Relevant bibliographies by topics / Local inhomogeneities

Academic literature on the topic 'Local inhomogeneities'

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Published: 25 May 2024

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Journal articles on the topic "Local inhomogeneities"

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Batllo, J., F. Goltsman, D. Kalinin, and J. Pous. "Seismic recognition of local inhomogeneities." Pure and Applied Geophysics PAGEOPH 132, no. 4 (February 1990): 639–52. http://dx.doi.org/10.1007/bf00876811.

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Martseniuk, Yurii P., Yevhen V. Siusko, and Yurii V. Kovtun. "Using microwave refraction to determine local inhomogeneities of a rotating plasma." Nukleonika 68, no. 1 (March 1, 2023): 19–24. http://dx.doi.org/10.2478/nuka-2023-0003.

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Abstract To determine the local inhomogeneities of a rotating plasma, the method based on microwave refraction was used. The method is based on spectral and correlation analysis of the reflected signals from the rotating plasma layer at normal and inclined microwave incidence. This method allowed us to determine local inhomogeneities of plasma electron density, angles of azimuthal displacement of grooves, and its angular frequency of rotation. Using an additional 4th horn antenna, in contrast to previous works, it was possible to find and analyze two regions with azimuthal inhomogeneities in the rotating plasma. Analysis of the reflected signals shows the presence of four grooves, and the angular frequency of rotation ω = 1.16 × 104 rad/s was also determined.
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Seppenwoolde, Jan-Henry, Mathilda van Zijtveld, and Chris J. G. Bakker. "Spectral characterization of local magnetic field inhomogeneities." Physics in Medicine and Biology 50, no. 2 (January 7, 2005): 361–72. http://dx.doi.org/10.1088/0031-9155/50/2/013.

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Tkeshelashvili, Lasha. "Discrete optical soliton scattering by local inhomogeneities." Photonics and Nanostructures - Fundamentals and Applications 11, no. 1 (February 2013): 95–101. http://dx.doi.org/10.1016/j.photonics.2012.10.001.

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Duvall, T. L., and A. G. Kosovichev. "New Developments in Local Area Helioseismology." Symposium - International Astronomical Union 203 (2001): 159–66. http://dx.doi.org/10.1017/s0074180900218974.

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Several techniques are used to study local areas in helioseismology, including time-distance helioseismology, acoustic imaging/holography, and ring diagram analysis. These techniques can be used to study flows, magnetic fields, and temperature inhomogeneities. The “local” area studied can be as small as a supergranule, or as large as the entire convection zone in the case of meridional circulation as studied by Giles and colleagues. Active regions have been studied with some interesting results, with complicated flow patterns below sunspots and detectable sound speed inhomogeneities in the 10 Mm below the spots. Another interesting result is the detection of sunspots on the back side of the Sun by Lindsey and Braun using the holography technique. A confirmation of their result using the time-distance technique is presented.
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Kushch, Volodymyr I., Igor Sevostianov, and Albert Giraud. "Local fields and effective conductivity tensor of ellipsoidal particle composite with anisotropic constituents." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, no. 2207 (November 2017): 20170472. http://dx.doi.org/10.1098/rspa.2017.0472.

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An accurate semi-analytical solution of the conductivity problem for a composite with anisotropic matrix and arbitrarily oriented anisotropic ellipsoidal inhomogeneities has been obtained. The developed approach combines the superposition principle with the multipole expansion of perturbation fields of inhomogeneities in terms of ellipsoidal harmonics and reduces the boundary value problem to an infinite system of linear algebraic equations for the induced multipole moments of inhomogeneities. A complete full-field solution is obtained for the multi-particle models comprising inhomogeneities of diverse shape, size, orientation and properties which enables an adequate account for the microstructure parameters. The solution is valid for the general-type anisotropy of constituents and arbitrary orientation of the orthotropy axes. The effective conductivity tensor of the particulate composite with anisotropic constituents is evaluated in the framework of the generalized Maxwell homogenization scheme. Application of the developed method to composites with imperfect ellipsoidal interfaces is straightforward. Their incorporation yields probably the most general model of a composite that may be considered in the framework of analytical approach.
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Holý, Václav, Marcin Kryśko, and Michał Leszczyński. "Diffuse X-ray scattering from local chemical inhomogeneities in InGaN layers." Journal of Applied Crystallography 51, no. 4 (June 12, 2018): 969–81. http://dx.doi.org/10.1107/s1600576718007173.

