946 research outputs found
Incorporating Literacy Props in Preschool Play
During my initial observations of my classroom where I will be conducting my six-week study, I noticed that my preschoolers could be participating in more literacy-related activities as they play in the different centers. It is clear that the preschoolers are engaging in oral language, yet there are many other opportunities for literacy-based play that could be occurring. My goal for this study is to incorporate developmentally appropriate literacy activities into center-based play. I plan to spend six weeks observing in my preschool classroom where I will gather data in the form of observations, field notes, and interviews of preschool teachers. Not only do I want to see how this study effects the development of preschoolers, but I also want to help my preschoolers in their acquisition of emergent literacy skills.
Through their study in a preschool classroom, Morrow and Rand ( 1991) discovered that by incorporating literacy objects into play settings with adult guidance, students were more likely to demonstrate literacy behaviors (p. 400). Therefore through my study, I propose to introduce new literacy materials into the play-based centers of the preschool classroom. I will then observe how the children interact with these materials by recording their behaviors. By gaining more insight into the incorporation of literacy props into play settings, I believe that this study will help me to improve my practice as an educator. In addition, I will also refine my skills as a researcher by learning how to thoroughly analyze data and identify limitations within my study
Modelling, reduction and analysis of Markov automata (extended version)
Markov automata (MA) constitute an expressive continuous-time compositional modelling formalism. They appear as semantic backbones for engineering frameworks including dynamic fault trees, Generalised Stochastic Petri Nets, and AADL. Their expressive power has thus far precluded them from effective analysis by probabilistic (and statistical) model checkers, stochastic game solvers, or analysis tools for Petri net-like formalisms. This paper presents the foundations and underlying algorithms for efficient MA modelling, reduction using static analysis, and most importantly, quantitative analysis. We also discuss implementation pragmatics of supporting tools and present several case studies demonstrating feasibility and usability of MA in practice
Analysis of Timed and Long-Run Objectives for Markov Automata
Markov automata (MAs) extend labelled transition systems with random delays
and probabilistic branching. Action-labelled transitions are instantaneous and
yield a distribution over states, whereas timed transitions impose a random
delay governed by an exponential distribution. MAs are thus a nondeterministic
variation of continuous-time Markov chains. MAs are compositional and are used
to provide a semantics for engineering frameworks such as (dynamic) fault
trees, (generalised) stochastic Petri nets, and the Architecture Analysis &
Design Language (AADL). This paper considers the quantitative analysis of MAs.
We consider three objectives: expected time, long-run average, and timed
(interval) reachability. Expected time objectives focus on determining the
minimal (or maximal) expected time to reach a set of states. Long-run
objectives determine the fraction of time to be in a set of states when
considering an infinite time horizon. Timed reachability objectives are about
computing the probability to reach a set of states within a given time
interval. This paper presents the foundations and details of the algorithms and
their correctness proofs. We report on several case studies conducted using a
prototypical tool implementation of the algorithms, driven by the MAPA
modelling language for efficiently generating MAs.Comment: arXiv admin note: substantial text overlap with arXiv:1305.705
Coupling of Active Motion and Advection Shapes Intracellular Cargo Transport
Intracellular cargo transport can arise from passive diffusion, active
motor-driven transport along cytoskeletal filament networks, and passive
advection by fluid flows entrained by such motor/cargo motion. Active and
advective transport are thus intrinsically coupled as related, yet different
representations of the same underlying network structure. A
reaction-advection-diffusion system is used here to show that this coupling
affects the transport and localization of a passive tracer in a confined
geometry. For sufficiently low diffusion, cargo localization to a target zone
is optimized either by low reaction kinetics and decoupling of bound and
unbound states, or by a mostly disordered cytoskeletal network with only weak
directional bias. These generic results may help to rationalize subtle features
of cytoskeletal networks, for example as observed for microtubules in fly
oocytes.Comment: revtex, 5 pages, 5 figures, to appear in PRL (http://prl.aps.org/
Asymmetric Optical Radiation Pressure Effects on Liquid Interfaces Under Intense Illumination
Deformations of horizontal liquid interfaces by optical radiation pressure
are generally expected to display similar behaviors whatever the direction of
propagation of the exciting laser beam is. In the present experiment we find
this expectation to be borne out, as long as the cw laser illumination is
moderate in strength. However, as a striking contrast in the case of high field
strengths, we find that either a large stable tether can be formed, or else
that a break-up of the interface can occur, depending on whether the laser beam
is upward or downward directed. Physically, the reason for this asymmetry can
be traced to whether total reflection can occur or not. We also present two
simple theoretical models, one based on geometrical optics, the other on wave
optics, that are able to illustrate the essence of the effect. In the case
leading to interface disruption our experimental results are compared with
those obtained by Zhang and Chang for water droplets under intense laser pulses
[Opt. Lett. \textbf{13}, 916 (1988)]. A key point in our experimental
investigations is to work with a near-critical liquid/liquid interface. The
surface tension becomes therefore significantly reduced, which thus enhances
the magnitude of the stationary deformations induced.Comment: 25 pages text, plus 6 figures. Discussion expanded. Submitted to JOSA
3D correlative single-cell imaging utilizing fluorescence and refractive index tomography
Cells alter the path of light, a fact that leads to well-known aberrations in
single cell or tissue imaging. Optical diffraction tomography (ODT) measures
the biophysical property that causes these aberrations, the refractive index
(RI). ODT is complementary to fluorescence imaging and does not require any
markers. The present study introduces RI and fluorescence tomography with
optofluidic rotation (RAFTOR) of suspended cells, quantifying the intracellular
RI distribution and colocalizing it with fluorescence in 3D. The technique is
validated with cell phantoms and used to confirm a lower nuclear RI for HL60
cells. Furthermore, the nuclear inversion of adult mouse photoreceptor cells is
observed in the RI distribution. The applications shown confirm predictions of
previous studies and illustrate the potential of RAFTOR to improve our
understanding of cells and tissues.Comment: 15 pages, 5 figure
The Relative Densities of Cytoplasm and Nuclear Compartments Are Robust against Strong Perturbation
The cell nucleus is a compartment in which essential processes such as gene transcription and DNA replication occur. Although the large amount of chromatin confined in the finite nuclear space could install the picture of a particularly dense organelle surrounded by less dense cytoplasm, recent studies have begun to report the opposite. However, the generality of this newly emerging, opposite picture has so far not been tested. Here, we used combined optical diffraction tomography and epi-fluorescence microscopy to systematically quantify the mass densities of cytoplasm, nucleoplasm, and nucleoli of human cell lines, challenged by various perturbations. We found that the nucleoplasm maintains a lower mass density than cytoplasm during cell cycle progression by scaling its volume to match the increase of dry mass during cell growth. At the same time, nucleoli exhibited a significantly higher mass density than the cytoplasm. Moreover, actin and microtubule depolymerization and changing chromatin condensation altered volume, shape, and dry mass of those compartments, whereas the relative distribution of mass densities was generally unchanged. Our findings suggest that the relative mass densities across membrane-bound and membraneless compartments are robustly conserved, likely by different as-of-yet unknown mechanisms, which hints at an underlying functional relevance. This surprising robustness of mass densities contributes to an increasing recognition of the importance of physico-chemical properties in determining cellular characteristics and compartments
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