Taux implicite d’impôt et détachement du dividende

En 1970, E. Elton et M. Gruber ont suggéré qu’il est possible d’estimer le taux d’impôt sur les dividendes de l’investisseur marginal à l’aide de la chute des cours des actions attribuable au détachement du dividende. Leur statistique est toujours en usage pour détecter les effets de clientèle à l’égard des dividendes et des structures financières ainsi que les conséquences des réformes fiscales.La présente recherche introduit l’incertitude dans le modèle en question et l’adapte à la structure fiscale canadienne. Les résultats empiriques suggèrent que la statistique proposée ne permet pas d’évaluer les taux d’impôt de façon fiable, qu’elle n'est pas liée statistiquement aux structures financières et qu’elle ne constitue pas un outil susceptible de déceler les effets de la réforme fiscale de 1971.In 1970, E. Elton and M. Gruber suggested that the price drop on ex-dividend days may be used as an estimator of the tax rate on dividends for the marginal investor. Their statistic is still being used to assess clientele effects for dividends and financial structures as well as the consequences of tax reforms. The authors reformulate the model to take into account uncertainty and the peculiar features of the Canadian tax laws. The empirical results suggest that the Elton and Gruber statistic does not provide reliable estimates of the tax rates, it is not correlated with financial structures and is not helpful to detect the effects of the Tax Reform of 1971

Effects of hypoxia on benthic macrofauna and bioturbation in the Estuary and Gulf of St. Lawrence, Canada

The bottom water in the 4300 m deep Lower St. Lawrence Estuary (LSLE) is persistently hypoxic in contrast to the normoxic bottom waters in the Gulf of St. Lawrence (GSL). We photographed the seabed at 11 stations in the Estuary and Gulf of St. Lawrence (EGSL) during the summers 2006 and 2007 and analysed the images to identify bioturbation traces (lebensspuren) and benthic macrofauna. The objective was to identify the environmental variables that influence the density and diversity of benthic macrofauna and bioturbation traces, and the differences that exist among regions with high, medium and low oxygen levels in the bottom water. The bottom water oxygen concentration is the variable that best explains the densities of total-traces as well as surface-traces. However, the density of these traces was higher in hypoxic regions than in well-oxygenated regions. The higher density of traces in the hypoxic region of the LSLE is mainly due to the activities of the surface deposit feeder Ophiura sp., which occurs in large numbers in this region. Possible explanations explored are stress behaviour of the organisms in response to hypoxia and different benthic macrofauna community structures between the hypoxic regions of the LSLE and the normoxic regions of the GSL. In the former, surface deposit feeders and low-oxygen tolerant species dominate over suspension feeders and low-oxygen intolerant species

First record of the European Giant File Clam, Acesta excavata (Bivalvia: Pectinoidea: Limidae), in the Northwest Atlantic

Two large bivalve specimens collected in Bay d’Espoir, a deep fjord situated on the south coast of Newfoundland, are described and identified as belonging to the species Acesta excavata (Fabricius 1779). In situ observations onboard the manned submersible PISCES IV and color videos have provided information on the vertical distribution, density and habitat of the species. Maximum abundances of about 15 large individuals/m2 occurred on sheltered rock outcrops at depth ranging from 550 to 775 m, where warm (6°C) continental slope water is found. Differences in shape and thickness between the valves of the two specimens appear to be related to the degree of exposure to rock falls (i.e., sheltered versus exposed habitat). Prior to this account, the European Giant File Clam had never been encountered west of the Azores Islands in the North Atlantic

Locomotion and Functional Spine Morphology of the Heart Urchin Brisaster fragilis

The heart urchin Brisaster fragilis is an important bioturbator found in the Estuary and Gulf of St. Lawrence. Several adaptations allow it to move within fine sediments (e.g., test shape, spine morphology, and distribution), which are compared here to those of its Pacific sibling species B. latifrons. While ventral spatulate spines and dorsal and anterolateral curvilinear spines are similar between the two species, anterior spines differ significantly: sigmoid-shaped for B. fragilis and curvilinear for B. latifrons. This morphological difference, in addition to a narrower plastron for B. fragilis, suggests a different digging strategy. In situ video observations of B. fragilis show a “dig and move” strategy: anterior spines “dig” forward at the sediment while the plastron spines “move” the urchin into the newly created space. B. latifrons on the other hand uses an oblique rocking motion. This suggests that generalizations derived from one or few species displaying similar body shapes may not be possible. Factors such as sediment depth (i.e., the amount of sediment above the urchin) are likely to affect movement and force the animal to employ a different digging strategy, even within a single species. The role of spines for locomotion is further discussed, with additional reference to tubercle morphology

