Sidelobe blanking with integration and target fluctuation

In radar systems, sidelobe blanking (SLB) is used to mitigate impulsive interference that enters the radar through sidelobes of the main antenna. SLB employs an auxiliary antenna channel with the output being compared with that of the main antenna channel and a decision is then made as to whether or not to blank the main channel output. SLB performance determination involves the evaluation of several probability functions. Based on the classical Maisel SLB architecture, this work extends previous performance results, in which detection was limited to the case of a single radar pulse with either Marcum or Swerling I target fluctuation. Probability expressions have been generalized to include both an arbitrary number of integrated pulses and target fluctuation models based on the gamma distribution. The Swerling fluctuation models are all special cases of the gamma distribution. Results are derived in terms of two generalized probability functions, one for detection and the other for blanking. With these generalized probability functions, the SLB design and performance results can be determined. Examples are presented and discussed.     

Composition of Interstellar Neutrals and the Origin of Anomalous Cosmic Rays

Knowledge of the elemental composition of the interstellar gas is of fundamental importance for understanding galactic chemical evolution. In addition to spectroscopic determinations of certain element abundance ratios, measurements of the composition of interstellar pickup ions and Anomalous Cosmic Rays (ACRs) have provided the principal means to obtain this critical information. Recent advances in our understanding of particle acceleration processes in the heliosphere and measurements by the Voyagers of the energy spectra and composition of energetic particles in the heliosheath provide us with another means of determining the abundance of the neutral components of the local interstellar gas. Here we compare the composition at the termination shock of six elements obtained from measurements of (a) pickup ions at ～5 AU, (b) ACRs in the heliosphere at ～70 AU, and (c) energetic particles as well as (d) ACRs in the heliosheath at ～100 AU. We find consistency among these four sets of derived neutral abundances. The average interstellar neutral densities at the termination shock for H, N, O, Ne and Ar are found to be 0.055±0.021 cm^?3, (1.44±0.45)×10^?5 cm^?3, (6.46±1.89)×10^?5 cm^?3, (8.5±3.3)×10^?6 cm^?3, and (1.08±0.49)×10^?7 cm^?3, respectively, assuming the He density is 0.0148±0.002 cm^?3.     

Performance Degradation Due to Specular Multipath Intersymbol Interference

Plots of performance degradation are used to compare the effects of fading and intersymbol interference in a two- component specular multipath digital communications channel. Similar plots are then used to compare two practical receivers designed to combat the interference. Degradation plots are shown to allow easy identification of each receiver's range of usefulness, as well as identification of variance bounds demanded of channel parameter estimates which the receivers require.     

Developing better artificial bones

Researchers at the Center for Commercial Applications of Combustion in Space at the Colorado School of Mines are preparing the Space-DRUMS (Dynamically Responding Ultrasonic Matrix Systems) materials processing facility for transport to the International Space Station. The Space-DRUMS uses acoustic pressure beams to maintain the position of a suspended liquid or solid. Space-DRUMS will be used to extend experiments with tricalcium phosphate in the development of artificial bone material.     

导风轮叶片偏置对高压比串列离心压气机性能的影响

为提升高压比串列离心压气机的性能,借鉴常规一体化离心叶轮中偏置分流叶片的方法,针对某高压比串列离心压气机,应用数值仿真手段分析了串列叶轮中导风轮叶片周向偏置对压气机流场和性能的影响。通过对不同导风轮叶片偏置方案下压气机流场的分析,建立了压气机流动损失与偏置参数的关联性。研究表明:采用较大的偏置参数γ可降低导风轮叶片1前缘的激波强度,改善激波作用导致的泄漏涡破碎和流动分离,但过大或过小的γ方案中导风轮叶顶会出现二次泄漏致使低能流体的掺混损失增加;γ=65%方案压气机综合性能最佳,其压比和效率较γ=50%分别提高了1.5%和1.4%;对于串列离心压气机导风轮叶片周向位置的优化,在避免导风轮叶顶形成较强二次泄漏的前提下,应考虑采用较大的偏置参数γ,同时应防止诱导轮尾迹流体参与导风轮的叶顶泄漏。     

High-Resolution, Radar Coherent Linear FM Microwave Source

The microwave CLFM study was directed to generating 14 ?s S-band pulses of 1000 MHz bandwidth and an rms phase error of a few degrees. Over 972 MHz bandwidth, the sampled phase error relative to the reference was 7 degrees rms and 17 degrees peak, with a maximum Fourier component of 4 degrees. The FM pulse train is generated by a gated BWO driven by a stable linearizing waveform. Phase coherency during each pulse is obtained by a sampling technique, where the phase is corrected at intervals of 1/6 ?s, the RF phase having changed an integral number of cycles in each interval. Multiplication of the BWO signal by the sampling pulse train results in band-limited phase error pulses which are applied in a feedback loop. Pulse-to-pulse coherency is obtained by phase lock of the BWO starting frequency to the crystal reference. Feedback leveling holds the output constant to 0.3 dB. The basic MITRE technique was originally demonstrated at 10 MHz in 1964. Range results measured with the X-band model radar using the CLFM generator are given and confirm the phase errors of the CLFM.     

Radar Doppler Spectra of Turbulent Ionized Wakes

The evaluation of the double convolution integrat involved in the expression of the radar response to scattering from a turbulent ionized wake is simplified by the approximation technique presented here, so that the Doppler spectrum parameters can be explicitly expressed in terms of the wake characteristics.     

The Tactical Communications Satellite

Early in 1969 the U. S. Air Force placed into synchronous orbit the largest communications satellite built to date. This vehicle, the tactical communications satellite (TACSAT), together with a variety of ground terminals, is designed to test experimentally and develop tactical communications concepts for all military services. This paper describes the spacecraft design focusing on the communications repeater. Measured performance characteristics affecting communications utilization of the spacecraft are presented.     

Ionization processes in the heliosphere — Rates and methods of their determination

The rates of the most important ionization processes acting in interplanetary space on interstellar H, He, C, O, Ne and Ar atoms are critically reviewed in the paper. Their long-term modulations in the period 1974 – 1994 are reexamined using updated information on relevant cross-sections as well as direct or indirect data on variations of the solar wind/solar EUV fluxes based on IMP 8 measurements and monitoring of the solar 10.7 cm radio emission. It is shown that solar cycle related variations are pronounced (factor of 3 between maximum and minimum) especially for species such as He, Ne, C for which photoionization is the dominant loss process. Species sensitive primarily to the charge-exchange (as H) show only moderate fluctuations 20% around average. It is also demonstrated that new techniques that make use of simultaneous observations of neutral He atoms on direct and indirect orbits, or simultaneous measurements of He⁺ and He⁺⁺ pickup ions and solar wind particles can be useful tools for narrowing the uncertainties of the He photoionization rate caused by insufficient knowledge of the solar EUV flux and its variations.