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Microhardness,Microstructure and Electrochemical Efficiency of an Al(Zn/xMg) Alloy after Thermal Treatment

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Journal of Materials Science & Technology 2012年第3期28卷 255-260页

作者： Socorro Valdez M.Suarez O.A.Fregoso J.A.Juárez-Islas instituto de ciencias fisicas-unam Av.Universidad S/N Col.Chamilpa062210CuernavacaMorelosMéxico instituto de Investigaciones en Materiales-unam Circuito escolar S/NCd.Universitaria04515MéxicoD.F.México

The influence of Mg on the microhardness,microstructure and electrochemical efficiency of Al（Zn/xMg） alloys have been ***（Zn/xMg） alloys were prepared by metal mould casting method to diminish the process cost and to generate an alloy with homogenous microstructure and less casting *** hardness,X-ray diffraction,scanning electron microscopy and transmission electron microscopy were performed to determine the Mg influence on the AlZn *** efficiency was used to relate the influence of Mg with the thermal treatment on the corrosion behavior of the Al（Zn/xMg） *** results reveals the presence of Al 32（MgZn） 49 phase for two events;the first is when the Mg content is above 5.49% in as-cast condition,and the second after the thermal treatment is carried out at 450℃ for 5 *** results also show that the microhardness and electrochemical efficiency have been influenced by the presence of Al 32（MgZn） 49 *** addition of Mg modifies the microstructure,increases the content of Al 32（MgZn） 49 phase and improves the electrochemical efficiency.

关键词： Al(Zn/xMg) alloy Microhardness Electrochemical efficiency Microstructures

Chaotic Lid-Driven Square Cavity Flows at Extreme Reynolds Numbers

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Communications in Computational Physics 2014年第3期15卷 596-617页

作者： Salvador Garcia instituto de ciencias fisicas y Matematicas Universidad Austral de ChileCasilla 567ValdiviaChile

This paper investigates the chaotic lid-driven square cavity flows at extreme Reynolds *** observations have been made from this ***,at extreme Reynolds numbers two principles add at the genesis of tiny,loose counterclockwise-or clockwise-rotating *** concerns the arousing of them owing to the influence of the clockwise-or counterclockwise currents nearby;the other,the arousing of counterclockwise-rotating eddies near attached to the moving(lid)top wall which moves from left to ***,unexpectedly,the kinetic energy soon reaches the qualitative temporal limit’s pace,fluctuating briskly,randomly inside the total kinetic energy range,fluctuations which concentrate on two distinct fragments:one on its upper side,the upper fragment,the other on its lower side,the lower fragment,switching briskly,randomly from each other;and further on many small fragments arousing randomly within both,switching briskly,randomly from one *** the Reynolds number Re→∞,both distance and then close,and the kinetic energy fluctuates shorter and shorter at the upper fragment and longer and longer at the lower fragment,displaying tall high spikes which enlarge and then *** the time t→∞(at the Reynolds number Re fixed)they recur from time to time with roughly the same *** the most part,at the upper fragment the leading eddy rotates clockwise,and at the lower fragment,in stark contrast,it rotates *** Re=109 the leading eddy-at its qualitative temporal limit’s pace—appears to rotate solely counterclockwise.

关键词： Navier-Stokes equations lid-driven square cavity flows chaos

Study of Branes with Variable Tension

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Communications in Theoretical Physics 2017年第11期67卷 595-599页

作者： Rodrigo Aros Milko Estrada departamento de ciencias fisicas Universidad Andres Bello department of Physics Universidad de Antofagasta instituto de Matematica Fisica y Estadistica Universidad de las Americas

In this work we study a brane world model with variable tension, which gives rise to four-dimensional cosmologies. The brane worlds obtained correspond to E?tv?s branes whose(internal) geometry can be casted as either a four-dimensional(A)dS_4 or a standard radiation period cosmology. The matter dominated period is discussed as well.

关键词： Randall–Sundrum brane world de Sitter hierarchy problem brane tension

FPn-Injective, FPn-Flat Covers and Preenvelopes, and Gorenstein AC-Flat Covers

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Algebra Colloquium 2018年第2期25卷 319-334页

作者： Daniel Bravo Sergio Estrada Alina Iacob instituto de ciencias fisicas y Matematicas Facultad de Ciencias Universidad Austral de Chile Valdivia Chile departamento de Matematicas Universidad de Murcia Campus de Espinardo 30100 Murcia Spain department of Mathematical Sciences Georgia Southern University Statesboro GA 30460 U.S.A

We prove that, for any n 〉 2, the classes of FPn-injective modules and of FPn-flat modules are both covering and preenveloping over any ring R. This includes the case of FP∞-injective and FP∞-flat modules （i.e., absolutely clean and, respectively, level modules）. Then we consider a generalization of the class of （strongly） Gorenstein flat modules, i.e., the （strongly） Gorenstein AC-flat modules （cycles of exact complexes of flat modules that remain exact when tensored with any absolutely clean module）. We prove that some of the properties of Gorenstein fiat modules extend to the class of Gorenstein AC-flat modules; for example, we show that this class is precovering over any ring R. We also show that （as in the case of Gorenstein flat modules） every Gorenstein AC-flat module is a direct summand of a strongly Gorenstein AC-flat module. When R is such that the class of Gorenstein AC-flat modules is closed under extensions, the converse is also true. Moreover, we prove that if the class of Gorenstein AC-flat modules is closed under extensions, then it is covering.

