In this study, a MATLAB&reg / code based on the Shooting and Bouncing Ray (SBR) algorithm is developed to compute the Radar Cross Section (RCS) of complex targets. SBR is based on ray tracing and combine Geometric Optics (GO) and Physical Optics (PO) approaches to compute the RCS of arbitrary scatterers. The presented algorithm is examined in two parts / the first part addresses a new aperture selection strategy named as &ldquo / conformal aperture&rdquo / , which is proposed and formulated to increase the performance of the code outside the specular regions, and the second part is devoted to testing the multiple scattering and shadowing performance of the code. The conformal aperture approach consists of a configuration that gathers all rays bouncing back from the target, and calculates their contribution to RCS. Multiple scattering capability of the algorithm is verified and tested over simple shapes. Ray tracing part of the code is also used as v a shadowing algorithm. In the first instance, simple shapes like sphere, plate, cylinder and polyhedron are used to model simple targets. With primitive shapes, complex targets can be modeled up to some degree. Later, patch representation is used to model complex targets accurately. In order to test the whole code over complex targets, a Computer Aided Design (CAD) format known as Stereo Lithography (STL) mesh is used. Targets that are composed in CAD tools are imported in STL mesh format and handled in the code. Different sweep geometries are defined to compute the RCS of targets with respect to aspect angles. Complex targets are selected according to their RCS characteristics to test the code further. In addition to these, results are compared with PO, Method of Moments (MoM) and Multilevel Fast Multipole Method (MLFMM) results obtained from the FEKO software. These comparisons enabled us to improve the code as possible as it is.

This thesis focuses on the underground transportation forms that began to emerge in city centers in the second half of the 20th century. Besides providing an illustration and evaluation of the selected case projects, the notions of speed and time are opened for discussion as significant concepts that interact to affect the physical formations both of cities and transport policies. The developments in urban transport technologies after the 1960s are also examined as leading factors in the development of today&rsquo / s multimodal and multilayered urban transportation hubs.

Power system protection is important for service reliability and quality assurance. Various faults may occur due to natural and artificial calamity. To reduce the outage duration and promptly restore power services, fault section estimate has to be done effectively with appeared fault alarms. Dispatchers could study the changed statuses of primary/back-up relays and circuit breakers to identify the fault section and fault types. It is difficult to process too many alarms under various conditions in a large power system. Single fault, multiple faults, single and multiple faults could coexist with the failed operation of relays and circuit breakers, or with the erroneous data communication. Dispatchers need more time to process the many uncertainties before identifying the fault. This thesis presents the use of artificial intelligence for fault section detection in substation with neural networks. Probabilistic Neural Networks (PNN) are proposed for fault detection system in substation. The proposed methodology will use primary/back-up information of protective relays and circuit breakers to detect the fault sections involving single fault, multiple faults, or fault with the failure operation of the relays and circuit breakers. This paper also presents a fuzzy theory-based method to identify fault types. It is derived to improve the inadequacy of making decisions by selecting a fixed threshold value and has the capability of non-deterministic decision making with a prior knowledge of uncertainties in fault location, fault resistance and the a size of loads. The proposed approach has been tested on a typical taipower system with accurate results.

