Artykuły w czasopismach: „Contrasting diffusivity”

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Lai, King C., i James W. Evans. "Complex oscillatory decrease with size in diffusivity of {100}-epitaxially supported 3D fcc metal nanoclusters". Nanoscale 11, nr 37 (2019): 17506–16. http://dx.doi.org/10.1039/c9nr05845a.

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Gaudiello, Antonio, i Ali Sili. "Homogenization of Highly Oscillating Boundaries with Strongly Contrasting Diffusivity". SIAM Journal on Mathematical Analysis 47, nr 3 (styczeń 2015): 1671–92. http://dx.doi.org/10.1137/140987225.

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Sili, Ali. "Diffusion through a composite structure with a high contrasting diffusivity". Asymptotic Analysis 89, nr 1-2 (2014): 173–87. http://dx.doi.org/10.3233/asy-141241.

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Nandakumaran, A. K., i Abu Sufian. "Strong contrasting diffusivity in general oscillating domains: Homogenization of optimal control problems". Journal of Differential Equations 291 (sierpień 2021): 57–89. http://dx.doi.org/10.1016/j.jde.2021.04.031.

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Perriot, Romain, i Blas P. Uberuaga. "Structural vs. intrinsic carriers: contrasting effects of cation chemistry and disorder on ionic conductivity in pyrochlores". Journal of Materials Chemistry A 3, nr 21 (2015): 11554–65. http://dx.doi.org/10.1039/c5ta01692d.

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Cation disorder liberates and enhances the mobility of structural carriers in pyrochlores. However, depending on the chemistry and type of defect, antisites can trap intrinsic carriers, and reduce the diffusivity.

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Sili, Ali. "Diffusion through a composite medium with a semi-periodic structure and high contrasting diffusivity". Asymptotic Analysis 98, nr 4 (11.07.2016): 309–24. http://dx.doi.org/10.3233/asy-161370.

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Sharma, Manju, i S. Yashonath. "How does contrasting dependence of impurity-atom diffusivity on the density of host disordered medium arise?" Indian Journal of Physics 83, nr 1 (styczeń 2009): 31–47. http://dx.doi.org/10.1007/s12648-009-0002-6.

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Jarníková, Tereza, Elise M. Olson, Susan E. Allen, Debby Ianson i Karyn D. Suchy. "A clustering approach to determine biophysical provinces and physical drivers of productivity dynamics in a complex coastal sea". Ocean Science 18, nr 5 (13.10.2022): 1451–75. http://dx.doi.org/10.5194/os-18-1451-2022.

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Abstract. The balance between ocean mixing and stratification influences primary productivity through light limitation and nutrient supply in the euphotic ocean. Here, we apply a hierarchical clustering algorithm (Ward's method) to four factors relating to stratification (wind energy, freshwater index, water-column-averaged vertical eddy diffusivity, and halocline depth), as well as to depth-integrated phytoplankton biomass, extracted from a biophysical ocean model of the Salish Sea. Running the clustering algorithm on 4 years of model output, we identify distinct regions of the model domain that exhibit contrasting wind and freshwater input dynamics, as well as regions of varying water-column-averaged vertical eddy diffusivity and halocline depth regimes. The spatial regionalizations in physical variables are similar in all 4 analyzed years. We also find distinct interannually consistent biological zones. In the northern Strait of Georgia and Juan de Fuca Strait, a deeper winter halocline and episodic summer mixing coincide with higher summer diatom abundance, while in the Fraser River stratified central Strait of Georgia, shallower haloclines and stronger summer stratification coincide with summer flagellate abundance. Cluster-based model results and evaluation suggest that the Juan de Fuca Strait supports more biomass than previously thought. Our approach elucidates probable physical mechanisms controlling phytoplankton abundance and composition. It also demonstrates a simple, powerful technique for finding structure in large datasets and determining boundaries of biophysical provinces.

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Ma, Ke, Mathijs Janssen, Cheng Lian i René van Roij. "Dynamic density functional theory for the charging of electric double layer capacitors". Journal of Chemical Physics 156, nr 8 (28.02.2022): 084101. http://dx.doi.org/10.1063/5.0081827.

