Modelling the ultraviolet environment at the surface of Mars and design of the Beagle 2 UV sensor

This thesis describes a multi-layer radiative transfer UV model which was used to aid in the design of the UV sensor on Beagle 2, which will soon provide the first ever in situ measurement of UV flux at the martian surface. The model uses the delta-Eddington approximation for diffuse flux and new low temperature gas absorption cross-sections and aerosol optical properties. Dust, H2O clouds and morning fogs are found to modify the martian surface UV spectrum. Dust storms have been shown to attenuate the surface UV flux by more than an order of magnitude, though some UV persists even at extremely high optical depths. The seasonal variation of surface UV irradiance was found to produce maximum exposure areas highly dependent upon dust activity over the martian year. Dust activity is also shown to distort the annual latitudinal dose, with high dust loading in the southern hemisphere resulting in a higher annual dose than in the north. The introduction of O3 abundances of 1.64 x 1017cm-2 into the model resulted in only partial protection for micro-organisms, since wavelengths shorter than 230 nm still penetrate to the surface. DNA-weighting of a martian UV spectrum shows the surface UV environment to be 103 times more damaging than on Earth. UV detection signatures of atmospheric phenomena and anticipated events for the case of Beagle 2 are presented: a dust devil encounter creates a double minimum profile in the UV flux, and solar eclipses by Phobos produce a single minimum. Clouds increase the diffuse/direct UV ratio, and fogs create a distinct dip in the morning profile when normalised to clear days

Radiative properties of IR materials

The objective of this thesis is to study the radiative properties of materials of interest in the infrared range of wavelengths. In particular, three distinct materials have been considered here - Erbium oxide, alumina and quartz. Erbium oxide has unique selective line emission, which gives a high emittance at a particular wavelength and low emittance in the rest of the infrared spectrum. It has applications in the design and development of thermophotovoltaic (TPV) generators. Because of its selective emission properties, erbium oxide assists in concentrating the radiant energy into a narrow band near the bandgap energy of the TPV cell, and this results in an efficient energy conversion. Lucalox and sapphire which are JR transparent materials are used as selective absorbers for increasing the efficiency of TPV generators. A novel spectral emissometer has been utilized for measurement of the temperature dependent radiative properties of erbium oxide, sapphire and lucalox. The experimental results presented in this thesis showed that the measurement of high temperature optical properties of these materials can be performed reliably with a novel non-contact, real-time approach using the spectral emissometer. The emissivity of erbium oxide is observed to be low and constant in the wavelength range of 2 to 5 microns and at various temperatures studied. Sapphire and lucalox exhibit almost similar characteristics in 1 to 3.3 micron region. All the materials investigated in this thesis are potential candidates for gate dielectrics in MOS technology

Open anterolateral fracture dislocation of ankle joint: a rare case report

Anterior ankle dislocation with associated compound bi-malleolar fracture is a rare injury. Ankle fracture dislocations most frequently occurs in young males caused by high energy trauma. The direction of the joint dislocation is determined by the position of the foot and the direction of the force being applied. A middle aged male presented to us with history of road traffic accident and was diagnosed to have anterior dislocation of right ankle joint with compound bi-malleolar fracture. Patient was taken to emergency operation theatre for wound debridement and immediate ankle reduction done under sedation. Due to wound contamination fracture fixation was delayed, once the wound healed bi-malleolar fracture fixation was done

Removal of Confined Ionic Liquid from a Metal Organic Framework by Extraction with Molecular Solvents

This work was supported in part by NSF Grant No. CHE-1223988 and by EPSRC Grant No. EP/K00090X/1.Peer reviewedPostprin

An Internally Consistent Approach for Modeling Solid-State Aggregation: II. Mean-Field Representation of Atomistic Processes

A detailed continuum (mean-field) model is presented that captures quantitatively the evolution of a vacancy cluster size distribution in crystalline silicon simulated directly by large-scale parallel molecular dynamics. The continuum model is parameterized entirely using the results of atomistic simulations based on the same empirical potential used to perform the atomistic aggregation simulation, leading to an internally consistent comparison across the two scales. It is found that an excellent representation of all measured components of the cluster size distribution can be obtained with consistent parameters only if the assumed physical mechanisms are captured correctly. In particular, the inclusion of vacancy cluster diffusion and a model to capture the dynamic nature of cluster morphology at high temperature are necessary to reproduce the results of the large-scale atomistic simulation. Dynamic clusters with large capture volumes at high temperature, which are the result of rapid cluster shape fluctuations, are shown to be larger than would be expected from static analyses, leading to substantial enhancement of the nucleation rate. Based on these results, it is shown that a parametrically consistent atomistic-continuum comparison can be used as a sensitive framework for formulating accurate continuum models of complex phenomena such as defect aggregation in solids

Internally Consistent Approach for Modeling Solid-State Aggregation: I. Atomistic Calculations of Vacancy Clustering in Silicon

A computational framework is presented for describing the nucleation and growth of vacancy clusters in crystalline silicon. The overall approach is based on a parametrically consistent comparison between two representations of the process in order to provide a systematic method for probing the details of atomic mechanisms responsible for aggregation. In this paper, the atomistic component of the overall framework is presented. First, a detailed set of targeted atomistic simulations are described that characterize fully the thermodynamic and transport properties of vacancy clusters over a wide range of sizes. It is shown that cluster diffusion is surprisingly favorable because of the availability of multiple, almost degenerate, configurations. A single large-scale parallel molecular dynamics simulation is then used to compute directly the evolution of the vacancy cluster size distribution in a supersaturated system initially containing 1000 uniformly distributed vacancies in a host lattice of 216,000 Si atoms at 1600 K. The results of this simulation are interpreted in the context of mean-field scaling theory based on the observed power-law evolution of the size distribution moments. It is shown that the molecular dynamics results for aggregation of vacancy clusters, particularly the evolution of the average cluster size, can be very well represented by a highly simplified mean-field model. A direct comparison to a detailed continuum model is made in a subsequent article