1,465 research outputs found
Evaluation and Repair of Blast Damaged Reinforced Concrete Beams
Ten reinforced concrete beams were constructed using standard concrete and A 615 Grade 60 reinforcing steel. Eight of the beams were then damaged using C-4 Composite high explosives to replicate the actual damage that a structural element may receive from a small bomb or other explosive device. The damaged beams were then evaluated and four of the beams were determined to have been damaged beyond reasonable repair. Of the other four damaged beams, two were repaired using carbon fiber reinforced polymer (FRP). The two repaired beams, two unrepaired beams, and two control beams were then tested in third-point loading to determine flexural strength capacity.
The load-deflection curves for the six beams were then analyzed to evaluate the effect of the FRP repairs. The two repaired beams demonstrated significant improvement in flexural strength over the unrepaired beams and equaled or exceeded the flexural strength of the undamaged control beams.
The study demonstrated that fiber reinforced polymers represent a viable option for the repair of blast damaged beams. The FRP repaired beams demonstrated a significant improvement in flexural capacity in comparison to their equivalently damaged counterparts
Are Recent Peculiar Velocity Surveys Consistent?
We compare the bulk flow of the SMAC sample to the predictions of popular
cosmological models and to other recent large-scale peculiar velocity surveys.
Both analyses account for aliasing of small-scale power due to the sparse and
non-uniform sampling of the surveys. We conclude that the SMAC bulk flow is in
marginal conflict with flat COBE-normalized Lambda-CDM models which fit the
cluster abundance constraint. However, power spectra which are steeper
shortward of the peak are consistent with all of the above constraints. When
recent large-scale peculiar velocity surveys are compared, we conclude that all
measured bulk flows (with the possible exception of that of Lauer & Postman)
are consistent with each other given the errors, provided the latter allow for
`cosmic covariance'. A rough estimate of the mean bulk flow of all surveys
(except Lauer & Postman) is ~400 km/s towards l=270, b=0.Comment: 8 pages, 3 figures. To appear in Proceedings of the Cosmic Flows
Workshop, Victoria, B. C., Canada, July 1999, eds. S. Courteau, M. Strauss,
and J. Willic
The SBF Survey of Galaxy Distances. II. Local and Large-Scale Flows
We present analysis of local large scale flows using the Surface Brightness
Fluctuation (SBF) Survey for the distances to 300 early-type galaxies. Our
models of the distribution function of mean velocity and velocity dispersion at
each point in space include a uniform thermal velocity dispersion and spherical
attractors whose position, amplitude, and radial shape are free to vary. Our
fitting procedure performs a maximum likelihood fit of the model to the
observations. We obtain a Hubble constant of Ho = 77 +/- 4 +/- 7 km/s/Mpc, but
a uniform Hubble flow is not acceptable fit to the data. Inclusion of two
attractors, one of whose fit location coincides with the Virgo cluster and the
other whose fit location is slightly beyond the Centaurus clusters nearly
explain the peculiar velocities, but the quality of the fit can be further
improved by the addition of a quadrupole correction to the Hubble flow.
Although the dipole and quadrupole may be genuine manifestations of more
distant density fluctuations, we find evidence that they are more likely due to
non-spherical attractors. We find no evidence for bulk flows which include our
entire survey volume (R < 3000 km/s); our volume is at rest with respect to the
CMB. The fits to the attractors both have isothermal radial profiles (v ~ 1/r)
over a range of overdensity between about 10 and 1, but fall off more steeply
at larger radius. The best fit value for the small scale, cosmic thermal
velocity is 180 +/- 14 km/s.Comment: 37 pages, AASTeX Latex, including 30 Postscript figures, submitted to
Astrophysical Journal, July 2, 199
Susan Reynolds
Susan Reynolds was elected to the British Academy after she had worked out a new framework for the medieval history of England, France, Germany and northern Italy. The breakthrough book was her Kingdoms and Communities in Western Europe 900–1300 (1984); it brought all levels of society together in a synthesis, and was a stunning achievement. Her subsequent Fiefs and Vassals (Oxford, 1994) left a generation reluctant even to use the word ‘feudalism’, and other important contributions continued until not long before she died. In 2001 she was honoured with a Festschrift entitled Law, Laity and Solidarities
The Courts’ Inconsistent Treatment of Bethel v. Fraser and the Curtailment of Student Rights
The majority of courts have cited Bethel v. Fraser in such a way as to give public school officials free reign to censor vulgar, lewd, or plainly offensive student speech. Some courts have gone a step further and prohibited student speech that contains offensive ideas. This article seeks to explain how the Fraser decision curtailed student rights recognized in the Supreme Court\u27s last pure student speech case, Tinker v. Des Moines Independent Community School District
Magneto-electrostatic trapping of ground state OH molecules
We report the magnetic confinement of neutral, ground state hydroxyl radicals
(OH) at a density of cm and temperature of 30
mK. An adjustable electric field of sufficient magnitude to polarize the OH is
superimposed on the trap in either a quadrupole or homogenous field geometry.
