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161.
162.
Christopher J. Mertens Jeremy R. Winick Richard H. Picard David S. Evans Manuel López-Puertas Peter P. Wintersteiner Xiaojing Xu Martin G. Mlynczak James M. Russell III 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Thermospheric infrared radiance at 4.3 μm is susceptible to the influence of solar-geomagnetic disturbances. Ionization processes followed by ion-neutral chemical reactions lead to vibrationally excited NO+ (i.e., NO+(v)) and subsequent 4.3 μm emission in the ionospheric E-region. Large enhancements of nighttime 4.3 μm emission were observed by the TIMED/SABER instrument during the April 2002 and October–November 2003 solar storms. Global measurements of infrared 4.3 μm emission provide an excellent proxy to observe the nighttime E-region response to auroral dosing and to conduct a detailed study of E-region ion-neutral chemistry and energy transfer mechanisms. Furthermore, we find that photoionization processes followed by ion-neutral reactions during quiescent, daytime conditions increase the NO+ concentration enough to introduce biases in the TIMED/SABER operational processing of kinetic temperature and CO2 data, with the largest effect at summer solstice. In this paper, we discuss solar storm enhancements of 4.3 μm emission observed from SABER and assess the impact of NO+(v) 4.3 μm emission on quiescent, daytime retrievals of Tk/CO2 from the SABER instrument. 相似文献
163.
164.
Although the physical organization of spatialinformation clearly influences how it is recognized,recalled, and mentally transformed, few studies haveexplored how different levels of organizationinteract. This study focused on 4- and 6-year-oldchildren's memory for spatial configurations andexamined the relative influence of two levels oforganization: symmetry (vertical, horizontal, or none)and codability (verbal or nonverbal). We predictedthat the influence of symmetry would be lesspronounced among the older children for whom thepatterns were more codable. The results partiallysupported this prediction: Older children'sreconstructions were accurate regardless of patternsymmetry; younger children's reconstructions ofvertically-symmetric patterns were more accurate thantheir reconstructions of horizontally-symmetric andasymmetric patterns. Taken together, the resultsrevealed an interaction between age and symmetry onthe accuracy of children's reconstructions, suggestingthat younger children were more sensitive than olderchildren to differences in pattern symmetry. Thus,different levels of organization may influencechildren's ability to recall spatial information andthe relative influence of these levels may changeduring development. 相似文献
165.
Michael W. Liemohn Yingjuan Ma Rudy A. Frahm Xiaohua Fang Janet U. Kozyra Andrew F. Nagy J. David Winningham James R. Sharber Stas Barabash Rickard Lundin 《Space Science Reviews》2006,126(1-4):63-76
Atmospheric photoelectrons have been observed well above the ionosphere of Mars by the ASPERA-3 ELS instrument on Mars Express.
To systematically interpret these observations, field lines from two global MHD simulations were analyzed for connectivity
to the dayside ionosphere (allowing photoelectron escape). It is found that there is a hollow cylinder behind the planet from
1–2 R
M away from the Mars-Sun line that has a high probability of containing magnetic field lines with connectivity to the dayside
ionosphere. These results are in complete agreement with the ELS statistics. It is concluded that the high-altitude photoelectrons
are the result of direct magnetic connectivity to the dayside at the moment of the measurement, and no extra trapping or bouncing
mechanisms are needed to explain the data. 相似文献
166.
Britt Charles L. Palmer David F. 《IEEE transactions on aerospace and electronic systems》1967,(1):123-135
This paper describes an experimental study of the effect of continuous wave (CW) interference and white noise on a second-order phase-lock loop. The reciprocal of the loop mean-square phase error is used as an index of performance, and the effect of interference levels that do not cause cycle skipping or loss of lock is described in terms of this index. Loop thresholds are determined by measurement of cycle-skipping rates. Stationary or slowly-sweeping CW interference caused a degradation in loop threshold of roughly 3 dB for every 6 dB of interference power above the noise power level. The effective loop signal-to-noise ratio was decreased approximately 1 dB at interference-to-noise power ratios of -3 dB. Interference levels equal to the signal level consistently caused loss of lock, regardless of the loop signal-to-noise ratio. 相似文献
167.
Nicholson WL Ricco AJ Agasid E Beasley C Diaz-Aguado M Ehrenfreund P Friedericks C Ghassemieh S Henschke M Hines JW Kitts C Luzzi E Ly D Mai N Mancinelli R McIntyre M Minelli G Neumann M Parra M Piccini M Rasay RM Ricks R Santos O Schooley A Squires D Timucin L Yost B Young A 《Astrobiology》2011,11(10):951-958
We report the first telemetered spaceflight science results from the orbiting Space Environment Survivability of Living Organisms (SESLO) experiment, executed by one of the two 10?cm cube-format payloads aboard the 5.5?kg Organism/Organic Exposure to Orbital Stresses (O/OREOS) free-flying nanosatellite. The O/OREOS spacecraft was launched successfully to a 72° inclination, 650?km Earth orbit on 19 November 2010. This satellite provides access to the radiation environment of space in relatively weak regions of Earth's protective magnetosphere as it passes close to the north and south magnetic poles; the total dose rate is about 15 times that in the orbit of the International Space Station. The SESLO experiment measures the long-term survival, germination, and growth responses, including metabolic activity, of Bacillus subtilis spores exposed to the microgravity, ionizing radiation, and heavy-ion bombardment of its high-inclination orbit. Six microwells containing wild-type (168) and six more containing radiation-sensitive mutant (WN1087) strains of dried B. subtilis spores were rehydrated with nutrient medium after 14 days in space to allow the spores to germinate and grow. Similarly, the same distribution of organisms in a different set of microwells was rehydrated with nutrient medium after 97 days in space. The nutrient medium included the redox dye Alamar blue, which changes color in response to cellular metabolic activity. Three-color transmitted intensity measurements of all microwells were telemetered to Earth within days of each of the 48?h growth experiments. We report here on the evaluation and interpretation of these spaceflight data in comparison to delayed-synchronous laboratory ground control experiments. 相似文献
168.
