Dissertations / Theses on the topic 'Multiple scattering'
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Nicholls, G. K. "Coherent multiple parton scattering." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358698.
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Chen, Xiaojun. "Multiple Scattering from Bubble Clouds." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_theses/36.
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Multiple scattering effects from bubble clouds are investigated in this study. A high performance, general purpose numerical tool for multiple scattering calculations is developed. This numerical tool is applied in three computational scenarios in this study. The total scattering cross section of a bubble cloud is investigated. Numerical results indicate that the resonant frequency of the bubble cloud is much lower than that of a single bubble. The variation of resonant frequency of multiple scattering is also studied. It is found that the resonant frequency decreases as the number of bubbles increases, or as the void fraction of the bubble cloud decreases. Phase distributions of bubble oscillations in various multiple scattering scenarios are presented. It is found that, at resonance, the bubbles synchronize to the same phase, which is indicative of the lowest mode of collective oscillation. At wave localization, half of the bubbles oscillate at phase 0 while the other half oscillate at phase Pi. An intuitive interpretation of this behavior is given.
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Li, Jun. "Coherent multiple scattering effect in DIS." [Ames, Iowa : Iowa State University], 2007.
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Broky, John. "Inverse Problems in Multiple Light Scattering." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5608.
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The interaction between coherent waves and material systems with complex optical properties is a complicated, deterministic process. Light that scatters from such media gives rise to random fields with intricate properties. It is common perception that the randomness of these complex fields is undesired and therefore is to be removed, usually through a process of ensemble averaging. However, random fields emerging from light matter interaction contain information about the properties of the medium and a thorough analysis of the scattered light allows solving specific inverse problems. Traditional attempts to solve these kinds of inverse problems tend to rely on statistical average quantities and ignore the deterministic interaction between the optical field and the scattering structure. Thus, because ensemble averaging inherently destroys specific characteristics of random processes, one can only recover limited information about the medium. This dissertation discusses practical means that go beyond ensemble averaging to probe complex media and extract additional information about a random scattering system. The dissertation discusses cases in which media with similar average properties can be differentiated by detailed examination of fluctuations between different realizations of the random process of multiple scattering. As a different approach to this type of inverse problems, the dissertation also includes a description of how higher-order field and polarization correlations can be used to extract features of random media and complex systems from one single realization of the light-matter interaction. Examples include (i) determining the level of multiple scattering, (ii) identifying non-stationarities in random fields, and (iii) extracting underlying correlation lengths of random electromagnetic fields that result from basic interferences. The new approaches introduced and the demonstrations described in this dissertation represent practical means to extract important material properties or to discriminate between media with similar characteristics even in situations when experimental constraints limit the number of realizations of the complex light-matter interaction.Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
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Voisey, Ruth. "Multiple wave scattering by quasiperiodic structures." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/multiple-wave-scattering-by-quasiperiodic-structures(1c366ad1-443a-4667-9d03-db77487ab1d1).html.
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Understanding the phenomenon of wave scattering by random media is a ubiquitous problem that has instigated extensive research in the field. This thesis focuses on wave scattering by quasiperiodic media as an alternative approach to provide insight into the effects of structural aperiodicity on the propagation of the waves. Quasiperiodic structures are aperiodic yet ordered so have attributes that make them beneficial to explore. Quasiperiodic lattices are also used to model the atomic structures of quasicrystals; materials that have been found to have a multitude of applications due to their unusual characteristics. The research in this thesis is motivated by both the mathematical and physical benefits of quasiperiodic structures and aims to bring together the two important and distinct fields of research: waves in heterogeneous media and quasiperiodic lattices. A review of the past literature in the area has highlighted research that would be beneficial to the applied mathematics community. Thus, particular attention is paid towards developing rigorous mathematical algorithms for the construction of several quasiperiodic lattices of interest and further investigation is made into the development of periodic structures that can be used to model quasiperiodic media. By employing established methods in multiple scattering new techniques are developed to predict and approximate wave propagation through finite and infinite arrays of isotropic scatterers with quasiperiodic distributions. Recursive formulae are derived that can be used to calculate rapidly the propagation through one- and two-dimensional arrays with a one-dimensional Fibonacci chain distribution. These formulae are applied, in addition to existing tools for two-dimensional multiple scattering, to form comparisons between the propagation in one- and two-dimensional quasiperiodic structures and their periodic approximations. The quasiperiodic distributions under consideration are governed by the Fibonacci, the square Fibonacci and the Penrose lattices. Finally, novel formulae are derived that allow the calculation of Bloch-type waves, and their properties, in infinite periodic structures that can approximate the properties of waves in large, or infinite, quasiperiodic media.
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Wubs, Cornelis Martijn. "Quantum optics and multiple scattering in dielectrics." [S.l : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2003. http://dare.uva.nl/document/70167.
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Berksoy-Bölük, Ebise Mualla. "Multiple scattering calculations of large inorganic systems." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74288.
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Self-consistent field multiple scattering (SCF-MS) calculations have been performed on the aluminium trihalides, AlX$ sb3$ (X = F, Cl, Br, I) and their dimers, Al$ sb2$X$ sb6$ and on the large organometallic compounds diphenyltin(IV) dichloride and diphenyllead(IV) dichloride monomers and dimers. All these molecules have nuclear quadrupole resonance (n.q.r.) active nuclei and strong or weak intermolecular halogen interaction. In addition, diphenyltin(IV) dichloride has a Mossbauer active $ sp{119}$Sn nuclei to study the isomer shift and quadrupole splitting. Calculations used the Vosko-Wilk-Nusair(VWN) exchange-correlation potential in addition to Slater's X$ alpha$ exchange potential and also a quasi-relativistic wavefunction for the heavy nuclei in these molecules. The VWN and X$ alpha$ n.q.r. results are compared for the aluminium trihalides. The non-relativistic and relativistic calculations which are very important for the hyperfine interactions are compared for diphenyltin(IV) dichloride and the calculated relativistic Mossbauer isomer shift and quadrupole splitting agree well with experiment. The electric field gradients, which are very sensitive to the charge distribution around the nuclei in the molecules, gave very important information, using the n.q.r. and Mossbauer results, about the intermolecular halogen interactions in these molecules, supporting the conclusions arrived at using the one-electron energies and the HOMO-LUMO gap, and from the wavefunction contours and density maps. The relative Lewis acidity order and ionization potentials are also studied in the aluminium trihalides. Qualitative interpretation and agreement with experiment were found whenever experiment was available. Electronic structure and n.q.r. comparison of the diphenyltin(IV) dichloride and diphenyllead(IV) dichloride monomers and dimers lead to the conclusion that the diphenyltin(IV) dichloride is a monomer and the diphenyllead(IV) dichloride is a polymer.
