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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

Time-scale calibration by U-Pb geochronology: Examples from the Triassic Period  

NASA Astrophysics Data System (ADS)

U-Pb zircon geochronology, pioneered by Tom Krogh, is a cornerstone for the calibration of the time scale. Before Krogh's innovations, U-Pb geochronology was essentially limited by laboratory blank Pb (typically hundreds of nanograms) inherent in the then existing zircon dissolution and purification methods. The introduction of high pressure HF dissolution combined with miniature ion exchange columns (1) reduced the blank by orders of magnitude and allowed mass-spectrometric analyses of minute amounts of material (picograms of Pb and U). Krogh also recognized the need for minimizing the effects of Pb loss, and the introduction of the air-abrasion technique was the method of choice for two decades (2), until the development of the combined annealing and chemical abrasion technique resulted in essentially closed system zircons (3). These are the prerequisite for obtaining precise (permil-level) and accurate radio-isotopic ages of individual zircons contained in primary volcanic ash deposits, which are primary targets for the calibration of the time scale if they occur within fossil bearing sediments. A prime example is the calibration of the Triassic time scale which improved significantly using these techniques. The ages for the base and the top of the Triassic are constrained by U-Pb ages to 252.3 (4) and 201.5 Ma (5), respectively. These dates also constrain the ages of major extinction events at the Permian-Triassic and Triassic-Jurassic boundaries, and are statistically indistinguishable from ages obtained for the Siberian Traps and volcanic products from the Central Atlantic Magmatic Province, respectively, suggesting a causal link. Ages for these continental volcanics, however, are mostly from the K-Ar (40Ar/39Ar) system which requires accounting and correcting for a systematic bias of ca 1 % between U-Pb and 40Ar/39Ar isotopic ages (the 40Ar/39Ar ages being younger) (6). Robust U-Pb age constraints also exist for the Induan- Olenekian boundary (251.2 Ma, (7)) and the Early-Middle Triassic (Olenekian-Anisian) boundary (247.2 Ma, (8, 9)), resulting in a surprisingly short duration of the Early Triassic which has implications for the timing of biotic recovery and major changes in ocean chemistry during this time. Furthermore, the Anisian-Ladinian boundary is constrained to 242.0 Ma by new U-Pb and 40Ar/39Ar ages. Radio-isotopic ages for the Late Triassic are scarce and the only reliable and biostratigraphically controlled age is from an upper Carnian tuff dated to 230.9 Ma (10), yielding a duration of more than 35 Ma for the Late Triassic. The resulting time-scale is at odds with the most recent compilation (11) but arguably more accurate because it is entirely based on U-Pb analyses applied to closed-system zircons with uncertainties at the permil level or better. 1. T. E. Krogh, Geochimica et Cosmochimica Acta 37, 485 (1973); 2. T. E. Krogh, Geochimica et Cosmochimica Acta 46, 637 (1982); 3. J. M. Mattinson, Chemical Geology 220, 47 (2005); 4. R. Mundil, K. R. Ludwig, I. Metcalfe, P. R. Renne, Science 305, 1760 (2004); 5. U. Schaltegger, J. Guex, A. Bartolini, B. Schoene, M. Ovtcharova, Earth and Planetary Science Letters 267, 266 (2008); 6. R. Mundil, P. R. Renne, K. K. Min, K. R. Ludwig, in Eos Trans. AGU, Fall Meet. Suppl. (2006), vol. 87(52), pp. V21A-0543; 7. T. Galfetti et al., Earth and Planetary Science Letters 258, 593 (2007). 8. M. Ovtcharova et al., Earth and Planetary Science Letters 243, 463 (2006). 9. J. Ramezani et al., Earth and Planetary Science Letters 256, 244 (2007). 10. S. Furin et al., Geology 34, 1009 (2006); 11. J. G. Ogg, in A Geologic Time Scale 2004 F. M. Gradstein, J. G. Ogg, A. G. Smith, Eds. (University Press, Cambridge, 2004) pp. 271-306.

Mundil, R.

2009-05-01

3

The late Permian\\/early Triassic magnetic polarity time scale and plate motions of south China  

Microsoft Academic Search

Fossiliferous stratigraphic sections spanning the Permian-Triassic boundary in south China have yielded a well-defined magnetic polarity sequence for the Lower Triassic and a more poorly defined sequence in the upper Permian. Four sections comprising more than 1100 continuous meters of stratigraphic section display a sequence of 11 major reversals of polarity within the Early Triassic (Griesbachian to Sapthian stages) and

M. Steiner; J. Ogg; Z. Zhang; S. Sun

1989-01-01

4

High-precision U-Pb zircon geochronological constraints on the End-Triassic Mass Extinction, the late Triassic Astronomical Time Scale and geochemical evolution of CAMP magmatism  

NASA Astrophysics Data System (ADS)

Mass extinction events that punctuate Earth's history have had a large influence on the evolution, diversity and composition of our planet's biosphere. The approximate temporal coincidence between the five major extinction events over the last 542 million years and the eruption of Large Igneous Provinces (LIPs) has led to the speculation that climate and environmental perturbations generated by the emplacement of a large volume of magma in a short period of time triggered each global biologic crisis. Establishing a causal link between extinction and the onset and tempo of LIP eruption has proved difficult because of the geographic separation between LIP volcanic deposits and stratigraphic sequences preserving evidence of the extinction. In most cases, the uncertainties on available radioisotopic dates used to correlate between geographically separated study areas often exceed the duration of both the extinction interval and LIP volcanism by an order of magnitude. The "end-Triassic extinction" (ETE) is one of the "big five" and is characterized by the disappearance of several terrestrial and marine species and dominance of Dinosaurs for the next 134 million years. Speculation on the cause has centered on massive climate perturbations thought to accompany the eruption of flood basalts related to the Central Atlantic Magmatic Province (CAMP), the most aerially extensive and volumetrically one of the largest LIPs on Earth. Despite an approximate temporal coincidence between extinction and volcanism, there lacks evidence placing the eruption of CAMP prior to or at the initiation of the extinction. Estimates of the timing and/or duration of CAMP volcanism provided by astrochronology and Ar-Ar geochronology differ by an order of magnitude, precluding high-precision tests of the relationship between LIP volcanism and the mass extinction, the causes of which are dependent upon the rate of magma eruption. Here we present high precision zircon U-Pb ID-TIMS geochronologic data for eight CAMP flows and sills from the eastern U.S. and Morocco. These data are used first to independently test the astronomically calibrated time scale and sediment accumulation rates within the Triassic-Jurassic rift basins along the eastern North America. The U-Pb, paleontological, magnetostratigraphic and astronomical data are combined to constrain the onset and duration of the CAMP and clarify the temporal relationship between the CAMP and the ETE. The dataset together allows more precise estimates of eruptive volume per unit time, a requirement for rigorous evaluation of climate-driven models for the extinction.

Blackburn, T. J.; Olsen, P. E.; Bowring, S. A.; McLean, N. M.; Kent, D. V.; Puffer, J. H.; McHone, G.; Rasbury, T.

2012-12-01

5

Integrated Upper Carnian to Lower Norian biochronology and implications for the Upper Triassic magnetic polarity time scale  

NASA Astrophysics Data System (ADS)

We summarize the ammonoid, conodont and halobiid biochronology of the Upper Carnian to Lower Norian, based on a discussion of data in the Alps, Sicily, Balkans, Turkey, Himalayas and Timor. With this integrated biostratigraphic scale, the Pizzo Mondello section (Sicily) can be recalibrated and the Carnian-Norian boundary more precisely located there. As a result, the magnetostratigraphy of this section is now in good agreement with previous results from Turkey, although the latter series are more condensed. Cross-correlation of available magnetostratigraphic data from marine Tethyan sections allow us to construct a composite Upper Carnian to Upper Norian geomagnetic polarity time scale (GPTS). This GPTS leads us to question previously proposed magnetobiostratigraphic and chronostratigraphic correlations within the Upper Triassic Newark non-marine sedimentary sequence.

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

2002-10-01

6

The continental Permian-Triassic boundary in the Netherlands: Implications for the geomagnetic polarity time scale  

NASA Astrophysics Data System (ADS)

In Central and NW Europe, the transition from the Permian to the Triassic (i.e., the Zechstein-Buntsandstein boundary interval) is developed mainly in red bed facies. This continental sedimentary succession is marked by relatively high sedimentation rates providing a high temporal resolution favorable for magnetic polarity stratigraphy. Here, we present a Zechstein to Lower Buntsandstein magnetostratigraphy obtained from the c. 100 m thick Everdingen-1 core from the Netherlands. Seven magnetozones (EV1n to EV4n) and five submagnetozones (EV1n.1r to EV3r.1n) have been delineated. The Everdingen-1 magnetostratigraphy has been integrated into the well-established high-resolution Zechstein-Buntsandstein stratigraphic framework, and verifies the geomagnetic polarity record from Central Germany. This confirms the hypothesis of nearly synchronous base-level cycles within the interior of the Central European Basin. These cycles are related to solar-induced ~ 100 ka eccentricity cycles. The most distinctive feature of the Everdingen-1 magnetostratigraphy is a transition from a thin reverse to a thick dominantly normal magnetic polarity interval. This reversal predates both the terrestrial mass extinction, which is indicated by a palynofloral turnover and a major sediment provenance change at the base of the Buntsandstein, and the marine Permian-Triassic Boundary (PTB). The PTB is located within the lowermost Buntsandstein and is approximated by the last occurrence of the conchostracan Falsisca postera and a negative excursion in the carbon isotope record. According to the Buntsandstein cyclostratigraphy, the R/N reversal predates the marine end-Permian extinction event by about 0.1 Ma and the marine biostratigraphic PTB by about 0.2 Ma. The thick normal magnetozone is estimated to have lasted c. 700 ka, and roughly coincides with the main phase of Siberian Trap volcanism.

Szurlies, Michael; Geluk, Mark C.; Krijgsman, Wout; Kürschner, Wolfram M.

2012-02-01

7

Early Triassic magnetic polarity time scale—integration of magnetostratigraphy, ammonite zonation and sequence stratigraphy from stratotype sections (Canadian Arctic Archipelago)  

NASA Astrophysics Data System (ADS)

Stratotypes defining the stages of the Early Triassic (Griesbachian, Dienerian, Smithian and Spathian) are located on Ellesmere and Axel Heiberg islands in the northern Canadian Arctic. Ammonite-rich horizons are within a clastic outer shelf-to-slope facies of thick progradational wedges of mudstones and siltstones. Three sections were sampled for magnetostratigraphy and interpreted for transgressive and regressive pulses of sedimentation. Using the ammonite zonation as a guide, the transgressive-regressive cycles and magnetostratigraphies have been correlated among the sections and to the published Triassic sequence stratigraphy time scale, thus enabling definition of the magnetic polarity pattern for the upper Griesbachian to Smithian stages in multiple sections. The magnetic polarity and associated sequence stratigraphy pattern for the lower Griesbachian and for the Spathian were derived from single sections. The Griesbachian and Dienerian stages each have two pairs of normal- and reversed-polarity chrons; the Smithian is predominantly of normal polarity, and the Spathian is predominantly of reversed polarity. This magnetic polarity time scale may help to resolve age correlations of North American redbed facies and to define the Permian-Triassic boundary. After correction for variable structural orientations, the mean directions of magnetization from the three sites converge at 296° declination, 57° inclination ( k = 60, ? 95 = 16.5° ; equivalent pole = 41°N, 161°E; paleolatitude = 38°N), which is consistent with the pole derived from nearby Early Permian volcanics and supports a postulated post-Early Triassic, pre-Tertiary counterclockwise rotation of this region with respect to cratonic North America.

Ogg, James G.; Steiner, Maureen B.

1991-10-01

8

Calibration of the Permo-Triassic Magnetostratigraphic Time Scale: Constraints from the Dewey Lake Formation, West Texas  

NASA Astrophysics Data System (ADS)

Magnetostratigraphy is potentially a powerful tool for deciphering the high resolution chronostratigraphy of events across the Permo-Triassic boundary, but few well-dated polarity reversals exist to serve as calibration. Red beds of the Dewey Lake Formation (DLF) of West Texas span three reversed polarity intervals (Steiner, 2001) in a section of the DLF at Caprock Canyons State Park, where two tuffs occur. Sanidine separated from these tuffs was analyzed by 40Ar/39Ar methods. Single crystal laser fusion 40Ar/39Ar analyses of 40 grains from the upper tuff yield a weighted mean age of 249.9 ± 2.4 Ma (2? errors here and throughout). The clustering of single crystal data provides some assurance against xenocrystic contamination. Two age spectra from multigrain sanidine separates from the lower tuff yielded integrated ages of 248.9 ± 2.8 Ma and 249.7 ± 2.8 Ma and consistent plateau ages of 249.2 ± 2.4 Ma and 249.6 ± 2.4 Ma. Two age spectra from multigrain upper tuff sanidines lack strict plateaus but with overall flat age spectra, with integrated ages of 249.7 ± 2.8 Ma and 250.3 ± 2.8 Ma and plateau-like segments (>70% of 39Ar released) with ages of 249.9 ± 2.6 Ma and 249.9 ± 2.6 Ma, respectively. These results, compared with 40Ar/39Ar data (using the same FCs = 28.02 Ma standard calibration) from the GSSP section at Meishan, China, suggest that the Permo-Triassic boundary (249.8 Ma; recalculated from Renne et al., 1995) definitely occurs within the lower Dewey Lake Formation. The two tuffs, which bracket a normal to reverse geomagnetic polarity transition polarity (Steiner, 2001), have indistinguishable ages. The age of this Permo-Triassic polarity transition is thus best represented by the weighed average of their ages, ca. 249.7 Ma (based on accepted calibrations of the 40Ar/39Ar system). Further such constraints will facilitate high-resolution comparison of terrestrial and marine records across this critical time interval.

Chang, S.; Knight, K. B.; Renne, P. R.

2005-12-01

9

A 70 million year astronomical time scale for the deep-sea bedded chert sequence (Inuyama, Japan): Implications for Triassic-Jurassic geochronology  

NASA Astrophysics Data System (ADS)

The astronomical time scale (ATS) has provided high-resolution geochronology. However, the early Mesozoic ATS is still under construction partly due to the lack of continuous pelagic sequences of the early Mesozoic. Here we present ca. ?70 Myr long ATS constructed from the early Mesozoic deep-sea bedded chert sequence exposed in the Inuyama area, central Japan. The sedimentary rhythms of bedded chert display a full range of climatic precession related cycles; ?20-kyr cycle as a chert-shale couplet and ?100-, 405-, 2000- to 4000-, and 10,000-kyr cycles as chert bed thickness variation. The newly established ATS (Inuyama-ATS) is tuned by 405-kyr eccentricity cycle and is anchored at the end-Triassic radiolarian extinction level as 201.4±0.2 Ma. This Inuyama-ATS gives ages consistent with the radiometric ages projected to the Inuyama deep-sea sequence using biostratigraphy and carbon isotope stratigraphy. The Inuyama-ATS provides the age constraints for the Triassic and Jurassic stage boundaries, which support the “Long-Norian” option of Muttoni et al. (2004). Because the deep-sea bedded chert sequence covers a long time interval before the Cretaceous, the ATS for the bedded chert will serve as a template for the astrochronology of Mesozoic and older ages.

Ikeda, Masayuki; Tada, Ryuji

2014-08-01

10

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

11

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

12

High precision time calibration of the Permo-Triassic boundary mass extinction by U-Pb geochronology  

NASA Astrophysics Data System (ADS)

U-Pb dating using Chemical Abrasion, Isotope Dilution Thermal Ionization Mass Spectrometry (CA-ID-TIMS) is the analytical method of choice for geochronologists, who are seeking highest temporal resolution and a high degree of accuracy for single grains of zircon. The use of double-isotope tracer solutions, cross-calibrated and assessed in different EARTHTIME labs, coinciding with the reassessment of the uranium decay constants and further improvements in ion counting technology led to unprecedented precision better than 0.1% for single grain, and 0.05% for population ages, respectively. These analytical innovations now allow calibrating magmatic and biological timescales at resolution adequate for both groups of processes. To construct a revised and high resolution calibrated time scale for the Permian-Triassic boundary (PTB) we use (i) high-precision U-Pb zircon age determinations of a unique succession of volcanic ash beds interbedded with shallow to deep water fossiliferous sediments in the Nanpanjiang Basin (South China) combined with (ii) accurate quantitative biochronology based on ammonoids and conodonts and (iii) carbon isotope excursions across the PTB. Using these alignments allows (i) positioning the PTB in different depositional environments and (ii) solving age/stratigraphic contradictions generated by the index, water depth-controlled conodont Hindeodus parvus, whose diachronous first occurrences are arbitrarily used for placing the base of the Triassic. This new age framework provides the basis for a combined calibration of chemostratigraphic records with high-resolution biochronozones of the Late Permian and Early Triassic. Besides the general improvement of the radio-isotopic calibration of the PTB at the ±100 ka level, this will also lead to a better understanding of cause and effect relations involved in this mass extinction.

Baresel, Björn; Bucher, Hugo; Brosse, Morgane; Schaltegger, Urs

2014-05-01

13

Fluvial/tidal interaction at the southern Tethyan strandline during Triassic Mukheiris times in central Jordan  

NASA Astrophysics Data System (ADS)

The Triassic (Anisian) Mukheiris Formation is exposed along the northeastern margins of the Dead Sea area, and encompasses all those sediments preserved between the Triassic Hisban and Iraq al Amir formations. It attains a thickness of at least 108 m, and comprises two subdivisions defined here: a lower tidal unit and an upper fluvial unit. The presence of fossiliferous limestones and marlstones in the lower member, and the presence of thin, rhythmic tidal bedding, flaser bedding and oscillation ripple marks suggests deposition in a tidally influenced shallow water, marine environment. The erosively based, fining-upward cycles of non-fossiliferous, unidirectional cross-bedded quartz arenites, and paucity of siltstones and mudstones in the lower part of the fluvial unit indicate that deposition occurred within a braided mixed load fluvial system. The increased proportion of fines ratio in the upper part suggests a change to a more meandering fluvial system. The spatial and temporal arrangement of tidal/fluvial facies during Mukheiris times may be related to fluctuations of the Tethyan strandline due to fluctuations in relative sea level and the development of alternating transgressive and regressive events.

Makhlouf, Issa M.

2003-01-01

14

Late Triassic Magneto-biostratigraphy From Sicily  

NASA Astrophysics Data System (ADS)

The aim of this study is to contribute to the development of an integrated geologic time scale for the Late Triassic that relates marine and nonmarine facies using the global record of geomagnetic polarity reversals. The 427 m-thick Upper Triassic ma- rine limestone section at Pizzo Mondello in the Sicani Mountains of western Sicily is characterized by high quality of exposure, accessibility, and stratigraphic continu- ity. Magnetostratigraphic and biostratigraphic data from Pizzo Mondello are presented and correlated with the Newark reference sequence of polarity reversals.

Muttoni, G.; Nicora, A.; Kent, D. V.; di Stefano, P.; Lowrie, W.

15

Timing is everything: ecological vs. evolutionary pacing of Triassic-Jurassic carbon cycle disruptions  

NASA Astrophysics Data System (ADS)

Eruption of Earth's largest flood basalt, the Central Atlantic Magmatic Province (CAMP) has been proposed as the trigger for a major carbon cycle disruption at the Triassic-Jurassic mass extinction interval at ~201 Ma. Inferred from negative excursions in the carbon isotopic composition (?13C) of carbonate and organic matter, this perturbation has been linked to massive dissociation of isotopically light, methane-rich gas hydrates caused by volcanogenic CO2-induced global warming. However, both the sequence and duration of the CAMP eruptions relative to the carbon cycle perturbation remain circumstantial and indirect, because the data have been from stratigraphic sections far from the flood basalts and without accumulation rate constraints. Here we use a record of atmospheric (?13C) from specific molecules (nC25 - nC32 n-alkanes) diagnostic of terrestrial plant leaf waxes from astronomically-paced cyclical lacustrine strata in which CAMP flood basalts are interbedded to directly examine the relationship between the (?13C) excursions and their durations. We show that the flood basalts postdate the abrupt start of a ~400 ky negative excursion coincident with the initiation of the mass extinction event, but predate a protracted 1.5 m.y. negative excursion. Based on a modified BLAG carbon cycle model, the timing and long durations of our (?13C) excursions are incompatible with CAMP-triggered gas hydrate release. Instead, we suggest that the (?13C) pattern is more consistent with a catastrophically-triggered functional reorganization of the biosphere, part of which involved the ascent of dinosaurs to ecological dominance, playing out over evolutionary time.

Whiteside, J. H.; Olsen, P. E.; Eglinton, T. I.

2007-12-01

16

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

17

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.

18

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

19

Timing of the Permian-Triassic biotic crisis: implications from new zircon U/Pb age data (and their limitations)  

NASA Astrophysics Data System (ADS)

The most profound biotic crisis in the Earth's history, causing the near extinction of both terrestrial and marine life, occurred at the end of the Permian period about 253 Myr ago and marks the Paleozoic-Mesozoic era boundary. The cause of this event is still a matter of vigorous debate, with both brief and catastrophic as well as gradual mechanisms having been proposed. Similar to a recent landmark study, this study uses the U-Pb method on zircons from the uppermost Permian/lowermost Triassic ash fall deposits at Meishan (Zhejiang Province, SE China) in order to examine time and rate constraints for these events. The results of both this study and previous work show that for these ash layers, the effects of Pb loss are combined with varying amounts and sources of inheritance, resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases. Though the effects of Pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid (as opposed to commonly applied air abrasion) prior to analysis, the presence within a single ash layer of multiple generations of older xenocrysts (in many cases only slightly older than the depositional age) has made quantitative interpretation even more difficult. When these combined phenomena bias individual zircon ages by less than a percent, they are extremely difficult to deconvolute, and, if multi-grain analyses are used, can become impossible to recognize (because of the resulting age averaging). Monte Carlo simulations using actual measurements of individual zircon crystals show that age excursions due to Pb loss and xenocrystic contamination for the Meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi-grain zircon samples are compared. Thus this study uses only high-precision analyses of single crystals, whether from our work or that of previous studies. Three main conclusions have emerged. First, our data require a significant increase in the age of the Permian-Triassic boundary by more than 2 myr compared to the previous study, which shifts the age to a value older than 253 Ma. Second, neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis. Third, even large suites of very high-quality, single-zircon U-Pb analyses for these tuffs cannot, in most cases, yield objective, reliable, and robust dates with accuracies at the sub-myr level - though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible. The last conclusion is not an indictment of zircon U/Pb dating in general (other rocks and other zircon populations can - and do - behave very differently), and further technical advances will likely improve our ability to prepare grains or sub-grains of adequately enhanced quality for analysis. Consequently, the results of the present study strongly suggest that for problems requiring time-scale accuracy, inferences from zircon U-Pb dating must be based on sufficiently large suites of single-crystal or crystal domain, high-precision analyses (<1% error) that are realistically interpreted.

Mundil, Roland; Metcalfe, Ian; Ludwig, Kenneth R.; Renne, Paul R.; Oberli, Felix; Nicoll, Robert S.

2001-04-01

20

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  

Microsoft Academic Search

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

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

2011-01-01

21

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

22

Interactive Geological Time Scale  

NSDL National Science Digital Library

This time scale allows students to select multiple time periods from a list and view them on a highlighted display. It shows the relationship between eon, era, period, sub-period, and epoch and also includes the date in mega-annum (Ma) or millions of years before present. The scale reflects the changes in the Cenozoic Era (Tertiary and Quaternary have been eliminated and the Neogene modified) in the most recent International Stratigraphic Charts.

23

Irreversibility time scale.  

PubMed

Entropy creation rate is introduced for a system interacting with thermostats (i.e., for a system subject to internal conservative forces interacting with "external" thermostats via conservative forces) and a fluctuation theorem for it is proved. As an application, a time scale is introduced, to be interpreted as the time over which irreversibility becomes manifest in a process leading from an initial to a final stationary state of a mechanical system in a general nonequilibrium context. The time scale is evaluated in a few examples, including the classical Joule-Thompson process (gas expansion in a vacuum). PMID:16822023

Gallavotti, G

2006-06-01

24

Pangea Megasequences of Tethyan Gondwana-margin reflect global changes of climate and tectonism in Late Palaeozoic and Early Triassic times—A review  

Microsoft Academic Search

The maximum concentration of continental crust at the Pangea stage is characterized by a specific depositional sequence generally referred to as the Pangea Megasequence. Extending in time from the Late Carboniferous to the middle of the Triassic, the succession exhibits similar trends across the whole of Gondwana. Invariably, the sequence was initiated by Late Carboniferous to Early Permian glacial and

H. Wopfner; X. C. Jin

2009-01-01

25

Basin scale evolution of formation waters: a diagenetic and formation water study of the Triassic Chaunoy Formation, Paris Basin  

Microsoft Academic Search

Formation waters and their movements within basins are commonly attributed with responsibility for patterns of cementation and porosity-loss within reservoirs and aquifers. It is thus important to understand when and how waters move in the subsurface. We have studied the evolution and movement of formation water in the Triassic Chaunoy Formation of the Paris Basin, NW Europe to define the

R. H Worden; M. L Coleman; J-M Matray

1999-01-01

26

Timing of the End-Triassic Extinctions on Land: the Moenave Formation on the Southern Colorado Plateau, USA  

NASA Astrophysics Data System (ADS)

Strata of the Moenave Formation on and adjacent to the southern Colorado Plateau in Utah-Arizona, USA represent one of the best known and most stratigraphically continuous, complete and fossiliferous terrestrial sections across the Triassic-Jurassic boundary. We present here a synthesis of new biostratigraphic and magnetostratigraphic data collected from the Moenave Formation across the outcrop belt, which extends from the St. George area in southwestern Utah to the Tuba City area in northern Arizona. These include, palynomorphs, conchostracans and vertebrate fossils (including footprints) and a composite polarity record based on four 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 conchostracan) allow us to place the Triassic-Jurassic boundary relatively precisely in the middle part of the Whitmore Point Member of the Moenave Formation. This placement supports the conclusion that terrestrial extinctions preceded marine extinctions across the Triassic-Jurassic boundary and likely were unrelated to CAMP volcanism.

Lucas, S. G.; Tanner, L. H.; Geissman, J. W.; Hurley, L. L.; Kozur, H.; Heckert, A.; Kuerschner, W.; Weems, R.

2010-12-01

27

Timing of the End-Triassic Extinctions on Land: the Moenave Formation on the Southern Colorado Plateau, USA  

Microsoft Academic Search

Strata of the Moenave Formation on and adjacent to the southern Colorado Plateau in Utah-Arizona, USA represent one of the best known and most stratigraphically continuous, complete and fossiliferous terrestrial sections across the Triassic-Jurassic boundary. We present here a synthesis of new biostratigraphic and magnetostratigraphic data collected from the Moenave Formation across the outcrop belt, which extends from the St.

S. G. Lucas; L. H. Tanner; J. W. Geissman; L. L. Hurley; H. Kozur; A. Heckert; W. Kuerschner; R. Weems

2010-01-01

28

Hamiltonian Systems on Time Scales  

Microsoft Academic Search

Linear and nonlinear Hamiltonian systems are studied on time scales T. We unify symplectic flow properties of discrete and continuous Hamiltonian systems. A chain rule which unifies discrete and continuous settings is presented for our so-called alpha derivatives on generalized time scales. This chain rule allows transformation of linear Hamiltonian systems on time scales under simultaneous change of independent and

Calvin D. Ahlbrandt; Martin Bohner; Jerry Ridenhour

2000-01-01

29

Timing of the Early Triassic carbon cycle perturbations inferred from new U–Pb ages and ammonoid biochronozones  

Microsoft Academic Search

Based on analyses of single, thermally annealed and chemically abraded zircons, a new high-precision U–Pb age of 251.22±0.20 Ma is established for a volcanic ash layer within the “Kashmirites densistriatus beds” of early Smithian age (Early Triassic) from the Luolou Formation (northwestern Guangxi, South China). This new date, together with recalculated uncertainties of previous U–Pb ages from the same section [M.

Thomas Galfetti; Hugo Bucher; Maria Ovtcharova; Urs Schaltegger; Arnaud Brayard; Thomas Brühwiler; Nicolas Goudemand; Helmut Weissert; Peter A. Hochuli; Fabrice Cordey; Kuang Guodun

2007-01-01

30

Geologic time scale bookmark  

USGS Publications Warehouse

This bookmark, designed for use with U.S. Geological Survey activities at the 2nd USA Science and Engineering Festival (April 26–29, 2012), is adapted from the more detailed Fact Sheet 2010–3059 "Divisions of Geologic Time." The information that it presents is widely sought by educators and students.

U.S. Geological Survey

2012-01-01

31

Three-dimensional accommodation analysis of the Triassic in the Paris Basin: a new approach in unravelling the basin evolution with time  

NASA Astrophysics Data System (ADS)

The mechanisms governing the development of the Paris Basin throughout the Triassic are regarded as being the result of superimposed and successive processes. In this study, the Triassic succession of the Paris Basin was re-interpreted in a sequence stratigraphic context, using essentially wireline log data. From this, a series of isopach maps, lithofacies maps and palaeobathymetric maps was produced for each sequence. Three-dimensional accommodation analysis was then carried out sequence by sequence, over the entire basin to produce a precise, detailed accommodation history for the entire Triassic succession. Previous studies have proposed that the Triassic was deposited during a rift period in a transtensional stress regime, with the formation of a trough superposed onto three fault systems derived from the Variscan structural framework. In this study, Scythian to Ladinian sediments (Buntsandstein and Muschelkalk) record the stress regime that prevailed over much of NW Europe. The basin architecture at this time is in continuity with the neighbouring Germanic Basin. Our three-dimensional accommodation modelling shows that the stress regime changed during the Carnian and the late Norian (Keuper). The Carnian events are marked by (1) the creation of a large depocentre infilled with halite, and (2) a northwest migration of this depocentre during the mid-late Carnian along with deposition of the Grès-à-Roseaux, an extensive fluvial deposit. This documents renewed strike-slip movement along the Bray fault. The Norian events involved major tectonic uplift on the basin margins, producting fan delta progradation into the basin. Rotation of the previous depocentre axis occurs on the downthrown side of the Bray fault. This may be viewed as a consequence of sinistral strike-slip displacement along the Bray fault, forming a local transpressive stress regime. The following Liassic cycle commenced with the Rhaetic sequences and illustrates a complete change in the stress regime. This corresponds with the new stress regime which prevailed over northwest Europe during the Liassic cycle. Accommodation curves from the basin complement this interpretation recognising two major accommodation phases which are separated by a significant unconformity. Both phases record periods of accelerating accommodation followed by a more uniform phase of decelerating accommodation. The accelerating phases correspond to periods of rapid accommodation space creation and result in thick evaporite deposits. They correspond to 'rift pulses' which occurred in the remote North Atlantic and Tethyan domain. Each accommodation phase is proposed to correspond to lithospheric stretching pulses followed by a relaxation period. This study illustrates the importance of sequence stratigraphy coupled with three-dimensional accommodation analysis in refining important stages in the basin evolution with time.

Goggin, Valerie; Jacquin, Thierry; Gaulier, Jean Michel

1997-12-01

32

Triassic Reefs of the Tethys  

Microsoft Academic Search

\\u000a The evolution of Triassic reefs started with a long-lasting global crisis of the metazoan reef ecosystem after the Permian—Triassic\\u000a mass extinction (about 12 Ma), followed by a relatively rapid recovery during the Middle Triassic. Reef systems were differentiated\\u000a during the Upper Triassic but were severely affected by a global crisis at the Triassic—Jurasic boundary. The present contribution\\u000a is focused on

Erik Flügel; Baba Senowbari-Daryan

33

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

34

A Geologic Time Scale 2004  

NASA Astrophysics Data System (ADS)

This may be the most straightforward book review imaginable to write. Just buy this book and use it! You will not regret it.Verlyn Klinkenborg's 23 August 2005 editorial in the New York Times (“Grasping the depth of time as a first step in understanding evolution”) serves as a most timely way begin a review of A Geologic Time Scale 2004 (GTS2004). Klinkenborg writes, “One of the most powerful limits to the human imagination is our inability to grasp, in a truly intuitive way the depths of terrestrial and cosmological time.”

Geissman, John W.

35

Triassic and Jurassic-Cretaceous deposits in the Western Chukotka: geodynamic implications, provenance studies and deformation  

NASA Astrophysics Data System (ADS)

Studied region is situated in western Chukotka, in Northeast Russia. We examine the part of Chukotka microplate, the key element in the evolution of the Amerasian basin. The Triassic of Chukotka is represented by up to 5 km of deposits. Triassic terrigeneous deposits consist of three different complexes: Lower-Middle Triassic, Upper Triassic Carnian, and Norian. All the complexes are represented by rhythmic intercalation of sandstones, siltstones and mudstones. Clastic material was carried by large rivers, possessing large reservoir on neighbouring continent. Progradation of delta system in deeper regions is observed. During the Triassic, sedimentation was represented by continental slope progradation. Petrographic study of mineral composition has established the sandstones as graywackes and lithic arenites, according to Pettijohn classification (1981). Sandstones with clasts of rock fragments of lower metamorphic grade rocks dominate at the base of Triassic deposits, sandstones with fragments of higher grade metamorphic rocks dominate in the Later Triassic deposits. This different shows that the Triassic represents an unroofing sequence sours of erosional processes that produced the clastic material eroded more deeply buried rocks through time. Detrital zircons from Triassic sedimentary rocks were collected for constain its paleogeographic links to source terranes. Zircons populations from these three samples are very similar, and youngest zircon ages show peaks at 236-255 Ma. Besides, we are dating the 9 samples for K-Ar and Rb-Sr methods. Data are similar and show 200-204 Ma, and we suppose that this isotopic data indicate the age of first stage of deformation in Chukotka's basin. The Jurassic-Cretaceous of Chukotka is represented by up to 3 km of deposits. The sedimentary complexes are enriched by organic matter, and fresh clastic materials. Fragments of shales, sometimes laminated or cleaved are their indicator constituents. Sandstones are arkosic. The chemical composition and mineral assemblages are different from Triassic sandstone. Besides, Upper Jurassic sandstones differs from Cretaceous sandstones. Our investigations indicate that Triassic, Upper Jurassic, and Lower Cretaceous sedimentary basins were related to different source provenance. In the paper will discuss the sedimentation, provenances, and geodynamic settings of Triassic and Jurassic-Cretaceous deposits. The studied part of western Chukotka is composed of variably deformed, folded and cleaved rhythmic deposits. Widely distributed and intensively deformed Triassic sequences (Tuchkova et al., 2007) and J-K units both intruded by Aptian-Albian postcollisional plutons and dikes (Katkov et al., 2010). Collisional-related fabric and subsequent granitoids are complicated by small-scale latest normal faults, in particular related to the westernmost segment of South Chukchi (Hope) basin development in Upper Cretaceous (?)-Cenozoic. Intensity of the compressional deformation of Jurassic-Cretaceous rocks is significantly less than in Triassic sequence. Work was supported by RBRR projects 11-05-00787, 11-05-00074, Scientific school # NSh-5177.2012.5, kontrakts No. 04.740.11.0190, and 01/14/20/11.

Tuchkova, M.

2012-04-01

36

Instantaneous scale and the short-time scale transform  

Microsoft Academic Search

The concept of instantaneous scale, ci, is developed and it is shown that it is given by ci=tØ'(t) where Ø'( t) is the derivative of the phase of the signal. Formulas for average scale, scale bandwidth, and scale group delay are obtained. The scale transform, the short time scale transform, the analytic scale signal, and other related concepts are defined

LEON COHEN

1992-01-01

37

The Concise Geologic Time Scale  

NASA Astrophysics Data System (ADS)

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 most up to date, international standard, as ratified by the International Commission on Stratigraphy and the International Union of Geological Sciences. This book is an essential reference for all geoscientists, including researchers, students, and petroleum and mining professionals. The presentation is non-technical and illustrated with numerous colour charts, maps and photographs. The book also includes a detachable laminated card of the complete time scale for use as a handy reference in the office, laboratory or field.

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

38

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

39

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

40

Multiple Time Scale Decomposition of Discrete Time Markov Chains,  

National Technical Information Service (NTIS)

The multiple time scale decomposition of discrete time, finite state Markov chains is addressed. In previous works, the behavior of a continuous time Markov chain is approximated using a fast time scale, epsilon-independent, continuous time process, and a...

J. R. Rohlicek, A. S. Willsky

1988-01-01

41

Time scales, their users, and leap seconds  

Microsoft Academic Search

Numerous time scales exist to address specific user requirements. Accurate dynamical time scales (barycentric, geocentric and terrestrial) have been developed based on the theory of relativity. A family of time scales has been developed based on the rotation of the Earth that includes Universal Time (specifically UT1), which serves as the traditional astronomical basis of civil time. International Atomic Time

P. Kenneth Seidelmann; John H. Seago

2011-01-01

42

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

43

Multiple-scale facies and reservoir quality variations within a dolomite body – Outcrop analog study from the Middle Triassic, SW German Basin  

Microsoft Academic Search

This study focuses on a porous dolomite body in the proximal part of an epeiric carbonate ramp (Triassic Muschelkalk, South German Basin), analogous to hydrocarbon-bearing dolomite reservoirs in the Middle East (e.g. Khuff and Arab Formations).The dolomite body is made up of shoal, lagoonal and peritidal facies types and is built by a three-fold hierarchy of cycles (3rd-order to 5th-order).

