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When tapping a blast furnace, a break-through of gas through the taphole at the end of a cast needs to be prevented, both to preserve a healthy state of the taphole and to prevent gas and dust from escaping into the environment. In this paper, two acoustic techniques are presented that can be used to prevent gas emissions from the taphole at the end of a cast. The first approach is by using the spectral analysis of the recorded data, the second approach uses a neural network to recognize the popping sounds that announce the slag–gas interface is approaching the taphole level. It was found that with both methods the end of the cast is detected about 4–2 min before the cast is ended.

The refractory thickness of the blast furnace hearth is a critical parameter for the safe operation of a blast furnace. A replacement of the refractory comes with high costs and, therefore, unnecessary repairs should be avoided. A promising method to estimate the refractory thickness is the impact-echo method. For the interpretation of impact-echo, often, the peaks in the spectrum of the measured signal are associated with the echo from an interface. In this paper, it is shown that this method should be used with care when applied to multi-layered structures. An alternative approach is presented for the calculation of the thickness of multi-layered structures. This method solves the wave equation based on transmission line theory. The formula is checked against 2D finite element analysis and for simple layered structures, good agreement is found. Three cases are simulated using finite element models. Both the impact-echo method and the proposed method overestimate the refractory thickness.

Cooperation for public goods poses a dilemma, where individuals are tempted to free ride on others’ contributions. Classic solutions involve monitoring, reputation maintenance and costly incentives, but there are important collective actions based on simple and cheap cues only, for example, unplanned protests and revolts. This can be explained by an Ising model with the assumption that individuals in uncertain situations tend to conform to the local majority in their network. Among initial defectors, noise such as rumors or opponents’ provocations causes some of them to cooperate accidentally. At a critical level of noise, these cooperators trigger a cascade of cooperation. We find an analytic relationship between the phase transition and the asymmetry of the Ising model, which in turn reflects the asymmetry of cooperation and defection. This study thereby shows that in principle, the dilemma of cooperation can be solved by nothing more than a portion of random noise, without rational decision-making.

The zeta potential is one of the most important parameters influencing the electrokinetic coupling. Most reservoir rocks are saturated or partially saturated by natural water containing various types of ions (mostly monovalent and divalent ions). Therefore, understanding how the zeta potential behaves for mixtures of electrolytes is very important. In this work, measurements of the zeta potential for four different silica-based samples saturated by seven different mixtures of monovalent and divalent electrolytes are then carried out at a fixed ionic strength. It is seen that the magnitude of the measured zeta potential decreases with increasing divalent cation fraction. The experimental results are then explained by a model developed for mixtures of monovalent and divalent electrolytes. The result shows that the theoretical model is able to reproduce the main trend of the variation of the zeta potential with divalent cation fractions. Additionally, the model can fit the experimental data reported in literature well for reasonable values of the input parameters.

