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1

An extended Cretaceous-Tertiary (K/T) stable isotope record. Implications for paleoclimate and the nature of the K/T boundary event  

NASA Technical Reports Server (NTRS)

In order to obtain a detailed single site record of marine productivity and temperature across the Cretaceous-Tertiary (K/T) boundary, both delta C-13 and delta O-18 values were measured in paired surface and deep water microfossil and nannofossil samples of mid-latitude South Atlantic Deep Sea Drilling Project (DSDP) Site 528. Additionally, the percent sedimentary carbonate content of the rock samples from which the analyzed fossil samples were taken, were determined. The analyzed interval spanned the last approximately 1 million years of the Cretaceous (the Abathomphalus mayaroensis foraminiferal zone) and the first approximately 9 million years of the Tertiary (the Paleocene). Paired samples were analyzed every 150 cm of the entire 165 m sampled interval (1 sample per recovered DSDP section), every 20 cm for 2.0 m below and 2.5 m above the K/T boundary, and every 0.25 cm immediately below, at, and above the K/T boundary clay. The Cretaceous-Tertiary boundary and earliest Paleocene record of DSDP Site 528 is marked by at least two strong decreases in the surface-to-deep delta C-13 gradient (one at the K/T boundary (66.4 mybp1) and one approximately 150,000 to 200,000 years later). Both of these decreases co-occur with radical decreases in percent carbonate content and appear to indicate not one, but two, strong decreases in marine primary productivity during the analyzed interval.

Dhondt, Steven

1988-01-01

2

The Cretaceous-Tertiary Boundary (K-T) Interval in Badlands National Park, South Dakota  

NSDL National Science Digital Library

Philip W. Stoffer and USGS colleagues wrote this report (.pdf format) on the marine K-T boundary interval that occurs throughout the Badlands National Park region of South Dakota. Data from marine sediments (supported by paleontological correlation, sequence stratigraphy, magnetostratigraphy, and strontium isotope geochronology) suggest that several asteroid impacts may be preserved in the Badlands. The deposits are thought to represent late Maestrichtian events or possibly the terminal K-T event.

Chamberlain, John A.; Messina, Paula.; Stoffer, Philip W.; Terry, Dennis O.

2001-01-01

3

Carbon isotopic compositions of organic matter across continental Cretaceous-Tertiary (K-T) boundary sections: Implications for paleoenvironment after the K-T impact event  

USGS Publications Warehouse

To assess the environmental perturbation induced by the impact event that marks the Cretaceous-Tertiary (K-T) boundary, concentrations and isotopic compositions of bulk organic carbon were determined in sedimentary rocks that span the terrestrial K-T boundary at Dogie Creek, Montana, and Brownie Butte, Wyoming in the Western Interior of the United States. The boundary clays at both sites are not bounded by coals. Although coals consist mainly of organic matter derived from plant tissue, siliceous sedimentary rocks, such as shale and clay, may contain organic matter derived from microbiota as well as plants. Coals record ??13C values of plant-derived organic matter, reflecting the ??13C value of atmospheric CO2, whereas siliceous sedimentary rocks record the ??13C values of organic matter derived from plants and microbiota. The microbiota ??13C value reflects not only the ??13C value of atmospheric CO2, but also biological productivity. Therefore, the siliceous rocks from these sites yields information that differs from that obtained previously from coal beds. Across the freshwater K-T boundary at Brownie Butte, the ??13C values decrease by 2.6??? (from - 26.15??? below the boundary clay to - 28.78??? above the boundary clay), similar to the trend in carbonate at marine K-T sites. This means that the organic ??13C values reflect the variation of ??13C of atmospheric CO2, which is in equilibrium with carbon isotopes at the ocean surface. Although a decrease in ??13C values is observed across the K-T boundary at Dogie Creek (from - 25.32??? below the boundary clay to - 26.11??? above the boundary clay), the degree of ??13C-decrease at Dogie Creek is smaller than that at Brownie Butte and that for marine carbonate. About 2??? decrease in ??13C of atmospheric CO2 was expected from the ??13C variation of marine carbonate at the K-T boundary. This ??13C-decrease of atmospheric CO2 should affect the ??13C values of organic matter derived from plant tissue. As such a decrease in ??13C value was not observed at Dogie Creek, a process that compensates the ??13C-decrease of atmospheric CO2 should be involved. For example, the enhanced contribution of 13C-enriched organic matter derived from algae in a high-productivity environment could be responsible. The ??13C values of algal organic matter become higher than, and thus distinguishable from, those of plant organic matter in situations with high productivity, where dissolved HCO3- becomes an important carbon source, as well as dissolved CO2. As the ??13C-decrease of atmospheric CO2 reflected a reduction of marine productivity, the compensation of the ??13C decrease by the enhanced activity of the terrestrial microbiota means that the microbiota at freshwater environment recovered more rapidly than those in the marine environment. A distinct positive ??13C excursion of 2??? in the K-T boundary clays is superimposed on the overall decreasing trend at Dogie Creek; this coincides with an increase in the content of organic carbon. We conclude that the K-T boundary clays include 13C-enriched organic matter derived from highly productive algae. Such a high biological productivity was induced by phenomena resulting from the K-T impact, such as nitrogen fertilization and/or eutrophication induced by enhanced sulfide formation. The high productivity recorded in the K-T boundary clays means that the freshwater environments (in contrast to marine environments) recovered rapidly enough to almost immediately (within 10??yr) respond to the impact-related environmental perturbations. ?? 2006 Elsevier B.V. All rights reserved.

Maruoka, T.; Koeberl, C.; Bohor, B.F.

2007-01-01

4

The Cretaceous/ Tertiary Boundary At Iridium Hill, Garfield County, Montana  

NSDL National Science Digital Library

The goal of this virtual field trip to Iridium Hill, Montana is to investigate the disappearance of dinosaur fossils above the Cretaceous/ Tertiary boundary. The site provides rock outcrop photos of Cretaceous and Tertiary strata (Hell Creek and Fort Union Formations), stratigraphic sections and supporting text for this classic iridium-bearing locality. Topics include the K/T boundary, iridium concentrations, stratigraphy, sedimentology and, fluvial and lacustrine depositional environments.

Limited, Athro

5

Fullerenes in the cretaceous-tertiary boundary layer  

SciTech Connect

High-pressure liquid chromatography with ultraviolet-visible spectral analysis of toluene extracts of samples from two Cretaceous-Tertiary (K-T) boundary sites in New Zealand has revealed the presence of C[sub 60] at concentrations of 0.1 to 0.2 parts per million of the associated soot. This technique verified also that fullerenes are produced in similar amounts in the soots of common flames under ambient atmospheric conditions. Therefore, the C[sub 60] in the K-T boundary layer may have originated in the extensive wildfires that were associated with the cataclysmic impact event that terminated the Mezozoic era about 65 million years ago.

Heymann, D.; Chibante, L.P.F.; Smalley, R.E. (Rice Univ., Houston, TX (United States)); Brooks, R.R. (Massey Univ., Palmerston North (New Zealand)); Wolbach, W.S. (Illinois Wesleyan Univ., Bloomington, IL (United States))

1994-07-29

6

The Western North American Cretaceous-Tertiary (K-T) boundary interval and its content of shock-metamorphosed minerals: Implications concerning the K-T boundary impact-extinction theory  

NASA Technical Reports Server (NTRS)

At 20 sites in the Raton Basin of Colorado and New Mexico, and at several other sites in Wyoming, Montana, and Canada, a pair of claystone units, an Ir abundance anomaly, and a concentration of shock-metamorphosed minerals mark the palynological K-T boundary. The K-T boundary claystone, which is composed of kaolinite and small amounts of illite/smectite mixed-layer clay, is similar in most respects to kaolinite tonstein layers in coal beds. At some, but not all, K-T boundary localities, the boundary claystone contains solid kaolinite and hollow and solid goyazite spherules, 0.05 to 1.2 mm in diameter. The upper unit, the K-T boundary impact layer, consists chiefly of kaolinite and various amounts of illite/smectite mixed-layer clay. The impact layer and boundary claystone are similar chemically, except that the former has slightly more Fe, K, Ba, Cr, Cu, Li, V, and Zn than the latter. The facts that the boundary claystone and impact layer contain anomalous amounts of Ir, comprise a stratigraphic couplet at Western North American sites, and form thin, discrete layers, similar to air-fall units (volcanic or impact), suggest that the claystone units are of impact origin. Significantly, the impact layer contains as much as 2 percent clastic mineral grains, about 30 percent of which contain multiple sets of shock lamellae. Only one such concentration of shocked minerals has been found near the K-T boundary. The type of K-T boundary shock-metamorphosed materials (quartzite and metaquartzite) in the impact layer and the lack of shock lamellae in quartz and feldspar of pumice lapilli and granitic xenoliths in air-fall pumice units of silicic tuffs, such as the Bishop Tuff, eliminate the possibility that the shock-metamorphosed minerals in the K-T impact layer are of volcanic origin. The global size distribution and abundance of shock-metamorphosed mineral grains suggest that the K-T impact occurred in North America.

Izett, G. A.

1988-01-01

7

Palynology and sedimentology across a new marine Cretaceous-Tertiary boundary section on Nuussuaq, West Greenland  

Microsoft Academic Search

A new northern high-latitude Cretaceous-Tertiary (K-T) boundary section has been studied at Annertuneq on the north coast of Nuussuaq, West Greenland. The boundary section is situated in a succession of homogeneous dark mudstone deposited in a marine-slope environment. Identification of the boundary is based on the presence of the latest Maastrichtian palynomorphs Palynodinium grallator, Disphaerogena carposphaeropsis, Manumiella spp., and Wodehouseia

Henrik Nøhr-Hansen; Gregers Dam

1997-01-01

8

40Ar/39Ar age of Cretaceous-Tertiary boundary tektites from Haiti  

USGS Publications Warehouse

40Ar/39Ar dating of tektites discovered recently in Cretaceous-Tertiary (K-T) boundary marine sedimentary rocks on Haiti indicates that the K-T boundary and impact event are coeval at 64.5 ?? 0.1 million years ago. Sanidine from a bentonite that lies directly above the K-T boundary in continental, coal-bearing, sedimentary rocks of Montana was also dated and has a 40Ar/39Ar age of 64.6 ?? 0.2 million years ago, which is indistinguishable statistically from the age of the tektites.

Izett, G.A.; Dalrymple, G.B.; Snee, L.W.

1991-01-01

9

Wildfires and animal extinctions at the Cretaceous\\/Tertiary boundary  

Microsoft Academic Search

Persuasive models of the ejection of material at high velocities from the Chicxulub asteroid impact marking the Cretaceous\\/Tertiary boundary have led to the conclusion that upon return, that material, heated in passage through the upper atmosphere, generated a high level of infrared energy density over the Earth's surface. That radiant energy has been considered to be a direct source of

Robert K. Adair

2010-01-01

10

Biostratigraphy of the Cretaceous\\/Tertiary boundary in the Sirwan Valley (Sulaimani Region, Kurdistan, NE Iraq)  

Microsoft Academic Search

The Cretaceous\\/Tertiary (K\\/T) boundary sequence, which crops out in the studied area is located within the High Folded Zone, in the Sirwan Valley, northeastern Iraq. These units mainly consist of flysch and flysch-type successions of thick clastic beds of Tanjero\\/Kolosh Formations. A detailed lithostratigraphic study is achieved on the outcropping uppermost part of the Upper Cretaceous successions (upper part of

Khalid Mahmood Sharbazheri; Imad Mahmood Ghafor; Qahtan Ahmad Muhammed

2009-01-01

11

Biostratigraphy of the Cretaceous/Tertiary boundary in the Sirwan Valley (Sulaimani Region, Kurdistan, NE Iraq)  

NASA Astrophysics Data System (ADS)

The Cretaceous/Tertiary (K/T) boundary sequence, which crops out in the studied area is located within the High Folded Zone, in the Sirwan Valley, northeastern Iraq. These units mainly consist of flysch and flysch-type successions of thick clastic beds of Tanjero/Kolosh Formations. A detailed lithostratigraphic study is achieved on the outcropping uppermost part of the Upper Cretaceous successions (upper part of Tanjero Formation) and the lowermost part of the Kolosh Formation. On the basis of the identified planktonic foraminiferal assemblages, five biozones are recorded from the uppermost part of Tanjero Formation and four biozones from the lower part of the Kolosh Formation (Lower Paleocene) in the Sirwan section. The biostratigraphic correlations based on planktonic foraminiferal zonations showed a comparison between the biostratigraphic zones established in this study and other equivalents of the commonly used planktonic zonal scheme around the Cretaceous/Tertiary boundary in and outside Iraq.

Sharbazheri, Khalid Mahmood; Ghafor, Imad Mahmood; Muhammed, Qahtan Ahmad

2009-10-01

12

Paleoenvironmental changes across the Cretaceous–Tertiary boundary at Koshak, Kazakhstan, based on planktic foraminifera and clay mineralogy  

Microsoft Academic Search

The Koshak section of the Mangyshlack Peninsula, Kazakhstan, is one of the most complete Cretaceous–Tertiary (K–T) transitions known from the boreal Paratethys. Cretaceous species richness is low (11 to 13 species), except for a peak of 20 species near the K\\/T boundary in the uppermost Maastrichtian (top 50 cm) that represents the temporary incursion of low-latitude taxa. This maximum species

Alfonso Pardo; Thierry Adatte; Gerta Keller; Hedi Oberhänsli

1999-01-01

13

Changes in coiling direction of Cibicidoides pseudoacutus (Nakkady) across the Cretaceous–Tertiary boundary of Tunisia: palaeoecological and biostratigraphic implications  

Microsoft Academic Search

The analysis of coiling direction preference in the benthic foraminifera Cibicidoides pseudoacutus (Nakkady) has been carried out across the Cretaceous–Tertiary boundary (K–T boundary) from four Tunisian sections representing a palaeobathymetric transect from a middle–outer neritic to lower upper bathyal depositional setting. Our study reveals that C. pseudoacutus developed a preference for sinistral coiling in a short time period during the

Simone Galeotti; Rodolfo Coccioni

2002-01-01

14

Iridium, sulfur isotopes and rare earth elements in the Cretaceous-Tertiary boundary clay at Stevns Klint, Denmark  

Microsoft Academic Search

Microbial activity and redox-controlled precipitation have been of major importance in the process of metal accumulation in the strongly Ir-enriched Cretaceous-Tertiary (K-T) boundary clay, the Fish Clay, at Stevns Klint in Denmark. Two important findings support this view: 1. 1) Kerogen, recovered by leaching the Fish Clay in HCl and HF, shows an Ir concentration of 1100 ppb; this represents

Birger Schmitz; Per Andersson; Jeremy Dahl

1988-01-01

15

Oceanic primary productivity and dissolved oxygen levels at the Cretaceous\\/Tertiary boundary: Their decrease, subsequent warming, and recovery  

Microsoft Academic Search

Thirty-six different geochemical and foraminiferal analyses were conducted on samples collected at closely spaced intervals across the Cretaceous\\/Tertiary (K\\/T) boundary exposed at Caravaca, Spain. A rapid reduction in the gradient between delta13C values in fine fraction carbonate and benthic foraminiferal calcite and a decrease in the abundance of phosphorus (a proxy for organic carbon) and calcium were recorded in sediments

Kunio Kaiho; Yoshimichi Kajiwara; Kazue Tazaki; Masato Ueshima; Nobuyori Takeda; Hodaka Kawahata; Tetsuya Arinobu; Ryoshi Ishiwatari; Akio Hirai; Macros A. Lamolda

1999-01-01

16

Palynologically calibrated vertebrate record from North Dakota consistent with abrupt dinosaur extinction at the Cretaceous-Tertiary boundary  

USGS Publications Warehouse

New data from 17 Cretaceous-Tertiary (K-T) boundary sections and 53 vertebrate sites in the Hell Creek and Fort Union Formations in southwestern North Dakota document a 1.76 m barren interval between the highest Cretaceous vertebrate fossils and the palynologically recognized K-T boundary. The boundary is above the formational contact at 15 localities and coincident with it at two, demonstrating that the formational contact is diachronous. Dinosaurs are common in the highest Cretaceous vertebrate samples and a partial dinosaur skeleton in the Fort Union Formation is the highest recorded Cretaceous vertebrate fossil in this area.

Pearson, D.A.; Schaefer, T.; Johnson, K.R.; Nichols, D.J.

2001-01-01

17

Orbital Cyclicities Above and Below the Cretaceous-Tertiary Boundary, Umbria-Marche Region, Italy  

NASA Technical Reports Server (NTRS)

In the Umbria-Marche region of central Italy, the deep basinal carbonate Scaglia Rossa Formation contains an important sequence of Cretaceous-Tertiary strata including a detailed paleomagnetic record and the distal impactoclastic Cretaceous-Tertiary boundary clay layer. In addition to this significant paleomagnetic and impactoclastic record, the Scaglia Rossa also contains potentially important stratigraphic evidence of relatively long-term oceanic and atmospheric consequences of the Cretaceous-Tertiary bolide catastrophe, which we will describe for the first time herein. Additional information is contained in the original extended abstract.

King, D. T., Jr.; Petruny, L. W.; Rampino, M. R.; Prokoph, A.; Pope, K.; Fischer, A. G.; Montanari, A.; Ocampo, A. C.

2000-01-01

18

Wildfires and animal extinctions at the Cretaceous/Tertiary boundary  

NASA Astrophysics Data System (ADS)

Persuasive models of the ejection of material at high velocities from the Chicxulub asteroid impact marking the Cretaceous/Tertiary boundary have led to the conclusion that upon return, that material, heated in passage through the upper atmosphere, generated a high level of infrared energy density over the Earth's surface. That radiant energy has been considered to be a direct source of universal wildfires, which were presumed to be a major cause of plant and animal species extinctions. The extinction of many animal species, especially the dinosaurs, has also been attributed to the immediate lethal effects of the radiation. I find that the absorption of the radiation by the atmosphere, by cloud formations, and by ejecta drifting in the lower atmosphere reduced the radiation at the surface to a level that cannot be expected to have generated universal fires. Although the reduced radiation will have likely caused severe injuries to many animals, such insults alone seem unlikely to have generated the overall species extinctions that have been deduced.

Adair, Robert K.

2010-06-01

19

Deccan volcanism at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

The accuracy with which one can claim that Deccan trap volcanism occurred at the Cretaceous-Tertiary boundary (KTB) over a very short time interval is of key importance in deciding whether a volcanic origin of the KTB events should be taken seriously. In the two years since paleomagnetic, paleontological and geodynamic evidence was published, further data have become available and the case now appears to be well constrained. The Ar-40/Ar-39 results from six labs have yielded some 24 reliable plateau ages that narrow the age range to 65 to 69 Ma. Moreover, it appears that a significant part of this range results from inter-lab spread and possible minor alteration. Paleontology demonstrates that volcanism started in the Maestrichtian, more precisely in the A. mayaroensis zone. Paleomagnetism shows that volcanism spanned only 3 chrons and only one correlation remains possible, that of the main central reversed chron with 29R. Therefore, whereas Ar-40/Ar-39 is able only to restrict the duration of volcanism to some 4 Ma, paleomagnetism restricts it to 0.5 Ma. Using some geochemical indicators such as C-13 as proxy, it is suggested that volcanism actually consists of a few shorter events of unequal magnitude. Extrusion rates may be as high as 100 cu km/yr and fissure lengths as long as several 100 km. Such a scenario appears to be at least as successful as others in accounting for most anomalies observed at the KTB. Particularly important are Iridium and other platinum group elements (PGE) profiles, Sr-87/Sr-86, C-13, 0-18, other exotic geochemical signatures, spherules, soot, shocked minerals, selective and stepwise extinctions. The environmental impact of CO2 possibly released during explosive phases of volcanism, and SO2 released during effusive phases, and the ability of volcanism to ensure worldwide distribution of KTB products are now all addressed. In conclusion, the case for a causal link between internal hotspot activity, birth of the Reunion hotspot itself as the Deccan and KTB events appears to rest on an increasingly stronger basis.

Courtillot, V.; Vandamme, D.; Besse, J.

1988-01-01

20

40Ar-39Ar dating of the Manson impact structure: A cretaceous-tertiary boundary crater candidate  

USGS Publications Warehouse

The mineralogy of shocked mineral and lithic grains in the Cretaceous-Tertiary (K-T) boundary claystone worldwide is most consistent with a bolide impact on a continent. Both the concentrations and sizes of these shocked grains are greatest in the western interior of North America. These data suggest that the Manson impact structure in north-central Iowa is a viable candidate for the K-T boundary impact event. Argon-40-argon-39 age spectrum dating of shocked microcline from the crystalline central uplift of the Manson impact structure indicates that there was severe argon-40 loss at 65.7 ?? 1.0 million years ago, an age that is indistinguishable from that of the K-T boundary, within the limits of analytical precision.

Kunk, M.J.; Izett, G.A.; Haugerud, R.A.; Sutter, J.F.

1989-01-01

21

Mineralogy of Cretaceous/Tertiary boundary clays in the Chicxulub structure in northern Yucatan  

NASA Technical Reports Server (NTRS)

The Cretaceous/Tertiary (K/T) boundary clay layer is thought to be derived from ejecta material from meteorite impact, based on the anomalous concentrations of noble metals in the layer. Because of recent findings of a half-meter thick ejecta deposit at the K/T boundary in Haiti, efforts have focused on locating a large impact feature in the Caribbean and the Gulf of Mexico. One of the leading candidates for the site of a large impact is the Chicxulub structure located on the northern Yucatan Peninsula in Mexico. The Chicxulub structure is a subsurface zone of upper Cretaceous igneous rocks, carbonates, and breccias. The structure has been interpreted to be a 200 km diameter; however, there is some question to the size of the structure or to the fact that it even is an impact feature. Little is known about the mineralogy of this structure; the objective of this study was to determine the clay mineralogy of core samples from within the Chicxulub structure.

Ming, D. W.; Sharpton, Virgil L.; Schuraytz, B. C.

1991-01-01

22

Palynology and sedimentology across a new marine Cretaceous-Tertiary boundary section on Nuussuaq, West Greenland  

NASA Astrophysics Data System (ADS)

A new northern high-latitude Cretaceous-Tertiary (K-T) boundary section has been studied at Annertuneq on the north coast of Nuussuaq, West Greenland. The boundary section is situated in a succession of homogeneous dark mudstone deposited in a marine-slope environment. Identification of the boundary is based on the presence of the latest Maastrichtian palynomorphs Palynodinium grallator, Disphaerogena carposphaeropsis, Manumiella spp., and Wodehouseia quadrispina below the boundary and on the first occurrence of the earliest Danian species Senoniasphaera inornata above the boundary. Variations in sporomorph and dinoflagellate cyst abundances indicate latest Maastrichtian regression followed by early Danian transgression. The transgressive phase can be subdivided into three high-frequency transgressive-regressive cycles. Each cycle indicates upwelling and transgression, mixing with low-latitudinal water masses, and ocean conditions suggested by the peak occurrences of Senegalinium spp., Trithyrodinium fragile, and Spongodinium delitiense, respectively.

Nøhr-Hansen, Henrik; Dam, Gregers

1997-09-01

23

The Cretaceous/ Tertiary boundary: sedimentology and micropalaeontology at El Mulato section, NE Mexico  

E-print Network

The Cretaceous/ Tertiary boundary: sedimentology and micropalaeontology at El Mulato section, NE and sedimentological analysis of this transition at the El Mulato section (NE Mexico), in order to infer the little Palaeogene Velasco Formation, there is a 2-m-thick Clastic Unit. Strati- graphical and sedimentological ana

Royer, Dana

24

Geologic framework of nonmarine cretaceous-tertiary boundary sites, raton basin, new Mexico and colorado.  

PubMed

Iridium concentrations are anomalously high at the palynological Cretaceous-Tertiary boundary in fluvial sedimentary rocks of the lower part of the Raton Formation at several localities in the Raton Basin of New Mexico and Colorado. The iridium anomaly is associated with a thin bed of kaolinitic claystone in a discontinuous carbonaceous shale and coal sequence. PMID:17742933

Pillmore, C L; Tschudy, R H; Orth, C J; Gilmore, J S; Knight, J D

1984-03-16

25

A new Cretaceous-Tertiary boundary locality in the western powder River basin, Wyoming: biological and geological implications  

USGS Publications Warehouse

A newly discovered Cretaceous-Tertiary (K-T) boundary locality in the western Powder River basin, Wyoming, is characterized by a palynologically defined extinction horizon, a fern-spore abundance anomaly, a strong iridium anomaly, and shock-metamorphosed quartz grains. Detailed microstratigraphic analyses show that about one third of the palynoflora (mostly angiosperm pollen) disappeared abruptly, placing the K-T boundary within a distinctive, 1- to 2-cm-thick claystone layer. Shocked quartz grains are concentrated at the top of this layer, and although fern-spore and iridium concentrations are high in this layer, they reach their maximum concentrations in a 2-cm-thick carbonaceous claystone that overlies the boundary claystone layer. The evidence supports the theory that the K-T boundary event was associated with the impact of an extraterrestrial body or bodies. Palynological analyses of samples from the K-T boundary interval document extensive changes in the flora that resulted from the boundary event. The palynologically and geochemically defined K-T boundary provides a unique time-line of use in regional basin analysis. ?? 1992.

Nichols, D. J.; Brown, J. L.; Attrep, Jr. , M.; Orth, C. J.

1992-01-01

26

Cretaceous/Tertiary boundary in the Eastern Carpathians: evidence from stable isotopes, mineralogy and calcareous nannoplancton  

NASA Astrophysics Data System (ADS)

This study presents the first integrated analyses of stable isotopes, mineralogical, and calcareous nannofossil data from a continuous Upper Campanian to Maastrichtian red bed sequence, including the K/T boundary interval, situated in the bend area of the Romanian Carpathians. The semi-quantitative calcareous nannofossil investigations have focused on six taxonomic groups, such as Watznaueria barnesae, Micula spp., Boreal nannofossils, Tethyan nannofossils, Braarudosphaera bigelowii, and the calcareous dinoflagellate genus Thoracosphaera. The nannofosil investigations show that the sequence spans the Upper Campanian and the whole Maastrichtian stage, including the K/T boundary. Calcite is present in all samples and varies from values up to 70 % down to 2 %. Its concentration varies in opposite direction with the concentration of layer silicates (smectite, chlorite, illite). Quartz and feldspars are plotted together and their content varies between 20 and 40 % and show no systematic fluctuations or long term trends. The delta 13C and d18O values are constant in the Upper Campanian and lower Maastrichtian red marls of the Gura Beliei Formation. In the upper Maastrichtian, lithological, mineralogical and nannofossil changes, together with several negative delta 13C and delta 18O excursions suggest instability of the ecosystems related to climatic changes and/or late Cretaceous tectonic phase. At the Cretaceous/Tertiary boundary, both d13C and d18O values show a negative excursion. Above the Cretaceous nannofossil mass extinction, successive blooms of the dinoflagellate genus Thoracosphaera and of the nannofossil species Braarudosphaera bigelowii were identified. Each of these blooms is marked by successive increases in productivity and positive delta 13C excursions.

Bojar, A.-V.; Melinte-Dobrinescu, M. C.; Bojar, H.-P.

2009-04-01

27

Step-wise extinctions at the Cretaceous-Tertiary boundary and their climatic implications  

NASA Technical Reports Server (NTRS)

A comparative study of planktonic foraminifera and radiolarian assemblages from the Cretaceous-Tertiary (K-T) boundary section of the Beloc Formation in the southern Peninsula of Haiti, and the lowermost Danian sequence of the Micara Formation in southern Cuba reveals a remarkable pattern of step-wise extinctions. This pattern is consistent in both places despite the widely different lithologies of the two formations. Because of a step-wise extinction and the delayed disappearance of taxa known to be more representative of cooler water realms, it is inferred that a cooling trend which characterized the close of the Maastrichtian and the onset of the Tertiary had the major adverse effect on the existing biota. Although repetitive lithologic and faunal fluctuations throughout the Maastrichtian sediments found at Deep Sea Drilling Project (DSDP) site 146/149 in the Caribbean Sea indicate variations reminiscent of known climatically induced cycles in the Cenozoic, rapid biotic succession appears to have taken place during a crisis period of a duration greater than 2 mission years. Widespread and abundant volcanic activities recorded in the Caribbean area during the crisis period gives further credence to earlier contention that intense volcanism may have played a major role in exhacerbating pre-existing climatic conditions during that time.

Maurrasse, Florentin J-M. R.

1988-01-01

28

Geochemical evidence for suppression of pelagic marine productivity at the Cretaceous/Tertiary boundary  

USGS Publications Warehouse

The normal, biologically productive ocean is characterized by a gradient of the 13C/12C ratio from surface to deep waters. Here we present stable isotope data from planktonic and benthic micro-fossils across the Cretaceous/Tertiary boundary in the North pacific, which reveal a rapid and complete breakdown in this biologically mediated gradient. The fluxes of barium (a proxy for organic carbon) and CaCO3 also decrease significantly at the time of the major marine plankton extinctions. The implied substantial reduction in oceanic primary productivity persisted for ???0.5 Myr before the carbon isotope gradient was gradually re-established. In addition, the stable isotope and preservational data indicate that environmental change, including cooling, began at least 200 kyr before the Cretaceous/Tertiary boundary, and a peak warming of ???3 ??C occurred 600 kyr after the boundary event. ?? 1989 Nature Publishing Group.

Zachos, J. C.; Arthur, M. A.; Dean, W. E.

1989-01-01

29

Biotic, geochemical, and paleomagnetic changes across the Cretaceous\\/Tertiary boundary at Braggs, Alabama  

Microsoft Academic Search

Exposed near Braggs, Alabama, is one of the few well-studied, nearly continuous shallow-marine Cretaceous\\/Tertiary boundary sections; it allows a glimpse of the biotic and environmental changes that occurred in the latest Cretaceous to earliest Paleocene. Paleomagnetic, strontium isotopic, and biostratigraphic data closely constrain the age of a series of lithologic, geochemical, and biotic variations and suggest that no more than

Douglas S. Jones; Paul A. Mueller; Jonathan R. Bryan; Jon P. Dobson; James E. T. Channell; James C. Zachos; Michael A. Arthur

1987-01-01

30

Main Deccan Trap Eruptions occurred close to the Cretaceous-Tertiary Boundary: increasing Multiproxy Evidence  

Microsoft Academic Search

Recent studies indicate that the bulk (80%) of the Deccan trap eruptions occurred over less than 0.8 m.y. in magnetic polarity C29r spanning the Cretaceous-Tertiary boundary (KTB) (Chenet et al, 2007, 2008). Detailed multiproxy studies from several sections from southeastern India (Rajhamundry, Andhra Pradesh) and central India (Jilmili, Madhya Pradesh) place the KTB event near the end of the main

Thierry Adatte; Gerta Keller

2010-01-01

31

Evidence for the recovery of terrestrial ecosystems ahead of marine primary production following a biotic crisis at the Cretaceous-Tertiary boundary  

USGS Publications Warehouse

The fossil record demonstrates that mass extinction across the Cretaceous–Tertiary (K–T) boundary is more severe in the marine than the terrestrial realm. We hypothesize that terrestrial ecosystems were able to recover faster than their marine counterparts. To test this hypothesis, we measured sedimentary ?13C as a tracer for global carbon cycle changes and compared it with palaeovegetational changes reconstructed from palynomorphs and cuticles across the K–T boundary at Sugarite, New Mexico, USA. Different patterns of perturbation and timescales of recovery of isotopic and palaeobotanical records indicate that the ?13C excursion reflects the longer recovery time of marine versus terrestrial ecosystems.

Beerling, D.J.; Lomax, B.H.; Upchurch, G.R., Jr.; Nichols, D.J.; Pillmore, C.L.; Handley, L.L.; Scrimgeour, C.M.

2001-01-01

32

Palynological and iridium anomalies at Cretaceous-Tertiary boundary, south-central Saskatchewan  

USGS Publications Warehouse

The Cretaceous-Tertiary boundary in south-central Saskatchewan is marked by coincident anomalies in abundance of iridium and fern spores at the extinction level of a suite of Cretaceous pollen taxa. Evidence of disruption of the terrestrial flora includes the fern-spore abundance anomaly and local extinction of as much as 30 percent of angiosperm species. The reorganized earliest Tertiary flora is made up largely of surviving species that assumed new roles of dominance. Persistence of climatically sensitive taxa across the boundary indicates that if paleoclimate was altered by the terminal Cretaceous event, it returned quickly to the pre-event condition.

Nichols, D.J.; Jarzen, D.M.; Orth, C.J.; Oliver, P.Q.

1986-01-01

33

Marine and continental K-T boundary clays compared  

NASA Technical Reports Server (NTRS)

Detailed geochemical and mineralogical studies (1 to 5) of sediments across the Cretaceous-Tertiary (K-T) boundary at Stevns Klint, Karlstrup, Nye Klov, Dania, and Kjolby Gaard in Denmark, at Limhamn in Sweden, at Caravaca in Spain, at Waipara and Woodside Creek in New Zealand, at Trinidad in Colorado, and at various sites in Montana, have induced conclusions and reflections which are given and briefly discussed.

Schmitz, B.

1988-01-01

34

Macro-invertebrates and the Cretaceous-Tertiary boundary  

NASA Astrophysics Data System (ADS)

Most of Cretaceous macro-invertebrate groups such as ammonites, inoceramids, belemnites, and rudists whow a gradual decline towards the C/T boundary, and some of them disappear long before the boundary level itself. As in the terrestrial vertebrates, their disappearance is unrelated to an extraterrestrial impact as suggested by the widespread iridium anomaly occurring at the boundary. It is also unrelated to fluctuations in temperature, which have been recognized near the boundary level but which can probably be better correlated with such an event. The decline of ammonites is gradual and at the same time periodic in nature. Periodic events occurring through the Upper Cretaceous and the Phanerozoic as a whole are sea level changes. Indeed, the pattern of global transgressions and regressions shows a striking similarity with increasing and decreasing ammonite diversity. In contrast, the turnover in calcareous plankton of oceanic surface waters as well as in angiosperms (Aquilapollenites Province) is a later and "instantaneous" event which can be related with observed fluctuations in temperature, the iridium anomaly, and presumed impact at the boundary level.

Wiedmann, Jost

35

Biospheric effects of a large extraterrestrial impact: Case study of the cretaceous/tertiary boundary crater  

NASA Technical Reports Server (NTRS)

The Chicxulub impact crater, buried in the Yucatan carbonate platform in Mexico, is the site of the impact purported to have caused mass extinctions at the Cretaceous/Tertiary (K/T) boundary. A recently discovered Chicxulub ejecta deposit in Belize contains evidence of carbonate vaporization and precipitation from the vapor plume. Sulfate clasts are almost absent in the Belize ejecta, but are abundant in the coarse ejecta near the crater rim, hwich may reflect the greater abundance of sulfates deep in the target section. The absence of sulfate precipitates in Belize may indicate that most of the vaporized sulfur was deposited in the upper atmosphere. Hydrocode modeling of the impact indicates that between 0.4 to 7.0 x 10(exp 17) g of sulfur were vaporized by the impact in sulfates. Laser experiments indicate that SO2, SO3, and SO4 are produced, and that complex chemical reactions between plume constituents occur during condensation. The sulfur released as SO3 or SO4 converted rapidly into H2HO4 aerosol. A radiative transfer model coupled with a model of coagulation predicts that the aerosol prolonged the initial blackout period caused by impact dust only if it contained impurities. The sulfur released as SO2 converted to aerosol slowly due to the rate limiting oxidation of SO2. Radiative transfer calculations combined with rates of acid production, coagulation, and diffusion indicate that solar transmission was reduced to 10-20 percent of normal for a period of 8-13 years. This reduction produced a climate forcing (cooling) of -300 Wm(exp -2), which far exceeded the +8 Wm(exp -2) greenhouse warming caused by the CO2 released through the vaporization of carbonates, and therefore produced a decade of freezing and near-freezing temperatures. Several decades of moderate warming followed the decade of severe cooling due to the long residence time of CO2. The prolonged impact winter may have been a major cause of the K/T extinctions.

Pope, Kevin O.

1995-01-01

36

Biospheric effects of a large extraterrestrial impact: Case study of the Cretaceous/Tertiary boundary crater  

NASA Technical Reports Server (NTRS)

The Chicxulub Crater in Yucatan, Mexico, is the primary candidate for the impact that caused mass extinctions at the Cretaceous/Tertiary boundary. The target rocks at Chicxulub contain 750 to 1500 m of anhydrite (CaSO4), which was vaporized upon impact, creating a large sulfuric acid aerosol cloud. In this study we apply a hydrocode model of asteroid impact to calculate the amount of sulfuric acid produced. We then apply a radiative transfer model to determine the atmospheric effects. Results include 6 to 9 month period of darkness followed by 12 to 26 years of cooling.

Pope, Kevin O.

1994-01-01

37

Trace element and isotope geochemistry of Cretaceous-Tertiary boundary sediments: identification of extra-terrestrial and volcanic components  

NASA Technical Reports Server (NTRS)

Trace element and stable isotope analyses were performed on a series of sediment samples crossing the Cretaceous-Tertiary (K-T) boundary from critical sections at Aumaya and Sopelano, Spain. The aim is to possibly distinguish extraterrestrial vs. volcanic or authigenic concentration of platinum group and other elements in K-T boundary transitional sediments. These sediments also have been shown to contain evidence for step-wise extinction of several groups of marine invertebrates, associated with negative oxygen and carbon isotope excursions occurring during the last million years of the Cretaceous. These isotope excursions have been interpreted to indicate major changes in ocean thermal regime, circulation, and ecosystems that may be related to multiple events during latest Cretaceous time. Results to date on the petrographic and geochemical analyses of the Late Cretaceous and Early Paleocene sediments indicate that diagenesis has obviously affected the trace element geochemistry and stable isotope compositions at Zumaya. Mineralogical and geochemical analysis of K-T boundary sediments at Zumaya suggest that a substantial fraction of anomalous trace elements in the boundary marl are present in specific mineral phases. Platinum and nickel grains perhaps represent the first direct evidence of siderophile-rich minerals at the boundary. The presence of spinels and Ni-rich particles as inclusions in aluminosilicate spherules from Zumaya suggests an original, non-diagenetic origin for the spherules. Similar spherules from southern Spain (Caravaca), show a strong marine authigenic overprint. This research represents a new approach in trying to directly identify the sedimentary mineral components that are responsible for the trace element concentrations associated with the K-T boundary.

Margolis, S. V.; Doehne, E. F.

1988-01-01

38

A non-catastrophist explanation for the iridium anomaly at the Cretaceous/Tertiary boundary  

NASA Technical Reports Server (NTRS)

The iridium (Ir) anomaly at the Cretaceous/Tertiary (C/T) boundary can be explained by dissolution of normal pelagic limestones producing an insoluble clay residue containing Ir-rich meteoritic material. Further concentration of Ir and other trace metals in the clay can be explained by deposition under reducing conditions. Clay-mineral analyses indicate that the boundary clay is similar to locally derived clays in the limestones above and below the boundary, and contains no detectable exotic components. This supports a terrestrial origin for the boundary clay. The genesis of the boundary clay is attributed to changes in ocean chemistry (pH and oxygenation), leading to an interval of widespread dissolution of carbonate sequences in the oceans, and culminating in the development of submarine pyritic hardgrounds and a disconformity of global extent.

Rampino, M. R.

1982-01-01

39

A Major Meteorite Impact on the Earth 65 Million Years Ago: Evidence from the Cretaceous-Tertiary Boundary Clay  

Microsoft Academic Search

Evidence for a major meteorite impact on the earth 65 million years ago is shown by the presence of meteoritic debris in the ``fish clay'' from Denmark representing the Cretaceous-Tertiary boundary Noble metals (iridium, osmium, gold, platinum, rhenium, ruthenium, palladium, nickel, and cobalt), which are sensitive indicators of meteorites and are normally depleted on the terrestrial surface by factors of

R. Ganapathy

1980-01-01

40

Chicxulub impact predates the K-T boundary mass extinction.  

PubMed

Since the early l990s the Chicxulub crater on Yucatan, Mexico, has been hailed as the smoking gun that proves the hypothesis that an asteroid killed the dinosaurs and caused the mass extinction of many other organisms at the Cretaceous-Tertiary (K-T) boundary 65 million years ago. Here, we report evidence from a previously uninvestigated core, Yaxcopoil-1, drilled within the Chicxulub crater, indicating that this impact predated the K-T boundary by approximately 300,000 years and thus did not cause the end-Cretaceous mass extinction as commonly believed. The evidence supporting a pre-K-T age was obtained from Yaxcopoil-1 based on five independent proxies, each with characteristic signals across the K-T transition: sedimentology, biostratigraphy, magnetostratigraphy, stable isotopes, and iridium. These data are consistent with earlier evidence for a late Maastrichtian age of the microtektite deposits in northeastern Mexico. PMID:15004276

Keller, Gerta; Adatte, Thierry; Stinnesbeck, Wolfgang; Rebolledo-Vieyra, Mario; Fucugauchi, Jaime Urrutia; Kramar, Utz; Stüben, Doris

2004-03-16

41

Iridium and trace element measurements from the Cretaceous-Tertiary boundary, site 752, Broken Ridge, Indian Ocean  

NASA Technical Reports Server (NTRS)

Fourteen samples spanning a 2.5 m interval that includes the Cretaceous-Tertiary (K/T) boundary from Hole 752B near the crest of Broken Ridge in the eastern Indian Ocean were studied in order to search for anomalous enrichments of iridium (Ir) and shock-metamorphosed quartz grains. No allogenic quartz grains larger than 10 microns were observed, hence the presence of quartz containing diagnostic evidence of shock-metamorphism could not be confirmed. Two Ir anomalies of 2.2 +/- 0.6 and 2.0 +/- 0.4 parts per billion (ppb) were measured in samples of dark green ash-bearing chalk at depths of 357.93 and 358.80 m below seafloor, respectively. These samples containing anomalous enrichments of Ir were taken from approximately 82 cm above and 5 cm below the extinction level of Globotruncanids. Our results are consistent with those of Michel et al., who observe elevated concentrations of Ir at these depths in addition to a larger Ir anomaly associated with the extinction level of Globotruncanids.

Schuraytz, B. C.; O'Connell, S.; Sharpton, V. L.

1991-01-01

42

Iridium profile for 10 million years across the Cretaceous-Tertiary boundary at Gubbio (Italy)  

NASA Technical Reports Server (NTRS)

The iridium anomaly at the Cretaceous-Tertiary (KT) boundary was discovered in the pelagic limestone sequence at Gubbio on the basis of 12 samples analyzed by neutron activation analysis (NAA) and was interpreted as indicating impact of a large extraterrestrial object at exactly the time of the KT mass extinction. Continuing controversy over the shape of the Ir profile at the Gubbio KT boundary and its interpretation called for a more detailed follow-up study. Analysis of a 57-meter-thick, 10-million-year-old part of the Gubbio sequence using improved NAA techniques revealed that there is only one Ir anomaly at the KT boundary, but this anomaly shows an intricate fine structure, the origin of which cannot yet be entirely explained. The KT Ir anomaly peaks in a 1-centimeter-thick clay layer, where the average Ir concentration is 3000 parts per trillion (ppt); this peak is flanked by tails with Ir concentrations of 20 to 80 ppt that rise above a background of 12 to 13 ppt. The fine structure of the tails is probably due in part to lateral reworking, diffusion, burrowing, and perhaps Milankovitch cyclicity.

Alvarez, Walter; Asaro, Frank; Montanari, Alessandro

1990-01-01

43

Osmium-187/osmium-186 in manganese nodules and the Cretaceous-Tertiary boundary  

SciTech Connect

As a result of the radioactive decay of rhenium-187 (4.6 x 10/sup 10/ years) the osmium-187/osmium-186 ratio changes in planetary systems as a function of time and the rhenium-187/osmium-186 ratio. For a value of the rhenium-187/osmium-186 ratio of about 3.2, typical of meteorites and the earth's mantle, the present-day osmium-187/osmium-186 ratio is about 1. The earth's continental crust has an estimated rhenium-187/osmium-186 ratio of about 400, so that for a mean age of the continent of 2 x 10/sup 9/ years, a present-day osmium-187/osmium-186 ratio of about 10 is expected. Marine manganese nodules show values (6 to 8.4) compatible with this expectation if allowance for a 25 percent mantle osmium supply to the oceans is allowed. The Cretaceous-Tertiary boundary iridium-rich layer in the marine section at Stevns Klint, Denmark, yields an osmium-187/osmium-186 ratio of 1.65, and the one in a continental section in the Raton Basin, Colorado, is 1.29. The simplest explanation is that these represent osmium imprints of predominantly meteoritic origin.

Luck, J.M.; Turekian, K.K.

1983-11-11

44

Cretaceous/Tertiary Boundary at Ocean Drilling Program Site 1138 and Paleobiogeography of Calcareous Nannofossil Genus Hornibrookina in the Early Paleocene  

NASA Astrophysics Data System (ADS)

A biostratigraphically complete, but bioturbated, Cretaceous/Tertiary (K/T) boundary was recovered by Ocean Drilling Project (ODP) Leg 183 on the Central Kerguelen Plateau (CKP). The K/T boundary was placed at 490.97 mbsf at a dramatic color change in the sediment. The sediment changed from a white chalk in the Cretaceous to a greenish clayey-chalk just above the K/T boundary, then grades back into a white chalk in the early Paleocene. Bulk carbonate isotopic analysis reveals a decrease in the ? 13C of 0.5\\permil across the boundary, similar to that recorded at other high-latitude K/T boundaries. Calcareous nannofossils from the boundary interval were divided into three groups for study following Pospichal and Wise (1990). The three groups, "Cretaceous," "Tertiary," and "Survivor," show sequential change across the boundary. Below the color change, Cretaceous taxa are the most abundant with Prediscosphaera stoveri consisting of over 30% of the assemblage. Survivor taxa (Neocrepidolithus, Markalius inversus, and Placozygus sigmoides) are rare. At the color change, nannofossil abundances are much diminished and poorly preserved. Most of the taxa identified are Cretaceous taxa with very few survivor taxa. Above the color change, nannofossils become more abundant and better preserved. The survivor taxa become more abundant and the new Tertiary taxa (Hornibrookina and Cruciplacolithus) also increase in abundance, while the reworked Cretaceous taxa are a significant part of the assemblage just above the boundary, they become increasingly rare as you move up the column until they disappear in NA5 (CP3). Abundance and distribution of the genus Hornibrookina can be used to identify water mass boundaries in the early Paleocene. Hornibrookina is known to acme at high-latitude (> 60\\deg S) Sites 690 and 738, while becoming less abundant with decreasing latitudes. This trend is documented at Sites 1135 and 750 (55-60\\deg S), Sites 1138 (53\\deg S) and 752 (50\\deg S) with Hornibrookina abundances being common, rare and single, respectively. These abundance patterns delineate cool water mass boundaries across the Kerguelen Plateau in the earliest Paleocene.

Arney, J. E.; Wise, S. W.

2001-12-01

45

Cretaceous-tertiary boundary spherules and Cenozoic microtektites: Similarities and differences  

NASA Technical Reports Server (NTRS)

Bohor and Betterton pointed out that the K-T spherules can be divided into three groups. Their Type 1 spherules appear to be found in or adjacent to North America, particularly the Western Interior and in Haiti and Mexico. The Type 1 spherules occur in the lower part of the K-T boundary clay below an Ir anomaly. It is the Type 1 spherules which are most similar to microtektites. The discovery of K-T boundary spherules in Beloc, Haiti, and Mimbral, Mexico, with residual tektite-like glass cores supports the hypothesis that the Type 1 spherules are diagenetically altered microtektites. The similarities and differences of the Type 1 K-T boundary spherules to previously described Cenozoic microtektites are discussed.

Glass, B. P.; Bohor, Bruce F.; Betterton, William J.

1993-01-01

46

Osmium187\\/osmium-186 in manganese nodules and the Cretaceous-Tertiary boundary  

Microsoft Academic Search

The Os-187\\/Os-186 ratio in the Cretaceous-Tertiary transition was examined to test the hypothesis that a meteoritic impact was responsible for the large-scale extinction of species which occurred soon after. Mantle and meteoritic material have a ratio currently of about 1, while crustal material would yield a ratio of about 10. A large sample of manganese nodule ratios was analyzed to

J. M. Luck; K. K. Turekian

1983-01-01

47

New Evidence links Deccan Traps to the Cretaceous-Tertiary Boundary Mass Extinction  

NASA Astrophysics Data System (ADS)

Recent studies indicate that Deccan Trap volcanism began with a relatively minor eruption phase (~6% of total volume) during the late Maastrichtian magnetic polarity C30n. The main eruption phase (~80%) occurred over a short period in C29r just below the Cretaceous-Tertiary boundary (KTB) and the last Deccan phase (~14%) erupted in the early Danian C29n. Multiproxy studies from sections in Meghalaya (NE India), Jhilmili in central India (Madhya Pradesh), 6 quarry outcrops from Rajahmundry (SE India), 10 deep wells from the Krishna-Godavari Basin (K-G) (Andhra Pradesh) place the KTB mass extinction near the end of the main Deccan phase coincident with the mass extinction. These studies show that the second and third phase of eruptions each produced the world's largest and longest lava megaflows ~1500 km across India through the K-G Basin into the Bay of Bengal. These megaflows are separated by sand, silt and shale which record the mass extinction across an interval that spans zones CF1-CF2 and most of the nannofossil Micula prinsii zone and is correlative with the rapid global warming and subsequent cooling near the end of the Maastrichtian. The mass extinction began preceding the first of the four mega-flows in C29r. Planktic foraminifera suffered a 50% drop in species richness. Survivors suffered another 50% drop after the first mega-flow, leaving just 7 to 8 survivor species. No recovery occurred between the next three mega-flows and the mass extinction was complete with the last phase-2 megaflow at the KTB. The last phase of Deccan volcanism and its 3 to 4 megaflows in the early Danian C29n (zone P1b) delayed biotic recovery of marine plankton. Correlative with these intense volcanic phases, climate changed from humid/tropical to arid conditions and returned to normal tropical humidity after the last phase of volcanism. Similar environmental conditions, mass extinction and delayed recovery patterns are observed in Meghalaya, NE India.The mass extinction was likely the consequence of rapid and massive volcanic CO2 and SO2 gas emissions, leading to high continental weathering rates, global warming, cooling, acid rains, ocean acidification and a carbonate crisis in the marine environment.

Adatte, T.; Keller, G.

2012-04-01

48

The Origin of Fullerenes in the 65 Myr Old Cretaceous/Tertiary Boundary  

NASA Technical Reports Server (NTRS)

In this work we have searched for extraterrestrial (ET) helium (He) in fullerenes isolated from several K/T boundary (KTB) sediments. Measurements of He in these KTB fullerene residues revealed He-3/He-4 ratios that can only be explained as ET in origin.

Becker, L.; Poreda, R. J.; Bunch, T. E.

2000-01-01

49

Ar-40 to Ar-39 ages of the large impact structures Kara and Manicouagan and their relevance to the Cretaceous-Tertiary and the Triassic-Jurassic boundary  

NASA Astrophysics Data System (ADS)

Since the discovery of the Ir enrichment in Cretaceous-Tertiary boundary clays in 1980, the effects of a 10-km asteroid impacting on the Earth 65 Ma ago have been discussed as the possible reason for the mass extinction--including the extinction of the dinosaurs--at the end of the Cretaceous. But up to now no crater of this age that is large enough (ca. 200 km in diameter) has been found. One candidate is the Kara Crater in northern Siberia. Kolesnikov et al. determined a K-Ar isochron of 65.6 +/- 0.5 Ma, indistinguishable from the age of the K-T boundary and interpreted this as confirmation of earlier proposals that the Kara bolide would have been at least one of the K-T impactors. Koeberl et al. determined Ar-40 to Ar-39 ages ranging from 70 to 82 Ma and suggested an association to the Campanian-Maastrichtian boundary, another important extinction horizon 73 Ma ago. We dated four impact melts, KA2-306, KA2-305, SA1-302, and AN9-182. Results from the investigation are discussed.

Trieloff, M.; Jessberger, E. K.

50

Ar-40 to Ar-39 ages of the large impact structures Kara and Manicouagan and their relevance to the Cretaceous-Tertiary and the Triassic-Jurassic boundary  

NASA Technical Reports Server (NTRS)

Since the discovery of the Ir enrichment in Cretaceous-Tertiary boundary clays in 1980, the effects of a 10-km asteroid impacting on the Earth 65 Ma ago have been discussed as the possible reason for the mass extinction--including the extinction of the dinosaurs--at the end of the Cretaceous. But up to now no crater of this age that is large enough (ca. 200 km in diameter) has been found. One candidate is the Kara Crater in northern Siberia. Kolesnikov et al. determined a K-Ar isochron of 65.6 +/- 0.5 Ma, indistinguishable from the age of the K-T boundary and interpreted this as confirmation of earlier proposals that the Kara bolide would have been at least one of the K-T impactors. Koeberl et al. determined Ar-40 to Ar-39 ages ranging from 70 to 82 Ma and suggested an association to the Campanian-Maastrichtian boundary, another important extinction horizon 73 Ma ago. We dated four impact melts, KA2-306, KA2-305, SA1-302, and AN9-182. Results from the investigation are discussed.

