1,290 research outputs found
Dilatometer Based Liquefaction Potential of Sites in the Imperial Valley
The liquefaction potential of several sites in the Imperial Valley, south California, is evaluated on the basis of standard penetration, cone, and dilatometer test data. The performance of the soil deposits at these sites during past earthquakes has been documented in earlier studies. Since the dilatometer parameter Kd is expected to reflect factors (e.g. fabric, prestress, preshaking, aging) affecting liquefaction potential to a certain extent (Marchetti, 1982), this paper primarily focuses on this parameter as an index for evaluating liquefaction potential. A tentative boundary curve (in terms of stress ratio vs. Kd) for evaluating liquefaction potential that takes advantage of earlier boundaries is proposed. A promising index which combines dynamic and static dilatometer tests is also proposed
Total cross sections for positrons scattered elastically from helium based on new measurements of total ionization cross sections
An improved technique is presented for employing the 2.3m spectrometer to measure total ionization cross sections, Q sub ion, for positrons incident on He. The new ionization cross section agree with the values reported earlier. Estimates are also presented of total elastic scattering cross section, Q sub el, obtained by subtracting from total scattering cross sections, Q sub tot, reported in the literature, the Q sub ion and Q sub Ps (total positronium formation cross sections) and total excitation cross sections, Q sub ex, published by another researcher. The Q sub ion and Q sub el measured with the 3m high resolution time-of-flight spectrometer for 54.9eV positrons are in accord with the results from the 2.3m spectrometer. The ionization cross sections are in fair agreement with theory tending for the most part to be higher, especially at 76.3 and 88.5eV. The elastic cross section agree quite well with theory to the vicinity of 50eV, but at 60eV and above the experimental elastic cross sections climb to and remain at about 0.30 pi a sub o sq while the theoretical values steadily decrease
Performance of Fill Soils During the Loma Prieta Earthquake
The results of high quality in situ test results obtained at Hunter\u27s Point Naval Station both before and after the Lorna Prieta earthquake are presented. The interpretation of these tests and the results of subsequent numerical ground motion analyses are validated by the observed response at that site during the event. Data show that densification of the loose fill soils occurred as a result of the seismic activity and corroborate the observed surface deformations
Chaotic motion of space charge wavefronts in semiconductors under time-independent voltage bias
A standard drift-diffusion model of space charge wave propagation in
semiconductors has been studied numerically and analytically under dc voltage
bias. For sufficiently long samples, appropriate contact resistivity and
applied voltage - such that the sample is biased in a regime of negative
differential resistance - we find chaos in the propagation of nonlinear fronts
(charge monopoles of alternating sign) of electric field. The chaos is always
low-dimensional, but has a complex spatial structure; this behavior can be
interpreted using a finite dimensional asymptotic model in which the front
(charge monopole) positions and the electrical current are the only dynamical
variables.Comment: 12 pages, 8 figure
Gist and verbatim communication concerning medication risks/benefits
To describe the information about medication risks/benefits that rheumatologists provide during patient office visits, the gist that patients with rheumatoid arthritis (RA) extract from the information provided, and the relationship between communication and medication satisfaction
Analytic and geometric properties of photoinduced effects in noncentrosymmetric crystals: photovoltaic current and optical rectification
An original dispersion relation between the stationary coherent nonlinear
optical responses by current and polarisation is obtained. The dispersion
relation provides a new complimentary tool that can be employed to study
light-induced charge transport models and facilitate experimental data
analysis. It is shown that the origin of the coherent current and the
dc-polarisation induced in a noncentrosymmetric crystal under illumination is
related to the theory of the Berry phase and can be represented in terms of the
renormalised geometric potentials. This renormalisation originates from the
extra phase difference acquired by a carrier in the light field on the quantum
transition between the electronic bands. The gauge invariance of the
corresponding expressions for the current and the polarisation is demonstrated.Comment: 7 page
Stationary solutions of driven fourth- and sixth-order Cahn-Hilliard type equations
New types of stationary solutions of a one-dimensional driven sixth-order
Cahn-Hilliard type equation that arises as a model for epitaxially growing
nano-structures such as quantum dots, are derived by an extension of the method
of matched asymptotic expansions that retains exponentially small terms. This
method yields analytical expressions for far-field behavior as well as the
widths of the humps of these spatially non-monotone solutions in the limit of
small driving force strength which is the deposition rate in case of epitaxial
growth. These solutions extend the family of the monotone kink and antikink
solutions. The hump spacing is related to solutions of the Lambert
function. Using phase space analysis for the corresponding fifth-order
dynamical system, we use a numerical technique that enables the efficient and
accurate tracking of the solution branches, where the asymptotic solutions are
used as initial input. Additionally, our approach is first demonstrated for the
related but simpler driven fourth-order Cahn-Hilliard equation, also known as
the convective Cahn-Hilliard equation
Diagnostic criterion for crystallized beams
Small ion crystals in a Paul trap are stable even in the absence of laser
cooling. Based on this theoretically and experimentally well-established fact
we propose the following diagnostic criterion for establishing the presence of
a crystallized beam: Absence of heating following the shut-down of all cooling
devices. The validity of the criterion is checked with the help of detailed
numerical simulations.Comment: REVTeX, 11 pages, 4 figures; submitted to PR
Results from a Search for Light-Mass Dark Matter with a P-type Point Contact Germanium Detector
We report on several features present in the energy spectrum from an ultra
low-noise germanium detector operated at 2,100 m.w.e. By implementing a new
technique able to reject surface events, a number of cosmogenic peaks can be
observed for the first time. We discuss several possible causes for an
irreducible excess of bulk-like events below 3 keVee, including a dark matter
candidate common to the DAMA/LIBRA annual modulation effect, the hint of a
signal in CDMS, and phenomenological predictions. Improved constraints are
placed on a cosmological origin for the DAMA/LIBRA effect.Comment: 4 pages, 4 figures. v2: submitted version. Minimal changes in
wording, one reference adde
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