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1

High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs  

NASA Astrophysics Data System (ADS)

The Triassic time scale is poorly constrained due to a paucity of high-precision radiometric ages. We present a 206Pb/238U age of 230.91 ± 0.33 Ma (error includes all known sources) for zircon from an ash bed in the upper Carnian (Upper Triassic) of southern Italy that requires a major revision of the Triassic time scale. For example, the Norian stage is lengthened to more than 20 m.y. The section containing the ash bed is correlated with other Tethyan sections and, indirectly, with the Newark astronomical polarity time scale (APTS). The dating provides also a minimum age for some important climatic and biotic events that occurred during the Carnian. We note a coincidence between these events and the eruption of the large igneous province of Wrangellia, but the possible link between volcanism and climatic and biotic events requires further scrutiny.

Furin, Stefano; Preto, Nereo; Rigo, Manuel; Roghi, Guido; Gianolla, Piero; Crowley, James L.; Bowring, Samuel A.

2006-12-01

2

Improving the Upper Triassic numerical time scale from cross-correlation between Tethyan marine sections and the continental Newark basin sequence  

Microsoft Academic Search

Magnetostratigraphic cross-correlations between biochronologically well-dated Tethyan marine sections and the astronomically tuned sedimentary sequence from the continental Newark basin (eastern North America) help to improve the Upper Triassic time scale. We show here that the most recent radiometric results constraining the age of the base and top of the Upper Triassic (?237 and ?200 Ma, respectively) strengthen the chronostratigraphic calibration

Yves Gallet; Leopold Krystyn; Jean Besse; Jean Marcoux

2003-01-01

3

A nonmarine record of eccentricity forcing through the Upper Triassic of southwest England and its correlation with the Newark Basin astronomically calibrated geomagnetic polarity time scale from North America  

NASA Astrophysics Data System (ADS)

The Late Triassic was a time of major environmental change, yet the precise chronology of events is poorly constrained owing to the nonmarine nature of most preserved Upper Triassic strata and the difficulty in correlating sections. St. Audrie's Bay, southwest England, has been the focus of many studies on this interval of time and is one of the proposed sections for the base Jurassic global stratotype section and point (GSSP). In this study, lacustrine deposits exposed at St. Audrie's Bay have been used to construct a floating astronomical time scale for ˜3.7 m.y. of the Late Triassic based on the recognition of ˜100 k.y. eccentricity cycles in rock color. In addition, we have correlated this time scale with an existing magnetostratigraphy through the same succession and produced an astronomically calibrated record of geomagnetic polarity. Using a novel statistical procedure, we have determined the correlation between this succession and the Late Triassic geomagnetic polarity time scale of the Newark Basin, North America, on which the current (2004) geological time scale is based. Our results show unequivocally that the studied St. Audrie's Bay succession represents part of the Norian and we demonstrate for the first time that cyclostratigraphy can be used in the correlation of Mesozoic strata between North America and Europe.

Kemp, David B.; Coe, Angela L.

2007-11-01

4

Status Report on the 40Ar/39Ar and U/Pb Dating of Tuffs in the Dewey Lake Formation of West Texas Towards Constraining the Permo-Triassic Magnetostratigraphic Time Scale  

NASA Astrophysics Data System (ADS)

A detailed magnetic polarity time scale for the Permo-Triassic Boundary interval, critical for correlating events in marine and terrestrial paleoenvironments, is not yet well-established. Recently, late Permian magnetostratigraphic studies have been reported for non-marine sections in Europe and South Africa (Szurlies et al., 2003; Nawrocki, 2004; Ward et al., 2005). However, these sections are devoid of index fossil suitable for correlation with marine successions and also lack age constraints from radioisotopic dating methods. In other words, it is dubious to correlate these magnetostratigraphic data with the GSSP Permo-Triassic boundary and mass extinction. The Dewey Lake red beds formation of West Texas, believed to be the youngest Permian formation in North America, has yielded high-quality paleomagnetic data (Molina-Garza et al., 1989; Steiner, 2001) and contains several silicic tuffs potentially enabling high-resolution calibration of the magnetic polarity time scale in this critical age range. The tuffs have yet to be placed into a regional stratigraphic or magnetostratigraphic framework, and it is unclear exactly how many distinct eruptive units are represented by the 7 distinct samples collected to date from widely separated (>160 km) localities. 40Ar/39Ar (sanidine and biotite) and U/Pb (zircon) studies reveal that all 7 sampled tuffs were probably erupted within several hundred ka of the Permo-Triassic boundary as dated at the Meishan GSSP section (Renne et al., 1995; Mundil et al., 2004) but results thus far are inadequate to convincingly resolve age differences between the various samples. U/Pb dating of some samples is severely challenged by Pb-loss from the zircons despite application of the Mattinson (2005) annealing/chemical abrasion technique. 40Ar/39Ar data have been obtained from as many as four different irradiations in order to reduce neutron fluence related error. We observe the familiar ~1% bias between U/Pb and 40Ar/39Ar ages. Biotite microprobe data, zircon U/Th TIMS data, and the absence of sanidine from some samples serve to help correlate or distinguish some samples despite irresolvable age differences; existing data suggest that 4 distinct tuffs are present in the Dewey Lake Formation. Resolving their ages convincingly will require further work, but it is clear from our results combined with previous magnetostratigraphic data that magnetic polarity reversals were relatively frequent in the latest Permian. Thus the uniqueness of correlations elsewhere with the Permo-Triassic boundary based on magnetostratigraphy alone are not well-founded.

Chang, S.; Renne, P. R.; Mundil, R.

2007-12-01

5

A Mesozoic time scale  

Microsoft Academic Search

We present an integrated geomagnetic polarity and stratigraphic time scale for the Triassic, Jurassic, and Cretaceous periods of the Mesozoic Era, with age estimates and uncertainty limits for stage boundaries. The time scale uses a suite of 324 radiometric dates, including high-resolution Ar-40\\/Ar-39 age estimates. This framework involves the observed ties between (1) radiometric dates, biozones, and stage boundaries, and

Felix M. Gradstein; Frits P. Agterberg; James G. Ogg; Jan Hardenbol; Paul van Veen; Jacques Thierry; Zehui Huang

1994-01-01

6

Isoarborinol through geological times: Evidence for its presence in the Permian and Triassic  

Microsoft Academic Search

Optical rotation measurements and HPLC chiral separations using a ?-cyclodextrin phase, performed on aromatic hydrocarbons isolated from diverse geological sources, and belonging to the arborane or fernane triterpenoid series, have shown that isoarborinol, one of the possible biological precursors, was abundantly present at the time of deposition of Permian and Triassic sediments. This fact considerably reinforces the hypothesis that arborane

V. Hauke; P. Adam; J.-M. Trendel; P. Albrecht; L. Schwark; M. Vliex; H. Hagemann; W. Püttmann

1995-01-01

7

Residence time indicators in groundwater: the East Midlands Triassic sandstone aquifer  

Microsoft Academic Search

The East Midlands Triassic (Sherwood Sandstone) aquifer which has been the subject of detailed radiometric age studies, is used to investigate both inert and reactive constituents of groundwater as indicators of residence time. Detailed resampling of the aquifer in 1992 has provided a considerable body of new inorganic geochemistry data, though without radiocarbon. Several inert indicators are defined including the

W. M Edmunds; P. L Smedley

2000-01-01

8

The time has changed: Middle Triassic climate changes revealed by carbon isotopes  

NASA Astrophysics Data System (ADS)

The Middle Triassic stratigraphy in Europe can be subdivided into a marine section of the Germanic and Paris Basin and a continental red-bed succession of Western Europe (Irish Basin, Wessex Basin). The link between the marine and continental is uncertain due to a lack of biostratigraphic information but recent palaeomagnetic studies have given a better understanding of the two environments (Hounslow et. al, 2001). In this study we have produced geochemical evidence which emphasize the implications of the palaeomagnetic data. We show that the marine and continental strata can be correlated using carbon isotopes. Throughout Europe the Middle Triassic is characterized by limestone deposits of the Muschelkalk Formation that contain evidence of a hiatus in sedimentation due to sea-level fall in the Middle Muschelkalk with the consequent deposition of evaporites. The Sherwood Sandstone Group (SSG) characterizes the Middle Triassic of Western Europe. The SSG is dominated by fluvial deposits with intercalated floodplain deposits, sand-flats and playas, which are penetrated by dolocretes and calcretes. The abundance of fluvial channels and sandflats are dependent on the fluvial activity and the water table height. In both depositional environments water plays a major role in the type of sediment. The volume of water is controlled by the prevalent climate. Climate signals are stored in carbon isotopes in both the marine Muschelkalk and the continental SSG. Carbon isotopes from the SSG from the Corrib Field, Slyne Basin, west of Ireland and from the Muschelkalk of the Germanic Basin have thus been interpreted in terms of climate change linked to stratigraphy. The continental sediments show a distinct positive carbon isotope excursion (taken from dolocretes), which is interpreted to present a more arid climate. In contrast the marine limestones exhibit a negative carbon isotopes excursion from a sea level low stand for the same time interval. The plot of both carbon isotopes curves against depth (using the Anisian-Ladinian boundary as a correlation marker) with a correction of sediment thickness show the same general climatic conditions for the Middle Triassic in Europe. Carbon isotope data from the Muschelkalk of the Germanic Basin and the SSG of the Slyne Basin reveal that the Middle Triassic was a time that witnessed a change from a humid to an arid climate with less fluvial activity in the continental parts and evaporite deposition in the marine part of Europe. References: Hounslow, M.W., McIntosh, G. &Jenkins, G.(2001): Magnetostratigraphy of the Middle Triassic: Sherwood Sandstone Group, South Devon, UK, EGS Nice

Schmid, S.; Worden, R.; Fisher, Q.

2003-04-01

9

Recognising ocean acidification in deep time: An evaluation of the evidence for acidification across the Triassic-Jurassic boundary  

NASA Astrophysics Data System (ADS)

While demonstrating ocean acidification in the modern is relatively straightforward (measure increase in atmospheric CO2 and corresponding ocean chemistry change), identifying palaeo-ocean acidification is problematic. The crux of this problem is that the rock record is a constructive archive while ocean acidification is essentially a destructive (and/or inhibitory) phenomenon. This is exacerbated in deep time without the benefit of a deep ocean record. Here, we discuss the feasibility of, and potential criteria for, identifying an acidification event in deep time. Furthermore, we investigate the evidence for ocean acidification during the Triassic-Jurassic (T-J) boundary interval, an excellent test case because 1) it occurs in deep time, beyond the reach of deep sea drilling coverage; 2) a potential trigger for acidification is known; and 3) it is associated with one of the 'Big Five' mass extinctions which disproportionately affected modern-style invertebrates. Three main criteria suggest that acidification may have occurred across the T-J transition. 1) The eruption of the Central Atlantic Magmatic Province (CAMP) and the associated massive and rapid release of CO2 coincident with the end-Triassic mass extinction provide a suitable trigger for an acidification event (full carbonate undersaturation in the surface ocean is possible but improbable). 2) Tentative evidence for a global paucity of carbonate across the end-Triassic mass extinction versus the adjacent stratigraphy is consistent with a predicted sedimentary response to acidification. 3) The end-Triassic mass extinction was particularly selective against acid-sensitive organisms (more so than perhaps any other extinction event) and temporarily eliminated coral reefs. Therefore multiple lines of evidence are consistent with a T-J ocean acidification event within our current resolution to recognise such events in deep time. The conclusion that the end-Triassic extinction was influenced by acidification implies that short-term acidification perturbations may have long-term effects on ecosystems, a repercussion that has previously not been established. Although anthropogenic emissions are more rapid than any event in the geologic record, events such as the T-J can serve as partial analogues for the present anthropogenic carbon release. Since the T-J was such a pronounced crisis for both modern-style marine invertebrates and scleractinian reefs, it is of particular interest in terms of informing projections about the effects of modern ocean acidification.

Greene, Sarah E.; Martindale, Rowan C.; Ritterbush, Kathleen A.; Bottjer, David J.; Corsetti, Frank A.; Berelson, William M.

2012-06-01

10

Position of the Triassic-Jurassic boundary and timing of the end-Triassic extinctions on land: Data from the Moenave Formation on the southern Colorado Plateau, USA  

USGS Publications Warehouse

Strata of the Moenave Formation on and adjacent to the southern Colorado Plateau in Utah-Arizona, U.S.A., represent one of the best known and most stratigraphically continuous, complete and fossiliferous terrestrial sections across the Triassic-Jurassic boundary. We present a synthesis of new biostratigraphic and magnetostratigraphic data collected from across the Moenave Formation outcrop belt, which extends from the St. George area in southwestern Utah to the Tuba City area in northern Arizona. These data include palynomorphs, conchostracans and vertebrate fossils (including footprints) and a composite polarity record based on four overlapping magnetostratigraphic sections. Placement of the Triassic-Jurassic boundary in strata of the Moenave Formation has long been imprecise and debatable, but these new data (especially the conchostracans) allow us to place the Triassic-Jurassic boundary relatively precisely in the middle part of the Whitmore Point Member of the Moenave Formation, stratigraphically well above the highest occurrence of crurotarsan body fossils or footprints. Correlation to marine sections based on this placement indicates that major terrestrial vertebrate extinctions preceded marine extinctions across the Triassic-Jurassic boundary and therefore were likely unrelated to the Central Atlantic Magmatic Province (CAMP) volcanism. ?? 2011 Elsevier B.V.

Lucas, S. G.; Tanner, L. H.; Donohoo-Hurley, L. L.; Geissman, J. W.; Kozur, H. W.; Heckert, A. B.; Weems, R. E.

2011-01-01

11

Geological Time Scale  

NSDL National Science Digital Library

This document describes how geologic time is approached in discussions of geologic topics. The uses of relative time and absolute time are compared, and a geologic time scale is provided to represent both concepts. References are provided.

12

Global Triassic tetrapod biostratigraphy and biochronology  

Microsoft Academic Search

Eight, temporally successive assemblage zones of tetrapod fossils provide the basis for dividing Triassic time into eight land-vertebrate faunachrons. These land-vertebrate faunachrons, their type assemblage zones, and their approximate correlation to the standard global chronostratigraphic scale are (ascending order): (1) Lootsbergian (Lystrosaurus Assemblage Zone, Balfour, Katberg and Burgersdorp formations, Karoo basin, South Africa) = late Dorashamian–Induan; (2) Nonesian (Cynognathus Assemblage

Spencer G Lucas

1998-01-01

13

GSA Geologic Time Scale  

NSDL National Science Digital Library

This Geological Society of America (GSA) site contains a detailed geologic time scale as an educational resource. It may be downloaded to a larger size, and includes all Eras, Eons, Periods, Epochs and ages as well as magnetic polarity information.

1999-01-01

14

Integration on time scales  

Microsoft Academic Search

In this paper we study the process of Riemann and Lebesgue integration on time scales. The relationship of the Riemann and Lebesgue integrals is considered and a criterion for Riemann integrability is established.

Gusein Sh. Guseinov

2003-01-01

15

Permain-Triassic Life Crisis on Land  

NASA Astrophysics Data System (ADS)

Recent advances in radiometric dating and isotopic stratigraphy have resulted in a different placement of the Permian-Triassic boundary within the sedimentary sequence of the Sydney Basin of southeastern Australia. This boundary at 251 million years ago was a time of abrupt decline in both diversity and provincialism of floras in southeastern Australia and extinction of the Glossopteris flora. Early Triassic vegetation was low in diversity and dominated by lycopods and voltzialean conifers. The seed fern Dicroidium appeared in the wake of Permian-Triassic boundary floral reorganization, but floras dominated by Dicroidium did not attain Permian levels of diversity and provinciality until the Middle Triassic (244 million years ago).

Retallack, G. J.

1995-01-01

16

The Geologic Time Scale  

NSDL National Science Digital Library

This site contains a large, easy to read, detailed geologic time scale for the Phanerozoic Eon (544 million years ago - Present). This is the period of time, also known as an eon, between the end of the Precambrian and today. The Phanerozoic begins with the start of the Cambrian period, 544 million years ago. It encompasses the period of abundant, complex life on Earth. The chart includes the Era, Period or System, and the Epoch or Series and features a brief description of each.

17

Web Geologic Time Scale  

NSDL National Science Digital Library

The University of California-Berkeley Museum of Paleontology (last mentioned in the June 16, 1995 Scout Report) has recently updated its Web Geologic Time Scale, an online feature that helps users learn about the geologic timeline and explore related museum exhibits. The familiar geologic timeline appears on the main page of the Web site, with hypertext links for each division of time. Every page of the Web Geologic Time Machine site is liberally sprinkled with links to related UCMP Web pages; think of it as a portal to all online information available from the museum. Altogether, this Web site provides a well-organized and comprehensive resource for learning how the planet has changed over time, and would be a great addition to earth or life sciences classroom material for a broad range of grades.

1994-01-01

18

How severe is the modern biotic crisis?—A comparison of global change and biotic crisis between Permian-Triassic transition and modern times  

Microsoft Academic Search

A comparison of the modern condition with the Permian-Triassic Boundary (PTB) times was made to estimate how severe the modern\\u000a biotic crisis is. About the global changes, the two periods are correlative in carbon dioxide concentration and carbon isotope\\u000a negative excursion, UV strengthening, temperature increase, ocean acidification, and weathering enhancement. The following\\u000a tendencies of biotic crises are also correlative: acceleration

Hongfu Yin; Weihong He; Shucheng Xie

2011-01-01

19

Time scales in fragmentation  

SciTech Connect

The problem of fragmentation of excited finite systems is explored in the frame of classical molecular dynamics experiments of two-dimensional Lennard-Jones drops. The main objective of this work is to get information about the relative value of the relevant characteristic time scales (CTS) for this kind of process. We investigate the CTS for fragment formation, the stabilization of the radial flux, and the internal {open_quotes}temperature.{close_quotes} It is found that the asymptotic fragments are realized early in phase space, when the system is still dense, by the time the radial flux attains its asymptotic value. It is also shown that the temperature of the system during the breakup is quite homogenous with respect to the expected profile if local thermal equilibration takes place. Special emphasis is put on the investigation of the time scale of stabilization of the statistical properties of the mass spectrum, which is related to the kind of information carried by the asymptotic fragments. {copyright} {ital 1997} {ital The American Physical Society}

Strachan, A.; Dorso, C.O. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellon I, Ciudad Universitaria, Nunez 1428, Buenos Aires (Argentina)

1997-02-01

20

A Geologic Time Scale 2004  

Microsoft Academic Search

A successor to A Geologic Time Scale 1989 (Cambridge, 1990), this volume introduces the theory and methodology behind the construction of the new time scale, before presenting the scale itself in extensive detail. An international team of over forty stratigraphic experts develops the most up-to-date international stratigraphic framework for the Precambrian and Phanerozoic eras. A large wallchart summarizing the time

Felix M. Gradstein; James G. Ogg; Alan G. Smith

2005-01-01

21

Relation of Middle and Late Triassic strata of N-C Nevada to contemporaneous strata of southern Nevada and Utah  

SciTech Connect

Middle and Late Triassic shelf strata in north-central Nevada comprising dominantly carbonate rocks of the Star Peak Group and overlying siliciclastic and carbonate rocks are overlain tectonically by predominantly siliciclastic basinal strata. Late Triassic slope strata are preserved in the East and Humboldt Ranges. At present, these Triassic rocks are separated from contemporaneous deposits of Utah by roughly 300 km over which time-equivalent ( ) strata are limited to a small, isolated outcrop near Currie, NV. Mesozoic and Cenozoic tectonics and widespread absence of Triassic rocks immediately to the east complicate the relation between the north-central Nevada section and Triassic rocks of southern Nevada and Utah. The gap in Triassic rocks may have resulted from erosion of intervening strata or from tectonic separation of originally contiguous stratal sequences. Some depositional facies of the shelf uniformly cover the preserved outcrop area and do not constrain the scale of the depositional system. Where facies variations are present, they suggest sediment sources to the east and north and deeper water to the west. Facies patterns, however, were influenced by local tectonics and changes in sediment source and supply. Late Triassic strata of N-C Nevada probably are the shallow-marine equivalents of fluvial and lacustrine rocks to the east. Local tectonics and changes in sediment influx require caution regarding interpretation of the original proximity of preserved stratal sequences.

Elison, M.W.

1993-04-01

22

Stability of Pulsar Time Scale.  

NASA Astrophysics Data System (ADS)

It is well known, that stability of pulsar period in the barycenter of Solar system depends on different effects. The stability is determined by both physical conditions in pulsar and processes along the way of signal propagation which affect the pulse time of arrival (TOA). In the presentation it will be discussed stability of pulsar time scale based on the long term millisecond pulsar timing. It will be considered an influence of the propagation conditions along the pulsar signal way. In this presentation it will be considered an influence of microlensing to TOA, as well. This effect can put a natural limit for pulsar time scale stability.

Sazhin, M. V.; Pshirkov, M. S.

2006-08-01

23

Timing and Extent of Magmatism Associated With the Permo-Triassic Siberian Large Igneous Province: The Biggest Gets Bigger.  

NASA Astrophysics Data System (ADS)

The generation of large igneous provinces, and whether or not they are responsible for mass extinctions, are hotly debated. The Siberian Traps represent the remnants of the largest Phanerozoic continental flood basalt province, with an estimated original size of 4 x 106 km2 and an original combined volume of at least 2 x 106 km3 (Milanovskiy, 1976). The province may also be responsible for the Permo-Triassic mass extinction at 251 Ma. Despite recent intensive research on the province, the extent and duration of extrusive and related magmatism are still controversial. Although several areas surrounding the Siberian craton have been attributed to the Siberian Traps volcanic activity, the full extent remains conjectural as precise age determinations and chemical correlations between units are missing. Basaltic, gabbroic and rhyolitic rocks occur throughout the West Siberian Basin beneath a thick succession of Mesozoic and Cenozoic sediments. Thicknesses of the lava sequences vary but exceed 2 km in places. Areas with basalt and dolerite rocks supposedly related to the Siberian Traps are also reported further to the north of the Siberian craton, on the Taimyr Peninsula, along the eastern border of the Urals (Chelyabinsk) and in the polar Urals (Vorkuta), and to the south within the Kuznetsk Basin (Kuzbass) and Semeitau (Kazakhstan) areas. We have obtained widespread early Triassic sample material from across Siberia, and present an assessment of published and new geochemical and isotopic age data. Basalts from the West Siberian Basin, and the Chelyabinsk, Kuzbass, Vorkuta regions have chemical characteristics typical of evolved, crustally- contaminated continental flood basalts (e.g., low Mg#, negative Nb anomaly) showing affinities with the Nadezhdinsky suite of the main traps from the Noril'sk area. The Nadezhdinsky suite is known to immediately precede the supposedly main pulse of volcanism that extruded over large areas of the craton. The data indicate that the basalts and associated rhyolites are likely to be a part of the greater Siberian LIP, although it is not yet possible, with the currently available data, to define the duration of activity. We review of the challenges of explaining the generation of the Siberian Large Igneous Province.

Reichow, M. K.; Saunders, A. D.; Pringle, M. S.; Puchkov, V. N.; Safonova, I. Y.; Fedoseev, G. S.; Buslov, M. M.

2006-12-01

24

Stability of Pulsar Time Scale  

Microsoft Academic Search

It is well known, that stability of pulsar period in the barycenter of Solar system depends on different effects. The stability is determined by both physical conditions in pulsar and processes along the way of signal propagation which affect the pulse time of arrival (TOA). In the presentation it will be discussed stability of pulsar time scale based on the

M. V. Sazhin; M. S. Pshirkov

2006-01-01

25

Deep Time: The Geologic Time Scale  

NSDL National Science Digital Library

This page examines the issues involved in teaching students about the geologic time scale. There are suggestions for tackling troublesome issues in class as well as activities that can be used to clarify how geoscientists look at deep time. Five main concepts with which students struggle when thinking about Deep Time are addressed here: imagining or comprehending big numbers; the difference between relative and numerical age; the concept of "timescales"; the ways we know about the age of the Earth and other materials; and resolving perceived issues with religious beliefs.

2007-01-01

26

Developing an IGS time scale.  

PubMed

Currently, the International GPS Service (IGS) provides a set of clock products for both satellites and tracking receivers, tabulated at 5-min intervals. These products allow users to determine consistent coordinates and clock values for an isolated GPS receiver with an internal accuracy at the few-cm level. However, because the underlying time scale for the IGS combined clocks is based on a linear alignment to broadcast GPS Time for each day separately, the day-to-day stability of this reference is poor. We show the results of a new filter package written to automate the production of an integrated IGS frequency scale based on a dynamically weighted ensemble of the included frequency standards. The new scale is loosely steered to GPS Time. PMID:12839170

Senior, Ken; Koppang, Paul; Ray, Jim

2003-06-01

27

The history of the Arabian platform evolution in the Late Permian and Triassic  

SciTech Connect

On the basis of comprehensive investigations of the Upper Permian and Triassic sequences of the Arabian platform, three stages were recognized, corresponding to distinct time intervals. The first stage corresponds to the Latest Permian-Early Triassic, the second - to the Early-Middle Triassic, the third - to the Late Triassic. Special maps were plotted for the second and third stages, reflecting major paleogeographic and paleotectonic events. An effort was made to test the oil potential of the sequences.

Bebeshev, I.I. [Geological Institute, Moscow (Russian Federation)

1995-03-01

28

THE VERTEBRATE FAUNA OF THE UPPER TRIASSIC CHINLE FORMATION IN NORTHERN ARIZONA  

Microsoft Academic Search

The Upper Triassic Chinle Formation of the southwestern United States preserves one of the most taxonomically diverse records of Late Triassic vertebrates in North America. This record spans at least 25 million years from the Late Carnian to the near end of the Triassic Period (Lucas, 1998). It is a time of faunal turnover, with earlier basal archosaur and temnospondyl

RANDALL B. IRMIS

29

The Concise Geologic Time Scale  

Microsoft Academic Search

This concise handbook presents a summary of Earth's history over the past 4.5 billion years as well as a brief overview of contemporaneous events on the Moon, Mars and Venus. The authors have been at the forefront of chronostratigraphic research and initiatives to create an international geologic time scale for many years, and the charts in this book present the

James G. Ogg; Gabi Ogg; Felix M. Gradstein

2008-01-01

30

Developing an IGS time scale  

Microsoft Academic Search

Currently, the International GPS Service (IGS) provides a set of clock products for both satellites and tracking receivers, tabulated at 5-min intervals. These products allow users to determine consistent coordinates and clock values for an isolated GPS receiver with an internal accuracy at the few-cm level. However, because the underlying time scale for the IGS combined clocks is based on

Ken Senior; Paul Koppang; Jim Ray

2003-01-01

31

Developing an IGS time scale  

Microsoft Academic Search

Currently, the International GPS Service (IGS) provides a set of clock products for both satellites and tracking receivers, tabulated at 5-minute intervals. These products provide users with sufficient information to determine consistent coordinates and clock values for an isolated GPS receiver with a precision at roughly the 5-cm level. However, because the underlying time scale for the IGS combined clocks

Ken Senior; Paul Koppang; Demetrios Matsakis

2001-01-01

32

Variations in Os- and Mo-isotope compositions and trace element abundances across the Permo-Triassic boundary, Meishan, China: Proxy evidence for large-scale oceanic anoxia?  

NASA Astrophysics Data System (ADS)

We have carried out Os-isotope analyses, and major and trace element determinations, on samples from the Permo-Triassic section at Meishan B sections, adjacent to the GSSP, China, to assess environmental change at the P-Tr boundary (Bed 27) and the underlying main extinction horizon (Bed 25). Major and trace element abundances were determined by XRF on 38 samples from a 2.3-metre interval of limestone, shale and dolomitic marl from Bed 24a to Bed 32. Re, Os and Mo abundances, and Os-isotope compositions, were determined on a subset of 26 samples, predominantly dark-coloured mudrocks; new Mo-isotope data will be presented. Initial 187Os/188Os(t=250Ma) ranges from 0.3 to 2, with no obvious pattern of change up-section. The data thus provide no unambiguous evidence at Meishan for major perturbation of seawater 187Os/188Os in this region of Palaeotethys, at least at the scale of the sampling. This is unlike early Jurassic and end-Cretaceous boundary sections, and mid-Cretaceous OAE intervals, which record substantial shifts in seawater 187Os/188Os that clearly reflect the influence of LIP emplacement. Major changes in elemental abundances occur between Beds 24 and Bed 27, accompanying the documented excursion in d13C. Redox- and biologically-sensitive elements such as Cu, Ni, P, V and Zn show strong fluctuations in abundance throughout Bed 24, even when abundances are normalised using Al2O3 to minimise the effects of carbonate dilution. In the lower part of Bed 27, however, the Al2O3-normalised concentrations of these elements decrease by an order of magnitude, and remain consistently low in the overlying Triassic marls. The relative decreases in Re and Os abundances throughout Bed 27 are even more substantial. Whilst these decreases are partly an artefact of Al-normalisation, the changes are accompanied by large increases in ratios involving lithogenous elements such as REE, Nb, Zr, Th and Ti. The data thus record a dramatic change in the marine depositional environment at Meishan, particularly within Bed 27, although levels of redox-sensitive elements were also very low within the upper part of Bed 24. A possible cause of these changes may have been an increase in the flux of terrigenous material, but this is not reflected by any obvious changes in 187Os/188O. Alternatively, these observations may reflect the occurrence of widespread oceanic anoxia in distal but contiguous water masses that caused a sudden reduction in the abundance of redox-sensitive elements in seawater. If the Meishan seas were fully open with Paleotethys, then seawater anoxia was global, as suggested by other studies. These results, combined with new Mo-isotope data, will shed further light on the phenomenon of marine anoxia in the vicinity of the P-Tr boundary and its relationship to the largest mass extinction of the Phanerozoic.

Cohen, A. S.; Saunders, A.; Zhang, H.; Li, J.

2009-12-01

33

Triassic-Jurassic marine anoxia in response to massive carbon release from CAMP?  

NASA Astrophysics Data System (ADS)

The end-Triassic mass extinction [~201.3 Ma], marked by marine and terrestrial ecosystem collapse and global marine biodiversity loss, coincides with the onset of extensive volcanic activity and emplacement of the Central Atlantic Magmatic Province (CAMP). Massive and rapid greenhouse gas release from surface basalts, subsurface organic rich strata and ocean-floor clathrate-hydrates had a profound impact on the global exogenic carbon cycle and it dramatically increased atmospheric pCO2 values. Although Permian-Triassic [~252 Ma] and early Toarcian [~183 Ma] volcanic carbon release is thought to have initiated global ocean anoxic events, ocean redox changes at the end-Triassic mass extinction are poorly constrained. Marine anoxia is only suggested by organic-rich, finely laminated sediment deposition in marginal marine basins. We studied the biostratigraphically well-constrained Triassic-Jurassic marine sedimentary record from St. Audrie's Bay (UK), which is astronomically calibrated to the continental geomagnetic polarity time-scale (GPTS) of the continental Newark basin. This marine geological archive is marked by precession paced black-shale deposition, similar to Neogene Mediterranean sapropels. We studied redox-sensitive trace element concentrations (e.g. Mo, U, V, Cu, Ni), iron-speciation (FeHR/FeT, FePY/FeHR) and ?34S-pyrite through the end-Triassic mass extinction and subsequent 3 million years of the lower Jurassic. We observe direct stratigraphic correlation between CAMP flood basalt emplacement, strong atmospheric pCO2 increase and development of marine anoxia. This now allows evaluation of mechanistic relations between massive greenhouse gas emissions initiated by CAMP volcanism, subsequent environmental change and upper Triassic and lower Jurassic biotic response.

Ruhl, M.; Bjerrum, C. J.; Canfield, D. E.; Frei, R.

2012-04-01

34

Late Triassic volcanic activity in South-East Asia: New stratigraphical, geochronological and paleontological evidence from the Luang Prabang Basin (Laos)  

NASA Astrophysics Data System (ADS)

Relative and absolute time constraints in the Permian–Triassic from SE Asia.Continental deposits including tuffites provide evidence for Late Triassic fluvial reworking.At least ˜10 Ma of active volcanism during Late Triassic sedimentation.Discovery of a new Dicynodont skull, Kannemeyeriidae family.Potential Permian-Triassic unconformity within the Indochina Block.

Blanchard, Sébastien; Rossignol, Camille; Bourquin, Sylvie; Dabard, Marie-Pierre; Hallot, Erwan; Nalpas, Thierry; Poujol, Marc; Battail, Bernard; Jalil, Nour-Eddine; Steyer, Jean-Sébastien; Vacant, Renaud; Véran, Monette; Bercovici, Antoine; Diez, José Bienvenido; Paquette, Jean-Louis; Khenthavong, Bounxou; Vongphamany, Sotsy

2013-07-01

35

Time scales in cognitive neuroscience.  

PubMed

Cognitive neuroscience boils down to describing the ways in which cognitive function results from brain activity. In turn, brain activity shows complex fluctuations, with structure at many spatio-temporal scales. Exactly how cognitive function inherits the physical dimensions of neural activity, though, is highly non-trivial, and so are generally the corresponding dimensions of cognitive phenomena. As for any physical phenomenon, when studying cognitive function, the first conceptual step should be that of establishing its dimensions. Here, we provide a systematic presentation of the temporal aspects of task-related brain activity, from the smallest scale of the brain imaging technique's resolution, to the observation time of a given experiment, through the characteristic time scales of the process under study. We first review some standard assumptions on the temporal scales of cognitive function. In spite of their general use, these assumptions hold true to a high degree of approximation for many cognitive (viz. fast perceptual) processes, but have their limitations for other ones (e.g., thinking or reasoning). We define in a rigorous way the temporal quantifiers of cognition at all scales, and illustrate how they qualitatively vary as a function of the properties of the cognitive process under study. We propose that each phenomenon should be approached with its own set of theoretical, methodological and analytical tools. In particular, we show that when treating cognitive processes such as thinking or reasoning, complex properties of ongoing brain activity, which can be drastically simplified when considering fast (e.g., perceptual) processes, start playing a major role, and not only characterize the temporal properties of task-related brain activity, but also determine the conditions for proper observation of the phenomena. Finally, some implications on the design of experiments, data analyses, and the choice of recording parameters are discussed. PMID:23626578

Papo, David

2013-04-19

36

Time scales in cognitive neuroscience  

PubMed Central

Cognitive neuroscience boils down to describing the ways in which cognitive function results from brain activity. In turn, brain activity shows complex fluctuations, with structure at many spatio-temporal scales. Exactly how cognitive function inherits the physical dimensions of neural activity, though, is highly non-trivial, and so are generally the corresponding dimensions of cognitive phenomena. As for any physical phenomenon, when studying cognitive function, the first conceptual step should be that of establishing its dimensions. Here, we provide a systematic presentation of the temporal aspects of task-related brain activity, from the smallest scale of the brain imaging technique's resolution, to the observation time of a given experiment, through the characteristic time scales of the process under study. We first review some standard assumptions on the temporal scales of cognitive function. In spite of their general use, these assumptions hold true to a high degree of approximation for many cognitive (viz. fast perceptual) processes, but have their limitations for other ones (e.g., thinking or reasoning). We define in a rigorous way the temporal quantifiers of cognition at all scales, and illustrate how they qualitatively vary as a function of the properties of the cognitive process under study. We propose that each phenomenon should be approached with its own set of theoretical, methodological and analytical tools. In particular, we show that when treating cognitive processes such as thinking or reasoning, complex properties of ongoing brain activity, which can be drastically simplified when considering fast (e.g., perceptual) processes, start playing a major role, and not only characterize the temporal properties of task-related brain activity, but also determine the conditions for proper observation of the phenomena. Finally, some implications on the design of experiments, data analyses, and the choice of recording parameters are discussed.

Papo, David

2013-01-01

37

Triassic in Iran  

Microsoft Academic Search

Summary  Except of the Nakhlak and Aghdarband regions, Lower and Middle Triassic strata in Iran consist almost exclusively of carbonate\\u000a rocks built on vast platforms along the shelves of the Paleo- and Neotethys. The depositional environments varied from shallow\\u000a shelf sea to lagoonal and near-shore tidal flats, becoming even evaporitic towards the coastal regions of the Persian Gulf.\\u000a During the early

Kazem Seyed-Emami

2003-01-01

38

The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation  

PubMed Central

Background Archosaurs (birds, crocodilians and their extinct relatives including dinosaurs) dominated Mesozoic continental ecosystems from the Late Triassic onwards, and still form a major component of modern ecosystems (>10,000 species). The earliest diverse archosaur faunal assemblages are known from the Middle Triassic (c. 244 Ma), implying that the archosaur radiation began in the Early Triassic (252.3–247.2 Ma). Understanding of this radiation is currently limited by the poor early fossil record of the group in terms of skeletal remains. Methodology/Principal Findings We redescribe the anatomy and stratigraphic position of the type specimen of Ctenosauriscus koeneni (Huene), a sail-backed reptile from the Early Triassic (late Olenekian) Solling Formation of northern Germany that potentially represents the oldest known archosaur. We critically discuss previous biomechanical work on the ‘sail’ of Ctenosauriscus, which is formed by a series of elongated neural spines. In addition, we describe Ctenosauriscus-like postcranial material from the earliest Middle Triassic (early Anisian) Röt Formation of Waldhaus, southwestern Germany. Finally, we review the spatial and temporal distribution of the earliest archosaur fossils and their implications for understanding the dynamics of the archosaur radiation. Conclusions/Significance Comprehensive numerical phylogenetic analyses demonstrate that both Ctenosauriscus and the Waldhaus taxon are members of a monophyletic grouping of poposauroid archosaurs, Ctenosauriscidae, characterised by greatly elongated neural spines in the posterior cervical to anterior caudal vertebrae. The earliest archosaurs, including Ctenosauriscus, appear in the body fossil record just prior to the Olenekian/Anisian boundary (c. 248 Ma), less than 5 million years after the Permian–Triassic mass extinction. These earliest archosaur assemblages are dominated by ctenosauriscids, which were broadly distributed across northern Pangea and which appear to have been the first global radiation of archosaurs.

Butler, Richard J.; Brusatte, Stephen L.; Reich, Mike; Nesbitt, Sterling J.; Schoch, Rainer R.; Hornung, Jahn J.

2011-01-01

39

How severe is the modern biotic crisis?—A comparison of global change and biotic crisis between Permian-Triassic transition and modern times  

NASA Astrophysics Data System (ADS)

A comparison of the modern condition with the Permian-Triassic Boundary (PTB) times was made to estimate how severe the modern biotic crisis is. About the global changes, the two periods are correlative in carbon dioxide concentration and carbon isotope negative excursion, UV strengthening, temperature increase, ocean acidification, and weathering enhancement. The following tendencies of biotic crises are also correlative: acceleration of extinction rates accompanied by parabolic curve of extinction with a turning interval representing the critical crisis; decline of the three main ecosystems: reefs, tropical rain forests and marine phytoplankton. It is also interesting to note that certain leading organism in both periods undergo accelerated evolution during the crisis. The comparison shows that the modern crisis is about at the turning point from decline to decimation. The extinction curve is now parabolic, and the extinction rate has been accelerated, but the decimation is not yet in real. This is also justified by the modern situation of the three main ecosystems. Modern biotic decline may worsen into decimation and mass extinction but may also get better and recover to ordinary evolution. Since human activities are the main cause of the deterioration of environments and organisms, mankind should be responsible and able to strive for the recovery of the crisis. For the future of mankind, Homo sapiens may become extinct, i.e., disappear without leaving descendants, or evolve into a new and more advanced species, i.e., disappear but leave descendants. For a better future, mankind should be conscious of the facing danger and act as a whole to save biodiversity and harmonize with the environments.

Yin, Hongfu; He, Weihong; Xie, Shucheng

2011-03-01

40

Stability of Rasch Scales Over Time  

Microsoft Academic Search

Item response theory (IRT) methods are generally used to create score scales for large-scale tests. Research has shown that IRT scales are stable across groups and over time. Most studies have focused on items that are dichotomously scored. Now Rasch and other IRT models are used to create scales for tests that include polytomously scored items. When tests are equated

Catherine S. Taylor; Yoonsun Lee

2009-01-01

41

Scaling regimes of composite rainfall time series  

Microsoft Academic Search

The scaling behaviour of rainfall is analysed both for a range of scales in time and for a given scale in intensity using the statistics of the Fourier transform and the cumulative probability distribution. The analyses are applied to sets of long time series of daily rainfall (26 (8) files of 45 (90) years at 13 European stations) and sets

Klaus Fraedrich; Chris Larnder

1993-01-01

42

New constraints on the End-Triassic (Upper Norian Rhaetian) magnetostratigraphy  

NASA Astrophysics Data System (ADS)

The end-Triassic was marked by one of the five important Phanerozoic global mass extinctions. The construction of a detailed magnetic polarity time scale for this period, that would integrate data from marine and terrestrial realms, is thus of particular interest. We report new magnetostratigraphic data from the Oyuklu section located in southwestern Turkey, which allow one to propose a complete late Upper Norian (Sevatian 2) to Rhaetian magnetic polarity sequence. Two correlations are discussed between the new Tethyan marine sequence and the (continental) magnetic polarity record previously determined from the Newark basin in eastern North America. Both options suggest that the Rhaetian is at least partly missing in the Newark basin, which would reconcile most Late Triassic magnetostratigraphic results and biotic features obtained from marine and continental environments. Following our preferred correlation, the Rhaetian would have a duration as short as ˜ 2 Myr, and ˜ 4.5 Myr if the Sevatian 2 zone is included as part of the Rhaetian.

Gallet, Yves; Krystyn, Leopold; Marcoux, Jean; Besse, Jean

2007-03-01

43

Microbialites and geochemistry of the Early Triassic enigma?  

NASA Astrophysics Data System (ADS)

The Permian-Triassic mass extinction, 252 Myr ago, is the most devastating global-scale event ever recorded. Ecological and environmental changes during this interval are commonly assumed to be associated with numerous perturbations (i.e. productivity changes, acidification, redox changes, eustatism) that still remain elusive. The present study focus on the relationships between the redox conditions within the water column, the successive sedimentary deposits and marine community turnovers. Our study is based on new Early Triassic sections from the western USA Basin that preserve diversified reefs and bioaccumulations that contain microbialites and various benthic and pelagic organisms (e.g. serpulids, bivalves, ostracods, gastropods, cephalopods). Such a sedimentary prisitine record provides interesting new prospects to decipher the relationships between lithology, microbial structures and the geochemistry of the water column. Three outcrops were studied: the Mineral Mountains, the Confusion Range and the Pahvant Range, that record a general transgressive trend from proximal to distal deposits during the Smithian substage. Continental to open marine conditions are deduced from sedimentological studies and are related to variations of the microbialite meso- and micro-structures over a short time scale. Hydrodynamics and bathymetry are shown to be the major parameters that influence the morphology and distribution of these microbialites. Additionally to the study of the different microbialites structures and associated depositional environments, the chemiotratigraphic record of both carbon isotopes and major elements indicate a complex and a wide range of variations at short time scale. Carbon isotopes vary from -5 to 2 ‰PDB and FeHR/FeT ratio, after iron speciation, indicate a broad range of variation between 0.1 and 1.5. On the one hand, these analyses suggest potential transient oxygen depletion within the water column. On the other hand, fluctuations of these geochemical proxies seem to be influenced by lithology. We thus suggest that biogeochemical cycles of carbon and iron in the studied sections were influenced by the paleo-bathymetry and the distal to proximal polarity between the three locations. A second order control on the water column geochemistry is also probably the consequence of the microbially-induced carbonate precipitation. This study suggests that the Early Triassic paleoenvironments with the western USA basin were highly variable in terms of sedimentology and geochemistry, but also suggest a low oxygen concentration within the water column during the Smithian substage.

Bour, Ivan; Vennin, Emmanuelle; Thomazo, Christophe; Brayard, Arnaud; Olivier, Nicolas; Escarguel, Gilles; Bylund, Kevin G.; Jenks, Jim; Stephen, Daniel A.

2013-04-01

44

A novel proxy links CAMP volcanism with end-Triassic mass extinction and early Jurassic evolution  

NASA Astrophysics Data System (ADS)

Global mass extinction events are marked by a major loss of terrestrial and marine biodiversity and the global collapse of ecosystems during times of extensive volcanic activity and the emplacement of large igneous provinces (LIPs). Large-scale greenhouse gas release, initiated by volcanism, had a profound impact on global geochemical cycles (e.g. initiating strong perturbations in ?13C records). Hence, these events may be regarded as natural deep-time analogues for studying mechanistic feedbacks between rapid and large/scale greenhouse gas emissions, environmental change and biotic crises. Such studies require high resolution stratigraphic correlation between volcanic activity, disruption of global geochemical cycles and biotic crises, which at present is poorly constrained. Here we present a novel proxy that records explosive continental volcanic activity in distant marine shale sediments. The proxy builds on the relative abundance of the trace elements Lu, Hf, Y and Nb (monitored as the (Lu/ Hf)/(Y/ Nb)-ratio). We test the method on a marine sedimentary record comprising Central Atlantic Magmatic Province (CAMP) volcanism and the associated end-Triassic global mass extinction, at ~201.38 Ma. We show that the onset of sharp well-defined peaks in the (Lu/ Hf)/(Y/ Nb)-ratio coincides with the end-Triassic biotic crisis. Subsequent subordinate peaks closely correspond to periods of early Jurassic biotic radiation and evolution. Large-scale volcanic activity therefore not only initiated the end-Triassic mass extinction, it possibly also actively punctuated and regulated the pace of early Jurassic evolution. Further, the proxy also records the timing of Siberian Traps volcanism relative to the end-Permian mass extinction, the largest extinction in Earth's history. Hence, this proxy for the first time allows causality studies between increased volcanic activity, disruption of global geochemical cycles and global biodiversity loss, in unprecedented stratigraphic resolution. End-Triassic changes in biodiversity and extinction and evolution of species is most severe in the marine realm. Reactive iron and trace element data (e.g. Mo, U) suggest strong changes in water column redox-conditions and anoxia and euxinia coinciding with CAMP volcanic activity. This suggests that the end-Triassic mass extinction in the marine realm maybe mostly related to marine anoxia, initiated by volcanism driven greenhouse gas release, in at least marginal marine basins.

Ruhl, M.; Bjerrum, C. J.; Frei, R.

2011-12-01

45

Gondwana's climate history inferred from the palynological record of South Africa's coal deposits: the Early Triassic wet intermezzo  

NASA Astrophysics Data System (ADS)

Permian-Triassic coals of the South African Karoo Basin play a central role in the study and interpretation of Gondwana's climate history and related vegetational changes in time and space. The palynological record of the coal-bearing formations reveals major phases of climate amelioration succeeding the Permo-Carboniferous Gondwana glaciations. Subsequent to the melting of the Dwyka ice, cold to cool-temperate climate conditions prevailed during the Early Permian and a continuous change to hot and dry climate conditions of the Late Permian and Triassic was inferred from sedimentological and palaeontological data so far. The here presented new palynological and geochemical data from the Early Triassic Molteno coal (Stormberg Group) point to a short-term switch from dry to wet climate conditions. To date, this wet intermezzo of Gondwana's early Mesozoic climate history has been overlooked in the Molteno coal of the Karoo Basin. The spore/pollen ratios, used as a proxy for humidity changes, indicate a significant climatic change corresponding to a prominent C-isotope excursion. Ongoing studies will provide a detailed palynological inventory of the Early Triassic coal deposits on an intra-Gondwanic scale, contributing to the interpretation of early Mesozoic palaeoclimates.

Götz, Annette E.

2013-04-01

46

Estimates of expansion time scales  

NASA Astrophysics Data System (ADS)

Monte Carlo simulations of the expansion of a spacefaring civilization show that descendants of that civilization should be found near virtually every useful star in the Galaxy in a time much less than the current age of the Galaxy. Only extreme assumptions about local population growth rates, emigration rates, or ship ranges can slow or halt an expansion. The apparent absence of extraterrestrials from the solar system suggests that no such civilization has arisen in the Galaxy.

Jones, E. M.

47

Multiple time scales in survival analysis  

Microsoft Academic Search

In some problems in survival analysis there may be more than one plausible measure of time for each individual. For example mileage may be a better indication of the age of a car than months. This paper considers the possibility of combining two (or more) time scales measured on each individual into a single scale. A collapsibility condition is proposed

David Oakes

1995-01-01

48

Multiple time scale methods in tokamak magnetohydrodynamics  

SciTech Connect

Several methods are discussed for integrating the magnetohydrodynamic (MHD) equations in tokamak systems on other than the fastest time scale. The dynamical grid method for simulating ideal MHD instabilities utilizes a natural nonorthogonal time-dependent coordinate transformation based on the magnetic field lines. The coordinate transformation is chosen to be free of the fast time scale motion itself, and to yield a relatively simple scalar equation for the total pressure, P = p + B/sup 2//2..mu../sub 0/, which can be integrated implicitly to average over the fast time scale oscillations. Two methods are described for the resistive time scale. The zero-mass method uses a reduced set of two-fluid transport equations obtained by expanding in the inverse magnetic Reynolds number, and in the small ratio of perpendicular to parallel mobilities and thermal conductivities. The momentum equation becomes a constraint equation that forces the pressure and magnetic fields and currents to remain in force balance equilibrium as they evolve. The large mass method artificially scales up the ion mass and viscosity, thereby reducing the severe time scale disparity between wavelike and diffusionlike phenomena, but not changing the resistive time scale behavior. Other methods addressing the intermediate time scales are discussed.

Jardin, S.C.

1984-01-01

49

Sedimentology, stratigraphy, and micropalaeontology of the Upper Triassic reefal series in Eastern Sulawesi (Indonesia)  

Microsoft Academic Search

An Upper Triassic (Upper Norian-Rhaetian) carbonate complex, composed of open marine to reefal deposits, has been investigated for the first time in Eastern Sulawesi. The age is based on the occurrence of benthic foraminifera, and also of the Upper Sevatian to Rhaetian conodont Misikella posthernsteini Kozur and Mock. Palynological assemblages contain Upper Triassic-Lower Jurassic palynomorphs. The scleractinian coral Retiophyllia seranica

Rossana Martini; Daniel Vachard; Louisette Zaninetti; Simonetta Cirilli; Jean-Jacques Cornée; Bernard Lathuilière; Michel Villeneuve

1997-01-01

50

Tetrapod association and palaeoenvironment of the Los Colorados Formation (Argentina): a significant sample from Western Gondwana at the end of the Triassic  

Microsoft Academic Search

The Los Colorados Formation constitutes a continuous continental succession deposited in Western Argentina during the Late Triassic, a time period that is crucial to the record of the faunistic turnover at the Triassic–Jurassic boundary. Many authors have pointed out that its rich tetrapod fauna represents a unique transitional assemblage with elements typical of both Late Triassic and Early Jurassic. However,

Andrea B. Arcucci; Claudia A. Marsicano; Alberto T. Caselli

2004-01-01

51

New palaeomagnetic data from Central Iran and a Triassic palaeoreconstruction  

NASA Astrophysics Data System (ADS)

New pole positions for Triassic and Cretaceous times have been obtained from volcanic and sedimentary sequences in Central Iran. These new results confirm the general trend of the Apparent Polar Wander Path (APWP) of the Central-East-Iran microplate (CEIM) from the Triassic through the Tertiary as published by Soffel and Förster (1983, 1984). Two new palaeopoles for the Triassic of the CEIM have been obtained; limestones and tuffs from the Nakhlak region yield a mean direction of 094.0°/25.0°, N=12, k=4.1, ?95=24.7°, after bedding correction, corresponding to a palaeopole position of 310.8°E 3.9°S, and volcanic rocks from the Sirjan regions yield a mean direction of 114.5°/35.1°, N=44, k=45.9, ?95=3.2° after bedding correction and a palaeopole position of 295.8°E 10.3°N. Combining these with the two previously published results yields a new palaeopole position of 317.5°E 12.7°N, for the Triassic of the CEIM, thus confirming that large counterclockwise rotations of the CEIM have occurred since the Triassic time. New results have also been obtained from Cretaceous limestones from the Saghand region of the CEIM. The mean direction of 340.7°/26.3°, N=33, k=44.3, ?95=3.8°, and the corresponding palaeopole position of 283.1°E 64.4°N, is in agreement with previously determined Cretaceous palaeopole positions of the CEIM. Furthermore, results have also been obtained from Triassic dolomite, limestone, sandstone and siltstone from the Natanz region, which is located to the west of the CEIM. A total of 161 specimens from 44 cores taken at five sites gave a mean direction of the five sites at 033.3°/25.1°, N= 5, k=69.0, ?95=9.3° and a palaeopole position of 167.2°E 53.7°N. They pass the positive fold test of McElhinny (1964) on the level of 99% confidence. This pole position is in fairly good agreement with the mean Triassic pole position of the Turan Plate (149°E 49°N). It indicates that the area of Natanz has not undergone the large counterclockwise rotation relative to the Turan plate since the Triassic, which has been shown for the CEIM. A Triassic palaeogeographic reconstruction of Iran, Arabia (Gondwana) and the Turan Plate (Eurasia) is also presented.

Soffel, H. C.; Davoudzadeh, M.; Rolf, C.; Schmidt, S.

