Infrared continuum observations of the solar atmosphere

The far-infrared wavelengths (10 microns to 1 mm) were used to study the spatial and temporal structure of the solar atmosphere. Observational results were obtained on flares, faculae, sunspots, and on the center-to-limb intensity distribution, as well as on time variability within these regions. A program of precise monitoring of slow variations in the integrated solar luminosity was shown to be feasible, and initial steps to implement observations were completed

Performance of turbo multi-user detectors in space-time coded DS-CDMA systems

Includes bibliographical references (leaves 118-123).In this thesis we address the problem of improving the uplink capacity and the performance of a DS-CDMA system by combining MUD and turbo decoding. These two are combined following the turbo principle. Depending on the concatenation scheme used, we divide these receivers into the Partitioned Approach (PA) and the Iterative Approach (IA) receivers. To enable the iterative exchange of information, these receivers employ a Parallel Interference Cancellation (PIC) detector as the first receiver stage

Linear and nonlinear optical pulse characterisation

Developmental work on the generation and measurement of ultrashort pulses has been performed. A colliding pulse, passively mode-locked (CPM) ring dye laser has been investigated by spectral analysis and the nonlinear technique of second harmonic generation autocorrelation. Two systems for the intracavity compensation of group velocity dispersion (GVD) have been experimentally compared in the CPM laser. Initially one scheme, utilising Gires-Toumois interferometers, has achieved pulse durations of 64 fs. A second technique employing a four-prism sequence within the cavity gave typical pulse durations of -40 fs and focussing adjustments within the jets achieved durations as short as 19 fs for the first time. A realtime interferometric autocorrelator was constructed and detailed theoretical work has been performed to model the resultant fringe resolved autocorrelations as a function of pulseshape and frequency chirp. Spectral and autocorrelation analysis of the CPM laser led to the inference that the laser pulse intensity profiles were distinctly asymmetric. The main sources of frequency chirp within the laser cavity were assessed in order to find possible explanations for this type of laser behaviour. The linear pulse measurement technique employing synchroscan streak cameras was also critically assessed in terms of the available temporal resolutions as a function of phase noise in the RF deflection signal. Two streak tube designs, the Photochron II and the Photochron IV, have been experimentally compared employing the CPM laser as a test pulse source. Optimisation of the synchronisation circuitry has allowed the notable achievement of a temporal resolution of 0.93ps for the Photochron IV streak camera. A computer-interfaced readout system incorporating a charge coupled device (CCD) sensor has been developed which allows the recording of synchroscan streak events with a digitisation accuracy up to 12 bits. Preliminary experimentation was also performed to investigate the feasibility of incorporating a electron sensitive CCD structure within the envelope of the streak camera. It is intended that such a streak camera will be incorporated in a spaceborne laser ranging system and a theoretical assessment of the expected instrument performance has been performed. The above investigations have direct relevance to other types of ultrashort pulse sources and their application in optical communications, time-resolved spectroscopy and ultrafast electrooptic sampling

Advanced passive communication satellite systems comparison studies. Volume 2 - Technical discussion Final report

Passive communication satellites feasibility for Comsat system - Vol.

Implementation of an experimental program to investigate the performance characteristics of OMEGA navigation

A theoretical formulation of differential and composite OMEGA error is presented to establish hypotheses about the functional relationships between various parameters and OMEGA navigational errors. Computer software developed to provide for extensive statistical analysis of the phase data is described. Results from the regression analysis used to conduct parameter sensitivity studies on differential OMEGA error tend to validate the theoretically based hypothesis concerning the relationship between uncorrected differential OMEGA error and receiver separation range and azimuth. Limited results of measurement of receiver repeatability error and line of position measurement error are also presented

Multi-fuel operation of modern engines; on board fuel identification

Modern engines require enhancement of electronic controls to achieve better fuel economy, higher power density and satisfactory emissions levels while operating safely. Military vehicles should be capable to run safely and efficiently on any fuel available in the field, therefore on-board fuel identification and adaptation of engine controls to the type of fuel becomes extremely important. In these conditions, the use of an inexpensive, nonintrusive sensor is highly desirable. The development of a technique based on the measurement of the instantaneous crankshaft speed and engine dynamics could be a convenient solution. Several such methods have been elaborated at the Center for Automotive Research (CAR) in the Mechanical Engineering Department at Wayne State University. Each of these methods yields plausible results regarding on-board fuel identification