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Diffuse X-ray scattering from random chemical inhomogeneities in epitaxial layers of InGaN/GaN was simulated using linear elasticity theory and kinematical X-ray diffraction. The simulation results show the possibility of determining the r.m.s. deviations of the local In content and its lateral correlation length from reciprocal-space maps of the scattered intensity. The reciprocal-space distribution of the intensity scattered from inhomogeneities is typical and it can be distinguished from other sources of diffuse scattering such as threading or misfit dislocations.
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REYNOLDS, JOSEPH P., GERALD J. IAFRATE, and JUN HE. "BLOCH DYNAMICS IN SPATIALLY LOCAL INHOMOGENEOUS ELECTRIC FIELDS." International Journal of High Speed Electronics and Systems 11, no. 02 (June 2001): 425–53. http://dx.doi.org/10.1142/s0129156401000903.

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The influence of local inhomogeneities on the electric field dependent properties of Bloch electrons is studied. The homogeneous electric field is described through the use of the vector potential, and the instantaneous Wannier functions of the homogeneous field dependent Hamiltonian are used as bases states to depict Bloch dynamics and properties. Model examples are treated using Slater-Koster inhomogeneities and nearest-neighbor tight-binding band structure in a one dimensional, single-band analysis. Detailed analysis is presented for the special case of a constant electric field; here the influence of localization due to the presence of the electric field is shown to clearly affect the energy spectrum of the Bloch electron for a single and double impurity configuration.
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Cabaço, M. I., M. Besnard, T. Tassaing, and Y. Danten. "Local density inhomogeneities detected by Raman scattering in supercritical hexafluorobenzene." Pure and Applied Chemistry 76, no. 1 (January 1, 2004): 141–46. http://dx.doi.org/10.1351/pac200476010141.

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The influence of the local density inhomogeneities in supercritical hexafluorobenzene C6F6 has been assessed using Raman spectroscopy. The polarized and depolarized profiles associated with the "breathing" mode of the molecule has been analyzed for the fluid in a wide density range, namely under isothermal conditions. The evolution upon the density of the band center position of the isotropic profile along the near-critical isotherm showed an anomalous behavior, characterized by a plateau in the density range (0.6 < ρ* = ρ/ρC < 1.3), which is not observed along the isotherm T* ~ 1.11. It has been interpreted as due to the existence of local-density inhomogeneities and the density enhancement factor has been evaluated. The rotational dynamics of the main symmetry axis of the molecule is governed by a diffusional process. The rotational correlation time τ2R exhibits an anomalous behavior (plateau regime) for both isotherms. These findings put in evidence the existence of local density inhomogeneities in a pure fluid and show that Raman spectroscopy is well adapted to investigate these phenomena.
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Rose, M. A., J. Barnett, D. Wendland, F. V. E. Hensling, J. M. Boergers, M. Moors, R. Dittmann, T. Taubner, and F. Gunkel. "Local inhomogeneities resolved by scanning probe techniques and their impact on local 2DEG formation in oxide heterostructures." Nanoscale Advances 3, no. 14 (2021): 4145–55. http://dx.doi.org/10.1039/d1na00190f.

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Using c-AFM and s-SNOM, we show the influence of local inhomogeneities on the LAO/STO 2DEG formation by mapping its distribution. The nanoscopic arrangement of insulating regions alters the conductive behavior down to low temperatures.
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Dissertations / Theses on the topic "Local inhomogeneities"

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Tsoulka, Polyxeni. "Local inhomogeneities in polycrystalline wide band gap Culn1-xGaxSe2 thin-films." Thesis, Nantes, 2019. http://www.theses.fr/2019NANT4009/document.

