Quasi-periodic oscillations, trapped inertial waves and strong toroidal magnetic fields in relativistic accretion discs

The excitation of trapped inertial waves (r-modes) by warps and eccentricities in the inner regions of a black hole accretion disc may explain the high-frequency quasi-periodic oscillations (HFQPOs) observed in the emission of Galactic X-ray binaries. However, it has been suggested that strong vertical magnetic fields push the oscillations' trapping region toward the innermost stable circular orbit (ISCO), where conditions could be unfavourable for their excitation. This paper explores the effects of large-scale magnetic fields that exhibit \textit{both} toroidal and vertical components, through local and global linear analyses. We find that a strong toroidal magnetic field can reduce the detrimental effects of a vertical field: in fact, the isolation of the trapping region from the ISCO may be restored by toroidal magnetic fields approaching thermal strengths. The toroidal field couples the r-modes to the disc's magneto-acoustic response and inflates the effective pressure within the oscillations. As a consequence, the restoring force associated with the vertical magnetic field's tension is reduced. Given the analytical and numerical evidence that accretion discs threaded by poloidal magnetic field lines develop a strong toroidal component, our result provides further evidence that the detrimental effects of magnetic fields on trapped inertial modes are not as great as previously thought.Comment: 16 pages, 6 figures, MNRAS accepte

Dynamical tides in Jupiter and other rotationally flattened planets and stars with stable stratification

We develop a numerical method for directly computing the dissipative dynamical tidal response of rapidly rotating, oblate stars and gaseous planets with realistic internal structures. Applying these calculations to neutrally and stably stratified polytropes, we identify the most relevant resonances in models with rotation rates up to nearly the mass-shedding limit. We then compute the dynamical tidal response for Jupiter interior models including both stably stratified and convective regions. These calculations show that resonances involving mixed waves with both gravito-inertial and purely inertial character are capable of explaining a discrepancy between observations and hydrostatic calculations of Jupiter's response to tidal forcing by Io. This result contrasts with recent work that excluded Jupiter's rotational flattening, and opens the door to resonances involving a wider range of internal oscillation modes than previously considered.Comment: 15 pages, 12 figures, accepted for publication in MNRAS (comments welcome

Is Dropping out of High School More Likely after Stressful Life Events?

High school dropout is typically viewed as the result of long-held vulnerabilities such as learning problems. This research brief, by PRC visiting scholars Véronique Dupéré and Eric Dion and PRC faculty research associate Robert Crosnoe and colleagues, shows that recent stressful life events can lead to a student dropping out.Population Research Cente

ON SOME LENGTH PROBLEMS FOR ANALYTIC FUNCTIONS

Let A be the class of functions f(z) = z+Σ^^__a_n z^n which are analytic in the unit disk D={z : |z|<1}. Let C(r) be the closed curve which is the image of the circle |z|=r < 1 under the mapping ω= f(z), L(r) the length of C(r), and let A(r) be the area enclosed by the curve C(r). It was shown in [13] that if f∈A, f is starlike with respect to the origin, and for 0 < r < 1, A(r ) < A, an absolute constant, then (0.1) L(r) = O(log(1/(1-r))) as r → 1. It is the purpose of this work to prove, using a modified methods than that in [13], a strengthened form of (0.1) for Bazilevic functions, strongly starlike functions and for close-to-convex functions

Dynamical tidal Love numbers of rapidly rotating planets and stars

Tidal interactions play an important role in many astrophysical systems, but uncertainties regarding the tides of rapidly rotating, centrifugally distorted stars and gaseous planets remain. We have developed a precise method for computing the dynamical, non-dissipative tidal response of rotating planets and stars, based on summation over contributions from normal modes driven by the tidal potential. We calculate the normal modes of isentropic polytropes rotating at up to $\simeq90\%$ of their critical breakup rotation rates, and tabulate fits to mode frequencies and tidal overlap coefficients that can be used to compute the frequency-dependent, non-dissipative tidal response (via potential Love numbers $k_{\ell m}$). Although fundamental modes (f-modes) possess dominant tidal overlap coefficients at (nearly) all rotation rates, we find that the strong coupling of retrograde inertial modes (i-modes) to tesseral ($\ell>|m|$) components of the tidal potential produces resonances that may be relevant to gas giants like Jupiter and Saturn. The coupling of f-modes in rapid rotators to multiple components of both the driving tidal potential and the induced gravitational field also affect the tesseral response, leading to significant deviations from treatments of rotation that neglect centrifugal distortion and high-order corrections. For very rapid rotation rates ($\gtrsim 70\%$ of breakup), mixing between prograde f-modes and i-modes significantly enhances the sectoral ($\ell=|m|$) tidal overlap of the latter. The tidal response of very rapidly rotating, centrifugally distorted planets or stars can also be modified by resonant sectoral f-modes that are secularly unstable via the Chandrasekhar-Friedman-Schutz (CFS) mechanism.Comment: 19 pages, 9 figures, 4 tables, accepted for publication in Ap

