Particle Sizes of Fumed Oxides: A New Approach Using PCS Signals

Fumed oxides produced in gas‐phase processes, such as silicas and aluminum oxide, consist of a cluster of aggregated primary particles. The aggregate size of these particles is an important variable in many applications. However, current procedures for measuring particle sizes all assume that the particles have a spherical shape and are thus not truly capable of determining aggregate size. The results of such particle size measurements are consequently called “equivalent spherical diameter” (ESD), but these results vary from method to method. This publication shows that it is feasible to use the number of primary particles per aggregate, rather than the ESD, as a measure for the particle size of clusters of this type. The method is based on dynamic light scattering (photon correlation spectroscopy, PCS), which has proven itself in the analysis of fumed oxides. A numerical simulation based on random, computer‐generated model aggregates is used to modify the well‐known Stokes‐Einstein equation so that the number of primary particles can be determined.     

Modification of spontaneous emission rate in planar dielectric microcavities – seen as superradiance and subradiance

The modification of the spontaneous emission rate of an atom in a cavity can be seen as superradiance/subradiance induced by virtual image dipoles. This result is used to gain physical insight why the spontaneous emission is enhanced or suppressed in various cavity geometries. A general model for spontaneous emission engineering, which simultaneously handles dispersive and lossy cavities, is derived.     

Spectral measurement of the caesium D2 line with a tunable heterodyne interferometer

The optical properties of a caesium atomic beam driven on a resonant hyperfine transition in the D₂ line were studied as a function of the probe laser frequency. Using a third off-resonant laser system, a heterodyne interferometer allowed simultaneous absorption and phase shift measurements of either the probe or the coupling laser. The signal features of the probe and coupling laser transmitted intensities showed strong differences in the vicinity of the hyperfine transitions excited by the probe laser. Regular absorption signals and electromagnetically induced transparency were found in either transmitted intensities. Furthermore, light induced birefringence of the probe laser was measured.     

On radiative transfer in water spray curtains using the discrete ordinates method

Radiative transfer through water spray curtains has been presently addressed in conditions similar to devices used in fire protection systems. The radiation propagation from the heat source through the medium is simulated using a 2D Discrete Ordinates Method. The curtain is treated as an absorbing and anisotropically scattering medium, made of droplets injected in a mixing of air, water vapor and carbon dioxide. Such a participating medium requires a careful treatment of its spectral response in order to model the radiative transfer accurately. This particular problem is dealt with using a correlated-K method. Radiative properties for the droplets are calculated applying the Mie theory. Transmissivities under realistic conditions are then simulated after a validation thanks to comparisons with some experimental data available in the literature. Owing to promising results which are already observed in this case of uncoupled radiative problem, next step will be to combine the present study with a companion work dedicated to the careful treatment of the spray dynamics and of the induced heat transfer phenomena.     

Computational study of low energy ion surface hyperchanneling

Classical ion trajectory simulations using the scattering and recoiling imaging code (SARIC) have been applied to study the low energy ion surface hyperchanneling phenomenon. It was found that the ion-surface interaction geometry, projectile type, surface chemisorbed hydrogen, and phonon amplitudes had a profound effect on the scattered ion trajectories. It is possible to determine the surface Debye temperature through analysis of the scattering yields and angular distributions. The simulations will find application in delineation of classical ion trajectories for specific as well as generic ion surface interactions.     

Schrödinger operators with nonlocal point interactions

Schrödinger operators with nonlocal point interactions are considered as new solvable models with point interactions. Examples in one and three dimensions are discussed. Corresponding direct and inverse scattering problems in one dimension are also discussed.     

Measurement of Young''s modulus of cementitious materials using an electro-optic holographic technique

The electro-optic holographic technique has already been used to determine Young's dynamic modulus in homogeneous materials based on the resonance frequency of the analysed samples. This paper shows a modification of the determination method of this frequency that speeds up this process thus obtaining Young's modulus. Based on the visualisation of real time fringes drawn by exciting the rods at the 1000–10,000 Hz range, the proposed method allows us to determine their resonance frequencies.

This procedure has been used in the analysis of non-homogeneous materials such as mortar and concrete. The results obtained by this method show good correlation with those determined by the conventional compression method established by Una Norma Española (UNE) regulations, but with a smaller variability as far as measurements are concerned. The variation coefficient is less than 1% with the optical method as opposed to 3% with the compression technique.     

Determination of Average Wall Thickness of Mesoporous Silica

Mesoporous silica formed by the condensation of silica oligomers around self-assembled surfactant micelle templates has recently attracted much interest owing to its potential for use in catalytic or adsorbent applications1. Much attention has been focused on characterization of its pore structure by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), N2 adsorption, small angle X-ray scattering (SAXS) et al., but seldom concerning its average wall thickness2-7. This shor…     

Mie theory 1908, on the mobile phone 2008

Hundred years ago Gustav Mie published his famous paper on the theory of light scattering by spherical particles. It has been programmed in many programming languages since invention of the computer. Nowadays with the mobile phone becoming an educational tool it would be of interest to port a Mie scattering application to a Java enabled hand set. The objective of this paper is to investigate the feasibility of porting existing Mie software to a hand held device. We will show that the mobile phone can be an advanced programming environment for the Mie theory and we will present some exemplary computational results.     

光固化快速成型中光敏树酯的光学特性对成型的影响

研究了光固化快速成型中光敏树酯的光化学过程、光敏树脂与固化光源的匹配性以及对光吸收特性和固化特征,分析了这些因素对成型过程的影响,为快速成型机的实际应用提供了参考.