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961.
The NASA Performance Assessment Workstation was used to assess cognitive performance changes in eight males subjected to seventeen days of 6 degrees head-down bed rest. PAWS uses six performance tasks to assess directed and divided attention, spatial, mathematical, and memory skills, and tracking ability. Subjective scales assess overall fatigue and mood state. Subjects completed training trials, practice trials, bed rest trials, and recovery trials. The last eight practice trials and all bed rest trials were performed with subjects lying face-down on a gurney. In general, there was no apparent cumulative effect of bed rest. Following a short period of performance stabilization, a slight but steady trend of performance improvement was observed across all trials. For most tasks, this trend of performance improvement was enhanced during recovery. No statistically significant differences in performance were observed when comparing bed rest with the control period. Additionally, fatigue scores showed little change across all periods. 相似文献
962.
We review aspects of anomalous cosmic rays (ACRs) that bear on the solar modulation of energetic particles in the heliosphere. We show that the latitudinal and radial gradients of these particles exhibit a 22-year periodicity in concert with the reversal of the Sun's magnetic field. The power-law index of the low energy portion of the energy spectrum of ACRs at the shock in 1996 appears to be -1.3, suggesting that the strength of the solar wind termination shock at the helioequatorial plane is relatively weak, with s 2.8. The rigidity dependence of the perpendicular interplanetary mean free path in the outer heliosphere for particles with rigidities between 0.2 and 0.7 GV varies approximately as R2, where R is particle rigidity. There is evidence that ACR oxygen is primarily multiply charged above 20 MeV/nuc and primarily singly-charged below 16 MeV/nuc. The location of the termination shock was at 65 AU in 1987 and 85 AU in 1994. 相似文献
963.
Eigenstructure Assignment for Linear Systems 总被引:2,自引:0,他引:2
Andry A.N. Shapiro E.Y. Chung J.C. 《IEEE transactions on aerospace and electronic systems》1983,(5):711-729
The use of feedback (full state, output, and constrained output) is considered as a means of shaping the transient response of linear time invariant systems. The underlying importance of the eigenstructure (eigenvalues/eigenvectors) is highlighted. Also, the important results and techniques are presented along with a brief literature review. An extensive flight control example is presented which should give direction to the application of eigenstructure assignment in diverse areas. 相似文献
964.
The practical implementation of the ESPRIT algorithm into direction-finding system architecture is considered. In particular, the problems of phase ambiguity resolution for extended array separations and multidimensional azimuth/elevation estimation are addressed. Generalized solutions for these problems are proposed, and a bearing quality indicator that provides a measure of credibility associated with each angle-of-arrival estimate is developed. Plots of computer simulated performance are presented in order to assess the probability of detection, of failure to alarm, and of false alarm as a function of azimuthal separation and period of signal observation 相似文献
965.
Ion-induced nucleation has been suggested to be a potentially important mechanism for atmospheric aerosol formation. Ions
are formed in the background atmosphere by galactic cosmic rays. A possible connection between galactic cosmic rays and cloudiness
has been However, the predictions of current atmospheric nucleation models are highly uncertain because the models are usually
based on the liquid drop model that estimates cluster thermodynamics based on bulk properties (e.g., liquid drop density and
surface tension). Sulfuric acid (H2SO4) and water are assumed to be the most important nucleating agents in the free troposphere. Measurements of the molecular
thermodynamics for the growth and evaporation of cluster ions containing H2SO4 and H2O were performed using a temperature-controlled laminar flow reactor coupled to a linear quadrupole mass spectrometer as well
as a temperature-controlled ion trap mass spectrometer. The measurements were complemented by quantum chemical calculations
of the cluster ion structures. The analysis yielded a complete set of H2SO4 and H2O binding thermodynamics extending from molecular cluster ions to the bulk, based on experimental thermodynamics for the small
clusters. The data were incorporated into a kinetic aerosol model to yield quantitative predictions of the rate of ion-induced
nucleation for atmospheric conditions. The model predicts that the negative ion-H2SO4-H2O nucleation mechanism is an efficient source of new particles in the middle and upper troposphere. 相似文献
966.
Urkowitz [1]has discussed the detection of a deterministic signal of unknown structure in the presence of flat, band-limited, Gaussian noise of known power density. That analysis is extended here to the case where jamming or other conditions preclude knowledge of the noise power density. The chi-square statistic of Urkowitz is replaced with Fisher's variance-ratio statistic, using a separate set of noise samples to estimate the unknown noise power density. Curves are given to show the additional degradation of perform over that due to ignorance of the signal structure, caused by ignorance of the noise power density. 相似文献
967.
