Radio and Microwave Spectroscopy of Some Complexes of Vanadium, Niobium and Tantalum

The thesis is subdivided into five main parts, which are summarised separately below. Part I This first part of the thesis is introductory in nature. The basic magnetic and electrostatic interactions which are of importance in understanding the form of electron paramagnetic resonance and nuclear quadrupole resonance spectra are discussed with particular reference to transition metal complexes of the type studied in this work. The way in which these spectra can be interpreted to obtain information about various aspects of the electronic structures of transition metal complexes is also discussed, and finally the spectrometers used in carrying out this work are described briefly. Part II This section describes a study of some oxovanadium (IV) chelates and their adducts with ethanol and pyridine. The X-band epr spectra of some five- and six-membered ring chelates 2+ of the VO2+ ion have been recorded in solution at room temperature and in magnetically dilute glasses at 77K. This study indicates that the chelates form adducts with pyridine and with ethanol, and that they are readily oxidised, especially in hydroxylic solvents, to oxovanadium (V) complexes. The oxidation may be reversible in some cases. A method is described for deriving very accurate values of the spin Hamiltonian parameters from glassy spectra of these complexes, which have effective C2v symmetry, and the parameters which were derived in this way are listed, together with the band maxima in the visible-u. v. spectra of the complexes. The spin Hamiltonian parameters are equated to the atomic orbital coefficients in some of the molecular orbitals involved in the bonding in the complexes, and it is thereby shown that whereas the in-plane d-bonding in the complexes is fairly covalent, the delocalisation of the unpaired electron onto the ligands via in-plane pi -bonding is very slight. The weak C2v component of the ligand field in these complexes mixes a small amount of 3dz2 and 4s orbital character into the 3d x2-y2 orbital which contains the unpaired electron, and the magnetic resonance data is used to estimate the extent of this mixing. Mixing 3d z2 character into the orbital containing the unpaired electron accounts for the in-plane anisotropy of the g- and hyperfine tensor components. Mixing in 4s character accounts for characteristic differences between the hyperfine tensor components observed for the five- and six-membered ring chelates, and for the differences in the changes which occur in these when additional complexing with solvent molecules takes place. The principal values of the hyperfine tensor components and the isotropic contribution to hyperfine coupling can be used to distinguish between five- and six-membered ring chelates. Part III This section describes a study of the complexes (pi-C5-H5)2 MX2 where M = vanadium (IV), niobium (IV) or tantalum (IV) and X = Cl-, SCN-, OCN-, CN- or -C5H5-. The epr spectra of these compounds have been recorded at room temperature and in magnetically dilute glasses at 77K; and these spectra have been analysed in detail. From Huckel L.C.A.O. molecular orbital calculations carried out on the complex (pi-C5H5)2 VCl2, the metal ion spin-orbit coupling constants Sv and S Nb in these complexes are estimated to be 133 cm-1 and 490 cm-1 respectively. Spin Hamiltonian parameters are listed for each substance, and are equated to the atomic orbital coefficients in some of the molecular orbitals involved in bonding in these complexes, and good agreement is obtained between the values derived in this way and those derived from the molecular orbital calculations. Except for the cyanides, in each case the unpaired electron lies essentially in a non-bonding nd z2 metal ion orbital, mixed with a small amount of the corresponding metal ion nd x2-y orbital, the Z-axis coinciding with the C2 axis of the compound; in the cyanides the unpaired electron is delocalised into px orbitals on the ligands. The bonding of the metal ion to the cyclopentadienide rings and to the other ligands X is almost completely covalent, the bonding to the cyclopentalienide rings being stronger than that to the ligands X. Several redistribution complexes of the type (pi-C5H5)2 MXY have also been detected and characterised by their epr spectre. epr techniques can be used to distinguish compounds of the type (pi-C5H5)2 MX2 from other compounds which contain vanadium (IV) and niobium (IV). The difference between the epr spectra arising from complexes containing tantalum (IV) and those containing vanadium (IV) or niobium (IV) may be due to the presence of a large quadrupolar interaction in the tantalum complexes. Part IV This section deals with a detailed study of the linewidths in the epr spectra of solutions of the complexes (pi-C5H5)2 VCl2, (pi-C5H5)2 NbCl2 and (pi-C5H5)2 Nb(pi-C5H5)2 as a function of temperature. In the case of the complexes (pi-C5H5)2 VCl2 and (pi-C5H5)2 NbCl2 these studies have been used to estimate the size of the proton and chlorine nuclear hyperfine coupling constants in these complexes, and hence to estimate the extent to which the unpaired electron in the complexes is delocalised on to the ligands. (Abstract shortened by ProQuest.)