Streaming potential in rocks is the electrical potential developing when an ionic fluid flows through the pores of rocks. The zeta potential is a key parameter of streaming potential and it depends on many parameters such as the mineral composition of rocks, fluid properties, temperature etc. Therefore, the zeta potential is different for various rocks and liquids. In this work, streaming potential measurements are performed for five rock samples saturated with six different monovalent electrolytes. From streaming potential coefficients, the zeta potential is deduced. The experimental results are then explained by a theoretical model. From the model, the surface site density for different rocks and the binding constant for different cations are found and they are in good agreement with those reported in literature. The result also shows that (1) the surface site density of Bentheim sandstone mostly composed of silica is the largest of five rock samples; (2) the binding constant is almost the same for a given cation but it increases in the order KMe(Na+) < KMe(K+) < KMe(Cs+) for a given rock.References Corwin R. F., Hoovert D.B., 1979. The self-potential method in geothermal exploration. Geophysics 44, 226-245. Dove P.M., Rimstidt J.D., 1994. Silica-Water Interactions. Reviews in Mineralogy and Geochemistry 29, 259-308. Glover P.W.J., Walker E., Jackson M., 2012. Streaming-potential coefficient of reservoir rock: A theoretical model. Geophysics, 77, D17-D43. Ishido T. and Mizutani H., 1981. Experimental and theoretical basis of electrokinetic phenomena in rock-water systems and its applications to geophysics. Journal of Geophysical Research, 86, 1763-1775. Jackson M., Butler A., Vinogradov J., 2012. Measurements of spontaneous potential in chalk with application to aquifer characterization in the southern UK: Quarterly Journal of Engineering Geology & Hydrogeology, 45, 457-471. Jouniaux L. and T. Ishido, 2012. International Journal of Geophysics. Article ID 286107, 16p. Doi:10.1155/2012/286107. Kim S.S., Kim H.S., Kim S.G., Kim W.S., 2004. Effect of electrolyte additives on sol-precipitated nano silica particles. Ceramics International 30, 171-175. Kirby B.J. and Hasselbrink E.F., 2004. Zeta potential of microfluidic substrates: 1. Theory, experimental techniques, and effects on separations. Electrophoresis, 25, 187-202. Kosmulski M., and Dahlsten D., 2006. High ionic strength electrokinetics of clay minerals. Colloids and Surfaces, A: Physicocemical and Engineering Aspects, 291, 212-218. Lide D.R., 2009, Handbook of chemistry and physics, 90th edition: CRC Press. Luong Duy Thanh, 2014. Electrokinetics in porous media, Ph.D. Thesis, University of Amsterdam, the Netherlands. Luong Duy Thanh and Sprik R., 2016a. Zeta potential in porous rocks in contact with monovalent and divalent electrolyte aqueous solutions, Geophysics, 81, D303-D314. Luong Duy Thanh and Sprik R., 2016b. Permeability dependence of streaming potential coefficient in porous media. Geophysical Prospecting, 64, 714-725. Luong Duy Thanh and Sprik R., 2016c. Laboratory Measurement of Microstructure Parameters of Porous Rocks. VNU Journal of Science: Mathematics-Physics 32, 22-33. Mizutani H., Ishido T., Yokokura T., Ohnishi S., 1976. Electrokinetic phenomena associated with earthquakes. Geophysical Research Letters, 3, 365-368. Ogilvy A.A., Ayed M.A., Bogoslovsky V.A., 1969. Geophysical studies of water leakage from reservoirs. Geophysical Prospecting, 17, 36-62. Onsager L., 1931. Reciprocal relations in irreversible processes. I. Physical Review, 37, 405-426. Revil A. and Glover P.W.J., 1997. Theory of ionic-surface electrical conduction in porous media. Physical Review B, 55, 1757-1773. Scales P.J., 1990. Electrokinetics of the muscovite mica-aqueous solution interface. Langmuir, 6, 582-589. Behrens S.H. and Grier D.G., 2001. The charge of glass and silica surfaces. The Journal of Chemical Physics, 115, 6716-6721. Stern O., 1924. Zurtheorieder electrolytischendoppelschist. Z. Elektrochem, 30, 508-516. Tchistiakov A.A., 2000. Physico-chemical aspects of clay migration and injectivity decrease of geothermal clastic reservoirs: Proceedings World Geothermal Congress, 3087-3095. Wurmstich B., Morgan F.D., 1994. Modeling of streaming potential responses caused by oil well pumping. Geophysics, 59, 46-56.

In nature, liquids often circulate in channels textured with leaflets, cilia, or porous walls that deform with the flow. These soft structures are optimized to passively control flows and have inspired the design of novel microfluidic and soft-robotic devices. Yet, the relationship between the geometry of the soft structures and the flow properties remains so far poorly understood. Here, taking inspiration from the lymphatic system, we devise millifluidic valves, dressed with asymmetric soft leaflets that feature on-demand asymmetric flow properties, which we harness to induce flow rectification and pumping. We demonstrate that the functional mechanism at play involves an interplay between geometry, asymmetry, and fluid-structure interaction-induced nonlinearity. Our results open the way to a better characterization of biological leaflet malformations and to more accurate control of flows for microfluidics and soft-robotic systems.

