18,242 research outputs found
A study of citizens' apathy toward civic responsibility in two communities with contrasting socio-economic status
Thesis (M.S.)--Boston Universit
F-14 modeling study
Preliminary results in the application of a closed loop pilot/simulator model to the analysis of some simulator fidelity issues are discussed in the context of an air to air target tracking task. The closed loop model is described briefly. Then, problem simplifications that are employed to reduce computational costs are discussed. Finally, model results showing sensitivity of performance to various assumptions concerning the simulator and/or the pilot are presented
Scattering of 42 MeV /6.7-pJ/ alpha particles from even isotopes of cadmium. Supplement 1 - Absolute cross sections
Absolute cross sections for scattering of 42 MeV alpha particles from even isotopes of cadmiu
Elastic and inelastic scattering of 42-MeV alpha particles from even tellurium isotopes
Angular distributions of elastic and inelastic scattering of 42-MeV alpha particles measured for even tellurium isotope
Persistent individual bias in a voter model with quenched disorder
Many theoretical studies of the voter model (or variations thereupon) involve
order parameters that are population-averaged. While enlightening, such
quantities may obscure important statistical features that are only apparent on
the level of the individual. In this work, we ask which factors contribute to a
single voter maintaining a long-term statistical bias for one opinion over the
other in the face of social influence. To this end, a modified version of the
network voter model is proposed, which also incorporates quenched disorder in
the interaction strengths between individuals and the possibility of
antagonistic relationships. We find that a sparse interaction network and
heterogeneity in interaction strengths give rise to the possibility of
arbitrarily long-lived individual biases, even when there is no
population-averaged bias for one opinion over the other. This is demonstrated
by calculating the eigenvalue spectrum of the weighted network Laplacian using
the theory of sparse random matrices.Comment: 15 pages, 7 figure
Exploration of Ground Penetrating Radar and Time Domain Reflectometry Methods for the Determination of Pavement Dielectric Constant
Traditionally, densities of newly built roadways are checked by direct sampling (cores) or by nuclear density gauge measurements. For roadway engineers, density of asphalt pavement surfaces is essential to determine pavement quality. Unfortunately, field measurements of density by direct sampling or by nuclear measurement are slow processes. Therefore, I have explored the use of rapidly-deployed ground penetrating radar (GPR) as an alternative means of determining pavement quality. The dielectric constant of pavement surface may be a substructure parameter that correlates with pavement density, and can be used as a proxy when density of asphalt is not known from nuclear or destructive methods. The dielectric constant of the asphalt can be determined using ground penetrating radar (GPR). In order to use GPR for evaluation of road surface quality, the relationship between dielectric constants of asphalt and their densities must be established. Field measurements of GPR were taken at four highway sites in Houghton and Keweenaw Counties, Michigan, where density values were also obtained using nuclear methods in the field. Laboratory studies involved asphalt samples taken from the field sites and samples created in the laboratory. These were tested in various ways, including, density, thickness, and time domain reflectometry (TDR).
In the field, GPR data was acquired using a 1000 MHz air-launched unit and a ground-coupled unit at 200 and 500 MHz. The equipment used was owned and operated by the Michigan Department of Transportation (MDOT) and available for this study for a total of four days during summer 2005 and spring 2006. The analysis of the reflected waveforms included “routine” processing for velocity using commercial software and direct evaluation of reflection coefficients to determine a dielectric constant. The dielectric constants computed from velocities do not agree well with those obtained from reflection coefficients. Perhaps due to the limited range of asphalt types studied, no correlation between density and dielectric constant was evident.
Laboratory measurements were taken with samples removed from the field and samples created for this study. Samples from the field were studied using TDR, in order to obtain dielectric constant directly, and these correlated well with the estimates made from reflection coefficients. Samples created in the laboratory were measured using 1000 MHz air-launched GPR, and 400 MHz ground-coupled GPR, each under both wet and dry conditions.
