The structures of four compounds representing each of the organic (natural product), inorganic and organometallic classes of compounds have been determined by single-crystal X-ray diffraction, and the methods employed in solution of the structures have been discussed briefly. For all four structures, the intensity data were collected on a single-crystal diffractometer with [formula omitted] radiation and a scintillation counter. The structure of the alkaloid, daphmacrine methiodide (acetone solvate), was determined from heavy-atom Patterson and Fourier syntheses, and refined by block-diagonal least-squares methods to a final R value of 0.089 for 1834 observed reflections. The absolute configuration was determined by the anomalous dispersion method. The molecule consists of two cage-structures which are linked by a chain of two carbon atoms, and the bond lengths and valency angles do not differ from normal values. 2 4-, For both exo-tricyclo [formula omitted] silver nitrate and silver nitrate itself, the silver ion was determined from Patterson syntheses to be lying in a pseudo-special position, so that the resulting electron-density maps exhibited pseudo-symmetry. A trial-and-error method based on detailed study of the shape of the Ag-Ag Patterson peaks was adopted to find the exact location of the silver ions, and from the resulting electron-density maps the true light atom peaks could be discerned from their images. The refinement was carried out by full-matrix least-squares, and the final R for the complex of silver nitrate was 0.105 and for silver nitrate was 0.067. The structure of the complex consists of thick layers perpendicular to the a crystallographic axis, and separated by ½ a. The silver ion is coordinated roughly tetrahedrally to the double bond of the hydrocarbon (in the exo-position, [formula omitted]), and to three nitrate groups [formula omitted]. The layers are held together by van der Waals forces. The silver nitrate structure consists of layers of silver ions parallel to the b crystallographic axis, and separated by ½ b, with the nitrate groups bridging the gap between layers. Previously observed inequalities in the N—O distances have been removed, all three bond lengths in the nitrate ion being 1.26 (l)Ǻ. The anisotropic thermal motion has been described. The N,N-dimethyl(ferrocenylmethyl)ammonium tetrachlorozincate hydrate structure contains seven heavy atoms, and it was not possible to resolve the Patterson peaks because of the overlap. A direct sign-determining procedure was employed to locate the heavy atoms, and the light atoms were located from resulting electron-density maps. The structure was refined to a final R value of 0.068 for 2012 observed reflections. The mean bond distances are Fe-C = 2. 04Ǻ and C-C (cyclopentadienyl rings) = 1.43Ǻ. Groups of four cations, two anions and two water molecules (two formula units), are linked around centres of symmetry by N-H...Cl (3.11Ǻ), N-H...0 (2.76Ǻ) and 0-H...Cl (3.05, 3.17Ǻ) hydrogen bonds. / Science, Faculty of / Chemistry, Department of / Graduate

Acetyltriphenylgermane, (C₆H₅)₃GeCOCH₃, crystallizes in the monoclinic system with a = 15.30, b = 14.53, c = 7.68Å, and β = 94.8°. The space group is P2₁/c and there are four molecules per unit cell, thus each molecule forms an asymmetric unit in the cell. The intensities of 2537 reflections were measured by means of a scintillation counter using CuKα radiation. The structure was determined by heavy atom Patterson and Fourier synthesis and refinement was by least-squares methods. The final discrepancy, R, for 1834 observed reflections is 0.075. The compound was found to be tetrahedral about the germanium atom, with only small deviations caused by the spreading of the phenyl rings. The phenyl rings are planar with a mean C-C bond distance of 1.383 Å, mean C-C-C bond angle of 120.0°, and a mean C-H bond distance of 1.09 Å. Intermolecular interaction causes one ring to deviate from a symmetric propeller orientation. Two Ge-C bond distances were found: Ge-Cphenyl distance of 1.945 Å and Ge-Cacetyl distance of 2.011 Å. The longer Ge-C bond is attributed to contribution from a resonance structure in which there is no formal bond between germanium and the carbonyl carbon, resulting in a partial negative charge on the oxygen and a partial positive charge on the germanium. This is supported by the electronegativity difference between carbon and germanium. The C=O bond distance is 1.20 Å. / Science, Faculty of / Chemistry, Department of / Graduate

