Time-resolved photoelectron imaging of model biological chromophores

Investigating the underlying forces that have a key role in light-matter interactions is crucial to understanding many fundamental processes that occur in nature. This thesis describes a series of experiments investigating model biological chromophores, providing an insight into the photochemistry of “ultraviolet selfprotection” schemes, invoked in many molecules involved in the protection of flora and fauna from the potentially damaging effects of excess ultraviolet radiation. These experiments are achieved through the application of time-resolved photoelectron imaging (TR-PEI) supported by high-level computational chemistry calculations. This thesis will set out both the motivation for the work, consisting of a comprehensive literature review of the subject, as well as an in-depth description of the optical set-up, laser system and spectrometer, as well as non-trivial data handling approaches involved in performing the experiments. This will lead on to work concerning the model chromophore aniline (and several aniline derived systems), guaiacol and finally a series of tertiary aliphatic amines. To conclude, various potential avenues of future work are discussed, considering both the experimental methodology and possible molecules of interest building upon the work described within this thesis

Following the relaxation dynamics of photoexcited aniline in the 273-266 nm region using time-resolved photoelectron imaging

Scanning tunnelling microscopy (STM) and Auger electron spectroscopy (AES) have been used to investigate the growth morphology of ultra-thin Pb films on the Ni3Al(111) face at room temperature. A previous study [K. Miśków and A. Krupski Appl Surf Sci 273, 2013, 554] using low-energy electron diffraction (LEED) and real time Auger intensity recording has demonstrated that an initial two-dimensional growth of the first Pb monolayer thick ‘wetting layer’ takes place. With further deposition and for T = 300 K, flat three atomic-layer-high islands are grown. Above 350 K, the Stranski–Krastanov growth mode was observed. In the current study, the analysis of STM measurements indicate and confirm that for coverage θ = 1.0 ML two-dimensional growth of the first Pb monolayer took place. Above θ > 1.0 ML, a three-dimensional growth of the Pb islands was observed with a strongly preferred atomic-scale ‘magic height (N),’ hexagonal shape and flat-tops. At coverage θ = 3.5 ML, only islands containing N = 3, 5, 7 and 11 atomic layers of Pb are observed. At the higher coverage θ = 5.5 ML, three types of regular hexagonal islands with side lengths of 25, 30 and 45 nm are observed. Furthermore, three different island adsorption configurations rotated by 10° ± 1° and 30° ± 6° with respect to each other were observed. After an annealing at T = 400 K of 5.5 ML of lead deposited at RT on the Ni3Al(111) the morphology of the surface changes. Post-anneal, islands of Pb are observed above the ‘wetting layer’ with an estimated average size and diameter of 768 ± 291 nm2 and 38.17 ± 6.56 nm and constant uniform height of two atomic layers (N = 2)

Time-resolved photoionization spectroscopy of mixed Rydberg-valence states:indole case study

Time-resolved photoelectron imaging reveals subtle new mechanistic insight into the ultraviolet relaxation dynamics of gas-phase indole.</p

The role of novel Rydberg-valence behaviour in the non-adiabatic dynamics of tertiary aliphatic amines

Time-resolved photoelectron imaging was used to study non-adiabatic relaxation dynamics in N,N-dimethylisopropylamine, N,N-dimethylpropylamine and N-methylpyrrolidine following excitation at 200 nm.</p

Bottom interacting sound at 50 km range in a deep ocean environment

Author Posting. © Acoustical Society of America, 2012. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 132 (2012): 2224-2231, doi:10.1121/1.4747617.Data collected during the 2004 Long-range Ocean Acoustic Propagation Experiment provide absolute intensities and travel times of acoustic pulses at ranges varying from 50 to 3200 km. In this paper a subset of these data is analyzed, focusing on the effects of seafloor reflections at the shortest transmission range of approximately 50 km. At this range bottom-reflected (BR) and surface-reflected, bottom-reflected energy interferes with refracted arrivals. For a finite vertical receiving array spanning the sound channel axis, a high mode number energy in the BR arrivals aliases into low mode numbers because of the vertical spacing between hydrophones. Therefore, knowledge of the BR paths is necessary to fully understand even low mode number processes. Acoustic modeling using the parabolic equation method shows that inclusion of range-dependent bathymetry is necessary to get an acceptable model-data fit. The bottom is modeled as a fluid layer without rigidity, without three dimensional effects, and without scattering from wavelength-scale features. Nonetheless, a good model-data fit is obtained for sub-bottom properties estimated from the data.This work was supported by the Office of Naval Research, Code 322, Grant Nos. N00014- 10-1-0987, N00014-11-1-0194, and N00014-10-1-0510

Frequency of Agenesis Palmaris Longus through Clinical Examination - An East African Study

INTRODUCTION: The Palmaris longus, one of the most variable muscles in the body both flexes the wrist and tenses the palmar fascia. It is used by surgeons as a source of tendon graft and racial differences in its variation have been documented. We sought to determine the frequency of the absence of the Palmaris longus in an East African population. METHODS: A prospective study was conducted using ten common clinical tests among patients and students in a large teaching hospital in East Africa to determine the presence of a Palmaris longus. RESULTS: The overall rate of absence was 4.4% with unilateral absence at 3.3% and bilateral absence at 1.1%. The overall difference between males and females was not statistically significant (p = 0.605). Participants were more likely to have absence in their non dominant hand. DISCUSSION: Our findings though in contrast to many studies worldwide, it concurs with most studies done in the African setting. These differences may be due to the higher levels of manual labour and the more use of the right hand in these activities. The frequency of the absence of Palmaris longus in East Africa has been determined. Surgeons should acquaint themselves with prevalence in their areas of practice

Dislocation Kinks in Copper: Widths, Barriers, Effective Masses, and Quantum Tunneling

We calculate the widths, migration barriers, effective masses, and quantum tunneling rates of kinks and jogs in extended screw dislocations in copper, using an effective medium theory interatomic potential. The energy barriers and effective masses for moving a unit jog one lattice constant are close to typical atomic energies and masses: tunneling will be rare. The energy barriers and effective masses for the motion of kinks are unexpectedly small due to the spreading of the kinks over a large number of atoms. The effective masses of the kinks are so small that quantum fluctuations will be important. We discuss implications for quantum creep, kink--based tunneling centers, and Kondo resonances