Periodic and chaotic dynamical systems follow deterministic equations such as Newton's laws of motion. To distinguish the difference between two systems, the initial conditions have an important role. Chaotic behaviors or dynamics are characterized by sensitivity to initial conditions. Mathematically, a chaotic system is defined as a system very sensitive to initial conditions. A small difference in initial conditions causes unpredictability in the final outcome. If error is measured from the initial state, the relative error grows exponentially. Prediction becomes impossible and finally, chaotic systems can come to become stochastic system. To make chaotic motion, the number of variables in the system should be above three and there should be non-linear terms coupling several of the variables in the equation of motion. Phase space is defined as the space spanned by the coordinate and velocity vectors. In our case, mixing zone is phase space. With the above characteristics - the initial condition sensitivity of a chaotic system, our plan is to find most efficient chaotic stirrer. In this thesis, we present four methods to measure mixing state based on the chaotic dynamics theory. The Lyapunov exponent is a measure of the sensitivity to initial conditions and can be used to calculate chaotic strength. We can decide the chaotic state with one real number and measure efficiency of the chaotic mixer and find the optimum frequency. The Poincare section method provides a means for viewing the phase space diagram so that the motion is observed periodically. To do this, the trajectory is sectioned at regular intervals. With the Poincare section method, we can find 'islands' considered as bad mixed zones so that the mixing state can be measured qualitatively. With the chaotic dynamics theory, the initial length of the interface can grow exponentially in a chaotic system. We will show the above characteristics of the chaotic system to prove as fact that our model is an efficient chaotic mixer. The final goal for making chaotic stirrer is how to implement efficient dispersed particles. The box counting method is focused on measurement of the particles dispersing state. We use snap shots of the mixing process and with these snap shots, we devise a plan to measure particles' dispersing rate using the box-counting method.

"Enhanced index fund" is an investment strategy, combining active and passive management elements, for index tracking and return enhancing through disciplined market timing, stock selection and leverage activities. Though enhanced index funds have been well developed globally, there is only one enhanced index fund in Taiwan - "Polaris/P-Shares Taiwan Dividend+ ETF". Taiwan's stock market falls between weak form and semi-strong form efficiency. With the growth of Taiwan's mutual fund industry size, the enhanced index funds have very good chance to become the main investment instruments of institutional investors, index investors, and pensions. This study attempts to build enhanced index funds, then analyzes the performance and checks the feasibility of launching such products in Taiwan. In this study, we select "TSEC Taiwan 50 index (TW50)" as the benchmark index. The innovative "Multi-section Adjustment Model" divides the original weights of constituent stocks into two sections. Each section is adjusted through parameters. The "multi-factor model section" is responsible for the delivery of enhanced return, while the "cash dividend yield section" is used to provide excess cash dividend yield. The investment target is set for less than 1.5 percent tracking error, at least 1 percent tracking difference, and higher cash dividend yield than the benchmark. Building methodology can be divided into "fixed parameter model" and "floating parameters model" according to its update frequency. Empirical studies show that: (1) The enhanced index fund built from the "fixed parameter model" not only exhibits risk slightly lower than the benchmark, but also enjoys higher return. (2) In the short-term, the performance of the enhanced index fund built from "floating parameters model" is difficult to predict; in the long-term, however, the risk is lower and the return is higher than TW50. The cumulative return from the "fixed parameter model" is higher than the "floating parameters model" by about 2 percent. (3) The effectiveness of the parameters used to control the optimal weight distribution is decreasing over time, so it is necessary to update parameters regularly. (4) Raising "enhancement multiplier" will cause higher tracking error, but also bring higher tracking difference. This result proves that "multi-factor model section" works nicely and has its contribution. (5) As the "section allotment" and/or "fixed rate" getting lower, there will be more and more weights distributed to the cash dividend yield level, resulting in higher cash dividend yield. It means the "cash dividend yield section" has its merit as well. (6) Regular parameter updates to the "floating parameters model" helps to reduce the tracking error and, at the same time, maintain positive tracking difference. Considering the perpetual life of real world funds, "floating parameters model" should be a better building methodology. "Multi-Section Adjustment Model" has following advantages: (1) Its concept is intuitive and easy to use. (2) Sections can be customized based on investment objectives. (3) It is easy to analyze the impacts and trade-off among the parameters.

