Adaptive multibeam phased array design for a Spacelab experiment

The parametric tradeoff analyses and design for an Adaptive Multibeam Phased Array (AMPA) for a Spacelab experiment are described. This AMPA Experiment System was designed with particular emphasis to maximize channel capacity and minimize implementation and cost impacts for future austere maritime and aeronautical users, operating with a low gain hemispherical coverage antenna element, low effective radiated power, and low antenna gain-to-system noise temperature ratio

Compressive Sampling of Speech Signals

Compressive sampling is an evolving technique that promises to effectively recover a sparsesignal from far fewer measurements than its dimension. The compressive sampling theoryassures almost an exact recovery of a sparse signal if the signal is sensed randomly where thenumber of the measurements taken is proportional to the sparsity level and a log factor of thesignal dimension. Encouraged by this emerging technique, we study the application ofcompressive sampling to speech signals.The speech signal is very dense in its natural domain; however speech residuals obtainedfrom linear prediction analysis of speech are nearly sparse. We apply compressive sampling tospeech signals, not directly but on the speech residuals obtained by conventional and robustlinear prediction techniques. We use a random measurement matrix to acquire the data then use§¤-1 minimization algorithms to recover the data. The recovered residuals are then used tosynthesize the speech signal. It was found that the compressive sampling process successfullyrecovers speech recorded both in clean and noisy environments. We further show that the qualityof the speech resulting from the compressed sampling process can be considerably enhanced byspectrally shaping the error spectrum. The recovered speech quality is said to be of high qualitywith SNR up to 15 dB at a compression factor of 0.4

Intrinsic Limits of Dimensionality and Richness in Random Multipath Fields

We study the dimensions or degrees of freedom of farfield multipath that is observed in a limited, source-free region of space. The multipath fields are studied as solutions to the wave equation in an infinite-dimensional vector space. We prove two universal upper bounds on the truncation error of fixed and random multipath fields. A direct consequence of the derived bounds is that both fixed and random multipath fields have an effective finite dimension. For circular and spherical spatial regions, we show that this finite dimension is proportional to the radius and area of the region, respectively. We use the Karhunen-Loève (KL) expansion of random multipath fields to quantify the notion of multipath richness. The multipath richness is defined as the number of significant eigenvalues in the KL expansion that achieve 99% of the total multipath energy. We establish a lower bound on the largest eigenvalue. This lower bound quantifies, to some extent, the well-known reduction of multipath richness with reducing the angular power spread of multipath angular power spectrum

A Mechanistic Investigation of Cytochrome C Nitrite Reductase Catalyzed Reduction of Nitrite to Ammonia: The Search for Catalytic Intermediates

Cytochrome c Nitrite Reductase (ccNiR) is a periplasmic homodimeric decaheme enzyme that catalyzes the reduction of nitrite to ammonium in a process that involves six electrons and eight protons. Under standard assay conditions, which use a strong reducing agent as an electron source, catalysis takes place rapidly without producing detectable intermediates. However, intermediates do accumulate when weaker reducing agents are employed, allowing the ccNiR mechanism to be studied. Herein, the early stages of Shewanella oneidensis ccNiR-catalyzed nitrite reduction were investigated in isolation by using the weak reducing agents N,N,N’,N’-tetramethyl-p-phenylenediamine (TMPD) and the 2-electron reduced form of indigo trisulfonate. Experiments were done with the wild type enzyme (wtccNiR) as well as with R103Q, Y206F, and H257Q variants.A UV/Vis stopped-flow investigation of the reaction between nitrite-loaded wtccNiR and TMPD revealed for the first time that the reaction proceeds via a transient 1-electron reduced intermediate. Generation of this species is pH-independent, whereas its decay to a previously characterized 2-electron reduced intermediate is fastest at pH 6.8 and significantly slower at higher pH. The pH dependence is ascribed to the rate-limiting cleavage of the nitrite N – O bond, which requires a prior di-protonation predicted to be slow in earlier computational studies. Under steady-state conditions, S. oneidensis ccNiR catalyzed the slow 1-electron reduction of nitrite to nitric oxide, which was monitored by tracking the concomitant appearance of the colored TMPD+ radical product. The rate of TMPD+ formation was found to be directly proportional to the concentration of TMPD+ at low TMPD concentrations, providing important insights about the mechanism of NO˙ release. The steady-state studies also showed that nitrite is a substrate inhibitor of NO˙ release when TMPD is the electron source, probably because it blocks exit by NO˙ through the nitrite entry channel. The H257Q variant of ccNiR was found to have 1/400th of the wild type enzyme’s nitrite reductase activity in the standard assay in which methyl viologen monocation radical is the electron source, but nearly normal hydroxylamine reductase activity. This demonstrated that H257 is essential for nitrite reduction but not for reduction of hydroxylamine, a putative intermediate in the catalytic process. UV/Vis spectropotentiometry showed that the nitrite-loaded active site of H257Q still reduced at fairly high applied potential, but the reduction was by one electron, whereas the wild type is reduced in a concerted 2-electron step. The experiments with the variant, coupled with the pH-dependent stopped flow experiments with wtccNiR, confirm H257’s importance in facilitating nitrite reduction, but suggest that its role is to modulate the pKa values of one or more of the waters that form a complex hydrogen bonding network in the active site. This view is more conservative than earlier theoretical predictions of direct histidine involvement in nitrite diprotonation leading to N – O bond cleavage

