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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. Variability of the Inter-Tropical Convergence Zone Related to Changes in Inter-Hemispheric Dust Load

    NASA Astrophysics Data System (ADS)

    Dawson, E.; Evans, S. M.; Ginoux, P. A.

    2016-12-01

    Dust is a key forcing agent in climate and has major societal impacts on health, agriculture, and transportation. Dust varies on inter-annual to millennial timescales up to a factor of 20 between glacial and interglacial periods. Over the 20th century, desert dust has doubled over much of the globe. In addition, dust has strong spatial heterogeneity producing disparate radiative forcing. Hemispheric asymmetry in dust concentrations has been observed between ice cores in Greenland and Antarctica and more recently between Australia and Africa in the 1970's. Our objective is to assess the impact of such hemispheric dust asymmetry on climate with an emphasis on the Inter-Tropical Convergence Zone (ITCZ). We perform a set of experiments with the GFDL coupled climate models (CM3), modifying dust emission in each hemisphere by 0, 1, 2, and 5 times preindustrial levels. Dust load follows the imposed emission, which reduces the net radiative flux at the surface and top of the atmosphere. When dust load is asymmetric, we find that the radiative forcing is similarly asymmetric, generating an inter-hemispheric transfer of energy through the atmosphere and ocean and an associated shift in precipitation along the ITCZ. We find a linear relationship between radiative forcing and tropical precipitation asymmetry in the Atlantic. Our results show that dust plays a significant role in determining the latitudinal position of the ITCZ. Understanding this relationship is crucial for accurately predicting dust feedbacks and the effects of dust on future climate. This relationship is also important for understanding past climate variability such as the mid-Holocene and Last Glacial Maximum.

  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

    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.

  7. 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

    2017-06-01

    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.

  8. 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

  9. Evolution of the Lorenz energy cycle in the Inter-Tropical Convergence Zone in the South American sector of the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    da Silva, Ligia; Vieira, Luis Eduardo; Satyamurty, Prakki

    We investigate the evolution of the Lorenz energy cycle in the Intertropical Convergence Zone (ITCZ) in the South American sector of the Atlantic. We compute the evolution of the zonal and eddy components of kinetic and potential energies using reanalysis data. We identify the ITCZ using the outgoing long-wave radiation (OLR) data. We realize a wavelet decomposition of the time series to study the ITCZ variability and to detect long-term trends. We also investigate trends in the evolution of the sea-surface temperature (SST) and sea-level pressure (SLP) in the ITCZ region. Furthermore, connections with the variability of the South Pacific circulation are examined employing the southern oscillation index (SOI) as a proxy. We found a strong annual cycle in all the energy components with high peaks in austral summer. Approximately 91

  10. 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

  11. 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

  12. The Intertropical Convergence Zone

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Intertropical Convergence Zone, or ITCZ, is the region that circles the Earth, near the equator, where the trade winds of the Northern and Southern Hemispheres come together. The intense sun and warm water of the equator heats the air in the ITCZ, raising its humidity and causing it to rise. As the air rises it cools, releasing the accumulated moisture in an almost perpetual series of thunderstorms. Variation in the location of the ITCZ 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. This image is a combination of cloud data from NOAA's newest Geostationary Operational Environmental Satellite (GOES-11) and color land cover classification data. The ITCZ is the band of bright white clouds that cuts across the center of the image. For more GOES images, visit the GOES Project Science site. Image Courtesy GOES Project Science Office

  13. The Intertropical Convergence Zone

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Intertropical Convergence Zone, or ITCZ, is the region that circles the Earth, near the equator, where the trade winds of the Northern and Southern Hemispheres come together. The intense sun and warm water of the equator heats the air in the ITCZ, raising its humidity and causing it to rise. As the air rises it cools, releasing the accumulated moisture in an almost perpetual series of thunderstorms. Variation in the location of the ITCZ 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. This image is a combination of cloud data from NOAA's newest Geostationary Operational Environmental Satellite (GOES-11) and color land cover classification data. The ITCZ is the band of bright white clouds that cuts across the center of the image. For more GOES images, visit the GOES Project Science site. Image Courtesy GOES Project Science Office

  14. Observation of Southward Shift of the North Pacific Intertropical Convergence Zone

    NASA Astrophysics Data System (ADS)

    Chiu, L.; Gao, S.

    2014-12-01

    One of the major feature of tropical precipitation is the seasonal movement of the Inter-Tropical Convergence Zone (ITCZ). Linear trend analyses of observational rainfall data show global trend patterns of opposite changes near the ITC regions. High-resolution monthly oceanic rainfall data derived from microwave observations by the Remote Sensing Systems are examined to characterize the trend and variability of the North Pacific Inter-tropical Convergence Zone (ITCZ) for the period 1988-2012. Position of the ITCZ is defined as the centroid of rain band between 15°N and equator for each longitude. The climatology captures the seasonal cycle of meridional migration of the ITCZ. The North Pacific ITCZ location shows significant southward shift of 0.3-0.5° decade-1 in the annual mean and in all seasons except for northern spring with El Niño-Southern Oscillation signal removed. Empirical orthogonal function analyses of the ITCZ position anomalies in the northern summer and autumn indicates a distinct difference in the ITCZ long-term variability between the western North Pacific and the eastern North Pacific, with more pronounced southward shift in the western North Pacific. The technique is applied to other rainfall data sets to characterize the temporal and spatial variability of the ITCZ movements.

  15. 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.

  16. Stratospheric aerosols in the intertropical convergence zone, Panama Canal zone

    NASA Technical Reports Server (NTRS)

    Farlow, N. H.; Ferry, G. V.; Lem, H. Y.; Hayes, D. M.

    1979-01-01

    To investigate whether injection sources of the stratospheric aerosol layer could be detected in the tropical stratosphere, an examination of the aerosol vertical and horizontal size distribution around the Intertropical Convergence Zone (ITCZ) at the Panama Canal Zone was performed during the summer of 1977. By comparing these data with similar measurements in temperate and polar regions, it was hoped to discover variations in particle size that would indicate whether a young aerosol is forming and entering the stratosphere at the ITCZ; where the aerosol matures; and finally, where it reenters the troposphere. The methods used in the investigations and the results obtained from the analyses are described.

  17. 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

  18. Comparison between the South Pacific Convergence Zone and South Atlantic Convergence Zone in January 1979

    NASA Technical Reports Server (NTRS)

    Vincent, Dayton G.; Hurrell, James W.; Huang, Huo-Jin

    1986-01-01

    Using one of the FGGE data sets, the eddy potential and eddy kinetic energy budgets during the period of January 10-27, 1979 were derived for the regions containing the South Pacific Convergence Zone (SPCZ) and the South Atlantic Convergence Zone. A complete set of energy equations developed by Brennan and Vincent (1980) was partitioned into zonal and eddy components; the eddy forms of energy were derived from a grid point's departure from the zonal average over a 5-deg latitude belt. The results of the analysis indicate that the eddy kinetic energy content (KE) is greater than the eddy available potential energy content (AE) throughout the period. Both AE and KE show large losses beginning when the SPCZ enters a decaying state: AE shows a gradual but slow decrease until after January 22, when it decreases rapidly; KE oscillates, reaching a maximum on January 22 before a rapid decrease.

  19. 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.

  20. 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.

  1. Impact of the overriding plate rheology on convergence zone dynamics.

    NASA Astrophysics Data System (ADS)

    Hertgen, Solenn; Yamato, Philippe; Guillaume, Benjamin; van Hunen, Jeroen

    2017-04-01

    Most of deformation at the Earth's surface is localized at plate boundaries. This deformation can be accommodated in very different ways depending on the tectonic setting. In the case of convergence zones, the deformation is typically simplified and classified as follows: - intra-oceanic convergence, when convergence involves two oceanic lithospheres, which generally leads to the subduction/obduction initiation and to the formation of an island arc; - convergence between an oceanic and a continental lithosphere, which is mainly accommodated by subduction and can lead to the formation of a mountain range at the plate boundary; - convergence involving two continental lithospheres, which is accommodated by collision and leads to the formation of a mountain range produced by the stacking of crustal slices. Different materials are thus involved (i.e., oceanic crust, continental crust, sediments). Depending on the context (oceanic or continental subduction), they can form contrasted structures in terms of units size, morphology and metamorphism (e.g., Alps vs. Andes/Altiplano-Puna). Moreover, some convergent zones with apparently similar tectonic settings (e.g., continent/continent convergence) show very different patterns of deformation with either very localized deformation (e.g., the Alps) or, at the opposite, deformation distributed over thousands of kilometers (e.g, Himalayas/Tibet). Finally, other convergent zones from different tectonic settings seem to show similar structures (e.g., Tibet plateau and Altiplano-Puna plateaus). Although the mechanism of plate convergence appears to be the same in each case, the structures obtained at the surface seem to be unique. Rheology of both the subducting plate and of the plate interface is known to influence the convergence zones dynamics. However, very few studies have addressed the role of the overriding plate rheology in details, while it may also exert a large control on the deformation style at plate boundaries. In

  2. 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

  3. OH measurement near the intertropical convergence zone in the Pacific

    NASA Technical Reports Server (NTRS)

    Davis, L. I., Jr.; James, John V.; Wang, Charles C.; Guo, Chuan; Morris, Peter T.; Fishman, Jack

    1987-01-01

    Airborne measurements of OH were made near the Intertropical Convergence Zone in the Pacific, and the averaged results for each data run were compared with those calculated from a photochemical model. The measured OH concentrations were found to vary along the flight path. Possible causes for the observed variations are discussed.

  4. Convection in the east Pacific Intertropical Convergence Zone

    NASA Astrophysics Data System (ADS)

    Raymond, David J.

    2017-01-01

    The eastern tropical Pacific exhibits a strong, cross-equatorial sea surface temperature (SST) gradient, which drives a southerly flow in the atmospheric boundary layer. Convergence in this flow is generally considered to drive deep convection in the east Pacific Intertropical Convergence Zone. However, results from cloud modeling and recent field programs provide an alternative thermodynamic mechanism for controlling this convection. While shallow convection responds to boundary layer convergence, deep convection appears to be controlled by a combination of convective inhibition, surface moist entropy fluxes, tropospheric relative humidity, and moist convective instability. These factors explain the sharp minimum in infrared brightness temperature near 8°N while boundary layer convergence occurs over a much broader range of latitudes.

  5. Multiple Convergence Zone Acoustic Telemetry Feasibility Test Report

    DTIC Science & Technology

    1991-11-01

    oseq oseqr body Multiple Convergence Zone Acoustic Telemetry Feasibility Tesi ReportNovemrber 6. 199153 53 pack oseq=[ipfill([- 1 1 -1I1 -1 -111 -1 -1...Convergpnce Zonc Acoumtic Telcmetry Feasibdity Tesi Rertm.Nvcmbcr 6, 199180 80 oseq=oseq.*exp((sqrt(- I )*2*pi*(fO/fs))*(O: 1 :length(oseq)- I)); pnstrn...Stella Sanchez -Wade Pell Marine Science Library Documents Section University of Rhode Island Scripps Institution of Oceanography Narragansett Bay Campus

  6. 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.

  7. Migrations and dynamics of the intertropical convergence zone.

    PubMed

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

    2014-09-04

    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.

  8. The South Pacific convergence zone (SPCZ): A review

    NASA Technical Reports Server (NTRS)

    Vincent, Dayton G.

    1994-01-01

    The circulation features associated with the South Pacific convergence zone (SPCZ) and its accompanying cloud band are reviewed and discussed. The paper focuses on the following topics: location, structure, and characteristics of the SPCZ; theories and observations concerning its existence; the significance and scope of the SPCZ in global-scale circulation patterns; quasi-periodic changes in its location and strength; and synoptic-scale features within its regional influence (e.g., cyclones, subtropical jets). It concludes with some challenging problems for the future.

  9. Marine debris collects within the North Pacific Subtropical Convergence Zone.

    PubMed

    Pichel, William G; Churnside, James H; Veenstra, Timothy S; Foley, David G; Friedman, Karen S; Brainard, Russell E; Nicoll, Jeremy B; Zheng, Quanan; Clemente-Colón, Pablo

    2007-08-01

    Floating marine debris, particularly derelict fishing gear, is a hazard to fish, marine mammals, turtles, sea birds, coral reefs, and even human activities. To ameliorate the economic and environmental impact of marine debris, we need to efficiently locate and retrieve dangerous debris at sea. Guided by satellite-derived information, we made four flights north of Hawaii in March and April 2005. During these aerial surveys, we observed over 1800 individual pieces of debris, including 122 derelict fishing nets. The largest debris concentrations were found just north of the North Pacific Transition Zone Chlorophyll Front (TZCF) within the North Pacific Subtropical Convergence Zone (STCZ). Debris densities were significantly correlated with sea-surface temperature (SST), chlorophyll-a concentration (Chla), and the gradient of Chla. A Debris Estimated Likelihood Index (DELI) was developed to predict where high concentrations of debris would be most likely in the North Pacific during spring and early summer.

  10. New criterion to select the South Atlantic Convergence Zone

    NASA Astrophysics Data System (ADS)

    Ferraz, S. E.; Ambrizzi, T.; Rocha, R. P.

    2007-05-01

    The South Atlantic Convergence Zone (SACZ) is a climatic aspect of the intraseasonal scale that produces intense precipitation in Southeast Brazil during summer Austral. The SACZ is characterized for a high variability convective region located in eastern Cordilheiras of the Andes with northeast-southeast orientation. In addition extend Southeast Amazon until South Atlantic (Zhou and Lau 1998; Liebmann et al, 1999; Carvalho et al, 2004). The many works that studied SACZ (Carvalho, Jones e Liebmann, 2004; Jones et al, 2004, for example) long wave radiation (ROL), is used which proxy of precipitation. In the first moment, it describes the position of event; however the precipitation is more adequate, principally in the used data series obtain of the climatic models. A study of the characterization of the South Atlantic Convergence Zone (SACZ) is presented. It was determined 48 events of ZCAS between 1995 to 2005 during the November to March period. Based on rainfall data, a new criterion was defined in order to select the SACZ events and their results were compared with the previous events. The results indicated that the new criterion did a good job in representing the SACZ. For this reason, um test with climatic model data series (REGCM3 Model, Giorgi et al., 1993) is presented.

  11. Eastern margin variability of the South Pacific Convergence Zone

    NASA Astrophysics Data System (ADS)

    Lintner, Benjamin R.; Neelin, J. David

    2008-08-01

    The influence of low-level inflow wind and its high-frequency variability on the spatial characteristics of the eastern margin of the South Pacific Convergence Zone (SPCZ) is examined. Compositing daily and 5-day mean low-level wind, precipitation, and tropospheric moisture data reveals a clear relationship between high-frequency zonal inflow variations and the eastern SPCZ margin, with relaxation of trade wind intensity associated with increased moisture near the mean eastern SPCZ margin and an eastward displacement of the convection. An idealized 2-dimensional model demonstrates that variations in dry air inflow cause tropospheric moisture and precipitation variations akin to those observed. In this prototype, factors affecting the extent of SPCZ variability are also important to the mean margin position. SPCZ margin shifts under natural variability thus offer an observational target against which to evaluate simulated interactions of inflow air mass characteristics with convection.

  12. 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

  13. Why the South Pacific Convergence Zone is diagonal

    NASA Astrophysics Data System (ADS)

    van der Wiel, Karin; Matthews, Adrian J.; Joshi, Manoj M.; Stevens, David P.

    2016-03-01

    During austral summer, the majority of precipitation over the Pacific Ocean is concentrated in the South Pacific Convergence Zone (SPCZ). The surface boundary conditions required to support the diagonally (northwest-southeast) oriented SPCZ are determined through a series of experiments with an atmospheric general circulation model. Continental configuration and orography do not have a significant influence on SPCZ orientation and strength. The key necessary boundary condition is the zonally asymmetric component of the sea surface temperature (SST) distribution. This leads to a strong subtropical anticyclone over the southeast Pacific that, on its western flank, transports warm moist air from the equator into the SPCZ region. This moisture then intensifies (diagonal) bands of convection that are initiated by regions of ascent and reduced static stability ahead of the cyclonic vorticity in Rossby waves that are refracted toward the westerly duct over the equatorial Pacific. The climatological SPCZ is comprised of the superposition of these diagonal bands of convection. When the zonally asymmetric SST component is reduced or removed, the subtropical anticyclone and its associated moisture source is weakened. Despite the presence of Rossby waves, significant moist convection is no longer triggered; the SPCZ disappears. The diagonal SPCZ is robust to large changes (up to ±6 °C) in absolute SST (i.e. where the SST asymmetry is preserved). Extreme cooling (change <-6 °C) results in a weaker and more zonal SPCZ, due to decreasing atmospheric temperature, moisture content and convective available potential energy.

  14. 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.

  15. Dependence of earthquake size distributions on convergence rates at subduction zones

    SciTech Connect

    Mccaffrey, R.

    1994-10-01

    The correlation of numbers of thrust earthquakes of moment magnitude 7 or greater in this century at subduction zones with convergence rate results from a combination of lower recurrence intervals for earthquakes of a given size where slip rates are high and peak in the global distribution of subduction zone convergence rates at high values (55 to 90 mm/yr). Hence, physical mechanisms related to convergence rate, such as plate interface force, slab pull, or thermal effects, are not required to explain the distribution of large earthquakes with convergence rate. The seismic coupling coefficient ranges from 10% to 100% at subduction zone segments where convergence is faster than 45 mm/yr but does not correlate with rate. The coefficient is generally orders of magnitude lower at rates below 40 mm/yr which may be due to long recurrence intervals and a short sampling period (94 years).

  16. Dynamics and energetics of the South Pacific convergence zone during FGGE SOP-1

    NASA Technical Reports Server (NTRS)

    Vincent, D. G.; Robertson, F. R.

    1984-01-01

    The major objectives are to: (1) diagnose the physical processes responsible for the maintenance of the South Pacific Convergence Zone (SPCZ); and (2) examine the role of the SPCZ in the large-scale circulation patterns of the Southern Hemisphere.

  17. 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.

  18. Hydrodynamic convergence of hydropressured and geopressured zones, Central Texas, Gulf of Mexico Basin, USA

    NASA Astrophysics Data System (ADS)

    Dutton, Alan R.; Nicot, Jean-Philippe; Kier, Katherine S.

    2006-09-01

    Freshwater moving downdip in the Carrizo-Wilcox aquifer, Central Texas, USA, and saltwater and hydrocarbons moving updip from a geopressured zone come together in a groundwater convergence zone, marked by (1) a hydraulic-gradient reversal, (2) “updip” oil fields, and (3) the downdip limit of potable water beyond which there is a marked increase in salinity. Data combined from groundwater-supply and petroleum-extraction industries document the interface between the hydropressured and geopressured zones. The hydraulic-head gradient updip of the convergence zone is 0.001 to 0.002, directed toward the coast; farther downdip it is -0.02 to -0.04, directed inland. Salinity increases from <400 mg/L near the outcrop, to ˜3,000 mg/L at the downdip limit of potable water, to >100,000 mg/L in the geopressured zone. Upward-directed flow paths probably predominate in the convergence zone. The convergence zone in the study area lies within only 30-50 km of the outcrop because updip extensional faulting offsets permeable aquifer units against low-permeability strata and restricts the downdip flux of recharged water. The major elements of the convergence zone may have been in place since the Miocene development of circulation in the updip coastal aquifer following incision of river valleys and lowering of base level.

  19. Effects of growth parameters on silicon molten zone formed by infrared convergent-heating floating zone method

    NASA Astrophysics Data System (ADS)

    Hossain, Md. Mukter; Watauchi, Satoshi; Nagao, Masanori; Tanaka, Isao

    2017-02-01

    The effects of rotation rate, filament size, mirror shape, and crystal diameter on the shape of the silicon molten zones prepared using the infrared convergent-heating floating zone method were examined. The crystal rotation rate did not significantly affect the shape of the feed-melt or crystal-melt interfaces, gap between the crystal and feed, zone length, or lamp power required to form the molten zone. More efficient heating was achieved using lamps with smaller filaments and ellipsoidal mirrors with higher eccentricity. The convexity of both the feed and the crystal sides of the molten zone decreased with increasing crystal diameter. However, the required lamp power, gap, and zone length increased with increasing crystal diameter. The stability of the molten zone seemed to reduce with increasing crystal diameter. The minimum melt width divided by the crystal diameter was found to be a good parameter to describe the stability of the molten zone.

  20. 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.

  1. South Pacific convergence zone and global-scale circulations

    NASA Technical Reports Server (NTRS)

    Vincent, Dayton G.; Robertson, Franklin R.

    1990-01-01

    Current research is focused on four topics. First, the GLA Global Circulation Model (GCM) is used for a series of experiments to examine the relationship between tropical heating and subtropical westerly wind maxima. Second, barotropic and baroclinic energy mechanisms associated with summertime subtropical wind maxima in the Southern Hemisphere is studied. Third, tropical/extratropical interactions in the Southern Hemisphere summer circulation is studied; the focus is on the importance of the 30 to 60 day tropical oscillation as a cause of enhancing the subtropical westerly winds. Finally, a study of precipitation efficiency in the tropics, comparing mean monthly distributions of precipitation over a three-year period to precipitable water and moisture convergency is being conducted.

  2. Stability and a fast calculation method of travel speed of pulse peak in convergence zone

    NASA Astrophysics Data System (ADS)

    Ren, Yun; Zhang, RenHe; Wang, Jun; Guo, YongGang; Luo, WenYu

    2014-07-01

    A long-range sound propagation experiment was conducted in the West Pacific Ocean in summer 2013. The signals received by a towed array indicate that the travel speed of pulse peak (TSPP) in the convergence zones is stable. Therefore, an equivalent sound speed can be used at all ranges in the convergence zones. A fast calculation method based on the beam-displacement ray-mode (BDRM) theory and convergence zone theory is proposed to calculate this equivalent sound speed. The computation speed of this proposed method is over 1000 times faster than that of the conventional calculation method based on the normal mode theory, with the computation error less than 0.4% compared with the experimental result. Also, the effect of frequency and sound speed profile on the TSPP is studied with the conventional and fast calculation methods, showing that the TSPP is almost independent of the frequency and sound speed profile in the ocean surface layer.

  3. Aerosol forcing of the position of the intertropical convergence zone since AD 1550

    NASA Astrophysics Data System (ADS)

    Ridley, Harriet E.; Asmerom, Yemane; Baldini, James U. L.; Breitenbach, Sebastian F. M.; Aquino, Valorie V.; Prufer, Keith M.; Culleton, Brendan J.; Polyak, Victor; Lechleitner, Franziska A.; Kennett, Douglas J.; Zhang, Minghua; Marwan, Norbert; MacPherson, Colin G.; Baldini, Lisa M.; Xiao, Tingyin; Peterkin, Joanne L.; Awe, Jaime; Haug, Gerald H.

    2015-03-01

    The position of the intertropical convergence zone is an important control on the distribution of low-latitude precipitation. Its position is largely controlled by hemisphere temperature contrasts. The release of aerosols by human activities may have resulted in a southward shift of the intertropical convergence zone since the early 1900s (refs , , , , ) by muting the warming of the Northern Hemisphere relative to the Southern Hemisphere over this interval, but this proposed shift remains equivocal. Here we reconstruct monthly rainfall over Belize for the past 456 years from variations in the carbon isotope composition of a well-dated, monthly resolved speleothem. We identify an unprecedented drying trend since AD 1850 that indicates a southward displacement of the intertropical convergence zone. This drying coincides with increasing aerosol emissions in the Northern Hemisphere and also marks a breakdown in the relationship between Northern Hemisphere temperatures and the position of the intertropical convergence zone observed earlier in the record. We also identify nine short-lived drying events since AD 1550 each following a large volcanic eruption in the Northern Hemisphere. We conclude that anthropogenic aerosol emissions have led to a reduction of rainfall in the northern tropics during the twentieth century, and suggest that geographic changes in aerosol emissions should be considered when assessing potential future rainfall shifts in the tropics.

  4. 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.

  5. The Curtain Effect in a Multiple Convergence Zone Environment: Part 1. Implications for Ambient Noise.

    DTIC Science & Technology

    1991-01-24

    prepared under Project No. A20022, principal investigator P. Herstein . It contains the oral and written presentation, "The Curtain Effect in a Multiple...Convergence Zone Environment: Part 1 - Implications for Ambient Noise." The authors wish to express their graditude to Peter D. Herstein (Code 33A) for

  6. Convergence zones for Type I migration: an inward shift for multiple planet systems

    NASA Astrophysics Data System (ADS)

    Cossou, C.; Raymond, S. N.; Pierens, A.

    2013-05-01

    Earth-mass planets embedded in gaseous protoplanetary disks undergo Type I orbital migration. In radiative disks an additional component of the corotation torque scaling with the entropy gradient across the horseshoe region can counteract the general inward migration, Type I migration can then be directed either inward or outward depending on the local disk properties. Thus, special locations exist in the disk toward which planets migrate in a convergent way. Here we present N-body simulations of the convergent migration of systems of low-mass (M = 1-10M⊕) planets. We show that planets do not actually converge in convergence zones. Rather, they become trapped in chains of mean motion resonances. This causes the planets' eccentricities to increase to high enough values to affect the structure of the horseshoe region and weaken the positive corotation torque. The zero-torque equilibrium point of the resonant chain of planets is determined by the sum of the attenuated corotation torques and unattenuated differential Lindblad torques acting on each planet. The effective convergence zone is shifted inward. Systems with several planets can experience stochastic migration as a whole due to continuous perturbations from planets entering and leaving resonances.

  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. Observations of blocking-induced convergence zones and effects on precipitation in complex terrain

    NASA Astrophysics Data System (ADS)

    Wesley, Douglas A.; Pielke, Roger A.

    Through an extensive set of observations, including standard surface measurements, Doppler radar, routine National Weather Service radiosondes and special Cross-chain Loran Atmospheric Sounding System (CLASS) data, two case studies of wintertime storms on the east slopes of the Rocky Mountains of Colorado are presented (9-10 February 1988 and 30-31 March 1988). The emphases are the effects of blocking-induced convergence zones on snowfall distributions, snow crystal production mechanisms and banded reflectivity structure. As shown by the analysis of a typical Front Range storm, cold air damming can frequently lead to convergence zones and enhanced precipitation east of the mountains. The meso-fronts often form in place just east of the foothills, and are sensitive to the nature of the low-level synoptic easterly flow. For other upslope situations, the convergence zone does not appear as a meso-front, but as a less distinct area of convergence. Measured vertical profiles associated with the blocked surface patterns reveal a distincly layered temperature and wind structure. These soundings, along with surface measurements of wind, moisture and snow crystal types, enable some microphysical interpretation to be made concerning snowfall production in zones of ascent aloft, which are related to frontal surface as well as lifting at the top of the blocking-induced cold pool. Predominance of heavily rimed, dendritic aggregates implies lifting associated with the layered vertical structure in both storms. Bands of enhanced Doppler reflectivity exhibit significant correlation with snowfall intensity. The two case studies demonstrate that distinctly different patterns of blocking and convergence can appear in Colorado Front Range storms, each resulting in a unique snowfall distribution.

  9. 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

  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.

    2005-04-01

    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

  12. 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

  13. 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

  14. 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

  15. 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

  16. Extended-range prediction of South Atlantic convergence zone rainfall with calibrated CFSv2 reforecast

    NASA Astrophysics Data System (ADS)

    Hirata, Fernando E.; Grimm, Alice M.

    2017-08-01

    During the 2010-2011 wet season in Brazil, widespread landslides triggered by heavy rainfall killed hundreds of people and displaced nearly 35,000. The extreme precipitation was associated with the formation of the South Atlantic convergence zone (SACZ). Even though the physical mechanisms behind the formation and persistence of subtropical convergence zones are still unclear, we demonstrate that early predictions of heavy rainfall in the SACZ region are possible. Precipitation rate hindcasts from the NCEP Climate Forecast System version 2 are calibrated with the aid of a gridded precipitation dataset. When the calibration was applied to the 2010-2011 events, the hindcasts were able to depict both active and break phases of the SACZ with up to 2 weeks in advance during a period of relatively weak intraseasonal variability associated with the Madden-Julian Oscillation (MJO).

  17. 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

  18. Tectonics, Fluids, and the Seismogenic Zone: Four Decades of Drilling at Convergent Margins (Invited)

    NASA Astrophysics Data System (ADS)

    Moore, J. C.; All Dsdp, Odp,; Iodp Convergent Margin Scientific Parties

    2010-12-01

    Investigations of Tectonics, Fluids, and the Seismogenic Zone are three disciplines that have driven convergent margin drilling. Each of these major themes sequentially evolved as centerpieces of drilling as the intellectual framework and the requisite technologies developed. Each remains active today. In the 1970s and early 1980s, initial results from testing plate tectonic theory defined the nature of progressive accretion, and conversely, tectonic erosion at convergent margins. With the more robust D/V JOIDES Resolution, investigation of fluid pressure, compositions, migration paths, and sediment/rock permeability became possible. 3D seismic data, first available in the early 1990s, detailed fluid migration paths inferred from porewater geochemical anomalies, emphasizing the importance of faults as fluid conduits. 3D seismic volumes also resulted in extraordinary insights on the structure and tectonics of convergent margins. In the mid 1990s packer testing and long-term monitoring of fault zones provided the first estimates of in situ fluid pressures, permeabilities, and variation of the latter with effective stress. Experimental studies, and hydrological and geomechanical modeling have provided critical perspectives on the observational data. During the late 1990s and 2000s the convergent margin community focused on earthquake processes in the Seismogenic Zone Experiment (SEIZE). Understanding of tectonics and fluids, plus monitoring, 3D seismic imaging, Logging While Drilling technology, and D/V Chikyu riser drilling capability have all contributed to emergent accomplishments of SEIZE. Some key results of this program include 1) estimates of material flux into the seismogenic zone, 2) measurement of stress orientation and magnitude across the margin of SW Japan, 3) recognition of high velocity fault slip at shallow depths, 4) correlation of monitored variations in fluid pressure and composition with seismic events, and 5) the initiation of a deep riser hole

  19. Insurgency Season: The Link between the Intertropical Convergence Zone and Insurgencies in Equatorial Africa

    DTIC Science & Technology

    2008-04-23

    hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and...completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of...Convergence Zone ( ITCZ ) creates distinct wet and dry seasons throughout the region. During the wet season, widespread flooding and inclement weather dominate

  20. A Framework for the Origin of the Diagonally Oriented South Atlantic and South Pacific Convergence Zones

    NASA Astrophysics Data System (ADS)

    van der Wiel, K.; Matthews, A. J.; Stevens, D. P.; Joshi, M. M.

    2014-12-01

    We present a conceptual framework for the diagonal orientation of the South Pacific Convergence Zone (SPCZ) and South Atlantic Convergence Zone (SACZ), based on observations of tropical-extratropical interactions, Rossby wave theory, and vorticity calculations. Wave trains propagate eastward along the Southern Hemisphere subtropical jet, with initially quasi-circular vorticity centres. In the zonally sheared environment on the equatorward flank of the jet, these vorticity centres become elongated and develop a northwest-southeast tilt. Ray tracing diagnostics in a non-divergent, barotropic Rossby wave framework then explain the observed equatorward propagation of these diagonal vorticity structures toward the westerly ducts over the equatorial Pacific and Atlantic. The baroclinic component of these circulations leads to ascent and destabilisation ahead of the cyclonic vorticity anomaly in the wave. Over the high sea surface temperatures in this region, deep convection is triggered. Latent heat release forces ascent and strong upper-tropospheric divergence, with an associated anticyclonic vorticity tendency. In a vorticity budget, this cancels out the advective cyclonic vorticity tendency in the wave train over the SPCZ, and dissipates the wave within a day. The mean SPCZ is then comprised of the sum of these pulses of diagonal bands of precipitation. These mechanisms also operate in the SACZ. However, the vorticity anomalies in the wave trains are stronger, and the precipitation and negative feedback from the divergence and anticyclonic vorticity tendency are weaker, resulting in continued propagation of the wave and a more diffuse diagonal convergence zone.

  1. Estimates of Projection Overlap and Zones of Convergence within Frontal-Striatal Circuits

    PubMed Central

    Lehman, Julia; Jacobson, Moriah; Haber, Suzanne N.

    2014-01-01

    Frontal-striatal circuits underlie important decision processes, and pathology in these circuits is implicated in many psychiatric disorders. Studies have shown a topographic organization of cortical projections into the striatum. However, work has also shown that there is considerable overlap in the striatal projection zones of nearby cortical regions. To characterize this in detail, we quantified the complete striatal projection zones from 34 cortical injection locations in rhesus monkeys. We first fit a statistical model that showed that the projection zone of a cortical injection site could be predicted with considerable accuracy using a cross-validated model estimated on only the other injection sites. We then examined the fraction of overlap in striatal projection zones as a function of distance between cortical injection sites, and found that there was a highly regular relationship. Specifically, nearby cortical locations had as much as 80% overlap, and the amount of overlap decayed exponentially as a function of distance between the cortical injection sites. Finally, we found that some portions of the striatum received inputs from all the prefrontal regions, making these striatal zones candidates as information-processing hubs. Thus, the striatum is a site of convergence that allows integration of information spread across diverse prefrontal cortical areas. PMID:25031393

  2. 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.

  3. Determination of rainfall and condensational heating in the South Pacific convergence zone during FGGE SOP-1

    NASA Technical Reports Server (NTRS)

    Robertson, F. R.

    1984-01-01

    The role of cloud related diabatic processes in maintaining the structure of the South Pacific Convergence Zone is discussed. The method chosen to evaluate the condensational heating is a diagnostic cumulus mass flux technique which uses GOES digital IR data to characterize the cloud population. This method requires as input an estimate of time/area mean rainfall rate over the area in question. Since direct observation of rainfall in the South Pacific is not feasible, a technique using GOES IR data is being developed to estimate rainfall amounts for a 2.5 degree grid at 12h intervals.

  4. Natural Disasters in Southeastern Brazil Associated with the South Atlantic Convergence Zone

    NASA Astrophysics Data System (ADS)

    Teixeira Nery, Jonas; Malvestio, Leônidas

    2017-04-01

    This study analyzed rains in southeastern Brazil associated with the South Atlantic Convergence Zone (SACZ), which resulted in several disasters over the study area. The study period was from 1976 to 2010 and data were obtained from the National Water Agency (ANA) and Department of Water and Energy (DAEE) of the state of São Paulo. Outgoing Longwave Radiation (OLR) data were also used to analyze SACZ, which is an important dynamics influencing spring and summer in this region. A close relationship between SACZ intensity and economic and life losses in the study area was observed.

  5. Toward understanding the double Intertropical Convergence Zone pathology in coupled ocean-atmosphere general circulation models

    NASA Astrophysics Data System (ADS)

    Zhang, Xuehong; Lin, Wuyin; Zhang, Minghua

    2007-06-01

    This paper first analyzes structures of the double Intertropical Convergence Zone (ITCZ) in the central equatorial Pacific simulated by three coupled ocean-atmosphere general circulation models in terms of sea surface temperatures, surface precipitation, and surface winds. It then describes the projection of the double ITCZ in the equatorial upper ocean. It is shown that the surface wind convergences, associated with the zonally oriented double rainbands on both sides of the equator, also correspond to surface wind curls that are favorable to Ekman pumping immediately poleward of the rainbands. The pumping results in a thermocline ridge south of the equator in the central equatorial Pacific, causing a significant overestimation of the eastward South Equatorial Counter Current that advects warm water eastward. A positive feedback mechanism is then described for the amplification of the double ITCZ in the coupled models from initial biases in stand-alone atmospheric models through the following chain of interactions: precipitation (atmospheric latent heating), surface wind convergences, surface wind curls, Ekman pumping, South Equatorial Counter Current, and eastward advection of ocean temperature. This pathology provides a possible means to address the longstanding double ITCZ problem in coupled models.

  6. Diagnosing inflow-moisture-precipitation relationships along the South Pacific Convergence Zone

    NASA Astrophysics Data System (ADS)

    Lintner, B. R.; Neelin, J.

    2009-12-01

    The tropical South Pacific is characterized by an area of large-scale atmospheric subsidence to the east and strong low-level convergence and deep convection, i.e., the South Pacific Convergence Zone (SPCZ), to the west. The spatial transition between these subsiding and convecting regimes manifests strong variability on multiple timescales and presents challenges for simulation, both of which underscore the need for understanding the interplay of dynamics and thermodynamics controlling the SPCZ margins. Here, the effect of one potential source of margin variability, the low-level trades, is examined. Composite analysis reveals high-frequency relationships among reanalysis inflow wind variability and observed column water vapor and precipitation along the SPCZ, with strengthening of the trades along the eastern tropical SPCZ margin associated with a reduction of column water vapor and precipitation. A simple analytic prototype for idealized convective margins situated in regions of substantial low-level inflow from a relatively dry oceanic region into the convection zone is used to interpret the observed inflow-moisture-precipitation relationships. Building on insights from this prototype, diagnostics of relevance for model evaluation and intercomparison and bias mitigation in the vicinity of the SPCZ or similar areas in other ocean basins are also discussed.

  7. Influence of the intertropical convergence zone on the East Asian monsoon

    NASA Astrophysics Data System (ADS)

    Yancheva, Gergana; Nowaczyk, Norbert R.; Mingram, Jens; Dulski, Peter; Schettler, Georg; Negendank, Jörg F. W.; Liu, Jiaqi; Sigman, Daniel M.; Peterson, Larry C.; Haug, Gerald H.

    2007-01-01

    The Asian-Australian monsoon is an important component of the Earth's climate system that influences the societal and economic activity of roughly half the world's population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits, but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct. Here we present high-resolution records of the magnetic properties and the titanium content of the sediments of Lake Huguang Maar in coastal southeast China over the past 16,000years, which we use as proxies for the strength of the winter monsoon winds. We find evidence for stronger winter monsoon winds before the Bølling-Allerød warming, during the Younger Dryas episode and during the middle and late Holocene, when cave stalagmites suggest weaker summer monsoons. We conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone. Similar migrations of the intertropical convergence zone have been observed in Central America for the period AD 700 to 900 (refs 4-6), suggesting global climatic changes at that time. From the coincidence in timing, we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the Tang dynasty in China and the Classic Maya in Central America.

  8. 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

  9. 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.

  10. Influence of the intertropical convergence zone on the East Asian monsoon.

    PubMed

    Yancheva, Gergana; Nowaczyk, Norbert R; Mingram, Jens; Dulski, Peter; Schettler, Georg; Negendank, Jörg F W; Liu, Jiaqi; Sigman, Daniel M; Peterson, Larry C; Haug, Gerald H

    2007-01-04

    The Asian-Australian monsoon is an important component of the Earth's climate system that influences the societal and economic activity of roughly half the world's population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits, but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct. Here we present high-resolution records of the magnetic properties and the titanium content of the sediments of Lake Huguang Maar in coastal southeast China over the past 16,000 years, which we use as proxies for the strength of the winter monsoon winds. We find evidence for stronger winter monsoon winds before the Bølling-Allerød warming, during the Younger Dryas episode and during the middle and late Holocene, when cave stalagmites suggest weaker summer monsoons. We conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone. Similar migrations of the intertropical convergence zone have been observed in Central America for the period ad 700 to 900 (refs 4-6), suggesting global climatic changes at that time. From the coincidence in timing, we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the Tang dynasty in China and the Classic Maya in Central America.

  11. Breaking Rossby Waves, Moisture Streamers, and the Southern Hemisphere Diagonal Convergence Zones

    NASA Astrophysics Data System (ADS)

    Panetta, R. L.; Ramotowski, M.

    2014-12-01

    A combination of satellite observations (principally GPCP) and ECMWF reanalyses were used to examine the major diagonal convergence zones in the Southern Hemisphere. Time-lag height anomalies composited on high rainfall events in sub-tropical and mid-latitude sections of the climatological zones showed nearly equivalent barotropic wave packets propagating into the regions from higher latitudes, in a manner easily interpretable in terms of the structure of low-pass-filtered pv gradients. To examine the moisture field with which the wave vertical motion field interacted in producing precipitation, animations were first constructed from daily fields of PV on the 330-theta surface superposed on total column water (TCW). The animations showed frequent events of anticyclonic breaking of mid-latitude Rossby waves, coincidental with the development of streamers of total column water (TCW) drawn out of the tropics, into the subtropics and mid-latitudes just downstream of parallel PV streamers in the breaking waves. Vertical cross sections through selected streamers showed locally high levels of moisture extending through most of the troposphere, with dynamically consistent vertical motion fields. Although major streamer events with NW-SE tilt could be seen in the animations, TCW streamers were in fact seen with many orientations and in many locations around the hemisphere. An objective method was developed to classify TCW streamers by their horizontal tilt. When applied to observations from the 20 year period 1991-2012, the method showed that TCW streamers with NW-SE tilt preferentially occurred in the three climatological diagonal convergence zones regions during austral summer, but only in the SPCZ and SACZ regions during austral winter.

