Covariance-Adaptive Slice Sampling

We describe two slice sampling methods for taking multivariate steps using the crumb framework. These methods use the gradients at rejected proposals to adapt to the local curvature of the log-density surface, a technique that can produce much better proposals when parameters are highly correlated. We evaluate our methods on four distributions and compare their performance to that of a non-adaptive slice sampling method and a Metropolis method. The adaptive methods perform favorably on low-dimensional target distributions with highly-correlated parameters

e+e- pair production from nucleon targets in the resonance region

We present consistent theoretical descriptions of the $\pi N \to e^+e^- N$ and $\gamma N \to e^+e^- N$ reactions on proton and neutron targets for total center of mass energies $\sqrt s$ ranging between 1.50 GeV and 1.75 GeV. These reactions are complementary to study the coupling of low-lying baryon resonances to vector meson-nucleon channels. We show in particular how the resonant structure of the amplitudes for both processes generates specific and large quantum interferences between $\rho$- and $\omega$-meson decays into $e^+e^-$ pairs. Data on the $\pi N \to e^+e^- N$ and $\gamma N \to e^+e^- N$ reactions are expected in the near future from the HADES program at GSI and from dilepton studies with CLAS at JLab.Comment: 6 pages, 6 figures, Paper presented at Hirschegg 2004, 'Probing nuclei and nucleons with electrons and photons', January 12th-16th, 200

Study of the threshold behavior of the η\etaN scattering amplitude through the associated photoproduction of ϕ\phi- and η\eta-mesons

We suggest that the $\gamma p \to \phi \eta p$ reaction cross section, in the kinematics where the $\eta p$ invariant mass in the final state lies between the threshold value (m$_p$+m$_\eta$) and the N*(1535) resonance mass, is largely determined by the $\eta N$ scattering amplitude close to threshold. The initial photon energy is chosen in the range $4 < E_\gamma^{Lab} < 5$ GeV, in order to reach low (absolute) values of the squared 4-momentum transfer from the initial photon to the final $\phi$-meson. In these conditions, we expect the t-channel $\pi^0$- and $\eta$-meson exchanges to drive the dynamics underlying the $\gamma p \to \phi \eta p$ process. We show that the $\eta$-exchange is the dominating contribution to the cross section while the $\pi^0$-exchange is negligible. The $\eta$-$\pi^0$ interference is of the order of $20 - 30$. The sign of this term is not known and alters significantly our results. Data on the $\gamma p \to \phi \eta p$ process would be therefore very useful to help unravelling the behavior of the $\eta p$ scattering amplitude close to threshold and assessing the possibility of producing $\eta$-nucleus bound states.Comment: 8 pages, 6 figures, Invited talk at MESON 2006, June 9th-13th, 2006, Cracow (Poland

Sororities at Gettysburg College During the Haaland Era, 1990-2004

From 1990 to 2004, Gettysburg College’s Greek system dominated student social life and, due to its prominence (and notoriety), attracted the attention of not only students but also faculty and administration during the era of President Gordon A. Haaland. Although fraternities were often the more influential and problematic Greek organizations on campus, Gettysburg’s sororities played a major role in the lives of female students -- offering women a chance to join a community of other women, participate in philanthropy events, and engage in Greek social life. Throughout the Haaland era, Gettysburg’s sororities consisted of a combination of Sigma Kappa, Alpha Xi Delta, Alpha Delta Pi, Chi Omega, Delta Gamma, Gamma Phi Beta, and Sigma Sigma Sigma. During the 14 years, some of these sororities were added, some disappeared, and all witnessed a reduction in membership by the end of Haaland’s presidency. Some sororities had more problematic reputations than others or hazed new members, but sororities were not often perceived as negatively as fraternities were by college faculty and administration -- primarily due to sororities’ lack of chapter houses. Nevertheless, sororities experienced the same administrative changes to Greek life that their male counterparts did, including three shifts in rush/pledge program timing. Beyond these broad changes, other transformations during the Haaland era were more specific to sororities, including the creation of new chapter rooms and the adoption of No Frills Rush

An index to characterize the spatial distribution of land use within watersheds and implications for river network nutrient removal and export

The spatial distribution of land use and associated nutrient inputs may influence the efficacy of in-stream nutrient removal; however, the effect of source location on N removal and watershed N export has not been quantified. We present the skewness index, a metric to quantify the spatial distribution of land use within watersheds. Using this index and a river network nitrogen removal model, we quantified the effect of varying the location of developed land use within two watersheds on nutrient removal and export. The quantity and location of developed land use as well as runoff affected nitrogen removal and export. Because river network nitrogen removal is bypassed when sources are skewed toward the watershed mouth, varying the location of land use alone can double aquatic nitrogen removal. Nutrient sources skewed toward the distant headwaters maximized in-stream removal which in turn can reduce watershed export

