A study of the polar current systems using the IMS meridian chains of magnetometers

Magnetic field data from a meridian chain of observatories and the recently developed computer codes constitute a powerful tool in studying substorm current systems in the polar region. In this paper, we summarize some of the results obtained from the IMS Alaska meridian chain of observatories. The basic data are the average daily magnetic field variations for 50 successive days (March 9–April 27, 28) which represent a moderately disturbed period. With the aid of the two computer codes, we obtained the distribution of the following quantities in the polar ionosphere in invariant-MLT coordinates: (1) the total ionospheric current; (2) the Pedersen current; (3) the Hall current; (4) the field-aligned currents; (5) the Pedersen-associated field-aligned currents; (6) the Hall-associated field-aligned currents; (7) the electric potential; (8) the Joule heat production rate; (9) the auroral particle energy injection rate; (10) the total energy dissipation rate. All these quantities are related to each other self-consistently at every point under the initial assumptions used in the computation. By using a model of the magnetosphere, the following quantities in the polar ionosphere are projected onto the equatorial plane and the Y — Z plane at X = -20 R _E: (11) the Pedersen current counterpart; (12) the Hall current counterpart; (13) the electric potential; (14) the Pedersen-associated field-aligned currents; (15) the Hall-associated field-aligned currents. These distribution patterns serve as an important basis for studying the generation mechanisms of substorm current systems and the magnetosphere-ionosphere coupling process.     

Preliminary results from the solar wind experiment on the ISEE-2 satellite

The EGD plasma experiment, launched on board of the ISEE-2 spacecraft, is briefly described. Preliminary results concerning three bow shock crossings occurred in November 1977 are discussed. Our attention is focused on some non-thermal features of the distribution function of proton velocities: in particular, we discuss double peaked structures of solar wind spectra and flows of particles backstreaming from the bow shock.     

The relationship between field-aligned currents and the auroral electrojets: A review

The recent development of several new observational techniques as well as of advanced computer simulation codes has contributed significantly to our understanding of dynamics of the three-dimensional current system during magnetospheric substorms. This paper attempts to review the main results of the last decade of research in such diverse fields as electric fields and currents in the high-latitude ionosphere and field-aligned currents and their relationship to the large-scale distribution of auroras and auroral precipitation. It also contains discussions on some efforts in synthesizing the vast amount of the observations to construct an empirical model which connects the ionospheric currents with field-aligned currents. While our understanding has been greatly improved during the last decade, there is much that is as yet unsettled. For example, we have reached only a first approximation model of the three-dimensional current system which is not inconsistent with integrated, ground-based and space observations of electric and magnetic fields. We have just begun to unfold the cause of the field-aligned currents both in the magnetosphere and ionosphere. Dynamical behaviour of the magnetosphere-ionosphere coupling relating to substorm variability can be an important topic during the coming years.On leave of absence from Kyoto Sangyo University, Kyoto 603, Japan.     

面向航天器系统级测试的虚拟测试方法及应用

航天器总体设计正确性和接口实现正确性的及时验证,是提高航天器这类复杂系统可靠性的重要手段。本文提出一种基于模型检测的虚拟测试方法。方法采用窗口树模型(WTM)对复杂系统进行建模,采用状态转移图(STG)作为系统规约刻画系统行为的正确性。方法通过提出基于自动机的模型检测机制,实现了一种面向航天器系统级测试的虚拟测试平台(VTP)原型系统。该平台支持虚拟测试准备、虚拟测试执行和虚拟测试评估等功能,模拟并实现复杂系统总体设计正确性的验证和接口实现正确性的验证。     

Role of ionospheric effects and plasma sheet dynamics in the formation of auroral arcs

