Search for Lorentz and CPT violation effects in Muon spin precession

The spin precession frequency of muons stored in the (g-2) storage ring has been analyzed for evidence of Lorentz and CPT violation. Two Lorentz and CPT violation signatures were searched for a nonzero delta omega a(=omega a mu+ - omega a mu-) and a sidereal variation of omega a mu+/-). No significant effect is found, and the following limits on the standard-model extension parameters are obtained: bZ = -(1.0+/-1.1) x 10(-23) GeV; (m mu dZ0 + HXY)=(1.8+/-6.0) x 10(-23) GeV; and the 95% confidence level limits b perpendicular mu+ <1.4 x 10(-24) GeV and b perpendicular mu- <2.6 x 10(-24) GeV.     

Review of Terahertz Tomography Techniques

Terahertz and millimeter waves penetrate various dielectric materials, including plastics, ceramics, crystals, and concrete, allowing terahertz transmission and reflection images to be considered as a new imaging tool complementary to X-Ray or Infrared. Terahertz imaging is a well-established technique in various laboratory and industrial applications. However, these images are often two-dimensional. Three-dimensional, transmission-mode imaging is limited to thin samples, due to the absorption of the sample accumulated in the propagation direction. A tomographic imaging procedure can be used to acquire and to render three-dimensional images in the terahertz frequency range, as in the optical, infrared or X-ray regions of the electromagnetic spectrum. In this paper, after a brief introduction to two dimensional millimeter waves and terahertz imaging we establish the principles of tomography for Terahertz Computed tomography (CT), tomosynthesis (TS), synthetic aperture radar (SAR) and time-of-flight (TOF) terahertz tomography. For each technique, we present advantages, drawbacks and limitations for imaging the internal structure of an object.     

Synthese,purification et analyses du tetrafluorure (SeF4) et de l'oxydifluorure de selenium (SeOF2) Enthalpie de fusion et enthalpie de vaporisation de SeOF2

Selenium tetrafluoride and selenium oxydifluoride have been prepared and various analyses (chemical, thermal, microsublimation, mass spectrometry) have been performed on pure samples. The temperature and heat of fusion and heat of vaporisation of SeOF₂ have been determined.

     

Mechanism of photo-oxidation of an elastomer

Ultraviolet irradiation in air of various elastomeric substances results in crosslinks, chain scissions and oxidation functions. The quantum yields of the different processes and the oxygen balance have been determined in the case of a model system. These results make it possible to propose a mechanism of photo-oxidation which agrees well with the experimental data. The rôle played by hydroperoxide functions has been recognised and demonstrated; their sensitised generation and decomposition have been explained in terms of energy transfer phenomena. Lastly, changes in the macromolecular chains and network formation have been followed. The results demonstrate quantitatively how light energy is absorbed by impurity in a polymer and is transferred to potential radical sites (hydroperoxides). Chain radical reactions develop in the material, leading predominantly to photocrosslinking simultaneously with a chain scission process which allows spatial reorganisation of the polymer medium.     

Determination de l'enthalpie de formation standard du tetrafluorure de tellure par calorimetrie de combustion dans le fluor et par calorimetrie de reaction

The standard enthalpy of formation of tellurium tetrafluoride has been determined: by combustion in fluorine:

by reaction in a normal solution of soda:

     

Characterization and purification of polyunsaturated fatty acids from microalgae by gas chromatography-mass spectrometry and countercurrent chromatography

Summary The present study was undertaken in order to characterize then to purify fatty acids from marine phytoplankton. From a crude mixture of fatty acid methyl esters it was possible to isolate by countercurrent chromatography a mixture of four polyunsaturated fatty acid methyl ester identified as being hexadecatrienoic acid methyl ester, octadecatetraenoic acid methyl ester, eicosapentaenoic acid methyl ester and docosahexaenoic acid methyl ester by gas chromatography coupled with mass spectrometry in electron impact and in positive-ion chemical ionization mode. The four polyunsaturated fatty acids are in different ratios in mixtures from the two microorganisms:Skeletonema costatum andIsochrysis galbana.     

Effect of spacer insertion in a commonly used dithienosilole/benzothiadiazole-based low band gap copolymer for polymer solar cells

Dithienosilole-benzothiadiazole based low bandgap copolymers remain promising material for organic photovoltaics. A new copolymer, poly[(4,4′-dioctyldithieno[3,2-b:2′,3′-d]silole-2,6-diyl)-alt-{4,7-bis[2-(3-hexyl)thienyl]-2,1,3-benzothiadiazole-5,5′-diyl}] (PDTSDTBT) was designed by introducing a thiophene spacer bearing a hexyl chain at β-position in the main backbone and compared to its analog poly[(4,4′-dioctyldithieno[3,2-b:2′,3′-d]silole-2,6-diyl)-alt-(2,1,3-benzothiadiazole-4,7-diyl)] (PDTSBT). In PDTSDTBT, linear alkyl chains on silicon were chosen due to facile and cheap access and the inserted 3-hexylthiophene units were chosen to increase solubility and molar mass, a weak point with PDTSBT. The two parameters are important to optimize photovoltaic performances. To compare characteristics, PDTSDTBT of molar masses greater than, and equal to a sample of PDTSBT, were prepared. Pd-catalyzed Stille cross-coupling reactions in a micro-wave reactor to promote an efficient copolymerisations. A strong absorption ranging from 370 nm to 800 nm and a good thermal stability were observed. PDTSDTBT showed better solubility and higher degree of crystallinity. Facile synthesis of high molar masses meant that higher efficiencies, around 40% greater, could be obtained with PDTSDTBT. The polymer was demonstrated to be susceptible to improvement through the use of device-additives. For example, under initial optimisations using PDTSDTBT:PC₆₀BM blend at a ratio of 1:1 delivered a power conversion efficiency of 2.13% with J_SC = 7.73 (mA/cm²), under AM 1.5 (100 mW/cm²) illumination.     

Free energy landscapes for the thermodynamic understanding of adsorption-induced deformations and structural transitions in porous materials

Soft porous crystals are flexible metal-organic frameworks that respond to physical stimuli such as temperature, pressure, and gas adsorption by large changes in their structure and unit cell volume. While they have attracted a lot of interest, molecular simulation methods that directly couple adsorption and large structural deformations in an efficient manner are still lacking. We propose here a new Monte Carlo simulation method based on non-Boltzmann sampling in (guest loading, volume) space using the Wang-Landau algorithm, and show that it can be used to fully characterize the adsorption properties and the material's response to adsorption at thermodynamic equilibrium. We showcase this new method on a simple model of the MIL-53 family of breathing materials, demonstrating its potential and contrasting it with the pitfalls of direct, Boltzmann simulations. We furthermore propose an explanation for the hysteretic nature of adsorption in terms of free energy barriers between the two metastable host phases.     

Prescribing the Jacobian in critical spaces

We consider the Sobolev space $X = W^{s,p} \left( {\mathbb{S}^m ;\mathbb{S}^{k - 1} } \right)$ . We prove the existence of a robust distributional Jacobian Ju for u ∈ X, provided sp ≥ k ? 1; this generalizes a result of Bourgain, Brezis, and the second author [10] dealing with the case m = k. We identify the image of the map X ? u ? Ju in the critical case sp = k ? 1. This extends a result of Alberti, Baldo, and Orlandi [2] for s = 1 and p = k ? 1. We also present a new, analytical, dipole construction method.