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481.
A.T. Karpachev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3202-3212
The comparison of the IRI model with the foF2 distribution in the equatorial anomaly region obtained by topside sounding onboard the Interkosmos-19 satellite has been carried out. The global distribution of foF2 in terms of LT-maps was constructed by averaging Intercosmos-19 data for summer, winter, and equinox. These maps, in fact, represent an empirical model of the equatorial anomaly for high solar activity F10.7 ~ 200. The comparison is carried out for the latitudinal foF2 profiles in the characteristic longitudinal sectors of 30, 90, 210, 270, and 330°, as well as for the longitudinal variations in foF2 over the equator. The largest difference between the models (up to 60%) for any season was found in the Pacific longitudinal sector of 210°, where there are a few ground-based sounding stations. Considerable discrepancies, however, are sometimes observed in the longitudinal sectors, where there are many ground-based stations, for example, in the European or Indian sector. The discrepancies reach their maximum at 00 LT, since a decay of the equatorial anomaly begins before midnight in the IRI model and after midnight according to the Interkosmos-19 data. The discrepancies are also large in the morning at 06 LT, since in the IRI model, the foF2 growth begins long before sunrise. In the longitudinal variations in foF2 over the equator at noon, according to the satellite data, four harmonics are distinguished in the June solstice and at the equinox, and three harmonics in the December solstice, while in the IRI model only two and one harmonics respectively are revealed. In diurnal variations in foF2 and, accordingly, in the equatorial anomaly intensity, the IRI model does not adequately reproduce even the main, evening extremum. 相似文献
482.
John A. Arredondo 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(1):111-121
In this paper we find the families of relative equilibria for the three body problem in the plane, when the interaction between the bodies is given by a quasi-homogeneous potential. The number of the relative equilibria depends on the values of the masses and on the size of the system, measured by the moment of inertia. 相似文献
483.
J.T. Rudd D.M. Oliveira A. Bhaskar A.J. Halford 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(1):317-326
In this paper, we investigate temporal and spatial magnetosphere response to the impact of interplanetary (IP) shocks with different inclinations and speeds on the Earth’s magnetosphere. A data set with more than 500 IP shocks is used to identify positive sudden impulse (SI+) events as expressed by the SuperMAG partial ring current index. The SI+ rise time (RT), defined as the time interval between compression onset and maximum SI+ signature, is obtained for each event. We use RT and a model suggested by Takeuchi et al. (2002) to calculate the geoeffective magnetospheric distance (GMD) in the shock propagation direction as a function of shock impact angle and speed for each event. GMD is a generalization of the geoeffective magnetosphere length (GML) suggested by Takeuchi et al. (2002), defined from the subsolar point along the X line toward the tail. We estimate statistical GMD and GML values which are then reported for the first time. We also show that, similarly to well-known results for RT, the highest correlation coefficient for the GMD and impact angle is found for shocks with high speeds and small impact angles, and the faster and more frontal the shock, the smaller the GMD. This result indicates that the magnetospheric response depends heavily on shock impact angle. With these results, we argue that the prediction and forecasting of space weather events, such as those caused by coronal mass ejections, will not be accurately accomplished if the disturbances’ angles of impact are not considered as an important parameter within model and observation scheme capabilities. 相似文献
484.
485.
Velocities of fluid flows and solid objects can be measured by performing photon count correlations on laser light scattered from the measuring region, the most common optical configuration being the laser Doppler system. A statistical analysis for the counting process is presented for both the constant velocity case and for turbulent fluid flows with formulations for specific laser Doppler configurations. For turbulent flow, relationships are derived for the shape of the count correlation in terms of the mean velocity and rms turbulent intensity, taking into account the shape of the turbulence correlation curve. Experimental results recorded for both a constant velocity solid object and for an unseeded turbulent air flow in a wind tunnel are presented, and, in the latter case, comparisons are made with hot-wire measurements. 相似文献
486.
Barnard T.W. Wasserman J. Schroeder J.B. 《IEEE transactions on aerospace and electronic systems》1972,(2):156-160
A system concept for remote measurement of vehicle orientation with only passive devices mounted on a vehicle is presented. Three channels of polarization-modulated light are used to determine all three degrees of freedom of vehicle orientation. Two important system components are described, a polarization rotator and a retroreflector which leaves the polarization state invariant. Also, the method of data reduction is outlined and the system accuracy is discussed. 相似文献
487.
Optical guidance for autonomous landing of spacecraft 总被引:7,自引:0,他引:7
Miso T. Hashimoto T. Ninomiya K. 《IEEE transactions on aerospace and electronic systems》1999,35(2):459-473
An autonomous rendezvous guidance scheme for spacecraft to descend to small celestial bodies by using optical information is presented. First, a new guidance, navigation, and control (GNC) method based on fixation-point (FP) inheritance is proposed. A spacecraft can safely descend toward the target point on the celestial body by tracking and autonomously renewing the FPs on the surface. Next, we deal with the method of extracting the FPs. A spatial band-pass filter (BPF) is applied to pictures taken to enhance features having comparable size with the tracking window. Local variance of the filtered image is used as a criterion of the extraction. Then, the relative information between the spacecraft and the celestial body (position, velocity, attitude, etc.) is calculated from the image coordinates and the range measurements of the FPs from the spacecraft. To suppress observation noise and improve navigation accuracy, an application of the extended Kalman filter is also presented. Finally, simulations are conducted to verify the guidance precision and the fuel consumption of the proposed guidance scheme 相似文献
488.
