Topological gauge fixing

We implement the metric-independent Fock-Schwinger gauge in the abelian quantum Chern-Simons field theory defined in ${\mathbb R}^3$. The expressions of the various components of the propagator are determined. Although the gauge field propagator differs from the Gauss linking density, we prove that its integral along two oriented knots is equal to the linking number

Three-dimensional flow and thermal structure in glass melting furnaces : Part II. Effects of batch blanket and bubbles

This paper is the second part of a parametric study of the flow and thermal structures in glass melting furnaces with a throat. The effects of the following parameters are discussed: a) the batch velocity, b) the melting temperature, c) the submerged depth of the batch, d) the wall heat losses, and e) the thickness of glass melt containing gas bubbles under the batch. The study indicates that the partially submerged batch and heat losses through the refractories have a strong impact on both the longitudinal and spanwise flow patterns of the molten glass. These physical phenomena must be accounted for if one wants to realistically simulate the natural convection circulation of the molten glass in the bath

Masse obscure pour une certaine pensée de l'imprégnation résineuse

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Tuning thermal conductivity of nanoporous crystalline silicon by surface passivation: A molecular dynamics study

Surface passivation of nanoporous crystalline silicon can reduce its thermal conductivity. This was established using equilibrium molecular dynamics simulations. The porosity varied from 8% to 38% while the pore diameter ranged from 1.74 to 2.93 nm. Hydrogen and oxygen passivation reduced thermal conductivity by 11% to 17% and 37% to 51% depending on porosity at 500 K, respectively. The hydrogen passivation effect decreased with increasing temperature. Vibrational spectra of oxygen overlapped with those of silicon at low frequencies. Therefore, oxygen passivation enhanced phonon scattering at solid matrix boundaries, resulting in stronger thermal conductivity reduction than that caused by hydrogen passivation

Restrained shrinkage cracking of cementitious composites containing soft PCM inclusions: A paste (matrix) controlled response

The addition of phase change materials (PCMs) has been proposed as a means to mitigate thermal cracking in cementitious materials. However, the addition of PCMs, i.e., soft inclusions, degrades the compressive strength of cementitious composites. From a strength-of-materials viewpoint, such reductions in strength are suspected to increase the tendency of cementitious materials containing PCMs to crack under load (e.g., volume instability-induced stresses resulting from thermal and/or hygral deformations). Based on detailed assessments of free and restrained shrinkage, elastic modulus, and tensile strength, this study shows that the addition of PCMs does not alter the cracking sensitivity of the material. In fact, the addition of PCMs (or other soft inclusions) enhances the cracking resistance as compared to a plain cement paste or composites containing equivalent dosages of (stiff) quartz inclusions. This is because composites containing soft inclusions demonstrate benefits resulting from crack blunting and deflection, and improved stress relaxation. As a result, although the tensile stress at failure remains similar, the time to failure (i.e., macroscopic cracking) of PCM-containing composites is considerably extended. More generally, the outcomes indicate that dosages of soft(er) inclusions, and the resulting decrease in compressive strength does not amplify the cracking risk of cementitious composites

Thermal Conductivity of Pure Silica MEL and MFI Zeolite Thin Films

This paper reports the room temperature cross-plane thermal conductivity of pure silica zeolite (PSZ) MEL and MFI thin films. PSZ MEL thin films were prepared by spin coating a suspension of MEL nanoparticles in 1-butanol solution onto silicon substrates followed by calcination and vapor-phase silylation with trimethylchlorosilane. The mass fraction of nanoparticles within the suspension varied from 16% to 55%. This was achieved by varying the crystallization time of the suspension. The thin films consisted of crystalline MEL nanoparticles embedded in a nonuniform and highly porous silica matrix. They featured porosity, relative crystallinity, and MEL nanoparticles size ranging from 40% to 59%, 23% to 47% and 55 nm to 80 nm, respectively. PSZ MFI thin films were made by in situ crystallization, were b-oriented, fully crystalline, and had a 33% porosity. Thermal conductivity of these PSZ thin films was measured at room temperature using the 3ω method. The cross-plane thermal conductivity of the MEL thin films remained nearly unchanged around 1.02±0.10 W m−1 K−1 despite increases in (i) relative crystallinity, (ii) MEL nanoparticle size, and (iii) yield caused by longer nanoparticle crystallization time. Indeed, the effects of these parameters on the thermal conductivity were compensated by the simultaneous increase in porosity. PSZ MFI thin films were found to have similar thermal conductivity as MEL thin films even though they had smaller porosity. Finally, the average thermal conductivity of the PSZ films was three to five times larger than that reported for amorphous sol-gel mesoporous silica thin films with similar porosity and dielectric constant

Étude archéométallurgique du dépôt de grands bronzes du sanctuaire gallo-romain du Vieil-Evreux (Eure)

Cet article présente les résultats d’une étude archéométallurgique réalisée sur un important dépôt de bronze découvert en 1840 sur le site du sanctuaire gallo-romain du Vieil-Evreux. De récentes découvertes de fragments au sein du sanctuaire, ainsi qu’une relecture des données d’archives, ont amené à redéfinir la nature et le contexte de ce dépôt.This article reports the results of an archeometallurgical study carried out on an important bronze hoard discovered in 1840 on the gallo-roman sanctuary of Vieil-Evreux. Recent excavations provided other fragments, and a study of the archive data, led to redefine the nature and context of this hoard. The work was conducted by the C2RMF, in collaboration with the CEA Le Ripault and the MADE, and the analytical procedure involved the use of multiple techniques such as radiography, tomography, endoscopy, or the determination of elemental composition by ICP-AES of the various pieces of bronze. Two main results were obtained so far. The first is directly related to the understanding of the Vieil-Evreux site by determining the minimal number of statues in the bronze hoard and more accurate the identification of their iconography. The second, more general, is to integrate and compare the data in the research program concerning the study of the manufacturing techniques of the Greek and Roman large bronze statues (including the study of the lost wax process and the welding process)

Foaming of E-Glass II (Report for G Plus Project for PPG)

In a previous study, the effect of the furnace atmosphere on E glass foaming was investigated with the specific goal to understand the impact of increased water content on foaming in oxy-fired furnaces. The present study extended the previous study and focused on the effect of glass batch chemical composition on E-glass foaming. The present study also included reruns of foam tests performed in a previous study, which resulted in the same trend: the foaming extent increased nearly linearly with the heating rate and no foam was produced when CO2 + 55% H2O atmosphere was introduced at 300°C. It was shown that the lack of foaming in the test with CO2 + 55% H2O atmosphere introduced at 300°C was caused by a loss of sulfate at T <1250°C because of higher water content at the early stages of melting. The tests with new batches in the present study showed that replacing quicklime with limestone tend to decrease foaming, possibly caused by increased sulfate loss during early stages of melting in the batch with limestone. The batches where Na2SO4 was replaced with NaNO3, NaNO3 + CeO2, or CeO2, produced only very limited foaming regardless of the replacing components. As expected, the foaming extent increased as the sulfate content in the batch increased. The results of the present study suggest that foaming can be reduced by using limestone over quicklime and by decreasing the sulfate addition to a minimum required for refining