The OH is confined by an overall potential established via molecular state
mixing induced by the combined electric and magnetic fields acting on the
molecule's electric dipole and magnetic dipole moments, respectively. An
effective molecular Hamiltonian including Stark and Zeeman terms has been
constructed to describe single molecule dynamics inside the trap. Monte Carlo
simulation using this Hamiltonian accurately models the observed trap dynamics
in various trap configurations. Confinement of cold polar molecules in a
magnetic trap, leaving large, adjustable electric fields for control, is an
important step towards the study of low energy dipole-dipole collisions.Comment: 4 pages, 4 figure
OH hyperfine ground state: from precision measurement to molecular qubits
We perform precision microwave spectroscopy--aided by Stark deceleration--to
reveal the low magnetic field behavior of OH in its ^2\Pi_{3/2} ro-vibronic
ground state, identifying two field-insensitive hyperfine transitions suitable
as qubits and determining a differential Lande g-factor of
1.267(5)\times10^{-3} between opposite parity components of the
\Lambda-doublet. The data are successfully modeled with an effective hyperfine
Zeeman Hamiltonian, which we use to make a tenfold improvement of the
magnetically sensitive, astrophysically important \Delta F=\pm1 satellite-line
frequencies, yielding 1720529887(10) Hz and 1612230825(15) Hz.Comment: 4+ pages, 3 figure
The excitation of the far ultraviolet electroglow emissions on Uranus, Saturn, and Jupiter
We propose that the diffuse FUV emissions of H and H_2 in excess of photoelectron excitation observed from the sunlit atmospheres of Uranus, Saturn, and Jupiter are produced by electric field acceleration of photoelectrons and ions locally in the upper atmospheres. This in situ acceleration is required to satisfy the many observational constraints on the altitude distribution, exciting particle energy, and total input energy requirements of the electroglow mechanism. We further suggest that a primary mechanism leading to this acceleration is an ionospheric dynamo, which is created in the same manner as the Earth's dynamo. The calculated altitude of charge separation by the neutral wind drag on ions across magnetic field lines is consistent with the observed peaks in electroglow emissions from the Voyager ultraviolet spectrometer limb scan data on both Saturn (near the homopause) and Uranus (just above the homopause). This dynamo action therefore appears to initiate the acceleration process, which must have the form of field-aligned potentials to accelerate the magnetized electrons. We propose that these field-aligned potentials are due to anomalous resistivity, which results from sufficiently high field-aligned currents in the ionosphere to generate plasma instabilities and therefore runaway electrons and ions above some critical lower initial energy. There are multiple candidate processes for inducing these currents, including polarization in the equivalent F regions and inner magnetospheric convection, and each of these processes should exhibit latitudinal structure. The acceleration of low-energy electrons in an H_2 atmosphere preferentially results in FUV radiation and further ionization, whereas electron acceleration in a nitrogen/oxygen atmosphere such as the Earth' is dominated by elastic scattering and thus results in electric currents. Individual electron and proton collisions with H_2 molecules will result in excitation, ionization, and heating, so that considerable enhancement of the ionospheric density and heating of the upper atmosphere will accompany the FUV emission
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