Um die anderen Arten von Veröffentlichungen zu diesem Thema anzuzeigen, folgen Sie diesem Link: Mean field optimal transport.
Zeitschriftenartikel zum Thema „Mean field optimal transport“
Geben Sie eine Quelle nach APA, MLA, Chicago, Harvard und anderen Zitierweisen an
Machen Sie sich mit Top-50 Zeitschriftenartikel für die Forschung zum Thema "Mean field optimal transport" bekannt.
Neben jedem Werk im Literaturverzeichnis ist die Option "Zur Bibliographie hinzufügen" verfügbar. Nutzen Sie sie, wird Ihre bibliographische Angabe des gewählten Werkes nach der nötigen Zitierweise (APA, MLA, Harvard, Chicago, Vancouver usw.) automatisch gestaltet.
Sie können auch den vollen Text der wissenschaftlichen Publikation im PDF-Format herunterladen und eine Online-Annotation der Arbeit lesen, wenn die relevanten Parameter in den Metadaten verfügbar sind.
Sehen Sie die Zeitschriftenartikel für verschiedene Spezialgebieten durch und erstellen Sie Ihre Bibliographie auf korrekte Weise.
1
Baudelet, Sebastian, Brieuc Frénais, Mathieu Laurière, Amal Machtalay und Yuchen Zhu. „Deep learning for mean field optimal transport“. ESAIM: Proceedings and Surveys 77 (2024): 145–75. http://dx.doi.org/10.1051/proc/202477145.
Der volle Inhalt der QuelleAnnotation:
Mean field control (MFC) problems have been introduced to study social optima in very large populations of strategic agents. The main idea is to consider an infinite population and to simplify the analysis by using a mean field approximation. These problems can also be viewed as optimal control problems for McKean-Vlasov dynamics. They have found applications in a wide range of fields, from economics and finance to social sciences and engineering. Usually, the goal for the agents is to minimize a total cost which consists in the integral of a running cost plus a terminal cost. In this work, we consider MFC problems in which there is no terminal cost but, instead, the terminal distribution is prescribed as in optimal transport problem. By analogy with MFC, we call such problems mean field optimal transport problems (or MFOT for short) since they can be viewed as a generalization of classical optimal transport problems when mean field interactions occur in the dynamics or the running cost function. We propose three numerical methods based on neural networks. The first one is based on directly learning an optimal control. The second one amounts to solve a forward-backward PDE system characterizing the solution. The third one relies on a primal-dual approach. We illustrate these methods with numerical experiments conducted on two families of examples.
2
Cao, Haoyang, Xin Guo und Mathieu Laurière. „Connecting GANs, Mean-Field Games, and Optimal Transport“. SIAM Journal on Applied Mathematics 84, Nr. 4 (01.07.2024): 1255–87. http://dx.doi.org/10.1137/22m1499534.
Der volle Inhalt der Quelle
3
Liu, Jiakun, und Grégoire Loeper. „Optimal transport with discrete long-range mean-field interactions“. Bulletin of Mathematical Sciences 10, Nr. 02 (12.05.2020): 2050011. http://dx.doi.org/10.1142/s1664360720500113.
Der volle Inhalt der QuelleAnnotation:
We study an optimal transport problem where, at some intermediate time, the mass is either accelerated by an external force field or self-interacting. We obtain the regularity of the velocity potential, intermediate density, and optimal transport map, under the conditions on the interaction potential that are related to the so-called Ma–Trudinger–Wang condition from optimal transport [X.-N. Ma, N. S. Trudinger and X.-J. Wang, Regularity of potential functions of the optimal transportation problems, Arch. Ration. Mech. Anal. 177 (2005) 151–183.].
4
Di Persio, Luca, und Matteo Garbelli. „From Optimal Control to Mean Field Optimal Transport via Stochastic Neural Networks“. Symmetry 15, Nr. 9 (08.09.2023): 1724. http://dx.doi.org/10.3390/sym15091724.
Der volle Inhalt der QuelleAnnotation:
In this paper, we derive a unified perspective for Optimal Transport (OT) and Mean Field Control (MFC) theories to analyse the learning process for Neural Network algorithms in a high-dimensional framework. We consider a Mean Field Neural Network in the context of MFC theory referring to the mean field formulation of OT theory that may allow the development of efficient algorithms in a high-dimensional framework while providing a powerful tool in the context of explainable Artificial Intelligence.
5
Ruthotto, Lars, Stanley J. Osher, Wuchen Li, Levon Nurbekyan und Samy Wu Fung. „A machine learning framework for solving high-dimensional mean field game and mean field control problems“. Proceedings of the National Academy of Sciences 117, Nr. 17 (09.04.2020): 9183–93. http://dx.doi.org/10.1073/pnas.1922204117.
Der volle Inhalt der QuelleAnnotation:
Mean field games (MFG) and mean field control (MFC) are critical classes of multiagent models for the efficient analysis of massive populations of interacting agents. Their areas of application span topics in economics, finance, game theory, industrial engineering, crowd motion, and more. In this paper, we provide a flexible machine learning framework for the numerical solution of potential MFG and MFC models. State-of-the-art numerical methods for solving such problems utilize spatial discretization that leads to a curse of dimensionality. We approximately solve high-dimensional problems by combining Lagrangian and Eulerian viewpoints and leveraging recent advances from machine learning. More precisely, we work with a Lagrangian formulation of the problem and enforce the underlying Hamilton–Jacobi–Bellman (HJB) equation that is derived from the Eulerian formulation. Finally, a tailored neural network parameterization of the MFG/MFC solution helps us avoid any spatial discretization. Our numerical results include the approximate solution of 100-dimensional instances of optimal transport and crowd motion problems on a standard work station and a validation using a Eulerian solver in two dimensions. These results open the door to much-anticipated applications of MFG and MFC models that are beyond reach with existing numerical methods.
6
Sivilevičius, Henrikas, und Mindaugas Martišius. „FIELD INVESTIGATION AND ASSESSMENT ON THE WEAR OF ASPHALT PAVEMENT MILLING MACHINE PICKS“. Transport 36, Nr. 6 (09.02.2022): 499–509. http://dx.doi.org/10.3846/transport.2021.16443.
Der volle Inhalt der QuelleAnnotation:
Deteriorated asphalt pavement material is recycled applying proved technologies based on scientific principles and practical experience. The asphalt pavement layer during rehabilitation process is loosened by a mobile transport machine fracturing into the required material grading and called Reclaimed Asphalt Pavement (RAP). RAP is extracted while cutting asphalt chip in required depth at optimal speed by mean of changeable picks installed in a toolholder of milling machine rotating drum. During interaction with the asphalt pavement to be demolished, the wear of picks appears, and the dimensions of their elements decrease. Methodology and results of a field experimental research allowed statistically to determine and evaluate the wear dynamics of picks from 2 manufacturers are provided in this paper. The results provide that length of pick, diameter of carbide tip and diameter of steel body of picks from these manufacturers were decreasing proportionally to milled asphalt pavement surface. Applying the Fisher’s criterion it was found that the variances of the reduction of these geometrical parameters are the same and they satisfy the normal distribution according to the Kolmogorov’s criterion. All values of Student’s criterion calculated statistics were higher than the critical values, which indicated that the wear intensiveness of the picks of the 2 manufacturers differed significantly. These data can be used to select suitable picks for the milling machine according to their wear intensity.
7
BARTON, ALISTAIR, und NASSIF GHOUSSOUB. „Dynamic and stochastic propagation of the Brenier optimal mass transport“. European Journal of Applied Mathematics 30, Nr. 6 (20.03.2019): 1264–99. http://dx.doi.org/10.1017/s0956792519000032.
Der volle Inhalt der QuelleAnnotation:
Similar to how Hopf–Lax–Oleinik-type formula yield variational solutions for Hamilton–Jacobi equations on Euclidean space, optimal mass transportations can sometimes provide variational formulations for solutions of certain mean-field games. We investigate here the particular case of transports that maximize and minimize the following ‘ballistic’ cost functional on phase space TM, which propagates Brenier’s transport along a Lagrangian L, $$b_T(v, x):=\inf\left\{\langle v, \gamma (0)\rangle +\int_0^TL(t, \gamma (t), {\dot \gamma}(t))\, dt; \gamma \in C^1([0, T], M); \gamma(T)=x\right\}\!,$$ where $M = \mathbb{R}^d$, and T >0. We also consider the stochastic counterpart: \begin{align*} \underline{B}_T^s(\mu,\nu):=\inf\left\{\mathbb{E}\left[\langle V,X_0\rangle +\int_0^T L(t, X,\beta(t,X))\,dt\right]\!; X\in \mathcal{A}, V\sim\mu,X_T\sim \nu\right\}\!, \end{align*} where $\mathcal{A}$ is the set of stochastic processes satisfying dX = βX (t, X) dt + dWt, for some drift βX (t, X), and where Wt is σ(Xs: 0 ≤ s ≤ t)-Brownian motion. Both cases lead to Lax–Oleinik-type formulas on Wasserstein space that relate optimal ballistic transports to those associated with dynamic fixed-end transports studied by Bernard–Buffoni and Fathi–Figalli in the deterministic case, and by Mikami–Thieullen in the stochastic setting. While inf-convolution easily covers cost minimizing transports, this is not the case for total cost maximizing transports, which actually are sup-inf problems. However, in the case where the Lagrangian L is jointly convex on phase space, Bolza-type dualities – well known in the deterministic case but novel in the stochastic case – transform sup-inf problems to sup–sup settings. We also write Eulerian formulations and point to links with the theory of mean-field games.
8
Igbida, Noureddine, und Van Thanh Nguyen. „Optimal partial transport problem with Lagrangian costs“. ESAIM: Mathematical Modelling and Numerical Analysis 52, Nr. 5 (September 2018): 2109–32. http://dx.doi.org/10.1051/m2an/2018001.
Der volle Inhalt der QuelleAnnotation:
We introduce a dual dynamical formulation for the optimal partial transport problem with Lagrangian costs cL(x,y) := ξ∈Lip([0,1];ℝN)inf {∫01 L(ξ(t), ξ˙(t))dt : ξ(0) = x, ξ(1) = y} based on a constrained Hamilton–Jacobi equation. Optimality condition is given that takes the form of a system of PDEs in some way similar to constrained mean field games. The equivalent formulations are then used to give numerical approximations to the optimal partial transport problem via augmented Lagrangian methods. One of advantages is that the approach requires only values of L and does not need to evaluate cL(x, y), for each pair of endpoints x and y, which comes from a variational problem. This method also provides at the same time active submeasures and the associated optimal transportation.