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FILHO, ERNANDES VIEIRA. "ANALYSIS OF MULTIPLE SCATTERING IN CASSEGRAIN ANTENNAS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1988. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=14490@1.
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TELECOMUNICAÇÕES BRASILEIRAS S/AEsta dissertação tem por objetivo analisar, a partir da Teoria Geométrica da Difração, o efeito de espalhamento mútuo entre as superfícies refletoras no diagrama de irradiação de antenas Cassegrain. São apresentados resultados numéricos evidenciando todas as contribuições de campos difratados de até 3ª. ordem.
It is the purpose of this dissertation to analyse, via the Geometrical theory of Diffraction, the effect of mutual scattering between reflector surfaces on the radiation pattern of Cassegrain antennas. Numerical results highlight the contributions of the complete set of up to 3(rd) order diffracted fields.
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Greis, Jan R. "Multiple coulomb scattering of muons in MICE." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/97733/.
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The Muon Ionisation Cooling Experiment (MICE) was designed to provide the first demonstration of muon ionisation cooling by passing a muon beam through a cooling channel consisting of low-Z absorber material as well as radio-frequency (RF) cavities, with the net effect of a reduction in transverse momentum spread at constant total momentum. The performance that can be achieved in such a cooling channel depends on both energy loss and multiple coulomb scattering in the absorber, the latter of which is currently not understood to very high precision for muons. Verification of muon multiple scattering algorithms - especially in low-Z materials - is therefore crucial for accurate modelling of a muon ionisation cooling channel, which would be used in future facilities such as a Neutrino Factory or a Muon Collider. A track matching algorithm was implemented in order to combine locally reconstructed detector output for further processing and analysis. Multiple coulomb scattering of muons in the lithium hydride (LiH) MICE absorber has been studied in the presence of magnetic fields using a convolution method, which has the advantage over typically used deconvolution methods in that it does not depend on the chosen value of the regularisation strength parameter. It does, however, only allow comparison between data and Monte Carlo, rather than direct extraction of the “true" scattering distributions. The presence of magnetic fields - while providing significantly superior momentum resolution - introduces additional systematic errors, mainly due to the uncertainties the field maps used. The results of this analysis provide support for the use of convolution methods and suggest that scattering algorithms in GEANT4 have significantly improved since the time of MuScat (which was an experiment designed specifically to measure muon scattering in a variety of materials). There is some indication that they may have changed from vastly overestimating to slightly underestimating large angle scatters though the uncertainties on the final results are insufficiently small to make definite statements on this point.
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Nugent, John Columba. "Multiple Coulomb scattering in the MICE experiment." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/7984/.
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The International Muon Ionisation Cooling Experiment (MICE) aims to give the first demonstration of ionisation cooling. MICE will use a low Z absorber to first reduce the momentum of a muon beam; then use a series of radio-frequency (RF) cavities to restore its longitudinal momentum. This action will reduce the overall phase-space volume of the muon beam. The goal of MICE is to reduce the emittance of a muon beam by 5\% and to measure the change in emittance to a precision of 1%. In 2011 MICE took data in its Step I configuration with the goal of understanding the muon beam that will serve the MICE experiment. In order to evaluate the expected performance of the beam using extensive simulation data the MICE user software had to be installed on the Grid. A G4beamline model of the MICE muon beam was updated and validated with Step I data and used for production jobs on the Grid. The results presented in this thesis demonstrate that the simulation is in good agreement with data. These data were also used to determine the pion contamination in the MICE muon beam using the Time-Of-Flight (TOF) and Kloe-light (KL) detectors. The measurement of ionisation cooling in MICE relies on the selection of a pure sample of muons that traverse the experiment. To make this selection, the MICE Muon Beam is designed to deliver a beam of muons with less than ~1% contamination. The upper limit for the pion contamination measured in this thesis is less than 1.4% at 90% C.L., including systematic uncertainties. A similar procedure applied to the G4Beamline and MAUS Monte Carlo simulation yields a pion contamination of less than 1.7% at 90\% C.L., including statistical and systematic errors. The expectation from the simulated MICE Muon Beam is for a contamination of (0.22 +/- 0.01)%. Therefore, the MICE Muon Beam is able to meet the stringent pion-contamination requirements for the study of ionisation cooling. In 2015 and 2016, MICE took data in its Step IV configuration giving the first measurement of multiple scattering with the MICE apparatus. In this thesis the results of the measurement of the scattering of muons in gaseous xenon and lithium hydride are reported. The motivation for the gaseous xenon measurement is to benchmark Multiple Coulomb Scattering (MCS) in a high-Z material, in order to perform further measurements of MCS in the MICE experiment. From this baseline the same analysis was applied to the lithium hydride data, a material for which it is essential to accurately model the MCS for the demonstration of ionisation cooling for muon acceleration. Results from this analysis are compared to GEANT4 simulations and to predictions from an analytical formula advocated by the Particle Data Group (PDG).
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Wallin, Marina. "Multiple electromagnetic scattering by spheres using the T-matrix formulation." Thesis, Umeå universitet, Institutionen för fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-105606.
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Low observable technology is used in order to prevent detection, or to delay detection. Radar cross section is an important parameter in aircraft survivability since it measures how detectable an object is with radar. To find the radar cross section Maxwell's equations are solved numerically in the time-domain using a finite difference scheme. This numerical method called Finite Difference Time Domain is very suitable for structures including complex materials. However, this numerical method needs to be verified for large scale simulations, due to numerical dispersion errors. Therefore it is desirable to verify the accuracy of the numerical simulations. In this project, the analytical solution to the multiple scattering by two spheres is implemented using the T-matrix formulation. The analytical solution to the scattering problem is first validated with the analytical Mie-series solution then compared to the Finite Difference Time Domain implementation. The results imply that the difference between the numerical and analytical solution is larger for higher frequencies and larger computational volumes.Smygteknik används för att förhindra detektering, eller för att fördröja detektion av ett flygplan. Radarmålarea är en viktig parameter för skyddsprestanda hos flygplan eftersom den mäter hur detekterbar ett föremål är med radar. För att hitta radarmålarean löses Maxwells ekvationer numeriskt i tidsdomänen med hjälp av ett finit differensschema. Den numeriska metoden som kallas Finita differensmetoden i tidsdomän, är mycket lämplig för strukturer med komplexa material. Den numeriska metoden behöver valideras för storskaliga simuleringar eftersom det förekommer felaktigheter på grund av den numeriska dispersionen. Därför är det önskvärt att kontrollera riktigheten av de numeriska simuleringarna. I detta projekt, är den analytiska lösningen till multipelspridning av två sfärer implementerad med hjälp av T-matrismetoden. Den analytiska lösningen på spridningsproblemet valideras först mot den analytiska Mie-serielösningen och sedan jämförs den med resultatet av simuleringarna med Finita differensmetoden i tidsdomän. Resultaten antyder att skillnaden mellan den numeriska och analytiska lösningen är större för högre frekvenser och större beräkningsvolymer.
