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Published Article / A reference carrier signal should be regenerated from a received partial response (PR) signal in order to facilitate optimal demodulation of the received signal. This paper describes the development and evaluation of such a carrier recovery system using DSP techniques. The relative phase of a free-running local oscillator at the receiver is synchronized with the carrier signal of a received 49 quadrature partial response signal (49QPRS). Synchronization is achieved and maintained by means of a process of cross-correlation.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / This paper will present methods to both measure the unmodulated carrier power of a modulated signal and to estimate the unmodulated carrier power level from the measured power spectrum. The unmodulated carrier power level is needed to convert measured spectra into units of dBc.

published_or_final_version / Botany / Doctoral / Doctor of Philosophy

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

Thesis advisor: Torsten Fiebig / This dissertation examines the chemistry and photophysics of semiconductor quantum dots with the intent of studying their capabilities and limitations as they pertain to photovoltaic technologies. Specifically, experiments are presented detailing the first time-resolved measurements of electron transfer in electronically coupled quantum rods. Electron transfer from the conduction band of CdTe was measured to occur on the 400 fs timescale (<italic>k_ET</italic> = 2.5 x 10<super>12</super> s<super>-1</super>), more than 500x faster than previously believed. Additionally, the direct optical promotion of an electron from the valence band of CdTe was observed, occurring on the timescale of the pump pulse (~50 fs). Based on the determined injection rates, a carrier separation efficiency of > 90% has been calculated suggesting these materials are sufficient for use in solar energy capture applications where efficient carrier separation is critical. To this end, model photovoltaic cells were fabricated, and their power conversion efficiency and photon-to-current generation efficiency characterized. In devices based of CdSe and heteromaterial quantum rods we observed fill-factors on the order of 10-20% though with power conversion efficiencies of < 0.02%. It was discovered that using a high temperature annealing step, while critical to get electrochemically stable photoelectrodes, was detrimental to quantum confinement effects and likely removed any hQR specific capabilities. Additionally, a detailed study on the role of nucleotide triphosphate chemistry in stabilizing emissive CdS nanoparticles is presented. Specifically it was observed that in a neutral pH environment, GTP selectively stabilizes CdS quantum dots with diameters of ~4 nm while the other naturally occurring ribonucleotides do not yield emissive product. The selectivity is dependent on the presence of the nucleophilic N-7 electrons near a triphosphate pocket for Cd<super>2+</super> complexation as well as an exocyclic amine to stabilize the resulting product particles. However, in an elevated pH environment, the nucleobase specificity is relaxed and all NTPs yield photo-emissive quantum dots with PLQEs as high as 10%. / Thesis (PhD) — Boston College, 2009. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Sulfur, an essential element required by the cell for the biosynthesis of crucial compounds, such as amino acids, co-factors and vitamins, is found most abundantly in the form of sulfate. In order to cross the lipid bilayer for cell usage, sulfate, being a negatively charged ion, requires an energetically `friendly' passageway. This could be accomplished via an ion channel that allows the flow of sulfate into the cell along its concentration gradient, or via an active transport system that allows sulfate to be taken up by the cell when it is in scarcity in the environment, against its concentration gradient, like the ABC transporter and sodium or proton-coupled symporters. The subject of this dissertation, CysZ, is a bacterial sulfate transport protein that does not belong to any known superfamily of canonical transporters or channels with no distinguishing features that could hint at its functional mechanism. We have undertaken a structural and functional approach to further understanding the role of CysZ in sulfate transport. In this dissertation, we report the structure of CysZ, its functional role in sulfate uptake and have suggested a mechanistic hypothesis for the passage of sulfate through CysZ along with the exciting future directions that might follow.

Coherent transmission system has been extensively studied in recent years, and it can use different modulation formats and different detection techniques. The modulation formats are ASK (Amplitude shift keying), PSK (Phase shift keying), and FSK (Frequency shift keying). The detection techniques are Homodyne detection and Heterodyne detection, and they need a laser in the receiver called as the LO (Local oscillator). In the previous study, the BPSK (Binary phase shift keying) modulation format was investigated, and the pilot carrier method realized the Homodyne Detection. The merit of the pilot carrier is that it do not need the LO in the receiver. In this master thesis, the QPSK (Quadrature phase shift keying) modulation format is investigated using the pilot carrier method, The BER is calculated using the matlab program. The performance of 20G bit/s, 50 km transmission system using the BPSK and the QPSK is compared to clarify the merits and demerits of the QPSK modulation.

Single Carrier Frequency Domain Equalization (SC-FDE) utilize Time Division multiple Access with Zero-padding under ultra-wideband¡Ait can improve Inter-Block Interference(IBI) and Multi-Access Interference(MAI) to get good performance¡AThis system even can eliminate multi-access interference. Concept of TDMA can avoid the same time to transmit different user¡¦s data with zero-padding algorithm. This method can efficiency to solve multi-access interference. In this thesis, we will utilize property of two dimension to solve multi-access interference between each others. Zero-padding have good capability the same to Cyclic prefix and can save transmitter power. In this thesis, we will not use CDMA of method because it do not need to much analysis of mathematics, moreover, we can provide low cost and low complexity for system to get low error rate. Finally we to be aimed at improve IBI and MAI to simulation under ultra-wideband, then simulation will show thesis of method is high performance than traditional of method.

In this thesis, a joint symbol timing and carrier frequency offset estimator is proposed for orthogonal frequency division multiplexing (OFDM) systems. The estimator exploits both redundancy in the cyclic prefix and pilot symbols for channel estimation. The proposed scheme includes a transparent sequence that is added to the OFDM symbol in frequency domain. Comparing with conventional methods, the proposed architecture has the advantage of better bandwidth usage since it does not require extra sub-carriers. The PAPR problem can be suppressed due to constant envelope property of the added sequence in time domain. Moreover, the optimal power allocation ratio of the transparent sequence is determined by minimizing the bit error rate of the system using simulation experiments.