Bastian Simon Koehrer; Christian Heymann; Frank Prousa; Thomas Aigner

2010-01-01

44

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

45

Improving the Geologic Time Scale (Jean Baptiste Lamarck Medal Lecture)  

NASA Astrophysics Data System (ADS)

The Geologic Time Scale (GTS) provides the framework for the physical, chemical and biological processes on Earth. The time scale is the tool "par excellence" of the geological trade, and insight in its construction, strength, and limitations enhances its function and its utility. Earth scientists should understand how time scales are constructed and its myriad of physical and abstract data are calibrated, rather than merely using ages plucked from a convenient chart or card. Calibration to linear time of the succession of events recorded in the rocks on Earth has three components: (1) the standard stratigraphic divisions and their correlation in the global rock record, (2) the means of measuring linear time or elapsed durations from the rock record, and (3) the methods of effectively joining the two scales, the stratigraphic one and the linear one. Under the auspices of the International Commission on Stratigraphy (ICS), the international stratigraphic divisions and their correlative events are now largely standardized, especially using the GSSP (Global Stratigraphic Section and Point) concept. The means of measuring linear time or elapsed durations from the rock record are objectives in the EARTH TIME and GTS NEXT projects, that also are educating a new generation of GTS dedicated scientists. The U/Pb, Ar/Ar and orbital tuning methods are intercalibrated, and external error analysis improved. Existing Ar/Ar ages become almost 0.5% older, and U/Pb ages stratigraphically more realistic. The new Os/Re method has potential for directly dating more GSSP's and its correlative events. Such may reduce scaling uncertainty between the sedimentary levels of an age date and that of a stage boundary. Since 1981, six successive Phanerozoic GTS have been published, each new one achieving higher resolution and more users. The next GTS is scheduled for 2011/2012, with over 50 specialists taking part. New chapters include an expanded planetary time scale, sequence stratigraphy, Osmium, Carbon and Oxygen stratigraphy, the Cryogenian period, history of the plants, hominid prehistory, and last but not least the Anthropocene. The Cambrian Period is radically improved with 10 standard stages and detailed trilobite biochronology. Ordovician now has a stable international stages and graptolites scale. The integration of a refined 100 and 400 ka sedimentary cycles scale and a truly high-resolution U/Pb ages scale for the Mississippian is a major step towards the global Carboniferous GTS. The Devonian GTS leaves to be desired with lack of firm definitions for its upper boundary, and the long Emsian stage; it also lacks age dates. Its stages scaling is disputed. The Rhaetian and Norian stages in the Triassic and the Berriasian stage in the Cretaceous urgently require lower boundary definitions, and also boundary age dates. The single ~400 ka eccentricity component is very stable and can extend orbital tuning from the Cenozoic well into the Mesozoic portion of the GTS. Jurassic and Cretaceous now have long orbitally tuned segments. A completely astronomical-tuned Geological Time Scale (AGTS) for the Cenozoic is within reach showing unprecedented accuracy, precision and resolution. Burdigalian in the Miocene, and Lutetian, Bartonian and Priabonian stages in the Eocene still require formal definition. The K/T boundary will become about 0.5 ± 0.1 Ma older. After 25 years of research and authorship in the GTS it behoves me to especially thank my colleagues James Ogg, Frits Agterberg, John McArthur and Roger Cooper for longstanding collaboration. As a final note I urge construction of more regional time scales(like developed ‘down under') calibrated to the standard global GTS, to scale regional rock units.

Gradstein, Felix M.

2010-05-01

46

Dating the end-Triassic and Early Jurassic mass extinctions, correlative large igneous provinces, and isotopic events  

Microsoft Academic Search

The end-Triassic marks one of the five biggest mass extinctions, and was followed by a well-known second-order extinction event in the Early Jurassic. Previously pub- lished geological time scales were inadequate for correlation of extinctions with other global events and to unravel their dynamics. Here we present a revised time scale based on high-precision U-Pb ages integrated with ammonoid biochronology

Jozsef Palfy; Paul L. Smith; James K. Mortensen

47

Feedback systems and multiple time-scales  

NASA Technical Reports Server (NTRS)

A study is conducted of feedback design for systems with multiple time-scale structure uncovering an intrinsic time-scale structure for a state feedback system with full state output. From this a multiple time-scale asymptotic observer and a system with state feedback via a two time-scale asymptotic observer is considered. Finally more general results for a restricted class of systems are obtained.

Silva-Madriz, R.

1986-01-01

48

Time scales, their users, and leap seconds  

NASA Astrophysics Data System (ADS)

Numerous time scales exist to address specific user requirements. Accurate dynamical time scales (barycentric, geocentric and terrestrial) have been developed based on the theory of relativity. A family of time scales has been developed based on the rotation of the Earth that includes Universal Time (specifically UT1), which serves as the traditional astronomical basis of civil time. International Atomic Time (TAI) is also maintained as a fundamental time scale based on the output of atomic frequency standards. Coordinated Universal Time (UTC) is an atomic scale for worldwide civil timekeeping, referenced to TAI, but with epoch adjustments via so-called leap seconds to remain within one second of UT1. A review of the development of the time scales, the status of the leap-second issue, and user considerations and perspectives are discussed. A description of some more recent applications for time usage is included.

Seidelmann, P. Kenneth; Seago, John H.

2011-08-01

49

Stability of Rasch Scales over Time  

ERIC Educational Resources Information Center

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.…

Taylor, Catherine S.; Lee, Yoonsun

2010-01-01

50

Introduction to the time scale problem  

SciTech Connect

As motivation for the symposium on extended-scale atomistic methods, I briefly discuss the time scale problem that plagues molecular dynamics simulations, some promising recent developments for circumventing the problem, and some remaining challenges.

Voter, A. F.

2002-01-01

51

Establishment of a Brazilian Atomic Time Scale.  

National Technical Information Service (NTIS)

The Atomic Time Scale at the Time Service Division of the National Observatory in Rio de Janeiro (ONRJ) has been carried out by commercial cesium clocks. The UTC(ONRJ) time scale based on a single commercial cesium clock selected from the ensemble of cloc...

R. Jose de Carvalho

2006-01-01

52

Carbon cycle changes during the Triassic-Jurassic transition  

Microsoft Academic Search

The end-Triassic is regarded as one of the five major mass extinction events of the Phanerozoic. This time interval is marked by up to 50% of marine biodiversity loss and major changes in terrestrial ecosystems. Mass extinction events are often marked by changes in the global carbon cycle. The reality and nature of C-cycle changes at the Triassic-Jurassic (T-J) transition

M. Ruhl

2010-01-01

53

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

54

Relaxation Processes and Time Scale Transformation.  

National Technical Information Service (NTIS)

Stochastic processes with a special class of non-stationary transition rates (NSTR) that can be related to stationary rates (STR) by time scale transformations are considered. Calculations are carried out on the time scale on which the process has STR and...

S. Teitler, A. K. Rajagopal, K. L. Ngai

1982-01-01

55

Dynamic equations on time scales: a survey  

Microsoft Academic Search

The study of dynamic equations on time scales, which goes back to its founder Stefan Hilger (1988), is an area of mathematics that has recently received a lot of attention. It has been created in order to unify the study of differential and difference equations. In this paper we give an introduction to the time scales calculus. We also present

Ravi Agarwal; Martin Bohner; Donal O'Regan; Allan Peterson

2002-01-01

56

Kalman plus weights: a time scale algorithm  

NASA Technical Reports Server (NTRS)

KPW is a time scale algorithm that combines Kalman filtering with the basic time scale equation (BTSE). A single Kalman filter that estimates all clocks simultaneously is used to generate the BTSE frequency estimates, while the BTSE weights are inversely proportional to the white FM variances of the clocks. Results from simulated clock ensembles are compared to previous simulation results from other algorithms.

Greenhall, C. A.

2001-01-01

57

Analysing Forced Oscillators with Multiple Time Scales  

Microsoft Academic Search

We present a novel formulation, called the WaMPDE, for solving systems with forced autonomous components. An important feature of the WaMPDE is its ability to capture frequency modulation (FM) in a natural and compact man- ner. This is made possible by a key new concept: that of warped time, related to normal time through separate time scales. Using warped time,

Onuttom Narayan; Jaijeet S. Roychowdhury

1999-01-01

58

Metaphor for the geologic time scale  

NSDL National Science Digital Library

This assignment serves as an introduction to the geologic time scale and to help students visualize the long time intervals between major events in Earth's history. The assignment encourages students to choose a metaphor for geologic time, research major events throughout Earth' history, and calculate how much (cumulative) of their metaphor each time interval represents.

Thompson, Cara

59

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

60

A Morphological Time-Scale for Rivers.  

National Technical Information Service (NTIS)

To predict changes in the geometry of a river due to human interference, a morphological time-scale, characterizing processes of degradation (erosion) and aggradation of rivers was defined. Processes of degradation and aggradation of rivers have a speed d...

M. Devries

1975-01-01

61

Long term stability of atomic time scales  

NASA Astrophysics Data System (ADS)

International Atomic Time TAI gets its stability from some 400 atomic clocks worldwide that generate the free atomic scale EA L and its accuracy from a small number of primary frequency standards (PFS) which frequency measurements are used to steer the EAL frequency. Because TAI is computed in "real - time" (every month) and has operational constraints, it is not optimal and the BIPM computes in deferred time another time scale TT(BIPM), which is based on a weighted average of the evaluations of TAI frequency by the PFS. We show that a point has been reached where the stability of atomic time scales, the accuracy of primary frequency standards, and the capabilities of frequency transfer are approximately at a similar level, in the low 10 - 16 in relative frequency. The goal is now to reach and surpass 1x10 - 16 and the three fields are in various stages of advancement towards this aim. We review the stability and accuracy recently achieved by frequency standards, focusing on primary frequency standards on one hand, and on new secondary realizations e.g. based on optical transitions on the other hand. We study how these performances can translate to the performance of atomic time scales, and the possible implications of the availability of new high - accuracy frequency standards operating on a regular basis. Finally we show how time transfer is trying to keep up with the progresses of frequency standards. Time transfer is presently the limiting factor at short averaging time (e.g. 1 - 2 weeks) but it should not be limiting the long term stability of atomic time scales, which is the main need of many applications in astronomy.

Petit, Gérard; Arias, Elisa Felicitas

2012-08-01

62

Time scales of turbulent relative dispersion.  

PubMed

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. PMID:23214642

Bitane, Rehab; Homann, Holger; Bec, Jérémie

2012-10-01

63

Length and Time Scales in Continental Drift  

NASA Astrophysics Data System (ADS)

Nonlinear feedback between continents and the mantle through thermal blanketing has long been surmised as a mechanism for continental drift and Wilson cycles. Paleomagnetism provides ample evidence for large scale (10,000 km) continental motion on time scales of several hundred million years, indicative of large scale mantle circulation. While much has been learned about the interactions between continents and mantle flow from analog and numerical modeling studies in two and three dimensions, a rigorous sensitivity study on the effects of continents in high resolution 3D spherical mantle convection models has yet to be pursued. As a result, a quantitative understanding of the scales of continental motion as they relate to relevant fluid dynamic processes is lacking. Here we focus on the effect of continental size. Continents covering 30% of the surface are representative of a supercontinent such as Pangea, smaller continents (10% of Earth's surface) are representative of present day Asia, and still smaller continents (3% of Earth's surface) are similar to present day Antarctica. These continents are introduced into simple end-member mantle flow regimes characterized by combinations of bottom or internal heating and uniform or layered mantle viscosity. We find that large scale mantle structure, and correspondingly the large scale displacement of continents, depends not only on mantle heating mode and radial viscosity structure, but also on continental size. Supercontinents promote heterogeneity on the largest scales (spherical harmonic degree one), especially when combined with strong bottom heating and a high viscosity lower mantle. Degree one heterogeneities in turn drive cyclical continental motion, with continents moving from the hot to the cold hemisphere on time scales of several hundred million years. Smaller continents are unable to initiate degree one convection. As a result, their motion is governed by shorter length and time scales. We apply these insights toward understanding the motion of several continents to study the aggregation and dispersal of continental groups.

Phillips, B. R.; Bunge, H.

2003-12-01

64

Early Triassic therapsid footprints from the Sydney basin, Australia  

Microsoft Academic Search

A large rock slab collected in 1913 from the roof of the Bellambi Colliery in the southern Sydney Basin bears fossil tracks that are now known from recent radiometric and chemostratigraphic dating to be earliest Triassic, rather than latest Permian, in age. The tracks show two distinctive features of reptiles: scale impressions and claw marks. Both manus and pes are

Gregory J. Retallack

1996-01-01

65

The Geologic Time Scale in Historical Perspective  

NSDL National Science Digital Library

This brief discussion of the development of the Geologic Time Scale begins with Nicolas Steno in 1669 whose ideas have become known as the principles of original horizontal deposition and superposition. Next are James Hutton in 1795 and Charles Lyell in the early 1800s who supported the principle of uniformitarianism. The work of William Smith and the principle of faunal succession is also noted. The site goes on to explain how and why the scale is divided as it is.

66

Time-scale segmentation of respiratory sounds.  

PubMed

Respiratory sounds are composed of various events: normal and so-called adventitious sounds. These phenomena present a wide range of characteristics which make difficult their analysis with a single technique. Adapted time-frequency and time-scale techniques allow to fit best, under constraints, the accuracy of analysis of a time segmentation and, by the way, make feasible the study of complex signals. We present here new approaches based only on the wavelet packet decomposition to segment respiratory sounds. PMID:9754684

Ademovic, E; Pesquet, J C; Charbonneau, G

1998-06-01

67

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

68

Scaling physiological pharmacokinetic models by physiological time  

SciTech Connect

This paper shows that a multicompartment physiological pharmacokinetic model, used to account for inhalation exposure to volatile chlorohydrocarbons in mammalian species, can be made species-independent if chronological time is re-expressed in terms of physiological time. Physiological time is defined as chronological time divided by species body weight to the 1/4 power. We demonstrate the usefulness of this time scaling of the multicompartment physiological pharmacokinetic model by using it to model the inhalation of the volatile chlorinated hydrocarbon tetrachloroethylene in mice, rats, and humans. 8 refs., 2 figs.

Ward, R.C.; Travis, C.C.

1987-01-01

69

Filling the Triassic Geochronologic Gap: A Continuous Cored Record of Continental Environmental Change in Western North America  

NASA Astrophysics Data System (ADS)

The Triassic Period (252.2-201.6 Ma) is bracketed by two mass extinctions, witnessed the evolution of the major groups of modern tetrapods, saw giant bolide impacts, and was typified by generally high atmospheric CO2 and a lack of ice at the poles. Testing hypotheses relevant to these major features of the Triassic, as well as problems related to the Earth system in general, requires temporally well-defined records of environmental and biotic change, especially in terrestrial environments, which until recently were lacking. The NSF and ICDP funded ~500 m long core at Petrified Forest National Park, scheduled to be drilled in Fall, 2013, is part of an interdisciplinary, multi-institutional, Colorado Plateau Coring Project, and is a major step towards providing a network of such records. The core will recover virtually the entire pre-Owl-Rock-Member Late Triassic age Chinle and underlying Early-Middle Triassic age Moenkopi formations. A core is required despite excellent outcrop and a long and distinguished history of study because of ambiguities in local correlation, a lack of constraints on the temporal duration and resolution of biotic events, and an inability to make clear global correlations. Specifically, by integrating a densely sampled paleomagnetic record with high-resolution radioisotopic ages in unquestioned superposition, the new core will allow us to test at least five sets of hypotheses: (1) were marine and continental biotic turnover events in the Late Triassic coupled? (2) was there high faunal provinciality during the existence of the supercontinent of Pangea?; (3) is the time scale of the Newark basin astronomically calibrated GPTS for the Triassic accurate, particularly for the Norian age part that is relevant for mapping the chaotic evolution of the Solar System, as well as global correlations?; (4) is the supposed Carnian-Norian boundary in the Chinle actually a late middle Norian extinction coinciding with the 215.5 Ma Manicouagan impact?; (5) is the stratigraphic record in the Triassic a reflection of changes in local climate due to plate motion through climate belts or changes in global climate driven by other processes, such as CO2 fluctuations? The Petrified Forest core will thus be key to unambiguous testing of these ideas, and observations from it promise to fundamentally change the certainty and specificity of the questions that relate the rich surface record from the Chinle and Moenkopi to Earth system processes.

Olsen, P. E.; Kent, D. V.; Geissman, J. W.; Mundil, R.; Gehrels, G. E.; Irmis, R. B.; Whiteside, J. H.; Schaller, M. F.

2013-12-01

70

Time-scaling in irreversible thermodynamics  

Microsoft Academic Search

We consider linear dynamical systems with motions characterized by two different time-scales. In practice the dynamical matrix in the phenomenological equations of motion often exhibits a strong coupling of the slow and fast variables. It is shown on the basis of the Onsager symmetry relations that a simple transformation of variables leads to a weak coupling. After the transformation one

U. Geigenmüller; B. U. Felderhof; U. M. Titulaer

1983-01-01

71

ISOTOPIC DATING AND THE GEOLOGIC TIME SCALE  

Microsoft Academic Search

The intensive research on isotopic methods of age determination at a ; number of laboratories has produced new methods, advances in experimental ; techniques, and many additional measurements. These developments are reviewed ; with particular reference to the effect of the new age determinations on the ; geologic time scale. The age of the planet now appears to be about

Kulp

1955-01-01

72

Assessing the record and causes of Late Triassic extinctions  

USGS Publications Warehouse

Accelerated biotic turnover during the Late Triassic has led to the perception of an end-Triassic mass extinction event, now regarded as one of the "big five" extinctions. Close examination of the fossil record reveals that many groups thought to be affected severely by this event, such as ammonoids, bivalves and conodonts, instead were in decline throughout the Late Triassic, and that other groups were relatively unaffected or subject to only regional effects. Explanations for the biotic turnover have included both gradualistic and catastrophic mechanisms. Regression during the Rhaetian, with consequent habitat loss, is compatible with the disappearance of some marine faunal groups, but may be regional, not global in scale, and cannot explain apparent synchronous decline in the terrestrial realm. Gradual, widespread aridification of the Pangaean supercontinent could explain a decline in terrestrial diversity during the Late Triassic. Although evidence for an impact precisely at the boundary is lacking, the presence of impact structures with Late Triassic ages suggests the possibility of bolide impact-induced environmental degradation prior to the end-Triassic. Widespread eruptions of flood basalts of the Central Atlantic Magmatic Province (CAMP) were synchronous with or slightly postdate the system boundary; emissions of CO2 and SO2 during these eruptions were substantial, but the contradictory evidence for the environmental effects of outgassing of these lavas remains to be resolved. A substantial excursion in the marine carbon-isotope record of both carbonate and organic matter suggests a significant disturbance of the global carbon cycle at the system boundary. Release of methane hydrates from seafloor sediments is a possible cause for this isotope excursion, although the triggering mechanism and climatic effects of such a release remain uncertain. ?? 2003 Elsevier B.V. All rights reserved.

Tanner, L. H.; Lucas, S. G.; Chapman, M. G.

2004-01-01

73

Reccurent Early Triassic marine anoxia, impacts of volcanics?  

NASA Astrophysics Data System (ADS)

NW Pangea records a complex history of recurrent development of anoxia through the Permo-Triassic Biotic Crises. The Early Triassic record from the Smithian strato-type in the Sverdrup Basin, as well as for the more open ocean setting of Svalbard, have organic carbon isotope records that closely correspond to major fluctuations in the inorganic carbon records from the Tethys, demonstrating truly global perturbations of the carbon cycle occurred during this time. Geochemical proxies for anoxia are strongly correlated with carbon isotopes, whereby negative shifts in ?13Corg are associated with shifts to more anoxic to euxinic conditions, and positive shifts are related to return to more oxic conditions. Rather than a delayed or prolonged recovery, the Early Triassic is characterized better by a series of aborted biotic recoveries related to shifts back to ocean anoxia, potentially driven by recurrent volcanism.

Grasby, Stephen; Beauchamp, Benoit; Sanei, Hamed

2014-05-01

74

A Triassic aquatic protorosaur with an extremely long neck.  

PubMed

By Middle Triassic time, a number of reptile lineages had diversified in shallow epicontinental seas and intraplatform basins along the margins of parts of Pangea, including the giraffe-necked protorosaurid reptile Tanystropheus from the Western Tethys (Europe and the Middle East), which grew to approximately 5 to 6 m long. Here we report another long-necked fossil, Dinocephalosaurus, from southwestern China, recently collected in Middle Triassic marine deposits approximately 230 million years old. This taxon represents unambiguous evidence for a fully aquatic protorosaur. Its extremely elongated neck is explained as an adaptation for aquatic life, perhaps for an increase in feeding efficiency. PMID:15448262

Li, Chun; Rieppel, Olivier; LaBarbera, Michael C

2004-09-24

75

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

76

Accuracy metrics for judging time scale algorithms  

NASA Technical Reports Server (NTRS)

Time scales have been constructed in different ways to meet the many demands placed upon them for time accuracy, frequency accuracy, long-term stability, and robustness. Usually, no single time scale is optimum for all purposes. In the context of the impending availability of high-accuracy intermittently-operated cesium fountains, we reconsider the question of evaluating the accuracy of time scales which use an algorithm to span interruptions of the primary standard. We consider a broad class of calibration algorithms that can be evaluated and compared quantitatively for their accuracy in the presence of frequency drift and a full noise model (a mixture of white PM, flicker PM, white FM, flicker FM, and random walk FM noise). We present the analytic techniques for computing the standard uncertainty for the full noise model and this class of calibration algorithms. The simplest algorithm is evaluated to find the average-frequency uncertainty arising from the noise of the cesium fountain's local oscillator and from the noise of a hydrogen maser transfer-standard. This algorithm and known noise sources are shown to permit interlaboratory frequency transfer with a standard uncertainty of less than 10(exp -15) for periods of 30-100 days.

Douglas, R. J.; Boulanger, J.-S.; Jacques, C.

1994-01-01

77

The end-triassic mass extinction event  

NASA Technical Reports Server (NTRS)

The end-Triassic is the least studied of the five major episodes of mass extinction recognized in the Phanerozoic, and the Triassic-Jurassic boundary is not precisely defined in most parts of the world, with a paucity of good marine sections and an insufficiency of biostratigraphically valuable fossils. Despite these limitations it is clear that there was a significant episode of mass extinction, affecting many groups, in the Late Norian and the existing facts are consistent with it having taken place at the very end of the period. The best record globally comes from marine strata. There was an almost complete turnover of ammonites across the T-J boundary, with perhaps no more than one genus surviving. About half the bivalve genera and most of the species went extinct, as did many archaeogastropods. Many Paleozoic-dominant brachiopods also disappeared, as did the last of the conodonts. There was a major collapse and disappearance of the Alpine calcareous sponge. Among terrestrial biota, a significant extinction event involving tetrapods was recognized. With regard to possible environmental events that may be postulated to account for the extinctions, there is no evidence of any significant global change of climate at this time. The existence of the large Manicouagan crater in Quebec, dated as about late or end-Triassic, has led to the suggestion that an impact event might be implicated, but so far despite intensive search no unequivocal iridium anomaly or shocked quartz was discovered. On the other hand there is strong evidence for significant marine regression in many parts of the world. It is proposed therefore that the likeliest cause of the marine extinctions is severe reduction in habitat area caused either by regression of epicontinental seas, subsequent widespread anoxia during the succeeding transgression, or a combination of the two.

Hallam, A.

1988-01-01

78

A comment on the use of flushing time, residence time, and age as transport time scales  

USGS Publications Warehouse

Applications of transport time scales are pervasive in biological, hydrologic, and geochemical studies yet these times scales are not consistently defined and applied with rigor in the literature. We compare three transport time scales (flushing time, age, and residence time) commonly used to measure the retention of water or scalar quantities transported with water. We identify the underlying assumptions associated with each time scale, describe procedures for computing these time scales in idealized cases, and identify pitfalls when real-world systems deviate from these idealizations. We then apply the time scale definitions to a shallow 378 ha tidal lake to illustrate how deviations between real water bodies and the idealized examples can result from: (1) non-steady flow; (2) spatial variability in bathymetry, circulation, and transport time scales; and (3) tides that introduce complexities not accounted for in the idealized cases. These examples illustrate that no single transport time scale is valid for all time periods, locations, and constituents, and no one time scale describes all transport processes. We encourage aquatic scientists to rigorously define the transport time scale when it is applied, identify the underlying assumptions in the application of that concept, and ask if those assumptions are valid in the application of that approach for computing transport time scales in real systems.

Monsen, N. E.; Cloern, J. E.; Lucas, L. V.; Monismith, S. G.

2002-01-01

79

Short-time scale behavior modeling within long-time scale fuel cycle evaluations  

SciTech Connect

Typically, short-time and long-time scales in nuclear energy system behavior are accounted for with entirely separate models. However, long-term changes in system characteristics do affect short-term transients through material variations. This paper presents an approach to consistently account for short-time scales within a nuclear system lifespan. The reported findings and developments are of significant importance for small modular reactors and other nuclear energy systems operating in autonomous modes. It is necessary to simulate the short time-scale kinetic behavior of the reactor as well as the long time-scale dynamics that occur with fuel burnup. The former is modeled using the point kinetics equations, while the latter is modeled by the Bateman equations. (authors)

Johnson, M.; Tsvetkov, P. [Dept. of Nuclear Engineering, Texas A and M Univ., 3133 TAMU, College Station, TX 77843 (United States); Lucas, S. [Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415 (United States)

2012-07-01

80

Relative Geologic Time and the Geologic Time Scale  

NSDL National Science Digital Library

Students are given a short introduction to fossils, strata, Steno's law of superposition, and the development of the geologic time scale from initial description of systems, through the realization that fossils could be used to correlate between systems, to the assembly of the modern geologic time scale. Then, each student in the course is given a sheet of paper with a simple stratigraphic column and associated fossils representing a geologic system on one side and a short description of the location and history of discovery of the system on the other. On a large wall, students then assemble four geologic columns from their systems representing mainland Europe, Great Britain, the Eastern U.S. and the Western U.S. using the fossils illustrated on their sheets to correlate systems. The instructor guides this process by placing the first system on the wall and by providing some narration as the columns take shape. Europe and Great Britain are assembled first, one sheet at a time, providing when completed the framework of the modern geologic time scale. Once this is up on the wall, the remaining students can assemble the other two columns in minutes using fossils to correlate between American and European systems. A temporal gap in the Grand Canyon sequence provides an opportunity to discuss the incompleteness of the rock record in any one place and a system composed of igneous and metamorphic rocks with no fossils is used to point out the difference between radiometric (absolute) and biostratigraphic (relative) dating.

Bennington, Bret

81

Towards a quaternary time scale*1  

NASA Astrophysics Data System (ADS)

Nine first-appearance datums (FADs), twenty-three last-appearance datums (LADs), and three other micropaleontological datums are related to the magnetic-reversal, oxygen-isotope, and calcite-dissolution/coarse-fraction time scales to provide a preliminary basis for subdivision of the Quaternary in deep-sea sediments. The magnetic-reversal, oxygen-isotope, and calcite-dissolution/coarse-fraction scales have been correlated by determination on the same core materials, and absolute dates applied by {40K}/{40Ar} or 14C dating of materials in known positions on one or another of these scales. FADS and LADs have been determined in cores for which either a magnetic-reversal, oxygen-isotope, or calcite-dissolution/coarse-fraction scale has also been available. Altogether 3 FADs and 5 LADs based on diatoms, 4 FADs and 5 LADs based on calcareous nannoplankton, 1 FAD and 8 LADs based on radiolarians, 1 FAD and 5 LADs based on planktonic foraminifers, 2 acme datums, and 1 ratio reversal datum have been determined, and absolute dates inferred by interpolation from known dates on the reference time scales. Some of the FADs and LADs apply or are synchronous only over limited areas of the oceans; others appear to be synchronous throughout the oceans. The base of the Quaternary is set at the top of the Olduvai event at 1.7 my. Four FADs, twelve LADs, two acme datums, and one ratio reversal datum occur above the base of the Quaternary at an average rate of about 1 per 100,000 yr. Five FADs and twelve LADs are recognized in the 0.8-my interval between the top of the Olduvai event and the Gauss/Matuyama Boundary at 2.5 my at an average incidence of about 1 per 50,000 yr.

Berggren, W. A.; Burckle, L. H.; Cita, M. B.; Cooke, H. B. S.; Funnell, B. M.; Gartner, S.; Hays, J. D.; Kennett, J. P.; Opdyke, N. D.; Pastouret, L.; Shackleton, N. J.; Takayanagi, Y.

1980-05-01

82

Mesozoic cyclostratigraphy, the 405-kyr orbital eccentricity metronome, and the Astronomical Time Scale (Invited)  

NASA Astrophysics Data System (ADS)

Mesozoic cyclostratigraphy from around the world is being assessed to construct a continuous Astronomical Time Scale (ATS) based on Earth’s cyclic orbital parameters. The recognition of a prevalent sedimentary cycling with a ~400-kyr period associated with forcing by the stable 405-kyr orbital eccentricity variation is an important development. Numerous formations spanning 10 to 20 myr (and longer) intervals in the Cretaceous, Jurassic and Triassic clearly express this dominant cycle and provide a robust basis for 405-kyr-scale calibration of the ATS. This 405-kyr metronome will enable extension of the well-defined Cenozoic ATS for scaling of the past quarter-billion years of Earth history. This astronomical calibration has a resolution comparable to the 1% to 0.1% precision for radioisotope dating of Mesozoic ash beds, with the added benefit of providing continuous stratigraphic coverage between dated beds. Extended portions of the Mesozoic ATS have already provided new insights into long-standing geologic problems of seafloor spreading, tectonics, eustasy, and paleoclimate change. Ongoing work is focused on closing gaps in coverage and on collecting duplicate cyclostratigraphic records for the entire Mesozoic Era.

Hinnov, L.; Ogg, J. G.

2009-12-01

83

Permo-Triassic boundary and Lower to Middle Triassic in South Tibet  

NASA Astrophysics Data System (ADS)

The abundance of conodonts increases sharply across the Permian/Triassic boundary in South Tibet, and as a consequence Griesbachian assemblages are much better defined than Changxingian ones. The " Otoceras latilobatum bed", representing the base of the Triassic at Selong, is a condensed biocalcirudite including abundant macrofossils (crinoids, corals, bryozoans, brachiopods) of Permian aspect associated with a varied conodont assemblage (including Hindeodus parvus) of early Griesbachian age. Condensation and reworking at the P/T boundary is interpreted as related to starvation and subaqueous erosion/redeposition during rapid transgression at the base of the Triassic rather than to subaerial exposure during a first-order sea-level drop. All of the Lower Triassic is strongly condensed, particularly in the west (Gyirong and Selong) where total thickness is 6.5 m at most, to 8.5 m; thickness is more comparable with other Himalayan localities at Tulong, where the Dienerian to Spathian section reaches 20 m. As in central Nepal, carbonate intervals dated as early Griesbachian to Dienerian, early to mid-Smithian and latest Smithian to earliest Aegean are separated by two mudrock intervals (locally reduced to millimetric interbeds) dated as late Dienerian or earliest Smithian and late Smithian. Condensed wackestone/packstone intervals were deposited during transgressive stages on the outermost shelf to continental slope. During highstand stages, mudrock intervals slowly accumulated on the outer shelf, whereas only a thin veneer of mud was deposited close to the shelf-break. Oceanic currents, intruding onto the outermost shelf during peak transgressions, are inferred to be the main causes of winnowing and resuspension of mud during the Spathian, when oxidized packstones in "Ammonitico Rosso" facies were deposited at Tulong. Grey limestones locally with bacterial mats or containing agglutinated foraminifers and intercalated black mudrocks indicate instead dysoxic conditions, which were widespread from Griesbachian to Smithian times. The Middle Triassic is mostly represented by marls and marly wackestones with crinoids, pelagic bivalves and benthic foraminifers. A notable increase in silty to sandy quartzo-feldspathic detritus is recorded at mid-Aegean times, and very fine-grained subarkoses characterize the mid-Anisian section at Tulong. Terrigenous supply was renewed probably in the Early Carnian, but accumulation rates sharply increased only in the latest Carnian and Norian.

Garzanti, E.; Nicora, A.; Rettori, R.

1998-04-01

84

Microbial biodiversity in Alpine Permo-Triassic rock salt  

Microsoft Academic Search

Alpine Permo-Triassic rock salt (age 200-250 million years) was shown several times to contain living extremely halophilic Archaea. These organisms might stem from ancient populations that became entrapped and persisted in the rock salt since then. For this reason, rock salt is considered a promising model system for the search for bacterial extraterrestrial life. In our studies on biodiversity in

C. Radax; H. Wieland; M. Pfaffenhuemer; S. Leuko; S. Rittmann; G. Weidler; C. Gruber; H. Stan-Lotter

2003-01-01

85

Cell water dynamics on multiple time scales  

PubMed Central

Water–biomolecule interactions have been extensively studied in dilute solutions, crystals, and rehydrated powders, but none of these model systems may capture the behavior of water in the highly organized intracellular milieu. Because of the experimental difficulty of selectively probing the structure and dynamics of water in intact cells, radically different views about the properties of cell water have proliferated. To resolve this long-standing controversy, we have measured the 2H spin relaxation rate in living bacteria cultured in D2O. The relaxation data, acquired in a wide magnetic field range (0.2 mT–12 T) and analyzed in a model-independent way, reveal water dynamics on a wide range of time scales. Contradicting the view that a substantial fraction of cell water is strongly perturbed, we find that ?85% of cell water in Escherichia coli and in the extreme halophile Haloarcula marismortui has bulk-like dynamics. The remaining ?15% of cell water interacts directly with biomolecular surfaces and is motionally retarded by a factor 15 ± 3 on average, corresponding to a rotational correlation time of 27 ps. This dynamic perturbation is three times larger than for small monomeric proteins in solution, a difference we attribute to secluded surface hydration sites in supramolecular assemblies. The relaxation data also show that a small fraction (?0.1%) of cell water exchanges from buried hydration sites on the microsecond time scale, consistent with the current understanding of protein hydration in solutions and crystals.

Persson, Erik; Halle, Bertil

2008-01-01

86

South Atlantic Spreading Velocities and Time Scales  

NASA Astrophysics Data System (ADS)

Plate reconstructions based on hierarchical spherical rotations have been around for many years. For the breakup of Pangea and Gondwana, these reconstructions are based on two major sources: magnetic isochrons and geological evidence for the onset of rifting and the tightness of the fit between continents. These reconstructions imply spreading velocities and it is the changes in velocities that can be used to probe questions of the forces moving plates around. In order to calculate the velocities correctly though, the importance of the choice of geologic time scale is often ignored. In this talk, we focus on the South Atlantic and calculate the spreading velocity errors implied by the choice of time scale for three major epochs: the Cenozoic and Late Mesozoic, the Cretaceous Quiet Zone and the Late Cretaceous to the Early Jurassic. In addition, we report the spreading velocities implied through these phases by various available magnetic isochron-derived reconstructions and the geological fits for South America and Africa used by large scale global reconstruction as well as in recent papers. Finally, we will highlight the implications for the choice of the mantle reference frame on African plate velocities.

Clark, S. R.; Smethurst, M. A.; Bianchi, M. C.

2013-12-01

87

A perspective on time: Loss frequencies, time scales, and lifetimes  

NASA Astrophysics Data System (ADS)

The need to describe the Earth system and its components with a quantity that has units of time is ubiquitous since the 1970s work of Bolin, Rodhe and Junge. These quantities are often used as metrics of the system to describe the duration or cumulative impact of an action, such as in global-warming and ozone-depletion potentials, as in the SPARC lifetime re-assessment. The quantity designated "lifetime" is often calculated inconsistently and/or misused when applied to the subsequent evaluations of impacts. A careful set of definitions and derivations is needed to ensure that we are reporting, publishing, and comparing the same quantities. There are many different ways to derive metrics of time, and they describe different properties of the system. Here we carefully define several of those metrics - denoted here as loss frequency, time scale, and lifetime - and demonstrate which properties of the system they describe. Three generalizable examples demonstrate (i) how the non-linear chemistry of tropospheric ozone makes simple approaches for tracking pollution in error; (ii) why the lifetime of a gas depends on the history of emissions, and (iii) when multiple reservoirs generate time scales quite separate from the traditionally defined lifetime. Proper use of the many "time" parameters in a system, however, gives a very powerful understanding of the response to anthropogenic perturbations.

Prather, Michael; Holmes, Christopher

2013-04-01

88

Scaling laws from geomagnetic time series  

USGS Publications Warehouse

The notion of extended self-similarity (ESS) is applied here for the X - component time series of geomagnetic field fluctuations. Plotting nth order structure functions against the fourth order structure function we show that low-frequency geomagnetic fluctuations up to the order n = 10 follow the same scaling laws as MHD fluctuations in solar wind, however, for higher frequencies (f > l/5[h]) a clear departure from the expected universality is observed for n > 6. ESS does not allow to make an unambiguous statement about the non triviality of scaling laws in "geomagnetic" turbulence. However, we suggest to use higher order moments as promising diagnostic tools for mapping the contributions of various remote magnetospheric sources to local observatory data. Copyright 1998 by the American Geophysical Union.

Voros, Z.; Kovacs, P.; Juhasz, A.; Kormendi, A.; Green, A. W.

1998-01-01

89

Truncation of scales by time relaxation  

NASA Astrophysics Data System (ADS)

We study a time relaxation regularization of flow problems proposed and tested extensively by Stolz and Adams. The aim of the relaxation term is to drive the unresolved fluctuations in a computational simulation to zero exponentially fast by an appropriate and often problem dependent choice of its coefficient; this relaxation term is thus intermediate between a tunable numerical stabilization and a continuum modeling term. Our aim herein is to understand how this term, by itself, acts to truncate solution scales and to use this understanding to give insight into parameter selection.

Layton, William; Neda, Monika

2007-01-01

90

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.

91

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

92

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

93

Multiple time scale analysis of macrotransport processes  

NASA Astrophysics Data System (ADS)

Convective and diffusive transport of a Brownian tracer corpuscle is analyzed within a multidimensional space decomposed into local (internal) and global (external) subspaces. Multiple time scale methods are employed to successively eliminate from the kinetic equation governing the multidimensional microtransport process its dependence upon each of the internal coordinates. The resulting long-time equation describing the residual global-space macrotransport process derived by this systematic perturbation procedure is shown to accord with the well-established results of generalized Taylor dispersion theory, heretofore obtained by ad hoc arguments. By way of example, this macrotransport description is used to analyze the Taylor dispersion of a solute in a Poiseuille-type solvent flow occuring within a rectangular duct of small, but non-zero, aspect ratio. Elementary dispersion results obtained by ignoring the side walls apply only for relatively short times; for longer times the perturbing presence of the side walls acts to substantially increase the axial dispersivity, even in the limit of zero aspect ratio-where intuition would strongly suggest otherwise.

Pagitsas, M.; Nadim, A.; Brenner, H.

1986-04-01

94

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

95

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

96

Early Triassic stromatolites as post-mass extinction disaster forms  

NASA Astrophysics Data System (ADS)

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 extinctions 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, Jennifer K.; Bottjer, David J.

1992-10-01

97

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

98

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

99

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

100

Gamma-ray burster recurrence time scales  

NASA Technical Reports Server (NTRS)

In the decade since gamma-ray bursters (GRBs) were discovered by Klebesadel et al. (1973), many models have been proposed to explain the GRB phenomenon. A difficulty is related to the small number of predictions which would make it possible to evaluate the models. One verifiable prediction is the recurrence time scale, tau-gamma. One method to measure tau-gamma is to look for possible cases of recurrence as indicated by overlapping error boxes. The analysis considered in the present investigation is composed of three procedures. One of these involves a search through known error regions for cases where the error regions overlap. In addition, the number of overlaps expected by chance coincidence alone has been determined, and a calculation has been performed regarding the number of overlaps which are expected due to recurrence for various assumed tau-gamma and luminosity functions.

Schaefer, B. E.; Cline, T. L.

