Classical Limit of Demagnetization in a Field Gradient

We calculate the rate of decrease of the expectation value of the transverse component of spin for spin-1/2 particles in a magnetic field with a spatial gradient, to determine the conditions under which a previous classical description is valid. A density matrix treatment is required for two reasons. The first arises because the particles initially are not in a pure state due to thermal motion. The second reason is that each particle interacts with the magnetic field and the other particles, with the latter taken to be via a 2-body central force. The equations for the 1-body Wigner distribution functions are written in a general manner, and the places where quantum mechanical effects can play a role are identified. One that may not have been considered previously concerns the momentum associated with the magnetic field gradient, which is proportional to the time integral of the gradient. Its relative magnitude compared with the important momenta in the problem is a significant parameter, and if their ratio is not small some non-classical effects contribute to the solution. Assuming the field gradient is sufficiently small, and a number of other inequalities are satisfied involving the mean wavelength, range of the force, and the mean separation between particles, we solve the integro- partial differential equations for the Wigner functions to second order in the strength of the gradient. When the same reasoning is applied to a different problem with no field gradient, but having instead a gradient to the z-component of polarization, the connection with the diffusion coefficient is established, and we find agreement with the classical result for the rate of decrease of the transverse component of magnetization.Comment: 22 pages, no figure

Radiation Hardness of Perovskite Solar Cells Based on Aluminum‐Doped Zinc Oxide Electrode Under Proton Irradiation

Due to their high specific power and potential to save both weight and stow volume, perovskite solar cells have gained increasing interest to be used for space applications. However, before they can be deployed into space, their resistance to ionizing radiations such as high‐energy protons must be demonstrated. In this report, we investigate the effect of 150 keV protons on the performance of perovskite solar cells based on aluminium‐doped zinc oxide (AZO) transparent conducting oxide (TCO). Record power conversion efficiency of 15% and 13.6% were obtained for cells based on AZO under AM1.5G and AM0 illumination, respectively. We demonstrate that perovskite solar cells can withstand proton irradiation up to 1013 protons.cm−2 without significant loss in efficiency. At this irradiation dose, Si or GaAs solar cells would be completely or severely degraded when exposed to 150 keV protons. From 1014 protons.cm−2, a decrease in short‐circuit current of the perovskite cells is observed, which is consistent with interfacial degradation due to deterioration of the Spiro‐OMeTAD HTL during proton irradiation. Using a combination of non‐destructive characterization techniques, results suggest that the structural and optical properties of perovskite remain intact up to high fluence levels. Although shallow trap states are induced by proton irradiation in perovskite bulk at low fluence levels, they can release charges efficiently and are not detrimental to the cell's performance. This work highlights the potential of perovskite solar cells based on AZO TCO to be used for space applications and give a deeper understanding of interfacial degradation due to proton irradiation

Mechanical Stability and Decohesion of Sol-Fel Hybrid Coatings on Metallic Substrates

ABSTRACT The mechanical properties and adhesion behaviour of coatings based on organically modified silanes and synthesized using sol-gel technology were assessed using nano-indentation and microtensile testing, respectively. The relationship between the film structure and its mechanical response is examined. It is shown that the mechanical properties (hardness and Young's modulus) of the coatings is influenced dramatically by the organic substituent and the presence of an oxide layer thermally grown on the substrate material prior to deposition plays an important role on the film/substrate adhesion behaviour. Keywords: Sol-gel, cracking, debonding, adhesion. INTRODUCTION The adhesion and mechanical stability of thin film coatings on substrates is increasingly becoming a key issue in device reliability as technology driven products demand smaller, thinner and more complex functional coatings. It is well known that the reliability of metallurgical protective coatings and microelectronic circuits containing multilayered thin film structures is strongly influenced by their interfacial properties, namely strength, fracture resistance and adhesion. Hence, characterizing and understanding the cracking evolution, debonding behavior and adhesion performance of thin films subject to external applied stresses is crucial when planning such applications. By using micro-mechanical in-situ tensile experiments it is possible to detect and analyze the critical conditions for cracking and debonding of the thin film Sol-gel hybrid coatings, also known as "ormosils" (organically modified silicates), up to several hundred nanometers thick are used to modify the functional behavior of the inorganic component for plastic and metal surfaces to confer wear/abrasion resistance and corrosion protection, respectively Characterization of the film cracking and debonding is achieved primarily by in-situ optical microscopy and subsequent scanning electron microscopy (SEM). Load-partial unload data from nanoindentation of the coatings on copper were used to determine the film properties and to provide data for future fracture and adhesion analyses. Implications concerning the influence of the thermal oxide layer on the interfacial adhesion behavior of the sol-gel coatings are discussed. EXPERIMENTAL Sol-gel coating solutions were prepared by adding a 0.01 M solution of HNO 3 to a mixture of the inorganic constituent tetraethylorthosilicate (TEOS) and the organic constituent glycidoxypropyltrimethoxysilane (GTMS) in ethanol. The solutions prepared were: (i) 100% TEO