At the ionospheric level, the substorm onset (expansion phase) is marked by the initial brightening and subsequent breakup of a pre-existing auroral arc. According to the field line resonance (FLR) wave model, the substorm-related auroral arc is caused by the field-aligned current carried by FLRs. The FLRs are standing shear Alfvén wave structures that are excited along the dipole/quasi-dipole lines of the geomagnetic field. The FLRs (that can cause auroral arc) thread from the Earthward edge of the plasma sheet and link the auroral arc to the plasma sheet region of 6–15 R _E. The region is associated with magnetic fluctuations that result from the nonlinear wave-wave interactions of the cross-field current-instability. The instability (excited at the substorm onset) disrupts the cross-tail current which is built up during the growth phase of the substorms and results in magnetic fluctuations. The diversion of the current to polar regions can lead to auroral arc intensification. The current FLR model is based on the amplitude equations that describe the nonlinear space-time evolution of FLRs in the presence of ponderomotive forces exerted by large amplitude FLRs (excited during substorms). The present work will modify the FLR wave model to include the effects arising from magnetic fluctuations that result from current disruption near the plasma sheet (6–15 R _E). The nonlinear evolution of FLRs is coupled with the dynamics of plasma sheet through a momentum exchange term (resulting from magnetic fluctuations due to current disruption) in the generalized Ohm's law. The resulting amplitude equations including the effects arising from magnetic fluctuations can be used to study the structure of the auroral arcs formed during substorms. We have also studied the role of feedback mechanism (in a dipole geometry of the geomagnetic field) in the formation of the discrete auroral arc observed on the nightside magnetosphere. The present nonlinear dispersive model (NDM) is extended to include effects arising from the low energy electrons originating from the plasma sheet boundary layer. These electrons increase the ionospheric conductivity in a localized patch and enhance the field-aligned current through a feedback mechanism. The feedback effects were studied numerically in a dipole geometry using the the NDM. The numerical studies yield the magnitude of the field-aligned current that is large enough to form a discrete auroral arc. Our studies provide theoretical support to the observational work of Newell et al. that the feedback instability plays a major role in the formation of the discrete auroral arcs observed on the nightside magnetosphere.     

Air motions in the tropical stratosphere deduced from satellite tracking of horizontally floating balloons

Between June and November of 1970, 26 constant level balloons were released from Ascension Island (8 S) for flight at 30 and 50 mb. The balloons were positioned by the Interrogation, Recording and Location System (IRLS) aboard the Nimbus D satellite. In general, balloon positioning appeared to be accurate to within a few kilometers, although occasionally there was doubt as to whether the balloon position was to the right or left of the satellite subtrack. Eight of the flights at 50 mb and three of the flights at 30 mb were tracked for more than one month, and one 50 mb flight was tracked continuously for more than 5 months while making 7 circumnavigations of the Earth. From the satellite-determined 12-hourly balloon positions in the tropics, 223 smoothed 24-hour-average zonal and meridional winds were obtained at 30 mb and 693 such winds were obtained at 50 mb. Near the equator the balloons moved from east to west at a speed of about 23 ms^–1 at 50 mb and 28 ms^–1 at 30 mb, while undergoing a mean northward drift of approximately 0.1 ms^–1. The northward drift was a maximum in the Northern Hemisphere winter, suggesting a weak upward extension of the Hadley Cell to 50 mb. Superimposed on this drift were oscillations in meridional velocity of about 2-month period, with these oscillations also most pronounced in the Northern Hemisphere winter. Small (1–3 ms^–1) short-period fluctuations in meridional velocity were evident directly above the equator at 50 mb. These waves appear to move westward at speeds of 30–40 ms^–1 and to have a wavelength of about 90° longitude. They were responsible for transporting small amounts of westerly momentum into the winter hemisphere. Fluctuations in zonal velocity (Kelvin waves) were also delineated by flights near the equator. These waves appear to move eastward at speeds of 30–40 ms^–1 and to have a wavelength of 360° longitude. Some comparisons are made between these IRLS data and the data obtained from GHOST balloon flights at the same heights in early 1969.     

