Relevant bibliographies by topics / Tensor dependent diffusion

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  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Book chapters
  5. Conference papers

Academic literature on the topic 'Tensor dependent diffusion'

Author: Grafiati
Published: 4 June 2021
Last updated: 6 February 2022

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Journal articles on the topic "Tensor dependent diffusion"

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Sajib, Saurav Z. K., Munish Chauhan, Oh In Kwon, and Rosalind J. Sadleir. "Magnetic-resonance-based measurement of electromagnetic fields and conductivity in vivo using single current administration—A machine learning approach." PLOS ONE 16, no. 7 (July 22, 2021): e0254690. http://dx.doi.org/10.1371/journal.pone.0254690.

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Diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) is a newly developed technique that combines MR-based measurements of magnetic flux density with diffusion tensor MRI (DT-MRI) data to reconstruct electrical conductivity tensor distributions. DT-MREIT techniques normally require injection of two independent current patterns for unique reconstruction of conductivity characteristics. In this paper, we demonstrate an algorithm that can be used to reconstruct the position dependent scale factor relating conductivity and diffusion tensors, using flux density data measured from only one current injection. We demonstrate how these images can also be used to reconstruct electric field and current density distributions. Reconstructions were performed using a mimetic algorithm and simulations of magnetic flux density from complementary electrode montages, combined with a small-scale machine learning approach. In a biological tissue phantom, we found that the method reduced relative errors between single-current and two-current DT-MREIT results to around 10%. For in vivo human experimental data the error was about 15%. These results suggest that incorporation of machine learning may make it easier to recover electrical conductivity tensors and electric field images during neuromodulation therapy without the need for multiple current administrations.
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Hanyga, Andrzej, and Richard L. Magin. "A new anisotropic fractional model of diffusion suitable for applications of diffusion tensor imaging in biological tissues." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2170 (October 8, 2014): 20140319. http://dx.doi.org/10.1098/rspa.2014.0319.

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An anomalous anisotropic diffusion equation is constructed in which the order of the spatial pseudo-differential operator is generalized to be distributed with a directionally dependent distribution. A time fractional version of this equation is also considered. First, it is proved that the equation is positivity-preserving and properly normalized. Second, the existence of a smooth Green's function solution is proved. Finally, an expression for the diffusive flux density for this new fractional order process is calculated. This approach may find utility in modelling diffusion tensor imaging data in the white matter of the human brain where both the apparent diffusion coefficient and the order of the pseudo-differential operator are anisotropic.
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KOPIETZ, PETER. "THOULESS NUMBER AND SPIN DIFFUSION IN QUANTUM HEISENBERG FERROMAGNETS." Modern Physics Letters B 07, no. 27 (November 20, 1993): 1747–59. http://dx.doi.org/10.1142/s0217984993001788.

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Using an analogy between the conductivity tensor of electronic systems and the spin stiffness tensor of spin systems, we introduce the concept of the Thouless number g0 and the dimensionless frequency-dependent conductance g(ω) for quantum spin models. It is shown that spin diffusion implies the vanishing of the Drude peak of g(ω), and that the spin diffusion coefficient Ds is proportional to g0. We develop a new method based the Thouless number to calculate D s , and present results for D s in the nearest-neighbor quantum Heisenberg ferromagnet at infinite temperatures for arbitrary dimension d and spin S.
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Ben-Sira, Liat, Noam Goder, Haim Bassan, Shlomi Lifshits, Yaniv Assaf, and Shlomi Constantini. "Clinical benefits of diffusion tensor imaging in hydrocephalus." Journal of Neurosurgery: Pediatrics 16, no. 2 (August 2015): 195–202. http://dx.doi.org/10.3171/2014.10.peds13668.