1985-01-01

101

Permian-Triassic thermal anomaly of the active margin of South America as a result of plate kinematics reorganization  

NASA Astrophysics Data System (ADS)

From Permian to Triassic times, tectonic plate reorganization provoked Pangaea breakup, counterclockwise rotation of Gondwana, closing of the Paleo-Tethys Ocean and opening of the Neo-Tethys oceanic realm. Meanwhile, the switch from arc volcanism to widespread S-type magmatism along the western South American active margin around 275-265 Ma is symptomatic of the onset of a large-scale Permian-Triassic thermal anomaly (PTTA)affecting the whole margin. Here we report metamorphic and U-Pb geochronological results from the El Oro metamorphic complex in the forearc zone of southwestern Ecuador, which recorded the last step, at 230-225 Ma, of the PTTA. The change in the drift direction of Gondwana from north to east at ca. 270 Ma was related to plate reorganization and provoked the verticalization of the subducted Panthalassa slab. As the slab verticalized, strong heat advection produced a high heat flow beneath the active margin inducing the development of a huge thermal anomaly responsible for the PTTA, which lasted 30 Ma. This voluminous magmatic activity culminated at the Permian-Triassic boundary, and may have contributed to the degradation of life conditions on the Earth surface.

Riel, Nicolas; Jaillard, Etienne; Guillot, Stéphane; Martelat, Jean-Emmanuel; Braun, Jean

2013-04-01

102

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

103

End-Triassic Mass Extinction Event.  

National Technical Information Service (NTIS)

The end-Triassic is the least studied of the five major episodes of mass extinction recognized in the Phanerozoic, and the Triassic-Jurassic boundary is not precisely defined in most parts of the world, with a paucity of good marine sections and an insuff...

A. Hallam

1988-01-01

104

Triassic alluvial braidplain and braided river deposits of the La Ternera Formation, Atacama region, northern Chile  

NASA Astrophysics Data System (ADS)

The La Ternera Formation is a thick (>2,100 m) succession of terrigenous clastic sediments, with andesitic and basaltic intercalations, exposed in the Quebrada de Paipote area of the Atacama Region, northern Chile. The strata were deposited in an active rift basin during Late Triassic to (?) Early Jurassic times. The lower 1,000 m of the studied elastic succession comprises pebbly granule paraconglomerates, unconformably overlying Upper Paleozoic sedimentary successions, volcanics, and granitoids. These sediments were derived from the east and are interpreted as braid-plain deposits. The upper 800 m of the succession comprises interbedded orthoconglomerates, sandstones and mudstones. Abundant plant fossils include trees in growth position and carbonaceous horizons. Small scale depositional cycles were the product of migrating braided-river channel systems. Larger scale successions resulted from tectonic uplift. The sediments of the La Ternera Formation were derived predominantly from a tectonically uplifted area of Upper Paleozoic acidic volcanic and plutonic rocks (Pantanoso Formation, Choiyoi Group). Active uplift on the eastern margin of the sedimentary basin probably occurred along north-south trending faults. Continued subsidence of the basin resulted in a Sinemurian to Bajocian marine transgression. Occurrences of Triassic andesitic and basaltic volcanic rocks both to the west and the east of the La Ternera formation suggest deposition in an intea-volcanic graben or half-graben.

Bell, C. M.; Suárez, M.

1995-01-01

105

Smithian and Spathian (Early Triassic) ammonoid assemblages from terranes: Paleoceanographic and paleogeographic implications  

NASA Astrophysics Data System (ADS)

Early Triassic paleobiogeography is characterised by the stable supercontinental assembly of Pangea. However, at that time, several terranes such as the South Kitakami Massif (SK), South Primorye (SP) and Chulitna (respectively, and presently located in Japan, eastern Russia and Alaska) straddled the vast oceans surrounding Pangea. By means of quantitative biogeographical methods including Cluster Analysis, Non-metric Multidimensional Scaling and Bootstrapped Spanning Network applied to Smithian and Spathian (Early Triassic) ammonoid assemblages; we analyze similarity relationships between faunas and suggest paleopositions for the above-cited terranes. Taxonomic similarities between faunas indicate that primary drivers of the ammonoid distribution were Sea Surface Temperature and currents. Possible connections due to current-controlled faunal exchanges between both sides of the Panthalassa are shown and terranes such as SK, SP and Chulitna played an important role as stepping stones in the dispersal of ammonoids. SK and SP terranes show strong sub-equatorial affinities during the Smithian, thus suggesting a location close to South China. At the same time, the Chulitna terrane shows strong affinities with equatorial faunas of the eastern Panthalassa. This paleoceanographic pattern was markedly altered during the Spathian, possibly indicating significant modifications of oceanic circulation at that time, as illustrated by the development of a marked intertropical faunal belt across Tethys and Panthalassa.

Brayard, Arnaud; Escarguel, Gilles; Bucher, Hugo; Brühwiler, Thomas

2009-11-01

106

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

107

An electronic time scale in chemistry  

PubMed Central

Ultrafast, subfemtosecond charge migration in small peptides is discussed on the basis of computational studies and compared with the selective bond dissociation after ionization as observed by Schlag and Weinkauf. The reported relaxation could be probed in real time if the removal of an electron could be achieved on the attosecond time scale. Then the mean field seen by an electron would be changing rapidly enough to initiate the migration. Tyrosine-terminated tetrapeptides have a particularly fast charge migration where in <1 fs the charge arrives at the other end. A femtosecond pulse can be used to observe the somewhat slower relaxation induced by correlation between electrons of different spins. A slower relaxation also is indicated when removing a deeper-lying valence electron. When a chromophoric amino acid is at one end of the peptide, the charge can migrate all along the peptide backbone up to the N end, but site-selective ionization is probably easier to detect for tryptophan than for tyrosine.

Remacle, F.; Levine, R. D.

2006-01-01

108

Shallow marine sedimentary facies in the earliest Triassic (Griesbachian) Cordilleran miogeocline, U.S.A.  

NASA Astrophysics Data System (ADS)

Permian history in the Cordilleran miogeocline, U.S.A., ended with an erosional interval of 1 to 22 million years. Previous studies of this event focused on unrepresented time, faunal extinction, regional truncation, or physical evidence in local areas. Another way to view this unconformity is to examine the nature of shallow marine sediments deposited on the erosional surface during the earliest Triassic (Griesbachian) transgression. As part of this study, the rate of the initial Mesozoic flood was estimated by determining the extent of the oldest Triassic conodont biozone within the study area. The calculated rate of transgression over 194,000 km 2 occupied by this biozone, within the 270,000 km 2 depositional area of the earliest Triassic Dinwoody Formation, is orders of magnitude greater than those suggested for eustatic sea-level change related to glaciation or plate tectonic processes. The rapidity of transgression, paucity of reworked material at the base of the Triassic, a general lack of local relief, and nearly conformable relations of Permian and Triassic rocks throughout the region suggest that the Triassic sea advanced across a featureless plain. The earliest Triassic sediments described in this study are restricted to the basal 2 m of the Dinwoody Formation. The generalized geographic distribution of facies within the depositional basin follows: evaporites are restricted to the northeast, Lingula-bearing dolomite characterizes the north-central, sandstone is locally present in the northwest and central areas, the southern part is dominated by shaly-bedded siltstone with some thin limestone interbeds, and calcareous, silty shale is present in the west toward the basin center. The similarity of basalmost Triassic depositional environments to those of the earlier Permian documents tectonic rejuvenation of a previous paleogeographic regime that strongly controlled Early Triassic sedimentation.

Paull, Rachel K.; Paull, Richard A.

1994-11-01

109

Triassic and Jurassic structural development along the Tornquist Zone, Denmark  

NASA Astrophysics Data System (ADS)

In the Danish area the old crustal weakness zone, the Tornquist Zone, was repeatedly reactivated during the Triassic and Jurassic/Early Cretaceous, causing minor dextral movements along the major boundary faults. These tectonic events were minor as compared to the tectonic events of the Late Carboniferous/Early Permian and the Late Cretaceous/Early Tertiary, although a dynamic structural and stratigraphical analysis indicate that the zone was highly active compared to the surrounding areas. During the Middle to Late Permian the area was exposed to erosion and became a peneplane. A regional Triassic subsidence produces seismic onlap towards the northeast, where the youngest Triassic sediment is found, supercropping the Precambrian basement. During mainly the Early Triassic, several of the major Early Permian faults became reactivated, probably with dextral strike-slip along the Børglum Fault. The Jurassic-Early Cretaceous subsidence became restricted primarily to the area between the two main faults in the Tornquist Zone, the Grenå-Helsingborg Fault and the Børglum Fault. This restricted basin development indicates a change in the regional stress field that seems to have come into existence during the transition between the Triassic and the Jurassic. The subsidence in the Middle Jurassic and the Late Jurassic-Early Cretaceous follows the Early Jurassic pattern with local subsidence in the Tornquist Zone, but even more restricted to the zone. The subsidence seems to have decreased in the Middle Jurassic; hereafter subsidence increased again during Late Jurassic/Early Cretaceous times. A set of small faults were generated during the Mesozoic internally in the Tornquist Zone. This fault pattern indicates a broad transfer of strike-slip/oblique-slip motion from the Grenå-Helsingborg Fault to the Børglum Fault.

Mogensen, Tommy E.

1995-12-01

110

Length, time, and energy scales of photosystems  

Microsoft Academic Search

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-Å scale of the membrane thickness. Electron tunneling is nearly as rapid at the shortest distances, but becomes physiologically too slow well before 20 Å. Diffusion, which starts out

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

2003-01-01

111

An optimal modification of a Kalman filter for time scales  

NASA Technical Reports Server (NTRS)

The Kalman filter in question, which was implemented in the time scale algorithm TA(NIST), produces time scales with poor short-term stability. A simple modification of the error covariance matrix allows the filter to produce time scales with good stability at all averaging times, as verified by simulations of clock ensembles.

Greenhall, C. A.

2003-01-01

112

A Major Unconformity Between Permian and Triassic Strata at Cape Kekurnoi, Alaska Peninsula: Old and New Observations on Stratigraphy and Hydrocarbon Potential  

USGS Publications Warehouse

A major angular unconformity separates carbonates and shales of the Upper Triassic Kamishak Formation from an underlying unnamed sequence of Permian agglomerate, volcaniclastic rocks (sandstone), and limestone near Puale Bay on the Alaska Peninsula. For the first time, we photographically document the angular unconformity in outcrop, as clearly exposed in a seacliff ~1.3 mi (2.1 km) west of Cape Kekurnoi in the Karluk C?4 and C?5 1:63,360-scale quadrangles. This unconformity is also documented by examination of core chips, ditch cuttings, and (or) open-hole electrical logs in two deep oil-and-gas-exploration wells (Humble Oil & Refining Co.?s Bear Creek No. 1 and Standard Oil Co. of California?s Grammer No. 1) drilled along the Alaska Peninsula southwest of Puale Bay. A third well (Richfield Oil Corp.?s Wide Bay Unit No. 1), south of and structurally on trend with the other two wells, probed deeply into the Paleozoic basement, but Triassic strata are absent, owing to either a major unconformity or a large fault. Here we briefly review current and newly acquired data on Permian and Triassic rocks of the Puale Bay-Becharof Lake-Wide Bay area on the basis of an examination of surface and subsurface materials. The resulting reinterpretation of the Permian and Triassic stratigraphy has important economic ramifications for oil and gas exploration on the Alaska Peninsula and in the Cook Inlet basin. We also present a history of petroleum exploration targeting Upper Triassic reservoirs in the region.

Blodgett, Robert B.; Sralla, Bryan

2008-01-01

113

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

PubMed

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. PMID:23129649

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

2012-11-20

114

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

115

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

116

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

117

Current and future realizations of coordinate time scales  

NASA Astrophysics Data System (ADS)

Two atomic time scales maintained at the International Bureau of Weights and Measures (BIPM) are realizations of terrestrial time: International Atomic Time (TAI) and TT(BIPM). They are calculated from atomic clocks realizing proper time in national laboratories. The algorithm for the calculation of TAI has been designed to optimize the frequency stability and accuracy of the time scale. Plans for the future improvement of the reference time scales are presented.

Arias, E. Felicitas

2010-01-01

118

Time domain modeling of plasmas at RF time-scales  

NASA Astrophysics Data System (ADS)

Results from tokamak experiments such as PPPL's NSTX indicate that significant anomalous power absorption can occur in the edge of the fusion plasma. Understanding of this phenomenon is a critical issue for analysis of RF heating scenarios on the ITER fusion experiment. Two probable edge absorption candidates, rf sheath losses and parametric decay instability, are both inherently non-linear, and likely to depend significantly on non-axi-symmetric geometric detail in the vicinity of the antenna structures. Analysis of these phenomenon is beyond the capabilities of existing axi-symmetric frequency-domain linear-solvers used for analysis of heating and current drive in core fusion plasma, and so we are augmenting our analysis capability with the time-domain 3-D general-geometry electromagnetic and particle-in-cell simulation framework, Vorpal [1]. This framework is a modern object-oriented software package, which has demonstrated fast scalable operation on clusters of over 1000 cpu's, a necessity for this type of calculation. We have successfully introduced into this framework an implicit plasma solver [2], in order to accurately treat electromagnetic plasma wave characteristics in the wide range of plasma conditions occurring from edge plasma to core plasma, including situations where the plasma frequency is not resolvable at the rf time-scales of interest, and including sharp plasma resonances and cutoff behaviours common in the rf regime. We present benchmarking of this new plasma solver for 1-D, 2-D, and 3-D scenarios. We also discuss implementation plans for non-linear sheath boundary models, non-linear edge-plasma conditions leading to parametric decay, and also tracking of high-energy particles in core-heating scenarios, where issues of finite-banana-width effects and superadiabaticity remain outside the scope of the existing frequency-domain solvers.

Smithe, David N.

2007-07-01

119

Dynamic equations on time scales: A survey  

Microsoft Academic Search

Abstract: The studyofdynam9equations ontim scales, which goes back to its founder Stefan Hilger (1988), is an area ofm\\/8#xW#\\/;9that has recently received a lot of attention. It has been created in order to unify the study of di#erential anddi#erence equations. In this paper we give an introduction to the tim scales calculus. We also present various propertiesof the exponential function on

R. Agarwal; M. Bohner; D. O'regan; A. Peterson

2000-01-01

120

Late Permian–early Middle Triassic back-arc basin development in West Qinling, China  

NASA Astrophysics Data System (ADS)

The Late Permian-early Middle Triassic strata of the northern West Qinling area, northeastern Tibetan Plateau, are composed of sediment gravity flow deposits. Detailed sedimentary facies analysis indicates these strata were deposited in three successive deep-marine environments. The Late Permian-early Early Triassic strata of the Maomaolong Formation and the lowest part of the Longwuhe Formation define a NW-SE trending proximal slope environment. Facies of the Early Triassic strata composing the middle and upper Longwuhe Formation are consistent with deposition in a base-of-slope apron environment, whereas facies of the Middle Triassic Anisian age Gulangdi Formation are more closely associated with a base-of-slope fan depositional environment. The lithofacies and the spatial-temporal changes in paleocurrent data from these strata suggest the opening of a continental margin back-arc basin system during Late Permian to early Middle Triassic time in the northern West Qinling. U-Pb zircon ages for geochemically varied igneous rocks with diabasic through granitic compositions intruded into these deep-marine strata range from 250 to 234 Ma. These observations are consistent with extensional back-arc basin development and rifting between the Permian-Triassic Eastern Kunlun arc and North China block during the continent-continent collision and underthrusting of the South China block northward beneath the Qinling terrane of the North China block. Deep-marine sedimentation ended in the northern West Qinling by the Middle Triassic Ladinian age, but started in the southern West Qinling and Songpan-Ganzi to the south. We attribute these observations to southward directed rollback of Paleo-Tethys oceanic lithosphere, continued attenuation of the West Qinling on the upper plate, local post-rift isostatic compensation in the northern West Qinling area, and continued opening of a back-arc basin in the southern West Qinling and Songpan-Ganzi. Rollback and back-arc basin development during Late Permian to early Middle Triassic time in the West Qinling area explains: the truncated map pattern of the Eastern Kunlun arc, the age difference of deep-marine sediment gravity flow deposits between the Late Permian-early Middle Triassic northern West Qinling and the late Middle Triassic-Late Triassic southern West Qinling and Songpan-Ganzi, and the discontinuous trace of ophiolitic rocks associated with the Anyemaqen-Kunlun suture.

Li, Lin; Meng, Qingren; Pullen, Alex; Garzione, Carmala N.; Wu, Guoli; Wang, Yanling; Ma, Shouxian; Duan, Liang

2014-06-01

121

Reappraisal of Displacement of Northern Cordilleran Terranes Since the Triassic and Jurassic  

NASA Astrophysics Data System (ADS)

Triassic-Jurassic paleomagnetic data from the Cordillera of Canada had initially indicated displacements of about 1000 km from the south. Later, as a result of revisions in the APW path for North America, it was contended that there had been no such displacements. The Cordilleran data are from Wrangellia (Nicolai/Karmutsen (225 Ma) and Bonanza (195 Ma) formations) and Stikinia (Hazelton (195-180 Ma) and Stuhinni (~210 Ma) formations). These are two largest exotic superterranes in the Cordillera. Data all are from massive lavas (mainly) or diabase sills whose bedding attitudes are well controlled and whose magnetizations are believed to record accurately the field direction. On the other hand, several of the APW paths determined from North America that were sometimes used for reference are dominated by results from sedimentary rocks, which recently published work using directional distributions and anisotropy measurements has demonstrated are commonly affected by inclination flattening, for example, Late Triassic and Early Jurassic sedimentary rocks in rift basins of eastern North America. When corrected for inclination flattening, sedimentary data agree with inclinations from coeval igneous rocks when these data are available, for example, 200 Ma CAMP volcanics, but don't support the J1 cusp, previously a cornerstone of many APW paths for North America. In order to avoid possible shallow bias in latitude determinations, we make a special effort to avoid errors arising from inclination-flattening in sedimentary rocks by (1) using only data from sedimentary rocks that have been corrected for inclination-flattening, and by rejecting all other sedimentary data, and (2) incorporating igneous data from all other major continents. Relative to present geography the global APW path relative to North America begins in Mongolia in the Early Triassic, trends north-northwest towards the estuary of the Ob River by the end of the Early Jurassic, where it lingers before rapidly moving to the vicinity of Nunivak Island by the end of the Jurassic (and then boomerangs to the Cretaceous standstill position in the Chukchi Sea). Cordilleran magnetizations always have inclinations that are shallower than expected from the reference path. There is therefore no ambiguity about the sense of displacements - they are always from the south relative to cratonic North America. However, within these structurally disrupted terranes, only individual poles and not their paths can be constructed and there are uncertainties in relating individual results to the global polarity time-scale, and so we cannot say, from the paleomagnetic evidence alone, whether the terranes were in the southern or the northern hemisphere during the early Mesozoic. Assuming the closest (northern hemisphere) position, all the Cordilleran terrane strata nevertheless give displacements of about 1000 km or more. The Nicolai of Alaska yields a displacement of ~2500 km which reflects the strong northward motion of SE Alaska in the Tertiary. We believe this settles the debate: Triassic and Jurassic rocks of Wrangellia and Stikinia all have been displaced significantly from the south. Notable also are the strong anticlockwise rotations of 40°-60° from the Nicolai (Triassic), Bonanza and Hazelton (Jurassic), which have been observed also by Enkin throughout the stratigraphy of the Skeena fold- belt of central Stikinia. The Karmutsen (Triassic) of Vancouver Island shows a huge 150° anticlockwise rotation, perhaps a composite of several deformation phases.

Kent, D. V.; Irving, E.

2008-12-01

122

A Quaternary Geomagnetic Instability Time Scale  

NASA Astrophysics Data System (ADS)

Reversals and excursions of Earth's geomagnetic field create marker horizons that are readily detected in sedimentary and volcanic rocks worldwide. An accurate and precise chronology of these geomagnetic field instabilities is fundamental to understanding several aspects of Quaternary climate, dynamo processes, and surface processes. For example, stratigraphic correlation between marine sediment and polar ice records of climate change across the cryospheres benefits from a highly resolved record of reversals and excursions. The temporal patterns of dynamo behavior may reflect physical interactions between the molten outer core and the solid inner core or lowermost mantle. These interactions may control reversal frequency and shape the weak magnetic fields that arise during successive dynamo instabilities. Moreover, weakening of the axial dipole during reversals and excursions enhances the production of cosmogenic isotopes that are used in sediment and ice core stratigraphy and surface exposure dating. The Geomagnetic Instability Time Scale (GITS) is based on the direct dating of transitional polarity states recorded by lava flows using the 40Ar/39Ar method, in parallel with astrochronologic age models of marine sediments in which O isotope and magnetic records have been obtained. A review of data from Quaternary lava flows and sediments yields a GITS comprising 10 polarity reversals and 27 excursions during the past 2.6 million years. Nine of the ten reversals bounding chrons and subchrons are associated with 40Ar/39Ar ages of transitionally-magnetized lava flows. The tenth, the Guass-Matuyama chron boundary, is tightly bracketed by 40Ar/39Ar dated ash deposits. Of the 27 well-documented excursions, 14 occurred during the Matuyama chron and 13 during the Brunhes chron; 19 have been dated directly using the 40Ar/39Ar method on transitionally-magnetized volcanic rocks and form the backbone of the GITS. Excursions are clearly not the rare phenomena once thought. Rather, during the Quaternary period, they occur nearly three times as often as full polarity reversals. I will address analytical issues, including the size and consistency of system blanks, that have led to the recognition of minor (1%) discrepencies between the 40Ar/39Ar age for a particular reversal or excursion and the best astrochronologic estimates from ODP sediment cores. For example, re-analysis of lava flows from Haleakala volcano, Maui that record in detail the Matuyama-Brunhes polarity reversal have been undertaken with blanks an order of magntitude smaller and more stable than was common a decade ago. Using the modern astrochronologic calibration of 28.201 Ma for the age of the Fish Canyon sanidine standard, results thus far yield an 40Ar/39Ar age of 772 × 11 ka for the reversal that is identical to the most precise and accurate astrochronologic age of 773 × 2 ka for this reversal from ODP cores. Similarly, new dating of sanidine in the Cerro Santa Rosa I rhyolite dome, New Mexico reveals an age of 932 × 5 ka for the excursion it records, in perfect agreement with astrochronologically dated ODP core records. Work underway aims at refining the 40Ar/39Ar ages that underpin the entire GITS by further eliminating the bias between the radioisotopic and astrochronologically determined ages for several reversals and excursions.

Singer, B. S.

2013-12-01

123

Time scales in energy balance climate models 2: The intermediate time solutions  

Microsoft Academic Search

We demonstrated in a companion paper (Watts et al., this issue) that the transient response of a globally averaged upwelling diffusion energy balance climate model depends upon three time scales: the mixed-layer thermal-response time scale, the thermocline thermal-response time scale, and the upwelling time scale. These time scales are defined and interpreted physically in that paper. The asymptotic solution for

Michael C. Morantine; Robert G. Watts

1994-01-01

124

Tethyan magnetostratigrapy from Pizzo Mondello and correlation to the Late Triassic Newark APTS  

NASA Astrophysics Data System (ADS)

We present magnetostratigraphic data and preliminary C13 and O18 stable isotope data from an expanded (?430m-thick) Upper Triassic marine section at Pizzo Mondello from the Sicani Basin of Sicily and review biostratigraphic data from the literature that can be used to define the location of the Carnian/Norian and Norian/Rhaetian boundaries. Pizzo Mondello offers good potentials for magnetostratigraphic correlation of marine biostratigraphic and chemostratigraphic data with the continental Newark astrochronological time scale (APTS) for development of an integrated Late Triassic time scale. The relatively stable average values of 18O centered around 0‰ are a strong indication that the Cherty Limestone at Pizzo Mondello suffered very little diagenetic overprinting. The Carnian/Norian boundary at Pizzo Mondello seems to be associated with a positive shift of C13 although further work is necessary to evaluate its paleoenvironmental significance. A statistical approach was applied to evaluate various Pizzo Mondello to Newark magnetostratigraphic correlations. Two correlation options, neither unequivocal, have the highest and nearly equivalent correlation coefficients. Option #1 predicts the base of Pizzo Mondello to be correlative with the middle part of the Newark APTS, whereas in Option #2 the base of Mondello starts towards the early part of the Newark APTS. According to sampling density and average sediment accumulation rates of 20-30m/m.y., polarity intervals with durations equal to or less than ?170 k.y. may have been undersampled at Pizzo Mondello. Accordingly, we filtered the high resolution Newark APTS and performed further statistical correlations from which we conclude that Option #2 is preferred. With this option, the Carnian/Norian boundary based on conodonts corresponds to basal Newark magnetozone E7 at about 228 Ma (adopting Newark astrochronology), implying a long Norian with a duration of 20m.y. and a Rhaetian of about 6 m.y. duration. These ages are in fact not inconsistent with the few high quality radiometric dates that are available for Late Triassic time scale calibration. We suggest that Pizzo Mondello is a good candidate for a GSSP for the base of the Norian whereas we find that sections of the "Hallstatt" type , which may be more fossiliferous but have erratic and typically very low average rates of sediment accumulation, are more difficult to correlate with each other and with expanded sections such as Pizzo Mondello and the Newark.

Muttoni, G.; Kent, D. V.; Olsen, P. E.; Bernasconi, S.; Lowrie, W.; Martín Hernández, F.; di Stefano, P.

2003-04-01

125

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

126

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

127

New Early Jurassic Tetrapod Assemblages Constrain Triassic-Jurassic Tetrapod Extinction Event  

NASA Astrophysics Data System (ADS)

The discovery of the first definitively correlated earliest Jurassic (200 million years before present) tetrapod assemblage (Fundy basin, Newark Supergroup, Nova Scotia) allows reevaluation of the duration of the Triassic-Jurassic tetrapod extinction event. Present are tritheledont and mammal-like reptiles, prosauropod, theropod, and ornithischian dinosaurs, protosuchian and sphenosuchian crocodylomorphs, sphenodontids, and hybodont, semionotid, and palaeonisciform fishes. All of the families are known from Late Triassic and Jurassic strata from elsewhere; however, pollen and spore, radiometric, and geochemical correlation indicate an early Hettangian age for these assemblages. Because all ``typical Triassic'' forms are absent from these assemblages, most Triassic-Jurassic tetrapod extinctions occurred before this time and without the introduction of new families. As was previously suggested by studies of marine invertebrates, this pattern is consistent with a global extinction event at the Triassic-Jurassic boundary. The Manicouagan impact structure of Quebec provides dates broadly compatible with the Triassic-Jurassic boundary and, following the impact theory of mass extinctions, may be implicated in the cause.

Olsen, P. E.; Shubin, N. H.; Anders, M. H.

1987-08-01

128

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

129

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

130

Why is the internet traffic bursty in short time scales?  

Microsoft Academic Search

Internet traffic exhibits multifaceted burstiness and correlation structure over a wide span of time scales. Previous work analyzed this structure in terms of heavy-tailed session characteristics, as well as TCP timeouts and congestion avoidance, in relatively long time scales. We focus on shorter scales, typically less than 100-1000 milliseconds. Our objective is to identify the actual mechanisms that are responsible

Hao Jiang; Constantinos Dovrolis

2005-01-01

131

The origin of TCP traffic burstiness in short time scales  

Microsoft Academic Search

Internet traffic exhibits multifaceted burstiness and correlation structure over a wide span of time scales. Previous work analyzed this structure in terms of heavy-tailed session characteristics, as well as TCP timeouts and congestion avoid- ance, in relatively long time scales. We focus on shorter scales, typically less than 100-1000 milliseconds. Our objective is to identify the actual mechanisms that are

Hao Jiang; Constantinos Dovrolis

2004-01-01

132

Development of a pulsar-based time-scale  

NASA Astrophysics Data System (ADS)

Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA) project we develop the first pulsar-based time-scale that has a precision comparable to the uncertainties in International Atomic Time-scales (TAI). Our ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the free atomic time-scale Échelle Atomique Libre. The EPS can be used to detect fluctuations in atomic time-scales and therefore can lead to a new realization of Terrestrial Time, TT(PPTA11). We successfully follow features known to affect the frequency of the TAI, and we find marginally significant differences between TT(PPTA11) and TT(BIPM11). We discuss the various phenomena that lead to a correlated signal in the pulsar timing residuals and therefore limit the stability of the pulsar time-scale.

Hobbs, G.; Coles, W.; Manchester, R. N.; Keith, M. J.; Shannon, R. M.; Chen, D.; Bailes, M.; Bhat, N. D. R.; Burke-Spolaor, S.; Champion, D.; Chaudhary, A.; Hotan, A.; Khoo, J.; Kocz, J.; Levin, Y.; Oslowski, S.; Preisig, B.; Ravi, V.; Reynolds, J. E.; Sarkissian, J.; van Straten, W.; Verbiest, J. P. W.; Yardley, D.; You, X. P.

2012-12-01

133

On time scales and time synchronization using LORAN-C as a time reference signal  

NASA Technical Reports Server (NTRS)

The long term performance of the eight LORAN-C chains is presented in terms of the Coordinated Universal Time (UTC) of the U.S. Naval Observatory (USNO); and the use of the LORAN-C navigation system for maintaining the user's clock to a UTC scale is described. The atomic time scale and the UTC of several national laboratories and observatories relative to the international atomic time are reported. Typical performance of several NASA tracking station clocks, relative to the USNO master clock, is also presented.

Chi, A. R.

1974-01-01

134

Detecting time series motifs under uniform scaling  

Microsoft Academic Search

Time series motifs are approximately repeated patterns found within the data. Such motifs have utility for many data min- ing algorithms, including rule-discovery, novelty-detection, summarization and clustering. Since the formalization of the problem and the introduction of ecient linear time al- gorithms, motif discovery has been successfully applied to many domains, including medicine, motion capture, robotics and meteorology. In this

Dragomir Yankov; Eamonn J. Keogh; Jose Medina; Bill Chiu; Victor B. Zordan

2007-01-01

135

Advances in Time-Scale Algorithms.  

National Technical Information Service (NTIS)

The term clock is usually used to refer to a device that counts a nearly periodic signal. A group of clocks, called an ensemble: is often used for time keeping in mission critical applications that cannot tolerate loss of time due to the failure of a sing...

S. R. Stein

1992-01-01

136

Time relaxation of ac susceptibility on very short time scales  

Microsoft Academic Search

We present an experimental method enabling measurements of time dependence of ac susceptibility down to 1 ms after a steplike change of the applied dc magnetic field. An analog-digital converter has been used to collect the transient of the current, signaling the change of the dc magnetic field. The time window for investigation of magnetic time relaxation phenomena, as studied

Ivica Zivkovic; Ðuro Drobac; Mladen Prester

2005-01-01

137

Early Triassic marine biotic recovery: the predators' perspective.  

PubMed

Examining the geological past of our planet allows us to study periods of severe climatic and biological crises and recoveries, biotic and abiotic ecosystem fluctuations, and faunal and floral turnovers through time. Furthermore, the recovery dynamics of large predators provide a key for evaluation of the pattern and tempo of ecosystem recovery because predators are interpreted to react most sensitively to environmental turbulences. The end-Permian mass extinction was the most severe crisis experienced by life on Earth, and the common paradigm persists that the biotic recovery from the extinction event was unusually slow and occurred in a step-wise manner, lasting up to eight to nine million years well into the early Middle Triassic (Anisian) in the oceans, and even longer in the terrestrial realm. Here we survey the global distribution and size spectra of Early Triassic and Anisian marine predatory vertebrates (fishes, amphibians and reptiles) to elucidate the height of trophic pyramids in the aftermath of the end-Permian event. The survey of body size was done by compiling maximum standard lengths for the bony fishes and some cartilaginous fishes, and total size (estimates) for the tetrapods. The distribution and size spectra of the latter are difficult to assess because of preservation artifacts and are thus mostly discussed qualitatively. The data nevertheless demonstrate that no significant size increase of predators is observable from the Early Triassic to the Anisian, as would be expected from the prolonged and stepwise trophic recovery model. The data further indicate that marine ecosystems characterized by multiple trophic levels existed from the earliest Early Triassic onwards. However, a major change in the taxonomic composition of predatory guilds occurred less than two million years after the end-Permian extinction event, in which a transition from fish/amphibian to fish/reptile-dominated higher trophic levels within ecosystems became apparent. PMID:24647136

Scheyer, Torsten M; Romano, Carlo; Jenks, Jim; Bucher, Hugo

2014-01-01

138

Permo-Triassic boundary and Lower to Middle Triassic in South Tibet  

Microsoft Academic Search

The abundance of conodonts increases sharply across the Permian\\/Triassic boundary in South Tibet, and as a consequence Griesbachian assemblages are much better defined than Changxingian ones. The “Otoceras latilobatum bed”, representing the base of the Triassic at Selong, is a condensed biocalcirudite including abundant macrofossils (crinoids, corals, bryozoans, brachiopods) of Permian aspect associated with a varied conodont assemblage (including Hindeodus

E. Garzanti; A. Nicora; R. Rettori

1998-01-01

139

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

2013-01-01

140

Lower Triassic lacustrine sediments in La Coipa area, Atacama, Chile  

NASA Astrophysics Data System (ADS)

Lower Triassic lacustrine sediments in an area of at least 300 km 2 at the La Coipa Mine area (26°50' S, 69°15' W), in northern Chile, indicate a large, actively subsiding lake, which was at one time evaporitic. This lake was surrounded by highlands dominated by outcrops of Late Paleozoic volcanic rocks and granitoids. An open lacustrine environment includes black hemipelagic shales with intercalated thin and medium-grained turbidites probably representing a channel-levee complex. The coarse-grained, lake margin sediments are dominated by debris-flow deposits and turbidites with intercalated black shales. These represent either the subaqueous part of a fan delta (formed during low-stand) or subaqueous talus (formed in a high stand). The Lower Triassic age, given by palynomorphs, represents the first documentation of strata of this age in Chile and apparently in the Andes. It indicates that basins of probable extensional origin were forming prior to the previously accepted Middle-Late Triassic age.

Suárez, M.; Bell, C. M.; Hutter, T.

1995-01-01

141

Uppermost permian reefs and permo-triassic sedimentary facies from the southeastern margin of Sichuan Basin, China  

Microsoft Academic Search

Summary  A large-scale, gradual transition from an epicontinental marine regime, prevailing during most of the Paleozoic, to continental\\u000a (?molasse) red beds of Upper Triassic and younger age is documented within the Permo-Triassic sequence of marine carbonate\\u000a and siliciclastic rocks of the western Yangzi Platform in southern China. Large portions of the Yangzi Platform (along with\\u000a the Tarim and Sino-Korea Platforms, one

Joachim W. Reinhardt

1988-01-01

142

Scaling Physiological Pharmacokinetic Models by Physiological Time.  

National Technical Information Service (NTIS)

This paper shows that a multicompartment physiological pharmacokinetic model, used to account for inhalation exposure to volatile chlorohydrocarbons in mammalian species, can be made species-independent if chronological time is re-expressed in terms of ph...

R. C. Ward C. C. Travis

1987-01-01

143

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

144

Real-time scale selection in hybrid multi-scale representations  

Microsoft Academic Search

Local scale information extracted from visual data in a bottom- up manner constitutes an important cue for a large number of visual tasks. This article presents a framework for how the computation of such scale descriptors can be performed in real time on a standard computer. The proposed scale selection framework is expressed within a novel type of multi-scale representation,referred

Tony Lindeberg; Lars Bretzner

2003-01-01

145

Milankovitch and sub-Milankovitch cycles of the Early Triassic Daye Formation, South China and their geochronological and paleoclimatic implications  

NASA Astrophysics Data System (ADS)

The most profound mass extinction in the Phanerozoic occurred at the end of the Permian, with global loss of nearly 90% of marine invertebrate species and 70% of terrestrial vertebrate genera. Recent studies suggested that volcanisms represented by the Siberian Trap were most likely cause of the end-Permian extinction. The post-extinction periods in the Early Triassic was characterized by low biodiversity, reduced abundance and size of invertebrates, hiatus in coal deposition, anomalously high sediment fluxes, and large perturbations of the carbon cycle, which have been interpreted as the consequence of persistently unfavorable environmental conditions. However, the time framework for the Early Triassic geological, biological and geochemical events is traditionally established by conodont biostratigraphy, but the absolute duration of condont biozones are not well constrained. In this study, a rock magnetic cyclostratigraphy, based on high-resolution analysis (2440 samples) of magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) intensity variations, was developed for the 55.1-m-thick, Early Triassic Daye Formation at the Daxiakou section, Hubei province in South China. The Daye Formation shows exceptionally well-preserved lithological cycles with alternations of thin-bedded mudstone, marl and limestone, which are closely tracked by the MS and ARM variations. Power spectral, wavelet and amplitude modulation (AM) analysis of the ARM and MS series reveal strong evidence for the presence of Milankovitch to sub-Milankovitch frequencies dominated by precession index signal and 4-5 ka cycles. Cycles expressed by variations in MS and ARM were likely controlled by the input of fine-grained detrital magnetite, which in turn may be driven by astronomically induced changes in monsoon intensity in the equatorial eastern Tethys during the Early Triassic greenhouse period. On the basis of the 100-ka tuning results, the astronomically constrained duration of the Induan stage is 1.162 Ma, with the Griesbachian and Dienerian substage of 491ka and 671 ka, respectively. The new astronomical time scale also provides time constraints for the conodont and bivalve biozones, the carbonate carbon isotope (?13C) records and magnetic polarity zones of the Lower Triassic Daye Formation. Time constraints for the conodont biozones include 34 ka for Hindeodus parvus , 24 ka for Isarcicella stachei-I. isarcica, 367 ka for Neogondolella planate-Ng. carinata, 66 ka for Neogondolella discreta, 255 ka for Neospathodus kummeli and 416 ka for Neospathodus dieneri. The Early Smithian negative ?13C shift near the Indun/Olenekian boundary may have happened within 430 ka. Global comparison indicates that Milankovitch and 4-5 ka sub-Milankovitch forcing depositional rhythms may have been common in tropical and sub-tropical carbonate platforms during Early and Middle Triassic time. The ultimate control on the 4-5 ka cycles may have been millennial-scale fluctuations in solar insolation.

Wu, H.; Zhang, S.; Feng, Q.; Jiang, G.; Li, H.; Yang, T.

2011-12-01

146

Diffusion Time-Scale of Porous Pressure-Sensitive Paint.  

National Technical Information Service (NTIS)

Pressure-sensitive paint (PSP) is an optical pressure sensor that utilizes the oxygen quenching of luminescence. PSP measurements in unsteady aerodynamic flows require fast time response of the paint. There are two characteristic time-scales that are rela...

