Posterior inference on the degrees of freedom parameter in multivariate-t regression models

Economics

A search for rapid optical variability in radio-quiet quasars

The detection of rapid variability on a time-scale of hours in radio-quiet quasars (RQQSOs) could be a powerful discriminator between starburst, accretion disc and relativistic jet models of these sources. This paper contains an account of a dedicated search for rapid optical variability in RQQSOs. The technique used differential photometry between the RQQSO and stars in the same field of view of the CCD. The 23 RQQSOs that were observed all have high luminosities (-27 1. The total amount of observation time was about 60 hours and these observations are part of an ongoing programme, started in September 1990, to search for rapid variability in RQQSOs. No evidence for short-term variability greater than about 0.1 magnitudes was detected in any of the 23 sources, however long-term variability was recorded for the radio-quiet quasar PG 2112+059. The finding charts are included here because they identify the RQQSO and the reference stars used in the photometry, and hence are available for use by other observers.Comment: Accepted for publication in A&AS. 10 pages, 3 figures. Figure 1 (finding charts) available by anonymous ftp from: bermuda.ucd.ie:/pub/outgoing/charts.eps.g

Regression models under competing covariance matrices: A Bayesian perspective

Economics

A Bayesian note on competing correlation structures in the dynamic linear regression model

Economics

The CIO role expectations instrument: validation and model testing

The validation of IS instruments has not been given the attention that it deserves. This study uses component-based structural equation modelling (PLS/SEM) to investigate the psychometric properties and possible modelling of the CIO role expectations instrument based on data obtained from 174 Australian CIOs. Results show that the CIO role expectation instrument has exhibited solid validity and reliability indices despite some minor weaknesses. The results also demonstrate the possibility to model the constructs of this instrument in different null and hierarchical models, and the validity of this instrument to measure the CIO role in different types of industries not just the healthcare sector in which it was developed. The results provide support for CIO role theory on two central issues: (1) CIOs are fulfilling a configuration of roles not just one specific role (2) the CIO roles can be grouped into two major categories: supply side roles and demand side roles

Hyperbolic Metamaterial Resonator-Antenna Scheme for Large, Broadband Emission Enhancement and Single Photon Collection

We model the broadband enhancement of single-photon emission from color centres in silicon carbide nanocrystals coupled to a planar hyperbolic metamaterial, HMM resonator. The design is based on positioning the single photon emitters within the HMM resonator, made of a dielectric index-matched with silicon-carbide material. The broadband response results from the successive resonance peaks of the lossy Fabry Perot structure modes arising within the high-index HMM cavity. To capture this broadband enhancement in the single photon emitters spontaneous emission, we placed a simple gold based cylindrical antenna on top of the HMM resonator. We analyzed the performance of this HMM coupled antenna structure in terms of the Purcell enhancement, quantum efficiency, collection efficiency and overall collected photon rate. For perpendicular dipole orientation relative to the interface, the HMM coupled antenna resonator leads to a significantly large spontaneous emission enhancement with Purcell factor of the order of 250 along with a very high average total collected photon rate, CPR of about 30 over a broad emission spectrum, 700 nm to 1000 nm. The peak CPR increases to about 80 at 900 nm, corresponding to the emission of silicon-carbide quantum emitters. This is a state of the art improvement considering the previous computational designs have reported a maximum average CPR of 25 across the nitrogen-vacancy centre emission spectrum, 600 nm to 800 nm with the highest value being about 40 at 650 nm

Adiabatic optical entanglement between electron spins in separate quantum dots

We present an adiabatic approach to the design of entangling quantum operations with two electron spins localized in separate InAs/GaAs quantum dots via the Coulomb interaction between optically-excited localized states. Slowly-varying optical pulses minimize the pulse noise and the relaxation of the excited states. An analytic "dressed state" solution gives a clear physical picture of the entangling process, and a numerical solution is used to investigate the error dynamics. For two vertically-stacked quantum dots we show that, for a broad range of dot parameters, a two-spin state with concurrence $C>0.85$ can be obtained by four optical pulses with durations $\sim 0.1 - 1$ ns.Comment: 7 pages, 5 figure

On Describing Multivariate Skewness: A Directional Approach

Most multivariate measures of skewness in the literature measure the overall skewness of a distribution. While these measures are perfectly adequate for testing the hypothesis of distributional symmetry, their relevance for describing skewed distributions is less obvious. In this article, we consider the problem of characterising the skewness of multivariate distributions. We define directional skewness as the skewness along a direction and analyse parametric classes of skewed distributions using measures based on directional skewness. The analysis brings further insight into the classes, allowing for a more informed selection of particular classes for particular applications. In the context of Bayesian linear regression under skewed error we use the concept of directional skewness twice. First in the elicitation of a prior on the parameters of the error distribution, and then in the analysis of the skewness of the posterior distribution of the regression residuals.Bayesian methods, Multivariate distribution, Multivariate regression, Prior elicitation, Skewness.

Proxy Access and Optimal Standardization in Corporate Governance: An Empirical Analysis

According to the conventional wisdom, “one size does not fit all” in corporate governance. Firms are heterogeneous with respect to their governance needs, implying that the optimal corporate governance structure must also vary from firm to firm. This one-size-does-not-fit-all axiom has featured prominently in arguments against numerous corporate law regulatory initiatives, including the SEC’s failed Rule 14a-11—an attempt to impose mandatory, uniform “proxy access” on all public companies—which the D.C. Circuit struck down for inadequate cost–benefit analysis. This Article presents an alternative theory as to the role of standardization in corporate governance—in which investors prefer standardized terms—and empirical evidence that is consistent with this theory. Under my theory, shareholders prefer standardization because they must incur considerable transaction costs to exercise control rights that contain idiosyncratic terms. Standardization reduces these transaction costs. Consistent with this theory, I find that standardization, not heterogeneity, has pervaded the post–Rule 14a-11 private ordering of proxy access. Shareholder proposals and adopted bylaws alike have converged around standardized terms, and regression analysis suggests that this standardization reflects shareholder preferences. Moreover, employing a regression-discontinuity design, I find evidence indicating that markets have generally reacted favorably to the passage of these standardized proposals. However, robustness checks cast some doubt on the internal validity of this regression-discontinuity design, and thus these results should be taken with a grain of salt. My theory and empirical findings have important implications for longstanding normative debates in corporate law. With a proper understanding of the role of standardization in corporate governance, the one-size-fits-all critique—though not baseless—takes on a different meaning. Although lawmakers would still do well to retain a presumption in favor of default rules instead of mandatory rules, the need for heterogeneity does not appear to be as great as some have supposed, and lawmakers may benefit from a greater focus on encouraging optimal standardization instead of optimal heterogeneity. These insights bear both on optimal regulatory design in the abstract and on the wisdom of currently pending federal legislation in a more concrete way