Trieloff, M.; Jessberger, E. K.

1992-01-01

51

Comet dust as a source of amino acids at the Cretaceous/Tertiary boundary  

NASA Technical Reports Server (NTRS)

It is suggested here that the large amounts of apparently extraterrestrial amino acids detected recently in rocks at the K/T boundary at Stevns Klint, Denmark were actually deposited with the dust from a giant comet trapped in the inner solar system, a fragment of which comprised the K/T impactor. Amino acids or their precursors in the comet dust would have been swept up by the earth both before and after the impact, but any conveyed by the impactor itself would have been destroyed. The observed amino acid layers would thus have been deposited without an impact.

Zahnle, Kevin; Grinspoon, David

1990-01-01

52

Evidence for a single impact at the Cretaceous-Tertiary boundary from trace elements  

NASA Technical Reports Server (NTRS)

Not only meteoritic elements (Ir, Ni, Au, Pt metals), but also some patently non-meteoritic elements (As, Sb) are enriched at the K-T boundary. Eight enriched elements at 7 K-T sites were compared and it was found that: All have fairly constant proportions to Ir and Kilauea (invoked as an example of a volcanic source of Ir by opponents of the impact theory) has too little of 7 of these 8 elements to account for the boundary enrichments. The distribution of trace elements at the K-T boundary was reexamined using data from 11 sites for which comprehensive are available. The meteoritic component can be assessed by first normalizing the data to Ir, the most obviously extraterrestrial element, and then to Cl chondrites. The double normalization reduces the concentration range from 11 decades to 5 and also facilitates the identification of meteoritic elements. At sites where trace elements were analyzed in sub-divided samples of boundary clay, namely, Caravaca (SP), Stevns Klint (DK), Flaxbourne River (NZ) and Woodside Creek (NZ), Sb, As and Zn are well correlated with Ir across the boundary implying a common deposition mechanism. Elemental carbon is also enriched by up to 10,000 x in boundary clay from 5 K-T sides and is correlated with Ir across the boundary at Woodside Creek. While biomass would appear to be the primary fuel source for this carbon a contribution from a fossil fuel source may be necessary in order to account for the observed C abundance.

Gilmour, Iain; Anders, Edward

1988-01-01

53

Macrofossil extinction patterns at Bay of Biscay Cretaceous-Tertiary boundary sections  

NASA Technical Reports Server (NTRS)

Researchers examined several K-T boundary cores at Deep Sea Drilling Project (DSDP) core repositories to document biostratigraphic ranges of inoceramid shell fragments and prisms. As in land-based sections, prisms in the deep sea cores disappear well before the K-T boundary. Ammonites show a very different extinction pattern than do the inoceramids. A minimum of seven ammonite species have been collected from the last meter of Cretaceous strata in the Bay of Biscay basin. In three of the sections there is no marked drop in either species numbers or abundance prior to the K-T boundary Cretaceous strata; at the Zumaya section, however, both species richness and abundance drop in the last 20 m of the Cretaceous, with only a single ammonite specimen recovered to date from the uppermost 12 m of Cretaceous strata in this section. Researchers conclude that inoceramid bivalves and ammonites showed two different times and patterns of extinction, at least in the Bay of Biscay region. The inoceramids disappeared gradually during the Early Maestrichtian, and survived only into the earliest Late Maestrichtian. Ammonites, on the other hand, maintained relatively high species richness throughout the Maestrichtian, and then disappeared suddenly, either coincident with, or immediately before the microfossil extinction event marking the very end of the Cretaceous.

Ward, Peter D.; Macleod, Kenneth

1988-01-01

54

Extinction and survival of plant life following the Cretaceous/Tertiary boundary event, Western Interior, North America ( USA).  

USGS Publications Warehouse

The palynological Cretaceous/Tertiary boundary is recognized in the northern part of the Western Interior by the abrupt disappearance of a few characteristic Cretaceous pollen genera. In the southern part, the boundary is recognized by the disappearance of a somewhat different group of pollen. The abrupt change in both regions takes place precisely at the stratigraphic horizon at which boundary clay layers containing anomalously high concentrations of iridium are found. All the principal Cretaceous pollen genera that disappear regionally have been reported from Tertiary rocks in other parts of North America. Differential apparent extinction and/or survival reflects a pronounced temporary disruption of plant life immediately after the impact event. Some Cretaceous plants must have persisted in refugia to have provided the propagules for the rapid recovery of the flora. No massive total extinction of plant genera at the end of the Cretaceous can be seen from the palynologic record. -from Authors

Tschudy, R.H.; Tschudy, B.D.

1986-01-01

55

Main Deccan Trap Eruptions occurred close to the Cretaceous-Tertiary Boundary: increasing Multiproxy Evidence  

NASA Astrophysics Data System (ADS)

Recent studies indicate that the bulk (80%) of the Deccan trap eruptions occurred over less than 0.8 m.y. in magnetic polarity C29r spanning the Cretaceous-Tertiary boundary (KTB) (Chenet et al, 2007, 2008). Detailed multiproxy studies from several sections from southeastern India (Rajhamundry, Andhra Pradesh) and central India (Jilmili, Madhya Pradesh) place the KTB event near the end of the main Deccan eruptive phase and indicate that Deccan volcanism could have been a major contributor to the mass extinction (Keller et al., 2008, 2009). Geochemical, mineralogical and micropaleontogical evidence from localities outside India suggest that this megapulse took place in the uppermost Maastrichtian C29r (CF2-CF1 transition). For example, a rapid shift in 187Os/188Os ratios observed in three deep-sea sections (Atlantic, Pacific and Indian Oceans) are interpreted to mark the onset of the main Deccan pulse in C29r (Robinson et al., 2009). Foraminiferal oxygen isotope data from DSDP Site 525 (South Atlantic) show a short rapid global warming in C29r (Li and Keller, 1998) coincident with the decline in 187Os/188Os ratios. This warming is also observed in the terrestrial plant record (Wilf 2003). A coeval increase in weathering observed in Site 525 and Tunisia (Adatte et al., 2002) is marked by dominant kaolinite clay assemblages. In the same interval a significant decrease in bulk carbonate content suggests acidification due to volcanic SO2. Enhanced dissolution is also observed at DSDP Site 527 and Gubbio, Italy. Calcareous microfossils (planktic foraminifera and nannofossils) experienced major stress conditions expressed by species dwarfing, decreased diversity and decreased abundance (Keller, 2005). These observations indicate that Deccan volcanism played a key role in increasing atmospheric CO2 levels that resulted in global warming and enhanced greenhouse effect, which coupled with high SO2 emission increased biotic stress and predisposed faunas to eventual extinction at the KTB. Adatte, T. Keller, G. & Stinnesbeck, W. (2002). PPP 178; 3-4, Pages 165-196. Chenet, A-L., Quidelleur, X., Fluteau, F., Courtillot, V., 2007. EPSL. 263, 1-15. Chenet, A-L., Fluteau, F., Courtillot, V., Gerard, M., Subbarao, K.V., 2008. J. Geophys. Res. 113, B04101. Li, L., Keller, G., 1998c. Geology 26, 995-998. Keller, G. 2005. Lithos, 79, 3-4, 317-341. Keller, G., Adatte, T., Gardin, S., Bartolini, A., Bajpai, S., 2008. EPSL 268, 293-311. Keller, G., Adatte, T., Bajpai, S., Mohabey, D.M., Widdowson, M., Khosla, A., Sharma, R., Khosla, S. C., Gertsch, B., Fleitmann, D., Sahni, A. 2009.. EPSL, 282, 1-4, 10-23 Robinson, Ravizza, G., Coccioni, R. Peucker-Ehrenbrink, B. Norris, R. 2009. EPSL, 281, 3-4, 159-158. Wilf, P., Johnson, K.R., Huber, B.T., 2003. PNAS 100, 599-604.

Adatte, Thierry; Keller, Gerta

2010-05-01

56

Iridium, shocked minerals, and trace elements across the Cretaceous/Tertiary boundary at Maud Rise, Wedell Sea, and Walvis Ridge, South Atlantic Ocean  

NASA Technical Reports Server (NTRS)

Sediments spanning a 5 meter section across the Cretaceous-Tertiary boundary at ODP holes 689B and 690D, Maud Rise, Wedell Sea and hole 527, Walvis Ridge, are being analyzed for shock deformation, PGE's and other trace elements (including REE's). Mineral separates from each sample were studied with optical microscopy to determine the distribution and microstructural state of quartz and feldspar present in the sediments. Samples from Maud Rise were taken of the K/T transition and at about 50 cm intervals above and below it. These samples consist of carbonate-rich sediments, with the K/T transition marked by a change from white Maastrichtian oozes to a greenish ooze with higher concentrations of altered volcanic clay and vitric ash. The Walvis Ridge site is characterized by more clay-rich sediments with average carbonate content about 60 to 70 percent. Initial results from RNAA studies indicate that iridium is present in all the Maud Rise samples in concentrations equal to or greater than 0.01 ppb (whole-rock basis). Preliminary results from optical microscopy indicate the occurrence of shock mosaicism in quartz and feldspar in all of the samples studied. The pervasiveness of shock mosaicism and presence of planar features to 2 meters from the K/T boundary indicates that a single impact or volcanic explosion 66 ma may be ruled out as responsible for the K/T event. A similar conclusion may be drawn independently from the distribution of iridium and other trace elements. Regardless of the source of the shock waves and sediment contamination, multiple events are required over a ca.0.5 my timespan; currently we favor endogenous sources.

Huffman, Alan R.; Crocket, James H.; Carter, Neville L.

1988-01-01

57

Dynamic deformation of volcanic ejecta from the Toba caldera: possible relevance to Cretaceous/Tertiary boundary phenomena  

SciTech Connect

Plagioclase and biotite phenocrysts in ignimbrites erupted from the Toba caldera, Sumatra, show microstructures and textures indicative of shock stress levels higher than 10 GPa. Strong dynamic deformation has resulted in intense kinking in biotite and, with increasing shock intensity, the development of plagioclase of planar features, shock mosaicism, incipient recrystallization, and possible partial melting. Microstructures in quartz indicative of strong shock deformation are rare, however, and many shock lamellae, if formed, may have healed during post-shock residence in the hot ignimbrite; they might be preserved in ash falls. Peak shock stresses from explosive silicic volcanism and other endogenous processes may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures, possibly including shock features observed near the Cretaceous/Tertiary boundary. 38 references, 3 figures.

Carter, N.L.; Officer, C.B.; Chesner, C.A.; Rose, W.I.

1986-05-01

58

Biogeochemical and ecological consequences of dissolved organic carbon released from soot particles from global firestorms at the Cretaceous/Tertiary boundary: Was the Strangelove Ocean a blackwater ocean?  

NASA Astrophysics Data System (ADS)

Phytoplankton productivity in the oceans was suppressed for about 200,000 years after the Cretaceous/Tertiary (K/T) boundary event, and many species of marine calcareous plankton became extinct at the boundary. Proposed causes for what has been called the "Strangelove Ocean" include acidification of oceanic surface waters and effects associated with deposition from a global cloud of firestorm ash. We evaluate the potential effects on the marine ecosystem of leaching of dissolved organic carbon (DOC) from firestorm soot particles. Based upon the quantity of soot deposited in the clay layer at the K/T boundary, we estimate that DOC concentrations in oceanic surface waters increased by at least a factor of two. These results are also supported by extrapolations based upon DOC increases in lakes and streams associated with deposition of ash in Rocky Mountain National Park from the Yellowstone fire of 1988. The soluble soot-derived humic substances would have had different chemical properties than marine humic substances, including a more aromatic character, greater absorptivity for visible light and greater quinone content. These humic substances could have acted as stress-inducing xenobiotic compounds and could have changed the physical and chemical characteristics of the marine environment. Cellular uptake of these humic compounds could have also inhibited calcite precipitation by coccolithophorids and foraminifera, contributing to the greater extinction of these species compared to dinoflagellates. Calculations show that the greater light absorption by the firestorm-derived humic substances would have decreased the depth of the mixed zone, limiting the dilution of the DOC pulse, and would have decreased the depth of the photic zone, spatially restructuring marine ecosystems.

McKnight, D. M.; Steinberg, C.; Baron, J. S.

2002-12-01

59

Energy, volatile production, and climatic effects of the Chicxulub Cretaceous\\/Tertiary impact  

Microsoft Academic Search

A comprehensive analysis of volatiles in the Chicxulub impact strongly supports the hypothesis that impact-generated sulfate aerosols caused over a decade of global cooling, acid rain, and disruption of ocean circulation, which contributed to the mass extinction at the Cretaceous\\/Tertiary (K\\/T) boundary. The crater size, meteoritic content of the K\\/T boundary clay, and impact models indicate that the Chicxulub crater

Kevin O. Pope; Kevin H. Baines; Adriana C. Ocampo; Boris A. Ivanov

1997-01-01

60

Impact mineralogy and chemistry of the cretaceous-tertiary boundary at DSDP site 576  

NASA Technical Reports Server (NTRS)

We have identified the K/T boundary in pelagic clay sediments from cores at DSDP Site 576 in the western North Pacific. Detailed geochemical and trace mineralogical analyses of this boundary section are in progress and initial results indicate similarities and differences relative to the only other clay core investigated in detail; DSDP Site 596, a locality in the western South Pacific. Peak Ir concentrations of 13 ng/g in DSDP Hole 576B are virtually identical with those observed in the South Pacific, but in the North Pacific this peak is much narrower and the integrated Ir fluence of 85 ng cm(exp -2) is 4 times lower (320 in Hole 596). Of the 34 elements measured, only Ir and Cr were found to have anomalous concentrations in K/T boundary samples. Trace mineral residues were obtained by washing away clays and sequential chemical leaches (including HF) to remove typical hydrogenous and biogenous sediment components (e.g., zeolites and radiolarian opal). We attempted to quantitatively recover the entire trace mineral assemblage for grains greater than 30 micrometers in diameter. Our mineral residues were dominated by two phases: quartz and magnesioferrite spinel. Other non-opaque mineral grains we have positively identified were trace K-feldspar, plagioclase, corundum, and muscovite. Of these only K-feldspar exhibited planar deformation features (PDF). We have not found abundant plagioclase, as in the South Pacific suggesting that this phase was either not preserved in the North Pacific, or that in the south, it has a non-impact (i.e., volcanic) source. PDF in quartz were commonly obscured by secondary overgrowths on the surfaces of quartz grains, presumably from diagenetic reprecipitation of silica dissolved from opaline radiolarian tests that are common in these sediments. However, careful examination revealed that most grains had multiple sets of PDF. Of the 133 quartz grains greater than 30 micrometers analyzed, 62 percent showed evidence of shock. The largest shocked grain recovered to date had a maximum diameter of 160 micrometers, consistent with other sites in the Pacific.

Bostwick, Jennifer A.; Kyte, Frank T.

1993-01-01

61

Combined osmium and strontium isotopic study of the Cretaceous-Tertiary boundary at Sumbar, Turkmenistan: A test for an impact vs. a volcanic hypothesis  

Microsoft Academic Search

Osmium and strontium isotopic ratios at the Cretaceous-Tertiary boundary at Sumbar, Turkmenistan, display a negative hyperbolic covariation superimposed on the long-term trend, which displays a positive covariation. The minimum ratio for Os and the maximum ratio for Sr occur at the boundary clay. Volcanism with a mantle or crustal source cannot account for the isotopic data. The low 187-Os\\/188-Os and

Thomas Meisel; Urs Krähenbühl; Michael A. Nazarov

1995-01-01

62

Tektites in Cretaceous-Tertiary boundary rocks on Haiti and their bearing on the Alvarez impact extinction hypothesis  

USGS Publications Warehouse

Relic tektites are associated with a Pt-group metal abundance anomaly and shocked minerals in a thin marl bed that marks the K-T boundary on Haiti. The presence of these three impact-produced materials at the precise K-T boundary enormously strengthens the Alvarez impact extinction hypothesis. The Haitian tektites are the first datable impact products in K-T boundary rocks, and 40Ar-39Ar ages of the glass show that the K-T boundary and impact event are coeval at 64.5 ?? 0.1 Ma. -from Author

Izett, G.A.

1991-01-01

63

Extended period of K/T boundary mass extinction in the marine realm  

NASA Technical Reports Server (NTRS)

The Cretaceous/Tertiary (K/T) boundary mass extinction has been widely recognized as a nearly instantaneous catastrophy among marine plankton such as foraminifera. However, the suddenness of this extinction event may have been overemphasized because most pelagic K/T boundary sequences are stratigraphically incomplete and generally lack the earliest Tertiary (Zones P0 and P1a) either due to carbonate dissolution and/or non-deposition. Stratigraphically complete sections appear to be restricted to continental shelf regions with high sedimentation rates and deposition well above the CCD. Such sections have been recovered from El Kef, Tunisia (1) and Brazos River, Texas. Quantitative foraminiferal analysis of these sections indicate an extinction pattern beginning below the K/T boundary and ending above the boundary. These data imply that the mass extinction event was not geologically instantaneous, but occurred over an extended period of time. Evidence supporting this conclusion is discussed.

Keller, G.

1988-01-01

64

New method for the measurement of osmium isotopes applied to a New Zealand Cretaceous/Tertiary boundary shale  

USGS Publications Warehouse

The determination of osmium content and isotopic abundances in geological materials has received increasing attention in recent years following the proposal of Alvarez et al.1 that mass extinctions at the end of the Cretaceous period were caused by the impact of a large (???10km) meteorite which left anomalously high iridium levels as a geochemical signature in the boundary shales. Here we report a new and simple method for measuring osmium in geological materials, involving fusion of the sample with sodium peroxide, distillation of the osmium as the tetroxide using perchloric acid, extraction into chloroform, and absorption of the chloroform extract onto graphite powder before instrumental neutron activation analysis. In a variant of this technique, the chloroform extract is back-extracted into an aqueous phase and the osmium isotopes are determined by plasma-source mass spectrometry (ICPMS). We have used this method on the Woodside Creek (New Zealand) Cretaceous/Tertiary boundary clay and have obtained the first osmium content (6g ng g-1) for this material. The 187Os/186Os ratio is 1.12??0.16, showing a typical non-crustal signature. This combined distillation-extraction- ICPMS method will prove to be useful for measuring osmium isotopes in other geological materials. ?? 1986 Nature Publishing Group.

Lichte, F.E.; Wilson, S.M.; Brooks, R.R.; Reeves, R.D.; Holzbecher, J.; Ryan, D.E.

1986-01-01

65

Search for fullerenes C 60and C 70in Cretaceous–Tertiary boundary sediments from Turkmenistan, Kazakhstan, Georgia, Austria, and Denmark  

Microsoft Academic Search

Fullerenes C60and C70have been found previously in sediments from the Cretaceous-Tertiary boundary (KTB) sites of Woodside Creek and Flaxbourne River (both New Zealand). Additional discoveries from Caravaca (Spain), Sumbar and Malyi Balkhan (Turkmenistan) and Stevns Klint (Denmark) are reported here. Fullerenes were not found in the KTB sediment from Elendgraben (Austria), nor in acid-demineralized sediments from Koshak (Kazakhstan) and Tetri

D. Heymann; A. Korochantsev; M. A. Nazarov; J. Smit

1996-01-01

66

40Ar-39Ar Ages of the Large Impact Structures Kara and Manicouagan and their Relevance to the Cretaceous-Tertiary and the Triassic-Jurassic Boundary  

NASA Astrophysics Data System (ADS)

Since the discovery of the iridium enrichment in Cretaceous- Tertiary boundary clays by Alvarez et al. (1980) the search for the crater of the K/T impactor is in progress. Petrographic evidence at the K/T boundary material points towards an impact into an ocean as well as onto the continental crust, multiple K/T impacts are now being considered (Alvarez and Asaro, 1990). One candidate is the Kara crater in northern Siberia of which Kolesnikov et al. (1988) determined a K-Ar isochrone age of 65.6 +- 0.5 Ma, regarding this as indicating that the Kara bolide is at least one of the K/T impactors. Koeberl et al. (1990) determined ^40Ar-^39Ar ages of six impact melts ranging from 70 to 82 Ma and suggested rather an association to the Campanian- Maastrichtian boundary, another important extinction horizon 73 Ma ago (Harland et al., 1982). We dated with the ^40Ar-^39Ar technique four impact melts, KA2- 306, KA2-305, SA1-302 and AN9-182. The spectra have rather well- defined plateaus, shown with highly extended age scales (Fig. 1). The plateau ages range from 69.3 to 71.7 Ma. Our data do not support an association either with the Cretaceous-Tertiary or with the Campanian-Maastrichtian boundary. We deduce an age of 69-71 Ma for the Kara impact structure. Nazarov et al. (1991) have demonstrated by isotopic hydrogen studies that the Kara bolide impacted on dry land, while the last regression at the target area before the end of the Cretaceous occurred 69-70 Ma ago. Our data are consistent with an impact shortly after the regression. We further dated impact metamorphic anorthosite samples (10BD5 and 10BD3C) of the Manicouagan crater, Canada, which may be related to the Triassic-Jurassic boundary (McLaren and Goodfellow, 1990). The samples consist of two different phases, one degassing at low temperatures yielding a plateau age of 212 Ma and another phase which was degassed during the cratering event to varying degrees with apparent ages increasing up to 950 Ma, the age of the target rocks (Wolfe, 1971). The low temperature plateaux are in agreement with the crater age of 212 Ma (Grieve, 1991) and do not improve the age of the impact structure. Anyway, while the crater age is quite accurate the ages of the adjacent geologic boundaries seem to be not. The last revision of the Triassic-Jurassic boundary (Harland et al., 1982) approved an age of 213 Ma, while later an age of 208 Ma was determined (Palmer, 1983). We think as far as ages are concerned it is not yet possible to conclude or exclude an association of the impact with the boundary until the age of the boundary is determined more precisely. References: Alvarez, L.W. , Alvarez, W., Asaro, F. and Michel, H.V. (1980) Science, 208, 1095-1108. Alvarez, L.W. and Asaro, F. (1990) Scient. Amer., 362. Grieve, R.A.F. (1991) Met., 26, 175- 194. Harland, W.B., Cox, A.V., Llewellyn, P.G., Pickton, C.A.G., Smith, A.G., and Walters, R. (1982) A geologic time scale. Cambridge Univ. Press. Koeberl, C., Sharpton, V.L., Murali, A.V. and Burke, K. (1990) Geology, 18, 50-53. Kolesnikov, E.M., Nazarov, M.A., Badjukov, D.D. and Shukolyukov, Y.A. (1988) Conf. on Glob. Catastr. in Earth Hist. LPI, Houston, Texas (abstract), 99-100. McLaren, D.J., and Goodfellow, W.D. (1990) Ann. Rev. Earth Planet. Sci., 18, 123-171. Nazarov, M.A., Devirts, A.L., Lagutina, E.P., Alekseev, A.S., Badjukov, D.D. and Shukolyukov, Y.A. (1991) Lunar Planet. Sci. (abstract) 22, 961. Palmer, A.R. (1983) Geology, 11, 503-504. Wolfe, S.H. (1971) J. Geophys. Res., 76, 5424-5436.

Trieloff, M.; Jessberger, E. K.

1992-07-01

67

Combined osmium and strontium isotopic study of the Cretaceous-Tertiary boundary at Sumbar, Turkmenistan: A test for an impact vs. a volcanic hypothesis  

NASA Astrophysics Data System (ADS)

Osmium and strontium isotopic ratios at the Cretaceous-Tertiary boundary at Sumbar, Turkmenistan, display a negative hyperbolic covariation superimposed on the long-term trend, which displays a positive covariation. The minimum ratio for Os and the maximum ratio for Sr occur at the boundary clay. Volcanism with a mantle or crustal source cannot account for the isotopic data. The low 187-Os/188-Os and the high 87-Sr/86-Sr ratios can be explained by an impact, whereby Os was derived from the bolide and the 87Sr/86Sr ratio was enhanced by acid rain and/or a tsunami following the event.

Meisel, Thomas; Krähenbühl, Urs; Nazarov, Michael A.

1995-04-01

68

A Search for Soot from Global Wildfires in Central Pacific Cretaceous-Tertiary Boundary and Other Extinction and Impact Horizon Sediments  

NASA Technical Reports Server (NTRS)

Hypotheses of global wildfires following the Cretaceous-Tertiary (KT) boundary impact are supported by high concentrations of elemental carbon (3.6 mg cm-3) and soot (1.8 mg cm-2) in DSDP Site 465, which was located several thousand kilometers from potential continental sources at 65 Ma. Soot is not preserved at four other central Pacific KT localities, but this is attributed to loss during oxic diagenesis. We find no evidence for wildfires related to major impacts in the late Eocene or to Ir anomalies and extinctions in the late Cenomanian.

Wolbach, Wendy S.; Widicus, Susanna; Kyte, Frank T.

2003-01-01

69

The causes for geographical variations in OS187/OS186 at the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

Researchers at Yale has approached the problem of the osmium isotopic composition of marine deposits formed in contact with both oxidized and reduced bottom waters. The measured (187) Os/(186) Os ratios of modern bulk sediment can be explained using mixing equations involving continental detrital, volcaniclastic, cosmogenic and hydrogeneous components. These studies show that sediments deposited under reducing marine conditions contain a hydrogenous component which is enriched in Re and has a radiogenic (187) Os/(186) Os ratio. The presence of such a hydrogenous component in the marine fish clay at Stevns Klint can account for the elevation of its (187) Os/(186) Os ration above the expected meteoritic value. Mass balance considerations require the Re/Os ratio of the phase precipitated from the terminal Cretaceous sea at Stevns Klint to have been about one tenth the value observed in contemporary deposits in the Black Sea, assuming Re has not been lost (or Os gained) subsequent to precipitation. In continental sections, the elevation of the (187) Os/(186) Os ratio in boundary layers may be due to precipitation from continental waters of crustally-derived radiogenic osmium either contemporaneous with the meteoritic (or mantle) osmium deposition or later during diagenesis.

Turekian, K. K.; Esser, B. K.; Ravizza, G. E.

1988-01-01

70

Plants and the K-T Boundary  

NASA Astrophysics Data System (ADS)

In Plants and the K--T Boundary, two of the world's leading experts in palynology and paleobotany provide a comprehensive account of the fate of land plants during the 'great extinction' about 65 million years ago. They describe how the time boundary between the Cretaceous and Paleogene Periods (the K--T boundary) is recognized in the geological record, and how fossil plants can be used to understand global events of that time. There are case studies from over 100 localities around the world, including North America, China, Russia and New Zealand. The book concludes with an evaluation of possible causes of the K--T boundary event and its effects on floras of the past and present. This book is written for researchers and students in paleontology, botany, geology and Earth history, and everyone who has been following the course of the extinction debate and the K--T boundary paradigm shift.

Nichols, Douglas J.; Johnson, Kirk R.

71

An expanded Cretaceous?Tertiary transition in a pelagic setting of the Southern Alps (central-western Tethys)  

Microsoft Academic Search

An integrated micropalaeontological (planktonic foraminifera and calcareous nannofossils), mineralogical and stable isotope investigation was carried out across the Cretaceous\\/Tertiary (K\\/T) boundary in a previously undescribed hemipelagic section (Forada section) cropping out in the Piave River Valley (Southern Alps, Belluno Province, NE Italy). Our results suggest that an apparently complete K\\/T transition with an expanded basal Danian is preserved in the

Eliana Fornaciari; Luca Giusberti; Valeria Luciani; Fabio Tateo; Claudia Agnini; Jan Backman; Massimo Oddone; Domenico Rio

2007-01-01

72

Paleoecology of the Cretaceous^Tertiary mass extinction in planktonic foraminifera  

E-print Network

Paleoecology of the Cretaceous^Tertiary mass extinction in planktonic foraminifera Gerta Keller a Paleobiogeographic patterns of the Cretaceous^Tertiary (K^T) mass extinction in planktonic foraminifera in Tunisia; K^T planktonic foraminifera 1. Introduction The mass extinction in planktonic foraminifera across

Keller, Gerta

73

Detritus in K/T boundary clays of western North America - Evidence against a single oceanic impact  

NASA Technical Reports Server (NTRS)

Understanding the crustal signature of impact ejecta contained in the Cretaceous/Tertiary (K/T) boundary layer is crucial to constraining the possible site(s) of the postulated K/T impact event. The relatively unaltered clastic constituents of the boundary layer at widely separated outcrops within the western interior of North America are not compatible with a single oceanic impact but require instead an impact site on a continent or continental margin. On the other hand, chemical compositions of highly altered K/T boundary layer components in some marine sections have suggested to others an impact into oceanic crust. We suspect that post-depositional alteration within the marine setting accounts for this apparent oceanic affinity. If, however, this is not the case, multiple simultaneous impacts, striking continent as well as ocean floor, would seem to be required.

Sharpton, V. L.; Schuraytz, B. C.; Burke, K.; Murali, A. V.; Ryder, G.

1990-01-01

74

Constraints on the Nature and Distribution of Iridium Host Phases at the Cretaceous-Tertiary Boundary: Implications for Projectile Identity and dispersal on impact  

NASA Technical Reports Server (NTRS)

Among Cretaceous-Tertiary boundary sites worldwide, variations in the concentrations and ratios of elements commonly enriched in meteorites complicate traditional geochemical attempts at impactor identification. Yet they may provide constraints on the physical and chemical processes associated with large-body disruption and dispersal, as well as with diagenesis of projectile components. To this end, we continue our efforts to identify the mineral host-phases of projectile-derived elements, particularly for Ir, and to document their partitioning between crater deposits and ejecta resulting from the Chicxulub basin-forming impact. Building on earlier work, we used INAA to measure Ir concentrations in successively smaller splits of finely powdered impact melt breccia from the Chicxulub Crater in Mexico (sample Y6Nl9-R(b)), and K/T boundary fish clay from Stevns Klint, Denmark (sample FC-1, split from 40 kg of homogenized material intended as an analytical standard). Results for the Chicxulub sample show a heterogeneous Ir distribution and document that at least five discrete Ir-bearing host phases were isolated in subsequent splits, having Ir masses equivalent to pure Ir spheres from about 0.8 to about 3.5 mm in diameter. Three of these are within a sufficiently reduced mass of powder to warrant searching for them using backscattered electron microscopy. In contrast, successively smaller splits of the Stevns Klint fish clay show no statistically significant deviation from the reported value of 32 +/- 2 ng/g Ir, suggesting a uniform Ir host-phase distribution. For the smallest split obtained thus far (100 +/- 40 ng/g Ir), a pure Ir sphere of equivalent Ir mass would be <0.05 min in diameter. (n.b. Although homogenizing and sieving of FC-1 to <75 min obviously obscured variations in stratigraphic distribution, it is unlikely to have affected the size-frequency distribution of Ir host phases.) We previously identified micrometer-scale Ir host phases by electron microscopy in melt-rock samples from two widely separated drill holes at the Chicxulub Basin, including a replicate split of Y6-NI9-R. One is an aggregate of subhedral Ir metal grains enclosed in silicate, in which no other Pt group elements (PGE) were detected. A second particle with twice the mass as the first, concentrated predominantly in a single grain, is associated with minor concentrations of Os, Ru, and Pt, and with adhering particles of corundum and perovskite. A third Ir-rich particle, with a greater apparent Os concentration, was identified before being lost as a result of charging under the electron beam. In addition to demonstrating the preservation of projectile components within the Chicxulub Crater, analogous phase associations in Ca- and Al-rich inclusions (CAI) from C2 and C3 chondrites suggest to us that these melt-rock Ir host phases are relics from a carbonaceous chondrite K/T boundary impactor Although the obviously low Ru/Ir ratios of the Chicxulub Ir host phases are qualitatively consistent with suggested PGE fractionation with distance during condensation in an ejecta cloud, it seems difficult to explain the accumulation of the about 3 x 10(exp 11) Ir atoms required to form a about 10(exp -10) g nugget of pure Ir metal within a jet of vaporized projectile expanding at 1-4 km/s, or to effectively exclude or remove commonly alloyed PGE and siderophile elements by fractionation processes resulting from condensation, oxidation, sulfidization, exsolution, or autometamorphism during cooling of the melt. We do not dismiss the importance of these processes entirely; on the contrary, other geochemical and mineralogical aspects of the melt rocks require them, and condensation from the expanding ejecta cloud appears to best explain the primary Ir host-phase distribution in the fish clay, as well as the high Ir concentrations associated with spinel-bearing spheroids at the K/T boundary in the Pacific Ocean . If the "relict" hypothesis is correct, micronuggets of other PGEs and alloys, not detected by our INAA screening, should also occur in

Schuraytz, B. C.; Lindstrom, D. J.; Sharpton, V. L.

1997-01-01

75

Impact wave deposits provide new constraints on the location of the K/T boundary impact  

NASA Technical Reports Server (NTRS)

All available evidence is consistent with an impact into oceanic crust terminating the Cretaceous Period. Although much of this evidence is incompatible with an endogenic origin, some investigators still feel that a volcanic origin is possible for the Cretaceous/Tertiary (K/T) boundary clay layers. The commonly cited evidence for a large impact stems from delicate clay layers and their components and the impact site has not yet been found. Impact sites have been suggested all over the globe. The impact is felt to have occurred near North America by: the occurrence of a 2 cm thick ejecta layer only at North American locales, the global variation of shocked quartz grain sizes peaking in North America, the global variation of spinel compositions with most refractory compositions occurring in samples from the Pacific region and possibly uniquely severe plant extinctions in the North American region. The K/T boundary interval was investigated as preserved on the banks of the Brazos River, Texas. The K/T fireball and ejecta layers with associated geochemical anomalies were found interbedded with this sequence which apparently allows a temporal resolution 4 orders of magnitude greater than typical K/T boundary sections. A literature search reveals that such coarse deposits are widely preserved at the K/T boundary. Impact wave deposits have not been found elsewhere on the globe, suggesting the impact occurred between North and South America. The coarse deposits preserved in Deep Sea Drilling Project (DSDP) holes 151-3 suggest the impact occurred nearby. Subsequent tectonism has complicated the picture.

Hildebrand, A. R.; Boynton, W. V.

1988-01-01

76

Deccan volcanism and K-T boundary signatures  

NASA Technical Reports Server (NTRS)

The Deccan Traps in the Indian subcontinent represent one of the most extensive flood basalt provinces in the world. These basalts occur mainly as flat-lying, subaerially erupted tholeiitic lava flows, some of which are traceable for distances of more than 100 km. Offshore drilling and geophysical surveys indicate that a part of the Deccan subsided or was downfaulted to the west beneath the Arabian Sea. The presence of 1 to 5 m thick intertrappean sediments deposited by lakes and rivers indicates periods of quiescence between eruptions. The occurrence of numerous red bole beds among the flows suggests intense weathering of flow tops between eruptive intervals. Although the causative relationship of the Cretaceous-Tertiary (K-T) biotic extinctions to Deccan volcanism is debatable, the fact that the main Deccan eruptions straddle the K-T event appears beyond doubt from the recent Ar-40/Ar-39 ages of various Deccan flows. This temporal relationship of the K-T event with Deccan volcanism makes the petrochemical signatures of the entire Deccan sequence (basalt flows, intercalated intertrappean sediments, infratrappean Lameta beds (with dinosaur fossils), and the bole beds) pertinent to studies of the K-T event. The results of ongoing study is presented.

Murali, A. V.; Schuraytz, B. C.; Parekh, P. P.

1988-01-01

77

Rb-Sr, Sm-Nd, K-Ca, O, and H isotopic study of Cretaceous-Tertiary boundary sediments, Caravaca, Spain Evidence for an oceanic impact site  

NASA Astrophysics Data System (ADS)

The results of isotopic and trace-element-abundance analyses of Ir-enriched Cretaceous-Tertiary-boundary clay sediments from Caravaca, Spain, and of adjacent carbonate and marl layers, are presented. Acetic-acid and HCl leachates and residues were analyzed by isotope dilution to determine K, Rb, Sr, Sm, and Nd concentrations and Sr-87/Sr-86 and Nd-143/Nd-144 ratios. The stable isotope ratios delta-D, delta-(C-13), and delta-(0-18) were also determined. The results are presented in tables and graphs and compared with published data on the Caravaca sediments and on samples from other locations. The boundary clay is found to be distinguished from the adjacent layers by its isotopic ratios and to be of mainly terrestrial, lithospheric (deeper than 3-km) origin. Although submarine-weathering effects are evident and difficult to quantify, the degree of variation in Ni, Ir, Sr, and REE concentrations is considered too large to be attributed to postdepositional processes alone. These findings are seen as evidence for the ocean impact of a large single asteroid producing a worldwide blanket of ejecta, a large injection of water vapor into the atmosphere, and perhaps a gigantic tsunami, at the end of the Cretaceous period.

Depaolo, D. J.; Kyte, F. T.; Marshall, B. D.; O'Neil, J. R.; Smit, J.

1983-09-01

78

Coeval Ar-40/Ar-39 ages of 65.0 million years ago from Chicxulub crater melt rock and Cretaceous-Tertiary boundary tektites  

NASA Technical Reports Server (NTRS)

Ar-40/Ar-39 dating of drill-core samples of a glassy melt rock recovered from beneath a massive impact breccia contained with the 180-kilometer subsurface Chicxulub crater yields well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from Ar-40/Ar-39 ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The Ar-40/Ar-39 ages, in conjunction with geochemical and petrological similarities, strengthen the suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.

Swisher, Carl C., III; Grajales-Nishimura, Jose M.; Montanari, Alessandro; Margolis, Stanley V.; Claeys, Philippe; Alvarez, Walter; Renne, Paul; Cedillo-Pardo, Esteban; Maurrasse, Florentin J.-M. R.; Curtis, Garniss H.

1992-01-01

79

Collapse of florisitic diversity coincident with a fungal spike and iridium anomaly at the Cretaceous-Tertiary boundary in New Zealand  

NASA Astrophysics Data System (ADS)

Analysis of pollen and spore assemblages from both terrestrial and near-shore marine sediments in New Zealand had revealed an instant, extensive destruction of land plants directly associated with the Cretaceous-Tertiary boundary (KTB) event, (Vajda et al., 2001). A recent palynological investigation, based on millimeter resolution sampling of the terrestrial KTB sediments at Moody Creek Mine, Greymouth coalfield, New Zealand has been carried out. The sediments were deposited in a terrestrial wetland environment and the KTB is defined within a coal seam. Preliminary results of the high-resolution investigation reveal a diverse vascular plant spore/pollen flora (>80 species) that was replaced by an assemblage impoverished in vascular plant pollen and spores, but rich in fungal spores. The "barren" layer is coincident with the extinction of several miospore taxa and contains an iridium abundance of 3ppb. The fungal spike covers 5 mm, and is followed by a 40-cm interval with abundant fern spores. The relative abundance of fern spores, increases from 25% below the boundary to 98% in the sediment following the KTB. We argue that the abrupt palynofloristic changes at this high southern palaeolatitude site are evidence of massive disruptions to terrestrial plant communities as a consequence of the Chicxulub impact. Palynofloristic evidence indicates that the complex mire and forest vegetation was totally devastated at the time of impact. Global cooling and several months with extremely low light levels following the impact, perhaps in combination with extensive wildfires would explain the devastation of the vegetation. The "barren" layer at the KTB corresponds to immediate post-impact conditions with low light levels and dust-related cooling unfavorable to forest growth but favoring saprophytic fungi. The recovery succession is initiated by opportunistic species of ground ferns, the plants best adapted to low light, lowered temperatures and high acidity. Vajda, V., Raine, I. &Hollis, C. (2001). Science, Vol. 294, p. 1700-1702.

Vajda, V.; Raine, J. I.

2003-04-01

80

Geochemistry of K/T boundaries in India and contributions of Deccan volcanism  

NASA Technical Reports Server (NTRS)

Three possible Cretaceous/Tertiary (K/T) boundary sections in the Indian subcontinent were studied for their geochemical and fossil characteristics. These include two marine sections of Meghalaya and Zanskar and one continental section of Nagpur. The Um Sohryngkew river section of Meghalaya shows a high iridium, osmium, iron, cobalt, nickel and chromium concentration in a 1.5 cm thick limonitic layer about 30 cm below the planktonic Cretaceous-Palaeocene boundary identified by the characteristic fossils. The Bottaccione and Contessa sections at Gubbio were also analyzed for these elements. The geochemical pattern at the boundary at the Um Sohryngkew river and Gubbio sections are similar but the peak concentrations and the enrichment factors are different. The biological boundary is not as sharp as the geochemical boundary and the extinction appears to be a prolonged process. The Zanskar section shows, in general, similar concentration of the siderophile, lithophile and rare earth elements but no evidence of enrichment of siderophiles has so far been observed. The Takli section is a shallow inter-trappean deposit within the Deccan province, sandwiched between flow 1 and flow 2. The geochemical stratigraphy of the inter-trappeans is presented. The various horizons of ash, clay and marl show concentration of Fe and Co, generally lower than the adjacent basalts. Two horizons of slight enrichment of iridium are found within the ash layers, one near the contact of flow 1 and other near the contact of flow 2, where iridium occurs at 170 and 260 pg/g. These levels are lower by a factor of 30 compared to Ir concentration in the K/T boundary in Meghalaya section. If the enhanced level of some elements in a few horizons of the ash layer are considered as volcanic contribution by some fractionation processes than the only elements for which it occurs are REE, Ir and possibly Cr.

Bhandari, N.; Gupta, M.; Pandey, J.; Shukla, P. N.

1988-01-01

81

The Cretaceous-Tertiary extinction: A lethal mechanism involving anhydrite target rocks  

USGS Publications Warehouse

The Chicxulub Crater, Yucatan, Mexico, is a leading contender as the site for the impact event that caused the Cretaceous-Tertiary (K-T) extinctions. A considerable thickness of anhydrite (CaSO4) forms part of the target rock. High temperatures resulting from impact would drive SO2 off from the anhydrite. Hundreds of billions of tonnes of sulfuric acid aerosol would thus enter the stratosphere and cause considerable cooling of the Earth's surface, decrease photosynthesis by orders of magnitude, deplete the ozone layer, and permit increased UV radiation to reach the Earth's surface. Finally, the aerosol would fall back to Earth as acid rain and devastate land and some lacustrine biota and near-surface marine creatures. The presence of anhydrite in the Chicxulub target rock may thus help explain the many extinctions observed at the K-T boundary. ?? 1992.

Brett, R.

1992-01-01

82

The global Cretaceous-Tertiary fire: Biomass or fossil carbon  

NASA Technical Reports Server (NTRS)

The global soot layer at the K-T boundary indicates a major fire triggered by meteorite impact. However, it is not clear whether the principal fuel was biomass or fossil carbon. Forests are favored by delta value of C-13, which is close to the average for trees, but the total amount of elemental C is approximately 10 percent of the present living carbon, and thus requires very efficient conversion to soot. The PAH was analyzed at Woodside Creek, in the hope of finding a diagnostic molecular marker. A promising candidate is 1-methyl-7-isopropyl phenanthrene (retene,), which is probably derived by low temperature degradation of abietic acid. Unlike other PAH that form by pyrosynthesis at higher temperatures, retene has retained the characteristic side chains of its parent molecule. A total of 11 PAH compounds were identified in the boundary clay. Retene is present in substantial abundance. The identification was confirmed by analysis of a retene standard. Retene is characteristic of the combustion of resinous higher plants. Its formation depends on both temperature and oxygen access, and is apparently highest in oxygen-poor fires. Such fires would also produce soot more efficiently which may explain the high soot abundance. The relatively high level of coronene is not typical of a wood combustion source, however, though it can be produced during high temperature pyrolysis of methane, and presumably other H, C-containing materials. This would require large, hot, low O2 zones, which may occur only in very large fires. The presence of retene indicates that biomass was a significant fuel source for the soot at the Cretaceous-Tertiary boundary. The total amount of elemental C produced requires a greater than 3 percent soot yield, which is higher than typically observed for wildfires. However, retene and presumably coronene imply limited access of O2 and hence high soot yield.

Gilmour, Iain; Guenther, Frank

1988-01-01

83

Terrestrial ecosystem destabilization at the K/T boundary in southwestern North Dakota, USA.  

NASA Astrophysics Data System (ADS)

Much of the debate regarding mass extinction events tend to discuss the relationship between such events relative to the moment and timing of internal or external factors (such as volcanism, impact(s), climate, sea-level changes and so on). However, the details of the extinction process itself is still poorly understood, and most of the analysis are based on biodiversity patterns without integrating the biogeographic and environmental context. Another way of approaching the problem would be to propose precise paleoenvironment reconstructions and analyzing their evolution through time, which allows for the understanding of such processes. The badlands of southwestern North Dakota provides some of the most prolific exposures of the continental Cretaceous/Tertiary (K/T) boundary in the world. The stratigraphical context indicates that the K/T boundary is coincident or lies in close proximity to the contact between the Hell Creek and the Fort Union Formations. In this area, a series of eight stratigraphical sections across a 40 km north-south transect were studied. These sections bracket the formational contact on a 10 m stratigraphical interval. Reconstruction of the depositional environment was undertaken at a centimeter scale by using sedimentological data, as well as palynological, paleobotanical and palaeontological content of the strata, using the K/T boundary as a precise chronological datum of correlation between the sections. Results shows a consistent evolution of pattern across the entire study area : 1) The uppermost 10 to 20 cm of the Hell Creek Formation always corresponds to a sequence of dark rooted mudstone. Pollen content is consistent with a Cretaceous age and displays a diversity of terrestrial taxa. 2) Immediately above, the formation contact lies at the lower part of the first laterally traceable lignite horizon. The K/T boundary indicators (iridium anomaly, shocked quartz, fern spike and boundary claystone) are located at or adjacent to this stratigraphical interval, when preserved. 3) Within or just above the formation contact coal, the relative abundance of palynological taxa indicative of the Cretaceous (K-taxa) drop significantly without significant subsequent recovery. 4) Above the formation contact lignite, lithology systematically the lithology consistently appears as a 1-2 m thick dark mudstone sequence. The palynological record of this interval is dominated by freshwater taxa (Pediastrum sp. and Penetetrapites sp.) indicating general flooding in the study area. 5) Change in the sedimentation style in comparison of the Hell Creek is reflected by the preservation of variegated beds, multiple lignite seams and small scale meandering river systems. The palynological content attest for reworking and erosion. Conclusions shows that both palaeoenviroments and biodiversity patterns stay consistent throughout the Hell Creek Formation, with the exception of its uppermost part. The vertebrate and plant communities underwent a significant change at this time coincident with the evidence for a impact scenario or catastrophic event of massive scale. Beginning at the very end of the Cretaceous and continuing up into the overlying Fort Union Formation, the area was experiencing the onset of a transgression cycle which contributed to widespread ponding. Following the impact, modifications in the environment caused by land denudation, changes in sea level and drainage patterns promoted run-off and reworking. The destabilization of terrestrial ecosystems in southwestern North Dakota is coincident with markers of the K/T boundary that supports a catastrophic event taking place over a very short duration.

Bercovici, Antoine; Pearson, Dean; Villanueva-Amadoz, Uxue

2010-05-01

84

Explosive volcanism, shock metamorphism and the K-T boundary  

NASA Technical Reports Server (NTRS)

The issue of whether shocked quartz can be produced by explosive volcanic events is important in understanding the origin of the K-T boundary constituents. Proponents of a volcanic origin for the shocked quartz at the K-T boundary cite the suggestion of Rice, that peak overpressures of 1000 kbars can be generated during explosive volcanic eruptions, and may have occurred during the May, 1980 eruption of Mt. St. Helens. Attention was previously drawn to the fact that peak overpressures during explosive eruptions are limited by the strength of the rock confining the magma chamber to less than 8 kbars even under ideal conditions. The proposed volcanic mechanisms for generating pressures sufficient to shock quartz are further examined. Theoretical arguments, field evidence and petrographic data are presented showing that explosive volcanic eruptions cannot generate shock metamorphic features of the kind seen in minerals at the K-T boundary.

Desilva, S. L.; Sharpton, V. L.

1988-01-01

85

Nanodiamonds and Carbon Spherules from Tunguska, the K/T Boundary, and the Younger Dryas Boundary Layer  

NASA Astrophysics Data System (ADS)

More than a dozen markers, including nanodiamonds (NDs) and carbon spherules (CS), occur in a sedimentary layer marking the onset of the Younger Dryas (YD) cooling episode at ~12.9 ka. This boundary layer, called the YDB, has been found at nearly forty locations across North America, Europe, and Asia, although not all markers are present at any given site. Firestone et al. (2007) and Kennett et al. (2008, 2009) proposed that these markers resulted from a cosmic impact/airburst and impact-related biomass burning. Here we report features common to the YDB event, the Cretaceous-Tertiary (K/T) impact, and the Tunguska airburst of 1908. In sediments attributed to each event, we and other researchers have recovered NDs either inside or closely associated with CS, which appear to be the high-temperature by-products of biomass burning. CS range in diameter from about 500 nanometers to 4 millimeters with a mean of ~100 microns, and they typically contain NDs, including lonsdaleite (hexagonal diamonds), in the interior matrix and in the crust. To date, CS and NDs have been found in the K/T layer in the United States, Spain, and New Zealand. Similarly, CS and NDs have been found in the YDB layer in the United States, Canada, United Kingdom, Belgium, the Netherlands, Germany, and France. Thus far, every site examined contains NDs and/or CS in the K/T and YDB layers; conversely, we have yet to detect CS associated with NDs in any non-YDB sediments tested. Five allotropes of NDs have been identified in association with CS: cubic diamonds, lonsdaleite, n-diamonds, p-diamonds, and i-carbon, which are differentiated by slight variations in their crystalline structure. All allotropes have been identified using scanning electron microscopy (SEM), high-resolution electron microscopy (HREM), and transmission electron microscopy (TEM) with confirmation by selected area diffraction (SAED). Lonsdaleite is found on Earth only in three instances: (1) in the laboratory, where it is produced by shock synthesis under a high-temperature-high-pressure regime (~1000°C to 1700°C at 15 GPa) or by carbon vapor deposition (CVD) under a very-high-temperature-low-pressure regime (~13,000°C at 300 Torr) (Maruyama et al., 1993); (2) after arrival on Earth inside extraterrestrial material; and (3) as a result of high-temperature cosmic impact/airbursts. Lonsdaleite associated with CS has been found in sediments only at the K/T, the YDB, and Tunguska, consistent with the hypothesis that all three events have cosmic origins, although the nature of the impactors may have been different.

Wittke, J. H.; Bunch, T. E.; West, A.; Kennett, J.; Kennett, D. J.; Howard, G. A.

2009-12-01

86

K-T magmatism of western Rajasthan, India: Manifestation of Reunion plume activity or extensional lithospheric tectonics?  

Microsoft Academic Search

A number of alkaline plutons have been recorded at the K-T (Cretaceous-Tertiary) boundary in western Rajasthan, India. Significant magmatism occurred at Mundwara, Barmer, Sarnu-Dandali and Tavider. The evolution of the Cambay-Sanchor-Barmer rift during the K-T period resulted in these alkaline complexes at the rift margins. Sedimentary basins are developed in the Barmer and Jaiselmer regions. The magmatism of Mundwara and

K. Sharma

2004-01-01

87

Catastrophic volcanism as a cause of shocked features found at the K/T boundary and in cryptoexplosion structures  

NASA Technical Reports Server (NTRS)

The presence of quartz grains containing shock lamellae at the Cretaceous/Tertiary (K/T) boundary is viewed by many as the single most compelling evidence of meteoritic or cometary impact because there is no known endogenous mechanism for producing these features. Similarly the presence of shocked quartz, shatter cones, coesite and stishovite at cryptoexplosion structures is comonly taken as conclusive evidence of impact. However, several recent studies have cast doubt on this interpretation. It is argued that basaltic volcanism, although not normally explosive, can under exceptional circumstances produce overpressures sufficiently high to produce shock features. The exceptional circumstances include a high content of volatiles, usually CO2, and no preestablished pathway to the surface. Rapid cooling of the saturated basaltic magma can occur if it underlies a cooler more evolved magma in a chamber. Initial slow cooling and partial exsolution of the volatiles will cause the density of the basaltic magma to become less than that of the overlying magma, leading to overturning and mixing. Gas will escape the magma chamber along planar cracks once the pressure becomes sufficiently high. In the vicinity of the crack tip there is a smallscale deviatoric stress pattern which is thought to be sufficiently high to produce transient cracks along secondary axes in the quartz crystals, causing the planar features. The CO2-rich fluid inclusions which have been found along planar elements of quartz in basement rocks of the Vredefort Dome were likely to have been emplaced by such a process. If the mechanism described is capable of producing shocked features as above, it would require a reassessment of the origin of many cryptoexplosion structures as well as seriously weakening the case for an impact origin of the K/T event.