In the deep burn research of Very High Temperature Reactor (VHTR), it is desired to make an accurate estimation of absorption cross sections and absorption rates in burnable poison (BP) pins. However, in traditional methods, multi-group cross sections are generated from single bundle calculations with specular reflection boundary condition, in which the energy spectral effect in the core environment is not taken into account. This approximation introduces errors to the absorption cross sections especially for BPs neighboring reflectors and control rods. In order to correct the BP absorption cross sections in whole core diffusion calculations, energy spectrum reconstruction (ESR) methods have been developed to reconstruct the fine group spectrum (and in-core continuous energy spectrum). Then, using the reconstructed spectrum as boundary condition, a BP pin cell local transport calculation serves an imbedded module within the whole core diffusion code to iteratively correct the BP absorption cross sections for improved results. The ESR methods were tested in a 2D prismatic High Temperature Reactor (HTR) problem. The reconstructed fine-group spectra have shown good agreement with the reference spectra. Comparing with the cross sections calculated by single block calculation with specular reflection boundary conditions, the BP absorption cross sections are effectively improved by ESR methods. A preliminary study was also performed to extend the ESR methods to a 2D Pebble Bed Reactor (PBR) problem. The results demonstrate that the ESR can reproduce the energy spectra on the fuel-outer reflector interface accurately.

<p>Aircrafttrajectory optimization is traditionally used forminimizing fuel consumption or time when going from one flightstate to another. This thesis presents a possible approach toincorporate tactical constraints in aircraft trajectoryoptimization.</p><p>The stealth technology of today focuses on making thetactics already in use more effective. Since tactics andstealth are closely interrelated, new and better results may beobtained if both aspects are considered simultaneously. Simplyreducing the radar cross section area in some directionswithout considering tactical aspects may result in little, ifany, improvement.</p><p>Flight tests have been performed in cooperation withEricsson Microwave Systems and the Swedish Air Force FlightAcademy. The aircraft used was the subsonic jet trainer Saab105, designated SK60 by the Swedish Air Force. The results showa decrease of 40% in the time interval between the instant theaircraft was first detected until it could pass above the radarstation. This corresponds to a reduced radar cross section(RCS) in the direction from the aircraft to the radar of almost90%, if classical RCS reduction techniques would have beenapplied.</p><p>If a modern aircraft with stealth properties would be used,the proposed methodology is believed to increase the possibleimprovements further. This is because the variation of themagnitude of RCS in different directions is greater for a shapeoptimized aircraft, which is the property exploited by thedeveloped method.</p><p>The methods presented are indeed an approach utilizing theideas of the network centric warfare (NCW) concept. Themethodology presented depends on accurate information about theadversary, while also providing up-to-date information to theother users in the information network.</p><p>The thesis focuses on aircraft but the methods are generaland may be adapted for missiles, shipsor land vehicles. Theproposed methods are also economically viable since they areuseful for existing platforms without costly modifications. Themethods presented are not limited to radar threats only. Thereasons for using radar in this thesis are the availablenon-classified data and that radar is known to pose a majorthreat against aircraft.</p>

<p>When simulating target seekers, there is a great need for computationally efficient, target models. This report considers a study of radar target modelling based on Inverse Synthetic Aperture Radar (ISAR) measurements of generic aircraft. The results underlie future modelling of full-size air targets. </p><p>A method is developed for two-dimensional modelling of aspect-dependent target scattering. The approach taken is to generate point-scatterer models of two targets, where each point scatterer is defined according to its position and radar cross section (RCS), estimated from ISAR images. The scattered energy contributions from all point scatterers are summed to simulate a radar return signal. To validate the models, the modelled radar target centre is compared to the true radar target centre, which is determined from ISAR images. </p><p>The method is presented to be promising for modelling air targets with large, persistent radar cross section.</p>

Die Arbeit beschäftigt sich mit Faltungsoperatoren auf Kegeln, die in Lebesgueräumen L^p(R^2) (1<p<\infty) von Funktionen auf der Ebene wirken. Es werden asymptotische Spektraleigenschaften der zugehörigen Finite Sections studiert. Im Falle p=2 (Hilbertraum) wird das Invertierbarkeitsproblem von Operatoren vom Faltungstyp auf Kegeln mit Hilfe der Methode der Standard-Modell-Algebren untersucht.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2009. / Härtill 4 uppsatser.