Dynamics of strong and radiative decays of Ds mesons

The positive parity scalar D$_{s0}^*$(2317) and axial-vector D$_{s1}^*$(2460) charmed strange mesons are generated by coupled-channel dynamics through the s-wave scattering of Goldstone bosons off the pseudoscalar and vector D(D$_s$)-meson ground states. The attraction leading to the specific masses of these states reflects the chiral symmetry breaking scale which characterizes the Weinberg-Tomozawa interaction in the chiral Lagrangian. Chiral corrections to order Q$_\chi^2$ are calculated and found to be small. The D$_{s0}^*$(2317) and D$_{s1}^*$(2460) mesons decay either strongly into the isospin-violating $\pi^0$D$_s$ and $\pi^0$D$_s^*$ channels or electromagnetically. We show that the $\pi^0$-$\eta$ and (K$^0$D$^+$-K$^+$D$^0$) mixings act constructively to generate strong widths of the order of 140 keV. The one-loop contribution to the radiative decay amplitudes of scalar and axial-vector states is calculated using the electromagnetic Lagrangian to chiral order Q$_\chi^2$. We show the importance of taking into account processes involving light vector mesons explicitly in the dynamics of electromagnetic decays to obtain a satisfactory description of the available data.Comment: Contribution to the Meson 2008 Conference, June 6-10, Cracow, Polan

Learning to Imagine

For the purpose of this discussion, we posit that there are essentially four overarching reasons we educate. They are: preparing students for democratic participation, providing access to knowledge and critical thinking, enabling all students to take advantage of life's opportunities, and enabling students to lead rich and rewarding personal lives. None of these can be achieved fully without attention to the role of imagination. While we acknowledge that not all would agree with our definition of purposes, our comprehensive vision, we believe, can serve our children and our society well

The πN→e+e−N\pi N \to e^+e^- N reaction close to the vector meson production threshold

The $\pi^-p \to e^+e^- n$ and $\pi^+n \to e^+e^- p$ reaction cross sections are calculated below and in the vicinity of the vector meson ($\rho^0$, $\omega$) production threshold. These processes are largely responsible for the emission of $e^+e^-$ pairs in pion-nucleus reactions and contribute to the dilepton spectra observed in relativistic heavy ion collisions. They are dominated by the decay of low-lying baryon resonances into vector meson-nucleon channels. The vector mesons materialize subsequently into $e^+e^-$ pairs. Using $\pi N\to \rho^0 N$ and $\pi N \to \omega N$ amplitudes calculated in the center of mass energy interval $1.4<\sqrt s <1.8$ GeV, we compute the $\pi^-p \to e^+e^- n$ and $\pi^+n \to e^+e^- p$ reaction cross sections in these kinematics. Below the vector meson production threshold, the $\rho^0 - \omega$ interference in the $e^+e^-$ channel appears largely destructive for the $\pi^-p \to e^+e^- n$ cross section and constructive for the $\pi^+n \to e^+e^- p$ cross section. The pion beam and the HADES detector at GSI offer a unique possibility to measure these effects. Such data would provide strong constraints on the coupling of vector meson-nucleon channels to low-lying baryon resonances.Comment: Talk given at the Budapest'02 Workshop on Quark and Hadron Dynamics, Budapest (Hungary), March 3rd-7th, 200

Internet Sexual Predators: Protecting Children in the Global Community

The Internet, serving as the largest network of computers in the world, has provided the horizontal parallax over which all can participate in communication and transaction, education and entertainment4 It also serves a community of participants and beneficiaries whose goals are not always shared or legal. The rise of this advanced technology has led to a new red light district. Unlike the physical spaces available for the distribution of pornography and sexual favors for money, the Internet, with its lack of structure, has led to an unimaginable amount of pornography available for any on-line spectator.\u27 Information necessary for consummation of transactions in the sex economy worldwide is more easily available than ever before. Moreover, children worldwide are now at greater risk than ever before. In Part II of this Article, I discuss how the Internet puts children at greater risk. Part III is an examination of cases arising out of Internet use that led to abuse of children. Part IV explores the Internet and the mail-order bride business as it affects children outside the United States. In Part V, I discuss crimes involving what is termed virtual abuse. Part VI covers legislative responses to the problem. In Part VII, I examine jurisdictional problems encountered with crimes involving cyberspace. Finally, Part VIII provides my conclusions and a caveat