Étude théorique et expérimentale d’une modulation simplifiée par déplacement de fréquence d’indice 1/2 à phase continue

The minimum shift keying modulation (MSK)to which a lot of recent publications have been done,presents some advantage about linear and non-linear distortions towards common 2 or 4 Phase Shift Keying (PSK)modulations. The simplified MSK modulation described in this paper is obtained by linear filtering of a coherent 2 phase shift keying modulation. Then the demodulator can be implemented with a matched filter followed by a coherent demodulator using only one carrier recovery circuit. In the first part of this paper, the modulator and the demodulator are described. After, some theorical results in the presence of noise and other impairments are given. In CCETT laboratories at Rennes, a modem has been realized at a data rate of 2,048 Mbit/s and performs at 0,8 dB of the theoretical results.     

Sem observations of the microstructure of frost deteriorated and self-healed concretes

The microcracking and self healing mechanisms of concrete exposed to rapid freezing and thawing in water and subsequently kept in water have been investigated by Scanning Electron Microscopy (SEM). Non air entrained concretes of water/binder ratio 0.40 with 0 and 5 % silica fume were studied. Damage was measured as loss in resonance frequency and compressive strength. After frost exposure, concrete beams were stored three months in water. During this time resonance frequency largely recovered, whereas compressive strength showed smaller recovery. On Secondary Electron Images (SEI) of fractured surfaces hydration products mainly of the C-S-H type were seen traversing cracks at several locations after self healing, but not directly after freeze/thaw. Back Scattered Electron Images (BSEI) showed that the cracks due to freeze/thaw testing were of 1–10 μm width. The cracks traversed the paste and followed the interfaces of most larger aggregate particles. On BSEI self healing was seen on 300–1000 X magnification as partly closing of several cracks smaller than 5 μm. This was most clearly seen by switching between SEI and BSEI modes. In BSEI-mode the re-hydration products appeared less dense and the cracks appeared wider than in the SEI-mode.     

The revival of personal services in cities: An expression of polarization?

Journal of Housing and the Built Environment -     

Numerical model and experimental validation of heat storage with phase change materials

This paper describes the numeric model developed to simulate heat transfer in phase change materials (PCM) plunged in water tank storage. This model, based on the enthalpy approach, takes into account the conduction and the convection into PCM as well as at the interface between PCM and water of the storage. Furthermore, hysterisis and subcooling are also included. This model has been implemented in an existing TRNSYS type of water tank storage. It allows the simulation of a water storage tank filled with PCM modules made of different materials and different shapes such as cylinders, plates or spheres bed. Comparisons between measurements and simulations has been undertake to evaluate the potential of this model.     

Insight into silicate-glass corrosion mechanisms

The remarkable chemical durability of silicate glass makes it suitable for a wide range of applications. The slowdown of the aqueous glass corrosion kinetics that is frequently observed at long time is generally attributed to chemical affinity effects (saturation of the solution with respect to silica). Here, we demonstrate a new mechanism and highlight the impact of morphological transformations in the alteration layer on the leaching kinetics. A direct correlation between structure and reactivity is revealed by coupling the results of several structure-sensitive experiments with numerical simulations at mesoscopic scale. The sharp drop in the corrosion rate is shown to arise from densification of the outer layers of the alteration film, leading to pore closure. The presence of insoluble elements in the glass can inhibit the film restructuring responsible for this effect. This mechanism may be more broadly applicable to silicate minerals.     

Sensitivity variation of doped Fricke gel irradiated with monochromatic synchrotron X rays between 33.5 and 80 keV

An experimental binary radiotherapy proposes the concomitant use of a high-Z compound and synchrotron X rays for enhancing radiation dose selectively in tumours by a photoelectric effect. This study aimed at measuring the resulting dose enhancement in irradiated material. A doped Fricke gel dosemeter model was manufactured with 10 mg ml(-1) of iodine (Telebrix) or barium (Micropaque). Samples were irradiated with a monochromatic synchrotron beam at 33.5, 50, 65 and 80 keV. The ensuing enhancement of the sensitivity of the dosemeter was derived from the nuclear magnetic resonance relaxation rates measured at different X-ray doses. Our results demonstrate (1) the preservation of a linear relationship between relaxation rates and X-ray doses for dosemeters doped with high-Z atoms and (2) a clear energy-dependent sensitivity enhancement for barium-doped Fricke gels. This enhancement was neither reproducible with iodinated compounds nor clearly related to the expected dose enhancement factor. However 1% barium sulphate in the gel could significantly improve the gel's response when it was irradiated by low-energy X rays.     

Thin compound-eye camera

An artificial compound-eye objective fabricated by micro-optics technology is adapted and attached to a CMOS sensor array. The novel optical sensor system with an optics thickness of only 0.2 mm is examined with respect to resolution and sensitivity. An optical resolution of 60 x 60 pixels is determined from captured images. The scaling behavior of artificial compound-eye imaging systems is analyzed. Cross talk between channels fabricated by different technologies is evaluated, and the influence on an extension of the field of view by addition of a (Fresnel) diverging lens is discussed. The lithographic generation of opaque walls between channels for optical isolation is experimentally demonstrated.