259 research outputs found
Macroelement modeling of shallow foundations
The paper presents a new macroelement model for shallow foundations. The
model is defined through a non-linear constitutive law written in terms of some
generalized force and displacement parameters. The linear part of this
constitutive law comes from the dynamic impedances of the foundation. The
non-linear part comprises two mechanisms. One is due to the irreversible
elastoplastic soil behavior: it is described with a bounding surface
hypoplastic model, adapted for the description of the cyclic soil response. An
original feature of the formulation is that the bounding surface is considered
independently of the surface of ultimate loads of the system. The second
mechanism is the detachment that can take place at the soil-footing interface
(foundation uplift). It is totally reversible and non-dissipative and can thus
be described by a phenomenological non-linear elastic model. The macroelement
is qualitatively validated by application to soil-structure interaction
analyses of simple real structures
Rupture sismique des fondations par perte de capacité portante: Le cas des semelles circulaires
International audienceWithin the context of earthquake-resistant design of shallow foundations, the present study is concerned with the determination of the seismic bearing capacity of a circular footing resting on the surface of a heterogene-ous purely cohesive semi-infinite soil layer. In the first part of the paper, a database, containing case histories of civil engineering structures that sustained a foundation seismic bearing capacity failure, is briefly pre-sented, aiming at a better understanding of the studied phenomenon and offering a number of case studies useful for validation of theoretical computations. In the second part of the paper, the aforementioned problem is addressed using the kinematic approach of the Yield Design theory, thus establishing optimal upper bounds for the ultimate seismic loads supported by the soil-footing system. The results lead to the establishment of some very simple guidelines that extend the existing formulae for the seismic bearing capacity contained in the European norms (proposed for strip footings on homogeneous soils) to the case of circular footings and to that of heterogeneous cohesive soils
Some consequences of a spatially varying cosmological constant in a spherically symmetric distribution of matter
This paper investigates the effects of the spatial variation of the cosmological constant Λ on the spacetime geometry within and outside a massive object. It is seen that the variation of Λ with the radial coordinate introduces non-trivial changes leading to spacetime closing on itself around a massive object. It may also be possible to generate interior solutions that lead to flat rotation curves of galaxies
Validation of a Piles Dynamic Analysis Computer Code Through In Situ Tests
In order to qualify the CLAPIFOU code, which computes the dynamic response of a pile foundation subjected to earthquake or harmonic forces, a test campaign was carried out on piles, to full scale, on pile groups of 2 x 1 piles and 2 x 3 piles on the Plancoet site. The purpose of the study is to compare the results of the experiments and the digital simulations with the computer code. The comparison is good but confirms the need for a good knowledge of the soil\u27s characteristics
Electron density in the quiet solar coronal transition region from SoHO/SUMER measurements of S VI line radiance and opacity
Context: The sharp temperature and density gradients in the coronal
transition region are a challenge for models and observations.
Aims: We set out to get linearly- and quadratically-weighted average electron
densities in the region emitting the S VI lines, using the observed opacity and
the emission measure of these lines.
Methods: We analyze SoHO/SUMER spectroscopic observations of the S VI lines,
using the center-to-limb variations and radiance ratios to derive the opacity.
We also use the Emission Measure derived from radiance at disk center.
Results: We get an opacity at S VI line center of the order of 0.05. The
resulting average electron density is 2.4 10^16 m^-3 at T = 2 10^5 K. This
value is higher than the values obtained from radiance measurements.
Conversely, taking a classical value for the density leads to a too high value
of the thickness of the emitting layer.