Electrokinetic phenomena are the result of a coupling between a fluid flow and an electric current flow in porous rocks. The zeta potential is an important parameter that influences the electrokinetic coupling. Most reservoir rocks are saturated or partially saturated by natural water containing various types of ions. Therefore, it is important to understand how the zeta potential and therefore the electric double layer (EDL) behave for different types of ions or electrolytes. Types of electrolytes influence the zeta potential most by affecting the surface charge — by changing the thickness of the EDL and the exact location of the shear plane. To study the dependence of the zeta potential on various electrolytes, we have carried out streaming potential measurements for consolidated rock samples saturated by monovalent and divalent electrolytes. From streaming potential coefficients, the zeta potential is obtained for different systems of electrolytes and rocks. The experimental results of silica-based rocks are then compared with theoretical models. For 1:1 or 1:2 electrolytes, a theoretical model for the zeta potential that has been available in literature is used. For 2:2 or 2:1 electrolytes, we have developed a new model to calculate the Stern potential and the zeta potential. The comparison found that the theoretical models can explain the main behavior of the zeta potential against types of electrolytes and types of silica-based rocks. The results show that the zeta potential for monovalent electrolytes is higher than that for divalent electrolytes. The zeta potential of the silica-based samples is higher than that of the nonsilica-based samples when they are saturated by the same types of electrolyte.

Large density fluctuations developing near the phase transition point of the binary mixture affect physical parameters directly related to the electrokinetic coupling coefficient. Here the first electrokinetic measurements for a porous rock sample are carried out with a critical binary mixture of triethylamine-water, especially around the phase transition point. From the measured streaming potential coefficient, the zeta potential is obtained for the critical composition. The results show that there is no anomaly in the streaming potential coefficient as the temperature approaches the demixing temperature. It is also seen that the streaming potential coefficient and the zeta potential in magnitude decreases with increasing temperature. This observation is opposite to what has been observed in literature. It means that the properties of the electric double layer for the mixtures are different from those for aqueous electrolytes. Additionally, the zeta potential for the critical composition is predicted to fluctuate around the critical point.

In theory, the streaming potential coefficient depends not only on the zeta potential but also on the permeability of the rocks that partially determines the surface conductivity of the rocks. However, in practice, it is hard to show the permeability dependence of streaming potential coefficients because of the variation of zeta potential from sample to sample. To study permeability dependence of streaming potential, including the effects of the variation of the zeta potential and surface conductance due to the difference in mineral compositions between samples, we perform measurements on 12 consolidated samples, including natural and artificial samples saturated with 7 different NaCl solutions to determine the streaming potential coefficients. The results have shown that the streaming potential coefficients strongly depend on the permeability of the samples for low fluid conductivity. When the fluid conductivity is larger than than 0.50 S/m for the natural samples or 0.25 S/m for the artificial ceramic samples, the streaming potential coefficient is independent of permeability. This behavior is quantitatively explained by a theoretical model.

Particulate fillers are often used to enhance the properties of soft materials; polymer composites often contain nanometer-sized particles to improve reinforcement, for example. The rationale for using nanometer-sized particles remains unclear, however, and classical micromechanical models cannot account for a scale dependent reinforcement. The systems studied here reveal that the reinforcement increases with decreasing filler size. A new relation is proposed, based only on the particle size, volume fraction, and relative moduli of filler and matrix, that describes the experimental results for reinforcement of both filled rubbers and a model system. (C) 2015 Elsevier Ltd. All rights reserved.

We study the ergodic -- non-ergodic transition in a generalized Dicke model with independent co- and counter rotating light-matter coupling terms. By studying level statistics, the average ratio of consecutive level spacings, and the quantum butterfly effect (out-of-time correlation) as a dynamical probe, we show that the ergodic -- non-ergodic transition in the Dicke model is a consequence of the proximity to the integrable limit of the model when one of the couplings is set to zero. This can be interpreted as a hint for the existence of a quantum analogue of the classical Kolmogorov-Arnold-Moser theorem. Besides, we show that there is no intrinsic relation between the ergodic -- non-ergodic transition and the precursors of the normal -- superradiant quantum phase transition., 5 pages, 4 figures

