The carrier envelope (CE) phase of a femtosecond laser was stabilized. The laser produces an ultra stable comb of frequency spanning the visible region and basically is an optical frequency synthesizer and ready for the frequency domain applications. In this context, the CW stability of the Ti:sapphire laser is discussed to provide a procedure for the femtosecond laser adjustments. In addition, the pulse trains emitted by the femtosecond laser are described analytically to provide a theoretical basis for carrier envelope phase stabilization. An f to 2f interferometer was used to detect the carrier envelope offset frequency, and a fast photo diode was employed to measure the repetition rate. Two similar designed phase lock loops are used to stabilize both the carrier envelope offset frequency and the repetition rate to the respective reference frequencies. The stability reaches 100mHz for the carrier envelope offset frequency and 10mHz for the repetition rate for a period of up to an hour. Doppler free iodine saturation spectroscopy was set up to provide a precise frequency reference to which a CW dye laser can be locked on. The near future goal is to accurately measure this frequency stabilized dye laser with the optical frequency synthesizer.

Due to the uncertainties introduced by the propagation channel, and RF and mixed signal circuits imperfections, digital communication receivers require efficient and robust signal acquisition algorithms for timing and carrier recovery, and interfer- ence rejection. The main theme of this work is the development of efficient and robust signal synchronization and interference rejection schemes for narrowband, wideband and ultra wideband communications systems. A series of novel signal acquisition schemes together with their performance analysis and comparisons with existing state-of-the- art results are introduced. The design effort is first focused on narrowband systems, and then on wideband and ultra wideband systems. For single carrier modulated narrowband systems, it is found that conventional timing recovery schemes present low efficiency, e.g., certain feedback timing recov- ery schemes exhibit the so-called hang-up phenomenon, while another class of blind feedforward timing recovery schemes presents large self-noise. Based on a general re- search framework, we propose new anti-hangup algorithms and prefiltering techniques to speed up the feedback timing recovery and reduce the self-noise of feedforward tim- ing estimators, respectively. Orthogonal frequency division multiplexing (OFDM) technique is well suited for wideband wireless systems. However, OFDM receivers require high performance car-rier and timing synchronization. A new coarse synchronization scheme is proposed for efficient carrier frequency offset and timing acquisition. Also, a novel highly accurate decision-directed algorithm is proposed to track and compensate the residual phase and timing errors after the coarse synchronization step. Both theoretical analysis and computer simulations indicate that the proposed algorithms greatly improve the performance of OFDM receivers. The results of an in-depth study show that a narrowband interference (NBI) could cause serious performance loss in multiband OFDMbased ultra-wideband (UWB) sys- tems. A novel NBI mitigation scheme, based on a digital NBI detector and adaptive analog notch filter bank, is proposed to reduce the effects of NBI in UWB systems. Simulation results show that the proposed NBI mitigation scheme improves signifi- cantly the performance of a standard UWB receiver (this improvement manifests as a signal-to-noise ratio (SNR) gain of 9 dB).

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 165-172).

published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

In Arabidopsis thaliana, a gene family encodes acyl-CoA-binding proteins (ACBPs) conserved at the acyl-CoA-binding domain which facilitates the binding to acyl-CoA esters. These ACBPs, designated ACBP1 to ACBP6, range in size from 10.4 to 73.1 kD. Previous studies have shown that the the overexpression of ACBP1 or ACBP2 in Arabidopsis likely promotes repair of lipid membranes and result in enhanced tolerance to lead and cadmium, respectively. Microarray data (http://bar.utoronto.ca/) revealed that the expression of ACBP1 and ACBP2 is also regulated by other abiotic stresses, such as cold and drought, suggestive of their association with these environmental pressures. The aim of this study is to investigate and better understand the roles of ACBP1 and ACBP2 in different stress responses. It has been previously observed that the expression of both ACBP1 and ACBP4 is lead [Pb(II)]-inducible and recombinant ACBP1 and ACBP4 bind Pb(II) in vitro. In this study, ACBP1 and ACBP4 were overexpressed in Brassica juncea to test if these ACBPs could be extended for application in Pb(II) phytoremediation in transgenic B. juncea. On freezing (-12 to -8 °C) treatment, ACBP1-overexpressing Arabidopsis was freezing sensitive and accumulated more phosphatidic acid (PA), but less phosphatidylcholine (PC), in contrast to acbp1 mutant plants which were freezing tolerant and had reduced PA and elevated PC levels. Such changes in PC and PA were consistent with the expression of the mRNA encoding phospholipase D1 (PLD1), a major enzyme that promotes the hydrolysis of PC to PA. In contrast, the expression of phospholipase D (PLD), which plays a positive role in freezing tolerance, was up-regulated in acbp1 mutant plants and down-regulated in ACBP1-overexpressing plants. Reduced PLD1 expression and decreased hydrolysis of PC to PA may enhance membrane stability in the acbp1 mutant plants. Given that recombinant ACBP1 binds PA and acyl-CoA esters in vitro, the expression of PLD1 and PLD could be regulated by PA or acyl-CoAs maintained by ACBP1, if ACBP1 were to resemble the yeast 10-kD ACBP by its capability to modulate gene expression during stress responses. Interestingly, another membrane-associated ACBP, ACBP2, which shows high (76.9%) conservation in amino acid homology to ACBP1, did not appear to be affected by freezing treatment. Besides freezing stress, ACBP1, as well as ACBP2, have been observed to participate in abscisic acid (ABA) signaling. They both promote ABA signaling in seed germination and seedling development, while only ACBP2 is involved in the drought response. The overexpression of ACBP2 in Arabidopsis up-regulated reactive oxygen species (ROS) production culminating in reduction in stomatal aperture and water loss in guard cells, thereby enhancing drought tolerance. For tests in phytoremediation, B. juncea was selected for overexpression of ACBP1 and ACBP4 because it is fast-growing, has a higher biomass than Arabidopsis, and is known to be a good accumulator of Pb(II). However, results of Pb(II) treatment for two days showed that the overexpression of ACBP1 or ACBP4 in B. juncea did not significantly improve Pb(II) tolerance. Nevertheless, B. juncea overexpressing ACBP1 did accumulate Pb(II) in roots whereas ACBP4-overexpressing B. juncea lines accumulated Pb(II) in both shoots and roots. Given that B. juncea has a larger biomass than Arabidopsis, it is likely that the duration of Pb(II)-incubation tested in this study was not drastic enough for comparison, and the incubation time should be further extended for Pb(II) translocation. In addition, future studies on Arabidopsis should be conducted to better understand the mechanism of ACBP4-mediated Pb(II) accumulation using Arabidopsis acbp4 mutant and ACBP4-overexpressing plants. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Master / Master of Philosophy

