36,931 research outputs found
Short-range Magnetic interactions in the Spin-Ice compound HoTiO
Magnetization and susceptibility studies on single crystals of the pyrochlore
HoTiO are reported for the first time. Magnetization
isotherms are shown to be qualitatively similar to that predicted by the
nearest neighbor spin-ice model. Below the lock-in temperature, K, magnetization is consistent with the locking of spins along
[111] directions in a specific two-spins-in, two-spins-out arrangement. Below
the magnetization for displays a two step behavior
signalling the breaking of the ice rules.Comment: 4 pages, 3 figure
On the ionization potential of molecular oxygen
The ionization potential of O2 was measured by the technique of high resolution photoelectron spectroscopy taking into account the influence of rotational structure on the shape of the vibrational bands. A value of 12.071 + or - .001 eV (1027.1 + or - 0.1 A) was found for the ionization potential. A lowering of the ionization potential caused by a branch-head when delta N = -2 gave an appearance potential for ionization of 12.068 + or - .001 eV (1027.4 + or - 0.1 A)
Vibrational intensity distributions for continuum photoionization of oxygen
Results from measurements of vibrational intensity distributions for continuum photoionization of O2 are reported. Measurements were made using the 584 and 304 A He lines. The photoionization cross section of O2 shows a substantial dip in magnitude over a 20 A band centered about 590 A; thus the possibility exists that a 584 A photoelectron spectrum of O2 includes an autoionized contribution and the vibrational intensity distributions may not correspond to those of continuum ionization. Oxygen photoionization cross section shows no structure around 304 A and purley continuum ionization is expected
Collecting efficiency of a cylindrical mirror electron energy analyzer with preretarding lens
The electron collecting efficiency of a cylindrical mirror energy analyzer incorporating retardation of the electrons prior to analysis has been determined over the range 0 to 30 eV by two methods. The first method requires the use of a vacuum ultraviolet monochromator to produce monoenergetic electrons of different energies; the second method involves measuring the energy-brightness relationship of the retarding optics and should be applicable to any deflection analyzer with pre-retarding optics. The results of the two methods are compared and the limitations of the latter method are discussed
Vibrational intensity distributions in the photoelectron spectrum of hydrogen
The intensity distribution over the H2(+) vibrational levels up to a quantum number of 15 was measured for H2 photoelectron spectra at a photon wavelength of 584 A. The data show reasonable agreement with recent calculations only in the quantum number of 0 through 8. The higher levels are populated significantly lower than predicted by theory
Photoionization branching ratios and vibrational intensity distribution for N2, CO; and CO2 between 53 and 75 nm
The probability of radiation producing ions in specific electronic and vibrational levels was documented. For example, when a narrow band-pass of solar ionizing photons is incident on an atmospheric species it is now possible to describe, accurately, how the radiant energy is shared among the various electronic states of the ions produced. The molecules studied were N2, CO, and CO2. These molecules were photoionized by radiation between 53 and 75 nm. The effects of autoionization are discussed and continuum vibrational intensities are tabulated and compared with theoretical Franck-Condon factors where available. The branching ratios and partial cross sections for ionization into various electronic states are tabulated
Electron density and temperature measurements in the exhaust of a mpd source
Electron density and temperature profiles measured in exhaust of magnetoplasma-dynamic sourc
Independent Orbiter Assessment (IOA): Assessment of instrumental subsystem FMEA/CIL
The McDonnell Douglas Astronautics Company (MDAC) was selected in June 1986 to perform an Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL). The IOA effort first completed an analysis of the Instrumentation hardware, generating draft failure modes and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. The IOA results were then compared to the NASA FMEA/CIL baseline. A resolution of each discrepancy from the comparison is provided through additional analysis as required. The results of that comparison for the Orbiter Instrumentation hardware are documented. The IOA product for Instrumentation analysis consisted of 107 failure mode worksheets that resulted in 22 critical items being identified. Comparison was made to the Pre 51-L NASA baseline with 14 Post 51-L FMEAs added, which consists of 96 FMEAs and 18 CIL items. This comparison produced agreement on all but 25 FMEAs which caused differences in 5 CIL items
New Prospects in Fixed Target Searches for Dark Forces with the SeaQuest Experiment at Fermilab
An intense, 120 GeV proton beam incident on an extremely long, iron target
generates enormous numbers of light-mass particles that also decay within that
target. If one of these particles decays to a final state with a hidden gauge
boson, or if such a particle is produced as a result of the initial collision,
then that weakly interacting, hidden-sector particle may traverse the remainder
of the target and be detected downstream through its possible decay to an
, , or final state. These conditions can be
realized through an extension of the SeaQuest experiment at Fermilab, and in
this initial investigation we consider how it can serve as an ultrasensitive
probe of hidden vector gauge forces, both Abelian and non-Abelian. A light,
weakly coupled hidden sector may well explain the dark matter established
through astrophysical observations, and the proposed search can provide
tangible evidence for its existence --- or, alternatively, constrain a "sea" of
possibilities.Comment: 14 pages, 8 figures; improved sensitivity analysis and cross-checks;
small shifts in the expected limits; conclusions unchanged; refs. adde
Power processor design considerations for a solar electric propulsion spacecraft
Propulsion power processor design options are described. The propulsion power processor generated the regulated dc voltages and currents from a solar array source of a solar electric propelled spacecraft. The power processor consisted of 12 power supplies that provide the regulated voltages and currents necessary to power a 30-cm mercury ion thruster. The design options for processing unregulated solar array power and for generating the regulated power required by each supply are studied. The technical approaches utilized in the developed design and the technological limitation of the identified design options are discussed. Alternate approaches for delivering power to a number of mercury ion thrusters and methods of optimizing are described. It was concluded that this power processor design should be considered for application in solar electric propulsion missions of the future
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