关键词： FPn-injective module FPn-flat module Ding injective module GorensteinAC-flat module

A POSTERIORI ERROR ANALYSIS OF A FULLY-MIXED FINITE ELEMENT METHOD FOR A TWO-DIMENSIONAL FLUID-SOLID INTERACTION PROBLEM

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Journal of Computational Mathematics 2015年第6期33卷 606-641页

作者： Carolina Dominguez Gabriel N. Gatica salim meddahi instituto de ciencias fisicas y Matemdticas facultad de ciencias universidad austral de chile Avenida Eduardo Morales Miranda - Campus isla teja valdivia chile CI2 MA and departamento de Ingenieria Matematica Universidad de concapcion casilla 160 concepcion chile departamento de Matemdticas Facultad de ciencias universidad de oiede calvo satela s/n oviedo espana

In this paper we develop an a posteriori error analysis of a fully-mixed finite element method for a fluid-solid interaction problem in 2D. The media are governed by the elas-todynamic and acoustic equations in time-harmonic regime, respectively, the transmission conditions are given by the equilibrium of forces and the equality of the corresponding normal displacements, and the fluid is supposed to occupy an annular region surrounding the solid, so that a Robin boundary condition imitating the behavior of the sommerfeld condition is imposed on its exterior boundary. Dual-mixed approaches are applied in both domains, and the governing equations are employed to eliminate the displacenent a of the solid and the pressure p of the fluid. In addition, since both transmission conditions become essential, they are enforced weakly by means of two suitable lahrange multipliers The unknowns of the solid and the fluid are then approximated by a conforming galerkin scheme defined in terms of PEERS elements in the solid, Raviart-Thomas of lowest order in the fluid, and continuous piecewise linear functions on the boundary, As the main con-tribution of this work, we derive a reliable and efficient residual-based a posteriori error estimator for the aforedescribed coupled problem. Some numerical results confirming the properties of the estimator are also reported.

关键词： Mixed finite elements Helmholtz equation Elastodynamic equation A poste- riori error analysis

Capturing Near-Equilibrium Solutions: A Comparison between High-Order Discontinuous Galerkin Methods and Well-Balanced Schemes

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Communications in Computational Physics 2019年第6期26卷 1-34页

作者： Maria Han Veiga David A.Velasco-Romero Remi Abgrall Romain Teyssier Institute of Computational Science University of ZurichSwitzerland Institute of Mathematics University of ZurichSwitzerland Universidad Autonoma del Estado de Morelos Mexico instituto de ciencias fisicas Universidad Nacional Aut́onoma de ḾexicoMexico

Equilibrium or stationary solutions usually proceed through the exact balance between hyperbolic transport terms and source terms. Such equilibrium solutions are affected by truncation errors that prevent any classical numerical scheme from capturing the evolution of small amplitude waves of physical significance. In order to overcome this problem, we compare two commonly adopted strategies: going to very high order and reduce drastically the truncation errors on the equilibrium solution, or design a specific scheme that preserves by construction the equilibrium exactly, the so-called well-balanced approach. We present a modern numerical implementation of these two strategies and compare them in details, using hydrostatic but also dynamical equilibrium solutions of several simple test cases. Finally, we apply our methodology to the simulation of a protoplanetary disc in centrifugal equilibrium around its star and model its interaction with an embedded planet, illustrating in a realistic application the strength of both methods.

关键词： Numerical methods benchmark well-balanced methods discontinuous Galerkin methods

Alternative approaches for estimating missing climate data:application to monthly precipitation records in South- Central Chile

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Forest Ecosystems 2018年第4期5卷 390-399页

作者： Alonso Barrios Guillermo Trincado Rene Garreaud Escuela de Graduados Facultad de Ctencias Forestales y Recursos Naturales Universidad Austral de ChileBox 567ValdiviaChile departamento de ciencias Forestales Facuitad de Ingenieria ForestalUnlversidad del Tolima Box 6299 Ibague Colombia instituto de Bosques y Sociedad Facultad de Ciencias Forestales y Recursos NaturalesUniversidad Austraide ChileBox 567 ValdiviaChile departamento de Geofistca Facultad de Ciencias Fisicas y MatematicasUniversidad de ChileSantiagoChile