The pharmaceutical compounding: acquisition of competences by PBL and out of class strategie

La formulación magistral, una de las actividades profesionales más representativas del farmacéutico, consiste en la elaboración, de acuerdo con una prescripción médica, de un medicamento personalizado, adaptado a un paciente concreto, en un compromiso profesional de solucionar un problema de salud específico. La amplia oferta de medicamentos industriales ha reducido considerablemente esta actividad, que a pesar de todo, debe considerarse una herramienta de futuro en sintonía con la tendencia personalizadora actual de la medicina y las necesidades del paciente. Los conocimientos y competencias requeridas para dicha actividad profesional se introducen actualmente en la carrera de Farmacia mediante una asignatura optativa. En el presente trabajo se presenta el planteamiento metodológico diseñado por el Grupo de Innovación Docente de Tecnología Farmacéutica (GIDTF) y el grupo e-Galenica, ambos de la Universidad de Barcelona, para esta asignatura. Dicha metodología esta basada en el Aprendizaje Basado en Problemas (ABP) incluyendo tutorías y prácticas de campo, apoyada en estrategias no presenciales como foro de debate, recursos on-line, cuestionarios y tareas de autoevaluación a través de la plataforma Moodle del Campus Virtual de la UB. Se evalúan asimismo los resultados académicos y las respuestas de los estudiantes a las encuestas realizadas en relación al sistema de impartición de la asignatura.The pharmaceutical compounding, one of the most representative professional activities of pharmacists, involves the preparation of an individualized medicine tailored to a specific patient in a professional commitment to solve a specific health problem, according to a prescription. The wide range of industrial medicine has significantly reduced this activity, which nevertheless should be considered a tool of the future in line with the current trend of personalizing medicine and patient needs. The knowledge and competences required for this professional activity are introduced to the students of Pharmacy through an optional subject. In this paper we present the methodological approach developed for this subject by the Teaching Innovation Group of Pharmaceutical Technology (GIDTF) and e-Galenica group, both from the University of Barcelona. This methodology is based on Problem-Based Learning (PBL) including tutorials and practices in other centres, supported by out of class strategies as discussion forum, online resources, self-assessment questionnaires and work through the platform Moodle of Virtual Campus UB. The academic performance and student responses to surveys in relation to the didactic methodology are also assessed

Introduction to galenic pharmacy: a challenge in the first year of pharmacy

Este curso académico 2009-2010 se implanta el nuevo plan de estudios de Farmacia en la Universidad de Barcelona, diseñado según los planteamientos del EEES. Como consecuencia, y por primera vez en la historia de la Facultad de Farmacia de la UB, se imparte una asignatura troncal de cariz galénico en el primer año de la carrera. Esto constituye un nuevo reto para el Grupo de Innovación Docente de Tecnología Farmacéutica (GIDTF), dado que la asignatura Introducción a la Farmacia Galénica se ha de impartir a grandes grupos de estudiantes, al inicio de su carrera, mediante sesiones teóricas de 1,5 h. Excepcionalmente en este curso académico, la asignatura se imparte en el primer semestre y se repite en el segundo. En este trabajo se presenta el planteamiento metodológico presencial diseñado para esta asignatura, apoyado en estrategias no presenciales como foro de debate, recursos on-line, cuestionarios y tareas de autoevaluación a través de la plataforma Moodle del Campus Virtual de la UB, puesto que el equipo docente considera prioritario iniciar al estudiante en el uso de la misma en el primer año de carrera. Se han efectuado encuestas de satisfacción a los estudiantes que se han evaluado, así también como los resultados académicos obtenidos. En el análisis de los puntos fuertes y débiles de la metodología empleada, se han detectado evaluaciones positivas y también aspectos que podrían mejorarse, estableciendo las medidas correctoras adecuadas. En cuanto a los resultados académicos, han sido muy satisfactorios.This academic year 2009-2010, the new curriculum of Pharmacy according to the premises of the EHEA is started at the University of Barcelona. As a result, for the first time in the history of the Faculty of Pharmacy of UB, an obligatory galenic subject will be given during the first year of the career. This is a new challenge for Teaching Innovation Group of Pharmaceutical Technology (GIDTF), as the subject Introduction to Galenic Pharmacy is given by a team of teachers to large groups of students who began its career, through theoretical sessions of 1.5 h. The subject will be taught exceptionally this academic year in the first semester and repeated in the second. In this paper we present the methodological approach designed to face this subject, supported by virtual strategies as discussion forum, online resources, self-assessment test and work through the platform Moodle of the Virtual Campus UB, as the team considers it a priority to initiate the student in using it in the first year of pharmacy study. Were carried out satisfaction surveys to students and we have evaluated them, as well as academic performance. Through the analysis of the methodology, we detected positive evaluations and areas for improvement that have been used to establish appropriate corrective measures. Academic results have been very satisfactory.Este trabajo forma parte del proyecto de innovación docente 2009PID-UB/28 de la Universidad de Barcelona

