Algorithmes de Newton-min polyédriques pour les problèmes de complémentarité

The semismooth Newton method is a very efficient approach for computing a zero of a large class of nonsmooth equations. When the initial iterate is sufficiently close to a regular zero and the function is strongly semismooth, the generated sequence converges quadratically to that zero, while the iteration only requires to solve a linear system.If the first iterate is far away from a zero, however, it is difficult to force its convergence using linesearch or trust regions because a semismooth Newton direction may not be a descent direction of the associated least-square merit function, unlike when the function is differentiable. We explore this question in the particular case of a nonsmooth equation reformulation of the nonlinear complementarity problem, using the minimum function. We propose a globally convergent algorithm using a modification of a semismooth Newton direction that makes it a descent direction of the least-square function. Instead of requiring that the direction satisfies a linear system, it must be a feasible point of a convex polyhedron; hence, it can be computed in polynomial time. This polyhedron is defined by the often very few inequalities, obtained by linearizing pairs of functions that have close negative values at the current iterate; hence, somehow, the algorithm feels the proximity of a "bad kink" of the minimum function and acts accordingly.In order to avoid as often as possible the extra cost of having to find a feasible point of a polyhedron, a hybrid algorithm is also proposed, in which the Newton-min direction is accepted if a sufficient-descent-like criterion is satisfied, which is often the case in practice. Global convergence to regular points is proved; the notion of regularity is associated with the algorithm and is analysed with care.L'algorithme de Newton semi-lisse est très efficace pour calculer un zéro d'une large classe d'équations non lisses. Lorsque le premier itéré est suffisamment proche d'un zéro régulier et si la fonction est fortement semi-lisse, la suite générée converge quadratiquement vers ce zéro, alors que l'itération ne requière que la résolution d'un système linéaire.Cependant, si le premier itéré est éloigné d'un zéro, il est difficile de forcer sa convergence par recherche linéaire ou régions de confiance, parce que la direction de Newton semi-lisse n'est pas nécessairement une direction de descente de la fonction de moindres-carrés associée, contrairement au cas où la fonction à annuler est différentiable. Nous explorons cette question dans le cas particulier d'une reformulation par équation non lisse du problème de complémentarité non linéaire, en utilisant la fonction minimum. Nous proposons un algorithme globalement convergent, utilisant une direction de Newton semi-lisse modifiée, qui est de descente pour la fonction de moindres-carrés. Au lieu de requérir la satisfaction d'un système linéaire, cette direction doit être intérieur à un polyèdre convexe, ce qui peut se calculer en temps polynomial. Ce polyèdre est défini par souvent très peu d'inégalités, obtenus en linéarisant des couples de fonctions qui ont des valeurs négatives proches à l'itéré courant; donc, d'une certaine manière, l'algorithme est capable d'estimer la proximité des "mauvais plis" de la fonction minimum et d'agir en conséquence.De manière à éviter au si souvent que possible le coût supplémentaire lié au calcul d'un point admissible de polyèdre, un algorithme hybride est également proposé, dans lequel la direction de Newton-min est acceptée si un critère de décroissance suffisante est vérifié, ce qui est souvent le cas en pratique. La convergence globale vers des points régulier est démontrée; la notion de régularité est associée à l'algorithme et est analysée avec soin

Les prix à la pompe à Québec réagissent-ils plus rapidement aux hausses qu'aux baisses du coût de l'essence?

Dans plusieurs marchés de l’essence, les prix semblent s’ajuster plus rapidement après des hausses que des baisses des coûts. Cet ajustement asymétrique pourrait entraîner un surcoût pour les automobilistes puisque les prix descendent plus lentement qu’ils le devraient. Plusieurs études ont été réalisées sur le sujet et la plupart indiquent la présence du phénomène. Au Québec, les rares études ont toutefois apporté des résultats mitigés. Ce mémoire vise à tester la présence d’ajustement asymétrique du prix de l’essence à Québec. Nous estimons trois modèles à correction d’erreur et deux d’entre eux indiquent la présence d’asymétrie. En particulier, nous trouvons que l’asymétrie s’observe en fonction de la marge bénéficiaire des essenceries et non du signe des variations des coûts, contrairement à ce que confirment plusieurs études. Plus précisément, le prix semble s’ajuster plus rapidement lorsque la marge est basse. Toutefois, nous estimons que l’asymétrie engendre un surcoût minime pour les automobilistes

Financial Well-being of Frontline Healthcare Workers: The Importance of Employer Benefits

