Radar imagery provides an all-weather and 24 h coverage, making it ideal for critical defence applications. In some applications, multiple images acquired of an area need to be registered for further processing. Such ...
详细信息
Radar imagery provides an all-weather and 24 h coverage, making it ideal for critical defence applications. In some applications, multiple images acquired of an area need to be registered for further processing. Such situations arise for battlefield surveillance based on satellite imagery. The registration has to be done between an earlier (reference) image and a new (live) image. For automated surveillance, registration is a prerequisite for change detection. Speed is essential due to large volumes of data involved and the need for quick responses. The registration transformation is quite simple, being mainly a global translation. (Scale and rotation corrections can be applied based on known camera parameters). The challenge lies in the fact that the radar images are not as feature-rich as optical images and the image content variation can be as high as 90 per cent. Even though the change on the ground may not be drastic, seasonal variations can significantly alter the radar signatures of ground, vegetation, and water bodies. This necessitates a novel approach different from the techniques developed for optical images. An algorithm has been developed that leads to fast registration of radar images, even in the presence of specular noise and significant scene content variation. The key features of this approach are adaptability to sensor/terrain types, ability to handle large content variations and false positive rejection. The present work shows that this algorithm allows for various cost-performance trade-offs, making it suitable for a wide variety of applications. The algorithm, in various cost-performance configurations, is tested on a sot of ERS images. Results of such tests have been reported, indicating the performance of the algorithm for various cost-performance trade-offs.
Heat treating is a dangerous occupation. Furnaces are inevitably hot and the treatment atmospheres comprise a wide range of potentially dangerous gases. This article outlines the potential hazards associated with the ...
详细信息
Heat treating is a dangerous occupation. Furnaces are inevitably hot and the treatment atmospheres comprise a wide range of potentially dangerous gases. This article outlines the potential hazards associated with the use of furnaces, particularly when atmospheres are employed that have risks of explosions, burning, toxic effects and asphyxiation. It suggests ways in which those risks can be minimised and reviews the guidance provided by some relevant safety standards.
Two novel navigation-guidance-based methods are presented for on-line-robotic-interception of fast-maneuvering objects. For the first method, an ideal proportional navigation-guidance (IPNG) technique is used during p...
详细信息
Two novel navigation-guidance-based methods are presented for on-line-robotic-interception of fast-maneuvering objects. For the first method, an ideal proportional navigation-guidance (IPNG) technique is used during phase I of the two-phase robot trajectory planning and control strategy. For the second method, an augmented form of the IPNG (AIPNG) technique is suggested for phase I, when a reliable estimation of the acceleration of the target can be provided to the interceptor. Both techniques are modified to reflect the greater mobility of a robotic manipulator over an airborne interceptor. The convergence analyses of both methods are detailed and compared to that of a conventional moving-object tracking method. Computer simulations clearly illustrate the effectiveness of the IPNG-based interception methods over pure tracking-based techniques proposed in the cited literature. (C) 2000 John Wiley gr Sons, Inc.
An innovative approach is followed for analysing flight control command for tactical missile guidance with a variable manoeuvering target. The moving orthogonal coordinate system of classical differential geometry cur...
详细信息
An innovative approach is followed for analysing flight control command for tactical missile guidance with a variable manoeuvering target. The moving orthogonal coordinate system of classical differential geometry curve theory is similar to the stability axis system utilised in atmospheric flight mechanics. Based on this similarity, the Frenet-Serret formula is used to study the characteristics of a pseudomissile pointing velocity vector and used to design a new control command for tactical missile guidance. The closed-form solution for the rate of rotation of the line of sight vector, characteristic of the pseudomissile pointing velocity vector, together with a miss vector are used to study the capture capability of this control command. The region of miss is derived in terms of the tangential component of the kinematics equation. A sufficient initial condition, which can guarantee capture under arbitrary target manoeuvres with bounding information, is proposed.
With all the guidance on ISO 9001:2000 already published, you would think everyone would understand the process approach as a basic concept of the revised standard. Jeffrey H. Hooper discussed this approach in an earl...
详细信息
With all the guidance on ISO 9001:2000 already published, you would think everyone would understand the process approach as a basic concept of the revised standard. Jeffrey H. Hooper discussed this approach in an earlier article in Quality Progress, and chapters two, eight, 11, 12, 20, 30 and 42 in the ASQ ISO 9001:2000 Handbook deal extensively with the topic. In addition, International Organization for Standardization, known as ISO, Technical Committee 176 provides a guidance document (ISO/TC 176/SC2 N544R) available for free download.
In the present work it is presented an implementation of two specific functions which are going to be of growing importance in Advanced Surface Movement guidance and Control Systems (A-SMGCS). Namely the two functions...