The statistical properties of wave propagation in classical chaotic systems are of fundamental interest in physics and are the basis for diagnostic tools in materials science. The statistical properties depend in particular also on the presence of time reversal invariance in the system, which can be verified independently by time reversal reconstruction experiments. As a model system to test the combination of statistical properties with the ability to perform time reversal reconstruction we investigated chaotic systems with time reversal invariance using ultrasonic waves in aluminum cavities. After excitation of the samples with a short acoustic pulse the reverberation responses were recorded and analyzed. In the analysis of the spectral density of the recorded responses we explicitly included the fact that not all resonances are detected. Reversibility of the excited wave dynamics in the cavity after a time delay was studied by reconstruction of the excitation pulse in time reversal experiments. The statistical properties of resonance frequencies in the cavities were obtained from the reverberant responses. The distribution of the transmission intensities displays random division of intensity between cavity waves in narrow frequency bands. The distribution of frequency spacing between neighboring cavity resonances and the spectral rigidity agree with the predictions for the Gaussian Orthogonal Ensemble. This agreement is achieved if a fraction of typically 25 percent of resonances is not detected in the experiment. The normalized amplitude of the pulse that is reconstructed in the time reversal experiments decays exponentially with the time delay between the original excitation pulse and the end of the reversed oscillation track. The exponential behavior exists for time delays longer than the inverse of the nearest neighbor resonance spacing.

We studied the effect of sodium chloride on the phase behaviour of the symmetric triblock copolymer F68 in water using direct visual observation, viscometry, small-angle x-ray scattering and microscopy. We found that salt has a destabilizing effect. The transitions from unimer to micellar solution and from micellar solution to BCC micellar crystal occurred some 20??C lower in 1?M NaCl than in the salt-free system. Salt also induced a region of liquid?liquid coexistence in the phase diagram at F68 concentrations ?wt%, with the lower critical solution temperature (or critical point) occurring at ~80??C in 1?M NaCl. At this salt concentration and , liquid?liquid phase separation becomes metastable. A homogeneous micellar solution at this temperature first separated into coexisting dilute and dense micellar liquids, and then the dense liquid would transform into a transparent () and turbid () mesophase. We tentatively identified these as the BCC cubic and lamellar (L?) phases respectively. A more complex sequence of observations at a Pluronic concentration of 34?wt% confirms this picture. A phase diagram for F68 in 1?M NaCl consistent with all of our observations is proposed, as well as a 'rule of thumb' for interpreting the effect of salt on Pluronic phase behaviour.

We studied the spontaneous emulsification and droplet growth mechanism in trans-anethol/water/ethanol solutions, also known as the beverage ouzo, using dynamic light scattering spectroscopy. This simple ternary mixture is a generic example of a system that forms microemulsions spontaneously when brought into the two-phase region. The volume fraction of the dispersed phase was found to profoundly affect the growth rates of the droplets, which is a new finding that has not been predicted by the Lifshitz-Slyozov-Wagner theory. Time-dependent measurements show that the droplet growth is governed by Ostwald ripening (OR), and no coalescence was observed. Furthermore, the OR rates increase with increasing oil concentration at low alcohol content. We attribute this behavior to enhanced droplet-droplet interactions. At high ethanol concentrations, we found that the measured rates decreased as the oil concentration increased. The OR growth mechanism completely correlates with changes in droplet size. The kinetics of droplet growth shows that the ripening has a saturation limit at a droplet radius of about 1.5 mum. Thus, formed emulsions remain stable for months.

A four channel scaler for counting applications has been designed and built using a standard high transfer rate parallel computer interface bus parallel data card. The counter section is based on standard complex programmable logic device integrated circuits. With a 200 MHz Pentium based host PC a sustained counting and data transfer with channel widths as short as 200 ns for a single channel is realized. The use of the multichannel scaler is demonstrated in dynamic light scattering experiments. The recorded traces are analyzed with wavelet and other statistical techniques to obtain transient changes in the properties of the scattered light.

Nanosized filler particles enhance the mechanical properties of polymer composites in a size-dependent fashion. This is puzzling, because classical elasticity is inherently scale-free, and models for the elasticity of composite systems never predict a filler-size dependence. Here, we study the industrially important system of silica-filled rubbers, together with a well-characterized model-filled crosslinked gel and show that at high filler content both the linear and nonlinear elastic properties of these systems exhibit a unique scaling proportional to the cube of the volume fraction divided by the particle size. This remarkable behavior makes it possible to predict the full mechanical response of particle-filled rubbers for small but finite deformations based solely on the rheology of the matrix and the size and modulus of the filler particles.

We have performed enhanced backscattering experiments in a high gain random laser, under circumstances where a stationary theory predicts the laser intensity to diverge. Above the laser threshold the observed backscatter cone changes only gradually, not showing any signs of the divergence. We present measurements and theory-generalized laser equations with a diffusive transport term for pump and laser light-to explain the observed behavior. The population dynamics prevent an indefinite growth of the intensity. Time dependence is essential for a theory of random lasers above the laser threshold.

