661 research outputs found
The limits of filopodium stability
Filopodia are long, finger-like membrane tubes supported by cytoskeletal
filaments. Their shape is determined by the stiffness of the actin filament
bundles found inside them and by the interplay between the surface tension and
bending rigidity of the membrane. Although one might expect the Euler buckling
instability to limit the length of filopodia, we show through simple energetic
considerations that this is in general not the case. By further analyzing the
statics of filaments inside membrane tubes, and through computer simulations
that capture membrane and filament fluctuations, we show under which conditions
filopodia of arbitrary lengths are stable. We discuss several in vitro
experiments where this kind of stability has already been observed.
Furthermore, we predict that the filaments in long, stable filopodia adopt a
helical shape
Developmental Changes in Sleep Oscillations during Early Childhood
Although quantitative analysis of the sleep electroencephalogram (EEG) has uncovered important aspects of brain activity during sleep in adolescents and adults, similar findings from preschool-age children remain scarce. This study utilized our time-frequency method to examine sleep oscillations as characteristic features of human sleep EEG. Data were collected from a longitudinal sample of young children (n=8; 3 males) at ages 2, 3, and 5 years. Following sleep stage scoring, we detected and characterized oscillatory events across age and examined how their features corresponded to spectral changes in the sleep EEG. Results indicated a developmental decrease in the incidence of delta and theta oscillations. Spindle oscillations, however, were almost absent at 2 years but pronounced at 5 years. All oscillatory event changes were stronger during light sleep than slow-wave sleep. Large interindividual differences in sleep oscillations and their characteristics (e.g., “ultrafast” spindle-like oscillations, theta oscillation incidence/frequency) also existed. Changes in delta and spindle oscillations across early childhood may indicate early maturation of the thalamocortical system. Our analytic approach holds promise for revealing novel types of sleep oscillatory events that are specific to periods of rapid normal development across the lifespan and during other times of aberrant changes in neurobehavioral function
土地家屋調査士のための法律学(1) : 土地家屋調査士の業務
1連載開始に際して 2「弁護士」型業務の獲得 3認定土地家屋調査士 4調査士志望者の減
Complexity Measures from Interaction Structures
We evaluate new complexity measures on the symbolic dynamics of coupled tent
maps and cellular automata. These measures quantify complexity in terms of
-th order statistical dependencies that cannot be reduced to interactions
between units. We demonstrate that these measures are able to identify
complex dynamical regimes.Comment: 11 pages, figures improved, minor changes to the tex
Quantifying structure in networks
We investigate exponential families of random graph distributions as a
framework for systematic quantification of structure in networks. In this paper
we restrict ourselves to undirected unlabeled graphs. For these graphs, the
counts of subgraphs with no more than k links are a sufficient statistics for
the exponential families of graphs with interactions between at most k links.
In this framework we investigate the dependencies between several observables
commonly used to quantify structure in networks, such as the degree
distribution, cluster and assortativity coefficients.Comment: 17 pages, 3 figure
Quantum Oscillations of Photocurrents in HgTe Quantum Wells with Dirac and Parabolic Dispersions
We report on the observation of magneto-oscillations of terahertz radiation
induced photocurrent in HgTe/HgCdTe quantum wells (QWs) of different widths,
which are characterized by a Dirac-like, inverted and normal parabolic band
structure. The photocurrent data are accompanied by measurements of
photoresistance (photoconductivity), radiation transmission, as well as
magneto-transport. We develop a microscopic model of a cyclotron-resonance
assisted photogalvanic effect, which describes main experimental findings. We
demonstrate that the quantum oscillations of the photocurrent are caused by the
crossing of Fermi level by Landau levels resulting in the oscillations of spin
polarization and electron mobilities in spin subbands. Theory explains a
photocurrent direction reversal with the variation of magnetic field observed
in experiment. We describe the photoconductivity oscillations related with the
thermal suppression of the Shubnikov-de Haas effect.Comment: 16 pages, 13 figure
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