Orientador: Gastão Inácio Krein / Banca: Maria Teresa Climaco dos Santos Thomaz / Banca: Gabriel Santos Menezes / Resumo: A presente dissertação tem como objetivo principal fazer uma revisão sobre o uso de estados coerentes para calcular a função de partição gran canônica de sistemas fermiônicos, sem empregar integrais de trajetória. Após discutir um método de cálculo baseado numa expansão de altas temperaturas, formulamos uma teoria de perturbação otimizada empregando campos auxiliares via transformação de Hubbard-Stratonovich. Aproximações não perturbativas tradicionais de campo médio tipo Hartree-Fock e de BCS são obtidas em ordem zero da teoria de perturbação otimizada. Correções não perturbativas à aproximação de ordem zero são implementadas usando uma expansão em potências de uma interação modificada, em que os efeitos dos campos médios são subtraídos da interação original do Hamiltoniano da teoria / Abstract: The primary aim of the dissertation is to review the use of coherent states for the calculation of the grand canonical partition function for fermion Systems, without employing path integrals. After discussing a calculational method based on a high temperature expansion, we formulate an optimized perturbation theory employing external fields via the Hubbard-Stratonovich transformation. Traditional non-perturbative mean field approximations like Hartree-Fock and BCS are obtained in zeroth order in the optimized perturbation theory. Non-perturbative corrections to the zeroth order approximation are implemented through a power series expansion of a modified interaction, where the effects of the mean fields are subtracted from the original interaction of the Hamiltonian of the theory / Mestre

In this paper, we propose a rate-compatible forward error-correcting (FEC) scheme based on low-density-parity check (LDPC) codes together with its software reconfigurable unified field-programmable gate array (FPGA) architecture. By FPGA emulation, we demonstrate that the proposed class of rate-compatible LDPC codes based on puncturing and generalized LDPC coding with an overhead from 25% to 46% provides a coding gain ranging from 12.67 to 13.8 dB at a post-FEC bit-error rate (BER) of 10(-15). As a result, the proposed rate-compatible codes represent one of the strong FEC candidates of soft-decision FEC for both short-haul and long-haul optical transmission systems.

As quantum systems can never be isolated from their environment entirely, it is expected that the spacetime fluctuations will influence their evolution. In particular, the environmental interaction may cause the loss of quantum superpositions, or decoherence. In this thesis, we examine the effects of the quantised environmental background on a range of bosonic fields in the formalism of open quantum systems. We first quantise linearised gravity in a gauge invariant way, using Dirac's constraint quantisation. We then use the influence functional technique to obtain an exact master equation for general bosonic matter interacting with weak gravity. As an application of this, we investigate the decoherence of free scalar, electromagnetic and gravitational fields. For long-time decoherence, under the Markov approximation, the dissipative terms in the master equation vanish, leading to no decay of quantum interferences. As a short-time effect, we study the master equation for a many particle state of a free scalar field, massive or massless and relativistic or non-relativistic. We find that in this case, the particles exhibit a counterintuitive behaviour of bundling towards the same quantum state that is not shared by the single particle master equation. Such collective effects, as well as possible long-time decoherence for fields in an external potential may have important implications in setting limits for precision measurements and astronomical observations.

Thesis advisor: Patricia A. Tabloski / This randomized pilot intervention study examined the influence of two self regulatory techniques, coherent breathing and meditation, in reducing perceived stress and anxiety scores, and increasing holistic wellness scores in college freshmen and sophomores. Too much stress is well documented throughout the literature to have adverse effects on physical, mental and spiritual health. Stress has been identified by college students as a barrier to academic performance. Both coherent breathing and meditation inhibit the secretion of stress hormone production responsible for the persistent state of sympathetic dominance experienced with daily living. A total sample of 37 Boston College freshmen and 3 sophomores was recruited for random assignment into three groups, meditation, n=14, coherent breathing n=14, and reading group as a control, n=12. The instruction of the intervention techniques was conducted through an 8 hour weekend workshop on two dates, October 2010, and September 2011. Participants were asked to practice their respective techniques daily for three weeks. All groups met once weekly throughout the duration of the study. Univariate ANOVA was conducted on pre and post test change of scores for the following instruments: Cohen's Perceived Stress Scale(PSS), Speilberger's State-Trait Anxiety Index, (STAI), and the Mind Body Spirit Wellness Behavior Characteristic Index (MBS-WBCI). The two self regulatory stress management techniques of coherent breathing and meditation demonstrated positive effects for this self selected small sample of freshmen and sophomores at Boston College. Participants of both intervention groups experienced reductions in perceived stress, state and trait anxiety scores, as well as increases in holistic wellness scores, as compared with controls. The favorable results achieved from this study strongly support future research investigations with larger samples and expanded populations. The implementation of mandatory college life skills courses incorporating these techniques could advance the potential for evaluating these techniques in a true randomized sample. The college environment provides an ideal opportunity for introducing prevention and early intervention techniques addressing mental health issues for students in their formative years. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Connell School of Nursing. / Discipline: Nursing.

