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Sample records for inter-tropical convergence zone

  1. The ocean's role in setting the mean position of the Inter-Tropical Convergence Zone

    NASA Astrophysics Data System (ADS)

    Marshall, J.; Donohoe, A.; Ferreira, D.; McGee, D.

    2014-04-01

    Through study of observations and coupled climate simulations, it is argued that the mean position of the Inter-Tropical Convergence Zone (ITCZ) north of the equator is a consequence of a northwards heat transport across the equator by ocean circulation. Observations suggest that the hemispheric net radiative forcing of climate at the top of the atmosphere is almost perfectly symmetric about the equator, and so the total (atmosphere plus ocean) heat transport across the equator is small (order 0.2 PW northwards). Due to the Atlantic ocean's meridional overturning circulation, however, the ocean carries significantly more heat northwards across the equator (order 0.4 PW) than does the coupled system. There are two primary consequences. First, atmospheric heat transport is southwards across the equator to compensate (0.2 PW southwards), resulting in the ITCZ being displaced north of the equator. Second, the atmosphere, and indeed the ocean, is slightly warmer (by perhaps 2 °C) in the northern hemisphere than in the southern hemisphere. This leads to the northern hemisphere emitting slightly more outgoing longwave radiation than the southern hemisphere by virtue of its relative warmth, supporting the small northward heat transport by the coupled system across the equator. To conclude, the coupled nature of the problem is illustrated through study of atmosphere-ocean-ice simulations in the idealized setting of an aquaplanet, resolving the key processes at work.

  2. Inter-Tropical Convergence Zone Shifts During the Last Glacial Cycle Near the Line Islands Ridge.

    NASA Astrophysics Data System (ADS)

    Reimi Sipala, M. A.; Marcantonio, F.

    2015-12-01

    This research focuses on the shift in the inter-tropical convergence zone (ITCZ) during the last glacial cycle. Deep sea sediments from the Central Equatorial Pacific (CEP) are used to quantify and isolate the sources and sinks of atmospheric dust. Dust records and influences climate affecting a wide range of process from Earth's Albedo to carbon export. Our aim is to determine the provenance of windblown dust deposited in the CEP near the Line Islands Ridge using radiogenic Nd and Pb isotopes, and to infer the location of the ITCZ and the changes of atmospheric transport through ice-age climate transitions. We focus on three cores from the CEP, along a meridional transect at approximately 160° W --- 0° 28' N (ML1208-17PC), 4° 41' N (ML1208-31BB), and 7 ° 2'N (ML1208-31BB). Radiogenic isotopes (Sr, Nd, Pb) have been successfully used to distinguish between different potential dust sources in the aluminosilicates fractions of Pacific Sediments. Our preliminary data suggest that the equatorial core (17PC) predominantly receives its dust from South America and South American volcanics South America (206Pb/204Pb = 18.62, 207Pb/204Pb = 15.63, 208Pb/204Pb = 38.62; ; ɛNd = ~ -5). The middle core, which more closely reflects the modern position of the ITCZ, has varied dust provenance through time, at times consistent with Asian Loess (average ratios are 206Pb/204Pb = 18.88, 207Pb/204Pb = 15.69, 208Pb/204Pb = 39.06; ɛNd = ~ -7) and Asian Volcanics (ɛNd = ~-1) suggesting a shift in the ITCZ south of 4N before the LGM. Our results for the most northern core are forthcoming. Prior to Holocene time, the changes in Pb isotope ratios in both cores appear to be in anti-phase; the northern core becomes less radiogenic up to the LGM, while the southern core becomes more radiogenic. This is potentially due to a weakening of the ITCZ during glacial times. A secondary aim of this work is to determine if the ITCZ migrated further south than core 17PC during Heinrich stage II.

  3. The Inter-Tropical Convergence Zone: A causal mechanism for Pb isotope cyclicity in Tropical Atlantic sediment cores

    NASA Astrophysics Data System (ADS)

    Abouchami, W.; Zabel, M.

    2003-04-01

    Lead isotopic compositions of bulk sediment cores from the Tropical Atlantic can be used to infer variations in the provenance of terrigenous input to the Tropical Atlantic during Pleistocene climate cycles. Pb isotope data were obtained using the triple spike method (Galer, 1999) on bulk sediments cores and cover the last six Marine Isotope Stages. The 200-ka high precision (2σ ˜100 ppm) Pb isotope records of the Ceará Rise (Western Atlantic, core GeoB1523-1, 3^o49'N, 41^o37'W, 3292 m) and Sierra Leone Rise (Eastern Atlantic, core GeoB2910-1, 4^o50'N, 21^o03'W, 2703 m) cores show a clear glacial-interglacial cyclicity, reflected by alternating unradiogenic Pb and radiogenic Pb. Changes in the relative proportions of the glacial (unradiogenic) and interglacial (radiogenic) Pb source(s) can be explained by changes in the erosional regime (chemical vs. physical) as a function of prevailing climate, combined with different mechanisms of Pb transport to the oceans (predominantly eolian in the Eastern Atlantic vs. riverine in the Western Atlantic). We interpret these regional changes as reflecting shifts in the mean latitude of the Inter-Tropical Convergence Zone that affects the hydrological cycle over South America and the wind systems over Africa. Our results strongly favor an increase in winter wind transport (rather than glacial hyper aridity) as the cause of enhanced glacial terrigenous fluxes observed in the Tropical Atlantic (Ruddiman, 1997). The two Atlantic Pb isotopic records exhibit strong correlations with Pleistocene sea level fluctuations, providing evidence for global teleconnection between tropical records and high latitude climate. Galer, S.J.G. (1999). Optimal double and triple spiking for high precision lead isotopic measurements. Chem. Geol. 154, 255-274. Ruddiman, W. F. (1997). Tropical Atlantic terrigenous fluxes since 25,000 yrs B.P., Mar. Geol., 136, 189-207.

  4. Response of the Pacific inter-tropical convergence zone to global cooling and initiation of Antarctic glaciation across the Eocene Oligocene Transition.

    PubMed

    Hyeong, Kiseong; Kuroda, Junichiro; Seo, Inah; Wilson, Paul A

    2016-08-10

    Approximately 34 million years ago across the Eocene-Oligocene transition (EOT), Earth's climate tipped from a largely unglaciated state into one that sustained large ice sheets on Antarctica. Antarctic glaciation is attributed to a threshold response to slow decline in atmospheric CO2 but our understanding of the feedback processes triggered and of climate change on the other contents is limited. Here we present new geochemical records of terrigenous dust accumulating on the sea floor across the EOT from a site in the central equatorial Pacific. We report a change in dust chemistry from an Asian affinity to a Central-South American provenance that occurs geologically synchronously with the initiation of stepwise global cooling, glaciation of Antarctica and aridification on the northern continents. We infer that the inter-tropical convergence zone of intense precipitation extended to our site during late Eocene, at least four degrees latitude further south than today, but that it migrated northwards in step with global cooling and initiation of Antarctic glaciation. Our findings point to an atmospheric teleconnection between extratropical cooling and rainfall climate in the tropics and the mid-latitude belt of the westerlies operating across the most pivotal transition in climate state of the Cenozoic Era.

  5. Inter-model diversity of Arctic amplification caused by global warming and its relationship with the Inter-tropical Convergence Zone in CMIP5 climate models

    NASA Astrophysics Data System (ADS)

    Yim, Bo Young; Yeh, Sang-Wook; Kug, Jong-Seong

    2016-08-01

    Surface-based Arctic amplification (AA) has experienced a remarkable increase in recent decades. Therefore, it is important to understand how Arctic warming might change in response to global warming. By analyzing the Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model dataset, we examine how AA correlates with changes in tropical Pacific precipitation in response to global warming. It is found that that the changes in the latitudinal position of the Inter-tropical Convergence Zone (ITCZ) are associated to the simulated AA strength in the CMIP5 climate models. Specifically, AA tends to be stronger (weaker) in models where the ITCZ shifts relatively more northward (southward). Further analysis indicates that the inter-model diversity of AA strength in the CMIP5 climate models is related to the changes in large-scale atmospheric circulation associated with the meridional shift of the ITCZ. These results emphasize a close relationship between AA and changes in tropical Pacific precipitation in response to global warming.

  6. Response of the Pacific inter-tropical convergence zone to global cooling and initiation of Antarctic glaciation across the Eocene Oligocene Transition

    PubMed Central

    Hyeong, Kiseong; Kuroda, Junichiro; Seo, Inah; Wilson, Paul A.

    2016-01-01

    Approximately 34 million years ago across the Eocene–Oligocene transition (EOT), Earth’s climate tipped from a largely unglaciated state into one that sustained large ice sheets on Antarctica. Antarctic glaciation is attributed to a threshold response to slow decline in atmospheric CO2 but our understanding of the feedback processes triggered and of climate change on the other contents is limited. Here we present new geochemical records of terrigenous dust accumulating on the sea floor across the EOT from a site in the central equatorial Pacific. We report a change in dust chemistry from an Asian affinity to a Central-South American provenance that occurs geologically synchronously with the initiation of stepwise global cooling, glaciation of Antarctica and aridification on the northern continents. We infer that the inter-tropical convergence zone of intense precipitation extended to our site during late Eocene, at least four degrees latitude further south than today, but that it migrated northwards in step with global cooling and initiation of Antarctic glaciation. Our findings point to an atmospheric teleconnection between extratropical cooling and rainfall climate in the tropics and the mid-latitude belt of the westerlies operating across the most pivotal transition in climate state of the Cenozoic Era. PMID:27507793

  7. Response of the Pacific inter-tropical convergence zone to global cooling and initiation of Antarctic glaciation across the Eocene Oligocene Transition

    NASA Astrophysics Data System (ADS)

    Hyeong, Kiseong; Kuroda, Junichiro; Seo, Inah; Wilson, Paul A.

    2016-08-01

    Approximately 34 million years ago across the Eocene–Oligocene transition (EOT), Earth’s climate tipped from a largely unglaciated state into one that sustained large ice sheets on Antarctica. Antarctic glaciation is attributed to a threshold response to slow decline in atmospheric CO2 but our understanding of the feedback processes triggered and of climate change on the other contents is limited. Here we present new geochemical records of terrigenous dust accumulating on the sea floor across the EOT from a site in the central equatorial Pacific. We report a change in dust chemistry from an Asian affinity to a Central-South American provenance that occurs geologically synchronously with the initiation of stepwise global cooling, glaciation of Antarctica and aridification on the northern continents. We infer that the inter-tropical convergence zone of intense precipitation extended to our site during late Eocene, at least four degrees latitude further south than today, but that it migrated northwards in step with global cooling and initiation of Antarctic glaciation. Our findings point to an atmospheric teleconnection between extratropical cooling and rainfall climate in the tropics and the mid-latitude belt of the westerlies operating across the most pivotal transition in climate state of the Cenozoic Era.

  8. Response of the Pacific inter-tropical convergence zone to global cooling and initiation of Antarctic glaciation across the Eocene Oligocene Transition.

    PubMed

    Hyeong, Kiseong; Kuroda, Junichiro; Seo, Inah; Wilson, Paul A

    2016-01-01

    Approximately 34 million years ago across the Eocene-Oligocene transition (EOT), Earth's climate tipped from a largely unglaciated state into one that sustained large ice sheets on Antarctica. Antarctic glaciation is attributed to a threshold response to slow decline in atmospheric CO2 but our understanding of the feedback processes triggered and of climate change on the other contents is limited. Here we present new geochemical records of terrigenous dust accumulating on the sea floor across the EOT from a site in the central equatorial Pacific. We report a change in dust chemistry from an Asian affinity to a Central-South American provenance that occurs geologically synchronously with the initiation of stepwise global cooling, glaciation of Antarctica and aridification on the northern continents. We infer that the inter-tropical convergence zone of intense precipitation extended to our site during late Eocene, at least four degrees latitude further south than today, but that it migrated northwards in step with global cooling and initiation of Antarctic glaciation. Our findings point to an atmospheric teleconnection between extratropical cooling and rainfall climate in the tropics and the mid-latitude belt of the westerlies operating across the most pivotal transition in climate state of the Cenozoic Era. PMID:27507793

  9. Twin Convergence Zones

    NASA Technical Reports Server (NTRS)

    2002-01-01

    NASA's QuikSCAT satellite has confirmed a 30-year old largely unproven theory that there are two areas near the equator where the winds converge year after year and drive ocean circulation south of the equator. By analyzing winds, QuikSCAT has found a year-round southern and northern Intertropical Convergence Zone. This find is important to climate modelers and weather forecasters because it provides more detail on how the oceans and atmosphere interact near the equator. The Intertropical Convergence Zone (ITCZ) is the region that circles the Earth near the equator, where the trade winds of both the Northern and Southern Hemispheres come together. North of the equator, strong sun and warm water of the equator heats the air in the ITCZ, drawing air in from north and south and causing the air to rise. As the air rises it cools, releasing the accumulated moisture in an almost perpetual series of thunderstorms. Satellite data, however, has confirmed that there is an ITCZ north of the equator and a parallel ITCZ south of the equator. Variation in the location of the ITCZ is important to people around the world because it affects the north-south atmospheric circulation, which redistributes energy. It drastically affects rainfall in many equatorial nations, resulting in the wet and dry seasons of the tropics rather than the cold and warm seasons of higher latitudes. Longer term changes in the ITCZ can result in severe droughts or flooding in nearby areas. 'The double ITCZ is usually only identified in the Pacific and Atlantic Oceans on a limited and seasonal basis,' said Timothy Liu, of NASA's Jet Propulsion Laboratory and California Institute of Technology, Pasadena, Calif., and lead researcher on the project. In the eastern Pacific Ocean, the southern ITCZ is usually seen springtime. In the western Atlantic Ocean, the southern ITCZ was recently clearly identified only in the summertime. However, QuikSCAT's wind data has seen the southern ITCZ in all seasons across the

  10. Convergence Zone over the Patagonian Shelf

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The bright waters off the east coast of Argentina mark the convergence of the Malvinas and Brazil Currents. The interaction of the two currents brings nutrients from the dark ocean depths to the sunlit surface, resulting in dense blooms of phytoplankton, especially in the spring and early summer. The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) imaged the area on November 29, 2001. For more information, read Convergence Zones: Where the Action Is Image courtesy the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

  11. The 1977 intertropical convergence zone experiment

    NASA Technical Reports Server (NTRS)

    Poppoff, I. G. (Editor); Page, W. A. (Editor); Margozzi, A. P. (Editor)

    1979-01-01

    Data are presented from the 1977 Intertropical Convergence Zone (ITCZ) Experiment conducted in the Panama Canal Zone in July 1977. Measurements were made daily over a 16-day period when the ITCZ moved across the Canal Zone. Two aircraft (Learjet and U-2) flew daily and provided data from horizontal traverses at several altitudes to 21.3 km of ozone, temperature, pressure, water vapor, aerosols, fluorocarbons, methane, nitrous oxide, nitric oxide, and nitric acid. Balloonsondes flown four times per day provided data on ozone, wind fields, pressure, temperature, and humidities to altitudes near 30 km. Rocketsondes provided daily data to altitudes near 69 km. Satellite photography provided detailed cloud information. Descriptions of individual experiments and detailed compilations of all results are provided.

  12. Preferred latitudes of the intertropical convergence zone

    NASA Technical Reports Server (NTRS)

    Waliser, Duane E.; Somerville, C. J.

    1994-01-01

    The latitude preference of the intertropical convergence zone (ITCZ) is examined on the basis of observations, theory, and a modeling analysis. Observations show that convection is enhanced at latitudes of about 4 deg to 10 deg relative to the equator, even in regions where the sea surface temperature (SST) is maximum on the equator. Both linear shallow-water theory and a moist primitive equation model suggest a new explanation for the off-equatorial latitude preference of the ITCZ that requires neither the existence of zonally propagating disturbances nor an off-equatorial maximum in SST. The shallow-water theory indicates that a finite-width, zonally oriented, midtropospheric heat source (i.e., an ITCZ) produces the greatest local low-level convergence when placed a finite distance away from the equator. This result suggests that an ITCZ is most likely to be supported via low-level convergence of moist energy when located at these "preferred" latitudes away from the equator. For a plausible range of heating widths and damping parameters, the theoretically predicted latitude is approximately equal to the observed position (s) of the ITCZ (s). Analysis with an axially symmetric, moist, primitive equation model indicates that when the latent heating field is allowed to be determined internally, a positive feedback develops between the midtropospheric latent heating and the low-level convergence, with the effect of enhancing the organization of convection at latitudes of about 4 deg to 12 deg. Numerical experiments show that (1) two peaks in convective precipitation develop straddling the equator when the SST maximum is located on the equator; (2) steady ITCZ-like structures form only when the SST maximum is located away from the equator; and (3) peaks in convection can develop away from the maximum in SST, with a particular preference for latitudes of about 4 deg to 12 deg, even in the ('cold') hemisphere without the SST maximum. The relationship between this

  13. A Northward Shift of the North Atlantic Ocean Intertropical Convergence Zone in Response to Summertime Saharan Dust Outbreaks

    NASA Technical Reports Server (NTRS)

    Wilcox, Eric M.; Lau, K. M.; Kim, Kyu-Myong

    2010-01-01

    The influence on the summertime North Atlantic Ocean inter-tropical convergence zone (ITCZ) of Saharan dust outbreaks is explored using nine years of continuous satellite observations and atmospheric reanalysis products. During dust outbreak events rainfall along the ITCZ shifts northward by 1 to 4 degrees latitude. Dust outbreaks coincide with warmer lower-tropospheric temperatures compared to low dust conditions, which is attributable to advection of the warm Saharan Air Layer, enhanced subtropical subsidence, and radiative heating of dust. The enhanced positive meridional temperature gradient coincident with dust outbreaks is accompanied by an acceleration of the easterly winds on the n011h side of the African Easterly Jet (AEJ). The center of the positive vorticity region south of the AEJ moves north drawing the center of low-level convergence and ITCZ rainfall northward with it. The enhanced precipitation on the north side of the ITCZ occurs in spite of widespread sea surface temperature cooling north of the ITCZ owing to reduced surface solar insolation by dust scattering.

  14. Rainfall Morphology in Semi-Tropical Convergence Zones

    NASA Technical Reports Server (NTRS)

    Shepherd, J. Marshall; Ferrier, Brad S.; Ray, Peter S.

    2000-01-01

    Central Florida is the ideal test laboratory for studying convergence zone-induced convection. The region regularly experiences sea breeze fronts and rainfall-induced outflow boundaries. The focus of this study is the common yet poorly-studied convergence zone established by the interaction of the sea breeze front and an outflow boundary. Previous studies have investigated mechanisms primarily affecting storm initiation by such convergence zones. Few have focused on rainfall morphology yet these storms contribute a significant amount precipitation to the annual rainfall budget. Low-level convergence and mid-tropospheric moisture have both been shown to correlate with rainfall amounts in Florida. Using 2D and 3D numerical simulations, the roles of low-level convergence and mid-tropospheric moisture in rainfall evolution are examined. The results indicate that time-averaged, vertical moisture flux (VMF) at the sea breeze front/outflow convergence zone is directly and linearly proportional to initial condensation rates. This proportionality establishes a similar relationship between VMF and initial rainfall. Vertical moisture flux, which encompasses depth and magnitude of convergence, is better correlated to initial rainfall production than surface moisture convergence. This extends early observational studies which linked rainfall in Florida to surface moisture convergence. The amount and distribution of mid-tropospheric moisture determines how rainfall associated with secondary cells develop. Rainfall amount and efficiency varied significantly over an observable range of relative humidities in the 850- 500 mb layer even though rainfall evolution was similar during the initial or "first-cell" period. Rainfall variability was attributed to drier mid-tropospheric environments inhibiting secondary cell development through entrainment effects. Observationally, 850-500 mb moisture structure exhibits wider variability than lower level moisture, which is virtually always

  15. Eddies, streams, and convergence zones in turbulent flows

    NASA Technical Reports Server (NTRS)

    Hunt, J. C. R.; Wray, A. A.; Moin, P.

    1988-01-01

    Recent studies of turbulent shear flows have shown that many of their important kinematical and dynamical properties can be more clearly understood by describing the flows in terms of individual events or streamline patterns. These events or flow regions are studied because they are associated with relatively large contributions to certain average properties of the flow, for example kinetic energy, Reynolds stress, or to particular processes in the flow, such as mixing and chemical reactions, which may be concentrated at locations where streamlines converge for fast chemical reactions (referred to as convergence or C regions), or in recirculating eddying regions for slow chemical reactions. The aim of this project was to use the numerical simulations to develop suitable criteria for defining these eddying or vortical zones. The C and streaming (S) zones were defined in order to define the whole flow field. It is concluded that homogeneous and sheared turbulent flow fields are made up of characteristic flow zones: eddy, C, and S zones. A set of objective criteria were found which describe regions in which the streamlines circulate, converge or diverge, and form high streams of high velocity flow.

  16. Understanding the South Pacific Convergence Zone and Its Impacts

    NASA Astrophysics Data System (ADS)

    Power, Scott

    2011-02-01

    International Workshop on the South Pacific Convergence Zone; Apia, Samoa, 24-26 August 2010 ; During the Southern Hemisphere summer the South Pacific Convergence Zone (SPCZ) in the southwestern Pacific Ocean produces the largest rainfall band in the world. The SPCZ tends to move northeast during southern winter and El Niño and move southwest during southern summer and La Niña. These changes in position have a profound influence on climate (e.g., rainfall, winds, and tropical cyclone frequencies) and life in most of the nations in the southwestern Pacific. Despite the importance of the SPCZ to the region and its prominence in the general circulation of the Southern Hemisphere, the SPCZ has been studied relatively little compared with convergence zones in the Northern Hemisphere. An international workshop on the SPCZ was held in Samoa and brought together 30 experts from Australia, the Cook Islands, Fiji, France, India, New Caledonia, New Zealand, Samoa, the Solomon Islands, Tonga, Tuvalu, the United Kingdom, the United States, and Vanuatu.

  17. Migrations and dynamics of the intertropical convergence zone.

    PubMed

    Schneider, Tapio; Bischoff, Tobias; Haug, Gerald H

    2014-09-01

    Rainfall on Earth is most intense in the intertropical convergence zone (ITCZ), a narrow belt of clouds centred on average around six degrees north of the Equator. The mean position of the ITCZ north of the Equator arises primarily because the Atlantic Ocean transports energy northward across the Equator, rendering the Northern Hemisphere warmer than the Southern Hemisphere. On seasonal and longer timescales, the ITCZ migrates, typically towards a warming hemisphere but with exceptions, such as during El Niño events. An emerging framework links the ITCZ to the atmospheric energy balance and may account for ITCZ variations on timescales from years to geological epochs.

  18. The intertropical convergence zone of the eastern Pacific revisited

    NASA Astrophysics Data System (ADS)

    Hastenrath, Stefan

    2002-03-01

    The Intertropical Convergence Zone (ITCZ) complex over the eastern Pacific is re-examined from the NCEP-NCAR 40 year reanalysis and other data. Consistent with earlier work, the new analysis yields for July-August: a surface position of the near-equatorial wind confluence at 12°N; the cross-equatorial flow changing from divergent to convergent at the latitude of recurvature from southeasterly to southwesterly; strongest convergence in the surface layer to the south of the wind confluence, with this feeding vigorous ascending motion and compensating divergence in the upper troposphere; and the interface between cross-equatorial flow and northeast trades sloping southward at 1 : 1500. An easterly speed maximum in the mid troposphere over the equator is consistent with the 4 year rawin record at Galapagos. The new coarse-resolution dataset fails to capture a well-developed Intertropical Divergence Zone. The annual cycle features for the wind confluence and the ITCZ a position closest to the equator in February, a northward migration to June, southward shift in July and August, and a northernmost location in September. This behaviour is paralleled by maxima in the frequency of the Temporal weather systems and rainfall on the Pacific side of Central America in June and September. Regarding the climatic variability, with an anomalously far southerly position of the wind confluence, Central American rainfall tends to be deficient, and such a combination of departures is common in the warm phase of the southern oscillation. The long-term evolution is characterized by a warming trend of equatorial Pacific waters and weakening of cross-equatorial wind, while trends in the latitude position of the wind confluence and in Central American rainfall are not significant.

  19. Large deglacial shifts of the Pacific Intertropical Convergence Zone

    PubMed Central

    Jacobel, A. W.; McManus, J. F.; Anderson, R. F.; Winckler, G.

    2016-01-01

    The position of the Intertropical Convergence Zone (ITCZ) is sensitive to changes in the balance of heat between the hemispheres which has fundamental implications for tropical hydrology and atmospheric circulation. Although the ITCZ is thought to experience the largest shifts in position during deglacial stadial events, the magnitude of shifts has proven difficult to reconstruct, in part because of a paucity of high-resolution records, particularly those including spatial components. Here we track the position of the ITCZ from 150 to 110 ka at three sites in the central equatorial Pacific at sub-millennial time resolution. Our results provide evidence of large, abrupt changes in tropical climate during the penultimate deglaciation, coincident with North Atlantic Heinrich Stadial 11 (∼136–129 ka). We identify this event both as a Northern Hemisphere increase in aeolian dust and as a shift in the mean position of the ITCZ a minimum of 4° southwards at 160° W. PMID:26794654

  20. Large deglacial shifts of the Pacific Intertropical Convergence Zone.

    PubMed

    Jacobel, A W; McManus, J F; Anderson, R F; Winckler, G

    2016-01-01

    The position of the Intertropical Convergence Zone (ITCZ) is sensitive to changes in the balance of heat between the hemispheres which has fundamental implications for tropical hydrology and atmospheric circulation. Although the ITCZ is thought to experience the largest shifts in position during deglacial stadial events, the magnitude of shifts has proven difficult to reconstruct, in part because of a paucity of high-resolution records, particularly those including spatial components. Here we track the position of the ITCZ from 150 to 110 ka at three sites in the central equatorial Pacific at sub-millennial time resolution. Our results provide evidence of large, abrupt changes in tropical climate during the penultimate deglaciation, coincident with North Atlantic Heinrich Stadial 11 (∼136-129 ka). We identify this event both as a Northern Hemisphere increase in aeolian dust and as a shift in the mean position of the ITCZ a minimum of 4° southwards at 160° W. PMID:26794654

  1. Regional climate model projections of the South Pacific Convergence Zone

    NASA Astrophysics Data System (ADS)

    Evans, J. P.; Bormann, K.; Katzfey, J.; Dean, S.; Arritt, R.

    2016-08-01

    This study presents results from regional climate model (RCM) projections for the south-west Pacific Ocean. The regional models used bias corrected sea surface temperatures. Six global climate models (GCMs) were used to drive a global variable resolution model on a quasi-uniform 60 km grid. One of these simulations was used to drive three limited area regional models. Thus a four member ensemble was produced by different RCMs downscaling the same GCM (GFDL2.1), and a six member ensemble was produced by the same RCM (Conformal Cubic Atmospheric Model—CCAM) downscaling six different GCMs. Comparison of the model results with precipitation observations shows the differences to be dominated by the choice of RCM, with all the CCAM simulations performing similarly and generally having lower error than the other RCMs. However, evaluating aspects of the model representation of the South Pacific Convergence Zone (SPCZ) does not show CCAM to perform better in this regard. In terms of the future projections of the SPCZ for the December-January-February season, the ensemble showed no consensus change in most characteristics though a majority of the ensemble members project a decrease in the SPCZ strength. Thus, similar to GCM based studies, there is large uncertainty concerning future changes in the SPCZ and there is no evidence to suggest that future changes will be outside the natural variability. These RCM simulations do not support an increase in the frequency of zonal SPCZ events.

  2. The Formation of Cores of Giant Planets at Convergence Zones of Planetary Migration

    NASA Astrophysics Data System (ADS)

    Sirono, Sin-iti; Katayama, Masahumi

    2016-10-01

    The formation of solid cores in giant planets of mass ∼ 10 {M}\\oplus is numerically simulated following the scenario of Sándor et al. In this scenario, there are two convergence zones, corresponding to the outer and inner edges of the dead zone, where the torque exerted on planetary embryos by the gas nebula is zero. At the outer edge of the dead zone, anticyclonic vortices accumulate infalling dust aggregates, and planetary embryos are continuously formed in this scenario. We performed N-body simulations and show that massive objects of ≃ 10 {M}\\oplus are formed in ∼2.5 Myr, starting from the embryos. The largest object is formed at the inner convergence zone, although planetary embryos are placed at the outer convergence zone. This is due to the scattering of embryos from the outer to the inner convergence zone, and the shorter damping timescale of eccentricity at the inner convergence zone compared to the outer one. We varied the migration timescale due to the torque from gas by changing the gas surface density around the convergence zones. We found that there is a critical migration timescale below which 10 {M}\\oplus -sized objects are formed. Furthermore, we conducted simulations in which the gas surface density evolves according to viscous accretion. The largest object is also formed at the inner convergence zone irrespective of the strength of turbulence. Throughout the simulations, the location of the largest mass is the inner convergence zone. We confirmed that the formation timescale of a core of a Jovian planet can be explained in this scenario.

  3. Geophysical study of the structure and processes of the continental convergence zones: Alpine-Himalayan belt

    NASA Technical Reports Server (NTRS)

    Toksoz, M. N.; Molnar, P.

    1983-01-01

    Studies of the structure of the continental collision zones using seismic and body waves, theoretical modelling of the thermal regime of the convergence processes, and studies of earthquake mechanisms and deformation aspects of the model are covered.

  4. Architecture of orogenic belts and convergent zones in Western Ishtar Terra, Venus

    NASA Technical Reports Server (NTRS)

    Head, James W.; Vorderbruegge, R. W.; Crumpler, L. S.

    1989-01-01

    Linear mountain belts in Ishtar Terra were recognized from Pioneer-Venus topography, and later Arecibo images showed banded terrain interpreted to represent folds. Subsequent analyses showed that the mountains represented orogenic belts, and that each had somewhat different features and characteristics. Orogenic belts are regions of focused shortening and compressional deformation and thus provide evidence for the nature of such deformation, processes of crustal thickening (brittle, ductile), and processes of crustal loss. Such information is important in understanding the nature of convergent zones on Venus (underthrusting, imbrication, subduction), the implications for rates of crustal recycling, and the nature of environments of melting and petrogenesis. The basic elements of four convergent zones and orogenic belts in western Ishtar Terra are identified and examined, and then assess the architecture of these zones (the manner in which the elements are arrayed), and their relationships. The basic nomenclature of the convergent zones is shown.

  5. Characteristics of the convergence zone at the eastern edge of the Pacific warm pool

    NASA Astrophysics Data System (ADS)

    Maes, Christophe; Picaut, Joël; Kuroda, Yoshifumi; Ando, Kentaro

    2004-06-01

    The characteristics of the convergence zone at the eastern edge of the equatorial Pacific warm pool are studied using a compilation of in-situ current and salinity measurements during the period 1992-2001. The displacement of the convergence zone is observed, for the first time, as far west as 140°E in the far western Pacific, mainly during La Niña periods, and near 140°W in the central Pacific during the 1997-98 El Niño. The convergence zone may be associated with a salinity front dividing the fresh waters of the warm pool from the salty waters upwelled in the central equatorial Pacific. Despite a zonal displacement ranging over about one fifth of the equatorial circumference of the earth, the characteristics of the main parameters involved in the air-sea interactions are nearly constant on each side of the convergence zone/salinity front. These results suggest that coupled models used for El Niño research and forecasting should be able to reproduce these important features.

  6. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2005-09-01

    Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and

  7. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2005-09-01

    Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and

  8. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2005-04-01

    Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and

  9. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2005-06-01

    Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and

  10. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2005-08-01

    Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and

  11. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2005-05-01

    Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and

  12. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2005-01-01

    Call for Papers: Convergence

    Guest Editors: Thomas E. Darcie, University of Victoria Robert Doverspike, AT&T Martin Zirngibl, Lucent Technologies

    Coordinating Associate Editor: Steven K. Korotky, Lucent Technologies

    The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly

  13. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2004-12-01

    Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These

  14. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2005-03-01

    Call for Papers: Convergence Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and

  15. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2005-02-01

    Call for Papers: Convergence Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and

  16. Convergence

    NASA Astrophysics Data System (ADS)

    Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

    2005-01-01

    Call for Papers: Convergence

    Guest Editors: Thomas E. Darcie, University of Victoria Robert Doverspike, AT&T Martin Zirngibl, Lucent Technologies

    Coordinating Associate Editor: Steven K. Korotky, Lucent Technologies

    The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly

  17. Extension and gold mineralisation in the hanging walls of active convergent continental shear zones

    NASA Astrophysics Data System (ADS)

    Upton, Phaedra; Craw, Dave

    2014-07-01

    Orogenic gold-bearing quartz veins form in mountain belts adjacent to convergent tectonic boundaries. The vein systems, hosted in extensional structures within compressively deformed rocks, are a widespread feature of these orogens. In many cases the extensional structures that host gold-bearing veins have been superimposed on, and locally controlled by, compressional structures formed within the convergent orogen. Exploring these observations within the context of a three-dimensional mechanical model allows prediction of mechanisms and locations of extensional zones within convergent orogens. Our models explore the effect of convergence angle and mid-crustal strength on stress states and compare them to the Southern Alps and Taiwan. The dilatation zones coincide with the highest mountains, in the hanging walls of major plate boundary faults, and can extend as deep as the brittle-ductile transition. Extensional deformation is favoured in the topographic divide region of oblique orogens with mid-lower crustal rheology that promotes localisation rather than diffuse deformation. In the near surface, topography influences the stress state to a depth approximately equal to the topographic relief, bringing the rock closer to failure and rotating σ1 to near vertical. The distribution of gold-bearing extensional veins may indicate the general position of the topographic divide within exhumed ancient orogens.

  18. Geophysical study of the structure and processes of the continental convergence zones: Alpine-Himalayan Belt

    NASA Technical Reports Server (NTRS)

    Toksoez, M. N.

    1981-01-01

    The seismic wave velocity structure in the crust and upper mantle region beneath the Tibetan plateau was studied in detail. Also, a preliminary study of the uppermost mantle P wave velocity beneath Iran and Turkey was carried out, and the results are compared with those for the Tibetan plateau. These two studies compose the bulk of the efforts on the observational aspects of continental collision zones in addition to satellite derived data. On the theoretical aspects the thermal evolution of converging plate boundaries was explored using a finite difference scheme.

  19. Seismotectonics of the Eastern Himalayan System and Indo-Burman Convergence Zone Using Seismic Waveform Inversion

    NASA Astrophysics Data System (ADS)

    Kumar, A.; Mitra, S.; Suresh, G.

    2014-12-01

    The Eastern Himalayan System (east of 88°E) is distinct from the rest of the India-Eurasia continental collision, due to a wider zone of distributed deformation, oblique convergence across two orthogonal plate boundaries and near absence of foreland basin sedimentary strata. To understand the seismotectonics of this region we study the spatial distribution and source mechanism of earthquakes originating within Eastern Himalaya, northeast India and Indo-Burman Convergence Zone (IBCZ). We compute focal mechanism of 32 moderate-to-large earthquakes (mb >=5.4) by modeling teleseismic P- and SH-waveforms, from GDSN stations, using least-squares inversion algorithm; and 7 small-to-moderate earthquakes (3.5<= mb <5.4) by modeling local P- and S-waveforms, from the NorthEast India Telemetered Network, using non-linear grid search algorithm. We also include source mechanisms from previous studies, either computed by waveform inversion or by first motion polarity from analog data. Depth distribution of modeled earthquakes reveal that the seismogenic layer beneath northeast India is ~45km thick. From source mechanisms we observe that moderate earthquakes in northeast India are spatially clustered in five zones with distinct mechanisms: (a) thrust earthquakes within the Eastern Himalayan wedge, on north dipping low angle faults; (b) thrust earthquakes along the northern edge of Shillong Plateau, on high angle south dipping fault; (c) dextral strike-slip earthquakes along Kopili fault zone, between Shillong Plateau and Mikir Hills, extending southeast beneath Naga Fold belts; (d) dextral strike-slip earthquakes within Bengal Basin, immediately south of Shillong Plateau; and (e) deep focus (>50 km) thrust earthquakes within IBCZ. Combining with GPS geodetic observations, it is evident that the N20E convergence between India and Tibet is accommodated as elastic strain both within eastern Himalaya and regions surrounding the Shillong Plateau. We hypothesize that the strike

  20. Atlanta ariejansseni, a new species of shelled heteropod from the Southern Subtropical Convergence Zone (Gastropoda, Pterotracheoidea)

    PubMed Central

    Wall-Palmer, Deborah; Burridge, Alice K.; Peijnenburg, Katja T.C.A.

    2016-01-01

    Abstract The Atlantidae (shelled heteropods) is a family of microscopic aragonite shelled holoplanktonic gastropods with a wide biogeographical distribution in tropical, sub-tropical and temperate waters. The aragonite shell and surface ocean habitat of the atlantids makes them particularly susceptible to ocean acidification and ocean warming, and atlantids are likely to be useful indicators of these changes. However, we still lack fundamental information on their taxonomy and biogeography, which is essential for monitoring the effects of a changing ocean. Integrated morphological and molecular approaches to taxonomy have been employed to improve the assessment of species boundaries, which give a more accurate picture of species distributions. Here a new species of atlantid heteropod is described based on shell morphology, DNA barcoding of the Cytochrome Oxidase I gene, and biogeography. All specimens of Atlanta ariejansseni sp. n. were collected from the Southern Subtropical Convergence Zone of the Atlantic and Indo-Pacific oceans suggesting that this species has a very narrow latitudinal distribution (37–48°S). Atlanta ariejansseni sp. n. was found to be relatively abundant (up to 2.3 specimens per 1000 m3 water) within this narrow latitudinal range, implying that this species has adapted to the specific conditions of the Southern Subtropical Convergence Zone and has a high tolerance to the varying ocean parameters in this region. PMID:27551204

  1. Atlanta ariejansseni, a new species of shelled heteropod from the Southern Subtropical Convergence Zone (Gastropoda, Pterotracheoidea).

    PubMed

    Wall-Palmer, Deborah; Burridge, Alice K; Peijnenburg, Katja T C A

    2016-01-01

    The Atlantidae (shelled heteropods) is a family of microscopic aragonite shelled holoplanktonic gastropods with a wide biogeographical distribution in tropical, sub-tropical and temperate waters. The aragonite shell and surface ocean habitat of the atlantids makes them particularly susceptible to ocean acidification and ocean warming, and atlantids are likely to be useful indicators of these changes. However, we still lack fundamental information on their taxonomy and biogeography, which is essential for monitoring the effects of a changing ocean. Integrated morphological and molecular approaches to taxonomy have been employed to improve the assessment of species boundaries, which give a more accurate picture of species distributions. Here a new species of atlantid heteropod is described based on shell morphology, DNA barcoding of the Cytochrome Oxidase I gene, and biogeography. All specimens of Atlanta ariejansseni sp. n. were collected from the Southern Subtropical Convergence Zone of the Atlantic and Indo-Pacific oceans suggesting that this species has a very narrow latitudinal distribution (37-48°S). Atlanta ariejansseni sp. n. was found to be relatively abundant (up to 2.3 specimens per 1000 m(3) water) within this narrow latitudinal range, implying that this species has adapted to the specific conditions of the Southern Subtropical Convergence Zone and has a high tolerance to the varying ocean parameters in this region.

  2. Atlanta ariejansseni, a new species of shelled heteropod from the Southern Subtropical Convergence Zone (Gastropoda, Pterotracheoidea).

    PubMed

    Wall-Palmer, Deborah; Burridge, Alice K; Peijnenburg, Katja T C A

    2016-01-01

    The Atlantidae (shelled heteropods) is a family of microscopic aragonite shelled holoplanktonic gastropods with a wide biogeographical distribution in tropical, sub-tropical and temperate waters. The aragonite shell and surface ocean habitat of the atlantids makes them particularly susceptible to ocean acidification and ocean warming, and atlantids are likely to be useful indicators of these changes. However, we still lack fundamental information on their taxonomy and biogeography, which is essential for monitoring the effects of a changing ocean. Integrated morphological and molecular approaches to taxonomy have been employed to improve the assessment of species boundaries, which give a more accurate picture of species distributions. Here a new species of atlantid heteropod is described based on shell morphology, DNA barcoding of the Cytochrome Oxidase I gene, and biogeography. All specimens of Atlanta ariejansseni sp. n. were collected from the Southern Subtropical Convergence Zone of the Atlantic and Indo-Pacific oceans suggesting that this species has a very narrow latitudinal distribution (37-48°S). Atlanta ariejansseni sp. n. was found to be relatively abundant (up to 2.3 specimens per 1000 m(3) water) within this narrow latitudinal range, implying that this species has adapted to the specific conditions of the Southern Subtropical Convergence Zone and has a high tolerance to the varying ocean parameters in this region. PMID:27551204

  3. Influence of the inter tropical discontinuity on Harmattan dust deposition in Ghana

    NASA Astrophysics Data System (ADS)

    Lyngsie, G.; Olsen, J. L.; Awadzi, T. W.; Fensholt, R.; Breuning-Madsen, H.

    2013-09-01

    The Harmattan is a dry dust-laden continental wind, and in the boreal winter Harmattan dust plumes affects many West African countries, including Ghana. When the Harmattan is strongest the southern part of Ghana is affected by the Inter Tropical Discontinuity (ITD). In this study, we investigate if the ITD functions as a barrier, preventing long transported Harmattan dust to settle south of, and below, it. This is done by analyzing a Harmattan dust outbreak, mapped using Earth observation (EO) data from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard the Meteosat Second Generation (MSG) platform, coupled with data from West African AERONET stations, and comparing these observations with wind data from NOAA's Air Resources Laboratory (ARL) program and the mineral suite of samples from seasonal dust deposits in north and south Ghana. In northern Ghana traces of minerals indicate a weak influence of particles from an arid environment, which is found consistent with the mapped dust plumes and NE wind directions. In southern Ghana the mineral composition show no sediments of an arid origin, the mapped dust plumes is less intense, and the surface wind directions and wind mass trajectories are more varying with lower wind speeds. Based on the results of this study it is concluded that dust deposited, or measured near ground, in the Harmattan period under the ITD, and south of it, does not contain material from the Chad Basin due to the local winds conditions.

  4. Tracking the extent of the South Pacific Convergence Zone since the early 1600s

    NASA Astrophysics Data System (ADS)

    Linsley, Braddock K.; Kaplan, Alexey; Gouriou, Yves; Salinger, Jim; Demenocal, Peter B.; Wellington, Gerard M.; Howe, Stephen S.

    2006-05-01

    The South Pacific Convergence Zone (SPCZ) is the largest and most persistent spur of the Intertropical Convergence Zone. At the southeastern edge of the SPCZ near 170°W and 15°-20°S a surface ocean salinity frontal zone exists that separates fresher Western Pacific Warm Pool water from saltier and cooler waters in the east. This salinity front is known to shift east and west with the phase of the El Niño Southern Oscillation. We have generated subannually resolved and replicated coral oxygen isotopic time series from Fiji (17°S, 179°E) and Rarotonga (21.5°S, 160°W) that have recorded interannual displacements of the salinity front over the last 380 years and also indicate that at lower frequencies the decadal mean position of the salinity front, and eastern extent of the SPCZ, has shifted east-west through 10° to 20° of longitude three times during this interval. The most recent and largest shift began in the mid 1800s as the salinity front progressively moved eastward and salinity decreased at both sites. Our results suggest that sea surface salinity at these sites is now at the lowest levels recorded and is evidence for an unprecedented expansion of the SPCZ since the mid 1800s. The expansion of the SPCZ implies a gradual change in the South Pacific to more La Niña-like long-term mean conditions. This observation is consistent with the ocean thermostat mechanism for the Pacific coupled ocean-atmosphere system, whereby exogenous heating of the atmosphere would result in greater warming in the western Pacific and a greater east-west surface temperature gradient.

  5. Spatial evolution of Zagros collision zone in Kurdistan, NW Iran: constraints on Arabia-Eurasia oblique convergence

    NASA Astrophysics Data System (ADS)

    Sadeghi, Shahriar; Yassaghi, Ali

    2016-04-01

    Stratigraphy, detailed structural mapping and a crustal-scale cross section across the NW Zagros collision zone provide constraints on the spatial evolution of oblique convergence of the Arabian and Eurasian plates since the Late Cretaceous. The Zagros collision zone in NW Iran consists of the internal Sanandaj-Sirjan, Gaveh Rud and Ophiolite zones and the external Bisotoun, Radiolarite and High Zagros zones. The Main Zagros Thrust is the major structure of the Zagros suture zone. Two stages of oblique deformation are recognized in the external part of the NW Zagros in Iran. In the early stage, coexisting dextral strike-slip and reverse dominated domains in the Radiolarite zone developed in response to deformation partitioning due to oblique convergence. Dextral-reverse faults in the Bisotoun zone are also compatible with oblique convergence. In the late stage, deformation partitioning occurred during southeastward propagation of the Zagros orogeny towards its foreland resulting in synchronous development of orogen-parallel strike-slip and thrust faults. It is proposed that the first stage was related to Late Cretaceous oblique obduction, while the second stage resulted from Cenozoic collision. The Cenozoic orogen-parallel strike-slip component of Zagros oblique convergence is not confined to the Zagros suture zone (Main Recent Fault) but also occurred in the external part (Marekhil-Ravansar fault system). Thus, it is proposed that oblique convergence of Arabian and Eurasian plates in Zagros collision zone initiated with oblique obduction in the Late Cretaceous followed by oblique collision in the late Tertiary, consistent with global plate reconstructions.

  6. Tracking the extent of the South Pacific Convergence Zone since 1619 AD

    NASA Astrophysics Data System (ADS)

    Linsley, B. K.; Kaplan, A.; Gouriou, Y.; Salinger, J.; Demenocal, P. B.; Wellington, G. M.; Howe, S. S.

    2005-12-01

    Enhanced convection and rainfall in the oceanic sectors of the Intertropical Convergence Zone (ITCZ) is one of the predicted outcomes of increasing greenhouse gas emissions and rising average global temperatures. However due to the current limited understanding of the past extent and variability of the convergence zones prior to ~1900, it has not been possible to determine pre-anthropogenic ``baseline'' convergence zone variability in order to test these predictions. Here we examine the past extent and variability of the South Pacific Convergence Zone (SPCZ), the largest and most persistent spur of the ITCZ, using multiple cores from massive coral colonies extending back to 1619. At the southeastern edge of the SPCZ near 170°W and 15°-20°S a surface ocean salinity frontal zone exists that separates fresher Western Pacific Warm Pool water from saltier and cooler waters in the east. Previous analysis of instrumental sea surface temperature (SST), sea surface salinity (SSS), and precipitation records in the SPCZ - SSS front region beginning in 1976 indicate that the amplitudes of the interannual signals in SST and precipitation are an order of magnitude less than the amplitude of the seasonal cycle, whereas for SSS, the interannual signal of 1 to 1.5 p.s.u. is double the amplitude of the seasonal signal. This analysis confirms that in the SPCZ region, SSS is higher and SST and precipitation are lower during El Niño events. The opposite occurs during La Niña events. We have generated sub-annually resolved and replicated coral oxygen isotopic time-series from Fiji (17°S, 179°E) and Rarotonga (21.5°S, 160°W) that record this same relationship between annual SST and interannual SSS. Calibration of the trends in these oxygen isotope records against instrumental SST and coral Sr/Ca from Fiji demonstrates that at lower frequencies the decadal mean position of the salinity front, and eastern extent of the SPCZ, has shifted east-west through 10° to 20° of longitude

  7. Spatial evolution of Zagros collision zone in Kurdistan - NW Iran, constraints for Arabia-Eurasia oblique convergence

    NASA Astrophysics Data System (ADS)

    Sadeghi, S.; Yassaghi, A.

    2015-09-01

    Stratigraphy, detailed structural mapping and crustal scale cross section of the NW Zagros collision zone evolved during convergence of the Arabian and Eurasian plates were conducted to constrain the spatial evolution of the belt oblique convergence since Late Cretaceous. Zagros orogeny in NW Iran consists of the Sanandaj-Sirjan, Gaveh Rud and ophiolite zones as internal, and Bisotoun, Radiolarite and High Zagros zones as external parts. The Main Zagros Thrust is known as major structures of the Zagros suture zone. Two stages of deformation are recognized in the external parts of Zagros. In the early stage, presence of dextrally deformed domains beside the reversely deformed domains in the Radiolarite zone as well as dextral-reverse faults in both Bisotoun and Radiolarite zones demonstrates partitioning of the dextral transpression. In the late stage, southeastward propagation of the Zagros orogeny towards its foreland resulted in synchronous development of orogen-parallel strike-slip and pure thrust faults. It is proposed that the first stage related to the late Cretaceous oblique obduction, and the second stage is resulted from Cenozoic collision. Cenozoic orogen-parallel strike-slip component of Zagros oblique faulting is not confined to the Zagros suture zone (Main Recent) but also occurred in the more external part (Marekhil-Ravansar fault system). Thus, it is proposed that oblique convergence of Arabia-Eurasia plates occurred in Zagros collision zone since the Late Cretaceous.

  8. Obliquity pacing of the western Pacific Intertropical Convergence Zone over the past 282,000 years.

    PubMed

    Liu, Yi; Lo, Li; Shi, Zhengguo; Wei, Kuo-Yen; Chou, Chien-Ju; Chen, Yi-Chi; Chuang, Chih-Kai; Wu, Chung-Che; Mii, Horng-Sheng; Peng, Zicheng; Amakawa, Hiroshi; Burr, George S; Lee, Shih-Yu; DeLong, Kristine L; Elderfield, Henry; Shen, Chuan-Chou

    2015-01-01

    The Intertropical Convergence Zone (ITCZ) encompasses the heaviest rain belt on the Earth. Few direct long-term records, especially in the Pacific, limit our understanding of long-term natural variability for predicting future ITCZ migration. Here we present a tropical precipitation record from the Southern Hemisphere covering the past 282,000 years, inferred from a marine sedimentary sequence collected off the eastern coast of Papua New Guinea. Unlike the precession paradigm expressed in its East Asian counterpart, our record shows that the western Pacific ITCZ migration was influenced by combined precession and obliquity changes. The obliquity forcing could be primarily delivered by a cross-hemispherical thermal/pressure contrast, resulting from the asymmetric continental configuration between Asia and Australia in a coupled East Asian-Australian circulation system. Our finding suggests that the obliquity forcing may play a more important role in global hydroclimate cycles than previously thought. PMID:26602034

  9. Response of the intertropical convergence zone to zonally asymmetric subtropical surface forcings

    NASA Astrophysics Data System (ADS)

    Shaw, Tiffany A.; Voigt, Aiko; Kang, Sarah M.; Seo, Jeongbin

    2015-11-01

    The energetic framework predicts no shift of the zonal mean Intertropical Convergence Zone (ITCZ) in response to zonally asymmetric forcings (zonal warming and cooling regions with zero zonal mean) assuming radiative feedbacks are linear. Here we show the ITCZ shifts southward in response to a zonally asymmetric forcing in the Northern Hemisphere subtropics in a slab ocean aquaplanet model. The southward shift is consistent with decreased zonal mean energy input to the atmosphere due to cloud radiative effect changes in the cooling region. When cloud-radiative feedbacks are disabled the ITCZ shifts northward consistent with changes in the warming region where increased energy input via surface heat fluxes and stationary Rossby-wave transport dominate. Competition between cooling and warming regions leads to changes in gross moist stability. Our results show rectification of zonally asymmetric forcings play an important role in zonal mean ITCZ dynamics and highlight the importance of assessing the momentum budget when interpreting ITCZ shifts.

  10. Relative influences of the Interdecadal Pacific Oscillation and ENSO on the South Pacific Convergence Zone

    NASA Astrophysics Data System (ADS)

    Folland, C. K.; Renwick, J. A.; Salinger, M. J.; Mullan, A. B.

    2002-07-01

    The South Pacific Convergence Zone (SPCZ), one of the most extensive features of the global atmospheric circulation, is shown to vary its location according to both the polarity of the El Niño/Southern Oscillation (ENSO), and of the Interdecadal Pacific Oscillation (IPO). We first demonstrate that the IPO can be regarded as the quasi-symmetric Pacific-wide manifestation of the Pacific Decadal Oscillation that has been described for the North Pacific. Shifts in the position of the SPCZ related to ENSO on interannual time scales and to the IPO on decadal time scales appear to be of similar magnitude and are largely linearly independent. A station pressure-based index of variations in SPCZ latitude is shown to be significantly related to the polarity of the IPO when ENSO influences are accounted for. Movements of this sensitive section of the SPCZ have occurred in phase with those of the IPO since the 1890s.

  11. Obliquity pacing of the western Pacific Intertropical Convergence Zone over the past 282,000 years

    PubMed Central

    Liu, Yi; Lo, Li; Shi, Zhengguo; Wei, Kuo-Yen; Chou, Chien-Ju; Chen, Yi-Chi; Chuang, Chih-Kai; Wu, Chung-Che; Mii, Horng-Sheng; Peng, Zicheng; Amakawa, Hiroshi; Burr, George S.; Lee, Shih-Yu; DeLong, Kristine L.; Elderfield, Henry; Shen, Chuan-Chou

    2015-01-01

    The Intertropical Convergence Zone (ITCZ) encompasses the heaviest rain belt on the Earth. Few direct long-term records, especially in the Pacific, limit our understanding of long-term natural variability for predicting future ITCZ migration. Here we present a tropical precipitation record from the Southern Hemisphere covering the past 282,000 years, inferred from a marine sedimentary sequence collected off the eastern coast of Papua New Guinea. Unlike the precession paradigm expressed in its East Asian counterpart, our record shows that the western Pacific ITCZ migration was influenced by combined precession and obliquity changes. The obliquity forcing could be primarily delivered by a cross-hemispherical thermal/pressure contrast, resulting from the asymmetric continental configuration between Asia and Australia in a coupled East Asian–Australian circulation system. Our finding suggests that the obliquity forcing may play a more important role in global hydroclimate cycles than previously thought. PMID:26602034

  12. Evidence for self-refraction in a convergence zone: NPE (Nonlinear progressive wave equation) model results

    NASA Technical Reports Server (NTRS)

    Mcdonald, B. Edward; Plante, Daniel R.

    1989-01-01

    The nonlinear progressive wave equation (NPE) model was developed by the Naval Ocean Research and Development Activity during 1982 to 1987 to study nonlinear effects in long range oceanic propagation of finite amplitude acoustic waves, including weak shocks. The NPE model was applied to propagation of a generic shock wave (initial condition provided by Sandia Division 1533) in a few illustrative environments. The following consequences of nonlinearity are seen by comparing linear and nonlinear NPE results: (1) a decrease in shock strength versus range (a well-known result of entropy increases at the shock front); (2) an increase in the convergence zone range; and (3) a vertical meandering of the energy path about the corresponding linear ray path. Items (2) and (3) are manifestations of self-refraction.

  13. 3D Thermochemical Numerical Model of a Convergent Zone With an Overriding Plate

    NASA Astrophysics Data System (ADS)

    Mason, W. G.; Moresi, L.; Betts, P. G.

    2008-12-01

    We have created a new three dimensional thermochemical numerical model of a convergent zone, in which a viscoplastic oceanic plate subducts beneath a viscous overriding plate, using the finite element Geoscience research code Underworld. Subduction is initiated by mantle flow induced by the gravitational instability of a slab tip, and buoyancy of the overriding plate. A cold thermal boundary layer envelopes both plates, and is partially dragged into the mantle along with the subducting slab. The trench rolls back as the slab subducts, and the overriding plate follows the retreating trench without being entrained into the upper mantle. The model is repeated with the overriding plate excluded, to analyse the influence of the overriding plate. The overriding plate retards the rate of subduction. Maximum strain rates, evident along the trench in the absence of an overriding plate, extend to a greater depth within the subducted portion of the slab in the presence of an overriding plate.

  14. Airborne pressure and temperature measurements during the 1977 intertropical convergence zone experiment

    NASA Technical Reports Server (NTRS)

    Munoz, R. M.

    1979-01-01

    During the 1977 ITCZ (Intertropical Convergence Zone) experiment in Panama two aircraft and numerous balloon-borne radiosonde instruments were equipped to measure pressure and temperature. The experiment was a coordinated effort to evaluate the meteorological conditions that prevailed from July 17 through 31, 1977. A critical analysis of the data collected on one of the aircraft (the Lear jet) operating at altitudes to 13,000 m for about 2 hr each day during most days of the experiment is presented. The discussion includes a comparison of the vertical profiles of potential temperature obtained from the Learjet with those obtained from balloons launched at Ft. Sherman. Time histories of pressure, temperature, and potential temperature, as observed from the Learjet are also presented.

  15. Obliquity pacing of the western Pacific Intertropical Convergence Zone over the past 282,000 years.

    PubMed

    Liu, Yi; Lo, Li; Shi, Zhengguo; Wei, Kuo-Yen; Chou, Chien-Ju; Chen, Yi-Chi; Chuang, Chih-Kai; Wu, Chung-Che; Mii, Horng-Sheng; Peng, Zicheng; Amakawa, Hiroshi; Burr, George S; Lee, Shih-Yu; DeLong, Kristine L; Elderfield, Henry; Shen, Chuan-Chou

    2015-01-01

    The Intertropical Convergence Zone (ITCZ) encompasses the heaviest rain belt on the Earth. Few direct long-term records, especially in the Pacific, limit our understanding of long-term natural variability for predicting future ITCZ migration. Here we present a tropical precipitation record from the Southern Hemisphere covering the past 282,000 years, inferred from a marine sedimentary sequence collected off the eastern coast of Papua New Guinea. Unlike the precession paradigm expressed in its East Asian counterpart, our record shows that the western Pacific ITCZ migration was influenced by combined precession and obliquity changes. The obliquity forcing could be primarily delivered by a cross-hemispherical thermal/pressure contrast, resulting from the asymmetric continental configuration between Asia and Australia in a coupled East Asian-Australian circulation system. Our finding suggests that the obliquity forcing may play a more important role in global hydroclimate cycles than previously thought.

  16. Sahelian dust lifting in the inter-tropical discontinuity region: Lidar observations and mesoscale modelling

    NASA Astrophysics Data System (ADS)

    Bou Karam, D.; Flamant, C.; Tulet, P.; Chaboureau, J.; Dabas, A.; Chong, M.; Reitebuch, O.

    2007-12-01

    Airbone lidar observations acquired with the LEANDRE 2 system during 3 flights of the SAFIRE Falcon 20 in the framework of the AMMA Special Observing Period (SOP) 2a1 (July 2006) over western Niger, revealed the existence of desert dust uptakes in the region of the inter-tropical discontinuity (ITD) in the morning hours. Complementary observations provided by dropsondes released from the same platform as well as airborne wind measurements made from another platform (the DLR Falcon 20, flying in coordination with the SAFIRE Falcon 20) evidenced that the lifting was associated with the leading edge of the monsoon low level jet, and to be transported southward by the harmattan, above the monsoon layer. A 10-day numerical simulation, using the mesoscale model Meso-NH (including the dust emission box Dust Entrainment And Deposition model), was conducted to assess the representativity of the observed phenomenon as well as the mechanisms associated with the Sahelian dust emissions. The Meso-NH simulation (initialized by and nudged with ECMWF analyses) was carried out on a 2000 km x 2000 km domain (20-km horizontal resolution) centered at 20°N and 7°E, that included the Falcons flight track, as well as numerous AMMA-related ground-based measurement sites (Tamanrasset, Agadez, Niamey/Banizoumbou, etc..) for validation purposes. In the simulation, large dust uptakes associated with the leading edge of the monsoon flow, with a dust concentration reaching 2000μg/m3, and to be transported southward by the harmattan, above the monsoon layer, were well reproduced. On the other hand, the simulation suggested the existence of dust emissions associated with the harmattan flow which were not observed by airborne lidar measurements. The reason for the discrepancy between the model results and the lidar observations is investigated.

  17. Characterization of the variability of the South Pacific Convergence Zone using satellite and reanalysis wind products

    NASA Astrophysics Data System (ADS)

    Kidwell, Autumn; Lee, Tong; Jo, Young-Heon; Yan, Xiao-hai

    2016-04-01

    The South Pacific Convergence Zone (SPCZ), the largest rain band worldwide during austral summer, is important to atmospheric circulation (including cyclone genesis) and ocean circulation. Previous studies of the SPCZ have focused on parameters such as outgoing longwave radiation or precipitation. However, wind convergence is fundamental causing the variations of these parameters. In this study, the SPCZ variability is examined using ocean surface wind products derived from NASA's QuickSCAT (1999-2009) and ESA's ASCAT (2007 onward) satellite scatterometers and ERA-Interim atmospheric reanalysis (1981 onward). From these products, indices were developed to characterize the SPCZ strength, area, and centroid location. Excellent agreement is found in terms of the temporal variations of the indices derived from the satellites and reanalysis wind products, despite some small differences in the time-mean SPCZ strength. The SPCZ strength, area, and centroid latitude have a dominant seasonal cycle. In contrast, the SPCZ centroid longitude is dominated by intraseasonal variability due to the influence by the Madden-Julian Oscillation. The SPCZ indices are all correlated with El Niño-Southern Oscillation indices. Interannual and intraseasonal variations of SPCZ strength during strong El Niño are approximately twice as large as the respective seasonal variations. SPCZ strength depends more on the intensity of El Niño rather than the central- vs. eastern-Pacific type. The longer ERA-Interim product is also used to examine decadal variations of the SPCZ indices. The change from positive to negative Pacific Decadal Oscillation phase around 1999 resulted in a westward shift of the SPCZ centroid longitude, much smaller interannual swing in centroid latitude, and a decrease in SPCZ area. This study improves the understanding of the variations of the SPCZ on multiple time scales and reveals the variations of SPCZ strength not reported previously. The diagnostics analyses can be

  18. Aqua-planet simulations of the formation of the South Atlantic convergence zone

    NASA Technical Reports Server (NTRS)

    Nieto Ferreira, Rosana; Chao, Winston C.

    2013-01-01

    The impact of Amazon Basin convection and cold fronts on the formation and maintenance of the South Atlantic convergence zone (SACZ) is studied using aqua-planet simulations with a general circulation model. In the model, a circular patch of warm sea-surface temperature (SST) is used to mimic the effect of the Amazon Basin on South American monsoon convection. The aqua-planet simulations were designed to study the effect of the strength and latitude of Amazon Basin convection on the formation of the SACZ. The simulations indicate that the strength of the SACZ increases as the Amazon convection intensifies and is moved away from the equator. Of the two controls studied here, the latitude of the Amazon convection exerts the strongest effect on the strength of the SACZ. An analysis of the synoptic-scale variability in the simulations shows the importance of frontal systems in the formation of the aqua-planet SACZ. Composite time series of frontal systems that occurred in the simulations show that a robust SACZ occurs when fronts penetrate into the subtropics and become stationary there as they cross eastward of the longitude of the Amazon Basin. Moisture convergence associated with these frontal systems produces rainfall not along the model SACZ region and along a large portion of the northern model Amazon Basin. Simulations in which the warm SST patch was too weak or too close to the equator did not produce frontal systems that extended into the tropics and became stationary, and did not form a SACZ. In the model, the SACZ forms as Amazon Basin convection strengthens and migrates far enough southward to allow frontal systems to penetrate into the tropics and stall over South America. This result is in agreement with observations that the SACZ tends to form after the onset of the monsoon season in the Amazon Basin.

  19. Massive barite deposits in the convergent margin off Peru: Implications for fluid circulation within subduction zones

    NASA Astrophysics Data System (ADS)

    Aquilina, L.; Dia, A. N.; Boulègue, J.; Bourgois, J.; Fouillac, A. M.

    1997-03-01

    The convergent margin of Peru, characterized by an extensional tectonic regime and the lack of a well-developed accretionary prism, has been investigated by a deep-sea submersible during the Nautiperc cruise (March-April, 1991). This allowed the collection of fluid samples, soft sediments, and barite concretions in the vicinity of biological communities associated with fluid steps. Major and trace element contents as well as strontium, oxygen, hydrogen, and sulfur isotopic compositions have been measured on fluid and/or solid samples to constrain the nature and origin of fluid circulating in this extensional tectonic context. Chemical variations with respect to bottom seawater composition have been recorded in the fluid samples and suggest the presence of a nonlocal component in the fluid expelled at the seafloor. The major variations correspond to elevations of the Cl, Na, and the Ba contents as well as the 87Sr /86Sr ratios. This is interpreted as the expulsion of a radiogenic, continent-related (basinal brine and/or meteoric water) fluid. Massive barite concretions have been collected at the seafloor in two areas of major fluid venting. The radiogenic signature (strontium isotopic composition) of the barite concretions implies that they are related to the nonlocal deep fluid component identified in the fluid samples. Furthermore, it is shown that these barite deposits testify to a hot, short, and intensive fluid circulation event. Compared to subduction zones that exhibit venting fluid with a strong oceanic water signature, the nature and origin of venting fluid along the subduction zone of Peru are different. The extensional tectonic regime of the Peru continental margin, locally associated with a dense E-W trending fault network, is an agent which may help to drain continent-related fluid as deep as the subduction scarp at the trench-slope boundary.

  20. Century-scale movement of the Atlantic Intertropical Convergence Zone linked to solar variability

    USGS Publications Warehouse

    Poore, R.Z.; Quinn, T.M.; Verardo, S.

    2004-01-01

    The abundance of the planktic foraminifer Globigerinoides sacculifer in Gulf of Mexico (GOM) sediments is a proxy for the influx of Caribbean surface waters (the Loop Current) into the GOM. Penetration of the Loop Current into the GOM is related to the position of the Intertropical Convergence Zone (ITCZ): northward migration of the ITCZ results in increased incursion of the Loop Current into the GOM; southward migration of the ITCZ results in decreased penetration of the Loop Current into the GOM. Abundance variations of G. sacculifer in a sediment core from the Pigmy Basin in the GOM show distinct century-scale cyclicity over the last 5,000 years. The periodicity of these abundance variations is similar to the century-scale periodicity observed in proxy records of solar variability, which suggests that the average position of the ITCZ and thus Holocene century-scale variability in the Caribbean-GOM region is linked to solar variability. Copyright 2004 by the American Geophysical Union.

