342 research outputs found
Ion beam modification of the Ni-Si solid-phase reaction: The influence of substrate damage and nitrogen impurities introduced by ion implantation
No full textsponsorship: The authors are grateful to the FWO Vlaanderen (G.0 761.12 N), the KU Leuven BOF (GOA/14/007 and C14/18/074) and the Bilateral Cooperation between Flanders and South Africa, and the National Research Foundation of South Africa (UID 85498) for providing financial support. We acknowledge the SOLEIL Synchrotron for provision of synchrotron radiation facilities and beamtime. (FWO Vlaanderen|G.0 761.12 N, KU Leuven BOF|GOA/14/007, KU Leuven BOF|C14/18/074, Bilateral Cooperation between Flanders and South Africa, National Research Foundation of South Africa|UID 85498)status: Publishe
Interaction of germanium with platinum group metals in lateral diffusion couples
No full textExisting materials and technologies in the semiconductor industry are approaching their physical limits as device sizes decrease significantly below 100 nm. The challenges of achieving the required lateral abruptness of semiconductor junctions and low junction leakage as well as low contact resistance require a careful rebuilding of the fundamental physics and materials platform on which to base a reliable manufacturing capability. As feature size continues to decrease, interconnects will also pose increasingly difficult challenges in terms of physics and materials. The study of lateral diffusion couples is particularly well suited for dealing with the above concerns. This thesis looks at metal-germanium systems of the Platinum Group Metals (PG Ms). It is of particular relevance to study possible applications of PG Ms in South Africa, the country being one of the major producers of these metals in the world today. The diffusion lengths in standard thin-film couples range from a few angstroms to several thousand angstroms. In lateral diffusion couples, phase formation could extend to lengths of around 100 µm. Solid-state interactions in both thin-film and bulk diffusion couples can therefore be investigated using lateral diffusion couples. In particular the transition between the two types of interactions can be studied
Growth, Structure and Prediction of the Thermal Internal Boundary Layer
No full textThe Thermal internal Boundary Layer (TIBL) is a dynamic and turbulent mesoscale feature of the coastal atmosphere that forms over the land during conditions of onshore flow. The TIBL develops as an adjustment of the atmospheric boundary layer to the discontinuities of temperature and roughness that occur at the interface between the underlying marine and terrestrial surfaces. The resulting formation of a characteristically convex mixed layer below relatively stable air aloft has serious implications for the dispersion of pollutants in shoreline environments. Although a wide range of research relating to various features of the TIBL may be found in the literature, relatively few broadly-based studies have been performed. This study has employed both airborne and surface measurements to obtain a comprehensive spatial and temporal data set, in order to elucidate aspects of the characteristic structure and behaviour of the TIBL. TIBL growth was found to follow a diurnal pattern, the initially irregular boundary becoming more uniform during the day as a steady balance between various factors was achieved. The TIBL was associated with a layer of uniform wind speed anti direction flowing perpendicular to the coastline, within which warmer temperatures and changes in relative humidity and moisture content were observed. The temperature structure of the onshore flow strongly influenced the intensity of turbulence encountered in the TIBL and the degree of entrainment aloft. Patterns of turbulent properties displayed significant increases in the TIBL, which were relatively abrupt near the surface and more gradual towards the top of the TIBL. Measurements of sensible heat flux revealed strong undulations in TIBL structure due to transitory eddies and thermal upcurrents. Certain theoretically based predictive equations of TIBL height displayed the best overall performance out of eight selected models, and some promise was shown by an empirical formulation. TIBL development was generally complex and irregular within the first few kilometres of the shore, while further inland more regular TIBL formation enabled the relatively accurate observation and prediction of TIBL height
On the scope of the referential hierarchy in the typology of grammatical relations
No full textIn the late seventies, Bernard Comrie was one of the first linguists to explore the effects of the referential hierarchy (RH) on the distribution of grammatical relations (GRs). The referential hierarchy is also known in the literature as the animacy, empathy or indexibability hierarchy and ranks speech act participants (i.e. first and second person) above third persons, animates above inanimates, or more topical referents above less topical referents. Depending on the language, the hierarchy is sometimes extended by analogy to rankings of possessors above possessees, singulars above plurals, or other notions. In his 1981 textbook, Comrie analyzed RH effects as explaining (a) differential case (or adposition) marking of transitive subject ("A") noun phrases in low RH positions (e.g. inanimate or third person) and of object ("P") noun phrases in high RH positions (e.g. animate or first or second person), and (b) hierarchical verb agreement coupled with a direct vs. inverse distinction, as in Algonquian (Comrie 1981: Chapter 6)
Cloning and expression of two isoforms of guanylate cyclase C (GC-C) from the European eel (Anguilla anguilla)
No full textComplementary DNA fragments for two isoforms of particulate guanylate cyclase C (GC-C) were cloned from the intestine of the European eel (Anguilla anguilla). Both isoforms exhibited higher nucleotide and amino acid sequence homologies to members of the GC-C family from other species than the related guanylate cyclase A or B (GC-A or GC-B) isoforms from the eel. Northern blots indicated that probes for both isoforms, termed GC-C1 and GC-C2, selectively hybridised to 4.8-kb transcripts in the intestine and the kidney. Expression of the GC-C2 transcript in the intestine was increased by 100% following the transfer of yellow FW-acclimated eels to SW. Likewise developmental maturation of yellow eels into pre-migratory silver eels resulted in a significant increase (60%) in the intestinal expression of GC-C2. No changes in expression of GC-C2 were seen in the kidney under any condition. RT-PCR indicated that the GC-C2 isoform is only expressed in anterior and mid-gut segments in FW-acclimated yellow eels. However, expression is also extended to the posterior gut segment when yellow eels are acclimated to SW or following developmental transformation into silver eels. (C) 2001 Elsevier Science Inc. All rights reserved.</p