9
Miatselskaya, N. S., A. I. Bril, A. P. Chaikovsky, Yu Yu Yukhymchuk, G. P. Milinevski und A. A. Simon. „OPTIMAL INTERPOLATION OF AERONET RADIOMETRIC NETWORK OBSERVATIONS FOR THE EVALUATION OF THE AEROSOL OPTICAL DEPTH DISTRIBUTION IN THE EASTERN EUROPEAN REGION“. Journal of Applied Spectroscopy 89, Nr. 2 (18.03.2022): 246–53. http://dx.doi.org/10.47612/0514-7506-2022-89-2-246-253.
Der volle Inhalt der QuelleAnnotation:
The application of the optimal interpolation method for the assimilation of the observational data of aerosol optical thickness (AOT), which are sparse in space and time, in the chemical transport model is herein validated. Assuming the negligible error of AOT observations in the AERONET ground-based radiometric network, spatial and temporal correlation functions of the errors in the results of the AOT simulated by the GEOS-Chem chemical transport model are obtained. The optimal interpolation method is applied to the AERONET data using the GEOS-Chem results as a background field for the Eastern European region for 2015–2016. It is shown that the use of the optimal interpolation method permits to reduce the root-mean-square error of the AOT estimation by more than a third in places where there are no AERONET stations in comparison with the model results.
10
Hassanzadeh, Pedram, Gregory P. Chini und Charles R. Doering. „Wall to wall optimal transport“. Journal of Fluid Mechanics 751 (24.06.2014): 627–62. http://dx.doi.org/10.1017/jfm.2014.306.
Der volle Inhalt der QuelleAnnotation:
AbstractThe calculus of variations is employed to find steady divergence-free velocity fields that maximize transport of a tracer between two parallel walls held at fixed concentration for one of two constraints on flow strength: a fixed value of the kinetic energy (mean square velocity) or a fixed value of the enstrophy (mean square vorticity). The optimizing flows consist of an array of (convection) cells of a particular aspect ratio $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\varGamma $. We solve the nonlinear Euler–Lagrange equations analytically for weak flows and numerically – as well as via matched asymptotic analysis in the fixed energy case – for strong flows. We report the results in terms of the Nusselt number ${\mathit{Nu}}$, a dimensionless measure of the tracer transport, as a function of the Péclet number ${\mathit{Pe}}$, a dimensionless measure of the strength of the flow. For both constraints, the maximum transport ${\mathit{Nu}}_{\mathit{MAX}}({\mathit{Pe}})$ is realized in cells of decreasing aspect ratio $\varGamma _{\mathit{opt}}({\mathit{Pe}})$ as ${\mathit{Pe}}$ increases. For the fixed energy problem, ${\mathit{Nu}}_{\mathit{MAX}} \sim {\mathit{Pe}}$ and $\varGamma _{\mathit{opt}} \sim {\mathit{Pe}}^{-1/2}$, while for the fixed enstrophy scenario, ${\mathit{Nu}}_{\mathit{MAX}} \sim {\mathit{Pe}}^{10/17}$ and $\varGamma _{\mathit{opt}} \sim {\mathit{Pe}}^{-0.36}$. We interpret our results in the context of buoyancy-driven Rayleigh–Bénard convection problems that satisfy the flow intensity constraints, enabling us to investigate how the transport scalings compare with upper bounds on ${\mathit{Nu}}$ expressed as a function of the Rayleigh number ${\mathit{Ra}}$. For steady convection in porous media, corresponding to the fixed energy problem, we find ${\mathit{Nu}}_{\mathit{MAX}} \sim {\mathit{Ra}}$ and $\varGamma _{\mathit{opt}} \sim {\mathit{Ra}}^{-1/2}$, while for steady convection in a pure fluid layer between stress-free isothermal walls, corresponding to fixed enstrophy transport, ${\mathit{Nu}}_{\mathit{MAX}} \sim {\mathit{Ra}}^{5/12}$ and $\varGamma _{\mathit{opt}} \sim {\mathit{Ra}}^{-1/4}$.
11
Fu, Guosheng, Stanley Osher, Will Pazner und Wuchen Li. „Generalized optimal transport and mean field control problems for reaction-diffusion systems with high-order finite element computation“. Journal of Computational Physics 508 (Juli 2024): 112994. http://dx.doi.org/10.1016/j.jcp.2024.112994.
Der volle Inhalt der Quelle
12
BARMAN, H., und N. S. VIDHYADHIRAJA. „TRANSPORT AND SPECTRA IN THE HALF-FILLED HUBBARD MODEL: A DYNAMICAL MEAN FIELD STUDY“. International Journal of Modern Physics B 25, Nr. 18 (20.07.2011): 2461–79. http://dx.doi.org/10.1142/s0217979211100977.
Der volle Inhalt der QuelleAnnotation:
We present an improved numerical implementation of the iterated perturbation theory, for use as an impurity solver for lattice models within dynamical mean field theory (DMFT). We demonstrate higher resolution of spectral and transport features and a reduced computational expense. Using this implementation, we study the issues of scaling and universality in spectral and transport properties of the particle-hole symmetric Hubbard model within DMFT. We re-examine experimental results for pressure-dependent resistivity in Selenium doped NiS2and thermal hysteresis on V2O3and find qualitative agreement. A systematic study of spectral weight transfer in optical conductivity is carried out.
13
Bai, Siqi, Yongjie Luo und Qun Wan. „Transfer Learning for Wireless Fingerprinting Localization Based on Optimal Transport“. Sensors 20, Nr. 23 (07.12.2020): 6994. http://dx.doi.org/10.3390/s20236994.
Der volle Inhalt der QuelleAnnotation:
Wireless fingerprinting localization (FL) systems identify locations by building radio fingerprint maps, aiming to provide satisfactory location solutions for the complex environment. However, the radio map is easy to change, and the cost of building a new one is high. One research focus is to transfer knowledge from the old radio maps to a new one. Feature-based transfer learning methods help by mapping the source fingerprint and the target fingerprint to a common hidden domain, then minimize the maximum mean difference (MMD) distance between the empirical distributions in the latent domain. In this paper, the optimal transport (OT)-based transfer learning is adopted to directly map the fingerprint from the source domain to the target domain by minimizing the Wasserstein distance so that the data distribution of the two domains can be better matched and the positioning performance in the target domain is improved. Two channel-models are used to simulate the transfer scenarios, and the public measured data test further verifies that the transfer learning based on OT has better accuracy and performance when the radio map changes in FL, indicating the importance of the method in this field.
14
Chamier-Gliszczyński, Norbert. „Optimal Design for the Environment of the Means Transportation: A Case Study of Reuse and Recycling Materials“. Solid State Phenomena 165 (Juni 2010): 244–49. http://dx.doi.org/10.4028/www.scientific.net/ssp.165.244.
Der volle Inhalt der QuelleAnnotation:
In the paper a topic of environmentally-oriented optimal design of means of transport is presented focusing on the example of reuse and recycling of materials. The following was applied in the field of environmental analysis of transport means: LCA (Life Cycle Assessment), LCC, LCI, DfE, DfR, DfD, end-of-life, assembly, disassembly, recycling, reuse, modeling of material separation. Results of the analysis enabled identification of components of transport means that dominate with respect to generated unfavorable environmental interactions. This allowed indicating areas, where modifications can strongly improve environmental image of means of transportation.
15
Ma, Zhimin, und Guoqi Han. „Reconstruction of the Surface Inshore Labrador Current from SWOT Sea Surface Height Measurements“. Remote Sensing 11, Nr. 11 (28.05.2019): 1264. http://dx.doi.org/10.3390/rs11111264.
Der volle Inhalt der QuelleAnnotation:
Utilizing a high-resolution (2-km) coastal ocean model output off Eastern Newfoundland, this paper explores the potential for reconstructing the sea surface height (SSH) and the surface inshore Labrador Current from high-resolution SSH data of the upcoming Surface Water and Ocean Topography (SWOT) satellite mission. The model results are evaluated against in-situ data from tide gauges and nadir altimetry for the period from June to October, 2010. The hourly model SSH output is used as true SSH and sampled along-swath with expected measurement errors by using a SWOT simulator, which produces SWOT-like data. We reconstruct half-day SSH fields from the SWOT-like data using optimal interpolation and average them into weekly fields. The average normalized root-mean-square difference between the weekly reconstructed SSH field and the model SSH filed is 0.07 for the inshore Labrador Current. Between the geostrophic surface current derived from the reconstructed SSH field and the model surface current, the average normalized root-mean-square difference is 0.26 for the inshore Labrador Current. For the surface unit-depth transport of the inshore Labrador Current, the normalized root-mean-square differences are 0.32–0.38 between the reconstructed current and the model current.
16
Dooley, Ciara, Steve Elgar, Britt Raubenheimer und Levi Gorrell. „Estimating Surfzone Currents with Near-Field Optical Remote Sensing“. Journal of Atmospheric and Oceanic Technology 42, Nr. 1 (Januar 2025): 33–46. https://doi.org/10.1175/jtech-d-24-0015.1.
Der volle Inhalt der QuelleAnnotation:
Abstract Currents transport sediment, larvae, pollutants, and people across and along the surfzone, creating a dynamic interface between the coastal ocean and shore. Previous field studies of nearshore flows primarily have relied on relatively low spatial resolution deployments of in situ sensors, but the development of remote sensing techniques using optical imagery and naturally occurring foam as a flow tracer has allowed for high spatial resolution observations (on the order of a few meters) across the surfzone. Here, algorithms optical current meter (OCM) and particle image velocimetry (PIV) are extended from previous surfzone applications and used to estimate both cross-shore and alongshore 2-, 10-, and 60-min mean surface currents in the nearshore using imagery from both oblique and nadir viewing angles. Results are compared with in situ current meters throughout the surfzone for a wide range of incident wave heights, directions, and directional spreads. Differences between remotely sensed flows and in situ current meters are smallest for nadir viewing angles, where georectification is simplified. Comparisons of 10-min mean flow estimates from a nadir viewing angle with in situ estimates of alongshore and cross-shore currents had correlations r2 = 0.94 and 0.51 with root-mean-square differences (RMSDs) = 0.07 and 0.16 m s−1 for PIV and r2 = 0.88 and 0.44 with RMSDs = 0.08 and 0.22 m s−1 for OCM. Differences between remotely sensed and in situ cross-shore current estimates are at least partially owing to the difference between onshore-directed mass flux on the surface and offshore-directed undertow in the mid–water column.
