M.Ing. (Electrical & Electronic Engineering) / Please refer to full text to view abstract

Adaptive modulation has been actively researched as a means to increase spectral efficiency of wireless communications systems. In general, analytic closed form models have been derived for the performance of the communications system as a function of the control parameters. However, in systems where general error correction coding is employed, it may be difficult to derive closed form performance functions of the communications systems. In addition, in closed form optimization, real time adaptation is not possible. Systems designed with deterministic state optimization are developed offline for a certain set of parameters and hardwired into mobile devices. In this thesis we present stochastic learning algorithms for adaptive modulation design. The algorithms presented allow for adaptive modulation system design in-dependent of error correction coding and modulation constellation requirements. In real time, the performance of the system is measured and stochastic approximation techniques are used to learn the optimal transmission parameters of the system. The technique is applied to Software Defined Radio (SDR) platforms, an emerging wireless technology which is currently being researched as a means of designing intelligent communications devices. The fundamental property that sets SDR apart from traditional radios is that the communications parameters are controlled in software, allowing for real-time control of physical layer communications. Our treatment begins by modeling the time evolution of the adaptive modulation process as a general state space Markov chain. We show the existence and uniqueness of the invariant measure and model performance functions as expectations with respect to the invariant measure. We consider constrained and unconstrained throughput optimization. We show that the cost functions considered are convex. Next we present stochastic approximation algorithms that are used to estimate the gradient of the cost function given only noisy estimates. We conclude by presenting simulation results obtained by the presented method. The learning based method is able to achieve the maximum throughput as dictated by exhaustive Monte Carlo simulation of the communications system, which provide an upper bound on performance. In addition, the learning algorithm is able to optimize communications under various error correction schemes. The tracking abilities of the algorithm are also demonstrated. We see that the proposed method is able to track optimal throughput settings as constraints are changed in time. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The drastic increase in the number of internet users and the general convergence of all other communication systems into an optical system have brought a sharp rise in demand for bandwidth and calls for high capacity transmission networks. Large unamplified transmission reach is another contributor in reducing deployment costs of an optical communication system. Spectrally efficient modulation formats are suggested as a solution to overcome the problems associated with limited channels and bandwidth of dense wavelength division multiplexing (DWDM) optical communication systems. Higher order modulation formats which are considered to be spectrally efficient and can increase the transmission capacity by transmitting more information in the amplitude, phase, polarization or a combination of all was studied. Different detection technologies are to be implemented to suit a particular higher order modulation format. In this research multilevel modulation formats, different detection technologies and a digital signal processing aided receiver were studied in a practical optical transmission system. The work in this thesis started with the implementation of the traditional amplitude shift keying (ASK) modulation and a differential phase shift keying (DPSK) modulation systems as they form the basic building block in the design of higher order modulation formats. Results obtained from using virtual photonics instruments (VPI)simulation software, receiver sensitivity for 10Gbpsnon-return-to-zero (NRZ), amplitude phase shift keying (ASK) and DPSK signals were measured to be -22.7 dBm and -22.0 dBm respectively. Performance comparison for the two modulation formats were done over different transmission distances. ASK also known as On-Off keying (OOK) performed better for shorter lengths whereas DPSK performed better for longer lengths of up to90km.Experimental results on a 10 Gbps NRZ- ASK signal gave a receiver sensitivity of -21.1 dBm from digital signal processing (DSP) aided receiver against -19.8 dBm from the commercial bit error ratio tester (BERT) yielding a small difference of 1.3 dB hence validating the reliability and accuracy of the digital signal processing (DSP) assisted receiver. Traditional direct detection scheme and coherent detection scheme performances were evaluated again on a 10 Gbps NRZ ASK signal. Coherent detection that can achieve a large unamplified transmission reach and has a higher passive optical splitting ratio was first evaluated using the VPI simulation software. Simulation results gave a receiver sensitivity of -30.4 dBm forcoherent detection and -18.3 dBm for direct detection, yielding a gain in receiver sensitivity of 12.1 dB. The complex coherently detected signal, from the experimental setup gave a receiver sensitivity of -20.6 dBm with a gain in receiver sensitivity of 3.5 dBm with respect to direct detection. A multilevel pulse amplitude modulation (4-PAM) that doubles the data rate per channel from10 Gbps to 20 Gbps by transmitting more information in the amplitude of the carrier signal was implemented. This was achieved by modulating the optical amplitude with an electrical four level amplitude shift keyed (ASK) signal. A receiver consisting of a single photodiode, three decision circuits and a decoding logic circuit was used to receive and extract the original transmitted data. A DSP aided receiver was used to evaluate the link performance. A receiver sensitivity of -12.8 dBm is attained with a dispersion penalty of about 7.2 dB after transmission through 25 km of G.652 fibre.