52

Imperfect scaling of time and space–time rainfall  

Microsoft Academic Search

Scale invariance is the most fertile concept to be introduced in stochastic rainfall modeling in 15 years. In particular, a form of scale invariance called multifractality has been exploited to construct parsimonious representations of rainfall in time and space and address fundamental problems of hydrology such as rainfall extremes, downscaling, and forecasting. However, several authors have observed that rainfall is

Daniele Veneziano; Pierluigi Furcolo; Vito Iacobellis

2006-01-01

53

Scale anomaly as the origin of time  

NASA Astrophysics Data System (ADS)

We explore the problem of time in quantum gravity in a point-particle analogue model of scale-invariant gravity. If quantized after reduction to true degrees of freedom, it leads to a time-independent Schrödinger equation. As with the Wheeler-DeWitt equation, time disappears, and a frozen formalism that gives a static wavefunction on the space of possible shapes of the system is obtained. However, if one follows the Dirac procedure and quantizes by imposing constraints, the potential that ensures scale invariance gives rise to a conformal anomaly, and the scale invariance is broken. A behaviour closely analogous to renormalization-group (RG) flow results. The wavefunction acquires a dependence on the scale parameter of the RG flow. We interpret this as time evolution and obtain a novel solution of the problem of time in quantum gravity. We apply the general procedure to the three-body problem, showing how to fix a natural initial value condition, introducing the notion of complexity. We recover a time-dependent Schrödinger equation with a repulsive cosmological force in the `late-time' physics and we analyse the role of the scale invariant Planck constant. We suggest that several mechanisms presented in this model could be exploited in more general contexts.

Barbour, Julian; Lostaglio, Matteo; Mercati, Flavio

2013-05-01

54

Development of the time management environment (TiME) scale  

Microsoft Academic Search

Purpose – The purpose of this paper is to propose an integrative model of time management, and in particular develop a scale to measure organizational variables which would facilitate and support time management practices. The research also examined whether the time management environment is related to turnover intentions and stress. Design\\/methodology\\/approach – Three studies are reported. Study 1 sampled 262

Christopher D. B. Burt; Alexandra Weststrate; Caroline Brown; Felicity Champion

2010-01-01

55

Ion-Beam Sculpting Time Scales  

NASA Astrophysics Data System (ADS)

A study of ion sculpting dynamics in SiO2 and SiN using periodically pulsed ion beams reveals material transport that depends strongly on the time structure of the pulsed beams. It is found that significant nanoscale matter transport can occur over second long time scales after the ion beam has been extinguished. A simple phenomenological model described the dynamics of ion beam sculpting in terms of two material time scales. The model accounts for the surprising observation of enhanced matter transport affected by pulsed ion beams over continuous ion beam exposure.

Stein, Derek; Li, Jiali; Golovchenko, Jene A.

2002-12-01

56

Paleomagnetic age constrains and magneto-mineralogic implications for the Triassic paleosurface in Europe  

NASA Astrophysics Data System (ADS)

The reconstruction of paleosurfaces represents a unique tool to access the evolution of ancient continents. Paleosurfaces contribute to the study of global changes through paleoweathering features/profiles and record uplift and subsidence of the ancient continents driven by crustal geodynamics and plate tectonics. However, age constraints for basement paleosurfaces are often difficult to obtain since the geological record of ancient land surfaces is usually limited, fragmented by unconformities and scrambled by successive superimposed evolutions, leaving a patchwork of relict landforms and weathering products, discontinuous over time and space. The crystalline basement of European Paleozoic massifs, consisting of igneous and metamorphic rocks, often show Permo-Triassic overprints resulting in underestimated age determinations. These remagnetisations are ubiquitous [e.g. Edel & Schneider, 1995], affecting many emerged Paleozoic rocks in Europe. The rejuvenated age estimations are attributed to an alteration of the primary paleomagnetic signal and carried by secondary hematite [Ricordel et al., 2007; Preeden et al., 2009; Preeden, 2009]. Moreover, published paleomagnetic ages [Ricordel et al., 2007] showed a strong relationship between the remagnetization and the development of pinkish-red crystalline facies associated to the albitized underlying rocks of the Morvan Massif (France). Parcerisa et al. [2009] performed further field and petrographic analyses and proposed that the albitization was linked to the precipitation of secondary haematite. Since hematite forms under oxidising conditions one may deduce that the remagnetization occurring in the Paleozoic crystalline rocks formed during the exposure of these rocks at the Permo-Triassic (paleo)surface. The extent of the altered zone (~200 m in depth) points to a sodium enriched groundwater environment [Thiry et al., 2009]. Demonstrating that the albitized facies are of supergenic origin and bound to the Triassic paleosurface deeply renews the ideas about the evolution of basement areas. The recognition of the Triassic paleosurface on widespread basements in Europe will provide spatio-temporal benchmarks to constrain the ablation of these massifs since the Triassic. This will be a major contribution to the geodynamic modelling of continental evolution of Europe. To deepen our understanding of this paleoalteration phenomenon on a supra-regional scale and to obtain a reasonable distribution of paleomagnetic age determinations, we aim to acquire more tie points for this Permo-Triassic surface, which was preserved in the crystalline basement of Europe throughout the Mesozoic and Cenozoic epochs. We will present results from paleomagnetic investigations as well as magneto-mineralogic analyses of the profiles through albitized granite and porphyry from the Sudetes in SW-Poland and the Catalonian Mountains in NE-Spain, for which preliminary age estimations have been carried out. Further European Paleozoic sample sites are in process. Depending on the depth situation of the sampled facies compared to the weathering profile, the Triassic paleomagnetic ages show dispersion towards rather older ages at the top and younger ages at the bottom of the sequence. This seems to correlate with the results from magneto-mineralogical analyses which show a decreasing hematite concentration with depth. The oldest ages are carried by a single component, identified as single-domain secondary hematite inclusions in the secondary albite crystals. With increasing depth the samples are rather characterized by a two-component signal, still showing (younger) Triassic ages for both components. These were identified as secondary hematite and maghemite. The latter is most probably a product of either low-temperature magnetite oxidation or precipitates during the albitization of the primary rock. These processes are both linked to less oxidising conditions than at the top of the weathering profile. A systematic interpretation of the paleomagnetic ages and the identification of the magnetic carrier assem

Franke, Christine; Thiry, Medard; Gomez-Gras, David; Jelenska, Maria; Kadzialko-Hofmokl, Magdalena; Lagroix, France; Parcerisa, David; Spassov, Simo; Szuszkiewicz, Adam; Turniak, Krzysztof

2010-05-01

57

Time scales involved in emergent market coherence  

NASA Astrophysics Data System (ADS)

In addressing the question of the time scales characteristic for the market formation, we analyze high-frequency tick-by-tick data from the NYSE and from the German market. By using returns on various time scales ranging from seconds or minutes up to 2 days, we compare magnitude of the largest eigenvalue of the correlation matrix for the same set of securities but for different time scales. For various sets of stocks of different capitalization (and the average trading frequency), we observe a significant elevation of the largest eigenvalue with increasing time scale. Our results from the correlation matrix study can be considered as a manifestation of the so-called Epps effect. There is no unique explanation of this effect and it seems that many different factors play a role here. One of such factors is randomness in transaction moments for different stocks. Another interesting conclusion to be drawn from our results is that in the contemporary markets the emergence of significant correlations occurs on time scales much smaller than in the more distant history.

Kwapie?, J.; Dro?d?, S.; Speth, J.

2004-06-01

58

Time scales of turbulent relative dispersion  

NASA Astrophysics Data System (ADS)

Tracers in a turbulent flow separate according to the celebrated t3/2 Richardson-Obukhov law, which is usually explained by a scale-dependent effective diffusivity. Here, supported by state-of-the-art numerics, we revisit this argument. The Lagrangian correlation time of velocity differences increases too quickly for validating this approach, but acceleration differences decorrelate on dissipative time scales. Phenomenological arguments are used to relate the behavior of separations to that of a “local energy dissipation,” defined as the average ratio between the cube of the longitudinal velocity difference and the distance between the two tracers. This quantity is shown to stabilize on short time scales and this results in an asymptotic diffusion ?t1/2 of velocity differences. The time of convergence to this regime is shown to be that of deviations from Batchelor's initial ballistic regime, given by a scale-dependent energy dissipation time rather than the usual turnover time. It is finally demonstrated that the fluid flow intermittency should not affect this long-time behavior of the relative motion.

Bitane, Rehab; Homann, Holger; Bec, Jérémie

2012-10-01

59

Optimal time scale for spike-time reliability  

PubMed Central

Use of spike timing to encode information requires that neurons respond with high temporal precision and with high reliability. Fast fluctuating stimuli are known to result in highly reproducible spike times across trials, whereas constant stimuli result in variable spike times. Here, we have investigated how spike-time reliability depends on the time scale of fluctuations of the input stimuli in real neurons (mitral cells in the olfactory bulb and pyramidal cells in the neocortex) as well as in neuron models (integrate-and-fire and Hodgkin-Huxley) with intrinsic noise. In all cases we found that for firing frequencies in the beta/gamma range, spike reliability is maximal when the input includes fluctuations on the time scale of a few milliseconds (2-5 ms), coinciding with the time scale of fast synapses, and decreases substantially for faster and slower inputs. In addition, we show mathematically that the existence of an optimal time scale for spike-time reliability is a general feature of neurons. Finally, we comment how these findings relate to the mechanisms that cause neuronal synchronization.

Galan, Roberto F.; Ermentrout, G. Bard; Urban, Nathaniel N.

2008-01-01

60

Paleomagnetism and Magnetostratigraphy of the Upper Triassic Chinle Group in North Central, Western and Eastern New Mexico  

Microsoft Academic Search

The Upper Triassic Chinle Group spans most of the Late Triassic and was deposited by a large scale fluvial system. Chinle Group strata are composed of predominantly red to purple mudstones with lesser orange siltstones and buff to red sandstones. In the Chama Basin, north-central New Mexico, both lower and upper Chinle strata are well-exposed and sections at several localities

K. E. Zeigler; J. W. Geissman

2007-01-01

61

Imperfect scaling of time and space time rainfall  

NASA Astrophysics Data System (ADS)

Scale invariance is the most fertile concept to be introduced in stochastic rainfall modeling in 15 years. In particular, a form of scale invariance called multifractality has been exploited to construct parsimonious representations of rainfall in time and space and address fundamental problems of hydrology such as rainfall extremes, downscaling, and forecasting. However, several authors have observed that rainfall is scale invariant only in approximation and within limited ranges. Here, we make a systematic analysis of the deviations of time and space time rainfall from multifractality. We use a flexible multiplicative cascade model, which produces multifractality as a special case while allowing deviations from scale invariance to occur. By fitting the model to rainfall records from different climates and over land or ocean, we find significant and consistent departures from multifractality in both the alternation of wet and dry conditions and the fluctuations of precipitation intensity when it rains. The fractal dimension of the rain support increases with increasing rain rate and the (multiplicative) fluctuations are larger at smaller scales and for lighter rainfall. A plausible explanation of these departures from scaling is that the rate of water vapor condensation in the atmosphere is a multifractal process in three space dimensions plus time, but multifractality is destroyed when the condensation rate is integrated to produce rainfall intensity at fixed altitudes.

Veneziano, Daniele; Furcolo, Pierluigi; Iacobellis, Vito

2006-05-01

62

Triassic deposits of the Chukotka Arctic continental margin (sedimentary implications and detrital zircon data)  

NASA Astrophysics Data System (ADS)

Triassic clastic deposits of Chukotka are represented by rhythmic intercalation of sandstones, siltstones and mudstones. During the Triassic, sedimentation was represented by continental slope progradation. Detrital zircons from Triassic sedimentary rocks were collected for constrain its paleogeographic links to source terranes. Zircons populations from three Chukotka's samples are very similar, and youngest zircon ages show peaks at 236-255 Ma (Miller et al., 2006). Lower Triassic sandstones from the Chaun subterrane do not contain the young population 235-265 Ma that is characteristic of the Upper Triassic rocks from the Anyui subterrane and Wrangel Island. The young zircon population is missing also from the coeval Sadlerochit Group (Alaska) and Blind Fiord Formation of the Sverdrup basin (Miller et al., 2006; Omma et al., 2011). Our data of Triassic sandstones of Wrangel island demonstrate detrital zircons ages dominated by Middle Triassic (227-245 Ma), Carboniferous (309-332 Ma) and Paleoproterozoic (1808-2500 Ma) ages. The new data on Chukotka show that populations of detrital zircons from Chukotka, the Sverdrup basin, and Alaska, the Sadlerochit Mountains included, demonstrate greater similarity than it was previously thought. Consequently, it may be assumed that they originate from a single source situated in the north. The data on zircon age of gabbro-dolerite magmatism in eastern Chukotka (252 Ma. Ledneva et al., 2011) and K-Ar ages obtained for sills and small intrusive bodies (Geodynamics…, 2006) in Lower Triassic deposits allow the local provenance. The presence of products of synchronous magmatism and shallow-water facies in the Lower Triassic sequences confirm this assumption. At the same time, coeval zircons appear only in the Upper Triassic strata. It is conceivable that the young zircon population originates from intrusive, not volcanic rocks, which were subjected to erosion only in the Late Triassic. In our opinion, the assumption of the local source with synchronous magmatism is consistent with the evolution of the petrological-mineralogical and geochemical compositions in the Triassic sandstones of Chukotka. Similar zircon peaks in Triassic rocks of northern Wrangel Island, Sverdrup basin, and Alaska indicate the same provenances for the Triassic periods. It is possible that all obtained data may indirectly support existence of the hypothetical "Hyperborean Platform" or Crockerland-Arctida microcontinent Work was supported by RBRR projects 11-05-00787, 11-05-00074, Scientific school # NSh-5177.2012.5, kontrakts 01/14/20/11; and we are extremely grateful to the TGS company for execution of a joint research project "Geological history of Wrangel Island".

Tuchkova, Marianna; Sokolov, Sergey; Verzhbitsky, Vladimir

2013-04-01

63

TimeScale Modification of Speech Signals  

Microsoft Academic Search

This paper presents methods for independently modifying the time and pitch scale of acoustic sig- nals, with an emphasis on speech signals. The algorithms developed here use parametric (sinu- soidal) modelling techniques introduced by other authors, but new perspectives on the role of vocal tract decomposition and maintaining phase relationships between sinusoidal tracks are derived that achieve improved output quality

Brett Ninness; Soren John Henriksen

2008-01-01

64

Global coal gap between Permian-Triassic extinction and Middle Triassic recovery of peat-forming plants  

Microsoft Academic Search

Early Triassic coals are unknown, and Middle Triassic coals are rare and thin. The Early Triassic coal gap began with extinction of peat-forming plants at the end of the Permian (ca. 250 Ma), with no coal known anywhere until Middle Triassic (243 Ma). Permian levels of plant diversity and peat thickness were not recovered until Late Triassic (230 Ma). Tectonic

G. J. Retallack; J. J. Veevers; R. Morante

1996-01-01

65

Time scales of memory, learning, and plasticity.  

PubMed

After only about 10 days would the storage capacity of our nervous system be reached if we stored every bit of input. The nervous system relies on at least two mechanisms that counteract this capacity limit: compression and forgetting. But the latter mechanism needs to know how long an entity should be stored: some memories are relevant only for the next few minutes, some are important even after the passage of several years. Psychology and physiology have found and described many different memory mechanisms, and these mechanisms indeed use different time scales. In this prospect we review these mechanisms with respect to their time scale and propose relations between mechanisms in learning and memory and their underlying physiological basis. PMID:23160712

Tetzlaff, Christian; Kolodziejski, Christoph; Markelic, Irene; Wörgötter, Florentin

2012-11-18

66

A new chronology for the end-Triassic mass extinction  

NASA Astrophysics Data System (ADS)

The transition from the Triassic to Jurassic Period, initiating the 'Age of the dinosaurs', approximately 200 Ma, is marked by a profound mass extinction with more than 50% genus loss in both marine and continental realms. This event closely coincides with a period of extensive volcanism in the Central Atlantic Magmatic Province (CAMP) associated with the initial break-up of Pangaea but a causal relationship is still debated. The Triassic-Jurassic (T-J) boundary is recently proposed in the marine record at the first occurrence datum of Jurassic ammonites, post-dating the extinction interval that concurs with two distinct perturbations in the carbon isotope record. The continental record shows a major palynological turnover together with a prominent change in tetrapod taxa, but a direct link to the marine events is still equivocal. Here we develop an accurate chronostratigraphic framework for the T-J boundary interval and establish detailed trans-Atlantic and marine-continental correlations by integrating astrochronology, paleomagnetism, basalt geochemistry and geobiology. We show that the oldest CAMP basalts are diachronous by 20 kyr across the Atlantic Ocean, and that these two volcanic pulses coincide with the end-Triassic extinction interval in the marine realm. Our results support the hypotheses of Phanerozoic mass extinctions resulting from emplacement of Large Igneous Provinces (LIPs) and provide crucial time constraints for numerical modelling of Triassic-Jurassic climate change and global carbon-cycle perturbations.

Deenen, M. H. L.; Ruhl, M.; Bonis, N. R.; Krijgsman, W.; Kuerschner, W. M.; Reitsma, M.; van Bergen, M. J.

2010-03-01

67

Early Triassic stromatolites as post-mass extinction disaster forms  

SciTech Connect

Aftermaths of mass extinctions have been thought to be characterized by relaxation of ecological constraints accompanied by increased prominence of opportunistic generalists. Such taxa, termed 'disaster forms,' have been shown to increase dramatically in range and abundance after several mass extinction events. The Cambrian-Ordovician stromatolite decline in normal-marine level-bottom environments has been explained as a direct or indirect consequence of increases in ecological constraints, such as greater levels of predation and/or bioturbation of microbial communities, caused by early Paleozoic benthic invertebrate evolution and diversification. Thus, one would predict that in post-Ordovician strata, stromatolites might appear in normal-marine level-bottom environments as disaster forms in the aftermaths of mass extinction particularly devastating to the benthic biota, such as during Early Triassic time. Mounded stromatolites are present in two beds (up to 1.5 m thick) of the Lower Triassic (Spathian) Virgin Limestone Member (Moenkopi Formation) in the southwestern Spring Mountains of Nevada. Stromatolites from level-bottom normal-marine subtidal environments have also been described from other Lower Triassic strata in North America, Europe, and Asia. These stromatolites, unusual in level-bottom normal-marine settings, may have developed locally during the long aftermath (4-5 m.y.) of the Permian-Triassic mass extinction because of partial relaxation of the ecological constraints that typically restricted them from unstressed subtidal, normal-marine, level-bottom environments.

Schubert, J.K.; Bottjer, D.J. (Univ. of Southern California, Los Angeles (United States))

1992-10-01

68

CO2 and the end-Triassic mass extinction.  

PubMed

The end of the Triassic period was marked by one of the largest and most enigmatic mass-extinction events in Earth's history and, with few reliable marine geochemical records, terrestrial sediments offer an important means of deciphering environmental changes at this time. Tanner et al. describe an isotopic study of Mesozoic fossil soils which suggests that the atmospheric concentration of carbon dioxide (pCO2) across the Triassic-Jurassic boundary was relatively constant (within 250 p.p.m.v.), but this is inconsistent with high-resolution evidence from the stomatal characters of fossil leaves. Here I show that the temporal resolution of the fossil-soil samples may have been inadequate for detecting a transient rise in pCO2. I also show that the fossil-soil data are consistent with a large increase in pCO2 across the Triassic-Jurassic boundary when variations in the stable carbon isotope (denoted as delta13C) in terrestrial plant leaves are taken into account. These factors suggest that the linkage between pCO2, global warming and the end-Triassic mass extinction remains intact. PMID:11807542

Beerling, David

2002-01-24

69

Astronomical constraints on the duration of the early Jurassic Hettangian stage and recovery rates following the end-Triassic mass extinction (St Audrie's Bay/East Quantoxhead, UK)  

NASA Astrophysics Data System (ADS)

The end-Triassic environmental crisis with major extinctions in the marine realm is followed by successive recovery in the lower Jurassic Hettangian Stage. Accurate timing of events is however still poorly constrained. In this study, combined field observations and physical and chemical proxy records, covering the uppermost Triassic and lower Jurassic marine successions of St Audrie's Bay and East Quantoxhead (UK), have been used to construct a floating astronomical time-scale of ˜ 2.5 Myr in length. This time-scale is based on the recognition of meters thick cycles in limestone and (black) shale predominance and concurrent variability in physical and chemical proxy records. Three to five individual black-shale beds occur within these meter-scale sedimentary bundles and are interpreted to reflect precession-controlled changes in monsoon intensity, while the bundles are interpreted as forced by the ˜ 100-kyr eccentricity cycle. On the basis of these findings, we propose an astronomically constrained duration of the Hettangian stage of 1.8 Myr in the UK and unequal duration of Hettangian ammonite zones ( Psilocerasplanorbis zone: ˜ 250 kyr; Alsatitesliasicus zone: ˜ 750 kyr; Schlotheimiaangulata zone: ˜ 800 kyr). Within this astronomical framework, the extinction interval and coinciding negative CIE represent 1 to 2 precession cycles (˜ 20-40 kyr). The amount of time succeeding the end-Triassic negative carbon isotope excursion (CIE) and preceding the first Jurassic ammonite occurrence (in the UK) is constrained to 6 climatic precession cycles (˜ 120 kyr). Cyclostratigraphic correlation to the astronomically-tuned sedimentary record of the continental Newark basin (USA) allows to locate the stratigraphic position of the marine defined Triassic-Jurassic and Hettangian-Sinemurian boundary in the continental realm. Continuous low ?13C TOC values throughout the Hettangian and early Sinemurian, succeeding volcanic activity in the Central Atlantic Magmatic Province (CAMP), may suggest a long-term change in Earth's global biogeochemical cycles, which do not fully recover for several million years.

Ruhl, M.; Deenen, M. H. L.; Abels, H. A.; Bonis, N. R.; Krijgsman, W.; Kürschner, W. M.

2010-06-01

70

Upper Triassic stratigraphy and paleobiogeography of Kotel'nyi Island (New Siberian Islands)  

NASA Astrophysics Data System (ADS)

The thorough study of the Upper Triassic reference section located at the Tikhaya River in the central part of Kotel'nyi Island and characterized by uniform clayey lithology and containing diverse cephalopod, molluscan, and radiolarian assemblages made it possible to specify its structure and paleontological characteristic and establish for the first time the upper Anisian Sirenites yakutensis Zone. It is shown that different Late Triassic faunal groups are represented by mixed dominant Boreal and subordinate Tethyan elements. Such proportions are observable through the entire section beginning from the lower Carnian to upper Norian layers. The peculiar taxonomic composition of Late Triassic radiolarian and cephalopod assemblages provides grounds for attributing the region to an autonomous paleobiochore (New Siberian subprovince). The occurrence of both Siberian and Canadian elements in the Late Triassic faunas emphasizes the specific position of this paleobiochore determined by wide connections between basins at that time.

Bragin, N. Yu.; Konstantinov, A. G.; Sobolev, E. S.

2012-11-01

71

The Geologic Time Scale: The Development of Life through time  

NSDL National Science Digital Library

This text assists in understanding time relationships and how life on Earth has changed over time. The dates shown were compiled from several available sources. The first page shows some important events in Earth history, presented in the order in which they occurred. The data are also shown on the scale of a calendar year. On the second sheet is a chart showing the geologic eras, systems, and series. On the chart, each dot, number, or letter represents 1 million years. The dots get older as you read down the chart, or to the right along a row. They represent millions of years before present (mybp) and show the ages of the oldest known fossils of selected animals or the time of an event. Not all of the items are shown on the chart because of space limitations.

72

Time sequence and time scale of intermediate mass fragment emission  

SciTech Connect

Semiperipheral collisions in the {sup 124}Sn+{sup 64}Ni reaction at 35 MeV/nucleon were studied using the forward part of the Charged Heavy Ion Mass and Energy Resolving Array. Nearly completely determined ternary events involving projectilelike fragments (PLF), targetlike fragments (TLF), and intermediate mass fragments (IMF) were selected. A new method of studying the reaction mechanism, focusing on the analysis of the correlations between relative velocities in the IMF+PLF and IMF+TLF subsystems, is proposed. The relative velocity correlations provide information on the time sequence and time scale of the neck fragmentation processes leading to production of IMFs. It is shown that the majority of light IMFs are produced within 40-80 fm/c after the system starts to reseparate. Heavy IMFs are formed at times of about 120 fm/c or later and can be viewed as resulting from two-step (sequential) neck rupture processes.

De Filippo, E.; Pagano, A.; Cardella, G.; Lanzano, G.; Papa, M.; Pirrone, S.; Politi, G. [INFN, Sezione di Catania and Dipartimento di Fisica e Astronomia, Universita di Catania (Italy); Wilczynski, J. [A. Soltan Institute for Nuclear Studies, Swierk/Warsaw (Poland); Amorini, F.; Anzalone, A.; Baran, V.; Bonasera, A.; Cavallaro, S.; Colonna, M.; Di Toro, M.; Giustolisi, F.; Iacono-Manno, M.; La Guidara, E.; Lanzalone, G.; Maiolino, C. [INFN, Laboratori Nazionali del Sud and Dipartimento di Fisica e Astronomia, Universita di Catania (Italy)] [and others

2005-04-01

73

Parametric instabilities in picosecond time scales  

SciTech Connect

The coupling of intense laser light with plasmas is a rich field of plasma physics, with many applications. Among these are inertial confinement fusion (ICF), x-ray lasers, particle acceleration, and x-ray sources. Parametric instabilities have been studied for many years because of their importance to ICF; with laser pulses with duration of approximately a nanosecond, and laser intensities in the range 10{sup 14}--10{sup 15}W/cm{sup 2} these instabilities are of crucial concern because of a number of detrimental effects. Although the laser pulse duration of interest for these studies are relatively long, it has been evident in the past years that to reach an understanding of these instabilities requires their characterization and analysis in picosecond time scales. At the laser intensities of interest, the growth rate for stimulated Brillouin scattering (SBS) is of the order of picoseconds, and of an order of magnitude shorter for stimulated Raman scattering (SRS). In this paper the authors discuss SBS and SRS in the context of their evolution in picosecond time scales. They describe the fundamental concepts associated with their growth and saturation, and recent work on the nonlinear treatment required for the modeling of these instabilities at high laser intensities.

Baldis, H.A. [Lawrence Livermore National Lab., CA (United States); Rozmus, W. [Alberta Univ., Edmonton, AB (Canada). Dept. of Physics; Labaune, C.; Mounaix, Ph.; Pesme, D.; Baton, S. [Ecole Polytechnique, Palaiseau (France); Tikhonchuk, V.T. [P.N. Lebedev Physics Inst., Moscow (Russian Federation)

1993-03-01

74

Length, time, and energy scales of photosystems.  

PubMed

The design of photosynthetic systems reflects the length scales of the fundamental physical processes. Energy transfer is rapid at the few angstrom scale and continues to be rapid even at the 50-A scale of the membrane thickness. Electron tunneling is nearly as rapid at the shortest distances, but becomes physiologically too slow well before 20 A. Diffusion, which starts out at a relatively slow nanosecond time scale, has the most modest slowing with distance and is physiologically competent at all biologically relevant distances. Proton transfer always operates on the shortest angstrom scale. The structural consequences of these distance dependencies are that energy transfer networks can extend over large, multisubunit and multicomplex distances and take leaps of 20 A before entering the domain of charge separating centers. Electron transfer systems are effectively limited to individual distances of 15 A or less and span the 50 A dimensions of the bioenergetic membrane by use of redox chains. Diffusion processes are generally used to cover the intercomplex electron transfer distances of 50 A and greater and tend to compensate for the lack of directionality by restricting the diffusional space to the membrane or the membrane surface, and by multiplying the diffusing species through the use of pools. Proton transfer reactions act over distances larger than a few angstroms through the use of clusters or relays, which sometimes rely on water molecules and which may only be dynamically assembled. Proteins appear to place a premium on robustness of design, which is relatively easily achieved in the long-distance physical processes of energy transfer and electron tunneling. By placing cofactors close enough, the physical process is relatively rapid compared to decay processes. Thus suboptimal conditions such as cofactor orientation, energy level, or redox potential level can be tolerated and generally do not have to be finely tuned. The most fragile regions of design tend to come in areas of complex formation and catalysis involving proton management, where relatively small changes in distance or mutations can lead to a dramatic decrease in turnover, which may already be limiting the overall speed of energy conversion in these proteins. Light-activated systems also face a challenge to robust function from the ever-present dangers of high redox potential chemistry. This can turn the protein matrix and wandering oxygen molecules into unintentional redox partners, which in the case of PSII requires the frequent, costly replacement of protein subunits. PMID:12629967

Moser, Christopher C; Page, Christopher C; Cogdell, Richard J; Barber, James; Wraight, Colin A; Dutton, P Leslie

2003-01-01

75

Carbon-cycle disturbances and environmental change preceding the end-Triassic mass extinction  

NASA Astrophysics Data System (ADS)

The end-Triassic mass extinction [~201.3 Ma], marked by marine and terrestrial ecosystem collapse and global marine biodiversity loss, coincides with the onset of extensive volcanic activity and emplacement of the Central Atlantic Magmatic Province (CAMP). Massive and rapid greenhouse gas release from basalts, subsurface organic rich strata and ocean-floor clathrates, had a profound impact on the global exogenic carbon cycle and caused dramatically increased atmospheric pCO2 values. A recent study however suggests global carbon cycle disturbance already (possibly ~100 kyr) before the end-Triassic mass extinction. 13C depleted atmospheric carbon injection at this event may have resulted from Late Triassic dike and sill intrusions possibly releasing thermogenic methane from subsurface organic-rich sediments. We now studied an extended, up to 1 million year long, Late Triassic marine sedimentary record from the western Tethian Eiberg basin (Northern Calcareous Alps, Austria). Sediments were deposited in the deepest part of the Eiberg basin (very close to the base Jurassic Global Stratotype Section and Point at Kuhjoch). High-resolution ?13CTOC, ?13CCARB-Bulk and ?13CCARB-Brachiopods from this record show distinct 1-2‰ ?13C negative excursions throughout the latest Triassic. This suggests disturbance of the global exogenic carbon cycle already long before the end-Triassic mass extinction. Regular alternations between (laminated) black-shales and carbonate deposition also indicate periodic changes in the palaeo-environment. Variations in the ?18OCARB record, coinciding with ?13C negative excursions, suggest climatic warming. But, distinct negative shifts may also indicate increased fresh-water input along the upper-Triassic western Tethys continental margin. Volcanic activity and palaeo-environmental change occurring already before the end-Triassic mass extinction, may have progressively weakened marine ecosystems, ultimately leading to large-scale marine biodiversity loss.

Ruhl, M.; Ullmann, C. V.; Mette, W.; Korte, C.

2012-04-01

76

Deep-sea record of impact apparently unrelated to mass extinction in the Late Triassic  

PubMed Central

The 34-million-year (My) interval of the Late Triassic is marked by the formation of several large impact structures on Earth. Late Triassic impact events have been considered a factor in biotic extinction events in the Late Triassic (e.g., end-Triassic extinction event), but this scenario remains controversial because of a lack of stratigraphic records of ejecta deposits. Here, we report evidence for an impact event (platinum group elements anomaly with nickel-rich magnetite and microspherules) from the middle Norian (Upper Triassic) deep-sea sediment in Japan. This includes anomalously high abundances of iridium, up to 41.5 parts per billion (ppb), in the ejecta deposit, which suggests that the iridium-enriched ejecta layers of the Late Triassic may be found on a global scale. The ejecta deposit is constrained by microfossils that suggest correlation with the 215.5-Mya, 100-km-wide Manicouagan impact crater in Canada. Our analysis of radiolarians shows no evidence of a mass extinction event across the impact event horizon, and no contemporaneous faunal turnover is seen in other marine planktons. However, such an event has been reported among marine faunas and terrestrial tetrapods and floras in North America. We, therefore, suggest that the Manicouagan impact triggered the extinction of terrestrial and marine organisms near the impact site but not within the pelagic marine realm.

Onoue, Tetsuji; Sato, Honami; Nakamura, Tomoki; Noguchi, Takaaki; Hidaka, Yoshihiro; Shirai, Naoki; Ebihara, Mitsuru; Osawa, Takahito; Hatsukawa, Yuichi; Toh, Yosuke; Koizumi, Mitsuo; Harada, Hideo; Orchard, Michael J.; Nedachi, Munetomo

2012-01-01

77

EDITORIAL: Special issue on time scale algorithms  

NASA Astrophysics Data System (ADS)

This special issue of Metrologia presents selected papers from the Fifth International Time Scale Algorithm Symposium (VITSAS), including some of the tutorials presented on the first day. The symposium was attended by 76 persons, from every continent except Antarctica, by students as well as senior scientists, and hosted by the Real Instituto y Observatorio de la Armada (ROA) in San Fernando, Spain, whose staff further enhanced their nation's high reputation for hospitality. Although a timescale can be simply defined as a weighted average of clocks, whose purpose is to measure time better than any individual clock, timescale theory has long been and continues to be a vibrant field of research that has both followed and helped to create advances in the art of timekeeping. There is no perfect timescale algorithm, because every one embodies a compromise involving user needs. Some users wish to generate a constant frequency, perhaps not necessarily one that is well-defined with respect to the definition of a second. Other users might want a clock which is as close to UTC or a particular reference clock as possible, or perhaps wish to minimize the maximum variation from that standard. In contrast to the steered timescales that would be required by those users, other users may need free-running timescales, which are independent of external information. While no algorithm can meet all these needs, every algorithm can benefit from some form of tuning. The optimal tuning, and even the optimal algorithm, can depend on the noise characteristics of the frequency standards, or of their comparison systems, the most precise and accurate of which are currently Two Way Satellite Time and Frequency Transfer (TWSTFT) and GPS carrier phase time transfer. The interest in time scale algorithms and its associated statistical methodology began around 40 years ago when the Allan variance appeared and when the metrological institutions started realizing ensemble atomic time using more than one single atomic clock. An international symposium dedicated to these topics was initiated in 1972 as the first International Symposium on Atomic Time Scale Algorithms and it was the beginning of a series: 1st Symposium: organized at the NIST (NBS at that epoch) in 1972, 2nd Symposium: again at the NIST in 1982, 3rd Symposium: in Italy at the INRIM (IEN at that epoch) in 1988, 4th Symposium: in Paris at the BIPM in 2002 (see Metrologia 40 (3), 2003) 5th Symposium: in San Fernando, Spain at the ROA in 2008. The early symposia were concerned with establishing the basics of how to estimate and characterize the behavior of an atomic frequency standard in an unambiguous and clearly identifiable way, and how to combine the reading of different clocks to form an optimal time scale within a laboratory. Later, as atomic frequency standards began to be used as components in larger systems, interest grew in understanding the impact of a clock in a more complex environment. For example, use of clocks in telecommunication networks in a Synchronous Digital Hierarchy created a need to measure the maximum time error spanned by a clock in a certain interval. Timekeeping metrologists became interested in estimating time deviations and time stability, so they had to find ways to convert their common frequency characteristics to time characteristics. Tests of fundamental physics provided a motivation for launching atomic frequency standards into space in long-lasting missions, whose high-precision measurements might be available for only a few hours a day, yielding a series of clock data with many gaps and outliers for which a suitable statistical analysis was necessary to extract as much information as possible from the data. In the 21st century, the field has been transformed by the advent of atomic-clock-based Global Navigation Satellite Systems (GNSS), the steady increase in precision brought about by rapidly improving clocks and measurement systems, and the growing number of relatively inexpensive small clock ensembles. Although technological transformations have raised the

Matsakis, Demetrios; Tavella, Patrizia

2008-12-01

78

Time scales in nuclear giant resonances  

SciTech Connect

We propose a general approach to characterise fluctuations of measured cross sections of nuclear giant resonances. Simulated cross sections are obtained from a particular, yet representative, self-energy that contains all information about fragmentations. Using a wavelet analysis, we demonstrate the extraction of time scales of cascading decays into configurations of different complexity of the resonance. We argue that the spreading widths of collective excitations in nuclei are determined by the number of fragmentations as seen in the power spectrum. An analytic treatment of the wavelet analysis using a Fourier expansion of the cross section confirms this principle. A simple rule for the relative lifetimes of states associated with hierarchies of different complexity is given.

Heiss, W. D. [National Institute for Theoretical Physics, Stellenbosch Institute for Advanced Study, and Institute of Theoretical Physics, University of Stellenbosch, 7602 Matieland (South Africa); Nazmitdinov, R. G. [Department de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, RU-141980 Dubna (Russian Federation); Smit, F. D. [iThemba LABS, Post Office Box 722, Somerset West 7129 (South Africa)

2010-03-15

79

Optimum synthesis for time scale generation.  

PubMed

A time scale can be regarded as a synthesis of readings from precise clocks. Usually such synthesis is based on the principle of weighted averaging, which balances the contribution of each clock according to its noise level. It is well known that there are five different noise processes in precise clocks. Therefore, a good synthesis should balance each of those noise levels. Most existing algorithms control only one or two noise types. If an algorithm can control all five noise types simultaneously, we consider it to be optimum. The key point of constructing an optimum algorithm is the separation of all five noise types. In this paper, an optimum algorithm is presented using the half-integrating/half-differentiating model by which the five noise types are separated correctly. Performances of the new algorithm are demonstrated with simulated and real data. PMID:18238481

Zhu, S; Wei, G

1999-01-01

80

Time Horizon and Social Scale in Communication  

NASA Astrophysics Data System (ADS)

In 2009 our center (CRED) published a first version of The Psychology of Climate Change Communication. In it, we attempted to summarize facts and concepts from psychological research that could help guide communication. While this work focused on climate change, most of the ideas are at least partly applicable for communication about a variety of natural hazards. Of the many examples in this guide, I mention three. Single-action bias is the human tendency to stop considering further actions that might be needed to deal with a given hazard, once a single action has been taken. Another example is the importance of group affiliation in motivating voluntary contributions to joint action. A third concerns the finding that group participation enhances understanding of probabilistic concepts and promotes action in the face of uncertainty. One current research direction, which goes beyond those included in the above publication, focuses on how time horizons arise in the thinking of individuals and groups, and how these time horizons might influence hazard preparedness. On the one hand, individuals sometimes appear impatient, organizations look for immediate results, and officials fail to look beyond the next election cycle. Yet under some laboratory conditions and in some subcultures, a longer time horizon is adopted. We are interested in how time horizon is influenced by group identity and by the very architecture of planning and decision making. Institutional changes, involving long-term contractual relationships among communities, developers, insurers, and governments, could greatly increase resilience in the face of natural hazards. Communication about hazards, in the context of such long-term contractual relationships might look very different from communication that is first initiated by immediate threat. Another new direction concerns the social scale of institutions and of communication about hazards. Traditionally, insurance contracts share risk among a large number of insurees: each contributes a small premium toward a fund that is adequate to cover the large losses that occasionally occur. Participatory processes are needed that extend risk sharing to larger social scales and that reduce adversarial relationships between insurers, insurees, insurance regulators, and governments that intervene or fail to intervene on an ad hoc rather than a contractual basis.

Krantz, D. H.

2010-12-01

81

Basin-scale time reversal communications.  

PubMed

During November 1994, broadband acoustic signals were transmitted from a 75-Hz source to a 20-element, 700-m vertical array at approximately 3250 km range in the eastern North Pacific Ocean as part of the acoustic engineering test (AET) of the acoustic thermometry of ocean climate program [Worcester et al., J. Acoust. Soc. Am. 105, 3185-3201 (1999)]. The AET tomography signal can be treated as a binary-phase shift-keying communication signal with an information rate of 37.5 bitss. With the multipath arrivals spanning 5-8 sec, these data represent an extreme case of intersymbol interference. The AET array data are processed using time reversal combined with frequent channel updates to accommodate channel variations over the 20-min long reception, followed by a single channel decision-feedback equalizer. The almost error-free performance using all 20 array elements demonstrates the feasibility of time reversal communications at basin scale. Further, comparable performance of single receive element communications integrating over multiple transmissions indicates that the ocean provided temporal diversity that is as effective as the spatial diversity provided by the array. PMID:19173408

Song, H C; Kuperman, W A; Hodgkiss, W S

2009-01-01

82

Global exponential stability of delayed BAM network on time scale  

Microsoft Academic Search

Some sufficient conditions are derived to ensure the global exponential stability of delayed bi-directional associative memory (BAM) neural network on time scale, using the time scale calculus theory and the Liapunov functional method. The conditions possess highly important significance and can be easily checked in practice by simple algebraic methods. This is the first time applying the time scale calculus

Anping Chen; Dejun Du

2008-01-01

83

Trophic network models explain instability of Early Triassic terrestrial communities  

PubMed Central

Studies of the end-Permian mass extinction have emphasized potential abiotic causes and their direct biotic effects. Less attention has been devoted to secondary extinctions resulting from ecological crises and the effect of community structure on such extinctions. Here we use a trophic network model that combines topological and dynamic approaches to simulate disruptions of primary productivity in palaeocommunities. We apply the model to Permian and Triassic communities of the Karoo Basin, South Africa, and show that while Permian communities bear no evidence of being especially susceptible to extinction, Early Triassic communities appear to have been inherently less stable. Much of the instability results from the faster post-extinction diversification of amphibian guilds relative to amniotes. The resulting communities differed fundamentally in structure from their Permian predecessors. Additionally, our results imply that changing community structures over time may explain long-term trends like declining rates of Phanerozoic background extinction

Roopnarine, Peter D; Angielczyk, Kenneth D; Wang, Steve C; Hertog, Rachel

2007-01-01

84

Trophic network models explain instability of Early Triassic terrestrial communities.  

PubMed

Studies of the end-Permian mass extinction have emphasized potential abiotic causes and their direct biotic effects. Less attention has been devoted to secondary extinctions resulting from ecological crises and the effect of community structure on such extinctions. Here we use a trophic network model that combines topological and dynamic approaches to simulate disruptions of primary productivity in palaeocommunities. We apply the model to Permian and Triassic communities of the Karoo Basin, South Africa, and show that while Permian communities bear no evidence of being especially susceptible to extinction, Early Triassic communities appear to have been inherently less stable. Much of the instability results from the faster post-extinction diversification of amphibian guilds relative to amniotes. The resulting communities differed fundamentally in structure from their Permian predecessors. Additionally, our results imply that changing community structures over time may explain long-term trends like declining rates of Phanerozoic background extinction. PMID:17609191

Roopnarine, Peter D; Angielczyk, Kenneth D; Wang, Steve C; Hertog, Rachel

2007-09-01

85

Detection of crossover time scales in multifractal detrended fluctuation analysis  

NASA Astrophysics Data System (ADS)

Fractal is employed in this paper as a scale-based method for the identification of the scaling behavior of time series. Many spatial and temporal processes exhibiting complex multi(mono)-scaling behaviors are fractals. One of the important concepts in fractals is crossover time scale(s) that separates distinct regimes having different fractal scaling behaviors. A common method is multifractal detrended fluctuation analysis (MF-DFA). The detection of crossover time scale(s) is, however, relatively subjective since it has been made without rigorous statistical procedures and has generally been determined by eye balling or subjective observation. Crossover time scales such determined may be spurious and problematic. It may not reflect the genuine underlying scaling behavior of a time series. The purpose of this paper is to propose a statistical procedure to model complex fractal scaling behaviors and reliably identify the crossover time scales under MF-DFA. The scaling-identification regression model, grounded on a solid statistical foundation, is first proposed to describe multi-scaling behaviors of fractals. Through the regression analysis and statistical inference, we can (1) identify the crossover time scales that cannot be detected by eye-balling observation, (2) determine the number and locations of the genuine crossover time scales, (3) give confidence intervals for the crossover time scales, and (4) establish the statistically significant regression model depicting the underlying scaling behavior of a time series. To substantive our argument, the regression model is applied to analyze the multi-scaling behaviors of avian-influenza outbreaks, water consumption, daily mean temperature, and rainfall of Hong Kong. Through the proposed model, we can have a deeper understanding of fractals in general and a statistical approach to identify multi-scaling behavior under MF-DFA in particular.

Ge, Erjia; Leung, Yee

2012-05-01

86

Detection of crossover time scales in multifractal detrended fluctuation analysis  

NASA Astrophysics Data System (ADS)

Fractal is employed in this paper as a scale-based method for the identification of the scaling behavior of time series. Many spatial and temporal processes exhibiting complex multi(mono)-scaling behaviors are fractals. One of the important concepts in fractals is crossover time scale(s) that separates distinct regimes having different fractal scaling behaviors. A common method is multifractal detrended fluctuation analysis (MF-DFA). The detection of crossover time scale(s) is, however, relatively subjective since it has been made without rigorous statistical procedures and has generally been determined by eye balling or subjective observation. Crossover time scales such determined may be spurious and problematic. It may not reflect the genuine underlying scaling behavior of a time series. The purpose of this paper is to propose a statistical procedure to model complex fractal scaling behaviors and reliably identify the crossover time scales under MF-DFA. The scaling-identification regression model, grounded on a solid statistical foundation, is first proposed to describe multi-scaling behaviors of fractals. Through the regression analysis and statistical inference, we can (1) identify the crossover time scales that cannot be detected by eye-balling observation, (2) determine the number and locations of the genuine crossover time scales, (3) give confidence intervals for the crossover time scales, and (4) establish the statistically significant regression model depicting the underlying scaling behavior of a time series. To substantive our argument, the regression model is applied to analyze the multi-scaling behaviors of avian-influenza outbreaks, water consumption, daily mean temperature, and rainfall of Hong Kong. Through the proposed model, we can have a deeper understanding of fractals in general and a statistical approach to identify multi-scaling behavior under MF-DFA in particular.

Ge, Erjia; Leung, Yee

2013-04-01

87

The differential equations on time scales through impulsive differential equations  

Microsoft Academic Search

In this paper we investigate differential equations on certain time scales with transition conditions (DETC) on the basis of reduction to the impulsive differential equations (IDE). DETC are in some sense more general than dynamic equations on time scales [M. Bohner, A. Peterson, Dynamic equations on time scales, in: An Introduction With Applications, Birkhäuser Boston, Inc., Boston, MA, 2001, p.

M. U. Akhmet; M. Turan

2006-01-01

88

Osmium isotope evidence for a large Late Triassic impact event.  

PubMed

Anomalously high platinum group element concentrations have previously been reported for Upper Triassic deep-sea sediments, which are interpreted to be derived from an extraterrestrial impact event. Here we report the osmium (Os) isotope fingerprint of an extraterrestrial impact from Upper Triassic chert successions in Japan. Os isotope data exhibit a marked negative excursion from an initial Os isotope ratio ((187)Os/(188)Osi) of ~0.477 to unradiogenic values of ~0.126 in a platinum group element-enriched claystone layer, indicating the input of meteorite-derived Os into the sediments. The timing of the Os isotope excursion coincides with both elevated Os concentrations and low Re/Os ratios. The magnitude of this negative Os isotope excursion is comparable to those found at Cretaceous-Paleogene boundary sites. These geochemical lines of evidence demonstrate that a large impactor (3.3-7.8?km in diameter) produced a global decrease in seawater (187)Os/(188)Os ratios in the Late Triassic. PMID:24036603

Sato, Honami; Onoue, Tetsuji; Nozaki, Tatsuo; Suzuki, Katsuhiko

2013-09-16

89

Osmium isotope evidence for a large Late Triassic impact event  

PubMed Central

Anomalously high platinum group element concentrations have previously been reported for Upper Triassic deep-sea sediments, which are interpreted to be derived from an extraterrestrial impact event. Here we report the osmium (Os) isotope fingerprint of an extraterrestrial impact from Upper Triassic chert successions in Japan. Os isotope data exhibit a marked negative excursion from an initial Os isotope ratio (187Os/188Osi) of ?0.477 to unradiogenic values of ?0.126 in a platinum group element-enriched claystone layer, indicating the input of meteorite-derived Os into the sediments. The timing of the Os isotope excursion coincides with both elevated Os concentrations and low Re/Os ratios. The magnitude of this negative Os isotope excursion is comparable to those found at Cretaceous–Paleogene boundary sites. These geochemical lines of evidence demonstrate that a large impactor (3.3–7.8?km in diameter) produced a global decrease in seawater 187Os/188Os ratios in the Late Triassic.

Sato, Honami; Onoue, Tetsuji; Nozaki, Tatsuo; Suzuki, Katsuhiko

2013-01-01

90

The Triassic detrital units in the East-Mediterranean realm: back-arcs opening and Cimmerian collision  

NASA Astrophysics Data System (ADS)

Late Permian and principally Triassic detrital units play an important role in deciphering the geodynamic evolution of the East-Mediterranean area. Some of these units are related to diffuse rifting along the southern margin of Eurasia, whereas others reflect the Cimmerian collision between Gondwana and post-Variscan Eurasia-derived terranes. Several differences within these Triassic detrital units should be noted: they have a different timing of deposition, they are found in autochthonous, para-autochthonous or allochthonous position, and they have different types of substratum and cover series. In addition, the nature of the recycled material is also decisive to make the difference between orogen and rift-related sediments. The investigated sandstones, breccias and conglomerates usually range in age from the Anisian (Scythian?) to the Late Triassic (sometimes Liassic) and are especially well-developed during the Carnian-Norian interval. From the Late Permian to the Late Triassic, the Variscan Cordillera was affected by orogen-scale collapse, leading to widespread rifting, related to slab roll-back of the northward subducting Palaeotethys. This provoked the opening of a series of back-arc basins (i.e. Meliata-Hallstatt, Maliac and Pindos oceans). At the same time, this subduction detached by slab-pull a series of Cimmerian terranes along the northern border of Gondwana and opened the Neotethys to the south of them. The final closure of the Palaeotethys (Cimmerian Event) between the Taurus and the Anatolian terranes produced at places large flysch-molasse deposits often sealed by Jurassic platforms. In southern Europe, the diffuse rifting along the southern margin of Eurasia is recognized in the Carnic Alps. The Carboniferous fore-arc flysch basin (Hochwipfel and Dimon fms) is sealed by a shallow-water sequence of Pennsylvanian-Early Permian age (Pramolo, Rattendorf and Trogkofel groups). The Late Permian rifting is marked by the deposition of the Val Gardena Sandstone and the Bellerophon Fm. This rifting phase is sealed by the Werfen Fm. and the Serla Dolomite. The second phase of rifting is marked by the deposition of the Braies group during the upper Anisian (locally sealed by the latest Anisian-early Carnian Sciliar Dolomite), followed by the deposition of the Buchenstein ("Pietra Verde" pro parte), Wengen (turbiditic sandstones) and San Cassiano Fms until the lower Carnian. This second episode is locally sealed by the Cassian Dolomite and the Val Degano Fm. The third rifting phase is marked by the deposition of the Carnian Dürrenstein Fm, sealed by the late Carnian Raibl Fm. and the Norian Dolomia Principale. On the Turkish transect, the detrital units belonging to the allochthonous series are post-Variscan Anatolian-derived nappes and are often associated with widespread volcanism. They are generally situated at the base of sequences showing shallow marine sedimentation that pass up to pelagic conditions and finish with flysch/wildflysch deposits. The Meliata-Hallstatt "signal" is well-known in the Silická Brezová composite section (Slovakia). The lower to middle Carnian is made of shallow water limestone followed by a rapid subsidence during the lower upper Carnian and the deposition of pelagic limestones, crinoid limestones, calcarenites and micrites themselves followed by Hallstatt Limestones during the entire Norian and lower Rhaetian. The Maliac "signal" is clearly identifiable in the Karaburun Peninsula. The pelagic development made of limestones and radiolarites usually starts during the Spathian above shallow water limestones. The pelagic sedimentation continues during the middle Triassic and the lower Carnian. During the middle Carnian, the sedimentation passes to shallow water limestones and this situation persists during the Upper Triassic and sometimes even higher up. Volcanic events are common in the Spathian and in the Middle Triassic. Late Carnian cherts associated with pillow-lavas of Maliac origin are found on the northern edge of the composite Anatolian-Tauric plat

Moix, P.; Stampfli, G. M.

2009-04-01

91

Geologic Time Scale 2004 - why, how, and where next!  

Microsoft Academic Search

A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. Key features of the new scale are outlined, how it was constructed, and how it can be improved Since Geologic Time Scale 1989 by Harland and his team, many developments have taken place: (1) Stratigraphic standardization through the work of the International Commission on Stratigraphy

Felix Gradstein; James Ogg

2004-01-01

92

Linking Response-Time Parameters onto a Common Scale  

ERIC Educational Resources Information Center

|Although response times on test items are recorded on a natural scale, the scale for some of the parameters in the lognormal response-time model (van der Linden, 2006) is not fixed. As a result, when the model is used to periodically calibrate new items in a testing program, the parameter are not automatically mapped onto a common scale. Several…

van der Linden, Wim J.

2010-01-01

93

Biogeography of Triassic tetrapods: evidence for provincialism and driven sympatric cladogenesis in the early evolution of modern tetrapod lineages  

PubMed Central

Triassic tetrapods are of key importance in understanding their evolutionary history, because several tetrapod clades, including most of their modern lineages, first appeared or experienced their initial evolutionary radiation during this Period. In order to test previous palaeobiogeographical hypotheses of Triassic tetrapod faunas, tree reconciliation analyses (TRA) were performed with the aim of recovering biogeographical patterns based on phylogenetic signals provided by a composite tree of Middle and Late Triassic tetrapods. The TRA found significant evidence for the presence of different palaeobiogeographical patterns during the analysed time spans. First, a Pangaean distribution is observed during the Middle Triassic, in which several cosmopolitan tetrapod groups are found. During the early Late Triassic a strongly palaeolatitudinally influenced pattern is recovered, with some tetrapod lineages restricted to palaeolatitudinal belts. During the latest Triassic, Gondwanan territories were more closely related to each other than to Laurasian ones, with a distinct tetrapod fauna at low palaeolatitudes. Finally, more than 75 per cent of the cladogenetic events recorded in the tetrapod phylogeny occurred as sympatric splits or within-area vicariance, indicating that evolutionary processes at the regional level were the main drivers in the radiation of Middle and Late Triassic tetrapods and the early evolution of several modern tetrapod lineages.

Ezcurra, Martin D.

