Journal articles on the topic 'Multi-scale limit'
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Khoei, A. R., and M. Jahanshahi. "Multi-scale modeling of plastic deformations in nano-scale materials; Transition to plastic limit." International Journal for Numerical Methods in Engineering 109, no. 8 (November 29, 2016): 1180–216. http://dx.doi.org/10.1002/nme.5327.
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MINH, C. HA, FR BOUSSU, A. IMAD, T. KANIT, and D. CRÉPIN. "MULTI-SCALE MODEL TO PREDICT THE BALLISTIC IMPACT BEHAVIOR OF MULTI-LAYER PLAIN-WOVEN FABRICS." International Journal of Computational Methods 11, no. 03 (June 2014): 1343011. http://dx.doi.org/10.1142/s0219876213430111.
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This paper presents a multi-scale model that can predict the ballistic impact behavior of multi-layer plain-woven fabrics using the finite element method (FEM). Multi-layer fabrics of 30.5 × 30.5 cm, woven by high performance yarns Kevlar® 29 3000 denier, are impacted by a 0.3 fragment simulating projectile (FSP). Using a multi-scale approach, behavior of multi-layer fabrics subjected to different impact velocities is numerically analyzed. Ballistic limit of the fabric can also be predicted. The multi-scale model shows an effective gain of computation time in comparison with current mesoscopic ones. Computational results show a good agreement with experimental data.
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Jung, M., T. F. Illenseer, and W. J. Duschl. "Multi-scale simulations of black hole accretion in barred galaxies." Astronomy & Astrophysics 614 (June 2018): A105. http://dx.doi.org/10.1051/0004-6361/201731688.
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Due to the non-axisymmetric potential of the central bar, in addition to their characteristic arms and bar, barred spiral galaxies form a variety of structures within the thin gas disk, such as nuclear rings, inner spirals, and dust lanes. These structures in the inner kiloparsec are extremely important in order to explain and understand the rate of black hole feeding. The aim of this work is to investigate the influence of stellar bars in spiral galaxies on the thin self-gravitating gas disk. We focus on the accretion of gas onto the central supermassive black hole and its time-dependent evolution. We conducted multi-scale simulations simultaneously resolving the galactic disk and the accretion disk around the central black hole. In all the simulations we varied the initial gas disk mass. As an additional parameter we chose either the gas temperature for isothermal simulations or the cooling timescale for non-isothermal simulations. Accretion was either driven by a gravitationally unstable or clumpy accretion disk or by energy dissipation in strong shocks. Most of the simulations show a strong dependence of the accretion rate at the outer boundary of the central accretion disk (r < 300 pc) on the gas flow at kiloparsec scales. The final black hole masses reach up to ~109 M⊙ after 1.6 Gyr. Our models show the expected influence of the Eddington limit and a decline in growth rate at the corresponding sub-Eddington limit.
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Kyoya, Takashi, Kenjiro Terada, and Toshikazu Kawamoto. "Multi-scale limit load analysis for discontinuous rock mass based on the homogenization method." International Journal for Numerical and Analytical Methods in Geomechanics 23, no. 10 (August 25, 1999): 995–1019. http://dx.doi.org/10.1002/(sici)1096-9853(19990825)23:10<995::aid-nag21>3.0.co;2-b.
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Cotter, C. J., G. A. Gottwald, and D. D. Holm. "Stochastic partial differential fluid equations as a diffusive limit of deterministic Lagrangian multi-time dynamics." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, no. 2205 (September 2017): 20170388. http://dx.doi.org/10.1098/rspa.2017.0388.
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In Holm (Holm 2015 Proc. R. Soc. A 471 , 20140963. ( doi:10.1098/rspa.2014.0963 )), stochastic fluid equations were derived by employing a variational principle with an assumed stochastic Lagrangian particle dynamics. Here we show that the same stochastic Lagrangian dynamics naturally arises in a multi-scale decomposition of the deterministic Lagrangian flow map into a slow large-scale mean and a rapidly fluctuating small-scale map. We employ homogenization theory to derive effective slow stochastic particle dynamics for the resolved mean part, thereby obtaining stochastic fluid partial equations in the Eulerian formulation. To justify the application of rigorous homogenization theory, we assume mildly chaotic fast small-scale dynamics, as well as a centring condition. The latter requires that the mean of the fluctuating deviations is small, when pulled back to the mean flow.