A comparison between nocturnal aural counts of passerines and radar reflectivity from a Canadian weather surveillance radar

Using a Canadian weather surveillance radar (CWSR), we assessed the relationship between aural passerine counts and radar reflectivity during autumn migration on 16 nights. Reflectivity was positively correlated on all but 1 night with the number of birds detected aurally, but the correlation strength varied between -0.58 and 0.93 among nights (mean ± SD = 0.69 ± 0.42). Using linear mixed-effects models with aural counts nested within nights, we found that the number of birds detected by observers increased with reflectivity. The slope of this relationship did not vary between observers, nor was it affected by time since sunset, but the number of birds detected aurally tended to be lower when ambient noise levels were high. We know that the radar was relatively sensitive to low bird densities, because the intercept was slightly positive and its 95% confidence interval marginally included zero. However, the relationship between the number of birds detected aurally and reflectivity varied significantly among nights. Such variation was likely caused by a combination of (interacting) factors, including bird species and behavior (e.g., calling rate, flight altitude), influencing bird detectability by the observers and the radar. The weather radar network of the United States (NEXRAD) is already used for bird migration studies, and we conclude that the use of CWSR can extend NEXRAD's coverage farther north by hundreds of kilometers, thereby increasing our understanding of how birds use the North American landscapes during migration. Nous avons étudié la relation entre un dénombrement auditif de passereaux et la réflectivité d'un radar de surveillance météorologique canadien (CWSR), durant la migration automnale, pendant 16 nuits. La réflectivité radar était positivement corrélée avec le nombre d'oiseaux détectés auditivement pour toutes les nuits, exception d'une, mais la puissance de cette relation variait de -0.58 à 0.93 (moyenne ± écart-type = 0.69 ± 0.42). En utilisant des modèles linéaires à effets mixtes où les dénombrements auditifs étaient nichés de manière intra-nuit, nous avons confirmé que le nombre d'oiseaux détectés par les observateurs s'accroissait avec la réflectivité. La pente de cette relation ne variait pas entre les observateurs comme elle n'était pas affectée par le temps écoulé depuis le coucher du soleil, mais le nombre d'oiseaux détectés auditivement tendait àdiminuer quand le bruit ambiant était plus élevé. Le radar s'est avéré être relativement sensible à une faible densité d'oiseaux, puisque la valeur de l'intercepte était légèrement positive et ses intervalles de confiance de 95% incluaient marginalement le zéro. Cependant, la relation entre le nombre d'oiseaux détectés auditivement et la réflectivité variait significativement entre les nuits. Une telle variation est vraisemblablement attribuable à la combinaison (ou l'interaction) de facteurs incluant les espèces d'oiseaux présentes et leurs comportements (e.g. taux de cris, altitude de vol), ce qui influence la détectabilité des oiseaux par les observateurs, mais aussi par le radar. Le réseau de radars météo (NEXRAD) des États-Unis est déjà utilisé dans des études de la migration des oiseaux et nous concluons que l'utilisation des CWSR pourrait permettent une extension vers le nord de plusieurs centaines de kilomètres de la couverture du réseau NEXRAD, permettant d'accroître la compréhension de l'utilisation des paysages nord américains par les oiseaux durant leur migration

Prospectives

Tiré de: Prospectives, vol. 19, no 1/2/3, février/avril/oct. 1983.Titre de l'écran-titre (visionné le 24 janv. 2013

Weather effects on autumn nocturnal migration of passerines on opposite shores of the St. Lawrence estuary

