1,302 research outputs found
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 Ă©crit : du partage Ă l'enrichissement de contenus
En 2006, le catalogue des collections patrimoniales numérisées élaboré par le ministÚre de la Culture, Patrimoine numérique, recense prÚs de 1 150 fonds ou collections numérisés. On sait peu que 44 % de ce patrimoine désormais numérique proviennent des archives départementales et 27 % des bibliothÚques 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 avÚnement comme des modalités de ses usages.
Lâimpact du numĂ©rique dans le champ du patrimoine Ă©crit nâa pas encore produit tous ses effets et le systĂšme nâa pas encore trouvĂ© son Ă©quilibre. Des effets attendus ne sont pas avĂ©rĂ©s, comme lâaffirmation de la notion de patrimoine Ă©crit susceptible de transcender les pĂ©rimĂštres professionnels et dâĂ©largir les publics. Dâautres, inattendus ou sous-estimĂ©s, jouent Ă plein, comme la redĂ©finition de la relation entre les institutions patrimoniales et leurs publics et lâirruption du secteur privĂ© dans les modalitĂ©s de diffusion des donnĂ©es publiques, y compris patrimoniales
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 âSaturday Sessions.â There, architects, engineers and students met for weekly reviews at IIT and then a lengthy and lively lunch at Bertucciâs 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 Goldsmithâs 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
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 CDM 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 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 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 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&
string scattering
The group theoretic method is extended to include fields with a background
charge. This formalism is used to compute the tree level scattering for
strings. The scattering amplitudes involve Ising model correlation functions. A
detailed study of the four tachyon amplitude shows that the string must
possess additional states in its spectrum associated with intercept and
the energy operator of the Ising model.Comment: 11 pages, KCL-TH-92-4/NI 9200
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