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Sun, Xiangkun, Changwei Zhou, Mohamed Ichchou, Jean-Pierre Lainé, and Abdel-Malek Zine. "Multi-Scale Homogenization of Transversal Waves in Periodic Composite Beams." International Journal of Applied Mechanics 09, no. 03 (April 2017): 1750039. http://dx.doi.org/10.1142/s1758825117500399.
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This paper deals with the deduction of new homogenized models for the flexural wave in bi-periodic beams. According to the homogenization theory, the long-wave assumption is used and the valid frequency range of homogenized models is limited to the first Bragg band gap. However, the classical homogenization method, whose idea is taking the component’s mean values as effective material properties, has limitations in mimicking the dispersive behavior and the real valid frequency range is far less than the limit. Thus, enriched homogenized models, derived by the multi-scale asymptotic homogenization method, are proposed to provide more accurate homogenization models with larger real valid frequency range. The new homogenized models are validated by investigating the dispersion relation in the infinite case and the frequency response function in the finite case. Wave finite element method (WFEM) are used to provide associated references. A parametric study is carried out in the infinite case while two different boundary conditions are considered in the finite case.
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Vulliez, Margot, Matthew A. Gleason, Aurélien Souto-Lebel, Yann Quinsat, Claire Lartigue, Steven P. Kordell, Adam C. Lemoine, and Christopher A. Brown. "Multi-scale Curvature Analysis and Correlations with the Fatigue Limit on Steel Surfaces after Milling." Procedia CIRP 13 (2014): 308–13. http://dx.doi.org/10.1016/j.procir.2014.04.052.
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Xiao, Liang, Yan Li, Huangqing Xiao, Zheren Zhang, and Zheng Xu. "Electromechanical Transient Modeling of Line Commutated Converter-Modular Multilevel Converter-Based Hybrid Multi-Terminal High Voltage Direct Current Transmission Systems." Energies 11, no. 8 (August 13, 2018): 2102. http://dx.doi.org/10.3390/en11082102.
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A method for electromechanical modeling of line commutated converter (LCC)-modular multilevel converter (MMC)-based hybrid multi-terminal High Voltage Direct Current Transmission (HVDC) systems for large-scale power system transient stability study is proposed. Firstly, the general idea of modeling the LCC-MMC hybrid multi-terminal HVDC system is presented, then the AC-side and DC-side models of the LCC/MMC are established. Different from the conventional first-order DC-side model of the MMC, an improved second-order DC-side model of the MMC is established. Besides considering the firing angle limit of the LCC, a sequential power flow algorithm is proposed for the initialization of LCC-MMC hybrid multi-terminal HVDC system. Lastly, simulations of small scale and large scale power systems embedded with a three-terminal LCC-MMC hybrid HVDC system are performed on the electromechanical simulation platform PSS/E. It is demonstrated that if the firing angle limit is not considered, the accuracy of the power flow solutions will be greatly affected. Steady state calculation and dynamic simulation show that the developed LCC-MMC hybrid MTDC model is accurate enough for electromechanical transient stability studies of large-scale AC/DC system.
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Yang, Mao, Yu Cui, Dawei Huang, Xin Su, and Gang Wu. "Multi-time-scale coordinated optimal scheduling of integrated energy system considering frequency out-of-limit interval." International Journal of Electrical Power & Energy Systems 141 (October 2022): 108268. http://dx.doi.org/10.1016/j.ijepes.2022.108268.
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Hart, W. S., P. K. Maini, C. A. Yates, and R. N. Thompson. "A theoretical framework for transitioning from patient-level to population-scale epidemiological dynamics: influenza A as a case study." Journal of The Royal Society Interface 17, no. 166 (May 2020): 20200230. http://dx.doi.org/10.1098/rsif.2020.0230.