Loper, D. E.; Mccartney, K.

1988-01-01

88

UPb Isotopic Ages of the K\\/T Impact Event and its Target Rocks from Shocked Zircons  

Microsoft Academic Search

U-Pb isotopic results for individual zircon grains from the fire- ball ejecta layer of the Cretaceous\\/Tertiary (K\\/T) boundary claystone, Raton Basin, Colorado, lie on a Pb loss line between 550 +- 10 Ma and 65.5 +- 3 Ma. This implies that the target area is dominated by rocks of the older age, and that grains plotting near the younger end

B. F. Bohor; T. E. Krogh; S. L. Kamo

1992-01-01

89

Large meteorite impacts: The K/T model  

NASA Technical Reports Server (NTRS)

The Cretaceous/Tertiary (K/T) boundary event represents probably the largest meteorite impact known on Earth. It is the only impact event conclusively linked to a worldwide mass extinction, a reflection of its gigantic scale and global influence. Until recently, the impact crater was not definitively located and only the distal ejecta of this impact was available for study. However, detailed investigations of this ejecta's mineralogy, geochemistry, microstratigraphy, and textures have allowed its modes of ejection and dispersal to be modeled without benefit of a source crater of known size and location.

Bohor, B. F.

1992-01-01

90

Cretaceous-Tertiary findings, paradigms and problems  

NASA Technical Reports Server (NTRS)

The asteroid hypothesis has stimulated numerous studies of the paleontological record at Cretaceous/Tertiary time as well as of geological indicators of environmental crisis preserved in the rock record. Both extinctions and geological anomalies often occur at times that do not appear to be synchronous or instantaneous. The record includes paleontological indicators of dinosaurs, terrestrial flora, marine planktonic organisms, and shallow water marine macrofauna and geological phenomena include occurrences of iridium and other platinum metals, trace elements, clay mineralogy, shocked minerals, soot, microspherules, and isotopes of osmium, strontium and carbon. These findings are reviewed in the context of the alternate hypotheses of an exogenic cause, involving either a single asteroid impact or multiple commentary impacts, and an endogenic cause, involving intense global volcanism and major sea level regression.

Officer, C. B.; Drake, C. L.

1988-01-01

91

Impact winter and the Cretaceous/Tertiary extinctions: Results of a Chicxulub asteroid impact model  

NASA Technical Reports Server (NTRS)

The Chicxulub impact crater in Mexico is the site of the impact purported to have caused mass extinctions at the Cretaceous/Tertiary (K/T) boundary. 2-D hydrocode modeling of the impact, coupled with studies of the impact site geology, indiate that between 0.4 and 7.0 x 10(exp 17) g of sulfur were vaporized by the impact into anhydrite target rocks. A small portion of the sulfur was released as SO3 or SO4, which converted rapidly into H2SO4 aerosol and fell as acid rain. A radiative transfer model, coupled with a model of coagulation indicates that the aerosol prolonged the initial blackout period caused by impact dust only if the aerosol contained impurities. A larger portion of sulfur was released as SO2, which converted to aerosol slowly, due to the rate-limiting oxidation of SO2. Our radiative transfer calculations, combined with rates of acid production, coagulation, and diffusion indicate that solar transmission was reduced to 10-20% of normal for a period of 8-13 yr. This reduction produced a climate forcing (cooling) of -300 W/sq.m, which far exceeded the +8 W/sq.m greenhouse warming, caused by the CO2 released through the vaporization of carbonates, and therefore produced a decade of freezing and near-freezing temperatures. Several decades of moderate warming followed the decade of severe cooling due to the long residence time of CO2. The prolonged impact winter may have been a major cause of the K/T extinctions.

Pope, Kevin O.; Baines, Kevin H.; Ocampo, Adriana C.; Ivanov, Boris A.

1994-01-01

92

Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact  

NASA Technical Reports Server (NTRS)

A comprehensive analysis of volatiles in the Chicxulub impact strongly supports the hypothesis that impact-generated sulfate aerosols caused over a decade of global cooling, acid rain, and disruption of ocean circulation, which contributed to the mass extinction at the Cretaceous/Tertiary (K/T) boundary. The crater size, meteoritic content of the K/T boundary clay, and impact models indicate that the Chicxulub crater was formed by a short period comet or an asteroid impact that released 0.7-3.4 x 10(31) ergs of energy. Impact models and experiments combined with estimates of volatiles in the projectile and target rocks predict that over 200 gigatons (Gt) each of SO2 and water vapor, and over 500 Gt of CO2, were globally distributed in the stratosphere by the impact. Additional volatiles may have been produced on a global or regional scale that formed sulfate aerosols rapidly in cooler parts of the vapor plume, causing an early, intense pulse of sulfuric acid rain. Estimates of the conversion rate of stratospheric SO2 and water vapor to sulfate aerosol, based on volcanic production of sulfate aerosols, coupled with calculations of diffusion, coagulation, and sedimentation, demonstrate that the 200 Gt stratospheric SO2 and water vapor reservoir would produce sulfate aerosols for 12 years. These sulfate aerosols caused a second pulse of acid rain that was global. Radiative transfer modeling of the aerosol clouds demonstrates (1) that if the initial rapid pulse of sulfate aerosols was global, photosynthesis may have been shut down for 6 months and (2) that for the second prolonged aerosol cloud, solar transmission dropped 80% by the end of first year and remained 50% below normal for 9 years. As a result, global average surface temperatures probably dropped between 5 degrees and 31 degrees K, suggesting that global near-freezing conditions may have been reached. Impact-generated CO2 caused less than 1 degree K greenhouse warming and therefore was insignificant compare to the sulfate cooling. The magnitude of sulfate cooling depends largely upon the rate of ocean mixing as surface waters cool, sink, and are replaced by upwelling of deep ocean water. This upwelling apparently drastically altered ocean stratification and circulation, which may explain the global collapse of the delta 13C gradient between surface and deep ocean waters at the K/T boundary.

Pope, K. O.; Baines, K. H.; Ocampo, A. C.; Ivanov, B. A.

1997-01-01

93

The Cretaceous-Tertiary Impact Crater and the Cosmic Projectile that Produced it  

NASA Astrophysics Data System (ADS)

Evidence gathered to date from topographic data, geophysical data, well logs, and drill-core samples indicates that the buried Chicxulub basin, the source crater for the approximately 65 Ma Cretaceous-Tertiary (K/T) boundary deposits, is approximately 300 km in diameter. A prominent topographic ridge and a ring of gravity anomalies mark the position of the basin rim at approximately 150 km from the center. Wells in this region recovered thick sequences of impact-generated breccias at 200-300 m below present sea level. Inside the rim, which has been severely modified by erosion following impact, the subsurface basin continues to deepen until near the center it is approximately 1 km deep. The best planetary analog for this crater appears to be the 270 km-diameter Mead basin on Venus. Seismic reflection data indicate that the central zone of downward displacement and excavation (the transient crater is approximately 130 km in diameter, consistent with previous studies of gravity anomaly data). Our analysis of projectile characteristics utilizes this information, coupled with conventional scaling relationships, and geochemical constraints on the mass of extraterrestrial material deposited within the K/T boundary layer. Results indicate that the Chicxulub crater would most likely be formed by a long-period comet composed primarily of nonsilicate materials (ice, hydrocarbons, etc.) and subordinate amounts (less than or equal to 50 percent) primitive chondritic material. This collision would have released the energy equivalent to between 4 x 108 and 4 x 109 megatons of TNT. Studies of terrestrial impact rates suggest that such an event would have a mean production rate of approximately 1.25 x 10-9 y-1. This rate is considerably lower than that of the major mass extinctions over the last 250 million years (approximately 5 x 10-7 y-1. Consequently, while there is substantial circumstantial evidence establishing the cause-effect link between the Chicxulub basin forming event and the K/T biological extinctions, the results of our analysis do not support models of impact as a common or singular causative agent of mass extinctions on Earth.

Sharpton, Virgil L.; Marín, Luis E.

1997-05-01

94

Provenance of the K/T boundary layers  

NASA Technical Reports Server (NTRS)

An array of chemical, physical and isotopic evidence indicates that an impact into oceanic crust terminated the Cretaceous Period. Approximately 1500 cu km of debris, dispersed by the impact fireball, fell out globally in marine and nonmarine environments producing a 2 to 4 mm thick layer (fireball layer). In North American locales, the fireball layer overlies a 15 to 25 mm thick layer of similar but distinct composition. This 15 to 25 mm layer (ejecta layer) may represent approximately 1000 cu km of lower energy ejecta from a nearby impact site. Isotopic and chemical evidence supports a mantle provenance for the bulk of the layers. The extraordinary REE pattern of the boundary clays was modelled as a mixture of oceanic crust, mantle, and approximately 10 percent continental material. The results are presented. If the siderophiles of the ejecta layer were derived solely from the mantle, a test may be available to see if the siderophile element anomaly of the fireball layer had an extraterrestrial origin. Radiogenic Os-187 is depleted in the mantle relative to an undifferentiated chondritic source. Os-187/Os-186 ratios of 1.049 and 1.108 were calculated for the ejecta and fireball layers, respectively.

Hildebrand, A. R.; Boynton, W. V.

1988-01-01

95

Stratigraphy and sedimentology of the K/T boundary deposit in Haiti  

NASA Technical Reports Server (NTRS)

The K/T boundary sequence is exposed in uplifted carbonate sediments of the southwest peninsula of Haiti. It is found at 15 localities within the Beloc formation, a sequence of limestone and marls interpreted as a monoclinal nappe structure thrust to the north. This tectonic deformation has affected the K/T boundary deposit to varying degrees. In some cases the less competent K/T deposit has acted as a slip plane leading to extensive shearing of the boundary layer, as well as duplication of the section. The presence of glassy tektites, shocked quartz, and an Ir anomaly directly link the deposit to a bolide impact. Stratigraphic and sedimentological features of the tripartite sequence indicate that it was formed by deposition from ballistic fallout of coarse tektites, emplacement of particle gravity flows and fine grained fallout of widely dispersed impact ejecta.

Carey, S.; Sigurdsson, H.; Dhondt, S.; Espindola, J. M.

1993-01-01

96

Extraterrestrial Cause for the Cretaceous-Tertiary Extinction  

Microsoft Academic Search

Platinum metals are depleted in the earth's crust relative to their cosmic abundance; concentrations of these elements in deep-sea sediments may thus indicate influxes of extraterrestrial material. Deep-sea limestones exposed in Italy, Denmark, and New Zealand show iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65

Luis W. Alvarez; Walter Alvarez; Frank Asaro; Helen V. Michel

1980-01-01

97

Geomagnetic polarity stratigraphy and nannofossil biostratigraphy at the K\\/T boundary section near Beloc, Haiti  

Microsoft Academic Search

A 54-meter-thick stratigraphic section of limestone and chalk from the Cretaceous and Tertiary Beloc Formation in southern Haiti is correlated to the geomagnetic polarity time scale using paleomagnetic and nannofossil data. The controversial K\\/T boundary layer at Beloc occurs within a thick zone of reversed magnetic polarity correlative to chron C29r (from 18 m above to 25 m below the

Mickey C. Van Fossen; James E. T. Channell; Timothy J. Bralower

1995-01-01

98

Geochemical evidence for combustion of hydrocarbons during the K-T impact event  

PubMed Central

It has been proposed that extensive wildfires occurred after the Cretaceous–Tertiary (K-T) impact event. An abundance of soot and pyrosynthetic polycyclic aromatic hydrocarbons (pPAHs) in marine K-T boundary impact rocks (BIRs) have been considered support for this hypothesis. However, nonmarine K-T BIRs, from across North America, contain only rare occurrences of charcoal yet abundant noncharred plant remains. pPAHs and soot can be formed from a variety of sources, including partial combustion of vegetation and hydrocarbons whereby modern pPAH signatures are traceable to their source. We present results from multiple nonmarine K-T boundary sites from North America and reveal that the K-T BIRs have a pPAH signature consistent with the combustion of hydrocarbons and not living plant biomass, providing further evidence against K-T wildfires and compelling evidence that a significant volume of hydrocarbons was combusted during the K-T impact event. PMID:19251660

Belcher, Claire M.; Finch, Paul; Collinson, Margaret E.; Scott, Andrew C.; Grassineau, Nathalie V.

2009-01-01

99

Magnetic properties and Moessbauer analyses of glass from the K-T boundary, Beloc, Haiti  

NASA Technical Reports Server (NTRS)

The experimental magnetic susceptibility, the temperature-independent component of the magnetic susceptibility, the magnetization, and the Curie constant have been measured for a number of specimens of glass from the K-T boundary found at Beloc, Haiti, and the results are compared with those of similar measurements of tektites. Because the Fe(3+)/Fe(2+) ratio is needed to calculate the magnetic parameters, Moessbauer spectroscopic measurements were also made. The data were consistent with the classification of the Beloc glasses as tektites.

Senftle, F. E.; Thorpe, A. N.; May, L.; Barkatt, A.; Adel-Hadadi, M. A.; Marbury, G. S.; Izett, G.; Sigurdsson, H.; Maurasse, F. J.-M. R.

1993-01-01

100

First Evidence for a Massive Extinction Event Affecting Bees Close to the K-T Boundary  

PubMed Central

Bees and eudicot plants both arose in the mid-late Cretaceous, and their co-evolutionary relationships have often been assumed as an important element in the rise of flowering plants. Given the near-complete dependence of bees on eudicots we would expect that major extinction events affecting the latter would have also impacted bees. However, given the very patchy distribution of bees in the fossil record, identifying any such extinctions using fossils is very problematic. Here we use molecular phylogenetic analyses to show that one bee group, the Xylocopinae, originated in the mid-Cretaceous, coinciding with the early radiation of the eudicots. Lineage through time analyses for this bee subfamily show very early diversification, followed by a long period of seemingly no radiation and then followed by rapid diversification in each of the four constituent tribes. These patterns are consistent with both a long-fuse model of radiation and a massive extinction event close to the K-T boundary. We argue that massive extinction is much more plausible than a long fuse, given the historical biogeography of these bees and the diversity of ecological niches that they occupy. Our results suggest that events near the K-T boundary would have disrupted many plant-bee relationships, with major consequences for the subsequent evolution of eudicots and their pollinators. PMID:24194843

Rehan, Sandra M.; Leys, Remko; Schwarz, Michael P.

2013-01-01

101

Environmental effects of an impact-generated dust cloud - Implications for the Cretaceous-Tertiary extinctions  

NASA Technical Reports Server (NTRS)

A model of the evolution and radiative effects of a debris cloud from a hypothesized impact event at the Cretaceous-Tertiary boundary suggests that the cloud could have reduced the amount of light at the earth's surface below that required for photosynthesis for several months and, for a somewhat shorter interval, even below that needed for many animals to see. For 6 months to 1 year, the surface would cool; the oceans could cool only a few degrees Celsius at most, but the continents might cool a maximum of 40 Kelvin. Extinctions in the ocean may have been caused primarily by the temporary cessation of photosynthesis, but those on land may have been primarily induced by a combination of lowered temperatures and reduced light.

Pollack, J. B.; Toon, O. B.; Ackerman, T. P.; Mckay, C. P.; Turco, R. P.

1983-01-01

102

Spatial and Temporal variations of the Haitian K\\/T Boundary record: implications concerning the event or events  

Microsoft Academic Search

Abstract Evidence of physical disruptions caused by the postulated bolide impact at the close of the Maastrichtian is clearly defined in the record of the K\\/T boundary (KTB) layer from different sites in the Southern Peninsula of Haiti. Lithologic and biostratigraphic record of the KTB layer from the different sites also show varying degrees of mixing, yielding faunal components within

Florentin. Jm. R. Maurrasse; Marcos A. Lamolda; Roque Aguado; Danuta Peryt; Gautam Sen

103

Environmental effects of Deccan volcanism across the Cretaceous-Tertiary transition in Meghalaya, India  

NASA Astrophysics Data System (ADS)

The Um Sohryngkew section of Meghalaya, NE India, located 800-1000 km from the Deccan volcanic province, is one of the most complete Cretaceous-Tertiary boundary (KTB) transitions worldwide with all defining and supporting criteria present: mass extinction of planktic foraminifera, first appearance of Danian species, ? 13C shift, Ir anomaly (12 ppb) and KTB red layer. The geochemical signature of the KTB layer indicates not only an extraterrestrial signal (Ni and all Platinum Group Elements (PGEs)) of a second impact that postdates Chicxulub, but also a significant component resulting from condensed sedimentation (P), redox fluctuations (As, Co, Fe, Pb, Zn, and to a lesser extent Ni and Cu) and volcanism. From the late Maastrichtian C29r into the early Danian, a humid climate prevailed (kaolinite: 40-60%, detrital minerals: 50-80%). During the latest Maastrichtian, periodic acid rains (carbonate dissolution; CIA index: 70-80) associated with pulsed Deccan eruptions and strong continental weathering resulted in mesotrophic waters. The resulting super-stressed environmental conditions led to the demise of nearly all planktic foraminiferal species and blooms (> 95%) of the disaster opportunist Guembelitria cretacea. These data reveal that detrimental marine conditions prevailed surrounding the Deccan volcanic province during the main phase of eruptions in C29r below the KTB. Ultimately these environmental conditions led to regionally early extinctions followed by global extinctions at the KTB.

Gertsch, B.; Keller, G.; Adatte, T.; Garg, R.; Prasad, V.; Berner, Z.; Fleitmann, D.

2011-10-01

104

The Disposition of Pt, Pd, Ir, Os, and Ru in Marine Sediments and the K/T Boundary  

NASA Technical Reports Server (NTRS)

The marine record of platinum group elements (PGEs) and Os isotopic compositions provides information on different inputs of PGEs into the oceans. Some studies based on a smaller subset of the PGEs suggest that the PGEs may suffer post-depositional mobility during diagenesis. In some K/T boundary clays, Kyte and others showed that the relative abundances of Pt, Pd, Ir, and Os can differ significantly from chondritic, which is the signature expected from fallout of the meteorite impact. In some K/T boundary sections, elevated Ir concentrations are observed as far as 1 meter from the cm-thick boundary clay containing the meteoritic ejecta. The purpose of this study was to characterize Pt, Pd, Ir, Os, and Ru abundances in zones including the K/T boundary. We determined PGE abundances of boundary clays at two hemipelagic sites (Stevns Klint, Denmark and Caravaca, Spain) in which previous studies by Kyte and others showed that the Ir anomaly is confined to within a few cm. We also analyzed two pelagic Pacific sites: a boundary clay from the north Pacific (Hole 465A) characterized by a 0.5 m thick Ir anomaly and a transect across the K/T boundary from the south Pacific (Hole 596) where the Ir anomaly spans 2 m. The Stevns Klint, Caravaca, and north Pacific sites are characterized by abundant marls and limestones in the section, whereas the south Pacific site is dominated by clays. Samples were spiked with isotopic tracers, mixed with a flux, S and Ni, and equilibrated by fusion. PGEs were extracted from the Ni and analyzed on a Finnigan Element ICP-MS. We find that the narrow Caravaca and Stevns Klint boundary clays have relative PGE abundance patterns indistinguishable from chondritic values. The two Pacific sites were found to have nearly identical PGE patterns but have ratios at the peak, which differ from chondritic values as found earlier by Evans et al. The Pacific sites were found to have nearly identical PGE patterns but are extremely depleted in OS (Os/Ir = 0.07-0.15) and slightly enriched in Pd and Pt relative to Ir.

Lee, Cin-Ty; Wasserburg, Gerald; Kyte, Frank

2003-01-01

105

Spatial and Temporal variations of the Haitian K\\/T Boundary record: implications concerning the event or events Variaciones espaciales y temporales del registro del límite K\\/T en Haiti: implicaciones acerca del evento o eventos  

Microsoft Academic Search

Evidence of physical disruptions caused by the postulated bolide impact at the close of the Maastrichtian is clearly defined in the record of the K\\/T boundary (KTB) layer from different sites in the Southern Peninsula of Haiti. Lithologic and biostratigraphic record of the KTB layer from the different sites also show varying degrees of mixing, yielding faunal components within a

R. Maurrasse; Marcos A. Lamolda; Roque Aguado; Danuta Peryt; Gautam Sen

106

Avian evolution, Gondwana biogeography and the Cretaceous-Tertiary mass extinction event  

Microsoft Academic Search

The fossil record has been used to support the origin and radiation of modern birds (Neornithes) in Laurasia after the Cretaceous^Tertiary mass extinction event, whereas molecular clocks have suggested a Cretaceous origin for most avian orders. These alternative views of neornithine evolution are examined using an independent set of evidence, namely phylogenetic relationships and historical biogeography. Phylogenetic relationships of basal

Joel Cracraft

2001-01-01

107

History and controls of subsidence in the Late Cretaceous-Tertiary Great Valley forearc basin, California  

Microsoft Academic Search

Analysis of the Upper Cretaceous-Tertiary fill of the Great Valley forearc basin of California reveals a complicated history of subsidence partitioned in time and space. Western, oceanward parts of the basin record subsidence, then uplift, in apparent response to the angle and rate of descent of the underlying subducting plate. Specifically, uplift in the forearc basin corresponds to the onset

Ian W. Moxon; Stephan A. Graham

1987-01-01

108

History and controls of subsidence in the Late Cretaceous: Tertiary Great Valley forearc basin, California  

Microsoft Academic Search

Analysis of the Upper Cretaceous-Tertiary fill of the Great Valley forearc basin of California reveals a complicated history of subsidence partitioned in time and space. Western, oceanward parts of the basin record subsidence, then uplift, in apparent response to the angle and rate of descent of the underlying subducting plate. Specifically, uplift in the forearc basin corresponds to the onset

Ian W. Moxon; Stephan A. Graham

1987-01-01

109

Iridium enrichment in volcanic dust from blue ice fields, Antarctica, and possible relevance to the K/T boundary event  

NASA Technical Reports Server (NTRS)

The analysis of samples of volcanic ash dust layers from the Lewis Cliff/Beardmore Glacier in Antarctica shows that some of the samples contain Ir concentrations up to 7.5 ppb. It is shown that the Ir is positively correlated with Se, As, Sb, and other volcanogenic elements. The results show that Ir may be present in some volcanic ash deposits, suggesting that the Ir in the K/T boundary clays is not necessarily of cosmic origin, but may have originated from mantle reservoirs tapped during extensive volcanic eruptions possibly triggered by impact events.

Koeberl, Christian

1989-01-01

110

Mineralogy and phase-chemistry of the Cretaceous/Tertiary section in the Lattengebirge, Bavarian Alps  

NASA Technical Reports Server (NTRS)

The Lattengebirge K/T section reveals three distinct Ir spikes. Two of them are contained in the K/T transition zone sensu-strictu termed clayey interval, with 4.4 ppb Ir at the actual K/T boundary, and 2.8 ppb Ir 10 cm above the boundary. The highest Ir enrichment of 9 ppb, however, was detected in semi-cleaned organic material from a thin sandstone layer of Upper Maastrichtian age at 16 cm below the boundary. In this layer various discernible phases are preserved, contrasting with the worldwide observed K/T transition zones which are generally entirely composed of diagenetically altered materials. Given that, important clues to understanding the Cretaceous terminal events may be provided. The phases of the Cretaceous Ir bearing layer at Lattengebirge consist of: sandstone fragmental minerals in a carbonate matrix, coal which is partly burnt, melt glasses presumably of combustion-metamorphic origin, and sulfides, mainly chalcopyrite, contained in the coal. Like many known K/T sections and the Lattengebirge boundary sensu-strictu, the Cretaceous horizon is enriched in Ir and chalcophile elements as well. Although the Lattengebirge section offers the freshest materials, including melt glasses, of all K/T localities investigated, no unequivocal evidence of formation by impact has been found there.

Graup, G.

1988-01-01

111

Impact mechanics of the Cretaceous-Tertiary extinction bolide  

NASA Technical Reports Server (NTRS)

An examination of the mechanics of asteroidal, cometary, and meteor swarm impact on the earth determined if the enrichment of projectile material in the K-T layer is consistent with melts and impact breccias on the earth and moon, the size of the impacters, the distribution of the kinetic energy, and the sequence of impacts that could give rise to observed extinction phenomena. Flows resulting from spherical projectile impacts onto layers of air, water, and silicates were modeled and Eulerian finite difference algorithms were employed to solve conservation equations and equations of state. A range of speeds and impacter densities were considered, along with sizes from 0.17 km, which would be consumed in the atmosphere, to a 10 km object, which would have had a diameter greater than a reference 7.1 km atmosphere depth. It is concluded that an impact of the K-T bolide could result in global biotic extinction and worldwide material deposition.

Okeefe, J. D.; Ahrens, T. J.

1982-01-01

112

Impact mechanics of the Cretaceous-Tertiary extinction bolide  

NASA Astrophysics Data System (ADS)

An examination of the mechanics of asteroidal, cometary, and meteor swarm impact on the earth determined if the enrichment of projectile material in the K-T layer is consistent with melts and impact breccias on the earth and moon, the size of the impacters, the distribution of the kinetic energy, and the sequence of impacts that could give rise to observed extinction phenomena. Flows resulting from spherical projectile impacts onto layers of air, water, and silicates were modeled and Eulerian finite difference algorithms were employed to solve conservation equations and equations of state. A range of speeds and impacter densities were considered, along with sizes from 0.17 km, which would be consumed in the atmosphere, to a 10 km object, which would have had a diameter greater than a reference 7.1 km atmosphere depth. It is concluded that an impact of the K-T bolide could result in global biotic extinction and worldwide material deposition.

Okeefe, J. D.; Ahrens, T. J.

1982-07-01

113

Calcareous nannofossil biostratigraphy and paleoecology of the Cretaceous–Tertiary transition in the central eastern desert of Egypt  

Microsoft Academic Search

The Gebel Qreiya and nearby Wadi Hamama sections of the central Eastern Desert are among the most complete K\\/T boundary sequences known from Egypt. The two sections were analyzed spanning an interval from l.83 Myr below to about 3 Myr above the K\\/T boundary. A 1-cm-thick red clay layer at the K\\/T boundary at Gebel Qreiya contains an Ir anomaly

Abdel Aziz A. M. Tantawy

2003-01-01

114

Altered spherules of impact melt and associated relic glass from the K/T boundary sediments in Haiti  

NASA Technical Reports Server (NTRS)

Partially to wholly altered glass spherules produced by impact-induced shock melting have been found in the K/T boundary sediments of Haiti which also contain grains of shocked quartz. The relic glass has an approximately dacitic composition, and although grossly similar in composition to most previously described tektite glasses, it is slightly enriched in Ca and slightly depleted in Si, suggesting the Haitian glass was produced either from a target with a greater fraction of carbonate and anhydrite lithologies and fewer silicate units than the targets from which most other tektites were produced, and/or from one with a significant mafic component. The composition of the glass can best be reconciled with a continental margin terrane, consistent with studies of shocked mineral phases reported elsewhere. The thickness of the deposit in which the impact spherules occur indicates the source of the ejecta was in the proto-Caribbean region.

Kring, David A.; Boynton, William V.

1991-01-01

115

Trace-element composition of Chicxulub crater melt rock, K/T tektites and Yucatan basement  

NASA Technical Reports Server (NTRS)

The Cretaceous/Tertiary (K/T) boundary Chicxulub impact is the best preserved large impact in the geologic record. The Chicxulub crater has been buried with no apparent erosion of its intracrater deposits, and its ejecta blanket is known and is well preserved at hundreds of localities globally. Although most of the molten material ejected from the crater has been largely altered, a few localities still preserve tektite glass. Availability of intra- and extracrater impact products as well as plausible matches to the targeted rocks allows the comparison of compositions of the different classes of impact products to those of the impacted lithologies. Determination of trace-element compositions of the K/T tektites, Chicxulub melt rock, and the targeted Yucatan silicate basement and carbonate/evaporite lithologies have been made using instrumental neutron activation analysis (INAA) and inductively coupled plasma mass spectrometry (ICP-MS). Some sample splits were studied with both techniques to ensure that inter-laboratory variation was not significant or could be corrected. The concentration of a few major and minor elements was also checked against microprobe results. Radiochemical neutron activation analysis (RNAA) was used to determine Ir abundances in some samples.

Hildebrand, A. R.; Gregoire, D. C.; Attrep, M., Jr.; Claeys, P.; Thompson, C. M.; Boynton, W. V.

1993-01-01

116

GEOL 104 Dinosaurs: A Natural History Homework 6: The Cretaceous-Tertiary Extinction  

E-print Network

Agents and Physical Evidence There are three environmental changes at or near the K/T boundary that might, starting around 69 Ma and ending around 65 Ma. Expected effects: o Change planetary albedo (reflectivity), changing both amount of heat absorbed by Earth and that heat's distribution o Change in oceanic circulation

Holtz Jr., Thomas R.

117

Paleosols and the Cretaceous/Tertiary transition in the Big Bend region of Texas  

SciTech Connect

A marked change in paleosols coincides with Cretaceous/Tertiary transition in fluvial sediments of the Big Bend region in Texas. Early Paleocene paleosols exhibit thick, black epipedons and a greater depth to the argillic and petrocalcic horizons compared to Late Cretaceous paleosols. These features and comparison with modern soils suggest that early Paleocene soils developed under conditions of higher rainfall and cooler temperatures than did Late Cretaceous soils. The change in paleosols occurs abruptly at the highest occurrence of dinosaur bones in the section.

Lehman, T.M. (Texas Tech Univ., Lubbock (USA))

1990-04-01

118

The K-T Extinction  

NSDL National Science Digital Library

This chapter from the book History of Life describes the results of the K-T extinction and looks at the Impact theory and a giant volcanic eruption as possible causes. The essay covers the catastrophic scenarios for extinction that could result from these events. After reviewing the paleontological record across the K-T boundary, the author concludes that it is not clear that the catastrophes themselves can explain the extinction patterns that we see in the fossil record.

Cowen, Richard

119

Bolide impacts, acid rain, and biospheric traumas at the Cretaceous-Tertiary boundary  

Microsoft Academic Search

Two plausible projectiles are considered: an ice-rich long-period comet and a much smaller rock-metal asteroid. In the framework of a proposal addressed by Lewis et al. (1982), it is shown that, while the impact projectiles themselves do not shock-heat the atmosphere very extensively, the supersonic plume of water vapor and rock produced on impact does shock the atmosphere up to

Ronald G. Prinn; Bruce Fegley Jr.

1987-01-01

120

Seawater strontium isotopes, acid rain, and the Cretaceous-Tertiary boundary  

NASA Technical Reports Server (NTRS)

A large bolide impact at the end of the Cretaceous would have produced significant amounts of nitrogen oxides by shock heating of the atmosphere. The resulting acid precipitation would have increased continental weathering greatly and could be an explanation for the observed high ratio of strontium-87 to strontium-86 in seawater at about this time, due to the dissolution of large amounts of strontium from the continental crust. Spikes to high values in the seawater strontium isotope record at other times may reflect similar episodes.

Macdougall, J. D.

1988-01-01

121

Nature and timing of extinctions in Cretaceous-Tertiary planktic foraminifera preserved in Deccan intertrappean sediments of the Krishna-Godavari Basin, India  

NASA Astrophysics Data System (ADS)

In C29r below the Cretaceous-Tertiary boundary (KTB) massive Deccan Trap eruptions in India covered an area the size of France or Texas and produced the world’s largest and longest lava megaflows 1500 km across India through the Krishna-Godavari (K-G) Basin into the Bay of Bengal. Investigation of ten deep wells from the K-G Basin revealed four lava megaflows separated by sand, silt and shale with the last megaflow ending at or near the KTB. The biologic response in India was swift and devastating. During Deccan eruptions prior to the first megaflow, planktic foraminifera suffered 50% species extinctions. Survivors suffered another 50% extinctions after the first megaflow leaving just 7-8 species. No recovery occurred between the next three megaflows and the mass extinction was complete with the last mega-flow at or near the KTB. The last phase of Deccan volcanism occurred in the early Danian C29n with deposition of another four megaflows accompanied by delayed biotic recovery of marine plankton. Correlative with these intense volcanic phases, climate changed from humid/tropical to arid conditions and returned to normal tropical humidity after the last phase of volcanism. The global climatic and biotic effects attributable to Deccan volcanism have yet to be fully investigated. However, preliminary studies from India to Texas reveal extreme climate changes associated with high-stress environmental conditions among planktic foraminifera leading to blooms of the disaster opportunist Guembelitria cretacea during the late Maastrichtian.

Keller, G.; Adatte, T.; Bhowmick, P. K.; Upadhyay, H.; Dave, A.; Reddy, A. N.; Jaiprakash, B. C.

2012-08-01

122

The high oxygen atmosphere toward the end-Cretaceous; a possible contributing factor to the K/T boundary extinctions and to the emergence of C(4) species.  

PubMed

Angiosperm plants were grown under either the present day 21 kPa O(2) atmosphere or 28 kPa, as estimated for the end-Cretaceous (100-65 MyBP). CO(2) was held at different levels, within the 24-60 Pa range, as also estimated for the same period. In C(3) Xanthium strumarium and Atriplex prostrata, leaf area and net photosynthesis per unit leaf area, were reduced by the high O(2), while the whole-plant respiration/photosynthesis ratio increased. The high O(2) effects were strongest under 24 Pa, but still significant under 60 Pa CO(2). Growth was reduced by high O(2) in these C(3) species, but not in Flaveria sp., whether C(3), C(4), or intermediary grown under light intensities <350 micromol m(-2) s(-1) PPF. Photosynthesis of C(3) Flaveria sp. was reduced by high O(2), but only at light intensities >350 micromol m(-2) s(-1) PPF. It is concluded that the high O(2) atmosphere at the end-Cretaceous would have reduced growth of at least some of the vegetation, thus adversely affecting dependent fauna. The weakened biota would have been predisposed to the consequences of volcanism and the K/T boundary bolide impact. Conversely, photosynthesis and growth of C(4) Zea mays and Atriplex halimus were little affected by high, 28 kPa, O(2). This suggests an environmental driver for the evolution of C(4) physiology. PMID:11413216

Gale, J; Rachmilevitch, S; Reuveni, J; Volokita, M

2001-04-01

123

Strangelove ocean at era boundaries, terrestrial or extraterrestrial cause  

NASA Technical Reports Server (NTRS)

Negative perturbations in carbon-isotope value of calcite in pelagic sediments were found at times of biotic crisis, marking horizons which are, or were proposed as era boundaries: Cretaceous/Tertiary (K/T), Permian/Triassic (P/T), and Precambrian/Cambrian (PreC/C). The anomaly was also found at several other mass-extinction horizons, such as terminal Ordovician, Frasnian-Famenian, etc. Studies of K/T boundary indicate that only the planktic fraction of the sediments has the negative isotope anomaly, whereas the benthic fraction has the same value across the boundary. This geochemical signal is thus considered a record of strangelove ocean, or an ocean where isotope fractionation of dissolved carbonate ions in surface waters (by biotic function of planktic organisms) has been significantly reduced because of the drastic reduction of the biomass in the oceans. The reduction of marine biomass at each of the era boundaries was related to chemical pollution of the oceans as a consequence of a catastrophic event; a pH decrease of 0.5 could inhibit the fertility of planktons. Studies of earthquakes, volcanic eruptions, and meteorite-impact occurrences have indicated a linearly inverse log/log relationship between the magnitude and frequency of events. The frequency of era boundaries in geologic history supports the postulate that the rare events causing those biotic crises were large bolide-impacts.

Hsue, Kenneth J.

1988-01-01

124

Formation of the Shelf-edge Cretaceous-Tertiary contact off the southeastern U.S. Coast  

USGS Publications Warehouse

Submarine erosion, associated with changes in position of the proto-Gulf Stream, was the dominant mechanism controlling the formation of the Cretaceous-Tertiary unconformity in AMCOR borehole 6004. Paleontologic evidence indicates that this unconformity, which is marked by a gravelly-sand enriched in glauconitic and phosphoritic concretions, represents a hiatus of about 7 m.y. Both Cretaceous and Paleocene sediments contain middle-outer neritic foraminiferal assemblages that become more diverse with distance from the contact. Of the elemental abundances measured, Al, Ba, Co, Fe, Ga, K, Mg/Ca, Mo, Ni, P, Sr/Ca, V, Y, and Zn show a strong positive correlation with proximity to the contact, probably as a result of the concentration of authigenic and heavy minerals present as lag sediments on the erosion surface. ?? 1986.

Poppe, L.J.; Hathaway, J.C.; Hall, R.E.; Commeau, R.F.

1986-01-01

125

Iridium abundance patterns across extinction boundaries  

SciTech Connect

The authors are measuring elemental abundances, with emphasis on high sensitivity Ir assay, across biological crisis zones in the fossil record. Samples are measured in an automated neutron activation analysis system, with radiochemical separations for the heavy Pt-group elements and Au. They are collaborating with paleontologic and stratigraphic experts to home-in on the boundaries, and to date they have performed at least one set of measurements across the following transition and extinction boundaries: Precambrian/Cambrian(Pc/C); 2 U. Cambrian biomere boundaries; the basal Ordovician; Ordovician;/Silurian; U. Devonian Frasnian/Famennian (F/F); Devonian/Miss.; Miss./Penn.; Permian/Triassic (P/Tr); Triassic/Jurassic; L. Jurassic Toarcian; Cretaceous/Tertiary (K/T); and the U. Eocene. The authors work on K/T sequences that were deposited under freshwater conditions in the western interior of North America supports the Alvarez asteroid impact hypothesis. The Earth has been struck many times in the Phanerozoic by large impactors that probably have done tremendous damage to the local environment. However, to day scientists have not found any firm chemical evidence for the association of impacts with global extinctions older than the massive terminal Cretaceous event, which might have been unique in the Phanerozoic. Although they have measured a moderate Ir and Pt anomaly in the F/F boundary zone in NW Australia, their evidence indicates that these and several other elements were enriched from seawater by bacteria. Although the authors data, except for the U. Eocene, do not support the periodic comet swarm-global extinction arguments, much more work is needed to resolve this issue.

Orth, C.J.; Gilmore, J.S.; Oliver, P.Q.; Quintana, L.R.

1985-01-01

126

Patterns of megafloral change across the Cretaceous-Tertiary boundary in the Northern Great Plains and Rocky Mountains  

NASA Technical Reports Server (NTRS)

The spatial and temporal distribution of vegetation in the terminal Cretaceous of Western Interior North America was a complex mosaic resulting from the interaction of factors including a shifting coastline, tectonic activity, a mild, possibly deteriorating climate, dinosaur herbivory, local facies effects, and a hypothesized bolide impact. In order to achieve sufficient resolution to analyze this vegetational pattern, over 100 megafloral collecting sites were established, yielding approximately 15,000 specimens, in Upper Cretaceous and lower Paleocene strata in the Williston, Powder River, and Bighorn basins in North Dakota, Montana, and Wyoming. These localities were integrated into a lithostratigraphic framework that is based on detailed local reference sections and constrained by vertebrate and palynomorph biostratigraphy, magnetostratigraphy, and sedimentary facies analysis. A regional biostratigraphy based on well located and identified plant megafossils that can be used to address patterns of floral evolution, ecology, and extinction is the goal of this research. Results of the analyses are discussed.

Johnson, Kirk R.; Hickey, Leo J.

1988-01-01

127

Comparison of the magnetic properties and Mossbauer analysis of glass from the Cretaceous-Tertiary boundary, Beloc, Haiti, with tektites  

NASA Technical Reports Server (NTRS)

The magnetic properties of black Beloc glass have been measured. The Curie constant, the magnetization, and the magnetic susceptibility of the Beloc glass fall within the known ranges observed for tektites. However, the temperature-independent component of the magnetic susceptibility is slightly higher than that found for tektites. Moreover, it is not possible to match the experimental magnetic data for the Beloc glass with the calculated values using the previously reported Fe(3+)/Fe(2+) ratio of 0.7. The oxidation state of Fe was therefore redetermined by Mossbauer measurements, and the Fe(3+)/Fe(2+) ratio was found to be 0.024 plus or minus 0.015. Using the redetermined value of the ratio, the magnetic parameters were again calculated using formulas that are applicable to tektites, and good agreement was found between the calculated and experimental values. The experimental magnetic measurements and the redetermined Fe(3+)/Fe(2+) ratio of the Beloc glass specimens are essentially the same as those found for tektite glass.

Thorpe, A. N.; Senftle, F. E.; May, L.; Barkatt, A.; Adel-Hadadi, M. A.; Marbury, G. S.; Izett, G. A.; Maurrasse, F. R.

1994-01-01

128

GEOLOGY, TAPHONOMY, AND PALEOECOLOGY OF A UNIQUE UPPER CRETACEOUS BONEBED NEAR THE CRETACEOUS-TERTIARY BOUNDARY IN SOUTH DAKOTA  

E-print Network

This research examines a Konzentrat-Lagerstätte, the Bone Butte site, in the Upper Cretaceous Hell Creek Formation of South Dakota. Field data from a diverse multispecific bonebed in Harding County, South Dakota, including ...

DePalma, Robert Anthony

2010-04-27

129

PALEOCEANOGRAPHY,VOL. 1, NO. 2, PAGES 97-117, JUNE 1986 THE CRETACEOUS/TERTIARY BOUNDARY  

E-print Network

patterns of plank- tonic foraminifera in a continuous carbon- ate sequence spanning the Cretaceous disap- pearance of almost all Maastrichtian plank- tonic foraminifera. Coincident with these extinctions than those of the other plank- tonic foraminifera. Such a relationship might suggest that G. eugubina

Zachos, James

130

Proportions of coarse and fine clay across the Cretaceous-Tertiary boundary in Milam, Falls, and Travis Counties, Texas  

E-print Network

PROPOBTIO ~S OF CO. IBSE . ~~ID FINE CLsY . , CROSS THE CHETHCEOUS-TEHTI. BY SOUND iHY IN idlLiLVn FRILLS?, U3D TBiaVIS COUNTII'S, TL'XiiS A Thesis John Charle - Smith Sub. 'nitted to the Graduate College of' Texas AKYi University in partial f... Charles Smith ~ppr ved as to style and content by: (Chairman of Com! ' ee) (He d of', ' artment, ( !I!ber) / c Ql, January, 1966 TaBLE Oi' COi1T~~~'JTB iicEnowledgments -bstract introduction Page vii Objective of the investigation Beasons...

Smith, John Charles

2012-06-07

131

The role of Deccan volcanism during the K-T mass extinction  

NASA Astrophysics Data System (ADS)

The potential role of major volcanic provinces has long been neglected as potential cause for major mass extinctions in Earth's history. This is despite the fact that volcanic activity is implicated in four of the five Phanerozoic mass extinctions, whereas a large asteroid impact is only associated with the K-T mass extinction. After 28 years of nearly unchallenged perception that a large impact (Chicxulub) on Yucatan caused the end-Cretaceous mass extinction, this theory is facing its most serious challenge from Deccan volcanism in India. Recent advances in Deccan volcanic studies show that Deccan Trap volcanism began with a relatively minor eruption phase (~6% of total volume) during the late Maastrichtian magnetic polarity C30n. The main eruption phase (~80%) occurred over a short period in C29r just below the Cretaceous-Tertiary boundary (KTB) and the last Deccan phase (~14%) erupted in the early Danian C29n. Multiproxy studies from sections in Meghalaya (NE India), Jhilmili in central India (Madhya Pradesh), 6 quarry outcrops from Rajahmundry (SE India), 10 deep wells from the Krishna-Godavari Basin (K-G) (Andhra Pradesh) place the KTB mass extinction near the end of the main Deccan phase coincident with the mass extinction. These studies show that the second and third phase of eruptions each produced the world's largest and longest lava megaflows ~1500 km across India through the K-G Basin into the Bay of Bengal. These megaflows are separated by sand, silt and shale which record the mass extinction across an interval that spans zones CF1-CF2 and most of the nannofossil Micula prinsii zone and is correlative with the rapid global warming and subsequent cooling near the end of the Maastrichtian. The mass extinction began preceding the first of the four mega-flows in C29r. Planktic foraminifera suffered a 50% drop in species richness. Survivors suffered another 50% drop after the first mega-flow, leaving just 7 to 8 survivor species. No recovery occurred between the next three mega-flows and the mass extinction was complete with the last phase-2 megaflow at the KTB. The last phase of Deccan volcanism and its 3 to 4 megaflows in the early Danian C29n (zone P1b) delayed biotic recovery of marine plankton. Correlative with these intense volcanic phases, climate changed from humid/tropical to arid conditions and returned to normal tropical humidity after the last phase of volcanism. Similar environmental conditions, mass extinction and delayed recovery patterns are observed in Meghalaya, NE India. The mass extinction was likely the consequence of rapid and massive volcanic CO2 and SO2 gas emissions, leading to high continental weathering rates, global warming, cooling, acid rains, ocean acidification and a carbonate crisis in the marine environment. Combined with an impact, Deccan volcanism can thus explain both the KTB mass extinction and the long delayed biotic recovery that has been an enigma for so long. But added to impact catastrophe, a cascade of rapid massive volcanic eruptions and their complex destructive interactions with Earth's equilibrium may have done the deed. The observed climate, faunal and floral changes may have been triggered by Deccan volcanism as a result of massive CO2 and SO2 emissions.

Adatte, T.; Keller, G.; Gertsch, B.

2012-12-01

132

K-T impact(s): Continental, oceanic or both  

NASA Technical Reports Server (NTRS)

Although geochemical and mineralogical evidence indicate that a major accretionary event occurred at the K-T boundary, no impact crater of suitable size and age was recognized. The 35 km Manson Structure, Iowa, was suggested recently as a possibility and Ar-40/Ar-39 determinations indicate that its formation age is indistinguishable from that of the K-T boundary. In order to test a possible association between Manson and the K-T boundary clay, the geochemistry and mineralogy of the K-T boundary clays at the Scollard Canyon section, Alberta and the Starkville South section, Colorado are compared with three dominant lithologies affected by the Manson impact: Proterozoic red clastics, underlying late-state granites, and gneisses. The chemical and mineralogical makeup of the Scollard Canyon boundary clay and its clastic constituents are presented, commenting on the implications for impact models. An impact into crystalline material of continental affinity appears to be required to explain the mineralogy and chemistry of the Scollard Canyon (and other Western N. American K-T sections). The low REE abundances of some K-T boundary layers are unusual but perhaps attempts should be made to understand the contributions of individual crustal components (e.g., carbonates, arkoses) as well as the potential for alteration involving these and other elements during and after impact-induced vaporization, before mantle excavation is invoked. If further studies confirm the results of published studies of marine boundary clays that indicate an oceanic target, attention must be paid to the possibility that multiple impacts occurred at the K-T boundary - one or more on the continents and one or more in the ocean.

Sharpton, V. L.; Schuraytz, B. C.; Murali, A. V.; Ryder, G.; Burke, K.

1988-01-01

133

Shock-induced devolatization of calcium sulfate and implications for K-T extinctions  

NASA Technical Reports Server (NTRS)

Calcium sulfate devolatization during the impact at Chicxulub, Mexico and dispersal in the stratosphere of the resultant sulfuric acid aerosol have been suggested as a possible mechanism for the Cretaceous-Tertiary extinctions. In this paper, we investigated two shock-induced devolatization reactions of calcium sulfate up to 42 GPa in the laboratory: CaSO4 + SiO2 yields CaSiO3 + SO3(degassed) and CaSO4 yields CaO + SO2(degassed) + 1/2 O2(degassed). We found both to proceed to a much less extent than calculated by equilibrium thermodynamic calculations. Reaction products are found to be 10(exp -2) times those calculated for equilibrium. Consequently our estimate of the amount of sulfur oxides degassed into the atmosphere from shock devolatization of CaS04 in the Chicxulub lithographic section (6x10(exp 15)-2x10(exp 16)g in sulfur mass) is lower by a factor of 70 to 400 than previous estimates; the related environmental stress arising from the resultant global cooling of approximately 4 K and fallout of acid rain does not appear to suffice to explain the widespread K-T extinctions.

Chen, Guangqing; Tyburczy, James A.; Ahrens, Thomas J.

1993-01-01

134

Shock-induced devolatilization of calcium sulfate and implications for K-T extinctions  

NASA Technical Reports Server (NTRS)

The devolatilization of calcium sulfate, which is present in the target rock of the Chicxulub, Mexico impact structure, and dispersal in the stratosphere of the resultant sulfuric acid aerosol have been suggested as a possible mechanism for the Cretaceous-Tertiary extinctions. We measured the amount of SO2 produced from two shock-induced devolatilization reactions of calcium sulfate up to 42 GPa in the laboratory. We found both to proceed to a much lower extent than calculated by equilibrium thermodynamic calculations. Reaction products are found to be approx. 10(exp -2) times those calculated for equilibrium. Upon modeling the quantity of sulfur oxides degassed into the atmosphere from shock devolatilization of CaSO4 in the Chicxulub lithographic section, the resulting 9 x 10(exp 16) to 6 x 10(exp 17) g (in sulfur mass) is lower by a factor of 10-100 than previous upper limit estimates, the related environmental stress arising from the resultant global cooling and fallout of acid rain is insufficient to explain the widespread K-T extinctions.

Chen, Guangqing; Tyburczy, James A.; Ahrens, Thomas J.

1994-01-01

135

The carbon-isotope shift at the Permian\\/Triassic boundary in the southern Alps is gradual  

Microsoft Academic Search

Carbon isotope ratios in marine carbonate rocks have been shown to shift at some of the time boundaries associated with extinction events; for example, Cretaceous\\/Tertiary1 and Ordovician\\/ Silurian2. The Permian\\/Triassic boundary, the greatest extinction event of the Phanerozoic3, is also marked by a large delta13C depletion4,5. New carbon isotope results from sections in the southern Alps show that this depletion

Mordeckai Magaritz; Richard Bart; Aymon Baud; William T. Holser

1988-01-01

136

Search for extractable fullerenes in clays from the cretaceous/tertiary boundary of the Woodsite Creek and Flaxbourne River sites, New Zealand  

SciTech Connect

When fullerenes were first discovered to form spontaneously in condensing carbon vapors, it was suggested that they might be widely distributed in the Universe. Searchers for fullerenes in meteorites were unsuccessful, but C[sub 60] and C[sub 70] were reported to occur on Earth in samples of shungite, a meta-anthracite from a deposit near Shunga, Russia, and in [open quotes]fulgurite[close quotes], a substance formed when lightning strikes certain soils or rocks. The occurrence of fullerenes in shungite is particularly surprising since fullerene synthesis in the laboratory has always involved gas phase chemistry at temperatures over 1000[degrees]C. Such conditions may be attained during lightning strikes, but shungite is believed to have formed from carbonaceous material creeping into fissures of a Precambrian rock which metamorphosed under extreme pressures. If the original carbonaceous material did not already contain fullerenes perhaps from wildfires, they must have formed during the metamorphism by as yet unknown solid- or liquid-phase mechanisms.

Heymann, D.; Chibante, L.P.F.; Smalley, R.E. (Rice Univ., Houston, TX (United States)); Wolbach, W.S. (Wesleyan Univ., Bloomington, IL (United States)); Brooks, R.R. (Massey Univ., Palmerston North (New Zealand))

1994-08-01

137

The succession of Vertebratesand Plants across the Cretaceous-Tertiary boundary in the Tremp Formation, Ager valley (South-central Pyrenees, Spain)  

Microsoft Academic Search

The Tremp Formation red beds in the Ager valley (Fontllonga section, Lleida, Spain) have yieldedplants (macrorests, palynomorphs) and vertebrates (teeth, bones, eggshells and footprints) at different levels from Early Maastrichtian to Early Palaeocene. A decrease in diversity affected both, plants and vertebrates, but not synchronously. Plant diversity decreases early in the Maastrichtian, while the change in vertebrate assemblages (sudden extinction

Nieves López-Martínez; M Fernández-Marrón; Maria F. Valle

1999-01-01

138

Darkness after the K-T impact: Effects of soot  

NASA Technical Reports Server (NTRS)

Dust from the K-T impact apparently settled from the atmosphere in less than 6 months, restoring sunlight to minimum photosynthesis levels in about 4 months. However, the discovery of a global soot component in the boundary clay makes it necessary to reconsider the problem, as soot particles not only are smaller (0.1 vs. about 0.5 micrometer) and thus settle more slowly, but also are better light absorbers (optical depth of 13 mg soot cm(-2) about 1800; and are more resistant to rainout. Still, the darkness cannot have lasted very much longer than 6 months, else no larger animals would have survived. Perhaps the soot coagulated with the rock dust and fell out with it. Evidence on this point may be sought at a relatively undisturbed K-T boundary site, such as Woodside Creek, N.Z. There the boundary clay and lowermost Tertiary strata are finely laminated and show large chemical and isotopic differences on a millimeter scale, apparently representing a detailed time sequence. Researchers studied a 3 m section across the boundary at this site, analyzing the principal forms of carbon (soot, elemental C, kerogen, and carbonate) as well as 33 elements. Correlations among the elements were sought. Apparently soot came early and coagulated with the ejecta, staying with them for the primary fallout and in the next 5 cm, but then parting company, perhaps due to size sorting.

