1,053 research outputs found
Bound states and scattering in quantum waveguides coupled laterally through a boundary window
We consider a pair of parallel straight quantum waveguides coupled laterally
through a window of a width in the common boundary. We show that such
a system has at least one bound state for any . We find the
corresponding eigenvalues and eigenfunctions numerically using the
mode--matching method, and discuss their behavior in several situations. We
also discuss the scattering problem in this setup, in particular, the turbulent
behavior of the probability flow associated with resonances. The level and
phase--shift spacing statistics shows that in distinction to closed
pseudo--integrable billiards, the present system is essentially non--chaotic.
Finally, we illustrate time evolution of wave packets in the present model.Comment: LaTeX text file with 12 ps figure
A treatise on the Surveyor lunar landing dynamics and an evaluation of pertinent telemetry data returned by Surveyor I
Dynamic behavior of Surveyor landing system and surface material during lunar landin
The T2K Side Muon Range Detector
The T2K experiment is a long baseline neutrino oscillation experiment aiming
to observe the appearance of {\nu} e in a {\nu}{\mu} beam. The {\nu}{\mu} beam
is produced at the Japan Proton Accelerator Research Complex (J-PARC), observed
with the 295 km distant Super- Kamiokande Detector and monitored by a suite of
near detectors at 280m from the proton target. The near detectors include a
magnetized off-axis detector (ND280) which measures the un-oscillated neutrino
flux and neutrino cross sections. The present paper describes the outermost
component of ND280 which is a side muon range detector (SMRD) composed of
scintillation counters with embedded wavelength shifting fibers and Multi-Pixel
Photon Counter read-out. The components, performance and response of the SMRD
are presented.Comment: 13 pages, 19 figures v2: fixed several typos; fixed reference
A computer code for forward calculation and inversion of the H/V spectral ratio under the diffuse field assumption
During a quarter of a century, the main characteristics of the
horizontal-to-vertical spectral ratio of ambient noise HVSRN have been
extensively used for site effect assessment. In spite of the uncertainties
about the optimum theoretical model to describe these observations, several
schemes for inversion of the full HVSRN curve for near surface surveying have
been developed over the last decade.
In this work, a computer code for forward calculation of H/V spectra based on
the diffuse field assumption (DFA) is presented and tested.It takes advantage
of the recently stated connection between the HVSRN and the elastodynamic
Green's function which arises from the ambient noise interferometry theory.
The algorithm allows for (1) a natural calculation of the Green's functions
imaginary parts by using suitable contour integrals in the complex wavenumber
plane, and (2) separate calculation of the contributions of Rayleigh, Love,
P-SV and SH waves as well. The stability of the algorithm at high frequencies
is preserved by means of an adaptation of the Wang's orthonormalization method
to the calculation of dispersion curves, surface-waves medium responses and
contributions of body waves.
This code has been combined with a variety of inversion methods to make up a
powerful tool for passive seismic surveying.Comment: Published in Computers & Geosciences 97, 67-7
Uncertainty quantification for classical effective potentials
Effective potentials are an essential ingredient of classical molecular dynamics simulations. Little is understood of the errors incurred in representing the complex energy landscape of an atomic configuration by an effective potential containing considerably fewer parameters. This thesis details the introduction of an uncertainty quantification framework into the potential fitting process within the potfit force matching code. The probabilistic sloppy model method has been implemented within potfit as a means to quantify the uncertainties in analytic potential parameters, and in subsequent quantities measured using the fitted potential. Uncertainties in the effective potential are propagated through molecular dynamics simulations to obtain uncertainties in quantities of interest, which are a measure of the confidence in the model predictions.
The implementation has been designed to fit flexibly within the existing potfit workflow, and is generalised to work with any potential model or material. The uncertainty quantification software contains a variety of controllable parameters, which provide the user with diagnostic capabilities to understand the nature of the fitting landscape defined by their potential model and reference data. The implementation is available for use by the materials modelling community as part of the open source potfit software.
The uncertainty quantification technique is demonstrated using three potentials for nickel: two simple pair potentials, Lennard-Jones and Morse, and a local density dependent EAM potential. A sloppy model fit to ab initio reference data is constructed for each potential to calculate the uncertainties in lattice constants, elastic constants and thermal expansion. These can be used to show the unsuitability of pair potentials for nickel. In contrast, with EAM we observe a decreased uncertainty in the model predictions. This shows that our method can capture the effects of the error incurred in the potential generation process without resorting to comparison with experiment or ab inito calculations, which is an essential part to assess the predictive power of molecular dynamics simulations
Energy Selecting Electron Microscopy
One of the major improvements in transmission electron microscopy over the last years is the addition of the capability of producing images with electrons that have specific narrow energy bands out of the total spectrum of energies they possess after having passed through the specimen. Though the idea is not new, the power of this application is only beginning to be recognized. Most simply, selection of elastically scattered electrons permits increased contrast in high resolution i mages in bright field, dark field, and diffraction. The use of combined elastic and inelastic signals adds entirely new contrast mechanisms, partially independent of thickness, partly Z-related. Finally, selection of element specific inelastic events permits elemental mapping with spatial resolutions of 0.3 -0.5 nm and detection sensitivities of about 30 to 50 atoms. Consideration of resolution, sensitivity, image points of analysis and acquisition time leads to a combined improvement of about 1013 times over X-ray microanalysis
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Efficient solution of the multichannel LĂŒscher determinant condition through eigenvalue decomposition
We present a method for efficiently finding solutions of L\"uscher's
quantisation condition, the equation which relates two-particle scattering
amplitudes to the discrete spectrum of states in a periodic spatial volume of
finite extent such as that present in lattice QCD. The approach proposed is
based on an eigenvalue decomposition in the space of coupled-channels and
partial-waves, which proves to have several desirable and simplifying features
that are of great benefit when considering problems beyond simple elastic
scattering of spinless particles. We illustrate the method with a toy model of
vector-vector scattering featuring a high density of solutions, and with an
application to explicit lattice QCD energy level data describing and
scattering in several coupled channels
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