48,709 research outputs found
Shatter cones: Diagnostic impact signatures
Uniquely fractured target rocks known as shatter cones are associated with more than one half the world's 120 or so presently known impact structures. Shatter cones are a form of tensile rock failure in which a positive conical plug separates from a negative outer cup or mold and delicate ornaments radiating from an apex are preserved on surfaces of both portions. Although distinct, shatter cones are sometimes confused with other striated geologic features such as ventifacts, stylolites, cone-in-cone, slickensides, and artificial blast plumes. Complete cones or solitary cones are rare, occurrences are usually as swarms in thoroughly fractured rock. Shatter cones may form in a zone where an expanding shock wave propagating through a target decays to form an elastic wave. Near this transition zone, the expanding primary wave may strike a pebble or other inhomogeneity whose contrasting transmission properties produce a scattered secondary wave. Interference between primary and secondary scattered waves produce conical stress fields with axes perpendicular to the plane of an advancing shock front. This model supports mechanism capable of producing such shatter cone properties as orientation, apical clasts, lithic dependence, and shock pressure zonation. Although formational mechanics are still poorly understood, shatter cones have become the simplest geologic field criterion for recognizing astroblemes (ancient terrestrial impact structures)
Shattering Thresholds for Random Systems of Sets, Words, and Permutations
This paper considers a problem that relates to the theories of covering
arrays, permutation patterns, Vapnik-Chervonenkis (VC) classes, and probability
thresholds. Specifically, we want to find the number of subsets of
[n]:={1,2,....,n} we need to randomly select, in a certain probability space,
so as to respectively "shatter" all t-subsets of [n]. Moving from subsets to
words, we ask for the number of n-letter words on a q-letter alphabet that are
needed to shatter all t-subwords of the q^n words of length n. Finally, we
explore the number of random permutations of [n] needed to shatter
(specializing to t=3), all length 3 permutation patterns in specified
positions. We uncover a very sharp zero-one probability threshold for the
emergence of such shattering; Talagrand's isoperimetric inequality in product
spaces is used as a key tool.Comment: 25 page
Breccia dikes from the Beaverhead Impact structure, southwest Montana
While shatter cones are generally accepted as indicators of meteorite impact, older petrologic features are not widely recognized in the geologic community. Breccia dikes are one such feature. They are found in many large impact structures occurring over an area at least as extensively as shatter cones. Breccia dikes will survive moderate degrees of metamorphism and tectonism, unlike many other microscopic features (shocked quartz grains, high-pressure polymorphs, etc.) and even large-scale features such as annular or bowl-shaped topographic features. Thus, they are important diagnostic criteria, especially for large, poorly preserved impact structures. The Beaverhead Impact structure is a recently discovered, deeply eroded impact structure in southwestern Montana. The remains of the structure are delineated by the occurrence of shatter cones, found in an area greater than 200 sq km, occurring within the Cabin thrust plate, part of the Cretaceous Sevier fold and thrust system. The distribution of shatter cones is further truncated by Tertiary normal faults. The present remains represent an allochthonous fragment of a larger structure
Ethanol Vapours to Complement or Replace Sulfur Dioxide Fumigation of Table Grapes
Recent studies have shown that dipping table grapes in ethanol solutions at harvest improved storage of the fruit. We report here the first results obtained by treating "Chasselas" table grapes (Vitis vinifera) with ethanol vapours over the storage period. We tested the effect of ethanol at 0, 4 and 8 g/kg fruit during cold storage for 2, 4 and 6 weeks. We measured berry shatter, stem browning, Botrytis rot incidence and sensory appreciation by tasting panels. Ethanol vapours reduced Botrytis rot incidence and berry shatter, but hastened stem browning. Sensory analyses did not detect any differences between treatments
How Protons Shatter Colored Glass
We consider the implications of the Color Glass Condensate for the central
region of p+A collisions. We compute the k_t distribution of radiated gluons
and their rapidity distribution dN/dy analytically, both in the perturbative
regime and in the region between the two saturation momenta. We find an
analytic expression for the number of produced gluons which is valid when the
saturation momentum of the proton is much less than that of the nucleus. We
discuss the scaling of the produced multiplicity with A. We show that the slope
of the rapidity density dN/dy provides an experimental measure for the
renormalization-group evolution of the color charge density of the Color Glass
Condensate (CGC). We also argue that these results are easily generalized to
collisions of nuclei of different A at central rapidity, or with the same A but
at a rapidity far from the central region.Comment: 9 pages, RevTex, 3 Figures; some typos corrected, the scaling of
^2 with dN/dy is derive
Analysis and Development of lgbokoda Clay as a Binder for Synthetic Moulding Sand
Clay obtained from lgbokoda in the southwestern part of Nigeria has been analysed and developed
as a binder for synthetic moulding sand. The analysis was compared with the analytical
results obtained for the pre-treated bentonite clay imported from the U.S.A. and used by the
Nigerian Foundries Ltd. (NFL). X-ray analysis indicated the presence of kaolin, illite and montmorillonite
(parent mineral of bentonite), with kaolin having the highest percentage in the lgbokoda
clay and montmorillonite was further confirmed by the flame test which shows the existence
of exchangeable cations not present in kaolin. The effects of mixing varying amounts of clay,
tempering water and sand on moulding properties were investigated. The green and dry strength
and shatter index of the mixtures were determined. The green and the dry strength (both in shear
and compression) of the lgbokoda test clay, mixed with the sub angular lagoon silica sand and
determined at optimum water content, give good values for synthetic moulding sand. The shatter
index test shows a decrease in collapsibility as the water content decreases at constant clay addition.
lgbokoda clay is more collapsible but less tough than bentonite as shown by the shatter inde
Shatter cones in Illinois: Evidence for metoeritic impacts at Glasford and Des Plaines
Shatter cone fragments were recovered from rock cores at two previously suspected, but heretofore unverified, impact structures in Illinois. Both sites are buried features known from geophysical surveys and drill holes. Shatter cones are accepted widely as field criteria of meteoritic impact. Detection of these shock indicators in both the Glasford Structure and the Des Plains Disturbance upgrades these sites in Earth's inventory of known and suspected impact structures from possible impact sites with compatible structure and morphology to probable impact structures which possess also evidence of shock metamorphism
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