9,746 research outputs found
Method for analyzing radiation sensitivity of integrated circuits
A method for analyzing the radiation sensitivity of an integrated circuit is described to determine the components. The application of a narrow radiation beam to portions of the circuit is considered. The circuit is operated under normal bias conditions during the application of radiation in a dosage that is likely to cause malfunction of at least some transistors, while the circuit is monitored for failure of the irradiated transistor. When a radiation sensitive transistor is found, then the radiation beam is further narrowed and, using a fresh integrated circuit, a very narrow beam is applied to different parts of the transistor, such as its junctions, to locate the points of greatest sensitivity
Suspension flow: do particles act as mixers?
Recently, Roht et al. [J. Contam. Hydrol. 145, 10-16 (2013)] observed that
the presence of suspended non-Brownian macroscopic particles decreased the
dispersivity of a passive solute, for a pressure-driven flow in a narrow
parallel-plates channel at low Reynolds number. This result contradicts the
idea that the streamline distortion caused by the random diffusive motion of
the particles increases the dispersion and mixing of the solute. Therefore, to
estimate the influence of this motion on the dispersivity of the solute, and
investigate the origin of the reported decrease, we experimentally studied the
probability density functions (pdf) of the particle velocities, and
spatio-temporal correlations, in the same experimental configuration. We
observed that, as the mean suspension velocity exceeds a critical value, the
pdf of the streamwise velocities of the particles markedly changes from a
symmetric distribution to an asymmetric one strongly skewed to high velocities
and with a peak of most probable velocity close to the maximum velocity. The
latter observations and the analysis of suspension microstructure indicate that
the observed decrease in the dispersivity of the solute is due to particle
migration to the mid-plane of the channel, and consequent flattening of the
velocity profile. Moreover, we estimated the contribution of particle diffusive
motion to the solute dispersivity to be three orders of magnitude smaller than
the reported decrease, and thus negligible. Solute dispersion is then much more
affected by how particles modify the flow velocity profile across the channel,
than by their diffusive random motion
Velocity fluctuations and population distribution in clusters of settling particles at low Reynolds number
A study on the spatial organization and velocity fluctuations of non Brownian
spherical particles settling at low Reynolds number in a vertical Hele-Shaw
cell is reported. The particle volume fraction ranged from 0.005 to 0.05, while
the distance between cell plates ranged from 5 to 15 times the particle radius.
Particle tracking revealed that particles were not uniformly distributed in
space but assembled in transient settling clusters. The population distribution
of these clusters followed an exponential law. The measured velocity
fluctuations are in agreement with that predicted theoretically for spherical
clusters, from the balance between the apparent weight and the drag force. This
result suggests that particle clustering, more than a spatial distribution of
particles derived from random and independent events, is at the origin of the
velocity fluctuations.Comment: 13 pages, 8 figure
Small-Signal Amplification of Period-Doubling Bifurcations in Smooth Iterated Maps
Various authors have shown that, near the onset of a period-doubling
bifurcation, small perturbations in the control parameter may result in much
larger disturbances in the response of the dynamical system. Such amplification
of small signals can be measured by a gain defined as the magnitude of the
disturbance in the response divided by the perturbation amplitude. In this
paper, the perturbed response is studied using normal forms based on the most
general assumptions of iterated maps. Such an analysis provides a theoretical
footing for previous experimental and numerical observations, such as the
failure of linear analysis and the saturation of the gain. Qualitative as well
as quantitative features of the gain are exhibited using selected models of
cardiac dynamics.Comment: 12 pages, 7 figure
Stability of an oscillating tip in Non-Contact Atomic Force Microscopy: theoretical and numerical investigations
This paper is a theoretical and a numerical investigation of the stability of
a tip-cantilever system used in Non-Contact Atomic Force Microscopy (NC-AFM)
when it oscillates close to a surface. No additional dissipative force is
considered. The theoretical approach is based on a variationnal method
exploiting a coarse grained operation that gives the temporal dependence of the
nonlinear coupled equations of motion in amplitude and phase of the oscillator.
Stability criterions for the resonance peak are deduced and predict a stable
behavior of the oscillator in the vicinity of the resonance. The numerical
approach is based on results obtained with a virtual NC-AFM developped in our
group. The effect of the size of the stable domain in phase is investigated.
