Convergent sequences of perturbative approximations for the anharmonic oscillator II. Compact time approach

We present an alternative pathway in the application of the variation improvement of ordinary perturbation theory exposed in [1] which can preserve the internal symmetries of a model by means of a time compactification.Comment: 21 pages, 4 Postscript figures available through anonymous ftp at ftp://algol.lpm.univ-montp2.fr ; replaces version which could not be postscripted presumably for lack of figures.uu fil

Convergent sequences of perturbative approximations for the anharmonic oscillator I. Harmonic approach

We present numerical evidence that a simple variational improvement of the ordinary perturbation theory of the quantum anharmonic oscillator can give a convergent sequence of approximations even in the extreme strong coupling limit, the purely anharmonic case. Some of the new techniques of this paper can be extended to renormalizable field theories.Comment: 29 pages, 12 Postscript figures available through anonymous ftp at ftp://algol.lpm.univ-montp2.fr ; replaces earlier version which could not be postscripted presumably due to lack of figures.uu fil

Applications of high pressure differential scanning calorimetry to aviation fuel thermal stability research

High pressure differential scanning calorimetry (DSC) was studied as an alternate method for performing high temperature fuel thermal stability research. The DSC was used to measure the heat of reaction versus temperature of a fuel sample heated at a programmed rate in an oxygen pressurized cell. Pure hydrocarbons and model fuels were studied using typical DSC operating conditions of 600 psig of oxygen and a temperature range from ambient to 500 C. The DSC oxidation onset temperature was determined and was used to rate the fuels on thermal stability. Kinetic rate constants were determined for the global initial oxidation reaction. Fuel deposit formation is measured, and the high temperature volatility of some tetralin deposits is studied by thermogravimetric analysis. Gas chromatography and mass spectrometry are used to study the chemical composition of some DSC stressed fuels

Renormalization Group Improved Optimized Perturbation Theory: Revisiting the Mass Gap of the O(2N) Gross-Neveu Model

We introduce an extension of a variationally optimized perturbation method, by combining it with renormalization group properties in a straightforward (perturbative) form. This leads to a very transparent and efficient procedure, with a clear improvement of the non-perturbative results with respect to previous similar variational approaches. This is illustrated here by deriving optimized results for the mass gap of the O(2N) Gross-Neveu model, compared with the exactly know results for arbitrary N. At large N, the exact result is reproduced already at the very first order of the modified perturbation using this procedure. For arbitrary values of N, using the original perturbative information only known at two-loop order, we obtain a controllable percent accuracy or less, for any N value, as compared with the exactly known result for the mass gap from the thermodynamical Bethe Ansatz. The procedure is very general and can be extended straightforwardly to any renormalizable Lagrangian model, being systematically improvable provided that a knowledge of enough perturbative orders of the relevant quantities is available.Comment: 18 pages, 1 figure, v2: Eq. (4.5) corrected, comments adde

Les usages en ligne du patrimoine écrit : du partage à l'enrichissement de contenus

En 2006, le catalogue des collections patrimoniales numérisées élaboré par le ministère de la Culture, Patrimoine numérique, recense près de 1 150 fonds ou collections numérisés. On sait peu que 44 % de ce patrimoine désormais numérique proviennent des archives départementales et 27 % des bibliothèques municipales, ce qui place ces deux services culturels locaux largement devant tous les autres. Cette constatation liminaire invite à poser la question des patrimoines écrits numériques en Pays-de-la-Loire, des conditions de son avènement comme des modalités de ses usages. L’impact du numérique dans le champ du patrimoine écrit n’a pas encore produit tous ses effets et le système n’a pas encore trouvé son équilibre. Des effets attendus ne sont pas avérés, comme l’affirmation de la notion de patrimoine écrit susceptible de transcender les périmètres professionnels et d’élargir les publics. D’autres, inattendus ou sous-estimés, jouent à plein, comme la redéfinition de la relation entre les institutions patrimoniales et leurs publics et l’irruption du secteur privé dans les modalités de diffusion des données publiques, y compris patrimoniales

