145 research outputs found
The Dunkl-Coulomb problem in the plane
The Dunkl-Coulomb system in the plane is considered. The model is defined in
terms of the Dunkl Laplacian, which involves reflection operators, with a
potential. The system is shown to be maximally superintegrable and
exactly solvable. The spectrum of the Hamiltonian is derived algebraically
using a realization of in terms of Dunkl operators. The
symmetry operators generalizing the Runge-Lenz vector are constructed. On
eigenspaces of fixed energy, the invariance algebra they generate is seen to
correspond to a deformation of by reflections. The exact
solutions are given as products of Laguerre polynomials and Dunkl harmonics on
the circle.Comment: Two-columns, 6 p
Tapered, tubular polyester fabric
A tapered tubular polyester sleeve is described to serve as the flexible foundation for a spacesuit limb covering. The tube has a large end and a small end with a length to be determined. The ratio of taper is also determined by scale factors. All the warp yarns extend to the large end. A requisite number of warp yarns extend the full length of the sleeve. Other warp yarns extend from the large end but are terminated along the length of the sleeve. It is then woven with a filling yarn which extends in a full circle along the full length of the sleeve to thereby define the tapered sleeve. The sleeve after fabrication is then placed on a mandrel, heated in an oven, and then attached to the arm or other limb of the spacesuit
Initiation et propagation de la corrosion dans un élément de béton armé
La corrosion des aciers dâarmatures rĂ©sultant de la pĂ©nĂ©tration des ions chlorure est un problĂšme important qui rĂ©duit de maniĂšre significative la durĂ©e de vie des structures en bĂ©ton armĂ© exposĂ©es Ă un environnement maritime ou Ă des sels de dĂ©glaçage. Ce mĂ©moire prĂ©sente une Ă©tude de lâinitiation de la corrosion sur des Ă©prouvettes de mortier armĂ© ainsi quâune Ă©tude du comportement de barres dâarmature corrodĂ©es. Lâobjectif gĂ©nĂ©ral des travaux de maĂźtrise Ă©tait dâĂ©tudier lâinfluence rĂ©elle de la minĂ©ralogie du ciment sur les mĂ©canismes dâinitiation de la corrosion des armatures. En plus de contribuer Ă lâĂ©laboration dâun outil de prĂ©diction de la durĂ©e de vie des ouvrages en bĂ©ton armĂ© exposĂ©s Ă la pĂ©nĂ©tration des ions chlorure, ce projet a permis de gĂ©nĂ©rer des informations permettant aux ingĂ©nieurs de la pratique et aux gestionnaires dâouvrages dâoptimiser la formulation des bĂ©tons et dâamĂ©liorer la durabilitĂ© des structures. Le projet Ă©tait sĂ©parĂ© en deux parties. La premiĂšre partie portait sur lâidentification dâune concentration seuil en ions chlorure requise pour initier la corrosion. Les Ă©prouvettes de mortier ont Ă©tĂ© soumises Ă des conditions dâexpositions contrĂŽlĂ©es (cycles de mouillage-sĂ©chage). LâĂ©volution de la corrosion a Ă©tĂ© suivie par des mĂ©thodes Ă©lectrochimiques non-destructives. Les diffĂ©rents facteurs Ă lâĂ©tude ont Ă©tĂ© le rapport eau sur ciment (e/c), la minĂ©ralogie du ciment et le type de prĂ©paration des barres dâarmature. Les rĂ©sultats de lâĂ©tude de la pĂ©nĂ©tration des ions chlorure dans les matĂ©riaux cimentaires et de sa consĂ©quence sur lâinitiation de la corrosion sont prĂ©sentĂ©s. La deuxiĂšme partie du projet Ă©tait dâĂ©tudier lâeffet de la corrosion sur les propriĂ©tĂ©s mĂ©caniques des armatures. Les rĂ©sultats de la mise en traction de barres ayant des degrĂ©s de corrosion spĂ©cifiques sont Ă©galement prĂ©sentĂ©s. Selon les rĂ©sultats obtenus, une diminution du rapport e/c et une augmentation de la teneur en C3A ont Ă©tĂ© deux facteurs favorisant un temps dâinitiation de la corrosion plus Ă©levĂ©. De plus, les barres prĂ©parĂ©es au jet de sable ont offert une meilleure rĂ©sistance Ă la corrosion que les barres brossĂ©es. En outre, le temps de fissuration des Ă©prouvettes semblaient ĂȘtre indĂ©pendant du rapport e/c et de la minĂ©ralogie (teneur en C3A). La concentration critique en ions chlorure totaux requise pour initier la corrosion, trouvĂ©e au cours de lâĂ©tude, a Ă©tĂ© dâenviron 0,3 % en masse de mortier sec ou 1,2 % en masse de ciment. Cette