12,791 research outputs found
Shock temperatures in calcite (CaCO3): Implication for shock induced decomposition
The temperatures induced in crystalline calcite upon planar shock compression (95â160 GPa) are reported from two-stage light gas-gun experiments. The temperatures are obtained fitting 6-channel optical pyrometer radiances in the 450 to 900 nm range, to a Planck radiation law temperature varied from 3300 to 5400 K. Calculations demonstrate that the temperatures are some 400 to 1350 K lower than if either shock-induced melting and/or disproportionation of calcite behind the shock front was not occurring. Here calcite is modeled as disproportionating into a molecular liquid, or a solid CaO plus CO2 gas. For temperature calculations, specific heat at constant volume for one mole of CO2 is taken to be 6.7R as compared to 9R in the solid state; whereas calcite and CaO have their solid state values (15R and 6R). Calculations also suggest that the onset of decomposition in calcite to CaO and CO2 during loading occurs at ~75±10 GPa, along the Hugoniot whereas decomposition begins upon unloading from 18 GPa. The 18 GPa value is based on comparison of VISAR measurements of particle velocity profiles induced upon isentropic expansion with one-dimensional numerical simulation
Spin observables and the determination of the parity of in photoproduction reactions
Spin observables in the photoproduction of the are explored for
the purpose of determining the parity of the . Based on reflection
symmetry in the scattering plane, we show that certain spin observables in the
photoproduction of the can be related directly to its parity. We
also show that measurements of both the target nucleon asymmetry and the polarization may be useful in determining the parity of in
a model-independent way. Furthermore, we show that no combination of spin
observables involving only the polarization of the photon and/or nucleon in the
initial state can determine the parity of unambiguously.Comment: LaTeX, 11 pages, minor revisio
Research study of some RAM antennas Final report, 18 Nov. 1964 - 18 Jun. 1965
Input impedance and radiation pattern determinations for cylindrical gap, waveguide excited and circular waveguide slot antenna array
Cross sections for the excitation of isovector charge-exchange resonances in 208Tl
The Glauber approximation for the treatment of heavy-ion scattering, has
already been shown to give reliable predictions for the reaction cross section
in the particular case of intermediate energy charge-exchange processes. In the
present work, we couple a Glauber-type model to microscopic Random Phase
Approximation calculations of the charge-exchange excitations of Pb.
The aim is to solve the longstanding question whether the very elusive
charge-exchange isovector monopole has been really identified in the past
experiments, or other multipoles were prevalent in the observed spectra.Comment: text + 4 figures; accepted for publication in Phys. Rev.
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Hydropyrolysis of high molecular weight organic matter in Murchison
Hydropyrolysis of the Murchison macromolecular material releases polyaromatic compounds including phenanthrene, carbazole, fluoranthene, pyrene, chrysene, perylene, benzoperylene and coronene units with varying degrees of alklyation
A study of acute respiratory disease in families exposed to different levels of Air pollution in the Great Salt Lake basin, Utah, 1971-1972 and 1972-1973.
The reported incidence of acute respiratory illness in families exposed to different concentrations of air pollution was studied during two consecutive school years. The purpose of the study was to determine the effect of increased exposure to sulfur dioxide and suspended particulate matter. In each of four study communities, the mothers of approximately 250 white families were contacted biweekly to obtain information regarding the occurrence of respiratory symptoms in each family member. Annual mean ambient sulfur dioxide concentrations in one community for the three years included in the study (1971-1973) were well above the current air quality standard of 80 micrograms/m3, while in the other three communities the annual sulfur dioxide concentrations were much lower (usually less than 40 micrograms/m3). Suspended particulate matter concentrations in high sulfur dioxide community were close to the limit designated by the annual standard (75 micrograms/m3) but actual exposures in the four communities probably were not excessive. Regression analyses of the data collected showed inconsistent associations between illness rates and educational attainment of the head of household, crowding in the home, bronchitis in parents or smoking of parents. However, once the effects of these factors were removed the adjusted rates showed little association with community of residence. It was concluded that the higher concentrations of sulfur dioxide in the Utah atmosphere could not be the cause of increases in acute respiratory illness in the exposed populations
STR-926: FOOTFALL-INDUCED VIBRATION: PREDICTION AND CONTROL STRATEGIES
Footfalls can produce vibrations that are irritating to occupants, or disruptive to vibration-sensitive spaces in hospitals and research laboratories. This paper describes, using case studies, techniques that can be used to predict vibrations, and mitigation strategies to control them. Firstly, pedestrian loading on footbridges is described. Stochastic simulations are conducted in which a number of pedestrians with random weights, walking speeds, and walking paths cross a bridge with random spacing. The resulting vibration response of the bridge is determined to estimate the peak acceleration of the bridge. For the case considered, tuned mass dampers (TMDs) were subsequently installed on the bridge to increase the effective damping of two modes. Next, crowd loading on stadia and ballroom structures is considered. For these structures, the crowd-structure interaction must be considered since the mass of the crowd is a significant fraction of the mass of the structure, which alters the dynamic response of the system. In the case presented, TMDs are considered to reduce the vibrations associated with crowd excitation. Lastly, the vibrations associated with a pedestrian walking in a corridor adjacent to a vibration-sensitive room in a hospital or research facility are described. Maintaining low vibrations in these hospitals and laboratories is critical as the operation of equipment may be adversely affected by vibrations that are well below the threshold of human perception. Typical mitigation strategies for these vibrations include positioning sensitive equipment near columns or increasing the stiffness or mass of the floor
Coherent laminar and turbulent motion of toroidal vortex bundles
Motivated by experiments performed in superfluid helium, we study numerically
the motion of toroidal bundles of vortex filaments in an inviscid fluid. We
find that the evolution of these large-scale vortex structures involves the
generalised leapfrogging of the constituent vortex rings. Despite three
dimensional perturbations in the form of Kelvin waves and vortex reconnections,
toroidal vortex bundles retain their coherence over a relatively large distance
(compared to their size), in agreement with experimental observations.Comment: 22 pages, 12 figure
Intersecting D5-brane models with massive vector-like leptons
We construct eight-stack intersecting D5-brane models, with an orbifold
transverse space, that yield the (non-supersymmetric) standard model up to
vector-like leptons. The matter includes right-chiral neutrinos and the models
have the renormalisable Yukawa couplings to tachyonic Higgs doublets needed to
generate mass terms for {\it all} matter, including the vector-like leptons.
The models are constrained by the requirement that twisted tadpoles cancel,
that the gauge boson coupled to the weak hypercharge does not get a
string-scale mass via a generalised Green-Schwarz mechanism, and that there are
no surviving, unwanted gauged U(1) symmetries coupled to matter.
Gauge coupling constant ratios close to those measured are easily obtained
for reasonable values of the parameters, consistently with having the string
scale close to the electroweak scale, as required to avoid the hierarchy
problem. Unwanted (colour-triplet, charged-singlet, and neutral-singlet) scalar
tachyons can be removed by a suitable choice of the parameters.Comment: 15 pages, LaTeX fil
Starsat: A space astronomy facility
Preliminary design and analyses of a versatile telescope for Spacelab missions are presented. The system is an all-reflective Korsch three-mirror telescope with excellent performance characteristics over a wide field and a broad spectral range, making it particularly suited for ultraviolet observations. The system concept is evolved around the utilization of existing hardware and designs which were developed for other astronomy space projects
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