These results are in particularly good agreement with the theoretical
predictions. Also they show the influence of the phase shifter in the feedback
loop and the way it can affect the damping signal
Comparative genomics and mutagenesis analyses of choline metabolism in the marine Roseobacter clade
Choline is ubiquitous in marine eukaryotes and appears to be widely distributed in surface marine waters; however, its metabolism by marine bacteria is poorly understood. Here, using comparative genomics and molecular genetic approaches, we reveal that the capacity for choline catabolism is widespread in marine heterotrophs of the marine Roseobacter clade (MRC). Using the model bacterium Ruegeria pomeroyi, we confirm that the betA, betB and betC genes, encoding choline dehydrogenase, betaine aldehyde dehydrogenase and choline sulfatase, respectively, are involved in choline metabolism. The betT gene, encoding an organic solute transporter, was essential for the rapid uptake of choline but not glycine betaine (GBT). Growth of choline and GBT as a sole carbon source resulted in the re-mineralization of these nitrogen-rich compounds into ammonium. Oxidation of the methyl groups from choline requires formyltetrahydrofolate synthetase encoded by fhs in R.pomeroyi, deletion of which resulted in incomplete degradation of GBT. We demonstrate that this was due to an imbalance in the supply of reducing equivalents required for choline catabolism, which can be alleviated by the addition of formate. Together, our results demonstrate that choline metabolism is ubiquitous in the MRC and reveal the role of Fhs in methyl group oxidation in R.pomeroyi
Security of high-dimensional quantum key distribution protocols using Franson interferometers
Franson interferometers are increasingly being proposed as a means of
securing high-dimensional energy-time entanglement-based quantum key
distribution (QKD) systems. Heuristic arguments have been proposed that purport
to demonstrate the security of these schemes. We show, however, that such
systems are vulnerable to attacks that localize the photons to several
temporally separate locations. This demonstrates that a single pair of Franson
interferometers is not a practical approach to securing high-dimensional
energy-time entanglement based QKD. This observations leads us to investigate
the security of modified Franson-based-protocols, where Alice and Bob have two
or more Franson interferometers. We show that such setups can improve the
sensitivity against attacks that localize the photons to multiple temporal
locations. While our results do not constituting a full security proof, they do
show that a single pair of Franson interferometers is not secure and that
multiple such interferometers could be a promising candidate for experimentally
realizable high-dimensional QKD.Comment: 14 pages (single column format
Competition between Electromagnetically Induced Transparency and Raman Processes
We present a theoretical formulation of competition among electromagnetically
induced transparency (EIT) and Raman processes. The latter become important
when the medium can no longer be considered to be dilute. Unlike the standard
formulation of EIT, we consider all fields applied and generated as interacting
with both the transitions of the scheme. We solve Maxwell equations
for the net generated field using a fast-Fourier-transform technique and obtain
predictions for the probe, control and Raman fields. We show how the intensity
of the probe field is depleted at higher atomic number densities due to the
build up of multiple Raman fields.Comment: 3.5 pages, 7 figure
Direct imaging of a digital-micromirror device for configurable microscopic optical potentials
Programable spatial light modulators (SLMs) have significantly advanced the
configurable optical trapping of particles. Typically, these devices are
utilized in the Fourier plane of an optical system, but direct imaging of an
amplitude pattern can potentially result in increased simplicity and
computational speed. Here we demonstrate high-resolution direct imaging of a
digital micromirror device (DMD) at high numerical apertures (NA), which we
apply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a
(1200 x 1920) pixel DMD and commercially available 0.45 NA microscope
objectives, finding that atoms confined in a hybrid optical/magnetic or
all-optical potential can be patterned using repulsive blue-detuned (532 nm)
light with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5%
of the diffraction limit. The result is near arbitrary control of the density
the BEC without the need for expensive custom optics. We also introduce the
technique of time-averaged DMD potentials, demonstrating the ability to produce
multiple grayscale levels with minimal heating of the atomic cloud, by
utilising the high switching speed (20 kHz maximum) of the DMD. These
techniques will enable the realization and control of diverse optical
potentials for superfluid dynamics and atomtronics applications with quantum
gases. The performance of this system in a direct imaging configuration has
wider application for optical trapping at non-trivial NAs.Comment: 9 page
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