3,501 research outputs found
Conformal Invariance and Shape-Dependent Conductance of Graphene Samples
For a sample of an arbitrary shape, the dependence of its conductance on the
longitudinal and Hall conductivity is identical to that of a rectangle. We use
analytic results for a conducting rectangle, combined with the semicircle model
for transport coefficients, to study properties of the monolayer and bilayer
graphene. A conductance plateau centered at the neutrality point, predicted for
square geometry, is in agreement with recent experiments. For rectangular
geometry, the conductance exhibits maxima at the densities of compressible
quantum Hall states for wide samples, and minima for narrow samples. The
positions and relative sizes of these features are different in the monolayer
and bilayer cases, indicating that the conductance can be used as a tool for
sample diagnostic.Comment: 9 pages, 6 figure
A microscopic view on contact angle selection
We discuss the equilibrium condition for a liquid that partially wets a solid
on the level of intermolecular forces. Using a mean field continuum
description, we generalize the capillary pressure from variation of the free
energy and show at what length scale the equilibrium contact angle is selected.
After recovering Young's law for homogeneous substrates, it is shown how
hysteresis of the contact angle can be incorporated in a self-consistent
fashion. In all cases the liquid-vapor interface takes a nontrivial shape,
which is compared to models using a disjoining pressure.Comment: 12 pages, 6 figure
Crossâscale seismic anisotropy analysis in metamorphic rocks from the COSCâ1 borehole in the Scandinavian Caledonides
Metamorphic and deformed rocks in thrust zones show particularly high seismic anisotropy causing challenges for seismic imaging and interpretation. A good example is the Seve Nappe Complex in central Sweden, an old exhumed orogenic thrust zone that is characterized by a strong but incoherent seismic reflectivity and considerable seismic anisotropy. However, only little is known about their origin in relation to composition and structural influences on measurements at different seismic scales. Here, we present a new integrative study of crossâscale seismic anisotropy analyses combining mineralogical composition, microstructural analyses and seismic laboratory experiments from the COSCâ1 borehole, which sampled a 2.5 kmâdeep section of metamorphic rocks deformed in an orogenic root now preserved in the Lower Seve Nappe. While there is strong crystallographic preferred orientation in most samples in general, variations in anisotropy depend mostly on bulk mineral composition and dominant core lithology as shown by a strong correlation between these. This relationship enables to identify three distinct seismic anisotropy facies providing a continuous anisotropy profile along the borehole. Moreover, comparison of laboratory seismic measurements and electronâbackscatter diffraction data reveals a strong scaleâdependence, which is more pronounced in the highly deformed, heterogeneous samples. This highlights the need for comprehensive crossâvalidation of microscale anisotropy analyses with additional lithological data when integrating seismic anisotropy over seismic scales
Stretching and squeezing of sessile dielectric drops by the optical radiation pressure
We study numerically the deformation of sessile dielectric drops immersed in
a second fluid when submitted to the optical radiation pressure of a continuous
Gaussian laser wave. Both drop stretching and drop squeezing are investigated
at steady state where capillary effects balance the optical radiation pressure.
A boundary integral method is implemented to solve the axisymmetric Stokes flow
in the two fluids. In the stretching case, we find that the drop shape goes
from prolate to near-conical for increasing optical radiation pressure whatever
the drop to beam radius ratio and the refractive index contrast between the two
fluids. The semi-angle of the cone at equilibrium decreases with the drop to
beam radius ratio and is weakly influenced by the index contrast. Above a
threshold value of the radiation pressure, these "optical cones" become
unstable and a disruption is observed. Conversely, when optically squeezed, the
drop shifts from an oblate to a concave shape leading to the formation of a
stable "optical torus". These findings extend the electrohydrodynamics approach
of drop deformation to the much less investigated "optical domain" and reveal
the openings offered by laser waves to actively manipulate droplets at the
micrometer scale
Network Anomaly Classification by Support Vector Classifiers Ensemble and Non-linear Projection Techniques
Network anomaly detection is currently a challenge due to the number of different attacks and the number of potential attackers. Intrusion detection systems aim to detect misuses or network anomalies in order to block ports or connections, whereas firewalls act according to a predefined set of rules. However, detecting the specific anomaly provides valuable information about the attacker that may be used to further protect the system, or to react accordingly. This way, detecting network intrusions is a current challenge due to growth of the Internet and the number of potential intruders. In this paper we present an intrusion detection technique using an ensemble of support vector classifiers and dimensionality reduction techniques to generate a set of discriminant features. The results obtained using the NSL-KDD dataset outperforms previously obtained classification rates
