Optical Properties of InGaN/GaN QW with the Same Well-Plus-Barrier Thickness

Optical properties of wurtzite violet InGaN/GaN quantum well (QW) structures, with the same well-plus-barrier thickness, grown by metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates, were investigated using temperature-dependent photoluminescence (TDPL) and excitation-power-dependent photoluminescence (PDPL). Two samples were compared: one had a thicker well (InGaN/GaN 3/5 nm); the other had a thicker barrier (InGaN/GaN 2/6 nm). It was found that the GaN barrier thickness in the InGaN/GaN MQWs plays an important role in determining the optical characteristics of the MQWs. The peak energy of the two samples varied with temperature in an S-shape. The thicker-barrier sample had a higher turning point from blueshift to redshift, indicating a stronger localization effect. From the Arrhenius plot of the normalized integrated PL intensity, it was found that the activation energy of the nonradiative process also increased with a thicker barrier thickness. The radiation recombination process was dominated in the sample of the thicker barrier, while the non-radiation process cannot be negligible in the sample of the thicker well.

Time-like Proton Form Factors with Initial State Radiation Technique

Electromagnetic form factors are fundamental quantities describing the internal structure of hadrons. They can be measured with scattering processes in the space-like region and annihilation processes in the time-like region. The two regions are connected by crossing symmetry. The measurements of the proton electromagnetic form factors in the time-like region using the initial state radiation technique are reviewed. Recent experimental studies have shown that initial state radiation processes at high luminosity electron-positron colliders can be effectively used to probe the electromagnetic structure of hadrons. The BABAR experiment at the B-factory PEP-II in Stanford and the BESIII experiment at BEPCII (an electron positron collider in the τ-charm mass region) in Beijing have measured the time-like form factors of the proton using the initial state radiation process e+e−→pp¯γ. The two kinematical regions where the photon is emitted from the initial state at small and large polar angles have been investigated. In the first case, the photon is in the region not covered by the detector acceptance and is not detected. The Born cross section and the proton effective form factor have been measured over a wide and continuous range of the the momentum transfer squared q2 from the threshold up to 42 (GeV/c)2. The ratio of electric and magnetic form factors of the proton has been also determined. In this report, the theoretical aspect and the experimental studies of the initial state radiation process e+e−→pp¯γ are described. The measurements of the Born cross section and the proton form factors obtained in these analyses near the threshold region and in the relatively large q2 region are examined. The experimental results are compared to the predictions from theory and models. Their impact on our understanding of the nucleon structure is discussed.

Degradation of Selected Antidepressants Sertraline and Citalopram in Ultrapure Water and Surface Water Using Gamma Radiation

Gamma radiation was applied to degradation selected antidepressants in ultrapure water and surface water. Additionally, the influence of typical radical scavengers like carbonate, nitrate and humic acid was determined. The cytotoxicity towards liver cells HepG2 and colon cells Caco2 were measured during the radiation process. It was found that radiation technology, specifically ionizing radiation, can achieve satisfactory degradation efficiency with both SER and CIT. It was shown that the process of decomposition of the tested antidepressants with the highest efficiency occurs in the reaction with the hydroxyl radical.

Time-Like Proton Form Factors in Initial State Radiation Process

The measurements of the proton electromagnetic form factors in the time-like region using the initial state radiation technique are reviewed. Recent experimental studies have shown that initial state radiation processes at high luminosity electron-positron colliders can be effectively used to probe the electromagnetic structure of hadrons. The BABAR experiment at the B-factory PEP-II in Stanford and the BESIII experiment at the $\tau$-charm factory BEPC-II in Beijing have measured the time-like form factors of the proton using the initial state radiation process $e^{+}e^{-}\to pbar{p}\gamma$. The two kinematical regions where the photon is emitted from the initial state at small and large polar angles have been investigated. In the first case the photon is in the region not covered by the detector acceptance and is not detected. The Born cross section and the proton effective form factor have been measured over a wide and continuous range of the the momentum transfer squared $q^2$ from threshold up to ~42 (GeV/c)$^2$. The ratio of electric and magnetic form factors of the proton has been also determined. In this report, the theoretical aspect and the experimental studies of the initial state radiation process $e^{+}e^{-}\to p\bar{p}\gamma$ are described. The measurements of the Born cross section and the proton form factors obtained in these analyses near the threshold region and in the relatively large $q^2$ region are examined. The experimental results are compared to the predictions from theory and models. Their impact on our understanding of the nucleon structure is discussed.