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Knotts, Michael E. "Experimental studies of multiple scattering by rough surfaces." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/30269.
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Heitner, Gabriele Heike. "Multiple scattering for diffraction enhanced X-ray imaging." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976522632.
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Azizoglu, Suha Alp. "Time Domain Scattering From Single And Multiple Objects." Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609413/index.pdf.
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The importance of the T-matrix method is well-known when frequency domain scattering problems are of interest. With the relatively recent and wide-spread interest in time domain scattering problems, similar applications of the T-matrix method are expected to be useful in the time domain. In this thesis, the time domain spherical scalar wave functions are introduced, translational addition theorems for the time domain spherical scalar wave functions necessary for the solution of multiple scattering problems are given, and the formulation of time domain scattering of scalar waves by two spheres and by two scatterers of arbitrary shape is presented. The whole analysis is performed in the time domain requiring no inverse Fourier integrals to be evaluated. Scattering examples are studied in order to check the numerical accuracy, and demonstrate the utility of the expressions.
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Turek, Gabriella. "Multiple scattering from submerged bodies dissimilar acoustical properties." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/17056.
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Hang, Zhihong. "Light organization of small particles by multiple scattering /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202008%20HANG.
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Barnett, David M. "On multiple optical scattering in a scanning nephelometer." Thesis, Boston Spa, U.K. : British Library Document Supply Centre, 2000. http://ethos.bl.uk/OrderDetails.do?did=1&uin=uk.bl.ethos.323870.
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Langridge, David J. "Multiple scattering theory for supported nanoscale metal chains." Thesis, University of Bath, 2002. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250942.
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Lange, Arnaud Guy Lucien. "A multilevel multipole method for modelling elastic-wave multiple scattering in fibre-reinforced composites." Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405583.
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Mujat, Claudia. "MULTIPLE SCATTERING OF LIGHT IN INHOMOGENEOUS MEDIA AND APPLICATIONS." Doctoral diss., University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4455.
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Light scattering-based techniques are being developed for non-invasive diagnostics of inhomogeneous media in various fields, such as medicine, biology, and material characterization. However, as most media of interest are highly scattering and have a complex structure, it is difficult to obtain a full analytical solution of the scattering problem without introducing approximations and assumptions about the properties of the system under consideration. Moreover, most of the previous studies deal with idealized scattering situations, rarely encountered in practice. This dissertation provides new analytical, numerical, and experimental solutions to describe subtle effects introduced by the properties of the light sources, and by the boundaries, absorption and morphology of the investigated media. A novel Monte Carlo simulation was developed to describe the statistics of partially coherent beams after propagation through inhomogeneous media. The Monte Carlo approach also enabled us to study the influence of the refractive index contrast on the diffusive processes, to discern between different effects of absorption in multiple scattering, and to support experimental results on inhomogeneous media with complex morphology. A detailed description of chromatic effects in scattering was used to develop new models that explain the spectral dependence of the detected signal in applications such as imaging and diffuse reflectance measurements. The quantitative and non-invasive characterization of inhomogeneous media with complex structures, such as porous membranes, diffusive coatings, and incipient lesions in natural teeth was then demonstrated.Ph.D.
Optics and Photonics
Optics and Photonics;
Optics
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Gibbs, Andrew James. "Numerical methods for high frequency scattering by multiple obstacles." Thesis, University of Reading, 2017. http://centaur.reading.ac.uk/73458/.
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For problems of time harmonic wave scattering, standard numerical methods (using piecewise polynomial approximation spaces) require the computational cost to grow with the frequency of the problem, in order to maintain a fixed accuracy. This can make many problems of practical interest difficult or impossible to solve at high frequencies. The Hybrid Numerical Asymptotic Boundary Element Method (HNA BEM) overcomes this by enriching the approximation space with oscillatory basis functions, in such a way that accuracy may be maintained with a computational cost that grows only modestly with frequency. HNA methods have previously been developed for a range of problems, including screens in two and three dimensions, also convex, non-convex and penetrable polygons in two dimensions. To date, all HNA methods have been developed for problems of plane wave scattering by a single obstacle. The key aim of this thesis is to extend the HNA method to multiple obstacles. A range of extensions to the HNA method are made in this thesis. Previous HNA methods for convex polygons use an approximation space on two overlapping meshes, here we use HNA on a single mesh. This single-mesh approach is easier to implement, and we prove that the frequency-dependence of the size of the approximation space is the same as for the overlapping mesh. We generalise HNA theory to provide a priori error estimates for a broader range of incident fields than just the plane wave, including point sources, beam sources, and Herglotz-type incidence. We also extend the HNA ansatz to include multiple obstacles. In addition to the development of HNA methods, we also consider other ideas and developments related to multiple scattering problems. This includes the first (to the best knowledge of the author) mesh and frequency explicit condition for wellposedness of Galerkin BEM for multiple scattering. We investigate numerical implementation of Embedding Formulae, which provide the far-field pattern for any incident plane wave, given the far-field patterns induced by a small (frequency independent) number of plane waves. We establish points at which a naive implementation of the theory can cause numerical instabilities and present alternative, numerically stable Embedding Formulae. We also extend the Embedding Formulae to produce the far-field pattern of any Herglotz-type wave. The recently developed Tmatrom method, a numerically stable T-matrix method, is explored as an alternative means of extending the HNA method from single to multiple obstacles. Tmatrom typically requires a number of single scattering problems to be solved, and this number grows (more than) linearly with the frequency of the problem. Using the numerically stable Embedding Formulae, we show that Tmatrom can be applied by solving a number of problems that depends only on the geometry of the obstacle, and not the frequency of the incident wave.
