Advances in nanofabrication have bolstered the development of new optical devices with potential uses ranging from conventional optoelectronics, such as lasers and solar cells, to novel devices, like single photon or entangled photon sources. Quantum encryption of optical communications, in particular, requires devices that couple efficiently to an optical fiber and emit, on demand, indistinguishable photons. With these goals in mind, ultrafast spectroscopy is used to study the electron dynamics in epitaxially grown InAs/GaAs quantum dots (QDs). Quantifying the behavior of these systems is critical to the development of more efficient devices. Studies of two newly developed InGaAs QD structures, quantum dot clusters (QDCs) and QDs embedded in photonic wires, are presented herein. GaAs photonic wires with diameters in the range of 200 to 250 nm support only the fundamental HE11 guided mode. To fully quantify these new systems, the emission dynamics of QDs contained within wires in a large range of diameters are studied. Time correlated single photon counting measurements of the ground state exciton lifetimes are in very good agreement with predicted theoretical values for the spontaneous emission rates. For diameters smaller than 200 nm, QD emission into the HE11 mode is strongly inhibited and non-radiative processes dominate the decay rate. The best small diameter wires exhibit inhibition factors as high as 16, on par with the current state of the art for photonic crystals. The QDCs are the product of a hybrid growth technique that combines droplet heteroepitaxy with standard Stranski-Krastanov growth to create many different geometries of QDs. The work presented in this dissertation concentrates specifically on hexa-QDCs consisting of six InAs QDs around a GaAs nanomound. The first ever spectral and temporal properties of QDs within individual hexa-QDCs are presented. The QDs exhibit narrow exciton resonances with good temperature stability, indicating that excitons are well confined within individual QDs. A distinct biexponential decay is observed even at the single QD level. This behavior suggests that non-radiative decay mechanisms and exciton occupation of dark states play a significant role in the recombination dynamics in the QDCs. / text

Analysis of the genomic sequences of Streptococcus mutans UA159 and Group B Streptococcus (GBS) strains Streptococcus agalactiae NEM316 and S. agalactiae 2603V/R indicated the presence of two putative collagenase genes in each organism. smcol1 from S. mutans was previously cloned and analyzed and the results indicated that the enzyme belonged to the U32 family of collagenases/peptidases. This enzyme shares homology with the prtC of Porphyromonas gingivalis, one of the principal examples of the U32 family of peptidases. Considering the potential role of these enzymes in the pathogenicity of P. gingivalis (periodontitis or gum disease), GBS (premature rupture of the amniochorionic membrane) and S. mutans (dental root decay), it is necessary to study these enzymes and establish their role in the virulence of these organisms. Toward this goal the present study has focused on cloning collagenase 2 (smcol2) from S. mutans and cloning collagenase 1 (gbscol1), and collagenase 2 (gbscol2), from GBS. The information obtained will contribute to a further understanding of the U32 peptidase family.

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The surface-induced dissociation (SID) method is introduced into a Bruker matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI TOF MS) as an efficient ion fragmentation method. Ion trajectory calculations using the SIMION 7.0 ion optics program are performed and results are combined with simple unimolecular decay calculations in order to study the kinetics of the SID processes. In this instrument, the observation time frame for SID fragments lies in the submicrosecond region, allowing the specific detection of submicrosecond fragmentation channels. MALDI-produced protonated peptides in the mass range of 700 - 1500 Da and radical ions produced by laser irradiation of fullerenes C60 and C70 are fragmented at a gold surface coated with a self-assembled monolayer of alkanethiol to obtain TOF SID TOF mass spectra. For the SID of peptides in the hyperthermal energy regime, a fragmentation time frame of tens to a few hundreds of nanoseconds was calculated for the observed fast fragmentation channels (Chapters 3 and 4). Theoretical and experimental peak shape comparisons assuming unimolecular decay kinetics indicated a log rate constant in the range 6 - 7 (Chapter 4). Energy and mass resolved kinetic studies are also carried out. The contribution of special structural features to peptide fragmentation and the possibility of different fragmentation mechanisms such as sequential and parallel pathways are investigated. The results indicate a unimolecular decay process for observed fast peptide fragments ruling out a surface-shattering mechanism. Fullerene ions, especially C60+., showed a fragmentation behavior producing C2n+. fragments with an even number of C units at collision energies in the range of 100 - 400 eV (Chapter 5). At around 400 eV, additional small fragments appeared that are apart by only a single C unit. According to the calculated fragmentation times and the theoretical and experimental peak shape comparisons assuming unimolecular decay kinetics, both these processes may be approximated by parallel fast unimolecular decay processes with fragmentation time frames of tens to hundreds of nanoseconds although the poor theoretical and experimental peak shape matching for example in the decay of C60+. to C19+. may suggest deviations from a one-step unimolecular decay process.

