排序方式: 共有41条查询结果,搜索用时 15 毫秒
31.
Holt John M. Anderson Ronald M. 《IEEE transactions on aerospace and electronic systems》1968,(2):305-314
The time required to execute a successful escape maneuver must be deduced from considerations of the following times: time required to gain adequate altitude separation, delay time due to pilot reaction, aircraft servo-system delay, delay due to missed data, delay due to data arrival time, alarm delay due to ? errors, time to stop turning, and time to level off. Since each of these times is a random variable, the required escape time must be determined in a probabilistic sense. By assigning appropriate probability density functions to each of the times involved, formulas are derived for the escape times required by the CAS hazard logic. The results of a simulation of 10 000 aircraft encounters verify the suitability of the formulas. 相似文献
32.
Ronald L. Moore Alphonse C. Sterling G. Allen Gary Jonathan W. Cirtain David A. Falconer 《Space Science Reviews》2011,160(1-4):73-94
The observed magnetic field configuration and signatures of reconnection in the large solar magnetic eruptions that make major flares and coronal mass ejections and in the much smaller magnetic eruptions that make X-ray jets are illustrated with cartoons and representative observed eruptions. The main reconnection signatures considered are the imaged bright emission from the heated plasma on reconnected field lines. In any of these eruptions, large or small, the magnetic field that drives the eruption and/or that drives the buildup to the eruption is initially a closed bipolar arcade. From the form and configuration of the magnetic field in and around the driving arcade and from the development of the reconnection signatures in coordination with the eruption, we infer that (1) at the onset of reconnection the reconnection current sheet is small compared to the driving arcade, and (2) the current sheet can grow to the size of the driving arcade only after reconnection starts and the unleashed erupting field dynamically forces the current sheet to grow much larger, building it up faster than the reconnection can tear it down. We conjecture that the fundamental reason the quasi-static pre-eruption field is prohibited from having a large current sheet is that the magnetic pressure is much greater than the plasma pressure in the chromosphere and low corona in eruptive solar magnetic fields. 相似文献
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34.
Wiens Roger C. Neugebauer Marcia Reisenfeld Daniel B. Moses Ronald W. Nordholt Jane E. Burnett Donald S. 《Space Science Reviews》2003,105(3-4):601-626
The design and operation of the Genesis Solar-Wind Concentrator relies heavily on computer simulations. The computer model
is described here, as well as the solar wind conditions used as simulation inputs, including oxygen charge state, velocity,
thermal, and angular distributions. The simulation included effects such as ion backscattering losses, which also affect the
mass fractionation of the instrument. Calculations were performed for oxygen, the principal element of interest, as well as
for H and He. Ion fluences and oxygen mass fractionation are determined as a function of radius on the target. The results
were used to verify that the instrument was indeed meeting its requirements, and will help prepare for distribution of the
target samples upon return of the instrument to earth. The actual instrumental fractionation will be determined at that time
by comparing solar-wind neon isotope ratios measured in passive collectors with neon in the Concentrator target, and by using
a model similar to the one described here to extrapolate the instrumental fractionation to oxygen isotopes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
35.
Nordholt Jane E. Wiens Roger C. Abeyta Rudy A. Baldonado Juan R. Burnett Donald S. Casey Patrick Everett Daniel T. Kroesche Joseph Lockhart Walter L. MacNeal Paul McComas David J. Mietz Donald E. Moses Ronald W. Neugebauer Marcia Poths Jane Reisenfeld Daniel B. Storms Steven A. Urdiales Carlos 《Space Science Reviews》2003,105(3-4):561-599
The primary goal of the Genesis Mission is to collect solar wind ions and, from their analysis, establish key isotopic ratios
that will help constrain models of solar nebula formation and evolution. The ratios of primary interest include 17O/16O and 18O/16O to ±0.1%, 15N/14N to ±1%, and the Li, Be, and B elemental and isotopic abundances. The required accuracies in N and O ratios cannot be achieved
without concentrating the solar wind and implanting it into low-background target materials that are returned to Earth for
analysis. The Genesis Concentrator is designed to concentrate the heavy ion flux from the solar wind by an average factor
of at least 20 and implant it into a target of ultra-pure, well-characterized materials. High-transparency grids held at high
voltages are used near the aperture to reject >90% of the protons, avoiding damage to the target. Another set of grids and
applied voltages are used to accelerate and focus the remaining ions to implant into the target. The design uses an energy-independent
parabolic ion mirror to focus ions onto a 6.2 cm diameter target of materials selected to contain levels of O and other elements
of interest established and documented to be below 10% of the levels expected from the concentrated solar wind. To optimize
the concentration of the ions, voltages are constantly adjusted based on real-time solar wind speed and temperature measurements
from the Genesis ion monitor. Construction of the Concentrator required new developments in ion optics; materials; and instrument
testing and handling.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
36.