The roles of motivation and ability in controlling the consequences of stereotype suppression
Two experiments investigated the conditions under which previously suppressed stereotypes are applied in impression formation. In Experiment 1, the extent to which a previously suppressed racial stereotype influenced subsequent impressions depended on the race of the target who was subsequently encountered. Whereas impressions of race-unspecified targets were assimilated to the stereotype following its suppression, no such effects were observed when the target belonged to the racial group whose stereotype had been initially suppressed. These results demonstrate that when perceivers are motivated to avoid stereo-typing individuals, the influence of a stereotype that has been previously activated through suppression is minimized. Experiment 2 demonstrated that these processing goals effectively reduce the impact of suppression-activated stereotypes only when perceivers have sufficient capacity to enact the goals. These results suggest that both sufficient motivation and capacity are necessary to prevent heightened stereotyping following stereotype suppression
The HADES Tracking System
The tracking system of the dielectron spectrometer HADES at GSI Darmstadt is
formed out of 24 low-mass, trapezoidal multi-layer drift chambers providing in
total about 30 square meter of active area. Low multiple scattering in the in
total four planes of drift chambers before and after the magnetic field is
ensured by using helium-based gas mixtures and aluminum cathode and field
wires. First in-beam performance results are contrasted with expectations from
simulations. Emphasis is placed on the energy loss information, exploring its
relevance regarding track recognition.Comment: 6 pages, 4 figures, presented at the 10th Vienna Conference on
Instrumentation, Vienna, February 2004, to be published in NIM A (special
issue
Inhalation exposure methodology.
Modern man is being confronted with an ever-increasing inventory of potentially toxic airborne substances. Exposures to these atmospheric contaminants occur in residential and commercial settings, as well as in the workplace. In order to study the toxicity of such materials, a special technology relating to inhalation exposure systems has evolved. The purpose of this paper is to provide a description of the techniques which are used in exposing laboratory subjects to airborne particles and gases. The various modes of inhalation exposure (whole body, head only, nose or mouth only, etc.) are described at length, including the advantages and disadvantages inherent to each mode. Numerous literature citations are included for further reading. Among the topics briefly discussed are the selection of appropriate animal species for toxicological testing, and the types of inhalation studies performed (acute, chronic, etc.)
Electrowetting-on-Dielectric Actuation of a Vertical Translation and Angular Manipulation Stage
Adhesion and friction during physical contact of solid components in microelectromechanical systems (MEMS) often lead to device failure. Translational stages that are fabricated with traditional silicon MEMS typically face these tribological concerns. This work addresses these concerns by developing a MEMS vertical translation, or focusing, stage that uses electrowetting-on-dielectric (EWOD) as the actuating mechanism. EWOD has the potential to eliminate solid-solid contact by actuating through deformation of liquid droplets placed between the stage and base to achieve stage displacement. Our EWOD stage is capable of linear spatial manipulation with resolution of 10âÎŒm over a maximum range of 130âÎŒm and angular deflection of approximately ±1°, comparable to piezoelectric actuators. We also developed a model that suggests a higher intrinsic contact angle on the EWOD surface can further improve the translational range, which was validated experimentally by comparing different surface coatings. The capability to operate the stage without solid-solid contact offers potential improvements for applications in micro-optics, actuators, and other MEMS devices.United States. Office of Naval ResearchNational Science Foundation (U.S.). Graduate Research Fellowship Program (Grant 1122374)National Science Foundation (U.S.) (Major Research Instrumentation Grant for Rapid Response Research (MRI-RAPID)
Identification of the Beutler-Fano formula in eigenphase shifts and eigentime delays near a resonance
Eigenphase shifts and eigentime delays near a resonance for a system of one
discrete state and two continua are shown to be functionals of the Beutler-
Fano formulas using appropriate dimensionless energy units and line profile
indices. Parameters responsible for the avoided crossing of eigenphase shifts
and eigentime delays are identified. Similarly, parameters responsible for the
eigentime delays due to a frame change are identified. With the help of new
parameters, an analogy with the spin model is pursued for the S matrix and time
delay matrix. The time delay matrix is shown to comprise three terms, one due
to resonance, one due to a avoided crossing interaction, and one due to a frame
change. It is found that the squared sum of time delays due to the avoided
crossing interaction and frame change is unity.Comment: 17 pages, 3 figures, RevTe
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