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Understanding the radiation chemistry of water is important in many disciplines including the nuclear industry, astrochemistry, and medicine. In recent years, low-energy electrons have been paid much greater attention, due to their abundance and reactivity in irradiated materials. Electrons with energies < 20 eV may interact via the dissociative electron attachment (DEA) mechanism, which has been found to cause single-strand breaks in DNA.DEA in water involves the capture of a low energy electron by a neutral water molecule into an outer orbital and is generally accompanied by excitation of the H2O molecule, causing it to dissociate. The aim of this work is to study the OH radical produced in DEA to H2O using laser-induced fluorescence (LIF).A high-vacuum chamber equipped with low energy electron gun, molecular beam and laser system was built for gas-phase studies of DEA in water. LIF spectra were recorded from OH formed by dissociation of gas-phase H2O, for determination of the rotational and vibrational state distributions. In addition to the gas-phase studies, low-energy (100 eV) electron-stimulated reactions in layered H2O/CO/H2O ices were investigated using a combination of temperature-programmed desorption (TPD) and infrared reflection-absorption spectroscopy (IRAS).For CO trapped within approximately 50 mono-layers of the vacuum interface both reduction and oxidation products were observed including HCO, H2CO, H3CO and CH3OH, and CO2. Concentration profiles of CO versus film thickness showed two zones in the film: a near-surface zone of preferential oxidation, and a zone of preferential reduction deeper in the film. A Monte Carlo model was developed based on diffusion of H atoms through the ice lattice, which supported the experimental results.

Electrocardiogram (ECG) is a noninvasive technology widely used in health care systems for diagnosis of heart diseases, and a wearable ECG sensor with long-term monitoring is necessary for real-time heart disease detection. However, the conventional ECG is restricted considering the physical size and power consumption of the system. In this thesis, we propose a Wireless ECG System with Bluetooth Low Energy (BLE) and Compressed Sensing (CS). The proposed Wireless ECG System includes an ECG sensor board based on a BLE chip, an Android application and a web service with a database. The ECG signal is first collected by the ECG Sensor Board and then transmitted to the Android application through BLE protocol. At last, the ECG signal is uploaded to the cloud database from the Android app. We also introduce Compressed Sensing into our system with a novel sparse sensing matrix, data compression and a modified Compressive Sampling Matching Pursuit (CoSaMP) reconstruction algorithm. Experiment results show that the amount of data transmitted is reduced by about 57% compared to not using Compressed Sensing, and reconstruction time is 64% less than using Orthogonal Matching Pursuit (OMP) or Iterative Re-weighted Least Squares (IRLS) algorithm. / Graduate

The Internet of things is a scenario where devices such as lighting, household appliances, sensors etc. are connected and communicate with each other via Internet. This puts a demand for a good infrastructure around these devices. One way to handle this is to use radio as a means of communication and let the devices forward each other's traffic in what is known as a mesh network. This thesis explores different radio standards that can be used to create a mesh network for sensors. Two different approaches to mesh networking using Bluetooth Low Energy was implemented and evaluated. One approach works by letting all devices broadcast every message they receive, a rather brute force approach. The other approach worked by letting the network find routes between all the nodes in the network and then establishes a connection between the nodes that want to communicate via intermediate nodes. It was found that the rebroadcast approach in idle mode used 3.36 mAh while the connection approach used 0.47 mAh for the same configuration. Another test was performed where the percentage of successfully delivered messages was measured. For the rebroadcast approach it was 75 % and for connection it was 58 %. Tweaking the connection network to not be able to adapt to changes increased the throughput to 77 %. During the testing numerous ways for improving performance were thought of but not implemented. The need for synchronizing the devices clocks and establishing protocol for when to send and receive became apparent when working with the rebroadcast network. In the connection network there were problems with that the routing maintenance led to unavailable units and reduced performance. / Sakernas internet, Internet of Things är ett scenario där elektriska apparater så som belysning, hushållsmaskiner, sensorer mm är anslutna och kommunicerar med varandra via internet. Men så många anslutna enheter ställer stora krav på infrastrukturen kring enheterna. Ett sätt att lösa problemen kring infrastruktur är att låta enheterna kommunicera via radio och låta dem vidarebefordra varandras datatrafik i en typ av nätverkstopologi som kallas för meshnätverk. Det här examensarbetet utforskar möjliga radiostandarder som kan användas för att skapa ett meshnätverk för just sensorer. Två typer av meshnätverk implementerades med Bluetooth Low Energy och deras styrkor och svagheter utvärderades. En av dessa gick ut på att enheterna i nätverket sände ut meddelanden som alla kunde ta och sedan att de som lyckades ta emot i sin tur sände meddelandena vidare. Det är en enkel metod som är lätt att implementera.Den andra metoden gick ut på att nätverket tog reda på sin konfiguration och vilken rutt som ska tas via andra enheter för att nå den man vill. När enheterna sen vill kommunicera så upprättar de en anslutning via enheterna längs rutten. Två saker som jämfördes mellan metoderna var strömförbrukning och andel lyckade sändningar. För samma nätverk så drog återsändnings nätverket 3.36 mA och anslutningsnätverket 0.47 mA. Antalet lyckade sändningar testades i ett annat scenario och där kom 75 % av meddelanden i återsändningsnätverket fram och motsvarande siffra för anslutningsnätverket var 58\%. Vidare testades det att stänga av utbytet av rutt information och sökningar efter nya enheter i anslutningsnätverket och då kom 77 % av meddelanden fram. I återsändningsnätverket insåg man att det fanns ett behov av att synkronisera klockorna i enheterna och etablera ett protokoll för hur när man ska sända och ta emot.I anslutningsnätverket så uppstod problem med att enheterna blev otillgängliga när de synkroniserade sin konfiguration vilket ledde till försämrad prestanda.

