An unsteady Reynolds Averaged Navier-Stokes (URANS) based turbulence model, the Spalart-Allmaras (SA) model, was used to investigate the flow pulsation phenomenon in compound rectangular channels for isothermal flows. The computational fluid dynamics (CFD) commercial package ANSYS CFX-11.0 was used for the simulations. The studied geometry was composed of two rectangular subchannels connected by a gap, on which experiments were conducted by Meyer and Rehme [34] and were used for the validation of the numerical results. Two case studies were selected to study the effect of the advection scheme. The results using the first order upwind advection scheme had clear symmetry and periodicity. The frequency of the flow pulsations was underpredicted by almost a factor of two. Due to the inevitable numerical diffusion of the first order upwind scheme, it was more appropriate to use a second order accurate in space advection scheme for comparison with the experiments. The span-wise velocity contours and the velocity vector plots at planes parallel to the bulk flow, together with the time traces of the velocity components at selected monitor points showed the expected cross-flow mixing between the subchannels through the gap. Although the SA model does not solve directly for the turbulence kinetic energy, a kinetic energy associated with the unsteady solutions of the momentum equations was evaluated and qualitatively compared with the experimental turbulence kinetic energy. The calculated kinetic energy followed the trends of the experimental turbulence kinetic energy at the gap area, predicting two peaks at the edges of the gap. The dynamics of the gap pulsations were quantitatively described through temporal auto-correlation and auto-power spectral density functions and the numerical predictions were in agreement with the experiments. Studies on the effect of the Reynolds number and the computational length of the domain were also carried out. The numerical results reproduced the relationship between the Reynolds number and the frequency of the auto-power spectral density functions. The impact of the channel length was tested by simulating a longer channel. It was found that the channel length did not significantly affect the predictions. Simulations were also performed using the (kappa) -(epsilon) model. While flow pulsations were predicted with this model, the frequency of the pulsation was in poor agreement with the experimentally measured value. / Thesis / Master of Applied Science (MASc)

The increasing use of visible and near infrared light in therapeutic and diagnostic techniques has created a need to model its propagation in tissue. One of the fundamental objectives of such a model is the noninvasive evaluation of the optical properties of tissue. The focus of this thesis was the development of the diffusion approximation in the semi-infinite, slab, cylindrical and spherical geometries. This development required the derivation of approximate boundary conditions which included the zero, extrapolated and partial current boundary conditions. Calculations of the fluence and its related quantities arising from the extrapolated boundary condition were found to be in excellent agreement with the results of the more rigorous partial current boundary condition. A preliminary evaluation of the validity of diffusion theory was performed by comparing its predictions to exact analytical calculations of the fluence in an infinite medium as well as Monte Carlo simulations of the reflectance and transmittance in 1-dimensional planar geometries. In all cases the agreement at late times was excellent. A practical test of the diffusion model was accomplished with the analysis of the reflectance data from a phantom of known optical properties in both the semi-infinite and slab geometries. The model performed well at low concentrations of added absorber, but a considerable discrepancy was found at the highest concentration. A systematic examination of the accuracy of the diffusion model as a function of the fundamental parameters is required to resolve this inconsistency. Approximate expressions describing the equivalent information in the frequency domain were also developed for a semi-infinite medium. These expressions were then used to analyze the phase and modulation obtained from phantoms of known optical properties. Once again reasonable results were obtained at low concentrations of added absorber while a significant discrepancy arose at the highest concentration. The resolution of these discrepancies requires further investigation. / Thesis / Master of Engineering (ME)

The groundwork has been completed for a large new research initiative involving the development of diode lasers for moderate power ultrashort pulse generation. This thesis reports on the status of three core areas of this initiative: InGaAsP/GaAs diode laser design and characterization, split contact device testing, and thin film interference filter deposition and characterization. Two new short wavelength diode laser designs have been realized and tested. A 980 nm laser was designed, using an InGaAsP barrier/waveguide region. This showed improved far field performance and better contact isolation as compared to an existing 980 nm laser using GaAs barriers. A laser emitting at 850 nm was also designed using GaAs quantum wells surrounded by a new quaternary waveguide region. A test arrangement was developed to facilitate the measurement of IV and LI curves for split contact lasers. Numerous lasers were tested, indicating that short absorber sections and narrow gap widths are preferable for use as saturable absorbing regions in a passively mode locked diode laser. Finally, thin film silicon oxynitride interference filters have been designed, deposited, and characterized for several antireflecting and high reflectance coatings on semiconductor laser facets. A comparison ofsingle layer AR coatings accounting for the modal reflectivity was performed. A four layer high reflectance coating with a peak broadband reflectance of over 90% was deposited on a laser facet. / Thesis / Master of Engineering (ME)

