Improved tracking of maneuvering targets: The use of turn-ratedistributions for acceleration modeling

Tactically maneuvering targets are difficult to track since acceleration cannot be observed directly and the accelerations are induced by human control or an autonomous guidance system therefore they are not subject to deterministic models. A common tracking system is the two-state Kalman filter with a Singer maneuver model where the second-order statistics of acceleration is the same as a first-order Markov process. The Singer model assumes a uniform probability distribution on the targets acceleration which is independent of the x and y direction. In practice, it is expected that targets have constant forward speed and an acceleration vector normal to the velocity vector, a condition not present in the Singer model. The work of Singer is extended by presenting a maneuver model which assumes constant forward speed and a probability distribution on the targets turn-rate. Details of the model are presented along with sample simulation results     

基于CFD技术的鼻腔输药的流动特性研究

鼻腔输药作为一种新颖的输药方式,具有方便可靠的特点,不仅可以适用于局部而且适用于全身用药,已经受到广泛的重视。但由于人类的呼吸道复杂的立体结构使得鼻腔输药成为生物医药研究的一个长期的挑战。利用CFD(计算流体动力学,Computational Fluid Dynamics)技术对鼻腔输药的流动特性进行研究,对一个基于真实的人类鼻腔解剖的3D模型的输药的流动过程进行了分析,着重研究了不同的药物颗粒的流动和沉淀特性。利用CFD的商用软件FLUENT在层流情况下对不同的密度、直径和流动速率的药物颗粒在鼻腔中流动进行了数值模拟,并对计算结果进行了比较分析。CFD研究的结果为鼻腔输药这种新颖的药物输送方式的优化设计提供了依据。     

Observational Manifestation of Chaos in the Gaseous Disk of the Grand Design Spiral Galaxy NGC 3631

The main goal of the paper is to demonstrate the presence of chaotic trajectories in the gaseous disk of a real spiral galaxy. As an example we have chosen NGC 3631. First, we show the stationarity of the 3-D velocity field restored from the observed line-of-sight velocity field of the gaseous disk. That allows to analyse behaviour of the trajectories of the fluid particles (gas clouds) in the disk, calculating the corresponding observed streamlines. We estimate the Lyapunov characteristic numbers using their independence of the metrics and show the existence of chaotic trajectories outside the vortices which are present in the velocity field, and in the vicinity of the saddle point. Related spectra of the stretching numbers for some trajectories are also calculated.     

Covariance matrix estimation for adaptive CFAR detection incompound-Gaussian clutter

We address the estimation of the structure of the covariance matrix and its application to adaptive radar detection of coherent pulse trains in clutter-dominated disturbance modeled as a compound-Gaussian process. For estimation purposes we resort to range cells in spatial proximity with that under test and assume that these cells, free of signal components, can be clustered into groups of data with one and the same value of the texture. We prove that, plugging the proposed estimator of the structure of the covariance matrix into a previously derived detector, based upon the generalized likelihood ratio test (GLRT), leads to an adaptive detector which ensures the constant false alarm rate (CFAR) property with respect to the clutter covariance matrix as well as the statistics of the texture. Finally, we show that this adaptive receiver has an acceptable loss with respect to its nonadaptive counterpart in cases of relevant interest for radar applications     

Medium PRF set selection using evolutionary algorithms

This paper presents a new and novel method of selecting multiple pulse repetition frequency (PRF) sets for use in medium PRF pulsed-Doppler radars. Evolutionary algorithms are used to minimise the blind areas in the range/Doppler space. The evolutionary algorithm allows optimal solutions to be generated quickly, far faster than with exhaustive searches, and is fully automatic, unlike existing techniques. The evolved solutions compare very favorably against the results of both an exhaustive search and existing published PRF set selection methods. This evolutionary approach to generation of PRF sets is a major advance in medium PRF radar design.     

