S and Q Matrices Reloaded: applications to open, inhomogeneous, and complex cavities

We present a versatile numerical algorithm for computing resonances of open dielectric cavities. The emphasis is on the generality of the system's configuration, i.e. the geometry of the (main) cavity (and possible inclusions) and the internal and external dielectric media (homogeneous and inhomogeneous). The method is based on a scattering formalism to obtain the position and width of the (quasi)-eigenmodes. The core of the method lies in the scattering S-matrix and its associated delay Q-matrix which contain all the relevant information of the corresponding scattering experiment. For instance, the electromagnetic near- and far-fields are readily extracted. The flexibility of the propagation method is displayed for a selected system.Comment: 15th International Conference on Transparent Optical Networks (2013

Phase Space Engineering in Optical Microcavities I: Preserving near-field uniformity while inducing far-field directionality

Optical microcavities have received much attention over the last decade from different research fields ranging from fundamental issues of cavity QED to specific applications such as microlasers and bio-sensors. A major issue in the latter applications is the difficulty to obtain directional emission of light in the far-field while keeping high energy densities inside the cavity (i.e. high quality factor). To improve our understanding of these systems, we have studied the annular cavity (a dielectric disk with a circular hole), where the distance cavity-hole centers, d, is used as a parameter to alter the properties of cavity resonances. We present results showing how one can affect the directionality of the far-field while preserving the uniformity (hence the quality factor) of the near-field simply by increasing the value of d. Interestingly, the transition between a uniform near- and far-field to a uniform near- and directional far-field is rather abrupt. We can explain this behavior quite nicely with a simple model, supported by full numerical calculations, and we predict that the effect will also be found in a large class of eigenmodes of the cavity.Comment: 12th International Conference on Transparent Optical Network

Déglaciation et émersion des terres de l’ouest de l’île d’Anticosti, golfe du Saint-Laurent, Québec

La géomorphologie et les dépôts quaternaires de la partie ouest de l'île d'Anticosti sont principalement associés à la glaciation du Wisconsinien supérieur et à la déglaciation au contact de la mer postglaciaire de Goldthwait. Le till de l'île a été mis en place au Wisconsinien supérieur au cours de la dernière avancée de l'inlandsis laurentidien. La dynamique de la glace à l'époque démontre une faible capacité d'érosion, le front du glacier se maintenant probablement près de la côte sud (actuelle) de l'île. Lors de la déglaciation, une calotte résiduelle s'est maintenue sur l'île. Une récurrence, survenue vers 12 500 ans BP, a permis l'édification de la moraine de Sainte-Marie. Cette moraine est formée de bourrelets morainiques sur la côte sud et d'épandages proglaciaires dans l'ouest et au nord de l'île. La calotte a existé pendant environ 1000 ans. Au cours de sa fonte, la mise en place du till d'Elsie s'est faite en association avec celles de nombreuses moraines de De Geer au nord des bourrelets de la moraine de Sainte-Marie, parallèlement à la côte. Une dernière récurrence venant du nord a permis la mise en place de la moraine de la rivière à l'Huile, probablement vers 9000 - 9500 ans BP, ce qui serait contradictoire avec les données provenant de la Côte-Nord du Saint-Laurent. Entre 11 000 et 9000 ans BP, le taux d'émersion a été de 2 m par siècle; il s'est abaissé par la suite à 25 cm par siècle.The Quaternary geomorphology and deposits of the western part of Anticosti Island are primarily associated with the late Wisconsinan glaciation and with déglaciation in contact with the Goldthwait Sea. The surface till was deposited during the late Wisconsinan readvance of the Laurentide ice sheet. The ice sheet had little eroding ability at that time and its margin was probably maintained near the south coast of the Anticosti Island. During déglaciation a residual ice cap remained and readvanced around 12 500 yrs BP and deposited the Sainte-Marie Moraine. The moraine consists of several morainic ridges on the south coast and proglacial outwash deposits on the west and north coasts. The ice cap remained for about 1000 years. During its breakup, Elsie Till was deposted in association with numerous De Geer moraines to the north of the Sainte-Marie Moraine, parallel to the south coast. A final readvance from the north resulted in the formation of the Rivière à l'Huile Moraine along the north coast between 9000 and 9500 yrs BP. Those dates are in conflict with the chronology of the North Shore of the St. Lawrence River. Between 11 000 and 9000 yrs BP, the rate of emersion was 2 m/century and subsequently it decreased to 25 cm/ century.Die Géomorphologie und die Ablagerungen des Quarter im westlichen Teil der lnsel Anticosti werden vor allem mit der spâteren Wisconsin-Eiszeit in Zusammenhang gebracht und mit der Enteisung in Verbindung mit dem GoId-waith-Meer. Die Grundmorâne wurde wàhrend des spâteren Wisconsin Rùckvorstosses der Laurentides Eisdecke abgelagert. Die Eisdecke hatte damais eine sehr geringe Erosionsfàhigkeit, und ihre Grenze befand sich wahrscheinlich in der Nahe der Sudkuste der Anticosti-lnsel. Wahrend der Enteisung blieb eine Resteiskalotte, die etwa 12500 Jahre v.u.Z. aufs Neue vordrang und die Sainte-Marie Morâne ablagerte. Die Morâne besteht aus mehreren Morànen-Rippen an der Sudkuste und aus proglazialen ausgewaschenen Ablagerungen an der West- und Nordkùste. Die Eiskalotte blieb etwa 1000 Jahre. Wâhrend ihres Schmelzens lagerte sich die Elsie-Moràne ab, zusammen mit zahireichen de Geer Moranen im Norden der Sainte-Marie Morâne, parallel zur Sudkuste. Ein letzter RuckvorstoR von Norden fuhrte zur Bildung der Rivière à l'Huile Morâne, entlang der Nordkuste zwischen 9000 und 9500 Jahren v.u.Z. Dièse Daten stehen in Widerspruch zu der Chronologie der Nordkùste des Lorenz-Stroms. Zwischen 11000 und 9000 Jahren v.u.Z. war die Auftauchrate 2m/Jahrhundert und danach nahm sie ab bis zu 25cm/Jahrhundert