17
Baral, P. C. „Study of frequency- and temperature-dependent electrical transport in heavy fermion systems“. International Journal of Modern Physics B 31, Nr. 12 (10.05.2017): 1750081. http://dx.doi.org/10.1142/s0217979217500813.
Der volle Inhalt der QuelleAnnotation:
This paper focuses on the frequency- and temperature-dependent electrical transport properties of heavy fermion (HF) systems. For this, Kondo lattice model (KLM) with Coulomb correlation between [Formula: see text]–[Formula: see text] electrons at the same site is considered. The Hamiltonian is treated in mean-field approximation (MFA) for the Kondo hybridization and Heisenberg-type interaction to get mean-field Hamiltonian and it is written after the Fourier transformation. The Hartree–Fock-type approximation is considered for the Coulomb repulsion between [Formula: see text]–[Formula: see text] electrons, the perturbed part of the Hamiltonian. The two Green’s functions for the conduction and [Formula: see text]-electrons are calculated to define the self-energy. Then the frequency- and temperature-dependent optical conductivity and resistivity are calculated by using the Kubo’s formula within the linear dynamical response approach. They are studied by varying the model parameters. The anomalies and results obtained are compared with experimental data.
18
VOLCHENKOV, D. „THE BENDING INSTABILITY IN THE VORTICITY TRANSPORT THROUGH A TURBULENT FLOW: FEEDBACK CHAOS CONTROLLING AND DYNAMICAL SYMMETRY BREAKING“. International Journal of Modern Physics B 15, Nr. 08 (30.03.2001): 1147–64. http://dx.doi.org/10.1142/s0217979201004666.
Der volle Inhalt der QuelleAnnotation:
The model of a large-scale injection into a turbulent flow of immiscible fluid is considered. The long-time, large-scale asymptotic behavior of the energy dissipation rate ∊ is analyzed in the framework of renormalization group approach. It is shown that if the ordinary Kolmogorov dissipation regime (∊= const , in the inertial range) becomes unstable, the alternative asymptotic behavior would come true. In contrast to the standard Navier–Stokes turbulence, the alternative dissipation spectrum ∊(k) has a minimum, which means that an optimal eddy size ℓ exists in the model. This phenomenon provokes the flow into turbulence damping (the "bending effect" in combustion) or stimulates the magnetohydrodynamic system to a generation of a large-scale mean magnetic field ("turbulent dynamo" effect).
19
Sahoo, Sushant Kumar, Anju Pansari und Bijaya Kumar Sahoo. „Built-in-polarization effect on relaxation time and mean free path of phonons in AlxGa1−xN/GaN heterostructure“. Modern Physics Letters B 30, Nr. 08 (30.03.2016): 1650097. http://dx.doi.org/10.1142/s0217984916500974.
Der volle Inhalt der QuelleAnnotation:
In this paper, we have theoretically investigated the effect of built-in-polarization field on various phonon scattering mechanisms in Al[Formula: see text]Ga[Formula: see text]N/GaN heterostructure. The built-in-polarization field enhances the elastic constant, phonon velocity and Debye frequency of Al[Formula: see text]Ga[Formula: see text]N alloy. As a result, various phonon scattering mechanisms are modified. Important phonon scattering mechanisms such as normal scattering, Umklapp scattering, point defect scattering, dislocation scattering and phonon–electron scattering processes have been considered. The combined relaxation time due to above scattering mechanisms has also been computed as a function of phonon frequency for various Al contents at room temperature. Our result shows that built-in-polarization field suppresses scattering rates leading to enhanced combined relaxation time. Increased relaxation time implies longer phonon mean free path and enhanced optical and thermal transport properties. The result can be used to determine the effect of built-in-polarization field on optical and thermal properties of Al[Formula: see text]Ga[Formula: see text]N/GaN heterostructure and will be useful, particularly, for improvement of thermoelectric performance of Al[Formula: see text]Ga[Formula: see text]N/GaN heterostructure through polarization engineering.
20
Brand, Evelien, Lars De Sloover, Alain De Wulf, Anne-Lise Montreuil, Sander Vos und Margaret Chen. „Cross-Shore Suspended Sediment Transport in Relation to Topographic Changes in the Intertidal Zone of a Macro-Tidal Beach (Mariakerke, Belgium)“. Journal of Marine Science and Engineering 7, Nr. 6 (01.06.2019): 172. http://dx.doi.org/10.3390/jmse7060172.
Der volle Inhalt der QuelleAnnotation:
Sediment transport is a key element in intertidal beach morphodynamics, but measurements of sediment transport are often unreliable. The aim of this study is to quantify and investigate cross-shore sediment transport and the resulting topographic changes for a tide-dominated, sandy beach. Two fortnight-long field experiments were carried out during which hydrodynamics and sediment dynamics were measured with optical and acoustic sensors, while the beach topography was surveyed with a permanent terrestrial laser scanner. Suspended sediment was generally well-mixed and currents were largest at approximately 1.5 m above the bed, which resulted in a peak in sediment transport at 1/3 of the high tide level. The mean transport direction was onshore during calm conditions (wave height <0.6 m) thanks to tidal currents and offshore during energetic conditions due to undertow. Oscillatory transport was always onshore because of wave asymmetry but it was subordinate to mean transport. The intertidal zone showed an alternation of erosion and accretion with formation of morphological features during energetic (no storm) conditionsand smoothening of the morphology during calm conditions. A good qualitative and quantitative agreement was found between the daily cross-shore suspended load and beach volume changes, especially during calm conditions.
21
Michelin, Sébastien, und Eric Lauga. „Unsteady feeding and optimal strokes of model ciliates“. Journal of Fluid Mechanics 715 (09.01.2013): 1–31. http://dx.doi.org/10.1017/jfm.2012.484.
Der volle Inhalt der QuelleAnnotation:
AbstractThe flow field created by swimming micro-organisms not only enables their locomotion but also leads to advective transport of nutrients. In this paper we address analytically and computationally the link between unsteady feeding and unsteady swimming on a model micro-organism, the spherical squirmer, actuating the fluid in a time-periodic manner. We start by performing asymptotic calculations at low Péclet number ($\mathit{Pe}$) on the advection–diffusion problem for the nutrients. We show that the mean rate of feeding as well as its fluctuations in time depend only on the swimming modes of the squirmer up to order ${\mathit{Pe}}^{3/ 2} $, even when no swimming occurs on average, while the influence of non-swimming modes comes in only at order ${\mathit{Pe}}^{2} $. We also show that generically we expect a phase delay between feeding and swimming of $1/ 8\mathrm{th} $ of a period. Numerical computations for illustrative strokes at finite $\mathit{Pe}$ confirm quantitatively our analytical results linking swimming and feeding. We finally derive, and use, an adjoint-based optimization algorithm to determine the optimal unsteady strokes maximizing feeding rate for a fixed energy budget. The overall optimal feeder is always the optimal steady swimmer. Within the set of time-periodic strokes, the optimal feeding strokes are found to be equivalent to those optimizing periodic swimming for all values of the Péclet number, and correspond to a regularization of the overall steady optimal.
22
Zhou, Zeyang, und Jun Huang. „Position Calculation for Front Fin of Rocket Forebody Using Variable Step Scheme“. Aerospace 11, Nr. 8 (27.07.2024): 617. http://dx.doi.org/10.3390/aerospace11080617.
Der volle Inhalt der QuelleAnnotation:
In order to determine the installation position of the front fin on the example rocket forebody, an optimized method based on a comprehensive evaluation indicator and variable step search is presented. The comprehensive indicator consists of four weight coefficients, two lateral aerodynamic forces and two aerodynamic moments. The computational fluid dynamics method based on a shear stress transport turbulence model is established to analyze the flow field characteristics of the forebody. The results indicate that under equal weight coefficients, the presented search algorithm can provide an optimized solution for the front fin to achieve the minimum value of the comprehensive evaluation indicator. When the range of the current wing movement changes or the weight coefficient distribution changes, this search algorithm can still provide the optimal solution and some feasible solutions. Under the given conditions, there is a difference between the optimal solution of the aerodynamic force priority and that of the aerodynamic moment priority. For the case of the aerodynamic moment priority, the mean level of the pressure coefficient corresponding to the optimal solution on the given observation plane is low. The presented method is effective in learning the appropriate installation position of the rocket’s front fins.
23
Blatnický, Miroslav, Ján Dižo, Milan Sága, Juraj Gerlici und Erik Kuba. „Design of a Mechanical Part of an Automated Platform for Oblique Manipulation“. Applied Sciences 10, Nr. 23 (27.11.2020): 8467. http://dx.doi.org/10.3390/app10238467.
Der volle Inhalt der QuelleAnnotation:
Handling machines are increasingly being used in all sectors of the industry. Knowledge of the theory of transport and handling machines are basic prerequisites for their further technical development. Development in the field of manipulators is reflected not only in their high technical level, but also in increasing safety and economy. The article presents results of research focused on the complete engineering design of a manipulator, which will serve as a mean of the oblique transport of pelletised goods. The manipulator takes the form of a platform moving between two destinations by means of an electromotor. The engineering design of the platform including the track and a working principle is described. The design includes analytical and numerical calculations of main loaded components of the platform. Extensive functional and dimensional calculations serve as the base for preparation of the technical documentation. An important step will be the creation of a parametric model of the force and moment load acting on a platform drivetrain. Based on this, optimal parameters of an electromotor and its dimensional calculation are performed.
24
Ravindra L. Pardhi. „Fault Identification in Optical Transport Network Using CNN“. Journal of Electrical Systems 20, Nr. 7s (04.05.2024): 2151–56. http://dx.doi.org/10.52783/jes.3934.
Der volle Inhalt der QuelleAnnotation:
The growing diversity Regarding the provision of information and services transmitted Using optical technology transport networks (OTN) has made network survival a crucial issue in current study. Fault detection refers to the process of identifying faults that arise from various issues such as packet loss, disconnection, and others in the OTN. The determination of the fault location in an OTN is highly significant in the analysis of the resilience of optical networks. This study presents a fault diagnosis system that utilises a Convolutional Neural Network (CNN), focusing primarily on distinguishing between hard faults (HF) and soft faults (SF). The CNN is implemented in where the fault is situated domain of OTN to determine the presence or absence of potential fault locations. The notion An F-Measure is implemented in order to quantify the impact of positioning.utilising Location, time, mean squared error (MSE), and F-measure. The scientific investigation demonstrates that the suggested CNN neural network achieves the highest performance. The suggested CNN has a reduced localization time and achieves an F1-score of 0.98 after 85 iterations. This level of accuracy and real-time performance fulfils the requirements for fault identification. Hence, there is significant potential and practical utility in incorporating neural networks in the field of identifying and locating faults in optical transport networks.