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OBJECT The object of this study was to use diffusion tensor imaging (DTI) to evaluate and characterize white matter changes in hydrocephalus. METHODS The authors performed a retrospective analysis of DTI in a cohort of patients with hydrocephalus (n = 35), 19 of whom had both pre- and postsurgical imaging studies. These patient’s DTI values were compared with values extracted from age-dependent trend lines computed from a healthy subject group (n = 70, age span 14 months-14 years). Several DTI parameters in different regions of interest (ROIs) were evaluated to find the most sensitive parameters for clinical decision making in hydrocephalus. RESULTS Compared with healthy controls, patients with active hydrocephalus had a statistically significant change in all DTI parameters. The most sensitive and specific DTI parameter for predicting hydrocephalus was axial diffusivity (λ1) measured at the level of the corona radiata. Diffusion tensor imaging parameters correlated with several conventional radiological parameters in the assessment of hydrocephalus but were not superior to them. There was no convincing correlation between clinical disease severity and DTI parameters. When examining the pre- and postsurgical effect, it was found that DTI may be a sensitive tool for estimating tissue improvement. CONCLUSIONS This large-cohort study with a multidisciplinary approach combining clinical, neurological, radiological, and multiple DTI parameters revealed the most sensitive DTI parameters for identifying hydrocephalus and suggested that they may serve as an important tool for the disorder’s quantitative radiological assessment.
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Chen, Bin, Hua Guo, and Allen W. Song. "Correction for direction-dependent distortions in diffusion tensor imaging using matched magnetic field maps." NeuroImage 30, no. 1 (March 2006): 121–29. http://dx.doi.org/10.1016/j.neuroimage.2005.09.008.

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Mueller, Karsten, Alfred Anwander, Harald E. Möller, Annette Horstmann, Jöran Lepsien, Franziska Busse, Siawoosh Mohammadi, et al. "Sex-Dependent Influences of Obesity on Cerebral White Matter Investigated by Diffusion-Tensor Imaging." PLoS ONE 6, no. 4 (April 11, 2011): e18544. http://dx.doi.org/10.1371/journal.pone.0018544.

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Thiessen, Jonathan D., Trevor J. Vincent, Sheryl L. Herrera, and Melanie Martin. "Diffusion Tensor Metric Measurements as a Function of Diffusion Time in the Rat Central Nervous System." Magnetic Resonance Insights 5 (January 2012): MRI.S10692. http://dx.doi.org/10.4137/mri.s10692.

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MRI and Monte Carlo simulated data of pulsed gradient spin echo experiments were used to study the effects of diffusion time, gradient strength and b-value on diffusion tensor (DT) metrics using real and simulated fixed rat spines. Radial (λ⊥) in grey matter and simulation data, axial (λ||) in both grey and white matter in fixed rat spinal cords and mean diffusivity in all tissues showed a significant decrease with diffusion time at b = 1 μm2/ms. All diffusivities significantly decreased with b-value at g = 116 mT/m and at Δeff = 23 ms. The fractional anisotropy (FA) significantly increased with diffusion time at b = 1 μm2/ms in the simulation data and grey matter. FA significantly increased in white matter and simulation data and significantly decreased in grey matter with b-value at g = 116 mT/m and at Δeff = 23 ms. These data suggest that DTI metrics are highly dependent on pulse sequence parameters.
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Chanraud, Sandra, Michel Reynaud, Michèle Wessa, Jani Penttilä, Nikoleta Kostogianni, Arnaud Cachia, Eric Artiges, et al. "Diffusion Tensor Tractography in Mesencephalic Bundles: Relation to Mental Flexibility in Detoxified Alcohol-Dependent Subjects." Neuropsychopharmacology 34, no. 5 (July 9, 2008): 1223–32. http://dx.doi.org/10.1038/npp.2008.101.

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Li, J., W. Shi, M. Li, Z. Wang, H. He, J. Xian, B. Lv, and F. Yan. "Time-dependent diffusion tensor changes of optic nerve in patients with indirect traumatic optic neuropathy." Acta Radiologica 55, no. 7 (September 2014): 855–63. http://dx.doi.org/10.1177/0284185113506900.

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Kusumi, Ryosuke, Fumiko Kimura, and Tsunehisa Kimura. "Single Crystal Solid-State NMR of Magnetically Oriented Powder." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C1086. http://dx.doi.org/10.1107/s205327331408913x.

