L’évolution du lit du Saint-Laurent dans le secteur de Contrecoeur (Québec) depuis un siècle

Des levés hydrographiques du gouvernement canadien datant de 1898, 1945 et 1988, ont été comparés afin d'établir la cartographie des changements survenus au lit du Saint-Laurent dans le secteur de Contrecoeur, à mi-chemin entre Montréal et Sorel. Depuis 1850, la dynamique hydrosédimentaire de ce tronçon long de 8 km a dû se rééquilibrer au fur et à mesure de l'agrandissement du chenal de navigation maritime. Au moyen d'un logiciel de géomatique, des modèles bathymétriques détaillés ont été élaborés à partir des cartes de levés historiques fournies par le Service hydrographique du Canada. Après ajustement des cadres géographiques et du zéro des cartes, les patrons spatiaux de changements bathymétriques consécutifs à l'érosion ou à la sédimentation ont pu être déterminés par comparaison de ces modèles. Les cartes qui en résultent illustrent les principales étapes de l'agrandissement de la voie maritime ainsi que l'évolution des dépôts de déblais de dragage. Il appert, par exemple, qu'un volume important de déblais laissé à la marge ouest du chenal entre 1898 et 1945 a été dispersé vers l'aval entre 1945 et 1988, après avoir été remis en suspension par les courants et les vagues en marge du chenal maritime. L'intérêt principal de notre étude réside néanmoins dans l'éclairage nouveau qu'il donne à la dynamique d'ensemble du lit fluvial, bien au delà du chenal dragué. Entre 1898 et 1988, de vastes secteurs du lit ont été recouverts de 0,5 à 1 m additionnel de sédiments. Le chenal central à l'ouest de l'île Saint-Ours semble particulièrement touché, le taux moyen de sédimentation y ayant été de 1,5 cm/a entre 1945 et 1988. L'instabilité du lit s'est accélérée depuis 1945 et semble être attribuable, en partie du moins, à la perturbation de l'équilibre hydrosédimentaire causée par l'agrandissement répété du chenal maritime.Canadian government hydrographie surveys from 1898, 1945 and 1988 are compared to reveal long-term patterns of bathymétrie change in the St. Lawrence River, in the Contrecoeur area between Montréal and Sorel. Since 1850, the hydraulic and sedimentary balance of this reach has been affected by repeated dredging to expand the main navigation channel. Using GIS software, detailed bathymétrie models of the reach for each of the years 1898, 1945 and 1988 were produced by interpolation through the archival soundings for each of these periods provided by the Canadian Hydrographie Service. After careful adjustment of reference water planes and planimetric coordinate systems, maps of bed changes were derived by comparing the different models. Major expansions of the navigation channel can be followed as well as the evolution of the main dredge spoil areas. In particular, considerable volumes of dredge spoil deposited at the margin of the ship channel between 1898 and 1945 are seen to have been re-entrained and dispersed downstream by 1988. Most interestingly, the maps of bed changes reveal substantial rates of sediment deposition over much of the river bed, well away from the ship channel. Over wide areas, deposition of between 0.5 and 1 m of new sediment since 1898 is observed. Bed aggradation has been particularly intense in the central channel west of Ile Saint-Ours, where it has averaged 1.5 cm/year between 1945 and 1988. In part at least, this tendency to bed aggradation over much of the river may be a reaction to the man-made concentration of the flow in the enlarged ship channel.Hydrographische Vermessungen von 1898, 1945 und 1988 wurden verglichen, um die Veranderungen im Bett des Sankt Lorenz im Bereich von Contrecoeur kartographisch festzuhalten. Seit 1850 musste die hydrosedimentare Dynamik dieses 8 km Iangen Stùckes entsprechend der Verbreiterung der Seewegfahrrinne jeweils ein neues Gleichgewicht finden. Mit Hilfe einer geomatischen Software wurden detaillierte Tiefenmodelle erstellt, ausgehend von Karten historischer Vermessungen, die der kanadische hydrographische Service zur Verfugung stellte. Nach Abstimmung der geographischen Rahmen und der Planimetrie konnten durch Vergleich dieser Modelle die ràumlichen Muster der Tiefenverànderungen aufgrund von Erosion oder Sedimentierung bestimmt werden. Die so entstandenen Karten illustrieren die wichtigsten Etappen der Vergrosserung des Seewegs sowie die Entwicklung der AbIagerungen von Baggeraushubmaterial. Es scheint, z.B. dass eine bedeutende Menge von Aushubmaterial, das man am westlichsten Rand der Fahrrinne zwischen 1898 und 1945 liess, zwischen 1945 und 1988 stromabwàrts verstreut wurde, nachdem es durch Stromungen und Wellen am Rand des Seewegs wieder aufgelôst worden war. Das Hauptinteresse unserer Untersuchung bes-teht jedoch in dem neuen Licht, das sie auf die Gesamtdynamik des Flussbettes wirft, weit iiber die ausgebaggerte Fahrrinne hinaus. Zwischen 1898 und 1988 wurden weite Abschnitte des Flussbettes mit einer zusàtzlichen Sedimentschicht von 0,5 bis 1 m bedeckt. Die zentrale Fahrrinne westlich von der lnsel St. Ours scheint besonders betroffen, die durchschnittliche Sedimentierungsrate war hier 1,5cm/Jahr zwischen 1945 und 1988. Die Labilitat des Flussbettes hat sich seit 1945 beschleunigt und scheint mindestens zum Teil auf die Stôrung des hydro-sedimentaren Gleichgewichts durch die wiederholte Vergrosserung des Seewegs zurùckzufùhren zu sein