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Les cellules solaires à base de CuIn1-xGaxSe2 sont des dispositifs en couches minces permettant d’atteindre des hauts rendements de conversion photovoltaïque. Le CuIn1-xGaxSe2 est un absorbeur permettant d’adapter l’énergie de la bande interdite de la cellule solaire en changeant la teneur en Ga. Le rendement record de conversion photovoltaïque actuel a été obtenu pour x~0.3, alors que la théorie indique qu’il devrait être obtenu pour un x~0.7. L’origine de cette limite pour x élevé reste en débat. Dans cette thèse, on étudie deux origines liées aux interfaces internes de CuIn1-xGaxSe2 à savoir i) le changement d’élément ségrégé aux joints de grains pour des fortes et faibles teneurs en Ga et ii) la ségrégation défavorable du séléniure du cuivre au volume ou à la surface. Dans une première partie, une étude par premiers principes (DFT) montre que la ségrégation substitutionnelle de l’In par Ga (ou de Ga par In) n’est pas favorisée dans un joint de macle. Dans le cas plus général d’une surface notre étude sur les forces motrices de ségrégation montre qu’il est plus facile de faire ségréger une impureté d’In qui se trouve dans une matrice de CuGaSe2 que l’inverse. Dans la seconde partie, les résultats expérimentaux du CuIn1-xGaxSe2 indiquent qu’en augmentant le taux de Ga la couche devient plus inhomogène. Cela est dû aux inhomogénéités locales de concentration en Cu dans la couche. L’origine de ce phénomène est liée à la cinétique de la formation de CuGaSe2 qui est lente et à la faible diffusion du Cu et du Ga. Nous proposons une étape de relaxation supplémentaire pendant la co-évaporation de CuIn1-xGaxSe2 qui permet de faciliter la croissance des grains, d’améliorer l’homogénéité de la couche et d’atteindre l’équilibre attendu
Amongst the different semiconductor materials used as absorber layers, polycrystalline CuIn1-xGaxSe2 is one of the most promising materials in the thin-film photovoltaic technology. Due to the high efficiency, stability and band gap tunability with x, thin-film solar cells based on CuIn1-xGaxSe2 absorber layer are already industrially implemented. Moreover, in the multi-junction solar cell technology the aim of reaching higher efficiencies while keeping the fabrication costs low, makes the wide band gap indium-free CuGaSe2 absorber layer an interesting candidate as a top cell in a hybrid tandem solar cell based on c-Si bottom cell. However, the actual energy conversion efficiency strongly decreases for x larger than 0.3 and it does not follow the theoretical predictions indicating better performances for x around 0.7. The difficulty to obtain a high device performance for large x has been a worldwide question for several years and many theories have been proposed to explain the limited conversion efficiency. A possible cause of the limited CuIn1-xGaxSe2 performance for large x involves the local inhomogeneities at the inter- or intra-grain regions, since the nature of the accumulated species or compound at the interfaces can be detrimental or beneficial for the solar cell efficiency. In this thesis we investigate two possible phenomena that are likely to occur at the CIGSe interfaces i) a preferential elemental segregation at the grain boundaries and ii) the detrimental copper selenide surface segregation or bulk precipitation. In this work, the elemental segregation is investigated at equilibrium by coupling ab initio calculations and thermodynamic modeling. Our results indicate that substitutional (InGa or GaIn antisite) cannot be expected in the most frequently present interfaces such as the twin grain boundaries. A complementary and simple analysis of the main segregation driving forces was also studied in order to understand the segregation in the more general cases, such as the surface segregation. Our calculations show that In is slightly more favorable to segregate at the surface rather than Ga. The experimental analysis on CuIn1-xGaxSe2 films at intermediate and large x reveals that increasing x the Cu content in the CuIn1-xGaxSe2 film can locally differ, creating detrimental Cu-enriched domains within the bulk of the film. This phenomenon is due to the slow kinetics at large x and the reduced Cu and Ga interdiffusion. In this work, we propose a strategy to avoid these local inhomogeneities by applying a relaxation stage during the CuIn1-xGaxSe2 deposition process. This stage improves the photovoltaic performance, since it leads to a long-range equilibration, grain growth, annihilation of voids and a close to stoichiometry bulk which was expected
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Bobenko, N. G., V. E. Egorushkin, N. V. Melnikova, and A. N. Ponomarev. "The Electron Density of States in Graphene on a Substrate with a Local Structural Disorder." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35212.