2010-01-01

94

Time Ephemeris and General Relativistic Scale Factor  

Microsoft Academic Search

Time ephemeris is the location-independent part of the transformation formula relating two time coordinates such as TCB and TCG (Fukushima 2009). It is computed from the corresponding (space) ephemerides providing the relative motion of two spatial coordinate origins such as the motion of geocenter relative to the solar system barycenter. The time ephemerides are inevitably needed in conducting precise four

Toshio Fukushima

2010-01-01

95

Time ephemeris and general relativistic scale factor  

Microsoft Academic Search

Time ephemeris is the location-independent part of the transformation formula relating two time coordinates such as TCB and TCG (Fukushima 1995). It is computed from the corresponding (space) ephemerides providing the relative motion of two spatial coordinate origins such as the motion of geocenter relative to the solar system barycenter. The time ephemerides are inevitably needed in conducting precise four

Toshio Fukushima

2010-01-01

96

The development of the Middle Triassic tectonical controlled Germanic Basin of Central Europe and the palaeoenvironmental related distribution of marine and terrestrial reptiles  

Microsoft Academic Search

Nine Middle Triassic paleogeographical maps comprising the uppermost Upper Bunter, Lower to Middle Muschelkalk and Upper Muschelkalk to Lower Keuper time frame (Diedrich 2008b) show the marine ingression and regression cycle of the Middle Triassic Germanic Basin (Diedrich 2010c). For bathymetrical and palaeoenvironmental interpretations especially reptiles and their footprints are used. This Germanic Basin as analogon for the Arabian Gulf

Cajus G. Diedrich

2010-01-01

97

Rift-related Triassic Alpine magmatism traced by U-Pb dating and Hafnium isotopes of detrital zircons  

NASA Astrophysics Data System (ADS)

The geodynamic setting and source of syn-sedimentary Triassic igneous activity in the Alpine Tethys is a matter of discussion since long time. There are two contrasting models proposed, either within an extensional environment (e.g. Crisci et al., 1984) or in a subduction-related setting (e.g. Castellarin, 1988); the latter in particular is based on the apparent calc-alkaline geochemical signature. We analyse Triassic and Jurassic sandstones from the southern margin of the Alpine Tethys. Laser-ablation ICP-MS methods are used to date the detrital zircons and to evaluate Hf-isotope ratios in order to characterise the time and type of magmas in which the zircons crystallised. For analyses we have chosen the Early Triassic Fuorn Formation and the Middle Triassic Prosanto and Altein formations (Upper Austroalpine Silvretta nappe), the Middle Jurassic Saluver Formation (Lower Austroalpine Err nappe), the Middle Triassic Buchenstein Formation and the early Late Triassic Val Sabbia Formation (South Alpine domain). The detrital zircon U-Pb ages reveal a main sourcing of the Triassic sandstones in coeval igneous rocks, and alternatively, in Permian igneous and volcaniclastic (Verruccano type) rocks. Triassic re-melting of older continental crust is documented by the presence of post-Variscan, Variscan and older inherited cores in the detrital zircons. A mixed mantle-crust source of the Triassic melts is confirmed by the Hf-isotope ratios. Finally, Triassic rift-related igneous activity developed in a similar crustal setting as the post-Variscan magmatism. We conclude that the Triassic magmas formed through partial melting of the upper mantle, which was deeply modified during the previous Variscan orogeny (Crisci et al. 1984). The rising melts included crustal material, and the apparent calc-alkaline signature was inherited due to recycling of previous subduction-related orogenic cycle products. With regard to the obtained epsilon Hafnium values of the detrital zircons, the post-Variscan (Permian) extension and Triassic Alpine rifting were continuous processes.

Beltran-Triviño, Alejandro; Winkler, Wilfried; Bussien, Denise; von Quadt, Albrecht

2013-04-01

98

Scale-Limited Activating Sets and Multiperiodicity for Threshold-Linear Networks on Time Scales.  

PubMed

The existing results for multiperiodicity of threshold-linear networks (TLNs) are scale-free on time evolution and hence exhibit some restrictions. Due to the nature of the scale-limited activating set, it is interesting to study the dynamical properties of neurons on time scales. In this paper we analyze and obtain results concerning nondivergence, attractivity, and multiperiodic dynamics of TLNs on time scales. Using the notion of exponential functions on time scales, we obtain results for scale-limited type criteria for boundedness and global attractivity of TLNs. Moreover, by constructing simple algebraic inequalities over scale-limited activating sets, we achieve results regarding multiperiodicity of TLNs. This will show that each scale-limited activating set depends on scale-synchronous self-excitation, and the existence of inactive neurons will slow down convergence of TLNs. At the end of the paper, we perform computer simulations to illustrate the obtained new theories. PMID:23757562

Huang, Zhenkun; Raffoul, Youssef N; Cheng, Chang-Yuan

2013-05-03

99

Palaeogeography of Late Triassic red-beds in Singapore and the Indosinian Orogeny  

NASA Astrophysics Data System (ADS)

A red-bed facies of the Upper Triassic Jurong Formation has been logged on Sentosa Island, Singapore. An overall coarsening and thickening-upward pattern is well developed. The lower part of the section is dominated by purple-red, massive to finely laminated illite-smectite-kaolin-rich mudstones containing thin, discontinuous lenses of fine sandstone marked by low-angle lamination and small ripples. One dinosaur-like foot print has been discovered in a loose block of red mudstone. It is concluded that this is a lacustrine sequence and it is proposed to name the lake, Lake Sentosa. The upper part of the sequence consists of flat-laminated to trough cross-bedded medium-grained sandstone and granule to cobble conglomerates alternating with purple-red mudstone. The mudstone-sandstone packages are arranged in decametre-scale coarsening-upward cycles. The channelling and decimetre-scale cross-bedding characterising the sandstone and conglomeratic beds is evidence for deposition by flashy fluvial flood processes, possibly feeding into the lake as a fresh water delta. One possible dinosaur trackway in granule size conglomerate has been located. Detrital zircon U-Pb ages vary from 2.7 Ba to 209 Ma with significant populations at ˜245 Ma and 220 Ma. These ages throw light on the timing of the Indosinian Orogeny. The molasse red-beds of the Jurong Formation were deposited in a half graben formed in the hangingwall of the Bukit Timah Fault when central Peninsular Malaysia went into extension following the climax of the Indosinian Orogeny in the Late Triassic.

Oliver, Grahame; Prave, Anthony

2013-10-01

100

General entanglement scaling laws from time evolution.  

PubMed

We establish a general scaling law for the entanglement of a large class of ground states and dynamically evolving states of quantum spin chains: we show that the geometric entropy of a distinguished block saturates, and hence follows an entanglement-boundary law. These results apply to any ground state of a gapped model resulting from dynamics generated by a local Hamiltonian, as well as, dually, to states that are generated via a sudden quench of an interaction as recently studied in the case of dynamics of quantum phase transitions. We achieve these results by exploiting ideas from quantum information theory and tools provided by Lieb-Robinson bounds. We also show that there exist noncritical fermionic systems and equivalent spin chains with rapidly decaying interactions violating this entanglement-boundary law. Implications for the classical simulatability are outlined. PMID:17155303

Eisert, Jens; Osborne, Tobias J

2006-10-12

101

Time and scale evolutionary EVD and detection  

Microsoft Academic Search

Optimal detection of a known signal in nonstationary noise requires tracking the eigenvalue decomposition (EVD) of the noise data over time. To take advantage of information in the long-term, as well as short-term, correlation lags we turn to EVD over wavelet subspaces. We develop a multirate EVD updating method over multiresolution subspaces and find maximum detectability nodes on wavelet binary

Nurgun Erdol; Spyros Kyperountas; Branko Petljanski

2001-01-01

102

Molecular carbon isotope variations in core samples taken at the Permian-Triassic boundary layers in southern China  

NASA Astrophysics Data System (ADS)

Stable carbon isotope composition (?13C) of carbonate sediments and the molecular (biomarker) characteristics of a continuous Permian-Triassic (PT) layer in southern China were studied to obtain geochemical signals of global change at the Permian-Triassic boundary (PTB). Carbonate carbon isotope values shifted toward positive before the end of the Permian period and then shifted negative above the PTB into the Triassic period. Molecular carbon isotope values of biomarkers followed the same trend at and below the PTB and remained negative in the Triassic layer. These biomarkers were acyclic isoprenoids, ranging from C15 to C40, steranes (C27 dominates) and terpenoids that were all significantly more abundant in samples from the Permian layer than those from the Triassic layer. The Triassic layer was distinguished by the dominance of higher molecular weight (waxy) n-alkanes. Stable carbon isotope values of individual components, including n-alkanes and acyclic isoprenoids such as phytane, isop-C25, and squalane, are depleted in ?13C by up to 8-10‰ in the Triassic samples as compared to the Permian. Measured molecular and isotopic variations of organic matter in the PT layers support the generally accepted view of Permian oceanic stagnation followed by a massive upwelling of toxic deep waters at the PTB. A series of large-scale (global) outgassing events may be associated with the carbon isotope shift we measured. This is also consistent with the lithological evidence we observed of white thin-clay layers in this region. Our findings, in context with a generally accepted stagnant Permian ocean, followed by massive upwelling of toxic deep waters might be the major causes of the largest global mass extinction event that occurred at the Permian-Triassic boundary.

Wang, Ruiliang; Zhang, Shuichang; Brassell, Simon; Wang, Jiaxue; Lu, Zhengyuan; Ming, Qingzhong; Wang, Xiaomei; Bian, Lizeng

2012-07-01

103

Examination of hypotheses for the Permo-Triassic boundary extinction by carbon cycle modeling  

PubMed Central

The biological extinction that occurred at the Permian–Triassic boundary represents the most extensive loss of species of any known event of the past 550 million years. There have been a wide variety of explanations offered for this extinction. In the present paper, a number of the more popular recent hypotheses are evaluated in terms of predictions that they make, or that they imply, concerning the global carbon cycle. For this purpose, a mass balance model is used that calculates atmospheric CO2 and oceanic ?13C as a function of time. Hypotheses considered include: (i) the release of massive amounts of CO2 from the ocean to the atmosphere resulting in mass poisoning; (ii) the release of large amounts of CO2 from volcanic degassing; (iii) the release of methane stored in methane hydrates; (iv) the decomposition and oxidation of dead organisms to CO2 after sudden mass mortality; and (v) the long-term reorganization of the global carbon cycle. The modeling indicates that measured short-term changes in ?13C at the boundary are best explained by methane release with mass mortality and volcanic degassing contributing in secondary roles. None of the processes result in excessively high levels of atmospheric CO2 if they occurred on time scales of more than about 1,000 years. The idea of poisoning by high levels of atmospheric CO2 depends on the absence of subthermocline calcium carbonate deposition during the latest Permian. The most far-reaching effect was found to be reorganization of the carbon cycle with major sedimentary burial of organic matter shifting from the land to the sea, resulting in less burial overall, decreased atmospheric O2, and higher atmospheric CO2 for the entire Triassic Period.

Berner, Robert A.

2002-01-01

104

Constraints on Early Triassic carbon cycle dynamics from paired organic and inorganic carbon isotope records  

NASA Astrophysics Data System (ADS)

Large ?13C excursions, anomalous carbonate precipitates, low diversity assemblages of small fossils, and evidence for marine euxinia in uppermost Permian and Lower Triassic strata bear more similarity to Neoproterozoic carbonates than to the remainders of the Permian and Triassic systems. Middle Triassic diversification of marine ecosystems coincided with the waning of anoxia and stabilization of the global carbon cycle, suggesting that environment-ecosystem linkages were important to biological recovery. However, the Earth system behavior responsible for these large ?13C excursions remains poorly constrained. Here we present a continuous Early Triassic ?13Corg record from south China and use it to test the extent to which Early Triassic excursions in ?13Ccarb record changes in the ?13C of marine dissolved inorganic carbon (DIC). Regression analysis demonstrates a significant positive correlation between ?13Corg and ?13Ccarb across multiple sections that span a paleoenvironmental gradient. Such a correlation is incompatible with diagenetic alteration because no likely mechanism will alter both ?13Corg and ?13Ccarb records in parallel and therefore strongly indicates a primary depositional origin. A simple explanation for this correlation is that a substantial portion of the preserved Corg was derived from the contemporaneous DIC pool, implying that the observed excursions reflect variation in the ?13C of the exogenic carbon reservoir (ocean, atmosphere, biomass). These findings support existing evidence that large ?13C excursions are primary and therefore strengthen the case that large-scale changes to the carbon cycle were mechanistically linked to the low diversity and small size of Early Triassic fossils. Associated sedimentary and biogeochemical phenomena further suggest that similar associations in Neoproterozoic and Cambrian strata may reflect the same underlying controls.

Meyer, K. M.; Yu, M.; Lehrmann, D.; van de Schootbrugge, B.; Payne, J. L.

2013-01-01

105

Paleomagnetic data from Triassic strata, Zuni uplift, New Mexico: Further evidence of large-magnitude Triassic apparent polar wander of North America  

NASA Astrophysics Data System (ADS)

Upper Carnian (~225 Ma) strata of the Bluewater Creek Formation of the Chinle Group of the Colorado Plateau, western New Mexico, contain predominantly reverse polarity characteristic magnetizations of high coercivity and distributed unblocking temperature up to 695°C. Data from a syndepositional structure suggest acquisition of a stable remanence during or soon after deposition. The mean paleomagnetic pole for 13 virtual geomagnetic poles (VGP) accepted (of 17 sites collected) is located at 55.2°N, 87.5°E (A95=6.7°, K=39.7). The angular distance between this pole and the mean of recently published middle and late Norian (~210 Ma) poles from overlying strata is 12.5°, supporting the hypothesis that significant apparent polar wander occurred during Late Triassic time. Furthermore, the Bluewater Creek pole lies to the west (6.1°, angular distance) of the cratonic reference pole for Carnian time supporting the hypothesis of a small Colorado Plateau rotation since the early Mesozoic. Anisian strata of the Moenkopi Formation contain dual polarity magnetizations of high coercivity and distributed unblocking temperatures up to 690°C. The mean VGP of six sites yields is located at 53.1°N, 96.3°E (A95=6.4°, K=109.2), which is similar to previously determined Middle Triassic poles. Triassic paleomagnetic poles from southwest North America from strata in continuous stratigraphic succession, both on and off the Colorado Plateau, are not consistent with the hypothesis of a Late Triassic stand still of the geomagnetic pole.

Molina Garza, Roberto S.; Geissman, John W.; Gomez, Alfred; Horton, Brian

1998-10-01

106

Image Denoising Using Similarities in the TimeScale Plane  

Microsoft Academic Search

This paper presents a de-noising method that recognizes similarities in the image through the time scale behaviour of wavelet\\u000a coefficients. Wavelet details are represented as linear combination of predefined atoms whose center of mass traces trajectories\\u000a in the time scale plane (from fine to coarse scale). These trajectories are the solution of a proper ordinary differential\\u000a equation and characterize atoms

Vittoria Bruni; Domenico Vitulano

2008-01-01

107

Preliminary evaluation of time scales based on hydrogen masers  

Microsoft Academic Search

Two experimental time scales based on ensembles of hydrogen masers were generated and compared with a variety of other references both internal and external to NIST. The masers all had some type of active cavity control to reduce frequency drift due to cavity changes, The first experimental time scale, TA2M, was generated over the interval from MJD 49050 to 49190

Marc A. Weiss; Fred L. Walls

1996-01-01

108

Evidence from ammonoids and conodonts for multiple Early Triassic mass extinctions.  

PubMed

Ammonoids and conodonts, being characterized by exceptionally high background rates of origination and extinction, were vulnerable to global environmental crises, which characteristically intensified background rates of extinction. Thus, it is not surprising that these taxa suffered conspicuous mass extinctions at the times of three negative Early Triassic global carbon isotopic excursions that resembled those associated with the two preceding Permian mass extinctions. In keeping with their high rates of origination, both the ammonoids and conodonts rediversified dramatically between the Early Triassic crises. Other marine taxa, characterized by much lower intrinsic rates of origination, were held at low levels of diversity by the Early Triassic crises; because global mass extinctions affect all marine life, these taxa must have experienced relatively modest expansions and contractions that have yet to be discovered, because they do not stand out in the fossil record and because the stratigraphic ranges of these taxa, being of little value for temporal correlation, have not been thoroughly studied. PMID:19721005

Stanley, Steven M

2009-08-31

109

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

110

Scaling the Martian Walls of Time  

NASA Astrophysics Data System (ADS)

On Earth, when scientists want to investigate planetary history they take a core sample, with deeper fragments corresponding to older materials. In essence, descending through sedimentary layers is like going back in time. But creating a robot capable of taking samples more than a few meters below the planetary surface is still beyond the current available technology. The cliffhanger idea takes advantage of the natural surface features of Mars to explore the history of the planet without digging. So interesting and difficult questions can be answered not with the brute force of a drill, but with creative mission design. Penn State University HEDS-UP team has designed a novel Mars mission approach. A main Lander with a Rover and a Cliffhanger will land near cliffs of Valles Mariners. Especially design cannon (gas, guided munitions or rocket) will deploy a long rope into the canyon. The rover will carry the cliffhanger to the edge of Valles Marineris following the rope, attach the cliffhanger to the rope. The Cliffhanger will then climb a 2 km down the rope and will allow the team to study sedimentary layers of rock on the side of the cliff. Samples and high-resolution images will be taken and delivered to the Lander for further investigation (optical multispectral imaging microscope, spectrometry) and sending the results to Earth. The robot has been designed to have the capability for locomotion at any angle (including somewhat uphill slopes) but maximum effective After the mission of rope-climbing is completed, the Rover am Lander will embark on another long-term mission to provide meteorological and geological data over a long period of time (long-term Mars Observatory), and perform acoustic and seismic experiments on the surface of Mars in preparation for human arrival.

Thornton, Nikki; Yagloski, Joseph; Fledderman, Joe; OMarr, Gregg; Weber, Ben; Carlins, Chris; Krishna, Shubh; Sloan, Kevin; Merriman, Taite; Borowski, David

2000-01-01

111

Time scales of tunneling decay of a localized state  

SciTech Connect

Motivated by recent time-domain experiments on ultrafast atom ionization, we analyze the transients and time scales that characterize, aside from the relatively long lifetime, the decay of a localized state by tunneling. While the tunneling starts immediately, some time is required for the outgoing flux to develop. This short-term behavior depends strongly on the initial state. For the initial state, tightly localized so that the initial transients are dominated by over-the-barrier motion, the time scale for flux propagation through the barrier is close to the Buettiker-Landauer traversal time. Then a quasistationary, slow-decay process follows, which sets ideal conditions for observing diffraction in time at longer times and distances. To define operationally a tunneling time at the barrier edge, we extrapolate backward the propagation of the wave packet that escaped from the potential. This extrapolated time is considerably longer than the time scale of the flux and density buildup at the barrier edge.

Ban, Yue; Muga, J. G. [Department of Physical Chemistry, Universidad del Pais Vasco UPV-EHU, E-48080 Bilbao (Spain); Sherman, E. Ya. [Department of Physical Chemistry, Universidad del Pais Vasco UPV-EHU, E-48080 Bilbao (Spain); IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao (Spain); Buettiker, M. [Departement de Physique Theorique, Universite de Geneve, CH-1211 Geneve 4 (Switzerland)

2010-12-15

112

Chron E23r, paleosecular variation, CAMP volcanism and the end-Triassic extinction event (Invited)  

NASA Astrophysics Data System (ADS)

In the early Mesozoic rift basins of eastern North America, CAMP lava flows occur within normal polarity Chron E24n, which according to cycle stratigraphy has a duration of nearly four McLaughlin (405 kyr) cycles, or ~1.6 Ma. In the Newark basin, the level marking the end-Triassic extinction event occurs one Van Houten cycle (20 kyr) before the first CAMP basalt and is preceded within another Van Houten cycle by reverse polarity Chron E23r, one of the shortest (~25 kyr) polarity intervals recognized in the Newark astronomically-tune polarity time scale. This tight chronostratigraphic sequence of events-E23r followed by end-Triassic event and then CAMP lavas within E24n-has been replicated in several sections [1] and a key element (end-Triassic palynofloral turnover preceding the first CAMP lava) is recorded in the Fundy basin of Nova Scotia, where the initial CAMP eruption (North Mountain Basalt) has a rather precise U-Pb (206Pb/238U) zircon date of 201.27± 0.03 Ma [2]. However, two magnetic excursions were found within the Intermediate Basalt (39Ar/40Ar date of 199.9± 0.5 Ma) in the Central High Atlas Mountains of Morocco and correlated to E23r [3, 4], which would imply that the underlying (Lower) basalt unit occurred before and therefore in a possible causal relationship to the end-Triassic extinction event. Paleomagnetic study of the Moroccan basalts also revealed variations in magnetic directions, which were interpreted as a record of secular variation and thus might prove useful for identification of CAMP lavas [4]. We sampled most of the lava flows in the Fundy basin that comprise the ~300 m-thick North Mountain Basalt in outcrop (30 sites) as well as in several industry cores drilled near Margaretsville (GAV-77-3, AV-C-1-4), Freeport (AV-C-1-1), and Westport (AV-C-1-2) in Nova Scotia. We find only two directional groupings for the entire North Mountain Basalt, a finding that basically confirms the results of Carmichael and Palmer [5]. We have yet to find evidence in the Fundy basin for the two excursions that have been reported in the Intermediate basalt (and variously correlated to E23r. However, the progression of VGP clusters corresponding to the directional groups for the North Mountain Basalt resemble those reported by Knight et al. [4] for the Lower and Intermediate lavas from Morocco. We thus speculate that the episodic volcanicity associated with initial phases of CAMP can be correlated over (predrift) distances of ~1000 km on submillennial time-scales of paleosecular variation. 1, Olsen, P.E. et al. 2002, Geol. Soc. Amer. Spec. Paper 356:505-522; 2, Schoene, B. et al., 2006, Geochim. Cosmochim. Acta 70:426-445; 3, Marzoli, A. et al., 2004, Geology 32:973-976; 4, Knight, A.B. et al., 2004, Earth Planet. Sci. Lett. 228:143-160; 5, Carmichael, C.M., Palmer, H. C., 1968, Jour. Geophys. Res. 73:2811-2822.

Kent, D. V.; Wang, H.; Olsen, P. E.

2009-12-01

113

Time Scales for Achieving Astronomical Consensus  

NASA Astrophysics Data System (ADS)

The history of science can be recounted in many ways: by addressing the work of one person or school; by starting with the ancients and working chronologically up to the present; by focusing on a particular century; or by tracing a particular important idea as far back and forward as it can be found. The present discussion does none of these. Rather, it adopts the ordering of a standard introductory astronomy textbook, from the solar system via stars and galaxies, to the universe as a whole, and in each regime picks out a few issues that were controversial or wrongly decided for a long time. For each, I attempt to identify a duration of the period of uncertainty or error and some of the causes of the confusion. This is surely not an original idea, though I am not aware of having encountered it elsewhere, and it is not one that is likely to appeal to most 21st century historians of science, for whom the question "Who first got it right?" is not necessarily an important, or even appropriate, one. Some of the stories have been told as historical introductions to conferences and are here summarized and brought up to date. Others I had not previously addressed.

Trimble, Virginia

114

Tectonic evolution of the Songpan Garzê and adjacent areas (NE Tibet) from Triassic to Present : a synthesis.  

NASA Astrophysics Data System (ADS)

The 12th May 2008 Wenchuan earthquake in the Longmen Shan occurred on a large thrust fault largely inherited from an Indosinian structure itself probably controlled by an older structural heritage of the South China block continental margin. Within the whole northeast Tibet region, such a structural inheritance has had a major impact on the Tertiary deformation. It appears of primary importance to assess the pre-Tertiary tectonic evolution of the main blocks involved to understand the actual deformation in the eastern edge of Tibet. Over the past decades, the Proterozoic to Cenozoic tectonic, metamorphic and geochronologic history of the Longmen Shan and Songpan Garzê area have been largely studied. We present a synthesis of the tectonic evolution of the Songpan Garzê fold and thrust belt from Triassic to present. The Songpan-Garzê belt was formed during closure of a wide oceanic basin filled with a thick (5 to 15 km) sequence of Triassic flyschoid sediments [10]. Closure of the basin due to Triassic subduction involved strong shortening, intense folding and faulting of the Triassic series. A large-scale décollement, that presently outcrops along the eastern boundary of the belt (Danba area), allowed the growth of a wide and thick accretionary wedge [9]. It develops in the Paleozoic and Triassic series and separates the accretionary prism from an autochthonous crystalline basement [5, 12, 6] which shares many similarities with the basement of the Yangtze Craton (0.7-0.9 Ga). To the north and northwest, below the thickened Triassic series of the belt, the composition (oceanic or continental) of the basement remains unknown. During the Indosinian orogeny the emplacement of orogenic granites (220 - 150 Ma) was associated to crustal thickening [12, 13, 17, 15]. The isotopic composition of granitoids shows that their magma source were predominantly derived from melting of the proterozoic basement with varying degrees of sedimentary material and negligible mantle source contribution. In the Danba area, the décollement outcrops in a large tertiary antiform with a NNW-SSE axis [6, 12, 18]. It has been exhumed too in the hanging wall of the NE-SW faults of the Tertiary Longmen-Shan belt that marks the present day transition from the Tibetan plateau to the Sichuan basin. These faults have episodically absorbed significant shortening since the Late Triassic [3]. The amount and precise timing of post-triassic deformation are difficult to constrain especially because of the difficulty to isolate the tertiary thermochronological signal from the protracted late Triassic - Cretaceous thermal history (e.g. [14]). Nonetheless it is generally accepted that Jurassic - Cretaceous tectonism did not modified the general Triassic architecture of eastern Tibet contrarily to the Tertiary deformation (e.g. [2, 12, 5, 14]). The long-term cooling histories obtained on Mesozoic granites and on the metamorphic series of the Danba dome are very similar showing a very slow and regular cooling during Jurassic and Cretaceous, confirming the absence of major tectonic event between c.a. 150 and 30 Ma [16, 7, 6, 12, 18]. Low temperature thermochronology data indicate that final exhumation and cooling occurred in the Tertiary with an acceleration between 10 and 5 Ma along the major tectonic structures [11, 12, 1, 16, 7,14, 8]. Within the Longmen Shan range, a total denudation of 7 to 10 km is estimated for the late Cenozoic period [1, 7, 4]. Similar amounts of late Tertiary denudation have been estimated along an east-west section across the Xianshuihe fault [16]. 1 : Arne et al., (1997), Tectonophysics 280, 239-256. 2 : Burchfield et al. (1995), International Geology Review 37, 661-735. 3 : Chen and Wilson, (1996), Journal of Structural Geology 18, 413-440. 4 : Clark et al., (2005), Geology 33, 525-528. 5 : Harrowfield and Wilson, (2005), Journal of Structural Geology 27, 101-117. 6 : Huang et al., (2003), Journal of Metamorphic Geology 21(3), 223-240. 7 : Kirby et al., (2002), Tectonics 21(1), 10.1029/2000TC001246. 8 : Lai et al., (2007), Science in Ch

Roger, F.; Jolivet, M.; Malavieille, J.

2009-04-01

115

Causality across rainfall time scales revealed by continuous wavelet transforms  

NASA Astrophysics Data System (ADS)

Rainfall variability occurs over a wide range of time scales owing to processes initiated by cloud microphysics and sustained by atmospheric circulation. A central topic in rainfall research is to determine whether rainfall variability at a given scale is caused by dynamics acting at some other scales. Random multiplicative cascades (RMCs) are standard approaches for describing rainfall variability across such a wide range of time scales. Their popularity stems from their ability to reproduce rainfall self-similarity and long-range correlations as well as intermittency buildup at finer scales. However, standard RMCs only predict instantaneous flow of variance (energy or activity) from large to fine scales and cannot account for scale-wise causal relationships. Such relationships reveal themselves through noninstantaneous cascade mechanisms, namely, large-scale events influencing finer-scale events at later times (i.e., forward causal cascade) or conversely (inverse causal cascade). The presence of causal cascade signatures within the rainfall process is explored here using both continuous wavelet decomposition (CWT) and scale-by-scale causality measures such as cross-scale correlation and linearized transfer entropy. The causality hypothesis is further tested against results from toy models, surrogate data, and a scalar turbulence time series (water vapor) to ensure that rainfall causality is not an artifact of the estimation method or resulting from the redundancy in CWT. The analysis demonstrates the presence of causal cascades (mainly forward) in rainfall series when sampled at fine temporal resolutions (seconds). These causal relationships tend to vanish when rainfall is aggregated at coarser time scales (hours and longer).

Molini, Annalisa; Katul, Gabriel G.; Porporato, Amilcare

2010-07-01

116

Magnetostratigraphy of Permian/Triassic boundary sequences in the Cis-Urals, Russia: No evidence for a major temporal hiatus  

NASA Astrophysics Data System (ADS)

During the last five years there has been considerable doubt over the age of the continental uppermost Permian Russian stages, the Kazanian and Tatarian. Traditionally they have been regarded as Late Permian but were re-dated as Middle Permian in the 2004 international time scale, despite fossil evidence that the Tatarian, at least, is Late Permian. These debated ages are tested by magnetostratigraphic study of five sections spanning the Permian Triassic Boundary (PTB) of the SE Urals in the Orenburg region of Russia. The Upper Permian and Lower Triassic of this region have a well documented vertebrate fauna whose evolution has a significant bearing on our understanding of the PTB mass extinction event. If the Tatarian is viewed as Mid Permian, then the Late Permian in Russia is marked by a 9-10 Ma stratigraphic gap. The palaeomagnetic data yield a distinct series of polarity zones that provide clear local and regional correlation and are readily tied to a recently compiled global magnetostratigraphic record. On the basis of this correlation the sampled sections span the upper Guadalupian to Induan stages without any obvious break, so confirming the traditional view that the Tatarian is Late Permian in age. Anomalies in the magnetic inclination are consistent with sediment compaction (inclination shallowing, a common phenomenon of red beds) but declination anomalies between these sites and elsewhere in Russia may suggest localised vertical axis rotation.

Taylor, Graeme K.; Tucker, Christopher; Twitchett, Richard J.; Kearsey, Timothy; Benton, Michael J.; Newell, Andrew J.; Surkov, Mikhail V.; Tverdokhlebov, Valentin P.

2009-04-01

117

Latest Triassic onset of the Central Atlantic Magmatic Province (CAMP) volcanism in the Fundy Basin (Nova Scotia): New stratigraphic constraints  

NASA Astrophysics Data System (ADS)

In this paper we investigate the stratigraphic relationship between the emplacement of the CAMP basalts and the Triassic-Jurassic (Tr-J) boundary in the Fundy Basin (Nova Scotia, Canada). This is one of the best exposed of the synrift basins of eastern North America (ENA) formed as a consequence of the rifting that led to the formation of the Atlantic Ocean. The Triassic palynological assemblages found in the sedimentary rocks below (uppermost Blomidon Formation) and just above the North Mountain Basalt (Scots Bay Member of the McCoy Brook Formation) indicate that CAMP volcanism, at least in Nova Scotia, is entirely of Triassic age, occurred in a very short time span, and may have triggered the T-J boundary biotic and environmental crisis. The palynological assemblage from the Blomidon Formation is characterised by the dominance of the Circumpolles group (e.g. Gliscopollis meyeriana, Corollina murphyae, Classopollis torosus) which crosses the previously established Tr-J boundary. The Triassic species Patinasporites densus disappears several centimetres below the base of the North Mountain basalt, near the previously interpreted Tr-J boundary. The lower strata of the Scots Bay Member yielded a palynological assemblage dominated by Triassic bisaccate pollens (e.g Lunatisporites acutus, L. rhaeticus Lueckisporites sp., Alisporites parvus) with minor specimens of the Circumpolles group. Examination of the state of preservation and thermal alteration of organic matter associated with the microfloral assemblages precludes the possibility of recycling of the Triassic sporomorphs from the older strata. Our data argue against the previous definition of the Tr-J boundary in the ENA basins, which was based mainly on the last occurrence of P. densus. Consequently, it follows that the late Triassic magnetostratigraphic correlations should be revised considering that chron E23r, which is correlated with the last occurrence of P. densus in the Newark basin, does not occur at the Tr-J boundary but marks rather a late Triassic (probably Rhaetian) reversal.

Cirilli, S.; Marzoli, A.; Tanner, L.; Bertrand, H.; Buratti, N.; Jourdan, F.; Bellieni, G.; Kontak, D.; Renne, P. R.

2009-09-01

118

Learning Across Time Scales: Science, Policy, Management, and Communication  

NASA Astrophysics Data System (ADS)

This presentation will draw together common themes raised in the session and discuss lessons learned across time scales and their implications for managers and policy makers concerned with both climate change and variability. Session themes will be examined in the context of the upcoming World Summit on Sustainable Development (WSSD) and considered as opportunities for linking climate change policy discussions with lessons learned from the study of adaptation on seasonal to interannual time scales. The presentation will raise questions about future research directions, discuss recommendations for promoting learning across time scales, and explore options for better communicating the links between climate change and variability.

Stewart, M. M.

2002-05-01

119

Mantle plume: The invisible serial killer — Application to the Permian–Triassic boundary mass extinction  

Microsoft Academic Search

The Earth experienced a severe mass extinction at the Permian–Triassic boundary (PTB) about 252 million years ago. This biological catastrophe was accompanied by major changes in geochemical composition of the atmosphere and ocean and the appearance of sedimentary features which had not occurred since the Precambrian time. The eruption of the largest continental flood basalt, the Siberian Traps, overlapped this mass

Ezat Heydari; Nasser Arzani; Jamshid Hassanzadeh

2008-01-01

120

Redescription of the dental features of an Early Triassic ichthyosaur, Utatsusaurus hataii  

Microsoft Academic Search

Utatsusaurus hataii is represented by exceptionally well preserved material for an Early Triassic ichthyosaur, but the preparation was incomplete at the time of the original description. Preparation of the holotype reveals new information concerning dental features. A principal diagnostic character of U. hataii is its isodont dentition, originally described as comprising very slender, needle-sharp teeth set in distinct alveoli. That

Ryosuke Motani

1996-01-01

121

Floral changes across the Triassic\\/Jurassic boundary linked to flood basalt volcanism  

Microsoft Academic Search

One of the five largest mass extinctions of the past 600million years occurred at the boundary of the Triassic and Jurassic periods, 201.6million years ago. The loss of marine biodiversity at the time has been linked to extreme greenhouse warming, triggered by the release of carbon dioxide from flood basalt volcanism in the central Atlantic Ocean. In contrast, the biotic

B. van de Schootbrugge; T. M. Quan; S. Lindström; W. Püttmann; C. Heunisch; J. Pross; J. Fiebig; R. Petschick; H.-G. Röhling; S. Richoz; Y. Rosenthal; P. G. Falkowski

2009-01-01

122

Real-Time Communication for Large Scale Distributed Control Systems  

Microsoft Academic Search

Because of their scale, complexity and requirement of ex- pandability, Large Scale Distributed Control Systems (LSDCS) are usu- ally created in a multistep integration process. To succeed, it has to be governed by well-defined information architecture, appropriate commu- nication infrastructure and the supervisory role of the time notion taken into consideration from the very beginning of the design stage. Mutual

Mariusz Postol

123

Optimal multi-scale patterns in time series streams  

Microsoft Academic Search

We introduce a method to discover optimal local patterns, which concisely describe the main trends in a time series. Our approach examines the time series at multiple time scales (i.e., window sizes) and efficiently discovers the key patterns in each. We also introduce a criterion to select the best window sizes, which most concisely capture the key oscillatory as well

Spiros Papadimitriou; Philip S. Yu

2006-01-01

124

Carbon-14 time scale extended: comparison of chronologies.  

PubMed

Thermal diffusion isotopic enrichment of carbon-14 has extended the radiocarbon dating range to about 75,000 years ago. Twenty-eight samples obtained up to June 1976, mainly from northwest Europe, were dated. Consideration of the basic assumptions of carbon-14 dating and of the sources of contamination indicates that the ages are generally reliable. Together with the pollen analytic and stratigraphic the dates yield a more detailed radiocarbon time scale for climatic variations in northwest Europe, showing three early glacial interstades. The radiocarbon time scale agrees with the Camp Century chronology and with the thorium-230 ages of corals representing high sea level stands on New Guinea. Ther is a discrepancy between the radiocarbon time scale and the deep-sea chronology, which may be due to correlation errors. With a modified interpretation of the correlation, all four time scales agree within the estimated experimental uncertainties of the dating techniques used. PMID:17847309

Grootes, P M

1978-04-01

125

Shape invariant time-scale and pitch modification of speech  

Microsoft Academic Search

The simplified linear model of speech production predicts that when the rate of articulation is changed, the resulting waveform takes on the appearance of the original, except for a change in the time scale. A time-scale modification system that preserves this shape-invariance property during voicing is developed. This is done using a version of the sinusoidal analysis-synthesis system that models

Thomas F. Quatieri; Robert J. McAulay

1992-01-01

126

Geometric structure of multiple time-scale nonlinear dynamical systems  

Microsoft Academic Search

A new methodology to analyze time-scale structure of smooth finite-dimensional nonlinear dynamical systems is developed. This approach does not assume apriori knowledge of slow and fast variables for special coordinates that simplify the form of the nonlinear dynamics. Conventional approaches to analyze time-scale structure of nonlinear dynamics such as singular perturbation theory proceed from such specialized apriori knowledge which is

Sanjay Bharadwaj

1999-01-01

127

Large Deviations for Two-Time-Scale Diffusions, with Delays  

SciTech Connect

We consider the problem of large deviations for a two-time-scale reflected diffusion process, possibly with delays in the dynamical terms. The Dupuis-Ellis weak convergence approach is used. It is perhaps the most intuitive and simplest for the problems of concern. The results have applications to the problem of approximating optimal controls for two-time-scale systems via use of the averaged equation.

Kushner, Harold J., E-mail: hjk@dam.brown.ed [Brown University, Applied Math (United States)

2010-12-15

128

A wavelet-based multiscale ensemble time-scale algorithm.  

PubMed

The wide-spread availability of ensembles of high-performance clocks has motivated interest in time-scale algorithms. There are many such algorithms in use today in applications ranging from scientific to commercial. Although these algorithms differ in key aspects and are sometimes tailored for specific applications and mixtures of clocks, they all share the goal of combining measured time differences between clocks to form a reference time scale that is more stable than any of the clocks in the ensemble. A new approach to forming time scales is presented here, the multiscale ensemble timescale (METS) algorithm. This approach is based on a multiresolution analysis afforded by the discrete wavelet transform. The algorithm does not assume a specific parametric model for the clocks involved and hence is well-suited for an ensemble of highly disparate clocks. The approach is based on an appealing optimality criterion which yields a reference time scale that is more stable than the constituent clocks over all averaging intervals (scales). The METS algorithm is presented here in detail and is shown in a simulation study to compare favorably with a time-scale algorithm based on Kalman filtering. PMID:22481786

Percival, Donald B; Senior, Kenneth L

2012-03-01

129

Characteristic Time Scales of Characteristic Magmatic Processes and Systems  

NASA Astrophysics Data System (ADS)

Every specific magmatic process, regardless of spatial scale, has an associated characteristic time scale. Time scales associated with crystals alone are rates of growth, dissolution, settling, aggregation, annealing, and nucleation, among others. At the other extreme are the time scales associated with the dynamics of the entire magmatic system. These can be separated into two groups: those associated with system genetics (e.g., the production and transport of magma, establishment of the magmatic system) and those due to physical characteristics of the established system (e.g., wall rock failure, solidification front propagation and instability, porous flow). The detailed geometry of a specific magmatic system is particularly important to appreciate; although generic systems are useful, care must be taken to make model systems as absolutely realistic as possible. Fuzzy models produce fuzzy science. Knowledge of specific time scales is not necessarily useful or meaningful unless the hierarchical context of the time scales for a realistic magmatic system is appreciated. The age of a specific phenocryst or ensemble of phenocrysts, as determined from isotopic or CSD studies, is not meaningful unless something can be ascertained of the provenance of the crystals. For example, crystal size multiplied by growth rate gives a meaningful crystal age only if it is from a part of the system that has experienced semi-monotonic cooling prior to chilling; crystals entrained from a long-standing cumulate bed that were mechanically sorted in ascending magma may not reveal this history. Ragged old crystals rolling about in the system for untold numbers of flushing times record specious process times, telling more about the noise in the system than the life of typical, first generation crystallization processes. The most helpful process-related time scales are those that are known well and that bound or define the temporal style of the system. Perhaps the most valuable of these times comes from the observed durations and rates of volcanism. There can be little doubt that the temporal styles of volcanism are the same as those of magmatism in general. Volcano repose times, periodicity, eruptive fluxes, acoustic emission structures, lava volumes, longevity, etc. must also be characteristic of pluton-dominated systems. We must therefore give up some classical concepts (e.g., instantaneous injection of crystal-free magma as an initial condition) for any plutonic/chambered system and move towards an integrated concept of magmatism. Among the host of process-related time scales, probably the three most fundamental of any magmatic system are (1) the time scale associated with crystal nucleation (J) and growth (G) (tx}=C{1(G3 J)-{1}/4; Zieg & Marsh, J. Pet. 02') along with the associated scales for mean crystal size (L) and population (N), (2) the time scale associated with conductive cooling controlled by a local length scale (d) (tc}=C{2 d2/K; K is thermal diffusivity), and (3) the time scale associated with intra-crystal diffusion (td}=C{3 L2/D; D is chemical diffusivity). It is the subtle, clever, and insightful application of time scales, dovetailed with realistic system geometry and attention paid to the analogous time scales of volcanism, that promises to reveal the true dynamic integration of magmatic systems.

Marsh, B. D.

2004-05-01

130

Evaluating compositional turnover of brachiopod communities during the end-Triassic mass extinction (Northern Calcareous Alps): Removal of dominant groups, recovery and community reassembly  

Microsoft Academic Search

This study highlights the role of large-scale physical perturbations in mediating biotic replacements and shows that an environmental disturbance at the Triassic\\/Jurassic (T\\/J) boundary correlates with abrupt and substantial changes in the composition of brachiopod communities. Disturbance changed the phylogenetic structure of Early Jurassic brachiopod communities owing to a removal of higher taxa that were abundant in the Late Triassic.

Adam Tomašových; Miloš Siblík

2007-01-01

131

Deep-water asymmetric cycles and progradation of carbonate platforms governed by high-frequency eustatic oscillations (Triassic of the Dolomites, Italy)  

Microsoft Academic Search

The basinal San Cassiano Formation (Triassic, Dolomites, Italy) is interfingered with clinostratified megabreccia slope deposits of coeval carbonate platforms, and to a large extent is composed of metre-scale thickening, coarsening-upward cycles. These asymmetrical cycles, often representing bundles of five coarsening-upward sequences, are interpreted as platformbasin interactions governed by fourth- and fifth-order eustatic oscillations. According to this model, progradation of Triassic

Daniele Masetti; Claudio Neri; Alfonso Bosellini

1991-01-01

132

Triassic/Jurassic faulting patterns of Conecuh Ridge, southwest Alabama  

SciTech Connect

Two major fault systems influenced Jurassic structure and deposition on the Conecuh Ridge, southwest Alabama. Identification and dating of these fault systems are based on seismic-stratigraphic interpretation of a 7-township grid in Monroe and Conecuh Counties. Relative time of faulting is determined by fault geometry and by formation isopachs and isochrons. Smackover and Norphlet Formations, both Late Jurassic in age, are mappable seismic reflectors and are thus reliable for seismicstratigraphic dating. The earlier of the 2 fault systems is a series of horsts and grabens that trends northeast-southwest and is Late Triassic to Early Jurassic in age. The system formed in response to tensional stress associated with the opening of the Atlantic Ocean. The resulting topography was a series of northeast-southwest-trending ridges. Upper Triassic Eagle Mills and Jurassic Werner Formations were deposited in the grabens. The later fault system is also a series of horsts and grabens trending perpendicular to the first. This system was caused by tensional stress related to a pulse in the opening of the Gulf of Mexico. Faulting began in Early Jurassic and continued into Late Jurassic, becoming progressively younger basinward. At the basin margin, faulting produced a very irregular shoreline. Submerged horst blocks became centers for shoaling or carbonate buildups. Today, these blocks are exploration targets in southwest Alabama.

Hutley, J.K.

1985-02-01

133

Conodont paleoecology of Lower Triassic Thaynes Formation  

SciTech Connect

The Lower Triassic (Smithian) Thaynes Formation represents a broad spectrum of paleoenvironments. Samples arranged along a generalized depth-salinity environmental gradient from tidal flats to a relatively deep, commonly dysaerobic, basin yielded a conodont fauna of 30 form elements. Association and similarity analysis were used to group the conodont elements into eight conodont entities, reflecting both biologic association (multielement apparatuses) and ecologic association (biofacies). Simple chi-square tests and discriminant analyses, using the eight conodont entities, and indicate presence of three distinctive conodont biofacies related to the generalized environmental gradient. The restricted inner shelf biotope was characterized by a conodont fauna dominated by Parachirognathus. The outer shelf biotope was distinguished by a diverse conodont fauna including the distinctive form Furnishius. The biotope farthest offshore consists of a low diversity conodont fauna composed primarily of species of Neogondolella. Some early Triassic conodonts such as Neospathodus and Ellisonia triassica are ubiquitous, and provide the foundation for a inter-basinal conodont zonation. Early Triassic conodont biotopes can be arranged along a generalized environmental gradient that probably reflects changes in hydrographic factors (e.g., salinity, temperature, and energy) which affected the distribution of conodonts.

Carr, T.R.

1983-03-01

134

The drift Hystory of Iran from the Ordovician to the Triassic  

NASA Astrophysics Data System (ADS)

New Late Ordovician, Permian, and Triassic paleomagnetic data from Iran are presented. These data, in conjunction with data from the literature, provide insights on the drift history of Iran as part of Cimmeria during the Ordovician-Triassic. A robust agreement of paleomagnetic poles of Iran and West Gondwana is observed for the Late Ordovician-earliest Carboniferous, indicating that Iran was part of Gondwana during that time. Data for the Late Permian-early Early Triassic indicate that Iran resided on subequatorial palaeolatitudes, clearly disengaged from the parental Gondwanan margin in the southern hemisphere as the result of the opening of the Neotethys Ocean along the eastern margin of Gondwana during the Permian. Since possibly the late Early Triassic, Iran was located in the northern hemisphere close to the Eurasian margin. This northward drift brought Iran to cover much of the Paleotethys in ~35 Myr at an average plate speed of ~7-8 cm/yr. As a novel conclusion, we find that timing, rates, and geometry of Cimmerian tectonics are broadly compatible with the transformation of Pangea from an Irvingian B to a Wegenerian A-type configuration with Neo-Tethyan opening taking place contemporaneously essentially in the Permian.

Muttoni, G.; Mattei, M.; Marco, B.; Zanchi, A.; Gaetani, M.; Berra, F.; Kent, D. V.; Angiolini, L.

2009-05-01

135

Feather-like development of Triassic diapsid skin appendages  

NASA Astrophysics Data System (ADS)

Of the recent sauropsid skin appendage types, only feathers develop from a cylindrical epidermal invagination, the follicle, and show hierarchical branching. Fossilized integuments of Mesozoic diapsids have been interpreted as follicular and potential feather homologues, an idea particularly controversially discussed for the elongate dorsal skin projections of the small diapsid Longisquama insignis from the Triassic of Kyrgyzstan. Based on new finds and their comparison with the type material, we show that Longisquama’s appendages consist of a single-branched internal frame enclosed by a flexible outer membrane. Not supporting a categorization either as feathers or as scales, our analysis demonstrates that the Longisquama appendages formed in a two-stage, feather-like developmental process, representing an unusual early example for the evolutionary plasticity of sauropsid integument.

Voigt, Sebastian; Buchwitz, Michael; Fischer, Jan; Krause, Daniel; Georgi, Robert

2009-01-01

136

Wavelet analysis and scaling properties of time series  

Microsoft Academic Search

We propose a wavelet based method for the characterization of the scaling behavior of nonstationary time series. It makes use of the built-in ability of the wavelets for capturing the trends in a data set, in variable window sizes. Discrete wavelets from the Daubechies family are used to illustrate the efficacy of this procedure. After studying binomial multifractal time series

P. Manimaran; Prasanta K. Panigrahi; Jitendra C. Parikh

2005-01-01

137

Evidence of dynamic scaling in space-time rainfall  

Microsoft Academic Search

As in any evolving process, including rainfall, variability in space and time are not independent of each other but depend in a way particular to the process at hand. Understanding and quantifying the space-time dependences in a process over a range of scales is not always easy because these dependences may be hidden under complex patterns with pronounced statistical variability

V. Venugopal; Efi Foufoula-Georgiou; Victor Sapozhnikov

1999-01-01

138

SNO+ Liquid Scintillator Characterization: Timing, Quenching, and Energy Scale  

NASA Astrophysics Data System (ADS)

This contribution describes laboratory measurements designed to investigate the optical properties of linear alkybenzene (LAB). Presented here is the measurement of the scintillation light timing profiles due to alpha and beta-particle excitation, the calculation of alpha/beta discrimination capability based on these timing distributions, and the investigation of electron energy scale.

O'Sullivan, E.; Wan Chan Tseung, H. S.; Tolich, N.; O'Keeffe, H. M.; Chen, M.

2012-08-01

139

Physical Process Time and Space Scales Related to River Restoration  

Microsoft Academic Search

River restoration studies need to consider stream dynamics, evolution, rates of adjustment, and relative effects of various human disturbances. The history of stream channel adjustment typically needs to be investigated over a time scale of decades to centuries to include the time before human disturbance. An investigation of historical change will help with understanding the processes of physical change, how

T. Randle; J. Boutry

2005-01-01

140

PREDICTIVE ADAPTIVE FEEDFORWARD CONTROL OF A TIME SCALED SOLAR PLANT  

Microsoft Academic Search

This paper concerns the control of a solar energy collector field using predictive feedforward adaptive control techniques based on multiple identifiers. The ACUREX field used in these work is described by a partial differential equation (PDE). The plant is characterized by: non linearity, fast accessible disturbances and time varying dynamics. The dynamic dependency on flow is overcome by time-scaling. The

R. N. Silva; J. M. Lemos

141

Remagnetization of Variscan massifs and reconstruction of the Triassic paleosurface in Europe  

NASA Astrophysics Data System (ADS)

Basement rocks (such as e.g. granites and rhyolithes) of European Variscan massifs often show Permo-Triassic remagnetization [e.g. Edel & Schneider, 1995, Geophys. J. Int., 122, 858-876; Edel et al., 1997, C.R.AS. Paris, Earth Planet. Sci., 325, 479-486] resulting in underestimated age determinations. These rejuvenated ages are attributed to an alteration of the primary paleomagnetic signal recently carried by the neo-formation of secondary hematite [Preeden et al., 2009, Geophys. Res. Abstr. EGU, 11, 365,]. Hematite forms under oxic conditions. Thus, one may deduce that the remagnetization of Paleozoic crystalline rocks occurs once the basement rocks are exposed at the Permo-Triassic (paleo)surface. Permo-Triassic remagnetizations are ubiquitous, affecting many emerged Paleozoic rocks in Europe and suggesting a major weathering event under oxic conditions. Previously published paleomagnetic ages [Ricordel et al., 2007, Palaeo3, 251, 268-282] showed a relationship between remagnetization and the development of pink-reddish facies associated to the albitized underlying rocks of the Morvan Massif (France). Parcerisa et al. [2009, Int. J. Earth Sci., doi: 10.1007/s00531-008-0405-1] performed further petrographic analyses and proposed a geochemical model for the genesis of this type of alteration. The extent of the altered zone (> 100 m in depth) points to a sodium enriched groundwater environment [Thiry et al., 2009, Geophs Res. Abstr. EGU, 11, 4103]. The Na+ enrichment is likely related to the Triassic environment characterized by widespread salt deposits, such as leaching of salt, marine aerosols, periodic/episodic contribution of seawater or evaporative solutions. Demonstrating that the albitized facies are of supergenic origin and bound to the Triassic paleosurface deeply renews the ideas about the evolution of basement areas. The recognition of the Triassic paleosurface on widespread basements in Europe will provide spatio-temporal benchmarks to constrain the ablation of these massifs since the Triassic. This will be a major contribution to the geodynamic modelling of these areas. To deepen our understanding of this paleoalteration phenomenon on a supra-regional scale, we aim to acquire more tie points for this Paleozoic surface, which was preserved in the crystalline basement of Europe throughout the Mesozoic and Cenozoic epoch. Therefore we will present results on paleomagnetic investigations as well as petrographic analyses of the profiles through albitized granite and porphyry from the Sudetes in SW-Poland and the Catalonian Mountains in NE-Spain.

Franke, C.; Thiry, M.; Jelenska, M.; Kodzialko-Hofmokl, M.; Lagroix, F.; Parcerisa, D.; Szuszkiewicz, A.; Turniak, K.

2009-12-01

142

Zircon U-Pb geochronology links the end-Triassic extinction with the Central Atlantic Magmatic Province.  

PubMed

The end-Triassic extinction is characterized by major losses in both terrestrial and marine diversity, setting the stage for dinosaurs to dominate Earth for the next 136 million years. Despite the approximate coincidence between this extinction and flood basalt volcanism, existing geochronologic dates have insufficient resolution to confirm eruptive rates required to induce major climate perturbations. Here, we present new zircon uranium-lead (U-Pb) geochronologic constraints on the age and duration of flood basalt volcanism within the Central Atlantic Magmatic Province. This chronology demonstrates synchroneity between the earliest volcanism and extinction, tests and corroborates the existing astrochronologic time scale, and shows that the release of magma and associated atmospheric flux occurred in four pulses over about 600,000 years, indicating expansive volcanism even as the biologic recovery was under way. PMID:23519213

Blackburn, Terrence J; Olsen, Paul E; Bowring, Samuel A; McLean, Noah M; Kent, Dennis V; Puffer, John; McHone, Greg; Rasbury, E Troy; Et-Touhami, Mohammed

2013-03-21

143

Two typical time scales of the piston effect.  

