Ultrafast Transient Dynamics of Adsorbates on Surfaces Deciphered: The Case of CO on Cu(100)

Time-resolved vibrational spectroscopy constitutes an invaluable experimental tool for monitoring hot-carrier induced surface reactions. However, the absence of a full understanding on the precise microscopic mechanisms causing the transient spectral changes has been limiting its applicability. Here we introduce a robust first-principles theoretical framework that successfully explains both the nonthermal frequency and linewidth changes of the CO internal stretch mode on Cu(100) induced by femtosecond laser pulses. Two distinct processes engender the changes: electron-hole pair excitations underlie the nonthermal frequency shifts, while electron-mediated vibrational mode coupling gives rise to linewidth changes. Furthermore, the origin and precise sequence of coupling events are finally identified.Comment: Article as accepted for publication in Physical Review Letters; 5 pages, 2 figures, 1 tabl

Third order superintegrable systems separating in polar coordinates

A complete classification is presented of quantum and classical superintegrable systems in $E_2$ that allow the separation of variables in polar coordinates and admit an additional integral of motion of order three in the momentum. New quantum superintegrable systems are discovered for which the potential is expressed in terms of the sixth Painlev\'e transcendent or in terms of the Weierstrass elliptic function

Infinite families of superintegrable systems separable in subgroup coordinates

A method is presented that makes it possible to embed a subgroup separable superintegrable system into an infinite family of systems that are integrable and exactly-solvable. It is shown that in two dimensional Euclidean or pseudo-Euclidean spaces the method also preserves superintegrability. Two infinite families of classical and quantum superintegrable systems are obtained in two-dimensional pseudo-Euclidean space whose classical trajectories and quantum eigenfunctions are investigated. In particular, the wave-functions are expressed in terms of Laguerre and generalized Bessel polynomials.Comment: 19 pages, 6 figure

A shrinking Compact Symmetric Object: J11584+2450?

We present multi-frequency multi-epoch Very Long Baseline Array (VLBA) observations of J11584+2450. These observations clearly show this source, previously classified as a core-jet, to be a compact symmetric object (CSO). Comparisons between these new data and data taken over the last 9 years shows the edge brightened hot spots retreating towards the core (and slightly to the west) at approximately 0.3c. Whether this motion is strictly apparent or actually physical in nature is discussed, as well as possible explanations, and what implications a physical contraction of J11584+2450 would have for current CSO models.Comment: 16 pages, 6 figures, 5 tables. Accepted for publication in Ap

The Development of Writing Centers in Japanese Higher Education

This dissertation introduces the concept of literate histories as a way of looking into a student writer’s path as a developing writer and their relationship with writing activities and institutions that sponsor writing. Using the concept of literate histories as an analytical lens, this dissertation examines how the US-born idea of writing centers had entered and is spreading in the changing Japanese higher educational system. Specifically, through a detailed examination of university writing centers, it aims to understand the growing exigency of writing in Japanese higher education and how writing centers can serve as sponsors of writing to student writers in an evolving context. The writing center movement has its roots in progressive education, however, the writing center has historically been associated with remedial work in the U.S. The writing center movement has spread to Japan, and universities across Japan are taking the initiative to advance the idea of fostering independent writers through one-on-one instruction at the writing center. Through ethnographic observations of tutoring sessions and interviews, this research presents an alternative view of the writing center. Specifically, through the lens of literate histories, it demonstrates how the writing center can serve as sponsors of writing to university student writers of diverse backgrounds. From this view, the writing center work is no longer remedial but is a resource that may help students in enacting disciplinary identities through the teaching of writing. Finally, writing center researchers have emphasized the importance of replicable, aggregable, and data-support (RAD) research in recent years. This dissertation, which offers a historical account of teaching of writing in Japanese education, offers a methodological contribution to writing center research by adding new codes to analyze tutor-tutee conversations and in turn, aims to advance writing center work