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Steponavicius, Raimundas. "Estimation of chemical information in scattering media using radiative transfer theory to remove multiple scattering effects." Thesis, University of Newcastle Upon Tyne, 2011. http://hdl.handle.net/10443/1094.
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Two approaches for removing multiple light scattering effects using the radiative transfer theory in order to improve the performance of multivariate calibration models have been proposed namely: partial correction of multiple scattering effects and full correction of multiple scattering effects. The first approach is applicable for predicting the concentration of a scattering-absorbing (particulate) component as well as the concentration of an absorbing only species. The second approach is applicable only for estimation of the concentration of an absorbing only species. Application of the first approach to a simulated four component system showed that it will lead to calibration models which perform appreciably better than when empirically scatter corrected measurements of total transmittance or total reflectance are used. The validity of the method was tested experimentally using a two-component (polystyrene-water) and a fourcomponent (polystyrene - ethanol - water - deuterated water) system. The proposed methodology of partial correction showed significantly better performance than the empirically pre-processed direct measurements (total transmittance, total reflectance and collimated transmittance) in all experiments. The results of applying the full correction approach showed that despite all errors the performance of PLS calibration model built on the corrected bulk absorption coefficient was marginally better than the performance of PLS model built on uncorrected bulk absorption coefficient. Finally, the benchmarking analysis revealed that there is still a significant potential for an improvement in the prediction performance in the quantitative analysis of turbid samples.
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Tse, Ka-ki. "Multiple scattering of waves by dense random distributions of particles for applications in light scattering by noble metal nanoparticles and microwave scattering by terrestrial snow /." access full-text access abstract and table of contents, 2009. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ee-b23750558f.pdf.
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Thesis (Ph.D.)--City University of Hong Kong, 2009."Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references.
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Linder, Tomas, Torbjörn Löfqvist, Coppel Ludovic Gustafsson, Magnus Neuman, and Per Edström. "Lateral light scattering in fibrous media." Mittuniversitetet, Avdelningen för naturvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-18657.
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Lateral light scattering in fibrous media is investigated by computing the modulation transfer function (MTF) of 22 paper samples using a Monte Carlo model. The simulation tool uses phase functions from infinitely long homogenous cylinders and the directional inhomogeneity of paper is achieved by aligning the cylinders in the plane. The inverse frequency at half maximum of the MTF is compared to both measurements and previous simulations with isotropic and strongly forward single scattering phase functions. It is found that the conical scattering by cylinders enhances the lateral scattering and therefore predicts a larger extent of lateral light scattering than models using rotationally invariant single scattering phase functions. However, it does not fully reach the levels of lateral scattering observed in measurements. It is argued that the hollow lumen of a wood fiber or dependent scattering effects must be considered for a complete description of lateral light scattering in paper.PaperOpt
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Cheng, Chung-Chieh. "Propagation of transverse optical coherence in random multiple-scattering media /." view abstract or download file of text, 1999. http://wwwlib.umi.com/cr/uoregon/fullcit?p9955916.
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Thesis (Ph. D.)--University of Oregon, 1999.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 131-135). Also available for download via the World Wide Web; free to University of Oregon users. Address: http://wwwlib.umi.com/cr/uoregon/fullcit?p9955916.
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VIEIRA, RENATO J. R. "Laser a base de pó de neodímio com granulação nanometrica." reponame:Repositório Institucional do IPEN, 2011. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10014.
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Made available in DSpace on 2014-10-09T12:33:49Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:04:36Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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Norman, Rachel. "Simultaneous detection of multiple explosives using surface enhanced Raman scattering." Thesis, University of Strathclyde, 2016. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27074.
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There remains a continuing threat of terrorist/insurgent attacks on military/civilian personnel and key strategic infrastructures both within the UK mainland and in operational theatres. The development of a novel, innovative, low cost, field deployable bionanosensor, which will have the capability to detect low levels of explosive in a multiplexed fashion is required. The use of the specific interaction between small molecules and biological capture molecules such as antibodies coupled with the detection technique of surface enhanced Raman scattering (SERS) allows a ‘one shot’ analysis. This research makes use of antibody functionalised silver nanoparticles for the detection of the explosives TNT, RDX and PETN by surface enhanced Raman scattering (SERS). Commercially available antibodies specific for TNT and RDX have been modified to specifically orientate ‘flat’ on the surface of silver nanoparticles bringing the target close enough to the metal surface to allow an intrinsic SERS signal of the target molecule to be obtained. Quantitative detection of TNT and RDX explosives was achieved, with pM sensitivity demonstrated for RDX. Furthermore, TNT was detected in two different types of dirt, natural and synthetic dirt in order to mimic a more realistic matrix in which TNT would be found in the field. However, for the detection of PETN, it was required to develop a method to modify a PETN antibody in-house, to specifically orientate ‘flat’ on the nanoparticles surface similarly to the commercially available antibodies. This was achieved by using carbodiimide chemistry and the antibody was purified by cartridge centrifugation and HPLC. The PETN modified antibody was then functionalised onto silver nanoparticles and detection of PETN was achieved by SERS. In addition, PCA was used to allow multiplexed analysis based on unique Raman bands for the three different explosives which could be clearly identified in the SERS spectra. Finally, TNT was detected by using magnetic nanoparticles which were functionalised with a terminal amine group in combination with FITC modified TNT antibody functionalised silver nanoparticles. This assay was designed to allow for the formation of a Meisenheimer complex in the presence of TNT, between the amine functionalised magnetic nanoparticles and the TNT. Furthermore, the TNT antibody functionalised silver nanoparticles also binds to TNT, aggregating the nanoparticles. The magnetic nanoparticles were subsequently used to remove the nanoparticle assembly from the matrix, resulting in a concentrated sample on the magnet, resulting in an increase in SERS.
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Hart, John Francis. "A new multiple scattering technique for X-ray photoelectron diffraction." Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30673.
