4,300 research outputs found
Spatial Organization of the Cytoskeleton enhances Cargo Delivery to Specific Target Areas on the Plasma Membrane of Spherical Cells
Intracellular transport is vital for the proper functioning and survival of a
cell. Cargo (proteins, vesicles, organelles, etc.) is transferred from its
place of creation to its target locations via molecular motor assisted
transport along cytoskeletal filaments. The transport efficiency is strongly
affected by the spatial organization of the cytoskeleton, which constitutes an
inhomogeneous, complex network. In cells with a centrosome microtubules grow
radially from the central microtubule organizing center towards the cell
periphery whereas actin filaments form a dense meshwork, the actin cortex,
underneath the cell membrane with a broad range of orientations. The emerging
ballistic motion along filaments is frequently interrupted due to constricting
intersection nodes or cycles of detachment and reattachment processes in the
crowded cytoplasm. In order to investigate the efficiency of search strategies
established by the cell's specific spatial organization of the cytoskeleton we
formulate a random velocity model with intermittent arrest states. With
extensive computer simulations we analyze the dependence of the mean first
passage times for narrow escape problems on the structural characteristics of
the cytoskeleton, the motor properties and the fraction of time spent in each
state. We find that an inhomogeneous architecture with a small width of the
actin cortex constitutes an efficient intracellular search strategy.Comment: 14 pages, 9 figure
Generalized van der Waals theory of liquid-liquid phase transitions
In the framework of the thermodynamic perturbation theory for fluids we study
how the phase diagram of an isotropic repulsive soft-core attractive potential,
where a liquid-liquid phase transition exists in addition to the standard
gas-liquid phase transition, changes by varying the parameters of the
potential. We show that existence of the liquid-liquid transition is determined
by the interplay of the parameters of the potential and the structure of a
reference liquid.Comment: 5 pages, 6 figure
Black Students Get an Edge in Reading
The purpose of this article is not so much to report that minority children are having trouble in learning to read all kinds of children are for that matter·· but to point out that with the proper kind of instruction black children can do as well as other children. Consider briefly the findings of a few research studies documenting contentions about the reading acquisition problems that numbers of black children have
Super-resolution imaging and estimation of protein copy numbers at single synapses with DNA-PAINT
In the brain, the strength of each individual synapse is defined by the complement of proteins present or the "local proteome." Activity-dependent changes in synaptic strength are the result of changes in this local proteome and posttranslational protein modifications. Although most synaptic proteins have been identified, we still know little about protein copy numbers in individual synapses and variations between synapses. We use DNA-point accumulation for imaging in nanoscale topography as a single-molecule super-resolution imaging technique to visualize and quantify protein copy numbers in single synapses. The imaging technique provides near-molecular spatial resolution, is unaffected by photobleaching, enables imaging of large field of views, and provides quantitative molecular information. We demonstrate these benefits by accessing copy numbers of surface AMPA-type receptors at single synapses of rat hippocampal neurons along dendritic segments
Temporal and spatial dynamics of competitive parapatry in chewing lice
We synthesize observations from 1979 to 2016 of a contact zone involving two subspecies of pocket gophers (Thomomys bottae connectens and T. b. opulentus) and their respective chewing lice (Geomydoecus aurei and G. centralis) along the Rio Grande Valley in New Mexico, U.S.A., to test predictions about the dynamics of the zone. Historically, the natural flood cycle of the Rio Grande prevented contact between the two subspecies of pocket gophers. Flood control measures completed in the 1930s permitted contact, thus establishing the hybrid zone between the pocket gophers and the contact zone between their lice (without hybridization). Since that time, the pocket gopher hybrid zone has stabilized, whereas the northern chewing louse species has replaced the southern louse species at a consistent rate of similar to 150 m/year. The 0.2-0.8 width of the replacement zone has remained constant, reflecting the constant rate of chewing louse species turnover on a single gopher and within a local pocket gopher population. In contrast, the full width of the replacement zone (northernmost G. centralis to southernmost G. aurei) has increased annually. By employing a variety of metrics of the species replacement zone, we are better able to understand the dynamics of interactions between and among the chewing lice and their pocket gopher hosts. This research provides an opportunity to observe active species replacement and resulting distributional shifts in a parasitic organism in its natural setting
Implications of Piagetian Theory for Correlating Art and Reading
Piaget tells us that we know something to the extent that we act on it. Because art facilitates the right kinds of action for knowing, or learning, correlating art and reading may well be the vehicle to growth in and enjoyment of communication skills. Therefore, art not only contributes to reading development but also contributes to both the cognitive and the affective development needed for success in all academic areas
Spin configuration in a frustrated ferromagnetic/antiferromagnetic thin film system
We have studied the magnetic configuration in ultrathin antiferromagnetic Mn
films grown around monoatomic steps on an Fe(001) surface by spin-polarized
scanning tunneling microscopy/spectroscopy and ab-initio-parametrized
self-consistent real-space tight binding calculations in which the spin
quantization axis is independent for each site thus allowing noncollinear
magnetism. Mn grown on Fe(001) presents a layered antiferromagnetic structure.
In the regions where the Mn films overgrows Fe steps the magnetization of the
surface layer is reversed across the steps. Around these defects a frustration
of the antiferromagnetic order occurs. Due to the weakened magnetic coupling at
the central Mn layers, the amount of frustration is smaller than in Cr and the
width of the wall induced by the step does not change with the thickness, at
least for coverages up to seven monolayers.Comment: 10 pages, 5 figure
Structural Properties and Relative Stability of (Meta)Stable Ordered, Partially-ordered and Disordered Al-Li Alloy Phases
We resolve issues that have plagued reliable prediction of relative phase
stability for solid-solutions and compounds. Due to its commercially important
phase diagram, we showcase Al-Li system because historically density-functional
theory (DFT) results show large scatter and limited success in predicting the
structural properties and stability of solid-solutions relative to ordered
compounds. Using recent advances in an optimal basis-set representation of the
topology of electronic charge density (and, hence, atomic size), we present DFT
results that agree reasonably well with all known experimental data for the
structural properties and formation energies of ordered, off-stoichiometric
partially-ordered and disordered alloys, opening the way for reliable study in
complex alloys.Comment: 7 pages, 2 figures, 2 Table
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