On the genus "Asplenium" in the Iberian Peninsula"

The Asplenium species recorded from the Iberian peninsula comprise diploids and tetraploids, and of the latter, both auto- and allotetraploids occur. Evidence from the meiotic pairing behaviour of the chromosomes in synthetic hybrids is adduced to show how the mode of origin and interrelationships of such species can be elucidated, and specific reference is made to Asplenium foresiense, A. majoricum, A. petrarchae and A. billotii. The suggested occurrence of autopolyploidy in Asplenium cuneifolium is also discussed. Evidence is presented which shows that in the British Isles and Corsica serpentine plants previously regarded as autotetraploid derivatives of A. cuneifolium are in fact allotetraploid and almost certainly just specialized serpentine forms of Asplenium adiantum-nigrum. It is suggested that such forms of A. adiantum-nigrum could occur also on serpentine rocks elsewhere in western Europe, for example, in Spain and France.Las especies del genero Asplenium, registradas en la Peninsula Ibérica, comprenden citotipos diploides y tetraploides, siendo estos últimos tanto autotetraploides como alotetraploides. Del apareamiento miótico de los cromosomas en los híbridos sintéticos se aducen pruebas para mostrar como se pueden dilucidar el modo de origen y las interrelaciones de tales especies, y se hace referencia específica a Asplenium foresiense, A. majoricum, A. petrarchae y A. billotii. También se discute la cuestión de la autopoliploidía de A. cuneifolium que habia sido sugerida previamente. Se ofrecen datos experimentales que muestran que en las Islas Británicas y en Córcega las plantas que crecen sobre serpentinas, anteriormente consideradas como un derivado autotetraploidal de A. cuneifolium, son en realidad alotetraploides y, casi con certeza, no son más que formas serpentinícolas especializadas de A. adiantum-nigrum. Se sugiere que tales formas de A. adiantum-nigrum pueden existir también sobre serpentinas en otras partes de Europa occidental, por ejemplo, en España o Francia

Impact production of NO and reduced species

It has recently been suggested that a reported spike in seawater (87)Sr/(86)Sr at the K-T boundary is the signature of an impact-generated acid deluge. However, the amount of acid required is implausibly large. Some about 3 x 10 to the 15th power moles of Sr must be weathered from silicates to produce the inferred Sr spike. The amount of acid required is at least 100 and probably 1000 times greater. Production of 3 x 10 to the 18th power moles of NO is clearly untenable. The atmosphere presently contains only 1.4 x 10 to the 20th power moles of N-sub 2 and 3.8 x 10 to the 19th power moles of O sub 2 If the entire atmosphere were shocked to 2000 K and cooled within a second, the total NO produced would be about 3 x 10 to the 18th power moles. This is obviously unrealistic. A (still to short) cooling time of 10th to the 3rd power sec reduces NO production by an order of magnitude. In passing, we note that if the entire atmosphere had in fact been shocked to 2000 K, acid rain would have been the least of a dinosaur's problems. Acid rain as a mechanism poses poses other difficulties. Recently deposited carbonates would have been most susceptable to acid attack. The researchers' preferred explanation is simply increased continental erosion following ecological trauma, coupled with enchanced levels of CO-sub 2

The Stability of the orbits of Earth-mass planets in and near the habitable zones of known exoplanetary systems

We have shown that Earth-mass planets could survive in variously restricted regions of the habitable zones (HZs) of most of a sample of nine of the 93 main-sequence exoplanetary systems confirmed by May 2003. In a preliminary extrapolation of our results to the other systems, we estimate that roughly a third of the 93 systems might be able to have Earth-mass planets in stable, confined orbits somewhere in their HZs. Clearly, these systems should be high on the target list for exploration for terrestrial planets. We have reached this conclusion by launching putative Earth-mass planets in various orbits and following their fate with a mixed-variable symplectic integrator

Topography and tectonics of the intersections of fracture zone with central rifts.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1969.Bibliography: leaves 13-15.M.S

Flexurally-resisted uplift of the Tharsis Province, Mars

The tectonic style of Mars is dominated by vertical motion, perhaps more than any of the terrestrial planets. The imprint of this tectonic activity has left a surface widely faulted even though younger volcanism has masked the expression of tectonism in many places. Geological activity associated with the Tharsis and, to a lesser extent, Elysium provinces is responsible for a significant portion of this faulting, while the origins of the remaining features are enigmatic in many cases. The origin and evolution of the Tharsis and Elysium provinces, in terms of their great elevation, volcanic activity, and tectonic style, has sparked intense debate over the last fifteen years. Central to these discussions are the relative roles of structural uplift and volcanic construction in the creation of immense topographic relief. For example, it is argued that the presence of very old and cratered terrain high on the Tharsis rise, in the vicinity of Claritas Fossae, points to structural uplift of an ancient crust. Others have pointed out, however, that there is no reason that this terrain could not be of volcanic origin and thus part of the constructional mechanism

Origin and thermal evolution of Mars

The thermal evolution of Mars is governed by subsolidus mantle convection beneath a thick lithosphere. Models of the interior evolution are developed by parameterizing mantle convective heat transport in terms of mantle viscosity, the superadiabatic temperature rise across the mantle, and mantle heat production. Geological, geophysical, and geochemical observations of the compositon and structure of the interior and of the timing of major events in Martian evolution are used to constrain the model computations. Such evolutionary events include global differentiation, atmospheric outgassing, and the formation of the hemispherical dichotomy and Tharsis. Numerical calculations of fully three-dimensional, spherical convection in a shell the size of the Martian mantle are performed to explore plausible patterns of Martian mantel convection and to relate convective features, such as plumes, to surface features, such as Tharsis. The results from the model calculations are presented

Best Practices in Second Stage Labor Care: Maternal Bearing Down and Positioning

Despite evidence of adverse fetal and maternal outcomes from the use of sustained Valsalva bearing down efforts, current second-stage care practices are still characterized by uniform directions to “push” forcefully upon complete dilatation of the cervix while the woman is in a supine position. Directed pushing might slightly shorten the duration of second stage labor, but can also contribute to deoxygenation of the fetus; cause damage to urinary, pelvic, and perineal structures; and challenge a woman’s confidence in her body. Research on the second stage of labor care is reviewed, with a focus on recent literature on maternal bearing down efforts, the “laboring down” approach to care, second-stage duration, and maternal position. Clinicians can apply the scientific evidence regarding the detrimental effects of sustained Valsalva bearing down efforts and supine positioning by individualizing second stage labor care and supporting women’s involuntary bearing down sensations that can serve to guide her behaviors

Kinks, rings, and rackets in filamentous structures

Carbon nanotubes and biological filaments each spontaneously assemble into kinked helices, rings, and "tennis racket" shapes due to competition between elastic and interfacial effects. We show that the slender geometry is a more important determinant of the morphology than any molecular details. Our mesoscopic continuum theory is capable of quantifying observations of these structures, and is suggestive of their occurrence in other filamentous assemblies as well.Comment: This paper was originally published in PNAS 100: 12141-12146 (2003). The present version has corrected Eq. 3, A1, and A2, and some minor typo