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This thesis is concerned with the development and application of a new method of performing multiple scattering calculations of X-ray Photoelectron Diffraction (XPD) from periodic surfaces. The technique is based on the dynamical theory of Reflection High Energy Electron Diffraction (RHEED), allowing more efficient access to high photoelectron energies (1000eV and above) than is available using present calculational schemes. Convergence tests have been performed to identify the limitations of the present method. The method is applied to two overlayer systems for which XPD experimental data is available, c(2 x 2)S and c(2 x 2)O on Ni(001). For the c(2 x 2)S system, which is relatively well understood and therefore a good test system, data at four emission (take-off) angles is fitted, giving optimum agreement with the S atoms occupying hollow sites at a vertical adsorption height of between 1.30A and 1.35A. The agreement is improved slightly for the lowest two take-off angles by an outward relaxation in the top Ni-Ni layer spacing. Comparison is made with single scattering calculations for the system and the present method shown to be far superior at the lowest take-off angle. This clearly demonstrates the importance of multiple scattering at grazing emission angles. For the c(2 x 2)O system, data at two take-off angles is fitted giving optimum agreement with the O atoms in hollow sites at an adsorption height of 0.75A. By allowing a small outward relaxation in the top Ni-Ni layer spacing, an almost equally good fit to the data is found at an adsorption height of 0.80A. An offcentre bonding site which has been proposed, in which the O atoms are displaced from their hollow sites by 0.3A in the [110] direction has been considered and ruled out.
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Liu, Zunping. "Three-dimensional multiple scattering of elastic waves by spherical inclusions." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/386.
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Thomas, Stefan [Verfasser]. "Multiple scattering approach for excitations in complex systems / Stefan Thomas." Halle (Saale) : Universitäts- und Landesbibliothek Sachsen-Anhalt, Halle, Hochschulschriften, 2017. http://d-nb.info/113302243X/34.
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Wong, Gary Ka Ning. "Optical feedback and multiple frequency interaction in stimulated Brillouin scattering." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47719.
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Feldman, Andrew F. "Multiple scattering of microwaves from soil surface and vegetation canopies." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119332.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 67-71).
A multiple scattering radiative transfer model is developed for use in global retrieval algorithms of microwave geophysical parameters. This attempts to both improve soil moisture and vegetation attenuation and scattering parameter retrievals under moderate to dense canopy covers and capture the full microwave vegetation signature. The model is developed using a ray tracing method of first-order interactions with canopy constituents larger than 21 cm (e.g. woody biomass). It introduces only one new variable, [omega]₁ representing scattering from these constituents, making it almost as computationally efficient to implement as the commonly used tau-omega (zeroth-order) model. With concerns for vegetation cover changes with climate change, there is motivation to monitor vegetation cover properties and respective available surface water availability. The retrieval of microwave vegetation attenuation and scattering parameters provides a unique opportunity to monitor vegetation parameters in addition to commonly used optical remote sensing of vegetation techniques. The model is applied within the recently developed and hereby enhanced Multi-Temporal Dual Channel Algorithm (MT-DCA) framework. The algorithm is implemented over Africa using SMAP 36 km brightness temperature radiometric measurements using both zeroth and first-order radiative transfer models. The first-order radiative transfer model is determined to be more sensitive to surface emission resulting in an improved surface emission signature from retrievals. The retrieved [omega]₁ are also greatest in forests noting the presence of woody biomass and resulting in first-order emission contributing to 5% of the total emission. Consequently, changes from zeroth to first-order retrievals occur primarily in vegetated regions where [omega]₁ is non-zero. Non-zero [omega]₁ additionally results in improved fit of parameters to SMAP measurements. Without a comprehensive forest in-situ measurement campaign, it is inconclusive whether the introduced first-order radiative transfer model improves retrievals over SMAP and SMOS baseline retrievals. Additionally, further work in developing global retrieval algorithms aimed at retrieving both surface and vegetation microwave parameters amongst moderate to dense vegetation is encouraged.
by Andrew F. Feldman.
S.M.
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Mendoza, Jonathan Michael. "Nanostructures and alloys : multiple scattering and nonlinearities in phonon transport." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87962.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 95-102).
Understanding how thermal transport is affected by disorder is crucial to the prediction and engineering of novel materials suitable for thermoelectric and device applications. Ab initio methods have demonstrated accurate calculations of the lattice contribution to thermal conductivity in semiconductors and dielectrics. Effective field theories and scattering theory have been combined to model alloys and systems with embedded nanostructures. The simplest of such effective field theories, the Virtual Crystal approximation, fails to capture short-length scale information due to the inherent coarse graining of the approximation. Additionally, these methods do not take multiple scattering effects into account. In order to address these issues, Green's function methods are developed to handle multiple scattering phenomena in systems with large numbers of impurities. Explicit calculations from the Green's functions method are able to capture the deviation from the dilute alloy limit in disordered systems. Multiple scattering theory developed in this thesis allows for a more precise description of the interaction between phonons and nanostructures. The phonon Green's function is computed from the dispersion relation obtained from Density Functional Theory. Multiple scattering theory predicts resonance scattering that is not accounted for in first order theory. Understanding how these resonances behave in large disordered systems yields insight into thermal transport in alloys. When impurities become closely spaced, the resonances couple and broaden over a range of frequencies that depends upon the strength of the coupling and the number of impurities. These resonant states become significantly coupled in silicon germanium alloys of concentrations over ten percent. Scattering rates, angle dependent scattering amplitudes, and local density of states calculations are subsequently performed for nanostructured germanium slabs embedded in a silicon host. The strong coupling between the densely packed system of impurities causes significant broadening over a wide range of phonon frequencies. The strong coupling highlights the importance of using Green's functions to capture high frequency effects. Furthermore, scattering rate calculations as a function of frequency highlight the transition from the Rayleigh regime to the geometric limit. Although approximations exist that describe the low and high frequency behavior, the transition between the two regimes requires multiple scattering theory. The lowest frequency peak in the nanostructure density of states corresponds to the transition frequency between the long and short wavelength asymptotic limits. Angle dependent scattering also provides insight into the transition between the Rayleigh and high frequency limits. The scattering phase functions exhibit isotropic scattering at long wavelengths, which are characteristic of the Rayleigh regime. As phonon frequencies increase, the scattering profile takes on a much more anisotropic profile reminiscent of interfacial scattering at frequencies away from the band edge. High frequency phonon scattering is reminiscent of particle scattering off of hard boundaries.
by Jonathan Michael Mendoza.
S.M.
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Hejazi, Nooghabi Aida. "Green's function retrieval from noise correlation in multiple scattering media." Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS609.pdf.
