Experimental studies of surface and gas-phase processes relevant to the interstellar medium and planetary atmospheres

The interstellar medium (ISM) is the region of space between stars, where star and planet formation occurs. Molecular hydrogen is vitally important to the chemistry that happens in the ISM, as it initiates most of the reactions. The molecules that result from these reactions act as a coolant for the huge molecular clouds that collapse to form stars. The abundance of molecular hydrogen in the ISM is too high to form through gas phase processes alone. The accepted formation mechanism for H_2 is via heterogeneous catalysis on the surface of interstellar dust grains. These dust grains make up approximately 1% mass of the ISM and are carbonaceous or silicate in composition. The experiment presented in this thesis has been designed to probe ro-vibrational energy of nascent HD formed on an interstellar dust grain analogue. The experiment involves the use of two atom sources, to produce H and D atoms, ultrahigh vacuum chambers and cryogenic cooling to obtain conditions relevant to the ISM. The laser technique of resonance enhanced multiphoton ionisation (REMPI) is employed to state selectively ionise the HD, in order to investigate the internal energy of the newly formed HD when itdesorbs from the highly orientated pyrolitic graphite surface. The results are presented here and are compared to other theoretical and experimental studies; the astrophysical implications are discussed. Also included in this thesis is a study of the electron impact ionisation of OCS using pulsed time-of-flight in conjunction with a 2-D coincidence technique. The experimentalset-up allows fragment ions to be formed by dissociative single, double and triple ionisation to be detected and quantified. The relative partial ionisation cross sections (PICS) and precursor specific relative PICS are derived as well as information on OCS^{2+}. OCS is found in the atmospheres of Jupiter and Venus, where it may exist in a doubly charged state, OCS has been observed in the interstellar medium

Station coordinates in the standard earth 3 system and radiation-pressure perturbations from ISAGEX camera data

Simultaneous and individual camera observations of GEOS 1, GEOS 2, Pageos, and Midas 4 obtained during the International Satellite Geodesy Experiment are utilized to determine station coordinates. The Smithsonian Astrophysical Observatory Standard Earth III system of coordinates is used to tie the geometrical network to a geocentric system and as a reference for calculating satellite orbits. A solution for coordinates combining geometrical and dynamical methods is obtained, and a comparison between the solutions and terrestrial data is made. The radiation-pressure and earth-albedo perturbations for Pageos are very large, and Pageos' orbits are used to evaluate the analytical treatment of these perturbations. Residual effects, which are probably of interest to aeronomists, remain in the Pageos orbits

Preliminary report of dinosaur tracks in Qwa Qwa, South Africa

We record the presence of tridactyl dinosaur tracks preserved on a siltstone surface in a watercourse in a north eastern Free State game park

Modeling large scale species abundance with latent spatial processes

Modeling species abundance patterns using local environmental features is an important, current problem in ecology. The Cape Floristic Region (CFR) in South Africa is a global hot spot of diversity and endemism, and provides a rich class of species abundance data for such modeling. Here, we propose a multi-stage Bayesian hierarchical model for explaining species abundance over this region. Our model is specified at areal level, where the CFR is divided into roughly $37{,}000$ one minute grid cells; species abundance is observed at some locations within some cells. The abundance values are ordinally categorized. Environmental and soil-type factors, likely to influence the abundance pattern, are included in the model. We formulate the empirical abundance pattern as a degraded version of the potential pattern, with the degradation effect accomplished in two stages. First, we adjust for land use transformation and then we adjust for measurement error, hence misclassification error, to yield the observed abundance classifications. An important point in this analysis is that only $28$ of the grid cells have been sampled and that, for sampled grid cells, the number of sampled locations ranges from one to more than one hundred. Still, we are able to develop potential and transformed abundance surfaces over the entire region. In the hierarchical framework, categorical abundance classifications are induced by continuous latent surfaces. The degradation model above is built on the latent scale. On this scale, an areal level spatial regression model was used for modeling the dependence of species abundance on the environmental factors.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS335 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Local forest structure variability increases resilience to wildfire in dry western U.S. coniferous forests.

