Variability of the interplanetary medium at 1 A.U. over 24 years: 1963–1986

A survey is presented of hourly averages of observations of the interplanetary medium, made by satellites close to the Earth (i.e. at l a.u.) in the years 1963-1986. This survey therefore covers two complete solar cycles (numbers 20 and 21). The distributions and solar-cycle variations of IMF field strength, B, and its northward component (in GSM coordinates), B(z), and of the solar-wind density, n, speed, v, and dynamic pressure, P, are discussed. Because of their importance to the terrestrial magnetosphere/ionosphere, particular attention is given to B(z) and P. The solar-cycle variation in the magnitude and variability of B(z) previously reported for cycle 20, is also found for cycle 21. However, the solar-wind data show a number of differences between cycles 20 and 21. The average dynamic pressure is found to show a solar-cycle variation and a systematic increase over the period of the survey. The minimum of dynamic pressure at sunspot maximum is mainly due to reduced solar-wind densities in cycle 20, but lower solar-wind speed in cycle 21 is a more significant factor. The distribution of the duration of periods of stable polarity of the IMF B(z) component shows that the magnetosphere could achieve steady state for only a small fraction of the time and there is some evidence for a solar-cycle variation in this fraction. It is also found that the polarity changes in the IMF B(z) fall into two classes: one with an associated change in solar-wind dynamic pressure, the other without such a change. However, in only 20% of cases does the dynamic pressure change exceed 50%

Casi-mercados, segregación escolar y desigualdad educativa: una trilogía con final abierto

La expansión de las lógicas de casi-mercado en la (re)configuración de los regímenes educativos ha hecho mella tanto en la articulación de la oferta como en la gestión de la demanda escolar. En lo relativo a la demanda, la potenciación del casi-mercado se ha plasmado, principalmente, en la extensión de políticas de distinta índole dirigidas a ampliar el margen formal de elección escolar por parte de las familias. En el terreno de la oferta, y más allá de las vías abiertas a la privatización de la enseñanza, el mismo proceso ha comportado la devolución a las escuelas de mayores márgenes de autonomía, en diversos campos (curricular, gestión de personal y presupuestos, admisión de alumnos...). En este artículo se repasan, desde una perspectiva europea y crítica, algunos de los principales peligros atribuibles a estos procesos, fundamentalmente relacionados con la segregación escolar, y se señalan algunas claves explicativas para contribuir a comprender su naturaleza e implicaciones

A role for intestinal mycoplasmas in the aetiology of Crohn's disease?

The definitive version is available at www.blackwell-synergy.comCrohn's disease (CD) is an inflammatory disorder of the gastrointestinal tract. The cause is unknown but clinical studies indicate that luminal factors and bacteria in the gut are involved in disease aetiology, although the infective organisms that have been implicated in CD, such as atypical mycobacteria and helicobacters, do not explain the various lesions that occur throughout the digestive tract. However, there is some evidence to suggest that mycoplasmas may be associated with CD. For example, mycoplasmas have been linked to colitis in dogs, while intracellular structures similar in morphology to these organisms have been observed in epithelial cells by electron microscopy of CD tissue. Lipids such as cholesterol are required for the growth of some mycoplasmas and dietary studies where the fat content in enteral formula diets was reduced have been demonstrated to have significant therapeutic value in patients with CD. Further support for mycoplasmal involvement in CD derives from improvements in inflammatory indices following the use of antibiotics known to be effective against mycoplasma infections, such as clarithromycin, rifabutin and clofazimine.W.E.W. Roediger and G.T. Macfarlan

Pines

Pinus is the most important genus within the Family Pinaceae and also within the gymnosperms by the number of species (109 species recognized by Farjon 2001) and by its contribution to forest ecosystems. All pine species are evergreen trees or shrubs. They are widely distributed in the northern hemisphere, from tropical areas to northern areas in America and Eurasia. Their natural range reaches the equator only in Southeast Asia. In Africa, natural occurrences are confined to the Mediterranean basin. Pines grow at various elevations from sea level (not usual in tropical areas) to highlands. Two main regions of diversity are recorded, the most important one in Central America (43 species found in Mexico) and a secondary one in China. Some species have a very wide natural range (e.g., P. ponderosa, P. sylvestris). Pines are adapted to a wide range of ecological conditions: from tropical (e.g., P. merkusii, P. kesiya, P. tropicalis), temperate (e.g., P. pungens, P. thunbergii), and subalpine (e.g., P. albicaulis, P. cembra) to boreal (e.g., P. pumila) climates (Richardson and Rundel 1998, Burdon 2002). They can grow in quite pure stands or in mixed forest with other conifers or broadleaved trees. Some species are especially adapted to forest fires, e.g., P. banksiana, in which fire is virtually essential for cone opening and seed dispersal. They can grow in arid conditions, on alluvial plain soils, on sandy soils, on rocky soils, or on marsh soils. Trees of some species can have a very long life as in P. longaeva (more than 3,000 years)