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L'interférométrie de bruit ambiant est une approche pour estimer la réponse impulsionnelle entre deux récepteurs sans source active. Cette thèse contribue à l'évaluation de la robustesse et de la précision de la reconstruction de la fonction de Green par la corrélation du bruit ambiant dans les milieux réverbérants. Plus précisément, on distingue les rôles respectifs de la partie balistique et coda des signaux dans les corrélations. Ensuite, nous nous concentrons sur un milieu réverbérant incluant un diffuseur. Nous estimons de manière passive la force du diffuseur en utilisant l'interférométrie du bruit ambiant. Dans la dernière partie de ce travail, nous nous concentrons sur un milieu réverbérant contenant les inclusions résonantes. Notre but est d'évaluer le comportement de la corrélation dans ce type de milieu. Nous avons construit un de ces matériaux au laboratoire qui est constitué des tiges verticales à la surface d'une plaque mince élastique. Nous trouvons que les différents comportements sont bien cohérents avec les régimes qui correspondent à la bande de propagation ou interdite. Comme la partie sismique, nous appliquons la technique de corrélation aux données réelles récupérées lors de l'expérience METAFORET. Nos résultats sont sont en accord avec le comportement diffusant des arbres dans les gammes de fréquence correspondanteAmbient-noise interferometry is an approach to estimate the transient response between two receivers without an active source. The method consists of cross-correlating recordings of ambient vibrations at a pair of passive instruments that act only as receivers. This dissertation contributes to evaluating the robustness and accuracy of Green's function reconstruction by cross-correlation of noise, disentangling the respective roles of ballistic and reverberated ('coda') signals. We focus our study on a strongly reverberating medium. We conduct a suite of experiments on a highly reverberating thin duralumin plate. We find that the coda of the arrivals contribute the most to retrieval of the Green's function. We also develop an analytical model that predicts the dependence of symmetry of the cross-correlations on the number of sources. Next, we focus on a reverberating medium with a scatterer. We passively estimate the scattering strength of the scatterer by implementing ambient-noise interferometry. In the last part, we focus on a reverberating medium with locally resonant scatterers which acts as a metamaterial. Our objective is to assess the behaviour of the cross-correlation in such a medium. We build an example of such materials in the laboratory by attaching an array of rods, arranged in a sub-wavelength order, to the surface of a thin elastic plate. We find different behaviours which are consistent with the regimes that correspond to propagation band and bandgap. We next apply the cross-correlation technique to the real data obtained in METAFORET experiment. Our findings are consistent with the resonating behaviour of trees at the corresponding frequency bands
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Zhang, Song. "A spontaneous Raman scattering system for in-cylinder multiple species measurement." Thesis, Brunel University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397816.
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Li, Wen-Hao. "Significance of multiple scattering in remotely sensed images of natural surfaces /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/6743.
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Pidcott, Celeste. "Multiple scattering and particle identification in the Muon Ionisation Cooling Experiment." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/90723/.
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The Muon Ionisation Cooling experiment aims to measure the effect of passing through low Z materials on the emittance of muons. This process is dependent on energy loss and multiple scattering through the material, which is currently not well understood for muons, and so it is necessary to study these effects. These studies require muon samples with high purity, greater than 99.9% upstream of the MICE cooling channel, for which strong particle identification is required. A Global Particle Identification software framework has been developed, its performance assessed, and then applied to both Monte Carlo and MICE data. Monte Carlo studies have shown that the software can achieve the required purity. An analysis of multiple scattering of muons through Lithium Hydride has also been presented, using a method designed for the presence of magnetic fields in the cooling channel. This has been applied for Monte Carlo input in both the presence and absence of fields, and for data taken in the absence of fields, which is all of the scattering data taken thus far in MICE. The results of these studies have been compared with both the Wentzel-VI model of scattering implemented in Geant4 and with the PDG approximation for multiple scattering, which has shown that Wentzel-VI underestimates the widths of the scattering distributions, while the PDG approximation overestimates their widths, in particular the width of the distributions of the 3D space angle.
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Bozzo, Alessio <1979>. "Atmospheric radiative transfer in multiple scattering conditions. Application to NWP models." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1874/1/bozzo_alessio_tesi.pdf.
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High spectral resolution radiative transfer (RT) codes are essential tools in the study of the radiative energy transfer in the Earth atmosphere and a support for the development of parameterizations for fast RT codes used in climate and weather prediction models. Cirrus clouds cover permanently 30% of the Earth's surface, representing an important contribution to the Earth-atmosphere radiation balance.
The work has been focussed on the development of the RT model LBLMS. The model, widely tested in the infra-red spectral range, has been extended to the short wave spectrum and it has been used in comparison with airborne and satellite measurements to study the optical properties of cirrus clouds. A new database of single scattering properties has been developed for mid latitude cirrus clouds. Ice clouds are treated as a mixture of ice crystals with various habits. The optical properties of the mixture are tested in comparison to radiometric measurements in selected case studies. Finally, a parameterization of the mixture for application to weather prediction and global circulation models has been developed. The bulk optical properties of ice crystals are parameterized as functions of the effective dimension of measured particle size distributions that are representative of mid latitude cirrus clouds. Tests with the Limited Area Weather Prediction model COSMO have shown the impact of the new parameterization with respect to cirrus cloud optical properties based on ice spheres.
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Bozzo, Alessio <1979>. "Atmospheric radiative transfer in multiple scattering conditions. Application to NWP models." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1874/.
Full textAbstract:
High spectral resolution radiative transfer (RT) codes are essential tools in the study of the radiative energy transfer in the Earth atmosphere and a support for the development of parameterizations for fast RT codes used in climate and weather prediction models. Cirrus clouds cover permanently 30% of the Earth's surface, representing an important contribution to the Earth-atmosphere radiation balance.
The work has been focussed on the development of the RT model LBLMS. The model, widely tested in the infra-red spectral range, has been extended to the short wave spectrum and it has been used in comparison with airborne and satellite measurements to study the optical properties of cirrus clouds. A new database of single scattering properties has been developed for mid latitude cirrus clouds. Ice clouds are treated as a mixture of ice crystals with various habits. The optical properties of the mixture are tested in comparison to radiometric measurements in selected case studies. Finally, a parameterization of the mixture for application to weather prediction and global circulation models has been developed. The bulk optical properties of ice crystals are parameterized as functions of the effective dimension of measured particle size distributions that are representative of mid latitude cirrus clouds. Tests with the Limited Area Weather Prediction model COSMO have shown the impact of the new parameterization with respect to cirrus cloud optical properties based on ice spheres.
