8,716 research outputs found
Direct Scattering for the Benjamin-Ono Equation with Rational Initial Data
We compute the scattering data of the Benjamin-Ono equation for arbitrary
rational initial conditions with simple poles. Specifically, we obtain explicit
formulas for the Jost solutions and eigenfunctions of the associated spectral
problem, yielding an Evans function for the eigenvalues and formulas for the
phase constants and reflection coefficient.Comment: 16 Pages, 2 Figure
pde2path - A Matlab package for continuation and bifurcation in 2D elliptic systems
pde2path is a free and easy to use Matlab continuation/bifurcation package
for elliptic systems of PDEs with arbitrary many components, on general two
dimensional domains, and with rather general boundary conditions. The package
is based on the FEM of the Matlab pdetoolbox, and is explained by a number of
examples, including Bratu's problem, the Schnakenberg model, Rayleigh-Benard
convection, and von Karman plate equations. These serve as templates to study
new problems, for which the user has to provide, via Matlab function files, a
description of the geometry, the boundary conditions, the coefficients of the
PDE, and a rough initial guess of a solution. The basic algorithm is a one
parameter arclength continuation with optional bifurcation detection and
branch-switching. Stability calculations, error control and mesh-handling, and
some elementary time-integration for the associated parabolic problem are also
supported. The continuation, branch-switching, plotting etc are performed via
Matlab command-line function calls guided by the AUTO style. The software can
be downloaded from www.staff.uni-oldenburg.de/hannes.uecker/pde2path, where
also an online documentation of the software is provided such that in this
paper we focus more on the mathematics and the example systems
pde2path - version 2.0: faster FEM, multi-parameter continuation, nonlinear boundary conditions, and periodic domains - a short manual
pdepath 2.0 is an upgrade of the continuation/bifurcation package pde2path
for elliptic systems of PDEs over bounded 2D domains, based on the Matlab
pdetoolbox. The new features include a more efficient use of FEM, easier
switching between different single parameter continuations, genuine
multi-parameter continuation (e.g., fold continuation), more efficient
implementation of nonlinear boundary conditions, cylinder and torus geometries
(i.e., periodic boundary conditions), and a general interface for adding
auxiliary equations like mass conservation or phase equations for continuation
of traveling waves. The package (library, demos, manuals) can be downloaded at
www.staff.uni-oldenburg.de/hannes.uecker/pde2pat
Radiation Damage and Recovery Properties of Common Plastics PEN (Polyethylene Naphthalate) and PET (Polyethylene Terephthalate) Using a 137Cs Gamma Ray Source Up To 1 MRad and 10 MRad
Polyethylene naphthalate (PEN) and polyethylene teraphthalate (PET) are cheap
and common polyester plastics used throughout the world in the manufacturing of
bottled drinks, containers for foodstuffs, and fibers used in clothing. These
plastics are also known organic scintillators with very good scintillation
properties. As particle physics experiments increase in energy and particle
flux density, so does radiation exposure to detector materials. It is therefore
important that scintillators be tested for radiation tolerance at these
generally unheard of doses. We tested samples of PEN and PET using laser
stimulated emission on separate tiles exposed to 1 MRad and 10 MRad gamma rays
with a 137Cs source. PEN exposed to 1 MRad and 10 MRad emit 71.4% and 46.7% of
the light of an undamaged tile, respectively, and maximally recover to 85.9%
and 79.5% after 5 and 9 days, respectively. PET exposed to 1 MRad and 10 MRad
emit 35.0% and 12.2% light, respectively, and maximally recover to 93.5% and
80.0% after 22 and 60 days, respectively
Synchronization in the presence of time delays and inertia: Stability criteria
Linear stability of synchronized states in networks of delay-coupled oscillators depends on the type of interaction, the network, and oscillator properties. For inert oscillator response, found ubiquitously from biology to engineering, states with time-dependent frequencies can arise. These generate side bands in the frequency spectrum or lead to chaotic dynamics. The time delay introduces multistability of synchronized states and an exponential term in the characteristic equation. Stability analysis using the resulting transcendental characteristic equation is a difficult task and is usually carried out numerically. We derive criteria and conditions that enable fast and robust analytical linear stability analysis based on the system parameters. These apply to arbitrary network topologies, identical oscillators, and delays
Conceptual designs study for a Personnel Launch System (PLS)
A series of conceptual designs for a manned, Earth to Low Earth Orbit transportation system was developed. Non-winged, low L/D vehicle shapes are discussed. System and subsystem trades emphasized safety, operability, and affordability using near-term technology. The resultant conceptual design includes lessons learned from commercial aviation that result in a safe, routine, operationally efficient system. The primary mission for this Personnel Launch System (PLS) would be crew rotation to the SSF; other missions, including satellite servicing, orbital sortie, and space rescue were also explored
Failure modes and gradual degradation due to large electrical stresses in GaAs/AlGaAs heterojunction bipolar transistors
Characterization of photomultiplier tubes in a novel operation mode for Secondary Emission Ionization Calorimetry
Hamamatsu single anode R7761 and multi-anode R5900-00-M16 Photomultiplier
Tubes have been characterized for use in a Secondary Emission (SE) Ionization
Calorimetry study. SE Ionization Calorimetry is a novel technique to measure
electromagnetic shower particles in extreme radiation environments. The
different operation modes used in these tests were developed by modifying the
conventional PMT bias circuit. These modifications were simple changes to the
arrangement of the voltage dividers of the baseboard circuits. The PMTs with
modified bases, referred to as operating in SE mode, are used as an SE detector
module in an SE calorimeter prototype, and placed between absorber materials
(Fe, Cu, Pb, W, etc.). Here, the technical design of different operation modes,
as well as the characterization measurements of both SE modes and the
conventional PMT mode are reported
In situ determination of hydraulic conductivity and hydraulic head in shallow coastal sediments
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