The end of continental growth by TTG magmatism   总被引：1，自引：0，他引：1  

Angelique Laurie  Gary Stevens  Jeroen van Hunen 《地学学报》2013,25(2):130-136

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Sampling Bias and Class Imbalance in Maximum-likelihood Logistic Regression     

Thomas?OommenEmail author  Laurie?G.?Baise  Richard?M.?Vogel 《Mathematical Geosciences》2011,43(1):99-120

Logistic regression is a widely used statistical method to relate a binary response variable to a set of explanatory variables and maximum likelihood is the most commonly used method for parameter estimation. A maximum-likelihood logistic regression (MLLR) model predicts the probability of the event from binary data defining the event. Currently, MLLR models are used in a myriad of fields including geosciences, natural hazard evaluation, medical diagnosis, homeland security, finance, and many others. In such applications, the empirical sample data often exhibit class imbalance, where one class is represented by a large number of events while the other is represented by only a few. In addition, the data also exhibit sampling bias, which occurs when there is a difference between the class distribution in the sample compared to the actual class distribution in the population. Previous studies have evaluated how class imbalance and sampling bias affect the predictive capability of asymptotic classification algorithms such as MLLR, yet no definitive conclusions have been reached.  相似文献   

Environments in a Changing World     

Laurie Jackson 《New Zealand geographer》2002,58(1):54-55

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Development and analysis of echo classification using time delays     

Tremblay  R.J. Lytle  D.W. 《Oceanic Engineering, IEEE Journal of》1996,21(2):205-215

The results from an investigation of an analytically based method for determining the performance of echo classifiers are presented. In particular, the problem of classifying echo waveforms reflected from objects that are composed of multiple scatterers is considered. The time delays between the multiple echo returns from the individual scattering centers that characterize an object are investigated as features. A generic stochastic point scatterer model is developed for representing the classes of reflecting objects which are of interest. The model allows for uncertainty in prior knowledge about the exact relative location of the individual component scatterers or uncertainty in the delay measurements. A classifier decision algorithm, in the form of a general optimum Bayesian binary classification decision rule suitable for a large variety of classification problems, is derived for the case when the orientation of the reflecting object is known. The case of unknown aspect angle is addressed through the numerical implementation and analysis of two classifiers. The associated performance for all three classifiers is obtained in terms of the probability of error and tied to standard sonar equation parameters. Example binary classification problems are presented and analyzed and some general observations made. A pragmatic framework is established within which complex echo classification issues can be further examined  相似文献   

Simulation of the interannual variability of the wind-driven Arctic sea-ice cover during 1958–1998     

G. Arfeuille  L. A. Mysak  L. -B. Tremblay 《Climate Dynamics》2000,16(2-3):107-121

A thermodynamic-dynamic sea-ice model based on a granular material rheology developed by Tremblay and Mysak is used to study the interannual variability of the Arctic sea-ice cover during the 41-year period 1958–98. Monthly wind stress forcing derived from the National Centers for Environmental Prediction (NCEP) Reanalysis data is used to produce the year-to-year variations in the sea-ice circulation and thickness. We focus on analyzing the variability of the sea-ice volume in the Arctic Basin and the subsequent changes in sea-ice export into the Greenland Sea via Fram Strait. The relative contributions of the Fram Strait sea-ice thickness and velocity anomalies to the sea-ice export anomalies are first investigated, and the former is shown to be particularly important during several large export events. The sea-ice export anomalies for these events are next linked to prior sea-ice volume anomalies in the Arctic Basin. The origin and evolution of the sea-ice volume anomalies are then related to the sea-ice circulation and atmospheric forcing patterns in the Arctic. Large sea-ice export anomalies are generally preceded by large volume anomalies formed along the East Siberian coast due to anomalous winds which occur when the Arctic High is centered closer than usual to this coastal area. When the center of this High relocates over the Beaufort Sea and the Icelandic Low extends far into the Arctic Basin, the ice volume anomalies are transported to the Fram Strait region via the Transpolar Drift Stream. Finally, the link between the sea-ice export and the North Atlantic Oscillation (NAO) index is briefly discussed. The overall results from this study show that the Arctic Basin and its ice volume anomalies must be considered in order to fully understand the export through Fram Strait. Received: 27 January 1999 / Accepted: 8 July 1999  相似文献   

Preferential low-pH dissolution of pyroxene in plagioclase-pyroxene mixtures: Implications for martian surface materials     

Amy C. McAdam  Mikhail Yu. Zolotov  Laurie A. Leshin 《Icarus》2008,196(1):90-96

Acid weathering of plagioclase-pyroxene mixtures has been investigated with an open system kinetic dissolution model. The modeling reveals that elevated plagioclase/pyroxene ratios observed in some low-albedo martian regions and atmospheric dust could be partially caused by preferential dissolution of pyroxenes at pHs below ∼3-4. Surface materials with smaller grain sizes, affected by lower pH fluids, and/or exposed to longer durations of acid weathering would be enriched in plagioclase. If preferential dissolution is responsible for the observed mineral ratios, the dissolution process likely occurred on a large scale, such as weathering by acid atmospheric precipitates. If dissolution was continuous, modeled timeframes required to produce a high plagioclase/pyroxene ratio are short on geologic timescales; however, it is likely that acid weathering on Mars was episodic, possibly occurring over a longer period of time.  相似文献   

Three-dimensional liquefaction potential analysis using geostatistical interpolation   总被引：1，自引：0，他引：1  