PubMed

The existence of a fourth mode of heat transfer near the critical point, named the piston effect, has been known for more than a decade. The typical time scale of temperature relaxation due to this effect was first predicted by Onuki [Phys. Rev A 41, 2256 (1990)], and this author's formula has been extensively used since then to predict the thermal behavior of near-critical fluids. Recent studies, however, pointed out that the critical divergence of the bulk viscosity could have a strong influence on piston-effect-related processes. In this paper, we conduct a theoretical analysis of near-critical temperature relaxation showing that the piston effect is not governed by one (as was until now believed) but by two typical time scales. These two time scales exhibit antagonistic asymptotic behaviors as the critical point is approached: while the classical piston-effect time scale (as predicted by Onuki ) goes to zero at the critical point (critical speeding up), the second time scale (related to bulk viscosity) goes to infinity (critical slowing down). Based on this property, an alternative method for measuring near-critical bulk viscosity is proposed. PMID:16089870

Carlès, Pierre; Dadzie, Kokou

2005-06-28

144

Surface field measurements of scale models in the time domain  

Microsoft Academic Search

Time-domain measurement have been performed of the surface densities of current and charge induced on scale models when illuminated by a transient electromagnetic pulse in order to provide test points to validate numerical models. three bodies--a cylinder, a crossed-cylinder, and a 1:100 scale model 747 aircraft were used in the experiments. Responses were measured for objects in a simulated free

H. S. Cabayan

1981-01-01

145

A scale model of multivariate rainfall time series  

Microsoft Academic Search

A multivariate time-series model that uses a factor-analytic approach is shown to provide an effective description of both monthly and annual rainfall in south Florida. In the case of monthly rainfall, the scale model shows that deviations from monthly means are caused primarily by large-scale phenomena that have temporal structure. These sort of phenomena are not accounted for by using

David A. Chin

1995-01-01

146

Non-parametric techniques for pitch-scale and time-scale modification of speech  

Microsoft Academic Search

Time-scale and, to a lesser extent, pitch-scale modifications of speech and audio signals are the subject of major theoretical and practical interest. Applications are numerous, including, to name but a few, text-to-speech synthesis (based on acoustical unit concatenation), transformation of voice characteristics, foreign language learning but also audio monitoring or film\\/soundtrack post-synchronization. To fulfill the need for high-quality time and

Eric Moulines; Jean Laroche

1995-01-01

147

Physics in space-time with scale-dependent metrics  

NASA Astrophysics Data System (ADS)

We construct three-dimensional space R?3 with the scale-dependent metric and the corresponding Minkowski space-time M?,?4 with the scale-dependent fractal (DH) and spectral (DS) dimensions. The local derivatives based on scale-dependent metrics are defined and differential vector calculus in R?3 is developed. We state that M?,?4 provides a unified phenomenological framework for dimensional flow observed in quite different models of quantum gravity. Nevertheless, the main attention is focused on the special case of flat space-time M1/3,14 with the scale-dependent Cantor-dust-like distribution of admissible states, such that DH increases from DH=2 on the scale ??0 to DH=4 in the infrared limit ??0, where ?0 is the characteristic length (e.g. the Planck length, or characteristic size of multi-fractal features in heterogeneous medium), whereas DS?4 in all scales. Possible applications of approach based on the scale-dependent metric to systems of different nature are briefly discussed.

Balankin, Alexander S.

2013-10-01

148

Early-middle Triassic paleomagnetic result from the Hexi corridor, and the relationship between the North China and Tarim blocks  

NASA Astrophysics Data System (ADS)

A paleomagnetic study was carried out on early-middle Triassic red beds at Jingtai area of Hexi corridor. The characteristic higher temperature component (HTC) isolated by stepwise thermal demagnetization exhibits dual polarity, which passed the fold and reversal tests at the 95% confidence level. Compared with paleomagnetic coveal results from the NCB, this result suggests that the paleolatitude differences between the observed at Jingtai area and those expected from the NCB reference early and/or middle Triassic poles are -0.9+/-7.3 degrees and 4.9+/-5.9 degrees, respectively. This implies that the Hexi Corridor was the extension of the NCB by the middle Triassic. However, in comparison with early and middle Triassic results from the NCB, an anticlockwise rotation of studied area relative to the NCB with 22.8+/-4.9 degress or 24+/-4.4 degrees, is detected, which might be illustrated by the ball-bearing model. Our results are different from the data obtained from the Tarim block, which include the discrimination of declinations, as well as paleolatitudes. The result indicates that Jingtai area, the western part of the NCB, and Tarim block, were not connected with each other during the early-middle Triassic. The amalgamation between the NCB and Tarim block may be late by the Jurassic, through the Cenozoic evolution of the large scale left lateral displacement of the Altyn Tage fault and the orogenic process within the Qilian fold belt.

Yang, Z.; Liu, J.; Tong, Y.; Yuan, W.

2009-12-01

149

Minimum variability time-scales of long and short GRBs  

NASA Astrophysics Data System (ADS)

We have investigated the time variations in the light curves from a sample of long and short Fermi/GBM gamma-ray bursts (GRBs) using an impartial wavelet analysis. The results indicate that in the source frame, the variability time-scales for long bursts differ from that for short bursts, variabilities of the order of a few milliseconds are not uncommon and an intriguing relationship exists between the minimum variability time and the burst duration.

MacLachlan, G. A.; Shenoy, A.; Sonbas, E.; Dhuga, K. S.; Cobb, B. E.; Ukwatta, T. N.; Morris, D. C.; Eskandarian, A.; Maximon, L. C.; Parke, W. C.

2013-06-01

150

Investigating the Geologic Time Scale: Creating posters to Display Trends in Geologic Time  

NSDL National Science Digital Library

This observational inquiry activity involving careful descriptions of rocks and fossil including age will be used to create a scalar accurate geologic time scale. Students will observe and learn that the geologic time scale was created based on changes in fossil, rock, and atmospheric changes.

Atkins, Kim

151

The displaced eugeoclinal rocks in the El Paso Mountains and northern Mojave Desert: A Triassic sliver  

SciTech Connect

Many workers have drawn attention to the displaced eugeoclinal rocks in the northern Mojave Desert and El Paso Mountains and their importance in models for the development of an active continental margin in the western Cordillera. Existing models can generally for either strike-slip juxtaposition or thrust emplacement. New field data, U-Pb zircon geochronology, and isotopic data for metasedimentary rocks and plutons in the northern Mojave Desert and El Paso Mountains shed light on the timing and mechanism of emplacement of the eugeoclinal allocthon. The observations and data above indicate that Early Triassic plutons in the northern Mojave Desert came through oceanic lithosphere but later Jurassic plutons intercepted continental lithosphere. The authors suggest a model where eugeoclinal rocks were deposited on oceanic crust which was initially brought southward along a strike-slip fault and later thrust eastward over the cratonal assemblage. Permian thrusting is incompatible with their data and observations. Intrusion of lower Triassic strata by Early Triassic plutons in the Lane Mountain area permits some Early Triassic thrusting but the oceanic affinity of the plutons implies that thrusting did not involve continental lithosphere.

Miller, J.S.; Glazner, A.F. (Univ. of North Carolina, Chapel Hill, NC (United States). Dept. of Geology); Walker, J.D.; Martin, M.W. (Univ. of Kansas, Lawrence, KS (United States). Dept. of Geology)

1993-04-01

152

Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks  

PubMed Central

The biotic recovery from Earth’s most severe extinction event at the Permian-Triassic boundary largely reestablished the preextinction structure of marine trophic networks, with marine reptiles assuming the predator roles. However, the highest trophic level of today's marine ecosystems, i.e., macropredatory tetrapods that forage on prey of similar size to their own, was thus far lacking in the Paleozoic and early Mesozoic. Here we report a top-tier tetrapod predator, a very large (>8.6 m) ichthyosaur from the early Middle Triassic (244 Ma), of Nevada. This ichthyosaur had a massive skull and large labiolingually flattened teeth with two cutting edges indicative of a macropredatory feeding style. Its presence documents the rapid evolution of modern marine ecosystems in the Triassic where the same level of complexity as observed in today’s marine ecosystems is reached within 8 My after the Permian-Triassic mass extinction and within 4 My of the time reptiles first invaded the sea. This find also indicates that the biotic recovery in the marine realm may have occurred faster compared with terrestrial ecosystems, where the first apex predators may not have evolved before the Carnian.

Frobisch, Nadia B.; Frobisch, Jorg; Sander, P. Martin; Schmitz, Lars; Rieppel, Olivier

2013-01-01

153

Extinction trajectories of benthic organisms across the Triassic–Jurassic boundary  

Microsoft Academic Search

We analysed diversity and abundance patterns of benthic organisms across the Triassic–Jurassic (T-J) boundary based on the Paleobiology Database (PBDB), which compiles palaeontological collection data on a global scale. While Sepkoski's [Sepkoski, J.J. Jr., 2002. A compendium of fossil marine animal genera. Bulletins of American Paleontology 363, 1–563] compendium on the stratigraphic ranges of marine animal genera suggests that the

Wolfgang Kiessling; Martin Aberhan; Benjamin Brenneis; Peter J. Wagner

2007-01-01

154

Hans-Jörg Rheinberger on biological time scales.  

PubMed

H.-J. Rheinberger (in Rheinberger 2002) analyzed the history of biological time concepts in very short compass. He begins with Newtonian time and Buffon's attempts to handle biological time. He then suggests an architectonic structure to account for three distinctive sorts of biological time. I summarize Rheinberger's account in this valuable essay, but criticize the architectonic as overly hierarchical (though Rheinberger also recognized relevant reticulation within the article) and for failing to appreciate sufficiently the interweaving of time scales in biological interactions. PMID:23888821

Burian, Richard M

2013-01-01

155

Space-time scaling laws for self-triggered control  

Microsoft Academic Search

Abstract—Feedback,control,laws,have,been,traditionally treated as periodic,tasks when,implemented,on digital plat- forms. However, the growing complexity of systems calls for efficient implementations,of control tasks that reduce,resource utilization while keeping,desired levels of performance.,In this paper,we,drop,the periodicity assumption,in favour,of self- triggered,strategies for the execution,of control,laws. Such strategies determine,the,next,execution,time,based,on,the current state of the plant. Under the self-triggered policy, the inter-execution times scale in a predictable,manner:,a scaling of

Adolfo Anta; Paulo Tabuada

2008-01-01

156

Palaeoecology of the pseudoplanktonic Triassic crinoid Traumatocrinus from Southwest China  

Microsoft Academic Search

Colonies of Traumatocrinus (Echinodermata, Crinoidea, Encrinida) attached to driftwood from the Late Triassic (Carnian) Xiaowa Formation of the Guanling area (Guizhou, Southwest China) give evidence for a pseudoplanktonic lifestyle of this specialized offshoot of the otherwise benthic Middle Triassic family Encrinidae. The stem of Traumatocrinus individuals may exceed 11 m in length. Colonies attached by root cirri to logs of driftwood

Hans Hagdorn; Xiaofeng Wang; Chuanshang Wang

2007-01-01

157

The Permo-Triassic Extinction  

NSDL National Science Digital Library

This website covers details about the Permian extinction, which occurred about 250 million years ago. It contains a paleontological overview of the extinction, discussing the life present at that time, evidence for the extinction, and what types of lifeforms disappeared. Other sections discuss various theories about what caused the mass-extinction including volcanism, impacts, climate change, glaciation, Pangea and other proposed theories.

158

Arthropods in amber from the Triassic Period.  

PubMed

The occurrence of arthropods in amber exclusively from the Cretaceous and Cenozoic is widely regarded to be a result of the production and preservation of large amounts of tree resin beginning ca. 130 million years (Ma) ago. Abundant 230 million-year-old amber from the Late Triassic (Carnian) of northeastern Italy has previously yielded myriad microorganisms, but we report here that it also preserves arthropods some 100 Ma older than the earliest prior records in amber. The Triassic specimens are a nematoceran fly (Diptera) and two disparate species of mites, Triasacarus fedelei gen. et sp. nov., and Ampezzoa triassica gen. et sp. nov. These mites are the oldest definitive fossils of a group, the Eriophyoidea, which includes the gall mites and comprises at least 3,500 Recent species, 97% of which feed on angiosperms and represents one of the most specialized lineages of phytophagous arthropods. Antiquity of the gall mites in much their extant form was unexpected, particularly with the Triassic species already having many of their present-day features (such as only two pairs of legs); further, it establishes conifer feeding as an ancestral trait. Feeding by the fossil mites may have contributed to the formation of the amber droplets, but we find that the abundance of amber during the Carnian (ca. 230 Ma) is globally anomalous for the pre-Cretaceous and may, alternatively, be related to paleoclimate. Further recovery of arthropods in Carnian-aged amber is promising and will have profound implications for understanding the evolution of terrestrial members of the most diverse phylum of organisms. PMID:22927387

Schmidt, Alexander R; Jancke, Saskia; Lindquist, Evert E; Ragazzi, Eugenio; Roghi, Guido; Nascimbene, Paul C; Schmidt, Kerstin; Wappler, Torsten; Grimaldi, David A

2012-08-27

159

Arthropods in amber from the Triassic Period  

PubMed Central

The occurrence of arthropods in amber exclusively from the Cretaceous and Cenozoic is widely regarded to be a result of the production and preservation of large amounts of tree resin beginning ca. 130 million years (Ma) ago. Abundant 230 million-year-old amber from the Late Triassic (Carnian) of northeastern Italy has previously yielded myriad microorganisms, but we report here that it also preserves arthropods some 100 Ma older than the earliest prior records in amber. The Triassic specimens are a nematoceran fly (Diptera) and two disparate species of mites, Triasacarus fedelei gen. et sp. nov., and Ampezzoa triassica gen. et sp. nov. These mites are the oldest definitive fossils of a group, the Eriophyoidea, which includes the gall mites and comprises at least 3,500 Recent species, 97% of which feed on angiosperms and represents one of the most specialized lineages of phytophagous arthropods. Antiquity of the gall mites in much their extant form was unexpected, particularly with the Triassic species already having many of their present-day features (such as only two pairs of legs); further, it establishes conifer feeding as an ancestral trait. Feeding by the fossil mites may have contributed to the formation of the amber droplets, but we find that the abundance of amber during the Carnian (ca. 230 Ma) is globally anomalous for the pre-Cretaceous and may, alternatively, be related to paleoclimate. Further recovery of arthropods in Carnian-aged amber is promising and will have profound implications for understanding the evolution of terrestrial members of the most diverse phylum of organisms.

Schmidt, Alexander R.; Jancke, Saskia; Lindquist, Evert E.; Ragazzi, Eugenio; Roghi, Guido; Nascimbene, Paul C.; Schmidt, Kerstin; Wappler, Torsten; Grimaldi, David A.

2012-01-01

160

Time Scale Calculus - a new perspectives for synthetic seismogram calculations  

NASA Astrophysics Data System (ADS)

Synthetic, numerically generated seismograms are one of the key factors of any interpretation of recorded seismic data. At the early stage of development, calculation of full seismic waveforms was impossible due to a limited computational resource so we were forced to used only some selected characteristics of seismic waves relatively easy for numerical calculations like first arrival times, maximum amplitude, approximate source spectra, to name a few. Continues development of computational resources as well as progress in numerical techniques has opened possibilities of generation the full, 3-component seismograms incorporating many physically important elements like wave attenuation, anisotropy or randomness of the media. Although achieved results are impressive we still need new numerical methods to tackle existing problems with the synthetic seismogram generation. In this contribution we present a novel approach to discretization of the wave equation which brings together continues and discrete numerical analysis of the seismic waves. The foundations of this new technique, called Time Scale Calculus, have been formulated by Hilger in late eighties and is very dynamically developing. The Time scale calculus, due to its universality seems to have a great potential when practical applications are considered. Thus we have decided to bring the Time Scale calculus concept closer to geophysical, or more precisely to seismological applications. This presentation is intend as a basic introduction to the time scales calculus considered from seismological point of view. We shortly present and discuss the possibility of using the Time Scales (TS) technique for solving the simplest acoustic 2D wave equation keeping in mind its particular applications for mining induced seismicity.

Waskiewicz, Kamil; Debski, Wojciech

2013-04-01

161

Wavelet analysis and scaling properties of time series  

Microsoft Academic Search

We propose a wavelet based method for the characterization of the scaling\\u000abehavior of non-stationary time series. It makes use of the built-in ability of\\u000athe wavelets for capturing the trends in a data set, in variable window sizes.\\u000aDiscrete wavelets from the Daubechies family are used to illustrate the\\u000aefficacy of this procedure. After studying binomial multifractal time series

P. Manimaran; Prasanta K. Panigrahi; Jitendra C. Parikh

2005-01-01

162

Lunar Crater Rays Point to a New Lunar Time Scale  

Microsoft Academic Search

The Lunar Time Scale should be reevaluated -- suggest remote sensing studies of lunar crater rays by B. Ray Hawke (University of Hawaii) and colleagues at the University of Hawaii, NovaSol, Cornell University, National Air and Space Museum, and Northwestern University. These scientists have found that the mere presence of crater rays is not a reliable indicator that the crater

L. M. V. Martel

2004-01-01

163

Two typical time scales of the piston effect  

Microsoft Academic Search

The existence of a fourth mode of heat transfer near the critical point, named the piston effect, has been known for more than a decade. The typical time scale of temperature relaxation due to this effect was first predicted by Onuki [Phys. Rev A 41, 2256 (1990)], and this author's formula has been extensively used since then to predict the

Pierre Carlès; Kokou Dadzie

2005-01-01

164

Modelling of UV radiation variations at different time scales  

Microsoft Academic Search

Solar UV radiation variability in the period 1976-2006 is discussed with respect to the relative changes in the solar global radiation, ozone content, and cloudiness. All the variables were decomposed into separate components, representing variations of different time scales, using wavelet multi-resolution decomposition. The response of the UV radiation to the changes in the solar global radiation, ozone content, and

J. L. Borkowski

2008-01-01

165

Loss rates and time scales for sodium at Mercury  

NASA Astrophysics Data System (ADS)

The time scales and loss rates for sodium in the exosphere of Mercury are studied here. Sodium comes from release processes occurring at the planetary surface; the amount of surface sodium that is available for release (mostly through thermal- or photon-stimulated desorption) is limited. Loss processes deplete the surface concentration of sodium, which is continuously refilled by diffusion from the interior of regolith grains or by chemical sputtering. Ejected sodium particles may either escape the gravity, also aided by the radiation pressure acceleration, or be photoionized, or fall back onto the surface. Falling particles may either stick to the surface or bounce. A Monte Carlo model, simulating all these processes, is used to obtain the exosphere densities, the global loss rates at different true anomaly angles, and typical time scales for small-term variations, taking into account planet's orbit and rotation speed. Assuming an impulsive event, which causes the enhancement of sodium in the exosphere, the model gives the time scales for the exosphere to recover to a steady-state condition. It is found that time scales go from one or two hour (close to perihelion) to half day (close to aphelion). The escape probability ranges from 20% at perihelion and aphelion up to 40% at true anomaly angles of about 60° and 300°.

Mura, Alessandro

2012-04-01

166

Variational methods for two resonant problems on time scales  

Microsoft Academic Search

Using variational methods we study the generalization of two classical second order periodic problems in the context of time scales. On the one hand, we study a forced pendulum-type equation. On the other hand, we obtain solutions for a bounded nonlinearity under Landesman-Lazer type conditions.

P. Amster; P. De Nápoli; C. C. Tisdell

167

Time and frequency scale modification of speech signals  

Microsoft Academic Search

This paper presents new and improved methods for independently modifying the time and pitch scale of acoustic signals, with an emphasis on speech signals. The algorithms developed here use parametric (sinusoidal) modelling techniques introduced by other authors, but new ideas are presented here that achieve improved output quality with decreased computational load. In particular, speech quality is improved by using

Brett Ninness; Soren John Henriksen

2000-01-01

168

Separatrix Splitting for Systems With Three Time Scales  

Microsoft Academic Search

An exact expression for the determinant of the splitting matrix is derived for three degrees of freedom systems with three time scales: it allows us to analyze the asymptotic behaviour needed to amend the large angles theorem proposed in Ann. Inst. H. Poincaré, B-60, 1, 1994. The asymptotic validity of Melnikov's integrals is proved for the class of models considered,

G. Gallavotti; G. Gentile; V. Mastropietro

1997-01-01

169

Separatrix Splitting for Systems with Three Time Scales  

Microsoft Academic Search

An exact expression for the determinant of the splitting matrix is derived for three degrees of freedom systems with three time scales: it allows us to analyze the asymptotic behaviour needed to amend the large angles theorem proposed in Ann. Inst. H. Poincaré, B-60, 1 (1994). The asymptotic validity of Mel'nikov's integrals is proved for the class of models considered,

G. Gallavotti; G. Gentile; V. Mastropietro

1999-01-01

170

The time-scale of escape from star clusters  

Microsoft Academic Search

In this paper a cluster is modelled as a smooth potential (due to the cluster stars) plus the steady tidal field of the Galaxy. In this model there is a minimum energy below which stars cannot escape. Above this energy, however, the time-scale on which a star escapes varies with the orbital parameters of the star (mainly its energy) in

T. Fukushige; D. C. Heggie

2000-01-01

171

Gott Time Machines, BTZ Black Hole Formation, and Choptuik Scaling  

NASA Astrophysics Data System (ADS)

We study the formation of Bañados-Teitelboim-Zanelli black holes by the collision of point particles. It is shown that the Gott time machine, originally constructed for the case of vanishing cosmological constant, provides a precise mechanism for black hole formation. As a result, one obtains an exact analytic understanding of the Choptuik scaling.

Birmingham, Danny; Sen, Siddhartha

2000-02-01

172

Time Flies When You're Learning About Scale!  

NSDL National Science Digital Library

Not many students would forget to say "Dinosaurs!" if you mention the Jurassic period, yet the word scale only conjures up ideas of measuring objects. Most students automatically think of measuring mass, volume, or distance, and not necessarily time. In t

Taylor, Amy R.; Jones, M. G.; Falvo, Michael R.

2009-04-01

173

Extensions of certain integral inequalities on time scales  

Microsoft Academic Search

In this work, we establish Hölder’s inequality, Minkowski’s inequality and Jensen’s inequality on time scales via the nabla integral and diamond-? dynamic integral, which is defined as a linear combination of the delta and nabla integrals.

Umut Mutlu Özkan; Mehmet Zeki Sarikaya; Hüseyin Yildirim

2008-01-01

174

METAS New Time Scale Generation System - A Progress Report.  

National Technical Information Service (NTIS)

Up to now, UTC (CH) has been defined as a paper time scale which is computed for a single epoch every day: UTC 00:00. In 2006, we have started to phase in the hardware for a new system, still under development, which should allow us to define UTC (CH) as ...

C. Schlunegger G. Dudle L. Bernier

2007-01-01

175

Development of the Free Time Motivation Scale for Adolescents.  

ERIC Educational Resources Information Center

Developed a self-report measure of adolescent free time motivation based in self-determination theory, using data from 634 seventh graders. The scale measured five forms of motivation (amotivation, external, introjected, identified, and intrinsic motivation). Examination of each of the subscales indicated minimally acceptable levels of fit. The…

Baldwin, Cheryl K.; Caldwell, Linda L.

2003-01-01

176

Modeling of streamflow processes at different time scales  

Microsoft Academic Search

The analysis and modeling of streamflow processes has attracted the attention of water resources specialists for several decades. A number of models have been suggested in the past for representing seasonal and annual streamflow processes. The topic addressed in this paper centers around the compatibility of stochastic models of streamflow at different time scales. More specifically, given a model for

Paolo Bartolini; Jose D. Salas

1993-01-01

177

Characterization of a binary karst aquifer using process time scales  

NASA Astrophysics Data System (ADS)

Within "a theoretical framework for the interpretation of karst spring signals" (Covington, EGU2012-853-1) process length scales that characterize the travel distances required for damping pulses of physicochemical parameters of spring waters such as electrical conductivity and temperature were derived (Covington et al., J. Geophys. Res., 2012). These length scales can be converted to corresponding process time scales characterizing the travel times needed for damping the pulses. This is particularly convenient if the travel distance is unknown. In this case the time lag between the increase of spring discharge and subsequent physicochemical responses at the spring may provide an estimate of the travel time. In binary karst aquifers with localized recharge from a sinking stream, the recharge pulse can be directly observed and thus travel times are readily obtained from the time delay of the physicochemical spring responses. If the spring response is strongly damped travel times can be inferred from artificial tracer testing. In this work, time scales for carbonate dissolution and heat transport were used for characterizing the binary Lurbach-Tanneben karst aquifer (Austria). This aquifer receives allogenic recharge from the sinking stream Lurbach and is drained by two springs, namely the Hammerbach and the Schmelzbach. The two springs show different thermal responses to two recharge events in December 2008: Whereas the temperature of the Schmelzbach responds within one day after the flood pulse in the Lurbach, the temperature signal is strongly damped at the Hammerbach. The evaluation based on the thermal time scale thus suggests that the Schmelzbach spring is fed by conduits with hydraulic diameters at least in the order of decimetres. In contrast, the damping of the thermal responses at the Hammerbach may be due to lower hydraulic diameters and/or longer residence times. Interestingly, the Hammerbach did show thermal responses in the time before a flood event in August 2005. This suggests that this flood event may have caused a change of the properties of the Hammerbach aquifer such that temperature pulses are more strongly damped than before. As opposed to the thermal responses the electrical conductivity appears to be less affected by this change, which suggests that the hydraulic diameters are still sufficiently large to permit the propagation of chemical signals.

Birk, Steffen; Wagner, Thomas

2013-04-01

178

MHD turbulence theory, cascade, time scale and nonlocality*  

NASA Astrophysics Data System (ADS)

The magnetohydrodynamic (MHD) approximation has been quite successful in space plasma physics and astrophysics. In particular, many manifestations of turbulence and other nonlinear phenomena in astrophysical plasma are explainable from a MHD turbulence perspective. In this talk, the fundamental physical processes involving energy transfer and interacting scales in incompressible MHD turbulence, including triadic interactions, are addressed. After reviewing the proposed isotropic and anisotropic energy spectra, the cascade process is discussed in detail along with the response of the small scales to large-scale anisotropy and mean magnetic field. We will stress the interplay between the external time scale and turbulence nonlinear time scale. The eddy-damped quasi-normal Markovian (EDQNM) closure model and direct numerical simulations will be used to illustrate some of these points. Finally, the application to the subgrid modeling for large-eddy simulation of MHD turbulence is discussed. *Work performed for the US DOE by UC LLNL under contract W-7405-Eng-48 and was supported by NSF under grant ATM 9814045.

Zhou, Ye

2001-10-01

179

From Permo-Triassic lithospheric thinning to Jurassic rifting at the Adriatic margin: Petrological and geochronological record in Valtournenche (Western Italian Alps)  

NASA Astrophysics Data System (ADS)

Slices of polycyclic metasediments (marbles and meta-cherts) are tectonically amalgamated with the polydeformed basement of the Dent Blanche tectonic system along a major Alpine shear zone in the Western Alps (Becca di Salé area, Valtournenche Valley). A combination of techniques (structural analysis at various scales, metamorphic petrology, geochronology and trace element geochemistry) was applied to determine the age and composition of accessory phases (titanite, allanite and zircon) and their relation to major minerals. The results are used to reconstruct the polyphase structural and metamorphic histories, comprising both pre-Alpine and Alpine cycles. The pre-Alpine evolution is associated with low-pressure high-temperature metamorphism related to Permo-Triassic lithospheric thinning. In meta-cherts, microtextural relations indicate coeval growth of allanite and garnet during this stage, at ~ 300 Ma. Textures of zircon also indicate crystallisation at HT conditions; ages scatter from 263 to 294 Ma, with a major cluster of data at ~ 276 Ma. In impure marble, U-Pb analyses of titanite domains (with variable Al and F contents) yield apparent 206Pb/238U dates range from Permian to Jurassic. Chemical and isotopic data suggest that titanite formed at Permian times and was then affected by (extension-related?) fluid circulation during the Triassic and Jurassic, which redistributed major elements (Al and F) and partially opened the U-Pb system.The Alpine cycle lead to early blueschist facies assemblages, which were partly overprinted under greenschist facies conditions. The strong Alpine compressional overprint disrupted the pre-Alpine structural imprint and/or reactivated earlier structures. The pre-Alpine metamorphic record, preserved in these slices of metasediments, reflects the onset of the Permo-Triassic lithospheric extension to Jurassic rifting.

Manzotti, Paola; Rubatto, Daniela; Darling, James; Zucali, Michele; Cenki-Tok, Bénédicte; Engi, Martin

2012-08-01

180

Multiple time scale based reduction scheme for nonlinear chemical dynamics  

NASA Astrophysics Data System (ADS)

A chemical reaction is often characterized by multiple time scales governing the kinetics of reactants, products and intermediates. We eliminate the fast relaxing intermediates in autocatalytic reaction by transforming the original system into a new one in which the linearized part is diagonal. This allows us to reduce the dynamical system by identifying the associated time scales and subsequent adiabatic elimination of the fast modes. It has been shown that the reduced system sustains the robust qualitative signatures of the original system and at times the generic form of the return map for the chaotic system from which complex dynamics stems out in the original system can be identified. We illustrate the scheme for a three-variable cubic autocatalytic reaction and four-variable peroxidase-oxidase reaction.

Das, D.; Ray, D. S.

2013-07-01

181

Scaling of average sending time on weighted Koch networks  

NASA Astrophysics Data System (ADS)

Random walks on weighted complex networks, especially scale-free networks, have attracted considerable interest in the past. But the efficiency of a hub sending information on scale-free small-world networks has been addressed less. In this paper, we study random walks on a class of weighted Koch networks with scaling factor 0 < r <= 1. We derive some basic properties for random walks on the weighted Koch networks, based on which we calculate analytically the average sending time (AST) defined as the average of mean first-passage times (MFPTs) from a hub node to all other nodes, excluding the hub itself. The obtained result displays that for 0 < r < 1 in large networks the AST grows as a power-law function of the network order with the exponent, represented by log43r+1r, and for r = 1 in large networks the AST grows with network order as N ln N, which is larger than the linear scaling of the average receiving time defined as the average of MFPTs for random walks to a given hub node averaged over all starting points.

Dai, Meifeng; Liu, Jie

2012-10-01

182

Wavelet analysis and scaling properties of time series.  

PubMed

We propose a wavelet based method for the characterization of the scaling behavior of nonstationary time series. It makes use of the built-in ability of the wavelets for capturing the trends in a data set, in variable window sizes. Discrete wavelets from the Daubechies family are used to illustrate the efficacy of this procedure. After studying binomial multifractal time series with the present and earlier approaches of detrending for comparison, we analyze the time series of averaged spin density in the 2D Ising model at the critical temperature, along with several experimental data sets possessing multifractal behavior. PMID:16383481

Manimaran, P; Panigrahi, Prasanta K; Parikh, Jitendra C

2005-10-18

183

Probing Fission Time Scales with Neutrons and GDR Gamma Rays  

SciTech Connect

The time scales for nuclear fission have been explored using both pre-and postfission neutrons and GDR gamma rays. Four systems were investigated: 133-MeV 16O + 176Yb and 208Pb and 104-MeV 4He + 188Os and 209Bi. Fission fragments were measured in coincidence with PPACs. The neutrons were detected using eight detectors from the DEMON array, while gamma rays were measured using the US BaF2 array. The pre-and postfission gamma rays were determined using moving source fits parallel and perpendicular to the fission fragment emission directions. The time scales for fission for the neutrons were determined using the neutron clock technique. The gamma-ray data were fitted using a statistical model calculation based on the code CASCADE. The results of the fits from both data types were used to extract nuclear friction coefficients, ?, and fission time scales. The ? values ranged from 7 to 20, while the fission times were (31-105) 10?21 s. From Yadernaya Fizika, Vol. 66, No. 6, 2003, pp. 1199-1203.

Schmitt, R. P. [Texas A& M University; Botting, Tye [Texas A& M University; Chubarian, G G [Texas A& M University; Wolf, K [Texas A& M University; Hurst, B J [Texas A& M University; Jabs, H [Texas A& M University; Hamelin, M [Texas A& M University; Bacak, A [Texas A& M University; Oganessian, Yuri Ts. [FLNR-JINR, Russia; Itkis, M. G. [FLNR-JINR, Russia; Kozulin, E M [FLNR-JINR, Russia; Kondratiev, N. A. [FLNR-JINR, Russia; Salamatin, V S [FLNR-JINR, Russia; Pokrovsky, I V [FLNR-JINR, Russia; Hanappe, F [Universite Libre de Bruxelles, Brussels, Belgium; de Goes Brennand, E. [Universite Libre de Bruxelles, Brussels, Belgium; Huck, A [CRN, Strasbourg, France; Stuttge, L [CRN, Strasbourg, France; Liatard, E [CRN, Strasbourg, France; Beene, James R [ORNL; Varner Jr, Robert L [ORNL; Halbert, Melvyn L [ORNL; Gan, Ning [ORNL

2003-06-01

184

Testing a scaling law for the earthquake recurrence time distributions  

NASA Astrophysics Data System (ADS)

The earthquake recurrence time distribution in a given space-time window is being studied, using earthquake catalogues from different seismic regions (Southern California, Canada, and Central Asia). The quality of the available catalogues, taking into account the completeness of the magnitude, is examined. Based on the analysis of the catalogues, it was determined that the probability densities of the earthquake recurrence times can be described by a universal gamma distribution, in which the time is normalized with the mean rate of occurrence. The results show a deviation from the gamma distribution at the short interevent times, suggesting the existence of clustering. This holds from worldwide to local scales and for quite different tectonic environments.

Marekova, Elisaveta

2012-06-01

185

Short time scale variability in the solar wind.  

NASA Astrophysics Data System (ADS)

Existing observations of the interplanetary medium over short time scales are incomplete due to lack of steerable telescopes dedicated for such observations. Consequently, understanding of fast interplanetary disturbances and their association to the solar and geomagnetic activity has been inadequate. A programme of interplanetary scintillation observations was, thus, initiated using the Ooty Radio Telescope, where a few strong scintillating sources were monitored over a period of one year. These observations show significant interplanetary activity over a time scale of few minutes to hours. The disturbances observed during the monitoring programme can be understood with a simple model for interplanetary scattering produced by dense plasma objects moving at high velocities. This model was used to associate the events with their origin on the Sun and subsequent geomagnetic activity produced at Earth.

Gothoskar, P.; Pramesh Rao, A.

1995-06-01

186

HMC algorithm with multiple time scale integration and mass preconditioning  

NASA Astrophysics Data System (ADS)

We present a variant of the HMC algorithm with mass preconditioning (Hasenbusch acceleration) and multiple time scale integration. We have tested this variant for standard Wilson fermions at ?=5.6 and at pion masses ranging from 380 to 680 MeV. We show that in this situation its performance is comparable to the recently proposed HMC variant with domain decomposition as preconditioner. We give an update of the “Berlin Wall” figure, comparing the performance of our variant of the HMC algorithm to other published performance data. Advantages of the HMC algorithm with mass preconditioning and multiple time scale integration are that it is straightforward to implement and can be used in combination with a wide variety of lattice Dirac operators.

Urbach, C.; Jansen, K.; Shindler, A.; Wenger, U.

2006-01-01

187

Permeability models of porous media: Characteristic length scales, scaling constants and time-dependent electrokinetic coupling  

NASA Astrophysics Data System (ADS)

Four important models that describe the fluid permeability of geological porous media and that are derived from different physical approaches have been rewritten in a generic form that implies a characteristic scale length and scaling constant for each model. The four models have been compared theoretically and using experimental data from 22 bead packs and 188 rock cores from a sand-shale sequence in the UK sector of the North Sea. The Kozeny-Carman model did not perform well because it takes no account of the connectedness of the pore network, and should no longer be used. The other three models (Schwartz, Sen and Johnson (SSJ), Katz and Thompson (KT) and the so-called RGPZ) all performed well when used with their respective length scales and scaling constants. Surprisingly, we have found that the SSJ and KT models are extremely similar, such that their characteristic scale lengths and scaling constants are almost identical even though they are derived using extremely different approaches; the SSJ model by weighting the Kozeny-Carman model using the local electric field, the KT model using entry radii from fluid imbibition measurements. The experimentally determined scaling constants for each model were found to be cSSJ ? cKT ? 8/3 ? cRGPZ/3. Use of these models with AC electrokinetic theory has also allowed us to show that these scaling constants are also related to the a value in the RGPZ model and the m* value in time-dependent electrokinetic theory, and then derive a relationship between the electrokinetic transition frequency and the RGPZ scale length, which we have validated using experimental data. The practical implication of this work for permeability prediction is that the Katz and Thompson model should be used when fluid imbibition data is available, while the RGPZ model should be used when electrical data is available.

Glover, Paul; Walker, Emile

2010-05-01

188

Adaptive Haar transforms with arbitrary time and scale splitting  

NASA Astrophysics Data System (ADS)

The Haar transform is generalized to the case of an arbitrary time and scale splitting. To any binary tree we associate an orthogonal system of Haar-type functions - tree-structured Haar (TSH) functions. Unified fast algorithm for computation of the introduced tree-structured Haar transforms is presented. It requires 2(N - 1) additions and 3N - 2 multiplications, where N is transform order or, equivalently, the number of leaves of the binary tree.

Egiazarian, Karen O.; Astola, Jaakko T.

2001-05-01

189

On transport phenomena and equilibration time scales in thermodenuders  

NASA Astrophysics Data System (ADS)

This paper presents a theoretical and experimental investigation of thermodenuders that addresses two controversial issues: 1) equilibration time scales and 2) the need for an activated carbon (AC) denuder in the cooling section. We describe a plug flow model for transport phenomena in a TD, which can be used to simulate the rate of vapor build-up in the gas phase and the corresponding change in particle size distribution. Model simulations were found to have excellent agreement with experiments performed with pure and mixed dicarboxylic acid aerosols. Both simulations and experiments showed that the aerosols approached equilibrium within reasonable residence times (15 s-30 s) for aerosol concentrations and size distributions typical for laboratory measurements. However, for size distributions relevant for ambient aerosols, equilibration time scales were much larger than residence times available with current TD designs. We have also performed dimensional analysis on the problem of equilibration in TDs, and derived a dimensionless equilibration parameter which can be used to determine the residence time needed for an aerosol of given size distribution and kinetic properties to approach equilibrium. It is also shown theoretically and empirically that aerosol volatility has no effect on the equilibration time scales. Model simulations and experiments showed that with aerosol size distributions relevant to both ambient and laboratory measurements re-condensation in the cooling section, with and without an AC denuder, was negligible. Thus, there is no significant benefit in using an AC denuder in the cooling section. Due to the risk of stripping volatile material from the aerosol, the use of AC denuders in the cooling section should be avoided. Finally, we present a rationale for why ? C is the proper measure of volatility, while using mass fraction remaining (MFR) can be misleading.

Saleh, R.; Shihadeh, A.; Khlystov, A.

2010-07-01

190

Modeling of streamflow processes at different time scales  

NASA Astrophysics Data System (ADS)

The analysis and modeling of streamflow processes has attracted the attention of water resources specialists for several decades. A number of models have been suggested in the past for representing seasonal and annual streamflow processes. The topic addressed in this paper centers around the compatibility of stochastic models of streamflow at different time scales. More specifically, given a model for monthly flows, the models for the processes obtained by aggregation, i.e., models for bimonthly, quarterly, etc., time scales, are derived. Likewise, parameter space and covariance properties of such derived processes as well as the relationship of such properties of different time scales are given. These concepts are applied to modeling streamflow of the Niger River. The developments are restricted to the family of periodic autoregressive moving average (PARMA) processes. For instance, it was found that monthly flows based on the PARMA(2, 1) process leads to PARMA(2, 2) bimonthly flows and stationary ARMA(2, 2) annual flows. Furthermore, applications to modeling the Niger River flows suggest that one can reproduce the seasonal and annual second-order statistics without using disaggregation if PARMA models are used for modeling the seasonal flows.

Bartolini, Paolo; Salas, Jose D.

1993-08-01

191

Approximate aggregation of linear discrete models with two time scales: re-scaling slow processes to the fast scale  

Microsoft Academic Search

Mathematical models used in ecology often inherit the complexity found in nature and thus are governed by a large number of variables. Aggregation of variables methods is used to make such models mathematically tractable by building an approximate system governing fewer variables. We extend here aggregation methods for linear discrete models with processes occurring at different time scales. In practical

Tri Nguyen-Huu; Rafael Bravo de la Parra; Pierre Auger

2011-01-01

192

Scale dependence of the directional relationships between coupled time series  

NASA Astrophysics Data System (ADS)

Using the cross-correlation of the wavelet transformation, we propose a general method of studying the scale dependence of the direction of coupling for coupled time series. The method is first demonstrated by applying it to coupled van der Pol forced oscillators and coupled nonlinear stochastic equations. We then apply the method to the analysis of the log-return time series of the stock values of the IBM and General Electric (GE) companies. Our analysis indicates that, on average, IBM stocks react earlier to possible common sector price movements than those of GE.

Shirazi, Amir Hossein; Aghamohammadi, Cina; Anvari, Mehrnaz; Bahraminasab, Alireza; Rahimi Tabar, M. Reza; Peinke, Joachim; Sahimi, Muhammad; Marsili, Matteo

2013-02-01

193

A methodological bias toward overestimation of molecular evolutionary time scales.  

PubMed

There is presently a conflict between fossil- and molecular-based evolutionary time scales. Molecular approaches for dating the branches of the tree of life frequently lead to substantially deeper times of divergence than those inferred by paleontologists. The discrepancy between molecular and fossil estimates persists despite the booming growth of sequence data sets, which increasingly feeds the interpretation that molecular estimates are older than stratigraphic dates because of deficiencies in the fossil record. Here we show that molecular time estimates suffer from a methodological handicap, namely that they are asymmetrically bounded random variables, constrained by a nonelastic boundary at the lower end, but not at the higher end of the distribution. This introduces a bias toward an overestimation of time since divergence, which becomes greater as the length of the molecular sequence and the rate of evolution decrease. PMID:12060757

Rodriguez-Trelles, Francisco; Tarrio, Rosa; Ayala, Francisco J

2002-06-11

194

Exceptional vertebrate biotas from the Triassic of China, and the expansion of marine ecosystems after the Permo-Triassic mass extinction  

NASA Astrophysics Data System (ADS)

The Triassic was a time of turmoil, as life recovered from the most devastating of all mass extinctions, the Permo-Triassic event 252 million years ago. The Triassic marine rock succession of southwest China provides unique documentation of the recovery of marine life through a series of well dated, exceptionally preserved fossil assemblages in the Daye, Guanling, Zhuganpo, and Xiaowa formations. New work shows the richness of the faunas of fishes and reptiles, and that recovery of vertebrate faunas was delayed by harsh environmental conditions and then occurred rapidly in the Anisian. The key faunas of fishes and reptiles come from a limited area in eastern Yunnan and western Guizhou provinces, and these may be dated relative to shared stratigraphic units, and their palaeoenvironments reconstructed. The Luoping and Panxian biotas, both from the Guanling Formation, are dated as Anisian (Pelsonian) on the basis of conodonts and radiometric dates, the former being slightly older than the latter. The Xingyi biota is from the Zhuganpo Formation, and is Ladinian or early Carnian, while the Guanling biota is from the overlying Xiaowa Formation, dated as Carnian. The first three biotas include extensive benthos and burrowing in the sediments, and they were located in restricted basins close to shore. Further, even though the Luoping and Panxian biotas are of similar age, their faunas differ significantly, reflecting perhaps palaeogeographically isolated basins. Between the time of the Xingyi and Guanling biotas, there was a major transgression, and the Guanling biota is entirely different in character from the other three, being dominated by pelagic forms such as large floating crinoids attached to logs, very large ichthyosaurs and thalattosaurs, and pseudoplanktonic bivalves, with no benthos and no burrowing. Phylogenetic study of the fishes and marine reptiles shows apparently explosive diversification among 20 actinopterygian lineages very early in the Early Triassic, but a later expansion of marine reptile groups, in the late Olenekian and early Anisian. This offset in diversification patterns is matched by comparisons of feeding guild categories and body size data. New research tools will shed considerable light on the phylogenetic and ecological implications of recovery of mairne vertebrates in the Triassic.

Benton, Michael J.; Zhang, Qiyue; Hu, Shixue; Chen, Zhong-Qiang; Wen, Wen; Liu, Jun; Huang, Jinyuan; Zhou, Changyong; Xie, Tao; Tong, Jinnan; Choo, Brian

2013-10-01

195

On balanced approximations for time integration of multiple time scale systems  

Microsoft Academic Search

The effect of various numerical approximations used to solve linear and nonlinear problems with multiple time scales is studied in the framework of modified equation analysis (MEA). First, MEA is used to study the effect of linearization and splitting in a simple nonlinear ordinary differential equation (ODE), and in a linear partial differential equation (PDE). Several time discretizations of the

D. A. Knoll; L. Chacon; L. G. Margolin; V. A. Mousseau

2003-01-01

196

Dynamic voltage scaling for multitasking real-time systems with uncertain execution time  

Microsoft Academic Search

Dynamic voltage scaling (DVS) for real-time systems has been extensively studied to save energy. Previous studies consider the probabilistic distributions of tasks' execution time to assist DVS in task scheduling. These studies use probability information for intra-task frequency scheduling but do not sufficiently explore the opportunities for inter- task scheduling to save more energy. This paper presents a new approach

Changjiu Xian; Yung-hsiang Lu

2006-01-01

197

Time scaling with efficient time-propagation techniques for atoms and molecules in pulsed radiation fields  

SciTech Connect

We present an ab initio approach to solving the time-dependent Schroedinger equation to treat electron- and photon-impact multiple ionization of atoms or molecules. It combines the already known time-scaled coordinate method with a high-order time propagator based on a predictor-corrector scheme. In order to exploit in an optimal way the main advantage of the time-scaled coordinate method, namely, that the scaled wave packet stays confined and evolves smoothly toward a stationary state, of which the squared modulus is directly proportional to the electron energy spectra in each ionization channel, we show that the scaled bound states should be subtracted from the total scaled wave packet. In addition, our detailed investigations suggest that multiresolution techniques like, for instance, wavelets are the most appropriate ones to represent the scaled wave packet spatially. The approach is illustrated in the case of the interaction of a one-dimensional model atom as well as atomic hydrogen with a strong oscillating field.

Hamido, Aliou; Frapiccini, Ana Laura; Piraux, Bernard [Institute of Condensed Matter and Nanosciences, Universite Catholique de Louvain, Batiment de Hemptinne, 2, chemin du cyclotron, B-1348 Louvain-la Neuve (Belgium); Eiglsperger, Johannes [Institut fuer Theoretische Physik, Universitaet Regensburg, D-93040 Regensburg (Germany); Physik Departement, Technische Universitaet Muenchen, D-85747 Garching (Germany); Madronero, Javier [Physik Departement, Technische Universitaet Muenchen, D-85747 Garching (Germany); Mota-Furtado, Francisca; O'Mahony, Patrick [Department of Mathematics, Royal Holloway, University of London, Egham, TW20 0EX Surrey (United Kingdom)

2011-07-15

198

Thermopeaking in alpine streams: event characterization and time scales  

NASA Astrophysics Data System (ADS)

The present study provides a detailed quantification of the "thermopeaking" phenomenon, which consists of sharp intermittent alterations of stream thermal regime associated with hydropeaking releases from hydroelectricity plants. The study refers to the Noce River (Northern Italy), a typical hydropower-regulated Alpine stream, where water stored in highaltitude reservoirs often has a different temperature compared to the receiving bodies. The analysis is based on a river water temperature dataset that has been continuously collected for one year at 30' intervals in four different sections along the Noce River. A suitable threshold-based procedure is developed to quantify the main characteristics of thermopeaking, which is responsible for thermal alterations at different scales. The application of Wavelet Transform allows to separately investigate thermal regime alterations at sub-daily, daily and weekly scales. Moreover, at a seasonal scale, patterns of "warm" and "cold" thermopeaking can be clearly detected and quantified. The study highlights the relevance of investigating a variety of short-term alterations at multiple time scales for a better quantitative understanding of the complexity that characterises the river thermal regime. The outcomes of the analysis raise important interdisciplinary research questions concerning the effects of thermopeaking and of the related short- and medium-term effects on biological communities, which have been rather poorly investigated in ecological studies.

Zolezzi, Guido; Siviglia, Annunziato; Toffolon, Marco; Maiolini, Bruno

2010-05-01

199

High-resolution correlation of the late Triassic (Raetian) to the early Jurassic (Toarcian) between Pelagic sequence of Panthalassa and terrestrial sequence of Pangea using Milankovitch cycles  

NASA Astrophysics Data System (ADS)

Milankovitch forcing is one of the main drivers of cyclic climate changes, and cyclicities of Milankovitch cycles recorded in sedimentary rhythms would give a clue to establish the astronomically calibrated age model. Bedded cherts consist of rhythmical alternations of a chert bed and a shale bed, which are considered to have been formed as a result of cyclic changes in accumulation rate of biogenic SiO2 under extremely slow and continuous accumulation of pelagic clay. Although Milankovitch cycle origin of bedded chert was suggested by several arthors (e.g. Hori et al., 1993), such an origin has been still unproved. Ikeda et al. (2008) demonstrated the Milankovitch cycle origin of the middle Triassic bedded chert based on the similarities in the hierarchy of dominant cyclicities and the nature of amplitude modulation between Milankovitch cycles and the chert bed thickness cycles. However, because the errors of age determinations in the middle Triassic bedded chert are too large, we could not orbitally tune the bedded chert sequence to the astronomical time scale. In this study, we extend our research to the upper Triassic (Raetian) to lower Jurassic (Toarcian) bedded chert sequence and demonstrate its Milankovitch cycle origin. The Triassic/Jurassic (T/J) boundary was recognized as a radiolarian faunal turnover (Carter & Hori, 2005). Because the astronomically calibrated cyclostratigraphy was already established using the upper Triassic (Carnian) to lower Jurassic (Hettangian) lacustrine sequences of Pangea including the T/J boundary horizon (e.g. Olsen & Kent, 1999; Whiteside et al., 2007), we could compare our bedded chert sequence with them. We conducted geologic survey at Katsuyama section (e.g. Carter & Hori, 2005), in Inuyama area, central Japan. The average duration of ca. 20 ky for a chert-shale couplet based on radiolarian biostratigraphy is consistent with the assumption that a chert-shale couplet represents a precession cycle. Spectral analysis of bed number series of chert bed thickness revealed ca. 5, 20, and 200beds cycles that correspond to ca. 100, 400, and ca. 3500 ky eccentricity cycles, respectively. The similarity in the hierarchy of dominant periodicities between Milankovitch cycles and chert bed thickness cycles strongly support the idea that the cyclicities in thickness of a chert bed of upper Triassic to lower Jurassic bedded chert sequence were paced by Milankovitch cycles. We try to import the astronomically calibrated cyclostratigraphy for the lacustrine sequence in Newark basin (Olsen & Kent, 1999; Whiteside et al., 2007) into the bedded chert sequence in Inuyama by using the T/J boundary as a datum level. This correlation suggests that the radiolarian faunal turnover in Panthalassa is almost synchronous (~ ca. 100 ky) with the faunal and floral turnover in Pangea. Such a cyclostratigraphic correlation between pelagic bedded chert sequence and terrestrial lacustrine sequence will also provide useful information on the detailed process and mechanism of environmental changes at the T/J boundary and its relation with mass extinction.

Ikeda, M.; Tada, R.; Sakuma, H.

2009-12-01

200

Time Scale Hierarchies in the Functional Organization of Complex Behaviors  

PubMed Central

Traditional approaches to cognitive modelling generally portray cognitive events in terms of ‘discrete’ states (point attractor dynamics) rather than in terms of processes, thereby neglecting the time structure of cognition. In contrast, more recent approaches explicitly address this temporal dimension, but typically provide no entry points into cognitive categorization of events and experiences. With the aim to incorporate both these aspects, we propose a framework for functional architectures. Our approach is grounded in the notion that arbitrary complex (human) behaviour is decomposable into functional modes (elementary units), which we conceptualize as low-dimensional dynamical objects (structured flows on manifolds). The ensemble of modes at an agent’s disposal constitutes his/her functional repertoire. The modes may be subjected to additional dynamics (termed operational signals), in particular, instantaneous inputs, and a mechanism that sequentially selects a mode so that it temporarily dominates the functional dynamics. The inputs and selection mechanisms act on faster and slower time scales then that inherent to the modes, respectively. The dynamics across the three time scales are coupled via feedback, rendering the entire architecture autonomous. We illustrate the functional architecture in the context of serial behaviour, namely cursive handwriting. Subsequently, we investigate the possibility of recovering the contributions of functional modes and operational signals from the output, which appears to be possible only when examining the output phase flow (i.e., not from trajectories in phase space or time).

Perdikis, Dionysios; Huys, Raoul; Jirsa, Viktor K.

