Phreatomagmatic deposits and stratigraphic reconstruction at Debunscha Maar (Mt Cameroon volcano)

The Debunscha Maar (DM) is located on the southwest flank of Mount Cameroon, an active stratovolcano on the Cameroon volcanic line (CVL). Here, we present the physical characteristics of the pyroclastic deposits at DM with the aim of deciphering tephra emplacement mechanisms, evolution of water–magma interaction and reconstructing the stratigraphy beneath the maar. From GPS measurements, the crater has long and short axes of 500 m and 320 m, respectively. Generally, the pyroclastic deposits are well stratified and present a variety of depositional bed forms including structureless/massive beds, massive beds with faint internal stratifications, inversely graded beds, lens- shaped units, impact sags, cross lamination, planar beds as well as dune-like beds. Clast sizes include ash, lapilli-tuff, bombs and blocks (pyroclastic breccia), with clast lithologies consisting of entrained lithics of porous ankaramite pillow lavas, lithified sediments (sandstone and shale) and juvenile material. The porous ankaramite pillow lavas have glassy margins and vesicle zonations typical of pillow lavas formed by subaqueous eruption. The pillow fragments are more common in early-formed eruption products at the base of the deposit. The lithified sandstones show planar laminations and together with the shales occur predominantly in stratigraphic positions above the ankaramite pillow lavas. The juvenile materials include basaltic bombs with low vesicularity (b15%) and moderate vesicularity (15–50%). The bombs have chilled surfaces and their abundance increases towards the top of the deposit. The presence of accretionary lapilli, fragments of country-rock and juvenile clasts with ragged surfaces as well as curved and chilled margins, is unambiguous evidence in support of phreatomagmatic activity. Of the observed lithic clasts, only the pillow lavas would appear to have the porosity necessary to furnish the required amount of water to feed the phreatomagmatic maar eruption. The clast stratigraphy suggests that the maar is underlain by ankaramite pillow lava that erupted on a consolidated sedimentary substratum. Studying deposits resulting from maar eruptions has a direct implication for hazards assessment at areas of active maar volcanism because many surface processes occur around such volcanoes well after the eruptive activities have stopped

Future exploration of Venus (post-Pioneer Venus 1978)

A comprehensive study was performed to determine the major scientific unknowns about the planet Venus to be expected in the post-Pioneer Venus 1978 time frame. Based on those results the desirability of future orbiters, atmospheric entry probes, balloons, and landers as vehicles to address the remaining scientific questions were studied. The recommended mission scenario includes a high resolution surface mapping radar orbiter mission for the 1981 launch opportunity, a multiple-lander mission for 1985 and either an atmospheric entry probe or balloon mission in 1988. All the proposed missions can be performed using proposed space shuttle upper stage boosters. Significant amounts of long-lead time supporting research and technology developments are required to be initiated in the near future to permit the recommended launch dates

Methane emission by alpaca and sheep fed on lucerne hay or grazed on pastures of perennial ryegrass/white clover or birdsfoot trefoil

Based on the knowledge that alpaca (Lama pacos) have a lower fractional outflow rate of feed particles (particulate FOR) from their forestomach than sheep (San Martin 1987), the current study measured methane (CH4) production and other digestion parameters in these species in three successive experiments (1, 2 and 3): Experiment 1, lucerne hay fed indoors; Experiment 2, grazed on perennial ryegrass/white clover pasture (PRG/WC); and Experiment 3, grazed on birdsfoot trefoil (Lotus corniculatits) pasture (Lotus). Six male alpaca and six castrated Romney sheep were simultaneously and successively fed on the forages either ad libitium or at generous herbage allowances (grazing). CH4 production (g/day) (using the sulphur hexafluoride tracer technique), voluntary feed intake (VFI), diet quality, and protozoa counts and volatile fatty acid concentrations in samples of forestomach contents were determined. In addition, feed digestibility, energy and nitrogen (N) balances and microbial N supply from the forestomach (using purine derivatives excretion) were measured in Experiment 1. Diets selected by alpaca were of lower quality than those selected by sheep, and the voluntary gross energy intakes (GEI, MJ) per kg of liveweight(0.75) were consistently lower (P0.05) in their CH4 yields (% GEI) when fed on lucerne hay (5.1 v. 4.7), but alpaca had a higher CH4 yield when fed on PRG/WC (9.4 v. 7.5, P0.05) in diet N partition or microbial N yield, but alpaca had higher (P<0.05) neutral detergent fibre digestibility (0.478 v. 0.461) and lower (P<0.01) urinary energy losses (5.2 v. 5.8 % GEI) than sheep. It is suggested that differences between these species in forestomach particulate FOR might have been the underlying physiological mechanism responsible for the differences in CH4 yield, although the between-species differences in VFI and diet quality also had a major effect on it

Upper critical field divergence induced by mesoscopic phase separation in the organic superconductor (TMTSF)2ReO4

Due to the competition of two anion orders, (TMTSF)2ReO4, presents a phase coexistence between semiconducting and metallic (superconducting) regions (filaments or droplets) in a wide range of pressure. In this regime, the superconducting upper critical field for H parallel to both c* and b' axes present a linear part at low fields followed by a divergence above a cross-over field. This cross-over corresponds to the 3D-2D decoupling transition expected in filamentary or granular superconductors. The sharpness of the transition also demonstrates that all filaments are of similar sizes and self organize in a very ordered way. The distance between the filaments and their cross-section are estimated.Comment: 4 pages, 4 figure

