298 research outputs found
The fission yeast FANCM ortholog directs non-crossover recombination during meiosis
Peer reviewedPostprin
Locally induced quantum interference in scanning gate experiments
We present conductance measurements of a ballistic circular stadium
influenced by a scanning gate. When the tip depletes the electron gas below, we
observe very pronounced and regular fringes covering the entire stadium. The
fringes correspond to transmitted modes in constrictions formed between the
tip-induced potential and the boundaries of the stadium. Moving the tip and
counting the fringes gives us exquisite control over the transmission of these
constrictions. We use this control to form a quantum ring with a specific
number of modes in each arm showing the Aharonov-Bohm effect in low-field
magnetoconductance measurements.Comment: 10 pages, 4 figure
Scanning-gate-induced effects and spatial mapping of a cavity
Tailored electrostatic potentials are the foundation of scanning gate
microscopy. We present several aspects of the tip-induced potential on the
two-dimensional electron gas. First, we give methods on how to estimate the
size of the tip-induced potential. Then, a ballistic cavity is formed and
studied as a function of the bias-voltage of the metallic top gates and probed
with the tip-induced potential. It is shown how the potential of the cavity
changes by tuning the system to a regime where conductance quantization in the
constrictions formed by the tip and the top gates occurs. This conductance
quantization leads to a unprecedented rich fringe pattern over the entire
structure. Finally, the effect of electrostatic screening of the metallic top
gates is discussed.Comment: 10 pages, 6 figure
Nonlinear Dynamics in Gene Regulation Promote Robustness and Evolvability of Gene Expression Levels
This is the final version of the article. Available from Public Library of Science via the DOI in this record.Cellular phenotypes underpinned by regulatory networks need to respond to evolutionary pressures to allow adaptation, but at the same time be robust to perturbations. This creates a conflict in which mutations affecting regulatory networks must both generate variance but also be tolerated at the phenotype level. Here, we perform mathematical analyses and simulations of regulatory networks to better understand the potential trade-off between robustness and evolvability. Examining the phenotypic effects of mutations, we find an inverse correlation between robustness and evolvability that breaks only with nonlinearity in the network dynamics, through the creation of regions presenting sudden changes in phenotype with small changes in genotype. For genotypes embedding low levels of nonlinearity, robustness and evolvability correlate negatively and almost perfectly. By contrast, genotypes embedding nonlinear dynamics allow expression levels to be robust to small perturbations, while generating high diversity (evolvability) under larger perturbations. Thus, nonlinearity breaks the robustness-evolvability trade-off in gene expression levels by allowing disparate responses to different mutations. Using analytical derivations of robustness and system sensitivity, we show that these findings extend to a large class of gene regulatory network architectures and also hold for experimentally observed parameter regimes. Further, the effect of nonlinearity on the robustness-evolvability trade-off is ensured as long as key parameters of the system display specific relations irrespective of their absolute values. We find that within this parameter regime genotypes display low and noisy expression levels. Examining the phenotypic effects of mutations, we find an inverse correlation between robustness and evolvability that breaks only with nonlinearity in the network dynamics. Our results provide a possible solution to the robustness-evolvability trade-off, suggest an explanation for the ubiquity of nonlinear dynamics in gene expression networks, and generate useful guidelines for the design of synthetic gene circuits.This work was funded by the UK Engineering and Physical Sciences Research Council, grant number EP/I017445/1
Scanning gate experiments: from strongly to weakly invasive probes
An open resonator fabricated in a two-dimensional electron gas is used to
explore the transition from strongly invasive scanning gate microscopy to the
perturbative regime of weak tip-induced potentials. With the help of numerical
simulations that faithfully reproduce the main experimental findings, we
quantify the extent of the perturbative regime in which the tip-induced
conductance change is unambiguously determined by properties of the unperturbed
system. The correspondence between the experimental and numerical results is
established by analyzing the characteristic length scale and the amplitude
modulation of the conductance change. In the perturbative regime, the former is
shown to assume a disorder-dependent maximum value, while the latter linearly
increases with the strength of a weak tip potential.Comment: 11 pages, 7 figure
Fingerprints of changes in the terrestrial carbon cycle in response to large reorganizations in ocean circulation
CO<sub>2</sub> and carbon cycle changes in the land, ocean and atmosphere are investigated using the comprehensive carbon cycle-climate model NCAR CSM1.4-carbon. Ensemble simulations are forced with freshwater perturbations applied at the North Atlantic and Southern Ocean deep water formation sites under pre-industrial climate conditions. As a result, the Atlantic Meridional Overturning Circulation reduces in each experiment to varying degrees. The physical climate fields show changes qualitatively in agreement with results documented in the literature, but there is a clear distinction between northern and southern perturbations. Changes in the physical variables, in turn, affect the land and ocean biogeochemical cycles and cause a reduction, or an increase, in the atmospheric CO<sub>2</sub> concentration by up to 20 ppmv, depending on the location of the perturbation. In the case of a North Atlantic perturbation, the land biosphere reacts with a strong reduction in carbon stocks in some tropical locations and in high northern latitudes. In contrast, land carbon stocks tend to increase in response to a southern perturbation. The ocean is generally a sink of carbon although large reorganizations occur throughout various basins. The response of the land biosphere is strongest in the tropical regions due to a shift of the Intertropical Convergence Zone. The carbon fingerprints of this shift, either to the south or to the north depending on where the freshwater is applied, can be found most clearly in South America. For this reason, a compilation of various paleoclimate proxy records of Younger Dryas precipitation changes are compared with our model results. The proxy records, in general, show good agreement with the model's response to a North Atlantic freshwater perturbation
Electrolyte gate dependent high-frequency measurement of graphene field-effect transistor for sensing applications
We performed radiofrequency (RF) reflectometry measurements at 2.4 GHz on
electrolyte-gated graphene field-effect transistors (GFETs) utilizing a tunable
stub-matching circuit for impedance matching. We demonstrate that the gate
voltage dependent RF resistivity of graphene can be deduced even in the
presence of the electrolyte which is in direct contact with the graphene layer.
The RF resistivity is found to be consistent with its DC counterpart in the
full gate voltage range. Furthermore, in order to access the potential of
high-frequency sensing for applications, we demonstrate time-dependent gating
in solution with nanosecond time resolution.Comment: 14 pages, 4 figure
Scaling of 1/f noise in tunable break-junctions
We have studied the voltage noise of gold nano-contacts in
electromigrated and mechanically controlled break-junctions having resistance
values that can be tuned from 10 (many channels) to 10 k
(single atom contact). The noise is caused by resistance fluctuations as
evidenced by the dependence of the power spectral density
on the applied DC voltage . As a function of the normalized noise
shows a pronounced cross-over from for low-ohmic
junctions to for high-ohmic ones. The measured powers of 3
and 1.5 are in agreement with -noise generated in the bulk and reflect the
transition from diffusive to ballistic transport
The multilevel trigger system of the DIRAC experiment
The multilevel trigger system of the DIRAC experiment at CERN is presented.
It includes a fast first level trigger as well as various trigger processors to
select events with a pair of pions having a low relative momentum typical of
the physical process under study. One of these processors employs the drift
chamber data, another one is based on a neural network algorithm and the others
use various hit-map detector correlations. Two versions of the trigger system
used at different stages of the experiment are described. The complete system
reduces the event rate by a factor of 1000, with efficiency 95% of
detecting the events in the relative momentum range of interest.Comment: 21 pages, 11 figure
Slx8 removes Pli1-dependent protein-SUMO conjugates including SUMOylated Topoisomerase I to promote genome stability
Peer reviewedPublisher PD
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