acase@tulane.edu / The ability of humans to regenerate complex tissue structures after amputation is not completely absent. Clinical reports have described random spontaneous cases of digit tip regeneration in young adults. Regeneration of a structure such as a limb or a digit requires tight orchestration of environmental cues and cells that come together and coordinate the regeneration of the missing body part. Studies on animal models have been crucial to have a better understanding on relevant components and mechanisms that are involved in epimorphic regeneration. Mechanistic studies however, are difficult to perform due to the lack of spatial and temporal control of microenvironmental factors. The overall approach of this proposal is to develop a blastema-like in vitro model to conduct comparative studies between connective tissue cells from regeneration-competent (P3) and incompetent (P2) regions of the mouse digit tip, and to control the cellular microenvironment to modulate P2 cells regeneration-incompetent behavior. A 3D spheroid culture model was identified to serve as a 3D biomimetic blastema model that preserves the inherent regenerative properties of regeneration-incompetent and regeneration-competent phenotypes. Relevant factors associated with either wound healing or a regenerative response, were evaluated in both P2 and P3 cells cultured as spheroids. It was found that the expression of wound healing markers, particularly known to be involved in scar tissue formation, were significantly higher in P2 spheroids. Conversely, the expression of markers indicative of a regeneration-permissive microenvironment was significantly higher in P3 spheroids. We evaluated the effects of oxygen modulation in P2 during 2D expansion and/or during 3D spheroid culture and found that preconditioning of P2 cells in 2D increases P2 cell number and promotes spontaneous aggregation. We also found that modulation of oxygen concentration during 3D culture significantly decreases expression of both, wound healing and regenerative markers. This physiologically relevant in vitro model provides a platform to characterize cellular processes involved in the wound healing and regenerative responses. Additionally, it allows for the incorporation of environmental cues, such as oxygen concentration, to better understand the key target mechanisms to shift the default wound response from scar formation to epimorphic regeneration. / 1 / Lina M. Quijano

Abstract From the very beginning of modern ionospheric science, different radar applications have been utilised in ionospheric measurements. The most sophisticated ionospheric radars are the incoherent scatter radars, which detect the extremely weak scattering of radio waves from thermal fluctuations in the ionospheric plasma. Besides the low signal level, the stochastic nature of the scattering process causes further complications to the measurements. The scattering produces a zero-mean random signal, whose autocorrelation function contains the information of the ionospheric plasma parameters. Incoherent scatter radars have been used for about half a century, but the demanding task of developing transmission modulation and data analysis is still in progress. In this thesis, a statistical inversion based method for removing range ambiguities from the autocorrelation functions, lag profile inversion, is applied to incoherent scatter radar data. The data have been recorded with the EISCAT incoherent scatter radars, located in Northern Fennoscandia. The method is first applied to standard EISCAT experiments, the results giving strong evidence that the method is applicable for the purpose, and it provides results of at least equal quality with the present standard methods. In subsequent studies, new radar modulation methods are developed, which may provide significant improvements to the present incoherent scatter radar experiments. All the methods have been tested with a real radar, and lag profile inversion has been successfully applied to the recorded data. The methods are also put to use in order to measure the predicted effects of artificial heating of the free electrons in the D-region of the ionosphere.

No description available.