Quantum cryptography offers a wonderful source for current and future research. The idea started in the early 1970s, and it continues to inspire work and development toward a popular goal, large-scale communication networks with strong security guarantees, based on quantum-mechanical properties. Quantum cryptography builds on the idea of exploiting physical properties to establish secure cryptographic operations. A particular quantum-based protocol has gathered interest in recent years for its use of mesoscopic coherent states. The AlphaEta protocol has been designed to exploit properties of coherent states of light to transmit data securely over an optical channel. AlphaEta aims to draw security from the uncertainty of any measurement of the transmitted coherent states due to intrinsic quantum noise. We propose a framework to combine this protocol with classical preprocessing, taking into account error-correction for the optical channel and establishing a strong provable security guarantee. Integrating a state-of-the-art solution for fast authenticated encryption is straightforward, but in this case the security analysis requires heuristic reasoning. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

The coherent system has been extensively studied in recent years. The reasons are that receiver sensitivity is better than Intensity Modulation with Direct Detection (IM/DD) and the spectral efficiency of wavelength division multiplexing (WDM) is increased. The modulation formats of the coherent system are Amplitude shift keying (ASK), Phase shift keying (PSK), and Frequency shift keying (FSK). The detection techniques are Homodyne detection and Heterodyne detection, both of them need a laser light source in the receiver called as the Local oscillator (LO). In the previous study, the Quadrature phase shift keying (QPSK) modulation format with Pseudo Random Binary Sequence (PRBS) 27-1 to transmit 51km was investigated, and the pilot carrier method realized the Homodyne Detection. The merit of the pilot carrier is that the LO is not necessary in the receiver. In this master thesis, the optical signal of the QPSK modulation format with PRBS 215-1 is transmitted over 500km using the pilot carrier method. A WDM system demonstration is also conducted to increase the system capacity. The Bit error rate (BER) is calculated by the MATLAB program. The BER performance of 20G bit/s, 500 km transmission system using the QPSK with single channel and multiplexed channels were measured.

Coherent control of laser induced processes is based on the quantum interference among multiple excitation pathways. Progress in the field has been fueled by advances in pulse shaping techniques, allowing modulation of phase and amplitude across the bandwidth of ultra short pulses. This dissertation makes use of coherent control technique for the optimization of two-photon fluorescence (TPF) and its applications in selective excitation for biomedical imaging. Different physical processes, e.g. TPF, second harmonic generation (SHG) and their ratios (e.g. TPF/SHG) were optimized by using feedback control pulse shaping technique with an evolutionary algorithm. Various nonlinear effects, e.g. filamentation, intensity clamping and white light generation were studied using two-photon fluorescence and Z-scan technique with different dyes and biomarkers. Simultaneous measurements of different nonlinear effects were performed. Novel methods were proposed and implemented to obtain two-photon excitation characteristics in intensity-resolved manner. Understanding of these nonlinear effects can give new solution to the issues of spatial resolution and molecular contrast for cellular and tissue imaging.