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In this paper we have obtained expression for the contribution to DOS with the help of the method of the temperature Green functions. Multiple elastic electron scattering by impurities and structural inhomogeneities in graphene on a substrate, has been taken into account. The resulting expression for the contribution to DOS depends on temperature, concentration of impurities and the type of short-range order (structural heterogeneity). When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35212
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Liu, Xuerong. "X-ray diffuse scattering studies of the local structural inhomogeneities in high temperature superconductors." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3339219.

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Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed February 6, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 126-131).
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Chakraborty, Akash. "Effets des inhomogénéités nanométriques sur les propriétés magnétiques de systèmes magnétiques dilués." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00947328.

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Cette thèse est principalement consacrée à l'étude des inhomogénéités de taille nanométrique dans les systèmes magnétiques désordonnés ou dilués. La présence d'inhomogénéités, souvent mise en évidence dans de nombreux matériaux, donne lieu à des propriétés physiques intéressantes et inattendues. La possibilité de ferromagnétisme à l'ambiante dans certains matéraux a généré un grand enthousiasme en vue d'application dans la spintronique. Cependant, d'un point de vue fondamental la physique de ces systèmes reste peu explorée et mal comprise. Dans ce manuscrit, on se propose de fournir une étude théorique complète et détaillée des effets des inhomogenéités de tailles nanométriques sur les propriétés magnétiques dans les systèmes dilués. Tout d'abord, on montre que l'approche RPA locale autocohérente est l'outil le plus adapté et fiable pour un traitement approprié du désordre et de la percolation. Nous avons implémenté cet outil et étudié dans un premier temps, les propriétés magnétiques dynamiques d'un modèle Heisenberg dilué (couplages premiers voisins) sur un reseau cubique simple. Nous avons reproduit précisémment la disparition de l'ordre à longue portée au seuil de percolation et comparé ce travail à des études précédentes. Dans le cadre d'un Hamiltonien minimal (modèle $V$-$J$) nous avons ensuite étudié en détails les propriétés magnétiques de (Ga,Mn)As (température critique, excitations magnétiques, stiffness,..). Nous avons obtenu de très bon accords avec les calculs textit{ab initio} et les résulats expérimentaux. Finalement, nous avons étudié les effets des inhomogénéités dans les sytèmes dilués. Nous avons montré, qu'inclure des inhomogenéités pourrait s'averer être une voie très efficace et prometteuse pour dépasser l'ambiante dans de nombreux matériaux. Nous avons pu obtenir une augmentation colossale de la température critique dans certains cas comparée à celle des systèmes dilués homogènes. Nous avons atteint une augmentation de 1600% dans certains cas. Nous avons également analysé les effets des inhomogénéités sur les courbes d'aimantations, elles sont inhabituelles et peu conventionelles dans ces systèmes. Les spectres d'excitations magnétiques sont très complexes, avec des structures très riches, et présentent de nombreux modes discrets à haute energie. De plus, nos calculs ont montré que la ''spin-stiffness" est fortement supprimé par l'introduction d'inhomogénéités. Il reste encore de nombreuses voies à explorer, ce travail devrait servir de base à de futures études théoriques et expérimentales des systèmes inhomogènes.
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Reinhardt, Jörg [Verfasser]. "Inversion for local stress field inhomogeneities / vorgelegt von Jörg Reinhardt." 2007. http://d-nb.info/984776834/34.

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Kuen-HsienWu and 吳坤憲. "Measurement and Modeling of Local Seebeck Coefficient in Thermoelectric Inhomogeneities." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/58082402134254649541.