Foliar Micronutrient Application for High-Yield Maize

Nebraska soils are generally micronutrient sufficient. However, critical levels for current yields have not been validated. From 2013 to 2015, 26 on-farm paired comparison strip-trials were conducted across Nebraska to test the effect of foliar-applied micronutrients on maize (Zea mays L.) yield and foliar nutrient concentrations. Treatments were applied from V6 to V14 at sites with 10.9 to 16.4 Mg ha−1 yield. Soils ranged from silty clays to fine sands. Soil micronutrient availability and tissue concentrations were all above critical levels for deficiency. Significant grain yield increases were few. Micronutrient concentrations for leaf growth that occurred after foliar applications were increased 4 to 9 mg Zn kg−1 at 5 of 17 sites with application of 87 to 119 g Zn ha−1, 12 to 16 mg kg−1 Mn at 2 of 17 sites with application of 87 to 89 g Mn ha−1, and an average of 8.1 mg kg−1 Fe across 10 sites showing signs of Fe deficiency with application of 123 g foliar Fe ha-1. Foliar B concentration was not affected by B application. Increases in nutrient concentrations were not related to grain yield responses except for Mn (r = 0.54). The mean, significant grain yield response to 123 g foliar Fe ha−1 was 0.4 Mg ha−1 for the 10 sites with Fe deficiency symptoms. On average, maize yield response to foliar Fe application can be profitable if Fe deficiency symptoms are observed. Response to other foliar micronutrient applications is not likely to be profitable without solid evidence of a nutrient deficiency

Effect of potassium nitrate intake on lactating dairy cows

A report on Department of Dairy Husbandry Research Project 55, Diet and Growth--p. [2].Digitized 2007 AES

The reaction of formic acid with RaneyTM copper

The interaction of formic acid with RaneyTM Cu proves to be complex. Rather than the expected generation of a monolayer of bidentate formate, we find the formation of a Cu(II) compound. This process occurs by direct reaction of copper and formic acid; in contrast, previous methods are by solution reaction. This is a rare example of formic acid acting as an oxidant rather than, as more commonly found, a reductant. The combination of diffraction, spectroscopic and computational methods has allowed this unexpected process to be characterized

Starlight Demonstration of the Dragonfly Instrument: an Integrated Photonic Pupil Remapping Interferometer for High Contrast Imaging

In the two decades since the first extra-solar planet was discovered, the detection and characterization of extra-solar planets has become one of the key endeavors in all of modern science. Recently direct detection techniques such as interferometry or coronography have received growing attention because they reveal the population of exoplanets inaccessible to Doppler or transit techniques, and moreover they allow the faint signal from the planet itself to be investigated. Next-generation stellar interferometers are increasingly incorporating photonic technologies due to the increase in fidelity of the data generated. Here, we report the design, construction and commissioning of a new high contrast imager; the integrated pupil-remapping interferometer; an instrument we expect will find application in the detection of young faint companions in the nearest star-forming regions. The laboratory characterisation of the instrument demonstrated high visibility fringes on all interferometer baselines in addition to stable closure phase signals. We also report the first successful on-sky experiments with the prototype instrument at the 3.9-m Anglo-Australian Telescope. Performance metrics recovered were consistent with ideal device behaviour after accounting for expected levels of decoherence and signal loss from the uncompensated seeing. The prospect of complete Fourier-coverage coupled with the current performance metrics means that this photonically-enhanced instrument is well positioned to contribute to the science of high contrast companions.Comment: 10 pages, 7 figures, accepted to Mon. Not. of Roy. Ast. Soc., 201

Education Deans: Challenges and Stress

Abstract: This study explored issues facing deans within higher education, specifically deans of doctoral granting schools/colleges of education. The study explored key challenges/issues and related stress education deans experience at research universities

Nitrogen response functions targeted to technology extrapolation domains in Ethiopia using CERES-maize