Investigation of wavelength tunable laser modules for use in future optically switched dense wavelength division multiplexed networks

This thesis investigates the use of fast wavelength tunable laser modules in future optically switched dense wavelength division multiplexed networks (DWDM). The worldwide demand for increasingly greater broadband access has thus far been satisfied by the use of DWDM networks, enabled by the development of the erbium doped amplifier. However as this demand continues to grow electronic switching at network nodes will become a limiting factor, creating a potential bandwidth mismatch between the fibre capacities and switching capacity. Optical switching has been proposed to overcome this electronic bottleneck and fully utilize the enormous bandwidth offered by fibre. Fast tunable lasers (TLs) are a key technology in this area, enabling fast wavelength switching. Experimental work involving the fast wavelength switching of sampled grating distributed Bragg reflector TL modules is presented. Spurious mode generation during wavelength tuning is shown to cause severe cross-channel interference on other data channels in a DWDM test bed. Bit error rate (BER) results demonstrate that a integrated semiconductor optical amplifier can greatly reduce system degradation caused by asynchronous switching of multiple TLs. This is achieved by optically blanking the laser output during channel transition for a period of 60 ns. Immediately after the blanking period a wavelength drift due to the TL module wavelength locking is found to cause cross channel interference and introduce an error floor >1 e-4 on the BER performance characteristic of an adjacent channel in a 12.5 GHz spaced DWDM network. This drift is characterised, using a selfheterodyne and a filter based approach – Error free performance is subsequently demonstrated by using an extended blanking period of 260 ns or by using subcarrier multiplexing transmission and phase selective demodulation before detection. A DWDM optical label switching system, utilizing 40 Gbit/s payload data with low data rate labels placed on a 40 GHz sub-carrier and using TL transmitters is presented. Channel performance is monitored on a static channel as a second data channel is tuned into an adjacent channel on a 100 GHz spaced grid. Error free performance is demonstrated only for the channel payload – Time resolved BER results in agreement with the TL wavelength drift are measured and demonstrate a detrimental influence of the drift on the sub-carrier label performance

Advanced borehole seismic imaging techniques for mineral exploration

The thesis examines the current VSP application in mineral exploration in Australia and identifies the challenges and studies in which domain these challenges could be mitigated. In particular, the advancements can be seen in the equipment domain, by applying DAS technology, and in the processing domain, by utilising the full-waveform inversion techniques. Finally, the thesis demonstrates how advanced VSP techniques address the identified challenges and introduces a high-resolution dataset to assist subsurface characterisation

Wireless Sensing System for Load Testing and Rating of Highway Bridges

Structural capacity evaluation of bridges is an increasingly important topic in the effort to deal with the deteriorating infrastructure. Most bridges are evaluated through subjective visual inspection and conservative theoretical rating. Diagnostic load test has been recognized as an effective method to accurately assess the carrying capacity of bridges. Traditional wired sensors and data acquisition (DAQ) systems suffer drawbacks of being labor intensive, high cost, and time consumption in installation and maintenance. For those reasons, very few load tests have been conducted on bridges.;This study aims at developing a low-cost wireless bridge load testing & rating system that can be rapidly deployed on bridges for structural evaluation and load rating. Commercially available wireless hardware is integrated with traditional analogue sensors and the appropriate rating software is developed. The wireless DAQ system can work with traditional strain gages, accelerometers as well as other voltage producing sensors. A wireless truck position indicator (WVPI) is developed and used for measuring the truck position during load testing. The software is capable of calculating the theoretical rating factors based on AASHTO Load Resistance Factor Rating (LRFR) codes, and automatically produces the adjustment factor through load testing data. A simplified finite element model was used to calculate deflection & moment distribution factors in order to reduce the amount of instrumentation used in field tests. The system was used to evaluate the structural capacity of Evansville Bridge in Preston County, WV. The results show that the wireless bridge load testing & rating system can effectively be implemented to evaluate the real capacity of bridges with remarkable advantages: low-cost, fast deployment and smaller crew

Discrete Wavelet Transforms

The discrete wavelet transform (DWT) algorithms have a firm position in processing of signals in several areas of research and industry. As DWT provides both octave-scale frequency and spatial timing of the analyzed signal, it is constantly used to solve and treat more and more advanced problems. The present book: Discrete Wavelet Transforms: Algorithms and Applications reviews the recent progress in discrete wavelet transform algorithms and applications. The book covers a wide range of methods (e.g. lifting, shift invariance, multi-scale analysis) for constructing DWTs. The book chapters are organized into four major parts. Part I describes the progress in hardware implementations of the DWT algorithms. Applications include multitone modulation for ADSL and equalization techniques, a scalable architecture for FPGA-implementation, lifting based algorithm for VLSI implementation, comparison between DWT and FFT based OFDM and modified SPIHT codec. Part II addresses image processing algorithms such as multiresolution approach for edge detection, low bit rate image compression, low complexity implementation of CQF wavelets and compression of multi-component images. Part III focuses watermaking DWT algorithms. Finally, Part IV describes shift invariant DWTs, DC lossless property, DWT based analysis and estimation of colored noise and an application of the wavelet Galerkin method. The chapters of the present book consist of both tutorial and highly advanced material. Therefore, the book is intended to be a reference text for graduate students and researchers to obtain state-of-the-art knowledge on specific applications