A measurement of solar neutrinos below 1 MeV of energy will further our knowledge of the neutrino's mass and mixing properties and will provide a probe to possible physics beyond the standard model of particle physics, as well as advance our understanding of energy production in the Sun. Borexino is a liquid scintillator detector that will measure the neutrino energy spectrum to the lowest energy threshold to date. It has been designed to measure the flux of the mono-energetic neutrinos produced by electron capture on 7Be in the Sun's core, which will produce a Compton-like edge in the energy spectrum. Because of the low count rate, Borexino requires extremely low backgrounds, and a good understanding of the backgrounds that do exist. Although the purification techniques used for the scintillator lowered the radioactive contaminates to levels never before achieved, cuts must still be made to the data. At Virginia Tech, we have developed an internal source calibration program that will be able to give us a thorough understanding of both the pulse shape discrimination efficiency and the energy and time response of Borexino. Energy calibration for alphas, betas, and gammas (energy scales) can be accomplished with such sources. When the calibration source is used in conjunction with an accurate source location system any spatial dependencies can be found. The system will use different types of sources at various energies to give the required information to make the cuts needed to extract believable physics from the detector. / Ph. D.

This research focuses on the design of an Extended Reality simulator for training medical professionals in Advanced Trauma Life Support (ATLS) and pulse palpation. Existing pulse simulators have the disadvantages of being bulky, expensive, and unsuitable to be used as training tools. In addition, none of the simulators were designed to incorporate the auditory feedback of the pulse, a crucial component of continuous pulse monitoring. The developed simulator incorporates haptic, visual, and auditory feedback modes. In this work, we also conduct a comparative user study to determine the effect of multimodal feedback on different participants. Participants trained in the Audio-Haptic scenario outperformed those trained in the Haptic only scenario. These values could also be correlated with qualitative user feedback indicating that Audio-Haptic interactions were perceived as superior. With this simulator, we hope to provide medical professionals with an immersive and realistic training tool for learning the skill of palpating pulse. / Master of Science / The medical field demands accurate and precise procedures to be performed by doctors, with no room for error. Traditional training methods consist of the trainer demonstrating the technique and the student duplicating it, which increases the risk of medical errors. Advanced Trauma Life Support (ATLS) is a program designed by the American College of Surgeons to teach physicians a systematic approach to treating trauma patients. Palpating and classifying pulses is one of the steps involved in the ATLS procedure. The majority of existing ATLS and pulse simulators are not fully integrated with haptic and auditory feedback, and there has been very little research on this topic. This work describes the design and development of an Extended Reality ATLS simulator with a pulse simulator for medical student training. We conduct a user study to determine how the Audio-Haptic scenario affects the learnability of palpating pulses and ATLS procedures. Our ATLS simulator aims to provide a comprehensive training module for emergency trauma response practice for medical professionals.

The goal of this project was to determine the feasibility of non-invasively monitoring the blood gases of construction workers for carbon monoxide exposure via pulse oximetry. In particular, this study sought to understand the impact of motion artifacts caused by the worker's activities and to determine if those activities would prevent the blood gas sensor from detecting the onset of carbon monoxide poisoning. This feasibility study was conducted using a blood oxygen sensor rather than a blood carbon monoxide sensor for several reasons. First, blood gas sensors that measure blood carbon monoxide are not readily available in suitable physical form factors. Second, sensors for blood oxygen and blood carbon monoxide operate on the same physical principles and thus will be affected in the same way by worker motions. Finally, using a blood oxygen sensor allowed the study to be conducted without exposing the human subjects to carbon monoxide. A user study was conducted to determine the distribution of motion artifacts that would be created during a typical work day. By comparing that distribution to a worst-case estimate of time to impairment, the probability that helmet will adequately monitor the worker can be established. The results of the study show that the helmet will provide a measurement capable of warning the user of on setting carbon monoxide poisoning with a probability greater than 99%. / Master of Science