<p>Stability is the ability of a system to reject noise and maintain or return to the desired movement pattern and is an important feature of a motor system. In contrast, maneuverability is the ability of a system to transition between different motor states. A system that prioritizes stability inhibits its ability to transition between different motor states in a dexterous fashion. Since stability and maneuverability are opposing characteristics of a system, stability could be traded off to increase maneuverability. This study focuses on isometric finger force production, and its goals were to identify whether (1) the amount of information available about an upcoming motor transition influences the reduction in stability of total isometric force produced by the fingers, (2) stability reduction was correlated with greater maneuverability, i.e., less time for initiating a change in the total force, (3) the amount of stability reduction is correlated across tasks with different amount of information regarding the upcoming force changes, and (4) the times required to change force correlated across tasks with different informational content. </p> <p>Twenty-nine young adults (17 women; age, 23.3 ± 4.3 years) participated in this study and completed three different finger force tasks. For each task, the participants modulated the total pressing force produced by the four fingers of their right hand to track a target presented on a computer screen. In each task, participants began by producing a consistent (10% of their maximum voluntary contraction, MVC) background force with their fingers. In the Steady task, the target remained stationary and participants knew the target would not move. In the Reaction Time (RT) task, the target moved randomly in the vertical direction and participants knew that this could happen at any point in time. In the Self-paced task, participants started producing a background force and then produced a quick increase in total force using a predefined target that was displayed at the beginning of the trial, and visible throughout the trial. </p> <p>The uncontrolled manifold analysis was used to assess the stability of the total force during each task. This assessment was performed when the participants produced the same force (10% MVC), but expected different upcoming force changes, and had different amount of information about these upcoming force changes. This analysis yielded a stability index, and measures of the variance structure in the finger forces, computed across multiple repetitions. The reaction time and the movement time in the RT and the Self-paced tasks, respectively, was computed to quantify maneuverability. </p> <p>In contrast to previous findings and our expectations, the stability index was not statistically different for the Steady, RT, and Self-paced tasks, meaning that stability of the total force was not reduced in response to the mere expectation of an upcoming change in total force. However, the stability index reduced immediately before individuals changed their total force in the Self-paced tasks, which supports findings from previous studies. The stability modulation between the Steady and RT tasks did not correlate with the RT, and the stability modulation between the Steady and Self-paced tasks did not correlate with the movement time. Therefore, this study did not reveal a stability-maneuverability trade-off in isometric finger force production tasks. The movement time for the RT and Self-paced tasks were also not correlated. However, the novel finding of this study was that participants changed stability similarly for the RT and Self-paced tasks.</p> <p>Finally, the variance components obtained from the uncontrolled manifold analysis were higher in the RT task compared to the Steady task, consistent with previous reports. In fact, the increase in the performance error (greater variability in total force) while expecting to change total force in uncertain conditions (RT tasks) is the most striking and consistent result across multiple similar studies. This result indicates that despite the inconsistent results regarding the stability index, the performance of the current task (producing a constant total force) is hampered by the uncertainty and the expectation of upcoming changes in total force.</p> <p>It is likely that the stability-maneuverability trade-off is not essential for young, healthy adults in manual force production tasks. Investigations that include participants across the lifespan will shed light on this relation and help identify whether it plays a salient role in understanding loss of manual dexterity with healthy aging. </p>

The physical characteristics (i.e., nanostructure and stiffness) of the extracellular matrix where cells reside have been shown to profoundly affect numerous cellular events in vivo and also been employed to modulate cell behavior in vitro, yet how these physical cues regulate cell behavior is still elusive. Therefore, we engineered a variety of nanotopographies with different shapes and dimensions, and investigated how the nanotopographical cue, through focal adhesions-cytoskeleton-nucleus pathway, affected cell phenotype and function. We further designed and fabricated well-defined substrates which had either identical biochemical cue (adhesive ligand presentation) but different nanotopographical cues or identical nanotopography but different biochemical cues, and dissected the roles of these cues in cell modulation. In addition, we revealed that the human mesenchymal stem cells (hMSCs) could obtain nanotopographical memory from the past culture environment, and the nanotopographical memory influenced the future fate decision of the hMSCs. Moreover, we evaluated the effects of substrate nanotopographical and stiffness cues on the fibrogenesis of human lung fibroblasts in response to carbon nanotubes and highlighted the significance of these physical cues in the development of physiologically relevant in vitro models for nanotoxicological study. The mechanistic understanding of the physical regulation of cell behaviors will provide important insight into the advancement of cell culture technologies and the recreation of biomimetic in vitro tissue/organ models.

Communication systems have remained almost unchanged since the invention of the superheterodyne receiver in 1918 by the US engineer Edwin Armstrong. With the introduction of multiple-input-multiple-output (MIMO) technologies, Index Modulation appears to be the promising technology to revolutionize the traditional radio-frequency (RF) chain. Index modulation is a high-spectrum, energy-efficient, simple digital communication technique that uses the states of the building blocks of a communication system. In this study, we have focused on the use of radiation patterns scattered by antenna arrays or a metasurface as indices that are encoded as data bits. Initially, we explore sets of 𝑁tx transmitting point source antennas located on the XY plane; we assume that every antenna has phase tunability capability. The phase, the position in space, and the size of the array determine the shape of the far-field radiation pattern. Following the antenna excitation, a set of 𝑁rx receiver antennas spread at specific locations of the spherical space measures the incoming power signal, allowing the sampling of the radiation pattern that is demodulated into information bits.This work is focused on the characterization of the measured radiation patterns under different system and channel variables and their direct effect on the Bit Error Rate.

Variable-rate technologies coupled with broadcast spray systems serve to reduce chemical inputs, misapplication of chemicals, and environmental pollution, thus improving profitability and sustainability. Sprayer variable rate control involves using pulse width modulation (PWM) solenoids and/or direct chemical injection to adjust the application rate. The objectives of this research were to: outfit a conventional broadcast sprayer with PWM and direct inject technologies; evaluate the accuracy of the PWM system to control application rate for strait line and turn segments; and characterize the direct injection system’s transport delay time. For the PWM evaluation, the mean flow rate and coefficient of variation of individual nozzles indicated consistent performance. For the direct injection evaluation, the manufacturer recommended plumbing scheme and injection point location resulted in unsatisfactory delay times, ranging from 105 to 150s for the 8 km h-1 (5 mph) speed and 60 to 90s for the 16 km h-1 (10 mph) speed.