STEREO/Extreme Ultraviolet Imager (EUVI) Event Catalog 2006 – 2012     

Markus J. Aschwanden  Jean-Pierre Wülser  Nariaki V. Nitta  James R. Lemen  Sam Freeland  William T. Thompson 《Solar physics》2014,289(3):919-938

We generated an event catalog with an automated detection algorithm based on the entire EUVI image database observed with the two Solar Terrestrial Relations Observatory (STEREO)-A and -B spacecraft over the first six years of the mission (2006?–?2012). The event catalog includes the heliographic positions of some 20?000 EUV events, transformed from spacecraft coordinates to Earth-based coordinates, and information on associated GOES flare events (down to the level of GOES A5-class flares). The 304 Å wavelength turns out to be the most efficient channel for flare detection (79?% of all EUVI event detections), while the 171 Å (4?%), 195 Å (10?%), and the 284 Å channel (7?%) retrieve substantially fewer flare events, partially due to the suppressing effect of EUV dimming, and partially due to the lower cadence in the later years of the mission. Due to the Sun-circling orbits of STEREO-A and -B, a large number of flares have been detected on the farside of the Sun, invisible from Earth, or seen as partially occulted events. The statistical size distributions of EUV peak fluxes (with a power-law slope of α _P =2.5±0.2) and event durations (with a power-law slope of α _T =2.4±0.3) are found to be consistent with the fractal-diffusive self-organized criticality model. The EUVI event catalog is available on-line at secchi.lmsal.com/EUVI/euvi_autodetection/euvi_events.txt and may serve as a comprehensive tool to identify stereoscopically observed flare events for 3D reconstruction and to study occulted flare events.  相似文献   

Kinematic hardening of soft clay in simple shear     

Alexander Puzrin  Sam Frydman  Mark Talesnick 《国际地质力学数值与分析法杂志》1995,19(11):769-791

In a separate paper, the authors have proposed a normalized, non-degrading form of the shear stress–shear strain relationship for undrained, cyclic simple shear of soft clay. This relationship is described in the present paper, and it is seen to include a single fatigue parameter—the mean effective stress. Application of the relationship therefore requires knowledge of the history of the mean effective stress during any loading history. The present paper proposes an effective stress path model which may be used for prediction of this history. The model is developed within the framework of bounding surface kinematic and isotropic hardening plasticity. It incorporates an isotropic hardening bounding surface, and a kinematic hardening yield surface, in which the elastic region vanishes, and so the yield surface reduces to the stress point. The normalized shear stress–shear strain relationship, developed on the basis of Iwan's model, is used to establish the shape of the cap of the bounding surface. A new translation rule is also incorporated in the model, allowing improved prediction of stress path development within the bounding surface during regular or irregular cyclic loading. Use of the proposed model to simulate the behaviour of soft clay in laboratory undrained cyclic simple shear tests shows excellent qualitative agreement, with most of the major features of the actual behaviour being predicted.  相似文献   

Seismic analysis of infinite pile groups in liquefiable soil     

Assaf Klar  Sam Frydman  Rafael Baker 《Soil Dynamics and Earthquake Engineering》2004,24(8):565-575

Numerical analysis of an infinite pile group in a liquefiable soil was considered in order to investigate the influence of pile spacing on excess pore pressure distribution and liquefaction potential. It was found that an optimal pile spacing exists resulting in minimal excess pore pressure. It was also found that certain pile group configurations might reduce liquefaction potential, compared to free field conditions. It was observed that for closely spaced piles and low frequency of loading, pile spacing has little influence on the response of the superstructure.  相似文献   

Step heating of Ar/Ar standard mineral mixtures: Investigation of a fine-grained bulk sediment provenance tool     

Sam VanLaningham  Darren F. Mark 《Geochimica et cosmochimica acta》2011,75(9):2324-2335

