518 research outputs found
Recommended from our members
Spring 1976 Conference Issue
Herbicide Evaluation for Crabgrass Control 1974-1975 (page 3) Growth Retardants on a Kentucky Bluegrass and Red Fescue Turf Stand (4) Herbicide trials on Broadleaf Weeds 1975 (4) Dollar Spot Fungicide Control Trials--1975 (6) GOLD-N, A Sulphur-coated Urea from ICI (8) Turf Conference Program (10) Priorities Given for OSHA Inspection Stops (19) UMass Turf Research Fund (19
Controlled Irradiative Formation of Penitentes
Spike-shaped structures are produced by light-driven ablation in very
different contexts. Penitentes 1-4 m high are common on Andean glaciers, where
their formation changes glacier dynamics and hydrology. Laser ablation can
produce cones 10-100 microns high with a variety of proposed applications in
materials science. We report the first laboratory generation of
centimeter-scale snow and ice penitentes. Systematically varying conditions
allows identification of the essential parameters controlling the formation of
ablation structures. We demonstrate that penitente initiation and coarsening
requires cold temperatures, so that ablation leads to sublimation rather than
melting. Once penitentes have formed, further growth of height can occur by
melting. The penitentes intially appear as small structures (3 mm high) and
grow by coarsening to 1-5 cm high. Our results are an important step towards
understanding and controlling ablation morphologies.Comment: Accepted for publication in Physical Review Letter
Scattering map for two black holes
We study the motion of light in the gravitational field of two Schwarzschild
black holes, making the approximation that they are far apart, so that the
motion of light rays in the neighborhood of one black hole can be considered to
be the result of the action of each black hole separately. Using this
approximation, the dynamics is reduced to a 2-dimensional map, which we study
both numerically and analytically. The map is found to be chaotic, with a
fractal basin boundary separating the possible outcomes of the orbits (escape
or falling into one of the black holes). In the limit of large separation
distances, the basin boundary becomes a self-similar Cantor set, and we find
that the box-counting dimension decays slowly with the separation distance,
following a logarithmic decay law.Comment: 20 pages, 5 figures, uses REVTE
Floating stones off El Hierro, Canary Islands: xenoliths of pre-island sedimentary origin in the early products of the October 2011 eruption
The eruption that started off the south coast of El Hierro, Canary Islands, in October 2011 has emitted intriguing eruption products found floating in the sea. These specimens appeared as floating volcanic "bombs" that have in the meantime been termed "restingolites" (after the close-by village of La Restinga) and exhibit cores of white and porous pumice-like material. Currently the nature and origin of these "floating stones" is vigorously debated among researchers, with important implications for the interpretation of the hazard potential of the ongoing eruption. The "restingolites" have been proposed to be either (i) juvenile high-silica magma (e.g. rhyolite), (ii) remelted magmatic material (trachyte), (iii) altered volcanic rock, or (iv) reheated hyaloclastites or zeolite from the submarine slopes of El Hierro. Here, we provide evidence that supports yet a different conclusion. We have collected and analysed the structure and composition of samples and compared the results to previous work on similar rocks found in the archipelago. Based on their high silica content, the lack of igneous trace element signatures, and the presence of remnant quartz crystals, jasper fragments and carbonate relicts, we conclude that "restingolites" are in fact xenoliths from pre-island sedimentary rocks that were picked up and heated by the ascending magma causing them to partially melt and vesiculate. They hence represent messengers from depth that help us to understand the interaction between ascending magma and crustal lithologies in the Canary Islands as well as in similar Atlantic islands that rest on sediment/covered ocean crust (e.g. Cape Verdes, Azores). The occurrence of these "restingolites" does therefore not indicate the presence of an explosive high-silica magma that is involved in the ongoing eruption
CO2 bubble generation and migration during magma-carbonate interaction
