Vision requires the photoreceptors in the eye to rapidly respond to changes in light intensity. These processes are accomplished within rod photoreceptors by the visual pigment rhodopsin that initiates a downstream signaling cascade called phototransduction. Rhodopsin is composed of an apoprotein opsin that is covalently bonded with light sensitive 11-cis retinal. Rhodopsin is activated when 11-cis retinal is photoisomerized into all-trans retinal. This isomerization initiates the phototransduction cascade that culminates in a change in current at the plasma membrane. Rhodopsin, once activated ("bleached"), can no longer absorb photons to activate phototransduction, and must be regenerated through the visual cycle. To enable the photoreceptors to respond to rapid changes in light intensities, phototransduction must terminate in a timely manner. Deactivation involves phosphorylation of activated rhodopsin by rhodopsin kinase, and then binding of visual arrestin. Exposing rods to daylight bleaches a large proportion of rhodopsin molecules. This exposure leads to desensitization of the photoreceptors and phosphorylation of bleached rhodopsin. Full recovery of receptor sensitivity is achieved when rhodopsin is recycled and regenerated through a series of steps to its ground state. The last step in this process is the dephosphorylation of rhodopsin. This dissertation focuses on how rhodopsin dephosphorylation affects rod sensitivity. I exploited a novel observation; mouse retinae when isolated from the retinal pigment epithelium (and eye cup), display blunted rhodopsin dephosphorylation. Isoelectric focusing followed by Western blot analysis of retinal homogenate from bleached isolated retinae showed little dephosphorylation of rhodopsin for up to four hours in darkness, even under conditions when rhodopsin was completely regenerated. Microspectrophotometric measurements of rhodopsin spectra show that regenerated phospho-rhodopsin has the same molecular photosensitivity as unphosphorylated rhodopsin and that flash responses measured by trans-retinal electroretinogram or single cell suction electrode recording displayed dark-adapted kinetics. Single quantal responses displayed normal dark-adapted kinetics, but rods were only half as sensitive as those containing exclusively unphosphorylated rhodopsin. I propose a revised model in which light-exposed retinae contain a mixed population of phosphorylated and unphosphorylated rhodopsin. Moreover, complete dark-adaptation can only occur when all rhodopsin has been dephosphorylated, a process that requires more than three hours in complete darkness.

Philosophiae Doctor - PhD / We present a new sample of distant powerful radio galaxies, in order to study their host-galaxy properties and provide targets for future observations of Hi absorption with new radio telescopes. We cross-match the Sydney University Molonglo Sky Survey radio catalogue at 843 MHz with the VISTA Hemisphere Survey near-infrared catalogue using the Likelihood Ratio technique, producing contour plots as a way to inspect by eye a subset of bright sources to validate the automated technique. We then use the Dark Energy Survey optical and near-infrared wavelength data to obtain photometric redshifts of the radio sources. We find a total of 249 radio sources with photometric redshifts over a 148 square degree region. By fitting the optical and near-infrared photometry with spectral synthesis models, we determine the stellar masses and star-formation rates of the radio sources. We find typical stellar masses of 1011−1012 M for the powerful high-redshift radio galaxies. We also find a population of low-mass blue galaxies. We then report results from the first search for associated Hi 21 cm line absorption with the new MeerKAT radio telescope (shared-risk early science programme). We used a 16-antenna sub-array of MeerKAT to carry out a survey for Hi absorption in the host galaxies of nine powerful (L1.4 GHz > 1026 W Hz−1 ) radio galaxies at cosmological distances (z = 0.29 to 0.54). We found no evidence of absorption with 5σ optical depth detection limits. We only obtain a tentative absorption towards a radio source 3C 262 at z = 0.44 with significant ongoing star formation at a rate of 10.5 M yr−1 . The source consists of two radio lobes separated by 28.5 kpc with no evidence of a compact core. If the absorption arises from neutral gas from an extended disc, the line is redshifted by 79(21) km s−1 with respect to the nucleus and has an average Hi column density across the source of NHI ∼ 7 × 1019−20 cm−2 , which is consistent with the rate of star formation. But after further tests, we find that the Hi detection towards 3C 262 is likely to be an artefact. We conclude that the new correlator with 32 k channel resolution will be needed before searching for its associated absorption in MIGHTEE data.

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A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, February 6, 2015. / We explore indirect detections of Dark Matter, focusing on deep radio observations of six dwarf spheroidal galaxies (dSph), Carina, Fornax, BootesII, Hercules, Segue2, Sculptor. We discuss the WIMP Dark Matter particle annihilation process and describe brie y the particles produced in this process. We consider the emissions, which can result from electrons and positrons produced. We describe why dSph are the best observational targets for indirect Dark Matter detection at radio frequencies. We describe the theoretical framework for predicting Dark Matter synchrotron emissions and make some predictions for the six dSph of interest to us. We discuss ATCA observations of these dSph and explore the background source subtraction process in detail. We obtain an upper limit on the WIMP mass and compare our results to various other experiments. We discuss prospects for this work towards attaining an indirect Dark Matter detection.

No description available.

