Polarization effects in microwave diversity imaging of perfectlyconducting cylinders

A theoretical vector development is derived for the directly and mutually scattered wavefield of two cylinders in a bistatic measuring system. The approach is first to give an expression for the field scattered from a single cylinder illuminated by a right-hand circularly polarized plane wave. This expression is then extended to the case of the directly scattered (or first-order) field of two cylinders. The mutually scattered (or second-order) field of two cylinders is then formulated in terms of a coherent summation of the scattered field from each cylinder due to the incident wave scattered from the other cylinder. In order to simplify computational tasks, only the second-order scattered field is analytically derived; this is called the mutually scattered field. The total wavefield scattered by two cylinders becomes the coherent superposition of the directly scattered component and the mutually scattered component for each polarization. The use of an automated microwave imaging facility employing frequency, polarization and angular diversity to verify the results of theoretical analysis is described. The analytical and experimental results are shown to be in good agreement. The results show that the effects of polarization state transformation or change in the mutually scattered field component are more pronounced than in the directly scattered component     

A natural partitioning scheme for parallel simulation of multibody systems

A parallel partitioning scheme based on physical-co-ordinate variables is presented to systematically eliminate system constraint forces and yield the equations of motion of multibody dynamics systems in terms of their independent co-ordinates. Key features of the present scheme include an explicit determination of the independent co-ordinates, a parallel construction of the null space matrix of the constraint Jacobian matrix, an easy incorporation of the previously developed two-stage staggered solution procedure and a Schur complement based parallel preconditioned conjugate gradient numerical algorithm.     

Towards parallel I/O in finite element simulations

I/O issues in finite element analysis on parallel processors are addressed. Viable solutions for both local and shared memory multiprocessors are presented. The approach is simple but limited by currently available hardware and software systems. Implementation is carried out on a CRAY-2 system. Performance results are reported.     

Microwave imaging of moving objects

Microwave images for objects in motion can be obtained with quality as good as those obtained in the stationary case if the signal waveforms, data acquisition systems, and image reconstruction algorithms are cleverly designed. The principle of imaging for objects in motion is to eliminate the gross Doppler effect of the echo signals and only reserve the differential Doppler information to reconstruct the image. Accordingly, requirements for parameters of the signal waveform are established. Two steps are involved in the image reconstruction algorithm: range alignment and phase compensation. Focused images of complex-shaped targets with simulated motion have been obtained experimentally.     

Surgical treatment of fixed subvalvular aortic stenosis. Immediate and long-term hemodynamic results

Forty patients operated on for fixed subvalvular aortic stenosis underwent cardiac catheterization preoperatively, immediately after coming off cardiopulmonary bypass and at long-term (1 to 14 years later, average 7 +/- 3.9 years). The age range was 3 to 50 years (average 15 +/- 12 years) with 27 (68%) aged under 18 years. Twenty-seven patients were male. The stenosis was the thin membranous type in 29, the fibromuscular collar type in 5, the tunnel type in 5 others and related to supernumerary mitral tissue in the remaining patient. Significant other pathology was associated in 13 cases. In addition to excision of the membrane or the fibromuscular ring, the surgeons performed myotomy in 6 cases, myomectomy in 12 cases, large resection of muscular and fibrous tissue in tunnels, and aortic valve replacement in 3 cases. There was no operative fatality. Permanent cardiac pacing was required in 1 patient for complete atrioventricular block. The peak systolic pressure gradient fell from 87 +/- 32 to 31 +/- 10 mmHg (p < 0.0001) at the immediate control: it remained > 30 and even 50 mmHg in 3 patients (7.5%), 2 of whom had tunnel types and the other the supernumerary mitral tissue. The gradient increased in the long-term to 42 +/- 11 mmHg, 1 patient with a membrane developed a gradient of 40 mmHg and 4 others (10%) developed a gradient > 50 mmHg (3 tunnels and 1 membrane). The 5 patients with tunnel types either had a residual stenosis or restenosis and underwent aorto-ventriculoplasty by Konno's procedure 1 to 8 years later. This operation should be the procedure of first intention, even in small children: the large resection is only acceptable when it cannot be performed or when aortic ring hypoplasia is mild. There is no residual stenosis and restenosis is rare (2.5%) in the membranous and fibromuscular types, probably because of the widespread use of myotomy and myomectomy. In the absence of severe associated malformations, surgery in only justified when peak systolic pressure gradients are > or = 50 mmHg.     

Three‐dimensional finite element calculations in acoustic scattering using arbitrarily shaped convex artificial boundaries

We report on a generalization of the Bayliss–Gunzburger–Turkel non‐reflecting boundary conditions to arbitrarily shaped convex artificial boundaries. For elongated scatterers such as submarines, we show that this generalization can improve significantly the computational efficiency of finite element methods applied to the solution of three‐dimensional acoustic scattering problems. Copyright © 2001 John Wiley & Sons, Ltd.     

Noise filtering in binary pictures by combinatorial techniques

Filtering of noise in binary pictures includes both the filling of spurious gaps and the elimination of spurious connections. This paper describes a method which performs these operations by examining pairs of boundary points of the various objects in the picture. The current implementation uses only distance criteria, but it can be extended by taking into account local shape information.     

Hardware Simulator Design for MIMO Propagation Channel on Shipboard at 2.2 GHz

A wireless communication system can be tested either in actual conditions or with a hardware simulator reproducing actual conditions. With a hardware simulator it is possible to freely simulate a desired radio channel, making it possible to test “on table” mobile radio equipments. This paper presents new architectures for the digital block of a hardware simulator of MIMO propagation channels. This simulator can be used for LTE and WLAN IEEE 802.11ac applications, in indoor and outdoor environments. However, in this paper, specific architectures of the digital block of the simulator for shipboard environment are presented. A hardware simulator must reproduce the behavior of the radio propagation channel. Thus, a measurements campaign has been conducted to obtain the impulse responses of the shipboard channel using a channel sounder designed and realized at IETR. After the presentation of the channel sounder, the channel impulse responses are described and implemented. Then, the new architectures of the digital block of the hardware simulator, implemented on a Xilinx Virtex-IV FPGA are presented. The accuracy, the occupation on the FPGA and the latency of the architectures are analyzed.     

Optimization methods applied for solving the short-term hydrothermal coordination problem

Short-term hydrothermal coordination (STHTC) is a very complicated optimization problem. It is a dynamic large-scale non-linear problem and requires solving unit commitment and economic power load dispatch problems. From this perspective, many successful and powerful optimization methods and algorithms have been employed to solve this problem. These optimization methodologies and techniques are widely diverse and have been the subject of ongoing enhancements over the years. This paper presents a survey of literature on the various optimization methods applied to solve the STHTC problem. A review and a methodology-based classification of most of the publications on the topic are presented.