涡轮发动机复杂区域的结构化网格生成技术

通过对二维泊松方程增加伪时间项，采用时间推进法求解生成二维网格，利用拉格朗日插值生成三维网格，给出了一种在涡轮发动机复杂区域中生成结构化网格的计算方法。该方法很好地保证了网格的质量和正交性。大量的计算算例表明该网格的生成方法和区域分解算法相结合可以对复杂区域流场的流动细节进行很好的模拟。     

Creating a space exploration industry

The article provides an overview of funding for space exploration to the Moon and Mars under NASA's direction, and presents an argument for the creation of a commercial space industry.     

Estimation of the covariance matrix for dependent signal samples:polarization diversity systems

The problem of the estimation of covariance matrices in multichannel radar system when signal samples are statistically dependent is addressed. An optimal maximum likelihood (ML) estimate is derived. Probability characteristics and sensitivity to signal models of the estimate are evaluated for a polarization diversity system     

Retrieval of a wind profile from the Galileo Probe telemetry signal

Ultrastable oscillators onboard the Galileo Probe and Orbiter will permit very accurate determinations of the frequency of the Probe's telemetry signal as the Probe descends from a pressure level of several hundred mb to a level of about 20 bars. Analysis of the time-varying frequency can provide, in principle, a unique and important definition of the vertical profile of the zonal wind speed in the Jovian atmosphere. In this paper, we develop a protocol for retrieving the zonal wind profile from the Doppler shift of the measured frequency; assess the impact of a wide range of error sources on the accuracy of the retrieved wind profile; and perform a number of simulations to illustrate our technique and to assess the likely accuracy of the retrieval.Because of unavoidably large uncertainties in the absolute frequencies of the oscillators, we use time-differenced frequencies in our analysis. Nevertheless, it is possible to recover absolute wind speeds as well as wind shears, since the Orbiter/Probe geometry changes significantly during the Probe relay link. We begin with the full relativistic Doppler shift equation. Through the use of power series expansions and a basis function representation of the wind profiles, we reduce the basic equation to a set of linear equations that can be solved with standard linear least-squares techniques.There are a very large number of instrumental and environmental factors that can introduce errors into the measured signal or to the recovery of zonal winds from the data. We provide estimates of the magnitudes of all these error sources and consider the degree to which they may be reduced by a posteriori information as well as the results of calibration tests. The most important error source is the a posteriori uncertainty in the Probe's entry longitude. The accuracy of the retrieved winds is also limited by errors in the Probe's descent velocity, as obtained from atmospheric parameters measured by several Probe experiments, and in the a posteriori knowledge of secular drifts in the oscillators' frequencies during the relay link, due, for example, to aging and radiation damage.Our simulations indicate that zonal winds may be retrieved from the Doppler data to an accuracy of several m s^-1. Therefore, it may be possible to discriminate among alternative models for the basic drive of the zonal winds, since they differ significantly in the implied zonal wind profile.     

如何给学习者一个全新的学习环境

通过对传统学习环境概念的阐释以及对一些有代表意义的建构主义学习环境定义的分析，提出关于建构主义学习环境的概念及其基本特点，论述了建构主义学习环境设计与教学设计之间的区别，建构主义学习环境的本质和设计过程中应注意的问题。     

Linear FM signal parameter estimation from discrete-timeobservations

The authors consider the problem of estimating the parameters of a complex linear FM signal from a finite number of noisy discrete-time observations. An estimation algorithm is proposed, and its asymptotic (large sample) performance is analyzed. The algorithm is computationally simple, consisting of two fast Fourier transforms (FFTs) accompanied by one-dimensional searches for maxima. The variance of the estimates is shown to be close to the Cramer-Rao lower bound when the signal-to-noise ratio is 0 dB and above. The authors applied the algorithm to the problem of estimating the kinematic parameters of an accelerating target by pulse-Doppler radar. A representative test case was used to exhibit the usefulness of the algorithm for this problem, and to verify the analytical results by Monte Carlo simulations     

Problems of complex safety of helicopter operation with regard for real expenditure of its service life

The methodical grounds for helicopter operation with respect to the technical condition for the state of the art of aeronautical engineering are analyzed and generalized. The most essential engineering solutions on developing the systems for monitoring the helicopter operating conditions are considered. The promising lines for further development of these systems are designated.     