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Multi-scale epidemic forecasting models have been used to inform population-scale predictions with within-host models and/or infection data collected in longitudinal cohort studies. However, most multi-scale models are complex and require significant modelling expertise to run. We formulate an alternative multi-scale modelling framework using a compartmental model with multiple infected stages. In the large-compartment limit, our easy-to-use framework generates identical results compared to previous more complicated approaches. We apply our framework to the case study of influenza A in humans. By using a viral dynamics model to generate synthetic patient-level data, we explore the effects of limited and inaccurate patient data on the accuracy of population-scale forecasts. If infection data are collected daily, we find that a cohort of at least 40 patients is required for a mean population-scale forecasting error below 10%. Forecasting errors may be reduced by including more patients in future cohort studies or by increasing the frequency of observations for each patient. Our work, therefore, provides not only an accessible epidemiological modelling framework but also an insight into the data required for accurate forecasting using multi-scale models.
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de Oliveira Gomes, André, and Pedro Catuogno. "Moderate Averaged Deviations for a Multi-Scale System with Jumps and Memory." Dynamics 3, no. 1 (March 14, 2023): 171–201. http://dx.doi.org/10.3390/dynamics3010011.
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This work studies a two-time-scale functional system given by two jump diffusions under the scale separation by a small parameter ε→0. The coefficients of the equations that govern the dynamics of the system depend on the segment process of the slow variable (responsible for capturing delay effects on the slow component) and on the state of the fast variable. We derive a moderate deviation principle for the slow component of the system in the small noise limit using the weak convergence approach. The rate function is written in terms of the averaged dynamics associated with the multi-scale system. The core of the proof of the moderate deviation principle is the establishment of an averaging principle for the auxiliary controlled processes associated with the slow variable in the framework of the weak convergence approach. The controlled version of the averaging principle for the jump multi-scale diffusion relies on a discretization method inspired by the classical Khasminkii’s averaging principle.
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Engquist, B., and P. E. Souganidis. "Asymptotic and numerical homogenization." Acta Numerica 17 (April 25, 2008): 147–90. http://dx.doi.org/10.1017/s0962492906360011.
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Homogenization is an important mathematical framework for developing effective models of differential equations with oscillations. We include in the presentation techniques for deriving effective equations, a brief discussion on analysis of related limit processes and numerical methods that are based on homogenization principles. We concentrate on first- and second-order partial differential equations and present results concerning both periodic and random media for linear as well as nonlinear problems. In the numerical sections, we comment on computations of multi-scale problems in general and then focus on projection-based numerical homogenization and the heterogeneous multi-scale method.
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Pu, Can, Runzi Song, Radim Tylecek, Nanbo Li, and Robert Fisher. "SDF-MAN: Semi-Supervised Disparity Fusion with Multi-Scale Adversarial Networks." Remote Sensing 11, no. 5 (February 27, 2019): 487. http://dx.doi.org/10.3390/rs11050487.
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Refining raw disparity maps from different algorithms to exploit their complementary advantages is still challenging. Uncertainty estimation and complex disparity relationships among pixels limit the accuracy and robustness of existing methods and there is no standard method for fusion of different kinds of depth data. In this paper, we introduce a new method to fuse disparity maps from different sources, while incorporating supplementary information (intensity, gradient, etc.) into a refiner network to better refine raw disparity inputs. A discriminator network classifies disparities at different receptive fields and scales. Assuming a Markov Random Field for the refined disparity map produces better estimates of the true disparity distribution. Both fully supervised and semi-supervised versions of the algorithm are proposed. The approach includes a more robust loss function to inpaint invalid disparity values and requires much less labeled data to train in the semi-supervised learning mode. The algorithm can be generalized to fuse depths from different kinds of depth sources. Experiments explored different fusion opportunities: stereo-monocular fusion, stereo-ToF fusion and stereo-stereo fusion. The experiments show the superiority of the proposed algorithm compared with the most recent algorithms on public synthetic datasets (Scene Flow, SYNTH3, our synthetic garden dataset) and real datasets (Kitti2015 dataset and Trimbot2020 Garden dataset).