  12. 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.

  13. Features of the Caucasian segment of the Alpine-Himalayan-Indonesian Convergence Zone

    NASA Astrophysics Data System (ADS)

    Sharkov, E.

    2012-04-01

    The Caucasus Mountain System is a part of the Cenozoic Alpine-Himalayan-Indonesian Convergence Zone (AHICZ) which lasted throughout Eurasia from Western Mediterranean to Western Pacific. This belt has been formed after closure of the Mesozoic Tethys and is marked by mountains building processes, appearance of riftogenic structures, numerous late Cenozoic basaltic plateaus, and chain of often within-continental andesite-latite volcanic arcs, which trace suture zones of the continental plates collision. Caucasus Mountains are located in eastern part of the proper Alpine Zone in zone of Arabian-Eurasian syntaxis and appeared as a result of submeridional pressure which generated by oncoming moving of these plates. The Great Caucasus is represent the south border of the Eurasian plate, uplifted along the Main Caucasian Fault (Thrust). The latter is a part of super-regional deep-seated fault ranged from the Kopetdag through Caspian Sea, Caucasus and Crimea; very likely, that its further continuation is Tornquist-Teisseyre Zone. This superfault separates areas of Alpine convergence from Eurasian plate sensu stricto. The Caucasus occurred between Black and Caspian seas with passive margins and oceanic crust, covered by sediments of 10-15 km thick. Depressions of the seas form large "downfall", or caldrons which cut off pre-Pliocene structures of Caucasus and Kopetdag. These seas are, probably, small remnants of the Tethys which gradually shallowing in the Miocene (Zonenshain, Le Pichon, 1986). New essential deepening of the Black Sea and South-Caspian deep began in the Pliocene- Quaternary; it occurred simultaneously with uprising of Crimea and Caucasus, which were not marked in relief before (Grachev, 2000). Large positive isostatic anomaly beneath the Trans-Caucasian Transverse Uplift (TCTU) of the Great Caucasus and Lesser Caucasus, which stretch out to Arabian plate, occurred between "subsides" Black and especially Caspian seas with neutral to negative isostatic

  14. Wave Accumulation and the Formation of the South Atlantic Convergence Zone

    NASA Astrophysics Data System (ADS)

    Hirata, F. E.; Webster, P. J.; Hoyos, C.; Kim, H.

    2011-12-01

    Convectively active phases of the South Atlantic Convergence Zone (SACZ) are associated with extreme episodes of rainfall over a large and densely inhabited area of Eastern South America. The SACZ is usually defined as a northwest-southeast oriented band of cloudiness extending from the Amazon basin into the South Atlantic Ocean with a varying spectral structure along its axis. Close to the equator, intraseasonal and synoptic variations are less energetic. To the southeast, intraseasonal variability peaks over the Brazilian coast south of 12oS and synoptic disturbances gain importance in the subtropics over the ocean. The spectral structure and orientation of the SACZ strongly resembles features observed in the South Pacific Convergence Zone (SPCZ). Widlansky et al. (2010) showed that the group speed of synoptic Rossby waves is reduced in a region of negative zonal stretching deformation in the vicinity of the SPCZ, causing wave energy density to accumulate. They also demonstrate that the zonal SST gradient determines the location of the negative zonal stretching deformation region and, consequently, the orientation of the convergence zone. On the other hand, a recent paper by Ferreira et al. (2011) proposed that the onset of the first SACZ of the season is triggered after a change in behavior of propagating troughs forced by the development of the Bolivian High. This upper-level high has its origins associated with Amazon convection and enhances anticyclonic shear in the northern flank of the subtropical jet. The horizontal shear causes the transient extratropical disturbances to thin and tilt westward. Here we present evidences that the increasing strength of the upper-level high during late spring contributes to the increase of horizontal anticyclonic shear in the northern flank of the subtropical jet and to a more negative zonal stretching deformation in the subtropical SACZ domain. Both factors may act in concert to alter the shape and propagation of synoptic

  15. 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.

  16. Cyclone development in the South Pacific convergence zone during FGGE, 10-17 January 1979

    NASA Technical Reports Server (NTRS)

    Vincent, D. G.

    1985-01-01

    An analysis is presented of the life cycles of three different South Pacific cyclones. Emphasis is given to two of the cyclones which propagate south-eastward along the western edge of the South Pacific convergence zone (SPCZ) and reach middle latitudes before decaying. The analysis is based on imagery from the GOES-West Satellite and on data from the European Center for Medium Range Weather Forecasts (EMWF). A comparison between estimates of the mean sea level pressure in the vicinity of the cyclones taken at observation stations and from ECMWF predictions shows good agreement when the cyclone disturbances are above grid-scale. The propagation characteristics of the cyclones are discussed in detail.

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

    NASA Astrophysics Data System (ADS)

    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

    2015-11-01

    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.

  18. Negative ocean--atmosphere feedback in the South Atlantic Convergence Zone

    NASA Astrophysics Data System (ADS)

    de Almeida, R. F.; Nobre, P.; Haarsma, R. J.; Campos, E. J.

    2007-05-01

    The temporal evolution of the coupled variability between the South Atlantic Convergence Zone (SACZ) and the underlying sea surface temperature (SST) during austral summer is investigated using monthly data from the NCEP/NCAR reanalysis. A maximum covariance analysis shows that the SACZ is intensified [weakened] by warm [cold] SST anomalies in the beginning of summer, drifting northward. This migration is accompanied by the cooling [warming] of the underlying oceanic anomalies. The results confirm earlier analyses using numerical models, and suggest the existence of a negative feedback between the SACZ and the underlying South Atlantic SST field. A linear regression of daily anomalies of SST and omega at 500 hPa to the equations of a stochastic oscillator reveals a negative ocean--atmosphere feedback in the western South Atlantic, stronger during January and February and directly underneath the oceanic band of the SACZ.

  19. Disentangling the air-sea interaction in the South Atlantic Convergence Zone

    NASA Astrophysics Data System (ADS)

    tirabassi, giulio; masoller, cristina; barreiro, marcelo

    2014-05-01

    Air-sea interaction in the region of the South Atlantic Convergence Zone (SACZ) is disentangled using Granger causality as a measure of directional coupling. Calculation of the area weighted connectivity indicates that the SACZ region is the one with largest mutual air-sea connectivity in the south Atlantic basin during summertime. Focusing on the leading mode of daily coupled variability, Granger causality allows distinguishing four regimes characterized by different coupling: there are years in which the forcing is mainly directed from the atmosphere to the ocean, years in which the ocean forces the atmosphere, years in which the influence is mutual, and years in which the coupling is not significant. A composite analysis shows that ocean-driven events have atmospheric anomalies that develop first and are strongest over the ocean, while in events without coupling anomalies develop from the continent where they are strongest and have weaker oceanic extension.

  20. Negative ocean-atmosphere feedback in the South Atlantic Convergence Zone

    NASA Astrophysics Data System (ADS)

    De Almeida, R. A. F.; Nobre, P.; Haarsma, R. J.; Campos, E. J. D.

    2007-09-01

    The temporal evolution of the coupled variability between the South Atlantic Convergence Zone (SACZ) and the underlying sea surface temperature (SST) during austral summer is investigated using monthly data from the NCEP/NCAR reanalysis. A maximum covariance analysis shows that the SACZ is intensified [weakened] by warm [cold] SST anomalies in the beginning of summer, drifting northward. This migration is accompanied by the cooling [warming] of the original oceanic anomalies. The results confirm earlier analyses using numerical models that suggest the existence of a negative feedback between the SACZ and the underlying South Atlantic SST field. A linear regression of daily anomalies of SST and omega at 500 hPa to the equations of a stochastic oscillator reveals a negative ocean-atmosphere feedback in the western South Atlantic, stronger during January and February directly underneath the oceanic band of the SACZ.

  1. 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.

  2. 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

  3. A diagnosis of two cyclones in the South Pacific Convergence Zone

    NASA Technical Reports Server (NTRS)

    Vincent, D. G.; Kann, D. M.

    1985-01-01

    The evolution of three cyclones which originated in the South Pacific Convergence Zone, two of which propagated into middle latitudes, are traced. The analysis is based on IR imagery from GOES-W, island meteorological station data, and estimates of heat and moisture budget residuals. A European Center for Medium-range Weather Forecasting Level III-b analysis was used to model the cyclones. The northward-propagating storms exhibited strong vertical shear of the horizontal wind, implicating baroclinic effects in the development of the storms. The processes which enhanced storm intensification are discussed. Attention is given to the spatial and temporal behavior of dynamic atmospheric components which were significant to baroclinicity and latent heat release, which the analysis demonstrates were coupled processes.

  4. A diagnosis of two cyclones in the South Pacific Convergence Zone

    NASA Technical Reports Server (NTRS)

    Vincent, D. G.; Kann, D. M.

    1985-01-01

    The evolution of three cyclones which originated in the South Pacific Convergence Zone, two of which propagated into middle latitudes, are traced. The analysis is based on IR imagery from GOES-W, island meteorological station data, and estimates of heat and moisture budget residuals. A European Center for Medium-range Weather Forecasting Level III-b analysis was used to model the cyclones. The northward-propagating storms exhibited strong vertical shear of the horizontal wind, implicating baroclinic effects in the development of the storms. The processes which enhanced storm intensification are discussed. Attention is given to the spatial and temporal behavior of dynamic atmospheric components which were significant to baroclinicity and latent heat release, which the analysis demonstrates were coupled processes.

  5. 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.

  6. Decadal Variability in the South Atlantic Convergence Zone and Changes in Precipitation over Southeastern Brazil

    NASA Astrophysics Data System (ADS)

    Zilli, M. T.; Carvalho, L. V.

    2014-12-01

    The present study examines the role of the South Atlantic Convergence Zone (SACZ) in the observed extreme precipitation changes along the southeast coast of Brazil (-18°S to -25°S). This area is under the influence of the South American Monsoon System (SAMS) and its main feature, the SACZ, which together are related to extreme precipitation events during the wet season (Oct-Mar). Previous studies suggest that one possible change in convergence zones behavior due to climate change is an increase in precipitation intensity at their central portion at the expense of moisture advected from their margin. By analyzing extremes in daily precipitation during the wet season based on more than 70 years of rain gauge data, we identified a positive trend in the intensity of precipitation and a reduction in the number of rainy days over the north portion of southeast coast. Further south, the tendency was for an overall increase in total precipitation. This spatial pattern in extreme precipitation trends along the coast is likely linked to changes in the characteristics of the SACZ. In this study we investigate decadal variations in the SACZ intensity, location and persistence using a multivariate daily index obtained with combined EOF analysis. The variables considered are zonal and meridional winds, temperature and specific humidity at low levels, derived from two different reanalysis datasets: NCEP/NCAR Reanalysis 1 and CFSR. The extent and spatial variability of the SACZ is investigated with daily Outgoing Longwave Radiation (OLR). The focus of this analysis is on intense SACZ events according to the SACZ index. Mechanisms associated with the decadal variability of the SACZ are also explored and include changes in sea surface temperature, the low-level Jet east of the Andes, and changes in circulation and moisture transport over South America and the South Atlantic Ocean.

  7. A Case Study of Mesoscale Cyclonic Vortices Associated with the South Atlantic Convergence Zone

    NASA Astrophysics Data System (ADS)

    Leal de Quadro, M. F.; Faus da Silva Dias, M. A.; Herdies, D. L.; Goncalves, L.

    2014-12-01

    The objective of this work is to study the behavior of mesoscale cyclonic vortices (MCVs) over South America, principally those that form in association with the South Atlantic Convergence Zone (SACZ), with a view toward identifying the basic characteristics of the formation of these MCVs. Two case studies were conducted over the Continental Amazonia Zone, simulated using the BRAMS model, showing the relationship between the mesovortices formation and the convective activity near its formation region. A thermodynamic analysis of two selected MCVs, embedded in the SACZ, highlights some salient features of these intense MCVs. Both systems are associated with strong upward vertical motion throughout practically the whole troposphere, before and during formation. This motion creates a transport of moisture into the upper troposphere and the surface fluxes of sensible and latent heat are reduced when the MCVs are operating. These systems that form in more than one level in the troposphere are more intense and are associated with greater precipitation rates (over 150 mm). Another striking feature is that these systems dissipate quickly. With respect to the horizontal wind, there is no similarity in pattern between the two cases. The first case, where the base of the vortex formed at 925 hPa and extended to 875 hPa, was characterized by convergence of winds from the south - west of the vortex - with winds from the north - east of the vortex. In the second case, which extended from 800 hPa to 775 hPa, we can clearly see the motion, originating in central Brazil, transporting moisture toward the vortex and certainly serving as a local factor contributing significantly to the moisture balance in the region.

  8. Cenozoic paleo-environmental evolution of the Pamir-Tien Shan convergence zone

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Sun, Donghuai; Chen, Fahu; Wang, Fei; Li, Baofeng; Popov, Sergej V.; Wu, Sheng; Zhang, Yuebao; Li, Zaijun

    2014-02-01

    The retreat of the Tethys Sea and the uplift of the Tibetan Plateau play the critical roles in driving Asian climatic changes during the Cenozoic. In the Pamir-Tien Shan convergence zone, over 3000 m of Cenozoic successions, consisting of marine deposits in the lower, continental clay and fine sand in the middle, and molasse in the upper part, record the evolution of the Tethys Sea, the Asian aridification, and the deformation of the Pamir. In this work, the existing biostratigraphic subdivisions and new electronic spinning resonance dating results were used to assign ages to formations within the Ulugqat section. Sedimentary facies analysis and multi-proxy indices were used to reconstruct the paleo-environmental evolution. The results show: (1) the Pamir-Tien Shan convergence zone has undergone progressive environmental changes from shallow marine before ˜34 Ma to arid land at ˜23 Ma and finally to inter-mountain basin by ˜5.3 Ma; (2) the overall increase in mean size of grains, decrease in redness, in magnetic susceptibility, and in proportion of the ultrafine component of the sediments studied revealed a long-term strengthening in potential energy to transporting medium, cooling, and enhanced continental aridity, respectively; (3) the easternmost edge of the Tethys Sea prevailed in the western Tarim Basin from late Cretaceous to early Cenozoic, and finally retreated from this region around the Eocene-Oligocene transition, which in turn strengthened the Asian aridification; (4) accumulation of molasse with an upper age of ˜1 Ma suggests that the deformation front of the Pamir migrated to this area at or before that time.

  9. Multi-Decadal Rainfall Variability under the South Pacific Convergence Zone from 1570-2005

    NASA Astrophysics Data System (ADS)

    Partin, J. W.; Quinn, T. M.; Shen, C.; Taylor, F. W.; Banner, J. L.; Maupin, C. R.; lin, K.; Sinclair, D. J.; Huh, C.

    2011-12-01

    The Pacific Ocean Basin undergoes natural climate variability on decadal to multi-decadal timescales. Ocean-atmosphere feedbacks drive a complex cycle in tropical and extra-tropical winds and zonal sea-surface temperatures (SST) resulting in basin-scale climate reorganizations. The Pacific Ocean zonal SST gradient responds to upwelling of cold waters near the equator transported by shallow Pacific Meridional Overturning Circulation (PMOC), which in turn responds to changes in winds. However, the frequency, timing, and magnitude of past decadal changes in the Pacific are largely unknown. To address this question, we developed a U-Th dated, 430-year stable oxygen isotope (δ18O) cave record of past precipitation in Vanuatu, a location whose climate is heavily influenced by variability in the South Pacific Convergence Zone (SPCZ). The δ18O-based precipitation record shows repeating cycles that are ~25-50 years in duration and correspond to ~115 mm/month of rainfall change that can occur in as fast as 5 years - a change larger and quicker than the 1976 regime shift. The stalagmite δ18O to rainfall amount conversion is based on the "amount effect" observed at similar tropical sites. The "Little Ice Age" (LIA) section of the record exhibits no trend in precipitation, hence no change in the strength or position of the SPCZ over Vanuatu. This result suggests a disconnection between changes in the SPCZ and the Intertropical Convergence Zone (ITCZ), which does exhibit a southerly shift during the LIA period. Changes in PMOC via ocean-atmosphere feedbacks most likely explain the decadal shifts in SPCZ strength through alteration of the tropical Pacific zonal SST gradient and subsequent trade wind response. Periods of high paleo-rainfall in Vanuatu (strong PMOC, increased zonal SST gradient and increased trade winds) correlate with historical accounts of little to no El Niño activity implying that Pacific Basin mean state regulates interannual variability.

  10. Dynamics and energetics of the South Pacific Convergence Zone during FGGE SOP-1

    NASA Technical Reports Server (NTRS)

    Vincent, D. G.

    1985-01-01

    The major research objectives are to diagnose the physical processes responsible for the maintenance of the South Pacific Convergence Zone (SPCZ) and to examine the role of the SPCZ in the large-scale circulation patterns of the Southern Hemisphere. To accomplish these objectives researchers used several data sources which include: a modified set of Level III-b upper air analyses, originally produced by ECMWF (Vincent, 1982); subjectively analyzed surface analyses for the South Pacific based on island station reports (Vincent, 1985); outgoing longwave radiation values supplied to us by NOAA/NESDIS; and equivalent black body temperatures and precipitation rates derived by Robertson. In the past year researchers found that wave number four plays an inportant role in the Southern Hemisphere tropics during the 15-day period when the sPCZ was a dominant feature, particularly with regard to the baroclinic conversion of potential to kinetic energy (Huang and Vincent, 1985). The convectively-active SPCZ area was found to make a significant contribution to this conversion process; thus, it appears that baroclinic effects and latent heating are important in maintaining the SPCZ. Recently efforts concentrated on two research tasks, an examination of cyclone activity within the SPCZ (Kann, 1985; Vincent, 1985; Vincent and Kann, 1985) and a study of the heat and moisture budgets in the South Pacific (Miller, et al., 1985). It was found that cyclonic disturbances occurred with regularity in the Zone from 10 to 17 January.

  11. Dynamics and energetics of the South Pacific Convergence Zone during FGGE SOP-1

    NASA Technical Reports Server (NTRS)

    Vincent, D. G.

    1985-01-01

    The major research objectives are to diagnose the physical processes responsible for the maintenance of the South Pacific Convergence Zone (SPCZ) and to examine the role of the SPCZ in the large-scale circulation patterns of the Southern Hemisphere. To accomplish these objectives researchers used several data sources which include: a modified set of Level III-b upper air analyses, originally produced by ECMWF (Vincent, 1982); subjectively analyzed surface analyses for the South Pacific based on island station reports (Vincent, 1985); outgoing longwave radiation values supplied to us by NOAA/NESDIS; and equivalent black body temperatures and precipitation rates derived by Robertson. In the past year researchers found that wave number four plays an inportant role in the Southern Hemisphere tropics during the 15-day period when the sPCZ was a dominant feature, particularly with regard to the baroclinic conversion of potential to kinetic energy (Huang and Vincent, 1985). The convectively-active SPCZ area was found to make a significant contribution to this conversion process; thus, it appears that baroclinic effects and latent heating are important in maintaining the SPCZ. Recently efforts concentrated on two research tasks, an examination of cyclone activity within the SPCZ (Kann, 1985; Vincent, 1985; Vincent and Kann, 1985) and a study of the heat and moisture budgets in the South Pacific (Miller, et al., 1985). It was found that cyclonic disturbances occurred with regularity in the Zone from 10 to 17 January.

  12. The South ``West'' Pacific Convergence Zone: Large-scale feedback on atmospheric subsidence to the east

    NASA Astrophysics Data System (ADS)

    Widlansky, M. J.; Webster, P. J.; Hoyos, C.

    2010-12-01

    Three semi-permanent convective cloud bands exist in the Southern Hemisphere extending southeastward from the equator, through the tropics, and into the subtropics. The most prominent of these features occurs in the South Pacific during summer and is referred to as the South Pacific Convergence Zone (SPCZ). Similar cloud bands, with less intensity, exist in the South Indian and Atlantic basins. To the east of each convective zone is a large-scale region of atmospheric subsidence. We attempt to explain the physical mechanisms that promote the diagonal orientation of the SPCZ and also teleconnections that may exist with stratocumulus cloud cover in the southeastern Pacific. It is argued that slowly varying sea surface temperature patterns produce upper tropospheric wind fields that vary substantially in longitude (∂U/∂x). Regions where 200 hPa zonal winds decrease with longitude (i.e., negative zonal stretching deformation, or ∂U/∂x<0) reduce the group speed of the eastward propagating synoptic (3-6 day period) Rossby waves and locally increase the wave energy density. Such a region of wave accumulation occurs in the vicinity of the SPCZ (see Figure), thus providing a hypothesis for the diagonal orientation and a physical basis for earlier observations that the zone traps eastward propagating synoptic disturbances. Controlled numerical experiments and composites of observed life cycles of synoptic waves confirm that disturbances slow in the SPCZ. From the hypothesis comes a more general theory accounting for the SPCZ’s spatial orientation and the lack of disturbances to the east. December-February climatology of 200 hPa zonal winds (shading) and negative zonal stretching deformation (red contours). Large black box located at 20°S-35°S, 165°W-135°W encloses the diagonal region of the SPCZ. 240 W m-2 OLR contour outlined by blue lines.

  13. 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.

  14. 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

  15. The Shallow-to-Deep Convective Transition Over an Idealized Mesoscale Convergence Zone

    NASA Astrophysics Data System (ADS)

    Rousseau-Rizzi, R.; Kirshbaum, D. J.; Yau, P. M.

    2015-12-01

    The initiation of deep convection within a conditionally unstable atmosphere requires air parcels to reach their level of free convection, above which latent-heat release generates positive buoyancy. However, air parcels that satisfy this condition often fail to undergo deep ascent due to mitigating factors such as entrainment and adverse perturbation vertical pressure gradients. Recent studies suggest that the transition from shallow-to-deep convection may additionally require the formation of evaporative cold pools, a sufficient cloud-layer lapse rate, gradual moistening of the mid-troposphere through shallow-cumulus detrainment, and/or the fortuitous development of new cumuli through the remnants of their predecessors. In this study, we use cloud-resolving simulations of cumulus convection over an idealized surface-based convergence zone to study the mechanisms and sensitivities of deep-convection initiation forced by mesoscale ascent. The surface convergence forms in response to a localized diurnal heating anomaly over an otherwise homogenous and unheated surface, producing an organized boundary-layer updraft with a maximal amplitude of around 3 m/s over the center of the heat source. It gives rise to a line of cumuli that gradually deepens and, in some cases, transitions into deep convection. Detailed analysis of the simulations reveals several notable aspects of cumulus evolution, including that its vertical development is not uniquely determined by the combination of surface forcing and surface-based convective inhibition (CIN), as some have suggested. In addition, the specific mechanism by which deep convection first develops is sensitive to the environmental conditions, which implies that no single mechanism always explains the shallow-to-deep transition. For example, with a thermal tracking algorithm developed for the purpose, it can be shown that, in a marginally unstable atmosphere, the total water perturbation induced locally by decaying cumuli has an

  16. 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.

  17. The Preferred Latitudes of the Intertropical Convergence Zone: Observations and Theory

    NASA Astrophysics Data System (ADS)

    Waliser, Duane Edward

    1992-01-01

    The latitude preference of the Intertropical Convergence Zone (ITCZ) is examined on the basis of observations, theory, and a modeling analysis. Observational analysis indicates that a dynamical mechanism in the atmosphere is acting to position the ITCZ(s) away from the equator to latitudes of about 4-10^circ, even in regions where the SST is maximum on the equator. Earlier theories for this off-equatorial preference of the ITCZ are reviewed and a new explanation is presented based on analogous results from a forced, linear shallow-water model and a moist primitive equation model. The results from the simplified model show that finite-width mid-level tropospheric heating (i.e. an ITCZ) induces the greatest low-level convergence when the heating is placed a finite distance away from the equator. The results from the primitive equation model show that when the latent heating field is not specified but is determined internally, the above phenomena leads to a positive feedback between the heating field and the induced low-level convergence that favors ITCZ development at latitudes of about 4-10^ circ. The relationship between this mechanism and earlier theories is discussed, as are implications concerning the roles played by mid-level latent heating and SST-gradients in forcing the low-level atmospheric circulation, as well as, other implications on related aspects of tropical meteorology and oceanography. In addition to the above results, comparative analyses of long-record satellite indices of tropical convection reveal that the Highly Reflective Cloud (HRC) data set is generally superior to the Outgoing Longwave Radiation data set for studies of tropical deep convection. Further, analysis of the relationship between these two data sets and local SST reveals that monthly SSTs in excess of about 29.5^circC tend to occur only under conditions of diminished local convection. This new and important finding helps to further define the complex relationship between SST and

  18. Characteristics of summertime daily rainfall variability over South America and the South Atlantic Convergence Zone

    NASA Astrophysics Data System (ADS)

    Todd, M. C.; Washington, R.; James, T.

    This paper presents an objective analysis of the structure of daily rainfall variability over the South American/South Atlantic region (15°-60°W and 0°-40°S) during individual austral summer months of November to March. From EOF analysis of satellite derived daily rainfall we find that the leading mode of variability is represented by a highly coherent meridional dipole structure, organised into 2 extensive bands, oriented northwest to southeast across the continent and Atlantic Ocean. We argue that this dipole structure represents variability in the meridional position of the South Atlantic Convergence Zone (SACZ). During early and later summer, in the positive (negative) phase of the dipole, enhanced (suppressed) rainfall over eastern tropical Brazil links with that over the subtropical and extra-tropical Atlantic and is associated with suppressed (enhanced) rainfall over the sub-tropical plains and adjacent Atlantic Ocean. This structure is indicative of interaction between the tropical, subtropical and temperate zones. Composite fields from NCEP reanalysis products (associated with the major positive and negative events) show that in early and late summer the position of the SACZ is associated with variability in: (a) the midlatitude wave structure, (b) the position of the continental low, and (c) the zonal position of the South Atlantic Subtropical High. Harmonic analysis of the 200hPa geopotential anomaly structure in the midlatitudes indicates that reversals in the rainfall dipole structure are associated primarily with variability in zonal wave 4. There is evidence of a wave train extending throughout the midlatitudes from the western Pacific into the SACZ region. During positive (negative) events the largest anomalous moisture advection occurs within westerlies (easterlies) primarily from Amazonia (the South Atlantic). In both phases a convergent poleward flow results along the leading edge of the low-level trough extending from the tropics into

  19. Interactions between sea surface temperature over the South Atlantic Ocean and the South Atlantic Convergence Zone

    NASA Astrophysics Data System (ADS)

    Chaves, Rosane Rodrigues; Nobre, Paulo

    2004-02-01

    Interactions between the sea surface temperature (SST) over the South Atlantic Ocean (40°S-Equador) and the South Atlantic Convergence Zone (SACZ) were studied through numerical experiments with an atmospheric general circulation model (AGCM) and an ocean general circulation model (OGCM). The AGCM experiments showed that warm SST anomalies over the South Atlantic tend to intensify the SACZ and shift it northward, while cool SST anomalies over the South Atlantic tend to weaken the SACZ. The OGCM experiments, on the other hand, showed that the intensification of the SACZ contributes to cool the underlying ocean through the reduction of incident shortwave solar radiation, causing the appearance of cold SST anomalies or the weakening of pre-existing warm SST anomalies. The most important finding in this work was the predominance of the cloud/shortwave - SST negative thermodynamic feedback between the atmosphere and the ocean over the southwest tropical Atlantic, this is one order of magnitude larger than the dynamic feedback associated with Ekman pumping. The latter was verified only during strong SACZ events. The results suggest that negative SST anomalies often observed underlying the SACZ represent an ocean response to atmospheric forcing.

  20. Seasonal prediction of the South Pacific Convergence Zone in the austral wet season

    NASA Astrophysics Data System (ADS)

    Charles, A. N.; Brown, J. R.; Cottrill, A.; Shelton, K. L.; Nakaegawa, T.; Kuleshov, Y.

    2014-11-01

    The position and orientation of the South Pacific Convergence Zone (SPCZ), modulated by the El Niño-Southern Oscillation (ENSO), determine many of the potentially predictable interannual variations in rainfall in the South Pacific region. In this study, the predictability of the SPCZ in austral summer is assessed using two coupled (ocean-atmosphere) global circulation model (CGCM)-based seasonal prediction systems: the Japan Meteorological Agency's Meteorological Research Institute Coupled Ocean-Atmosphere General Circulation Model (JMA/MRI-CGCM) and the Australian Bureau of Meteorology's Predictive Ocean-Atmosphere Model for Australia (POAMA-M24). Forecasts of austral summer rainfall, initialized in November are assessed over the period 1980-2010. The climatology of CGCM precipitation in the SPCZ region compares favorably to rainfall analyses over subsets of years characterizing different phases of ENSO. While the CGCMs display biases in the mean SPCZ latitudes, they reproduce interannual variability in austral summer SPCZ position indices for forecasts out to 4 months, with temporal correlations greater than 0.6. The summer latitude of the western branch of the SPCZ is predictable with correlations of the order of 0.6 for forecasts initialized as early as September, while the correlation for the eastern branch only exceeds 0.6 for forecasts initialized in November. Encouragingly, the models are able to simulate the large displacement of the SPCZ during zonal SPCZ years 1982-1983, 1991-1992, and 1997-1998.

  1. 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

    2016-02-24

    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.

  2. 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

  3. Regional energy budget control of the intertropical convergence zone and application to mid-Holocene rainfall

    NASA Astrophysics Data System (ADS)

    Boos, William R.; Korty, Robert L.

    2016-12-01

    Shifts in the latitude of the intertropical convergence zone--a region of intense tropical rainfall--have often been explained through changes in the atmospheric energy budget, specifically through theories that tie rainfall to meridional energy fluxes. These quantitative theories can explain shifts in the zonal mean, but often have limited relevance for regional climate shifts, such as a period of enhanced precipitation over Saharan Africa during the mid-Holocene. Here we present a theory for regional tropical rainfall shifts that utilizes both zonal and meridional energy fluxes. We first identify a qualitative link between zonal and meridional energy fluxes and rainfall variations associated with the seasonal cycle and the El Niño/Southern Oscillation. We then develop a quantitative theory based on these fluxes that relates atmospheric energy transport to tropical rainfall. When applied to the orbital configuration of the mid-Holocene, our theory predicts continental rainfall shifts over Africa and Southeast Asia that are consistent with complex model simulations. However, the predicted rainfall over the Sahara is not sufficient to sustain vegetation at a level seen in the palaeo-record, which instead requires an additional large energy source such as that due to reductions in Saharan surface albedo. We thus conclude that additional feedbacks, such as those involving changes in vegetation or soil type, are required to explain changes in rainfall over Africa during the mid-Holocene.

  4. Link between the double-Intertropical Convergence Zone problem and cloud biases over the Southern Ocean

    PubMed Central

    Hwang, Yen-Ting; Frierson, Dargan M. W.

    2013-01-01

    The double-Intertropical Convergence Zone (ITCZ) problem, in which excessive precipitation is produced in the Southern Hemisphere tropics, which resembles a Southern Hemisphere counterpart to the strong Northern Hemisphere ITCZ, is perhaps the most significant and most persistent bias of global climate models. In this study, we look to the extratropics for possible causes of the double-ITCZ problem by performing a global energetic analysis with historical simulations from a suite of global climate models and comparing with satellite observations of the Earth’s energy budget. Our results show that models with more energy flux into the Southern Hemisphere atmosphere (at the top of the atmosphere and at the surface) tend to have a stronger double-ITCZ bias, consistent with recent theoretical studies that suggest that the ITCZ is drawn toward heating even outside the tropics. In particular, we find that cloud biases over the Southern Ocean explain most of the model-to-model differences in the amount of excessive precipitation in Southern Hemisphere tropics, and are suggested to be responsible for this aspect of the double-ITCZ problem in most global climate models. PMID:23493552

  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. 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.

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

    USGS Publications Warehouse

    van Hengstrum, Peter J.; Donnelly, Jeffrey P.; Fall, Patricia L.; Toomey, Michael; 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. 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.

  9. Enhanced Ionospheric Plasma Bubble Generation in More Active Atmospheric Intertropical Convergence Zone

    NASA Astrophysics Data System (ADS)

    Yue, X.; Li, G.; Otsuka, Y.; Ning, B.; Abdu, M. A.; Yamamoto, M.; Wan, W.; Liu, L.; Abadi, P.

    2016-12-01

    Using two low latitude steerable backscatter radars in Southeast Asia, the Kototabang (0.2°S, 100.3°E; dip lat 10.4°S) and Sanya (18.4°N, 109.6°E; dip lat 12.8°N) VHF radars, the characteristics of equatorial plasma bubbles (backscatter plumes) during the autumn equinox of 2012-2013 over the two sites separated in longitude by 1000 km were simultaneously investigated. The beam steering measurements reveal frequent occurrences of multiple plumes over both radar sites. We find that the total numbers of nights with plume/bubble (i.e., occurrence rates) at the two closely located longitudes (Kototabang and Sanya) are comparable. But interestingly, the total number of nights with locally generated bubble (i.e., generation rate) over Kototabang is clearly more than that over Sanya. Further analysis reveals that a more active Intertropical Convergence Zone (ITCZ) is situated around the longitude of Kototabang. Considering that the two stations are separated only by about 9° in longitude where the magnetic declination and the magnetic equator offset from the geographic equator are almost the same, we surmise that the evening pre-reversal enhancement of the eastward electric field (PRE) was unlikely to cause any difference in the bubble generation rate between the two longitudes. The enhanced ionospheric bubble generation at Kototabang longitude could be caused by a higher gravity wave activity associated with the more active ITCZ.

  10. Link between the double-Intertropical Convergence Zone problem and cloud biases over the Southern Ocean.

    PubMed

    Hwang, Yen-Ting; Frierson, Dargan M W

    2013-03-26

    The double-Intertropical Convergence Zone (ITCZ) problem, in which excessive precipitation is produced in the Southern Hemisphere tropics, which resembles a Southern Hemisphere counterpart to the strong Northern Hemisphere ITCZ, is perhaps the most significant and most persistent bias of global climate models. In this study, we look to the extratropics for possible causes of the double-ITCZ problem by performing a global energetic analysis with historical simulations from a suite of global climate models and comparing with satellite observations of the Earth's energy budget. Our results show that models with more energy flux into the Southern Hemisphere atmosphere (at the top of the atmosphere and at the surface) tend to have a stronger double-ITCZ bias, consistent with recent theoretical studies that suggest that the ITCZ is drawn toward heating even outside the tropics. In particular, we find that cloud biases over the Southern Ocean explain most of the model-to-model differences in the amount of excessive precipitation in Southern Hemisphere tropics, and are suggested to be responsible for this aspect of the double-ITCZ problem in most global climate models.

  11. 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.

  12. 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

  13. 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

  14. Influence of Anomalous Heat Sources on the South Atlantic Convergence Zone Low-Frequency Variability

    NASA Astrophysics Data System (ADS)

    Andrade, F.; Aravéquia, J.

    2014-12-01

    This study identifies the locations of anomalous heat sources (AHS) that promote low-frequency variations in three components of South America Monsoon System (SAMS) associated with South Atlantic Convergence Zone (SACZ) behavior, which are: 1) the Northeastern Brazilian trough in 200hPa (NBT); 2) the Bolivian High in 200hPa (BH); and 3) the trough in 500hPa on the southeastern of South America (TS). The AHS are identified through combined analysis between anomalous outgoing longwave radiation (OLR) observed fields, only for January months from 1982 to 2011, and influence functions (IF) fields produced for January climatology basic state from numerical simulations of a global atmospheric circulation model that include in each solution of temperature tendency equation a thermal forcing in a specific grid point of model domain to mimic a diabatic heating vertical profile observed in deep convective clouds. Statistically significant linear correlations are observed among each of those components from SAMS and OLR. For NBT and BH the largest correlations are concentrated in equatorial regions, SACZ and subtropical oceans. On the other side, TS circulation correlates with convective dipole between eastern of tropical Indian Ocean and western of tropical Pacific Ocean, besides anomalous convection on the Africa, the subtropical South Pacific Ocean and the SACZ. IF for different atmospheric levels show that NBT and BH (TS) variations are related to AHS in tropical Pacific/Atlantic Oceans and SACZ (subtropical South Pacific Ocean), possibly connected with the El Niño-Southern Oscillation (Madden-Julian Oscillation - MJO). Generally, an intensification of NBT (BH) could be produced by El Niño, intensified SACZ and/or equatorial Atlantic reduced convection (by La Niña and/or SACZ/equatorial Atlantic intensified convection), whilst an intensified TS could be produced by reduced convection in central-western of subtropical South Pacific Ocean resulting from MJO variability.

  15. 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.

  16. 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.

  17. Oscillations of the Intertropical Convergence Zone and the genesis of easterly waves Part II: numerical verification

    NASA Astrophysics Data System (ADS)

    Toma, Violeta E.; Webster, Peter John

    2010-03-01

    A companion paper (Part I: Toma and Webster 2008), argued that the characteristics of the mean Intertropical Convergence Zone (ITCZ) arise from instabilities associated with the strong cross-equatorial pressure gradient (CEPG) that exists in the eastern Pacific Ocean as a result of the latitudinal sea-surface temperature (SST) gradient. Furthermore, it was argued that instabilities of the mean ITCZ resulted in the in situ development of easterly waves. Thus, in Part I, it was hypothesized that the mean and transient state of eastern Pacific convection was due to local processes and less so to the advection of waves from the North Atlantic Ocean. To test this hypothesis and, at the same time, consider others such as a possible role of the equatorial and subtropical orography in generating local instabilities, a series of controlled numerical experiments are designed using the WRF regional model. The domain of the model was configured to include the western Atlantic Ocean, the Isthmus of Panama and the eastern Pacific Ocean to 155°W. Lateral boundaries were set at 40°N and 40°S, thus containing the mountains of Central America, the Andes and the Sierra Madre of Mexico. In a series of experiments, analysis products were used as boundary conditions that were successively updated four times per day, set as 10-day running average fields or as running mean monthly fields. Finally, the model was run with topography essentially eliminated over the land areas. Although there are differences between the details of the resultant fields, the location of mean convection and the form of the transients remain the same. It is concluded, in support of the theoretical and diagnostic studies of Part I that orographic forcing or waves generated in the North Atlantic Ocean are not the major causes of the mean and transient nature of disturbances in the eastern Pacific.

  18. Precipitation Changes Throughout the South Pacific Convergence Zone During the Last 2000 Years

    NASA Astrophysics Data System (ADS)

    Maloney, A. E.; Nelson, D. B.; Sachs, J. P.

    2016-12-01

    The South Pacific Convergence Zone (SPCZ) is the southern hemisphere's most prominent precipitation feature extending 3000km southeastwards from Papua New Guinea to French Polynesia. Seasonal and interannual variability in SPCZ rainfall is well characterized by satellite data, however an understanding of this feature prior to the instrumental record is lacking. Rainfall in the western tropical Pacific is difficult to reconstruct due to a dearth of archives that are both high-resolution and continuous. Here we present molecular fossil hydroclimate reconstructions from the last 2000 years. The hydrogen isotopic composition of the algal lipid biomarker dinosterol was measured in 10 freshwater lake sediment cores from 7 lakes on 4 islands in Vanuatu, the Solomon Islands, and Wallis and Futuna. Coretop δ2Hdinosterol values were well correlated with satellite-derived rainfall rates, providing a transfer function for deriving precipitation rates from sedimentary δ2Hdinosterol values. The Vanuatu and Wallis records indicate that the south-western portion of the SPCZ was driest during the transition from the Medieval Warm Period (MWP) to the Little Ice Age (LIA) (1200-1400 CE) with rainfall rates as low as 2mm/day compare to more typical values of 4mm/day. Conversely, the central SPCZ (Solomon Islands) experienced the driest conditions ( 5mm/day) during the MWP (600-1200 CE) and has maintained high ( 9mm/day) rainfall rates since the LIA. The tropical water cycle influences global climate and these quantitative precipitation records are important for understanding SPCZ natural variability.