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Tang, Chin Hang. "Transport of light in metal nano-particle chains using a multiple scattering approach /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202008%20TANG.
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Markou, Christos. "Event topologies and multiple parton scattering processes in high energy pp⁻ collisions." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47558.
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Riley, Douglas J. "Single and multiple electromagnetic scattering by dielectric obstacles from a resonance perspective." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/71273.
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A new application of the singularity expansion method (SEM) is explored. This application combines the classical theory of wave propagation through a multiple scattering environment and the SEM. Since the SEM is generally considered a theory for surface currents on conducting scatterers, extensions are made which permit, under certain conditions, a singularity expansion representation of the electromagnetic field scattered by a dielectric scatterer. Application of this expansion is then made to the multiple scattering case using both single and multiple interactions. A resonance scattering tensor form is used for the SEM description which leads to an associated tensor form of the solution to the multiple scattering problem with each SEM pole effect appearing explicitly. The coherent field is determined for both spatial and SEM parameter random variations.
A numerical example for the case of an ensemble of lossy dielectric spheres is made. Accurate resonance expansions for the single scattering problem are derived, and resonance trajectories based on the Debye relaxation model for the refractive index are introduced. Application of the resonance expansions to the multiple scattering results for a slab containing a distribution of spheres with varying radii is made. Conditions are discussed for when the hybrid theory is appropriate.Ph. D.
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Mounaix, Mickaël. "Matricial approaches for spatio-temporal control of light in multiple scattering media." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066562/document.
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L’imagerie optique à travers des milieux diffusants, comme des milieux biologiques ou de la peinture blanche, reste un challenge car l’information spatiale portée par la lumière incidente est mélangée par les évènements multiples de diffusion. Toutefois, les modulateurs spatiaux de lumière (SLM) disposent de millions de degrés de liberté pour contrôler le profil spatial de la lumière en sortie du milieu, en forme de tavelure (speckle), avec des techniques de modulation du front d’onde. Cependant, si le laser génère une impulsion brève, le signal transmis s’allonge temporellement, car le milieu diffusant répond différemment pour les diverses composantes spectrales de l’impulsion. Nous avons développé, au cours de cette thèse, des méthodes de contrôle du profil spatiotemporel d’une impulsion brève transmise à travers un milieu diffusant. En mesurant la Matrice de Transmission Multi-Spectrale ou Résolue-Temporellement, la propagation de l’impulsion peut être totalement décrite dans le domaine spectral ou temporel. Avec des techniques de manipulation du front d’onde, les degrés de libertés spectraux/temporel peuvent être ajustés avec un unique SLM via la diversité spectrale du milieu diffusant. Nous avons démontré, de manière déterministe, la focalisation spatio-temporelle d’une impulsion brève après propagation dans un milieu diffusant, avec une compression temporelle proche de la durée initiale de l’impulsion, à différentes positions de l’espace-temps. Nous avons également démontré un façonnage contrôlé du profil temporel de l’impulsion, notamment avec la génération d’impulsions doubles. Nous exploitons cette focalisation spatio-temporelle pour exciter un processus optique non-linéaire, la fluorescence à deux photons. Cette approche ouvre des perspectives intéressantes pour le contrôle cohérent, l’étude de l’interaction lumière-matière ainsi que l’imagerie multi-photoniqueOptical imaging through highly disordered media such as biological tissue or white paint remains a challenge as spatial information gets mixed because of multiple scattering. Nonetheless, spatial light modulators (SLM) offer millions of degrees of freedom to control the spatial speckle pattern at the output of a disordered medium with wavefront shaping techniques. However, if the laser generates a broadband ultrashort pulse, the transmitted signal becomes temporally broadened as the medium responds disparately for the different spectral components of the pulse. We have developed methods to control the spatio-temporal profile of the pulse at the output of a thick scattering medium. By measuring either the Multispectral or the Time- Resolved Transmission Matrix, we can fully describe the propagation of the broadband pulse either in the spectral or temporal domain. With wavefront shaping techniques, one can control both spatial and spectral/temporal degrees of freedom with a single SLM via the spectral diversity of the scattering medium. We have demonstrated deterministic spatio-temporal focusing of an ultrashort pulse of light after the medium, with a temporal compression almost to its initial time-width in different space-time position, as well as different temporal profile such as double pulses. We exploit this spatio-temporal focusing beam to enhance a non-linear process that is two-photon excitation. It opens interesting perspectives in coherent control, light-matter interactions and multiphotonic imaging
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Erez, Ilana. "The concept of virtual events: application to the attenuation of internal multiples." Texas A&M University, 2006. http://hdl.handle.net/1969.1/4254.
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Modern seismic imaging tools for oil and gas exploration and production (E&P)
assume that seismic data contain responses only of waves that bounce (e.g., reflect,
diffract) only once at each interface in the subsurface. This type of response is called
a primary. Unfortunately, actual seismic data also contain responses of waves that
bounce at several interfaces in the subsurface. This type of response is called a
multiple.
In general, multiples in seismic data fall into two categories: (1) events that
bounce at least once at the free surface in addition to any other bounce in the sub-
surface and (2) events that do not bounce at the free surface but instead inside the
subsurface, at two or more interfaces. The first category has the greater amount of
energy; therefore most of the research and development efforts in E&P have so far
focused on attenuating this category of multiples accurately.
At present, more knowledge of the subsurface is expected from seismic imaging. To avoid any misinterpretation of these details, there is a growing need in the
E&P industry to also attenuate the second category of multiples, known as internal
multiples.
In this work I describe a new method of attenuation of internal multiples. The
method consists of predicting the internal multiples and then subtracting them from
the data. The prediction of internal multiples from seismic data is made possible by
the discovery of a new type of seismic scattering event known as a virtual event. Seismic virtual events constitute a calculational device, which is becoming an
important part of seismic data processing. Virtual events combine forward and back-
ward wave propagation in such a way that their convolution with real events allows
us to predict internal multiples.
In addition to showing how virtual events can be constructed from real seismic
events, I also show that virtual events obey physical laws, despite their counterintuitive wavepath.
I have illustrated the findings in this thesis with synthetic examples. In particu-
lar, I have shown the effectiveness of my internal-multiple-attenuation method for a
1D data set, which includes several primaries and internal multiple interferences.