The Lunar Orbiter Laser Altimeter Investigation on the Lunar Reconnaissance Orbiter Mission 总被引:3,自引:0,他引:3
David E. Smith Maria T. Zuber Glenn B. Jackson John F. Cavanaugh Gregory A. Neumann Haris Riris Xiaoli Sun Ronald S. Zellar Craig Coltharp Joseph Connelly Richard B. Katz Igor Kleyner Peter Liiva Adam Matuszeski Erwan M. Mazarico Jan F. McGarry Anne-Marie Novo-Gradac Melanie N. Ott Carlton Peters Luis A. Ramos-Izquierdo Lawrence Ramsey David D. Rowlands Stephen Schmidt V. Stanley Scott III George B. Shaw James C. Smith Joseph-Paul Swinski Mark H. Torrence Glenn Unger Anthony W. Yu Thomas W. Zagwodzki 《Space Science Reviews》2010,150(1-4):209-241
The Lunar Orbiter Laser Altimeter (LOLA) is an instrument on the payload of NASA’s Lunar Reconnaissance Orbiter spacecraft (LRO) (Chin et al., in Space Sci. Rev. 129:391–419, 2007). The instrument is designed to measure the shape of the Moon by measuring precisely the range from the spacecraft to the lunar surface, and incorporating precision orbit determination of LRO, referencing surface ranges to the Moon’s center of mass. LOLA has 5 beams and operates at 28 Hz, with a nominal accuracy of 10 cm. Its primary objective is to produce a global geodetic grid for the Moon to which all other observations can be precisely referenced. 相似文献
37.
G. Randall Gladstone S. Alan Stern Kurt D. Retherford Ronald K. Black David C. Slater Michael W. Davis Maarten H. Versteeg Kristian B. Persson Joel W. Parker David E. Kaufmann Anthony F. Egan Thomas K. Greathouse Paul D. Feldman Dana Hurley Wayne R. Pryor Amanda R. Hendrix 《Space Science Reviews》2010,150(1-4):161-181
38.
Albert William S. Rensink Ronald A. Beusmans Jack M. 《Spatial Cognition & Computation》1999,1(2):131-144
This study presents two experiments that examine howindividuals learn relative directions betweenlandmarks in a desktop virtual environment. Subjectswere presented snapshot images of different virtualenvironments containing distinguishing landmarks anda road network. Following the presentation of eachvirtual environment, subjects were given a relativedirection test. The relative direction test involvedindicating the direction of hidden landmarks fromdifferent vantage points in the environment. Half ofthese vantage points were presented during thelearning phase, while the other half were novel.Results showed that subjects learned relativedirections between landmarks equally well when sceneswere presented in either a sequential or random order.Furthermore, viewing a configuration of landmarks ina desktop virtual environment from multipleperspectives produced a viewpoint dependentrepresentation in memory. Subjects had significantlygreater response times for new viewing perspectives,as compared to previously viewed scenes. Thisviewpoint dependent representation of the environmentpersisted despite learning under conditions ofspatio-temporal discontinuity and changes to anenvironmental frame of reference. 相似文献
39.
The Lunar Reconnaissance Orbiter Laser Ranging Investigation 总被引:1,自引:0,他引:1
Maria T. Zuber David E. Smith Ronald S. Zellar Gregory A. Neumann Xiaoli Sun Richard B. Katz Igor Kleyner Adam Matuszeski Jan F. McGarry Melanie N. Ott Luis A. Ramos-Izquierdo David D. Rowlands Mark H. Torrence Thomas W. Zagwodzki 《Space Science Reviews》2010,150(1-4):63-80
The objective of the Lunar Reconnaissance Orbiter (LRO) Laser Ranging (LR) system is to collect precise measurements of range that allow the spacecraft to achieve its requirement for precision orbit determination. The LR will make one-way range measurements via laser pulse time-of-flight from Earth to LRO, and will determine the position of the spacecraft at a sub-meter level with respect to ground stations on Earth and the center of mass of the Moon. Ranging will occur whenever LRO is visible in the line of sight from participating Earth ground tracking stations. The LR consists of two primary components, a flight system and ground system. The flight system consists of a small receiver telescope mounted on the LRO high-gain antenna that captures the uplinked laser signal, and a fiber optic cable that routes the signal to the Lunar Orbiter Laser Altimeter (LOLA) instrument on LRO. The LOLA instrument receiver records the time of the laser signal based on an ultrastable crystal oscillator, and provides the information to the onboard LRO data system for storage and/or transmittal to the ground through the spacecraft radio frequency link. The LR ground system consists of a network of satellite laser ranging stations, a data reception and distribution facility, and the LOLA Science Operations Center. LR measurements will enable the determination of a three-dimensional geodetic grid for the Moon based on the precise seleno-location of ground spots from LOLA. 相似文献
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