7,436 research outputs found
Element Level Bridge Inspection: Benefits and Use of Data for Bridge Management
In 2012, Congress passed the Moving Ahead for Progress in the 21st Century Act (MAP-21) and committed to the development of a data-driven, risk based approach to asset management in the United States. This law requires the collection and submission of element level bridge inspection data for all National Highway System bridges, in addition to the National Bridge Inspection condition rating data. Ultimately, the data collected during element level bridge inspections should satisfy the requirements of the Federal Highway Administration and MAP-21 and be utilized by INDOT to evaluate bridge condition, predict deterioration, and guide decision making.
The objective of this project is to develop recommendations for element level bridge inspection techniques, data collection, and inspector training based on a survey of INDOT peer agencies and a literature review of existing research and bridge inspection guidance. In order to collect consistent and reliable data, a rigorous inspector training program and detailed quality control procedures are necessary. INDOT must provide inspectors with the tools to be successful, including clearly defined expectations and instructions, comprehensive training and technical support, and effective inspection equipment. Similarly, robust quality control measures and periodic performance testing should be implemented to improve inspection quality and assess the agency’s performance
Cooling in the X-ray halo of the rotating, massive early-type galaxy NGC 7049
The relative importance of the physical processes shaping the thermodynamics
of the hot gas permeating rotating, massive early-type galaxies is expected to
be different from that in non-rotating systems. Here, we report the results of
the analysis of XMM-Newton data for the massive, lenticular galaxy NGC 7049.
The galaxy harbours a dusty disc of cool gas and is surrounded by an extended
hot X-ray emitting gaseous atmosphere with unusually high central entropy. The
hot gas in the plane of rotation of the cool dusty disc has a multi-temperature
structure, consistent with ongoing cooling. We conclude that the rotational
support of the hot gas is likely capable of altering the multiphase
condensation regardless of the ratio, which is here
relatively high, . However, the measured ratio of cooling time and
eddy turnover time around unity (-ratio ) implies significant
condensation, and at the same time, the constrained ratio of rotational
velocity and the velocity dispersion (turbulent Taylor number)
indicates that the condensing gas should follow non-radial orbits forming a
disc instead of filaments. This is in agreement with hydrodynamical simulations
of massive rotating galaxies predicting a similarly extended multiphase disc.Comment: 11 pages, 12 figures, accepted for publication in MNRA
Jost Function for Singular Potentials
An exact method for direct calculation of the Jost function and Jost
solutions for a repulsive singular potential is presented. Within this method
the Schrodinger equation is replaced by an equivalent system of linear
first-order differential equations, which after complex rotation, can easily be
solved numerically. The Jost function can be obtained to any desired accuracy
for all complex momenta of physical interest, including the spectral points
corresponding to bound and resonant states. The method can also be used in the
complex angular-momentum plane to calculate the Regge trajectories. The
effectiveness of the method is demonstrated using the Lennard-Jones (12,6)
potential. The spectral properties of the realistic inter-atomic He4-He4
potentials HFDHE2 and HFD-B of Aziz and collaborators are also investigated.Comment: 12 pages, latex, 2 eps-figures, submitted to Phys.Rev.
Semiclassical ionization dynamics of the hydrogen molecular ion in an electric field of arbitrary orientation
Quasi-static models of barrier suppression have played a major role in our
understanding of the ionization of atoms and molecules in strong laser fields.