The X-ray emission from a plasma focus has been studied using time integrated and streak photography. The plasma focus, a small volume of very dense and hot plasma was created in a coaxial plasma gun driven by a fast current pulse of period T ~ 2 μsec which was produced by discharging a condensor bank of V = 12-15 kV, and C = 84 μf. Measurements have shown that a diffuse X-ray emitting plasma column is formed in the 'early' pinch stage, which extends a few centimeters in the axial direction, has expansion velocities of between 2-6 x 10⁷ cm/sec. and lasts for 30-60 nsec. In the following 10-30 nsec. X-ray emission occurs from small plasma regions which have little or no axial velocity. The distance between these "hot" spots are of the order of half a centimeter. These measurements and observations of the X-ray emitting regions are consistent with results obtained by Peacock and Mather. By comparing their results with those of this experiment it is concluded that the appearance of the isolated X-ray sources is associated with the m = 0 instability. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Many techniques for measuring neutron star radii rely on absolute flux measurements in the X-rays. As a result, one of the fundamental uncertainties in these spectroscopic measurements arises from the absolute flux calibrations of the detectors being used. Using the stable X-ray burster, GS 1826-238, and its simultaneous observations by Chandra HETG/ACIS-S and RXTE/PCA as well as by XMM-Newton EPIC-pn and RXTE/PCA, we quantify the degree of uncertainty in the flux calibration by assessing the differences between the measured fluxes during bursts. We find that the RXTE/PCA and the Chandra gratings measurements agree with each other within their formal uncertainties, increasing our confidence in these flux measurements. In contrast, XMM-Newton EPIC-pn measures 14.0 +/- 0.3% less flux than the RXTE/PCA. This is consistent with the previously reported discrepancy with the flux measurements of EPIC-pn, compared with EPIC MOS1, MOS2, and ACIS-S detectors. We also show that any intrinsic time-dependent systematic uncertainty that may exist in the calibration of the satellites has already been implicity taken into account in the neutron star radius measurements.

Nanoparticles as novel materials have unique properties due to their incredibly small sizes. Ensembles of nanoparticles not only collect their intrinsic properties but also generate new ones when nanoparticles are sufficiently close. One important way of forming nanostructures entails the assembly of nanoparticle monolayers at liquid interfaces. It is important to understand how the iron oxide nanoparticles transport in a liquid phase and on a liquid/liquid interface and self-assemble into nanostructures over time. As a preliminary research topic before the comprehensive small angle X-ray scattering (SAXS) study, real-time optical reflection of incident p-polarized light near Brewster’s angle shows that after drop-casting iron oxide nanoparticle heptane dispersion on top of a diethylene glycol (DEG) liquid substrate, an iron oxide nanoparticle layer forms at the DEG/heptane interface, and it self-limits to one monolayer even when there are excess nanoparticles dispersed in the upper heptane phase. As is needed for the high time resolution and X-ray exposure minimization requirements of kinetics studies, a new cell with walls at angles is designed to significantly reduce the size of the meniscus, which enables the collection of much larger signals in the SAXS images of ordered arrays of nanoparticles at liquid/air interfaces, along with the observation of extremely high degrees of order. Spatial and temporal SAXS scans show that 8.6 and 11.8 nm iron oxide nanoparticles in heptane drop-cast on top of a heptane layer atop a DEG layer are trapped at the DEG/heptane interface to generally form a single ordered, hexagonally close-packed monolayer, and this occurs long before the heptane evaporates. The morphology of the monolayer is independent of the number of nanoparticles used in the formation process. Many nanoparticles remain dispersed in the heptane after this nanoparticle assembly. Assembly occurs faster than expected from considering only the diffusion of nanoparticles from the drop-cast site to this liquid/liquid interface. And, on the same time scale there is a concomitant decrease in the SAXS form factor from disordered nanoparticles. X-ray beam transmission at different vertical heights characterizes the heptane and DEG bulk and interfacial regions, while monitoring the time dependence of SAXS at and near the DEG/heptane interface gives a clear picture of the evolution of nanoparticle assembly at this liquid/liquid interface. These SAXS observations of self-limited nanoparticle monolayer formation at the DEG/heptane interface are consistent with those using the less direct method of real-time optical reflection monitoring of that interface.

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No / Although the study of palaeopathology is less developed for avian bones than for human or other vertebrate remains, skeletal pathologies have been noted in the bones of a range of bird species of all periods, from many parts of the world. Such studies make use of x-radiographs as an aid to differential diagnosis, to image features of the pathology that may not be apparent to the unassisted eye. Bird bones are often thin yet highly mineralised, and offer a particular challenge to the radiographer. Conventional medical or veterinary radiographic techniques are not optimal for ancient material, yet are commonly applied. Here we show that the quality of the x-ray image can be greatly enhanced by applying quite simple techniques. Furthermore, digitisation of the x-radiograph allows commercially available image manipulation software to be used to add further enhancement and to explore specific details of the image. We demonstrate the use of these techniques in the investigation of a number of avian palaeopathology specimens.