Explicit formulas for the generalized Hermite polynomials in superspace

We provide explicit formulas for the orthogonal eigenfunctions of the supersymmetric extension of the rational Calogero-Moser-Sutherland model with harmonic confinement, i.e., the generalized Hermite (or Hi-Jack) polynomials in superspace. The construction relies on the triangular action of the Hamiltonian on the supermonomial basis. This translates into determinantal expressions for the Hamiltonian's eigenfunctions.Comment: 19 pages. This is a recasting of the second part of the first version of hep-th/0305038 which has been splitted in two articles. In this revised version, the introduction has been rewritten and a new appendix has been added. To appear in JP

Exact operator solution of the Calogero-Sutherland model

The wave functions of the Calogero-Sutherland model are known to be expressible in terms of Jack polynomials. A formula which allows to obtain the wave functions of the excited states by acting with a string of creation operators on the wave function of the ground state is presented and derived. The creation operators that enter in this formula of Rodrigues-type for the Jack polynomials involve Dunkl operators.Comment: 35 pages, LaTeX2e with amslate

Probing the Birth and Ultrafast Dynamics of Hydrated Electrons at the Gold/Liquid Water Interface via an Optoelectronic Approach

The hydrated electron has fundamental and practical significance in radiation and radical chemistry, catalysis and radiobiology. While its bulk properties have been extensively studied, its behavior at buried solid/liquid interfaces is still unclear due to the lack of effective tools to characterize this short-lived species in between two condensed matter layers. In this study, we develop a novel optoelectronic technique for the characterization of the birth and structural evolution of solvated electrons at the metal/liquid interface with a femtosecond time resolution. We thus recorded for the first time their transient spectra (in a photon energy range from 0.31 to 1.85 eV) in situ with a time resolution of 50 fs. The transient species show state-dependent optical transition behaviors from being isotropic in the hot state to perpendicular to the surface in the trapped and solvated states. The technique will enable a better understanding of hot electron-driven reactions at electrochemical interfaces