  19. Connections between the Intertropical Convergence Zone and the Caribbean Low Level Jet in Central America

    NASA Astrophysics Data System (ADS)

    Hidalgo, H. G.; Durán-Quesada, A.; Amador, J.; Alfaro, E. J.

    2013-05-01

    This study explores statistical connections between the displacements and strength of the Intertropical Convergence Zone (ITCZ) and the Caribbean Low Level Jet (CLLJ). Indicators of the strength and position of the ITCZ include the latitude (LATC) and longitude (LONC) of the center of mass of precipitation and the mean domain precipitation (Pdomain) in a region bounded by coordinates 10 oS and 25 oN and 100 - 55 oW. The CLLJ was indexed using the average zonal wind velocity at 925 hPa over a region bounded by 7.5 - 12.5 oN and 85 - 75 oW. Preliminary analyses show that there is a strong correlation (0.82) between summer (JJA) LATC and JJA CLLJ index for the period 1979 - 2010; this correlation is lower in other seasons (0.63 for Autumn, 0.20 for Winter and 0.49 for Spring). These correlations were verified in the zonal wind composites at 925 hPa for the 5 lowest and 5 highest years of LATC. LONC does not seem to have the same strong relationship with the CLLJ. At daily level, composites show that precipitation in the Central America region is influenced by Pdomain, LATC, and the CLLJ index. From the comparison between the highest and lowest years of LATC, a strong contrast is observed for the evaporation over the Caribbean and the moisture transport to Central America. Moisture uptake increases significantly for the lowest LATC which corresponds to a stronger CLLJ. Composites of Sea Surface Temperature for the 5 years of highest and lowest LATC show some relationship with ENSO, although there is a disproportionate influence of the 1997-98 El Niño that may be affecting the results. There is however a consistent feature: during years of high LATC, there are warm anomalies in the tropical Atlantic off the coast of Venezuela, that are not present during years of low LATC.

  20. Assessment of seasonal prediction of South Pacific Convergence Zone using APCC multi-model ensembles

    NASA Astrophysics Data System (ADS)

    Kim, Ok-Yeon

    2017-07-01

    We have quantified and examined the South Pacific convergence zone (SPCZ) characteristics for the purpose of its seasonal prediction, by defining two orientation indices, strength and area. The multi-model ensemble (MME) tends to simulate the ENSO-associated shift of SPCZ orientation, especially for the 1-month forecast lead. The migration of the SPCZ orientation indices associated with ENSO phases is clear in the observation and the MME. The variation of the SPCZ strength and area associated with ENSO phases is not as clear as in the SPCZ orientation. In spite of marginal changes in the SPCZ strength and area related to ENSO phases, the SPCZ strength becomes a bit stronger during El Niño and weaker during La Niña, which is represented in individual models and MME. The performance of the MME in simulating the variability of the SPCZ orientation, strength and area is also examined. We found that the MME reasonably predicts the observed interannual variability of the western portion of the SPCZ, with systematic and marginal shift southward. Compared to the western part of the SPCZ, the MME seems to have a limitation in predicting the variability of the eastern part. In comparison to the SPCZ orientation, the MME is not capable of predicting the strength and area of the SPCZ. The interannual variability of the SPCZ strength in the MME is systematically weaker compared to that in the analysis. By comparison with SPCZ orientation and strength, the SPCZ area is not resolved in the MME. The SPCZ is a main source of precipitation in the South Pacific, and the SPCZ predictability also influences high impact weather prediction such as tropical cyclones. Therefore, skillful predictions of seasonal variability of the SPCZ could benefit users who utilize the seasonal forecasting information for their decision making in many applicable sectors.

  1. The South Atlantic Coupled Variability and the South Atlantic Convergence Zone

    NASA Astrophysics Data System (ADS)

    Bombardi, Rodrigo Jose

    The dominant mode of coupled variability over the South Atlantic Ocean is known as "South Atlantic Dipole" (SAD) and is characterized by a dipole in sea surface temperature (SST) anomalies with centers over the tropical and the extratropical South Atlantic. Previous studies have shown that variations in SST related to SAD modulate large-scale patterns of precipitation over the Atlantic Ocean. Here we show that variations in the South Atlantic SST are associated with changes in daily precipitation over eastern South America. This study is based on observational and regional atmospheric modeling. Rain gauge precipitation, satellite derived sea surface temperature and reanalysis data are used to investigate the variability of the subtropical and tropical South Atlantic and impacts on precipitation. SAD phases are assessed by performing Singular Value Decomposition (SVD) analysis of sea level pressure and SST anomalies. We show that during neutral El Nino-Southern Oscillation (ENSO) events, SAD plays an important role in modulating cyclogenesis and the characteristics of the South Atlantic Convergence Zone (SACZ). Positive SST anomalies over the extratropical South Atlantic (SAD negative phase) are related to increased cyclogenesis near southeast Brazil as well as the migration of extratropical cyclones further north. As a consequence, these systems organize convection and increase precipitation over eastern South America. Numerical experiments forced with prescribed SST anomalies showed that even though the Atlantic SST affects the position of the cyclone associated with the SACZ, the atmospheric response and precipitation patters over land were opposite from the observational results. On the other hand, experiments forced with prescribed anomalous driving fields showed that the atmospheric component of SAD plays a significant role for the right position and intensity of precipitation associated with the SACZ. SAD negative anomalies provide the low-level and upper

  2. How Does Intertropical Convergence Zone Variation Impact on Tropical Cyclone in the Northern Hemisphere?

    NASA Astrophysics Data System (ADS)

    Ma, Liping; Williams, Richard

    2017-04-01

    Enhanced sea surface temperature is expected to be favourable for more tropical cyclone formation. However, a surprising result emerges from the analysis of the frequency of tropical cyclones in the global tropical oceans in the northern hemisphere. The frequency of tropical cyclones positively correlates with a strengthening and northward movement of the Intertropical Convergence Zone (ITCZ hereafter). There is a different regional character for the tropical cyclones activity: in the Western North Pacific, the number of tropical cyclones has been decreasing since 1960s, whereas in the Eastern North Pacific and North Atlantic, the number of tropical cyclones has been increasing since 1949 and 1984 respectively. Most of the tropical cyclones in the tropical oceans are generated within the ITCZ (called the monsoon trough in the Western North Pacific, and the easterly wave in the Eastern North Pacific and North Atlantic). At the same time, there are changes in the strength and position of the ITCZ. In the Western North Pacific, ITCZ strength has been weakening and its position has been moving equatorward since the 1960s when the tropical cyclones frequency decreased. In the Eastern North Pacific, the ITCZ has been strengthening and moving northward where the tropical cyclone frequency has been increasing since 1949. In North Atlantic, since the mid-1980s, the ITCZ has been strengthening and moving northward and the tropical cyclone numbers have been increasing uniformly since then. To understand the differing regional response, the ITCZ may be viewed as a planetary wave undulating around the planet along the tropics. The trough phase is correlated with where the tropical cyclone numbers reduce, such as in the Western North Pacific since 1960s; conversely, its peak phase in the tropical oceans is where the frequency of tropical cyclones increases, such as in the tropical Eastern North Pacific since 1949 and North Atlantic since 1984 In conclusion, this research reveals

  3. 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

  4. Teleconnection between the South Atlantic convergence zone and the southern Indian Ocean: Implications for tropical cyclone activity

    NASA Astrophysics Data System (ADS)

    DeBlander, Evan; Shaman, Jeffrey

    2017-01-01

    A link between anomalous austral summer convection over the South Atlantic convergence zone (SACZ) and atmospheric conditions over the South Indian Ocean is investigated. Interannual north-south shifts in the SACZ produce a dipole of anomalous convection and precipitation over South America. The South Atlantic convergence zone index (SACZI) capturing this variability is presented and associated with a midlatitude Rossby wave train that propagates from South America eastward and south of Africa before curving north into the tropical Indian Ocean. This wave train is reproduced using Rossby wave ray tracing and simulations with a linearized barotropic vorticity equation model forced with divergence and convergence consistent with the observed dipole of anomalous convection. The wave train acts to excite anomalies in wind shear and relative humidity over the tropical south Indian Ocean, which in turn impact tropical cyclone (TC) genesis and distribution over this region. We find that changes in the wind shear and relative humidity associated with the SACZI effect changes in TC genesis, which result in a change in observed TC days over portions of the South Indian Ocean.

  5. 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.

  6. 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.

  7. 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

  8. Control of Saharan mineral dust transport to Barbados in winter by the Intertropical Convergence Zone over West Africa

    NASA Astrophysics Data System (ADS)

    Doherty, O. M.; Riemer, N.; Hameed, S.

    2012-10-01

    The reasons for the inter-annual variability of dust transport from the Sahara across the Atlantic are not well-understood. Here we address this issue by defining three new climate indices that capture the position and intensity of the zone of near-surface convergence over West Africa, a part of the global Intertropical Convergence Zone (ITCZ). We then relate these indices to a 38-year record of mineral dust concentrations at Barbados focusing on the winter season. The results show that the latitudinal displacement of the ITCZ over West Africa and the dust load in Barbados are statistically significantly correlated with a correlation coefficient ofr= -0.69. A southward movement of the ITCZ corresponds to an increased dust load at Barbados. This correlation represents an improvement upon previous results, which focused on traditional teleconnection indices such as the North Atlantic Oscillation or the El-Niño-Southern Oscillation. From analyzing composites of wind and precipitation we conclude that for the winter season, the inter-annual variability of the Barbados dust load is related to changes in near-surface northeasterly winds in semi-arid regions in North Africa coincident with the movement of the ITCZ. Changes in precipitation appear to only play a minor role.

  9. Response of the South Pacific Convergence Zone to imposed circulation and moisture perturbations in an intermediate level complexity model

    NASA Astrophysics Data System (ADS)

    Niznik, M. J.; Lintner, B. R.

    2014-12-01

    Previous research has identified a connection between the strength of low-level trade wind inflow from the relatively dry southeastern Pacific basin and the position of the South Pacific Convergence Zone (SPCZ). This circulation-precipitation relationship has been noted in composite analysis applied to reanalysis data as well as to output from current generation climate models, although the causality is ambiguous. Additionally, given that prior studies exhibit deep vertical structures associated with changes to low-level inflow east of the SPCZ, the relationship between low-level inflow variability and the propagation of upper level mid-latitude synoptic disturbances into the SPCZ remains unclear. Thus, forcing models with prescribed circulation and moisture anomalies may be instructive for untangling the dynamic and thermodynamic contributions to such interactions, as well as their potential causality. To that end, we use the Quasi-equilibrium Tropical Circulation Model 2 (QTCM2), an intermediate complexity model with a separate boundary layer of fixed height imposed at the base of the free troposphere, to explore the response of the SPCZ, and more broadly convection across the South Pacific, to perturbed low- and upper-level circulation and moisture fields east of its climatological position. Preliminary results suggest a strong precipitation response to strengthened low-level trade wind inflow, hypothesized to be the result of increased convergence in the climatological SPCZ, with an associated decrease in Intertropical Convergence Zone (ITCZ) precipitation. Conversely, there is a limited precipitation response to weakened low-level trade wind inflow despite a notable (2-3 g kg-1) increase in specific humidity, suggesting the climatological low-level inflow is already associated with the necessary moisture threshold for deep convection. Ultimately, these results suggest dynamics play a stronger role than thermodynamics in the interaction as modeled by QTCM2.

  10. 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.

  11. 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.

  12. Using a <670> zone axis for convergent beam electron diffraction measurements of lattice strain in strained silicon.

    PubMed

    Diercks, D R; Kaufman, M J; Irwin, R B; Jain, A; Robertson, L; Weijtmans, J W; Wise, R

    2010-08-01

    Convergent beam electron diffraction patterns of silicon from the gate channel region of a complementary metal-oxide-semiconductor transistor with recessed Si(.82)Ge(.18) stressors were analysed using three zone axes: <230>, <340> and <670>. Values measured using these axes were compared with each other with regards to strain along the [110] and the [001] directions. It was demonstrated that strain measurements made using all three axes showed reasonable agreement with each other: an increase in the [110] compressive strain and a switch from compressive to tensile strain in the [001] with decreasing distance below the gate. It was also observed that the strain calculations using the <230> axis had the lowest uncertainty whereas the <670> axis allowed for measurements closest to the gate due to the improved lateral resolution at that tilt angle.

  13. 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

  14. 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. © 2013 German Botanical Society and The Royal Botanical Society of the Netherlands.

  15. North Atlantic Oscillation Influence on Precipitation Variability around the Southeast African Convergence Zone.

    NASA Astrophysics Data System (ADS)

    McHugh, Maurice J.; Rogers, Jeffrey C.

    2001-09-01

    The relationship between the North Atlantic oscillation (NAO) and austral summer (December-February) rainfall variability over southeastern Africa is described. Thirty-one stations in 0°-16°S and 25°-40°E have statistically significant correlations to the NAO index over varying periods of record starting since 1895 and form a regional normalized rainfall index of southeast African rainfall (SEAR) correlated to the NAO index (NAOI) at r = 0.48 over 1894/95-1989/90, although the relationship is r = 0.70 since 1958. The spectrum of the SEAR index has significant amplitude at 7.6 yr, a periodicity commonly associated with the NAO, and the NAOI/SEAR cospectrum has its largest power at this periodicity. NCEP-NCAR reanalysis data, extending from 1958/59 to 1995/96 are used to evaluate moisture and circulation field variations associated with both NAO and SEAR indices. Precipitable water over southeastern Africa varies significantly such that anomalously high (low) convective rainfall occurs over southeast Africa when the NAO is weak (strong). Unusually wet summers are associated with anomalous equatorial westerly flow originating in the subtropical Atlantic and traversing the continent. Relatively dry summers are associated with increased southeasterly monsoon flow originating over the subtropical Indian Ocean. The NAO linkage to southeastern African rainfall is especially pronounced in 300-hPa zonal winds where five highly significant elongated bands of alternating zonal wind anomalies extend from the Atlantic Arctic to equatorial Africa. The latter 300-hPa equatorial band exhibits westerly (easterly) flow during wet (dry) austral summers and undergoes regional divergence (convergence) over southeastern Africa. The westerly flow, along with orographic uplift, has an element of instability due to the vertical component of the Coriolis parameter that assists rain production during wet summer. Potential interactions between the NAO and ENSO in producing regional

  16. Oscillations of the intertropical convergence zone and the genesis of easterly waves. Part I: diagnostics and theory

    NASA Astrophysics Data System (ADS)

    Toma, Violeta E.; Webster, Peter J.

    2010-03-01

    We examine the mean and transient state of the intertropical convergence zone (ITCZ) by analyzing data and using simple theory. We concentrate on the tropical eastern Pacific Ocean noting that there exists in this region a well-developed mean ITCZ. Furthermore, it is a region where there has been considerable discussion in the literature of whether easterly waves develop in situ or propagate westwards from the Atlantic Ocean. The region is typical of tropical regions where there is a strong cross-equatorial pressure gradient (CEPG): mean convection well removed from the equator but located equatorward of the maximum sea-surface temperature (SST) and minimum sea level pressure (MSLP). Further to the west, near the dateline where the CEPG is much smaller, convection is weaker and collocated with SST and MSLP extrema. It is argued that in regions of significant CEPG that the near-equatorial tropical system is inertially unstable and that the rectification of the instability for a given CEPG determines the location and intensity of the climatological ITCZ. Using simple theoretical arguments, we develop an expression for the mean latitude of the ITCZ as a function of the CEPG. We note on a day-by-day basis that the ITCZ is highly transient state with variability occurring on 3-8 day time scales. Transients with amplitudes about half of the mean ITCZ, propagate northwards from the near-equatorial southern hemisphere as anomalous meridional oscillations, eventually amplifying convection in the vicinity of the mean ITCZ. It is argued that in these longitudes of strong CEPG the mean ITCZ is continually inertially unstable with advections of anticylonic vorticity across the equator resulting in the creation of an oscillating divergence-convergence doublet. The low-level convergence produces convection and the resultant vortex tube stretching generates cyclonic vorticity which counteracts the northward advection of anticylonic vorticity. During a cycle, the mid

  17. Convergent margin structure and tectonics of the Java subduction zone (105°E-122°E)

    NASA Astrophysics Data System (ADS)

    Kopp, H.; Barckhausen, U.; Djajadihardja, Y.; Engels, M.; Flueh, E. R.; Hindle, D. A.; Lueschen, E.; Mueller, C.; Planert, L.; Reichert, C. J.; Shulgin, A. A.; Wittwer, A.

    2009-12-01

    The Java margin is the site of oceanic subduction of the Indo-Australian plate underneath the Indonesian archipelago. Data from a suite of geophysical experiments conducted between 1997-2006 using RV SONNE as platform include seismic and seismological studies, potential field measurements and high-resolution seafloor bathymetry mapping. Tomographic inversions provide an image of the ongoing deformation of the forearc and the deep subsurface. We investigate the role of various key mechanisms that shape the first-order features characterizing the present margin architecture. Our results show a high variability in subduction zone processes along the Java margin, ranging from accretionary subduction to erosive processes to zero-budget mass transfer. These variations are closely linked to changes in character of the incoming plate. Off Western Java (105°E -109°E), near-full accretion of the trench sediment fill is associated with a well-developed accretionary prism fronting a 4 km deep forearc basin. The Central Java segment (109°E -115°E) experiences the collision of an oceanic plateau dotted with numerous seamounts, causing large-scale uplift of the forearc, coupled with erosion of the frontal prism and correlated mass wasting processes. Intense deformation of the forearc basin results from thrusting and compressional forces. In the neighbouring segment farther to the east (115°E-119°E), the lack of significant sediment input to the trench supports the notion that recycling of upper plate material in the forearc sustains the massive outer high observed here adjacent to a mature forearc basin. The incoming oceanic plate of the Argo Abyssal plain is devoid of a sediment drape and the original spreading fabric overprinted by bending-related faulting near the trench shape its morphology. The transition zone from the Java margin to the Banda Arc (119°E-122°E) experiences the early stages of continent-island arc collision associated with the convergence of the

  18. Combined obliquity and precession pacing of western Pacific Intertropical Convergence Zone over the past 282,000 years

    NASA Astrophysics Data System (ADS)

    Shen, C. C.; Yi, L.; Lo, L.; Shi, Z.; Wei, K. Y.; Chou, C. J.; Chen, Y. C.; Chuang, C. K.; WU, C. C.; Mii, H. S.; Amakawa, H.; Burr, G.; Lee, S. Y.; DeLong, K. L.; Elderfield, H.

    2015-12-01

    The Intertropical convergence Zone (ITCZ) encompasses the heaviest rain belt on Earth. Few direct long-term records, especially in the Pacific, limit our understanding of long-term natural variability necessary to predict future ITCZ changes. Here we present a tropical precipitation record from the Southern Hemisphere covering the past 282,000 years, inferred from of rare earth elements (REEs) to Ca ratios in the planktonic foraminifer Globigerinoides ruber shell calcite, of a marine sedimentary core MD05-2925 (9o20.60'S, 151o27.54'E; water depth 1661 m), 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. This 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, supported by model simulations. Our finding suggests that the obliquity forcing may play a more important role in global hydroclimate cycles than previously thought.

  19. Simulating the influence of the South Atlantic dipole on the South Atlantic convergence zone during neutral ENSO

    NASA Astrophysics Data System (ADS)

    Bombardi, Rodrigo J.; Carvalho, Leila M. V.; Jones, Charles

    2014-10-01

    The South Atlantic Convergence Zone (SACZ) is an intrinsic characteristic of the South American Summer Monsoon. In a recent study, we verified that the main mode of coupled variability over the South Atlantic (South Atlantic Dipole (SAD)) plays a role in modulating the position of extratropical cyclones that affect the SACZ precipitation. In this study, we perform numerical experiments to further investigate the mechanisms between SAD and the SACZ. Numerical experiments forced with prescribed SST anomalies showed that, even though the Atlantic SST affects the position of the cyclone associated with the SACZ, the atmospheric response and precipitation patterns over land are opposed to the observations. On the other hand, experiments forced with prescribed anomalous driving fields showed that the atmospheric component of SAD plays a significant role for the right position and intensity of precipitation associated with the SACZ. SAD negative anomalies provide the low-level and upper-level atmospheric support for the intensification of the cyclone at surface and for the increase in precipitation over the land portion of the SACZ. Therefore, the numerical experiments suggest that, during El Niño Southern Oscillation neutral conditions, the SACZ precipitation variability associated with SAD is largely dependent on the atmospheric variability rather than the underlying SST.

  20. Simulated precipitation response to SST forcing and potential predictability in the region of the South Atlantic convergence zone

    NASA Astrophysics Data System (ADS)

    Barreiro, Marcelo; Chang, Ping; Saravanan, R.

    2005-01-01

    The sensitivity of the precipitation response in the South Atlantic convergence zone (SACZ) to sea surface temperature (SST) anomaly is investigated by an inter-model comparison study of ensembles of multidecadal integrations of two atmospheric general circulation models (AGCMs)—version 1 of the NASA Seasonal-to-Interannual Prediction Project (NSIPP-1) model, and the NCAR community climate model (CCM3) version 3.6.6. Despite the different physical parameterizations, the two models consistently show an SST-forced signal located mainly over the oceanic portion of the SACZ. The signal has interannual-to-decadal timescales, and consists of a shift and strengthening of the SACZ toward anomalous warm waters. A potential predictability analysis reveals that the maximum predictable variance is about 50% of the total SACZ variance over the ocean, but the signal attenuates rapidly toward the South American continent. This result implies that the land portion of the SACZ is primarily dominated by the internal variability, thereby having a limited potential predictability at seasonal timescales.

  1. Active and inactive phases of the South Pacific Convergence Zone and changes in global circulation patterns - A case study

    NASA Technical Reports Server (NTRS)

    Huang, H.-J.; Vincent, D. G.

    1988-01-01

    A set of FGGE Level III-b analyses produced at the NASA Goddard Laboratory for Atmospheres (GLA) is used to examine changes that occur in the global-scale circulation features during the period, January 10 - February 13,1979. In the first two weeks of this period, the South Pacific Convergence Zone (SPCZ) and its convective cloud band were observed to be dominant features of the circulation. Subsequent to January 24, there were marked changes in the global-scale circulation, particularly in the Southern Hemisphere tropics. Concomitant with these changes was the disappearance of the SPCZ and its cloud band. The primary purpose of this study is to compare some general circulation parameters, which frequently correspond to deep convection, for two 15-day periods: January 10-24, when the SPCZ was very convectively active, and January 28 - February 11 when it was inactive. Daily variations of some parameters are also shown. It is seen that distinct changes occur in each parameter by the end of the first period, particularly in the vicinity of the SPCZ. Suggestions are offered regarding mechanisms which might be responsible for the observed changes.

  2. Persistent decadal-scale rainfall variability in the tropical South Pacific Convergence Zone through the past six centuries

    NASA Astrophysics Data System (ADS)

    Maupin, C. R.; Partin, J. W.; Shen, C.-C.; Quinn, T. M.; Lin, K.; Taylor, F. W.; Banner, J. L.; Thirumalai, K.; Sinclair, D. J.

    2013-10-01

    Observations and reconstructions of decadal-scale climate variability are necessary to place predictions of future global climate change into temporal context (Goddard et al., 2012). This is especially true for decadal-scale climate variability that originates in the Pacific Ocean (Deser et al., 2004; Dong and Lu, 2013). We focus here on the western tropical Pacific (Solomon Islands; ~ 9.5° S, ~ 160° E), a region directly influenced by: the South Pacific Convergence Zone (SPCZ), the West Pacific Warm Pool (WPWP), the Pacific Walker Circulation (PWC), and the Hadley Circulation. We calibrate δ18O variations in a fast growing stalagmite to local rainfall amount and produce a 600 yr record of rainfall variability from the zonally oriented, tropical portion of the SPCZ. We present evidence for large (~ 1.5 m), persistent and decade(s)-long shifts in total annual rainfall amount in the Solomon Islands since 1416 ± 5 CE. The timing of the decadal changes in rainfall inferred from the 20th century portion of the stalagmite δ18O record coincide with previously identified decadal shifts in Pacific ocean-atmosphere behavior (Clement et al., 2011; Deser et al., 2004). The 600 yr Solomons stalagmite δ18O record indicates that decadal oscillations in rainfall are a robust characteristic of SPCZ-related climate variability, which has important implications to water resource management in this region.

  3. Persistent decadal-scale rainfall variability in the tropical South Pacific Convergence Zone through the past six centuries

    NASA Astrophysics Data System (ADS)

    Maupin, C. R.; Partin, J. W.; Shen, C.-C.; Quinn, T. M.; Lin, K.; Taylor, F. W.; Banner, J. L.; Thirumalai, K.; Sinclair, D. J.

    2014-07-01

    Modern Pacific decadal variability (PDV) has global impacts; hence records of PDV from the pre-instrumental period are needed to better inform models that are used to project future climate variability. We focus here on reconstructing rainfall in the western tropical Pacific (Solomon Islands; ~ 9.5° S, ~160° E), a region directly influenced by PDV, using cave deposits (stalagmite). A relationship is developed between δ18O variations in the stalagmite and local rainfall amount to produce a 600 yr record of rainfall variability from the South Pacific Convergence Zone (SPCZ). We present evidence for large (~1.5 m), abrupt, and periodic changes in total annual rainfall amount on decadal to multidecadal timescales since 1423 ± 5 CE (Common Era) in the Solomon Islands. The timing of the decadal changes in rainfall inferred from the 20th century portion of the stalagmite δ18O record coincides with previously identified decadal shifts in PDV-related Pacific ocean-atmosphere behavior (Clement et al., 2011; Deser et al., 2004). The Solomons record of PDV is not associated with variations in external forcings, but rather results from internal climate variability. The 600 yr Solomon Islands stalagmite δ18O record indicates that decadal oscillations in rainfall are a persistent characteristic of SPCZ-related climate variability.

  4. Active and inactive phases of the South Pacific Convergence Zone and changes in global circulation patterns - A case study

    NASA Technical Reports Server (NTRS)

    Huang, H.-J.; Vincent, D. G.

    1988-01-01

    A set of FGGE Level III-b analyses produced at the NASA Goddard Laboratory for Atmospheres (GLA) is used to examine changes that occur in the global-scale circulation features during the period, January 10 - February 13,1979. In the first two weeks of this period, the South Pacific Convergence Zone (SPCZ) and its convective cloud band were observed to be dominant features of the circulation. Subsequent to January 24, there were marked changes in the global-scale circulation, particularly in the Southern Hemisphere tropics. Concomitant with these changes was the disappearance of the SPCZ and its cloud band. The primary purpose of this study is to compare some general circulation parameters, which frequently correspond to deep convection, for two 15-day periods: January 10-24, when the SPCZ was very convectively active, and January 28 - February 11 when it was inactive. Daily variations of some parameters are also shown. It is seen that distinct changes occur in each parameter by the end of the first period, particularly in the vicinity of the SPCZ. Suggestions are offered regarding mechanisms which might be responsible for the observed changes.

  5. Observations of SKS splitting beneath the Central and Southern External Dinarides in the Adria-Eurasia convergence zone

    NASA Astrophysics Data System (ADS)

    Subašić, Senad; Prevolnik, Snježan; Herak, Davorka; Herak, Marijan

    2017-05-01

    Seismic anisotropy beneath the greater region of the Central and Southern External Dinarides is estimated from observations of SKS splitting. The area is located in the broad and complex Africa-Eurasia convergent plate boundary zone, where the Adriatic microplate interacts with the Dinarides. We analyzed recordings of 12 broadband seismic stations located in the Croatian coastal region. Evidence of seismic anisotropy was found beneath all stations. Fast axis directions are oriented approximately in the NE-SW to NNE-SSW direction, perpendicularly to the strike of the Dinarides. Average delay times range between 0.6 and 1.0 s. A counter-clockwise rotation in average fast axis directions was observed for the stations in the northern part with respect to the stations in the southern part of the studied area. Fast axis directions coincide with the assumed direction of asthenospheric flow through a slab-gap below the Northern and Central External Dinarides, with the maximum tectonic stress orientation in the crust, and with fast directions of Pg and Sg-waves in the crust. These observations suggest that the detected SKS birefringence is primarily caused by the preferred lattice orientation of mantle minerals generated by the asthenospheric flow directed SW-NE to SSW-NNE, with a possible contribution from the crust.

  6. Observation-based 3-D view of aerosol radiative properties over Indian Continental Tropical Convergence Zone: implications to regional climate

    NASA Astrophysics Data System (ADS)

    Jai Devi, J.; Tripathi, S. N.; Gupta, Tarun; Singh, B. N.; Gopalakrishnan, V.; Dey, Sagnik

    2011-11-01

    Spatial and vertical distributions of aerosol radiative properties over Indian Continental Tropical Convergence Zone (CTCZ) up to 6 km altitude during the pre-monsoon and monsoon seasons of 2008 have been measured and reported for the first time. Inter-seasonal and intra-seasonal comparisons of different aerosol properties below and above the boundary layer are carried out in and among different regions of CTCZ. During pre-monsoon, aerosol layers were found to be present up to altitude as high as 6 km over the Indo-Gangetic Plains and Himalayan foothills. A large increase in absorption coefficients (by two to five times) near the Himalayan foothills and coastal India than the background values may be attributed to extensive biomass burning as supported by fire counts data. During monsoon, the aerosols were mostly confined to lower troposphere. However, absorbing aerosols were found to rebuild much faster than scattering aerosols after rains. Heating rates were very high over urban city of Bareilly peaking around 2 km during the pre-monsoon. The HR values over urban Kanpur during monsoon were comparable to Bareilly during pre-monsoon. Negligible latitudinal gradient of heating rate from the Himalayan foothill to central India was observed during both the seasons.

  7. 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

  8. Diapir versus along-channel ascent of crustal material during plate convergence: Constrained by the thermal structure of subduction zones

    NASA Astrophysics Data System (ADS)

    Liu, Ming-Qi; Li, Zhong-Hai; Yang, Shao-Hua

    2017-09-01

    Subduction channel processes are crucial for understanding the material and energy exchange between the Earth's crust and mantle. Crustal rocks can be subducted to mantle depths, interact with the mantle wedge, and then exhume to the crustal depth again, which is generally considered as the mechanism for the formation of ultrahigh-pressure metamorphic rocks in nature. In addition, the crustal rocks generally undergo dehydration and melting at subarc depths, giving rise to fluids that metasomatize and weaken the overlying mantle wedge. There are generally two ways for the material ascent from subarc depths: one is along subduction channels; the other is through the mantle wedge by diapir. In order to study the conditions and dynamics of these contrasting material ascent modes, systematic petrological-thermo-mechanical numerical models are constructed with variable thicknesses of the overriding and subducting continental plates, ages of the subducting oceanic plate, as well as the plate convergence rates. The model results suggest that the thermal structures of subduction zones control the thermal condition and fluid/melt activity at the slab-mantle interface in subcontinental subduction channels, which further strongly affect the material transportation and ascent mode. The thick overriding continental plate and the low-angle subduction style induced by young subducting oceanic plate both contribute to the formation of relatively cold subduction channels with strong overriding mantle wedge, where the along-channel exhumation occurs exclusively to result in the exhumation of HP-UHP metamorphic rocks. In contrast, the thin overriding lithosphere and the steep subduction style induced by old subducting oceanic plate are the favorable conditions for hot subduction channels, which lead to significant hydration and metasomatism, melting and weakening of the overriding mantle wedge and thus cause the ascent of mantle wedge-derived melts by diapir through the mantle wedge

  9. 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.

  10. Extreme Precipitation Events in Southeastern South America and Large-Scale Convective Patterns in the South Atlantic Convergence Zone.

    NASA Astrophysics Data System (ADS)

    Carvalho, Leila M. V.; Jones, Charles; Liebmann, Brant

    2002-09-01

    The occurrence of daily extreme precipitation events in southeast South America (São Paulo, Brazil) and the spatial features of convective activity in the South Atlantic convergence zone (SACZ) are investigated. Precipitation data from surface stations in São Paulo state from 1979 to 1996 are used to determine the frequency of occurrence of extremely heavy daily precipitation events. Daily averages of outgoing longwave radiation (OLR) are examined to characterize convective activity in the SACZ. OLR features are identified with factor analysis. Two factors explain 65% of the total variance of the convective activity patterns in tropical South America and characterize events according to the intensity and extent of the OLR features over the Atlantic Ocean. The combination of factors indicates that 35% of extreme precipitation events occurred when convective activity in the SACZ was intense over large parts of tropical South America, which includes São Paulo, but with less extent toward the Atlantic Ocean. Warm SST episodes (El Niño) seem to modulate the occurrence of extremes associated with intense convection in the SACZ displaced northward of São Paulo and toward the Atlantic Ocean. The remaining events associated with weak convective activity in the SACZ suggest the role of transient systems producing extreme precipitation in São Paulo. The important contribution of the present work is the documentation of the role of orographic features for the regional distribution of extreme precipitation in São Paulo. It is shown that the regional distribution of extreme precipitation depends on both the intensity and form of the convection in the SACZ.

  11. The South Atlantic Convergence Zone: Intensity, Form, Persistence, and Relationships with Intraseasonal to Interannual Activity and Extreme Rainfall.

    NASA Astrophysics Data System (ADS)

    Carvalho, Leila M. V.; Jones, Charles; Liebmann, Brant

    2004-01-01

    The characteristics of intensity, geographical location, and persistence of the South Atlantic convergence zone (SACZ) during the austral summer are investigated. Intensity and spatial features of the SACZ are identified by performing a factor analysis of structural properties of outgoing longwave radiation (OLR) data. The first two leading factors explain 65% of the total variance of structural properties and characterize the SACZ according to intensity and location (oceanic versus continental). An index is constructed based on the magnitude of the factor scores to identify intense (weak) and oceanic (continental) SACZ. The intense SACZ category is associated with negative OLR anomalies over a large area of tropical South America, extending from the western Amazon to the Atlantic Ocean. The weak SACZ category is observed with positive OLR anomalies over tropical South America and negative OLR anomalies over southeastern South America. Oceanic and continental aspects of the SACZ are related to a midlatitude wave train pattern. The Madden Julian oscillation (MJO) modulates intense SACZ events with persistence longer than 3 days. Interannual variability of persistent events indicates that the ratio of oceanic to continental SACZ as well as their frequency depends on the phase of El Niño Southern Oscillation (ENSO). Occurrence of extreme rainfall in Brazil is discussed in the context of variations in the SACZ and MJO. Intense (weak) SACZ increases (decreases) the 95th daily rainfall percentile over central-eastern Brazil compared to the climatology. Oceanic (continental) SACZ increases (decreases) the 95th daily rainfall percentile over southeastern Brazil. The MJO phase characterized by suppression of convective activity over Indonesia and enhancement over the central Pacific increases the 95th daily rainfall percentile over north-northeastern Brazil, whereas opposite features are observed for the phase of the MJO characterized by the enhancement of convection over

  12. Maintenance of the intertropical convergence zones and the large-scale tropical circulation on a water-covered earth

    SciTech Connect

    Hess, P.G.; Rasch, P.J. ); Battisti, D.S. )

    1993-03-01

    How the surface boundary heating (sea surface temperature) and cumulus adjustment process affect the location, structure, energetics, and dynamics of the intertropical convergence zones (ITCZs) is investigated. A series of experiments is performed with a general circulation model where the lower boundary is specified to be water at a fixed sea surface temperature (SST), an aqua planet. All experiments are run using equinoctal insolation with no longitudinal variation in SST. Two different convective parameterization schemes (Kuo and moist convective adjustment) and several different zonally symmetric SST distributions are used in these experiments. The location of the ITCZ is found to be sensitive to the convective parameterization scheme and the SST distribution. The model with the moist convective adjustment scheme produces an ITCZ over the tropical SST maximum, even under conditions where the SST gradient is weak. By contrast, the model with the Kuo convective parameterization is not as sensitive to SST distribution: the model with the Kuo scheme yields two ITCZs straddling the equator at approximately 7[degrees]latitude for a wide variety of SST distributions, including when the warmest water is located on the equator. The location of the ITCZ affects the structure and strength of both the time-mean Hadley cells and the subtropical jets. Furthermore, the equatorial wave spectrum is strongly influenced by the type of cumulus parameterization scheme used. The [open quotes]convective characteristics[close quotes] for each parameterization scheme are presented in detail to elucidate the influence of the large-scale environment on convection. 52 refs., 15 figs., 2 tabs.

  13. Fast and slow shifts of the zonal-mean intertropical convergence zone in response to an idealized anthropogenic aerosol

    DOE PAGES

    Voigt, Aiko; Pincus, Robert; Stevens, Bjorn; ...

    2017-04-03

    Previous modeling work showed that aerosol can affect the position of the tropical rain belt, i.e., the intertropical convergence zone (ITCZ). Yet it remains unclear which aspects of the aerosol impact are robust across models, and which are not. Here we present simulations with seven comprehensive atmosphere models that study the fast and slow impacts of an idealized anthropogenic aerosol on the zonal-mean ITCZ position. The fast impact, which results from aerosol atmospheric heating and land cooling before sea-surface temperature (SST) has time to respond, causes a northward ITCZ shift. Yet the fast impact is compensated locally by decreased evaporationmore » over the ocean, and a clear northward shift is only found for an unrealistically large aerosol forcing. The local compensation implies that while models differ in atmospheric aerosol heating, this does not contribute to model differences in the ITCZ shift. The slow impact includes the aerosol impact on the ocean surface energy balance and is mediated by SST changes. The slow impact is an order of magnitude more effective than the fast impact and causes a clear southward ITCZ shift for realistic aerosol forcing. Models agree well on the slow ITCZ shift when perturbed with the same SST pattern. However, an energetic analysis suggests that the slow ITCZ shifts would be substantially more model-dependent in interactive-SST setups due to model differences in clear-sky radiative transfer and clouds. In conclusion, we also discuss implications for the representation of aerosol in climate models and attributions of recent observed ITCZ shifts to aerosol.« less

  14. Circulation, moisture, and precipitation relationships along the South Pacific Convergence Zone in reanalyses and CMIP5 models

    NASA Astrophysics Data System (ADS)

    Niznik, M. J.; Lintner, B. R.; Langenbrunner, B.; Neelin, J.

    2013-12-01

    One theorized control on the position of the South Pacific Convergence Zone (SPCZ) is the amount of low-level inflow from the relatively dry southeastern Pacific basin. Building on the analysis of observed SPCZ-region synoptic scale variability by Lintner and Neelin (2008), composite analysis is performed here on two reanalysis products as well as output from 17 models in phase five of the Coupled Model Intercomparison Project (CMIP5). Using low-level zonal wind as a compositing index, it is shown that the CMIP5 ensemble mean, as well as many of the individual models, captures patterns of wind, specific humidity, and precipitation anomalies resembling those obtained for reanalysis fields between weak- and strong-inflow phases. Lead-lag analysis of both the reanalyses and models is used to develop a conceptual model for the formation of each composite phase. This analysis indicates that an equatorward displaced Southern Hemisphere storm track and an eastward displaced equatorial eastern Pacific westerly [wind] duct are features of the weak-inflow phase, though as indicated by additional composite analyses based on these features, each appears to account weakly for the details of the low-level inflow composite anomalies. To further identify intermodel differences in the SPCZ region, Principle Uncertainty Pattern (PUP) analysis is performed using simulated precipitation. Sorting the models into groups based on the each PUP reveals key circulation and moisture anomalies associated with distinct precipitation patterns. Despite the presence of well-known biases in the CMIP5 simulations of SPCZ region climate, the models appear to have some fidelity in simulating synoptic scale relationships between low-level winds, moisture, and precipitation, consistent with observations and simple theoretical understanding of interactions of dry air inflow with deep convection.