Modèle des déterminants des buts de maîtrise chez des élèves du primaire

La présente étude s’appuie sur une série d’hypothèses décrivant les liens entre la motivation de l’enseignant et la poursuite des buts de maîtrise chez des élèves de quatrième et sixième années du primaire. Les données ont été recueillies à l’aide du Questionnaire de l’environnement socioéducatif. Elles révèlent que ces liens sont essentiellement indirects. Ce sont plutôt les pratiques d’enseignement et surtout les composantes du climat scolaire qui contribuent à la poursuite des buts de maîtrise. Toutefois, le niveau d’engagement affectif de l’enseignant influence directement les pratiques pédagogiques. Ces résultats confirment l’ensemble des hypothèses de départ.The present study is based on a series of assumptions describing the relationships between the motivation of the teacher and the pursuit of self-control goals for pupils of fourth and sixth grades of primary school. The data were collected using the socio-educational environment questionnaire. They reveal that these relationships are primarily of indirect nature. It is rather the practices and especially the components of the school climate that contribute directly to the pursuit of self-control goals. However, the level of the teachers’ emotional commitment directly influences teaching practices. These results ultimately confirm all of the initial assumptions.El presente estudio se fundamenta en una serie de hipótesis que describen los vínculos entre la motivación del docente y la prosecución de metas de dominio en alumnos de cuarto y de sexto grado de primaria. Los datos han sido colectados por medio del cuestionario del entorno socio-educativo. Revelan que los vínculos son esencialmente de tipo indirecto. Son más bien las prácticas y aún más los componentes del ambiente escolar que contribuyen directamente a la prosecución de metas de dominio. Sin embargo, el nivel de compromiso afectivo del docente influye directamente en las prácticas pedagógicas. Finalmente, estos resultados confirman el conjunto de hipótesis iniciales.Diese Studie stützt sich auf eine Reihe von Hypothesen, die die Zusammenhänge zwischen der Motivation des Lehrers und der Verfolgung der Beherrschungsziele bei Schülern vierter und sechster Klasse in der Grundschule beschreiben. Die Daten wurden gesammelt mit der Hilfe von Fragebogen des sozialpädagogischen Umfelds. Sie zeigen auf, daß diese Zusammenhänge im wesentlichen indirekt sind. Es sind eher die Praktiken und besonders die Bestandteile des Schulklimas, die direkt zur Verfolgung der Beherrschungsziele beitragen. Das Gefühlvolle Verpflichtungsniveau des Lehrers beeinflusst jedoch die pädagogischen Praktiken direkt. Diese Ergebnisse bestätigen letzten Endes die Anfangshypothesen im Großen und Ganzen

Consommation de psychotropes et délinquance : de bons prédicteurs de l’abandon scolaire ?

Although empirical links between deviant behavior and school dropout have been extensively demonstrated, the specific influence of drug use and delinquency on school dropout is still not clear and varies across studies. One reason for this lack of consistency may rests upon the way samples of dropouts have been analysed. Recently, Janosz, Le Blanc, Boulerice and Tremblay (1996) constructed and validated a typology of school dropout highlithing the social and psychological diversity of this population. Using a longitudinal sample of adolescents (N=791), we analyzed the predictive relationships of family rebelliousness, drug use and delinquency on school dropout. The results showed an important variability in the predictive relationships according to the type of dropouts. The necessity of considering the psychosocial heterogeneity of dropouts when conducting such studies is discussed

Reciprocal Prospective Associations Between Depressive Symptoms and Perceived Relationship With Parents in Early Adolescence

