980 research outputs found
Knockouts, Robustness and Cell Cycles
The response to a knockout of a node is a characteristic feature of a
networked dynamical system. Knockout resilience in the dynamics of the
remaining nodes is a sign of robustness. Here we study the effect of knockouts
for binary state sequences and their implementations in terms of Boolean
threshold networks. Beside random sequences with biologically plausible
constraints, we analyze the cell cycle sequence of the species Saccharomyces
cerevisiae and the Boolean networks implementing it. Comparing with an
appropriate null model we do not find evidence that the yeast wildtype network
is optimized for high knockout resilience. Our notion of knockout resilience
weakly correlates with the size of the basin of attraction, which has also been
considered a measure of robustness.Comment: 11 pages, 3 figures, 3 table
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
Orbital photogalvanic effects in quantum-confined structures
We report on the circular and linear photogalvanic effects caused by
free-carrier absorption of terahertz radiation in electron channels on
(001)-oriented and miscut silicon surfaces. The photocurrent behavior upon
variation of the radiation polarization state, wavelength, gate voltage and
temperature is studied. We present the microscopical and phenomenological
theory of the photogalvanic effects, which describes well the experimental
results. In particular, it is demonstrated that the circular (photon-helicity
sensitive) photocurrent in silicon-based structures is of pure orbital nature
originating from the quantum interference of different pathways contributing to
the absorption of monochromatic radiation.Comment: 8 pages, 5 figures, two culumne
Photoexcitation of valley-orbit currents in (111)-oriented silicon metal-oxide-semiconductor field-effect transistors
We demonstrate the injection of pure valley-orbit currents in multivalley semiconductors and present the phenomenological theory of this effect. We studied photoinduced transport in (111)-oriented silicon metaloxide-semiconductor field effect transistors at room temperature. By shining circularly polarized light on exact oriented structures with six equivalent valleys, nonzero electron fluxes within each valley are generated, which
compensate each other and do not yield a net electric current. By disturbing the balance between the valley fluxes, we demonstrate that the pure valley-orbit currents can be converted into a measurable electric current
Predicting sex from brain rhythms with deep learning
We have excellent skills to extract sex from visual assessment of human faces, but assessing sex from human brain rhythms seems impossible. Using deep convolutional neural networks, with unique potential to find subtle differences in apparent similar patterns, we explore if brain rhythms from either sex contain sex specific information. Here we show, in a ground truth scenario, that a deep neural net can predict sex from scalp electroencephalograms with an accuracy of >80% (p < 10-5), revealing that brain rhythms are sex specific. Further, we extracted sex-specific features from the deep net filter layers, showing that fast beta activity (20-25 Hz) and its spatial distribution is a main distinctive attribute. This demonstrates the ability of deep nets to detect features in spatiotemporal data unnoticed by visual assessment, and to assist in knowledge discovery. We anticipate that this approach may also be successfully applied to other specialties where spatiotemporal data is abundant, including neurology, cardiology and neuropsychology
Chaos or Noise - Difficulties of a Distinction
In experiments, the dynamical behavior of systems is reflected in time
series. Due to the finiteness of the observational data set it is not possible
to reconstruct the invariant measure up to arbitrary fine resolution and
arbitrary high embedding dimension. These restrictions limit our ability to
distinguish between signals generated by different systems, such as regular,
chaotic or stochastic ones, when analyzed from a time series point of view. We
propose to classify the signal behavior, without referring to any specific
model, as stochastic or deterministic on a certain scale of the resolution
, according to the dependence of the -entropy,
, and of the finite size Lyapunov exponent,
, on .Comment: 24 pages RevTeX, 9 eps figures included, two references added, minor
corrections, one section has been split in two (submitted to PRE
Helicity sensitive terahertz radiation detection by dual-grating-gate high electron mobility transistors
We report on the observation of a radiation helicity sensitive photocurrent
excited by terahertz (THz) radiation in dual-grating-gate (DGG)
InAlAs/InGaAs/InAlAs/InP high electron mobility transistors (HEMT). For a
circular polarization the current measured between source and drain contacts
changes its sign with the inversion of the radiation helicity. For elliptically
polarized radiation the total current is described by superposition of the
Stokes parameters with different weights. Moreover, by variation of gate
voltages applied to individual gratings the photocurrent can be defined either
by the Stokes parameter defining the radiation helicity or those for linear
polarization. We show that artificial non-centrosymmetric microperiodic
structures with a two-dimensional electron system excited by THz radiation
exhibit a dc photocurrent caused by the combined action of a spatially periodic
in-plane potential and spatially modulated light. The results provide a proof
of principle for the application of DGG HEMT for all-electric detection of the
radiation's polarization state.Comment: 7 pages, 4 figure
Photon helicity driven electric currents in graphene
We report on the observation of photon helicity driven currents in graphene.
The directed net electric current is generated in single layer graphene by
circularly polarized terahertz laser radiation at normal as well as at oblique
incidence and changes its sign upon reversing the radiation helicity. The
phenomenological and microscopic theories of the observed photocurrents are
developed. We demonstrate that under oblique incidence the current is caused by
the circular photon drag effect in the interior of graphene sheet. By contrast,
the effect at normal incidence stems from the sample edges, which reduce the
symmetry and result in an asymmetric scattering of carriers driven by the
radiation field. Besides a photon helicity dependent current we also observe
photocurrents in response to linearly polarized radiation. The microscopic
mechanisms governing this effect are discussed.Comment: 13 pages, 7 figure
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