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Cai, Liang-Wu 1965. "Full-scale simulation of multiple scattering of elastic waves in fiber reinforced composites." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9573.
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Stark, Holger. "Physics of inhomogeneous nematic liquid crystals colloidal dispersions and multiple scattering of light /." [S.l. : s.n.], 1999. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB8921083.
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Gerken, Jan Erik. "Modular Graph Forms and Scattering Amplitudes in String Theory." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21829.
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In dieser Dissertation untersuchen wir die Niedrigenergieentwicklung von Streuamplituden geschlossener Strings auf Einschleifenniveau (d.h. auf Genus eins) in einem zehndimensionalen Minkowski-Hintergrund mit Hilfe einer speziellen Klasse von Funktionen, den sogenannten modularen Graphenformen. Diese erlauben eine systematische Berechnung der Niedrigenergieentwicklung und erfüllen viele nicht-triviale algebraische- und Differentialgleichungen. Wir studieren diese Relationen detailliert und leiten Basiszerlegungen für eine große Zahl modularer Graphenformen her. Eines der Ergebnisse dieser Dissertation ist ein Mathematica-Paket, welches diese Vereinfachungen automatisiert.
Wir benutzen diese Techniken, um die führenden Niedrigenergieordnungen der Streuamplitude von vier Gluonen im heterotischen String auf Einschleifenniveau zu berechnen.
Für Stringamplituden auf Baumniveau bildet die Einwertigkeitsabbildung multipler Zetawerte offene Stringamplituden auf geschlossene Stringamplituden ab. Wir zeigen, dass ein bestimmter Vorschlag für die Definition einer geeigneten einschleifen-Verallgemeinerung, der sogenannten elliptische Einwertigkeitsabbildung, nicht alle Terme im heterotischen String reproduzieren kann.
Ferner studieren wir eine Erzeugendenfunktion, die vermutlich die Torusintegrale aller perturbativen Theorien geschlossener Strings enthält. Wir bestimmen eine Differentialgleichung, die von dieser Erzeugendenfunktion erfüllt wird und lösen sie mit Hilfe von pfadgeordneten Exponentialen, was auf iterierte Integrale von holomorphen Eisensteinreihen führt. Da eine ähnliche Konstruktion im offenen String zur Verfügung steht, eröffnet dies außerdem eine neue Perspektive auf die elliptische Einwertigkeitsabbildung.In this thesis, we investigate the low-energy expansion of scattering amplitudes of closed strings at one-loop level (i.e. at genus one) in a ten-dimensional Minkowski background using a special class of functions called modular graph forms. These allow for a systematic evaluation of the low-energy expansion and satisfy many non-trivial algebraic and differential relations. We study these relations in detail, leading to basis decompositions for a large number of modular graph forms which greatly reduce the complexity of the expansions of the integrals appearing in the amplitude. One of the results of this thesis is a Mathematica package which automatizes these simplifications. We use these techniques to compute the leading low-energy orders of the scattering amplitude of four gluons in the heterotic string at one-loop level. For tree-level string amplitudes, the single-valued map of multiple zeta values maps open-string amplitudes to closed-string amplitudes. The definition of a suitable one-loop generalization, a so-called elliptic single-valued map, is an active area of research and we show that a certain conjectural definition for this map, which was successfully applied to maximally supersymmetric amplitudes, cannot reproduce all terms in the heterotic string which has half-maximal supersymmetry. In order to arrive at a more systematic treatment of modular graph forms and at a different perspective on the elliptic single-valued map, we then study a generating function which conjecturally contains the torus integrals of all perturbative closed-string theories. We determine a differential equation satisfied by this generating function and solve it in terms of path-ordered exponentials, leading to iterated integrals of holomorphic Eisenstein series. Since a similar construction is available for the open string, this opens a new perspective on the elliptic single-valued map.
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Sengers, Lynn H. Ailes. "Particle shape corrections to Twersky's formalism for multiple scattering in a random particulate medium." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-06102009-063037/.
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Ba, Abdoulaye Sidiki. "Étude de la transmission acoustique de métaplaques localement résonantes." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0228/document.
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Les matériaux acoustiques super absorbants, sub-longueur d’ondes et large bande, ouvrent de nouvelles perspectives prometteuses pour l’isolation sonore. Dans ce contexte, nous avons conçu et synthétisé des structures hétérogènes comportant des microbilles sphériques de silicone poreux « ultra-lentes », distribuées dans des matrices aqueuses ou élastomériques. Dans un premier temps, nous avons démontré pourquoi la vitesse du son est aussi basse dans les silicones poreux (<100 m/s) comparativement à celle de milieux homogènes (~1000 m/s). Ce fort contraste de propriétés acoustiques entre phases étant susceptible d’induire des propriétés extrêmement diffusantes des microbilles, nous avons étudié l’impact de la nature de la matrice et de l’arrangement (aléatoire ou périodique) des microbilles sur les propriétés acoustiques d’échantillons se présentant sous forme de plaques sub-longueurs d’ondes à faces parallèles. Nous avons montré que la présence de minima prononcés dans le coefficient de transmission de ces métaplaques était pilotée par la résonance monopolaire des microbilles, et était fortement conditionnée par la nature de la matrice environnante. Enfin, toutes les mesures ultrasonores de l’étude ont été confrontées avec succès à des prédictions issues de modèles de diffusion multipleAcoustic metamaterials may behave like sub-wavelength and broadband sound-absorbers, opening thus new promising routes for sound insulation. In this context, we have designed and achieved heterogeneous structures composed of soft porous silicone rubber microbeads with ultra-low sound speeds, dispersed in various aqueous or elastomeric matrices. First, we show why the sound speed is so low in soft porous silicone rubber materials (<100m/s) in comparison with soft homogeneous materials (~1000m/s). Such a large sound-speed contrast resulting in strongly scattering properties of the microbeads, we have studied the influence of the matrix characteristics as well as the arrangement of microbeads (random or ordered) on the acoustic properties of the samples in form of sub-wavelength slabs. We have evidenced deep and wide minima of acoustic transmission due to the strong monopolar resonances of the microbeads, which strongly depend on the properties of the surrounding matrix. All our ultrasonic measurements have been compared with theoretical predictions based on various Multiple Scattering Theories, revealing an excellent quantitative agreement
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Kapodistrias, Georgios. "A theoretical and experimental study on multiple scattering from bubbles, with emphasis on scattering from a bubble located close to the air-sea interface /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/7150.
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