Chiral filtration and Faraday rotation in multi-Weyl semimetals

In Weyl semimetals with broken inversion and time-reversal symmetries, the Maxwell equations are modified by the presence of the axion terms $\mathbf{b}$ and $b_{0}$ where, in the simplest case of a two-node Weyl semimetal, $2\hslash \mathbf{b}$ is the vector that connects two Weyl nodes in momentum space and $2\hslash b_{0}$ is the separation in energy of the two Dirac points of these nodes. These axion terms modify the behavior of electromagnetic waves inside a Weyl semimetal leading to a number of unique optical properties such as non-reciprocal propagation, circular and linear dichroism, birefringence and Faraday and Kerr rotations in the absence of a magnetic field. These effects can be used to design optical devices that act as broadband chiral filters, circular polarizers or tunable optical isolators. In this paper, we study in detail how the Faraday and Kerr rotations as well as the transmission and reflection of light incident on a slab of Weyl semimetal can be controlled by varying the different parameters characterizing the Weyl semimetal such as the axion terms, the Fermi level and Fermi velocity, the background dielectric constant, the scattering time for intraband scattering, the width of the semimetal and the dielectric constant of the dielectrics on each side of the semimetal slab. We extend our analysis to Weyl nodes with Chern number $n=1,2,3$.Comment: 18 pages, 14 figure

Magneto-optical Kerr effect in Weyl semimetals with broken inversion and time-reversal symmetries

The topological nature of the band structure of a Weyl semimetal leads to a number of unique transport and optical properties. For example, the description of the propagation of an electromagnetic wave in a Weyl semimetal with broken time-reversal and inversion symmetry, for example, requires a modification of the Maxwell equations by the axion field $\theta \left( \mathbf{r},t\right) =2\mathbf{b}\cdot \mathbf{r}-2b_{0}t,$ where $2$ is the separation in wave vector space between two Weyl nodes of opposite chiralities and $2\hslash b_{0}$ is their separation in energy. In this paper, we study theoretically how the axion terms $b_{0}$ and $\bf{b}$ modify the frequency behavior of the Kerr rotation and ellipticity angles $\theta_{K}\left( \omega \right)$ and $\psi_{K}\left( \omega \right)$ in a Weyl semimetal. Both the Faraday and Voigt configurations are considered since they provide different information on the electronic transitions and plasmon excitation. We derive the Kerr angles firstly without an external magnetic field where the rotation of the polarization is only due to the axion terms and secondly in a strong magnetic field where these terms compete with the gyration effect of the magnetic field. In this latter case, we concentrate on the ultra-quantum limit where the Fermi level lies in the chiral Landau level and the Kerr and ellipticity angles have more complex frequency and magnetic field behaviors.Comment: 21 pages with 14 PDF figure

Étude de l'effet Kerr dans les semimétaux de Weyl avec termes d'axion

L’objectif de cet ouvrage est de déterminer de comprendre les propriétés optiques des semi-métaux de Weyl de façon à aider la détermination d’applications technologiques. Les semi-métaux de Weyl sont des matériaux topologiques qui présentent des points autour desquels la structure de bande est linéaire. Ces points apparaissent en paires nommées noeuds de Weyl et sont responsables de plusieurs propriétés électroniques étonnantes. De façon à mieux comprendre l’impact de ces propriétés sur l’optique, cet ouvrage couvre certaines étapes nécessaires à l’étude de l’angle de Kerr (angle décrivant la capacité du solide à modifier l’orientation de la polarisation dans la lumière réfléchie). La première étape est de présenter un modèle simple pouvant décrire encapsuler les caractéristiques d’un semi-métal de Weyl. Le modèle du continuum est alors employé pour fournir les états propres du système. Les états propres avec et sans champ magnétique externe appliqué sont alors obtenus et permettent de caractériser l’interaction avec la lumière. En effet, la seconde étape est d’obtenir l’expression de la conductivité. Seul un survol rapide des étapes sera présenté puisque d’autres ouvrages couvrent déjà ces calculs. Une fois l’expression de la conductivité déterminée, il convient alors d’évaluer l’interaction entre la lumière et les charges dans le solide. Pour arriver à cette fin, la troisième étape est de résoudre les équations de Maxwell et les équations de frontière. Cependant, il sera alors question d’inclure les termes d’axion. La présence de ces termes nécessite d’introduire une nouvelle façon de résoudre les équations de Maxwell qui sera alors présentée. Finalement, une analyse de l’effet de ces termes sera présentée. Dans cette analyse, certaines caractéristiques innovantes seront mises en évidence. Parmi cellesci, sera notablement avancée une possible triréfringence, une technique expérimentale pour déterminer la valeur des termes d’axion et un moyen de contrôler la polarisation de la lumière de façon flexible

