941 research outputs found
Determination of structural state of calcic plagioclases by an X-ray powder technique
B(20o1t - 20<zot)v ersusI (2d1131{1 2|pzo't - 4gcrartf)o r calcic plagioclasesd eterminedf rom
X-ray powder data distinguishesa mong structural statesa nd provides a rough estimateo f plagioclase
composition. A linear relationship betweenB and I for plagioclaseso f a particular structural state is
related to the apparent linear relationships between p* and composition 7* and composition for
these feldspars
In-Vivo Messung der Blutflussgeschwindigkeitsverteilung distal zu künstlichen Aortenklappen mittels der Magnetresonanz-Phasenkontrast-Technik
A transition from river networks to scale-free networks
A spatial network is constructed on a two dimensional space where the nodes
are geometrical points located at randomly distributed positions which are
labeled sequentially in increasing order of one of their co-ordinates. Starting
with such points the network is grown by including them one by one
according to the serial number into the growing network. The -th point is
attached to the -th node of the network using the probability: where is the degree of the -th node
and is the Euclidean distance between the points and . Here
is a continuously tunable parameter and while for one gets
the simple Barab\'asi-Albert network, the case for
corresponds to the spatially continuous version of the well known Scheidegger's
river network problem. The modulating parameter is tuned to study the
transition between the two different critical behaviors at a specific value
which we numerically estimate to be -2.Comment: 5 pages, 5 figur
High-Performance GPU Implementation of PageRank with Reduced Precision Based on Mantissa Segmentation
On D0-branes in Gepner models
We show why and when D0-branes at the Gepner point of Calabi-Yau manifolds
given as Fermat hypersurfaces exist.Comment: 22 pages, substantial improvements in sections 2 and 3, references
added, version to be publishe
Directed Fixed Energy Sandpile Model
We numerically study the directed version of the fixed energy sandpile. On a
closed square lattice, the dynamical evolution of a fixed density of sand
grains is studied. The activity of the system shows a continuous phase
transition around a critical density. While the deterministic version has the
set of nontrivial exponents, the stochastic model is characterized by mean
field like exponents.Comment: 5 pages, 6 figures, to be published in Phys. Rev.
Oxidation and emission of methane in a monomictic lake (Rotsee, Switzerland)
The build-up of methane in the hypolimnion of the eutrophic Lake Rotsee (Lucerne, Switzerland) was monitored over a full year. Sources and sinks of methane in the water column were characterized by measuring concentrations and carbon isotopic composition. In fall, high methane concentrations (up to 1mM) were measured in the anoxic water layer. In the oxic layer, methane concentrations were much lower and the isotopic composition shifted towards heavy carbon isotopes. Methane oxidation rates peaked at the interface between oxic and anoxic water layers at around 8-10m depth. The electron balance between the oxidants oxygen, sulphate, and nitrate, and the reductants methane, sulphide and ammonium, matched very well in the chemocline during the stratified season. The profile of carbon isotopic composition of methane showed strong indications for methane oxidation at the chemocline (including the oxycline). Aerobic methane oxidizing bacteria were detected at the interface using fluorescence in situ hybridization. Sequencing the responsible organisms from DGGE bands revealed that aerobic methanotrophs type I closely related to Methylomonas were present. Sulphate consumption occurred at the sediment surface and, only towards the end of the stagnation period, matched with a zone of methane consumption. In any case, the flux of sulphate below the chemocline was not sufficient to oxidize all the methane and other oxidants like nitrate, iron or manganese are necessary for the observed methane oxidation. Although most of the methane was oxidized either aerobically or anaerobically, Lake Rotsee was still a source of methane to the atmosphere with emission rates between 0.2mgCH4m−2day−1 in February and 7mgCH4m−2day−1 in Novembe
X-Ray Diffraction and Chemical Study of Secondary Minerals from Deep Sea Drilling Project Leg 51, Holes 417A and 417D
Secondary minerals found in fracture fillings and in fragments of altered
basalt from Holes 417A and 417D were studied by both X-ray
diffraction and chemical techniques. Minerals found in fracture fillings
from Hole 417A are dominated by montmorillonite, "protoceládonite,"
analcite, and lesser saponite; celadonite and ferrosaponite are the characteristic
secondary minerals in Hole 417D fracture fillings. Assuming that
minerals found in such fracture fillings reflect the composition of the
secondary fluids that produced them, it is apparent that those from Hole
417A were dominantly Al-rich, while those from Hole 417D were more
enriched in Fe, Mg, and K. X-ray diffraction study of bulk samples
support such fundamental differences in secondary mineralogy. In addition,
the X-ray data on bulk samples suggest that primary plagioclase is
the feldspar in Hole 417D rocks, and secondary potassium feldspar is the
feldspar in Hole 417A altered rocks.
Using available published data on secondary miner?1" found in other
altered oceanic crust, it is possible to interpret the differences in secondary
mineralogy that exist between the two sites. Secondary minerals
present in Hole 417D rocks are believed to have formed under hydrothermally
influenced, low temperature, nonoxidative diagenesis;
whereas, those present in Hole 417A were produced under similarly low
temperatures, but much more highly oxidizing conditions. The fundamental
differences in secondary mineralogy between the two sites can be
best explained by the accompanying remobilization of elements that involved
plagioclase alteration in Hole 417A rocks. A comparison of the
composition of Hole 417A and 417D secondary minerals with those found
in younger crust suggests that the age of crust, influenced by the changing
conditions of alteration, control the chemistry of secondary minerals
found in available pore spaces in altered rocks. Minerals found in young
crust (<15 m.y.B.P.) are highly Mg-rich; minerals found in crust of
intermediate age (—15-50 m.y.B.P.) are dominantly enriched in Fe and
Mg; and those found in older crust have higher contents of Al and K
Eastern Pacific spreading rate fluctuation and its relation to Pacific area volcanic episodes
Sea-floor spreading rates from four locations along the Nazca-Pacific plate boundary and one along the Juan de Fuca-Pacific plate boundary show variations over the past 2.4 m.y., with decreasing rates prior to the Jaramillo to Olduvai time interval (0.92-1.73 m.y. ago) and increasing rates since then. Other Pacific area volcanic phenomena in mid-plate and convergent-boundary settings also show minima about 1.3-1.5 m.y. ago and a maximum at present and another maximum about 5 m.y. ago: extrusion rates along the Hawaiian Ridge; volcanic episodes associated with calc-alkalic provinces of western Oregon and Central America; temporal variations in the SiO2 content of Aleutian ash layers; and the number of deep-sea ash layers. These phenomena may fluctuate in response to changing spreading rates. During times of more rapid spreading increased shear and melting along lithospheric boundaries may occasion increased volcanic activity, whereas during times of less rapid spreading volcanic activity may be less intense.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23637/1/0000601.pd
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