25
Yamamoto, A., Y. Hasegawa und N. Kasagi. „Optimal control of dissimilar heat and momentum transfer in a fully developed turbulent channel flow“. Journal of Fluid Mechanics 733 (23.09.2013): 189–220. http://dx.doi.org/10.1017/jfm.2013.436.
Der volle Inhalt der QuelleAnnotation:
AbstractSustained friction drag reduction and heat transfer augmentation are simultaneously achieved in a fully developed channel flow where the averaged transport equations and wall boundary conditions for momentum and heat have identical form. Zero-net-mass-flux wall blowing and suction is assumed as a control input and its spatio-temporal distribution is determined based on optimal control theory. When the root-mean-square value of the control input is 5 % of the bulk mean velocity, the friction drag is decreased by 24 % from the uncontrolled value, whereas the heat transfer is more than doubled. Optimizations with different amplitudes of the control input and different Reynolds numbers reveal that the optimal control inputs commonly exhibit the property of a downstream travelling wave, whose wavelength is ∼250 in wall units and phase velocity is ∼30 % of the bulk mean velocity. Detailed analyses of the controlled velocity and thermal fields show that the travelling wave input contributes to dissimilar heat transfer enhancement through two distinct mechanisms, i.e. direct modification of the coherent velocity and thermal fields and an indirect effect on the random fields. The present results show that the divergence-free velocity vector and the conservative scalar are essentially different, and this is a key to achieving dissimilar heat transfer enhancement in turbulent shear flows.
26
Alzraiee, A. H., D. Baú und A. Elhaddad. „Estimation of heterogeneous aquifer parameters using centralized and decentralized fusion of hydraulic tomography data from multiple pumping tests“. Hydrology and Earth System Sciences Discussions 11, Nr. 4 (11.04.2014): 4163–208. http://dx.doi.org/10.5194/hessd-11-4163-2014.
Der volle Inhalt der QuelleAnnotation:
Abstract. Characterization of spatial variability of hydraulic properties of groundwater systems at high resolution is essential to simulate flow and transport phenomena. This paper investigates two schemes to invert transient hydraulic head data resulting from multiple pumping tests for the purpose of estimating the spatial distributions of the hydraulic conductivity, K, and the specific storage, Ss, of an aquifer. The two methods are centralized fusion and decentralized fusion. The centralized fusion of transient data is achieved when data from all pumping tests are processed concurrently using a central inversion processor, whereas the decentralized fusion inverts data from each pumping test separately to obtain optimal local estimates of hydraulic parameter, which are consequently fused using the Generalized Millman Formula, an algorithm for merging multiple correlated or uncorrelated local estimates. For both data fusion schemes, the basic inversion processor employed is the Ensemble Kalman Filter, which is employed to assimilate the temporal moments of the transient hydraulic head measurements resulting from multiple pumping tests. Assimilating the temporal moments instead of the hydraulic head transient data themselves is shown to provide a significant improvement in computational efficiency. Additionally, different assimilation strategies to improve the estimation of Ss are investigated. Results show that estimation of the K and Ss distributions using temporal moment analysis is fairly good; however, the centralized inversion scheme consistently outperforms the decentralized inversion scheme. Investigations on the sensitivity of the inversion estimates to errors in geostatistical parameters of the random fields of K and Ss reveal that the estimates are not sensitive to errors in the correlation length and the variance of hydraulic properties, but are noticeably sensitive to errors in the stationary mean. The proposed inversion schemes are expanded to estimate the geostatistical parameters of the K and Ss fields. The results show that the estimation of the true stationary mean of the K field and, to a lesser degree, the stationary mean of the Ss field can be successfully achieved, while the estimation of correlation length and standard deviation for both the K and Ss fields are not as effective.
27
Popova, T. A., und A. P. Popov. „A Formalised Approach to Optimal Adoption of a Complex of Technical Means“. World of Transport and Transportation 19, Nr. 3 (02.12.2021): 45–52. http://dx.doi.org/10.30932/1992-3252-2021-19-3-5.
Der volle Inhalt der QuelleAnnotation:
The research relates to the field of automation of technological preparation of production in transport equipment manufacturing sector and proposes the concept of choosing the optimal design model for a complex of technical means within a control system in automated production. The factors characterising the dynamics of the processes have been studied, and the corresponding mathematical models have been drawn up, considering the cost characteristics and the economic feasibility of adopting integratedtechnical means.The main objective of this work is to propose consideration of all parameters that have weight, including the dynamics of technical and economic processes. It is shown that cost characteristics are direct indicators of economic efficiency of the implemented complex of technical means.Methodically, this work was carried out based on economic and mathematical analysis of adoption of a complex of technical means at a transport equipment manufacturing enterprise considering approaches previously suggested by researchers.Thus, for the most accurate determination of the final cost of a certain product option, it is necessary to consider all factors of design decisions. Based on these data, a model of cost characteristics of products is built, analysing which it is possible to select the optimal product design, optimal assemblies and units with specific components and specific quality indicators. This allows obtaining the optimal technological version of the design solution during manufacturing.A method of searching for an optimal production cycle when introducing an automated production system is proposed. It is proposed to consider the losses associated with temporary freezing of funds, including the need to perform a convolution of optimization criteria. To formalise the process of making optimal decisions, it is also proposed to harmonise the products and market needs. Besides, the search methodology should include the search for an optimal group of employees responsible for implementation of specific and narrowly focused tasks, which makes it possible to improve the quality indicators of automated production with an adopted complex of technical means (CTM).To minimise the time spent on entire commissioning of a product from the development stage to receipt of the finished product, it is required to speed up the development work. This can be done by increasing production capacity, as well as by reducing the time of partial cycles of the structure’s existence.Even though the model is becoming excessively redundant, we suppose that introduction of additional elements is necessary to consider all the nuances that help choosing the best solution regarding optimisation issues, which will allow determining of the full economic efficiency of the complex.
28
Tirpitz, Jan-Lukas, Udo Frieß, François Hendrick, Carlos Alberti, Marc Allaart, Arnoud Apituley, Alkis Bais et al. „Intercomparison of MAX-DOAS vertical profile retrieval algorithms: studies on field data from the CINDI-2 campaign“. Atmospheric Measurement Techniques 14, Nr. 1 (04.01.2021): 1–35. http://dx.doi.org/10.5194/amt-14-1-2021.
Der volle Inhalt der QuelleAnnotation:
Abstract. The second Cabauw Intercomparison of Nitrogen Dioxide measuring Instruments (CINDI-2) took place in Cabauw (the Netherlands) in September 2016 with the aim of assessing the consistency of multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of tropospheric species (NO2, HCHO, O3, HONO, CHOCHO and O4). This was achieved through the coordinated operation of 36 spectrometers operated by 24 groups from all over the world, together with a wide range of supporting reference observations (in situ analysers, balloon sondes, lidars, long-path DOAS, direct-sun DOAS, Sun photometer and meteorological instruments). In the presented study, the retrieved CINDI-2 MAX-DOAS trace gas (NO2, HCHO) and aerosol vertical profiles of 15 participating groups using different inversion algorithms are compared and validated against the colocated supporting observations, with the focus on aerosol optical thicknesses (AOTs), trace gas vertical column densities (VCDs) and trace gas surface concentrations. The algorithms are based on three different techniques: six use the optimal estimation method, two use a parameterized approach and one algorithm relies on simplified radiative transport assumptions and analytical calculations. To assess the agreement among the inversion algorithms independent of inconsistencies in the trace gas slant column density acquisition, participants applied their inversion to a common set of slant columns. Further, important settings like the retrieval grid, profiles of O3, temperature and pressure as well as aerosol optical properties and a priori assumptions (for optimal estimation algorithms) have been prescribed to reduce possible sources of discrepancies. The profiling results were found to be in good qualitative agreement: most participants obtained the same features in the retrieved vertical trace gas and aerosol distributions; however, these are sometimes at different altitudes and of different magnitudes. Under clear-sky conditions, the root-mean-square differences (RMSDs) among the results of individual participants are in the range of 0.01–0.1 for AOTs, (1.5–15) ×1014molec.cm-2 for trace gas (NO2, HCHO) VCDs and (0.3–8)×1010molec.cm-3 for trace gas surface concentrations. These values compare to approximate average optical thicknesses of 0.3, trace gas vertical columns of 90×1014molec.cm-2 and trace gas surface concentrations of 11×1010molec.cm-3 observed over the campaign period. The discrepancies originate from differences in the applied techniques, the exact implementation of the algorithms and the user-defined settings that were not prescribed. For the comparison against supporting observations, the RMSDs increase to a range of 0.02–0.2 against AOTs from the Sun photometer, (11–55)×1014molec.cm-2 against trace gas VCDs from direct-sun DOAS observations and (0.8–9)×1010molec.cm-3 against surface concentrations from the long-path DOAS instrument. This increase in RMSDs is most likely caused by uncertainties in the supporting data, spatiotemporal mismatch among the observations and simplified assumptions particularly on aerosol optical properties made for the MAX-DOAS retrieval. As a side investigation, the comparison was repeated with the participants retrieving profiles from their own differential slant column densities (dSCDs) acquired during the campaign. In this case, the consistency among the participants degrades by about 30 % for AOTs, by 180 % (40 %) for HCHO (NO2) VCDs and by 90 % (20 %) for HCHO (NO2) surface concentrations. In former publications and also during this comparison study, it was found that MAX-DOAS vertically integrated aerosol extinction coefficient profiles systematically underestimate the AOT observed by the Sun photometer. For the first time, it is quantitatively shown that for optimal estimation algorithms this can be largely explained and compensated by considering biases arising from the reduced sensitivity of MAX-DOAS observations to higher altitudes and associated a priori assumptions.
29
Zhang, Yinchao, Yize Zheng, Wangshu Tan, Pan Guo, Qingyue Xu, Su Chen, Ruiqi Lin, Siying Chen und He Chen. „Two Practical Methods to Retrieve Aerosol Optical Properties from Coherent Doppler Lidar“. Remote Sensing 14, Nr. 11 (04.06.2022): 2700. http://dx.doi.org/10.3390/rs14112700.