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Solid-state NMR spectroscopy is one of the most widely used methods for investigating crystal structures, along with the X-ray and neutron diffraction methods. Solid-state NMR can provide structural information including isotropic chemical shift, dipolar and quadrupolar couplings, spin diffusion, and chemical shift tensor. Among these, the chemical shift tensor is of particular significance because the electronic environment around a nucleus is directly reflected on the chemical shift tensor. However, full information of the chemical shift tensor, including principal values and axes, is difficult to obtain experimentally because a large single crystal is required for the measurement. On the other hand, we have proposed the use of a magnetically oriented microcrystal array (MOMA) as an alternative to a single crystal.[1,2] A MOMA is a composite in which microcrystals are aligned three-dimensionally, prepared by using a time-dependent magnetic field. We recently demonstrated that the13C chemical shift tensors of L-alanine crystal can be completely determined by application of the standard procedure in the single-crystal rotation method to a MOMA of L-alanine microcrystals,[3] as shown in Figure 1. The L-alanine MOMA produces sharp resonance peaks without resolution enhancement by magic angle spinning (MAS). In addition, we observed that the positions of the13C resonance peaks vary systematically as a function of the angle ψ that is the sample-rotation angle about the axis inclined by the magic angle with respect to the NMR magnetic field. From the ψ-dependence of the chemical shifts,13C chemical shift tensor was completely determined. We confirmed that the combination of MOMA with the single-crystal rotation method can be applied to other nuclei such as31P and15N. These results clearly show that the MOMA method is a powerful tool for obtaining full information of the chemical shift tensor from a microcrystalline powder without MAS.
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Dissertations / Theses on the topic "Tensor dependent diffusion"

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Piatkowski, Jakub Przemyslaw. "Probing the brain's white matter with diffusion MRI and a tissue dependent diffusion model." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8850.

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While diffusion MRI promises an insight into white matter microstructure in vivo, the axonal pathways that connect different brain regions together can only partially be segmented using current methods. Here we present a novel method for estimating the tissue composition of each voxel in the brain from diffusion MRI data, thereby providing a foundation for computing the volume of different pathways in both health and disease. With the tissue dependent diffusion model described in this thesis, white matter is segmented by removing the ambiguity caused by the isotropic partial volumes: both grey matter and cerebrospinal fluid. Apart from the volume fractions of all three tissue types, we also obtain estimates of fibre orientations for tractography as well as diffusivity and anisotropy parameters which serve as proxy indices of pathway coherence. We assume Gaussian diffusion of water molecules for each tissue type. The resulting three-tensor model comprises one anisotropic (white matter) compartment modelled by a cylindrical tensor and two isotropic compartments (grey matter and cerebrospinal fluid). We model the measurement noise using a Rice distribution. Markov chain Monte Carlo sampling techniques are used to estimate posterior distributions over the model’s parameters. In particular, we employ a Metropolis Hastings sampler with a custom burn-in and proposal adaptation to ensure good mixing and efficient exploration of the high-probability region. This way we obtain not only point estimates of quantities of interest, but also a measure of their uncertainty (posterior variance). The model is evaluated on synthetic data and brain images: we observe that the volume maps produced with our method show plausible and well delineated structures for all three tissue types. Estimated white matter fibre orientations also agree with known anatomy and align well with those obtained using current methods. Importantly, we are able to disambiguate the volume and anisotropy information thus alleviating partial volume effects and providing measures superior to the currently ubiquitous fractional anisotropy. These improved measures are then applied to study brain differences in a cohort of healthy volunteers aged 25-65 years. Lastly, we explore the possibility of using prior knowledge of the spatial variability of our parameters in the brain to further improve the estimation by pooling information among neighbouring voxels.
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Larsson, Karl. "Scale-Space Methods as a Means of Fingerprint Image Enhancement." Thesis, Linköping University, Department of Science and Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2282.

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The usage of automatic fingerprint identification systems as a means of identification and/or verification have increased substantially during the last couple of years. It is well known that small deviations may occur within a fingerprint over time, a problem referred to as template ageing. This problem, and other reasons for deviations between two images of the same fingerprint, complicates the identification/verification process, since distinct features may appear somewhat different in the two images that are matched. Commonly used to try and minimise this type of problem are different kinds of fingerprint image enhancement algorithms. This thesis tests different methods within the scale-space framework and evaluate their performance as fingerprint image enhancement methods.

The methods tested within this thesis ranges from linear scale-space filtering, where no prior information about the images is known, to scalar and tensor driven diffusion where analysis of the images precedes and controls the diffusion process.

The linear scale-space approach is shown to improve correlation values, which was anticipated since the image structure is flattened at coarser scales. There is however no increase in the number of accurate matches, since inaccurate features also tends to get higher correlation value at large scales.

The nonlinear isotropic scale-space (scalar dependent diffusion), or the edge- preservation, approach is proven to be an ill fit method for fingerprint image enhancement. This is due to the fact that the analysis of edges may be unreliable, since edge structure is often distorted in fingerprints affected by the template ageing problem.