A case study of combined winter road snow plowing and de-icer spreading

In this article, we address a winter maintenance problem where the streets need to be plowed and gritted in a sequence that depends on the class of the road. The maintenance fleet includes vehicles equipped for plowing, some for spreading, and some for both at once. The objective is to complete the operations as rapidly as possible while considering street hierarchy, turn restrictions, heterogeneous speeds, and street–vehicle compatibility. An adaptive large neighborhood search framework is developed to solve the problem. Analysis of the results obtained can provide both a good basis for vehicle routing and help managers plan long-term policies and investments.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Pour créer des collaborations fructueuses au sein des écosystèmes d’innovation, se rencontrer ne suffit pas

Les initiatives visant à développer un écosystème favorable à la création et à la croissance des entreprises et/ou de l’innovation reposent sur l’idée de réunir une diversité d’acteurs. Les interactions sociales, ouvertes et diversifiées, deviennent alors du soutien et des moteurs de l’innovation. Déterminantes du succès des écosystèmes, elles sont pensées comme « faciles » tant à faire exister qu’à multiplier. Dans le présent article, nous revenons sur quelques constats de base de la sociologie des réseaux, puis utilisons le concept d’homophilie pour examiner la faisabilité sociologique de cette multiplication et de cette diversification des relations. L’analyse s’appuie sur l’étude de deux cas exemplaires. D’une part, l’écosystème montréalais de startups dans le secteur numérique, où l’absence d’homophilie explique la relative rareté des collaborations et, d’autre part, l’Esplanade, un accélérateur et espace collaboratif montréalais dédié à l’entrepreneuriat et à l’innovation sociale, où la ressemblance des acteurs explique les nombreuses collaborations observées.Initiatives to develop an ecosystem conducive to the creation and growth of businesses and/or innovation are based on the idea of bringing together a diversity of actors. Open and diversified social interactions then support and drive innovation. These determining factors of ecosystem success are perceived as “easy” both to achieve and to multiply. In this article, we return to some basic findings of network sociology and use the homophily concept to examine the sociological feasibility of this multiplication and diversification of relationships. The analysis is based on the study of two exemplary cases: the case of the Montreal startup ecosystem in the digital field, where the absence of homophily explains the relative scarcity of collaboration, and the case of l’Esplanade, a Montreal business accelerator and collaborative network dedicated to entrepreneurship and social innovation, where the commonality of the actors explains the significant collaboration observed

Solving the large-scale min-max K-rural postman problem for snow plowing

International audienceThis article studies the snow plow routing problem, which is a modified version of the min–max problem with k-vehicles for arc routing on a mixed graph with hierarchy. Each arc or edge is given a priority and instead of minimizing the overall finishing time, we minimize the latest finishing time for each priority class. We consider turn restrictions, route balancing, and variable vehicle speeds in a real large-scale network. To solve the problem, we present a graph transformation from a directed rural postman problem with turn penalties to an asymmetric traveling salesman problem. We then make the following modifications to the metaheuristics to better handle the constraints: development of new neighborhood operators, several applications of the same destruction operators before repair of the solution, and a dynamic arc-grouping procedure when links are removed or inserted. We tested our methodology on three real networks with 1,626 to 2,146 street segments and 613 to 723 intersections. The results show that our approach can improve the solution, and the grouping procedure is helpful. The results also show that some operators perform better than others; the network topology seems to explain these variations. Finally, we validated our methodology by comparing to some routes planned in the past and to some routes obtained from a commercial solver

Brain omega-3 polyunsaturated fatty acids modulate microglia cell number and morphology in response to intracerebroventricular amyloid-β 1-40 in mice

Abstract Background Neuroinflammation is a proposed mechanism by which Alzheimer’s disease (AD) pathology potentiates neuronal death and cognitive decline. Consumption of omega-3 polyunsaturated fatty acids (PUFA) is associated with a decreased risk of AD in human observational studies and exerts protective effects on cognition and pathology in animal models. These fatty acids and molecules derived from them are known to have anti-inflammatory and pro-resolving properties, presenting a potential mechanism for these protective effects. Methods Here, we explore this mechanism using fat-1 transgenic mice and their wild type littermates weaned onto either a fish oil diet (high in n-3 PUFA) or a safflower oil diet (negligible n-3 PUFA). The fat-1 mouse carries a transgene that enables it to convert omega-6 to omega-3 PUFA. At 12 weeks of age, mice underwent intracerebroventricular (icv) infusion of amyloid-β 1-40. Brains were collected between 1 and 28 days post-icv, and hippocampal microglia, astrocytes, and degenerating neurons were quantified by immunohistochemistry with epifluorescence microscopy, while microglia morphology was assessed with confocal microscopy and skeleton analysis. Results Fat-1 mice fed with the safflower oil diet and wild type mice fed with the fish oil diet had higher brain DHA in comparison with the wild type mice fed with the safflower oil diet. Relative to the wild type mice fed with the safflower oil diet, fat-1 mice exhibited a lower peak in the number of labelled microglia, wild type mice fed with fish oil had fewer degenerating neurons, and both exhibited alterations in microglia morphology at 10 days post-surgery. There were no differences in astrocyte number at any time point and no differences in the time course of microglia or astrocyte activation following infusion of amyloid-β 1-40. Conclusions Increasing brain DHA, through either dietary or transgenic means, decreases some elements of the inflammatory response to amyloid-β in a mouse model of AD. This supports the hypothesis that omega-3 PUFA may be protective against AD by modulating the immune response to amyloid-β