2011-01-01

201

From Depth Scale to Time Scale: Transforming Sediment Image Color Data into a High-Resolution Time Series  

Microsoft Academic Search

High-resolution time-scales are important for the precise correlation of spatially distributed geological records, and further development of process-oriented models used to predict climate change and other terrestrial processes. The extraction of digital line-scan data from images of laminated sediments provides a tool for the rapid and non-invasive analysis of sedimentary records, including sediment and ice cores, and tree ring growth

Andreas Prokoph; R. Patterson

202

A Hierarchy of Time-Scales and the Brain  

PubMed Central

In this paper, we suggest that cortical anatomy recapitulates the temporal hierarchy that is inherent in the dynamics of environmental states. Many aspects of brain function can be understood in terms of a hierarchy of temporal scales at which representations of the environment evolve. The lowest level of this hierarchy corresponds to fast fluctuations associated with sensory processing, whereas the highest levels encode slow contextual changes in the environment, under which faster representations unfold. First, we describe a mathematical model that exploits the temporal structure of fast sensory input to track the slower trajectories of their underlying causes. This model of sensory encoding or perceptual inference establishes a proof of concept that slowly changing neuronal states can encode the paths or trajectories of faster sensory states. We then review empirical evidence that suggests that a temporal hierarchy is recapitulated in the macroscopic organization of the cortex. This anatomic-temporal hierarchy provides a comprehensive framework for understanding cortical function: the specific time-scale that engages a cortical area can be inferred by its location along a rostro-caudal gradient, which reflects the anatomical distance from primary sensory areas. This is most evident in the prefrontal cortex, where complex functions can be explained as operations on representations of the environment that change slowly. The framework provides predictions about, and principled constraints on, cortical structure–function relationships, which can be tested by manipulating the time-scales of sensory input.

Kiebel, Stefan J.; Daunizeau, Jean; Friston, Karl J.

2008-01-01

203

A new Triassic procolophonoid reptile and its implications for procolophonoid survivorship during the Permo-Triassic extinction event.  

PubMed Central

A reptile specimen from the Lystrosaurus Assemblage Zone of the Beaufort Group, lowermost Triassic of South Africa, represents a new procolophonoid parareptile. Sauropareion anoplus gen. et sp. nov. is identified as the sister taxon of Procolophonidae in a phylogenetic analysis of procolophonoids. Stratigraphic calibration of the most parsimonious tree reveals that four of the six procolophonoid lineages originating in the Permian Period extended into the succeeding Triassic Period. This relatively high taxic survivorship (67%) across the Permo-Triassic boundary strongly suggests that procolophonoids were little if at all affected by the mass extinction event that punctuated the end of the Palaeozoic Era (ca. 251 million years ago).

Modesto, S; Sues, H D; Damiani, R

2001-01-01

204

Decay of surface nanostructures via long-time-scale dynamics  

SciTech Connect

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The authors have developed a new approach for extending the time scale of molecular dynamics simulations. For infrequent-event systems, the category that includes most diffusive events in the solid phase, this hyperdynamics method can extend the simulation time by a few orders of magnitude compared to direct molecular dynamics. The trajectory is run on a potential surface that has been biased to raise the energy in the potential basins without affecting the transition state region. The method is described and applied to surface and bulk diffusion processes, achieving microsecond and millisecond simulation times. The authors have also developed a new parallel computing method that is efficient for small system sizes. The combination of the hyperdynamics with this parallel replica dynamics looks promising as a general materials simulation tool.

Voter, A.F.; Stanciu, N.

1998-11-01

205

A New Measure of Time Perspective: Initial Psychometric Findings for the Balanced Time Perspective Scale (BTPS)  

Microsoft Academic Search

The development and initial validation of a new scale of balanced time perspective is reported. A balanced time perspective is defined here as a frequent and equal tendency to think about both one's past and future in positive ways. Sixty-seven men and 79 women ranging in age from 18–46 years (M = 21.3, SD = 4.42) completed the Balanced Time

Jeffrey Dean Webster

2011-01-01

206

Multiple-Time Scaling and Universal Behavior of the Earthquake Interevent Time Distribution  

SciTech Connect

The interevent time distribution characterizes the temporal occurrence in seismic catalogs. Universal scaling properties of this distribution have been evidenced for entire catalogs and seismic sequences. Recently, these universal features have been questioned and some criticisms have been raised. We investigate the existence of universal scaling properties by analyzing a Californian catalog and by means of numerical simulations of an epidemic-type model. We show that the interevent time distribution exhibits a universal behavior over the entire temporal range if four characteristic times are taken into account. The above analysis allows us to identify the scaling form leading to universal behavior and explains the observed deviations. Furthermore, it provides a tool to identify the dependence on the mainshock magnitude of the c parameter that fixes the onset of the power law decay in the Omori law.

Bottiglieri, M.; Godano, C.; Lippiello, E. [Department of Environmental Sciences and CNISM, Second University of Naples, Caserta (Italy); Arcangelis, L. de [IfB, ETH, Schafmattstr. 6, 8093 Zuerich (Switzerland) and Department of Information Engineering and CNISM, Second University of Naples, Aversa (Italy)

2010-04-16

207

Ti diffusion in quartz inclusions: implications for metamorphic time scales  

NASA Astrophysics Data System (ADS)

Quartz inclusions in garnet from samples collected from the staurolite zone in central New England are zoned in cathodoluminescence (CL). The CL intensity is interpreted to be a proxy for Ti concentration and the zoning attributed to Ti diffusion into the quartz grains driven by Ti exchange between quartz and enclosing garnet as a function of changing temperature. The CL zoning has been interpreted using a numerical diffusion model to constrain the time scales over which the diffusion has occurred. Temperature-time histories are sensitive to the presumed peak temperature but not to other model parameters. The total time of the metamorphic heating and cooling cycle from around 450 °C to the peak temperature (550-600 °C) back to 450 °C is surprisingly short and encompasses only 0.2-2 million years for peak temperatures of 600-550 °C. The metamorphism was accompanied by large-scale nappe and dome formation, and it is suggested that this occurred as a consequence of in-sequence thrusting resulting in a mid-crustal ductile duplex structure.

Spear, Frank S.; Ashley, Kyle T.; Webb, Laura E.; Thomas, Jay B.

2012-12-01

208

The circadian clock and glucocorticoids - Interactions across many time scales.  

PubMed

Glucocorticoids are steroid hormones of the adrenal gland that are an integral component of the stress response and regulate many physiological processes, including metabolism and immune response. Their release into the blood is highly dynamic and occurs in about hourly pulses, the amplitude of which is modulated in a daytime dependent fashion. In addition, in many species seasonal changes in basal glucocorticoid levels have been reported. In their target tissues, glucocorticoids bind to cytoplasmic receptors of the nuclear receptor superfamily. Upon binding, these receptors regulate transcription in a highly dynamic fashion, which involves stochastic binding to regulatory DNA elements on a time scale of seconds and heat shock protein mediated receptor-ligand complex recycling within minutes. The glucocorticoid hormone system interacts with another highly dynamic system, the circadian clock. The circadian clock is an endogenous biological timing mechanism that allows organisms to anticipate regular daily changes in their environment. It regulates daily rhythms of glucocorticoid release by a variety of mechanisms, modulates glucocorticoid signaling and is itself influenced by glucocorticoids. Here, we discuss mechanisms, functions and interactions of the circadian and glucocorticoid systems across time scales ranging from seconds (DNA binding by transcriptional regulators) to years (seasonal rhythms). PMID:23707790

Dickmeis, Thomas; Weger, Benjamin D; Weger, Meltem

2013-05-21

209

Did an Impact Trigger the Permian-Triassic Extinction?  

NSDL National Science Digital Library

NASA Astrobiology Institute news story on new evidence of a 251-million year-old impact crater off the western coast of Australia that may have caused the "Great Dying", the Permian-Triassic extinction event.

Morrison, David

2004-07-16

210

Measurement of hyperpolarized gas diffusion at very short time scales  

NASA Astrophysics Data System (ADS)

We present a new pulse sequence for measuring very-short-time-scale restricted diffusion of hyperpolarized noble gases. The pulse sequence is based on concatenating a large number of bipolar diffusion-sensitizing gradients to increase the diffusion attenuation of the MR signal while maintaining a fundamentally short diffusion time. However, it differs in several respects from existing methods that use oscillating diffusion gradients for this purpose. First, a wait time is inserted between neighboring pairs of gradient pulses; second, consecutive pulse pairs may be applied along orthogonal axes; and finally, the diffusion-attenuated signal is not simply read out at the end of the gradient train but is periodically sampled during the wait times between neighboring pulse pairs. The first two features minimize systematic differences between the measured (apparent) diffusion coefficient and the actual time-dependent diffusivity, while the third feature optimizes the use of the available MR signal to improve the precision of the diffusivity measurement in the face of noise. The benefits of this technique are demonstrated using theoretical calculations, Monte-Carlo simulations of gas diffusion in simple geometries, and experimental phantom measurements in a glass sphere containing hyperpolarized 3He gas. The advantages over the conventional single-bipolar approach were found to increase with decreasing diffusion time, and thus represent a significant step toward making accurate surface-to-volume measurements in the lung airspaces.

Carl, Michael; Wilson Miller, G.; Mugler, John P.; Rohrbaugh, Scott; Tobias, William A.; Cates, Gordon D.

2007-12-01

211

Time scales in the context of general relativity.  

PubMed

Towards 1967, the accuracy of caesium frequency standards reached such a level that the relativistic effect could not be ignored anymore. Corrections began to be applied for the gravitational frequency shift and for distant time comparisons. However, these corrections were not applied to an explicit theoretical framework. Only in 1991 did the International Astronomical Union provide metrics (then improved in 2000) for a definition of space-time coordinates in reference systems centred at the barycentre of the Solar System and at the centre of mass of the Earth. In these systems, the temporal coordinates (coordinate times) can be realized on the basis of one of them, the International Atomic Time (TAI), which is itself a realized time scale. The definition and the role of TAI in this context will be recalled. There remain controversies regarding the name to be given to the unit of coordinate times and to other quantities appearing in the theory. However, the idea that astrometry and celestial mechanics should adopt the usual metrological rules is progressing, together with the use of the International System of Units, among astronomers. PMID:21930569

Guinot, Bernard

2011-10-28

212

The beginning of the Buntsandstein cycle (Early–Middle Triassic) in the Catalan Ranges, NE Spain: Sedimentary and palaeogeographic implications  

NASA Astrophysics Data System (ADS)

The Early–Middle Triassic siliciclastic deposits of the Catalan Ranges, NE Spain, are dominated by aeolian sediments indicating a predominance of arid climate during this time span, in sharp contrast with the coeval fluvial sediments found in the Castilian Branch of the Iberian Ranges, 300 km to the SW.

Galán-Abellán, Belén; López-Gómez, José; Barrenechea, José F.; Marzo, Mariano; De la Horra, Raúl; Arche, Alfredo

2013-10-01

213

Multiple time-scale methods in particle simulations of plasmas  

SciTech Connect

This paper surveys recent advances in the application of multiple time-scale methods to particle simulation of collective phenomena in plasmas. These methods dramatically improve the efficiency of simulating low-frequency kinetic behavior by allowing the use of a large timestep, while retaining accuracy. The numerical schemes surveyed provide selective damping of unwanted high-frequency waves and preserve numerical stability in a variety of physics models: electrostatic, magneto-inductive, Darwin and fully electromagnetic. The paper reviews hybrid simulation models, the implicitmoment-equation method, the direct implicit method, orbit averaging, and subcycling.

Cohen, B.I.

1985-02-14

214

Viscosity, fission time scale and deformation of 156Dy  

NASA Astrophysics Data System (ADS)

In the fusion-fission reaction 40Ar + 116Cd --> 156Dy* --> fission, at Eb = 216 MeV and 238 MeV, ?-rays were measured in coincidence with fission fragments. The interpretation of the ?-ray spectra is done with the help of a modified version of the statistical-model code CASCADE. The spectra can be reproduced with nuclear viscosities in the range 0.01 < ?< 4. The extracted fission time scale is of the order of 10-19 s. The CASCADE analysis seems to favor a prolate deformation with ?~ 0.45.

van't Hof, G.; Bacelar, J. C. S.; Diószegi, I.; Harakeh, M. N.; Hesselink, W. H. A.; Kalantar-Nayestanaki, N.; Kugler, A.; van der Ploeg, H.; Plompen, A. J. M.; van Schagen, J. P. S.

1998-08-01

215

Biogenic calcium phosphate transformation in soils over millennial time scales  

Microsoft Academic Search

Background, aim, and scope  Changes in bioavailability of phosphorus (P) during pedogenesis and ecosystem development have been shown for geogenic calcium\\u000a phosphate (Ca-P). However, very little is known about long-term changes of biogenic Ca-P in soil.\\u000a \\u000a \\u000a \\u000a Materials and methods  Long-term transformation characteristics of biogenic Ca-P were examined using anthropogenic soils along a chronosequence from\\u000a centennial to millennial time scales.\\u000a \\u000a \\u000a \\u000a Results and discussion  Phosphorus

Shinjiro Sato; Eduardo G. Neves; Dawit Solomon; Biqing Liang; Johannes Lehmann

2009-01-01

216

Scaling in a Continuous Time Model for Biological Aging  

NASA Astrophysics Data System (ADS)

In this paper, we consider a generalization to the asexual version of Penna model for biological aging, where we take a continuous time limit. The genotype associated to each individual is an interval of real numbers over which Dirac ?-functions are defined, representing genetically programmed diseases to be switched on at defined ages of the individual life. We discuss two different continuous limits for the evolution equation and two different mutation protocols, to be implemented during reproduction. Exact stationary solutions are obtained and scaling properties are discussed.

de Almeida, R. M. C.; Thomas, G. L.

217

Time scales and relaxation dynamics in quantum-dot lasers  

SciTech Connect

We analyze a three-variable rate equation model that takes into account carrier capture and Pauli blocking in quantum dot semiconductor lasers. The exponential decay of the relaxation oscillations is analyzed from the linearized equations in terms of three key parameters that control the time scales of the laser. Depending on their relative values, we determine two distinct two-variable reductions of the rate equations in the limit of large capture rates. The first case leads to the rate equations for quantum well lasers, exhibiting relaxation oscillations dynamics. The second case corresponds to dots nearly saturated by the carriers and is characterized by the absence of relaxation oscillations.

Erneux, Thomas; Viktorov, Evgeny A.; Mandel, Paul [Universite Libre de Bruxelles, Optique Nonlineaire Theorique, Campus Plaine, Code Postal 231, 1050 Brussels (Belgium)

2007-08-15

218

Aram Chaos outflow channel: water volume and time scale  

NASA Astrophysics Data System (ADS)

The evaluation of the water volume and the formative time scale needed to carve the outflow channels represents a fundamental process for the validation of their evolutive models. We calculate these attributes for the Aram channels and we compared the results with the volume of liquid water that was produced in a single chaotization event of the Aram Chaos. The analysis suggests that a single rapid and catastrophic event is sufficient to carve the channel and the volume of flood is compatible with the volume of liquid water release in a single chaotization event of the Aram Chaos.

Roda, M.; Kleinhans, M. G.; Zegers, T. E.

2012-09-01

219

Triassic plant fossils from Pollock Road, Southland, New Zealand  

Microsoft Academic Search

Pole. M. S., & Raine. J. I., 1994:03:28. Triassic plant fossils from Pollock Road, Southland. New Zealand. Alcheringa 18, 147–159. ISSN 0311-5518.Sedimentary rocks of the Murihiku Supergroup considered to be latest Triassic (Rhaetian), crop out about 10 m below the Glenham Porphyry, near Glenham, New Zealand. They contain the vegetative macrofossils Marchantites sp. (Hepaticae), Pachydermophyllum praecordillerae (Frenguelli) Retallack and Pachydermophyllum

MIKE S. POLE; J. I. RAINE

1994-01-01

220

In-situ detrital zircon geochronology and Hf isotopic analyses from Upper Triassic Tethys sequence strata  

NASA Astrophysics Data System (ADS)

Marine sedimentary rocks of the Tethyan Himalayan sequence exposed south of the India-Asia suture and north of the high Himalayan mountain belt are widely attributed to India's passive margin along the southern margin of the Neo-Tethys ocean. The focus of this study are the Tethyan sequence strata exposed in southern Tibet that yield U-Pb detrital zircon age probability spectra and ?Hf values that are in stark contrast with Tethyan sequence strata of known Indian affinity. The rocks of the Upper Triassic Songre and Nieru Formations, exposed < 10 km south of the India-Asia suture, yield populations of U-Pb zircon ages in the range of ~ 450-220 Ma. Detrital zircon crystals of this age are not known to populate India affinity Tethyan sequence strata. The youngest cluster of ages, in the range of ~ 266-224 Ma, typically have juvenile ?Hf (T) values (+ 5.5-+13.5). Zircon ages and ?Hf (T) values in this range are consistent with igneous rocks of the Lhasa terrane on the northern margin of the Neo-Tethys ocean during Triassic time or with a hypothesized juvenile arc source from within the Neo-Tethys ocean. Collectively these unexpected results highlight the current uncertainties over the nature Neo-Tethys ocean and tectonic setting of the southern Lhasa prior to the India-Asia collision. We propose that the Upper Triassic age northern Tethyan Himalayan strata studied here represent an independent terrane from the widely studied southern Tethyan Himalayan strata. These rocks where isolated from the southern Tethyan Himalayan strata during Late Triassic time. This isolation was the result of a bathymetric barrier within the Neo-Tethys ocean such as a spreading center or an inter-Tethys arc system.

Guangwei, Li; Xiaohan, Liu; Alex, Pullen; Lijie, Wei; Xiaobing, Liu; Feixin, Huang; Xuejun, Zhou

2010-09-01

221

First occurrence of tetrapod footprints from the continental Triassic of the Sidi Said Maachou area (Western Meseta, Morocco)  

NASA Astrophysics Data System (ADS)

The Sidi Said Maachou area in the Moroccan western Meseta preserves a succession, up to 400 m thick, of hitherto poorly studied continental Triassic deposits. Recent detailed geological mapping proposes a lithostratigraphic subdivision of the predominantly red-coloured siliciclastic deposits into three formations. Laminated mudstones and fine-grained sandstones in the upper part of the Oued Oum Er Rbiaa Formation have the most interesting fossil content including plant impressions, rhizoliths, fish scales, and invertebrate and vertebrate traces. These biogenic remains are partially associated with tool marks, microbially induced sedimentary structures, oscillation ripples, desiccation cracks, and halite pseudomorphs, suggesting sedimentation in a playa-like, fluvio-lacustrine system under semiarid conditions. All tetrapod footprints from these beds are assigned to Brachychirotherium parvum and indistinguishable from other occurrences of the ichnogenus in Central Europe and North America. Supposed trackmakers are archosaurs of the crocodile stem-group (Crurotarsi) that were widely spread over Triassic Pangaea. Because Brachychirotherium is only known from Late Triassic (Carnian-Rhaetian) deposits, the same age is attributed to the footprint horizon of the Oued Oum Er Rbiaa Formation. This is the first record of Brachychirotherium on the African continent and the first record of Triassic tetrapod footprints in Morocco outside of the High Atlas.

Hminna, Abdelkbir; Voigt, Sebastian; Klein, Hendrik; Saber, Hafid; Schneider, Jörg W.; Hmich, Driss

2013-04-01

222

Polymorphism in ferroic functional elements. Bridging length and time scales  

NASA Astrophysics Data System (ADS)

The present study describes an approach for the scale-bridging modeling of ferroic materials as functional elements in micro- and nanoelectronic devices. Ferroic materials are characterized by temperature-dependent complex ordering phenomena of the internal magnetic, electronic, and structural degrees of freedom with several involved length and time scales. Hence, the modelling of such compounds is not straightforward, but relies on a combination of electronic-structure-based methods like ab-initio and density-functional schemes with classical particle-based approaches given by Monte-Carlo simulations with Ising, lattice-gas, or Heisenberg Hamiltonians, which incorporate material-specific parameters both from theory and experiment. The interplay of those methods is demonstrated for device concepts based on electroceramic materials like ferroelectrics and multiferroics, whose functionality is closely related with their propensity towards structural and magnetic polymorphism. In the present case, such scale-bridging techniques are employed to aid the development of an organic field effect transistor on a ferroelectric substrate generated by the self-assembly of field-sensitive molecules on the surfaces of ferroic oxides. Electronic-structure-based methods yield the microscopic properties of the oxide, the surface, the molecules, and the respective interactions. They are combined with classical particle-based methods on a scale-hopping basis. This combination allows to study the morphology evolution during the self-assembly of larger adsorbate arrays on the (defective) oxide surface and to investigate the interplay of low-temperature magnetic ordering phenomena with the ferroelectric functionality at higher temperatures in multiferroic oxides like the hexagonal manganites. The combination of density-functional data with classical continuum modelling also yielded a model Hamiltonian for the quick determination of the properties of a gate structure based on bio-functionalized carbon nanotubes.

Gemming, S.; Luschtinetz, R.; Chaplygin, I.; Seifert, G.; Loppacher, C.; Eng, L. M.; Kunze, T.; Olbrich, C.

2007-10-01

223

Coupling among electroencephalogram gamma signals on a short time scale.  

PubMed

An important goal in neuroscience is to identify instances when EEG signals are coupled. We employ a method to measure the coupling strength between gamma signals (40-100 Hz) on a short time scale as the maximum cross-correlation over a range of time lags within a sliding variable-width window. Instances of coupling states among several signals are also identified, using a mixed multivariate beta distribution to model coupling strength across multiple gamma signals with reference to a common base signal. We first apply our variable-window method to simulated signals and compare its performance to a fixed-window approach. We then focus on gamma signals recorded in two regions of the rat hippocampus. Our results indicate that this may be a useful method for mapping coupling patterns among signals in EEG datasets. PMID:20811477

McAssey, Michael P; Hsieh, Fushing; Smith, Anne C

2010-07-29

224

Multiple-time-scale motion in molecularly linked nanoparticle arrays.  

PubMed

We explore the transport of electrons between electrodes that encase a two-dimensional array of metallic quantum dots linked by molecular bridges (such as ?,? alkaline dithiols). Because the molecules can move at finite temperatures, the entire transport structure comprising the quantum dots and the molecules is in dynamical motion while the charge is being transported. There are then several physical processes (physical excursions of molecules and quantum dots, electronic migration, ordinary vibrations), all of which influence electronic transport. Each can occur on a different time scale. It is therefore not appropriate to use standard approaches to this sort of electron transfer problem. Instead, we present a treatment in which three different theoretical approaches-kinetic Monte Carlo, classical molecular dynamics, and quantum transport-are all employed. In certain limits, some of the dynamical effects are unimportant. But in general, the transport seems to follow a sort of dynamic bond percolation picture, an approach originally introduced as formal models and later applied to polymer electrolytes. Different rate-determining steps occur in different limits. This approach offers a powerful scheme for dealing with multiple time scale transport problems, as will exist in many situations with several pathways through molecular arrays or even individual molecules that are dynamically disordered. PMID:23199199

George, Christopher; Szleifer, Igal; Ratner, Mark

2012-12-11

225

Complex Processes from Dynamical Architectures with Time-Scale Hierarchy  

PubMed Central

The idea that complex motor, perceptual, and cognitive behaviors are composed of smaller units, which are somehow brought into a meaningful relation, permeates the biological and life sciences. However, no principled framework defining the constituent elementary processes has been developed to this date. Consequently, functional configurations (or architectures) relating elementary processes and external influences are mostly piecemeal formulations suitable to particular instances only. Here, we develop a general dynamical framework for distinct functional architectures characterized by the time-scale separation of their constituents and evaluate their efficiency. Thereto, we build on the (phase) flow of a system, which prescribes the temporal evolution of its state variables. The phase flow topology allows for the unambiguous classification of qualitatively distinct processes, which we consider to represent the functional units or modes within the dynamical architecture. Using the example of a composite movement we illustrate how different architectures can be characterized by their degree of time scale separation between the internal elements of the architecture (i.e. the functional modes) and external interventions. We reveal a tradeoff of the interactions between internal and external influences, which offers a theoretical justification for the efficient composition of complex processes out of non-trivial elementary processes or functional modes.

Perdikis, Dionysios; Huys, Raoul; Jirsa, Viktor

2011-01-01

226

How noise contributes to time-scale invariance of interval timing.  

PubMed

Time perception in the suprasecond range is crucial for fundamental cognitive processes such as decision making, rate calculation, and planning. In the vast majority of species, behavioral manipulations, and neurophysiological manipulations, interval timing is scale invariant: the time-estimation errors are proportional to the estimated duration. The origin and mechanisms of this fundamental property are unknown. We discuss the computational properties of a circuit consisting of a large number of (input) neural oscillators projecting on a small number of (output) coincidence detector neurons, which allows time to be coded by the pattern of coincidental activation of its inputs. We show that time-scale invariance emerges from the neural noise, such as small fluctuations in the firing patterns of its input neurons and in the errors with which information is encoded and retrieved by its output neurons. In this architecture, time-scale invariance is resistant to manipulations as it depends neither on the details of the input population nor on the distribution probability of noise. PMID:23767576

Oprisan, Sorinel A; Buhusi, Catalin V

2013-05-29

227

How noise contributes to time-scale invariance of interval timing  

NASA Astrophysics Data System (ADS)

Time perception in the suprasecond range is crucial for fundamental cognitive processes such as decision making, rate calculation, and planning. In the vast majority of species, behavioral manipulations, and neurophysiological manipulations, interval timing is scale invariant: the time-estimation errors are proportional to the estimated duration. The origin and mechanisms of this fundamental property are unknown. We discuss the computational properties of a circuit consisting of a large number of (input) neural oscillators projecting on a small number of (output) coincidence detector neurons, which allows time to be coded by the pattern of coincidental activation of its inputs. We show that time-scale invariance emerges from the neural noise, such as small fluctuations in the firing patterns of its input neurons and in the errors with which information is encoded and retrieved by its output neurons. In this architecture, time-scale invariance is resistant to manipulations as it depends neither on the details of the input population nor on the distribution probability of noise.

Oprisan, Sorinel A.; Buhusi, Catalin V.

2013-05-01

228

Depositional history of Lower Triassic Dinwoody Formation, Bighorn basin, Wyoming and Montana  

SciTech Connect

The Lower Triassic Dinwoody Formation in the Bighorn basin of Wyoming and Montana records the northeasternmost extent of the widespread and rapid Griesbachian transgression onto the Wyoming shelf. Depositional patterns document a progressive change from sparsely fossiliferous, inner-shelf marine conditions in the southwest and west to restricted, marginal-marine environments to the north and east. Characteristic lithologies include greenish-gray calcareous or dolomitic mudstone and siltstone, very thin to thick beds of gypsum, and thin-bedded, commonly laminated dolomite. A formation thickness of approximately 20 m persists throughout most of the basin but diminishes abruptly near the northern and eastern limits of deposition. The Dinwoody is disconformable on the Ervay Member of the Permian Park City Formation except in the northeasternmost part of the basin, where it locally overlies the Pennsylvanian Tensleep Sandstone. Considering the significant time interval involved, physical evidence at the Permian-Triassic boundary is generally limited to an abrupt lithologic change from light-colored shallow marine or intertidal Permian dolomite to greenish-gray Dinwoody siltstone. The Dinwoody grades vertically as well as laterally to the east and north into red beds of the Lower Triassic Red Peak Formation of the Chugwater Group. The Early Triassic depositional environment in the present-day Bighorn basin was hostile. A sparse molluscan fauna was observed at only one of the 20 sections studied, and no conodonts were recovered from Dinwoody carbonates. Significant amounts of gypsum within the Dinwoody suggest periodic high evaporation from hypersaline waters on a low-energy shallow shelf during intervals of reduced terrigenous sediment supply from the north and east. However, sufficient organic material was present to create reducing conditions, as evidenced by greenish rock color and abundant pyrite.

Paull, R.A.; Paull, R.K.

1986-08-01

229

Time and space scale analysis of the climate entropy budget  

NASA Astrophysics Data System (ADS)

Either in models or in measurements entropy production and fluxes are generally estimated starting from the ratio of temperature and energy fluxes. Given the nonlinearity of the definition of entropy production, this quantities depend on the time and space resolution involved. It is therefore fundamental for observational and theoretical purposes to know how the climate entropy budget is affected by different time-space coarse graining and what are the errors involved when certain time means (e.g. annual) are used in place of others (e.g. daily). Referring to the entropy budget studied in Pascale et al. (2011), we study the effect of combined space and time averaging of the material entropy production (direct and indirect formula), entropy production due to kinetic energy dissipation, hydrological cycle and ocean turbulence. For the time analysis a 50-year run is taken. Time coarse graining shows that material entropy production decreases as the averaging period is increased. Daily cycle and seasonal cycle are the main signals which can be observed. In the indirect formula (based on radiative fields, Goody 2000) an underestimate of 4% and 10% is found associated with neglecting daily and seasonal correlations. The direct formula is less sensitive and shows errors of 2% and 4% respectively and mainly due to response of the hydrological cycle. The material entropy production due to small-scale ocean turbulence shows a sharp decrease (~ 45%) corresponding to the seasonal cycle and associated with the seasonal thermocline variations. We then take into account also a space coarse graining in which energy fluxes and temperature are re-gridded over space grids of coarser resolution. We find that entropy budget terms decreases when the space resolution is decreased as would be expected from general coarse-graining theory. Our results suggest that the model in consideration, although not designed for dealing with entropy production, behaves consistently with the second law of thermodynamics.

Lucarini, V.; Pascale, S.

2012-04-01

230

Monitoring bacterial community structure and variability in time scale in full-scale anaerobic digesters.  

PubMed

Using a high-throughput pyrosequencing technology, this study assessed bacterial community structure and time-scale variability in great detail in seven full-scale anaerobic digesters operated variously in terms of influent substrate, digestion temperature, and reactor configuration. Pyrosequencing generated a total of 83,774 sequence reads from 40 digester sludge samples collected monthly for six months. The highest number of sequence reads were detected within Proteobacteria (20.5%), followed by those within Bacteroidetes (19.7%), Firmicutes (17.8%), and Chloroflexi (4.8%). The relative composition of bacterial populations was varied within the digesters as well as between the digesters, and the bacterial community structures were mainly influenced by digestion temperature. Detailed bacterial community structures were assessed by analyzing the operational taxonomic units (OTUs) based on 97% sequence similarity, which resulted in a total of 9051 OTUs. Among these, a total of 31 core OTUs were analyzed and inferred phylogenetically, which enabled us to classify the sequences within an unclassified phylum. Unclassified sequences were mostly affiliated with the sequences within Spirochaetes and Firmicutes. Interestingly, numerically dominant novel phylotypes (18% of the total sequence reads) presumably involved in anaerobic digestion within Spirochaetes were identified. Temporal variability was further explored using a non-metric multidimensional scaling ordination which demonstrated that the variability of the bacterial community within the digesters was smaller than between digesters. Correlation analysis demonstrated that digester performance and operational conditions affected the pattern of bacterial community in the ordination. Additionally, a multi-response permutation procedure revealed that the bacterial communities within the digesters were more similar than those belonging to other digesters statistically, demonstrating a patchiness of the digesters in the distribution of bacterial populations. Overall, this study revealed the correlation of bacterial community structure and time-scale variability with digester performance and operating conditions. PMID:22426622

Lee, Sang-Hoon; Kang, Hyun-Jin; Lee, Young Haeng; Lee, Taek Jun; Han, Keumsuk; Choi, Youngjun; Park, Hee-Deung

2012-03-19

231

Time-scales of granite magmatism: from source to emplacement  

NASA Astrophysics Data System (ADS)

Many granite (sensu-lato) bodies in the upper crust originated as partial melts in the mid- to lower crust. Their formation involves four separate, but inter-related processes: generation, segregation, ascent and emplacement. These processes were traditionally thought to occur over long time-scales (c. 1-10 M.y.), but this view has recently been challenged. Quantitative studies have suggested that melt generation following the intrusion of mantle-derived basalt, ascent of granite magma through dykes, and emplacement of tabular plutons accommodated by lateral fault opening and vertical movement of roof and floor, can occur over much shorter time-scales (c. 0.01 M.y. 1 M.y.). However, what is missing is a quantitative understanding of the time-scales over which granite melt can segregate from its partially molten protolith. Melt flow along grain edges can be driven by buoyancy, and space to accommodate the melt provided by compaction of the solid matrix. Previous studies suggested that this process is very slow, but they neglected the coupled physical and chemical processes which occur as buoyant melt migrates upwards through the steep thermal gradient above a hot basalt intrusion. A new quantitative model of melt generation and segregation via buoyancy-driven compaction includes these coupled processes, and suggests that granite magma can segregate rapidly following the onset of melting. Combining this model with magma ascent via dykes, and using reasonable values of the governing physical parameters, suggests that emplacement of a 100 km3 pluton in the upper crust can be complete within c. 50,000 y. of the onset of melting in the lower crust. Melt generation results from the intrusion of mantle-derived basalt with a thickness of 250m, over an area of 900 km2. The segregated granite magma accumulates at the top of the partially molten source region, where it flows laterally to a localised area of dyke formation and then upwards to the emplacement level. Repeated intrusion of basalt into thickening lower crust leads to the formation of multiple plutons.

Jackson, M. D.

2006-12-01

232

Time Scale Dependent SGD due to the Sea Level Change  

NASA Astrophysics Data System (ADS)

Submarine groundwater discharge (SGD) is defined as the groundwater outflux across the ocean-land interface. In this study, the variation of amount of SGD due to the sea level change is investigated by means of numerical simulation. Numerical code FEFLOW (Diersh et al., 2005) is used to conduct the simulation and the effect of sea level change on the variation of SGD with different time scales from diurnal cycle to glacial cycle is evaluated. The simulation results indicate that generally, the increase of amplitude of sea level leads to the increase of SGD while the increase of period of sea level change cause more complicated pattern of the variation of SGD. These variations are changed with the aquifer properties, especially, hydraulic conductivity. The simulation results show that the sea level change with different period and amplitude leads to the variation of total SGD and it may explain the unknown source of the unexpectedly high amount of SGD.

Lee, K.; Lee, E.; Hyun, Y.

2009-12-01

233

Large-scale structure of time evolving citation networks  

NASA Astrophysics Data System (ADS)

In this paper we examine a number of methods for probing and understanding the large-scale structure of networks that evolve over time. We focus in particular on citation networks, networks of references between documents such as papers, patents, or court cases. We describe three different methods of analysis, one based on an expectation-maximization algorithm, one based on modularity optimization, and one based on eigenvector centrality. Using the network of citations between opinions of the United States Supreme Court as an example, we demonstrate how each of these methods can reveal significant structural divisions in the network and how, ultimately, the combination of all three can help us develop a coherent overall picture of the network's shape.

Leicht, E. A.; Clarkson, G.; Shedden, K.; Newman, M. E. J.

2007-09-01

234

Bounded diffusive motion on two different time scales in solid  

SciTech Connect

High-energy-resolution quasielastic neutron scattering on three complementary spectrometers has been used to investigate molecular diffusive motion in solid nano- to bulk-sized particles of the alkane n-C32H66. The crystalline-to-plastic and plastic-to-fluid phase transition temperatures are observed to decrease as the particle size decreases. In all samples, localized molecular diffusive motion in the plastic phase occurs on two different time scales: a 'fast' motion corresponding to uniaxial rotation about the long molecular axis; and a 'slow' motion attributed to conformational changes of the molecule. Contrary to the conventional interpretation in bulk alkanes, the fast uniaxial rotation begins in the low-temperature crystalline phase.

Wang, S.-K. [University of Missouri, Columbia; Mamontov, Eugene [ORNL; Bai, M. [University of Missouri, Columbia; Hansen, F.Y. [Technical University of Denmark; Taub, H. [University of Missouri, Columbia; Copley, J.R.D. [National Institute of Standards and Technology (NIST); Garcia Sakai, V [University of Maryland and NIST; Gasparovic, Goran [NCNR and University of Maryland; Jenkins, Timothy [NCNR and University of Maryland; Tyagi, M. [NCNR and University of Maryland; Herwig, Kenneth W [ORNL; Neumann, D. A. [National Institute of Standards and Technology (NIST); Montfrooij, W. [University of Missouri, Columbia; Volkmann, U. G. [Pontifica Universidad Catolica de Chile

2010-01-01

235

Time-scale modelling of the invasive species Robinia pseudoacacia  

NASA Astrophysics Data System (ADS)

Our contribution is part of the TransEcoNet project (Transnational Ecological Networks in Central Europe) that aims to investigate transboundary ecological networks across Central Europe. An objective of this project is to contribute towards awareness rising on the value and role of ecological networks. This poster presents the activities that are carried out in Pomurje region, Slovenia as our case study area. Pomurje region borders with Austria in the north, to Hungary in the east, and to Croatia in the south. We are investigating the spread of the invasive species Robinia pseudacacia and the underlying causes, and assess landscape scale ecological dynamics (e.g. Mura River floodplains) in ecological networks. The study comprises investigation and mapping of the R. pseudacacia spread with time-series analysis to understand its spatial dynamics. The preliminary studies show that the R. pseudacacia had the most expanded in the region since 1980s. Some of the surfaces were cut and converted back to fields. This reflects the socioeconomic situation in the region. The further study will include statistic, GIS (geographical information systems) and remote sensing techniques. We will apply various character data: satellite imagery, IR-orthophotos, digital elevation models, including LIDAR, contemporary and historical maps, and other spatial/non-spatial data sources. The outputs will include reconstruction of R. pseudacacia-dynamics in the recent decade, modelling the distribution of R. pseudacacia in relation to abiotic environmental factors and land use, and modelling (prediction) the expected distribution of R. pseudacacia in case of climate and land use change. Keywords: invasive species, Robinia pseudacacia, spatial analysis, time-scale analysis, remote sensing, land use change, climate change

Tomaž, Podobnikar; Andraž, Ä.?Arni; Imelda, Somodi

2010-05-01

236

Geologic history of Florida-Bahama platform, Triassic through Paleocene  

SciTech Connect

This study is based on top-to-bottom examination of samples from 146 wells from the Florida-Bahama platform. Following Triassic graben formation, three different structural configurations develop through time. In the Late Jurassic-Coahuilan, a northwestern and southeastern sedimentary province were separated by the Sarasota arch, located on the west Florida shelf. Modern basin configurations, which began to appear in the Comanchean, were modified by tectonics in Cuba in the early Gulfian. From the Late Jurassic through the Comanchean, the continental margin was occupied by a carbonate complex that restricted marine circulation in some areas. In the southeast, this barrier caused the deposition of lagoonal carbonates and anhydrites; in the north, clastics were deposited. Carbonate-evaporite deposition in the south ended at the close of the Comanchean and was followed by the deposition of chalk and chalky limestone in the Gulfian. During this epoch, the rapid subsidence of the Blake Plateau basin to bathal depths and the collapse of the Florida straits were associated with tectonic activity in northern Cuba. By the middle Gulfian, the Rebecca Shoal barrier reef had appeared on the upthrown northern side of the straits. This barrier reef expanded to encircle the Florida peninsula completely, at which time the Cedar Keys (Paleocene) lagoonal dolomite-anhydrite deposition was initiated.

Winston, G.O.

1988-02-01

237

An aborted Triassic Ocean in west Siberia  

NASA Astrophysics Data System (ADS)

A small buried oceanic basin named the Obsky paleo-ocean has been found in West Siberia. It developed from 235 to 218 m.y. during the Triassic by rift propagation and seafloor spreading inside the west Siberian region of the continent. During the postspreading period the Obsky paleo-ocean did not collapse but instead was covered intact by a layer of sediments with a thickness of up to 15 km. This conclusion is based on detailed interpretation of geophysical and geological data. Striped magnetic anomalies marking the paleo-ocean spreading have been separated from the total magnetic field. They have been dated and interpreted within the framework of the Vine-Matthews concept. Seismic and gravitational data have permitted delineation of the Obsky paleo-ocean depression and contouring of the basement relief within its bounds. Investigation of the Obsky paleo-ocean basalts by means of deep boreholes has indicated that they are chemically similar to oceanic tholeiites and has also confirmed the presence of strong residual magnetism in them. Spreading of the Obsky paleo-ocean was a stage in the initial disintegration of Pangea at the Paleozoic-Mesozoic boundary. The presence of a north trending buried spreading center along the axial zone of West Siberia accounts for many features of the Mesozoic-Cenozoic history of the region and its present-day structure.

Aplonov, Sergei

1988-12-01

238

Dynamic time scale for the Lagrangian subgrid-scale model based on Rice's formula  

NASA Astrophysics Data System (ADS)

The dynamic formulation of Smagorinsky's subgrid-scale model for Large Eddy Simulations (LES) requires averaging to avoid instability due to extreme fluctuations. For complex-geometry flows a Lagrangian approach is often useful [see Meneveau, Lund, and Cabot, JFM 319 (1996)]. However, an ad-hoc choice of the relaxation timescale must be made, often based on resolved strain-rates and stresses at the grid- scale. Recently, Park and Mahesh [Phys. Fluids 21, 065106 (2009)] proposed the attractive notion of using statistics of the error signal itself to determine a timescale dynamically. We extend this approach by using Rice's formula to dynamically estimate the time between mean-crossings of the error signal and set the averaging timescale to be twice this value. The approach requires accumulating Lagrange-averaged square error and its time-derivative squared, which is done using the Eulerian approximation as proposed in the original model. For validation, LES of flow in a channel and through an array of cubes are compared with experimental results. Distributions of the dynamic coefficient, error, and dynamic timescale are shown as a function of distance from the wall. Computational efficiency and memory requirements are also discussed.

Verhulst, Claire; Meneveau, Charles

2011-11-01

239

Early Triassic palaeomagnetic results from the Ryeongnam Block, Korean Peninsula: the eastern extension of the North China Block  

NASA Astrophysics Data System (ADS)

Greenish sandstones in the Early Triassic Nogam Formation of the Ryeongnam Block, Korean Peninsula were collected at 23 sites for palaeomagnetic study. A high-temperature magnetization component with unblocking temperatures of 670-690 degC was isolated from seven sites and yielded a positive fold test at the 95 per cent confidence level. The high-temperature component is interpreted to be of primary origin because the folding age is Middle Triassic. The Early Triassic palaeomagnetic direction for the Ryeongnam Block after tilt correction is D=347.1 deg, I=23.8 deg (?95=5.5 deg). The palaeomagnetic pole (62.5 degN, 336.8 degE, A95=4.7 deg) shows good agreement with the coeval pole for the North China Block, suggesting that the Ryeongnam Block has been part of the North China Block at least since Early Triassic times. A tectonic history of the Korean Peninsula includes obduction of the eastern part of the South China Block onto the central part of the Korean Peninsula in the Permian, with the Ryeongnam Block geographically isolated from the main part of the North China Block. Collision of the North and South China blocks commenced initially at the Korean Peninsula, and suturing of the two blocks progressed westwards.

Uno, Koji

1999-12-01

240

Lunar Crater Rays Point to a New Lunar Time Scale  

NASA Astrophysics Data System (ADS)

The Lunar Time Scale should be reevaluated -- suggest remote sensing studies of lunar crater rays by B. Ray Hawke (University of Hawaii) and colleagues at the University of Hawaii, NovaSol, Cornell University, National Air and Space Museum, and Northwestern University. These scientists have found that the mere presence of crater rays is not a reliable indicator that the crater is young, as once thought, and that the working definition of the Copernican/Eratosthenian (C/E) boundary should be reconsidered. The team used Earth-based spectral and radar data with FeO, TiO2, and optical maturity maps derived from Clementine UVVIS images to determine the origin and composition of selected lunar ray segments. They conclude that the optical maturity parameter, which uses chemical analyses of lunar samples as its foundation, should be used to redefine the C/E boundary. Under this classification, the Copernican System would be defined as the time required for an immature surface to reach full optical maturity.

Martel, L. M. V.

2004-09-01

241

IPS Observations of Short-Time Scale Interplanetary Activity  

NASA Astrophysics Data System (ADS)

We have carried out a program of continuous Interplanetary Scintillation (IPS) monitoring of the interplanetary activity using Ooty Radio Telescope (ORT). From May 1990 to March 1991, during the 22nd, solar maximum, a few radio sources were monitored to provide long stretches of IPS data with a high-time resolution of few minutes. These observations covered 0.3 to 0.8 AU region (12° to 70° elongations) around the sun at several heliographic latitudes. During the observation, we detected 33 short-time scale IPS events which had significant variation in the scintillation index and solar wind velocity. These were considered to be due to travelling interplanetary disturbances. A multi-component model of plasma density enhancement was developed to estimate the geometry and physical properties of these IPS events. Detailed analysis of 20 of these events suggests, 1. fast IPS events were interplanetary signatures of Coronal Mass Ejections (CMEs), 2. the average mass and energy of these events was ˜ 1016 gm and 1033 erg respectively,3. 80% of IPS events were associated with X-ray flares on the sun and 50% were associated with geomagnetic activity at earth. Detailed study of the multicomponent model suggests IPS observations at smaller elongations (hence at higher radio frequencies) are more suited to detect fast-moving interplanetary disturbances such as produced by CMEs.

Gothoskar, Pradeep; Pramesh Rao, A.

1996-03-01

242

Use of a Walk Through Time to Facilitate Student Understandings of the Geological Time Scale  

NASA Astrophysics Data System (ADS)

Students often have difficulties in appreciating just how old the earth and the universe are. While they can simply memorize a number, they really do not understand just how big that number really is, in comparison with other, more familiar student referents like the length of a human lifetime or how long it takes to eat a pizza. (See, e.g., R.D. Trend 2001, J. Research in Science Teaching 38(2): 191-221) Students, and members of the general public, also display such well-known misconceptions as the "Flintstone chronology" of believing that human beings and dinosaurs walked the earth at the same time. (In the classic American cartoon "The Flintstones," human beings used dinosaurs as draft animals. As scientists we know this is fiction, but not all members of the public understand that.) In an interdisciplinary undergraduate college class that dealt with astronomy, cosmology, and biological evolution, I used a familiar activity to try to improve student understanding of the concept of time's vastness. Students walked through a pre-determined 600-step path which provided a spatial analogy to the geological time scale. They stopped at various points and engaged in some pre-determined discussions and debates. This activity is as old as the hills, but reports of its effectiveness or lack thereof are quite scarce. This paper demonstrates that this activity was effective for a general-audience, college student population in the U.S. The growth of student understandings of the geological time scale was significant as a result of this activity. Students did develop an understanding of time's vastness and were able to articulate this understanding in various ways. This growth was monitored through keeping track of several exam questions and through pre- and post- analysis of student writings. In the pre-writings, students often stated that they had "no idea" about how to illustrate the size of the geological time scale to someone else. While some post-time walk responses simply restated what was done in the walk through time, some students were able to develop their own ways of conceptualizing the vastness of the geological time scale. A variety of findings from student understandings will be presented. This work has been supported in part by the Distinguished Scholars Program of the National Science Foundation (DUE-0308557).

Shipman, H. L.

2004-12-01

243

Economies of Scale in e-Government: Time for Evidence  

Microsoft Academic Search

The presence of economies of scale has been often taken for granted in the discussion of many eGovernment implementation issues. This paper discusses this assumption by showing that empirical evidence in favor of economies of scale may be considered context dependent. Although the analysis carried out does not lead to discard the presence of economies of scale in the provision

Enrico Ferro; Marco Cantanmessa; Emilio Paolucci

2004-01-01

244

A biologically plausible model of time-scale invariant interval timing  

Microsoft Academic Search

The temporal durations between events often exert a strong influence over behavior. The details of this influence have been\\u000a extensively characterized in behavioral experiments in different animal species. A remarkable feature of the data collected\\u000a in these experiments is that they are often time-scale invariant. This means that response measurements obtained under intervals\\u000a of different durations coincide when plotted as

Rita Almeida; Anders Ledberg

2010-01-01

245

Full-Scale and Time-Scale Heating Experiments at Stripa: Preliminary Results. Technical Project Report No. 11.  

National Technical Information Service (NTIS)

Two full-scale heating experiments and a time-scale heating experiment have recently been started in granite 340 meters below surface. The purpose of the full-scale heating experiments is to assess the near-field effects of thermal loading for the design ...

N. G. W. Cook M. Hood

1978-01-01

246

What is the time scale for ?-helix nucleation?  

PubMed

Helix formation is an elementary process in protein folding, influencing both the rate and mechanism of the global folding reaction. Yet, because helix formation is less cooperative than protein folding, the kinetics are often multiexponential, and the observed relaxation times are not straightforwardly related to the microscopic rates for helix nucleation and elongation. Recent ultrafast spectroscopic measurements on the peptide Ac-WAAAH(+)-NH(2) were best fit by two relaxation modes on the ?0.1-1 ns time scale, (1) apparently much faster than had previously been experimentally inferred for helix nucleation. Here, we use replica-exchange molecular dynamics simulations with an optimized all-atom protein force field (Amber ff03w) and an accurate water model (TIP4P/2005) to study the kinetics of helix formation in this peptide. We calculate temperature-dependent microscopic rate coefficients from the simulations by treating the dynamics between helical states as a Markov process using a recently developed formalism. The fluorescence relaxation curves obtained from simulated temperature jumps are in excellent agreement with the experimentally determined results. We find that the kinetics are multiphasic but can be approximated well by a double-exponential function. The major processes contributing to the relaxation are the shrinking of helical states at the C-terminal end and a faster re-equilibration among coil states. Despite the fast observed relaxation, the helix nucleation time is estimated from our model to be 20-70 ns at 300 K, with a dependence on temperature well described by Arrhenius kinetics. PMID:21480610

De Sancho, David; Best, Robert B

2011-04-11

247

Triassic Sequence Geological Development of the Arctic with focus on Svalbard and the Barents Shelf.  

National Technical Information Service (NTIS)

Triassic rocks are of great interest for exploration in Arctic areas as they have proved to include both good hydrocarbon source rocks and potential hydrogen reservoir rocks. In this thesis, the stratigraphy and sedimentology of the Arctic Triassic succes...

A. Moerk

1998-01-01

248

Climatically driven biogeographic provinces of Late Triassic tropical Pangea  

PubMed Central

Although continents were coalesced into the single landmass Pangea, Late Triassic terrestrial tetrapod assemblages are surprisingly provincial. In eastern North America, we show that assemblages dominated by traversodont cynodonts are restricted to a humid 6° equatorial swath that persisted for over 20 million years characterized by “semiprecessional” (approximately 10,000-y) climatic fluctuations reflected in stable carbon isotopes and sedimentary facies in lacustrine strata. More arid regions from 5–20°N preserve procolophonid-dominated faunal assemblages associated with a much stronger expression of approximately 20,000-y climatic cycles. In the absence of geographic barriers, we hypothesize that these variations in the climatic expression of astronomical forcing produced latitudinal climatic zones that sorted terrestrial vertebrate taxa, perhaps by excretory physiology, into distinct biogeographic provinces tracking latitude, not geographic position, as the proto-North American plate translated northward. Although the early Mesozoic is usually assumed to be characterized by globally distributed land animal communities due to of a lack of geographic barriers, strong provinciality was actually the norm, and nearly global communities were present only after times of massive ecological disruptions.

Whiteside, Jessica H.; Grogan, Danielle S.; Olsen, Paul E.; Kent, Dennis V.

2011-01-01

249

Return to Coalsack Bluff and the Permian Triassic boundary in Antarctica  

NASA Astrophysics Data System (ADS)

Coalsack Bluff was the first discovery site in Antarctica for the latest Permian to earliest Triassic reptile Lystrosaurus. This together with discovery of Permian Glossopteris leaves during the heroic age of Antarctic exploration, indicated not only that Antarctica was part of Gondwanaland, but also that Antarctic rocks recorded faunas from the greatest of all mass extinctions at the Permian-Triassic boundary. Pinpointing the exact stratigraphic level of this life crisis has recently become possible using ? 13C values in terrestrial organic matter. Multiple, short-lived events of 13C depletion may reflect carbon cycle crises, with the isotopic change a measure of terrestrial and atmospheric disequilibrium. Additional evidence for ecosystem reorganization came from changes in paleosol types and their root traces. Such studies previously completed at the Antarctic localities of Graphite Peak, Mount Crean, Portal Mountain, Shapeless Mountain and Allan Hills, are here extended to Coalsack Bluff. Carbon isotopic values in Permian rocks at Coalsack Bluff average - 23.08 ± 0.25‰, but begin to decline within the last coal with leaves ( Glossopteris), roots ( Vertebraria) and permineralized stumps ( Araucarioxylon) of glossopterids. The low point in ä 13C values is - 27.19‰ at 5.6 m above the last coal, which is capped by unusually abundant pyrite, and a claystone breccia with common clasts of redeposited clayey soils. Above this are massive quartz-rich sandstones of braided streams, considered a geomorphic response to deforestation and soil erosion following the mass extinction. Distinctive berthierine-bearing paleosols (Dolores pedotype) within these sandstones have unoxidized iron taken as evidence of severe groundwater hypoxia. Other paleosols at this stratigraphic level are like those in other Early Triassic rocks of Antarctica, which indicate unusually warm and humid conditions for such high paleolatitude lowlands. Waterlogging is also indicated by newly discovered kinds of paleosol (Ernest pedotype) with groundwater calcretes. The lack of peat accumulation in such waterlogged lowlands, berthierine in paleosols and large negative carbon isotopic shift at Coalsack Bluff support the idea of atmospheric pollution with methane from submarine and permafrost clathrates as a cause for the Permian-Triassic mass extinction. Hypoxic soils would have killed lowland plants by preventing root respiration and hypoxic air would have challenged vertebrates with pulmonary edema. Causes for catastrophic methane release remain unclear. Flood basalt eruptions, dolerite intrusions into coal measures, submarine landslides, tectonic faulting, and bolide impact suggested for episodes of methane release at other times are also plausible for the Permian-Triassic boundary.

