GE积极应对防务预算削减

针对防务预算削减的局面,GE公司把准市场发展趋势,集中资金发展重点项目,将商业发动机的运作方式移植到军事领域,力图减小防务预算缩减带来的不利影响。     

Lunar ground penetrating radar: Minimizing potential data artifacts caused by signal interaction with a rover body

Ground-penetrating radar (GPR) is the leading geophysical candidate technology for future lunar missions aimed at mapping shallow stratigraphy (<5 m). The instrument’s exploration depth and resolution capabilities in lunar materials, as well as its small size and lightweight components, make it a very attractive option from both a scientific and engineering perspective. However, the interaction between a GPR signal and the rover body is poorly understood and must be investigated prior to a space mission. In doing so, engineering and survey design strategies should be developed to enhance GPR performance in the context of the scientific question being asked. This paper explores the effects of a rover (simulated with a vertical metal plate) on GPR results for a range of heights above the surface and antenna configurations at two sites: (i) a standard GPR testing site with targets of known position, size, and material properties, and; (ii) a frozen lake for surface reflectivity experiments. Our results demonstrate that the GPR antenna configuration is a key variable dictating instrument design, with the XX polarization considered optimal for minimizing data artifact generation. These findings could thus be used to help guide design requirements for an eventual flight instrument.     

Structure of the migrating diurnal tide in the Whole Atmosphere Community Climate Model (WACCM)

As part of an ongoing effort to understand the migrating diurnal tide generated by the NCAR Whole Atmosphere Community Climate Model, version 3 (WACCM3), we compare the WACCM3 migrating diurnal tide in the horizontal wind and temperature fields to similar results from the Global Scale Wave Model (GSWM). The WACCM3 diurnal tidal wind fields are also compared to tropical radar measurements at Kauai (22°N, 200.2°E) and Rarotonga (21.3°S, 199.7°E). The large-scale features of the WACCM3 results, such as the global spatial structure and the semiannual amplitude variation are in general agreement with past tidal studies; however, several differences do exist. WACCM3 exhibits a much higher degree of hemispheric asymmetry, lower overall amplitudes around the equinoxes, and peaks which are more confined in latitude when compared with the GSWM. Factors which may contribute to such differences between WACCM3 and GSWM are the solar heating profiles from ozone and water vapor, dissipation, and the zonal mean zonal winds. We find that the internally generated heating in WACCM3 and eddy dissipation values are both smaller than the values specified in the GSWM; the eddy dissipation fields and zonal mean zonal winds of the two models also display measurable differences in spatial structure. Comparisons with radar data show several differences in spatial and seasonal structure. In particular, the diurnal tide zonal winds in WACCM3 above Kauai are considerably larger in amplitude than those observed in the radar data, due to contributions from nonmigrating tidal components including wave numbers eastward 1 through 3, westward 2, and stationary components, which interfere constructively with the migrating component around equinox in WACCM3.     

Optimal combination of InSAR and GPS for measuring interseismic crustal deformation

High spatial resolution measurements of interseismic deformation along major faults are critical for understanding the earthquake cycle and for assessing earthquake hazard. We propose a new remove/filter/restore technique to optimally combine GPS and InSAR data to measure interseismic crustal deformation, considering the spacing of GPS stations in California and the characteristics of interseismic signal and noise using InSAR. To constrain the longer wavelengths (>40 km) we use GPS measurements, combined with a dislocation model, and for the shorter wavelength information we rely on InSAR measurements. Expanding the standard techniques, which use a planar ramp to remove long wavelength error, we use a Gaussian filter technique. Our method has the advantage of increasing the signal-to-noise ratio, controlling the variance of atmosphere error, and being isotropic. Our theoretical analysis indicates this technique can improve the signal-to-noise ratio by up to 20%. We test this method along three segments of the San Andreas Fault (Southern section near Salton Sea, Creeping section near Parkfield and Mojave/Big Bend section near Los Angeles), and find improvements of 26%, 11% and 8% in these areas, respectively. Our data shows a zone of uplift to the west of the Creeping section of the San Andreas Fault and an area of subsidence near the city of Lancaster. This work suggests that after only 5 years of data collection, ALOS interferograms will provide a major improvement in measuring details of interseismic deformation.     

High-Energy Atmospheric Physics: Terrestrial Gamma-Ray Flashes and Related Phenomena

It is now well established that both thunderclouds and lightning routinely emit x-rays and gamma-rays. These emissions appear over wide timescales, ranging from sub-microsecond bursts of x-rays associated with lightning leaders, to sub-millisecond bursts of gamma-rays seen in space called terrestrial gamma-ray flashes, to minute long glows from thunderclouds seen on the ground and in or near the cloud by aircraft and balloons. In particular, terrestrial gamma-ray flashes (TGFs), which are thought to be emitted by thunderclouds, are so bright that they sometimes saturate detectors on spacecraft hundreds of kilometers away. These TGFs also generate energetic secondary electrons and positrons that are detected by spacecraft in the inner magnetosphere. It is generally believed that these x-ray and gamma-ray emissions are generated, via bremsstrahlung, by energetic runaway electrons that are accelerated by electric fields in the atmosphere. In this paper, we review this newly emerging field of High-Energy Atmospheric Physics, including the production of runaway electrons, the production and propagation of energetic radiation, and the effects of both on atmospheric electrodynamics.     

Titan’s new pole: Implications for the Huygens entry and descent trajectory and landing coordinates

The European Space Agency’s Huygens probe separated from the NASA Cassini spacecraft on 25 December 2004, after having been attached for a 7-year interplanetary journey and three orbits around Saturn. The probe reached the predefined NASA/ESA interface point on 14 January 2005 at 09:05:52.523 (UTC). It performed a successful entry and descent sequence and softly landed on Titan’s surface on the same day at 11:38:10.77 (UTC) with a speed of about 4.54 m/s. Since the publication of the official project entry and descent trajectory reconstruction effort by the Descent Trajectory Working Group in 2007 (referred to as DTWG#4) various other efforts have been performed and published. This paper presents an overview of the most relevant reconstructions and compares their methodologies and results. Furthermore, the results of a new reconstruction effort (DTWG#5) are presented, which is based on the same methodology as DTWG#4 but takes into account new estimates of Titan’s pole coordinates which were derived from radar images of different Cassini Titan flybys. It can be shown that the primary effect can be observed in the meridional direction which is represented by a stark southward shift of the trajectory by about 0.3 deg. A much smaller effect is seen in the zonal direction (i.e., less than 0.01 deg in the west to east direction). The revised probe landing coordinates are 192.335 deg W and 10.573 deg S. A comparison of these coordinates with results of recent landing site investigations using visual and radar images of the Cassini VIMS instrument shows excellent agreement of the two independently derived landing coordinates, i.e., longitude and latitude residuals of respectively 0.035 deg and 0.007 deg.     

Thermoviscoelastic Analysis of Stress in Composite Structures- Micro-to-Structural Approach

Manufacturing of composite materials is usually accompanied with residual stresses. These stresses should be evaluated and assessed. To this end, a micromechanical model for periodic material whose temperature dependent constituents behave as thermorheologically complex materials （TCM） has been developed. This model, referred as the high fidelity generalized method of cells （HFGMC）, takes into account the detailed interaction be- tween the fiber and resin, their volume ratios, the fibers distribution and their waviness. This model is linked, in conjunction with a special UMAT subroutine, to the ABAQUS finite element code for prediction of the response of thermoviscoelastic composite structures during cool down process. The present investigation shows the effect of the cool down rate on the residual stress developed in the composite cylindrical structures.