  15. Fast and slow shifts of the zonal-mean intertropical convergence zone in response to an idealized anthropogenic aerosol

    NASA Astrophysics Data System (ADS)

    Voigt, Aiko; Pincus, Robert; Stevens, Bjorn; Bony, Sandrine; Boucher, Olivier; Bellouin, Nicolas; Lewinschal, Anna; Medeiros, Brian; Wang, Zhili; Zhang, Hua

    2017-04-01

    Previous modeling work showed that aerosol can affect the position of the tropical rain belt, i.e., the intertropical convergence zone (ITCZ). Yet, it remains unclear which aspects of the aerosol impact are robust across models, and which are not. Here, we present simulations with seven comprehensive atmosphere models that study the fast and slow impacts of an idealized anthropogenic aerosol on the zonal-mean ITCZ position. The fast impact, which results from aerosol atmospheric heating and land cooling before sea-surface temperature (SST) have time to respond, causes a northward ITCZ shift. Yet, the fast impact is compensated locally by decreased evaporation over the ocean, and a clear northward shift is only found for an unrealistically large aerosol forcing. The local compensation implies that while models differ in atmospheric aerosol heating, this does not contribute to model differences in the ITCZ shift. The slow impact includes the aerosol impact on the ocean surface energy balance and is mediated by SST changes. The slow impact is an order of magnitude more effective than the fast impact and causes a clear southward ITCZ shift already for realistic aerosol forcing. Models agree well on the slow ITCZ shift when perturbed with the same SST pattern. However, an energetic analysis suggests that the slow ITCZ shifts would be substantially more model dependent in interactive-SST setups due to model differences in clear-sky radiative transfer and clouds. We also discuss implications for the representation of aerosol in climate models and attributions of recent observed ITCZ shifts to aerosol.

  16. Fast and slow shifts of the zonal-mean intertropical convergence zone in response to an idealized anthropogenic aerosol

    NASA Astrophysics Data System (ADS)

    Voigt, Aiko; Pincus, Robert; Stevens, Bjorn; Bony, Sandrine; Boucher, Olivier; Bellouin, Nicolas; Lewinschal, Anna; Medeiros, Brian; Wang, Zhili; Zhang, Hua

    2017-06-01

    Previous modeling work showed that aerosol can affect the position of the tropical rain belt, i.e., the intertropical convergence zone (ITCZ). Yet it remains unclear which aspects of the aerosol impact are robust across models, and which are not. Here we present simulations with seven comprehensive atmosphere models that study the fast and slow impacts of an idealized anthropogenic aerosol on the zonal-mean ITCZ position. The fast impact, which results from aerosol atmospheric heating and land cooling before sea-surface temperature (SST) has time to respond, causes a northward ITCZ shift. Yet the fast impact is compensated locally by decreased evaporation over the ocean, and a clear northward shift is only found for an unrealistically large aerosol forcing. The local compensation implies that while models differ in atmospheric aerosol heating, this does not contribute to model differences in the ITCZ shift. The slow impact includes the aerosol impact on the ocean surface energy balance and is mediated by SST changes. The slow impact is an order of magnitude more effective than the fast impact and causes a clear southward ITCZ shift for realistic aerosol forcing. Models agree well on the slow ITCZ shift when perturbed with the same SST pattern. However, an energetic analysis suggests that the slow ITCZ shifts would be substantially more model-dependent in interactive-SST setups due to model differences in clear-sky radiative transfer and clouds. We also discuss implications for the representation of aerosol in climate models and attributions of recent observed ITCZ shifts to aerosol.

  17. Rainfall Variability under the South Pacific Convergence Zone as Reconstructed from a Speleothem Record (1670-2005) from Vanuatu

    NASA Astrophysics Data System (ADS)

    Partin, J. W.; Quinn, T. M.; Shen, C.; Maupin, C. R.; Lin, K.; Taylor, F. W.; Sinclair, D. J.; Banner, J. L.

    2010-12-01

    The tropical Pacific exhibits known climate changes on interannual timescales during El Niño-Southern Oscillation (ENSO) events causing global socio-economic impacts. On decadal timescales, climate changes associated with oscillations in the tropical Pacific have been postulated, such as the Pacific Decadal Oscillation (PDO). However, the instrumental record is too short and too sparse to allow reliable and convincing evaluation of such decadal-scale oscillations. A fast-growing speleothem (~1-3 mm/year) collected from the island of Espirito Santo, Vanuatu (15.5°S, 167°E), which is located under the South Pacific Convergence Zone (SPCZ) yields a record of rainfall variability spanning ~1670 - 2005 Common Era (CE), as dated by U-Th disequilibrium techniques. Close agreement between speleothem stable oxygen isotopic composition (δ18O) and the amount of rainfall from nearby Pekoa Airport demonstrates the ability of the speleothem to record hydrologic changes above-ground. While the speleothem grows fast enough to capture the annual cycle, mixing of rain and groundwaters in the overlying bedrock dampens this δ18O signal. However, interannual changes in speleothem δ18O, or reconstructed rainfall, of ~0.6 ‰ appear to capture events associated with ENSO and subsequent reorganizations of the SPCZ. The speleothem sample offers the opportunity to record local expressions of ENSO-related changes in rainfall for the last several hundred years. The speleothem record complements previously published coral records from Vanuatu of oceanic changes to provide a broader picture of pre-instrumental ENSO variability in the region. The speleothem δ18O record also exhibits concentrations of variance on the decadal scale, which correlate with variations associated with the PDO. The amplitude of this decadal signal is large (~1.5 ‰), which serves to highlight the sensitivity of SPCZ rainfall to decadal-scale changes in the tropical Pacific ocean-atmosphere system.

  18. Effect of zone size on the convergence of exact solutions for diffusion in single phase systems with planar, cylindrical or spherical geometry

    NASA Technical Reports Server (NTRS)

    Unnam, J.; Tenney, D. R.

    1981-01-01

    Exact solutions for diffusion in single phase binary alloy systems with constant diffusion coefficient and zero-flux boundary condition have been evaluated to establish the optimum zone size of applicability. Planar, cylindrical and spherical interface geometry, and finite, singly infinite, and doubly infinite systems are treated. Two solutions are presented for each geometry, one well suited to short diffusion times, and one to long times. The effect of zone-size on the convergence of these solutions is discussed. A generalized form of the diffusion solution for doubly infinite systems is proposed.

  19. Comparative analysis of geodynamic activity of the Caucasian and Eastern Mediterranean segments of the Alpine-Himalayan convergence zone

    NASA Astrophysics Data System (ADS)

    Chelidze, Tamaz; Eppelbaum, Lev

    2013-04-01

    The Alpine-Himalayan convergence zone (AHCZ) underwent recent transverse shortening under the effect of collisional compression. The process was accompanied by rotation of separate microplates. The Caucasian and Eastern Mediterranean regions are segments of the of the AHCZ and are characterized by intensive endogenous and exogenous geodynamic processes, which manifest themselves in occurrence of powerful (with magnitude of 8-9) earthquakes accompanied by development of secondary catastrophic processes. Large landslides, rock falls, avalanches, mud flows, etc. cause human deaths and great material losses. The development of the aforesaid endogenous processes is set forth by peculiarities of the deep structure of the region and an impact of deep geological processes. The Caucasus is divided into several main tectonic terranes: platform (sub-platform, quasi-platform) and fold-thrust units. Existing data enable to perform a division of the Caucasian region into two large-scale geological provinces: southern Tethyan and northern Tethyan located to the south of and to the north of the Lesser Caucasian ophiolite suture, respectively. The recent investigations show that the assessments of the seismic hazard in these regions are not quite correct - for example in the West Caucasus the seismic hazard can be significantly underestimated, which affects the corresponding risk assessments. Integrated analysis of gravity, magnetic, seismic and thermal data enables to refine the assessment of the seismic hazard of the region, taking into account real rates of the geodynamic movements. Important role play the last rheological constructions. According to Reilinger et al. (2006) tectonic scheme, the West flanking of the Arabian Plate manifests strike-slip motion, when the East Caucasian block is converging and shortening. The Eastern Mediterranean is a tectonically complex region located in the midst of the progressive Afro-Eurasian collision. The recent increasing geotectonic

  20. 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

  1. Revisiting the Numerical Convergence of Cohesive-Zone Models in Simulating the Delamination of Composite Adhesive Joints by Using the Finite-Element Analysis

    NASA Astrophysics Data System (ADS)

    Liu, P. F.; Gu, Z. P.; Hu, Z. H.

    2016-11-01

    Delamination is the dominating failure mechanism in composite adhesive joints. A deep insight into the delamination failure mechanism requires advanced numerical methods. Currently, cohesive-zone models (CZMs), in combination with the finite-element analysis (FEA), have become powerful tools for modeling the initiation and growth of delaminations in composites. However, ensuring the numerical convergence in the CZMs used for a delamination analysis of three-dimensional (3D) composite structures is always a challenging issue due to the "snap-back" instability in the nonlinear implicit FEA, which arises mainly from the cohesive softening behavior. Based on the midplane interpolation technique, first numerical techniques for implementing 3D bilinear and exponential CZMs by using ABAQUS-UEL (user element subroutine) are developed in this paper. In particular, a viscous regularization by introducing the damping effect into the stiffness equation is used to improve the convergence. Two examples, a single-lap composite joint and a composite skin/stiffener panel under tension, demonstrate the numerical technique developed. Then, the effect of cohesion parameters on the numerical convergence based on the viscous regularization is studied.

  2. 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.

  3. 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

  4. Caucasian-Arabian Syntaxis (Alpine-Himalayan convergence zone): an example of continental collision above mantle plume head

    NASA Astrophysics Data System (ADS)

    Sharkov, Evgenii; Lebedev, Vladimir

    2017-04-01

    1. The Caucasian-Arabian segment of the huge Cenozoic Alpine-Himalayan collisional belt consists on two domains: the EW-striking Greater Caucasus to the north and the Caucasian-Arabian Syntaxis (CAS) to the south. The CAS includes arc-like tectonic domains of the Lesser Caucasus and Eastern Anatolia and is characterized by a large NS-trending positive isostatic anomaly, which suggests presence of a mantle plume head underneath. 2. The Greater Caucasus in essence represents the southern margin of the Eurasian plate; it is uplifted over the Main Caucasian Fault, which is part of the Kopetdag-Caucasian-TransEuropean Megafault. 3. The Alpine structure of the Caucasus formed by NS horizontal compression generated by interaction of two plates: the Arabian indenter and the East European Craton. In the late Cenozoic, that plate interaction resulted in the transverse shortening of the CAS to 400 km, mainly at the expense of the territory south of the Main Caucasian Fault. 4. The seismic data available do not reveal any subduction zone beneath the Great Caucasus. However, beneath transitional fold and thrust zone between north margin of Arabian plate (Bitlis-Zagros Fault) and the Great Caucasus, two steep north-directed seismic zone occurred which trace up to 50-70 km depth. They look like as possibly peculiar "embryonic" subduction zones, where crustal material involves in descending currents. We suggest that mention above shortening was due to two major causes: (1) the tectonic "diffluence" of crustal material apart from the Arabian indenter, in front of the East European Craton, and (2) involving another part of material in descending flows. . 5. The CAS includes a Neogene-Quaternary volcanic belt, which is extended from Eastern Anatolia and to the Lesser Caucasus and farther to the Greater Caucasus. The belt is dominated by two types of volcanic rocks: (1) extensive plateau basalts possessing geochemical characteristics of intra-plate (plume-related) rocks, and (2) calc

  5. Variability of the Tropical Atlantic and Pacific SSS Minimum Zones and Their Relations to the ITCZ and SPCZ (1979-2013)

    NASA Astrophysics Data System (ADS)

    Delcroix, Thierry; Tchilibou, Michel; Alory, Gael; Reverdin, Gilles; Arnault, Sabine

    2017-04-01

    This study focuses on the time-space variability of the low Sea Surface Salinity (SSS) waters located from the West to the East within about 2°N-12°N in the Atlantic and Pacific oceans and within about 6°S-16°S in the western Pacific. The analysis is based on a combination of in situ SSS observations collected in the last 3.5 decades from voluntary observing ships, TAO/TRITON and PIRATA moorings, Argo floats and (few) CTD profiles. We show that the mean positions of the Atlantic and Pacific low SSS waters are tightly related to the local minimum in Evaporation minus Precipitation (E-P) budget linked to the Inter Tropical Convergence Zones (ITCZ) and South Pacific Convergence Zone (SPCZ). We also show that the meridional position of the SSS minima varies both at seasonal time scale, with an overall poleward displacement in summer (or winter in the western Pacific ITCZ), and at interannual time scale in relation with ENSO and the Atlantic meridional mode, with however subtle differences in timing between the western, central and eastern basins. The role of the ITCZ- and SPCZ-related E-P budget in these seasonal and interannual changes is examined. We further document long-term meridional migrations of these low SSS waters in the last 3.5 decades and discuss whether or not they are consistent with documented decadal variability and/or expected global change effects.

  6. Soft tissue stability at the facial aspect of gingivally converging abutments in the esthetic zone: a pilot clinical study.

    PubMed

    Rompen, Eric; Raepsaet, Nicolas; Domken, Olivier; Touati, Bernard; Van Dooren, Eric

    2007-06-01

    The literature indicates that 0.5 to 1.5 mm of gingival recession most often occurs within the first months after implant placement or abutment connection. The purpose of this pilot study was to evaluate the effect of a concave transmucosal profile on the vertical stability of soft tissues at the facial aspect of dental implants. Fifty-four implants were placed in esthetically demanding sites in 41 patients (17 women, 24 men; age range of 23 to 62 years, mean 40.3 years; 5 smokers), primarily following a 1-stage approach. Twenty-five implants were placed immediately after extraction. Experimental concave titanium (n=49) and zirconia abutments (n=5) were used, and a provisional crown was placed at the same session. Digital photographs were made perpendicularly to the facial aspect of the teeth at abutment placement, and at 1, 3, 6, 12, 18, and 24 months, and enlarged views were subsequently analyzed by an independent examiner. Vertical changes in soft tissue levels were measured, and the definitive esthetic result was evaluated subjectively (poor to excellent). Data were analyzed with descriptive statistics. Twenty-four implants were evaluated at 24 months, 20 at 18 months, and 8 at 12 months. Vertical augmentation or no recession in soft tissue was observed in 87% of the situations, and in no situation was recession greater than 0.5 mm found. The gingival level remained stable at 12, 18, and 24 months. The average esthetic outcome was rated as 4.5 (very good to excellent) on a 0- to 5-point scale. The concave, gingivally converging abutments used in the study allowed for above-average soft tissue outcomes.

  7. Overriding plate structure of the Nicaragua convergent margin: Relationship to the seismogenic zone of the 1992 tsunami earthquake

    NASA Astrophysics Data System (ADS)

    Sallarès, Valentí; Meléndez, Adrià; Prada, Manuel; Ranero, César R.; McIntosh, Kirk; Grevemeyer, Ingo

    2013-09-01

    We present 2-D seismic velocity models and coincident multichannel seismic reflection images of the overriding plate and the inter-plate boundary of the Nicaragua convergent margin along two wide-angle seismic profiles parallel and normal to the trench acquired in the rupture area of the 1992 tsunami earthquake. The trench-perpendicular profile runs over a seamount subducting under the margin slope, at the location where seismological observations predict large coseismic slip. Along this profile, the igneous basement shows increasing velocity both with depth and away from the trench, reflecting a progressive decrease in upper-plate rock degree of fracturing. Upper mantle-like velocities are obtained at ˜10 km depth beneath the fore-arc Sandino basin, indicating a shallow mantle wedge. A mismatch of the inter-plate reflector in the velocity models and along coincident multichannel seismic profiles under the slope is best explained by ˜15% velocity anisotropy, probably caused by subvertical open fractures that may be related to fluid paths feeding known seafloor seepage sites. The presence of a shallow, partially serpentinized mantle wedge, and the fracture-related anisotropy are supported by gravity analysis of velocity-derived density models. The downdip limit of inter-plate seismicity occurs near the tip of the inferred mantle wedge, suggesting that seismicity could be controlled by the presence of serpentinite group minerals at the fault gouge. Near the trench, the inferred local increase of normal stress produced by the subducting seamount in the plate boundary may have made this fault segment unstable during earthquake rupture, which could explain its tsunamigenic character.

  8. Neotectonics and seismicity of a slowly deforming segment of the Adria-Europe convergence zone - the northern Dinarides fold-and-thrust belt

    NASA Astrophysics Data System (ADS)

    Ustaszewski, Kamil; Herak, Marijan; Tomljenović, Bruno; Herak, Davorka; Matej, Srebrenka

    2014-05-01

    With GPS-derived shortening rates of c. 3-5 mm/a, the Adria-Europe convergence zone across the fold-and-thrust belt of the Dinarides (Balkan Peninsula) is a slowly deforming plate boundary by global standards. We have analysed the active tectonics and instrumental seismicity of the northernmost segment of this fold-and-thrust belt at its border to the Pannonian Basin. This area hosts a Maastrichtian collisional suture formed by closure of Mesozoic fragments of the Neotethys, overprinted by Miocene back-arc extension, which led to the exhumation of greenschist- to amphibolite-grade rocks in several core complexes. Geological, geomorphological and reflection seismic data provide evidence for a compressive or transpressive reactivation of extensional faults after about 5 Ma. The study area represents the seismically most active region of the Dinarides apart from the Adriatic Sea coast and the area around Zagreb. The strongest instrumentally recorded earthquake (27 October 1969) affected the city of Banja Luka (northern Bosnia and Herzegovina). Fault plane solutions for the main shock (ML 6.4) and its largest foreshock (ML 6.0) indicate reverse faulting along ESE-WNW-striking nodal planes and generally N-S trending pressure axes. The spatial distribution of epicentres and focal depths, analyses of the macroseismic field and fault-plane solutions for several smaller events suggest on-going shortening in the internal Dinarides. Our results therefore imply that current Adria-Europe convergence is widely distributed across c. 300 km, rendering the entire Dinarides fold-and-thrust belt a slowly deforming plate boundary.

  9. Correcting for Precipitation Effects in Satellite-Based Passive Microwave Tropical Cyclone Intensity Estimates

    DTIC Science & Technology

    2005-08-05

    approaching the convection in the intertropical convergence zone (ITCZ). TB2 is relatively unaffected by humidity so it exhibits a very sharp TB gradient...tower in the inter-tropical convergence zone (ITCZ), thus affecting upper-level sounding channels more for the same window channel depression. A second...possible explanations are offered, both centered on difference between convective clouds in the inter-tropical convergence zone (ITCZ), where the slopes

  10. 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.; hide

    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.

  11. Modern Spatial Rainfall Rate is well Correlated with Coretop δ2Hdinosterol in the South Pacific Convergence Zone: A Tool for Quantitative Reconstructions of Rainfall Rate

    NASA Astrophysics Data System (ADS)

    Sear, D. A.; Maloney, A. E.; Nelson, D. B.; Sachs, J. P.; Hassall, J. D.; Langdon, P. G.; Prebble, M.; Richey, J. N.; Schabetsberger, R.; Sichrowsky, U.; Hope, G.

    2015-12-01

    The South Pacific Convergence Zone (SPCZ) is the Southern Hemisphere's most prominent precipitation feature extending southeastward 3000 km from Papua New Guinea to French Polynesia. Determining how the SPCZ responded to climate variations before the instrumental record requires the use of indirect indicators of rainfall. The link between the hydrogen isotopic composition of fluxes of water though the hydrologic cycle, lake water, and molecular fossil 2H/1H ratios make hydrogen isotopes a promising tool for improving our understanding of this important climate feature. An analysis of coretop sediment from freshwater lakes in the SPCZ region indicates that there is a strong spatial relationship between δ2Hdinosterol and mean annual precipitation rate. The objectives of this research are to use 2H/1H ratios of the biomarker dinosterol to develop an empirical relationship between δ2Hdinosterol and modern environmental rainfall rates so that we may quantitatively reconstruct several aspects of the SPCZ's hydrological system during the late Holocene. The analysis includes lake sediment coretops from the Solomon Islands, Wallis Island, Vanuatu, Tahiti, Samoa, New Caledonia, and the Cook Islands. These islands span range of average modern precipitation rates from 3 to 7 mm/day and the coretop sediment δ2Hdinosterol values range from -240‰ to -320‰. Applying this regional coretop calibration to dated sediment cores reveals that the mean annual position and/or intensity of the SPCZ has not been static during the past 2000 years.

  12. 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.

  13. Modern Spatial Rainfall Rate is well Correlated with Coretop δ2Hdinosterol in the South Pacific Convergence Zone: a Tool for Quantitative Reconstructions

    NASA Astrophysics Data System (ADS)

    Maloney, A. E.; Nelson, D. B.; Sachs, J. P.; Hassall, J. D.; Sear, D. A.; Langdon, P. G.; Prebble, M.; Richey, J. N.; Schabetsberger, R.; Sichrowsky, U.; Hope, G.

    2016-02-01

    The South Pacific Convergence Zone (SPCZ) is the Southern Hemisphere's most prominent precipitation feature extending southeastward 3000 km from Papua New Guinea to French Polynesia. Determining how the SPCZ responded to climate variations before the instrumental record requires the use of indirect indicators of rainfall. The link between the hydrogen isotopic composition of water fluxes though the hydrologic cycle, lake water, and molecular fossil 2H/1H ratios make hydrogen isotopes a promising tool for improving our understanding of this important climate feature. An analysis of coretop sediment from freshwater lakes in the SPCZ region indicates that there is a strong spatial relationship between δ2Hdinosterol and mean annual precipitation rate. The objectives of this research are to use 2H/1H ratios of the biomarker dinosterol to develop an empirical relationship between δ2Hdinosterol and modern environmental rainfall rates so that we may quantitatively reconstruct several aspects of the SPCZ's hydrological system during the late Holocene. The analysis includes lake sediment coretops from the Solomon Islands, Wallis Island, Vanuatu, Tahiti, Samoa, New Caledonia, and the Cook Islands. These islands span range of average modern precipitation rates from 3 to 7 mm/day and the coretop sediment δ2Hdinosterol values range from -240‰ to -320‰. Applying this regional coretop calibration to dated sediment cores reveals that the mean annual position and/or intensity of the SPCZ has not been static during the past 2000 years.

  14. Interhemispheric Orbital-Scale Asymmetry of the Intertropical Convergence Zone Movement at the Asia-Pacific Realm over the Past 3 Glacial-Interglacial Cycles

    NASA Astrophysics Data System (ADS)

    Yi, L.; Shen, C. C.; Lo, L.; Shi, Z.; Wei, K. Y.; Chou, C. J.; WU, C. C.; Mii, H. S.; Chuang, C. K.; Amakawa, H.; Burr, G. S.; Chen, Y. C.

    2014-12-01

    The Intertropical convergence Zone (ITCZ) is the heaviest rain belt on earth and provides global water-resources for human populations around the world. Here we present a tropical precipitation record from the Southern Hemisphere covering the past 284,000 years, inferred from a marine sedimentary sequence of planktonic foraminifera collected off the eastern coast of Papua New Guinea (PNG). The foraminiferal tests of Globigerinoides ruber were sampled from a marine sediment core MD05-2925 (9o20.60'S, 151o27.54'E; water depth 1661 m). Using inductively coupled plasma sector field mass spectrometric (ICP-SF-MS) techniques with 2s precision of 2-6%, we measured rare earth elements (REEs) to Ca ratios in the planktonic foraminifer to reconstruct precipitation and make inferences about the orbital-timescale evolution of the Pacific ITCZ. In addition to precessional feature, which is expressed in the East Asian counterpart, our record shows that the Pacific ITCZ migration was dominantly influenced by obliquity changes. Model simulations suggest that this obliquity forcing could be primarily delivered by a meridional thermal/pressure contrast, resulting from the asymmetric continental configuration between Asia and Australia in a coupled East Asian-Australian circulation system.

  15. 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

  16. Convergence Insufficiency

    MedlinePlus

    ... report of improvement in symptoms. What is the method of treatment for convergence insufficiency? Convergence insufficiency can ... be brought in to the office visit. Which method of treatment will be used for an individual ...

  17. 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.

  18. Fast and slow shifts of the zonal-mean intertropical convergence zone in response to an idealized anthropogenic aerosol: AEROSOL IMPACT ON THE ITCZ

    DOE PAGES

    Voigt, Aiko; Pincus, Robert; Stevens, Bjorn; ...

    2017-04-23

    Previous modeling work showed that aerosol can affect the position of the tropical rain belt, i.e., the intertropical convergence zone (ITCZ). Yet it remains unclear which aspects of the aerosol impact are robust across models, and which are not. Here we present simulations with seven comprehensive atmosphere models that study the fast and slow impacts of an idealized anthropogenic aerosol on the zonal-mean ITCZ position. The fast impact, which results from aerosol atmospheric heating and land cooling before sea-surface temperature (SST) has time to respond, causes a northward ITCZ shift. Yet the fast impact is compensated locally by decreased evaporationmore » over the ocean, and a clear northward shift is only found for an unrealistically large aerosol forcing. The local compensation implies that while models differ in atmospheric aerosol heating, this does not contribute to model differences in the ITCZ shift. The slow impact includes the aerosol impact on the ocean surface energy balance and is mediated by SST changes. The slow impact is an order of magnitude more effective than the fast impact and causes a clear southward ITCZ shift for realistic aerosol forcing. Models agree well on the slow ITCZ shift when perturbed with the same SST pattern. However, an energetic analysis suggests that the slow ITCZ shifts would be substantially more model-dependent in interactive-SST setups due to model differences in clear-sky radiative transfer and clouds. We also discuss implications for the representation of aerosol in climate models and attributions of recent observed ITCZ shifts to aerosol.« less

  19. Movement of the Intertropical Convergence Zone during the mid-pleistocene transition and the response of atmospheric and surface ocean circulations in the central equatorial Pacific

    NASA Astrophysics Data System (ADS)

    Seo, Inah; Lee, Yong Il; Kim, Wonnyon; Yoo, Chan Min; Hyeong, Kiseong

    2015-11-01

    This paper investigates the causes of a brief, but prominent, cooling episode (1.1-0.8 Ma) that occurred in the equatorial upwelling region of the Atlantic and Pacific during the mid-Pleistocene transition (MPT) using temporal changes in dust provenance, regional hydrology, and surface productivity recorded in a deep-sea sediment core from the central equatorial Pacific. The 87Sr/86Sr and ɛNd values of the inorganic silicate fraction indicate deposition of dust from Australia and Central/South America before 0.8 Ma, but a gradual increase in Asian dust deposition after 0.8 Ma. The change in dust provenance was accompanied by an increased dust flux and a decrease in surface productivity and salinity. These changes can be explained by the southward movement of the Intertropical Convergence Zone (ITCZ) and North Equatorial Counter Current (NECC) and the direct influence of these features on the site after 0.8 Ma. Our results, together with previously published Atlantic data, suggest the northward position of the ITCZ between 1.1 and 0.9 Ma, and the southward position thereafter. The meridional movement of the ITCZ is in phase with the cooling and warming trend in upwelling regions in the equatorial Pacific and Atlantic, which suggests strengthening of southeast trades relative to its northern counterpart between 1.1 and 0.9 Ma as a plausible cause of this brief cooling event. The southward movement of the ITCZ from 0.9 to 0.8 Ma indicates more significant cooling in the Northern Hemisphere (NH) than in the Southern Hemisphere, which is supportive of the interpretation that the NH ice sheet expanded significantly and stabilized after 0.9 Ma.

  20. 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.

  1. 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

  2. Reconstruction of precipitation variability in the Strait of Yucatan associated with latitudinal shifts in the position of the Intertropical Convergence Zone since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Staines-Urías, Francisca; Seidenkrantz, Marit-Solveig; Fischel, Andrea; Kuijpers, Antoon

    2017-04-01

    The elemental composition of sediments from gravity core HOLOVAR11-03 provides a ca. 40 ka record of past climate variability in the Strait of Yucatan, between the Caribbean Sea and the Gulf of Mexico, a region where precipitation variability is determined by the seasonal position of the Intertropical Convergence Zone (ITCZ). Within this region, sea level pressure decreases and rainfall increases as the ITCZ moves north of the equator in response to increased solar insolation in the Northern Hemisphere during boreal summer. In contrast, as the ITCZ retracts southward towards the equator during boreal winter, rainfall diminishes and the regional sea level pressure gradient strengthens. On interannual, multidecadal and millennial timescales, fluctuations in the average latitudinal position of the ITCZ in response to insolation forcing modulate the intensity and duration of the seasonal regimens, determining average regional precipitation and, ultimately, the elemental composition of the marine sedimentary record. Regionally, higher titanium and iron content in marine sediments reflect greater terrigenous input from inland runoff, indicating greater precipitation, hence a more northerly position of the ITCZ. Correspondingly, Ti and Fe concentration data were used to reconstruct regional rainfall variability since the Last Glacial Maxima (LGM ˜24 cal ka BP). HOLOVAR11-03 age model (based on 4 AMS 14C dates obtained from multi-specific samples of planktic foraminifera) shows stable sedimentation rates in the area throughout the cored period. Nonetheless, higher terrestrial mineral input is observed since the LGM and all through the last glacial termination (24 to 12 cal ka BP), indicating a period of increased precipitation. In contrast, lower Ti and Fe values are typical for the period between 12 and 8 cal ka BP, indicating reduced precipitation. A positive trend characterizes the following interval, showing a return to wetter conditions lasting until 5 cal ka BP

  3. Latitudinal Position and Trends of the Intertropical Convergence Zone (ITCZ) and its Relationship with Upwelling in the Southern Caribbean Sea and Global Climate Indices

    NASA Astrophysics Data System (ADS)

    Carlock, Brett Edmond

    The Intertropical Convergence Zone (ITCZ) is a feature that results from the ocean-atmosphere interactions in the tropics around the world. The ITCZ is characterized by surface wind convergence, tall storm clouds, and it forms a belt of high time-averaged precipitation around the globe. The ITCZ undergoes seasonal migrations between 5°S and 15°N roughly following the subsolar point on Earth with the seasons, with a mean annual position located slightly above the Equator, between 2° and 5°N. This study tested the hypothesis that there was a northward shift in the median position of the ITCZ in the first decade of the 2000's relative to the 1900's. This hypothesis has been posed in the literature given a weakening in the intensity of the Trade Winds observed in the southern Caribbean Sea during the first decade of the 2000's, with concomitant ecological impacts due to weakening in coastal wind-driven upwelling. The hypothesis was tested by analyzing variations in the monthly latitudinal position of the ITCZ over the Atlantic Ocean relative to the median position computed for the period 1987-2011. The position of the ITCZ was derived from satellite-derived ocean surface wind measurements collected from 1987 to 2011. A Mann-Kendall analysis and a Monte Carlo simulation were used to test for trends in the median cross-basin latitudinal position of the ITCZ. The study included an analysis of regional changes across the tropical central Atlantic (50°W to 15°W), the Western Atlantic (50°W to 30°W), and the Eastern Atlantic (30°W to 15°W) within the tropics. The results show a slight southward trend in the median position of the ITCZ over the central Atlantic and also in the Eastern Atlantic in the first decade of the 2000's relative to the 1990's. While this trend is barely significant, it is likely simply due to interannual variation in the average annual position of the ITCZ. The data were also examined for the timing and persistence of a double ITCZ in the

  4. Investigating the Climatic Transition Zone in Guyana, South America

    NASA Astrophysics Data System (ADS)

    Bovolo, C.; Pereira, R.; Parkin, G.; Kilsby, C. G.; Wagner, T.

    2010-12-01

    The climate of Guyana is influenced by the seasonal oscillation of the rain-bearing Inter-Tropical-Convergence Zone over the northern part of South America, producing two wet seasons on the coast and one wet season inland. The transition zone between the two climate regimes also corresponds to a distinct vegetation transition between intact and highly biodiverse rainforests in northern and central Guyana, and open, savannah type vegetation in the southwest. Coastal Guyana has been shown to be highly susceptible to El Niño Southern Oscillation (ENSO) events, with El-Niño conditions most likely to result in drought; however a brief analysis of available observations suggests that an opposite effect may exist inland. Geographically sparse meteorological records of variable quality (especially inland) have so far precluded detailed climatic studies of the Guianas. It is important therefore, to establish the climate regime of the area and to analyse the influence of ENSO on the region in order to derive baselines against which the impacts of any future landuse change or climate change can be measured. The impacts of climatic variations on the ecosystem services of the area can then also begin to be determined. This study compares the ECMWF ERA40 reanalysis dataset for the period 1957-2002 at a ~125 km2 (1.125 degree) resolution against available areally averaged meteorological observations in the Guyanas to determine if reanalysis data can be used to supplement observations in data-poor areas. Mean differences (biases) and correlations are examined comparing the seasonal cycles and the yearly, monthly and monthly anomaly time series. Results show that maps of average annual reanalysis precipitation for the region compare favourably against observations, although the model underestimates precipitation in some zones of higher elevation. ERA40 also appears slightly positively biased on the coast and negatively biased inland. Correlations between observed and modelled

  5. 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.

  6. Convergent chaos

    NASA Astrophysics Data System (ADS)

    Pradas, Marc; Pumir, Alain; Huber, Greg; Wilkinson, Michael

    2017-07-01

    Chaos is widely understood as being a consequence of sensitive dependence upon initial conditions. This is the result of an instability in phase space, which separates trajectories exponentially. Here, we demonstrate that this criterion should be refined. Despite their overall intrinsic instability, trajectories may be very strongly convergent in phase space over extremely long periods, as revealed by our investigation of a simple chaotic system (a realistic model for small bodies in a turbulent flow). We establish that this strong convergence is a multi-facetted phenomenon, in which the clustering is intense, widespread and balanced by lacunarity of other regions. Power laws, indicative of scale-free features, characterize the distribution of particles in the system. We use large-deviation and extreme-value statistics to explain the effect. Our results show that the interpretation of the ‘butterfly effect’ needs to be carefully qualified. We argue that the combination of mixing and clustering processes makes our specific model relevant to understanding the evolution of simple organisms. Lastly, this notion of convergent chaos, which implies the existence of conditions for which uncertainties are unexpectedly small, may also be relevant to the valuation of insurance and futures contracts.

  7. Evidence for the development of a convergent setting in the Southern Alps domain during the early Mesozoic: insights from the Finero Complex (Ivrea-Verbano Zone)

    NASA Astrophysics Data System (ADS)

    Giovanardi, T.; Zanetti, A.; Mazzucchelli, M.; Tiepolo, M.; Vannucci, R.; Morishita, T.

    2012-04-01

    The Finero Mafic-Ultramafic Complex is located in the northernmost sector of the Ivrea-Verbano Zone (hereafter IVZ, Southern Alps). It consists of a pervasively metasomatized dunitic-harzburgitic phlogopite-amphibole-rich mantle unit surrounded by a layered and strongly hydrous mafic-ultramafic pluton (the Finero Mafic Complex) that underplated the lower crust of the Adria plate. A number of different geodynamic scenarios, among which i) aborted rifting processes, ii) mantle plume activity and iii) development of a subduction zone, have been proposed to account for the mantle metasomatism and the melts intrusion in the Finero area. All these scenarios, however, are commonly considered from pre-Hercynian to Permian in age, in analogy with the petrogenetic processes which occurred in the central and southern sectors of IVZ. In this contribution, new geochronological and petrochemical data are presented, along with a review of the literature age determinations, which suggest that the metasomatic events of the Finero mantle unit, as well as the emplacement of the layered intrusion, occurred over a time span covering Middle Triassic to Lower Jurassic. Trace element and isotopic evidence point to the occurrence of large amount of crustal component in the melts migrating through the mantle unit, which, consistently with regional structural features, has been proposed to be related development of roll-back subduction during the early Mesozoic. In this scenario, the intrusion of the Finero Mafic Complex predates the mantle metasomatism and occurred during Upper Anisian-Ladinian, as a consequence of the uprising of melts produced by large degrees of fluid-assisted partial melting in a supra-subduction regime. The mantle unit and the mafic-ultramafic complex were tectonically juxtaposed later on, possibly during the opening of the Middle Jurassic Neo-Tethys.

  8. 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.

  9. 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.

  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. 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

  12. Subseasonal Variations of Rainfall in South America in the Vicinity of the Low-Level Jet East of the Andes and Comparison to Those in the South Atlantic Convergence Zone.

    NASA Astrophysics Data System (ADS)

    Liebmann, Brant; Kiladis, George N.; Vera, Carolina S.; Celeste Saulo, A.; Carvalho, Leila M. V.

    2004-10-01

    Regional and large-scale circulation anomalies associated with variations in rainfall downstream of the South American low-level jet are identified and compared to those in the South Atlantic convergence zone (SACZ). Composites of precipitation associated with strong jets reveal an approximate doubling of the quantities one would expect from climatology, with an evolution of the rainfall pattern from south to north. The occurrence of extreme precipitation events follows a similar pattern. Meridional cross sections of composite wind reveal a distinct low-level jet near 20°S and a baroclinic development farther south that appears to force the jet. Geopotential height, temperature, and large-scale wind composites suggest that this developing disturbance is tied to a wave train that originates in the midlatitude Pacific and turns equatorward as it crosses the Andes Mountains. Similar composites based on SACZ rainfall reveal similar features, but of opposite sign, suggesting that the phase of the wave as it crosses the Andes Mountains determines whether rainfall will be enhanced downstream of the jet or in the SACZ. The alternate suppression or enhancement of rainfall in these adjacent regions results in a precipitation “dipole.” Many previous studies have found a similar out-of-phase relationship over many time scales. The phase of the Madden Julian oscillation (MJO) is composited relative to anomalous precipitation events, revealing statistically relevant amplitudes associated with rainfall both downstream of the jet and in the SACZ. The MJO is a particularly interesting intraseasonal oscillation because it has some predictability. It is speculated that the slowly varying dipole that has been observed is a consequence of the preferred phasing of synoptic waves due to variations of the planetary-scale basic-state flow, which is at times associated with the MJO.


  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.

    2017-01-01

    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. Latitudinal variations in intermediate depth ventilation and biological production over northeastern Pacific Oxygen Minimum Zones during the last 60 ka

    NASA Astrophysics Data System (ADS)

    Cartapanis, Olivier; Tachikawa, Kazuyo; Bard, Edouard

    2012-10-01

    of the Inter Tropical Convergence Zone (ITCZ). Latitudinal variations of the OMZ intensity reflected the relative influence of the northern and southern intermediate water masses whose oxygenation was driven by high latitude climates and productivity over the intermediate water pathway.

  16. 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

  17. 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."…

  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. Fabric stability in oblique convergence and divergence

    NASA Astrophysics Data System (ADS)

    Teyssier, Christian; Tikoff, Basil

    1999-08-01

    Forward modeling of transpression-transtension, assuming homogeneous strain and a direct relationship between finite strain axes and foliation-lineation in tectonites, investigates fields of stability of foliation and lineation orientations in oblique convergence and divergence. Vertical foliation-horizontal lineation (VF-HL) develop for angles of convergence-divergence between 0 and 20°. With increasing finite strain, this narrow window of stability is further reduced; lineation switches to vertical in transpression and foliation switches to horizontal in transtension. If a shear zone contains VF-HL, it either developed as a zone very close to pure wrenching, or recorded low finite strain. The stability of VF-HL at high strain and higher angles of convergence is enhanced by lateral extrusion of material along transpression zones. VF-HL may be stabilized in magmatic bodies that progressively intrude transtension zones, if the wrench component of deformation partitions within them. Alternatively, if these bodies are dike-like, cool fast, and do not record large deformation, they take up the extension component of transtension through anisotropic volume addition, leaving a larger component of wrench deformation in the country rocks; this effect stabilizes VF-HL effectively at low strain, but only marginally so at high strain.

  20. Convergence, adaptation, and constraint.

    PubMed

    Losos, Jonathan B

    2011-07-01

    Convergent evolution of similar phenotypic features in similar environmental contexts has long been taken as evidence of adaptation. Nonetheless, recent conceptual and empirical developments in many fields have led to a proliferation of ideas about the relationship between convergence and adaptation. Despite criticism from some systematically minded biologists, I reaffirm that convergence in taxa occupying similar selective environments often is the result of natural selection. However, convergent evolution of a trait in a particular environment can occur for reasons other than selection on that trait in that environment, and species can respond to similar selective pressures by evolving nonconvergent adaptations. For these reasons, studies of convergence should be coupled with other methods-such as direct measurements of selection or investigations of the functional correlates of trait evolution-to test hypotheses of adaptation. The independent acquisition of similar phenotypes by the same genetic or developmental pathway has been suggested as evidence of constraints on adaptation, a view widely repeated as genomic studies have documented phenotypic convergence resulting from change in the same genes, sometimes even by the same mutation. Contrary to some claims, convergence by changes in the same genes is not necessarily evidence of constraint, but rather suggests hypotheses that can test the relative roles of constraint and selection in directing phenotypic evolution. © 2011 The Author(s). Evolution© 2011 The Society for the Study of Evolution.