Solid state diffusion in Pd₂Si
No full textThe atomic transport processes ocurring in the Pd/Si system have been investigated. The Pd₂Si system has been studied to try and establish the mechanism(s) of diffusion by which the growth of Pd₂Si proceeds under thermal annealing. Using a deposited Ti marker, the dominant moving species during Pd₂Si formation in the temperature range 250-400°C has been determined to be silicon. Palladium transport appears to occur during the initial stages of formation of Pd₂Si. Once several hundred angstrom of Pd₂Si has been formed, palladium transport seems to be replaced by silicon transport. Silicon tracer experiments, in conjunction with Si selfdiffusion measurements. indicate that silicon mobility is exceptionally high during the formation of Pd₂Si on Si substrate. During growth. the mobility of silicon is orders of magnitude higher than under equilibrium conditions. This is thought to suggest a vacancy mechanism of diffusion, and is expected that large numbers of vacancies are generated at the growth interface during silicide formation. Silicon self-diffusion in Pd₂Si has been investigated. The results indicate that grain-boundary diffusion could be operative under equilibrium conditions. Under the assumption that grain-boundary diffusion does occur during thermal annealing in the range 350-550°C, it is deduced that at all times the grain-boundary diffusivity is so much greater than the lattice diffusivity, that the grain-boundaries are effectively able to act as sources for the grains. The activation energy for lattice self-diffusion of silicon in Pd₂Si which has grown on Si substrate, has been determined to be 0.8±0.3eV. This value is thought to support recent kinetic results which indicate that the activation energy for growth of Pd₂Si is in the region of 1eV
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Mapping a Wind–Modified Urban Heat Island in Tucson, Arizona (with Comments on Integrating Research and Undergraduate Learning)
No full textTucson, Arizona, is an example of the many cities in the southwestern United States experiencing rapid growth and urban sprawl over the last several decades. The accompanying extensive modification of land use and land cover leads to many environmental impacts, including urban heat islands. The primary aim of this paper is to expand knowledge of the phenomenon for Tucson, by quantifying the amount of urban warming, and by mapping temperature patterns over the city and examining related aspects of the local-scale atmospheric circulation. The secondary aim is to document how an applied empirical research project was integrated into an introductory undergraduate climatology class via active learning. The paper begins and concludes with general and practical comments on combining the research and educational aspects of the project. An analysis of 30-yr temporal trends in urban and nonurban minimum temperatures across the region shows the rate of urban warming to be about three-quarters of the general regional warming. Tucson's urban heat island is ~3°C over the last century, with >2°C of this warming in the last 30 years. The annual average urban warming trend over the last three decades is 0.071°C y r 1 with the strongest effect in March and the weakest effect in November. There is evidence that the latter is caused by strong, near-surface winds under stable conditions. A case study is presented comprising field measurements and map analysis of urban temperatures and supporting variables for 13 February 1999. Measurements include comprehensive mapping using vehicle-mounted thermistors and numerous local meteorological observations from around the city. Wind speeds during the field measurements were somewhat stronger than is typical of heat island studies, up to 12 m s_ 1 . Nonetheless, because of terrain-induced flows and land surface heterogeneity, complex temperature patterns were observed. Several transient katabatic flows off surrounding mountain ranges were detected, leading to localized cold pockets. Locally warm areas in other parts of the city are associated with terrain sheltering or local land surface heating. The central city showed a possible urban heating pattern with temperatures ~2°C higher than upwind rural air.6 month embargoThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
The formation of epitaxially stabilized nickel and cobalt silicides by pulsed laser annealing
No full textBibliography: leaves 56-58.The formation of epitaxially stabilised nickel and cobalt silicides by pulsed laser annealing has been investigated. Thermally grown NiSi and CoSi and Si substrate were irradiated with laser pulses in the energy density range between 0.4 - 1.0 J/cm² in an attempt to produce epitaxially stabilized silicides. The analysis was carried out using well established RBS and channelling techniques. In the bulk form, and in thin films, NiSi has an orthorhombic MnP crystal structure and cannot grow epitaxially on the cubic silicon substrate and channelling is nto observed in the silicides thus prepared. Since NiSi melts at a temperature 400°C below silicon, it is possible to melt the whole NiSi film without melting the substrate. The presence of channelling in the NiSi film observed after laser annealing at lower energy densities was an indication that complete melting of the film had occured allowing for re-ordering of atoms in the melt
The effects of annealing on phase transformation in platinum-molybdenum coatings
No full textIncludes bibliographical references.The thermodynamic study of platinum binary systems has both fundamental and applied aspects. It is due to the fact that the formation of ordered phases increases the strength and surface hardness and could also have an impact on surface activity and chemical properties. The changes in mechanical, physical and chemical properties could be of significant importance in enhancing the performance of platinum-based systems in their respective applications, such as gas sensors, catalyst, fuel cells and superconductors. In this investigation, the phase transformation in Pt-Mo coated systems induced by thermal annealing was studied by X-ray diffraction, scanning electron microscope, transmission electron microscope, energy dispersive X-ray emission and Rutherford backscattering spectrometry. The phase analysis showed the presence of several intermetalic phases, Pt2Mo, PtMo and Pt2Mo3 which were observed to nucleate in sequence when the annealing time and temperature were extended. RBS analysis showed an increase in coating thickness after annealing which has been attributed to the formation of the Pt-Mo phases
Cloning and expression of guanylin and guanylate cyclase-C in the European eel, Anguilla anguilla
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