Der volle Inhalt der QuelleAnnotation:
Complexly distributed aerosol particles have significant impacts on climate and environmental changes. As one of the vital atmospheric power sources, the wind field deeply affects the distribution and transport of aerosol particles. For a more comprehensive investigation of the aerosols flux and transport mechanism, two retrieval methods of aerosol optical properties (backscatter coefficient and extinction coefficient at 1550 nm) from coherent Doppler lidar (CDL) observation are proposed in this paper. The first method utilizes the calculated aerosol backscatter coefficient (532 nm) from Mie-scattering lidar datasets and the iterative Fernald method to retrieve aerosol optical property profiles during joint measurements with CDL and Mie-scattering lidar. After verifying the correctness of the first method compared with AERONET datasets, we proposed the second retrieval method. Using the forward integral Fernald method with near-ground reference aerosol extinction coefficient calculated by atmospheric visibility, aerosol optical properties at 1550 nm could be obtained. Thirty-six-day joint measurements with two lidars were specially designed and conducted to verify the correctness of these retrieval methods. The validation results of these two methods indicate great performances, where the mean relative errors are 0.0272 and 0.1656, and the correlation coefficients are 0.9306 and 0.9197, respectively. In conclusion, the feasibility of these two retrieval methods extends the capability of CDL to detect aerosol optical properties and also provides a possibility to observe the aerosol distribution and transport process comprehensively, which is a great promotion of aerosol transport studies development.
30
Mutalip, А. А., Y. А. Ussenov, А. K. Akildinova, М. K. Dosbolayev, М. Т. Gabdullin und Т. S. Ramazanov. „Determination of the reduced electric field in surface dielectric barrier discharge plasmas“. Bulletin of the Karaganda University. "Physics" Series 103, Nr. 3 (30.09.2021): 35–44. http://dx.doi.org/10.31489/2021ph3/35-44.
Der volle Inhalt der QuelleAnnotation:
In this paper, the experimental determination of the reduced electric field (E/n) in plasma of dielectric coplanar surface barrier discharge (DCSBD) at atmospheric pressure was demonstrated. The plasma characteristics and the experimental setup properties were described, and the optical emission spectrum of the plasma was also measured. The results of optical emission spectroscopy showed the presence of nitrogen molecular bands in the emission spectrum of DCSBD. In particular, the second positive and the first negative systems, as well as low intensity OH and NO lines were identified. The main transport properties of electrons, such as mobility, mean average energy, and diffusion coefficients were calculated using the BOLSIG+ open source software. The dependence of the ratio of intensities of the nitrogen spectral lines on the reduced electric field, the dependence of the E/n on plasma power, and the dependence of the electron energy distribution function (EEDF) on E/n were obtained. An algorithm in the form of a block diagram for determining the reduced electric field by the BOLSIG + program and experimentally measured spectral line intensities are presented. The utilized method is quite simple, accessible and versatile.
31
Dai, Guangyao, Kangwen Sun, Xiaoye Wang, Songhua Wu, Xiangying E, Qi Liu und Bingyi Liu. „Dust transport and advection measurement with spaceborne lidars ALADIN and CALIOP and model reanalysis data“. Atmospheric Chemistry and Physics 22, Nr. 12 (20.06.2022): 7975–93. http://dx.doi.org/10.5194/acp-22-7975-2022.
Der volle Inhalt der QuelleAnnotation:
Abstract. In this paper, a long-term large-scale Saharan dust transport event which occurred between 14 and 27 June 2020 is tracked with the spaceborne lidars ALADIN (Atmospheric Laser Doppler Instrument) and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) together with ECMWF (European Centre for Medium-Range Forecasts) and HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory model) analysis. We evaluate the performance of ALADIN and CALIOP on the observations of dust optical properties and wind fields and explore the possibility of tracking the dust events and calculating the dust mass advection with the combination of satellite and model data. The dust plumes are identified with the AIRS/Aqua Dust Score Index and with the vertical feature mask product from CALIOP. The emission, dispersion, transport and deposition of the dust event are monitored using the data from AIRS/Aqua, CALIOP and HYSPLIT. With the quasi-synchronized observations by ALADIN and CALIOP, combined with the wind field and relative humidity, the dust advection values are calculated. From this study, it is found that the dust event generated on 14 and 15 June 2020 from the Sahara in North Africa dispersed and moved westward over the Atlantic Ocean, finally being deposited in the western Atlantic Ocean, the Americas and the Caribbean Sea. During the transport and deposition processes, the dust plumes are trapped in the northeasterly trade-wind zone between latitudes of 5∘ and 30∘ N and altitudes of 0 and 6 km. Aeolus provided the observations of the dynamics of this dust transport event in the Saharan Air Layer (SAL). From the measurement results on 19 June 2020, the dust plumes are captured quasi-simultaneously over the emission region (Western Sahara), the transport region (middle Atlantic) and the deposition region (western Atlantic) individually, which indicates that the dust plume area over the Atlantic on the morning of this day is quite enormous and that this dust transport event is massive and extensive. The quasi-synchronization observation results of 15, 16, 19, 24 and 27 June by ALADIN and CALIOP during the entire transport process show good agreement with the Dust Score Index data and the HYSPLIT trajectories, which indicates that the transport process of the same dust event is tracked by ALADIN and CALIOP, verifies that the dust transport spent around 2 weeks from the emission to the deposition and achieved the respective observations of this dust event's emission phase, development phase, transport phase, descent phase and deposition phase. Finally, the advection values for different dust parts and heights on 19 June and on the entire transport routine during transportation are computed. On 19 June, the mean dust advection values are about 1.91±1.21 mg m−2 s−1 over the emission region, 1.38±1.28 mg m−2 s−1 over the transport region and 0.75±0.68mgm-2s-1 over the deposition region. In the whole lifetime of the dust event, the mean dust advection values were about 1.51±1.03mgm-2s-1 on 15 June 2020, 2.19±1.72mgm-2s-1 on 16 June 2020, 1.38±1.28mgm-2s-1 on 19 June 2020, 1.60±1.08mgm-2s-1 on 24 June 2020 and 1.03±0.60mgm-2s-1 on 27 June 2020. During the dust development stage, the mean advection values gradually increased and reached their maximum on 16 June with the enhancement of the dust event. Then, the mean advection values decreased during the transport and the deposition of the dust over the Atlantic Ocean, the Americas and the Caribbean Sea.
32
Chazette, Patrick, Cyrille Flamant, Julien Totems, Marco Gaetani, Gwendoline Smith, Alexandre Baron, Xavier Landsheere, Karine Desboeufs, Jean-François Doussin und Paola Formenti. „Evidence of the complexity of aerosol transport in the lower troposphere on the Namibian coast during AEROCLO-sA“. Atmospheric Chemistry and Physics 19, Nr. 23 (11.12.2019): 14979–5005. http://dx.doi.org/10.5194/acp-19-14979-2019.
Der volle Inhalt der QuelleAnnotation:
Abstract. The evolution of the vertical distribution and optical properties of aerosols in the free troposphere, above stratocumulus, is characterized for the first time over the Namibian coast, a region where uncertainties on aerosol–cloud coupling in climate simulations are significant. We show the high variability of atmospheric aerosol composition in the lower and middle troposphere during the Aerosols, Radiation and Clouds in southern Africa (AEROCLO-sA) field campaign (22 August–12 September 2017) around the Henties Bay supersite using a combination of ground-based, airborne and space-borne lidar measurements. Three distinct periods of 4 to 7 d are observed, associated with increasing aerosol loads (aerosol optical thickness at 550 nm ranging from ∼0.2 to ∼0.7), as well as increasing lofted aerosol layer depth and top altitude. Aerosols are observed up to 6 km above mean sea level during the later period. Aerosols transported within the free troposphere are mainly polluted dust (predominantly dust mixed with smoke from fires) for the first two periods (22 August–1 September 2017) and smoke for the last part (3–9 September) of the field campaign. As shown by Lagrangian back-trajectory analyses, the main contribution to the aerosol optical thickness over Henties Bay is shown to be due to biomass burning over Angola. Nevertheless, in early September, the highest aerosol layers (between 5 and 6 km above mean sea level) seem to come from South America (southern Brazil, Argentina and Uruguay) and reach Henties Bay after 3 to 6 d. Aerosols appear to be transported eastward by the midlatitude westerlies and towards southern Africa by the equatorward moving cut-off low originating from within the westerlies. All the observations show a very complex mixture of aerosols over the coastal regions of Namibia that must be taken into account when investigating aerosol radiative effects above stratocumulus clouds in the southeast Atlantic Ocean.
33
Foures, D. P. G., C. P. Caulfield und P. J. Schmid. „Optimal mixing in two-dimensional plane Poiseuille flow at finite Péclet number“. Journal of Fluid Mechanics 748 (28.04.2014): 241–77. http://dx.doi.org/10.1017/jfm.2014.182.
Der volle Inhalt der QuelleAnnotation:
AbstractWe consider the nonlinear optimisation of the mixing of a passive scalar, initially arranged in two layers, in a two-dimensional plane Poiseuille flow at finite Reynolds and Péclet numbers, below the linear instability threshold. We use a nonlinear-adjoint-looping approach to identify optimal perturbations leading to maximum time-averaged energy as well as maximum mixing in a freely evolving flow, measured through the minimisation of either the passive scalar variance or the so-called mix-norm, as defined by Mathew, Mezić & Petzold (Physica D, vol. 211, 2005, pp. 23–46). We show that energy optimisation appears to lead to very weak mixing of the scalar field whereas the optimal mixing initial perturbations, despite being less energetic, are able to homogenise the scalar field very effectively. For sufficiently long time horizons, minimising the mix-norm identifies optimal initial perturbations which are very similar to those which minimise scalar variance, demonstrating that minimisation of the mix-norm is an excellent proxy for effective mixing in this finite-Péclet-number bounded flow. By analysing the time evolution from initial perturbations of several optimal mixing solutions, we demonstrate that our optimisation method can identify the dominant underlying mixing mechanism, which appears to be classical Taylor dispersion, i.e. shear-augmented diffusion. The optimal mixing proceeds in three stages. First, the optimal mixing perturbation, energised through transient amplitude growth, transports the scalar field across the channel width. In a second stage, the mean flow shear acts to disperse the scalar distribution leading to enhanced diffusion. In a final third stage, linear relaxation diffusion is observed. We also demonstrate the usefulness of the developed variational framework in a more realistic control case: mixing optimisation by prescribed streamwise velocity boundary conditions.