  1. The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin

    PubMed Central

    van Hengstum, Peter J.; Donnelly, Jeffrey P.; Fall, Patricia L.; Toomey, Michael R.; Albury, Nancy A.; Kakuk, Brian

    2016-01-01

    Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval. PMID:26906670

  2. Factors Affecting the Latitudinal Location of the Intertropical Convergence Zone in a GCM

    NASA Technical Reports Server (NTRS)

    Chao, Winston C.; Chen, Baode

    2002-01-01

    The dominant role of the latitudinal peak of the sea surface temperature (SST) in determining the latitudinal location of the intertropical convergence zone (ITCZ) is well-known. However, the roles of the other factors are less well-known and are the topic of this study. These other factors include the inertial stability, the interaction between convection and surface fluxes and the interaction between convection and radiation. Since these interactions involve convection, in a model they involve the cumulus parameterization scheme. These factors are studied with a general circulation model with uniform SST and solar angle. Under the aforementioned model settings, the latitudinal location of the ITCZ is the latitude where the balance of two types of attraction on the ITCZ, both due to earth's rotation, exists. Directly related to the Coriolis parameter, the first type pulls the ITCZ toward the equator and is not sensitive to model design changes. Related to the convective circulation, the second type pulls the ITCZ poleward and is sensitive to model design changes. Due to the shape and the magnitude of the attractors, the balance of the two types of attractions is reached either at the equator or more than 10 degrees away from the equator. The former case results in a single ITCZ over the equator and the latter case a double ITCZ straddling the equator.

  3. Impact of the Madden-Jullian oscillation on Rainfall over the South Pacific Convergence Zone

    NASA Astrophysics Data System (ADS)

    Pariyar, Sunil Kumar; Keenlyside, Noel; Bhatt, Bhuwan Chandra; Koseki, Shunya; Spengler, Thomas

    2016-04-01

    Impacts of Madden-Jullian oscillation (MJO) on southern summertime rainfall over the south Pacific convergence zone (SPCZ) is investigated. For this, the real-time multivariate daily MJO series 1 (RMM1) and 2 (RMM2) are used to measure the intensity and different phases of the MJO. For rainfall, daily 3B42 TRMM rainfall data are used and composite analysis is done in all eight different phases of the MJO. By analyzing the daily rainfall for the period 1998-2014, it is found that the MJO significantly modulates the distribution of rainfall over the SPCZ region. Multiple regression analysis (daily rainfall regressed with RMM1 and RMM2) shows noticeable impact of the MJO on rainfall over the SPCZ with explained variance of up to 14%. The phase composite analysis shows considerable changes in rainfall over the SPCZ region during the MJO life cycle with episodes of enhanced and supressed convection. When the MJO is in phase 2,3, and 4 negative rainfall anomalies (up to 6 mm day-1) are observed along the SPCZ. While during phase 6,7,and 8, SPCZ experiences positive rainfall anomaly (up to 8 mm day-1). Spectral analysis of daily rainfall data over the SPCZ (160E-180E,5S-15S) shows the maximum spectral peak within the range of intraseasonal periods of 30-90 days. This indicates that the intraseasonal variation in rainfall over the SPCZ is typically associated with the MJO.

  4. The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin.

    PubMed

    van Hengstum, Peter J; Donnelly, Jeffrey P; Fall, Patricia L; Toomey, Michael R; Albury, Nancy A; Kakuk, Brian

    2016-01-01

    Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval. PMID:26906670

  5. The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin

    NASA Astrophysics Data System (ADS)

    van Hengstum, Peter J.; Donnelly, Jeffrey P.; Fall, Patricia L.; Toomey, Michael R.; Albury, Nancy A.; Kakuk, Brian

    2016-02-01

    Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval.

  6. Diabatic heating profiles over the continental convergence zone during the monsoon active spells

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, Rajib; Sur, Sharmila; Joseph, Susmitha; Sahai, A. K.

    2013-07-01

    The present paper aims to bring out the robust common aspects of spatio-temporal evolution of diabatic heating during the monsoon intraseasonal active phases over the continental tropical convergence zone (CTCZ). The robustness of spatio-temporal features is determined by comparing the two state-of-the art reanalyses: NCEP Climate Forecast System reanalysis and Modern ERA Retrospective Analysis. The inter-comparison is based on a study period of 26 years (1984-2009). The study confirms the development of deep heating over the CTCZ region during the active phase and is consistent between the two datasets. However, the detailed temporal evolution of the vertical structure (e.g., vertical tilts) of heating differs at times. The most important common feature from both the datasets is the significant vertical redistribution of heating with the development of shallow (low level) heating and circulation over the CTCZ region 3-7 days after the peak active phase. The shallow circulation is found to be associated with increased vertical shear and relative vorticity over certain regions in the subcontinent. This increased vertical shear and relative vorticity in the lower levels could be crucial in the sustenance of rainfall after the peak active phase. Model experiments with linear dynamics affirm the role of shallow convection in increasing the lower level circulation as observed.

  7. The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin.

    PubMed

    van Hengstum, Peter J; Donnelly, Jeffrey P; Fall, Patricia L; Toomey, Michael R; Albury, Nancy A; Kakuk, Brian

    2016-01-01

    Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval.

  8. Coral oxygen isotope records of interdecadal climate variations in the South Pacific Convergence Zone region

    NASA Astrophysics Data System (ADS)

    Bagnato, Stefan; Linsley, Braddock K.; Howe, Stephen S.; Wellington, Gerard M.; Salinger, Jim

    2005-06-01

    The South Pacific Convergence Zone (SPCZ), a region of high rainfall, is a major feature of subtropical Southern Hemisphere climate and contributes to and interacts with circulation features across the Pacific, yet its past temporal variability and forcing remain only partially understood. Here we compare coral oxygen isotopic (δ18O) series (spanning A.D. 1997-1780 and A.D. 2001-1776) from two genera of hermatypic corals in Fiji, located within the SPCZ, to examine the fidelity of these corals in recording climate change and SPCZ interdecadal dynamics. One of these coral records is a new 225-year subannually resolved δ18O series from the massive coral Diploastreaheliopora. Diploastrea's use in climate reconstructions is still relatively new, but this coral has shown encouragingly similar interannual variability to Porites, the coral genus most commonly used in Pacific paleoclimate studies. In Fiji we observe that interdecadal δ18O variance is also similar in these two coral genera, and Diploastrea contains a larger-amplitude interdecadal signal that more closely tracks instrumental-based indices of Pacific interdecadal climate change and the SPCZ than Porites. Both coral δ18O series record greater interdecadal variability from ˜1880 to 1950, which is consistent with the observations of Folland et al. (2002), who reported higher variability in SPCZ position before 1945. These observations indicate that Diploastrea will likely provide a significant new source of long-term climate information from the SPCZ region.

  9. Study of the variability of Atlantic Intertropical Convergence Zone using multivariate indices

    NASA Astrophysics Data System (ADS)

    Nóbile Tomaziello, A.; Gandu, A.; Carvalho, L. V.

    2013-05-01

    Ana Carolina Nóbile Tomaziello, Adilson Wagner Gandu Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo, Brazil carolnobile@model.iag.usp.br; adwgandu@model.iag.usp.br Leila Maria Véspoli de Carvalho Department of Geography, University of California, Santa Barbara, United States leila@eri.ucsb.edu The variability of Atlantic Intertropical Convergence Zone (ITCZ) is studied using multivariate indices based on the first and second combined EOF (EOFc) of anomalies of zonal and meridional wind's components, specific humidity, and air temperature at 850 mb, and precipitation. The EOFc's spatial domain encompassed tropical Atlantic Ocean and part of Brazilian Northeast and western Africa. Silva and Carvalho (2007) described a similar index in order to characterize the South American monsoon. First and second modes of EOFc describe successfully ITCZ's main features. Composites for the percentile of 25% (75%) for EOFc-1 show convection (suppression), and easterly and south (westerly and north) wind anomalies in ITCZ. There are negative anomalies of humidity over central Brazil when there are positive ones over ITCZ, and vice-versa. For the second mode, composites for the percentile of 25% (75%) show convection (suppression), westerly and south (easterly and north) wind anomalies in ITCZ, and negative (positive) anomalies of temperature in tropical Atlantic. Negative (positive) anomalies of humidity in northern and northwestern South America, and central Brazil are accompanied by positive (negative) ones in tropical north Atlantic. Convergence (divergence) of meridional wind in tropical Atlantic is associated with divergence (convergence) over southern and part of southeastern Brazil. EOFc-2 illustrates a possible relationship between SACZ and ITCZ and also shows a Pacific-South America (PSA) like pattern teleconnecting Indian and Pacific Oceans to South America. The PSA-like wave train has opposite phases for percentiles of 25% and 75

  10. Exploring Coral Reconstructions of Intertropical Convergence Zone Oscillations over Central America During the Common Era

    NASA Astrophysics Data System (ADS)

    Brenner, L. D.; Linsley, B. K.; Dassie, E. P.; Dunbar, R. B.

    2013-12-01

    A thorough understanding of the Intertropical Convergence Zone (ITCZ), visible as a band of clouds where the northeastern and southeastern trade winds converge near the equator, is a crucial pillar in supplementing regional climate models. These types of models are used for the creation of comprehensive water management policies, as well as flood prediction and remediation programs. Seasonal and interannual shifts in the position of the ITCZ control precipitation throughout much of the tropics. However, lower frequency decadal and century variability of the ITCZ remains poorly constrained and understood. We sampled a Porites sp. coral head off the northeast coast of Coiba Island, Pacific side of Panamá (7°25'58.80'N, 81°45'57.60'W), and conducted both stable isotope (δ18O and δ13C) and trace element (Sr/Ca) analysis. The δ18O record from the Coiba Island coral (IC4A-2) suggests that changes in the amount of precipitation, which regulate the sea surface salinity (SSS) at this location, are the dominant factors modulating the various periodicities in this coral stable isotope record. Instrumental gridded sea surface temperature (SST) data from the region portray an irregular and small (2°C) annual cycle, supported by the Sr/Ca record, which mirrors the 2°C envelope. From these analyses we were able to reconstruct precipitation and SST history over this area and therefore the variability of the ITCZ at this location. While the majority of the variability (>50%) in the δ18O record is owed to the seasonal cycle, a decadal signal accounts for a significant portion of the remaining total variance (~10%). There is no similar decadal cycle apparent in the instrumental SSTs from the area or the IC4A-2 Sr/Ca record, suggesting that the proxy history is dominated by precipitation fluctuations. Furthermore, El Niño Southern Oscillation (3-8yr cycle) appears as a meager component in the total variance, also supported by earlier work from nearby Secas Island, which

  11. Intraseasonal variability of the Atlantic Intertropical Convergence Zone during austral summer and winter

    NASA Astrophysics Data System (ADS)

    Tomaziello, Ana Carolina Nóbile; Carvalho, Leila M. V.; Gandu, Adilson W.

    2016-09-01

    The Atlantic Intertropical Convergence Zone (A-ITCZ) exhibits variations on several time-scales and plays a crucial role in precipitation regimes of northern South America and western Africa. Here we investigate the variability of the A-ITCZ on intraseasonal time-scales during austral summer (November-March) and winter (May-September) based on a multivariate index that describes the main atmospheric features of the A-ITCZ and retains its variability on interannual, semiannual, and intraseasonal time-scales. This index is the time coefficient of the first combined empirical orthogonal function mode of anomalies (annual cycle removed) of precipitation, and zonal and meridional wind components at 850 hPa from the climate forecast system reanalysis (1979-2010). We examine associations between the intraseasonal variability of the A-ITCZ and the activity of the Madden-Julian oscillation (MJO). We show that during austral summer intraseasonal variability of the A-ITCZ is associated with a Rossby wave train in the Northern Hemisphere. In austral winter this variability is associated with the propagation of a Rossby wave in the Southern Hemisphere consistent with the Pacific-South American pattern. Moreover, we show that intense A-ITCZ events on intraseasonal time-scales are more frequent during the phase of MJO characterized by convection over western Pacific and suppression over the Indian Ocean. These teleconnection patterns induce anomalies in the trade winds and upper level divergence over the equatorial Atlantic that modulate the intensity of the A-ITCZ.

  12. More extreme swings of the South Pacific convergence zone due to greenhouse warming.

    PubMed

    Cai, Wenju; Lengaigne, Matthieu; Borlace, Simon; Collins, Matthew; Cowan, Tim; McPhaden, Michael J; Timmermann, Axel; Power, Scott; Brown, Josephine; Menkes, Christophe; Ngari, Arona; Vincent, Emmanuel M; Widlansky, Matthew J

    2012-08-16

    The South Pacific convergence zone (SPCZ) is the Southern Hemisphere's most expansive and persistent rain band, extending from the equatorial western Pacific Ocean southeastward towards French Polynesia. Owing to its strong rainfall gradient, a small displacement in the position of the SPCZ causes drastic changes to hydroclimatic conditions and the frequency of extreme weather events--such as droughts, floods and tropical cyclones--experienced by vulnerable island countries in the region. The SPCZ position varies from its climatological mean location with the El Niño/Southern Oscillation (ENSO), moving a few degrees northward during moderate El Niño events and southward during La Niña events. During strong El Niño events, however, the SPCZ undergoes an extreme swing--by up to ten degrees of latitude toward the Equator--and collapses to a more zonally oriented structure with commensurately severe weather impacts. Understanding changes in the characteristics of the SPCZ in a changing climate is therefore of broad scientific and socioeconomic interest. Here we present climate modelling evidence for a near doubling in the occurrences of zonal SPCZ events between the periods 1891-1990 and 1991-2090 in response to greenhouse warming, even in the absence of a consensus on how ENSO will change. We estimate the increase in zonal SPCZ events from an aggregation of the climate models in the Coupled Model Intercomparison Project phases 3 and 5 (CMIP3 and CMIP5) multi-model database that are able to simulate such events. The change is caused by a projected enhanced equatorial warming in the Pacific and may lead to more frequent occurrences of extreme events across the Pacific island nations most affected by zonal SPCZ events.

  13. Numerical simulation of formation of cyclone vortex flows in the intratropical zone of convergence and their early detection

    NASA Astrophysics Data System (ADS)

    Mingalev, I. V.; Astaf'eva, N. M.; Orlov, K. G.; Chechetkin, V. M.; Mingalev, V. S.; Mingalev, O. V.

    2012-05-01

    Mechanisms of formation of cyclonic vortices in the tropical atmosphere of the Earth are investigated in the intratropical zone of convergence using numerical simulation made with the complete system of equations of gas dynamics taking into account transport of infrared radiation, phase transitions of water vapor into microdrops of water and ice particles, and sedimentation of these drops and ice particles in the field of gravity force. Observational data on the structure of dominant air streams, which are formed in the intratropical zone of convergence over the North Atlantic in the periods of its highest thermodynamic intensity and instability, are used in the initial and boundary conditions of the model. Formation of cyclonic vortex flows is obtained numerically at sufficiently strong bending of the intratropical zone of convergence. The results of numerical modeling are compared with the data of satellite microwave monitoring: global radio thermal fields of the Earth from the electronic collection GLOBAL-Field allowing one to study the structure of atmospheric motions in a wide range of space-time scales.

  14. Western Atlantic Intertropical Convergence Zone Variability Over the Last Full Glacial Cycle

    NASA Astrophysics Data System (ADS)

    Drenzek, N.; Hughen, K.; Sessions, A.; Bice, M.; Eglinton, T.

    2006-12-01

    Precipitation associated with the modern Intertropical Convergence Zone (ITCZ) in the Atlantic Basin is sensitive to fluctuations in both local insolation1 and remote North Atlantic2,3 and equatorial Pacific4 climate. Reconstructing the pattern and timing of precipitation change in regions influenced by the ITCZ may therefore clarify the mechanisms driving Quaternary climate change in, and the teleconnections between, low and high latitudes. In order to establish a record of ITCZ variability in the western tropical Atlantic, we measured the stable carbon and hydrogen isotopic compositions of individual vascular plant lipids preserved in Cariaco Basin sediments at sub-millennial resolution over the last glacial cycle. High frequency oscillations in the δ13C values of long chain fatty acids during Marine Isotope Stage 3, reflecting changes in the relative proportion of C3 vs C4 vegetation, and hence humidity, in northern South America, appear to coincide with Dansgaard- Oeschger (D-O) variability in high latitude ice cores. Positive (negative) excursions occur during stadial (interstadial) periods, with the largest enrichments associated with Heinrich Events in the North Atlantic. Corresponding D/H ratios also indicate rapid shifts in ambient humidity, although more work is needed to fully constrain the effect of glacial conditions on the isotopic composition of paleoprecipitation. These millennial scale fluctuations are superimposed upon a longer term oscillation with significant power near the 21 kyr spectral band. Together, these data imply that the ITCZ in this region of the tropics responded to both high and low latitude forcing over the late Quaternary. For example, the proportion of C4 plants rapidly increased at the onset of stadial periods in the North Atlantic, suggesting that a southward deflection of the ITCZ gave rise to more arid conditions in northern South America. The converse was true for interstadials. Moreover, the amplitude of these millennial

  15. Climatological mean tropical Atlantic surface wind convergence : analysis of the drivers in reanalyses

    NASA Astrophysics Data System (ADS)

    Diakhaté, Moussa; lazar, Alban; De Coëtlogon, Gaelle; Gaye, Amadou

    2016-04-01

    Using atmosphere mixed layer models, satellites data and the Climate Forecast System Reanalyses datasets over the 2000-2009 decade, we provide an analysis of the monthly-mean climatological surface wind convergence budget over the tropical Atlantic, as well as its month to moth variations. Relative influence of Sea Surface Temperature relative to free troposphere is particularly examined. Regarding the monthly-mean budget, the marine Inter-Tropical Convergence Zone (ITCZ) appears to be split into two parts. There is an "oceanic part" (defined as the region between 10-50°W), with north and south sides largely controlled by surface pressure driven convergence, to the opposite to the center dominated by free troposphere forces. East and west stands a "coastal part" (African and Northeastern Brazilian coasts), where horizontal advection and pressure contributions control surface wind convergence, with the pressure beeing the first order driver. This pressure contribution is largely dominated by horizontal gradients within the surface boundary layer, likely closely related to SST. On the other hand, month-to-month changes are controlled by geostrophic balance dominated by the free troposphere, with likely less influence of SST changes.

  16. Stem tilting in the inter-tropical cactus Echinocactus platyacanthus: an adaptive solution to the trade-off between radiation acquisition and temperature control.

    PubMed

    Herce, M F; Martorell, C; Alonso-Fernandez, C; Boullosa, L F V V; Meave, J A

    2014-05-01

    While plants require radiation for photosynthesis, radiation in warm deserts can have detrimental effects from high temperatures. This dilemma may be solved through plant morphological attributes. In cold deserts, stem tilting keeps reproductive organs warm by increasing radiation interception at the cost of decreased annual light interception. Conversely, little is known about stem tilting in warm deserts. We hypothesised that stem tilting in Echinocactus platyacanthus prevents high temperatures near the apex, where reproduction occurs. The study was conducted in the warm, inter-tropical portion of the Chihuahuan Desert, Mexico. We found that cacti preferentially tilted towards the south, which reduced temperatures of reproductive organs during the hot season, but increased total annual near-apex PAR interception. Tilting also maximised reproduction, a likely consequence of temperature control but perhaps also of the difficulty in translocating photosynthates in cacti; therefore, annual energy acquisition near floral meristems may be largely allocated to reproduction. Unlike plants of higher latitudes, in inter-tropical deserts sunlight at noon comes either from the north or the south, depending on the season, and thus stem tilting may more strongly affect total annual radiation received in different portions of the stem. Inter-tropical cacti can synchronise reproduction with irradiance peaks if flowering occurs in a specific (north or south) portion of the stem; also, they effectively solve the conflict between maximising annual PAR interception and minimising temperature at the hottest time of day. Notably, the two inter-tropical cacti in which stem tilting has been studied successfully solve this conflict.

  17. A study of the dynamics of the Intertropical Convergence Zone (ITCZ) in a symmetric atmosphere-ocean model

    NASA Technical Reports Server (NTRS)

    Charney, J. G.; Kalnay, E.; Schneider, E.; Shukla, J.

    1988-01-01

    A numerical model of the circulation of a coupled axisymmetric atmosphere-ocean system was constructed to investigate the physical factors governing the location and intensity of the Intertropical Convergence Zone (ITCZ) over oceans and over land. The results of several numerical integrations are presented to illustrate the interaction of the individual atmospheric and oceanic circulations. It is shown that the ITCA cannot be located at the equator because the atmosphere-ocean system is unstable for lateral displacements of the ITCA from an equilibrium position at the equator.

  18. Seismogenic Coupling at Convergent Margins - Geophysical Observations from the South American Subduction Zone and the Alpine Rock Record

    NASA Astrophysics Data System (ADS)

    Oncken, O.

    2008-12-01

    Convergent continental margins are the Earth's principal locus of important earthquake hazards with nearly all interplate megathrust earthquakes (M>8) in the seismogenic coupling zone between the converging plates. Despite the key importance of this zone, the processes that shape it are poorly understood. This is underscored by a number of novel observations attributed to processes in the interface zone that are attracting increasing attention: silent slip events, non-volcanic tremors, afterslip, locked patches embedded in a creeping environment, etc. We here compare the rock record from a field study with recent results from two major geophysical experiments (ANCORP and TIPTEQ) that have imaged the South Chilean subduction zone at the site of the largest historically recorded earthquake (Valdivia, 1969; Mw = 9.5) and the plate boundary in Northern Chile, where a major seismic event is expected in the near future (Iquique segment). The reflection seismic data exhibit well defined changes of reflectivity and Vp/Vs ratio along the plate interface that can be correlated with different parts of the coupling zone as well as with changes during the seismic cycle. Observations suggest an important role of the hydraulic system. The rock record from the exhumed Early Tertiary seismogenic coupling zone of the European Alps provides indications for the mechanisms and processes responsible for the geophysical images. Fabric formation and metamorphism in a largely preserved subduction channel chiefly record the deformation conditions of the pre-collisional setting along the plate interface. We identify an unstable slip domain from pseudotachylytes occurring in the temperature range between 200-300°C. This zone coincides with a domain of intense veining in the subduction mélange with mineral growth into open cavities, indicating fast, possibly seismic, rupture. Evidence for transient near-lithostatic fluid pressure as well as brittle fractures competing with mylonitic shear

  19. Idealized Simulations of the Effects of Amazon Convection and Baroclinic Waves on the South Atlantic Convergence Zone

    NASA Technical Reports Server (NTRS)

    Ferreira, Rosana Nieto; Suarez, Max J.; Nigam, Sumant; Einaudi, Franco (Technical Monitor)

    2001-01-01

    The South Atlantic Convergence Zone (SACZ) is a NW-SE oriented, stationary region of enhanced convergence and convection that extends southeastward from the ITCZ convection anchored over the Amazon region. On daily satellite images each SACZ episode is seen as a progression of one or several midlatitude cold fronts that intrude into the subtropics and tropics, becoming stationary over southeastern Brazil for a few days. Previous studies have shown that while Amazon convection plays a fundamental role in the formation of the SACZ, Atlantic sea surface temperatures and the Andes Mountains play a relatively minor role in the strength and location of the SACZ. The role of interactions between Amazon convection and midlatitude baroclinic waves in establishing the origin, position, and maintenance of the SACZ is studied here using idealized dry, multilayer global model simulations that do not include the effects of topography. The model simulations produce SACZ-like regions of low-level convergence in the presence of Amazon convection embedded in a mean-flow that contains propagating baroclinic waves. The results of these simulations indicate that Amazon convection plays two fundamental roles in the formation and location of the SACZ. First, it produces a NW-SE oriented region of low-level convergence to the SE of Amazon convection. Second, it produces a storm-track region and accompanying stronger midlatitude baroclinic waves in the region of the SACZ. It is suggested that in the presence of moist effects, the 'seedling' SACZ regions produced in these simulations can be enhanced to produce the observed SACZ.

  20. Segregation behavior in a stationary vertical zone with converging interfaces - Pressure-induced segregation effects

    NASA Technical Reports Server (NTRS)

    Kim, K. M.; Witt, A. F.; Gatos, H. C.

    1974-01-01

    Crystal growth and segregation were investigated in a confined vertical melt zone in which the upper solid-melt interface advanced under destabilizing and the lower interface under stabilizing thermal gradients. A technique reported by Kim et al. (1972) was used in the study. The experimental results are discussed, giving attention to interface morphology and growth rate and questions of dopant segregation. Dopant inhomogeneities formed simultaneously in both advancing interfaces can be explained on the basis of pressure induced segregation effects.

  1. Balloon-borne ozonesonde and rocket temperature and wind data gathered during the July 1977 intertropical convergence zone experiment

    NASA Technical Reports Server (NTRS)

    Schmidlin, F. J.; Kloos, G.

    1979-01-01

    In middle latitudes, it is possible for large concentrations of stratospheric air to be brought down to the tropopause through folds or breaks in the tropopause. The exchange of air from the tropopause into higher altitudes is not well understood. Thus, the ITCZ (Intertropical Convergence Zone) experiment, conducted from July 16 through July 31, 1977, included a series of balloon-borne ozone soundings. The results of these soundings are presented and explain in the vertical exchange of air and provide information on the short vertical scales-of-motion. Rocketsonde data was also gathered in the ITCZ experiment in support of a stratospheric scales-of-motion study. The investigation was to determine whether rocketsonde and satellite information currently used yield information on the stratospheric horizontal wave spectrum and its importance with respect to tropospheric and mesospheric interaction and transport.

  2. Deformation zone ‘jumps’ in a young convergent setting; the Lengguru fold-and-thrust belt, New Guinea Island

    NASA Astrophysics Data System (ADS)

    Bailly, V.; Pubellier, M.; Ringenbach, J.-C.; de Sigoyer, J.; Sapin, F.

    2009-12-01

    The Lengguru fold-and-thrust belt in West Papua (Indonesia) has all the characteristics of a young orogen involved in a rapidly changing tectonic setting. The analysis of the young wedge shows however that its internal shortening has ceased recently, and that it is nowadays suffering severe extension. Recent topographic data, marine industrial seismic lines and drilling, were used with field observations and measurements to create detailed cross-sections and a new structural map. The study allows us to distinguish two superimposed prisms composed of stacked Mesozoic marine sediments of the Australian margin against a crustal buttress. The construction of these two wedges is younger than 11 Myr. The structures of the Lengguru belt external zones are sealed by an unconformable clastic series, indicating that the construction of the Lengguru prism had aborted suddenly due to a change in the way the Australian and Pacific plate convergence was accommodated. At that time, the internal zones probably started to exhume and the tectonic regime became extensional. Nowadays the internal part of the Lengguru fold-and-thrust belt is undergoing an active east-west extension. We believe that the extension observed in the Lengguru wedge is coeval with a transition from a compressive to a transtensional regime illustrated in the Central Range of Papua, and the onset of the Tarera-Aiduna and Paniai left-lateral faults. The structure of the Lengguru belt therefore results from events occurring over a very short time span; a previous Late Miocene northeast-southwest compression linked to the subduction process, a second from Middle Miocene to Early Pliocene and a Late Pliocene-Quaternary global extension in the whole range. The evolution is compared with that of the Seram wedge and the Misool-Onin-Kumawa continental ridge to the west; where deformation is accommodated at a localized zone which jumps as convergence between Australian and Pacific plate proceeds. This evolution of the

  3. Trade-off between morphological convergence and opportunistic diet behavior in fish hybrid zone

    PubMed Central

    Corse, Emmanuel; Costedoat, Caroline; Pech, Nicolas; Chappaz, Rémi; Grey, Jonathan; Gilles, André

    2009-01-01

    Background The invasive Chondrostoma nasus nasus has colonized part of the distribution area of the protected endemic species Chondrostoma toxostoma toxostoma. This hybrid zone is a complex system where multiple effects such as inter-species competition, bi-directional introgression, strong environmental pressure and so on are combined. Why do sympatric Chondrostoma fish present a unidirectional change in body shape? Is this the result of inter-species interactions and/or a response to environmental effects or the result of trade-offs? Studies focusing on the understanding of a trade-off between multiple parameters are still rare. Although this has previously been done for Cichlid species flock and for Darwin finches, where mouth or beak morphology were coupled to diet and genetic identification, no similar studies have been done for a fish hybrid zone in a river. We tested the correlation between morphology (body and mouth morphology), diet (stable carbon and nitrogen isotopes) and genomic combinations in different allopatric and sympatric populations for a global data set of 1330 specimens. To separate the species interaction effect from the environmental effect in sympatry, we distinguished two data sets: the first one was obtained from a highly regulated part of the river and the second was obtained from specimens coming from the less regulated part. Results The distribution of the hybrid combinations was different in the two part of the sympatric zone, whereas all the specimens presented similar overall changes in body shape and in mouth morphology. Sympatric specimens were also characterized by a larger diet behavior variance than reference populations, characteristic of an opportunistic diet. No correlation was established between the body shape (or mouth deformation) and the stable isotope signature. Conclusion The Durance River is an untamed Mediterranean river despite the presence of numerous dams that split the river from upstream to downstream. The

  4. Elastic thickness structure of the Andaman subduction zone: Implications for convergence of the Ninetyeast Ridge

    NASA Astrophysics Data System (ADS)

    Ratheesh Kumar, R. T.; Windley, B. F.; Rajesh, V. J.; Santosh, M.

    2013-12-01

    We use the Bouguer coherence (Morlet isostatic response function) technique to compute the spatial variation of effective elastic thickness (Te) of the Andaman subduction zone. The recovered Te map resolves regional-scale features that correlate well with known surface structures of the subducting Indian plate and the overriding Burma plate. The major structure on the India plate, the Ninetyeast Ridge (NER), exhibits a weak mechanical strength, which is consistent with the expected signature of an oceanic ridge of hotspot origin. However, a markedly low strength (0 < Te < 3 km) in that region, where the NER is close to the Andaman trench (north of 10°N), receives our main attention in this study. The subduction geometry derived from the Bouguer gravity forward modeling suggests that the NER has indented beneath the Andaman arc. We infer that the bending stresses of the viscous plate, which were reinforced within the subducting oceanic plate as a result of the partial subduction of the NER buoyant load, have reduced the lithospheric strength. The correlation, Te < Ts (seismogenic thickness) reveals that the upper crust is actively deforming beneath the frontal arc Andaman region. The occurrence of normal-fault earthquakes in the frontal arc, low Te zone, is indicative of structural heterogeneities within the subducting plate. The fact that the NER along with its buoyant root is subducting under the Andaman region is inhibiting the subduction processes, as suggested by the changes in trench line, interrupted back-arc volcanism, variation in seismicity mechanism, slow subduction, etc. The low Te and thinned crustal structure of the Andaman back-arc basin are attributed to a thermomechanically weakened lithosphere. The present study reveals that the ongoing back-arc spreading and strike-slip motion along the West Andaman Fault coupled with the ridge subduction exerts an important control on the frequency and magnitude of seismicity in the Andaman region.

  5. Thermodynamic and kinematic characteristics of low-level convergent zones observed by the mobile integrated profiling system

    NASA Astrophysics Data System (ADS)

    Karan, Haldun

    Thermodynamic and kinematic characteristics of convergent boundary zones (CBZs) over various geographic regions in a broad range of environmental conditions are investigated through analysis of the Mobile Integrated Profiling System (MIPS), Doppler radar, atmospheric sounding, and surface data. The MIPS sensors provide very fine temporal kinematic and thermodynamic profiles of the atmospheric boundary layer ( ABL) and CBZ properties, including enhanced 915 MHz backscatter within the CBZ, an increase in integrated water vapor within the updrafts of the CBZ, variations in file convective boundary layer depth, and increases in ceilometer backscatter that are typically coincident with the arrival of cooler, moister air when the CBZs are associated with gust fronts, retrograding drylines, and shallow cold fronts. An analysis of over 50 gust frontal passages reveals that morphological structures and dynamical properties of gust fronts resemble laboratory simulated density currents and numerical simulations of outflow boundaries. Characteristics of a retrograding dryline and a shallow cold front sampled during IHOP 2002 project suggest a close resemblance to density currents. Gust frontal updrafts appear to be greatly affected by the adjacent boundary layer stability and interaction between the ambient shear and gust frontal circulation. Gust frontal updrafts were stronger and more vertically oriented when gust fronts were moving against the ambient flow. Interaction between gust fronts and horizontal convective rolls are investigated through radar derived wind field, Z reflectivity factors, and MIPS data sets. Convective initiation occurs more efficiently at intersection points between horizontal convective rolls and gust fronts when the HCR axes intersect the gust front at a large angle. In contrast, convection initiation was absent when HCRs were parallel to an approaching gust front which systematically encountered roll updrafts and downdrafts. A collision of two

  6. Numerical Study of the Intertropical Convergence Zone Over the Indian Ocean During the 1997 and 1998 Northeast Monsoon Episodes

    NASA Astrophysics Data System (ADS)

    Roswintiarti, O.; Raman, S.; Mohanty, U. C.

    - The hydrostatic Naval Research Laboratory/North Carolina State University (NRL/NCSU) model was used to study the mesoscale dynamics and diurnal variability of the Intertropical Convergence Zone (ITCZ) over the Indian Ocean in the short-range period. To achieve this objective the initial conditions from two northeast monsoon episodes (29 January, 1997 and 29 January, 1998) were run for 48-hour simulations using a triple-nested grid version of the model with 1.5°×1.5°, 0.5°×0.5° and 0.17°×0.17° resolutions. The 1997 case represents a typical northeast monsoon episode, while the 1998 case depicts an abnormal monsoon episode during an El Niño event.Comparisons between the model-produced and analyzed mean circulation, wind speed, and associated rainfall for different spatial scales are presented. During the active northeast monsoon season in 1997, the major low-level westerly winds and associated high rainfall rates between 0° and 15°S were simulated reasonably well up to 24 hours. During the 1998 El Niño event, the model was capable of simulating weak anomalous easterly winds (between 0° and 15°S) with much lower rainfall rates up to 48 hours. In both simulations, the finest grid size resulted in largest rainfall rates consistent with Outgoing Longwave Radiation data.The model performance was further evaluated using the vertical profiles of the vertical velocity, the specific humidity and temperature differences between the model outputs and the analyses. It is found that during a typical northeast monsoon year, 1997, the water vapor content in the middle troposphere was largely controlled by the low-level convergence determined by strong oceanic heat flux gradient. In contrast, during the 1998 El Niño year moisture was present only in the lower troposphere. Due to strong subsidence associated with Walker circulation over the central and eastern Indian Ocean, deep convection was not present. Finally, the diurnal variations of the maximum rainfall

  7. Investigating Rainfall Variability in the South Pacific Convergence Zone using the Geochemistry of Stalagmites from the Solomon Islands

    NASA Astrophysics Data System (ADS)

    Sekhon, N.; Quinn, T. M.; Partin, J. W.; Edwards, R. L.; Cheng, H.

    2015-12-01

    The South Pacific Convergence Zone (SPCZ), which extends southeastward from New Guinea to Tahiti, is the largest perennial rainfall feature in the Southern Hemisphere. The position of the SPCZ and its associated rainfall varies significantly on multidecadal timescales, as documented by instrumental and climate proxy data. For example, stalagmite δ18O records (rainfall proxy) from Espiritu Santo, Vanuatu (Partin et al., 2013) and Guadalcanal, Solomon Islands (Maupin et al., 2014), document large (~1‰), abrupt changes in stalagmite δ18O on multidecadal timescales over the past 600 years that arise from internal variability in the climate system. The proxy data agree with the type of rainfall changes observed in the instrumental record, such as the change across 1976/77, but the older changes are larger in relative magnitude. We expand on these earlier studies of rainfall variability in the SPCZ system using stable isotope variations in stalagmites from two other locations in the Solomon Islands (Munda, New Georgia, 8.3°S, 157.3°E; Suku, Nggela Pile (9.8° S, 160.2° E). These stalagmites range in age from about 400 CE to 1850 CE, based on U-Th dating, and have relatively fast growth rates (60 to 300 µm/yr). Stalagmite δ18O time series were generated from sub-samples milled every 500 µm, or approximately 1 to 8 years per data point. Initial results from these two new Solomon Island stalagmites not only confirm the presence of multidecadal variability in stalagmite δ18O identified in previous studies, but suggest that the same amplitude of variability has occurred over several windows of time during the past 1600 years. When complete, these new proxy rainfall records from Munda and Suku will further constrain the pattern and mechanism of SPCZ rainfall variability in western tropical Pacific region.

  8. Active flexural-slip faulting: A study from the Pamir-Tian Shan convergent zone, NW China

    NASA Astrophysics Data System (ADS)

    Li, Tao; Chen, Jie; Thompson, Jessica A.; Burbank, Douglas W.; Yang, Xiaodong

    2015-06-01

    The flexural-slip fault (FSF), a type of secondary fault generated by bed-parallel slip, occurs commonly and plays an important role in accommodating fold growth. Although the kinematics and mechanics of FSFs are well studied, relatively few field observations or geometric models explore its geomorphic expression. In the Pamir-Tian Shan convergent zone, NW China, suites of well-preserved FSF scarps displace fluvial terraces in the Mingyaole and Wulagen folds. Integrating interpretations of Google Earth images, detailed geologic and geomorphic mapping, and differential GPS measurements of terrace surfaces, we summarize geomorphic features that typify these faults and create kinematic models of active flexural-slip faulting. Our study indicates the following: (i) FSF scarps commonly occur near synclinal hinges, irrespective of whether (a) the dip direction of beds on either side of the hinge is unidirectional or in opposite directions, (b) the hinge is migrating or fixed, or (c) the hinge shape is narrow and angular or wide and curved. (ii) Active FSFs are likely to produce higher scarps on steeper beds, whereas lower or no topographic scarps typify gentler beds. (iii) Tilt angles of the terrace surface displaced above FSFs progressively decrease farther away from the hinge, with abrupt changes in slope coinciding with FSF scarps; the changes in tilt angle and scarp height have a predictable geometric relationship. (iv) Active FSFs can accommodate a significant fraction of total slip and play a significant role in folding deformation. (v) Active FSFs may be used to assess seismic hazards associated with active folds and associated blind thrusts.

  9. Tectonic evidence for the ongoing Africa-Eurasia convergence in central Mediterranean foreland areas: A journey among long-lived shear zones, large earthquakes, and elusive fault motions

    NASA Astrophysics Data System (ADS)

    di Bucci, Daniela; Burrato, Pierfrancesco; Vannoli, Paola; Valensise, Gianluca

    2010-12-01

    We investigate the role of the Africa-Eurasia convergence in the recent tectonic evolution of the central Mediterranean. To this end we focused on two sectors of the Adriatic-Hyblean foreland of the Apennine-Maghrebian chain as they allow tectonic evidence for relative plate motions to be analyzed aside from the masking effect of other more local tectonic phenomena (e.g., subduction, chain building, etc.). We present a thorough review of data and interpretations on two major shear zones cutting these foreland sectors: the E-W Molise-Gondola in central Adriatic and the N-S Vizzini-Scicli in southern Sicily. The selected foreland areas exhibit remarkable similarities, including an unexpectedly high level of seismicity and the presence of the investigated shear zones since the Mesozoic. We analyze the tectonic framework, active tectonics, and seismicity of each of the foreland areas, highlighting the evolution of the tectonic understanding. In both areas, we find that current strains at midcrustal levels seem to respond to the same far-field force oriented NNW-SSE to NW-SE, similar to the orientation of the Africa-Eurasia convergence. We conclude that this convergence plays a primary role in the seismotectonics of the central Mediterranean and is partly accommodated by the reactivation of large Mesozoic shear zones.

  10. Deformation kinematics along oblique convergent plate boundary zones in the western United States, Japanese Islands, and Pakistan

    NASA Astrophysics Data System (ADS)

    Shen-Tu, Bingming

    transmitted from the Japan trench. Horizontal strain rate and velocity field that accommodate India-Eurasia plate motion in Pakistan are determined based on constraints from geological and geodetic information in the region. The optimal model that yields a strain rate field consistent with observed geologic, seismologic, and geodetic data gives 17--28 mm/yr of left-lateral strike-slip motion along the Chaman fault zone, 3--6 mm/yr of east-west convergence and 5--14 mm/yr of north-south left-lateral shear across the roughly NS trending Sulaiman Range. (Abstract shortened by UMI.)

  11. The Asian Monsoon Links to Solar Changes and the Intertropical Convergence Zone and 1300 Years of Chinese Human Susceptibility

    NASA Astrophysics Data System (ADS)

    Yu, E.; Hsu, Y.; Lee, T.

    2011-12-01

    Here we present a new paleoclimatic record from a sediment core recovered in Lake Liyutan in central Taiwan over the last 1300 years. The age model is based on 2 AMS 14C dates. Adjustments of age were using the well-dated records from a near by lake sediment core. The Lake Liyutan sediments record the strength of the summer monsoon in two independent ways: (1) the magnetic parameters (ARM/χ, ARM, anhysteresis remenent magnetization; χ, Volume susceptibility) and magnetic susceptibility, and (2) total organic carbon content, organic C/N elemental ratio and δ13Corg of the sediments as a result of changes in different organic matter origins and terrigenous detritus dilution due to precipitation. All the proxy records are 10 to 30- year-resolution. Weaker summer monsoon phases reconstructed from the Lake Liyutan correlate with higher δ18O at Dongge and Hulu caves, which indicates lower summer precipitation rates. Moreover, it is interesting to find that the strong winter monsoon from the Lake Huguang Maar records show a synchronous relationship with weaker summer monsoon from the caves and the Lake Liyutan. From the coincidence in timing, these records were explained by migrations in the intertropical convergence zone. In addition, the weak Asian summer monsoon in the Lake Liyutan corresponds with lowering Northern Hemisphere summer insolation recorded at Dongge cave. Climate variations influenced the agricultural productivity, health risk, and conflict level of preindustrial societies. We note that, on the basis of our new lake record, major changes in Chinese dynasties occurred when the summer monsoon strength was weaker and rainfall was reduced. The Tang dynasty began to ebb in the eighth century, and it fully collapsed in AD907, then the dynastic transitions to the Five Dynasties and Ten Kingdoms period. The weak summer monsoon and reduced rainfall was indicated in the coincidence in timing of the sediment core LYT-3A from Lake Liyutan during 1100 - 1000BP. In

  12. Fluid budgets at convergent plate margins: Implications for the extent and duration of fault-zone dilation

    USGS Publications Warehouse

    Saffer, D.M.; Bekins, B.A.

    1999-01-01

    Faults at convergent plate boundaries are important conduits for fluid escape, and recent evidence suggests that fluid expulsion along them is both transient and heterogeneous. For the Nankai and Barbados convergent margins, we have used numerical models to investigate the long-term partitioning of expelled fluids between diffuse flow and flow along connected high-permeability fault conduits. For a simple case of spatial heterogeneity, we estimated the extent of high-permeability conduits necessary to maintain a balance between incoming and expelled fluids. For the case of transient expulsion, we constrained the duration of elevated permeability required to balance the fluid budgets. Comparison of modeled and observed geochemical profiles suggests that the initiation of connected flow conduits is delayed with respect to the time of accretion into each accretionary complex and may be related to burial below a critical depth, either where the overlying wedge is sufficiently thick to prevent fluid escape to the sea floor or where sediments behave brittlely.

  13. Forcing, properties, structure, and antecedent synoptic climatology of the Snake River Plain Convergence Zone of eastern Idaho: Analyses of observations and numerical simulations

    NASA Astrophysics Data System (ADS)

    Andretta, Thomas A.

    The Snake River Plain Convergence Zone (SPCZ) is a convergent shear zone generated by synoptic-scale post cold-frontal winds in the planetary boundary layer (PBL) interacting with the complex topography of eastern Idaho. The SPCZ produces clouds and occasional precipitation over time scales of 6--12 hours in a significant area of mesoscale dimensions (10--50 x 10 3 km2). This meso-beta-scale feature also contributes to the precipitation climatology in a semi-arid plain. The SPCZ is climatologically linked to the passage of synoptic-scale cold fronts and typically occurs in the fall and winter months with the highest frequencies in October, November, and January. The Snake River Plain of eastern Idaho is covered by a dense surface mesonetwork of towers with sensible weather measurements, single Doppler weather radar, regional soundings, and operational model sources. The ability of numerical weather prediction models to simulate the SPCZ depends on several factors: the accuracy of the large scale flow upstream of the zone, terrain resolution, grid scale, boundary layer parameterizations of stability, cumulus parameterizations, and microphysics schemes. This dissertation explores several of these issues with the aforementioned observations and with the Weather Research and Forecasting-Advanced Research WRF (WRF-ARW) model simulations of selected SPCZ events. This dissertation first explains the conceptual models of the flow patterns related to the genesis of the SPCZ in light of other well-documented topographically-generated zones. The study then explores the links between the theoretical models and observations of the SPCZ in several episodes. With this foundation, the dissertation then tests several hypotheses relating to the horizontal and vertical zone structure, topographic sensitivity on the zone structure, and boundary layer evolution of the zone through the use of high resolution nested grid numerical simulations. The SPCZ consists of windward and leeward

  14. Age, tectonic evolution and origin of the Aswa Shear Zone in Uganda: Activation of an oblique ramp during convergence in the East African Orogen

    NASA Astrophysics Data System (ADS)

    Saalmann, K.; Mänttäri, I.; Nyakecho, C.; Isabirye, E.

    2016-05-01

    Shear Zone activation is linked to underthrusting of the Congo Craton and coeval high-grade metamorphism and intense deformation in the orogen interior. During E-W convergence between ca. 690 and 650 Ma, the NE-dipping ASZ was activated as an oblique ramp leading to deflection of the transport direction and concentration of non-coaxial strain and sinistral shear along the shear zone system. During progressive convergence, between ca. 645 and 620 Ma, sinistral shearing along ASZ changed to ductile-brittle deformation mechanisms, while thrusting took place in Pan-African belts in eastern and western Uganda. Late-orogenic brittle sinistral reactivation of the ASZ can be regarded as the result of continent collision and closure of the Mozambique ocean further to the east, that potentially caused lateral escape manifested in NW-SE striking sinistral shear zones in Kenya and the southern Arabina-Nubian Shield between 620 and 570 Ma.

  15. Incipient extension along the active convergent margin of Nubia in Sicily, Italy: Cefalù-Etna seismic zone

    NASA Astrophysics Data System (ADS)

    Billi, Andrea; Presti, Debora; Orecchio, Barbara; Faccenna, Claudio; Neri, Giancarlo

    2010-08-01

    Recent geodetic data are compatible with NNE-SSW tectonic extension at a rate of ˜5 mm/yr in Sicily, southern Italy, within a broader region of net active compression along the Nubian plate margin (northern Africa). The structures that accommodate such extensional regime and its cause are still unknown. From field structural surveys and seismological analyses, the geometry, kinematics, structural architecture, and seismic potential of an extensional seismic zone linking Cefalù and Mount Etna in central eastern Sicily are defined. The zone includes high-angle WNW striking normal and right-lateral strike-slip faults and subordinate north and NNE striking strike-slip faults either right or left lateral. The occurrence of small discontinuous faults and the absence of related depressions and sedimentary basins suggest that the extensional regime is still in an incipient stage. The ongoing seismic activity possibly reactivates preexisting faults. Instrumentally and historically recorded earthquakes are lower than about 6 in magnitude, and destructive events are historically unknown since at least 1300 A.D. This apparent upper bound of earthquake magnitudes is consistent with the maximum magnitude values estimated from the length of the longest mapped faults and sources of seismic swarms, which all together suggest a value between 6 and 6.5 as the maximum expected magnitude that can be proposed at the present stage of investigation for earthquakes in the study area. Lateral extension on preexisting faults and upwelling of melt mantle material beneath Mount Etna are considered viable processes to explain, at least in part, the active extensional tectonics along the Cefalù-Etna seismic zone. Strike-slip seismic faulting beneath Mount Etna may be part of a previously proposed diffuse transfer zone affecting northeastern Sicily and including the Tindari Fault.

  16. Quantitative zone-axis convergent-beam electron diffraction (CBED) studies of metals. II. Debye-Waller-factor measurements.

    PubMed

    Saunders; Fox; Midgley

    1999-05-01

    Quantitative CBED techniques, such as the ZAPMATCH zone-axis pattern-matching method [Bird & Saunders (1992). Ultramicroscopy, 45, 241-251], have been applied with great success to the accurate refinement of low-order structure factors. The major limitation on the accuracy of the structure-factor measurements is uncertainty in the Debye-Waller factors describing the temperature-dependent atomic vibrations. While X-ray and neutron diffraction tech-niques are both capable of accurate measurements of Debye-Waller factors, the frequent use of liquid-nitrogen-cooled samples in CBED experiments means that previous measurements are rarely available at the temperatures required. This has prompted attempts to determine Debye-Waller factors from electron diffraction data obtained under experimental conditions that match those used for the quantitative CBED work. In this paper, the possibility of extracting accurate Debye-Waller factors from the low-order reflections of a zone-axis CBED pattern is investigated. In this way, the Debye-Waller factors and structure factors could be obtained from the same data set. With this new approach, it is shown that errors lower than +/-0.02 Å(2) can be obtained for the measurement of Debye-Waller factors from room- and liquid-nitrogen-temperature nickel and copper <110> zone-axis data. The results obtained are compared with previous measurements and theoretical predictions. PMID:10926691

  17. Evolution and timing of tectonic events in the Arabia-Eurasia convergence zone as inferred from igneous geochemistry from the EarthChem database

    NASA Astrophysics Data System (ADS)

    Lieu, W. K.; Stern, R. J.

    2011-12-01

    The timing of tectonic events in the Anatolia-Iranian region can be inferred from analysis of igneous rocks. Magmatic activities in the region are generally associated with the convergence of the African-Arabian and Eurasian plates and the subduction of the Neotethys Ocean. Ancillary processes such as subduction of continental crust, delamination of upper plate lithosphere or lower crust, or asthenospheric decompression accompanying post-collisional relaxation also contribute to the composition of igneous rocks. Here we use geochemical data gathered from the EarthChem database to assess broad chemical implications of Cenozoic tectonic activities of the convergence region. We search for geochemical signal of the timing of first contact of the subducting Arabian and overriding Eurasian continental crust. Of particular interest is how igneous rock compositions vary during the transition from pre- to post-contact of the continental crusts. Also, is there a geographic variation along the convergence zone during this tectonic transition? We generate maps and geochemical plots for four different epochs and two different regions since Cenozoic time: Iran and Anatolia in the Eocene, Oligocene, Miocene and Plio-Quaternary. This board, region-scaled analysis of major and trace element patterns suggests the following tectonic events: Subduction-related medium K calc-alkaline igneous rocks reflect Eocene subduction of the Neo-Tethys oceanic lithosphere. Oligocene igneous rocks are characterized by K2O-SiO2 trends scattering to higher silica and alkaline content, which may reflect subduction of stretched continental margin lithosphere and sediments. A bimodal pattern of potash-silica trends during Miocene time may mark the transition from subduction-related to intra-plate magmatism, perhaps signaling contact between the continental crust of Arabia-Africa with Eurasia. Pliocene and younger igneous rocks show an intra-plate and ocean island basalt trend, as the region's activities

  18. Convergence Insufficiency

    MedlinePlus

    ... Eye Terms Conditions Frequently Asked Questions Español Condiciones Chinese Conditions Convergence Insufficiency En Español Read in Chinese What is convergence insufficiency? Convergence insufficiency is the ...

  19. Early Cambrian granitoids of North Gondwana margin in the transition from a convergent setting to intra-continental rifting (Ossa-Morena Zone, SW Iberia)

    NASA Astrophysics Data System (ADS)

    Sánchez-García, T.; Pereira, M. F.; Bellido, F.; Chichorro, M.; Silva, J. B.; Valverde-Vaquero, P.; Pin, Ch.; Solá, A. R.

    2014-07-01

    Two distinct Cambrian magmatic pulses are recognized in the Ossa-Morena Zone (SW Iberia): an early rift-(ER) and a main rift-related event. This Cambrian magmatism is related to intra-continental rifting of North Gondwana that is thought to have culminated in the opening of the Rheic Ocean in Lower Ordovician times. New data of whole-rock geochemistry (19 samples), Sm-Nd-Sr isotopes (4 samples) and ID-TIMS U-Pb zircon geochronology (1 sample) of the Early Cambrian ER plutonic rocks of the Ossa-Morena Zone are presented in this contribution. The ER granitoids (Barreiros, Barquete, Calera, Salvatierra de los Barros and Tablada granitoid Massifs) are mostly peraluminous granites. The Sm-Nd isotopic data show moderate negative ɛNdt values ranging from -3.5 to +0.1 and TDM ages greatly in excess of emplacement ages. Most ER granitoids are crustal melts. However, a subset of samples shows a transitional anorogenic alkaline tendency, together with more primitive isotopic signatures, documenting the participation of lower crust or mantle-derived sources and suggesting a local transient advanced stage of rifting. The Barreiros granitoid is intrusive into the Ediacaran basement of the Ossa-Morena Zone (Série Negra succession) and has yielded a crystallization age of 524.7 ± 0.8 Ma consistent with other ages of ER magmatic pulse. This age: (1) constrains the age of the metamorphism developed in the Ediacaran back-arc basins before the intrusion of granites and (2) defines the time of the transition from the Ediacaran convergent setting to the Lower Cambrian intra-continental rifting in North Gondwana.

  20. Real-time three-dimensional color doppler evaluation of the flow convergence zone for quantification of mitral regurgitation: Validation experimental animal study and initial clinical experience

    NASA Technical Reports Server (NTRS)

    Sitges, Marta; Jones, Michael; Shiota, Takahiro; Qin, Jian Xin; Tsujino, Hiroyuki; Bauer, Fabrice; Kim, Yong Jin; Agler, Deborah A.; Cardon, Lisa A.; Zetts, Arthur D.; Panza, Julio A.; Thomas, James D.

    2003-01-01

    BACKGROUND: Pitfalls of the flow convergence (FC) method, including 2-dimensional imaging of the 3-dimensional (3D) geometry of the FC surface, can lead to erroneous quantification of mitral regurgitation (MR). This limitation may be mitigated by the use of real-time 3D color Doppler echocardiography (CE). Our objective was to validate a real-time 3D navigation method for MR quantification. METHODS: In 12 sheep with surgically induced chronic MR, 37 different hemodynamic conditions were studied with real-time 3DCE. Using real-time 3D navigation, the radius of the largest hemispherical FC zone was located and measured. MR volume was quantified according to the FC method after observing the shape of FC in 3D space. Aortic and mitral electromagnetic flow probes and meters were balanced against each other to determine reference MR volume. As an initial clinical application study, 22 patients with chronic MR were also studied with this real-time 3DCE-FC method. Left ventricular (LV) outflow tract automated cardiac flow measurement (Toshiba Corp, Tokyo, Japan) and real-time 3D LV stroke volume were used to quantify the reference MR volume (MR volume = 3DLV stroke volume - automated cardiac flow measurement). RESULTS: In the sheep model, a good correlation and agreement was seen between MR volume by real-time 3DCE and electromagnetic (y = 0.77x + 1.48, r = 0.87, P <.001, delta = -0.91 +/- 2.65 mL). In patients, real-time 3DCE-derived MR volume also showed a good correlation and agreement with the reference method (y = 0.89x - 0.38, r = 0.93, P <.001, delta = -4.8 +/- 7.6 mL). CONCLUSIONS: real-time 3DCE can capture the entire FC image, permitting geometrical recognition of the FC zone geometry and reliable MR quantification.

  1. Band structure of silicene on zirconium diboride (0001) thin-film surface: Convergence of experiment and calculations in the one-Si-atom Brillouin zone

    NASA Astrophysics Data System (ADS)

    Lee, Chi-Cheng; Fleurence, Antoine; Yamada-Takamura, Yukiko; Ozaki, Taisuke; Friedlein, Rainer

    2014-08-01

    So far, it represents a challenging task to reproduce angle-resolved photoelectron (ARPES) spectra of epitaxial silicene by first-principles calculations. Here, we report on the resolution of the previously controversial issue related to the structural configuration of silicene on the ZrB2(0001) surface and its band structure. In particular, by representing the band structure in a large Brillouin zone associated with a single Si atom, it is found that the imaginary part of the one-particle Green's function follows the spectral weight observed in ARPES spectra. By additionally varying the in-plane lattice constant, the results of density functional theory calculations and ARPES data obtained in a wide energy range converge into the "planarlike" phase and provide the orbital character of electronic states in the vicinity of the Fermi level. It is anticipated that the choice of a smaller commensurate unit cell for the representation of the electronic structure will be useful for the study of epitaxial two-dimensional materials on various substrates in general.

  2. Sediment dispersal system in the Taiwan-South China Sea collision zone along a convergent margin in the perspective of source to sink

    NASA Astrophysics Data System (ADS)

    Hsiung, K.; Yu, H.

    2011-12-01

    Through a large-scale examination of the morpho-sedimentary features on seafloor in the Taiwan-Luzon convergent margin, we determined the main sediment dispersal system which stretches from 23°N to 20°N and displays as an aligned linear sediment pathway, consisting of the Penghu Canyon, the deep-sea Penghu Channel and northern Manila Trench. The seafloor of South China Sea (SCS) north of 21°N are underlain by a triangle-shaped collision basin, resulting from oblique collision between the Luzon Arc and Chinese margin, and is mainly occupied by two juxtaposed slopes, the SCS and Kaoping slopes. The Penghu Canyon is located along the tilting basin axis where is the physiographic boundary separating the SCS and Kaoping slopes. Progressive subsidence of the basin floor from this nearby uplifted Taiwan orogen results in the linear basin axis deepening and tilting towards the open SCS, serving as a longitudinal sediment conduit. Two major tributary canyons of the Formosa and Kaoping and small channels and gullies on both slopes join into the axial Penghu Canyon and form a dendritic canyon drainage system in this collision basin. The canyon drainage system is characteristic of lateral sediment supply from flank slopes and axial sediment transport down-canyon following the tilting basin axis. The significance of the collision basin in term of source to sink is that terrestrial and shallow marine sediments derived from nearby Taiwan orogen, Chinese margin and the Taiwan Strait are transported to and accumulated in the collision basin, serving as a temporary sediment sink and the major marine transport route along the basin axis. The multi-sourced sediments in the collision basin are then delivered down-dip via the Penghu Canyon to the deep-sea Penghu Channel and ultimately to the final destination of the Manila Trench, representing a regional longitudinal sediment dispersal route along the convergent margin between Taiwan and Luzon. A comparison with other examples is a

  3. Sediment dispersal system in the Taiwan-South China Sea collision zone along a convergent margin: A comparison with the Papua New Guinea collision zone of the western Solomon Sea

    NASA Astrophysics Data System (ADS)

    Hsiung, Kan-Hsi; Yu, Ho-Shing

    2013-01-01

    Through a large-scale examination of the morpho-sedimentary features on sea floors in the Taiwan-Luzon convergent margin, we determined the main sediment dispersal system which stretches from 23°N to 20°N and displays as an aligned linear sediment pathway, consisting of the Penghu Canyon, the deep-sea Penghu Channel and northern Manila Trench. The seafloor of South China Sea north of 21°N are underlain by a triangle-shaped collision marine basin, resulting from oblique collision between the Luzon Arc and Chinese margin, and are mainly occupied by two juxtaposed slopes, the South China Sea and Kaoping Slopes, and a southward tilting basin axis located along the Penghu Canyon. Two major tributary canyons of the Formosa and Kaoping and small channels and gullies on both slopes join into the axial Penghu Canyon and form a dendritic canyon drainage system in this collision marine basin. The canyon drainage system is characteristic of lateral sediment supply from flank slopes and axial sediment transport down-canyon following the tilting basin axis. The significance of the collision marine basin in term of source to sink is that sediments derived from nearby orogen and continental margins are transported to and accumulated in the collision basin, serving as a temporary sediment sink and major marine transport route along the basin axis. The comparison of the Taiwan-South China Sea collision zone with the Papua New Guinea collision zone of the western Solomon Sea reveals remarkable similarities in tectonic settings and sedimentary processes that have resulted in similar sediment dispersal systems consisting of (1) a canyon drainage network mainly in the collision basin and (2) a longitudinal sediment transport system comprising a linear connection of submarine canyon, deep-sea channel and oceanic trench beyond the collision marine basin.

  4. Partitioning of oblique convergence in the Northern Andes subduction zone: Migration history and the present-day boundary of the North Andean Sliver in Ecuador

    NASA Astrophysics Data System (ADS)

    Alvarado, A.; Audin, L.; Nocquet, J. M.; Jaillard, E.; Mothes, P.; Jarrín, P.; Segovia, M.; Rolandone, F.; Cisneros, D.

    2016-05-01

    Along the Ecuadorian margin, oblique subduction induces deformation of the overriding continental plate. For the last 15 Ma, both exhumation and tectonic history of Ecuador suggest that the northeastward motion of the North Andean Sliver (NAS) was accompanied by an eastward migration of its eastern boundary and successive progressively narrowing restraining bends. Here we present geologic data, earthquake epicenters, focal mechanisms, GPS results, and a revised active fault map consistent with this new kinematic model. All data sets concur to demonstrate that active continental deformation is presently localized along a single major fault system, connecting fault segments from the Gulf of Guayaquil to the eastern Andean Cordillera. Although secondary faults are recognized within the Cordillera, they accommodate a negligible fraction of relative motion compared to the main fault system. The eastern limit is then concentrated rather than distributed as first proposed, marking a sharp boundary between the NAS, the Inca sliver, and the Subandean domain overthrusting the South American craton. The NAS limit follows a northeast striking right-lateral transpressional strike-slip system from the Gulf of Guayaquil (Isla Puná) to the Andean Cordillera and with the north-south striking transpressive faults along the eastern Andes. Eastward migration of the restraining belt since the Pliocene, abandonment of the sutures and reactivation of north-south striking ancient fault zones lead to the final development of a major tectonic boundary south and east of the NAS, favoring its extrusion as a continental sliver, accommodating the oblique convergence of the Nazca oceanic plate toward South America.

  5. Interdecadal-decadal climate variability from multicoral oxygen isotope records in the South Pacific Convergence Zone region since 1650 A.D.

    NASA Astrophysics Data System (ADS)

    Linsley, Braddock K.; Zhang, Peipei; Kaplan, Alexey; Howe, Stephen S.; Wellington, Gerard M.

    2008-06-01

    In the South Pacific, interdecadal-decadal oceanic and atmospheric variability, referred to as the Interdecadal Pacific Oscillation (IPO), is most pronounced in the South Pacific Convergence Zone (SPCZ) salinity front region. Here we have used annual average oxygen isotope (δ18O) time series from five coral cores collected from Fiji and Tonga in this region to construct a Fiji-Tonga Interdecadal-Decadal Pacific Oscillation (F-T IDPO) index of low-frequency (>9 and <55 years) climate variability back to 1650 A.D. We first demonstrate the consistency between this F-T IDPO index and a mean sea level (MSL) pressure-based SPCZ position index (SPI) (1891-2000), thus verifying the ability of coral δ18O to record past interdecadal-decadal climatic variations in this region back to 1891. The F-T IDPO index is then shown to be synchronous with the IPO index (1856-2000), suggesting that this coral-based index effectively represents the interdecadal-decadal scale climate variance back to 1650. The regularity of the F-T IDPO index indicates that interdecadal-decadal variability in the SPCZ region has been relatively constant over the past 350 years with a mean frequency of ˜20 years (variance peaks near 11 and 35 years). There is a consistent antiphase correlation of the F-T IDPO index and the interdecadal-decadal components in equatorial Pacific coral δ18O series from Maiana and Palmyra. This observation indicates that the eastward expansion (westward contraction) of the eastern salinity front of the Western Pacific Warm Pool (WPWP) occurs simultaneously (±<1 year) with the westward (eastward) shift of the SPCZ salinity front during positive IPO (negative IPO) phases. This is the same relationship observed during the phases of the El Niño Southern Oscillation.

  6. Sequence stratigraphy, structural style, and age of deformation of the Malaita accretionary prism (Solomon arc-Ontong Java Plateau convergent zone)

    NASA Astrophysics Data System (ADS)

    Phinney, Eric J.; Mann, Paul; Coffin, Millard F.; Shipley, Thomas H.

    2004-10-01

    Possibilities for the fate of oceanic plateaus at subduction zones range from complete subduction of the plateau beneath the arc to complete plateau-arc accretion and resulting collisional orogenesis. Deep penetration, multi-channel seismic reflection (MCS) data from the northern flank of the Solomon Islands reveal the sequence stratigraphy, structural style, and age of deformation of an accretionary prism formed during late Neogene (5-0 Ma) convergence between the ˜33-km-thick crust of the Ontong Java oceanic plateau and the ˜15-km-thick Solomon island arc. Correlation of MCS data with the satellite-derived, free-air gravity field defines the tectonic boundaries and internal structure of the 800-km-long, 140-km-wide accretionary prism. We name this prism the "Malaita accretionary prism" or "MAP" after Malaita, the largest and best-studied island exposure of the accretionary prism in the Solomon Islands. MCS data, gravity data, and stratigraphic correlations to islands and ODP sites on the Ontong Java Plateau (OJP) reveal that the offshore MAP is composed of folded and thrust faulted sedimentary rocks and upper crystalline crust offscraped from the Solomon the subducting Ontong Java Plateau (Pacific plate) and transferred to the Solomon arc. With the exception of an upper, sequence of Quaternary? island-derived terrigenous sediments, the deformed stratigraphy of the MAP is identical to that of the incoming Ontong Java Plateau in the North Solomon trench. We divide the MAP into four distinct, folded and thrust fault-bounded structural domains interpreted to have formed by diachronous, southeast-to-northwest, and highly oblique entry of the Ontong Java Plateau into a former trench now marked by the Kia-Kaipito-Korigole (KKK) left-lateral strike-slip fault zone along the suture between the Solomon arc and the MAP. The structural style within each of the four structural domains consists of a parallel series of three to four fault propagation folds formed by the

  7. Variations of the tropical Atlantic and Pacific SSS minimum zones and their relations to the ITCZ and SPCZ rain bands (1979-2009)

    NASA Astrophysics Data System (ADS)

    Tchilibou, M.; Delcroix, T.; Alory, G.; Arnault, S.; Reverdin, G.