Navigating towards the future: transitioning from terrestrial radio navigation to satellite navigation and airborne surveillance

This paper presents a proposal for transitioning from terrestrial-based navigation aids to implementing satellite and airborne surveillance as the primary navigation means. The transition occurs through several steps. First, the installation and use of modern navigation and surveillance equipment is mandated by the regulatory organizations. The installations should take place in a sequenced fashion to allow time for companies to absorb the initial cost. Next, the existing network of terrestrial navigation aids is down-sized leaving only the areas of heaviest use in service. At this point, the global positioning system (GPS) will be deemed the primary method of terrestrial and oceanic travel. Finally, terrestrial navigation stations will be available around airports and the remaining stations will be put in a standby condition for use in the event of a national emergency. This paper will discuss the security benefits and examples of cost savings through implementation of these steps.     

A study of flight-critical computer system recovery from spaceradiation-induced error

It is well known that space radiation, containing energetic particles such as protons and ions, can cause anomalies in digital avionics onboard satellites, spacecraft, and aerial vehicles flying at high altitude. Semiconductor devices embedded in these applications become more sensitive to space radiation as the features shrink in size. One of the adverse effects of space radiation on avionics is a transient error known as single event upset (SEU). Given that it is caused by bit-flips in computer memory, SEU does not result in a damaged device. However, the SEU induced data error propagates through the run-time operational flight program, causing erroneous outputs from a flight-critical computer system. This study was motivated by a need for a cost-effective solution to keep flight-critical computers functioning after SEU occurs. The result of the study presents an approach to recover flight-critical computer systems from SEU induced error by using an identity observer array. The identity observers replicate the state data of the controller in distinct data partitions. The faulty controller can be recovered by replacing data image of the faulty data partition with that of the healthy data partition. The methodology of applying such an approach from the fault tolerant control perspective is presented. The approach is currently being tested via computer simulation     

A new iterative algorithm for geolocating a known altitude target using TDOA and FDOA measurements in the presence of satellite location uncertainty

This paper considers the problem of geolocating a target on the Earth surface whose altitude is known previously using the target signal time difference of arrival(TDOA) and frequency difference of arrival(FDOA) measurements obtained at satellites. The number of satellites available for the geolocation task is more than sufficient and their locations are subject to random errors. This paper derives the constrained Crame′r-Rao lower bound(CCRLB) of the target position, and on the basis of the CCRLB analysis, an approximately efficient constrained maximum likelihood estimator(CMLE) for geolocating the target is established. A new iterative algorithm for solving the CMLE is then proposed, where the updated target position estimate is shown to be the globally optimal solution to a generalized trust region sub-problem(GTRS) which can be found via a simple bisection search. First-order mean square error(MSE) analysis is conducted to quantify the performance degradation when the known target altitude is assumed to be precise but indeed has an unknown but deterministic error. Computer simulations are used to compare the performance of the proposed iterative geolocation technique with those of two benchmark algorithms. They verify the approximate efficiency of the proposed algorithm and the validity of the MSE analysis.     

Periodic X-ray outbursts from A0535+26, 2S1145-619 and GX301-2

We report Ariel V(SSI) observations of three X-ray pulsars A0535+26, 2S1145-619 and GX301-2 (2S1223-624). These sources exhibit X-ray outbursts which appear, on the basis of observations extending over 5 years, to have recurrence periods of 110 days, 187.5 days and 41.4 days respectively. If these periods are orbital in origin, the observed X-ray modulation may be explained in terms of an appreciable orbital eccentricity giving rise to time variable accretion. (In the case of GX301-2 published pulse timing data already provide independent evidence for a 41.4 day orbital period and an eccentricity e 0.4). The optical counterparts are all early-type stars; A0535+26 and 2S1145-619 are identified with Be main sequence stars and GX301-2 with a B2 supergiant which also shows an emission line spectrum. The implications of the observations in relation to possible mass transfer mechanisms in such systems are discussed.     

