3,555 research outputs found
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
Multipole nonlinearity of metamaterials
We report on the linear and nonlinear optical response of metamaterials
evoked by first and second order multipoles. The analytical ground on which our
approach bases permits for new insights into the functionality of
metamaterials. For the sake of clarity we focus here on a key geometry, namely
the split-ring resonator, although the introduced formalism can be applied to
arbitrary structures. We derive the equations that describe linear and
nonlinear light propagation where special emphasis is put on second harmonic
generation. This contribution basically aims at stretching versatile and
existing concepts to describe light propagation in nonlinear media towards the
realm of metamaterials.Comment: 7 pages, 3 figure
Phase Separation in Charge-Stabilized Colloidal Suspensions: Influence of Nonlinear Screening
The phase behavior of charge-stabilized colloidal suspensions is modeled by a
combination of response theory for electrostatic interparticle interactions and
variational theory for free energies. Integrating out degrees of freedom of the
microions (counterions, salt ions), the macroion-microion mixture is mapped
onto a one-component system governed by effective macroion interactions. Linear
response of microions to the electrostatic potential of the macroions results
in a screened-Coulomb (Yukawa) effective pair potential and a one-body volume
energy, while nonlinear response modifies the effective interactions [A. R.
Denton, \PR E {\bf 70}, 031404 (2004)]. The volume energy and effective pair
potential are taken as input to a variational free energy, based on
thermodynamic perturbation theory. For both linear and first-order nonlinear
effective interactions, a coexistence analysis applied to aqueous suspensions
of highly charged macroions and monovalent microions yields bulk separation of
macroion-rich and macroion-poor phases below a critical salt concentration, in
qualitative agreement with predictions of related linearized theories [R. van
Roij, M. Dijkstra, and J.-P. Hansen, \PR E {\bf 59}, 2010 (1999); P. B. Warren,
\JCP {\bf 112}, 4683 (2000)]. It is concluded that nonlinear screening can
modify phase behavior but does not necessarily suppress bulk phase separation
of deionized suspensions.Comment: 14 pages of text + 9 figure
Sound modes broadening for Fibonacci one dimensional quasicrystals
We investigate vibrational excitation broadening in one dimensional Fibonacci
model of quasicrystals (QCs). The chain is constructed from particles with two
masses following the Fibonacci inflation rule. The eigenmode spectrum depends
crucially on the mass ratio. We calculate the eigenstates and eigenfunctions.
All calculations performed self-consistently within the regular expansion over
the three wave coupling constant. The approach can be extended to three
dimensional systems. We find that in the intermediate range of mode coupling
constants, three-wave broadening for the both types of systems (1D Fibonacci
and 3D QCs) depends universally on frequency. Our general qualitative
conclusion is that for a system with a non-simple elementary cell phonon
spectrum broadening is always larger than for a system with a primitive cell
(provided all other characteristics are the same).Comment: 2o pages, 15 figure
How mRNA localization and protein synthesis sites influence dendritic protein distribution and dynamics
In this issue ofNeuron,Fonkeu et al. (2019)present a mathematical model of mRNA and protein synthesis,degradation, diffusion, and trafficking in neuronal dendrites. The model can predict the spatial distributionand temporal dynamics of proteins along dendrites. The authors use the model to account forin situimagingdata of CaMKII⍺mRNA and protein in hippocampal neurons
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