prohibitively expensive.Results: We present a method that incorporates spatial information by means of tailored, probability distributed time-delays. These distributions can be directly obtained by single in silico or a suitable set of in vitro experiments and are subsequently fed into a delay stochastic simulation algorithm (DSSA), achieving a good compromise between computational costs and a much more accurate representation of spatial processes such as molecular diffusion and translocation between cell compartments. Additionally, we present a novel alternative approach based on delay differential equations (DDE) that can be used in scenarios of high molecular concentrations and low noise propagation.Conclusions: Our proposed methodologies accurately capture and incorporate certain spatial processes into temporal stochastic and deterministic simulations, increasing their accuracy at low computational costs. This is of particular importance given that time spans of cellular processes are generally larger (possibly by several orders of magnitude) than those achievable by current spatially-resolved stochastic simulators. Hence, our methodology allows users to explore cellular scenarios under the effects of diffusion and stochasticity in time spans that were, until now, simply unfeasible. Our methodologies are supported by theoretical considerations on the different modelling regimes, i.e. spatial vs. delay-temporal, as indicated by the corresponding Master Equations and presented elsewhere
Exact Product Formation Rates for Stochastic Enzyme Kinetics
The
rate of product formation is an important measure of the speed
of enzyme reactions. Classical studies of enzyme reactions have been
conducted in dilute solutions and under conditions that justified
the substrate abundance assumption. However, such assumption is well-known
to break down in the context of cellular biochemistry. Instead, the
concentration of available substrate can become rate limiting. Here
we use the chemical master equation to obtain expressions for the
instantaneous and time averaged rate of product formation without
invoking the conventional substrate abundance assumption. The expressions
are derived for a broad range of enzyme reaction mechanisms, including
those that involve one or many enzyme molecules, require multiple
substrates, and exhibit cooperativity and substrate inhibition. Novel
results include: (i) the relationship between the average rate of
product formation (calculated over the time it takes for the reaction
to finish) and the substrate concentration, for a Michaelis–Menten
(MM) reaction with one enzyme molecule, is approximately given by
a logarithmically corrected MM form; (ii) intrinsic noise decreases
the sharpness of cooperative switches but enhances the filtering response
of substrate inhibition; (iii) the relationship between the initial
average rate of product formation and the initial substrate concentration
for a MM reaction with no reversible reaction and with any number
of enzyme and substrate molecules is a sum of Michaelis–Menten
equations
Detection of Atmospheric Muon Neutrinos with the IceCube 9-String Detector
The IceCube neutrino detector is a cubic kilometer TeV to PeV neutrino
detector under construction at the geographic South Pole. The dominant
population of neutrinos detected in IceCube is due to meson decay in cosmic-ray
air showers. These atmospheric neutrinos are relatively well-understood and
serve as a calibration and verification tool for the new detector. In 2006, the
detector was approximately 10% completed, and we report on data acquired from
the detector in this configuration. We observe an atmospheric neutrino signal
consistent with expectations, demonstrating that the IceCube detector is
capable of identifying neutrino events. In the first 137.4 days of livetime,
234 neutrino candidates were selected with an expectation of 211 +/-
76.1(syst.) +/- 14.5(stat.) events from atmospheric neutrinos
- …