  1. Nonaccommodative convergence excess.

    PubMed

    von Noorden, G K; Avilla, C W

    1986-01-15

    Nonaccommodative convergence excess is a condition in which a patient has orthotropia or a small-angle esophoria or esotropia at distance and a large-angle esotropia at near, not significantly reduced by the addition of spherical plus lenses. The AC/A ratio, determined with the gradient method, is normal or subnormal. Tonic convergence is suspected of causing the convergence excess in these patients. Nonaccommodative convergence excess must be distinguished from esotropia with a high AC/A ratio and from hypoaccommodative esotropia. In 24 patients treated with recession of both medial recti muscles with and without posterior fixation or by posterior fixation alone, the mean correction of esotropia was 7.4 prism diopters at distance and 17 prism diopters at near.

  2. Convergence of estuarine channels

    NASA Astrophysics Data System (ADS)

    Dronkers, Job

    2017-07-01

    Tide-dominated coastal plain estuaries have typically up-estuary convergent tidal channels. Analysis of estuarine characteristics indicates a dependence of the convergence length on relative tidal amplitude, relative intertidal area and river flow velocity. In order to explain these relationships we investigate a condition for continuity of net sediment transport throughout the estuary, corresponding to morphodynamic equilibrium. We show, by using an analytical solution of the tidal equations, that this condition is equivalent to a condition on the convergence length. This condition is evaluated for 21 estuaries in different regions of the world. It appears that the convergence length determined in this way can explain observed convergence lengths for the considered set of estuaries. The dependence of the convergence length on different estuarine characteristics is analysed by solving the fully coupled hydro-morphodynamic equations. We show that this dependence limits the range of variation of the tidal velocity amplitude. The analysis provides insight in the morphological response of estuaries to human interventions. The condition can easily be evaluated to yield an estimate of this response.

  3. 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.

  4. On the weight convergence of Elman networks.

    PubMed

    Song, Qing

    2010-03-01

    An Elman network (EN) can be viewed as a feedforward (FF) neural network with an additional set of inputs from the context layer (feedback from the hidden layer). Therefore, instead of the offline backpropagation-through-time (BPTT) algorithm, a standard online (real-time) backpropagation (BP) algorithm, usually called Elman BP (EBP), can be applied for EN training for discrete-time sequence predictions. However, the standard BP training algorithm is not the most suitable for ENs. A low learning rate can improve the training of ENs but can also result in very slow convergence speeds and poor generalization performance, whereas a high learning rate can lead to unstable training in terms of weight divergence. Therefore, an optimal or suboptimal tradeoff between training speed and weight convergence with good generalization capability is desired for ENs. This paper develops a robust extended EBP (eEBP) training algorithm for ENs with a new adaptive dead zone scheme based on eEBP training concepts. The adaptive learning rate and adaptive dead zone optimize the training of ENs for each individual output and improve the generalization performance of the eEBP training. In particular, for the proposed eEBP training algorithm, convergence of the ENs' weights with the adaptive dead zone estimates is proven in the sense of Lyapunov functions. Computer simulations are carried out to demonstrate the improved performance of eEBP for discrete-time sequence predictions.

  5. 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,…

  6. 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).

  7. 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,…

  8. 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.)

  9. 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.)

  10. The Forcing of 25-Knot Winds at Hickam and Andersen AFB

    DTIC Science & Technology

    2007-03-01

    reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching...existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding...creating an Inter-tropical Convergence Zone ( ITCZ ). (From Elsberry, Chapter 1) ..........11 Figure 7. Convergence zone where Coriolis has had time

  11. 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…

  12. 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…

  13. Safety Zones

    EPA Pesticide Factsheets

    These are established primarily to reduce the accidental spread of hazardous substances by workers or equipment from contaminated areas to clean areas. They include the exclusion (hot) zone, contamination reduction (warm) zone, and support (cold) zone.

  14. Homology, convergence and parallelism.

    PubMed

    Ghiselin, Michael T

    2016-01-05

    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. © 2015 The Author(s).

  15. Grand network convergence.

    PubMed

    Bader, Joel S

    2011-06-17

    A report of the Systems Biology: Networks meeting, Cold Spring Harbor, USA, 22-26 March 2011.The success of the human genome project has provided a model for an analogous interactome project to map how proteins, genes, metabolites and other regulatory components interact to transform a biochemical soup into a living system. These maps promise to serve as a framework for models that predict how a biological system responds to a perturbation or an input, which is relevant to gene mutations and therapeutic treatment in human disease, and as a framework for designing new systems in synthetic biology.Three major themes arose during the 2011 meeting: technological drivers and data generation, algorithmic advances, and convergence on biological applications with context-sensitive networks.

  16. Homology, convergence and parallelism

    PubMed Central

    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

  17. 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.

  18. 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.

  19. Convergent ablator performance measurements

    SciTech Connect

    Hicks, D. G.; Spears, B. K.; Braun, D. G.; Sorce, C. M.; Celliers, P. M.; Collins, G. W.; Landen, O. L.; Olson, R. E.

    2010-10-15

    The velocity and remaining ablator mass of an imploding capsule are critical metrics for assessing the progress toward ignition of an inertially confined fusion experiment. These and other convergent ablator performance parameters have been measured using a single streaked x-ray radiograph. Traditional Abel inversion of such a radiograph is ill-posed since backlighter intensity profiles and x-ray attenuation by the ablated plasma are unknown. To address this we have developed a regularization technique which allows the ablator density profile {rho}(r) and effective backlighter profile I{sub 0}(y) at each time step to be uniquely determined subject to the constraints that {rho}(r) is localized in radius space and I{sub 0}(y) is delocalized in object space. Moments of {rho}(r) then provide the time-resolved areal density, mass, and average radius (and thus velocity) of the remaining ablator material. These results are combined in the spherical rocket model to determine the ablation pressure and mass ablation rate during the implosion. The technique has been validated on simulated radiographs of implosions at the National Ignition Facility [Miller et al., Nucl. Fusion 44, 228 (2004)] and implemented on experiments at the OMEGA laser facility [Boehly et al., Opt. Commun. 133, 495 (1997)].

  20. Some Observations on Grid Convergence

    NASA Technical Reports Server (NTRS)

    Salas, manuel D.

    2006-01-01

    It is claimed that current practices in grid convergence studies, particularly in the field of external aerodynamics, are flawed. The necessary conditions to properly establish grid convergence are presented. A theoretical model and a numerical example are used to demonstrate these ideas.

  1. 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.

  2. Dynamics of the Intertropical Convergence Zone of the East Pacific

    NASA Astrophysics Data System (ADS)

    Raymond, D. J.; Raga, G.; Bretherton, C.; Deszoeke, S.; Molinari, J.; Lopez-Carrillo, C.; Fuchs, Z.

    2002-12-01

    Intensive observations were made of the atmosphere in the tropical east Pacific during September and October 2001 as a part of the EPIC (East Pacific Study of Climate) project. During this period the most intense deep convection was associated with the existence of marine layer top (810 - 850 nit{mb}) westerly winds, while more suppressed convection generally occurred with marine layer top easterlies. The distribution of convection can be explained on the basis of a quasi-equilibrium theory in which surface latent and sensible heat fluxes are balanced by deep convective downdrafts in the control of the vertically averaged entropy in the marine layer. Since downdrafts presumably occur in proportion to the updrafts responsible for them, surface heat fluxes exert a lagged control over convection. The lag occurs because convection appears to respond directly to the conditional instability of the marine layer and marine layer destabilization by surface heat fluxes can take some time. More intense convection occurs during marine layer top westerlies because the surface winds, and hence surface heat fluxes, are stronger in this case. The surface winds are stronger because the geostrophic pressure gradient associated with the westerlies aloft reinforces the surface pressure gradient produced by the north-south variation in the marine layer temperature. This latter gradient results from the northward increase in sea surface temperature in the east Pacific.

  3. Giant lobelias exemplify convergent evolution.

    PubMed

    Givnish, Thomas J

    2010-01-14

    Giant lobeliads on tropical mountains in East Africa and Hawaii have highly unusual, giant-rosette growth forms that appear to be convergent on each other and on those of several independently evolved groups of Asteraceae and other families. A recent phylogenetic analysis by Antonelli, based on sequencing the widest selection of lobeliads to date, raises doubts about this paradigmatic example of convergent evolution. Here I address the kinds of evidence needed to test for convergent evolution and argue that the analysis by Antonelli fails on four points. Antonelli's analysis makes several important contributions to our understanding of lobeliad evolution and geographic spread, but his claim regarding convergence appears to be invalid. Giant lobeliads in Hawaii and Africa represent paradigmatic examples of convergent evolution.

  4. Convergence and the multidimensional niche.

    PubMed

    Harmon, Luke J; Kolbe, Jason J; Cheverud, James M; Losos, Jonathan B

    2005-02-01

    Convergent evolution has played an important role in the development of the ecological niche concept. We investigated patterns of convergent and divergent evolution of Caribbean Anolis lizards. These lizards diversified independently on each of the islands of the Greater Antilles, producing the same set of habitat specialists on each island. Using a phylogenetic comparative framework, we examined patterns of morphological convergence in five functionally distinct sets of morphological characters: body size, body shape, head shape, lamella number, and sexual size dimorphism. We find evidence for convergence among members of the habitat specialist types for each of these five datasets. Furthermore, the patterns of convergence differ among at least four of the five datasets; habitat specialists that are similar for one set of characters are often greatly different for another. This suggests that the habitat specialist niches into which these anoles have evolved are multidimensional, involving several distinct and independent aspects of morphology.

  5. Giant lobelias exemplify convergent evolution

    PubMed Central

    2010-01-01

    Giant lobeliads on tropical mountains in East Africa and Hawaii have highly unusual, giant-rosette growth forms that appear to be convergent on each other and on those of several independently evolved groups of Asteraceae and other families. A recent phylogenetic analysis by Antonelli, based on sequencing the widest selection of lobeliads to date, raises doubts about this paradigmatic example of convergent evolution. Here I address the kinds of evidence needed to test for convergent evolution and argue that the analysis by Antonelli fails on four points. Antonelli's analysis makes several important contributions to our understanding of lobeliad evolution and geographic spread, but his claim regarding convergence appears to be invalid. Giant lobeliads in Hawaii and Africa represent paradigmatic examples of convergent evolution. PMID:20074322

  6. 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.

  7. Zone lines

    Treesearch

    Kevin T. Smith

    2001-01-01

    Zone lines are narrow, usually dark markings formed in decaying wood. Zone lines are found most frequently in advanced white rot of hardwoods, although they occasionally are associated both with brown rot and with softwoods.

  8. 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. Copyright © 2014 Elsevier Inc. All rights reserved.

  9. Optimality Functions and Lopsided Convergence

    DTIC Science & Technology

    2015-03-16

    Royset and E.Y. Pee . Rate of convergence analysis of discretization and smoothing algorithms for semi-infinite minimax problems. Journal of Optimization Theory and Applications, 155(3):855– 882, 2012. 17

  10. Spaces of Ideal Convergent Sequences

    PubMed Central

    Mursaleen, M.; Sharma, Sunil K.

    2014-01-01

    In the present paper, we introduce some sequence spaces using ideal convergence and Musielak-Orlicz function ℳ = (Mk). We also examine some topological properties of the resulting sequence spaces. PMID:24592143

  11. Convergence palsy secondary to amoxicillin.

    PubMed

    Pérez-Roca, F; Alfaro Juárez, A; Sánchez Merino, C; Navarro Mingorance, A

    2016-12-01

    We present the case of an 11-year-old boy with acute diplopia in near vision secondary to transient convergence palsy, possibly in relation to amoxicillin. Convergence palsy is an uncommon eye disorder. The causes are reviewed, and amoxicilin is identified as presumptive etiologic agent. This is the first case reported. Copyright © 2016 Sociedad Española de Oftalmología. Publicado por Elsevier España, S.L.U. All rights reserved.

  12. The camera convergence problem revisited

    NASA Astrophysics Data System (ADS)

    Allison, Robert S.

    2004-05-01

    Convergence of the real or virtual stereoscopic cameras is an important operation in stereoscopic display systems. For example, convergence can shift the range of portrayed depth to improve visual comfort; can adjust the disparity of targets to bring them nearer to the screen and reduce accommodation-vergence conflict; or can bring objects of interest into the binocular field-of-view. Although camera convergence is acknowledged as a useful function, there has been considerable debate over the transformation required. It is well known that rotational camera convergence or 'toe-in' distorts the images in the two cameras producing patterns of horizontal and vertical disparities that can cause problems with fusion of the stereoscopic imagery. Behaviorally, similar retinal vertical disparity patterns are known to correlate with viewing distance and strongly affect perception of stereoscopic shape and depth. There has been little analysis of the implications of recent findings on vertical disparity processing for the design of stereoscopic camera and display systems. We ask how such distortions caused by camera convergence affect the ability to fuse and perceive stereoscopic images.

  13. NONSURGICAL TREATMENT OF CONVERGENT STRABISMUS

    PubMed Central

    Tour, Robert L.

    1959-01-01

    It is generally agreed that surgical treatment of convergent strabismus should be withheld until all other less traumatic approaches have proved ineffectual. There are four categories of nonsurgical treatment. One is psychiatric. Too often psychiatric problems in the causation of convergent strabismus are either overlooked or unrecognized. Another is the proper employment of optical devices. For example, spectacle lenses to eliminate the need for excessive accommodation with its associated convergence excess, and the employment of prisms in the lenses to permit the two eyes to see as a unit even though they may not be properly anatomically oriented. Another kind of treatment is orthoptics, the use of exercises and rather complex optical equipment in a laboratory to train the patient in coordination between the two eyes. Treatment with drugs is based on the fact that certain drugs reduce the effort necessary for accommodation (much as eye-glasses do) and therefore lessen the stimulus toward convergence which may possibly tend toward the development of convergent strabismus. PMID:13662849

  14. Convergence methods on time scales

    NASA Astrophysics Data System (ADS)

    Turan, Ceylan; Duman, Oktay

    2013-10-01

    In this paper, we introduce the concepts of lacunary statistical convergence and strongly lacunary Cesàro summability of delta measurable functions on time scales and obtain some inclusion results between them. We also display some examples containing discrete and continuous cases.

  15. 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.

  16. Thin-skinned deformation and plate driving forces associated with convergent margins

    SciTech Connect

    Davis, D.M.

    1983-08-01

    Several aspects of the mechanics of convergent margins are investigated. A quantitative model for the mechanics of thin skinned deformation in accretionary wedges and thrust belts, and a test of plate driving forces, including those at convergence zones, against the absolute velocities of the plates since the late Cretaceous are presented. Constraints are provided which are used to draw conclusions about the state of stress in the lithosphere.

  17. A Smart Climatology of Evaporation Duct Height and Surface Radar Propagation in the Indian Ocean

    DTIC Science & Technology

    2007-09-01

    Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction...searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the col lection of information. Send...Atmosphere Data Set IO Indian Ocean IOZM Indian Ocean Zonal Mode ITCZ Inter-tropical Convergence Zone LN La Nina LTM Long-Term Mean

  18. Inclusion of Sea-Surface Temperature Variation in the U.S. Navy Ensemble-Transform Global Ensemble Prediction System

    DTIC Science & Technology

    2012-10-13

    hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and...completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information...that in SSTidf there is a strengthened Inter-Tropical Convergence Zone ( ITCZ ) in these regions, with deeper convection (i.e., colder convec- tive cloud

  19. Salt Transport in the Near-Surface Layer in the Monsoon-Influenced Indian Ocean Using HYCOM

    DTIC Science & Technology

    2010-08-04

    hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and...completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of...the significant role of advection for the distribution of freshwater and the Ekman processes. The Inter-Tropical Convergence Zone ( ITCZ ) is seen to

  20. The Switchover from NOGAPS to NAVGEM 1.1 Atmospheric Forcing in GOFS and ACNFS

    DTIC Science & Technology

    2013-08-20

    reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions...searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments...shortwave radiation along the Inter-Tropical Convergence Zone ( ITCZ ) and tropical Indian and west Pacific Oceans. However, across much of the rest of the

  1. 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.

  2. Convergence.

    ERIC Educational Resources Information Center

    Hancock, Alan

    1984-01-01

    Characterizes the development over the past 30 years of the communication technologies employed in education by examining technological developments, structure of individual media, objectives and audiences of media systems, access to communications technologies, appropriateness of technology in new environments, social impact, and policy…

  3. Convergence.

    ERIC Educational Resources Information Center

    Hancock, Alan

    1984-01-01

    Characterizes the development over the past 30 years of the communication technologies employed in education by examining technological developments, structure of individual media, objectives and audiences of media systems, access to communications technologies, appropriateness of technology in new environments, social impact, and policy…

  4. 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.

  5. 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.

  6. Rapid Convergence and Subduction at the Intersections of Fronts

    NASA Astrophysics Data System (ADS)

    D'Asaro, E. A.

    2016-12-01

    An array of 300 surface drifters drogued to follow the top 0.6m of the ocean were deployed in the northern Gulf of Mexico near the Deep Water Horizon spill site in January of 2016. As expected, the array spread from its initial 15x15km scale with the second moment increasing at a rate roughly consistent with historical dispersion curves. More surprisingly, a large fraction of the drifters accumulated within a km-scale submesoscale eddy and grouped into clusters often only a few meters apart. This occurred due to surface convergence, as opposed to purely confluence, with convergence rates of many f feeding downward-going subduction zones with vertical velocities of a few centimeters per second. These convergences preferentially occurred at density fronts and in particular at junctions of density fronts on the periphery of submesoscale eddies. These observations complement the traditional view of lateral dispersion of surface particles by mesoscale eddies with a competing submesocale convergence and provide direct observations of the strong vertical exchanges associated with submesoscale eddies and fronts.

  7. Converging beam optical Fourier transforms

    NASA Astrophysics Data System (ADS)

    Puang-ngern, Srisuda; Almeida, Silverio P.

    1985-08-01

    The classical, most often used, system for performing the optical Fourier transform is by using parallel coherent beam illumination. Lenses used in this method can become quite costly. In this paper we present results obtained using converging beam illumination which is suitable for many applications and is less expensive than the parallel beam method. The input objects for which the Fourier transforms were made are transparencies of snowflakes.

  8. Adaptive sampling in convergent beams.

    PubMed

    Espinosa, Julián; Mas, David; Pérez, Jorge; Illueca, Carlos

    2008-09-01

    Numerical calculation of convergent Fresnel patterns through fast Fourier transform usually requires a large number of samples to fulfill the Nyquist sampling condition around the focus. From polynomial decomposition of the wavefront it is possible to determine which polynomial orders are the main contributors to the number of samples. This information can be used to properly modify the initial wavefront and relax the Nyquist condition thus giving a more efficient numerical algorithm.

  9. Open questions in the ethics of convergence.

    PubMed

    Khushf, George

    2007-01-01

    After historically situating NBIC Convergence in the context of earlier bioethical debate on genetics, ten questions are raised in areas related to the ethics of Convergence, indicating where future research is needed.

  10. Mesh Convergence Requirements for Composite Damage Models

    NASA Technical Reports Server (NTRS)

    Davila, Carlos G.

    2016-01-01

    The ability of the finite element method to accurately represent the response of objects with intricate geometry and loading renders the finite element method as an extremely versatile analysis technique for structural analysis. Finite element analysis is routinely used in industry to calculate deflections, stress concentrations, natural frequencies, buckling loads, and much more. The method works by discretizing complex problems into smaller, simpler approximations that are valid over small uniform domains. For common analyses, the maximum size of the elements that can be used is often be determined by experience. However, to verify the quality of a solution, analyses with several levels of mesh refinement should be performed to ensure that the solution has converged. In recent years, the finite element method has been used to calculate the resistance of structures, and in particular that of composite structures. A number of techniques such as cohesive zone modeling, the virtual crack closure technique, and continuum damage modeling have emerged that can be used to predict cracking, delaminations, fiber failure, and other composite damage modes that lead to structural collapse. However, damage models present mesh refinement requirements that are not well understood. In this presentation, we examine different mesh refinement issues related to the representation of damage in composite materials. Damage process zone sizes and their corresponding mesh requirements will be discussed. The difficulties of modeling discontinuities and the associated need for regularization techniques will be illustrated, and some unexpected element size constraints will be presented. Finally, some of the difficulties in constructing models of composite structures capable of predicting transverse matrix cracking will be discussed. It will be shown that to predict the initiation and propagation of transverse matrix cracks, their density, and their saturation may require models that are

  11. 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

  12. Convergence of m-bonacci 'golden ratios'

    NASA Astrophysics Data System (ADS)

    Ahrens, K.; Brown, D. A.; Kramer, A.

    2014-05-01

    This paper proves that the ratios of consecutive terms of the m-bonacci sequence converge to a limit φm < 2 and, as m → ∞, these φm converge to 2. Further, it is shown that the generating functions for the m-bonacci sequences converge pointwise to the geometric series.

  13. 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.

  14. "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…

  15. "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…

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. Convergence across the northwest Himalaya from GPS measurements

    NASA Astrophysics Data System (ADS)

    Banerjee, P.; Bürgmann, R.

    2002-07-01

    Horizontal velocities of 26 Global Positioning System (GPS) stations in the northwest Himalayan region provide new constraints on the partitioning of India-Eurasia convergence and elastic strain accumulation about the locked Main Frontal Thrust (MFT). The northwest-striking Karakorum fault slips at 11 +/- 4 mm/yr and contributes to east-west extension of southern Tibet and westward motion of the northwest Himalaya towards Nanga Parbat, rather than playing a role in eastward extrusion of Tibet. Crustal shortening across the Himalaya occurs within a zone centered about 100 km north of the Siwalik Foothills and the MFT. Model inversions of the GPS data indicate that the MFT is locked over a width of ~100 km. Comparison with geologic MFT-slip-rate estimates suggests that this zone is building up a slip deficit at a rate of 14 +/- 1 mm/yr and will eventually fail in future great earthquakes.

  1. Convergence of the moments of inertia in f-p-g shell nuclei

    NASA Astrophysics Data System (ADS)

    Tabor, S. L.

    1992-01-01

    A survey of the kinematic moments of inertia of A~=80 nuclei shows a tendency to converge toward the rigid-body values of 20 to 25 ħ2/MeV at rotational frequencies above 0.6 MeV/ħ. The moments of the even-even isotopes approach the convergence zone from much lower values. The farther from the center of the shell, the lower the initial values are and the more rapid is the rise. By contrast, the moments of inertia of the odd-odd nuclei start from higher values and decrease into the convergence zone. The values for odd-A nuclei are generally intermediate, usually starting somewhat below the final value and increasing into the 20 to 25 ħ2/MeV region. The quadrupole deformations inferred from lifetimes in the even-even nuclei show no systematic change with spin, in contrast to the moments of inertia.

  2. Convergent Validity of the PUTS

    PubMed Central

    Brandt, Valerie Cathérine; Beck, Christian; Sajin, Valeria; Anders, Silke; Münchau, Alexander

    2016-01-01

    Premonitory urges are a cardinal feature in Gilles de la Tourette syndrome. Severity of premonitory urges can be assessed with the “Premonitory Urge for Tic Disorders Scale” (PUTS). However, convergent validity of the measure has been difficult to assess due to the lack of other urge measures. We investigated the relationship between average real-time urge intensity assessed by an in-house developed real-time urge monitor (RUM), measuring urge intensity continuously for 5 min on a visual analog scale, and general urge intensity assessed by the PUTS in 22 adult Tourette patients (mean age 29.8 ± 10.3 SD, 19 males). Additionally, underlying factors of premonitory urges assessed by the PUTS were investigated in the adult sample using factor analysis and were replicated in 40 children and adolescents diagnosed with Tourette syndrome (mean age 12.05 ± 2.83 SD, 31 males). Cronbach’s α for the PUTS 10 was acceptable (α = 0.79) in the adult sample. Convergent validity between average real-time urge intensity scores (as assessed with the RUM) and the 10-item version of the PUTS (r = 0.64) and the 9-item version of the PUTS (r = 0.66) was good. A factor analysis including the 10 items of the PUTS and average real-time urge intensity scores revealed three factors. One factor included the average real-time urge intensity score and appeared to measure urge intensity, whereas the other two factors can be assumed to reflect the (sensory) quality of urges and subjective control, respectively. The factor structure of the 10 PUTS items alone was replicated in a sample of children and adolescents. The results indicate that convergent validity between the PUTS and the real-time urge assessment monitor is good. Furthermore, the results suggest that the PUTS might assess more than one dimension of urges, and it may be worthwhile developing different subscales of the PUTS assessing premonitory urges in terms of intensity and quality, as well as

  3. Formal convergence characteristics of elliptically constrained incremental Newton-Raphson algorithms

    NASA Technical Reports Server (NTRS)

    Padovan, J.; Arechaga, T.

    1982-01-01

    Various aspects of the convergence, uniqueness, and existence properties associated with solutions generated via the elliptically constrained incremental Newton-Raphson (ECINR) algorithm are analyzed. Several theorems are developed, and the formal behavior of the elliptically constrained scheme developed by Padovan (1981) is discussed in detail. Consideration is given to global and local rates of convergence, to the determination of the occurrence of safety zones wherein the algorithm yields inherently convergent results, to formal limitations on the class of functions which the scheme can be applied to solve, and to single and multidimensional formalisms on existence uniqueness and convergence. Special attention is given to functions whose Jacobian matrix exhibit positive, negative, semi and indefinite properties. Several significant advantages of ECINR over the classical INR are mentioned.

  4. Formal convergence characteristics of elliptically constrained incremental Newton-Raphson algorithms

    NASA Technical Reports Server (NTRS)

    Padovan, J.; Arechaga, T.

    1982-01-01

    Various aspects of the convergence, uniqueness, and existence properties associated with solutions generated via the elliptically constrained incremental Newton-Raphson (ECINR) algorithm are analyzed. Several theorems are developed, and the formal behavior of the elliptically constrained scheme developed by Padovan (1981) is discussed in detail. Consideration is given to global and local rates of convergence, to the determination of the occurrence of safety zones wherein the algorithm yields inherently convergent results, to formal limitations on the class of functions which the scheme can be applied to solve, and to single and multidimensional formalisms on existence uniqueness and convergence. Special attention is given to functions whose Jacobian matrix exhibit positive, negative, semi and indefinite properties. Several significant advantages of ECINR over the classical INR are mentioned.

  5. Particles Acceleration in Converged Shocks

    NASA Astrophysics Data System (ADS)

    Wang, Xin

    2016-07-01

    Observations show that there is a proton spectral ``break" with E_{break} at 1-10MeV in some large CME-driven shocks. However, the understanding of this energy spectral ``break" from the diffusive shock acceleration theory still remains uncertain. Although previous numerical methods can hardly predict this ``break" from current theoretical models due to high computational expense, the present paper focuses on simulating this energy spectrum in converged two shocks by Monte Carlo numerical method. Considering the Dec 13 2006 CME-driven shock interaction with an Earth bow shock, we examine whether the energy spectral ``break" could occur on an interaction between two shocks. As result, we indeed obtain the maximum proton energy up to 10MeV, and we further find a proton spectral ``break" appears distinctly at the energy ˜5MeV.

  6. 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.

  7. Feedback between mountain belt growth and plate convergence

    NASA Astrophysics Data System (ADS)

    Iaffaldano, Giampiero; Bunge, Hans-Peter; Dixon, Timothy H.

    2006-10-01

    While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that link remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at zones of plate convergence are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less clear, as are the main factors controlling long-term changes in plate motion. The ability to consider past as well as present plate motions provides significant additional constraints, because changes in plate motion are necessarily driven by changes in one or more driving or resisting forces, which may be inferred from independent data. Here we present for the first time a model that explicitly links global mantle convection and lithosphere models to infer plate motion changes as far back as Miocene time. By accurately predicting observed convergence rates over the past 10 m.y., we demonstrate that surface topography generated at convergent margins is a key factor controlling the long-term evolution of plate motion. Specifically, the topographic load of large mountain belts and plateaus consumes a significant amount of the driving force available for plate tectonics by increasing frictional forces between downgoing and overriding plates.

  8. 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.

  9. Genome-Wide Convergence during Evolution of Mangroves from Woody Plants.

    PubMed

    Xu, Shaohua; He, Ziwen; Guo, Zixiao; Zhang, Zhang; Wyckoff, Gerald J; Greenberg, Anthony; Wu, Chung-I; Shi, Suhua

    2017-04-01

    When living organisms independently invade a new environment, the evolution of similar phenotypic traits is often observed. An interesting but contentious issue is whether the underlying molecular biology also converges in the new habitat. Independent invasions of tropical intertidal zones by woody plants, collectively referred to as mangrove trees, represent some dramatic examples. The high salinity, hypoxia, and other stressors in the new habitat might have affected both genomic features and protein structures. Here, we developed a new method for detecting convergence at conservative Sites (CCS) and applied it to the genomic sequences of mangroves. In simulations, the CCS method drastically reduces random convergence at rapidly evolving sites as well as falsely inferred convergence caused by the misinferences of the ancestral character. In mangrove genomes, we estimated ∼400 genes that have experienced convergence over the background level of convergence in the nonmangrove relatives. The convergent genes are enriched in pathways related to stress response and embryo development, which could be important for mangroves' adaptation to the new habitat.

  10. 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.

  11. Convergence Analysis of LMS based Adaptive filter

    NASA Astrophysics Data System (ADS)

    Rai, Amrita; Kohli, Amit Kumar

    2010-11-01

    A standard algorithm for LMS-filter simulation, tested with several convergence criteria is presented in this paper. We analyze the steady-state mean square error (MSE) convergence of the LMS algorithm when random functions are used as reference inputs. In this paper, we make a more precise analysis using the deterministic nature of the reference inputs and their time-variant correlation matrix. Simulations performed under MATLAB show remarkable differences between convergence criteria with various value of the step size.

  12. Systematically Accelerated Convergence of Path Integrals

    SciTech Connect

    Bogojevic, A.; Balaz, A.; Belic, A.

    2005-05-13

    We present a new analytical method that systematically improves the convergence of path integrals of a generic N-fold discretized theory. Using it we calculate the effective actions S{sup (p)} for p{<=}9, which lead to the same continuum amplitudes as the starting action, but that converge to that continuum limit as 1/N{sup p}. We checked this derived speedup in convergence by performing Monte Carlo simulations on several different models.

  13. Testing hypotheses of convergence with multivariate data: morphological and functional convergence among herbivorous lizards.

    PubMed

    Stayton, C Tristan

    2006-04-01

    Despite its importance to evolutionary theory, convergence remains an understudied phenomenon and is usually investigated using qualitative data. This paper advances a new, multidimensional view of convergence. Three patterns indicative of convergence are discussed, and techniques to discover and test convergent patterns in a quantitative framework are developed. These concepts and methods are applied to a dataset of digitized coordinates on 1554 lizard skulls and 1292 lower jaws to test hypotheses of convergence among herbivorous lizards. Encompassing seven independent acquisitions of herbivory, this lizard sample provides an ideal natural experiment for exploring ideas of convergence among different systems (here, morphological and functional). Three related questions are addressed: (1) Do herbivorous lizards show evidence of convergence in skull and lower jaw morphology? (2) What, if any, is the morphospace pattern associated with this convergence? (3) Is it possible to predict the direction of convergence using functional models? Relative warp analysis and permutation tests reveal that the skulls and lower jaws of herbivorous lizards do show evidence of convergence. Herbivore skulls deviate from their carnivorous or omnivorous sister groups toward the same area of morphospace. Without a phylogenetic perspective, this pattern would not be recognizable. Lower jaws of herbivores are not convergent in morphology but are convergent in function: herbivores deviate away from their carnivorous sister groups toward higher values of mechanical advantage. These results illustrate the desirability of quantitative methods, informed by phylogenetic information, in the study of convergence.

  14. 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

  15. 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.

  16. Lack of convergence in aquatic Anolis lizards.

    PubMed

    Leal, Manuel; Knox, Alison K; Losos, Jonathan B

    2002-04-01

    Why convergent evolution occurs among some species occupying similar habitats but not among others is a question that has received surprisingly little attention. Caribbean Anolis lizards, known for their extensive convergent evolution among islands in the Greater Antilles, are an appropriate group with which to address this question. Despite the well-documented pattern of between-island convergence, some Greater Antillean anoles are not obviously part of the convergence syndrome. One example involves aquatic anoles--species that are found near to and readily enter streams-which have evolved independently twice in the Caribbean and also twice on mainland Central America. Despite being found in similar habitats, no previous study has investigated whether aquatic anoles represent yet another case of morphological convergence. We tested this hypothesis by collecting morphological data for seven aquatic anole species and 29 species from the six convergent types of Greater Antillean habitat specialists. We failed to find evidence for morphological convergence: the two Caribbean aquatic species are greatly dissimilar to each other and to the Central American species, which, however, may be convergent upon each other. We suggest two possible reasons for this lack of convergence in an otherwise highly convergent system: either there is more than one habitat type occupied by anoles in the proximity of water, or there is more than one way to adapt to a single aquatic habitat. We estimate that almost all of the 113 species of Greater Antillean anoles occupy habitats that are also used by distantly related species, but only 15% of these species are not morphologically similar to their distantly related ecological counterparts. Comparative data from other taxa would help enlighten the question of why the extent of convergence is so great in some lineages and not in others.

  17. 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.

  18. Seismic coupling and uncoupling at subduction zones

    NASA Technical Reports Server (NTRS)

    Ruff, L.; Kanamori, H.

    1983-01-01

    Some of the correlations concerning the properties of subduction zones are reviewed. A quantitative global comparison of many subduction zones reveals that the largest earthquakes occur in zones with young lithosphere and fast convergence rates. Maximum earthquake size is directly related to the asperity distribution on the fault plane. This observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface. Plate age and rate can control asperity distribution directly through the horizontal compressive stress associated with the vertical and horizontal velocities of subducting slabs. The basalt to eclogite phase change in the down-going oceanic crust may be largely responsible for the uncoupling of subduction zones below a depth of about 40 km.

  19. Ecomorphological convergence of cave communities.

    PubMed

    Trontelj, Peter; Blejec, Andrej; Fišer, Cene

    2012-12-01

    Extreme selective environments are commonly believed to funnel evolution toward a few predictable outcomes. Caves are well-known extreme environments with characteristically adapted faunas that are similar in appearance, physiology, and behavior all over the world, even if not closely related. Morphological diversity between closely related cave species has been explained by difference in time since colonization and different ecological influence from the surface. Here, we tested a more classical hypothesis: morphological diversity is niche-based, and different morphologies reflect properties of microhabitats within caves. We analyzed seven communities with altogether 30 species of the subterranean amphipod (crustacean) genus Niphargus using multivariate morphometrics, multinomial logit models cross-validation, and phylogenetic reconstruction. Species clustered into four distinct ecomorph classes-small pore, cave stream, cave lake, and lake giants-associated with specific cave microhabitats and of multiple independent phylogenetic origins. Traits commonly regarded as adaptations to caves, such as antenna length, were shown to be related to microhabitat parameters, such as flow velocity. These results demonstrate that under the selection pressure of extreme environment, the ecomorphological structure of communities can converge. Thus, morphological diversity does not result from adaptive response to temporal and ecological gradients, but from fine-level niche partitioning. © 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.

  20. 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

  1. Convergence of a Linear Recursive Sequence

    ERIC Educational Resources Information Center

    Tay, E. G.; Toh, T. L.; Dong, F. M.; Lee, T. Y.

    2004-01-01

    A necessary and sufficient condition is found for a linear recursive sequence to be convergent, no matter what initial values are given. Its limit is also obtained when the sequence is convergent. Methods from various areas of mathematics are used to obtain the results.

  2. 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.

  3. Selective Grammatical Convergence: Learning from Desirable Speakers

    ERIC Educational Resources Information Center

    Lev-Ari, Shiri

    2016-01-01

    Models of language learning often assume that we learn from all the input we receive. This assumption is particularly strong in the domain of short-term and long-term grammatical convergence, where researchers argue that grammatical convergence is mostly an automatic process insulated from social factors. This article shows that the degree to…

  4. Numerical simulation of converging shock waves

    NASA Astrophysics Data System (ADS)

    Yee, Seokjune; Abe, Kanji

    We can achieve the high pressure and high temperature state of gas if the shock wave converges stably. In order to check the stability of the converging shock wave, we introduce two kinds of perturbed initial conditions. The Euler equations of conservation form are integrated by using explicit Non-Muscl TVD finite difference scheme.

  5. Selective Grammatical Convergence: Learning from Desirable Speakers

    ERIC Educational Resources Information Center

    Lev-Ari, Shiri

    2016-01-01

    Models of language learning often assume that we learn from all the input we receive. This assumption is particularly strong in the domain of short-term and long-term grammatical convergence, where researchers argue that grammatical convergence is mostly an automatic process insulated from social factors. This article shows that the degree to…

  6. Convergence of a Linear Recursive Sequence

    ERIC Educational Resources Information Center

    Tay, E. G.; Toh, T. L.; Dong, F. M.; Lee, T. Y.

    2004-01-01

    A necessary and sufficient condition is found for a linear recursive sequence to be convergent, no matter what initial values are given. Its limit is also obtained when the sequence is convergent. Methods from various areas of mathematics are used to obtain the results.

  7. Measuring phonetic convergence in speech production

    PubMed Central

    Pardo, Jennifer S.

    2013-01-01

    Phonetic convergence is defined as an increase in the similarity of acoustic-phonetic form between talkers. Previous research has demonstrated phonetic convergence both when a talker listens passively to speech and while talkers engage in social interaction. Much of this research has focused on a diverse array of acoustic-phonetic attributes, with fewer studies incorporating perceptual measures of phonetic convergence. The current paper reviews research on phonetic convergence in both non-interactive and conversational settings, and attempts to consolidate the diverse array of findings by proposing a paradigm that models perceptual and acoustic measures together. By modeling acoustic measures as predictors of perceived phonetic convergence, this paradigm has the potential to reconcile some of the diverse and inconsistent findings currently reported in the literature. PMID:23986738

  8. The continental collision zone, South Island, New Zealand: Comparison of geodynamical models and observations

    SciTech Connect

    Beaumont, C.; Hamilton, J.; Fullsack, P.; Kamp, P.J.J.

    1996-02-10

    In this report geodynamical models are used to test the applicability of the mantle subduction model to the compressional character and evaluation of the South Island continental convergence zone of New Zealand.

  9. Propagation of converging spherical deformation waves in a heteromodular elastic medium

    NASA Astrophysics Data System (ADS)

    Ragozina, V. E.; Dudko, O. V.

    2016-07-01

    The unsteady one-dimensional boundary-value problem of shock deformation of a medium bounded by a sphere is solved. The propagation of converging deformation wave fronts in an elastic material with different tensile and compressive strengths is studied. A boundary condition is obtained that provides the formation of a converging spherical shock wave with constant velocity. The impact conditions on the boundary of the heteromodular sphere are determined that can lead to the formation of a transition zone (a spherical layer of constant density) between the compression and tension regions.

  10. Kaiser Permanente's Convergent Medical Terminology.

    PubMed

    Dolin, Robert H; Mattison, John E; Cohn, Simon; Campbell, Keith E; Wiesenthal, Andrew M; Hochhalter, Brad; LaBerge, Diane; Barsoum, Rita; Shalaby, James; Abilla, Alan; Clements, Robert J; Correia, Carol M; Esteva, Diane; Fedack, John M; Goldberg, Bruce J; Gopalarao, Sridhar; Hafeza, Eza; Hendler, Peter; Hernandez, Enrique; Kamangar, Ron; Kahn, Rafique A; Kurtovich, Georgina; Lazzareschi, Gerry; Lee, Moon H; Lee, Tracy; Levy, David; Lukoff, Jonathan Y; Lundberg, Cyndie; Madden, Michael P; Ngo, Trongtu L; Nguyen, Ben T; Patel, Nikhilkumar P; Resneck, Jim; Ross, David E; Schwarz, Kathleen M; Selhorst, Charles C; Snyder, Aaron; Umarji, Mohamed I; Vilner, Max; Zer-Chen, Roy; Zingo, Chris

    2004-01-01

    This paper describes Kaiser Permanente's (KP) enterprise-wide medical terminology solution, referred to as our Convergent Medical Terminology (CMT). Initially developed to serve the needs of a regional electronic health record, CMT has evolved into a core KP asset, serving as the common terminology across all applications. CMT serves as the definitive source of concept definitions for the organization, provides a consistent structure and access method to all codes used by the organization, and is KP's language of interoperability, with cross-mappings to regional ancillary systems and administrative billing codes. The core of CMT is comprised of SNOMED CT, laboratory LOINC, and First DataBank drug terminology. These are integrated into a single poly-hierarchically structured knowledge base. Cross map sets provide bi-directional translations between CMT and ancillary applications and administrative billing codes. Context sets provide subsets of CMT for use in specific contexts. Our experience with CMT has lead us to conclude that a successful terminology solution requires that: (1) usability considerations are an organizational priority; (2) "interface" terminology is differentiated from "reference" terminology; (3) it be easy for clinicians to find the concepts they need; (4) the immediate value of coded data be apparent to clinician user; (5) there be a well defined approach to terminology extensions. Over the past several years, there has been substantial progress made in the domain coverage and standardization of medical terminology. KP has learned to exploit that terminology in ways that are clinician-acceptable and that provide powerful options for data analysis and reporting.