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Liu, Guangmao, Jiangtao Chen, Runrun Li, Jialin Jin, and Yuying Cheng. "Multi-agent technology based voltage grading control method for distribution network." ITM Web of Conferences 47 (2022): 03012. http://dx.doi.org/10.1051/itmconf/20224703012.
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It is one of the challenges to solve the power quality problems such as voltage fluctuation and voltage exceeding limit caused by the largescale grid connection of distributed photovoltaic (DPV). Considering the operation speed of voltage regulation control in distribution network, this paper proposes a voltage hierarchical control method based on multi-agent structure. The mathematical models of this method are divided into dualtime scale global optimization model and event-triggered voltage regional autonomy model, aiming at solving the problem of operation safety of voltage exceeding limit. The method is verified by a specific example. The results show that this method can respond quickly to the change of power grid voltage, and help to reduce the risk of voltage exceeding the limit, and improve the operation economy of distribution network.
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Qin, Fang, Lele Zhang, Geng Chen, and Christoph Broeckmann. "Lower bound limit and shakedown analysis of orthotropic material." Mathematics and Mechanics of Solids 25, no. 11 (June 7, 2020): 2037–49. http://dx.doi.org/10.1177/1081286520918004.
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We present in this study a new approach for predicting the plastic and shakedown limits of structures composed of orthotropic materials. In this approach, the Hill yield criterion is introduced to Melan’s theorem. By formulating the problem by means of the finite element method and solving the resulting large-scale nonlinear optimization problem we successfully predict the plastic and shakedown limits of structures having complex geometries made from multi-orthotropic materials. Several numerical examples are elaborated in this study for evaluating the accuracy, general applicability, as well as the efficiency of the established numerical scheme. Overall, the study confirms that the direct method can be extended and adopted as a viable means for design and analysis of structures made of orthotropic materials.
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Adeleke, T. B., R. O. Edokpia, M. K. Onifade, and N. B. Chime. "Development of a Multi-criteria Decision Model for Nigerian Refinery Bottlenecks." European Journal of Engineering and Technology Research 6, no. 5 (July 29, 2021): 80–83. http://dx.doi.org/10.24018/ejers.2021.6.5.2492.
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Production systems are continually surrounded by bottleneck problems that limit their overall performances. The petroleum industry today faces a lot of challenges which border on production bottlenecks that tend to limit production throughput and hence output. The purpose of this study is to provide a decision support strategy for refinery operators and mangers as well as other stakeholders. The multi-criteria models used were the Analytical Hierarchy Process (AHP) and the Test of Preference by Similarity to Ideal Solution (TOPSIS). A 9-point saaty scale and 10-point linguistic scale questionnaires were used to elicit responses from experts in the refinery. The statistical computations with the Multi-criteria Decision Model were carried out with the aid of (AHP -OS) BPMSG software on nine criteria which are bottleneck variables which impact on refinery operations and the comparison was made by nine decision makers who are refinery experts while TOPSIS was used for alternatives selection. The result of the AHP showed the contributing weights of individual criterion with “Government Interference” ranking first, exerting a weight of 19.84%. The result also generated a normalized total matrix which is approximately one (1), consistency index of 0.09694 and a consistency ratio of 0.06685 which is within acceptable limit and finally from TOPSIS modeling, “Denationalization” with the highest value of 0.7598 was found to be closest to the ideal solution for the optimal refinery performance. This study has developed a multi-criteria decision model for selecting the best alternative for optimal performance based on inputs from experts and this provides a veritable framework that serves as a decision support strategy for policy makers and stakeholders in the operations of the refinery.
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Adeleke, T. B., R. O. Edokpia, M. K. Onifade, and N. B. Chime. "Development of a Multi-criteria Decision Model for Nigerian Refinery Bottlenecks." European Journal of Engineering and Technology Research 6, no. 5 (July 29, 2021): 80–83. http://dx.doi.org/10.24018/ejeng.2021.6.5.2492.