I carried out systematic studies on the assembly history of dark matter halos, using numerical simulations and semi-analytical methods. First, I look into dark halo mass assembly history. I confirmed that the halo mass assembly is divided into a fast accretion phase and a slow accretion phase. These two phases are found to be separated by the epoch when the dark halo potential reaches its maximum. The fast accretion phase is dominated by mergers, especially major mergers; the slow accretion phase is dominated by slow mass accretion. Each halo experiences about 3±2 major mergers since its main progenitor had a mass equal to 1 percent of halo mass. However, the average redshift at which these major mergers occur is strongly mass dependent. Secondly, I investigate the formation times and the assembly bias of dark halos. I use eight different definitions of halo formation times to characterize the different aspects of the halo assembly history. I find that these formation times have different dependence on halo mass. While some formation times characterize well the hierarchical nature of halo formation, the trend is reversed for other definitions of the formation time. In addition, the formation-time dependence of halo bias is quite strong for some definitions of formation time but weak or absent for others. Thirdly, I study sub-halo mass function in the halo assembly history, with the generally known unevolved sub-halo mass functions (USMFs). I find that for subhalos that merge into the main progenitor of a present-day halo, their USMF can be well described by a universal functional form; the same conclusion can also be reached for the USMF of all sub-halos that have merged during the entire halo merging history. In these two cases, the USMFs do not seem to depend on the redshift of the host halo either. However, due to the mass loss caused by dynamical effects, only small part of the accreted halos survived and became sub-structures in the present-day dark halos. In the cluster-sized halos, 30% survived sub-halos are sub-subhalos. The sub-halo mass function at given accretion time (redshift) is also investigated to find the origin of the statistics mentioned above.

Indiana University-Purdue University Indianapolis (IUPUI) / Tolerance is a diagnostic criterion for alcohol use disorder (AUD) and dependence and is often measured metabolically or behaviorally by comparing blood ethanol concentrations (BEC) or locomotor performance to an ethanol (EtOH) challenge before and after a drinking history, respectively. To explore another aspect of chronic behavioral tolerance in a family history positive (FH+) model of AUD, crossed High Alcohol Preferring (cHAP) mice were allowed to respond instrumentally for an EtOH reinforcer after either a five-week history of continuous home cage two-bottle choice (2BC) drinking or a concurrent five-week water-drinking period. Additionally, some of these animals were placed back into the operant box after home cage drinking histories to respond in extinction, allowing for the quantification of alcohol-motivated seeking alone in the absence of EtOH taking and its intoxicating effects. The results demonstrate that an alcohol history does not lead to a subsequent increase in active lever responding or inactive lever responding when compared to water-drinking controls. However, female cHAP mice with an EtOH-drinking history respond more on the inactive lever in extinction compared to water controls, suggesting that home cage EtOH history potentiates variation in responding in extinction. Overall, female mice responded more on the active lever and drank more alcohol in the reinforced condition, but again, there was not an effect of drinking history on this sex-specific effect. Together these results suggest that while female cHAPs, regardless of drinking history, are more motivated to work to drink EtOH, reinforced and non-reinforced instrumental responding are not reliable readouts for tolerance in cHAP mice compared to other endpoints such as drinking in the dark (DID) assays.

The thesis explores the relationship of light, architecture, and humans focusing on both the mathematics of solar movement that informs the architecture and the experiential and spiritual response of human perception to it. The exploration uses the celestial realm as the inspiration and canvas that the design process was built on. The light tunnels, the design concept explored in detail, investigate the consequences of architectural form and space in combination with volumetric, reflected, dispersed, or absorbed light. The design process transforms an instrument derived from the sun dial to a living piece of architecture that responds to human perception to variably objectify and reveal spiritual conditions of the celestial sky. / Master of Architecture / The thesis explores the relationship of light, architecture and humans focusing on both the movement of the sun and the perceptive response to it. The Pilgrimage of the 'temples of inexplicable' is a complex with several pavilions that engage with light and dark to create a space that allows the coexistence of spirituality and science in harmony. The thesis looks into one pavilion in detail – The light tunnels that investigate the movement of the light source, its nature as an object or revelation, and the human perception. The design process transforms an instrument to a living piece of architecture.

Although astrophysical evidence supports the existence of dark matter (DM), it remains one of the unanswered questions left by the Standard Model (SM) of Particle Physics. However, under hypotheses of new interactions, the production of dark matter can be detected as an excess of events with large missing transverse momentum (p_T^miss) over the SM background process. This thesis documents a search for new particles at the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC), targeting events where large p_T^miss and energetic jets are produced in a proton-proton collision at 13 TeV. The data were collected from 2017 to 2018 during the second half of LHC Run-II. The analysis also targets events where a jet is produced from W or Z bosons identified by a deep-neural-network-based tagger. Multiple control regions targeting specific background processes are defined which estimate background yield in the signal region through a simultaneous fit across control regions of all search channels. The result for the Run-II data corresponding to an integrated luminosity of 137 fb^-1 is obtained by combining this analysis with the previously published 2016 data. No excess of events is observed compared to the SM background expectations. The result of this search is interpreted in several new physics models, including simplified dark matter models, large extra dimension model (ADD), Higgs portal models, and leptoquark models. Limits are set on model parameters providing the most stringent direct constraints on dark matter search from colliders.