  11. 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

  12. 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

  13. Latest extension of the Laujar fault in a convergence setting (Sierra Nevada, Betic Cordillera)

    NASA Astrophysics Data System (ADS)

    Martínez-Martos, Manuel; Galindo-Zaldívar, Jesus; Sanz de Galdeano, Carlos; García-Tortosa, Francisco Juan; Martínez-Moreno, Francisco José; Ruano, Patricia; González-Castillo, Lourdes; Azañón, José Miguel

    2017-02-01

    The present-day relief of the Betic Cordillera formed since the Late Miocene through the regional N-S to NW-SE Africa-Eurasia convergence that developed large folds. The Laujar Fault Zone is a south-dipping E-W oriented structure located at the northern boundary of the Alpujarran Corridor Neogene intramontane basin, which separates Sierra Nevada and Sierra de Gador antiforms, in the Internal Zones of the Betic Cordillera. The fault zone acted in a first stage as a dextral strike-slip fault. Currently it moves as a normal fault evidenced by striated calcretes, also in agreement with regional continuous GPS (CGPS) data that support the hypothesis of an active N-S extension in the fault area. In order to analyse the deep geometry of the Laujar Fault Zone, we combined several geophysical techniques (gravity, magnetic, electric resistivity tomography and audio-magnetotelluric data) with field geological observations. Fault surfaces seem to join at a southward-dipping shallow detachment level, including faults covered by the sedimentary infill. The fault zone was developed in a previously weakened area by wrench faults parallel to the Alpujarran Corridor. The recent normal activity of this fault zone may be a consequence of a change in the Africa-Eurasia convergence orientation, which implies a decrease in the N-S compression component. This structure along the southern limb of Sierra Nevada antiform evidences the gravitational collapse of previously thickened crust in a regional compressional context simultaneous to metamorphic core uplift.

  14. Canonical forms of unconditionally convergent multipliers☆

    PubMed Central

    Stoeva, D.T.; Balazs, P.

    2013-01-01

    Multipliers are operators that combine (frame-like) analysis, a multiplication with a fixed sequence, called the symbol, and synthesis. They are very interesting mathematical objects that also have a lot of applications for example in acoustical signal processing. It is known that bounded symbols and Bessel sequences guarantee unconditional convergence. In this paper we investigate necessary and equivalent conditions for the unconditional convergence of multipliers. In particular, we show that, under mild conditions, unconditionally convergent multipliers can be transformed by shifting weights between symbol and sequence, into multipliers with symbol (1) and Bessel sequences (called multipliers in canonical form). PMID:23564973

  15. Canonical forms of unconditionally convergent multipliers.

    PubMed

    Stoeva, D T; Balazs, P

    2013-03-01

    Multipliers are operators that combine (frame-like) analysis, a multiplication with a fixed sequence, called the symbol, and synthesis. They are very interesting mathematical objects that also have a lot of applications for example in acoustical signal processing. It is known that bounded symbols and Bessel sequences guarantee unconditional convergence. In this paper we investigate necessary and equivalent conditions for the unconditional convergence of multipliers. In particular, we show that, under mild conditions, unconditionally convergent multipliers can be transformed by shifting weights between symbol and sequence, into multipliers with symbol (1) and Bessel sequences (called multipliers in canonical form).

  16. 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.

  17. 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

  18. Svecofennian orogeny in an evolving convergent margin setting

    NASA Astrophysics Data System (ADS)

    Korja, Annakaisa

    2015-04-01

    The dominant tectonic mode changes from extension to convergence at around 1.9 Ga in Fennoscandian. The lithological record suggests short lived subduction-related magmatic events followed by deformation and low-pressure high temperature metamorphism. At around 1.8 Ga the subduction systems seem to have stabilized implying continuous supply of oceanic lithosphere. The evolution of the convergent margin is recorded in the rock record and crustal architecture of the long lived Svecofennian orogeny (1.9-1.7 Ga). A closer look at the internal structure of the Svecofennian orogen reveals distinct regional differences. The northern and central parts of the Svecofennian orogen that have been formed during the initial accretionary phase - or compilation of the nucleus - have a thick three-layer crust and with thick mafic lower crust (10-30 km) and block-like internal architecture. Reflection profiles (FIRE1-3) image listric structures flattening on crustal scale décollement zones at the upper-middle crust and middle-upper crust boundaries. The crustal architecture together with large volumes of exposed granitoid rocks suggests spreading of the orogen and the development of an orogenic plateau west of the continental convergence boundary. The architecture is reminiscent of a large hot orogen. Within the western and southwestern part of the Svecofennian orogen (BABEL B, 1, 2, 3&4), which have been envisioned to have formed during continuous subduction phase, the crust is thinner (45-50 km) and it is hosting crustal blocks having one to two crustal layers. Layering is poorly developed in crustal blocks that are found S-SW of NE-dipping mantle reflections previously interpreted as paleo-subduction zones. Within these blocks, the crustal scale reflective structures dip NE (prowedge) or form pop-up wedges (uplifted plug) above the paleo-subduction zones. Crustal blocks with well-developed two-layer crust are located NE of the paleo-subduction zone. The architecture can be

  19. 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.

  20. Morphological and molecular convergences in mammalian phylogenetics.

    PubMed

    Zou, Zhengting; Zhang, Jianzhi

    2016-09-02

    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.

  1. 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.

  2. 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.

  3. Cultivate technology convergence for product innovation.

    PubMed

    Wilkinson, J Malcolm

    2006-04-01

    Technologies from diverse scientific disciplines are being combined to drive innovation in medical devices. How technology convergence and innovation could be further stimulated is explored here using developments in imaging and point-of-care devices as examples.

  4. Convergence results for elliptic quasivariational inequalities

    NASA Astrophysics Data System (ADS)

    Sofonea, Mircea; Benraouda, Ahlem

    2017-02-01

    In this paper, we state and prove various convergence results for a general class of elliptic quasivariational inequalities with constraints. Thus, we prove the convergence of the solution of a class of penalized problems to the solution of the original inequality, as the penalty parameter converges to zero. We also prove a continuous dependence result of the solution with respect the convex set of constraints. Then, we consider a mathematical model which describes the equilibrium of an elastic rod attached to a nonlinear spring. We derive the variational formulation of the model which is in a form of an elliptic quasivariational inequality for the displacement field. We prove the unique weak solvability of the model, and then we state and prove two convergence results and provide their corresponding mechanical interpretation.

  5. Convergence of Attitudes among College Students

    ERIC Educational Resources Information Center

    Whatley, Alice E.; Appel, Victor H.

    1973-01-01

    Attempts to determine whether the intersex convergence phenomenon could be applicable to the measured attitudes of collegiate samples. Both sexes seemed to be moving toward a more liberal view on issues related to marriage and the family. (Author)

  6. 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

  7. 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.

  8. 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

  9. [Convergence in health: dream or reality?].

    PubMed

    Comín Novella, D

    1997-01-01

    In the last fifty years the distance between the poorest and the richest countries, measured in income per capita, has augmented. Keeping in mind the absence of economic convergence, this paper use the life expectancy data compiled by the World Bank for 125 countries to examine whether their health levels have converged in the period 1960-1992. In order to answer this question we apply the concepts of beta and sigma convergence and the evolution of the distribution developed in the economic literature. The most relevant results that arise from the analysis are that 1) there is convergence in the health levels in the world during the period 1960-89, 2) the existence of convergence is not sensible to the measure used but it is to the variable used to proxy the health level, 3) the speed of convergence fell down from the eighties, and 4) the African countries reduced the distance from their health level to the levels of the rest of the world but, within Africa, the differences increased along 1960-92. These evidences suggest a nonlinear relation between health and income per capita.

  10. Auto convergence for stereoscopic 3D cameras

    NASA Astrophysics Data System (ADS)

    Zhang, Buyue; Kothandaraman, Sreenivas; Batur, Aziz Umit

    2012-03-01

    Viewing comfort is an important concern for 3-D capable consumer electronics such as 3-D cameras and TVs. Consumer generated content is typically viewed at a close distance which makes the vergence-accommodation conflict particularly pronounced, causing discomfort and eye fatigue. In this paper, we present a Stereo Auto Convergence (SAC) algorithm for consumer 3-D cameras that reduces the vergence-accommodation conflict on the 3-D display by adjusting the depth of the scene automatically. Our algorithm processes stereo video in realtime and shifts each stereo frame horizontally by an appropriate amount to converge on the chosen object in that frame. The algorithm starts by estimating disparities between the left and right image pairs using correlations of the vertical projections of the image data. The estimated disparities are then analyzed by the algorithm to select a point of convergence. The current and target disparities of the chosen convergence point determines how much horizontal shift is needed. A disparity safety check is then performed to determine whether or not the maximum and minimum disparity limits would be exceeded after auto convergence. If the limits would be exceeded, further adjustments are made to satisfy the safety limits. Finally, desired convergence is achieved by shifting the left and the right frames accordingly. Our algorithm runs real-time at 30 fps on a TI OMAP4 processor. It is tested using an OMAP4 embedded prototype stereo 3-D camera. It significantly improves 3-D viewing comfort.

  11. Effect of genetic convergence on phylogenetic inference.

    PubMed

    Christin, Pascal-Antoine; Besnard, Guillaume; Edwards, Erika J; Salamin, Nicolas

    2012-03-01

    Phylogenetic reconstructions are a major component of many studies in evolutionary biology, but their accuracy can be reduced under certain conditions. Recent studies showed that the convergent evolution of some phenotypes resulted from recurrent amino acid substitutions in genes belonging to distant lineages. It has been suggested that these convergent substitutions could bias phylogenetic reconstruction toward grouping convergent phenotypes together, but such an effect has never been appropriately tested. We used computer simulations to determine the effect of convergent substitutions on the accuracy of phylogenetic inference. We show that, in some realistic conditions, even a relatively small proportion of convergent codons can strongly bias phylogenetic reconstruction, especially when amino acid sequences are used as characters. The strength of this bias does not depend on the reconstruction method but varies as a function of how much divergence had occurred among the lineages prior to any episodes of convergent substitutions. While the occurrence of this bias is difficult to predict, the risk of spurious groupings is strongly decreased by considering only 3rd codon positions, which are less subject to selection, as long as saturation problems are not present. Therefore, we recommend that, whenever possible, topologies obtained with amino acid sequences and 3rd codon positions be compared to identify potential phylogenetic biases and avoid evolutionarily misleading conclusions. Copyright © 2011 Elsevier Inc. All rights reserved.

  12. Coeval emplacement and orogen-parallel transport of gold in oblique convergent orogens

    NASA Astrophysics Data System (ADS)

    Upton, Phaedra; Craw, Dave

    2016-12-01

    Varying amounts of gold mineralisation is occurring in all young and active collisional mountain belts. Concurrently, these syn-orogenic hydrothermal deposits are being eroded and transported to form placer deposits. Local extension occurs in convergent orogens, especially oblique orogens, and facilitates emplacement of syn-orogenic gold-bearing deposits with or without associated magmatism. Numerical modelling has shown that extension results from directional variations in movement rates along the rock transport trajectory during convergence, and is most pronounced for highly oblique convergence with strong crustal rheology. On-going uplift during orogenesis exposes gold deposits to erosion, transport, and localised placer concentration. Drainage patterns in variably oblique convergent orogenic belts typically have an orogen-parallel or sub-parallel component; the details of which varies with convergence obliquity and the vagaries of underlying geological controls. This leads to lateral transport of eroded syn-orogenic gold on a range of scales, up to > 100 km. The presence of inherited crustal blocks with contrasting rheology in oblique orogenic collision zones can cause perturbations in drainage patterns, but numerical modelling suggests that orogen-parallel drainage is still a persistent and robust feature. The presence of an inherited block of weak crust enhances the orogen-parallel drainage by imposition of localised subsidence zones elongated along a plate boundary. Evolution and reorientation of orogen-parallel drainage can sever links between gold placer deposits and their syn-orogenic sources. Many of these modelled features of syn-orogenic gold emplacement and varying amounts of orogen-parallel detrital gold transport can be recognised in the Miocene to Recent New Zealand oblique convergent orogen. These processes contribute little gold to major placer goldfields, which require more long-term recycling and placer gold concentration. Most eroded syn

  13. 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

  14. 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.

  15. Possibilities for global governance of converging technologies

    NASA Astrophysics Data System (ADS)

    Roco, Mihail C.

    2008-01-01

    The convergence of nanotechnology, modern biology, the digital revolution and cognitive sciences will bring about tremendous improvements in transformative tools, generate new products and services, enable opportunities to meet and enhance human potential and social achievements, and in time reshape societal relationships. This paper focuses on the progress made in governance of such converging, emerging technologies and suggests possibilities for a global approach. Specifically, this paper suggests creating a multidisciplinary forum or a consultative coordinating group with members from various countries to address globally governance of converging, emerging technologies. The proposed framework for governance of converging technologies calls for four key functions: supporting the transformative impact of the new technologies; advancing responsible development that includes health, safety and ethical concerns; encouraging national and global partnerships; and establishing commitments to long-term planning and investments centered on human development. Principles of good governance guiding these functions include participation of all those who are forging or affected by the new technologies, transparency of governance strategies, responsibility of each participating stakeholder, and effective strategic planning. Introduction and management of converging technologies must be done with respect for immediate concerns, such as privacy, access to medical advancements, and potential human health effects. At the same time, introduction and management should also be done with respect for longer-term concerns, such as preserving human integrity, dignity and welfare. The suggested governance functions apply to four levels of governance: (a) adapting existing regulations and organizations; (b) establishing new programs, regulations and organizations specifically to handle converging technologies; (c) building capacity for addressing these issues into national policies and

  16. 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. © 2013 John Wiley & Sons Ltd.

  17. Advancing Understanding of Earthquakes by Drilling an Eroding Convergent Margin

    NASA Astrophysics Data System (ADS)

    von Huene, R.; Vannucchi, P.; Ranero, C. R.

    2010-12-01

    A program of IODP with great societal relevance is sampling and instrumenting the seismogenic zone. The zone generates great earthquakes that trigger tsunamis, and submarine slides thereby endangering coastal communities containing over sixty percent of the earth’s population. To asses and mitigate this endangerment it is urgent to advance understanding of fault dynamics that allows more timely anticipation of hazardous seismicity. Seismogenesis on accreting and eroding convergent plate boundaries apparently differ because of dissimilar materials along the interplate fault. As the history of instrumentally recorded earthquakes expands the difference becomes clearer. The more homogeneous clay, silt and sand subducted at accreting margins is associated with great earthquakes (M 9) whereas the fragmented upper plate rock that can dominate subducted material along an eroding margin plate interface is associated with many tsunamigenic earthquakes (Bilek, 2010). Few areas have been identified where the seismogenic zone can be reached with scientific drilling. In IODP accreting margins are studied on the NanTroSeize drill transect off Japan where the ultimate drilling of the seismogenic interface may occur by the end of IODP. The eroding Costa Rica margin will be studied in CRISP where a drill program will begin in 2011. The Costa Rican geophysical site survey will be complete with acquisition and processing of 3D seismic data in 2011 but the entire drilling will not be accomplished in IODP. It is appropriate that the accreting margin study be accomplished soon considering the indications of a pending great earthquake that will affect a country that has devoted enormous resources to IODP. However, understanding the erosional end-member is scientifically as important to an understanding of fault mechanics. Transoceanic tsunamis affect the entire Pacific rim where most subduction zones are eroding margins. The Costa Rican subduction zone is less complex operationally and

  18. Dynamics and energetics of the South Pacific Convergence Zone during FGGE SOP-1 and South Pacific Convergence Zone and global-scale

    NASA Technical Reports Server (NTRS)

    Vincent, Dayton G.; Robertson, Franklin R.; Huang, Huo-Jin; Kann, Deirdre M.; Hurrell, James W.; Pedigo, Catherine B.

    1989-01-01

    Significant accomplishments (papers published, conference presentations, and education degrees) are presented. The focus of the current research is outlined. Plans for the coming year are discussed briefly.

  19. 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.

  20. 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

  1. Experimental and numerical analysis of convergent nozzlex

    NASA Astrophysics Data System (ADS)

    Srinivas, G.; Rakham, Bhupal

    2017-05-01

    In this paper the main focus was given to convergent nozzle where both the experimental and numerical calculations were carried out with the support of standardized literature. In the recent years the field of air breathing and non-air breathing engine developments significantly increase its performance. To enhance the performance of both the type of engines the nozzle is the one of the component which will play a vital role, especially selecting the type of nozzle depends upon the vehicle speed requirement and aerodynamic behavior at most important in the field of propulsion. The convergent nozzle flow experimental analysis done using scaled apparatus and the similar setup was arranged artificially in the ANSYS software for doing the flow analysis across the convergent nozzle. The consistent calculation analysis are done based on the public literature survey to validate the experimental and numerical simulation results of convergent nozzle. Using these two experimental and numerical simulation approaches the best fit results will bring up to meet the design requirements. However the comparison also made to meet the reliability of the work on design criteria of convergent nozzle which can entrench in the field of propulsion applications.

  2. 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.

  3. Uplift of Zagros Mountains slows plate convergence

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2013-05-01

    Research has indicated that mountain ranges can slow down the convergence between two tectonic plates on timescales as short as a few million years, as the growing mountains provide enough tectonic force to impact plate motions. Focusing on the convergence of the Arabian and Eurasian plates at the Zagros mountain range, which runs across Iran and Iraq, Austermann and Iaffaldano reconstructed the relative motion of the plates using published paleomagnetic data covering the past 13 million years, as well as current geodetic measurements. They show that the convergence of the two plates has decreased by about 30% over the past 5 million years. Looking at the geological record to infer past topography and using a computer model of the mantle-lithosphere system, the authors examined whether the recent uplift across the Zagros Mountains could have caused the observed slowdown. They also considered several other geological events that might have influenced the convergence rate, but the authors were able to rule those out as dominant controls. The authors conclude that the uplift across the Zagros Mountains in the past 5 million years did indeed play a key role in slowing down the convergence between the Eurasian and Arabian plates. (Tectonics, doi:10.1002/tect.20027, 2013)

  4. Providing plastic zone extrusion

    DOEpatents

    Manchiraju, Venkata Kiran; Feng, Zhili; David, Stan A.; Yu, Zhenzhen

    2017-04-11

    Plastic zone extrusion may be provided. First, a compressor may generate frictional heat in stock to place the stock in a plastic zone of the stock. Then, a conveyer may receive the stock in its plastic zone from the compressor and transport the stock in its plastic zone from the compressor. Next, a die may receive the stock in its plastic zone from the conveyer and extrude the stock to form a wire.

  5. Landing Zone and Drop Zone Criteria

    DTIC Science & Technology

    2017-05-01

    Report Approved for public release; distribution is unlimited. Prepared for Army Terrestrial Environmental Modeling and Intelligence System (ARTEMIS...for the Army Terrestrial Environmental Model - ing and Intelligence System (ARTEMIS) program under Work Item 9K3D08 for the Geospatial Remote...Compatible Use Zone APZ Accident Potential Zone APZ-LZ Accident Potential Zone–Landing Zone ARTEMIS Army Terrestrial Environmental Modeling and

  6. 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.

  7. Convergence studies in meshfree peridynamic simulations

    SciTech Connect

    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 accurate 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.

  8. Convergence Properties of KKR Green Function Methods

    NASA Astrophysics Data System (ADS)

    Moghadam, N. Y.; Stocks, G. M.; Zhang, X.-G.; Nicholson, D. M. C.; Shelton, W. A.; Wang, Yang; Faulkner, J. S.

    1998-03-01

    Most multiple scattering theory (MST) electronic structure methods (e.g. KKR, KKR-CPA, impurity Greens function, O[N] LSMS method(Yang Wang et al. Phys. Rev. Letters 75), 2867,(1995)) make use of a expression for the single particle Green function that is based on a single center expansion(J. S. Faulkner and G. M. Stocks, Phys. Rev. B 21),3222, (1980). Because the electronic structure is rapidly convergent in angular momentum, l, the multiple scattering equations are typically truncated at l_max <= 4. Using the LSMS method as illustrative we show that the Green function and, therefore, the cell densities of states and charge density converge more slowly requiring l_max ~ 8 arrow 12 even for muffin-tin potentails. We discuss the consequences of this for previous MST based work, and show that this slow convergence can be trivially accommodated within the LSMS method.

  9. Convergence studies in meshfree peridynamic simulations

    SciTech Connect

    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 accurate 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.

  10. Theoretical convergence guarantees for cooperative coevolutionary algorithms.

    PubMed

    Panait, Liviu

    2010-01-01

    Cooperative coevolutionary algorithms have the potential to significantly speed up the search process by dividing the space into parts that can each be conquered separately. However, recent research presented theoretical and empirical arguments that these algorithms tend to converge to suboptimal solutions in the search space, and are thus not fit for optimization tasks. This paper details an extended formal model for cooperative coevolutionary algorithms, and uses it to explore possible reasons these algorithms converge to optimal or suboptimal solutions. We demonstrate that, under specific conditions, this theoretical model will converge to the globally optimal solution. The proofs provide the underlying theoretical foundation for a better application of cooperative coevolutionary algorithms. We demonstrate the practical advantages of applying ideas from this theoretical work to a simple problem domain.

  11. On phonetic convergence during conversational interaction.

    PubMed

    Pardo, Jennifer S

    2006-04-01

    Following research that found imitation in single-word shadowing, this study examines the degree to which interacting talkers increase similarity in phonetic repertoire during conversational interaction. Between-talker repetitions of the same lexical items produced in a conversational task were examined for phonetic convergence by asking a separate set of listeners to detect similarity in pronunciation across items in a perceptual task. In general, a listener judged a repeated item spoken by one talker in the task to be more similar to a sample production spoken by the talker's partner than corresponding pre- and postinteraction utterances. Both the role of a participant in the task and the sex of the pair of talkers affected the degree of convergence. These results suggest that talkers in conversational settings are susceptible to phonetic convergence, which can mark nonlinguistic functions in social discourse and can form the basis for phenomena such as accent change and dialect formation.

  12. Convergence studies in meshfree peridynamic simulations

    DOE PAGES

    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. Science and technology convergence: with emphasis for nanotechnology-inspired convergence

    NASA Astrophysics Data System (ADS)

    Bainbridge, William S.; Roco, Mihail C.

    2016-07-01

    Convergence offers a new universe of discovery, innovation, and application opportunities through specific theories, principles, and methods to be implemented in research, education, production, and other societal activities. Using a holistic approach with shared goals, convergence seeks to transcend existing human limitations to achieve improved conditions for work, learning, aging, physical, and cognitive wellness. This paper outlines ten key theories that offer complementary perspectives on this complex dynamic. Principles and methods are proposed to facilitate and enhance science and technology convergence. Several convergence success stories in the first part of the 21st century—including nanotechnology and other emerging technologies—are discussed in parallel with case studies focused on the future. The formulation of relevant theories, principles, and methods aims at establishing the convergence science.

  14. Relict basin closure during initial suturing accommodates continental convergence with minimal crustal shortening or reduction in convergence rates

    NASA Astrophysics Data System (ADS)

    Cowgill, E.; Forte, A. M.; Niemi, N. A.; Mumladze, T.; Elashvili, M.; Javakhishvili, Z.; Trexler, C.

    2013-12-01

    In both the Indo-Eurasian and Arabia-Eurasian (Ab-Eu) collisions, documented post-collisional crustal shortening is hundreds to thousands of kilometers less than the amount of plate convergence determined from independent plate reconstructions. We propose that relict-basin closure may help resolve such shortening deficits, based on a synthesis of the late Cenozoic evolution of the Greater Caucasus Mountains in the Ab-Eu collision zone. This range is located ~700 km north of the Bitlis suture and defines the northern margin of the Ab-Eu collision zone between the Black and Caspian seas. The range formed from late Cenozoic tectonic inversion of the Greater Caucasus basin, a relict Mesozoic back-arc basin that originally formed in the Jurassic during north-dipping subduction of Neo-Tethys and rifting of the Lesser Caucasus arc from the southern margin of Eurasia (i.e., Scythia). This basin was originally wide enough to prevent sedimentary exchange of turbidites across it, as shown by provenance studies using U-Pb detrital zircon geochronology. The floor of the relict basin now forms a NE-dipping slab that extends to at least 158 km depth beneath the central and eastern Greater Caucasus, as revealed by a new earthquake compilation. Miocene to Quaternary felsic volcanic and intrusive rocks in the Greater Caucasus have geochemical signatures and eruptive centers similar to those in continental margin arcs. Based on these data we propose the Ab-Eu collision occurred in two stages. The first (soft collision) started when Arabia collided with Eurasia, closed the Bitlis suture, and caused the locus of convergence to jump ~700 km north to the Greater Caucasus basin. Initial exhumation of the Greater Caucasus started at ~25-30 Ma and continued until ~ 5 Ma at rates of a few °C/Ma during north-directed subduction of the back-arc basin, with little structural evidence of this crustal shortening preserved. The second phase (hard collision) started at ~ 5 Ma, when the relict

  15. Deterministic convergence in iterative phase shifting

    SciTech Connect

    Luna, Esteban; Salas, Luis; Sohn, Erika; Ruiz, Elfego; Nunez, Juan M.; Herrera, Joel

    2009-03-10

    Previous implementations of the iterative phase shifting method, in which the phase of a test object is computed from measurements using a phase shifting interferometer with unknown positions of the reference, do not provide an accurate way of knowing when convergence has been attained. We present a new approach to this method that allows us to deterministically identify convergence. The method is tested with a home-built Fizeau interferometer that measures optical surfaces polished to {lambda}/100 using the Hydra tool. The intrinsic quality of the measurements is better than 0.5 nm. Other possible applications for this technique include fringe projection or any problem where phase shifting is involved.

  16. Experience and convergence in spiritual direction.

    PubMed

    Evans, Jean

    2015-02-01

    The practice of spiritual direction concerns the human experience of God. As praxis, spiritual direction has a long tradition in Western Christianity. It is a process rooted in spirituality with theology as its foundation. This paper explores the convergences between aspects of philosophy (contemplative awareness), psychology (Rogerian client-centered approach) and phenomenology. There are significant points of convergence between phenomenology and spiritual direction: first, in Ignatius of Loyola's phenomenological approach to his religious experience; second, in the appropriation by spiritual directors of concepts of epochē and empathy; third, in the process of "unpacking" religious experience within a spiritual direction interview.

  17. Antibiotics from microbes: converging to kill.

    PubMed

    Fischbach, Michael A

    2009-10-01

    As genetically encoded small molecules, antibiotics are phenotypes that have resulted from mutation and natural selection. Advances in genetics, biochemistry, and bioinformatics have connected hundreds of antibiotics to the gene clusters that encode them, allowing these molecules to be analyzed using the tools of evolutionary biology. This review surveys examples of convergent evolution from microbially produced antibiotics, including the convergence of distinct gene clusters on similar phenotypes and the merger of distinct gene clusters into a single functional unit. Examining antibiotics through an evolutionary lens highlights the versatility of biosynthetic pathways, reveals lessons for combating antibiotic resistance, and provides an entry point for studying the natural roles of these natural products.

  18. 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.

  19. Metamorphism in Plate Boundary Zones

    NASA Astrophysics Data System (ADS)

    Brown, M.

    2005-12-01

    Accretionary orogenic systems (AOS) form at sites of subduction of oceanic lithosphere; these systems dominate during supercontinent break-up and dispersal. Collisional orogenic systems (COS) form where ocean basins close and subduction ultimately ceases; these systems dominate during crustal aggregation and assembly of supercontinents. It follows that COS may be superimposed on AOS, although AOS may exist for 100s Ma without terminal collision. AOS are of two types, extensional-contractional AOS in dominantly extensional arc systems, and terrane-dominated AOS in which accretion of allochthonous elements occurs during oblique convergence. On modern Earth, regional metamorphism occurs in plate boundary zones. Blueschists are created in the subduction zone and ultra-high pressure metamorphic (UHPM) rocks are created in collision zones due to deep subduction of continental lithosphere; granulites are created deep under continental and oceanic plateaus and in arcs and collision zones [high-pressure (HP) granulites, ultra-high temperature (UHT) granulites]. In extensional-contractional AOS, basement generally is not exposed, primitive volcanic rocks occur through the history, rift basins step oceanward with time, and a well-defined arc generally is absent. LP-HT metamorphism is dominant, with looping, CW or CCW P-T-t paths and peak metamorphic mineral growth syn-to-late in relation to tectonic fabrics. UHT and HP granulites are absent, and although rare, blueschists may occur early, but UHPM is not recorded. Short-lived contractional phases of orogenesis probably relate to interruptions in the continuity of subduction caused by features on the ocean plate, particularly plateaus. Extensive granite (s.l.) magmatism accompanies metamorphism. Examples include the Lachlan Orogen, Australia, the Acadian Orogen, NE USA and Maritime Canada, and the Proterozoic orogens of the SW USA. At plate boundaries, oblique convergence is partitioned into two components, one directed more

  20. 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…

  1. Sweet! Generation "D" Takes on Media Convergence.

    ERIC Educational Resources Information Center

    Tarpenning, David; Schaub, Laura

    2002-01-01

    Notes that professional journalists continually emphasize the need for developing skills for all delivery systems. Proposes that students interested in journalism should learn about technology and develop projects without the guidance of a teacher or advisor. Describes students' experience with media convergence in a summer journalism workshop.…

  2. [Conservative and surgical treatment of convergence excess].

    PubMed

    Ehrt, O

    2016-07-01

    Convergence excess is a common finding especially in pediatric strabismus. A detailed diagnostic approach has to start after full correction of any hyperopia measured in cycloplegia. It includes measurements of manifest and latent deviation at near and distance fixation, near deviation after relaxation of accommodation with addition of +3 dpt, assessment of binocular function with and without +3 dpt as well as the accommodation range. This diagnostic approach is important for the classification into three types of convergence excess, which require different therapeutic approaches: 1) hypo-accommodative convergence excess is treated with permanent bifocal glasses, 2) norm-accommodative patients should be treated with bifocals which can be weaned over years, especially in patients with good stereopsis and 3) non-accommodative convergence excess and patients with large distance deviations need a surgical approach. The most effective operations include those which reduce the muscle torque, e. g. bimedial Faden operations or Y‑splitting of the medial rectus muscles.

  3. Convergence of some asynchronous nonlinear multisplitting methods

    NASA Astrophysics Data System (ADS)

    Szyld, Daniel B.; Xu, Jian-Jun

    2000-09-01

    Frommer's nonlinear multisplitting methods for solving nonlinear systems of equations are extended to the asynchronous setting. Block methods are extended to include overlap as well. Several specific cases are discussed. Sufficient conditions to guarantee their local convergence are given. A numerical example is presented illustrating the performance of the new approach.

  4. Convergence of coupled cluster perturbation theory

    NASA Astrophysics Data System (ADS)

    Eriksen, Janus J.; Kristensen, Kasper; Matthews, Devin A.; Jørgensen, Poul; Olsen, Jeppe

    2016-12-01

    The convergence of a recently proposed coupled cluster (CC) family of perturbation series [J. J. Eriksen et al., J. Chem. Phys. 140, 064108 (2014)], in which the energetic difference between two CC models—a low-level parent and a high-level target model—is expanded in orders of the Møller-Plesset (MP) fluctuation potential, is investigated for four prototypical closed-shell systems (Ne, singlet CH2, distorted HF, and F-) in standard and augmented basis sets. In these investigations, energy corrections of the various series have been calculated to high orders and their convergence radii have been determined by probing for possible front- and back-door intruder states, the existence of which would make the series divergent. In summary, we conclude how it is primarily the choice of the target state, and not the choice of the parent state, which ultimately governs the convergence behavior of a given series. For example, restricting the target state to, say, triple or quadruple excitations might remove intruders present in series which target the full configuration interaction limit, such as the standard MP series. Furthermore, we find that whereas a CC perturbation series might converge within standard correlation consistent basis sets, it may start to diverge whenever these become augmented by diffuse functions, similar to the MP case. However, unlike for the MP case, such potential divergences are not found to invalidate the practical use of the low-order corrections of the CC perturbation series.

  5. 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

  6. Convergent evolution in plant specialized metabolism.

    PubMed

    Pichersky, Eran; Lewinsohn, Efraim

    2011-01-01

    Plants synthesize a multitude of compounds that contribute to adaptation to their ecological niches. Such compounds serve as attractants of other living organisms beneficial to the plants or as defense against other biotic as well as abiotic agents. Selection for increased fitness, a never-ending process, has resulted in each plant lineage synthesizing a distinct set of specialized metabolites appropriate for its environment. The total number of specialized metabolites found in the plant kingdom far exceeds the capacity of any one plant genome to encode the necessary enzymes, and just as a plant lineage acquires the ability to make new specialized compounds during evolution, it also loses the ability to make others. Although the ability of plants to make novel, specialized metabolites continues to evolve, there are also many examples in which different plants have independently evolved the ability to make compounds already present in other plant lineages or to make different compounds that fulfill the same role-both are examples of convergent evolution. Here, we discuss many examples of convergent evolution in specialized metabolism. There are many genetic and biochemical mechanisms that can give rise to convergent evolution, and we conclude that, overall, convergent evolution in plant specialized metabolism is surprisingly common.

  7. 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…

  8. 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…

  9. 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…

  10. 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,…

  11. Bandlimited image extrapolation with faster convergence.

    PubMed

    Cahana, D; Stark, H

    1981-08-15

    The Gerchberg-Papoulis (GP) algorithm has been widely discussed in the literature in connection with band-limited or space-limited image extrapolation. Despite its seemingly superior noise-resistant properties over earlier superresolution schemes, the GP algorithm generally exhibits very slow convergence thereby making the choice of starting point critical. We discuss how additional a priori information, such as the low-pass projection of the image (LPI), can be incorporated in the algorithm to decrease the initial error between the starting point of the recursion and the true signal. We also investigate how convergence rates might be improved by (1) using the LPI in each iteration to achieve a double per cycle correction, and (2) applying adaptive thresholding. Somewhat surprisingly, it was found that using the LPI had only a minor effect on the rate of convergence. On the other hand, when combined with adaptive thresholding the use of the LPI both significantly reduced the starting point error and improved the rate of convergence.

  12. 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…

  13. 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,…

  14. 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…

  15. Converging Oceaniac Internal Waves, Somalia, Africa

    NASA Image and Video Library

    1988-10-03

    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.

  16. The convergence coefficient across political systems.

    PubMed

    Gallego, Maria; 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.

  17. 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…

  18. 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. Copyright © 2010 Elsevier Ltd. All rights reserved.

  19. 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.

  20. 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.

  1. Design and application of three-zone annular filters

    NASA Astrophysics Data System (ADS)

    Liu, Ximin; Liu, Liren; Liu, De'an; Bai, Lihua

    2006-10-01

    We design three-zone annular filters to be applied to optical storage system. The designed filters extend the depth of focus and realize transverse superresolution simultaneously, which will improve the performance of optical storage system greatly. And we propose two feasible schemes to improve imaging resolution of three-dimensional imaging system. One scheme depends on a complex filter formed by cascading of a three-zone phase filter and a three-zone amplitude filter. The complex filter converge the optimized transverse superresolution and the optimized axial superresolution of two different filters onto a single filter. It can improve the three-dimensional imaging performances greatly. Another scheme depends on a single three-zone complex filter. We propose a three-zone complex filter with phase shift 0.8[pi], which presents bigger design margin, better imaging quality and stronger three-dimensional superresolution capability.

  2. Volcanism and aseismic slip in subduction zones

    SciTech Connect

    Acharya, H.

    1981-01-10

    The spatial and temporal relationship of volcanism to the occurrence of large earthquakes and convergent plate motion is examined. The number of volcanic eruptions per year in a convergent zone is found to be linearly related to the aseismic slip component of plate motion. If the aseismic slip rate is low (coupling between converging plates is strong), then the primary manifestation of tectonic activity is the occurrence of large earthquakes with only infrequent volcanic activity. If, however, the aseismic slip rate is high (coupling is weak), then there are few large earthquakes, and volcanism is the principal manifestation of tectonic activity. This model is consistent with the spatial distribution of large earthquakes and active volcanoes in the circum-Pacific area. It is tested by examining the extent of volcanic activity in the rupture zones of the 1952--1973 sequence of earthquakes in the Japan--Kurile Islands area. The number of volcanic euptions along these zones during the interval between large earthquakes is used to compute the aseismic slip rates for these segments, based on the relationship developed in this study. The aseismic slip rates so computed agree with those determined from the earthquake history of the area and rates of plate motion. The agreement suggests that in the interval between large earthquakes, the aseismic plate motion is manifested in a specific number of volcanic eruptions. Therefore in areas with adequate historial data it should be possible to use the model developed in this study to monitor volcanic eruptions for long-term prediction of large earthquakes.

  3. NUMERICAL CONVERGENCE IN SMOOTHED PARTICLE HYDRODYNAMICS

    SciTech Connect

    Zhu, Qirong; Li, Yuexing; Hernquist, Lars

    2015-02-10

    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 N{sub nb} → ∞, where N is the total number of particles, h is the smoothing length, and N{sub nb} 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 N{sub nb} fixed. We demonstrate that if N{sub nb} 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 N{sub nb} is increased systematically as the resolution is improved. Using analytic arguments, we derive an optimal compromise scaling for N{sub nb} by requiring that this source of error balance that present in the smoothing procedure. For typical choices of the smoothing kernel, we find N{sub nb} ∝N {sup 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 {sup 1} {sup +} {sup δ}), where δ ≈ 0.5, with a weak dependence on the form of the smoothing kernel.

  4. Multidimensional Convergence in Future 5G Networks

    NASA Astrophysics Data System (ADS)

    Ruffini, Marco

    2017-02-01

    Future 5G services are characterised by unprecedented need for high rate, ubiquitous availability, ultra-low latency and high reliability. The fragmented network view that is widespread in current networks will not stand the challenge posed by next generations of users. A new vision is required, and this paper provides an insight on how network convergence and application-centric approaches will play a leading role towards enabling the 5G vision. The paper, after expressing the view on the need for an end-to-end approach to network design, brings the reader into a journey on the expected 5G network requirements and outlines some of the work currently carried out by main standardisation bodies. It then proposes the use of the concept of network convergence for providing the overall architectural framework to bring together all the different technologies within a unifying and coherent network ecosystem. The novel interpretation of multi-dimensional convergence we introduce leads us to the exploration of aspects of node consolidation and converged network architectures, delving into details of optical-wireless integration and future convergence of optical data centre and access-metro networks. We then discuss how ownership models enabling network sharing will be instrumental in realising the 5G vision. The paper concludes with final remarks on the role SDN will play in 5G and on the need for new business models that reflect the application-centric view of the network. Finally, we provide some insight on growing research areas in 5G networking.

  5. On the Convergence of Stresses in Fretting Fatigue.

    PubMed

    Pereira, Kyvia; Bordas, Stephane; Tomar, Satyendra; Trobec, Roman; Depolli, Matjaz; Kosec, Gregor; Abdel Wahab, Magd

    2016-07-29

    Fretting is a phenomenon that occurs at the contacts of surfaces that are subjected to oscillatory relative movement of small amplitudes. Depending on service conditions, fretting may significantly reduce the service life of a component due to fretting fatigue. In this regard, the analysis of stresses at contact is of great importance for predicting the lifetime of components. However, due to the complexity of the fretting phenomenon, analytical solutions are available for very selective situations and finite element (FE) analysis has become an attractive tool to evaluate stresses and to study fretting problems. Recent laboratory studies in fretting fatigue suggested the presence of stress singularities in the stick-slip zone. In this paper, we constructed finite element models, with different element sizes, in order to verify the existence of stress singularity under fretting conditions. Based on our results, we did not find any singularity for the considered loading conditions and coefficients of friction. Since no singularity was found, the present paper also provides some comments regarding the convergence rate. Our analyses showed that the convergence rate in stress components depends on coefficient of friction, implying that this rate also depends on the loading condition. It was also observed that errors can be relatively high for cases with a high coefficient of friction, suggesting the importance of mesh refinement in these situations. Although the accuracy of the FE analysis is very important for satisfactory predictions, most of the studies in the literature rarely provide information regarding the level of error in simulations. Thus, some recommendations of mesh sizes for those who wish to perform FE analysis of fretting problems are provided for different levels of accuracy.

