Matching at one loop for the four-quark operators in NRQCD

The matching coefficients for the four-quark operators in NRQCD (NRQED) are calculated at one loop using dimensional regularization for ultraviolet and infrared divergences. The matching for the electromagnetic current follows easily from our results. Both the unequal and equal mass cases are considered. The role played by the Coulomb infrared singularities is explained in detail

Evolution of the metal load in a reach of the Odiel River affected by acid mine drainage (Huelva province)

This work quantifies the impact of the first acid mine discharges to the Odiel River and studies the variation of the dissolved and particulate pollutant load. The acid mine discharges cause the progressive deterioration of the river water quality, resulting in processes that favor the precipitation of the non-conservative elements (Fe, Al, As or Pb), while the more soluble ones (Mn, Co or Ni) remain in solution. Cu and Zn have an intermediate behavior due to be affected by sorption/coprecipitation processes. The dissolved pollutant load at the end of the reach is around 5000 kg/day of Al, 1900 kg/day of Fe, 860 kg/day of Zn, 643 kg/day of Mn, 385 kg/day of Cu and lower amounts of other metals. The total metal load may be up to 21 times the dissolve load in the case of Fe and among 3-4 times for As and PbEste trabajo cuantifica la repercusión de los primeros vertidos de mina en un tramo del Río Odiel y se estudian las variaciones de la carga metálica disuelta y particulada. La confluencia de las sucesivas descargas ácidas de mina provoca el empeoramiento progresivo de la calidad del agua, dando lugar a procesos que favorecen la precipitación de elementos no conservativos (Fe, Al, As o Pb) mientras que los elementos más móviles (Mn, Co o Ni) permanecen en disolución. Cu y Zn poseen un comportamiento intermedio debido a que están afectados por procesos de adsorción/coprecipitación. La carga disuelta transportada al final del tramo es aproximadamente 5000 kg/día de Al, 1900 kg/día de Fe, 860 kg/día de Zn, 643 kg/día de Mn, 385 kg/día de Cu y cantidades inferiores de otros metales. La carga metálica total es hasta 21 veces superior a la disuelta en el caso del Fe y entre 3-4 veces superior para As y P

Community Assets for Health Model and Assessment Scale: A Delphi-Based Analysis and Expert Validation

The salutogenesis theory of Aaron Antonovsky and the Health Assets Model of Morgan and Ziglio have given rise to a notable interest in defining the resources available to individuals and the community to maintain or improve their health and well-being. The present study began by identifying the universal dimensions of Community Assets for Health, and then analyzed and validated an assessment scale following the Delphi method. A high degree of consensus was achieved among 13 experts from different disciplines. The results of the content analysis and statistical analysis led to a reconfiguring of an instrument that is so far unique in its approach. It is composed of 103 items across 14 dimensions (utility, intention, previous use, affordability, proximity, walkability, connectivity, intelligibility, identity, design, safety, diversity, public dimension, and sustainability)

FOULING MONITORING AND CLEANING OPTIMISATION IN A HEAT EXCHANGER NETWORK OF A CRUDE DISTILLATION UNIT

Fouling in preheat networks of crude distillation units (CDU) plays an important role in energy consumption. In this work a procedure to monitor the performance of the heat exchanger network (HEN) and to optimize the cleaning strategies is presented. The procedure is based on a rigorous simulation of the HEN using Hysys (from Aspen Technology). The simulation is used to estimate the service overall heat transfer coefficient with real operational data acquired from the unit’s Plant Information System (PI). The clean overall heat transfer coefficient is calculated for each one of the individual heat exchangers with a rigorous simulation using TASC (rigorous heat exchanger simulator also from Aspen Technology), embedded into Hysys. A comparison between the service and clean overall heat transfer coefficients provides the actual performance for each individual heat exchanger and for the complete HEN. The first step is to collect the HEN operative data from the Plant Information System and to perform an ad-hoc preprocessing of each individual exchanger data (i.e., feed and product inlet and outlet temperatures and flow rates) in order to identify stable periods from which the mentioned calculations will be performed. As the feed/products flow rates and unit operating conditions are constantly changing, the steady intervals detection is a very important task because calculations performed with data of unstable operation time intervals could be erroneous and produce non-sense results. The overall procedure is managed from an Excel environment, which performs the needed calls to PI and Hysys/TASC simulators in order to calculate each exchanger fouling and HEN overall performance under the actual fouling situation. Excel also commands the evaluation of the cleaning policies economics, searching between several pre-defined cleaning alternatives. Results of the above mentioned methodology applied to a complex feed preheat HEN of the Topping IV CDU of REPSOL YPF Luján de Cuyo Refinery, Argentina, are presented

