43,036 research outputs found
Comparison of Optical, Radio, and Acoustical Detectors for Ultrahigh-Energy Neutrinos
For electromagnetic cascades induced by electron-neutrinos in South Pole ice,
the effective volume per detector element (phototube, radio antenna, or
acoustic transducer) as a function of cascade energy is estimated, taking
absorption and scattering into account. A comparison of the three techniques
shows that the optical technique is most effective for energies below ~0.5 PeV,
that the radio technique shows promise of being the most effective for higher
energies, and that the acoustic method is not competitive. Due to the great
transparency of ice, the event rate of AGN ne-induced cascades is an order of
magnitude greater than in water. For hard source spectra, the rate of Glashow
resonance events may be much greater than the rate for non-resonant energies.
The radio technique will be particularly useful in the study of Glashow events
and in studies of sources with very hard energy spectra.Comment: 22 pages Postscript, including 4 figure
Thermal expansion of mantle minerals at high pressures - A theoretical study
Recent experimental work has shown that the pressure dependence of the thermal expansion coefficient can be expressed as:
( Ī± / Ī± 0 ) = ( Ļ / Ļ 0 ( - Ī“ T ā ( 1 )
where Ī“_{T}, the AndersonāGruneisen parameter, is assumed to be independent of pressure, and for the materials studied has a value that lies between 4 and 6. Calculation of Ī“_{T} from seismic data, however, appears to suggest a contradictory value of between 2 and 3 for mantleāforming phases. Using an atomistic model based on our previously successful manyābody interatomic potential set (THBl), we have performed calculations to obtain values of Ī“_{T} for four major mantleāforming minerals. Our model results are in excellent agreement with experimental data, yielding values of between 4 and 6 for forsterite and MgO, and values in the same range for MgSiO_{3-}perovskite and Ī³āMg_{2}SiO_{4}. Moreover, the calculations confirm that Ī“_{T} is indeed constant with pressure up to the coreāmantle boundary. The apparent conflict between the values of Ī“_{T} predicted from seismic data and those obtained from experiment, and now from theory, is discussed
Relativistic astrophysics
The design, experimental testing, and calibration (error analysis) of a high resolution Cerenkov-scintillation detector is presented. The detector is capable of detecting iron isotopes and heavy ions of cosmic rays, and of performing direct measurements of individual neighboring isotopes at charge resolution 26. It utilizes Lexan (trademark) sheets, and has been used in flight packages of balloons and on the Skylab. The detector will be able to provide more information on violet astrophysical processes, such as thermonuclear reactions on neutron stars. Ground support and display equipment which are to be used in conjunction with the detector are also discussed
Lunar surface cosmic ray experiment
The galactic cosmic ray and solar flare experiment on Apollo 16 is reported. The published papers presented describe the experiment, equipment, data processing techniques, and operational history. The principle findings include: (1) The composition of heavy ions in interplanetary space at energies between approximately 30 and 130 MeV/nucleon is the same, within experimental errors. (2) The ability of a Lexan stack to determine simultaneously the energy spectra of major elements from He up to Fe in the energy interval 0.2 to 30 MeV/nucleon revealed systematic changes in the composition of solar flare particles as a function of energy. (3) Heavy ions emitted in a solar flare appear to be completely stripped of electrons, and are not in charge equilibrium at the time of acceleration and releases from the sun
Feedback laws for fuel minimization for transport aircraft
The Theoretical Mechanics Branch has as one of its long-range goals to work toward solving real-time trajectory optimization problems on board an aircraft. This is a generic problem that has application to all aspects of aviation from general aviation through commercial to military. Overall interest is in the generic problem, but specific problems to achieve concrete results are examined. The problem is to develop control laws that generate approximately optimal trajectories with respect to some criteria such as minimum time, minimum fuel, or some combination of the two. These laws must be simple enough to be implemented on a computer that is flown on board an aircraft, which implies a major simplification from the two point boundary value problem generated by a standard trajectory optimization problem. In addition, the control laws allow for changes in end conditions during the flight, and changes in weather along a planned flight path. Therefore, a feedback control law that generates commands based on the current state rather than a precomputed open-loop control law is desired. This requirement, along with the need for order reduction, argues for the application of singular perturbation techniques
Critical properties of the Kitaev-Heisenberg model
We study critical properties of the Kitaev-Heisenberg model on the honeycomb
lattice at finite temperatures which might describe the physics of the quasi
two-dimensional compounds, NaIrO and LiIrO. The model undergoes
two phase transitions as a function of temperature. At low temperature, thermal
fluctuations induce magnetic long-range order by order-by-disorder mechanism.
Magnetically ordered state with the spontaneously broken symmetry
persists up to a certain critical temperature. We find that there is an
intermediate phase between the low-temperature ordered phase and the
high-temperature disordered phase. The finite-sized scaling analysis suggests
that the intermediate phase is a critical Kosterlitz-Thouless phase with
continuously variable exponents. We argue that the intermediate phase has been
actually observed above the low-temperature magnetically ordered phase in
NaIrO, and likely in LiIrO.Comment: 5 pages, 6 figure
On some properties of the water-vapor spectrum and their relations to atmospheric radiation
In the present paper we investigate the physical consequences of the fact that the water vapor spectrum in the far infrared consists of a large number of narrow lines. It will be shown that the average width of these lines is much smaller than the intervals which could be resolved with the spectrographs used hitherto. For thick layer of vapor complete absorption is nevertheless reached in most parts of the spectrum. It can be shown that under such circumstances the total absorption is approximately proportional to the air pressure in the absorbing layers and is inversely proportional to the square root of the absolute temperature. There is an additional variation with temperature of a more complex type which cannot yet be quantitatively evaluated from the available measurements, but it is probably not very large
An annotated checklist of Wisconsin sap and short-winged flower beetles (Coleoptera: Nitidulidae, Kateretidae)
A survey of Wisconsin Nitidulidae and Kateretidae yielded 78 species through analysis of literature records, museum and private collections, and three years of field research (2000-2002). Twenty-seven species (35% of the Wisconsin fauna) represent new state records, having never been previously recorded from the state. Wisconsin distribution, along with relevant collecting techniques and natural history information, are summarized. The Wisconsin nitidulid and kateretid faunae are compared to reconstructed and updated faunal lists for Illinois, Indiana, Michigan, Minnesota, Ohio, and south-central Canada. Literature and distributional records suggest at least 11 additional nitidulid species may occur in Wisconsin
- ā¦