The nonlinear anisotropic scale-space (tensor dependent diffusion), or coherence-enhancing, method does not give any overall improvements of the number of accurate matches. It is however shown that for a certain type of template ageing problem, where the deviating structure does not significantly affect the ridge orientation, the nonlinear anisotropic diffusion is able to accurately match correlation pairs that resulted in a false match before they were enhanced.

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Isobe, Masanori. "Polymorphism within a neuronal activity-dependent enhancer of NgR1 is associated with corpus callosum morphology in humans." Kyoto University, 2015. http://hdl.handle.net/2433/202673.

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Fick, Rutger. "Modélisation avancée du signal dMRI pour la caractérisation de la microstructure tissulaire." Thesis, Université Côte d'Azur (ComUE), 2017. http://www.theses.fr/2017AZUR4006/document.

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Cette thèse est dédiée à améliorer la compréhension neuro-scientifique à l'aide d'imagerie par résonance magnétique de diffusion (IRMd). Nous nous concentrons sur la modélisation du signal de diffusion et l'estimation par IRMd des biomarqueurs liés à la microstructure, appelé «Microstructure Imaging». Cette thèse est organisée en trois parties. Dans partie I nous commençons par la base de l'IRMd et un aperçu de l'anisotropie en diffusion. Puis nous examinons la plupart des modèles de microstructure utilisant PGSE, en mettant l'accent sur leurs hypothèses et limites, suivi par une validation par l'histologie de la moelle épinière de leur estimation. La partie II présente nos contributions à l'imagerie en 3D et à l’estimation de microstructure. Nous proposons une régularisation laplacienne de la base fonctionnelle MAP, ce qui nous permet d'estimer de façon robuste les indices d'espace q liés au tissu. Nous appliquons cette approche aux données du Human Connectome Project, où nous l'utilisons comme prétraitement pour d'autres modèles de microstructure. Enfin, nous comparons les biomarqueurs dans une étude ex-vivo de rats Alzheimer à différents âges. La partie III présente nos contributions au représentation de l’espace qt - variant sur l'espace q 3D et le temps de diffusion. Nous présentons une approche initiale qui se concentre sur l'estimation du diamètre de l'axone depuis l'espace qt. Nous terminons avec notre approche finale, où nous proposons une nouvelle base fonctionnelle régularisée pour représenter de façon robuste le signal qt, appelé qt-IRMd. Ce qui permet l'estimation des indices d’espace q dépendants du temps, quantifiant la dépendance temporelle du signal IRMd
This thesis is dedicated to furthering neuroscientific understanding of the human brain using diffusion-sensitized Magnetic Resonance Imaging (dMRI). Within dMRI, we focus on the estimation and interpretation of microstructure-related markers, often referred to as ``Microstructure Imaging''. This thesis is organized in three parts. Part I focuses on understanding the state-of-the-art in Microstructure Imaging. We start with the basic of diffusion MRI and a brief overview of diffusion anisotropy. We then review and compare most state-of-the-art microstructure models in PGSE-based Microstructure Imaging, emphasizing model assumptions and limitations, as well as validating them using spinal cord data with registered ground truth histology. In Part II we present our contributions to 3D q-space imaging and microstructure recovery. We propose closed-form Laplacian regularization for the recent MAP functional basis, allowing robust estimation of tissue-related q-space indices. We also apply this approach to Human Connectome Project data, where we use it as a preprocessing for other microstructure models. Finally, we compare tissue biomarkers in a ex-vivo study of Alzheimer rats at different ages. In Part III, we present our contributions to representing the qt-space - varying over 3D q-space and diffusion time. We present an initial approach that focuses on 3D axon diameter estimation from the qt-space. We end with our final approach, where we propose a novel, regularized functional basis to represent the qt-signal, which we call qt-dMRI. Our approach allows for the estimation of time-dependent q-space indices, which quantify the time-dependence of the diffusion signal
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Nel, Amoré Elsje. "The solar-cycle dependence of the heliospheric diffusion tensor / Amoré Elsje Nel." Thesis, 2015. http://hdl.handle.net/10394/16076.