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Production systems are continually surrounded by bottleneck problems that limit their overall performances. The petroleum industry today faces a lot of challenges which border on production bottlenecks that tend to limit production throughput and hence output. The purpose of this study is to provide a decision support strategy for refinery operators and mangers as well as other stakeholders. The multi-criteria models used were the Analytical Hierarchy Process (AHP) and the Test of Preference by Similarity to Ideal Solution (TOPSIS). A 9-point saaty scale and 10-point linguistic scale questionnaires were used to elicit responses from experts in the refinery. The statistical computations with the Multi-criteria Decision Model were carried out with the aid of (AHP -OS) BPMSG software on nine criteria which are bottleneck variables which impact on refinery operations and the comparison was made by nine decision makers who are refinery experts while TOPSIS was used for alternatives selection. The result of the AHP showed the contributing weights of individual criterion with “Government Interference” ranking first, exerting a weight of 19.84%. The result also generated a normalized total matrix which is approximately one (1), consistency index of 0.09694 and a consistency ratio of 0.06685 which is within acceptable limit and finally from TOPSIS modeling, “Denationalization” with the highest value of 0.7598 was found to be closest to the ideal solution for the optimal refinery performance. This study has developed a multi-criteria decision model for selecting the best alternative for optimal performance based on inputs from experts and this provides a veritable framework that serves as a decision support strategy for policy makers and stakeholders in the operations of the refinery.
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Ekanga, Trésor. "Localization in the multi-particle tight-binding Anderson model at low energy." Reviews in Mathematical Physics 32, no. 03 (September 20, 2019): 2050009. http://dx.doi.org/10.1142/s0129055x20500099.
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We consider the multi-particle tight-binding Anderson model and prove that its lower spectral edge is non-random under some mild assumptions on the inter-particle interaction and the random external potential. We also adapt to the low energy regime the multi-particle multi-scale analysis initially developed by Chulaevsky and Suhov in the high disorder limit, if the marginal probability distribution of the i.i.d. random variables is log-Hölder continuous and we obtain the spectral exponential and strong dynamical localization near the bottom of the spectrum.
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Liao, Yuchen. "Multi-point distribution of discrete time periodic TASEP." Probability Theory and Related Fields 182, no. 3-4 (January 16, 2022): 1053–131. http://dx.doi.org/10.1007/s00440-021-01107-8.
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AbstractWe study the one-dimensional discrete time totally asymmetric simple exclusion process with parallel update rules on a spatially periodic domain. A multi-point space-time joint distribution formula is obtained for general initial conditions. The formula involves contour integrals of Fredholm determinants with kernels acting on certain discrete spaces. For a class of initial conditions satisfying certain technical assumptions, we are able to derive large-time, large-period limit of the joint distribution, under the relaxation time scale $$t=O(L^{3/2})$$ t = O ( L 3 / 2 ) when the height fluctuations are critically affected by the finite geometry. The assumptions are verified for the step and flat initial conditions. As a corollary we obtain the multi-point distribution of discrete time TASEP on the whole integer lattice $${\mathbb {Z}}$$ Z by taking the period L large enough so that the finite-time distribution is not affected by the boundary. The large time limit for the multi-time distribution of discrete time TASEP on $${\mathbb {Z}}$$ Z is then obtained for the step initial condition.
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Yano, J. I. "Mass-flux subgrid-scale parameterization in analogy with multi-component flows: a formulation towards scale independence." Geoscientific Model Development 5, no. 6 (November 21, 2012): 1425–40. http://dx.doi.org/10.5194/gmd-5-1425-2012.