    2015-07-01

    This study focuses on the time-space variability of the low Sea Surface Salinity (SSS) waters extending zonally within 2°N-12°N in the Atlantic and Pacific and within 6°S-16°S in the western third of the Pacific. The analysis is based on a combination of in situ SSS observations collected in the last three decades from voluntary observing ships, TAO/TRITON and PIRATA moorings, Argo floats, and (few) CTD profiles. The mean latitudes of the Atlantic and Pacific low SSS waters appear 1°-3° further poleward than the Evaporation minus Precipitation (E-P) minima linked to the Inter Tropical Convergence Zones (ITCZ) and South Pacific Convergence Zone (SPCZ). At the seasonal time scale, the E-P minima migrate poleward in summer hemispheres, leading the migration of the SSS minima by 2-3 months in the Atlantic ITCZ, Pacific SPCZ, and in the eastern part of the Pacific ITCZ. On the other hand, the seasonal displacements of E-P and SSS minima are in antiphase in the central and western parts of the Pacific ITCZ. At the interannual time scale, the E-P and SSS minima migrate poleward during La Nina events in the Pacific and during the positive phase of the Atlantic Meridional Dipole (AMD) in the Atlantic (and vice versa during El Nino and the negative phase of the AMD). We further document long-term (1979-2009) meridional migrations of the E-P and SSS minima, especially in the SPCZ region, and discuss whether or not they are consistent with documented SST and wind stress trends.

  8. Combined Regional Gravity Model of the Andean Convergent Subduction Zone and Its Application to Crustal Density Modelling in Active Plate Margins

    NASA Astrophysics Data System (ADS)

    Hosse, M.; Pail, R.; Horwath, M.; Holzrichter, N.; Gutknecht, B. D.

    2014-11-01

    The Central Andean subduction system is one of the most active geological structures on Earth. Although there have been a few previous studies, the structure and dynamics of the system are still not well understood. In the present study, we determine a combined regional gravity model of the Andean convergent subduction region for constraining lithospheric models. After a thorough validation and cleaning of the terrestrial gravity and height databases, the method of Least Squares Collocation was applied to consistently combine terrestrial and satellite gravity data, putting much emphasis on the stochastic modelling of the individual data components. As a result, we computed the first high-resolution regional gravity model of the study region that includes GOCE satellite gravity information. The inclusion of GOCE is an essential distinction from the independent global gravity model EGM2008. Validation against EGM2008 reveals that our regional solution is very consistent in regions where terrestrial gravity data are available, but shows systematic differences in areas with terrestrial data gaps. Artefacts in the EGM2008 of up to 150 mGal could be identified. The new combined regional model benefits from the very homogeneous error characteristics and accuracy of GOCE gravity data in the long-to-medium wavelengths down to 80-100 km. Reliable density modelling became possible also in the region of Central Andes, which lacks terrestrial gravity data. Finally, density models were adapted to fit the new regional gravity field solution. The results clearly demonstrate the capabilities of GOCE to better constrain lithospheric models.

  9. Why does continental convergence stop

    SciTech Connect

    Hynes, A.

    1985-01-01

    Convergence between India and Asia slowed at 45 Ma when they collided, but continues today. This requires that substantial proportions of the Indian and/or Asian lithospheric mantle are still being subducted. The resulting slab-pull is probably comparable with that from complete lithospheric slabs and may promote continued continental convergence even after collision. Since descending lithospheric slabs are present at all collision zones at the time of collision such continued convergence may be general after continental collisions. It may cease only when there is a major (global) plate reorganization which results in new forces on the convergent continents that may counteract the slab-pull. These inferences may be tested on the late Paleozoic collision between Gondwanaland and Laurasia. This is generally considered to have been complete by mid-Permian time (250 Ma). However, this may be only the time of docking of Gondwanaland with North America, not that of the cessation of convergence. Paleomagnetic polar-wander paths for the Gondwanide continents exhibit consistently greater latitudinal shifts from 250 Ma to 200 Ma than those of Laurasia when corrected for post-Triassic drift, suggesting that convergence continued through late Permian well into the Triassic. It may have been accommodated by crustal thickening under what is now the US Coastal Plain, or by strike-slip faulting. Convergence may have ceased only when Pangea began to fragment again, in which case the cause for its cessation may be related to the cause of continental fragmentation.

  10. Do convergent developmental mechanisms underlie convergent phenotypes?

    NASA Technical Reports Server (NTRS)

    Wray, Gregory A.

    2002-01-01

    Convergence is a pervasive evolutionary process, affecting many aspects of phenotype and even genotype. Relatively little is known about convergence in developmental processes, however, nor about the degree to which convergence in development underlies convergence in anatomy. A switch in the ecology of sea urchins from feeding to nonfeeding larvae illustrates how convergence in development can be associated with convergence in anatomy. Comparisons to more distantly related taxa, however, suggest that this association may be limited to relatively close phylogenetic comparisons. Similarities in gene expression during development provide another window into the association between convergence in developmental processes and convergence in anatomy. Several well-studied transcription factors exhibit likely cases of convergent gene expression in distantly related animal phyla. Convergence in regulatory gene expression domains is probably more common than generally acknowledged, and can arise for several different reasons. Copyright 2002 S. Karger AG, Basel.

  11. Decadal and lower frequency changes in the South Pacific Convergence Zone (SPCZ) salinity front gradient over the last 210 years and relationship to Pacific-wide climate

    NASA Astrophysics Data System (ADS)

    Linsley, B. K.; Dassie, E. P.; Wu, H. C.; Wellington, G. M.

    2010-12-01

    Along the southeastern edge of the SPCZ near 170°W and 15°-20°S a surface ocean salinity frontal zone exists that separates fresher water under the SPCZ from significantly saltier and cooler waters to the east in the South Pacific central gyre. Instrumental sea surface salinity (SSS) data from this region indicate that temporal variability in the SSS difference between Fiji and Tonga is closely coupled to the phase of ENSO. The SSS difference increases by 1.0 to 1.5 p.s.s. during La Niña events and decreases by a comparable magnitude to no difference (0.0 p.s.s.) during El Niño events. The cause of this gradient change is directly related to the position of the salinity front. During La Niña events the salinity front shifts SE as the S. Equatorial Current (SEC) weakens and the zone of maximum rainfall in the SPCZ moves over Fiji, making Fiji fresher than Tonga. During El Niño events, the SEC advects higher salinity water from the east and the SPCZ shifts NE making the SSS difference between Fiji and Tonga close to zero. Using replicated coral δ18O and SSS records over the last 50 years, (Dassie et al., 2010, this meeting) demonstrate that Porites corals from Fiji and Tonga accurately record interannual changes in this SSS difference across the salinity front. Here we evaluate decadal-scale and lower frequency changes in the coral δ18O difference between Fiji and Tonga using replicated Porites coral δ18O records from Fiji (Savusavu Bay, n=2; Vanua Balavu (200km E. of Savusavu Bay, n=2) and Tonga (n=2). Our previous work with coral δ18O records from the region indicates that interannual and lower frequency changes in δ18O are predominantly driven by changes in SSS (Linsley et al., 2006, G^3). Earlier evidence from instrumental salinity data and coral δ18O records indicate that the SPCZ has been expanding SE since the mid 19th century. Our new coral δ18O reconstruction of the SSS gradient provides more details and indicates a reduced or non

  12. Imaging the structure of the Northern Lesser Antilles (Guadeloupe - Virgin Island) to assess the tectonic and thermo-mechanical behavior of an arcuate subduction zone that undergoes increasing convergence obliquity

    NASA Astrophysics Data System (ADS)

    Laurencin, M.; Marcaillou, B.; Klingelhoefer, F.; Jean-Frederic, L.; Graindorge, D.; Bouquerel, H.; Conin, M.; Crozon, J.; De Min, L.; De Voogd, B.; Evain, M.; Heuret, A.; Laigle, M.; Lallemand, S.; Lucazeau, F.; Pichot, T.; Prunier, C.; Rolandone, F.; Rousset, D.; Vitard, C.

    2015-12-01

    Paradoxically, the Northern Lesser Antilles is the less-investigated and the most tectonically and seismically complex segment of the Lesser Antilles subduction zone: - The convergence obliquity between the North American and Caribbean plates increases northward from Guadeloupe to Virgin Islands raising questions about the fore-arc tectonic partitioning. - The margin has undergone the subduction of the rough sediment-starved Atlantic Ocean floor spiked with ridges as well as banks docking, but the resulting tectonic deformation remains hypothetical in the absence of a complete bathymetry and of any seismic line. - Recent geodetic data and low historical seismic activity suggest a low interplate coupling between Saint-Martin and Anegada, but the sparse onshore seismometers located far from source zone cast doubt on this seismic gap. To shed new light on these questions, the ANTITHESIS project, 5 Marine Geophysical legs totaling 72 days, aims at recording a complete bathymetric map, deep and shallow seismic reflexion lines, wide-angle seismic data, heat-flow measurements and the seismic activity with a web of sea-bottom seismometers. Our preliminary results suggest that: - A frontal sliver of accretionary prism is stretched and expulsed northward by 50km along the left-lateral Bunce fault that limits the prism from the margin basement as far southward as 18.5°N. So far, this structure is the only interpreted sign of tectonic partitioning in the fore-arc. - The Anegada Passage extends eastward to the accretionary prism through strike-slip faults and pull-apart basins that possibly form a lef-lateral poorly-active system inherited from a past tectonic phase, consistently with geodetic and seismologic data. - The anomalously cold interplate contact, consistent with a low interseismic coupling, is possibly due to fluid circulation within the shallow crustal aquifer or a depressed thermal structure of the oceanic crust related to the slow-spreading at the medio

  13. Variability in warm-season atmospheric circulation and precipitation patterns over subtropical South America: relationships between the South Atlantic convergence zone and large-scale organized convection over the La Plata basin

    NASA Astrophysics Data System (ADS)

    Mattingly, Kyle S.; Mote, Thomas L.

    2016-03-01

    Warm-season precipitation variability over subtropical South America is characterized by an inverse relationship between the South Atlantic convergence zone (SACZ) and precipitation over the central and western La Plata basin of southeastern South America. This study extends the analysis of this "South American Seesaw" precipitation dipole to relationships between the SACZ and large, long-lived mesoscale convective systems (LLCSs) over the La Plata basin. By classifying SACZ events into distinct continental and oceanic categories and building a logistic regression model that relates LLCS activity across the region to continental and oceanic SACZ precipitation, a detailed account of spatial variability in the out-of-phase coupling between the SACZ and large-scale organized convection over the La Plata basin is provided. Enhanced precipitation in the continental SACZ is found to result in increased LLCS activity over northern, northeastern, and western sections of the La Plata basin, in association with poleward atmospheric moisture flux from the Amazon basin toward these regions, and a decrease in the probability of LLCS occurrence over the southeastern La Plata basin. Increased oceanic SACZ precipitation, however, was strongly related to reduced atmospheric moisture and decreased probability of LLCS occurrence over nearly the entire La Plata basin. These results suggest that continental SACZ activity and large-scale organized convection over the northern and eastern sections of the La Plata basin are closely tied to atmospheric moisture transport from the Amazon basin, while the warm coastal Brazil Current may also play an important role as an evaporative moisture source for LLCSs over the central and western La Plata basin.

  14. A Fiji multi-coral δ18O composite approach to obtaining a more accurate reconstruction of the last two-centuries of the ocean-climate variability in the South Pacific Convergence Zone region

    NASA Astrophysics Data System (ADS)

    Dassié, Emilie P.; Linsley, Braddock K.; Corrège, Thierry; Wu, Henry C.; Lemley, Gavin M.; Howe, Steve; Cabioch, Guy

    2014-12-01

    The limited availability of oceanographic data in the tropical Pacific Ocean prior to the satellite era makes coral-based climate reconstructions a key tool for extending the instrumental record back in time, thereby providing a much needed test for climate models and projections. We have generated a unique regional network consisting of five Porites coral δ18O time series from different locations in the Fijian archipelago. Our results indicate that using a minimum of three Porites coral δ18O records from Fiji is statistically sufficient to obtain a reliable signal for climate reconstruction, and that application of an approach used in tree ring studies is a suitable tool to determine this number. The coral δ18O composite indicates that while sea surface temperature (SST) variability is the primary driver of seasonal δ18O variability in these Fiji corals, annual average coral δ18O is more closely correlated to sea surface salinity (SSS) as previously reported. Our results highlight the importance of water mass advection in controlling Fiji coral δ18O and salinity variability at interannual and decadal time scales despite being located in the heavy rainfall region of the South Pacific Convergence Zone (SPCZ). The Fiji δ18O composite presents a secular freshening and warming trend since the 1850s coupled with changes in both interannual (IA) and decadal/interdecadal (D/I) variance. The changes in IA and D/I variance suggest a re-organization of climatic variability in the SPCZ region beginning in the late 1800s to period of a more dominant interannual variability, which could correspond to a southeast expansion of the SPCZ.

  15. Convergence Is Real

    ERIC Educational Resources Information Center

    Enyeart, Mike; Staman, E. Michael; Valdes, Jose J., Jr.

    2007-01-01

    The concept of convergence has evolved significantly during recent years. Today, "convergence" refers to the integration of the communications and computing resources and services that seamlessly traverse multiple infrastructures and deliver content to multiple platforms or appliances. Convergence is real. Those in higher education, and especially…

  16. Convergent flow stove

    SciTech Connect

    Engblom, D.W.

    1986-02-25

    An apparatus for burning combustible solid organic material such as wood is described in a environment in which combustion is directed downwardly. The apparatus consists of: A. A fuel chamber having a closed upper portion and a major dimension in the vertical direction such that the fuel chamber is generally upright, B. A combustion zone in the lower portion of the fuel chamber defined by a convergent outflow passage at the bottom of the fuel chamber and a pair of walls on opposite sides of the lower portion, the walls being sloped inwardly toward one another at the outflow passage, and the outflow passage comprising a gap between the walls, C. A Hearth element forming each the sloping wall, the hearth element including I. At least one row of spaced slots extending into the interior of the hearth element and a lateral air inlet channel connected to the slots of each row and a source of combustion air, and II. A flue outlet communicating with the outflow passage, the flue outlet including spaced, parallel tubes in the hearth element, with the tubes being juxtaposed the slots and extending perpendicular to the air inlet channels, D. Means connected to the flue outlet to permit exhaustion of flue gases from the apparatus, and E. means for loading fuel into the fuel chamber.

  17. Mnemonic convergence in the human hippocampus

    PubMed Central

    Backus, Alexander R.; Bosch, Sander E.; Ekman, Matthias; Grabovetsky, Alejandro Vicente; Doeller, Christian F.

    2016-01-01

    The ability to form associations between a multitude of events is the hallmark of episodic memory. Computational models have espoused the importance of the hippocampus as convergence zone, binding different aspects of an episode into a coherent representation, by integrating information from multiple brain regions. However, evidence for this long-held hypothesis is limited, since previous work has largely focused on representational and network properties of the hippocampus in isolation. Here we identify the hippocampus as mnemonic convergence zone, using a combination of multivariate pattern and graph-theoretical network analyses of functional magnetic resonance imaging data from humans performing an associative memory task. We observe overlap of conjunctive coding and hub-like network attributes in the hippocampus. These results provide evidence for mnemonic convergence in the hippocampus, underlying the integration of distributed information into episodic memory representations. PMID:27325442

  18. Development of the Scale for "Convergence Thinking" in Engineering

    ERIC Educational Resources Information Center

    Park, Sungmi

    2016-01-01

    Purpose: The purpose of this paper is to define the concept of "convergence thinking" as a trading zone for knowledge fusion in the engineering field, and develops its measuring scale. Design/ Methodology/Approach: Based on results from literature review, this study clarifies a theoretical ground for "convergence thinking."…

  19. The cumulative effect of convergent seismic waves

    NASA Astrophysics Data System (ADS)

    Guglielmi, A. V.

    2015-11-01

    This methodical note is devoted to the nonlinear impact of convergent seismic waves on a medium. Special attention is paid to the similarity and distinctions of the phenomena occurring in the Earth, on one hand, and on the Moon and Mercury, on the other hand. The importance of the experimental and theoretical study of the round-the-world seismic echo which induces repeated shocks in the epicentral zones of the earthquakes is noted.

  20. The Convergence Years

    ERIC Educational Resources Information Center

    Kolodzy, Janet; Grant, August E.; DeMars, Tony R.; Wilkinson, Jeffrey S.

    2014-01-01

    The emergence of the Internet, social media, and digital technologies in the twenty-first century accelerated an evolution in journalism and communication that fit under the broad term of convergence. That evolution changed the relationship between news producers and consumers. It broke down the geographical boundaries in defining our communities,…

  1. Convergence of Arnoldi method

    SciTech Connect

    Nevanlinna, O.

    1994-12-31

    This note summarizes some results on (a monitored version of) the Arnoldi method in Hilbert spaces. The interest in working in infinite dimensional spaces comes partly from the fact that only then can one have meaningful asymptotical statements (which hopefully give some light to the convergence of Arnoldi in large dimensional problems with iteration indices far less than the dimension).

  2. Converging or Diverging Lens?

    ERIC Educational Resources Information Center

    Branca, Mario

    2013-01-01

    Why does a lens magnify? Why does it shrink objects? Why does this happen? The activities that we propose here are useful in helping us to understand how lenses work, and they show that the same lens can have different magnification capabilities. A converging lens can also act as a diverging lens. (Contains 4 figures.)

  3. Knowledge Convergence and Collaborative Learning

    ERIC Educational Resources Information Center

    Jeong, Heisawn; Chi, Michelene T. H.

    2007-01-01

    This paper operationalized the notion of knowledge convergence and assessed quantitatively how much knowledge convergence occurred during collaborative learning. Knowledge convergence was defined as an increase in common knowledge where common knowledge referred to the knowledge that all collaborating partners had. Twenty pairs of college students…

  4. Homology, convergence and parallelism.

    PubMed

    Ghiselin, Michael T

    2016-01-01

    Homology is a relation of correspondence between parts of parts of larger wholes. It is used when tracking objects of interest through space and time and in the context of explanatory historical narratives. Homologues can be traced through a genealogical nexus back to a common ancestral precursor. Homology being a transitive relation, homologues remain homologous however much they may come to differ. Analogy is a relationship of correspondence between parts of members of classes having no relationship of common ancestry. Although homology is often treated as an alternative to convergence, the latter is not a kind of correspondence: rather, it is one of a class of processes that also includes divergence and parallelism. These often give rise to misleading appearances (homoplasies). Parallelism can be particularly hard to detect, especially when not accompanied by divergences in some parts of the body. PMID:26598721

  5. Series that Converge Absolutely but Don't Converge

    ERIC Educational Resources Information Center

    Kantrowitz, Robert; Schramm, Michael

    2012-01-01

    If a series of real numbers converges absolutely, then it converges. The usual proof requires completeness in the form of the Cauchy criterion. Failing completeness, the result is false. We provide examples of rational series that illustrate this point. The Cantor set appears in connection with one of the examples.

  6. Creating Concepts from Converging Features in Human Cortex.

    PubMed

    Coutanche, Marc N; Thompson-Schill, Sharon L

    2015-09-01

    To make sense of the world around us, our brain must remember the overlapping features of millions of objects. Crucially, it must also represent each object's unique feature-convergence. Some theories propose that an integration area (or "convergence zone") binds together separate features. We report an investigation of our knowledge of objects' features and identity, and the link between them. We used functional magnetic resonance imaging to record neural activity, as humans attempted to detect a cued fruit or vegetable in visual noise. Crucially, we analyzed brain activity before a fruit or vegetable was present, allowing us to interrogate top-down activity. We found that pattern-classification algorithms could be used to decode the detection target's identity in the left anterior temporal lobe (ATL), its shape in lateral occipital cortex, and its color in right V4. A novel decoding-dependency analysis revealed that identity information in left ATL was specifically predicted by the temporal convergence of shape and color codes in early visual regions. People with stronger feature-and-identity dependencies had more similar top-down and bottom-up activity patterns. These results fulfill three key requirements for a neural convergence zone: a convergence result (object identity), ingredients (color and shape), and the link between them.

  7. Geotectonic framework of Japanese convergent margin

    SciTech Connect

    Taira, A.; Tokuyama, H.

    1986-07-01

    A synthesis of recent marine geophysical and geologic investigations around Japan uses data obtained by the Ocean Research Institute of the University of Tokyo, the Hydrographic Office and Geological Survey of Japan, and the Japan National Oil Company. This work reveals the contrasting characteristics of forearc and back-arc morphotectonics around Japanese subduction zones. From the north, the following feature can be summarized. The Kuril Trench off Hokkaido shows a pile of trench deposits as much as 2-sec two-way traveltime in thickness. Despite this thickness, there is little evidence of deformation related to the accretionary processes. The authors propose that subduction of the thick trench fill is occurring at this boundary. The Japan Trench is characterized by massive slumping processes and debris accumulation at the toe of the overriding plate. Dai-ichi Kashima seamount at the trench has been broken in half by normal faulting related to bending of the oceanic lithosphere into the subduction zone. Forearc subsidence is also evident on various profiles. The authors believe that the inner wall of the Japan Trench has been eroded tectonically at least from the Miocene to the Pliocene. Three plates interacting at the trench triple junction (Japan, Sagami, and Ogasawara Trenches) created a complex framework of convergent margin tectonics, including highly oblique convergence, forearc sliver collision, and pull-apart basin. The conspicuous features observed in the Izu-Bonin arc are forearc ophiolite (serpentinite diapir) and back-arc rifting close to the volcanic arc. As a result of intraplate shortening related to the Izu-Bonin arc collision against Honshu, the Shikoku basin oceanic crust was ruptured and uplifted, forming a high called the Zenisu Ridge. The Nankai Trough has been filled by turbidites transported through the Suraga Trough area from the Izu collision zone.

  8. The Convergence of Intelligences

    NASA Astrophysics Data System (ADS)

    Diederich, Joachim

    Minsky (1985) argued an extraterrestrial intelligence may be similar to ours despite very different origins. ``Problem- solving'' offers evolutionary advantages and individuals who are part of a technical civilisation should have this capacity. On earth, the principles of problem-solving are the same for humans, some primates and machines based on Artificial Intelligence (AI) techniques. Intelligent systems use ``goals'' and ``sub-goals'' for problem-solving, with memories and representations of ``objects'' and ``sub-objects'' as well as knowledge of relations such as ``cause'' or ``difference.'' Some of these objects are generic and cannot easily be divided into parts. We must, therefore, assume that these objects and relations are universal, and a general property of intelligence. Minsky's arguments from 1985 are extended here. The last decade has seen the development of a general learning theory (``computational learning theory'' (CLT) or ``statistical learning theory'') which equally applies to humans, animals and machines. It is argued that basic learning laws will also apply to an evolved alien intelligence, and this includes limitations of what can be learned efficiently. An example from CLT is that the general learning problem for neural networks is intractable, i.e. it cannot be solved efficiently for all instances (it is ``NP-complete''). It is the objective of this paper to show that evolved intelligences will be constrained by general learning laws and will use task-decomposition for problem-solving. Since learning and problem-solving are core features of intelligence, it can be said that intelligences converge despite very different origins.

  9. South Pacific convergence zone and global-scale circulations

    NASA Technical Reports Server (NTRS)

    Vincent, Dayton G.

    1991-01-01

    The major goals of the research can be classified under three categories: (1) heat and moisture budget studies in the tropics; (2) the role of tropical forcing on subtropical wind maxima in the Southern Hemisphere; and (3) general circulation modeling of low latitude circulations. Research related to the first goal included budget estimates of precipitation, as well as a comparison to rainfall rates observed at numerous island stations. It also included a comparison between observed and satellite estimates of precipitable water. Results and methods used to achieve this goal are given. Included in the second research goal were diagnostic studies of the intraseasonal oscillation which is known to be an important component of organized tropical convection. Also, the role of extratropical forcing on subtropical wind maxima was examined through the use of Eliassen-Palm (EP) fluxes. Again, results and procedural details are discussed in section 3. To accomplish the third research goal, the GLA general circulation model (GCM) was ported to Purdue University and successfully used in a number of control and experimental runs to investigate the significance of tropical heating on subtropical and extratropical circulation features. As with the first two research goals, results and methodology are detailed. Documentation of publications, theses, conference preprint papers, and other scientific information relevant to the research results and significant accomplishments achieved under the contract are given. Finally, the conclusions of the sponsored research are given.

  10. Convergence insufficiency and vision therapy.

    PubMed

    McGregor, Mary Lou

    2014-06-01

    There is no standard meaning of the term "vision therapy", and for this reason it is often a controversial topic between some members of the ophthalmic and optometric community. Most pediatric ophthalmologists avoid using the term because it is nonspecific. Convergence Insufficiency (CI) is a binocular visual problem that causes problems and symptoms with near fixation. There is consensus among eye care professionals that convergence therapy is effective in treating CI. Convergence therapy is not effective in treating learning disabilities, but can sometimes relieve symptoms that might be a barrier to reading.

  11. Lithospheric Convergence Preceded Extension in the Pannonian-Carpathian System

    NASA Astrophysics Data System (ADS)

    Houseman, Gregory; Stuart, Graham; Dando, Ben; Hetenyi, Gyorgy; Lorinczi, Piroska; Hegedus, Endre; Brueckl, Ewald

    2010-05-01

    The continuing collision of the Adriatic block with European continental lithosphere has its clearest expression now in the Alpine collision zone. Recent tomographic images of the upper mantle beneath the eastern Alps and western Pannonian Basin support the interpretation that in the Early Miocene the collision zone extended further east: a steeply dipping seismically fast structure stretches downward beneath the Eastern Alps reaching to the base of the transition zone, consistent with the long history of convergence in this region. This high velocity structure also extends eastward beneath the extensional Pannonian Basin. The high velocity anomaly beneath the Basin is strongly developed in transition zone depths (410 to 660 km) but the anomaly weakens upward. High velocities beneath the center of the extensional basin are unexpected because there is substantive evidence that the onset of extension in the Pannonian domain at around 17 Ma produced rapid extension of the lithosphere and replacement of the lower part of the lithosphere by hot asthenosphere. These deeper structures, however, must be explained by the long history of convergence that preceded the extension of the basin. Further evidence of a history of sustained convergence in the present Pannonian region is found in the depression of the 660 km seismic discontinuity beneath the Alps (Lombardi et al., EPSL, 2009) and also beneath the Pannonian Basin (Hetenyi et al., GRL, 2009). The 660 km discontinuity in both places is depressed by as much as 40 km, whereas the 410 km discontinuity is at approximately nominal depths. Evidently in both regions relatively dense material derived from the mid-Miocene collision sits stagnant on top of the 660 km discontinuity, where further descent is obstructed by the negative Clapeyron slope of the spinel-to-perovskite phase transition and/or the high viscosity of the lower mantle. The rapid extension of the Intra-Carpathian Basins in the Mid-Miocene (between about 17 and

  12. Trophic convergence drives morphological convergence in marine tetrapods.

    PubMed

    Kelley, Neil P; Motani, Ryosuke

    2015-01-01

    Marine tetrapod clades (e.g. seals, whales) independently adapted to marine life through the Mesozoic and Caenozoic, and provide iconic examples of convergent evolution. Apparent morphological convergence is often explained as the result of adaptation to similar ecological niches. However, quantitative tests of this hypothesis are uncommon. We use dietary data to classify the feeding ecology of extant marine tetrapods and identify patterns in skull and tooth morphology that discriminate trophic groups across clades. Mapping these patterns onto phylogeny reveals coordinated evolutionary shifts in diet and morphology in different marine tetrapod lineages. Similarities in morphology between species with similar diets-even across large phylogenetic distances-are consistent with previous hypotheses that shared functional constraints drive convergent evolution in marine tetrapods.

  13. Convergent Creativity: From Arthur Cropley (1935-) Onwards

    ERIC Educational Resources Information Center

    Tan, Ai-Girl

    2015-01-01

    Arthur Cropley's view on convergent thinking is reviewed, with reflections on the relations of divergent and convergent processes and the roles of knowledge and convergent creativity. While divergence is about considering and generating multiplicity, possibility, difference, originality, and so on; convergence is about relating, associating,…

  14. Convergence of a Catalan Series

    ERIC Educational Resources Information Center

    Koshy, Thomas; Gao, Zhenguang

    2012-01-01

    This article studies the convergence of the infinite series of the reciprocals of the Catalan numbers. We extract the sum of the series as well as some related ones, illustrating the power of the calculus in the study of the Catalan numbers.

  15. Convective initiation by topographically induced convergence forcing over the Dabie Mountains on 24 June 2010

    NASA Astrophysics Data System (ADS)

    Wang, Qiwei; Xue, Ming; Tan, Zhemin

    2016-10-01

    The initiation of convective cells in the late morning of 24 June 2010 along the eastward extending ridge of the Dabie Mountains in the Anhui region, China, is studied through numerical simulations that include local data assimilation. A primary convergence line is found over the ridge of the Dabie Mountains, and along the ridge line several locally enhanced convergence centers preferentially initiate convection. Three processes responsible for creating the overall convergence pattern are identified. First, thermally-driven upslope winds induce convergence zones over the main mountain peaks along the ridge, which are shifted slightly downwind in location by the moderate low-level easterly flow found on the north side of a Mei-yu front. Second, flows around the main mountain peaks along the ridge create further convergence on the lee side of the peaks. Third, upslope winds develop along the roughly north-south oriented valleys on both sides of the ridge due to thermal and dynamic channeling effects, and create additional convergence between the peaks along the ridge. The superposition of the above convergence features creates the primary convergence line along the ridge line of the Dabie Mountains. Locally enhanced convergence centers on the primary line cause the initiation of the first convection cells along the ridge. These conclusions are supported by two sensitivity experiments in which the environmental wind (dynamic forcing) or radiative and land surface thermal forcing are removed, respectively. Overall, the thermal forcing effects are stronger than dynamic forcing given the relatively weak environmental flow.

  16. Initiation of deep convection along boundary layer convergence lines in a semitropical environment

    SciTech Connect

    Fankhauser, J.C.; Crook, N.A.; Tuttle, J.; Miller, L.J.; Wade, C.G.

    1995-02-01

    The initiation of deep convection through forcing along boundary layer convergence lines is examined using observations from the Convection and Precipitation/Electrification (CaPE) Experiment conducted in east-central Florida during the summer of 1991. The study is concerned with the evolution and interaction of two converging air masses that were initially separated by an intervening boundary layer characterized by neutral stability and horizontal convective rolls. As anticipated, major thunderstorms erupt when the east coast breeze eventually collides with thunderstorm outflows from the west, but unexpected convection takes place prior to their merger along a well-defined confluence zone associated with a persistent quasi-stationary roll vortex signature. In this study, complementary interactions between roll vortex convergence lines and the sea-breeze front are not sufficient to trigger deep convection. However, organized convergence along the eastward-spreading thunderstorm outflows did interact periodically with roll vortex convergence maxima to initiate a new series of new storms. Results from two-dimensional numerical model simulations replicate many of the observed boundary layer features. Surface heating produces circulations similar to sea-breeze frontal zones that appear near the coastlines and progress steadily toward each other as the interior boundary layer deepens. Vertical velocity maxima develop over the associated convergence zones, but weaker periodic maxima also occur within the interior air mass at intervals similar to the spacing of observed horizontal roll vortices.

  17. Concept Convergence in Empirical Domains

    NASA Astrophysics Data System (ADS)

    Ontañón, Santiago; Plaza, Enric

    How to achieve shared meaning is a significant issue when more than one intelligent agent is involved in the same domain. We define the task of concept convergence, by which intelligent agents can achieve a shared, agreed-upon meaning of a concept (restricted to empirical domains). For this purpose we present a framework that, integrating computational argumentation and inductive concept learning, allows a pair of agents to (1) learn a concept in an empirical domain, (2) argue about the concept's meaning, and (3) reach a shared agreed-upon concept definition. We apply this framework to marine sponges, a biological domain where the actual definitions of concepts such as orders, families and species are currently open to discussion. An experimental evaluation on marine sponges shows that concept convergence is achieved, within a reasonable number of interchanged arguments, and reaching short and accurate definitions (with respect to precision and recall).

  18. Trace gas concentrations, intertropical convergence, atmospheric fronts, and ocean currents in the tropical Pacific

    NASA Technical Reports Server (NTRS)

    Wilkniss, P. E.; Rodgers, E. B.; Swinnerton, J. W.; Larson, R. E.; Lamontagne, R. A.

    1979-01-01

    Descriptions of the intertropical convergence zones (ITCZ) in the tropical Pacific have been obtained from shipboard measurements of Rn-222, CO, and CH4 in combination with conventional meteorological data and satellite images. The intertropical convergence zone is marked by light shifting waves near an area of heavy cloud cover and precipitation, and appears to be located north and south of the south equatorial current. A 'second' ITCZ with the same atmospheric features was encountered just north of the south equatorial current in the Southern Hemisphere. Atmospheric Rn-222 increases north of the ITCZ and serves as a sensitive indicator for this atmospheric boundary.

  19. Converging shocks for DSD modelling

    NASA Astrophysics Data System (ADS)

    Matignon, Christophe

    2013-06-01

    Modelling of pyrotechnic systems requires both, a good understanding and precise prediction capabilities of the dynamics of detonation. When using insensitive high explosives IHE (such as TATB-based explosives) the interaction of the detonation front with the confinement can lead to very different detonation velocities. One of the most popular engineering tools used to model this behaviour is the Detonation Shock Dynamics (DSD). In the DSD assumption, the detonation front propagates at a normal shock velocity (Dn) which depends only on its local curvature (κ). For divergent detonations, the DSD limit is very well established both experimentally and theoretically and one can easily propose a model (which obeys the 1D quasi-steady weakly curved detonation theory) to reproduce this behavior. We propose to extend the DSD theory to slightly convergent detonation fronts and to validate it against experimental data. Two series of experiments were carried out. The first series was designed to collect precise information regarding converging detonation. Usually, in such configurations, the detonation is non steady, making precise and simultaneous measurements of velocity and curvature difficult to achieve. The originality of the proposed setup is to drive a self similar convergent detonation at constant speed in an IHE rod by an external explosive tube of greater detonation velocity (allowing an accurate recording of both velocity and curvature). A wide range EOS/reaction rate model (inspired from previous works of Wescott et al.) was then calibrated to reproduce both the strong shock initiation and the newly extended (Dn- κ) law. This model can be used to perform either direct numerical simulation (DNS) on fine resolved mesh grid, or its reduced PZR model (DSD based) on a much coarser grid. This model was then successfully validated against the second series of experiments involving a detonation propagating around an obstacle and exhibiting a non steady converging front

  20. Convergence analysis of combinations of different methods

    SciTech Connect

    Kang, Y.

    1994-12-31

    This paper provides a convergence analysis for combinations of different numerical methods for solving systems of differential equations. The author proves that combinations of two convergent linear multistep methods or Runge-Kutta methods produce a new convergent method of which the order is equal to the smaller order of the two original methods.

  1. "Nanoselves": NBIC and the Culture of Convergence

    ERIC Educational Resources Information Center

    Venkatesan, Priya

    2010-01-01

    The subject of this essay is NBIC convergence (nanotechnology, biotechnology, information technology and cognitive science convergence). NBIC convergence is a recurring trope that is dominated by the paradigm of integration of the sciences. It is largely influenced by the considerations of social and economic impact, and it assumes positivism in…

  2. Ecomorphological convergence in planktivorous surgeonfishes.

    PubMed

    Friedman, S T; Price, S A; Hoey, A S; Wainwright, P C

    2016-05-01

    Morphological convergence plays a central role in the study of evolution. Often induced by shared ecological specialization, homoplasy hints at underlying selective pressures and adaptive constraints that deterministically shape the diversification of life. Although midwater zooplanktivory has arisen in adult surgeonfishes (family Acanthuridae) at least four independent times, it represents a clearly specialized state, requiring the capacity to swiftly swim in midwater locating and sucking small prey items. Whereas this diet has commonly been associated with specific functional adaptations in fishes, acanthurids present an interesting case study as all nonplanktivorous species feed by grazing on benthic algae and detritus, requiring a vastly different functional morphology that emphasizes biting behaviours. We examined the feeding morphology in 30 acanthurid species and, combined with a pre-existing phylogenetic tree, compared the fit of evolutionary models across two diet regimes: zooplanktivores and nonzooplanktivorous grazers. Accounting for phylogenetic relationships, the best-fitting model indicates that zooplanktivorous species are converging on a separate adaptive peak from their grazing relatives. Driving this bimodal landscape, zooplanktivorous acanthurids tend to develop a slender body, reduced facial features, smaller teeth and weakened jaw adductor muscles. However, despite these phenotypic changes, model fitting suggests that lineages have not yet reached the adaptive peak associated with plankton feeding even though some transitions appear to be over 10 million years old. These findings demonstrate that the selective demands of pelagic feeding promote repeated - albeit very gradual - ecomorphological convergence within surgeonfishes, while allowing local divergences between closely related species, contributing to the overall diversity of the clade. PMID:26809907

  3. Weak {}^* convergence of operator means

    NASA Astrophysics Data System (ADS)

    Romanov, Alexandr V.

    2011-12-01

    For a linear operator U with \\Vert U^n\\Vert \\le \\operatorname{const} on a Banach space X we discuss conditions for the convergence of ergodic operator nets T_\\alpha corresponding to the adjoint operator U^* of U in the {W^*O}-topology of the space \\operatorname{End} X^*. The accumulation points of all possible nets of this kind form a compact convex set L in \\operatorname{End} X^*, which is the kernel of the operator semigroup G=\\overline{\\operatorname{co}}\\,\\Gamma_0, where \\Gamma_0=\\{U_n^*, n \\ge 0\\}. It is proved that all ergodic nets T_\\alpha weakly {}^* converge if and only if the kernel L consists of a single element. In the case of X=C(\\Omega) and the shift operator U generated by a continuous transformation \\varphi of a metrizable compactum \\Omega we trace the relationships among the ergodic properties of U, the structure of the operator semigroups L, G and \\Gamma=\\overline{\\Gamma}_0, and the dynamical characteristics of the semi-cascade (\\varphi,\\Omega). In particular, if \\operatorname{card}L=1, then a) for any \\omega \\in\\Omega the closure of the trajectory \\{\\varphi^n\\omega, n \\ge 0\\} contains precisely one minimal set m, and b) the restriction (\\varphi,m) is strictly ergodic. Condition a) implies the {W^*O}-convergence of any ergodic sequence of operators T_n \\in \\operatorname{End} X^* under the additional assumption that the kernel of the enveloping semigroup E(\\varphi,\\Omega) contains elements obtained from the `basis' family of transformations \\{\\varphi^n, n \\ge 0\\} of the compact set \\Omega by using some transfinite sequence of sequential passages to the limit.

  4. Seismotectonic constraints on the convergence rate between the Rivera and North American plates

    NASA Astrophysics Data System (ADS)

    Kostoglodov, Vladimir; Bandy, William

    1995-09-01

    There are two significantly different types of models for the convergence rate between the Rivera and North American plates. The first type, the high-rate model (Bandy, 1992), predicts convergence rates of approximately 5.0 cm/yr near the southern end of the Rivera-North America subduction zone and between 2.0 and 3.0 cm/yr at its northern end. In contrast, the second type, the low-rate model (e.g., DeMets and Stein, 1990), predicts convergence rates of between 2.0 and 3.3 cm/yr near the southern end of the Rivera-North America subduction zone and between 0.6 and 1.7 cm/yr at its northern end. Seismotectonic relationships, which relate seismic characteristics of subduction zones (maximum magnitudes, maximum seismic depths, etc.) to plate tectonic parameters (convergence rates, age of the oceanic lithosphere, etc.) provide a means of distinguishing between the two different models. Three such relationships suggest that the Rivera-North American and Cocos-North American convergence rates should be roughly equal across the Rivera-Cocos plate boundary, favoring the high-rate model. Employing the high-rate model, one can evaluate the magnitude and distribution of the strike-slip component of forearc motion, Vss, produced by oblique convergence between the Rivera and North American plates. The analysis indicates both a progressive increase and clockwise reorientation of Vss northwestward along the plate contact zone of the Rivera-North America subduction zone. Such a distribution in Vss should produce a northwestward movement of and NW-SE oriented extension within the interior of the Jalisco Block, consistent with previous proposals of Jalisco Block motions. Also, such a distribution in Vss should produce a slight clockwise rotation of the Jalisco Block in the vicinity of Bahia de Banderas, consistent with paleomagnetic data.

  5. Convergent instability in the ionosphere

    SciTech Connect

    Ponyatov, A.A.

    1994-04-01

    A linear theory of the convergent instability (CI) of ionospheric plasma associated with the nonuniform nature of its regular motion is examined. The conditions under which CI appears in the E- and F-layers for vertical ion motion caused by various physical factors are analyzed. The possibility of small-scale strongly geomagnetic-field-aligned nonuniformities of electron concentration (l{sub min} {approximately} 10-30 m) is demonstrated. The altitude dependence of collision frequency is shown to play a large role in CI.

  6. Global Warming Attenuates the Tropical Atlantic-Pacific Teleconnection

    PubMed Central

    Jia, Fan; Wu, Lixin; Gan, Bolan; Cai, Wenju

    2016-01-01

    Changes in global sea surface temperature (SST) since the end of last century display a pattern of widespread warming intercepted by cooling in the eastern equatorial Pacific and western coasts of the American continent. Studies have suggested that the cooling in the eastern equatorial Pacific may be partly induced by warming in the North Atlantic. However, it remains unknown how stable this inter-tropical teleconnection will be under global warming. Here we show that the inter-tropical teleconnection from the tropical Atlantic to Pacific weakens substantially as the CO2 concentration increases. This reduced impact is related to the El Niño-like warming of the tropical Pacific mean state, which leads to limited seasonal migration of the Pacific inter-tropical convergence zone (ITCZ) and weakened ocean heat transport. A fast decay of the tropical Atlantic SST anomalies in a warmer climate also contributes to the weakened teleconnection. Our study suggests that as greenhouse warming continues, the trend in the tropical Pacific as well as the development of ENSO will be less frequently interrupted by the Atlantic because of this attenuation. The weakened teleconnection is also supported by CMIP5 models, although only a few of these models can capture this inter-tropical teleconnection. PMID:26838053

  7. Global Warming Attenuates the Tropical Atlantic-Pacific Teleconnection.

    PubMed

    Jia, Fan; Wu, Lixin; Gan, Bolan; Cai, Wenju

    2016-02-03

    Changes in global sea surface temperature (SST) since the end of last century display a pattern of widespread warming intercepted by cooling in the eastern equatorial Pacific and western coasts of the American continent. Studies have suggested that the cooling in the eastern equatorial Pacific may be partly induced by warming in the North Atlantic. However, it remains unknown how stable this inter-tropical teleconnection will be under global warming. Here we show that the inter-tropical teleconnection from the tropical Atlantic to Pacific weakens substantially as the CO2 concentration increases. This reduced impact is related to the El Niño-like warming of the tropical Pacific mean state, which leads to limited seasonal migration of the Pacific inter-tropical convergence zone (ITCZ) and weakened ocean heat transport. A fast decay of the tropical Atlantic SST anomalies in a warmer climate also contributes to the weakened teleconnection. Our study suggests that as greenhouse warming continues, the trend in the tropical Pacific as well as the development of ENSO will be less frequently interrupted by the Atlantic because of this attenuation. The weakened teleconnection is also supported by CMIP5 models, although only a few of these models can capture this inter-tropical teleconnection.

  8. Ocular Convergence Deficits in Schizophrenia

    PubMed Central

    Bolding, Mark S.; Lahti, Adrienne C.; Gawne, Timothy J.; Hopkins, Kristine B.; Gurler, Demet; Gamlin, Paul D.

    2012-01-01

    Individuals with schizophrenia (SZ) have been reported to exhibit a higher prevalence of convergence insufficiency (CI) than the “normal” adult population. The purpose of this study was to determine if individuals with SZ exhibit clinical signs of CI and to determine if the Convergence Insufficiency Symptom Survey (CISS) is an effective instrument for identifying CI in this population. Twenty participants with SZ and 20 healthy controls (HC) completed the study. The prevalence of CI (15%) in the SZ group was slightly higher than reported norms, but the difference was not significant. The SZ group had significantly higher scores on the CISS than the HC group, but the CISS scores did not correlate with clinical measures of CI in individuals with SZ. The only exception was that SZ patients had a significantly reduced fusional reserve as determined by Sheard’s criteria. Further study is needed to determine why individuals with SZ reported symptoms associated with CI even though clinical measures did not support this diagnosis. PMID:23087652

  9. Professional convergence in forensic practice.

    PubMed

    Mercer, D; Mason, T; Richman, J

    2001-06-01

    This paper outlines the development and convergence of forensic science and secure psychiatric services in the UK, locating the professionalization of forensic nursing within a complex web of political, economic, and ideological structures. It is suggested that a stagnation of the therapeutic enterprise in high and medium security provision has witnessed an intrusion of medical power into the societal body. Expanding technologies of control and surveillance are discussed in relation to the move from modernity to postmodernity and the ongoing dynamic of medicalized offending. Four aspects of globalization are identified as impacting upon the organization and application of forensic practice: (i) organized capitalism and the exhaustion of the welfare state; (ii) security versus danger and trust versus risk; (iii) science as a meta-language; and (iv) foreclosure as a mechanism of censorship. Finally, as a challenge for the profession, some predictions are offered about the future directions or demise of forensic nursing.

  10. Mosaic Convergence of Rodent Dentitions

    PubMed Central

    Lazzari, Vincent; Charles, Cyril; Tafforeau, Paul; Vianey-Liaud, Monique; Aguilar, Jean-Pierre; Jaeger, Jean-Jacques; Michaux, Jacques; Viriot, Laurent

    2008-01-01

    Background Understanding mechanisms responsible for changes in tooth morphology in the course of evolution is an area of investigation common to both paleontology and developmental biology. Detailed analyses of molar tooth crown shape have shown frequent homoplasia in mammalian evolution, which requires accurate investigation of the evolutionary pathways provided by the fossil record. The necessity of preservation of an effective occlusion has been hypothesized to functionally constrain crown morphological changes and to also facilitate convergent evolution. The Muroidea superfamily constitutes a relevant model for the study of molar crown diversification because it encompasses one third of the extant mammalian biodiversity. Methodology/Principal Findings Combined microwear and 3D-topographic analyses performed on fossil and extant muroid molars allow for a first quantification of the relationships between changes in crown morphology and functionality of occlusion. Based on an abundant fossil record and on a well resolved phylogeny, our results show that the most derived functional condition associates longitudinal chewing and non interlocking of cusps. This condition has been reached at least 7 times within muroids via two main types of evolutionary pathways each respecting functional continuity. In the first type, the flattening of tooth crown which induces the removal of cusp interlocking occurs before the rotation of the chewing movement. In the second type however, flattening is subsequent to rotation of the chewing movement which can be associated with certain changes in cusp morphology. Conclusion/Significance The reverse orders of the changes involved in these different pathways reveal a mosaic evolution of mammalian dentition in which direction of chewing and crown shape seem to be partly decoupled. Either can change in respect to strong functional constraints affecting occlusion which thereby limit the number of the possible pathways. Because convergent

  11. Cosmic Convergence: Art and Science

    NASA Astrophysics Data System (ADS)

    Mayo, Elizabeth A.; Zisholtz, E.; Hilton, H.

    2010-01-01

    The I.P. Stanback Museum and Planetarium is a major educational and teaching resource for South Carolina State University, K-12 schools, other universities and the community of Orangeburg and well beyond. The concept of creating a museum with a planetarium on the campus of SC State was ahead of its time. Today scholars are writing about the unity of creative disciplines. Through its integration of the arts, humanities and sciences, the Stanback, the only art museum with a planetarium at any of the Historically Black Colleges and Universities and one of the few in the nation, stands in the forefront of modern thinking. Cosmic Convergence: Art and Science, opening at the I.P. Stanback Museum and Planetarium in February 2010, will feature the works of Mildred Thompson (1936-2003), a prominent African American artist who worked in the media of painting, drawing, print making, sculpture, and photography. Thompson’s artwork shows the strong influences of her interest in physics, astronomy, and metaphysics as well as music and spiritualism. “My work in the visual arts is, and has always been, a continuous search for understanding. It is an expression of purpose and reflects a personal interpretation of the Universe.” Cosmic Convergence will explore the meeting of Art and Science through Mildred Thompson's work and the scientific basis of that work. The paintings and sculptures of the exhibit will be combined with astronomical images showing both the reality and interpretation of the surrounding Universe. Support for this work was provided by the NSF PAARE program to South Carolina State University under award AST-0750814.

  12. Estimator reduction and convergence of adaptive BEM.

    PubMed

    Aurada, Markus; Ferraz-Leite, Samuel; Praetorius, Dirk

    2012-06-01

    A posteriori error estimation and related adaptive mesh-refining algorithms have themselves proven to be powerful tools in nowadays scientific computing. Contrary to adaptive finite element methods, convergence of adaptive boundary element schemes is, however, widely open. We propose a relaxed notion of convergence of adaptive boundary element schemes. Instead of asking for convergence of the error to zero, we only aim to prove estimator convergence in the sense that the adaptive algorithm drives the underlying error estimator to zero. We observe that certain error estimators satisfy an estimator reduction property which is sufficient for estimator convergence. The elementary analysis is only based on Dörfler marking and inverse estimates, but not on reliability and efficiency of the error estimator at hand. In particular, our approach gives a first mathematical justification for the proposed steering of anisotropic mesh-refinements, which is mandatory for optimal convergence behavior in 3D boundary element computations.

  13. Estimator reduction and convergence of adaptive BEM

    PubMed Central

    Aurada, Markus; Ferraz-Leite, Samuel; Praetorius, Dirk

    2012-01-01

    A posteriori error estimation and related adaptive mesh-refining algorithms have themselves proven to be powerful tools in nowadays scientific computing. Contrary to adaptive finite element methods, convergence of adaptive boundary element schemes is, however, widely open. We propose a relaxed notion of convergence of adaptive boundary element schemes. Instead of asking for convergence of the error to zero, we only aim to prove estimator convergence in the sense that the adaptive algorithm drives the underlying error estimator to zero. We observe that certain error estimators satisfy an estimator reduction property which is sufficient for estimator convergence. The elementary analysis is only based on Dörfler marking and inverse estimates, but not on reliability and efficiency of the error estimator at hand. In particular, our approach gives a first mathematical justification for the proposed steering of anisotropic mesh-refinements, which is mandatory for optimal convergence behavior in 3D boundary element computations. PMID:23482248

  14. Marital assortment and phenotypic convergence: longitudinal evidence.

    PubMed

    Caspi, A; Herbener, E S

    1993-01-01

    This study provides a direct test of whether the observed similarity of spouses is due to initial assortment rather than to convergence of phenotypes. With data from three well-known longitudinal studies, phenotypic convergence is examined using both variable- and person-centered analyses. The longitudinal evidence does not support the hypothesis that couples increasingly resemble each other with time. Spouse correlations most likely reflect initial assortment at marriage and not the convergence of phenotypes.

  15. On the frequency-magnitude distribution of converging boundaries

    NASA Astrophysics Data System (ADS)

    Marzocchi, W.; Laura, S.; Heuret, A.; Funiciello, F.

    2011-12-01

    The occurrence of the last mega-thrust earthquake in Japan has clearly remarked the high risk posed to society by such events in terms of social and economic losses even at large spatial scale. The primary component for a balanced and objective mitigation of the impact of these earthquakes is the correct forecast of where such kind of events may occur in the future. To date, there is a wide range of opinions about where mega-thrust earthquakes can occur. Here, we aim at presenting some detailed statistical analysis of a database of worldwide interplate earthquakes occurring at current subduction zones. The database has been recently published in the framework of the EURYI Project 'Convergent margins and seismogenesis: defining the risk of great earthquakes by using statistical data and modelling', and it provides a unique opportunity to explore in detail the seismogenic process in subducting lithosphere. In particular, the statistical analysis of this database allows us to explore many interesting scientific issues such as the existence of different frequency-magnitude distributions across the trenches, the quantitative characterization of subduction zones that are able to produce more likely mega-thrust earthquakes, the prominent features that characterize converging boundaries with different seismic activity and so on. Besides the scientific importance, such issues may lead to improve our mega-thrust earthquake forecasting capability.

  16. Mobilization of beryllium in the sedimentary column at convergent margins

    USGS Publications Warehouse

    You, C.-F.; Morris, J.D.; Gieskes, J.M.; Rosenbauer, R.; Zheng, S.H.; Xu, X.; Ku, T.-L.; Bischoff, J.L.

    1994-01-01

    Studies of Be distributions in subduction zone sediments will help to understand questions regarding the enrichments of cosmogenic Be-10 in arc volcanic rocks. Analyses of Be-10 and Be-9 in sediments of Ocean Drilling Program Site 808, Nankai Trough and Be-9 in porewaters of Site 808 and Sites 671 and 672, Barbados ridge complex, show significant decreases in solid phase Be-10 and large increases of porewater Be-9 at the location of the de??collement zone and below or at potential flow conduits. These data imply the potential mobilization of Be during pore fluid expulsion upon sediment burial. Experiments involving reaction between a de??collement sediment and a synthetic NaCl-CaCl2 solution at elevated pressure and temperatures were conducted in an attempt to mimic early subduction zone processes. The results demonstrate that Be is mobilized under elevated pressure and temperature with a strong pH dependence. The Be mobilization provides an explanation of Be-10 enrichment in arc volcanic rocks and supports the argument of the importance of the fluid processes in subduction zones at convergent margins. ?? 1994.

  17. Geophysical constraints on geodynamic processes at convergent margins: A global perspective

    NASA Astrophysics Data System (ADS)

    Artemieva, Irina; Thybo, Hans; Shulgin, Alexey

    2016-04-01

    Convergent margins, being the boundaries between colliding lithospheric plates, form the most disastrous areas in the world due to intensive, strong seismicity and volcanism. We review global geophysical data in order to illustrate the effects of the plate tectonic processes at convergent margins on the crustal and upper mantle structure, seismicity, and geometry of subducting slab. We present global maps of free-air and Bouguer gravity anomalies, heat flow, seismicity, seismic Vs anomalies in the upper mantle, and plate convergence rate, as well as 20 profiles across different convergent margins. A global analysis of these data for three types of convergent margins, formed by ocean-ocean, ocean-continent, and continent-continent collisions, allows us to recognize the following patterns. (1) Plate convergence rate depends on the type of convergent margins and it is significantly larger when, at least, one of the plates is oceanic. However, the oldest oceanic plate in the Pacific ocean has the smallest convergence rate. (2) The presence of an oceanic plate is, in general, required for generation of high-magnitude (M N 8.0) earthquakes and for generating intermediate and deep seismicity along the convergent margins. When oceanic slabs subduct beneath a continent, a gap in the seismogenic zone exists at depths between ca. 250 km and 500 km. Given that the seismogenic zone terminates at ca. 200 km depth in case of continent-continent collision, we propose oceanic origin of subducting slabs beneath the Zagros, the Pamir, and the Vrancea zone. (3) Dip angle of the subducting slab in continent-ocean collision does not correlate neither with the age of subducting oceanic slab, nor with the convergence rate. For ocean-ocean subduction, clear trends are recognized: steeply dipping slabs are characteristic of young subducting plates and of oceanic plates with high convergence rate, with slab rotation towards a near-vertical dip angle at depths below ca. 500 km at very high

  18. Oblique convergence and the lobate mountain belts of western Pakistan

    NASA Astrophysics Data System (ADS)

    Haq, Saad S. B.; Davis, Dan M.

    1997-01-01

    The thin-skinned structures of the Pakistani convergent margin have formed as a consequence of the relative motion between India and Eurasia. Most of the resultant motion is being accommodated along or near the current edge of the Eurasian plate: the southwest-northeast striking Chaman fault zone. It has been observed at oblique margins that the total plate motion is resolved into a component parallel to the margin, accommodated through strike-slip faulting, and a component normal to the margin taken up as contraction. However, the orientations of structures along the Pakistani convergent margin in and around the Sulaiman lobe and Sulaiman Range cannot be explained simply by resolving the plate motion vector into components normal and parallel to the plate boundary. Our modeling suggests that the complex juxtaposition of strike-slip faults with thrust faults of various orientations can be explained by the presence of a block centered upon the Katawaz basin that translates along the southwest-northeast structural barrier of the Chaman fault zone, moving with respect to both Eurasia and India. As this relatively rigid block moves northeastward relative to Asia, it causes deformation of the sedimentary cover and is responsible for much of the structural complexity in the Pakistani foreland. Our simple model explains several first-order features of this oblique margin, such as the eastward-facing Sulaiman Range, the strike-slip Kingri fault (located between the Sulaiman lobe and Sulaiman Range), and the reentrant at Sibi. This leads us to conclude that very complex structural and geometric relationships at oblique convergent plate boundaries can result from the accommodation of strain with simple initial geometric constraints.

  19. The Convergence of European Business Cycles 1980--2004

    NASA Astrophysics Data System (ADS)

    Ormerod, P.

    2005-09-01

    The degree of convergence of the business cycles of the economies of the European Union is a key policy issue. In particular, a substantial degree of convergence is needed if the European Central Bank is to be capable of setting a monetary policy which is appropriate to the stage of the cycle of the Euro zone economies. I consider the annual rates of real GDP growth on a quarterly basis in the main economies of the EU (France, Germany, Italy, UK, Spain, Belgium and the Netherlands) over the period 1980Q1--2004Q4. An important empirical question is the degree to which the correlations between these growth rates contain true information rather than noise. The technique of random matrix theory is able to answer this question, and has been applied successfully in the physics journals to financial markets data. I find that the correlations between the growth rates of most of the core EU economies contain substantial amounts of true information, and exhibit considerable stability over time. Even in the late 1970s and early 1980s, these economies moved together closely over the course of the business cycle. There was a slight loosening at the time of German re-unification, but the economies have moved back into close synchronisation. The same result holds when Spain is added to the group of core EU countries. However, the problems of the German economy which arose from the early 1990s onwards has led to Germany becoming increasingly less synchronised with the rest of the core EU. Further, the results obtained with a data set of the converged EU core plus the UK show no real convergence between the UK and this group of economies.

  20. New concurrent iterative methods with monotonic convergence

    SciTech Connect

    Yao, Qingchuan

    1996-12-31

    This paper proposes the new concurrent iterative methods without using any derivatives for finding all zeros of polynomials simultaneously. The new methods are of monotonic convergence for both simple and multiple real-zeros of polynomials and are quadratically convergent. The corresponding accelerated concurrent iterative methods are obtained too. The new methods are good candidates for the application in solving symmetric eigenproblems.

  1. Converging finite-strength shocks

    NASA Astrophysics Data System (ADS)

    Axford, R. A.; Holm, D. D.

    1981-01-01

    The converging shock problem was first solved by Guderley and later by Landau and Stanyukovich for infinitely strong shocks in an ideal gas with spherical and cylindrical symmetry. This problem is solved herein for finite-strength shocks and a non-ideal-gas equation of state with an adiabatic bulk modulus of the type Bs= {- v∂ p}/{∂ v| s} = ( p +B) f( v) , where B is a constant with the dimensions of pressure, and f(v) is an arbitrary function of the specific volume. Self-similar profiles of the particle velocity and thermodynamic variables are studied explicitly for two cases with constant specific heat at constant volume; the Tait-Kirkwood-Murnaghan equation, f(v) = constant, and the Walsh equation, f(v) = v/A, where A = constant. The first case reduces to the ideal gas when B = 0. In both cases the flow behind the shock front exhibits an unbalanced buoyant force instability at a critical Mach number which depends upon equation-of-state parameters.

  2. Hepatitis C Virus Antigenic Convergence

    PubMed Central

    Campo, David S.; Dimitrova, Zoya; Yokosawa, Jonny; Hoang, Duc; Perez, Nestor O.; Ramachandran, Sumathi; Khudyakov, Yury

    2012-01-01

    Vaccine development against hepatitis C virus (HCV) is hindered by poor understanding of factors defining cross-immunoreactivity among heterogeneous epitopes. Using synthetic peptides and mouse immunization as a model, we conducted a quantitative analysis of cross-immunoreactivity among variants of the HCV hypervariable region 1 (HVR1). Analysis of 26,883 immunological reactions among pairs of peptides showed that the distribution of cross-immunoreactivity among HVR1 variants was skewed, with antibodies against a few variants reacting with all tested peptides. The HVR1 cross-immunoreactivity was accurately modeled based on amino acid sequence alone. The tested peptides were mapped in the HVR1 sequence space, which was visualized as a network of 11,319 sequences. The HVR1 variants with a greater network centrality showed a broader cross-immunoreactivity. The entire sequence space is explored by each HCV genotype and subtype. These findings indicate that HVR1 antigenic diversity is extensively convergent and effectively limited, suggesting significant implications for vaccine development. PMID:22355779

  3. Formation of polarity convergences underlying shoot outgrowths.

    PubMed

    Abley, Katie; Sauret-Güeto, Susanna; Marée, Athanasius Fm; Coen, Enrico

    2016-08-01

    The development of outgrowths from plant shoots depends on formation of epidermal sites of cell polarity convergence with high intracellular auxin at their centre. A parsimonious model for generation of convergence sites is that cell polarity for the auxin transporter PIN1 orients up auxin gradients, as this spontaneously generates convergent alignments. Here we test predictions of this and other models for the patterns of auxin biosynthesis and import. Live imaging of outgrowths from kanadi1 kanadi2 Arabidopsis mutant leaves shows that they arise by formation of PIN1 convergence sites within a proximodistal polarity field. PIN1 polarities are oriented away from regions of high auxin biosynthesis enzyme expression, and towards regions of high auxin importer expression. Both expression patterns are required for normal outgrowth emergence, and may form part of a common module underlying shoot outgrowths. These findings are more consistent with models that spontaneously generate tandem rather than convergent alignments.

  4. Formation of polarity convergences underlying shoot outgrowths.

    PubMed

    Abley, Katie; Sauret-Güeto, Susanna; Marée, Athanasius Fm; Coen, Enrico

    2016-01-01

    The development of outgrowths from plant shoots depends on formation of epidermal sites of cell polarity convergence with high intracellular auxin at their centre. A parsimonious model for generation of convergence sites is that cell polarity for the auxin transporter PIN1 orients up auxin gradients, as this spontaneously generates convergent alignments. Here we test predictions of this and other models for the patterns of auxin biosynthesis and import. Live imaging of outgrowths from kanadi1 kanadi2 Arabidopsis mutant leaves shows that they arise by formation of PIN1 convergence sites within a proximodistal polarity field. PIN1 polarities are oriented away from regions of high auxin biosynthesis enzyme expression, and towards regions of high auxin importer expression. Both expression patterns are required for normal outgrowth emergence, and may form part of a common module underlying shoot outgrowths. These findings are more consistent with models that spontaneously generate tandem rather than convergent alignments. PMID:27478985

  5. Evolution of the Mariana Convergent Plate Margin System

    NASA Astrophysics Data System (ADS)

    Fryer, Patricia

    1996-02-01

    The Mariana convergent plate margin system of the western Pacific provides opportunities for studying the tectonic and geochemical processes of intraoceanic plate subduction without the added complexities of continental geology. The system's relative geologic simplicity and the well-exposed sections of lithosphere in each of its tectonic provinces permit in situ examination of processes critical to understanding subduction tectonics. Its general history provides analogs to ancient convergent margin terranes exposed on land and helps to explain the chemical mass balance in convergent plate margins. The Mariana convergent margin's long history of sequential formation of volcanic arcs and extensional back arc basins has created a series of volcanic arcs at the eastern edge of the Philippine Sea plate. The trenchward edge of the overriding plate has a relatively sparse sediment cover. Rocks outcropping on the trench's inner slope are typical of the early formed suprasubduction zone's lithosphere and have been subjected to various processes related to its tectonic history. Pervasive forearc faulting has exposed crust and upper mantle lithosphere. Many large serpentinized peridotite seamounts are within 100 km of the trench axis. From these we can learn the history of regional metamorphism and observe and sample active venting of slab fluids. Ocean drilling recovered suprasubduction zone lava sequences erupted since the Eocene that suggest that the forearc region remains volcanologically dynamic. Seismic studies and seafloor mapping show evidence of deformation throughout forearc evolution. Large portions of uplifted southern forearc are exposed at the larger islands. Active volcanoes at the base of the eastern boundary fault of the Mariana Trough vary in size and composition along strike and record regional differences in source composition. Their locations along strike of the arc are controlled in part by cross-arc structures that also facilitate formation of submarine

  6. Data Convergence - An Australian Perspective

    NASA Astrophysics Data System (ADS)

    Allen, S. S.; Howell, B.

    2012-12-01

    Coupled numerical physical, biogeochemical and sediment models are increasingly being used as integrators to help understand the cumulative or far field effects of change in the coastal environment. This reliance on modeling has forced observations to be delivered as data streams ingestible by modeling frameworks. This has made it easier to create near real-time or forecasting models than to try to recreate the past, and has lead in turn to the conversion of historical data into data streams to allow them to be ingested by the same frameworks. The model and observation frameworks under development within Australia's Commonwealth and Industrial Research Organisation (CSIRO) are now feeding into the Australian Ocean Data Network's (AODN's) MARine Virtual Laboratory (MARVL) . The sensor, or data stream, brokering solution is centred around the "message" and all data flowing through the gateway is wrapped as a message. Messages consist of a topic and a data object and their routing through the gateway to pre-processors and listeners is determined by the topic. The Sensor Message Gateway (SMG) method is allowing data from different sensors measuring the same thing but with different temporal resolutions, units or spatial coverage to be ingested or visualized seamlessly. At the same time the model output as a virtual sensor is being explored, this again being enabled by the SMG. It is only for two way communications with sensor that rigorous adherence to standards is needed, by accepting existing data in less than ideal formats, but exposing them though the SMG we can move a step closer to the Internet Of Things by creating an Internet of Industries where each vested interest can continue with business as usual, contribute to data convergence and adopt more open standards when investment seems appropriate to that sector or business.Architecture Overview

  7. On the Local Convergence of Pattern Search

    NASA Technical Reports Server (NTRS)

    Dolan, Elizabeth D.; Lewis, Robert Michael; Torczon, Virginia; Bushnell, Dennis M. (Technical Monitor)

    2000-01-01

    We examine the local convergence properties of pattern search methods, complementing the previously established global convergence properties for this class of algorithms. We show that the step-length control parameter which appears in the definition of pattern search algorithms provides a reliable asymptotic measure of first-order stationarity. This gives an analytical justification for a traditional stopping criterion for pattern search methods. Using this measure of first-order stationarity, we analyze the behavior of pattern search in the neighborhood of an isolated local minimizer. We show that a recognizable subsequence converges r-linearly to the minimizer.