Validity and Sensitivity of a Brief Psychomotor Vigilance Test (PVT-B) to Total and Partial Sleep Deprivation 总被引:2,自引:0,他引:2
The Psychomotor Vigilance Test (PVT) objectively assesses fatigue-related changes in alertness associated with sleep loss, extended wakefulness, circadian misalignment, and time on task. The standard 10-min PVT is often considered impractical in applied contexts. To address this limitation, we developed a modified brief 3-min version of the PVT (PVT-B). The PVT-B was validated in controlled laboratory studies with 74 healthy subjects (34 female, aged 22-45 years) that participated either in a total sleep deprivation (TSD) study involving 33 hours awake (N=31 subjects) or in a partial sleep deprivation (PSD) protocol involving 5 consecutive nights of 4 hours time in bed (N=43 subjects). PVT and PVT-B were performed regularly during wakefulness. Effect sizes of 5 key PVT outcomes were larger for TSD than PSD and larger for PVT than for PVT-B for all outcomes. Effect size was largest for response speed (reciprocal response time) for both the PVT-B and the PVT in both TSD and PSD. According to Cohen's criteria, effect sizes for the PVT-B were still large (TSD) or medium to large (PSD, except for fastest 10% RT). Compared to the 70% decrease in test duration the 22.7% (range 6.9%-67.8%) average decrease in effect size was deemed an acceptable trade-off between duration and sensitivity. Overall, PVT-B performance had faster response times, more false starts and fewer lapses than PVT performance (all p<0.01). After reducing the lapse threshold from 500 ms to 355 ms for PVT-B, mixed model ANOVAs indicated no differential sensitivity to sleep loss between PVT-B and PVT for all outcome variables (all P>0.15) but the fastest 10% response times during PSD (P<0.001), and effect sizes increased from 1.38 to 1.49 (TSD) and 0.65 to 0.76 (PSD), respectively. In conclusion, PVT-B tracked standard 10-min PVT performance throughout both TSD and PSD, and yielded medium to large effect sizes. PVT-B may be a useful tool for assessing behavioral alertness in settings where the duration of the 10-min PVT is considered impractical, although further validation in applied settings is needed. 相似文献
169.
??EIT waves?? are large-scale coronal bright fronts (CBFs) that were first observed in 195 Å images obtained using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). Commonly called ??EIT waves??, CBFs typically appear as diffuse fronts that propagate pseudo-radially across the solar disk at velocities of 100?C700 km?s?1 with front widths of 50?C100 Mm. As their speed is greater than the quiet coronal sound speed (c s ??200 km?s?1) and comparable to the local Alfvén speed (v A ??1000 km?s?1), they were initially interpreted as fast-mode magnetoacoustic waves ( $v_{f}=(c_{s}^{2} + v_{A}^{2})^{1/2}$ ). Their propagation is now known to be modified by regions where the magnetosonic sound speed varies, such as active regions and coronal holes, but there is also evidence for stationary CBFs at coronal hole boundaries. The latter has led to the suggestion that they may be a manifestation of a processes such as Joule heating or magnetic reconnection, rather than a wave-related phenomena. While the general morphological and kinematic properties of CBFs and their association with coronal mass ejections have now been well described, there are many questions regarding their excitation and propagation. In particular, the theoretical interpretation of these enigmatic events as magnetohydrodynamic waves or due to changes in magnetic topology remains the topic of much debate. 相似文献
170.
Valerie C. Thomas Joseph M. Makowski G. Mark Brown John F. McCarthy Dominick Bruno J. Christopher Cardoso W. Michael Chiville Thomas F. Meyer Kenneth E. Nelson Betina E. Pavri David A. Termohlen Michael D. Violet Jeffrey B. Williams 《Space Science Reviews》2011,163(1-4):175-249
The Dawn spacecraft is designed to travel to and operate in orbit around the two largest main belt asteroids, Vesta and Ceres. Developed to meet a ten-year life and fully redundant, the spacecraft accommodates an ion propulsion system, including three ion engines and xenon propellant tank, utilizes large solar arrays to power the engines, carries the science instrument payload, and hosts the hardware and software required to successfully collect and transmit the scientific data back to Earth. The launch of the Dawn spacecraft in September 2007 from Cape Canaveral Air Force Station was the culmination of nearly five years of design, development, integration and testing of this unique system, one of the very few scientific spacecraft to rely on ion propulsion. The Dawn spacecraft arrived at its first destination, Vesta, in July 2011, where it will conduct science operations for twelve months before departing for Ceres. 相似文献