Effectiveness of a treat-to-target strategy in patients with moderate to severely active rheumatoid arthritis treated with abatacept

Abstract Background To compare a treat-to-target (T2T) approach and routine care (RC) in adults with active to severely active rheumatoid arthritis (RA) initiating subcutaneous abatacept. Methods A 12-month cluster-randomized trial in active RA patients treated with abatacept was conducted. Physicians were randomized to RC or T2T with a primary endpoint of achieving sustained Clinical Disease Activity Index (CDAI) low disease activity (LDA) at two consecutive assessments approximately 3 months apart. Additional outcomes included Simple Disease Activity Index (SDAI), Disease Activity Score 28-CRP (DAS28-CRP), Routine Assessment of Patient Index Data 3 (RAPID3), and the Health Assessment Questionnaire-Disability Index (HAQ-DI). Time to achieve therapeutic endpoints was assessed with survival analysis. Results Among the 284 enrolled patients, 130 were in the T2T group and 154 in RC. Primary endpoint was achieved by 36.9% and 40.3% of patients in T2T and RC groups, respectively. No significant between-group differences were observed in the odds of achieving secondary outcomes, except for a higher likelihood of CDAI LDA in the T2T group vs. RC (odds ratio [95% confidence interval]: 1.33 [1.03–1.71], p = 0.0263). Compared with RC, patients in the T2T group achieved SDAI remission significantly faster (Kaplan–Meier-estimated mean [standard error]: 14.0 [0.6] vs. 19.3 [0.8] months, p = 0.0428) with a trend toward faster achievement of CDAI LDA/remission, DAS28-CRP remission, and HAQ-DI minimum clinically important difference. Conclusions Patients managed per T2T and those under RC experienced significant improvements in RA disease activity at 12 months of abatacept treatment. T2T was associated with higher odds of CDAI LDA and a shorter time to achieving therapeutic endpoints. Trial registration Name of the registry: ClinicalTrials.gov. Trial registrations: NCT03274141 . Date of registration: September 6, 2017

The effects of n-6 polyunsaturated fatty acid deprivation on the inflammatory gene response to lipopolysaccharide in the mouse hippocampus

Abstract Background Neuroinflammation is thought to contribute to psychiatric and neurological disorders such as major depression and Alzheimer’s disease (AD). N-6 polyunsaturated fatty acids (PUFA) and molecules derived from them, including linoleic acid- and arachidonic acid-derived lipid mediators, are known to have pro-inflammatory properties in the periphery; however, this has yet to be tested in the brain. Lowering the consumption of n-6 PUFA is associated with a decreased risk of depression and AD in human observational studies. The purpose of this study was to investigate the inflammation-modulating effects of lowering dietary n-6 PUFA in the mouse hippocampus. Methods C57BL/6 male mice were fed either an n-6 PUFA deprived (2% of total fatty acids) or an n-6 PUFA adequate (23% of total fatty acids) diet from weaning to 12 weeks of age. Animals then underwent intracerebroventricular surgery, in which lipopolysaccharide (LPS) was injected into the left lateral ventricle of the brain. Hippocampi were collected at baseline and following LPS administration (1, 3, 7, and 14 days). A microarray (n = 3 per group) was used to identify candidate genes and results were validated by real-time PCR in a separate cohort of animals (n = 5–8 per group). Results Mice administered with LPS had significantly increased Gene Ontology categories associated with inflammation and immune responses. These effects were independent of changes in gene expression in any diet group. Results were validated for the effect of LPS treatment on astrocyte, cytokine, and chemokine markers, as well as some results of the diets on Ifrd2 and Mfsd2a expression. Conclusions LPS administration increases pro-inflammatory and lipid-metabolizing gene expression in the mouse hippocampus. An n-6 PUFA deprived diet modulated inflammatory gene expression by both increasing and decreasing inflammatory gene expression, without impairing the resolution of neuroinflammation following LPS administration