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We consider the charging of a model capacitor comprised of two planar electrodes and an electrolyte. Upon switching on a voltage difference, electric double layers build up in this setup, which we characterize with a classical dynamic density functional theory (DDFT) that accounts for electrostatic correlations and for molecular excluded volume of finite-sized ions and solvent molecules. Our DDFT predicts the electrode charge Q( t) to form exponentially with two timescales: at early times, the system relaxes on the RC time, namely, λ D L/[ D(2 + σ/ λ D)], with λ D being the Debye length, L being the electrode separation, σ being the ion diameter, and D being the ionic diffusivity. Contrasting an earlier DDFT study, this early-time response does not depend on the applied potential. At late times, the capacitor relaxes with a relaxation time proportional to the diffusion time L2/ D.

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Hariri, Saeed. "Near-Surface Transport Properties and Lagrangian Statistics during Two Contrasting Years in the Adriatic Sea". Journal of Marine Science and Engineering 8, nr 9 (4.09.2020): 681. http://dx.doi.org/10.3390/jmse8090681.

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This paper describes the near-surface transport properties and Lagrangian statistics in the Adriatic semi-enclosed basin using synthetic drifters. Lagrangian transport models were used to simulate synthetic trajectories from the mean flow fields obtained by the Massachusetts Institute of Technology general circulation model (MITgcm), implemented in the Adriatic from October 2006 until December 2008. In particular, the surface circulation properties in two contrasting years (2007 had a mild winter and cold fall, while 2008 had a normal winter and hot summer) are compared here. In addition, the Lagrangian statistics for the entire Adriatic Basin after removing the Eulerian mean circulation for numerical particles were calculated. The results indicate that the numerical particles were slower in this simulation when compared with the real drifters. This is because of the reduced energetic flow field generated by the MIT general circulation model during the selected years. The numerical results showed that the balanced effects of the wind-driven recirculation in the northernmost area(which would be a sea response to the Bora wind field) and the Po River discharge cause the residence times to be similar during the two selected years (182 and 185 days in 2007 and 2008, respectively). Furthermore, the mean angular momentum, diffusivity, and Lagrangian velocity covariance values are smaller than in the real drifter observations, while the maximum Lagrangian integral time scale is the same.

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Mesarchaki, E., C. Kräuter, K. E. Krall, M. Bopp, F. Helleis, J. Williams i B. Jähne. "Measuring air–sea gas-exchange velocities in a large-scale annular wind–wave tank". Ocean Science 11, nr 1 (28.01.2015): 121–38. http://dx.doi.org/10.5194/os-11-121-2015.

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Abstract. In this study we present gas-exchange measurements conducted in a large-scale wind–wave tank. Fourteen chemical species spanning a wide range of solubility (dimensionless solubility, α = 0.4 to 5470) and diffusivity (Schmidt number in water, Scw = 594 to 1194) were examined under various turbulent (u10 = 0.73 to 13.2 m s−1) conditions. Additional experiments were performed under different surfactant modulated (two different concentration levels of Triton X-100) surface states. This paper details the complete methodology, experimental procedure and instrumentation used to derive the total transfer velocity for all examined tracers. The results presented here demonstrate the efficacy of the proposed method, and the derived gas-exchange velocities are shown to be comparable to previous investigations. The gas transfer behaviour is exemplified by contrasting two species at the two solubility extremes, namely nitrous oxide (N2O) and methanol (CH3OH). Interestingly, a strong transfer velocity reduction (up to a factor of 3) was observed for the relatively insoluble N2O under a surfactant covered water surface. In contrast, the surfactant effect for CH3OH, the high solubility tracer, was significantly weaker.

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Mesarchaki, E., C. Kräuter, K. E. Krall, M. Bopp, F. Helleis, J. Williams i B. Jähne. "Measuring air–sea gas exchange velocities in a large scale annular wind-wave tank". Ocean Science Discussions 11, nr 3 (23.06.2014): 1643–89. http://dx.doi.org/10.5194/osd-11-1643-2014.