Frontline healthcare workers – especially direct care workers (DCWs), such as home health aides, struggle due to low pay, lack of benefits, and difficult working conditions. The need for these workers is growing. Unless frontline healthcare jobs improve, positions may be difficult to fill, and care for vulnerable members of society may be compromised. In this study, we surveyed 2,321 frontline healthcare workers and conducted in-depth interviews with 30 of these workers concerning pay, benefits, work conditions, and financial well-being. Key survey findings included: Only 39% of workers were eligible for at least four out of five major benefits (e.g., health, retirement). Compared to all U.S. workers, workers had less access to health, retirement, paid leave, dental, and tuition benefits. On average, the proportion of workers who said various benefits were important to them was 41 percentage points higher than the proportion of workers who had access to these benefits. Probabilities that workers had access to most major benefits were: 138% higher among workers with college degrees compared to workers without degrees 206% higher among workers in facility-based settings such as hospitals compared to workers in home health or private duty settings and 24% lower among Black compared to white workers. Black workers, workers without college degrees, and workers in home health or private duty settings had significantly higher rates of 9 out of 10 financial difficulties such as problems paying bills. The greater the number of major benefits to which workers had access, the lower their probabilities for experiencing all 10 financial difficulties – after controlling for income and other factors. For example, the probability of experiencing food insufficiency drops by 28% from having three benefits compared to one. 59% of workers changed jobs at least once in the past year. 34% of workers are somewhat or very likely to leave their current job in the next year. Workers with a greater number of major benefits to which they had access and those with higher levels of job satisfaction were less likely to consider leaving. In-depth interviewers revealed that workers struggle with challenging work conditions, such as severe staffing shortages. Work is physically and emotionally demanding, and burnout is high. Despite this, they want to remain in healthcare. Pay is the primary factor when considering a job change, yet workers yearned for more tuition assistance to support career development, more help with childcare, and less expensive health insurance. Many workers rely on public benefits and find it stressful to navigate benefits cliffs - the possibility of losing public benefits when income rises above income limits. Based on these key findings, we outline a set of recommendations for employers, policymakers, and other stakeholders to improve pay, benefits, and work conditions for frontline health workers, especially DCWs, such as: Offering a core package of major benefits: health insurance, paid leave, retirement, dental, and childcare assistance and ensuring workers can afford health insurance premiums. Increasing spending on home and community-based services (HCBS) via Medicaid to raise pay for frontline healthcare workers. Increasing federal funding for childcare subsidies and fixing benefits cliffs

Accuracy of unguided and ultrasound guided Coracohumeral ligament infiltrations – a feasibility cadaveric case series

Coracohumeral ligament (CHL) thickening, contracture, and fibroplasia have been identified in glenohumeral idiopathic adhesive capsulitis (GHIAC). The CHL is the main structure responsible for the range of motion limitations. Favorable outcomes have been reported with CHL surgical release. Intra-articular glenohumeral joint corticosteroid infiltrations are utilized to disrupt the inflammatory process and reduce pain in GHIAC. The aim of this study was to investigate whether the CHL could be accurately targeted with a periligamentous infiltration

The association between parameters of physical activity and olfactory function—the importance of frequency and moderate intensity

IntroductionOverall physical activity (PA) has been linked to decreased olfactory dysfunction and could improve olfactory function. Additionally, decreased olfactory function can contribute to reduced overall PA levels, given its association with neurodegenerative disorders. This study aims to examine the relationship between specific PA parameters (duration, frequency, intensity) and olfactory function in adults.MethodsA total of 3,527 participants from the National Health and Nutrition Examination Survey (NHANES) 2013–2014 underwent assessments for weekly PA duration, frequency, and intensity, alongside a smell test (including odors such as chocolate, strawberry, grape, onion, smoke, natural gas, leather, and soap). Correlation analyses and binary logistic regressions using SPSS were used to evaluate associations.ResultsThe total smell score exhibited small yet significant positive correlations with the duration, frequency, and volume of moderate PA (correlation coefficients ranging between 0.05 and 0.08; all p ≤ 0.05) and frequency of vigorous PA (correlation coefficient of 0.05; p < 0.05). For moderate PA, the duration, frequency, and volume were significantly and positively associated with the ability to correctly detect the smell of grapes while the frequency was significantly and positively associated with the ability to identify smoke and leather odors (odds ratios ranging from 1.01 to 1.07; p < 0.05). For vigorous PA, the frequency of PA was positively associated with the detection of grape smell (odds ratio of 1.05; p < 0.05).ConclusionSome parameters of an active lifestyle are associated with improved odds of accurately identifying odors by up to 7.4%. Moderate PA duration, frequency, and volume were linked to better olfactory scores, while high-intensity PA had limited associations

Structure and dynamics of the deoxyguanosine-sensing riboswitch studied by NMR-spectroscopy

