Tidal stream generators, current state and potential opportunities for condition monitoring

Tidal power industry has made significant progress towards commercialization over the past decade. Significant investments from sector leaders, strong technical progress and positive media coverage have established the credibility of this specific renewable energy source. However, its progress is being retarded by operation and maintenance problems, which results in very low operational availability times, as low as 25 %. This paper presents a literature review of the current state of tidal device operators as well as some commercial tidal turbine condition monitoring solutions. Furthermore, an overview is given of the global tidal activity status (tidal energy market size and geography), the key industry activity and the regulations-standards related with tidal energy industry. Therefore, the main goal of this paper is to provide a bird’s view of the current status of the tidal power industry to serve as a roadmap for the academia regarding the real needs of the tidal power industry

New tools for assessing personal exposure near urban air pollution hotspots

During the last decade, researchers and policy makers have focused on the development and deployment of air pollution mitigation measures invoking solutions based on technology transfer. This term encompasses the synthesis of air quality monitoring, primarily by networks of inexpensive sensors, remote sensing and numerical modelling, as tools for supporting policy makers and disseminating air quality information to the citizens. It has been recognised that localised concentration maxima developing around traffic sources represent an exposure contribution of major epidemiological significance. The ability, therefore, of an integrated air quality management system to reliably assess personal exposure heavily depends on the consistent numerical treatment of multiscale interactions which determine the flow and dispersion structures in these fine spatial scales. Moreover, it is important to incorporate innovative methodologies for enhancing the stability and error-resilience of the sensor networks themselves. The approach presented in this work focuses on the utilisation of latest developments both in sensor technology and numerical air quality modelling, so as to provide end products able to support regulatory assessment and environmental information services. A peer-to-peer network of air quality measuring devices is deployed in six urban areas in the Balkan region in order to provide real time air quality data over areas of high population and emissions density. The coupled mesoscale modelling system MEMO/ MARS-aero and the mesomicro MEMICO two-way coupling methodology implement the physical modelling core of the system in the respective spatial scales. These modelling tools are used to estimate, integrate and complement the sensor data on pollutant levels in predictions of high temporal and spatial resolution in order to highlight pollution hot spots. In the case of fine particulate matter, special adaptations are incorporated in the emissions and chemical transformation treatment in order to provide consistent number concentration fields, which constitute the most relevant exposure metric

Convincing students that their groupmates' success can increase, not diminish, their own success

Both theory and research support the use of group activities to aid student learning. However, some students are reluctant to learn with peers for fear that the peers will gain more. The article attempts to address this fear. This article provides educators with explanations to give their students as to why, even in norm referenced assessment environments, by helping their groupmates, students are positively, not negatively, impacting their own success on assessments. The article opens with a review of assessment options: norm referenced, criterion referenced and ipsative. Next, Social Interdependence Theory is explained for the insights it might offer as to how students view their peers' success. The article's third section summarises some of the research on peer learning, in particular research on what forms of peer interaction might best promote learning. Finally, the article examines three contexts in which norm referencing is applied - standardised exams, class grades and class ranking – and concludes that the chances are small of groupmates' success diminishing the success of students who have helped their groupmates. This conclusion is reached based, first, on mathematical calculations and, most importantly, on the research based premise that when students provide elaborated help to groupmates, the helpers are likely to boost their own scores

Pulsed high magnetic field measurement via a Rubidium vapor sensor

We present a new technique to measure pulsed magnetic fields based on the use of Rubidium in gas phase as a metrological standard. We have therefore developed an instrument based on laser inducing transitions at about 780~nm (D2 line) in a Rubidium gas contained in a mini-cell of 3~mm~x~3~mm cross section. To be able to insert such a cell in a standard high field pulsed magnet we have realized a fibred probe kept at a fixed temperature. Transition frequencies for both the $\pi$ (light polarization parallel to the magnetic field) and $\sigma$ (light polarization perpendicular to the magnetic field) configurations are measured by a commercial wavemeter. One innovation of our sensor is that in addition of monitoring the light transmitted by the Rb cell, which is usual, we also monitor the fluorescence emission of the gas sample from a very small volume with the advantage of reducing the impact of the field inhomogeneity on the field measurement. Our sensor has been tested up to about 58~T.Comment: Submitted to Review Scientific Instrument

Multi-Step Homogenization of Thermoelastic Multi-Scale Tubes with Wavy Layers

In this paper we present a multi-step homogenization scheme of a tube made of numerous wavy cylindrical layers exhibiting periodicity with respect to both the radial and the angular direction. The proposed homogenization is a combination of successive semi-analytical, cell-problem-based, homogenization steps and a possible, micromechanics-based, homogenization in the interior of every layer. Every step of cell-problem based homogenization gives analytical expressions for the homogenized stiffness, thermal expansion and thermal conductivity

Percutaneous pulmonary valve implantation alters electrophysiologic substrate

BACKGROUND: Percutaneous pulmonary valve implantation (PPVI) is first‐line therapy for some congenital heart disease patients with right ventricular outflow tract dysfunction. The hemodynamics improvements after PPVI are well documented, but little is known about its effects on the electrophysiologic substrate. The objective of this study is to assess the short‐ and medium‐term electrophysiologic substrate changes and elucidate postprocedure arrhythmias. METHODS AND RESULTS: A retrospective chart review of patients undergoing PPVI from May 2010 to April 2015 was performed. A total of 106 patients underwent PPVI; most commonly these patients had tetralogy of Fallot (n=59, 55%) and pulmonary insufficiency (n=60, 57%). The median follow‐up time was 28 months (7‐63 months). Pre‐PPVI, 25 patients (24%) had documented arrhythmias: nonsustained ventricular tachycardia (NSVT) (n=9, 8%), frequent premature ventricular contractions (PVCs) (n=6, 6%), and atrial fibrillation/flutter (AF/AFL) (n=10, 9%). Post‐PPVI, arrhythmias resolved in 4 patients who had NSVT (44%) and 5 patients who had PVCs (83%). New arrhythmias were seen in 16 patients (15%): 7 NSVT, 8 PVCs, and 1 AF/AFL. There was resolution at medium‐term follow‐up in 6 (86%) patients with new‐onset NSVT and 7 (88%) patients with new‐onset PVCs. There was no difference in QRS duration pre‐PPVI, post‐PPVI, and at medium‐term follow‐up (P=0.6). The median corrected QT lengthened immediately post‐PPVI but shortened significantly at midterm follow‐up (P<0.01). CONCLUSIONS: PPVI reduced the prevalence of NSVT. The majority of postimplant arrhythmias resolve by 6 months of follow‐up