T. Liu N. Teduka M. Kameda K. Asai

2001-01-01

147

Permo-Triassic vertebrate extinctions: A program  

NASA Technical Reports Server (NTRS)

Since the time of the Authors' study on this subject, a great deal of new information has become available. Concepts of the nature of extinctions have changed materially. The Authors' conclusion that a catastrophic event was not responsible for the extinction of vertebrates has modified to the extent that hypotheses involving either the impact of a massive extra-terrestrial body or volcanism provide plausible but not currently fully testable hypotheses. Stated changes resulted in a rapid decrease in organic diversity, as the ratio of origins of taxa to extinctions shifted from strongly positive to negative, with momentary equilibrium being reached at about the Permo-Triassic boundary. The proximate causes of the changes in the terrestrial biota appear to lie in two primary factors: (1) strong climatic changes (global mean temperatures, temperature ranges, humidity) and (2) susceptibility of the dominant vertebrates (large dicynodonts) and the glossopteris flora to disruption of the equlibrium of the world ecosystem. The following proximate causes have been proposed: (1) rhythmic fluctuations in solar radiation, (2) tectonic events as Pangea assembled, altering land-ocean relationships, patterns of wind and water circulation and continental physiography, (3) volcanism, and (4) changes subsequent to impacts of one or more massive extra terrestrial objects, bodies or comets. These hypotheses are discussed.

Olson, E. C.

1988-01-01

148

Relations between the scales of length, time and mass  

Microsoft Academic Search

It is considered the model of the homogeneous and isotropic universe. The scale of length is defined via the laboratory scale of time by the motion of photon. This leads to the appearance of the inertial forces. The properties of the space and time are defined both by these inertial forces and by the matter. Within the framework of classical

D. L. Khokhlov

1999-01-01

149

Singular perturbation and time scale approaches in discrete control systems  

NASA Technical Reports Server (NTRS)

After considering a singularly perturbed discrete control system, a singular perturbation approach is used to obtain outer and correction subsystems. A time scale approach is then applied via block diagonalization transformations to decouple the system into slow and fast subsystems. To a zeroth-order approximation, the singular perturbation and time-scale approaches are found to yield equivalent results.

Naidu, D. S.; Price, D. B.

1988-01-01

150

Corrected Late Triassic latitudes for continents adjacent to the North Atlantic.  

PubMed

We use a method based on a statistical geomagnetic field model to recognize and correct for inclination error in sedimentary rocks from early Mesozoic rift basins in North America, Greenland, and Europe. The congruence of the corrected sedimentary results and independent data from igneous rocks on a regional scale indicates that a geocentric axial dipole field operated in the Late Triassic. The corrected paleolatitudes indicate a faster poleward drift of approximately 0.6 degrees per million years for this part of Pangea and suggest that the equatorial humid belt in the Late Triassic was about as wide as it is today. PMID:15653500

Kent, Dennis V; Tauxe, Lisa

2005-01-14

151

Permian-Carboniferous and Permian-Triassic magmatism in the rift zone bordering the Tethyan margin of southern Pangea  

Microsoft Academic Search

Magma was emplaced in the India-Australia rift zone along the Tethyan margin during Permian-Carboniferous and Permian-Triassic time. Permian-Carboniferous alkalic granite and basaltic and rhyolitic lava flows and tuffs formed at the same time as right-lateral transtension of Pangea, as recorded by the magmatic rocks of neocratonic post-Variscan Europe and post-Kanimblan eastern Australia. Permian-Triassic tholeiitic basalt in India, alkalic magmatic rocks

J. J. Veevers; R. C. Tewari

1995-01-01

152

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

153

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

154

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

155

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

156

Death in Guizhou — Late Triassic drowning of the Yangtze carbonate platform  

NASA Astrophysics Data System (ADS)

The Yangtze platform in south China formed a stable palaeogeographic element from the Late Proterozoic to the end of the Middle Triassic with deposition of shallow-water carbonates during much of this time. A portion of the Yangtze platform in south-central Guizhou drowned at the transition from Permian to Triassic, as the south-adjacent Nanpanjiang basin encroached about 100 km northward, but a new, stable platform margin was established that persisted through the Early and Middle Triassic. This long history as a stable carbonate platform ended at the transition from the Ladinian to the Carnian. The latest Ladinian rocks, the Yangliujing Formation, are 490 m of shoaling-upward carbonate cycles of grapestone and bioclastic grainstone, fenestral limestone, and stromatolitic dolomudstone, commonly overprinted by extensive subaerial diagenesis. The beginning of the Carnian is marked by a rapid transition to medium-dark-grey, nodular lime mudstones containing ammonoids, conodonts and thin-shelled bivalves, the Zhuganpo Formation. The upper part of this thin pelagic limestone contains many muddy intraclasts, some slightly bored and encrusted, indicating incipient cementation. The overlying Wayao Formation is a condensed black shale with thin interbeds of dark-grey, manganiferous lime mudstone near the base. Ammonoids, conodonts, thin-shelled bivalves, and articulated crinoid stems are abundant. Fine-grained greywacke with sole marks forms prominent bundles within grey, calcareous shale in the overlying Laishike Formation. Ammonoids and thin-shelled bivalves occur sporadically in this 810-m-thick unit. Calcareous shale with thicker-shelled bivalves and packages of cleaner, coarser-grained sandstone characterize the Banan Formation, 460 m thick. The sandstone units generally coarsen and thicken upward, with ripples, medium-scale trough cross-beds, and rare U-tube burrows. Quartzose, coal-bearing siliciclastics 690 m thick form the overlying Huobachong Formation. Thick-bedded, cross-stratified sandstone and conglomerates are amalgamated into thinning- and fining-upward intervals separated by blocky mudstones. This fining-upward motif continues into the overlying Erqiao Formation, but coals are lacking. At the beginning of the Late Triassic (Carnian) the previously stable Yangtze platform, on which peritidal limestones were forming, was drowned and covered by dark lime mud that was cemented into intraclasts and nodular lime mudstone. Black shale and manganiferous pelagic limestone formed a condensed interval, recording maximum submergence. Turbidite sandstone and shale of the Laishike flysch filled the accommodation space of 800 m created during drowning of the Yangtze platform, leading to deposition of shoaling-upward shelf and paralic sandstones and shales, but without significant carbonate production. The succeeding fining-upward siliciclastics are interpreted as braided-stream deposits with coals that mark minor marine incursions. The shallow-shelf and braided-stream deposits form a molasse 1500 m thick. It was apparently derived from the west, in contrast to the underlying flysch where palaeocurrent directions are from the north or northeast. The entire Yangtze platform became emergent during the Late Triassic and was never submerged again. Subtle local differences in the drowning sequences indicate differential subsidence and suggest that tectonics played a role in the death of the Yangtze platform.

Enos, Paul; Wei Jiayong; Lehrmann, Daniel J.

1998-06-01

157

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

158

Time flies, a new molecular time-scale for brachyceran fly evolution without a clock.  

PubMed

The insect order Diptera, the true flies, contains one of the four largest Mesozoic insect radiations within its suborder Brachycera. Estimates of phylogenetic relationships and divergence dates among the major brachyceran lineages have been problematic or vague because of a lack of consistent evidence and the rarity of well-preserved fossils. Here, we combine new evidence from nucleotide sequence data, morphological reinterpretations, and fossils to improve estimates of brachyceran evolutionary relationships and ages. The 28S ribosomal DNA (rDNA) gene was sequenced for a broad diversity of taxa, and the data were combined with recently published morphological scorings for a parsimony-based phylogenetic analysis. The phylogenetic topology inferred from the combined 28S rDNA and morphology data set supports brachyceran monophyly and the monophyly of the four major brachyceran infraorders and suggests relationships largely consistent with previous classifications. Weak support was found for a basal brachyceran clade comprising the infraorders Stratiomyomorpha (soldier flies and relatives), Xylophagomorpha (xylophagid flies), and Tabanomorpha (horse flies, snipe flies, and relatives). This topology and similar alternative arrangements were used to obtain Bayesian estimates of divergence times, both with and without the assumption of a constant evolutionary rate. The estimated times were relatively robust to the choice of prior distributions. Divergence times based on the 28S rDNA and several fossil constraints indicate that the Brachycera originated in the late Triassic or earliest Mesozoic and that all major lower brachyceran fly lineages had near contemporaneous origins in the mid-Jurassic prior to the origin of flowering plants (angiosperms). This study provides increased resolution of brachyceran phylogeny, and our revised estimates of fly ages should improve the temporal context of evolutionary inferences and genomic comparisons between fly model organisms. PMID:14668115

Wiegmann, Brian M; Yeates, David K; Thorne, Jeffrey L; Kishino, Hirohisa

2003-12-01

159

Separation of time scales in aircraft trajectory optimization  

NASA Technical Reports Server (NTRS)

Two methods for analyzing the time-scale properties of aircraft trajectory optimization problems are presented. Time-scale properties must be identified before solutions can be obtained by using singular perturbation methods. Both methods only require a knowledge of the state equations, the aircraft characteristics, and the bounds on the state and control variables. Although these methods give only rough estimates of time-scale separation, they do not require that an 'exact' optimal trajectory be known, as do the more rigorous methods, and they are an improvement on the ad hoc methods currently in use. The two methods are applied to an example problem for a high performance aircraft.

Ardema, M. D.; Rajan, N.

1983-01-01

160

Multiple time scale complexity analysis of resting state FMRI.  

PubMed

The present study explored multi-scale entropy (MSE) analysis to investigate the entropy of resting state fMRI signals across multiple time scales. MSE analysis was developed to distinguish random noise from complex signals since the entropy of the former decreases with longer time scales while the latter signal maintains its entropy due to a "self-resemblance" across time scales. A long resting state BOLD fMRI (rs-fMRI) scan with 1000 data points was performed on five healthy young volunteers to investigate the spatial and temporal characteristics of entropy across multiple time scales. A shorter rs-fMRI scan with 240 data points was performed on a cohort of subjects consisting of healthy young (age 23 ± 2 years, n = 8) and aged volunteers (age 66 ± 3 years, n = 8) to investigate the effect of healthy aging on the entropy of rs-fMRI. The results showed that MSE of gray matter, rather than white matter, resembles closely that of f (-1) noise over multiple time scales. By filtering out high frequency random fluctuations, MSE analysis is able to reveal enhanced contrast in entropy between gray and white matter, as well as between age groups at longer time scales. Our data support the use of MSE analysis as a validation metric for quantifying the complexity of rs-fMRI signals. PMID:24242271

Smith, Robert X; Yan, Lirong; Wang, Danny J J

2014-06-01

161

Liquidity spillover in international stock markets through distinct time scales.  

PubMed

This paper identifies liquidity spillovers through different time scales based on a wavelet multiscaling method. We decompose daily data from U.S., British, Brazilian and Hong Kong stock markets indices in order to calculate the scale correlation between their illiquidities. The sample is divided in order to consider non-crisis, sub-prime crisis and Eurozone crisis. We find that there are changes in correlations of distinct scales and different periods. Association in finest scales is smaller than in coarse scales. There is a rise on associations in periods of crisis. In frequencies, there is predominance for significant distinctions involving the coarsest scale, while for crises periods there is predominance for distinctions on the finest scale. PMID:24465918

Righi, Marcelo Brutti; Vieira, Kelmara Mendes

2014-01-01

162

Hydromagnetic interpretation of short time scale structures in solar flares  

Microsoft Academic Search

Hydromagnetic interpretation of the solar flare short time scale structure indicated in microwave and hard X-ray emission during the impulsive phase is presented. The main assumption is that the plasma ejection from the current sheet may be considered as a forced convection by an isolated source. From this point of view some analogies with small scale short lasting hydrodynamic and

V. M. Dermendjiev

1986-01-01

163

Structural Decomposition of Multiple Time Scale Markov Processes,  

National Technical Information Service (NTIS)

A straightforward algorithm for the multiple time scale decomposition of singularly perturbed Markov processes has been presented. That algorithm provides a uniform approximation of the probability transition function over the interval t > or = 0 through ...

J. R. Rohlicek A. S. Willsky

1987-01-01

164

Constraints on the paleogeographic evolution of the North China Craton during the Late Triassic-Jurassic  

NASA Astrophysics Data System (ADS)

This paper reports U-Pb-Hf isotopes of detrital zircons from Late Triassic-Jurassic sediments in the Ordos, Ningwu, and Jiyuan basins in the western-central North China Craton (NCC), with the aim of constraining the paleogeographic evolution of the NCC during the Late Triassic-Jurassic. The early Late Triassic samples have three groups of detrital zircons (238-363 Ma, 1.5-2.1 Ga, and 2.2-2.6 Ga), while the latest Late Triassic and Jurassic samples contain four groups of detrital zircons (154-397 Ma, 414-511 Ma, 1.6-2.0 Ga, and 2.2-2.6 Ga). The Precambrian zircons in the Late Triassic-Jurassic samples were sourced from the basement rocks and pre-Late Triassic sediments in the NCC. But the initial source for the 238-363 Ma zircons in the early Late Triassic samples is the Yinshan-Yanshan Orogenic Belt (YYOB), consistent with their negative zircon ?Hf(t) values (-24 to -2). For the latest Late Triassic and Jurassic samples, the initial source for the 414-511 Ma zircons with ?Hf(t) values of -18 to +9 is the Northern Qinling Orogen (NQO), and that for the 154-397 Ma zircons with ?Hf(t) values of -25 to +12 is the YYOB and the southeastern Central Asian Orogenic Belt (CAOB). In combination with previous data of late Paleozoic-Early Triassic sediments in the western-central NCC and Permian-Jurassic sediments in the eastern NCC, this study reveals two shifts in detrital source from the late Paleozoic to Jurassic. In the Late Permian-Early Triassic, the western-central NCC received detritus from the YYOB, southeastern CAOB and NQO. However, in the early Late Triassic, detritus from the CAOB and NQO were sparse in basins located in the western-central NCC, especially in the Yan'an area of the Ordos Basin. We interpret such a shift of detrital source as result of the uplift of the eastern NCC in the Late Triassic. In the latest Late Triassic-Jurassic, the southeastern CAOB and the NQO restarted to be source regions for basins in the western-central NCC, as well as for basins in the eastern NCC. The second shift in detrital source suggests elevation of the orogens surrounding the NCC and subsidence of the eastern NCC in the Jurassic, arguing against the presence of a paleo-plateau in the eastern NCC at that time. It would be subsidence rather than elevation of the eastern NCC in the Jurassic, due to roll-back of the subducted paleo-Pacific plate and consequent upwelling of asthenospheric mantle.

Li, Hong-Yan; Huang, Xiao-Long

2013-07-01

165

Diffusion Time-Scale of Porous Pressure-Sensitive Paint  

NASA Technical Reports Server (NTRS)

Pressure-sensitive paint (PSP) is an optical pressure sensor that utilizes the oxygen quenching of luminescence. PSP measurements in unsteady aerodynamic flows require fast time response of the paint. There are two characteristic time-scales that are related to the time response of PSP. One is the luminescent lifetime representing an intrinsic physical limit for the achievable temporal resolution of PSP. Another is the time-scale of oxygen diffusion across the PSP layer. When the time-scale of oxygen diffusion is much larger than the luminescent lifetime, the time response of PSP is controlled by oxygen diffusion. In a thin homogenous polymer layer where diffusion is Fickian, the oxygen concentration 1021 can be described by the diffusion equation in one-dimension.

Liu, Tianshu; Teduka, Norikazu; Kameda, Masaharu; Asai, Keisuke

2001-01-01

166

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

167

Interest point detection and scale selection in space-time  

Microsoft Academic Search

Several types of interest point detectors have been proposed for spatial images. This paper investigates how this notion can be gener- alised to the detection of interesting events in space-time data. Moreover, we develop a mechanism for spatio-temporal scale selection and detect events at scales corresponding to their extent in both space and time. To detect spatio-temporal events, we build

Ivan Laptev; Tony Lindeberg

2003-01-01

168

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

169

Short time scale monitoring of SiO sources  

Microsoft Academic Search

We present the results of a short time scale monitoring of SiO maser emission (v=1 J=1-0 transition) in four known strong sources. These sources were monitored nightly for a period of about a month. The aim of these observations is to investigate the possible presence of variations in the maser lines on time scales of a few days to weeks,

F. P. Pijpers; J. R. Pardo; V. Bujarrabal

1994-01-01

170

Short-time scaling of variable ordering of OBDDs  

Microsoft Academic Search

A short-time scaling criterion of variable ordering of OBDDs is proposed. By this criterion it is easy and fast to determine\\u000a which one is better when several variable orders are given, especially when they differ 10% or more in resulted BDD size from\\u000a each other. An adaptive variable order selection method, based on the short-time scaling criterion, is also presented.

Wangning Long; Yinghua Min; Shiyuan Yang; Shibai Tong

1997-01-01

171

Short-time scale variability in some Be stars  

Microsoft Academic Search

The short-time scale spectroscopic variability of some Be stars has been investigated with an optical fiber spectrograph and a CCD camera. Findings on a time-scale of hours and days include: (1) weak changes in the H-alpha emission line profile of gamma Cas; (2) changes in the structure and the intensity of the H-alpha emission line core and sometimes in the

H. Hubert; B. Dagostinoz; A. M. Hubert; M. Floquet

1987-01-01

172

Geomagnetic secular variations at the Permo-Triassic boundary  

NASA Astrophysics Data System (ADS)

Study of changes in geomagnetic secular variations through geological time is essential to document the Earth's magnetic field evolution and provides an important constraint for geodynamo modeling. Moreover, knowledge of the secular variations value for any specific geological epoch (paleosecular variations - PSV) may give an additional tool to constrain the duration of emplacement and cooling of various magmatic bodies including flows, dykes and sills. In this report we present the result of study of the PSV at the Permo-Triassic boundary (~252 Ma), based on the paleomagnetic data, obtained from numerous (N>100) volcanic flows of the Siberian traps exposed in series of sections located in Norilsk and Maymecha-Kotuy regions in the North-West and North of the Siberian platform. Our data, taken together with similar data from other regions (Sementau, East Kazakhstan; Emeichan, China) indicates that the amplitude of PSV at the Permo-Triassic boundary was about the same or a little lower than in Late Cenozoic during last 5 milllions years. The low (comparing with expected one) value of PSV recorded in several large sills from Angara-Bratsk region (southern Siberian platform) indicates that these sills was formed very fast during the time interval less than, at least, several thousand years. Especially this conclusion is interesting for so called Tolstomyss sill, which, in fact, represents a huge field of associated tuffs, sills, dykes and volcanics, extended over the distance more than 200 km. This result can be considered as a further indication of very fast emplacement of the Siberian traps and their link with the Permo-Triassic catastrophe.

Pavlov, Vladimir; Veselovskiy, Roman; Fetisova, Anna; Latyshev, Anton; Fluteau, Frederic

2014-05-01

173

The Late Triassic bivalve Monotis in accreted terranes of Alaska  

USGS Publications Warehouse

Late Triassic bivalves of the genus Monotis occur in at least 16 of the lithotectonic terranes and subterranes that together comprise nearly all of Alaska, and they also occur in the Upper Yukon region of Alaska where Triassic strata are regarded as representing non-accretionary North America. On the basis of collections made thus far, 14 kinds of Monotis that differ at the species or subspecies level can be recognized from alaska. These are grouped into the subgenera Monotis (Monotis), M. (Pacimonotis), M. (Entomonotis), and M. (Eomonotis). In places, Monotis shells of one kind or another occur in rock-forming abundance. On the basis of superpositional data from Alaska, as well as from elsewhere in North America and Far Eastern Russia, at least four distince biostratigraphic levels can be discriminated utilizing Monotis species. Different species of M. (Eomonotis) characterize two middle Norian levels, both probably within the supper middle Norian Columbianus Ammonite Zone. Two additional levels are recognized in the lower upper Norian Cordilleranus Ammonite Zone utilizing species of M. (Monotis) or M. (Entomonotis), both of which subgenera are restricted to the late Norian. An attached-floating mode of life is commonly attributed to Monotis; thus, these bivalves would have been pseudoplanktonic surface dwellers that were sensitive to surface-water temperature and paleolatitude. Distinctly different kinds of Monotis occur at different paleolatitudes along the Pacific and Arctic margins of the North American craton inboard of the accreted terranes. Comparison between thse craton-bound Monotis faunas and those of the Alaskan terranes in southern Alaska south of the Denali fault were paleoequatorial in latitude during Late Triassic time. Among these terranes, the Alexander terrane was possibly in the southern hemisphere at that time. Terranes of northern Alaska, on the other hand, represent middle, possibly high-middle, northern paleolatitudes.

Silberling, N. J.; Grant-Mackie, J. A.; Nichols, K. M.

1997-01-01

174

Signatures of discrete scale invariance in Dst time series  

NASA Astrophysics Data System (ADS)

Self-similar systems are characterized by continuous scale invariance and, in response, the existence of power laws. However, a significant number of systems exhibits discrete scale invariance (DSI) which in turn leads to log-periodic corrections to scaling that decorate the pure power law. Here, we present the results of a search of log-periodic corrections to scaling in the squares of Dst index increments which are taken as proxies of the energy dissipation rate in the magnetosphere. We show that Dst time series exhibit DSI and discuss the consequence of this feature, as well as the possible implications of Dst DSI on space weather forecasting efforts.

Balasis, Georgios; Papadimitriou, Constantinos; Daglis, Ioannis A.; Anastasiadis, Anastasios; Athanasopoulou, Labrini; Eftaxias, Konstantinos

2011-07-01

175

Detrital Zircon Link Between Headwaters and Terminus of the Upper Triassic Chinle-Dockum Paleoriver System  

PubMed

New detrital-zircon geochronologic data reveal that a through-going paleoriver connected Texas with Nevada in Late Triassic time. Sandstone from the Upper Triassic Santa Rosa Sandstone (Dockum Group) from northwestern Texas contains a detrital zircon suite nearly identical to that found in western Nevada in the Upper Triassic Osobb Formation (Auld Lang Syne Group, correlative with the Chinle Formation). The Santa Rosa Sandstone was derived in large part from the eroded Cambrian core of the Amarillo-Wichita uplift, as evidenced by abundant zircons with ages of 515 to 525 million years. Other zircon grains in the sandstone are Permian, Devonian, Proterozoic, and Archean in age and, with the exception of the Archean grain, are also matched by the population in the Nevada strata. PMID:8688060

Riggs; Lehman; Gehrels; Dickinson

1996-07-01

176

Permo-Triassic oblique extension in the Potrerillos-Uspallata area, western Argentina  

NASA Astrophysics Data System (ADS)

The Permo-Triassic evolution of southwestern South America was characterized by the development of a great amount of volcanism under extensional conditions. Structural analyses of faults developed contemporaneously with this volcanism in the key area of Potrerillos-Uspallata suggest the existence of an oblique extensional setting controlled by the presence of a pre-existing lithospheric anisotropy. A clear parallelism between the trace of an inferred Devonian suture zone, the Late Paleozoic San Rafael orogenic belt and the Permo-Triassic rifting suggests that Early and Late Paleozoic tectonic inheritance permitted the reactivation of a NNW-trending zone of lithospheric weakness. The reactivation of this pre-existing weak zone during Late Permian to Early Triassic times has resulted in the generation of a new complex fault system, which concentrated the oblique-slip normal displacement related to a NNE-SSW stretching (N23°E).

Giambiagi, Laura; Martinez, Amancay N.

2008-11-01

177

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

2009-09-01

178

Russian national time scale long-term stability  

NASA Technical Reports Server (NTRS)

The Institute of Metrology for Time and Space NPO 'VNIIFTRI' generates the National Time Scale (NTS) of Russia -- one of the most stable time scales in the world. Its striking feature is that it is based on a free ensemble of H-masers only. During last two years the estimations of NTS longterm stability based only on H-maser intercomparison data gives a flicker floor of about (2 to 3) x 10(exp -15) for averaging times from 1 day to 1 month. Perhaps the most significant feature for a time laboratory is an extremely low possible frequency drift -- it is too difficult to estimate it reliably. The other estimations, free from possible inside the ensemble correlation phenomena, are available based on the time comparison of NTS relative to the stable enough time scale of outer laboratories. The data on NTS comparison relative to the time scale of secondary time and frequency standards at Golitzino and Irkutsk in Russia and relative to NIST, PTB and USNO using GLONASS and GPS time transfer links gives stability estimations which are close to that based on H-maser intercomparisons.

Alshina, A. P.; Gaigerov, B. A.; Koshelyaevsky, N. B.; Pushkin, S. B.

1994-01-01

179

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

180

Supraregional seismites in Triassic - Jurassic boundary strata  

NASA Astrophysics Data System (ADS)

The end-Triassic mass extinction event (201.564 Ma) was synchronous with the earliest volcanic phase during the emplacement of the Central Atlantic Magmatic Province (CAMP), a large igneous province (LIP) formed during the initial breakup of Pangea. Volcanic degassing of CO2 and other volatile gases, and/or thermogenic methane, from the CAMP is generally regarded as the main cause of the end-Triassic biotic crisis. However, discrepancies in the durations of the ETE (50 Kyrs) and the CAMP volcanism (600 Kyrs) as well as temporal offsets between carbon cycle perturbations and biotic turnovers suggest a more complex scenario that require further studies of the temporal succession of events in Triassic-Jurassic (TJ) boundary strata. Here, we present and examine multiple episodes of soft-sediment deformation (seismite) within uppermost Rhaetian marine and terrestrial strata of Denmark, Sweden and Germany. These seismites are stratigraphically constrained by palynology and C-isotopes to the latest Rhaetian, and are synchronous to the single seismite layer from the UK, which similarly predates the T/J boundary, and has been explained by an extraterrestrial bolide impact. Instead, we argue that the multiple episodes of soft-sediment deformation, interbedded by undisturbed strata, were formed from repeated intense earthquake activity restricted to an interval within the latest Rhaetian bracketed by two negative excursions in ?13C and also containing palynological evidence for deforestation and fern proliferation. The fact that these biotic changes coincide with repeated seismic activity has implications for the end-Triassic extinction and the CAMP scenario. We discuss the temporal position of the seismites in regards to other end-Triassic events, and argue that their supraregional distribution in pre-TJ-boundary strata of NW Europe may be linked to intensified earthquake activity during CAMP emplacement, rather than an extraterrestrial impact.

Lindström, Sofie; Pedersen, Gunver K.; van de Schootbrugge, Bas; Johansson, Leif; Petersen, Henrik I.; Dybkjær, Karen; Weibel, Rikke; Hansen, Katrine H.; Erlström, Mikael; Alwmark, Carl; Nielsen, Lars Henrik; Oschmann, Wolfgang; Tegner, Christian

2014-05-01

181

Evolution of a Permo-Triassic sedimentary melange, Grindstone terrane, east-central Oregon  

USGS Publications Warehouse

Perceives the Grindstone rocks to be a sedimentary melange composed of Paleozoic limestone slide and slump blocks that became detached from a carbonate shelf fringing a volcanic knoll or edifice in Late Permian to Middle Triassic time and were intermixed with Permian and Triassic slope to basinal clastic and volcaniclastic rocks in a forearc basin setting. Paleogeographic affinities of the Grindstone limestone faunas and volcaniclastic debris in the limestone and clastic rocks all indicate deposition in promixity to an island-arc system near the North American craton. -from Authors

Blome, C. D.; Nestell, M. K.

1991-01-01

182

Time/scale-adjusted dyadic wavelet packet bases  

NASA Astrophysics Data System (ADS)

This paper generalizes the dyadic wavelet packet bases (DWP), developed by Coifman and Wickerhauser, to time/scale-adjusted DWP bases. These generalized DWP bases provide more flexibility in matching the time-scale characteristics of the input signal. Development of these generalized bases is achieved by combining the previously defined time-invariant DWP bases of Pesquet, Krim, Carfantan, and Proakis with a generalized scale sampling. The generalized scale sampling extends the usual dyadic sampling by adding a real-valued offset parameter to the integer power of two in the scale parameter. This offset parameter value is taken between zero and one. By combining both scale and translation generalizations, signal components existing between consecutive dyadic scales, or consecutive time translations, may be captured. It is shown how these DWP coefficients may be generated from a two step process; first projecting the input signal onto an appropriate space. Then, performing the usual wavelet low and highpass filtering operations, followed by downsampling. The projection operation is shown to be equivalent to a filtering operation. An expression for the filter taps is derived, and basic properties are proven. A translation-invariant transform defined on these scale-adjusted wavelet packets, is developed. An application to transient detection is presented, by developing a transient detector based on this transform. ROC curves, generated by Monte- Carlo simulation, are presented demonstrating detector performance. Detector performance is shown to be independent of the signal translation. It is further shown how matching the basis functions to the time-scale-frequency characteristics of the transient can provide improved detection performance.

del Marco, Stephen P.

1996-03-01

183

The "terminal Triassic catastrophic extinction event" in perspective: a review of carboniferous through Early Jurassic terrestrial vertebrate extinction patterns  

USGS Publications Warehouse

A catastrophic terminal Triassic extinction event among terrestrial vertebrates is not supported by available evidence. The current model for such an extinction is based on at least eight weak or untenable assumptions: (1) a terminal Triassic extinction-inducing asteroid impact occurred, (2) a terminal Triassic synchronous mass extinction of terrestrial vertebrates occurred, (3) a concurrent terminal Triassic marine extinction occurred, (4) all terrestrial vertebrate families have similar diversities and ecologies, (5) changes in familial diversity can be gauged accurately from the known fossil record, (6) extinction of families can be compared through time without normalizing for changes in familial diversity through time, (7) extinction rates can be compared without normalizing for differing lengths of geologic stages, and (8) catastrophic mass extinctions do not select for small size. These assumptions have resulted in unsupportable and (or) erroneous conclusions. Carboniferous through Early Jurassic terrestrial vertebrate families mostly have evolution and extinction patterns unlike the vertebrate evolution and extinction patterns during the terminal Cretaceous event. Only the Serpukhovian (mid Carboniferous) extinction event shows strong analogy to the terminal Cretaceous event. Available data suggest no terminal Triassic extinction anomaly, but rather a prolonged and nearly steady decline in the global terrestrial vertebrate extinction rate throughout the Triassic and earliest Jurassic. ?? 1992.

Weems, R. E.

1992-01-01

184

Plate tectonic controls on atmospheric CO2 levels since the Triassic  

NASA Astrophysics Data System (ADS)

Climate trends on time-scales of 10's to 100's of millions of years are controlled by changes in solar luminosity, continent distribution and atmosphere composition. Plate tectonics affect geography, but also atmosphere composition through volcanic degassing of CO2 at subduction zones and mid-ocean ridges. So far, such degassing estimates were based on reconstructions of ocean floor production for the last 150 Million years (Myr) and indirectly, through sea level inversion before 150 Myr. Here we quantitatively estimate CO2 degassing by reconstructing lithosphere subduction evolution, using recent advances in combining global plate reconstructions and present-day structure of the mantle. First, we estimate that since the Triassic (250-200 Myr) until Present, the total paleo-subduction zone length reached up to ~200% of the present-day value. Comparing our subduction zone lengths with previously reconstructed ocean-crust production rates over the past 140 Myr suggests average global subduction rates have been constant, ~6 cm/year: Higher ocean-crust production is associated with longer total subduction length. We compute a Strontium isotope record based on subduction zone length, which agrees well with geological records supporting the validity of our approach: The total subduction zone length is proportional to the summed arc- and ridge volcanic CO2 production and thereby to global volcanic degassing at plate boundaries. We therefore use our degassing curve as input for the GEOCARBSULF model to estimate atmospheric CO2 levels since the Triassic. Our calculated CO2 levels for the mid-Mesozoic differ from previous modeling results and are more consistent with available proxy data.

van der Meer, Douwe; Zeebe, Richard; van Hinsbergen, Douwe; Sluijs, Appy; Spakman, Wim; Torsvik, Trond

2014-05-01

185

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

186

Palaeoenvironments and palaeotectonics of the arid to hyperarid intracontinental latest Permian- late Triassic Solway basin (U.K.)  

NASA Astrophysics Data System (ADS)

The late Permian to late Triassic sediments of the Solway Basin consist of an originally flat-lying, laterally persistent and consistent succession of mature, dominantly fine-grained red clastics laid down in part of a very large intracontinental basin. The complete absence of body or trace fossils or palaeosols indicates a very arid (hyperarid) depositional environment for most of the sediments. At the base of the succession, thin regolith breccias and sandstones rest unconformably on basement and early Permian rift clastics. Overlying gypsiferous red silty mudstones, very fine sandstones and thick gypsum were deposited in either a playa lake or in a hypersaline estuary, and their margins. These pass upwards into thick-bedded, multi-storied, fine- to very fine-grained red quartzo-felspathic and sublithic arenites in which even medium sand is rare despite channels with clay pebbles up to 30 cm in diameter. Above, thick trough cross-bedded and parallel laminated fine-grained aeolian sandstones (deposited in extensive barchanoid dune complexes) pass up into very thick, multicoloured mudstones, and gypsum deposited in marginal marine or lacustrine sabkha environments. The latter pass up into marine Lower Jurassic shales and limestones. Thirteen non-marine clastic lithofacies are arranged into five main lithofacies associations whose facies architecture is reconstructed where possible by analysis of large exposures. The five associations can be compared with the desert pavement, arid ephemeral stream, sabkha, saline lake and aeolian sand dune environments of the arid to hyperarid areas of existing intracontinental basins such as Lake Eyre and Lake Chad. The accommodation space in such basins is controlled by gradual tectonic subsidence moderated by large fluctuations in shallow lake extent (caused by climatic change and local variation) and this promotes a large-scale layer-cake stratigraphy as exemplified in the Solway basin. Here, the dominant fine-grained mature sandstones above the local basal reg breccias suggest water-reworking of wind-transported sediment, as in the northern part of the Lake Chad basin. Growth faulting occurs in places in the Solway basin, caused by underlying evaporite movement, but these faults did not significantly affect pre-late Triassic sedimentation and did not expose pre-Permian units above the basal breccias. There is no evidence of post-early Permian rifting anywhere during deposition of the late Permian to middle Triassic British succession although the succession is often interpreted with a rift-basin model. The arid to hyperarid palaeoclimate changed little during deposition of the Solway basin succession, in contrast to Lakes Eyre and Chad: and this is attributed to tectonic and palaeolatitude stability. Unlike the later Mesozoic- Cenozoic, only limited plate movements took place during the Triassic in western Europe, palaeolatitude changed little, and the Solway Basin remained in the northern latitudinal desert belt from early to mid-Triassic times. However, the influence of the early Triassic impoverished biota on environmental interpretations needs further study.

Brookfield, Michael E.

2008-10-01

187

Scaling Behavior of the Time-Dependent SGEMP Boundary Layer  

Microsoft Academic Search

The analysis and results given here show that boundary layer dynamics obeys very useful scaling laws which permit one solution of the basic equations to hold for many cases. In particular, during the time that the X-ray pulse is linearly rising, or when the pulse time history changes slowly after a rapid rise, (or when the pulse behaves as any

N. J. CarronandC; C. L. Longmire

1978-01-01

188

High quality time-scale modification for speech  

Microsoft Academic Search

We present a new and simple method for speech rate modification that yields high quality rate-modified speech. Earlier algorithms either required a significant amount of computation for good quality output speech or resulted in poor quality rate-modified speech. The algorithm we describe allows arbitrary linear or nonlinear scaling of the time axis. The algorithm operates in the time domain using

Salim Roucos

1985-01-01

189

Short time-scale structural variation in 3C 273  

Microsoft Academic Search

The results of VLBI observations at 22 GHz and 43 GHz of the quasar 3C 273 are presented Hybrid maps and modelfitting were made to look for any short time-scale structural variation in the jet. The jet structure did not show dramatic changes during the 42 days in which 3C 273 was observed 5 times at almost 10 day intervals.

F. Mantovani; C. Valerio; W. Junor; I. McHardy

1999-01-01

190

Current and Future Realizations of Coordinate Time Scales  

NASA Astrophysics Data System (ADS)

Time metrology provides references for experiments in the vicinity of a clock and also for applications in astro-geodetic sciences on extended environments, where time constitutes a coordinate in a space-time coordinate system. Only a coordinate time scale can be the basis of a world-time reference. We adopt a rotating geocentric reference system where the time-coordinate is the geocentric coordinate time. Such a time scale is constructed from a clock ensemble with an appropriate algorithm. The choice of the algorithm will depend on the interval over which the frequency stability is to be assured, on the compromise between frequency stability and accuracy, and should be adapted to the type of standards and the techniques used for their comparison. This algorithm should produce a time scale more stable and accurate than any of the individual participating clocks. To profit at best the quality of the time and frequency standards, algorithms should be in the framework of general relativity. International atomic time (TAI) is a realization of terrestrial time maintained at the Bureau International des Poids et Mesures from data of industrial atomic clocks and primary frequency standards in time metrology laboratories. TAI is calculated from thirty-day data sets and is published monthly with adelay of about 15 days after the last date of data. The frequency stability of TAI at one month is better than 0.4 ×10-15, and its frequency accuracy is of order 10-15. However, long term drifts limit the stability of TAI making it inadequate for some applications. Another atomic time scale is calculated under the acronym TT(BIPMYY) using an algorithm that eliminates the instabilities of TAI. This presentation describes TAI and TT(BIPMYY) and tries to predict their features in view of the progress in atomic physics and technology.

Felicitas Arias, Elisa

2009-05-01

191

Auroral Substorm Time Scales: Seasonal and IMF Variations  

NASA Technical Reports Server (NTRS)

The time scales and phases of auroral substorm, activity are quantied in this study using the hemispheric power computed from Polar Ultraviolet Imager (UVI) images. We have applied this technique to several hundred substorm events and we are able to quantify how the characterist act, of substorms vary with season and IMF Bz orientation. We show that substorm time scales vary more strongly with season than with IMF Bz orientation. The recovery time for substorm. activity is well ordered by whether or not the nightside oral zone is sunlit. The recovery time scales for substorms occurring in the winter and equinox periods are similar and are both roughly a factor of two longer than in summer when the auroral oval is sunlit. Our results support the hypothesis that the ionosphere plays an active role in governing the dynamics of the aurora.

