Effect of microstructure and temperature on the erosion rates and mechanisms of modified EB PVD TBCs

Thermal barrier coatings (TBCs) have now been used in gas turbine engines for a number of decades and are now considered to be an accepted technology. As there is a constant drive to increase the turbine entry temperature, in order to increase engine efficiency, the coatings operate in increasingly hostile environments. Thus there is a constant drive to both increase the temperature capabilities of TBCs while at the same time reducing their thermal conductivities. The thermal conductivity of standard 7 wt% yttria stabilized zirconia (7YSZ) electron beam (EB) physical vapour deposited (PVD) TBCs can be reduced in two ways: the first by modification of the microstructure of the TBC and the second by addition of ternary oxides. By modifying the microstructure of the TBC such that there are more fine pores, more photon scattering centres are introduced into the coatings, which reduce the heat transfer by radiation. While ternary oxides will introduce lattice defects into the coating, which increases the phonon scattering, thus reducing the thermal conductivity via lattice vibrations. Unfortunately, both of these methods can have a negative effect on the erosion resistance of EB PVD TBCs. This paper compares the relative erosion rates of ten different EB PVD TBCs tested at 90à ° impact at room temperature and at high temperature and discusses the results in term of microstructural and temperature effects. It was found that by modifying the coating deposition, such that a low density coating with a highly â  featheredâ  microstructure formed, generally resulted in an increase in the erosion rate at room temperature. When there was a significant change between the room temperature and the high temperature erosion mechanism it was accompanied by a significant decrease in the erosion rate, while additions of dopents was found to significantly increase the erosion rate at room and high temperature. However, all the modified coatings still had a lower erosion rate than a plasma sprayed coatings. So, although, relative to a standard 7YSZ coating, the modified coatings have a lower erosion resistance, they still perform better than PS TBCs and their lower thermal conductivities could make them viable alternatives to 7YSZ for use in gas turbine en

Synthesis and evaluation of some novel nucleotide derivatives as potential anti-AIDS drugs.

Many nucleoside analogues are known to inhibit human immunodeficiency virus (HIV), the causative agent of the disease acquired immunodeficiency syndrome (AIDS). In order to act these nucleosides must be phosphorylated to their corresponding 5'-triphosphates, which can then inhibit reverse-transcriptase (RT), a key viral enzyme. These phosphorylations are catalysed by cellular kinases. The synthesis of a number of nucleoside 5'-dialkyl phosphates is described in this thesis, along with the results of the biological evaluation of some of these derivatives against HIV. It was thought that the 5'-dialkyl phosphates might have been able to act as prodrugs for the corresponding 5'-monophosphates. Firstly the synthesis of 5'-dialkyl phosphates of 3'-0-mesylthymidine, 3'-0-acetylthymidine and 3'-0-ethylthymidine is described, along with the synthesis of some 5'-dialkyl phosphates of 3'-azido-3'-deoxythymidine, 2',3'-dideoxycytidine and 2',3'-dideoxyadenosine. However, when tested, all of the above 5'-dialkyl phosphates were found to be inactive against HIV in vitro. It was thought that this inactivity arose from the metabolic stability of the simple dialkyl esterifying groups present in these compounds. With this in mind some nucleoside 5'-bis(2,2,2-trihaloethyl) phosphate derivatives were synthesised as it was hoped that 2,2,2- trihaloethyl groups would be more labile than simple alkyl ones. Both 3'-azido-3'-deoxythymidine 5'-bis(2,2,2-trifluoroethyl) phosphate and 3'-azido-3'-deoxythymidine 5'-bis(2,2,2-trichloroethyl) phosphate were found to be inhibitors of HIV in vitro. In view of these results, the synthesis of some 5'-bis(2,2,2-trihaloethyl) phosphate derivatives of 2',3'-dideoxycytidine and 3'-fluoro-3'-deoxythymidine was undertaken. The synthesis of some mixed 5'-(alkyl 2,2,2-trihaloethyl) phosphate derivatives of 3'-azido-3'-deoxythymidine was also carried out. The 5'-bis(2,2,2-trichloroethyl) phosphates of 3'-0-mesylthymidine, 3'-0-acetylthymidine, 3'-0-ethylthymidine and 3'-amino-3'-deoxythymidine were also synthesised. As 3'-azido-3'-deoxythymidine 5'-bis(2,2,2-trichloroethyl) phosphate was able to inhibit HIV in vitro, the 5'-bis(2-chloroethyl) phosphate and the 5'-bis(2,2-dichloroethyl) phosphate of 3'-azido-3'-deoxythymidine were prepared, in order to ascertain if these compounds were able to inhibit HIV also. The 5'-bis(2-chloroethyl) phosphate of 3'-azido- 3'-deoxythymidine does indeed display activity against HIV in vitro. An attempt was made to synthesise a thymidine 5'-dialkyl phosphonate species, by a Michaelis-Arbuzov type reaction between 5'-bromo-5'-deoxythymidine and diethyl phosphite. However, it was only possible to isolate a 3'-hydrogenphosphate species from this reaction. As the method by which 3'-azido-3'-deoxythymidine 5'-bis(2,2,2-trichloroethyl) phosphate acts as an inhibitor of HIV probably involves the hydrolysis of the phosphate moiety to either the 5'-monophosphate or the parent nucleoside, some studies on the hydrolysis of 3'-azido-3'-deoxythymidine 5'-bis(2,2,2-trichloroethyl) phosphate at a variety of pH were carried out