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Long-term cosmic-ray modulation studies using ab initio numerical modulation models require an understanding of the solar-cycle dependence of the heliospheric diffusion tensor. Such an understanding requires information as to possible solar-cycle dependences of various basic turbulence quantities. In this study, 1-minute resolution data for the N-component of the heliospheric magnetic field spanning from 1974 to 2012 is analysed using second-order structure functions constructed assuming a simple three-stage power-law frequency spectrum. This spectrum is motivated observationally and theoretically, and has an inertial, an energycontaining and a cutoff-range at small frequencies to ensure a finite energy density. Of the turbulence quantities calculated from 27-day averaged second-order structure functions, only the magnetic variance and the spectral level show a significant solar-cycle dependence, much less so the spectral index in the energy range. The spectral indices in the inertial range, as well as the turnover and cutoff scales do not appear to depend on the level of solar activity. The ratio of the variance to the square of the magnetic field also appears to be solar-cycle independent. These results suggest that the dominant change in the spectrum over several solar-cycles is its level. Comparisons of the results found in this study with relevant published observations of turbulence quantities are very favourable. Furthermore, when the magnetic variances and heliospheric magnetic magnitudes calculated in this study are used as inputs for theoretically motivated expressions for the mean free paths and turbulence-reduced drift lengthscale, clear solar-cycle dependencies in these quantities are seen. Values for the diffusion and drift lengthscales during the recent unusual solar minimum are found to be significantly higher than during previous solar minima.
MSc (Space Physics), North-West University, Potchefstroom Campus, 2015
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Books on the topic "Tensor dependent diffusion"

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Andersen, Jørgen Goul. 22. The impact of public policies. Oxford University Press, 2017. http://dx.doi.org/10.1093/hepl/9780198737421.003.0024.

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This chapter examines the effects of public policy. It first considers economic paradigms and approaches to welfare and documents the overriding historical changes in approaches to the economy, from Keynesian ideas of macro-economic steering to more market-oriented economic perspectives. It then explores the idea of institutional complementarity as expressed in the typologies of welfare regimes, varieties of capitalism, and flexicurity. It also looks at some of the empirical analyses of the effects of welfare policies and the tension between welfare and economic efficiency. Finally, it looks at policy feedback, path dependence, policy learning, social learning, policy transfer and policy diffusion, and policy convergence.
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Book chapters on the topic "Tensor dependent diffusion"

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Algethami, Hanan, Fred C. Lam, Rafael Rojas, and Ekkehard M. Kasper. "PreSurgical and Surgical Planning in Neurosurgical Oncology - A Case-Based Approach to Maximal Safe Surgical Resection in Neurosurgery." In Neurosurgery [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.99155.

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Use of functional neuroimaging capabilities such as fMRI, DTI, MRP, MRS, AS-PET-CT, SPECT, and TMS as noninvasive tools to visualize intrinsic brain and spine morphology in relation to function have developed over the past 30 years. Amongst these imaging modalities, functional magnetic resonance imaging (fMRI) is of particular interest since it follows the physiological coupling between neuronal electrical activity and metabolic structural (cellular) activity as it relates to tissue vascularity and perfusion states. This structure–function synesis (from the Greek noun, σύνεσις = being together), leads to three effects that contribute to the fMRI signal: an increase in the blood flow velocity, a change in the mean blood volume, and most importantly, alterations in the blood oxygenation level. The latter effect has lent to the development of blood-oxygenation-level-dependent or BOLD fMRI, which has been used in establishing the topographic relationship between eloquent cortex and neurosurgical planning. As an adjunct to this modality, MRI-based diffusion tensor imaging (DTI) allows further detailed radiographic assessment of fiber tracts in the brain in relationship to the surgical lesion of interest. Herein we review the roles of fMRI and DTI for presurgical mapping to allow for maximal safe resection procedures in neurosurgery with case-based illustrations.
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Newnham, Robert E. "Diffusion and ionic conductivity." In Properties of Materials. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780198520757.003.0021.

