Muonium as a shallow center in GaN

A paramagnetic muonium (Mu) state with an extremely small hyperfine parameter was observed for the first time in single-crystalline GaN below 25 K. It has a highly anisotropic hyperfine structure with axial symmetry along the [0001] direction, suggesting that it is located either at a nitrogen-antibonding or a bond-centered site oriented parallel to the c-axis. Its small ionization energy (=< 14 meV) and small hyperfine parameter (--10^{-4} times the vacuum value) indicate that muonium in one of its possible sites produces a shallow state, raising the possibility that the analogous hydrogen center could be a source of n-type conductivity in as-grown GaN.Comment: 4 figures, to be published in Phys. Rev. Letter

A REVIEW OF GEOMETRIC MODELS AND SELF-CALIBRATION METHODS FOR TERRESTRIAL LASER SCANNERS

Terrestrial laser scanning has been shown to be an invaluable technology for engineering measurement applications such as structural deformation measurement and rockfall monitoring. In order to ensure the quality of the data captured for these and other applications, all systematic instrument errors must be properly modelled, calibrated and corrected prior to using the data in subsequent stability or deformation analyses. In one popular modelling approach, the range and angular observations from a laser scanner are augmented with additive model terms that describe the systematic errors. Self-calibration methods can then be used in order to estimate the coefficients of these models. This paper provides a review of the current state-of-the-art of terrestrial laser scanner systematic error models and self-calibration methods, supported by real-dataset examples that demonstrate the need for these processes

Requiem for a Heavyweight

Homily at the funeral of Garry McCarthy CSSp, Gerald Fitzgerald CSSpFr. Mac, Sister kathleen Lichti CS

Gamma-Ray Burst Detection with INTEGRAL/SPI

The spectrometer SPI, one of the two main instruments of the INTEGRAL spacecraft, has strong capabilities in the Field of Gamma-Ray Burst (GRB) detections. In its 16 degree Field of view (FoV) SPI is able to trigger and to localize GRBs. With its large anticoincidence shield (ACS) of 512 kg of BGO crystals SPI is able to detect GRBs quasi omnidirectionally with a very high sensitivity. The ACS GRB alerts will provide GRB arrival times with high accuracy but with no or very rough positional information. The expected GRB detection rate in SPI's FoV will be one per month and for the ACS around 300 per year. At MPE two SPI software contributions to the real-time INTEGRAL burst-alert system (IBAS) at the INTEGRAL science data centre ISDC have been developed. The SPI-ACS branch of IBAS will produce burst alerts and light-curves with 50 ms resolution. It is planned to use ACS burst alerts in the 3rd interplanetary network. The SPI-FoV branch of IBAS is currently under development at MPE. The system is using the energy and timing information of single and multiple events detected by the Germanium-camera of SPI. Using the imaging algorithm developed at the University of Birmingham the system is expected to locate strong bursts with an accuracy of better than 1 degree.Comment: 11 pages, 5 figure

Automated Calibration of Mobile Cameras for 3D Reconstruction of Mechanical Pipes

This manuscript provides a new framework for calibration of optical instruments, in particular mobile cameras, using large-scale circular black and white target fields. New methods were introduced for (i) matching targets between images; (ii) adjusting the systematic eccentricity error of target centers; and (iii) iteratively improving the calibration solution through a free-network self-calibrating bundle adjustment. It was observed that the proposed target matching effectively matched circular targets in 270 mobile phone images from a complete calibration laboratory with robustness to Type II errors. The proposed eccentricity adjustment, which requires only camera projective matrices from two views, behaved synonymous to available closed-form solutions, which require several additional object space target information a priori. Finally, specifically for the case of the mobile devices, the calibration parameters obtained using our framework was found superior compared to in-situ calibration for estimating the 3D reconstructed radius of a mechanical pipe (approximately 45% improvement)

Robust Detection of Non-overlapping Ellipses from Points with Applications to Circular Target Extraction in Images and Cylinder Detection in Point Clouds

This manuscript provides a collection of new methods for the automated detection of non-overlapping ellipses from edge points. The methods introduce new developments in: (i) robust Monte Carlo-based ellipse fitting to 2-dimensional (2D) points in the presence of outliers; (ii) detection of non-overlapping ellipse from 2D edge points; and (iii) extraction of cylinder from 3D point clouds. The proposed methods were thoroughly compared with established state-of-the-art methods, using simulated and real-world datasets, through the design of four sets of original experiments. It was found that the proposed robust ellipse detection was superior to four reliable robust methods, including the popular least median of squares, in both simulated and real-world datasets. The proposed process for detecting non-overlapping ellipses achieved F-measure of 99.3% on real images, compared to F-measures of 42.4%, 65.6%, and 59.2%, obtained using the methods of Fornaciari, Patraucean, and Panagiotakis, respectively. The proposed cylinder extraction method identified all detectable mechanical pipes in two real-world point clouds, obtained under laboratory, and industrial construction site conditions. The results of this investigation show promise for the application of the proposed methods for automatic extraction of circular targets from images and pipes from point clouds