High-precision half-life and branching-ratio measurements for the superallowed beta+ emitter 26Alm were performed at the TRIUMF-ISAC radioactive ion beam facility located in Vancouver, Canada. The branching ratio measurement was performed with the 8pi Spectrometer, an array of 20 high-purity germanium detectors, in conjunction with SCEPTAR, a plastic scintillator array used to detect the emitted beta particles. An upper limit of <= 12 ppm at 90% confidence level was found for the second forbidden beta + decay of 26Alm to the first 2+ state at 1809 keV in 26Mg. An inclusive upper limit of <= 15 ppm at 90% confidence level was found when considering all possible non-analogue beta +/EC decay branches of 26Alm, resulting in a superallowed branching ratio of 100.0000+0−0.0015%. The half-life measurement was performed using a 4pi continuous-flow gas proportional counter and fast tape transport system. The resulting value for the 26Alm half-life, T1/2 = 6.34654(76) s, is consistent with, but 2.5 times more precise than, the previous world average, and represents the single most precisely measured half-life of any superallowed emitting nucleus to date. Combining these results with world-average Q-value measurements yields a superallowed beta -decay ft value of 3037.58(60) s, the most precisely determined ft value for any superallowed emitting nucleus to date. Combined with the small, and precisely quoted, theoretical isospin-symmetry-breaking corrections for this nucleus, the corrected Ft value for 26Alm of 3073.1(12) s is also the most precisely determined for any superallowed emitter by nearly a factor of two and now rivals the precision of all the other 12 precisely measured superallowed beta decays combined. The high-precision experimental ft value for 26Alm superallowed decay reported here provides a new benchmark to refine theoretical models of isospin-symmetry-breaking effects in superallowed Fermi beta decays.

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<p>Two separate experimental searches for second-order weak nuclear decays to excited final states were conducted. Both experiments were carried out at the Kimballton Underground Research Facility to provide shielding from cosmic rays. The first search is for the two-neutrino double-beta decay of 96Zr to excited final states of the daughter nucleus, 96Mo. As a by product of this experiment, the beta decay of 96Zr was also investigated. Two coaxial high-purity germanium detectors were used in coincidence to detect gamma rays produced by the daughter nucleus as it de-excited to the ground state. After collecting 1.92 years of data with 17.91 g of enriched 96Zr, half-life limits at the level of 10^20 yr were produced. Measurements of this decay are important to test neutrinoless double-beta decay nuclear matrix element calculations, which are necessary to extract the neutrino mass from a measurement of the neutrinoless double-beta decay half-life. </p><p>The second experiment is a search for the resonantly-enhanced neutrinoless double-electron capture decay of 156Dy to excited states in 156Gd. Double-electron capture is a possible experimental alternative to neutrinoless-double beta decay, which could distinguish the Dirac or Majorana nature of the neutrino. Two clover high-purity germanium detectors were used in coincidence to investigate the decay. A 213.5 mg enriched 156Dy sample was observed for 0.635 year, producing half-life limits of 10^17 yr. The limits produced by both of these experiments are currently the most stringent limits available for these decays.</p> / Dissertation