Mechanisms and Clinical Consequences of Vascular Calcification

Vascular calcification has severe clinical consequences and is considered an accurate predictor of future adverse cardiovascular events, including myocardial infarction and stroke. Previously vascular calcification was thought to be a passive process which involved the deposition of calcium and phosphate in arteries and cardiac valves. However, recent studies have shown that vascular calcification is a highly regulated, cell-mediated process similar to bone formation. In this article, we outline the current understanding of key mechanisms governing vascular calcification and highlight the clinical consequences. By understanding better the molecular pathways and genetic circuitry responsible for the pathological mineralization process novel drug targets may be identified and exploited to combat and reduce the detrimental effects of vascular calcification on human health

Semiclassical transmission across transition states

It is shown that the probability of quantum-mechanical transmission across a phase space bottleneck can be compactly approximated using an operator derived from a complex Poincar\'e return map. This result uniformly incorporates tunnelling effects with classically-allowed transmission and generalises a result previously derived for a classically small region of phase space.Comment: To appear in Nonlinearit

Order in de Broglie - Bohm quantum mechanics

A usual assumption in the so-called {\it de Broglie - Bohm} approach to quantum dynamics is that the quantum trajectories subject to typical `guiding' wavefunctions turn to be quite irregular, i.e. {\it chaotic} (in the dynamical systems' sense). In the present paper, we consider mainly cases in which the quantum trajectories are {\it ordered}, i.e. they have zero Lyapunov characteristic numbers. We use perturbative methods to establish the existence of such trajectories from a theoretical point of view, while we analyze their properties via numerical experiments. Using a 2D harmonic oscillator system, we first establish conditions under which a trajectory can be shown to avoid close encounters with a moving nodal point, thus avoiding the source of chaos in this system. We then consider series expansions for trajectories both in the interior and the exterior of the domain covered by nodal lines, probing the domain of convergence as well as how successful the series are in comparison with numerical computations or regular trajectories. We then examine a H\'{e}non - Heiles system possessing regular trajectories, thus generalizing previous results. Finally, we explore a key issue of physical interest in the context of the de Broglie - Bohm formalism, namely the influence of order in the so-called {\it quantum relaxation} effect. We show that the existence of regular trajectories poses restrictions to the quantum relaxation process, and we give examples in which the relaxation is suppressed even when we consider initial ensembles of only chaotic trajectories, provided, however, that the system as a whole is characterized by a certain degree of order.Comment: 25 pages, 12 figure

Forces on a boiling bubble in a developing boundary layer, in microgravity with g-jitter and in terrestrial conditions

Terrestrial and microgravity flow boiling experiments were carried out with the same test rig, comprising a locally heated artificial cavity in the center of a channel near the frontal edge of an intrusive glass bubble generator. Bubble shapes were in microgravity generally not far from those of truncated spheres,which permitted the computation of inertial lift and drag from potential flow theory for truncated spheres approximating the actual shape. For these bubbles, inertial lift is counteracted by drag and both forces are of the same order of magnitude as g-jitter. A generalization of the Laplace equation is found which applies to a deforming bubble attached to a plane wall and yields the pressure difference between the hydrostatic pressures in the bubble and at the wall, p. A fully independent way to determine the overpressure p is given by a second Euler-Lagrange equation. Relative differences have been found to be about 5% for both terrestrial and microgravity bubbles. A way is found to determine the sum of the two counteracting major force contributions on a bubble in the direction normal to the wall from a single directly measurable quantity. Good agreement with expectation values for terrestrial bubbles was obtained with the difference in radii of curvature averaged over the liquid-vapor interface, (1/R2 − 1/R1), multiplied with the surface tension coefficient, σ. The new analysis methods of force components presented also permit the accounting for a surface tension gradient along the liquid-vapor interface. No such gradients were found for the present measurements

Time-delayed feedback control in astrodynamics

In this paper we present time-delayed feedback control (TDFC) for the purpose of autonomously driving trajectories of nonlinear systems into periodic orbits. As the generation of periodic orbits is a major component of many problems in astodynamics we propose this method as a useful tool in such applications. To motivate the use of this method we apply it to a number of well known problems in the astrodynamics literature. Firstly, TDFC is applied to control in the chaotic attitude motion of an asymmetric satellite in an elliptical orbit. Secondly, we apply TDFC to the problem of maintaining a spacecraft in a periodic orbit about a body with large ellipticity (such as an asteroid) and finally, we apply TDFC to eliminate the drift between two satellites in low Earth orbits to ensure their relative motion is bounded

Cliff Roosting by Migrant Semipalmated Sandpipers, Calidris pusilla, at Farrier's Cove, Shepody Bay, New Brunswick

An observation of Semipalmated Sandpipers roosting on a cliff face in Shepody Bay, New Brunswick, suggests changes from “traditional” roosting sites. Sandpipers may be altering their roosting patterns due to pressures from avian predators such as the recent, and successful, re-introduction of the Peregrine Falcon