published_or_final_version / Physics / Master / Master of Philosophy

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by Chu Hon Yue. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1990. / Bibliography: leaves 91-93. / ACKNOWLEDGEMENT --- p.i / ABSTRACT --- p.ii / Chapter I. --- INTRODUCTION --- p.1 / Chapter II. --- LOW ENERGY ELECTRON DIFFRACTION --- p.4 / Chapter 2.1. --- LEED EXPERIMENT --- p.4 / Chapter 2.2. --- LEED CRYSTALLOGRAPHY：I(E) CURVE --- p.7 / Chapter 2.3. --- AN OUTLINE OF THE PHYSICS OF LEED --- p.8 / Chapter 2.3.1. --- LEED Process In One-Dimensional Surface --- p.8 / Chapter 2.3.2. --- LEED Process In Three-Dimensional Surface --- p.11 / Chapter 2.3.3. --- Surface With An Overlayer --- p.12 / Chapter 2.3.4. --- The Muffin-Tin Model And The Inner Potential --- p.13 / Chapter 2.3.5. --- The Phase Shift --- p.17 / Chapter 2.3.6. --- Thermal Effects --- p.19 / Chapter III. --- DYNAMICAL LEED CALCULATION： THE RENORMALIZED FORWARD SCATTERING PERTURBATION METHOD --- p.22 / Chapter IV. --- THE ZANAZZI-JONA RELIABILITY FACTOR --- p.30 / Chapter V. --- CALCULATIONS AND RESULTS --- p.33 / Chapter 5.1. --- EXPERIMENTAL I(E) CURVES --- p.33 / Chapter 5.2. --- CALCULATED I(E) CURVES --- p.36 / Chapter 5.2.1. --- Top Site --- p.4o / Chapter 5.2.2. --- Bridge Site --- p.41 / Chapter 5.2.3. --- Hollow Site --- p.42 / Chapter VI. --- DISCUSSIONS AND CONCLUSIONS --- p.44 / APPENDIX I --- p.51 / TABLES --- p.52 / I(E) CURVES AND CONTOUR MAPS --- p.61 / APPENDIX II --- p.79 / MAIN PROGRAMME FOR Rh(100)-c(2x2) -S --- p.80 / INPUT PARAMETERS FOR TOP SITE --- p.85 / INPUT PARAMETERS FOR BRIDGE SITE --- p.87 / INPUT PARAMETERS FOR HOLLOW SITE --- p.89 / REFERENCES --- p.91

archives@tulane.edu / The electronic, spin, phonon and magnetic behavior govern the electrodynamics of solid materials. The different compositions and symmetries mix all the degrees of freedom leading to varieties of interesting phenomena such as metal-to-insulator transition, nonreciprocal directional dichroism and topological states. The study of the behavior of electrons, spins and phonons is crucial to reveal the physics behind the mysterious phenomena. The nature of terahertz time domain spectroscopy (THz TDS) which has low photon energy and contains phase information makes this technique very powerful to probe the physics of spins, electrons, phonons and magnons where the resonance energy is in the THz range. The multiferroic materials are studied by using THz-TDS with strong dc magnetic field. Multiferroic material is one of complex materials that simultaneously contain ferroelectricity and magnetism. Many fascinating physical phenomena are discovered in multiferroics, including magneto-dielectric effect and nonreciprocal directional dichroism. The magneto-dielectric effect, change in dielectric function in applied magnetic field, is studied in multiferroic CaBaCo4O7. We analyze the dynamics of phonons to clarify the individual phonon contribution to the magneto-dielectric effect. We observe giant nonreciprocal directional dichroism in the multiferroic material FeZnMo3O8, which is defined as the difference in absorption coefficient for linearly polarized light waves travelling in the opposite direction. A spin excitation is determined as the origin of nonreciprocal effect in the multiferroic FeZnMo3O8 by using THz-TDS. The nonreciprocal effect from magneto-chiral dichroism is also observed in BaCoSiO4 crystal where the material simultaneously possesses the chiral structure and magnetization. The polarimetry of transmitted THz light through BaCoSiO4 is carefully analyzed. We attribute the change in polarization in the zero magnetic field to the chirality of the structure. Nonlinearity of semiconductor InSb due to intense THz electric field is investigated quantitatively by using THz-TDS. The effective mass approximation breaks down when the intense THz pulse is applied to the semiconductor. We develop a predictive model that replaces the effective mass with a realistic band structure and retains the Drude parameters, the electron density and scattering rate, to accurately calculate the experimental observations (saturable absorption and amplitude-dependent refractive index) in InSb. / 1 / Shukai Yu