27,687 research outputs found
On Krein-like theorems for noncanonical Hamiltonian systems with continuous spectra: application to Vlasov-Poisson
The notions of spectral stability and the spectrum for the Vlasov-Poisson
system linearized about homogeneous equilibria, f_0(v), are reviewed.
Structural stability is reviewed and applied to perturbations of the linearized
Vlasov operator through perturbations of f_0. We prove that for each f_0 there
is an arbitrarily small delta f_0' in W^{1,1}(R) such that f_0+delta f_0f_0$ is perturbed by an area preserving rearrangement, f_0 will
always be stable if the continuous spectrum is only of positive signature,
where the signature of the continuous spectrum is defined as in previous work.
If there is a signature change, then there is a rearrangement of f_0 that is
unstable and arbitrarily close to f_0 with f_0' in W^{1,1}. This result is
analogous to Krein's theorem for the continuous spectrum. We prove that if a
discrete mode embedded in the continuous spectrum is surrounded by the opposite
signature there is an infinitesimal perturbation in C^n norm that makes f_0
unstable. If f_0 is stable we prove that the signature of every discrete mode
is the opposite of the continuum surrounding it.Comment: Submitted to the journal Transport Theory and Statistical Physics. 36
pages, 12 figure
Definition, analysis and development of an optical data distribution network for integrated avionics and control systems. Part 2: Component development and system integration
Fiber optic transmission is emerging as an attractive concept in data distribution onboard civil aircraft. Development of an Optical Data Distribution Network for Integrated Avionics and Control Systems for commercial aircraft will provide a data distribution network that gives freedom from EMI-RFI and ground loop problems, eliminates crosstalk and short circuits, provides protection and immunity from lightning induced transients and give a large bandwidth data transmission capability. In addition there is a potential for significantly reducing the weight and increasing the reliability over conventional data distribution networks. Wavelength Division Multiplexing (WDM) is a candidate method for data communication between the various avionic subsystems. With WDM all systems could conceptually communicate with each other without time sharing and requiring complicated coding schemes for each computer and subsystem to recognize a message. However, the state of the art of optical technology limits the application of fiber optics in advanced integrated avionics and control systems. Therefore, it is necessary to address the architecture for a fiber optics data distribution system for integrated avionics and control systems as well as develop prototype components and systems
On the Classification of 6D SCFTs and Generalized ADE Orbifolds
We study (1,0) and (2,0) 6D superconformal field theories (SCFTs) that can be
constructed in F-theory. Quite surprisingly, all of them involve an orbifold
singularity C^2 / G with G a discrete subgroup of U(2). When G is a subgroup of
SU(2), all discrete subgroups are allowed, and this leads to the familiar ADE
classification of (2,0) SCFTs. For more general U(2) subgroups, the allowed
possibilities for G are not arbitrary and are given by certain generalizations
of the A- and D-series. These theories should be viewed as the minimal 6D
SCFTs. We obtain all other SCFTs by bringing in a number of E-string theories
and/or decorating curves in the base by non-minimal gauge algebras. In this way
we obtain a vast number of new 6D SCFTs, and we conjecture that our
construction provides a full list.Comment: v3: 47 pages, 3 figures, clarifications added, typos corrected,
references added, and Mathematica file update
Jovian vortices and jets
We explore the conditions required for isolated vortices to exist in sheared
zonal flows and the stability of the underlying zonal winds. This is done using
the standard 2-layer quasigeostrophic model with the lower layer depth becoming
infinite; however, this model differs from the usual layer model because the
lower layer is not assumed to be motionless but has a steady configuration of
alternating zonal flows [1]. Steady state vortices are obtained by a simulated
annealing computational method introduced in [2], generalized and applied in
[3] in fluid flow, and used in the context of magnetohydrodynamics in [4-6].
