The Wardle Instability in Interstellar Shocks: I. Nonlinear Dynamical Evolution

The nonlinear evolution of unstable C-type shocks in weakly ionized plasmas is studied by means of time-dependent magnetohydrodynamical simulations. This study is limited to shocks in magnetically dominated plasmas (in which the Alfven speed in the neutrals greatly exceeds the sound speed), and microphysical processes such as ionization and recombination are not followed. Both two-dimensional simulations of planar perpendicular and oblique C-type shocks, and fully three-dimensional simulation of a perpendicular shock are presented.Comment: 20 pages, 7 Postscript figures, LaTeX, accepted by Ap.

High Levels of Circularly Polarized Emission from the Radio Jet in NGC 1275 (3C 84)

We present multi-frequency, high resolution VLBA circular polarization images of the radio source 3C 84 in the center of NGC 1275. Our images reveal a complex distribution of circular polarization in the inner parsec of the radio jet, with local levels exceeding 3% polarization, the highest yet detected with VLBI techniques. The circular polarization changes sign along the jet, making 3C 84 also the first radio jet to show both signs of circular polarization simultaneously. The spectrum and changing sign of the circular polarization indicate that it is unlikely to be purely intrinsic to the emitted synchrotron radiation. The Faraday conversion process makes a significant and perhaps dominant contribution to the circular polarization, and the observed spectrum suggests the conversion process is near saturation. The sign change in the circular polarization along the jet may result from this saturation or may be due to a change in magnetic field order after an apparent bend in the jet. From the small spatial scales probed here, ~ 0.15 pc, and the comparably high levels of circular polarization inferred for the intra-day variable source PKS 1519-273, we suggest a connection between small spatial scales and efficient production of circular polarization.Comment: 4 pages, accepted in ApJ Letter

Enhancing the decision-making process of project managers in the built environment: An integrated approach

A study of the project manager’s (PM) function must be to examine: what their role is, their skills, and training needed. The project manager needs wide perspective regarding the classic management functions of control, coordination, communication, and the settling of performance standards. If the PM is a professional, their performance must be of the highest standard, and must be accountable for a high level of productivity. This is the project manager’s Achilles heel. Another problem is the absence of feedback during the early stages through to completion of the project. During the project’s life the relative importance of their responsibilities may change several times, including the constant changing of the dynamic environment. The PM will aim for a balanced emphasis; they will try to be flexible so they can adapt to new circumstances as they occur. The PM needs tried and tested methods to aid his decision making. This paper posits an integrated development and use of methods such as; scenario planning, effectuation, and reflective thinking to enhance decision making. The paper concludes with potential benefits that this method brings to the PM when fully understood and tested in the application domain

SULLA AND THE ‘PROPHECY’ OF CAESAR’S DESTRUCTION OF THE OPTIMATES (SUET. IUL. 1.3)

The extant life of Julius Caesar by Suetonius begins with the dictator Sulla predicting that Caesar will destroy the Optimates, i.e., undo all that Sulla himself had achieved. In presenting Sulla’s forecast Suetonius uniquely in examples of divinatory material in the Lives appears to be ambiguous as to its divinatory status. This paper examines how Suetonius secures credibility for this piece of ‘prophecy’ and considers the role of Sulla’s words in the economy of the Life

The use of chronosequences in studies of ecological succession and soil development

1. Chronosequences and associated space-for-time substitutions are an important and often necessary tool for studying temporal dynamics of plant communities and soil development across multiple time-scales. However, they are often used inappropriately, leading to false conclusions about ecological patterns and processes, which has prompted recent strong criticism of the approach. Here, we evaluate when chronosequences may or may not be appropriate for studying community and ecosystem development. 2. Chronosequences are appropriate to study plant succession at decadal to millennial time-scales when there is evidence that sites of different ages are following the same trajectory. They can also be reliably used to study aspects of soil development that occur between temporally linked sites over time-scales of centuries to millennia, sometimes independently of their application to shorter-term plant and soil biological communities. 3. Some characteristics of changing plant and soil biological communities (e.g. species richness, plant cover, vegetation structure, soil organic matter accumulation) are more likely to be related in a predictable and temporally linear manner than are other characteristics (e.g. species composition and abundance) and are therefore more reliably studied using a chronosequence approach. 4. Chronosequences are most appropriate for studying communities that are following convergent successional trajectories and have low biodiversity, rapid species turnover and low frequency and severity of disturbance. Chronosequences are least suitable for studying successional trajectories that are divergent, species-rich, highly disturbed or arrested in time because then there are often major difficulties in determining temporal linkages between stages. 5. Synthesis. We conclude that, when successional trajectories exceed the life span of investigators and the experimental and observational studies that they perform, temporal change can be successfully explored through the judicious use of chronosequences

Extreme scattering events and Galactic dark matter

Extreme Scattering Events (ESEs) are attributed to radio-wave refraction by a cloud of free-electrons crossing the line-of-sight. We present a new model in which these electrons form the photo-ionized 'skin' of an underlying cool, self-gravitating cloud in the Galactic halo. In this way we avoid the severe over-pressure problem which afflicts other models. The UV flux in the Galactic halo naturally generates electron densities of the right order. We demonstrate, for the first time, a good reproduction of the prototypical ESE in the quasar 0954+658. The neutral clouds are a few AU in radius and have masses less than about 10^{-3} solar. The observed rate of ESEs implies that a large fraction of the mass of the Galaxy is in this form.Comment: 5 pp incl 3 figs, LaTeX, uses aas2pp4.sty. Minor revisions. ApJ Letters in pres

From Slavery to Same-Sex Marriage: Comity Versus Public Policy in Inter-jurisdictional Recognition of Controversial Domestic relations

Recognition across state and national borders of controversial forms of domestic relationships have existed throughout the history of conflict of laws, creating tension between two important principles: respect for comity and protection of valued domestic public policies. Drawing upon several examples, and particularly the history of international and intrastate recognition of slavery (a “domestic relationship”) in Anglo-American history, the article shows that despite the comity-based presumption of respect for legal status created in other jurisdictions, when strong public policies protective of domestic relations and status have been implicated, American states consistently have declined to give interstate recognition to those controversial forms of domestic relationship that are being imported. The article examines several examples of this and reviews the principles that are historically established in dealing with such conflicts, and suggests the relevance of this history and these principles for interstate recognition of same-sex marriage and other controversial contemporary domestic relationships