We investigate the hydrodynamic interaction in suspensions of charged colloidal silica spheres. The volume fraction as well as the range of the electrostatic repulsion between the spheres is varied. Using a combination of dynamic x-ray scattering, cross-correlated dynamic light scattering, and small angle x-ray scattering, the hydrodynamic function Hq is determined experimentally. The effective hydrodynamic interactions are found to be screened, if the range of the direct interaction is relatively long and the static density correlations are strong. This observation of effective hydrodynamic screening is in marked contrast to hard-sphere-like systems. Colloidal suspensions have intriguing static and dynamic properties due to their composite nature and the mesoscopic length scales involved. Colloids interact by direct forces, such as electrostatic or hard-sphere repulsions, and hydrodynamic forces mediated by the suspending fluid [1,2]. Whereas the static properties of colloidal suspensions are strikingly similar to those of molecular fluids, the important role of the suspending medium leads to significant differences in the dynamical behavior. The complex viscoelastic and diffusional properties of colloidal suspensions depend on the interplay between direct and hydrodynamic interactions. This interplay is governed by the ratio of the different length scales in the system [3], such as particle radius, interparticle distance, and the range of the interactions. Unraveling these fascinating effects is

We have performed optical reflectivity experiments and band structure diffraction calculations on fcc photonic crystals, consisting of air spheres in titania ( $\mathrm{TiO}{}_{2}$). The spectra reveal Bragg peaks whose large widths agree well with the calculations. The peaks overlap in many directions, causing the propagation of light to be limited by Bragg reflection to $45%$ of the $4\ensuremath{\pi}$ solid angle. This illustrates that the air-sphere crystals interact so strongly with light that an unprecedented limitation in the directions of propagation of light in photonic crystals is achieved.

We present near infrared total transmission measurements through samples of randomly packed silicon powders. At different wavelengths we analyze in detail the scattering properties and the effects of residual absorption. The lowest value of kls, where k is the wave vector and ls is the scattering mean free path, is 3.2. We also observe that kls is nearly constant over a wide wavelength range. This phenomenon is associated with the high polydispersity of the particles. We use the energy density coherent potential approximation to explain our measurements.

r 3 divergence at the origin. To incorporate these microscopic interactions local-field corrections are introduced. The approach is still macroscopic in nature, but the electric field at the radiating dipole, the local field, is different from the macroscopic field to incorporate local interactions. Macroscopic derivations of the local-field correction often imply the use of a cavity around the radiating dipole. The specific choice of the cavity is subtle matter [10], greatly complicating the interpretation of these models. Two limiting cases for a local-field model have been proposed. The empty-cavity model [11], in which the atom is inside a real empty spherical cavity in the dielectric, leads to

Seismoelectric effects and streaming potentials play an important role in geophysical applications. The key parameter for those phenomena is the streaming potential coupling coefficient, which is, for example, dependent on the zeta potential of the interface of the porous rocks. Comparison of an existing theoretical model to experimental data sets from available published data for streaming potentials has been performed. However, the existing experimental data sets are based on samples with dissimilar fluid conductivity, pH of pore fluid, temperature, and sample compositions. All those dissimilarities may cause the observed deviations. To critically assess the models, we have carried out streaming potential measurement as a function of electrolyte concentration and temperature for a set of well-defined consolidated samples. The results show that the existing theoretical model is not in good agreement with the experimental observations when varying the electrolyte concentration, especially at low electrolyte concentration. However, if we use a modified model in which the zeta potential is considered to be constant over the electrolyte concentration, the model fits the experimental data well in a whole range of concentration. Also, for temperature dependence, the comparison shows that the theoretical model is not fully adequate to describe the experimental data but does describe correctly the increasing trend of the coupling coefficient as function of temperature.

We determined orientational relaxation times for rhodamine 700 dye in glycerol-water mixtures using time-resolved fluorescence depolarization. It appears that the orientational relaxation time varies linearly with the viscosity of the solvent between 1 and 60 cP, in accordance with the Perrin-Stokes-Einstein model with stick boundary conditions. Previously others have found that for two anionic dyes in glycerol-water and a cationic dye in glycerol-ethylene glycol mixtures, the orientational relaxation time becomes less sensitive to the viscosity at very high viscosities (>25 cP at least). We discuss the influence of dye and solvent on the relation between orientational relaxation time and viscosity, which suggests that the relaxation time as a function of viscosity can be scaled on a common curve.