Wolbach, Wendy S.; Anders, Edward; Orth, Charles J.

1988-01-01

139

KT boundary impact glasses from the Gulf of Mexico region  

NASA Technical Reports Server (NTRS)

Cretaceous-Tertiary boundary (KTB) tektite glasses occur at several sites around the Gulf of Mexico. Contrary to rumor among KTB workers, glass fragments have been found by several researchers in the base of the spherule bed at Arroyo el Mimbral in NE Mexico. The presence of green, red, and transparent glass fragments at Mimbral only, demonstrates that the Mimbral glass is not a laboratory contamination by Beloc glass. The chemistry and ages of the glass are consistent with an origin from the Chixculub impact crater in Yucatan. No evidence supports a volcanic origin for the KTB glasses. A discussion of tektite glass from the KT boundary is presented.

Claeys, Philippe; Alvarez, Walter; Smit, Jan; Hildebrand, A. R.; Montanari, Alessandro

1993-01-01

140

Valence quarks and $k_T$ factorisation  

E-print Network

We study in the $k_T$ factorisation framework jet production at LHC energies. In particular we are interested in valence quark and gluon initiated jets. The calculation of the relevant hard matrix element is presented. A CCFM like evolutionequation for valence quark distribution is solved and the cross section for valence quark and gluon initiated process is calculated using Monte Carlo event generator CASCADE.

Michal Deák; Hannes Jung; Krzysztof Kutak

2008-07-15

141

Magnetic microspherules associated with the K/T and upper Eocene extinction events  

NASA Technical Reports Server (NTRS)

Magnetic microspherules were identified in over 20 K/T boundary sites, and in numerous Deep Sea Drilling Project (DSDP) cores from the Caribbean and Pacific, synchronous with the extinction of several radiolarian species near the end of the Eocene. The K/T magnetic spherules are of particular interest as carriers of Ir and other siderophiles generally found in abundance in K/T boundary clay. Furthermore the textures and unusual chemistry of their component magnetic phases indicate an origin at high temperature, possibly related to (an) unusual event(s) marking the end of the Cretaceous and Eocene periods. Their origin, along with the non-magnetic (sanidine) spheules, is generally ascribed directly to megaimpact events hypothesized to have periodically disrupted life on Earth. A survey of microspherical forms associated with known meteorite and impact derived materials reveals fundamental differences from the extinction related spherules. Low temperature magnetic experiments on the K/T and Upper Eocene spheroids indicate that, unlike tektites, extremely small superparamagnetic carriers are not present in abundance. The extensive subaerial exposure of Cretaceous combustible black shale during sea level regression in the latest Cretaceous represents a potential source for the magnetic spheroids found in certain K/T boundary clays. The recent discovery of high Ir abundances distributed above and below the K/T boundary within shallow water sediments in Israel, which also contain the most extensive known zones of combustion metamorphism, the so called Mottled Zone, adds a further dramatic footnote to the proposed association between the magnetic spheroids and combustion of organic shales. Interestingly, the Mottled Zone also contains the rare mineral magnesioferrite, which was identified both within the K/T magnetic spheroids and as discrete crystals in boundary clay from marine and continental sites.

Cisowski, Stanley M.

1988-01-01

142

Synchroneity of the K-T oceanic mass extinction and meteorite impact: Blake Nose, western North Atlantic  

USGS Publications Warehouse

A 10-cm-thick layer of green spherules occurs precisely at the biostratigraphic boundary between the Cretaceous and Paleogene (K-T boundary) at Ocean Drilling Program Site 1049 (lat 30??08???N, long 76??06???W). The spherulitic layer contains abundant rock fragments (chalk, limestone, dolomite, chert, mica books, and schist) as well as shocked quartz, abundant large Cretaceous planktic foraminifera, and rounded clasts of clay as long as 4 mm interpreted as altered tektite glass probably derived from the Chicxulub impact structure. Most of the Cretaceous foraminifera present above the spherule layer are not survivors since small specimens are conspicuously rare compared to large individuals. Instead, the Cretaceous taxa in Paleocene sediments are thought to be reworked. The first Paleocene planktic foraminifera and calcareous nannofossil species are recorded immediately above the spherule bed, the upper part of which contains an iridium anomaly. Hence, deposition of the impact ejecta exactly coincided with the biostratigraphic K-T boundary and demonstrates that the impact event was synchronous with the evolutionary turnover in the oceans. These results are consistent with a reanalysis of the biostratigraphy of the K-T boundary stratotype, which argues that shallow-marine K-T boundary sections are not biostratigraphically more complete than deep-sea K-T boundary sites.

Norris, R. D.; Huber, B. T.; Self-Trail, J.

1999-01-01

143

Projectile-Target Mixing in Melted Ejecta Formed During a Hypervelocity Impact Cratering Event.  

National Technical Information Service (NTIS)

Tektites contain little to no projectile contamination while, in contrast, some distal ejecta deposits can be relatively projectile-rich (e.g. the Cretaceous-Tertiary (K-T) boundary clay). This compositional difference motivated an experimental study of h...

N. J. Evans, T. J. Ahrens, M. Shahinpoor, W. W. Anderson

1993-01-01

144

Dinosaur bone beds and mass mortality: Implications for the K-T extinction  

NASA Technical Reports Server (NTRS)

Mass accumulations of fossilized large terrestrial vertebrate skeletons (bone beds: BB) provide a test for K-T catastrophic extinction hypotheses. The two major factors contributing to BB formation are mode of death and sedimentation rate. Catastrophic mass mortality (CMM) is the sudden death of numerous individuals where species, age, health, gender, or social ranking offer no survivorship advantage. Noncatastrophic mass mortality (NCMM) occurs over time and is strongly influenced by species, age, or gender. In addition to cause of death, sedimentation rate is also important in BB formation. Models of BBs can be made. The CMM drops all individuals in their tracks, therefore, the BB should reflect the living population with respect to species, age, or gender. The NCMM results in monospecific BBs skewed in the direction of the less fit, usually the very young or very old, or towards a specific gender. The NCMM and AM BBs may become more similar the more spread out over time NCMM deaths occur because carcasses are widely scattered requiring hydraulic accumulation, and the greater time allows for more disarticulation and weathering. The CMM and NCMM BB appear to be dominated by social animals. Applying this and the characteristics of mortality patterns to the uppermost Cretaceous Hell Creek Formation indicates that only NCMM and AM BB occur. Furthermore, NCMM BB are rare in the upper third of the Hell Creek. Near the K-T boundary, only AM BB are known. The absence of CMM and NCMM BB appears to be real reflecting a decrease in population levels of some dinosaurs prior to the K-T event. The absence of CMM suggests that the K-T event did not lead to an instantaneous extinction of dinosaurs. Nor was there a protracted die-off due to an asteroid impact winter, because no NCMM BB are known at or near the K-T boundary.

Carpenter, Kenneth

1988-01-01

145

QCD jet rates with the inclusive generalized k t algorithms  

NASA Astrophysics Data System (ADS)

We derive generating functions, valid to next-to-double logarithmic accuracy, for QCD jet rates according to the inclusive forms of the k t , Cambridge/Aachen and anti- k t algorithms, which are equivalent at this level of accuracy. We compare the analytical results with jet rates and average jet multiplicities from the SHERPA event generator, and study the transition between Poisson-like and staircase-like behaviour of jet ratios.

Gerwick, Erik; Schumann, Steffen; Gripaios, Ben; Webber, Bryan

2013-04-01

146

Determination of rapid Deccan eruptions across the Cretaceous-Tertiary boundary using paleomagnetic secular variation: 2. Constraints from analysis of eight new sections and synthesis for a 3500-m-thick composite section  

Microsoft Academic Search

The present paper completes a restudy of the main lava pile in the Deccan flood basalt province (trap) of India. Chenet et al. (2008) reported results from the upper third, and this paper reports the lower two thirds of the 3500-m-thick composite section. The methods employed are the same, i.e., combined use of petrology, volcanology, chemostratigraphy, morphology, K-Ar absolute dating,

Anne-Lise Chenet; Vincent Courtillot; Frédéric Fluteau; Martine Gérard; Xavier Quidelleur; S. F. R. Khadri; K. V. Subbarao; Thor Thordarson

2009-01-01

147

Diffractive Vector Meson Production in k_t-Factorization Approach  

E-print Network

We describe the current status of the diffractive vector meson production calculations within the k_t-factorization approach. Since the amplitude of the vector meson production off a proton is expressed via the differential gluon structure function (DGSF), we take a closer look at the latter and present results of our new improved determination of the DGSF from the structure function F_2p. Having determined the differential glue, we proceed to the k_t-factorization results for the production of various vector mesons. We argue that the properties of the vector meson production can reveal the internal spin-angular and radial structure of the vector meson.

I. P. Ivanov; N. N. Nikolaev

2002-06-28

148

Heavy quark impact factor in kT-factorization  

E-print Network

We present the calculation of the finite part of the heavy quark impact factor at next-to-leading logarithmic accuracy in a form suitable for phenomenological studies such as the calculation of the cross-section for single bottom quark production at the LHC within the kT-factorization scheme.

Grigorios Chachamis; Michal Deak; German Rodrigo

2013-10-24

149

Prompt photon production with $k_T-$factorization  

E-print Network

We consider the prompt photon production at modern high energy colliders in the framework of $k_T-$factorization approach. We compare our theoretical predictions with recent experimental data at HERA and Tevatron, empahasizing the distinction between our theoretical predictions and the results of NLO QCD calculations. Finally, we extrapolate our predictions to LHC energies.

A. V. Lipatov; N. P. Zotov

2006-11-30

150

Nanofósiles del límite Cretácico\\/Terciario cerca de Beloc (Haití): bioestratigrafía, composición de las asociaciones e implicaciones paleoclimáticas  

Microsoft Academic Search

Abstract The Beloc Formation, (Southern Peninsula of Haiti) includes a well preserved record of the Cretaceous\\/Tertiary boundary ma- terials with a distinct spherulithic layer interpreted as a result of the Chicxulub impact. A quantitative nannofossil study of four sections spanning the K\\/T boundary,has led to identify the interval corresponding,to the Micula murus\\/Nephrolithus frequens (CC25c\\/CC26a) Subzones and a thick Micula prinsii(CC26b)

Roque Aguado; Marcos A. Lamolda; Florentin J-M; R. Maurrasse

151

Investigating a 65-Ma-Old Smoking Gun: Deep Drilling of the Chicxulub Impact Structure  

NASA Technical Reports Server (NTRS)

The Phanerozoic paleontological record is marked by several biological extinction events. One of them,at the Cretaceous/Tertiary (K/T) boundary was responsible for the demise of about 50% of genera and 75% of species, including the dinosaurs.These drastic and abrupt changes in the development of life on Earth puzzled paleontologists in the past. Many a cause was put forward to account for them, amongst them climate changes, disease, or overspecialization.

Dressler, B.; Sharpton, V. L.; Morgan, J.; Buffler, R.; Moran, D.; Smit, J.; Stoeffler, D.; Urrutia, J.

2003-01-01

152

Iridium in marine organisms from the Gulf of Mexico  

E-print Network

the scientific and popular literature of possible causes of the Iridium (Ir) enrichment in Cretaceous-Tertiary (K-T) boundary sediments and the concomitant biological extinctions (65 m. y. BP). No published data exist for Ir in marine biota, therefore... and also caused the very large biological extinctions (Alvarez et al. , 1984; Brooks et al. , 1984; Kasmer et al. , 1984). The meteorite impact theory has generated much discussion in both the scientific and popular literature. Since 1980 many articles...

Wells, Mona Cara

2012-06-07

153

Primary Mineralogical and Chemical Characteristics of the Major K/T and Late Eocene Impact Deposits  

NASA Technical Reports Server (NTRS)

Three well-characterized, distal impact deposits at the WT boundary and in upper Eocene sediments serve as a baseline for understanding other proposed impact deposits. All contain abundant spherules, evidence of shock metamorphism, and the largest have significant extraterrestrial components (ETCs). The K/T and the Eocene cpx-spherule (cpxS) deposits are global - likely from the events that produced the 180 km Chicxulub and 100 km Popigai craters. The Eocene North American microtektite (NAM) deposit is regional and likely from the event that produced the 45 km Chesapeake Bay crater. These deposits all contain abundant spherules formed from both shock-melted target and mixtures of target and projectile in the ejecta plume. Spherules constitute most of the mass of the distal ejecta. K/T spherules in regional deposits around the Gulf of Mexico are from low-velocity, target-rich ejecta. These can be a few mm in size and form deposits 10s of cm thick. Globally deposited KIT spherules from the plume (typically a few hundred micron size) are both target- and projectile-rich. When well preserved, the global deposits are 3 mm thick. Eocene cpxS deposits are similar to distal K/T with both target- and projectile-rich varieties (Le., glassy microtektite, and cpx spherules). They are smaller on average than WT spherules, concentrated in the 125-250 micron and smaller fractions. They are invariably bioturbated, but the initial deposit was probably less than 1 mm thick. The NAM are composed entirely of target-rich glass. They are similar in size to the cpxS. Size is an important criterion for distal ejecta because droplet size in the impact plume is proportional to the energy of the impact. Both the JUT and cpxS deposits are characterized by well-defined ETCs, commonly measured by Ir. The total Ir deposited is about 55 ng per square cm in WT sediments, and about 11 ng for the cpxS layer. This 5/1 proportion in Ir is generally consistent with the approx.1.8/1 ratio in crater diameters. The NAM have no significant ETC. This may be a function of the smaller impact. It indicates there was no significant projectile-rich plume deposit.

Kyte, Frank T.

2004-01-01

154

What Effect Do They Have? Direct Hit at the K-T Boundary  

NSDL National Science Digital Library

This is a lesson about the effects of large impacts. Learners will use critical thinking skills to evaluate and apply data from a narrative to a scientific selection process, will demonstrate or visualize simulations of some of the effects of a huge impact, and will write a point of view narrative. Materials and vocabulary lists, and advanced preparation and procedural tips are included. This is lesson 14 of 19 in Exploring Meteorite Mysteries.

155

Terrestrial Acidification at the K/T Boundary James R. Lyons*  

E-print Network

on geochemically constraining the production of acid during the KT impact. The potential importance of acid timescale as stratospheric SO2 was slowly converted to sulfuric acid aerosol [9-11]. Evaporite deposits the KTB [1] and acid leaching of base cations at North American KTB sites [2]. Continental weathering

Stewart, Sarah T.

156

What Caused the Mass Extinction Recorded at the K-T Boundary  

NSDL National Science Digital Library

Exploring Earth Investigations are Internet-based activities that use animations, interactive graphics, and unique imagery to help students gather information about a particular Earth science theme, issue, or concept.

TERC (www.terc.edu)

157

Carbon dioxide emissions from Deccan volcanism and a K/T boundary greenhouse effect  

NASA Technical Reports Server (NTRS)

A greenhouse warming caused by increased emissions of carbon dioxide from the Deccan Traps volcanism has been suggested as the cause of the terminal Cretaceous extinctions on land and in the sea. Total eruptive and noneruptive CO2 output by the Deccan eruptions (from 6 to 20 x 10 to the 16th moles) over a period of several hundred thousand years is estimated based on best estimates of the CO2 weight fraction of the original basalts and basaltic melts, the fraction of CO2 degassed, and the volume of the Deccan Traps eruptions. Results of a model designed to estimate the effects of increased CO2 on climate and ocean chemistry suggest that increases in atmospheric pCO2 due to Deccan Traps CO2 emissions would have been less than 75 ppm, leading to a predicted global warming of less than 1 C over several hundred thousand years. It is concluded that the direct climate effects of CO2 emissions from the Deccan eruptions would have been too weak to be an important factor in the end-Cretaceous mass extinctions.

Caldeira, Ken; Rampino, Michael R.

1990-01-01

158

A detailed taxonomy of Upper Cretaceous and lower Tertiary Crassatellidae in the Eastern United States; an example of the nature of extinction at the boundary  

USGS Publications Warehouse

Current theories on the causes of extinction at the CretaceousTertiary boundary have been based on previously published data; however, few workers have stopped to ask the question, 'How good is the basic data set?' To test the accuracy of the published record, a quantitative and qualitative analysis of the Crassatellidae (Mollusca, Bivalvia) of the Gulf and Mid-Atlantic Coastal Plains of the United States for the Upper Cretaceous and lower Tertiary was conducted. Thirty-eight species names and four generic names are used in publications for the Crassatellidae within the geographic and stratigraphic constraints of this analysis. Fourteen of the 38 species names are represented by statistically valid numbers of specimens and were tested by using canonical discriminant analysis. All 38 names, with the exception of 1 invalid name and 4 names for which no representative specimen could be located, were evaluated qualitatively. The results show that the published fossil record is highly inaccurate. Only 8 valid, recognizable species exist in the Crassatellidae within the limits of this study, 14 names are synonymized, and 11 names are represented by indeterminate molds or poorly preserved specimens. Three of the four genera are well founded; the fourth is based on the juvenile of another genus and therefore synonymized. This detailed taxonomic analysis of the Crassatellidae illustrates that the published fossil record is not reliable. Calculations of evolutionary and paleobiologic significance based on poorly defined, overly split fossil groups, such as the Crassatellidae, are biased in the following ways: Rates of evolution and extinction are higher, Faunal turnover at mass extinctions appears more catastrophic, Species diversity is high, Average species durations are shortened, and Geographic ranges are restricted. The data on the taxonomically standardized Crassatellidae show evolutionary rates one-quarter to one-half that of the published fossil record; faunal change at the Cretaceous-Tertiary boundary that was not catastrophic; a constant number of species on each side of the Cretaceous-Tertiary boundary; a decrease in abundance in the Tertiary; and lower species diversity, longer average species durations, and expanded geographic ranges. Similar detailed taxonomic studies need to be conducted on other groups of organisms to test the patterns illustrated for the Crassatellidae and to determine the extent and direction of the bias in the published fossil record. Answers to our questions about evolutionary change cannot be found in the literature but rather with the fossils themselves. Evolution and extinction occur within small populations of species groups, and it is only through detailed analysis of these groups that we can achieve an understanding of the causes and effects of evolution and extinction.

Wingard, G. Lynn

1993-01-01

159

T H I N K T A N K O N Enhancing Obesity  

E-print Network

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 ObesityT H I N K T A N K O N Enhancing Obesity Research at the National Heart,Lung, andBlood Institute U Institute #12;#12;T H I N K T A N K O N Enhancing Obesity Research at the National Heart,Lung, and

Bandettini, Peter A.

160

The CretaceousTertiary Mass Extinction, Chicxulub Impact,  

E-print Network

of Planet Earth, DOI 10.1007/978-90-481-3428-1_25, © Springer Science+Business Media B.V. 2012 #12;760 G on Yucatan in 1991 (Hildebrand et al. 1991), and the subsequent media and public fascination with it): This theory unquestionably has great sex appeal. The largest and most fascinating creatures that ever roamed

Keller, Gerta

161

Violation of kT factorization in quark production from the Color Glass Condensate  

E-print Network

We examine the violation of the kT factorization approximation for quark production in high energy proton-nucleus collisions. We comment on its implications for the open charm and quarkonium production in collider experiments.

H. Fujii; F. Gelis; R. Venugopalan

2005-10-05

162

First Look at kT Measurements Using di-jet Correlations  

SciTech Connect

The intrinsic parton transverse momentum kT is associated to Fermi motion of the confined partons within a nucleon. In this work we concentrate effort to investigate this phenomena in di-jets simulated in the ALICE framework, for p+p collisions. The goal of this analysis is to determine the sensitivity of the observed parameters, such as, momentum imbalance and acoplanarity, on the magnitude of kT.

Dominguez, Isabel; Cuautle, Eleazar; Paic, Guy [Departamento de Fisica de Altas Energias, Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico (Mexico); Diaz, Rafael [Helsinki Institute of Physics, University of Jyvaeskylae, FI-40014 Jyvaeskylae (Finland); Morsch, Andreas [CERN, PH-Division, 1211 Geneva (Switzerland)

2008-07-02

163

Quasistellar spectrum for neutron activation measurements at kT=5keV  

NASA Astrophysics Data System (ADS)

We have measured the neutron energy spectrum of the 18O(p,n)18F reaction at a proton energy of 2582 keV, 8 keV above the reaction threshold. At this energy the resulting neutron spectrum resembles almost perfectly a Maxwellian distribution at a thermal energy of kT=5.1±0.1keV. Since all neutrons are emitted in a forward cone of 140? opening angle, this reaction can be used for neutron activation measurements similar to the 7Li(p,n)7Be reaction, which is known for producing a thermal spectrum with kT=25keV. Measured neutron capture cross sections at kT=5.1keV and kT=25keV can be used to interpolate to kT=8keV, which characterizes the dominant neutron exposure during s-process nucleosynthesis in thermally pulsing low-mass AGB stars. In a first application of this new method the Maxwellian-averaged neutron capture cross section of 138Ba was measured to be /vT=13.0±0.5mb at kT=5.1keV.

Heil, M.; Dababneh, S.; Juseviciute, A.; Käppeler, F.; Plag, R.; Reifarth, R.; O'Brien, S.

2005-02-01

164

Accelerating free breathing myocardial perfusion MRI using multi coil radial k-t SLR  

PubMed Central

The clinical utility of myocardial perfusion MR imaging (MPI) is often restricted by the inability of current acquisition schemes to simultaneously achieve high spatio-temporal resolution, good volume coverage, and high signal to noise ratio. Moreover, many subjects often find it difficult to hold their breath for sufficiently long durations making it difficult to obtain reliable MPI data. Accelerated acquisition of free breathing MPI data can overcome some of these challenges. Recently, an algorithm termed as k ? t SLR has been proposed to accelerate dynamic MRI by exploiting sparsity and low rank properties of dynamic MRI data. The main focus of this paper is to further improve k ? t SLR and demonstrate its utility in considerably accelerating free breathing MPI. We extend its previous implementation to account for multi-coil radial MPI acquisitions. We perform k ? t sampling experiments to compare different radial trajectories and determine the best sampling pattern. We also introduce a novel augmented Lagrangian framework to considerably improve the algorithm's convergence rate. The proposed algorithm is validated using free breathing rest and stress radial perfusion data sets from two normal subjects and one patient with ischemia. k ? t SLR was observed to provide faithful reconstructions at high acceleration levels with minimal artifacts compared to existing MPI acceleration schemes such as spatio-temporal constrained reconstruction (STCR) and k ? t SPARSE/SENSE. PMID:24077063

Lingala, Sajan Goud; DiBella, Edward; Adluru, Ganesh; McGann, Christopher; Jacob, Mathews

2013-01-01

165

Higgs boson production at hadron colliders in the k_T-factorization approach  

E-print Network

We consider the Higgs boson production at high energy hadron colliders in the framework of the k_T-factorization approach. The attention is focused on the dominant gluon-gluon fusion subprocess. We calculate the total cross section and transverse momentum distributions of the inclusive Higgs production using unintegrated gluon distributions in a proton obtained from the full CCFM evolution equation. We show that k_T-factorization gives a possibility to investigate the associated Higgs boson and jets production. We calculate the transverse momentum distributions and study the Higgs-jet and jet-jet azimuthal correlations in the Higgs + one or two jet production processes. We demonstrate the importance of the higher-order corrections within the k_T-factorization approach. These corrections should be developed and taken into account in the future applications.

A. V. Lipatov; N. P. Zotov

2005-01-18

166

Nuclear k_T in d+Au Collisions from Multiparticle Jet Reconstruction at STAR  

E-print Network

This paper presents the most recent nuclear k_T measurements from STAR derived from multiparticle jet reconstruction of d+Au and p+p collisions at sqrt(s)=200 GeV. Since jets reconstructed from multiple particles are relatively free of fragmentation biases, nuclear k_T can be measured with greater certainty in this way than with traditional di-hadron correlations. Multi-particle jet reconstruction can also be used for a direct measurement of the fragmentation function.

Thomas Henry

2005-11-01

167

High Temperature Structural Study of Gd-Doped Ceria by Synchrotron X-ray Diffraction (673 K ? T ? 1073 K).  

PubMed

The crystallographic features of Gd-doped ceria were investigated at the operating temperature of solid oxides fuel cells, where these materials are used as solid electrolytes. (Ce1-xGdx)O2-x/2 samples (x = 0.1, 0.3, 0.5, 0.7) were prepared by coprecipitation of mixed oxalates, treated at 1473 K in air, and analyzed by synchrotron X-ray diffraction in the temperature range 673 K ? T ? 1073 K at the Elettra synchrotron radiation facility located in Trieste, Italy. In the whole temperature span a boundary was found at x ? 0.2 between a CeO2-based solid solution (for x ? 0.2) and a structure where Gd2O3 microdomains grow within the CeO2 matrix, taking advantage of the similarity between Gd(3+) and Ce(4+) sizes; the existence of the boundary at x ? 0.2 was confirmed also by measurements of ionic conductivity performed by impedance spectroscopy. Similar to what observed at room temperature, the trend of the cell parameter shows the presence of a maximum; with increasing temperature, the composition corresponding to the maximum moves toward lower Gd content. This evidence can be explained by analyzing the behavior of the coefficient of thermal expansion as a function of composition. PMID:25192043

Artini, Cristina; Pani, Marcella; Lausi, Andrea; Masini, Roberto; Costa, Giorgio A

2014-10-01

168

Global Blackout Following the K/T Chicxulub Impact: Results of Impact and Atmospheric Modeling.  

National Technical Information Service (NTIS)

Several recent studies have suggested that shock decomposition of anhydrite (CaSO4) target rocks during the K/T Chicxulub impact would have ejected tremendous amounts of sulfur gas into the stratosphere. One of the many potential biospheric effects of thi...

K. O. Pope, A. C. Ocampo, K. H. Baines, B. A. Ivanov

1993-01-01

169

Restoration of $k_T$ factorization for low $p_T$ hadron hadroproduction  

E-print Network

We discuss the applicability of the $k_T$ factorization theorem to low-$p_T$ hadron production in hadron-hadron collision in a simple toy model, which involves only scalar particles and gluons. It has been shown that the $k_T$ factorization for high-$p_T$ hadron hadroproduction is broken by soft gluons in the Glauber region, which are exchanged among a transverse-momentum-dependent (TMD) parton density and other subprocesses of the collision. We explain that the contour of a loop momentum can be deformed away from the Glauber region at low $p_T$, so the above residual infrared divergence is factorized by means of the standard eikonal approximation. The $k_T$ factorization is then restored in the sense that a TMD parton density maintains its universality. Because the resultant Glauber factor is independent of hadron flavors, experimental constraints on its behavior are possible. The $k_T$ factorization can also be restored for the transverse single-spin asymmetry in hadron-hadron collision at low $p_T$ in a similar way, with the residual infrared divergence being factorized into the same Glauber factor.

Chun-peng Chang; Hsiang-nan Li

2009-04-27

170

Fatigue of aluminium-lithium alloys K. T. Venkateswara Rao and R. O. Ritchie  

E-print Network

Fatigue of aluminium-lithium alloys K. T. Venkateswara Rao and R. O. Ritchie Aluminium in commercial and military aircraft. In this review, the cyclic fatigue strength and fatigue crack propagation. Compared with traditional aerospace aluminium alloys, results on the fatigue of binary AI-Li, experimental

Ritchie, Robert

171

Methods of Emittance Measurement K.T. McDonald and D.P. Russell  

E-print Network

Methods of Emittance Measurement K.T. McDonald and D.P. Russell Joseph Henry Laboratories moments of a two-dimensional density in conjugate coordinates are combined to form the emittance, which remains invari- ant under idealized beam transport. Four different methods of emittance measurement

McDonald, Kirk

172

Cartesian SENSE and k-t SENSE reconstruction using commodity graphics hardware.  

PubMed

This study demonstrates that modern commodity graphics cards (GPUs) can be used to perform fast Cartesian SENSE and k-t SENSE reconstruction. Specifically, the SENSE inversion is accelerated by up to two orders of magnitude and is no longer the time-limiting step. The achieved reconstruction times are now well below the acquisition times, thus enabling real-time, interactive SENSE imaging, even with a large number of receive coils. The fast GPU reconstruction is also beneficial for datasets that are not acquired in real time. We demonstrate that it can be used for interactive adjustment of regularization parameters for k-t SENSE in the same way that one would adjust window and level settings. This enables a new way of performing imaging reconstruction, where the user chooses the setting of tunable reconstruction parameters, in real time, depending on the context in which the images are interpreted. PMID:18306398

Hansen, Michael S; Atkinson, David; Sorensen, Thomas S

2008-03-01

173

Shock-induced vaporization of anhydrite and global cooling from the K\\/T impact  

Microsoft Academic Search

Discovery of abundant anhydrite (CaSO4) and gypsum (CaSO4·2H2O) in the otherwise carbonate sediment comprising the upper 3 km thick layer of the target rock at the K\\/T impact site has prompted research on these minerals. Evaluation of the severity of the proposed extinction mechanism involving injection of impact-generated SO2 and SO3 into the stratosphere entails determination of criteria for shock-induced

Satish C. Gupta; Thomas J. Ahrens; Wenbo Yang

2001-01-01

174

Heavy quark production at HERA in k_t factorization supplemented with CCFM evolution  

E-print Network

The application of k_t - factorization, supplemented with the CCFM small-x evolution equation, to heavy quark production is discussed. Differential cross sections of b-b_bar production and also inelastic J/psi production as measured at HERA are compared to the hadron level CCFM Monte Carlo generator CASCADE, using the unintegrated gluon density obtained within the CCFM evolution approach from a fit to HERA F_2 data.

H. Jung

2001-10-26

175

Accelerated Phase-Contrast Cine MRI Using k-t SPARSE-SENSE  

PubMed Central

Phase-contrast (PC) cine MRI is a promising method for assessment of pathologic hemodynamics, including cardiovascular and hepatoportal vascular dynamics, but its low data acquisition efficiency limits the achievable spatial and temporal resolutions within clinically acceptable breath-hold durations. We propose to accelerate PC cine MRI using an approach which combines compressed sensing and parallel imaging (k-t SPARSE-SENSE). We validated the proposed 6-fold accelerated PC cine MRI against 3-fold accelerated PC cine MRI with parallel imaging (generalized autocalibrating partially parallel acquisitions). With the programmable flow pump, we simulated a time varying waveform emulating hepatic blood flow. Normalized root mean square error between two sets of velocity measurements was 2.59%. In multiple blood vessels of 12 control subjects, two sets of mean velocity measurements were in good agreement (mean difference = –0.29 cm/s; lower and upper 95% limits of agreement = –5.26 and 4.67 cm/s, respectively). The mean phase noise, defined as the standard deviation of the phase in a homogeneous stationary region, was significantly lower for k-t SPARSE-SENSE than for generalized autocalibrating partially parallel acquisitions (0.05 ± 0.01 vs. 0.19 ± 0.06 radians, respectively; P < 0.01). The proposed 6-fold accelerated PC cine MRI pulse sequence with k-t SPARSE-SENSE is a promising investigational method for rapid velocity measurement with relatively high spatial (1.7 mm × 1.7 mm) and temporal (~35 ms) resolutions. PMID:22083998

Kim, Daniel; Dyvorne, Hadrien A.; Otazo, Ricardo; Feng, Li; Sodickson, Daniel K.; Lee, Vivian S.

2012-01-01

176

Z and W production associated with quark-antiquark pair in k_T-factorization at the LHC  

E-print Network

We calculate and analyze Z and W production in association with quark-antiquark pair in k_T-factorization. Numerical calculations are performed using the Monte Carlo generator CASCADE for proton proton collisions at LHC energy. We compare total and differential cross sections calculated in k_T-factorization approach with total differential cross sections obtained in LO and NLO calculations in collinear factorization approach. We provide strong evidence that some of the effects of the NLO and even higher order collinear calculation are already included in the LO k_T-factorization calculation.

M. Deak; F. Schwennsen

2008-05-24

177

Heavy quark and quarkonium production at CERN LEP2: k_T-factorization versus data  

E-print Network

We present calculations of heavy quark and quarkonium production at CERN LEP2 in the k_T-factorization QCD approach. Both direct and resolved photon contribution are taken into account. The conservative error analisys is performed. The unintegrated gluon distribution in the photon is taken from the full CCFM evolution equation. The traditional color-singlet mechanism to describe non-perturbative transition of heavy quark pair into a final quarkonium is used. Our analisys covers polarization properties of heavy quarkonia at moderate and large transverse momenta. We find that the total and differential open charm production cross sections are consistent with the recent experimental data taken by the L3, OPAL and ALEPH collaborations. At the same time the DELPHI data for the inclusive J/Psi production exceed our predictions but experimental uncertainties are too large to claim a significant inconsistency. The bottom production in photon-photon collisions at CERN LEP2 is hard to explain within the k_T-factorization formalism.

A. V. Lipatov; N. P. Zotov

2004-12-19

178

Breakdown of kT-factorization and J/Psi production in dA collisions  

E-print Network

In spite of the sweeping coherence effects in high energy hadron and nuclei collisions, $k_T$-factorization can be recovered for the inclusive gluon production in $pA$ collisions at the leading logarithmic order. In open charm production at RHIC $k_T$-factorization holds numerically with about 10-20% accuracy. This allows to extrapolate the cold nuclear matter effect observed in light and charm meson production in $dA$ collisions to that in $AA$ ones. Unlike the open charm, the breakdown of factorization in $J/\\psi$ production is severe. Indeed, already at the lowest order in gluon density the main contribution to the inclusive cross section is proportional to the square of gluon density in the nucleus. As a consequence, one cannot infer the cold nuclear matter effect on $J/\\psi$ production in $AA$ collisions from that in $dA$. We present the calculation of $J/\\psi$ multiplicity in the framework of the CGC (color glass condensate)/saturation and show that it agrees with the experimental data.

Kirill Tuchin

2010-12-19

179

Diffractive production of vector mesons in Deep Inelastic Scattering within k_t-factorization approach  

E-print Network

In this work we give a theoretical description of the elastic vector meson production in diffractive DIS developed within the k_t-factorization formalism. Since the k_t-factorization scheme does not require large values of Q^2+m_V^2, we conduct an analysis that is applicable to all values of Q^2 from photo- up to highly virtual production of vector mesons. The basic quantity in this approach -- the unintegrated gluon structure function -- was for the first time extracted from the experimental data on F_{2p}, thoroughly investigated, and consistently used in the vector meson production calculation. Moreover, by limiting ourselves to the lowest Fock state of the vector meson, we were able to construct in a closed form the theory of spin-angular coupling in the vector meson. This allowed us for the first time to address the production of a vector meson in a given spin-angular state. We performed an extensive analytical and numerical investigation of the properties of 1S, 2S, and D-wave vector meson production reactions. Treating the physical ground state vector mesons as purely 1S states, we observed a good overall agreement with all available experimental data on vector meson production. For the excited states, our analysis predicts a picture which is remarkably different from 1S-state, so that such reactions can be regarded as potential sources of new information on the structure of excited states in vector mesons.

I. P. Ivanov

2003-03-06

180

Bl k t T h l F l C l dBlanket Technology, Fuel Cycle and Tritium Self Sufficiency  

E-print Network

Bl k t T h l F l C l dBlanket Technology, Fuel Cycle and Tritium Self Sufficiency M h d Abd and Technology Center (UCLA) President Council of Energy Research and Education Leaders CEREL (USA to date. Th bl k t i l t ith lti l f ti d lti l t i l· The blanket is a complex system, with multiple

Abdou, Mohamed

181

Modeling study of infrasonic detection of 1 kT atmospheric blast  

SciTech Connect

A modified version of the ``Pierce code``, which provides a theoretical prediction of acoustic-gravity pressure waveforms generated by explosions in the atmosphere, has been used to simulate detectable signal amplitudes from a 1 kT atmospheric detonation at high latitudes upton distances of about 1,000 kilometers from the source. Realistic prevailing winds and temperature profiles have been included in these simulations and propagation results for with wind and counter wind conditions are presented. En route, the code has been successfully ported from a CRAY/UNICOS platform to a more general UNIX/workstation environment in FORTRAN90. The effects of seasonal variations of winds and temperature at high latitudes will be presented at the symposium.

Dighe, K.A.; Whitaker, R.W.; Armstrong, W.T.

1998-12-31

182

Open charm production at the LHC - $k_{t}$-factorization approach  

E-print Network

We discuss inclusive production of open charm in proton-proton scattering at LHC. The calculation is performed within the $k_t$-factorization approach. Different models of unintegrated gluon distributions (UGDF) from the literature are used. The theoretical transverse momentum as well as (pseudo)rapidity distributions of charmed mesons are compared with recent experimental data of ATLAS, ALICE and LHCb collaborations. Only the calculation with Kimber-Martin-Ryskin (KMR) UGDF gives results comparable to experimental ones. All other popular models of UGDF significantly underpredict experimental data. Several sources of uncertainties of the theoretical predictions are also studied in details. In addition we discuss correlations between $D$ and $\\bar D$ mesons. Good description of experimental distribution in invariant mass and in relative azimuthal angle between $D$ and $\\bar D$ mesons is achieved for the KMR UGDF. The considered correlation observables measured by the LHCb experiment were not discussed in other approaches in the literature.

Rafal Maciula; Antoni Szczurek

2013-01-14

183

Prompt photon and associated heavy quark production at hadron colliders with k T -factorization  

NASA Astrophysics Data System (ADS)

In the framework of the k T -factorization approach, the production of prompt photons in association with a heavy (charm or beauty) quarks at high energies is studied. The consideration is based on the {O}( {? ?_s^2} ) off-shell amplitudes of gluon-gluon fusion and quark-(anti)quark interaction subprocesses. The unintegrated parton densities in a proton are determined using the Kimber-Martin-Ryskin prescription. The analysis covers the total and differential cross sections and extends to specific angular correlations between the produced prompt photons and muons originating from the semileptonic decays of associated heavy quarks. Theoretical uncertainties of our evaluations are studied and comparison with the results of standard NLO pQCD calculations is performed. Our numerical predictions are compared with the recent experimental data taken by the D? and CDF collaborations at the Tevatron. Finally, we extend our results to LHC energies.

Lipatov, A. V.; Malyshev, M. A.; Zotov, N. P.

2012-05-01

184

Acceleration of tissue phase mapping by k-t BLAST: a detailed analysis of the influence of k-t-BLAST for the quantification of myocardial motion at 3T  

PubMed Central

Background The assessment of myocardial motion with tissue phase mapping (TPM) provides high spatiotemporal resolution and quantitative motion information in three directions. Today, whole volume coverage of the heart by TPM encoding at high spatial and temporal resolution is limited by long data acquisition times. Therefore, a significant increase in imaging speed without deterioration of the quantitative motion information is required. For this purpose, the k-t BLAST acceleration technique was combined with TPM black-blood functional imaging of the heart. Different k-t factors were evaluated with respect to their impact on the quantitative assessment of cardiac motion. Results It is demonstrated that a k-t BLAST factor of two can be used with a marginal, but statistically significant deterioration of the quantitative motion data. Further increasing the k-t acceleration causes substantial alteration of the peak velocities and the motion pattern, but the temporal behavior of the contraction is well maintained up to an acceleration factor of six. Conclusions The application of k-t BLAST for the acceleration of TPM appears feasible. A reduction of the acquisition time of almost 45% could be achieved without substantial loss of quantitative motion information. PMID:21223566

2011-01-01

185

A neutron source to measure stellar neutron capture cross sections at kT=5 keV  

NASA Astrophysics Data System (ADS)

Since 1980 the 7Li(p,n)7Be reaction was intensively used for activation measurements. With a proton energy of E=1911 keV the resulting neutron spectrum resembles a Maxwell-Boltzmann distribution with a thermal energy of kT=25 keV. Therefore, this neutron source is ideal to determine Maxwellian-averaged neutron capture cross sections (MACS) close to a temperature of 250 million Kelvin (kT=23 keV) which is typical for the s process in red giant stars. Meanwhile, detailed stellar models indicate that the dominant neutron exposure of the main s-process component in low mass AGB stars occurs at a lower temperature of 90 million Kelvin (kT=8 keV). Hence, the necessary stellar reaction rates had to be extrapolated from 25 keV to the lower thermal energy. In order to avoid the corresponding additional uncertainties, we report on the 18O(p,n)18F neutron source, which allows one to produce a Maxwell-Boltzmann spectrum close to the lower thermal energy of kT=8 keV. First results of activation measurements for 138Ba(n,?)139Ba, 139La(n,?)140La, and 175Lu(n,?)176Lum will be presented.

Heil, M.; Dababneh, S.; Käppeler, F.; Plag, R.; Juseviciute, A.; Winckler, N.; Reifarth, R.; O'Brien, S.

2005-07-01

186

Robust Position Control of a Tilt-Wing Quadrotor C. Hancer, K. T. Oner, E. Sirimoglu, E. Cetinsoy, M. Unel  

E-print Network

Robust Position Control of a Tilt-Wing Quadrotor C. Hancer, K. T. Oner, E. Sirimoglu, E. Cetinsoy, M. Unel Abstract-- This paper presents a robust position controller for a tilt-wing quadrotor on 2D GPS data for quadrotor vehicles. Using the proposed algorithm, the vehicle is able to keep

Yanikoglu, Berrin

187

Kaon Electromagnetic Form Factor within the $k_T$ Factorization Formalism and It's Light-Cone Wave Function  

E-print Network

We present a systematical study on the kaon electromagnetic form factors $F_{K^{\\pm},K^0,\\bar{K}^0}(Q^2)$ within the $k_T$ factorization formalism, where the transverse momentum effects, the contributions from the different helicity components and different twist structures of the kaon light-cone (LC) wave function are carefully analyzed for giving a well understanding of the hard contributions at the energy region where pQCD is applicable. The right power behavior of the hard contribution from the higher helicity components and from the higher twist structures can be obtained by keeping the $k_T$ dependence in the hard amplitude. Our results show that the $k_T$ dependence in LC wave function affects the hard and soft contributions substantially and the power-suppressed terms (twist-3 and higher helicity components) make an important contribution below $Q^2\\sim several GeV^2$ although they drop fast as $Q^2$ increasing. The parameters of the proposed model wave function can be fixed by the first two moments of its distribution amplitude and other conditions. By varying the first two moments $a^K_1(1GeV)$ and $a^K_2(1GeV)$ with the region of $0.05\\pm0.02$ and $0.10\\pm 0.05$ respectively, we find that the uncertainty of the kaon electromagnetic form factor is rather small.

Xing-Gang Wu; Tao Huang

2008-03-29

188

A framework for generalized reference image reconstruction methods including HYPR-LR, PR-FOCUSS, and k-t FOCUSS  

PubMed Central

Purpose To investigate the relationships among HYPR-LR, PR-FOCUSS, and k-t FOCUSS by showing how each method relates to a generalized reference image reconstruction method. That is, the generalized series model employs a fixed reference image and multiplicative corrections - that model is extended here to consider reference images more broadly, both in image space and in transform spaces (x-t and x-f spaces), and that can evolve with iteration. Materials and Methods Theoretical relationships between the methods are derived. Computer simulations are done to compare HYPR-LR to one iteration of PR-FOCUSS. The generalized reference approaches applied in the x-t or x-f domain are compared using computer simulation, five cardiac cine imaging datasets and six myocardial perfusion datasets. Results PR-FOCUSS and HYPR-LR gave comparable errors, with PR-FOCUSS slightly outperforming HYPR-LR. The baseline image is important to the performance of k-t FOCUSS and x-t FOCUSS as demonstrated by results from cardiac cine imaging. For cardiac perfusion reconstructions with the use of a temporal average image as the baseline image, k-t FOCUSS gave lower errors than x-t FOCUSS. Conclusion HYPR-LR and PR-FOCUSS are closely related: both work for radial sampling and use reference images in the x-t domain; HYPR-LR is an approximate implementation of the generalized reference framework, while PR-FOCUSS is a conjugate gradient implementation of the generalized reference framework. The superiority of generalized reference approaches applied in the x-t or x-f domain was sensitive to the characteristics of the acquired data and to the baseline image used. PMID:21780232

Chen, Liyong; Samsonov, Alexey; DiBella, Edward V.R.

2011-01-01

189

Discovery and focused study of the Chicxulub impact crater  

NASA Astrophysics Data System (ADS)

Three decades ago, a landmark paper by Alvarez et al. [1980] proposed that an asteroid impact 65.5 million years ago was the cause of the mass extinction of about 75% of species, including the dinosaurs, at the boundary between the Cretaceous and Paleogene periods (K-Pg), formerly known as the Cretaceous-Tertiary (K-T) boundary. Alvarez et al. used geochemical studies on carbonate sequences from Italy, Denmark, and New Zealand to study the boundary layer, which was enriched in iridium and other platinum group elements (PGEs) at concentrations well above background levels. They associated these enrichments with the collision of an asteroid that injected large amounts of pulverized debris into the atmosphere, resulting in blockage of solar radiation, global cooling, and a shutdown of photosynthesis.

Urrutia-Fucugauchi, Jaime; Camargo-Zanoguera, Antonio; Pérez-Cruz, Ligia

2011-06-01

190

Color-singlet direct J/?and ?' production at Tevatron in the k_t factorization approach  

E-print Network

Direct $J/\\psi$ and $\\psi'$ production rates at Tevatron are calculated in the $k_t$-factorization approach within the color-singlet model. In this approach, the production rates are enhanced by a factor of 20 compared to the naive collinear parton model. However, the theoretical predictions are still below the experimental data by at least one order of magnitude. This means that to explain charmonium productions at Tevatron, we still need to call for the contributions from color-octet channels or other production mechanisms.

F. Yuan; K. T. Chao

2000-08-29

191

Measurement of k T splitting scales in W? ?? events at ?{s} = 7 TeV with the ATLAS detector  

NASA Astrophysics Data System (ADS)

A measurement of splitting scales, as defined by the k T clustering algorithm, is presented for final states containing a W boson produced in proton-proton collisions at a centre-of-mass energy of 7 TeV. The measurement is based on the full 2010 data sample corresponding to an integrated luminosity of 36 pb-1 which was collected using the ATLAS detector at the CERN Large Hadron Collider. Cluster splitting scales are measured in events containing W bosons decaying to electrons or muons. The measurement comprises the four hardest splitting scales in a k T cluster sequence of the hadronic activity accompanying the W boson, and ratios of these splitting scales. Backgrounds such as multi-jet and top-quark-pair production are subtracted and the results are corrected for detector effects. Predictions from various Monte Carlo event generators at particle level are compared to the data. Overall, reasonable agreement is found with all generators, but larger deviations between the predictions and the data are evident in the soft regions of the splitting scales.

Aad, G.; Abajyan, T.; Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdelalim, A. A.; Abdinov, O.; Aben, R.; Abi, B.; Abolins, M.; AbouZeid, O. S.; Abramowicz, H.; Abreu, H.; Acharya, B. S.; Adamczyk, L.; Adams, D. L.; Addy, T. N.; Adelman, J.; Adomeit, S.; Adragna, P.; Adye, T.; Aefsky, S.; Aguilar-Saavedra, J. A.; Agustoni, M.; Ahlen, S. P.; Ahles, F.; Ahmad, A.; Ahsan, M.; Aielli, G.; Åkesson, T. P. A.; Akimoto, G.; Akimov, A. V.; Alam, M. A.; Albert, J.; Albrand, S.; Aleksa, M.; Aleksandrov, I. N.; Alessandria, F.; Alexa, C.; Alexander, G.; Alexandre, G.; Alexopoulos, T.; Alhroob, M.; Aliev, M.; Alimonti, G.; Alison, J.; Allbrooke, B. M. M.; Allison, L. J.; Allport, P. P.; Allwood-Spiers, S. E.; Almond, J.; Aloisio, A.; Alon, R.; Alonso, A.; Alonso, F.; Altheimer, A.; Alvarez Gonzalez, B.; Alviggi, M. G.; Amako, K.; Amelung, C.; Ammosov, V. V.; Amor Dos Santos, S. P.; Amorim, A.; Amoroso, S.; Amram, N.; Anastopoulos, C.; Ancu, L. S.; Andari, N.; Andeen, T.; Anders, C. F.; Anders, G.; Anderson, K. J.; Andreazza, A.; Andrei, V.; Anduaga, X. S.; Angelidakis, S.; Anger, P.; Angerami, A.; Anghinolfi, F.; Anisenkov, A.; Anjos, N.; Annovi, A.; Antonaki, A.; Antonelli, M.; Antonov, A.; Antos, J.; Anulli, F.; Aoki, M.; Aperio Bella, L.; Apolle, R.; Arabidze, G.; Aracena, I.; Arai, Y.; Arce, A. T. H.; Arfaoui, S.; Arguin, J.-F.; Argyropoulos, S.; Arik, E.; Arik, M.; Armbruster, A. J.; Arnaez, O.; Arnal, V.; Artamonov, A.; Artoni, G.; Arutinov, D.; Asai, S.; Ask, S.; Åsman, B.; Asquith, L.; Assamagan, K.; Astalos, R.; Astbury, A.; Atkinson, M.; Auerbach, B.; Auge, E.; Augsten, K.; Aurousseau, M.; Avolio, G.; Axen, D.; Azuelos, G.; Azuma, Y.; Baak, M. A.; Baccaglioni, G.; Bacci, C.; Bach, A. M.; Bachacou, H.; Bachas, K.; Backes, M.; Backhaus, M.; Backus Mayes, J.; Badescu, E.; Bagnaia, P.; Bai, Y.; Bailey, D. C.; Bain, T.; Baines, J. T.; Baker, O. K.; Baker, S.; Balek, P.; Balli, F.; Banas, E.; Banerjee, P.; Banerjee, Sw.; Banfi, D.; Bangert, A.; Bansal, V.; Bansil, H. S.; Barak, L.; Baranov, S. P.; Barber, T.; Barberio, E. L.; Barberis, D.; Barbero, M.; Bardin, D. Y.; Barillari, T.; Barisonzi, M.; Barklow, T.; Barlow, N.; Barnett, B. M.; Barnett, R. M.; Baroncelli, A.; Barone, G.; Barr, A. J.; Barreiro, F.; Barreiro Guimarães da Costa, J.; Bartoldus, R.; Barton, A. E.; Bartsch, V.; Basye, A.; Bates, R. L.; Batkova, L.; Batley, J. R.; Battaglia, A.; Battistin, M.; Bauer, F.; Bawa, H. S.; Beale, S.; Beau, T.; Beauchemin, P. H.; Beccherle, R.; Bechtle, P.; Beck, H. P.; Becker, K.; Becker, S.; Beckingham, M.; Becks, K. H.; Beddall, A. J.; Beddall, A.; Bedikian, S.; Bednyakov, V. A.; Bee, C. P.; Beemster, L. J.; Beermann, T. A.; Begel, M.; Behar Harpaz, S.; Belanger-Champagne, C.; Bell, P. J.; Bell, W. H.; Bella, G.; Bellagamba, L.; Bellomo, M.; Belloni, A.; Beloborodova, O.; Belotskiy, K.; Beltramello, O.; Benary, O.; Benchekroun, D.; Bendtz, K.; Benekos, N.; Benhammou, Y.; Benhar Noccioli, E.; Benitez Garcia, J. A.; Benjamin, D. P.; Benoit, M.; Bensinger, J. R.; Benslama, K.; Bentvelsen, S.; Berge, D.; Bergeaas Kuutmann, E.; Berger, N.; Berghaus, F.; Berglund, E.; Beringer, J.; Bernat, P.; Bernhard, R.; Bernius, C.; Bernlochner, F. U.; Berry, T.; Bertella, C.; Bertin, A.; Bertolucci, F.; Besana, M. I.; Besjes, G. J.; Besson, N.; Bethke, S.; Bhimji, W.; Bianchi, R. M.; Bianchini, L.; Bianco, M.; Biebel, O.; Bieniek, S. P.; Bierwagen, K.; Biesiada, J.; Biglietti, M.; Bilokon, H.; Bindi, M.; Binet, S.; Bingul, A.; Bini, C.; Biscarat, C.; Bittner, B.; Black, C. W.; Black, J. E.; Black, K. M.; Blair, R. E.; Blanchard, J.-B.; Blazek, T.; Bloch, I.; Blocker, C.; Blocki, J.; Blum, W.; Blumenschein, U.; Bobbink, G. J.; Bobrovnikov, V. S.; Bocchetta, S. S.; Bocci, A.; Boddy, C. R.; Boehler, M.; Boek, J.; Boek, T. T.; Boelaert, N.; Bogaerts, J. A.; Bogdanchikov, A.; Bogouch, A.; Bohm, C.; Bohm, J.; Boisvert, V.; Bold, T.; Boldea, V.; Bolnet, N. M.; Bomben, M.; Bona, M.; Boonekamp, M.; Bordoni, S.; Borer, C.; Borisov, A.; Borissov, G.; Borjanovic, I.; Borri, M.; Borroni, S.; Bortfeldt, J.; Bortolotto, V.; Bos, K.; Boscherini, D.; Bosman, M.; Boterenbrood, H.; Bouchami, J.; Boudreau, J.; Bouhova-Thacker, E. V.; Boumediene, D.; Bourdarios, C.; Bousson, N.; Boutouil, S.; Boveia, A.; Boyd, J.; Boyko, I. R.; Bozovic-Jelisavcic, I.; Bracinik, J.; Branchini, P.; Brandt, A.; Brandt, G.; Brandt, O.; Bratzler, U.; Brau, B.; Brau, J. E.; Braun, H. M.; Brazzale, S. F.; Brelier, B.; Bremer, J.; Brendlinger, K.; Brenner, R.; Bressler, S.; Bristow, T. M.; Britton, D.; Brochu, F. M.; Brock, I.; Brock, R.; Broggi, F.; Bromberg, C.; Bronner, J.; Brooijmans, G.; Brooks, T.; Brooks, W. K.; Brown, G.; Bruckman de Renstrom, P. A.; Bruncko, D.; Bruneliere, R.; Brunet, S.; Bruni, A.; Bruni, G.; Bruschi, M.; Bryngemark, L.; Buanes, T.