Retallack, Gregory J.; Greaver, Tara; Jahren, A. Hope

2007-01-01

250

Evidence for prosauropod dinosaur gastroliths in the Bull Run Formation (Upper Triassic, Norian) of Virginia  

USGS Publications Warehouse

Definitive criteria for distinguishing gastroliths from sedimentary clasts are lacking for many depositional settings, and many reported occurrences of gastroliths either cannot be verified or have been refuted. We discuss four occurrences of gastrolith-like stones (category 6 exoliths) not found within skeletal remains from the Upper Triassic Bull Run Formation of northern Virginia, USA. Despite their lack of obvious skeletal association, the most parsimonious explanation for several characteristics of these stones is their prolonged residence in the gastric mills of large animals. These characteristics include 1) typical gastrolith microscopic surface texture, 2) evidence of pervasive surface wear on many of these stones that has secondarily removed variable amounts of thick weathering rinds typically found on these stones, and 3) a width/length-ratio modal peak for these stones that is more strongly developed than in any population of fluvial or fanglomerate stones of any age found in this region. When taken together, these properties of the stones can be explained most parsimoniously by animal ingestion and gastric-mill abrasion. The size of these stones indicates the animals that swallowed them were large, and the best candidate is a prosauropod dinosaur, possibly an ancestor of the Early Jurassic gastrolith-producing prosauropod Massospondylus or Ammosaurus. Skeletal evidence for Upper Triassic prosauropods is lacking in the Newark Supergroup basins; footprints (Agrestipus hottoni and Eubrontes isp.) from the Bull Run Formation in the Culpeper basin previously ascribed to prosauropods are now known to be underprints (Brachychirotherium parvum) of an aetosaur and underprints (Kayentapus minor) of a ceratosaur. The absence of prosauropod skeletal remains or footprints in all but the uppermost (upper Rhaetian) Triassic rocks of the Newark Supergroup is puzzling because prosauropod remains are abundant elsewhere in the world in Upper Triassic (Carnian, Norian, and lower Rhaetian) continental strata. The apparent scarcity of prosauropods in Upper Triassic strata of the Newark Supergroup is interpreted as an artifact of ecological partitioning, created by the habitat range and dietary preferences of phytosaurs and by the preservational biases at that time within the lithofacies of the Newark Supergroup basins.

Weems, R. E.; Culp, M. J.; Wings, O.

2007-01-01

251

Scale relativity and fractal space-time: Applications to quantum physics, cosmology and chaotic systems  

Microsoft Academic Search

The theory of scale relativity is a new approach to the problem of the origin of fundamental scales and of scaling laws in physics, that consists of generalizing Einstein's principle of relativity (up to now applied to motion laws) to scale transformations. Namely, we redefine space-time resolutions as characterizing the state of scale of the reference system and require that

L. Nottale

1996-01-01

252

Late Permian to Late Triassic palaeomagnetic data from Iran: constraints on the migration of the Iranian block through the Tethyan Ocean and initial destruction of Pangaea  

NASA Astrophysics Data System (ADS)

A palaeomagnetic study of Late Permian to early Jurassic rocks from the Alborz and Sanandaj-Sirjan zones in Iran and a compilation of selected palaeopoles from the Carboniferous to the present provide an updated history of the motion of the Iranian block within the Tethys Ocean. The Iran assemblage, part of Gondwana during the Palaeozoic, rifted away by the end of the Permian. We ascertain the southern-hemisphere palaeoposition of Iran at that time using magnetostratigraphy and show that it was situated close to Arabia, near to its relative position today. A northward transit of this block during the Triassic is shown, with an estimated expansion rate of the Neotethyan ridge of 100-140 km Myr-1. The northward convergence with respect to Eurasia ended during the Ladinian (Middle Triassic), and is marked by a collision in the northern hemisphere with the Turan platform, which was the southern margin of the Eurasian continent at that time. No north-south component of shortening is evidenced north of Iran afterwards. An analysis of the declinations from the Late Permian to the present shows different, large rotations, emphasizing the important tectonic phases suffered since the Triassic. Finally, we propose palaeomagnetic reconstructions of the Tethys area during the Late Permian and the Late Triassic, showing that the Palaeotethys Ocean was narrower than previously thought, and did not widen its gate to the Panthalassa before the Triassic period.

Besse, J.; Torcq, F.; Gallet, Y.; Ricou, L. E.; Krystyn, L.; Saidi, A.

1998-10-01

253

Science at the Time-scale of the Electron  

NASA Astrophysics Data System (ADS)

Replace this text with your abstract Ever since the invention of the laser 50 years ago and its application in nonlinear optics, scientists have been striving to extend coherent laser beams into the x-ray region of the spectrum. Very recently however, the prospects for tabletop coherent sources, with attosecond pulse durations, at very short wavelengths even in the hard x-ray region of the spectrum at wavelengths < 1nm, have brightened considerably. These advances are possible by taking nonlinear optics techniques to an extreme, and are the direct result of a new ability to manipulate electrons on the fastest, attosecond, time-scales of our natural world. My talk will discuss new experimental data that demonstrates high harmonic generation of laser-like, fully coherent, 10 attosecond duration, soft x-ray beams at photon energies around 0.5keV. Several applications will also be discussed, including making a movie of how electron orbitals in a molecule change shape as a molecule breaks apart, following how fast a magnetic material can flip orientation, understanding how fast heat flows in a nanocircuit, or building a microscope without lenses. [4pt] [1] T. Popmintchev et al., ``Phase matched upconversion of coherent ultrafast laser light into the soft and hard x-ray regions of the spectrum'', PNAS 106, 10516 (2009). [0pt] [2] C. LaOVorakiat et al., ``Ultrafast Soft X-Ray Magneto-Optics at the M-edge Using a Tabletop High-Harmonic Source'', Physical Review Letters 103, 257402 (2009). [0pt] [3] M. Siemens et al. ``Measurement of quasi-ballistic heat transport across nanoscale interfaces using ultrafast coherent soft x-ray beams'', Nature Materials 9, 26 (2010). [0pt] [4] K. Raines et al., ``Three-dimensional structure determination from a single view,'' Nature 463, 214 (2010). [0pt] [5] W. Li et al., ``Time-resolved Probing of Dynamics in Polyatomic Molecules using High Harmonic Generation'', Science 322, 1207 (2008).

Murnane, Margaret

2010-03-01

254

Super ENSO and global climate oscillations at millennial time scales.  

PubMed

The late Pleistocene history of seawater temperature and salinity variability in the western tropical Pacific warm pool is reconstructed from oxygen isotope (delta18O) and magnesium/calcium composition of planktonic foraminifera. Differentiating the calcite delta18O record into components of temperature and local water delta18O reveals a dominant salinity signal that varied in accord with Dansgaard/Oeschger cycles over Greenland. Salinities were higher at times of high-latitude cooling and were lower during interstadials. The pattern and magnitude of the salinity variations imply shifts in the tropical Pacific ocean/atmosphere system analogous to modern El Niño-Southern Oscillation (ENSO). El Niño conditions correlate with stadials at high latitudes, whereas La Niña conditions correlate with interstadials. Millennial-scale shifts in atmospheric convection away from the western tropical Pacific may explain many paleo-observations, including lower atmospheric CO2, N2O, and CH4 during stadials and patterns of extratropical ocean variability that have tropical source functions that are negatively correlated with El Niño. PMID:12114618

Stott, Lowell; Poulsen, Christopher; Lund, Steve; Thunell, Robert

2002-07-12

255

Detonation initiation on the microsecond time scale: DDTs  

SciTech Connect

Spatially resolved, thermal power deposition of limited duration into a finite volume of reactive gas is the initiator for a deflagration-to-detonation transition (DDT) on the microsecond time scale. The reactive Euler equations with one-step Arrhenius kinetics are used to derive novel formulas for velocity and temperature variation that describe the physical phenomena characteristic of DDTs. A nonlinear transformation of the variables is shown to yield a canonical equation system, independent of the activation energy. Numerical solutions of the reactive Euler equations are used to describe the detailed sequence of reactive gas dynamic processes leading to an overdriven planar detonation far from the power deposition location. Results are presented for deposition into a region isolated from the planar boundary of the reactive gas as well as for that adjacent to the boundary. The role of compressions and shocks reflected from the boundary into the partially reacted hot gas is described. The quantitative dependences of DDT evolution on the magnitude of thermal power deposition and activation energy are identified.

Kuehn, Jeffery A [ORNL; Kassoy, Dr. David R [University of Colorado; Nabity, Mr. Matthew W. [University of Colorado; Clarke, Dr. John F. [Cranfield University

2006-01-01

256

Detonation initiation on the microsecond time scale: DDTs  

SciTech Connect

Spatially resolved, thermal power deposition of limited duration into a finite volume of reactive gas is the initiator for a deflagration-to-detonation transition (DDT) on the microsecond time scale. The reactive Euler equations with one-step Arrhenius kinetics are used to derive novel formulas for velocity and temperature variation that describe the physical phenomena characteristic of DDTs. A transformation of the variables is shown to yield a canonical equation system, independent of the activation energy. Numerical solutions of the reactive Euler equations are used to describe the detailed sequence of reactive gasdynamic processes leading to an overdriven planar detonation far from the power deposition location. Results are presented for deposition into a region isolated from the planar boundary of the reactive gas as well as for that adjacent to the boundary. The role of compressions and shocks reflected from the boundary into the partially reacted hot gas is described. The quantitative dependences of DDT evolution on the magnitude of thermal power deposition and activation energy are identified.

Kassoy, Dr. David R [University of Colorado; Kuehn, Jeffery A [ORNL; Nabity, Mr. Matthew W. [University of Colorado; Clarke, Dr. John F. [Cranfield University

2008-01-01

257

Evaluating the uncertainty of predicting future climate time series at the hourly time scale  

NASA Astrophysics Data System (ADS)

A stochastic downscaling methodology is developed to generate hourly, point-scale time series for several meteorological variables, such as precipitation, cloud cover, shortwave radiation, air temperature, relative humidity, wind speed, and atmospheric pressure. The methodology uses multi-model General Circulation Model (GCM) realizations and an hourly weather generator, AWE-GEN. Probabilistic descriptions of factors of change (a measure of climate change with respect to historic conditions) are computed for several climate statistics and different aggregation times using a Bayesian approach that weights the individual GCM contributions. The Monte Carlo method is applied to sample the factors of change from their respective distributions thereby permitting the generation of time series in an ensemble fashion, which reflects the uncertainty of climate projections of future as well as the uncertainty of the downscaling procedure. Applications of the methodology and probabilistic expressions of certainty in reproducing future climates for the periods, 2000 - 2009, 2046 - 2065 and 2081 - 2100, using the 1962 - 1992 period as the baseline, are discussed for the location of Firenze (Italy). The climate predictions for the period of 2000 - 2009 are tested against observations permitting to assess the reliability and uncertainties of the methodology in reproducing statistics of meteorological variables at different time scales.

Caporali, E.; Fatichi, S.; Ivanov, V. Y.

2011-12-01

258

Evidence for Triassic salt domes in the Tunisian Atlas from gravity and geological data  

Microsoft Academic Search

Detailed gravity data were analyzed to constrain two controversial geological models of evaporitic structures within the Triassic diapiric zone (Triassic massifs of Jebel Debadib and Ben Gasseur) of the northern Tunisian Atlas. Based on surface observations, two geological models have been used to explain the origin of the Triassic evaporitic bodies: (1) salt dome\\/diapiric structure or (2) a “salt glacier”.

Chokri Jallouli; Mongi Chikhaoui; Ahmed Braham; Mohamed Moncef Turki; Kevin Mickus; Ramdhane Benassi

2005-01-01

259

A Late Triassic traversodont cynodont from the Newark Supergroup of North Carolina  

Microsoft Academic Search

A new traversodont cynodont, Plinthogomphodon herpetairus, is described on the basis of a partial snout from Late Triassic strata of the Newark Supergroup exposed in the Deep River basin (Durham sub-basin) of North Carolina. In the structure of its upper postcanine teeth, Plinthogomphodon most closely resembles Boreogomphodon from the Upper Triassic (Carnian) of Virginia and Luangwa from the Middle Triassic

Hans-Dieter Sues; Paul E. Olsen; Joseph G. Carter

1999-01-01

260

Evidence for recurrent Early Triassic massive volcanism from quantitative interpretation of carbon isotope fluctuations  

Microsoft Academic Search

Carbon cycle disturbance associated with mass extinction at the end of the Permian Period continued through the Early Triassic, an interval of approximately 5 million years. Coincidence of carbon cycle stabilization with accelerated Middle Triassic biotic recovery suggests a link between carbon cycling and biodiversity, but the cause of Early Triassic carbon isotope excursions remains poorly understood. Previous modeling studies

Jonathan L. Payne; Lee R. Kump

2007-01-01

261

Evidence for recurrent Early Triassic massive volcanism from quantitative interpretation of carbon isotope fluctuations  

Microsoft Academic Search

Carbon cycle disturbance associated with mass extinction at the end of the Permian Period continued through the Early Triassic, an interval of approximately 5 million years. Coincidence of carbon cycle stabilization with accelerated Middle Triassic biotic recovery suggests a link between carbon cycling and biodiversity, but the cause of Early Triassic carbon isotope excursions remains poorly understood. Previous modeling studies have

Jonathan L. Payne; Lee R. Kump

2007-01-01

262

Multiple dolomitization events in Triassic latemar buildup, the dolomites, northern Italy  

SciTech Connect

Partially dolomitized grainstones of the Middle Triassic Latemar buildup (Dolomites, northern Italy) exhibit a range of texturally distinct dolomite types. Petrographic and field observations of spatial associations and cross-cutting relationships among dolomites allow unravelling of the paragenesis of dolomitization events. Three generations of dolomite are preserved in the Latemar. Microdolomite, the earliest generation, occurs as replacement of allochems and as cement in thin (5-15 cm) exposure caps of meter-scale subtidal cycles. These dolomite crusts are texturally and chemically analogous to the Holocene supratidal crusts of Florida and the Bahamas. Saddle dolomite cements, the second generation, fill or line pores and fractures through the platform. The final generation is massive replacement of limestone by coarse, crystalline dolomite, which occupies a 2-3 km/sup 3/ mushroom-shaped zone in the center of the buildup and includes a wide array of fabrics. Here, subtidal limestones are altered to porous sucrosic dolomite, while microdolomite caps are altered to dense dolomite mosaics. Saddle dolomite cements remain as relics surrounded by replacement rhombs. Two important conclusions are (1) early dolomite is preserved as poorly ordered microdolomite (unless overprinted by a later dolomitization event) and accounts for an insignificant volume of the Latemar dolomite, and (2) saddle dolomite cements, often regarded as late-stage burial, occur before massive replacement. Standard textural classification of Latemar dolomites hindered the resolution of the timing of dolomitization events. Instead, paragenetic relationships provided a powerful tool for grouping dolomites into generations representing specific diagenetic events in specific dolomitizing environments.

Wilson, E.N.

1988-02-01

263

Probing time-dependent molecular dipoles on the attosecond time scale.  

PubMed

Photoinduced molecular processes start with the interaction of the instantaneous electric field of the incident light with the electronic degrees of freedom. This early attosecond electronic motion impacts the fate of the photoinduced reactions. We report the first observation of attosecond time scale electron dynamics in a series of small- and medium-sized neutral molecules (N(2), CO(2), and C(2)H(4)), monitoring time-dependent variations of the parent molecular ion yield in the ionization by an attosecond pulse, and thereby probing the time-dependent dipole induced by a moderately strong near-infrared laser field. This approach can be generalized to other molecular species and may be regarded as a first example of molecular attosecond Stark spectroscopy. PMID:23909314

Neidel, Ch; Klei, J; Yang, C-H; Rouzée, A; Vrakking, M J J; Klünder, K; Miranda, M; Arnold, C L; Fordell, T; L'Huillier, A; Gisselbrecht, M; Johnsson, P; Dinh, M P; Suraud, E; Reinhard, P-G; Despré, V; Marques, M A L; Lépine, F

2013-07-18

264

Two-phase micro- and macro-time scales in particle-laden turbulent channel flows  

NASA Astrophysics Data System (ADS)

The micro- and macro-time scales in two-phase turbulent channel flows are investigated using the direct numerical simulation and the Lagrangian particle trajectory methods for the fluid- and the particle-phases, respectively. Lagrangian and Eulerian time scales of both phases are calculated using velocity correlation functions. Due to flow anisotropy, micro-time scales are not the same with the theoretical estimations in large Reynolds number (isotropic) turbulence. Lagrangian macro-time scales of particle-phase and of fluid-phase seen by particles are both dependent on particle Stokes number. The fluid-phase Lagrangian integral time scales increase with distance from the wall, longer than those time scales seen by particles. The Eulerian integral macro-time scales increase in near-wall regions but decrease in out-layer regions. The moving Eulerian time scales are also investigated and compared with Lagrangian integral time scales, and in good agreement with previous measurements and numerical predictions. For the fluid particles the micro Eulerian time scales are longer than the Lagrangian ones in the near wall regions, while away from the walls the micro Lagrangian time scales are longer. The Lagrangian integral time scales are longer than the Eulerian ones. The results are useful for further understanding two-phase flow physics and especially for constructing accurate prediction models of inertial particle dispersion.

Wang, Bing; Manhart, Michael

2012-06-01

265

Controls on the Time Scale of Carbonate Neutralization of Carbon Dioxide Released to the Atmosphere  

Microsoft Academic Search

Once released to the atmosphere, carbon dioxide is removed on a range of time scales. On the time scale of years to centuries, carbon dioxide removal from the atmosphere is dominated by transport processes within the ocean. On the time scale of hundreds of thousands of years, carbon dioxide removal from the atmosphere is dominated by processes related to the

K. Caldeira; L. Cao

2007-01-01

266

Diffusion-limited adsorption to a spherical geometry: The impact of curvature and competitive time scales  

Microsoft Academic Search

Although the time scale governing diffusion-limited transport of soluble species from solution onto a planar interface is well understood, the time scale governing transport onto a spherical interface is not. The time scales that have been proposed in the literature for spherical interfaces do not capture the correct asymptotic behavior for increasing bubble radius and do not capture previously reported

Nicolas J. Alvarez; Lynn M. Walker; Shelley L. Anna

2010-01-01

267

Clockwise rotation of the Korean Peninsula with respect to the North China Block inferred from an improved Early Triassic palaeomagnetic pole for the Ryeongnam Block  

NASA Astrophysics Data System (ADS)

In order to detect a possible clockwise rotation of the Korean Peninsula with respect to the North China Block, Early Triassic rocks in the Ryeongnam Block, Korean Peninsula have been restudied. Sandstones in the Nogam Formation were collected at four sites for palaeomagnetic study. A high-temperature magnetization component with an unblocking temperature of 690°C is isolated from all sites and yields a positive fold test at the 95 per cent confidence level. This high-temperature component is interpreted to be of primary origin because folding is Middle Triassic in age. The primary directions together with previously reported ones give a new Early Triassic mean direction (D=347.4°, I=23.8°, ?95=5.1°) and corresponding palaeomagnetic pole (62.6°N, 336.1°E, A95=4.2°) for the Ryeongnam Block. This improved Early Triassic pole for the Ryeongnam Block is located to the west of the coeval poles for the North China Block. It is therefore concluded that the Ryeongnam Block underwent clockwise rotation of 10°-15° with respect to the North China Block. Because the amount of rotation observed in the present study is comparable with rotations observed in Cretaceous results from the Ryeongnam Block and in the Triassic-Cretaceous results from other blocks in the Korean Peninsula, the whole of the Korean Peninsula appears to have been subjected to clockwise rotation in Tertiary times.

Uno, Koji

2000-12-01

268

Diffusion-limited adsorption to a spherical geometry: The impact of curvature and competitive time scales  

NASA Astrophysics Data System (ADS)

Although the time scale governing diffusion-limited transport of soluble species from solution onto a planar interface is well understood, the time scale governing transport onto a spherical interface is not. The time scales that have been proposed in the literature for spherical interfaces do not capture the correct asymptotic behavior for increasing bubble radius and do not capture previously reported experimental observations of the effect of concentration. This paper develops a diffusion-limited time scale that is dependent on an intrinsic length scale termed the spherical depletion depth. The time scale is determined by considering a specific example of diffusion-limited transport of surfactant species to a water-air interface and is verified using numerical simulations and experiments. This newly derived diffusion time scale will have a significant impact on our understanding of fundamental phenomena at spherical fluid-fluid and fluid-solid interfaces, especially those involving micrometer and nanometer length scales.

Alvarez, Nicolas J.; Walker, Lynn M.; Anna, Shelley L.

2010-07-01

269

New Paleoenvironmental and Biotic Records from the Triassic-Jurassic Boundary Interval of the Algarve Basin, Portugal  

NASA Astrophysics Data System (ADS)

Studies of carbonate, bulk organic, and compound-specific stable isotopes of carbon have shown that the Triassic-Jurassic boundary interval (including the end-Triassic mass extinction) displays major, global perturbations to the carbon cycle. These records are instrumental not only in reconstructing environmental change, as they are thought to reflect ecosystem instability and changing atmospheric gas inventories, but, due to their global nature, can be useful tools for stratigraphic correlation. The Algarve Basin, a deformed, extensional basin in the south of Portugal, has potential for yielding insight into the dramatic paleoenvironmental and faunal changes that occurred during the latest Triassic through earliest Jurassic. During this time interval, the basin records an evolution from continental to marginal marine sediments that are interbedded with radioisotopically dated Central Atlantic Magmatic Province (CAMP) basalts, thought to be a major causative agent in the end-Triassic mass extinction. Recent field excavations in the Algarve Basin have documented terrestrial vertebrate remains at multiple horizons, including a rich bone bed densely packed with well-preserved remains of large stereospondyl temnospondyls (skull length up to ~1 meter) positioned close to the Triassic-Jurassic boundary. These stereospondyls may represent some of the latest surviving members of their groups in Europe, and occur in a time interval in which stereospondyl material is scarce and represented primarily by isolated and fragmentary material. Unfortunately, the paleoenvironmental and chronologic framework of the Algarve Basin is not well constrained, despite its importance as a critical record of this time in Earth history. We present a preliminary bulk organic carbon isotope record of early Mesozoic rift-basin sediments from the Algarve Basin. This record exhibits significant variability, but appears to record a trend towards more negative values at the top of the section, though this needs better constraint with further sampling. Although the potential for changes in the source of organic material can be expected to have an effect on the overall signal, the presence of depleted ?13C values in proximity to CAMP basalts relative to stratigraphically lower sections points to the potential for identifying key negative excursions associated with Triassic-Jurassic boundary events in the Algarve Basin.

Kasprak, A. H.; Whiteside, J. H.; Lopes, F. M.; Brusatte, S. L.; Butler, R. J.; Mateus, O.

2010-12-01

270

Palaeontology: A polydactylous amniote from the Triassic period  

Microsoft Academic Search

The earliest four-limbed vertebrates, or tetrapods, lived between 370 million and 354 million years ago, during the Late Devonian period, and typically had more than five digits (polydactyly). We have discovered that a preaxial form of polydactyly, in which extra digits are positioned anterior to the first digit, has unexpectedly re-emerged in a marine reptile from the Early Triassic period

Xiao-Chun Wu; Zhan Li; Bao-Chun Zhou; Zhi-Ming Dong

2003-01-01

271

A reinterpretation of the Upper Triassic ichthyosaur Shonisaurus  

Microsoft Academic Search

Shonisaurus, from the Upper Triassic (Carnian) of Nevada, is represented by some 40 individuals. However, many comprise only a few elements, and not one of the skeletons is complete. Furthermore, preservation is often poor, so information is limited. Reaching lengths of up to 15 m, possibly slightly more, Shonisaurus was about the size of a Gray Whale. The only other

Chris Mcgowan; Ryosuke Motani

1999-01-01

272

A new mixosaurid ichthyosaur from the Middle Triassic of China  

Microsoft Academic Search

We describe the new ichthyosaur taxon Mixosaurus panxianensis, sp. nov., from the Middle Triassic of Guizhou Province, China. Diagnostic characters of the new species include a short posteroventral jugal process and the absence of external contact between jugal and quadratojugal. The morphologic description of the type specimens amends the knowledge of the postorbital region and the postcranium of the Mixosauridae.

Da-yong Jiang; Lars Schmitz; Wei-Cheng Hao; Yuan-Lin Sun

2006-01-01

273

Depositional environments of the Triassic Gosford formation, Sydney basin  

Microsoft Academic Search

A matrix of the primary sedimentary features of modern depositional environments has been used as a key for the interpretation of the environments of deposition of the Gosford Formation, which comprises the uppermost 212 m of the Triassic Narrabeen Group on the Central Coast of New South Wales.The formation is interpreted as a fluvial deposit in in?channel and floodplain environments.

K. L. McDonnell

1974-01-01

274

A new chronology for the end-Triassic mass extinction  

Microsoft Academic Search

The transition from the Triassic to Jurassic Period, initiating the ‘Age of the dinosaurs’, approximately 200Ma, is marked by a profound mass extinction with more than 50% genus loss in both marine and continental realms. This event closely coincides with a period of extensive volcanism in the Central Atlantic Magmatic Province (CAMP) associated with the initial break-up of Pangaea but

M. H. L. Deenen; M. Ruhl; N. R. Bonis; W. Krijgsman; W. M. Kuerschner; M. Reitsma; M. J. van Bergen

2010-01-01

275

Late Triassic charcoal from Petrified Forest National Park, Arizona, USA  

Microsoft Academic Search

Fossil charcoal has been found in the Late Triassic Chinle Formation in Petrified Forest National Park, a location that is world famous for its silicified tree trunks. The material consists of charcoalified secondary wood, and has sufficiently well preserved plant anatomy to show it may be described as ‘araucarian type’, although it does display some minor differences from the anatomies

Timothy P Jones; Sidney Ash; Isabel Figueiral

2002-01-01

276

Triassic and Jurassic rocks at Currie, Nevada Preliminary paleontologic evidence  

SciTech Connect

A sequence of continental rocks overlies the Lower Triassic Thaynes Formation in a poorly exposed syncline near Currie in northeastern NV. The authors recognize four lithostratigraphic units above the Thaynes near Currie and provide new paleontologic data. In ascending order, unit 1 (120 ft) consists of reddish-brown, very fine grained sandstone. Unit 2 (50 ft) consists of light-gray, trough cross-stratified, coarse-grained, conglomeratic sandstone. Unit 3 (at least 500 ft) consists of green, red, and brown sandstone and mudstone. Unit 4 occurs as isolated outcrops of reddish-orange, fine- to medium-grained sandstone. New fossil evidence, while not definitive, constrain the age of this sequence. Plant megafossils in unit 1 include (1) a specimen with narrow ovate leaves, possibly from an early Mesozoic conifer and (2) abundant fragments of probable Neocalamites. The presence of these fossils and the absence of any angiosperm leaves or wood fragments suggest an early Mesozoic age. Ostracodes in unit 3 are exclusively Darwinula sp., and their association with conchostracans in the absence of younger ostracodes suggests a Triassic age. Finally, two small outcrops, previously mapped as Triassic/Jurassic, contain the gastropods Pilidae indet. and Lymnaea sp., which resemble Late Cretaceous to Paleocene faunas. The sequence is similar to the nearest Lower Mesozoic section on the Colorado Plateau at Cove Fort, Utah, 165 miles to the southeast. The authors' new evidence supports the longstanding correlation of units 1--4 with the Lower Triassic Moenkopi Formation (part), the Shinarump and Petrified Forest Members of the Upper Triassic Chinle Formation, and the Lower Jurassic Navajo Sandstone of the Plateau. These rocks at Currie demonstrate that the Early Mesozoic depositional systems of the Colorado Plateau extended at least this far west and provide constraints on Early Mesozoic tectonism in the eastern Great Basin.

Johnson, E.A.; Dubiel, R.F.; Brouwers, E.M. (Geological Survey, Denver, CO (United States)); Litwin, R.J. (Geological Survey, Reston, VA (United States)); Ash, S.R. (Weber State Coll., Ogden, UT (United States)); Good, S.C. (State Univ. Coll., Cortland, NY (United States))

1993-04-01

277

Oil and gas potential of the Triassic in west Siberia  

SciTech Connect

Permian-Triassic rocks are widely spread within the West Siberian basin, and they include volcanics, volcanoclastics, and clastics. Their thickness varies from tens of meters of 3000 m. Recently, three commercial oil pools have been discovered in Triassic effusive-sedimentary rocks. These discoveries, together with other geological and geochemical data, identify the Triassic complex as a major play. Oil-bearing intervals have been found in three different types of sequences; a fourth also may be prospective. The first type is represented by lacustrine-terrigenous sediments, which comprise oil-saturated sandstones interbedded with basalts (the Turin series). Oil influxes were obtained in the Yakhlinskaya and Triyurtin-skaya structures in the Shaim region. The second type is distinguished from the first by the presence of coal-bearing intervals in the upper part. Oil was produced in the Yerofeyev area of the Chelyabinsk garben. The third type differs from the other two by the presence of potassic rhyolites and dacites. Their age is not precisely dated, and supposedly they are of Permian age. The largest oil influxes have been obtained from fractured and eroded rocks of this type in the Rogozhnikovskaya and other places in the Krasnoleninsk region. Rhyodacites often underlie Turin basalts, but locally they occur in the upper part of the series. Triassic and Permian-Trissic rocks of the three types are overlain by Jurassic and Cretaceous rocks with a large break. The fourth type of section is completely terrigenous (Tampei series). It is developed in the northern part of west Siberia. Here Triassic sediments are overlain by the Jurassic complex without a break. According to well-log data, productive horizons occur at Urengoy and Beregovaya (in the Urengoy region).

Bochkarev, V.S.; Kulakhmetov, N.KH.; Nesterov, I.I. (ZapSibNIGNI, Tyumen (Russian Federation))

1993-09-01

278

Spatial scaling of optical fluctuations during substorm-time aurora  

NASA Astrophysics Data System (ADS)

A study of statistical features of auroras during substorm activity is presented, emphasizing characteristics which are commonly applied to turbulent flows. Data from all-sky television (TV) observations from the Barentsburg observatory (Svalbard) have been used. Features of the probability density function (PDF) of auroral fluctuations have been examined at different spatial scales. We find that the observed PDFs generally have a non-Gaussian, heavy-tailed shape. The generalized structure function (GSF) for the auroral luminosity fluctuations has been analyzed to determine the scaling properties of the higher (up to 6) order moments, and the evolution of the scaling indices during the actual substorm event has been determined. The scaling features obtained can be interpreted as signatures of turbulent motion of the magnetosphere-ionosphere plasma. Relations to previously obtained results of avalanche analysis of the same event, as well as possible implications for the validity of self-organized criticality models and turbulence models of the substorm activity, are discussed.

Kozelov, B. V.; Rypdal, K.

2007-05-01

279

Sedimentary evolution of the continental Early-Middle Triassic Cañizar Formation (Central Spain): Implications for life recovery after the Permian-Triassic crisis  

NASA Astrophysics Data System (ADS)

The Permian-Triassic transition (P-T) was marked by important geochemical perturbations and the largest known life crisis. Consequences of this event, as oxygen-depleted conditions and the unusual behavior of the carbon cycle, were prolonged during the Early Triassic interval delaying the recovery of life in both terrestrial and marine ecosystems. Studies on Lower Triassic sediments of continental origin, as in the case of Western Europe, are especially problematic due to the scarcity of fossils and absence of precise dating. The Cañizar Fm. is an Early-Middle Triassic unit of continental origin of the SE Iberian Ranges, E Spain. A detailed sedimentary study of this unit allows a shedding of light on some unresolved problems of the continental deposits of this age.The top of this unit is dated as early Anisian by means of a pollen association, while the age of its base is here estimated as late Smithian or Smithian-Spathian transition. Different facies associations and architectural elements have been defined in this unit. In the western and central parts of the basin, this unit shows sedimentary characteristics of fluvial deposits with locally intercalated aeolian sediments, while in the eastern part there is an alternation of both aeolian and fluvial deposits. Sedimentary structures also indicate changes in the climate conditions, mainly from arid to semiarid. Two marked arid periods when well-preserved aeolian sediments developed during early-middle Spathian and Spathian-Anisian transition. They alternated with two semiarid but more humid periods during the late Spathian and early Anisian. These conditions basically correspond with the general arid and very arid conditions described for central-western European plate during the same period of time. The Ateca-Montalbán High, in the northern border of the study basin, must have represented an important topographic barrier in the western Tethys separating aeolian dominated areas to the N and NE from fluvial dominated areas to the south.The Cañizar Fm. has been subdivided into six members (A-F) separated by seven (1-7) major bounding surfaces (MBS). These surfaces are well recognized laterally over hundred of km and they represent 104-105 My. MBS-5 is considered to be of late Spathian age and it is a clear indication of tectonic activity, represented by a mild unconformity. This event represents a change in the sedimentary characteristics (reactivation) of the unit and from here to the top of the unit are found the first signals of biotic recovery, represented by tetrapod footprints, plants, roots and bioturbation. All of these characteristics and the estimated age represented by the MBS-5 event permit this surface to be related to the coeval Hardegsen unconformity of Central-Western Europe. These first signals of biotic recovery can thus be related to an increased oxygen supply due to the new created paleogeographical corridors in the context of this tectonic activity. These biotic signals occurred 5 My after the Permian-Triassic limit crisis; a similar delay as occurred in other coeval and neighboring basins.

López-Gómez, José; Galán-Abellán, Belén; de La Horra, Raúl; Barrenechea, José F.; Arche, Alfredo; Bourquin, Sylvie; Marzo, Mariano; Durand, Marc

2012-04-01

280

What time is it? Choice of time origin and scale in extended proportional hazards models.  

PubMed

The analysis of telemetry data offers many unique challenges due to both the observation process and the complexity of the underlying system (e.g., risk of mortality may be influenced by both age and a wide range of environmental variables). Although semi-parametric proportional hazards (SPPH) models have been proposed for analyzing ecological data, recent applications have failed to address the importance of choosing an appropriate time origin and scale for analysis. We compared models fit to a long-term deer (Odocoileus spp.) survival data set using three alternative survival timescales: age, time since start of study, and time since 6 June (with a seasonally recurrent timescale). Temporal variability in risk resulted from multiple sources (e.g., changes in hunting pressure, winter severity), and the risk of mortality varied nonlinearly with age (highest risk for young and older individuals). Age-varying hazards were represented well using regression splines, but temporal variability was more difficult to model using parametric assumptions. Annual survival estimates using the three timescales differed considerably. The model using a study-based timescale most closely tracked temporal patterns in risk. Given the difficulties in modeling temporal variability using parametric assumptions, we recommend this approach over an age-based or recurrent timescale when using SPPH models to evaluate the impact of large (naturally occurring or experimental) disturbances or to estimate annual age-specific survival rates. Lastly, we discuss the strengths and limitations of SPPH models relative to fully parametric approaches. PMID:19569383

Fieberg, John; DelGiudice, Glenn D

2009-06-01

281

The Triassic dicynodont Kombuisia (Synapsida, Anomodontia) from Antarctica, a refuge from the terrestrial Permian-Triassic mass extinction.  

PubMed

Fossils from the central Transantarctic Mountains in Antarctica are referred to a new species of the Triassic genus Kombuisia, one of four dicynodont lineages known to survive the end-Permian mass extinction. The specimens show a unique combination of characters only present in this genus, but the new species can be distinguished from the type species of the genus, Kombuisia frerensis, by the presence of a reduced but slit-like pineal foramen and the lack of contact between the postorbitals. Although incomplete, the Antarctic specimens are significant because Kombuisia was previously known only from the South African Karoo Basin and the new specimens extend the taxon's biogeographic range to a wider portion of southern Pangaea. In addition, the new finds extend the known stratigraphic range of Kombuisia from the Middle Triassic subzone B of the Cynognathus Assemblage Zone into rocks that are equivalent in age to the Lower Triassic Lystrosaurus Assemblage Zone, shortening the proposed ghost lineage of this taxon. Most importantly, the occurrence of Kombuisia and Lystrosaurus mccaigi in the Lower Triassic of Antarctica suggests that this area served as a refuge from some of the effects of the end-Permian extinction. The composition of the lower Fremouw Formation fauna implies a community structure similar to that of the ecologically anomalous Lystrosaurus Assemblage Zone of South Africa, providing additional evidence for widespread ecological disturbance in the extinction's aftermath. PMID:19956920

Fröbisch, Jörg; Angielczyk, Kenneth D; Sidor, Christian A

2009-12-03

282

Permo-Triassic rifting in the southern Appalachians: New seismic evidence from the Durham basin, North Carolina  

Microsoft Academic Search

The Permo-Triassic unconformity is perhaps the most important hiatus in the Appalachian-Variscan orogen, embracing both the terminal phase of plate consolidation and the onset of plate break-up that culminated in the opening of the central Atlantic Ocean. Yet events documenting this critical tectonic reversal have been obscured or erased through erosion, non-deposition and\\/or deep burial. Now for the first time

W. Manspeizer; A. E. Gates

1994-01-01

283

The carbon and sulfur cycles and atmospheric oxygen from middle Permian to middle Triassic  

NASA Astrophysics Data System (ADS)

The results of a theoretical isotope mass balance model are presented for the time dependence of burial and weathering-plus-degassing fluxes within the combined long-term carbon and sulfur cycles. Averaged data for oceanic ? 13C and ? 34S were entered for every million years from 270 to 240 Ma (middle Permian to middle Triassic) to study general trends across the Permian-Triassic boundary. Results show a drop in the rate of global organic matter burial during the late Permian and a predominance of low values during the early-to-middle Triassic. This overall decrease with time is ascribed mainly to epochs of conversion of high biomass forests to low biomass herbaceous vegetation resulting in a decrease in the production of terrestrially derived organic debris. Additional contributions to lessened terrestrial carbon burial were increased aridity and a drop in sea level during the late Permian which led to smaller areas of low-lying coastal wetlands suitable for coal and peat deposition. Mirroring the drop in organic matter deposition was an increase in the burial of sedimentary pyrite, and a dramatic increase in the calculated global mean ratio of pyrite-S to organic-C. High S/C values resulted from an increase of deposition in marine euxinic basins combined with a decrease in the burial of low-pyrite associated terrestrial organic matter. The prediction of increased oceanic anoxia during the late Permian and early Triassic agrees with independent studies of the composition of sedimentary rocks. Weathering plus burial fluxes for organic carbon and pyrite sulfur were used to calculate changes in atmospheric oxygen. The striking result is a continuous drop in O 2 concentration from ˜30% to ˜13% over a twenty million year period. This drop was brought about mainly by a decrease in the burial of terrestrially derived organic matter. but with a possible contribution from the weathering of older organic matter on land. It must have exerted a considerable influence on animal evolution because of the role of O 2 in respiration. Some examples are the extinction of many vertebrates, loss of giant insects and amphibians, and the restriction of animals to low elevations. It is concluded that the extinction of plants may have contributed to the extinction of animals.

Berner, Robert A.

2005-07-01

284

Sponges from the Middle Triassic reef limestone of the Aggtelek Karst (NE Hungary)  

NASA Astrophysics Data System (ADS)

The hypercalcified sponge fauna of the Middle Triassic (Anisian-Ladinian) reef limestone exposed between Aggtelek-Jósvaf?-Égerszög (northern Hungary) is described. Almost all the identified species are chambered sponges ("sphinctozoa"). Only two fragments of a not determinable species of non-chambered species ("inozoa") were identified. Hexactinellid sponges are not found. The majority of the Middle Anisian "sphinctozoans" are absolutely different genera, not known from the Permian reefs. The sponge fauna of the Triassic pioneer reefs in the Aggtelek Karst are distinctly small-scaled occurring in "Tubiphytes"-dominated carbonates. The following taxa are described: Amblysiphonella sp., Celyphia zoldana Ott, Pisa & Farabegoli, Colospongia catenulata catenulata Ott, C. catenulata macrocatenulata Scholz, Follicatena cautica Ott, Kovacsia baloghi (Kovács), Solenolmia manon manon (Münster), S. radiata Senowbari-Daryan & Riedel, Olangocoelia otti Bechstädt & Brandner, Thaumastocoelia dolomitica Senowbari-Daryan, Zühlke, Bechstädt & Flügel, Thaumastocoelia cf., Th. cassiana Steinmann.

Senowbari-Daryan, Baba; Kovács, Sándor; Velledits, Felicitász

2011-10-01

285

Scaling up Dynamic Time Warping to Massive Dataset  

Microsoft Academic Search

There has been much recent interest in adapting da ta mining algorithms to time series databases. Many of these algorithms nee d to compare time series. Typically some variation or extension of Euclidean distance is used. However, as we demonstrate in this paper, Euclidean distance can b e an extremely brittle distance measure. Dynamic time warping (DTW) has been suggested

Eamonn J. Keogh; Michael J. Pazzani

1999-01-01

286

Permian Triassic palynofloral transition in Chintalapudi area, Godavari Graben, Andhra Pradesh, India  

NASA Astrophysics Data System (ADS)

The entire 606 m-thick sedimentary sequence in borecore MCP-7 from Chintalapudi area, Chintalapudi sub-basin has been lithologically designated as Kamthi Formation. However, the palynological investigation revealed five distinct palynoassemblages, which essentially fall under two groups, one group (Palynoassemblage-I, II and III) having dominance of striate disaccates along with presence of some stratigraphically significant taxa, belongs to Late Permian (Raniganj) palynoflora, while the other group (Palynoassemblages IV and V) shows sharp decline in percentage of characteristic taxa of first group, i.e., striate disaccates, and consequent rise or dominance of taeniate and cingulate cavate spores, belongs to Early Triassic (Panchet) palynoflora. Palynoassemblage-I, II and III (Group I) are characterized by dominance of striate disaccates chiefly, Striatopodocarpites spp. and Faunipollenites spp. along with presence of rare but stratigraphically significant taxa, viz., Gondisporites raniganjensis, Falcisporites nuthaliensis, Klausipollenites schaubergeri, Chordasporites sp., Striomonosaccites, ovatus, Crescentipollenites multistriatus, Verticipollenites debiles, Strotersporites crassiletus, Guttulapollenites hannonicus, G. gondwanensis, Hamiapollenites insolitus, Corisaccites alutus, Lunatisporites ovatus, Weylandites spp. and Vitreisporites pallidus. Palynoassemblage-I is distinguished by significant presence of Densipollenites spp. while Palynoassemblage-II shows significant presence of Crescentipollenites spp. and Palynoassemblage-III differs from the above two assemblages in having significant presence of Guttulapollenites hannonicus. Palynoassemblage-IV (Group II) is characterized by high percentage of taeniate disaccates chiefly Lunatisporites spp., while Palynoassemblage-V (Group II) is characterized by cingulate-cavate trilete spores chiefly, Lundbladispora spp. and Densoisporites spp. Striate disaccates show a sharp decline in these two assemblages. In Chintalapudi area Late Permian and Early Triassic palynoflora has been recorded for the first time indicating existence of Raniganj and Panchet sediments as well. The study further supports the earlier studies of Jha and Srivastava (1996) that Kamthi Formation represents Early Triassic (=Panchet Formation) overlying Raniganj equivalent sediments with a gradational contact.

Jha, Neerja; Chary, M. Basava; Aggarwal, Neha

2012-10-01

287

Paleoclimate cycles and tectonic controls on fluvial, lacustrine, and eolian strata in upper Triassic Chinle Formation, San Juan basin  

SciTech Connect

Sedimentologic study of the Upper Triassic Chinle Formation in the San Juan basin (SJB) indicates that Late Triassic paleoclimate and tectonic movements influenced the distribution of continental lithofacies. The Shinarump, Monitor Butte, and Petrified Forest Members in the lower part of the Chinle consist of complexly interfingered fluvial, floodplain, marsh, and lacustrine rocks; the Owl Rock and Rock Point Members in the upper part consists of lacustrine-basin and eolian sandsheet strata. Facies analysis, vertebrate and invertebrate paleontology, and paleoclimate models demonstrate that the Late Triassic was dominated by tropical monsoonal circulation, which provided abundant precipitation interspersed with seasonally dry periods. Owl Rock lacustrine strata comprise laminated limestones that reflect seasonal monsoonal precipitation and larger scale, interbedded carbonates and fine-grained clastics that represent longer term, alternating wet and dry climatic cycles. Overlying Rock Point eolian sand-sheet and dune deposits indicate persistent alternating but drier climatic cyclicity. Within the Chinle, upward succession of lacustrine, alternating lacustrine/eolian sand-sheet, and eolian sand-sheet/dune deposits reflects an overall decrease in precipitation due to the northward migration of Pangaea out of low latitudes dominated by monsoonal circulation.

Dubiel, R.F. (Geological Survey, Denver, CO (USA))

1989-09-01

288

The lower Triassic microbiolites in Chaohu region, East China and their contribution to the early Triassic recovery  

NASA Astrophysics Data System (ADS)

The lower Triassic is well preserved in Chaohu Region, Anhui Province, East China. It can be divided into Yinkeng Formation (80 meters thick, was formed during the Indian and early Smitian), Helongshan Formation (21 meters thick, was formed during the end Smithian) and Nanlinghu Formation (more than 157 meters thick, was formed during the Spathian) from bottom to top. It is mainly composed of carbonatites such as micrite limestones and nodular limestones, as well as shales and calcareous marls. The lower Triassic in this area has been well researched for more than a decade, and many fossils such as ammonites, bivalves, fishes, ichthyosaurus, conodonts, and ichnofossils have been found, but the microbiolites have been neglected. Microbiolites were mainly outcropped in the Helongshan Formaiton and the lower Nanlinghu Formation. In the lower Helongshan Formaiton, tens microbial mat layers and thin bedded calcareous marl layers formed cyclothems which have been named as nodular limstones. The thin-section observation of the microbial mats indicate that many films and thin-shell bivalve fragments deposited almost horizontally. In the upper Helongshan Formaiton, six microstromatolite bioherm layers were outcropped in the thin bedded calcareous marl layers. The diameter of the stromatolite column is about 2 millimeters, the bioherms are lenticular and no more than 3 centimeters thick in the central, their diameters change from 5 centimeters to 30 centimeters, calcareous marls were deposited around the bioherms, and many ammonoids, bivalves and burrows were found in such layers. The microfacies differentiation of the stromatolites such as the basement, reef core and the capping beds can be recognised clearly in thin sections. Several microstromatolite layers were outcropped in the micritic limestones with a stable thickness of 15 millimeters in the lower Nanlinghu Formation and the stromatolite column look like the ones in the Helongshan Formation. Few microbiolites have been found in the middle and upper Nanlinghu Formation. The macro fossil association of the lower Triassic in Chaohu region is quite different in different Formations. Ammonoids and bivalves can be found in the whole lower Triassic strata, and they are especially dominant in the Yinkeng Formation and lower Helongshan Formaiton, worms and borrowing animals can be found in the middle Helongshan Formation, fishes can be found in the uppermost Helongshan Formation and the lower Nanlinghu Formation, and the oldest ichthyosaurus in the world can be found in the upper Nanlinghu Formation. According to the changing characters of the fossil association in this area, it is indicated that the high-level ecosystem had been formed in this area in the late early Triassic, and the appearance of the microbiolites in the Helongshan Formation might be the milestone for the early Triassic recovery. Though the global recovery process after the Permian-Triassic mass extinction might be postponed to the end of the early Triassic, regional recovery process in Chaohu region might start at the end Smithian and actualized at the middle Spathian. The microbioilites might be the original impetus for the early Triassic recovery. Key words: microbiolites, early Triassic, regional recovery, Chaohu region Acknowledgments This work is supported by the grants from National Natural Science Fundation of China (No. 40902096 and No.J0830522) and the IGCP 572 program. * Corresponding author: zhihai.jia@gmail.com

Jia, Zhihai; Zhang, Liwei; Hong, Tianqiu

2010-05-01

289

Modeling the response to changes in tropospheric methane concentration: Application to the Permian-Triassic boundary  

NASA Astrophysics Data System (ADS)

We discuss model experiments valid for the Permian-Triassic boundary in which we explore the impact of changes in tropospheric methane concentration. For scenarios relevant to methane clathrate release, we consider surface methane concentration with values up to 5000 times its preindustrial concentration. We employ a comprehensive three-dimensional tropospheric-stratospheric model with chemistry that allows for the feedbacks between chemistry and climate. We show that stratospheric ozone starts collapsing for methane surface concentrations on the order of 1000 times their preindustrial concentration. At 5000 times, more than half of the total ozone column has disappeared. As a result a large rise (up to a factor of 7) in surface UV-B radiation is found. Other chemical consequences include a rise in CO and ozone surface concentrations; although becoming very large (up to 17 ppmv for CO), neither seems to reach lethal values according to present-day life forms. Finally, we show that tropospheric OH does not collapse for any of the scenarios; a corollary of this is a finite methane lifetime (45 years at the most). As a result, if methane were to increase significantly enough over a short period, the associated UV-B increase and/or deterioration of surface conditions could provide an explanation for the landmass extinction at the Permian-Triassic boundary.

Lamarque, J.-F.; Kiehl, J. T.; Shields, C. A.; Boville, B. A.; Kinnison, D. E.

2006-09-01

290

Global terrestrial biogeochemistry: Perturbations, interactions, and time scales  

SciTech Connect

Global biogeochemical processes are being perturbed by human activity, principally that which is associated with industrial activity and expansion of urban and agricultural complexes. Perturbations have manifested themselves at least since the beginning of the 19th Century, and include emissions of CO{sub 2} and other pollutants from fossil fuel combustion, agricultural emissions of reactive nitrogen, and direct disruption of ecosystem function through land conversion. These perturbations yield local impacts, but there are also global consequences that are the sum of local-scale influences. Several approaches to understanding the global-scale implications of chemical perturbations to the Earth system are discussed. The lifetime of anthropogenic CO{sub 2} in the atmosphere is an important concept for understanding the current and future commitment to an altered atmospheric heat budget. The importance of the terrestrial biogeochemistry relative to the lifetime of excess CO{sub 2} is demonstrated using dynamic, aggregated models of the global carbon cycle.

Braswell, B.H. Jr.

1996-12-01

291

Metamorphic and volcanic quartz of the siliciclastic Tipuma Formation, West Papua, Indonesia: an insight into Triassic palaeogeography of northern Australia  

NASA Astrophysics Data System (ADS)

The origin and Triassic evolution of the Bird's Head of West Papua has been a subject of active discussion. Many interpretations have been proposed for the Triassic evolution, from active margin to passive margin models. The Bird's Head region is underlain by Australian continental crust and has a relatively complete stratigraphy from Palaeozoic to Recent. The Tipuma Formation is a Mesozoic siliciclastic sequence and a potentially important reservoir. Its sedimentation may record parts of the region's Mesozoic tectonic history, including several phases of rifting. Little is known about the variations in lithologies and their composition, and nothing is known about its provenance. The Tipuma Formation is dominated by red to cream well-bedded mudstone, sandstone and conglomerate. It rests unconformably on the Kemum Formation and is overlain by the Cretaceous Jass Formation. It is difficult to assess the depositional age of the Tipuma Formation due to the absence of fossils. The suggested Triassic age is based solely on its stratigraphic position. The Tipuma Formation was previously thought to be deposited in a stable continental setting. Detrital modes indicate acid plutonic, metamorphic, and recycled sedimentary source rocks for the Tipuma Formation sandstones. Angular volcanic quartz and elongate euhedral zircons suggest a contribution from previously unrecognised contemporaneous acid volcanics. New interpretations suggest that the widespread Permo-Triassic volcanic activity in the Bird's Head was caused by subduction associated with an Andean-type active margin and that the Tipuma Formation was deposited in a fluvial setting close to the volcanic arc. Cathodoluminescence (CL) characteristics of quartz depend on variations in temperature, pressure, and geochemical environment during crystal growth and subsequent events. The CL colour spectra of quartz can be correlated with the formation conditions of the quartz. They can therefore be used as a provenance indicator along with other techniques. Quartz from Tipuma Formation sandstone is dominated by quartz of low-T metamorphic and volcanic origin and only with little plutonic quartz. This strongly suggests an input of detritus derived from contemporaneous acid volcanic rocks and some local low-grade metamorphic rocks. The results confirm assessment based on zircon study of the main contemporaneous volcanic activity, which waned or ceased during deposition of the Middle Member of the Tipuma Formation. Widespread Permo-Triassic volcanic activity in the Bird's Head possibly caused contact metamorphism in the area with uplift and erosion of low-T metamorphic rocks. The Tasman Line continues from Eastern Australia through New Guinea, into the Bird's Head region. At least since the Triassic, the Bird's Head has been part of the Gondwana margin and for the first time, we can provide compelling evidence that volcanic activity has played a major role in this region.

Gunawan, Indra; Hall, Robert; Augustsson, Carita

2013-04-01

292

Duration and Eruptive Chronology of CAMP: Implications for Central Atlantic Rifting and the Triassic-Jurassic Boundary  

NASA Astrophysics Data System (ADS)

The Central Atlantic Magmatic Province (CAMP) is among the largest igneous provinces on Earth, emplaced synchronously with or just prior to the Triassic-Jurassic boundary ca. 200 Ma. In great part due to the controversial connection between the occurrence of CAMP and the events of the Triassic-Jurassic boundary, the demand for better constraints on the duration and eruptive chronology of this province has increased. A careful review and selection of available ages, as well as 16 new ages from the Carolinas, Newark basin (US), French Guyana and Morocco are presented. Judicious selection yields a total of 59 dates for CAMP, ranging from 202 to 190 Ma covering every part of the CAMP. Extrusive activity commenced abruptly around 200 Ma, reaching peak volume and intensity around 199 Ma on the African margin. The main period of CAMP magmatism is confirmed as brief, but is suggested to consist of at least two phases over 1.5 Ma, during which time data suggest a southward migration of the magmatism from the Africa-North American margins towards South America. Two volumetrically minor, but distinctive magmatic peaks at 195 and 192 Ma are mirrored in data from all three continents, highlighted by our statistical approach. Despite significant advances in our understanding of the chronology of CAMP, we emphasize that the lack of a well-defined Triassic-Jurassic boundary age, as well as an absence of relevant comparison between U/Pb and Ar/Ar data for this time period remain limiting factors to unambiguously linking CAMP in time with the events of the Triassic-Jurassic boundary.