Background: Over the last decades interest has grown on how climate change impacts forest resources. However,one of the main constraints is that meteorological stations are riddled with missing climatic data. This study compared five approaches for estimating monthly precipitation records: inverse distance weighting(IDW), a modification of IDW that includes elevation differences between target and neighboring stations(IDW_m), correlation coefficient weighting(CCW), multiple linear regression(MLR) and artificial neural networks(ANN).Methods: A complete series of monthly precipitation records(1995-2012) from twenty meteorological stations located in central Chile were used. Two target stations were selected and their neighboring stations, located within a radius of25 km(3 stations) and 50 km(9 stations), were identified. Cross-validation was used for evaluating the accuracy of the estimation approaches. The performance and predictive capability of the approaches were evaluated using the ratio of the root mean square error to the standard deviation of measured data(RSR), the percent bias(PBIAS), and the NashSutcliffe efficiency(NSE). For testing the main and interactive effects of the radius of influence and estimation approaches,a two-level factorial design considering the target station as the blocking factor was ***: ANN and MLR showed the best statistics for all the stations and radius of influence. However, these approaches were not significantly different with IDW_m. Inclusion of elevation differences into IDW significantly improved IDW_m estimates. In terms of precision, similar estimates were obtained when applying ANN, MLR or IDW_m, and the radius of influence had a significant influence on their estimates, we conclude that estimates based on nine neighboring stations located within a radius of 50 km are needed for completing missing monthly precipitation data in regions with complex ***: It is concluded that approaches based on ANN

关键词： Climatological data Cross-validation Artificial neural networks Multiple linear regression

Nitrate regulates rhizobial and mycorrhizal symbiosis in common bean(Phaseolus vulgaris L.)

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Journal of Integrative Plant Biology 2014年第3期56卷 281-298页

作者： Kalpana Nanjareddy Lourdes Blanco Manoj‐Kumar Arthikala Xochitl Alvarado Affantrange Federico Sánchez Miguel Lara Genómica Funcional de Eucariotes Centro de Ciencias Genómicas Universidad Nacional Autónoma de México UNAM Apartado Postal 510‐3Cuernavaca Morelos 62271 México Escuela Nacional de Estudios Superiores‐unam León Blvd.UNAM 2011 Predio El Saucillo y El PotreroComunidad de los Tepetates León Gto.C.P.37684 Mexico departamento de Biología Molecular de Plantas Instituto de BiotecnologíaUniversidad Nacional Autónoma de México UNAM Apartado Postal 510‐3 Cuernavaca Morelos 62271 México

Nitrogen-limited conditions are considered to be a prerequisite for legume-rhizobial symbiosis, but the effects of nitrate-rich conditions on symbiotic status remain poorly understood. We addressed this issue by examining rhizobial （Rhizobim tropici） and arbusclar mycorrhizal （Glomus intraradices） symbiosis in Phaseolus vulgaris L. cv. Negro Jamapa under nitrate pre-incubation and continuous nitrate conditions. Our results indicate that nitrate pre-incubation, independent of the concentration, did not affect nodule development. However, the continuous supply of nitrate at high concentrations impaired nodule maturation and nodule numbers. Low nitrate conditions, in addition to positively regulating nodule number, biomass, and nitrogenase activity, also extended the span of nitrogen-fixing activity. By contrast, for arbuscular mycorrhizae, continuous 1o and 50mmol/L nitrate increased the percent root length colonization, concomitantly reduced arbuscule size, and enhanced ammonia transport without affecting phosphate transport. Therefore, in this manuscript, we have proposed the importance of nitrate as a positive regulator in promoting both rhizobial and mycorrhizal symbiosis in the common bean.

关键词： Arbuscule common bean mycorrhiza nitrate nodule Rhizobium

Arylhydrazones derivatives Containing a Benzothiazole Moiety, Efficient Ligands in the Palladium-Catalyzed Mizoroki-Heck and Suzuki-Miyaura Cross-coupling Reactions under IR Irradiation

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Chinese Journal of Chemistry 2017年第12期35卷 1881-1888页

作者： Fernando Ortega-Jiménez José Guillermo Penieres-Carrillo José Guadalupe López-Cortés M. Carmen Ortega-Alfaro Selene Lagunas-Rivera departamento de Cieneias Qulmicas Facultad de Estudios Superiores Cuautitlān-UNAM Campo i Avenida lro. de Mayo s/n Cuautitlán Izcalli C.P. 54740 Estado de México México instituto de Qulmiea unam Circuito Exterior Ciudad Universitaria Coyoacán C.P. 04360 Cuidad de México México instituto de ciencias Nucleares UNAM Circuito Exterior Ciudad Universitaria Coyoacán C.P. 04360 Ciudad de México México Catedrático CONA CyT-TecNM-instituto Tecnológico de Tuxtla Gutiérrez Carretera Panamericana Km 1080 Col Juan Crispin Tuxtla Gutiérrez C.P. 29050 Chiapas México

A simple arylhydrazone containing the benzothiazole moiety which may be used as an efficient ligand in the palladium-catalyzed Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions, under infrared irradiation as an alternative source of energy, is presented. The reactions proceeded with extremely high efficiency under mild conditions and produced very good yields.

关键词： arylhydrazones palladium-catalyzed cross-coupling reaction IR-irradiation