concentration seuil a pu ĂȘtre Ă©valuĂ©e avec prĂ©cision Ă lâaide dâĂ©prouvettes avec et sans barres. De plus, la concentration critique a semblĂ© indĂ©pendante de la teneur en C3A, du type de prĂ©paration de barres (brossĂ© ou prĂ©parĂ© au jet de sable) et du rapport e/c.Chloride-induced corrosion of steel reinforcement is an important issue that greatly decreases the service life of all concrete structures exposed to marine environments or de-icing salts. This study analysed the phenomenon of corrosion initiation on reinforced mortar specimens and the behavior of several corroded reinforcing bars. The main objective of the study was to observe the actual influence of cement mineralogy on the various mechanisms of corrosion initiation on steel reinforcement. Contributing to the elaboration of a tool that will be able to predict the service life of a reinforced concrete structures exposed to chlorides, this research also allowed to put forward new information for the civil engineering community, helping engineers and owners optimizing concrete formulations, and improving the durability of concrete constructions. The project was divided in two parts. The first one is aimed at isolating a threshold concentration of chloride-ions that would initiate corrosion. The mortar specimens were exposed to chloride-ions in a controlled environment, by chloride ponding, and the evolution of corrosion was observed with non-destructive electrochemical measurements. Different factors were taken into consideration during these tests: the water/cement ratio, the cement mineralogy, and the various type of reinforcing bars preparation. Going trough this paper, you will learn about the consequences that come from the variation of these factors on the corrosion initiation. The second part of the project studied the effects of corrosion on the mechanical properties of steel reinforcement. The data that resulted from the traction tests, on the bars, at different corrosion levels, are also presented in this document. According to the results of the study, reducing the water/cement ratio and increasing the C3A content led to a longer corrosion initiation time. As for the cracking time of the different mortar specimens, it appeared to be independent from these two factors. Moreover, sandblasted bars were found to be a lot more resistant to corrosion than the brushed bars. In the end, the critical concentration of chloride-ions was found to be around 0.3% by weight of dry mortar or 1.2% by weight of cement. This threshold value was precisely evaluated studying different specimens with and without bars. Furthermore, this threshold value seems independent of the concentration of C3A, the type of bar preparation or the water/cement ratio
Functionalized polyhydroquinolines from amino acids using a key one-pot cyclization cascade and application to the synthesis of (±)-Î7-mesembrenone
Substituted polyhydroquinolines are ubiquitous skeletal cores found in drugs and bioactive natural products. As a new route to access this motif, we successfully developed a one-pot cyclization cascade with high chemocontrol and diastereoselectivi-ty. The sequence generates two cycles, three carbon-carbon bonds, and an all-carbon quaternary center in a highly conver-gent process. Functionalized polyhydroquinolines and congeners are accessible from commercially available amino acids. This versatile and robust strategy was applied to the synthesis of (±)-D7-mesembrenon
Direct inscription of on-surface waveguides in polymers using a mid-ir fiber laser
A detailed study of photo-inscribed optical waveguides in PMMA and polycarbonate using a mid-IR laser is presented. The wavelength of the laser is tuned near the absorption peaks of stretching C-H molecular bonds and the focused beam is scanned onto the surface of planar polymer samples. For the first time, we report the formation of optical waveguides in both polymers through resonant absorption of the laser beam. The optical properties of the waveguides were thoroughly assessed. An elliptic Gaussian mode is guided at the surface of both polymers. Insertion losses of 3.1 dB for a 30 mm long on-surface waveguide inscribed in PMMA were recorded. Such waveguides can interact with the external medium through evanescent coupling. As a proof of concept, the surface waveguides are used as highly sensitive refractometric sensors. An attenuation dynamical range of 35 dB was obtained for a liquid that matches the index of the PMMA substrate. Our results pave the way for large scale manufacturing of low cost biocompatible photonic devices