We present results of experiments on the transport of light through thin random media. Total transmission and time-resolved propagation measurements were performed using strongly scattering samples of varying thickness $L$. For $L/\ensuremath{\ell}l8$, where $\ensuremath{\ell}$ is the transport mean free path, the observed decay times from the long-time exponential behavior exhibit strong deviations from diffusion theory and radiative transport theory, whereas the total transmission measurements do not. For the thinnest sample $(L/\ensuremath{\ell}\ensuremath{\simeq}2)$ a reduction of the diffusion coefficient with a factor of 2 was observed.

The influence of photonic band structures on optical diffraction has been studied with colloidal crystals with large refractive index ratios up to 1.45 and polarizibilities per volume as large as 0.6. It is found that the apparent Bragg spacings are strongly dependent on the wavelength of light. The dynamical diffraction theory that correctly describes weak photonic effects encountered in x-ray diffraction also breaks down. Two simple models are presented that give a much better description of the diffraction of photonic crystals. @S01631829~96!06523-X#

Reliable phase‐sensitive time‐resolved interferometry with ultrashort pulsed lasers is performed with the use of a closed scanning Michelson interferometer in combination with a fixed Mach–Zehnder interferometer at the front end. The technique is based on measuring the full phase and frequency properties of the pulse distortion of an ultrashort optical pulse introduced by linear or nonlinear interaction with a sample. The necessary stability and reproducibility to perform an interferometric measurement is provided by a commercially available Fourier transform spectrometer enabling time‐resolved measurements from the IR well into the visible part of the optical spectrum. The feasibility of the technique is demonstrated by measuring the distortion introduced by an etalon and a surface‐plasmon polariton.

We present results of an experimental study on the effect of the inclusion of ferroelectric thiourea particles in paraelectric amorphous KBr on the ferroelectric phase transition. The phase transition as a function of temperature has been observed with optical second‐harmonic generation (SHG) of infrared light. The Curie temperature Tc shows a minimum as a function of the volume fraction x of thiourea in the composites at x=0.4. We describe the experimentally observed density dependence of the Curie temperature in a phenomenological mean‐field model.

We quantify the effects of axial diffusion and lateral flow on the decorrelation of the Fourier-domain OCT signal. The local and fast measurement of random and directional motion of particles is aimed to quantify tissue perfusion. © OSA 2012.

We present simulations of the decorrelation rate for a high and a low coherence light source in heterodyne light scattering geometry. Light scatters on an ensemble of particles of which the particle trajectories are calculated using a forced-diffusion model. The low coherence signal is constructed in the Fourier domain (as in Fourier-domain optical coherence tomography).

We present results of an experimental study on the reaction kinetics of a one-dimensional diffusion-reaction system, on a picosecond to millisecond time scale. Tetramethylammonium manganese trichloride (TMMC) is a perfect model system to study this problem. Time-resolved luminescence of TMMC has been measured over nine decades in time. The nonexponential shape of the luminescence decay curves depends strongly on exciting laser power. This is shown to result from a fusion reaction (A+A\ensuremath{\rightarrow}A) between photogenerated excitons, which is very well described by the diffusion-limited single-species fusion model for initial exciton densities 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ (fraction of the number of sites). At higher initial exciton densities the diffusion process, and thus the reaction rate, is significantly influenced by the heat produced in the fusion reaction. This is supported by Monte Carlo simulations.

We present theoretical and experimental results of the leading order angular correlations of second harmonic light generated inside random media, for both the transmission and reflection geometries. We find the striking result that correlations in reflection of the second harmonic light scales with the sample thickness L, in sharp contrast to the corresponding short-range correlation function in reflection of the fundamental light in the linear scattering regime, which scales with mean free path ${\mathit{l}}^{\mathrm{*}}$.