2013-05-01

192

On the undersampling strategies to accelerate time-resolved 3D imaging using k-t-GRAPPA.  

PubMed

The purpose of this study was to explore how to optimally undersample and reconstruct time-resolved 3D data using a k-t-space-based GRAPPA technique. The performance of different reconstruction strategies was evaluated using data sets with different ratios of phase (N(y)) and partition (N(z)) encoding lines (N(y) × N(z) = 64-128 × 40-64) acquired in a moving phantom. Image reconstruction was performed for different kernel configurations and different reduction factors (R = 5, 6, 8, and 10) and was evaluated using regional error quantification and SNR analysis. To analyze the temporal fidelity of the different kernel configurations in vivo, time-resolved 3D phase contrast data were acquired in the thoracic aorta of two healthy volunteers. Results demonstrated that kernel configurations with a small kernel extension yielded superior results especially for more asymmetric data matrices as typically used in clinical applications. The application of k-t-GRAPPA to in vivo data demonstrated the feasibility of undersampling of time-resolved 3D phase contrast data set with a nominal reduction factors of up to R(net) = 8, while maintaining the temporal fidelity of the measured velocity field. Extended GRAPPA-based parallel imaging with optimized multidimensional reconstruction kernels has the potential to substantially accelerate data acquisitions in time-resolved 3D MRI. PMID:21437975

Jung, Bernd; Stalder, Aurélien F; Bauer, Simon; Markl, Michael

2011-10-01

193

Cretaceous–Tertiary convergence and continental collision, Sanandaj–Sirjan Zone, western Iran  

Microsoft Academic Search

The Sanandaj–Sirjan Zone contains the metamorphic core of the Zagros continental collision zone in western Iran. The zone has been subdivided into the following from southwest to northeast: an outer belt of imbricate thrust slices (radiolarite, Bisotun, ophiolite and marginal sub-zones, which consist of Mesozoic deep-marine sediments, shallow-marine carbonates, oceanic crust and volcanic arc, respectively) and an inner complexly deformed

M. Mohajjel; C. L Fergusson; M. R Sahandi

2003-01-01

194

The Cretaceous-Tertiary sea floor off Dronning Maud Land, Antarctica  

NASA Astrophysics Data System (ADS)

A study of the bathymetric and linear magnetic anomalies between Dronning Maud Land, Antarctica and the South West Indian Ridge (SWIR) revealed a Mesozoic sequence of linear magnetic anomalies, M0 to M12 (108-126 Ma), a fracture zone offset (˜- 130 km), and the Cretaceous magnetic quiet zone between isochrons M0 (108 Ma) and 34 (80 Ma). The study sheds light on: (1) the evolution of an anomalous "stretched" pattern of seafloor anomalies during magnetic isochrons M0 and 34, and the associated offset (> 10°) in some segments of the northeastern part of the SWIR; (2) continuation of a proposed buried fracture zone to the south, where it abuts the Astrid Ridge off Dronning Maud Land. The history of spreading is related to declining dynamic pressures at the plate margin due to the Kergeulen-Heard mantle plume during Cretaceous time (˜-110 Ma).

Rao, D. Gopala; Chaubey, A. K.; Ramprasad, T.

1992-05-01

195

Hydrogeologic characterization of the cretaceous-tertiary Coastal Plain sequence at the Savannah River Site  

SciTech Connect

Several hydrostratigraphic classification schemes have been devised to describe the hydrogeology at the Savannah River Site SRS. Central to these schemes is the one-to-one fixed relationship between the hydrostratigraphic units and the lithostratigraphic units currently favored for the Site. This fixed relationship has proven difficult to apply in studies of widely separated locations at the Site due to the various facies observed in the updip Coastal Plain sequence. A detailed analysis and synthesis of the geophysical, core, and hydrologic data available from more than 164 deep wells from 23 cluster locations both on the Site and in the surrounding region was conducted to provide the basis for a hydrostratigraphic classification scheme which could be applied to the entire SRS region. As a result, an interim hydrostratigraphic classification was developed that defines the regional hydrogeologic characteristics of the aquifers underlying the Site (Aadland et al., 1990). The hydrostratigraphic code accounts for and accommodates the rapid lateral variation in lithofacies observed in the region, and eliminates all formal'' connection between the hydrostratigraphic nomenclature and the lithostratigraphic nomenclature. The code is robust and can be made as detailed as is needed to characterize the aquifer units and aquifer zones described in Site-specific studies. 15 refs., 2 figs.

Aadland, R.K.

1990-01-01

196

Early Cretaceous &Tertiary metamorphic events of the Pelagonian Zone in the E. Thessaly area, Greece  

Microsoft Academic Search

The area occupied by what is known as the Pelagonian Zone is composed of several tectonic units showing different Alpine tectonometamorphic evolution. The lowermost unit is exposed as tectonic window in the Olympos and Ossa area and has been affected by a low grade metamorphism of post-Eocene age. Two main tectonometamorphic units are exposed as nappes over the Olympos window:

M. Perraki; G. Hoinkes; E. Mposkos; M. Thoeni

2003-01-01

197

The interaction of the cretaceous-tertiary extinction bolide with the atmosphere, ocean, and solid earth  

NASA Technical Reports Server (NTRS)

A number of investigations, including those reported by Orth et al. (1981), have provided physical evidence for the impact of an extraterrestrial object on earth 65 million years ago. This time corresponds to the end of the cretaceous period. This impact could, therefore, be responsible for the observed extinction of biological species at the end of the Mesozoic era. Among the species becoming extinct are found also flying and walking dinosaurs, which include all land animals that had masses greater than 25 kg. The present investigation is concerned with a study of the possibilities for the collision of earth with 10 km-size object, and the consequences produced by such a collision. It is found that the penetration of the atmosphere by the bolide creates a temporary hole in the atmosphere. The resulting flow fields can inject melt droplets and finely commuted solid particles into the atmosphere. Short-term effects of heating, followed by dust induced worldwide cooling, may provide several mechanisms for the observed extinction of the species.

Okeefe, J. D.; Ahrens, T. J.

1981-01-01

198

Borehole gravity surveys in the Cretaceous-Tertiary Sagavanirktok Formation, Kuparuk River oil field, Alaska  

SciTech Connect

Detailed borehole gravity surveys (sponsored by the US Department of Energy) were made in three wells in the Kuparuk River and westernmost Prudhoe Bay oil fields, Alaska from depths as shallow as 15 m to as great as 1,340 m through permafrost and underlying heavy oil bearing sandstones of the Sagavanirktok Formation. A subbituminous coal-bearing sequence and the stability field for methane hydrate occur partly within and partly below the permafrost zone, whose base, defined by the 0{degree}C isotherm, varies from 464 to 564 m. The surveys provided accurate, large-volume estimates of in-situ bulk density from which equivalent porosity was calculated using independent grain and pore-fluid density information. This density and porosity data helped to define the rock mass properties within the hydrate stability field and the thermal conductivity, seismic character, and compaction history of the permafrost. Bulk density of the unconsolidated to poorly consolidated sections ranges mostly from 1.9 to 2.3 g/cm{sup 3}. The shallow permafrost section appears to be slightly overcompacted in comparison to similar sedimentary sequences in nonpermafrost regions. The cause of this apparent overcompaction is unknown but may be due to freeze-thaw processes that have similarly affected sea floor and surficial deposits elsewhere in the Arctic. Fluctuations of bulk density appear to be controlled principally by (1) textural variations of the sediments, possibly exaggerated locally within the permafrost zone by excess ice, (2) presence or absence of carbonaceous material, and (3) type of pore-fluid (water-ice vs. water vs. hydrocarbons). As hypothetical models predict bulk-density is slightly lower opposite one interval of possible methane hydrate. Porosity may be as high as 40-45% for selected coarser grained units within the permafrost zone, and as high as 30-35% in a series of well sorted, heavy oil-bearing sandstones.

Beyer, L.A. (Geological Survey, Menlo Park, CA (USA))

1990-05-01

199

Bio-events in the continental realm during the Cretaceous/Tertiary transition: a multidisciplinary approach  

NASA Astrophysics Data System (ADS)

This study is a short progress report of a multidisciplinary cooperation. It deals with animal and plant biotas found in five nonmarine Maastrichtian-Paleocene sequences in southern Europe (southern France, north-east Spain). In addition, contributions on North America charophyte floras are taken into account.

Feist, Monique

200

Petroleum geology of Cretaceous-Tertiary rift basins in Niger, Chad, and Central African Republic  

SciTech Connect

This overview of the petroleum geology of rift basins in Niger, Chad, and Central African Republic (CAR) is based on exploration work by Exxon and partners in the years 1969-1991. The work included 50,000 km of modern reflection seismic, 53 exploration wells, 1,000,000 km[sup 2] of aeromagnetic coverage, and about 10,500 km of gravity profiles. The results outline ten Cretaceous and Tertiary rift basins, which constitute a major part of the West and Central African rift system (WCARS). The rift basins derive from a multiphased geologic history dating from the Pan-African (approximately 750-550 Ma) to the Holocene. WCARS in the study area is divided into the West African rift subsystem (WAS) and the Central African rift subsystem (WAS) and the Central African rift subsystem (CAS). WAS basins in Niger and Chad are chiefly extensional, and are filled by up to 13,000 m of Lower Cretaceous to Holocene continental and marine clastics. The basins contain five oil (19-43[degrees]API) and two oil and gas accumulations in Upper Cretaceous and Eocene sandstone reservoirs. The hydrocarbons are sourced and sealed by Upper Cretaceous and Eocene marine and lacustrine shales. The most common structural styles and hydrocarbon traps usually are associated with normal fault blocks. CAS rift basins in Chad and CAR are extensional and transtensional, and are filled by up to 7500 m of chiefly Lower Cretaceous continental clastics. The basins contain eight oil (15-39[degrees]API) and one oil and gas discovery in Lower and Upper Cretaceous sandstone reservoirs. The hydrocarbons are sourced by Lower Cretaceous shales and sealed by interbedded lacustrine and flood-plain shales. Structural styles range from simple fault blocks through complex flower structures. The main hydrocarbon traps are in contractional anticlines. Geological conditions favor the discovery of potentially commercial volumes of oil in WCARS basins, of Niger, Chad and CAR. 108 refs., 24 figs., 4 tabs.

Genik, G.J. (Exxon Exploration Co., Houston, TX (United States))

1993-08-01

201

k_T factorization is violated in production of high-transverse-momentum particles in hadron-hadron collisions  

E-print Network

We show that hard-scattering factorization is violated in the production of high-p_T hadrons in hadron-hadron collisions, in the case that the hadrons are back-to-back, so that k_T factorization is to be used. The explicit counterexample that we construct is for the single-spin asymmetry with one beam transversely polarized. The Sivers function needed here has particular sensitivity to the Wilson lines in the parton densities. We use a greatly simplified model theory to make the breakdown of factorization easy to check explicitly. But the counterexample implies that standard arguments for factorization fail not just for the single-spin asymmetry but for the unpolarized cross section for back-to-back hadron production in QCD in hadron-hadron collisions. This is unlike corresponding cases in e^+e^- annihilation, Drell-Yan, and deeply inelastic scattering. Moreover, the result endangers factorization for more general hadroproduction processes.

John Collins; Jian-Wei Qiu

2007-05-15

202

Boundary Crossing and Boundary Objects  

ERIC Educational Resources Information Center

Diversity and mobility in education and work present a paramount challenge that needs better conceptualization in educational theory. This challenge has been addressed by educational scholars with the notion of "boundaries", particularly by the concepts of "boundary crossing" and "boundary objects". Although studies on boundary crossing and…

Akkerman, Sanne F.; Bakker, Arthur

2011-01-01

203

Blast From the Past  

NSDL National Science Digital Library

A recently recovered deep-sea core supports theories that an asteroid collided with the earth 65 million years ago, around the time of the extinction of the dinosaurs. The Smithsonian Institution National Museum of Natural History's new site, Blast from the Past, contains details on this cataclysmic event. Colorful graphics provide conceptual illustrations of the asteroid impact and aftermath, accompanied by photographs of the deep-sea core. Text summaries, followed by bibliographic references, describe the asteroid hypothesis, the Cretaceous/Tertiary (K/T) boundary, and the utility of deep-sea cores. With links to other paleobiological sites and related museum exhibits, this site is a useful resource for those wanting to know more about fateful asteroid impacts.

204

Nozzle R&D for a 20-m/s, 1-cm-diameter Mercury Jet K.T. McDonald  

E-print Network

and the Influence of Nozzle Design, Chem. Eng. J. 7, 1 (1974), http://puhep1.princeton). However, advice on nozzle design is not very definitive. It seems good precede the nozzle by a largerNozzle R&D for a 20-m/s, 1-cm-diameter Mercury Jet K.T. McDonald Princeton U. MERIT Collider

McDonald, Kirk

205

Design and construction of a novel quad tilt-wing UAV E. Cetinsoy, S. Dikyar, C. Hancer, K.T. Oner, E. Sirimoglu, M. Unel  

E-print Network

Design and construction of a novel quad tilt-wing UAV E. Cetinsoy, S. Dikyar, C. Hancer, K.T. Oner 12 March 2012 Available online xxxx Keywords: UAV Quad tilt-wing Aerodynamic design Carbon composite VehIcle). SUAVI is an electric powered quad tilt-wing UAV that is capable of vertical takeoff

Ã?Â?nel, Mustafa

206

Interface mechanics of adhesiveless microtransfer printing processes H.-J. Kim-Lee, A. Carlson, D. S. Grierson, J. A. Rogers, and K. T. Turner  

E-print Network

electronics, advanced packaging schemes, and complex 3D microstructures that cannot be realizedInterface mechanics of adhesiveless microtransfer printing processes H.-J. Kim-Lee, A. Carlson, D microtransfer printing processes H.-J. Kim-Lee,1,a) A. Carlson,2 D. S. Grierson,1,b) J. A. Rogers,2 and K. T

Rogers, John A.

207

What's news about the Deccan traps emplacement ? An attempt to estimate the eruptive sequence of lava emplacement  

Microsoft Academic Search

Synchronism between Large Igneous Provinces formations and mass extinctions along the Phanerozoic is clearly evidenced and suggests that LIPs could be deeply involved in such environmental crisis. As example, the Cretaceous-Tertiary (K-T) mass extinction coincides with the emplacement of the Deccan continental flood basalts. However the climatic and environmental impact of the traps emplacement is not well known. One reason

A. Chenet; V. Courtillot; F. Fluteau; J. Besse; K. Subbarao; S. Khadri

2005-01-01

208

Measurement of the MACS of Ta181(n,?) at kT=30 keV as a test of a method for Maxwellian neutron spectra generation  

NASA Astrophysics Data System (ADS)

Measurement of the Maxwellian-Averaged Cross-Section (MACS) of the Ta(n,?)181 reaction at kT=30 keV by the activation technique using an innovative method for the generation of Maxwellian neutron spectra is presented. The method is based on the shaping of the proton beam to produce a desired neutron spectrum using the 7Li(p,n) reaction as a neutron source. The characterization of neutron spectra has been performed by combining measured proton distributions, an analytical description of the differential neutron yield in angle and energy of the 7Li(p,n) reaction, and with Monte Carlo simulations of the neutron transport. A measured value equal to 815±73 mbarn is reported for the MACS of the reaction Ta(n,?)181 at kT=30 keV. The MACS of the reaction Au(n,?)197 provided by KADoNiS has been used as a reference.

Praena, J.; Mastinu, P. F.; Pignatari, M.; Quesada, J. M.; García-López, J.; Lozano, M.; Dzysiuk, N.; Capote, R.; Martín-Hernández, G.

2013-11-01

209

Nozzle R&D for a 20-m/s, 1-cm-diameter Mercury Jet K.T. McDonald  

E-print Network

Title 1 Design Review 7-8 Feb 05 Cavitation is highly likely because of the low pressure at the nozzleNozzle R&D for a 20-m/s, 1-cm-diameter Mercury Jet K.T. McDonald Princeton U. Neutrino Factory. McDonald Muon Collaboration Meeting, Berkeley, Feb. 16, 2005 1 #12;The Best Nozzle is No Nozzle

McDonald, Kirk

210

(slope) and comparable absolute values for 30 K # T # 290 K and 0.5 T # H # 55 T (Fig. 3, inset). The quantum oscillations at low T  

E-print Network

its melting point for 24 h, and left to cool in a horizontal position. Regularly shaped sensors(slope) and comparable absolute values for 30 K # T # 290 K and 0.5 T # H # 55 T (Fig. 3, inset/r0 versus rxy /r0 rather than H/nr0. Nonetheless, b(T) rises steadily as rxx(T) falls, pointing

Breedveld, Victor

211

Iridium abundance measurements across bio-event horizons in the geological record  

NASA Technical Reports Server (NTRS)

Geochemical studies have been performed on thousands of rock samples collected across bio-event horizons in the fossil record using INAA for about 40 common and trace elements and radiochemical isolation procedures for Os, Ir, Pt, and Au on selected samples. These studies were begun soon after the Alvarez team announced their discovery of the Cretaceous-Tertiary (K-T) Ir anomaly in marine rock sequences in Europe. With their encouragement the Authors searched for the anomaly in nearby continental (freshwater coal swamp) deposits. In collaboration with scientists from the U.S.G.S. in Denver, the anomaly was located and it was observed that a floral crisis occurred at the same stratigraphic position as the Ir spike. Further work in the Raton Basin has turned up numerous well-preserved K-T boundary sections. Although the Authors have continued to study the K-T boundary and provide geochemical measurements for other groups trying to precisely locate it, the primary effort was turned to examining the other bio-events in the Phanerozoic, especially to those that are older than the terminal Cretaceous. A list of horizons that were examined in collaboration with paleontologists and geologists is given. Results are also given and discussed.

Orth, C. J.; Attrep, M., Jr.

1988-01-01

212

Complete mitochondrial DNA genome sequences show that modern birds are not descended from transitional shorebirds.  

PubMed Central

To test the hypothesis put forward by Feduccia of the origin of modern birds from transitional birds, we sequenced the first two complete mitochondrial genomes of shorebirds (ruddy turnstone and blackish oystercatcher) and compared their sequences with those of already published avian genomes. When corrected for rate heterogeneity across sites and non-homogeneous nucleotide compositions among lineages in maximum likelihood (ML), the optimal tree places palaeognath birds as sister to the neognaths including shorebirds. This optimal topology is a re-rooting of recently published ordinal-level avian trees derived from mitochondrial sequences. Using a penalized likelihood (PL) rate-smoothing process in conjunction with dates estimated from fossils, we show that the basal splits in the bird tree are much older than the Cretaceous-Tertiary (K-T) boundary, reinforcing previous molecular studies that rejected the derivation of modern birds from transitional shorebirds. Our mean estimate for the origin of modern birds at about 123 million years ago (Myr ago) is quite close to recent estimates using both nuclear and mitochondrial genes, and supports theories of continental break-up as a driving force in avian diversification. Not only did many modern orders of birds originate well before the K-T boundary, but the radiation of major clades occurred over an extended period of at least 40 Myr ago, thus also falsifying Feduccia's rapid radiation scenario following a K-T bottleneck. PMID:11958716

Paton, Tara; Haddrath, Oliver; Baker, Allan J

2002-01-01

213

Fingerprinting the K/T impact site and determining the time of impact by UPb dating of single shocked zircons from distal ejecta  

USGS Publications Warehouse

UPb isotopic dating of single 1-3 ??g zircons from K/T distal ejecta from a site in the Raton Basin, Colorado provides a powerful new tool with which to determine both the time of the impact event and the age of the basement at the impact site. Data for the least shocked zircons are slightly displaced from the 544 ?? 5 Ma primary age for a component of the target site, white those for highly shocked and granular grains are strongly displaced towards the time of impact at 65.5 ?? 3.0 Ma. Such shocked and granular zircons have never been reported from any source, including explosive volcanic rocks. Zircon is refractory and has one of the highest thermal blocking temperatures; hence, it can record both shock features and primary and secondary ages without modification by post-crystallization processes. Unlike shocked quartz, which can come from almost anywhere on the Earth's crust, shocked zircons can be shown to come from a specific site because basement ages vary on the scale of meters to kilometers. With UPb zircon dating, it is now possible to correlate ejecta layers derived from the same target site, test the single versus multiple impact hypothesis, and identify the target source of impact ejecta. The ages obtained in this study indicate that the Manson impact site, Iowa, which has basement rocks that are mid-Proterozoic in age, cannot be the source of K/T distal ejecta. The K/T distal ejecta probably originated from a single impact site because most grains have the same primary age. ?? 1993.

Krogh, T.E.; Kamo, S.L.; Bohor, B.F.

1993-01-01

214

Rapidity and kT dependence of HBT correlations in Au+Au collisions at 200 GeV with PHOBOS  

NASA Astrophysics Data System (ADS)

Two-particle correlations of identical charged pion pairs from Au+Au collisions at \\sqrt{s_{\\rm NN}} = 200 GeV were measured by the PHOBOS experiment at RHIC. Data for the most central (0 15%) events were analysed with Bertsch Pratt (BP) and Yano Koonin Podgoretskii (YKP) parametrizations using pairs with rapidities of 0.4 < y < 1.3 and transverse momenta 0.1 < kT < 1.4 GeV/c. The Bertsch Pratt radii decrease as a function of pair transverse momentum. The pair rapidity Ypgrpgr roughly scales with the source rapidity YYKP, indicating strong dynamical correlations.

Holzman, Burt; PHOBOS Collaboration; Back, B. B.; Baker, M. D.; Ballintijn, M.; Barton, D. S.; Betts, R. R.; Bickley, A. A.; Bindel, R.; Budzanowski, A.; Busza, W.; Carroll, A.; Decowski, M. P.; García, E.; George, N.; Gulbrandsen, K.; Gushue, S.; Halliwell, C.; Hamblen, J.; Heintzelman, G. A.; Henderson, C.; Hofman, D. J.; Hollis, R. S.; Holynski, R.; Holzman, B.; Iordanova, A.; Johnson, E.; Kane, J. L.; Katzy, J.; Khan, N.; Kucewicz, W.; Kulinich, P.; Kuo, C. M.; Lin, W. T.; Manly, S.; McLeod, D.; Mignerey, A. C.; Nouicer, R.; Olszewski, A.; Pak, R.; Park, I. C.; Pernegger, H.; Reed, C.; Remsberg, L. P.; Reuter, M.; Roland, C.; Roland, G.; Rosenberg, L.; Sagerer, J.; Sarin, P.; Sawicki, P.; Skulski, W.; Steinberg, P.; Stephans, G. S. F.; Sukhanov, A.; Tang, J.-L.; Tonjes, M. B.; Trzupek, A.; Vale, C.; van Nieuwenhuizen, G. J.; Verdier, R.; Wolfs, F. L. H.; Wosiek, B.; Wozniak, K.; Wuosmaa, A. H.; Wyslouch, B.

2004-08-01

215

Boundary inflation  

SciTech Connect

Inflationary solutions are constructed in a specific five-dimensional model with boundaries motivated by heterotic M theory. We concentrate on the case where the vacuum energy is provided by potentials on those boundaries. It is pointed out that the presence of such potentials necessarily excites bulk fields. We distinguish a linear and a non-linear regime for those modes. In the linear regime, inflation can be discussed in an effective four-dimensional theory in the conventional way. This effective action is derived by integrating out the bulk modes. Therefore, these modes do not give rise to excited Kaluza-Klein modes from a four-dimensional perspective. We lift a four-dimensional inflating solution up to five dimensions where it represents an inflating domain wall pair. This shows explicitly the inhomogeneity in the fifth dimension. We also demonstrate the existence of inflating solutions with unconventional properties in the non-linear regime. Specifically, we find solutions with and without an horizon between the two boundaries. These solutions have certain problems associated with the stability of the additional dimension and the persistence of initial excitations of the Kaluza-Klein modes. (c) 1999 The American Physical Society.

Lukas, Andre [Department of Physics, Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, (United Kingdom)] [Department of Physics, Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, (United Kingdom); Ovrut, Burt A. [Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396 (United States)] [Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6396 (United States); Waldram, Daniel [Department of Physics, Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544 (United States)] [Department of Physics, Joseph Henry Laboratories, Princeton University, Princeton, New Jersey 08544 (United States)

2000-01-15

216

Mass extinctions: Ecological selectivity and primary production  

NASA Astrophysics Data System (ADS)

If mass extinctions were caused by reduced primary productivity, then extinctions should be concentrated among animals with starvation-susceptible feeding modes, active lifestyles, and high-energy budgets. The stratigraphic ranges (by stage) of 424 genera of bivalves and 309 genera of articulate brachiopods suggest that there was an unusual reduction of primary productivity at the Cretaceous/Tertiary (K/T) boundary extinction. For bivalves at the K/T, there were (1) selective extinction of suspension feeders and other susceptible trophic categories relative to deposit feeders and other resistant categories, and (2) among suspension feed-ers, selective extinction of bivalves with active locomotion. During the Permian-Triassic (P/Tr) extinction and Jurassic background time, extinction rates among suspension feeders were greater for articulate brachiopods than for bivalves. But during the K/T event, extinction rates of articulates and suspension-feeding bivalves equalized, possibly because the low-energy budgets of articulates gave them an advantage when food was scarce.

Rhodes, Melissa Clark; Thayer, Charles W.

1991-09-01

217

Impact production of CO2 by the Cretaceous/Tertiary extinction bolide and the resultant heating of the earth  

NASA Technical Reports Server (NTRS)

Various observations and data demonstrate that sea level at the end of the Cretaceous was 150-200 m higher than at present, suggesting the possibility that the extinction bolide struck a shallow marine carbonate-rich sedimentary section. It is shown here that the impact of such a bolide (about 5 km in radius) onto a carbonate-rich terrane would increase the CO2 content of the atmosphere by a factor of two to ten. Additional dissolution of CO2 from the ocean's photic zone could release much larger quantities of CO2. The impact-induced release of CO2, by itself, would enhance atmospheric greenhouse heating and give rise to a worldwide increase in temperature from 2 K to 10 K for periods of 10,000 to 100,000 years.

O'Keefe, John D.; Ahrens, Thomas J.

1989-01-01

218

The geology, geochemistry and emplacement of the Cretaceous—Tertiary ophiolitic Nicoya Complex of the Osa Peninsula, southern Costa Rica  

NASA Astrophysics Data System (ADS)

The Nicoya Complex of the Osa Peninsula is essentially an obducted segment of oceanic crust comprising basaltic lavas and associated intrusive dolerite and gabbro, interstratified with lesser amounts of pelagic limestones, cherts and argillites. The sediments contain a minor clastic component and were deposited on an ocean floor of considerable relief and distant from a major landmass. The extrusive and intrusive basaltic rocks have geochemical affinities to large ion lithophile (LIL) element-enriched oceanic crust, and are interpreted to have formed in a back-arc basin analagous to the Mariana Trough, Lau Basin or Gulf of California. One sample has distinctly different geochemical characteristics and may represent a younger within-plate seamount. In the Late Cretaceous, an E-W-trending intra-oceanic trench/volcanic/back-arc system developed in association with an active southward-dipping subduction zone located south of the present-day southern Central American isthmus. Pelagic sediments and basaltic lavas accumulated in the back-arc over a period of at least 34 Ma spanning the Late Cretaceous and Early Tertiary. During this period there were three major volcanic events dated respectively as Santonian-Campanian (78.0 ± 2 Ma), Palaeocene (60.2 ± 7.6 Ma) and Middle Eocene (44.0 ± 4.4 Ma). Continuing northward movement of the southern plate caused overthrusting of the volcanic arc onto the northern plate and production of a thickened embryonic continental crust. Inferred reorganization of crustal stress in the Late Eocene caused fragmentation of the single ancestral plate into the Caribbean and "East Pacific" plates, with a flipping of the subduction zone accompanying development of the NE-dipping Middle America subduction zone and andesitic volcanism. During the Oligocene, the ancestral East Pacific plate split into the NE-moving Cocos plate and the eastward-moving Nazca plate, separated by the E-W-trending Colón spreading ridge and a series of N-S-trending transforms. The Cocos plate was subsequently split into two blocks separated by the Costa Rica Fracture Zone that extends northeastwards from the western end of the Colón Ridge to Costa Rica, which it divides into two distinctive volcanotectonic domains. To the north of the Costa Rica Fracture Zone, the Cocos plate is moving northeastwards and being consumed by the Middle America subduction zone, whereas the southern block is under the influence of the Colón spreading ridge with a N-S-oriented main stress axis. The N-S-trending Panama Fracture Zone can be extrapolated northwards via three submarine canyons on the continental slope to merge into a braided system of curved NW-trending coast-parallel wrench faults on which predominantly dextral strike-slip movement has produced pull-apart and tipped wedge basins with adjacent uplifted mini-horsts dating back to the Middle Pliocene. Therefore, although the Nicoya Complex of the Osa Peninsula was originally emplaced by accretion and thrusting related to pre-Oligocene plate movement, it owes its present-day exposure to post-Late Miocene wrench fault tectonics, with superimposed isostatic uplift.

Berrangé, J. P.; Thorpe, R. S.

1988-04-01

219

Cretaceous-Tertiary paleobathymetry of Labrador and Baffin shelves, and its significance to evolution of Labrador Sea  

SciTech Connect

The integrated micropaleontological and palynological analyses of 17 wells from offshore Labrador and southern Baffin Island allowed consistent assignments of biozones, ages, and depositional environments to the sections. Resolution attained is approximately at the stage level or finer. Interpretation of the foraminifera and palynomorphs from the Labrador Shelf indicates that the depositional environments were mainly neritic during the Early and early Late Cretaceous, changed to bathyal during the Maastrichtian to late Eocene, and returned to neritic during the Oligocene to Miocene. The sections drilled on the Baffin Shelf do not include Cretaceous sediments, but indicate bathyal environments from Paleocene to early Eocene, and neritic to nonmarine environments from late Eocene to Miocene. The Barremian to Campanian continental to neritic sediments from the Labrador Shelf correspond to the initial rifting phase of the Labrador-Greenland continental plate; whereas the Maastrichtian to late Eocene bathyal sediments correspond to the opening of the southern part of the Labrador Sea with the creation of oceanic crust. The Labrador Sea reached the Baffin shelf area during the Maastrichtian. The Oligocene to Miocene neritic to continental sediments of both the Labrador and Baffin Shelf areas correspond to the filling phase of the basin, with resulting buildup of the continental shelves and slopes.

Helenes, J.; Gradstein, F.

1988-03-01

220

Bouncing boundaries and breaking boundaries  

Microsoft Academic Search

New bio-technologies are currently forcing medicine to cross boundaries that might have seemed insuperable sometime ago. Specifically,\\u000a they now help to prolong human life beyond its natural process and to maintain it almost indefinitely. Consequently, death\\u000a takes on new meanings. For some it simply appears like an eventuality that can be postponed while, for others, death become\\u000a synonymous to extended

Joane Martel

1998-01-01

221

High pT direct photon and pi0 triggered azimuthal jet correlations and measurement of kT for isolated direct photons in p+p collisions at s=200GeV  

Microsoft Academic Search

Correlations of charged hadrons of 1kT, is obtained by comparing to a model incorporating a Gaussian kT smearing. The sensitivity of the associated charged hadron spectra to

A. Adare; S. Afanasiev; C. Aidala; N. N. Ajitanand; Y. Akiba; H. Al-Bataineh; J. Alexander; K. Aoki; L. Aphecetche; R. Armendariz; S. H. Aronson; J. Asai; E. T. Atomssa; R. Averbeck; T. C. Awes; B. Azmoun; V. Babintsev; M. Bai; G. Baksay; L. Baksay; A. Baldisseri; K. N. Barish; P. D. Barnes; B. Bassalleck; A. T. Basye; S. Bathe; S. Batsouli; V. Baublis; C. Baumann; A. Bazilevsky; S. Belikov; R. Bennett; A. Berdnikov; Y. Berdnikov; A. A. Bickley; J. G. Boissevain; H. Borel; K. Boyle; M. L. Brooks; H. Buesching; V. Bumazhnov; G. Bunce; S. Butsyk; C. M. Camacho; S. Campbell; B. S. Chang; W. C. Chang; J.-L. Charvet; S. Chernichenko; J. Chiba; C. Y. Chi; M. Chiu; I. J. Choi; R. K. Choudhury; T. Chujo; P. Chung; A. Churyn; V. Cianciolo; Z. Citron; C. R. Cleven; B. A. Cole; M. P. Comets; M. Connors; P. Constantin; M. Csanád; T. Csörgo; T. Dahms; S. Dairaku; K. Das; G. David; M. B. Deaton; K. Dehmelt; H. Delagrange; A. Denisov; D. D'Enterria; A. Deshpande; E. J. Desmond; O. Dietzsch; A. Dion; M. Donadelli; O. Drapier; A. Drees; K. A. Drees; A. K. Dubey; A. Durum; D. Dutta; V. Dzhordzhadze; Y. V. Efremenko; J. Egdemir; F. Ellinghaus; W. S. Emam; T. Engelmore; A. Enokizono; H. En'Yo; S. Esumi; K. O. Eyser; B. Fadem; D. E. Fields; M. Finger Jr.; F. Fleuret; S. L. Fokin; Z. Fraenkel; J. E. Frantz; A. Franz; A. D. Frawley; K. Fujiwara; Y. Fukao; T. Fusayasu; S. Gadrat; I. Garishvili; A. Glenn; H. Gong; M. Gonin; J. Gosset; Y. Goto; R. Granier de Cassagnac; N. Grau; S. V. Greene; M. Grosse Perdekamp; T. Gunji; H.-Å. Gustafsson; T. Hachiya; A. Hadj Henni; C. Haegemann; J. S. Haggerty; H. Hamagaki; R. Han; H. Harada; E. P. Hartouni; K. Haruna; E. Haslum; R. Hayano; M. Heffner; T. K. Hemmick; T. Hester; X. He; H. Hiejima; J. C. Hill; R. Hobbs; M. Hohlmann; W. Holzmann; K. Homma; B. Hong; T. Horaguchi; D. Hornback; S. Huang; T. Ichihara; R. Ichimiya; H. Iinuma; Y. Ikeda; K. Imai; J. Imrek; M. Inaba; Y. Inoue; D. Isenhower; L. Isenhower; M. Ishihara; T. Isobe; M. Issah; A. Isupov; D. Ivanischev; B. V. Jacak; J. Jia; J. Jin; O. Jinnouchi; B. M. Johnson; K. S. Joo; D. Jouan; F. Kajihara; S. Kametani; N. Kamihara; J. Kamin; M. Kaneta; J. H. Kang; H. Kanou; J. Kapustinsky; D. Kawall; A. V. Kazantsev; T. Kempel; A. Khanzadeev; K. M. Kijima; J. Kikuchi; B. I. Kim; D. H. Kim; D. J. Kim; E. Kim; S. H. Kim; E. Kinney; K. Kiriluk; Á. Kiss; E. Kistenev; A. Kiyomichi; J. Klay; C. Klein-Boesing; L. Kochenda; V. Kochetkov; B. Komkov; M. Konno; J. Koster; D. Kotchetkov; A. Kozlov; A. Král; A. Kravitz; J. Kubart; G. J. Kunde; N. Kurihara; K. Kurita; M. Kurosawa; M. J. Kweon; Y. Kwon; G. S. Kyle; R. Lacey; Y. S. Lai; J. G. Lajoie; D. Layton; A. Lebedev; D. M. Lee; K. B. Lee; M. K. Lee; T. Lee; M. J. Leitch; M. A. L. Leite; B. Lenzi; P. Liebing; T. Liska; A. Litvinenko; H. Liu; M. X. Liu; X. Li; B. Love; D. Lynch; C. F. Maguire; Y. I. Makdisi; A. Malakhov; M. D. Malik; V. I. Manko; E. Mannel; Y. Mao; L. Masek; H. Masui; F. Matathias; M. McCumber; P. L. McGaughey; N. Means; B. Meredith; Y. Miake; P. Mikes; K. Miki; T. E. Miller; A. Milov; S. Mioduszewski; M. Mishra; J. T. Mitchell; M. Mitrovski; A. K. Mohanty; Y. Morino; A. Morreale; D. P. Morrison; T. V. Moukhanova; D. Mukhopadhyay; J. Murata; S. Nagamiya; Y. Nagata; J. L. Nagle; M. Naglis; M. I. Nagy; I. Nakagawa; Y. Nakamiya; T. Nakamura; K. Nakano; J. Newby; M. Nguyen; T. Niita; B. E. Norman; R. Nouicer; A. S. Nyanin; E. O'Brien; S. X. Oda; C. A. Ogilvie; H. Ohnishi; K. Okada; M. Oka; O. O. Omiwade; Y. Onuki; A. Oskarsson; M. Ouchida; K. Ozawa; R. Pak; D. Pal; A. P. T. Palounek; V. Pantuev; V. Papavassiliou; W. J. Park; S. F. Pate; H. Pei; J.-C. Peng; H. Pereira; V. Peresedov; D. Yu. Peressounko; C. Pinkenburg; M. L. Purschke; A. K. Purwar; H. Qu; J. Rak; A. Rakotozafindrabe; I. Ravinovich; K. F. Read; S. Rembeczki; M. Reuter; K. Reygers; V. Riabov; Y. Riabov; D. Roach; G. Roche; S. D. Rolnick; A. Romana; M. Rosati; S. S. E. Rosendahl; P. Rosnet; P. Rukoyatkin; P. Ruzicka; V. L. Rykov; B. Sahlmueller; N. Saito; T. Sakaguchi; S. Sakai; K. Sakashita; H. Sakata; V. Samsonov; S. Sato; T. Sato; S. Sawada; K. Sedgwick; J. Seele; R. Seidl; A. Yu. Semenov; V. Semenov; R. Seto; D. Sharma; I. Shein; A. Shevel; T.-A. Shibata; K. Shigaki; M. Shimomura; K. Shoji; P. Shukla; A. Sickles; C. L. Silva; D. Silvermyr; C. Silvestre; K. S. Sim; B. K. Singh; C. P. Singh; V. Singh; S. Skutnik; M. Slunecka; A. Soldatov; R. A. Soltz; W. E. Sondheim; S. P. Sorensen; I. V. Sourikova; F. Staley; P. W. Stankus; E. Stenlund; M. Stepanov; A. Ster; S. P. Stoll; T. Sugitate; C. Suire; A. Sukhanov; J. Sziklai; T. Tabaru; S. Takagi; E. M. Takagui; A. Taketani; R. Tanabe; Y. Tanaka; S. Taneja; K. Tanida; M. J. Tannenbaum; A. Taranenko; P. Tarján; H. Themann; T. L. Thomas; M. Togawa; A. Toia; J. Tojo; L. Tomásek; Y. Tomita; H. Torii; R. S. Towell; V.-N. Tram; I. Tserruya; Y. Tsuchimoto; C. Vale; H. Valle

2010-01-01

222

Projectile-target mixing in melted ejecta formed during a hypervelocity impact cratering event  

NASA Technical Reports Server (NTRS)

Tektites contain little to no projectile contamination while, in contrast, some distal ejecta deposits can be relatively projectile-rich (e.g. the Cretaceous-Tertiary (K-T) boundary clay). This compositional difference motivated an experimental study of hypervelocity target-projectile mixing processes. We hope to scale up the results from these experiments and apply them to terrestrial impact structures like the Chicxulub Crater, Yucutan, Mexico, the leading contender as the site for the impact that caused the mass extinction that marks the K-T boundary. Shock decomposition of the approximately 500m thickness of anhydrite, or greater thickness of limestone, in the target rocks at Chicxulub may have been a critical mechanism for either global cooling via SO3, and subsequently H2SO4, formation, or possibly, global warming via increased CO2 formation. Understanding target-projectile mixing processes during hypervelocity impact may permit more accurate estimates of the amount of potentially toxic, target-derived material reaching stratospheric heights.

Evans, Noreen Joyce; Ahrens, Thomas J.; Shahinpoor, M.; Anderson, W. W.

1993-01-01

223

Manson impact structure, Iowa: First geochemical results for drill core M-1  

NASA Technical Reports Server (NTRS)

The Manson Impact Structure is a large complex impact crater centered ca. S km north of the town of Manson, Iowa. It is the largest intact impact structure recognized in the United States (35 km in diameter). Its Ar-40/Ar-39 age is indistinguishable from that of the Cretaceous-Tertiary (K-T) boundary. The Manson structure may be one element of the events at the K-T boundary. The crater is completely covered by Quaternary glacial sedimentary deposits that are normally underlain by Cretaceous clastic sediments and flat-lying carbonate sediments of Phanerozoic age, as well as Proterozoic red clastic, metamorphic, volcanic, and plutonic rock sequences. The study of a reflection seismic profile, provided by Amoco, was critical in interpreting the structure. In the 35 km diameter zone that marks the extension of the crater the normal rock sequence is disturbed due to the impact, and at the center of the structure granitic basement rocks are present that have been uplifted from about 4 km depth. Our studies consist of detailed petrological and geochemical characterization of all cores, with emphasis on a detailed description of all rock types found in the core samples and their relationship to target rocks. Geochemical data on samples from the Manson M-1 core are presented.

Koeberl, Christian; Anderson, Raymond R.; Hartung, Jack B.; Reimold, Wolf Uwe

1993-01-01

224

A method to obtain a Maxwell-Boltzmann neutron spectrum at kT=30 keV for nuclear astrophysics studies  

NASA Astrophysics Data System (ADS)

A method based on shaping the proton beam energy in order to shape the neutron beam energy to a desired form for accelerator-based neutron sources is proposed. An application to a superconductive RFQ proton accelerator of 5 MeV and 50 mA for the production of a stellar neutron spectrum at thermal energy equal to 30 keV using the 7Li(p,n)7Be reaction is investigated. The chosen energy beam shaper is a carbon foil which shapes the quasi-monochromatic proton beam to a quasi-Gaussian distribution: after the carbon foil, the beam is still shaped by chopping the Gaussian distribution at the reaction energy threshold. The obtained proton beam is impinged in a metallic lithium target. The concepts of the energy shaper, the proposed lithium target and the calculations performed to remove their power load are presented. Calculations show that a power density of 3 kW/cm2 can be sustained by the target which produces a forward-directed neutron source of 7.3×1010 neutrons/s. The obtained neutron spectrum resembles a Maxwell-Boltzmann distribution at kT=30 keV with a coefficient of determination of 0.997. The method is intended to be applied in activation analysis for measuring the Maxwellian-averaged neutron capture cross-section of elements of interest for astrophysics and validation of integral neutron data in the epithermal energy range.

Mastinu, P. F.; Martín Hernández, G.; Praena, J.

2009-04-01

225

Calcareous nannofossils from the uppermost Cretaceous and the lowermost Tertiary of central Texas  

E-print Network

as a o transitional interval of the Cretaceous/Tertiary boundary. It should be found everywhere in the world, unless it is missing because of a hiatus. Perch-Nielsen (1968-1973) systematically studied the coccoliths and related forms from Greenland... not be expected too far away from the Greenland Sea - Norwegian Sea passage (personal communication). THE SECTIONS The Cretaceous/Tertiary contact of the western Gu'lf Coast area extends in an arc from the Rio Grande eastward to San Antonio, from there north...

Jiang, Ming-Jung

2012-06-07

226

Two-Gluon Correlations in Heavy-Light Ion Collisions: Energy and Geometry Dependence, IR Divergences, and $k_T$-Factorization  

E-print Network

We study the properties of the cross section for two-gluon production in heavy-light ion collisions derived in our previous paper on the subject in the saturation/Color Glass Condensate framework. Concentrating on the energy and geometry dependence of the corresponding correlation functions we find that the two-gluon correlator is a much slower function of the center-of-mass energy than the one- and two-gluon production cross sections. The geometry dependence of the correlation function leads to stronger azimuthal near- and away-side correlations in the tip-on-tip U+U collisions than in the side-on-side U+U collisions, an exactly opposite behavior from the correlations generated by the elliptic flow of the quark-gluon plasma: a study of azimuthal correlations in the U+U collisions may thus help to disentangle the two sources of correlations. We demonstrate that the cross section for two-gluon production in heavy-light ion collisions contains a power-law infrared (IR) divergence even for fixed produced gluon momenta: while saturation effects in the target regulate some of the power-law IR-divergent terms in the lowest-order expression for the two-gluon correlator, other power-law IR-divergent terms remain, possibly due to absence of saturation effects in the dilute projectile. Finally we rewrite our result for the two-gluon production cross-section in a $k_T$-factorized form, obtaining a new factorized expression involving a convolution of one- and two-gluon Wigner distributions over both the transverse momenta and impact parameters. We show that the two-gluon production cross-section depends on two different types of unintegrated two-gluon Wigner distribution functions.

Yuri V. Kovchegov; Douglas E. Wertepny

2013-10-24

227

Vacuum Boundary Effects  

E-print Network

The effect of boundary conditions on the vacuum structure of quantum field theories is analysed from a quantum information viewpoint. In particular, we analyse the role of boundary conditions on boundary entropy and entanglement entropy. The analysis of boundary effects on massless free field theories points out the relevance of boundary conditions as a new rich source of information about the vacuum structure. In all cases the entropy does not increase along the flow from the ultraviolet to the infrared.

M. Asorey; J. M. Munoz-Castaneda

2008-03-18

228

The palaeoclimatology, palaeoecology and palaeoenvironmental analysis of mass extinction events  

Microsoft Academic Search

Although there is a continuum in magnitude of diversity loss between the smallest and largest biotic crisis, typically most authors refer to the largest five Phanerozoic events as “mass extinctions”. In the past 25 years the study of these mass extinction events has increased dramatically, with most focus being on the Cretaceous–Tertiary (K–T) event, although study of the end-Permian event

Richard J. Twitchett

2006-01-01

229

ArchiveofSID Journal of Sciences, Islamic Republic of Iran 18(2): 139-149 (2007) http://jsciences.ut.ac.ir  

E-print Network

ArchiveofSID Journal of Sciences, Islamic Republic of Iran 18(2): 139-149 (2007) http of Iran 2 Department of Geology, Faculty of Science, University of Tehran, Tehran, Islamic Republic the Cretaceous-Tertiary Boundary in Southwestern Iran B. Darvishzad,1,* E. Ghasemi-Nejad,2 S. Ghourchaei,2 and G

Keller, Gerta

230

CALCAREOUS NANNOPLANKTON BIOSTRATIGRAPHY OF THE CARPATHIAN TYPE UPPER CRETACEOUS-PALEOCENE DEPOSITS NEAR KLADORUB VILLAGE, VIDIN DISTRICT  

Microsoft Academic Search

The siltstone sequence of the Kladorub Formation, covering almost the entire Upper Campanian - Paleocene stratigraphic interval, is exposed in a restricted area near Kladorub Village in the West Fore-Balkan, NW Bulgaria. Some biostratigraphic and lithologic studies were recently made about the discovery of the Cretaceous\\/Tertiary boundary in this area. In the present study, a nannofossil biostratigraphic zonation is proposed

D. Sinnyovsky

2004-01-01

231

Experimental evidence that an asteroid impact led to the extinction of many species 65 million years ago  

SciTech Connect

The development of the theory that the mass extinction of the dinosaurs at the Cretaceous-Tertiary boundary was caused by an asteroid impact is reviewed. The personnel involved, the objections to the theory, and the evidence refuting those objections are presented chronologically. (ACR)

Alvarez, L.W.

1982-09-01

232

Numerical Boundary Condition Procedures  

NASA Technical Reports Server (NTRS)

Topics include numerical procedures for treating inflow and outflow boundaries, steady and unsteady discontinuous surfaces, far field boundaries, and multiblock grids. In addition, the effects of numerical boundary approximations on stability, accuracy, and convergence rate of the numerical solution are discussed.

1981-01-01

233

Boundary Conditions Copenhagen University  

E-print Network

Boundary Conditions Gerd Grubb Copenhagen University Lecture in memory of Lars H¨ormander 26th Nordic and 1st Nordic-European Congress of Mathematicians June 2013 Gerd Grubb Copenhagen University, and the people involved. Gerd Grubb Copenhagen University Boundary Conditions #12;On boundary conditions

Grubb, Gerd

234

High pT direct photon and ?0 triggered azimuthal jet correlations and measurement of kT for isolated direct photons in p+p collisions at s=200GeV  

NASA Astrophysics Data System (ADS)

Correlations of charged hadrons of 1kT, is obtained by comparing to a model incorporating a Gaussian kT smearing. The sensitivity of the associated charged hadron spectra to the underlying fragmentation function is tested and the data are compared to calculations using recent global fit results. The shape of the direct photon-associated hadron spectrum as well as its charge asymmetry are found to be consistent with a sample dominated by quark-gluon Compton scattering. No significant evidence of fragmentation photon correlated production is observed within experimental uncertainties.