Interplanetary origin of geomagnetic storms 总被引:8,自引:0,他引:8
Gonzalez Walter D. Tsurutani Bruce T. Clúa de Gonzalez Alicia L. 《Space Science Reviews》1999,88(3-4):529-562
Around solar maximum, the dominant interplanetary phenomena causing intense magnetic storms (Dst<−100 nT) are the interplanetary
manifestations of fast coronal mass ejections (CMEs). Two interplanetary structures are important for the development of storms,
involving intense southward IMFs: the sheath region just behind the forward shock, and the CME ejecta itself. Whereas the
initial phase of a storm is caused by the increase in plasma ram pressure associated with the increase in density and speed
at and behind the shock (accompanied by a sudden impulse [SI] at Earth), the storm main phase is due to southward IMFs. If
the fields are southward in both of the sheath and solar ejecta, two-step main phase storms can result and the storm intensity
can be higher. The storm recovery phase begins when the IMF turns less southward, with delays of ≈1–2 hours, and has typically
a decay time of 10 hours. For CMEs involving clouds the intensity of the core magnetic field and the amplitude of the speed
of the cloud seems to be related, with a tendency that clouds which move at higher speeds also posses higher core magnetic
field strengths, thus both contributing to the development of intense storms since those two parameters are important factors
in genering the solar wind-magnetosphere coupling via the reconnection process.
During solar minimum, high speed streams from coronal holes dominate the interplanetary medium activity. The high-density,
low-speed streams associated with the heliospheric current sheet (HCS) plasma impinging upon the Earth's magnetosphere cause
positive Dst values (storm initial phases if followed by main phases). In the absence of shocks, SIs are infrequent during
this phase of the solar cycle. High-field regions called Corotating Interaction Regions (CIRs) are mainly created by the fast
stream (emanating from a coronal hole) interaction with the HCS plasma sheet. However, because the Bz component is typically highly fluctuating within the CIRs, the main phases of the resultant magnetic storms typically have
highly irregular profiles and are weaker. Storm recovery phases during this phase of the solar cycle are also quite different
in that they can last from many days to weeks. The southward magnetic field (Bs) component of Alfvén waves in the high speed stream proper cause intermittent reconnection, intermittent substorm activity,
and sporadic injections of plasma sheet energy into the outer portion of the ring current, prolonging its final decay to quiet
day values. This continuous auroral activity is called High Intensity Long Duration Continuous AE Activity (HILDCAAs).
Possible interplanetary mechanisms for the creation of very intense magnetic storms are discussed. We examine the effects
of a combination of a long-duration southward sheath magnetic field, followed by a magnetic cloud Bs event. We also consider the effects of interplanetary shock events on the sheath plasma. Examination of profiles of very
intense storms from 1957 to the present indicate that double, and sometimes triple, IMF Bs events are important causes of such events. We also discuss evidence that magnetic clouds with very intense core magnetic
fields tend to have large velocities, thus implying large amplitude interplanetary electric fields that can drive very intense
storms. Finally, we argue that a combination of complex interplanetary structures, involving in rare occasions the interplanetary
manifestations of subsequent CMEs, can lead to extremely intense storms.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
489.
From magnetic fields and coronal heating observed in flares, active regions, quiet regions, and coronal holes, we propose
that exploding sheared core magnetic fields are the drivers of most of the dynamics and heating of the solar atmosphere, ranging
from the largest and most powerful coronal mass ejections and flares, to the vigorous microflaring and coronal heating in
active regions, to a multitude of fine-scale explosive events in the magnetic network, driving microflares, spicules, global
coronal heating, and, consequently, the solar wind.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
490.
K. Miyamoto M. Oka R. Yamamoto Y. Masuda T. Hoson S. Kamisaka J. Ueda 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(12):2033-2036
Activity of auxin polar transport in inflorescence axes of Arabidopsis thaliana grown under simulated microgravity conditions was studied in relation to the growth and development. Seeds were germinated and allowed to grow on an agar medium in test tubes on a horizontal clinostat. Horizontal clinostat rotation substantially reduced the growth of inflorescence axes and the productivity of seeds of Arabidopsis thaliana (ecotypes Landsberg erecta and Columbia), although it little affected seed germination, development of rosette leaves and flowering. The activity of auxin polar transport in inflorescence axes decreased when Arabidopsis plants were grown on a horizontal clinostat from germination stage, being ca. 60% of 1 g control. On the other hand, the auxin polar transport in inflorescence axes of Arabidopsis grown in 1 g conditions was not affected when the segments were exposed to various gravistimuli, including 3-dimensional clinorotation, during transport experiments. Pin-formed mutant of Arabidopsis, having a unique structure of the inflorescence axis with no flower and extremely low levels of the activity of auxin polar transport in inflorescence axes and endogenous auxin, did not continue its vegetative growth under clinostat rotation. These facts suggest that the development of the system of auxin polar transport in Arabidopsis is affected by microgravity, resulting in the inhibition of growth and development, especially during reproductive growth. 相似文献