Th. 3e cycle--Électronique, électrotech., autom.--Toulouse--I.N.P., 1979. N°: 40.

Three centuries ago, the concept of the Solar Sytem being formed from an unstable disc was initially proposed. This research examines this cosmogony by the classical technique of initially obtaining the density structure of steady state discs, and gravitational instability of such systems Is then investigated in order to examine correlations between observed phenomena in the Solar System and predictions of the theory. A fluid mechanical approach to the steadystate axisymmetric structure is formulated for isothermal and polytropic gas systems, with uniform or radially dependent rotation. The equations are reduced to a single quasi-linear elliptical partial differential equation governing density, and known external boundary conditions are necessary to yield an unique density solution. When the external density is non-zero, flattened discs are possible solutions of the basic system. Two asymptotic techniques in spherical and cylindrical coordinates are created to obtain approximate solutions of the steadystate structure. Both techniques show that a self-consistent disc is composed of a high-density central bulge encircled by a low-density flat outer disc. Gravitational instability in gaseous discs is now formulated by the linear perturbation of the fundamental variables, density, pressure, gravitational potential and velocity. As the Solar System is essentially a planar structure, axisymmetric radial instability along the equatorial plane of rotation is examined. Such ring type modes are shown to be unstable to shear and tend to self-coverage. A dispersion relation is obtained analytically which indicates that the wavelength between rings is approximately inversely proportional to the square root of the steadystate density at marginal stability. However for the pure gas disc, the wavelengths are too long for any correspondence with the present spacing of the Planets. As usual, the presence of dust is invoked close to the equatorial plane. Radial instability in this gas-dust disc has a dispersion relation for the resultant wave in which the gas and dust move together such that the density term is multiplied by the dust-gas mass loading ratio. Thus the wavelengths at neutral stability will be correspondingly shorter and a correlation of ring density maxima with Planetary positions in the Solar System is obtained for reasonable values of three dimensionless parameters. If any planets exist outside Pluto the theory shows their distance apart can be expected to be similar to that of the Outer Planets, 10 a.u. Solar Systems formed by this type of instability in self-gravitating dust-gas discs can be expected to have linearly increasing planetary distances close to the central Sun "(Titius-Bode Law) with a more constant spacing further out as illustrated by our Solar System. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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<p>Solid-state LED lighting is a promising technology to improve the energy efficiency of general illumination. The inherent modulation bandwidth of these devices can be exploited to provide a dual role as a communication device. This method of communication is termed visible light communications (VLC).</p> <p>Due to dispersive nature of the VLC channel, orthogonal frequency division multiplexing (OFDM) has been proposed to allow multi-user communication while mitigating the effects of inter-symbol interference (ISI). However, OFDM is in general not compatible with intensity modulation and direct detection (IM/DD) channels since it has both positive and negative amplitudes. Various techniques have been proposed that provide compatible optical OFDM signaling such as DC-biased OFDM, asymmetrically clipped optical OFDM (ACO-OFDM), and pulse amplitude modulated discrete multi-tone (PAM-DMT).</p> <p>This thesis develops spectrally factorized optical OFDM (SFO-OFDM) as a framework to implement OFDM on optical intensity channels. The drawbacks of conventional methods are mitigated in SFO-OFDM. Contrary to ACO-OFDM and PAM-DMT, the proposed technique uses all the available bandwidth for data modulation and does not require reserved subcarriers. Simulation results verify that SFO-OFDM has gain both in optical power efficiency and peak-to-average power ratio compared to conventional optical OFDM schemes.</p> <p>Furthermore in this thesis, a new receiver design for ACO-OFDM and PAM-DMT is proposed. Unlike conventional receivers that ignore the structure of the transmitted signal, the new detector exploits this structure to improve the optical power efficiency. By observing the time domain samples, a simple pairwise maximum likelihood detector is developed and used to remove half of the noise power. It is also shown by simulation results that employing the proposed detector design leads to a significant gain in optical power efficiency.</p> / Master of Applied Science (MASc)