On the basis of these observations, I conclude that dielectric constant of asphalt can be reliably measured from waveform amplitude analysis of GJPR data, based on the consistent agreement with that obtained in the laboratory using TDR. Because of the uniformity of asphalts studied here, any correlation between dielectric constant and density is not yet apparent
THE PERFORMANCE AND MODIFICATION OF RECYCLED ELECTRONIC WASTE PLASTICS FOR THE IMPROVEMENT OF ASPHALT PAVEMENT MATERIALS
Bulk electric waste plastics were recycled and reduced in size into plastic chips before pulverization or cryogenic grinding into powders. Two major types of electronic waste plastics were used in this investigation: acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS). This research investigation utilized two approaches for incorporating electronic waste plastics into asphalt pavement materials. The first approach was blending and integrating recycled and processed electronic waste powders directly into asphalt mixtures and binders; and the second approach was to chemically treat recycled and processed electronic waste powders with hydro-peroxide before blending into asphalt mixtures and binders. The chemical treatment of electronic waste (e-waste) powders was intended to strengthen molecular bonding between e-waste plastics and asphalt binders for improved low and high temperature performance. Superpave asphalt binder and mixture testing techniques were conducted to determine the rheological and mechanical performance of the e-waste modified asphalt binders and mixtures. This investigation included a limited emissions-performance assessment to compare electronic waste modified asphalt pavement mixture emissions using SimaPro and performance using MEPDG software. Carbon dioxide emissions for e-waste modified pavement mixtures were compared with conventional asphalt pavement mixtures using SimaPro. MEPDG analysis was used to determine rutting potential between the various e-waste modified pavement mixtures and the control asphalt mixture. The results from this investigation showed the following: treating the electronic waste plastics delayed the onset of tertiary flow for electronic waste mixtures, electronic waste mixtures showed some improvement in dynamic modulus results at low temperatures versus the control mixture, and tensile strength ratio values for treated e-waste asphalt mixtures were improved versus the control mixture
On the attenuation coefficient of monomode periodic waveguides
It is widely accepted that, on ensemble average, the transmission T of guided
modes decays exponentially with the waveguide length L due to small
imperfections, leading to the important figure of merit defined as the
attenuation-rate coefficient alpha = -/L. In this letter, we evidence
that the exponential-damping law is not valid in general for periodic monomode
waveguides, especially as the group velocity decreases. This result that
contradicts common beliefs and experimental practices aiming at measuring alpha
is supported by a theoretical study of light transport in the limit of very
small imperfections, and by numerical results obtained for two waveguide
geometries that offer contrasted damping behaviours
Theoretical Clues to the Ultraviolet Diversity of Type Ia Supernovae
The effect of metallicity on the observed light of Type Ia supernovae (SNe
Ia) could lead to systematic errors as the absolute magnitudes of local and
distant SNe Ia are compared to measure luminosity distances and determine
cosmological parameters. The UV light may be especially sensitive to
metallicity, though different modeling methods disagree as to the magnitude,
wavelength dependence, and even the sign of the effect. The outer density
structure, ^56 Ni, and to a lesser degree asphericity, also impact the UV. We
compute synthetic photometry of various metallicity-dependent models and
compare to UV/optical photometry from the Swift Ultra-Violet/Optical Telescope.
We find that the scatter in the mid-UV to near-UV colors is larger than
predicted by changes in metallicity alone and is not consistent with reddening.
We demonstrate that a recently employed method to determine relative abundances
using UV spectra can be done using UVOT photometry, but we warn that accurate
results require an accurate model of the cause of the variations. The abundance
of UV photometry now available should provide constraints on models that
typically rely on UV spectroscopy for constraining metallicity, density, and
other parameters. Nevertheless, UV spectroscopy for a variety of SN explosions
is still needed to guide the creation of accurate models. A better
understanding of the influences affecting the UV is important for using SNe Ia
as cosmological probes, as the UV light may test whether SNe Ia are
significantly affected by evolutionary effects.Comment: 10 pages. Submitted to Ap
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