CP violation is an important condition to explain the preponderance of baryons in our universe, yet the available CP violation in the Standard Model (SM) via the so-called Cabibbo-Kobayashi-Maskawa mechanism seems to not provide enough CP violation. Thus searching for new sources of CP violation is one of the central tasks of modern physics. In this thesis, we focus on a new possible source of CP violation which generates triple-product correlations in momenta which can appear in neutron and nuclear radiative β decay. We show that at low energies such a CP violating correlation may arise from the exotic coupling of nucleon, photon and neutrino that was proposed by Harvey, Hill, and Hill (HHH). One specialty of such an exotic HHH coupling is that it does not generate the well-known CP-violating terms such as ``D-term'', ``R-term'', and neutron electric dipole moment, in which particle's spins play critical role. We show that such a new HHH-induced CP violating effect is proportional to the imaginary part of c5gv, where gv is the vector coupling constant in neutron and nuclear β decay, and c5 is the phenomenological coupling constant that appears in chiral perturbation theory at O(M-2) with M referring to the nucleon or nuclear mass. We consider a possible non-Abelian hidden sector model, which is beyond the SM and may yield a nontrivial Im(c5). The available bounds on both Im(c5) and Im(gv) are considered, and a better limit on Im(c5) can come from a direct measurement in radiative beta decay. We calculate the competitive effect that arises from the general parameterization of the weak interaction that was proposed by Lee and Yang in 1956. We also show that in the proposed measurements, the CP-violating effect can be mimicked by the SM via final-state interactions (FSI). For a better determination of the bound of Im(c5), we consider the FSI-induced mimicking effect in full detail in O(α) as well as in leading recoil order. To face ongoing precision measurements of neutron radiative β decay of up to 1% relative error, we sharpen our calculations of the CP conserving pieces of neutron radiative β decay by considering the largest contributions in O(α2): the final-state Coulomb corrections as well as the contributions from two-photon radiation.

While neutrino oscillations indicate that neutrino flavors mix and that neutrinos have mass, they do not supply information on the absolute mass scale of the three flavors of neutrinos. Currently, the only viable way to determine this mass scale is through the observation of the theoretically predicted process of neutrinoless double-beta decay (0νββ). This yet-to-be-observed decay process is speculated to occur in a handful of nuclei and has predicted half-lives greater than 10²⁵ years. Observation of 0νββ is the goal of several large-scale, multinational efforts and consists of detecting a sharp peak in the summed β energies at the Q-value of the reaction. An exceptional candidate for the observation of 0νββ is ⁷⁶Ge, which offers an excellent combination of capabilities and sensitivities, and two such collaborations, MAJORANA and GERDA, propose tonne-scale experiments that have already begun initial phases using a fraction of the material. The absolute scale of the neutrino masses hinges on a matrix element, which depends on the ground-state wave functions for both the parent (⁷⁶Ge) and daughter (⁷⁶Se) nuclei in the 0νββ decay and can only be calculated from nuclear structure models. Efforts to provide information on the applicability of these models have been undertaken at the University of Kentucky Accelerator Laboratory using gamma-ray spectroscopy following inelastic scattering reactions with monoenergetic, accelerator-produced fast neutrons. Information on new energy levels and transitions, spin and parity assignments, lifetimes, multipole mixing ratios, and transition probabilities have been determined for ⁷⁶Se, the daughter of ⁷⁶Ge 0νββ, up to 3.0 MeV. Additionally, inaccuracies in the accepted level schemes have been addressed. Observation of 0νββ requires precise knowledge of potential contributors to background within the region of interest, i.e., approximately 2039 keV for ⁷⁶Ge. In addition to backgrounds resulting from surrounding materials in the experimental setup, ⁷⁶Ge has a previously observed 3952-keV level with a de-exciting 2040-keV γ ray. This γ ray constitutes a potential background for 0νββ searches, if this level is excited. The cross sections for this level and, subsequently, for the 2040-keV γ ray has been determined in the range from 4 to 5 MeV.