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The phenomenon of atomic and ionic migration in crystals is called solidstate diffusion, and its study has shed light on many problems of technological and scientific importance. Diffusion is intimately connected to the strength of metals at high temperature, to metallurgical processes used to control alloy properties, and to many of the effects of radiation on nuclear reactor materials. Diffusion studies are important in understanding the ionic conductivity of the materials used in fuel cells, the fabrication of semiconductor integrated circuits, the corrosion of metals, and the sintering of ceramics. When two miscible materials are in contact across an interface, the quantity of diffusing material which passes through the interface is proportional to the concentration gradient. The atomic flux J is given by where J is measured per unit time and per unit area, c is the concentration of the diffusing material per unit volume, and Z is the gradient direction. The proportionality factor D, the diffusion coefficient, is measured in units of m2/s. This equation is sometimes referred to as Fick’s First Law. It describes atomic transport in a form that is analogous to electrical resistivity (Ohm’s Law) or thermal conductivity. There are several objections to Fick’s Law, as discussed in Section 19.5. Strictly speaking, it is valid only for self-diffusion coefficients measured in small concentration gradients. Since J and Z are both vectors, the diffusion coefficient D is a second rank tensor. As with other symmetric second rank tensors, between one and six measurements are required to specify Dij , depending on symmetry. The relationship between structure and anisotropy is more apparent in PbI2. Lead iodide is isostructural with CdI2 in trigonal point group.m. The self-diffusion of Pb is much easier parallel to the layers where the Pb atoms are in close proximity to one another. Diffusion is more difficult along Z3 = [001] because Pb atoms have a very long jump distance in this direction. The mineral olivine, (Mg, Fe)2SiO4, is an important constituent of the deeper parts of the earth’s crust.
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Andersen, Jørgen Goul. "22. The Impact of Public Policies." In Comparative Politics, 395–416. Oxford University Press, 2020. http://dx.doi.org/10.1093/hepl/9780198820604.003.0022.

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This chapter examines the effects of public policy. It first considers economic paradigms and approaches to welfare and documents the overriding historical changes in approaches to the economy, from Keynesian ideas of macro-economic steering to more market-oriented economic perspectives. It then explores the idea of institutional complementarity, as expressed in the typologies of welfare regimes, varieties of capitalism, and flexicurity. It also looks at some of the empirical analyses of the effects of welfare policies and the tension between welfare and economic efficiency. Finally, it looks at policy feedback, path dependence, policy learning, social learning, policy transfer and policy diffusion, and policy convergence.
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Conference papers on the topic "Tensor dependent diffusion"

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Huang, Xing, Hui Shen, Zongtan Zhou, Xuyi Wang, Wei Hao, and Dewen Hu. "Anisotropic Asymmetry Analysis in Diffusion Tensor Images of Healthy an Heroin-dependent Subjects." In 2007 IEEE/ICME International Conference on Complex Medical Engineering. IEEE, 2007. http://dx.doi.org/10.1109/iccme.2007.4381877.

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El Afif, A., D. De Kee, R. Cortez, and D. P. Gaver. "Relationships Between Mass Transfer and Morphology in Deformable Complex Interfacial Systems." In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-32230.

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We propose a model for isothermal mass transport into immiscible complex fluids. The interface is described by two, space and time dependent, structural variables: a scalar Q(r,t) denoting the interfacial area density and a traceless symmetric second order tensor q(r,t) accounting for the shape anisotropy. The mass flux expression includes new contributions attributed to the dynamical changes of the interface. The diffusion-morphology coupling is found to influence both the mass transfer and the dynamics of the interface. The former exhibits non-Fickian behavior while the latter undergoes interfacial deformations that affect both its size and shape, creating internal stresses at the same time.
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Silva, Luis, and Alfonso Ortega. "CFD Analysis of the Vortex Dynamics Generated by a Synthetic Jet Impinging on a Heated Surface." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-64185.

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A canonical geometry has been used to investigate the flow and heat transfer of a purely oscillatory jet that is not influenced by the manner in which it is produced. Such a jet has been popularly termed a synthetic jet in the literature, and recently has been investigated for thermal management of electronics by causing the jet to impinge onto the heated surface. Because of its oscillatory nature, the impinging jet thus formed is dominated by vortices that are advected towards the surface. This surface-vortex interaction is key to understanding the fundamental mechanisms of convective heat transfer by the impinging synthetic jet and hence is the subject of the current investigation. The unsteady two-dimensional Navier-Stokes equations and the convection-diffusion equation were solved using a fully unsteady, two-dimensional finite volume approach in order to capture the complex time dependent flow field. Various vortex identification methods were investigated for proper identification of the train of vortices emanating from the jet and their evolution and eventual dissipation. Intuitive definitions of vortices such as spiraling streamlines, pressure minima and isovorticity surfaces suffer from inaccuracies. In the present work, the vortex-identification criteria employed was the Q-criterion (Hunt et al. 1988), which defines vortices as connected fluid regions with positive second invariant of the velocity gradient tensor. By tracking vortices, it was found that a primary vortex advecting parallel to the target surface gives rise to a secondary vortex with opposite net vorticity. It was found that the secondary vortex is largely responsible for enhancement of the heat transfer within the wall jet region. In addition it was found that in some situations vortex coalescence or pairing occurs, leading to degradation in the heat transfer enhancement due to the reduction in the frequency of vortices interacting with the surface.
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Wu, Yin, Chao Zou, Na Zhang, Guoxi Xie, Xin Liu, Fei Feng, and Yang Liu. "Preliminary study of B-value dependence of MR diffusion tensor imaging measurements in myocardium structure characterization." In 2010 3rd International Conference on Biomedical Engineering and Informatics (BMEI). IEEE, 2010. http://dx.doi.org/10.1109/bmei.2010.5639246.

