Search results for "Rayleigh"
showing 10 items of 182 documents
Anomalous tracer diffusion in film forming colloidal dispersions
2000
Film forming colloidal dispersions can be conceived as a material composed of interpenetrating hydrophobic (polymer) and hydrophilic (partially broken interfaces) phases where the transport properties of one phase are influenced by the geometric confinement effect imposed by the other. We studied the transport properties of film forming colloidal dispersions by introducing hydrophobic dye molecules into the colloidal particles and determining their motion with forced Rayleigh Scattering as a function of length scale (grating distance A) and water content. At water contents between 18 and 3 weight percent we find signatures of anomalous tracer diffusion, namely stretched exponential decay cu…
A Multi-Phase Decode-and-Forward Transmission Protocol in Cognitive Relay Networks: Outage Analysis and Relay Power Allocation
2015
Consider an underlay cognitive relay network with multiple source and destination pairs and that a decode-and-forward scheme is adopted at the relay. We propose a multi-phase transmission protocol in this paper which involves cooperation among source, relay and destination nodes. Given perfect interference elimination before decoding at the destination nodes, we derive closed-form expressions for outage probability calculation over Rayleigh fading channels. Furthermore, the optimal relay power allocation factor which leads to minimal outage probability is determined. Numerical results reveal the conditions under which satisfactory performance can be achieved based on the proposed scheme.
Ferroelectricity and structure of BaTiO grown on YBa Cu O thin films
2000
We have investigated the crystal structure and the ferroelectric properties of BaTiO3 thin films with YBa2Cu3O \(_{7 - \delta }\) as the bottom and Au as the top electrode. Epitaxial heterostructures of YBa2Cu3O \(_{7 - \delta }\) and BaTiO3 were prepared by dc and rf sputtering, respectively. The crystal structure of the films was characterised by X-ray diffraction. The ferroelectric behaviour of the BaTiO3 films was confirmed by hysteresis loop measurements using a Sawyer Tower circuit. We obtain a coercive field of 30 kV/cm and a remanent polarisation of 1.25 μC/cm2. At sub-switching fields the capacitance of the films obeys a relation analogous to the Rayleigh law. This behaviour indica…
Oil-in-Water fL Droplets by Interfacial Spontaneous Fragmentation and Their Electrical Characterization
2019
Inkjet printing is here employed for the first time as a method to produce femtoliter-scale oil droplets dispersed in water. In particular, picoliter-scale fluorinated oil (FC40) droplets are printed in the presence of perfluoro-1-octanol surfactant at a velocity higher than 5 m/s. Femtoliter-scale oil droplets in water are spontaneously formed through a fragmentation process at the water/air interface using minute amounts of nonionic surfactant (down to 0.003% v/v of Tween 80). This fragmentation occurs by a Plateau-Rayleigh mechanism at a moderately high Weber number (10(1)). A microfluidic chip with integrated microelectrodes allows droplets characterization in terms of number and diamet…
Simultaneous photonic and excitonic coupling in spherical quantum dot supercrystals
2020
Semiconductor nanocrystals, or quantum dots (QDs), simultaneously benefit from inexpensive low-temperature solution processing and exciting photophysics, making them the ideal candidates for next-generation solar cells and photodetectors. While the working principles of these devices rely on light absorption, QDs intrinsically belong to the Rayleigh regime and display optical behavior limited to electric dipole resonances, resulting in low absorption efficiencies. Increasing the absorption efficiency of QDs, together with their electronic and excitonic coupling to enhance charge carrier mobility, is therefore of critical importance to enable practical applications. Here, we demonstrate a ge…
Easy-use and low-cost fiber-based two-color dynamic light-scattering apparatus
2011
We present a small and compact two-color cross-correlation light-scattering setup designed to study the structure and dynamics of colloidal suspensions in the regime of considerable turbidity. Using a homemade concentric four-arm goniometer, combined with fiber-optical illumination and detection devices, allows an easy and long time stable alignment-even under a temperature variation of ∼5 °C. Tests with a nearly multiple scattering free suspension of small Rayleigh scatterers show intercepts in cross correlation near 0.4 over a wide range of scattering angles from 20° to 150°. Measuring slightly turbid samples in cross-correlation mode multiple scattering is sufficiently suppressed allowin…
Polyorganosiloxane-microgels as probes for forced Rayleigh scattering
2007
We describe the synthesis of microgel spheres of 10 nm radius which are suitable as probes to study diffusion by forced Rayleigh scattering (FRS), a holographic grating technique. Those particles are obtained by a copolycondensation in microemulsion. The main advantage of organosiloxanes compared to purely organic monomers as styrene or methacrylate is the simple chemical functionalization of the particles. A rich choice of silane monomers which may be copolycondensated with the standard monomer trimethoxymethylsilane are commercially available. One of those, chlorobenzyltrimethoxysilane, is used as a coupling agent to attach the photoreactive dye orthonitrostilbene (ONS) to the microgel sp…
Particle characterization using multiple scattering decorrelation methods: hard-sphere model system
2000
Applying static light scattering experiments, we characterize colloidal particles that are used as model hard-sphere systems in experiments investigating their crystallization kinetics. The particles comprise of a compact core of poly(methyl methacrylate) and short polymer hairs grafted onto the surface. We use a contrast variation procedure to determine the refractive index variation within the particles and observe that one component of the binary mixture used as a solvent penetrates the particles and masks completely the small polymer hairs. Making use of the determined refractive index variation, we obtain the average particle radius and its polydispersity from measurements of the parti…
Photoelectric fields in doped lithium niobate crystals
2019
Photoinduced light scattering (PILS) in nominally pure stoichiometric and congruent lithium niobate single crystals (LiNbO3), and ones doped with B³⁺, Cu²⁺, Zn²⁺, Mg²⁺, Gd³⁺, Y³⁺, Er³⁺ cations was studied. All crystals have a relatively low effect of photorefraction and are promising materials for frequency conversion, electro-optical modulators and shutters. It was found that the photovoltaic and diffusion fields for some crystals have a maximum at a wavelength of 514.5 nm. All the crystals studied are characterized by a maximum of the integral intensity of the speckle structure of the PILS at a wavelength of 514.5 nm.
Stable two -dimensional spatial solitons in heavy metal oxide glasses
2007
In this Communication, a stable self-confined propagation with ps near-infrared (NIR) pulses and over several Rayleigh lengths is demonstrated for the first time . Multiphoton absorption is shown to saturate the self-focusing response in a novel glass of the ternary system Nb2O5-O2-PbO (NPG) exhibiting a high refractive index (2-2.1) in the NIR and an energy gap of 3.52 eV. NPG belongs to the family of heavy metal oxides, widely studied for its fast and high nonlinearity in the infrared.