Comments with reply, on `A new look at nonseparable syntheticaperture radar processing' by A. Di Cenzo

The commenters point out that the idea using a two-dimensional digital correlation technique to perform synthetic-aperture-radar (SAR) processing, presented as new in the above-titled paper (see ibid., vol.24, p.218-23, May 1988), was described by them as early as 1978 and has since been described by other authors. They discuss some of these earlier studies. The author replies that he was unaware of the earlier work, and that he did not intend to convey the impression that the nonseparable transform domain processor that he presented was the first     

A SAR processor based on two-dimensional FFT codes

A synthetic aperture radar (SAR) processor approach based on two-dimensional fast Fourier transform (FFT) codes coupled with an asymptotic evaluation of the unit response function is presented. For the latter, no approximation is made to the distance function, so that the full range of geometric aberrations is analytically considered, enabling an effective reference filter to be designed. The two-dimensional FFTs were designed as to run on computers of very limited memory: the required FFT is computed by means of FFTs of lower order. Two FFT codes were considered: one is faster and allows full or reduced (quick look or multilook) resolution performance to be obtained easily; the second is slower but allows the use of a space-varying filter and/or investigations on limited portions (zoom) of the image. Both codes are suited to parallel processing, e.g. by a transputer net. A full discussion on computer memory and time requirements is presented as well as first examples of image processing results     

On adaptive multiband signal detection with the SMI algorithm

In a nonstationary and/or nonhomogeneous interference environment, an adaptive system for target detection may suffer a severe performance degradation due to the lack of a sufficient amount of data from which the system can learn (estimate) the statistics of the environment. The detection performance of an adaptive system, which employs a frequency diversity (multiband) signaling waveform and a multiband sample matrix inversion algorithm (SMI), is analyzed. By comparison with the corresponding single-band system under the chosen system constraint, it is shown that the multiband system can significantly outperform the single band when the amount of data available from a single frequency band is severely limited by the environment     

Simplified analysis of PWM converters using model of PWM switch.II. Discontinuous conduction mode

For pt.I see ibid., vol.26, no.3, p.490-6 (1990). According to the method of state-space averaging, when a pulsewidth modulation (PWM) converter enters discontinuous conduction mode (DCM), the inductor current state is lost from the average model of the converter. It is shown that there is neither theoretical nor experimental justification for the disappearance of the inductor state as claimed by the method of state-space averaging. For example, when the model of the PWM switch in DCM is substituted in the buck, boost, or buck-boost converter while the inductor is left intact, the average model has two poles: the first pole f_p1 agrees with the single pole of state-space averaging, while the second pole f_p2 occurs in the range f_p2⩾F_s/π. It is shown that the right-half plane zeros present in the control-to-output transfer functions of the boost, buck-boost, and Cuk converters in continuous conduction mode are also present in discontinuous conduction mode     

复材机身制造的自动化流水线工艺过程

AeroSuite给出了一个飞行器制造过程有效管理整个产品制造流程的解决方案。它包括FiberSIM复材工艺软件、SyncroFIT机身设计制造装配软件、对于首件鉴定过程的流程化的质量规划模块(QPE)。     

以高效加工机床设备服务我国装备制造业

<正>北京机电院高技术股份有限公司是北京市转制企业的成功典范,前身曾是北京市最大的科研院所,作为北京市65家第一批转制科研院所之一。在数控机床领域,公司始终致力于成为国内机床细分领域技术创新排头兵,作为京城控股中高端数控机     