Effet du débit sur la dynamique temporelle des algues périphytiques dans une rivière influencée par les activités agricoles

Le périphyton de la rivière Boyer Nord, une rivière affectée par les activités agricoles dans le sud du Québec (Canada), a été échantillonné toutes les deux semaines de la mi-mai à la fin septembre 1999 afin d'évaluer son évolution temporelle et d'identifier les variables potentielles qui le contrôlent. Les résultats montrent la grande variabilité temporelle de la biomasse périphytique (poids sec organique et chlorophylle a) et de la structure de la communauté de diatomées. La communauté d'algues benthiques dans la rivière Boyer était principalement composée de diatomées (Nitzschia, Cocconeis, Cymbella, Cyclotella), d'algues vertes (Scenedesmus, Pediastrum, Cosmarium, Closterium) et de cyanobactéries (Phormidium, Oscillatoria, Merismopedia). La pointe de débit observée durant la semaine précédant l'échantillonnage était fortement corrélée à plusieurs variables physico-chimiques (N-total, NH3-N, NO3-N, P-total, turbidité) et était le plus fortement corrélée aux changements temporels de la biomasse. La biomasse (chlorophylle a et poids sec organique) était négativement corrélée au phosphore total, ce qui reflète la relation avec le débit. Les changements temporels dans la composition spécifique des diatomées étaient régis par différentes variables physico-chimiques, selon les limites de tolérances et la valence écologique des espèces. Les algues périphytiques de cette communauté ont réagi aux variations de l'environnement à l'intérieur d'une période de 2 semaines puisque des changements majeurs dans la structure de l'assemblage de diatomées ont été observés lors de chaque échantillonnage. Ces observations montrent la forte variabilité de la biomasse et de la structure de la communauté périphytique dans les rivières enrichies par les éléments nutritifs et souligne l'influence majeure du débit dans ce type d'environnement.Periphyton in an agriculturally enriched river (Boyer River, Québec, Canada) was sampled from mid-May to the end of September 1999 to evaluate the temporal succession of periphyton and to identify potential controlling variables. The river is located on the south shore of the St. Lawrence River and discharges into it approximately 30 kilometres downstream (east) of Québec City. Land-use in the Boyer River watershed is 60% farmland and 40% forests. The site was chosen for its intense farming, accessibility and proximity to an automatic sampling station for water quality operated by the Québec Ministry of the Environment that continuously recorded pH, temperature, dissolved oxygen and discharge. Event water samples were collected for nutrients, turbidity, conductivity and suspended solids according to discharge. Periphyton growth was scraped every two weeks from rocks over a 10 meter reach, between mid-May and the end of September using a template, blade and toothbrush. Samples for chlorophyll a (Chl a) and ash-free-dry-weight (AFDW) were filtered on to Whatman GF/C glass fiber filters the same day and additional samples were preserved with paraformaldehyde-glutaraldehyde for taxonomic analysis. Chl a was extracted in 95% ethanol and quantified by spectrophotometry. AFDW was determined by drying the samples for 24 hours at 80ºC followed by combustion in a muffle furnace at 500ºC for 2 hours. Samples for diatom analysis were cleaned using a mixture of 1:1 sulphuric and nitric acid at 60°C and mounted on slides with Naphrax mounting medium. Diatoms were then identified and counted with a Zeiss Axiovert 10 inverted microscope at 1000X magnification. A minimum of 400 valves were enumerated for each sample. The presence of other algal constituents was also determined. Statistical analyses included Pearson correlations, stepwise regression analysis and analysis of variance.The chemical and physical properties of the river fluctuated substantially during the sampling season. Nutrient levels were consistently high with total N in the range of 1,2-7,2 mg/l and total P in the range of 0,07-0,37 mg/l, confirming the strong agricultural enrichment of the Boyer River. All measured nitrogen components (total-N, NH3-N, NO3-N) showed a decreasing trend during the sampling season while soluble reactive phosphorus (SRP), total dissolved P, conductivity, pH and temperature showed a general increase over the season. Oxygen levels were often well above or below saturation (29-176% of air equilibrium) indicating a strong biological influence on oxygen dynamics.Periphytic biomass (Chl a and AFDW) and diatom community