Chua, D.; Parks, G. K.; Brittnacher, M.; Germany, G. A.; Spann, J. F.; Six, N. Frank (Technical Monitor)

2002-01-01

192

How was the Triassic Songpan-Ganzi basin filled? A provenance study  

USGS Publications Warehouse

The Triassic Songpan-Ganzi complex comprises >200,000 km2 of 5-15 km thick turbiditic sediments. Although surrounded by several magmatic and orogenic belts, the Triassic high- and ultrahigh-pressure Qinling-Tongbai-Hong'an-Dabie (QTHD) orogen, located several hundred kilometers to the east, was proposed as its major source. Middle to Late Triassic samples from the northern and southern Songpan-Ganzi complex, studied using detrital white mica 40Ar/39Ar ages, Si-in-white mica content, and detrital zircon U/Pb ages, suggest that the northern Songpan-Ganzi deposystem obtained detritus from the north: the north China block, east Kunlun, northern Qaidam, Qilian, and western Qinling; the southern Songpan-Ganzi deposystem was supplied from the northeasterly located Paleozoic QTHD area throughout the Ladinian and received detritus from the Triassic Hong'an-Dabie orogen during the Carnian, indicative of exhumation of the orogen at that time. The QTHD orogen fed the Norian samples in the southeastern southern Songpan-Ganzi deposystem, signifying long drainage channels along the western margin of the south China block. An additional supply from the Emeishan magmatic province and/or the Yidun arc is suggested by the paucity of white mica in the southern Songpan-Ganzi deposystem. Mica ages of Rhaetian sediments from the northwestern Sichuan basin best correlate with those of the Triassic QTHD orogen. Our Si-in-white mica data demonstrate that the high- and ultrahigh-pressure rocks of the Hong'an-Dabie Shan were not exposed in the Middle to Late Triassic. Copyright 2007 by the American Geophysical Union.

Enkelmann, E.; Weislogel, A.; Ratschbacher, L.; Eide, E.; Renno, A.; Wooden, J.

2007-01-01

193

On Nonlinear Control Systems with Multiple Time Scales  

Microsoft Academic Search

An order reduction procedure for nonlinear control systems with multiple time scales is introduced. A limit system for the slowest motion describing the situation that all singular perturbation parameters vanish is constructed. For this purpose a refined two-scale averaging method is used in a way that allows a re-iteration. For vanishing control range the results reduce to the well-known Tychonoff

G. Grammel

2004-01-01

194

Short time scale monitoring of SiO sources  

Microsoft Academic Search

We present the results of a short time scale monitoring of SiO maser emission\\u000a(v=1 J=1-0 transition) in four known strong sources. These sources were\\u000amonitored nightly for a period of about a month. The aim of these observations\\u000ais to investigate the possible presence of variations in the maser lines on\\u000atime scales of a few days to weeks,

F. P. Pijpers; J. R. Pardo; V. Bujarrabal

1994-01-01

195

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

196

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

197

Tetrapod biostratigraphy and biochronology of the Triassic–Jurassic transition on the southern Colorado Plateau, USA  

Microsoft Academic Search

Nonmarine fluvial, eolian and lacustrine strata of the Chinle and Glen Canyon groups on the southern Colorado Plateau preserve tetrapod body fossils and footprints that are one of the world's most extensive tetrapod fossil records across the Triassic–Jurassic boundary. We organize these tetrapod fossils into five, time-successive biostratigraphic assemblages (in ascending order, Owl Rock, Rock Point, Dinosaur Canyon, Whitmore Point

Spencer G. Lucas; Lawrence H. Tanner

2007-01-01

198

Triassic Pollen Date Moroccan High Atlas and the Incipient Rifting of Pangea as Middle Carnian  

Microsoft Academic Search

Palynomorphs from the High Atlas Mountains south of Marrakech define the Minutosaccus-Patinasporites Concurrent Range Zone, which is time-stratigraphically equivalent to the Swiss and English middle Keuper, type Carnian of Austria, and North American Triassic beds in Virginia, North Carolina, Pennsylvania, New Jersey, Texas, New Mexico, and Arizona, thus dating an early episode of continental rifting between Africa and North America.

Harold L. Cousminer; Warren Manspeizer

1976-01-01

199

Late Precambrian to Triassic history of the East European Craton: dynamics of sedimentary basin evolution  

Microsoft Academic Search

During its Riphean to Palaeozoic evolution, the East European Craton was affected by rift phases during Early, Middle and Late Riphean, early Vendian, early Palaeozoic, Early Devonian and Middle-Late Devonian times and again at the transition from the Carboniferous to the Permian and the Permian to the Triassic. These main rifting cycles were separated by phases of intraplate compressional tectonics

A. M. Nikishin; P. A. Ziegler; R. A. Stephenson; S. A. P. L. Cloetingh; A. V. Furne; P. A. Fokin; A. V. Ershov; S. N. Boloytov; M. V. Korotaev; A. S. Alekseev; V. I. Gorbachev; E. V. Shipilov; A. C. Lankreijer; E. Yu. Bembinova; I. V. Shalimov

1996-01-01

200

An algorithm for the Italian atomic time scale  

NASA Technical Reports Server (NTRS)

During the past twenty years, the time scale at the IEN has been realized by a commercial cesium clock, selected from an ensemble of five, whose rate has been continuously steered towards UTC to maintain a long term agreement within 3 x 10(exp -13). A time scale algorithm, suitable for a small clock ensemble and capable of improving the medium and long term stability of the IEN time scale, has been recently designed taking care of reducing the effects of the seasonal variations and the sudden frequency anomalies of the single cesium clocks. The new time scale, TA(IEN), is obtained as a weighted average of the clock ensemble computed once a day from the time comparisons between the local reference UTC(IEN) and the single clocks. It is foreseen to include in the computation also ten cesium clocks maintained in other Italian laboratories to further improve its reliability and its long term stability. To implement this algorithm, a personal computer program in Quick Basic has been prepared and it has been tested at the IEN time and frequency laboratory. Results obtained using this algorithm on the real clocks data relative to a period of about two years are presented.

Cordara, F.; Vizio, G.; Tavella, P.; Pettiti, V.

1994-01-01

201

Large-scale fluctuations in underground muon time series  

SciTech Connect

We study the self-affine properties of intensity fluctuations of underground muons generated by primary cosmic rays of rigiditygreater than or equal to1600 GV. The muon time series were recorded at a vertical depth of 570 Hg/cm/sup 2/ during the years 1981--1983. This time interval includes a period of intense solar activity in the summer of 1982 which was characterized by the creation of large solar wind shocks and associated production of major interplanetary disturbances. The purpose of our analysis is to obtain from the behavior of the muon intensity some insight into the large-scale behavior of interplanetary magnetic field fluctuations and their effects on the propagation of high-rigidity galactic cosmic rays. The results give good evidence for fractal behavior of large-scale muon fluctuations in the range from a few hours to more than 10 days, with scaling exponent H varying according to the time interval analyzed. We find that the large time scale muon fluctuations evolve from a preshock condition in late 1981 to early 1982 characterized by a scaling exponent H = 0.28 and power spectrum f/sup -1.6/ to a condition with H = 0.07 and an f/sup 1.1/ power spectrum during the most intense solar activity in 1982, followed by a slow return in 1983 to the original preshock conditions (H = 0.14, f/sup -1.3/).

Bergamasco, L.; Provenzale, A.; Osborne, A.R.; Castagnoli, G.C.; Kudryavtsev, V.A.; Kuznetsov, V.A.; Ryazhkaya, O.G.

1989-03-01

202

The Galaxy Viewed at Very Short Time-Scales  

NASA Astrophysics Data System (ADS)

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 0540-69), dMe flare stars (CN Leo) and active galactic nucleii (Mkn 618). These observations, which were recorded during several nights of engineering time at SALT in early 2009, indicate that there are many types of astrophysical processes operating over very short time-scales in a wide variety of astronomical objects. The high-time resolution capability of the BVIT detector allowed emission features occurring on time-scales as short as tens of milli-seconds to be revealed. In particular, we have measured the optical period of the PSR 0540-69 pulsar to be 0.05065018808s and we have also detected several quasi-periodic oscillations operating on time-scales of < 0.5 s in the emitted flux from the X-ray transient source, GX 339-4. These preliminary data indicate that the new field of high time-resolution astronomy is providing important new insights into the transient nature of the Universe.

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

2010-01-01

203

Dynamics symmetries of Hamiltonian system on time scales  

NASA Astrophysics Data System (ADS)

In this paper, the dynamics symmetries of Hamiltonian system on time scales are studied. We study the symmetries and quantities based on the calculation of variation and Lie transformation group. Particular focus lies in: the Noether symmetry leads to the Noether conserved quantity and the Lie symmetry leads to the Noether conserved quantity if the infinitesimal transformations satisfy the structure equation. As the new application of result, at end of the article, we give a simple example of Noether symmetry and Lie symmetry on time scales.

Peng, Keke; Luo, Yiping

2014-04-01

204

Time scale analysis of a digital flight control system  

NASA Technical Reports Server (NTRS)

In this paper, consideration is given to the fifth order discrete model of an aircraft (longitudinal) control system which possesses three slow (velocity, pitch angle and altitude) and two fast (angle of attack and pitch angular velocity) modes and exhibits a two-time scale property. Using the recent results of the time scale analysis of discrete control systems, the high-order discrete model is decoupled into low-order slow and fast subsystems. The results of the decoupled system are found to be in excellent agreement with those of the original system.

Naidu, D. S.; Price, D. B.

1986-01-01

205

Relativistic fireballs - Energy conversion and time-scales  

NASA Technical Reports Server (NTRS)

The expansion energy of a relativistic fireball can be reconverted into radiation when it interacts with an external medium. For expansion with Lorentz factors greater than or approximately equal to 1000 into a typical galactic environment, the corresponding time-scale in the frame of the observer is of the order of seconds. This mechanism would operate in any cosmological scenario of gamma-ray bursts involving initial energies of order a percent of a stellar rest mass, and implies photon energies and time-scales compatible with those observed in gamma-ray bursts.

Rees, M. J.; Meszaros, P.

1992-01-01

206

Triassic-Jurassic atmospheric CO2 spike.  

PubMed

I question the claim by Tanner et al. that atmospheric CO2 levels remained constant across the Triassic-Jurassic boundary on the grounds of problems with stratigraphic completeness and contamination with atmospheric methane. Because methanogenic CH4 has a light isotope composition and oxidizes readily to CO2, methane-clathrate dissociation and oxidation events cannot be detected by palaeobarometers that use the carbon-isotope composition of palaeosol carbonate. PMID:11807543

Retallack, Gregory J

2002-01-24

207

Appropriate time scales for nonlinear analyses of deterministic jump systems  

NASA Astrophysics Data System (ADS)

In the real world, there are many phenomena that are derived from deterministic systems but which fluctuate with nonuniform time intervals. This paper discusses the appropriate time scales that can be applied to such systems to analyze their properties. The financial markets are an example of such systems wherein price movements fluctuate with nonuniform time intervals. However, it is common to apply uniform time scales such as 1-min data and 1-h data to study price movements. This paper examines the validity of such time scales by using surrogate data tests to ascertain whether the deterministic properties of the original system can be identified from uniform sampled data. The results show that uniform time samplings are often inappropriate for nonlinear analyses. However, for other systems such as neural spikes and Internet traffic packets, which produce similar outputs, uniform time samplings are quite effective in extracting the system properties. Nevertheless, uniform samplings often generate overlapping data, which can cause false rejections of surrogate data tests.

Suzuki, Tomoya

2011-06-01

208

Calculation of nanocolloidal liquid time scales by molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

Molecular dynamics, MD, simulations have been used to calculate the translational and rotational relaxation dynamics of model atomistically rough spherical nanocolloidal particles in solution at infinite dilution by immersing a single Lennard-Jones cluster in a molecularly discrete solvent. Key time scales characterizing colloidal particle dynamical relaxation were computed from time correlation functions. For translational motion these were ? v, the colloidal velocity relaxation time, ?f, the hydrodynamic relaxation time and the time scale for significant particle displacement, ?d. We show that ?v ? ?f when the relative mass density of the colloidal particle divided by the bulk density of the solvent is ca. ?*=20, in agreement with theoretical predictions. Preliminary evidence from the velocity autocorrelation functions, VACF, of the nanocolloidal particle also supports the theoretical treatments that the transition from the Liouville to Fokker-Planck description (evident by exponential decay in the VACF) is determined by both the colloidal particle mass and size. We calculated the relaxation times for angular velocity relaxation, ?? and reorientation, ?u and found them to scale reasonably well with the relaxation time for the free rotor, for size dependence but not so well for mass dependence. The angular velocity correlation function of 13 atom clusters departed from Langevin (exponential) relaxation also for ?*< 20. The rotational self-diffusion coefficient was also non-classical in this range.

Heyes, D. M.; Bra?ka, A. C.

209

Combined quantitative analysis and microfacies studies of ancient reefs: An integrated approach to Upper Permian and Upper Triassic reef carbonates (Sultanate of Oman)  

Microsoft Academic Search

Summary  The internal architecture of Upper Permian calcisponge reefs, Upper Triassic coral thickets, and Upper Triassic coral reef\\u000a communities of the Oman Mountains have been investigated. In order to gain comparable data sets, investigations were carried\\u000a out at different scales comprising quantitative data from outcrops and descriptions from thin-sections. Methods of quantitative\\u000a outcrop investigations were modified with reference to standard investigation

Oliver Weidlich; Michaela Bernecker; Erik Flügel

1993-01-01

210

Multiple-Time-Scale Concepts in Turbulent Transport Modeling  

NASA Technical Reports Server (NTRS)

Progress in developing a turbulence closure employing two or more independently calculated time scales with which to characterize the rates of progress of different turbulent interactions is reported. The energy containing part of the spectrum is divided into two regions which respond at different rates and in different ways to changes in the environment. The scheme may be regarded as providing an intermediate level of approximation between the relatively simple, but fallible, single-point closures and the vastly more elaborate two-point closures which have so far been applied only to simulating homogeneous flows. The proposed approach requires only slightly more computational effort than single-scale schemes. Computational results are reported for several thin shear flows which show striking improvement in the level of agreement with experiment over that obtained with models employing only one time scale.

Hanjalic, K.; Launder, B. E.; Schiestel, R.

1980-01-01

211

Satellite attitude prediction by multiple time scales method  

NASA Technical Reports Server (NTRS)

An investigation is made of the problem of predicting the attitude of satellites under the influence of external disturbing torques. The attitude dynamics are first expressed in a perturbation formulation which is then solved by the multiple scales approach. The independent variable, time, is extended into new scales, fast, slow, etc., and the integration is carried out separately in the new variables. The theory is applied to two different satellite configurations, rigid body and dual spin, each of which may have an asymmetric mass distribution. The disturbing torques considered are gravity gradient and geomagnetic. Finally, as multiple time scales approach separates slow and fast behaviors of satellite attitude motion, this property is used for the design of an attitude control device. A nutation damping control loop, using the geomagnetic torque for an earth pointing dual spin satellite, is designed in terms of the slow equation.

Tao, Y. C.; Ramnath, R.

1975-01-01

212

Relations between the scales of length, time and mass  

Microsoft Academic Search

It is considered the model of the homogeneous and isotropic universe. The\\u000ascale of length is defined via the laboratory scale of time by the motion of\\u000aphoton. This leads to the appearance of the inertial forces. The properties of\\u000athe space and time are defined both by these inertial forces and by the matter.\\u000aWithin the framework of classical

D. L. Khokhlov

1999-01-01

213

Measurement of hyperpolarized gas diffusion at very short time scales  

Microsoft Academic Search

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

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

2007-01-01

214

Units of relativistic time scales and associated quantities  

Microsoft Academic Search

This note suggests nomenclature for dealing with the units of various astronomical quantities that are used with the relativistic time scales TT, TDB, TCB and TCG. It is suggested to avoid wordings like ``TDB units'' and ``TT units'' and avoid contrasting them to ``SI units''. The quantities intended for use with TCG, TCB, TT or TDB should be called ``TCG-compatible'',

Sergei Klioner; N. Capitaine; W. M. Folkner; B. Guinot; T.-Y. Huang; S. M. Kopeikin; E. V. Pitjeva; P. K. Seidelmann; M. Soffel

2010-01-01

215

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

216

GNSS observations of deep convective time scales in the Amazon  

NASA Astrophysics Data System (ADS)

In the tropics, understanding the shallow-to-deep transition and organization of convection on the mesoscale is made difficult due the paucity of long-term high spatial/temporal resolution data. In this paper, data from the world's first long-term equatorial Global Navigational Satellite System meteorological station in Manaus (Central Amazon) is used to create a new metric, a water vapor convergence time scale, to characterize the temporal evolution of deep convection over a tropical continental region. From 3.5 years of data, 320 convective events were analyzed using a compositing analysis. Results reveal two characteristic time scales of water vapor convergence; an 8 h time scale of weak convergence and 4 h timescale of intense water vapor convergence associated with the shallow-to-deep convection transition. The 4 h shallow-to-deep transition time scale is particularly robust, regardless of convective intensity, seasonality, or nocturnal versus daytime convection. This new result provides a useful metric for both high resolution and global climate models to replicate.

Adams, D. K.; Gutman, Seth I.; Holub, Kirk L.; Pereira, Dulcineide S.

2013-06-01

217

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

218

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

219

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

220

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

221

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

222

Statistical Multiplexing of Multiple TimeScale Markov Streams  

Microsoft Academic Search

We study the problem of statistical multiplexing of cell streams which have correla- tions at multiple time-scales. Each stream is modeled by a singularly perturbed Markov- modulated process with some state transitions occurring much more infrequently than others. We develop a set of large deviations results to estimate the buffer overflow prob- abilities in various asymptotic regimes in the buffer

David N. C. Tse; Robert G. Gallager; John N. Tsitsiklis

1995-01-01

223

Sturm-Liouville eigenvalue problems on time scales  

Microsoft Academic Search

For Sturm—Liouville eigenvalue problems on time scales with separated boundary conditions we give an oscillation theorem and establish Rayleigh's principle. Our results not only unifly the corresponding theories for differential and difference equations, but are also new in the discrete case.

Ravi P. Agarwal; Martin Bohner; Patricia J. Y. Wong

1999-01-01

224

Nonequilibrium Physics at Short Time Scales: Formation of Correlations  

Microsoft Academic Search

It is a happy situation when similar concepts and theoretical techniques can be applied to widely different physical systems because of a deep similarity in the situations being studied. The book illustrates this well; it focuses on the description of correlations in quantum systems out of equilibrium at very short time scales, prompted by experiments with short laser pulses in

L Peliti

2005-01-01

225

A study of Venus rotation at short time scale  

Microsoft Academic Search

Venus which can be considered as the twin sister of the Earth in view of its global characteristics (size, density) has been the subject of many investigations to understand its slow retrograde rotation (243d) and its rather small obliquity (2°.63). Many of these studies concern the evolution of Venus rotation at very long time scales. Here we present a complete

L. Cottereau; J. Souchay

2009-01-01

226

ON LOWER AND UPPER SOLUTIONS WITHOUT ORDERING ON TIME SCALES  

Microsoft Academic Search

In order to enlarge the set of boundary value problems on time scales, for which we can use the lower and upper solutions technique to get existence of solutions, we extend this method to the case when the pair lacks ordering. We use the degree theory and a priori estimates to obtain the existence of solutions for the second-order Dirichlet

PETR STEHLIK

2006-01-01

227

Time scale algorithm: Definition of ensemble time and possible uses of the Kalman filter  

NASA Technical Reports Server (NTRS)

The comparative study of two time scale algorithms, devised to satisfy different but related requirements, is presented. They are ALGOS(BIPM), producing the international reference TAI at the Bureau International des Poids et Mesures, and AT1(NIST), generating the real-time time scale AT1 at the National Institute of Standards and Technology. In each case, the time scale is a weighted average of clock readings, but the weight determination and the frequency prediction are different because they are adapted to different purposes. The possibility of using a mathematical tool, such as the Kalman filter, together with the definition of the time scale as a weighted average, is also analyzed. Results obtained by simulation are presented.

Tavella, Patrizia; Thomas, Claudine

1990-01-01

228

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

2013-05-24

229

Aftermath of the Permian-Triassic mass extinction event: Paleoecology of Lower Triassic carbonates in the western USA  

Microsoft Academic Search

Paleoecologic study of invertebrate faunas from three successive Early Triassic seaways reveals that biotic recovery from the end-Permian mass extinction event was slow, and that full recovery did not occur until after the Early Triassic. Simple, cosmopolitan, opportunistic generalists, and low-diversity, low-complexity paleocommunities were characteristic of the entire Early Triassic in the Western USA. An increase in guild and taxonomic

Jennifer K. Schubert; David J. Bottjer

1995-01-01

230

The Available Time Scale: Measuring Foster Parents' Available Time to Foster  

ERIC Educational Resources Information Center

This article presents a new measure of available time specific to fostering, the Available Time Scale (ATS). It was tested with a national sample of 304 foster mothers and is designed to measure the amount of time foster parents are able to devote to fostering activities. The ATS has excellent reliability, and good support exists for its validity.…

Cherry, Donna J.; Orme, John G.; Rhodes, Kathryn W.

2009-01-01

231

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

232

Short time-scale surface changes on Io  

NASA Technical Reports Server (NTRS)

Imaging data from the Voyager 1 and 2 encounters with the Jupiter system provide a data set for the examination of short time-scale variations of surface features on Io. Clear evidence exists for variations near the known eruption sites and for other areas which appeared to have erupted between the encounters. Regions outside the known active eruption sites were examined in order to look for variations in the surface scattering properties which is due to undetected small-scale volcanic activity. The phase functions of many areas are intercompared in order to look for regions with phase functions outside the normal range for satellite surface properties. Areas with unusual scattering properties are related to small-scale eruptions of gas or particles. Determination of the distribution of these areas has strong implications for the resurfacing rates for Io.

Terrile, R. J.

1984-01-01

233

Earthquake magnitude time series: scaling behavior of visibility networks  

NASA Astrophysics Data System (ADS)

We present a statistical analysis of earthquake magnitude sequences in terms of the visibility graph method. Magnitude time series from Italy, Southern California, and Mexico are transformed into networks and some organizational graph properties are discussed. Connectivities are characterized by a scale-free distribution with a noticeable effect for large scales due to either the presence or the lack of large events. Also, a scaling behavior is observed between different node measures like betweenness centrality, clustering coefficient, nearest neighbor connectivity, and earthquake magnitude. Moreover, parameters which quantify the difference between forward and backward links, are proposed to evaluate the asymmetry of visibility attachment mechanism. Our results show an alternating average behavior of these parameters as earthquake magnitude changes. Finally, we evaluate the effects of reducing temporal and spatial windows of observation upon visibility network properties for main-shocks.

Aguilar-San Juan, B.; Guzmán-Vargas, L.

2013-11-01

234

Integrated Record of Terrestrial Biotic Change from the Upper Triassic Chinle Formation of northern New Mexico  

NASA Astrophysics Data System (ADS)

The Triassic Period was an interval of major biotic and environmental changes sandwiched between two major mass extinctions. During the Late Triassic (235-201.3 Ma), dinosaurs originated and diversified across Pangaea, and several major extant vertebrate groups also appeared for the first time. Unfortunately, few detailed stratigraphically-precise local-regional paleontological records exist for continental Triassic strata, which hinders any attempt to understand the tempo and mode of biotic change through the Late Triassic. We present a new stratigraphically well-constrained fossil vertebrate and palynomorph record (10-15 Ma in duration) from the upper Chinle Formation of the Chama Basin, northern New Mexico, an area that is famous for preserving one of the best records of early dinosaurs in North America. Our data indicate that vertebrate faunas were generally stable, experiencing only one identifiable species turnover event. Dinosaurs, although relatively diverse, were never abundant components of the fauna. Contemporaneous palynological records indicate that floral composition fluctuated considerably. The drought-tolerant conifer pollen Enzonalasporites and other gymnosperms such as Alisporites and Protodiploxypinus dominate most palynofloral assemblages, but there is a distinct increase in fern spore abundance near the top of the section. In combination with evidence of variability from organic carbon stable isotopes, these data indicate that the vertebrate fauna, including early dinosaurs, remained stable over millions of years despite living within a dynamic ecosystem associated with rapidly changing environmental conditions.

Irmis, R. B.; Lindström, S.; Dunlavey, M.; Whiteside, J. H.

2010-12-01

235

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

236

The Importance of Rotational Time-scales in Accretion Variability  

NASA Astrophysics Data System (ADS)

For the first few million years, one of the dominant sources of emission from a low mass young stellar object is from accretion. This process regulates the flow of material and angular moments from the surroundings to the central object, and is thought to play an important role in the definition of the long term stellar properties. Variability is a well documented attribute of accretion, and has been observed on time-scales of from days to years. However, where these variations come from is not clear. Th current model for accretion is magnetospheric accretion, where the stellar magnetic field truncates the disc, allowing the matter to flow from the disc onto the surface of the star. This model allows for variations in the accretion rate to come from many different sources, such as the magnetic field, the circumstellar disc and the interaction of the different parts of the system. We have been studying unbiased samples of accretors in order to identify the dominant time-scales and typical magnitudes of variations. In this way different sources of variations can be excluded and any missing physics in these systems identified. Through our previous work with the Long-term Accretion Monitoring Program (LAMP), we found 10 accretors in the ChaI region, whose variability is dominated by short term variations of 2 weeks. This was the shortest time period between spectroscopic observations which spanned 15 months, and rules out large scale processes in the disk as origins of this variability. On the basis of this study we have gone further to study the accretion signature H-alpha, over the time-scales of minutes and days in a set of Herbig Ae and T Tauri stars. Using the same methods as we used in LAMP we found the dominant time-scales of variations to be days. These samples both point towards rotation period of these objects as being an important time-scale for accretion variations. This allows us to indicate which are the most likely sources of these variations.

Costigan, Gráinne; Vink, Joirck; Scholz, Aleks; Testi, Leonardo; Ray, Tom

2013-07-01

237

Groundwater recharge of carbonate aquifers of the Silesian-Cracow Triassic (southern Poland) under human impact  

Microsoft Academic Search

A Triassic carbonate unit has been intensively drained by zinc and lead ore mines and numerous borehole fields since the nineteenth\\u000a century. Its groundwater recharge has increased due to: pumping of water from boreholes, mining activity, and urbanization.\\u000a An approach to determine the amounts of the recharge at a variety of spatial scales is presented in the paper. Different methods

Andrzej Kowalczyk; Andrzej J. Witkowski

2008-01-01

238

Thermal lens measurements in liquids on a submicrosecond time scale  

SciTech Connect

The use of the thermal lens method is shown to be quite suitable for kinetic studies of quenching on a submicrosecond time scale. The lower limit of time resolution that can be achieved is determined by the acoustic transit time, /tau//sub /ital a//, in the medium. A thermal lens signal with a 100-ns time constant due to the quenched triplet state of benzophenone is readily measured. The thermal lens method is superior to the photoacoustic (PA) method in the breadth of the accessible time range, and in the significantly fewer measurements required to obtain accurate data, including no requirement for a reference sample; it is also less sensitive to geometrical and laser power requirements than is the PA method.

Isak, S. J.; Komorowski, S. J.; Merrow, C. N.; Poston, P. E.; Eyring, E. M.

1989-03-01

239

Time scale of diffusion in molecular and cellular biology  

NASA Astrophysics Data System (ADS)

Diffusion is the driver of critical biological processes in cellular and molecular biology. The diverse temporal scales of cellular function are determined by vastly diverse spatial scales in most biophysical processes. The latter are due, among others, to small binding sites inside or on the cell membrane or to narrow passages between large cellular compartments. The great disparity in scales is at the root of the difficulty in quantifying cell function from molecular dynamics and from simulations. The coarse-grained time scale of cellular function is determined from molecular diffusion by the mean first passage time of molecular Brownian motion to a small targets or through narrow passages. The narrow escape theory (NET) concerns this issue. The NET is ubiquitous in molecular and cellular biology and is manifested, among others, in chemical reactions, in the calculation of the effective diffusion coefficient of receptors diffusing on a neuronal cell membrane strewn with obstacles, in the quantification of the early steps of viral trafficking, in the regulation of diffusion between the mother and daughter cells during cell division, and many other cases. Brownian trajectories can represent the motion of a molecule, a protein, an ion in solution, a receptor in a cell or on its membrane, and many other biochemical processes. The small target can represent a binding site or an ionic channel, a hidden active site embedded in a complex protein structure, a receptor for a neurotransmitter on the membrane of a neuron, and so on. The mean time to attach to a receptor or activator determines diffusion fluxes that are key regulators of cell function. This review describes physical models of various subcellular microdomains, in which the NET coarse-grains the molecular scale to a higher cellular-level, thus clarifying the role of cell geometry in determining subcellular function.

Holcman, D.; Schuss, Z.

2014-05-01

240

Space and Time Scales in Human-Landscape Systems  

NASA Astrophysics Data System (ADS)

Exploring spatial and temporal scales provides a way to understand human alteration of landscape processes and human responses to these processes. We address three topics relevant to human-landscape systems: (1) scales of human impacts on geomorphic processes, (2) spatial and temporal scales in river restoration, and (3) time scales of natural disasters and behavioral and institutional responses. Studies showing dramatic recent change in sediment yields from uplands to the ocean via rivers illustrate the increasingly vast spatial extent and quick rate of human landscape change in the last two millennia, but especially in the second half of the twentieth century. Recent river restoration efforts are typically small in spatial and temporal scale compared to the historical human changes to ecosystem processes, but the cumulative effectiveness of multiple small restoration projects in achieving large ecosystem goals has yet to be demonstrated. The mismatch between infrequent natural disasters and individual risk perception, media coverage, and institutional response to natural disasters results in un-preparedness and unsustainable land use and building practices.

Kondolf, G. Mathias; Podolak, Kristen

2014-01-01

241

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.

242

Genetic Programming for Multi-Time-Scale Modeling: First Results  

NASA Astrophysics Data System (ADS)

A bottleneck for effective multi-time-scale modeling of alloys is the computation of jump frequencies (or potential energy, PE, surface). We explore the use of genetic programming (GP)---a genetic algorithm that evolves computer programs---to create a local mapping of the jump frequency for any possible chemical or defect configuration that avoids explicit calculation of the entirety of the PE surface. We use a simple genetic program to perform symbolic regression of activation energies as a function of local configuration. To exemplify the ideas, we use (un)relaxed 2-D FCC Leonard-Jones A_xB_1-x alloy exhibiting phase segregation that includes a vacancy point defect. We show that the GP predicts activations energies within 0.5% for the relaxed case using only ˜3% of the total configuration space. These initial results hold promise to scale kinetics simulations, via kinetic Monte Carlo, by ˜9 orders in time over molecular dynamics.

Sastry, Kumara; Johnson, D. D.; Goldberg, D. E.

2003-03-01

243

The length and time scales of water's glass transitions.  

PubMed

Using a general model for the equilibrium dynamics of supercooled liquids, I compute from molecular properties the emergent length and time scales that govern the nonequilibrium relaxation behavior of amorphous ice prepared by rapid cooling. Upon cooling, the liquid water falls out of equilibrium whereby the temperature dependence of its relaxation time is predicted to change from super-Arrhenius to Arrhenius. A consequence of this crossover is that the location of the apparent glass transition temperature depends logarithmically on cooling rate. Accompanying vitrification is the emergence of a dynamical length-scale, the size of which depends on the cooling rate and varies between angstroms and tens of nanometers. While this protocol dependence clarifies a number of previous experimental observations for amorphous ice, the arguments are general and can be extended to other glass forming liquids. PMID:24908028

Limmer, David T

2014-06-01

244

Time scale of nuclear multifragmentation induced by light relativistic ions  

NASA Astrophysics Data System (ADS)

Nuclear fragmentation in a d (4.4 GeV) + Au collision was studied with a 4? setup FASA on the external beam of the Dubna Nuclotron. The IMF-IMF relative angle correlation function was analyzed using the statistical model of multifragmentation (SMM) with the main goal of estimating the total time scale of the process. It was found that the fragmentation of the hot nucleus was ˜100 fm/c delayed in respect to the collision moment.

Karnaukhov, V. A.; Avdeyev, S. P.; Botvina, A. S.; Kirakosyan, V. V.; Strekalovsky, O. V.; Rukoyatkin, P. A.; Karcz, W.; Norbeck, E.; Oeschler, H.

2012-12-01

245

The Fission Time Scale Measured with AN Atomic Clock  

Microsoft Academic Search

We present a new direct method of measuring the fission absolute time scale using an atomic clock based on the lifetime of a vacancy in the atomic K-shell. We studied the reaction 20Ne + 232Th --> 16O + 236U* at 30 MeV\\/u. The excitation energy of about 115 MeV in such a reaction is in the range where a fission

V. L. Kravchuk; H. W. Wilschut; M. Hunyadi; S. Kopecky; H. Löhner; A. Rogachevskiy; R. H. Siemssen; A. Krasznahorkay

2003-01-01

246

Solar Irradiance Variations on Active Region Time Scales  

NASA Technical Reports Server (NTRS)

The variations of the total solar irradiance is an important tool for studying the Sun, thanks to the development of very precise sensors such as the ACRIM instrument on board the Solar Maximum Mission. The largest variations of the total irradiance occur on time scales of a few days are caused by solar active regions, especially sunspots. Efforts were made to describe the active region effects on total and spectral irradiance.

Labonte, B. J. (editor); Chapman, G. A. (editor); Hudson, H. S. (editor); Willson, R. C. (editor)

1984-01-01

247

Extending the astronomical (polarity) time scale into the Miocene  

Microsoft Academic Search

An astronomical time scale is presented for the late Miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the Mediterranean to the 65°N summer insolation curve of La90[1,2] with present-day values for the dynamical ellipticity of the Earth and tidal dissipation by the moon. This correlation yields ages for all sedimentary cycles and hence also

F. J. Hilgen; W. Krijgsman; C. G. Langereis; L. J. Lourens; A. Santarelli; W. J. Zachariasse

1995-01-01

248

Quartz Rheology and Short-time-scale Crustal Instabilities  

Microsoft Academic Search

We present numerical results of thermal-mechanical feedback in crustal quartz rheology and contrast this behavior to the vastly\\u000a different character of an olivine mantle. In the numerical experiments quartz is found to have a very strong tendency for\\u000a short-time-scale instabilities, while our numerical experiments show that olivine has a decisive tendency for a stable thermally\\u000a lubricated slip. At the same

Klaus Regenauer-Lieb; David A. Yuen

2006-01-01

249

Short-time-scale features of the Earth's polar motion  

Microsoft Academic Search

The fundamental astrometric problem of high-accuracy interpolation and forecasting of the Earth's polar motion on short time scales from 1-2 to 10-30 days is studied. Hierarchies of interval length and parameter accuracy are established using appropriate models for the process. Filtering algorithms are adjusted using a weighted least squares fit of measurements of the International Earth Rotation Service (IERS). Best-fit

L. D. Akulenko; Yu. G. Markov; V. V. Perepelkin; L. V. Rykhlova

2009-01-01

250

Short time-scale variability in bright Seyfert galaxies  

Microsoft Academic Search

High-quality, long-slit CCD spectroscopic data were obtained to search for short time-scale (hour-day) variability in a sample of five Seyfert galaxies. The equivalent widths of all of the emission lines and the relative intensities of the Balmer lines were measured for each galaxy. No significant profile or flux variations were observed for any galaxy within errors, except for NGC 4151.

E. Xanthopoulos; M. M. De Robertis

1991-01-01

251

Quartz Rheology and Short-time-scale Crustal Instabilities  

Microsoft Academic Search

We present numerical results of thermal-mechanical feedback in crustal quartz rheology and contrast this behavior to the vastly\\u000a different character of an olivine mantle. In the numerical experiments quartz is found to have a very strong tendency for\\u000a short-time-scale instabilities, while our numerical experiments show that olivine has a decisive tendency for a stable thermally\\u000a lubricated slip. At the same

Klaus Regenauer-Lieb; David A. Yuen

252

Erratum: Short-time scaling behavior of growing interfaces  

Microsoft Academic Search

The short-time evolution of a growing interface is studied analytically and numerically for the Kadar-Parisi-Zhang (KPZ) universality class. The scaling behavior of response and correlation functions is reminiscent of the ``initial slip'' behavior found in purely dissipative critical relaxation (model A). Unlike model A the initial slip exponent for the KPZ equation can be expressed by the dynamical exponent z.

Michael Krech

1997-01-01

253

Variations in solar Lyman alpha irradiance on short time scales  

Microsoft Academic Search

Variations in solar UV irradiance at Lyman alpha are studied on short time scales (from days to months) after removing the long-term changes over the solar cycle. The SME\\/Lyman alpha irradiance is estimated from various solar indices using linear regression analysis. In order to study the nonlinear effects, Lyman alpha irradiance is modeled with a 5th-degree polynomial as well. It

J. M. Pap

1992-01-01

254

Short-time scaling behavior of growing interfaces  

Microsoft Academic Search

The short-time evolution of a growing interface is studied within the framework of the dynamic renormalization-group approach for the Kadar-Parisi-Zhang (KPZ) equation and for an idealized continuum model of molecular-beam epitaxy. The scaling behavior of response and correlation functions is reminiscent of the ``initial slip'' behavior found in purely dissipative critical relaxation (model A) and critical relaxation with conserved order

Michael Krech; Fachbereich Physik

1997-01-01

255

Multiple time scales of adaptation in auditory cortex neurons.  

PubMed

Neurons in primary auditory cortex (A1) of cats show strong stimulus-specific adaptation (SSA). In probabilistic settings, in which one stimulus is common and another is rare, responses to common sounds adapt more strongly than responses to rare sounds. This SSA could be a correlate of auditory sensory memory at the level of single A1 neurons. Here we studied adaptation in A1 neurons, using three different probabilistic designs. We showed that SSA has several time scales concurrently, spanning many orders of magnitude, from hundreds of milliseconds to tens of seconds. Similar time scales are known for the auditory memory span of humans, as measured both psychophysically and using evoked potentials. A simple model, with linear dependence on both short-term and long-term stimulus history, provided a good fit to A1 responses. Auditory thalamus neurons did not show SSA, and their responses were poorly fitted by the same model. In addition, SSA increased the proportion of failures in the responses of A1 neurons to the adapting stimulus. Finally, SSA caused a bias in the neuronal responses to unbiased stimuli, enhancing the responses to eccentric stimuli. Therefore, we propose that a major function of SSA in A1 neurons is to encode auditory sensory memory on multiple time scales. This SSA might play a role in stream segregation and in binding of auditory objects over many time scales, a property that is crucial for processing of natural auditory scenes in cats and of speech and music in humans. PMID:15548659

Ulanovsky, Nachum; Las, Liora; Farkas, Dina; Nelken, Israel

2004-11-17

256

Short time scale monitoring of SiO sources  

NASA Astrophysics Data System (ADS)

We present the results of a short time scale monitoring of SiO maser emission (v=1 J=1-0 transition) in four known strong sources. These sources were monitored nightly for a period of about a month. The aim of these observations is to investigate the possible presence of variations in the maser lines on time scales of a few days to weeks, due to sound waves propagating out from the central star. If sound waves are responsible for the mass loss of certain cool giants, as suggested by Pijpers & Hearn (1989) and Pijpers & Habing (1989), local variations in density and relative velocity are expected just above the stellar photosphere. These could give rise to variations in any narrow spectral line formed in this region, and therefore in particular in the SiO maser lines. Our observations indicate that variations in the line shape (leading to relative changes in the intensity of about 20%) occur in the SiO emission of Mira type stars, within short time scales of 10-20 days. The main component of the profile variability is consistent with a displacement of the velocity centroid of the dominant maser peaks, by about 1 km/s in the average. Apparent variations in the total line flux were also found, but could be partially due to calibration uncertainties.