The mfl-riboswitch regulates expression of ribonucleotide reductase subunit in Mesoplasma florum by binding to 2′-deoxyguanosine and thereby promoting transcription termination. We characterized the structure of the ligand-bound aptamer domain by NMR spectroscopy and compared the mfl-aptamer to the aptamer domain of the closely related purine-sensing riboswitches. We show that the mfl-aptamer accommodates the extra 2′-deoxyribose unit of the ligand by forming a more relaxed binding pocket than these found in the purine-sensing riboswitches. Tertiary structures of the xpt-aptamer bound to guanine and of the mfl-aptamer bound to 2′-deoxyguanosine exhibit very similar features, although the sequence of the mfl-aptamer contains several alterations compared to the purine-aptamer consensus sequence. These alterations include the truncation of a hairpin loop which is crucial for complex formation in all purine-sensing riboswitches characterized to date. We further defined structural features and ligand binding requirements of the free mfl-aptamer and found that the presence of Mg2+ is not essential for complex formation, but facilitates ligand binding by promoting pre-organization of key structural motifs in the free aptamer

Les retraites de rédaction structurées auprès des doctorant[e]s : Quelles conditions favorisent une expérience de rédaction légitime, productive et plaisante?

Thesis writing is challenging for many PhD candidates. To support them, structured writing retreats represent a strategy for consideration, although little has been documented on the topic. This article presents results from a mixed-method study (N = 210) combining questionnaires and interviews, aiming to understand the effects of Thesez-vous writing retreats to 1) document benefits of writing retreats, namely encouraging writing, legitimizing writing and ensuring a fulfilling experience, and to 2) identify conditions maximizing these benefits. More broadly, this article conveys the possibility to rethink and reframe thesis writing to create a productive, collective and pleasant experience. Keywords: thesis editing, writing retreats, benefits, flow, scientific productivityLa rédaction de la thèse est problématique pour nombre de doctorant[e]s. Pour les soutenir, la retraite de rédaction structurée semble une stratégie intéressante, mais peu de recherches ont tenté de la décrire. Cet article présente des résultats issus d’une étude mixte (N = 210), combinant questionnaires et entretiens pour mesurer et comprendre les effets des retraites Thèsez-vous en vue 1) d’en recenser les bénéfices, soit favoriser la productivité, légitimer la rédaction et vivre une expérience plaisante, et 2) d’identifier les conditions qui favorisent ces bénéfices. Ultimement, cet article contribue à l’identification de stratégies pour repenser et améliorer l’encadrement de la rédaction de thèse. Mots-clés : rédaction, retraite de rédaction, bénéfices, flow, productivité scientifiqu

Planetary Candidates Observed by Kepler IV: Planet Sample From Q1-Q8 (22 Months)

We provide updates to the Kepler planet candidate sample based upon nearly two years of high-precision photometry (i.e., Q1-Q8). From an initial list of nearly 13,400 Threshold Crossing Events (TCEs), 480 new host stars are identified from their flux time series as consistent with hosting transiting planets. Potential transit signals are subjected to further analysis using the pixel-level data, which allows background eclipsing binaries to be identified through small image position shifts during transit. We also re-evaluate Kepler Objects of Interest (KOI) 1-1609, which were identified early in the mission, using substantially more data to test for background false positives and to find additional multiple systems. Combining the new and previous KOI samples, we provide updated parameters for 2,738 Kepler planet candidates distributed across 2,017 host stars. From the combined Kepler planet candidates, 472 are new from the Q1-Q8 data examined in this study. The new Kepler planet candidates represent ~40% of the sample with Rp~1 Rearth and represent ~40% of the low equilibrium temperature (Teq<300 K) sample. We review the known biases in the current sample of Kepler planet candidates relevant to evaluating planet population statistics with the current Kepler planet candidate sample.Comment: 12 pages, 8 figures, Accepted ApJ Supplemen

Analysis of the Collective Behavior of a 10 by 10 Array of Fe3O4 Dots in a Large Micromagnetic Simulation

We report a full (3D) micromagnetic simulation of a set of 100 ferrite (Fe$_3$O$_4$) cylindrical dots, arranged in a 10 by 10 square (planar) array of side 3.27 $\mu$m, excited by an external in-plane magnetic field. The resulting power spectrum of magnetic excitations and the dynamical magnetization field at the resulting resonance modes were investigated. The absorption spectrum deviates considerably from that of a single particle reference simulation, presenting a mode-shifting and splitting effect. We found an inversion symmetry through the center of the array, in the sense that each particle and its inversion counterpart share approximately the same magnetization mode behavior. Magnonic designs aiming at synchronous or coherent tunings of spin-wave excitations at given spatially separated points within a regular square array may benefit from the new effects here described.Comment: 22 pages, 4 figures; accepted for publication in Physica E: Low-Dimensional Systems and Nanostructure