Convergent sequences of perturbative approximations for the anharmonic oscillator; 1, harmonic approach

We present numerical evidence that a simple variational improvement of the ordinary perturbation theory of the quantum anharmonic oscillator can give a convergent sequence of approximations even in the extreme strong coupling limit, the purely anharmonic case. Some of the new techniques of this paper can be extended to renormalizable field theories

Constraining the Λ\LambdaCDM and Galileon models with recent cosmological data

The Galileon theory belongs to the class of modified gravity models that can explain the late-time accelerated expansion of the Universe. In previous works, cosmological constraints on the Galileon model were derived, both in the uncoupled case and with a disformal coupling of the Galileon field to matter. There, we showed that these models agree with the most recent cosmological data. In this work, we used updated cosmological data sets to derive new constraints on Galileon models, including the case of a constant conformal Galileon coupling to matter. We also explored the tracker solution of the uncoupled Galileon model. After updating our data sets, especially with the latest \textit{Planck} data and BAO measurements, we fitted the cosmological parameters of the $\Lambda$CDM and Galileon models. The same analysis framework as in our previous papers was used to derive cosmological constraints, using precise measurements of cosmological distances and of the cosmic structure growth rate. We showed that all tested Galileon models are as compatible with cosmological data as the $\Lambda$CDM model. This means that present cosmological data are not accurate enough to distinguish clearly between both theories. Among the different Galileon models, we found that a conformal coupling is not favoured, contrary to the disformal coupling which is preferred at the $2.3\sigma$ level over the uncoupled case. The tracker solution of the uncoupled Galileon model is also highly disfavoured due to large tensions with supernovae and \textit{Planck}+BAO data. However, outside of the tracker solution, the general uncoupled Galileon model, as well as the general disformally coupled Galileon model, remain the most promising Galileon scenarios to confront with future cosmological data. Finally, we also discuss constraints coming from Lunar Laser Ranging experiment and gravitational wave speed of propagation.Comment: 22 pages, 17 figures, published version in A&

Myron Goldsmith: The Development of the Diagonally Braced Tube

Myron Goldsmith (1918-96) was a unique figure in the development of tall building design. He successfully blended the roles of architect, engineer and teacher throughout his tenure at Skidmore Owings and Merrill (SOM) and in the Department of Architecture at the Illinois Institute of Technology (IIT). Indeed, many of the projects supervised by Goldsmith and his colleagues, to include the pre-eminent structural engineer Dr. Fazlur Khan (1929-82), directly influenced built work. The few published studies of Goldsmith acknowledge, but do not fully explore, the innovations that Goldsmith oversaw as thesis advisor to many graduate students at IIT in the 1960s. An essential link between the student work and the large-scale office projects at SOM were the “Saturday Sessions.” There, architects, engineers and students met for weekly reviews at IIT and then a lengthy and lively lunch at Bertucci’s restaurant in Chicago. Goldsmith encouraged the free exchange of scholarly and practical ideas during these Saturday Sessions and we argue that this was a vital part of Goldsmith’s pedagogy. This paper will focus on a fascinating network of students, architects, and engineers that led to the innovation of the diagonally braced tube tall building

Experimental constraints on the uncoupled Galileon model from SNLS3 data and other cosmological probes

The Galileon model is a modified gravity theory that may provide an explanation for the accelerated expansion of the Universe. This model does not suffer from instabilities or ghost problems (normally associated with higher-order derivative theories), restores local General Relativity -- thanks to the Vainshtein screening effect -- and predicts late time acceleration of the expansion. In this paper, we derive a new definition of the Galileon parameters that allows us to avoid having to choose initial conditions for the Galileon field, and then test this model against precise measurements of the cosmological distances and the rate of growth of cosmic structures. We observe a small tension between the constraints set by growth data and those from distances. However, we find that the Galileon model remains consistent with current observations and is still competitive with the \Lambda CDM model, contrary to what was concluded in recent publications.Comment: 19 pages, 15 figures, accepted to Astronomy and Astrophysic