Pijpers, F. P.; Pardo, J. R.; Bujarrabal, V.

1994-06-01

257

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

258

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

259

Permean and Lower Triassic reservoir rocks of central Utah  

Microsoft Academic Search

Permian and Lower Triassic reservoir rocks throughout central Utah consist of beach and shallow water sandstones and shallow marine carbonates. These reservoirs are the Permian Cedar Mesa Sandstone, Toroweap Formation, White Rim Sandstone, Kaibab Formation, and the Lower Triassic Sinbad-Timpoweap carbonate member of the Moenkopi Formation. Depositional patterns of these stratigraphic units are controlled by the relative positions of the

1977-01-01

260

Geology and petroleum prospects of Upper Triassic sediments, Jordan  

Microsoft Academic Search

Subsurface Upper Triassic sediments of northern Jordan represent part of a regressive evaporitic-clastic succession that marks the shrinkage phase of the Late Triassic basin in the northern parts of the Arabian Plate. Sabkhas developed along the basin margin, whereas, oolitic shoals formed on the deeper parts of the carbonate platform. The basin reached a drewdown stage in the Risha, Palmyra

F. N Sadooni; A Dalqamouni

1998-01-01

261

A Decomposition of Time Scales for Iterative Computation of Time-Optimal Controls.  

National Technical Information Service (NTIS)

An iterative procedure, exploiting the multiple time scale properties of systems with slow and fast modes, is presented. This procedure solves the time-optimal problem for higher-order systems iteratively via the solutions of simple second-order problems....

S. H. Javid P. V. Kokotovic

1977-01-01

262

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

263

Improving the readability of time-frequency and time-scale representations by the reassignment method  

Microsoft Academic Search

In this paper, the use of the reassignment method, first applied by Kodera, Gendrin, and de Villedary (1976) to the spectrogram, is generalized to any bilinear time-frequency or time-scale distribution. This method creates a modified version of a representation by moving its values away from where they are computed, so as to produce a better localization of the signal components.

Franqois Auger; Patrick Flandrin

1995-01-01

264

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

265

The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania  

PubMed Central

The rise of dinosaurs was a major event in vertebrate history, but the timing of the origin and early diversification of the group remain poorly constrained. Here, we describe Nyasasaurus parringtoni gen. et sp. nov., which is identified as either the earliest known member of, or the sister–taxon to, Dinosauria. Nyasasaurus possesses a unique combination of dinosaur character states and an elevated growth rate similar to that of definitive early dinosaurs. It demonstrates that the initial dinosaur radiation occurred over a longer timescale than previously thought (possibly 15 Myr earlier), and that dinosaurs and their immediate relatives are better understood as part of a larger Middle Triassic archosauriform radiation. The African provenance of Nyasasaurus supports a southern Pangaean origin for Dinosauria.

Nesbitt, Sterling J.; Barrett, Paul M.; Werning, Sarah; Sidor, Christian A.; Charig, Alan J.

2013-01-01

266

The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania.  

PubMed

The rise of dinosaurs was a major event in vertebrate history, but the timing of the origin and early diversification of the group remain poorly constrained. Here, we describe Nyasasaurus parringtoni gen. et sp. nov., which is identified as either the earliest known member of, or the sister-taxon to, Dinosauria. Nyasasaurus possesses a unique combination of dinosaur character states and an elevated growth rate similar to that of definitive early dinosaurs. It demonstrates that the initial dinosaur radiation occurred over a longer timescale than previously thought (possibly 15 Myr earlier), and that dinosaurs and their immediate relatives are better understood as part of a larger Middle Triassic archosauriform radiation. The African provenance of Nyasasaurus supports a southern Pangaean origin for Dinosauria. PMID:23221875

Nesbitt, Sterling J; Barrett, Paul M; Werning, Sarah; Sidor, Christian A; Charig, Alan J

2013-02-23

267

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

268

Terrestrial Waters and Sea Level Variations on Interannual Time Scale  

NASA Technical Reports Server (NTRS)

On decadal to multi-decadal time scales, thermal expansion of sea waters and land ice loss are the main contributors to sea level variations. However, modification of the terrestrial water cycle due to climate variability and direct anthropogenic forcing may also affect sea level. For the past decades, variations in land water storage and corresponding effects on sea level cannot be directly estimated from observations because these are almost non-existent at global continental scale. However, global hydrological models developed for atmospheric and climatic studies can be used for estimating total water storage. For the recent years (since mid-2002), terrestrial water storage change can be directly estimated from observations of the GRACE space gravimetry mission. In this study, we analyse the interannual variability of total land water storage, and investigate its contribution to mean sea level variability at interannual time scale. We consider three different periods that, each, depend on data availability: (1) GRACE era (2003-2009), (2) 1993-2003 and (3) 1955-1995. For the GRACE era (period 1), change in land water storage is estimated using different GRACE products over the 33 largest river basins worldwide. For periods 2 and 3, we use outputs from the ISBA-TRIP (Interactions between Soil, Biosphere, and Atmosphere-Total Runoff Integrating Pathways) global hydrological model. For each time span, we compare change in land water storage (expressed in sea level equivalent) to observed mean sea level, either from satellite altimetry (periods 1 and 2) or tide gauge records (period 3). For each data set and each time span, a trend has been removed as we focus on the interannual variability. We show that whatever the period considered, interannual variability of the mean sea level is essentially explained by interannual fluctuations in land water storage, with the largest contributions arising from tropical river basins.

Llovel, W.; Becker, M.; Cazenave, A.; Jevrejeva, S.; Alkama, R.; Decharme, B.; Douville, H.; Ablain, M.; Beckley, B.

2011-01-01

269

Many roads to synchrony: Natural time scales and their algorithms  

NASA Astrophysics Data System (ADS)

We consider two important time scales—the Markov and cryptic orders—that monitor how an observer synchronizes to a finitary stochastic process. We show how to compute these orders exactly and that they are most efficiently calculated from the ?-machine, a process's minimal unifilar model. Surprisingly, though the Markov order is a basic concept from stochastic process theory, it is not a probabilistic property of a process. Rather, it is a topological property and, moreover, it is not computable from any finite-state model other than the ?-machine. Via an exhaustive survey, we close by demonstrating that infinite Markov and infinite cryptic orders are a dominant feature in the space of finite-memory processes. We draw out the roles played in statistical mechanical spin systems by these two complementary length scales.

James, Ryan G.; Mahoney, John R.; Ellison, Christopher J.; Crutchfield, James P.

2014-04-01

270

Optimal Control Modification for Time-Scale Separated Systems  

NASA Technical Reports Server (NTRS)

Recently a new optimal control modification has been introduced that can achieve robust adaptation with a large adaptive gain without incurring high-frequency oscillations as with the standard model-reference adaptive control. This modification is based on an optimal control formulation to minimize the L2 norm of the tracking error. The optimal control modification adaptive law results in a stable adaptation in the presence of a large adaptive gain. This study examines the optimal control modification adaptive law in the context of a system with a time scale separation resulting from a fast plant with a slow actuator. A singular perturbation analysis is performed to derive a modification to the adaptive law by transforming the original system into a reduced-order system in slow time. A model matching conditions in the transformed time coordinate results in an increase in the actuator command that effectively compensate for the slow actuator dynamics. Simulations demonstrate effectiveness of the method.

Nguyen, Nhan T.

2012-01-01

271

Time scale algorithms for an inhomogeneous group of atomic clocks  

NASA Technical Reports Server (NTRS)

Through the past 17 years, the time scale requirements at the National Research Council (NRC) have been met by the unsteered output of its primary laboratory cesium clocks, supplemented by hydrogen masers when short-term stability better than 2 x 10(exp -12)tau(sup -1/2) has been required. NRC now operates three primary laboratory cesium clocks, three hydrogen masers, and two commercial cesium clocks. NRC has been using ensemble averages for internal purposes for the past several years, and has a realtime algorithm operating on the outputs of its high-resolution (2 x 10(exp -13) s at 1 s) phase comparators. The slow frequency drift of the hydrogen masers has presented difficulties in incorporating their short-term stability into the ensemble average, while retaining the long-term stability of the laboratory cesium frequency standards. We report on this work on algorithms for an inhomogeneous ensemble of atomic clocks, and on our initial work on time scale algorithms that could incorporate frequency calibrations at NRC from the next generation of Zacharias fountain cesium frequency standards having frequency accuracies that might surpass 10(exp -15), or from single-trapped-ion frequency standards (Ba+, Sr+,...) with even higher potential accuracies. The requirements for redundancy in all the elements (including the algorithms) of an inhomogeneous ensemble that would give a robust real-time output of the algorithms are presented and discussed.

Jacques, C.; Boulanger, J.-S.; Douglas, R. J.; Morris, D.; Cundy, S.; Lam, H. F.

1993-01-01

272

The role of time scales in extrinsic noise propagation  

NASA Astrophysics Data System (ADS)

Cell-to cell variability in the number of proteins has been studied extensively experimentally. There are many sources of this stochastic variability or noise that can be classified as intrinsic, due to the stochasticity of chemical reactions and extrinsic, due to environmental differences. The different stages in the production of proteins in response to a stimulus, the signaling cascade before transcription, transcription, and translation are characterized by different time scales. We analyze how these time scales determine the effect of the reactions at each stage on different sources of noise. For example, even if intrinsic noise dominates the fluctuations in mRNA number, for typical degradation rates, extrinsic noise can dominate corresponding protein number fluctuations. Such results are important in determining the importance of intrinsic noise at earlier stages of a genetic network on the products of subsequent stages. We examine cases in which the dynamics of the extrinsic noise can lead to differences from cases in which extrinsic noise arises from static (in time) cell-to-cell variations. We will interpret the experiments of Pedraza et al*. in the light of these results. *J. M. Pedraza et al, Science 25 March 2005:Vol. 307. no. 5717, pp. 1965 - 1969.

Iyer-Biswas, Srividya; Pedraza, Juan Manuel; Jayaprakash, C.

2009-03-01

273

Measurement of hyperpolarized gas diffusion at very short time scales  

PubMed Central

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.

2007-01-01

274

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

275

Tectonic setting of the Late Triassic volcaniclastic series of the Luang Prabang Basin, Laos, and geodynamic implications from the Triassic to Jurassic in SE Asia  

NASA Astrophysics Data System (ADS)

The Luang Prabang Basin, located on the eastern margin of the Indochina block, is mainly composed of volcaniclastic continental deposits. The interpretation of U-Pb zircon geochronological dates shows that volcanism is contemporaneous with the sedimentation during the Late Triassic (c.a. 225 to 215 Ma; Blanchard et al., 2013, J. Asian Earth Sci., 70-71; 8-26). At the same time, volcanism is also known along the Eastern margin of the Indochina block (present day Thailand). There are currently two main contrasting interpretations concerning the tectonic setting related to these volcanic events: are they arc-related (e.g. Barr et al., 2006, J. Geol. Soc. London, 163; 1037-1046) or post collisional (e.g. Srichan et al., 2009, Island Arc, 18; 32-51)? We have performed geochemical analysis on both sedimentary and volcanic rocks of the Luang Prabang Basin in order to evaluate the relationships between the volcanic events and to propose a geodynamic interpretation. The geochemical characteristics of the Luang Prabang Late Triassic volcaniclastic and volcanic rocks are compatible with a volcanic arc setting. The confrontation of these results with the stratigraphic evolution of the eastern margin of the Indochina block leads to reconsider the Late Triassic to Jurassic geodynamic evolution of this area. Arc-related volcanism seems to occur during nearly the whole Triassic, implying a subduction of the Paleotethys beneath the Indochina block. As the stratigraphic record of north-eastern Thailand and western Myanmar shows an important stratigraphic gap spanning from the Early to the Middle Jurassic, the collision between the Indochina and the Sibumasu blocks likely occurred at that period.

Rossignol, Camille; Bourquin, Sylvie; Dabard, Marie-Pierre; Hallot, Erwan; Poujol, Marc; Nalpas, Thierry

2014-05-01

276

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

277

Separatrix Splitting for Systems with Three Time Scales  

NASA Astrophysics Data System (ADS)

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, which are polynomial perturbations. The technique for exhibiting cancellations is inspired by renormalization theory in quantum electrodynamics and uses an analogue of Dyson's equations to prove an infinite family of identities, due to symmetries, that remind us of Ward's identities.

Gallavotti, G.; Gentile, G.; Mastropietro, V.

278

Two time scale design of output feedback systems  

NASA Technical Reports Server (NTRS)

Singular perturbation techniques are used in this paper to develop a two time scale procedure for designing static gain output feedback controllers. It is shown that, if certain control spillover conditions are satisfied, control designs based on reduced-order models will stabilize the corrgsponding full system. Optimal output feedback control theory is used to derive the necessary conditions for the stabilizing gain matrix. The problem of stabilizing a model for a large space structure is used to illustrate the practicality of the approach.

Calise, A. J.; Moerder, D. D.

1984-01-01

279

Formation processes and time scales for meteorite parent bodies  

NASA Technical Reports Server (NTRS)

The transition from small particles suspended in the solar nebula to the planetesimals (asteroids) that became the parent bodies of meteorites is examined. Planetesimals probably grew by coagulation of grain aggregates that collided due to different rates of settling and drag-induced orbital decay. Their growth was accompanied by radial transport of solids, possibly sufficient to deplete the primordial mass in the asteroid zone, but with relatively little mixing. The formation of asteroid-sized planetesimals was probably rapid, on a time scale less than 1 Myr.

Weidenschilling, S. J.

1988-01-01

280

The Time and Space Scales of Extreme Precipitation (Invited)  

NASA Astrophysics Data System (ADS)

Energetic atmospheric processes such as tropical storms, Mesoscale Convection Systems, and heavy rain storms can generate extreme hydro-meteorological events that can be the driver of processes at the earths surface such as floods, debris flows, and landslides. An important aspect of these events is the duration and intensity of the precipitation. Characteristic time and space scales can be defined based on the storm duration, strength, and speed. This paper will examine these characteristics over the western U.S., Himalaya's, and the Andes focusing on MCS's, monsoon depressions, rain on snow events and tropical storms. The analysis will be based on both observations and model simulations of these storm types.

Rasmussen, R.; Rasmussen, K. L.; Sørland, S.

2013-12-01

281

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

282

Disruption time scales of star clusters in different galaxies  

NASA Astrophysics Data System (ADS)

The observed average lifetime of the population of star clusters in the Solar Neighbourhood, the Small Magellanic Cloud and in selected regions of M 51 and M 33 is compared with simple theoretical predictions and with the results of N-body simulations. The empirically derived lifetimes (or disruption times) of star clusters depend on their initial mass as tdisemp ? Mcl0.60 in all four galaxies. N-body simulations have shown that the predicted disruption time of clusters in a tidal field scales as tdispred ? trh0.75 tcr0.25, where trh is the initial half-mass relaxation time and tcr is the crossing time for a cluster in equilibrium. We show that this can be approximated accurately by tdispred ? Mcl0.62 for clusters in the mass range of about 103 to 106 M?, in excellent agreement with the observations. Observations of clusters in different extragalactic environments show that tdis also depends on the ambient density in the galaxies where the clusters reside. Linear analysis predicts that the disruption time will depend on the ambient density of the cluster environment as tdis ? rhmo_amb-1/2. This relation is consistent with N-body simulations. The empirically derived disruption times of clusters in the Solar Neighbourhood, in the SMC and in M 33 agree with these predictions. The best fitting expression for the disruption time is tdis=Cenv (Mcl/104 M?)0.62 (rhmoamb / M? pc-3)-0.5 where Mcl is the initial mass of the cluster and Cenv ? 300 - 800 Myr. The disruption times of star clusters in M 51 within 1-5 kpc from the nucleus, is shorter than predicted by about an order of magnitude. This discrepancy might be due to the strong tidal field variations in M 51, caused by the strong density contrast between the spiral arms and interarm regions, or to the disruptive forces from giant molecular clouds.

Lamers, H. J. G. L. M.; Gieles, M.; Portegies Zwart, S. F.

2005-01-01

283

Alignment of Noisy and Uniformly Scaled Time Series  

NASA Astrophysics Data System (ADS)

The alignment of noisy and uniformly scaled time series is an important but difficult task. Given two time series, one of which is a uniformly stretched subsequence of the other, we want to determine the stretching factor and the offset of the second time series within the first one. We adapted and enhanced different methods to address this problem: classical FFT-based approaches to determine the offset combined with a naïve search for the stretching factor or its direct computation in the frequency domain, bounded dynamic time warping and a new approach called shotgun analysis, which is inspired by sequencing and reassembling of genomes in bioinformatics. We thoroughly examined the strengths and weaknesses of the different methods on synthetic and real data sets. The FFT-based approaches are very accurate on high quality data, the shotgun approach is especially suitable for data with outliers. Dynamic time warping is a candidate for non-linear stretching or compression. We successfully applied the presented methods to identify steel coils via their thickness profiles.

Lipowsky, Constanze; Dranischnikow, Egor; Göttler, Herbert; Gottron, Thomas; Kemeter, Mathias; Schömer, Elmar

284

Estimating ventilation time scales using overturning stream functions  

NASA Astrophysics Data System (ADS)

A simple method for estimating ventilation time scales from overturning stream functions is proposed. The stream function may be computed using either geometric coordinates or a generalized vertical coordinate, such as potential density (salinity in our study). The method is tested with a three-dimensional circulation model describing an idealized semi-enclosed ocean basin ventilated through a narrow strait over a sill, and the result is compared to age estimates obtained from a passive numerical age tracer. The best result is obtained when using the stream function in salinity coordinates. In this case, the reservoir-averaged advection time obtained from the overturning stream function in salinity coordinates agrees rather well with the mean age of the age tracer, and the corresponding maximum ages agree very well.

Thompson, Bijoy; Nycander, Jonas; Nilsson, Johan; Jakobsson, Martin; Döös, Kristofer

2014-06-01

285

Nonlinear Dynamics of Extended Hydrologic Systems over long time scales  

NASA Astrophysics Data System (ADS)

We often view our knowledge of hydrology and hence of nature as intransient, at least over the time scales over which we study processes we wish to predict and understand. Over the last few decades, this assumption has come under question, largely because of the vocal expression of a changing climate, but also the recurrent demonstration of significant land use change, both of which significantly affect the boundary conditions for terrestrial hydrology that is our forte. Most recently, the concepts of hydromorphology and social hydrology have entered the discussion, and the notion that climate and hydrology influence human action, which in turn shapes hydrology, is being recognized. Finally, as a field, we seem to be coming to the conclusion that the hydrologic system is an open system, whose boundaries evolve in time, and that the hydrologic system, at many scales, has a profound effect on the systems that drive it -- whether they be the ecological and climatic systems, or the social system. What a mess! Complexity! Unpredictability! At a certain level of abstraction, one can consider the evolution of these coupled systems with nonlinear feedbacks and ask what types of questions are relevant in terms of such a coupled evolution? What are their implications at the planetary scale? What are their implications for a subsistence farmer in an arid landscape who may under external influence achieve a new transient hydro-ecological equilibrium? What are the implications for the economy and power of nations? In this talk, I will try to raise some of these questions and also provide some examples with very simple dynamical systems that suggest ways of thinking about some practical issues of feedback across climate, hydrology and human behavior.

Lall, Upmanu

2014-05-01

286

Dynamic response of materials on sub-nanosecond time scales  

NASA Astrophysics Data System (ADS)

During the past few years, substantial progress has been made in developing experimental techniques capable of investigating the response of materials to dynamic loading on nanosecond time scales and shorter, with multiple diagnostics probing different aspects of the behavior. These relatively short time scales are scientifically interesting because plastic flow and phase changes in common materials with simple crystal structures - such as iron - may be suppressed, allowing unusual states to be induced and the dynamics of plasticity and polymorphism to be explored. Loading by laser ablation can be particularly convenient. The TRIDENT laser has been used to impart shocks and isentropic compression waves from ˜1 to 200 GPa in a range of elements and alloys, with diagnostics including surface velocimetry (line-imaging VISAR), surface displacement (framed area imaging), x-ray diffraction (single crystal and polycrystal), ellipsometry, and Raman spectroscopy. A major motivation has been the study of the properties of beryllium under conditions relevant to the ICF fuel capsule: magnetically-driven shock and isentropic compression shots at Z were used to investigate the equation of state and shock melting characteristics, complemented by laser ablation experiments to investigate plasticity and heterogeneous response. These results will help to constrain acceptable tolerances on manufacturing, and possible loading paths, for ICF ignition experiments at the National Ignition Facility. Laser-based techniques are being developed further for future material dynamics experiments at NIF, where it should be possible to obtain high quality data on strength and phase changes up to at least 1 TPa.

Swift, Damian

2004-11-01

287

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

288

Reusable Launch Vehicle Control In Multiple Time Scale Sliding Modes  

NASA Technical Reports Server (NTRS)

A reusable launch vehicle control problem during ascent is addressed via multiple-time scaled continuous sliding mode control. The proposed sliding mode controller utilizes a two-loop structure and provides robust, de-coupled tracking of both orientation angle command profiles and angular rate command profiles in the presence of bounded external disturbances and plant uncertainties. Sliding mode control causes the angular rate and orientation angle tracking error dynamics to be constrained to linear, de-coupled, homogeneous, and vector valued differential equations with desired eigenvalues placement. Overall stability of a two-loop control system is addressed. An optimal control allocation algorithm is designed that allocates torque commands into end-effector deflection commands, which are executed by the actuators. The dual-time scale sliding mode controller was designed for the X-33 technology demonstration sub-orbital launch vehicle in the launch mode. Simulation results show that the designed controller provides robust, accurate, de-coupled tracking of the orientation angle command profiles in presence of external disturbances and vehicle inertia uncertainties. This is a significant advancement in performance over that achieved with linear, gain scheduled control systems currently being used for launch vehicles.

Shtessel, Yuri; Hall, Charles; Jackson, Mark

2000-01-01

289

Complex processes from dynamical architectures with time-scale hierarchy.  

PubMed

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. PMID:21347363

Perdikis, Dionysios; Huys, Raoul; Jirsa, Viktor

2011-01-01

290

The evidence for ocean acidification across the Triassic-Jurassic boundary  

NASA Astrophysics Data System (ADS)

The end-Triassic extinction is one of the "Big Five" mass extinctions of the Phanerozoic and until recently no consensus regarding the cause of this extinction has been established. Over the last decade, a robust temporal correlation between the eruption of the Central Atlantic Magmatic Province (CAMP) and the end-Triassic extinction has been established. This correlation has led to the speculation that the release of CO2 and volatiles from the CAMP flood basalts induced a carbon cycle perturbation that acidified the Triassic oceans. It has also been suggested that an acidification event could have been the key mechanism that caused the end-Triassic marine ecosystem collapse. By combining observations and data from multiple fields such as volcanology, paleoceanography, chemostratigraphy, paleontology, and sedimentology, one can assess whether or not there was an ocean acidification event and to what degree it contributed to the extinction. The eruption of the CAMP flood basalts began at the very end of the Triassic period, albeit before the official Triassic-Jurassic (T-J) boundary, (defined as the first Jurassic ammonite). CAMP is one of the largest continental flood basalts of the Phanerozoic (2-4 million cubic km) and was emplaced extremely rapidly (<1.6-2 Myr) in three to five pulses (possibly hundreds to tens of thousands of years). The massive injection of CAMP CO2 and other volcanic volatiles over such a short period of time would have caused a major change in ocean carbonate chemistry and, if short enough in duration, could have caused significant declines in oceanic carbonate saturation state (an ocean acidification event), possibly even undersaturating parts of the surface ocean with respect to aragonite and calcite. Although the change in saturation state of the ocean is extremely difficult to detect or quantify in the rock record, there is a distinct paucity of primary carbonate sediments in the T-J boundary interval, consistent with an ocean acidification event. Of the seventeen T-J boundary sections only three or four record potentially continuous carbonate deposition across the extinction interval, even so these carbonates are often marls and so may not be truly continuous. Finally, the end-Triassic extinction was particularly selective against pH-sensitive organisms (more so than perhaps any other extinction event). Not only was this extinction event one of the most severe extinctions of the 'Modern Fauna' in the geologic record, it also decimated reef ecosystems built by corals and hypercalcified sponges. End-Triassic extinction rates amongst acid-intolerant organisms and ecosystems are elevated and differ significantly from background extinction so that ocean acidification is a reasonable explanation for the interpreted extinction selectivity during this time interval. Given the volcanic, geochemical, sedimentological, and paleontological changes or events across the T-J interval it is likely that the end-Triassic extinction was heavily influenced by a CAMP-induced ocean acidification event. The dramatic taxonomic and ecosystem turnover at the T-J event implies that short-term acidification events may have long-term effects on ecosystems, a repercussion that has not previously been correlated with acidification events and has implications for future changes in ocean chemistry.

Martindale, R. C.; Greene, S. E.; Ritterbush, K. A.; Bottjer, D. J.; Corsetti, F. A.; Berelson, W.

2012-12-01

291

Quantifying catchment-scale mixing and its effect on time-varying travel time distributions  

NASA Astrophysics Data System (ADS)

Travel time distributions are often used to characterize catchment discharge behavior, catchment vulnerability to pollution and pollutant loads from catchments to downstream waters. However, these distributions vary with time because they are a function of rainfall and evapotranspiration. It is important to account for these variations when the time scale of interest is smaller than the typical time-scale over which average travel time distributions can be derived. Recent studies have suggested that subsurface mixing controls how rainfall and evapotranspiration affect the variability in travel time distributions of discharge. To quantify this relation between subsurface mixing and dynamics of travel time distributions, we propose a new transformation of travel time that yields transformed travel time distributions, which we call Storage Outflow Probability (STOP) functions. STOP functions quantify the probability for water parcels in storage to leave a catchment via discharge or evapotranspiration. We show that this is equal to quantifying mixing within a catchment. Compared to the similar Age function introduced by Botter et al. (2011), we show that STOP functions are more constant in time, have a clearer physical meaning and are easier to parameterize. Catchment-scale STOP functions can be approximated by a two-parameter beta distribution. One parameter quantifies the catchment preference for discharging young water; the other parameter quantifies the preference for discharging old water from storage. Because of this simple parameterization, the STOP function is an innovative tool to explore the effects of catchment mixing behavior, seasonality and climate change on travel time distributions and the related catchment vulnerability to pollution spreading.

van der Velde, Y.; Torfs, P. J. J. F.; van der Zee, S. E. A. T. M.; Uijlenhoet, R.

2012-06-01

292

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

293

The Triassic of Timor: Lithostratigraphy, chronostratigraphy and palaeogeography  

NASA Astrophysics Data System (ADS)

The palaeontologically rich and lithologically diverse Triassic successions of Timor provide a key stratigraphic and palaeontological link between northwestern Australia and other terranes of former eastern Gondwana (present-day Southeast Asia). Timor is now located in the zone of collision between the northern margin of the Australian continent and island arc terranes bordering the Eurasian plate, with the Triassic successions exposed in a fold-and-thrust belt and an extensive mélange complex. Three formal lithostratigraphic units have been defined previously within the main Triassic succession in Timor (Niof, Aitutu and Babulu formations), with a fourth, the Wai Luli Formation, primarily Jurassic in age but extending down into the Triassic. The Niof Formation (Anisian to Ladinian, possibly also Early Triassic) is a fine-grained deepwater succession, succeeded conformably by the Aitutu and Babulu formations (Ladinian to Norian/Rhaetian), which were deposited contemporaneously, with the Aitutu Formation continuing locally into the Lower Jurassic. The Aitutu Formation consists of deep shelf limestones interbedded with shales and marls, while the Babulu Formation is a deltaic to turbiditic siliciclastic succession. The Late Triassic to Jurassic Wai Luli Formation is characterised by marine shales and marls. Informal stratigraphic units include the Cephalopod Limestone Facies, a Rosso Ammonitico-type deposit, which contains an extremely rich fossil fauna (particularly ammonoids) and ranges through the entire Triassic; and the Fatu Limestone and Pualaca Facies which consists of shallow to marginal marine carbonates (mud mounds, oolitic limestones and reefs) restricted to the Late Triassic. Facies diversity was low during the Early Triassic and Anisian, but became more pronounced from the Ladinian and continuing through the Late Triassic, probably as a consequence of renewed tectonic extension. Triassic extension was not associated with major volcanism, unlike a previous phase of extension in the Early Permian. The Cablac Limestone Formation, originally defined as a Miocene stratigraphic element, is now recognised to be at least partly Late Triassic-Early Jurassic in age, with lithologies comparable to parts of the Fatu Limestone. The stratigraphy of these shallow marine carbonate sequences is clearly in need of rigorous revision, but it is not yet possible to suggest appropriate redefined formations.

Charlton, T. R.; Barber, A. J.; McGowan, A. J.; Nicoll, R. S.; Roniewicz, E.; Cook, S. E.; Barkham, S. T.; Bird, P. R.

2009-10-01

294

Global Precipitation Analyses at Monthly to 3-HR Time Scales  

NASA Technical Reports Server (NTRS)

Global precipitation analysis covering the last few decades and the impact of the new TRMM precipitation observations are discussed. The 20+ year, monthly, globally complete precipitation analysis of the World Climate Research Program's (WCRP/GEWEX) Global Precipitation Climatology Project (GPCP) is used to explore global and regional variations and trends and is compared to the much shorter TRMM(Tropica1 Rainfall Measuring Mission) tropical data set. A trend pattern that is a combination of both El Nino and La Nina precipitation features is evident in the 20-year data set. This pattern is related to an increase with time in the number of combined months of El Nino and La Nina during the 20 year period. Monthly anomalies of precipitation are related to ENSO variations with clear signals extending into middle and high latitudes of both hemispheres. The GPCP daily, 1deg latitude-longitude analysis, which is available from January 1997 to the present is described and the evolution of precipitation patterns on this time scale related to El Nino and La Nina is described. Finally, a TRMM-based 3-hr analysis is described that uses TRMM to calibrate polar-orbit microwave observations from SSM/I and geosynchronous IR observations and merges the various calibrated observations into a final, 3-hr resolution map. This TRMM standard product will soon be available for the entire TRMM period (January 1998- present). A real-time version of this merged product is being produced and is available at 0.25deg latitude-longitude resolution over the latitude range from 50degN-50degS. Images from this data set can be seen at the U.S. TRMM web site (trmm.gsfc.nasa.gov). Examples will be shown, including its use in monitoring flood conditions and relating weather-scale events to climate variations.

Adler, Robert F.; Huffman, George; Curtis, Scott; Bolvin, David; Nelkin, Eric

2002-01-01

295

Critical time scales for advection-diffusion-reaction processes.  

PubMed

The concept of local accumulation time (LAT) was introduced by Berezhkovskii and co-workers to give a finite measure of the time required for the transient solution of a reaction-diffusion equation to approach the steady-state solution [A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Biophys. J. 99, L59 (2010); A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Phys. Rev. E 83, 051906 (2011)]. Such a measure is referred to as a critical time. Here, we show that LAT is, in fact, identical to the concept of mean action time (MAT) that was first introduced by McNabb [A. McNabb and G. C. Wake, IMA J. Appl. Math. 47, 193 (1991)]. Although McNabb's initial argument was motivated by considering the mean particle lifetime (MPLT) for a linear death process, he applied the ideas to study diffusion. We extend the work of these authors by deriving expressions for the MAT for a general one-dimensional linear advection-diffusion-reaction problem. Using a combination of continuum and discrete approaches, we show that MAT and MPLT are equivalent for certain uniform-to-uniform transitions; these results provide a practical interpretation for MAT by directly linking the stochastic microscopic processes to a meaningful macroscopic time scale. We find that for more general transitions, the equivalence between MAT and MPLT does not hold. Unlike other critical time definitions, we show that it is possible to evaluate the MAT without solving the underlying partial differential equation (pde). This makes MAT a simple and attractive quantity for practical situations. Finally, our work explores the accuracy of certain approximations derived using MAT, showing that useful approximations for nonlinear kinetic processes can be obtained, again without treating the governing pde directly. PMID:22680446

Ellery, Adam J; Simpson, Matthew J; McCue, Scott W; Baker, Ruth E

2012-04-01

296

Critical time scales for advection-diffusion-reaction processes  

NASA Astrophysics Data System (ADS)

The concept of local accumulation time (LAT) was introduced by Berezhkovskii and co-workers to give a finite measure of the time required for the transient solution of a reaction-diffusion equation to approach the steady-state solution [A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Biophys. J.BIOJAU0006-349510.1016/j.bpj.2010.07.045 99, L59 (2010); A. M. Berezhkovskii, C. Sample, and S. Y. Shvartsman, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.83.051906 83, 051906 (2011)]. Such a measure is referred to as a critical time. Here, we show that LAT is, in fact, identical to the concept of mean action time (MAT) that was first introduced by McNabb [A. McNabb and G. C. Wake, IMA J. Appl. Math.IJAMDM0272-496010.1093/imamat/47.2.193 47, 193 (1991)]. Although McNabb's initial argument was motivated by considering the mean particle lifetime (MPLT) for a linear death process, he applied the ideas to study diffusion. We extend the work of these authors by deriving expressions for the MAT for a general one-dimensional linear advection-diffusion-reaction problem. Using a combination of continuum and discrete approaches, we show that MAT and MPLT are equivalent for certain uniform-to-uniform transitions; these results provide a practical interpretation for MAT by directly linking the stochastic microscopic processes to a meaningful macroscopic time scale. We find that for more general transitions, the equivalence between MAT and MPLT does not hold. Unlike other critical time definitions, we show that it is possible to evaluate the MAT without solving the underlying partial differential equation (pde). This makes MAT a simple and attractive quantity for practical situations. Finally, our work explores the accuracy of certain approximations derived using MAT, showing that useful approximations for nonlinear kinetic processes can be obtained, again without treating the governing pde directly.

Ellery, Adam J.; Simpson, Matthew J.; McCue, Scott W.; Baker, Ruth E.

2012-04-01

297

Triassic alluvial braidplain and braided river deposits of the La Ternera Formation, Atacama region, northern Chile  

Microsoft Academic Search

The La Ternera Formation is a thick (>2,100 m) succession of terrigenous clastic sediments, with andesitic and basaltic intercalations, exposed in the Quebrada de Paipote area of the Atacama Region, northern Chile. The strata were deposited in an active rift basin during Late Triassic to (?) Early Jurassic times.The lower 1,000 m of the studied elastic succession comprises pebbly granule

C. M Bell; M Suárez

1995-01-01

298

Triassic pollen date moroccan high atlas and the incipient rifting of pangea as middle carnian.  

PubMed

Palynomorphs from the High Atlas Mountains south of Marrakech define the Minutosaccus-Patinasporites Concurrent Range Zone, which is time-stratigraphically equivalent to the Swiss and English middle Keuper, type Carnian of Austria, and North American Triassic beds in Virginia, North Carolina, Pennsylvania, New Jersey, Texas, New Mexico, and Arizona, thus dating an early episode of continental rifting between Africa and North America. PMID:17792703

Cousminer, H L; Manspeizer, W

1976-03-01

299

Palaeoenvironmental changes and vegetation history during the Triassic-Jurassic transition  

Microsoft Academic Search

The Triassic-Jurassic (T-J) boundary, ~200 Ma, is known as one of the ‘big five’ mass extinctions in Earth’s history. The T-J transition is characterized by a major extinction in the marine realm but evidence for floral turnover is ambiguous. Palynological records across the T-J boundary are controversially discussed because of the paucity of sections with a sufficient time resolution and\\/or

N. R. Bonis

2010-01-01

300

The stochastic background: scaling laws and time to detection for pulsar timing arrays  

NASA Astrophysics Data System (ADS)

We derive scaling laws for the signal-to-noise ratio of the optimal cross-correlation statistic, and show that the large power-law increase of the signal-to-noise ratio as a function of the observation time T that is usually assumed holds only at early times. After enough time has elapsed, pulsar timing arrays enter a new regime where the signal to noise only scales as \\sqrt{T}. In addition, in this regime the quality of the pulsar timing data and the cadence become relatively unimportant. This occurs because the lowest frequencies of the pulsar timing residuals become gravitational-wave dominated. Pulsar timing arrays enter this regime more quickly than one might naively suspect. For T = 10 yr observations and typical stochastic background amplitudes, pulsars with residual root-mean-squares of less than about 1??s are already in that regime. The best strategy to increase the detectability of the background in this regime is to increase the number of pulsars in the array. We also perform realistic simulations of the NANOGrav pulsar timing array, which through an aggressive pulsar survey campaign adds new millisecond pulsars regularly to its array, and show that a detection is possible within a decade, and could occur as early as 2016.

Siemens, Xavier; Ellis, Justin; Jenet, Fredrick; Romano, Joseph D.

2013-11-01

301

Magma-sediment interaction during the emplacement of syn-sedimentary silicic and mafic intrusions and lavas into and onto Triassic strata (Circum-Rhodope Belt, northern Greece)  

NASA Astrophysics Data System (ADS)

Within the Circum-Rhodope Belt in northern Greece, Middle Triassic neritic carbonate metasediments are locally intercalated with quartz-feldspar-phyric metarhyolites. In the same belt, Upper Triassic pelagic lime-marl-layered metasediments are similarly intercalated with low-grade metamorphosed basalt, dolerite and minor andesite and trachydacite. We interpret these sequences as due to magmatism active during the rifting event that eventually led to the opening of the Vardar Ocean. Despite the overprint of Late Jurassic deformation and low greenschist metamorphism, peperitic textures produced by magma-wet sediment interaction are well preserved at the contacts between the silicic volcanic rocks and the originally wet unconsolidated neritic carbonate sediments, suggesting contemporaneous magmatism and sedimentation. The mafic and intermediate volcanic rocks lack peperitic textures at their contacts with the pelagic sedimentary rocks. Thin margin parallel banding in the sedimentary members of the sequence indicates thermally affected original contacts with the mafic volcanic rocks only locally and at a microscopic scale. The absence of peperite in this case is attributed to the consolidated state of the sediments at the time of the mafic magma emplacement.