We conducted quantitative textural analysis of vesicles in high temperature and pressure carbonate assimilation
experiments (1200 °C, 0.5 GPa) to investigate CO2 generation and subsequent bubble migration from carbonate
into magma. We employed Mt. Merapi (Indonesia) and Mt. Vesuvius (Italy) compositions as magmatic starting
materials and present three experimental series using (1) a dry basaltic-andesite, (2) a hydrous basaltic-andesite
(2 wt% H2O), and (3) a hydrous shoshonite (2 wt% H2O). The duration of the experiments was varied from 0 to
300 s, and carbonate assimilation produced a CO2-rich fluid and CaO-enriched melts in all cases. The rate of carbonate assimilation, however, changed as a function of melt viscosity, which affected the 2D vesicle number,
vesicle volume, and vesicle size distribution within each
experiment. Relatively low-viscosity melts (i.e. Vesuvius experiments) facilitated efficient removal of bubbles
from the reaction site. This allowed carbonate assimilation to continue unhindered and large volumes of CO2 to beliberated, a scenario thought to fuel sustained CO2-driven eruptions at the surface. Conversely, at higher viscosity
(i.e. Merapi experiments), bubble migration became progressively
inhibited and bubble concentration at the reaction site caused localised volatile over-pressure that can eventually trigger short-lived explosive outbursts. Melt
viscosity therefore exerts a fundamental control on carbonate assimilation rates and, by consequence, the style of
CO2-fuelled eruptions
CO2 bubble generation and migration during magma–carbonate interaction
We conducted quantitative textural analysis of vesicles in high temperature and pressure carbonate assimilation experiments (1200 °C, 0.5 GPa) to investigate CO2 generation and subsequent bubble migration from carbonate into magma. We employed Mt. Merapi (Indonesia) and Mt. Vesuvius (Italy) compositions as magmatic starting materials and present three experimental series using (1) a dry basaltic-andesite, (2) a hydrous basaltic-andesite (2 wt% H2O), and (3) a hydrous shoshonite (2 wt% H2O). The duration of the experiments was varied from 0 to 300 s, and carbonate assimilation produced a CO2-rich fluid and CaO-enriched melts in all cases. The rate of carbonate assimilation, however, changed as a function of melt viscosity, which affected the 2D vesicle number, vesicle volume, and vesicle size distribution within each experiment. Relatively low-viscosity melts (i.e. Vesuvius experiments) facilitated efficient removal of bubbles from the reaction site. This allowed carbonate assimilation to continue unhindered and large volumes of CO2 to be liberated, a scenario thought to fuel sustained CO2-driven eruptions at the surface. Conversely, at higher viscosity (i.e. Merapi experiments), bubble migration became progressively inhibited and bubble concentration at the reaction site caused localised volatile over-pressure that can eventually trigger short-lived explosive outbursts. Melt viscosity therefore exerts a fundamental control on carbonate assimilation rates and, by consequence, the style of CO2-fuelled eruptions
Recommended from our members
October 1966
Massachusetts Turf and Lawn Grass CouncilBetter Turf Through Research and Educatio
Classical Scattering for a driven inverted Gaussian potential in terms of the chaotic invariant set
We study the classical electron scattering from a driven inverted Gaussian
potential, an open system, in terms of its chaotic invariant set. This chaotic
invariant set is described by a ternary horseshoe construction on an
appropriate Poincare surface of section. We find the development parameters
that describe the hyperbolic component of the chaotic invariant set. In
addition, we show that the hierarchical structure of the fractal set of
singularities of the scattering functions is the same as the structure of the
chaotic invariant set. Finally, we construct a symbolic encoding of the
hierarchical structure of the set of singularities of the scattering functions
and use concepts from the thermodynamical formalism to obtain one of the
measures of chaos of the fractal set of singularities, the topological entropy.Comment: accepted in Phy. Rev.
Recommended from our members
July 1964
Turf and Lawn Grass Association
Better turf through research and Educatio
Recommended from our members
February 1967 Conference Issue
Massachusetts Turf and Lawn Grass CouncilBetter Turf Through Research and Educatio
- …