  6. On the Convergence of Stresses in Fretting Fatigue

    PubMed Central

    Pereira, Kyvia; Bordas, Stephane; Tomar, Satyendra; Trobec, Roman; Depolli, Matjaz; Kosec, Gregor; Abdel Wahab, Magd

    2016-01-01

    Fretting is a phenomenon that occurs at the contacts of surfaces that are subjected to oscillatory relative movement of small amplitudes. Depending on service conditions, fretting may significantly reduce the service life of a component due to fretting fatigue. In this regard, the analysis of stresses at contact is of great importance for predicting the lifetime of components. However, due to the complexity of the fretting phenomenon, analytical solutions are available for very selective situations and finite element (FE) analysis has become an attractive tool to evaluate stresses and to study fretting problems. Recent laboratory studies in fretting fatigue suggested the presence of stress singularities in the stick-slip zone. In this paper, we constructed finite element models, with different element sizes, in order to verify the existence of stress singularity under fretting conditions. Based on our results, we did not find any singularity for the considered loading conditions and coefficients of friction. Since no singularity was found, the present paper also provides some comments regarding the convergence rate. Our analyses showed that the convergence rate in stress components depends on coefficient of friction, implying that this rate also depends on the loading condition. It was also observed that errors can be relatively high for cases with a high coefficient of friction, suggesting the importance of mesh refinement in these situations. Although the accuracy of the FE analysis is very important for satisfactory predictions, most of the studies in the literature rarely provide information regarding the level of error in simulations. Thus, some recommendations of mesh sizes for those who wish to perform FE analysis of fretting problems are provided for different levels of accuracy. PMID:28773760

  7. Convergence of semantics and emotional expression within the IFG pars orbitalis.

    PubMed

    Belyk, Michel; Brown, Steven; Lim, Jessica; Kotz, Sonja A

    2017-04-08

    Humans communicate through a combination of linguistic and emotional channels, including propositional speech, writing, sign language, music, but also prosodic, facial, and gestural expression. These channels can be interpreted separately or they can be integrated to multimodally convey complex meanings. Neural models of the perception of semantics and emotion include nodes for both functions in the inferior frontal gyrus pars orbitalis (IFGorb). However, it is not known whether this convergence involves a common functional zone or instead specialized subregions that process semantics and emotion separately. To address this, we performed Kernel Density Estimation meta-analyses of published neuroimaging studies of the perception of semantics or emotion that reported activation in the IFGorb. The results demonstrated that the IFGorb contains two zones with distinct functional profiles. A lateral zone, situated immediately ventral to Broca's area, was implicated in both semantics and emotion. Another zone, deep within the ventral frontal operculum, was engaged almost exclusively by studies of emotion. Follow-up analysis using Meta-Analytic Connectivity Modeling demonstrated that both zones were frequently co-activated with a common network of sensory, motor, and limbic structures, although the lateral zone had a greater association with prefrontal cortical areas involved in executive function. The status of the lateral IFGorb as a point of convergence between the networks for processing semantic and emotional content across modalities of communication is intriguing since this structure is preserved across primates with limited semantic abilities. Hence, the IFGorb may have initially evolved to support the comprehension of emotional signals, being later co-opted to support semantic communication in humans by forming new connections with brain regions that formed the human semantic network.

  8. It Takes Two to Tango: The Timing of the India -Eurasia Collision and the Origin of the Super-Fast India-Eurasia Convergence Rates.

    NASA Astrophysics Data System (ADS)

    Jagoutz, O. E.; Royden, L.; Holt, A.; Becker, T. W.

    2014-12-01

    The pre-collisional convergence history of India and Eurasia displays highly variable convergence rates, including anomalously high rates of ~120-180 mm/a between ~70 and 50 Ma. As the subduction zone forces play a key role in driving plate tectonic understanding the subduction zone configuration in the Tethyan ocean is essential to understand the observed variation in convergence rates. It has long been established that two subduction systems existed between India and Eurasia since the break up of Gondwana: An intra oceanic subduction system (in the equatorial part of the ocean) and a continental subduction system on the southern Eurasian margin. As relicts of both subduction systems are now incorporated in the Himalayan and Tibetan collision zone, reconstruction of the pre-collisional geometry and the timing of the collision between India and the different subduction system is challenging. However, in recent years it has become increasingly more obvious that India likely originally collided with the intra oceanic subduction system first and only subsequently with the Eurasia margin (e.g., Aitchison et al., 2007 JGR, Bouilhol et al, 2013 EPSL). In this presentation, we summarize the geological evidence that allows us to reconstruct the configuration of the subduction system in the Tehtyan ocean and the timing of the India-Arc and India Eurasia collision. These constraints guide 3D subduction zone models that are used to evaluate the role of two subduction zones for the variable India-Eurasia Convergence rates. Model convergence rates of up to 140 mm/yr are in agreement with observed rates from 120 Ma to present, except for a short-lived spike in rate at ~62-66 Ma, which may be attributed to the Reunion plume. The end of anomalously fast convergence is due to the entry of buoyant Indian continental lithosphere into this intra-oceanic subduction zone at 50 Ma and not to the collision of India with Eurasia, which had little effect before 40 Ma.

  9. 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

  10. The Interaction of Strike-Slip and Convergent Deformation in the Alpine Belt of New Zealand

    NASA Astrophysics Data System (ADS)

    Houseman, G. A.; Billen, M. I.

    2002-12-01

    The South Island of New Zealand provides a type example of transpressional deformation in the continental environment. Oblique convergence between the Pacific and Australian plates is absorbed partly by strike-slip motion parallel to the Alpine Fault and partly by horizontal convergence perpendicular to the fault. The distribution of strike-parallel deformation observed geodetically is consistent with the theoretical deformation of a thin viscous sheet (England et al., J. Geophys. Res., 90, 3551-3557, 1985). In this model the displacement rate, and hence the strain-rate, decays exponentially away from a strike-slip boundary. The observed exponential length scale is consistent with an along-strike length of the zone of about 450 km, and a stress vs strain-rate exponent of the non-linear viscous constitutive law, of about n = 3. This strike-parallel deformation field implies an effective viscosity distribution across the orogen in which viscosity increases exponentially with distance from the boundary (the Alpine Fault). The length scale of this exponential increase is about 60 km, but the total width of the weak zone depends on the background viscosity level. Weakening of the lithosphere in the region adjacent to the boundary has a key influence on the progress of convergent deformation in the orthogonal direction. Firstly, the weakening localizes the convergent deformation. Secondly, and perhaps more significantly, it promotes the local rate of development of gravitational instability in which the relatively dense mantle lithosphere in the zone of shortening sinks into and is replaced by asthenosphere. The development of instability is affected by other factors also, including the buoyancy of the crustal layer and the strength of crust relative to mantle. Shear induced weakening explains why downwelling can develop relatively quickly in transpressional zones, while in typical continental environments lithosphere appears relatively stable to convective disturbances

  11. On domains of convergence in optimization problems

    NASA Technical Reports Server (NTRS)

    Diaz, Alejandro R.; Shaw, Steven S.; Pan, Jian

    1990-01-01

    Numerical optimization algorithms require the knowledge of an initial set of design variables. Starting from an initial design x(sup 0), improved solutions are obtained by updating the design iteratively in a way prescribed by the particular algorithm used. If the algorithm is successful, convergence is achieved to a local optimal solution. Let A denote the iterative procedure that characterizes a typical optimization algorithm, applied to the problem: Find x belonging to R(sup n) that maximizes f(x) subject to x belonging to Omega contained in R(sup n). We are interested in problems with several local maxima (x(sub j))(sup *), j=1, ..., m, in the feasible design space Omega. In general, convergence of the algorithm A to a specific solution (x(sub j))(sup *) is determined by the choice of initial design x(sup 0). The domain of convergence D(sub j) of A associated with a local maximum (x(sub j))(sup *) is a subset of initial designs x(sup 0) in Omega such that the sequence (x(sup k)), k=0,1,2,... defined by x(sup k+1) = A(x(sup k)), k=0,1,... converges to (x(sub j))(sup *). The set D(sub j) is also called the basin of attraction of (x(sub j))(sup *). Cayley first proposed the problem of finding the basin of attraction for Newton's method in 1897. It has been shown that the basin of attraction for Newton's method exhibits chaotic behavior in problems with polynomial objective. This implies that there may be regions in the feasible design space where arbitrarily close starting points will converge to different local optimal solutions. Furthermore, the boundaries of the domains of convergence may have a very complex, even fractal structure. In this paper we show that even simple structural optimization problems solved using standard gradient based (first order) algorithms exhibit similar features.

  12. Convergence characteristics of the multiple input, multiple output LMS algorithm

    NASA Technical Reports Server (NTRS)

    Snyder, Scott D.; Hansen, Colin H.; Clark, Robert L.

    1992-01-01

    The convergence characteristics of the multiple input, multiple output LMS algorithm, as applied to active noise and vibration control systems, are examined. The mean square error during the convergence process, as well as the final converged value, are examined analytically and in computer simulation. It is shown that the ratio of number of error sensors to number of control sources has a significant influence upon both the converging and converged value of the mean square error. Other active control system variables, such as the inherent time delays and structural/acoustic transfer functions, are also shown to have a significant influence upon the convergence process.

  13. Convergence characteristics of the multiple input, multiple output LMS algorithm

    NASA Technical Reports Server (NTRS)

    Snyder, Scott D.; Hansen, Colin H.; Clark, Robert L.

    1992-01-01

    The convergence characteristics of the multiple input, multiple output LMS algorithm, as applied to active noise and vibration control systems, are examined. The mean square error during the convergence process, as well as the final converged value, are examined analytically and in computer simulation. It is shown that the ratio of number of error sensors to number of control sources has a significant influence upon both the converging and converged value of the mean square error. Other active control system variables, such as the inherent time delays and structural/acoustic transfer functions, are also shown to have a significant influence upon the convergence process.

  14. 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.

  15. Requirements for Instrument Approaches to Converging Runways,

    DTIC Science & Technology

    1981-09-01

    PERSPECTIVE 2-1 2.1 Definition 2-1 2.2 Types of Converging Runways 2-1 2.2.1 Intersecting Approach Streams 2-3 2.2.2 Intersecting Runways 2-3 2.2.3...Therefore, a methodology to define and characterize ’e converging approaches is presented in this chapter. 2.1 Definition If two runways are not parallel...c nter of ARC, the positive X-direction is paralel to IA, and the positive Y-direction is parallel to TC,i C-1 *z / ,i// \\2D 2B0 C-2 FIUE w 4Z a!w wV

  16. 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.

  17. 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.

  18. Antibiotics From Microbes: Converging To Kill

    PubMed Central

    Fischbach, Michael A.

    2011-01-01

    Summary As genetically encoded small molecules, antibiotics are phenotypes that have resulted from mutation and natural selection. Advances in genetics, biochemistry, and bioinformatics have connected hundreds of antibiotics to the gene clusters that encode them, allowing these molecules to be analyzed using the tools of evolutionary biology. This review surveys examples of convergent evolution from microbially produced antibiotics, including the convergence of distinct gene clusters on similar phenotypes and the merger of distinct gene clusters into a single functional unit. Examining antibiotics through an evolutionary lens highlights the versatility of biosynthetic pathways, reveals lessons for combating antibiotic resistance, and provides an entry point for studying the natural roles of these natural products. PMID:19695947

  19. A Numerical, Literal, and Converged Perturbation Algorithm

    NASA Astrophysics Data System (ADS)

    Wiesel, William E.

    2017-09-01

    The KAM theorem and von Ziepel's method are applied to a perturbed harmonic oscillator, and it is noted that the KAM methodology does not allow for necessary frequency or angle corrections, while von Ziepel does. The KAM methodology can be carried out with purely numerical methods, since its generating function does not contain momentum dependence. The KAM iteration is extended to allow for frequency and angle changes, and in the process apparently can be successfully applied to degenerate systems normally ruled out by the classical KAM theorem. Convergence is observed to be geometric, not exponential, but it does proceed smoothly to machine precision. The algorithm produces a converged perturbation solution by numerical methods, while still retaining literal variable dependence, at least in the vicinity of a given trajectory.

  20. 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

  1. [Orthoptic treatment efficiency in convergence insufficiency treatment].

    PubMed

    Dragomir, M; Truş, L; Chirilă, D; Stîngu, C

    2001-01-01

    We studied a group of 162 patients(89 females, 73 males), with ages between 15-30 years, who complained of blurred vision at near work. 98 patients(60.4%) were diagnosed with convergence insufficiency (C.I.), the rest of 64 patients(39.6%) had: low refractive errors, heterophoria and intermittent heterotropia. Patients with convergence insufficiency were divided in 3 groups: group 1(34 patients--34.6%) were treated with orthoptic exercises and near point exercises at home, group 2 (34 patients--34.6%) were treated with only near point exercises at home and control group 3 (30 patients--30.8%) without treatment. The result of the treatment of C.I. was good at 25 patients(73.5%) of group 1, at 8 patients(23.5%) of group 2 while in group 3 at only one patient the symptoms disappeared.

  2. On the convergence of validity interval analysis.

    PubMed

    Maire, F

    2000-01-01

    Validity interval analysis (VIA) is a generic tool for analyzing the input-output behavior of feedforward neural networks. VIA is a rule extraction technique that relies on a rule refinement algorithm. The rules are of the form R(i)-->R(0) which reads if the input of the neural network is in the region R(i), then its output is in the region R(0), where regions are axis parallel hypercubes. VIA conjectures, then refines and checks rules for inconsistency. This process can be computationally expensive, and the rule refinement phase becomes critical. Hence, the importance of knowing the complexity of these rule refinement algorithms. In this paper, we show that the rule refinement part of VIA always converges in one run for single-weight-layer networks, and has an exponential average rate of convergence for multilayer networks. We also discuss some variations of the standard VIA formulae.

  3. Broadband converging plano-concave lens.

    PubMed

    Yang, Rui; Lei, Zhenya; Chen, Lei; Zhang, Jiawei; Wang, Zhaoxu; Xie, Yongjun

    2013-07-01

    A plano-concave lens with source-tailored geometric profile and transformational gradient index is proposed for broadband illumination. Such a design, capable of focusing and collimating the electromagnetic fields, fulfils the functionality of a converging lens and can also achieve a steerable beam and multiple beams efficiently. Nonresonant synthesis with a perforated dielectric plate and dielectric rod arrays is demonstrated for the lensing realization, promising a wide operating frequency band in the practical implementation.

  4. Convergent designs for electrogenesis and electroreception.

    PubMed

    Hopkins, C D

    1995-12-01

    New- and old-world tropical electric fish lack a common electrical ancestor, suggesting that the mechanisms of signal generation and recognition evolved independently in the two groups. Recent research on convergent designs for electrogenesis and electroreception has focused on the structure of electric organs, the neural circuitry controlling the pacemaker driving the electric organ, and the neural circuitry underlying time coding of electric waveforms.

  5. 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

  6. A Practical, Convergent Method for Glycopeptide Synthesis

    DTIC Science & Technology

    1993-07-23

    deprotection, the overall yield from oligosaccharide to glycopeptide is low. This may be acceptable for monosaccharides or for oligosaccharides which...in Figure 3. GIcNAcNH2 (1) is commercially available. Chitobiose constitutes the disaccharide core of N-linked sugars; the peracetylated compound (2...glycopeptides containing this sugar cannot be easily prepared by non- convergent methods. 43 The peracetylated disaccharide (5) was synthesized from L

  7. Convergence of the Naval Information Infrastructure

    DTIC Science & Technology

    2004-06-01

    REPORT TYPE AND DATES COVERED Master’s Thesis 4. TITLE AND SUBTITLE: Convergence of the Naval Information Infrastructure 6. AUTHOR( S ) James A...Knoll 5. FUNDING NUMBERS 7. PERFORMING ORGANIZATION NAME( S ) AND ADDRESS(ES) Naval Postgraduate School Monterey, CA 93943-5000 8. PERFORMING...ORGANIZATION REPORT NUMBER 9. SPONSORING /MONITORING AGENCY NAME( S ) AND ADDRESS(ES) N/A 10. SPONSORING/MONITORING AGENCY REPORT NUMBER 11

  8. Sequences of Rational Numbers Converging to Surds

    ERIC Educational Resources Information Center

    Fletcher, Rodney

    2010-01-01

    In this sequence 1/1, 7/5, 41/29, 239/169 and so on, Thomas notes that the sequence converges to square root of 2. By observation, the sequence of numbers in the numerator of the above sequence, have a pattern of generation which is the same as that in the denominator. That is, the next term is found by multiplying the previous term by six and…

  9. 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.

  10. Uniform Convergence to Equilibrium for Granular Media

    NASA Astrophysics Data System (ADS)

    Bolley, François; Gentil, Ivan; Guillin, Arnaud

    2013-05-01

    We study the long time asymptotics of a nonlinear, nonlocal equation used in the modelling of granular media. We prove a uniform exponential convergence to equilibrium for degenerately convex and nonconvex interaction or confinement potentials, improving in particular results by J. A. Carrillo, R. J. McCann and C. Villani. The method is based on studying the dissipation of the Wasserstein distance between a solution and the steady state.

  11. New Type Continuities via Abel Convergence

    PubMed Central

    Albayrak, Mehmet

    2014-01-01

    We investigate the concept of Abel continuity. A function f defined on a subset of ℝ, the set of real numbers, is Abel continuous if it preserves Abel convergent sequences. Some other types of continuities are also studied and interesting result is obtained. It turned out that uniform limit of a sequence of Abel continuous functions is Abel continuous and the set of Abel continuous functions is a closed subset of continuous functions. PMID:24883393

  12. Variational Convergence Of Bifunctions: Motivating Applications

    DTIC Science & Technology

    2011-01-01

    Research Office (ARO) W911NS1010246 and Fondap- Matematicas Aplicadas, Universidad de Chile 1 Variational convergence of bifunctions The analysis of...The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing...problems. 1 . REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 13. SUPPLEMENTARY NOTES The views, opinions and/or findings contained in this report are those

  13. Theoretical modeling of converging and diverging detonation waves in solid and gaseous explosives. CONF-830704--7

    SciTech Connect

    Tarver, C.M.; Urtiew, P.A.

    1983-01-01

    The ignition and growth reactive flow model of shock initiation and detonation is shown to accurately calculate detonation velocity-radius data on spherically diverging and converging detonation waves in the solid explosive PBX-9404. Comparison of calculations with the ignition and growth Zeldovich-von Neumann-Doring (ZND)-type model and with a simple Chapman-Jouguet (CJ) model for converging detonation waves in the solid explosive LX-17 shows that the additional momentum associated with a finite thickness reaction zone in the ZND model causes a slightly more rapid acceleration of the detonation wave front. The theory of converging detonation waves is briefly reviewed. The effects of the final reaction product state, the variability of the heat of reaction, and the equations of state are discussed for converging detonation waves in gaseous and solid explosives. It is postulated that the reaction product states follow a locus of Chapman-Jouguet (CJ) states as the detonation velocity and pressure increase. In converging gaseous detonations the heat of reaction decreases and the adiabatic exponent increases as the detonation velocity increases. In converging detonations in solid explosives equation of state uncertainties dominate the calculations, and more experimental data on overdriven detonation waves are required for improved modeling.

  14. Non-LTE radiative transfer with lambda-acceleration - Convergence properties using exact full and diagonal lambda-operators

    NASA Technical Reports Server (NTRS)

    Macfarlane, J. J.

    1992-01-01

    We investigate the convergence properties of Lambda-acceleration methods for non-LTE radiative transfer problems in planar and spherical geometry. Matrix elements of the 'exact' A-operator are used to accelerate convergence to a solution in which both the radiative transfer and atomic rate equations are simultaneously satisfied. Convergence properties of two-level and multilevel atomic systems are investigated for methods using: (1) the complete Lambda-operator, and (2) the diagonal of the Lambda-operator. We find that the convergence properties for the method utilizing the complete Lambda-operator are significantly better than those of the diagonal Lambda-operator method, often reducing the number of iterations needed for convergence by a factor of between two and seven. However, the overall computational time required for large scale calculations - that is, those with many atomic levels and spatial zones - is typically a factor of a few larger for the complete Lambda-operator method, suggesting that the approach should be best applied to problems in which convergence is especially difficult.

  15. 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

  16. Crenulative Turbulence in a Converging Nonhomogeneous Material

    SciTech Connect

    Romero, Casildo 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.

  17. 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.

  18. 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

  19. Bandlimited image extrapolation with faster convergence

    NASA Astrophysics Data System (ADS)

    Cahana, D.; Stark, H.

    1981-08-01

    Techniques for increasing the convergence rate of the extrapolation algorithm proposed by Gerchberg (1974) and Papoulis (1975) for image restoration applications are presented. The techniques involve the modification of the Gerchberg-Papoulis algorithm to include additional a priori data such as the low-pass projection of the image either by the inclusion of the data at the start of the recursion to reduce the starting-point error, or by use of the low-pass image in each iteration to correct twice in the frequency domain. The performance of the GP algorithm and the two modifications presented in the restorations of a signal consisting of widely separated spectral components of equal magnitude and a signal with spectral components grouped in passbands is compared, and it is found that while both modifications reduced the starting point error, the convergence rate of the second technique was not substantially greater than that of the first despite the additional iterative frequency-plane correction. A significant improvement in the starting-point errors and convergence rates of both modified algorithms is obtained, however, when they are combined with adaptive thresholding in the presence of low noise levels and a signal with relatively well spaced impulse-type spectral components.

  20. Convergence Behavior of Bird's Sophisticated DSMC Algorithm

    NASA Astrophysics Data System (ADS)

    Gallis, M. A.; Torczynski, J. R.; Rader, D. J.

    2007-11-01

    Bird's standard Direct Simulation Monte Carlo (DSMC) algorithm has remained almost unchanged since the mid-1970s. Recently, Bird developed a new DSMC algorithm, termed ``sophisticated DSMC'', which significantly modifies the way molecules both move and collide. The sophisticated DSMC algorithm is implemented in a one-dimensional DSMC code, and its convergence behavior is investigated for one-dimensional Fourier flow, where an argon-like hard-sphere gas is confined between two parallel, motionless, fully accommodating walls with unequal temperatures. As in previous work, the primary convergence metric is the ratio of the DSMC-calculated thermal conductivity to the theoretical value. The convergence behavior of sophisticated DSMC is compared to that of standard DSMC and to the predictions of Green-Kubo theory. The sophisticated algorithm significantly reduces the computational resources needed to maintain a fixed level of accuracy. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  1. 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.

  2. Determinants of compliance with malaria chemoprophylaxis among French soldiers during missions in inter-tropical Africa.

    PubMed

    Resseguier, Noémie; Machault, Vanessa; Ollivier, Lénaick; Orlandi-Pradines, Eve; Texier, Gaetan; Pradines, Bruno; Gaudart, Jean; Buguet, Alain; Tourette-Turgis, Catherine; Rogier, Christophe

    2010-02-03

    The effectiveness of malaria chemoprophylaxis is limited by the lack of compliance whose determinants are not well known. The compliance with malaria chemoprophylaxis has been estimated and analysed by validated questionnaires administered before and after the short-term missions (about four months) in five tropical African countries of 2,093 French soldiers from 19 military companies involved in a prospective cohort study. "Correct compliance" was defined as "no missed doses" of daily drug intake during the entire mission and was analysed using multiple mixed-effect logistic regression model. The averaged prevalence rate of correct compliance was 46.2%, ranging from 9.6%to 76.6% according to the companies. Incorrect compliance was significantly associated with eveningness (p = 0.028), a medical history of clinical malaria (p < 0.001) and a perceived mosquito attractiveness inferior or superior to the others (p < 0.007). Correct compliance was significantly associated with the systematic use of protective measures against mosquito bites (p < 0.001), the type of military operations (combat vs. training activities, p < 0.001) and other individual factors (p < 0.05). The identification of circumstances and profiles of persons at higher risk of lack of compliance would pave the way to specifically targeted strategies aimed to improve compliance with malaria chemoprophylaxis and, therefore, its effectiveness.

  3. Determinants of compliance with malaria chemoprophylaxis among French soldiers during missions in inter-tropical Africa

    PubMed Central

    2010-01-01

    Background The effectiveness of malaria chemoprophylaxis is limited by the lack of compliance whose determinants are not well known. Methods The compliance with malaria chemoprophylaxis has been estimated and analysed by validated questionnaires administered before and after the short-term missions (about four months) in five tropical African countries of 2,093 French soldiers from 19 military companies involved in a prospective cohort study. "Correct compliance" was defined as "no missed doses" of daily drug intake during the entire mission and was analysed using multiple mixed-effect logistic regression model. Results The averaged prevalence rate of correct compliance was 46.2%, ranging from 9.6%to 76.6% according to the companies. Incorrect compliance was significantly associated with eveningness (p = 0.028), a medical history of clinical malaria (p < 0.001) and a perceived mosquito attractiveness inferior or superior to the others (p < 0.007). Correct compliance was significantly associated with the systematic use of protective measures against mosquito bites (p < 0.001), the type of military operations (combat vs. training activities, p < 0.001) and other individual factors (p < 0.05). Conclusions The identification of circumstances and profiles of persons at higher risk of lack of compliance would pave the way to specifically targeted strategies aimed to improve compliance with malaria chemoprophylaxis and, therefore, its effectiveness. PMID:20128921

  4. Convergence of a Moran model to Eigen's quasispecies model.

    PubMed

    Dalmau, Joseba

    2017-03-02

    We prove that a Moran model converges in probability to Eigen's quasispecies model in the infinite population limit. We show further that the invariant probability measure of the Moran model converges to the unique stationary solution of Eigen's quasispecies model.

  5. ON THE CONVERGENCE OF THE ENSEMBLE KALMAN FILTER

    PubMed Central

    Mandel, Jan; Cobb, Loren; Beezley, Jonathan D.

    2013-01-01

    Convergence of the ensemble Kalman filter in the limit for large ensembles to the Kalman filter is proved. In each step of the filter, convergence of the ensemble sample covariance follows from a weak law of large numbers for exchangeable random variables, the continuous mapping theorem gives convergence in probability of the ensemble members, and Lp bounds on the ensemble then give Lp convergence. PMID:24843228

  6. Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda).

    PubMed

    Nesbitt, Sterling J; Norell, Mark A

    2006-05-07

    Living archosaurs comprise birds (dinosaurs) and crocodylians (suchians). The morphological diversity of birds and stem group dinosaurs is tremendous and well-documented. Suchia, the archosaurian group including crocodylians, is generally considered more conservative. Here, we report a new Late Triassic suchian archosaur with unusual, highly specialized features that are convergent with ornithomimid dinosaurs. Several derived features of the skull and postcranial skeleton are identical to conditions in ornithomimids. Such cases of extreme convergence in multiple regions of the skeleton in two distantly related vertebrate taxa are rare. This suggests that these archosaurs show iterative patterns of morphological evolution. It also suggests that this group of suchians occupied the adaptive zone that was occupied by ornithomimosaurs later in the Mesozoic.

  7. 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.

  8. Influence of South Pacific Subtropical Dipole on South Pacific Convergence Precipitation

    NASA Astrophysics Data System (ADS)

    Wang, F.

    2016-12-01

    This study analyses the influence of the South Pacific Subtropical Dipole(SPSD) on South Pacific Convergence Zone(SPCZ) and explores its dynamic processes by using SST data HadISST of Hadley center and atmospheric reanalysis data of NCEP-NCAR. Analyses show that South Pacific Subtropical Dipole is linearly independent of ENSO, and SPSD with a strong phase locking peaks in summer(12 2). The location of SPCZ precipitation during January-March is remarkably affected by SPSD event during December-February, and SPCZ precipitation zone moves north and the location of precipitation moves south during negative dipole event. Northeast pole (warmer SST) has positive precipitation anomaly because of lower pressure and convergence of moisture in this area during positive dipole event years. However southwest pole (cooler SST) with higher pressure is dominated by divergence of moisture in order to less precipitation, so SPCZ precipitation zone moves north and the location of precipitation is opposite during negative dipole event. The results of this study provide more knowledge of relationship between SPSD and SPCZ, and it's better to understand climate change and air-sea interaction in south Pacific

  9. Introduction to the structures and processes of subduction zones

    NASA Astrophysics Data System (ADS)

    Zheng, Yong-Fei; Zhao, Zi-Fu

    2017-09-01

    Subduction zones have been the focus of many studies since the advent of plate tectonics in 1960s. Workings within subduction zones beneath volcanic arcs have been of particular interest because they prime the source of arc magmas. The results from magmatic products have been used to decipher the structures and processes of subduction zones. In doing so, many progresses have been made on modern oceanic subduction zones, but less progresses on ancient oceanic subduction zones. On the other hand, continental subduction zones have been studied since findings of coesite in metamorphic rocks of supracrustal origin in 1980s. It turns out that high-pressure to ultrahigh-pressure metamorphic rocks in collisional orogens provide a direct target to investigate the tectonism of subduction zones, whereas oceanic and continental arc volcanic rocks in accretionary orogens provide an indirect target to investigate the geochemistry of subduction zones. Nevertheless, metamorphic dehydration and partial melting at high-pressure to ultrahigh-pressure conditions are tectonically applicable to subduction zone processes at forearc to subarc depths, and crustal metasomatism is the physicochemical mechanism for geochemical transfer from the slab to the mantle in subduction channels. Taken together, these provide us with an excellent opportunity to find how the metamorphic, metasomatic and magmatic products are a function of the structures and processes in both oceanic and continental subduction zones. Because of the change in the thermal structures of subduction zones, different styles of metamorphism, metasomatism and magmatism are produced at convergent plate margins. In addition, juvenile and ancient crustal rocks have often suffered reworking in episodes independent of either accretionary or collisional orogeny, leading to continental rifting metamorphism and thus rifting orogeny for mountain building in intracontinental settings. This brings complexity to distinguish the syn

  10. Introduction to the structures and processes of subduction zones

    NASA Astrophysics Data System (ADS)

    Zheng, Yong-Fei; Zhao, Zi-Fu

    2017-09-01

    Subduction zones have been the focus of many studies since the advent of plate tectonics in 1960s. Workings within subduction zones beneath volcanic arcs have been of particular interest because they prime the source of arc magmas. The results from magmatic products have been used to decipher the structures and processes of subduction zones. In doing so, many progresses have been made on modern oceanic subduction zones, but less progresses on ancient oceanic subduction zones. On the other hand, continental subduction zones have been studied since findings of coesite in metamorphic rocks of supracrustal origin in 1980s. It turns out that high-pressure to ultrahigh-pressure metamorphic rocks in collisional orogens provide a direct target to investigate the tectonism of subduction zones, whereas oceanic and continental arc volcanic rocks in accretionary orogens provide an indirect target to investigate the geochemistry of subduction zones. Nevertheless, metamorphic dehydration and partial melting at high-pressure to ultrahigh-pressure conditions are tectonically applicable to subduction zone processes at forearc to subarc depths, and crustal metasomatism is the physicochemical mechanism for geochemical transfer from the slab to the mantle in subduction channels. Taken together, these provide us with an excellent opportunity to find how the metamorphic, metasomatic and magmatic products are a function of the structures and processes in both oceanic and continental subduction zones. Because of the change in the thermal structures of subduction zones, different styles of metamorphism, metasomatism and magmatism are produced at convergent plate margins. In addition, juvenile and ancient crustal rocks have often suffered reworking in episodes independent of either accretionary or collisional orogeny, leading to continental rifting metamorphism and thus rifting orogeny for mountain building in intracontinental settings. This brings complexity to distinguish the syn

  11. An Ensemble Approach in Converging Contents of LMS and KMS

    ERIC Educational Resources Information Center

    Sabitha, A. Sai; Mehrotra, Deepti; Bansal, Abhay

    2017-01-01

    Currently the challenges in e-Learning are converging the learning content from various sources and managing them within e-learning practices. Data mining learning algorithms can be used and the contents can be converged based on the Metadata of the objects. Ensemble methods use multiple learning algorithms and it can be used to converge the…

  12. Independent molecular basis of convergent highland adaptation in maize

    USDA-ARS?s Scientific Manuscript database

    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 ...

  13. Automatized convergence of optoelectronic simulations using active machine learning

    NASA Astrophysics Data System (ADS)

    Rouet-Leduc, Bertrand; Hulbert, Claudia; Barros, Kipton; Lookman, Turab; Humphreys, Colin J.

    2017-07-01

    A fundamental problem of optoelectronic simulations is to achieve convergence. We use statistical analysis and machine learning to effectively guide the selection of the next device to be examined based upon the expected convergence of the simulation. This active learning strategy rapidly constructs a model that predicts Poisson-Schrödinger simulations of devices and that simultaneously produces fully converged simulations.

  14. 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…

  15. 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…

  16. Societal response to nanotechnology: converging technologies-converging societal response research?

    NASA Astrophysics Data System (ADS)

    Ronteltap, Amber; Fischer, Arnout R. H.; Tobi, Hilde

    2011-10-01

    Nanotechnology is an emerging technology particularly vulnerable to societal unrest, which may hinder its further development. With the increasing convergence of several technological domains in the field of nanotechnology, so too could convergence of social science methods help to anticipate societal response. This paper systematically reviews the current state of convergence in societal response research by first sketching the predominant approaches to previous new technologies, followed by an analysis of current research into societal response to nanotechnology. A set of 107 papers on previous new technologies shows that rational actor models have played an important role in the study of societal response to technology, in particular in the field of information technology and the geographic region of Asia. Biotechnology and nuclear power have, in contrast, more often been investigated through risk perception and other affective determinants, particularly in Europe and the USA. A set of 42 papers on societal response to nanotechnology shows similarities to research in biotechnology, as it also builds on affective variables such as risk perception. Although there is a tendency to extend the rational models with affective variables, convergence in social science approaches to response to new technologies still has a long way to go. The challenge for researchers of societal response to technologies is to converge to some shared principles by taking up the best parts from the rational actor models dominant in information technology, whilst integrating non-rational constructs from biotechnology research. The introduction of nanotechnology gives a unique opportunity to do so.

  17. 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.

  18. 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.

  19. New Madrid Seismic Zone

    DTIC Science & Technology

    2007-11-02

    NEW MADRID SEISMIC ZONE BY COLONEL J.DAVID NORWOOD United States Army DISTRIBUTION STATEMENT A...mCTBB l USAWC STRATEGY RESEARCH PROJECT New Madrid Seismic Zone by J. David Norwood, COL, USA Michael A. Pearson, COL, USA Project Advisor The...ABSTRACT AUTHOR: J. David Norwood, Colonel, U.S. Army TITLE: New Madrid Seismic Zone FORMAT: Strategy Research Project DATE: 22 April 1998 . PAGES:

  20. 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.

  1. 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.

  2. Response of the Intertropical Convergence Zone to Southern Hemisphere cooling during Ordovician glaciation

    NASA Astrophysics Data System (ADS)

    Armstrong, H.; Baldini, J.; Challands, T.; Owen, A.

    2007-12-01

    Difficulties in quantifying environmental conditions (particularly pCO2 and palaeobathymetry) and oversimplification in parameterization are major limitations on what deep time climate models can tell us about the dynamic behaviour of the Earth's climate. Research is still focussed at understanding climate proxy data and the best climate proxy datasets available for the Early Palaeozoic are those from palaeo-tropical latitudes. At the present day the tropics are the main source of the atmosphere's heat and water vapour; changes in tropical dynamics have a major influence on the Earth's climate. On the global scale, the position of the ITCZ affects pole-ward heat transport and latitudinal temperature gradients and is a critical feedback mechanism, sensitive to ice volume changes, during glaciation. Ocean water beneath the ITCZ is warm, has reduced salinity and is characterised by light δ18O(carb). Stable isotope records from low latitude Upper Ordovician limestone (from Nevada, Arctic Canada and Estonia) are interpreted as showing a pattern of predicted and coincident shifts in the position of subtropical and tropical water masses associated with the developing Hirnantian glaciation. We hypothesize that these changes reflect a shift in the position of the ITCZ that tracked the pattern of climate change during the Late Ordovician. We argue for a discrete palaeo-ITCZ, the location of which was controlled by ice volume changes. The repositioning of the ITCZ resulted in climatic belt re-organization resulting in complex feedbacks into the ocean-climate system that were a likely contributor to the Late Ordovician mass extinction.

  3. The Sea Breeze Convergence Zone and Its Relationship to Fair Weather Electricity in East Central Florida

    DTIC Science & Technology

    1993-01-01

    and Rodebust 1948; Gentry and Moore 1954; Estoque 1962; Frank et al. 1967; Neumann 1971; Pielke 1974; Blanchard and Lopez 1985; Waston et al. 1987...convection and boundary layer interactions. J. Appl. Meteor., 21, 953-977. Estoque , M.A., 1962: The sea breeze as a function of the prevailing synoptic

  4. 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.

  5. Rapid convergent evolution in wild crickets.

    PubMed

    Pascoal, Sonia; Cezard, Timothee; Eik-Nes, Aasta; Gharbi, Karim; Majewska, Jagoda; Payne, Elizabeth; Ritchie, Michael G; Zuk, Marlene; Bailey, Nathan W

    2014-06-16

    The earliest stages of convergent evolution are difficult to observe in the wild, limiting our understanding of the incipient genomic architecture underlying convergent phenotypes. To address this, we capitalized on a novel trait, flatwing, that arose and proliferated at the start of the 21st century in a population of field crickets (Teleogryllus oceanicus) on the Hawaiian island of Kauai. Flatwing erases sound-producing structures on male forewings. Mutant males cannot sing to attract females, but they are protected from fatal attack by an acoustically orienting parasitoid fly (Ormia ochracea). Two years later, the silent morph appeared on the neighboring island of Oahu. We tested two hypotheses for the evolutionary origin of flatwings in Hawaii: (1) that the silent morph originated on Kauai and subsequently introgressed into Oahu and (2) that flatwing originated independently on each island. Morphometric analysis of male wings revealed that Kauai flatwings almost completely lack typical derived structures, whereas Oahu flatwings retain noticeably more wild-type wing venation. Using standard genetic crosses, we confirmed that the mutation segregates as a single-locus, sex-linked Mendelian trait on both islands. However, genome-wide scans using RAD-seq recovered almost completely distinct markers linked with flatwing on each island. The patterns of allelic association with flatwing on either island reveal different genomic architectures consistent with the timing of two mutational events on the X chromosome. Divergent wing morphologies linked to different loci thus cause identical behavioral outcomes--silence--illustrating the power of selection to rapidly shape convergent adaptations from distinct genomic starting points. Copyright © 2014 Elsevier Ltd. All rights reserved.

  6. Convergence of Fourier series in classical systems

    NASA Astrophysics Data System (ADS)

    Galoyan, L. N.; Grigoryan, M. G.; Kobelyan, A. Kh

    2015-07-01

    The following results are proved:there exists an integrable function such that any subsequence of the Cesàro means of negative order of the Fourier series of this function diverges almost everywhere; the values of an arbitrary integrable function can be changed on a set (independent of this function) of arbitrarily small measure so that the Fourier series with respect to both the Franklin system and the Haar system of the 'modified' function will be absolutely convergent almost everywhere on [ 0,1 ] there exists a continuous function which features an unremovable absolute divergence. Bibliography: 47 titles.

  7. 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.

  8. Mobile systems; From chaos to convergence

    NASA Astrophysics Data System (ADS)

    Swain, R. S.

    An outline of the two most recent and significant mobile communication developments in Europe is given. These are the Global System for Mobility (GSM) and Digital European Cordless Telecoms (DECT). A summary of advanced communications research is also presented, and the topics covered include the following: Research into Advanced Communications in Europe (RACE); 3rd-generation mobile communication systems; a common unified Universal Mobile Telecommunications Service (UMTS); convergence of mobile radio services; and equipment interface standardization. Finally, a brief review is given of the areas where further antenna and propagation research is needed: handset antennas, in-building propagation, and full system emulation.