structure showed major fluctuations over time. The temporal changes in biomass were most strongly correlated (negatively) with peak discharge during the preceding week (AFDW : r=-0,748, p < 0,05; and Chl a : r=-0,649, p < 0,05). This discharge variable was strongly correlated (positively) with several physico-chemical variables (total-N, NH3-N, NO3-N, total-P, turbidity). The negative correlation between biomass and total phosphorus suggested that algae in the Boyer River were not nutrient-limited. However, stepwise regressions showed that variations in diatom-specific composition over time were regulated by various physico-chemical variables linked to environmental preferences and tolerance of each species. Navicula seminulum, Navicula cf. subminusculus and Navicula saprophila were strongly influenced by the peak discharge during the week preceding the sampling (R2 =0,76, F(1,8) =25,7, p 0,001; R2 =0,66, F(1,8) =15,82, p < 0,05 and R2=0,55, F(1,8) =9,85, p < 0,05, respectively). Cymbella silesiaca, Cocconeis placentula, Cyclotella meneghiniana and Navicula saprophila were strongly correlated with temperature (R2 =0,58, F(1,8) =11,08, p < 0,05; R2 =0,61, F(1,8) =28,15, p 0,001; R2 =0,41, F(1,8) =5,65, p < 0,05 and R2 =0,59, F(1,8) =11,38, p < 0,005, respectively). Diatoma vulgaris was mostly influenced by suspended solids plus discharge (R2 =0,4, F(1,8) =5,38, p < 0,05; and R2 =0,86, F(1,7) =20,72, p < 0,005, respectively). The abundance of Navicula lanceolata was strongly correlated with conductivity (R2 =45, F(1,8) =6,55, p < 0,05) while that of Nitzschia spp. correlated with total dissolved phosphorus (R2 =49, F(1,8) =7,63, p < 0,05). No significant influence of the physico-chemical environment was observed on Navicula cryptocephala or Surirella brebissonii. Benthic algae in this nutrient-rich ecosystem responded to environmental variations within 2 weeks since major changes in community composition were observed between all sampling dates. Although diatom community structure changed markedly during the sampling season, most of the observed species are indicative of nutrient-enriched rivers and streams.The results of this study show the dynamic nature of periphyton communities in nutrient-enriched rivers and streams and underscore the importance of discharge as a regulator of biomass. The rapid shifts in community structure also imply that benthic algae can be used as a sensitive measure of environmental conditions in agriculturally impacted ecosystems

Assessing medical student knowledge and attitudes about shared decision making across the curriculum: protocol for an international online survey and stakeholder analysis

Introduction: Shared decision making (SDM) is a goal of modern medicine; however, it is not currently embedded in routine care. Barriers include clinicians’ attitudes, lack of knowledge and training and time constraints. Our goal is to support the development and delivery of a robust SDM curriculum in medical education. Our objective is to assess undergraduate medical students’ knowledge of and attitudes towards SDM in four countries. Methods and analysis: The first phase of the study involves a web-based cross-sectional survey of undergraduate medical students from all years in selected schools across the United States (US), Canada and undergraduate and graduate students in the Netherlands. In the United Kingdom (UK), the survey will be circulated to all medical schools through the UK Medical School Council. We will sample students equally in all years of training and assess attitudes towards SDM, knowledge of SDM and participation in related training. Medical students of ages 18 years and older in the four countries will be eligible. The second phase of the study will involve semistructured interviews with a subset of students from phase 1 and a convenience sample of medical school curriculum experts or stakeholders. Data will be analysed using multivariable analysis in phase 1 and thematic content analysis in phase 2. Method, data source and investigator triangulation will be performed. Online survey data will be reported according to the Checklist for Reporting the Results of Internet E-Surveys. We will use the COnsolidated criteria for REporting Qualitative research for all qualitative data. Ethics and dissemination: The study has been approved for dissemination in the US, the Netherlands, Canada and the UK. The study is voluntary with an informed consent process. The results will be published in a peer-reviewed journal and will help inform the inclusion of SDM-specific curriculum in medical education worldwide