Despite their success, in the case of diatomic molecules these studies have so
far been restricted to fields aligned with the molecular axis. In this paper we
investigate the locations and heights of the potential barriers in the hydrogen
molecular ion in an electric field of arbitrary orientation. We find that the
barriers undergo bifurcations as the external field strength and direction are
varied. This phenomenon represents an unexpected level of intricacy even on
this most elementary level of the dynamics. We describe the dynamics of
tunnelling ionization through the barriers semiclassically and use our results
to shed new light on the success of a recent theory of molecular tunnelling
ionization as well as earlier theories that restrict the electric field to be
aligned with the molecular axis
Sub-threshold resonances in few-neutron systems
Three- and four-neutron systems are studied within the framework of the
hyperspherical approach with a local S-wave nn-potential. Possible bound and
resonant states of these systems are sought as zeros of three- and four-body
Jost functions in the complex momentum plane. It is found that zeros closest to
the origin correspond to sub-threshold (nnn) (1/2-) and (nnnn) (0+) resonant
states. The positions of these zeros turned out to be sensitive to the choice
of the --potential. For the Malfliet- Tjon potential they are
E(nnn)=-4.9-i6.9 (MeV) and E(nnnn)=-2.6-i9.0 (MeV). Movement of the zeros with
an artificial increase of the potential strength also shows an extreme
sensitivity to the choice of potential. Thus, to generate ^3n and ^4n bound
states, the Yukawa potential needs to be multiplied by 2.67 and 2.32
respectively, while for the Malfliet-Tjon potential the required multiplicative
factors are 4.04 and 3.59.Comment: Latex, 22 pages, no PS-figures, submitted to J.Phys.
Photoabsorption spectra of the diamagnetic hydrogen atom in the transition regime to chaos: Closed orbit theory with bifurcating orbits
With increasing energy the diamagnetic hydrogen atom undergoes a transition
from regular to chaotic classical dynamics, and the closed orbits pass through
various cascades of bifurcations. Closed orbit theory allows for the
semiclassical calculation of photoabsorption spectra of the diamagnetic
hydrogen atom. However, at the bifurcations the closed orbit contributions
diverge. The singularities can be removed with the help of uniform
semiclassical approximations which are constructed over a wide energy range for
different types of codimension one and two catastrophes. Using the uniform
approximations and applying the high-resolution harmonic inversion method we
calculate fully resolved semiclassical photoabsorption spectra, i.e.,
individual eigenenergies and transition matrix elements at laboratory magnetic
field strengths, and compare them with the results of exact quantum
calculations.Comment: 26 pages, 9 figures, submitted to J. Phys.
A complex ray-tracing tool for high-frequency mean-field flow interaction effects in jets
This paper presents a complex ray-tracing tool for the calculation of high-frequency Green’s functions in 3D mean field jet flows. For a generic problem, the ray solution suffers from three main deficiencies: multiplicity of solutions, singularities at caustics, and the determining of complex solutions. The purpose of this paper is to generalize, combine and apply existing stationary media methods to moving media scenarios. Multiplicities are dealt with using an equivalent two-point boundary-value problem, whilst non-uniformities at caustics are corrected using diffraction catastrophes. Complex rays are found using a combination of imaginary perturbations, an assumption of caustic stability, and analytic continuation of the receiver curve. To demonstrate this method, the ray tool is compared against a high-frequency modal solution of Lilley’s equation for an off-axis point source. This solution is representative of high-frequency source positions in real jets and is rich in caustic structures. A full utilization of the ray tool is shown to provide excellent results<br/
Corrections to the universal behavior of the Coulomb-blockade peak splitting for quantum dots separated by a finite barrier
Building upon earlier work on the relation between the dimensionless interdot
channel conductance g and the fractional Coulomb-blockade peak splitting f for
two electrostatically equivalent dots, we calculate the leading correction that
results from an interdot tunneling barrier that is not a delta-function but,
rather, has a finite height V and a nonzero width xi and can be approximated as
parabolic near its peak. We develop a new treatment of the problem for g much
less than 1 that starts from the single-particle eigenstates for the full
coupled-dot system. The finiteness of the barrier leads to a small upward shift
of the f-versus-g curve at small values of g. The shift is a consequence of the
fact that the tunneling matrix elements vary exponentially with the energies of
the states connected. Therefore, when g is small, it can pay to tunnel to
intermediate states with single-particle energies above the barrier height V.
The correction to the zero-width behavior does not affect agreement with recent
experimental results but may be important in future experiments.Comment: Title changed from ``Non-universal...'' to ``Corrections to the
universal...'' No other changes. 10 pages, 1 RevTeX file with 2 postscript
figures included using eps
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