14,359 research outputs found
Comparison of numerical methods for the calculation of cold atom collisions
Three different numerical techniques for solving a coupled channel
Schroedinger equation are compared. This benchmark equation, which describes
the collision between two ultracold atoms, consists of two channels, each
containing the same diagonal Lennard-Jones potential, one of positive and the
other of negative energy. The coupling potential is of an exponential form. The
methods are i) a recently developed spectral type integral equation method
based on Chebyshev expansions, ii) a finite element expansion, and iii) a
combination of an improved Numerov finite difference method and a Gordon
method. The computing time and the accuracy of the resulting phase shift is
found to be comparable for methods i) and ii), achieving an accuracy of ten
significant figures with a double precision calculation. Method iii) achieves
seven significant figures. The scattering length and effective range are also
obtained.Comment: 22 pages, 3 figures, submitted to J. Comput. Phys. documentstyle
[thmsa,sw20aip]{article} in .te
Far-field optical microscope with nanometer-scale resolution based on in-plane surface plasmon imaging
A new far-field optical microscopy technique capable of reaching
nanometer-scale resolution has been developed recently using the in-plane image
magnification by surface plasmon polaritons. This microscopy is based on the
optical properties of a metal-dielectric interface that may, in principle,
provide extremely large values of the effective refractive index n up to
100-1000 as seen by the surface plasmons. Thus, the theoretical diffraction
limit on resolution becomes lambda/2n, and falls into the nanometer-scale
range. The experimental realization of the microscope has demonstrated the
optical resolution better than 50 nm for 502 nm illumination wavelength.
However, the theory of such surface plasmon-based far-field microscope
presented so far gives an oversimplified picture of its operation. For example,
the imaginary part of the metal dielectric constant severely limits the
surface-plasmon propagation and the shortest attainable wavelength in most
cases, which in turn limits the microscope magnification. Here I describe how
this limitation has been overcome in the experiment, and analyze the practical
limits on the surface plasmon microscope resolution. In addition, I present
more experimental results, which strongly support the conclusion of extremely
high spatial resolution of the surface plasmon microscope.Comment: 23 pages, 9 figures, will be published in the topical issue on
Nanostructured Optical Metamaterials of the Journal of Optics A: Pure and
Applied Optics, Manuscript revised in response to referees comment
Classifying network attack scenarios using an ontology
This paper presents a methodology using network attack ontology to classify computer-based attacks. Computer network attacks differ in motivation, execution and end result. Because attacks are diverse, no standard classification exists. If an attack could be classified, it could be mitigated accordingly. A taxonomy of computer network attacks forms the basis of the ontology. Most published taxonomies present an attack from either the attacker's or defender's point of view. This taxonomy presents both views. The main taxonomy classes are: Actor, Actor Location, Aggressor, Attack Goal, Attack Mechanism, Attack Scenario, Automation Level, Effects, Motivation, Phase, Scope and Target. The "Actor" class is the entity executing the attack. The "Actor Location" class is the Actor‟s country of origin. The "Aggressor" class is the group instigating an attack. The "Attack Goal" class specifies the attacker‟s goal. The "Attack Mechanism" class defines the attack methodology. The "Automation Level" class indicates the level of human interaction. The "Effects" class describes the consequences of an attack. The "Motivation" class specifies incentives for an attack. The "Scope" class describes the size and utility of the target. The "Target" class is the physical device or entity targeted by an attack. The "Vulnerability" class describes a target vulnerability used by the attacker. The "Phase" class represents an attack model that subdivides an attack into different phases. The ontology was developed using an "Attack Scenario" class, which draws from other classes and can be used to characterize and classify computer network attacks. An "Attack Scenario" consists of phases, has a scope and is attributed to an actor and aggressor which have a goal. The "Attack Scenario" thus represents different classes of attacks. High profile computer network attacks such as Stuxnet and the Estonia attacks can now be been classified through the “Attack Scenario” class
Monitoring the Earthquake Activity in an Area with Shale Gas Potential in Southeastern New Brunswick, Canada
Isolation of microsatellite loci in the Capricorn silvereye, Zosterops lateralis chlorocephalus (Aves : Zosteropidae)
The Capricorn silvereye (Zosterops lateralis chlorocephalus
) is ideally suited to investigating the genetic basis of body size evolution. We have isolated and characterized a set of microsatellite markers for this species. Seven out of 11 loci were polymorphic. The number of alleles
detected ranged from two to five and observed heterozygosities between 0.12 and 0.67. One locus, ZL49, was found to be sex-linked. This moderate level of diversity is consistent with that expected in an isolated, island population
Review of the systems analysis of interactions between the thermal, lubricant, and combustion processes of diesel engines
Quantum many-body dynamics in a Lagrangian frame: II. Geometric formulation of time-dependent density functional theory
We formulate equations of time-dependent density functional theory (TDDFT) in
the co-moving Lagrangian reference frame. The main advantage of the Lagrangian
description of many-body dynamics is that in the co-moving frame the current
density vanishes, while the density of particles becomes independent of time.
Therefore a co-moving observer will see the picture which is very similar to
that seen in the equilibrium system from the laboratory frame. It is shown that
the most natural set of basic variables in TDDFT includes the Lagrangian
coordinate, , a symmetric deformation tensor , and a
skew-symmetric vorticity tensor, . These three quantities,
respectively, describe the translation, deformation, and the rotation of an
infinitesimal fluid element. Reformulation of TDDFT in terms of new basic
variables resolves the problem of nonlocality and thus allows to regularly
derive a local nonadiabatic approximation for exchange correlation (xc)
potential. Stationarity of the density in the co-moving frame makes the
derivation to a large extent similar to the derivation of the standard static
local density approximation. We present a few explicit examples of nonlinear
nonadiabatic xc functionals in a form convenient for practical applications.Comment: RevTeX4, 18 pages, Corrected final version. The first part of this
work is cond-mat/040835
On the QED Effective Action in Time Dependent Electric Backgrounds
We apply the resolvent technique to the computation of the QED effective
action in time dependent electric field backgrounds. The effective action has
both real and imaginary parts, and the imaginary part is related to the pair
production probability in such a background. The resolvent technique has been
applied previously to spatially inhomogeneous magnetic backgrounds, for which
the effective action is real. We explain how dispersion relations connect these
two cases, the magnetic case which is essentially perturbative in nature, and
the electric case where the imaginary part is nonperturbative. Finally, we use
a uniform semiclassical approximation to find an expression for very general
time dependence for the background field. This expression is remarkably similar
in form to Schwinger's classic result for the constant electric background.Comment: 27 pages, no figures; reference adde
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