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Abstract. In this study we present gas exchange measurements conducted in a large scale wind-wave tank. Fourteen chemical species spanning a wide range of solubility (dimensionless solubility, α = 0.4 to 5470) and diffusivity (Schmidt number in water, Scw = 594 to 1194) were examined under various turbulent (u10 = 0.8 to 15 m s−1 conditions. Additional experiments were performed under different surfactant modulated (two different concentration levels of Triton X-100) surface states. This paper details the complete methodology, experimental procedure and instrumentation used to derive the total transfer velocity for all examined tracers. The results presented here demonstrate the efficacy of the proposed method, and the derived gas exchange velocities are shown to be comparable to previous investigations. The gas transfer behaviour is exemplified by contrasting two species at the two solubility extremes, namely nitrous oxide (N2O) and methanol (CH3OH). Interestingly, a strong transfer velocity reduction (up to a factor of three) was observed for N2O under a surfactant covered water surface. In contrast, the surfactant affected CH3OH, the high solubility tracer only weakly.

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Sihi, Debjani, Xiaofeng Xu, Mónica Salazar Ortiz, Christine S. O'Connell, Whendee L. Silver, Carla López-Lloreda, Julia M. Brenner i in. "Representing methane emissions from wet tropical forest soils using microbial functional groups constrained by soil diffusivity". Biogeosciences 18, nr 5 (15.03.2021): 1769–86. http://dx.doi.org/10.5194/bg-18-1769-2021.

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Abstract. Tropical ecosystems contribute significantly to global emissions of methane (CH4), and landscape topography influences the rate of CH4 emissions from wet tropical forest soils. However, extreme events such as drought can alter normal topographic patterns of emissions. Here we explain the dynamics of CH4 emissions during normal and drought conditions across a catena in the Luquillo Experimental Forest, Puerto Rico. Valley soils served as the major source of CH4 emissions in a normal precipitation year (2016), but drought recovery in 2015 resulted in dramatic pulses in CH4 emissions from all topographic positions. Geochemical parameters including (i) dissolved organic carbon (C), acetate, and soil pH and (ii) hydrological parameters like soil moisture and oxygen (O2) concentrations varied across the catena. During the drought, soil moisture decreased in the slope and ridge, and O2 concentrations increased in the valley. We simulated the dynamics of CH4 emissions with the Microbial Model for Methane Dynamics-Dual Arrhenius and Michaelis–Menten (M3D-DAMM), which couples a microbial functional group CH4 model with a diffusivity module for solute and gas transport within soil microsites. Contrasting patterns of soil moisture, O2, acetate, and associated changes in soil pH with topography regulated simulated CH4 emissions, but emissions were also altered by rate-limited diffusion in soil microsites. Changes in simulated available substrate for CH4 production (acetate, CO2, and H2) and oxidation (O2 and CH4) increased the predicted biomass of methanotrophs during the drought event and methanogens during drought recovery, which in turn affected net emissions of CH4. A variance-based sensitivity analysis suggested that parameters related to aceticlastic methanogenesis and methanotrophy were most critical to simulate net CH4 emissions. This study enhanced the predictive capability for CH4 emissions associated with complex topography and drought in wet tropical forest soils.

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Tao, Peng, i Xiao Lin Shu. "Multiple Helium Atoms Diffusion in Tungsten: A Molecular Dynamic Simulation". Materials Science Forum 789 (kwiecień 2014): 549–53. http://dx.doi.org/10.4028/www.scientific.net/msf.789.549.

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The diffusion process of multiple He atoms in W is simulated by a molecular dynamics (MD) method with the W-H-He analytic bond-order potential. The diffusivities of different number of helium (He) atoms in W are determined by the mean squared displacement (MSD) method at different temperatures. The diffusivity-temperature (D-T) relationship is fitted to the Arrhenius equation to obtain the pre-factor and the diffusion barrier. Under the temperature of 1200K He atoms diffuse together, and above 1200K they separate from each other. When the number of He atoms is greater than three, all He atoms oscillate at the tetrahedral interstitial site (TIS) instead of diffusing under 400K. In the temperature range of 400-1200K, the diffusion barriers of He atoms, the number of which is from two to five, are 0.098, 0.170, 0.125 and 0.112eV, respectively. Contrasting with one He atom (0.058eV), the higher diffusion barriers reflect a greater difficulty in diffusion of multiple He atoms in W. In addition, when the number of He atoms is over five, vacancies are formed in W, and He atoms occupy the vacancies.

