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SEMI-QUANTITATIVE CHARACTERIZATION OF SEGMENT DISTRIBUTION IN LLDPE BASED ON THERMAL SEGREGATION

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Chinese Journal of Polymer Science 2002年第4期20卷 347-352页

作者： stephen Z.D.Cheng Maurice Morton Institute and Department of Polymer Science University of Akron Akron Lhio 44325-3909 USA

Based on successive multiple-step isothermal crystallization and self-nucleation annealing methods, a novel semi-quantitative method for the characterization of segment distribution in linear low density polyethylene (LLDPE) was established by treating the thermal analysis data using the Gibbs-Thomson equation. The method was used to describe the segment distribution of Ziegler-Natta catalyzed LLDPE (Z-N LLDPE), metallocene catalyzed LLDPE (m-LLDPE) and two commercial LLDPEs with wide molecular weight distribution. The differences of the results obtained from the two thermally treated samples were compared. The results of segment distribution of the polymers were discussed according to their microstructure data and were compared with their characteristics. It can be deduced from the results that this characterization method is effective to characterize the sequence structure of the branched ethylene copolymers.

关键词： characterization segment distribution linear low density polyethylene thermal segregation

Laplace plane and low inclination geosynchronous radar mission design

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Science China(Information Sciences) 2017年第6期60卷 62-71页

作者： stephen HOBBS Joan Pau SANCHEZ School of Aerospace Transport and Manufacturing Cranfield University

This study is inspired by the Laplace orbit plane property of requiring minimal station-keeping and therefore its potential use for long-term geosynchronous synthetic aperture radar(GEOSAR) imaging. A set of GEOSAR user requirements is presented and analysed to identify significant mission requirements. Imaging geometry and power demand are assessed as a function of relative satellite speed(which is determined largely by choice of orbit inclination). Estimates of the cost of station-keeping as a function of orbit inclination and right ascension are presented to compare the benefits of different orbit choices. The conclusion is that the Laplace plane(and more generally, orbits with inclinations up to 15°) are attractive choices for GEOSAR.

关键词： Laplace plane station-keeping geosynchronous inclination GEOSAR

Learning Convex Optimization Models

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IEEE/CAA Journal of Automatica Sinica 2021年第8期8卷 1355-1364页

作者： Akshay Agrawal Shane Barratt stephen Boyd Department of Electrical Engineering Stanford UniversityStanfordCA 94305 USA

A convex optimization model predicts an output from an input by solving a convex optimization *** class of convex optimization models is large,and includes as special cases many well-known models like linear and logistic *** propose a heuristic for learning the parameters in a convex optimization model given a dataset of input-output pairs,using recently developed methods for differentiating the solution of a convex optimization problem with respect to its *** describe three general classes of convex optimization models,maximum a posteriori(MAP)models,utility maximization models,and agent models,and present a numerical experiment for each.

关键词： Convex optimization differentiable optimization machine learning

On Iterative Algorithm and Perturbation Analysis for the Nonlinear Matrix Equation

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Communications on Applied Mathematics and Computation 2022年第3期4卷 1158-1174页

作者： Chacha stephen Chacha Department of Mathematics Physics and InformaticsMkwawa University College of EducationP.O.Box 2513IringaTanzania

In this study,an iterative algorithm is proposed to solve the nonlinear matrix equation X+A∗eXA=*** expressions for mixed and componentwise condition numbers with their upper bounds are derived to measure the sensitivity of the considered nonlinear matrix *** analysis for the derived condition numbers and the proposed algorithm are *** proposed iterative algorithm reduces the number of iterations significantly when incorporated with exact line *** condition number seems more reliable to detect the sensitivity of the considered equation than mixed condition number as validated by numerical examples.

关键词： Mixed condition number Componentwise condition number Iterative algorithm Perturbation analysis Exact line search

Characterization of isolated homogeneous hypersurface singularities in C^4

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Science China Mathematics 2006年第11期49卷 1576-1592页

作者： YAU stephen S T Department of Mathematics Statistics and Computer Science University of Illinois at ChicagoChicagoIL 60607-7045USA

Let V be a hypersurface with an isolated singularity at the origin in Cn+1. It is a natural question to ask when V is defined by weighted homogeneous polynomial or homogeneous polynomial up to biholomorphic change of coordinates. In 1971, a beautiful theorem of Saito gives a necessary and sufficient condition for V to be defined by a weighted homogeneous polynomial. For a two-dimensional isolated hypersurface singularity V, Xu and Yau found a coordinate free characterization for V to be defined by a homogeneous polynomial. Recently Lin and Yau gave necessary and sufficient conditions for a 3-dimensional isolated hypersurface singularity with geometric genus bigger than zero to be defined by a homogeneous polynomial. The purpose of this paper is to prove that Lin-Yau's theorem remains true for singularities with geometric genus equal to zero.

关键词： homogeneous polynomials, hypersurface singularity, weighted homogeneous polynomial, geometric genus.