Polycrystalline AlN thin films were reactively deposited onto Al layers on negatively biased glass and Si substrates at temperatures < 80 oC by coherent magnetron sputtering. The target-to-substrate distance is 17 cm. The microstructures and morphology of the films grown at different bias voltages on the substrates were investigated. Typical thickness of the deposited film is 600 nm. The films were amorphous when no bias was applied to the substrates. Diffraction peak of AlN (002) direction was observed at bias voltages of -180 and -210 V. At a bias voltage of -210 V, the (002) granular crystal with the maximum diameter of 80 nm was obtained. In addition to the AlN (002) direction, AlN (100) direction was observed when the bias voltage was increased to -240 and -270 V. The peak of (002) plane vanished at a bias voltage of -320 V. Moreover, the deposited AlN films have specular reflectance owning to the large target-to-substrate distance. The maximum roughness of the films was 47.2¡Ó5.0 nm at a bias voltage of -210 V. The hardness and microstructure of aluminum nitride (AlN) thin films prepared by long-distance magnetron sputtering at room temperature has been investigated. The hardness and microstructure of the films were found to vary greatly with different substrate biases. At a bias voltage of ¡V210 V, the (002) polycrystalline AlN with the maximum hardness of 17.5 GPa was observed. The water droplet contact angle under this bias condition is larger than 90¢X indicating that hydrophobicity can be obtained at the film surface. In addition, hardness of (002) AlN films prepared by sputtering of AlN target at room temperature and by reactive sputtering of Al target at 400¢XC were discussed and compared with that of AlN films prepared by long-distance reactive sputtering.

Loop heat pipes seem a promising approach for application in modern technologies where such thermal devices as cooling fans and radiators cannot satisfy overall requirements. Even though a loop heat pipe has a big potential to remove the thermal energy from a high heat flux source, the heat removal performance of heat pipes cannot be predicted well since a first principles of evaporation has not been established. An evaporation model based on statistical rate theory has been recently suggested by Ward and developed for a single pore by Oinuma. A loop heat pipe with coherent pore wick structure has been proposed as a design model. To limit product development risk and to enhance performance assurance, design model features and performance parameters have been carefully reviewed during the concept development phase and have been deliberately selected so as to be well-founded on the limited existing loop heat pipe knowledge base. A first principles evaporation model has been applied for evaporator geometry optimization. A number of iteration calculations have been performed to satisfy design and operating limitations. A set of recommendations for design optimization has been formulated. An optimal model has been found and proposed for manufacture and experimental investigation.

Optical coherence tomography (OCT) has been shown to be a versatile three-dimensional imaging tool in diagnostic medicine, combining micrometre-scale resolutions with fast acquisition times. This imaging modality uses the interference between light backscattered from a sample and light that has traversed a known reference path delay to determine the scattering profile over penetration depths of up to several millimetres in tissue. A novel OCT system is presented that uses nonlinear optics to process the backscattered light in the optical domain prior to standard Fourier-domain OCT acquisition and processing. The nonlinear optical effects experienced between short light pulses are strongly intensity-dependent, occurring only significantly when the pulses are temporally and spatially overlapped. These conditions allow for the creation of a user-controlled time gate that restricts the light backscattered from the sample to a narrow (~100 micrometres) depth field of view prior to detection. When strong and weak scattering interfaces exist across the sample depth range, the signal-to-noise ratio of the weaker scattering sites can be limited by the finite detector dynamic range in Fourier-domain OCT systems. By aligning the time gate temporal delay to the backscatter from the weak interfaces of interest, a user can completely remove the strong backscattered light and enhance imaging contrast. The nonlinear effect used in the current time-gated OCT design is sum-frequency generation, which provides an additional advantage of imaging at near infrared (1280 nm) wavelengths, used for long penetration depths in tissue, while detection is performed in the visible (504 nm) with silicon-based camera technology. With the reduced depth field of view, the number of sampling points required per depth scan is also proportionately reduced, permitting faster acquisition rates for the time-gated region of interest. A complete description of the time-gated OCT system design is presented, along with proof-of-concept images demonstrating contrast enhancement and operation in a highly scattering biological medium. Based on its successful initial performance, future development of this system is expected for its eventual use in many OCT imaging applications. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-01-15 20:05:41.665 / This work was funded by the Natural Sciences and Engineering Research Council and the Cancer Imaging Network of Ontario, supported by Cancer Care Ontario