Nomade, S.; Knight, K. B.; Beutel, E.; Renne, P. R.; Verati, C.; Feraud, G.; Marzoli, A.

2005-12-01

293

Quaternary landscape ecology: Relevant scales in space and time  

Microsoft Academic Search

Two primary goals of landscape ecologists are to (1) evaluate changes in ecological pattern and process on natural landscapes through time and (2) determine the ecological consequences of transforming natural land-scapes to cultural ones. Paleoecological techniques can be used to reconstruct past landscapes and their changes through time; use of paleoecological methods of investigation in combination with geomorphic and paleoethnobiological

Hazel R. Delcourt; Paul A. Delcourt

1988-01-01

294

Reproductive Timing in Marine Fishes: Variability, Temporal Scales, and Methods  

Microsoft Academic Search

Reproductive timing can be defined as the temporal pattern of reproduction over a lifetime. Although reproductive timing is highly variable in marine fishes, certain traits are universal, including sexual maturity, undergoing one or more reproductive cycles, participating in one or more spawning events within a reproductive cycle, release of eggs or offspring, aging, and death. These traits commonly occur at

Susan K. Lowerre-Barbieri; Konstantinos Ganias; Fran Saborido-Rey; Hilario Murua; John R. Hunter

2011-01-01

295

Scale of Viability and Minimal Time of Crisis  

Microsoft Academic Search

In this paper, we introduce and study the minimal time of a crisis map which measures the minimal time spent outside a given closed domain of constraints by trajectory solutions of a differential inclusion. The interest of such a notion is basically to tackle simultaneously viability and target issues. The main mathematical result characterizes the epigraph of the crisis map

L. Doyen; P. Saint-Pierre

1997-01-01

296

Scales and trends in 280-year observed rainfall time series  

Microsoft Academic Search

Daily rainfall observations in Padova (Italy) arguably constitute one of the longest observed rainfall time series in the world. Observations started in 1725 and were regularly annotated by the scientists who headed the Astronomic Observatory of Padova over more than two centuries. A patient work of data recovery from the original registries allowed the reconstruction of the entire precipitation time

S. Zanetti; M. Boni; M. Marani

2009-01-01

297

Compile-Time Dynamic Voltage Scaling Settings: Opportunities and Limits  

NSDL National Science Digital Library

The Parapet research group at Princeton University focuses on power-related issues in computer hardware and software design. Citing the importance of power efficiency both in mobile applications as well as in the general goal of shrinking technology sizes on chips, the authors of this paper discuss the role of dynamic voltage scaling (DVS) in managing power during runtime. This interesting technique enables control of "the power consumption by varying a processor's supply voltage...and clock frequency." The paper identifies specific factors that contribute to the effectiveness of DVS and considers the extent to which it can save power.

Xie, Fen; Martonosi, Margaret; Malik, Sharad

298

Modelling financial markets with agents competing on different time scales and with different amount of information  

NASA Astrophysics Data System (ADS)

We use agent-based models to study the competition among investors who use trading strategies with different amount of information and with different time scales. We find that mixing agents that trade on the same time scale but with different amount of information has a stabilizing impact on the large and extreme fluctuations of the market. Traders with the most information are found to be more likely to arbitrage traders who use less information in the decision making. On the other hand, introducing investors who act on two different time scales has a destabilizing effect on the large and extreme price movements, increasing the volatility of the market. Closeness in time scale used in the decision making is found to facilitate the creation of local trends. The larger the overlap in commonly shared information the more the traders in a mixed system with different time scales are found to profit from the presence of traders acting at another time scale than themselves.

Wohlmuth, Johannes; Andersen, Jørgen Vitting

2006-05-01

299

Joint time-scale and TDOA estimation: analysis and fast approximation  

Microsoft Academic Search

Relative motion (rm) between a signal source and a receiver causes a time scaling of the signal arriving at the receiver. When estimating the time-difference-of-arrival (TDOA) of a signal at two receivers, time scaling, when not properly accounted for, can introduce a bias that could dominate the estimation errors. Segmentization processing cannot reduce this bias. Following the derivation of the

Y. T. Chan; K. C. Ho

2005-01-01

300

Palaeomagnetism of Early Triassic limestones from the Huanan Block, South China: no evidence for separation between the Huanan and Yangtze blocks during the Early Mesozoic  

Microsoft Academic Search

There has been extensive debate on the timing of the collision between the Huanan and Yangtze blocks ever since Hsu and co-workers (Hsu et al. 1987, 1988) proposed a Mesozoic collision model for South China tectonics. We report new rock and palaeomagnetic data from an Early Triassic limestone formation from the Huanan Block that help to constrain its tectonic history.

Xiaodong Tan; Kenneth P. Kodama; Pengyan Wang; Dajun Fang

2000-01-01

301

Electrical Breakdown of Hydrogen and Helium on Subnanosecond Time Scales.  

National Technical Information Service (NTIS)

This report describes the experimental determination of the formative time lag data for hydrogen and helium. For subnanosecond risetime pulses, there are typically very few free electrons in the discharge space generated through ionization by external rad...

J. M. Gahl D. W. Scholfield N. Shimomura J. Lester

2000-01-01

302

The Galaxy Viewed at Very Short Time-Scales  

Microsoft Academic Search

We present high time-resolution astronomical observations recorded with the Berkeley Visible Image Tube (BVIT) photon counting detector mounted on the 10m South African Large Telescope (SALT). Relative B and V-band photometric fluxes were obtained as a function of time for targets that included Polar-type cataclysmic variables (UZ For, OY Car, V1033Cen), low-mass X-ray binaries (GX 339-4, UY Vol), pulsars (PSR

Navid Radnia; O. Siegmund; B. Welsh; J. Mcphate; D. Rogers; P. Charles; D. Buckley

2010-01-01

303

Scaled CMOS MEMS for real-time infrared scene generation  

NASA Astrophysics Data System (ADS)

CMOS/MEMS is used as a technique to create infrared emitters. A commercial CMOS process is used that, with a post-processing silicon etch, creates thermally isolated, electronically addressable polysilicon resistors suitable for infrared scene generation. Previous efforts have focused on 2.0 micron CMOS processes which require large suspended structures in order to accommodate the design rules. This work has successfully used a 1.2 micron commercial process with a post-processing silicon etch to scale down the emitter structure to 40 X 40 microns. This allows higher density arrays, and together with using the high value poly resistor available in the 1.2 micrometer process, allows lower current operation, significantly relaxing the design constraints previously encountered. A 128 X 128 design was fabricated in this process and is characterized using a microradiometer. A silicon-on-insulator thermal pixel array design with a further reduction in emitter dimensions is also presented.

Offord, Bruce W.; Marlin, H. Ronald; Bates, Richard L.; Perkins, Gordon C.; Hutchens, Chris; Huang, Derek

2000-07-01

304

Entanglement and confinement effects constraining polymer chain dynamics on different length and time scales  

Microsoft Academic Search

With the time constants usually considered to be characteristic for polymer dynamics, namely ?s (the segment fluctuation time), ?e (the entanglement time), and ?R (the longest Rouse relaxation time), the time scales of particular interest: (i) t?s; (ii) ?st?e; and (iii) ?et?R will be discussed and compared with experimental data. These ranges correspond to the chain-mode length scales: (i) ?b;

Rainer Kimmich

2010-01-01

305

A Novel Multiple-Time Scale Integrator for the Hybrid Monte Carlo Algorithm  

NASA Astrophysics Data System (ADS)

Hybrid Monte Carlo simulations that implement the fermion action using multiple terms are commonly used. By the nature of their formulation they involve multiple integration time scales in the evolution of the system through simulation time. These different scales are usually dealt with by the Sexton-Weingarten nested leapfrog integrator. In this scheme the choice of time scales is somewhat restricted as each time step must be an exact multiple of the next smallest scale in the sequence. A novel generalisation of the nested leapfrog integrator is introduced which allows for far greater flexibility in the choice of time scales, as each scale now must only be an exact multiple of the smallest step size.

Kamleh, Waseem

2011-05-01

306

A Novel Multiple-Time Scale Integrator for the Hybrid Monte Carlo Algorithm  

SciTech Connect

Hybrid Monte Carlo simulations that implement the fermion action using multiple terms are commonly used. By the nature of their formulation they involve multiple integration time scales in the evolution of the system through simulation time. These different scales are usually dealt with by the Sexton-Weingarten nested leapfrog integrator. In this scheme the choice of time scales is somewhat restricted as each time step must be an exact multiple of the next smallest scale in the sequence. A novel generalisation of the nested leapfrog integrator is introduced which allows for far greater flexibility in the choice of time scales, as each scale now must only be an exact multiple of the smallest step size.

Kamleh, Waseem [Special Research Centre for the Subatomic Structure of Matter and Department of Physics, University of Adelaide 5005 (Australia)

2011-05-24

307

Uranium comminution ages: Sediment transport and deposition time scales  

NASA Astrophysics Data System (ADS)

The uranium isotope comminution age is determined from the 234U/238U ratio and reflects the timescale associated with the transformation of bedrock to sediment. The comminution age is applicable to Late Pleistocene sediments and measures the amount of time elapsed since sediment generation by mechanical weathering and erosion. The age significance of the 234U/238U ratios is based on physical disruption of the 238U-decay series by recoil loss of 234Th that occurs in mineral grains smaller than 50 ?m. Results from study of fine-grained deep sea sediments in the North Atlantic Ocean, alluvial sediments in California and Australia, and modern glacial outwash are encouraging, but critical aspects of the method require further investigation. Particular issues are the effects of laboratory chemical leaching treatment on sediment samples and estimation of 234U loss rates as a function of grain size. In the North Atlantic marine environment the U isotope variations are inferred to reflect differences in the transport time of the sediment-the time elapsed between the generation of the small sediment particles by glacial action in Iceland and Fennoscandian source areas, and the time of deposition on the seafloor in the North Atlantic Ocean at a drift site south of Iceland. Calculated transport times vary from less than 10 kyr to about 400 kyr, and correlate with provenance and glacial cycles. Application to alluvial sediments in California and Australia suggests that where sediments are glacially-derived and transported short distances, the U comminution age may approximate the sedimentation age, but in larger basins that are not glaciated the sediments retain information about residence/transport times that can extend to ca. 400 kyr. To verify that initial 234U/238U ratios for glacial sediments are close to the secular equilibrium ratio, outwash from several major glaciers around the world was measured and found to be within ± 1% of the accepted equilibrium 234U/238U value.

DePaolo, Donald J.; Lee, Victoria E.; Christensen, John N.; Maher, Kate

2012-11-01

308

Probing single-photon ionization on the attosecond time scale.  

PubMed

We study photoionization of argon atoms excited by attosecond pulses using an interferometric measurement technique. We measure the difference in time delays between electrons emitted from the 3s(2) and from the 3p(6) shell, at different excitation energies ranging from 32 to 42 eV. The determination of photoemission time delays requires taking into account the measurement process, involving the interaction with a probing infrared field. This contribution can be estimated using a universal formula and is found to account for a substantial fraction of the measured delay. PMID:21561188

Klünder, K; Dahlström, J M; Gisselbrecht, M; Fordell, T; Swoboda, M; Guénot, D; Johnsson, P; Caillat, J; Mauritsson, J; Maquet, A; Taïeb, R; L'Huillier, A

2011-04-05

309

Probing Single-Photon Ionization on the Attosecond Time Scale  

SciTech Connect

We study photoionization of argon atoms excited by attosecond pulses using an interferometric measurement technique. We measure the difference in time delays between electrons emitted from the 3s{sup 2} and from the 3p{sup 6} shell, at different excitation energies ranging from 32 to 42 eV. The determination of photoemission time delays requires taking into account the measurement process, involving the interaction with a probing infrared field. This contribution can be estimated using a universal formula and is found to account for a substantial fraction of the measured delay.

Kluender, K.; Dahlstroem, J. M.; Gisselbrecht, M.; Fordell, T.; Swoboda, M.; Guenot, D.; Johnsson, P.; Mauritsson, J.; L'Huillier, A. [Department of Physics, Lund University, P.O. Box 118, 22100 Lund (Sweden); Caillat, J.; Maquet, A.; Taieeb, R. [Laboratoire de Chimie Physique-Matiere et Rayonnement, Universite Pierre et Marie Curie, 11, Rue Pierre et Marie Curie, 75231 Paris Cedex, 05 (France)

2011-04-08

310

A new Geologic Time Scale, with special reference to Precambrian and Neogene  

Microsoft Academic Search

A Geologic Time Scale (GTS2004) is presented that inte- grates currently available stratigraphic and geochrono- logic information. Key features of the new scale are out- lined, how it was constructed, and how it can be further improved. The accompanying International Strati- graphic Chart, issued under auspices of the Interna- tional Commission on Stratigraphy (ICS), shows the cur- rent chronostratigraphic scale

Felix M. Gradstein; James G. Ogg; Alan G. Smith; Wouter Bleeker; Lucas J. Lourens

311

Time scale and intensity dependency in multiplicative cascades for temporal rainfall disaggregation  

Microsoft Academic Search

Multiplicative random cascades (MRCs) can parsimoniously generate highly intermittent patterns similar to those in rainfall. The elemental MRC model parameter is the cascade weight, which determines how rainfall at one scale is partitioned at the next smallest scale in the cascade. While it is known that the probability density of these weights may vary with both time scale and rainfall

David E. Rupp; Richard F. Keim; Mina Ossiander; Marcela Brugnach; John S. Selker

2009-01-01

312

An unusual archosaurian from the marine Triassic of China  

NASA Astrophysics Data System (ADS)

A new Triassic archosaurian from China shows a number of aquatic specializations, of which the most striking is the extreme lateral compression of the long tail. Others that may also reflect aquatic adaptations include platelike scapula and coracoid, elongate neck with extremely long and slender ribs, and reduction of osteoderms. In contrast, its pelvic girdle and hind limb have no aquatic modifications. Anatomic features, taphonomy, and local geological data suggest that it may have lived in a coastal-island environment. This lifestyle, convergent with some Jurassic marine crocodyliforms that lived at least 40 million years later and the saltwater species of extant Crocodylus, contradicts with the prevailing view that Triassic archosaurians were restricted to nonmarine ecosystems. Its mosaic anatomy represents a previously unknown ecomorph within primitive archosaurians.

Li, Chun; Wu, Xiao-Chun; Cheng, Yen-Nien; Sato, Tamaki; Wang, Liting

2006-04-01

313

Ophiuroids discovered in the middle triassic hypersaline environment.  

PubMed

Echinoderms have long been considered to be one of the animal phyla that is strictly marine. However, there is growing evidence that some recent species may live in either brackish or hypersaline environments. Surprisingly, discoveries of fossil echinoderms in non-(open)marine paleoenvironments are lacking. In Wojkowice Quarry (Southern Poland), sediments of lowermost part of the Middle Triassic are exposed. In limestone layer with cellular structures and pseudomorphs after gypsum, two dense accumulations of articulated ophiuroids (Aspiduriella similis (Eck)) were documented. The sediments with ophiuroids were formed in environment of increased salinity waters as suggested by paleontological, sedimentological, petrographical and geochemical data. Discovery of Triassic hypersaline ophiuroids invalidates the paleontological assumption that fossil echinoderms are indicators of fully marine conditions. Thus caution needs to be taken when using fossil echinoderms in paleoenvironmental reconstructions. PMID:23185442

Salamon, Mariusz A; Nied?wiedzki, Robert; Lach, Rafa?; Brachaniec, Tomasz; Gorzelak, Przemys?aw

2012-11-19

314

First-passage times in complex scale-invariant media  

Microsoft Academic Search

How long does it take a random walker to reach a given target point? This quantity, known as a first-passage time (FPT), has led to a growing number of theoretical investigations over the past decade. The importance of FPTs originates from the crucial role played by first encounter properties in various real situations, including transport in disordered media, neuron firing

S. Condamin; O. Bénichou; V. Tejedor; R. Voituriez; J. Klafter

2007-01-01

315

Biochemical recovery time scales in elderly patients with osteomalacia  

Microsoft Academic Search

SUMMARY Osteomalacia is not rare in the UK and climatically similar countries, particularly in elderly people and those of Asian descent. Overt clinical osteomalacia is usually treated with a loading dose of vitamin D, followed by a regular supplement. However, little is known of the time taken to reach a stable biochemical state after starting treatment. Such information would shed

S C Allen

2004-01-01

316

Language, time, and person effects on attitude scale translations  

Microsoft Academic Search

Decentered translations into Spanish were obtained for 2 standard job attitude instruments, the Job Descriptive Index and the Index of Organizational Reactions. Bilingual employees working in different offices of a large retail organization responded to each instrument and its translation at 2 time periods. Complete data were obtained for 57 employees of Puerto Rican origin and for 71 employees of

Ralph Katerberg; Frank J. Smith; Stephen Hoy

1977-01-01

317

Brain connectivity at different time-scales measured with EEG  

PubMed Central

We present an overview of different methods for decomposing a multichannel spontaneous electroencephalogram (EEG) into sets of temporal patterns and topographic distributions. All of the methods presented here consider the scalp electric field as the basic analysis entity in space. In time, the resolution of the methods is between milliseconds (time-domain analysis), subseconds (time- and frequency-domain analysis) and seconds (frequency-domain analysis). For any of these methods, we show that large parts of the data can be explained by a small number of topographic distributions. Physically, this implies that the brain regions that generated one of those topographies must have been active with a common phase. If several brain regions are producing EEG signals at the same time and frequency, they have a strong tendency to do this in a synchronized mode. This view is illustrated by several examples (including combined EEG and functional magnetic resonance imaging (fMRI)) and a selective review of the literature. The findings are discussed in terms of short-lasting binding between different brain regions through synchronized oscillations, which could constitute a mechanism to form transient, functional neurocognitive networks.

Koenig, T; Studer, D; Hubl, D; Melie, L; Strik, W.K

2005-01-01

318

Brain connectivity at different time-scales measured with EEG.  

PubMed

We present an overview of different methods for decomposing a multichannel spontaneous electroencephalogram (EEG) into sets of temporal patterns and topographic distributions. All of the methods presented here consider the scalp electric field as the basic analysis entity in space. In time, the resolution of the methods is between milliseconds (time-domain analysis), subseconds (time- and frequency-domain analysis) and seconds (frequency-domain analysis). For any of these methods, we show that large parts of the data can be explained by a small number of topographic distributions. Physically, this implies that the brain regions that generated one of those topographies must have been active with a common phase. If several brain regions are producing EEG signals at the same time and frequency, they have a strong tendency to do this in a synchronized mode. This view is illustrated by several examples (including combined EEG and functional magnetic resonance imaging (fMRI)) and a selective review of the literature. The findings are discussed in terms of short-lasting binding between different brain regions through synchronized oscillations, which could constitute a mechanism to form transient, functional neurocognitive networks. PMID:16087445

Koenig, T; Studer, D; Hubl, D; Melie, L; Strik, W K

2005-05-29

319

Scaling spectra and return times of dynamical systems  

SciTech Connect

The grand canonical version of the spectrum of singularities formalism is presented, relying naturally upon certain Markov transition graphs. The structure of a graph is simply determined by the close return times of the dynamical system described. Thus, an intimate connection exists between the shape of the singularity curve and a small but interesting set of dynamical properties.

Feigenbaum, M.J.

1987-03-01

320

Triassic and Jurassic rocks at Currie, Nevada Preliminary paleontologic evidence  

Microsoft Academic Search

A sequence of continental rocks overlies the Lower Triassic Thaynes Formation in a poorly exposed syncline near Currie in northeastern NV. The authors recognize four lithostratigraphic units above the Thaynes near Currie and provide new paleontologic data. In ascending order, unit 1 (120 ft) consists of reddish-brown, very fine grained sandstone. Unit 2 (50 ft) consists of light-gray, trough cross-stratified,

E. A. Johnson; R. F. Dubiel; E. M. Brouwers; R. J. Litwin; S. R. Ash; S. C. Good

1993-01-01

321

The Triassic section north of Currie, Elko County, Nevada  

SciTech Connect

More than 600 m of Triassic strata are exposed just N of Currie, Nevada in secs. 8--9 T29N, R64E. The Thaynes Formation is 468 m of limestone, calcareous shale and siltstone that rest disconformably on the Permian Gerster Formation. A 7.7-m-thick interval of ammonite packstones is 8.8 m above the base of the Thaynes in the NW1/4NW1/SW1/4 sec. 8. Ammonites from these packstones indicate the Tardus Zone of late Smithian age. The Shinarump Formation of the Chinle Group (Upper Triassic) disconformably overlies the Thaynes Formation and is 19.4 m of trough-crossbedded, silica-pebble conglomerate and quartzarenite with silicified wood in the SW1/4SW1/4SW1/4 sec. 9. Shinarump crossbeds dip to the N. Chinle Group strata above the Shinarump are 169.2 m thick and consist of reddish brown siltstone, fine sandstone and minor micritic limestone. Ripple laminations and horizontal bedding are the dominant bedforms. These strata are assigned to the Rock Point Formation, the top of which is cut by a fault N of Currie. Upper Triassic nonmarine strata north of Currie are the northwesternmost outcrops of the Chinle Group. Rock Point strata here are tidal flat facies that indicate proximity of the Late Triassic shoreline in northeastern Nevada. However, it is likely that the Chinle Group strata N of Currie are allochthonous, having been originally deposited to the E in what is now Utah.

Lucas, S.G.; Goodspeed, T.H. (New Mexico Museum of Natural History, Albuquerque, NM (United States))

1993-04-01

322

Triassic shoshonites from the dolomites, northern Italy: Alkaline arc rocks in a strike-slip setting  

NASA Astrophysics Data System (ADS)

Triassic igneous rocks of the Dolomites are typical shoshonites, with high K2O/SiO2 and K2O/Na2O ratios, and low Fe contents. They have mid-ocean ridge basalt-like abundances of high field strength elements but are highly enriched in large ion lithophile (LIL) elements (Rb, Sr, Ba, K). The effects of crustal contamination and fractional crystallization have been superimposed on initial LIL element enrichment. Lavas of similar composition occur in Papua New Guinea, Fiji, the Absaroka Mountains, and the Eolian Islands. These suites are all associated with destructive plate margins but were not erupted until after subduction had ceased. Examination of Mediterranean paleogeography indicates that no subduction event which could have given rise to the shoshonites of the Dolomites occurred during the Triassic. In fact, the tectonic setting at the time of eruption of the lavas was probably one of strike-slip faulting. The suite may have inherited its "arc signature" from Permo-Carboniferous subduction of the ocean between Laurasia and Gondawanaland prior to the Hercynian orogeny.

Sloman, L. E.

1989-04-01

323

Chemostratigraphic reconstruction of biofacies: Molecular evidence linking cyst-forming dinoflagellates with pre-Triassic ancestors  

NASA Astrophysics Data System (ADS)

New data from numerous detailed mass-spectrometric studies have detected triaromatic dinosteroids in Precambrian to Cenozoic rock samples. Triaromatic dinosteroids are organic geochemicals derived from dinosterols, compounds known in modern organisms to be the nearly exclusive widely occurring products of dinoflagellates. We observed the ubiquitous occurrence of these dinosteroids in 49 Late Triassic through Cretaceous marine source rocks and the absence of them in 13 Permian-Carboniferous source rocks synergistic with the dinoflagellate cyst record. However, finding dinosteroids in lower Paleozoic and Precambrian strata presents challenging results for molecular paleontologists, evolutionary biologists, palynologists, and especially for those concerned with the food web at various times of biological crisis. Other than the few species known as parasites and symbionts, many other dinoflagellate species are important as primary producers. The presence of Precambrian to Devonian triaromatic dinosteroids gives chemostratigraphic evidence of dinoflagellates (or other organisms with similar chemosynthetic capabilities) in rocks significantly older than the oldest undisputed dinoflagellate fossils (dinoflagellate cysts from the Middle Triassic, ˜ 240 Ma), and older than the putative Silurian ˜ 420 Ma) dinocyst,Arpylorus antiquus (Calandra) Sargent, from Tunisia. This systematic chemostratigraphic approach can shed light not only on lineages of dinoflagellates and their precursors, but potentially on many other lineages, especially bacteria, algae, plants, and possibly some metazoans.

Moldowan, J. Michael; Dahl, Jeremy; Jacobson, Stephen R.; Huizinga, Bradley J.; Fago, Frederick J.; Shetty, Rupa; Watt, David S.; Peters, Kenneth E.

1996-02-01

324

Length scale and time scale effects on the plastic flow of fcc metals  

Microsoft Academic Search

We examine size scale and strain rate effects on single-crystal face-centered cubic (fcc) metals. To study yield and work hardening, we perform simple shear molecular dynamics simulations using the embedded atom method (EAM) on single-crystal nickel ranging from 100 atoms to 100 million atoms and at strain rates ranging from 107 to 1012 s?1. We compare our atomistic simulation results

M. F. Horstemeyer; M. I. Baskes; S. J. Plimpton

2001-01-01

325

Scaling in a continuous time model for biological aging  

Microsoft Academic Search

In this paper we consider a generalization to the asexual version of the\\u000aPenna model for biological aging, where we take a continuous time limit. The\\u000agenotype associated to each individual is an interval of real numbers over\\u000awhich Dirac $\\\\delta$--functions are defined, representing genetically\\u000aprogrammed diseases to be switched on at defined ages of the individual life.\\u000aWe discuss

R. M. C. de Almeida; G. L. Thomas

2000-01-01

326

Carbon, sulfur, oxygen and strontium isotope records, organic geochemistry and biostratigraphy across the Permian/Triassic boundary in Abadeh, Iran  

NASA Astrophysics Data System (ADS)

Pelagic deposits at Abadeh represent a complete biostratigraphic record across the Permian/Triassic boundary (PTB). The presumed water depth during deposition of these sediments was between 60 and 90 m. Similar to other Permian/Triassic boundary sections, the succession at Abadeh is characterised by a negative carbon isotope shift of approximately 4‰. The values start to decrease in the lower C. changxingensis - C. deflecta s.l. Zone, reach -0.12‰ (V-PDB) in the uppermost Permian just below the PTB, remain low to the early I. isarcica Zone (-0.32‰) and increase subsequently in the upper I. isarcica Zone. For the time interval of the PTB negative carbon isotope excursion, between the C. iranica and the I. isarcica Zones, no correlation exists between the ?13Ccarb and the ?18Ocarb. The above observations argue against the conclusion of Heydari et al. (2001) that the carbon isotope event at the P/T transition is an alteration artefact and not a global signal. The decrease in ?13Ccarb is accompanied by a ~5‰ (and potentially up to 10‰) increase in ?34SSSS. Together, these features are thought to reflect a complex global event, notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves. For the carbon isotope drop, other factors, such as the collapse of ocean primary productivity may also have played a role. The 87Sr/86Sr ratios of Dzhulfian seawater show only a minor increase from 0.70705 to 0.70710, reaching 0.70720 in the Dorashamian. The increase becomes steeper in the Early Triassic reaching 0.70754 in the N. dieneri Zone. The rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost Permian (C. meishanensis - H. praeparvus Zone) and the lack of a dense land vegetation in the Early Triassic, prior to the Spathian (Upper Olenekian).

Korte, Christoph; Kozur, Heinz W.; Joachimski, Michael M.; Strauss, Harald; Veizer, Ján; Schwark, Lorenz

2004-09-01

327

Bi-Plasma Interactions on Femtosecond Time-Scales  

SciTech Connect

Ultrafast THz radiation has important applications in materials science studies, such as characterizing transport properties, studying the vibrational response of materials, and in recent years, controlling materials and elucidating their response in intense electromagnetic fields. THz fields can be generated in a lab setting using various plasma-based techniques. This study seeks to examine the interaction of two plasmas in order to better understand the fundamental physics associated with femtosecond filamentation processes and to achieve more efficient THz generation in a lab setting. The intensity of fluorescence in the region of overlap was measured as a function of polarization, power, and relative time delay of the two plasma-generating laser beams. Results of time dependent intensity studies indicate strikingly similar behaviors across polarizations and power levels; a sudden intensity spike was observed at time-zero, followed by a secondary maxima and subsequent decay to the initial plasma intensity. Dependence of the intensity on the power through either beam arm was also observed. Spectral studies of the enhanced emission were also carried out. Although this physical phenomenon is still not fully understood, future studies, including further spectral analysis of the fluorescence overlap, could yield new insight into the ultrafast processes occurring at the intersection of femtosecond filaments, and would provide a better understanding of the mechanisms for enhanced THz production.

Not Available

2011-06-22

328

A potential biomarker for the Permian Triassic ecological crisis  

NASA Astrophysics Data System (ADS)

A unique biomarker, a C 33n-alkylcyclohexane ( n-heptacosylcyclohexane), which strongly increases in abundance within the extinction interval of the end-Permian ecological crisis, is here reported from the key Permian-Triassic (P-Tr) marine section in Greenland. Prior to this study, this compound had been known from Early Triassic organic-rich marine rocks and oils from the northern Perth Basin, Western Australia for two decades. We have identified the compound in high relative abundance in 29 samples from P-Tr marine sections from two separate paleogeographic localities, from Laurasia and Gondwana. Relative concentrations of the C 33n-alkylcyclohexane show similar changes to the relative abundances of extinct spinose acritarchs ( Veryhachium and Micrhystridium) indicating that the source organism of the C 33n-alkylcyclohexane is associated with the depositional environments/facies in which the acritarchs are identified. These organisms probably formed the cornerstone of the unique marine ecosystem that thrived in the extinction aftermath in the Early Triassic Ocean.

Grice, Kliti; Twitchett, Richard J.; Alexander, Robert; Foster, C. B.; Looy, Cindy

2005-07-01

329

Atmospheric carbon injection linked to end-Triassic mass extinction.  

PubMed

The end-Triassic mass extinction (~201.4 million years ago), marked by terrestrial ecosystem turnover and up to ~50% loss in marine biodiversity, has been attributed to intensified volcanic activity during the break-up of Pangaea. Here, we present compound-specific carbon-isotope data of long-chain n-alkanes derived from waxes of land plants, showing a ~8.5 per mil negative excursion, coincident with the extinction interval. These data indicate strong carbon-13 depletion of the end-Triassic atmosphere, within only 10,000 to 20,000 years. The magnitude and rate of this carbon-cycle disruption can be explained by the injection of at least ~12 × 10(3) gigatons of isotopically depleted carbon as methane into the atmosphere. Concurrent vegetation changes reflect strong warming and an enhanced hydrological cycle. Hence, end-Triassic events are robustly linked to methane-derived massive carbon release and associated climate change. PMID:21778394

Ruhl, Micha; Bonis, Nina R; Reichart, Gert-Jan; Sinninghe Damsté, Jaap S; Kürschner, Wolfram M

2011-07-22

330

A new chronology for the end-Triassic mass extinction  

NASA Astrophysics Data System (ADS)

The link between the end-Triassic mass extinction (~200 Ma), one of the big five, and the emplacement of the Central Atlantic Magmatic Province (CAMP), one of the biggest flood basalt provinces, has been controversial. Here we show with a multi-disciplinary approach that the onset of volcanism in Morocco is synchronous with the extinction events documented in the terrestrial Newark basin (US) and in the marine realm (UK). Roughly 20 kyr later the main pulse of initial CAMP volcanism is synchronously recorded throughout the rest of the northern CAMP province. This event also seems to be short-lived (<100 kyr), probably occurring in distinct instantaneous pulses. Additional cyclostratigraphic control on the marine St. Audrie's Bay Tr-J boundary section (UK) indicates that both these two CAMP pulses occurred before the recently defined (first occurrence Jurassic ammonites) Triassic Jurassic boundary. This boundary, which can be considered as a first recovery event, occurs about 6 precession cycles (~120 kyr) after the end-Triassic mass extinction level.

Deenen, Martijn H. L.; Ruhl, Micha; Bonis, Nina R.; Krijgsman, Wout; Kuerschner, Wolfram M.; van Bergen, Manfred J.

2010-05-01

331

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

332

The end-Triassic and Early Jurassic mass extinction records in the British Isles  

Microsoft Academic Search

WIGNALL, P.B. & BOND, D.P.G. 2008. The end-Triassic and Early Jurassic mass extinction records in the British Isles. Proceedings of the Geologists' Association, 119, 73-84. The complex crises of the end-Triassic and Early Jurassic (Toarcian) mass extinctions are well recorded in the British Isles where they coincide with major palaeoenvironmental changes. The end-Triassic extinction occurs within the quasi-marine Lilstock Formation,

Paul B. Wignall; David P. G. Bond

2008-01-01

333

A petrified Glossopteris flora from Collinson Ridge, central Transantarctic Mountains: Late Permian or Early Triassic?  

Microsoft Academic Search

The Permian–Triassic boundary in Gondwana has traditionally been based on lithology and a change from the glossopterid-dominated flora in the Permian to the Dicroidium-dominated flora in the Triassic. There have, however, been a few reports of Glossopteris occurring in the Lower Triassic of Tasmania, Antarctica, South Africa and India, usually as a minor element in floras dominated by Dicroidium. The

Hilary A. McManus; Edith L. Taylor; Thomas N. Taylor; James W. Collinson

2002-01-01

334

Facies analysis of Lofer cycles (Upper Triassic), in the Argolis Peninsula (Greece)  

Microsoft Academic Search

The Upper Triassic carbonate sediments of Argolis Peninsula are part of the Upper Triassic–Lower Jurassic extensive and thick neritic carbonate formations (Pantokrator facies) that formed at the passive Pelagonian margin and are considered as Dachstein-type platform carbonates. Facies analysis of the Upper Triassic “Lofer-type” lagoonal–peritidal cycles in the Dhidimi area, proved that cycles, although mostly incomplete, were regressive shallowing-upward. The

F. Pomoni-Papaioannou

2008-01-01

335

Invited Review Article: The statistical modeling of atomic clocks and the design of time scales  

SciTech Connect

I will show how the statistical models that are used to describe the performance of atomic clocks are derived from their internal design. These statistical models form the basis for time scales, which are used to define international time scales such as International Atomic Time and Coordinated Universal Time. These international time scales are realized by ensembles of clocks at national laboratories such as the National Institute of Standards and Technology, and I will describe how ensembles of atomic clocks are characterized and managed.

Levine, Judah [Time and Frequency Division and JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80305 (United States)

2012-02-15

336

Time scale of magma differentiation in arcs from protactinium-radium isotopic data  

NASA Astrophysics Data System (ADS)

Absolute chronology of magma differentiation processes has been a long-desired goal, given its importance in understanding magma chamber dynamics and its connection to a fundamental understanding of the style and frequency of volcanic eruptions. Broad estimates of the duration of magma differentiation and overall crustal residence times have been made based on a variety of indirect approaches, such as physical models of magma chamber cooling, rates of crystal growth and settling, and long-lived radiogenic isotopes. In contrast, combined 231Pa-235U data may provide a robust measure of the time scale of magma differentiation. Based on 231Pa-235U, 230Th-238U and 226Ra-230Th data from Taal volcano, Luzon Arc, Philippine Archipelago, we show that 231Pa-235U data may provide a robust direct measure of the time scale of magma differentiation. A closed-system magma fractionation model gives a 231Pa-235U differentiation time scale in the range of 30 k.y., while the 226Ra-230Th time scale is considerably younger. The time scales are reconciled if we consider either fluid-mixing or magma-mixing models. The fluid-mixing model gives a time scale of differentiation similar to the 231Pa-235U closed-system time scale and is supported by the 230Th-238U data. The magma-mixing model gives a considerably longer time, in the range of 55 k.y. The combined observations support the robustness of the 231Pa-235U chronology, indicating a differentiation time scale in the range of 30 k.y., although this time scale for other volcanoes may vary depending on size and thermal state of the magma chamber. The 226Ra-230Th closed-system model ages, which yield much younger estimates for magma differentiation, are not likely to reflect time scales of magma differentiation.

Asmerom, Yemane; Dufrane, S. Andrew; Mukasa, Samuel B.; Cheng, Hai; Edwards, R. Lawrence

2005-08-01

337

Thermal Time Scales in a Color Glass Condensate  

NASA Astrophysics Data System (ADS)

In a model of relativistic heavy ion collisions wherein the unconfined quark-gluon plasma is condensed into glass, we derive the Vogel-Fulcher-Tammann cooling law. This law is well known to hold true in condensed matter glasses. The high energy plasma is initially created in a very hot negative temperature state and cools down to the Hagedorn glass temperature at an ever decreasing rate. The cooling rate is largely determined by the QCD string tension derived from hadronic Regge trajectories. The ultimately slow relaxation time is characteristic of a color glass condensate.

Parihar, Vivek; Widom, Allan; Srivastava, Yogi

2006-04-01

338

Thermal time scales in a color glass condensate  

NASA Astrophysics Data System (ADS)

In a model of relativistic heavy-ion collisions wherein the unconfined quark-gluon plasma is condensed into glass, we derive the Vogel-Fulcher-Tammann cooling law. This law is well known to hold true in condensed matter glasses. The high-energy plasma is initially created in a very hot negative temperature state and cools down to the Hagedorn glass temperature at an ever decreasing rate. The cooling rate is largely determined by the QCD string tension derived from hadronic Regge trajectories. The ultimately slow relaxation time is a defining characteristic of a color glass condensate.

Parihar, V.; Widom, A.; Srivastava, Y. N.

2006-01-01

339

Time-scales, Meaning, and Availability of Information in a Global Brain  

Microsoft Academic Search

We note the importance of time-scales, meaning, and availability of information for the emergence of novel information meta-structures at a global scale. We discuss previous work in this area and develop future perspectives. We focus on the transmission of scientific articles and the integration of traditional conferences with their virtual ext ensions on the I nternet, their time-scales, and av

Carlos Gershenson; Gottfried Mayer-Kress; Atin Das; Pritha Das; Matus Marko

2003-01-01

340

Temperature responses to spectral solar variability on decadal time scales  

NASA Astrophysics Data System (ADS)

Two scenarios of spectral solar forcing, namely Spectral Irradiance Monitor (SIM)-based out-of-phase variations and conventional in-phase variations, are input to a time-dependent radiative-convective model (RCM), and to the GISS modelE. Both scenarios and models give maximum temperature responses in the upper stratosphere, decreasing to the surface. Upper stratospheric peak-to-peak responses to out-of-phase forcing are ˜0.6 K and ˜0.9 K in RCM and modelE, ˜5 times larger than responses to in-phase forcing. Stratospheric responses are in-phase with TSI and UV variations, and resemble HALOE observed 11-year temperature variations. For in-phase forcing, ocean mixed layer response lags surface air response by ˜2 years, and is ˜0.06 K compared to ˜0.14 K for atmosphere. For out-of-phase forcing, lags are similar, but surface responses are significantly smaller. For both scenarios, modelE surface responses are less than 0.1 K in the tropics, and display similar patterns over oceanic regions, but complex responses over land.

Cahalan, Robert F.; Wen, Guoyong; Harder, Jerald W.; Pilewskie, Peter

2010-04-01

341

RCBR: a simple and efficient service for multiple time-scale traffic  

Microsoft Academic Search

Variable bit-rate (VBR) compressed video traffic is expected to be a significant component of the traffic mix in integrated services networks. This traffic is hard to manage because it has strict delay and loss requirements while simul- taneously exhibiting burstiness at multiple time scales. We show that burstiness over long time scales, in conjunction with resource reservation using one-shot traffic

Matthias Grossglauser; Srinivasan Keshav; David N. C. Tse

1997-01-01

342

Mutual information function assesses autonomic information flow of heart rate dynamics at different time scales  

Microsoft Academic Search

The autonomic information flow (AIF) represents the complex communication within the Autonomic Nervous System (ANS). It can be assessed by the mutual information function (MIF) of heart rate fluctuations (HRF). The complexity of HRF is based on several interacting physiological mechanisms operating at different time scales. Therefore one prominent time scale for HRF complexity analysis is not given a priori.

Dirk Hoyer; Bernd Pompe; Ki H. Chon; Henning Hardraht; Carola Wicher; Ulrich Zwiener

2005-01-01

343

On Green's functions and positive solutions for boundary value problems on time scales  

Microsoft Academic Search

In this paper we offer a form of self-adjoint differential equations on time scales so that the associated Green's function is found symmetric in the usual sense. For this purpose together with the delta derivative we employ the nabla derivative as well. We introduce the concepts of Lebesgue delta and nabla integrals on time scales. Next, sign properties of the

F. Merdivenci Atici; G. Sh. Guseinov

2002-01-01

344

Abrupt changes in soil water content variability for various time scales and at different depths at the catchment scale  

NASA Astrophysics Data System (ADS)

A current challenge in hydrology is to observe, explain and model soil water content (SWC) patterns across multiple space-time scales. A promising technique for the assessment of SWC patterns at the catchment scale is the wireless sensor network. This technique has the potential to continuously monitor three-dimensional SWC fields with high spatial and temporal resolution, i.e. to detect abrupt changes in SWC patterns. The objective of this study was to analyze the dynamics of SWC patterns at the TERENO forest hydrologic observatory Wüstebach (0.27 km2) for different depths (surface and subsurface soil) and various time scales (annual, seasonal scale and wetting and drying periods). We used the SoilNet wireless network system developed at Forschungszentrum Jülich. SWC measurements were taken every 15 minutes in three depths (5, 20, 50 cm) at 150 locations using EC-5 and 5TE sensors (Decagon Devices). This particular analysis is based on hourly aggregated SWC data measured from 1st of August 2009 to 31st of July 2010. Descriptive statistics and geostatistics were used to investigate the data set depending on soil depth and time scale. We analyzed the mean SWC, standard deviation, coefficient of variation and geostatististical parameters (nugget, sill and range) as a function of time and mean SWC. We found that the dynamics of SWC variability depended on depth, mean soil moisture status, time scale and wetting versus drying period. The magnitude and the variability of the mean SWC, standard deviation, coefficient of variation, and the range decreased with depth depending on soil moisture status. As already observed by others, the standard deviation peaked at medium (critical) SWC, which means that during wetting the standard deviation increased for mean SWC below the critical SWC and decreased above the mean SWC (and vice versa for drying). In addition, we observed that the standard deviation was higher during wetting periods than during drying periods in the medium SWC range, leading to hysteresis effects during abrupt changes in soil moisture status. In the low and high SWC range, the relationship between standard deviation and mean SWC was linear. This systematic behaviour was independent of the time scale. The topography and shallow groundwater are important controls especially in very dry situations. Underlying factors that are variable in space and time and interact in a complex, non-linear way have still to be investigated. The results of this study demonstrated that the SoilNet sensor network was able to detect abrupt changes in SWC patterns at the catchment scale.

Rosenbaum, U.; Herbst, M.; Huisman, J. A.; Weuthen, A.; Petersen, T. J.; Western, A. W.; Vereecken, H.; Bogena, H. R.

2010-12-01

345

On the time scale of New World primate diversification.  

PubMed

New World primates comprise a diverse group of neotropical mammals that suddenly appeared in the Late Oligocene deposits of South America at around 26 million years ago (MYA). Platyrrhines seem to have separated from Old World anthropoids ca. 35 MYA, and their subsequent diversfication is not well documented in the fossil record. Therefore, molecular clock studies were conducted to unveil the temporal scenario for the evolution of the group. In this study, divergence times of all splits within platyrrhines until the generic level were investigated, using two different gene data sets under relaxed molecular clocks. Special attention was paid to the basal diversification of living platyrrhines and to the basal split of the modern Cebidae family, since these nodes were reported to be phylogenetically difficult to resolve. The results showed that analyses from various genomic regions are similar to estimates obtained by early single-gene studies. Living New World primates are descendants of ancestors that lived in the Early Miocene, at around 20 MYA, and modern Cebidae and Pitheciidae appeared ca. 16.9 and 15.6 MYA, respectively. The last common ancestor of living Atelidae is 12.4 million years old, making this clade the youngest New World primate family; at approximately the same time, modern Callitrichinae was evolving (11.8 MYA). The gap between the Platyrrhini/Catarrhini separation and the last common ancestor of living Platyrrhini may be as big as 20 million years. Paleontological and geoclimatological evidence corroborates that the sudden appearance of modern families may be a consequence of environmental changes during the Miocene. PMID:17133436

Schrago, Carlos G

2007-03-01

346

Event and time-scale characteristics of heart-rate dynamics  

NASA Astrophysics Data System (ADS)

The cardiac system shows various scale dynamic activities from secondly to yearly. Therefore multiple time-scale characteristics of heart dynamics have received much attention for understanding and distinguishing healthy and pathological cardiac systems. In this paper we expand the multiple time-scale analysis into event and time scales to investigate scale characteristics in healthy and pathologic cardiac systems. To do this, we define a measure based on symbolic dynamics, which calculates complexity at each time and event scale, called the unit time block entropy (UTBE). This measure allows a reliable comparison of experimental data through matching the number of words and the total measurement time at the same time for all RR interval sequences which are composed of the time durations between consecutive R waves of electrocardiograms. We apply the UTBE to the healthy heart-rate (HR) group and pathological HR groups and find that the RR interval acceleration is more effective than the RR interval in distinguishing each group. And we also find that the normal and pathological HR groups are clearly distinguished in some specific event and time-scale regions.

Lee, Uncheol; Kim, Seunghwan; Yi, S. H.

2005-06-01

347

Updating the planetary time scale: focus on Mars  

USGS Publications Warehouse

Formal stratigraphic systems have been developed for the surface materials of the Moon, Mars, Mercury, and the Galilean satellite Ganymede. These systems are based on geologic mapping, which establishes relative ages of surfaces delineated by superposition, morphology, impact crater densities, and other relations and features. Referent units selected from the mapping determine time-stratigraphic bases and/or representative materials characteristic of events and periods for definition of chronologic units. Absolute ages of these units in some cases can be estimated using crater size-frequency data. For the Moon, the chronologic units and cratering record are calibrated by radiometric ages measured from samples collected from the lunar surface. Model ages for other cratered planetary surfaces are constructed primarily by estimating cratering rates relative to that of the Moon. Other cratered bodies with estimated surface ages include Venus and the Galilean satellites of Jupiter. New global geologic mapping and crater dating studies of Mars are resulting in more accurate and detailed reconstructions of its geologic history.

Tanaka, Kenneth L;Quantin-Nataf, Cathy

2013-01-01

348

Temperature analysis of laser heated polymers on microsecond time scales  

NASA Astrophysics Data System (ADS)

To investigate the temperature profiles on laser heated polymer films, we track the thermal radiation with 1 ?s time and 1 ?m spatial resolution. The resulting two-dimensional temperature graphs are compared to finite element simulations in order to understand the heat conversion and flow. The temperature measurement setup consists of a NIR laser and an optical detection system, which includes high performance optics and a microsecond gated camera, equipped with several interference filters. In this way the thermal radiation is detected in the visible range with spectral resolution. Fitting the spectrum with Planck's law, two-dimensional micrographs of the temperature distribution are obtained. For polystyrene surfaces we were able to analyze the heating and the ablation behavior. Good agreement was found between experimental results and finite element simulations, when ablation is limited to a few tens of nanometers of the film thickness. Ablation of polystyrene starts at 150°C, 50 K above the glass transition temperature. We suggest a photomechanical ablation mechanism at that threshold fluence. For ablation at higher fluence and peak temperature, experiments indicate a thermal decomposition reaction. The temperature range of spinodal decomposition is not reached and can in our case be ruled out as ablation mechanism.

Kappes, Ralf S.; Schönfeld, Friedhelm; Li, Chen; Gutmann, Jochen S.; Butt, Hans-Jürgen

2012-03-01

349

Short time-scale periodicity in OJ 287  

NASA Astrophysics Data System (ADS)

We have studied short-term variations of the blazar OJ 287, suspected to host a supermassive black hole binary. In this study, we use a two-season optical R-band data set from 2004 to 2006 which consists of 3991 data points from the OJ 287 observation campaign. It has sections of dense time coverage, and is largely independent from previously published data. We find that these data confirm the existence of a ˜50 d periodic component, presumably related to the half-period of the innermost stable circular orbit (ISCO) of the primary black hole. In addition, we find several pseudo-periodic components in the 1-7 d range, most prominently at 3.5 d, which are likely Lorentz contracted jet re-emission of the 50 d component. The typical 50-d cycle exhibits a slow rise of brightness and a rapid dimming before the start of the new cycle. We explain this as being due to a spiral wave in the accretion disc which feeds the central black hole in this manner.

Pihajoki, P.; Valtonen, M.; Ciprini, S.

2013-10-01

350

Probabilistic eruption forecasting at short and long time scales  

NASA Astrophysics Data System (ADS)

Any effective volcanic risk mitigation strategy requires a scientific assessment of the future evolution of a volcanic system and its eruptive behavior. Some consider the onus should be on volcanologists to provide simple but emphatic deterministic forecasts. This traditional way of thinking, however, does not deal with the implications of inherent uncertainties, both aleatoric and epistemic, that are inevitably present in observations, monitoring data, and interpretation of any natural system. In contrast to deterministic predictions, probabilistic eruption forecasting attempts to quantify these inherent uncertainties utilizing all available information to the extent that it can be relied upon and is informative. As with many other natural hazards, probabilistic eruption forecasting is becoming established as the primary scientific basis for planning rational risk mitigation actions: at short-term (hours to weeks or months), it allows decision-makers to prioritize actions in a crisis; and at long-term (years to decades), it is the basic component for land use and emergency planning. Probabilistic eruption forecasting consists of estimating the probability of an eruption event and where it sits in a complex multidimensional time-space-magnitude framework. In this review, we discuss the key developments and features of models that have been used to address the problem.

Marzocchi, Warner; Bebbington, Mark S.

2012-10-01

351

Tectonically controlled magnetic fabrics in the Iberian Triassic basin  

NASA Astrophysics Data System (ADS)

A relationship between the orientation of the magnetic susceptibility ellipsoid and the strain ellipsoid has been demonstrated by using the anisotropy of magnetic susceptibility (AMS) in sedimentary rocks. Studies also interpret an early development of the magnetic fabric, which registers the stress pattern acting during deposition. But this primary fabric can be overwritten by successive deformation phases, and these changes have been registered even in weakly deformed sediments. This work studies the AMS registered in an inverted basin where no penetrative compression-related structures have been recognized. Although inversion took place, strata remain weakly deformed, with shallow dips in most part of the area. Triassic sedimentary rocks from the Castilian Branch of the Iberian Range (NE Spain) are studied. The Castilian Branch started to develop as a rift basin during the Late Permian-Early Triassic with NW-SE and NE-SW faults affecting Upper Permian materials. Buntsandstein red beds accumulated in asymmetric half-grabens with strong thickness variations related to their position within the troughs and highs. After the Mid-Triassic, a marine and transitional sedimentation spanned throughout the Iberian Range (Keuper and Muschelkalk). Jurassic to Upper Cretaceous deposits unconformably covered the Triassic sediments with thickness of a few hundreds of meters. During the Paleogene, tectonic inversion took place, developing gentle folds and steeply-dipping reverse faults, resulting from the reactivation of extensional Triassic faults. The particular lithology of the Buntsandstein red beds also allows determining the influence of ferromagnetic phases in the AMS. We analyzed 815 standard specimens from 55 sites in a KLY-3S Kappabridge (AGICO) susceptometer to obtain the bulk susceptibility and the orientation of the three main eigenvectors of the magnetic ellipsoid. In order to determine the magnetic carriers of the bulk susceptibility, 22 temperature dependent susceptibility curves (from 40 to 700°C) were carried out, combining the susceptometer with a CS-3 furnace. Sites are representative of all the red beds sectors from the Castilian Branch, limited by different extensional structures acting during Triassic rifting. The magnetic susceptibility ranges between 80 and 350 x 10-6 SI. Most of the thermomagnetic curves indicate the presence of a high fraction of hematite as ferromagnetic mineral. In other cases, hematite and phyllosilicates are present in the same proportion, usually coinciding with samples from sites with the lowest susceptibility values. In some cases neoformation of magnetite takes place during heating. Results show kmin always subperpendicular to the bedding plane, according to a sedimentary fabric. kmax indicates four main directions for the magnetic lineation: NW-SE, NNE-SSW and, less represented N-S and E-W. These variations in lineation directions are directly related to several tectonic events, and can be interpreted according to i) the direction of the major extensional structures nearest to each site (suggesting an extensional-influenced origin for the lineation), ii) the geographic position of the basin sectors, depending on their proximity to the inverted faults (that would suggest a partial tectonically-influenced secondary magnetic fabric), iii) the age of the studied rocks, suggesting a stronger influence of extensional features in Early Triassic rocks, progressively diminishing upwards within the sedimentary sequence.

García-Lasanta, C.; Oliva-Urcia, B.; Román-Berdiel, T.; Casas-Sainz, A.; Gil-Peña, I.; Sánchez-Moya, Y.; Sopeña, A.

2012-04-01

352

Proportional hazards regression in epidemiologic follow-up studies: an intuitive consideration of primary time scale.  