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Badin, Gualtiero, Richard G. Williams, Zhao Jing i Lixin Wu. "Water Mass Transformations in the Southern Ocean Diagnosed from Observations: Contrasting Effects of Air–Sea Fluxes and Diapycnal Mixing". Journal of Physical Oceanography 43, nr 7 (1.07.2013): 1472–84. http://dx.doi.org/10.1175/jpo-d-12-0216.1.

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Abstract Transformation and formation rates of water masses in the Southern Ocean are estimated in a neutral-surface framework using air–sea fluxes of heat and freshwater together with in situ estimates of diapycnal mixing. The air–sea fluxes are taken from two different climatologies and a reanalysis dataset, while the diapycnal mixing is estimated from a mixing parameterization applied to five years of Argo float data. Air–sea fluxes lead to a large transformation directed toward lighter waters, typically from −45 to −63 Sv (1 Sv ≡ 106 m3 s−1) centered at γ = 27.2, while interior diapycnal mixing leads to two weaker peaks in transformation, directed toward denser waters, 8 Sv centered at γ = 27.8, and directed toward lighter waters, −16 Sv centered at γ = 28.3. Hence, air–sea fluxes and interior diapycnal mixing are important in transforming different water masses within the Southern Ocean. The transformation of dense to lighter waters by diapycnal mixing within the Southern Ocean is slightly larger, though comparable in magnitude, to the transformation of lighter to dense waters by air–sea fluxes in the North Atlantic. However, there are significant uncertainties in the authors' estimates with errors of at least ±5 W m−2 in air–sea fluxes, a factor 4 uncertainty in diapycnal mixing and limited coverage of air–sea fluxes in the high latitudes and Argo data in the Pacific. These water mass transformations partly relate to the circulation in density space: air–sea fluxes provide a general lightening along the core of the Antarctic Circumpolar Current and diapycnal diffusivity is enhanced at middepths along the current.

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Chen, Bingzhang, i Sherwood Lan Smith. "CITRATE 1.0: Phytoplankton continuous trait-distribution model with one-dimensional physical transport applied to the North Pacific". Geoscientific Model Development 11, nr 1 (1.02.2018): 467–95. http://dx.doi.org/10.5194/gmd-11-467-2018.

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Abstract. Diversity plays critical roles in ecosystem functioning, but it remains challenging to model phytoplankton diversity in order to better understand those roles and reproduce consistently observed diversity patterns in the ocean. In contrast to the typical approach of resolving distinct species or functional groups, we present a ContInuous TRAiT-basEd phytoplankton model (CITRATE) that focuses on macroscopic system properties such as total biomass, mean trait values, and trait variance. This phytoplankton component is embedded within a nitrogen–phytoplankton-zooplankton–detritus–iron model that itself is coupled with a simplified one-dimensional ocean model. Size is used as the master trait for phytoplankton. CITRATE also incorporates trait diffusion for sustaining diversity and simple representations of physiological acclimation, i.e., flexible chlorophyll-to-carbon and nitrogen-to-carbon ratios. We have implemented CITRATE at two contrasting stations in the North Pacific where several years of observational data are available. The model is driven by physical forcing including vertical eddy diffusivity imported from three-dimensional general ocean circulation models (GCMs). One common set of model parameters for the two stations is optimized using the Delayed-Rejection Adaptive Metropolis–Hasting Monte Carlo (DRAM) algorithm. The model faithfully reproduces most of the observed patterns and gives robust predictions on phytoplankton mean size and size diversity. CITRATE is suitable for applications in GCMs and constitutes a prototype upon which more sophisticated continuous trait-based models can be developed.

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Costa, Felipe D., Otávio C. Acevedo, Luiz E. Medeiros, Rafael Maroneze, Franciano S. Puhales, Arlindo D. Carvalho Jr., Luis F. Camponogara, Daniel M. dos Santos i Luca Mortarini. "Stable Boundary Layer Regimes in Single-Column Models". Journal of the Atmospheric Sciences 77, nr 6 (21.05.2020): 2039–54. http://dx.doi.org/10.1175/jas-d-19-0218.1.