A persistent homology-based topological loss function for multi-class CNN segmentation of cardiac MRI

With respect to spatial overlap, CNN-based segmentation of short axis cardiovascular magnetic resonance (CMR) images has achieved a level of performance consistent with inter observer variation. However, conventional training procedures frequently depend on pixel-wise loss functions, limiting optimisation with respect to extended or global features. As a result, inferred segmentations can lack spatial coherence, including spurious connected components or holes. Such results are implausible, violating the anticipated topology of image segments, which is frequently known a priori. Addressing this challenge, published work has employed persistent homology, constructing topological loss functions for the evaluation of image segments against an explicit prior. Building a richer description of segmentation topology by considering all possible labels and label pairs, we extend these losses to the task of multi-class segmentation. These topological priors allow us to resolve all topological errors in a subset of 150 examples from the ACDC short axis CMR training data set, without sacrificing overlap performance.Comment: To be presented at the STACOM workshop at MICCAI 202

Medical students’ knowledge and attitudes towards shared decision-making: results from a multinational cross-sectional survey

Introduction: We aimed to conduct a multinational cross-sectional online survey of medical students' attitudes towards, knowledge of, and experience with shared decision-making (SDM). Methods: We conducted the survey from September 2016 until May 2017 using: 1) a convenience sample of students from four medical schools each in Canada, the US, and the Netherlands (n=12), and 2) all medical schools in the UK through the British Medical School Council (n=32). We also distributed the survey through social media. Results: 765 students read the information sheet and 619 completed the survey. Average age was 24, 69% were female. Mean SDM knowledge score was 83.6% (range:18.8%-100%; 95% CI 82.8%-84.5%). US students had the highest knowledge scores (86.2%, 95% CI 84.8%-87.6%). The mean risk communication score was 57.4% (range: 0%-100%; 95% CI 57.4%-60.1%). Knowledge did not vary with age, race, gender, school, or school year. Attitudes were positive, except 46% believed SDM could only be done with higher educated patients and 80.9% disagreed that physician payment should be linked to SDM performance (increased with years in training, p<.05). Attitudes did not vary due to any tested variable. Students indicated they were more likely than experienced clinicians to practice SDM (72.1% vs. 48.8%). 74.7% reported prior SDM training and 82.8% were interested in learning more about SDM. Discussion: SDM knowledge is high among medical students in all four countries. Risk communication is less well-understood. Attitudes indicate that further research is needed to understand how medical schools deliver and integrate SDM training into existing curricula

Advances and new applications using the acousto-optic effect in optical fibers

This work presents a short review of the current research on the acousto-optic mechanism applied to optical fibers. The role of the piezoelectric element and the acousto-optic modulator in the excitation of flexural and longitudinal acoustic modes in the frequency range up to 1.2 MHz is highlighted. A combination of the finite elements and the transfer matrix methods is used to simulate the interaction of the waves with Bragg and long period gratings. Results show a very good agreement with experimental data. Recent applications such as the writing of gratings under the acoustic excitation and a novel viscometer sensor based on the acousto-optic mechanism are discussed

Contrasted Effects of Diversity and Immigration on Ecological Insurance in Marine Bacterioplankton Communities

The ecological insurance hypothesis predicts a positive effect of species richness on ecosystem functioning in a variable environment. This effect stems from temporal and spatial complementarity among species within metacommunities coupled with optimal levels of dispersal. Despite its importance in the context of global change by human activities, empirical evidence for ecological insurance remains scarce and controversial. Here we use natural aquatic bacterial communities to explore some of the predictions of the spatial and temporal aspects of the ecological insurance hypothesis. Addressing ecological insurance with bacterioplankton is of strong relevance given their central role in fundamental ecosystem processes. Our experimental set up consisted of water and bacterioplankton communities from two contrasting coastal lagoons. In order to mimic environmental fluctuations, the bacterioplankton community from one lagoon was successively transferred between tanks containing water from each of the two lagoons. We manipulated initial bacterial diversity for experimental communities and immigration during the experiment. We found that the abundance and production of bacterioplankton communities was higher and more stable (lower temporal variance) for treatments with high initial bacterial diversity. Immigration was only marginally beneficial to bacterial communities, probably because microbial communities operate at different time scales compared to the frequency of perturbation selected in this study, and of their intrinsic high physiologic plasticity. Such local “physiological insurance” may have a strong significance for the maintenance of bacterial abundance and production in the face of environmental perturbations