Quantitative techniques that link sediments to their sources are needed to understand a range of tectonic, climate, and anthropogenic driven Earth surface processes. Many provenance techniques exist for sand-sized material but fewer are available for fine-grained sediment archives. In this respect, bulk ⁴⁰Ar/³⁹Ar ages from silt-sized sediment show potential, but many questions remain about the significance of a bulk sediment ⁴⁰Ar/³⁹Ar age. We interrogate bulk sediment ⁴⁰Ar/³⁹Ar ages by step heating mixtures of well-constrained ⁴⁰Ar/³⁹Ar mineral standards crushed to silt-sized. Silt-sized end member components Alder Creek Sanidine, Taylor Creek Sanidine and Heidelberg Biotite all yield plateau ages within uncertainty of their coarse-grained counterparts. High-resolution step heating (as many as 43 steps) of the mineral mixtures shows that biotite degasses first at lower temperatures compared to the two sanidines that degas generally in concert. Concordant age steps develop at both low and high temperatures and the transition from the isotope signal being dominated by one mineral phase to another is clearly observed. We show that age spectra for the mineral standard mixtures can be modeled and predicted for all mixtures by assuming a (simplistic) Gaussian distributed release of Ar, and by using the degassing maxima, variance, K concentration, and ⁴⁰Ar/³⁹Ar age of each monitor mineral. Thus, bulk sediment ⁴⁰Ar/³⁹Ar ages can be robust indicators of the average cooling/crystallization age of all contributing K-bearing minerals to a depositional center. Furthermore, we discuss the potential to deconvolve individual mineral age populations by model inversion. The application of this bulk sediment provenance technique should not be considered a replacement for single grain analyses. It should be applied to environments that do not provide sand-sized sediment archives (e.g., distal terrigenous sedimentary archives) when information about source changes through time are more important than precise sediment source identification.  相似文献   

Pb isotopic variability in the modern-Pleistocene Indus River system measured by ion microprobe in detrital K-feldspar grains   总被引：1，自引：0，他引：1  

Anwar Alizai  Peter D. Clift  Sam VanLaningham  Ali R. Tabrez  The Edinburgh Ion Microprobe Facility 《Geochimica et cosmochimica acta》2011,75(17):4771-4795

The western Himalaya, Karakoram and Tibet are known to be heterogeneous with regard to Pb isotope compositions in K-feldspars, which allows this system to be used as a sediment provenance tool. We used secondary ion mass spectrometry to measure the isotopic character of silt and sand-sized grains from the modern Sutlej and Chenab Rivers, together with Thar Desert sands, in order to constrain their origin. The rivers show a clear Himalayan provenance, contrasting with grains from the Indus Suture Zone, but with overlap to known Karakoram compositions. The desert dunes commonly show ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb values that are much higher than those seen in the rivers, most consistent with erosion from Nanga Parbat. This implies at least some origin from the trunk Indus, probably reworked by summer monsoon winds from the SW, a hypothesis supported by bulk Nd and U-Pb zircon dating. Further data collected from Holocene and Pleistocene sands shows that filled and abandoned channels on the western edge of the Thar Desert were sourced from Himalayan rivers before and at 6-8 ka, but that after that time the proportion of high isotopic ratio grains rose, indicating increased contribution from the Thar Desert dunes prior to ∼4.5 ka when flow ceased entirely. This may be linked to climatic drying, northward expansion of the Thar Desert, or changes in drainage style including regional capture, channel abandonment, or active local Thar tributaries. Our data further show a Himalayan river channel east of the present Indus, close to the delta, in the Nara River valley during the middle Holocene. While this cannot be distinguished from the Indus it is not heavily contaminated by reworking from the desert. The Pb system shows some use as a provenance tool, but is not effective at demonstrating whether these Nara sediments represent a Ghaggar-Hakra stream independent from the Indus. Our study highlights an important role for eolian reworking of floodplain sediments in arid rivers such as the Indus.  相似文献   