The profitability of fertilizer-N use can be optimized using N response functions specific to climate-based technology extrapolation domains (TED). Crop growth simulation can complement field research for targeting of response functions. The objective of this study was to target maize (Zea mays L.) N response functions to seven TED in Ethiopia through CERES-Maize simulation of continuous maize over 30 yr. The complete factorial set of treatments included seven levels of N in 25 kg ha−1 increments under no-till (NT) and conventional tillage (CT) systems. The CERES-Maize simulated experiments were done for two or three sites per TED. Nitrogen response functions were generated for each TED with tillage-specific functions for three TED with tillage × N interactions. The N rate responses for all TED fit curvilinear to plateau functions but with differing magnitudes and shapes of response. The mean yield with NT was 6% less than with CT, but the difference declined with increased N rate. The economically optimum N rate (EONR) ranged from 65 to 179 and 103 to 243 kg ha−1 for high and low-cost fertilizer-N, respectively. The EONR was 6% less and the profit cost ratio was 11% higher with CT compared to NT, indicating greater fertilizer-N need with NT than with CT. The application of N for maize was highly profitable for all TED. The EONR from CERES-Maize were higher than past field research results. This suggests that the CERES-Maize N response functions were most appropriate for well-managed crop production situations in Ethiopia

Adsorption of formate species on Cu(h,k,l) low index surfaces

We report a density functional theory study on the relative stability of formate species on Cu(h,k,l) low index surfaces using a range of exchange-correlation functionals. We find that these functionals predict similar geometries for the formate molecule adsorbed on the Cu surface. A comparison of the calculated vibrational transition energies of a perpendicular configuration of formate on Cu surface shows an excellent agreement with the experimental spectrum obtained from inelastic neutron spectroscopy. From the calculations on adsorption energy we find that formate is most stable on the Cu(110) surface as compared to Cu(111) and Cu(100) surfaces. Bader analysis shows that this feature could be related to the higher charge transfer from the Cu(110) surface and optimum charge density at the interfacial region due to bidirectional electron transfer between the formate and the Cu surface. Analysis of the partial density of states finds that in the –5.5 eV to –4.0 eV region, hybridization between O p and the non-axial Cu dyz and dxz orbitals takes place on the Cu(110) surface, which is energetically more favourable than on the other surfaces

X-ray behaviour of Circinus X-1 - I: X-ray Dips as a diagnostic of periodic behaviour

We examine the periodic nature of detailed structure (particularly dips) in the RXTE/ASM lightcurve of Circinus X-1. The significant phase wandering of the X-ray maxima suggests their identification with the response on a viscous timescale of the accretion disk to perturbation. We find that the X-ray dips provide a more accurate system clock than the maxima, and thus use these as indicators of the times of periastron passage. We fit a quadratic ephemeris to these dips, and find its predictive power for the X-ray lightcurve to be superior to ephemerides based on the radio flares and the full archival X-ray lightcurve. Under the hypothesis that the dips are tracers of the mass transfer rate from the donor, we use their occurrence rate as a function of orbital phase to explore the (as yet unconstrained) nature of the donor. The high $\dot{P}$ term in the ephemeris provides another piece of evidence that Cir X-1 is in a state of dynamical evolution, and thus is a very young post-supernova system. We further suggest that the radio ``synchrotron nebula'' immediately surrounding Cir X-1 is in fact the remnant of the event that created the compact object, and discuss briefly the evidence for and against such an interpretation.Comment: 11 pages, 11 figures, accepted for publication in MNRA

Fishes of the Choctawhatchee River System in Southeastern Alabama and Northcentral Florida

The diversity and distribution of fish species occurring in the Choctawhatchee River drainage in southeastern Alabama and northcentral Florida were surveyed to obtain historical baseline information. Three hundred seventy-four sites were evaluated for species diversity and distribution in the drainage, including compilation of unpublished records from southeastern natural history museums. The greatest diversity at any single site was 37 species. Sixty-eight sites were represented by 15 species or more, and 26 sites were represented by a single species. The most frequently encountered species includes Gambusia holbrooki, Percina nigrofasciata, Esox americanus, Notropis texanus, Lepomis macrochirus, Cyprinella n. sp. cf venusta, Notropis amplamala, and Aphredoderus sayanus. New records for Hybopsis n. sp. cf winchelli and Etheostoma parvipinne were found in the drainage, and range extensions were found for 14 other species. Our study increases the known number of fish species in the Choctawhatchee River drainage to 132 species and two hybrids, including 83 native freshwater, 10 introduced freshwater, 24 estuarine, and 17 marine species