A study of the SMC cluster NGC 330

We analyze the properties of the SMC cluster NGC 330 on the basis of a new CMD and of published effective temperatures and bolometric magnitudes for a smaller sample of stars (Caloi et al 1993, Stothers & Chin 1992a,b) to check for the kind of mixing taking place in massive stars. The existence of a few stars in the so-called HR gap led Stothers & Chin (1993) to claim that only models with semiconvective mixing and OPAL could match the HR diagram, whereas induced Caloi et al (1993) to conclude that neither semiconvective nor overshoot models are suited. The careful analysis of this cluster with new stellar models indicates that 1) models with convective overshoot and models with semiconvection can both explain the gross features of the HR diagram, 2) models with overshoot ought to be preferred.     

熵定律与大学教育可持续发展研究

本文针对在焙定律作用下，大学教育出现的无序化现象和各种有碍于大学教育可持续发展的因素进行了分析，并给出了解决这些问题的相应对策。     

圆棒拉伸试样蠕变过程中的应力应变分布分析

对光滑及切口圆棒试样进行有限元蠕变分析,得到了蠕变过程时的应力应变分布。在相同的平均净拉伸蠕变应力下,切口的存在使得最小截面上的平均Mises应力和平均轴向应力小于光滑试样。切口还导致蠕变时的应力松弛并使得试样的最大应力不再发生在切口根部。这可以用来简单解释切口对试样断裂寿命的影响。     

浦东机场卫星厅旅客捷运系统完成联合调试进入试运行阶段

4月22日,浦东机场三期扩建工程旅客捷运系统完成联合调试移交运营。6列捷运列车进行空车试运行,在不载客的情况下模拟演练载客运营下的行车组织方案,验证系统的可靠性,及时解决发现的问题,为列车正式运营后设施设备更加可靠、系统更加完善、管理更加熟练奠定基础。     

Initial results from the ISEE-1 and -2 plasma wave investigation

In this paper we present an initial survey of results from the plasma wave experiments on the ISEE-1 and -2 spacecraft which are in nearly identical orbits passing through the Earth's magnetosphere at radial distances out to about 22.5R_e. Essentially every crossing of the Earth's bow shock can be associated with an intense burst of electrostatic and whistler-mode turbulence at the shock, with substantial wave intensities in both the upstream and downstream regions. Usually the electric and magnetic field spectrum at the shock are quite similar for both spacecraft, although small differences in the detailed structure are sometimes apparent upstream and downstream of the shock, probably due to changes in the motion of the shock or propagation effects. Upstream of the shock emissions are often observed at both the fundamental, f_-^p, and second harmonic, 2f_p^-, of the electron plasma frequency. In the magnetosphere high resolution spectrograms of the electric field show an extremely complex distribution of plasma and radio emissions, with numerous resonance and cutoff effects. Electron density profiles can be obtained from emissions near the local electron plasma frequency. Comparisons of high resolution spectrograms of whistler-mode emissions such as chorus detected by the two spacecraft usually show a good overall similarity but marked differences in detailed structure on time scales less than one minute. Other types of locally generated waves, such as the (n+1/2)f_-^gelectron cyclotron waves, show a better correspondence between the two spacecraft. High resolution spectrograms of kilometric radio emissions are also presented which show an extremely complex frequency-time structure with many closely spaced narrow-band emissions.     

A numerical study of the fission hypothesis for rotating polytropes

Conclusions Our results show that n = 3/2 and n = 1/2 polytropes are dynamically unstable to non-axisymmetric perturbations if t 0.30, in rough agreement with linear theory. Instead of fission as the direct end product of dynamic instability in rapidly rotating, centrally condensed stars, it appears that a rapidly rotating star can, through gravitational torques, eject some high angular momentum material in its equatorial plane and settle down into a dynamically stable (lower t) configuration. The central object, at least in the detailed evolution described above, ends up as a stable traixial star! The assumption of reflection symmetry through the rotation axis needs to be relaxed before this evolutionary picture can be considered realistic and before meaningful comparisons can be made with the results of Lucy (1977) and Gingold and Monaghan (1978, 1979), who found odd modes to be of crucial importance.We cannot escape mentioning that the ejected disk/ring of material in our models may have some connection with the formation of planetary systems.This research was supported by National Science Foundation Grant No. AST-7821449.