Modification of the SAR step transform algorithm

When the basic step transform algorithm is used to compress synthetic-aperture radar (SAR) signals in azimuth, the linear FM rate and sampling rate must satisfy certain tight constraints. In practice, these constraints cannot be satisfied and errors are introduced into the compressed SAR image. A modification is described of the basic step transform which incorporates interpolation and resampling into the algorithm. These changes allow the removal of the constraints and make the step transform more useful for the compression of real data. An autofocusing capability is also included, without introducing much additional complexity     

Investigation of resonant modes and frequencies of plate vibrations as applied to turbomachine blades

The results of experimental and numerical investigations of resonant vibration frequencies and modes for rectangular cantilever plates of constant thickness are presented. The investigations are carried out using the methods of interference holography and finite elements, and the results may serve as basic references in determining resonant frequencies and modes of compressor and turbine blade vibrations.     

UVCS Observations and Modeling of Streamers

We present results derived from the analysis of an equatorial streamer structure as observed by the UVCS instrument aboard SOHO. From observations of the H I Lyα and Lyβ lines we infer the density and temperature of the plasma. We develop a preliminary axisymmetric, magnetostatic model of the corona which includes the effects of gas pressure gradients on the magnetic structure. We infer a coronal plasma β > 1 in the closed field regions and near the cusp of the streamer. We add to the model a parallel velocity field assuming mass flux conservation along magnetic flux tubes. We then compute the Lyα emissivity and the line-of-sight integrals to obtain images of Lyα intensity, taking into account projection effects and Doppler dimming. The images we obtain from this preliminary model are in good general agreement with the UVCS observations, both qualitatively and quantitatively. This revised version was published online in June 2006 with corrections to the Cover Date.     

Magnetic reconnection in solar coronal loops

Simulations of the evolution of kink modes in line-tied coronal loops are presented which demonstrate the occurrence of magnetic reconnection in the non-linear stage of the instability. In loops which do not carry a net axial current (and are confined by a potential purely axial field) the reconnection is limited to the initial current-carrying channel and no overall loss of confinement is observed. In loops which carry a net current on the other hand, reconnection progressively involves field lines at greater and greater distances from the axis and even regions where the field was initially potential, leading to a total disruption of the magnetic field topology.     

跨声速流自发凝结水滴的测量

应用基于多波长消光法原理发展的光学探针,测量了跨声速风洞中不同马赫数湿空气流自发凝结形成的水滴尺寸及浓度,并给出了实验结果     

Relativistic electron fluxes and dose rate variations during April–May 2010 geomagnetic disturbances in the R3DR data on ISS

Space radiation has been monitored successfully using the Radiation Risks Radiometer-Dosimeter (R3D) installed at the ESA EXPOSE-R (R3DR) facility outside of the Russian Zvezda module of the International Space Station (ISS) between March 2009 and January 2011. R3DR is a Liulin type spectrometer–dosimeter with a single Si PIN detector 2 cm² of area and 0.3 mm thick. The R3DR instrument accumulated about 2 million measurements of the absorbed dose rate and flux of 10 s resolution. The total external and internal shielding before the detector of R3DR device is 0.41 g cm⁻². The calculated stopping energy of normally incident particles to the detector is 0.78 MeV for electrons and 15.8 MeV for protons. After the Coronal Mass Ejection (CME) at 09:54 UTC on 3 April 2010, a shock was observed at the ACE spacecraft at 0756 UTC on 5 April, which led to a sudden impulse on Earth at 08:26 UTC. Nevertheless, while the magnetic substorms on 5 and 6 of April were moderate; the second largest in history of GOES fluence of electrons with energy >2 MeV was measured. The R3DR data show a relatively small amount of relativistic electrons on 5 April. The maximum dose rate of 2323 μGy day⁻¹ was reached on 7 April; by 9 April, a dose of 6600 μGy was accumulated. By the end of the period on 7 May 2010 a total dose of 11,587 μGy was absorbed. Our data were compared with AE-8 MIN, CRESS and ESA-SEE1 models using SPENVIS and with similar observations on American, Japanese and Russian satellites.