Machine Learning in Digital Signal Processing for Optical Transmission Systems

The future demand for digital information will exceed the capabilities of current optical communication systems, which are approaching their limits due to component and fiber intrinsic non-linear effects. Machine learning methods are promising to find new ways of leverage the available resources and to explore new solutions. Although, some of the machine learning methods such as adaptive non-linear filtering and probabilistic modeling are not novel in the field of telecommunication, enhanced powerful architecture designs together with increasing computing power make it possible to tackle more complex problems today. The methods presented in this work apply machine learning on optical communication systems with two main contributions. First, an unsupervised learning algorithm with embedded additive white Gaussian noise (AWGN) channel and appropriate power constraint is trained end-to-end, learning a geometric constellation shape for lowest bit-error rates over amplified and unamplified links. Second, supervised machine learning methods, especially deep neural networks with and without internal cyclical connections, are investigated to combat linear and non-linear inter-symbol interference (ISI) as well as colored noise effects introduced by the components and the fiber. On high-bandwidth coherent optical transmission setups their performances and complexities are experimentally evaluated and benchmarked against conventional digital signal processing (DSP) approaches. This thesis shows how machine learning can be applied to optical communication systems. In particular, it is demonstrated that machine learning is a viable designing and DSP tool to increase the capabilities of optical communication systems

Transport Barrier Formation on HBT-EP

The physics of the biasing induced L-H transition and the mechanism for E×B shear flow suppression of turbulence are investigated on HBT-EP. Detailed measurements of the transverse length scales, behavior, and propagation direction of the edge turbulence match what is expected for the ion temperature gradient (ITG) mode. In the scrape-off layer (SOL), radially propagating blob-filament turbulence is identified and characterized, with velocities, sizes, and distributions comparable to measurements on other devices. Through systematic studies of the effect of applied shear flow on the turbulence, it is found that the E×B suppression of turbulence matches what is expected by the spectral shift model [Staebler et al. 2013 Phys. Rev. Lett. 110 055003]. Namely, the application of shear flow tilts the turbulent eddies and shifts the mean radial wavenumber ⟨kr⟩ of the turbulence spectrum from near zero to finite values, leading to a reduction in the turbulence intensity. The investigation also shows that both the decorrelation model and quench rule are able to reproduce the measured reduction of the turbulence intensity with applied shear flow when appropriate parameters are chosen. However, the decorrelation model fails to explain the increase in the shear-wise correlation length measured with increasing applied shear, and the quench rule fails to capture the suppression of the turbulence to a finite intensity at high shear. It is found that the same shearing effect that tilts the eddy structures and shifts ⟨kr⟩, enhances the gradient in the Reynolds stress at the edge and suppresses the blob-filament turbulence in the SOL. Although the biasing levels leading up to the transition are shown to enhance the Reynolds stress in a radially varying manner, it is found that the high flow shear in the H-mode state completely quenches the Reynolds stress. A careful examination of the spatial structure and temporal dynamics of the forcing terms in both dithering and one-step transitions reveals that the biasing induced L-H transition is caused by a reduction in poloidal viscosity at high flow velocity, in agreement with neoclassical theory. Nevertheless, the Reynolds force is measured to be comparable to the force from the electrode current, allowing the turbulence driven stress to work synergistically (or antagonistically) with forces from the probe to achieve the critical poloidal flow velocities. The similarities between the transition criteria on HBT-EP and other devices indicate that reduction of poloidal viscosity leading to the transition to improved confinement regimes may be a universal trait among toroidal confinement devices. The application of resonant magnetic perturbations (RMPs) is shown to both reduce the Reynolds stress and increase the biasing threshold for the transition. The observed reduction in the Reynolds stress stems from a reduction in the intensity of the underlying turbulence; namely, a decrease in the amplitude of velocity fluctuations in regions where the Reynolds stress is high without an applied RMP. This study has therefore expanded the current understanding of transport barrier formation in magnetic confinement devices

Digital transmission systems operating over high frequency radio channels

Imperial Users onl