A method to calculate the resonance current in high-frequency series-resonant DC-DC converters is presented that includes the effect of the reverse-bias capacitance of output rectifiers and that of the primary inductance of the output transformer. A computer program developed as a tool to determine the amplitude of the resonance current for any given input and output conditions is also discussed. The results of the computer calculations agree well with experimental measurements 相似文献
968.
Deborah L. Domingue Patrick L. Koehn Rosemary M. Killen Ann L. Sprague Menelaos Sarantos Andrew F. Cheng Eric T. Bradley William E. McClintock 《Space Science Reviews》2007,131(1-4):161-186
The existence of a surface-bounded exosphere about Mercury was discovered through the Mariner 10 airglow and occultation experiments.
Most of what is currently known or understood about this very tenuous atmosphere, however, comes from ground-based telescopic
observations. It is likely that only a subset of the exospheric constituents have been identified, but their variable abundance
with location, time, and space weather events demonstrate that Mercury’s exosphere is part of a complex system involving the
planet’s surface, magnetosphere, and the surrounding space environment (the solar wind and interplanetary magnetic field).
This paper reviews the current hypotheses and supporting observations concerning the processes that form and support the exosphere.
The outstanding questions and issues regarding Mercury’s exosphere stem from our current lack of knowledge concerning the
surface composition, the magnetic field behavior within the local space environment, and the character of the local space
environment. 相似文献
969.
G. Gloeckler E. C. Roelof K. W. Ogilvie D. B. Berdichevsky 《Space Science Reviews》1995,72(1-2):321-326
Proton phase space densities in the solar wind frame from suprathermal velocities 10 km s–1 to 30,000 km s–1 (0.5 eV–5 MeV) were derived from combined SWICS and HISCALE measurements when Ulysses was at 5 AU and –24° heliolatitude. The period (19–23 January 1993) encompasses a forward/reverse shock pair (20 January, 0500 UT and 22 January, 0300 UT). Strong evidence is found for shock acceleration of pickup protons from interstellar hydrogen at all energies measured. 相似文献
970.
THE CLUSTER ION SPECTROMETRY (CIS) EXPERIMENT 总被引:5,自引:0,他引:5
H. RÈME J. M. Bosqued J. A. Sauvaud A. Cros J. Dandouras C. Aoustin J. Bouyssou Th. Camus J. Cuvilo C. Martz J. L. MÉDALE H. Perrier D. Romefort J. Rouzaud C. D'Uston E. MÖBIUS K. Crocker M. Granoff L. M. Kistler M. Popecki D. Hovestadt B. Klecker G. Paschmann M. Scholer C. W. Carlson D. W. Curtis R. P. Lin J. P. Mcfadden V. Formisano E. Amata M. B. Bavassano-CATTANEO P. Baldetti G. Belluci R. Bruno G. Chionchio A. Di Lellis E. G. Shelley A. G. Ghielmetti W. Lennartsson A. Korth H. Rosenbauer R. Lundin S. Olsen G. K. Parks M. Mccarthy H. Balsiger 《Space Science Reviews》1997,79(1-2):303-350
The Cluster Ion Spectrometry (CIS) experiment is a comprehensive ionic plasma spectrometry package on-board the four Cluster spacecraft capable of obtaining full three-dimensional ion distributions with good time resolution (one spacecraft spin) with mass per charge composition determination. The requirements to cover the scientific objectives cannot be met with a single instrument. The CIS package therefore consists of two different instruments, a Hot Ion Analyser (HIA) and a time-of-flight ion COmposition and DIstribution Function analyser (CODIF), plus a sophisticated dual-processor-based instrument-control and Data-Processing System (DPS), which permits extensive on-board data-processing. Both analysers use symmetric optics resulting in continuous, uniform, and well-characterised phase space coverage. CODIF measures the distributions of the major ions (H+, He+, He++, and O+) with energies from ~0 to 40 keV/e with medium (22.5°) angular resolution and two different sensitivities. HIA does not offer mass resolution but, also having two different sensitivities, increases the dynamic range, and has an angular resolution capability (5.6° × 5.6°) adequate for ion-beam and solar-wind measurements. 相似文献