Objective: Adolescent depressive symptoms are associated with difficult family relationships. Family systems and interpersonal theories of depression suggest that this association could reflect a circular process in which symptoms and family functioning affect each other over time. Few longitudinal studies have tested this hypothesis, and the results of these studies have been equivocal. In this study, we examine reciprocal prospective associations in early adolescence between depressive symptoms and 2 important aspects of parent–child relationships: communication and conflict. Methods: Participants were 3862 students who annually filled out self-reports. Path analysis was used to examine prospective associations between depressive symptoms and perceived communication and conflict with parents from the age of 12 to 13 and 14 to 15 years. Independence of these associations was assessed by controlling for family context (parental separation and family socioeconomic status) and adolescent behaviour problems (delinquent behaviours and substance use). Sex differences were evaluated with multiple group analysis. Results: Reciprocal prospective associations were found between depressive symptoms and perceived conflict with parents, but not between depressive symptoms and communication with parents. Depressive symptoms were found to predict poorer communication with parents over time, but communication was not predictive of lower depressive symptoms in subsequent years. All paths were sex-invariant and independent from family context and behaviour problems. Conclusion: This study highlights the importance of considering the potential impact of adolescent symptomatology on parent–child relationships and suggests that reciprocity may characterize the association between depressive symptoms and negative aspects of parent–child relationships. The role of adolescent perceptions in the interplay between depressive symptoms and family relationships remains to be clarified.Objectif : Les symptômes dépressifs des adolescents sont associés à des relations familiales difficiles. Les systèmes familiaux et les théories interpersonnelles de la dépression suggèrent que cette association pourrait refléter un processus circulaire dans lequel les symptômes et le fonctionnement familial exercent une influence les uns sur les autres avec le temps. Peu d’études longitudinales ont vérifié cette hypothèse, et elles ont conclu à des résultats équivoques. Dans cette étude, nous examinons les associations prospectives réciproques du début de l’adolescence entre les symptômes dépressifs et 2 aspects importants des relations parent–enfant : la communication et le conflit. Méthodes : Les participants étaient 3862 élèves qui remplissaient chaque année une autoévaluation. L’analyse des pistes causales a servi à examiner les associations prospectives entre les symptômes dépressifs et la communication et le conflit perçus avec les parents, de 12 à 13 ans et de 14 à 15 ans. L’indépendance de ces associations a été évaluée en contrôlant le contexte familial (séparation parentale et statut socioéconomique familial) et les problèmes de comportement de l’adolescent (comportements délinquants et utilisation de substances). Les différences selon le sexe ont été évaluées par une analyse de groupes multiples. Résultats : Des associations prospectives réciproques ont été observées entre les symptômes dépressifs et le conflit perçu avec les parents, mais non entre les symptômes dépressifs et la communication avec les parents. Les symptômes dépressifs prédisaient une communication médiocre avec les parents avec le temps, mais la communication ne prédisait pas de symptômes dépressifs plus faibles dans les années subséquentes. Toutes les pistes ne variaient pas selon le sexe et étaient indépendantes du contexte familial et des problèmes de comportement. Conclusion : Cette étude souligne l’importance de tenir compte de l’effet potentiel de la symptomatologie adolescente sur les relations parent–enfant, et suggère que la réciprocité peut caractériser l’association entre les symptômes dépressifs et les aspects négatifs des relations parent–enfant. Le rôle des perceptions des adolescents dans l’interaction entre les symptômes dépressifs et les relations familiales demeure à préciser

On the damping of tidally driven oscillations

Expansions in the oscillation modes of tidally perturbed bodies provide a useful framework for representing tidally induced flows. However, recent work has demonstrated that such expansions produce inaccurate predictions for secular orbital evolution when mode damping rates are computed independently. We explore the coupling of collectively driven modes by frictional and viscous dissipation, in tidally perturbed bodies that are both non-rotating and rigidly rotating. This exploration leads us to propose an alternative approach to treating the damping of tidally driven oscillations that accounts for dissipative mode coupling, but which does not require any information beyond the eigenfunctions and eigenfrequencies of adiabatic modes.Comment: 9 pages, 7 figures, revised after submission to MNRAS (comments welcome

Motivation et adaptation psychosociale des élèves du secondaire selon la localisation socioéconomique de leur école

L’objectif de cette recherche était de vérifier si la motivation à apprendre et l’adaptation psychosociale se distinguent selon le sexe et la localisation socioéconomique de l’école. Au total, 5 692 élèves de 24 écoles secondaires de divers milieux socioéconomiques ont rempli un questionnaire. Les analyses multivariées et univariées montrent que l’école a moins d’attrait pour les élèves de milieu favorisé, qu’ils sont moins orientés vers la tâche, plus orientés vers soi et ont une plus faible adaptation psychosociale que les élèves d’autres milieux. Quant aux élèves des écoles de milieu défavorisé, ils percevraient moins l’utilité de l’école. Ces résultats contredisent plusieurs idées généralement admises.The purpose of this study was to verify if students’ achievement motivation and school psychosocial adaptation differ according to sex and to the school’s socio-economic status. The subjects included 5692 students from 24 public secondary French schools who answered a self-report questionnaire about achievement motivation and psychosocial adaptation. Multivariate (MANOVA) and univariate analyses (ANOVA) showed that students from schools in high SES milieu have less attraction toward school, are less task-oriented and are more ego-oriented. Also, they tend to be less adapted than other students. For their part, students from schools in low SES milieu perceive less school utility. These results partially contradict general public perceptions about schools located in low SES areas.El objetivo del presente estudio es averiguar si la motivación para aprender y la adaptación psicosocial son distintas según el género y la ubicación socioeconómica de la escuela. En total, 5 692 alumnas y alumnos de 24 escuelas secundarias de diversos medios socioeconómicos llenaron un cuestionario. Los análisis multivariados y univariados demuestran que la escuela atrae menos a los alumnos de medio favorecido, que estos son menos orientados hacia la tarea, más orientados hacia sí mismo y tienen un nivel de adaptación psicosocial más bajo que los alumnos de otros medios. En cuanto a los alumnos procedentes de medio desfavorecido, perciben menos la utilidad de la escuela. Estos resultados contradicen varias ideas generalmente vinculadas