Altitude Limits for Rotating Vector Model Fitting of Pulsar Polarization

Traditional pulsar polarization sweep analysis starts from the point dipole rotating vector model (RVM) approximation. If augmented by a measurement of the sweep phase shift, one obtains an estimate of the emission altitude (Blaskiewicz, Cordes, & Wasserman). However, a more realistic treatment of field line sweepback and finite altitude effects shows that this estimate breaks down at modest altitude ~ 0.1R_{LC}. Such radio emission altitudes turn out to be relevant to the young energetic and millisecond pulsars that dominate the \gamma-ray population. We quantify the breakdown height as a function of viewing geometry and provide simple fitting formulae that allow observers to correct RVM-based height estimates, preserving reasonable accuracy to R ~ 0.3R_{LC}. We discuss briefly other observables that can check and improve height estimates

Laboratory measurements and methane photochemistry modeling

Methane is photolyzed by the solar UV in the stratosphere of Saturn. Subsequent photochemistry leads to the production of acetylene (C2H2) and diacetylene (C4H2). These species are produced where it is relatively warm (T is greater than or equal to 140 K), but the tropopause temperature of Saturn (approximately 80 K) is low enough that these two species may freeze out to their respective ices. Numerical models which include both photochemistry and condensation loss make predictions about the mixing ratios of these species and haze production rates. These models are dependent upon knowing reaction pathways and their associated kinetic reaction rate constants and vapor pressures. How uncertainties in the chemistry and improvements in the vapor pressures affect model predictions for Saturn are discussed

Uniform bounds for higher-order semilinear problems in conformal dimension

We establish uniform a-priori estimates for solutions of the semilinear Dirichlet problem \begin{equation} \begin{cases} (-\Delta)^m u=h(x,u)\quad&\mbox{in }\Omega,\\ u=\partial_nu=\cdots=\partial_n^{m-1}u=0\quad&\mbox{on }\partial\Omega, \end{cases} \end{equation} where $h$ is a positive superlinear and subcritical nonlinearity in the sense of the Trudinger-Moser-Adams inequality, either when $\Omega$ is a ball or, provided an energy control on solutions is prescribed, when $\Omega$ is a smooth bounded domain. The analogue problem with Navier boundary conditions is also studied. Finally, as a consequence of our results, existence of a positive solution is shown by degree theory.Comment: Minor correction

Love Thy Neighbour? Evidence from Ethnic Discrimination in Information Sharing within Villages

There is increasing evidence to suggest that a fundamental source of information for farmers on how to access and use new agricultural technologies comes from interacting with neighbours. Economic research on adoption of innovations in a rural context has only partially addressed the issue of how the social structure of a village can affect adoption and the final impact on productivity of farmers. This paper investigates the role of proximity interpreted not only in geographical terms but also along the line of ethnic similarities among neighbours (what we define as ?social proximity?). We use a panel dataset collected in C.te d?Ivoire to define the probability of accessing the knowledge network. The main results indicate that farmers from ethnic minorities are less likely to access, and benefit less from, extension services. But they seem to try to re-equalize their condition by putting more effort than dominant ethnic group neighbours in sharing information among themselves.economic development, technological change, growth

Convexity preserving interpolatory subdivision with conic precision

The paper is concerned with the problem of shape preserving interpolatory subdivision. For arbitrarily spaced, planar input data an efficient non-linear subdivision algorithm is presented that results in $G^1$ limit curves, reproduces conic sections and respects the convexity properties of the initial data. Significant numerical examples illustrate the effectiveness of the proposed method

Model Atmospheres for Low Field Neutron Stars

We compute model atmospheres and emergent spectra for low field (B<10^10 G) neutron stars, using new opacity and equation of state data from the OPAL project. These computations, incorporating improved treatments of flux transport and convective stability, provide spectra for hydrogen, solar abundance and iron atmospheres. We compare our results to high field magnetic atmospheres, available only for hydrogen. An application to apparently thermal flux from the low field millisecond pulsar PSR J0437--4715 shows that H atmospheres fit substantially better than Fe models. We comment on extension to high fields and the implication of these results for neutron star luminosities and radii.Comment: 13 pages, text errors in several formulae corrected for publication, 5 eps figures unchanged; to appear in ApJ, April 10, 199