We describe a new method to measure the decorrelation rate of the optical coherence tomography (OCT) magnitude simultaneously in space and time. We measure the decorrelation rate of the OCT magnitude in a Fourier-domain OCT system for a large range of translational diffusion coefficients by varying the sphere diameter. The described method uses the sensitivity advantage of Fourier-domain OCT over time-domain OCT to increase the particle diffusion imaging speed by a factor of 200. By coherent gating, we reduce the contribution of multiple scattering to the detected signal, allowing a quantitative study of diffusive particle dynamics in high concentration samples. We demonstrate that this technique is well suited to image diffusive particle dynamics in samples with a complex geometry as we measure the morphology and diffusive particle dynamics simultaneously with both high spatial and high temporal resolution.

We show experimentally that the electron distribution of a laser-heated metal is a InonthermalR distribution on the time scale of the electron-phonon (e-ph) energy relaxation time ${\mathrm{\ensuremath{\tau}}}_{\mathit{E}}$. We measured ${\mathrm{\ensuremath{\tau}}}_{\mathit{E}}$ in Ag and Au films as a function of lattice temperature (10--300 K) and laser-energy density (0.3--1.3 J ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$), combining femtosecond optical transient-reflection techniques with the surface-plasmon polariton resonance. Calculations support the experimental result that the nonthermal distribution leads to a IslowerR e-ph energy relaxation process below room temperature, compared to the thermalized limit.

The technique of accumulated photon echo is used in combination with a high-pressure diamond anvil cell to measure the splitting of the $^{4}$${\mathit{A}}_{2}$ ground state and the one-phonon spontaneous decay rate of the 2A\ifmmode\bar\else\textasciimacron\fi{}${(}^{2}$E) level at 1.5 K in ruby up to 4.3 GPa of hydrostatic pressure. The $^{4}$${\mathit{A}}_{2}$ ground-state splitting is found to be 0.383\ifmmode\pm\else\textpm\fi{}0.001 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at ambient pressure, and increases with a slope of +(6\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$/GPa. The spontaneous decay rate of 2A\ifmmode\bar\else\textasciimacron\fi{}${(}^{2}$E) increases only weakly with pressure. The pressure dependences of both quantities are accounted for in terms of the trigonal-field and spin-orbit-coupling parameters.

Accurate time-resolved stimulated Raman measurement of anomalous line broadening of a vibrational excitation weakly coupled to a lattice mode which shows critical slowing down is presented. Dephasing of the Raman-active internal ${\mathit{A}}_{1\mathit{g}}$ CN stretching mode in ferroelectric ${\mathrm{K}}_{4}$Fe(CN${)}_{6}$\ensuremath{\cdot}${3\mathrm{H}}_{2}$O is found to result from a superposition of energy-exchange dephasing from coupling to the internal ${\mathit{T}}_{1\mathit{g}}$ Fe-C?N bending mode and pure dephasing from coupling to the (tunneling motion of the) crystal water. Anomalous broadening of the ${\mathit{A}}_{1\mathit{g}}$ line at the Curie temperature (248.5 K) results from critical slowing down of the water reorientational tunneling motion.

We employed the surface plasmon resonance of a thin silver film to induce and detect nonequilibrium heating of the electron gas. We measured an increase of the electron temperature of 30 – 90 K and an electron-phonon energy relaxation time of 670(70) fs.

We present a study on surfactant vesicles that spontaneously move towards an oil droplet that is deposited on a glass substrate. Tracer particles in the surfactant solution show that the motion is not self-propelled: the vesicles are entrained by a macroscopic hydrodynamic flow. Measurements of the flow velocity suggest that the flow is of diffusio-osmotic nature. The surfactant is observed to move into the oil phase which creates a gradient in ion concentration in the vicinity of the droplet. As the diffusion coefficients of the surfactant's co- and counter-ions differ, a charge separation takes place and an electric field arises. This electric field then generates a hydrodynamic flow along the charged glass substrate in which the vesicles are entrained.

In modern multiple input multiple output (MIMO) wireless communication systems arrays of antennas are employed to enhance the data transfer rate. Scattering of the waves in the medium between the antennas can actually enhance the transfer capacity by decorrelating the available channels. Here it is shown that the transfer capacity between arrays of regularly spaced antennas depends intricately on the distance between the arrays and on the arrangement of scatterers. The relevant length scale is the Talbot distance L(Talbot) =2 d2/lambda known from optics as the distance where the self-imaging occurs of coherently illuminated gratings with d the grating period and lambda the wavelength. The modulation of singular values of the channel transfer matrix occurs at fractions of L(Talbot) .