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Valaparla, Sunil K., Feng Gao, Muhammad Abdul-Ghani, and Geoffrey D. Clarke. "Intramyocellular lipid dependence on skeletal muscle fiber type and orientation characterized by diffusion tensor imaging and1H-MRS." In SPIE Medical Imaging, edited by Sebastien Ourselin and Martin A. Styner. SPIE, 2014. http://dx.doi.org/10.1117/12.2041728.

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Freidin, Alexander B. "Chemical Affinity Tensor and Stress-Assist Chemical Reactions Front Propagation in Solids." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-64957.

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We consider a stress-assist chemical reaction front propagation in a deformable solid undergoing a localized chemical reaction between solid and gas constituents. The reaction is sustained by the diffusion of the gas constituent through the transformed solid material. We introduce a chemical transformations strain tensor that relates two reference configurations of solid constituents. Then mass, momentum and energy balances are written down for the open system considered and the expression of the entropy production due to the reaction front propagation in a solid with arbitrary constitutive equations is derived. As a result, the expression of the chemical affinity tensor is obtained. Kinetic equation for the chemical reactions front propagation is formulated in a form of the dependence of the front velocity on normal components of the chemical affinity tensor. The locking effect — blocking the reaction by stresses is demonstrated. Finally the kinetic equation for the bulk chemical reaction is derived in a form of the dependence of the reaction rate on the first invariant of the chemical affinity tensor.
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Chiravarambath, Sidharth, Narendra K. Simha, and Jack L. Lewis. "Poroviscoelastic Properties of Mouse Cartilage From Inverse Finite Elements and Indentation." In ASME 2007 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2007. http://dx.doi.org/10.1115/sbc2007-176688.

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Transgenic mice offer a novel way to probe structure function relationships in healthy and osteoarthritic cartilage. Indentation is a convenient method to measure mechanical properties of cartilage in the mouse. In order to reduce test data to material properties, test model geometry along with a material model needs to be assumed. Most recent developments support the use of a poroviscoelastic (PVE) model for cartilage. However, using this model makes separation of the flow-dependent and flow-independent viscoelastic parameters challenging. For cartilage from larger animals, Huang [1] showed that tensile tests have negligible flow-dependent response and hence can identify the flow-independent material parameters. A compression experiment can then be used to find only the flow-dependent parameters. However, limited cartilage volumes in mouse do not allow for tension tests, so mouse cartilage is primarily tested by indentation. Mak [2] has shown that fluid flow occurs mainly for times comparable to the gel diffusion time T = a2/Hκ where a is the tip size, H is the aggregate modulus and κ is permeability. Consequently, we propose use of two different sized indenters to separate flow-independent and dependent effects in mouse cartilage. One tip is small enough to make T negligible (say <0.1 s), then relaxation data will probe only the flow-independent response, whereas a second considerably larger tip will probe both flow-dependent and fluid flow effects. The data from the small indenter can be used to fit the flow-independent parameters; the data from the large indenter, in conjunction with parameters from the first fit, can be used to fit the flow-dependent parameters.
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8

McLeod, Logan S., Levent F. Degertekin, and Andrei G. Fedorov. "Grain Boundary Diffusion of Hydrogen in Nano-Structured Pd/Ag Alloy Membranes." In ASME 2008 3rd Energy Nanotechnology International Conference collocated with the Heat Transfer, Fluids Engineering, and Energy Sustainability Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/enic2008-53014.