Adare, A.; Afanasiev, S.; Aidala, C.; Ajitanand, N. N.; Akiba, Y.; Al-Bataineh, H.; Alexander, J.; Aoki, K.; Aphecetche, L.; Armendariz, R.; Aronson, S. H.; Asai, J.; Atomssa, E. T.; Averbeck, R.; Awes, T. C.; Azmoun, B.; Babintsev, V.; Bai, M.; Baksay, G.; Baksay, L.; Baldisseri, A.; Barish, K. N.; Barnes, P. D.; Bassalleck, B.; Basye, A. T.; Bathe, S.; Batsouli, S.; Baublis, V.; Baumann, C.; Bazilevsky, A.; Belikov, S.; Bennett, R.; Berdnikov, A.; Berdnikov, Y.; Bickley, A. A.; Boissevain, J. G.; Borel, H.; Boyle, K.; Brooks, M. L.; Buesching, H.; Bumazhnov, V.; Bunce, G.; Butsyk, S.; Camacho, C. M.; Campbell, S.; Chang, B. S.; Chang, W. C.; Charvet, J.-L.; Chernichenko, S.; Chiba, J.; Chi, C. Y.; Chiu, M.; Choi, I. J.; Choudhury, R. K.; Chujo, T.; Chung, P.; Churyn, A.; Cianciolo, V.; Citron, Z.; Cleven, C. R.; Cole, B. A.; Comets, M. P.; Connors, M.; Constantin, P.; Csanád, M.; Csörg?, T.; Dahms, T.; Dairaku, S.; Das, K.; David, G.; Deaton, M. B.; Dehmelt, K.; Delagrange, H.; Denisov, A.; D'Enterria, D.; Deshpande, A.; Desmond, E. J.; Dietzsch, O.; Dion, A.; Donadelli, M.; Drapier, O.; Drees, A.; Drees, K. A.; Dubey, A. K.; Durum, A.; Dutta, D.; Dzhordzhadze, V.; Efremenko, Y. V.; Egdemir, J.; Ellinghaus, F.; Emam, W. S.; Engelmore, T.; Enokizono, A.; En'Yo, H.; Esumi, S.; Eyser, K. O.; Fadem, B.; Fields, D. E.; Finger, M., Jr.; Finger, M.; Fleuret, F.; Fokin, S. L.; Fraenkel, Z.; Frantz, J. E.; Franz, A.; Frawley, A. D.; Fujiwara, K.; Fukao, Y.; Fusayasu, T.; Gadrat, S.; Garishvili, I.; Glenn, A.; Gong, H.; Gonin, M.; Gosset, J.; Goto, Y.; Granier de Cassagnac, R.; Grau, N.; Greene, S. V.; Grosse Perdekamp, M.; Gunji, T.; Gustafsson, H.-Å.; Hachiya, T.; Hadj Henni, A.; Haegemann, C.; Haggerty, J. S.; Hamagaki, H.; Han, R.; Harada, H.; Hartouni, E. P.; Haruna, K.; Haslum, E.; Hayano, R.; Heffner, M.; Hemmick, T. K.; Hester, T.; He, X.; Hiejima, H.; Hill, J. C.; Hobbs, R.; Hohlmann, M.; Holzmann, W.; Homma, K.; Hong, B.; Horaguchi, T.; Hornback, D.; Huang, S.; Ichihara, T.; Ichimiya, R.; Iinuma, H.; Ikeda, Y.; Imai, K.; Imrek, J.; Inaba, M.; Inoue, Y.; Isenhower, D.; Isenhower, L.; Ishihara, M.; Isobe, T.; Issah, M.; Isupov, A.; Ivanischev, D.; Jacak, B. V.; Jia, J.; Jin, J.; Jinnouchi, O.; Johnson, B. M.; Joo, K. S.; Jouan, D.; Kajihara, F.; Kametani, S.; Kamihara, N.; Kamin, J.; Kaneta, M.; Kang, J. H.; Kanou, H.; Kapustinsky, J.; Kawall, D.; Kazantsev, A. V.; Kempel, T.; Khanzadeev, A.; Kijima, K. M.; Kikuchi, J.; Kim, B. I.; Kim, D. H.; Kim, D. J.; Kim, E.; Kim, S. H.; Kinney, E.; Kiriluk, K.; Kiss, Á.; Kistenev, E.; Kiyomichi, A.; Klay, J.; Klein-Boesing, C.; Kochenda, L.; Kochetkov, V.; Komkov, B.; Konno, M.; Koster, J.; Kotchetkov, D.; Kozlov, A.; Král, A.; Kravitz, A.; Kubart, J.; Kunde, G. J.; Kurihara, N.; Kurita, K.; Kurosawa, M.; Kweon, M. J.; Kwon, Y.; Kyle, G. S.; Lacey, R.; Lai, Y. S.; Lajoie, J. G.; Layton, D.; Lebedev, A.; Lee, D. M.; Lee, K. B.; Lee, M. K.; Lee, T.; Leitch, M. J.; Leite, M. A. L.; Lenzi, B.; Liebing, P.; Liška, T.; Litvinenko, A.; Liu, H.; Liu, M. X.; Li, X.; Love, B.; Lynch, D.; Maguire, C. F.; Makdisi, Y. I.; Malakhov, A.; Malik, M. D.; Manko, V. I.; Mannel, E.; Mao, Y.; Mašek, L.; Masui, H.; Matathias, F.; McCumber, M.; McGaughey, P. L.; Means, N.; Meredith, B.; Miake, Y.; Mikeš, P.; Miki, K.; Miller, T. E.; Milov, A.; Mioduszewski, S.; Mishra, M.; Mitchell, J. T.; Mitrovski, M.; Mohanty, A. K.; Morino, Y.; Morreale, A.; Morrison, D. P.; Moukhanova, T. V.; Mukhopadhyay, D.; Murata, J.; Nagamiya, S.; Nagata, Y.; Nagle, J. L.; Naglis, M.; Nagy, M. I.; Nakagawa, I.; Nakamiya, Y.; Nakamura, T.; Nakano, K.; Newby, J.; Nguyen, M.; Niita, T.; Norman, B. E.; Nouicer, R.; Nyanin, A. S.; O'Brien, E.; Oda, S. X.; Ogilvie, C. A.; Ohnishi, H.; Okada, K.; Oka, M.; Omiwade, O. O.; Onuki, Y.; Oskarsson, A.; Ouchida, M.; Ozawa, K.; Pak, R.; Pal, D.; Palounek, A. P. T.; Pantuev, V.; Papavassiliou, V.; Park, J.; Park, W. J.; Pate, S. F.; Pei, H.; Peng, J.-C.; Pereira, H.; Peresedov, V.; Peressounko, D. Yu.; Pinkenburg, C.; Purschke, M. L.; Purwar, A. K.; Qu, H.; Rak, J.; Rakotozafindrabe, A.; Ravinovich, I.; Read, K. F.; Rembeczki, S.; Reuter, M.; Reygers, K.; Riabov, V.; Riabov, Y.; Roach, D.; Roche, G.; Rolnick, S. D.; Romana, A.; Rosati, M.; Rosendahl, S. S. E.; Rosnet, P.; Rukoyatkin, P.; Ruži?ka, P.; Rykov, V. L.; Sahlmueller, B.; Saito, N.; Sakaguchi, T.; Sakai, S.; Sakashita, K.; Sakata, H.; Samsonov, V.; Sato, S.; Sato, T.; Sawada, S.; Sedgwick, K.; Seele, J.; Seidl, R.; Semenov, A. Yu.; Semenov, V.; Seto, R.; Sharma, D.; Shein, I.; Shevel, A.; Shibata, T.-A.; Shigaki, K.; Shimomura, M.; Shoji, K.; Shukla, P.; Sickles, A.; Silva, C. L.; Silvermyr, D.; Silvestre, C.; Sim, K. S.; Singh, B. K.; Singh, C. P.; Singh, V.; Skutnik, S.; Slune?ka, M.; Soldatov, A.; Soltz, R. A.; Sondheim, W. E.

2010-10-01

235

The atmospheric boundary layer  

SciTech Connect

In this book, the author successfully reviews the current state of affairs in boundary-layer meteorology research. The book is organized into nine chapters. The first chapter is an introduction to the topic of the atmospheric boundary layer. The second chapter is a survey of turbulence theory. The third chapter reviews the similarity relationships that have been formulated for the various scaling regimes in the boundary layer. Chapter 4 deals with the deviations of the homogeneous boundary layer. In chapter 5 the boundary conditions for the atmospheric boundary layers are considered, that is, the energy fluxes at the earth's surface. In chapter 6 the characteristics and dynamics are discussed for the various prototypes of the atmospheric boundary layer, such as the convective and the stable boundary layer. Boundary-layer clouds are the subject of chapter 7. The final chapters, 8 and 9, discuss the use of boundary-layer meteorology in formulating parameterization schemes. In the preface of the book, the author states that his goal is to provide a book for researchers in atmospheric and associated sciences. The book will be an asset to any scientist active in boundary-layer meteorology or a related field.

Garratt, J.R.

1992-01-01

236

Boundary lubrication: Revisited  

NASA Technical Reports Server (NTRS)

A review of the various lubrication regimes, with particular, emphasis on boundary lubrication, is presented. The types of wear debris and extent of surface damage is illustrated for each regime. The role of boundary surface films along with their modes of formation and important physical properties are discussed. In addition, the effects of various operating parameters on friction and wear in the boundary lubrication regime are considered.

Jones, W. R., Jr.

1982-01-01

237

Nanoscale Boundary Lubrication Studies  

Microsoft Academic Search

\\u000a Boundary films are formed by physisorption, chemisorption, and chemical reaction. A good boundary boundary film physisorption\\u000a chemisorption lubricant should have a high degree of interaction between its molecules and the solid surface. As a general\\u000a rule, liquids are good lubricants when they are polar and thus able to grip solid surfaces perfluoropolyether (PFPE) (or be\\u000a adsorbed). In this chapter, we

Bharat Bhushan

238

Boundaries and dual relationships.  

PubMed

Ethical standards are core components of practice standards and codes of conduct for mental health practitioners. Practice standards and ethics related to boundaries are generally based on historical review, study of mental health services, and the impact of boundary crossing or boundary violations on clients receiving services. This article explores some common standards of ethical practice related to boundaries and dual or multiple relationships between mental health professionals and clients. The underlying conceptual basis for these standards and examples of questions encountered in clinical practice with sexual offenders are explored. PMID:20966164

Sawyer, Steven; Prescott, David

2011-09-01

239

The atmospheric boundary layer  

Microsoft Academic Search

In this book, the author successfully reviews the current state of affairs in boundary-layer meteorology research. The book is organized into nine chapters. The first chapter is an introduction to the topic of the atmospheric boundary layer. The second chapter is a survey of turbulence theory. The third chapter reviews the similarity relationships that have been formulated for the various

J. R. Garratt

1992-01-01

240

About positivity of green's functions for nonlocal boundary value problems with impulsive delay equations.  

PubMed

The impulsive delay differential equation is considered (Lx)(t) = x'(t) + ?(i=1)(m) p(i)(t)x(t - ?(i) (t)) = f(t), t ? [a, b], x(t j) = ?(j)x(t(j - 0)), j = 1,…, k, a = t0 < t1 < t2 < ?k < t k+1 = b, x(?) = 0, ? ? [a, b], with nonlocal boundary condition lx = ?(a)(b) ?(s)x'(s)ds + ?x(a) = c, ? ? L ? [a, b]; ?, c ? R. Various results on existence and uniqueness of solutions and on positivity/negativity of the Green's functions for this equation are obtained. PMID:24719584

Domoshnitsky, Alexander; Volinsky, Irina

2014-01-01

241

Behavior of carbonate shelf communities in the Upper Triassic of Nevada: Evidence of impact mediated faunal turnover  

SciTech Connect

The carbonate shelf sediments of the Luning and Gabbs Formations of Nevada span the last several million years of the Triassic. This richly fossiliferous sequence provides a relatively continuous record of benthic community behavior during a long interval of global biotic turnover. Upper Carnian-Lower Norian and Upper Norian sea floors in this region were inhabited by a variety of invertebrate communities, all of them mollusc-dominated. Across a range of offshore shelf to basinal environments and throughout repeated community replacements, the most abundant and diverse taxa were infaunal and epifaunal bivalves and ammonites. The sequence of Upper Triassic molluscan communities was interrupted by a Lower or Middle Norian interval of brachiopod-dominated faunas. Although preserved in similar offshore carbonate shelf sediments, these communities are nearly devoid of the infaunal bivalves and ammonites that characterize both older and younger assemblages in the section. This pattern, of a temporary replacement of molluscan communities by brachiopod faunas, mimics that reported for some shelf assemblages across the Cretaceous-Tertiary boundary. That brief resurgence of brachiopods is linked to a sharp drop in marine primary productivity, which suggests that a disruption of planktonic food chains may also have occurred early in the Norian. The timing and pattern of Carnian-Norian faunal and physical events and their resemblance to K/T sequences are consistent with the proposal that an asteroid impact played a role in the Upper Triassic faunal transition.

Hogler, J.A. (Univ. of California, Berkeley, CA (United States). Museum of Paleontology)

1993-04-01

242

Iridium in sediments containing large abundances of Australasian microtektites from DSDP hole 758B in the Eastern Indian Ocean and from DSDP hole 769A in the Sulu Sea  

NASA Technical Reports Server (NTRS)

Excess Ir found in sediments at the Cretaceous/Tertiary (K/T) boundary and in other (e.g., Pliocene) sediments from deep sea drilling cores is widely interpreted as evidence of major impact events. The Australasian tektites originated in an impact event approximately 0.77 Ma ago; microtektites have been found in deep-sea sediment cores from throughout the Indian Ocean, the Philippine Sea, and western Pacific Ocean, but Ir has not been previously reported in these horizons. The deep-sea record of tektites is of particular interest, because in contrast to most continental occurrences, the stratigraphy preserves the original depositional position. Recently several cores having exceptionally high contents of Australasian microtektites have been investigated, Glass and Wu found shocked quartz associated with the microtektites. We used neutron activation to determine concentrations of Ir and other elements in two cores bearing microtektites, one from Deep Sea Drilling Project (DSDP) hole 758B in the Eastern Indian Ocean and one from DSDP hole 769A in the Sulu Sea (near Mindanao, Philippines). The sedimentation age for the microtektite layers in core 758B lies between 0.73 - 0.78 Ma and agrees well with the mean laser-fusion Ar-40/Ar-39 age of Australasian tektites of 0.77 +/- 0.02 Ma by Izett et al. We are able to resolve a small positive Ir enhancement in 758B. Core 769A shows too much scatter to allow resolution of an Ir peak.

Schmidt, Gerhard; Zhou, Lei; Wasson, John T.

1993-01-01

243

Placenta-Specific Protein 1 Is Conserved throughout the Placentalia under Purifying Selection  

PubMed Central

Placental mammals (Placentalia) are a very successful group that, today, comprise 94% of all mammalian species. Recent phylogenetic analyses, coupled with new, quite complete fossils, suggest that the crown orders were all established rapidly from a common ancestor just after the Cretaceous/Tertiary (K/T) boundary 65 million years ago. Extensive molecular and morphologic evidence has led to a description of the common ancestor of all Placentalia in which a two-horned uterus and a hemochorial placenta are present. Thus, the process of placentation in which the placenta invades and anchors to the uterine epithelium was already established. One factor that has been suggested as a crucial component of this process is placenta-specific protein 1 (PLAC1). A phylogenetic analysis of the PLAC1 protein in 25 placental mammal species, representing nine of the sixteen crown orders of the Placentalia, suggests that this protein was present in the placental common ancestor in the form we see it today, that it evolved in the Placentalia and has been subject to the effects of purifying selection since its appearance. PMID:25180201

Devor, Eric J.

2014-01-01

244

Seeking the boundary of boundary extension.  

PubMed

Boundary extension (BE) is a remarkably consistent visual memory error in which participants remember seeing a more wide-angle image of a scene than was actually viewed (Intraub & Richardson, Journal of Experimental Psychology: Learning, Memory, and Cognition 15:179-187, 1989). Multiple stimulus factors are thought to contribute to the occurrence of BE, including object recognition, conceptual knowledge of scenes, and amodal perception at the view boundaries (Intraub, Wiley Interdisciplinary Reviews: Cognitive Science 3:117-127, 2012). In the present study, we used abstract scenes instead of images of the real world, in order to remove expectations based on semantic associations with objects and the schematic context of the view. Close-angle and wide-angle scenes were created using irregular geometric shapes rated by independent observers as lacking any easily recognizable structure. The abstract objects were tested on either a random-dot or a blank background in order to assess the influence of implied continuation of the image beyond its boundaries. The random-dot background conditions had background occlusion cues either present or absent at the image border, in order to test their influence on BE in the absence of high-level information about the scenes. The results indicate that high-level information about objects and schematic context is unnecessary for BE to occur, and that occlusion information at the image boundary also has little influence on BE. Contrary to previous studies, we also found clear BE for all conditions, despite using scenes depicting undetailed objects on a blank white background. The results highlighted the ubiquitous nature of BE and the adaptability of scene perception processes. PMID:23921509

McDunn, Benjamin A; Siddiqui, Aisha P; Brown, James M

2014-04-01

245

Discovering Plate Boundaries  

NSDL National Science Digital Library

Students are initially assigned to one of four maps of the world: Seismology, Volcanology, Geochronology or Topography. They are also given a map of the world's plate boundaries and are asked to classify the boundaries based upon the data from their assigned map. Students are then assigned to a tectonic plate, such that each plate group contains at least one "expert" on each map. As a group, they must classify their plate's boundaries using data from all four maps. Recent volcanic and seismic events are discussed in the plate tectonic context. Has minimal/no quantitative component Uses geophysics to solve problems in other fields

Henning, Alison

246

Boundaries and Topological Algorithms  

E-print Network

This thesis develops a model for the topological structure of situations. In this model, the topological structure of space is altered by the presence or absence of boundaries, such as those at the edges of objects. ...

Fleck, Margaret Morrison

1988-09-01

247

Mapping Plate Tectonic Boundaries  

NSDL National Science Digital Library

To prepare for this activity, students do background reading on Plate Tectonics from the course textbook. Students also participate in a lecture on the discovery and formulation of the unifying theory of plate tectonics, and the relationship between plate boundaries and geologic features such as volcanoes. Lastly, in lecture, students are introduced to a series of geologic hazards caused by certain plate tectonic interactions. The activity gives students practices at identifying plate boundaries and allows them to explore lesser known tectonically active regions.

Kerwin, Michael

248

Accretion rate of extraterrestrial matter: Iridium deposited over the last 70 million years  

NASA Technical Reports Server (NTRS)

In order to quantify the accretion rate of extraterrestrial matter during the Cenozoic, Ir concentrations were measured in a continuous series of 450 samples across most of the length of piston core LL44-GPC3. LL44-GPC3 is a 25-meter-long, large-diameter piston core of abyssal clay from the central North Pacific. This core contains a nearly continuous record of sedimentation over the last 70 Ma, as this site migrated from a region near the Equator in the late Cretaceous to its present position north of Hawaii. The first-cut survey across the core is nearing completion, and all of the conclusions of the earlier study, in which was reported the concentrations of Ir, Co, and Sb across 9 meters of this core, remain unchanged. The only strongly enhanced Ir concentrations occur at the Cretaceous-Tertiary (K-T) boundary and outside the K-T boundary Ir correlates well with Co, a terrestrial element which is largely present in hydrogenous ferromanganese oxide precipitates from seawater. Concentrations of both elements appear to be inversely correlated with the sedimentation rate. Although the K-T Ir anomaly is unique in magnitude in this core, there are several small bumps in the Ir profile which may reflect smaller accretionary events. The most promising Ir enhancement was observed in a 30 cm section approximately 1 m below the K-T boundary. Preliminary data suggest deposition of an excess across this interval at a time estimate to be approximate 1 Ma before the K-T impact event, but there is insufficient evidence at present to prove that this reflects enhanced accretion of extraterrestrial matter. A detailed model is being prepared of the chemical record of sedimentation in this core using a combined database of 39 elements in approximately 450 samples across the Cenozoic. Preliminary working model indicates that the only sedimentary sources which contribute significantly to the Ir budget in this core are the hydrogenous precipitates and extraterrestrial particulates.

Kyte, Frank T.

1988-01-01

249

Cretaceous–Tertiary structures and kinematics of the Serbomacedonian metamorphic rocks and their relation to the exhumation of the Hellenic hinterland (Macedonia, Greece)  

Microsoft Academic Search

The kinematic pattern and associated metamorphism of the predominant ductile deformation and the subsequent deformational\\u000a stages of the Serbomacedonian metamorphic rocks and granitoids are presented in terms of peri-Tethyan tectonics. A systematic\\u000a record of structural and metamorphic data gives evidence of a main top-to-ENE to ESE ductile flow of Cretaceous age (120–90?Ma)\\u000a associated with a crustal stretching and unroofing. A

A. Kilias; G. Falalakis; D. Mountrakis

1999-01-01

250

Characterizing Plate Boundaries  

NSDL National Science Digital Library

To prepare for this exercise students read about the processes that operate at plate boundaries and how they are related to the distinct patterns of seismicity, volcanism, surface elevations (e.g., ridges versus trenches), and seafloor ages characteristic of different boundary types. During the week the assignment is available online, students have access to: (1) an index map that locates three boundaries they are to study; and (2) four maps from Sawyer's Discovering Plate Boundaries website that provide the data mentioned above. Student tasks are to: (1) document patterns in each type of data along the three targeted boundaries; and (2) use these observations in conjunction with their understandings of the processes that operate along different types of boundaries to decide whether each of the targeted sites is most likely to be a divergent, convergent, or shear boundary. This activity gives students practice in map reading, interpreting the likely tectonic setting of a boundary by pulling together constraints from several types of data, and collaborating with their classmates in an online environment. The activity also provides a foundation for understanding a wide range of phenomena that are discussed later in the semester in the context of plate tectonic processes. Teaching Tips Adaptations that allow this activity to be successful in an online environment Sawyer's Discovering Plate Boundaries is a jigsaw exercise in which students collaboratively develop an empirical classification of plate boundaries by first studying an individual data set (e.g., seismicity) and then working as part of a multidisciplinary team to develop a composite classification for the boundaries of a single plate using several types of data. In order for the classification to be truly empirical, students are not introduced to the "traditional" classification of plate boundaries till the end of the exercise. In adapting this assignment to the online environment I have: (1) asked students to prepare by becoming familiar with the standard classification of plate boundaries and the processes that operate at them; (2) limited their work to three targeted boundaries of different types; and (3) provided guidance about which features to look for in the each data set. I have found that these modifications help online students, who often work alone "on their own schedules", to avoid getting "lost" and frustrated with the assignment and to compensate for the lack of collaborative input they would receive in a classroom setting. Elements of this activity that are most effective The success of this exercise is really seems to depend on how well a student follows the directions. If a student learns about the geologic differences among plate boundaries, makes careful observations, and thoughtfully compares his or her observations to the expected patterns he or she typically does quite well based on answers to the follow-up questions. If, on the other hand, a student simply looks up the types of the targeted boundaries on a map and then attempts to "back out" the observations that he or she thinks should fit, the result is often inconsistency and a poor score on the questions. (I can often tell which approach a student is taking based on the queries they post to the discussion board, but rarely seem to be able to get those who are trying to work backwards through the assignment to change direction.) Recommendations for other faculty adapting this activity to their own course: To date my experience developing an engaging online exercise to help students learn the principles of plate tectonics has only been partly successful. I think that having such an exercise is critical, however, because this topic provides the framework for so much of what we learn in the geosciences. Based on my efforts to adapt elements of Discovering Plate Boundaries to an online environment I would offer three recommendations. (1) Provide examples. Confronted with an unfamiliar map students are sometimes confused when asked to decide if seafloor age, for example, is uniform or variable along the length of a boundary. Showing them what you mean using snapshots from a map can often clear questions like this up quickly. Similarly, for written work a single example that gives them a clear sense of "what you're looking for" and can often head off a lot of questions. (2) Choose the boundaries you ask students to study carefully. The scarcity of documented volcanism along a mid-ocean ridge or the burial of seafloor age belts by sediment along a trench can result in student observations that are correct, but problematic for correctly assessing the nature of a boundary. (3) Stay on top of student questions and comments, and be prepared to make well-publicized "mid-course corrections" if something you thought was clear turns out to be misunderstood. These minor corrections happen naturally in face-to-face classes but can require real diligence to catch and correct in the online environment.

Hirt, Bill

251

Spectrum of local boundary operators from boundary form factor bootstrap  

E-print Network

Using the recently introduced boundary form factor bootstrap equations, we map the complete space of their solutions for the boundary version of the scaling Lee-Yang model and sinh-Gordon theory. We show that the complete space of solutions, graded by the ultraviolet behaviour of the form factors can be brought into correspondence with the spectrum of local boundary operators expected from boundary conformal field theory, which is a major evidence for the correctness of the boundary form factor bootstrap framework.

M. Szots; G. Takacs

2007-03-26

252

Measurement of the ratio of inclusive jet cross sections using the anti-kT algorithm with radius parameters R =0.5 and 0.7 in pp collisions at ?s =7 TeV  

NASA Astrophysics Data System (ADS)

Measurements of the inclusive jet cross section with the anti-kT clustering algorithm are presented for two radius parameters, R =0.5 and 0.7. They are based on data from LHC proton-proton collisions at ?s =7 TeV corresponding to an integrated luminosity of 5.0 fb-1 collected with the CMS detector in 2011. The ratio of these two measurements is obtained as a function of the rapidity and transverse momentum of the jets. Significant discrepancies are found comparing the data to leading-order simulations and to fixed-order calculations at next-to-leading order, corrected for nonperturbative effects, whereas simulations with next-to-leading-order matrix elements matched to parton showers describe the data best.

Chatrchyan, S.; Khachatryan, V.; Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Erö, J.; Fabjan, C.; Friedl, M.; Frühwirth, R.; Ghete, V. M.; Hartl, C.; Hörmann, N.; Hrubec, J.; Jeitler, M.; Kiesenhofer, W.; Knünz, V.; Krammer, M.; Krätschmer, I.; Liko, D.; Mikulec, I.; Rabady, D.; Rahbaran, B.; Rohringer, H.; Schöfbeck, R.; Strauss, J.; Taurok, A.; Treberer-Treberspurg, W.; Waltenberger, W.; Wulz, C.-E.; Mossolov, V.; Shumeiko, N.; Suarez Gonzalez, J.; Alderweireldt, S.; Bansal, M.; Bansal, S.; Cornelis, T.; De Wolf, E. A.; Janssen, X.; Knutsson, A.; Luyckx, S.; Mucibello, L.; Ochesanu, S.; Roland, B.; Rougny, R.; Van Haevermaet, H.; Van Mechelen, P.; Van Remortel, N.; Van Spilbeeck, A.; Blekman, F.; Blyweert, S.; D'Hondt, J.; Heracleous, N.; Kalogeropoulos, A.; Keaveney, J.; Kim, T. J.; Lowette, S.; Maes, M.; Olbrechts, A.; Strom, D.; Tavernier, S.; Van Doninck, W.; Van Mulders, P.; Van Onsem, G. P.; Villella, I.; Caillol, C.; Clerbaux, B.; De Lentdecker, G.; Favart, L.; Gay, A. P. R.; Léonard, A.; Marage, P. E.; Mohammadi, A.; Perniè, L.; Reis, T.; Seva, T.; Thomas, L.; Vander Velde, C.; Vanlaer, P.; Wang, J.; Adler, V.; Beernaert, K.; Benucci, L.; Cimmino, A.; Costantini, S.; Dildick, S.; Garcia, G.; Klein, B.; Lellouch, J.; Mccartin, J.; Ocampo Rios, A. A.; Ryckbosch, D.; Salva Diblen, S.; Sigamani, M.; Strobbe, N.; Thyssen, F.; Tytgat, M.; Walsh, S.; Yazgan, E.; Zaganidis, N.; Basegmez, S.; Beluffi, C.; Bruno, G.; Castello, R.; Caudron, A.; Ceard, L.; Da Silveira, G. G.; Delaere, C.; du Pree, T.; Favart, D.; Forthomme, L.; Giammanco, A.; Hollar, J.; Jez, P.; Komm, M.; Lemaitre, V.; Liao, J.; Militaru, O.; Nuttens, C.; Pagano, D.; Pin, A.; Piotrzkowski, K.; Popov, A.; Quertenmont, L.; Selvaggi, M.; Vidal Marono, M.; Vizan Garcia, J. M.; Beliy, N.; Caebergs, T.; Daubie, E.; Hammad, G. H.; Alves, G. A.; Correa Martins Junior, M.; Dos Reis Martins, T.; Pol, M. E.; Souza, M. H. G.; Aldá Júnior, W. L.; Carvalho, W.; Chinellato, J.; Custódio, A.; Da Costa, E. M.; De Jesus Damiao, D.; De Oliveira Martins, C.; Fonseca De Souza, S.; Malbouisson, H.; Malek, M.; Matos Figueiredo, D.; Mundim, L.; Nogima, H.; Prado Da Silva, W. L.; Santaolalla, J.; Santoro, A.; Sznajder, A.; Tonelli Manganote, E. J.; Vilela Pereira, A.; Bernardes, C. A.; Dias, F. A.; Tomei, T. R. Fernandez Perez; Gregores, E. M.; Lagana, C.; Mercadante, P. G.; Novaes, S. F.; Padula, Sandra S.; Genchev, V.; Iaydjiev, P.; Marinov, A.; Piperov, S.; Rodozov, M.; Sultanov, G.; Vutova, M.; Dimitrov, A.; Glushkov, I.; Hadjiiska, R.; Kozhuharov, V.; Litov, L.; Pavlov, B.; Petkov, P.; Bian, J. G.; Chen, G. M.; Chen, H. S.; Chen, M.; Du, R.; Jiang, C. H.; Liang, D.; Liang, S.; Meng, X.; Plestina, R.; Tao, J.; Wang, X.; Wang, Z.; Asawatangtrakuldee, C.; Ban, Y.; Guo, Y.; Li, Q.; Li, W.; Liu, S.; Mao, Y.; Qian, S. J.; Wang, D.; Zhang, L.; Zou, W.; Avila, C.; Carrillo Montoya, C. A.; Chaparro Sierra, L. F.; Florez, C.; Gomez, J. P.; Gomez Moreno, B.; Sanabria, J. C.; Godinovic, N.; Lelas, D.; Polic, D.; Puljak, I.; Antunovic, Z.; Kovac, M.; Brigljevic, V.; Kadija, K.; Luetic, J.; Mekterovic, D.; Morovic, S.; Sudic, L.; Attikis, A.; Mavromanolakis, G.; Mousa, J.; Nicolaou, C.; Ptochos, F.; Razis, P. A.; Finger, M.; Finger, M.; Abdelalim, A. A.; Assran, Y.; Elgammal, S.; Ellithi Kamel, A.; Mahmoud, M. A.; Radi, A.; Kadastik, M.; Müntel, M.; Murumaa, M.; Raidal, M.; Rebane, L.; Tiko, A.; Eerola, P.; Fedi, G.; Voutilainen, M.; Härkönen, J.; Karimäki, V.; Kinnunen, R.; Kortelainen, M. J.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Peltola, T.; Tuominen, E.; Tuominiemi, J.; Tuovinen, E.; Wendland, L.; Tuuva, T.; Besancon, M.; Couderc, F.; Dejardin, M.; Denegri, D.; Fabbro, B.; Faure, J. L.; Ferri, F.; Ganjour, S.; Givernaud, A.; Gras, P.; Hamel de Monchenault, G.; Jarry, P.; Locci, E.; Malcles, J.; Nayak, A.; Rander, J.; Rosowsky, A.; Titov, M.; Baffioni, S.; Beaudette, F.; Busson, P.; Charlot, C.; Daci, N.; Dahms, T.; Dalchenko, M.; Dobrzynski, L.; Florent, A.; Granier de Cassagnac, R.; Miné, P.; Mironov, C.; Naranjo, I. N.; Nguyen, M.; Ochando, C.; Paganini, P.; Sabes, D.; Salerno, R.; Sirois, Y.; Veelken, C.; Yilmaz, Y.; Zabi, A.; Agram, J.-L.; Andrea, J.; Bloch, D.; Brom, J.-M.; Chabert, E. C.; Collard, C.; Conte, E.; Drouhin, F.; Fontaine, J.-C.; Gelé, D.; Goerlach, U.; Goetzmann, C.; Juillot, P.; Le Bihan, A.-C.; Van Hove, P.; Gadrat, S.; Beauceron, S.; Beaupere, N.; Boudoul, G.; Brochet, S.; Chasserat, J.; Chierici, R.; Contardo, D.; Depasse, P.; El Mamouni, H.; Fan, J.; Fay, J.; Gascon, S.; Gouzevitch, M.; Ille, B.; Kurca, T.; Lethuillier, M.; Mirabito, L.; Perries, S.; Ruiz Alvarez, J. D.; Sgandurra, L.; Sordini, V.; Vander Donckt, M.; Verdier, P.

2014-10-01

253

Boundary layer simulator improvement  

NASA Technical Reports Server (NTRS)

Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.

Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.

1989-01-01

254

A compilation of information and data on the Manson impact structure  

NASA Technical Reports Server (NTRS)

A problem for the impact hypothesis for the Cretaceous-Tertiary (K-T) mass extinction is the apparent absence of an identifiable impact site. The Manson Impact Structure is a candidate because it is the largest recognized in the U.S.; it is relatively close to the largest and most abundant shocked quartz grains found at the K-T boundary; and its age is indistinguishable from that of the K-T boundary based on paleontological evidence, fission track dates, and preliminary Ar-40/Ar-39 measurements. The region of northwest central Iowa containing the Manson Impact Structure is covered by Quaternary glacial deposits underlain by Phanerozoic sedimentary rocks (mostly flat-lying carbonates) and Proterozoic red clastic, metamorphic, volcanic, and plutonic rocks. In a circular area about 22 miles (35 km) in diameter around Manson, Iowa, this normal sequence is absent or disturbed and near the center of the disturbed area granitic basement rocks have been uplifted some 20,000 ft (6000m). Attention was drawn to Manson initially by the unusual quality of the groundwater there. Within the structure three roughly concentric zones of rock associations have been identified: (1) displaced strata; (2) completely disrupted strata, and igneous and metamorphic rocks. Manson was established as an impact structure based on its circular shape, its central uplift, and the presence of shocked quartz within the granitic central uplift. A gravity survey identified locations of low-density brecciated rocks and high-density uplifted crystalline rocks, but the outer boundary of the structure could not be established. Aeromagnetic and ground magnetic surveys showed locations and depths of shallowly buried crystalline rock and the locations of faults. A refraction seismic survey identified the crystalline central uplift, determined that the average elevation of bedrock is 70 ft (20 m) higher outside the structure than within, and was used to map the bedrock topography within the structure. A connection between the Manson impact and the K-T boundary may be established or refuted through study of the impact energy, the impact time, and composition of host rock, possible impactors, and impact melts.

Hartung, Jack B.; Anderson, Raymond R.

1988-01-01

255

Cartographic Boundary Files  

NSDL National Science Digital Library

The Cartographic Boundary Files Web site from the US Census Bureau contains "generalized extracts from the Census Bureau's TIGER geographic database for use in a Geographic Information System (GIS) or similar mapping systems." The files are mainly from the 2000 census and contain such things as Congressional Districts, School Districts, Urbanized Areas, and more. The Descriptions and Metadata link gives users an idea of what is contained in each file before downloading, and the Download Boundary Files link lists each file that can than be downloaded, all available in several formats.

2001-01-01

256

Grain Boundaries, Misorientation Distributions,  

E-print Network

in the transmission electron microscope. #12;Reading · Pages 3-25 of Sutton & Balluffi · Pages 307-346 of Howe. 3 #12://jolisfukyu.tokai-sc.jaea.go.jp/fukyu/tayu/ACT02E/06/0603.htm In most crystalline solids, a grain boundary is very thin (one/two atoms). Disorder

Rollett, Anthony D.

257

Mapping Plate Boundaries  

NSDL National Science Digital Library

This in-class exercise, profiled on the Starting Point website, is intended to have the students discover plate boundaries based on the uneven geographic occurrence of geologic hazards. The website details the learning goals, teaching notes and materials, and context for this activity. It offers an extensive list of links to additional resources and materials for lecture on geologic hazards and plate tectonics.

Johnson, Rurik

2009-11-12

258

2000 CENSUS BLOCK BOUNDARIES  

EPA Science Inventory

This data set is a polygon shapefile of the boundaries of Census Blocks in New England derived from U.S. Census Bureau 2000 TIGER/Line data. Numerous attributes pertaining to population are included. TIGER, TIGER/Line, and Census TIGER are registered trademarks of the Bureau o...

259

RCRA TSD BOUNDARIES  

EPA Science Inventory

This is a shapefile of RCRA Treatment, Storage, and Disposal facility boundaries developed by PRC Environmental Management, Inc (PRC) per a Work Assignment from the U.S. EPA under the Resource Conservation and Recovery Act (RCRA) Enforcement, Permitting, and Assistance (REPA) Con...

260

Interstellar Boundary Explorer Lithograph  

NSDL National Science Digital Library

This is a lithograph that outlines the major mission highlights of the Interstellar Boundary Explorer, or IBEX, mission, a Small Explorer Earth-orbiting spacecraft that is designed to map the distant boundary between the solar wind from our Sun and the interstellar medium, the material between the stars. Short educational activities are included on the back of the lithograph. Learners will use a ball to represent the Earth to investigate the concepts of size and scale in relation to the IBEX mission: the size of the Moon compared to Earth, the distance from the Earth to the Moon on the same scale, the distance to the farthest point in IBEX's orbit, and the distance to the Sun and the edge of the heliosphere, also on the same scale.

261

Boundary layer stability calculations  

NASA Technical Reports Server (NTRS)

In this paper numerical calculation of the spatial stability of disturbances in the parallel and nonparallel Blasius boundary layers is considered. Chebyshev polynomials are used for discretization. The problem with the boundary condition at infinity is overcome, and the resulting nonlinear matrix eigenvalue problem is attacked directly. The secondary eigenvalue problem for three-dimensional disturbances is shown to be uniformly stable, and particular solutions of this problem generated by the Orr-Sommerfeld equation are shown. A numerical solution of the nonparallel problem is considered using Chebyshev polynomials. The matrix equations are analyzed directly and the problem of uniqueness of the nonparallel correction is settled by careful application of the Fredholm alternative. Nonparallel corrections to the streamwise eigenfunction are shown.

Bridges, Thomas J.; Morris, Philip J.

1987-01-01

262

Boundary layer simulator improvement  

NASA Technical Reports Server (NTRS)

High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.

Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.

1984-01-01

263

Maritime boundaries and ocean resources  

SciTech Connect

International maritime boundaries have become a major issue in international politics with the increasing exploitation of maritime resources, including mineral extraction from the sea bed, and the associated exstention of territorial waters and zones of exclusive economic activity. This book examines this important international problem. It considers the growth in the exploration of marine resources. It examines particular boundary disputes in different parts of the world and discusses the implications for international law, international politics and maritime activity and management. Contents. Antarctic maritime boundary problems; the law of the sea and the mediterranean; historical geography and the world court line of delimitation across the Gulf of Maine; maritime boundary delimitation worldwide: the current state of play; technical delimitation problems in the Mediterranean Sea; offshore boundaries and mineral resources; maritime boundaries and the emerging regional bases of world ocean management; recent delimitation decisions and trends in international law; maritime boundary problems in the Barents Sea; local government boundaries in U.K. coastal areas.

Blake, G.

1987-01-01

264

Topology of the Future Chronological Boundary: Universality for Spacelike Boundaries  

E-print Network

A method is presented for imputing a topology for any chronological set, i.e., a set with a chronology relation, such as a spacetime or a spacetime with some sort of boundary. This topology is shown to have several good properties, such as replicating the manifold topology for a spacetime and replicating the expected topology for some simple examples of spacetime-with-boundary; it also allows for a complete categorical characterization, in topological categories, of the Future Causal Boundary construction of Geroch, Kronheimer, and Penrose, showing that construction to have a universal property for future-completing chronological sets with spacelike boundaries. Rigidity results are given for any reasonable future completion of a spacetime, in terms of the GKP boundary: In the imputed topology, any such boundary must be homeomorphic to the GKP boundary (if all points have indecomposable pasts) or to a topological quotient of a closely related boundary (if boundaries are spacelike). A large class of warped-product-type spacetimes with spacelike boundaries is examined, calculating the GKP and other possible boundaries, and showing that the imputed topology gives expected results; included among these are the Schwarzschild singularity and those Robertson-Walker singularities which are spacelike.

Steven G. Harris

1999-07-19

265

The Hale solar sector boundary  

NASA Technical Reports Server (NTRS)

A Hale solar sector boundary is defined as the half (Northern Hemisphere or Southern Hemisphere) of a sector boundary in which the change of sector magnetic field polarity is the same as the change of polarity from a preceding spot to a following spot. Above a Hale sector boundary the green corona has maximum brightness, while above a non-Hale boundary the green corona has a minimum brightness. The Hale portion of a photospheric sector boundary tends to have maximum magnetic field strength, while the non-Hale portion has minimum field strength.

Svalgaard, L.; Wilcox, J. M.

1976-01-01

266

A classification of ecological boundaries  

USGS Publications Warehouse

Ecologists use the term boundary to refer to a wide range of real and conceptual structures. Because imprecise terminology may impede the search for general patterns and theories about ecological boundaries, we present a classification of the attributes of ecological boundaries to aid in communication and theory development. Ecological boundaries may differ in their origin and maintenance, their spatial structure, their function, and their temporal dynamics. A classification system based on these attributes should help ecologists determine whether boundaries are truly comparable. This system can be applied when comparing empirical studies, comparing theories, and testing theoretical predictions against empirical results.

Strayer, D. L.; Power, M. E.; Fagan, W. F.; Pickett, S. T. A.; Belnap, J.

2003-01-01

267

Black holes without boundaries  

E-print Network

We discuss some of the drawbacks of using event horizons to define black holes and suggest ways in which black holes can be described without event horizons, using trapping horizons. We show that these trapping horizons give rise to thermodynamic behavior and possibly Hawking radiation too. This raises the issue of whether the event horizon or the trapping horizon should be seen as the true boundary of a black hole. This difference is important if we believe that quantum gravity will resolve the central singularity of the black hole and clarifies several of the issues associated with black hole thermodynamics and information loss.

Alex B. Nielsen

2008-09-10

268

The boundaries of convection  

NASA Astrophysics Data System (ADS)

Convection in the solid interiors of the Earthlike planets is generally described by the slow creeping flow of silicates. The high viscosity and low speeds allows for the simplification of the governing equations to those of the Stokes equations at infinite Prandtl number. Laboratory simulations of this type of flow are generally carried out with high Prandtl number fluids and at speeds that cause laminar flow without a significant influence of inertial effects. Within the high viscosity, infinite Prandtl number convective flow the boundaries of convection play a special role compared to low Prandtl number flow. This creates difficulties in the comparison with theoretical scaling laws that are derived for infinite media or infinite Prandtl number. We have carried out a detailed comparison between laboratory and numerical simulations of thermal plumes in a cavity. We focus on the influence of the boundaries and develop numerical approaches to mitigate their effects in an effort to compare the new results with existing scaling laws for the velocity and temperature in the plume conduit. We provide a comparison for isoviscous and temperature-dependent rheology and describe the possible role of inertial effects within laboratory experiments.

van Keken, P. E.; Davaille, A. B.; Vatteville, J.; Touitou, F.

2009-12-01

269

Nanoscale Boundary Lubrication Studies  

NASA Astrophysics Data System (ADS)

Boundary films are formed by physisorption, chemisorption, and chemical reaction. With physisorption, no exchange of electrons takes place between the molecules of the adsorbate and those of the adsorbant. The physisorption process typically involves van der Waals forces, which are relatively weak. In chemisorption, there is an actual sharing of electrons or electron interchange between the chemisorbed species and the solid surface. The solid surfaces bond very strongly to the adsorption species through covalent bonds. Chemically reacted films are formed by the chemical reaction of a solid surface with the environment. The physisorbed film can be either monomolecularly or polymolecularly thick. The chemisorbed films are monomolecular, but stoichiometric films formed by chemical reaction can have a large film thickness. In general, the stability and durability of surface films decrease in the following order: chemically reacted films, chemisorbed films, and physisorbed films. A good boundary lubricant should have a high degree of interaction between its molecules and the sliding surface. As a general rule, liquids are good lubricants when they are polar and, thus, able to grip solid surfaces (or be adsorbed). In this chapter, we focus on PFPEs. We first introduce details of the commonly used PFPE lubricants; then present a summary of nanodeformation, molecular conformation, and lubricant spreading studies; followed by an overview of nanotribological properties of polar and nonpolar PFPEs studied by atomic force microscopy (AFM) atomic force microscope (AFM) and some concluding remarks.

Bhushan, Bharat; Liu, Huiwen

270

Nanoscale Boundary Lubrication Studies  

NASA Astrophysics Data System (ADS)

Boundary films are formed by physisorption, chemisorption, and chemical reaction. With physisorption, no exchange of electrons takes place between the molecules of the adsorbate and those of the adsorbant. The physisorption process typically involves van der Waals forces, which are relatively weak. In chemisorption, there is an actual sharing of electrons or electron interchange between the chemisorbed species and the solid surface. The solid surfaces bond very strongly to the adsorption species through covalent bonds. Chemically reacted films are formed by the chemical reaction of a solid surface with the environment. The physisorbed film can be either monomolecularly or polymolecularly thick. The chemisorbed films are monomolecular, but stoichiometric films formed by chemical reaction can have a large film thickness. In general, the stability and durability of surface films decrease in the following order: chemically reacted films, chemisorbed films, and physisorbed films. A good boundary lubricant should have a high degree of interaction between its molecules and the sliding surface. As a general rule, liquids are good lubricants when they are polar and, thus, able to grip solid surfaces (or be adsorbed). In this chapter, we focus on perfluoropolyethers (PFPEs). We first introduce details of the commonly used PFPE lubricants; then present a summary of nanodeformation, molecular conformation, and lubricant spreading studies; followed by an overview of nanotribological properties of polar and nonpolar PFPEs studied by atomic force microscopy (AFM) and some concluding remarks.

Bhushan, Bharat; Liu, Huiwen

271

Solubility of Fullerenes C60 and C70 in Water  

Microsoft Academic Search

Fullerenes C(sub)60 and C(sub)70, the all-carbon molecules with closed-cage structures, have been found naturally in soot-rich clays and marls at the Cretaceous-Tertiary boundary. All were marine sediments which were permeated by water even after the consolidated rocks had become uplifted above sea level. Because of this, one would like to know the solubilities of C(sub)60 and C(sub)70 in water in

D. Heymann

1996-01-01

272

The Blake Nose Cretaceous-Paleogene (Florida atlantic margin, ODP Leg 171 B): An exemplar record of the Maastrichtian-Danian transition [Le Cre??tace??-Pale??oge??ne du Blake Nose (marge atlantique de la Floride, campagne ODP 171 B) : Un enregistrement exemplaire de la transition Maastrichtien-Danien  

USGS Publications Warehouse

During ODP Leg 171B, devoted to the analysis of the Blake Plateau margin in front of Florida, 16 holes have been drilled in 5 distinct sites. The sites have documented a sedimentary succession ranging in age from Aptian to Eocene. Emphasis has been put on critical periods, comprising the Paleocene-Eocene transition, the Cretaceous-Tertiary boundary which has been cored in excellent conditions, the middle Maastrichtian extinctions and the Albian anoxic episodes.

Bellier, J. -P.; Marca, S.; Norris, R. D.; Kroon, D.; Klaus, A.; Alexander, I. T.; Bardot, L. P.; Barker, C. E.; Blome, C. D.; Clarke, L. J.; Erbacher, J.; Faul, K. L.; Holmes, M. A.; Huber, B. T.; Katz, M. E.; Macleod, K. G.; Martinez-Ruiz, F. C.; Mita, I.; Nakai, M.; Ogg, J. G.; Pak, D. K.; Pletsch, T. K.; Self-Trail, J. M.; Shackleton, N. J.; Smit, J.; Ussler, III, W.; Watkins, D. K.; Widmark, J.; Wilson, P. A.

1997-01-01

273

Meteoric smoke fallout over the Holocene epoch revealed by iridium and platinum in Greenland ice  

Microsoft Academic Search

An iridium anomaly at the Cretaceous\\/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65million years ago. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate or the nanophase material of the vaporized impactor. But the fate of platinum-group elements (such as iridium) that regularly

Paolo Gabrielli; Carlo Barbante; John M. C. Plane; Anita Varga; Sungmin Hong; Giulio Cozzi; Vania Gaspari; Frédéric A. M. Planchon; Warren Cairns; Christophe Ferrari; Paul Crutzen; Paolo Cescon; Claude F. Boutron

2004-01-01

274

Current status of the impact theory for the terminal Cretaceous extinction  

Microsoft Academic Search

Iridium is depleted in the earth's crust relative to its normal solar system abundance. Several hundred measurements by at least seven laboratories have disclosed an iridium abundance anomaly at the Cretaceous-Tertiary (C-T) boundary in 36 sites worldwide. Discovery of the first iridium anomaly in non-marine sediments, by Charles Orth and his colleagues, shows that the iridium was not extracted from

W. Alvarez; L. W. Alvarez; F. Asaro; H. V. Michel

1982-01-01

275

40K– 40Ar dating of the Main Deccan large igneous province: Further evidence of KTB age and short duration  

Microsoft Academic Search

Most mass extinctions coincide in time with outpourings of continental flood basalts (CFB). Some 20 years ago, it was shown [Courtillot, V., Besse, J., Vandamme, D., Montigny, R., Jaeger, J.-J., Cappetta, H., 1986. Deccan flood basalts at the Cretaceous\\/Tertiary boundary? Earth Planet. Sci. Lett. 80, 361–374; Courtillot, V., Feraud, G., Maluski, H., Vandamme, D., Moreau, M.G., Besse, J., 1988. Deccan flood

Anne-Lise Chenet; Xavier Quidelleur; Frédéric Fluteau; Vincent Courtillot; Sunil Bajpai

2007-01-01

276

Inverse boundary value problems with unknown boundaries: Optimal stability  

NASA Astrophysics Data System (ADS)

In this paper we obtain essentially best possible stability estimates for a class of inverse problems associated to elliptic boundary value problems in which the role of the unknown is played by an inaccessible part of the boundary and the role of the data is played by overdetermined boundary data for the elliptic equation assigned on the remaining, accessible, part of the boundary. We treat the case of arbitrary space dimension n?2 . Such problems arise in applied contexts of nondestructive testing of materials for either electric or thermal conductors, and are known to be ill-posed.

Alessandrini, Giovanni; Beretta, Elena; Rosset, Edi; Vessella, Sergio

277

Boundary layer transition studies  

NASA Technical Reports Server (NTRS)

A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated holes in the impervious test plate that used to establish the Blasius base flow. The suction is perturbed harmonically and data are averaged on the basis of the phase of the disturbance, for conditions corresponding to strong suction and without suction. The technique was enhanced by using up to nine multiple probes to reduce the experimental run-time. In both cases, 3D contour surfaces in the vicinity of the hole show highly 3D TS waves which fan out in the spanwise direction forming bow-shaped waves downstream. The case without suction has proved useful for evaluating calculation methods. With suction, the perturbations on the centerline are much stronger and decay less rapidly, while the TS waves in the far field are similar to the case without suction. Downstream, the contour surfaces of the TS waves develop spanwise irregularities which eventually form into clumps. The spanwise clumping is evidence of a secondary instability that could be associated with suction vortices. Designers of porous surfaces use Goldsmith's Criterion to minimize cross-stream interactions. It is shown that partial TS wave cancellation is possible, depending on the hole spacing, disturbance frequency and free-stream velocity. New high-performance Constant Temperature Hot-Wire Anemometers were designed and built, based on a linear system theory analysis that can be extended to arbitrary order. The motivation was to achieve the highest possible frequency reponse while ensuring overall system stability. The performance is equal to or superior to commercially available instruments at about 10% of the cost. Details, such as fabrication drawings and a parts list, have been published to enable the instrument to be construced by others.

Watmuff, Jonathan H.

1995-01-01

278

Boundary layer transition studies  

NASA Astrophysics Data System (ADS)

A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated holes in the impervious test plate that used to establish the Blasius base flow. The suction is perturbed harmonically and data are averaged on the basis of the phase of the disturbance, for conditions corresponding to strong suction and without suction.

Watmuff, Jonathan H.

1995-02-01

279

Below the Curie temperature Tc of a Heusler-alloy film, consisting of densely packed, but exchange- decoupled nanograins, the spontaneous magnetization Ms(T) and static in-plane susceptibility ?k (T) increase very slowly signalizing a suppression of magnetization fluctuations. The unpredicted vari  

Microsoft Academic Search

ation ?k (T) ? G 2 d(T), where Gd ? M 2 s is the intergranular dipolar coupling, and also the magnetic freezing observed in the dynamic susceptibility at lower temperatures is quantitatively reproduced by Monte Carlo (MC) simulations with 104 dipolar-coupled moments on a disordered triangular lattice. At high temperatures, the MC spin configurations clearly reveal a dense gas

Jurgen Kotzler; Detlef Gorlitz; Elena Y. Vedmedenko

280

Modeling the urban boundary layer  

NASA Technical Reports Server (NTRS)

A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and boundary problems, (5) nocturnal boundary layer, and (6) verification of models.

Bergstrom, R. W., Jr.

1976-01-01

281

Meteors and Meteorites  

NSDL National Science Digital Library

This resource covers meteors; meteor showers, such as Leonids; the relationship between meteor showers and comets; fireballs; classification of meteorites into chondrite, iron and carbonaceous chondrite meteorites; and meteorite impacts, including their velocities. There is information on a meteorite that may have come from the asteroid Vesta; a Mars meteorite that may hold evidence of life; the relation between the Cretaceous-Tertiary mass extinction (commonly known as the K-T Event), the Chicxulub crater in the Yucatan region of Mexico, and dinosaur extinction; and antarctic meteorites. There is also a video clip of the Peekskill fireball of 1992, and a photograph of the Barringer Crater of Arizona.

2007-06-05

282

Symbolic Boundary Work in Schools: Demarcating and Denying Ethnic Boundaries  

ERIC Educational Resources Information Center

This article examines the symbolic boundary work that is carried out at a school whose student population is heterogeneous in terms of ethnicity and class. Based on ethnography, the article demonstrates how the school's staff seeks to neutralize ethnic boundaries and their accompanying discourse, while the pupils try to bring ethnic…

Tabib-Calif, Yosepha; Lomsky-Feder, Edna

2014-01-01

283

Biodiversity during the Deccan volcanic eruptive episode  

NASA Astrophysics Data System (ADS)

This paper gives a detailed overview of biotic assemblages recovered from the Deccan trap intercalated sedimentary sequences (infra- and intertrappean beds) of peninsular India as a result of extensive research done during the last 20 years. The infra- and intertrappean beds contain remnants of Gondwanan forms such as myobatrachinae frogs, pelomedusid turtles, dinosaurs (i.e. titanosaurids and abelisaurids), and mammals. Apart from these Gondwanan elements, the infra- and intertrappean beds also contain forms of Laurasian affinity though recently doubt has been cast on such relationships. Based on previous fossil records, Laurasiatic forms were considered to be represented by a great variety of micro- and megavertebrate assemblages such as discoglossid and pelobatid frogs, anguid lizards, alligatorid crocodiles, palaeoryctid mammals, charophytes and ostracodes. The biotic assemblages show a remarkable similarity between the infra- and intertrappean beds indicating a short time period for the deposition of these Deccan volcano-sedimentary beds. The recovered biotic assemblages strongly indicate a Maastrichtian age for the initiation of Deccan volcanic activity and the sedimentary beds associated with it. The Cretaceous/Tertiary boundary as such remains to be defined in any known sections in sedimentary sequences in so far investigated localities of peninsular India. What have been identified are Maastrichtian age beds in the east-central and western Narmada river region on the basis of pollens, vertebrate assemblage and planktonic foraminiferas in infratrappean offshore sequences. A Palaeocene intertrappean bed at Lalitpur (Uttar Pradesh) that is among those lacking dinosaurian remains but having palynological assemblages similar to those from well established Palaeocene sequences, suggests the presence of Palaeocene intertrappeans, but the K/T boundary is yet to be properly defined.