Fitting gravimetric geoid models to vertical deflections

Regional gravimetric geoid and quasigeoid models are now commonly fitted to GPS-levelling data, which simultaneously absorbs levelling, GPS and quasi/geoid errors due to their inseparability. We propose that independent vertical deflections are used instead, which are not affected by this inseparability problem. The formulation is set out for geoid slopes and changes in slopes. Application to 1080 astrogeodetic deflections over Australia for the AUSGeoid98 model shows that it is feasible, but the poor quality of the historical astrogeodetic deflections led to some unrealistic values

New Confocal Hyperbola-based Ellipse Fitting with Applications to Estimating Parameters of Mechanical Pipes from Point Clouds

This manuscript presents a new method for fitting ellipses to two-dimensional data using the confocal hyperbola approximation to the geometric distance of points to ellipses. The proposed method was evaluated and compared to established methods on simulated and real-world datasets. First, it was revealed that the confocal hyperbola distance considerably outperforms other distance approximations such as algebraic and Sampson. Next, the proposed ellipse fitting method was compared with five reliable and established methods proposed by Halir, Taubin, Kanatani, Ahn and Szpak. The performance of each method as a function of rotation, aspect ratio, noise, and arc-length were examined. It was observed that the proposed ellipse fitting method achieved almost identical results (and in some cases better) than the gold standard geometric method of Ahn and outperformed the remaining methods in all simulation experiments. Finally, the proposed method outperformed the considered ellipse fitting methods in estimating the geometric parameters of cylindrical mechanical pipes from point clouds. The results of the experiments show that the confocal hyperbola is an excellent approximation to the true geometric distance and produces reliable and accurate ellipse fitting in practical settings

Regulation of the Pregnane X Receptor Signaling Pathway

Liver-enriched nuclear receptors (NRs) collectively function as metabolic and toxicological `sensors' that mediate liver-specific gene-activation in mammals. NR-mediated gene-environment interaction regulates important steps in the hepatic uptake, metabolism and excretion of glucose, fatty acids, lipoproteins, cholesterol, bile acids, and xenobiotics. While it is well-recognized that ligand-binding is the primary mechanism behind activation of NRs, recent research is revealing that multiple signal transduction pathways modulate NR-function in liver. The interface between specific signal transduction pathways and NRs helps to determine their overall responsiveness to various environmental and physiological stimuli. The pregnane x receptor (PXR, NR1I2) was identified in 1998 as a member of the NR superfamily of ligand-activated transcription factors. PXR is activated by a broad range of lipophilic compounds in a species-specific manner. The primary function ascribed to PXR is the homeostatic control of steroids, bile acids, and xenobiotics. This function is mediated through PXR's ability to coordinately activate gene expression and regulate the subsequent activity of phase I and phase II metabolic enzymes, as well as several membrane transporter proteins. While PXR likely evolved primarily to protect the liver from toxic assault, its activation also represents the molecular basis for an important class of drug-drug, herb-drug, and food-drug interactions. While ligand binding is the primary mode of PXR activation, several signal transduction pathways interface with the PXR protein to determine its overall responsiveness to environmental stimuli. Multiple signaling pathways modulate the activity of PXR, likely through direct alteration of the phosphorylation status of the receptor and its protein cofactors. Therefore, specific combinations of ligand binding and cell signaling pathways affect PXR-mediated gene activation and determine the overall biological response. This dissertation contributes to the molecular understanding of the regulation of PXR by novel agonists, cAMP-dependent protein kinase (PKA) signaling, and phosphorylation. The results presented here were primarily obtained from mouse and tissue culture systems. This dissertation identifies Tian Xian, a traditional Chinese herbal anti-cancer remedy, as a novel PXR activator. This evidence suggests that Tian Xian should be used cautiously by cancer patients taking chemotherapy due to its potential to increase the metabolism of co-administered medications. In addition, data presented here show that activation of PKA signaling modulates PXR activity in a species-specific manner. It is further revealed that PXR exists as phospho-protein in vivo and that the activation of PKA signaling modulates the phospho-threonine status of PXR. Finally, the potential phosphorylation sites within the PXR protein are identified. These phosphorylation sites are characterized, using a phosphomimetic and phospho-deficient site-directed mutagenesis based approach, based on their ability to modulate PXR activity. Taken together, the work presented in this dissertation contributes to understanding the interface between ligands, signal transduction pathways and PXR activity, which is critical for the development of safe and effective therapeutic strategies