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博士
國立成功大學
機械工程學系碩博士班
99
A Potential Seebeck Microprobe apparatus is described that a profile of Seebeck coefficients can be detected on a material sample surface for thermopower investigations. Due to its spatially resolved limit on detecting small inhomogeneities of dopants or composition changes, we here propose a constructive combination of ANSYS coupled-field numerical simulation and digital signal processing in order to improve the spatial resolution by deconvolution algorithm. The relevant transfer function, obtained from numerical calculations, was validated and successfully applied to theoretical and experimental data. The improvement in detecting thermoelectric bulk material sample was demonstrated, in which the spatial resolution of Potential Seebeck Microprobe is increased by the inverse of measured Seebeck signal. Also, the systemic preconditions (tip size, signal capture time and scan period), which are the main factors to affect the captured thermovoltages, were discussed in detail. In addition, for detecting thermoelectric film material sample, we found that the heat flow penetrating into substrate causes an additional Seebeck distortion, leading to a low spatial resolution. Therefore, a correct transfer function, according to the characteristic of Potential Seebeck Microprobe as a low-pass filter, is next proposed for the successful spatial resolution improvement. Finally, we provide an efficient route to use model order reduction, which reduces the transient three-dimensional analysis time, for searching the required transfer functions. Thus, we can fast perform significant improvements beyond the current measured resolution of Potential Seebeck Microprobe, which is the unique technique to detect the thermopower of thermoelectric inhomogeneities.
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Rakić, Aleksandar [Verfasser]. "On the influence of local inhomogeneities on cosmological observables : from galaxies to the microwave background / Aleksandar Rakić." 2007. http://d-nb.info/987842021/34.

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Book chapters on the topic "Local inhomogeneities"

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Bettin, A., and D. Gross. "Crack Propagation in Materials with Local Inhomogeneities under Thermal Load." In Lecture Notes in Engineering, 85–93. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-88479-5_9.

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Alex Polkanov, Yury. "A set of proposals to overcome the crisis in Atmospheric Remote Sensing Technologies." In Revolutionizing Earth Observation - New Technologies and Insights [Working Title]. IntechOpen, 2024. http://dx.doi.org/10.5772/intechopen.1004255.

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This chapter summarizes proposals to expand the capabilities of lidar measurements of the Earth’s atmosphere as a structural stratified medium with complex thermodynamics. The generalized structure of the revealed, statistically stable horizontal optical inhomogeneities of the surface layer and their dynamics are taken as an informative indicator of the thermodynamic stability of the atmosphere in the zone even beyond the limits of measurements. A special statistical method for analyzing the two identified structures is used. It is based on the separate fixation and statistical averaging of the intervals between local maxima and minima of the lidar backscattering signal and the analysis of the time dynamics of such an interval component of the signal during the night, under anticyclone conditions. It assumed that this approach makes it possible to identify certain statistically stable structures of atmospheric inhomogeneities of varying connectivity, depending on the overall thermodynamic stability of the atmosphere. In addition, a specific method is tested to search for emerging and temporarily stable anomalies of such a structure of atmospheric inhomogeneities, but associated with a violation of the thermodynamic stability of the atmosphere. Such a filtration method (identification of a certain anomaly against the background of an extended organized structure of inhomogeneities) showed high efficiency in model experiments compared to standard filtration methods.
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Plerrehumbert, R. T. "The Effect of Local Baroclinic Instability on Zonal Inhomogeneities of Vorticity and Temperature." In Advances in Geophysics, 165–82. Elsevier, 1986. http://dx.doi.org/10.1016/s0065-2687(08)60038-2.

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Cobbold, Richard S. C. "Ultrasound Imaging Arrays." In Foundations of Biomedical Ultrasound, 413–91. Oxford University PressNew York, NY, 2006. http://dx.doi.org/10.1093/oso/9780195168310.003.0007.

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Abstract Ultrasound images differ from their optical counterpart in that they map the local acoustic properties of the medium such as the density and compressibility as opposed to the optical properties. They are subject to distortion from a variety of sources, including diffraction, attenuation, dispersion, and inhomogeneities in the medium. Imaging arrays enable acoustic images to be obtained without the need for mechanical scanning of single-element transducers, and they can do so at a sufficiently high frame rate that avoids significant motion distortion caused by fast-moving structures such as those in the heart. Developments in transducers and array design, together with new signal-processing techniques, have enabled major improvements to be made in ultrasound contrast, resolution, dynamic range, frame rate, and signal-to-noise ratios (SNR). This chapter is the first of two concerned with the theory, design, and application of arrays for 2-D and 3-D imaging. It begins with a brief historical overview that describes how ultrasound imaging evolved from pulse-echo metal flaw detectors and was influenced by the techniques developed for radar during World War II. Simple CW excited 1-D arrays consisting of point source elements will first be examined. This leads to the concepts of beam focusing and steering using pulse-excited array elements of finite size.
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Epstein, Irving R., and John A. Pojman. "Waves and Patterns." In An Introduction to Nonlinear Chemical Dynamics. Oxford University Press, 1998. http://dx.doi.org/10.1093/oso/9780195096705.003.0011.