Reduction of Hydrogenated ZrO2 Nanoparticles by Water Desorption

Reduction of zirconia by water desorption from a hydrogenated surface is the topic of this study. The focus is on the role of nanostructuring the oxide reducibility measured by the cost of formation of oxygen vacancies by water desorption. We have performed density functional theory calculations using the Perdew-Burke-Ernzerhof + U approach and including dispersion forces on the adsorption, dissociation, diffusion of hydrogen on the ZrO2 (101) surface and on Zr16O32, Zr40O80, and Zr80O160 nanoparticles (NPs). The process involves the formation of a precursor state via diffusion of hydrogen on the surface of zirconia. The results show that O vacancy formation via H2O desorption is more convenient than via direct O-2 desorption. The formation of an OsH2 surface precursor state to water desorption is the ratedetermining step. This step is highly unfavorable on the ZrO2 (101) surface both thermodynamically and kinetically. On the contrary, on zirconia NPs, characterized by the presence of low coordinated ions, water desorption becomes accessible such that even at temperatures close to 450 K the reaction becomes exergonic. The study shows the role of nanostructuring on the chemical and electronic properties of an oxide

Improved cold-drawn eutectoid steel wires based on residual stress measurement and simulation: Part 2. optimization of mechanical properties

Cold-drawn eutectoid steel wires are used in prestressed concrete structures to provide compressive stresses to the concrete. For that purpose, they are loaded up to 60 to 70% of their tensile strength. Although the loading stress is lower than the elastic limit (around 85% of the tensile strength), failure may occur in service conditions due to stress corrosion. Wire failure reduces the load bearing capacity and may lead to catastrophic collapse of the prestressed structure. The risk of these failures can be increased by the presence of tensile residual stresses on the surface of the wires. Cold-drawing generates considerable residual stresses which, added to the service stresses, may seriously affect the mechanical properties and durability of the wires [1,2]. Until now, the measuring of residual stresses was considered more a scientific problem and even revealing their presence was a challenging task [3]. However, wire manufacturers were aware of the deleterious effect produced by the presence of tensile residual stresses at the surface of the wires after drawing. That is the reason why they consider residual stresses both dangerous and damaging, and hence attempt to reduce their influence by stress relieving treatments. But residual stresses may also have beneficial effects if we are able to obtain the desired profile. With the advent of powerful experimental techniques for measurement of residual stresses — such as neutron and X-ray diffractometers — and of faster computers to simulate numerically the wire drawing processes, this phenomenon is seen now in a new light. A significant research effort has been undertaken in recent years in order to understand, measure and control the residual stresses in cold-drawn wires [3-5]. In the first part of this paper [3], the advances on the measurement and simulation of residual stresses have been discussed. In this second part, the influence of residual stresses on the mechanical properties required by standards to this kind of wire (tensile, stress relaxation and stress corrosion tests) is reviewed. The control of residual stresses may play an important role in the design of new post-drawing treatments and the optimization of the performance of the wires

Control de las tensiones residuales como herramienta de mejora de los alambres de pretensado: 1. Caracterización de las tensiones residuales

