1,411 research outputs found
Calibrated Dynamic Response Analysis of Stafford Dam
Stafford Dam, an approximately 79-ft high compacted earthfill founded on stream alluvium approximately 40 feet thick, was shaken by the 1989 Lorna Prieta Earthquake. Records of the earthquake motions were obtained from seismographs located at the dam crest and at the right abutment on rock. Two-dimensional dynamic finite element analyses were performed to calibrate a model of the dam using the recorded motions. Excellent agreement between the recorded and calculated response was obtained by appropriate adjustments to material parameters based on shear wave velocity measurements. Various deconvolution methods for obtaining input bedrock motions to calculate the dam response are discussed
Response of Two Dams in the 1987 Whittier Narrows Earthquake
The 1987 Whittier Narrows earthquake (ML = 5.9) shook two dams, the Puddingstone and Cogswell dams, which were instrumented as part of the California Strong Motion Instrumentation Program (CSMIP). The resulting recorded accelerograms provided a valuable opportunity to investigate and evaluate the accuracy and reliability of conventional geotechnical procedures for evaluation of dynamic response characteristics of earth and rockfill dams. This paper presents the results of these studies, which provide insight regarding current techniques for dynamic soil property evaluation and the applicability of one- and two-dimensional analytical procedures to evaluation of the dynamic response of these types of dams
Site Response of Organic Soils
A primary source of uncertainty in any evaluation of the seismic stability of the Sacramento-San Joaquin Delta levee system is the site response characteristics of the shallow organic soils that commonly underlay the levees. This paper provides an overview of recent research on the site response characteristics of organic soils using centrifuge and numerical modeling. The centrifuge modeling effort included the development of techniques to measure the shear wave velocity profile for a centrifuge model while in-flight. One-dimensional site response analyses using an equivalent linear procedure were performed with the measured shear wave velocity profiles and the modulus reduction and damping relationships determined from prior laboratory studies. Good agreement was obtained between the numerical simulations and the centrifuge model recordings
Effects of Sample Disturbance and Consolidation Procedures on Cyclic Strengths of Intermediate Soils
Sampling and testing of soils to measure engineering properties, such as monotonic and cyclic undrained shear strengths, requires an understanding of the potential effects of sampling disturbance and the selection of appropriate laboratory testing procedures. For clays, past research has provided insights on how sampling methods and laboratory testing procedures can be used in practice to assess and minimize sample disturbance effects. For sands, past research has shown that conventional tube sampling techniques cause excessive disturbance to the soil fabric, such that subsequent measurement of monotonic or cyclic strengths can be greatly in error and misleading. For intermediate soils, the effects of disturbance and consolidation procedures on monotonic and cyclic strengths are not well understood. In the present study, a test protocol was developed to assess the effects that disturbance during sample extrusion, trimming, and mounting have on subsequent measurements of compressibility, monotonic undrained strength, and cyclic undrained strength. Detailed laboratory tests were performed on tube samples from deposits of low-plasticity silty clay, for which conventional sampling and testing were expected to work reasonably well, and low-plasticity clayey sand, for which the effects of sample disturbance were of primary concern. Test results using this protocol for these two soils are presented and discussed
Infrared Emission from Interstellar Dust. II. The Diffuse Interstellar Medium
We present a quantitative model for the infrared emission from dust in the
diffuse interstellar medium. The model consists of a mixture of amorphous
silicate grains and carbonaceous grains, each with a wide size distribution
ranging from molecules containing tens of atoms to large grains > 1 um in
diameter. We assume that the carbonaceous grains have polycyclic aromatic
hydrocarbon (PAH)-like properties at very small sizes, and graphitic properties
for radii a > 50 A. On the basis of recent laboratory studies and guided by
astronomical observations, we propose "astronomical" absorption cross sections
for use in modeling neutral and ionized PAHs from the far ultraviolet to the
far infrared. We also propose modifications to the far-infrared emissivity of
"astronomical silicate". We calculate energy distribution functions for small
grains undergoing "temperature spikes" due to stochastic absorption of
starlight photons, using realistic heat capacities and optical properties.
Using a grain size distribution consistent with the observed interstellar
extinction, we are able to reproduce the near-IR to submillimeter emission
spectrum of the diffuse interstellar medium, including the PAH emission
features at 3.3, 6.2, 7.7, 8.6, and 11.3um. The model is compared with the
observed emission at high Galactic latitudes as well as in the Galactic plane,
as measured by COBE and IRTS. We calculate infrared emission spectra for our
dust model heated by a range of starlight intensities, and we provide tabulated
dust opacities (extended tables available at
http://www.astro.princeton.edu/~draine/dust/dustmix.html)Comment: Final version published in ApJ, 554, 778 but with factor 1.086 error
in Table 6 and Fig. 16 corrected. Main change from astro-ph version 1 is
correction of typographical errors in Table 1, and correction of typo in eq.
(A2). 51 pages, 16 figures, Late
Linear connections with propagating spin-3 field in gravity
We show that Fronsdal's Lagrangian for a free massless spin-3 gauge field in
Minkowski spacetime is contained in a general Yang--Mills-like Lagrangian of
metric-affine gravity (MAG), the gauge theory of the general affine group in
the presence of a metric. Due to the geometric character of MAG, this can best
be seen by using Vasiliev's frame formalism for higher-spin gauge fields in
which the spin-3 frame is identified with the tracefree nonmetricity one-form
associated with the shear generators of GL(n,R). Furthermore, for specific
gravitational gauge models in the framework of full nonlinear MAG, exact
solutions are constructed, featuring propagating massless and massive spin-3
fields.Comment: References added. Minor corrections and clarifications. To be
published in Phys. Rev.