Light scattering from resonant two-level atoms on three-dimensional lattices can be described by a classical energy conserving t-matrix. The optical band structure of lattices filled with such atoms are calculated exactly in scalar approximation and displays, e.g., the formation of polariton gaps. The Einstein coefficient for spontaneous emission in a system with an inhomogeneous dielectric constant is shown to be proportional to part of the total density of states. This part is calculated for the dipolar lattice model.

In the accurate radiometric calibration of earth observation instruments, diffusers are used as “white-references”. In the frame of on-ground calibration campaigns of instruments such as SCIAMACHY, GOME2 and OMI (all using on-board diffusers), which took place at TNO TPD, a modulation of the reflectance signal in the spectral domain was discovered. This modulation appears when two spectra, recorded under slightly different conditions, are compared. This modulation, referred to here as Spectral features, reduces the accuracy of spectrometers as used in earth observation satellites. The spectral features are caused by speckle phenomena in the entrance slit of the spectrometer. The work reported here describes the origin of the spectral features, the measurements performed in order to reproduce and characterize this effect and the result of simulations performed on speckle patterns thanks to a dedicated analysis tool. A new set-up dedicated to spectral features measurements is also described.

Measurements of the angular-resolved-optical transmission through strongly scattering samples of porous gallium phosphide are described. Currently porous GaP is the strongest-scattering material for visible light. From these measurements the effective refractive index and the average reflectivity at the sample interface can be obtained. These parameters are of great importance for an accurate interpretation of optical experiments, and are for the first time determined in strongly scattering samples.

The quest for developing ever stronger interacting photonic materials has caused the birth of a widely expanding research field. Successful achievement of very strong elastic interaction between light and matter would allow demonstration of conceptually new physical phenomena, among which Anderson localization [1] and a full photonic bandgap [2, 3] are prime examples. Experimental realization of these phenomena would open new avenues in control and manipulation of light and matter [4], and could lead to fascinating new developments in quantum optics.

To determine the refractivity in situ, a time-resolved interferometric technique is used. The technique is based on cross correlating a reference pulse and a transmitted pulse from a 70-fs Ti:sapphire laser with the use of a commercially available Fourier-transform spectrometer. This approach enables us to obtain the pulse delay through the dense gas with 10-fs resolution in the refractive-index change. The resulting molecule Eu(fod), is optically excited with a pulsed, tripled Nd:YAG laser at 355 nm, and luminescence is detected in the red (614 nm). Radiative decay rates are in the convenient ms range and are recorded with a multichannel scaler. We present measurements on the radiative lifetime of Eu (fod), in supercritical CO/sub 2/ with varying refractive index. Different local field models are discussed.

The analogy between the propagation of electron waves and classical waves has led to a revival in the research of the transport of light in disordered scattering systems [1]. The first indications of the role of interference in multiple scattering has been indicated in experiments on enhanced backscattering in the late 1980’s [2]. Over the past decade many studies have been performed to characterize and understand this intricate interplay of scattering and interference [3]. The improved understanding of the optical systems stimulated the studies of the propagation of waves in disordered systems in general and applications in e.g. the field of medical imaging [4].

Anderson localization of light refers to an inhibition of wave transport in scattering media due to the interference of multiple scattered waves. We present wavelength dependent midinfrared optical transport measurements in slabs of randomly packed germanium (Ge) micron-sized particles, using a free electron laser as a tunable source of pulsed radiation. Because of their high refractive index and low absorption, Ge and similar semiconductors are excellent systems to study Anderson localization of light. To characterize the samples fully, we have employed several complementary optical techniques: total diffuse transmission, total diffuse reflection, coherent transmission, and time-resolved speckle interferometry. In this way we obtained the scattering ${(l}_{s})$ and transport (l) mean free paths, the absorption coefficient $(\ensuremath{\alpha}),$ the diffusion constant $(D),$ and the energy transport velocity ${(v}_{e}).$ These measurements have been made as a function of midinfrared wavelength, so that the scattering cross section and absorption coefficients can be varied in the same samples. We found that the Ge samples are close ${(kl}_{s}\ensuremath{\approx}3)$ to the localization transition, but still above it. Our measurements of ${l}_{s}$ and l suggest that l is renormalized due to interference at the proximity of the localization transition. We also found that the diffusion constant is significantly reduced in samples thinner than $\ensuremath{\approx}7l.$