6,422 research outputs found
Centrifuge modelling of cone penetration tests in layered soils
Penetration problems are important in many areas of geotechnical engineering, such as the prediction of pile capacity and interpretation of in situ test data. The cone penetration test is a proven method for evaluating soil properties, yet relatively little research has been conducted to understand the effect of soil layering on penetrometer readings. This paper focuses on the penetration of a probe within layered soils and investigates the layered soil effects on both penetration resistance and soil deformation. A series of centrifuge tests was performed in layered configurations of silica sand with varying relative density in a 180° axisymmetric model container. The tests allowed for the use of a half-probe for observation of the induced soil deformation through a poly(methyl methacrylate) window as well as a full-probe for measurement of penetration resistance within the central area of the container. The variations of penetration resistance and soil deformation characteristics as they relate to penetration depth, soil density and soil layering are examined. The results of deformation are also compared with previous experimental data to examine the effect of the axisymmetric condition. The effects of soil layering on both resistance and soil deformation are shown to be dependent on the relative properties between soil layers
Benchmark solutions of large-strain cavity contraction for deep tunnel convergence in geomaterials
To provide precise prediction of tunnelling-induced deformation of the surrounding geomaterials, a framework for derivation of rigorous large-strain solutions of unified spherical and cylindrical cavity contraction is presented for description of confinement-convergence responses for deep tunnels in geomaterials. Considering the tunnelling-induced large deformation, logarithmic strains are adopted for cavity contraction analyses in linearly elastic, non-associated Mohr–Coulomb, and brittle Hoek–Brown media. Compared with approximate solutions, the approximation error indicates the importance of release of small-strain restrictions for estimating tunnel convergence profiles, especially in terms of the scenarios with high stress condition and stiffness degradation under large deformation. The ground reaction curve is therefore predicted to describe the volume loss and stress relaxation around the tunnel walls. The stiffness of circular lining is calculated from the geometry and equivalent modulus of the supporting structure, and a lining installation factor is thus introduced to indicate the time of lining installation based on the prediction of spherical cavity contraction around the tunnel opening face. This study also provides a general approach for solutions using other sophisticated geomaterial models, and serves as benchmarks for analytical developments in consideration of nonlinear large-deformation behaviour and for numerical analyses of underground excavation
Quasi-16-day periodic meridional movement of the equatorial ionization anomaly
Based on the daytime location of the equatorial ionization anomaly (EIA)
crest derived from GPS observations at low latitude over China during the
2005–2006 stratospheric sudden warming (SSW), a quasi-16-day periodic
meridional movement of EIA crest with the maximum amplitude of about 2
degrees relative to the average location of EIA crest has been revealed. In
addition, periodic variations that are in phase with the meridional EIA
movement are also revealed in the equatorial electrojet (EEJ) and F2 layer
peak height (<i>hm</i>F2) over Chinese ionosonde stations Haikou and Chongqing. The
quasi-16-day periodic component in Dst index is weak, and the 16-day
periodic component does not exist in F10.7 index. Such large-scale periodic
meridional movement of EIA crest is likely related to the globally enhanced
stratospheric planetary waves coupled with anomalous stratospheric zonal
wind connected with SSW. In addition, such large-scale periodic movement of
EIA should be global, and can affect the ionospheric morphology around the
low-latitude belt near the EIA region. Further case analysis, simulation and
theoretical studies must proceed in order to understand the periodic
movements of EIA connected with the different periodic atmospheric
variations
Aircraft measurements of microphysical properties of subvisible cirrus in the tropical tropopause layer
International audienceSubvisible cirrus (SVC) clouds are often observed within the tropical tropopause layer (TTL). Some studies suggest that SVC has a significant impact on the earth radiation budget. The Costa Rica Aura Validation Experiment (CR-AVE) sponsored by the National Aeronautics and Space Administration (NASA) took place near San Jose, Costa Rica from 14 January?15 February 2006. The NASA WB-57F sampled SVC in the TTL from ?75°C to ?90°C with an improved set of cloud particle probes. The first digital images of ice particles in the TTL are compared with replicator images of ice particles collected in 1973 by a WB-57F in the TTL. The newer measurements reveal larger particles, on the order of 100 ?m compared with <50 ?m from the earlier measurements, and also different particle shapes. The 1973 particles were mainly columnar and trigonal, whereas the newer measurements are quasi-spherical and hexagonal plates. The WB-57F also measured very high water vapor contents with some instruments, up to 4 ppmv, and aerosols with mixed organics and sulfates. It is unknown whether these ambient conditions were present in the 1973 studies, and whether such conditions have an influence on particle shape and the development of the large particles. A companion paper (Jensen et al., 2008) presents crystal growth calculations that suggest that the high water vapor measurements are required to grow ice particles to the observed sizes of 100 ?m and larger
Real Scalar Field Scattering with Polynomial Approximation around Schwarzschild-de Sitter Black-hole
As one of the fitting methods, the polynomial approximation is effective to
process sophisticated problem. In this paper, we employ this approach to handle
the scattering of scalar field around the Schwarzschild-de Sitter black-hole.
