On the differential geometry of curves in Minkowski space

We discuss some aspects of the differential geometry of curves in Minkowski space. We establish the Serret-Frenet equations in Minkowski space and use them to give a very simple proof of the fundamental theorem of curves in Minkowski space. We also state and prove two other theorems which represent Minkowskian versions of a very known theorem of the differential geometry of curves in tridimensional Euclidean space. We discuss the general solution for torsionless paths in Minkowki space. We then apply the four-dimensional Serret-Frenet equations to describe the motion of a charged test particle in a constant and uniform electromagnetic field and show how the curvature and the torsions of the four-dimensional path of the particle contain information on the electromagnetic field acting on the particle.Comment: 10 pages. Typeset using REVTE

Effect of Polymer Hydration on the Kinetic Release of Drugs: A Study of Ibuprofen and Ketoprofen in HPMC Matrices

Samples of drug/hydroxypropylmethylcellulose (HPMC) mixtures and matrices (drug/HPMC mixtures plus excipients) were allowed to equilibrate in closed chambers with defined relative humidities (RHs). Their water uptake and drug release were evaluated by differential scanning calorimetry/thermogravimetric analysis and dissolution studies, respectively. Analysis of the thermal behaviors of the drug/HPMC mixtures and of the polymer alone, as functions of RH, leads to the conclusion that most of the hydration water is retained by the polymer, and points to the occurrence of different types of hydration water, from the strongly polymer-bound water molecules at RH values up to 81%, to the almost “free water” for RH values close to 100%. In addition, application of the Korsmeyer model to the dissolution results leads to the conclusion that the rate determining dissolution processes are predominantly of the fickian type.http://www.informaworld.com/10.1081/DDC-12001820

Temperature dependence of the magnetization processes in Co/Al oxide/Permalloy trilayers

The magnetization process of Co/Al oxide/Py trilayers and its evolution with the temperature have been analyzed. The particular behavior of the Co layers, including the shift of the hysteresis loops and a coercivity increase with the decrease of temperature, is related with the apparition of a CoO layer at the Co/Al-oxide interface

Self-efficacy, mental models and team adaptation: a first approach on football and futsal refereeing

Objective: Within the football and futsal refereeing context, even though referees work within teams, there is very little research considering the implications of team dynamics. In response, this study starts to address this gap in the literature by investigating the moderating effect of mental models on the relationship between self-efficacy beliefs and perceptions of team adaptation within the exciting context of professional and national football and futsal refereeing. Design: We obtained online questionnaires from 339 active football and futsal referees within the National and Professional league at two distinct points (April and May) within the football season. Results: Self-efficacy beliefs were positively associated with perceptions of team adaptation (only for football referees). Mental models were positively associated with team adaptation. Likewise, the moderation between mental models and self-efficacy beliefs was positively associated with perceptions of team adaptation (only for futsal referees). However, such an effect was only significant at the futsal referees’ level. Conclusion: This study emphasises the importance of mental models for team adaptation and the importance of self-efficacy beliefs in predicting perceptions of team adaptation. We hope that this study represents the first step in a greater appreciation of the salience of team dynamics and their impact on football and futsal referees’ performance and that future research can build upon our work.info:eu-repo/semantics/publishedVersio

Lessons from the 1914 Christmas truce

LISBOA-01-0145-FEDER-007722.We examine the historical phenomenon of truces, as these occurred during a period of severe warfare during World War I, around Christmas 1914. These were processes of resistance that could not have been planned (otherwise they would obviously have been thwarted by authority) and that occurred in a setting with continuously changing conditions. Our purpose in making this analysis is to identify the micro-foundations and behaviours of enacting resistance and forming a truce under conditions where planning and executing cannot be assumed to be orderly and linear. We discuss the battlefield context of intense competition and mutual suffering as an organizational setting, in order to provide a more precise explanation of how rules and structures can be (at least) temporarily suspended in the workplace. We rethink the construct of resistance as an act of improvisation; we do so by developing a framework that explains how resistance can emerge and be quashed in workplace settings that might appear at first sight to be immune. Therefore, we combine two themes that have largely been separated in theory: resistance and improvisation. Doing so opens new ground in three ways. First, we contribute to literature about resistance by explaining how it was constructed as action suspending rules and structures in hostile contexts. Second, we show the political-motivational dimension of improvisation. Third, we extend the notion of truces as not an end in itself (a temporary settlement) but as an avenue to achieve a real objective (e.g. to change the course of history for the better).authorsversionauthorsversionauthorsversionauthorsversionauthorsversionpublishe

Metrics with Prescribed Ricci Curvature near the Boundary of a Manifold

Suppose $M$ is a manifold with boundary. Choose a point $o\in\partial M$. We investigate the prescribed Ricci curvature equation \Ric(G)=T in a neighborhood of $o$ under natural boundary conditions. The unknown $G$ here is a Riemannian metric. The letter $T$ in the right-hand side denotes a (0,2)-tensor. Our main theorems address the questions of the existence and the uniqueness of solutions. We explain, among other things, how these theorems may be used to study rotationally symmetric metrics near the boundary of a solid torus $\mathcal T$. The paper concludes with a brief discussion of the Einstein equation on $\mathcal T$.Comment: 13 page

Influence of Cellulose Ether Mixtures on Ibuprofen Release: MC25, HPC and HPMC K100M

The influence of cellulose ether derivatives on ibuprofen release from matrix tablets was investigated. Raman spectroscopy and differential scanning calorimetry (DSC) experiments were used, in order to examine the compatibility between the matrix components: both excipients and ibuprofen. While both the DSC and Raman results did not detect any incompatibilities, DSC revealed the existence of some drug:excipient interactions, reflected by variations in the hydration/dehydration processes. Formulations containing mixtures of polymers with both low and high viscosity grades—methylcellulose (MC25) or hydroxypropylcellulose (HPC), and hydroxypropylmethylcellulose (HPMC K100M), respectively—were prepared by a direct compression method (using 20, 25, and 30% of either MC25 or HPC). The tablets were evaluated for their drug content, weight uniformity, hardness, thickness, tensile strength, friability, porosity, surface area, and volume. Parameters such as the mean dissolution time (MDT) and the dissolution efficiency (DE) were calculated in all cases. The solid formulations presently studied demonstrated a predominantly Fickian diffusion release mechanism.http://www.informaworld.com/10.1080/1083745060056134

Espondilolistesis traumática del axis asociada a fractura de odontoides: a propósito de un caso

Se presentan dos casos de espondilolistesis traumática del axis, tipo I de Effendi, asociadas a fractura de odontoides. En ninguno de los casos fue necesario realizar tratamiento quirúrgico, consiguiendo la consolidación de ambas fracturas mediante inmovilización con halo-chaleco.Two new case s of traumatic spondylolisthesis of the axis, Effendi's type I, associated to fracture of the odontoid process are reported. Surgical treatment wa s not necessary in any of the cases. Repair of both fractures wa s adrieved by means of inmovilization with halo-chest orthesis