Intensity forecast of tropical cyclones over North Indian Ocean using multilayer perceptron model: skill and performance verification     

Sutapa Chaudhuri  Debashree Dutta  Sayantika Goswami  Anirban Middey 《Natural Hazards》2013,65(1):97-113

The coastal regions of India are profoundly affected by tropical cyclones during both pre- and post-monsoon seasons with enormous loss of life and property leading to natural disasters. The endeavour of the present study is to forecast the intensity of the tropical cyclones that prevail over Arabian Sea and Bay of Bengal of North Indian Ocean (NIO). A multilayer perceptron (MLP) model is developed for the purpose and compared the forecast through MLP model with other neural network and statistical models to assess the forecast skill and performances of MLP model. The central pressure, maximum sustained surface wind speed, pressure drop, total ozone column and sea surface temperature are taken to form the input matrix of the models. The target output is the intensity of the tropical cyclones as per the T??number. The result of the study reveals that the forecast error with MLP model is minimum (4.70?%) whereas the forecast error with radial basis function network (RBFN) is observed to be 14.62?%. The prediction with statistical multiple linear regression and ordinary linear regression are observed to be 9.15 and 9.8?%, respectively. The models provide the forecast beyond 72?h taking care of the change in intensity at every 3-h interval. The performance of MLP model is tested for severe and very severe cyclonic storms like Mala (2006), Sidr (2007), Nargis (2008), Aila (2009), Laila (2010) and Phet (2010). The forecast errors with MLP model for the said cyclones are also observed to be considerably less. Thus, MLP model in forecasting the intensity of tropical cyclones over NIOs may thus be considered to be an alternative of the conventional operational forecast models.  相似文献   

Chemically stabilized soil organic carbon fractions in a reclaimed minesoil chronosequence: implications for soil carbon sequestration   总被引：1，自引：0，他引：1  

Sriroop Chaudhuri  Louis M. McDonald  Eugenia M. Pena-Yewtukhiw  Jeff Skousen  Mimi Roy 《Environmental Earth Sciences》2013,70(4):1689-1698

With adoption of appropriate reclamation strategies, minesoils can sequester significant amount of soil organic carbon (SOC). The objective of this study was to isolate different SOC fractions and coal-C in a reclaimed minesoil chronosequence and assess effects of increasing time since reclamation on each SOC fraction and selected soil properties. The chronosequence was comprised of four minesoils with time since reclamation ranging between 2 and 22 years. Total SOC (TSOC, summation of all SOC fractions), ranged between 20 and 8 g kg^?1, respectively, at the oldest (Mylan Park) and youngest (WVO1) minesite, indicating increasing SOC sequestration along the chronosequence. The humin fraction accounted for about 43 and 7 % of TSOC, respectively, at Mylan Park and WVO1, indicating increasing humification and biochemical stabilization of SOC with increasing time since reclamation. At WVO1, >60 % of TSOC was apportioned among the acid-hydrolysable (labile) and mineral-bound SOC fractions. Total soil carbon (TSC, TSOC + coal-C) were significantly (p < 0.05) related to the humin fraction in older minesoils, whereas with the acid-hydrolysable (labile) fraction in the younger minesoils indicating that C stabilization mechanisms differed substantially along the chronosequence. Coal-C was unrelated to any SOC fraction at all minesites indicating that SOC sequestration estimations in this chronosequence was unaffected by coal-C. Soil cation exchange capacity and electrical conductivity were significantly (p < 0.05) related to the humin fraction at Mylan Park while to the acid-hydrolysable and mineral-bound SOC fractions at WVO1 indicating that the relative influences of different SOC fractions on soil quality indicators differed substantially along the chronosequence.  相似文献   

Annual floods in New England (USA) and Atlantic Canada: synoptic climatology and generating mechanisms   总被引：1，自引：1，他引：0  

