Solid-spaced filters: an alternative for narrow-bandpass applications

Solid-spaced filters are composed of one or several thin wafers of excellent optical quality acting as Fabry-Perot spacer layers. We study the different steps of the design and the manufacture of filters following dense-wavelength-division-multiplexing specifications. The design method of such filters requires a tight synergy between numerical simulations and experimental characterizations to correct possible thickness errors. Experimental results of the manufacture and characterization of a three-cavity narrow-bandpass filter and of an interleaver filter are given.     

Large-scale optical-field measurements with geometric fibre constructs

Optical fields are measured using sequential arrangements of optical components such as lenses, filters, and beam splitters in conjunction with planar arrays of point detectors placed on a common axis. All such systems are constrained in terms of size, weight, durability and field of view. Here a new, geometric approach to optical-field measurements is presented that lifts some of the aforementioned limitations and, moreover, enables access to optical information on unprecedented length and volume scales. Tough polymeric photodetecting fibres drawn from a preform are woven into light-weight, low-optical-density, two- and three-dimensional constructs that measure the amplitude and phase of an electromagnetic field on very large areas. First, a three-dimensional spherical construct is used to measure the direction of illumination over 4pi steradians. Second, an intensity distribution is measured by a planar array using a tomographic algorithm. Finally, both the amplitude and phase of an optical wave front are acquired with a dual-plane construct. Hence, the problem of optical-field measurement is transformed from one involving the choice and placement of lenses and detector arrays to that of designing geometrical constructions of polymeric, light-sensitive fibres.     

Mechanical and interfacial properties of wood and bio-based thermoplastic composite

The aim of this investigation was to study a new family of wood polymer composites with thermoplastic elastomer matrix (pebax® copolymers) instead of commonly used WPC matrices. These copolymers are polyether-b-amide thermoplastic elastomers which present an important elongation at break and a melting point below 200 °C to prevent wood fibers degradation during processing. Moreover these polymers are synthesized from renewable resources and they present a hydrophilic character which allow them to interact with wood fibers. We have used two pebax® grade with different hardness and three types of wood fibers, so the influence of the matrix and wood fibers characteristics were evaluated. Composites were produced using a laboratory-size twin screw extruder to obtain composite pellets prior to injection moulding into tensile test samples. We have evaluated fibers/matrix interaction by differential scanning calorimetry (DSC), infrared spectroscopy (IRTF) and scanning electron microscopy (SEM). Then, the mechanical properties, through tensile test, were assessed. We also observed fibers dispersion into the matrix by tomography X. DSC, IRTF and SEM measurements confirmed the presence of strong interface interactions between polymer and wood. These interactions lead to good mechanical properties of the composites with a reinforcement effect of wood fibers due also to a good dispersion of fibers into the matrix without agglomerate.     

Effects of high pressure,high temperature and dilution on laminar burning velocities and Markstein lengths of iso-octane/air mixtures

Spherically expanding flames are employed to measure flame velocities, from which are derived the corresponding laminar burning velocities at zero stretch rate. Iso-octane/air mixtures at initial temperatures between 323 and 473 K, and pressures between 1 and 10 bar, are studied over an extensive range of equivalence ratios, using a high-speed shadowgraph system. Effects of dilution are investigated with nitrogen and for several dilution percentages (from 5 to 25 vol% N₂). Over 270 experimental values have been obtained, providing an exhaustive data base for iso-octane/air combustion. Experimental results are in excellent agreement with recently published experimental data. An explicit correlation giving the laminar burning velocity from the initial pressure, the initial temperature, the dilution rate, and the equivalence ratio is finally proposed. Computed results using the two kinetic schemes and the Cantera code are compared to the present measurements. It is found that the mechanisms yield substantially higher values of laminar flame velocities than the present experimental results. Effects of oxygen enrichment are also investigated. A linear trend relating the percentage of oxygen in air and the unstretched laminar burning velocity is observed. Effects of high pressure, high temperature, and high dilution rate on Markstein lengths are also studied. As already done for the laminar burning velocity, an empirical correlation is proposed to describe the Markstein length for burned gases as a function of initial temperature and pressure, for equivalence ratios between 0.9 and 1.1, which has never been done before in the literature.     

Production and characterization of plutonium dioxide particles as a quality control material for safeguards purposes

Plutonium (Pu) dioxide particles were produced from certified reference material (CRM) 136 solution (CRM 136-plutonium isotopic standard, New Brunswick Laboratory, Argonne, IL, U.S.A., 1987) using an atomizer system on December 3, 2009 after chemical separation of americium (Am) on October 27, 2009. The highest density of the size distribution of the particles obtained from 312 particles on a selected impactor stage was in the range of 0.7-0.8 μm. The flattening degree of 312 particles was also estimated. The isotopic composition of Pu and uranium (U) and the amount of Am were estimated by thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICPMS), and α-spectrometry. Within uncertainties the isotopic composition of the produced particles is in agreement with the expected values, which were derived from the decay correction of the Pu isotopes in the CRM 136. The elemental ratio of Am to Pu in the produced particles was determined on the 317th and 674th day after Am separation, and the residual amount of Am in the solution was estimated. The analytical results of single particles by micro-Raman-scanning electron microscopy (SEM)-energy-dispersive X-ray spectrometry (EDX) indicate that the produced particles are Pu dioxide. Our initial attempts to measure the density of two single particles gave results with a spread value accompanied by a large uncertainty.     

Parsimonious reduction of Gaussian mixture models with a variational-Bayes approach

Aggregating statistical representations of classes is an important task for current trends in scaling up learning and recognition, or for addressing them in distributed infrastructures. In this perspective, we address the problem of merging probabilistic Gaussian mixture models in an efficient way, through the search for a suitable combination of components from mixtures to be merged. We propose a new Bayesian modelling of this combination problem, in association to a variational estimation technique, that handles efficiently the model complexity issue. A main feature of the present scheme is that it merely resorts to the parameters of the original mixture, ensuring low computational cost and possibly communication, should we operate on a distributed system. Experimental results are reported on real data.     

The co-evolution of taxi drivers and their in-car navigation systems

The recent market success of in-car navigation systems creates an opportunity to investigate the appropriation of location-aware systems outside laboratory settings. Through ethnographical lenses, we study how this technology changed the practice of a massive community of its early adopters, the taxi drivers of Barcelona (Spain) and, specifically, their exploitation of pervasive geoinformation. The results show co-evolution: taxi drivers adapt to their in-car navigation systems and adapt them to their needs; in particular, there are evidences of an alteration of the learning processes and of technology appropriation to reduce stress rather than to improve efficiency. We argue that these findings can inform the design of next-generation location-based services.     

电池供电设备中的电荷泵

白色发光二极管(LED)广泛用于手持设备(如手机)以便从背后照亮彩色液晶显示器(LCD)或照明按键.LED的亮度与流经的电流量成正比,一般需要至少3V的正向电压.锂离子可充电电池因其相当高的能量密度而非常受欢迎,其输出电压可在4.2V(完全充电后)至3V(放电后)之间变化.该电压范围难以直接通过电池给LED供电,因此,需要某种形式的升压转换器.由于简单和成本低,自动调节式电荷泵特别适用于LED总电流为100mA的应用中.