Khosla, A.; Sahni, A.

2003-06-01

284

Boundary elements and nuclear organization  

Microsoft Academic Search

Functional compartmentalization of eukaryotic genomes is thought to be necessary for the proper regulation of gene expression. Chromatin insulators or boundary elements have been implicated in the establishment of this compartmentalization, as they may be involved in creating independent chromatin domains. Recent advances in understanding the mechanisms of insulator function suggest a role for boundary elements in determining transcriptional identity

Maya Capelson; Victor G. Corces

2004-01-01

285

Cell boundary fault detection system  

DOEpatents

An apparatus and program product determine a nodal fault along the boundary, or face, of a computing cell. Nodes on adjacent cell boundaries communicate with each other, and the communications are analyzed to determine if a node or connection is faulty.

Archer, Charles Jens (Rochester, MN); Pinnow, Kurt Walter (Rochester, MN); Ratterman, Joseph D. (Rochester, MN); Smith, Brian Edward (Rochester, MN)

2011-04-19

286

The Lithosphere-Asthenosphere Boundary  

E-print Network

The Lithosphere- Asthenosphere Boundary Karen M. Fischer,1 Heather A. Ford,1 David L. Abt,1 lithosphere that corresponds to a dry, chemically depleted layer over a hydrated, fertile asthenosphere. At the lithosphere-asthenosphere boundary beneath oceans and many Phanerozoic continental regions, ob- served seismic

Jellinek, Mark

287

Fractal Boundaries of Complex Networks  

E-print Network

We introduce the concept of boundaries of a complex network as the set of nodes at distance larger than the mean distance from a given node in the network. We study the statistical properties of the boundaries nodes of complex networks. We find that for both Erd\\"{o}s-R\\'{e}nyi and scale-free model networks, as well as for several real networks, the boundaries have fractal properties. In particular, the number of boundaries nodes {\\it B} follows a power-law probability density function which scales as $B^{-2}$. The clusters formed by the boundary nodes are fractals with a fractal dimension $d_{f} \\approx 2$. We present analytical and numerical evidence supporting these results for a broad class of networks. Our findings imply potential applications for epidemic spreading.

Jia Shao; Sergey V. Buldyrev; Reuven Cohen; Maksim Kitsak; Shlomo Havlin; H. Eugene Stanley

2008-04-11

288

Boundary control of scattering  

NASA Astrophysics Data System (ADS)

The essence of the acoustic scattering problem is to determine the acoustic fields that result from the presence of a body (scatterer) in a known ensonification field. The scattering problem is formulated as a constrained optimization problem solving for that surface admittance which minimizes radiated energy in a restricted subset of farfield directions. The imposed constraints are that the total field must satisfy the admittance boundary condition at the scatterer's surface, and the scattered field must satisfy both the Helmholtz equation and the radiation condition in the region exterior to the scatterer. For a specified surface admittance distribution, approximate solutions for the scattering problem are obtained by applying the discrete form of the axisymmetric Helmholtz integral representation coupled with a piecewise constant collocation scheme. Nonlinear minimization techniques are then used to find the admittance distribution that minimizes the scattered energy in a selected farfield angular sector. For this investigation, the scattering bodies are rotational ellipsoids and the surface admittance is both complex and axisymmetric. The ensonification field is a packet of plane waves containing a few sinusoidal waves with different frequencies or with a few directions of incidence. Three factors are found to directly affect optimization calculations for the acoustic fields that result from the scatterer's presence. First is the farfield sector over which minimization is desired. Second is the constraint imposed on the admittance distribution. The third factor is the convergence domain for the solutions to the direct scattering problem. The numerical simulations demonstrate that the Helmholtz integral representation coupled with nonlinear minimization techniques yield useful solutions. Further, the approach and numerical techniques provide credible estimates of optimal admittance distributions and the scattered fields over a range of spatial and geometric arrangements.

Bazow, Terence John

289

Vacuum Structure and Boundary Renormalization Group  

E-print Network

The vacuum structure is probed by boundary conditions. The behaviour of thermodynamical quantities like free energy, boundary entropy and entanglement entropy under the boundary renormalization group flow are analysed in 2D conformal field theories. The results show that whereas vacuum energy and boundary entropy turn out to be very sensitive to boundary conditions, the vacuum entanglement entropy is independent of boundary properties when the boundary of the entanglement domain does not overlap the boundary of the physical space. In all cases the second law of thermodynamics holds along the boundary renormalization group flow.

M. Asorey; J. M. Munoz-Castaneda

2007-12-28

290

Tracking Dynamic Boundaries Using Sensor Network  

Microsoft Academic Search

We examine the problem of tracking dynamic boundaries occurring in natural phenomena using a network of range sensors. Two main challenges of the boundary tracking problem are accurate boundary estimation from noisy observations and continuous tracking of the boundary. We propose Dynamic Boundary Tracking (DBTR), an algorithm that combines the spatial estimation and temporal estimation techniques. The regression-based spatial estimation

Subhasri Duttagupta; Krithi Ramamritham; Purushottam Kulkarni

2011-01-01

291

Optimal Transpiration Boundary Control for Aeroacoustics  

E-print Network

Optimal Transpiration Boundary Control for Aeroacoustics S. Scott Collis, Kaveh Ghayour transpiration boundary control of aeroacoustic noise in- troduces challenges beyond those encountered in direct of transpiration boundary conditions. Since we allow suction and blowing on the boundary, portions of the boundary

Heinkenschloss, Matthias

292

Orthogonal Boundary-Layer Flows  

NASA Astrophysics Data System (ADS)

A theoretical study is made for boundary-layer flows of different strengths intersecting each other at right angles. Analytic solutions are found for orthogonally interesecting Bickley jets, wall jets, wakes, and uniform shear flows. The equations for intersecting Blasius boundary layers and mixing layers are found and solved numerically. In all cases the development of the boundary-layer thickness for flow in the x-z plane is proportional to a fractional power of (x + z). Extensions of the work are envisioned to include plate transpiration and stretching for the wall-bounded flows.

Weidman, Patrick

2011-11-01

293

Cloud Boundaries During FIRE 2.  

National Technical Information Service (NTIS)

To our knowledge, previous observations of cloud boundaries have been limited to studies of cloud bases with ceilometers, cloud tops with satellites, and intermittent reports by aircraft pilots. Comprehensive studies that simultaneously record information...

T. Uttal, S. M. Shaver, E. E. Clothiaux, T. P. Ackerman

1993-01-01

294

Boundary Layer Control on Airfoils.  

ERIC Educational Resources Information Center

A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)

Gerhab, George; Eastlake, Charles

1991-01-01

295

Boundary conditions for quadrupolar metamaterials  

NASA Astrophysics Data System (ADS)

One of the long-standing problems in effective medium theories is using the knowledge of the bulk material response to predict the behavior of the electromagnetic fields at the material boundaries. Here, using a first principles approach, we derive the boundary conditions satisfied by the macroscopic fields at interfaces between reciprocal metamaterials with a quadrupolar-type response. Our analysis reveals that in addition to the usual Maxwellian-type boundary conditions for the tangential fields, in general—to ensure the conservation of the power flow and Lorentz reciprocity—it is necessary to enforce an additional boundary condition (ABC) at an interface between a quadrupolar material and a standard dielectric. It is shown that the ABC is related to the emergence of an additional wave in the bulk quadrupolar medium.

Silveirinha, Mário G.

2014-08-01

296

Finding Cadences through Boundary Entropy  

E-print Network

transcribed chord collections in RDF · Beatles Transcriptions all studio albums, 180 songs (Harte et al., 2005 to their entropy value. Highest ranking boundary entropy 3-grams over 180 Beatles songs (possible functional

Mauch, Matthias

297

no)boundaries Interdisciplinary Student Conference  

E-print Network

no)boundaries Interdisciplinary Student Conference 2012 Preliminary Conference Program March 31)Boundaries no)Boundaries is an annual interdisciplinary conference organized by the graduate students for student scholars (graduate and undergraduate) from across departments, disciplines, and universities

Giles, C. Lee

298

Boundary Condition for Modeling Semiconductor Nanostructures  

NASA Technical Reports Server (NTRS)

A recently proposed boundary condition for atomistic computational modeling of semiconductor nanostructures (particularly, quantum dots) is an improved alternative to two prior such boundary conditions. As explained, this boundary condition helps to reduce the amount of computation while maintaining accuracy.

Lee, Seungwon; Oyafuso, Fabiano; von Allmen, Paul; Klimeck, Gerhard

2006-01-01

299

Boundary characterization experiment series overview  

Microsoft Academic Search

Ocean acoustic propagation and reverberation in continental shelf regions is often controlled by the seabed and sea surface boundaries. A series of three multi-national and multi-disciplinary experiments was conducted between 2000-2002 to identify and measure key ocean boundary characteristics. The frequency range of interest was nominally 500-5000 Hz with the main focus on the seabed, which is generally considered as

Charles W. Holland; Roger C. Gauss; Paul C. Hines; Peter Nielsen; John R. Preston; Chris H. Harrison; Dale D. Ellis; Kevin D. LePage; John Osler; Redwood W. Nero; Dan Hutt; Altan Turgut

2005-01-01

300

Thermal boundaries analysis program document  

NASA Technical Reports Server (NTRS)

The digital program TBAP has been developed to provide thermal boundaries in the DD/M-relative velocity (D-V), dynamic pressure-relative velocity (q-V), and altitude-relative velocity (h-V) planes. These thermal boundaries are used to design and/or analyze shuttle orbiter entry trajectories. The TBAP has been used extensively in supporting the Flight Performance Branch of NASA in evaluating candidate trajectories for the thermal protection system design trajectory.

Evans, M. E.

1975-01-01

301

Near boundary flow over a two-dimensional waving boundary  

NASA Astrophysics Data System (ADS)

Results are presented from an experimental investigation into the hydrodynamic features of the unsteady near-boundary flow over an undulating mat. Experiments are performed in a recirculating water tunnel using Digital Particle Image Velocimetry (DPIV) and Laser Doppler Velocimetry (LDV) at Reynolds numbers up to 10^7. Like the fish body motion, a wave traveling down a flat plate produces an undulating motion that will affect the fluid near the plate boundary. In this near boundary region the evolution of turbulence is especially interesting as the boundary motion has been shown to result in suppression of turbulent structures. Taneda and Tomonari (1974) investigated the flow around a flexible waving mat, revealing a unique effect as the wave phase speed increased beyond the free stream velocity. It was observed that the flow began to relaminarize at the crests, and then eventually over the entire mat (troughs and crests), as the phase speed approached and then exceeded the velocity of the free stream. This result has an interesting correlation to a swimming fish, since the motion of its body is essentially that of a traveling wave. However, the waving plate offers a controlled experimental setting to further study the effects of an undulating motion on a boundary layer and the opportunity to draw a parallel with the hydrodynamics of swimming fish. Flow visualization results obtained from a study of the MIT RoboTuna will also be presented to illuminate similarities and differences between these two problems.

Techet, Alexandra H.; Triantafyllou, Michael S.

1999-11-01

302

Squirmer dynamics near a boundary.  

PubMed

The boundary behavior of axisymmetric microswimming squirmers is theoretically explored within an inertialess Newtonian fluid for a no-slip interface and also a free surface in the small capillary number limit, preventing leading-order surface deformation. Such squirmers are commonly presented as abridged models of ciliates, colonial algae, and Janus particles and we investigate the case of low-mode axisymmetric tangential surface deformations with, in addition, the consideration of a rotlet dipole to represent torque-motor swimmers such as flagellated bacteria. The resulting boundary dynamics reduces to a phase plane in the angle of attack and distance from the boundary, with a simplifying time-reversal duality. Stable swimming adjacent to a no-slip boundary is demonstrated via the presence of stable fixed points and, more generally, all types of fixed points as well as stable and unstable limit cycles occur adjacent to a no-slip boundary with variations in the tangential deformations. Nonetheless, there are constraints on swimmer behavior-for instance, swimmers characterized as pushers are never observed to exhibit stable limit cycles. All such generalities for no-slip boundaries are consistent with observations and more geometrically faithful simulations to date, suggesting the tangential squirmer is a relatively simple framework to enable predications and classifications for the complexities associated with axisymmetric boundary swimming. However, in the presence of a free surface, with asymptotically small capillary number, and thus negligible leading-order surface deformation, no stable surface swimming is predicted across the parameter space considered. While this is in contrast to experimental observations, for example, the free-surface accumulation of sterlet sperm, extensive surfactants are present, most likely invalidating the low capillary number assumption. In turn, this suggests the necessity of surface deformation for stable free-surface three-dimensional finite-size microswimming, as previously highlighted in a two-dimensional mathematical study of singularity swimmers [Crowdy et al., J. Fluid Mech. 681, 24 (2011)]. PMID:24483481

Ishimoto, Kenta; Gaffney, Eamonn A

2013-12-01

303

Calculation of State Specific Rate Coefficients for Non-Equilibrium Hypersonics Applications: from H(Psi) = E(Psi) to k(T) = A *exp(-E(sub a)/RT)  

NASA Technical Reports Server (NTRS)

Development of High-Fidelity Physics-Based Models to describe hypersonic flight through the atmospheres of Earth and Mars is underway at NASA Ames Research Center. The goal is to construct chemistry models of the collisional and radiative processes that occur in the bow shock and boundary layers of spacecraft during atmospheric entry that are free of empiricism. In this talk I will discuss our philosophy and describe some of our progress. Topics to be covered include thermochemistry, internal energy relaxation, collisional dissociation and radiative emission and absorption. For this work we start by solving the Schrodinger equation to obtain accurate interaction potentials and radiative properties. Then we invoke classical mechanics to compute state-specific heavy particle collision cross sections and reaction rate coefficients. Finally, phenomenological rate coefficients and relaxation times are determined from master equation solutions.

Jaffe, Richard; Schwenke, David; Chaban, Galina; Panesi, Marco

2014-01-01

304

Undulatory microswimming near solid boundaries  

NASA Astrophysics Data System (ADS)

The hydrodynamic forces involved in the undulatory microswimming of the model organism C. elegans are studied in proximity to solid boundaries. Using a micropipette deflection technique, we attain direct and time-resolved force measurements of the viscous forces acting on the worm near a single planar boundary as well as confined between two planar boundaries. We observe a monotonic increase in the lateral and propulsive forces with increasing proximity to the solid interface. We determine normal and tangential drag coefficients for the worm, and find these to increase with confinement. The measured drag coefficients are compared to existing theoretical models. The ratio of normal to tangential drag coefficients is found to assume a constant value of 1.5 ± 0.1(5) at all distances from a single boundary, but increases significantly as the worm is confined between two boundaries. In response to the increased drag due to confinement, we observe a gait modulation of the nematode, which is primarily characterized by a decrease in the swimming amplitude.

Schulman, R. D.; Backholm, M.; Ryu, W. S.; Dalnoki-Veress, K.

2014-10-01

305

Physics of magnetospheric boundary layers  

NASA Technical Reports Server (NTRS)

This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.

Cairns, Iver H.

1995-01-01

306

Unsteady turbulent boundary layer analysis  

NASA Technical Reports Server (NTRS)

The governing equations for an unsteady turbulent boundary layer on a swept infinite cylinder, composed of a continuity equation, a pair of momentum equations and a pair of turbulent energy equations which include upstream history efforts, are solved numerically. An explicit finite difference analog to the partial differential equations is formulated and developed into a computer program. Calculations were made for a variety of unsteady flows in both two and three dimensions but primarily for two dimensional flow fields in order to first understand some of the fundamental physical aspects of unsteady turbulent boundary layers. Oscillating free stream flows without pressure gradient, oscillating retarded free stream flows and monotonically time-varying flows have all been studied for a wide frequency range. It was found that to the lowest frequency considered, the lower frequency bound being determined by economic considerations (machine time), there were significant unsteady effects on the turbulent boundary layer.

Singleton, R. E.; Nash, J. F.; Carl, L. W.; Patel, V. C.

1973-01-01

307

Distributed Boundary Estimation using Sensor Networks  

Microsoft Academic Search

We examine the problem of determining boundaries occurring in natural phenomena using sensor networks. Sensor nodes remotely collect data about various points on the boundary. From this data, we estimate the boundary along with the confidence intervals using a regression relationship among sensor locations and the distances to the boundary. The confidence intervals are guaranteed to be narrower than a

Subhasri Duttagupta; Krithi Ramamritham; Parmesh Ramanathan

2006-01-01

308

Boundary Learning by Optimization with Topological Constraints  

Microsoft Academic Search

Recent studies have shown that machine learning can improve the accuracy of detecting object boundaries in images. In the standard approach, a boundary detector is trained by minimizing its pixel-level disagreement with human boundary tracings. This naive metric is problematic because it is overly sensitive to boundary locations. This problem is solved by metrics provided with the Berkeley Segmentation Dataset,

Viren Jain; Benjamin Bollmann; Mark Richardson; Daniel R. Berger; Moritz N. Helmstaedter; Kevin L. Briggman; Winfried Denk; Jared B. Bowden; John M. Mendenhall; Wickliffe C. Abraham; Kristen M. Harris; Narayanan Kasthuri; Ken J. Hayworth; Richard Schalek; Juan Carlos Tapia; Jeff W. Lichtman; H. Sebastian Seung

2010-01-01

309

Ego Boundary Disturbance in Juvenile Anorexia Nervosa.  

ERIC Educational Resources Information Center

Anorexics were compared to female depressed controls to measure boundary impairment. Anorexics scored higher on inner-outer and conceptual boundary disturbance and produced significantly more responses that emphasized the solidity of object boundaries. Boundary scores were unrelated to degree of weight loss and global symptom severity. (Author)

Strober, Michael; Goldenberg, Irene

1981-01-01

310

The Shaping of Communication across Boundaries  

ERIC Educational Resources Information Center

This article will consider the formative effect of boundaries between activities in directing and deflecting the attention of actors who are seeking to develop innovatory practice at these boundaries. Specific attention will be directed to practices of communication at these boundaries and also to the way in which these boundaries shape the…

Daniels, Harry

2011-01-01

311

BRST Invariant Boundary Conditions for Gauge Theories  

E-print Network

A systematic way of generating sets of local boundary conditions on the gauge fields in a path integral is presented. These boundary conditions are suitable for one--loop effective action calculations on manifolds with boundary and for quantum cosmology. For linearised gravity, the general proceedure described here leads to new sets of boundary conditions.

Ian G. Moss; Pedro J. Silva

1996-10-14

312

Boundary value methods for PDEs  

SciTech Connect

Many existing numerical schemes for the solution of partial differential equations c .an be derived by the method of lines. The PDEs are converted into a system of ordinary differential equations with initial conditions (longitudinal scheme) or boundary conditions (transverse scheme). This system may be stiff or singularly perturbed; then, a numerical method with a large stability region must be used for solving the resulting ODEs. This paper studies the behavior of a class of Boundary Value Methods when applied to partial differential equations discretized with both the longitudinal and the transversal scheme. Some numerical experiments illustrate that the performance of BVMs is the same for both schemes.

Mazzia, A. [IRMA, Bari (Italy); Mazzia, F. [Universita degli Studi di Bari (Italy); Trigiante, D. [Universita degli Studi di Firenze (Italy)

1994-12-31

313

Anomalous Diffusion with Absorbing Boundary  

E-print Network

In a very long Gaussian polymer on time scales shorter that the maximal relaxation time, the mean squared distance travelled by a tagged monomer grows as ~t^{1/2}. We analyze such sub-diffusive behavior in the presence of one or two absorbing boundaries and demonstrate the differences between this process and the sub-diffusion described by the fractional Fokker-Planck equation. In particular, we show that the mean absorption time of diffuser between two absorbing boundaries is finite. Our results restrict the form of the effective dispersion equation that may describe such sub-diffusive processes.

Yacov Kantor; Mehran Kardar

2007-10-31

314

Grain boundaries in complex oxides  

SciTech Connect

A quantitative comparison was achieved between space charge theory and segregation at grain boundaries in the model system TiO[sub 2]. The ionic space charge can be titrated from negative to positive potential. A space charge model was developed that includes the lattice defect chemistry. Defect formation energies in the Frenkel pair for TiO[sub 2] were studied. Grain boundary enthalpy was measured during coarsening. It was shown that it is the barium vacancy that forms near surfaces in donor-doped BaTiO[sub 3] electroceramics during oxidative-cooling.

Chiang, Yet-Ming.

1993-05-01

315

Microphysics of Low-Frequency Attenuation: Grain Boundaries, Heterophase Boundaries, Subgrain Boundaries, Spatiotemporal Scaling (Invited)  

NASA Astrophysics Data System (ADS)

The dynamical mechanical response of polycrystalline materials is effected by lattice defects: point defects, dislocations, subgrain boundaries, grain and heterophase boundaries—and larger-length-scale structures (e.g., groups or “rafts” of grains or of subgrains). That the response is temperature- and frequency-dependent indicates that an understanding of spatial scaling of these defects is critical in interpreting—and extrapolating—experimental results. We have engaged in an experimental effort to tease apart the effects of various defects on low-frequency attenuation. The power-law attenuation response (QG-1~f -m; m~0.3-0.5), described as the “high-temperature background” and characteristic, e.g., of Earth’s upper mantle, need not represent a distribution of grain sizes, as is often taught, but can represent different spatiotemporal scales of relaxation within a uniform microstructure. This presentation outlines various experimental studies we and others have undertaken—grain and heterophase boundary effects in peridotite and in ice/salt-hydrate eutectics; grain boundary and dislocation effects in ice; subgrain boundary effects in an intermetallic—and scrutinizes them relative to non-equilibrium thermodynamics and to Edward Hart’s state-variable model of inelastic deformation.

Cooper, R. F.; Sundberg, M. I.; McCarthy, C.

2009-12-01

316

AC conductivity scaling behavior in grain and grain boundary response regime of fast lithium ionic conductors  

NASA Astrophysics Data System (ADS)

AC conductivity spectra of Li-analogues NASICON-type Li1.5Al0.5Ge1.5P3O12 (LAGP), Li-Al-Ti-P-O (LATP) glass-ceramics and garnet-type Li7La2Ta2O13 (LLTO) ceramic are analyzed by universal power law and Summerfield scaling approaches. The activation energies and pre-exponential factors of total and grain conductivities are following the Meyer-Neldel (M-N) rule for NASICON-type materials. However, the garnet-type LLTO material deviates from the M-N rule line of NASICON-type materials. The frequency- and temperature-dependent conductivity spectra of LAGP and LLTO are superimposed by Summerfield scaling. The scaled conductivity curves of LATP are not superimposed at the grain boundary response region. The superimposed conductivity curves are observed at cross-over frequencies of grain boundary response region for LATP by incorporating the exp ( {{{ - (EAt - EAg )} {{{ - (EAt - EAg )} {kT}}} ) factor along with Summerfield scaling factors on the frequency axis, where EAt and EAg are the activation energies of total and grain conductivities, respectively.

Mariappan, C. R.

2014-05-01

317

Boundary correlation functions of integrable vertex models  

NASA Astrophysics Data System (ADS)

We review our recent work on the boundary correlation functions of integrable vertex models on an N × N lattice with domain wall boundary conditions. Particularly considered is the six vertex model. The general expression of the boundary correlation functions is obtained for the six vertex model by use of the quantum inverse scattering method. We also comment on the potential application of the boundary correlation functions, and the relation between the boundary correlation functions for the nineteen vertex model.

Motegi, Kohei

2012-02-01

318

Patients, friends, and relationship boundaries.  

PubMed Central

When patient and physician are close friends, both professional and personal relationships can suffer. Jointly exploring and setting explicit boundaries can help avoid conflict and maintain these valuable relationships. This is particularly important when the physician practises in a small community where such concurrent relationships are unavoidable. PMID:8292931

Rourke, J. T.; Smith, L. F.; Brown, J. B.

1993-01-01

319

BIRD STRIKE OUTSIDE AIRPORT BOUNDARIES  

Microsoft Academic Search

Most often, bird strike happens within airport area, i.e. inside strictly fenced and bounded area that is up to certain reasonable height under direct control and management of airport operator. However, it is known that bird strikes also happen outside airport boundaries, consequently in the area that is not under direct airport operator control. As serious threat to air traffic

Ante Matijaca

320

Science beyond the Classroom Boundaries  

ERIC Educational Resources Information Center

There have been many years of innovation in primary science education. Surprisingly, however, most of this has taken place within the confines of the classroom. What primary science has not yet done with universal success is step outside the classroom boundaries to use the school grounds for teaching and learning across all aspects of the science…

Feasey, Rosemary; Bianchi, Lynne

2011-01-01

321

Transgressing Boundaries through Learning Communities.  

ERIC Educational Resources Information Center

Cooperative education should adopt the learning communities model because (1) it situates learning in communities of inquirers who share meanings and ideas; (2) it related learning to experiences and the larger cultural context; and (3) it enables learning that has value and meaning. In co-op, learning communities help cross the boundaries between…

Howard, Adam; England-Kennedy, Elizabeth S.

2001-01-01

322

Suburb Boundaries and Residential Burglars  

Microsoft Academic Search

In examining home addresses of burglars and the addresses of their targets, this study found that burglars did not, as expected, work in their own neighbourhood. Most burglars (77%) travelled away from their home suburb to do their work, travelling an average of five kilometres to their target. There was no evidence that physical boundaries separating suburbs, such as carriageways

Jerry H. Ratcliffe; Adam Graycar

323

Pricing Options With Curved Boundaries  

Microsoft Academic Search

This paper provides a general valuation method for the European options whose payoff is restricted by curved boundaries contractually set on the underlying asset price process when it follows the geometric Brownian motion. Our result is based on the generalization of the Levy formula on the Brownian motion by T. W. Anderson in sequential analysis. We give the explicit probability

Naoto Kunitomo; Masayuki Ikeda

1992-01-01

324

HAWAII RCRA TSD FACILITY BOUNDARIES  

EPA Science Inventory

Polygon coverage of RCRA TSD facility boundaries in Hawaii. These are derived from original maps and descriptions located in the US EPA Region 9 Records Center files. Current TSD facility designations were extracted from the ARIS (RCRIS) database in June 1998. Auxiliary tables i...

325

Holographic duals of boundary CFTs  

NASA Astrophysics Data System (ADS)

New families of regular half-BPS solutions to 6-dimensional Type 4b supergravity with m tensor multiplets are constructed exactly. Their space-time consists of AdS 2 × S 2 warped over a Riemann surface with an arbitrary number of boundary components, and arbitrary genus. The solutions have an arbitrary number of asymptotic AdS 3 × S 3 regions. In addition to strictly single-valued solutions to the supergravity equations whose scalars live in the coset SO(5 , m) /SO(5) × SO( m), we also construct stringy solutions whose scalar fields are single-valued up to transformations under the U -duality group SO(5 , m; Z), and live in the coset SO(5 , m; Z)SO(5 , m) /SO(5) × SO( m). We argue that these Type 4b solutions are holographically dual to general classes of interface and boundary CFTs arising at the juncture of the end-points of 1+1-dimensional bulk CFTs. We evaluate their corresponding holographic entanglement and boundary entropy, and discuss their brane interpretation. We conjecture that the solutions for which ? has handles and multiple boundaries correspond to the near-horizon limit of half-BPS webs of dyonic strings and three-branes.

Chiodaroli, Marco; D'Hoker, Eric; Gutperle, Michael

2012-07-01

326

The seismotectonics of plate boundaries  

NASA Technical Reports Server (NTRS)

Research on the seismotectonics of plate boundaries is summarized. Instrumental development and an observational program designed to study various aspects of the seismotectonics of southern California and the northern Gulf of California are described. A unique superconducting gravimeter was further developed and supported under this program for deployment and operation at several sites. Work on Earth tides is also discussed.

Berger, J.; Brune, J. N.; Goodkind, J.; Wyatt, F.; Agnew, D. C.; Beaumont, C.

1981-01-01

327

The Double Absorbing Boundary method  

NASA Astrophysics Data System (ADS)

A new approach is devised for solving wave problems in unbounded domains. It has common features to each of two types of existing techniques: local high-order Absorbing Boundary Conditions (ABC) and Perfectly Matched Layers (PML). However, it is different from both and enjoys relative advantages with respect to both. The new method, called the Double Absorbing Boundary (DAB) method, is based on truncating the unbounded domain to produce a finite computational domain ?, and on applying a local high-order ABC on two parallel artificial boundaries, which are a small distance apart, and thus form a thin non-reflecting layer. Auxiliary variables are defined on the two boundaries and inside the layer bounded by them, and participate in the numerical scheme. The DAB method is first introduced in general terms, using the 2D scalar time-dependent wave equation as a model. Then it is applied to the 1D Klein-Gordon equation, using finite difference discretization in space and time, and to the 2D wave equation in a wave guide, using finite element discretization in space and dissipative time stepping. The computational aspects of the method are discussed, and numerical experiments demonstrate its performance.

Hagstrom, Thomas; Givoli, Dan; Rabinovich, Daniel; Bielak, Jacobo

2014-02-01

328

Five-parameter grain boundary distribution in grain boundary engineered brass  

E-print Network

Five-parameter grain boundary distribution in grain boundary engineered brass Chang-Soo Kim a , Yan of a five-parameter determination of grain boundary types to grain boundary engineered alpha- brass to a grain boundary engineered material, namely alpha-brass. 2. Experimental Specimens of alpha-brass

Rohrer, Gregory S.

329

The nonlinear boundary layer to the Boltzmann equation for cutoff soft potential with physical boundary condition  

Microsoft Academic Search

We consider the nonlinear boundary layer to the Boltzmann equation for cutoff soft potential with physical boundary condition, i.e., the Dirichlet boundary condition with weak diffuse effect. Under the assumption that the distribution function of gas particles tends to a global Maxwellian in the far field, we will show the boundary layer exist if the boundary data satisfy the solvability

Jie Sun; Qianzhu Tian

2011-01-01

330

Lagrangian Variational Framework for Boundary Value Problems  

E-print Network

A boundary value problem is commonly associated with constraints imposed on a system at its boundary. We advance here an alternative point of view treating the system as interacting "boundary" and "interior" subsystems. This view is implemented through a Lagrangian framework that allows to account for (i) a variety of forces including dissipative acting at the boundary; (ii) a multitude of features of interactions between the boundary and the interior fields when the boundary fields may differ from the boundary limit of the interior fields; (iii) detailed pictures of the energy distribution and its flow; (iv) linear and nonlinear effects. We provide a number of elucidating examples of the structured boundary and its interactions with the system interior. We also show that the proposed approach covers the well known boundary value problems.

Alexander Figotin; Guillermo Reyes

2014-07-22

331

SH Wave Scattering from Fractures using Boundary Element Method with Linear Slip Boundary Condition  

E-print Network

A boundary element method (BEM) combined with a linear slip boundary condition is proposed to calculate SH wave scattering from fractures. The linear slip boundary condition was proposed by Schoenberg (1980) to model elastic ...

Chen, Tianrun

2011-01-01

332

Cloud boundaries during FIRE 2  

NASA Technical Reports Server (NTRS)

To our knowledge, previous observations of cloud boundaries have been limited to studies of cloud bases with ceilometers, cloud tops with satellites, and intermittent reports by aircraft pilots. Comprehensive studies that simultaneously record information of cloud top and cloud base, especially in multiple layer cases, have been difficult, and require the use of active remote sensors with range-gated information. In this study, we examined a 4-week period during which the NOAA Wave Propagation Laboratory (WPL) 8-mm radar and the Pennsylvania State University (PSU) 3-mm radar operated quasi-continuously, side by side. By quasi-continuously, we mean that both radars operated during all periods when cloud was present, during both daytime and nighttime hours. Using this data, we develop a summary of cloud boundaries for the month of November for a single location in the mid-continental United States.

Uttal, Taneil; Shaver, Scott M.; Clothiaux, Eugene E.; Ackerman, Thomas P.

1993-01-01

333

Grain Boundary Cavitation in Molybdenum  

Microsoft Academic Search

THE formation of cavities at grain boundaries under creep conditions had been observed in many metals and may lead to intercrystalline failure1. We have observed such cavitation in molybdenum wires of 0.010 mm diam. heated by electron bombardment to temperatures between 1,500° and 2,500° C (that is, above 60 per cent of the absolute melting point) and strained a few

P. J. Bowles; G. A. Geach

1963-01-01

334

Continuous boundary local Fourier transform  

NASA Astrophysics Data System (ADS)

The Local Fourier Transform (LFT) provides a nice tool for concentrating both a signal and its Fourier transform. But there are certain properties of this algorithm that make it unattractive for various applications. In this paper, some of these disadvantages are explored, and a new approach to localized Fourier analysis is proposed, the continuous boundary local Fourier transform (CBLFT), which attempts to correct some of these shortcomings. Results ranging from segmentation to representation cost to compression are also presented.

Larson, Brons M.; Saito, Naoki

2001-12-01

335

Iridium and Spherules in Late Eocene Impact Deposits  

NASA Technical Reports Server (NTRS)

We have been independently examining the Ir (FTK) and spherule (SL) contents of recently discovered late Eocene impact deposits from the south Atlantic and western Indian oceans. These include ODP Sites 1090 [14,15], 709 [lo], and 699 [Liu in prep.]. Iridium abundances at these sites are within the typical range reported for late Eocene deposits, with peak concentrations between 100 and 1000 pg/g. In Table 1 we present estimated net Ir fluences (in ng Ir/cm ) for these and nine other sites. Although there are fewer sites than the K/T boundary, the average of 9 ng Ir/cm2 is probably a good estimate of the late Eocene global flux. This is enough Ir for a 6 km comet (assuming 250 ng/g Ir, p=1.5), is sufficient to produce the Popigai or Chesapeake Bay structures, and is 16% of the flux estimated for the K/T boundary (55 ng/cm2 [ 161). Figure 1 shows the relative abundances of Ir, glassy microtektites and cpx-bearing spherules in sediments from Sites 699 and 1090, which are separated by only 3100 km. Although these two sites have similar Ir anomalies, the abundances of spherules are quite different. Site 1090 has well-defined peaks for both types of spherules, with a peak of 562 cpx spheruledg, while Site 699 contains only a few glassy microtektites and no cpx spherules. While the different abundances of spherules may reflect a heterogeneous distribution of spherules on the Earth s surface, an equally likely cause of this difference may be differential preservation of spherules in the sediment. recovered are only a trace residue of the initial impact deposit. Earlier work found 0.22 ng/g Ir in glassy microtektites from Site 689 [17], an insufficient concentration to support 0.16 ng/g in the bulk sediment at this site. We measured 15 ng/g Ir in a group of 95 cpx spherules from Site 1090 with sizes from 63 to -200 pm, a set typical of the size distribution at this site. Although this is a significant concentration it also cannot support the Ir peak. We presently lack quantitative data on the mass concentration of cpx spherules in Site 1090 sediments, but it is certainly <1 mg/g in The impact record in the late Eocene is very different from that at the Cretaceous-Tertiary In contrast, the late Eocene probably experienced multiple impact events.

Kyte, F. T.; Liu, S.

2002-01-01

336

Boundary detection via dynamic programming  

NASA Astrophysics Data System (ADS)

This paper reports a new method for detecting optimal boundaries in multidimensional scene data via dynamic programming (DP). In its current form the algorithm detects 2-D contours on slices and differs from other reported DP-based algorithms in an essential way in that it allows freedom in 2-D for finding optimal contour paths (as opposed to a single degree of freedom in the published methods). The method is being successfully used in segmenting object boundaries in a variety of medical applications including orbital volume from CT images (for craniofacial surgical planning), segmenting bone in MR images for kinematic analysis of the joints of the foot, segmenting the surface of the brain from the inner surface of the cranial vault, segmenting pituitary gland tumor for following the effect of a drug on the tumor, segmenting the boundaries of the heart in MR images, and segmenting the olfactory bulb for verifying hypotheses related to the size of this bulb in certain disease states.

Udupa, Jayaram K.; Samarasekera, Supun; Barrett, William A.

1992-09-01

337

Tropical cyclone boundary layer shocks  

E-print Network

This paper presents numerical solutions and idealized analytical solutions of axisymmetric, $f$-plane models of the tropical cyclone boundary layer. In the numerical model, the boundary layer radial and tangential flow is forced by a specified pressure field, which can also be interpreted as a specified gradient balanced tangential wind field $v_{\\rm gr}(r)$ or vorticity field $\\zeta_{\\rm gr}(r)$. When the specified $\\zeta_{\\rm gr}(r)$ field is changed from one that is radially concentrated in the inner core to one that is radially spread, the quasi-steady-state boundary layer flow transitions from a single eyewall shock-like structure to a double eyewall shock-like structure. To better understand these structures, analytical solutions are presented for two simplified versions of the model. In the simplified analytical models, which do not include horizontal diffusion, the $u(\\partial u/\\partial r)$ term in the radial equation of motion and the $u[f+(\\partial v/\\partial r)+(v/r)]$ term in the tangential equat...

Slocum, Christopher J; Taft, Richard K; Schubert, Wayne H

2014-01-01

338

Beyond the no-slip boundary condition  

E-print Network

This paper offers a simple macroscopic approach to the question of the slip boundary condition to be imposed upon the tangential component of the fluid velocity at a solid boundary. Plausible reasons are advanced for ...

Brenner, Howard

339

Characterization of grain boundaries in silicon  

NASA Technical Reports Server (NTRS)

Zero-bias conductance and capacitance measurements at various temperatures were used to study trapped charges and potential barrier height at the boundaries. Deep-level transient spectroscopy (DLTS) was applied to measure the density of states at the boundary. A study of photoconductivity of grain boundaries in p-type silicon demonstrated the applicability of the technique in the measurement of minority carrier recombination velocity at the grain boundary. Enhanced diffusion of phosphorus at grain boundaries in three cast polycrystalline photovoltaic materials was studied. Enhancements for the three were the same, indicating that the properties of boundaries are similar, although grown by different techniques. Grain boundaries capable of enhancing the diffusion were found always to have strong recombination activities; the phenomena could be related to dangling bonds at the boundaries. Evidence that incoherent second-order twins of (111)/(115) type are diffusion-active is presented.

Cheng, L. J.; Shyu, C. M.; Stika, K. M.; Daud, T.; Crotty, G. T.

1983-01-01

340

ConcepTest: Divergent Boundary Sketch  

NSDL National Science Digital Library

The figure below was drawn by a student to show the relationship between earthquake epicenters (filled circles) and a divergent plate boundary (red line). The figure represents a boundary between two oceanic ...

341

15 CFR 922.90 - Boundary.  

Code of Federal Regulations, 2013 CFR

...SANCTUARY PROGRAM REGULATIONS Gray's Reef National Marine Sanctuary...922.90 Boundary. The Gray's Reef National Marine Sanctuary...square nautical miles of ocean waters and the submerged lands thereunder...Sanctuary boundary includes all waters and submerged lands...

2013-01-01

342

15 CFR 922.90 - Boundary.  

Code of Federal Regulations, 2010 CFR

...SANCTUARY PROGRAM REGULATIONS Gray's Reef National Marine Sanctuary...922.90 Boundary. The Gray's Reef National Marine Sanctuary...square nautical miles of ocean waters and the submerged lands thereunder...Sanctuary boundary includes all waters and submerged lands...

2010-01-01

343

15 CFR 922.90 - Boundary.  

Code of Federal Regulations, 2011 CFR

...SANCTUARY PROGRAM REGULATIONS Gray's Reef National Marine Sanctuary...922.90 Boundary. The Gray's Reef National Marine Sanctuary...square nautical miles of ocean waters and the submerged lands thereunder...Sanctuary boundary includes all waters and submerged lands...

2011-01-01

344

15 CFR 922.90 - Boundary.  

Code of Federal Regulations, 2012 CFR

...SANCTUARY PROGRAM REGULATIONS Gray's Reef National Marine Sanctuary...922.90 Boundary. The Gray's Reef National Marine Sanctuary...square nautical miles of ocean waters and the submerged lands thereunder...Sanctuary boundary includes all waters and submerged lands...

2012-01-01

345

50 CFR 600.105 - Intercouncil boundaries.  

Code of Federal Regulations, 2010 CFR

...c) South Atlantic and Gulf of Mexico Councils. The boundary coincides with the line of demarcation between the Atlantic Ocean and the Gulf of Mexico, which begins at the intersection of the outer boundary of the EEZ, as specified...

2010-10-01

346

50 CFR 600.105 - Intercouncil boundaries.  

Code of Federal Regulations, 2011 CFR

...c) South Atlantic and Gulf of Mexico Councils. The boundary coincides with the line of demarcation between the Atlantic Ocean and the Gulf of Mexico, which begins at the intersection of the outer boundary of the EEZ, as specified...

2011-10-01

347

Boundary element methods—An overview  

Microsoft Academic Search

Variational methods for boundary integral equations deal with the weak formulations of boundary integral equations. Their numerical discretizations are known as the boundary element methods. This paper gives an overview of the method from both theoretical and numerical point of view. It summarizes the main results obtained by the author and his collaborators over the last 30 years. Fundamental theory

George C. Hsiao

2006-01-01

348

Inverse Scattering on Matrices with Boundary Conditions  

E-print Network

We describe inverse scattering for the matrix Schroedinger operator with general selfadjoint boundary conditions at the origin using the Marchenko equation. Our approach allows the recovery of the potential as well as the boundary conditions. It is easily specialised to inverse scattering on star-shaped graphs with boundary conditions at the node.

M. Harmer

2007-02-21

349

Disturbance, Scale, and Boundary in Wilderness Management  

Microsoft Academic Search

Natural disturbances are critical to wilderness man- agement. This paper reviews recent research on natural distur- bance and addresses the problem of managing for disturbances in a world of human-imposed scales and boundaries. The dominant scale issue in disturbance management is the question of patch dynamic equilibrium. The dominant boundary issue in disturbance manage- ment is the effect of boundary

Peter S. White; Jonathan Harrod; Joan L. Walker; Anke Jentsch

2000-01-01

350

The Arabia-India plate boundary unveiled  

Microsoft Academic Search

Since the advent of Plate Tectonics, tectonic plate boundaries were explored on land as at sea for search of active faults where the destructive energy of earthquakes is released. Yet, some plate boundaries, less active or considered as less dangerous to humankind, escaped general attention and remained unknown to a large extent. Among them, the boundary between two major tectonic

M. Fournier; N. R. Chamot-Rooke; M. Rodriguez; C. Petit; P. Huchon; M. Beslier; B. Hazard

2009-01-01

351

Compressible turbulent boundary layer interaction experiments  

NASA Technical Reports Server (NTRS)

Four phases of research results are reported: (1) experiments on the compressible turbulent boundary layer flow in a streamwise corner; (2) the two dimensional (2D) interaction of incident shock waves with a compressible turbulent boundary layer; (3) three dimensional (3D) shock/boundary layer interactions; and (4) cooperative experiments at Princeton and numerical computations at NASA-Ames.

Settles, G. S.; Bogdonoff, S. M.

1981-01-01

352

Grain boundaries in high-Tc superconductors  

Microsoft Academic Search

Since the first days of high-Tc superconductivity, the materials science and the physics of grain boundaries in superconducting compounds have developed into fascinating fields of research. Unique electronic properties, different from those of the grain boundaries in conventional metallic superconductors, have made grain boundaries formed by high-Tc cuprates important tools for basic science. They are moreover a key issue for

H. Hilgenkamp; J. Mannhart

2002-01-01

353

Grain boundary characterization and energetics of superalloys  

Microsoft Academic Search

In many engineering alloys, there exists a wide distribution of grain sizes; we investigate the role of grain boundaries as a strengthening mechanism in such a material. The coincidental site lattice (CSL) model is a powerful mathematical tool to characterize grain boundaries (GBs) and identify ‘special’ boundaries, which display beneficial mechanical behavior. We define the CSL and describe a detailed

Michael D. Sangid; Huseyin Sehitoglu; Hans J. Maier; Thomas Niendorf

2010-01-01

354

Bayesian Areal Wombling for Geographical Boundary Analysis  

Microsoft Academic Search

In the analysis of spatially referenced data, interest often focuses not on prediction of the spatially indexed variable itself, but on boundary analysis, that is, the determina- tion of boundaries on the map that separate areas of higher and lower values. Existing boundary analysis methods are sometimes generically referred to as wombling, after a foundational article by Womble (1951). When

Haolan Lu; Bradley P. Carlin

2005-01-01

355

Mean Flow Boundary Conditions for Computational Aeroacoustics  

NASA Technical Reports Server (NTRS)

In this work, a new type of boundary condition for time-accurate Computational Aeroacoustics solvers is described. This boundary condition is designed to complement the existing nonreflective boundary conditions while ensuring that the correct mean flow conditions are maintained throughout the flow calculation. Results are shown for a loaded 2D cascade, started with various initial conditions.

Hixon, R.; Nallasamy, M.; Sawyer, S.; Dyson, R.

2003-01-01

356

THE BEHAVIOR OF THE FREE BOUNDARY NEAR THE FIXED BOUNDARY FOR A MINIMIZATION  

E-print Network

one. E.g., in the so-called Dam problem of reservoir (see [AG]) the free boundary is locally a smooth graph near the fixed boundary (boundary of the reservoir), and the angle of contact depends on the pressure function (the Dirichlet data) given on the boundary of the reservoir. In a recent work

Shahgholian, Henrik

357

A coupled level set-boundary integral method for moving boundary simulations  

Microsoft Academic Search

A numerical method for moving boundary problems based upon level set and boundary integral formulations is presented. The interface velocity is obtained from the boundary integral solution using a Galerkin technique for post-processing function gradients on the interface. We introduce a new level set technique for propagating free boundary values in time, and couple this to a narrow band level

M. Garzon; J. A. SETHIAN; L. Gray

2005-01-01

358

August, 2009 1. "Boundary element analysis of inclusions with corners" Engineering Analysis with Boundary Elements  

E-print Network

August, 2009 1 1. "Boundary element analysis of inclusions with corners" Engineering Analysis with Boundary Elements v31, pp 762­770,(2007) (With J. Maddi). 2. "Boundary element analysis of bonded joints. "An hr-method of Mesh Refinement for Boundary Element Method" Int. J. for Numerical Methods

Endres. William J.

359

Work-Family Boundary Strategies: Stability and Alignment between Preferred and Enacted Boundaries  

ERIC Educational Resources Information Center

Are individuals bounding work and family the way they would like? Much of the work-family boundary literature focuses on whether employees are segmenting or integrating work with family, but does not explore the boundaries workers would like to have, nor does it examine the fit between desired and enacted boundaries, or assess boundary stability.…

Ammons, Samantha K.

2013-01-01

360

Cylinder kernel expansion of Casimir energy with a Robin boundary  

E-print Network

approach based on the cylinder kernel [13, 14, 15]. We start our discussion by comparing cylinder kernel and heat kernel due to their similarity. The local heat kernel is de?ned by K(t;x;y) = 1X n=1 ?n(x)?currency1n(y)e?t!2n; (1.4) here !2n and ?n...(x) are the corresponding discrete spectrum and eigenfunctions of the problem @2u@t2 + r2u = 0. The global heat kernel can be obtained formally as trace over the local one K(t) = Tr(K(t;x;x)) = 1X n=1 e?t!2n (1.5) The less known local cylinder kernel is de?ned by T(t...

Liu, Zhonghai

2006-10-30

361

Model Reduction by Manifold Boundaries  

NASA Astrophysics Data System (ADS)

Understanding the collective behavior of complex systems from their basic components is a difficult yet fundamental problem in science. Existing model reduction techniques are either applicable under limited circumstances or produce "black boxes" disconnected from the microscopic physics. We propose a new approach by translating the model reduction problem for an arbitrary statistical model into a geometric problem of constructing a low-dimensional, submanifold approximation to a high-dimensional manifold. When models are overly complex, we use the observation that the model manifold is bounded with a hierarchy of widths and propose using the boundaries as submanifold approximations. We refer to this approach as the manifold boundary approximation method. We apply this method to several models, including a sum of exponentials, a dynamical systems model of protein signaling, and a generalized Ising model. By focusing on parameters rather than physical degrees of freedom, the approach unifies many other model reduction techniques, such as singular limits, equilibrium approximations, and the renormalization group, while expanding the domain of tractable models. The method produces a series of approximations that decrease the complexity of the model and reveal how microscopic parameters are systematically "compressed" into a few macroscopic degrees of freedom, effectively building a bridge between the microscopic and the macroscopic descriptions.

Transtrum, Mark K.; Qiu, Peng

2014-08-01

362

Modelling the transitional boundary layer  

NASA Technical Reports Server (NTRS)

Recent developments in the modelling of the transition zone in the boundary layer are reviewed (the zone being defined as extending from the station where intermittency begins to depart from zero to that where it is nearly unity). The value of using a new non-dimensional spot formation rate parameter, and the importance of allowing for so-called subtransitions within the transition zone, are both stressed. Models do reasonably well in constant pressure 2-dimensional flows, but in the presence of strong pressure gradients further improvements are needed. The linear combination approach works surprisingly well in most cases, but would not be so successful in situations where a purely laminar boundary layer would separate but a transitional one would not. Intermittency-weighted eddy viscosity methods do not predict peak surface parameters well without the introduction of an overshooting transition function whose connection with the spot theory of transition is obscure. Suggestions are made for further work that now appears necessary for developing improved models of the transition zone.

Narasimha, R.

1990-01-01

363

Boundary Layer Heights from CALIOP  

NASA Astrophysics Data System (ADS)

This work is focused on the development of a planetary boundary layer (PBL) height retrieval algorithm for CALIOP and validation studies. Our current approach uses a wavelet covariance transform analysis technique to find the top of the boundary layer. We use the methodology similar to that found in Davis et. al. 2000, ours has been developed to work with the lower SNR data provided by CALIOP, and is intended to work autonomously. Concurrently developed with the CALIOP algorithm we will show results from a PBL height retrieval algorithm from profiles of potential temperature, these are derived from Aircraft Meteorological DAta Relay (AMDAR) observations. Results from 5 years of collocated AMDAR - CALIOP retrievals near O'Hare airport demonstrate good agreement between the CALIOP - AMDAR retrievals. In addition, because we are able to make daily retrievals from the AMDAR measurements, we are able to observe the seasonal and annual variation in the PBL height at airports that have sufficient instrumented-aircraft traffic. Also, a comparison has been done between the CALIOP retrievals and the NASA Langley airborne High Spectral Resolution Lidar (HSRL) PBL height retrievals acquired during the GoMACCS experiment. Results of this comparison, like the AMDAR comparison are favorable. Our current work also involves the analysis and verification of the CALIOP PBL height retrieval from the 6 year CALIOP global data set. Results from this analysis will also be presented.

Kuehn, R.; Ackerman, S. A.; Holz, R.; Roubert, L.

2012-12-01

364

Transcending boundaries with Ira Hirsh  

NASA Astrophysics Data System (ADS)

Ira Hirsh has made many contributions to various fields of acoustics from speech, hearing, psychological and physiological acoustics, to musical and architectural acoustics. It was a privilege for me to have been his student in all these areas, and to have had him as a guide through masters and doctoral degree programs that focused on topics that lie at the boundaries connecting these disciplines. Ira was not a prescriptive advisor, imposing particular research topics or procedures on his graduate students. Rather, he encouraged originality, innovation, and personal goal setting. He would subtly suggest starting points and provide landmarks as references, rather than explicit directions leading to them. One had to navigate the path by ones own wits. This approach encouraged lateral, out-of-the box thinking, while also leading to respectful appreciation of historic trajectories in scientific research. During our time together, we worked on several aspects of music, including, rhythm, melody, pitch, and timber perception. Some of this work will be recapitulated, highlighting Ira's role in its exposition and development. His multidimensional personality, astute insights, colorful remarks, wry humor, care, and concern are qualities to be cherished-beyond the boundaries of campus, city, country, and contemporaneity.

Singh, Punita G.