  8. The evolution of forearc structures along an oblique convergent margin, central Aleutian Arc

    USGS Publications Warehouse

    Ryan, H.F.; Scholl, D. W.

    1989-01-01

    Multichannel seismic reflection data were used to determine the evolutionary history of the forearc region of the central Aleutian Ridge. Since at least late Miocene time this sector of the ridge has been obliquely underthrust 30?? west of orthogonal convergence by the northwestward converging Pacific plate at a rate of 80-90 km/m.y. Our data indicate that prior to late Eocene time the forearc region was composed of rocks of the arc massif thinly mantled by slope deposits. Beginning in latest Miocene or earliest Pliocene time, a zone of outer-arc structural highs and a forearc basin began to form. Initial structures of the zone of outer-arc highs formed as the thickening wedge underran, compressively deformed, and uplifted the seaward edge of the arc massive above a landward dipping backstop thrust. Forearc basin strata ponded arcward of the elevating zone of outer-arc highs. However, most younger structures of the zone of outer-arc highs cannot be ascribed simply to the orthogonal effects of an underrunning wedge. Oblique convergence created a major right-lateral shear zone (the Hawley Ridge shear zone) that longitudinally disrupted the zone of outer-arc highs, truncating the seaward flank of the forearc basin and shearing the southern limb of Hawley Ridge, an exceptionally large antiformal outer-arc high structure. Uplift of Hawley Ridge may be related to the thickening of the arc massif by westward directed basement duplexes. Great structural complexity, including the close juxtaposition of coeval structures recording compression, extension, differential vertical movements, and strike-slip displacement, should be expected, even within areas of generally kindred tectonostratigraphic terranes. -from Authors

  9. Transition from convergence to escape: Field evidence from the West Carpathians

    SciTech Connect

    Nemcok, M. ); Fleischmann, K.H.; Keith, J.F. Jr )

    1991-03-01

    A large data base of gravimetric, magnetic, seismic, paleomagnetic, lithostratigraphic, sedimentologic, fission-track, bore-hole, and structural information has been used to analyze the structural development of the West Carpathians. These data support a structural model for the evolution of this orogen from convergence to tectonic escape. The West Carpathians resulted from Cretaceous-Miocene convergence of the European and Apulian plates. Paleocene convergence was northeast directed. With progressive deformation, the central mountain front encountered a shallow wedge-shaped portion of the subducted European plate, which caused a sinistral deflection of convergence trajectories in the western portion of the chain. Beginning with Egerian/Eggenburgian collision and continuing to the present time, the orogen has consisted of two zones: a frontal shortening zone and an internal extensional/strike-slip zone. A cycle of deformation patterns is recognized along the frontal part of the orogen in which {sigma}{sub 1} remained normal to the West Carpathian front: orogen-vergent thrusting, intermediate back-thrusting, and strike-slip faulting. Tectonic escape along strike-slip fault sets oriented sub-parallel to the suture zone begun in early Badenian time in the westernmost West Carpathians. The final phase of thrusting becomes younger to the east. The principal compressive stress orientations in areas affected by escape were sub-horizontal and pointed to the location of the last thrust movements along the orogen front. With increased distance from the active collision-suture zone, the principal compressive stress orientations plunged more steeply, indicating a continuous change from a transtensional to an extensional stress regime.

  10. Strain accumulation along the Cascadia subduction zone

    USGS Publications Warehouse

    Murray, M.H.; Lisowski, M.

    2000-01-01

    We combine triangulation, trilateration, and GPS observations to determine horizontal strain rates along the Cascadia subduction zone from Cape Mendocino to the Strait of Juan de Fuca. Shear-strain rates are significantly greater than zero (95% confidence) in all forearc regions (26-167 nanoradians/yr), and are not significant in the arc and backarc regions. The deformation is primarily uniaxial contraction nearly parallel to Juan de Fuca-North America plate convergence (N55??-80??E). The strain rates are consistent with an elastic dislocation model for interseismic slip with a shallow 100-km wide locked zone and a deeper 75-km transition zone along the entire megathrust, except along the central Oregon coast where relatively lower strain rates are consistent with 30-40 km wide locked and transition zones.

  11. Topics in global convergence of density estimates

    NASA Technical Reports Server (NTRS)

    Devroye, L.

    1982-01-01

    The problem of estimating a density f on R sup d from a sample Xz(1),...,X(n) of independent identically distributed random vectors is critically examined, and some recent results in the field are reviewed. The following statements are qualified: (1) For any sequence of density estimates f(n), any arbitrary slow rate of convergence to 0 is possible for E(integral/f(n)-fl); (2) In theoretical comparisons of density estimates, integral/f(n)-f/ should be used and not integral/f(n)-f/sup p, p 1; and (3) For most reasonable nonparametric density estimates, either there is convergence of integral/f(n)-f/ (and then the convergence is in the strongest possible sense for all f), or there is no convergence (even in the weakest possible sense for a single f). There is no intermediate situation.

  12. Speeding Convergence In Simulations Of Hypersonic Flow

    NASA Technical Reports Server (NTRS)

    Flores, J.; Cheung, S.; Cheer, A.; Hafez, M.

    1991-01-01

    Report describes study aimed at accelerating rates of convergence of iterative schemes for numerical integration of equations of hypersonic flow of viscous and inviscid fluids. Richardson-type overrelaxation method applied.

  13. Morphological and molecular convergences in mammalian phylogenetics

    PubMed Central

    Zou, Zhengting; Zhang, Jianzhi

    2016-01-01

    Phylogenetic trees reconstructed from molecular sequences are often considered more reliable than those reconstructed from morphological characters, in part because convergent evolution, which confounds phylogenetic reconstruction, is believed to be rarer for molecular sequences than for morphologies. However, neither the validity of this belief nor its underlying cause is known. Here comparing thousands of characters of each type that have been used for inferring the phylogeny of mammals, we find that on average morphological characters indeed experience much more convergences than amino acid sites, but this disparity is explained by fewer states per character rather than an intrinsically higher susceptibility to convergence for morphologies than sequences. We show by computer simulation and actual data analysis that a simple method for identifying and removing convergence-prone characters improves phylogenetic accuracy, potentially enabling, when necessary, the inclusion of morphologies and hence fossils for reliable tree inference. PMID:27585543

  14. Convergent Validity of Four Innovativeness Scales.

    ERIC Educational Resources Information Center

    Goldsmith, Ronald E.

    1986-01-01

    Four scales of innovativeness were administered to two samples of undergraduate students: the Open Processing Scale, Innovativeness Scale, innovation subscale of the Jackson Personality Inventory, and Kirton Adaption-Innovation Inventory. Intercorrelations indicated the scales generally exhibited convergent validity. (GDC)

  15. Low-Convergence Magnetized Liner Inertial Fusion

    NASA Astrophysics Data System (ADS)

    Slutz, Stephen; Vesey, Roger; Sinars, Daniel; Sefkow, Adam

    2013-10-01

    Numerical simulations indicate that pulsed-power driven liner-implosions could produce substantial fusion yields if the deuterium-tritium (DT) fuel is first magnetized and preheated [S.A. Slutz et al., Phys. Plasmas 17, 056303 (2010)]. As with all inertial fusion, the implosions could be degraded by the Rayleigh-Taylor instability. Since highly convergent implosions are more susceptible to this instability, we have explored the necessary conditions to obtain significant fusion yield with low-convergence liner-implosions. Such low-convergence implosions can be obtained if the fuel is sufficiently preheated and magnetized. We present analytic and numerical studies of laser plasma heating, which indicate that low convergence implosions should be possible with sufficient laser energy. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contra.

  16. New convergence estimates for multigrid algorithms

    SciTech Connect

    Bramble, J.H.; Pasciak, J.E.

    1987-10-01

    In this paper, new convergence estimates are proved for both symmetric and nonsymmetric multigrid algorithms applied to symmetric positive definite problems. Our theory relates the convergence of multigrid algorithms to a ''regularity and approximation'' parameter ..cap alpha.. epsilon (0, 1) and the number of relaxations m. We show that for the symmetric and nonsymmetric ..nu.. cycles, the multigrid iteration converges for any positive m at a rate which deteriorates no worse than 1-cj/sup -(1-//sup ..cap alpha..//sup )///sup ..cap alpha../, where j is the number of grid levels. We then define a generalized ..nu.. cycle algorithm which involves exponentially increasing (for example, doubling) the number of smoothings on successively coarser grids. We show that the resulting symmetric and nonsymmetric multigrid iterations converge for any ..cap alpha.. with rates that are independent of the mesh size. The theory is presented in an abstract setting which can be applied to finite element multigrid and finite difference multigrid methods.

  17. Morphological and molecular convergences in mammalian phylogenetics.

    PubMed

    Zou, Zhengting; Zhang, Jianzhi

    2016-01-01

    Phylogenetic trees reconstructed from molecular sequences are often considered more reliable than those reconstructed from morphological characters, in part because convergent evolution, which confounds phylogenetic reconstruction, is believed to be rarer for molecular sequences than for morphologies. However, neither the validity of this belief nor its underlying cause is known. Here comparing thousands of characters of each type that have been used for inferring the phylogeny of mammals, we find that on average morphological characters indeed experience much more convergences than amino acid sites, but this disparity is explained by fewer states per character rather than an intrinsically higher susceptibility to convergence for morphologies than sequences. We show by computer simulation and actual data analysis that a simple method for identifying and removing convergence-prone characters improves phylogenetic accuracy, potentially enabling, when necessary, the inclusion of morphologies and hence fossils for reliable tree inference. PMID:27585543

  18. Acceleration of convergence of vector sequences

    NASA Technical Reports Server (NTRS)

    Sidi, A.; Ford, W. F.; Smith, D. A.

    1983-01-01

    A general approach to the construction of convergence acceleration methods for vector sequence is proposed. Using this approach, one can generate some known methods, such as the minimal polynomial extrapolation, the reduced rank extrapolation, and the topological epsilon algorithm, and also some new ones. Some of the new methods are easier to implement than the known methods and are observed to have similar numerical properties. The convergence analysis of these new methods is carried out, and it is shown that they are especially suitable for accelerating the convergence of vector sequences that are obtained when one solves linear systems of equations iteratively. A stability analysis is also given, and numerical examples are provided. The convergence and stability properties of the topological epsilon algorithm are likewise given.

  19. On Convergent Probability of a Random Walk

    ERIC Educational Resources Information Center

    Lee, Y.-F.; Ching, W.-K.

    2006-01-01

    This note introduces an interesting random walk on a straight path with cards of random numbers. The method of recurrent relations is used to obtain the convergent probability of the random walk with different initial positions.

  20. Interplay of plate convergence and arc migration in the central Mediterranean (Sicily and Calabria)

    NASA Astrophysics Data System (ADS)

    Nijholt, Nicolai; Govers, Rob; Wortel, Rinus

    2016-04-01

    Key components in the current geodynamic setting of the central Mediterranean are continuous, slow Africa-Eurasia plate convergence (~5 mm/yr) and arc migration. This combination encompasses roll-back, tearing and detachment of slabs, and leads to back-arc opening and orogeny. Since ~30 Ma the Apennnines-Calabrian and Gibraltar subduction zones have shaped the western-central Mediterranean region. Lithospheric tearing near slab edges and the accompanying surface expressions (STEP faults) are key in explaining surface dynamics as observed in geologic, geophysical and geodetic data. In the central Mediterranean, both the narrow Calabrian subduction zone and the Sicily-Tyrrhenian offshore thrust front show convergence, with a transfer (shear) zone connecting the distinct SW edge of the former with the less distinct, eastern limit of the latter (similar, albeit on a smaller scale, to the situation in New Zealand with oppositely verging subduction zones and the Alpine fault as the transfer shear zone). The ~NNW-SSE oriented transfer zone (Aeolian-Sisifo-Tindari(-Ionian) fault system) shows transtensive-to-strike slip motion. Recent seismicity, geological data and GPS vectors in the central Mediterranean indicate that the region can be subdivided into several distinct domains, both on- and offshore, delineated by deformation zones and faults. However, there is discussion about the (relative) importance of some of these faults on the lithospheric scale. We focus on finding the best-fitting assembly of faults for the transfer zone connecting subduction beneath Calabria and convergence north of Sicily in the Sicily-Tyrrhenian offshore thrust front. This includes determining whether the Alfeo-Etna fault, Malta Escarpment and/or Ionian fault, which have all been suggested to represent the STEP fault of the Calabrian subduction zone, are key in describing the observed deformation patterns. We first focus on the present-day. We use geodynamic models to reproduce observed GPS

  1. International Convergence on Geoscience Cyberinfrastructure

    NASA Astrophysics Data System (ADS)

    Allison, M. L.; Atkinson, R.; Arctur, D. K.; Cox, S.; Jackson, I.; Nativi, S.; Wyborn, L. A.

    2012-04-01

    There is growing international consensus on addressing the challenges to cyber(e)-infrastructure for the geosciences. These challenges include: Creating common standards and protocols; Engaging the vast number of distributed data resources; Establishing practices for recognition of and respect for intellectual property; Developing simple data and resource discovery and access systems; Building mechanisms to encourage development of web service tools and workflows for data analysis; Brokering the diverse disciplinary service buses; Creating sustainable business models for maintenance and evolution of information resources; Integrating the data management life-cycle into the practice of science. Efforts around the world are converging towards de facto creation of an integrated global digital data network for the geosciences based on common standards and protocols for data discovery and access, and a shared vision of distributed, web-based, open source interoperable data access and integration. Commonalities include use of Open Geospatial Consortium (OGC) and ISO specifications and standardized data interchange mechanisms. For multidisciplinarity, mediation, adaptation, and profiling services have been successfully introduced to leverage the geosciences standards which are commonly used by the different geoscience communities -introducing a brokering approach which extends the basic SOA archetype. Principal challenges are less technical than cultural, social, and organizational. Before we can make data interoperable, we must make people interoperable. These challenges are being met by increased coordination of development activities (technical, organizational, social) among leaders and practitioners in national and international efforts across the geosciences to foster commonalities across disparate networks. In doing so, we will 1) leverage and share resources, and developments, 2) facilitate and enhance emerging technical and structural advances, 3) promote

  2. Efficient Controls for Finitely Convergent Sequential Algorithms

    PubMed Central

    Chen, Wei; Herman, Gabor T.

    2010-01-01

    Finding a feasible point that satisfies a set of constraints is a common task in scientific computing: examples are the linear feasibility problem and the convex feasibility problem. Finitely convergent sequential algorithms can be used for solving such problems; an example of such an algorithm is ART3, which is defined in such a way that its control is cyclic in the sense that during its execution it repeatedly cycles through the given constraints. Previously we found a variant of ART3 whose control is no longer cyclic, but which is still finitely convergent and in practice it usually converges faster than ART3 does. In this paper we propose a general methodology for automatic transformation of finitely convergent sequential algorithms in such a way that (i) finite convergence is retained and (ii) the speed of convergence is improved. The first of these two properties is proven by mathematical theorems, the second is illustrated by applying the algorithms to a practical problem. PMID:20953327

  3. Convergence of gut microbiomes in myrmecophagous mammals.

    PubMed

    Delsuc, Frédéric; Metcalf, Jessica L; Wegener Parfrey, Laura; Song, Se Jin; González, Antonio; Knight, Rob

    2014-03-01

    Mammals have diversified into many dietary niches. Specialized myrmecophagous (ant- and termite-eating) placental mammals represent a textbook example of evolutionary convergence driven by extreme diet specialization. Armadillos, anteaters, aardvarks, pangolins and aardwolves thus provide a model system for understanding the potential role of gut microbiota in the convergent adaptation to myrmecophagy. Here, we expand upon previous mammalian gut microbiome studies by using high-throughput barcoded Illumina sequencing of the 16S rRNA gene to characterize the composition of gut microbiota in 15 species representing all placental myrmecophagous lineages and their close relatives from zoo- and field-collected samples. We confirm that both diet and phylogeny drive the evolution of mammalian gut microbiota, with cases of convergence in global composition, but also examples of phylogenetic inertia. Our results reveal specialized placental myrmecophages as a spectacular case of large-scale convergence in gut microbiome composition. Indeed, neighbour-net networks and beta-diversity plots based on UniFrac distances show significant clustering of myrmecophagous species (anteaters, aardvarks and aardwolves), even though they belong to phylogenetically distant lineages representing different orders. The aardwolf, which diverged from carnivorous hyenas only in the last 10 million years, experienced a convergent shift in the composition of its gut microbiome to become more similar to other myrmecophages. These results confirm diet adaptation to be a major driving factor of convergence in gut microbiome composition over evolutionary timescales. This study sets the scene for future metagenomic studies aiming at evaluating potential convergence in functional gene content in the microbiomes of specialized mammalian myrmecophages. PMID:24118574

  4. Convergence of gut microbiomes in myrmecophagous mammals.

    PubMed

    Delsuc, Frédéric; Metcalf, Jessica L; Wegener Parfrey, Laura; Song, Se Jin; González, Antonio; Knight, Rob

    2014-03-01

    Mammals have diversified into many dietary niches. Specialized myrmecophagous (ant- and termite-eating) placental mammals represent a textbook example of evolutionary convergence driven by extreme diet specialization. Armadillos, anteaters, aardvarks, pangolins and aardwolves thus provide a model system for understanding the potential role of gut microbiota in the convergent adaptation to myrmecophagy. Here, we expand upon previous mammalian gut microbiome studies by using high-throughput barcoded Illumina sequencing of the 16S rRNA gene to characterize the composition of gut microbiota in 15 species representing all placental myrmecophagous lineages and their close relatives from zoo- and field-collected samples. We confirm that both diet and phylogeny drive the evolution of mammalian gut microbiota, with cases of convergence in global composition, but also examples of phylogenetic inertia. Our results reveal specialized placental myrmecophages as a spectacular case of large-scale convergence in gut microbiome composition. Indeed, neighbour-net networks and beta-diversity plots based on UniFrac distances show significant clustering of myrmecophagous species (anteaters, aardvarks and aardwolves), even though they belong to phylogenetically distant lineages representing different orders. The aardwolf, which diverged from carnivorous hyenas only in the last 10 million years, experienced a convergent shift in the composition of its gut microbiome to become more similar to other myrmecophages. These results confirm diet adaptation to be a major driving factor of convergence in gut microbiome composition over evolutionary timescales. This study sets the scene for future metagenomic studies aiming at evaluating potential convergence in functional gene content in the microbiomes of specialized mammalian myrmecophages.

  5. Gene acquisition convergence between entomopoxviruses and baculoviruses.

    PubMed

    Thézé, Julien; Takatsuka, Jun; Nakai, Madoka; Arif, Basil; Herniou, Elisabeth A

    2015-04-01

    Organisms from diverse phylogenetic origins can thrive within the same ecological niches. They might be induced to evolve convergent adaptations in response to a similar landscape of selective pressures. Their genomes should bear the signature of this process. The study of unrelated virus lineages infecting the same host panels guarantees a clear identification of phyletically independent convergent adaptation. Here, we investigate the evolutionary history of genes in the accessory genome shared by unrelated insect large dsDNA viruses: the entomopoxviruses (EPVs, Poxviridae) and the baculoviruses (BVs). EPVs and BVs have overlapping ecological niches and have independently evolved similar infection processes. They are, in theory, subjected to the same selective pressures from their host's immune responses. Their accessory genomes might, therefore, bear analogous genomic signatures of convergent adaption and could point out key genomic mechanisms of adaptation hitherto undetected in viruses. We uncovered 32 homologous, yet independent acquisitions of genes originating from insect hosts, different eukaryotes, bacteria and viruses. We showed different evolutionary levels of gene acquisition convergence in these viruses, underlining a continuous evolutionary process. We found both recent and ancient gene acquisitions possibly involved to the adaptation to both specific and distantly related hosts. Multidirectional and multipartite gene exchange networks appear to constantly drive exogenous gene assimilations, bringing key adaptive innovations and shaping the life histories of large DNA viruses. This evolutionary process might lead to genome level adaptive convergence.

  6. Strong convergence for reduced free products

    NASA Astrophysics Data System (ADS)

    Pisier, Gilles

    2016-06-01

    Using an inequality due to Ricard and Xu, we give a different proof of Paul Skoufranis’s recent result showing that the strong convergence of possibly non-commutative random variables X(k) → X is stable under reduced free product with a fixed non-commutative random variable Y. In fact we obtain a more general fact: assuming that the families X(k) = {X i(k)} and Y(k) = {Y j(k)} are ∗-free as well as their limits (in moments) X = {Xi} and Y = {Yj}, the strong convergences X(k) → X and Y(k) → Y imply that of {X(k),Y(k)} to {X,Y }. Phrased in more striking language: the reduced free product is “continuous” with respect to strong convergence. The analogue for weak convergence (i.e. convergence of all moments) is obvious. Our approach extends to the amalgamated free product, left open by Skoufranis.

  7. Numerical Convergence In Smoothed Particle Hydrodynamics

    NASA Astrophysics Data System (ADS)

    Zhu, Qirong; Hernquist, Lars; Li, Yuexing

    2015-02-01

    We study the convergence properties of smoothed particle hydrodynamics (SPH) using numerical tests and simple analytic considerations. Our analysis shows that formal numerical convergence is possible in SPH only in the joint limit N → ∞, h → 0, and Nnb → ∞, where N is the total number of particles, h is the smoothing length, and Nnb is the number of neighbor particles within the smoothing volume used to compute smoothed estimates. Previous work has generally assumed that the conditions N → ∞ and h → 0 are sufficient to achieve convergence, while holding Nnb fixed. We demonstrate that if Nnb is held fixed as the resolution is increased, there will be a residual source of error that does not vanish as N → ∞ and h → 0. Formal numerical convergence in SPH is possible only if Nnb is increased systematically as the resolution is improved. Using analytic arguments, we derive an optimal compromise scaling for Nnb by requiring that this source of error balance that present in the smoothing procedure. For typical choices of the smoothing kernel, we find Nnb vpropN 0.5. This means that if SPH is to be used as a numerically convergent method, the required computational cost does not scale with particle number as O(N), but rather as O(N 1 + δ), where δ ≈ 0.5, with a weak dependence on the form of the smoothing kernel.

  8. Grid Convergence for Turbulent Flows(Invited)

    NASA Technical Reports Server (NTRS)

    Diskin, Boris; Thomas, James L.; Rumsey, Christopher L.; Schwoppe, Axel

    2015-01-01

    A detailed grid convergence study has been conducted to establish accurate reference solutions corresponding to the one-equation linear eddy-viscosity Spalart-Allmaras turbulence model for two dimensional turbulent flows around the NACA 0012 airfoil and a flat plate. The study involved three widely used codes, CFL3D (NASA), FUN3D (NASA), and TAU (DLR), and families of uniformly refined structured grids that differ in the grid density patterns. Solutions computed by different codes on different grid families appear to converge to the same continuous limit, but exhibit different convergence characteristics. The grid resolution in the vicinity of geometric singularities, such as a sharp trailing edge, is found to be the major factor affecting accuracy and convergence of discrete solutions, more prominent than differences in discretization schemes and/or grid elements. The results reported for these relatively simple turbulent flows demonstrate that CFL3D, FUN3D, and TAU solutions are very accurate on the finest grids used in the study, but even those grids are not sufficient to conclusively establish an asymptotic convergence order.

  9. Formation of polarity convergences underlying shoot outgrowths

    PubMed Central

    Abley, Katie; Sauret-Güeto, Susanna; Marée, Athanasius FM; Coen, Enrico

    2016-01-01

    The development of outgrowths from plant shoots depends on formation of epidermal sites of cell polarity convergence with high intracellular auxin at their centre. A parsimonious model for generation of convergence sites is that cell polarity for the auxin transporter PIN1 orients up auxin gradients, as this spontaneously generates convergent alignments. Here we test predictions of this and other models for the patterns of auxin biosynthesis and import. Live imaging of outgrowths from kanadi1 kanadi2 Arabidopsis mutant leaves shows that they arise by formation of PIN1 convergence sites within a proximodistal polarity field. PIN1 polarities are oriented away from regions of high auxin biosynthesis enzyme expression, and towards regions of high auxin importer expression. Both expression patterns are required for normal outgrowth emergence, and may form part of a common module underlying shoot outgrowths. These findings are more consistent with models that spontaneously generate tandem rather than convergent alignments. DOI: http://dx.doi.org/10.7554/eLife.18165.001 PMID:27478985

  10. Application of Convergence Confinement Analysis to the study of preceding displacement of a squeezing rock tunnel

    NASA Astrophysics Data System (ADS)

    Kitagawa, T.; Kumeta, T.; Ichizyo, T.; Soga, S.; Sato, M.; Yasukawa, M.

    1991-01-01

    This paper deals with a study on the geomechanical behavior of the rock mass around the tunnel. The Convergence Confinement Analysis is one of the most appropriate way to estimate this behavior. Elasto-plastic models proposed by Hoek and Brown, Egger and Kastner were adopted in this study. Measurements of the preceding displacement were performed in a road tunnel in Japan, the geology of which is Neogene squeezing mudstone. The measured data was compared with the results of Convergence Confinement Analysis. The preceding displacement was about 40% against the upper bench face converged displacement and 17% against the final converged displacement. Meanwhile, it increased drastically in lower bench excavation step. Back analysis was also executed to calculate the extension of the plastic zone of the rock mass, which was half of that estimated by Convergence Confinement Analysis in upper bench excavation step. But, in lower bench excavation step, the results of the two analyses were very similar. The support pressure and support stiffness were also calculated.

  11. Convergence Estimates for Multidisciplinary Analysis and Optimization

    NASA Technical Reports Server (NTRS)

    Arian, Eyal

    1997-01-01

    A quantitative analysis of coupling between systems of equations is introduced. This analysis is then applied to problems in multidisciplinary analysis, sensitivity, and optimization. For the sensitivity and optimization problems both multidisciplinary and single discipline feasibility schemes are considered. In all these cases a "convergence factor" is estimated in terms of the Jacobians and Hessians of the system, thus it can also be approximated by existing disciplinary analysis and optimization codes. The convergence factor is identified with the measure for the "coupling" between the disciplines in the system. Applications to algorithm development are discussed. Demonstration of the convergence estimates and numerical results are given for a system composed of two non-linear algebraic equations, and for a system composed of two PDEs modeling aeroelasticity.

  12. Convergence studies in meshfree peridynamic simulations

    DOE PAGESBeta

    Seleson, Pablo; Littlewood, David J.

    2016-04-15

    Meshfree methods are commonly applied to discretize peridynamic models, particularly in numerical simulations of engineering problems. Such methods discretize peridynamic bodies using a set of nodes with characteristic volume, leading to particle-based descriptions of systems. In this article, we perform convergence studies of static peridynamic problems. We show that commonly used meshfree methods in peridynamics suffer from accuracy and convergence issues, due to a rough approximation of the contribution to the internal force density of nodes near the boundary of the neighborhood of a given node. We propose two methods to improve meshfree peridynamic simulations. The first method uses accuratemore » computations of volumes of intersections between neighbor cells and the neighborhood of a given node, referred to as partial volumes. The second method employs smooth influence functions with a finite support within peridynamic kernels. Numerical results demonstrate great improvements in accuracy and convergence of peridynamic numerical solutions, when using the proposed methods.« less

  13. Testing Convergence Versus History: Convergence Dominates Phenotypic Evolution for over 150 Million Years in Frogs.

    PubMed

    Moen, Daniel S; Morlon, Hélène; Wiens, John J

    2016-01-01

    Striking evolutionary convergence can lead to similar sets of species in different locations, such as in cichlid fishes and Anolis lizards, and suggests that evolution can be repeatable and predictable across clades. Yet, most examples of convergence involve relatively small temporal and/or spatial scales. Some authors have speculated that at larger scales (e.g., across continents), differing evolutionary histories will prevent convergence. However, few studies have compared the contrasting roles of convergence and history, and none have done so at large scales. Here we develop a two-part approach to test the scale over which convergence can occur, comparing the relative importance of convergence and history in macroevolution using phylogenetic models of adaptive evolution. We apply this approach to data from morphology, ecology, and phylogeny from 167 species of anuran amphibians (frogs) from 10 local sites across the world, spanning ~160 myr of evolution. Mapping ecology on the phylogeny revealed that similar microhabitat specialists (e.g., aquatic, arboreal) have evolved repeatedly across clades and regions, producing many evolutionary replicates for testing for morphological convergence. By comparing morphological optima for clades and microhabitat types (our first test), we find that convergence associated with microhabitat use dominates frog morphological evolution, producing recurrent ecomorphs that together encompass all sampled species in each community in each region. However, our second test, which examines whether and how much species differ from their inferred optima, shows that convergence is incomplete: that is, phenotypes of most species are still somewhat distant from the estimated optimum for each microhabitat, seemingly because of insufficient time for more complete adaptation (an effect of history). Yet, these effects of history are related to past ecologies, and not clade membership. Overall, our study elucidates the dominant drivers of

  14. Testing Convergence Versus History: Convergence Dominates Phenotypic Evolution for over 150 Million Years in Frogs.

    PubMed

    Moen, Daniel S; Morlon, Hélène; Wiens, John J

    2016-01-01

    Striking evolutionary convergence can lead to similar sets of species in different locations, such as in cichlid fishes and Anolis lizards, and suggests that evolution can be repeatable and predictable across clades. Yet, most examples of convergence involve relatively small temporal and/or spatial scales. Some authors have speculated that at larger scales (e.g., across continents), differing evolutionary histories will prevent convergence. However, few studies have compared the contrasting roles of convergence and history, and none have done so at large scales. Here we develop a two-part approach to test the scale over which convergence can occur, comparing the relative importance of convergence and history in macroevolution using phylogenetic models of adaptive evolution. We apply this approach to data from morphology, ecology, and phylogeny from 167 species of anuran amphibians (frogs) from 10 local sites across the world, spanning ~160 myr of evolution. Mapping ecology on the phylogeny revealed that similar microhabitat specialists (e.g., aquatic, arboreal) have evolved repeatedly across clades and regions, producing many evolutionary replicates for testing for morphological convergence. By comparing morphological optima for clades and microhabitat types (our first test), we find that convergence associated with microhabitat use dominates frog morphological evolution, producing recurrent ecomorphs that together encompass all sampled species in each community in each region. However, our second test, which examines whether and how much species differ from their inferred optima, shows that convergence is incomplete: that is, phenotypes of most species are still somewhat distant from the estimated optimum for each microhabitat, seemingly because of insufficient time for more complete adaptation (an effect of history). Yet, these effects of history are related to past ecologies, and not clade membership. Overall, our study elucidates the dominant drivers of

  15. Large field cutoffs make perturbative series converge

    NASA Astrophysics Data System (ADS)

    Meurice, Yannick

    For λφ4 problems, convergent perturbative series can be obtained by cutting off the large field configurations. The modified series converge to values exponentially close to the exact ones. For λ larger than some critical value, the method outperforms Padé approximants and Borel summations. We discuss some aspects of the semi-classical methods used to calculate the modified Feynman rules and estimate the error associated with the procedure. We provide a simple numerical example where the procedure works despite the fact that the Borel sum has singularities on the positive real axis.

  16. Large field cutoffs make perturbative series converge

    NASA Astrophysics Data System (ADS)

    Meurice, Yannick

    2002-03-01

    For λφ 4 problems, convergent perturbative series can be obtained by cutting off the large field configurations. The modified series converge to values exponentially close to the exact ones. For λ larger than some critical value, the method outperforms Padé approximants and Borel summations. We discuss some aspects of the semi-classical methods used to calculate the modified Feynman rules and estimate the error associated with the procedure. We provide a simple numerical example where the procedure works despite the fact that the Borel sum has singularities on the positive real axis.

  17. On Iλ -statistical convergence of weight g

    NASA Astrophysics Data System (ADS)

    Savas, Ekrem

    2016-08-01

    In this paper, following a very recent and new approach of [M. Balcerzak, P. Das, M. Filipczak, and J. Swaczyna, Acta Math. Hungar. 147, 97-115 (2015)], we further generalize the recently introduced summability method of [E. Savas, and P. Das, Appl. Math. Lett. 24, 826-830 (2011)] and introduce the new notion namely, Iλ -statistical convergence of weight g, where g : ℕ → [0, ∞) is a function satisfying g(n) → ∞ and g(n) ↛ 0 as n → ∞. We mainly investigate certain properties of this convergence.

  18. GPS Monitoring of Subduction Zone Deformation in Costa Rica

    NASA Technical Reports Server (NTRS)

    Lundgren, Paul

    1997-01-01

    The subduction of the Cocos plate beneath Costa Rica is among the highest convergence rates in the world. The high subduction rate and nearness of the Nicoya Peninsula, Costa Rica to the Middle America Trench (MAT) provide a unique opportunity to map variations in interseismic strain of the crust above the seismogenic zone in response to variations in seismic coupling.

  19. Root apex transition zone as oscillatory zone.

    PubMed

    Baluška, František; Mancuso, Stefano

    2013-01-01

    Root apex of higher plants shows very high sensitivity to environmental stimuli. The root cap acts as the most prominent plant sensory organ; sensing diverse physical parameters such as gravity, light, humidity, oxygen, and critical inorganic nutrients. However, the motoric responses to these stimuli are accomplished in the elongation region. This spatial discrepancy was solved when we have discovered and characterized the transition zone which is interpolated between the apical meristem and the subapical elongation zone. Cells of this zone are very active in the cytoskeletal rearrangements, endocytosis and endocytic vesicle recycling, as well as in electric activities. Here we discuss the oscillatory nature of the transition zone which, together with several other features of this zone, suggest that it acts as some kind of command center. In accordance with the early proposal of Charles and Francis Darwin, cells of this root zone receive sensory information from the root cap and instruct the motoric responses of cells in the elongation zone.

  20. Root Apex Transition Zone As Oscillatory Zone

    PubMed Central

    Baluška, František; Mancuso, Stefano

    2013-01-01

    Root apex of higher plants shows very high sensitivity to environmental stimuli. The root cap acts as the most prominent plant sensory organ; sensing diverse physical parameters such as gravity, light, humidity, oxygen, and critical inorganic nutrients. However, the motoric responses to these stimuli are accomplished in the elongation region. This spatial discrepancy was solved when we have discovered and characterized the transition zone which is interpolated between the apical meristem and the subapical elongation zone. Cells of this zone are very active in the cytoskeletal rearrangements, endocytosis and endocytic vesicle recycling, as well as in electric activities. Here we discuss the oscillatory nature of the transition zone which, together with several other features of this zone, suggest that it acts as some kind of command center. In accordance with the early proposal of Charles and Francis Darwin, cells of this root zone receive sensory information from the root cap and instruct the motoric responses of cells in the elongation zone. PMID:24106493

  1. World health inequality: convergence, divergence, and development.

    PubMed

    Clark, Rob

    2011-02-01

    Recent studies characterize the last half of the twentieth century as an era of cross-national health convergence, with some attributing welfare gains in the developing world to economic growth. In this study, I examine the extent to which welfare outcomes have actually converged and the extent to which economic development is responsible for the observed trends. Drawing from estimates covering 195 nations during the 1955-2005 period, I find that life expectancy averages converged during this time, but that infant mortality rates continuously diverged. I develop a narrative that implicates economic development in these contrasting trends, suggesting that health outcomes follow a "welfare Kuznets curve." Among poor countries, economic development improves life expectancy more than it reduces infant mortality, whereas the situation is reversed among wealthier nations. In this way, development has contributed to both convergence in life expectancy and divergence in infant mortality. Drawing from 674 observations across 163 countries during the 1980-2005 period, I find that the positive effect of GDP PC on life expectancy attenuates at higher levels of development, while the negative effect of GDP PC on infant mortality grows stronger.

  2. Another Perspective: A Response to "Toward Convergence"

    ERIC Educational Resources Information Center

    Regelski, Thomas A.

    2013-01-01

    This response by Thomas A. Regelski was solicited to complement the lead article in this issue, "Toward Convergence: Adapting Music Education to Contemporary Society and Participatory Culture" by Evan S. Tobias. The author notes that many interesting and vital questions and alternatives that are often studiously ignored, overlooked, or taken for…

  3. Phonological Convergence in a Contracting Language Variety

    ERIC Educational Resources Information Center

    Bullock, Barbara E.; Gerfen, Chip

    2004-01-01

    Most work investigating the role of convergence in situations of language attrition has focused on the morpho-syntactic restructuring of the dying language variety. A central concern of such research has been untangling the factors driving the restructuring with an eye towards establishing whether the changes observed are best viewed as externally…

  4. Convergence as a Mechanism of Language Change

    ERIC Educational Resources Information Center

    Backus, Ad

    2004-01-01

    This issue of "Bilingualism: Language and Cognition" is about convergence, a type of language change that is contact-induced and results in greater similarity between two languages that are in contact with each other. In Backus (forthcoming), I have attempted an overview of contact-induced language change, focusing on causal factors, on mechanisms…

  5. Converging Oceaniac Internal Waves, Somalia, Africa

    NASA Technical Reports Server (NTRS)

    1988-01-01

    The arculate fronts of these apparently converging internal waves off the northeast coast of Somalia (11.5N, 51.5E) probably were produced by interaction with two parallel submarine canyons off the Horn of Africa. Internal waves are packets of tidally generated waves traveling within the ocean at varying depths and are not detectable by any surface disturbance.

  6. Culture and Social Psychology: Converging Perspectives

    ERIC Educational Resources Information Center

    Dimaggio, Paul; Markus, Hazel Rose

    2010-01-01

    Views of culture in psychology and sociology have converged markedly in the past two decades. Both have rejected what Adams and Markus (2004) refer to as the "entity" conception of culture--the view that culture is coherent, stable, and located in the heads of collectivities' members--in favor of more supple and dynamic constructs. Culture, in…

  7. The Convergence Coefficient across Political Systems

    PubMed Central

    Schofield, Norman

    2013-01-01

    Formal work on the electoral model often suggests that parties or candidates should locate themselves at the electoral mean. Recent research has found no evidence of such convergence. In order to explain nonconvergence, the stochastic electoral model is extended by including estimates of electoral valence. We introduce the notion of a convergence coefficient, c. It has been shown that high values of c imply that there is a significant centrifugal tendency acting on parties. We used electoral surveys to construct a stochastic valence model of the the elections in various countries. We find that the convergence coefficient varies across elections in a country, across countries with similar regimes, and across political regimes. In some countries, the centripetal tendency leads parties to converge to the electoral mean. In others the centrifugal tendency dominates and some parties locate far from the electoral mean. In particular, for countries with proportional electoral systems, namely, Israel, Turkey, and Poland, the centrifugal tendency is very high. In the majoritarian polities of the United States and Great Britain, the centrifugal tendency is very low. In anocracies, the autocrat imposes limitations on how far from the origin the opposition parties can move. PMID:24385886

  8. Convergent formal synthesis of (±)-roseophilin.

    PubMed

    Song, Chuanjun; Liu, Hui; Hong, Meiling; Liu, Yuanyuan; Jia, Feifei; Sun, Li; Pan, Zhenliang; Chang, Junbiao

    2012-01-01

    A facile convergent synthesis of the tricyclic core 2 of roseophilin is described, which represents the shortest route so far for the formal synthesis of roseophilin. The key step was a tandem pyrrole acylation-Nazarov cyclization reaction to form the cyclopenta[b]pyrrole moiety 4. PMID:22098172

  9. Collaborative Instructional Strategies to Enhance Knowledge Convergence

    ERIC Educational Resources Information Center

    Draper, Darryl C.

    2015-01-01

    To promote knowledge convergence through collaborative learning activities in groups, this qualitative case study involved a layered approach for the design and delivery of a highly collaborative learning environment incorporating various instructional technologies grounded in learning theory. In a graduate-level instructional technology course,…

  10. Governance Challenges of Technological Systems Convergence

    ERIC Educational Resources Information Center

    Whitman, Jim

    2006-01-01

    The convergence of several technological systems (especially nanotechnology, biotechnology, information technology, and robotics) has now been adopted as a strategic goal by several countries, most notably the United States and those of the European Union. The anticipated benefits and related fears of competitive disadvantage have brought together…

  11. Convergence behavior of a new DSMC algorithm.

    SciTech Connect

    Gallis, Michail A.; Rader, Daniel John; Torczynski, John Robert; Bird, Graeme A.

    2008-10-01

    The convergence rate of a new direct simulation Monte Carlo (DSMC) method, termed 'sophisticated DSMC', is investigated for one-dimensional Fourier flow. An argon-like hard-sphere gas at 273.15K and 266.644Pa is confined between two parallel, fully accommodating walls 1mm apart that have unequal temperatures. The simulations are performed using a one-dimensional implementation of the sophisticated DSMC algorithm. In harmony with previous work, the primary convergence metric studied is the ratio of the DSMC-calculated thermal conductivity to its corresponding infinite-approximation Chapman-Enskog theoretical value. As discretization errors are reduced, the sophisticated DSMC algorithm is shown to approach the theoretical values to high precision. The convergence behavior of sophisticated DSMC is compared to that of original DSMC. The convergence of the new algorithm in a three-dimensional implementation is also characterized. Implementations using transient adaptive sub-cells and virtual sub-cells are compared. The new algorithm is shown to significantly reduce the computational resources required for a DSMC simulation to achieve a particular level of accuracy, thus improving the efficiency of the method by a factor of 2.

  12. Professionalization in Universities and European Convergence

    ERIC Educational Resources Information Center

    Vivas, Amparo Jimenez; Hevia, David Menendez Alvarez

    2009-01-01

    The constant assessment of the quality of higher education within the framework of European convergence is a challenge for all those universities that wish their degrees and diplomas to reflect a unified Europe. As is the case in any assessment, change and review process, the quest to improve quality implies measuring achievement of the objectives…

  13. Diurnal cycle in convergence patterns in the boundary layer east of the Andes and convection

    NASA Astrophysics Data System (ADS)

    Nicolini, Matilde; Skabar, Yanina García

    2011-06-01

    . Mesoscale circulations are altered (still effecting mean divergence in the domain, which exhibits a diurnal oscillation) upon the initiation of deep convective circulations in the evening in an increasingly convectively unstable atmosphere driven by a persistent horizontal advection of heat and moisture at low levels and forced by convergence generated by the low-level jet and the presence of a frontal zone. Convection intensifies at night when its related convergence over the plains comes in phase with the convergence related to the nocturnal maximum in the low-level jet.

  14. A Numerical Study of Strain Partitioning and the Development of Forearc Slivers at Obliquely Convergent Margins

    NASA Astrophysics Data System (ADS)

    Koster, K. L.; Haq, S. S.; Flesch, L. M.

    2012-12-01

    Oblique relative plate motion is common at convergent margins, often with a significant component of margin-parallel motion. At such margins, relative plate motion is often accommodated as spatially distinct margin-normal thrusting and margin-parallel shear, leading to the development of fore-arc slivers. These crustal slivers are bounded trench-ward by thrust faults and arc-ward by a well developed margin-parallel strike-slip fault and are observed in about half of all modern convergent boundaries. Some modestly oblique convergent settings are known to develop fore-arc slivers while some higher obliquity margins fail to effectively partition the margin-parallel component of plate motion in a distinct zone. Analog modeling has shown that pure frictional wedges only produce fore-arc like sliver motion at very high obliquities, however, the presence of ductile layers at depth can localize shear at lower obliquities. We have performed finite-element numerical simulations of oblique convergent wedges, over a wide range of obliquities, governed by viscous behavior at depth in which we solve force-balance equations for Stokes flow using COMSOL Multiphysics to quantify the magnitude and style of stress. Our numerical models reproduce topographic profiles and surface velocity fields of similarly parameterized analog experiments and demonstrate a progressive localization of margin-parallel shear with wedge growth. We also observe the onset and localization of shear in all wedges of non-zero obliquity, which we quantify by comparing the magnitudes of principal compressional and extensional stress tensor axes to constrain the timing of the transition between intermediate and high partitioning of strain in evolving wedges. These results suggest, in conjunction with analog models, that viscous behavior at depth and increase in topography during convergence both work to localize margin-parallel shear in obliquely convergent wedges and gives a mechanism for the development of

  15. Contamination-free high capacity converging waves sonoreactors for the chemical industry.

    PubMed

    Dion, Jean-Luc

    2009-02-01

    A new sonoreactor technology is presented here which should give a decisive impulse to sonochemistry in various areas of chemical processing. These exclusive systems use high power converging acoustic waves in a tube to produce a relatively large volume confined acoustic cavitation zone in flowing liquid reagents under pressure. It is well known that numerous chemical reactions are strongly accelerated when they take place inside such a zone. The new cylindrical sonoreactors do not contaminate the processed liquids with erosion products as most other devices do since the cavitation zone is maintained away from the wall of the tube. The processing conditions can be widely varied with pressure, power, temperature, and flow rate. The processing capacity of the largest models may be up to several tons per hour, depending on the required cavitation energy per unit volume to produce the desired process enhancement, using an electric power input of about 50 kW. PMID:18789748

  16. The convergence of European business cycles 1978-2000

    NASA Astrophysics Data System (ADS)

    Ormerod, Paul; Mounfield, Craig

    2002-05-01

    The degree of convergence of the business cycles of the economies of the European Union (EU) is a key policy issue. In particular, a substantial degree of convergence is needed if the European Central Bank is to be capable of setting a monetary policy which is appropriate to the stage of the cycle of the Euro zone economies. We consider the annual rates of real GDP growth on a quarterly basis in the large core economies of the EU (France, Germany and Italy, plus The Netherlands) over the period 1978Q1-2000Q3. An important empirical question is the degree to which the correlations between these growth rates contain true information rather than noise. The technique of random matrix theory is able to answer this question, and has been recently applied successfully in the physics journals to financial markets data. We find that the correlations between the growth rates of the core EU economies contain substantial amounts of true information, and exhibit considerable stability over time. Even in the late 1970s and early 1980s, these economies moved together closely over the course of the business cycle. There was a slight loosening at the time of German re-unification, but the economies are now, if anything, even more closely correlated. As a benchmark for comparison, we add a series to the EU core data set which by construction is uncorrelated with these business cycles. We then analyse the EU core plus Spain, a country which has attached great importance to greater integration with Europe. In the early part of the period examined, the results are very similar to those obtained with the data set of the EU core plus the random series. However, there is a clear trend in the results, which provide strong evidence to support the view that the Spanish economy has now become closely converged with the core EU economies in terms of its movements over the business cycle. In contrast, the results obtained with a data set of the EU core plus the UK show no such trend. In the

  17. Vadose zone microbiology

    SciTech Connect

    Kieft, Thomas L.; Brockman, Fred J.

    2001-01-17

    The vadose zone is defined as the portion of the terrestrial subsurface that extends from the land surface downward to the water table. As such, it comprises the surface soil (the rooting zone), the underlying subsoil, and the capillary fringe that directly overlies the water table. The unsaturated zone between the rooting zone and the capillary fringe is termed the "intermediate zone" (Chapelle, 1993). The vadose zone has also been defined as the unsaturated zone, since the sediment pores and/or rock fractures are generally not completely water filled, but instead contain both water and air. The latter characteristic results in the term "zone of aeration" to describe the vadose zone. The terms "vadose zone," "unsaturated zone", and "zone of aeration" are nearly synonymous, except that the vadose zone may contain regions of perched water that are actually saturated. The term "subsoil" has also been used for studies of shallow areas of the subsurface immediately below the rooting zone. This review focuses almost exclusively on the unsaturated region beneath the soil layer since there is already an extensive body of literature on surface soil microbial communities and process, e.g., Paul and Clark (1989), Metting (1993), Richter and Markowitz, (1995), and Sylvia et al. (1998); whereas the deeper strata of the unsaturated zone have only recently come under scrutiny for their microbiological properties.

  18. Globally convergent autocalibration using interval analysis.

    PubMed

    Fusiello, Andrea; Benedetti, Arrigo; Farenzena, Michela; Busti, Alessandro

    2004-12-01

    We address the problem of autocalibration of a moving camera with unknown constant intrinsic parameters. Existing autocalibration techniques use numerical optimization algorithms whose convergence to the correct result cannot be guaranteed, in general. To address this problem, we have developed a method where an interval branch-and-bound method is employed for numerical minimization. Thanks to the properties of Interval Analysis this method converges to the global solution with mathematical certainty and arbitrary accuracy and the only input information it requires from the user are a set of point correspondences and a search interval. The cost function is based on the Huang-Faugeras constraint of the essential matrix. A recently proposed interval extension based on Bernstein polynomial forms has been investigated to speed up the search for the solution. Finally, experimental results are presented. PMID:15573823

  19. The genetic causes of convergent evolution.

    PubMed

    Stern, David L

    2013-11-01

    The evolution of phenotypic similarities between species, known as convergence, illustrates that populations can respond predictably to ecological challenges. Convergence often results from similar genetic changes, which can emerge in two ways: the evolution of similar or identical mutations in independent lineages, which is termed parallel evolution; and the evolution in independent lineages of alleles that are shared among populations, which I call collateral genetic evolution. Evidence for parallel and collateral evolution has been found in many taxa, and an emerging hypothesis is that they result from the fact that mutations in some genetic targets minimize pleiotropic effects while simultaneously maximizing adaptation. If this proves correct, then the molecular changes underlying adaptation might be more predictable than has been appreciated previously.

  20. Stability of spherical converging shock wave

    NASA Astrophysics Data System (ADS)

    Murakami, M.; Sanz, J.; Iwamoto, Y.

    2015-07-01

    Based on Guderley's self-similar solution, stability of spherical converging shock wave is studied. A rigorous linear perturbation theory is developed, in which the growth rate of perturbation is given as a function of the spherical harmonic number ℓ and the specific heats ratio γ. Numerical calculation reveals the existence of a γ-dependent cut-off mode number ℓc, such that all the eigenmode perturbations for ℓ > ℓc are smeared out as the shock wave converges at the center. The analysis is applied to partially spherical geometries to give significant implication for different ignition schemes of inertial confinement fusion. Two-dimensional hydrodynamic simulations are performed to verify the theory.

  1. Molecular mechanisms involved in convergent crop domestication.

    PubMed

    Lenser, Teresa; Theißen, Günter

    2013-12-01

    Domestication has helped to understand evolution. We argue that, vice versa, novel insights into evolutionary principles could provide deeper insights into domestication. Molecular analyses have demonstrated that convergent phenotypic evolution is often based on molecular changes in orthologous genes or pathways. Recent studies have revealed that during plant domestication the causal mutations for convergent changes in key traits are likely to be located in particular genes. These insights may contribute to defining candidate genes for genetic improvement during the domestication of new plant species. Such efforts may help to increase the range of arable crops available, thus increasing crop biodiversity and food security to help meet the predicted demands of the continually growing global population under rapidly changing environmental conditions.

  2. Non-surgical interventions for convergence insufficiency

    PubMed Central

    Scheiman, Mitchell; Gwiazda, Jane; Li, Tianjing

    2014-01-01

    Background Convergence insufficiency is a common eye muscle co-ordination problem in which the eyes have a strong tendency to drift outward (exophoria) when reading or doing close work. Symptoms may include eye strain, headaches, double vision, print moving on the page, frequent loss of place when reading, inability to concentrate, and short attention span. Objectives To systematically assess and synthesize evidence from randomized controlled trials (RCTs) on the effectiveness of non-surgical interventions for convergence insufficiency. Search strategy We searched The Cochrane Library, MEDLINE, EMBASE, Science Citation Index, the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com) and ClinicalTrials.gov (www.clinicaltrials.gov) on 7 October 2010. We manually searched reference lists and optometric journals. Selection criteria We included RCTs examining any form of non-surgical intervention against placebo, no treatment, sham treatment, or each other. Data collection and analysis Two authors independently assessed eligibility, risk of bias, and extracted data. We performed meta-analyses when appropriate. Main results We included six trials (three in children, three in adults) with a total of 475 participants. We graded four trials at low risk of bias. Evidence from one trial (graded at low risk of bias) suggests that base-in prism reading glasses was no more effective than placebo reading glasses in improving clinical signs or symptoms in children. Evidence from one trial (graded at high risk of bias) suggests that base-in prism glasses using a progressive addition lens design was more effective than progressive addition lens alone in decreasing symptoms in adults. At three weeks of therapy, the mean difference in Convergence Insufficiency Symptoms Survey (CISS) score was −10.24 points (95% confidence interval (CI) −15.45 to −5.03). Evidence from two trials (graded at low risk of bias) suggests that outpatient (or office-based as used in the

  3. Convergent strand array liquid pumping system

    NASA Technical Reports Server (NTRS)

    Collins, Earl R., Jr. (Inventor)

    1989-01-01

    A surface-tension liquid pumping system is provided by one or more arrays of converging solid monofilament fibers or metal wires (strands) spaced apart at an input end to gather liquid, and gathered close together at the opposite end where menisci forms between wetted strands to force liquid in the direction of convergence of the strands. The liquid pumping system is independent of gravity. It is illustrated as being used in a heat pump having a heating box to vaporize the liquid and a condensing chamber. Condensed liquid is returned by the pumping system to the heating box where it is again vaporized. A vapor tube carries the vapor to the condensing chamber. In that way, a closed system pumps heat from the heating box to the evaporating chamber and from there radiated to the atmosphere.

  4. Technologies for convergence in the metro network

    NASA Astrophysics Data System (ADS)

    Frankel, Michael Y.

    2005-02-01

    Traditional metro network architectures comprise multiple layers of networking equipment supporting a wide array of services and packet-oriented applications. Among others, these include WDM, SDH, ATM, Ethernet and IP, each requiring its own network elements and associated management solutions to perform its own independent networking functions. While these work well individually, the combined network is cumbersome and inefficient. Recent advancements in network technologies are now changing the way metro networks are designed. Multi-functional consolidation through technology integration and the standardization of protocol inter-networking methods are leading to a converged network solution in support of a diverse set of packet-aware service offerings. This presentation will explore new technologies that are enabling convergence in the metro network, both across layers and across services.

  5. Stability of spherical converging shock wave

    SciTech Connect

    Murakami, M.; Sanz, J.; Iwamoto, Y.

    2015-07-15

    Based on Guderley's self-similar solution, stability of spherical converging shock wave is studied. A rigorous linear perturbation theory is developed, in which the growth rate of perturbation is given as a function of the spherical harmonic number ℓ and the specific heats ratio γ. Numerical calculation reveals the existence of a γ-dependent cut-off mode number ℓ{sub c}, such that all the eigenmode perturbations for ℓ > ℓ{sub c} are smeared out as the shock wave converges at the center. The analysis is applied to partially spherical geometries to give significant implication for different ignition schemes of inertial confinement fusion. Two-dimensional hydrodynamic simulations are performed to verify the theory.

  6. Arieti and Bowlby: convergence and direct influence.

    PubMed

    Bacciagaluppi, Marco

    2015-09-01

    Arieti was a great specialist of schizophrenia and Bowlby was the initiator of attachment theory. Working independently on the two sides of the Atlantic, they converged on a range of topics, such as evolutionary theory, mourning, trauma, violence, and therapy as art and science. Later, Bowlby exerted a direct influence on Arieti, which Arieti acknowledged in his Love Can Be Found. Finally, the two authors cooperated in the second edition of the American Handbook of Psychiatry. PMID:26356777

  7. Guaranteed convergence of the Hough transform

    NASA Astrophysics Data System (ADS)

    Soffer, Menashe; Kiryati, Nahum

    1995-01-01

    The straight-line Hough Transform using normal parameterization with a continuous voting kernel is considered. It transforms the colinearity detection problem to a problem of finding the global maximum of a two dimensional function above a domain in the parameter space. The principle is similar to robust regression using fixed scale M-estimation. Unlike standard M-estimation procedures the Hough Transform does not rely on a good initial estimate of the line parameters: The global optimization problem is approached by exhaustive search on a grid that is usually as fine as computationally feasible. The global maximum of a general function above a bounded domain cannot be found by a finite number of function evaluations. Only if sufficient a-priori knowledge about the smoothness of the objective function is available, convergence to the global maximum can be guaranteed. The extraction of a-priori information and its efficient use are the main challenges in real global optimization problems. The global optimization problem in the Hough Transform is essentially how fine should the parameter space quantization be in order not to miss the true maximum. More than thirty years after Hough patented the basic algorithm, the problem is still essentially open. In this paper an attempt is made to identify a-priori information on the smoothness of the objective (Hough) function and to introduce sufficient conditions for the convergence of the Hough Transform to the global maximum. An image model with several application dependent parameters is defined. Edge point location errors as well as background noise are accounted for. Minimal parameter space quantization intervals that guarantee convergence are obtained. Focusing policies for multi-resolution Hough algorithms are developed. Theoretical support for bottom- up processing is provided. Due to the randomness of errors and noise, convergence guarantees are probabilistic.

  8. Design Calculations For NIF Convergent Ablator Experiments

    SciTech Connect

    Olson, R E; Hicks, D G; Meezan, N B; Callahan, D A; Landen, O L; Jones, O S; Langer, S H; Kline, J L; Wilson, D C; Rinderknecht, H; Zylstra, A; Petrasso, R D

    2011-10-25

    The NIF convergent ablation tuning effort is underway. In the early experiments, we have discovered that the design code simulations over-predict the capsule implosion velocity and shock flash rhor, but under-predict the hohlraum x-ray flux measurements. The apparent inconsistency between the x-ray flux and radiography data implies that there are important unexplained aspects of the hohlraum and/or capsule behavior.

  9. Design calculations for NIF convergent ablator experiments

    NASA Astrophysics Data System (ADS)

    Olson, R. E.; Hicks, D. G.; Meezan, N. B.; Callahan, D. A.; Landen, O. L.; Jones, O. S.; Langer, S. H.; Kline, J. L.; Wilson, D. C.; Rinderknecht, H.; Zylstra, A.; Petrasso, R. D.

    2013-11-01

    The NIF convergent ablation tuning effort is underway. In the early experiments, we have discovered that the design code simulations over-predict the capsule implosion velocity and shock flash ρr, but under-predict the hohlraum x-ray flux measurements. The apparent inconsistency between the x-ray flux and radiography data implies that there are important unexplained aspects of the hohlraum and/or capsule behavior.

  10. Convergence Creates Opportunities Across Health Care System

    PubMed Central

    Fox, Brent I.; Felkey, Bill G.

    2014-01-01

    Industrial design students at Auburn do a creativity exercise where they are asked to combine a common household appliance with an animal. Have you seen a snake light? In health technology, we have a similar opportunity. In the connection between jewelry and vital sign monitoring technology or household security and health status monitoring, we are witnessing active convergence that will benefit patients, providers, and health systems. PMID:24958948

  11. Convergence creates opportunities across health care system.

    PubMed

    Fox, Brent I; Felkey, Bill G

    2014-04-01

    Industrial design students at Auburn do a creativity exercise where they are asked to combine a common household appliance with an animal. Have you seen a snake light? In health technology, we have a similar opportunity. In the connection between jewelry and vital sign monitoring technology or household security and health status monitoring, we are witnessing active convergence that will benefit patients, providers, and health systems.

  12. Convergence creates opportunities across health care system.

    PubMed

    Fox, Brent I; Felkey, Bill G

    2014-04-01

    Industrial design students at Auburn do a creativity exercise where they are asked to combine a common household appliance with an animal. Have you seen a snake light? In health technology, we have a similar opportunity. In the connection between jewelry and vital sign monitoring technology or household security and health status monitoring, we are witnessing active convergence that will benefit patients, providers, and health systems. PMID:24958948

  13. [Bioethics and public health: epistemological convergences].

    PubMed

    Junges, Jose Roque; Zoboli, Elma Lourdes Campos Pavone

    2012-04-01

    This is a theoretical discussion about the epistemological statute of bioethics based on its convergences with public health, linked as scientific areas that came from the context of the second epistemological rupture, which questioned the critique to common sense inherent in modern science. The reapproximation with common sense in the second rupture means considering the determinants of environment and subjectivity in the methodology. Emerging from the second rupture, public health and bioethics include the social and subjective determinants in their analysis, with an enlarged and complex vision of human health and human actions involving environment, life and health. This requires a transdisciplinary focus in their approaches. What is the meaning of these premises for the epistemological statute of bioethics in its convergence with public health? As ethics, bioethics needs to be critical, but not aprioristic. The criticism of bioethics needs to come from the facticity of the social determinants expressed by the health iniquities. The only way to integrate criticism and facticity is hermeneutics, interpreting the significances constructed in the reality and become critical therefrom. This is the epistemological statute appropriate to bioethics in its convergence with public health.

  14. Cultural and Gender Convergence in Adolescent Drunkenness

    PubMed Central

    Kuntsche, Emmanuel; Kuntsche, Sandra; Knibbe, Ronald; Simons-Morton, Bruce; Farhat, Tilda; Hublet, Anne; Bendtsen, Pernille; Godeau, Emmanuelle; Demetrovics, Zsolt

    2014-01-01

    Objective To investigate time-trend changes in the frequency of drunkenness among European and North American adolescents. Design Cross-sectional surveys in the 1997/1998 and 2005/2006 Health Behaviour in School-Aged Children Study (HBSC). Setting High schools in 23 countries. Participants A sample of 77 586 adolescents aged 15 years was analyzed by means of hierarchical linear modeling. Main Outcome Measure The frequency of drunkenness. Results We observed a significant increase of about 40% in the mean frequency of drunkenness in all 7 participating Eastern European countries. This increase was evident among both genders, but most consistently among girls. Meanwhile, it declined in 13 of 16 Western countries, about 25% on average. Declines in Western countries were particularly notable among boys and in North America, Scandinavia, the United Kingdom, and Ireland. Despite this gender convergence, with few exceptions (Greenland, Norway, United Kingdom) boys continued to have a higher frequency of drunkenness in 2005/2006 than girls. Conclusions The confirmed cultural convergence implies that adoption and implementation of evidence-based measures to mitigate the frequency of adolescent drunkenness such as tax increases and restricting alcohol access and advertisement should get the same priority in Eastern European countries as in Western countries. Policy measures that might facilitate decreases in drunkenness such as server training and the promotion of alcohol-free leisure-time activities should be reinforced in Western countries. The gender convergence implies that prevention policy should be less exclusively focused on male adolescents. PMID:20921343

  15. Crenulative Turbulence in a Converging Nonhomogeneous Material

    SciTech Connect

    Romero, C.A.

    1999-01-01

    Crenulative turbulence is a nonlinear extension of the Bell-Plesset instability, usually observed in a converging system in which there is a nonhomogeneous response of stress to strain and/or strain rate. In general, crenelation occurs in any circumstance in which the mean flow streamlines converge the material more strongly than the compressibility can accommodate. Elements of the material slip past each other, resulting in local fluctuations in velocity from that of the mean flow, producing a type of turbulence that is more kinematic than inertial. For a homogeneous material, crenelation occurs at the atomic or molecular scale. With nonhomogeneous stress response at larger scales, the crenulative process can also occur at those larger scales. The results are manifested by a decrease in the rate of dissipation to heat, and by the configurationally-irreversible mixing of nonhomogeneities across any mean-flow-transported interface. We obtain a mathematical description of the crenulative process by means of Reynolds decomposition of the appropriate variables, and the derivation of transport equations for the second-order moments that arise in the mean-flow momentum and energy equations. The theory is illustrated by application to the spherical convergence of an incompressible fluid with nonhomogeneous distribution of kinematic viscosity.

  16. Convergent Coarseness Regulation for Segmented Images

    SciTech Connect

    Paglieroni, D W

    2004-05-27

    In segmentation of remotely sensed images, the number of pixel classes and their spectral representations are often unknown a priori. Even with prior knowledge, pixels with spectral components from multiple classes lead to classification errors and undesired small region artifacts. Coarseness regulation for segmented images is proposed as an efficient novel technique for handling these problems. Beginning with an over-segmented image, perceptually similar connected regions are iteratively merged using a method reminiscent of region growing, except the primitives are regions, not pixels. Interactive coarseness regulation is achieved by specifying the area {alpha} of the largest region eligible for merging. A region with area less than {alpha} is merged with the most spectrally similar connected region, unless the regions are perceived as spectrally dissimilar. In convergent coarseness regulation, which requires no user interaction, {alpha} is specified as the total number of pixels in the image, and the coarseness regulation output converges to a steady-state segmentation that remains unchanged as {alpha} is further increased. By applying convergent coarseness regulation to AVIRIS, IKONOS and DigitalGlobe images, and quantitatively comparing computer-generated segmentations to segmentations generated manually by a human analyst, it was found that the quality of the input segmentations was consistently and dramatically improved.

  17. Disparity and convergence in bipedal archosaur locomotion

    PubMed Central

    Bates, K. T.; Schachner, E. R.

    2012-01-01

    This study aims to investigate functional disparity in the locomotor apparatus of bipedal archosaurs. We use reconstructions of hindlimb myology of extant and extinct archosaurs to generate musculoskeletal biomechanical models to test hypothesized convergence between bipedal crocodile-line archosaurs and dinosaurs. Quantitative comparison of muscle leverage supports the inference that bipedal crocodile-line archosaurs and non-avian theropods had highly convergent hindlimb myology, suggesting similar muscular mechanics and neuromuscular control of locomotion. While these groups independently evolved similar musculoskeletal solutions to the challenges of parasagittally erect bipedalism, differences also clearly exist, particularly the distinct hip and crurotarsal ankle morphology characteristic of many pseudosuchian archosaurs. Furthermore, comparative analyses of muscle design in extant archosaurs reveal that muscular parameters such as size and architecture are more highly adapted or optimized for habitual locomotion than moment arms. The importance of these aspects of muscle design, which are not directly retrievable from fossils, warns against over-extrapolating the functional significance of anatomical convergences. Nevertheless, links identified between posture, muscle moments and neural control in archosaur locomotion suggest that functional interpretations of osteological changes in limb anatomy traditionally linked to postural evolution in Late Triassic archosaurs could be constrained through musculoskeletal modelling. PMID:22112652

  18. Convergence of quantum random walks with decoherence

    SciTech Connect

    Fan Shimao; Feng Zhiyong; Yang, Wei-Shih; Xiong Sheng

    2011-10-15

    In this paper, we study the discrete-time quantum random walks on a line subject to decoherence. The convergence of the rescaled position probability distribution p(x,t) depends mainly on the spectrum of the superoperator L{sub kk}. We show that if 1 is an eigenvalue of the superoperator with multiplicity one and there is no other eigenvalue whose modulus equals 1, then P(({nu}/{radical}(t)),t) converges to a convex combination of normal distributions. In terms of position space, the rescaled probability mass function p{sub t}(x,t){identical_to}p({radical}(t)x,t), x is an element of Z/{radical}(t), converges in distribution to a continuous convex combination of normal distributions. We give a necessary and sufficient condition for a U(2) decoherent quantum walk that satisfies the eigenvalue conditions. We also give a complete description of the behavior of quantum walks whose eigenvalues do not satisfy these assumptions. Specific examples such as the Hadamard walk and walks under real and complex rotations are illustrated. For the O(2) quantum random walks, an explicit formula is provided for the scaling limit of p(x,t) and their moments. We also obtain exact critical exponents for their moments at the critical point and show universality classes with respect to these critical exponents.