Black Hole Radiation, Greybody Factors, and Generalised Wick Rotation

<p>In this thesis we look at the intersection of quantum field theory and general relativity. We focus on Hawking radiation from black holes and its implications. This is done on two fronts. In the first we consider the greybody factors arising from a Schwarzschild black hole. We develop a new way to numerically calculate these greybody factors using the transfer matrix formalism and the product calculus. We use this technique to calculate some of the relevant physical quantities and consider their effect on the radiation process. The second front considers a generalisation of Wick rotation. This is motivated by the success of Wick rotation and Euclidean quantum field theory techniques to calculate the Hawking temperature. We find that, while an analytic continuation of the coordinates is not well defined and highly coordinate dependent, a direct continuation of the Lorentzian signature metric to Euclidean signature has promising results. It reproduces the Hawking temperature and is coordinate independent. However for consistency, we propose a new action for the Euclidean theory which cannot be simply the Euclidean Einstein-Hilbert action.</p>

Black Hole Radiation, Greybody Factors, and Generalised Wick Rotation

<p>In this thesis we look at the intersection of quantum field theory and general relativity. We focus on Hawking radiation from black holes and its implications. This is done on two fronts. In the first we consider the greybody factors arising from a Schwarzschild black hole. We develop a new way to numerically calculate these greybody factors using the transfer matrix formalism and the product calculus. We use this technique to calculate some of the relevant physical quantities and consider their effect on the radiation process. The second front considers a generalisation of Wick rotation. This is motivated by the success of Wick rotation and Euclidean quantum field theory techniques to calculate the Hawking temperature. We find that, while an analytic continuation of the coordinates is not well defined and highly coordinate dependent, a direct continuation of the Lorentzian signature metric to Euclidean signature has promising results. It reproduces the Hawking temperature and is coordinate independent. However for consistency, we propose a new action for the Euclidean theory which cannot be simply the Euclidean Einstein-Hilbert action.</p>

Generation in the regime with three resonance frequencies

If the group velocity of the wave is close to the bunch velocity, the bunch placed in the maximumum of the radiated pulse. It provides high effeciency of the electron-wave interaction. However, there are other factors related to particle dynamics, which have strong influence on the radiation process. In this paper the regime with three resonance frequencies is discussed. By varying the phase size of the electron bunch, the generation conditions at each of the frequencies can be changed. There are results for the spontaneous coherent super-radiative undulator emission in the terahertz frequency range from a short (as compared to the wavelength of the radiated wave) dense electron bunch. As a result, an electron bunch radiates two pulses with amplitudes of the radiated fields ∼ 10-70 MV/m.

Thermal Energy Production in an Electrochemical Cell and Heat Transfer to Its Dark Surroundings

The theoretical formulation presented in this abridged paper was developed to predict the transient cell average temperature of a lithium-based cell during its discharge in dark, extremely low material density surroundings where the predominant mechanism of heat exchange between its shroud surface and surroundings is the thermal radiation process for a given cell discharge current and its initial temperature. The average computed temperature of an ideal lithium-based button cell, such as Li(s)/electrolyte/CF(s), is presented as a function of time in the form of plots at two discharge currents as an example of the application of the derived formulation. The presented data are briefly discussed in light of the lithium-based cell component stability and its safe discharge operation.

Off-Grid Electrical Cell Lysis Microfluidic Device Utilizing Thermoelectricity and Thermal Radiation

Microfluidic devices have enormous potential and a wide range of applications. However, most applications end up as chip-in-a-lab systems because of power source constraints. This work focuses on reducing the reliance on the power network and expanding on the concept of a lab-on-a-chip for microfluidic devices. A cellulose-based radiator to reflect infrared (IR) radiation with wavelengths within the atmospheric window (8–13 µm) into outer space was fabricated. This process lowered the temperature inside the insulated environment. The difference in temperature was used to power a thermoelectric generator (TEG) and generate an electric current. This electric current was run through a DC-DC transformer to increase the voltage before being used to perform electrical cell lysis with a microfluidic device. This experimental setup successfully achieved 90% and 50% cell lysis efficiencies in ideal conditions and in field tests, respectively. This work demonstrated the possibility of utilizing the unique characteristics of a microfluidic device to perform an energy-intensive assay with minimal energy generated from a TEG and no initial power input for the system. The TEG system also required less maintenance than solar, wind, or hydroelectricity. The IR radiation process naturally allows for more dynamic working conditions for the entire system.

A Theory for Electromagnetic Radiation and Coupling

A theory for analyzing the radiative and reactive electromagnetic energies of a radiator in vacuum is presented. In vacuum, the radiative electromagnetic energies will depart from their sources and travel to infinity, generating a power flux in the space. However, the reactive electromagnetic energies are bounded to their sources. They appear and disappear almost in the same time with their sources, and their fluctuation also causes a power flux in the space. In the proposed theory, the reactive electromagnetic energies of a radiator are defined by postulating that they have properties similar to the self-energies in the charged particle theory. More importantly, in addition to a main term of source-potential products, the reactive energies contain a special energy term which will last to exist a short time after the sources disappear. This oscillating energy is related to the electric displacement and the vector potential, and seems to be responsible for energy exchanging between the reactive energy and the radiative energy in the radiation process, performing like the Schott energy term. As the Poynting vector describes the total power flux density related to the total electromagnetic energy, it should include the contributions of the propagation of the radiative energies and the fluctuation of the reactive energies. The mutual electromagnetic couplings between two radiators are also defined in a similar way in which the vector potential plays a central role. The reactive electromagnetic energies can be evaluated with explicit expressions in time domain and frequency domain. The theory is verified with the Hertzian dipole and numerical examples.