Asvesta, Argyro; Dimitriadis, Sarantis

2013-06-01

302

Variations in solar Lyman alpha irradiance on short time scales  

NASA Technical Reports Server (NTRS)

Variations in solar UV irradiance at Lyman alpha are studied on short time scales (from days to months) after removing the long-term changes over the solar cycle. The SME/Lyman alpha irradiance is estimated from various solar indices using linear regression analysis. In order to study the nonlinear effects, Lyman alpha irradiance is modeled with a 5th-degree polynomial as well. It is shown that the full-disk equivalent width of the He line at 1083 nm, which is used as a proxy for the plages and active network, can best reproduce the changes observed in Lyman alpha. Approximately 72 percent of the solar-activity-related changes in Lyman alpha irradiance arise from plages and the network. The network contribution is estimated by the correlation analysis to be about 19 percent. It is shown that significant variability remains in Lyman alpha irradiance, with periods around 300, 27, and 13.5d, which is not explained by the solar activity indices. It is shown that the nonlinear effects cannot account for a significant part of the unexplained variation in Lyman alpha irradiance. Therefore, additional events (e.g., large-scale motions and/or a systematic difference in the area and intensity of the plages and network observed in the lines of Ca-K, He 1083, and Lyman alpha) may explain the discrepancies found between the observed and estimated irradiance values.

Pap, J. M.

1992-01-01

303

Wood remains from the Late Triassic (Carnian) of Jordan and their paleoenvironmental implications  

NASA Astrophysics Data System (ADS)

During field work in the Triassic of Jordan fossil wood remains have been discovered at five horizons (S-1AR-S-5AR) of the Late Triassic (Carnian) Abu Ruweis Formation in NW Jordan. In most horizons wood remains are too badly preserved to allow for a detailed xylotomic investigation. Only two horizons provided material which exhibited anatomical details: (1) in horizon S-1AR we found rare and rather small fragments of woody charcoal exhibiting cellular details (representing the first macroscopic evidence of paleo-wildfires from the Late Triassic of the Middle East), and (2) in horizon S-5AR surfaces of partly compressed (gagatized) and partly permineralized wood fragments exhibited anatomical details that could be investigated by means of scanning electron microscopy. All wood remains that allow for a detailed investigation show features typical of gymnosperms, but at the moment nothing can be said about a more specific taxonomic affinity of most of the woods, although wood from horizon S-5AR exhibits characteristics of protopinoid wood. Our data provide evidence that gymnospermous woody vegetation cover has existed in the source areas of the sediments deposited in the Abu Ruweis Formation in Jordan and that this woody vegetation occasionally experienced wildfires. This, together with lithological data, provides evidence for a seasonally dry (maybe even arid) climate during deposition of the Abu Ruweis Formation. On a larger scale our findings contribute to the very scarce current knowledge about Late Triassic wildfires on the entire continent Gondwana, from where so far only three records of macro-charcoals, as undisputed evidence of paleo-wildfires, have been published from this period.

Abu Hamad, Abdalla M. B.; Jasper, André; Uhl, Dieter

2014-07-01

304

Nanosecond time scale, high power electrical wire explosion in water  

SciTech Connect

Experimental and magnetohydrodynamic simulation results of nanosecond time scale underwater electrical explosions of Al, Cu, and W wires are presented. A water forming line generator with current amplitude up to 100 kA was used. The maximum current rise rate and maximum Joule heating power achieved during wire explosions were dI/dt{<=}500 A/ns and 6 GW, respectively. Extremely high energy deposition of up to 60 times the atomization enthalpy was registered compared to the best reported result of 20 times the atomization enthalpy for energy deposition with a vacuum wire explosion. Discharge channel evolution and surface temperature were analyzed by streak shadow imaging and by a fast photodiode with a set of interference filters, respectively. A 1D magnetohydrodynamic simulation demonstrated good agreement with experimental parameters such as discharge channel current, voltage, radius, and temperature. Material conductivity was calculated to produce the best correlation between the simulated and experimentally obtained voltage. It is shown that material conductivity may significantly vary as a function of energy deposition rate.

Grinenko, A.; Krasik, Ya.E.; Efimov, S.; Fedotov, A.; Gurovich, V.Tz.; Oreshkin, V.I. [Physics Department, Technion, 32000 Haifa (Israel); Institute of High Current Electronics, SB RAN, 634055 Tomsk (Russian Federation)

2006-04-15

305

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

306

X-ray signatures: New time scales and spectral features  

NASA Technical Reports Server (NTRS)

The millisecond bursts from Cyg X-1 are investigated and the overall chaotic variability for the bulk of the Cyg X-1 emission is compared to that of Sco X-1, showing that the essential character is remarkably similar (i.e. shot noise) although the fundamental time scales involved differ widely, from a fraction of a second (for Cyg X-1) to a fraction of a day (for Sco X-1). Recent OSO-8 observations of spectra features attributable to iron are reviewed. In particular, line emission is discussed within the context of a model for thermal radiation by a hot evolved gas in systems as different as supernova remnants and clusters of galaxies. Newly observed spectral structure in the emission from the X-ray pulsar Her X-1 is reported.

Boldt, E. A.

1977-01-01

307

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

308

Control of Systems With Slow Actuators Using Time Scale Separation  

NASA Technical Reports Server (NTRS)

This paper addresses the problem of controlling a nonlinear plant with a slow actuator using singular perturbation method. For the known plant-actuator cascaded system the proposed scheme achieves tracking of a given reference model with considerably less control demand than would otherwise result when using conventional design techniques. This is the consequence of excluding the small parameter from the actuator dynamics via time scale separation. The resulting tracking error is within the order of this small parameter. For the unknown system the adaptive counterpart is developed based on the prediction model, which is driven towards the reference model by the control design. It is proven that the prediction model tracks the reference model with an error proportional to the small parameter, while the prediction error converges to zero. The resulting closed-loop system with all prediction models and adaptive laws remains stable. The benefits of the approach are demonstrated in simulation studies and compared to conventional control approaches.

Stepanyan, Vehram; Nguyen, Nhan

2009-01-01

309

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

310

Reid Roundabout Theorem for Symplectic Dynamic Systems on Time Scales  

SciTech Connect

The principal aim of this paper is to state and prove the so-called Reid roundabout theorem for the symplectic dynamic system (S) z{sup {delta}}= cal S {sub t}z on an arbitrary time scale Bbb T , so that the well known case of differential linear Hamiltonian systems (Bbb T = Bbb R ) and the recently developed case of discrete symplectic systems (Bbb T = Bbb Z ) are unified. We list conditions which are equivalent to the positivity of the quadratic functional associated with (S), e.g. disconjugacy (in terms of no focal points of a conjoined basis) of (S), no generalized zeros for vector solutions of (S), and the existence of a solution to the corresponding Riccati matrix equation. A certain normality assumption is employed. The result requires treatment of the quadratic functionals both with general and separated boundary conditions.

Hilscher, R. [Department of Mathematics, Masaryk University Brno, Janackovo nam. 2a, CZ-66295 Brno (Czech Republic)], E-mail: houska@math.muni.cz

2001-07-01

311

Partitioned transpression in the Triassic Aghdarband basin: evidence for a Cimmerian deformation in NE IRAN:  

NASA Astrophysics Data System (ADS)

The Lower-Middle Triassic Aghdarband Basin, NE Iran, consists of a strongly deformed arc-related marine succession deposited along the southern margin of Eurasia (Turan domain) in a highly mobile tectonic context. The marine deposits are unconformably covered by Upper Triassic continental beds, marking the Cimmerian collision of Iran with Eurasia. The Aghdarband Basin is a key-area for the study of the Cimmerian events, as the Triassic units were severely folded and thrust short time after the collision and were unconformably covered by the gently deformed Middle Jurassic succession which seals the Cimmerian structures. The Triassic deposits form a north-verging thrust stack interacting with an important left-lateral strike-slip shear zone exposed in the northernmost part of the basin. Transpressional structures as strike-slip faults and vertical folds are here associated with high angle reverse faults forming intricate positive flower structures. Systematic asymmetry of major and parasitic folds, as well as their geometrical features indicate that they generated in a left-lateral transpressional regime roughly coeval to thrust imbrication to the south, as a consequence of a marked strain partitioning. Aim of this presentation is to describe in detail the deformational structures of the Aghdarband region, based on structural mapping and detailed original mesoscopic field analyses, resuming from the excellent work performed in the '70s by Ruttner (1991). Our work is focused on the pre mid-Jurassic structures which can be related to the final stages of the Cimmerian deformation resulting from the oblique collision of the Iranian microplate with the southern margin of Eurasia, the so-called Turan domain. We will finally discuss the kinematic significance of the Late Triassic oblique convergence zone of Aghdarband in the frame of strain partitioning in transpressional deformation. Structural weakness favouring strain partitioning can be related to inversion of syn-sedimentary faults active during the Triassic, resulting from the reactivation of previous Palaeozoic structural lineaments which characterize the Turan domain. A right-lateral reactivation of the main left-lateral fault zone followed during Neogene and Quaternary as a consequence of the Arabia collision to the south

Zanchi, Andrea; Zanchetta, Stefano; Balini, Marco; Ghassemi, Mohammad Reza

2014-05-01

312

Towards a stable numerical time scale for the early Paleogene  

NASA Astrophysics Data System (ADS)

The construction of an astronomical time scale for the early Paleogene is hampered by ambiguities in the number, correlation and tuning of 405-kyr eccentricity related cycles in deep marine records from ODP cores and land-based sections. The two most competing age models result in astronomical ages for the K/Pg boundary that differ by ~750 kyr (~66.0 Ma of Vandenberghe et al. (2012) versus 65.25 Ma of Westerhold et al. (2012); these ages in turn are consistent with proposed ages for the Fish Canyon sanidine (FCs) that differ by ~300 kyr (28.201 Ma of Kuiper et al. (2008) versus 27.89 Ma of Westerhold et al. (2012)); an even older age of 28.294 Ma is proposed based on a statistical optimization model (Renne et al., 2011). The astronomically calibrated FCs age of 28.201 ± 0.046 Ma of Kuiper et al. (2008), which is consistent with the astronomical age of ~66.0 Ma for the K/Pg boundary, is currently adopted in the standard geological time scale (GTS2012). Here we combine new and published data in an attempt to solve the controversy and arrive at a stable nuemrical time scale for the early Paleogene. Supporting their younger age model, Westerhold et al. (2012) argue that the tuning of Miocene sections in the Mediterranean, which underlie the older FCs age of Kuiper et al. (2008) and, hence, the coupled older early Paleogene age model of Vandenberghe et al. (2012), might be too old by three precession cycles. We thoroughly rechecked this tuning; distinctive cycle patterns related to eccentricity and precession-obliquity interference make a younger tuning that would be consistent with the younger astronomical age of 27.89 Ma for the FCs of Westerhold et al. (2012) challenging. Next we compared youngest U/Pb zircon and astronomical ages for a number of ash beds in the tuned Miocene section of Monte dei Corvi. These ages are indistinguishable, indicating that the two independent dating methods yield the same age when the same event is dated. This is consistent with results of single crystal U/Pb zircon dating of the Fish Canyon tuff itself (Wotzlaw et al., 2013), which produced a youngest U/Pb age of 28.196 ± 0.038 Ma that is indistinguishable from the astronomically calibrated age of 28.201 ± 0.046 Ma for the FCs. Finally, youngest U/Pb zircon ages for ash layers that are found directly above the K/Pg boundary in North America are close to 65.9 Ma and thus consistent with the older astronomical age model with an age of ~66.0 Ma for the boundary. Summarizing, the new and published data summarized above unanimously favor the older option of the two alternative astronomical time scales for the early Paleogene. References Kuiper, K.F., A. Deino, F.J. Hilgen, W. Krijgsman, P.R. Renne, and J.R. Wijbrans, 2008. Synchronizing the Rock Clocks of Earth history. Science 320, 500-504. Renne, P.R., G. Balco, K.R. Ludwig, R. Mundil, and K. Min, 2011. Response to the comment by W.H. Schwarz et al. on "Joint determination of 40K decay constants and 40Ar*/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology". Geochim. Cosmochim. Acta 75, 5097-5100. Vandenberghe, N., F.J. Hilgen, and R.P. Speijer, 2012. The Paleogene Period. In: The Geological Time Scale 2012, Gradstein, F., et al., eds., Elsevier, pp. 855-921. Westerhold, T., U. Röhl, and J. Laskar, 2012. Time scale controversy: Accurate orbital calibration of the early Paleogene. Geochem. Geophys. Geosyst., 13, Q06015, doi:10.1029/2012GC004096. Wotzlaw, J.-F., U. Schaltegger, D.A. Frick, M.A. Dungan, A. Gerdes, and D. Günther, 2013. Tracking the evolution of large-volume silicic magma reservoirs from assembly to supereruption. Geology, doi:10.1130/G34366.1

Hilgen, Frederik; Kuiper, Klaudia; Sierro, Francisco J.; Wotzlaw, Jorn; Schaltegger, Urs; Sahy, Diana; Condon, Daniel

2014-05-01

313

Triassic-Jurassic mass extinction as trigger for the Mesozoic radiation of crocodylomorphs  

PubMed Central

Pseudosuchia, one of the two main clades of Archosauria (Reptilia: Diapsida), suffered a major decline in lineage diversity during the Triassic–Jurassic (TJ) mass extinction (approx. 201 Ma). Crocodylomorpha, including living crocodilians and their extinct relatives, is the only group of pseudosuchians that survived into the Jurassic. We reassess changes in pseudosuchian morphological diversity (disparity) across this time interval, using considerably larger sample sizes than in previous analyses. Our results show that metrics of pseudosuchian disparity did not change significantly across the TJ boundary, contrasting with previous work suggesting low pseudosuchian disparity in the Early Jurassic following the TJ mass extinction. However, a significant shift in morphospace occupation between Late Triassic and Early Jurassic taxa is recognized, suggesting that the TJ extinction of many pseudosuchian lineages was followed by a major and geologically rapid adaptive radiation of crocodylomorphs. This marks the onset of the spectacularly successful evolutionary history of crocodylomorphs in Jurassic and Cretaceous ecosystems.

Toljagic, Olja; Butler, Richard J.

2013-01-01

314

Triassic-Jurassic mass extinction as trigger for the Mesozoic radiation of crocodylomorphs.  

PubMed

Pseudosuchia, one of the two main clades of Archosauria (Reptilia: Diapsida), suffered a major decline in lineage diversity during the Triassic-Jurassic (TJ) mass extinction (approx. 201 Ma). Crocodylomorpha, including living crocodilians and their extinct relatives, is the only group of pseudosuchians that survived into the Jurassic. We reassess changes in pseudosuchian morphological diversity (disparity) across this time interval, using considerably larger sample sizes than in previous analyses. Our results show that metrics of pseudosuchian disparity did not change significantly across the TJ boundary, contrasting with previous work suggesting low pseudosuchian disparity in the Early Jurassic following the TJ mass extinction. However, a significant shift in morphospace occupation between Late Triassic and Early Jurassic taxa is recognized, suggesting that the TJ extinction of many pseudosuchian lineages was followed by a major and geologically rapid adaptive radiation of crocodylomorphs. This marks the onset of the spectacularly successful evolutionary history of crocodylomorphs in Jurassic and Cretaceous ecosystems. PMID:23536443

Toljagic, Olja; Butler, Richard J

2013-06-23

315

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

316

Lowermost Triassic (Griesbachian) microbial bindstone-cementstone facies, southwest Japan  

Microsoft Academic Search

Summary  On the basis of the lithostratigraphy and microscopic characters, the paper describes the facies interpretation of the upper\\u000a Upper Permian (Changhsingian) and Lower Triassic (Griesbachian to Spathian) carbonates of southwest Japan, with a focus upon\\u000a the lowermost Triassic (Griesbachian) microbial bindstone-cementstone. We emphasize the significant sediment-binding and stabilizing\\u000a agencies of microbes chiefly of cyanobacteria along with the syndepositional cementation for

Hiroyoshi Sano; Koichi Nakashima

1997-01-01

317

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

318

Structural studies of melting on the picosecond time scale.  

PubMed

Ultrafast structural studies of laser-induced melting have demonstrated that the solid-liquid phase transition can take place on a picosecond time scale in a variety of materials. Experimental studies using ångström wavelength X-rays from the sub-picosecond pulse source at Stanford (now retired) on non-thermal melting of semi-conductors, such as indium antimonide, employed the decay of a single Bragg-peak to measure the time component of the phase transition. These materials were found to start melting within one picosecond after the laser pulse. Recent computer simulations have described the thermal melting of ice induced by an infrared laser pulse. Here it was shown that melting can happen within a few picoseconds, somewhat slower than non-thermal melting in semi-conductors. These computer simulations are compatible with spectroscopy experiments on ice-melting, demonstrating that simulations form a very powerful complement to experiments targeting the process of phase-transitions. Here we present an overview of recent experimental and theoretical studies of melting, as well as new simulations of ice-melting where the effect of the size of the crystal on scattering is studied. Based on simulations of a near-macroscopic crystal, we predict the decay of the most intense Bragg peaks of ice following heating by laser pulse, by modeling the scattering from the melting sample in the simulations. PMID:18972022

Spoel, David van der; Maia, Filipe R N C; Caleman, Carl

2008-11-14

319

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

320

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

321

Multiple-Time Scaling and deviation from universality of the Earthquake Interevent Time Distribution  

NASA Astrophysics Data System (ADS)

The distribution of interevent times between subsequent earthquakes provides important information on the temporal organization of seismic catalogs. Universal scaling properties of this distribution have been evidenced for seismic catalogs of different geografic regions and for seismic sequences [1,2]. Recently, these universal features have been questioned and some criticisms have been raised [3,4]. We present an analysis of the Californian catalog and of numerical simulations of an epidemic-type model in order to investigate the existence of universal scaling properties. We show [5] 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 ?xes the onset of the power law decay in the Omori law. [1] P. Bak, K. Christensen, L. Danon, and T. Scanlon, . [2] A. Corral, Phys. Rev. Lett. 92, 108501 (2004). [3] S. Hainzl, C. Beauval, and F. Scherbaum, Bull. Seismol. Soc. Am. 96, 313 (2006). [4] S. Touati, M. Naylor, and I. G. Main, Phys. Rev. Lett. 102, 168501 (2009). [5] M. Bottiglieri, L. de Arcangelis, C. Godano, and E. Lippiello, Phys. Rev. Lett. 104, 158501 (2010)

Lippiello, E.; Godano, C.; de Arcangelis, L.; Bottiglieri, M.

2010-12-01

322

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

323

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

324

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

NASA Astrophysics Data System (ADS)

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 turnover in terrestrial ecosystems is not well understood, and cannot be readily reconciled with the effects of massive volcanism. Here we present pollen, spore and geochemical analyses across the Triassic/Jurassic boundary from three drill cores from Germany and Sweden. We show that gymnosperm forests in northwest Europe were transiently replaced by fern and fern-associated vegetation, a pioneer assemblage commonly found in disturbed ecosystems. The Triassic/Jurassic boundary is also marked by an enrichment of polycyclic aromatic hydrocarbons, which, in the absence of charcoal peaks, we interpret as an indication of incomplete combustion of organic matter by ascending flood basalt lava. We conclude that the terrestrial vegetation shift is so severe and wide ranging that it is unlikely to have been triggered by greenhouse warming alone. Instead, we suggest that the release of pollutants such as sulphur dioxide and toxic compounds such as the polycyclic aromatic hydrocarbons may have contributed to the extinction.

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

2009-08-01

325

Development of the Permian-Triassic sequence in the basin Fringe area, southern Netherlands  

SciTech Connect

Geological studies in the fringe area of the southern Permian basin led to new insights in the distribution and development of the Permian-Triassic sequence. During the Permian, the fringe area formed a platform, attached to the London-Brabant Massif, while during the Triassic it is characterized by strongly subsiding half grabens. In the southern Netherlands, Rotliegende sandstones and conglomerates have a much wider distribution than previously recognized. The Rotliegende deposits are capped by claystones and carbonates of the Upper Permian Zechstein. In the offshore, an important feeder system of clastics from the London-Brabant Massif was active during deposition of the Rotliegende and the Zechstein. In course of time, the location of major sandstone deposition shifted westward. Deposition of the Triassic Buntsandstein was controlled by the development of a large feeder system, which transported clastics from the Vosges northward, through the Roer Valley Graben and West netherlands Basin into the Off Holland Low. This system was responsible for the deposition of the economically important sheet sandstones of the Volpriehausen, Detfurth, Hardegsen, and Solling formations. A regional unconformity occurs below the Solling Formation. The sandstones are capped by claystones, evaporites, and sandstones of the Rot Formation. During deposition of the Muschelkalk, the differences in subsidence decreased and shallow marine sediments are interbedded with evaporites. Several unconformities occur within the Keuper. In the previous half grabens in the southern Netherlands, the Keuper is incomplete, which may be indicative for a possible reversal of the tectonic movements during this period.

Geluk, M.; Van Doorn, D.; Plomp, A.; Duin, E. (Geological Survey of the Netherlands, Haarlem (Netherlands))

1993-09-01

326

Bridging time-scale gaps via reaction path optimization  

NASA Astrophysics Data System (ADS)

In this talk I will present a series of new computational methodologies that can be applied to systematically investigate the mechanism, free energy profiles, and rates of large-scale conformational changes of biomolecules. First, we enhance the efficiency of reaction path optimization methods, which use a series of duplicated systems, or replicas, to represent a discrete path by using holonomic constraints instead of reparametrization or using penalty potential functions that may require force projections to maintain equal distances between replicas. As a result, this formulation allows a straightforward application of super-linear optimization schemes such as the Adopted Basis Newton Raphson method, which uses much fewer energy and force evaluations to optimize a path. Novel objective functions, such as Hamiltonian and action, have also been designed for the search of novel pathways in addition to minimum energy paths. We have also generalized this approach to compute minimum free energy paths of a reaction. Second, constraints for sampling on the hyper-planes along an optimized path have been developed for computing the potential of mean force using the blue- moon approach. For obtaining rate information, we propose to solve the time-dependent Fokker-Planck equation by using the free energy profiles along a path as input. I will present the studies of two important conformational changes using these methods: the cis-to- trans isomerization of an alanine dipeptide and the helix-to-hairpin transition of an amyloid beta peptide.

Chu, Jhih-Wei

2008-03-01

327

Existence results for time scale boundary value problem  

NASA Astrophysics Data System (ADS)

In this paper, we establish some existence results for positive solutions to a class of singular boundary value problem on time scale by using the Krasnosel'skii fixed point theorem. Two examples are presented as applications. The conditions we used in this paper are different from those in [D.R. Anderson, Eigenvalue intervals for a two-point boundary value problem on a measure chain, J. Comput. Appl. Math. 141 (2002) 57-64; C.J. Chyan, J. Henderson, Eigenvalues problems for nonlinear differential equations on a measure chain, J. Math. Anal. Appl. 245 (2000) 547-559; L.H. Erbe, A. Peterson Positive solutions for nonlinear differential equation on a measure chain, Math. Comput. Modelling 32 (2000) 571-585; L.H. Erbe, H.Y. Wang, On the existence of positive solutions of ordinary differential equations, Proc. Amer. Math. Soc. 120 (1994) 743-748; J. Henderson, H.Y. Wang, Positive solutions for nonlinear eigenvalue problems, J. Math. Anal. Appl. 208 (1997) 252-259; C.H. Hong, C.C. Yeh, Positive solutions for eigenvalue problems on a measure chain, Nonlinear Anal. 51 (2002) 499-507; W.C. Lian; W.F. Wong; C.C. Yeh, On the existence of positive solutions of nonlinear differential equations, Proc. Amer. Math. Soc. 124 (1996) 1117-1126; J. Liang, T.J. Xiao, Z.C. Hao, Positive solutions of singular differential equations on measure chain, Comput. Math. Appl. 49 (2005) 651-663].

Hao, Zhao-Cai; Liang, Jin; Xiao, Ti-Jun

2006-12-01

328

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

329

A Group Simulation of the Development of the Geologic Time Scale.  

ERIC Educational Resources Information Center

Explains how to demonstrate to students that the relative dating of rock layers is redundant. Uses two column diagrams to simulate stratigraphic sequences from two different geological time scales and asks students to complete the time scale. (YDS)

Bennington, J. Bret

2000-01-01

330

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

331

EON: software for long time simulations of atomic scale systems  

NASA Astrophysics Data System (ADS)

The EON software is designed for simulations of the state-to-state evolution of atomic scale systems over timescales greatly exceeding that of direct classical dynamics. States are defined as collections of atomic configurations from which a minimization of the potential energy gives the same inherent structure. The time evolution is assumed to be governed by rare events, where transitions between states are uncorrelated and infrequent compared with the timescale of atomic vibrations. Several methods for calculating the state-to-state evolution have been implemented in EON, including parallel replica dynamics, hyperdynamics and adaptive kinetic Monte Carlo. Global optimization methods, including simulated annealing, basin hopping and minima hopping are also implemented. The software has a client/server architecture where the computationally intensive evaluations of the interatomic interactions are calculated on the client-side and the state-to-state evolution is managed by the server. The client supports optimization for different computer architectures to maximize computational efficiency. The server is written in Python so that developers have access to the high-level functionality without delving into the computationally intensive components. Communication between the server and clients is abstracted so that calculations can be deployed on a single machine, clusters using a queuing system, large parallel computers using a message passing interface, or within a distributed computing environment. A generic interface to the evaluation of the interatomic interactions is defined so that empirical potentials, such as in LAMMPS, and density functional theory as implemented in VASP and GPAW can be used interchangeably. Examples are given to demonstrate the range of systems that can be modeled, including surface diffusion and island ripening of adsorbed atoms on metal surfaces, molecular diffusion on the surface of ice and global structural optimization of nanoparticles.

Chill, Samuel T.; Welborn, Matthew; Terrell, Rye; Zhang, Liang; Berthet, Jean-Claude; Pedersen, Andreas; Jónsson, Hannes; Henkelman, Graeme

2014-07-01

332

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

333

Studying the Dynamics of Problem Behavior across Multiple Time Scales: Prospects and Challenges.  

ERIC Educational Resources Information Center

As a commentary on the Special Issue, this paper discusses recent advances in the study of change across several time scales. It points out the importance of specifying time scales and putative patterns of change when characterizing problem behavior over developmental time scales. Methods for studying risk and protective mechanisms through…

Howe, George W.

2004-01-01

334

The Luoping biota: exceptional preservation, and new evidence on the Triassic recovery from end-Permian mass extinction  

PubMed Central

The timing and nature of biotic recovery from the devastating end-Permian mass extinction (252 Ma) are much debated. New studies in South China suggest that complex marine ecosystems did not become re-established until the middle–late Anisian (Middle Triassic), much later than had been proposed by some. The recently discovered exceptionally preserved Luoping biota from the Anisian Stage of the Middle Triassic, Yunnan Province and southwest China shows this final stage of community assembly on the continental shelf. The fossil assemblage is a mixture of marine animals, including abundant lightly sclerotized arthropods, associated with fishes, marine reptiles, bivalves, gastropods, belemnoids, ammonoids, echinoderms, brachiopods, conodonts and foraminifers, as well as plants and rare arthropods from nearby land. In some ways, the Luoping biota rebuilt the framework of the pre-extinction latest Permian marine ecosystem, but it differed too in profound ways. New trophic levels were introduced, most notably among top predators in the form of the diverse marine reptiles that had no evident analogues in the Late Permian. The Luoping biota is one of the most diverse Triassic marine fossil Lagerstätten in the world, providing a new and early window on recovery and radiation of Triassic marine ecosystems some 10 Myr after the end-Permian mass extinction.

Hu, Shi-xue; Zhang, Qi-yue; Chen, Zhong-Qiang; Zhou, Chang-yong; Lu, Tao; Xie, Tao; Wen, Wen; Huang, Jin-yuan; Benton, Michael J.

2011-01-01

335

The Luoping biota: exceptional preservation, and new evidence on the Triassic recovery from end-Permian mass extinction.  

PubMed

The timing and nature of biotic recovery from the devastating end-Permian mass extinction (252 Ma) are much debated. New studies in South China suggest that complex marine ecosystems did not become re-established until the middle-late Anisian (Middle Triassic), much later than had been proposed by some. The recently discovered exceptionally preserved Luoping biota from the Anisian Stage of the Middle Triassic, Yunnan Province and southwest China shows this final stage of community assembly on the continental shelf. The fossil assemblage is a mixture of marine animals, including abundant lightly sclerotized arthropods, associated with fishes, marine reptiles, bivalves, gastropods, belemnoids, ammonoids, echinoderms, brachiopods, conodonts and foraminifers, as well as plants and rare arthropods from nearby land. In some ways, the Luoping biota rebuilt the framework of the pre-extinction latest Permian marine ecosystem, but it differed too in profound ways. New trophic levels were introduced, most notably among top predators in the form of the diverse marine reptiles that had no evident analogues in the Late Permian. The Luoping biota is one of the most diverse Triassic marine fossil Lagerstätten in the world, providing a new and early window on recovery and radiation of Triassic marine ecosystems some 10 Myr after the end-Permian mass extinction. PMID:21183583

Hu, Shi-xue; Zhang, Qi-yue; Chen, Zhong-Qiang; Zhou, Chang-yong; Lü, Tao; Xie, Tao; Wen, Wen; Huang, Jin-yuan; Benton, Michael J

2011-08-01

336

Categorical Scaling of Time: Implications for Clock-Counter Models  

Microsoft Academic Search

Pigeons partitioned time into three intervals. Responses to one key could be reinforced after a short time, to a second key after an intermediate time, and to a third key after a long time. The values of the short, intermediate, and long times and the proportion of trials ending with reinforcement were varied. Absolute and relative response rates on each

J. Gregor Fetterman; Peter R. Killeen

1995-01-01

337

Tempo of the end-Permian event: High-resolution cyclostratigraphy at the Permian-Triassic boundary  

Microsoft Academic Search

The Permian-Triassic (P-T) boundary is marked by the most severe mass extinction in the geologic record. High-resolution cyclostratigraphy on a 104 yr scale across the P-T boundary in a core from the Carnic Alps (Austria) revealed significant cycles in the ratio ˜40:10:4.7:2.3 m, identified with Milankovitch cycles of ˜412:100:40:20 k.y. (eccentricity 1 and 2, obliquity, and precession). Wavelet analysis indicates

Michael R. Rampino; Andreas Prokoph; Andre Adler

2000-01-01

338

Climatically driven biogeographic provinces of Late Triassic tropical Pangea.  

PubMed

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. PMID:21571639

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

2011-05-31

339

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

340

Paleoenvironmental significance of carbonate microbialites from the uppermost Rhaetian (latest Triassic) southwestern United Kingdom  

NASA Astrophysics Data System (ADS)

Several upper Triassic sections of the southwestern United Kingdom contain a laterally extensive (2,000 km2), thin (~20 cm) unit of carbonate microbialites known regionally as the Cotham Marble. The microbialites occur as discrete mounds that range from about 0.5 to 2 meters in diameter and are internally composed of alternating dendritic and laminated mesofabrics. The dendritic portions are composed of microspar/micrite, contain abundant putative pyrite coated filamentous microfossils, and have elevated total organic carbon (TOC) relative to the interstitial fill. Here, we highlight two very striking features of the Cotham Marble microbialites which offer clues to local paleoenvironmental conditions across the end-Triassic mass extinction interval: (1) the microbialites contain extensive laterally continuous fabrics with mm-scale laminae that are represented in samples separated by at least 10 km and (2) the microbialites preserve fine, sub-mm scale details of microbial mat branching patterns. The proliferation and preservation of largely undisturbed, laterally continuous fabrics and delicate microbial mat textures indicate the microbialites were lithified very quickly likely from growth in waters with an anomalously high saturation state with respect to calcium carbonate. High saturation state possibly resulted from accelerated weathering conditions due to the emplacement of the Central Atlantic Magmatic Providence (CAMP). The fine-grained, dominantly micritic nature of the microbialites bears a strong textural resemblance to their Precambrian counterparts in contrast to the coarse-grained fabrics of modern marine microbialites. Such fine-grained textures are rare in Phanerozoic marine microbialites but are known to occur during other mass extinction episodes. Therefore, the Cotham Marble microbialites could indicate a brief return to microbial carbonate deposition as a consequence of the end-Triassic mass extinction.

Ibarra, Y.; Corsetti, F. A.; Greene, S. E.; Bottjer, D. J.

2013-12-01

341

Permo-Triassic collisional orogenesis and transition to intraplate sinistral shear in southeastern Mongolia  

NASA Astrophysics Data System (ADS)

Southeastern Mongolia is part of a vast accretionary complex involving Paleozoic arc terranes of the Altaid tectonic collage that collided with North China during closure of the Paleo-Asian Ocean. The region also records a complex history of post-collisional polyphase Triassic-Quaternary intraplate deformation. We present new 40Ar/39Ar and U/Pb titanite data that place temporal constraints on the evolution of collisional orogenesis and the transition to intraplate deformation in southeastern Mongolia where highly deformed and metamorphosed Lower-Upper Permian turbidite successions mark final closure of a remnant ocean basin between the Paleozoic arc terranes and the North China block. At Nomgon, the turbidite sequences are structurally bound by deformed metasediments, including marbles, of higher strain and metamorphic grade. 40Ar/39Ar step heating analyses of hornblende from a granitoid and white mica from muscovite schist along the SW and S margins of the turbidites yield plateau ages of 274 and 273 Ma, respectively. White mica from mylonitic rocks along the NW margin of the Nomgon block yielded a 40Ar/39Ar spectrum with a loss profile and 234 Ma weighted mean age. At Bulgan Uul, an offset correlative of the Nomgon section, the transition from marine to terrestrial sedimentation is cross-cut by an intermediate-mafic dike swarm for which hornblende yielded a 245 Ma 40Ar/39Ar plateau age. To the north and structurally below a carbonate klippe, hornblende from the metamorphosed and boudinaged equivalent of the dike gave a 40Ar/39Ar 227 Ma weighted mean age. Biotite from the same boudin and its host gneiss both yield complicated spectra but are consistent with Late Triassic metamorphism and deformation. Late Triassic metamorphic tectonites at Tavan Har record evidence for partial melting at amphibolite-facies conditions and multiple generations of intrusions. Field, petrographic, and U/Pb zircon analyses indicate that the protoliths of the metamorphic tectonites are Paleozoic volcanic and sedimentary sequences. U/Pb titanite data from amphibolites and amphibolite-facies gneisses yield an older population c. 274 Ma, and two younger populations at 244 and 224 Ma. The latter is consistent with 40Ar/39Ar data that constrain the timing of amphibolite-facies sinistral shear in the East Gobi Fault Zone (EGFZ). Taken together and integrated with ongoing studies, these data along strike of the EGFZ suggest that Permian collisional orogenesis in SE Mongolia continued until the Early Triassic and that the transition to intraplate sinistral shear along the NE-trending EGFZ occurred by the Late Triassic (Carnian), dissecting the closed oceanic basin.

Webb, L. E.; Taylor, J. P.; Heumann, M. J.; Johnson, C. L.; Stypula, M.; Kylander-Clark, A. R.

2011-12-01

342

Long-term oceanic changes prior the end-Triassic mass extinction  

NASA Astrophysics Data System (ADS)

A number of potential causes and kill mechanisms have been proposed for the end-Triassic mass extinction such as palaeoclimatic and sea-level variations, massive volcanism and ocean acidification. Recent analysis of the stomatal index and density of fossil leaves and geochemical research on pedogenic carbonate nodules are suggestive of rising atmospheric CO2 concentration and fluctuating climate in the Rhaetian. It seems therefore probable that the end-Triassic event was preceded by large climatic fluctuations and environmental perturbations in the Rhaetian which might have partly affected the composition and diversity of the terrestrial and marine biota prior to the end-Triassic interval. The Northern Calcareous Alps (NCA) has long been favored for the study of the Rhaetian, since the GSSP of the Triassic/Jurassic (T/J) boundary and other important T/J sections are situated in this region. However, the most famous Rhaetian sections in the NCA are composed of carbonates from the Koessen Formation and were situated in a large isolated intraplatform Basin (the Eiberg Basin), bordered to the south-east by a well-developed coral reef in the NW of the Tethys border. Several Rhaetian sections composed of marls and shales of the Zlambach Formation were deposited at the same time on the other side of this reef, in the oceanic Halstatt Basin, which was in direct connection to the Tethys. Here, we present new results on sedimentology, stable isotope and trace element analysis of both intraplatform and oceanic basin deposits in the NCA. Intraplatform Rhaetian sections from the Koessen Formation bear a few minor intervals of shales with enrichments in organic matter, some of which are associated to carbon isotopic excursions. Oceanic sections from the Hallstatt Basin are characterized at the base by very cyclic marl-limestone alternations. Higher up in the section, sediments progressively turn into pure shale deposits and the top of the Formation is characterized by organic-rich, laminated black shales. This interval of black shales is associated with a 2 per mil negative carbon isotopic excursion and a strong warming as suggested by fluctuations in oxygen isotopes. Forthcoming geochemical and paleontological analysis on these two Formations should help us : (1) better constrain the stratigraphy of the Rhaetian in the NCA by correlating geochemical and climatic events that took place both in the intraplaform (Eiberg) and oceanic (Hallstatt) Basin, (2) decipher localized vs large Tethyan anoxic events and associated carbon-cycle perturbations and (3) constrain the possible influence of Rhaetian climatic perturbations on the biota before the end-Triassic mass extinction.

Clémence, Marie-Emilie; Mette, Wolfgang; Thibault, Nicolas; Korte, Christoph

2014-05-01

343

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

344

Small-Time Scaling Beahviors of Internet Backbone Traffic: An Empirical Study  

Microsoft Academic Search

We study the small-time (sub-seconds) scaling behaviors of Internet backbone traffic, based on traces collected from OC3\\/12\\/48 links in a tier-1 ISP. We observe that for a majority of these traces, the (second-order) scaling exponents at small time scales (1ms - 100ms) are fairly close to 0.5, indicating that traffic fluctuations at these time scales are (nearly) uncorrelated. In addition,

Zhi-li Zhang; Vinay J. Ribeiro; Sue B. Moon; Christophe Diot

2003-01-01

345

Input-output description of linear systems with multiple time-scales  

NASA Technical Reports Server (NTRS)

It is pointed out that the study of systems evolving at multiple time-scales is simplified by studying reduced-order models of these systems valid at specific time-scales. The present investigation is concerned with an extension of results on the time-scale decomposition of autonomous systems to that of input-output systems. The results are employed to study conditions under which positive realness of a transfer function is preserved under singular perturbation. Attention is given to the perturbation theory for linear operators, the multiple time-scale structure of autonomous linear systems, the input-output description of two time-scale linear systems, the positive realness of two time-scale systems, and multiple time-scale linear systems.

Madriz, R. S.; Sastry, S. S.