Quasiparticle states of the Hubbard model near the Fermi level

The spectra of the t-U and t-t'-U Hubbard models are investigated in the one-loop approximation for different values of the electron filling. It is shown that the four-band structure which is inherent in the case of half-filling and low temperatures persists also for some excess or deficiency of electrons. Besides, with some departure from half-filling an additional narrow band of quasiparticle states arises near the Fermi level. The dispersion of the band, its bandwidth and the variation with filling are close to those of the spin-polaron band of the t-J model. For moderate doping spectral intensities in the new band and in one of the inner bands of the four-band structure decrease as the Fermi level is approached which leads to the appearance of a pseudogap in the spectrum.Comment: 8 pages, 7 figure

N=2 supersymmetric extension of the Tremblay-Turbiner-Winternitz Hamiltonians on a plane

The family of Tremblay-Turbiner-Winternitz Hamiltonians $H_k$ on a plane, corresponding to any positive real value of $k$, is shown to admit a ${\cal N} = 2$ supersymmetric extension of the same kind as that introduced by Freedman and Mende for the Calogero problem and based on an ${\rm osp}(2/2, \R) \sim {\rm su}(1,1/1)$ superalgebra. The irreducible representations of the latter are characterized by the quantum number specifying the eigenvalues of the first integral of motion $X_k$ of $H_k$. Bases for them are explicitly constructed. The ground state of each supersymmetrized Hamiltonian is shown to belong to an atypical lowest-weight state irreducible representation.Comment: 18 pages, no figur

An infinite family of superintegrable systems from higher order ladder operators and supersymmetry

We will discuss how we can obtain new quantum superintegrable Hamiltonians allowing the separation of variables in Cartesian coordinates with higher order integrals of motion from ladder operators. We will discuss also how higher order supersymmetric quantum mechanics can be used to obtain systems with higher order ladder operators and their polynomial Heisenberg algebra. We will present a new family of superintegrable systems involving the fifth Painleve transcendent which possess fourth order ladder operators constructed from second order supersymmetric quantum mechanics. We present the polynomial algebra of this family of superintegrable systems.Comment: 8 pages, presented at ICGTMP 28, accepted for j.conf.serie

Étude paléolimnologique de l'histoire trophique du lac Saint-Charles, réservoir d'eau potable de la Communauté Urbaine de Québec