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In this chapter, we will examine how diffusion can interact with the sort of nonlinear reaction kinetics that we have discussed in previous chapters to generate propagating waves of chemical reactivity and structured, sometimes spectacular, spatial patterns. One might argue, particularly if one were a physicist rather than a chemist, that the oscillatory phenomena that we have discussed thus far, and even the chaotic behavior that we will treat a bit later, can be just as easily generated by nonlinear electrical circuits, and that those circuits are much easier to work with than wet, smelly, and often toxic, chemicals. However, as far as chemistry goes, “spatial is special” in the sense that the spatial phenomena that we will discuss in this chapter are most naturally and conveniently generated in chemical systems. These same patterns also occur in a number of biological systems; the resemblance between a structure that develops in an inorganic chemical reaction and one found in a living organism can be startling. We are inclined to think of diffusion as tending to make a system more homogeneous, with it acting to reduce and ultimately to obliterate local fluctuations in the concentration of a chemical species. The spontaneous appearance of concentration gradients might seem to violate the Great Law (i.e., the Second Law of Thermodynamics), since the free energy should be at a minimum or the entropy at a maximum when concentrations are uniform. However, as we have seen in the case of temporal oscillation, a system far from equilibrium can generate spontaneous transient spatial inhomogeneities and, in an open system, sustained spatial patterns as well. The most common kind of chemical wave is the single propagating front, where, in an unstirred medium, there is a relatively sharp boundary between reacted and unreacted material, and this boundary or wavefront moves through the solution at an essentially constant speed. These waves are, of course, most noticeable when the reaction involves a color change. Many autocatalytic reactions exhibit this phenomenon of traveling waves.
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Conference papers on the topic "Local inhomogeneities"

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ROMANO, ANTONIO ENEA. "LOCAL INHOMOGENEITIES AND THE VALUE OF THE COSMOLOGICAL CONSTANT." In Proceedings of the First LeCosPA Symposium. WORLD SCIENTIFIC, 2013. http://dx.doi.org/10.1142/9789814449373_0019.

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Krause, H., and J. Engemann. "Measurement of local material inhomogeneities in magnetic garnet films." In International Conference on Magnetics. IEEE, 1990. http://dx.doi.org/10.1109/intmag.1990.734959.

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Yu, Tao. "Response of Love waves to local inhomogeneities: A model study." In SEG Technical Program Expanded Abstracts 1995. Society of Exploration Geophysicists, 1995. http://dx.doi.org/10.1190/1.1887293.

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Freyer, Richard, Uwe Hampel, M. Forejtek, and Cuong T. Luu. "Detection of local inhomogeneities in scattering media using tomographic reconstruction techniques." In BiOS Europe '95, edited by Britton Chance, David T. Delpy, and Gerhard J. Mueller. SPIE, 1995. http://dx.doi.org/10.1117/12.228680.

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Krit, Timofey, Valeriy Andreev, and Victor Kostikov. "Nonlinear moduli estimation for rubber-like media with local inhomogeneities elastography." In ICA 2013 Montreal. ASA, 2013. http://dx.doi.org/10.1121/1.4799568.

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Bekirov, B., I. Ivanchenko, M. Khruslov, and N. Popenko. "Numerical modeling the resonance X-band structures with local inhomogeneities inside." In 2016 IEEE International Conference on Mathematical Methods in Electromagnetic Theory (MMET). IEEE, 2016. http://dx.doi.org/10.1109/mmet.2016.7544049.

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Malev, Andrei V., and Evgeny A. Viktorov. "Solvable model in multimode dynamics including the case of local inhomogeneities." In Laser Optics, edited by Artur A. Mak. SPIE, 1994. http://dx.doi.org/10.1117/12.183164.

