Effects of adiabaticity and non-adiabaticity of dust charge fluctuation on the propagation of the dust ion acoustic waves in inhomogeneous dusty plasma

A theoretical investigation has been made for adiabatic positive and negative dust charge fluctuations on the propagation of dust-ion acoustic waves (DIAWs) in a weakly inhomogeneous, collisionless, unmagnetized dusty plasmas consisting of cold positive ions, stationary positively and negatively charged dust particles and isothermal electrons. The reductive perturbation method is employed to reduce the basic set of fluid equations to the variable coefficients Korteweg–de Vries (KdV) equation. Either compressive or rarefactive solitons are shown to exist depending on the critical value of the ion density, which in turn, depends on the inhomogeneous distribution of the ion. The dissipative effects of non-adiabatic dust charge variation has been studied which cause generation of dust ion acoustic shock waves governed by KdV-Burger (KdVB) equation. The results of the present investigation may be applicable to some dusty plasma environments, such as dusty plasma existing in polar mesosphere region.     

GPS-only gravity field recovery with GOCE,CHAMP, and GRACE

Gravity missions such as the Gravity field and steady-state Ocean Circulation Explorer (GOCE) are equipped with onboard Global Positioning System (GPS) receivers for precise orbit determination (POD), instrument time-tagging, and the extraction of the long wavelength part of the Earth’s gravity field. The very low orbital altitude of the GOCE satellite and the availability of dense 1 s GPS tracking data are ideal characteristics to exploit the contribution of GPS high-low Satellite-to-Satellite Tracking (hl-SST) to gravity field determination. We present gravity field solutions based on about 8 months of GOCE GPS hl-SST data from 2009 and compare the results with those obtained from the CHAllenging Minisatellite Payload (CHAMP) and Gravity Recovery And Climate Experiment (GRACE) missions. The very low orbital altitude of GOCE significantly improves gravity field recovery from GPS hl-SST data above degree 20, but not for the degrees below 20, where the quality of the spherical harmonic coefficients remains essentially unchanged. Despite the limited time span of GOCE data used, the gravity field of the Earth can be resolved up to about degree 115 using GPS data only. Empirically determined phase center variations (PCVs) of the GOCE onboard GPS helix antenna are, however, mandatory to achieve this performance.     

Impact of covariance information of kinematic positions on orbit reconstruction and gravity field recovery

Gravity missions are equipped with onboard Global Positioning System (GPS) receivers for precise orbit determination (POD) and for the extraction of the long wavelength part of the Earth’s gravity field. As positions of low Earth orbiters (LEOs) may be determined from GPS measurements at each observation epoch by geometric means only, it is attractive to derive such kinematic positions in a first step and to use them in a second step as pseudo-observations for gravity field determination. The drawback of not directly using the original GPS measurements is, however, that kinematic positions are correlated due to the ambiguities in the GPS carrier phase observations, which in principle requires covariance information be taken into account. We use GRACE data to show that dynamic or reduced-dynamic orbit parameters are not optimally reconstructed from kinematic positions when only taking epoch-wise covariance information into account, but that essentially the same orbit quality can be achieved as when directly using the GPS measurements, if correlations in time are taken into account over sufficiently long intervals. For orbit reconstruction covariances have to be considered up to one revolution period to avoid ambiguity-induced variations of kinematic positions being erroneously interpreted as orbital variations. For gravity field recovery the advantage is, however, not very pronounced.     

火星卫星的冻结轨道研究

冻结轨道是一种稳定的轨道,地球、火星、月球的卫星因引力场的南北不对称,都存在冻结轨道.由于主星体引力场的不同,它们卫星的冻结轨道也有不同的特性.地球卫星的冻结执道的偏心率非常小,对卫星遥感非常有利,国内外已有相当多的近地遥感卫星采用这种轨道.月球卫星的冻结轨道偏心率随轨道倾角的不同有很大的变化,对月球卫星冻结轨道的研究...     

