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Multiple Scattering (multiple + scattering)
Selected AbstractsSeismic interferometry, intrinsic losses and Q -estimation,GEOPHYSICAL PROSPECTING, Issue 3 2010Deyan Draganov ABSTRACT Seismic interferometry is the process of generating new seismic traces from the cross-correlation, convolution or deconvolution of existing traces. One of the starting assumptions for deriving the representations for seismic interferometry by cross-correlation is that there is no intrinsic loss in the medium where the recordings are performed. In practice, this condition is not always met. Here, we investigate the effect of intrinsic losses in the medium on the results retrieved from seismic interferometry by cross-correlation. First, we show results from a laboratory experiment in a homogeneous sand chamber with strong losses. Then, using numerical modelling results, we show that in the case of a lossy medium ghost reflections will appear in the cross-correlation result when internal multiple scattering occurs. We also show that if a loss compensation is applied to the traces to be correlated, these ghosts in the retrieved result can be weakened, can disappear, or can reverse their polarity. This compensation process can be used to estimate the quality factor in the medium. [source] The dynamic behavior of magnetic colloids in suspensionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Tina Autenrieth The dynamic behavior of magnetic colloidal particles in suspension is investigated. The particles of the core,shell colloid consist of a cobalt ferrite core embedded in a silica shell and are stabilized by surface charges. As the suspension is strongly opaque to visible light, it can not be probed by dynamic light scattering techniques as a result of strong multiple scattering as well as absorption effects. Therefore, the static and dynamic behavior is probed with small-angle X-ray scattering and X-ray photon correlation spectroscopy (XPCS), respectively. Using XPCS, we are able to study the diffusion coefficient of an opaque colloidal system as a function of the scattering vector. In this paper, we report on the behavior of the colloidal system in the absence of an external magnetic field, meaning that the magnetic moments of the particles are oriented randomly. We find no evidence for magnetic interactions in the static data, while the dynamic XPCS data deviate very significantly from the predictions of model calculations. [source] Fractal structure of basic silica gels with low Ca contentJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000F. Gaboriaud Several gels were produced by addition of low amounts of calcium ions to strongly basic silico-alkaline sols. These gels, previously studied by small-angle x-ray scattering (SAXS), small-angle neutron scattering (SANS) and elastic light scattering (ELS), were analysed over a wide range of scattering vectors extending from 8 x 10,4Å,1 up to 2 x 10,4Å. The joint use of various scattering techniques allowed us the simultaneous characterisation of coarse, medium and fine structural features of the studied gels. Clear discrepancies between SANS and earlier ELS results were attributed to effects of multiple scattering on light scattering experiments. The experimental results demonstrate that the studied gels are composed of aggregates exhibiting a fractal structure within a scale range extending from less than 10 to more than 1000 Å, with the same fractal dimension over the whole scale range. The fractal dimension and so the mechanism of aggregation depend on the initial sol composition and Ca content. The mechanism responsible for gel formation in precursor sols with low calcium concentration ([Ca2+] = 0.3 mol.L,1) is reaction limited cluster-cluster aggregation (RLCA). [source] Evaluation of double-crystal SANS data influenced by multiple scatteringJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000aroun Evaluation of small-angle neutron scattering (SANS) data is often complicated by multiple scattering effects if large particles of relatively high volume fraction have to be studied and dilution or contrast reduction is impossible. The use of pin-hole SANS instruments is often limited due to the contradictory requirements of high resolution and short wavelength needed to keep scattering contrast as low as possible. Double crystal (DC) SANS diffractometers of Bonse-Hart and bent-crystal type are useful alternatives in such cases, as they permit reaching very high resolution with thermal neutrons. A method for SANS data evaluation suited to DC instruments is presented. It includes the common scheme of the indirect Fourier transformation method, but takes multiple scattering into account. The scattering medium is described by the frequency function g(x) defined as the cosine Fourier transform of slit-smeared data. Although a simplistic model of polydisperse spheres is used to represent g(x), resulting g(x) function and some integral parameters are independent of this model. Tests on simulated data show, that the method reproduce well true values of microstructural parameters, though systematic errors are observed in the cases when the unscattered part of incident beam completely disappears. If the scattering power Low and high order light scattering in particulate mediaLASER PHYSICS LETTERS, Issue 8 2004I. V. Meglinski Abstract We present the results of a theoretical study providing details of propagation of laser radiation within disperse randomly inhomogeneous intermediately single-to-multiple scattering media. A quantitative analysis of scattering orders in the transition from single to multiple scattering is presented. Crossed source-detector fiber optics geometry used to separate the intensity of single scattering from higher scattering orders. The results demonstrate good agreement between analytical and Monte Carlo techniques. This validates the use of the Monte Carlo approach in the intermediate single-to-multiple scattering regime. The method used can be applied to verify analytical results against experiment via the Monte Carlo calculations that include imperfections of the experiment. (© 2004 by ASTRO, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Resolving Concentrated Particle Size Mixtures Using Dynamic Light ScatteringPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2007Michael Kaszuba Abstract Dynamic light scattering (DLS) is a technique used for measuring the size of molecules and particles undergoing Brownian motion by observing time-dependent fluctuations in the intensity of scattered light. The measurement of samples using conventional DLS instrumentation is limited to low concentrations due to the onset of a phenomenon called multiple scattering. The problems of multiple scattering have been addressed in a light scattering instrument incorporating non- invasive backscatter optics (NIBS). This novel optic arrangement maximizes the detection of scattered light while maintaining signal quality and allows for measurements of turbid samples. This paper discusses the ability of backscatter detection to accurately determine particle sizes at 1,%w/v sample concentrations and demonstrates the correct resolution of different size populations using a series of latex standard mixtures with known volume ratios. The concentration of 1,%w/v is much higher than can be measured on conventional dynamic light scattering instruments. [source] Two-wavelength inversion of multiply scattered soft X-ray intensities to charge densityACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2009J. C. H. Spence A method is described for reconstructing the two-dimensional real-space charge density of an isolated object from measurement of the soft X-ray transmission diffraction pattern when it is affected by strong multiple scattering. The Bloch-wave scattering-matrix approach is used to show that the diffracted amplitude depends only on a simple product of X-ray wavelength and sample thickness (unlike the case of relativistic electron diffraction) under reasonable approximations. The multislice formulation then gives the effect of a small change in wavelength, which involves only single scattering. Dynamical diffraction patterns are recorded at two adjacent wavelengths, phased by iterative methods, transformed to real space and divided to give a single-scattering wavefunction. This can then be used to produce a charge-density map. The extension of the method to tomography is discussed. Consideration is first also given to the possibility that absorption due to the photoelectric effect may be so severe for soft X-rays that multiple elastic scattering becomes so much less probable than photoelectric absorption that it may be neglected entirely. A discussion of signs in soft X-ray, positron and electron multiple-scattering theory is given. [source] Quantitative structure retrieval using scanning transmission electron microscopyACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2005S. D. Findlay A method is described that reconstructs the projected object potential using data recorded in the coherent imaging mode of a scanning transmission electron microscope. The technique is applicable in the presence of multiple scattering. It is not required that the thickness is known. Model examples exploring the nature of the data set required, the stability of the algorithm and the limitations on resolution are provided. [source]
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