Approximating Cross-validatory Predictive P-values with Integrated IS for Disease Mapping Models

An important statistical task in disease mapping problems is to identify out- lier/divergent regions with unusually high or low residual risk of disease. Leave-one-out cross-validatory (LOOCV) model assessment is a gold standard for computing predictive p-value that can flag such outliers. However, actual LOOCV is time-consuming because one needs to re-simulate a Markov chain for each posterior distribution in which an observation is held out as a test case. This paper introduces a new method, called iIS, for approximating LOOCV with only Markov chain samples simulated from a posterior based on a full data set. iIS is based on importance sampling (IS). iIS integrates the p-value and the likelihood of the test observation with respect to the distribution of the latent variable without reference to the actual observation. The predictive p-values computed with iIS can be proved to be equivalent to the LOOCV predictive p-values, following the general theory for IS. We com- pare iIS and other three existing methods in the literature with a lip cancer dataset collected in Scotland. Our empirical results show that iIS provides predictive p-values that are al- most identical to the actual LOOCV predictive p-values and outperforms the existing three methods, including the recently proposed ghosting method by Marshall and Spiegelhalter (2007).Comment: 21 page

Vortex melting and decoupling transitions in YBa2_{2}Cu4_{4}O8_{8} single crystals

The vortex correlation along the c-axis in high quality single crystals of YBa$_{2}$Cu$_{4}$O$_{8}$ has been investigated as a function of temperature T in different magnetic fields, using the quasi-flux transformer configuration. A simultaneous sharp drop associated with the vortex lattice melting is observed in both the primary and secondary voltages(V$_{top}$ and V$_{bot}$). Just above the melting temperature, the vortices form three-dimensional line liquid with the correlation length along the c direction $L_{c}\leq$ t, the sample thickness. The temperature where a resistive peak in R$_{bot}$ develops corresponds to the decoupling temperature T$_{d}$ at which the vortices loose their correlation along the c-direction and they dissolve into the two dimensional pancake vortices. The H-T phase diagram for the YBa$_{2}$Cu$_{4}$O$_{8}$ single crystal is obtained.Comment: 1 Text file, 3 eps figure

Investigation into the design of ultra-wideband (UWB) and multi-band antennas

University of Technology, Sydney. Faculty of Engineering.The rapid development of high speed wireless communications as well as other applications such as microwave imaging place extraordinary demands on spectrums for which ultra-wideband (UWB) and multi-band, e.g.: dual-band, techniques are useful. These UWB and multi-band services require UWB and multi-band antenna designs. Motivated by these applications, we first carried out the investigations on the family of square plate monopole (SPM) antennas for UWB applications. The family of square plate monopole (SPM) UWB antennas yields quite attractive features, viz.: ease of fabrication and freedom of dielectric material selection. Next, we considered the use of coplanar waveguide (CPW) fed printed UWB antenna for compact, body-worn applications. We investigated the antenna performance using empirical optimisation. The work on CPW-fed printed antennas has led to the development of multi-band antennas also. For UWB antennas, we have first considered the modifications of well know square plate monopole (SPM) antennas. Our approach differs from other similar approaches on SPM antennas published in the literature. We have introduced symmetrical modifications to both bottom and top portions of the SPM antenna element. This has led to the development of these types of symmetrically modified SPM antennas, viz.: symmetrically beveled SPM (SB-SPM) antenna, symmetrical semi-circular base SPM (SSCB-SPM) antenna and symmetrically notched SPM (SN-SPM) antenna. All these antennas have been empirically optimised using Feko® and the theoretical and experimental results are provided, in the point of view of reflection coefficient, radiation characteristics, phase response of antenna transfer function and time domain response. For better suiting the compact and body-worn UWB applications, we have investigated the design of CPW-fed printed antenna. We have explored the antenna characteristics using empirical optimisation. The theoretical and experimental results for the completed CPW-fed printed antenna are provided, in the point of view of reflection coefficient, radiation characteristics, phase response of antenna transfer function, group delay and time domain response. Lately, for multi-band antennas, we have investigated the design of multi-band printed antennas, which are fed by CPW, to suit emerging design requirements. Two CPW-fed dual-band printed antennas for GSM and DCS/PCS as well as DCS/PCS and IEEE 802.11b applications are proposed, which have C-shape and T-shape structures respective1y. The theoretical and experimental results for these antennas are provided, in the point of view of reflection coefficient and radiation characteristics. Due to the use of substrate material for the designs of UWB CPW-fed printed antenna as well as C-shaped and T-shaped dual-band CPW-fed printed antennas, the effects of substrate material tolerances on UWB characteristics and dual-band characteristics are investigated. Furthermore, as these UWB and dual-band CPW-fed printed antennas are the promising candidates for wireless body-worn applications, which include wireless body area network (WBAN), the interactions between them and lossy material, such as human tissue, are investigated, which might help to decide the suitability of them for wireless body-worn applications

Work Function of Single-wall Silicon Carbide Nanotube

Using first-principles calculations, we study the work function of single wall silicon carbide nanotube (SiCNT). The work function is found to be highly dependent on the tube chirality and diameter. It increases with decreasing the tube diameter. The work function of zigzag SiCNT is always larger than that of armchair SiCNT. We reveal that the difference between the work function of zigzag and armchair SiCNT comes from their different intrinsic electronic structures, for which the singly degenerate energy band above the Fermi level of zigzag SiCNT is specifically responsible. Our finding offers potential usages of SiCNT in field-emission devices.Comment: 3 pages, 3 figure

Chromospheric Evaporation in an X1.0 Flare on 2014 March 29 Observed with IRIS and EIS

Chromospheric evaporation refers to dynamic mass motions in flare loops as a result of rapid energy deposition in the chromosphere. These have been observed as blueshifts in X-ray and extreme-ultraviolet (EUV) spectral lines corresponding to upward motions at a few tens to a few hundreds of km/s. Past spectroscopic observations have also revealed a dominant stationary component, in addition to the blueshifted component, in emission lines formed at high temperatures (~10 MK). This is contradictory to evaporation models predicting predominant blueshifts in hot lines. The recently launched Interface Region Imaging Spectrograph (IRIS) provides high resolution imaging and spectroscopic observations that focus on the chromosphere and transition region in the UV passband. Using the new IRIS observations, combined with coordinated observations from the EUV Imaging Spectrometer, we study the chromospheric evaporation process from the upper chromosphere to corona during an X1.0 flare on 2014 March 29. We find evident evaporation signatures, characterized by Doppler shifts and line broadening, at two flare ribbons separating from each other, suggesting that chromospheric evaporation takes place in successively formed flaring loops throughout the flare. More importantly, we detect dominant blueshifts in the high temperature Fe XXI line (~10 MK), in agreement with theoretical predictions. We also find that, in this flare, gentle evaporation occurs at some locations in the rise phase of the flare, while explosive evaporation is detected at some other locations near the peak of the flare. There is a conversion from gentle to explosive evaporation as the flare evolves.Comment: ApJ in pres