详细信息
In the present work it is presented an implementation of two specific functions which are going to be of growing importance in Advanced Surface Movement guidance and Control Systems (A-SMGCS). Namely the two functions are Routing and guidance. Routing provides a means to suggest to the airport ground control a best path from any given point on the airfield to any other given point according to a number of constraints and rules. guidance provides an interface between the system and the pilot and provides guidance aids to the pilot in order to have the airplane on the route generated by the Routing function. Both Functions have been developed under the European Union “Vision” project, in the frame of the Telematics Application Program. A complete A-SMGCS is working now at Navia with simulation scenarios for various airports and will be installed and tested at, at least, two of them. The system is completely modular and can be installed in a number of configurations. In fact, every function is a self-contained program, communicating with each other by the means of computer networks
The dynamic mechanisms by which self-organizing circuits form in a developing nervous system remain to be elucidated. It is clear, however, that diffusible chemoattractants and chemorepelants as well as contact attrac...
详细信息
The dynamic mechanisms by which self-organizing circuits form in a developing nervous system remain to be elucidated. It is clear, however, that diffusible chemoattractants and chemorepelants as well as contact attraction and contact repulsion have been implicated in the establishment of connections between neurons and their targets, We will describe simulations based on the known biology of the whole sequence of events from the bundling of axons, guidance, pathfinding, to debundling and the final innervation of individual targets. (C) 2000 Elsevier Science B.V. All rights reserved.
The existing optimal guidance laws assume that the time-to-go is known exactly. The time-to-go is usually estimated and thus is a random variable. The Issue of optimal guidance with uncertain time-to-go is dealt with ...
详细信息
The existing optimal guidance laws assume that the time-to-go is known exactly. The time-to-go is usually estimated and thus is a random variable. The Issue of optimal guidance with uncertain time-to-go is dealt with here. A problem of control of linear discrete systems with unknown time-to-go is formulated and served. The solution is applied to derive guidance laws. The solution depends on the probability density function of the time-of-flight. This guidance law has the structure of a rendezvous guidance law where the guidance gains are time-dependent and depend on the distribution of the time-to-go. Examples that demonstrate these dependencies are presented.
During development, the formation of neural networks is reflected by the oriented extension of neurites. Using retinal ganglion cells (RGCs) as a model, we identified the yet uncharacterized chick semaphorin Sema3E/co...
详细信息
During development, the formation of neural networks is reflected by the oriented extension of neurites. Using retinal ganglion cells (RGCs) as a model, we identified the yet uncharacterized chick semaphorin Sema3E/collapsin-5 as a repulsive cue for outgrowing axons. Sema3E/collapsin-5 was highly regulated during retinal histogenesis, with peak expression during the period of intraretinal axon growth. Polymerase chain reaction analysis demonstrated Sema3E/collapsin-5 mRNA in retina layers, from which RGC axons are excluded. Neither isolated RGCs nor purified retinal Muller glia cells synthesized Sema3E/collapsin-5. Sema3E/ collapsin-5 receptor sites were visualized by alkaline phosphatase fusion proteins in the axon-rich optic fiber layer. Time-lapse video recording of chick in vitro cultures revealed a growth cone collapsing activity of recombinant Sema3E/collapsin-5. This effect was specific for RGCs, since dorsal root ganglia (DRG) neurons of the peripheral nervous system were not affected. Comparison with Sema3A/collapsin-1 displayed a reciprocal specificity, because Sema3A/collapsin-1 hampered exclusively DRG but not RGC growth cones. The collapsing effect was mediated by low cGMP levels, but not cAMP, as revealed by a set of agonists. In summary, the data suggest a possible role of chick Sema3E/collapsin-5 in restricting growth of retinal ganglion cell axons to the optic fiber layer. (C) 2002 Elsevier Science (USA).
Purpose: To evaluate initial technical success, procedural complications, and 12-month patency of duplex-guided angioplasty compared to conventional fluoroscopically-guided procedures. Methods: One hundred four patien...
详细信息
Purpose: To evaluate initial technical success, procedural complications, and 12-month patency of duplex-guided angioplasty compared to conventional fluoroscopically-guided procedures. Methods: One hundred four patients (65 men;mean age 69 years) who underwent duplex-guided femoropopliteal angioplasty were compared to 104 patients undergoing fluoroscopically-guide procedures who were matched for age, sex, baseline ankle-brachial index (ABI), and length and grade of lesion. Patients were followed for 12 months, and restenosis was assessed by ABI and duplex sonography. Results: Technical success was achieved in 88 (84.6%) patients from the duplex-guided group and in 102 (98.1%) control patients (p=0.001). Periprocedural complications occurred in 12.5% (n=13) and 18.3% (n=19), respectively (p=0.4). Contrast-induced transient renal impairment was observed in 7 (6.7%) patients in the fluoroscopic group. One hundred (96.1%) patients in the duplex and 102 (98.1%) patients in the fluoroscopic group completed the 12-month follow-up. Restenosis was found in 35 (39.8%) patients of the duplex group and in 38 (37.2%) patients of the fluoroscopic group (p=0.8). Conclusions: Technical success of duplex-guided procedures was significantly lower compared to fluoroscopic angioplasty;complications and 12-month patency were similar with both techniques. Duplex-guided angioplasty may be a feasible alternative, particularly for patients at high risk for contrast-induced complications.
暂无评论