En este artículo se resume el trabajo desarrollado por los autores durante estos últimos años para mejorar el comportamiento de las armaduras activas del hormigón pretensado mediante el control de sus tensiones residuales. En esta primera parte se examinan las técnicas de caracterización de dichas tensiones, sus dificultades y limitaciones, así como la interpretación de sus resultados. Se han realizado medidas de tensiones residuales con diferentes tratamientos, utilizando difracción de rayos X, de neutrones y de radiación sincrotrón. Asimismo se han realizado simulaciones numéricas. Las microestructura de los alambres de pretensado (finas láminas de ferrita y cementita muy deformadas y alineadas según la dirección de trefilado) complican de forma importante la obtención de un perfil de tensiones residuales en estos alambres. - This paper summarizes the work done by the authors during the last years in attempting to obtain accurate measurements and simulations of the residual stresses developed in prestressed concrete wires in order to improve their performance. In this first part of the study, the characterization of the residual stress distributions is examined: residual stresses in cold-drawn wires (subjected to different treatments) have been measured by neutron, synchrotron and X-ray diffraction and also, numerical simulations have been performed. Severe plastic deformation, anisotropy and the presence of cementite make experimental measurements and simulations in this kind of wires a difficult task. Experimental and numerical difficulties, limitations of different techniques and interpretation of the measurements have been discussed

The role of residual stresses in the performance and durability of prestressing steel wires

Residual stresses developed during wire drawing influence the mechanical behavior and durability of steel wires used for prestressed concrete structures, particularly the shape of the stress–strain curve, stress relaxation losses, fatigue life, and environmental cracking susceptibility. The availability of general purpose finite element analysis tools and powerful diffraction techniques (X-rays and neutrons) has made it possible to predict and measure accurately residual stress fields in cold-drawn steel wires. Work carried out in this field in the past decade, shows the prospects and limitations of residual stress measurement, how the stress relaxation losses and environmentally-assisted cracking are correlated with the profile of residual stresses and how the performance of steel wires can be improved by modifying such a stress profil

Medida de tensiones residuales para el control y mejora de la durabilidad de los alambres de pretensado

En la última década, la Comisión 9 de la fib, encargada de todo lo relativo a los materiales y sistemas de pretensado, ha dedicado una gran atención a la mejora de la durabilidad de las estructuras pretensadas. Uno de los aspectos que ha considerado de especial interés es el control del estado de tensiones residuales que presentan las armaduras activas, ya que influye significativamente en sus propiedades mecánicas y en su susceptibilidad a la corrosión bajo tensión. Hasta ahora, el problema de las tensiones residuales había pertenecido al ámbito científico, quedando alejado de la práctica ingenieril, pero todo parece indicar que en los próximos años las diferentes normas internacionales recogerán, entre sus requerimientos para el material, la certificación del nivel de tensiones residuales en su superficie. El Depto de Ciencia de Materiales de la UPM, liderado por Manuel Elices ha dedicado un considerable esfuerzo a entender, medir y controlar las tensiones residuales en las armaduras activas. Este artículo resume la experiencia de los autores, con la esperanza de acercar el problema de las tensiones residuales, su importancia y sus dificultades, al ámbito ingenieril

Influència dels valors d’eficàcia sobre la condició de guanyador o perdedor en waterpolo femení

Aquest estudi ha perseguit trobar els valors d’eficàcia en els marcs situacionals presents en el waterpolo i analitzar la relació entre aquests i la condició de guanyador o de perdedor. Es van registrar tots els partits femenins del X Campionat del Món, per fer-ne una anàlisi consensuada entre dos especialistes entrenats. S’han avaluat mitjançant coeficients les microsituacions de joc en igualtat numèrica, contraatac, replegament defensiu, desigualtat numèrica temporal simple i penal; se n’han obtingut valors d’eficàcia. Per al tractament estadístic es va realitzar una ANOVA d’un sol factor seguida per la prova de Tukey; s’han revelat diferències significatives en igualtat numèrica amb possessió i sense: en possibilitat (,005), concreció, definició i precisió (,000), resolució (,001) i exactitud (,017). En el contraatac i el replegament defensiu: en possibilitat, concreció, definició, resolució i precisió (,000) i exactitud (,001). En desigualtat numèrica temporal simple amb possessió i sense: en possibilitat (,020), concreció, definició, precisió i exactitud (,000) i resolució amb possessió (,002) i sense possessió (,003); prenent com a referència un valor de p<,05. Hi ha diferències significatives entre la condició de guanyador o perdedor en dotze coeficients d’eficàcia en igualtat numèrica, dotze en transició, dotze en desigualtat numèrica temporal simple i cap en el penal