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Abstract Two contrasting flow regimes exist in the stable boundary layer (SBL), as evidenced from both observational and modeling studies. In general, numerical schemes such as those used in numerical weather prediction and climate models (NWPCs) reproduce a transition between SBL regimes. However, the characteristics of such a transition depend on the turbulence parameterizations and stability functions used to represent the eddy diffusivity in the models. The main goal of the present study is to detail how the two SBL regimes occur in single-column models (SCMs) by analyzing the SBL structure and its dependence on external parameters. Two different turbulence closure orders (first order and an E–l model) and two types of stability functions (short and long tail) are considered. The control exerted by the geostrophic wind and the surface cooling rate on the model SBL regimes is addressed. The model flow presents a three-layer structure: a fully turbulent, weakly stable layer (WSL) next to the surface; a very stable layer (VSL) above that; and a laminar layer above the other two and toward the domain top. It is shown that the WSL and VSL are related to both SBL regimes, respectively. Furthermore, the numerically simulated SBL presents the two-layer structure regardless of the turbulence parameterization order and stability function used. The models also reproduce other features reported in recent observational studies: an S-shaped dependence of the thermal gradient on the mean wind speed and an independence of the vertical gradient of friction velocity δu* on the mean wind speed.

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Ranjitha Ruttala, Pratik Purohit, AninditaBhattacharjee, BinduKumari i Prasun K. Roy. "MRI-DTI Imaging Reveals Specific Neuro-degeneration Signature in Precuneus Node of Awareness Processing in Brain under Alzheimer’s Disease". JOURNAL OF ADVANCED APPLIED SCIENTIFIC RESEARCH 4, nr 4 (7.11.2022): 102–11. http://dx.doi.org/10.46947/joaasr442022460.

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Introduction:Alzheimer's disease(AD) displays progressive neurodegenerative atrophy, causing neuronal lossaffecting cognitive skills and memory. As precuneus is associated with episodic memory and is the reflexive self-awareness hub node, we consider precuneus as region-of-interest(ROI) for analysing AD.Objective:The main objective is find AD-caused alteration in nerve fibres, using diffusion tensor imaging(DTI) parameters like Mean Diffusivity(MD), Fractional Anisotropy(FA), and Nerve-tract Parameters, as number, length, volume, density, and thus, analyse the effect on precuneus by AD [when compared to normal subjects(CN)].Materials/Methods:Normals and Alzheimer’s subjects (n=50 each) were scanned with Siemens 3-tesla MRI-scanner. DTI parameters were estimated by DSI-FSL procedure, with statistical analysis usingt-test/ANOVA.Results:While ageing-process occurs in both AD and CN subjects, there is no change in “macro-structural” nerve fibre characteristics (e.g. Tract Indices: Number, density, volume, length). Contrastingly, there is significant alteration in “micro-structural” fibre characteristics, as increase in Mean Diffusivity(p=0.0006) and decrease in Fractional Anisotropy(p=0.0009) in Alzheimer's disease, when compared with normal subjects. Furthermore, comparing left-versus-right brain, Alzheimer’s patients (but not Normal subjects) show diminution in macro-structural nerve characteristics in left precuneus (compared to right precuneus): namely Tract’s number(p=0.0010), length(p=0.0107), volume(p=0.0225), density(p=0.0340).Conclusion:Under neurodegeneration, change in “micro-structural” nerve-fibre characteristics (Tract Indices), as opposed to “macro structural” fibre indices, can be hallmark for AD. Moreover, right precuneus is more protected in AD. Conversely, left precuneus has more neurodegeneration since its blood-flow is supplied by left common-carotid artery (unlike right common-carotid artery), this left artery arises directly from high-pressure aortic flow, transmitting turbulent hemodynamic stress to left precuneus.

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Nandakumaran, A. K., i Ali Sili. "Homogenization of a hyperbolic equation with highly contrasting diffusivity coefficients". Differential and Integral Equations 29, nr 1/2 (1.01.2016). http://dx.doi.org/10.57262/die/1448323252.

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Stewart, Andrew L., Nicole K. Neumann i Aviv Solodoch. "“Eddy” Saturation of the Antarctic Circumpolar Current by Standing Waves". Journal of Physical Oceanography, 23.01.2023. http://dx.doi.org/10.1175/jpo-d-22-0154.1.

