Bayesian Inference of a Multivariate Regression Model

We explore Bayesian inference of a multivariate linear regression model with use of a flexible prior for the covariance structure. The commonly adopted Bayesian setup involves the conjugate prior, multivariate normal distribution for the regression coefficients and inverse Wishart specification for the covariance matrix. Here we depart from this approach and propose a novel Bayesian estimator for the covariance. A multivariate normal prior for the unique elements of the matrix logarithm of the covariance matrix is considered. Such structure allows for a richer class of prior distributions for the covariance, with respect to strength of beliefs in prior location hyperparameters, as well as the added ability, to model potential correlation amongst the covariance structure. The posterior moments of all relevant parameters of interest are calculated based upon numerical results via a Markov chain Monte Carlo procedure. The Metropolis-Hastings-within-Gibbs algorithm is invoked to account for the construction of a proposal density that closely matches the shape of the target posterior distribution. As an application of the proposed technique, we investigate a multiple regression based upon the 1980 High School and Beyond Survey

The Mantle and Basalt-Crust Interaction Below the Mount Taylor Volcanic Field, New Mexico

The Mount Taylor Volcanic Field (MTVF) lies on the Jemez Lineament on the southeastern margin of the Colorado Plateau. The field is centered on the Mt. Taylor composite volcano and includes Mesa Chivato to the NE and Grants Ridge to the WSW. MTVF magmatism spans approximately 3.8-1.5 Ma (K-Ar). Magmas are dominantly alkaline with mafic compositions ranging from basanite to hy-basalt and felsic compositions ranging from ne-trachyte to rhyolite. We are investigating the state of the mantle and the spatial and temporal variation in basalt-crustal interaction below the MTVF by examining mantle xenoliths and basalts in the context of new mapping and future Ar-Ar dating. The earliest dated magmatism in the field is a basanite flow south of Mt. Taylor. Mantle xenolith-bearing alkali basalts and basanites occur on Mesa Chivato and in the region of Mt. Taylor, though most basalts are peripheral to the main cone. Xenolith-bearing magmatism persists at least into the early stages of conebuilding. Preliminary examination of the mantle xenolith suite suggests it is dominantly lherzolitic but contains likely examples of both melt-depleted (harzburgitic) and melt-enriched (clinopyroxenitic) mantle. There are aphyric and crystal-poor hawaiites, some of which are hy-normative, on and near Mt. Taylor, but many of the more evolved MTVF basalts show evidence of complex histories. Mt. Taylor basalts higher in the cone-building sequence contain >40% zoned plagioclase pheno- and megacrysts. Other basalts peripheral to Mt. Taylor and at Grants Ridge contain clinopyroxene and plagioclase megacrysts and cumulate-textured xenoliths, suggesting they interacted with lower crustal cumulates. Among the questions we are addressing: What was the chemical and thermal state of the mantle recorded by the basaltic suites and xenoliths and how did it change with time? Are multiple parental basalts (Si-saturated vs. undersaturated) represented and, if so, what changes in the mantle or in the tectonic regime allowed their coexistence or caused the transition