Mathias J. Collins  Johnathan P. Kirk  Joshua Pettit  Arthur T. DeGaetano  M. Sam McCown  Thomas C. Peterson 《自然地理学》2014,35(3):195-219

New England and Atlantic Canada are characterized by mixed flood regimes that reflect different storm types, antecedent land surface conditions, and flood seasonality. Mixed flood regimes are known to complicate flood risk analyses, yet the synoptic climatology and precipitation mechanisms that generate annual floods in this region have not been described in detail. We analyzed a set of long-term annual flood records at climate-sensitive stream gauges across the region and classified the synoptic climatology of each annual flood, quantitatively describing the precipitation mechanisms, and characterize flood seasonality. We find that annual floods here are dominantly generated by Great Lakes-sourced storms and Coastal lows, known locally as ‘nor’easters.’ Great Lakes storms tend to be associated with lower magnitude annual floods (<75th percentile) and Coastal lows are more clearly associated with higher magnitude events (>75th percentile). Tropical cyclones account for few of all annual floods, including extreme events, despite causing some of the region’s largest and most destructive floods. Late winter/early spring is when the greatest number of annual floods occur region wide, and rainfall is the dominant flood-producing mechanism. Rainfall in combination with snowmelt is also important. Both mechanisms are expected to be impacted by projected regional climate change. We find little evidence for associations between flood-producing synoptic storm types or precipitation mechanisms and large-scale atmospheric circulation indices or time periods, despite upward trends in New England annual flood magnitudes. To more completely investigate such associations, partial duration flood series that include more floods than just the largest of each year, and their associated synoptic climatologies and precipitation mechanisms, should be analyzed.  相似文献   

Temporal Accuracy in Urban Growth Forecasting: A Study Using the SLEUTH Model   总被引：2，自引：0，他引：2  

Gargi Chaudhuri  Keith C. Clarke 《Transactions in GIS》2014,18(2):302-320

This study attempts to establish multi‐temporal accuracy of the predicted maps produced by a land use change simulation model over time. Validation of the forecasted results is an essential part of predictive modeling and it becomes even more important when the models are used for decision making purposes. The present study uses a popular land use change model called SLEUTH to investigate the temporal trend of accuracy of the predicted maps. The study first investigates the trend of accuracy of the predicted maps from the immediate future to the distant future. Secondly, it investigates the impact of the prediction date range on the accuracy of the predicted maps. The objectives are tested for the city of Gorizia (Italy) using three sets of map comparison techniques, Kappa coefficients, Kappa Simulation and quantity disagreement and allocation disagreement. Results show that, in addition to the model's performance, the decrease in the accuracy of the predicted maps is dependent on factors such as urban history, uncertainty of input data and accuracy of reference maps.  相似文献   

Exhibitions     

Jiří Pánek  Alex Gekker  Sam Hind  Jana Wendler  Chris Perkins  Sybille Lammes 《The Cartographic journal》2013,50(3):285-301

In this paper we propose the use of ‘Encountering’ a location-based game (LBG) based on the Wherigo platform to facilitate interdisciplinary student learning about places on field courses. Deploying a mobile, digital map-based platform addresses significant challenges – such as the sacrifice of context specificity and methodological applicability and depth. It also runs the danger of ‘gamifying’ the fieldwork, blinding the participant to their own agency and emergent encounters. Interactive and layered digital map interfaces have affordances that can potentially overcome such challenges. We claim that one such affordance is the ability to play through the map. In other words, maps – and digital maps in particular – offer the possibility of decoupling results-orientated actions from free-form serendipitous engagement with the field. Our argument is two-fold. First, that LBG toolsets such as Wherigo can provide a ‘common ground’ for students engaging in place-based interdisciplinary research, by providing a material, cartographic basis for playful investigation. Second, that they can facilitate the production of ‘spaces of epistemological failure’, allowing students to challenge taken-for-granted conceptual and methodological axioms within and across disciplines.  相似文献