Cette étude utilise une approche paléolimnologique pour reconstituer l'histoire trophique du réservoir d'eau potable de la Communauté Urbaine de Québec (CUQ), le lac Saint-Charles. Ce lac manifeste présentement un manque d'oxygène près du fond à la fin de la stratification estivale et hivernale. L'étude révèle des changements dans la communauté diatomifère fossile depuis environ les 150 dernières années. L'événement ayant entraîné le plus de changements biologiques et physico-chimiques dans le bassin est la transformation hydrologique engendrée par la construction d'un barrage en 1934 qui éleva le niveau du lac d'environ 1,5 à 2 mètres. Par conséquent, il y eut des changements dans la structure des communautés de diatomées avec des effets sur le ratio espèces planctoniques / benthiques, sur la paléoproductivité et les caractéristiques physico-chimiques des sédiments suivant cette période. Les assemblages diatomifères indiquent que les conditions mésotrophes se sont maintenues pendant toute la période étudiée. L'analyse du phosphore total dans les sédiments et la reconstitution à partir des diatomées fossiles du phosphore total dans l'eau montrent une légère diminution de la concentration en phosphore avec le temps. Ces observations démontrent qu'il n'y a pas eu d'accélération du processus d'eutrophisation engendrée par les activités humaines. Par contre, l'analyse géochimique des sédiments révèle un apport plus important de métaux depuis la fin du 19e siècle, qui atteint un plateau vers la fin des années 70.This study adopted a combined paleolimnological-limnological approach towards evaluating the trophic history of Lake Saint-Charles, the drinking water reservoir for a population of 305,000 in the Québec City (Canada) region. Our limnological measurements indicate that the lake is currently in a state of advanced mesotrophy. Water column profiles during late summer stratification (September) showed that the bottom waters were anoxic, enriched in phosphorus (up to 17 µg total P L-1) and had a pH almost 2 units lower than the surface waters. Surface phytoplankton concentrations were high at this time of year with Chlorophyll a concentrations of up to 12 µg·L-1. At the end of winter stratification, oxygen concentrations were below saturation at all depths, ranging from 72% immediately under the ice to 4% at the bottom of the water column. This tendency towards eutrophic conditions was offset, however, by a rapid flushing rate (mean hydraulic residence time=23 days). Because there are concerns that the lake has experienced accelerated nutrient enrichment due to increased human activities in its drainage basin, the objectives of our paleolimnological approach were to document the recent trophic history of this lake, to estimate the extent of recent changes in trophic status, and to identify critical periods of past anthropogenic disturbances from the fossils of siliceous algae (diatoms; class Bacillariophyceae) preserved in its sediments. Quantitative estimates of past total phosphorus (TP) concentrations in the water column of Lake Saint-Charles were obtained by applying a diatom-TP reconstruction model developed for 54 lakes located in south-eastern Ontario to fossil diatom assemblages from a 28 cm long sediment core. The timing of changes in the fossil diatom record was estimated by210 Pb dating. The study reveals changes in fossil diatom assemblage composition during the past ca. 150 years, with the most striking biological and physico-chemical changes occurring immediately after 1934. This date coincides with the construction of a dam, which raised the lake water level by 1.5-2 m. This modification was accompanied by significant shifts in diatom community structure, especially in the planktonic/benthic ratio (with increases in planktonic diatoms Cyclotella stelligera and Aulacoseira distans), and by changes in the physico-chemical characteristics of the sediments. Paleoproductivity increased at the same time, but remained more or less stable following conservation efforts between 1950 and 1970 (e.g., construction of a sewage treatment system). The organic matter content of the sediments showed an increase in the order of 20% between 1850 and 1950, after which it remained constant. Fossil diatom community structure indicates that mesotrophic conditions have prevailed during the recent history of Lake Saint-Charles, and that diatoms typical of eutrophic conditions never became established in the lake. The geochemical analysis of phosphorus in the sediments as well as the diatom-inferred quantitative reconstruction of lake water total phosphorus reveals a slight decrease in total phosphorus over time, from close to 17 µg·L- prior to 1887 to about 13 µg·L- 1 in recent times. These observations suggest that Lake Saint-Charles has not experienced significant recent changes in trophic status due to increased human activities in its drainage basin. However, our geochemical analyses show a sharp rise in metal concentrations (especially Fe, Mn, Cu, Pb and Zn), beginning in the late 19th century, reaching a plateau by the late 1970s, which may be attributed to increased atmospheric pollution since the beginning of intense human colonization in the lake's catchment and surrounding areas. This in combination with the advanced mesotrophic status of the lake indicates the ongoing need for careful management of the watershed to prevent further changes in this important urban water resource

Invariants of Triangular Lie Algebras

Triangular Lie algebras are the Lie algebras which can be faithfully represented by triangular matrices of any finite size over the real/complex number field. In the paper invariants ('generalized Casimir operators') are found for three classes of Lie algebras, namely those which are either strictly or non-strictly triangular, and for so-called special upper triangular Lie algebras. Algebraic algorithm of [J. Phys. A: Math. Gen., 2006, V.39, 5749; math-ph/0602046], developed further in [J. Phys. A: Math. Theor., 2007, V.40, 113; math-ph/0606045], is used to determine the invariants. A conjecture of [J. Phys. A: Math. Gen., 2001, V.34, 9085], concerning the number of independent invariants and their form, is corroborated.Comment: LaTeX2e, 16 pages; misprints are corrected, some proofs are extende