Development of a floating tidal energy system suitable for use in shallow water

A proposal is made for the use of a traditional streamwaterwheel suspended between two floating catamaranNPL series demi-hulls as means of generating electricalpower. Two prototype devices, of lengths 1.6m and 4.5m,have been developed, constructed and tested. It was foundthat the concept is sound although greater investment isrequired with regards to the materials and bothhydrodynamic and aerodynamic design of the waterwheelto ensure an economically viable system. The workpresented concentrates on practical aspects associated withdesign, construction and trial testing in Southampton waterof the 4.5m prototype. The relatively low cost, ease ofdeployment, and the fact that conventional boat mooringsystems are effective, combine to make this an attractivealternative energy solution for remote communities

Observation of guanidine-carbon dioxide complexation in solution and its role in reaction of carbon dioxide and propargylamines

The first observation of guanidine-CO2 'activation' complexes in solution using ATR-FTIR is reported. While cyclic guanidines TBD and MTBD form stable and detectable complexes with CO2, other guanidines and tertiary amines do not. Correlation with catalytic activity of these amines/guanidines in reaction between CO2 and propargylamines indicated that the basicity of the catalyst, rather than its ability to form complexes with CO2, is the origin of catalytic activity

Blast initiation and propagation of cylindrical detonation in MAPP-air mixtures

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76403/1/AIAA-1974-149-579.pd

Comparison of Theoretical Starburst Photoionisation Models for Optical Diagnostics

We study and compare different examples of stellar evolutionary synthesis input parameters used to produce photoionisation model grids using the MAPPINGS V modelling code. The aim of this study is to (a) explore the systematic effects of various stellar evolutionary synthesis model parameters on the interpretation of emission lines in optical strong-line diagnostic diagrams, (b) characterise the combination of parameters able to reproduce the spread of local galaxies located in the star-forming region in the Sloan Digital Sky Survey, and (c) investigate the emission from extremely metal-poor galaxies using photoionisation models. We explore and compare the stellar input ionising spectrum (stellar population synthesis code [Starburst99, SLUG, BPASS], stellar evolutionary tracks, stellar atmospheres, star-formation history, sampling of the initial mass function) as well as parameters intrinsic to the H II region (metallicity, ionisation parameter, pressure, H II region boundedness). We also perform a comparison of the photoionisation codes MAPPINGS and CLOUDY. On the variations in the ionising spectrum model parameters, we find that the differences in strong emission-line ratios between varying models for a given input model parameter are small, on average ~0.1 dex. An average difference of ~0.1 dex in emission-line ratio is also found between models produced with MAPPINGS and CLOUDY. Large differences between the emission-line ratios are found when comparing intrinsic H II region parameters. We find that low-metallicity galaxies are better explained by a density-bounded H II region and higher pressures better encompass the spread of galaxies at high redshift.Comment: 33 pages, 26 figures, accepted for publication in Ap

Dobrushin-Kotecky-Shlosman theorem for polygonal Markov fields in the plane

We consider the so-called length-interacting Arak-Surgailis polygonal Markov fields with V-shaped nodes - a continuum and isometry invariant process in the plane sharing a number of properties with the two-dimensional Ising model. For these polygonal fields we establish a low-temperature phase separation theorem in the spirit of the Dobrushin-Kotecky-Shlosman theory, with the corresponding Wulff shape deteremined to be a disk due to the rotation invariant nature of the considered model. As an important tool replacing the classical cluster expansion techniques and very well suited for our geometric setting we use a graphical construction built on contour birth and death process, following the ideas of Fernandez, Ferrari and Garcia.Comment: 59 pages, new version revised according to the referee's suggestions and now publishe