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Abstract It is now well established that changes in the zonal wind stress over the ACC do not lead to changes in its baroclinicity nor baroclinic transport, a phenomenon referred to as “eddy saturation”. Previous studies provide contrasting dynamical mechanisms for this phenomenon: on one extreme, changes in the winds lead to changes the efficiency with which transient eddies transfer momentum to the sea floor; on the other, structural adjustments of the ACC’s standing meanders increase the efficiency of momentum transfer. In this study the authors investigate the relative importance of these mechanisms using an idealized, isopycnal channel model of the ACC. Via separate diagnoses of the model’s time-mean flow and eddy diffusivity, the authors decompose the model’s response to changes in wind stress into contributions from transient eddies and the mean flow. A key result is that holding the transient eddy diffusivity constant while varying the mean flow very closely compensates changes in the wind stress, whereas holding the mean flow constant and varying the eddy diffusivity does not. This implies that “eddy saturation” primarily occurs due to adjustments in the ACC’s standing waves/meanders, rather than due to adjustments of transient eddy behavior. The authors derive a quasi-geostrophic theory for ACC transport saturation by standing waves, in which the transient eddy diffusivity is held fixed, and thus provides dynamical insights into standing wave adjustment to wind changes. These findings imply that representing eddy saturation in global models requires adequate resolution of the ACC’s standing meanders, with wind-responsive parameterizations of the transient eddies being of secondary importance.

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Nandakumaran, A. K., Abu Sufian i Renjith Thazhathethil. "Homogenization with strong contrasting diffusivity in a circular oscillating domain with $$L^1$$ source term". Annali di Matematica Pura ed Applicata (1923 -), 9.09.2022. http://dx.doi.org/10.1007/s10231-022-01259-x.

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Park, Sohee, Young-Kyun Kwon, Mina Yoon i Changwon Park. "Role of Sr doping and external strain on relieving bottleneck of oxygen diffusion in La2−xSrxCuO4−δ". Scientific Reports 12, nr 1 (4.08.2022). http://dx.doi.org/10.1038/s41598-022-17376-9.

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AbstractIn many complex oxides, the oxygen vacancy formation is a promising route to modify the material properties such as a superconductivity and an oxygen diffusivity. Cation substitutions and external strain have been utilized to control the concentration and diffusion of oxygen vacancies, but the mechanisms behind the controls are not fully understood. Using first-principles calculations, we find how Sr doping and external strain greatly enhances the diffusivity of oxygen vacancies in La2−xSrxCuO4−δ (LSCO) in the atomic level. In hole-doped case (2x > δ), the formation energy of an apical vacancy in the LaO layer is larger than its equatorial counterpart by 0.2 eV that the bottleneck of diffusion process is for oxygen vacancies to escape equatorial sites. Such an energy difference can be reduced and even reversed by either small strain (< 1.5%) or short-range attraction between Sr and oxygen vacancy, and in turn, the oxygen diffusivity is greatly enhanced. For fully compensated hole case (2x ≦ δ), the formation energy of an apical vacancy becomes too high that most oxygen vacancies cannot move but would be trapped at equatorial sites. From our electronic structure analysis, we found that the contrasting change in the formation energy by Sr doping and external strain is originated from the different localization natures of electron carrier from both types of oxygen vacancies.

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Nelson, Mark C., Jessica Royer, Wen Da Lu, Ilana R. Leppert, Jennifer S. W. Campbell, Simona Schiavi, Hyerang Jin i in. "The Human Brain Connectome Weighted by the Myelin Content and Total Intra-Axonal Cross-Sectional Area of White Matter Tracts". Network Neuroscience, 2.08.2023, 1–68. http://dx.doi.org/10.1162/netn_a_00330.

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Abstract A central goal in neuroscience is the development of a comprehensive mapping between structural and functional brain features which facilitates mechanistic interpretation of brain function. However, the interpretability of structure-function brain models remains limited by a lack of biological detail. Here, we characterize human structural brain networks weighted by multiple white matter microstructural features including total intra-axonal cross-sectional area and myelin content. We report edge-weight-dependent spatial distributions, variance, small-worldness, rich club, hubs, as well as relationships with function, edge length and myelin. Contrasting networks weighted by the total intra-axonal cross-sectional area and myelin content of white matter tracts, we find opposite relationships with functional connectivity, an edge-length-independent inverse relationship with each other, and the lack of a canonical rich club in myelin-weighted networks. When controlling for edge length, networks weighted by either fractional anisotropy, radial diffusivity or neurite density show no relationship with whole-brain functional connectivity. We conclude that the co-utilization of structural networks weighted by total intra-axonal cross-sectional area and myelin content could improve our understanding of the mechanisms mediating the structure-function brain relationship.