A Blueprint for Short-Term Petroleum Supply Crises Management

For most North Carolinians, and for that matter, most Americans, thoughts of the Organization of Petroleum Exporting Countries' (OPEC) oil embargo during the winter and spring of 1973 do not provide pleasant memories. It was a time of personal hardship, dramatically changing daily routines, considerable inconvenience, and a deepened national recession. However, the embargo's end saw most of the population return to normal routines, changed somewhat to accomodate higher petroleum prices, but unhampered by fuel shortages. A sluggish economy began the long slow road to recovery. But suspicion still lingers that the problem of future petroleum embargoes, and subsequent economic and daily chaos, remained unaddressed. Would the national and state governments be able to respond quickly and boldly should another sudden supply interruption occur in the near future? Are we better prepared for this contingency in the near future, and if we are, at what levels of preparedness are we? This paper is written to dispel some of the apprehension which now surrounds any discussion of petroleum embargoes. Its focus is short term supply crisis management caused by an embargo or natural catastrophe such as a break in the Alaskan pipeline. It describes the legislated national goals which will be operating during the next supply denial and briefly details the national programs which have been developed around them. It closes with a summary of actions which have been taken in North Carolina, and some comments on the basic orientation of the management framework and its implications to state and local policy making

Sodium leak pathway and substrate binding order in the Na+-glucose cotransporter

The Na+-glucose cotransporter (SGLT1) expressed in Xenopus laevis oocytes was shown to generate a phlorizin-sensitive sodium leak in the absence of sugars. Using the current model for SGLT1, where the sodium leak was presumed to occur after two sodium ions are bound to the free carrier before glucose binding, a characteristic concentration constant (Kc) was introduced to describe the relative importance of the sodium leak versus Na+-glucose cotransport currents. Kc represents the glucose concentration at which the Na+-glucose cotransport current is equal to the sodium leak. As both the sodium leak and the Na+-glucose cotransport current are predicted to occur after the binding of two sodium ions, the model predicted that Kc should be sodium-independent. However, by using a two-microelectrode voltage-clamp technique, the observed Kc was shown to depend strongly on the external sodium concentration ([Na+]o): it was four times higher at 5 mM [Na+]o than at 20 mM [Na+]o. In addition, the magnitude of the sodium leak varied as a function of [Na+]o in a Michaelian fashion, and the sodium affinity constant for the sodium leak was 2–4 times lower than that for cotransport in the presence of low external glucose concentrations (50 or 100 microM), whereas the current model predicted a sigmoidal sodium dependence of the sodium leak and identical sodium affinities for the sodium leak and the Na+-glucose cotransport. These observations indicate that the sodium leak occurs after one sodium ion is associated with the carrier and agree with predictions from a model with the binding order sodium-glucose-sodium. This conclusion was also supported by experiments performed where protons replaced Na+ as a "driving cation.

Rodrigues Formula for the Nonsymmetric Multivariable Hermite Polynomial

Applying a method developed by Takamura and Takano for the nonsymmetric Jack polynomial, we present the Rodrigues formula for the nonsymmetric multivariable Hermite polynomial.Comment: 5 pages, LaTe

Shape Invariance in the Calogero and Calogero-Sutherland Models

We show that the Calogero and Calogero-Sutherland models possess an N-body generalization of shape invariance. We obtain the operator representation that gives rise to this result, and discuss the implications of this result, including the possibility of solving these models using algebraic methods based on this shape invariance. Our representation gives us a natural way to construct supersymmetric generalizations of these models, which are interesting both in their own right and for the insights they offer in connection with the exact solubility of these models.Comment: Latex file, 23 pages, no picture

Rodrigues Formula for the Nonsymmetric Multivariable Laguerre Polynomial

Extending a method developed by Takamura and Takano, we present the Rodrigues formula for the nonsymmetric multivariable Laguerre polynomials which form the orthogonal basis for the $B_{N}$-type Calogero model with distinguishable particles. Our construction makes it possible for the first time to algebraically generate all the nonsymmetric multivariable Laguerre polynomials with different parities for each variable.Comment: 6 pages, LaTe