Fourier methods for turbomachinery applications

Rapid increase in computing power has made a huge difference in scales and complexities of the problems in turbomachinery that we can tackle by use of computational fluid dynamics (CFD). It is recognised, however, that there is always a need for developing efficient methods for applications to blade designs. In a design cycle, a large number of flow solutions are sought to interact iteratively or concurrently with various options, opportunities and constraints from other disciplines. This basic requirement for fast prediction methods in a multi-disciplinary design environment remains unchanged, regardless of computer speed. And it must be recognised that the multi-disciplinary nature of blading design increasingly influences outcomes of advanced gas turbine and aeroengine developments. Recently there has been considerable progress in the Fourier harmonic modelling method development for turbomachinery applications. The main driver is to develop efficient and accurate computational methodologies and working methods for prediction and analysis of unsteady effects on aerothermal performance (loading and efficiency) and aeroelasticity (blade vibration due to flutter and forced response) in turbomachinery. In this article, the developments and applications of this type of methods in the past 20 years or so are reviewed. The basic modelling assumptions and various forms of implementations for the temporal Fourier modelling approach are presented and discussed. Computational examples for realistic turbomachinery configurations/flow conditions are given to illustrate the validity and effectiveness of the approach. Although the major development has been in the temporal Fourier harmonic modelling, some recent progress in use of the spatial Fourier modelling is also described with demonstration examples.     

A data-driven approach to modeling high-density terminal areas: A scenario analysis of the new Beijing,China airspace

Airports are being developed and expanded rapidly in China to accommodate and pro-mote a growing aviation market. The future Beijing Daxing International Airport (DAX) will serve as the central airport of the JingJinJi megaregion, knitting the Beijing, Tianjin, and Hebei regions together. DAX will be a busy airport from its inception, relieving congestion and accommodating growth from Beijing Capital International Airport (PEK), currently the second busiest airport in the world in passengers moved. We aim to model terminal airspace designs and possible conflicts in the future Beijing Multi-Airport System (MAS). We investigate standard arrival procedures and mathematically model current and future arrival trajectories into PEK and DAX by collecting large quantities of publicly available track data from historical arrivals operating within the Beijing terminal airspace. We find that (1) trajectory models constructed from real data capture aberrations and deviations from standard arrival procedures, validating the need to incorporate data on histor-ical trajectories with standard procedures when evaluating the airspace and (2) given all existing constraints, DAX may be restricted to using north and east arrival flows, constraining the capacity required to handle the increases in air traffic demand to Beijing. The results indicate that the termi-nal airspace above Beijing, and the future JingJinJi region, requires careful consideration if the full capacity benefits of the two major airports are to be realized.     

软件体系结构的探讨

软件体系结构是软件工程中的一个新兴研究领域,它与软件工程技术的发展有着密切的关系。首先,从软件工程技术的发展了解软件体系结构研究的必然性;然后,给出软件体系结构的概念描述,介绍有关体系结构研究的内容;最后,举出一个实例。     

OSIRIS-REx: Sample Return from Asteroid (101955) Bennu

In May of 2011, NASA selected the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) asteroid sample return mission as the third mission in the New Frontiers program. The other two New Frontiers missions are New Horizons, which explored Pluto during a flyby in July 2015 and is on its way for a flyby of Kuiper Belt object 2014 MU69 on January 1, 2019, and Juno, an orbiting mission that is studying the origin, evolution, and internal structure of Jupiter. The spacecraft departed for near-Earth asteroid (101955) Bennu aboard an United Launch Alliance Atlas V 411 evolved expendable launch vehicle at 7:05 p.m. EDT on September 8, 2016, on a seven-year journey to return samples from Bennu. The spacecraft is on an outbound-cruise trajectory that will result in a rendezvous with Bennu in November 2018. The science instruments on the spacecraft will survey Bennu to measure its physical, geological, and chemical properties, and the team will use these data to select a site on the surface to collect at least 60 g of asteroid regolith. The team will also analyze the remote-sensing data to perform a detailed study of the sample site for context, assess Bennu’s resource potential, refine estimates of its impact probability with Earth, and provide ground-truth data for the extensive astronomical data set collected on this asteroid. The spacecraft will leave Bennu in 2021 and return the sample to the Utah Test and Training Range (UTTR) on September 24, 2023.