We modeled migration intensity as a function of weather, using nightly migration measurements from Doppler surveillance weather radar during autumn migration on the north (Côte-Nord) and south (Gaspésie) shores of the St. Lawrence estuary, Québec, Canada. The radar had negative elevation angles, an uncommon characteristic among weather radars, which allowed simultaneous low-altitude monitoring of bird migration on each side of the estuary. Precipitation and wind both had strong effects on the intensity of migration. Very few birds migrated when >40% of the area had precipitation, especially when winds were strong. Light winds were associated with the strongest migration intensity, regardless of wind direction; in stronger winds, migration was likely only when winds were predominantly from the north. Days immediately after adverse weather events, which are assumed to lead to an accumulation of migrants, were associated with an increase in the intensity of migration in Côte-Nord, but not in Gaspésie. Time since the passage of a cold front had no effect in either region. Bird flight direction and behavior in relation to wind differed on each side of the estuary. On Côte-Nord, birds tended to migrate in a southwesterly direction along the St. Lawrence north coast, in a direction relatively unaffected by wind direction; they compensated or overcompensated for wind drift by following the coast. By contrast, birds in Gaspésie tended to fly in a more southerly direction. They migrated partially or almost fully downwind with only limited compensation, their flight direction often changing with wind direction. Nous avons modélisé l'intensité migratoire automnale en fonction de la météo, en utilisant des mesures de la migration nocturne prises à la fois sur la rive nord (Côte-Nord) et la rive sud (Gaspésie) de l'estuaire du Saint-Laurent, Québec, Canada, à l'aide d'un radar Doppler de surveillance météorologique. Ce radar effectue des balayages à des angles négatifs, une caractéristique rare chez les radars météo qui permet entre autres, de relever des données de migration d'oiseaux à basse altitude et simultanément de chaque côté de l'estuaire. Nos résultats montrent que les précipitations et le vent avaient de forts effets sur l'intensité migratoire. Peu d'oiseaux migraient quand 40% ou plus du territoire était affecté par des précipitations, particulièrement en combinaison avec des vents forts. Les plus fortes intensités migratoires étaient associés avec des vents légers, peu importe la direction du vent; par vents forts, la migration était plus probable quand les vents avaient une composante nord. Un événement de conditions météo adverses à la migration s'ensuivait d'une augmentation de l'intensité migratoire sur la Côte-Nord, mais pas en Gaspésie. Le passage d'un front froid n'avait aucun effet sur la migration dans l'une ou l'autre des deux régions. La direction de vol des oiseaux et leur comportement relativement au vent différaient de chaque côté de l'estuaire. Sur la Côte-Nord, les oiseaux avaient tendance à migrer vers Ie sud-ouest, Ie long de la rive nord du Saint-Laurent; cette direction de vol était peu affectée par la direction du vent et les oiseaux suivaient la côte en compensant ou surcompensant pour la dérive par les vents. En opposition, les oiseaux en Gaspésie avaient tendance à voler vers Ie sud; leur migration se faisait en suivant partiellement ou pleinement le vent avec peu de compensation et avec une direction de vol qui changeait souvent avec la direction du vent

Waking EEG functional connectivity in middle-aged and older adults with obstructive sleep apnea

Objectives: The present study aimed at investigating changes in waking electroencephalography (EEG), most specifically regarding spectral power and functional connectivity, in middle-aged and older adults with OSA. We also explored whether changes in spectral power or functional connectivity are associated with polysomnographic characteristics and/or neuropsychological performance. Methods: 19 OSA subjects (apnea-hypopnea index ≥ 20, age: 63.6 ± 6.4) and 22 controls (apneahypopnea index ≤ 10, age: 63.6 ± 6.7) underwent a full night of in-laboratory polysomnography followed by a waking EEG and a neuropsychological assessment. Waking EEG spectral power and imaginary coherence were compared between groups for all EEG frequency bands and scalp regions. Correlation analyses were performed between selected waking EEG variables, polysomnographic parameters and neuropsychological performance. Results: No group difference was observed for EEG spectral power for any frequency band. Regarding the imaginary coherence, when compared to controls, OSA subjects showed decreased EEG connectivity between frontal and temporal regions in theta and alpha bands as well as increased connectivity between frontal and parietal regions in delta and beta 1 bands. In the OSA group, these changes in connectivity correlated with lower sleep efficiency, lower total sleep time and higher apnea-hypopnea index. No relationship was found with neuropsychological performance. Conclusions: Contrary to spectral power, imaginary coherence was sensitive enough to detect changes in brain function in middle-aged and older subjects with OSA when compared to controls. Whether these changes in cerebral connectivity predict cognitive decline needs to be investigated longitudinally

L’histoire de l’art au Canada : pratiques actuelles d’une discipline universitaire

Pour répondre à l’étonnement admiratif de nos collègues français devant la popularité croissante de notre discipline au Canada auprès des étudiants, des chercheurs et du grand public dans un pays où l’histoire de l’art s’est développée depuis seulement une ou deux générations, j’ai proposé à trois enseignants universitaires – dont une muséologue directrice d’une galerie d’université – des thèmes de réflexion pour éclairer le phénomène et décrire la diversité des approches et des méthodes selo..

F.A.R.O.G. FORUM, Vol. 4 No. 1

https://digitalcommons.library.umaine.edu/francoamericain_forum/1054/thumbnail.jp