Unmanned aircraft navigation for shipboard landing using infrared vision

This paper addresses the problem of determining the relative position and orientation of an unmanned air vehicle with respect to a ship using three visible points of known separation. The, images of the points are obtained from an onboard infrared camera. The paper develops a numerical solution to this problem. Both simulation and flight test results are presented.     

Present-Day Sea Level Change: Observations and Causes

We investigate climate-related processes causing variations of the global mean sea level on interannual to decadal time scale. We focus on thermal expansion of the oceans and continental water mass balance. We show that during the 1990s where global mean sea level change has been measured by Topex/Poseidon satellite altimetry, thermal expansion is the dominant contribution to the observed 2.5 mm/yr sea level rise. For the past decades, exchange of water between continental reservoirs and oceans had a small, but not totally negligible contribution (about 0.2 mm/yr) to sea level rise. For the last four decades, thermal contribution is estimated to about 0.5 mm/yr, with a possible accelerated rate of thermosteric rise during the 1990s. Topex/Poseidon shows an increase in mean sea level of 2.5 mm/yr over the last decade, a value about two times larger than reported by historical tide gauges. This would suggest that there has been significant acceleration of sea level rise in the recent past, possibly related to ocean warming. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Genesis Solar-Wind Collector Materials

Genesis (NASA Discovery Mission #5) is a sample return mission. Collectors comprised of ultra-high purity materials will be exposed to the solar wind and then returned to Earth for laboratory analysis. There is a suite of fifteen types of ultra-pure materials distributed among several locations. Most of the materials are mounted on deployable panels (‘collector arrays’), with some as targets in the focal spot of an electrostatic mirror (the ‘concentrator’). Other materials are strategically placed on the spacecraft as additional targets of opportunity to maximize the area for solar-wind collection. Most of the collection area consists of hexagonal collectors in the arrays; approximately half are silicon, the rest are for solar-wind components not retained and/or not easily measured in silicon. There are a variety of materials both in collector arrays and elsewhere targeted for the analyses of specific solar-wind components. Engineering and science factors drove the selection process. Engineering required testing of physical properties such as the ability to withstand shaking on launch and thermal cycling during deployment. Science constraints included bulk purity, surface and interface cleanliness, retentiveness with respect to individual solar-wind components, and availability. A detailed report of material parameters planned as a resource for choosing materials for study will be published on a Genesis website, and will be updated as additional information is obtained. Some material is already linked to the Genesis plasma data website (genesis.lanl.gov). Genesis should provide a reservoir of materials for allocation to the scientific community throughout the 21st Century. This revised version was published online in August 2006 with corrections to the Cover Date.     

Public Attitudes Towards Space Science

Astronomy and space science, including their associated basic research activities, enjoy broad popular backing. People generally support them, and say that they follow their results with interest. This article summarizes some of the detailed results of public surveys in the United States, focusing on popular opinions and attitudes, and the somewhat paradoxical finding that despite being interested and supportive, people are often ignorant about the basic facts. I explore some of the reasons for the popularity of space science, and suggest ways of justifying space science research in the broader context of science research. I argue that vigorous and innovative education and outreach programs are important, and can be made even more effective. This revised version was published online in June 2006 with corrections to the Cover Date.     

Type II Solar Radio Bursts: Theory and Space Weather Implications

Recent data and theory for type II solar radio bursts are reviewed, focusing on a recent analytic quantitative theory for interplanetary type II bursts. The theory addresses electron reflection and acceleration at the type II shock, formation of electron beams in the foreshock, and generation of Langmuir waves and the type II radiation there. The theory's predictions as functions of the shock and plasma parameters are summarized and discussed in terms of space weather events. The theory is consistent with available data, has explanations for radio-loud/quiet coronal mass ejections (CMEs) and why type IIs are bursty, and can account for empirical correlations between type IIs, CMEs, and interplanetary disturbances. This revised version was published online in August 2006 with corrections to the Cover Date.