1984-01-01

346

Siberian Traps large igneous province: Evidence for two flood basalt pulses around the Permo-Triassic boundary and in the Middle Triassic, and contemporaneous granitic magmatism  

NASA Astrophysics Data System (ADS)

The Siberian Traps large igneous province is of enormous size (~ 7 × 106 km2) and volume (~ 4 × 106 km3). It contains effusive, intrusive and volcanoclastic rocks varying in compositions from ultramafic to felsic, though low-Ti basalts and their intrusive analogs are the predominant rock types. In this paper, we provide new 40Ar/39Ar ages for two lava units of the geographic center of the Siberian Traps, the Central Putorana region (240.9 ± 1.3/2.6/5.5 and 246.6 ± 1.4/2.7/5.6 Ma, where ages are calculated relative to Bern4M with an assigned age of 18.7 (± 0.096) Ma and errors are stated in the form ± x/y/z, where x and y and z are analytical, internal and external errors, respectively), three dolerite sills from the Angara-Taseevskaya syncline of the southeastern Siberian Traps (242.8 ± 1.3/2.6/5.0 Ma, 239.1 ± 1.1/2.5/4.9 Ma and 255.8 ± 4.7/5.3/6.9 Ma) and a lamproite dyke from the Noril'sk region (238.3 ± 1.3/2.6/5.3 Ma). In combination with available geochronologic data our results suggest that voluminous low-Ti basaltic magmatism appeared during different pulses. At least two volcanic pulses are recognized: at the Permo-Triassic boundary (~ 249 Ma or 252 Ma using the 40Ar/39Ar and U-Pb timescales, respectively) and about 10 Ma later in the Middle Triassic. Granitic magmatism overlapped in time with the two flood basalt pulses, but continued into the Late Triassic (~ 229 Ma using the U-Pb timescale). Prolonged magmatism of the Siberian Traps province is also supported by geologic observations and paleomagnetic data. New geochronologic findings are discussed in light of the different models for the origin of the Siberian Traps and applied to a Middle Triassic mass extinction event.

Ivanov, Alexei V.; He, Huayiu; Yan, Liekun; Ryabov, Viktor V.; Shevko, Artem Y.; Palesskii, Stanislav V.; Nikolaeva, Irina V.

347

Associated skeletons of a new middle Triassic "Rauisuchia" from Brazil.  

PubMed

For more than 30 million years, in early Mesozoic Pangea, "rauisuchian" archosaurs were the apex predators in most terrestrial ecosystems, but their biology and evolutionary history remain poorly understood. We describe a new "rauisuchian" based on ten individuals found in a single locality from the Middle Triassic (Ladinian) Santa Maria Formation of southern Brazil. Nine articulated and associated skeletons were discovered, three of which have nearly complete skulls. Along with sedimentological and taphonomic data, this suggests that those highly successful predators exhibited some kind of intraspecific interaction. Other monotaxic assemblages of Triassic archosaurs are Late Triassic (Norian-Rhaetian) in age, approximately 10 million years younger than the material described here. Indeed, the studied assemblage may represent the earliest evidence of gregariousness among archosaurs, adding to our knowledge on the origin of a behavior pattern typical of extant taxa. PMID:21445632

França, Marco Aurélio G; Ferigolo, Jorge; Langer, Max C

2011-05-01

348

Categorical scaling of time: implications for clock-counter models.  

PubMed

Pigeons partitioned time into three intervals. Responses to one key could be reinforced after a short time, to a second key after an intermediate time, and to a third key after a long time. The values of the short, intermediate, and long times and the proportion of trials ending with reinforcement were varied. Absolute and relative response rates on each key were an orderly function of time and showed approximately proportional changes with changes in the interval values, consistent with Weber's law, Gibbon's (1977) scalar expectancy theory, and Killeen and Fetterman's (1988) behavioral theory of timing (BeT). Standard deviations of the times at which subjects switched between successive keys increased more slowly within a condition than across conditions, as predicted by BeT. Increases and decreases in reinforcement probability produced both transient and longer lasting changes in timing behavior, once again, in accord with predictions of BeT. PMID:7844506

Fetterman, J G; Killeen, P R

1995-01-01

349

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

350

Kinematic restoration of the Mediterranean region since the Triassic  

NASA Astrophysics Data System (ADS)

The Mediterranean region is one of the most complexly deformed areas in the world and its tectonic evolution has been instrumental in the development of numerous fundamental geological principles and geodynamic concepts. Reconstructions of the Mediterranean region invariably demonstrated that the area had a complex paleogeography with ribbon continents or micro-plates and narrow, elongated ocean basins systems in Mesozoic time. A western and northern ocean basin system was genetically related to the Atlantic Ocean, opened in Jurassic time and is known as the Alpine Tethys Ocean. A southern and eastern basin system was genetically related to the Neotethys domain located between Gondwana and Eurasia and - in the Mediterranean realm - opened in Triassic to Jurassic times. Continental domains of variable size within and between these ocean systems rifted away from Eurasia or Africa. This mosaic of pieces of continental and oceanic lithosphere became consumed by a complex configuration of subduction zones that accommodated convergence between the African and Eurasian plates since middle Jurassic times. Since Oligocene time, the overriding plate above subduction zones throughout the Mediterranean region became extended, locally leading to formation of new ocean floor, as a result of roll-back of subducted slab segments, culminating in todays complex and strongly curved configuration of subduction zones and slab segments. An area such as the tectonically complex Mediterranean invites attempt to kinematic restoration, and various reconstructions are already available. However, by now such reconstructions are no more merely a translation of - frequently qualitative - geological data into a quantitative description of surface evolution: with the advent of 3-dimensional numerical modeling tools that can be kinematically driven by plate reconstructions, they become critical input for attempts to integrate surface evolution into mantle dynamics. An increasingly widely used platform for kinematic reconstructions is the freely available GPlates plate kinematic reconstruction software (http://www.gplates.org). We provide the first fully quantitatively described GPlates-based kinematic reconstruction of the Mediterranean region back to Triassic time. Classic plate reconstructions assume plate rigidity, and motion concentrated along discrete plate boundaries. Convergence between Africa-Europe plate boundary in the Mediterranean region is, however, associated with regionally distributed deformation. In this reconstruction, we attempt to restore this distributed deformation, which in practice means that we allow for polygons to change shape and area over time. This reconstruction may (i) be used as input for numerical models that aim to constrain the geodynamic evolution of (parts of) the Mediterranean history, (ii) allow comparing relative tectonic motions of the Mediterranean region to the mantle using mantle reference frames, and (iii) provide regional kinematic context for future geological studies. Upon final publication, all shape and rotation files of this reconstruction will be made publically available, which may serve as a platform for further improvement when new constraints demand so, or when the reader wishes to test different tectonic scenarios.

van Hinsbergen, Douwe; Torsvik, Trond; Matenco, Liviu; Schmid, Stefan; Maffione, Marco; Spakman, Wim

2014-05-01

351

TRIASSIC-JURASSIC BOUNDARY ON THE SOUTHERN MARGIN OF TETHYS: IMPLICATIONS OF FACIES, TECTONICS AND VOLCANISM  

Microsoft Academic Search

The facies changes, tectonics and magmatism across the Triassic-Jurassic boundary in the southern Tethyan margin have been studied in Egypt, Sudan, Jordan and Saudi Arabia. In Saudi Arabia and Jordan an unconformable contact is recognized between the Upper Triassic and Lower Jurassic rocks. This unconformity surface is marked by the truncation of the fluvial clastics of the uppermost Triassic before

MOHAMED A. KHALIFA

352

Permian-Triassic mass extinction event recorded in bedded chert sequence in southwest Japan  

Microsoft Academic Search

Rock types in southwest Japan change across the Permian-Triassic boundary. Late Permian bedded chert grades upward into latest Permian siliceous claystone, carbonaceous mudstone of unknown age, early Triassic siliceous claystone with carbonaceous mudstone and chert interbeds, and then into middle Triassic to Jurassic bedded chert. These stratigraphic lithologic variation also accompany the decline and recovery of radiolarians in the Changxingian

Yoshitaka Kakuwa

1996-01-01

353

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

354

TRIASSIC PALEOGEOGRAPHIC AND TECTONIC EVOLUTION OF SOUTHWESTERN LAURENTIA THROUGH JURASSIC TECTONIC OVERPRINT  

Microsoft Academic Search

The undeformed to broadly folded Triassic and Jurassic stratigra- phy of the Great Plains and Laramide broken foreland of the western North American craton belie the increasingly complex task of reassem- bling the Triassic paleogoeography and tectonic evolution of the Cordil- leran margin. Indeed, the location and configuration of the western mar- gin of the Triassic North American craton remain

JOHN E. MARZOLF

355

Paleomagnetic results from the TRiassic of the Yangtze Platform  

NASA Astrophysics Data System (ADS)

Two widely separated localities have been sampled from Triassic Formations of the Yangtze platforms. The first is from the border area between Sichuan and Guizhou provinces, where the Early Triassic Yelang Formation was sampled at 15 sites, located on both flanks of an anticline. Characteristic high-temperature components were isolated from nine sites, the remainder were severely overprinted by a recent field. Two polarities are present, one directed toward the northeast with shallow positive inclinations, and the other to the southwest with almost horizontal inclinations. The northeast group passes the fold test at the 95% level. The second area of study was from the city of Nanjing, Jiangsu Province, where 19 sites were drilled from three formations ranging in age from the lower to upper Triassic. The samples are severely overprinted with a component that is almost vertical and whose origin is unclear. However, in 23 of the samples, a high-temperature component was isolated directed to the northeast and positive and to the southwest and negative. The fold test is indeterminate. The pole positions from the two localities are Sichuan 46.3°N, 219.2°E, ?95 = 10.9°; Nanjing 44.8°N, 223.6°E, ?95 = 9.3°, which are not significantly different from each other and fall near two other recent studies of Triassic rocks from the Yangtze block. The pole positions given above are significantly different from the Triassic of Eurussia, Siberia, the North China block, and Thailand, indicating that these different components of eastern Asia were not sutured together in their present configuration until after the Triassic.

Opdyke, Neil D.; Huang, K.; Xu, G.; Zhang, W. Y.; Kent, D. V.

1986-08-01

356

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

357

Scaling up dynamic time warping for datamining applications  

Microsoft Academic Search

There has been much recent interest in adapting data mining algorithms to time series databases. Most of these algorithms need to compare time series. Typically some variation of Euclidean distance is used. However, as we demonstrate in this paper, Euclidean distance can be an extremely brittle distance measure. Dynamic time warping (DTW) has been suggested as a technique to allow

Eamonn J. Keogh; Michael J. Pazzani

2000-01-01

358

Fast stratocumulus time scale in mixed layer model and large eddy simulation  

NASA Astrophysics Data System (ADS)

mixed layer model (MLM) and large eddy simulation (LES) are used to analyze the internal response time scales of a stratocumulus-topped boundary layer (STBL). Three separate time scales are identified: a slow time scale associated with boundary layer deepening (several days), an intermediate thermodynamic time scale (approximately 1 day), and a fast time scale (6-12 h) for cloud water path adjustment associated with an internal entrainment-liquid flux (ELF) feedback. The nocturnal DYCOMSII-RF01 case study is used to establish and interpret the previously unidentified fast STBL adjustment time scale with the MLM. The role of the entrainment closure is investigated by repeating the analysis with several different closures. Nearly every closure considered exhibits a fast time scale. Perturbations are applied to the well-mixed CGILS stratocumulus case in both MLM and LES in order to elicit a short time scale response. Purely radiative perturbations do not project strongly onto the fast scale, while perturbations to the free tropospheric humidity do. A 2K surface and atmospheric temperature perturbation also projects strongly onto the fast scale. We show that the ELF adjustment mechanism behind the fast time scale is responsible for much of the steady state liquid water path response in the perturbed case, acting as a cloud-thinning feedback mechanism in a uniformly warmed climate.

Jones, C. R.; Bretherton, C. S.; Blossey, P. N.

2014-03-01

359

Detrital zircon provenance of the Late Triassic Songpan-Ganzi complex: Sedimentary record of collision of the North and South China blocks  

USGS Publications Warehouse

Using detrital zircon geochronology, turbidite deposystems fed from distinct sediment sources can be distinguished within the Songpan-Ganzi complex, a collapsed Middle to Late Triassic turbidite basin of central China. A southern Songpan-Ganzi deposystem initially was sourced solely by erosion of the Qinling-Dabie orogen during early Late Triassic time, then by Qinling-Dabie orogen, North China block, and South China block sources during middle to late Late Triassic time. A northern Songpan-Ganzi system was sourced by erosion of the Qinling-Dabie orogen and the North China block throughout its deposition. These separate deposystems were later tectonically amalgamated to form one complex and then uplifted as the eastern Tibet Plateau. ?? 2006 Geological Society of America.

Weislogel, A. L.; Graham, S. A.; Chang, E. Z.; Wooden, J. L.; Gehrels, G. E.; Yang, H.

2006-01-01

360

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

361

Time-delay quasars: Scales and orders of magnitudes  

NASA Astrophysics Data System (ADS)

We can think of a lensed quasar as taking the Hubble time, shrinking it by ˜10-11, and then presenting the result to us as a time delay; the shrinking factor is of the order of fractional sky-area that the lens occupies. This cute fact is a straightforward consequence of lensing theory, and enables a simple rescaling of time delays. Observed time delays have a 40-fold range, but after rescaling the range reduces to 5-fold. The latter range depends on details of the lens and lensing configuration - for example, quads have systematically shorter rescaled time delays than doubles - and is as expected from a simple model. The hypothesis that observed time-delay lenses all come from a generalized-isothermal family can be ruled out. But there is no indication of drastically different populations either.

Saha, P.

2004-02-01

362

Massive Red-Staining and Albitization of Feldspars in Paleozoic Basement Rocks of Western Europe and Their Association with the Triassic Palaeogeography  

NASA Astrophysics Data System (ADS)

Albitization of feldspars is a widespread mineral replacement process of the upper crust. An ubiquitous and pervasive red-staining albitization of feldspars has been observed in the feldspathic rocks of the Variscan basement in the Sudetes, Armorican, Morvan, Roc de Frausa and Montseny-Guilleries Massifs (Western Europe). These crystalline massifs were strongly eroded during Permian and Triassic times and suffered a long-lasting exposition in the Permian-Triassic palaeosurface. The albitized rocks contain minute Fe-oxides hoisted within the microporosity of the secondary albite. The intimate textural relationship between the Fe-oxides and the albite strongly suggest that they are coetaneous with albitization. The microscope, cathodoluminescence, SEM and EMPA analyses reveal that almost all plagioclases and some K-feldspars are albitized in those areas close to the Permian-Triassic palaeosurface. Moving downwards the palaeosurface the albitization of Variscan rocks progressively disappears. Field mapping of the albitized areas points to estimated thickness about 100-200m. In the uppermost parts of the profile almost all plagioclases are totally albitized and the rock shows a strong and pervasive reddening, whereas in the lowermost parts the mineral replacement is restricted to fractures and neighbouring walls and the rock in tinted with a soft pink colour. These observations suggest that albitization is linked to that palaeosurface and constitutes a paleoalteration profile beneath the Permian-Triassic palaeosurface. All these observations suggest that the mineral replacement could have been driven by descending Na+ rich brines related with or coming from the Permian-Triassic palaeosurface. Ricodel et al. (2007) determined a Triassic age for the paleomagnetic signature of the Fe-oxides hoisted within the microporosity of albite in the Morvan Massif. The narrow textural relationship between the Fe-oxides and the albite support the idea that this is the age of albitization in this massif. The similarities in the petrographycal and geometrical aspects between the five studied massifs strongly suggest that they could record a common albitization event that affected the basement rocks of the Permian-Triassic palaeosurface during Triassic times. Although albitization usually is a deep process which occurs at depths greater then 900 m, during the end of the Permian and the beginning of the Triassic geochemical conditions of the atmosphere and the hydrosphere were radically distinctive and without equal in the earth. This exclusive geochemical conditions should had a role in de development of unusual shallow chemical reactions. In this contexts albitization developed close to the surface. The shallow Triassic albitization of the Variscan basement of Western Europe, and maybe around the Triassic continental long-lasting world, can be a useful tool in the reconstruction of the continental areas around the Triassic basins. [1] Ricordel, C., Parcerisa, D., Thiry, M., Moreau, M. G., & Gómez-Gras, D. (2007). Triassic magnetic overprints related to albitization in granites from the Morvan Massif (France). Palaeogeography, Palaeoclimatology, Palaeoecology, 251, 268-282.

Fabrega, C.; Parcerisa, D.; Franke, C.; Thiry, M.; Yao, K.; Gómez-Gras, D.

2013-12-01

363

Absoluteness of Velocity Produced by Accelerating Process and Absolute Space-time Theory with Variable Scales  

Microsoft Academic Search

It is proved by means of the dynamical effects of special relativity that velocity caused by accelerating process is not a relative concept. The influence of accelerating process should be considered in space-time theory. Besides the Newtonian absolute space-time theory with invariable space-time scales and the Einstein relative space-time theory with variable space-time scales, there exists the third space-time theory,

Mei Xiaochun

2006-01-01

364

Time-scale invariance as an emergent property in a perceptron with realistic, noisy neurons  

PubMed Central

In most species, interval timing is time-scale invariant: errors in time estimation scale up linearly with the estimated duration. In mammals, time-scale invariance is ubiquitous over behavioral, lesion, and pharmacological manipulations. For example, dopaminergic drugs induce an immediate, whereas cholinergic drugs induce a gradual, scalar change in timing. Behavioral theories posit that time-scale invariance derives from particular computations, rules, or coding schemes. In contrast, we discuss a simple neural circuit, the perceptron, whose output neurons fire in a clockwise fashion (interval timing) based on the pattern of coincidental activation of its input neurons. We show numerically that time-scale invariance emerges spontaneously in a perceptron with realistic neurons, in the presence of noise. Under the assumption that dopaminergic drugs modulate the firing of input neurons, and that cholinergic drugs modulate the memory representation of the criterion time, we show that a perceptron with realistic neurons reproduces the pharmacological clock and memory patterns, and their time-scale invariance, in the presence of noise. These results suggest that rather than being a signature of higher-order cognitive processes or specific computations related to timing, time-scale invariance may spontaneously emerge in a massively-connected brain from the intrinsic noise of neurons and circuits, thus providing the simplest explanation for the ubiquity of scale invariance of interval timing.

Buhusi, Catalin V.; Oprisan, Sorinel A.

2013-01-01

365

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

366

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

367

Structure and dating errors in the geologic time scale and periodicity in mass extinctions  

NASA Technical Reports Server (NTRS)

Structure in the geologic time scale reflects a partly paleontological origin. As a result, ages of Cenozoic and Mesozoic stage boundaries exhibit a weak 28-Myr periodicity that is similar to the strong 26-Myr periodicity detected in mass extinctions of marine life by Raup and Sepkoski. Radiometric dating errors in the geologic time scale, to which the mass extinctions are stratigraphically tied, do not necessarily lessen the likelihood of a significant periodicity in mass extinctions, but do spread the acceptable values of the period over the range 25-27 Myr for the Harland et al. time scale or 25-30 Myr for the DNAG time scale. If the Odin time scale is adopted, acceptable periods fall between 24 and 33 Myr, but are not robust against dating errors. Some indirect evidence from independently-dated flood-basalt volcanic horizons tends to favor the Odin time scale.

Stothers, Richard B.

1989-01-01

368

Time-scale invariance as an emergent property in a perceptron with realistic, noisy neurons.  

PubMed

In most species, interval timing is time-scale invariant: errors in time estimation scale up linearly with the estimated duration. In mammals, time-scale invariance is ubiquitous over behavioral, lesion, and pharmacological manipulations. For example, dopaminergic drugs induce an immediate, whereas cholinergic drugs induce a gradual, scalar change in timing. Behavioral theories posit that time-scale invariance derives from particular computations, rules, or coding schemes. In contrast, we discuss a simple neural circuit, the perceptron, whose output neurons fire in a clockwise fashion based on the pattern of coincidental activation of its input neurons. We show numerically that time-scale invariance emerges spontaneously in a perceptron with realistic neurons, in the presence of noise. Under the assumption that dopaminergic drugs modulate the firing of input neurons, and that cholinergic drugs modulate the memory representation of the criterion time, we show that a perceptron with realistic neurons reproduces the pharmacological clock and memory patterns, and their time-scale invariance, in the presence of noise. These results suggest that rather than being a signature of higher order cognitive processes or specific computations related to timing, time-scale invariance may spontaneously emerge in a massively connected brain from the intrinsic noise of neurons and circuits, thus providing the simplest explanation for the ubiquity of scale invariance of interval timing. PMID:23518297

Buhusi, Catalin V; Oprisan, Sorinel A

2013-05-01

369

RCBR: A Simple and Efficient Service for Multiple TimeScale Traffic  

Microsoft Academic Search

Compressed video traffic is expected to be a significant component of the traffic mix in integrated services networks. This traffic is hard to manage, since it has strict delay and loss requirements, but at the same time, exhibits burstiness at multiple time-scales. In this paper, we observe that slow time-scale variations can cause sustained peaks in the source rate, substantially

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

1995-01-01

370

Modeling for scaling to humans: Time to get serious  

SciTech Connect

The subject matter for this 26th Annual Hanford Life Sciences Symposium evolved from the deliberations of a Task Group on Modeling for Scaling to Humans, which was established in January 1986 through the efforts of the Office of Health and Environmental Research of the Department of Energy (OHER/DOE). Several laboratories that utilize animals in radiobiological research sponsored by the OHER/DOE were extensively reviewed in the spring of 1985, and, as a result, OHER recommended establishment of eight task groups designed for selected purposes. The current membership of the Task Group on Modeling for Scaling to Humans is presented. Dr. James A. Mewhinney of the Lovelace Inhalation Toxicology Research Institute has been Chairman since these Task Groups were established. Ms. Judy Mahaffey of Battelle. Pacific Northwest Laboratories served as chairperson for this symposium, and the Task Group membership has served as the Program Committee. The OHER/DOE thanks all of them for their work as members of the Task Group as well as for their arranging such a potentially productive and informative meeting.

Thomas, R.G. (Department of Energy, Washington, DC (USA))

1989-01-01

371

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

372

Computational methods for time-scale analysis of nonlinear dynamical systems  

Microsoft Academic Search

Knowledge of the time-scale structure of a smooth finite dimensional nonlinear dynamical system provides the opportunity for model decomposition, if there are two or more disparate time-scales. A few benefits of such model decomposition are simplified control design and analysis and reduced computational effort in simulation. Singular perturbation theory provides the tools necessary to analyze and decompose a multiple time-scale

Shawn Iravanchy

2003-01-01

373

Singular perturbations and time scales (SPaTS) in discrete control systems-An overview  

NASA Technical Reports Server (NTRS)

Recent developments in the theory of singular perturbations and time scales (SPaTS) in discrete control systems are reviewed. Sources of discrete models and the effect of the discretizing interval on the model are examined. The analysis of two-time scale systems is presented to bring out typical characteristic features of SPaTS. In the control of the two-time scale systems, the important issue of multirate sampling is addressed.

Naidu, D. S.; Hibey, J. L.; Price, D. B.

1987-01-01

374

Horizontal Structure of 500 mb Height Fluctuations with Long, Intermediate and Short Time Scales  

Microsoft Academic Search

Maps of standard deviations and one-point correlation maps based on twice-daily data subjected to a variety of temporal filters are presented, in order to document the horizontal structure of 500 mb height fluctuations with different time scales. The filters have been chosen to isolate fluctuations with long time scales (periods much longer than 30 days), intermediate time scales (10-30 day

Maurice L. Blackmon; Y.-H. Lee; John M. Wallace

1984-01-01

375

Did an Impact Trigger the Permian-Triassic Extinction?  

NSDL National Science Digital Library

This resource, authored by David Morrison, contains the National Aeronautics and Space Administration's 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

2009-05-26

376

Triassic-Jurassic Mass Extinction: Evidence for Bolide Impact?  

Microsoft Academic Search

The Triassic-Jurassic (TJ) mass extinction event is one of the most severe in geologic history and is one of the five largest in the Phanerozoic with as many as 80% of the species lost. It is also one of the most poorly understood. Only a few geologic sections have been identified for the TJ extinction and most of those are

R. Perry; L. Becker; J. Haggart; R. Poreda

2003-01-01

377

Hamilton-Jacobi-Bellman equations and approximate dynamic programming on time scales.  

PubMed

The time scales calculus is a key emerging area of mathematics due to its potential use in a wide variety of multidisciplinary applications. We extend this calculus to approximate dynamic programming (ADP). The core backward induction algorithm of dynamic programming is extended from its traditional discrete case to all isolated time scales. Hamilton-Jacobi-Bellman equations, the solution of which is the fundamental problem in the field of dynamic programming, are motivated and proven on time scales. By drawing together the calculus of time scales and the applied area of stochastic control via ADP, we have connected two major fields of research. PMID:18632378

Seiffertt, John; Sanyal, Suman; Wunsch, Donald C

2008-08-01

378

Time scales of variability associated with Nordeste precipitation  

SciTech Connect

The Northeast section of Brazil, called the Nordeste, experiences flood and drought regimes as the norm rather than the exception. This region receives its principal dose of precipitation during March--April, subsequent to regions to the west and north due to its proximity to the southern Atlantic subtropical high. A weakening of this anticyclone and strengthening of its counterpart in the northern Atlantic during this season results in the farthest southward penetration of the ITCZ and the Nordeste rainy season. Fluctuations in the large-scale circulation of the atmosphere, such as ENSO, modulate the track of the ITCZ causing the interannual drought or flood conditions that plague this region. Empirical studies have shown that Nordeste rainfall is related to the sea-surface temperature (SST) in the tropical Atlantic Ocean. 16 refs., 4 figs.

Sperber, K.R. (Lawrence Livermore National Lab., CA (USA)); Hameed, S. (State Univ. of New York, Stony Brook, NY (USA). Inst. for Terrestrial and Planetary Atmospheres)

1991-06-01

379

Statistics of bedload transport over steep slopes: Separation of time scales and collective motion  

NASA Astrophysics Data System (ADS)

Steep slope streams show large fluctuations of sediment discharge across several time scales. These fluctuations may be inherent to the internal dynamics of the sediment transport process. A probabilistic framework thus seems appropriate to analyze such a process. In this paper, we present an experimental study of bedload transport over a steep slope flume for small to moderate Shields numbers. The sampling technique allows the acquisition of high-resolution time series of the solid discharge. The resolved time scales range from 10- 1 s up to 105 s. We show that two distinct time scales can be observed in the probability density function for the waiting time between moving particles. We make the point that the separation of time scales is related to collective dynamics. Proper statistics of a Markov process including collective entrainment are derived. The separation of time scales is recovered theoretically for low entrainment rates.

Heyman, J.; Mettra, F.; Ma, H. B.; Ancey, C.

2013-01-01

380

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

381

Time and length scales for diffusion in liquids.  

PubMed

The first six even moments of the displacement of a molecule in water and an atom in liquid argon are found by molecular dynamics simulations and compared with the moments predicted by diffusion theory. We find a noticeable difference between the moments higher than the second. The ratio between predicted and calculated moments approaches unity as 1/t for times larger than 10 ps. Continuous time random walk is used to explain this slow approach of the moments to their diffusion limit. PMID:12188692

Berezhkovskii, A M; Sutmann, G

2002-06-01

382

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

383

Time scales in the JPL and CfA ephemerides  

Microsoft Academic Search

Over the past decades, the IAU has repeatedly at- tempted to correct its definition of the basic fundamental argu- ment used in the ephemerides. Finally, they have defined a time system which is physically possible, according to the accepted standard theory of gravitation: TCB (\\

E. M. Standish

384

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

385

Space-time scales of internal waves: A progress report  

Microsoft Academic Search

We present a revised model for the distribution of internal wave energy in wave number frequency space. The model is empirical, guided by the following measurements: moored spectra and moored coherences for horizontal and vertical separations (MS, MHC, MVC as functions of frequency), towed spectra and towed vertical and time-lagged coherences (TS, TVC, TLC as functions of horizontal wave number),

Christopher Garrett; Walter Munk

1975-01-01

386

Time-Stepped Hybrid Simulation (TSHS) for Large Scale Networks  

Microsoft Academic Search

Data communication networks have been experienc- ing tremendous growth in size, complexity, and heterogeneity over the last decade. This trend poses a significant challenge to t he de- sign of scalable performance evaluation methodologies. In this paper we propose time-stepped hybrid simulation (TSHS) to deal with the scalability issue faced by traditional packet level dis- crete event simulation methods. TSHS

Yang Guo; Weibo Gong; Donald F. Towsley

2000-01-01

387

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

388

Astrobiology with haloarchaea from Permo-Triassic rock salt  

NASA Astrophysics Data System (ADS)

Several viable halophilic archaebacteria were isolated previously from rock salt of Permo-Triassic age in an Austrian salt mine; one of these strains was the first to be recognized as a novel species from subterranean halite and was designated Halococcus salifodinae. The halophilic microorganisms have apparently survived in the salt sediments over extremely long periods of time. Halobacteria could therefore be suitable model organisms for exploring the possibility of long-term survival of microbes on other planets, in particular, since extraterrestrial halite has been detected in meteorites and is assumed to be present in the subsurface ocean on Europa. Our efforts are directed at the identification of the microbial content of ancient rock salt and the development of procedures for the investigation of the halobacterial response to extreme environmental conditions. Using modified culture media, further halophilic strains were isolated from freshly blasted rock salt and bore cores; in addition, growth of several haloarchaea was substantially improved. Molecular methods indicated the presence of at least 12 different 16S rRNA gene species in a sample of Alpine rock salt, but these strains have not been cultured yet. The exploration of Mars is a target of space missions in the 21st century; therefore, testing the survival of haloarchaea under conditions comparable to present-day Mars, using a simulation chamber, was begun. Preliminary results with Halococcus and Halobacterium species suggested at least tenfold higher survival rates when cells were kept in liquid brines than under dry conditions; staining of cells with the LIVE DEAD kit, which discriminates between damaged and intact membranes, corroborated these data.

Stan-Lotter, H.; Radax, C.; Gruber, C.; Legat, A.; Pfaffenhuemer, M.; Wieland, H.; Leuko, S.; Weidler, G.; Kömle, N.; Kargl, G.

2002-10-01

389

The Pangea conundrum: Implications of new Paleomagnetic data from Permo-Triassic Araguainha Impact Crater (Central Brazil)  

NASA Astrophysics Data System (ADS)

This paper presents a new Permo-Triassic paleomagnetic pole for South America based on impact-related material from the Araguainha Dome. The relative position of southern and northern continents in Pangea between the Carboniferous and the Triassic has been a topic of intense debate for almost half a century, since when T. Irving has shown dramatic inconsistencies between the original A. Wegener's Pangea and the then-available paleomagnetic data. Recent compilations of paleomagnetic poles for both hemispheres of Pangea (Laurussia and Gondwana) seem to concur that part of those inconsistencies are related to the quality of the Carboniferous to Triassic paleomagnetic record and emphasize the urgent need for high-quality data for this time period. Permo-Triassic paleomagnetic data for South America were obtained mainly from sedimentary rocks, which are inherently affected by several recording problems such as inclination shallowing or remagnetization, also presenting large uncertainties in their ages. Thus, it is necessary to improve the database with paleomagnetic poles derived from igneous rocks carrying stable thermoremanent magnetization that can be easily dated. However, volcanic rocks are scarce for this time period at the central part of the continent. In this way, we targeted the well-dated melt impact material from the Araguainha dome. The Araguainha Dome is the biggest and oldest complex impact structure yet recognized in South America. It is 40 km wide and has excavated about 2500 meters of the sedimentary rocks of the Paraná basin, reaching the basement crystalline rocks. A multi-method dating of the impact melts provided a precise age for the impact at 254.7 ± 2.5 Ma overlapping the Permo-Triassic limit. The same impact-related melt sheets and dykes were sampled for paleomagnetic studies in 23 sites (138 specimens). Alternating field and thermal demagnetization indicate stable, usually univectorial magnetizations carried by magnetite and hematite. All sites but one show coherent directions along the same normal polarity with a resulting mean at Dec = 356.4°; Inc = -38.7°; N = 22; k = 95.6; ?95 = 3.2°, and a paleomagnetic pole at Lat= -83.7; Lon=340.2; K=87.6; A95=3.3°; SB=8.1°. The pole matches the apparent polar wander path built from a selection of high-quality poles from the West Gondwana (Domeier et al., 2012, Tectonophysics, doi:10.1016/j.tecto.2011.10.021). Our result provides a strong constraint on the position of Gondwana at the Permo-Triassic boundary and favors the Pangea A reconstruction.

Brandt, D.; Yokoyama, E.; Trindade, R. I.; Tohver, E.

2013-05-01

390

Crystallization time scales for polydisperse hard-sphere fluids  

NASA Astrophysics Data System (ADS)

We study the evolution of crystallization in dense mono- and polydisperse hard sphere fluids, initially quenched to an amorphous configuration. We use as signatures of crystallization both the decay of the reduced pressure Z and the increase in the local and global orientational order parameters Q¯6. For a given realization of the crystallization process these parameters show sudden changes, both large and small, separated by long periods of quiescence. However, averaging over a large number of realizations, a well-defined scenario for their evolution appears. We find an initial fast relaxation to a disordered state, followed by a period of slow variation, associated to the presence of nucleation events, followed by a fast change, composed of the growth of a few crystals with different orientations, and a final and slow coarsening in a domain-growth process. No clear scaling for this whole process was found. We also find that the transition to an stable glassy fluid is quite sharp as the polydispersity is increased, showing a probable first-order phase transition behavior. A well-defined boundary between crystallizing and permanently amorphous fluids should exist, at least for a region in packing fractions. We looked for segregation at large values of polydispersity, but no effects of this type were found.

Vargas, M. Cristina; Pérez-Ángel, Gabriel

2013-04-01

391

Time scales in rotating unstable Langevin-type dynamics.  

PubMed

In this Rapid Communication we propose a different and general characterization of rotating, unstable Langevin-type dynamics in the presence of an external force in the context of two dynamical representations x and y, using the passage time distribution. Here y is the transformed space of coordinates obtained by means of a time-dependent rotation matrix. The Langevin dynamics in the new y space defines an interesting concept of external force and internal noise due to rotation. The theory is applied to the characterization of rotational unstable systems of two (such as the laser system) and three variables, and stimulates its application in other fields, for instance, in plasma physics. PMID:11735880

Jiménez-Aquino, J I; Romero-Bastida, M

2001-11-01

392

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

NASA Astrophysics Data System (ADS)

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.

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

2010-02-01

393

Scaling up Self-Explanatory Simulators: Polynomial-time Compilation  

Microsoft Academic Search

Self-explanatory simulators have many potential applica­ tions, including supporting engineering activities, intelligent tutoring systems, and computer-based training systems. To fully realize this potential requires improving the technol­ ogy to efficiently generate highly optimized simulators. This paper describes an algorithm for compiling self- explanatory simulators that operates in polynomial time. It is capable of constructing self-explanatory simulators with thousands of parameters,

Kenneth D. Forbus; Brian Falkenhainer

1995-01-01

394

Does expressive timing in music performance scale proportionally with tempo?  

Microsoft Academic Search

Evidence is presented that expressive timing in music is not relationally invariant with global tempo. Our results stem from an analysis of repeated performances of Beethoven's variations on a Paisiello theme. Recordings were made of two pianists playing the pieces at three tempi. In contrast with the relational-invariance hypothesis (see Repp, 1994), between-tempo correlations were in general lower than within-tempo

Peter Desainl; Henkjan Honing

1994-01-01

395

IPS observations of short-time scale interplanetary activity  

Microsoft Academic Search

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

Pradeep Gothoskar; A. Pramesh Rao

1996-01-01

396

Cyclization of Rouse Chains at Long and Short Time Scales  

Microsoft Academic Search

We have investigated cyclization of a Rouse chain at long and short times by a Langevin dynamics simulation method. We measure S(t), the fraction of non-reacted chains, for chains lengths ranging from Z=5 to Z=800. Comparison is made with the closure approximations of Wilemski and Fixman and Doi and the renormalization group (RG) arguments of Friedman and O'Shaughnessy. The ratio

Chuck Yeung; Barry Friedman

2005-01-01

397

Cyclo-, magneto-, and bio-stratigraphic constraints on the duration of the CAMP event and its relationship to the Triassic-Jurassic boundary  

NASA Astrophysics Data System (ADS)

Early Mesozoic tholeiitic flood basalts of the Central Atlantic Magmatic Province (CAMP) are interbedded throughout much of their extent with cyclical lacustrine strata, allowing Milankovitch calibration of the duration of the extrusive episode. This cyclostratigraphy extends from the Newark basin of the northeastern US, where it was first worked out, to Nova Scotia and Morocco and constrains the outcropping extrusive event to less than 600 ky in duration, beginning roughly 20 ky after the Triassic-Jurassic boundary, and to within one pollen and spore zone and one vertebrate biochron. Based principally on the well-known Newark astronomically calibrated magnetic polarity time scale with new additions from the Hartford basin, the rather large scatter in recent radiometric dates from across CAMP (>10 m.y. ), centering on about ˜200 m.y., is not likely to be real. Rather, the existing paleomagnetic data from both intrusive and extrusive rocks suggest emplacement of nearly all the CAMP within less than 3 m.y. of nearly entirely normal polarity. The very few examples of reversed magnetizations suggest that some CAMP activity probably occurred just prior to the Triassic-Jurassic boundary. Published paleomagnetic and 40Ar/39Ar data from the Clubhouse Crossroads Basalt are reviewed and with new paleomagnetic data suggest that alteration and possible core misorientation could be responsible for the apparent differences with the CAMP. The Clubhouse Crossroads Basalt at the base of the Coastal Plain of South Carolina and Georgia provides a link to the volumetrically massive volcanic wedge of seaward dipping reflectors present in the subsurface off the southeastern US that may be part of the same igneous event, suggesting that the CAMP marks the formation of the oldest Atlantic oceanic crust.

Olsen, Paul E.; Kent, Dennis V.; Et-Touhami, Mohammed; Puffer, John

398

Multiscale Modeling and TimeScale Analysis of a Human Limb  

Microsoft Academic Search

A multi-scale modeling approach is proposed in this paper that assists the user in constructing musculoskeletal system models from sub-models describing various mechanisms on different levels on the length scale. In addition, dynamic time-scale analysis has been performed on the developed multi-scale models of various parts of a human limb: on wrist, elbow and shoulder characterized by different maximal muscle

Csaba Fazekas; ORGY KOZMANN; Katalin M. Hangos

2007-01-01

399

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

400

RAP: A Real-Time Communication Architecture for Large-Scale Wireless Sensor Networks.  

National Technical Information Service (NTIS)

Large-scale wireless sensor networks represent a new generation of real-time embedded systems with significantly different communication constraints from traditional networked systems. This paper presents RAP, a new real-time communication architecture fo...

C. Lu B. M. Blum T. F. Abdelzaher J. A. Stankovic T. He

2002-01-01

401

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)