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Goloborodko, Andrey A., Vitalij N. Kurashov, Dmytro V. Podanchuk, and Natalia S. Sutyagina. "Shack-Hartmann wavefront sensor for the determination of local inhomogeneities of the surface." In SPIE Proceedings, edited by Malgorzata Kujawinska and Oleg V. Angelsky. SPIE, 2008. http://dx.doi.org/10.1117/12.797117.

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Giusti, Andrea, Luca Magri, and Marco Zedda. "Flow Inhomogeneities in a Realistic Aeronautical Gas-Turbine Combustor: Formation, Evolution and Indirect Noise." In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-76436.

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Indirect noise generated by the acceleration of combustion inhomogeneities is an important aspect in the design of aeroengines because of its impact on the overall noise emitted by an aircraft and the possible contribution to combustion instabilities. In this study, a realistic rich-quench-lean combustor is numerically investigated, with the objective of quantitatively analyzing the formation and evolution of flow inhomogeneities and determine the level of indirect combustion noise in the nozzle guide vane (NGV). Both entropy and compositional noise are calculated in this work. A high-fidelity numerical simulation of the combustion chamber, based on the Large-Eddy Simulation (LES) approach with the Conditional Moment Closure (CMC) combustion model, is performed. The contributions of the different air streams to the formation of flow inhomogeneities are pinned down and separated with seven dedicated passive scalars. LES-CMC results are then used to determine the acoustic sources to feed an NGV aeroacoustic model, which outputs the noise generated by entropy and compositional inhomogeneities. Results show that non-negligible fluctuations of temperature and composition reach the combustor’s exit. Combustion inhomogeneities originate both from finite-rate chemistry effects and incomplete mixing. In particular, the role of mixing with dilution and liner air flows on the level of combustion inhomogeneities at the combustor’s exit is highlighted. The species that most contribute to indirect noise are identified and the transfer functions of a realistic NGV are computed. The noise level indicates that indirect noise generated by temperature fluctuations is larger that the indirect noise generated by compositional inhomogeneities, although the latter is not negligible and is expected to become louder in supersonic nozzles. It is also shown that relatively small fluctuations of the local flame structure can lead to significant variations of the nozzle transfer function, whose gain increases with the Mach number. This highlights the necessity of an on-line solution of the local flame structure, which is performed in this paper by CMC, for an accurate prediction of the level of compositional noise. This study opens new possibilities for the identification, separation and calculation of the sources of indirect combustion noise in realistic aeronautical gas turbines.
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10

Breitenstein, Otwin. "Lock-in Thermography-Based Local Efficiency Analysis of Solar Cells." In ISTFA 2012. ASM International, 2012. http://dx.doi.org/10.31399/asm.cp.istfa2012p0250.

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Abstract The electronic properties of solar cells, particularly multicrystalline silicon-based ones, are distributed spatially inhomogeneous, where regions of poor quality may degrade the performance of the whole cell. These inhomogeneities mostly affect the dark current-voltage (I-V) characteristic, which decisively affects the efficiency. Since the grid distributes the local voltage homogeneously across the cell and leads to lateral balancing currents, local light beam-induced current methods alone cannot be used to image local cell efficiency parameters. Lock-in thermography (LIT) is the method of choice for imaging inhomogeneities of the dark I-V characteristic. This contribution introduces a novel method for evaluating a number of LIT images taken at different applied biases. By pixel-wise fitting the data to a two diode model and taking into account local series resistance and short circuit current density data, realistically simulated images of the other cell efficiency parameters (open circuit voltage, fill factor, and efficiency) are obtained. Moreover, simulated local and global dark and illuminated I-V characteristics are obtained, also for various illumination intensities. These local efficiency data are expectation values, which would hold if a homogeneous solar cell had the properties of the selected region of the inhomogeneous cell. Alternatively, also local efficiency data holding for the cell working at its own maximum power point may be generated. The amount of degradation of different cell efficiency parameters in some local defect positions is an indication how dangerous these defects are for degrading this parameter of the whole cell. The method allows to virtually 'cut out' certain defects for checking their influence on the global characteristics. Thus, by applying this method, a detailed local efficiency analysis of locally inhomogeneous solar cells is possible. It can be reliably predicted how a cell would improve if certain defects could be avoided. This method is implemented in a software code, which is available.
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