John Coates(1945-2022):生命的礼赞

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数学译林 2024年第1期43卷 22-34,21页

作者： Barry Mazur stephen Lichtenbaum Andrew Wiles Leila Schneps Sujatha Mahesh Kakde 陆柱家(译) 张晓宇(校) 哈佛大学布朗大学牛津大学 Sorbonne大学不列颠哥伦比亚大学印度科学研究所不详

1.怀念John Coates Barry Mazur(马祖尔)JohnCoates(科茨)的数学工作范围很广,包括他的智力乐趣以及他激励和指导几代数学家的才华,是给我们所有人的礼物.在我认识他的初期,就能明显感受到他的活力和友谊,他乐意分享他的想法,欣赏别人... 详细信息

1.怀念John Coates Barry Mazur(马祖尔)JohnCoates(科茨)的数学工作范围很广,包括他的智力乐趣以及他激励和指导几代数学家的才华,是给我们所有人的礼物.在我认识他的初期,就能明显感受到他的活力和友谊,他乐意分享他的想法,欣赏别人的观点.1969年,他来到哈佛大学任Benjamin Peirce(皮尔斯)助理教授.在那里,他在对JohnTate(泰特)的纪念中写道,“非常局促的办公室”,它的“现实中的小规模”和“办公室之间的小咖啡室或走廊”为他提供了一个易于与他人互动的环境.Tate向他介绍了数学的各个方面,这将把他带到后来他做出巨大贡献的地方.

关键词：助理教授皮尔斯哈佛大学

Breather Dynamics of the Sine-Gordon Equation

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Communications in Theoretical Physics 2013年第6期59卷 664-670页

作者： stephen Johnson Anjan Biswas stephen Johnson and Anjan Biswas Department of Mathematical Sciences Delaware State University Department of Mathematics Faculty of Science King Abdulaziz University

This paper studies the adiabatic dynamics of the breather soliton of the sine-Gordon equation. The integrals of motion are found and then used in soliton perturbation theory to derive the differential equation governing the soliton velocity. Time-dependent functions arise and their properties are studied. These functions are found to be bounded and periodic and affect the soliton velocity. The soliton velocity is numerically plotted against time for different combinations of initial velocities and perturbation terms.

关键词： solitons phonons conservation laws perturbations numerics

A relational database of global U-Pb ages

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Geoscience Frontiers 2018年第3期9卷 877-891页

作者： stephen J.Puetz Progressive Science Institute HonoluluHI 96815USA

Enhanced understanding of how sampling techniques affect estimates of the global U-Pb age-distribution have, in turn, constrained U-Pb database design. Recent studies indicate that each continent has a unique age-distribution, as determined by zircon ages dated by the U-Pb isotope method. Likewise, broad regions within a continent also exhibit diverse age-distributions. To achieve a reliable estimate of the global distribution, the heterogenous composition of the continental crust requires sampling as many regions as feasibly possible. To attain this goal, and to provide a method for calculating age histograms, the records from a recent global U-Pb compilation are supplemented with 281,631 new records. These additions increase the database size to 700,598 records. In addition, the data are now restructured and made available as a relational database. After filtering the records by the six age-models included with the database, the results reveal two problems that might generally be unrecognized. First, an abrupt switch in the best-age at any given point(such as 1000 Ma) from ^(206)Pb/^(238)U ages to ^(207)Pb/^(206)Pb ages artificially depresses the age-distribution at the cutoff point. Second, rejecting analyses based on either absolute discordance or the magnitude of 2σ precision errors artificially depresses the age-distribution between 900 Ma and 2000 Ma. The results indicate that, when estimating the global U-Pb age-distribution, the methods for determining best-age and for rejecting records both require some attention. Possible solutions include using either an Accuracy Model or a Precision Model for estimating best-age, and then including all U-Pb records in the estimate, rather than rejecting any of them.

关键词： U-Pb age-distribution Histogram Global database Sampling Filtering Zircon

An integrated measurement and modeling methodology for estuarine water quality management

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Water Science and Engineering 2015年第1期8卷 9-19页

作者： Michael Hartnett stephen Nash Department of Civil Engineering National University of Ireland

This paper describes research undertaken by the authors to develop an integrated measurement and modeling methodology for water quality management of estuaries. The approach developed utilizes modeling and measurement results in a synergistic manner. Modeling results were initially used to inform the field campaign of appropriate sampling locations and times, and field data were used to develop accurate models. Remote sensing techniques were used to capture data for both model development and model validation. Field surveys were undertaken to provide model initial conditions through data assimilation and determine nutrient fluxes into the model domain. From field data, salinity re- lationships were developed with various water quality parameters, and relationships between chlorophyll a concentrations, transparency, and light attenuation were also developed. These relationships proved to be invaluable in model development, particularly in modeling the growth and decay of chlorophyll a. Cork Harbour, an estuary that regularly experiences summer algal blooms due to anthropogenic sources of nutrients, was used as a case study to develop the methodology. The integration of remote sensing, conventional fieldwork, and modeling is one of the novel aspects of this research and the approach developed has widespread applicability.

关键词： Estuarine modeling Hydrodynamics Water quality management Nutrients Phytoplankton Field measurements Remote sensing