Conclusions: The pressure derived from the Emission Measure method compares
well with previous determinations and implies a low opacity of 5 10^-3 to
10^-2. The fact that a direct derivation leads to a much higher opacity remains
unexplained, despite tentative modeling of observational biases. Further
measurements need to be done, and more realistic models of the transition
region need to be used.Comment: 11 pages, 9 figure
The Radiative Transport of Dust in Primordial Galaxies and Second-Generation Star Formation
We investigate the radiative transport of dust in primordial galaxies in the
presence of the UV radiation field from the first metal-free stars. We find
that dust created in the first supernova (SN) explosions can be driven through
the interior of the SN remnant to accumulate in the SN shells, where
second-generation stars may form from compressed cooling gas. This scenario
requires metal-free stars to form continuously over timescales of up to 10 Myr,
consistent with recent estimates. Silicate and graphite grains, as well as
iron-bearing magnetites, are transported to the shells for reasonable parameter
assumptions, but their relative yields from primordial SNe is an important
factor in the resulting abundance ratios. We compare the results of segregated
grain transport with the current nucleosynthetic data on extremely metal-poor
Galactic halo stars. Fossil signatures of this process may already have been
detected in those iron-poor stars with enhanced carbon and silicate elements
such as magnesium, silicon and oxygen. We discuss the implications of our
results for the transition from first- to second-generation star formation in
primordial galaxies, and the role played by the radiative transport of dust in
this process.Comment: Accepted by ApJ; 10 ApJ-style pages, 5 figures. Minor revisions with
added text, results and figures unchanged. Will appear in ApJ v. 640, 20
March 2006 issu
Numerical analysis of seismic wave amplification in Nice (France) and comparisons with experiments
The analysis of site effects is very important since the amplification of
seismic motion in some specific areas can be very strong. In this paper, the
site considered is located in the centre of Nice on the French Riviera. Site
effects are investigated considering a numerical approach (Boundary Element
Method) and are compared to experimental results (weak motion and
microtremors). The investigation of seismic site effects through numerical
approaches is interesting because it shows the dependency of the amplification
level on such parameters as wave velocity in surface soil layers, velocity
contrast with deep layers, seismic wave type, incidence and damping. In this
specific area of Nice, a one-dimensional (1D) analytical analysis of
amplification does not give a satisfactory estimation of the maximum reached
levels. A boundary element model is then proposed considering different wave
types (SH, P, SV) as the seismic loading. The alluvial basin is successively
assumed as an isotropic linear elastic medium and an isotropic linear
viscoelastic solid (standard solid). The thickness of the surface layer, its
mechanical properties, its general shape as well as the seismic wave type
involved have a great influence on the maximum amplification and the frequency
for which it occurs. For real earthquakes, the numerical results are in very
good agreement with experimental measurements for each motion component.
Two-dimensional basin effects are found to be very strong and are well
reproduced numerically
Molecular cloning and expression in photosynthetic bacteria of a soybean cDNA coding for phytoene desaturase, an enzyme of the carotenoid biosynthesis pathway.
Catalog of 93 Nova Light Curves: Classification and Properties
We present a catalog of 93 very-well-observed nova light curves. The light
curves were constructed from 229,796 individual measured magnitudes, with the
median coverage extending to 8.0 mag below peak and 26% of the light curves
following the eruption all the way to quiescence. Our time-binned light curves
are presented in figures and as complete tabulations. We also calculate and
tabulate many properties about the light curves, including peak magnitudes and
dates, times to decline by 2, 3, 6, and 9 magnitudes from maximum, the time
until the brightness returns to quiescence, the quiescent magnitude, power law
indices of the decline rates throughout the eruption, the break times in this
decline, plus many more properties specific to each nova class. We present a
classification system for nova light curves based on the shape and the time to
decline by 3 magnitudes from peak (t3). The designations are S for smooth light
curves (38% of the novae), P for plateaus (21%), D for dust dips (18%), C for
cusp-shaped secondary maxima (1%), O for quasi-sinusoidal oscillations
superposed on an otherwise smooth decline (4%), F for flat-topped light curves
(2%), and J for jitters or flares superposed on the decline (16%). Our
classification consists of this single letter followed by the t3 value in
parentheses; so for example V1500 Cyg is S(4), GK Per is O(13), DQ Her is
D(100), and U Sco is P(3).Comment: Astronomical Journal, in press, 19 figures, 73 page
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