  9. Problems Associated with Grid Convergence of Functionals

    NASA Technical Reports Server (NTRS)

    Salas, Manuel D.; Atkins, Harld L.

    2008-01-01

    The current use of functionals to evaluate order-of-convergence of a numerical scheme can lead to incorrect values. The problem comes about because of interplay between the errors from the evaluation of the functional, e.g., quadrature error, and from the numerical scheme discretization. Alternative procedures for deducing the order-property of a scheme are presented. The problem is studied within the context of the inviscid supersonic flow over a blunt body; however, the problem and solutions presented are not unique to this example.

  10. 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.

  11. 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.

  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. Digest: Imperfect convergence in butterfly wing patterns.

    PubMed

    Earl, Chandra; Guralnick, Robert P; Kawahara, Akito Y

    2017-02-27

    Butterfly wing patterns are among the most diverse morphological characteristics in nature, with many of the 18,000 or so described butterfly species readily distinguished by wing pattern alone. Wing pattern serves as one of the primary means of communication among species and is thus subject to strong natural selection for mimicry and warning color (aposematism). Convergent wing patterns are particularly evident across the butterfly genus Adelpha, suggesting this genus may be a good system to study the underlying mechanisms behind mimicry. This article is protected by copyright. All rights reserved.

  14. 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.

  15. 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.

  16. 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.

  17. Feedback between mountain belt growth and plate convergence revealed by forward and inverse tectonic models

    NASA Astrophysics Data System (ADS)

    Iaffaldano, G.; Bunge, H.; Dixon, T. H.; Buecker, M.

    2006-12-01

    While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that linkage remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at zones of plate convergence are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less clear. The ability to consider past as well as present plate motions provides significant additional constraints, because changes in plate motion are necessarily driven by changes in one or more driving or resisting forces, which may be inferred from independent data. Here we first exploit the capabilities of forward tectonic models of the Andean region to infer plate motion changes as far back as Miocene time. By accurately predicting observed convergence rates between Nazca and South America plates over the last 10 Myrs, we demonstrate for the first time that the topographic load of the Andes increases frictional forces between downgoing and overriding plates and thus consumes a significant amount of the driving force available for plate tectonics. This result suggests a strong feedback between mountain belt growth and plate convergence. We then test this notion by performing a numerical inversion of the same model. We use the Automatic Differentiation approach to generate a derivative code that relates convergence of the Nazca/South America plates to gross topography of the Andes mountain belt. We test the derivative code in a simple search algorithm to infer an optimal paleotopography of the Andes at 3.2 m.y. from the well-known history of Nazca/South America plate convergence. Our modeling result is in good agreement with independent published estimates of Andean paleotopography.

  18. Feedback Between Mountain Belt Growth and Plate Convergence Revealed by Forward and Inverse Tectonic Models

    NASA Astrophysics Data System (ADS)

    Iaffaldano, G.; Buecker, M.

    2009-05-01

    While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that linkage remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at convergent zones are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less clear. The ability to consider past as well as present plate motions provides significant additional constraints, because changes in plate motion must be necessarily driven by changes in one or more driving or resisting forces, which may be inferred from independent data. Here we first exploit the capabilities of forward global tectonic models focused on the Andean region to infer plate motion changes as far back as Miocene time. By accurately predicting observed convergence rates between Nazca and South America plates over the past 10 Myrs, we demonstrate that the topographic load of the Andes increases resistive forces between downgoing and overriding plates and thus consumes a significant amount of the driving force available for plate tectonics. This result suggests a strong feedback between mountain belt growth and plate convergence. We then test this notion by performing a numerical inversion of the same model. We use the Automatic Differentiation approach to generate a derivative code that relates convergence of the Nazca/South America plates to gross topography of the Andes mountain belt. We test the derivative code in a simple search algorithm to infer an optimal paleotopography of the Andes at 3.2 Myrs from the well-known history of Nazca/South America plate convergence. Our modeling result is in good agreement with independent published estimates of Andean paleotopography.

  19. 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.

  20. 231Pa excesses in arc volcanic rocks: Constraint on melting rates at convergent margins

    NASA Astrophysics Data System (ADS)

    Huang, Fang; Lundstrom, Craig C.

    2007-11-01

    The 231Pa-235U disequilibria provide greater ability to constrain the rate of mantle melting in convergent margin settings than the more often analyzed 238U-230Th-226Ra systems, which are strongly affected by fluid-addition processes from the subducting slab. Here we present new 231Pa-235U data for 12 samples from the Kick'em Jenny (KEJ) submarine volcano in the Southern Lesser Antilles to define the melting rate at a subduction zone with one of the lowest convergence rates. The KEJ samples have the highest average (231Pa)/(235U) yet measured in global arcs, consistent with other studies of the Southern Lesser Antilles lavas. These results reinforce the previously noted negative correlation between average (231Pa)/(235U) and convergence rate in all arc settings globally. We develop a model to explain this negative correlation and to better constrain melting rates at convergent margins. Assuming that the corner flow velocity is coupled to and equal to the subducting slab velocity, the melting rate, directly reflecting the flux of water added, becomes a linear function of subduction rate. This physical model is then coupled to three different melting models previously developed for calculating U-series disequilibria (reactive porous flow, dynamic, and flux melting). All three models reproduce the globally observed negative correlation between subduction rate and 231Pa excess. Although the style of melting cannot be easily discriminated, the good correspondence between models and observation provides an example of how geochemical and geophysical models can be linked to provide a self-consistent model of melt generation in convergent margin settings.

  1. 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.

  2. OpenMC In Situ Source Convergence Detection

    SciTech Connect

    Aldrich, Garrett Allen; Dutta, Soumya; Woodring, Jonathan Lee

    2016-05-07

    We designed and implemented an in situ version of particle source convergence for the OpenMC particle transport simulator. OpenMC is a Monte Carlo based-particle simulator for neutron criticality calculations. For the transport simulation to be accurate, source particles must converge on a spatial distribution. Typically, convergence is obtained by iterating the simulation by a user-settable, fixed number of steps, and it is assumed that convergence is achieved. We instead implement a method to detect convergence, using the stochastic oscillator for identifying convergence of source particles based on their accumulated Shannon Entropy. Using our in situ convergence detection, we are able to detect and begin tallying results for the full simulation once the proper source distribution has been confirmed. Our method ensures that the simulation is not started too early, by a user setting too optimistic parameters, or too late, by setting too conservative a parameter.

  3. No Genome-Wide Protein Sequence Convergence for Echolocation

    PubMed Central

    Zou, Zhengting; Zhang, Jianzhi

    2015-01-01

    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

  4. 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.

  5. 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

  6. 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.

  7. Surgery for residual convergence excess esotropia.

    PubMed

    Patel, Himanshu I; Dawson, Emma; Lee, John

    2011-12-01

    The outcome of bilateral medial rectus posterior fixation sutures +/- central tenotomy was assessed as a secondary procedure for residual convergence excess esotropia in 11 patients. Ten had previously undergone bilateral medial rectus recessions. One had recess/resect surgery on the deviating eye. The average preoperative near angle was 30 prism diopters with a range of 16 to 45 prism diopters. Eight patients underwent bilateral medial rectus posterior fixation sutures with central tenotomy. Two had bilateral medial rectus posterior fixation sutures only, and one had bilateral medial rectus posterior fixation suture, a lateral rectus resection, and an inferior oblique disinsertion. The postoperative near angle ranged from 4-30 prism diopters, with mean of 12 prism diopters. Five patients demonstrated some stereopsis preoperatively, all needing bifocals. Postoperatively, nine patients demonstrated an improvement in stereopsis, none needing bifocals. Two showed smaller near angles and better control without bifocals. Final stereopsis ranged from 30 seconds of arc to 800 seconds of arc. We feel that bilateral medial rectus posterior fixation sutures with or without central tenotomy is a viable secondary procedure for residual convergence excess esotropia.

  8. 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.

  9. 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

  10. 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)].

  11. RNA Polymerase II Collision Interrupts Convergent Transcription

    PubMed Central

    Hobson, David J.; Wei, Wu; Steinmetz, Lars M.; Svejstrup, Jesper Q.

    2012-01-01

    Summary Antisense noncoding transcripts, genes-within-genes, and convergent gene pairs are prevalent among eukaryotes. The existence of such transcription units raises the question of what happens when RNA polymerase II (RNAPII) molecules collide head-to-head. Here we use a combination of biochemical and genetic approaches in yeast to show that polymerases transcribing opposite DNA strands cannot bypass each other. RNAPII stops but does not dissociate upon head-to-head collision in vitro, suggesting that opposing polymerases represent insurmountable obstacles for each other. Head-to-head collision in vivo also results in RNAPII stopping, and removal of collided RNAPII from the DNA template can be achieved via ubiquitylation-directed proteolysis. Indeed, in cells lacking efficient RNAPII polyubiquitylation, the half-life of collided polymerases increases, so that they can be detected between convergent genes. These results provide insight into fundamental mechanisms of gene traffic control and point to an unexplored effect of antisense transcription on gene regulation via polymerase collision. PMID:23041286

  12. Exceptional Convergent Evolution in a Virus

    PubMed Central

    Bull, J. J.; Badgett, M. R.; Wichman, H. A.; Huelsenbeck, J. P.; Hillis, D. M.; Gulati, A.; Ho, C.; Molineux, I. J.

    1997-01-01

    Replicate lineages of the bacteriophage φX 174 adapted to growth at high temperature on either of two hosts exhibited high rates of identical, independent substitutions. Typically, a dozen or more substitutions accumulated in the 5.4-kilobase genome during propagation. Across the entire data set of nine lineages, 119 independent substitutions occurred at 68 nucleotide sites. Over half of these substitutions, accounting for one third of the sites, were identical with substitutions in other lineages. Some convergent substitutions were specific to the host used for phage propagation, but others occurred across both hosts. Continued adaptation of an evolved phage at high temperature, but on the other host, led to additional changes that included reversions of previous substitutions. Phylogenetic reconstruction using the complete genome sequence not only failed to recover the correct evolutionary history because of these convergent changes, but the true history was rejected as being a significantly inferior fit to the data. Replicate lineages subjected to similar environmental challenges showed similar rates of substitution and similar rates of fitness improvement across corresponding times of adaptation. Substitution rates and fitness improvements were higher during the initial period of adaptation than during a later period, except when the host was changed. PMID:9409816

  13. Revisiting approximate dynamic programming and its convergence.

    PubMed

    Heydari, Ali

    2014-12-01

    Value iteration-based approximate/adaptive dynamic programming (ADP) as an approximate solution to infinite-horizon optimal control problems with deterministic dynamics and continuous state and action spaces is investigated. The learning iterations are decomposed into an outer loop and an inner loop. A relatively simple proof for the convergence of the outer-loop iterations to the optimal solution is provided using a novel idea with some new features. It presents an analogy between the value function during the iterations and the value function of a fixed-final-time optimal control problem. The inner loop is utilized to avoid the need for solving a set of nonlinear equations or a nonlinear optimization problem numerically, at each iteration of ADP for the policy update. Sufficient conditions for the uniqueness of the solution to the policy update equation and for the convergence of the inner-loop iterations to the solution are obtained. Afterwards, the results are formed as a learning algorithm for training a neurocontroller or creating a look-up table to be used for optimal control of nonlinear systems with different initial conditions. Finally, some of the features of the investigated method are numerically analyzed.

  14. Simulations of 2-shock Convergence Scan Shots

    NASA Astrophysics Data System (ADS)

    Bradley, Paul; Olson, R. E.; Kline, J. L.; MacLaren, S. A.; Ma, T.; Salmonson, J. D.; Kyrala, G. A.; Pino, J.; Dewald, E.; Khan, S.; Sayre, D.; Ralph, J.; Turnbull, D.

    2016-10-01

    The 2-shock campaign is a joint Los Alamos/Livermore project to investigate the role of shock timing, asymmetry, and shock convergence on the performance of ignition relevant capsules. This campaign uses a simple two step pulse that makes it easier to correlate the effect of changing the laser pulse on the performance of the capsule. The 680 micron outer radius capsule has a CH +1 at% Si ablator approximately 175 microns thick surrounding a DD or HT gas region with fill densities between 0.0085 and 0.00094 g/cc. The capsules are indirectly driven inside a gold hohlraum that is 9.2 mm long by 5.75 mm in diameter. Some capsules had about 3 microns of CD on the inner surface. The CD inner surface capsules utilized HT fuel so that the DT yield arises from mixing of CD shell material into the tritium of the gas region. Our simulated results compare well to the experimental yield, ion temperature, burn width, x-ray size, convergence ratio, and radius versus time data. Work performed by Los Alamos National Laboratory under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy.

  15. Instability and Tsunamigenic Potential at Convergent Margins

    NASA Astrophysics Data System (ADS)

    von Huene, R.; Ranero, C. R.; Watts, P.

    2001-12-01

    Along many convergent margins multibeam echosounding navigated with GPS has revealed large slope failures that were probably tsunamigenic. Bathymetric data combined with seismic reflection imaging indicate multiple causes. The 55-km wide Nicoya Slump resulted from the steepening slope above an underthrusting seamount on the subducting oceanic plate. This slump may have generated a 27-m high wave. Several 5-7 km wide mid-slope slides off central Nicaragua probably resulted from steepening of the continental slope by tectonic erosion. They may have generated waves 6-7 m high. A 30 km wide mid-slope slump off northern Peru may have generated a 5 m high wave. Its cause will not be understood without better seismic reflection imaging but considerable fluid venting was observed across its headwall. In the Gulf of Alaska a large slide appears to have resulted from rapid sedimentation. Tsunamigenic slope failure along convergent margins is only beginning to be resolved and the causes vary. Subducted ocean floor relief, tectonically steepened slopes, and sites of rapid sedimentation can help target potential failure and possible future tsunami hazards.

  16. OPC solution by implementing fast converging methodology

    NASA Astrophysics Data System (ADS)

    Yang, Qing; Du, Yaojun

    2015-03-01

    Traditionally, the optical proximity correction (OPC) is to deliver the solution to ensure the nominal after-development-inspection (ADI) contours on target. As the technology node keeps shrinking to 28nm and beyond, the OPC is expected to cover the lithography process window (PW), etch PW, and overlay margin as well. As a result, more and more advanced functions are included in OPC to achieve the awareness of multiple cost functions, such as the nominal EPE, PW effective EPE, the enclosure of above and underneath layers, and so on. These inclusions are at the cost of the run time and complexity of OPC solution. In this paper, we demonstrated a methodology by adopting design rule check (DRC) algorithm in repair flow to fix hot spots. In accordance to OPC verification check, the subsequent DRC movements were applied to those hot spots only. With a straightforward recipe tuning, a fast convergence of OPC can be achieved. The results exhibit the run time improvement without compromising the OPC performance. We further evaluated by real cases the effects of the DRC-based repair algorithm on the error convergence and final repair effects, by comparing to the standard OPC solution.

  17. 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

  18. Posterior fixation suture and convergence excess esotropia.

    PubMed

    Steffen; Auffarth; Kolling

    1998-09-01

    The present study investigates the results of Cuppers' 'Fadenoperation' in patients with non-accommodative convergence excess esotropia. Particular attention is given to postoperative eye alignment at distance fixation. Group 1 (n=96) included patients with a 'normal' convergence excess. The manifest near angles (mean ET 16.73 degrees +/- 6.33 degrees, range 4 degrees -33 degrees ) were roughly twice the size of the distance angles (mean ET 6.50 degrees +/- 3.62 degrees, range 0 degrees -14 degrees ). These patients were treated with a bilateral fadenoperation of the medial recti without additional eye muscle surgery. Three months after surgery, the mean postoperative angles were XT 0.5 degrees +/- 3.3 degrees (range XT 11 degrees -ET 5 degrees ) for distance fixation, and ET 2.7 degrees +/- 3.6 degrees (range XT 5 degrees -ET 14 degrees ) for near fixation, respectively. Postoperative convergent angles at near fixation >ET 10 degrees were present in two patients (1.9%). Group 2 (n=21) included patients with a mean preoperative distance angle of ET 9.2 degrees +/- 3.7 degrees (range 6 degrees -16 degrees ) and a mean preoperative near angle of ET 23.4 degrees +/- 3.1 degrees (range 16 degrees -31 degrees ). These patients were operated on with a bilateral fadenoperation of the medial recti and a simultaneous recession of one or both medial rectus muscles. Mean postoperative angles were XT 0.5 degrees +/- 4.6 degrees (range XT 12 degrees -ET 7 degrees ) for distance fixation and ET 1.4 degrees +/- 4.5 degrees (range XT 8 degrees -ET 13 degrees ) for near fixation, respectively. In this group, 2 patients (10.6%) had a postoperative exotropia >XT 5 degrees at distance fixation, and two patients had residual esotropia>ET 10 degrees at near fixation. Group 3 (n=17) included patients with a pronounced non-accommodative convergence excess. Near angle values (mean of 17.8 degrees +/- 5.3 degrees, range ET 7 degrees -26 degrees ) were several times higher than the distance

  19. 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.

  20. 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.

  1. 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.

  2. Marginal Zone Lymphoma

    MedlinePlus

    ... zone lymphomas are a group of indolent (slow-growing) NHL B-cell lymphomas, which account for approximately 12 percent of all B-cell lymphomas. The median age for diagnosis is 65 years old. There are three types of marginal zone lymphoma: ...

  3. Longleaf pine site zones

    Treesearch

    Phillip J. Craul; John S. Kush; William D. Boyer

    2005-01-01

    The authors delineate six major climatic areas of the longleaf pine (Pinus palustris Mill.) region. They subdivide these areas into 21 site zones, each of which is deemed homogenous with respect to climate, physiography, and soils. The site zones are mapped and their climate, physiography, and soils described. The authors recommend that plantings of...

  4. 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…

  5. Urban Terrain Zone Characteristics

    DTIC Science & Technology

    1987-09-01

    function . An example of the interaction of some of these can result in an exposed surface of decorative brick veneer on a framed stracture . Or, a...Classification System for HOUT Studies . . . . . . . . .- ..- . . . . . . 14 2. Urban Terrain Zones Function /Morphology Relationship...By Function --All Cities Aggregated . . . . . . . . . . . . . . . . . . . 69 6. Building Types: Major Terrain Zones . . . . ...... 103 7. Urban Terrain

  6. 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…

  7. California tree seed zones

    Treesearch

    John M. Buck; Ronald S. Adams; Jerrold Cone; M. Thompson Conkle; William J. Libby; Cecil J. Eden; Michel J. Knight

    1970-01-01

    California forest tree seed zones were established originally by Fowells (1946), with revisions proposed by Roy (1963) and Schubert (1966). The Forest Tree Seed Committee of the Northern California Section, Society of American Foresters, has revised the original zones and updated the recording system described in the earlier reports. Fowells' (1946) Research Note...

  8. 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.

  9. What does convergent evolution mean? The interpretation of convergence and its implications in the search for limits to evolution

    PubMed Central

    Stayton, C. Tristan

    2015-01-01

    Convergent evolution is central to the study of life's evolutionary history. Researchers have documented the ubiquity of convergence and have used this ubiquity to make inferences about the nature of limits on evolution. However, these inferences are compromised by unrecognized inconsistencies in the definitions, measures, significance tests and inferred causes of convergent evolution. I review these inconsistencies and provide recommendations for standardizing studies of convergence. A fundamental dichotomy exists between definitions that describe convergence as a pattern and those that describe it as a pattern caused by a particular process. When this distinction is not acknowledged it becomes easy to assume that a pattern of convergence indicates that a particular process has been active, leading researchers away from alternative explanations. Convergence is not necessarily caused by limits to evolution, either adaptation or constraint; even substantial amounts of convergent evolution can be generated by a purely stochastic process. In the absence of null models, long lists of examples of convergent events do not necessarily indicate that convergence or any evolutionary process is ubiquitous throughout the history of life. Pattern-based definitions of convergence, coupled with quantitative measures and null models, must be applied before drawing inferences regarding large-scale limits to evolution. PMID:26640646

  10. What does convergent evolution mean? The interpretation of convergence and its implications in the search for limits to evolution.

    PubMed

    Stayton, C Tristan

    2015-12-06

    Convergent evolution is central to the study of life's evolutionary history. Researchers have documented the ubiquity of convergence and have used this ubiquity to make inferences about the nature of limits on evolution. However, these inferences are compromised by unrecognized inconsistencies in the definitions, measures, significance tests and inferred causes of convergent evolution. I review these inconsistencies and provide recommendations for standardizing studies of convergence. A fundamental dichotomy exists between definitions that describe convergence as a pattern and those that describe it as a pattern caused by a particular process. When this distinction is not acknowledged it becomes easy to assume that a pattern of convergence indicates that a particular process has been active, leading researchers away from alternative explanations. Convergence is not necessarily caused by limits to evolution, either adaptation or constraint; even substantial amounts of convergent evolution can be generated by a purely stochastic process. In the absence of null models, long lists of examples of convergent events do not necessarily indicate that convergence or any evolutionary process is ubiquitous throughout the history of life. Pattern-based definitions of convergence, coupled with quantitative measures and null models, must be applied before drawing inferences regarding large-scale limits to evolution.

  11. Crustal rheology controls on the Tibetan plateau formation during India-Asia convergence

    PubMed Central

    Chen, Lin; Capitanio, Fabio A.; Liu, Lijun; Gerya, Taras V.

    2017-01-01

    The formation of the Tibetan plateau during the India-Asia collision remains an outstanding issue. Proposed models mostly focus on the different styles of Tibetan crustal deformation, yet these do not readily explain the observed variation of deformation and deep structures along the collisional zone. Here we use three-dimensional numerical models to evaluate the effects of crustal rheology on the formation of the Himalayan-Tibetan orogenic system. During convergence, a weaker Asian crust allows strain far north within the upper plate, where a wide continental plateau forms behind the orogeny. In contrast, a stronger Asian crust suppresses the plateau formation, while the orogeny accommodates most of the shortening. The stronger Asian lithosphere is also forced beneath the Indian lithosphere, forming a reversed-polarity underthrusting. Our results demonstrate that the observed variations in lithosphere deformation and structures along the India-Asia collision zone are primarily controlled by the strength heterogeneity of the Asian continental crust. PMID:28722008

  12. Crustal rheology controls on the Tibetan plateau formation during India-Asia convergence.

    PubMed

    Chen, Lin; Capitanio, Fabio A; Liu, Lijun; Gerya, Taras V

    2017-07-19

    The formation of the Tibetan plateau during the India-Asia collision remains an outstanding issue. Proposed models mostly focus on the different styles of Tibetan crustal deformation, yet these do not readily explain the observed variation of deformation and deep structures along the collisional zone. Here we use three-dimensional numerical models to evaluate the effects of crustal rheology on the formation of the Himalayan-Tibetan orogenic system. During convergence, a weaker Asian crust allows strain far north within the upper plate, where a wide continental plateau forms behind the orogeny. In contrast, a stronger Asian crust suppresses the plateau formation, while the orogeny accommodates most of the shortening. The stronger Asian lithosphere is also forced beneath the Indian lithosphere, forming a reversed-polarity underthrusting. Our results demonstrate that the observed variations in lithosphere deformation and structures along the India-Asia collision zone are primarily controlled by the strength heterogeneity of the Asian continental crust.

  13. Crustal rheology controls on the Tibetan plateau formation during India-Asia convergence

    NASA Astrophysics Data System (ADS)

    Chen, Lin; Capitanio, Fabio A.; Liu, Lijun; Gerya, Taras V.

    2017-07-01

    The formation of the Tibetan plateau during the India-Asia collision remains an outstanding issue. Proposed models mostly focus on the different styles of Tibetan crustal deformation, yet these do not readily explain the observed variation of deformation and deep structures along the collisional zone. Here we use three-dimensional numerical models to evaluate the effects of crustal rheology on the formation of the Himalayan-Tibetan orogenic system. During convergence, a weaker Asian crust allows strain far north within the upper plate, where a wide continental plateau forms behind the orogeny. In contrast, a stronger Asian crust suppresses the plateau formation, while the orogeny accommodates most of the shortening. The stronger Asian lithosphere is also forced beneath the Indian lithosphere, forming a reversed-polarity underthrusting. Our results demonstrate that the observed variations in lithosphere deformation and structures along the India-Asia collision zone are primarily controlled by the strength heterogeneity of the Asian continental crust.

  14. 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.

  15. Comparison of bacterial and archaeal communities in depth-resolved zones in an LNAPL body.

    PubMed

    Irianni-Renno, Maria; Akhbari, Daria; Olson, Mitchell R; Byrne, Adam P; Lefèvre, Emilie; Zimbron, Julio; Lyverse, Mark; Sale, Thomas C; De Long, Susan K

    2016-04-01

    Advances in our understanding of the microbial ecology at sites impacted by light non-aqueous phase liquids (LNAPLs) are needed to drive development of optimized bioremediation technologies, support longevity models, and develop culture-independent molecular tools. In this study, depth-resolved characterization of geochemical parameters and microbial communities was conducted for a shallow hydrocarbon-impacted aquifer. Four distinct zones were identified based on microbial community structure and geochemical data: (i) an aerobic, low-contaminant mass zone at the top of the vadose zone; (ii) a moderate to high-contaminant mass, low-oxygen to anaerobic transition zone in the middle of the vadose zone; (iii) an anaerobic, high-contaminant mass zone spanning the bottom of the vadose zone and saturated zone; and (iv) an anaerobic, low-contaminant mass zone below the LNAPL body. Evidence suggested that hydrocarbon degradation is mediated by syntrophic fermenters and methanogens in zone III. Upward flux of methane likely contributes to promoting anaerobic conditions in zone II by limiting downward flux of oxygen as methane and oxygen fronts converge at the top of this zone. Observed sulfate gradients and microbial communities suggested that sulfate reduction and methanogenesis both contribute to hydrocarbon degradation in zone IV. Pyrosequencing revealed that Syntrophus- and Methanosaeta-related species dominate bacterial and archaeal communities, respectively, in the LNAPL body below the water table. Observed phylotypes were linked with in situ anaerobic hydrocarbon degradation in LNAPL-impacted soils.

  16. Reduced vergence adaptation is associated with a prolonged output of convergence accommodation in convergence insufficiency.

    PubMed

    Sreenivasan, Vidhyapriya; Bobier, William R

    2014-07-01

    Convergence insufficiency (CI) is a developmental visual anomaly defined clinically by a reduced near point of convergence, a reduced capacity to view through base-out prisms (fusional convergence); coupled with asthenopic symptoms typically blur and diplopia. Experimental studies show reduced vergence parameters and tonic adaptation. Based upon current models of accommodation and vergence, we hypothesize that the reduced vergence adaptation in CI leads to excessive amounts of convergence accommodation (CA). Eleven CI participants (mean age=17.4±2.3 years) were recruited with reduced capacity to view through increasing magnitudes of base out (BO) prisms (mean fusional convergence at 40 cm=12±0.9Δ). Testing followed our previous experimental design for (n=11) binocularly normal adults. Binocular fixation of a difference of Gaussian (DoG) target (0.2 cpd) elicited CA responses during vergence adaptation to a 12Δ BO. Vergence and CA responses were obtained at 3 min intervals over a 15 min period and time course were quantified using exponential decay functions. Results were compared to previously published data on eleven binocular normals. Eight participants completed the study. CI's showed significantly reduced magnitude of vergence adaptation (CI: 2.9Δ vs. normals: 6.6Δ; p=0.01) and CA reduction (CI=0.21 D, Normals=0.55 D; p=0.03). However, the decay time constants for adaptation and CA responses were not significantly different. CA changes were not confounded by changes in tonic accommodation (Change in TA=0.01±0.2D; p=0.8). The reduced magnitude of vergence adaptation found in CI patients resulting in higher levels of CA may potentially explain their clinical findings of reduced positive fusional vergence (PFV) and the common symptom of blur. Copyright © 2014 Elsevier B.V. All rights reserved.

  17. Contrasting patterns of adaptive sequence convergence among echolocating mammals.

    PubMed

    Lambert, Matthew J; Nevue, Alexander A; Portfors, Christine V

    2017-03-20

    Several recent studies have described genes demonstrating adaptive sequence convergence between echolocating bats and dolphin, suggesting that common selective pressures can induce common molecular changes, even in distantly related species. However, in the case of the auditory genes Otoferlin (Otof), Cadherin 23 (Cdh23) and Protocadherin 15 (Pcdh15), the reported sequence convergence was supported only by incongruent gene and species trees and counts of convergent substitutions. Therefore, it remains unclear whether echolocating bats and dolphin really do demonstrate evidence of adaptive sequence convergence, or whether there is simply a high level of random background convergence in these genes. To address this question, we estimated the number of convergent and divergent amino acid substitutions along all independent branches of a sufficiently deep phylogeny containing between 22 and 32 mammals for each gene, and compared convergence between the two proposed suborders of bat, Yangochiroptera and Yinpterochiroptera, and dolphin. We find no support for convergence between bats and dolphin in the gene Pcdh15. For the gene Otof we report minimal evidence for convergent evolution only between the Yinpterochiroptera and dolphin. Cdh23 displayed a high level of convergence between dolphin and the Yinpterochiroptera. In addition, dolphin and certain members of the Yangochiroptera that emit high frequency echolocation calls shared several unique convergent substitutions. These results indicate that the convergent evolution of Cdh23 was likely driven by selection for hearing above a certain frequency threshold. Moreover, the contrasting patterns of convergence between the two bat suborders and dolphin in all auditory genes studied thus far suggest echolocation may have evolved independently in the Yinpterochiroptera and Yangochiroptera.

  18. 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.

  19. 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

  20. Converging shocks in elastic-plastic solids

    NASA Astrophysics Data System (ADS)

    López Ortega, A.; 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=es(I1)+eh(ρ,ς), where es accounts for shear through the first invariant of the Cauchy-Green tensor, and eh 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., eh=eh(ρ), with a power-law dependence eh∝ρα, shock dynamics predicts that for a converging shock located at r=R(t) at time t, the Mach number increases as M∝[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∝R-(s-1) for strong shocks. A nonisothermal constitutive law, whose hydrostatic part eh is that of an ideal gas, is also tested, recovering the strong-shock limit M∝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 hydrostatic part of the energy essentially commands the strong-shock behavior, the shear

  1. Anomalous zones (domal)

    SciTech Connect

    Kupfer, D.H. )

    1990-09-01

    Each zone contains several anomalous salt properties (anomalous features). Zones cannot be characterized by any single property Zones are highly variable, lenticular, and discontinuous in detail; however, once established, they commonly have a predictable trend. The individual anomalous features can occur alone (locally in pairs) over areas of various sizes and shapes. These alone occurrences are not anomalous zones. Anomalous zones may be of any origin, and origin is not part of the definition. Typical origins include: primary (sedimentary), external sheath zone, separating two spines of salt, or caused by toroidal flow. The major importance of an anomalous zone is that it consists of various anomalous features distributed discontinuously along the zone. Thus, if three or more anomalous properties are observed together, one should look for others. The anomalous zones observed in the Gulf Coast thus far are vertical, linear, and semicontinuous. Most are reasonably straight, but some bend sharply, end abruptly, or coalesce. Textures in salt involve grain size, color (white to dark gray), grain shape, or grain distribution of the salt. Typical anomalous textures are coarse-grain, poikiloblastic, and friability. A change in color is commonplace and seldom anomalous. Structural anomalous features, broadly defined, account for most of the rest of the anomalous features. Not uncommonly they cause mining problems. Among the structural anomalous features: INCLUSIONS: Sediments, hydrocarbons, brine, gases. Common gases are air (as N{sub 2}), CH-compounds, CO{sub 2}, and H{sub 2}S. STRUCTURES: Sheared salt, undue stabbing or jointing, voids (crystal-lined pockets), permeability, increased porosity COMPOSITION: High anhydrite content, visible anhydrite as grains or boudins, very black salt = disseminated impurities such as clay.

  2. 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

  3. 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.

  4. 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.

  5. 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. Copyright © 2016 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.

  6. 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.

  7. Convergent Replication of Mouse Synthetic Prion Strains

    PubMed Central

    Ghaemmaghami, Sina; Colby, David W.; Nguyen, Hoang-Oanh B.; Hayashi, Shigenari; Oehler, Abby; DeArmond, Stephen J.; Prusiner, Stanley B.

    2014-01-01

    Prion diseases are neurodegenerative disorders characterized by the aberrant folding of endogenous proteins into self-propagating pathogenic conformers. Prion disease can be initiated in animal models by inoculation with amyloid fibrils formed from bacterially derived recombinant prion protein. The synthetic prions that accumulated in infected organisms are structurally distinct from the amyloid preparations used to initiate their formation and change conformationally on repeated passage. To investigate the nature of synthetic prion transformation, we infected mice with a conformationally diverse set of amyloids and serially passaged the resulting prion strains. At each passage, we monitored changes in the biochemical and biological properties of the adapting strain. The physicochemical properties of each synthetic prion strain gradually changed on serial propagation until attaining a common adapted state with shared physicochemical characteristics. These results indicate that synthetic prions can assume multiple intermediate conformations before converging into one conformation optimized for in vivo propagation. PMID:23438476

  8. 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.

  9. Convergence and Fluctuations of Regularized Tyler Estimators

    NASA Astrophysics Data System (ADS)

    Kammoun, Abla; Couillet, Romain; Pascal, Ferderic; Alouini, Mohamed-Slim

    2016-02-01

    This article studies the behavior of regularized Tyler estimators (RTEs) of scatter matrices. The key advantages of these estimators are twofold. First, they guarantee by construction a good conditioning of the estimate and second, being a derivative of robust Tyler estimators, they inherit their robustness properties, notably their resilience to the presence of outliers. Nevertheless, one major problem that poses the use of RTEs in practice is represented by the question of setting the regularization parameter $\\rho$. While a high value of $\\rho$ is likely to push all the eigenvalues away from zero, it comes at the cost of a larger bias with respect to the population covariance matrix. A deep understanding of the statistics of RTEs is essential to come up with appropriate choices for the regularization parameter. This is not an easy task and might be out of reach, unless one considers asymptotic regimes wherein the number of observations $n$ and/or their size $N$ increase together. First asymptotic results have recently been obtained under the assumption that $N$ and $n$ are large and commensurable. Interestingly, no results concerning the regime of $n$ going to infinity with $N$ fixed exist, even though the investigation of this assumption has usually predated the analysis of the most difficult $N$ and $n$ large case. This motivates our work. In particular, we prove in the present paper that the RTEs converge to a deterministic matrix when $n\\to\\infty$ with $N$ fixed, which is expressed as a function of the theoretical covariance matrix. We also derive the fluctuations of the RTEs around this deterministic matrix and establish that these fluctuations converge in distribution to a multivariate Gaussian distribution with zero mean and a covariance depending on the population covariance and the parameter $\\rho$.

  10. 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.

  11. The Converged Experience of Risk and Disease

    PubMed Central

    Aronowitz, Robert A

    2009-01-01

    Context: One underappreciated consequence of modern clinical and public health practices is that the experience of being at risk for disease has been converging with the experience of disease itself. This is especially true for certain chronic diseases, in which early diagnosis and aggressive treatment have led to symptom-less and sign-less disease and in which treatments have largely been aimed at altering the disease's future course. Methods: This article reviews the historical scholarship and medical literature pertinent to transformations in the chronic disease and risk experiences. Findings: The experience of chronic disease increasingly resembles or has become indistinguishable from risk because of (1) new clinical interventions that have directly changed the natural history of disease; (2) increased biological, clinical, and epidemiological knowledge about the risk of chronic disease; (3) the recruitment of larger numbers into chronic disease diagnoses via new screening and diagnostic technology and disease definitions; (4) new ways of conceptualizing efficacy; and (5) intense diagnostic testing and medical interventions. Conclusions: The converged experience of risk and disease has led to some unsettling and generally underappreciated consequences that might be subjected to more clinical and policy reflection and response: (1) some puzzling trends in medical decision making, such as the steep and uniform increase in the numbers of women across a broad spectrum of risk/disease in breast cancer who have opted for prophylactic mastectomies; (2) a larger and highly mobilized disease/risk population, resulting in an expanded market for interventions and greater clout for disease advocates; (3) shifts in the perceived severity of the disease, with ripple effects on how people experience and understand their illness and risk of disease; and (4) interventions that promise both to reduce the risk of disease and to treat its symptoms. PMID:19523124

  12. Species-specific contribution of volumetric growth and tissue convergence to posterior body elongation in vertebrates.

    PubMed

    Steventon, Ben; Duarte, Fernando; Lagadec, Ronan; Mazan, Sylvie; Nicolas, Jean-François; Hirsinger, Estelle

    2016-05-15

    Posterior body elongation is a widespread mechanism propelling the generation of the metazoan body plan. The posterior growth model predicts that a posterior growth zone generates sufficient tissue volume to elongate the posterior body. However, there are energy supply-related differences between vertebrates in the degree to which growth occurs concomitantly with embryogenesis. By applying a multi-scalar morphometric analysis in zebrafish embryos, we show that posterior body elongation is generated by an influx of cells from lateral regions, by convergence-extension of cells as they exit the tailbud, and finally by a late volumetric growth in the spinal cord and notochord. Importantly, the unsegmented region does not generate additional tissue volume. Fibroblast growth factor inhibition blocks tissue convergence rather than volumetric growth, showing that a conserved molecular mechanism can control convergent morphogenesis through different cell behaviours. Finally, via a comparative morphometric analysis in lamprey, dogfish, zebrafish and mouse, we propose that elongation via posterior volumetric growth is linked to increased energy supply and is associated with an overall increase in volumetric growth and elongation. © 2016. Published by The Company of Biologists Ltd.

  13. The Nazca-South American convergence rate and the recurrence of the great 1960 Chilean earthquake

    NASA Technical Reports Server (NTRS)

    Stein, S.; Engeln, J. F.; Demets, C.; Gordon, R. G.; Woods, D.

    1986-01-01

    The seismic slip rate along the Chile Trench estimated from the slip in the great 1960 earthquake and the recurrence history of major earthquakes has been interpreted as consistent with the subduction rate of the Nazca plate beneath South America. The convergence rate, estimated from global relative plate motion models, depends significantly on closure of the Nazca - Antarctica - South America circuit. NUVEL-1, a new plate motion model which incorporates recently determined spreading rates on the Chile Rise, shows that the average convergence rate over the last three million years is slower than previously estimated. If this time-averaged convergence rate provides an appropriate upper bound for the seismic slip rate, either the characteristic Chilean subduction earthquake is smaller than the 1960 event, the average recurrence interval is greater than observed in the last 400 years, or both. These observations bear out the nonuniformity of plate motions on various time scales, the variability in characteristic subduction zone earthquake size, and the limitations of recurrence time estimates.

  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.

    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).

  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.; 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).

  16. Xenopus Cdc42 regulates convergent extension movements during gastrulation through Wnt/Ca2+ signaling pathway.

    PubMed

    Choi, Sun-Cheol; Han, Jin-Kwan

    2002-04-15

    Rho GTPases are molecular switches that regulate many essential cellular processes, including actin dynamics, cell adhesion, cell-cycle progression, and transcription. We have isolated the Xenopus homolog of Rho GTPase Cdc42 and examined its potential role during gastrulation movements in early Xenopus embryos. XCdc42 is expressed in tissues undergoing extensive morphogenetic changes, such as the deep layers of involuting mesoderm and posterior neuroectoderm during gastrulation, and somitic mesoderm at neurula stages. Overexpression of either wild-type (WT) or dominant-negative (DN) XCdc42 interferes with convergent extension movements in intact embryos, activin-stimulated animal caps, and dorsal marginal zone explants. These effects occur without affecting mesodermal specification. Overexpression of WT or DN XCdc42 leads to the decrease and increase of cell adhesiveness of blastomeres, respectively, as demonstrated by the cell adhesion assay. In addition, when overexpressed, PKC-alpha, XWnt-5a, and Mfz-3 inhibit activin-induced convergent extension in animal cap explants. This inhibition can be rescued by coexpression of DN XCdc42, implying that XCdc42 acts downstream of the Wnt/Ca2+ signaling pathway involving PKC activation. XCdc42 also lies downstream of XWnt-5a in the regulation of Ca2+-dependent cell adhesion. Taken together, our results suggest that XCdc42 plays a role in the regulation of convergent extension movements during gastrulation through the protein kinase C-mediated Wnt/Ca2+ pathway.

  17. 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.

  18. 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.

  19. Disparity and convergence: Chinese provincial government health expenditures.

    PubMed

    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.

  20. 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