  19. On lacunary statistical convergence of order α in probability

    NASA Astrophysics Data System (ADS)

    Işık, Mahmut; Et, Kübra Elif

    2015-09-01

    In this study, we examine the concepts of lacunary statistical convergence of order α in probability and Nθ—convergence of order α in probability. We give some relations connected to these concepts.

  20. The Record of Collision and Accretion in the History of a Convergent Margin

    NASA Astrophysics Data System (ADS)

    Moresi, L. N.; Betts, P. G.; Miller, M. S.; Cayley, R. A.

    2014-12-01

    Convergent margins become congested when they try to swallow buoyant, exotic crust or an oceanic swell associated with anomalously buoyant plume material. Mountain belts (orogens) that form at these convergent plate margins are the sites of significant lateral continental growth. Modern examples of accretionary margins are the North American Cordillera and southwest Pacific. The geologic record is riddled with accretionary orogens, such as the Tasmanides along the eastern margin of the supercontinent Gondwana and the Altaides that formed on the southern margin of Laurasia. In modern and ancient examples of long lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back arc basin development, often related to subduction roll back and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. In previous work, (Mason et al, 2010), we found that buoyant material ingested by a subduction zone produces a relative advance of the local region of the trench (either reduced rollback or absolute advance) naturally leading to the characteristic indentation of the plate boundary by the plateau. Depending on the strength and buoyancy of the incoming anomaly relative to the oceanic lithosphere, it may be subducted or it may be accreted with the associated formation of a slab window. Extending this model to ocean-continent convergent zones (Moresi et al, 2014), we show how the indentation of buoyant exotic material also dominates terrane accretion. When large blocks of material congest a subduction zone, the subduction zone needs to undergo signficiant re-arrangement for convergence to continue. We have modelled this process and observe characteristic patterns in the deformation of the over-riding plate, in the timing of the escape of material from behind the indenter, and in the oroclinal geometry that remains once the collision has completed. References Mason, W. G., Moresi, L., Betts, P. G

  1. The Residue of Lithospheric Convergence in the Alpine-Pannonian-Carpathian system

    NASA Astrophysics Data System (ADS)

    Houseman, G. A.; Stuart, G. W.; Hetenyi, G.; Lorinczi, P.; Dando, B. D.

    2009-12-01

    The continuing collision of the Adriatic block with European continental lithosphere has its clearest expression now in the Alpine collision zone. In the Early Miocene the collision zone extended further east and included probably all of the regions within the Carpathian Mountain Range. In the Mid-Miocene between about 17 and 12 Ma, however, the Pannonian lithosphere extended rapidly and subsequently subsided, while convergence persisted in the Alps and the Carpathian arc. The change from convergence to extension in the Pannonian domain is associated with either rapid subduction roll-back or gravitational instability in which the lower part of the lithosphere was removed and replaced by hot asthenosphere. Throughout this time however, convergence has continued in the Alpine orogeny further west. It is surprising therefore to see similarities in the mantle transition zone beneath these two neighbouring regions whose lithospheres have, in the last 17 Myr at least, evolved in such different modes. New seismic images from beneath the Pannonian Basin (Hetenyi et al., GRL, in press) and from beneath the Alps (Lombardi et al., EPSL, 2009) show that both regions have a depressed 660 km discontinuity beneath a relatively normal-depth 410 km discontinuity. An important factor in both regions evidently is that relatively dense material derived from the mid-Miocene collision sits stagnant on top of the 660 km discontinuity, where further descent is obstructed by the negative Clapeyron slope of the spinel-to-perovskite phase transition and the high viscosity of the lower mantle. While the depression of the 660 km discontinuity beneath the Alps is directly associated with ongoing convergence, that beneath the Pannonian appears to be decoupled from the upper mantle circulation that accompanied the Miocene Pannonian extension. If the cold material at the base of the Pannonian upper mantle is the residue of lithospheric subduction, delamination, or gravitational instability, the

  2. Convergence to steady state of solutions of Burgers' equation

    NASA Technical Reports Server (NTRS)

    Kreiss, G.; Kreiss, H. O.

    1985-01-01

    Consider the initial boundary value problem for Burgers' equation. It is shown that its solutions converge, in time, to a unique steady state. The speed of the convergence depends on the boundary conditions and can be exponentially slow. Methods to speed up the rate of convergence are also discussed.

  3. Convergent and Divergent Thinking in the Context of Narrative Mysteries

    ERIC Educational Resources Information Center

    Wenzel, William G.; Gerrig, Richard J.

    2015-01-01

    This project demonstrates how narrative mysteries provide a context in which readers engage in creative cognition. Drawing on the concepts of convergent and divergent thinking, we wrote stories that had either convergent or divergent outcomes. For example, one story had a character give his girlfriend a ring (a convergent outcome), whereas the…

  4. Convergence and Divergence in Ethnic Divorce Patterns: A Research Note.

    ERIC Educational Resources Information Center

    Jones, F. L.

    1996-01-01

    Discusses divorce among ethnically heterogeneous couples. Uses Australian data from the 1970s to show that divorce risks are consistent with a modified model of behavioral convergence in which divorce rates for mixed marriages are largely a function of revealed group preferences for divorce and convergence between them. A convergence model may…

  5. Plate convergence, transcurrent faults and internal deformation adjacent to Southeast Asia and the western Pacific

    NASA Technical Reports Server (NTRS)

    Fitch, T. J.

    1971-01-01

    A model for oblique convergence between plates of lithosphere is proposed in which at least a fraction of slip parallel to the plate margin results in transcurrent movements on a nearly vertical fault which is located on the continental side of a zone of plate consumption. In an extreme case of complete decoupling only the component of slip normal to the plate margin can be inferred from underthrusting. Recent movements in the western Sunda region provide the most convincing evidence for decoupling of slip, which in this region is thought to be oblique to the plate margin. A speculative model for convergence along the margins of the Philippine Sea is constructed from an inferred direction of oblique slip in the Philippine region. This model requires that the triple point formed by the junction of the Japanese and Izu-Bonin trenches and the Nankai trough migrate along the Sagami trough.

  6. GPS constraints on interplate locking within the Makran subduction zone

    NASA Astrophysics Data System (ADS)

    Frohling, E.; Szeliga, W.

    2016-04-01

    The Makran subduction zone is one of the last convergent margins to be investigated using space-based geodesy. While there is a lack of historical and modern instrumentation in the region, a sparse sampling of continuous and campaign measurements over the past decade has allowed us to make the first estimates of convergence rates. We combine GPS measurements from 20 stations located in Iran, Pakistan and Oman along with hypocentral locations from the International Seismological Centre to create a preliminary 3-D estimate of the geometry of the megathrust, along with a preliminary fault-coupling model for the Makran subduction zone. Using a convergence rate which is strongly constrained by measurements from the incoming Arabia plate along with the backslip method of Savage, we find the Makran subduction zone appears to be locked to a depth of at least 38 km and accumulating strain.We also find evidence for a segmentation of plate coupling, with a 300 km long section of reduced plate coupling. The range of acceptable locking depths from our modelling and the 900 km along-strike length for the megathrust, makes the Makran subduction zone capable of earthquakes up to Mw = 8.8. In addition, we find evidence for slow-slip-like transient deformation events on two GPS stations. These observations are suggestive of transient deformation events observed in Cascadia, Japan and elsewhere.

  7. Unsustainable Groundwater Exploitation and Stochastic Regime Shifts: Converging Management Constraints

    NASA Astrophysics Data System (ADS)

    Rao, Suresh; Park, Jeryang

    2014-05-01

    Increasing water security concerns arise from projected increases in competing freshwater demands, resulting from rapid urbanization, growing affluent population, and the need for increased production of food and bio-energy. These global trends in concert with the convergence of three groups of threats are likely to exacerbate freshwater security issues: (1) increasing dependency on effectively non-renewable groundwater ("peak water"); (2) increasing groundwater quality impairment("land-use intensification") from larger contaminant loads delivered from the vadose zone and surface water; and (3) increasing uncertainties in groundwater demand/supply from climate change ("stochastic risks"). Here, we present a conceptual framework for exploring water security threats, with a consideration of aquifers as complex hydrological systems with two stable states. Regime shifts in groundwater pumping -- from "sufficient" to "insufficient" -- result from changes in both internal system dynamics and external forcing from stochastic divers (non-stationary demands, hydro-climatic patterns). Examples from recent related work, in groundwater and surface water systems and ecosystems, are briefly reviewed as a prelude to presentation of model simulations of hypothetical scenarios of regime-shifts (tipping points) involving groundwater quantity and quality constraints. In addition to three types of widely recognized tipping points, we introduce a new type, stochastic tipping, that contributes to unexpected, undesirable regime shifts, resulting in inability to meet groundwater pumping needs, even when the perceived precariousness is small and the system is far from bifurcation point (deterministic tipping). Implications to sustainable groundwater management are discussed.

  8. The night when the auroral and equatorial ionospheres converged

    NASA Astrophysics Data System (ADS)

    Martinis, C.; Baumgardner, J.; Mendillo, M.; Wroten, J.; Coster, A.; Paxton, L.

    2015-09-01

    An all-sky imaging system at the McDonald Observatory (30.67°N, 104.02°W, 40° magnetic latitude) showed dramatic ionospheric effects during a moderate geomagnetic storm on 1 June 2013. The auroral zone expanded, leading to the observation of a stable auroral red (SAR) arc. Airglow depletions associated with equatorial spread F (ESF) were also seen for the first time at such high magnetic latitude. Total electron content measurements from a Global Positioning System (GPS) receiver exhibited ionospheric irregularities typically associated with ESF. We explore why this moderate geomagnetic disturbance leads to such dramatic ionospheric perturbations at midlatitudes. A corotating interaction region-like driver and a highly contracted plasmasphere caused the SAR arc to occur at L shell ~ 2.3. For ESF at L ~ 2.1, timing of the storm intensification, alignment of the sunset terminator with the central magnetic meridian, and sudden variations in the westward auroral electrojet all combined to trigger equatorial irregularities that reached altitudes of ~ 7000 km. The SAR arc and ESF signatures at the ionospheric foot points of inner magnetosphere L shells (L ~ 2) represent a dramatic convergence of pole to equator/equator to pole coupling at midlatitudes.

  9. Convergence in [Formula: see text]-quasicontinuous posets.

    PubMed

    Ruan, Xiao-Jun; Xu, Xiao-Quan

    2016-01-01

    In this paper, we present one way to generalize [Formula: see text]-convergence and [Formula: see text]-convergence of nets for arbitrary posets by use of the cut operator instead of joins. Some convergence theoretical characterizations of [Formula: see text]-continuity and [Formula: see text]-quasicontinuity of posets are given. The main results are: (1) a poset P is [Formula: see text]-continuous if and only if the [Formula: see text]-convergence in P is topological; (2) P is [Formula: see text]-quasicontinuous if and only if the [Formula: see text]-convergence in P is topological.

  10. On Convergence Acceleration Techniques for Unstructured Meshes

    NASA Technical Reports Server (NTRS)

    Mavriplis, Dimitri J.

    1998-01-01

    A discussion of convergence acceleration techniques as they relate to computational fluid dynamics problems on unstructured meshes is given. Rather than providing a detailed description of particular methods, the various different building blocks of current solution techniques are discussed and examples of solution strategies using one or several of these ideas are given. Issues relating to unstructured grid CFD problems are given additional consideration, including suitability of algorithms to current hardware trends, memory and cpu tradeoffs, treatment of non-linearities, and the development of efficient strategies for handling anisotropy-induced stiffness. The outlook for future potential improvements is also discussed.

  11. Convergent strabismus in a white Bengal tiger.

    PubMed

    Bernays, M E; Smith, R I

    1999-03-01

    A white Bengal tiger was noted to have a convergent strabismus with poor vision since a cub. The tiger and a littermate with normal colouring and apparently normal eyes were anaesthetised for comparative ocular examination. A fundus typical of colour-dilute cats and dogs was noted in the white tiger. Except for strabismus, no abnormalities were observed. Electroretinography showed similar retinal function in both tigers. Possible causes of strabismus considered were an adaptation to genetically determined abnormal visual pathways related to lack of pigment, abnormalities of the abducent nerves and mechanical restricting conditions of the medial rectus muscles.

  12. High convergence implosion symmetry in cylindrical hohlraums

    SciTech Connect

    Amendt, P A; Bradley, D K; Hammel, B A; Landen, O L; Suter, L J; Turner, R E; Wallace, R J

    1999-09-01

    High convergence, hohlraum-driven implosions will require control of time-integrated drive asymmetries to 1% levels for ignition to succeed on the NIF. We review how core imaging provides such asymmetry measurement accuracy for the lowest order asymmetry modes, and describe recent improvements in imaging techniques that should allow detection of higher order asymmetry modes. We also present a simple analytic model explaining how the sensitivity of symmetry control to beam pointing scales as we progress from single ring per side Nova cylindrical hohlraum illumination geometries to NIF-like multiple rings per side Omega hohlraum illumination geometries and ultimately to NIF-scale hohlraums.

  13. Convergence Analysis of a Domain Decomposition Paradigm

    SciTech Connect

    Bank, R E; Vassilevski, P S

    2006-06-12

    We describe a domain decomposition algorithm for use in several variants of the parallel adaptive meshing paradigm of Bank and Holst. This algorithm has low communication, makes extensive use of existing sequential solvers, and exploits in several important ways data generated as part of the adaptive meshing paradigm. We show that for an idealized version of the algorithm, the rate of convergence is independent of both the global problem size N and the number of subdomains p used in the domain decomposition partition. Numerical examples illustrate the effectiveness of the procedure.

  14. Convergent strabismus in a white Bengal tiger.

    PubMed

    Bernays, M E; Smith, R I

    1999-03-01

    A white Bengal tiger was noted to have a convergent strabismus with poor vision since a cub. The tiger and a littermate with normal colouring and apparently normal eyes were anaesthetised for comparative ocular examination. A fundus typical of colour-dilute cats and dogs was noted in the white tiger. Except for strabismus, no abnormalities were observed. Electroretinography showed similar retinal function in both tigers. Possible causes of strabismus considered were an adaptation to genetically determined abnormal visual pathways related to lack of pigment, abnormalities of the abducent nerves and mechanical restricting conditions of the medial rectus muscles. PMID:10197239

  15. Multimedia reviews: multimedia convergence for clinicians.

    PubMed

    Taintor, Zebulon

    2003-12-01

    Introduction by the column editor: In this final column of the year, Dr. Taintor provides an overview of exciting technological developments via his report on the 2003 annual meeting of the American Association for Technology in Psychiatry (AATP). Advances-and convergences-in technology are providing clinicians with increasingly useful tools to enhance the effectiveness of their treatments, increase access to care, reduce errors, and save time. As Dr. Taintor notes, AATP's meeting is traditionally held in conjunction with the annual meeting of the American Psychiatric Association (APA). I hope that his report will encourage APA's members to attend some of next year's informative sessions.

  16. Adaptive control: Stability, convergence, and robustness

    NASA Technical Reports Server (NTRS)

    Sastry, Shankar; Bodson, Marc

    1989-01-01

    The deterministic theory of adaptive control (AC) is presented in an introduction for graduate students and practicing engineers. Chapters are devoted to basic AC approaches, notation and fundamental theorems, the identification problem, model-reference AC, parameter convergence using averaging techniques, and AC robustness. Consideration is given to the use of prior information, the global stability of indirect AC schemes, multivariable AC, linearizing AC for a class of nonlinear systems, AC of linearizable minimum-phase systems, and MIMO systems decouplable by static state feedback.

  17. Cubature on Wiener Space: Pathwise Convergence

    SciTech Connect

    Bayer, Christian Friz, Peter K.

    2013-04-15

    Cubature on Wiener space (Lyons and Victoir in Proc. R. Soc. Lond. A 460(2041):169-198, 2004) provides a powerful alternative to Monte Carlo simulation for the integration of certain functionals on Wiener space. More specifically, and in the language of mathematical finance, cubature allows for fast computation of European option prices in generic diffusion models.We give a random walk interpretation of cubature and similar (e.g. the Ninomiya-Victoir) weak approximation schemes. By using rough path analysis, we are able to establish weak convergence for general path-dependent option prices.

  18. Zone Refining by Laser

    NASA Technical Reports Server (NTRS)

    Griner, D. B.

    1986-01-01

    System developed for studying use of laser beam for zone-refining semiconductors and metals. Specimen scanned with focused CO2 laser beam in such way that thin zone of molten material moves along specimen sweeps impurities with it. Zone-melting system comprises microcomputer, laser, electromechanical and optical components for beam control, vacuum chamber that holds specimen, and sensor for determining specimen temperature.

  19. Convergent evolution of the genomes of marine mammals.

    PubMed

    Foote, Andrew D; Liu, Yue; Thomas, Gregg W C; Vinař, Tomáš; Alföldi, Jessica; Deng, Jixin; Dugan, Shannon; van Elk, Cornelis E; Hunter, Margaret E; Joshi, Vandita; Khan, Ziad; Kovar, Christie; Lee, Sandra L; Lindblad-Toh, Kerstin; Mancia, Annalaura; Nielsen, Rasmus; Qin, Xiang; Qu, Jiaxin; Raney, Brian J; Vijay, Nagarjun; Wolf, Jochen B W; Hahn, Matthew W; Muzny, Donna M; Worley, Kim C; Gilbert, M Thomas P; Gibbs, Richard A

    2015-03-01

    Marine mammals from different mammalian orders share several phenotypic traits adapted to the aquatic environment and therefore represent a classic example of convergent evolution. To investigate convergent evolution at the genomic level, we sequenced and performed de novo assembly of the genomes of three species of marine mammals (the killer whale, walrus and manatee) from three mammalian orders that share independently evolved phenotypic adaptations to a marine existence. Our comparative genomic analyses found that convergent amino acid substitutions were widespread throughout the genome and that a subset of these substitutions were in genes evolving under positive selection and putatively associated with a marine phenotype. However, we found higher levels of convergent amino acid substitutions in a control set of terrestrial sister taxa to the marine mammals. Our results suggest that, whereas convergent molecular evolution is relatively common, adaptive molecular convergence linked to phenotypic convergence is comparatively rare. PMID:25621460

  20. Convergent evolution of the genomes of marine mammals

    USGS Publications Warehouse

    Foote, Andrew D.; Liu, Yue; Thomas, Gregg W.C.; Vinař, Tomáš; Alföldi, Jessica; Deng, Jixin; Dugan, Shannon; van Elk, Cornelis E.; Hunter, Margaret; Joshi, Vandita; Khan, Ziad; Kovar, Christie; Lee, Sandra L.; Lindblad-Toh, Kerstin; Mancia, Annalaura; Nielsen, Rasmus; Qin, Xiang; Qu, Jiaxin; Raney, Brian J.; Vijay, Nagarjun; Wolf, Jochen B. W.; Hahn, Matthew W.; Muzny, Donna M.; Worley, Kim C.; Gilbert, M. Thomas P.; Gibbs, Richard A.

    2015-01-01

    Marine mammals from different mammalian orders share several phenotypic traits adapted to the aquatic environment and therefore represent a classic example of convergent evolution. To investigate convergent evolution at the genomic level, we sequenced and performed de novo assembly of the genomes of three species of marine mammals (the killer whale, walrus and manatee) from three mammalian orders that share independently evolved phenotypic adaptations to a marine existence. Our comparative genomic analyses found that convergent amino acid substitutions were widespread throughout the genome and that a subset of these substitutions were in genes evolving under positive selection and putatively associated with a marine phenotype. However, we found higher levels of convergent amino acid substitutions in a control set of terrestrial sister taxa to the marine mammals. Our results suggest that, whereas convergent molecular evolution is relatively common, adaptive molecular convergence linked to phenotypic convergence is comparatively rare.

  1. No genome-wide protein sequence convergence for echolocation.

    PubMed

    Zou, Zhengting; Zhang, Jianzhi

    2015-05-01

    Toothed whales and two groups of bats independently acquired echolocation, the ability to locate and identify objects by reflected sound. Echolocation requires physiologically complex and coordinated vocal, auditory, and neural functions, but the molecular basis of the capacity for echolocation is not well understood. A recent study suggested that convergent amino acid substitutions widespread in the proteins of echolocators underlay the convergent origins of mammalian echolocation. Here, we show that genomic signatures of molecular convergence between echolocating lineages are generally no stronger than those between echolocating and comparable nonecholocating lineages. The same is true for the group of 29 hearing-related proteins claimed to be enriched with molecular convergence. Reexamining the previous selection test reveals several flaws and invalidates the asserted evidence for adaptive convergence. Together, these findings indicate that the reported genomic signatures of convergence largely reflect the background level of sequence convergence unrelated to the origins of echolocation. PMID:25631925

  2. Convergent evolution of the genomes of marine mammals

    PubMed Central

    Foote, Andrew D.; Liu, Yue; Thomas, Gregg W.C.; Vinař, Tomáš; Alföldi, Jessica; Deng, Jixin; Dugan, Shannon; van Elk, Cornelis E.; Hunter, Margaret E.; Joshi, Vandita; Khan, Ziad; Kovar, Christie; Lee, Sandra L.; Lindblad-Toh, Kerstin; Mancia, Annalaura; Nielsen, Rasmus; Qin, Xiang; Qu, Jiaxin; Raney, Brian J.; Vijay, Nagarjun; Wolf, Jochen B. W.; Hahn, Matthew W.; Muzny, Donna M.; Worley, Kim C.; Gilbert, M. Thomas P.; Gibbs, Richard A.

    2015-01-01

    Marine mammals from different mammalian orders share several phenotypic traits adapted to the aquatic environment and are therefore a classic example of convergent evolution. To investigate convergent evolution at the genomic level, we sequenced and de novo assembled the genomes of three species of marine mammals (the killer whale, walrus and manatee) from three mammalian orders that share independently evolved phenotypic adaptations to a marine existence. Our comparative genomic analyses found that convergent amino acid substitutions were widespread throughout the genome, and that a subset were in genes evolving under positive selection and putatively associated with a marine phenotype. However, we found higher levels of convergent amino acid substitutions in a control set of terrestrial sister taxa to the marine mammals. Our results suggest that while convergent molecular evolution is relatively common, adaptive molecular convergence linked to phenotypic convergence is comparatively rare. PMID:25621460

  3. Analysis of Long-Term Anisotropic Convergence in Drifts Excavated in Callovo-Oxfordian Claystone

    NASA Astrophysics Data System (ADS)

    Guayacán-Carrillo, Lina-María; Sulem, Jean; Seyedi, Darius M.; Ghabezloo, Siavash; Noiret, Aurélien; Armand, Gilles

    2016-01-01

    The main purpose of this paper is to analyze the convergence measurements in drifts of the Underground Research Laboratory (URL) of the French National Radioactive Waste Management Agency (Andra), excavated in Callovo-Oxfordian claystone. These measurements show an anisotropic closure, which depends on the drift orientations with respect to the horizontal in situ stresses. This anisotropic character of the deformation is taken into account by assuming that the drifts section evolves following an elliptical shape. The characteristics of the deformed elliptical section are evaluated following the methodology proposed by Vu et al. (Rock Mech Rock Eng 46:231-246, 2013). Then, using the semi-empirical law proposed by Sulem et al. (Int J Rock Mech Min Sci Geomech Abstr 24:145-154, 1987), the convergence evolution is fitted independently for each axis of the ellipse. This method allows to distinguish two effects: the face advance and the time-dependent behavior of the ground. The results for the two drift orientations (along the major horizontal stress and perpendicular to it) show very close values for the parameters describing the time-dependent properties of the ground, the distance of influence of the face, and the extent of the decompressed zone around the drift. Finally, the model is validated by keeping these parameters as constants and by simulating the convergence data on a new drift. It is shown that with a period of about 40 days of convergence monitoring, the model can provide valuable insights for predictions of the convergence evolution in the long term.

  4. The Use of Domain Decomposition in Accelerating the Convergence of Quasihyperbolic Systems

    NASA Astrophysics Data System (ADS)

    Parent, Bernard; Sislian, Jean P.

    2002-06-01

    This paper proposes an alternate form of the active-domain method [K. Nakahashi and E. Saitoh, AIAA J.35, 1280 (1997)] that is applicable to streamwise separated flows. Named the "marching window," the algorithm consists of performing pseudo-time iterations on a minimal width subdomain composed of a sequence of cross-stream planes of nodes. The upstream boundary of the subdomain is positioned such that all nodes upstream exhibit a residual smaller than the user-specified convergence threshold. The advancement of the downstream boundary follows the advancement of the upstream boundary, except in zones of significant streamwise ellipticity, where a streamwise ellipticity sensor ensures its continuous progress. Compared to the standard pseudo-time-marching approach, the marching window decreases the work required for convergence by up to 24 times for flows with little streamwise ellipticity and by up to eight times for flows with large streamwise separated regions. Storage is reduced by up to six times by not allocating memory to the nodes not included in the computational subdomain. The marching window satisfies the same convergence criterion as the standard pseudo-time-stepping methods, hence resulting in the same converged solution within the tolerance of the user-specified convergence threshold. The algorithm is not restricted to a discretization stencil and pseudo-time-stepping scheme in particular and is used here with the Yee-Roe scheme and block-implicit approximate factorization solving the Favre-averaged Navier-Stokes (FANS) equations closed by the Wilcox kω turbulence model. The eigenstructure of the FANS equations is also presented.

  5. Convergent validity of a novel method for quantifying rowing training loads.

    PubMed

    Tran, Jacqueline; Rice, Anthony J; Main, Luana C; Gastin, Paul B

    2015-01-01

    Elite rowers complete rowing-specific and non-specific training, incorporating continuous and interval-like efforts spanning the intensity spectrum. However, established training load measures are unsuitable for use in some modes and intensities. Consequently, a new measure known as the T2minute method was created. The method quantifies load as the time spent in a range of training zones (time-in-zone), multiplied by intensity- and mode-specific weighting factors that scale the relative stress of different intensities and modes to the demands of on-water rowing. The purpose of this study was to examine the convergent validity of the T2minute method with Banister's training impulse (TRIMP), Lucia's TRIMP and Session-RPE when quantifying elite rowing training. Fourteen elite rowers (12 males, 2 females) were monitored during four weeks of routine training. Unadjusted T2minute loads (using coaches' estimates of time-in-zone) demonstrated moderate-to-strong correlations with Banister's TRIMP, Lucia's TRIMP and Session-RPE (rho: 0.58, 0.55 and 0.42, respectively). Adjusting T2minute loads by using actual time-in-zone data resulted in stronger correlations between the T2minute method and Banister's TRIMP and Lucia's TRIMP (rho: 0.85 and 0.81, respectively). The T2minute method is an appropriate in-field measure of elite rowing training loads, particularly when actual time-in-zone values are used to quantify load.

  6. Convergent validity of a novel method for quantifying rowing training loads.

    PubMed

    Tran, Jacqueline; Rice, Anthony J; Main, Luana C; Gastin, Paul B

    2015-01-01

    Elite rowers complete rowing-specific and non-specific training, incorporating continuous and interval-like efforts spanning the intensity spectrum. However, established training load measures are unsuitable for use in some modes and intensities. Consequently, a new measure known as the T2minute method was created. The method quantifies load as the time spent in a range of training zones (time-in-zone), multiplied by intensity- and mode-specific weighting factors that scale the relative stress of different intensities and modes to the demands of on-water rowing. The purpose of this study was to examine the convergent validity of the T2minute method with Banister's training impulse (TRIMP), Lucia's TRIMP and Session-RPE when quantifying elite rowing training. Fourteen elite rowers (12 males, 2 females) were monitored during four weeks of routine training. Unadjusted T2minute loads (using coaches' estimates of time-in-zone) demonstrated moderate-to-strong correlations with Banister's TRIMP, Lucia's TRIMP and Session-RPE (rho: 0.58, 0.55 and 0.42, respectively). Adjusting T2minute loads by using actual time-in-zone data resulted in stronger correlations between the T2minute method and Banister's TRIMP and Lucia's TRIMP (rho: 0.85 and 0.81, respectively). The T2minute method is an appropriate in-field measure of elite rowing training loads, particularly when actual time-in-zone values are used to quantify load. PMID:25083912

  7. Analysis of local strain in aluminum interconnects by convergent beam electron diffraction

    NASA Astrophysics Data System (ADS)

    Krämer, Stephan; Mayer, Joachim

    1999-11-01

    Energy filtered convergent beam electron diffraction (CBED) was used to investigate localized strain in aluminum interconnects. An analysis of the higher order Laue zone (HOLZ) line positions in CBED patterns makes it possible to measure the lattice strain with high accuracy (˜104) and high spatial resolution (10 to 100 nm). The strain development in a single grain was measured during thermal cycling between -170 °C and +100 °C. The grain showed reversible, elastic behavior over the whole temperature range building up large strains at low temperatures. By comparing with finite element simulations, a detailed understanding of the tri-axial strain state could be achieved.

  8. Globally convergent computation of chemical equilibrium composition.

    PubMed

    Patil, Sunil; Aiyer, R C; Sharma, K C

    2008-05-01

    We report the Newton-Raphson based globally convergent computational method for determination of chemical equilibrium composition. In the computation of chemical equilibrium composition, an appearance of nonpositive value of number of moles of any component leads to discrepancy. The process of conditional backtracking and adaptive set of refining factors for Newton-Raphson steps are employed to resolve the problem. The mathematical formulation proposed by Heuze et al. (J Chem Phys 1985, 83, 4734) has been solved using proposed computational method, instead of empirical iterative formulation, as proposed by them. Results for the same numerical example, used by Heuze et al. (J Chem Phys 1985, 83, 4734) and White et al. (J Chem Phys 1958, 28, 751) are presented in addition to decomposition of Cyclotrimethylenetrinitramine for fixed temperature and pressure. It is observed that the proposed method is efficient and globally convergent. An even noteworthy finding is that the set of refining factors can be chosen from the range 0.1 to eta, where eta may be greater than one depending on how smoothly system of nonlinear equations is dependant on corresponding variable. Related analysis and results are discussed.

  9. Design Calculations for NIF Convergent Ablator Experiments

    NASA Astrophysics Data System (ADS)

    Olson, R. E.; Callahan, D. A.; Hicks, D. G.; Landen, O. L.; Langer, S. H.; Meezan, N. B.; Spears, B. K.; Widmann, K.; Kline, J. L.; Wilson, D. C.; Petrasso, R. D.; Leeper, R. J.

    2010-11-01

    Design calculations for NIF convergent ablator experiments will be described. The convergent ablator experiments measure the implosion trajectory, velocity, and ablation rate of an x-ray driven capsule and are a important component of the U. S. National Ignition Campaign at NIF. The design calculations are post-processed to provide simulations of the key diagnostics -- 1) Dante measurements of hohlraum x-ray flux and spectrum, 2) streaked radiographs of the imploding ablator shell, 3) wedge range filter measurements of D-He3 proton output spectra, and 4) GXD measurements of the imploded core. The simulated diagnostics will be compared to the experimental measurements to provide an assessment of the accuracy of the design code predictions of hohlraum radiation temperature, capsule ablation rate, implosion velocity, shock flash areal density, and x-ray bang time. Post-shot versions of the design calculations are used to enhance the understanding of the experimental measurements and will assist in choosing parameters for subsequent shots and the path towards optimal ignition capsule tuning. *SNL, LLNL, and LANL are operated under US DOE contracts DE-AC04-94AL85000. DE-AC52-07NA27344, and DE-AC04-94AL85000.

  10. Design calculations for NIF convergent ablator experiments.

    SciTech Connect

    Callahan, Debra; Leeper, Ramon Joe; Spears, B. K.; Zylstra, A.; Seguin, F.; Landen, Otto L.; Petrasso, R. D.; Rinderknecht, H.; Kline, J. L.; Frenje, J.; Wilson, D. C.; Langer, S. H.; Widmann, K.; Meezan, Nathan B.; Hicks, Damien G.; Olson, Richard Edward

    2010-11-01

    Design calculations for NIF convergent ablator experiments will be described. The convergent ablator experiments measure the implosion trajectory, velocity, and ablation rate of an x-ray driven capsule and are a important component of the U. S. National Ignition Campaign at NIF. The design calculations are post-processed to provide simulations of the key diagnostics: (1) Dante measurements of hohlraum x-ray flux and spectrum, (2) streaked radiographs of the imploding ablator shell, (3) wedge range filter measurements of D-He3 proton output spectra, and (4) GXD measurements of the imploded core. The simulated diagnostics will be compared to the experimental measurements to provide an assessment of the accuracy of the design code predictions of hohlraum radiation temperature, capsule ablation rate, implosion velocity, shock flash areal density, and x-ray bang time. Post-shot versions of the design calculations are used to enhance the understanding of the experimental measurements and will assist in choosing parameters for subsequent shots and the path towards optimal ignition capsule tuning.

  11. Origin of weak lensing convergence peaks

    NASA Astrophysics Data System (ADS)

    Liu, Jia; Haiman, Zoltán

    2016-08-01

    Weak lensing convergence peaks are a promising tool to probe nonlinear structure evolution at late times, providing additional cosmological information beyond second-order statistics. Previous theoretical and observational studies have shown that the cosmological constraints on Ωm and σ8 are improved by a factor of up to ≈2 when peak counts and second-order statistics are combined, compared to using the latter alone. We study the origin of lensing peaks using observational data from the 154 deg2 Canada-France-Hawaii Telescope Lensing Survey. We found that while high peaks (with height κ >3.5 σκ , where σκ is the rms of the convergence κ ) are typically due to one single massive halo of ≈1 015M⊙ , low peaks (κ ≲σκ ) are associated with constellations of 2-8 smaller halos (≲1 013M⊙ ). In addition, halos responsible for forming low peaks are found to be significantly offset from the line of sight towards the peak center (impact parameter ≳ their virial radii), compared with ≈0.25 virial radii for halos linked with high peaks, hinting that low peaks are more immune to baryonic processes whose impact is confined to the inner regions of the dark matter halos. Our findings are in good agreement with results from the simulation work by Yang et al. [Phys. Rev. D 84, 043529 (2011)].

  12. Divergence and Convergence in Enzyme Evolution*

    PubMed Central

    Galperin, Michael Y.; Koonin, Eugene V.

    2012-01-01

    Comparative analysis of the sequences of enzymes encoded in a variety of prokaryotic and eukaryotic genomes reveals convergence and divergence at several levels. Functional convergence can be inferred when structurally distinct and hence non-homologous enzymes show the ability to catalyze the same biochemical reaction. In contrast, as a result of functional diversification, many structurally similar enzyme molecules act on substantially distinct substrates and catalyze diverse biochemical reactions. Here, we present updates on the ATP-grasp, alkaline phosphatase, cupin, HD hydrolase, and N-terminal nucleophile (Ntn) hydrolase enzyme superfamilies and discuss the patterns of sequence and structural conservation and diversity within these superfamilies. Typically, enzymes within a superfamily possess common sequence motifs and key active site residues, as well as (predicted) reaction mechanisms. These observations suggest that the strained conformation (the entatic state) of the active site, which is responsible for the substrate binding and formation of the transition complex, tends to be conserved within enzyme superfamilies. The subsequent fate of the transition complex is not necessarily conserved and depends on the details of the structures of the enzyme and the substrate. This variability of reaction outcomes limits the ability of sequence analysis to predict the exact enzymatic activities of newly sequenced gene products. Nevertheless, sequence-based (super)family assignments and generic functional predictions, even if imprecise, provide valuable leads for experimental studies and remain the best approach to the functional annotation of uncharacterized proteins from new genomes. PMID:22069324

  13. Geophysical study of the structure and processes of the continental convergence zones: Alpine-Himalayan Belt

    NASA Technical Reports Server (NTRS)

    Toksoz, M. Nafi; Molnar, Peter

    1988-01-01

    Intracontinental deformation occurrence and the processes and physical parameters that control the rates and styles of deformation were examined. Studies addressing specific mechanical aspects of deformation were reviewed and the studies of deformation and of the structure of specific areas were studied considering the strength of the material and the gravitational effect.

  14. NASA Experiment on Tropospheric-Stratospheric Water Vapor Transport in the Intertropical Convergence Zone

    NASA Technical Reports Server (NTRS)

    Page, William A.

    1982-01-01

    The following six papers report preliminary results obtained from a field experiment designed to study the role of tropical cumulo-nimbus clouds in the transfer of water vapor from the troposphere to the stratosphere over the region of Panama. The measurements were made utilizing special NOAA enhanced IR satellite images, radiosonde-ozonesondes and a NASA U-2 aircraft carrying. nine experiments. The experiments were provided by a group of NASA, NOAA, industry, and university scientists. Measurements included atmospheric humidity, air and cloud top temperatures, atmospheric tracer constituents, cloud particle characteristics and cloud morphology. The aircraft made a total of eleven flights from August 30 through September 18, 1980, from Howard Air Force Base, Panama; the pilots obtained horizontal and vertical profiles in and near convectively active regions and flew around and over cumulo-nimbus towers and through the extended anvils in the stratosphere. Cumulo-nimbus clouds in the tropics appear to play an important role in upward water vapor transport and may represent the principal source influencing the stratospheric water vapor budget. The clouds provide strong vertical circulation in the troposphere, mixing surface air and its trace materials (water vapor, CFM's sulfur compounds, etc.) quickly up to the tropopause. It is usually assumed that large scale mean motions or eddy scale motions transport the trace materials through the tropopause and into the stratosphere where they are further dispersed and react with other stratospheric constituents. The important step between the troposphere and stratosphere for water vapor appears to depend upon the processes occurring at or near the tropopause at the tops of the cumulo-nimbus towers. Several processes have been sugested: (1) The highest towers penetrate the tropopause and carry water in the form of small ice particles directly into the stratosphere. (2) Water vapor from the tops of the cumulonimbus clouds is transported somehow through the tropopause, the vapor pressure being controlled by the temperature at the tops of the clouds; the dryness of the stratosphere could be explained if most of the transport occurs in connection with very high clouds in regions with very high and cold tropopause. (3) Cumulo-nimbus anvils act as terrestrial-radiation shields allowing the ice particle temperatures near cloud tops to cool radiatively below the supersaturation point; this cooling would cause a vapor deposition on the ice particles which will settle out and thus act as water scavengers. The experiment was designed to collect information on these detailed physical processes near and above the tropopause in order to assess their importance and the role they play in controlling stratospheric water vapor humidity.

  15. Converging shocks in elastic-plastic solids.

    PubMed

    Ortega, A López; Lombardini, M; Hill, D J

    2011-11-01

    We present an approximate description of the behavior of an elastic-plastic material processed by a cylindrically or spherically symmetric converging shock, following Whitham's shock dynamics theory. Originally applied with success to various gas dynamics problems, this theory is presently derived for solid media, in both elastic and plastic regimes. The exact solutions of the shock dynamics equations obtained reproduce well the results obtained by high-resolution numerical simulations. The examined constitutive laws share a compressible neo-Hookean structure for the internal energy e=e(s)(I(1))+e(h)(ρ,ς), where e(s) accounts for shear through the first invariant of the Cauchy-Green tensor, and e(h) represents the hydrostatic contribution as a function of the density ρ and entropy ς. In the strong-shock limit, reached as the shock approaches the axis or origin r=0, we show that compression effects are dominant over shear deformations. For an isothermal constitutive law, i.e., e(h)=e(h)(ρ), with a power-law dependence e(h) is proportional to ρ(α), shock dynamics predicts that for a converging shock located at r=R(t) at time t, the Mach number increases as M is proportional to [log(1/R)](α), independently of the space index s, where s=2 in cylindrical geometry and 3 in spherical geometry. An alternative isothermal constitutive law with p(ρ) of the arctanh type, which enforces a finite density in the strong-shock limit, leads to M is proportional to R(-(s-1)) for strong shocks. A nonisothermal constitutive law, whose hydrostatic part e(h) is that of an ideal gas, is also tested, recovering the strong-shock limit M is proportional to R(-(s-1)/n(γ)) originally derived by Whitham for perfect gases, where γ is inherently related to the maximum compression ratio that the material can reach, (γ+1)/(γ-1). From these strong-shock limits, we also estimate analytically the density, radial velocity, pressure, and sound speed immediately behind the shock. While the

  16. Influence of the Convergence and Stepover Angles in the Structural Style of Strike-Slip Systems: Analogue Models

    NASA Astrophysics Data System (ADS)

    Gonzalez, D.; Pinto, L.

    2008-12-01

    The presented results of analogue models analyze the influence of the relation between the convergence angle and the stepover angle on strike-slip systems. The experiments include 2 stepovers arrays to generate both transpressional and transtensional zones. These experiments were prepared using 5 cm thick sandpack (sand diameter <500 μm, internal friction angle 30°, density 1,400 kg/m3) to simulate brittle deformation; the base of the model was formed by thin zinc base plates, one of them mobile, cut in such a way so as to produce restraining and releasing strike-slip stepovers; the rate convergence was constant. We carried out 3 series of experiments in which the convergence angles (0°-60°) and stepover angles (30°-60°) were varied systematically. Preliminary results indicate that by increasing the angle between the stepover and the convergence vector: a) the restraining area generated a positive flower structure that is progressively wider; b) progressively more reverse faults which absorb more shortening were generated. Locally, strike-slip faults in the positive flowers were accommodated by the geometry of the stepover base. Areas most complex involved the development of normal faults, which subsequently were inverted. In conclusion, the relation between the convergence and stepover angles is a main factor that determines the structural style of flowers structures on strike-slip systems. This work was done through the ACT-18 PBCT project.

  17. Influence of fault trend, bends, and convergence on shallow structure and geomorphology of the Hosgri strike-slip fault, offshore central California

    USGS Publications Warehouse

    Johnson, Samuel Y.; Watt, Janet T.

    2012-01-01

    Earthquake hazard assessments should incorporate a minimum rupture length of 110 km based on continuity of the Hosgri fault zone through this area. Lateral slip rates may vary along the fault (both to the north and south) as different structures converge and diverge but are probably in the geodetically estimated range of 2–4 mm/yr.

  18. Convergent evolution in primates and an insectivore

    SciTech Connect

    Boffelli, Dario; Cheng, Jan-Fang; Rubin, Edward M.

    2003-04-16

    The cardiovascular risk factor apolipoprotein(a) (apo(a)) has a puzzling distribution among mammals, its presence being limited to a subset of primates and a member of the insectivore lineage, the hedgehog. To explore the evolutionary history of apo(a), we performed extensive genomic sequence comparisons of multiple species with and without an apo(a) gene product, such as human, baboon, hedgehog, lemurand mouse. This analysis indicated that apo(a) arose independently in a subset of primates, including baboon and human, and an insectivore, the hedgehog, and was not simply lost by species lacking it. The similar structural domains shared by the hedgehog and primate apo(a) indicate that they were formed by a unique molecular mechanism involving the convergent evolution of paralogous genes in these distantspecies.

  19. Unstable resonators with excited converging wave

    SciTech Connect

    Hodgson, N. ); Weber, H. )

    1990-04-01

    This paper reports the properties of unstable resonators with an additional mirror inside or outside the resonator investigated, both experimentally and theoretically. The additional mirror excites the converging wave, and by this, output coupling is decreased without affecting beam quality. Experiments were performed with a pulsed Nd:YAG system. The theoretical model was based on the coupled Kirchhoff integrals and solved numerically. Agreement between theory and experiments indicates that this kind of resonator provides high focusability and maximum extraction efficiency simultaneously, even with low-gain media. This enables one to apply unstable resonators to solid-state lasers with low small-signal gain, like alexandrite or CW-pumped Nd:YAG.

  20. Nonlinear Resonance Cones and Converging Plasma Blobs

    NASA Astrophysics Data System (ADS)

    Agmon, Nathan; Pribyl, Patrick; Gekelman, Walter; Wise, Joe; Katz, Cami; Ha, Chis; Baker, Bob

    2013-10-01

    Electric field resonance cones have been shown to create density disturbances in cold, magnetized plasmas. Two circular antennas in the LAPTAG experimental plasma device were used to create converging, nonlinear resonance cones. The nonlinear electrostatic field is produced by large amplitude RF (ERF/nkTe >> 1). A movable probe, powered by a computerized motor and consisting of three mutually orthogonal electric dipoles, is used to measure the electric field of the cones which become distorted at large amplitudes. A 2D movable Langmuir probe was used to determine localized density perturbations after turn-off of the RF power. A density blob moving at 3-5 times the ion sound speed has been observed to propagate away (for at least 20 cm) from the focus of the cone. Two ring antennas produced colliding blobs. The physics of the collision will be described. Work performed at the Basic Plasma Science Facility supported by DOE and NSF.

  1. Positive Cardiovascular Health: A Timely Convergence.

    PubMed

    Labarthe, Darwin R; Kubzansky, Laura D; Boehm, Julia K; Lloyd-Jones, Donald M; Berry, Jarett D; Seligman, Martin E P

    2016-08-23

    Two concepts, positive health and cardiovascular health, have emerged recently from the respective fields of positive psychology and preventive cardiology. These parallel constructs are converging to foster positive cardiovascular health and a growing collaboration between psychologists and cardiovascular scientists to achieve significant improvements in both individual and population cardiovascular health. We explore these 2 concepts and note close similarities in the measures that define them, the health states that they aim to produce, and their intended long-term clinical and public health outcomes. We especially examine subjective health assets, such as optimism, that are a core focus of positive psychology, but have largely been neglected in preventive cardiology. We identify research to date on positive cardiovascular health, discuss its strengths and limitations thus far, and outline directions for further engagement of cardiovascular scientists with colleagues in positive psychology to advance this new field.

  2. Improving the Convergence of Reversible Samplers

    NASA Astrophysics Data System (ADS)

    Rey-Bellet, Luc; Spiliopoulos, Konstantinos

    2016-08-01

    In Monte-Carlo methods the Markov processes used to sample a given target distribution usually satisfy detailed balance, i.e. they are time-reversible. However, relatively recent results have demonstrated that appropriate reversible and irreversible perturbations can accelerate convergence to equilibrium. In this paper we present some general design principles which apply to general Markov processes. Working with the generator of Markov processes, we prove that for some of the most commonly used performance criteria, i.e., spectral gap, asymptotic variance and large deviation functionals, sampling is improved for appropriate reversible and irreversible perturbations of some initially given reversible sampler. Moreover we provide specific constructions for such reversible and irreversible perturbations for various commonly used Markov processes, such as Markov chains and diffusions. In the case of diffusions, we make the discussion more specific using the large deviations rate function as a measure of performance.

  3. Cylindrically converging blast waves in air

    NASA Astrophysics Data System (ADS)

    Matsuo, H.; Nakamura, Y.

    1981-07-01

    Cylindrically converging shock waves are produced by utilizing the detonation of cylindrical explosive shells. The production and the propagation of shock waves are observed by framing and streak camera photographs, and the trajectory of shock propagations is determined by using an electrical ionization probing system. The effect of the quantity of explosives on the stability, or the axial symmetry, of shock fronts and on the strength of shocks produced is investigated. It has been shown that, for practical purposes, the approximation of shock trajectories by Guderley's formulas would be sufficiently acceptable in an unexpectedly wide region near the implosion center, and that the axial symmetry of the shock front is improved by increasing the quantity of explosives, and thus, strong shocks are produced by merely increasing the quantity of explosives. The reflected diverging shock seems to be very stable. Piezoelectric elements have also been used to detect reflected diverging waves.

  4. Positive Cardiovascular Health: A Timely Convergence.

    PubMed

    Labarthe, Darwin R; Kubzansky, Laura D; Boehm, Julia K; Lloyd-Jones, Donald M; Berry, Jarett D; Seligman, Martin E P

    2016-08-23

    Two concepts, positive health and cardiovascular health, have emerged recently from the respective fields of positive psychology and preventive cardiology. These parallel constructs are converging to foster positive cardiovascular health and a growing collaboration between psychologists and cardiovascular scientists to achieve significant improvements in both individual and population cardiovascular health. We explore these 2 concepts and note close similarities in the measures that define them, the health states that they aim to produce, and their intended long-term clinical and public health outcomes. We especially examine subjective health assets, such as optimism, that are a core focus of positive psychology, but have largely been neglected in preventive cardiology. We identify research to date on positive cardiovascular health, discuss its strengths and limitations thus far, and outline directions for further engagement of cardiovascular scientists with colleagues in positive psychology to advance this new field. PMID:27539179

  5. Flow of foam through a convergent channel.

    PubMed

    Dollet, Benjamin; Bocher, Claire

    2015-11-01

    We study experimentally the flow of a foam confined as a bubble monolayer between two plates through a convergent channel. We quantify the velocity, the distribution and orientation of plastic events, and the elastic stress, using image analysis. We use two different soap solutions: a sodium dodecyl sulfate (SDS) solution, with a negligible wall friction between the bubbles and the confining plates, and a mixture containing a fatty acid, giving a large wall friction. We show that for SDS solutions, the velocity profile obeys a self-similar form which results from the superposition of plastic events, and the elastic deformation is uniform. For the other solution, the velocity field differs and the elastic deformation increases towards the exit of the channel. We discuss and quantify the role of wall friction on the velocity profile, the elastic deformation, and the rate of plastic events. PMID:26607260

  6. Convergent solid-phase synthesis of hirudin.

    PubMed

    Goulas, Spyros; Gatos, Dimitrios; Barlos, Kleomenis

    2006-02-01

    Hirudin variant 1 (HV1), a small protein consisting of 65 amino acids and three disulfide bonds, was synthesized by using Fmoc-based convergent methods on 2-chlorotrityl resin (CLTR). The linear sequence was assembled by the sequential condensation of 7 protected fragments, on the resin-bound 55-65 fragment. The conditions of fragment assembly were carefully studied to determine the most efficient synthetic protocol. Crude reduced [Cys(16, 28)(Acm)]-HV1 thus obtained was easily purified to homogeneity by RP-HPLC. Disulfide bridges were successfully formed by a two-step procedure, involving an oxidative folding step to form Cys(6)-Cys(14) and Cys(22)-Cys(39) linkages, followed by iodine oxidation to form the Cys(16)-Cys(28) bond. The correct disulfide bond alignment was established by peptide mapping using Staphylococcus aureus V8 protease at pH 4.5. PMID:15952245

  7. Spherically-Convergent, Advanced-Fuel Systems

    NASA Astrophysics Data System (ADS)

    Barnes, D. C.; Nebel, R. A.; Schauer, M. M.; Umstadter, K. R.

    1998-11-01

    Combining nonneutral electron confinement with spherical ion convergence leads to a cm sized reactor volume with high power density.(R. A. Nebel and D. C. Barnes, Fusion Technol.), to appear (1998); D. C. Barnes and R. A. Nebel, Phys. of Plasmas 5, 2498 (1998). This concept is being investigated experimentally,(D. C. Barnes, T. B. Mitchell, and M. M. Schauer, Phys. Plasmas) 4, 1745 (1997). and results will be reported. We argue that D-D operation of such a system offers all the advantages of aneutronic fusion cycles. In particular, no breeding or large tritium inventory is required, and material problems seem tractable based on previous LWR experience. In addition the extremely small unit size leads to a massively modular system which is easily maintained and repaired, suggesting a very high availability. It may also be possible to operate such a system with low or aneutronic fuels. Preliminary work in this direction will be presented.

  8. Evolution and disease converge in the mitochondrion.

    PubMed

    Mishmar, D; Zhidkov, I

    2010-01-01

    Mitochondrial DNA (mtDNA) mutations are long known to cause diseases but also underlie tremendous population divergence in humans. It was assumed that the two types of mutations differ in one major trait: functionality. However, evidence from disease association studies, cell culture and animal models support the functionality of common mtDNA genetic variants, leading to the hypothesis that disease-causing mutations and mtDNA genetic variants share considerable common features. Here we provide evidence showing that the two types of mutations obey the rules of evolution, including random genetic drift and natural selection. This similarity does not only converge at the principle level; rather, disease-causing mutations could recapitulate the ancestral DNA sequence state. Thus, the very same mutations could either mark ancient evolutionary changes or cause disease.

  9. Cooperative target convergence using multiple agents

    SciTech Connect

    Kwok, K.S.; Driessen, B.J.

    1997-10-01

    This work considers the problem of causing multiple (100`s) autonomous mobile robots to converge to a target and provides a follow-the-leader approach to the problem. Each robot has only a limited-range sensor for sending the target and also larger but also limited-range robot-to-robot communication capability. Because of the small amount of information available to the robots, a practical approach to improve convergence to the target is to have a robot follow the robot with the best quality of information. Specifically, each robot emits a signal that informs in-range robots what its status is. A robot has a status value of 0 if it is itself in range of the target. A robot has a status of 1 if it is not in range of the target but is in communication range of a robot that is in range of the target. A robot has a status of 2 if it is not in range of the target but is within range of another robot that has status 1, and so on. Of all the mobile robots that any given robot is in range of, it follows the one with the best status. The emergent behavior is the ant-like trails of robots following each other toward the target. If the robot is not in range of another robot that is either in range of the target or following another robot, the robot will assign-1 to its quality-of-information, and will execute an exhaustive search. The exhaustive search will continue until it encounters either the target or another robot with a nonnegative quality-of-information. The quality of information approach was extended to the case where each robot only has two-bit signals informing it of distance to in-range robots.

  10. Convergent perturbation theory for lattice models with fermions

    NASA Astrophysics Data System (ADS)

    Sazonov, V. K.

    2016-05-01

    The standard perturbation theory in QFT and lattice models leads to the asymptotic expansions. However, an appropriate regularization of the path or lattice integrals allows one to construct convergent series with an infinite radius of the convergence. In the earlier studies, this approach was applied to the purely bosonic systems. Here, using bosonization, we develop the convergent perturbation theory for a toy lattice model with interacting fermionic and bosonic fields.

  11. Disparity and Convergence: Chinese Provincial Government Health Expenditures

    PubMed Central

    Pan, Jay; Wang, Peng; Qin, Xuezheng; Zhang, Shufang

    2013-01-01

    The huge regional disparity in government health expenditures (GHE) is a major policy concern in China. This paper addresses whether provincial GHE converges in China from 1997 to 2009 using the economic convergence framework based on neoclassical economic growth theory. Our empirical investigation provides compelling evidence of long-term convergence in provincial GHE within China, but not in short-term. Policy implications of these empirical results are discussed. PMID:23977049

  12. A new look at the convergence of a famous sequence

    NASA Astrophysics Data System (ADS)

    Dobrescu, Mihaela

    2010-12-01

    A new proof for the monotonicity of the sequence ? is given as a special case of a large family of monotomic and bounded, hence convergent sequences. The new proof is based on basic calculus results rather than induction, which makes it accessible to a larger audience including business and life sciences students and faculty. The slow rate of convergence of the two sequences is also discussed, and convergence bounds are found.

  13. Linear perturbations of a Schwarzschild blackhole by thin disc - convergence

    NASA Astrophysics Data System (ADS)

    Čížek, P.; Semerák, O.

    2012-07-01

    In order to find the perturbation of a Schwarzschild space-time due to a rotating thin disc, we try to adjust the method used by [4] in the case of perturbation by a one-dimensional ring. This involves solution of stationary axisymmetric Einstein's equations in terms of spherical-harmonic expansions whose convergence however turned out questionable in numerical examples. Here we show, analytically, that the series are almost everywhere convergent, but in some regions the convergence is not absolute.

  14. Structural and stratigraphic evolution of Aleutian convergent-margin basins - ridge crest to trench floor

    SciTech Connect

    Scholl, D.W.; Ryan, H.F.; Geist, E.L.; Vallier, T.L.; Stevenson, A.J.; Childs, J.R. )

    1988-02-01

    The Aleutian Ridge lies along nearly 2000 km of the north Pacific's obliquely converging plate boundary with North America. Since middle Eocene time, convergent-margin basins have repeatedly formed here, typically as summit basins along the ridge crest, and as forearc basins on the landward trench slope. Summit and forearc basins formed as a consequence of plate-boundary coupling and the application of compressional and right-lateral shear stresses to the arc massif. Basins typically evolved along shear zones in response to transtensional processes, and as trailing-edge grabens behind rotating blocks of arc massif. In the late Cenozoic, high rates of trench sedimentation led to the growth of an accretionary complex that underthrust forearc basement. Wedging and improved plate coupling elevated and laterally shifted blocks of outer forearc rocks, creating much of the structural framework of the regionally extensive Aleutian Terrace forearc basin. Changes in plate-boundary conditions that affected the ridge's volcanic activity and regional elevation importantly influenced basinal sedimentation. Changes of greatest significance were a major shift in convergence direction and rate about 42 Ma (reduced volcanism), ridge underthrusting by increasingly younger ocean crust in Oligocene and Miocene time (arc elevation), and the combination of more orthogonal underthrusting and the subduction of a dead spreading center 5-10 Ma (arc subsidence).

  15. Structural and stratigraphic evolution of Aleutian convergent-margin basins - Ridge crest to trench floor

    SciTech Connect

    Scholl, D.W.; Ryan, H.F.; Geist, E.L.; Vallier, T.L.

    1988-01-01

    The Aleutian Ridge lies along nearly 2,000 km of the north Pacific's obliquely converging plate boundary with North America. Since middle Eocene time, convergent-margin basins have repeatedly formed here, typically as summit basins along the ridge crest, and as forecarc basins on the landward trench slope. Thick (1-4 km) sequences of terrigenous, hemipelagic, and biogenic debris have accumulated in these depressions, which are mostly intra-arc structures floored by arc-basement rocks. Summit and forearc basins formed as a consequence of plate-boundary coupling and the application of compressional and right-lateral shear stresses to the arc massif. Basins typically evolved along shear zones in response to transtensional processes, and as trailing-edge grabens behind rotating blocks of arc massif. In the late Cenozoic, high rates of trench sedimentation led to the growth of an accretionary complex that underthrust forearc basement. Wedging and improved plate coupling elevated and laterally shifted blocks of outer forearc rocks, creating much of the structural framework of the regionally extensive Aleutian Terrace forearc basin. Changes in plate-boundary conditions that affected the ridge's volcanic activity and regional elevation importantly influenced basinal sedimentation. Changes of greatest significant were a major shift in convergence direction and rate about 42 Ma (reduced volcanism), ridge underthrusting by increasingly younger ocean crust in Oligocena and Miocene time (arc elevation), and the combination of more orthogonal underthrusting and the subduction of a dead spreading center 5-120 Ma (arc subsidence).

  16. Fractal aspects and convergence of Newton`s method

    SciTech Connect

    Drexler, M.

    1996-12-31

    Newton`s Method is a widely established iterative algorithm for solving non-linear systems. Its appeal lies in its great simplicity, easy generalization to multiple dimensions and a quadratic local convergence rate. Despite these features, little is known about its global behavior. In this paper, we will explain a seemingly random global convergence pattern using fractal concepts and show that the behavior of the residual is entirely explicable. We will also establish quantitative results for the convergence rates. Knowing the mechanism of fractal generation, we present a stabilization to the orthodox Newton method that remedies the fractal behavior and improves convergence.

  17. Coefficients of convergent multiple Walsh-Paley series

    SciTech Connect

    Plotnikov, Mikhail G

    2012-09-30

    The paper is concerned with the behaviour of the coefficients of multiple Walsh-Paley series that are cube convergent to a finite sum. It is shown that even an everywhere convergent series of this kind may contain coefficients with numbers from a sufficiently large set that grow faster than any preassigned sequence. By Cohen's theorem, this sort of thing cannot happen for multiple trigonometric series that are cube convergent on a set of full measure - their coefficients cannot grow even exponentially. Null subsequences of coefficients are determined for multiple Walsh-Paley series that are cube convergent on a set of definite measure. Bibliography: 18 titles.

  18. Generalized monotonically convergent algorithms for solving quantum optimal control problems

    NASA Astrophysics Data System (ADS)

    Ohtsuki, Yukiyoshi; Turinici, Gabriel; Rabitz, Herschel

    2004-03-01

    A wide range of cost functionals that describe the criteria for designing optimal pulses can be reduced to two basic functionals by the introduction of product spaces. We extend previous monotonically convergent algorithms to solve the generalized pulse design equations derived from those basic functionals. The new algorithms are proved to exhibit monotonic convergence. Numerical tests are implemented in four-level model systems employing stationary and/or nonstationary targets in the absence and/or presence of relaxation. Trajectory plots that conveniently present the global nature of the convergence behavior show that slow convergence may often be attributed to "trapping" and that relaxation processes may remove such unfavorable behavior.

  19. Generalized monotonically convergent algorithms for solving quantum optimal control problems.

    PubMed

    Ohtsuki, Yukiyoshi; Turinici, Gabriel; Rabitz, Herschel

    2004-03-22

    A wide range of cost functionals that describe the criteria for designing optimal pulses can be reduced to two basic functionals by the introduction of product spaces. We extend previous monotonically convergent algorithms to solve the generalized pulse design equations derived from those basic functionals. The new algorithms are proved to exhibit monotonic convergence. Numerical tests are implemented in four-level model systems employing stationary and/or nonstationary targets in the absence and/or presence of relaxation. Trajectory plots that conveniently present the global nature of the convergence behavior show that slow convergence may often be attributed to "trapping" and that relaxation processes may remove such unfavorable behavior. PMID:15267426

  20. Experimental examination of strain field within GP zone in an Al-Zn-Mg-Cu alloy

    NASA Astrophysics Data System (ADS)

    Bai, P. C.; Liu, F.; Hou, X. H.; Zhao, C. W.; Xing, Y. M.

    2012-11-01

    The strain field of GP zone plays a very important role in strengthening of the precipitation-hardened aluminum alloys by prohibiting movement of dislocations; however, quantitative analysis about the strain field of the GP zone in the aluminum alloys has been seldom reported elsewhere. In this paper, the microstructure of GP zone in an Al-Zn-Mg-Cu alloy was explored by using high-resolution transmission electron microscopy (HRTEM), and the displacement field of lattice planes within the GP zone was experimentally measured by geometric phase analysis (GPA) technique; then, the quantitative results about strains of the distorted lattice planes within the GP zone were also obtained. It is found that the GP zone core is convergence region of the strains, and the maximum value of the compressive strains within the GP zone is about 7.6%.

  1. Strong convergence and convergence rates of approximating solutions for algebraic Riccati equations in Hilbert spaces

    NASA Technical Reports Server (NTRS)

    Ito, Kazufumi

    1987-01-01

    The linear quadratic optimal control problem on infinite time interval for linear time-invariant systems defined on Hilbert spaces is considered. The optimal control is given by a feedback form in terms of solution pi to the associated algebraic Riccati equation (ARE). A Ritz type approximation is used to obtain a sequence pi sup N of finite dimensional approximations of the solution to ARE. A sufficient condition that shows pi sup N converges strongly to pi is obtained. Under this condition, a formula is derived which can be used to obtain a rate of convergence of pi sup N to pi. The results of the Galerkin approximation is demonstrated and applied for parabolic systems and the averaging approximation for hereditary differential systems.

  2. Impact of contact lens zone geometry and ocular optics on bifocal retinal image quality

    PubMed Central

    Bradley, Arthur; Nam, Jayoung; Xu, Renfeng; Harman, Leslie; Thibos, Larry

    2014-01-01

    Purpose To examine the separate and combined influences of zone geometry, pupil size, diffraction, apodisation and spherical aberration on the optical performance of concentric zonal bifocals. Methods Zonal bifocal pupil functions representing eye + ophthalmic correction were defined by interleaving wavefronts from separate optical zones of the bifocal. A two-zone design (a central circular inner zone surrounded by an annular outer-zone which is bounded by the pupil) and a five-zone design (a central small circular zone surrounded by four concentric annuli) were configured with programmable zone geometry, wavefront phase and pupil transmission characteristics. Using computational methods, we examined the effects of diffraction, Stiles Crawford apodisation, pupil size and spherical aberration on optical transfer functions for different target distances. Results Apodisation alters the relative weighting of each zone, and thus the balance of near and distance optical quality. When spherical aberration is included, the effective distance correction, add power and image quality depend on zone-geometry and Stiles Crawford Effect apodisation. When the outer zone width is narrow, diffraction limits the available image contrast when focused, but as pupil dilates and outer zone width increases, aberrations will limit the best achievable image quality. With two-zone designs, balancing near and distance image quality is not achieved with equal area inner and outer zones. With significant levels of spherical aberration, multi-zone designs effectively become multifocals. Conclusion Wave optics and pupil varying ocular optics significantly affect the imaging capabilities of different optical zones of concentric bifocals. With two-zone bifocal designs, diffraction, pupil apodisation spherical aberration, and zone size influence both the effective add power and the pupil size required to balance near and distance image quality. Five-zone bifocal designs achieve a high degree of

  3. The definition, recognition, and interpretation of convergent evolution, and two new measures for quantifying and assessing the significance of convergence.

    PubMed

    Stayton, C Tristan

    2015-08-01

    Convergent evolution is an important phenomenon in the history of life. Despite this, there is no common definition of convergence used by biologists. Instead, several conceptually different definitions are employed. The primary dichotomy is between pattern-based definitions, where independently evolved similarity is sufficient for convergence, and process-based definitions, where convergence requires a certain process to produce this similarity. The unacknowledged diversity of definitions can lead to problems in evolutionary research. Process-based definitions may bias researchers away from studying or recognizing other sources of independently evolved similarity, or lead researchers to interpret convergent patterns as necessarily caused by a given process. Thus, pattern-based definitions are recommended. Existing measures of convergence are reviewed, and two new measures are developed. Both are pattern based and conceptually minimal, quantifying nothing but independently evolved similarity. One quantifies the amount of phenotypic distance between two lineages that is closed by subsequent evolution; the other simply counts the number of lineages entering a region of phenotypic space. The behavior of these measures is explored in simulations; both show acceptable Type I and Type II error. The study of convergent evolution will be facilitated if researchers are explicit about working definitions of convergence and adopt a standard toolbox of convergence measures.