34
Keating, Shane R., Andrew J. Majda und K. Shafer Smith. „New Methods for Estimating Ocean Eddy Heat Transport Using Satellite Altimetry“. Monthly Weather Review 140, Nr. 5 (01.05.2012): 1703–22. http://dx.doi.org/10.1175/mwr-d-11-00145.1.
Der volle Inhalt der QuelleAnnotation:
Abstract Attempts to monitor ocean eddy heat transport are strongly limited by the sparseness of available observations and the fact that heat transport is a quadratic, sign-indefinite quantity that is particularly sensitive to unresolved scales. In this article, a suite of stochastic filtering strategies for estimating eddy heat transport are tested in idealized two-layer simulations of mesoscale oceanic turbulence at high and low latitudes under a range of observation scenarios. A novel feature of these filtering strategies is the use of computationally inexpensive stochastic models to forecast the underlying nonlinear dynamics. The stochastic model parameters can be estimated by regression fitting to climatological energy spectra and correlation times or by adaptively learning these parameters “on-the-fly” from the observations themselves. The authors show that, by extracting high-wavenumber information that has been aliased into the low wavenumber band, “stochastically super-resolved” velocity fields with a nominal resolution increase of a factor of 2 or more can be derived. Observations of the upper-layer streamfunction are projected onto an empirical orthogonal function basis for the vertical structure to produce filtered estimates for both upper- and lower-layer streamfunctions and hence net heat transport. The resulting time-mean poleward eddy heat transport is significantly closer to the true value when compared with standard estimates based upon optimal interpolation. By contrast, the temporal variability of the heat transport is underestimated because of poor temporal resolution. Implications for estimating poleward eddy heat transport using current and next-generation altimeters are discussed.
35
Schmechtig, C., B. Marticorena, B. Chatenet, G. Bergametti, J. L. Rajot und A. Coman. „Simulation of the mineral dust content over Western Africa from the event to the annual scale with the CHIMERE-DUST model“. Atmospheric Chemistry and Physics 11, Nr. 14 (22.07.2011): 7185–207. http://dx.doi.org/10.5194/acp-11-7185-2011.
Der volle Inhalt der QuelleAnnotation:
Abstract. The chemistry and transport model CHIMERE-DUST have been used to simulate the mineral dust cycle over the Sahara in 2006. Surface measurements deployed during the AMMA field campaign allow to test the capability of the model to correctly reproduce the atmospheric dust load and surface concentrations from the daily to the seasonal time-scale. The simulated monthly mean Aerosol Optical Depths (AOD) and surface concentrations are significantly correlated with the measured ones. The simulated daily concentrations and hourly AOD are in the same range of magnitude than the observed ones despite relatively high simulated dust emissions. The level of agreement between the simulations and the observations has been quantified at different time scales using statistical parameters classically used to evaluate air quality models. The capability of the model to reproduce the altitude of the dust transport was tested for two contrasted cases of low and high altitude transport. These results highlight the sensitivity of the simulations to the surface winds used as external forcing and the necessity to further constrain the dust mass budget at the regional scale.
36
TARAPHDER, A., RAHUL PANDIT, H. R. KRISHNAMURTHY und T. V. RAMAKRISHNAN. „THE EXOTIC BARIUM BISMUTHATES“. International Journal of Modern Physics B 10, Nr. 08 (10.04.1996): 863–955. http://dx.doi.org/10.1142/s0217979296000362.
Der volle Inhalt der QuelleAnnotation:
We review the remarkable properties, including superconductivity, charge-density-wave ordering and metal–insulator transitions, of lead- and potassium-doped barium bismuthate. We will discuss some of the early theoretical studies of these systems. Our recent theoretical work, on the negative-U, extended-Hubbard model for these systems, will also be described. Both the large- and intermediate-U regimes of this model were examined, using mean-field and random-phase approximations, particularly with a view to fitting various experimental properties of these bismuthates. On the basis of our studies, we point out possibilities for exotic physics in these systems. We also emphasize the different consequences of electronic and phonon-mediated mechanisms for the negative U. We show that, for an electronic mechanism, the semiconducting phases of these bismuthates must be unique, with their transport properties dominated by charge±2eCooperon bound states. This can explain the observed difference between the optical and transport gaps. We propose other experimental tests for this novel mechanism of charge transport and comment on the effects of disorder.
37
Perri, B., und A. Brandenburg. „Spontaneous flux concentrations from the negative effective magnetic pressure instability beneath a radiative stellar surface“. Astronomy & Astrophysics 609 (Januar 2018): A99. http://dx.doi.org/10.1051/0004-6361/201730421.
Der volle Inhalt der QuelleAnnotation:
Context. The formation of sunspots requires the concentration of magnetic flux near the surface. The negative effective magnetic pressure instability (NEMPI) might be a possible mechanism for accomplishing this, but it has mainly been studied in simple systems using an isothermal equation of state without a natural free surface. Aims. We study NEMPI in a stratified Cartesian mean-field model where turbulence effects are parameterized. We use an ideal equation of state and include radiation transport, which establishes selfconsistently a free surface. Methods. We use a Kramers-type opacity with adjustable exponents chosen such that the deeper layers are approximately isentropic. No convection is therefore possible in this model, allowing us to study NEMPI with radiation in isolation. We restrict ourselves to two-dimensional models. We use artificially enhanced mean-field coefficients to allow NEMPI to develop, thereby making it possible to study the reason why it is much harder to excite in the presence of radiation. Results. NEMPI yields moderately strong magnetic flux concentrations a certain distance beneath the surface where the optical depth is unity. The instability is oscillatory and in the form of upward traveling waves. This seems to be a new effect that has not been found in earlier models without radiative transport. The horizontal wavelength is about ten times smaller than what has previously been found in more idealized isothermal models. Conclusions. In our models, NEMPI saturates at field strengths too low to explain sunspots. Furthermore, the structures appear too narrow and too far beneath the surface to cause significant brightness variations at the radiative surface. We speculate that the failure to reproduce effects resembling sunspots may be related to the neglect of convection.
38
Balakin, Vladimir V., Sergei V. Aleksikov und Valeri N. Azarov. „Ensuring the quality of atmospheric air on main streets and in residential buildings by means of planning and landscaping“. Hygiene and sanitation 102, Nr. 7 (30.08.2023): 639–47. http://dx.doi.org/10.47470/0016-9900-2023-102-7-639-647.
Der volle Inhalt der QuelleAnnotation:
Introduction. The level of concentration of toxic substances in the atmospheric air of main streets is largely determined by their aeration regime, established due to exposure to air flow of buildings and green spaces. Therefore, when developing master plans of cities and projects of detailed planning of residential formations to ensure hygienic standards for the expected content of emissions of motor transport in the air of transport communications and adjacent residential buildings, the influence of urban factors on wind speed and direction one should take into account.
The aim of the study is the justification and selection of urban planning measures to reduce atmospheric air pollution from main roads and streets by exhaust gases of motor transport.
Material and methods. Full-scale surveys of transport infrastructure facilities in large cities and modelling of the processes of dispersion of exhaust gases of cars in the air using models of residential buildings and green spaces.
Results. The regularities of the formation of the aeration regime of city streets and the dispersion of car emissions behind the landscaping strips and in residential buildings have been established. Optimal variants of planning, development and landscaping of main streets have been determined, ensuring the reduction of gas contamination of pedestrian zones, public spaces and residential areas.
Limitations. The choice of landscaping objects for urban roads and streets for field observations and modelling of car emissions dispersion processes is limited to strips of green spaces of a blown and dense construction, without taking into account the peculiarities of the transformation of the air flow and reducing gas pollution under the influence of landscaping strips of an openwork design.
Conclusions. Reduction of gas pollution of main roads and streets is ensured by choosing the direction of the route and planning, and building techniques. At the same time, it is necessary to use environmental protection linear-strip landscaping facilities of optimal design. At the same time, it should be borne in mind that frontal multi-sectional buildings and strips of green spaces of windproof dense construction stimulate the appearance of stable vortices with a closed circulation of impurities in street canyons and on sections of highways. When choosing urban planning solutions to ensure the quality of atmospheric air of transport communications and adjacent residential buildings in various landscape and climatic conditions, it is necessary to take into account the specifics of the tasks arising in this case to regulate the aeration regime and reclamation of the microclimate as a whole.
39
Kondragunta, S., P. Lee, J. McQueen, C. Kittaka, A. I. Prados, P. Ciren, I. Laszlo, R. B. Pierce, R. Hoff und J. J. Szykman. „Air Quality Forecast Verification Using Satellite Data“. Journal of Applied Meteorology and Climatology 47, Nr. 2 (01.02.2008): 425–42. http://dx.doi.org/10.1175/2007jamc1392.1.
Der volle Inhalt der QuelleAnnotation:
Abstract NOAA’s operational geostationary satellite retrievals of aerosol optical depths (AODs) were used to verify National Weather Service developmental (research mode) particulate matter (PM2.5) predictions tested during the summer 2004 International Consortium for Atmospheric Research on Transport and Transformation/New England Air Quality Study (ICARTT/NEAQS) field campaign. The forecast period included long-range transport of smoke from fires burning in Canada and Alaska and a regional-scale sulfate event over the Gulf of Mexico and the eastern United States. Over the 30-day time period for which daytime hourly forecasts were compared with observations, the categorical (exceedance defined as AOD > 0.55) forecast accuracy was between 0% and 20%. Hourly normalized mean bias (forecasts − observations) ranged between −50% and +50% with forecasts being positively biased when observed AODs were small and negatively biased when observed AODs were high. Normalized mean errors are between 50% and 100% with the errors on the lower end during the 18–22 July 2004 time period when a regional-scale sulfate event occurred. Spatially, the errors are small over the regions where sulfate plumes were present. The correlation coefficient also showed similar features (spatially and temporally) with a peak value of ∼0.6 during the 18–22 July 2004 time period. The dominance of long-range transport of smoke into the United States during the summer of 2004, neglected in the model predictions, skewed the model forecast performance. Enhanced accuracy and reduced normalized mean errors during the time period when a sulfate event prevailed show that the forecast system has skill in predicting PM2.5 associated with urban/industrial pollution events.
40
Duan, Jimiao, Zhi Kou, Huishu Liu, Keyu Lin, Sichen He und Shiming Chen. „Pour Point Prediction Method for Mixed Crude Oil Based on Ensemble Machine Learning Models“. Processes 12, Nr. 9 (23.08.2024): 1783. http://dx.doi.org/10.3390/pr12091783.