Rapid progress in ultra-intense laser technology has resulted in intensity levels surpassing 1022 W/cm2, reaching the highest possible density of electromagnetic energy amongst all controlled sources available in the laboratory. During recent decades, fast growth in available intensity has stimulated numerous studies based on the use of high intensity lasers as a unique tool for the initiation of nonlinear behavior in various basic systems: first molecules and atoms, then plasma resulting from the ionization of gases and solids, and, finally, pure vacuum. Apart from their fundamental importance, these studies reveal various mechanisms for the conversion of a laser pulse's energy into other forms, opening up new possibilities for generating beams of energetic particles and radiation with tailored properties. In particular, the cheapness and compactness of laser based sources of energetic protons are expected to make a revolution in medicine and industry.   In this thesis we study nonlinear phenomena in the process of laser radiation interacting with plasmas of ionized targets. We develop advanced numerical tools and use them for the simulation of laser-plasma interactions in various configurations relating to both current and proposed experiments. Phenomenological analysis of numerical results helps us to reveal several new effects, understand the physics behind them and develop related theoretical models capable of making general conclusions and predictions. We develop target designs to use studied effects for charged particle acceleration and for the generation of attosecond pulses of unprecedented intensity. Finally, we analyze prospects for experimental activity at the upcoming international high intensity laser facilities and uncover a basic effect of anomalous radiative trapping, which opens up new possibilities for fundamental science.

Classification of airborne laser scanning data using information about intensity and width of the recorded signal Abstract One of the basic tasks in analysing airborne laser scanning (ALS) data is filtration of mass 3D point cloud with purpose to create digital terrain model and digital surface model. New scanner generation (so called Full-waveform LiDAR) allows analysing the whole recorded signal. The recorded value of amplitude and signal width accordant with reflectance of different objects differs according to geometry of the objects. Objective of this thesis is to create a methodology for classification of ALS data in settled areas. This methodology will be based on number of reflections, amplitude of reflected signal, recorded signal width and on spatial attributes. At the same time it will be analysed how the parameters of amplitude and signal width are affected by characteristics of estate surface. It means which radiometrical characteristics (e.g. different roof materials) and geometrical characteristics (e.g. different roof inclination) belong to which amplitude and signal width. Basic question of this thesis is if amplitude and signal width are good attributes to improve the quality of filtration of mass 3D point cloud in chosen area and if so, how. Key words: classification, segmentation, LiDAR,...

The ability to numerically determine the received signal in an ultrasound pulse-echo system is very important for the development of new ultrasound applications, such as tissue characterization, complex object recognition, and identification of surface topology. The output signal from an ultrasound pulse-echo system depends on the transducer geometry, reflector shape, location and orientation, among others, therefore, only by numerical modeling can the output signal for a given measurement configuration be predicted. This thesis concerns about the numerical modeling and optimal design of annular array based ultrasound pulse-echo system for object recognition. Two numerical modeling methods have been implemented and evaluated for calculating received signal in a pulse-echo system. One is the simple, but computationally demanding Huygens Method and the other one is the computationally more efficient Diffraction Response for Extended Area Method (DREAM). The modeling concept is further extended for pulse-echo system with planar annular array. The optimal design of the ultrasound pulse-echo system is based on annular array transducer that gives us the flexibility to create a wide variety of insonifying fields and receiver characteristics. As the first step towards solving the optimization problem for general conditions, the problem of optimally identifying two specific reflectors is investigated. Two optimization methods, the straightforward, but computationally intensive Global Search Method and the efficient Waveform Alignment Method, have been investigated and compared.

Noninvasive pulse oximetry represents an area of potential interest to the army, because it could provide cost-effective, safe, fast and real-time physiological assessment in a combat injured soldier. Consequently, there is a need to develop a reliable, battery-powered, wearable pulse oximeter to acquire and process photoplethysmographic (PPG) signals using an optimized sensor configuration. A key requirement in the optimal design of a wearable wireless pulse oximeter is low power management without compromising signal quality. This research investigated the advantage gained by increasing the area of the photodetector and decreasing the light emitting diode (LED) driving currents to reduce the overall power requirement of a reflectance mode pulse oximeter sensor. In vitro and preliminary in vivo experiments were conducted to evaluate a multiple photodetector reflectance sensor setup to simulate a varying detection area. It was concluded that a reflection pulse oximeter sensor employing a large area photodetector is preferred over a similar transmission type sensor for extending the battery life of a wireless pulse oximeter intended for future telemedicine applications.