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Palladium and its alloys have long been used as hydrogen separation membranes due to their extremely high permeability and selectivity to hydrogen over all other gases [1]. The hydrogen permeation process begins with selective chemisorption of the gas onto the metal surface. As the adsorption process is the point in the permeation sequence where the majority of gases become excluded, it follows that a cleverly designed device could be created to take advantage of the so-called ‘fast’ diffusion paths of surface and grain-boundary diffusion to further enhance permeability without sacrificing selectivity. The contribution of grain-boundary diffusion to the overall permeation rate is dependent on the relative volume in the membrane occupied by grain-boundaries versus bulk material. Typically, grain boundaries only make up a miniscule fraction of the overall volume and therefore only contribute an appreciable amount to the overall diffusion process at temperatures low enough to make the bulk diffusion process nearly stagnant. However, in the case of a nanostructured membrane this paradigm is no longer valid. The fabrication methods associated with extremely thin membrane deposition typically lead to highly non-equilibrium microstructure with an average grain size on the order of tens of nanometers [2]. In order to exploit the potential advantages of grain boundary diffusion the nano-scale grains must persist throughout operation. To avoid the tendency for the grain structure to relax to a more equiaxed, coarse-grained morphology the self-diffusion of metal atoms in the film must be minimized by operating the membranes at a temperature much lower than the membrane melting temperature. Figure 1 shows the microstructural changes in a thin, sputtered, Pd/Ag alloy film before and after annealing. The initial fine-grained structure on the bottom surface of the membrane is due to a combination of low substrate temperature during deposition and the Ti adhesion layer onto which the Pd/Ag layer was deposited. After annealing at 400 C the grains have coarsened and the top and bottom structure are identical.
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9

Tretola, Giovanni, Konstantina Vogiatzaki, and Salvador Navarro-Martinez. "Detailed simulation of air-assisted spray atomization: effect of numerical scheme at intermediate Weber number." In ILASS2017 - 28th European Conference on Liquid Atomization and Spray Systems. Valencia: Universitat Politècnica València, 2017. http://dx.doi.org/10.4995/ilass2017.2017.4712.

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Numerical simulations are often used to understand spray atomisation and estimate the size of the liquid fragments.Several techniques (Level Set, Volume of Fluid, Smooth Particle Hydrodynamics, among others) exist to compute multiphase flows and potentially represent liquid-break-up. However, the complexity of the breakup process and the wide range of scales prevents the use of an unified approach to simulate the complete spray. Numerical techniques face different challenges depending on the spray characteristics. The incorrect representation of surface forces in capillary dominated flows, creates large parasitic currents that distort and in some cases destroy the interface. Methods that perform well in the capillary regime aim to capture the interface directly and the surface radius cur- vature is therefore larger than the mesh size. However, this creates large constrains on the mesh resolution and limits its applications to low Weber number flows, when there is no extensive atomization. Methods that simulate large Weber number flows (typical of industrial injectors) do not resolve the interface directly and the mesh is larger than the smallest radius of curvature. These models often have numerical or artificial diffusion that destroys small scale structures and alters the break-up. However, even at large Weber flows, the spray formation can be affected by errors due to the local imbalance between pressure and surface tension forces and interface curvature errors. Numerical schemes work around these problems by adjusting the amount of numerical diffusion of the scheme depending on the spray application. Intermediate Weber number sprays are well suited to study the performance of numerical methods as they exhibit hybrid behaviour between capillary flows and full atomization. In the present work an intermediate gas Weber of a laboratory air-blast atomiser is investigated using a volume of fluid approach. The amount of numerical diffusion is controlled by a compressive factor in the volume of fluid transport equation. The effect of the compressive term on spray atomization and droplet size distribution is explored. The results suggestthat the optimal amount of diffusion depends on the local Weber number.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4712
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10

Bothe, Dieter, and Andreas Alke. "Influence of Surfactants on the Dynamics of Fluid-Liquid Interfaces." In ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/fedsm2006-98141.

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In many two-phase fluid-liquid systems at least one phase contains surface active agents (surfactants for short) which are adsorbed preferentially at the interface Γ(t) due to minimization of free surface energy. Important examples are emulsification processes and bubbles rising in a bubble column through water containing a surfactant - unmeant as a contamination or by determined addition in order to increase the efficiency of the column. The adsorption of a surfactant at a fluid-liquid interface causes a decrease of the surface tension, depending on the area specific concentration cΓ of the adsorbed surfactant, i.e. σ=f(cΓ)(1) with a decreasing function f. The adsorbed surfactant is distributed on the interface due to convective and diffusive interfacial fluxes. The resulting spatial inhomogeneity leads to surface gradients of the surface tension, ∇Γσ(cΓ), which effect the hydrodynamics via the interfacial momentum jump condition [pI−S]nΓ=σκnΓ+∇Γσ(cΓ).(2) These additional so-called Marangoni stresses often result in a pronounced change of the dynamical behavior.
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