Der volle Inhalt der QuelleAnnotation:
Pipelines are the most common way to transport crude oil. The crude oil developed from different fields is mixed first and then transported. The pour point of mixed crude oil is very important for pipeline schemes and ensuring the safe, efficient, and flexible operation of the pipeline. An integrated machine learning model based on XGBoost is identified as optimal to predict the pour point of mixed crude oil by comprehensive comparison among six different types of machine learning models: multiple linear regression, random forest, support vector machine, LightGBM, backpropagation neural network, and XGBoost. A mixed crude oil pour point prediction model with strong engineering adaptability is proposed, focusing on enhancing the flexibility of machine learning model inputs (using density and viscosity instead of component crude oil pour points) and addressing challenges such as data volume and input missing in engineering scenarios. With the inputs of pour point Tg, density ρ, viscosity μ, and ratio Xi in component oils, the mean absolute error of the model prediction estimations after training with 8912 data is 1.12 °C, when the pour point Tg of the component crude oil is missing, the mean absolute error is 1.93 °C and the percentage of the predicted absolute error within 2 °C is 88.0%. This study can provide support for the intelligent control of flow properties of pipeline transport mixed oil.
41
Niu, Peining, Yan Mo, Baolin Yao, Zongze Yang, Yanqun Zhang und Dequan Zhang. „The Impact of Flow Channel Structural Parameters on Both the Hydraulic Performance and Anticlogging Abilities of Variable Flow Emitters“. Agronomy 14, Nr. 11 (31.10.2024): 2560. http://dx.doi.org/10.3390/agronomy14112560.
Der volle Inhalt der QuelleAnnotation:
Variable flow emitters are used in subsurface drip irrigation to address challenges in soil moisture transport. This study investigates the impact of flow channel structural parameters on the hydraulic performance and anticlogging ability of emitters using computational fluid dynamics (CFD) simulations and experimental tests. The results show that the realizable k–ε turbulence model can be used to simulate the flow field inside the variable flow emitter flow channel. The nRMSE between the measured (qm) and simulated (q) values of the flow rate is 11.23%, and the relative error between the measured (xm) and simulated (x) values of the flow index is 4.66%, which gives a high simulation accuracy. A polar analysis shows that the tooth angle (A) has the smallest effect on the effluent flow rate at 0.1 MPa (q0.1), x, and particle passage rate (η) of the variable flow emitter. Flow channel depth (D), tooth spacing (B), and tooth height (E) have a different order of precedence in the influence of the three indices, which are D > B > E > A, B > E > D > A and E > B > D > A, respectively. The value of η is positively correlated with the mean flow velocity (v) and the mean turbulent kinetic energy (k) in the flow channel, and η tends to increase and then decrease with the increase of x. The retention time of the particles in the flow channel is closely related to the magnitude of v and k. Three multivariate lin ear regression equations (R2 = 0.883–0.995) were constructed for q0.1, x, and η versus the flow channel structural parameters. The optimal design combination of channel structure parameters for different scenarios was determined using the scipy.optimize.minimize function in Python 3.8.0. The research results provide a reference for the optimal design of variable flow emitters.
42
Xu, Yibin, Hongguang Liu, Ping Gong, Pengfei Li, Ling Li, Qiang Xu, Bao Xue, Yaru Guo, Yao Zhang und Rumeng Tian. „Model-Based Optimization of Design Parameters of Subsurface Drain in Cotton Field under Mulch Drip Irrigation“. Water 14, Nr. 21 (24.10.2022): 3369. http://dx.doi.org/10.3390/w14213369.
Der volle Inhalt der QuelleAnnotation:
In this study, the influence of the relevant parameters of a subsurface pipe layout on soil water and salt transport in a cotton field under mulched drip irrigation is explored. Based on the measured data of the changes in the groundwater level and salt in the field, the DRAINMOD numerical model has been used for simulating the water and salt dynamics of a salinized cotton field under subsurface pipe drainage. The results of the investigation show that the DRAINMOD model can accurately simulate the changes in the hydrological conditions and the salt-leaching process in the study area. The average deviation between the simulated and measured values of the groundwater depth in 2013 and 2014 was −1.72 cm and 2.43 cm, the average absolute deviation was 3.84 cm and 2.43 cm, the root mean square error was 5.14 cm and 3.63 cm, and the correlation coefficient was 0.87 and 0.94, respectively. The average deviation between the simulated and measured values of soil salinity in 2013 and 2014 was −0.68 g/kg and −1.86 g/kg, the average absolute deviation was 1.60 g/kg and 1.99 g/kg, the root mean square error was 1.95 g/kg and 2.99 g/kg, and the correlation coefficient was 0.82 and 0.86, respectively, which are all within the acceptable error range. After validation, the model was used to simulate and analyze the desalination process of a cotton field in the study area for 27 different subsurface pipe layout modes. The projection pursuit classification model has been combined with the accelerated genetic algorithm based on real-number coding. The comprehensive benefits of the subsurface pipe layout were evaluated using the construction cost, average desalination rate, and relative yield of cotton as the evaluation indices. The results show that C11 (buried depth 2.1 m, spacing 30 m) is the optimal layout of the subsurface pipe. The results of this study can provide theoretical support and scientific guidance for the popularization and application of subsurface pipe salt discharge technology and drip irrigation under film in the arid inland areas of northwest China.
43
Pustogow, A., A. S. McLeod, Y. Saito, D. N. Basov und M. Dressel. „Internal strain tunes electronic correlations on the nanoscale“. Science Advances 4, Nr. 12 (Dezember 2018): eaau9123. http://dx.doi.org/10.1126/sciadv.aau9123.
Der volle Inhalt der QuelleAnnotation:
In conventional metals, charge carriers basically move freely. In correlated electron materials, however, the electrons may become localized because of strong Coulomb interactions, resulting in an insulating state. Despite considerable progress in the last decades, elucidating the driving mechanisms that suppress metallic charge transport, the spatial evolution of this phase transition remains poorly understood on a microscopic scale. Here, we use cryogenic scanning near-field optical microscopy to study the metal-to-insulator transition in an electronically driven charge-ordered system with a 20-nm spatial resolution. In contrast to common mean-field considerations, we observe pronounced phase segregation with a sharp boundary between metallic and insulating regions evidencing its first-order nature. Considerable strain in the crystal spatially modulates the effective electronic correlations within a few micrometers, leading to an extended “zebra” pattern of metallic and insulating stripes. We can directly monitor the spatial strain distribution via a gradual enhancement of the optical conductivity as the energy gap is depressed. Our observations shed new light on previous analyses of correlation-driven metal-insulator transitions.
44
Vérité, Jean, Clément Narteau, Olivier Rozier, Jeanne Alkalla, Laurie Barrier und Sylvain Courrech du Pont. „Equilibrium distance from long-range dune interactions“. Earth Surface Dynamics 13, Nr. 1 (13.01.2025): 23–39. https://doi.org/10.5194/esurf-13-23-2025.
Der volle Inhalt der QuelleAnnotation:
Abstract. Flow perturbations induced by dune topography affect sediment transport locally but can also be felt over long distances, altering the dynamics of isolated neighbouring dunes downstream. In order to work under optimal conditions that eliminate transverse flow components, collisions, and mass exchange between dunes, we study here these long-range interactions using a 2D numerical model where two equal-sized dunes lying on a non-erodible bed are exposed to a symmetric reversing flow. Depending on the initial spacing, dunes either attract or repel each other to eventually converge towards a steady-state spacing. This equilibrium distance decreases with flow strength and increases with the period of flow reorientation and dune size. It is mainly controlled by the reversing dune shape and the structure of the turbulent wake it generates, which continuously modulates the mean shear stress on the downstream dune. Under multi-directional wind regimes, these long-range flow perturbations offer an alternative mechanism for wavelength selection in linear dune fields with non-erodible interdune areas. Within these dune fields, estimates of mean shear stress could be used to assess the relative migration rate and the state of attraction or repulsion between neighbouring dunes.
45
Balika, S. D. „The effect of the stagnant layer on the photon mean-free-path length in concentrated suspensions of nanoparticles“. Physics of Aerodisperse Systems, Nr. 61 (09.12.2023): 142–49. http://dx.doi.org/10.18524/0367-1631.2023.61.290219.
Der volle Inhalt der QuelleAnnotation:
We analyze the possibility of evaluation of the thickness and refractive index of the stagnant layer in concentrated suspensions of nanoparticles through the transport characteristics of scattered light photons. The analysis is based on a physically-transparent generalization of the concept of the single scattering intensity off systems in which the number of particles within regions with linear sizes of order of the wavelength in the medium greatly exceeds unity. This generalization is carried out within the notion of compact groups of particles, makes it possible to go beyond the traditional Born approximation, and take into account many-particle effects contributed from those ranges of integration variables in the terms of the iteration series for the scattered field where the internal propagators have delta-function-type behavior. As a result, the evaluation of the photon transport characteristics becomes possible without a detailed modeling of many-particle scattering and correlation processes in the system.
The photon mean-free-path length is investigated theoretically as a function of the stagnant refractive index and that of the layer thickness to show a noticeable effect of both parameters on it. As the layer refractive index is increased at a fixed layer thickness, the mean-free-path length decreases because the suspension optical density increases. As a function of the layer thickness, the photon mean-free-path length reveals different types of behavior, depending on the relation between the refractive indices of the stagnant layer and base liquid. If the former is smaller than the latter, this behavior is increasing; in the opposite case, it is decreasing. An experimentally observed increase of the photon mean-free-path length with the particle concentration is usually explained as a manifestation of higher correlation effects. Our theory reveals that the presence of the stagnant layer make the situation more complicated, for both factors may either enhance or diminish each other. To resolve the issue, new specially-designed experiments are required to be set up.
46
Jin, Jae Sik, und Joon Sik Lee. „Electron–Phonon Interaction Model and Prediction of Thermal Energy Transport in SOI Transistor“. Journal of Nanoscience and Nanotechnology 7, Nr. 11 (01.11.2007): 4094–100. http://dx.doi.org/10.1166/jnn.2007.010.