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Mungoven, Tiffani J., Noemi Meylakh, Vaughan G. Macefield, Paul M. Macey i Luke A. Henderson. "Alterations in brain structure associated with trigeminal nerve anatomy in episodic migraine". Frontiers in Pain Research 3 (18.07.2022). http://dx.doi.org/10.3389/fpain.2022.951581.

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The pathophysiology of migraine remains to be elucidated. We have recently shown that interictal migraineurs exhibit reduced fractional anisotropy (FA) in the root entry zone of the trigeminal nerve when compared to controls, but it is not known if this altered nerve anatomy is associated with changes within the brainstem or higher cortical brain regions. Diffusion tensor imaging of the brain was used to calculate regional measures of structure, including mean diffusivity (MD), axial diffusivity (AX) and radial diffusivity (RD) in addition to voxel-based morphometry of T1-weighted anatomical images. Linear relationships between trigeminal nerve anatomy (FA) and MD throughout the brainstem and/or higher cortical regions were determined in both controls (n = 31, brainstem; n = 38, wholebrain) and interictal migraineurs (n = 32, brainstem; n = 38, wholebrain). Additionally, within the same brain areas, relationships of AX and RD with nerve FA were determined. We found that in both interictal migraine and control participants, decreasing trigeminal nerve FA was associated with significantly increased MD in brainstem regions including the spinal trigeminal nucleus and midbrain periaqueductal gray matter (PAG), and in higher brain regions such as the hypothalamus, insula, posterior cingulate, primary somatosensory and primary visual (V1) cortices. Whereas, both control and migraineur groups individually displayed significant inverse correlations between nerve FA and MD, in migraineurs this pattern was disrupted in the areas of the PAG and V1, with only the control group displaying a significant linear relationship (PAG controls r = –0.58, p = 0.003; migraineurs r = –0.25, p = 0.17 and V1 controls r = −0.52, p = 0.002; migraineurs r = –0.10, p = 0.55). Contrastingly, we found no gray matter volume changes in brainstem or wholebrain areas. These data show that overall, trigeminal nerve anatomy is significantly related to regional brain structure in both controls and migraineurs. Importantly, the PAG showed a disruption of this relationship in migraineurs suggesting that the anatomy and possibly the function of the PAG is uniquely altered in episodic migraine, which may contribute to altered orofacial pain processing in migraine.

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Dong, Dong, Koichi Hosomi, Nobuhiko Mori, Yoshi-ichiro Kamijo, Yohei Furotani, Daisuke Yamagami, Yu-ichiro Ohnishi i in. "White matter microstructural alterations in patients with neuropathic pain after spinal cord injury: a diffusion tensor imaging study". Frontiers in Neurology 14 (24.08.2023). http://dx.doi.org/10.3389/fneur.2023.1241658.

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BackgroundThrough contrastive analysis, we aimed to identify the white matter brain regions that show microstructural changes in patients with neuropathic pain (NP) after spinal cord injury (SCI).MethodsWe categorized patients with SCI into NP (n = 30) and non-NP (n = 15) groups. We extracted diffusion tensor maps of fractional anisotropy (FA) and mean (MD), axial (AD), and radial (RD) diffusivity. A randomization-based method in tract-based spatial statistics was used to perform voxel-wise group comparisons among the FA, MD, AD, and RD for nonparametric permutation tests.ResultsAtlas-based analysis located significantly different regions (p < 0.05) in the appointed brain atlas. Compared to the non-NP group, the NP group showed higher FA in the posterior body and splenium of the corpus callosum and higher AD in the corpus callosum, internal capsule, corona radiata, posterior thalamic radiation, sagittal stratum, external capsule, cingulum, fornix/stria terminalis, superior longitudinal fasciculus, and uncinate fasciculus.ConclusionThe results demonstrated that compared with the non-NP group, NP pathogenesis after SCI was potentially related to higher values in FA that are associated with microstructural changes in the posterior body and splenium of the corpus callosum, which could be regarded as central sensitization or network hyperexcitability.

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