  4. Converging cylindrical shocks in ideal magnetohydrodynamics

    SciTech Connect

    Pullin, D. I.; Mostert, W.; Wheatley, V.; Samtaney, R.

    2014-09-15

    We consider a cylindrically symmetrical shock converging onto an axis within the framework of ideal, compressible-gas non-dissipative magnetohydrodynamics (MHD). In cylindrical polar co-ordinates we restrict attention to either constant axial magnetic field or to the azimuthal but singular magnetic field produced by a line current on the axis. Under the constraint of zero normal magnetic field and zero tangential fluid speed at the shock, a set of restricted shock-jump conditions are obtained as functions of the shock Mach number, defined as the ratio of the local shock speed to the unique magnetohydrodynamic wave speed ahead of the shock, and also of a parameter measuring the local strength of the magnetic field. For the line current case, two approaches are explored and the results compared in detail. The first is geometrical shock-dynamics where the restricted shock-jump conditions are applied directly to the equation on the characteristic entering the shock from behind. This gives an ordinary-differential equation for the shock Mach number as a function of radius which is integrated numerically to provide profiles of the shock implosion. Also, analytic, asymptotic results are obtained for the shock trajectory at small radius. The second approach is direct numerical solution of the radially symmetric MHD equations using a shock-capturing method. For the axial magnetic field case the shock implosion is of the Guderley power-law type with exponent that is not affected by the presence of a finite magnetic field. For the axial current case, however, the presence of a tangential magnetic field ahead of the shock with strength inversely proportional to radius introduces a length scale R=√(μ{sub 0}/p{sub 0}) I/(2 π) where I is the current, μ{sub 0} is the permeability, and p{sub 0} is the pressure ahead of the shock. For shocks initiated at r ≫ R, shock convergence is first accompanied by shock strengthening as for the strictly gas-dynamic implosion. The

  5. Converging cylindrical shocks in ideal magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Pullin, D. I.; Mostert, W.; Wheatley, V.; Samtaney, R.

    2014-09-01

    We consider a cylindrically symmetrical shock converging onto an axis within the framework of ideal, compressible-gas non-dissipative magnetohydrodynamics (MHD). In cylindrical polar co-ordinates we restrict attention to either constant axial magnetic field or to the azimuthal but singular magnetic field produced by a line current on the axis. Under the constraint of zero normal magnetic field and zero tangential fluid speed at the shock, a set of restricted shock-jump conditions are obtained as functions of the shock Mach number, defined as the ratio of the local shock speed to the unique magnetohydrodynamic wave speed ahead of the shock, and also of a parameter measuring the local strength of the magnetic field. For the line current case, two approaches are explored and the results compared in detail. The first is geometrical shock-dynamics where the restricted shock-jump conditions are applied directly to the equation on the characteristic entering the shock from behind. This gives an ordinary-differential equation for the shock Mach number as a function of radius which is integrated numerically to provide profiles of the shock implosion. Also, analytic, asymptotic results are obtained for the shock trajectory at small radius. The second approach is direct numerical solution of the radially symmetric MHD equations using a shock-capturing method. For the axial magnetic field case the shock implosion is of the Guderley power-law type with exponent that is not affected by the presence of a finite magnetic field. For the axial current case, however, the presence of a tangential magnetic field ahead of the shock with strength inversely proportional to radius introduces a length scale R=sqrt{μ _0/p_0} I/(2 π ) where I is the current, μ0 is the permeability, and p0 is the pressure ahead of the shock. For shocks initiated at r ≫ R, shock convergence is first accompanied by shock strengthening as for the strictly gas-dynamic implosion. The diverging magnetic field

  6. Microgravity silicon zoning investigation

    NASA Technical Reports Server (NTRS)

    Kern, E. L.; Gill, G. L., Jr.

    1983-01-01

    A resistance heated zoner, suitable for early zoning experiments with silicon, was designed and put into operation. The initial power usage and size was designed for an shown to be compatible with payload carriers contemplated for the Shuttle. This equipment will be used in the definition and development of flight experiments and apparatus for float zoning silicon and other materials in microgravity.

  7. Float Zone Workshop

    NASA Technical Reports Server (NTRS)

    Naumann, R. J.

    1980-01-01

    A summary of the Analytical Float Zone Experiment System (AFZES) concept is presented. The types of experiments considered for such a facility are discussed. Reports from various industrial producers and users of float zone material are presented. Special emphasis is placed on state-of-the-art developments in low gravity manufacturing and their applications to space processing.

  8. Investigating Aquatic Dead Zones

    ERIC Educational Resources Information Center

    Testa, Jeremy; Gurbisz, Cassie; Murray, Laura; Gray, William; Bosch, Jennifer; Burrell, Chris; Kemp, Michael

    2010-01-01

    This article features two engaging high school activities that include current scientific information, data, and authentic case studies. The activities address the physical, biological, and chemical processes that are associated with oxygen-depleted areas, or "dead zones," in aquatic systems. Students can explore these dead zones through both…

  9. Coastal zone management

    NASA Technical Reports Server (NTRS)

    Tilton, E. L., III

    1975-01-01

    A panel of federal and state representatives concerned with coastal zone affairs discussed their problems in this area. In addition, several demonstrations of the application of remote sensing technology to coastal zone management were described. These demonstrations were performed by several agencies in a variety of geographical areas.

  10. Subduction of fracture zones

    NASA Astrophysics Data System (ADS)

    Constantin Manea, Vlad; Gerya, Taras; Manea, Marina; Zhu, Guizhi; Leeman, William

    2013-04-01

    Since Wilson proposed in 1965 the existence of a new class of faults on the ocean floor, namely transform faults, the geodynamic effects and importance of fracture zone subduction is still little studied. It is known that oceanic plates are characterized by numerous fracture zones, and some of them have the potential to transport into subduction zones large volumes of water-rich serpentinite, providing a fertile water source for magma generated in subduction-related arc volcanoes. In most previous geodynamic studies, subducting plates are considered to be homogeneous, and there is no clear indication how the subduction of a fracture zone influences the melting pattern in the mantle wedge and the slab-derived fluids distribution in the subarc mantle. Here we show that subduction of serpentinized fracture zones plays a significant role in distribution of melt and fluids in the mantle wedge above the slab. Using high-resolution tree-dimensional coupled petrological-termomechanical simulations of subduction, we show that fluids, including melts and water, vary dramatically in the region where a serpentinized fracture zone enters into subduction. Our models show that substantial hydration and partial melting tend to concentrate where fracture zones are being subducted, creating favorable conditions for partially molten hydrous plumes to develop. These results are consistent with the along-arc variability in magma source compositions and processes in several regions, as the Aleutian Arc, the Cascades, the Southern Mexican Volcanic Arc, and the Andean Southern Volcanic Zone.

  11. Relationship between outer forearc subsidence and plate boundary kinematics along the Northeast Japan convergent margin

    NASA Astrophysics Data System (ADS)

    Regalla, Christine; Fisher, Donald M.; Kirby, Eric; Furlong, Kevin P.

    2013-12-01

    Tectonic erosion along convergent plate boundaries, whereby removal of upper plate material along the subduction zone interface drives kilometer-scale outer forearc subsidence, has been purported to explain the evolution of nearly half the world's subduction margins, including part of the history of northeast Japan. Here, we evaluate the role of plate boundary dynamics in driving forearc subsidence in northeastern Japan. A synthesis of newly updated analyses of outer forearc subsidence, the timing and kinematics of upper plate deformation, and the history of plate convergence along the Japan trench demonstrate that the onset of rapid fore-arc tectonic subsidence is contemporaneous with upper plate extension during the opening of the Sea of Japan and with an acceleration in convergence rate at the trench. In Plio-Quaternary time, relative uplift of the outer forearc is contemporaneous with contraction across the arc and a decrease in plate convergence rate. The coincidence of these changes across the forearc, arc, backarc system appears to require an explanation at the scale of the entire plate boundary. Similar observations along other western Pacific margins suggest that correlations between forearc subsidence and major changes in plate kinematics are the rule, rather than the exception. We suggest that a significant component of forearc subsidence at the northeast Japan margin is not the consequence of basal tectonic erosion, but instead reflects dynamic changes in plate boundary geometry driven by temporal variations in plate kinematics. If correct, this model requires a reconsideration of the mass balance and crustal recycling of continental crust at nonaccretionary margins.

  12. Oblique sinistral transpression in the Arabian shield: The timing and kinematics of a Neoproterozoic suture zone

    USGS Publications Warehouse

    Johnson, P.R.; Kattan, F.

    2001-01-01

    The Hulayfah-Ad Dafinah-Ruwah fault zone is a belt of highly strained rocks that extends in a broad curve across the northeastern Arabian shield. It is a subvertical shear zone, 5-30 km wide and over 600 km long, and is interpreted as a zone of oblique sinistral transpression that forms the suture between the Afif terrane and the Asir-Jiddah-Hijaz-Hulayfah superterrane. Available data suggest that the terranes began to converge sometime after 720 Ma, were in active contact at about 680 Ma, and were in place, with suturing complete, by 630 Ma, The fault zone was affected by sinistral horizontal and local vertical shear, and simultaneous flattening and fault-zone-parallel extension. Structures include sinistral sense-of-shear indicators, L-S tectonite, and coaxial stretching lineations and fold axes. The stretching lineations switch from subhorizontal to subvertical along the fault zone indicating significant variation in finite strain consistent with an origin by oblique transpression. The sense of shear on the fault zone suggests sinistral trajectories for the converging terranes, although extrapolating the shear sense of the suture zone to infer far-field motion must be done with caution. The amalgamation model derived from the chronologic and structural data for the fault zone modifies an existing model of terrane amalgamation and clarifies the definitions of two deformational events (the Nabitah orogeny and the Najd fault system) that are widely represented in the Arabian shield. ?? 2001 Elsevier Science B.V.

  13. Testing Convergence for Global Accretion Disks

    NASA Astrophysics Data System (ADS)

    Hawley, John F.; Richers, Sherwood A.; Guan, Xiaoyue; Krolik, Julian H.

    2013-08-01

    Global disk simulations provide a powerful tool for investigating accretion and the underlying magnetohydrodynamic turbulence driven by magneto-rotational instability (MRI). Using them to accurately predict quantities such as stress, accretion rate, and surface brightness profile requires that purely numerical effects, arising from both resolution and algorithm, be understood and controlled. We use the flux-conservative Athena code to conduct a series of experiments on disks having a variety of magnetic topologies to determine what constitutes adequate resolution. We develop and apply several resolution metrics: langQz rang and langQ phirang, the ratio of the grid zone size to the characteristic MRI wavelength, αmag, the ratio of the Maxwell stress to the magnetic pressure, and \\langle B_R^2\\rangle /\\langle B_\\phi ^2\\rangle, the ratio of radial to toroidal magnetic field energy. For the initial conditions considered here, adequate resolution is characterized by langQz rang >= 15, langQ phirang >= 20, αmag ≈ 0.45, and \\langle B_R^2\\rangle /\\langle B_\\phi ^2\\rangle \\approx 0.2. These values are associated with >=35 zones per scaleheight H, a result consistent with shearing box simulations. Numerical algorithm is also important. Use of the Harten-Lax-van Leer-Einfeldt flux solver or second-order interpolation can significantly degrade the effective resolution compared to the Harten-Lax-van Leer discontinuities flux solver and third-order interpolation. Resolution at this standard can be achieved only with large numbers of grid zones, arranged in a fashion that matches the symmetries of the problem and the scientific goals of the simulation. Without it, however, quantitative measures important to predictions of observables are subject to large systematic errors.

  14. Convergence of controllers designed using state space methods

    NASA Technical Reports Server (NTRS)

    Morris, K. A.

    1991-01-01

    The convergence of finite dimensional controllers for infinite dimensional systems designed using approximations is examined. Stable coprime factorization theory is used to show that under the standard assumptions of uniform stabilizability/detectability, the controllers stabilize the original system for large enough model order. The controllers converge uniformly to an infinite dimensional controller, as does the closed loop response.

  15. Convergent evolution as natural experiment: the tape of life reconsidered.

    PubMed

    Powell, Russell; Mariscal, Carlos

    2015-12-01

    Stephen Jay Gould argued that replaying the 'tape of life' would result in radically different evolutionary outcomes. Recently, biologists and philosophers of science have paid increasing attention to the theoretical importance of convergent evolution-the independent origination of similar biological forms and functions-which many interpret as evidence against Gould's thesis. In this paper, we examine the evidentiary relevance of convergent evolution for the radical contingency debate. We show that under the right conditions, episodes of convergent evolution can constitute valid natural experiments that support inferences regarding the deep counterfactual stability of macroevolutionary outcomes. However, we argue that proponents of convergence have problematically lumped causally heterogeneous phenomena into a single evidentiary basket, in effect treating all convergent events as if they are of equivalent theoretical import. As a result, the 'critique from convergent evolution' fails to engage with key claims of the radical contingency thesis. To remedy this, we develop ways to break down the heterogeneous set of convergent events based on the nature of the generalizations they support. Adopting this more nuanced approach to convergent evolution allows us to differentiate iterated evolutionary outcomes that are probably common among alternative evolutionary histories and subject to law-like generalizations, from those that do little to undermine and may even support, the Gouldian view of life.

  16. Influence of Role-Switching on Phonetic Convergence in Conversation

    ERIC Educational Resources Information Center

    Pardo, Jennifer S.; Jay, Isabel Cajori; Hoshino, Risa; Hasbun, Sara Maria; Sowemimo-Coker, Chantal; Krauss, Robert M.

    2013-01-01

    The current study examined phonetic convergence when talkers alternated roles during conversational interaction. The talkers completed a map navigation task in which they alternated instruction Giver and Receiver roles across multiple map pairs. Previous studies found robust effects of the role of a talker on phonetic convergence, and it was…

  17. Economic Growth and the Ehrenfest Fleas:. the Convergence among Countries

    NASA Astrophysics Data System (ADS)

    di Gennaro, Luca; Garibaldi, Ubaldo

    The aim of this work is to predict the economic convergence among countries by using a generalization of Ehrenfest's urn. In particular this work shows that the Ehrenfest model captures the convergence among countries. A empirical analysis is presented on the European Union countries, the G7 countries and the emerging countries.

  18. The Convergent Validity of the Cognitive Preference Construct.

    ERIC Educational Resources Information Center

    Van Den Berg, Euwe; And Others

    1982-01-01

    Three cognitive preference instruments were administered to 71 college students and 37 tenth graders to measure cognitive preferences in a natural information processing (learning) situation and to assess convergent validity of cognitive preference construct and instrument validity of conventional tests. Strong evidence of convergent validity was…

  19. Managing the New Learning Agenda in a Converged Service Environment.

    ERIC Educational Resources Information Center

    Biddiscombe, Richard

    This paper describes the increasingly dynamic involvement of information professionals in the learning and teaching process in higher education. The converged service model at the University of Birmingham (United Kingdom) is described. Established in 1995, the converged service brought the university library, computing service, television service,…

  20. Value Creation Through Integrated Networks and Convergence

    SciTech Connect

    De Martini, Paul; Taft, Jeffrey D.

    2015-04-01

    Customer adoption of distributed energy resources and public policies are driving changes in the uses of the distribution system. A system originally designed and built for one-way energy flows from central generating facilities to end-use customers is now experiencing injections of energy from customers anywhere on the grid and frequent reversals in the direction of energy flow. In response, regulators and utilities are re-thinking the design and operations of the grid to create more open and transactive electric networks. This evolution has the opportunity to unlock significant value for customers and utilities. Alternatively, failure to seize this potential may instead lead to an erosion of value if customers seek to defect and disconnect from the system. This paper will discuss how current grid modernization investments may be leveraged to create open networks that increase value through the interaction of intelligent devices on the grid and prosumerization of customers. Moreover, even greater value can be realized through the synergistic effects of convergence of multiple networks. This paper will highlight examples of the emerging nexus of non-electric networks with electricity.

  1. Cylindrical converging shock initiation of reactive materials

    NASA Astrophysics Data System (ADS)

    Jenkins, Charles M.; Horie, Yasuyuki; Lindsay, Christopher Michael; Butler, George C.; Lambert, David; Welle, Eric

    2012-03-01

    Recent research has been conducted that builds on the Forbes et al. (1997) study of inducing a rapid solid state reaction in a highly porous core using a converging cylindrical shock driven by a high explosive. The high explosive annular charge used in this research to compress the center reactive core was comparable to PBXN-110. Some modifications were made on the physical configuration of the test item for scale-up and ease of production. The reactive materials (I2O5/Al and I2O5/Al/Teflon) were hand mixed and packed to a tap density of about 32 percent. Data provided by a Cordon 114 high speed framing camera and a Photon Doppler Velocimetry instrument provided exit gas expansion, core particle and cylinder wall velocities. Analysis indicates that the case expansion velocity differs according to the core formulation and behaved similar to the baseline high explosive core with the exit gas of the reactive materials producing comparable velocities. Results from CTH hydrocode used to model the test item compares favorably to the experimental results.

  2. Convergence of Hamiltonian systems to billiards.

    PubMed

    Collas, Peter; Klein, David; Schwebler, Hans-Peter

    1998-06-01

    We examine in detail a physically natural and general scheme for gradually deforming a Hamiltonian to its corresponding billiard, as a certain parameter k varies from one to infinity. We apply this limiting process to a class of Hamiltonians with homogeneous potential-energy functions and further investigate the extent to which the limiting billiards inherit properties from the corresponding sequences of Hamiltonians. The results are mixed. Using theorems of Yoshida for the case of two degrees of freedom, we prove a general theorem establishing the "inheritability" of stability properties of certain orbits. This result follows naturally from the convergence of the traces of appropriate monodromy matrices to the billiard analog. However, in spite of the close analogy between the concepts of integrability for Hamiltonian systems and billiards, integrability properties of Hamiltonians in a sequence are not necessarily inherited by the limiting billiard, as we show by example. In addition to rigorous results, we include numerical examples of certain interesting cases, along with computer simulations. (c) 1998 American Institute of Physics. PMID:12779750

  3. Convergent evolution of anti-bat sounds.

    PubMed

    Corcoran, Aaron J; Hristov, Nickolay I

    2014-09-01

    Bats and their insect prey rely on acoustic sensing in predator prey encounters--echolocation in bats, tympanic hearing in moths. Some insects also emit sounds for bat defense. Here, we describe a previously unknown sound-producing organ in Geometrid moths--a prothoracic tymbal in the orange beggar moth (Eubaphe unicolor) that generates bursts of ultrasonic clicks in response to tactile stimulation and playback of a bat echolocation attack sequence. Using scanning electron microscopy and high-speed videography, we demonstrate that E. unicolor and phylogenetically distant tiger moths have evolved serially homologous thoracic tymbal organs with fundamentally similar functional morphology, a striking example of convergent evolution. We compared E. unicolor clicks to that of five sympatric tiger moths and found that 9 of 13 E. unicolor clicking parameters were within the range of sympatric tiger moths. Remaining differences may result from the small size of the E. unicolor tymbal. Four of the five sympatric clicking tiger moth species were unpalatable to bats (0-20% eaten), whereas E. unicolor was palatable to bats (86% eaten). Based on these results, we hypothesize that E. unicolor evolved tymbal organs that mimic the sounds produced by toxic tiger moths when attacked by echolocating bats. PMID:24980483

  4. Bat echolocation calls: adaptation and convergent evolution

    PubMed Central

    Jones, Gareth; Holderied, Marc W

    2007-01-01

    Bat echolocation calls provide remarkable examples of ‘good design’ through evolution by natural selection. Theory developed from acoustics and sonar engineering permits a strong predictive basis for understanding echolocation performance. Call features, such as frequency, bandwidth, duration and pulse interval are all related to ecological niche. Recent technological breakthroughs have aided our understanding of adaptive aspects of call design in free-living bats. Stereo videogrammetry, laser scanning of habitat features and acoustic flight path tracking permit reconstruction of the flight paths of echolocating bats relative to obstacles and prey in nature. These methods show that echolocation calls are among the most intense airborne vocalizations produced by animals. Acoustic tracking has clarified how and why bats vary call structure in relation to flight speed. Bats using broadband echolocation calls adjust call design in a range-dependent manner so that nearby obstacles are localized accurately. Recent phylogenetic analyses based on gene sequences show that particular types of echolocation signals have evolved independently in several lineages of bats. Call design is often influenced more by perceptual challenges imposed by the environment than by phylogeny, and provides excellent examples of convergent evolution. Now that whole genome sequences of bats are imminent, understanding the functional genomics of echolocation will become a major challenge. PMID:17251105

  5. Conformal mapping and convergence of Krylov iterations

    SciTech Connect

    Driscoll, T.A.; Trefethen, L.N.

    1994-12-31

    Connections between conformal mapping and matrix iterations have been known for many years. The idea underlying these connections is as follows. Suppose the spectrum of a matrix or operator A is contained in a Jordan region E in the complex plane with 0 not an element of E. Let {phi}(z) denote a conformal map of the exterior of E onto the exterior of the unit disk, with {phi}{infinity} = {infinity}. Then 1/{vert_bar}{phi}(0){vert_bar} is an upper bound for the optimal asymptotic convergence factor of any Krylov subspace iteration. This idea can be made precise in various ways, depending on the matrix iterations, on whether A is finite or infinite dimensional, and on what bounds are assumed on the non-normality of A. This paper explores these connections for a variety of matrix examples, making use of a new MATLAB Schwarz-Christoffel Mapping Toolbox developed by the first author. Unlike the earlier Fortran Schwarz-Christoffel package SCPACK, the new toolbox computes exterior as well as interior Schwarz-Christoffel maps, making it easy to experiment with spectra that are not necessarily symmetric about an axis.

  6. Bat echolocation calls: adaptation and convergent evolution.

    PubMed

    Jones, Gareth; Holderied, Marc W

    2007-04-01

    Bat echolocation calls provide remarkable examples of 'good design' through evolution by natural selection. Theory developed from acoustics and sonar engineering permits a strong predictive basis for understanding echolocation performance. Call features, such as frequency, bandwidth, duration and pulse interval are all related to ecological niche. Recent technological breakthroughs have aided our understanding of adaptive aspects of call design in free-living bats. Stereo videogrammetry, laser scanning of habitat features and acoustic flight path tracking permit reconstruction of the flight paths of echolocating bats relative to obstacles and prey in nature. These methods show that echolocation calls are among the most intense airborne vocalizations produced by animals. Acoustic tracking has clarified how and why bats vary call structure in relation to flight speed. Bats using broadband echolocation calls adjust call design in a range-dependent manner so that nearby obstacles are localized accurately. Recent phylogenetic analyses based on gene sequences show that particular types of echolocation signals have evolved independently in several lineages of bats. Call design is often influenced more by perceptual challenges imposed by the environment than by phylogeny, and provides excellent examples of convergent evolution. Now that whole genome sequences of bats are imminent, understanding the functional genomics of echolocation will become a major challenge.

  7. Convergent evolution of anti-bat sounds.

    PubMed

    Corcoran, Aaron J; Hristov, Nickolay I

    2014-09-01

    Bats and their insect prey rely on acoustic sensing in predator prey encounters--echolocation in bats, tympanic hearing in moths. Some insects also emit sounds for bat defense. Here, we describe a previously unknown sound-producing organ in Geometrid moths--a prothoracic tymbal in the orange beggar moth (Eubaphe unicolor) that generates bursts of ultrasonic clicks in response to tactile stimulation and playback of a bat echolocation attack sequence. Using scanning electron microscopy and high-speed videography, we demonstrate that E. unicolor and phylogenetically distant tiger moths have evolved serially homologous thoracic tymbal organs with fundamentally similar functional morphology, a striking example of convergent evolution. We compared E. unicolor clicks to that of five sympatric tiger moths and found that 9 of 13 E. unicolor clicking parameters were within the range of sympatric tiger moths. Remaining differences may result from the small size of the E. unicolor tymbal. Four of the five sympatric clicking tiger moth species were unpalatable to bats (0-20% eaten), whereas E. unicolor was palatable to bats (86% eaten). Based on these results, we hypothesize that E. unicolor evolved tymbal organs that mimic the sounds produced by toxic tiger moths when attacked by echolocating bats.

  8. The deep structure of the North Anatolian Fault Zone

    NASA Astrophysics Data System (ADS)

    Fichtner, Andreas; Saygin, Erdinc; Taymaz, Tuncay; Cupillard, Paul; Capdeville, Yann; Trampert, Jeannot

    2013-07-01

    Multi-scale full waveform inversion of complete continental- and regional-scale seismograms reveals the crustal and upper-mantle signature of the North Anatolian Fault Zone which shapes the neotectonics of Turkey and the eastern Mediterranean. Within the crust, the fault zone is mostly bounded by several high-velocity blocks, suggesting that it developed along the edges of continental fragments with high rigidity. Below the crust, the surface expression of the eastern and central parts of the North Anatolian Fault Zone correlate with a pronounced low-velocity band that extends laterally over 600 km. Around 100 km depth, the low-velocity band merges into the shallow Anatolian asthenosphere, thereby providing a link to the Kırka-Afyon-Isparta Volcanic Field and the Central Anatolian Volcanics. We interpret the low-velocity band beneath the North Anatolian Fault Zone as the upper-mantle expression of the Tethyan sutures that formed 60-15 Ma ago as a result of Africa-Eurasian convergence. The structurally weak suture facilitated the formation of the younger (less than 10 Ma) crustal fault zone. In this sense, the North Anatolian Fault Zone is not only a crustal feature, but a narrow zone of weakness that extends into the upper mantle.

  9. Multi-zone furnace system

    SciTech Connect

    Orbeck, G.A.

    1986-05-06

    A multi-zone furnace is described which consists of: a furnace chamber having at least one heat zone and at least one zone adjacent to the heat zone and disposed along the length of the furnace chamber; the heat zone having a hearth at a level different from the hearth level of the adjacent zone; a walking beam conveyor disposed in the furnace chamber and operative in a short stroke mode to convey a product along the hearth of the heat zone, and in a long stroke mode to convey a product from the heat zone to the adjacent zone.

  10. Seismic reflection imaging of two megathrust shear zones in the northern Cascadia subduction zone.

    PubMed

    Calvert, Andrew J

    2004-03-11

    At convergent continental margins, the relative motion between the subducting oceanic plate and the overriding continent is usually accommodated by movement along a single, thin interface known as a megathrust. Great thrust earthquakes occur on the shallow part of this interface where the two plates are locked together. Earthquakes of lower magnitude occur within the underlying oceanic plate, and have been linked to geochemical dehydration reactions caused by the plate's descent. Here I present deep seismic reflection data from the northern Cascadia subduction zone that show that the inter-plate boundary is up to 16 km thick and comprises two megathrust shear zones that bound a >5-km-thick, approximately 110-km-wide region of imbricated crustal rocks. Earthquakes within the subducting plate occur predominantly in two geographic bands where the dip of the plate is inferred to increase as it is forced around the edges of the imbricated inter-plate boundary zone. This implies that seismicity in the subducting slab is controlled primarily by deformation in the upper part of the plate. Slip on the shallower megathrust shear zone, which may occur by aseismic slow slip, will transport crustal rocks into the upper mantle above the subducting oceanic plate and may, in part, provide an explanation for the unusually low seismic wave speeds that are observed there.

  11. Fault zone hydrogeology

    NASA Astrophysics Data System (ADS)

    Bense, V. F.; Gleeson, T.; Loveless, S. E.; Bour, O.; Scibek, J.

    2013-12-01

    Deformation along faults in the shallow crust (< 1 km) introduces permeability heterogeneity and anisotropy, which has an important impact on processes such as regional groundwater flow, hydrocarbon migration, and hydrothermal fluid circulation. Fault zones have the capacity to be hydraulic conduits connecting shallow and deep geological environments, but simultaneously the fault cores of many faults often form effective barriers to flow. The direct evaluation of the impact of faults to fluid flow patterns remains a challenge and requires a multidisciplinary research effort of structural geologists and hydrogeologists. However, we find that these disciplines often use different methods with little interaction between them. In this review, we document the current multi-disciplinary understanding of fault zone hydrogeology. We discuss surface- and subsurface observations from diverse rock types from unlithified and lithified clastic sediments through to carbonate, crystalline, and volcanic rocks. For each rock type, we evaluate geological deformation mechanisms, hydrogeologic observations and conceptual models of fault zone hydrogeology. Outcrop observations indicate that fault zones commonly have a permeability structure suggesting they should act as complex conduit-barrier systems in which along-fault flow is encouraged and across-fault flow is impeded. Hydrogeological observations of fault zones reported in the literature show a broad qualitative agreement with outcrop-based conceptual models of fault zone hydrogeology. Nevertheless, the specific impact of a particular fault permeability structure on fault zone hydrogeology can only be assessed when the hydrogeological context of the fault zone is considered and not from outcrop observations alone. To gain a more integrated, comprehensive understanding of fault zone hydrogeology, we foresee numerous synergistic opportunities and challenges for the discipline of structural geology and hydrogeology to co-evolve and

  12. Growth recovery zones.

    PubMed

    Siffert, R S; Katz, J F

    1983-05-01

    Growth arrest lines and zones have been reinvestigated. Sequential studies after dietary deprivation reveal transformations of the physis with diminution in formation of the zone of cell columns, resorption of previously formed bone, and cessation of new bone formation. At 6 weeks post diet restriction, the physis is prominently narrowed with transversely oriented, thin bone plaque sealing it from the subjacent marrow. Initially, restoration of stock diet thickens the bony plaque, creating a growth arrest line. Later the zone of osteogenesis adds new bone as a dense metaphyseal band.

  13. Evolution of Strain in Obliquely Convergent Analog Doubly-Vergent Wedges

    NASA Astrophysics Data System (ADS)

    Davis, D. M.; Haq, S. S.

    2012-12-01

    We have conducted a range of analog experiments across the parameter space from 0° to 70°, in which we have tracked the evolution of the model geometries and strain fields. Surface deformation is monitored by photographic analysis of the experiment and a plane laser is used to obtain precise topography of the developing pro and retro-wedges normal to strike At both high and low obliquities, our results are broadly consistent with theoretical expectations. At obliquities ranging from 0° to close to 60°, doubly-vergent wedges with the same combination of a broad, minimum taper pro-wedge and a narrower, maximum-taper double retro-wedge found in normal convergence at obliquities up to close to 60°. Above about 60° obliquity, though, the orogen continues to grow with a much greater degree of symmetry; it never develops the broad prowedge that characterizes the orogens at low to moderately high obliquities. This result is entirely consistent with the rotation of stresses and reversal in principal stress order associated with the transition from an essentially convergent orogen with some margin-parallel shear to transpression with dominant strike-slip, as described by various authors. This marked change in tectonic style and orogen shape at about 60° obliquity is accompanied by a change in the distribution of shear within the model. In normal convergence, there is no margin-parallel shear to be accommodated, so it is everywhere equal to zero. Margin-normal shortening is accommodated across the orogen, but, as taper is maintained, it occurs most rapidly near the deformation front (at left). In no case is there extension in these purely frictional models, unlike the case with a ductile layer at depth. At non-zero obliquities, there is also margin-parallel shear to be distributed across the margin. In addition to a broad zone centered on the topographic high (over the tip of the backstop), that shear is distributed across the prowedge, where it is accommodated in the

  14. Borrowed alleles and convergence in serpentine adaptation.

    PubMed

    Arnold, Brian J; Lahner, Brett; DaCosta, Jeffrey M; Weisman, Caroline M; Hollister, Jesse D; Salt, David E; Bomblies, Kirsten; Yant, Levi

    2016-07-19

    Serpentine barrens represent extreme hazards for plant colonists. These sites are characterized by high porosity leading to drought, lack of essential mineral nutrients, and phytotoxic levels of metals. Nevertheless, nature forged populations adapted to these challenges. Here, we use a population-based evolutionary genomic approach coupled with elemental profiling to assess how autotetraploid Arabidopsis arenosa adapted to a multichallenge serpentine habitat in the Austrian Alps. We first demonstrate that serpentine-adapted plants exhibit dramatically altered elemental accumulation levels in common conditions, and then resequence 24 autotetraploid individuals from three populations to perform a genome scan. We find evidence for highly localized selective sweeps that point to a polygenic, multitrait basis for serpentine adaptation. Comparing our results to a previous study of independent serpentine colonizations in the closely related diploid Arabidopsis lyrata in the United Kingdom and United States, we find the highest levels of differentiation in 11 of the same loci, providing candidate alleles for mediating convergent evolution. This overlap between independent colonizations in different species suggests that a limited number of evolutionary strategies are suited to overcome the multiple challenges of serpentine adaptation. Interestingly, we detect footprints of selection in A. arenosa in the context of substantial gene flow from nearby off-serpentine populations of A. arenosa, as well as from A. lyrata In several cases, quantitative tests of introgression indicate that some alleles exhibiting strong selective sweep signatures appear to have been introgressed from A. lyrata This finding suggests that migrant alleles may have facilitated adaptation of A. arenosa to this multihazard environment. PMID:27357660

  15. Borrowed alleles and convergence in serpentine adaptation

    PubMed Central

    Arnold, Brian J.; Lahner, Brett; DaCosta, Jeffrey M.; Weisman, Caroline M.; Hollister, Jesse D.; Salt, David E.; Bomblies, Kirsten; Yant, Levi

    2016-01-01

    Serpentine barrens represent extreme hazards for plant colonists. These sites are characterized by high porosity leading to drought, lack of essential mineral nutrients, and phytotoxic levels of metals. Nevertheless, nature forged populations adapted to these challenges. Here, we use a population-based evolutionary genomic approach coupled with elemental profiling to assess how autotetraploid Arabidopsis arenosa adapted to a multichallenge serpentine habitat in the Austrian Alps. We first demonstrate that serpentine-adapted plants exhibit dramatically altered elemental accumulation levels in common conditions, and then resequence 24 autotetraploid individuals from three populations to perform a genome scan. We find evidence for highly localized selective sweeps that point to a polygenic, multitrait basis for serpentine adaptation. Comparing our results to a previous study of independent serpentine colonizations in the closely related diploid Arabidopsis lyrata in the United Kingdom and United States, we find the highest levels of differentiation in 11 of the same loci, providing candidate alleles for mediating convergent evolution. This overlap between independent colonizations in different species suggests that a limited number of evolutionary strategies are suited to overcome the multiple challenges of serpentine adaptation. Interestingly, we detect footprints of selection in A. arenosa in the context of substantial gene flow from nearby off-serpentine populations of A. arenosa, as well as from A. lyrata. In several cases, quantitative tests of introgression indicate that some alleles exhibiting strong selective sweep signatures appear to have been introgressed from A. lyrata. This finding suggests that migrant alleles may have facilitated adaptation of A. arenosa to this multihazard environment. PMID:27357660

  16. Divergent and Convergent Evolution of Fungal Pathogenicity

    PubMed Central

    Shang, Yanfang; Xiao, Guohua; Zheng, Peng; Cen, Kai; Zhan, Shuai; Wang, Chengshu

    2016-01-01

    Fungal pathogens of plants and animals have multifarious effects; they cause devastating damages to agricultures, lead to life-threatening diseases in humans, or induce beneficial effects by reducing insect pest populations. Many virulence factors have been determined in different fungal pathogens; however, the molecular determinants contributing to fungal host selection and adaptation are largely unknown. In this study, we sequenced the genomes of seven ascomycete insect pathogens and performed the genome-wide analyses of 33 species of filamentous ascomycete pathogenic fungi that infect insects (12 species), plants (12), and humans (9). Our results revealed that the genomes of plant pathogens encode more proteins and protein families than the insect and human pathogens. Unexpectedly, more common orthologous protein groups are shared between the insect and plant pathogens than between the two animal group pathogens. We also found that the pathogenicity of host-adapted fungi evolved multiple times, and that both divergent and convergent evolutions occurred during pathogen–host cospeciation thus resulting in protein families with similar features in each fungal group. However, the role of phylogenetic relatedness on the evolution of protein families and therefore pathotype formation could not be ruled out due to the effect of common ancestry. The evolutionary correlation analyses led to the identification of different protein families that correlated with alternate pathotypes. Particularly, the effector-like proteins identified in plant and animal pathogens were strongly linked to fungal host adaptation, suggesting the existence of similar gene-for-gene relationships in fungus–animal interactions that has not been established before. These results well advance our understanding of the evolution of fungal pathogenicity and the factors that contribute to fungal pathotype formation. PMID:27071652

  17. Aeroacoustic Resonance with Convergent-Divergent Nozzles

    NASA Technical Reports Server (NTRS)

    Zaman, K. B. M. Q.; Dahl, M. D.

    1999-01-01

    Convergent-divergent nozzles, when run at off-design conditions, often undergo flow resonance accompanied by the emission of a tone. Apart from screech occurring at higher operating pressures, resonance is also common at lower Mach numbers near transonic as well as subsonic conditions. With data from six nozzles of different size and design Mach number, the present paper documents the characteristics of the latter phenomenon that is morphologically quite different from conventional screech. The resonance is due to a feedback loop internal to the nozzle and is apparently driven by unsteady laminar boundary layer separation near the throat of the nozzle. Appropriate boundary layer tripping prior to the throat is found to eliminate or alter most of the tones. The Helmholtz number of the resonance, based on the throat-to-exit length, is found to attain a value of approximately 0.15 at M(sub j)=1 for all nozzles. However, its variation with M(sub j) may be different and depend on the nozzle geometry. With nozzles having larger throat-to-exit angle of divergence, the frequency is found to increase, in some cases having stage jumps to lower frequencies, with increasing operating pressure. With nozzles having smaller angle of divergence, the frequency variation exhibits an increase followed by a decrease involving one prominent stage occurring around transonic (M(sub j)= 1) condition. While the mechanisms remain far from completely clear, a model involving downstream propagating aerodynamic disturbance together with acoustic feedback explains the overall frequency characteristics for most cases.

  18. Borrowed alleles and convergence in serpentine adaptation.

    PubMed

    Arnold, Brian J; Lahner, Brett; DaCosta, Jeffrey M; Weisman, Caroline M; Hollister, Jesse D; Salt, David E; Bomblies, Kirsten; Yant, Levi

    2016-07-19

    Serpentine barrens represent extreme hazards for plant colonists. These sites are characterized by high porosity leading to drought, lack of essential mineral nutrients, and phytotoxic levels of metals. Nevertheless, nature forged populations adapted to these challenges. Here, we use a population-based evolutionary genomic approach coupled with elemental profiling to assess how autotetraploid Arabidopsis arenosa adapted to a multichallenge serpentine habitat in the Austrian Alps. We first demonstrate that serpentine-adapted plants exhibit dramatically altered elemental accumulation levels in common conditions, and then resequence 24 autotetraploid individuals from three populations to perform a genome scan. We find evidence for highly localized selective sweeps that point to a polygenic, multitrait basis for serpentine adaptation. Comparing our results to a previous study of independent serpentine colonizations in the closely related diploid Arabidopsis lyrata in the United Kingdom and United States, we find the highest levels of differentiation in 11 of the same loci, providing candidate alleles for mediating convergent evolution. This overlap between independent colonizations in different species suggests that a limited number of evolutionary strategies are suited to overcome the multiple challenges of serpentine adaptation. Interestingly, we detect footprints of selection in A. arenosa in the context of substantial gene flow from nearby off-serpentine populations of A. arenosa, as well as from A. lyrata In several cases, quantitative tests of introgression indicate that some alleles exhibiting strong selective sweep signatures appear to have been introgressed from A. lyrata This finding suggests that migrant alleles may have facilitated adaptation of A. arenosa to this multihazard environment.

  19. The gray zone.

    PubMed

    Kisner, H J

    1998-01-01

    Think for a minute about the terms equivocal and indeterminate. Equivocal is defined as "of uncertain significance", and indeterminate is defined as "indefinite, uncertain". Now think of the context in which laboratory results are reported: either by using the exact words equivocal or indeterminate or cloaked in technical jargon (e.g., cytologic diagnoses "ASCUS" or "AGUS"). Clinicians expect (or at least want) laboratory results to be black or white (i.e., bimodally distributed), whereas laboratorians strive for the perfect shade of gray because of data that often are bimodal but overlapping. A consequence of this color war is "the gray zone" (often confused with the "twilight zone"), a noncommittal zone that leaves laboratorians and clinicians alike plenty of wiggle room, allowing us to interpret results on either side of the fence. This article examines the root causes of the gray zone, with several clinical examples of how it permeates laboratory interpretation.

  20. Cascadia Subduction Zone

    USGS Publications Warehouse

    Frankel, Arthur D.; Petersen, Mark D.

    2008-01-01

    The geometry and recurrence times of large earthquakes associated with the Cascadia Subduction Zone (CSZ) were discussed and debated at a March 28-29, 2006 Pacific Northwest workshop for the USGS National Seismic Hazard Maps. The CSZ is modeled from Cape Mendocino in California to Vancouver Island in British Columbia. We include the same geometry and weighting scheme as was used in the 2002 model (Frankel and others, 2002) based on thermal constraints (Fig. 1; Fluck and others, 1997 and a reexamination by Wang et al., 2003, Fig. 11, eastern edge of intermediate shading). This scheme includes four possibilities for the lower (eastern) limit of seismic rupture: the base of elastic zone (weight 0.1), the base of transition zone (weight 0.2), the midpoint of the transition zone (weight 0.2), and a model with a long north-south segment at 123.8? W in the southern and central portions of the CSZ, with a dogleg to the northwest in the northern portion of the zone (weight 0.5). The latter model was derived from the approximate average longitude of the contour of the 30 km depth of the CSZ as modeled by Fluck et al. (1997). A global study of the maximum depth of thrust earthquakes on subduction zones by Tichelaar and Ruff (1993) indicated maximum depths of about 40 km for most of the subduction zones studied, although the Mexican subduction zone had a maximum depth of about 25 km (R. LaForge, pers. comm., 2006). The recent inversion of GPS data by McCaffrey et al. (2007) shows a significant amount of coupling (a coupling factor of 0.2-0.3) as far east as 123.8? West in some portions of the CSZ. Both of these lines of evidence lend support to the model with a north-south segment at 123.8? W.

  1. Subduction zone tectonic studies to develop concepts for the occurrence of sediment subduction (Phase I). Final technical report

    SciTech Connect

    Hilde, T.W.C.

    1984-08-01

    The objective was to determine the fate of sediments at convergent lithospheric plate boundaries. The study focuses on the structures of the Circum-Pacific trenches and shallow portions of the associated subduction zones. Sediment distribution and the nature of sediment deformation was defined through the various stages of plate convergence to determine if the sediments are subducted or accreted. The controlling factors for sediment subduction and/or accretion were determined. 50 figs. (ACR)

  2. The importance of accurate convergence in addressing stereoscopic visual fatigue

    NASA Astrophysics Data System (ADS)

    Mayhew, Christopher A.

    2015-03-01

    Visual fatigue (asthenopia) continues to be a problem in extended viewing of stereoscopic imagery. Poorly converged imagery may contribute to this problem. In 2013, the Author reported that in a study sample a surprisingly high number of 3D feature films released as stereoscopic Blu-rays contained obvious convergence errors.1 The placement of stereoscopic image convergence can be an "artistic" call, but upon close examination, the sampled films seemed to have simply missed their intended convergence location. This failure maybe because some stereoscopic editing tools do not have the necessary fidelity to enable a 3D editor to obtain a high degree of image alignment or set an exact point of convergence. Compounding this matter further is the fact that a large number of stereoscopic editors may not believe that pixel accurate alignment and convergence is necessary. The Author asserts that setting a pixel accurate point of convergence on an object at the start of any given stereoscopic scene will improve the viewer's ability to fuse the left and right images quickly. The premise is that stereoscopic performance (acuity) increases when an accurately converged object is available in the image for the viewer to fuse immediately. Furthermore, this increased viewer stereoscopic performance should reduce the amount of visual fatigue associated with longer-term viewing because less mental effort will be required to perceive the imagery. To test this concept, we developed special stereoscopic imagery to measure viewer visual performance with and without specific objects for convergence. The Company Team conducted a series of visual tests with 24 participants between 25 and 60 years of age. This paper reports the results of these tests.

  3. Dentin Caries Zones

    PubMed Central

    Pugach, M.K.; Strother, J.; Darling, C.L.; Fried, D.; Gansky, S.A.; Marshall, S.J.; Marshall, G.W.

    2009-01-01

    Caries Detector staining reveals 4 zones in dentin containing caries lesions, but characteristics of each zone are not well-defined. We therefore investigated the physical and microstructural properties of carious dentin in the 4 different zones to determine important differences revealed by Caries Detector staining. Six arrested dentin caries lesions and 2 normal controls were Caries-Detector-stained, each zone (pink, light pink, transparent, apparently normal) being analyzed by atomic force microscopy (AFM) imaging for microstructure, by AFM nano-indentation for mechanical properties, and by transverse digital microradiography (TMR) for mineral content. Microstructure changes, and nanomechanical properties and mineral content significantly decreased across zones. Hydrated elastic modulus and mineral content from normal dentin to pink Caries-Detector-stained dentin ranged from 19.5 [10.6-25.3] GPa to 1.6 [0.0-5.0] GPa and from 42.9 [39.8-44.6] vol% to 12.4 [9.1-14.2] vol%, respectively. Even the most demineralized pink zone contained considerable residual mineral. PMID:19131321

  4. Γ-convergence of Variational Integrators for Constrained Systems

    NASA Astrophysics Data System (ADS)

    Schmidt, Bernd; Leyendecker, Sigrid; Ortiz, Michael

    2009-04-01

    For a physical system described by a motion in an energy landscape under holonomic constraints, we study the Γ-convergence of variational integrators to the corresponding continuum action functional and the convergence properties of solutions of the discrete Euler-Lagrange equations to stationary points of the continuum problem. This extends the results in Müller and Ortiz (J. Nonlinear Sci. 14:279-296, 2004) to constrained systems. The convergence result is illustrated with examples of mass point systems and flexible multibody dynamics.

  5. The convergence of spectral methods for nonlinear conservation laws

    NASA Technical Reports Server (NTRS)

    Tadmor, Eitan

    1987-01-01

    The convergence of the Fourier method for scalar nonlinear conservation laws which exhibit spontaneous shock discontinuities is discussed. Numerical tests indicate that the convergence may (and in fact in some cases must) fail, with or without post-processing of the numerical solution. Instead, a new kind of spectrally accurate vanishing viscosity is introduced to augment the Fourier approximation of such nonlinear conservation laws. Using compensated compactness arguments, it is shown that this spectral viscosity prevents oscillations, and convergence to the unique entropy solution follows.

  6. IS THERE CONVERGENCE ACROSS COUNTRIES? A SPATIAL APPROACH

    PubMed Central

    Berry, Heather; Guillen, Mauro F.; Hendi, Arun S.

    2014-01-01

    We analyze convergence across countries over the last half century as a result of globalizing forces. Drawing on theories of modernization, dependency, the world-system, political trade blocs, and the world-society, we consider economic, demographic, knowledge, financial, and political dimensions of convergence. Using a new methodology, we calculate the minimum volume ellipsoid encompassing different groupings of countries, finding that during the 1960–2009 period, countries have not evolved significantly closer or similar to one another, although groups of countries based on their core-periphery status or membership in trade blocs exhibit increasing internal convergence and divergence between one another. PMID:25580035

  7. Comparative Convergence Analysis of Nonlinear AMLI-Cycle Multigrid

    SciTech Connect

    Hu, Xiaozhe; Vassilevski, Panayot S.; Xu, Jinchao

    2013-04-30

    The purpose of our paper is to provide a comprehensive convergence analysis of the nonlinear algebraic multilevel iteration (AMLI)-cycle multigrid (MG) method for symmetric positive definite problems. We show that the nonlinear AMLI-cycle MG method is uniformly convergent, based on classical assumptions for approximation and smoothing properties. Furthermore, under only the assumption that the smoother is convergent, we show that the nonlinear AMLI-cycle method is always better (or not worse) than the respective V-cycle MG method. Finally, numerical experiments are presented to illustrate the theoretical results.

  8. On the Convergence of an Implicitly Restarted Arnoldi Method

    SciTech Connect

    Lehoucq, Richard B.

    1999-07-12

    We show that Sorensen's [35] implicitly restarted Arnoldi method (including its block extension) is simultaneous iteration with an implicit projection step to accelerate convergence to the invariant subspace of interest. By using the geometric convergence theory for simultaneous iteration due to Watkins and Elsner [43], we prove that an implicitly restarted Arnoldi method can achieve a super-linear rate of convergence to the dominant invariant subspace of a matrix. Moreover, we show how an IRAM computes a nested sequence of approximations for the partial Schur decomposition associated with the dominant invariant subspace of a matrix.

  9. Strain partitioning and the formation of forearc slivers at oblique convergent margins: Insight from numerical modeling

    NASA Astrophysics Data System (ADS)

    Koster, Kelvin

    Oblique relative plate motion is ubiquitous at convergent margins, often resulting in a significant component of motion parallel to the margin. Partitioning of relative plate motion can result in deformation that is accommodated as spatially distinct margin-parallel shear and margin-normal thrusting, and lead to the development and migration of crustal slivers. These slivers, bounded by thrust faults at the trench and arc-ward by a well-developed margin-parallel strike-slip fault, are observed at about half of all modern convergent boundaries. Some modestly oblique settings have developed fore-arc slivers while other margins, with higher obliquities, have failed to effectively partition plate motion into distinct zones suggesting mechanisms other than obliquity are important in partitioning. Analog modeling has shown that pure frictional wedges always partition deformation but produce sliver like motion and structures at only very high obliquities. The presence of ductile layers at depth in some analog models, however, can localize shear at much lower obliquities. In light of this, we have performed, for a wide range of obliquities, finite-element numerical simulations of convergent wedges with similar geometries and distributions in strength as layered analog models, with a basal ductile layer. For these models, we solve force-balance equations for Stokes flow using COMSOL Multiphysics in order to quantify the magnitude and style of stress. Our numerical models display a similar distribution of cross-sectional topography and surface velocity fields compared to their counter part oblique analog experiments. The numerical models also demonstrate a progressive localization of margin-parallel shear with the growth of wedge topography. All wedges with a non-zero obliquity eventually show the onset and localization of shear indicative of strike-slip deformation, which we quantify by calculating the principal horizontal stress field, as well as, the margin-normal and

  10. Convergence of semigroups with an application to the Carleman equation

    SciTech Connect

    Kaper, H.G.; Leaf, G.K.; Reich, S.

    1980-01-01

    A simple proof of a convergence result for nonlinear semigroups is presented which can be applied to obtain the fluid dynamical limit of Carleman's equation. In addition, a closed exponential generator of the limit semigroup is explicitly identified.

  11. Numerical Stability and Convergence of Approximate Methods for Conservation Laws

    NASA Astrophysics Data System (ADS)

    Galkin, V. A.

    We present the new approach to background of approximate methods convergence based on functional solutions theory for conservation laws. The applications to physical kinetics, gas and fluid dynamics are considered.

  12. Does healthcare financing converge? Evidence from eight OECD countries.

    PubMed

    Chen, Wen-Yi

    2013-12-01

    This study investigated the convergence of healthcare financing across eight OECD countries during 1960-2009 for the first time. The panel stationary test incorporating both shapes of multiple structural breaks (i.e., sharp drifts and smooth transition shifts) and cross-sectional dependence was used to provide reliable evidence of convergence in healthcare financing. Our results suggested that the public share of total healthcare financing in eight OECD countries has exhibited signs of convergence towards that of the US. The convergence of healthcare financing not only reflected a decline in the share of public healthcare financing in these eight OECD countries but also exhibited an upward trend in the share of public healthcare financing in the US over the period of 1960-2009.

  13. Heterotic quantum and classical computing on convergence spaces

    NASA Astrophysics Data System (ADS)

    Patten, D. R.; Jakel, D. W.; Irwin, R. J.; Blair, H. A.

    2015-05-01

    Category-theoretic characterizations of heterotic models of computation, introduced by Stepney et al., combine computational models such as classical/quantum, digital/analog, synchronous/asynchronous, etc. to obtain increased computational power. A highly informative classical/quantum heterotic model of computation is represented by Abramsky's simple sequential imperative quantum programming language which extends the classical simple imperative programming language to encompass quantum computation. The mathematical (denotational) semantics of this classical language serves as a basic foundation upon which formal verification methods can be developed. We present a more comprehensive heterotic classical/quantum model of computation based on heterotic dynamical systems on convergence spaces. Convergence spaces subsume topological spaces but admit finer structure from which, in prior work, we obtained differential calculi in the cartesian closed category of convergence spaces allowing us to define heterotic dynamical systems, given by coupled systems of first order differential equations whose variables are functions from the reals to convergence spaces.

  14. Simulating convergent extension by way of anisotropic differential adhesion.

    PubMed

    Zajac, Mark; Jones, Gerald L; Glazier, James A

    2003-05-21

    Simulations using the Extended Potts Model suggest that anisotropic differential adhesion can account for convergent extension, as observed during embryonic development of the frog Xenopus laevis for example. During gastrulation in these frogs, convergent extension produces longitudinal tissue growth from latitudinal elongation and migration of aligned constituent cells. The Extended Potts Model employs clustered points on a grid to represent subdivided cells with probabilistic displacement of cell boundaries such that small changes in energy drive gradual tissue development. For modeling convergent extension, simulations include anisotropic differential adhesion: the degree of attachment between adjacent elongated cells depends on their relative orientation. Without considering additional mechanisms, simulations based on anisotropic differential adhesion reproduce the hallmark stages of convergent extension in the correct sequence, with random fluctuations as sufficient impetus for cell reorganization. PMID:12727459

  15. Acquired convergence-evoked pendular nystagmus in multiple sclerosis.

    PubMed

    Barton, J J; Cox, T A; Digre, K B

    1999-03-01

    Nystagmus seen only with convergence is unusual. We describe four cases of acquired convergence-evoked pendular nystagmus in patients with multiple sclerosis. The nystagmus was horizontal and asymmetric in all patients. Eye movement recordings in one subject showed a conjugate rather than a convergent-divergent relationship of the phase of movement between the two eyes. All patients had evidence of optic neuropathy and cerebellar dysfunction. Occlusion of either eye during fixation of near targets led to divergent drift of the covered eye and a decrease in nystagmus. Intravenous scopolamine reduced nystagmus in one patient. Base-in prisms alleviated symptoms of oscillopsia at near and improving reading visual acuity. Convergence-evoked pendular nystagmus may be more common than currently appreciated, particularly among patients with multiple sclerosis.

  16. Does healthcare financing converge? Evidence from eight OECD countries.

    PubMed

    Chen, Wen-Yi

    2013-12-01

    This study investigated the convergence of healthcare financing across eight OECD countries during 1960-2009 for the first time. The panel stationary test incorporating both shapes of multiple structural breaks (i.e., sharp drifts and smooth transition shifts) and cross-sectional dependence was used to provide reliable evidence of convergence in healthcare financing. Our results suggested that the public share of total healthcare financing in eight OECD countries has exhibited signs of convergence towards that of the US. The convergence of healthcare financing not only reflected a decline in the share of public healthcare financing in these eight OECD countries but also exhibited an upward trend in the share of public healthcare financing in the US over the period of 1960-2009. PMID:24037490

  17. Beyond division: convergences between postmodern qualitative research and family therapy.

    PubMed

    De Haene, Lucia

    2010-01-01

    Starting from examples of postmodern research and therapeutic practice, we raise the question on the role of the research-therapy dichotomy within these approaches. The article aims to show the profound convergence between postmodern ethnographic research and constructionist, collaborative therapeutic approaches on a double, epistemological and practice level. First, we point out their converging development toward narrative and constructionist epistemologies. Second, an inquiry into the core features of these disciplinary activities' goal, process, and expert role reveals their profound convergence into a dialogical practice in which the boundaries between research and therapy are radically transgressed. We conclude by questioning the implications and acceptability of this convergence for researchers' and therapists' understanding of their practices.

  18. Functional zones in the auditory cortex of the echolocating bat, Myotis lucifugus.

    PubMed

    Wong, D; Shannon, S L

    1988-06-21

    Neurophysiological mapping experiments in the auditory cortex of the frequency-modulated bat, Myotis lucifugus, reveal 3 functional subregions: a tonotopic zone located dorsally, a delay-sensitive zone more ventrally, and an intermediate zone of major overlap. The unique finding of an overlapping cortical region representing both spectral and time-delay information of echoes is intriguing in view of a recent behavioral study suggesting the convergence of such echo cues in auditory perception. (Simmons et al., Soc. Neurosci. Abstr., 13 [1987] 870). PMID:3401773

  19. Bayesian Optimization Algorithm, Population Sizing, and Time to Convergence

    SciTech Connect

    Pelikan, M.; Goldberg, D.E.; Cantu-Paz, E.

    2000-01-19

    This paper analyzes convergence properties of the Bayesian optimization algorithm (BOA). It settles the BOA into the framework of problem decomposition used frequently in order to model and understand the behavior of simple genetic algorithms. The growth of the population size and the number of generations until convergence with respect to the size of a problem is theoretically analyzed. The theoretical results are supported by a number of experiments.

  20. Convergence of Density-Matrix Expansions for Nuclear Interactions

    SciTech Connect

    Carlsson, B. G.; Dobaczewski, J.

    2010-09-17

    We extend density-matrix expansions in nuclei to higher orders in derivatives of densities and test their convergence properties. The expansions allow for converting the interaction energies characteristic to finite- and short-range nuclear effective forces into quasilocal density functionals. We also propose a new type of expansion that has excellent convergence properties when benchmarked against the binding energies obtained for the Gogny interaction.

  1. Convergence of reinforcement learning algorithms and acceleration of learning

    NASA Astrophysics Data System (ADS)

    Potapov, A.; Ali, M. K.

    2003-02-01

    The techniques of reinforcement learning have been gaining increasing popularity recently. However, the question of their convergence rate is still open. We consider the problem of choosing the learning steps αn, and their relation with discount γ and exploration degree ɛ. Appropriate choices of these parameters may drastically influence the convergence rate of the techniques. From analytical examples, we conjecture optimal values of αn and then use numerical examples to verify our conjectures.

  2. On cylindrically converging shock waves shaped by obstacles

    SciTech Connect

    Eliasson, V; Henshaw, W D; Appelo, D

    2007-07-16

    Motivated by recent experiments, numerical simulations were performed of cylindrically converging shock waves. The converging shocks impinged upon a set of zero to sixteen regularly space obstacles. For more than two obstacles the resulting diffracted shock fronts formed polygonal shaped patterns near the point of focus. The maximum pressure and temperature as a function of number of obstacles were studied. The self-similar behavior of cylindrical, triangular and square-shaped shocks were also investigated.

  3. Relations between convergence rates in Schatten p-norms

    SciTech Connect

    Albini, Paolo; Toigo, Alessandro; Umanita, Veronica

    2008-01-15

    In quantum estimation theory and quantum tomography, the quantum state obtained by sampling converges to the ''true'' unknown density matrix under topologies that are different from the natural notion of distance in the space of quantum states, i.e., the trace class norm. In this paper, we address such problem, finding relations between the rates of convergence in the Schatten p-norms and in the trace class norm.

  4. Numerical Optimization of converging diverging miniature cavitating nozzles

    NASA Astrophysics Data System (ADS)

    Chavan, Kanchan; Bhingole, B.; Raut, J.; Pandit, A. B.

    2015-12-01

    The work focuses on the numerical optimization of converging diverging cavitating nozzles through nozzle dimensions and wall shape. The objective is to develop design rules for the geometry of cavitating nozzles for desired end-use. Two main aspects of nozzle design which affects the cavitation have been studied i.e. end dimensions of the geometry (i.e. angle and/or curvature of the inlet, outlet and the throat and the lengths of the converging and diverging sections) and wall curvatures(concave or convex). Angle of convergence at the inlet was found to control the cavity growth whereas angle of divergence of the exit controls the collapse of cavity. CFD simulations were carried out for the straight line converging and diverging sections by varying converging and diverging angles to study its effect on the collapse pressure generated by the cavity. Optimized geometry configurations were obtained on the basis of maximum Cavitational Efficacy Ratio (CER)i.e. cavity collapse pressure generated for a given permanent pressure drop across the system. With increasing capabilities in machining and fabrication, it is possible to exploit the effect of wall curvature to create nozzles with further increase in the CER. Effect of wall curvature has been studied for the straight, concave and convex shapes. Curvature has been varied and effect of concave and convex wall curvatures vis-à-vis straight walls studied for fixed converging and diverging angles.It is concluded that concave converging-diverging nozzles with converging angle of 20° and diverging angle of 5° with the radius of curvature 0.03 m and 0.1530 m respectively gives maximum CER. Preliminary experiments using optimized geometry are indicating similar trends and are currently being carried out. Refinements of the CFD technique using two phase flow simulations are planned.

  5. Convergence theorems for generalized nonexpansive multivalued mappings in hyperbolic spaces.

    PubMed

    Kim, Jong Kyu; Pathak, Ramesh Prasad; Dashputre, Samir; Diwan, Shailesh Dhar; Gupta, Rajlaxmi

    2016-01-01

    In this paper, we establish the existence of a fixed point for generalized nonexpansive multivalued mappings in hyperbolic spaces and we prove some [Formula: see text]-convergence and strong convergence theorems for the iterative scheme proposed by Chang et al. (Appl Math Comp 249:535-540, 2014) to approximate a fixed point for generalized nonexpansive multivalued mapping under suitable conditions. Our results are the extension and improvements of the recent well-known results announced in the current literature.

  6. Convergence theorems for generalized nonexpansive multivalued mappings in hyperbolic spaces.

    PubMed

    Kim, Jong Kyu; Pathak, Ramesh Prasad; Dashputre, Samir; Diwan, Shailesh Dhar; Gupta, Rajlaxmi

    2016-01-01

    In this paper, we establish the existence of a fixed point for generalized nonexpansive multivalued mappings in hyperbolic spaces and we prove some [Formula: see text]-convergence and strong convergence theorems for the iterative scheme proposed by Chang et al. (Appl Math Comp 249:535-540, 2014) to approximate a fixed point for generalized nonexpansive multivalued mapping under suitable conditions. Our results are the extension and improvements of the recent well-known results announced in the current literature. PMID:27386356

  7. A technique for accelerating the convergence of restarted GMRES

    SciTech Connect

    Baker, A H; Jessup, E R; Manteuffel, T

    2004-03-09

    We have observed that the residual vectors at the end of each restart cycle of restarted GMRES often alternate direction in a cyclic fashion, thereby slowing convergence. We present a new technique for accelerating the convergence of restarted GMRES by disrupting this alternating pattern. The new algorithm resembles a full conjugate gradient method with polynomial preconditioning, and its implementation requires minimal changes to the standard restarted GMRES algorithm.

  8. Forearc kinematics in obliquely convergent margins: Examples from Nicaragua and the northern Lesser Antilles

    NASA Astrophysics Data System (ADS)

    Turner, Henry L., III

    In this study, I use surface velocities derived from GPS geodesy, elastic half-space dislocation models, and modeled Coulomb stress changes to investigate deformation in the over-riding plate at obliquely convergent margins at the leading and trailing edges of the Caribbean plate. The two principal study areas are western Nicaragua, where the Cocos plate subducts beneath the Caribbean plate, and the northern Lesser Antilles, where the North American plate subducts beneath the Caribbean plate. In Nicaragua, plate convergence is rapid at 84 mm yr1 with a small angle of obliquity of 10° along a slightly concave portion of the Middle America Trench. GPS velocities for the period from 2000 to 2004 from sites located in the Nicaraguan forearc confirmed forearc sliver motion on the order of ˜14 mm yr1 in close agreement with the value predicted by DeMets (2001). These results are presented here in Chapter 3 and were reported in Geophysical Research Letters (Turner et al., 2007). GPS observations made on sites located in the interior and on the eastern coast of Nicaragua during the same time period were combined with new data from eastern Honduras to help better constrain estimates of rigid Caribbean plate motion (DeMets et al., 2007). Slip approaching the plate convergence rate along the Nicaraguan and El Salvadoran sections of the Middle America Trench was quantitatively demonstrated by finite element modeling of this section of the plate interface using GPS velocities from our Nicaraguan network together with velocities from El Salvador and Honduras as model constraints (Correa-Mora, 2009). The MW 6.9 earthquake that ruptured the seismogenic zone offshore Nicaragua on October 9, 2004 resulted in coseismic displacements and post-seismic motion at GPS sites in the central part of the Nicaraguan forearc that currently prevent extension of interseismic time-series in this region. An elastic half-space dislocation model was used to estimate coseismic displacements at these

  9. Cosmic Reionization on Computers: Numerical and Physical Convergence

    NASA Astrophysics Data System (ADS)

    Gnedin, Nickolay Y.

    2016-04-01

    In this paper I show that simulations of reionization performed under the Cosmic Reionization On Computers project do converge in space and mass, albeit rather slowly. A fully converged solution (for a given star formation and feedback model) can be determined at a level of precision of about 20%, but such a solution is useless in practice, since achieving it in production-grade simulations would require a large set of runs at various mass and spatial resolutions, and computational resources for such an undertaking are not yet readily available. In order to make progress in the interim, I introduce a weak convergence correction factor in the star formation recipe, which allows one to approximate the fully converged solution with finite-resolution simulations. The accuracy of weakly converged simulations approaches a comparable, ~20% level of precision for star formation histories of individual galactic halos and other galactic properties that are directly related to star formation rates, such as stellar masses and metallicities. Yet other properties of model galaxies, for example, their H i masses, are recovered in the weakly converged runs only within a factor of 2.

  10. Convergence in pigmentation at multiple levels: mutations, genes and function.

    PubMed

    Manceau, Marie; Domingues, Vera S; Linnen, Catherine R; Rosenblum, Erica Bree; Hoekstra, Hopi E

    2010-08-27

    Convergence--the independent evolution of the same trait by two or more taxa--has long been of interest to evolutionary biologists, but only recently has the molecular basis of phenotypic convergence been identified. Here, we highlight studies of rapid evolution of cryptic coloration in vertebrates to demonstrate that phenotypic convergence can occur at multiple levels: mutations, genes and gene function. We first show that different genes can be responsible for convergent phenotypes even among closely related populations, for example, in the pale beach mice inhabiting Florida's Gulf and Atlantic coasts. By contrast, the exact same mutation can create similar phenotypes in distantly related species such as mice and mammoths. Next, we show that different mutations in the same gene need not be functionally equivalent to produce similar phenotypes. For example, separate mutations produce divergent protein function but convergent pale coloration in two lizard species. Similarly, mutations that alter the expression of a gene in different ways can, nevertheless, result in similar phenotypes, as demonstrated by sister species of deer mice. Together these studies underscore the importance of identifying not only the genes, but also the precise mutations and their effects on protein function, that contribute to adaptation and highlight how convergence can occur at different genetic levels. PMID:20643733

  11. Convergence and Rate Analysis of Neural Networks for Sparse Approximation

    PubMed Central

    Balavoine, Aurèle; Romberg, Justin; Rozell, Christopher J.