Der volle Inhalt der QuelleAnnotation:
An electron–phonon interaction model is proposed and applied to thermal transport in semiconductors at micro/nanoscales. The high electron energy induced by the electric field in a transistor is transferred to the phonon system through electron–phonon interaction in the high field region of the transistor. Due to this fact, a hot spot occurs, which is much smaller than the phonon mean free path in the Si-layer. The full phonon dispersion model based on the Boltzmann transport equation (BTE) with the relaxation time approximation is applied for the interactions among different phonon branches and different phonon frequencies. The Joule heating by the electron–phonon scattering is modeled through the intervalley and intravalley processes for silicon by introducing average electron energy. The simulation results are compared with those obtained by the full phonon dispersion model which treats the electron–phonon scattering as a volumetric heat source. The comparison shows that the peak temperature in the hot spot region is considerably higher and more localized than the previous results. The thermal characteristics of each phonon mode are useful to explain the above phenomena. The optical mode phonons of negligible group velocity obtain the highest energy density from electrons, and resides in the hot spot region without any contribution to heat transport, which results in a higher temperature in that region. Since the acoustic phonons with low group velocity show the higher energy density after electron–phonon scattering, they induce more localized heating near the hot spot region. The ballistic features are strongly observed when phonon–phonon scattering rates are lower than 4 × 1010 s−1.
47
Jin, Jae Sik, und Joon Sik Lee. „Electron–Phonon Interaction Model and Prediction of Thermal Energy Transport in SOI Transistor“. Journal of Nanoscience and Nanotechnology 7, Nr. 11 (01.11.2007): 4094–100. http://dx.doi.org/10.1166/jnn.2007.18084.
Der volle Inhalt der QuelleAnnotation:
An electron–phonon interaction model is proposed and applied to thermal transport in semiconductors at micro/nanoscales. The high electron energy induced by the electric field in a transistor is transferred to the phonon system through electron–phonon interaction in the high field region of the transistor. Due to this fact, a hot spot occurs, which is much smaller than the phonon mean free path in the Si-layer. The full phonon dispersion model based on the Boltzmann transport equation (BTE) with the relaxation time approximation is applied for the interactions among different phonon branches and different phonon frequencies. The Joule heating by the electron–phonon scattering is modeled through the intervalley and intravalley processes for silicon by introducing average electron energy. The simulation results are compared with those obtained by the full phonon dispersion model which treats the electron–phonon scattering as a volumetric heat source. The comparison shows that the peak temperature in the hot spot region is considerably higher and more localized than the previous results. The thermal characteristics of each phonon mode are useful to explain the above phenomena. The optical mode phonons of negligible group velocity obtain the highest energy density from electrons, and resides in the hot spot region without any contribution to heat transport, which results in a higher temperature in that region. Since the acoustic phonons with low group velocity show the higher energy density after electron–phonon scattering, they induce more localized heating near the hot spot region. The ballistic features are strongly observed when phonon–phonon scattering rates are lower than 4 × 1010 s−1.
48
Graf, Anton Marius, Thomas Cochard, Kiana Amini, Shmuel Rubinstein und Michael Aziz. „Confocal Fluorescence Microscopy to Probe in Operando electrochemical Conversion“. ECS Meeting Abstracts MA2022-02, Nr. 1 (09.10.2022): 98. http://dx.doi.org/10.1149/ma2022-02198mtgabs.
Der volle Inhalt der QuelleAnnotation:
The development of electrochemical devices, such as flow batteries, fuel cells and electrolysers, is critical for the transition to a sustainable economy. Given the critical role of porous electrodes in the performance of these devices, understanding their structure-function relationship is crucial. Although porous electrodes with many different internal structures have been utilized, there is no clear consensus as to what features lead to what aspects of electrode performance. Transport in porous electrodes is commonly approximated by mean-field theories, which assumes a homogenous, Darcy-like permeability in the porous structure. Recent findings have challenged the suitability of these assumptions by revealing extreme heterogeneities in the electrolyte transport, on commercially relevant length scales exceeding the electrode pore size by an order of magnitude. [1] In this study, we introduce a new analytical method for electrochemical flow devices: 4D Confocal Optical Fluorescence Microscopy. This non-invasive in-situ analytical technique distinguishes between oxidized and reduced molecular species by their fluorescence spectra and maps out 3D molecular concentration fields with single-digit micron resolution (Figure 1). 3D movies, correlated with macroscopic chronoamperometry, add time as a fourth dimension. Thus, electrochemical conversion and species advection and diffusion can be monitored at heretofore unprecedented resolution, giving us new routes to understanding local phenomena in porous electrodes. We demonstrate this method by monitoring the reversible electrolytic reduction of 2,7 anthraquinone disulfonate (AQDS) to its corresponding hydroquinone, H2AQDS, in aqueous electrolyte in a transparent electrochemical cell. We monitor changes in the concentration field as a response to the variation of applied potential and current in real time. We correlate the fluorescence intensity of a particular band of wavelengths to the electrolyte state of charge. Furthermore, high sensitivity to non-linear optical effects enables us to capture the reversible formation of a dimer, specific to the AQDS/H2AQDS system, quantitatively in an operating battery. This new high-resolution 4D technique of characterizing operando electrochemical devices is expected to provide insight into the relationship between electrode microstructure and electrochemical performance features. Literature cited: [1] A.A. Wong, S.M. Rubinstein and M.J. Aziz, “Direct visualization of electrochemical reactions and heterogeneous transport within porous electrodes in operando by fluorescence microscopy” Cell Reports Phys. Sci. 2021, 100388; https://doi.org/10.1016/j.xcrp.2021.100388 Figure 1
49
Cescatti, Alessandro, Barbara Marcolla, Ignacio Goded und Carsten Gruening. „Optimal use of buffer volumes for the measurement of atmospheric gas concentration in multi-point systems“. Atmospheric Measurement Techniques 9, Nr. 9 (21.09.2016): 4665–72. http://dx.doi.org/10.5194/amt-9-4665-2016.
Der volle Inhalt der QuelleAnnotation:
Abstract. Accurate multi-point monitoring systems are required to derive atmospheric measurements of greenhouse gas concentrations both for the calculation of surface fluxes with inversion transport models and for the estimation of non-turbulent components of the mass balance equation (i.e. advection and storage fluxes) at eddy covariance sites. When a single analyser is used to monitor multiple sampling points, the deployment of buffer volumes (BVs) along sampling lines can reduce the uncertainty due to the discrete temporal sampling of the signal. In order to optimize the use of buffer volumes we explored various set-ups by simulating their effect on time series of high-frequency CO2 concentration collected at three Fluxnet sites. Besides, we proposed a novel scheme to calculate half-hourly weighted arithmetic means from discrete point samples, accounting for the probabilistic fraction of the signal generated in the averaging period. Results show that the use of BVs with the new averaging scheme reduces the mean absolute error (MAE) up to 80 % compared to a set-up without BVs and up to 60 % compared to the case with BVs and a standard, non-weighted averaging scheme. The MAE of CO2 concentration measurements was observed to depend on the variability of the concentration field and on the size of BVs, which therefore have to be carefully dimensioned. The optimal volume size depends on two main features of the instrumental set-up: the number of measurement points and the time needed to sample at one point (i.e. line purging plus sampling time). A linear and consistent relationship was observed at all sites between the sampling frequency, which summarizes the two features mentioned above, and the renewal frequency associated with the volume. Ultimately, this empirical relationship can be applied to estimate the optimal volume size according to the technical specifications of the sampling system.
50
Stein, Y., R. J. Dettmar, R. Beck, J. Irwin, T. Wiegert, A. Miskolczi, Q. D. Wang et al. „CHANG-ES“. Astronomy & Astrophysics 639 (Juli 2020): A111. http://dx.doi.org/10.1051/0004-6361/202037675.
Der volle Inhalt der QuelleAnnotation:
Context. Radio continuum observations of edge-on spiral galaxies reveal the appearance of radio halos as well as the large-scale structure of their magnetic fields. Furthermore, with multiple frequency observations, it is possible to deduce the transport mechanisms of the cosmic ray electrons (CREs). Aims. In order to gain a better understanding of the influence of cosmic rays (CRs) and magnetic fields in the disk-halo interface of edge-on spiral galaxies, we investigate the radio continuum halo, the magnetic field, and the transport processes of the CRs of the edge-on spiral galaxy NGC 4217 using CHANG-ES radio data at two frequencies, 6 GHz (C-band) and 1.5 GHz (L-band), and supplemental LOFAR data of this galaxy at 150 MHz. With additional X-ray Chandra data, we study the connection of radio features to the diffuse hot gas around NGC 4217. Methods. We investigate the total intensity (Stokes I) data in detail and determine the integrated spectral behavior. The radio scale heights of all three radio frequencies for NGC 4217 were extracted via exponential fits to the intensity profiles. From these, individual absolute flux densities of the disk and the halo were also calculated. Furthermore, we present magnetic field orientations from the polarization data using rotation measure synthesis (RM-synthesis), showing the large-scale ordered magnetic field of NGC 4217. After a separation of thermal and nonthermal emission, we calculated the resolved magnetic field strength via the revised equipartition formula. Additionally, we modeled the transport processes of CREs into the halo with the 1D model SPINNAKER. Results. NGC 4217 shows a large-scale X-shaped magnetic field structure, covering a major part of the galaxy with a mean total magnetic field strength in the disk of 9 μG. From the analysis of the rotation measure map at C-band, we found that the direction of the disk magnetic field is pointing inward. A helical outflow structure is furthermore present in the northwestern part of the galaxy, which is extended nearly 7 kpc into the halo. More polarized emission is observed on the approaching side of the galaxy, indicating that Faraday depolarization has to be considered at C-band. With a simplified galaxy disk model, we are able to explain the finding of higher polarized intensity on the approaching side. We generalize the model to predict that roughly 75% of edge-on spiral galaxies will show higher polarized intensity on the approaching side. Many loop and shell structures are found throughout the galaxy in total intensity at C-band. One structure, a symmetric off-center (to southwest of the disk) superbubble-like structure is prominent in total and polarized intensity, as well as in Hα and optical dust filaments. This is at a location where a second peak of total intensity (to the southwest of the disk) is observed, making this superbubble-like structure a possible result of a concentrated star formation region in the disk. The X-ray diffuse emission shows similarities to the polarized diffuse emission of NGC 4217. The flux density extension of the radio continuum halo increases toward lower frequencies. While the total flux density of the disk and halo are comparable at C-band, the contribution of the disk flux density decreases toward LOFAR to 18% of the total flux density. Dumbbell-shaped structures are present at C-band and at the LOFAR frequency. Total intensity profiles at the two CHANG-ES bands and the LOFAR frequency show a clear two-component behavior and were fit best with a two-component exponential fit. The halo scale heights are 1.10 ± 0.04 kpc, 1.43 ± 0.09 kpc, and 1.55 ± 0.04 kpc in C-band, L-band, and 150 MHz, respectively. The frequency dependence of these scale heights between C-band and L-band suggests advection to be the main transport process. The 1D CRE transport modeling shows that advection appears to be more important than diffusion.