丹麦,缔造2010年世博会的童话意境

2010年上海世博会,丹麦国家馆。由哥本哈根远道而来的安徒生童话著名人物——小美人鱼雕像,在中心水池恬静娴雅,悠闲自得地端坐着。这是一座完全拥有丹麦味道的雕塑作品,栩栩如生,届时约七千万人能有幸欣赏这一丹麦王国的象征。哥本哈根市议会目前已投票决定了将要送小美人鱼远离家乡参加2010年5月1日到10月31日在上海世博会的丹麦展台。这一决定结束了长期以来关于小美人鱼去与否的诸多纷争。     

一个房地产老板的通航梦想

2012年3月7日在浙江建德千岛湖通用机场上海东方通用航空公司的269C型直升机举行首飞仪式。上海东方通用航空的前身是上海东方航空教培公司,公司成立于1995年,至今已有17年的历史。上海东方通航是全国最早引进美国塞斯纳训练飞机的单位,也是全国最早具有甲类资质的通用航空企业。2009年公司主运营基地由上海龙华机场迁至浙江建德千岛湖通用机场,同年12月28日通过了民航商业(非运输)航空营运运行合格审定,正式成为第二家在浙江安家的通用航空企业,2011年又完成了直升机补充运行合格审     

Dynamics of air transport networks: A review from a complex systems perspective

Air transport systems are highly dynamic at temporal scales from minutes to years. This dynamic behavior not only characterizes the evolution of the system but also affect the system's functioning. Understanding the evolutionary mechanisms is thus fundamental in order to better design optimal air transport networks that benefits companies, passengers and the environment. In this review, we briefly present and discuss the state-of-the-art on time-evolving air transport net-works. We distinguish the structural analysis of sequences of network snapshots, ideal for long-term network evolution (e.g. annual evolution), and temporal paths, preferred for short-term dynamics (e.g. hourly evolution). We emphasize that most previous research focused on the first modeling approach (i.e. long-term) whereas only a few studies look at high-resolution temporal paths. We conclude the review highlighting that much research remains to be done, both to apply already available methods and to develop new measures for temporal paths on air transport networks. In particular, we identify that the study of delays, network resilience and optimization of resources (aircraft and crew) are critical topics.     

Design of a space-based radar signal processor

Space-based radar (SBR) is capable of providing flexible wide-area coverage of air, land, and sea targets. Numerous studies have been carried out in the United States and Canada in recent years to investigate different concepts for SBR. The design of a suitable radar signal processor (RSP) is challenging due to the effects caused by the moving platform on target integration and clutter spectral spread. A candidate RSP is described that uses a corporate fed array (CFA) antenna as its primary radar sensor. The algorithmic definitions of the signal processing functions are provided; the relationships between these functions and the reasons for their location in the signal processing chain are also discussed. In addition, techniques for reducing the computational requirements are also presented     

On the uniform sampling of a sinusoidal signal

It is generally accepted that a monochromatic signal such as sin 2πWt (W>0) must be sampled at a uniform rate greater than the ostensible Nyquist rate of 2W samples per to effect a reconstruction of the signal. It is shown that a sinusoid of frequency W Hz is completely determined by its samples taken at the uniform rate of 2r samples per second, where r>0 is arbitrary subject only to the restriction that W ≠kr for any positive integer k. In particular, a pure sinusoid may be sampled uniformly without loss of information at arbitrarily small rates     