Kevin M. Dawson  Laurie G. Baise   《Soil Dynamics and Earthquake Engineering》2005,25(5):369-381

We applied three-dimensional geostatistical interpolation to evaluate the extent of liquefiable materials at two sites that liquefied during the 1994 Northridge Earthquake. The sites were the Balboa Blvd site and the Wynne Ave. site located in the alluvial San Fernando Valley. The estimated peak ground accelerations at the sites are 0.84 g (Balboa Blvd) and 0.51 g (Wynne Ave.). These sites were chosen because surface effects due to liquefaction were not predicted using available techniques based on thickness and depth of liquefiable layers (Ishihara [Ishihara K. Stability of natural deposits during earthquakes. Proceedings of the 11th international conference on soil mechanics and foundation engineering, vol. 1. Rotterdam, The Netherlands: A.A. Balkema; 1985. p. 321–76.]) and the Liquefaction Potential Index (Iwasaki et al. [Iwasaki T, Tatsuoka F, Tokida K, Yasuda S. A practical method for assessing soil liquefaction potential based on case studies at various sites in Japan. In: Proceedings of the second international conference on microzonation, San Francisco; 1978. p. 885–96.]). During the earthquake, both sites experienced surface effects including ground cracking and extension as a result of liquefaction. Foundations and buried utilities were damaged at both sites. The sites were investigated after the event by researchers with the United States Geologic Survey using standard penetration tests (SPT) and cone penetration tests. In this paper, liquefaction potential was estimated for each soil sample using results from SPTs according to the updated Seed and Idriss simplified procedure. The probability of liquefaction was estimated by applying an indicator transform to the results of the liquefaction potential calculation. We compared our results to detailed geologic mapping of the sites performed by other researchers. Using geostatistical interpolation to estimate the probability of liquefaction is a useful supplement to geologic evaluation of liquefaction potential. The geostatistical analysis provides an estimate of the continuous volume of liquefiable soil along with an assessment of confidence in an interpolation. The probability of liquefaction volumes compare well with those predicted using geologic interpretations.  相似文献   

Behaviour and modelling of partial‐strength beam‐to‐column composite joints for seismic applications     

A. Braconi  W. Salvatore  R. Tremblay  O. S. Bursi 《地震工程与结构动力学》2007,36(1):142-161

A refined component model is proposed to predict the inelastic monotonic response of exterior and interior beam‐to‐column joints for partial‐strength composite steel–concrete moment‐resisting frames. The joint typology is designed to exhibit ductile seismic response through plastic deformation developing simultaneously in the column web panel in shear, the bolted end‐plate connection, the column flanges in bending and the steel reinforcing bars in tension. The model can handle the large inelastic deformations consistent with high ductility moment‐resisting frames. Slip response between the concrete slab and the beams was taken into account. A fibre representation was adopted for the concrete slab to accurately capture the non‐uniform stress distribution and progressive crushing of the concrete at the interface between the concrete slab and the column flange. The model is validated against results from full‐scale subassemblages monotonic physical tests performed at the University of Pisa, Italy. A parametric study is presented to illustrate the capabilities of the model and the behaviour of the joints examined. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Defining phases of bedload transport using piecewise regression     

Sandra E. Ryan  Laurie S. Porth  C. A. Troendle 《地球表面变化过程与地形》2002,27(9):971-990

Differences in the transport rate and size of bedload exist for varying levels of flow in coarse‐grained channels. For gravel‐bed rivers, at least two phases of bedload transport, with notably differing qualities, have been described in the literature. Phase I consists primarily of sand and small gravel moving at relatively low rates over a stable channel surface. Transport rates during Phase II are considerably greater than Phase I and more coarse grains are moved, including material from both the channel surface and subsurface. Transition from Phase I to Phase II indicates initiation and transport of grains comprising the coarse surface layer common in steep mountain channels. While the existence of different phases of transport is generally acknowledged, the threshold between them is often poorly defined. We present the results of the application of a piecewise regression analysis to data on bedload transport collected at 12 gravel‐bed channels in Colorado and Wyoming, USA. The piecewise regression recognizes the existence of different linear relationships over different ranges of discharge. The inflection, where the fitted functions intersect, is interpreted as the point of transition from Phase I to Phase II transport; this is termed breakpoint. A comparison of grain sizes moved during the two phases shows that coarse gravel is rarely trapped in the samplers during Phase I transport, indicating negligible movement of grains in this size range. Gravel larger than about D₁₆ of the channel surface is more consistently trapped during Phase II transport. The persistence of coarse gravel in bedload samples provides good evidence that conditions suitable for coarse grain transport have been reached, even though the size of the sediment approaches the size limits of the sampler (76 mm in all cases). A relative breakpoint (R_br) was defined by the ratio between the discharge at the breakpoint and the 1·5‐year flow (a surrogate for bankfull discharge) expressed as a percentage. The median value of R_br was about 80 percent, suggesting that Phase II begins at about 80 percent of the bankfull discharge, though the observed values of R_br ranged from about 60 to 100 percent. Variation in this value appears to be independent of drainage area, median grain size, sorting of bed materials, and channel gradient, at least for the range of parameters measured in 12 gravel‐bed channels. Published in 2002 by John Wiley & Sons, Ltd.  相似文献   

Ecology, Uncertainty and Policy: Managing Ecosystems for Sustainability     

Laurie Jackson 《New Zealand geographer》2002,58(1):52-53

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