    2013-01-01

    We present an analysis of the Locally Competitive Algotihm (LCA), which is a Hopfield-style neural network that efficiently solves sparse approximation problems (e.g., approximating a vector from a dictionary using just a few nonzero coefficients). This class of problems plays a significant role in both theories of neural coding and applications in signal processing. However, the LCA lacks analysis of its convergence properties, and previous results on neural networks for nonsmooth optimization do not apply to the specifics of the LCA architecture. We show that the LCA has desirable convergence properties, such as stability and global convergence to the optimum of the objective function when it is unique. Under some mild conditions, the support of the solution is also proven to be reached in finite time. Furthermore, some restrictions on the problem specifics allow us to characterize the convergence rate of the system by showing that the LCA converges exponentially fast with an analytically bounded convergence rate. We support our analysis with several illustrative simulations. PMID:24199030

  12. Cosmic Reionization On Computers: Numerical and Physical Convergence

    DOE PAGESBeta

    Gnedin, Nickolay Y.

    2016-04-01

    In this paper I show that simulations of reionization performed under the Cosmic Reionization On Computers (CROC) project do converge in space and mass, albeit rather slowly. A fully converged solution (for a given star formation and feedback model) can be determined at a level of precision of about 20%, but such a solution is useless in practice, since achieving it in production-grade simulations would require a large set of runs at various mass and spatial resolutions, and computational resources for such an undertaking are not yet readily available. In order to make progress in the interim, I introduce amore » weak convergence correction factor in the star formation recipe, which allows one to approximate the fully converged solution with finite resolution simulations. The accuracy of weakly converged simulations approaches a comparable, ~20% level of precision for star formation histories of individual galactic halos and other galactic properties that are directly related to star formation rates, like stellar masses and metallicities. Yet other properties of model galaxies, for example, their HI masses, are recovered in the weakly converged runs only within a factor of two.« less

  13. Convergence and rate analysis of neural networks for sparse approximation.

    PubMed

    Balavoine, Aurèle; Romberg, Justin; Rozell, Christopher J

    2012-09-01

    We present an analysis of the Locally Competitive Algorithm (LCA), which is a Hopfield-style neural network that efficiently solves sparse approximation problems (e.g., approximating a vector from a dictionary using just a few nonzero coefficients). This class of problems plays a significant role in both theories of neural coding and applications in signal processing. However, the LCA lacks analysis of its convergence properties, and previous results on neural networks for nonsmooth optimization do not apply to the specifics of the LCA architecture. We show that the LCA has desirable convergence properties, such as stability and global convergence to the optimum of the objective function when it is unique. Under some mild conditions, the support of the solution is also proven to be reached in finite time. Furthermore, some restrictions on the problem specifics allow us to characterize the convergence rate of the system by showing that the LCA converges exponentially fast with an analytically bounded convergence rate. We support our analysis with several illustrative simulations.

  14. Filopodial-Tension Model of Convergent-Extension of Tissues

    PubMed Central

    Swat, Maciej H.; Glazier, James A.

    2016-01-01

    In convergent-extension (CE), a planar-polarized epithelial tissue elongates (extends) in-plane in one direction while shortening (converging) in the perpendicular in-plane direction, with the cells both elongating and intercalating along the converging axis. CE occurs during the development of most multicellular organisms. Current CE models assume cell or tissue asymmetry, but neglect the preferential filopodial activity along the convergent axis observed in many tissues. We propose a cell-based CE model based on asymmetric filopodial tension forces between cells and investigate how cell-level filopodial interactions drive tissue-level CE. The final tissue geometry depends on the balance between external rounding forces and cell-intercalation traction. Filopodial-tension CE is robust to relatively high levels of planar cell polarity misalignment and to the presence of non-active cells. Addition of a simple mechanical feedback between cells fully rescues and even improves CE of tissues with high levels of polarity misalignments. Our model extends easily to three dimensions, with either one converging and two extending axes, or two converging and one extending axes, producing distinct tissue morphologies, as observed in vivo. PMID:27322528

  15. Semiautomatic fracture zone tracking

    NASA Astrophysics Data System (ADS)

    Wessel, Paul; Matthews, Kara J.; Müller, R. Dietmar; Mazzoni, Aline; Whittaker, Joanne M.; Myhill, Robert; Chandler, Michael T.

    2015-07-01

    Oceanic fracture zone traces are widely used in studies of seafloor morphology and plate kinematics. Satellite altimetry missions have resulted in high-resolution gravity maps in which all major fracture zones and other tectonic fabric can be identified, and numerous scientists have digitized such lineaments. We have initiated a community effort to maintain low-cost infrastructure that allows seafloor fabric lineaments to be stored, accessed, and updated. A key improvement over past efforts is our processing software (released as a GMT5 supplement) that allows for semiautomatic corrections to previously digitized fracture zone traces given improved gridded data sets. Here we report on our seafloor fabric processing tools, which complement our database of seafloor fabric lineations, magnetic anomaly identifications, and plate kinematic models.

  16. Convergent Beam Electron Diffraction Study of Bi-BASED High Temperature Superconducting Layered Compounds

    NASA Astrophysics Data System (ADS)

    Zhang, X. F.; Yan, Y. F.; Fung, K. K.

    Cleaved specimens of layered compounds Bi2Sr2(CaCuO2)nCuO6, n = 0, 1 and 2 phases have been studied by convergent beam electron diffraction. The identity and the symmetry of the phases have been determined from the higher order Laue zone (HOLZ) rings and the symmetry of their [001] patterns. In the case of Bi2Sr2CuO6, the [001] axial periodicity corresponds to the component of the wave vector of the monoclinic modulation along the c axis. Widely different axial periodicities have been obtained. This is interpreted as the manifestation of the variation of the monoclinic modulation. The presence of basal stacking fault lowers the symmetry of the [001] pattern.

  17. Strain Distribution Measurement in Stainless Steels by Convergent-Beam Electron Diffraction

    NASA Astrophysics Data System (ADS)

    Saito, Masakazu; Aoyama, Takashi; Nakata, Kiyotomo; Suzuki, Takaya

    1995-01-01

    A convergent-beam electron diffraction technique was utilized to measure local strain distributions in stainless steels. Electron beams were focused into {210} crystal planes and the higher order Laue zone (HOLZ) lines diffracted from {375} and {119} planes were characterized by measuring the distances between the intersections of these HOLZ lines. Four parameters, including strains in three directions and one magnification factor, were calculated based on the least squares method. Strain distributions near a chromium carbide precipitate were measured in sensitized SUS 304 and it was confirmed that parallel tensile strain and vertical compressive strain to the edge of the precipitate existed and that they decreased with the distance from the edge of precipitate.

  18. Strain Measurements in Thin Film Structures by Convergent Beam Electron Diffraction

    NASA Astrophysics Data System (ADS)

    Armigliato, A.; Balboni, R.; Benedetti, A.; Frabboni, S.; Tixier, A.; Vanhellemont, J.

    1997-12-01

    The Convergent Beam Electron Diffraction technique (CBED) has been applied to determine the lattice strain in Si{1-x}Gex/Si heterostructures and below patterned films on silicon substrates. The well known problem of the stress relaxation which occurs in thinned TEM samples has been overcome, in the case of the heterostructures, by applying the isotropic elasticity theory to the lattice constants measured along different crystallographic directions through the shift of the High Order Laue Zone (HOLZ) lines in the central disk of the CBED patterns. In this way bulk strain values have been obtained, in good agreement with values deduced from independent techniques. In patterned structures, the high spatial resolution of the CBED technique has been applied to determine the distribution of the components of the strain tensor induced into oxidized silicon substrates by Si3N4 stripes. A good agreement with the results obtained using numerical computations has been found.

  19. Improving spatial resolution of convergent beam electron diffraction strain mapping in silicon microstructures

    SciTech Connect

    Armigliato, A.; Balboni, R.; Frabboni, S.

    2005-02-07

    Despite the use of nanometer-sized probes in field emission transmission electron microscopes, the spatial resolution in strain analysis performed by convergent beam electron diffraction is limited in one direction by the need for tilting the cross-sectional sample in the electron microscope off the vertical <110> direction. We demonstrate that it is possible to improve this resolution by using the <340> zone axis, instead of the <230> one, which has recently become of common use in the analysis of silicon microdevices. Quantitative strain information with good sensitivity and accuracy can be obtained in the new axis. An example of application to the two-dimensional strain mapping in shallow trench isolation structures, obtained with a scanning attachment and a high-angle annular dark-field detector, is reported.

  20. Nuclear free zone

    SciTech Connect

    Christoffel, T.

    1987-07-01

    Health professionals have played a leading role in alerting and educating the public regarding the danger of nuclear war which has been described as the last epidemic our civilization will know. Having convinced most people that the use of nuclear weapons would mean intolerable consequences, groups such as Physicians for Social Responsibility have focused on the second critical question how likely is it that these weapons will be used. The oultlook is grim. This article describes the nuclear free zone movement, explores relevant legal questions, and shows how the political potential of nuclear free zones threatens to open a deep rift in the American constitutional system.

  1. Nasal field loss in cats reared with convergent squint: behavioural studies.

    PubMed Central

    Ikeda, H; Jacobson, S G

    1977-01-01

    1. The extent of the monocular visual field in cats reared with convergent squint in one eye was determined by a behavioural perimetry technique. 2. Significant reduction in the extent of the visual field was found in the squinting eyes. 3. The visual field defect is a graded one, located mainly in the nasal field, but in some cats extending into the temporal visual field. The defect includes a zone of absolute loss of response to stimuli at the extreme nasal field, adjacent areas of partial response and areas of 100% response in the periphery of the temporal field. 4. A direct relationship was found between the angle of horizontal deviation of the squinting eye and the amount of visual field loss: i.e. the larger the angle of squint, the greater the loss of nasal field. 5. It is suggested that the process leading to a loss in nasal visual field is independent of the loss of visual acuity in squinting cats, since the latter is not related to the angle of squint. 6. The significant loss in nasal visual field found by behavioural experiments in cats reared with a convergent squint thus correlates with comparable deficits found in the physiology and morphology of the lateral geniculate nucleus (Ikeda, Plant & Tremain, 1977), although the behaviourally determined loss of nasal field is greater than would be expected from the study of the response of the LGN neurones. PMID:903899

  2. Deformation partitioning during polyphase oblique convergence in the Karawanken Mountains, southeastern Alps

    NASA Astrophysics Data System (ADS)

    Polinski, Ralf K.; Eisbacher, Gerhard H.

    1992-11-01

    The Karawanken Mountains of southeastern Austria straddle the Insubric Line, a major fault zone that corresponds to the Austroalpine-South Alpine border of the eastern Alps. They display polyphase structural patterns that resulted from deformation partitioning at shallow crustal levels. Following a poorly constrained late Cretaceous deformation history, Paleogene contraction produced NW—SE-trending fold—thrust structures and possibly related sinistral (?) cross faults. Miocene deformation produced both NW- and SE-directed thrust faults and NW-striking high-angle dextral cross faults which merged with or displaced the W-striking Insubric Line. Distributed dextral strike-slip displacements of the order of 30-40 km and thrust displacement of 4-5 km along the northern Karawanken front initiated subsidence of a small foreland basin north of the Karawanken Mountains. Recent regional deformation seems to be concentrated along cross-cutting NNW-striking dextral faults within a shifting system of seismogenic transfer faults that probably merge with the convergent South Alpine thrust front to the west. There are conspicuous parallels in the style of deformation along the Karawanken Mountains with that found along other seismogenic convergent strike-slip faults, such as those of southern California, New Zealand and Anatolia.

  3. Convergent evolution and divergent selection: lizards at the White Sands ecotone.

    PubMed

    Rosenblum, Erica Bree

    2006-01-01

    Ecological transition zones, where organismal phenotypes result from a delicate balance between selection and migration, highlight the interplay of local adaptation and gene flow. Here, I study the response of an entire species assemblage to natural selection across a common ecotone. Three lizard species, distributed along a dramatic environmental gradient in substrate color, display convergent adaptation of blanched coloration on the gypsum dunes of White Sands National Monument. I investigate the role of gene flow in modulating phenotypic response to selection by quantifying color variation and genetic variation across the ecotone. I find species differences in degree of background matching and in genetic connectivity of populations across the ecotone. Differences among species in phenotypic response to selection scale precisely to levels of genetic isolation. Species with higher levels of gene flow across the ecotone exhibit less dramatic responses to selection. Results also reveal a strong signal of ecologically mediated divergence for White Sands lizards. For all species, phenotypic variation is better explained by habitat similarity than genetic similarity. Convergent evolution of blanched coloration at White Sands clearly reflects the action of strong divergent selection; however, adaptive response appears to be modulated by gene flow and demographic history and can be predicted by divergence-with-gene-flow models.

  4. Synaptic potentials evoked by convergent somatosensory and corticocortical inputs in raccoon somatosensory cortex: substrates for plasticity.

    PubMed

    Smits, E; Gordon, D C; Witte, S; Rasmusson, D D; Zarzecki, P

    1991-09-01

    1. "Unmasking" of weak synaptic connections has been suggested as a mechanism for the early changes in cortical topographic maps that follow alterations of sensory activity. For such a mechanism to operate, convergent sensory inputs must already exist in the normal cortex. 2. We tested for topographic and cross-modality convergence in primary somatosensory cortex of raccoon. The representation of glabrous skin of forepaw digits was chosen because, even though it is dominated by inputs from the glabrous skin of a single digit, it nevertheless comes to respond to stimulation of other digits when, e.g., a digit is removed. 3. Intracellular recordings were made from 109 neurons in the representation of glabrous skin of digit 4. Neurons were tested for somatosensory inputs with electrical and natural stimulation of digits. 4. Excitatory postsynaptic potentials (EPSPs) were evoked in 100% of the neurons (109/109) by electrical stimulation of glabrous skin of digit 4, and in 79% (31 of 39) by vibrotactile stimulation. 5. Glabrous skin of digit 4 was not the sole source of somatosensory inputs. A minority of neurons generated EPSPs after electrical stimulation of hairy skin of digit 4 (10 of 98 neurons, 10%). Electrical stimulation of digits 3 or 5 evoked EPSPs in 22 of 103 neurons (21%). Natural stimulation (vibrotactile or hair bending) was also effective in most of these latter cases (digit 3, 6/7; digit 5, 9/10). 6. Intracortical microstimulation of the "heterogeneous zone" was used to test for corticocortical connections to neurons in the glabrous zone.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1753280

  5. Convergence and non-convergence in ecological, phenotypic, and genetic divergence across replicate population pairs of lake and stream stickleback

    PubMed Central

    Kaeuffer, Renaud; Peichel, Catherine L.; Bolnick, Daniel I.; Hendry, Andrew P.

    2015-01-01

    Convergent (or parallel) evolution provides strong evidence for a deterministic role of natural selection: similar phenotypes evolve when independent populations colonize similar environments. In reality, however, independent populations in similar environments always show some differences: some non-convergent evolution is present. It is therefore important to explicitly quantify the convergent and non-convergent aspects of trait variation, and to investigate the ecological and genetic explanations for each. We performed such an analysis for threespine stickleback (Gasterosteus aculeatus) populations inhabiting lake and stream habitats in independent watersheds. Morphological traits differed in the degree to which lake-stream divergence was convergent across watersheds. Some aspects of this variation were correlated with ecological variables related to diet, presumably reflecting the strength and specifics of divergent selection. Furthermore, a genetic scan revealed some markers that diverged between lakes and streams in many of the watersheds and some that diverged in only a few watersheds. Moreover, some of the lake-stream divergence in genetic markers was associated within some of the lake-stream divergence in morphological traits. Our results suggest that convergent evolution, and deviations from it, are primarily the result of natural selection, which corresponds in only some respect to the dichotomous habitat classifications frequently used in such studies. PMID:22276537

  6. FORTRAN source listing for simulating three-dimensional convergent beam patterns with absorption by the Bloch wave method.

    PubMed

    Zuo, J M; Gjonnes, K; Spence, J C

    1989-05-01

    The FORTRAN source code is given for a computer program that calculates the two-dimensional intensity distribution in convergent-beam transmission electron microdiffraction (CBED) patterns from perfect crystals. The program uses the eigenvalue or Bloch-wave method. It allows three-dimensional dynamical diffraction, and so includes all higher-order Laue zone effects without approximation. No symmetry reduction is included. The program accepts noncentrosymmetric or centrosymmetric crystal structures and allows absorption corrections to be included. It uses the "EISPACK" subroutines for the diagonalisation of a general complex matrix. Up to 100 CBED disks may be included. The code is also available via "Bitnet."

  7. Zones of Peace.

    ERIC Educational Resources Information Center

    Evans, Judith L.; And Others

    1996-01-01

    Children affected by armed violence face a specific set of stressors and challenges which calls for appropriate programming. This Coordinator's Notebook focuses on how to work with children affected by organized violence in order to provide them the best possible early childhood experiences. It is divided into five sections. "Children as Zones of…

  8. Fast aurora zone analysis

    NASA Technical Reports Server (NTRS)

    Booker, Mattie

    1992-01-01

    The Flight Dynamics Facility (FDF) of the Flight Dynamics Division (FDD), of the Goddard Space Flight Center provides acquisition data to tracking stations and orbit and attitude services to scientists and mission support personnel. The following paper explains how a method was determined that found spacecraft entry and exit times of the aurora zone.

  9. Analysis of sponge zones for computational fluid mechanics

    SciTech Connect

    Bodony, Daniel J. . E-mail: bodony@stanford.edu

    2006-03-01

    The use of sponge regions, or sponge zones, which add the forcing term -{sigma}(q - q {sub ref}) to the right-hand-side of the governing equations in computational fluid mechanics as an ad hoc boundary treatment is widespread. They are used to absorb and minimize reflections from computational boundaries and as forcing sponges to introduce prescribed disturbances into a calculation. A less common usage is as a means of extending a calculation from a smaller domain into a larger one, such as in computing the far-field sound generated in a localized region. By analogy to the penalty method of finite elements, the method is placed on a solid foundation, complete with estimates of convergence. The analysis generalizes the work of Israeli and Orszag [M. Israeli, S.A. Orszag, Approximation of radiation boundary conditions, J. Comp. Phys. 41 (1981) 115-135] and confirms their findings when applied as a special case to one-dimensional wave propagation in an absorbing sponge. It is found that the rate of convergence of the actual solution to the target solution, with an appropriate norm, is inversely proportional to the sponge strength. A detailed analysis for acoustic wave propagation in one-dimension verifies the convergence rate given by the general theory. The exponential point-wise convergence derived by Israeli and Orszag in the high-frequency limit is recovered and found to hold over all frequencies. A weakly nonlinear analysis of the method when applied to Burgers' equation shows similar convergence properties. Three numerical examples are given to confirm the analysis: the acoustic extension of a two-dimensional time-harmonic point source, the acoustic extension of a three-dimensional initial-value problem of a sound pulse, and the introduction of unstable eigenmodes from linear stability theory into a two-dimensional shear layer.

  10. Indirectly driven, high-convergence implosions (HEP1)

    SciTech Connect

    Hatchett, S.P.; Cable, M.D.; Caird, J.A.

    1996-06-01

    High-gain inertial confinement fusion will most readily be achieved with hot-spot ignition, in which a relatively small mass of gaseous fuel at the center of the target is heated to 5-10 keV, igniting a larger surrounding mass of approximately isobaric fuel at higher density but lower temperature. Existing lasers are too low in energy to achieve thermonuclear gain, but hydrodynamically equivalent implosions using these lasers can demonstrate that the important, scalable parameters of ignition capsules are scientifically and technologically achievable. The experiments described in this article used gas-filled glass shells driven by x rays produced in a surrounding cavity, or hohlraum. These implosions achieved convergence ratios (initial capsule radius/ final fuel radius) high enough to fall in the range required for ignition-scale capsules, and they produced an imploded configuration (high-density glass with hot gas fill) that is equivalent to the hot-spot configuration of an ignition-scale capsule. Other recent laser-driven implosions have achieved high shell density but at lower convergences and without a well defined hot spot. Still other experiments have used very-low-density gas fill to reach high convergence with unshaped drive, but that approach results in a relatively low shell density. Moreover, even at the highest convergence ratios the implosions described here had neutron yields averaging 8% of that calculated for an idealized, clean, spherically symmetric implosion - much higher than previous high-convergence experiments.

  11. Convergence in pigmentation at multiple levels: mutations, genes and function

    PubMed Central

    Manceau, Marie; Domingues, Vera S.; Linnen, Catherine R.; Rosenblum, Erica Bree; Hoekstra, Hopi E.

    2010-01-01

    Convergence—the independent evolution of the same trait by two or more taxa—has long been of interest to evolutionary biologists, but only recently has the molecular basis of phenotypic convergence been identified. Here, we highlight studies of rapid evolution of cryptic coloration in vertebrates to demonstrate that phenotypic convergence can occur at multiple levels: mutations, genes and gene function. We first show that different genes can be responsible for convergent phenotypes even among closely related populations, for example, in the pale beach mice inhabiting Florida's Gulf and Atlantic coasts. By contrast, the exact same mutation can create similar phenotypes in distantly related species such as mice and mammoths. Next, we show that different mutations in the same gene need not be functionally equivalent to produce similar phenotypes. For example, separate mutations produce divergent protein function but convergent pale coloration in two lizard species. Similarly, mutations that alter the expression of a gene in different ways can, nevertheless, result in similar phenotypes, as demonstrated by sister species of deer mice. Together these studies underscore the importance of identifying not only the genes, but also the precise mutations and their effects on protein function, that contribute to adaptation and highlight how convergence can occur at different genetic levels. PMID:20643733

  12. Monte Carlo source convergence and the Whitesides problem

    SciTech Connect

    Blomquist, R. N.

    2000-02-25

    The issue of fission source convergence in Monte Carlo eigenvalue calculations is of interest because of the potential consequences of erroneous criticality safety calculations. In this work, the authors compare two different techniques to improve the source convergence behavior of standard Monte Carlo calculations applied to challenging source convergence problems. The first method, super-history powering, attempts to avoid discarding important fission sites between generations by delaying stochastic sampling of the fission site bank until after several generations of multiplication. The second method, stratified sampling of the fission site bank, explicitly keeps the important sites even if conventional sampling would have eliminated them. The test problems are variants of Whitesides' Criticality of the World problem in which the fission site phase space was intentionally undersampled in order to induce marginally intolerable variability in local fission site populations. Three variants of the problem were studied, each with a different degree of coupling between fissionable pieces. Both the superhistory powering method and the stratified sampling method were shown to improve convergence behavior, although stratified sampling is more robust for the extreme case of no coupling. Neither algorithm completely eliminates the loss of the most important fissionable piece, and if coupling is absent, the lost piece cannot be recovered unless its sites from earlier generations have been retained. Finally, criteria for measuring source convergence reliability are proposed and applied to the test problems.

  13. The Road to Convergence in Earthquake Frequency-Magnitude Statistics

    NASA Astrophysics Data System (ADS)

    Naylor, M.; Bell, A. F.; Main, I. G.

    2013-12-01

    The Gutenberg-Richter frequency-magnitude relation is a fundamental empirical law of seismology, but its form remains uncertain for rare extreme events. Convergence trends can be diagnostic of the nature of an underlying distribution and its sampling even before convergence has occurred. We examine the evolution of an information criteria metric applied to earthquake magnitude time series, in order to test whether the Gutenberg-Richter law can be rejecting in various earthquake catalogues. This would imply that the catalogue is starting to sample roll-off in the tail though it cannot yet identify the form of the roll-off. We compare bootstrapped synthetic Gutenberg-Richter and synthetic modified Gutenberg-Richter catalogues with the convergence trends observed in real earthquake data e.g. the global CMT catalogue, Southern California and mining/geothermal data. Whilst convergence in the tail remains some way off, we show that the temporal evolution of model likelihoods and parameters for the frequency-magnitude distribution of the global Harvard Centroid Moment Tensor catalogue is inconsistent with an unbounded GR relation, despite it being the preferred model at the current time. Bell, A. F., M. Naylor, and I. G. Main (2013), Convergence of the frequency-size distribution of global earthquakes, Geophys. Res. Lett., 40, 2585-2589, doi:10.1002/grl.50416.

  14. Independent Molecular Basis of Convergent Highland Adaptation in Maize.

    PubMed

    Takuno, Shohei; Ralph, Peter; Swarts, Kelly; Elshire, Rob J; Glaubitz, Jeffrey C; Buckler, Edward S; Hufford, Matthew B; Ross-Ibarra, Jeffrey

    2015-08-01

    Convergent evolution is the independent evolution of similar traits in different species or lineages of the same species; this often is a result of adaptation to similar environments, a process referred to as convergent adaptation. We investigate here the molecular basis of convergent adaptation in maize to highland climates in Mesoamerica and South America, using genome-wide SNP data. Taking advantage of archaeological data on the arrival of maize to the highlands, we infer demographic models for both populations, identifying evidence of a strong bottleneck and rapid expansion in South America. We use these models to then identify loci showing an excess of differentiation as a means of identifying putative targets of natural selection and compare our results to expectations from recently developed theory on convergent adaptation. Consistent with predictions across a wide parameter space, we see limited evidence for convergent evolution at the nucleotide level in spite of strong similarities in overall phenotypes. Instead, we show that selection appears to have predominantly acted on standing genetic variation and that introgression from wild teosinte populations appears to have played a role in highland adaptation in Mexican maize.

  15. Simulating Roll Clouds associated with Low-Level Convergence.

    NASA Astrophysics Data System (ADS)

    Prasad, A. A.; Sherwood, S. C.

    2015-12-01

    Convective initiation often takes place when features such as fronts and/or rolls collide, merge or otherwise meet. Rolls indicate boundary layer convergence and may initiate thunderstorms. These are often seen in satellite and radar imagery prior to the onset of deep convection. However, links between convergence driven rolls and convection are poor in global models. The poor representation of convection is the source of many model biases, especially over the Maritime Continent in the Tropics. We simulate low-level convergence lines over north-eastern Australia using the Weather Research and Forecasting (WRF) Model (version 3.7). The simulations are events from September-October 2002 driven by sea breeze circulations. Cloud lines associated with bore-waves that form along the low-level convergence lines are thoroughly investigated in this study with comparisons from satellite and surface observations. Initial simulations for a series of cloud lines observed on 4th October, 2002 over the Gulf of Carpentaria showed greater agreement in the timing and propagation of the disturbance and the low-level convergence, however the cloud lines or streets of roll clouds were not properly captured by the model. Results from a number of WRF simulations with different microphysics, cumulus and planetary boundary layer schemes, resolution and boundary conditions will also be discussed.

  16. PROBABILITY DISTRIBUTION FUNCTIONS OF COSMOLOGICAL LENSING: CONVERGENCE, SHEAR, AND MAGNIFICATION

    SciTech Connect

    Takahashi, Ryuichi; Oguri, Masamune; Sato, Masanori; Hamana, Takashi

    2011-11-20

    We perform high-resolution ray-tracing simulations to investigate probability distribution functions (PDFs) of lensing convergence, shear, and magnification on distant sources up to the redshift of z{sub s} = 20. We pay particular attention to the shot noise effect in N-body simulations by explicitly showing how it affects the variance of the convergence. We show that the convergence and magnification PDFs are closely related to each other via the approximate relation {mu} = (1 - {kappa}){sup -2}, which can reproduce the behavior of PDFs surprisingly well up to the high magnification tail. The mean convergence measured in the source plane is found to be systematically negative, rather than zero as often assumed, and is correlated with the convergence variance. We provide simple analytical formulae for the PDFs, which reproduce simulated PDFs reasonably well for a wide range of redshifts and smoothing sizes. As explicit applications of our ray-tracing simulations, we examine the strong-lensing probability and the magnification effects on the luminosity functions of distant galaxies and quasars.

  17. Adaptive processes drive ecomorphological convergent evolution in antwrens (Thamnophilidae).

    PubMed

    Bravo, Gustavo A; Remsen, J V; Brumfield, Robb T

    2014-10-01

    Phylogenetic niche conservatism (PNC) and convergence are contrasting evolutionary patterns that describe phenotypic similarity across independent lineages. Assessing whether and how adaptive processes give origin to these patterns represent a fundamental step toward understanding phenotypic evolution. Phylogenetic model-based approaches offer the opportunity not only to distinguish between PNC and convergence, but also to determine the extent that adaptive processes explain phenotypic similarity. The Myrmotherula complex in the Neotropical family Thamnophilidae is a polyphyletic group of sexually dimorphic small insectivorous forest birds that are relatively homogeneous in size and shape. Here, we integrate a comprehensive species-level molecular phylogeny of the Myrmotherula complex with morphometric and ecological data within a comparative framework to test whether phenotypic similarity is described by a pattern of PNC or convergence, and to identify evolutionary mechanisms underlying body size and shape evolution. We show that antwrens in the Myrmotherula complex represent distantly related clades that exhibit adaptive convergent evolution in body size and divergent evolution in body shape. Phenotypic similarity in the group is primarily driven by their tendency to converge toward smaller body sizes. Differences in body size and shape across lineages are associated to ecological and behavioral factors.

  18. PARTICLE-GAS DYNAMICS WITH ATHENA: METHOD AND CONVERGENCE

    SciTech Connect

    Bai Xuening; Stone, James M. E-mail: jstone@astro.princeton.ed

    2010-10-15

    The Athena magnetohydrodynamics code has been extended to integrate the motion of particles coupled with the gas via aerodynamic drag in order to study the dynamics of gas and solids in protoplanetary disks (PPDs) and the formation of planetesimals. Our particle-gas hybrid scheme is based on a second-order predictor-corrector method. Careful treatment of the momentum feedback on the gas guarantees exact conservation. The hybrid scheme is stable and convergent in most regimes relevant to PPDs. We describe a semi-implicit integrator generalized from the leap-frog approach. In the absence of drag force, it preserves the geometric properties of a particle orbit. We also present a fully implicit integrator that is unconditionally stable for all regimes of particle-gas coupling. Using our hybrid code, we study the numerical convergence of the nonlinear saturated state of the streaming instability. We find that gas flow properties are well converged with modest grid resolution (128 cells per pressure length {eta}r for dimensionless stopping time {tau} {sub s} = 0.1) and an equal number of particles and grid cells. On the other hand, particle clumping properties converge only at higher resolutions, and finer resolution leads to stronger clumping before convergence is reached. Finally, we find that the measurement of particle transport properties resulted from the streaming instability may be subject to error of about {+-}20%.

  19. Reflection of cylindrical converging shock wave over a plane wedge

    NASA Astrophysics Data System (ADS)

    Zhang, Fu; Si, Ting; Zhai, Zhigang; Luo, Xisheng; Yang, Jiming; Lu, Xiyun

    2016-08-01

    The cylindrical converging shock reflection over a plane wedge is investigated experimentally and numerically in a specially designed shock tube which converts a planar shock into a cylindrical one. When the converging shock is moving along the wedge, both the shock strength and the incident angle are changing, which provides the possibility for the wave transition. The results show that both regular reflection (RR) and Mach reflection (MR) are found on the wedge with different initial incident angles. The wave transitions from direct Mach reflection (DiMR) to inverse Mach reflection (InMR) and further to transitioned regular reflection (TRR) are observed with appropriate initial incident angles. The instability development in the shear layer and strong vortices formation near the wall are evident, which are ascribed not only to the interaction of two shear layers but also to the shock impact and the shock converging effect. Because of the flow unsteadiness after the converging shock, the detachment criterion provides a good estimation for the RR → MR transition, but fails to predict the DiMR → InMR transition, and MR is found to persist slightly below the mechanical equilibrium condition. A hysteresis process is found in the MR → TRR transition and becomes more apparent as the increase of the initial incident angle due to the shock converging effect.

  20. Evolution of parasitism along convergent lines: from ecology to genomics.

    PubMed

    Poulin, Robert; Randhawa, Haseeb S

    2015-02-01

    SUMMARY From hundreds of independent transitions from a free-living existence to a parasitic mode of life, separate parasite lineages have converged over evolutionary time to share traits and exploit their hosts in similar ways. Here, we first summarize the evidence that, at a phenotypic level, eukaryotic parasite lineages have all converged toward only six general parasitic strategies: parasitoid, parasitic castrator, directly transmitted parasite, trophically transmitted parasite, vector-transmitted parasite or micropredator. We argue that these strategies represent adaptive peaks, with the similarities among unrelated taxa within any strategy extending to all basic aspects of host exploitation and transmission among hosts and transcending phylogenetic boundaries. Then, we extend our examination of convergent patterns by looking at the evolution of parasite genomes. Despite the limited taxonomic coverage of sequenced parasite genomes currently available, we find some evidence of parallel evolution among unrelated parasite taxa with respect to genome reduction or compaction, and gene losses or gains. Matching such changes in parasite genomes with the broad phenotypic traits that define the convergence of parasites toward only six strategies of host exploitation is not possible at present. Nevertheless, as more parasite genomes become available, we may be able to detect clear trends in the evolution of parasitic genome architectures representing true convergent adaptive peaks, the genomic equivalents of the phenotypic strategies used by all parasites. PMID:24229807

  1. Accelerate OPC convergence with new iteration control methodology

    NASA Astrophysics Data System (ADS)

    Wang, Ching-Heng; Liu, Qingwei; Zhang, Liguo

    2008-10-01

    A dilemmatic trade-off that all OPC engineers are facing everyday is the convergence of the OPC result and the control of the OPC iteration times. Theoretically, infinite times of OPC iterations are needed to achieve a convergent and stable correction result. But actually there should always be a cut-off for the iteration time, for turnaround- time is always an important criteria for IC fabs. But considering the design layout becomes more complicated and pattern density becomes higher with the shrinkage of the critical dimension, fragmentation control during the OPC procedure is also becoming more and more sophisticated. Thus, to achieve a convergent correction result for all OPC fragments within limited correction iteration times now becomes a big challenge to OPC engineers. This work presents our study in a new OPC iteration control methodology. It can help to find an algorithm that always converges, and reduce the excessive use of parameter setting, commands and other involvement by the user. With this, we can reduce the run time required to obtain a convergent OPC solution.

  2. Convergence of sensory inputs upon projection neurons of somatosensory cortex.

    PubMed

    Zarzecki, P; Wiggin, D M

    1982-01-01

    Cortico-cortical neurons and pyramidal tract neurons of the cat were tested for convergent inputs from forelimb afferents. Neurons were recorded in cortical areas 1, 2, and 3a. Consideration was given to both suprathreshold and subthreshold inputs evoked by electrical stimulation of forelimb nerves. Individual cortico-cortical neurons and also pyramidal tract neurons were characterized by convergence of multiple somatosensory inputs from different regions of skin, from several muscle groups, and between group I deep afferents and low threshold cutaneous afferents. Certain patterns of afferent input varied with cytoarchitectonic area. There was, however, no difference between area 3a and areas 1-2 in the incidence of cross-modality convergence in the form of input from cutaneous and also deep nerves. Many of the inputs were subthreshold. Arguments are presented that these inputs, though subthreshold, must be considered for a role in cortical information processing. The convergent nature of the sensory inputs is discussed in relation to the proposed specificities of cortical columns. The patterns of afferent inputs reaching cortico-cortical neurons seem to be appropriate for them to have a role in the formation of sensory fields of motor cortex neurons. PT neurons of somatosensory cortex have possible roles as modifiers of ascending sensory systems, however, the convergent input which these PT neurons receive argues against a simple relationship between the modality of peripheral stimuli influencing them and the modality of the ascending tract neurons under their descending control. PMID:7140889

  3. Short‐term time step convergence in a climate model

    PubMed Central

    Rasch, Philip J.; Taylor, Mark A.; Jablonowski, Christiane

    2015-01-01

    Abstract This paper evaluates the numerical convergence of very short (1 h) simulations carried out with a spectral‐element (SE) configuration of the Community Atmosphere Model version 5 (CAM5). While the horizontal grid spacing is fixed at approximately 110 km, the process‐coupling time step is varied between 1800 and 1 s to reveal the convergence rate with respect to the temporal resolution. Special attention is paid to the behavior of the parameterized subgrid‐scale physics. First, a dynamical core test with reduced dynamics time steps is presented. The results demonstrate that the experimental setup is able to correctly assess the convergence rate of the discrete solutions to the adiabatic equations of atmospheric motion. Second, results from full‐physics CAM5 simulations with reduced physics and dynamics time steps are discussed. It is shown that the convergence rate is 0.4—considerably slower than the expected rate of 1.0. Sensitivity experiments indicate that, among the various subgrid‐scale physical parameterizations, the stratiform cloud schemes are associated with the largest time‐stepping errors, and are the primary cause of slow time step convergence. While the details of our findings are model specific, the general test procedure is applicable to any atmospheric general circulation model. The need for more accurate numerical treatments of physical parameterizations, especially the representation of stratiform clouds, is likely common in many models. The suggested test technique can help quantify the time‐stepping errors and identify the related model sensitivities.

  4. Independent Molecular Basis of Convergent Highland Adaptation in Maize

    PubMed Central

    Takuno, Shohei; Ralph, Peter; Swarts, Kelly; Elshire, Rob J.; Glaubitz, Jeffrey C.; Buckler, Edward S.; Hufford, Matthew B.; Ross-Ibarra, Jeffrey

    2015-01-01

    Convergent evolution is the independent evolution of similar traits in different species or lineages of the same species; this often is a result of adaptation to similar environments, a process referred to as convergent adaptation. We investigate here the molecular basis of convergent adaptation in maize to highland climates in Mesoamerica and South America, using genome-wide SNP data. Taking advantage of archaeological data on the arrival of maize to the highlands, we infer demographic models for both populations, identifying evidence of a strong bottleneck and rapid expansion in South America. We use these models to then identify loci showing an excess of differentiation as a means of identifying putative targets of natural selection and compare our results to expectations from recently developed theory on convergent adaptation. Consistent with predictions across a wide parameter space, we see limited evidence for convergent evolution at the nucleotide level in spite of strong similarities in overall phenotypes. Instead, we show that selection appears to have predominantly acted on standing genetic variation and that introgression from wild teosinte populations appears to have played a role in highland adaptation in Mexican maize. PMID:26078279

  5. Convergence of the solution method for variational inequalities

    SciTech Connect

    Panin, V.M.; Aleksandrova, V.M.

    1995-01-01

    We study the properties of the method proposed in literature for solving variational inequalities and its modifications. Linear convergence in the neighborhood of the solution is established for problems that satisfy second-order sufficient conditions. The problem of finding the solution x{sub *} of the variational inequality (F(x{sub *}), x-x{sub *}) {ge} 0, {forall} x {element_of} {Omega} = (x{element_of}R{sup n}{vert_bar} f{sub i}(x){le}O, i=1,...,l) has been studied by many authors. The numerical methods considered by them, despite their theoretically fast rate of convergence, usually converge only locally and are computationally highly complex, because each iteration solves auxiliary subproblems on the original nonlinear set {Omega}. In other methods, on the other hand, each iteration is efficiently executed and converges nonlocally to the solution, but we do not have the rate of convergence bounds which are typical for mathematical programming methods of the corresponding order.

  6. Analog models of convergence and divergence: perspectives of the tectonics of the Middle East

    NASA Astrophysics Data System (ADS)

    Mart, Yossi

    2010-05-01

    Three series of analog models of convergence and divergence of tectonic plates illuminate the possible tectonic processes that shaped the lithology of the Middle East since the early Miocene. The Mid-East geographic province extends from the Ionian Sea to the Arabian Sea, and comprises the Hellenic subduction zone, the Aegean back-arc basin, the motion of Anatolia southwestwards, the oblique collision of Arabia and Iran along the Zagros suture, and the continental break-up of the Gulf of Aden and the Red Sea. The tectonic evolution of all these diverse domains started in the Miocene nearly contemporaneously, and modeling suggests that the convergence and divergence, though derived from unrelated processes, their tectonics is intertwined. Centrifuge models of the initiation of subduction show the correlation between early subduction and the opening of its back-arc basin (Mart et al., 2005). The models emphasize the significance of extensive seawards roll-back of the deformation front when friction between the thrust slabs is reduced, and consequently, the pull within the overthrust slab that leads to its structural extension. That extension produced the Aegean domain with its volcanism and the exposure of its core complex, as well as the westwards displacement of Anatolia along the North and East Anatolian Faults. Sand-box models of oblique subduction, namely the gradual shift from subduction to collision along the convergence front, showed orthogonal patterns of extension in distal parts of the underthrust slab (Bellahsen et al., 2002). It is suggested that the extensional domains deflected the propagation of Carlsberg Ridge to swing 1200 and penetrate the Gulf of Aden in the early Miocene. The structural differences between the Gulf of Aden and the Red Sea can be accounted for by the results of sand-box experiments in oblique rifting (Mart and Dauteuil, 2000). The models suggest that oblique rifting, where the deviation from the normal extension was ca. 50, would

  7. An accelerated and convergent iterative algorithm in image reconstruction

    NASA Astrophysics Data System (ADS)

    Yan, Jianhua; Yu, Jun

    2007-05-01

    Positron emission tomography (PET) is becoming increasingly important in the field of medicine and biology. The maximum-likelihood expectation-maximization (ML-EM) algorithm is becoming more important than filtered back-projection (FBP) algorithm which can incorporate various physical models into image reconstruction scheme. However, ML-EM converges slowly. In this paper, we propose a new algorithm named AC-ML-EM (accelerated and convergent maximum likelihood expectation maximization) by introducing gradually decreasing correction factor into ML-EM. AC-ML-EM has a higher speed of convergence. Through the experiments of computer simulated phantom data and real phantom data, AC-ML-EM is shown faster and better quantitatively than conventional ML-EM algorithm.

  8. Exponential convergence through linear finite element discretization of stratified subdomains

    NASA Astrophysics Data System (ADS)

    Guddati, Murthy N.; Druskin, Vladimir; Vaziri Astaneh, Ali

    2016-10-01

    Motivated by problems where the response is needed at select localized regions in a large computational domain, we devise a novel finite element discretization that results in exponential convergence at pre-selected points. The key features of the discretization are (a) use of midpoint integration to evaluate the contribution matrices, and (b) an unconventional mapping of the mesh into complex space. Named complex-length finite element method (CFEM), the technique is linked to Padé approximants that provide exponential convergence of the Dirichlet-to-Neumann maps and thus the solution at specified points in the domain. Exponential convergence facilitates drastic reduction in the number of elements. This, combined with sparse computation associated with linear finite elements, results in significant reduction in the computational cost. The paper presents the basic ideas of the method as well as illustration of its effectiveness for a variety of problems involving Laplace, Helmholtz and elastodynamics equations.

  9. Two-level method with coarse space size independent convergence

    SciTech Connect

    Vanek, P.; Brezina, M.; Tezaur, R.; Krizkova, J.

    1996-12-31

    The basic disadvantage of the standard two-level method is the strong dependence of its convergence rate on the size of the coarse-level problem. In order to obtain the optimal convergence result, one is limited to using a coarse space which is only a few times smaller than the size of the fine-level one. Consequently, the asymptotic cost of the resulting method is the same as in the case of using a coarse-level solver for the original problem. Today`s two-level domain decomposition methods typically offer an improvement by yielding a rate of convergence which depends on the ratio of fine and coarse level only polylogarithmically. However, these methods require the use of local subdomain solvers for which straightforward application of iterative methods is problematic, while the usual application of direct solvers is expensive. We suggest a method diminishing significantly these difficulties.

  10. Convergent WKB Series--How Can It be ?

    SciTech Connect

    Ezawa, Hiroshi; Nakamura, Toru; Watanabe, Keiji

    2008-06-18

    Schroedinger equation for a polynomial potential with the highest order term having an even power and a positive coefficient is solved for high eigenvalues E{sub n} in two different ways after Liouville transformation, (a) converting the differential equation into integral equation and solving it iteratively and (b) by the WKB method. While the series solution in powers of 1/{radical}(E{sub n}) from (b) is known to diverge, we show that the one from (a) converges. We show then that asymptotic re-expansion of the convergent series from (a) agrees with the divergent series from (b). Actually, we have been able to show the agreement only up to order (1/{radical}(E{sub n})){sup 5}, but we believe that it holds to all orders. If this is true, the divergent WKB series can be reorganized into a convergent series, which is in fact obtained by the method of iteration (a)

  11. Converging paradigms for environmental health theory and practice.

    PubMed Central

    Parkes, Margot; Panelli, Ruth; Weinstein, Philip

    2003-01-01

    Converging themes from the fields of environmental health, ecology and health, and human ecology highlight opportunities for innovation and advancement in environmental health theory and practice. In this commentary we outline the role of research and applied programs that integrate biophysical and social sciences with environmental health practice in order to address deficiencies in each field when taken on its own. New opportunities for environmental health protection and promotion are outlined based on the three converging themes: integrated approaches to research and policy, methodological acknowledgment of the synergies between the social and biophysical environments, and incorporation of core ecosystem principles into research and practice. These converging themes are discussed in relation to their implications for new types of intervention to achieve health gains across different spatial and temporal scales at the interface between biophysical and social environments. PMID:12727592

  12. Searching for converging research using field to field citations

    PubMed Central

    Noyons, Ed. C. M.; Van Raan, Anthony F. J.

    2010-01-01

    We define converging research as the emergence of an interdisciplinary research area from fields that did not show interdisciplinary connections before. This paper presents a process to search for converging research using journal subject categories as a proxy for fields and citations to measure interdisciplinary connections, as well as an application of this search. The search consists of two phases: a quantitative phase in which pairs of citing and cited fields are located that show a significant change in number of citations, followed by a qualitative phase in which thematic focus is sought in publications associated with located pairs. Applying this search on publications from the Web of Science published between 1995 and 2005, 38 candidate converging pairs were located, 27 of which showed thematic focus, and 20 also showed a similar focus in the other, reciprocal pair. PMID:21297857

  13. Convergence of the frequency-size distribution of global earthquakes

    NASA Astrophysics Data System (ADS)

    Bell, Andrew F.; Naylor, Mark; Main, Ian G.

    2013-06-01

    The Gutenberg-Richter (GR) frequency-magnitude relation is a fundamental empirical law of seismology, but its form remains uncertain for rare extreme events. Here, we show that the temporal evolution of model likelihoods and parameters for the frequency-magnitude distribution of the global Harvard Centroid Moment Tensor catalog is inconsistent with an unbounded GR relation, despite if being the preferred model at the current time. During the recent spate of 12 great earthquakes in the last 8 years, record-breaking events result in profound steps in favor of the unbounded GR relation. However, between such events the preferred model gradually converges to the tapered GR relation, and the form of the convergence cannot be explained by random sampling of an unbounded GR distribution. The convergence properties are consistent with a global catalog composed of superposed randomly-sampled regional catalogs, each with different upper bounds, many of which have not yet sampled their largest event.

  14. Toward a convergence of regenerative medicine, rehabilitation, and neuroprosthetics.

    PubMed

    Aravamudhan, Shyam; Bellamkonda, Ravi V

    2011-11-01

    No effective therapeutic interventions exist for severe neural pathologies, despite significant advances in regenerative medicine, rehabilitation, and neuroprosthetics. Our current hypothesis is that a specific combination of tissue engineering, pharmacology, cell replacement, drug delivery, and electrical stimulation, together with plasticity-promoting and locomotor training (neurorehabilitation) is necessary to interact synergistically in order to activate and enable all damaged circuits. We postulate that various convergent themes exist among the different therapeutic fields. Therefore, the objective of this review is to highlight the convergent themes, which we believe have a common goal of restoring function after neural damage. The convergent themes discussed in this review include modulation of inflammation and secondary damage, encouraging endogenous repair/regeneration (using scaffolds, cell transplantation, and drug delivery), application of electrical fields to modulate healing and/or activity, and finally modulation of plasticity.

  15. Convergence of complex cognitive abilities in cetaceans and primates.

    PubMed

    Marino, Lori

    2002-01-01

    What examples of convergence in higher-level complex cognitive characteristics exist in the animal kingdom? In this paper I will provide evidence that convergent intelligence has occurred in two distantly related mammalian taxa. One of these is the order Cetacea (dolphins, whales and porpoises) and the other is our own order Primates, and in particular the suborder anthropoid primates (monkeys, apes, and humans). Despite a deep evolutionary divergence, adaptation to physically dissimilar environments, and very different neuroanatomical organization, some primates and cetaceans show striking convergence in social behavior, artificial 'language' comprehension, and self-recognition ability. Taken together, these findings have important implications for understanding the generality and specificity of those processes that underlie cognition in different species and the nature of the evolution of intelligence.

  16. Converging language streams in the human temporal lobe.

    PubMed

    Spitsyna, Galina; Warren, Jane E; Scott, Sophie K; Turkheimer, Federico E; Wise, Richard J S

    2006-07-12

    There is general agreement that, after initial processing in unimodal sensory cortex, the processing pathways for spoken and written language converge to access verbal meaning. However, the existing literature provides conflicting accounts of the cortical location of this convergence. Most aphasic stroke studies localize verbal comprehension to posterior temporal and inferior parietal cortex (Wernicke's area), whereas evidence from focal cortical neurodegenerative syndromes instead implicates anterior temporal cortex. Previous functional imaging studies in normal subjects have failed to reconcile these opposing positions. Using a functional imaging paradigm in normal subjects that used spoken and written narratives and multiple baselines, we demonstrated common activation during implicit comprehension of spoken and written language in inferior and lateral regions of the left anterior temporal cortex and at the junction of temporal, occipital, and parietal cortex. These results indicate that verbal comprehension uses unimodal processing streams that converge in both anterior and posterior heteromodal cortical regions in the left temporal lobe. PMID:16837579

  17. Adaptive sliding mode control - convergence and gain boundedness revisited

    NASA Astrophysics Data System (ADS)

    Zhu, Jiang; Khayati, Karim

    2016-04-01

    This paper reviews the main adaptive sliding mode controller (ASMC) designs for nonlinear systems with finite uncertainties of unknown bounds. Different statements of convergence referring to uniformly ultimate boundedness (UUB), asymptotic convergence (AC) and finite-time convergence (FTC) for ASMC shown in recent papers are analysed. Weaknesses and incomplete proofs apropos FTC are pointed out. Thereafter, a new approach is proposed to successfully demonstrate FTC of the so-called sliding variable. We identify a compensating phase and a reaching phase during the ASMC process. A new explicit form for estimating the upper-bound reaching time is provided for any bounded perturbation. An amended form of the real ASMC is recalled showing improved accuracy and chattering reduction. Finally, numerical and experimental applications are performed to convey the discussed results.

  18. Shock wave convergence in water with parabolic wall boundaries

    SciTech Connect

    Yanuka, D.; Shafer, D.; Krasik, Ya.

    2015-04-28

    The convergence of shock waves in water, where the cross section of the boundaries between which the shock wave propagates is either straight or parabolic, was studied. The shock wave was generated by underwater electrical explosions of planar Cu wire arrays using a high-current generator with a peak output current of ∼45 kA and rise time of ∼80 ns. The boundaries of the walls between which the shock wave propagates were symmetric along the z axis, which is defined by the direction of the exploding wires. It was shown that with walls having a parabolic cross section, the shock waves converge faster and the pressure in the vicinity of the line of convergence, calculated by two-dimensional hydrodynamic simulations coupled with the equations of state of water and copper, is also larger.

  19. Converging spherical wave propagation in a hemispherical solid lens

    NASA Astrophysics Data System (ADS)

    Zhang, Yaoju; Ye, Xuehua; Chen, Junfeng

    2006-06-01

    The propagation of converging spherical waves through a hemispherical solid lens (HSL) is studied, and the multiple reflections inside the HSL are considered. It is found that the reflectivity and transmissivity have an oscillatory behaviour related to the optical radius of the HSL. When the refractive index of the HSL is smaller than that of the sample, the small mismatch in refractive indices is preferable for transmission-mode microscopy. But when the refractive index of the HSL is larger than that of the sample, the reflectivity increases rapidly as the mismatch in refractive indices and the converging angle of incident light increase, the larger mismatch and converging angle are useful for reflection-mode microscopy. The magnitude of the whole reflectivity and its modulation depth are strongly sensitive to the incident polarization, which is also discussed.

  20. A fast algorithm for nonnegative matrix factorization and its convergence.

    PubMed

    Li, Li-Xin; Wu, Lin; Zhang, Hui-Sheng; Wu, Fang-Xiang

    2014-10-01

    Nonnegative matrix factorization (NMF) has recently become a very popular unsupervised learning method because of its representational properties of factors and simple multiplicative update algorithms for solving the NMF. However, for the common NMF approach of minimizing the Euclidean distance between approximate and true values, the convergence of multiplicative update algorithms has not been well resolved. This paper first discusses the convergence of existing multiplicative update algorithms. We then propose a new multiplicative update algorithm for minimizing the Euclidean distance between approximate and true values. Based on the optimization principle and the auxiliary function method, we prove that our new algorithm not only converges to a stationary point, but also does faster than existing ones. To verify our theoretical results, the experiments on three data sets have been conducted by comparing our proposed algorithm with other existing methods.

  1. Convergent structure of multitrophic communities over three continents.

    PubMed

    Segar, Simon T; Pereira, Rodrigo A S; Compton, Steve G; Cook, James M

    2013-12-01

    Ecological theory predicts that communities using the same resources should have similar structure, but evolutionary constraints on colonisation and niche shifts may hamper such convergence. Multitrophic communities of wasps exploiting fig fruits, which first evolved about 75MYA, do not show long-term 'inheritance' of taxonomic (lineage) composition or species diversity. However, communities on three continents have converged ecologically in the presence and relative abundance of five insect guilds that we define. Some taxa fill the same niches in each community (phylogenetic niche conservatism). However, we show that overall convergence in ecological community structure depends also on a combination of niche shifts by resident lineages and local colonisations of figs by other insect lineages. Our study explores new ground, and develops new heuristic tools, in combining ecology and phylogeny to address patterns in the complex multitrophic communities of insect on plants, which comprise a large part of terrestrial biodiversity.

  2. Modelling Iteration Convergence Condition for Single SAR Image Geocoding

    NASA Astrophysics Data System (ADS)

    Dong, Yuting; Liao, Minghsheng; Zhang, Lu; Shi, Xuguo

    2014-11-01

    Single SAR image geocoding is to determine the ground coordinate for each pixel in the SAR image assisted with an external DEM. Due to the uncertainty of the elevation of each pixel in SAR image, an iterative procedure is needed, which suffers from the problem of divergence in some difficult areas such as shaded and serious layover areas. This paper aims at theoretically analysing the convergence conditions that has not been intensively studied till now. To make the discussion easier, the Range-Doppler (RD) model is simplified and then the general surface is simplified into a planar surface. Mathematical deduction is carried out to derive the convergence conditions and the impact factors for the convergence speed are analysed. The theoretical findings are validated by experiments for both simulated and real surfaces.

  3. Vadose zone water fluxmeter

    DOEpatents

    Faybishenko, Boris A.

    2005-10-25

    A Vadose Zone Water Fluxmeter (WFM) or Direct Measurement WFM provides direct measurement of unsaturated water flow in the vadose zone. The fluxmeter is a cylindrical device that fits in a borehole or can be installed near the surface, or in pits, or in pile structures. The fluxmeter is primarily a combination of tensiometers and a porous element or plate in a water cell that is used for water injection or extraction under field conditions. The same water pressure measured outside and inside of the soil sheltered by the lower cylinder of the fluxmeter indicates that the water flux through the lower cylinder is similar to the water flux in the surrounding soil. The fluxmeter provides direct measurement of the water flow rate in the unsaturated soils and then determines the water flux, i.e. the water flow rate per unit area.

  4. The Pliny-Strabo trench region: A large shear zone resulting from slab tearing

    NASA Astrophysics Data System (ADS)

    Özbakır, Ali D.; Şengör, A. M. C.; Wortel, M. J. R.; Govers, R.

    2013-08-01

    The eastern part of the Hellenic subduction zone is composed of the Pliny and Strabo "trenches" that have been regarded as a zone of convergence between the subducting African lithosphere and the overriding Anatolian-Aegean plate. In the Pliny and Strabo "trenches", the oblique relative plate motion is generally thought to be accommodated by a typical strain partitioning consisting of strike-slip and convergence components. Notwithstanding the occurrence of strike-slip motion parallel with the Pliny-Strabo "trenches", trench-normal thrusting is not observed so far. Therefore, we conducted a detailed analysis to investigate the deformation mechanisms of the eastern part of the Hellenic Trench system. Our analyses of offshore faulting and mechanisms of earthquakes in the overriding Aegean lithosphere show that the region of the Pliny and Strabo "trenches" obeys the mechanics of the sinistral shear zone model of Tchalenko (1970). We propose that the trench perpendicular convergence is taken up by the Rhodes fold and thrust belt, which has been postulated off the southeast coast of Rhodes. Several regional P-wave tomography results give indications of a slow seismic anomaly under this zone, which is interpreted as a tear between the Hellenic and Cyprus subduction zones. The primary reason for such tear and its propagation is the ongoing rollback of the subducted part of the African lithosphere, also referred to as "the Aegean slab". Our work elucidates the surface expression of this tearing process in the form of the development of a shear zone between the Aegean lithosphere in the NW and the African lithosphere in the SE, the Pliny-Strabo Shear Zone.

  5. Peak exclusion, stochasticity and convergence of perturbative bias expansions in 1+1 gravity

    NASA Astrophysics Data System (ADS)

    Baldauf, Tobias; Codis, Sandrine; Desjacques, Vincent; Pichon, Christophe

    2016-03-01

    The Lagrangian peaks of a 1D cosmological random field representing dark matter are used as a proxy for a catalogue of biased tracers in order to investigate the small-scale exclusion in the two-halo term. The two-point correlation function of peaks of a given height is numerically estimated and analytical approximations that are valid inside the exclusion zone are derived. The resulting power spectrum of these tracers is investigated and shows clear deviations from Poisson noise at low frequencies. On large scales, the convergence of a perturbative bias expansion is discussed. Finally, we go beyond Gaussian statistics for the initial conditions and investigate the subsequent evolution of the two-point clustering of peaks through their Zel'dovich ballistic displacement, to clarify how exclusion effects mix up with scale-dependences induced by non-linear gravitational evolution. While the expected large-scale separation limit is recovered, significant deviations are found in the exclusion zone that tends in particular to be reduced at later times. Even though these findings apply to the clustering of 1D tracers, they provide useful insights into halo exclusion and its impact on the two-halo term.

  6. Flycatcher song in allopatry and sympatry--convergence, divergence and reinforcement.

    PubMed

    Haavie, J; Borge, T; Bures, S; Garamszegi, L Z; Lampe, H M; Moreno, J; Qvarnström, A; Török, J; Saetre, G-P

    2004-03-01

    The theory of reinforcement predicts that natural selection against the production of unfit hybrids favours traits that increase assortative mating. Whether culturally inherited traits, such as bird song, can increase assortative mating by reinforcement is largely unknown. We compared songs of pied (Ficedula hypoleuca) and collared flycatchers (F. albicollis) from two hybrid zones of different ages with songs from allopatric populations. Previously, a character divergence in male plumage traits has been shown to reinforce premating isolation in sympatric flycatchers. In contrast, we find that the song of the pied flycatcher has converged towards that of the collared flycatcher (mixed singing). However, a corresponding divergence in the collared flycatcher shows that the species differences in song characters are maintained in sympatry. Genetic analyses suggest that mixed song is not caused by introgression from the collared flycatcher, but rather due to heterospecific copying. Circumstantial evidence suggests that mixed song may increase the rate of maladaptive hybridization. In the oldest hybrid zone where reinforcement on plumage traits is most pronounced, the frequency of mixed singing and hybridization is also lowest. Thus, we suggest that reinforcement has reduced the frequency of mixed singing in the pied flycatcher and caused a divergence in the song of the collared flycatcher. Whether a culturally inherited trait promotes or opposes speciation in sympatry may depend on its plasticity. The degree of plasticity may be genetically determined and accordingly under selection by reinforcement.

  7. Contractile roots in succulent monocots: convergence, divergence and adaptation to limited rainfall.

    PubMed

    North, Gretchen B; Brinton, Erin K; Garrett, Tadao Y

    2008-08-01

    Contractile roots (CRs) that pull shoots further down in the soil are a possible example of convergent evolution in two monocot families, the Agavaceae and the Asphodelaceae. The association between CRs, water uptake and habitat aridity was investigated for agaves, yuccas and aloes by assessing the occurrence of CRs and the amount of root contraction for glasshouse-grown plants with respect to mean annual rainfall of their native habitats. Structural features of CRs as well as root hydraulic conductance were compared with those of non-contractile roots (NCRs). CRs occurred in 55% of the 73 species examined, including 64% of the agaves and 85% of the yuccas, but in none of the aloes despite the occurrence of CRs in related genera. The phylogenetic distribution of CRs was consistent with multiple acquisitions or losses of the trait. The amount of root contraction showed a highly significant negative relationship with mean annual rainfall, although other environmental factors may also be important. Radial hydraulic conductance of the basal (contractile) zone exceeded that of the midroot zone for CRs; for NCRs, the opposite was true. Thus, CRs in the species examined may provide a mechanism for greater water uptake near the soil surface in regions with limited rainfall. PMID:18507804

  8. Contractile roots in succulent monocots: convergence, divergence and adaptation to limited rainfall.

    PubMed

    North, Gretchen B; Brinton, Erin K; Garrett, Tadao Y

    2008-08-01

    Contractile roots (CRs) that pull shoots further down in the soil are a possible example of convergent evolution in two monocot families, the Agavaceae and the Asphodelaceae. The association between CRs, water uptake and habitat aridity was investigated for agaves, yuccas and aloes by assessing the occurrence of CRs and the amount of root contraction for glasshouse-grown plants with respect to mean annual rainfall of their native habitats. Structural features of CRs as well as root hydraulic conductance were compared with those of non-contractile roots (NCRs). CRs occurred in 55% of the 73 species examined, including 64% of the agaves and 85% of the yuccas, but in none of the aloes despite the occurrence of CRs in related genera. The phylogenetic distribution of CRs was consistent with multiple acquisitions or losses of the trait. The amount of root contraction showed a highly significant negative relationship with mean annual rainfall, although other environmental factors may also be important. Radial hydraulic conductance of the basal (contractile) zone exceeded that of the midroot zone for CRs; for NCRs, the opposite was true. Thus, CRs in the species examined may provide a mechanism for greater water uptake near the soil surface in regions with limited rainfall.

  9. Trojans in habitable zones.

    PubMed

    Schwarz, Richard; Pilat-Lohinger, Elke; Dvorak, Rudolf; Erdi, Balint; Sándor, Zsolt

    2005-10-01

    With the aid of numerical experiments we examined the dynamical stability of fictitious terrestrial planets in 1:1 mean motion resonance with Jovian-like planets of extrasolar planetary systems. In our stability study of the so-called "Trojan" planets in the habitable zone, we used the restricted three-body problem with different mass ratios of the primary bodies. The application of the three-body problem showed that even massive Trojan planets can be stable in the 1:1 mean motion resonance. From the 117 extrasolar planetary systems only 11 systems were found with one giant planet in the habitable zone. Out of this sample set we chose four planetary systems--HD17051, HD27442, HD28185, and HD108874--for further investigation. To study the orbital behavior of the stable zone in the different systems, we used direct numerical computations (Lie Integration Method) that allowed us to determine the escape times and the maximum eccentricity of the fictitious "Trojan planets." PMID:16225431

  10. Convergence acceleration of the Proteus computer code with multigrid methods

    NASA Technical Reports Server (NTRS)

    Demuren, A. O.; Ibraheem, S. O.

    1992-01-01

    Presented here is the first part of a study to implement convergence acceleration techniques based on the multigrid concept in the Proteus computer code. A review is given of previous studies on the implementation of multigrid methods in computer codes for compressible flow analysis. Also presented is a detailed stability analysis of upwind and central-difference based numerical schemes for solving the Euler and Navier-Stokes equations. Results are given of a convergence study of the Proteus code on computational grids of different sizes. The results presented here form the foundation for the implementation of multigrid methods in the Proteus code.

  11. Convergence Time towards Periodic Orbits in Discrete Dynamical Systems

    PubMed Central

    San Martín, Jesús; Porter, Mason A.

    2014-01-01

    We investigate the convergence towards periodic orbits in discrete dynamical systems. We examine the probability that a randomly chosen point converges to a particular neighborhood of a periodic orbit in a fixed number of iterations, and we use linearized equations to examine the evolution near that neighborhood. The underlying idea is that points of stable periodic orbit are associated with intervals. We state and prove a theorem that details what regions of phase space are mapped into these intervals (once they are known) and how many iterations are required to get there. We also construct algorithms that allow our theoretical results to be implemented successfully in practice. PMID:24736594

  12. Convergence time towards periodic orbits in discrete dynamical systems.

    PubMed

    San Martín, Jesús; Porter, Mason A

    2014-01-01

    We investigate the convergence towards periodic orbits in discrete dynamical systems. We examine the probability that a randomly chosen point converges to a particular neighborhood of a periodic orbit in a fixed number of iterations, and we use linearized equations to examine the evolution near that neighborhood. The underlying idea is that points of stable periodic orbit are associated with intervals. We state and prove a theorem that details what regions of phase space are mapped into these intervals (once they are known) and how many iterations are required to get there. We also construct algorithms that allow our theoretical results to be implemented successfully in practice.

  13. Globally convergent techniques in nonlinear Newton-Krylov

    NASA Technical Reports Server (NTRS)

    Brown, Peter N.; Saad, Youcef

    1989-01-01

    Some convergence theory is presented for nonlinear Krylov subspace methods. The basic idea of these methods is to use variants of Newton's iteration in conjunction with a Krylov subspace method for solving the Jacobian linear systems. These methods are variants of inexact Newton methods where the approximate Newton direction is taken from a subspace of small dimensions. The main focus is to analyze these methods when they are combined with global strategies such as linesearch techniques and model trust region algorithms. Most of the convergence results are formulated for projection onto general subspaces rather than just Krylov subspaces.