Quelles pratiques diffĂ©renciĂ©es pour lâenseignement de lâorthographe lexicale ? Une recension des Ă©crits
MalgrĂ© la quantitĂ© dâĂ©crits sur la diffĂ©renciation pĂ©dagogique, peu dâentre eux visent Ă appliquer son cadre conceptuel Ă des contenus scolaires. Cet article propose de croiser les pratiques en orthographe lexicale et ce cadre. Une recension des Ă©crits a Ă©tĂ© effectuĂ©e dans diffĂ©rentes bases de donnĂ©es. LâanasynthĂšse a Ă©tĂ© employĂ©e pour analyser les donnĂ©es recueillies et Ă©laborer une modĂ©lisation de la diffĂ©renciation en orthographe lexicale. De nombreuses pistes de diffĂ©renciation pĂ©dagogique sont proposĂ©es Ă la suite de cette catĂ©gorisation dans les quatre axes de la diffĂ©renciation pĂ©dagogique : contenu,processus, structure et production
Graph Positional and Structural Encoder
Positional and structural encodings (PSE) enable better identifiability of
nodes within a graph, as in general graphs lack a canonical node ordering. This
renders PSEs essential tools for empowering modern GNNs, and in particular
graph Transformers. However, designing PSEs that work optimally for a variety
of graph prediction tasks is a challenging and unsolved problem. Here, we
present the graph positional and structural encoder (GPSE), a first-ever
attempt to train a graph encoder that captures rich PSE representations for
augmenting any GNN. GPSE can effectively learn a common latent representation
for multiple PSEs, and is highly transferable. The encoder trained on a
particular graph dataset can be used effectively on datasets drawn from
significantly different distributions and even modalities. We show that across
a wide range of benchmarks, GPSE-enhanced models can significantly improve the
performance in certain tasks, while performing on par with those that employ
explicitly computed PSEs in other cases. Our results pave the way for the
development of large pre-trained models for extracting graph positional and
structural information and highlight their potential as a viable alternative to
explicitly computed PSEs as well as to existing self-supervised pre-training
approaches
Nonlinear increase, invisibility, and sign inversion of a localized fs-laser-induced refractive index change in crystals and glasses
Multiphoton absorption via ultrafast laser focusing is the only technology that allows a three-dimensional structural
modification of transparent materials. However, the magnitude of the refractive index change is rather limited,
preventing the technology from being a tool of choice for the manufacture of compact photonic integrated circuits.
We propose to address this issue by employing a femtosecond-laser-induced electronic band-gap shift (FLIBGS), which
has an exponential impact on the refractive index change for propagating wavelengths approaching the material
electronic resonance, as predicted by the KramersâKronig relations. Supported by theoretical calculations, based on a
modified Sellmeier equation, the Tauc law, and waveguide bend loss calculations, we experimentally show that several
applications could take advantage of this phenomenon. First, we demonstrate waveguide bends down to a
submillimeter radius, which is of great interest for higher-density integration of fs-laser-written quantum and photonic
circuits. We also demonstrate that the refractive index contrast can be switched from negative to positive, allowing
direct waveguide inscription in crystals. Finally, the effect of the FLIBGS can compensate for the fs-laser-induced
negative refractive index change, resulting in a zero refractive index change at specific wavelengths, paving the way
for new invisibility applications
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