New Insights on Geomagnetic Storms from Model Simulations Using Multi-Spacecraft Data

The forecast of the terrestrial ring current as a major contributor to the stormtime Dst index and a predictor of geomagnetic storms is of central interest to ‘space weather’ programs. We thus discuss the dynamical coupling of the solar wind to the Earth's magnetosphere during several geomagnetic storms using our ring current-atmosphere interactions model and coordinated space-borne data sets. Our model calculates the temporal and spatial evolution of H⁺, O⁺, and He⁺ ion distribution functions considering time-dependent inflow from the magnetotail, adiabatic drifts, and outflow from the dayside magnetopause. Losses due to charge exchange, Coulomb collisions, and scattering by EMIC waves are included as well. As initial and boundary conditions we use complementary data sets from spacecraft located at key regions in the inner magnetosphere, Polar and the geosynchronous LANL satellites. We present recent model simulations of the stormtime ring current energization due to the enhanced large-scale convection electric field, which show the transition from an asymmetric to a symmetric ring current during the storm and challenge the standard theories of (a) substorm-driven, and (b) symmetric ring current. Near minimum Dst there is a factor of ∼ 10 variation in the intensity of the dominant ring current ion specie with magnetic local time, its energy density reaching maximum in the premidnight to postmidnight region. We find that the O⁺ content of the ring current increases after interplanetary shocks and reaches largest values near Dst minimum; ∼ 60% of the total ring current energy was carried by O⁺ during the main phase of the 15 July 2000 storm. The effects of magnetospheric convection and losses due to collisions and wave-particle interactions on the global ring current energy balance are calculated during different storm phases and intercompared. This revised version was published online in August 2006 with corrections to the Cover Date.     

Needs and Tools for Future Gravity Measuring Missions

This paper compares the requirements that can be expected of gravity measuring missions with respect to the status of the instrumentation and satellite technologies. The error sources of gravity gradiometry and satellite-to-satellite tracking are analysed and the elements limiting the accuracy are identified. Proposed and approved future missions that will fly technologies of interest for gravity sensing are recalled. Areas of technical development of interest are reviewed. The article finishes with two possible conceptual missions presented as examples and with a chapter of conclusions. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Self-Consistent Determination of the Temperature Profile and The Magnetic Field Geometry in Winds of Late-Type Stars

Cool giant and supergiant stars generally present low velocity winds with high mass-loss rates. Several models have been proposed to explain the acceleration process of these winds. Although dust is known to be present in these objects, the radiation pressure on these particles is uneffective in reproducing the observed physical parameters of the wind. The most promising acceleration mechanism cited in the literature is the transference of momentum and energy from Alfvén waves to the gas. Usually, these models consider the wind to be isothermal. We present a stellar wind model in which the Alfvén waves are used as the main acceleration mechanism, and determine the temperature profile by solving the energy equation taking into account both the radiative losses and the wave heating. We also determine, self-consistently, the magnetic field geometry as the result of the competition between the magnetic field and the thermal pressure gradient. As the main result, we show that the magnetic geometry presents a super-radial index in the region where the gas pressure is increasing. However, this super-radial index is greater than that observed for the solar corona.     

井田制与租佃制的比较分析

井田制内含耕地资源所有权和经营权分离,租佃制则是耕地资源所有权与经营权分离的普遍化,二者都以耕地资源私有制和资源有偿利用为基础。给我们的启示是:公有资源按照所有权与经营权相分离的模式必产生公有制经济形式多样。     

连续分离铝熔体中夹杂物的分析

通过分析高频磁场作用下熔体连续处理时夹杂的去除效率表明，熔体连续处理条件下的夹杂去除效率比熔体静止时的略低，而夹杂与熔体之间的密度差对电磁分离时的去除效率影响不大。提高去除效率的有效途径是增大磁感应强度或降低分离器管径，但减小管径的同时需要提高磁场频率，以保持α/δ的值在2附近才可以取得最佳的分离效果。     

静触头部件的改制

对起动机电磁开关中静触头部件的改制工艺进行了介绍。实践表明,该工艺质量稳定,降低了生产成本,提高了经济效益。