Highway traffic control systems have been deployed to provide emergency vehicle preemption (EVP) at signalized intersections. Industry and transportation researchers have worked to develop analytical methods to establish the degree of benefit of emergency vehicle preemption to the emergency vehicle (EV) community and the impact on other road user groups. This thesis report illustrates the use of an analytical method to evaluate the potential impacts of EVP related to EV safety, and the potential delay to EVs and vehicles on the side street. The method uses EV-specific conflict point and delay analysis with video and other data collected in a field study conducted in Northern Virginia at the intersection of Southgate Drive and U.S. 1. EV related conflict points are characterized in terms of the EV/auto interaction geometry, the signal display, and the severity of potential crashes. EV related delay is characterized in terms of the EV/auto interaction geometry, the signal display, the level of service and the amount of delay to the EV. The EV/auto interaction, the queue length and the signal display characterize increase in delay to vehicles on the side street. The analysis indicates that the severity of EV-specific conflict points is significantly reduced with EVP. The delay to EV does not change significantly and the delay to the vehicles on the side street auto traffic increases. / Master of Science

Since its discovery, in the 1940's, radar (Radio Detection and Ranging) has become an important ranging sensor in many areas of technology and science. Most of the military and many civilian applications are unimaginable today without radar. With technology development, radar application areas have become larger and more available. One of these applications is Synthetic Aperture Radar (SAR), where an airborne radar is used to create high resolution images of the imaged scene. Although known since the 1950's, the SAR methods have been continuously developed and improved and new algorithms enabling real-time applications have emerged lately. Together with making the hardware components smaller and lighter, SAR has become an interesting sensor to be mounted on smaller unmanned aerial vehicles (UAV's). One important thing needed in the SAR algorithms is the estimate of the platform's motion, like position and velocity. Since this estimate is always corrupted with errors, particularly if lower grade navigation system, common in UAV applications, is used, the SAR images will be distorted. One of the most frequently appearing distortions caused by the unknown platform's motion is the image defocus. The process of correcting the image focus is called auto-focusing in SAR terminology. Traditionally, this problem was solved by methods that discard the platform's motion information, mostly due to the off-line processing approach, i.e. the images were created after the flight. Since the image (de)focus and the motion of the platform are related to each other, it is possible to utilise the information from the SAR images as a sensor and improve the estimate of the platform's motion. The auto-focusing problem can be cast as a sensor fusion problem. Sensor fusion is the process of fusing information from different sensors, in order to obtain best possible estimate of the states. Here, the information from sensors measuring platform's motion, mainly accelerometers, will be fused together with the information from the SAR images to estimate the motion of the flying platform. Two different methods based on this approach are tested on the simulated SAR data and the results are evaluated. One method is based on an optimisation based formulation of the sensor fusion problem, leading to batch processing, while the other method is based on the sequential processing of the radar data, leading to a filtering approach. The obtained results are promising for both methods and the obtained performance is comparable with the performance of a high precision navigation aid, such as Global Positioning System (GPS). / LINK-SIC

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International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / Our telemetry department has an application for a data categorization/compression of a high speed transient signal in a short period of time. Categorization of the signal reveals important system performance and compression is required because of the terminal nature of our telemetry testing. Until recently, the hardware for the system of this type did not exist. A new exploratory device from Intel has the capability to meet these extreme requirements. This integrated circuit is an analog neural network capable of performing 2 billion connections per second. The two main advantages of this chip over traditional hardware are the obvious computation speed of the device and the ability to compute a three layer feed-forward neural network classifier. The initial investigative development work using the Intel chip has been completed. The results from this proof of concept will show data categorization/compression performed on the neural network integrated circuit in real time. We will propose a preliminary design for a transient measurement system employing the Intel integrated circuit.

International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / This paper introduces a PPK intelligent demodulator used in the PCM--PPK (pulse position keying) telemetry system. It describes the basic requirement of the system for the PPK signal demodulator and analyses the insufficiancy of the full-hardware PPK demodulator. It also advances a PPK demodulating scheme based on the TMS32020 digital signal processor and a block diagram of the demodulator, states the method of detecting frame synchronization, analyses the precision of sync-building and gives the way of calculating the miss and error probability of frame sync. The result makes it clear that the demodulator based on TMS32020 has programmable feature for the bit rate and frame synchronization and realizes easily the system demand of the separate demodulating of output signals of the multi-channel receiver and then the synthesis processing of the realtime data.