A 'resilient' forest endures disturbance and is likely to persist. Resilience to wildfire may arise from feedback between fire behaviour and forest structure in dry forest systems. Frequent fire creates fine-scale variability in forest structure, which may then interrupt fuel continuity and prevent future fires from killing overstorey trees. Testing the generality and scale of this phenomenon is challenging for vast, long-lived forest ecosystems. We quantify forest structural variability and fire severity across >30 years and >1000 wildfires in California's Sierra Nevada. We find that greater variability in forest structure increases resilience by reducing rates of fire-induced tree mortality and that the scale of this effect is local, manifesting at the smallest spatial extent of forest structure tested (90 × 90 m). Resilience of these forests is likely compromised by structural homogenisation from a century of fire suppression, but could be restored with management that increases forest structural variability

Dentition and feeding niche of Endothiodon (Synapsida; Anomodontia).

Main articleThe cranial morphology and extensive dentition of the dicynodont therapsid Endothiodon are different from those of any other dicynodont and it clearly had a different feeding niche. Recently prepared material from Mozambique which has relatively well preserved dentition has revealed that the mode of tooth replacement of Endothiodon differs in the upper and lower jaws. The very high and narrow vaulted palate with a close fitting, pointed lower jaw indicates that Endothiodon had a small mouth with muscular cheeks and extensive cheek pouches, suggesting a browsing feeding niche.Non

Enhancing the Critical Current of a Superconducting Film in a Wide Range of Magnetic Fields with a Conformal Array of Nanoscale Holes

The maximum current (critical current) a type-II superconductor can transmit without energy loss is limited by the motion of the quantized magnetic flux penetrating into a superconductor. Introducing nanoscale holes into a superconducting film has been long pursued as a promising way to increase the critical current. So far the critical current enhancement was found to be mostly limited to low magnetic fields. Here we experimentally investigate the critical currents of superconducting films with a conformal array of nanoscale holes that have non-uniform density while preserving the local ordering. We find that the conformal array of nanoscle holes provides a more significant critical current enhancement at high magnetic fields. The better performance can be attributed to its arching effect that not only gives rise to the gradient in hole-density for pinning vortices with a wide range of densities but also prevent vortex channeling occurring in samples with a regular lattice of holes.Comment: 5 pages, 3 figure

A systematic review of three approaches for constructing physical activity messages: What messages work and what improvements are needed?

<p>Abstract</p> <p>Background</p> <p>To motivate individuals to adhere to a regular physical activity regime, guidelines must be supplemented with persuasive messages that are disseminated widely. While substantial research has examined effective strategies for disseminating physical activity messages, there has been no systematic effort to examine optimal message content. This paper reviews studies that evaluate the effectiveness of three approaches for constructing physical activity messages including tailoring messages to suit individual characteristics of message recipients (message tailoring), framing messages in terms of gains versus losses (message framing), and targeting messages to affect change in self-efficacy (i.e., a theoretical determinant of behavior change).</p> <p>Methods</p> <p>We searched the MEDLINE, PsycINFO, EMBASE and CINAHL databases up to July 2008. Relevant reference lists also were searched. We included intervention trials, field experiments, and laboratory-based studies that aimed to test the efficacy or effectiveness of tailored messages, framed messages and self-efficacy change messages among healthy adults. We used a descriptive approach to analyze emerging patterns in research findings. Based on this evidence we made recommendations for practice and future research.</p> <p>Results</p> <p>Twenty-two studies were identified. Twelve studies evaluated message tailoring. In 10 of these studies, tailored messages resulted in greater physical activity than a control message. Six studies evaluated framed messages. Five of these studies demonstrated that gain-framed messages lead to stronger intentions to be active compared to a control message. Moreover, a gain-frame advantage was evident in three of the four studies that assessed physical activity. Four studies evaluated self-efficacy change messages. The two studies that used an experimental design provide a clear indication that individuals' beliefs can be affected by messages that incorporate types of information known to be determinants of self-efficacy. Overall, strong evidence to support definitive recommendations for optimal message content and structure was lacking.</p> <p>Conclusions</p> <p>Additional research testing the optimal content of messages used to supplement physical activity guidelines is needed. Tailored messages, gain-framed messages, and self-efficacy change messages hold promise as strategies for constructing physical activity messages and should be a focus of future research.</p