The complex relationship between tortoise coordinate and radial coordinate is
replaced by the approximate polynomial. The Schrdinger-like equation,
the real boundary conditions and the polynomial approximation construct a full
Sturm-Liouville type problem. Then this boundary value problem can be solved
numerically according to two limiting cases: the first one is the Nariai
black-hole whose horizons are close to each other, the second one is when the
horizons are widely separated. Compared with previous results (Brevik and
Tian), the field near the event horizon and cosmological horizon can have a
better description.Comment: revtex4 source file, 11 pages, 8 figure
Future scenarios modeling of urban stormwater management response to impacts of climate change and urbanization
Future scenario modeling was used to investigate the effectiveness of urban stormwater infrastructure and its response to potential future changes. The changes of urban stormwater, both in-flow quantity and water quality, in response to climate change and urbanization were examined and tested in two highly developed urban catchments using the US Environmental Protection Agency’s Storm Water
Management Model. Similar responses were observed in the two catchments, despite their differences in size and land use. Flow quantity and water quality appeared to be more sensitive to urbanization factors than to climatic change. With respect to factors attributable to urbanization, urban
intensification (land use plus population density) had more of an effect than land-use changes alone. Low-impact development, as a key adaptation measure, could be effective in mitigating the adverse impacts of future changes on urban stormwater. The methodology developed in this study may be useful for urban stormwater planning and testing such plans against future urbanization and climate change scenarios
Time-dependent density-functional theory for open systems
By introducing the self-energy density functionals for the dissipative
interactions between the reduced system and its environment, we develop a
time-dependent density-functional theory formalism based on an equation of
motion for the Kohn-Sham reduced single-electron density matrix of the reduced
system. Two approximate schemes are proposed for the self-energy density
functionals, the complete second order approximation and the wide-band limit
approximation. A numerical method based on the wide-band limit approximation is
subsequently developed and implemented to simulate the steady and transient
current through various realistic molecular devices. Simulation results are
presented and discussed.Comment: 16 pages, 12 figure
Local stochastic non-Gaussianity and N-body simulations
Large-scale clustering of highly biased tracers of large-scale structure has
emerged as one of the best observational probes of primordial non-Gaussianity
of the local type (i.e. f_{NL}^{local}). This type of non-Gaussianity can be
generated in multifield models of inflation such as the curvaton model.
Recently, Tseliakhovich, Hirata, and Slosar showed that the clustering
statistics depend qualitatively on the ratio of inflaton to curvaton power \xi
after reheating, a free parameter of the model. If \xi is significantly
different from zero, so that the inflaton makes a non-negligible contribution
to the primordial adiabatic curvature, then the peak-background split ansatz
predicts that the halo bias will be stochastic on large scales. In this paper,
we test this prediction in N-body simulations. We find that large-scale
stochasticity is generated, in qualitative agreement with the prediction, but
that the level of stochasticity is overpredicted by ~30%. Other predictions,
such as \xi independence of the halo bias, are confirmed by the simulations.
Surprisingly, even in the Gaussian case we do not find that halo model
predictions for stochasticity agree consistently with simulations, suggesting
that semi-analytic modeling of stochasticity is generally more difficult than
modeling halo bias.Comment: v3: minor changes matching published versio
A Simple Model for Anisotropic Step Growth
We consider a simple model for the growth of isolated steps on a vicinal
crystal surface. It incorporates diffusion and drift of adatoms on the terrace,
and strong step and kink edge barriers. Using a combination of analytic methods
and Monte Carlo simulations, we study the morphology of growing steps in
detail. In particular, under typical Molecular Beam Epitaxy conditions the step
morphology is linearly unstable in the model and develops fingers separated by
deep cracks. The vertical roughness of the step grows linearly in time, while
horizontally the fingers coarsen proportional to . We develop scaling
arguments to study the saturation of the ledge morphology for a finite width
and length of the terrace.Comment: 20 pages, 12 figures; [email protected]
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