2002-05-01

365

Free boundary resistive modes in tokamaks  

NASA Astrophysics Data System (ADS)

There exist a number of observations of magnetohydrodynamic (MHD) activity that can be related to resistive MHD modes localized near the plasma boundary. To study the stability of these modes, a free boundary description of the plasma is essential. The resistive plasma-vacuum boundary conditions have been implemented in the fully toroidal resistive spectral code castor (Complex Alfvén Spectrum in Toroidal Geometry) [Proceedings of the 18th Conference on Controlled Fusion and Plasma Physics, Berlin, edited by P. Bachmann and D. C. Robinson (European Physical Society, Petit-Lancy, Switzerland, 1991), p. 89]. The influence of a free boundary, as compared to a fixed boundary on the stability of low-m tearing modes, is studied. It is found that the stabilizing (toroidal) effect of a finite pressure due the plasma compression is lost in the free boundary case for modes localized near the boundary. Since the stabilization due to the favorable average curvature in combination with a pressure gradient near the boundary is small, the influence of the pressure on the stability is much less important for free boundary modes than for fixed boundary modes.

Huysmans, G. T. A.; Goedbloed, J. P.; Kerner, W.

1993-05-01

366

Plasma transport near material boundaries  

SciTech Connect

The fluid theory of two-dimensional (2-d) plasma transport in axisymmetric devices is reviewed. The forces which produce flow across the magnetic field in a collisional plasma are described. These flows may lead to up-down asymmetries in the poloidal rotation and radial fluxes. Emphasis is placed on understanding the conditions under which the known 2-d plasma fluid equations provide a valid description of these processes. Attempts to extend the fluid treatment to less collisional, turbulent plasmas are discussed. A reduction to the 1-d fluid equations used in many computer simulations is possible when sources or boundary conditions provide a large enough radial scale length. The complete 1-d fluid equations are given in the text, and 2-d fluid equations are given in the Appendix.

Singer, C.E.

1985-06-01

367

Boundary layer theory and subduction  

SciTech Connect

Numerical models of thermally activated convective flow in Earth`s mantle do not resemble active plate tectonics because of their inability to model successfully the process of subduction, other than by the inclusion of artificial weak zones. Here we show, using a boundary layer argument, how the `rigid lid` style of convection favored by thermoviscous fluids leads to lithospheric stresses which may realistically exceed the yield stress and thus cause subduction ot occur through the visoc-plastic failure of lithospheric rock. An explicit criterion for the failure of the lid is given, which is sensitive to the internal viscosity eta(sub a) below the lid. For numbers appropriate to Earth`s mantle, this criterion is approximately eta(sub a) greater than 10(exp 21) Pa s.

Fowler, A.C. [Oxford Univ., Oxford (United Kingdom)

1993-12-01

368

Microgravity Effects on Plant Boundary Layers  

NASA Technical Reports Server (NTRS)

The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental boundary layers in roots and leaves and to determine the effects of air flow on boundary layer development. It is hypothesized that microgravity induces larger boundary layers around plant organs because of the absence of buoyancy-driven convection. These larger boundary layers may affect normal metabolic function because they may reduce the fluxes of heat and metabolically active gases (e.g., oxygen, water vapor, and carbon dioxide. These experiments are to test whether there is a change in boundary layer associated with microgravity, quantify the change if it exists, and determine influence of air velocity on boundary layer thickness under different gravity conditions.

Stutte, Gary; Monje, Oscar

2005-01-01

369

Grain boundary segregation and intergranular failure  

SciTech Connect

Trace elements and impurities often segregate strongly to grain boundaries in metals and alloys. Concentrations of these elements at grain boundaries are often 10/sup 3/ to 10/sup 5/ times as great as their overall concentration in the alloy. Because of such segregation, certain trace elements can exert a disproportionate influence on material properties. One frequently observed consequence of trace element segregation to grain boundaries is the occurrence of grain boundary failure and low ductility. Less well known are incidences of improved ductility and inhibition of grain boundary fracture resulting from trace element segregation to grain boundaries in certain systems. An overview of trace element segregation and intergranular failure in a variety of alloy systems as well as preliminary results from studies on Al 3% Li will be presented.

White, C.L.

1980-01-01

370

Hamiltonian boundary term and quasilocal energy flux  

SciTech Connect

The Hamiltonian for a gravitating region includes a boundary term which determines not only the quasilocal values but also, via the boundary variation principle, the boundary conditions. Using our covariant Hamiltonian formalism, we found four particular quasilocal energy-momentum boundary term expressions; each corresponds to a physically distinct and geometrically clear boundary condition. Here, from a consideration of the asymptotics, we show how a fundamental Hamiltonian identity naturally leads to the associated quasilocal energy flux expressions. For electromagnetism one of the four is distinguished: the only one which is gauge invariant; it gives the familiar energy density and Poynting flux. For Einstein's general relativity two different boundary condition choices correspond to quasilocal expressions which asymptotically give the ADM energy, the Trautman-Bondi energy and, moreover, an associated energy flux (both outgoing and incoming). Again there is a distinguished expression: the one which is covariant.

Chen, C.-M.; Nester, James M.; Tung, R.-S. [Department of Physics, National Central University, Chungli 32054, Taiwan (China); Department of Physics and Institute of Astronomy, National Central University, Chungli 32054, Taiwan (China); Center for Astrophysics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234 (China)

2005-11-15

371

Multiple solutions of a boundary layer problem  

NASA Astrophysics Data System (ADS)

The laminar boundary layer flow on a continuous moving porous flat plate with suction or injection is governed by the nonlinear differential equation f?(?)+f(?)f?(?)=0, with boundary conditions f(0)=-C,f'(0)=?,f'(+?)=1, where ? is the similarity variable, f( ?) is related to the stream function, and C and ? are constants. This paper presents a rigorous proof of the existence of multiple solutions to the boundary value problem by a shooting method on [0, ?).

Lu, Chunqing

2007-08-01

372

IMMPDAF Approach for Road-Boundary Tracking  

Microsoft Academic Search

Robust road-boundary extraction\\/tracking is one of the main problems in autonomous roadway navigation. Although the road boundary can be defined by various means including lane markings, curbs, and borders of vegetation, this paper focuses on road-boundary tracking using curbs. A vehicle-mounted (downward tilted) 2-D laser-measurement system is utilized to detect the curbs. The tracking problem is difficult because both the

K. R. S. Kodagoda; Shuzhi Sam Ge; Wijerupage Sardha Wijesoma; Arjuna P. Balasuriya

2007-01-01

373

Three-dimensional boundary layers approaching separation  

NASA Technical Reports Server (NTRS)

The theory of semi-similar solutions of the laminar boundary layer equations is applied to several flows in which the boundary layer approaches a three-dimensional separation line. The solutions obtained are used to deduce the nature of three-dimensional separation. It is shown that in these cases separation is of the "ordinary" type. A solution is also presented for a case in which a vortex is embedded within the three-dimensional boundary layer.

Williams, J. C., III

1976-01-01

374

Physicians’ experiences with patients who transgress boundaries  

Microsoft Academic Search

BACKGROUND: Boundary violations have been discussed in the literature, but most studies report on physician transgressions of boundaries\\u000a or sexual transgressions by patients. We studied the incidence of all types of boundary transgressions by patients and physicians’\\u000a responses to these transgressions.\\u000a \\u000a \\u000a METHODS: We surveyed 1,000 members of the Society of General Internal Medicine (SGIM) for the number of patient transgressions

Neil J. Farber; Dennis H. Novack; Julie Silverstein; Elizabeth B. Davis; Joan Weiner; E. Gil Boyer

2000-01-01

375

Characteristic boundary conditions for the Euler equations  

NASA Technical Reports Server (NTRS)

The boundary conditions are demonstrated for the quasi-one-dimensional Euler equations with the extension to two and three dimensions being straightforward. In this application an implicit finite-difference scheme is employed with the boundary conditions being applied implicitly. The boundary application uses both characteristic extrapolations and evaluations which distinguishes it from other theories. Flow fields with shocks are calculated with inflow-outflow conditions of supersonic-subsonic and subsonic-subsonic flow.

Pulliam, T. H.

1981-01-01

376

Turbulent boundary layers with secondary flow  

NASA Technical Reports Server (NTRS)

An experimental analysis of the boundary layer on a plane wall, along which the flow occurs, whose potential flow lines are curved in plane parallel to the wall is discussed. According to the equation frequently applied to boundary layers in a plane flow, which is usually obtained by using the pulse law, a generalization is derived which is valid for boundary layers with spatial flow. The wall shear stresses were calculated with this equation.

Grushwitz, E.

1984-01-01

377

Theories, Boundaries, and All of the Above  

Microsoft Academic Search

Our immediate challenge in computer-mediated communication (CMC) research has to do with refinement of theories, and the most important refinement has to do with the articulation of boundary conditions. Boundary conditions stipulate the contextual conditions in which different theoretical chains-of-events are expected to occur. Boundary specifications will help us understand when one theoretical process applies, or when a different one

Joseph B. Walther

2009-01-01

378

Scalar discrete nonlinear multipoint boundary value problems  

NASA Astrophysics Data System (ADS)

In this paper we provide sufficient conditions for the existence of solutions to scalar discrete nonlinear multipoint boundary value problems. By allowing more general boundary conditions and by imposing less restrictions on the nonlinearities, we obtain results that extend previous work in the area of discrete boundary value problems [Debra L. Etheridge, Jesus Rodriguez, Periodic solutions of nonlinear discrete-time systems, Appl. Anal. 62 (1996) 119-137; Debra L. Etheridge, Jesus Rodriguez, Scalar discrete nonlinear two-point boundary value problems, J. Difference Equ. Appl. 4 (1998) 127-144].

Rodriguez, Jesus; Taylor, Padraic

2007-06-01

379

Grain Boundaries: Their Microstructure and Chemistry  

NASA Astrophysics Data System (ADS)

Over recent years the understanding of grain boundaries, interphase boundaries and free surfaces has advanced greatly, leading to a clear recognition that these discontinuities make a significant contribution to the physical and mechanical properties of materials from multiphase metals and alloys to electronic materials. Grain Boundaries -Their Microstructure and Chemistry discusses the interrelationship between microstructure and chemistry of the grain boundary, with particular emphasis on the influence of the environment (air, liquid and liquid metal) and composition (bulk and impurity). This highly practical volume presents a brief background to interphase and grain boundaries, before considering in detail grain boundary composition and composition changes, and how grain boundary composition affects material properties. Very recent advances in techniques such as electron energy loss spectroscopy, high-resolution transmission electron microscopy and atom probe, and the facinating new insights into grain boundary, microstructure that they have revealed, are also discussed. Grain Boundaries - Their Microstructure and Chemistry is an indispensable text for design and safety engineers in many industries, including power and aerospace, as well as for materials scientists and engineers in academia and research institutes.

Flewitt, P. E. J.; Wild, R. K.

2001-04-01

380

Boundary assessment under uncertainty: A case study  

USGS Publications Warehouse

Estimating certain attributes within a geological body whose exact boundary is not known presents problems because of the lack of information. Estimation may result in values that are inadmissible from a geological point of view, especially with attributes which necessarily must be zero outside the boundary, such as the thickness of the oil column outside a reservoir. A simple but effective way to define the boundary is to use indicator kriging in two steps, the first for the purpose of extrapolating control points outside the body, the second to obtain a weighting function which expresses the uncertainty attached to estimations obtained in the boundary region. ?? 1993 International Association for Mathematical Geology.

Pawlowsky, V.; Olea, R.A.; Davis, J.C.

1993-01-01

381

Boundary denoising for open surface meshes  

NASA Astrophysics Data System (ADS)

Recently, applications of open surfaces in 3D have emerged to be an interesting research topic due to the popularity of range cameras such as the Microsoft Kinect. However, surface meshes representing such open surfaces are often corrupted with noises especially at the boundary. Such deformity needs to be treated to facilitate further applications such as texture mapping and zippering of multiple open surface meshes. Conventional methods perform denoising by removing components with high frequencies, thus smoothing the boundaries. However, this may result in loss of information, as not all high frequency transitions at the boundaries correspond to noises. To overcome such shortcoming, we propose a combination of local information and geometric features to single out the noises or unusual vertices at the mesh boundaries. The local shape of the selected mesh boundaries regions, characterized by the mean curvature value, is compared with that of the neighbouring interior region. The neighbouring interior region is chosen such that it is the closest to the corresponding boundary region, while curvature evaluation is independent of the boundary. The smoothing processing is done via Laplacian smoothing with our modified weights to reduce boundary shrinkage. The evaluation of the algorithm is done by noisy meshes generated from controlled model clean meshes. The Hausdorff distance is used as the measurement between the meshes. We show that our method produces better results than conventional smoothing of the whole boundary loop.

Lee, Wei Zhe; Lim, Wee Keong; Soo, Wooi King

2013-04-01

382

Metamorphism in Plate Boundary Zones  

NASA Astrophysics Data System (ADS)

Accretionary orogenic systems (AOS) form at sites of subduction of oceanic lithosphere; these systems dominate during supercontinent break-up and dispersal. Collisional orogenic systems (COS) form where ocean basins close and subduction ultimately ceases; these systems dominate during crustal aggregation and assembly of supercontinents. It follows that COS may be superimposed on AOS, although AOS may exist for 100s Ma without terminal collision. AOS are of two types, extensional-contractional AOS in dominantly extensional arc systems, and terrane-dominated AOS in which accretion of allochthonous elements occurs during oblique convergence. On modern Earth, regional metamorphism occurs in plate boundary zones. Blueschists are created in the subduction zone and ultra-high pressure metamorphic (UHPM) rocks are created in collision zones due to deep subduction of continental lithosphere; granulites are created deep under continental and oceanic plateaus and in arcs and collision zones [high-pressure (HP) granulites, ultra-high temperature (UHT) granulites]. In extensional-contractional AOS, basement generally is not exposed, primitive volcanic rocks occur through the history, rift basins step oceanward with time, and a well-defined arc generally is absent. LP-HT metamorphism is dominant, with looping, CW or CCW P-T-t paths and peak metamorphic mineral growth syn-to-late in relation to tectonic fabrics. UHT and HP granulites are absent, and although rare, blueschists may occur early, but UHPM is not recorded. Short-lived contractional phases of orogenesis probably relate to interruptions in the continuity of subduction caused by features on the ocean plate, particularly plateaus. Extensive granite (s.l.) magmatism accompanies metamorphism. Examples include the Lachlan Orogen, Australia, the Acadian Orogen, NE USA and Maritime Canada, and the Proterozoic orogens of the SW USA. At plate boundaries, oblique convergence is partitioned into two components, one directed more orthogonal to the strike of the trench than the convergence vector, and the other directed parallel to the strike of the trench. The orthogonal component is accommodated by subduction, but the margin-parallel component gives rise to block rotations and extension, strike-slip motion, and shortening within the upper plate. In some AOS, it has been argued that `paired' metamorphic belts characterize the metamorphic pattern. Commonly, this is a false construct that results from failure to recognize orogen-parallel terrane migration and the limitations of particular chronological datasets. Whereas a HP-LT (blueschist-eclogite) metamorphic belt may occur outboard, it is generally separated from a LP-HT (And-Sil type) metamorphic belt by a terrane boundary. These are terrane-dominated AOS. In some AOS an additional feature of the orogenic process is ridge subduction, which is reflected in the pattern of LP-HT metamorphism and the magmatism. Granulites may occur at the highest grade of metamorphism in the LP-HT belt, where granite (s.l.) magmatism is common, but UHPM occurs only rarely in the outboard HP-LT belt. Examples include the Mesozoic metamorphic belts of Japan and the North American Cordillera. COS commonly are characterized by syntectonic index minerals that record CW P-T-t paths and Barrovian-type metamorphic field gradients generated by thickening followed by exhumation. However, during the Neoproterozoic, ultra-high temperature granulite facies metamorphism is common in orogens that suture Gondwana, whereas during the Phanerozoic, metamorphism to high-pressure granulite/medium temperature eclogite facies and extreme UHPM conditions commonly occurs and may be more typical of younger COS; examples include the Alpides, the Qinling - Dabie Shan - Sulu orogens, the Variscides and the Caledonides.

Brown, M.

2005-12-01

383

The Influence of Grain Boundary Type upon Damage Evolution at Grain Boundary Interfaces  

SciTech Connect

In a prior work, it was found that grain boundary structure strongly influences damage evolution at grain boundaries in copper samples subjected to either shock compression or incipient spall. Here, several grain boundaries with different grain boundary structures, including a {Sigma}3 (10-1) boundary, are interrogated via conventional transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) to investigate the effects of atomic-scale structural differences on grain boundary strength and mobility. Boundaries are studied both before and after shock compression at a peak shock stress of 10 GPa. Results of the TEM and HRTEM work are used in conjunction with MD modeling to propose a model for shock-induced damage evolution at grain boundary interfaces that is dependent upon coincidence.

Perez-Bergquist, Alejandro G [Los Alamos National Laboratory; Brandl, Christian [Los Alamos National Laboratory; Escobedo, Juan P [Los Alamos National Laboratory; Trujillo, Carl P [Los Alamos National Laboratory; Cerreta, Ellen K [Los Alamos National Laboratory; Gray III, George T [Los Alamos National Laboratory; Germann, Timothy C [Los Alamos National Laboratory

2012-07-09

384

On local boundary CFT and non-local CFT on the boundary  

E-print Network

The holographic relation between local boundary conformal quantum field theories (BCFT) and their non-local boundary restrictions is reviewed, and non-vacuum BCFT's, whose existence was conjectured previously, are constructed.

K. -H. Rehren

2004-12-15

385

Effects of grain boundary constraints on properties of polycrystalline materials  

NASA Astrophysics Data System (ADS)

Grain boundary networks are engineered by increasing the fraction of boundaries which have favorable properties. Favorable boundaries have either low grain boundary misorientation or they are special boundaries, such as coincident site lattice boundaries. Significant improvement in properties such as corrosion resistance, critical current in superconductors and mechanical strength and toughness occur, provided percolating grain or grain boundary structures can be engineered. We demonstrate that grain boundary constraints shift percolation thresholds from their uncorrelated values and that the behavior near threshold is also modified. The origin of these behaviors is an enhanced clustering of weak boundaries induced by grain boundary constraints.

McGarrity, Kimberly; McGarrity, Erin; Duxbury, Phillip; Reed, Bryan; Holm, Elizabeth

2007-03-01

386

K/T age for the popigai impact event  

NASA Technical Reports Server (NTRS)

The multi-ringed POPIGAI structure, with an outer ring diameter of over 100 km, is the largest impact feature currently recognized on Earth with an Phanerozoic age. The target rocks in this relatively unglaciated region consist of upper Proterozoic through Mesozoic platform sediments and igneous rocks overlying Precambrian crystalline basement. The reported absolute age of the Popigai impact event ranges from 30.5 to 39 Ma. With the intent of refining this age estimate, a melt-breccia (suevite) sample from the inner regions of the Popigai structure was prepared for total fusion and step-wise heating Ar-40/Ar-39 analysis. Although the total fusion and step-heating experiments suggest some degree of age heterogeneity, the recurring theme is an age of around 64 to 66 Ma.

Deino, A. L.; Garvin, J. B.; Montanari, S.

1991-01-01

387

k(t) Factorization for Hard Processes in Nuclei  

SciTech Connect

Two widely proposed k{sub t}-dependent gluon distributions in the small-x saturation regime are investigated using two-particle back-to-back correlations in high energy scattering processes. The Weizsaecker-Williams gluon distribution, interpreted as the number density of gluon inside nucleus, is studied in the quark-antiquark jet correlation in deep inelastic scattering. On the other hand, the unintegrated gluon distribution, defined as the Fourier transform of the color-dipole cross section, is probed in the direct photon-jet correlation in pA collisions.

Dominguez, F.; Yuan, F.; Xiao, B.W.

2011-01-10

388

The K-T Transition in Meghalaya, NE India  

Microsoft Academic Search

The TEX86 paleotemperature proxy, based on tetraether membrane lipids derived from aquatic Crenarchaeota has been applied in a variety of marine and lacustrine systems. A recent study analyzing a suite of 50 globally distributed lakes for TEX86 discovered that this proxy does not appear to work in all lake systems and that the TEX86 correlates well with both annual and

B. Gertsch; G. Keller; T. Adatte; R. Garg; V. Prasad; Z. Berner; K. Ateequzzaman; D. Stueben

2008-01-01

389

Bibliography Abend, K., T. J. Harley, and L. N. Kanal  

E-print Network

(1985). A learning algorithm for boltzmann machines. Cognitive Science 9, 147­169. Adams, R. P., H. Wallach, and Z. Ghahramani (2010). Learning the structure of deep sparse graphical models. In AI Stochastic Gradient Fisher Scoring. In Intl. Conf. on Machine Learning. Airoldi, E., D. Blei, S. Fienberg

Murphy, Kevin Patrick

390

The SISCone and anti-k_t jet algorithms  

SciTech Connect

We illustrate how the midpoint and iterative cone (with progressive removal) algorithms fail to satisfy the fundamental requirements of infrared and collinear safety, causing divergences in the perturbative expansion. We introduce SISCone and the anti-k{sub t} algorithms as respective replacements that do not have those failures without any cost at the experimental level.

Soyez,G.

2008-04-07

391

Aging embrittlement and grain boundary  

NASA Astrophysics Data System (ADS)

“Clean” 3.5NiCrMoV steels with limited contents in trace elements (P, Sn, As, Sb) are commonly provided for manufacturing big rotor shafts. The possible increase in temperature in future steam turbines has promoted the development of “superclean” steels characterized by an extra drastic decrease of manganese and silicon contents. Their higher cost in comparison to “clean” steels leads to concern above which temperature they must be considered as mandatory for resisting aging embrittlement in operation. 3.5NiCrMoV “clean” steel samples (Mn = 0.30 pct; Si = 0.10 pct) were aged at 300 °C, 350 °C, and 400 °C for 10,000 hours up to 30,000 hours. No embrittlement results from aging at 300 °C and 350 °C, but holding at 400 °C is highly detrimental. Auger spectroscopy confirms that, when aging at 400 °C, phosphorus is the main embrittling trace element. It is suggested that grain boundary embrittlement is associated with the building of a layer that contains, on the one hand, Ni and P and, on the other hand, Mo and Cr.

Thauvin, G.; Lorang, G.; Leymonie, C.

1992-08-01

392

The Arctic Circumpolar Boundary Current  

NASA Astrophysics Data System (ADS)

We present high-resolution simulations and observational data as evidence of a fast current flowing along the shelf break of the Siberian and Alaskan shelves in the Arctic Ocean. Thus far, the Arctic Circumpolar Boundary Current (ACBC) has been seen as comprising two branches: the Fram Strait and Barents Sea Branches (FSB and BSB, respectively). Here we describe a new third branch, the Arctic Shelf Break Branch (ASBB). We show that the forcing mechanism for the ASBB is a combination of buoyancy loss and non-local wind, creating high pressure upstream in the Barents Sea. The potential vorticity influx through the St. Anna Trough dictates the cyclonic direction of flow of the ASBB, which is the most energetic large-scale circulation structure in the Arctic Ocean. It plays a substantial role in transporting Arctic halocline waters and exhibits a robust seasonal cycle with a summer minimum and winter maximum. The simulations show the continuity of the FSB all the way around the Arctic shelves and the uninterrupted ASBB between the St. Anna Trough and the western Fram Strait. The BSB flows continuously along the Siberian shelf as far as the Chukchi Plateau, where it partly diverges from the continental slope into the ocean interior. The Alaskan Shelf break Current (ASC) is the analog of the ASBB in the Canadian Arctic. The ASC is forced by the local winds and high upstream pressure in Bering Strait, caused by the drop in sea surface height between the Pacific and Arctic Oceans.

Aksenov, Yevgeny; Ivanov, Vladimir V.; Nurser, A. J. George; Bacon, Sheldon; Polyakov, Igor V.; Coward, Andrew C.; Naveira-Garabato, Alberto C.; Beszczynska-Moeller, Agnieszka

2011-09-01

393

8/28/12 Pushing Boundaries 1/2communication.ucsd.edu/ovasquez/boundaries.html  

E-print Network

8/28/12 Pushing Boundaries 1/2communication.ucsd.edu/ovasquez/boundaries.html CommWeb - Recent intercultural transactions, language socialization and schooling." Beth Warren, Technology and Education/2communication.ucsd.edu/ovasquez/boundaries.html 6 Moving Toward a Recognition Perspective 7 Meeting

394

Reection of equatorial Kelvin waves at eastern ocean boundaries Part I: hypothetical boundaries  

E-print Network

Re¯ection of equatorial Kelvin waves at eastern ocean boundaries Part I: hypothetical boundaries J of the orientation of the eastern ocean boundary on the behavior of equatorial Kelvin waves. The model is formulated are considered given the large latitudinal extent used in the model. Baroclinic equatorial Kelvin waves

Paris-Sud XI, Université de

395

A pure boundary element method approach for solving hypersingular boundary integral equations  

Microsoft Academic Search

This paper is concerned with discretization and numerical solution of a regularized version of the hypersingular boundary integral equation (HBIE) for the two-dimensional Laplace equation. This HBIE contains the primary unknown, as well as its gradient, on the boundary of a body. Traditionally, this equation has been solved by combining the boundary element method (BEM) together with tangential differentiation of

Georgios N. Lilis; Subrata Mukherjee

2007-01-01

396

A new discriminant analysis based on boundary\\/non-boundary pattern separation  

Microsoft Academic Search

In this paper, we propose a new discriminant analysis, named as linear boundary discriminant analysis (LBDA), which increases the class separability by differently emphasizing the boundary and non-boundary patterns. This is achieved by defining two novel scatter matrices and solving eigenproblem on the criterion described by these scatter matrices. As a result, the classification performance using the extracted features can

Jin Hee Na; Myoung Soo Park; Jin Young Choi

2009-01-01

397

Boundary conditions for the subdiffusion equation  

SciTech Connect

The boundary conditions for the subdiffusion equations are formulated using the continuous-time random walk model, as well as several versions of the random walk model on an irregular lattice. It is shown that the boundary conditions for the same equation in different models have different forms, and this difference considerably affects the solutions of this equation.

Shkilev, V. P., E-mail: shkilevv@ukr.net [National Academy of Sciences of Ukraine, Institute of Surface Chemistry (Ukraine)

2013-04-15

398

Millennial Values and Boundaries in the Classroom  

ERIC Educational Resources Information Center

Students' relationships with authority and information are changing rapidly, and this presents a new set of interpersonal boundary challenges for faculty. The topic of setting boundaries often conjures up thoughts of how to protect oneself. The intent of this chapter is to explore how good rapport between teacher and student can be developed and…

Espinoza, Chip

2012-01-01

399

FRACTIONAL LAPLACIAN PHASE TRANSITIONS AND BOUNDARY REACTIONS  

E-print Network

FRACTIONAL LAPLACIAN PHASE TRANSITIONS AND BOUNDARY REACTIONS: A GEOMETRIC INEQUALITY-called fractional Laplacian. The study of this nonlocal equation is made via a careful analysis of the following: Boundary reactions, Allen-Cahn phase transitions, frac- tional operators, Poincar´e-type inequality. 2000

400

Soliton equations solved by the boundary CFT  

NASA Astrophysics Data System (ADS)

Soliton equations are derived which characterize the boundary CFT à la Callan et al. Soliton fields of classical soliton equations are shown to appear as a neutral bound state of a pair of soliton fields of BCFT. One soliton amplitude under the influence of the boundary is calculated explicitly and is shown that it is frozen at the Dirichlet limit.

Saito, Satoru; Sato, Ryuichi

2003-11-01

401

Conference on Transport Phenomena with Moving Boundaries  

E-print Network

Conference on Transport Phenomena with Moving Boundaries 9th -10th October, Berlin, Germany VOF-of-Fluid (VOF) method. For the examination of mass transfer, single bubbles are held in counter require numerical methods that resolve the free phase boundary. Based on the VOF-method, mass transfer

Bothe, Dieter

402

Professional boundaries in learning disability care.  

PubMed

Healthcare staff providing care for people with a learning disability often deliver intimate personal care and have access to confidential information about vulnerable clients. Awareness of professional boundaries can help them to avoid either under- or over-involvement with patients and clients. Education and reflection can improve staff awareness of boundaries and help them reflect usefully on their relationships with clients. PMID:24960974

Bowler, Mandy; Nash, Peter

403

Boundary value problems for fractional diffusion equations  

Microsoft Academic Search

The fractional diffusion equation is solved for different boundary value problems, these being absorbing and reflecting boundaries in half-space and in a box. Thereby, the method of images and the Fourier–Laplace transformation technique are employed. The separation of variables is studied for a fractional diffusion equation with a potential term, describing a generalisation of an escape problem through a fluctuating

Ralf Metzler; Joseph Klafter

2000-01-01

404

Diamagnetic boundary layers: A kinetic theory  

Microsoft Academic Search

We present a kinetic theory for boundary layers associated with MHD tangential ‘discontinuities’ in a collisionless magnetized plasma such as those observed in the solar wind. The theory consists of finding self-consistent solutions of Vlasov's equation and Maxwell's equation for stationary, one-dimensional boundary layers separating two Maxwellian plasma states. Layers in which the current is carried by electrons are found

J. Lemaire; L. F. Burlaga

1976-01-01

405

Transport of Helium Grain Boundaries During Irradiation.  

National Technical Information Service (NTIS)

The rate of accumulation of helium at grain boundaries is one of the important parameters determining the integrity and lifetime of the structural components of a fusion reactor. A diffusion calculation is made of the flux of helium to a grain boundary. T...

B. N. Singh, A. J. E. Foreman

1986-01-01

406

AIAA 20042128 Boundary Layer Flow Control Using  

E-print Network

AIAA 2004­2128 Boundary Layer Flow Control Using AC Discharge Plasma Actuators Jamey Jacob, Propulsion Directorate Wright-Patterson Air Force Base, OH J. Estevadeordal ISSI, Dayton, OH AIAA 2nd Flow­4344 #12;Boundary Layer Flow Control Using AC Discharge Plasma Actuators Jamey Jacob Mechanical Engineering

Jacob, Jamey

407

Fast algorithm for locating head boundaries  

Microsoft Academic Search

The first step for human face recognition is to locate the head boundary in a head-and- shoulders image. An approach that uses adaptive contour models or `snakes' is described to solve this problem. Since we have a priori knowledge of the shape of a head, this active contour model is tailor-made for representing the head boundary. In this paper, a

Kin-Man Lam; Hong Yan

1994-01-01

408

1996 GTA BOUNDARIES Prepared for the  

E-print Network

1996 GTA BOUNDARIES Prepared for the Toronto Area Transportation Planning Data Collection Steering #12;PREFACE This report presents the 1996 GTA zone boundary definitions. The report is divided in two such as streets, rivers and railroad tracks. The 1996 GTA zones are significantly different from the 1991 GTA

Toronto, University of

409

15 CFR 922.101 - Boundary.  

...Ta'u Unit. The Ta'u Unit boundary is defined by...description. The Ta'u Unit boundary extends from Point...western coast to Point 2, Si'ufa'alele Point...which is directly south of Si'u Point. From Point...southern border of the unit. From Point 6, the...

2014-01-01

410

15 CFR 922.101 - Boundary.  

Code of Federal Regulations, 2013 CFR

...Ta'u Unit. The Ta'u Unit boundary is defined by...description. The Ta'u Unit boundary extends from Point...western coast to Point 2, Si'ufa'alele Point...which is directly south of Si'u Point. From Point...southern border of the unit. From Point 6, the...

2013-01-01

411

Transgressions and Transcendence: Surpassing Disciplinary Boundaries.  

ERIC Educational Resources Information Center

Discusses how women such as Amy Morris Homans, Susan B. Anthony, Elizabeth Cady Stanton, and Mary Wollstonecraft transgressed boundaries, allowing others to transcend old boundary limitations in physical education, examining the Boston Normal School of Gymnastics established for training women as directors of physical education over 100 years ago…

Wughalter, Emily H.

2002-01-01

412

Reconstruction of twist grain boundaries in gold  

SciTech Connect

The reconstruction of high-angle twist grain boundaries on the four densest atomic planes in gold are investigated using the recently developed method of grand-canonical simulated quenching. It is found that the grain boundaries on the two densest planes, (111) and (100), do not reconstruct, while those on the (110) and (113) planes do.

Phillpot, S.R.

1992-11-01

413

ABSORBING BOUNDARY CONDITIONS FOR ELECTROMAGNETIC WAVE PROPAGATION  

E-print Network

ABSORBING BOUNDARY CONDITIONS FOR ELECTROMAGNETIC WAVE PROPAGATION Xiaobing Feng y Abstract of the electromagnetic fields indi­ vidually. This boundary condition allows any wave motion generated within the domain, and the electromagnetic wave scattering related to antennas. Because of the limitations of both speed and memory

414

Boundary Integral Formulations for Homogeneous Material Bodies  

Microsoft Academic Search

There are many boundary integral formulations for the problem of electromagnetic scattering from and transmission into a homogeneous material body. The only formulations which give a unique solution at all frequencies are those which involve both electric and magnetic equivalent currents, and satisfy boundary conditions on both tangential E and tangential H. Formulations which involve only electric (or magnetic) equivalent

Roger F. Harrington

1989-01-01

415

School Boundary Debate Divides Minnesota Suburb  

ERIC Educational Resources Information Center

The author discusses how an assignment plan intended to keep schools socioeconomically balanced spurs a bitter debate in suburban Eden Prairie. The boundary debate in the 9,700-student Eden Prairie, Minnesota, district has been bruising. Eden Prairie adopted new school attendance boundaries this year based on socioeconomic balance, ensuring for…

Samuels, Christina A.

2011-01-01

416

8, 1074910790, 2008 Boundary-layer top  

E-print Network

lidar, a vertical-wind Doppler lidar, and ac- companying radiosonde profiling of temperatureACPD 8, 10749­10790, 2008 Boundary-layer top from lidar H. Baars et al. Title Page Abstract Chemistry and Physics Discussions Continuous monitoring of the boundary-layer top with lidar H. Baars, A

Paris-Sud XI, Université de

417

Decision Boundary Feature Extraction for Nonparametric Classification  

NASA Technical Reports Server (NTRS)

Feature extraction has long been an important topic in pattern recognition. Although many authors have studied feature extraction for parametric classifiers, relatively few feature extraction algorithms are available for nonparametric classifiers. A new feature extraction algorithm based on decision boundaries for nonparametric classifiers is proposed. It is noted that feature extraction for pattern recognition is equivalent to retaining 'discriminantly informative features' and a discriminantly informative feature is related to the decision boundary. Since nonparametric classifiers do not define decision boundaries in analytic form, the decision boundary and normal vectors must be estimated numerically. A procedure to extract discriminantly informative features based on a decision boundary for non-parametric classification is proposed. Experiments show that the proposed algorithm finds effective features for the nonparametric classifier with Parzen density estimation.

Lee, Chulhee; Landgrebe, David A.

1993-01-01

418

Transient response of a turbulent boundary layer  

NASA Technical Reports Server (NTRS)

A unique feature of the present ensemble-averaged measurements of a turbulent boundary layer's transient response to a spontaneous change in the free stream velocity distribution, is that the test boundary layer is a standard, steady, flat plate turbulent boundary layer at the entrance to the unsteady region, and is then subjected to sudden changes in free stream velocity distribution in the test section. These water tunnel tests were controlled by minicomputer. It is noted that the boundary layer development was relatively slow, with a characteristic time that was greater than the free stream time-of-flight by a factor of as much as 3. Response varied dramatically across the boundary layer, and the evolution of the turbulent stress field occurred on the same time scale as that of the ensemble-averaged velocity field.

Parikh, P. G.; Jayaraman, R.; Reynolds, W. C.; Carr, L. W.

1983-01-01

419

Boundary Layers of Air Adjacent to Cylinders  

PubMed Central

Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the boundary layer of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated boundary-layer thickness agreed with that determined for water vapor diffusion from a moistened cylindrical surface 2 cm in diameter. It correctly predicted the resistance for water vapor movement across the boundary layers adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The boundary-layer thickness decreased as the turbulence intensity increased. For a turbulence intensity representative of field conditions (0.5) and for ?windd between 200 and 30,000 cm2/second (where ?wind is the mean wind velocity and d is the cylinder diameter), the effective boundary-layer thickness in centimeters was equal to [Formula: see text]. PMID:16658855

Nobel, Park S.

1974-01-01

420

Decoupled temporal patterns of evolution and ecology in two post-Paleozoic clades  

NASA Technical Reports Server (NTRS)

Counts of taxonomic diversity are the prevailing standards for documenting large-scale patterns of evolution in the fossil record. However, the secular pattern of relative ecological importance between the bryozoan clades Cyclostomata and Cheilostomata is not reflected fully in compilations of generic diversity or within-fauna species richness, and the delayed ecological recovery of the Cheilostomata after the mass extinction at the Cretaceous-Tertiary boundary is missed entirely. These observations demonstrate that evolutionary success and ecological dominance can be decoupled and profoundly different, even over tens of millions of years.

McKinney, F. K.; Lidgard, S.; Sepkoski, J. J. Jr; Taylor, P. D.

1998-01-01

421

Gradual dinosaur extinction and simultaneous ungulate radiation in the hell creek formation.  

PubMed

Dinosaur extinction in Montana, Alberta, and Wyoming was a gradual process that began 7 million years before the end of the Cretaceous and accelerated rapidly in the final 0.3 million years of the Cretaceous, during the interval of apparent competition from rapidly evolving immigrating ungulates. This interval involves rapid reduction in both diversity and population density of dinosaurs. The last dinosaurs known are from a channel that contains teeth of Mantuan mammals, seven species of dinosaurs, and Paleocene pollen. The top of this channel is 1.3 meters above the likely position of the iridium anomaly, the Cretaceous/Tertiary boundary. PMID:17781415

Sloan, R E; Rigby, J K; VAN Valen, L M; Gabriel, D

1986-05-01

422

Effects of grain boundary constraint on properties of polycrystalline materials  

NASA Astrophysics Data System (ADS)

Grain boundary networks are engineered by increasing the fraction of boundaries which exhibit improved properties. Favourable boundaries have either low grain boundary misorientation or they are special boundaries, such as coincident site lattice boundaries. Significant improvement in properties such as corrosion resistance, critical current in superconductors and mechanical strength and toughness occur, provided percolating grain or grain boundary structures can be engineered. We develop computational models for grain boundary engineered polycrystals and demonstrate that grain boundary constraints modify the behaviour near the percolation threshold. We postulate that this is due to an enhanced clustering of weak boundaries induced by grain boundary constraints. In random grain structures the fraction of strong grain boundaries may be measured in two ways, either the length fraction, c, or the edge fraction ce. We find that grain boundary constraint shifts the length fraction threshold, c*, of Potts model polycrystals to higher values, while the edge fraction, ce*, remains almost the same in both correlated and uncorrelated grain structures.

McGarrity, E. S.; McGarrity, K. S.; Duxbury, P. M.; Reed, B. W.; Holm, E. A.

2007-06-01

423

Boundary definition of a multiverse measure  

NASA Astrophysics Data System (ADS)

We propose to regulate the infinities of eternal inflation by relating a late time cutoff in the bulk to a short-distance cutoff on the future boundary. The light-cone time of an event is defined in terms of the volume of its future light cone on the boundary. We seek an intrinsic definition of boundary volumes that makes no reference to bulk structures. This requires taming the fractal geometry of the future boundary and lifting the ambiguity of the conformal factor. We propose to work in the conformal frame in which the boundary Ricci scalar is constant. We explore this proposal in the Friedmann-Robertson-Walker approximation for bubble universes. Remarkably, we find that the future boundary becomes a round three-sphere, with smooth metric on all scales. Our cutoff yields the same relative probabilities as a previous proposal that defined boundary volumes by projection into the bulk along timelike geodesics. Moreover, it is equivalent to an ensemble of causal patches defined without reference to bulk geodesics. It thus yields a holographically motivated and phenomenologically successful measure for eternal inflation.

Bousso, Raphael; Freivogel, Ben; Leichenauer, Stefan; Rosenhaus, Vladimir

2010-12-01

424

Biogeochemistry of the Triassic-Jurassic Boundary  

NASA Astrophysics Data System (ADS)

New biostratigraphic and biogeochemical data are presented from Triassic-Jurassic (Tr-J) boundary sections at Kennecott Point, Queen Charlotte Islands (QCI), Canada, Muller Canyon, Nevada, USA, and Marokopa Beach, New Zealand. The New Zealand record shows two negative excursions in ?13Corg of approximately 2‰ associated with the Tr-J transition. The QCI and Nevada boundary sections show a consistent isotopic trend indicative of multiple major perturbations to the carbon cycle: one negative excursion in ?13Corg of 2‰ at the boundary and one positive excursion of 3 to 5‰ following the boundary. The post-Tr-J boundary positive excursion is especially prominent in boundary sections from QCI, where the high organic content of the black shales makes the rocks suitable for a survey of lipid biomarkers. New GC-MS data are presented from this locality, revealing changes in the distribution and abundance of alkanes, hopanes, and steranes across the Tr-J transition. Litho-, bio- and chemostratigraphy from these boundary localities do not support a single impact cause for the late Triassic extinctions, although impact events such as the Manicouagan may well have exerted significant stress on a biosphere still recovering from the Permian-Triassic mass extinction. The data support the idea of a degraded late Triassic environment persisting for millions of years and characterized by low atmospheric oxygen and high carbon dioxide associated with Central Atlantic Magmatic Province volcanism. Global warming and sea level change may have led to destabilization of seafloor methane hydrates and runaway greenhouse conditions.

Williford, K. H.; Ward, P. D.; Garrison, G. H.

2006-12-01

425

Absorbing Boundary Conditions for Numerical Simulation of Waves  

Microsoft Academic Search

In practical calculations, it is often essential to introduce artificial boundaries to limit the area of computation. Here we develop a systematic method for obtaining a hierarchy of local boundary conditions at these artificial boundaries. These boundary conditions not only guarantee stable difference approximations, but also minimize the (unphysical) artificial reflections that occur at the boundaries.

Bjorn Engquist; Andrew Majda

1977-01-01

426

Explicit boundary form factors: The scaling Lee-Yang model  

NASA Astrophysics Data System (ADS)

We provide explicit expressions for boundary form factors in the boundary scaling Lee-Yang model for operators with the mildest ultraviolet behavior for all integrable boundary conditions. The form factors of the boundary stress tensor take a determinant form, while the form factors of the boundary primary field contain additional explicit polynomials.

Hollo, L.; Laczko, Z. B.; Bajnok, Z.

2014-09-01

427

BOFFO - BOUNDARY FORCE METHOD FOR ORTHOTROPIC MATERIALS  

NASA Technical Reports Server (NTRS)

In the field of fracture mechanics, stress-intensity factors are important parameters for predicting fracture strengths and fatigue lives. BOFFO performs stress analysis of two-dimensional linear elastic orthotropic or composite bodies with or without cracks using the Boundary Force Method. The Boundary Force Method is versatile since complex geometries, crack configurations, and load distributions can be analyzed with ease. The BOFFO program is easy to use because only the boundaries of the region of interest are modeled using a built-in mesh generator. Stresses can be computed at any specified point in the body. Stress-intensity factor solutions and strain-energy release rates are computed for both mode I and mixed mode fracture problems. The Boundary Force Method is a numerical technique that uses the fundamental solutions for concentrated forces and moments in an infinite sheet to obtain the solution to the boundary value problem of interest. These fundamental solutions are used in the BOFFO program to exactly satisfy the stress-free conditions on the crack faces. The other boundary conditions are approximately satisfied by applying the appropriate sets of concentrated horizontal and vertical forces and moments along the boundary. The problem configuration is defined using two sets of axes. The global X- and Y-axes define the specimen boundaries, loads, and material properties. The local axes define the crack length and orientation. The user can specify four types of symmetry conditions: symmetry about the X-axis, symmetry about the Y-axis, symmetry about the X- and Y-axes, or no symmetry. The lines of symmetry are not modeled as boundaries. The accuracy of the solution depends on how well the boundary conditions are approximated, which in turn depends on the refinement of the boundary mesh. BOFFO uses the radial-line method for element mesh generation. BOFFO is written in FORTRAN V for execution on CDC CYBER 170 Series computers running NOS. The execution time and memory required depend on the number of boundary elements in the mesh. With twelve elements, the main memory requirement is 26K Cyber words. Input and output are tabular. BOFFO is available on a 9-track 1600 BPI ASCII Card Image format magnetic tape. This program was developed in 1990. CDC CYBER and NOS are trademarks of Control Data Corporation.

Bigelow, C. A.

1994-01-01

428

Classical BV Theories on Manifolds with Boundary  

NASA Astrophysics Data System (ADS)

In this paper we extend the classical BV framework to gauge theories on spacetime manifolds with boundary. In particular, we connect the BV construction in the bulk with the BFV construction on the boundary and we develop its extension to strata of higher codimension in the case of manifolds with corners. We present several examples including electrodynamics, Yang-Mills theory and topological field theories coming from the AKSZ construction, in particular, the Chern-Simons theory, the BF theory, and the Poisson sigma model. This paper is the first step towards developing the perturbative quantization of such theories on manifolds with boundary in a way consistent with gluing.

Cattaneo, Alberto S.; Mnev, Pavel; Reshetikhin, Nicolai

2014-08-01

429

Atomistic Simulation of Slow Grain Boundary Motion  

SciTech Connect

Existing atomistic simulation techniques to study grain boundary motion are usually limited to either high velocities or temperatures and are difficult to compare to realistic experimental conditions. Here we introduce an adapted simulation method that can access boundary velocities in the experimental range and extract mobilities in the zero driving force limit at temperatures as low as {approx}0.2T{sub m} (T{sub m} is the melting point). The method reveals three mechanistic regimes of boundary mobility at zero net velocity depending on the system temperature.

Deng Chuang; Schuh, Christopher A. [Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States)

2011-01-28

430

Prosodic boundary information modulates phonetic categorization.  

PubMed

Categorical perception experiments were performed on an English /b-p/ voice onset time (VOT) continuum with native (American English) and non-native (Korean) listeners to examine whether and how phonetic categorization is modulated by prosodic boundary and language experience. Results demonstrated perceptual shifting according to prosodic boundary strength: A longer VOT was required to identify a sound as /p/ after an intonational phrase than a word boundary, regardless of the listeners' language experience. This suggests that segmental perception is modulated by the listeners' computation of an abstract prosodic structure reflected in phonetic cues of phrase-final lengthening and domain-initial strengthening, which are common across languages. PMID:23862901

Kim, Sahyang; Cho, Taehong

2013-07-01

431

The Rivera-Cocos Plate Boundary Revisited  

NASA Astrophysics Data System (ADS)

The nature of the boundary between the Rivera and Cocos plates has long been controversial. Early studies (predominantly earthquake studies) suggested that it was a NE oriented left lateral transform boundary. With the collection of multi-beam bathymetric data during the SEAMAT cruise of the N/O Jean Charcot in 1987 it became clear that this early proposal was not entirely correct as no clear transform morphology was observed. Shortly after the SEAMAT campaign, three main proposals emerged to explain this lack of transform morphology. The first two proposals favored the results of earthquake studies over the new multibeam data. The first proposed that the boundary is indeed a left-lateral transform boundary, you just cannot see it. In other words, it was a diffuse boundary and the resolution of the multi-beam data was not sufficient to reveal the associated deformation. The second proposal was that it was an east-west oriented, dextral transform, the proposal being based on the results of an earthquake directivity analysis. The third proposal favored the morphologic data over the earthquake data and proposed that the plate boundary was not a transform boundary, but was instead a divergent boundary, at least near the Middle America Trench in what is now called the EL Gordo Graben. Implicit in this proposal was that the earthquake activity did not reflect plate motions but rather were the result of local stresses. Since 2002, several marine geophysical campaigns have been conducted in the area of the Rivera-Cocos plate boundary with the aim of resolving this debate. During the 2002 BART and FAMEX campaigns of the N/O L'ATALANTE, multibeam bathymetric and seafloor backscatter data were collected along the boundary. During the MARTIC04 and MARTIC05 campaigns of the B/O EL PUMA dense total field magnetic surveys were conducted covering the entire plate boundary. Lastly, the multibeam coverage obtained during the BART/FAMEX campaigns was extended northward during the MORTIC07 campaign of the B/O EL PUMA. In this talk we will present these new data (some of which have already been published) and discuss the constraints that these data impose on the nature of the Rivera-Cocos plate boundary.

Bandy, W. L.; Mortera-Gutierrez, C. A.; Michaud, F.; Ortega Ramírez, J.

2013-05-01

432

Characterization of internal boundary layer capacitors  

SciTech Connect

Internal boundary layer capacitors were characterized by scanning transmission electron microscopy and by microscale electrical measurements. Data are given for the chemical and physical characteristics of the individual grains and boundaries, and their associated electric and dielectric properties. Segregated internal boundary layers were identified with resistivities of 10/sup 12/-10/sup 13/ ..cap omega..-cm. Bulk apparent dielectric constants were 10,000-60,000. A model is proposed to explain the dielectric behavior in terms of an equivalent n-c-i-c-n representation of ceramic microstructure, which is substantiated by capacitance-voltage analysis.

Park, H. D.; Payne, D. A.

1980-05-01

433

An outflow boundary condition for aeroacoustic computations  

NASA Technical Reports Server (NTRS)

A formulation of boundary condition for flows with small disturbances is presented. The authors test their methodology in an axisymmetric jet flow calculation, using both the Navier-Stokes and Euler equations. Solutions in the far field are assumed to be oscillatory. If the oscillatory disturbances are small, the growth of the solution variables can be predicted by linear theory. Eigenfunctions of the linear theory are used explicitly in the formulation of the boundary conditions. This guarantees correct solutions at the boundary in the limit where the predictions of linear theory are valid.

Hayder, M. Ehtesham; Hagstrom, Thomas

1995-01-01

434

Connectivity in Random Grain Boundary Networks  

SciTech Connect

Mechanical properties of FCC metals and alloys can be improved by exercising control over the population of grain boundary types in the microstructure. The existing studies also suggest that such properties tend to have percolative mechanisms that depend on the topology of the grain boundary network. With the emergence of SEM-based automated electron backscatter diffraction (EBSD), statistically significant datasets of interface crystallography can be analyzed in a routine manner, giving new insight into the topology and percolative properties of grain boundary networks. In this work, we review advanced analysis techniques for EBSD datasets to quantify microstructures in terms of grain boundary character and triple junction distributions, as well as detailed percolation-theory based cluster analysis.

Kumar, M; Schuh, C A; King, W E

2002-10-22

435

Roughness effect on the Neumann boundary condition  

E-print Network

rugosity, called wall law. This approach is however different from that usually used in Dirichlet case rugosity. That allows to give an application to the water waves equation. Key words: Neumann boundary

Boyer, Edmond

436

15 CFR 922.130 - Boundary.  

Code of Federal Regulations, 2010 CFR

...Point. The shoreward Sanctuary boundary excludes a small area between Point Bonita and Point San Pedro. Pillar Point Harbor, Santa Cruz Harbor, Monterey Harbor, and Moss Landing Harbor are all excluded from the Sanctuary shoreward from the points...

2010-01-01

437

Topological analysis of the grain boundary space  

E-print Network

Grain boundaries and their networks have a profound influence on the functional and structural properties of every class of polycrystalline materials and play a critical role in structural evolution and phase transformations. ...

Patala, Srikanth

2011-01-01

438

Brownian walkers within subdiffusing territorial boundaries  

E-print Network

Inspired by the collective phenomenon of territorial emergence, whereby animals move and interact through the scent marks they deposit, we study the dynamics of a 1D Brownian walker in a random environment consisting of confining boundaries that are themselves diffusing anomalously. We show how to reduce, in certain parameter regimes, the non-Markovian, many-body problem of territoriality to the analytically tractable one-body problem studied here. The mean square displacement (MSD) of the 1D Brownian walker within subdiffusing boundaries is calculated exactly and generalizes well known results when the boundaries are immobile. Furthermore, under certain conditions, if the boundary dynamics are strongly subdiffusive, we show the appearance of an interesting non-monotonicity in the time dependence of the MSD, giving rise to transient negative diffusion.

Luca Giuggioli; Jonathan R. Potts; Stephen Harris

2011-02-04

439

Quadratic Functionals with General Boundary Conditions  

SciTech Connect

The purpose of this paper is to give the Reid 'Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in terms of Riccati equation solutions.

Dosla, Z.; Dosly, O. [Department of Mathematics, Masaryk University, Janackovo nam. 2a, 66295 Brno (Czech Republic)

1997-11-15

440

Theory and application of radiation boundary operators  

NASA Technical Reports Server (NTRS)

A succinct unified review is provided of the theory of radiation boundary operators. With the recent introduction of the on-surface radiation condition (OSRC) method and the continued growth of finite-difference and finite-element techniques for modeling electromagnetic wave scattering problems, the understanding and use of radiation boundary operators has become increasingly important. Results are presented to illustrate the application of radiation boundary operators in both these areas. Recent OSRC results include analysis of the scattering behavior of both electrically small and large cylinders, a reactively loaded acoustic sphere, and a simple reentrant duct. Radiation boundary operator results include the demonstration of the effectiveness of higher-order operators in truncating finite-difference time-domain grids.

Moore, Thomas G.; Kriegsmann, Gregory A.; Taflove, Allen; Blaschak, Jeffrey G.

1988-01-01