Field-dependent heat transport in the Kondo insulator SmB6 : phonons scattered by magnetic impurities
The thermal conductivity of the Kondo insulator SmB was measured
at low temperature, down to 70 mK, in magnetic fields up to 15 T, on single
crystals grown using both the floating-zone and the flux methods. The residual
linear term at is found to be zero in all samples, for
all magnetic fields, in agreement with previous studies. There is therefore no
clear evidence of fermionic heat carriers. In contrast to some prior data, we
observe a large enhancement of with increasing field. The effect of
field is anisotropic, depending on the relative orientation of field and heat
current (parallel or perpendicular), and with respect to the cubic crystal
structure. We interpret our data in terms of heat transport predominantly by
phonons, which are scattered by magnetic impurities.Comment: publish versio
Optical Spectroscopy of Galactic Cirrus Clouds: Extended Red Emission in the Diffuse Interstellar Medium
We present initial results from the first optical spectroscopic survey of
high latitude Galactic cirrus clouds. The observed shape of the cirrus spectrum
does not agree with that of scattered ambient Galactic starlight. This mismatch
can be explained by the presence of Extended Red Emission (ERE) in the diffuse
interstellar medium, as found in many other astronomical objects, probably
caused by photoluminescence of hydrocarbons. The integrated ERE intensity,
I_ERE \approx 1.2 x 10^{-5} erg s^{-1} cm^{-2} sr^{-1}, is roughly a third of
the scattered light intensity, consistent with recent color measurements of
diffuse Galactic light. The peak of the cirrus ERE (lambda_{0} \sim 6000 AA) is
shifted towards short (bluer) wavelengths compared to the ERE in sources
excited by intense ultraviolet radiation, such as HII regions (lambda_{0} sim
8000 AA); such a trend is seen in laboratory experiments on hydrogenated
amorphous carbon films.Comment: 7 pages, 2 figures. Accepted for publication in ApJ Letter
Seasonal home ranges and habitat selection of three elk (Cervus elaphus) herds in North Dakota
Changes in land use have resulted in range shifts of many wildlife species, including those entering novel environments, resulting in the critical need to understand their spatial ecology to inform ecosystem effects and management decisions. Dispersing elk (Cervus elaphus) were colonizing areas of suitable habitat in the Northern Great Plains, USA, resulting in crop depredation complaints in these areas. Although state resource managers had little information on these elk herds, limited evidence suggested temporal movements into Canada. We collected and analyzed essential information on home range and habitat selection for 3 elk herds residing in North Dakota. We captured 5 adult female elk in each study area, affixed global positioning system collars, and monitored them for 1 year (2016–2017). We estimated diel period, seasonal, and hunting season home ranges using Brownian Bridge Movement Models for each individual. We analyzed habitat selection using multinomial logit models to test for differences in use of land classes, and for departures from proportionate use based on random sampling; our predictor variables included individual elk, diel period, and season. Home ranges differed between the 3 herds, seasons, and diel period; gun and winter season home ranges were both larger than in summer, as was night when compared with day. Female elk generally restricted themselves to cover during the day and entered open areas at night and during winter months. Our results also suggest that elk in our study areas tended to seek more cover, and in the case of our Turtle Mountain study area, some cross into Canada during gun season. Our study provides a better understanding of the spatial ecology of elk in the Northern Great Plains while highlighting the need for enhanced international cooperative management efforts
Powerful H Line-cooling in Stephan's Quintet : I - Mapping the Significant Cooling Pathways in Group-wide Shocks
We present results from the mid-infrared spectral mapping of Stephan's
Quintet using the Spitzer Space Telescope. A 1000 km/s collision has produced a
group-wide shock and for the first time the large-scale distribution of warm
molecular hydrogen emission is revealed, as well as its close association with
known shock structures. In the main shock region alone we find 5.0
M of warm H spread over 480 kpc and
additionally report the discovery of a second major shock-excited H
feature. This brings the total H line luminosity of the group in excess of
10 erg/s. In the main shock, the H line luminosity exceeds, by a
factor of three, the X-ray luminosity from the hot shocked gas, confirming that
the H-cooling pathway dominates over the X-ray. [Si II]34.82m
emission, detected at a luminosity of 1/10th of that of the H, appears to
trace the group-wide shock closely and in addition, we detect weak
[FeII]25.99m emission from the most X-ray luminous part of the shock.
Comparison with shock models reveals that this emission is consistent with
regions of fast shocks (100 < < 300 km/s) experiencing depletion of
iron and silicon onto dust grains. Star formation in the shock (as traced via
ionic lines, PAH and dust emission) appears in the intruder galaxy, but most
strikingly at either end of the radio shock. The shock ridge itself shows
little star formation, consistent with a model in which the tremendous H
power is driven by turbulent energy transfer from motions in a post-shocked
layer. The significance of the molecular hydrogen lines over other measured
sources of cooling in fast galaxy-scale shocks may have crucial implications
for the cooling of gas in the assembly of the first galaxies.Comment: 23 pages, 15 figures, Accepted to Ap
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