General direction-of-arrival estimation: a signal subspace approach

A high-resolution algorithm is presented for resolving multiple incoherent and coherent plane waves that are incident on an array of sensors. The incident sources can be a mixture of narrowband and broadband sources, and, the geometry of the array is unrestricted. The algorithm makes use of a fundamental property possessed by those eigenvectors of the array spectral density matrix that are associated with eigenvalues that are larger than the sensor noise level. Specifically, it is shown that these eigenvectors can each be represented as linear combinations of the steering vectors identifying the incident plane waves. This property is then used to solve the important special cases of incoherent sources incident on a general array and coherent sources incident on an equispaced linear array. Simulation results are presented to illustrate the high-resolution performance achieved with this approach relative to that obtained with MUSIC and spatial smoothed MUSIC in which the coherent-signal-subspace focusing method is used     

建立民航维修专家系统的分析

简要介绍了专家系统的原理及构成.分析了“设计民航维修专家系统”的过程,目前加拿大正着手研制的“先进的维修软件系统”的概况.最后提出专家系统需要解决的关键技术问题及发展情况.     

Angle and polarization estimation in a coherent signal environment

It is shown how a uniform linear array of crossed dipoles may be used with the ESPRIT algorithm and spatial smoothing techniques to estimate the arrival directions and polarizations of incoming coherent plane waves. Some examples showing typical performance are presented. One method of smoothing can be used where it is necessary to estimate both the arrival angles and polarizations of signals. Two other methods can be used when only the arrival angles are of interest     

利用QED—200硅光电二极管自校准技术建立微光功率标准

着重介绍利用硅光二极管自校准技术建立激光功率标准的基本原理、实验装置的组成和实验结果。     

Optimum array detector for a weak signal in unknown noise

We study the design of constant false-alarm rate (CFAR) tests for detecting a rank-one signal in the presence of background Gaussian noise with unknown spatial covariance. We look at invariant tests, i.e., those tests whose performance is independent of the nuisance parameters, like the background noise covariance. Such tests are shown to have the desirable CFAR property. We characterize the class of all such tests by showing that any invariant decision statistic can be written as a function of two basic statistics which are in fact the adaptive matched filter (AMF) statistic and Kelly's generalized likelihood ratio statistic. Further, we establish an optimum test in the limit of low signal-to-noise ratio (SNR), the locally most powerful invariant (LMPI) test. We also derive the bound for the probability of detection of any invariant detector, at a fixed false-alarm rate, and compare the LMPI and the published detectors (Kelly and AMF) to it     

Efficient wideband signal parameter estimation using a radon-ambiguity transform slice

A novel efficient technique based on a single slice Radon-ambiguity transform (RAT) for time-delay and time-scale estimation is proposed. The proposed approach combines the narrowband cross-ambiguity function (NBCAF), the wideband cross-ambiguity function (WBCAF), and a single slice RAT to estimate multiple target parameters in noisy environments. The square modulus of Gaussian-enveloped linear frequency modulated (GLFM) signals has high-energy centrality in the ambiguity plane. Its peaks in the NBCAF fall along nearly straight lines whose slopes depend on the Doppler rates of the moving targets. These lines could be effectively detected by computing the entire Radon transform of the NBCAF for all possible angles; however, it is a computationally intensive procedure. It is shown that without calculating the entire RAT, it is possible to estimate target parameters using only a single slice of the RAT, i.e., using an appropriate projection of the NBCAF. It is demonstrated that the proposed method can successfully separate overlapping targets efficiently. The efficiency is achieved due to fast Fourier transform (FFT)-bascd processing, use of a single slice of RAT, and the use of only one-dimensional (1-D) searches.     

Differential GPS in a real time land vehicle environment-satellitebased Van Carrier Location System

The handling of containers in terminals requires, in particular in the application of “chaotic storekeeping”, optimal logistic organization-supported by technical and innovative methods. In this manner, it is possible to guarantee that the existing resources are used at maximal cost and time efficiency. The satellite supported DGPS location system represents a substantial contribution to this problem, which determines the container location during the pick-up and set-down phases in the decimeter range and transmits this information via data telemetry link to the central control office. This allows the realization of a fully automatic administration of the container storage facility, as well as integration into the company's data radio link and terminal control