Various cases of vortices with a constant potential vorticity anomaly atop
zonal winds and the stability of the underlying winds are considered using a
mix of computational and analytical techniques
Evolution from a molecular Rydberg gas to an ultracold plasma in a seeded supersonic expansion of NO
We report the spontaneous formation of a plasma from a gas of cold Rydberg
molecules. Double-resonant laser excitation promotes nitric oxide, cooled to 1
K in a seeded supersonic molecular beam, to single Rydberg states extending as
deep as 80 cm below the lowest ionization threshold. The density of
excited molecules in the illuminated volume is as high as 1 x 10
cm. This population evolves to produce prompt free electrons and a
durable cold plasma of electrons and intact NO ions.Comment: 4 pages (two column) 3 figures; smaller figure files, corrected typo
Use of accelerometry to investigate physical activity in dogs receiving chemotherapy
Objectives:
To perform a preliminary study to assess whether single-agent palliative or adjuvant chemotherapy has an impact on objectively measured physical activity in dogs.
Methods:
Fifteen dogs with neoplasia (treatment group) wore ActiGraph™ accelerometers for 5-day periods before, during and after receiving single-agent adjuvant or palliative chemotherapy. Mean 5-day total physical activity and time spent in three different intensities of activity (sedentary, light-moderate and vigorous) before, during and after receiving chemotherapy were compared to a group of 15 healthy dogs (control group). Results were also compared within the treatment group across time.
Results:
Prior to chemotherapy, treated dogs tended to be less active than control dogs. Treatment group dogs were slightly more active at restaging than they were prior to treatment but had similar activity levels to control dogs. Marked effects of chemotherapy on physical activity were not detected. Physical activity was slightly lower in treated dogs during chemotherapy when compared to control dogs but there was a slight increase in physical activity of treated dogs during chemotherapy when compared with pretreatment recordings. There was little change in the mean 5-day total physical activity between treated dogs during chemotherapy and at restaging but a mild decrease in time spent sedentary and increase in time spent in light-moderate activity at this comparison of time points.
Clinical Significance:
Single-agent adjuvant or palliative chemotherapy had minimal impact on physical activity levels in dogs with neoplasia
Effective transport barriers in nontwist systems
In fluids and plasmas with zonal flow reversed shear, a peculiar kind of transport barrier appears in the shearless region, one that is associated with a proper route of transition to chaos. These barriers have been identified in symplectic nontwist maps that model such zonal flows. We use the so-called standard nontwist map, a paradigmatic example of nontwist systems, to analyze the parameter dependence of the transport through a broken shearless barrier. On varying a proper control parameter, we identify the onset of structures with high stickiness that give rise to an effective barrier near the broken shearless curve. Moreover, we show how these stickiness structures, and the concomitant transport reduction in the shearless region, are determined by a homoclinic tangle of the remaining dominant twin island chains. We use the finite-time rotation number, a recently proposed diagnostic, to identify transport barriers that separate different regions of stickiness. The identified barriers are comparable to those obtained by using finite-time Lyapunov exponents.FAPESPCNPqCAPESMCT/CNEN (Rede Nacional de Fusao)Fundacao AraucariaUS Department of Energy DE-FG05-80ET-53088Physic
Atomic Classification of 6D SCFTs
We use F-theory to classify possibly all six-dimensional superconformal field
theories (SCFTs). This involves a two step process: We first classify all
possible tensor branches allowed in F-theory (which correspond to allowed
collections of contractible spheres) and then classify all possible
configurations of seven-branes wrapped over them. We describe the first step in
terms of "atoms" joined into "radicals" and "molecules," using an analogy from
chemistry. The second step has an interpretation via quiver-type gauge theories
constrained by anomaly cancellation. A very surprising outcome of our analysis
is that all of these tensor branches have the structure of a linear chain of
intersecting spheres with a small amount of possible decoration at the two
ends. The resulting structure of these SCFTs takes the form of a generalized
quiver consisting of ADE-type nodes joined by conformal matter. A collection of
highly non-trivial examples involving E8 small instantons probing an ADE
singularity is shown to have an F-theory realization. This yields a
classification of homomorphisms from ADE subgroups of SU(2) into E8 in purely
geometric terms, largely matching results obtained in the mathematics
literature from an intricate group theory analysis.Comment: v3: 123 pages, 23 figures, typos corrected. Included with the
submission are the Mathematica notebooks "Bases.nb" and
"Fiber_Enhancements.nb
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