Implications of mean field accretion disc theory for vorticity and magnetic field growth

In addition to the scalar Shakura-Sunyaev $\alpha_{ss}$ turbulent viscosity transport term used in simple analytic accretion disc modeling, a pseudoscalar transport term also arises. The essence of this term can be captured even in simple models for which vertical averaging is interpreted as integration over a half-thickness and one separately studies each hemisphere. The additional term highlights a complementarity between mean field magnetic dynamo theory and accretion disc theory treated as a mean field theory. Such pseudoscalar terms have been studied, and can lead to large scale magnetic field and vorticity growth. Here it is shown that vorticity can grow even in the simplest azimuthal and half-height integrated disc model, for which mean quantities depend only on radius. The simplest vorticity growth solutions seem to have scales and vortex survival times consistent those required for facilitating planet formation. Also it is shown that when the magnetic back-reaction is included to lowest order, the pseudoscalar driving the magnetic field growth and that driving the vorticity growth will behave differently with respect to shearing and non-shearing flows: the former can reverse sign in the two cases, while the latter will have the same sign.Comment: 17 Pages LaTex, revised versio

Writing for Balance: A Conversation with Doris Lessing

Earl G. Ingersoll has edited a collection of interviews with Doris Lessing, which OR Press will be publishing this spring. He teaches at SUNY College in Brockport, New York. Doris Lessing has published over 30 books, most recently African Laughter and The Real Thing: Stories and Sketches, both from HarperCollins 1992. She lives in London

Managing Drivers of Cost in the Construction of Nuclear Plants

To make a meaningful contribution toward clean, reliable, and economical future energy systems, nuclear power plants (NPPs) must be cost and risk competitive with other low-carbon technologies within near-term timeframes. Recent new builds in the United States and western Europe have suffered from two phenomena. First, they are expensive in absolute and relative terms: the cost per MW installed, along with the size of the plant, makes them among the most expensive power plants of any type. Second, they have all been delivered overbudget and late, making the construction of an NPP a risky investment, which in turn increases the cost of borrowing money for new projects

Response of a zonal climate-ice sheet model to the orbital perturbations during the Quaternary ice ages

The astronomical theory of the ice ages is investigated using a simple climate model which includes the ice sheets explicitly. A one-level, zonally averaged, seasonal energy-balance equation is solved numerically for sea-level temperature T as a function of latitude and month (similar to North, 1975). Seasonally varying snow cover (which affects planetary albedo) is included diagnostically by parameterizing monthly snowfall and snowmelt in simple ways. The net annual accumulation and ablation on the ice sheet surface at each latitude are computed using the same parameterizations as for snow cover above (with T corrected for ice sheet height using a lapse rate of -6.5 °C km^(-1)). Treatment of the ice sheets follows Weertman (1976) with ice flow approximated as perfect plasticity, which constrains the ice sheet profiles to be parabolic. The northern hemisphere's ice sheet is constrained to extend equatorward from 75°N (corresponding to the Arctic Ocean shoreline). Model ice age curves are generated for the last several 100 K years by computing the seasonal climate as above once every 2 K years, with insolation calculated from actual Earth orbit perturbations. The change in ice sheet size for each 2 K year time step depends only on the net annual snow budget integrated over the whole ice sheet surface. In these model runs, the equatorward tip of the northern hemisphere's ice sheet oscillates through ~7° in latitude, correctly simulating the phases and approximate amplitude of the higher frequency components (~43 Kyear and 22 Kyear) of the deep-sea core data (Hays et al., 1976). However, the model fails to simulate the dominant glacial-interglacial cycles (~100 to 120 Kyear) of this data. The sensitivity of the model ice age curves to various parameter changes is described, but none of these changes significantly improve the fit of the model ice age curves to the data. In the concluding section we generalize about the types of mechanisms that might yield realistic glacial-interglacial cycles

The Mars observer camera

A camera designed to operate under the extreme constraints of the Mars Observer Mission was selected by NASA in April, 1986. Contingent upon final confirmation in mid-November, the Mars Observer Camera (MOC) will begin acquiring images of the surface and atmosphere of Mars in September-October 1991. The MOC incorporates both a wide angle system for low resolution global monitoring and intermediate resolution regional targeting, and a narrow angle system for high resolution selective surveys. Camera electronics provide control of image clocking and on-board, internal editing and buffering to match whatever spacecraft data system capabilities are allocated to the experiment. The objectives of the MOC experiment follow

Living on the Precipice: A Conversation with Edward Albee

An edited version of the Writers Forum interview dated February 5, 1981. Speaking with Edward Albee were Stan Sanvel Rubin, the current director of·the Forum; Adam Lazarre, the former Dean of Fine Arts; and Mark Anderson, who teaches Renaissance and contemporary drama

Faith or Agnosticism?

48 p. ; 21 cmhttps://digitalcommons.pittstate.edu/hjbbb/1026/thumbnail.jp