  14. Assessing the validity of discourse analysis: transdisciplinary convergence

    NASA Astrophysics Data System (ADS)

    Jaipal-Jamani, Kamini

    2014-12-01

    Research studies using discourse analysis approaches make claims about phenomena or issues based on interpretation of written or spoken text, which includes images and gestures. How are findings/interpretations from discourse analysis validated? This paper proposes transdisciplinary convergence as a way to validate discourse analysis approaches to research. The argument is made that discourse analysis explicitly grounded in semiotics, systemic functional linguistics, and critical theory, offers a credible research methodology. The underlying assumptions, constructs, and techniques of analysis of these three theoretical disciplines can be drawn on to show convergence of data at multiple levels, validating interpretations from text analysis.

  15. Convergence of Series in Mittag-Leffler Type Functions

    NASA Astrophysics Data System (ADS)

    Paneva-Konovska, J.

    2010-11-01

    Explicit solutions of some kinds of fractional order (or multi-order) differential and integral equations involving Erdelyi-Kober (E-K) operators are representable by means of series in Mittag-Leffler type functions like those considered in this work. The domains of convergence of such expansions are found. The series behaviour on the boundary of these domains are studied. Cauchy-Hadamard, Abel, Tauber and Littlewood type theorems for such series are given. Asymptotic formulae for "large" values of indices of these functions, used in the proofs of the convergence theorems for the considered series, are also provided.

  16. Strain Partitioning and the Geometry of Oblique Plate Convergence

    NASA Astrophysics Data System (ADS)

    Guzman-Speziale, M.

    2004-05-01

    Strain partitioning occurs at convergent margins where oblique subduction takes place, a fact that has been known for a number of years. The geometry of plate subduction controls strain-partitioning mode in the forearc region. Deformation in the forearc depends on the direction of relative plate convergence, earthquake slip vectors, and trench-normal direction. Two basic angles are derived from these vectors: obliquity of plate convergence, the angle of plate motion direction and trench normal, and slip partitioning which is the angle between the earthquake slip vector and trench normal. Traditionally, oblique convergence models consider the trench (convergent margin) a straight line on a flat Earth. This is correct for small-scale (in the order of a few kilometers) models. However, earthquakes along convergent margins often have fault lengths of tens and even hundreds (for magnitude 7 or greater) of kilometers. On the other hand, the direction normal to the trench is usually calculated averaging contiguous points along the deepest part of the digitized bathymetry, yielding the local trend of the trench. The direction normal to the trench thus calculated varies greatly along a specific trench. In this work we propose an alternate treatment of the geometry of the trench. On a spherical Earth, trench segments form arcs of small circles. Usually, a trench of interest will contain a few (three-five) such segments, which can be fitted (in a least-squares sense) with small circles with a known center of curvature (or pole) on the surface of the Earth. Also known are the initial and final points. Instead of the standard direction normal to the trench, we use the average azimuth from the segment of small circle to its corresponding pole. We use this direction instead of trench normal and calculate obliquity of plate convergence. We test our model along the western Sunda arc, from the eastern Himalayan sintaxis to Sumatra. Five contiguos small circles were fitted to the

  17. Comparison of some tests for convergence of positive series

    NASA Astrophysics Data System (ADS)

    Bourchtein, Ludmila; Bourchtein, Andrei

    2016-04-01

    In this survey, aimed at professors and students of undergraduate analysis courses, two hierarchies of tests are considered. The first is originated from the ratio test and the second from the root test. The test construction techniques are exposed and relations between the tests in each family are discussed. The examples of convergent and divergent series clarify the range of application for each of the introduced tests and situations when they are not conclusive. The behaviour of the partial sums of these series is illustrated geometrically and the level of complexity of each series is evaluated in terms of the rate of its convergence or divergence.

  18. New formulations of monotonically convergent quantum control algorithms

    NASA Astrophysics Data System (ADS)

    Maday, Yvon; Turinici, Gabriel

    2003-05-01

    Most of the numerical simulation in quantum (bilinear) control have used one of the monotonically convergent algorithms of Krotov (introduced by Tannor et al.) or of Zhu and Rabitz. However, until now no explicit relationship has been revealed between the two algorithms in order to understand their common properties. Within this framework, we propose in this paper a unified formulation that comprises both algorithms and that extends to a new class of monotonically convergent algorithms. Numerical results show that the newly derived algorithms behave as well as (and sometimes better than) the well-known algorithms cited above.

  19. Converging prescription brand shares as evidence of physician learning.

    PubMed

    Walker, Doug

    2012-01-01

    Within a drug category, there is an optimal brand the physician could choose to prescribe based on the patient's particular condition and characteristics. Physicians desire to prescribe the best brand for each patient for professional, moral, and legal reasons. Ideally, detailing provides information that supports this effort. This study finds that, over time, the proportion of prescriptions written for each brand moves toward a stable distribution--a convergence in which each brand's share in the category appears to match the proportion of prescription writing opportunities where the brand is the best choice for the patient. Detailing supports this convergence.

  20. Convergence time towards periodic orbits in discrete dynamical systems.

    PubMed

    San Martín, Jesús; Porter, Mason A

    2014-01-01

    We investigate the convergence towards periodic orbits in discrete dynamical systems. We examine the probability that a randomly chosen point converges to a particular neighborhood of a periodic orbit in a fixed number of iterations, and we use linearized equations to examine the evolution near that neighborhood. The underlying idea is that points of stable periodic orbit are associated with intervals. We state and prove a theorem that details what regions of phase space are mapped into these intervals (once they are known) and how many iterations are required to get there. We also construct algorithms that allow our theoretical results to be implemented successfully in practice. PMID:24736594

  1. Radiant zone heated particulate filter

    DOEpatents

    Gonze, Eugene V [Pinckney, MI

    2011-12-27

    A system includes a particulate matter (PM) filter including an upstream end for receiving exhaust gas and a downstream end. A radiant zoned heater includes N zones, where N is an integer greater than one, wherein each of the N zones includes M sub-zones, where M is an integer greater than or equal to one. A control module selectively activates at least a selected one of the N zones to initiate regeneration in downstream portions of the PM filter from the one of the N zones, restricts exhaust gas flow in a portion of the PM filter that corresponds to the selected one of the N zones, and deactivates non-selected ones of the N zones.

  2. The role of the subcutaneous zone in karst hydrology

    NASA Astrophysics Data System (ADS)

    Williams, Paul W.

    1983-02-01

    The subcutaneous zone is the upper weathered layer of rock beneath the soil, but above the permanently saturated (phreatic) zone. It is of particular hydrological importance in karst because of its high secondary permeability, arising from the considerable chemical solution in this zone. However, corrosional enlargement of fissures diminishes with depth; thus permeability decreases in the same direction with the result that percolation is inhibited, except down widened master joints and faults. Storage of water consequently occurs in this zone, particularly after storms. The upper surface of this suspended saturated layer in the subcutaneous zone is defined by a perched water table, which slopes towards points of rapid vertical percolation. The potential induces lateral water movement converging on the most permeable areas such as beneath dolines. Leakage from the subcutaneous store sustains slow percolation in the vadose zone. Cross-correlation of rainfall with percolation rates in caves in New Mexico, U.S.A., and New Zealand reveal response lags of 2-14 weeks with no apparent relationship to depth below the surface. Other percolation sites show no correlation with rainfall; interpreted as being a consequence of considerable friction in tight fissure networks. The recognition of storage and rapid as well as very slow percolation from the subcutaneous zone requires re-interpretation of the components of hydrographs from karst springs and of some conceptual models of karst aquifers. The importance of subcutaneous storage in sustaining baseflow discharge at some sites must be recognised, as must the contribution of subcutaneous water to flood hydrographs. Methods of estimating the volumes of subcutaneous and phreatic components of karst-spring flood hydrographs are presented. The paper concludes with a discussion of the significance of subcutaneous hydrologic processes for an understanding of karst geomorphology. The desirability of explaining karst landform

  3. Analytical modelling of wave refraction and convergence on coral reef platforms: Implications for island formation and stability

    NASA Astrophysics Data System (ADS)

    Mandlier, Philipp Georg; Kench, Paul Simon

    2012-07-01

    An analytical model was constructed to simulate the refraction of waves on coral reef platforms comprising an idealised bathymetry of uniform depth and vertical reef faces. Model simulations were conducted to investigate the influence of key parameters such as reef shape and depth as well as wave period on the propagation behaviour of incident waves. Results of the refraction analysis demonstrate that different reef shapes produce characteristic patterns of wave convergence on reef surfaces. The location and stability of focal zones and hence wave convergence is largely controlled by the shape of platforms. Platform configuration further controls the distribution of wave energy across platform surfaces and determines the influence of incident wave forcing on different reef sections. Results have significant implications for sedimentation processes and hence the formation and stability of islands on reef platforms. Wave propagation patterns define sediment transport vectors and subsequently control the transport and deposition of different sized material. Platforms which promote marked wave convergence behaviour, such as elliptical and circular reefs, are more likely to retain sediment on reef surfaces, whereas narrow linear structures have a higher potential for the off-reef evacuation of sediment over leeward reef margins and the subsequent infill of deeper lagoonal areas. The study provides a physical basis for future investigations of reef hydrodynamics and platform sedimentation processes.

  4. Methane Production In Forearc Sediments At The Costa Rican Convergent Margin

    NASA Astrophysics Data System (ADS)

    Cardace, D.; Morris, J. D.; Peacock, A.; White, D. C.

    2004-12-01

    Plate tectonics creates suitable habitats for deep biosphere organisms, affecting the distribution of biological communities on Earth. Subduction zones, where crustal materials return to the planetary interior through plate convergence, expose active microbial communities in subducting seafloor sediments to a fresh chemical inventory as diagenesis, metamorphic reactions, and tectonically-induced fluid flow alter sediments and surrounding porewaters. The plate interface (the decollement) experiences persistent geochemical flux of light hydrocarbon- and metal-bearing fluids from depth. This project (1) examines the habitability of the decollement zone at the Costa Rican convergent margin from a geochemical perspective, (2) uses lipid biomarkers to describe biomass distribution in sediment samples adjacent to and within the decollement, and (3) cites methanogenesis as a likely metabolic strategy employed by the resident microbial community. Sterile plugs of sediment were recovered from cores taken during Leg 205 of the Ocean Drilling Program, in the Middle America Trench off Costa Rica. Samples are from the incoming carbonate section of Site 1253 at 370-437 meters below seafloor (mbsf), in the forearc sedimentary wedge at Site 1255 at 134-145 mbsf, and around an upper fault (153-220 mbsf) and in the decollement zone (305-366 mbsf) at Site 1254. Drilling mud and fluid were sampled to monitor potential microbial contamination. Samples were immediately frozen at -80ºC. Prior to analysis, samples were freeze-dried in preparation for serial extraction of DNA and lipids. DNA was identified by fluorometry in 13 of 26 samples tested. The DNA was screened for methanogens by real time polymerase chain reaction (PCR), employing ME1 and ME2 primers that amplify a 0.75-kb region of the alpha-subunit gene for methyl coenzyme M reductase (MCR). Methanogen-specific genes were detected in DNA extracted from one Site 1253 sample (at 436.9 mbsf in the basal carbonates) and four Site

  5. Extrapolating surface structures to depth in transpressional systems: the role of rheology and convergence angle deduced from analogue experiments

    NASA Astrophysics Data System (ADS)

    Hsieh, Shang Yu; Neubauer, Franz; Cloetingh, Sierd; Willingshofer, Ernst; Sokoutis, Dimitrios

    2014-05-01

    The internal structure of major strike-slip faults is still poorly understood, particularly how the deep structure could be inferred from its surface expression (Molnar and Dayem, 2011 and references therein). Previous analogue experiments suggest that the convergence angle is the most influential factor (Leever et al., 2011). Further analogue modeling may allow a better understanding how to extrapolate surface structures to the subsurface geometry of strike-slip faults. Various scenarios of analogue experiments were designed to represent strike-slip faults in nature from different geological settings. As such key parameters, which are investigated in this study include: (a) the angle of convergence, (b) the thickness of brittle layer, (c) the influence of a rheological weak layer within the crust, and (d) influence of a thick and rheologically weak layer at the base of the crust. The latter aimed to simulate the effect of a hot metamorphic core complex or an alignment of uprising plutons bordered by a transtensional/transpressional strike-slip fault. The experiments are aimed to explain first order structures along major transcurrent strike-slip faults such as the Altyn, Kunlun, San Andrea and Greendale (Darfield earthquake 2010) faults. The preliminary results show that convergence angle significantly influences the overall geometry of the transpressive system with greater convergence angles resulting in wider fault zones and higher elevation. Different positions, densities and viscosities of weak rheological layers have not only different surface expressions but also affect the fault geometry in the subsurface. For instance, rheological weak material in the bottom layer results in stretching when experiment reaches a certain displacement and a buildup of a less segmented, wide positive flower structure. At the surface, a wide fault valley in the middle of the fault zone is the reflection of stretching along the velocity discontinuity at depth. In models with a

  6. A possible transoceanic tsunami directed toward the U.S. west coast from the Semidi segment, Alaska convergent margin

    NASA Astrophysics Data System (ADS)

    von Huene, Roland; Miller, John J.; Dartnell, Peter

    2016-03-01

    The Semidi segment of the Alaska convergent margin appears capable of generating a giant tsunami like the one produced along the nearby Unimak segment in 1946. Reprocessed legacy seismic reflection data and a compilation of multibeam bathymetric surveys reveal structures that could generate such a tsunami. A 200 km long ridge or escarpment with crests >1 km high is the surface expression of an active out-of-sequence fault zone, recently referred to as a splay fault. Such faults are potentially tsunamigenic. This type of fault zone separates the relatively rigid rock of the margin framework from the anelastic accreted sediment prism. Seafloor relief of the ridge exceeds that of similar age accretionary prism ridges indicating preferential slip along the splay fault zone. The greater slip may derive from Quaternary subduction of the Patton Murray hot spot ridge that extends 200 km toward the east across the north Pacific. Estimates of tsunami repeat times from paleotsunami studies indicate that the Semidi segment could be near the end of its current inter-seismic cycle. GPS records from Chirikof Island at the shelf edge indicate 90% locking of plate interface faults. An earthquake in the shallow Semidi subduction zone could generate a tsunami that will inundate the US west coast more than the 1946 and 1964 earthquakes because the Semidi continental slope azimuth directs a tsunami southeastward.

  7. A possible transoceanic tsunami directed toward the U.S. west coast from the Semidi segment, Alaska convergent margin

    USGS Publications Warehouse

    von Huene, Roland; Miller, John J.; Dartnell, Peter

    2016-01-01

    The Semidi segment of the Alaska convergent margin appears capable of generating a giant tsunami like the one produced along the nearby Unimak segment in 1946. Reprocessed legacy seismic reflection data and a compilation of multibeam bathymetric surveys reveal structures that could generate such a tsunami. A 200 km long ridge or escarpment with crests >1 km high is the surface expression of an active out-of-sequence fault zone, recently referred to as a splay fault. Such faults are potentially tsunamigenic. This type of fault zone separates the relatively rigid rock of the margin framework from the anelastic accreted sediment prism. Seafloor relief of the ridge exceeds that of similar age accretionary prism ridges indicating preferential slip along the splay fault zone. The greater slip may derive from Quaternary subduction of the Patton Murray hot spot ridge that extends 200 km toward the east across the north Pacific. Estimates of tsunami repeat times from paleotsunami studies indicate that the Semidi segment could be near the end of its current inter-seismic cycle. GPS records from Chirikof Island at the shelf edge indicate 90% locking of plate interface faults. An earthquake in the shallow Semidi subduction zone could generate a tsunami that will inundate the US west coast more than the 1946 and 1964 earthquakes because the Semidi continental slope azimuth directs a tsunami southeastward.

  8. Interplay of plutonism and regional deformation in an obliquely convergent arc, southern Coast Belt, British Columbia

    NASA Astrophysics Data System (ADS)

    Brown, E. H.; Talbot, J. L.; McClelland, W. C.; Feltman, J. A.; Lapen, T. J.; Bennett, J. D.; Hettinga, M. A.; Troost, M. L.; Alvarez, K. M.; Calvert, A. T.

    2000-06-01

    The Coast Plutonic Complex is an extensive zone of continental growth that formed along the Mesozoic convergent margin of northwestern North America. The orogeny creating this belt involved terrane accretion and assembly, massive upward transfer and emplacement of sial in the form of batholiths constituting a magmatic arc, and transformation of broad tracts of sedimentary and volcanic rocks into crystalline continental crust, all operating in more or less the same space and time. The mechanisms and interplay of these orogenic processes are well displayed in the Harrison Lake area of the southern Coast Belt, British Columbia. Great structural relief across the area exhibits a present-day architecture defined by thin, thrust-stacked terrane sheets and early concordant pluton sheets folded on a macroscopic scale, all truncated by oblique dextral-reverse faults and overlain by later floored plutons. Construction of this complex began with terrane assembly on orogen-normal thrusts during a lull in plutonism in the Early Cretaceous. Low-grade metamorphism during this event indicates only modest crustal thickening. Subsequent plutons intruded into the assembled terranes appear to be composites of sheets. Early pluton sheets are now steeply dipping due to folding but were likely intruded as horizontal bodies. Large ovoid post folding plutons are mostly subhorizontal floored bodies, at least in part sheeted. These plutons are underlain by Barrovian mineralogic aureoles that indicate downward vertical displacement of 10 km or more during plutonism, suggesting pluton emplacement by vertical inflation. Magmatic fabrics in these bodies, and the discordant relation of plutons to regional structures, preclude emplacement in active fault zones. Penetrative strain aureoles flanking plutons are mostly limited to zones a few hundred meters wide, and regional tectonic structures are widely preserved. Tectonic deformation of the arc is characterized by contraction and strike-slip, not

  9. Convergent evolution of 'creepers' in the Hawaiian honeycreeper radiation.

    PubMed

    Reding, Dawn M; Foster, Jeffrey T; James, Helen F; Pratt, H Douglas; Fleischer, Robert C

    2009-04-23

    Natural selection plays a fundamental role in the ecological theory of adaptive radiation. A prediction of this theory is the convergent evolution of traits in lineages experiencing similar environments. The Hawaiian honeycreepers are a spectacular example of adaptive radiation and may demonstrate convergence, but uncertainty about phylogenetic relationships within the group has made it difficult to assess such evolutionary patterns. We examine the phylogenetic relationships of the Hawaii creeper (Oreomystis mana), a bird that in a suite of morphological, ecological and behavioural traits closely resembles the Kauai creeper (Oreomystis bairdi), but whose mitochondrial DNA (mtDNA) and osteology suggest a relationship with the amakihis (Hemignathus in part) and akepas (Loxops). We analysed nuclear DNA sequence data from 11 relevant honeycreeper taxa and one outgroup to test whether the character contradiction results from historical hybridization and mtDNA introgression, or convergent evolution. We found no evidence of past hybridization, a phenomenon that remains undocumented in Hawaiian honeycreepers, and confirmed mtDNA and osteological evidence that the Hawaii creeper is most closely related to the amakihis and akepas. Thus, the morphological, ecological and behavioural similarities between the evolutionarily distant Hawaii and Kauai creepers represent an extreme example of convergent evolution and demonstrate how natural selection can lead to repeatable evolutionary outcomes.

  10. New convergence results for the scaled gradient projection method

    NASA Astrophysics Data System (ADS)

    Bonettini, S.; Prato, M.

    2015-09-01

    The aim of this paper is to deepen the convergence analysis of the scaled gradient projection (SGP) method, proposed by Bonettini et al in a recent paper for constrained smooth optimization. The main feature of SGP is the presence of a variable scaling matrix multiplying the gradient, which may change at each iteration. In the last few years, extensive numerical experimentation showed that SGP equipped with a suitable choice of the scaling matrix is a very effective tool for solving large scale variational problems arising in image and signal processing. In spite of the very reliable numerical results observed, only a weak convergence theorem is provided establishing that any limit point of the sequence generated by SGP is stationary. Here, under the only assumption that the objective function is convex and that a solution exists, we prove that the sequence generated by SGP converges to a minimum point, if the scaling matrices sequence satisfies a simple and implementable condition. Moreover, assuming that the gradient of the objective function is Lipschitz continuous, we are also able to prove the {O}(1/k) convergence rate with respect to the objective function values. Finally, we present the results of a numerical experience on some relevant image restoration problems, showing that the proposed scaling matrix selection rule performs well also from the computational point of view.

  11. Emerging interdisciplinary fields in the coming intelligence/convergence era

    NASA Astrophysics Data System (ADS)

    Noor, Ahmed

    2012-09-01

    Dramatic advances are in the horizon resulting from rapid pace of development of several technologies, including, computing, communication, mobile, robotic, and interactive technologies. These advances, along with the trend towards convergence of traditional engineering disciplines with physical, life and other science disciplines will result in the development of new interdisciplinary fields, as well as in new paradigms for engineering practice in the coming intelligence/convergence era (post-information age). The interdisciplinary fields include Cyber Engineering, Living Systems Engineering, Biomechatronics/Robotics Engineering, Knowledge Engineering, Emergent/Complexity Engineering, and Multiscale Systems engineering. The paper identifies some of the characteristics of the intelligence/convergence era, gives broad definition of convergence, describes some of the emerging interdisciplinary fields, and lists some of the academic and other organizations working in these disciplines. The need is described for establishing a Hierarchical Cyber-Physical Ecosystem for facilitating interdisciplinary collaborations, and accelerating development of skilled workforce in the new fields. The major components of the ecosystem are listed. The new interdisciplinary fields will yield critical advances in engineering practice, and help in addressing future challenges in broad array of sectors, from manufacturing to energy, transportation, climate, and healthcare. They will also enable building large future complex adaptive systems-of-systems, such as intelligent multimodal transportation systems, optimized multi-energy systems, intelligent disaster prevention systems, and smart cities.

  12. Converging Supergranular Flows and the Formation of Coronal Plumes

    NASA Astrophysics Data System (ADS)

    Wang, Y.-M.; Warren, H. P.; Muglach, K.

    2016-02-01

    Earlier studies have suggested that coronal plumes are energized by magnetic reconnection between unipolar flux concentrations and nearby bipoles, even though magnetograms sometimes show very little minority-polarity flux near the footpoints of plumes. Here we use high-resolution extreme-ultraviolet (EUV) images and magnetograms from the Solar Dynamics Observatory (SDO) to clarify the relationship between plume emission and the underlying photospheric field. We find that plumes form where unipolar network elements inside coronal holes converge to form dense clumps, and fade as the clumps disperse again. The converging flows also carry internetwork fields of both polarities. Although the minority-polarity flux is sometimes barely visible in the magnetograms, the corresponding EUV images almost invariably show loop-like features in the core of the plumes, with the fine structure changing on timescales of minutes or less. We conclude that the SDO observations are consistent with a model in which plume emission originates from interchange reconnection in converging flows, with the plume lifetime being determined by the ∼1 day evolutionary timescale of the supergranular network. Furthermore, the presence of large EUV bright points and/or ephemeral regions is not a necessary precondition for the formation of plumes, which can be energized even by the weak, mixed-polarity internetwork fields swept up by converging flows.

  13. Converging Supergranular Flows and the Formation of Coronal Plumes

    NASA Technical Reports Server (NTRS)

    Wang, Y.-M.; Warren, H. P.; Muglach, K.

    2016-01-01

    Earlier studies have suggested that coronal plumes are energized by magnetic reconnection between unipolar flux concentrations and nearby bipoles, even though magnetograms sometimes show very little minority-polarity flux near the footpoints of plumes. Here we use high-resolution extreme-ultraviolet (EUV) images and magnetograms from the Solar Dynamics Observatory (SDO) to clarify the relationship between plume emission and the underlying photospheric field. We find that plumes form where unipolar network elements inside coronal holes converge to form dense clumps, and fade as the clumps disperse again. The converging flows also carry internetwork fields of both polarities. Although the minority-polarity flux is sometimes barely visible in the magnetograms, the corresponding EUV images almost invariably show loop-like features in the core of the plumes, with the fine structure changing on timescales of minutes or less. We conclude that the SDO observations are consistent with a model in which plume emission originates from interchange reconnection in converging flows, with the plume lifetime being determined by the approximately 1-day evolutionary timescale of the supergranular network. Furthermore, the presence of large EUV bright points and/or ephemeral regions is not a necessary precondition for the formation of plumes, which can be energized even by the weak, mixed-polarity internetwork fields swept up by converging flows.

  14. Seeking Convergent Evidence of Epistemological Beliefs: A Novel Survey

    ERIC Educational Resources Information Center

    Briell, Jeremy E.; Elen, Jan; Clarebout, Geraldine

    2013-01-01

    Introduction: This paper explains the development and testing of a novel paper-and-pencil measure designed to support inferences of five epistemological belief dimensions based on three forms of evidence. The three evidence types are anticipated to converge at a single theoretical level, permitting better-supported inferences than existing survey…

  15. Uniform Convergence of a Sequence of Functions at a Point

    ERIC Educational Resources Information Center

    Klippert, J.; Williams, G.

    2002-01-01

    It is well known that the uniform limit of a sequence of continuous real-valued functions defined on an interval I is itself continuous. However, if the convergence is pointwise, the limit function need not be continuous (take f[subscript n](x) = x[superscript n] on [0, 1], for example). Boas has shown that the pointwise limit function of a…

  16. Converged Librarian/Academic Roles in the 'Wired' University.

    ERIC Educational Resources Information Center

    Dugdale, Christine

    New technologies allow universities to extend pedagogical practices, enhance learning experiences and develop self-managed lifelong learners. To take full advantage of evolving technologies, multi-skilled teaching and development teams are required with a merging and converging of academic and librarian roles. Conclusions are reported from the…

  17. The Converging Literacies Center: An Integrated Model for Writing Programs

    ERIC Educational Resources Information Center

    Carter, Shannon; Dunbar-Odom, Donna

    2009-01-01

    The Converging Literacies Center (CLiC) is a deeply integrated model for writing programs, bringing together the writing center, first-year writing, basic writing, professional development activities, graduate coursework, and research activities to re-imagine and support twenty-first-century literacies. What is unique about CLiC is not merely the…

  18. Paths of convergence for agriculture, health, and wealth

    PubMed Central

    Dubé, Laurette; Pingali, Prabhu; Webb, Patrick

    2012-01-01

    This special feature calls for forward thinking around paths of convergence for agriculture, health, and wealth. Such convergence aims for a richer integration of smallholder farmers into national and global agricultural and food systems, health systems, value chains, and markets. The articles identify analytical innovation, where disciplines intersect, and cross-sectoral action where single, linear, and siloed approaches have traditionally dominated. The issues addressed are framed by three main themes: (i) lessons related to agricultural and food market growth since the 1960s; (ii) experiences related to the integration of smallholder agriculture into national and global business agendas; and (iii) insights into convergence-building institutional design and policy, including a review of complexity science methods that can inform such processes. In this introductory article, we first discuss the perspectives generated for more impactful policy and action when these three themes converge. We then push thematic boundaries to elaborate a roadmap for a broader, solution-oriented, and transdisciplinary approach to science, policies, and actions. As the global urban population crosses the 50% mark, both smallholder and nonsmallholder agriculture are keys in forging rural–urban links, where both farm and nonfarm activities contribute to sustainable nutrition security. The roadmaps would harness the power of business to reduce hunger and poverty for millions of families, contribute to a better alignment between human biology and modern lifestyles, and stem the spread of noncommunicable chronic diseases. PMID:22826252

  19. Defending Symbolic Convergence Theory from an Imaginary Gunn

    ERIC Educational Resources Information Center

    Bormann, Ernest G.; Cragan, John F.; Shields, Donald C.

    2003-01-01

    Joshua Gunn calls for the creation of a new post-humanist, -Marxist, -Freudian approach to rhetorical criticism that would combine literary, critical, and psychoanalytic methods in a new "popular imaginary" paradigm. While urging acceptance of his new paradigm, Gunn advances three major criticisms of symbolic convergence theory (SCT): (1) SCT is…

  20. Evaluating the Convergence of Muscle Appearance Attitude Measures

    ERIC Educational Resources Information Center

    Cafri, Guy; Thompson, J. Kevin

    2004-01-01

    There has been growing interest in the assessment of a muscular appearance. Given the importance of assessing muscle appearance attitudes, the aim of this study was to explore the convergence of the Drive for Muscularity Scale, Somatomorphic Matrix, Contour Drawing Rating Scale, Male Figure Drawings, and the Muscularity Rating Scale. Participants…

  1. Functional convergence in bat and toothed whale biosonars.

    PubMed

    Madsen, P T; Surlykke, A

    2013-09-01

    Echolocating bats and toothed whales hunt and navigate by emission of sound pulses and analysis of returning echoes to form a self-generated auditory scene. Here, we demonstrate a striking functional convergence in the way these two groups of mammals independently evolved the capability to sense with sound in air and water.

  2. Representational System Predicate Use and Convergence in Counseling: Gloria Revisited.

    ERIC Educational Resources Information Center

    Mercier, Mary Ann; Johnson, Marilyn

    1984-01-01

    Analayzed transcripts of Three Approaches to Psychotherapy (Shostrom, 1966) for counselor and client representational system predicate use. Although different patterns of predicate use emerged, only limited support for Neurolinguistic Programming theory was found. The findings of different patterns of predicate use were related to convergence and…

  3. A New Look at the Convergence of a Famous Sequence

    ERIC Educational Resources Information Center

    Dobrescu, Mihaela

    2010-01-01

    A new proof for the monotonicity of the sequence [image omitted] is given as a special case of a large family of monotomic and bounded, hence convergent sequences. The new proof is based on basic calculus results rather than induction, which makes it accessible to a larger audience including business and life sciences students and faculty. The…

  4. Improving convergence in smoothed particle hydrodynamics simulations without pairing instability

    NASA Astrophysics Data System (ADS)

    Dehnen, Walter; Aly, Hossam

    2012-09-01

    The numerical convergence of smoothed particle hydrodynamics (SPH) can be severely restricted by random force errors induced by particle disorder, especially in shear flows, which are ubiquitous in astrophysics. The increase in the number NH of neighbours when switching to more extended smoothing kernels at fixed resolution (using an appropriate definition for the SPH resolution scale) is insufficient to combat these errors. Consequently, trading resolution for better convergence is necessary, but for traditional smoothing kernels this option is limited by the pairing (or clumping) instability. Therefore, we investigate the suitability of the Wendland functions as smoothing kernels and compare them with the traditional B-splines. Linear stability analysis in three dimensions and test simulations demonstrate that the Wendland kernels avoid the pairing instability for all NH, despite having vanishing derivative at the origin (disproving traditional ideas about the origin of this instability; instead, we uncover a relation with the kernel Fourier transform and give an explanation in terms of the SPH density estimator). The Wendland kernels are computationally more convenient than the higher order B-splines, allowing large NH and hence better numerical convergence (note that computational costs rise sublinear with NH). Our analysis also shows that at low NH the quartic spline kernel with NH ≈ 60 obtains much better convergence than the standard cubic spline.

  5. Paths of convergence for agriculture, health, and wealth.

    PubMed

    Dubé, Laurette; Pingali, Prabhu; Webb, Patrick

    2012-07-31

    This special feature calls for forward thinking around paths of convergence for agriculture, health, and wealth. Such convergence aims for a richer integration of smallholder farmers into national and global agricultural and food systems, health systems, value chains, and markets. The articles identify analytical innovation, where disciplines intersect, and cross-sectoral action where single, linear, and siloed approaches have traditionally dominated. The issues addressed are framed by three main themes: (i) lessons related to agricultural and food market growth since the 1960s; (ii) experiences related to the integration of smallholder agriculture into national and global business agendas; and (iii) insights into convergence-building institutional design and policy, including a review of complexity science methods that can inform such processes. In this introductory article, we first discuss the perspectives generated for more impactful policy and action when these three themes converge. We then push thematic boundaries to elaborate a roadmap for a broader, solution-oriented, and transdisciplinary approach to science, policies, and actions. As the global urban population crosses the 50% mark, both smallholder and nonsmallholder agriculture are keys in forging rural-urban links, where both farm and nonfarm activities contribute to sustainable nutrition security. The roadmaps would harness the power of business to reduce hunger and poverty for millions of families, contribute to a better alignment between human biology and modern lifestyles, and stem the spread of noncommunicable chronic diseases.

  6. The Convergent Validity of the Cognitive Preference Construct. Draft Copy.

    ERIC Educational Resources Information Center

    van den Berg, Euwe; And Others

    Reported is a study designed to investigate the convergent validity of the cognitive preference construct and to develop new techniques for analyzing cognitive preference data. The cognitive preference construct was invented to help evaluate the science curricula of the sixties based on the assumption that a student's intellectual approach to…

  7. Interactive Patterns and Conceptual Convergence during Student Collaborations in Science

    ERIC Educational Resources Information Center

    Oliveira, Alandeom W.; Sadler, Troy D.

    2008-01-01

    This study examines cognitive and social processes in group interactions that shape collaborative learning in science classrooms. Three small groups of students were observed while working collaboratively on explaining the burning of a candle under a jar. The learning environment served as a context for examination of conceptual convergence, a…

  8. Convergent Validity of Group Tests of Cognitive Development.

    ERIC Educational Resources Information Center

    Stefanich, Greg P.; And Others

    1983-01-01

    Investigated convergent validity of individual Piaget/Inhelder clinical task interviews with Reasoning Test (Ankney and Joyce), Logical Reasoning Test (Burney), and Classroom Test of Formal Operations (Lawson). Indicates that correlations obtained are not sufficiently strong to warrant selection/categorization of individual students based on their…

  9. Convergence and Professional Identity in the Academic Library

    ERIC Educational Resources Information Center

    Wilson, Kerry M.; Halpin, Eddie

    2006-01-01

    This paper discusses the effects of operational convergence, and the subsequent growth of the hybrid library model, upon the professional self-identity of academic library staff. The role of professionalism as a concept and motivational driver within contemporary academic librarianship is examined. Main themes of investigation include the extent…

  10. Convergence of broad-scale migration strategies in terrestrial birds.

    PubMed

    La Sorte, Frank A; Fink, Daniel; Hochachka, Wesley M; Kelling, Steve

    2016-01-27

    Migration is a common strategy used by birds that breed in seasonal environments. Selection for greater migration efficiency is likely to be stronger for terrestrial species whose migration strategies require non-stop transoceanic crossings. If multiple species use the same transoceanic flyway, then we expect the migration strategies of these species to converge geographically towards the most optimal solution. We test this by examining population-level migration trajectories within the Western Hemisphere for 118 migratory species using occurrence information from eBird. Geographical convergence of migration strategies was evident within specific terrestrial regions where geomorphological features such as mountains or isthmuses constrained overland migration. Convergence was also evident for transoceanic migrants that crossed the Gulf of Mexico or Atlantic Ocean. Here, annual population-level movements were characterized by clockwise looped trajectories, which resulted in faster but more circuitous journeys in the spring and more direct journeys in the autumn. These findings suggest that the unique constraints and requirements associated with transoceanic migration have promoted the spatial convergence of migration strategies. The combination of seasonal atmospheric and environmental conditions that has facilitated the use of similar broad-scale migration strategies may be especially prone to disruption under climate and land-use change.

  11. Convergent Flows: Humanities Scholars and Their Interactions with Electronic Texts

    ERIC Educational Resources Information Center

    Sukovic, Suzana

    2008-01-01

    This article reports research findings related to converging formats, media, practices, and ideas in the process of academics' interaction with electronic texts during a research project. The findings are part of the results of a study that explored interactions of scholars in literary and historical studies with electronic texts as primary…

  12. Paths of convergence for agriculture, health, and wealth.

    PubMed

    Dubé, Laurette; Pingali, Prabhu; Webb, Patrick

    2012-07-31

    This special feature calls for forward thinking around paths of convergence for agriculture, health, and wealth. Such convergence aims for a richer integration of smallholder farmers into national and global agricultural and food systems, health systems, value chains, and markets. The articles identify analytical innovation, where disciplines intersect, and cross-sectoral action where single, linear, and siloed approaches have traditionally dominated. The issues addressed are framed by three main themes: (i) lessons related to agricultural and food market growth since the 1960s; (ii) experiences related to the integration of smallholder agriculture into national and global business agendas; and (iii) insights into convergence-building institutional design and policy, including a review of complexity science methods that can inform such processes. In this introductory article, we first discuss the perspectives generated for more impactful policy and action when these three themes converge. We then push thematic boundaries to elaborate a roadmap for a broader, solution-oriented, and transdisciplinary approach to science, policies, and actions. As the global urban population crosses the 50% mark, both smallholder and nonsmallholder agriculture are keys in forging rural-urban links, where both farm and nonfarm activities contribute to sustainable nutrition security. The roadmaps would harness the power of business to reduce hunger and poverty for millions of families, contribute to a better alignment between human biology and modern lifestyles, and stem the spread of noncommunicable chronic diseases. PMID:22826252

  13. On a Cubically Convergent Iterative Method for Matrix Sign

    PubMed Central

    Sharifi, M.; Karimi Vanani, S.; Khaksar Haghani, F.; Arab, M.; Shateyi, S.

    2015-01-01

    We propose an iterative method for finding matrix sign function. It is shown that the scheme has global behavior with cubical rate of convergence. Examples are included to show the applicability and efficiency of the proposed scheme and its reciprocal. PMID:25954769

  14. Convergence Analysis of a Cascade Architecture Neural Network

    NASA Technical Reports Server (NTRS)

    Duong, Tuan A.; Stubberub, Allen R.; Daud, Taher; Thakoor, Anil

    1997-01-01

    In this paper, we present a mathematical foundation, including a convergence analysis, for cascading architecture neural networks. From this, a mathematical foundation for the casade correlation learning algorithm can also be found. Furthermore, it becomes apparent that the cascade correlation scheme is a special case of an efficient hardware learning algorithm called Cascade Error Projection.

  15. Characteristics of Convergence Learning Experience Using an Educational Documentary Film

    ERIC Educational Resources Information Center

    Shin, Jongho; Cho, Eunbyul

    2015-01-01

    The purpose of the study was to investigate the characteristics of convergence learning experience when learners study integrated learning contents from various academic subjects. Specifically, cognitive and emotional experiences and their changes over time were investigated. Eight undergraduate and graduate students participated in the study.…

  16. Capitalism, Identity Politics, and Queerness Converge: LGBT Employee Resource Groups

    ERIC Educational Resources Information Center

    Githens, Rod P.

    2009-01-01

    Lesbian, gay, bisexual, and transgender (LGBT) employee resource groups have brought about substantial organizational change within corporations. Capitalist structures have enabled these changes to occur more quickly in the private sector than within the public sector. In this article, I explore how capitalism has converged with two approaches of…

  17. Structural and Convergent Validity of the Homework Performance Questionnaire

    ERIC Educational Resources Information Center

    Pendergast, Laura L.; Watkins, Marley W.; Canivez, Gary L.

    2014-01-01

    Homework is a requirement for most school-age children, but research on the benefits and drawbacks of homework is limited by lack of psychometrically sound measurement of homework performance. This study examined the structural and convergent validity of scores from the newly developed Homework Performance Questionnaire -- Teacher Scale (HPQ-T).…

  18. Aspired Convergence, Cherished Diversity: Dealing with the Contradictions of Bologna

    ERIC Educational Resources Information Center

    Witte, Johanna

    2008-01-01

    This article addresses the inherent tension in the Bologna process between the aim of convergence and the will to maintain the diversity of national higher education (HE) systems, as well as the decentralised and autonomous nature of national policy formulation on Bologna reforms. Starting from an analytical discussion of the concepts of…

  19. Assessing the Validity of Discourse Analysis: Transdisciplinary Convergence

    ERIC Educational Resources Information Center

    Jaipal-Jamani, Kamini

    2014-01-01

    Research studies using discourse analysis approaches make claims about phenomena or issues based on interpretation of written or spoken text, which includes images and gestures. How are findings/interpretations from discourse analysis validated? This paper proposes transdisciplinary convergence as a way to validate discourse analysis approaches to…

  20. Convergent and Divergent Validity of the Learning Transfer System Inventory

    ERIC Educational Resources Information Center

    Holton, Elwood F., III; Bates, Reid A.; Bookter, Annette I.; Yamkovenko, V. Bogdan

    2007-01-01

    The Learning Transfer System Inventory (LTSI) was developed to identify a select set of factors with the potential to substantially enhance or inhibit transfer of learning to the work environment. It has undergone a variety of validation studies, including construct, criterion, and crosscultural studies. However, the convergent and divergent…

  1. Investigating Convergence Patterns for Numerical Methods Using Data Analysis

    ERIC Educational Resources Information Center

    Gordon, Sheldon P.

    2013-01-01

    The article investigates the patterns that arise in the convergence of numerical methods, particularly those in the errors involved in successive iterations, using data analysis and curve fitting methods. In particular, the results obtained are used to convey a deeper level of understanding of the concepts of linear, quadratic, and cubic…

  2. Secondary Trainee Teachers' Understanding of Convergence and Continuity.

    ERIC Educational Resources Information Center

    Eade, Frank

    2003-01-01

    Explores the understanding that students who are training to be secondary mathematics teachers have of elementary concepts in mathematical analysis. Research involved probing students' conceptual understanding of convergence and continuity and associated reasoning. Concludes that even mathematically well-qualified students have difficulties with…

  3. Considering the Interest-Convergence Dilemma in STEM Education

    ERIC Educational Resources Information Center

    Baber, Lorenzo DuBois

    2015-01-01

    This study examines tensions between universalist ideology and racial/ethnic inequalities in STEM education. Using data collected from qualitative interviews with STEM diversity administrators at 10 research-intensive, public universities, the study considers programmatic goals through an interest-convergence framework. Emerging patterns reveal…

  4. Language Policies in North and South Korea: Divergence and Convergence.

    ERIC Educational Resources Information Center

    Song, Jae Jung

    1994-01-01

    Argues that the language policies in North and South Korea are in some respects divergent and in others convergent. The North uses more nativized words, while the South retains Sino-Korean words. Awareness of each other's policies and their implications in the event of reunification is evident in the regressive measures taken. (23 references) (CK)

  5. Smartphones and Time Zones

    NASA Astrophysics Data System (ADS)

    Baird, William; Secrest, Jeffery; Padgett, Clifford; Johnson, Wayne; Hagrelius, Claire

    2016-09-01

    Using the Sun to tell time is an ancient idea, but we can take advantage of modern technology to bring it into the 21st century for students in astronomy, physics, or physical science classes. We have employed smartphones, Google Earth, and 3D printing to find the moment of local noon at two widely separated locations. By reviewing GPS time-stamped photos from each place, we are able to illustrate that local noon is longitude-dependent and therefore explain the need for time zones.

  6. Saturated Zone Colloid Transport

    SciTech Connect

    H. S. Viswanathan

    2004-10-07

    This scientific analysis provides retardation factors for colloids transporting in the saturated zone (SZ) and the unsaturated zone (UZ). These retardation factors represent the reversible chemical and physical filtration of colloids in the SZ. The value of the colloid retardation factor, R{sub col} is dependent on several factors, such as colloid size, colloid type, and geochemical conditions (e.g., pH, Eh, and ionic strength). These factors are folded into the distributions of R{sub col} that have been developed from field and experimental data collected under varying geochemical conditions with different colloid types and sizes. Attachment rate constants, k{sub att}, and detachment rate constants, k{sub det}, of colloids to the fracture surface have been measured for the fractured volcanics, and separate R{sub col} uncertainty distributions have been developed for attachment and detachment to clastic material and mineral grains in the alluvium. Radionuclides such as plutonium and americium sorb mostly (90 to 99 percent) irreversibly to colloids (BSC 2004 [DIRS 170025], Section 6.3.3.2). The colloid retardation factors developed in this analysis are needed to simulate the transport of radionuclides that are irreversibly sorbed onto colloids; this transport is discussed in the model report ''Site-Scale Saturated Zone Transport'' (BSC 2004 [DIRS 170036]). Although it is not exclusive to any particular radionuclide release scenario, this scientific analysis especially addresses those scenarios pertaining to evidence from waste-degradation experiments, which indicate that plutonium and americium may be irreversibly attached to colloids for the time scales of interest. A section of this report will also discuss the validity of using microspheres as analogs to colloids in some of the lab and field experiments used to obtain the colloid retardation factors. In addition, a small fraction of colloids travels with the groundwater without any significant retardation

  7. Liquid zone seal

    DOEpatents

    Klebanoff, Leonard E.

    2001-01-01

    A seal assembly that provides a means for establishing multiple pressure zones within a system. The seal assembly combines a plate extending from the inner wall of a housing or inner enclosure that intersects with and is immersed in the fluid contained in a well formed in a tray contained within the enclosure. The fluid is a low vapor pressure oil, chemically inert and oxidation resistant. The use of a fluid as the sealing component provides a seal that is self-healing and mechanically robust not subject to normal mechanical wear, breakage, and formation of cracks or pinholes and decouples external mechanical vibrations from internal structural members.

  8. Widespread convergence in toxin resistance by predictable molecular evolution.

    PubMed

    Ujvari, Beata; Casewell, Nicholas R; Sunagar, Kartik; Arbuckle, Kevin; Wüster, Wolfgang; Lo, Nathan; O'Meally, Denis; Beckmann, Christa; King, Glenn F; Deplazes, Evelyne; Madsen, Thomas

    2015-09-22

    The question about whether evolution is unpredictable and stochastic or intermittently constrained along predictable pathways is the subject of a fundamental debate in biology, in which understanding convergent evolution plays a central role. At the molecular level, documented examples of convergence are rare and limited to occurring within specific taxonomic groups. Here we provide evidence of constrained convergent molecular evolution across the metazoan tree of life. We show that resistance to toxic cardiac glycosides produced by plants and bufonid toads is mediated by similar molecular changes to the sodium-potassium-pump (Na(+)/K(+)-ATPase) in insects, amphibians, reptiles, and mammals. In toad-feeding reptiles, resistance is conferred by two point mutations that have evolved convergently on four occasions, whereas evidence of a molecular reversal back to the susceptible state in varanid lizards migrating to toad-free areas suggests that toxin resistance is maladaptive in the absence of selection. Importantly, resistance in all taxa is mediated by replacements of 2 of the 12 amino acids comprising the Na(+)/K(+)-ATPase H1-H2 extracellular domain that constitutes a core part of the cardiac glycoside binding site. We provide mechanistic insight into the basis of resistance by showing that these alterations perturb the interaction between the cardiac glycoside bufalin and the Na(+)/K(+)-ATPase. Thus, similar selection pressures have resulted in convergent evolution of the same molecular solution across the breadth of the animal kingdom, demonstrating how a scarcity of possible solutions to a selective challenge can lead to highly predictable evolutionary responses. PMID:26372961

  9. Widespread convergence in toxin resistance by predictable molecular evolution

    PubMed Central

    Ujvari, Beata; Casewell, Nicholas R.; Sunagar, Kartik; Arbuckle, Kevin; Wüster, Wolfgang; Lo, Nathan; O’Meally, Denis; Beckmann, Christa; King, Glenn F.; Deplazes, Evelyne; Madsen, Thomas

    2015-01-01

    The question about whether evolution is unpredictable and stochastic or intermittently constrained along predictable pathways is the subject of a fundamental debate in biology, in which understanding convergent evolution plays a central role. At the molecular level, documented examples of convergence are rare and limited to occurring within specific taxonomic groups. Here we provide evidence of constrained convergent molecular evolution across the metazoan tree of life. We show that resistance to toxic cardiac glycosides produced by plants and bufonid toads is mediated by similar molecular changes to the sodium-potassium-pump (Na+/K+-ATPase) in insects, amphibians, reptiles, and mammals. In toad-feeding reptiles, resistance is conferred by two point mutations that have evolved convergently on four occasions, whereas evidence of a molecular reversal back to the susceptible state in varanid lizards migrating to toad-free areas suggests that toxin resistance is maladaptive in the absence of selection. Importantly, resistance in all taxa is mediated by replacements of 2 of the 12 amino acids comprising the Na+/K+-ATPase H1–H2 extracellular domain that constitutes a core part of the cardiac glycoside binding site. We provide mechanistic insight into the basis of resistance by showing that these alterations perturb the interaction between the cardiac glycoside bufalin and the Na+/K+-ATPase. Thus, similar selection pressures have resulted in convergent evolution of the same molecular solution across the breadth of the animal kingdom, demonstrating how a scarcity of possible solutions to a selective challenge can lead to highly predictable evolutionary responses. PMID:26372961

  10. Short‐term time step convergence in a climate model

    PubMed Central

    Rasch, Philip J.; Taylor, Mark A.; Jablonowski, Christiane

    2015-01-01

    Abstract This paper evaluates the numerical convergence of very short (1 h) simulations carried out with a spectral‐element (SE) configuration of the Community Atmosphere Model version 5 (CAM5). While the horizontal grid spacing is fixed at approximately 110 km, the process‐coupling time step is varied between 1800 and 1 s to reveal the convergence rate with respect to the temporal resolution. Special attention is paid to the behavior of the parameterized subgrid‐scale physics. First, a dynamical core test with reduced dynamics time steps is presented. The results demonstrate that the experimental setup is able to correctly assess the convergence rate of the discrete solutions to the adiabatic equations of atmospheric motion. Second, results from full‐physics CAM5 simulations with reduced physics and dynamics time steps are discussed. It is shown that the convergence rate is 0.4—considerably slower than the expected rate of 1.0. Sensitivity experiments indicate that, among the various subgrid‐scale physical parameterizations, the stratiform cloud schemes are associated with the largest time‐stepping errors, and are the primary cause of slow time step convergence. While the details of our findings are model specific, the general test procedure is applicable to any atmospheric general circulation model. The need for more accurate numerical treatments of physical parameterizations, especially the representation of stratiform clouds, is likely common in many models. The suggested test technique can help quantify the time‐stepping errors and identify the related model sensitivities. PMID:27660669

  11. Free-Tropospheric Moisture Convergence and Tropical Convective Regimes

    NASA Astrophysics Data System (ADS)

    Masunaga, H.

    2014-12-01

    It is known that quiescent periods with only shallow cumuli prevalent are frequently observed even in the deep Tropics, which is considered from the climatological perspectives as an area harboring vigorous deep convection. It is argued in this work that the free-tropospheric (FT) moisture convergence is a crucial factor for separating the stable maintenance of isolated shallow cumuli in the quiescent periods from the self-sustaining growth of organized convective systems in the dynamic periods over tropical oceans. The analysis is based on a variety of satellite measurements including Aqua AIRS T and q soundings and QuikSCAT surface wind, composited with reference to the time before or after the occurrence of precipitating clouds detected by TRMM PR. The FT moisture convergence and updraft moisture flux at cloud base are then derived from this dataset under large-scale moisture budget constraint (see Figure). Free-tropospheric precipitation efficiency (FTPE), or the ratio of precipitation to updraft moisture flux at cloud base, is introduced as a measure of convective intensity (rather than the population) over the large-scale domain. The following hypothesis is discussed in light of the analysis results. Isolated shallow cumuli would stay shallow when large-scale FT moisture is diverging (although moisture is weakly converging when integrated over the whole troposphere) since an increase in cumulus population would be counteracted by an additional moisture divergence in the FT. When large-scale FT convergence is positive, in contrast, developing clouds would induce a more moisture input and allow an unstable growth to a highly organized convective system. Zero FT moisture convergence may serve as the neutrality separating the negative feedback acting in the quiescent regime from the positive feedback instrumental for the dynamic regime.

  12. Temperature Models for the Mexican Subduction Zone

    NASA Astrophysics Data System (ADS)

    Manea, V. C.; Kostoglodov, V.; Currie, C.; Manea, M.; Wang, K.

    2002-12-01

    It is well known that the temperature is one of the major factors which controls the seismogenic zone. The Mexican subduction zone is characterized by a very shallow flat subducting interplate in its central part (Acapulco, Oaxaca), and deeper subduction slabs northern (Jalisco) and southern (Chiapas). It has been proposed that the seismogenic zone is controlled, among other factors, by a temperature. Therefore, we have developed four two-dimensional steady state thermal models for Jalisco, Guerrero, Oaxaca and Chiapas. The updip limit of the seismogenic zone is taken between 100 §C and 150 §C, while the downdip limit is thought to be at 350 §C because of the transition from stick-slip to stable-sliding. The shape of the subducting plate is inferred from gravity and seismicity. The convergence velocity between oceanic and continental lithospheric plates is taken as the following: 5 cm/yr for Jalisco profile, 5.5 for Guerrero profile, 5.8 for Oaxaca profile, and 7.8 for Chiapas profile. The age of the subducting plates, since they are young, and provides the primary control on the forearc thermal structure, are as the following: 11 My for Jalisco profile, 14.5 My for Guerrero profile, 15 My for Oaxaca profile, and 28 My for Chiapas profile. We also introduced in the models a small quantity of frictional heating (pore pressure ratio 0.98). The value of 0.98 for pore pressure ratio was obtained for the Guerrero profile, in order to fit the intersection between the 350 §C isotherm and the subducting plate at 200 Km from trench. The value of 200 km coupling zone from trench is inferred from GPS data for the steady interseismic period and also for the last slow aseismic slip that occurred in Guerrero in 2002. We have used this value of pore pressure ratio (0.98) for all the other profiles. For the others three profiles we obtained the following coupling extents: Jalisco - 100 km, Oaxaca - 170 km and Chiapas - 125 km (from the trench). Independent constrains of the

  13. The deep structure of the North Anatolian Fault Zone (Invited)

    NASA Astrophysics Data System (ADS)

    Fichtner, A.; Cupillard, P.; Saygin, E.; Trampert, J.; Taymaz, T.; Capdeville, Y.

    2013-12-01

    Multi-scale full waveform inversion of complete continental- and regional-scale seismograms reveals the crustal and upper-mantle signature of the North Anatolian Fault Zone which shapes the neotectonics of Turkey and the eastern Mediterranean. Within the crust, the fault zone is mostly bounded by several high-velocity blocks, suggesting that it developed along the edges of continental fragments with high rigidity. Below the crust, the surface expression of the eastern and central parts of the North Anatolian Fault Zone correlate with a pronounced low-velocity band that extends laterally over 600 km. Around 100 km depth, the low-velocity band merges into the shallow Anatolian asthenosphere, thereby providing a link to the Kirka-Afyon-Isparta Volcanic Field and the Central Anatolian Volcanics. We interpret the low-velocity band beneath the North Anatolian Fault Zone as the upper-mantle expression of the Tethyan sutures that formed 60-15 Ma ago as a result of Africa-Eurasian convergence. The structurally weak suture facilitated the formation of the younger (less than 10 Ma) crustal fault zone. In this sense, the North Anatolian Fault Zone is not only a crustal feature, but a narrow zone of weakness that extends into the upper mantle. Horizontal slices through the isotropic S velocity, vS, at 20 km (a) and 40 km (b) depth. Indicated are the surface expressions of the North Anatolian Fault Zone (NAFZ). The North Anatolian Fault (NAF) marks the northern boundary of the NAFZ. Dashed rectangles mark regions that are amplified in the two leftmost panels of the figure. Dotted ellipses indicate thin (20-30 km) crust as inferred from receiver function analysis (Vanacore et al., GJI 2013). Key to marked features: ATB: Anatolide-Tauride Block, IZ: Istanbul Zone, KM: Krsehir Massif, SZ: Sakarya Zone. Horizontal slices through the isotropic S velocity, vs, at 70 km and 150 km depth beneath Europe and western Asia. The Anatolian region where shorter-period data have been

  14. Terranes and suture zones in east central Alaska

    NASA Astrophysics Data System (ADS)

    Churkin, M., Jr.; Foster, H. L.; Chapman, R. M.; Weber, F. R.

    1982-05-01

    East central Alaska, with its 17 terranes, forms a part of the mosaic of allochthonous terranes that join the North American and Siberian plates. These terranes range from continental and continental margin, such as the Tatonduk with its thick well-bedded succession of marine shelf rocks, to seamount, arc, and ocean floor terranes. The Yukon crystalline terrane, the largest described here, is a composite of at least four subterranes juxtaposed across the Tintina fault with the Tatonduk terrane, a northwestern extension of the North American plate in Alaska. Inboard of the Yukon crystalline terrane are packets of closely appressed microterranes separated from the Tatonduk and other terranes belonging to North America by major suture zones. These microterranes lie between North America and the mosaic of accretionary terranes that form the more southerly part of Alaska. The most obviously allochthonous microterranes within the suture zones are the Woodchopper Canyon, an Early Devonian basaltic seamount, and the White Mountains, an Ordovician volcanic arc terrane capped by Silurian and Devonian carbonate bank deposits. The nearest counterpart of these terranes is the Alexander terrane in southeastern Alaska. The Tintina fault of Mesozoic and Cenozoic age, like the Denali fault, primarily follows old suture zones that separate terranes. Strike slip faulting developed after collision in places where further convergence was oblique to the terrane margins. Where terranes met head-on, their leading edges lie along a multiple set of high-angle faults that outline microterranes in accretion zones.

  15. Serpentinite in Active Suprasubduction-Zone Regions and Preserved Terrestrial Sections: Observations; Modeling; and Implications

    NASA Astrophysics Data System (ADS)

    Fryer, P.

    2012-12-01

    Exposures of serpentinized mantle of the overriding plate in the trench-proximal regions of nonaccretionary, intraoceanic forearcs have been extensively studied. Deposits of what were formerly called "sedimentary" serpentinite bodies on land are well documented all over the world. The deposits are variously categorized as mylonitized peridotite that was metamorphosed after obduction of an ophiolite section; olistostromes derived from sections of fault-exposed, serpentinized mantle; diapiric intrusions from point sources or along faults (as ridges); and flows from serpentinite mud volcanoes. The structures and compositions of serpentinite exposures help to differentiate between potential origins and protoliths. Theoretical studies of dehydration reactions, coupled with models of the thermal structure of subduction zones, provide constraints on the nature of fluids liberated from the subducting slab for various convergence angles and rates. These fluids are the source for serpentinization of the suprasubduction-zone mantle. The parameters for degree and distribution of serpentinite in such environments must be, however, constrained in each instance by the forcing functions operating within a given convergent margin. Spatial, i.e., down-dip increases in temperature and pressure vary with convergence angle and rate. Whereas most models assume continuous dehydration of the slab, in reality dehydration events are likely episodic and thus temporal effects must also be considered. We know that suprasubduction-zone serpentinization can begin early in the evolution of a convergent margin and that extensive faulting of a forearc region is necessary for emplacement of serpentinite deposits on the seafloor in active margins. Recent studies of Archean exposures of serpentinized peridotitic deposits suggest that the processes we observe in today's active convergent margins likely also took place during the earliest stages of tectonic cycling of the Earth's lithosphere. The

  16. Subduction-zone magnetic anomalies and implications for hydrated forearc mantle

    USGS Publications Warehouse

    Blakely, R.J.; Brocher, T.M.; Wells, R.E.

    2005-01-01

    Continental mantle in subduction zones is hydrated by release of water from the underlying oceanic plate. Magnetite is a significant byproduct of mantle hydration, and forearc mantle, cooled by subduction, should contribute to long-wavelength magnetic anomalies above subduction zones. We test this hypothesis with a quantitative model of the Cascadia convergent margin, based on gravity and aeromagnetic anomalies and constrained by seismic velocities, and find that hydrated mantle explains an important disparity in potential-field anomalies of Cascadia. A comparison with aeromagnetic data, thermal models, and earthquakes of Cascadia, Japan, and southern Alaska suggests that magnetic mantle may be common in forearc settings and thus magnetic anomalies may be useful in mapping hydrated mantle in convergent margins worldwide. ?? 2005 Geological Society of America.

  17. Convergent evolution across the Australian continent: ecotype diversification drives morphological convergence in two distantly related clades of Australian frogs.

    PubMed

    Vidal-García, M; Keogh, J S

    2015-12-01

    Animals from different clades but subject to similar environments often evolve similar body shapes and physiological adaptations due to convergent evolution, but this has been rarely tested at the transcontinental level and across entire classes of animal. Australia's biome diversity, isolation and aridification history provide excellent opportunities for comparative analyses on broad-scale macroevolutionary patterns. We collected morphological and environmental data on eighty-four (98%) Australian hylid frog species and categorized them into ecotypes. Using a phylogenetic framework, we tested the hypothesis that frogs from the same ecotype display similar body shape patterns: (i) across all the Australian hylids, and (ii) through comparison with a similar previous study on 127 (97%) Australian myobatrachid species. Body size and shape variation did not follow a strong phylogenetic pattern and was not tightly correlated with environment, but there was a stronger association between morphotype and ecotype. Both arboreal and aquatic frogs had long limbs, whereas limbs of fossorial species were shorter. Other terrestrial species were convergent on the more typical frog body shape. We quantified the strength of morphological convergence at two levels: (i) between fossorial myobatrachid and hylid frogs, and (ii) in each ecomorph within the hylids. We found strong convergence within ecotypes, especially in fossorial species. Ecotypes were also reflected in physiological adaptations: both arboreal and cocooned fossorial frogs tend to have higher rates of evaporative water loss. Our results illustrate how adaptation to different ecological niches plays a crucial role in morphological evolution, boosting phenotypic diversity within a clade. Despite phylogenetic conservatism, morphological adaptation to repeatedly emerging new environments can erase the signature of ancestral morphotypes, resulting in phenotypic diversification and convergence both within and between diverse

  18. Convergent evolution across the Australian continent: ecotype diversification drives morphological convergence in two distantly related clades of Australian frogs.

    PubMed

    Vidal-García, M; Keogh, J S

    2015-12-01

    Animals from different clades but subject to similar environments often evolve similar body shapes and physiological adaptations due to convergent evolution, but this has been rarely tested at the transcontinental level and across entire classes of animal. Australia's biome diversity, isolation and aridification history provide excellent opportunities for comparative analyses on broad-scale macroevolutionary patterns. We collected morphological and environmental data on eighty-four (98%) Australian hylid frog species and categorized them into ecotypes. Using a phylogenetic framework, we tested the hypothesis that frogs from the same ecotype display similar body shape patterns: (i) across all the Australian hylids, and (ii) through comparison with a similar previous study on 127 (97%) Australian myobatrachid species. Body size and shape variation did not follow a strong phylogenetic pattern and was not tightly correlated with environment, but there was a stronger association between morphotype and ecotype. Both arboreal and aquatic frogs had long limbs, whereas limbs of fossorial species were shorter. Other terrestrial species were convergent on the more typical frog body shape. We quantified the strength of morphological convergence at two levels: (i) between fossorial myobatrachid and hylid frogs, and (ii) in each ecomorph within the hylids. We found strong convergence within ecotypes, especially in fossorial species. Ecotypes were also reflected in physiological adaptations: both arboreal and cocooned fossorial frogs tend to have higher rates of evaporative water loss. Our results illustrate how adaptation to different ecological niches plays a crucial role in morphological evolution, boosting phenotypic diversity within a clade. Despite phylogenetic conservatism, morphological adaptation to repeatedly emerging new environments can erase the signature of ancestral morphotypes, resulting in phenotypic diversification and convergence both within and between diverse

  19. The Pinto shear zone; a Laramide synconvergent extensional shear zone in the Mojave Desert region of the southwestern United States

    USGS Publications Warehouse

    Wells, M.L.; Beyene, M.A.; Spell, T.L.; Kula, J.L.; Miller, D.M.; Zanetti, K.A.

    2005-01-01

    The Pinto shear zone is one of several Late Cretaceous shear zones within the eastern fringe of the Mesozoic magmatic arc of the southwest Cordilleran orogen that developed synchronous with continued plate convergence and backarc shortening. We demonstrate an extensional origin for the shear zone by describing the shear-zone geometry and kinematics, hanging wall deformation style, progressive changes in deformation temperature, and differences in hanging wall and footwall thermal histories. Deformation is constrained between ???74 and 68 Ma by 40Ar/39Ar thermochronology of the exhumed footwall, including multi-diffusion domain modeling of K-feldspar. We discount the interpretations, applied in other areas of the Mojave Desert region, that widespread Late Cretaceous cooling results from refrigeration due to subduction of a shallowly dipping Laramide slab or to erosional denudation, and suggest alternatively that post-intrusion cooling and exhumation by extensional structures are recorded. Widespread crustal melting and magmatism followed by extension and cooling in the Late Cretaceous are most consistent with production of a low-viscosity lower crust during anatexis and/or delamination of mantle lithosphere at the onset of Laramide shallow subduction. ?? 2005 Elsevier Ltd. All rights reserved.

  20. Convergence of olfactory and vomeronasal projections in the rat basal telencephalon.

    PubMed

    Pro-Sistiaga, Palma; Mohedano-Moriano, Alicia; Ubeda-Bañon, Isabel; Del Mar Arroyo-Jimenez, Maria; Marcos, Pilar; Artacho-Pérula, Emilio; Crespo, Carlos; Insausti, Ricardo; Martinez-Marcos, Alino

    2007-10-01

    Olfactory and vomeronasal projections have been traditionally viewed as terminating in contiguous non-overlapping areas of the basal telencephalon. Original reports, however, described areas such as the anterior medial amygdala where both chemosensory afferents appeared to overlap. We addressed this issue by injecting dextran amines in the main or accessory olfactory bulbs of rats and the results were analyzed with light and electron microscopes. Simultaneous injections of different fluorescent dextran amines in the main and accessory olfactory bulbs were performed and the results were analyzed using confocal microscopy. Similar experiments with dextran amines in the olfactory bulbs plus FluoroGold in the bed nucleus of the stria terminalis indicate that neurons projecting through the stria terminalis could be integrating olfactory and vomeronasal inputs. Retrograde tracing experiments using FluoroGold or dextran amines confirm that areas of the rostral basal telencephalon receive inputs from both the main and accessory olfactory bulbs. While both inputs clearly converge in areas classically considered olfactory-recipient (nucleus of the lateral olfactory tract, anterior cortical amygdaloid nucleus, and cortex-amygdala transition zone) or vomeronasal-recipient (ventral anterior amygdala, bed nucleus of the accessory olfactory tract, and anteroventral medial amygdaloid nucleus), segregation is virtually complete at posterior levels such as the posteromedial and posterolateral cortical amygdalae. This provides evidence that areas so far considered receiving a single chemosensory modality are likely sites for convergent direct olfactory and vomeronasal inputs. Therefore, areas of the basal telencephalon should be reclassified as olfactory, vomeronasal, or mixed chemosensory structures, which could facilitate understanding of olfactory-vomeronasal interactions in functional studies.