Spectrum sensing is the process of identifying the frequencies of a spectrum in which Signals Of Interest (SOI) are present. In case of continuous time signals present in a wideband spectrum, the information rate is seen to be much less than that suggested by its bandwidth and are therefore known as sparse signals. A review of the literature in [1] and [2] indicates that two of the many techniques used in wideband spectrum sensing of sparse signals are the Wideband Compressive Radio Receiver (WCRR) for multitoned signals and the mixed analog digital system for multiband signals. In both of these techniques even though the signals are sampled at sub-Nyquist rates using Compressive Sampling (CS), the recovery algorithms used by them are different from that of CS. In WCRR, a simple correlation function is used for the detection of carrier frequencies and in a mixed analog digital system, a simple digital algorithm is used for the identification of frequency support. Through a literature survey, we could identify that a VHSIC hardware descriptive ModelSim simulation model for wideband spectrum sensing of multitoned and multiband signals using sub Nyquist sampling does not exist. If a ModelSim simulation model can be developed using VHDL codes, it can be easily adapted for FPGA implementation leading to the development of a realistic hardware prototype for use in Cognitive Radio (CR) communication systems. The research work reported through this dissertation deals with the implementation of simulation models of WCRR and mixed analog digital system in ModelSim by making use of VHDL coding. Algorithms corresponding to different blocks contained in the conceptual design of these models have been formulated prior to the coding phase. After the coding phase, analyses of the models are performed using test parameter choices to ensure that they meet the design requirements. Different parametric choices are then assigned for the parametric study and a sufficient number of iterations of these simulations were carried out to verify and validate these models. / MIng (Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2014

Denna studie bestod i att undersöka situationen på marknaden angående framdriftsanläggningar för LNG-tankfartyg. Syftet med arbetet var att skapa en relevant bild av hur situationen ser ut idag och genom intervjuer ta reda på hur den kan komma att förändras. Genom en litteraturstudie undersöktes läget på marknaden och utifrån det kunde relevanta frågor utformas. Efter att frågorna hade utformats tog författarna kontakt med olika företag som var anknutna till marknaden för LNG-tankfartyg. Intervjuer med företagen genomfördes och dessa har gjort det möjligt att analysera hur läget kan komma att förändras. Studien har visat att det finns ett system, DFDE, som dominerar fartygsbeställningar i dagsläget. Det finns även nyare system som består av gasdrivna tvåtaktsmotorer som förväntas ta över en del av marknaden. Andra system såsom ånganläggningar och anläggningar med gasturbin finns tillgängliga men de ligger inte i fokus i dagsläget. / This study consisted of analysing the current situation on the market for propulsion systems for LNG-carriers. The purpose of the study was to create a relevant picture of what the situation looks like today and through interviews try to predict how the situation might come to change. By using already existing literature the authors reviewed the situation on the market as it is today and formed relevant questions. After the questions had been formed the authors contacted several companies associated with the LNG-carrier market. Interviews with these companies were carried out and it is through these interviews possible to analyse how the situation might come to change. The study has shown that there is one system that dominates the market for LNG-carrier propulsion, DFDE. There is however a new system, with dual-fuel two stroke engines that is expected to take over a part of the market in the near future. Other propulsion systems such as steam propulsion plant and a system with a gas turbine exist on the market but the interest in these systems is limited.