Local Union Officers' Donations to a Political Action Committee

Durant les années 80, les syndicats américains ont grandement accru leurs activités politiques en partie en réaction stratégique à la réduction du nombre de leurs membres. Une caractéristique importante de cet effort est la contribution financière aux campagnes présidentielles et des membres du Congrès par des comités d'action politique (CAP). En vertu de la loi électorale fédérale, les syndicats peuvent prélever auprès de leurs membres, sur une base volontaire, des sommes d'argent CAP pouvant servir, dans des limites prévues, aux campagnes électorales générales et celles des primaires pour les candidats à la présidence et au Congrès. Les dirigeants syndicaux locaux élus peuvent jouer un grand rôle dans cet effort syndical de ramasser des fonds CAP puisqu'ils représentent un groupe important de donateurs potentiels et que leurs dons personnels peuvent influencer leurs membres. Cependant, le seul statut de dirigeants locaux n'implique pas un comportement homogène. Peu de recherche empirique a porté sur les dirigeants locaux en soi, aussi nous avons eu recours à une documentation pertinente plus large dans les domaines tels la participation politique générale, la participation politique des syndiqués et l'incitation des employés à se joindre à des groupes d'intérêts pour des fins politiques. À partir de cela, nous proposons des hypothèses spécifiques eu égard aux variables socio-psychologiques, démographiques, économiques, régionales et expérimentales pouvant influencer les dons CAP des dirigeants syndicaux locaux.Nous avons vérifié nos hypothèses à l'aide d'analyses de régression de données colligées suite à une enquête menée auprès de 700 dirigeants locaux des Métallurgistes unis d'Amérique (Métallos) qui ont tous suivi des séminaires commandités par le syndicat international. Les résultats révèlent une variation considérable dans les dons qu'ont eux-mêmes rapportés les dirigeants locaux. Cependant, en moyenne, ces dons excèdent de beaucoup ceux des membres. Chez les dirigeants, les résultats démontrent que l'implication dans le syndicat est un bon prédicteur de dons CAP. Les résultats suggèrent que les Métallos et les syndicats américains en général pourraient accroître leur niveau actuel d'action politique en permettant aux dirigeants locaux de ramasser de l'argent CAP par une éducation de base et par le fait d'inculquer un plus grand sentiment d'engagement syndical.During the 1980s, unions in the United States significantly increased their political activity, partly as a strategic response to declining membership. An important aspect of this effort is contributing money to congressional and presidential candidates through political action committees (PACs). U.S. federal election campaign laws allow unions to raise PAC money from members on a strictly uoluntary basis. Elected local union officers may play an important part in union PAC fundraising, as they are a sizable cadre of potential donors and their donations may send powerful signais to rank-and-file to donate as well. This paper examines the PAC donations among a sample of elected local union officers of the United Steelworkers of America (USW). The descriptive results show significant variation in officers' PAC donations. Regression analyses show that union commitment is a significant predictor of PAC support as is location in a non-right-to-work state. The results have implications for promoting union PAC fundraising efforts, and hence the potential of U.S. unions to rely on political action as a strategy for resurgence

Measurement of electrical properties of electrode materials for the bakelite Resistive Plate Chambers

Single gap (gas gap 2 mm) bakelite Resistive Plate Chamber (RPC) modules of various sizes from 10 cm \times 10 cm to 1 m \times 1 m have been fabricated, characterized and optimized for efficiency and time resolution. Thin layers of different grades of silicone compound are applied to the inner electrode surfaces to make them smooth and also to reduce the surface resistivity. In the silicone coated RPCs an efficiency > 90% and time resolution \sim 2 ns (FWHM) have been obtained for both the streamer and the avalanche mode of operation. Before fabrication of detectors the electrical properties such as bulk resistivity and surface resistivity of the electrode materials are measured carefully. Effectiveness of different silicone coating in modifying the surface resistivity was evaluated by an instrument developed for monitoring the I-V curve of a high resistive surface. The results indicate definite correlation of the detector efficiency for the atmospheric muons and the RPC noise rates with the surface resistivity and its variation with the applied bias voltage. It was also found that the surface resistivity varies for different grades of silicone material applied as coating, and the results are found to be consistent with the detector efficiency and noise rate measurements done with these RPCs.Comment: 9 Pages, 6 figure

Measurement of electrical properties of electrode materials for the bakelite Resistive Plate Chambers

Single gap (gas gap 2 mm) bakelite Resistive Plate Chamber (RPC) modules of various sizes from 10 cm \times 10 cm to 1 m \times 1 m have been fabricated, characterized and optimized for efficiency and time resolution. Thin layers of different grades of silicone compound are applied to the inner electrode surfaces to make them smooth and also to reduce the surface resistivity. In the silicone coated RPCs an efficiency > 90% and time resolution \sim 2 ns (FWHM) have been obtained for both the streamer and the avalanche mode of operation. Before fabrication of detectors the electrical properties such as bulk resistivity and surface resistivity of the electrode materials are measured carefully. Effectiveness of different silicone coating in modifying the surface resistivity was evaluated by an instrument developed for monitoring the I-V curve of a high resistive surface. The results indicate definite correlation of the detector efficiency for the atmospheric muons and the RPC noise rates with the surface resistivity and its variation with the applied bias voltage. It was also found that the surface resistivity varies for different grades of silicone material applied as coating, and the results are found to be consistent with the detector efficiency and noise rate measurements done with these RPCs.Comment: 9 Pages, 6 figure