Diseño y construcción de las bóvedas por cruceros en España durante el siglo XVI

The aim of this text is to present the historical guidelines, design and construction of the grid crossing vaults built in Spain during the 16th century to show how the Gothic tradition of building ribbed vaults could be adapted to classical aesthetic principles. In the Andalusia of the 16th century, both a Renaissance classical architecture and another extraordinarily evolved Gothic one reached, at the same time, their full development, taking place between them interesting knowledge, stylistic and technical transfers. In this respect, the grid crossing vaults are a remarkable example of the formal autonomy of Gothic ribs which, without losing their medieval construction principles, are capable of adapting themselves to Renaissance models. We will see how in the grid crossing vaults, the Gothic crossings adapted themselves to the shape of a classical grid structure, drawing on the surface of the vault a design of caissons according to the stricter Roman Canon.El objetivo de este texto es dar a conocer las pautas históricas, de diseño y construcción de las bóvedas por cruceros erigidas en España durante el siglo XVI, como muestra de cómo la tradición gótica de construir bóvedas con nervaduras pudo adaptarse a los principios estéticos clásicos. En la Andalucía del siglo XVI, una arquitectura clásica renacentista y otra gótica extraordinariamente evolucionada alcanzaron, al mismo tiempo, su pleno desarrollo; entre ambas se produjeron interesantes transferencias de conocimiento, estilísticas y técnicas. En este sentido, las bóvedas por cruceros constituyen un notable ejemplo de autonomía formal de la nervadura gótica que, sin perder sus principios constructivos medievales, es capaz de adaptarse a modelos renacentistas. Veremos como en las bóvedas por cruceros, las crucerías góticas se adaptan a la forma de una trama reticular clásica, dibujando sobre la superficie de la bóveda un diseño de casetones conforme al canon romano más estricto

From resource to document: Scaffolding content and organising student learning in teachers’ documentation work on the teaching of series

We examine teachers’ use of resources as they prepare to teach the topic of numerical series of real numbers in order to identify how their personal relationship with mathematical content—and its teaching—interacts with their use of a commonly used textbook. We describe this interplay between textbook and personal relationship, a term coined in the Anthropological Theory of the Didactic (ATD, Chevallard, 2003), in the terms of documentation work (resources, aims, rules of action, operational invariants), a key construct from the documentational approach (DA, Gueudet & Trouche, 2009). We do so in the case of five post-secondary teachers who use the same textbook as a main resource to teach the topic. Documentational analysis of interviews with the teachers led to the identification of their aims and rules of action (the what and how of their resource use as they organise their teaching of the topic) as well as the operational invariants (the why for this organisation of their teaching). We describe the teachers’ documentation work in two sets of aims/rules of action: scaffolding mathematical content (series as a stepping stone to learning about Taylor polynomials and Maclaurin series) and organising student learning about series through drill exercises, visualisation, examples, and applications. Our bridging (networking) of theoretical constructs originating in one theoretical framework (personal relationship, ATD) with the constructs of a different, yet compatible, framework (documentation work, DA) aims to enrich the latter (teachers’ documentation work) with the individual agency (teachers’ personal relationship with the topic) provided by the former

An experimental and kinetic modelling study of the oxidation of the four isomers of butanol

Butanol, an alcohol which can be produced from biomass sources, has received recent interest as an alternative to gasoline for use in spark ignition engines and as a possible blending compound with fossil diesel or biodiesel. Therefore, the autoignition of the four isomers of butanol (1-butanol, 2-butanol, iso-butanol, and tert-butanol) has been experimentally studied at high temperatures in a shock tube and a kinetic mechanism for description of their high-temperature oxidation has been developed. Ignition delay times for butanol/oxygen/argon mixtures have been measured behind reflected shock waves at temperatures and pressures ranging from approximately 1200 to 1800 K and 1 to 4 bar. Electronically excited OH emission and pressure measurements were used to determine ignition delay times. A detailed kinetic mechanism has been developed to describe the oxidation of the butanol isomers and validated by comparison to the shock tube measurements. Reaction flux and sensitivity analysis indicate that the consumption of 1 butanol and iso-butanol, the most reactive isomers, takes place primarily by H-atom abstraction resulting in the formation of radicals, the decomposition of which yields highly reactive branching agents, H-atoms and OH radicals. Conversely, the consumption of tert butanol and 2-butanol, the least reactive isomers, takes place primarily via dehydration, resulting in the formation of alkenes, which lead to resonance stabilized radicals with very low reactivity. To our knowledge, the ignition delay measurements and oxidation mechanism presented here for 2-butanol, iso-butanol, and tert butanol are the first of their kind.