PubMed

In epidemiologic cohort studies of chronic diseases, such as heart disease or cancer, confounding by age can bias the estimated effects of risk factors under study. With Cox proportional-hazards regression modeling in such studies, it would generally be recommended that chronological age be handled nonparametrically as the primary time scale. However, studies involving baseline measurements of biomarkers or other factors frequently use follow-up time since measurement as the primary time scale, with no explicit justification. The effects of age are adjusted for by modeling age at entry as a parametric covariate. Parametric adjustment raises the question of model adequacy, in that it assumes a known functional relationship between age and disease, whereas using age as the primary time scale does not. We illustrate this graphically and show intuitively why the parametric approach to age adjustment using follow-up time as the primary time scale provides a poor approximation to age-specific incidence. Adequate parametric adjustment for age could require extensive modeling, which is wasteful, given the simplicity of using age as the primary time scale. Furthermore, the underlying hazard with follow-up time based on arbitrary timing of study initiation may have no inherent meaning in terms of risk. Given the potential for biased risk estimates, age should be considered as the preferred time scale for proportional-hazards regression with epidemiologic follow-up data when confounding by age is a concern. PMID:22517300

Cologne, John; Hsu, Wan-Ling; Abbott, Robert D; Ohishi, Waka; Grant, Eric J; Fujiwara, Saeko; Cullings, Harry M

2012-07-01

353

A Lagrangian subgrid-scale model with dynamic estimation of Lagrangian time scale for large eddy simulation of complex flows  

NASA Astrophysics Data System (ADS)

The dynamic Lagrangian averaging approach for the dynamic Smagorinsky model for large eddy simulation is extended to an unstructured grid framework and applied to complex flows. The Lagrangian time scale is dynamically computed from the solution and does not need any adjustable parameter. The time scale used in the standard Lagrangian model contains an adjustable parameter ?. The dynamic time scale is computed based on a ``surrogate-correlation'' of the Germano-identity error (GIE). Also, a simple material derivative relation is used to approximate GIE at different events along a pathline instead of Lagrangian tracking or multi-linear interpolation. Previously, the time scale for homogeneous flows was computed by averaging along directions of homogeneity. The present work proposes modifications for inhomogeneous flows. This development allows the Lagrangian averaged dynamic model to be applied to inhomogeneous flows without any adjustable parameter. The proposed model is applied to LES of turbulent channel flow on unstructured zonal grids at various Reynolds numbers. Improvement is observed when compared to other averaging procedures for the dynamic Smagorinsky model, especially at coarse resolutions. The model is also applied to flow over a cylinder at two Reynolds numbers and good agreement with previous computations and experiments is obtained. Noticeable improvement is obtained using the proposed model over the standard Lagrangian model. The improvement is attributed to a physically consistent Lagrangian time scale. The model also shows good performance when applied to flow past a marine propeller in an off-design condition; it regularizes the eddy viscosity and adjusts locally to the dominant flow features.

Verma, Aman; Mahesh, Krishnan

2012-08-01

354

Increased Atmospheric SO2 Detected from Changes in Leaf Physiognomy across the Triassic-Jurassic Boundary Interval of East Greenland  

PubMed Central

The Triassic–Jurassic boundary (Tr–J; ?201 Ma) is marked by a doubling in the concentration of atmospheric CO2, rising temperatures, and ecosystem instability. This appears to have been driven by a major perturbation in the global carbon cycle due to massive volcanism in the Central Atlantic Magmatic Province. It is hypothesized that this volcanism also likely delivered sulphur dioxide (SO2) to the atmosphere. The role that SO2 may have played in leading to ecosystem instability at the time has not received much attention. To date, little direct evidence has been presented from the fossil record capable of implicating SO2 as a cause of plant extinctions at this time. In order to address this, we performed a physiognomic leaf analysis on well-preserved fossil leaves, including Ginkgoales, bennettites, and conifers from nine plant beds that span the Tr–J boundary at Astartekløft, East Greenland. The physiognomic responses of fossil taxa were compared to the leaf size and shape variations observed in nearest living equivalent taxa exposed to simulated palaeoatmospheric treatments in controlled environment chambers. The modern taxa showed a statistically significant increase in leaf roundness when fumigated with SO2. A similar increase in leaf roundness was also observed in the Tr–J fossil taxa immediately prior to a sudden decrease in their relative abundances at Astartekløft. This research reveals that increases in atmospheric SO2 can likely be traced in the fossil record by analyzing physiognomic changes in fossil leaves. A pattern of relative abundance decline following increased leaf roundness for all six fossil taxa investigated supports the hypothesis that SO2 had a significant role in Tr–J plant extinctions. This finding highlights that the role of SO2 in plant biodiversity declines across other major geological boundaries coinciding with global scale volcanism should be further explored using leaf physiognomy.

Bacon, Karen L.; Belcher, Claire M.; Haworth, Matthew; McElwain, Jennifer C.

2013-01-01

355

A robust two-time-scale control design for a pneumatic vibration isolator  

Microsoft Academic Search

Active pneumatic vibration isolators have been widely studied as the use of precision equipment increases. This paper focuses on the robust two-time-scale control design of an active pneumatic vibration isolator using the singular perturbation method and time delay control (TDC). The singular perturbation method, or more generally, the two-time-scale approach to feedback design is used to cope with the ill-conditioning

Dong Ki Han; Pyung Hun Chang

2007-01-01

356

Dual-time scale crystal plasticity FE model for cyclic deformation of Ti alloys  

Microsoft Academic Search

A dual-time scale finite element model is developed in this paper for simulating cyclic deformation in a Titanium alloy Ti-6242.\\u000a The material is characterized by crystal plasticity constitutive relations. Modeling cyclic deformation using conventional\\u000a time integration algorithms in a single time scale can be prohibitive for crystal plasticity computations. Typically 3D crystal\\u000a plasticity based fatigue simulations found in the literature

Sivom Manchiraju; Kedar Kirane; Somnath Ghosh

2007-01-01

357

Global correlations of mid Early Triassic events: The Induan/Olenekian boundary in the Dolomites (Italy)  

NASA Astrophysics Data System (ADS)

The Dolomites (Southern Alps, Italy) are a reference-area for research on the end-Permian mass extinction and its Early Triassic aftermath. The effects on shallow marine benthic biota are recorded in the Werfen Formation, a thick mixed carbonate-siliciclastic sedimentary succession. Only in its lower (Griesbachian) and upper (Spathian) parts, this formation is bio-chronologically constrained by means of conodonts and ammonoids, whilst no significant bioevent occurs in its middle part. This represents an impediment to the biochronologic recognition of the Induan/Olenekian boundary (IOB). The Bulla/Pufels (Val Gardena) succession is a key-section for the P/T boundary and Early Triassic for global correlation due to the abundance of studies on biostratigraphy (mostly on conodonts), magnetostratigraphy and chemostratigraphy carried out there by stratigraphers of various nationalities. Recent chemostratigraphic studies have permitted the recognition of some carbon isotope positive peaks, the strongest of which is considered to approximate the IOB. However, various authors have reached different conclusions on the position of the maximum peak and thus on the IOB location. This leads to important stratigraphic consequences for the calibration of conodont biostratigraphy. The critical revision of the traditional stratigraphic units (litho- and biostratigraphy), under-evaluated in most of the recent literature, and magneto-, chemo- and sequence stratigraphic units allowed herein an integrated stratigraphic scale for the Bulla/Pufels section to be proposed. This contribution highlights the mid Early Triassic Dolomites record for regional and global correlations. The most significant results attained herein regard the different lithostratigraphic subdivisions of the middle Werfen Formation and its consequences on the position of the IOB with respect to the conodont and bivalve biostratigraphy and sequence stratigraphic units. The upper part of the section is attributed herein to the Gastropod Oolite Member, which is represented by the lithozone A, a predominant supratidal episode, and the lower part of the subtidal lithozone B. Between the lithozones A and B, a sequence boundary of 3th order (Sc2/Sc3) is located. The maximum carbon isotope excursion is near this boundary, which therefore approximates the IOB in the Dolomites. This proposal suggests a Dienerian age for the FO of the conodont Pachycladina obliqua, which occurs about 60 m below the stage boundary. No significant biotic event, either for molluscs or conodonts, occurred across this stage boundary.

Posenato, Renato

2008-12-01

358

Palaeogeographic evolution of the marine Middle Triassic marine Germanic Basin changements - With emphasis on the carbonate tidal flat and shallow marine habitats of reptiles in Central Pangaea  

NASA Astrophysics Data System (ADS)

More than seventy-five vertebrate track-sites have been found in Central Europe in 243-246.5 m.y. old Triassic coastal intertidal to sabkha carbonates. In the western part of the very flat Triassic intracontinental Germanic Basin, the carbonate strata contain at least 22 laterally extensive track horizons (called megatracksites). In contrast, in the eastern part of the basin only six megatracksites extended to near the centre of the Basin during marine low stands. Marine ingression and the development of extensive coastal marine environments began during the Aegean (Anisian) stage. This incursion began in the region of the eastern Carpathian and Silesian gates and spread westward due to the development of a tectonically controlled intracratonic basin. The tectonic origin of this basin made it susceptible to tsunamis and submarine earthquakes, which constituted very dangerous hazards for coastal terrestrial and even marine reptiles. The shallow sea that spread across the Germanic Basin produced extensive tidal flats that at times formed extensive inter-peninsular bridges between the Rhenish and Bohemian Massifs. The presence of these inter-peninsular bridges explains the observed distribution and movement of reptiles along coastal Europe and the northern Tethys Seaway during the Middle Triassic epoch. Two small reptiles, probably Macrocnemus and Hescherleria, left millions of tracks and trackways known as Rhynchosauroides and Procolophonichnium in the Middle Triassic coastal intertidal zone. The great abundance of their tracks indicates that their trackmakers Macrocnemus and Hescherleria were permanent inhabitants of this environment. In sharp contrast, tracks of other large terrestrial reptiles are quite rare along the coastal margins of the Germanic Basin, for example the recently discovered archaeosaur tracks and trackways referable to Isochirotherium, which most probably were made by the carnivore Ticinosuchus. Smaller medium-sized predatory thecodont reptiles, possibly Euparkeria, probably made the Brachychirotherium trackways that have been found across much of Central Europe. Large lepidosaurs such as Tanystrophaeus probably hunted in the tidal ponds and channels, where they locally produced Synaptichnium tracks. Recently discovered tracks made by a basal prosauropod are the world's oldest record of this group of dinosaurs, occurring in beds that have an age of about 243.5 Ma. (Pelsonian substage). This shows that very large prosauropods existed much earlier than was previously believed. These prosauropod tracks, along with tracks of small bipedal dinosaurs found in the Alps and Eastern France, show that by the middle part of the Middle Triassic the radiation and diversification of dinosaurs was already in progress. In the Germanic Basin, aquatic-adapted paraxial swimming sauropterygians are not known to have left tracks, except for occasional subaquatic swimming scratch-mark "trackways" within the coastal tidal flat zone. Marine-adapted aquatic reptiles migrated into the Germanic Basin with increasing frequency in the upper part of the Middle Triassic, when the bathymetry of the Germanic Basin was at its deepest following a strong regression that occurred due to basin uplift in the middle part of the Middle Triassic. These large marine reptiles included Pistosaurus, the ichthyosaurs Cymbospondylus or Mixosaurus, and many placodonts such as Cyamodus, Placodus and Paraplacodus, which fed on macroalgae and seem to have been the Triassic sea cows of their day. The distribution of these reptiles was mainly controlled by tectonics, but eustatic changes in sea level also were important and produced widespread environmental changes across the tidal flats up until their disappearance in the Germanic Basin in the late Middle Triassic. The initial break-up of Pangaea already had started in Middle Triassic time, and this event had begun to drastically change environments all over Central Europe. It is very interesting that dinosaurs began to diversify at exactly this time, and it seems likely that this was a direct

Diedrich, Cajus G.

2009-01-01

359

Contrasting Triassic ferroan granitoids from northwestern Liaoning, North China: Magmatic monitor of Mesozoic decratonization and a craton-orogen boundary  

NASA Astrophysics Data System (ADS)

The diversity exhibited by ferroan granitoids testifies to multiple distinct crustal and mantle processes generally within extensional environments and thus holds the key to monitoring important geodynamic and crustal evolutionary processes and calibrating terrane tectonic affinity. This study documents three Middle to Late Triassic ferroan granitoid suites from northwestern Liaoning, North China, and proposes distinct petrogenetic scenarios for each. The Middle Triassic (ca. 238 Ma) Ping'andi (PAD) granites are mainly calc-alkali and peraluminous. Their radiogenic whole-rock Nd and zircon Hf isotopic signatures argue for an origin consistent with partial melting of a juvenile quartzofeldspathic crust formed by prior mantle-derived magmatic underplating and their differentiations. By contrast, the Late Triassic (ca. 220 Ma) Dashaoleng (DSL) and Sijiazi (SJZ) suites show an evolved character from alkali-calcic to alkali and from metaluminous to peraluminous. Their variably evolved whole-rock Sr-Nd and mixed zircon Hf isotopic compositions suggest that both suites were formed by variable mixing between depleted mantle-derived mafic magma and old crust-derived felsic magma, with distinctively higher input from juvenile components in the DSL suite. These contrasting ferroan granitoid suites not only provide a spatial marker for monitoring juxtaposition of the North China Craton (NCC) and the Central Asian Orogenic Belt (CAOB) along a lithospheric-scale boundary fault in the region, but also present a temporal snapshot that records a southwardly-progressing crustal growth scenario possibly in response to lithospheric dripping within a post-orogenic extensional regime. The cratonic scale synthesis further indicates that diachronous decratonization pattern of the NCC might record episodic response of the craton to evolved plate tectonic processes with two contrasting Phanerozoic orogenic systems.

Zhang, Xiaohui; Yuan, Lingling; Xue, Fuhong; Zhang, Yanbin

2012-07-01

360

Scaling Behavior of the First Arrival Time of a Random-Walking Magnetic Domain  

SciTech Connect

We report a universal scaling behavior of the first arrival time of a traveling magnetic domain wall into a finite space-time observation window of a magneto-optical microscope enabling direct visualization of a Barkhausen avalanche in real time. The first arrival time of the traveling magnetic domain wall exhibits a nontrivial fluctuation and its statistical distribution is described by universal power-law scaling with scaling exponents of 1.34 {+-} 0.07 for CoCr and CoCrPt films, despite their quite different domain evolution patterns. Numerical simulation of the first arrival time with an assumption that the magnetic domain wall traveled as a random walker well matches our experimentally observed scaling behavior, providing an experimental support for the random-walking model of traveling magnetic domain walls.

Im, M.-Y.; Lee, S.-H.; Kim, D.-H.; Fischer, P.; Shin, S.-C.

2008-02-04

361

Scaling behavior of the first arrival time of a random-walking magnetic domain.  

PubMed

We report a universal scaling behavior of the first arrival time of a traveling magnetic domain wall into a finite space-time observation window of a magneto-optical microscope enabling direct visualization of a Barkhausen avalanche in real time. The first arrival time of the traveling magnetic domain wall exhibits a nontrivial fluctuation and its statistical distribution is described by universal power-law scaling with scaling exponents of 1.34+/-0.07 for CoCr and CoCrPt films, despite their quite different domain evolution patterns. Numerical simulation of the first arrival time with an assumption that the magnetic domain wall traveled as a random walker well matches our experimentally observed scaling behavior, providing an experimental support for the random-walking model of traveling magnetic domain walls. PMID:18518241

Im, M-Y; Lee, S-H; Kim, D-H; Fischer, P; Shin, S-C

2008-04-23

362

Task difficulty and the time scales of warm-up and motor learning.  

PubMed

The authors investigated the influence of task difficulty on warm-up decrement and learning across practice sessions. Three groups of participants practiced a star-tracing task over 3 consecutive days with different levels (e.g., easy, medium, hard) of task difficulty. The performance data were modeled with a 2 time scale function that represented the transient, fast time scale process of warm-up decrement superimposed with the persistent, slow time scale process of learning. Movement time decreased as a function of practice with the most difficult condition exhibiting the greatest reduction though still the longest movement time. The 2 time scale model provided a better fit to the data than an exponential or power law function and showed that the 3 difficulty conditions exhibited similar rates of change for the respective slow (i.e., learning) and fast (i.e., warm-up decrement) time scale processes that varied by an order of magnitude. Task difficulty was inversely related to the initial level of warm-up decrement but not the rate of performance recovery early in a practice session. The findings support the postulation that there is a persistent learned component to the initial conditions in subsequent practice sessions but that there is a common time scale of accommodating the transient process of warm-up decrement. PMID:23611248

Joseph, Morina E; King, Adam C; Newell, Karl M

2013-04-23

363

Approaches to scaling up physiologically based soil-plant models in space and time  

Microsoft Academic Search

Summary Many broad-scale, environmental phenomena can be investigated by extrapolating from detailed study of events at a small scale. This paper evaluates approaches to the use of physiologically based soil-plant models for addressing broad-scale, environmental issues. When the space and time domains of a soil-plant simulator are extended, there is an increase in the variability of soil, plant, and weather

R. J. Luxmoore; A. W. King; M. L. Tharp

2010-01-01

364

Time scale and intensity dependency in multiplicative cascades for temporal rainfall disaggregation  

NASA Astrophysics Data System (ADS)

Multiplicative random cascades (MRCs) can parsimoniously generate highly intermittent patterns similar to those in rainfall. The elemental MRC model parameter is the cascade weight, which determines how rainfall at one scale is partitioned at the next smallest scale in the cascade. While it is known that the probability density of these weights may vary with both time scale and rainfall intensity, nearly all previous studies have considered either time scale or intensity separately. We examined the simultaneous dependency of the weights on both factors and assessed the impacts of explicitly including these dependencies in the MRC model. On the basis of the observed relationships between cascade weights and time scale and intensity, four progressively more "dependent" models were constructed to disaggregate a long time series of daily rainfall to hourly intervals. We found that inclusion of the intensity dependency on the model parameters that generate dry intervals greatly improved performance. For the relatively small range of time scales over which the rainfall was disaggregated, varying model parameters with time scale resulted in minor improvement.

Rupp, David E.; Keim, Richard F.; Ossiander, Mina; Brugnach, Marcela; Selker, John S.

2009-07-01

365

Scaling of mean first-passage time as efficiency measure of nodes sending information on scale-free Koch networks  

NASA Astrophysics Data System (ADS)

Random walks on complex networks, especially scale-free networks, have attracted considerable interest in the past few years. A lot of previous work showed that the average receiving time (ART), i.e., the average of mean first-passage time (MFPT) for random walks to a given hub node (node with maximum degree) averaged over all starting points in scale-free small-world networks exhibits a sublinear or linear dependence on network order N (number of nodes), which indicates that hub nodes are very efficient in receiving information if one looks upon the random walker as an information messenger. Thus far, the efficiency of a hub node sending information on scale-free small-world networks has not been addressed yet. In this paper, we study random walks on the class of Koch networks with scale-free behavior and small-world effect. We derive some basic properties for random walks on the Koch network family, based on which we calculate analytically the average sending time (AST) defined as the average of MFPTs from a hub node to all other nodes, excluding the hub itself. The obtained closed-form expression displays that in large networks the AST grows with network order as N ln N, which is larger than the linear scaling of ART to the hub from other nodes. On the other hand, we also address the case with the information sender distributed uniformly among the Koch networks, and derive analytically the global mean first-passage time, namely, the average of MFPTs between all couples of nodes, the leading scaling of which is identical to that of AST. From the obtained results, we present that although hub nodes are more efficient for receiving information than other nodes, they display a qualitatively similar speed for sending information as non-hub nodes. Moreover, we show that that AST from a starting point (sender) to all possible targets is not sensitively affected by the sender's location. The present findings are helpful for better understanding random walks performed on scale-free small-world networks.

Zhang, Zhongzhi; Gao, Shuyang

2011-03-01

366

Correlation of upper Triassic strata between southern Colorado Plateau and southern High Plains, New Mexico  

SciTech Connect

Almost 600 m of Upper Triassic strata are exposed in the Hagan basin. They pertain to the basal Agua Zarca member of the Chinle Formation (as much as 80 m), overlain by about 500 m of mud-rock-dominated red beds of the Petrified Forest Member of the Chinle Formation. The top of the Triassic section here is the 5.5-24 m-thick Correo Sandstone Bed of Chinle Formation, which is disconformably overlain by the medial silty member of the Middle Jurassic Entrada Sandstone. At Lamy, approximately 370 m of Upper Triassic strata represent the westernmost outcrops of the Triassic section typical of the Tucumcari basin. This Triassic section consists of about 140 m of Santa Rosa Formation (divisible into three members) overlain by a mud-rock-dominated section (Chinle Formation) split by a medial sandy interval, the Cuervo member (Trujillo Formation of the Palo Duro basin). The youngest Triassic strata near Lamy are rhythmically bedded sediments of the Redonda Member. Based on lithologic similarity, stratigraphic position, and limited paleontological data, the central New Mexico Upper Triassic strata support for the following correlations (from west to east): (1) Shinarump = Agua Zarca = Santa Rosa; (2) lower Petrified Forest = lower shale member of the Chinle = Tecovas; (3) Sonsela = Poleo = Cuervo = Trujillo; (4) upper Petrified Forest = upper shale member of the Chinle; and (5) Owl Rock = Redonda = Correo. These correlations reflect homotaxis of sedimentary cycles across a broad region of the southern Western Interior during the Late Triassic.

Lucas, S.G. (New Mexico Museum of Natural History, Albuquerque (USA))

1989-09-01

367

Triassic rocks of the Black Forest-Haldon area, Mackenzie Country, South Island, New Zealand  

Microsoft Academic Search

Tightly folded marine sedimentary rocks, most or all of Triassic age, form the low hills on the north-east shore of Lake Benmore. They are separated from foliated sandstone and phyllite above and to the east by the Black Forest Thrust, which dips gently eastward.The sedimentary sequence in rocks known to be Triassic is, from the base: large lenticular sandstone bodies

Lucy M. Force; Eric R. Force

1978-01-01

368

Reevaluation of alleged bees' nests from the Upper Triassic of Arizona  

Microsoft Academic Search

Published records of supposed Triassic bees' nests are based on trace fossils in silicified wood and in sandstone in Upper Triassic strata of the Chinle Group in Petrified Forest National Park, Arizona. A critical, firsthand restudy of these trace fossils indicates that they lack diagnostic features of bees' nests, such as cells with smooth linings and spiral closure caps. Indeed,

Spencer G. Lucas; Nicholas J. Minter; Adrian P. Hunt

2010-01-01

369

Pseudoctenis cornelii nov. spec. (cycadalean foliage) from the Carnian (Upper Triassic) of Lunz, Lower Austria  

Microsoft Academic Search

Pseudoctenis (cycadalean foliage) is a characteristic element of Rhaetian (uppermost Triassic) and Jurassic floras from Europe. Here we describe a new species, Pseudoctenis cornelii, from the Carnian flora of Lunz in Lower Austria that provides the earliest persuasive evidence for this genus in the European Triassic. The new species is included in Pseudoctenis based on macromorphology and epidermal anatomy; a

Christian POTT; Hans KERP; Michael KRINGS

370

A Triassic tetrapod footprint assemblage from southern South America: palaeobiogeographical and evolutionary implications  

Microsoft Academic Search

A new Triassic tetrapod track assemblage recorded from levels of the Cuyana Basin (west-central Argentina) is described. The tracks came from multiple track-bearing horizons of the Upper Triassic (Carnian) Portezuelo Formation that indicate recurrent playa to mudflat conditions in a marginal lacustrine succession. This footprint assemblage is the most important one described up to now for the lower Mesozoic of

Claudia A Marsicano; Silvia P Barredo

2004-01-01

371

A new temnospondyl amphibian from the Lower Triassic of South America  

Microsoft Academic Search

A new temnospondyl from the Early Triassic Buena Vista Formation (Paraná Basin) in Uruguay is described. The specimen is represented by a skull table fragment which includes the left orbit, and, although fairly incomplete, shows close affinities with the basal temnospondyl clade (Dvinosaurus + Tupilakosauridae). Previously, members of this clade were only known from Upper Permian and Lower Triassic deposits

C. A. Marsicano; D. Perea; M. Ubilla

2000-01-01

372

Palaeomagnetism and magnetostratigraphy of the Permian and Triassic of Spitsbergen: a review of progress and challenges  

Microsoft Academic Search

Permian and Triassic sediments from Svalbard provide a testing ground for evaluating concepts about the polarity and configuration of the geomagnetic field during the Palaeozoic-Mesozoic transition. This review examines existing palaeomagnetic and magnetostratigraphic data and also reexamines the issue of partial remagnetization of these sediments. Permian and Triassic palaeomagnetic poles from Spitsbergen demonstrate a close similarity to the stable-Europe apparent

Mark W. Hounslow; Jerzy Nawrocki

2008-01-01

373

A critical re?evaluation of the Late Triassic dinosaur taxa of North America  

Microsoft Academic Search

The North American Triassic dinosaur record has been repeatedly cited as one of the most complete early dinosaur assemblages. The discovery of Silesaurus from Poland and the recognition that Herrerasaurus and Eoraptor may not be theropods have forced a re?evaluation of saurischian and theropod synapomorphies. Here, we re?evaluate each purported Triassic dinosaur from North America on a specimen by specimen

Sterling J. Nesbitt; Randall B. Irmis; William G. Parker

2007-01-01

374

Time scale defined by the fractal structure of the price fluctuations in foreign exchange markets  

NASA Astrophysics Data System (ADS)

In this contribution, a new time scale named C-fluctuation time is defined by price fluctuations observed at a given resolution. The intraday fractal structures and the relations of the three time scales: real time (physical time), tick time and C-fluctuation time, in foreign exchange markets are analyzed. The data set used is trading prices of foreign exchange rates; US dollar (USD)/Japanese yen (JPY), USD/Euro (EUR), and EUR/JPY. The accuracy of the data is one minute and data within a minute are recorded in order of transaction. The series of instantaneous velocity of C-fluctuation time flowing are exponentially distributed for small C when they are measured by real time and for tiny C when they are measured by tick time. When the market is volatile, for larger C, the series of instantaneous velocity are exponentially distributed.

Kumagai, Yoshiaki

2010-04-01

375

The Theory of Scale Relativity: Non-Dieren tiable Geometry and Fractal Space-Time1  

Microsoft Academic Search

The aim of the theory of scale relativity is to derive the physical behavior of a non-dieren tiable and fractal space-time and of its geodesics (with which particles are identied), under the constraint of the principle of the relativity of scales. We mainly study in this contribution the eects induced by internal fractal structures on the motion in standard space.

Laurent NOTTALE

2004-01-01

376

Evolutionary dynamics of gastropod size across the end-Permian extinction and through the Triassic recovery interval  

Microsoft Academic Search

A global database of gastropod sizes from the Permian through the Middle Triassic doc- uments trends in gastropod shell size and permits tests of the suggestion that Early Triassic gas- tropods were everywhere unusually small. Analysis of the database shows that no specimens of unambiguous Early Triassic age larger than 2.6 cm have been reported, in contrast to common 5-

Jonathan L. Payne

2005-01-01

377

Bridging time scales in cellular decision making with a stochastic bistable switch  

PubMed Central

Background Cellular transformations which involve a significant phenotypical change of the cell's state use bistable biochemical switches as underlying decision systems. Some of these transformations act over a very long time scale on the cell population level, up to the entire lifespan of the organism. Results In this work, we aim at linking cellular decisions taking place on a time scale of years to decades with the biochemical dynamics in signal transduction and gene regulation, occuring on a time scale of minutes to hours. We show that a stochastic bistable switch forms a viable biochemical mechanism to implement decision processes on long time scales. As a case study, the mechanism is applied to model the initiation of follicle growth in mammalian ovaries, where the physiological time scale of follicle pool depletion is on the order of the organism's lifespan. We construct a simple mathematical model for this process based on experimental evidence for the involved genetic mechanisms. Conclusions Despite the underlying stochasticity, the proposed mechanism turns out to yield reliable behavior in large populations of cells subject to the considered decision process. Our model explains how the physiological time constant may emerge from the intrinsic stochasticity of the underlying gene regulatory network. Apart from ovarian follicles, the proposed mechanism may also be of relevance for other physiological systems where cells take binary decisions over a long time scale.

2010-01-01

378

Parametric scaling studies of the energy confinement time for neutral beam heated Heliotron E plasmas  

Microsoft Academic Search

A kinetic analysis of the global energy confinement time for neutral beam heated Heliotron E plasmas has been performed with a 1-D, time independent transport analysis code, PROCTR-Mod. From a regression analysis of a representative sample selection of the presented data sets, the global energy confinement time, , is found to scale as , where ? = 0.53 0.10, ?

F. Sano; Y. Takeiri; K. Hanatani; H. Zushi; M. Sato; S. Sudo; T. Mutoh; K. Kondo; H. Kaneko; T. Mizuuchi; H. Okada; S. Morimoto; K. Itoh; S. Besshou; M. Nakasuga; Y. Nakamura; N. Noda; K. Akaishi; O. Motojima; M. Wakatani; T. Obiki; A. Iiyoshi; M. Murakami; H. C. Howe

1990-01-01

379

The role of topography on catchment-scale water residence time  

Microsoft Academic Search

The age, or residence time, of water is a fundamental descriptor of catchment hydrology, revealing information about the storage, flow pathways, and source of water in a single integrated measure. While there has been tremendous recent interest in residence time estimation to characterize watersheds, there are relatively few studies that have quantified residence time at the watershed scale, and fewer

K. J. McGuire; J. J. McDonnell; M. Weiler; C. Kendall; B. L. McGlynn; J. M. Welker; J. Seibert

2005-01-01

380

Fine-scale variation in the timing of reproduction in titmice and chickadees  

Microsoft Academic Search

Variation among female songbirds in the timing of clutch initiation has been studied, nearly continu- ously, for at least the last 60 years. Rather than a focus on control of broad timing patterns across sea- sons (Chapter 4), this research has concerned itself with fine-scale adjustment of reproductive timing for strategic breeding purposes. It has benefited from long-term data sets

Scott M. Ramsay; Ken A. Otter

381

Dominant time scale for brittle fragmentation of vesicular magma by decompression  

Microsoft Academic Search

Brittle fragmentation was examined in a vesicular material analogous to magma, in this case, maltose syrup with bubbles. All the key time scales for magma fragmentation are controlled in the experiment using a rapid decompression facility. It was found that the onset of fragmentation can be well characterized using the Maxwell relaxation time ?r and the decompression time ?tdec, in

Masaharu Kameda; Hideaki Kuribara; Mie Ichihara

2008-01-01

382

Time operators in stroboscopic wave-packet basis and the time scales in tunneling  

SciTech Connect

We demonstrate that the time operator that measures the time of arrival of a quantum particle into a chosen state can be defined as a self-adjoint quantum-mechanical operator using periodic boundary conditions and applied to wave functions in energy representation. The time becomes quantized into discrete eigenvalues; and the eigenstates of the time operator, i.e., the stroboscopic wave packets introduced recently [Phys. Rev. Lett. 101, 046402 (2008)], form an orthogonal system of states. The formalism provides simple physical interpretation of the time-measurement process and direct construction of normalized, positive definite probability distribution for the quantized values of the arrival time. The average value of the time is equal to the phase time but in general depends on the choice of zero time eigenstate, whereas the uncertainty of the average is related to the traversal time and is independent of this choice. The general formalism is applied to a particle tunneling through a resonant tunneling barrier in one dimension.

Bokes, P. [Department of Physics, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology, Ilkovicova 3, SK-812 19 Bratislava (Slovakia) and ETSF, Department of Physics, University of York, Heslington, York YO10 5DD (United Kingdom)

2011-03-15

383

Can inertial electrostatic confinement work beyond the ion-ion collisional time scale.  

National Technical Information Service (NTIS)

Inertial electrostatic confinement systems are predicated on a non-equilibrium ion distribution function. Coulomb collisions between ions cause this distribution to relax to a Maxwellian on the ion-ion collisional time-scale. The power required to prevent...

W. M. Nevins

1995-01-01

384

Existence of positive periodic solutions for functional differential equations with impulse effects on time scales  

NASA Astrophysics Data System (ADS)

By using a fixed point theorem of strict-set-contraction, some criteria are established for the existence of positive periodic solutions for a functional differential equation with delays and impulses on time scales.

Zhang, Hongtao; Li, Yongkun

2009-01-01

385

Palaeomagnetic investigation on Early-Middle Triassic sediments of the North China block: a new Early Triassic palaeopole and its tectonic implications  

NASA Astrophysics Data System (ADS)

Palaeomagnetic and rock magnetic study is reported of Early-Middle Triassic terrestrial sediments from the Jiaocheng and Yushe areas, Shanxi province. Thermomagnetic analysis indicates that magnetite and haematite are the main magnetic carriers. Thermal demagnetization shows that the majority of Early Triassic specimens from the Jiaocheng area contain an intermediate-temperature component (ITC) between 500 -250 °C and a high-temperature component (HTC) between 500-680 °C. The ITC has a negative fold test and might be a Cretaceous or recent overprint. The HTC contains both normal and reversed polarities with positive fold and C-level reversal tests. We interpret the HTC as primary magnetization. Unfortunately, we failed to isolate a meaningful mean direction from Middle Triassic rocks of the Yushe area. New Early Triassic palaeopole from the Jiaocheng area confirms an ~ 10° counter-clockwise displacement of the Taihang Early Triassic palaeopoles relative to their Ordos counterparts. This study thus suggests that the North China block (NCB) has generally behaved as rigid block since the Early Triassic, but there might be an ~9° counter-clockwise rotation of the Taihang terrane with respect to stable NCB in the Late Triassic. The slight rotation of the Taihang terrane does not bear significantly on what has been previously concluded concerning the Mesozoic history of the NCB-South China block (SCB) collision. However, Triassic palaeomagnetic data from stable NCB indicate that the east end of the NCB and SCB did not undergo large convergence or significant opposite latitudinal displacement after the initial contact at the end of the Late Permian.

Huang, Baochun; Shi, Ruiping; Wang, Yongcheng; Zhu, Rixiang

2005-01-01

386

Facies and diagenetic evaluation of the Permian–Triassic boundary interval and basal Triassic carbonates: shallow and deep ramp sections, Hungary  

Microsoft Academic Search

The Permian–Triassic boundary and basal Triassic shallow-marine successions were studied and correlated in sections of two\\u000a structural units in Hungary (Transdanubian Range and Bükk units). Core sections in the Transdanubian Range unit recovered\\u000a inner ramp deposits whereas outcrops in the Bükk unit expose deposits of the deeper ramp area of the western Tethys. The inner\\u000a ramp section (studied ca. 10 m

Kinga Hips; János Haas

2009-01-01

387

Dependence of evaporation on meteorological variables at different time-scales and intercomparison of estimation methods  

Microsoft Academic Search

This paper consists of two parts. In the first part, the significance of five major factors, including solar radiation, vapour pressure deficit, relative humidity, wind speed and air temperature, that control evaporation were evaluated comparatively at different time-scales using the data from Changines station in Switzerland. The comparative evaluation was made at hourly, daily, 10-day and monthly time-scales. It was

C.-Y. Xu; V. P. Singh

1998-01-01

388

Mixed TimeScale Generalized Fair Scheduling for Amplify-and-Forward Relay Networks  

Microsoft Academic Search

We devise an optimization framework for generalized proportional fairness (GPF) under different time scales for amplify-and-forward (AF) relay networks. In GPF scheduling, a single input parameter is used to change the fairness from throughput optimal, to proportionally fair and asymptotically to max-min fair. We extend the GPF scheduling to include a new input parameter, which determines the time-scale of fairness

Alireza Sharifian; Petar Djukic; Halim Yanikomeroglu; Jietao Zhang

2010-01-01

389

Output feedback control of doubly-fed induction generator based on multi-time scale model  

Microsoft Academic Search

A doubly-fed induction machine is an electrical asynchronous three phases machine with open rotor windings which can be fed by external voltages. In this paper a new control system of a doubly-fed induction generator based on multi-time scale model is presented. After established the detailed model, the simplified model based on the multi-time scale theory was given. In simplified model,

X. Y. Li; X. H. Chen; G. Q. Tang

2008-01-01

390

Priority Based Real-Time Communication for Large Scale Wormhole Networks  

Microsoft Academic Search

As advances are made in parallel processing technology, an increasing number of real-time applications are being developed for large-scale parallel processors. Since the wormhole network is a popular communication system used in the new generation of large-scale parallel multiprocessors, real-time communication support on wormhole networks becomes an important issue. We evaluate a priority mapping scheme, a priority adjustment scheme and

Jong-pyng Li; Matt W. Mutka

1994-01-01

391

Paleomagnetism and Magnetostratigraphy of the Upper Triassic Chinle Group in North- Central, Western and Eastern New Mexico  

NASA Astrophysics Data System (ADS)

The Upper Triassic Chinle Group spans most of the Late Triassic and was deposited by a large scale fluvial system. Chinle Group strata are composed of predominantly red to purple mudstones with lesser orange siltstones and buff to red sandstones. In the Chama Basin, north-central New Mexico, both lower and upper Chinle strata are well-exposed and sections at several localities have been sampled to develop a more complete magnetic reversal chronology for the Late Triassic of the American Southwest. Localities in eastern and west- central New Mexico were also sampled for comparative purposes. Sampling at all sections concentrated on hematitic mudrocks and these materials typically carry a well-defined, well-grouped, dual polarity magnetization dominated by pigmentary hematite with laboratory unblocking temperatures about 660C we interpret as a primary, Late Triassic remanence (e.g., Painted Desert Mbr., corrected grand mean: D = 182.9°, I = 4.4°, ?95 = 2.9°, k = 61.7, N/No = 40/45 sites (14 levels of N polarity, 26 levels of R polarity). The Shinarump Formation (lowest unit of the Chinle Group) failed to yield interpretable magnetizations. The Salitral, Poleo, Petrified Forest and Rock Point formations all yielded magnetizations with either south or north-seeking declinations and shallow inclinations, comparable to those of the Painted Desert Member(e.g.: Poleo Formation grand mean: D = 183.1°, I = 0.3deg, ?95 = 5.7°, k = 33.9, N/No = 20/30). Although the Chinle Group of New Mexico was sampled at a relatively coarse sampling interval, the composite, yet incomplete,magnetic reversal chronology derived from these sections compares, at a gross scale, to similar age strata from Arizona, eastern North America and the Tethyan region of southern Europe. Chinle Group strata of Carnian age (based on palynostratigraphy) are of mixed polarity. Lower Norian strata are dominantly of reverse polarity and upper Norian strata are of mixed polarity. Paleopoles calculated from averaged VGPs show very little motion along the apparent polar wander path throughout the Carnian (Salitral Fm. Pole: 56.9°N, 62.0°E, A95 = 4.8°) and early Norian (Petrified Forest Fm., Painted Desert Member: 55.3°N, 67.3°E, A95 = 3.2°), followed by a shift in the pole position in the Late Norian (Rock Point Fm.: 58.5°N, 42.4°E, A95 = 14.8deg).

Zeigler, K. E.; Geissman, J. W.

2007-12-01

392

Dissected paleotopography and base-level changes in a Triassic fluvial sequence  

NASA Astrophysics Data System (ADS)

At one stratigraphic level in Petrified Forest National Park in Arizona, fluvial mudrocks of the Chinle Formation are truncated by areally extensive deep scours that are filled dominantly by pedogenically modified mudrocks. Color differences between paleosols, developed on scoured and scour-fill deposits, facilitate recognition of the dissected interval. The mudstone-filled scour system records a period of channel incision and widespread gullying caused by lowered base level. Although it is difficult to document subsidence rates in the Chinle basin, the tectonic setting suggests that the enormous scour system could be the result of fluctuations in regional thermal activity during Late Triassic time. Similar scour and fill should occur in other fluvial sequences; however, because they both truncate and are filled by mudrocks, identification can be difficult. Recognition of them is important because they are indicators of base-level fluctuations and thus are useful in unraveling the depositional history of a basin.

Kraus, Mary J.; Middleton, Larry T.

1987-01-01

393

Alongshore Shear-Dispersion of Surfzone Drifters: The Effect of a Finite Lagrangian Time-Scale  

NASA Astrophysics Data System (ADS)

GPS-tracked surfzone drifters were used to investigate surfzone dispersion. For the 2006 Huntington Beach (HB06) data, the alongshore diffusivity is related to the magnitude of the mean alongshore current V0 [Spydell et al. JGR 2009]. In particular the asymptotic alongshore diffusivity ?yy was approximately consistent with a "shear dispersion" scaling [e.g., Taylor 1953] ?yy = K V02 ?D, where K is a constant, and ?D=Ls2/?xx is the cross-shore diffusion time for surfzone width Ls and cross-shore diffusivity ?xx. However, the value of the constant K obtained from the in-situ data is more than three times that expected for the classic Taylor shear dispersion model that assumes uncorrelated Lagrangian velocities at all times. Lagrangian velocities in the surfzone are correlated and eventually become decorrelated at times longer than the Lagrangian time-scale ?L. A theory for shear-dispersion that includes the effect of a finite Lagrangian time-scale is presented. The shear-enhanced alongshore diffusivity for this model has a different scaling ?yy ˜ C V02(?D?L)1/2 where C is a constant given by the theory. This scaling better explains the HB06 data than the classic shear dispersion scaling. This new theory may have application in other geophysical fluid dynamics settings.

Spydell, M. S.; Feddersen, F.

2010-12-01

394

The Pangea Problem: Insights from New Permo-Triassic Paleomagnetic Data from Gondwana  

NASA Astrophysics Data System (ADS)

Assuming the widely accepted Pangea reconstruction, the so called ‘A-fit’ wherein the eastern margin of North America abuts northwest Africa (e.g. Bullard et al., 1965), Permian and Triassic paleopoles from Gondwana and Laurasia do not statistically coincide, unless heavy filtering is applied to the existing global paleomagnetic database. Forcing a fit of these paleopoles, while maintaining the internal geometry of the supercontinent, results in an unacceptable overlap of continental elements on the order of 10 degrees (~1000 km). To alleviate this problem, alternative paleogeographies and non-dipole field (NDF) models have been invoked. Alternative reconstructions are unfavorable geologically, as they inevitably require large transformative events (i.e. a 3500 km transcontinental megashear) for which there is little structural evidence. NDF arguments lack a causative mechanism, and undermine a central tenet of paleomagnetism, the geocentric axial dipole (GAD) hypothesis. Given the implications of these solutions, it is important to first examine the possibility that the problem could be an artifact of flawed data, arising from erroneous age assignments or directional biases rooted in local block rotations, shallowed inclinations, unrecognized remagnetizations, etc. Experiments with data filtering add credence to this notion, as cratonic overlap is reduced by using only high-quality paleopoles - but at the expense of severely thinning the dataset. In order to test this hypothesis more rigorously, new high-quality Mid-to-Late Permian and Early Triassic paleomagnetic data have been collected from Argentina. Our sampling strategy targeted volcanics to minimize the effects of inclination shallowing, and AMS/AARM was employed to improve structural control. Coupled thermal/AF demagnetization and rock magnetic experiments were utilized to fully characterize the magnetic components and remanence carriers. Age constraints on the volcanics have been improved with new geochronologic work and early/primary magnetic acquisition is demonstrable through stability tests. These new results refute the necessity of alternative reconstructions or NDF models during Late Permian-Early Triassic time, as the paleomagnetic data allow Gondwana and Laurasia to be restored to a tight ‘A-type’ fit, without producing impossible continental overlap. Thus, alternative reconstructions of Pangea should be restricted to the Late Carboniferous-Early Permian, and the transformative megashearing event must have occurred prior to the Late Permian, if at all.

Domeier, M. M.; van der Voo, R.; Tomezzoli, R.; Torsvik, T. H.; Tohver, E.; Hendriks, B.; Vizan, H.; Dominguez, A. R.

2009-12-01

395

Evolutionary and Ecological Sequelae of Mass Extinctions: Examples From the Continental Triassic-Jurassic Boundary  

NASA Astrophysics Data System (ADS)

The Triassic-Jurassic boundary at ˜200 Ma marks one of the five major mass-extinctions of the Phanerozoic and, depending on the metrics used, was similar in magnitude to the K-T mass extinction. In continental environments about 50% of all tetrapod families are eliminated and although floral diversity change is difficult to gauge, a similar proportion of palynomorph taxa disappear at the boundary. The extinction event appears to have been very abrupt, followed by a roughly 900 ky super-greenhouse period characterized by increased precipitation. We hypothesize a series of biological consequences of the drop in diversity and associated super-greenhouse based on observations of the earliest Jurassic assemblages, largely from eastern North America. 1) The drop in diversity results in a collapse of ecological interactions that tend to stabilize the composition of regional biotas and buffer them from invading forms. Triassic assemblages show considerable biogeographic provinciality despite the existence of Pangea, but the earliest Jurassic assemblages were extraordinarily homogenous with many vertebrate genera being essentially global in distribution. 2) Initially the post-boundary terrestrial assemblages were comprised of eurytopic trophic generalists, with animal communities with few herbivores, but abundant carnivores and detritivores subsisting on aquatic-based food webs. The earliest Jurassic tetrapod footprint record is overwhelmingly dominated by the footprints of ceratosaurian theropod dinosaurs, the latter having skull characteristics usually associated at least in part with piscivory. 3) The dramatic size changes over very short periods of time were likely due to an absence of competition (i.e., ecological release). The maximum size of theropod dinosaur footprints increased by about 25% within 10 ky following the boundary, corresponding to a doubling of mass. 4) Representatives of clades with intrinsically high rates of speciation tend to form species flocks after the boundary. Species flocks of semionotid fishes dominated earliest Jurassic giant rift lakes in eastern North America, but not Triassic or later Early Jurassic lakes in the same basins. Based on footprint data, it is quite possible that there were also species flocks of morphologically similar ceratosaurian theropod dinosaurs in the Early Jurassic.

Olsen, P. E.; Whiteside, J. H.

2003-12-01

396

Recovery from the most profound mass extinction of all time  

PubMed Central

The end-Permian mass extinction, 251 million years (Myr) ago, was the most devastating ecological event of all time, and it was exacerbated by two earlier events at the beginning and end of the Guadalupian, 270 and 260?Myr ago. Ecosystems were destroyed worldwide, communities were restructured and organisms were left struggling to recover. Disaster taxa, such as Lystrosaurus, insinuated themselves into almost every corner of the sparsely populated landscape in the earliest Triassic, and a quick taxonomic recovery apparently occurred on a global scale. However, close study of ecosystem evolution shows that true ecological recovery was slower. After the end-Guadalupian event, faunas began rebuilding complex trophic structures and refilling guilds, but were hit again by the end-Permian event. Taxonomic diversity at the alpha (community) level did not recover to pre-extinction levels; it reached only a low plateau after each pulse and continued low into the Late Triassic. Our data showed that though there was an initial rise in cosmopolitanism after the extinction pulses, large drops subsequently occurred and, counter-intuitively, a surprisingly low level of cosmopolitanism was sustained through the Early and Middle Triassic.

Sahney, Sarda; Benton, Michael J

2008-01-01

397

Scaling behaviour of the time-fractional Kardar-Parisi-Zhang equation  

NASA Astrophysics Data System (ADS)

The scaling behaviour of the time-fractional Kardar-Parisi-Zhang (TFKPZ) equation in (1 + 1) dimensions is investigated by scaling analysis and numerical simulations. The surface morphology and critical exponents with different fractional orders are obtained. The analytical results are consistent with the corresponding numerical solutions based on a Caputo-type fractional derivative. We find that, similar to the normal Kardar-Parisi-Zhang equation, anomalous behaviour does not appear in the TFKPZ model according to the scaling idea of local slope and numerical evidence. However, there exists significant finite-time effect of local scaling exponents in the TFKPZ system. Our results also imply that memory effects can affect the scaling behaviour of evolving fractional surface growth.

Xia, Hui; Tang, Gang; Ma, Jingjie; Hao, Dapeng; Xun, Zhipeng

2011-07-01

398

Synchronous Wildfire Activity Rise and Mire Deforestation at the Triassic-Jurassic Boundary  

PubMed Central

The end-Triassic mass extinction event (?201.4 million years ago) caused major faunal and floral turnovers in both the marine and terrestrial realms. The biotic changes have been attributed to extreme greenhouse warming across the Triassic–Jurassic (T–J) boundary caused by massive release of carbon dioxide and/or methane related to extensive volcanism in the Central Atlantic Magmatic Province (CAMP), resulting in a more humid climate with increased storminess and lightning activity. Lightning strikes are considered the primary source of wildfires, producing charcoal, microscopically recognized as inertinite macerals. The presence of polycyclic aromatic hydrocarbons (PAHs) of pyrolytic origin and allochthonous charcoal in siliciclastic T–J boundary strata has suggested widespread wildfire activity at the time. We have investigated largely autochthonous coal and coaly beds across the T–J boundary in Sweden and Denmark. These beds consist of predominantly organic material from the in situ vegetation in the mires, and as the coaly beds represent a substantial period of time they are excellent environmental archives. We document a remarkable increase in inertinite content in the coal and coaly beds across the T–J boundary. We show estimated burning temperatures derived from inertinite reflectance measurements coupled with palynological data and conclude that pre-boundary late Rhaetian mire wildfires included high-temperature crown fires, whereas latest Rhaetian–Sinemurian mire wildfires were more frequent but dominated by lower temperature surface fires. Our results suggest a major change in the mire ecosystems across the T–J boundary from forested, conifer dominated mires to mires with a predominantly herbaceous and shrubby vegetation. Contrary to the overall regional vegetation for which onset of recovery commenced in the early Hettangian, the sensitive mire ecosystem remained affected during the Hettangian and did not start to recover until around the Hettangian–Sinemurian boundary. Decreasing inertinite content through the Lower Jurassic suggests that fire activity gradually resumed to considerable lower levels.

Petersen, Henrik I.; Lindstrom, Sofie

2012-01-01

399

Synchronous wildfire activity rise and mire deforestation at the triassic-jurassic boundary.  

PubMed

The end-Triassic mass extinction event (?201.4 million years ago) caused major faunal and floral turnovers in both the marine and terrestrial realms. The biotic changes have been attributed to extreme greenhouse warming across the Triassic-Jurassic (T-J) boundary caused by massive release of carbon dioxide and/or methane related to extensive volcanism in the Central Atlantic Magmatic Province (CAMP), resulting in a more humid climate with increased storminess and lightning activity. Lightning strikes are considered the primary source of wildfires, producing charcoal, microscopically recognized as inertinite macerals. The presence of polycyclic aromatic hydrocarbons (PAHs) of pyrolytic origin and allochthonous charcoal in siliciclastic T-J boundary strata has suggested widespread wildfire activity at the time. We have investigated largely autochthonous coal and coaly beds across the T-J boundary in Sweden and Denmark. These beds consist of predominantly organic material from the in situ vegetation in the mires, and as the coaly beds represent a substantial period of time they are excellent environmental archives. We document a remarkable increase in inertinite content in the coal and coaly beds across the T-J boundary. We show estimated burning temperatures derived from inertinite reflectance measurements coupled with palynological data and conclude that pre-boundary late Rhaetian mire wildfires included high-temperature crown fires, whereas latest Rhaetian-Sinemurian mire wildfires were more frequent but dominated by lower temperature surface fires. Our results suggest a major change in the mire ecosystems across the T-J boundary from forested, conifer dominated mires to mires with a predominantly herbaceous and shrubby vegetation. Contrary to the overall regional vegetation for which onset of recovery commenced in the early Hettangian, the sensitive mire ecosystem remained affected during the Hettangian and did not start to recover until around the Hettangian-Sinemurian boundary. Decreasing inertinite content through the Lower Jurassic suggests that fire activity gradually resumed to considerable lower levels. PMID:23077574

Petersen, Henrik I; Lindström, Sofie

2012-10-15

400

Time Scales in the Approach to Equilibrium of Macroscopic Quantum Systems  

NASA Astrophysics Data System (ADS)

We prove two theorems concerning the time evolution in general isolated quantum systems. The theorems are relevant to the issue of the time scale in the approach to equilibrium. The first theorem shows that there can be pathological situations in which the relaxation takes an extraordinarily long time, while the second theorem shows that one can always choose an equilibrium subspace, the relaxation to which requires only a short time for any initial state.

Goldstein, Sheldon; Hara, Takashi; Tasaki, Hal

2013-10-01

401

Early Triassic carbon isotope excursions from South China: proxies for devastation and restoration of marine ecosystems following the end-Permian mass extinction  

Microsoft Academic Search

Early Triassic carbon isotopes are measured based on 1422 carbonate bulk samples from 10 Lower Triassic sections in different palaeogeographic settings in South China. Early Triassic fluctuation of d13C is used as a proxy for environmental change to discuss the devastation and restoration of marine ecosystems following the biggest Phanerozoic mass extinction at the end of the Permian. Early Triassic

Tong Jinnan; Zuo Jingxun

2007-01-01

402

Applications of time-frequency and time-scale transforms to ultra-wideband radar transient signal detection  

NASA Astrophysics Data System (ADS)

In this paper we use a non-stationary approach and analyze ultra-wideband (UWB) radar data using time-frequency and time-scale transformations. The time-frequency transformations considered are the Short-Time Fourier Transform (STFT), the Wigner-Ville Distribution (WD), the Instantaneous Power Spectrum (IPS), and the ZAM transform. Two discrete implementations of the Wavelet Transform (DWT) are also investigated: the decimated A- trous algorithm proposed by Holschneider et al, which uses non-orthogonal wavelets; and the Mallat algorithm, which employs orthogonal wavelets. The transients under study are UWB radar returns from a boat (with and without corner reflector) in the presence of sea clutter, multipath, and radio frequency interferences (RFI). Results show that all time-frequency and time-scale transforms clearly detect the transient radar returns corresponding to the boat with a corner reflector. However, as the radar cross section of the target decreases (boat without a corner reflector), results change drastically as the RFI component dominates the signal. Simulations show that the Instantaneous Power Spectrum may be better adapted for localizing the transient among the time-frequency techniques studied. The decimated A-trous algorithm has the best time resolution of the techniques studied as the return appears better localized in the scalogram.

Fargues, Monique P.; Brooks, William A.

1993-11-01

403