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Abstract. A generalized mass-flux formulation is presented, which no longer takes a limit of vanishing fractional areas for subgrid-scale components. The presented formulation is applicable to a~situation in which the scale separation is still satisfied, but fractional areas occupied by individual subgrid-scale components are no longer small. A self-consistent formulation is presented by generalizing the mass-flux formulation under the segmentally-constant approximation (SCA) to the grid–scale variabilities. The present formulation is expected to alleviate problems arising from increasing resolutions of operational forecast models without invoking more extensive overhaul of parameterizations. The present formulation leads to an analogy of the large-scale atmospheric flow with multi-component flows. This analogy allows a generality of including any subgrid-scale variability into the mass-flux parameterization under SCA. Those include stratiform clouds as well as cold pools in the boundary layer. An important finding under the present formulation is that the subgrid-scale quantities are advected by the large-scale velocities characteristic of given subgrid-scale components (large-scale subcomponent flows), rather than by the total large-scale flows as simply defined by grid-box average. In this manner, each subgrid-scale component behaves as if like a component of multi-component flows. This formulation, as a result, ensures the lateral interaction of subgrid-scale variability crossing the grid boxes, which are missing in the current parameterizations based on vertical one-dimensional models, and leading to a reduction of the grid-size dependencies in its performance. It is shown that the large-scale subcomponent flows are driven by large-scale subcomponent pressure gradients. The formulation, as a result, furthermore includes a self-contained description of subgrid-scale momentum transport. The main purpose of the present paper is to appeal the importance of this new possibility suggested herein to the numerical weather forecast community with implications for the other parameterizations (cloud fraction, mesoscale organization) as well as resolution-dependence of parameterizations.
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Luo, Zhao, Zhendong Zhu, Zhiyuan Zhang, Jinghui Qin, Hao Wang, Zeyong Gao, and Zhichao Yang. "Multi-Time-Scale Rolling Optimal Dispatch for Grid-Connected AC/DC Hybrid Microgrids." Processes 7, no. 12 (December 16, 2019): 961. http://dx.doi.org/10.3390/pr7120961.
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In order to reduce the impact of the randomness and volatility of renewable energy on the economic operation of AC/DC hybrid microgrids, a multi-time-scale rolling optimization strategy is proposed for the grid-connected AC/DC hybrid microgrids. It considers the source-load uncertainty declined with time scale reduction, and the scheduling cooperation problem of different units on different time scales. In this paper, we propose a three-time-scale optimal strategy of the day-ahead, intraday and real-time dispatching stage and a two-level rolling optimal strategy of the intraday and real-time stage, aiming at minimizing the operating cost. We added the power penalty cost in the rolling optimization model to limit the energy state of the energy storage system in the constraint, and improve the power correction and tracking effect of the rolling optimization. A typical-structure AC/DC hybrid microgrid is analyzed in this paper and the simulation results are shown to demonstrate the feasibility and effectiveness of the proposed multi-time-scale rolling optimal dispatch.
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Wang, Ling, Hongqiao Wang, and Guangyuan Fu. "Multi-Nyström Method Based on Multiple Kernel Learning for Large Scale Imbalanced Classification." Computational Intelligence and Neuroscience 2021 (June 13, 2021): 1–11. http://dx.doi.org/10.1155/2021/9911871.
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Extensions of kernel methods for the class imbalance problems have been extensively studied. Although they work well in coping with nonlinear problems, the high computation and memory costs severely limit their application to real-world imbalanced tasks. The Nyström method is an effective technique to scale kernel methods. However, the standard Nyström method needs to sample a sufficiently large number of landmark points to ensure an accurate approximation, which seriously affects its efficiency. In this study, we propose a multi-Nyström method based on mixtures of Nyström approximations to avoid the explosion of subkernel matrix, whereas the optimization to mixture weights is embedded into the model training process by multiple kernel learning (MKL) algorithms to yield more accurate low-rank approximation. Moreover, we select subsets of landmark points according to the imbalance distribution to reduce the model’s sensitivity to skewness. We also provide a kernel stability analysis of our method and show that the model solution error is bounded by weighted approximate errors, which can help us improve the learning process. Extensive experiments on several large scale datasets show that our method can achieve a higher classification accuracy and a dramatical speedup of MKL algorithms.
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Dai, Shibin, and Keith Promislow. "Geometric evolution of bilayers under the functionalized Cahn–Hilliard equation." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 469, no. 2153 (May 8, 2013): 20120505. http://dx.doi.org/10.1098/rspa.2012.0505.
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We use a multi-scale analysis to derive a sharp interface limit for the dynamics of bilayer structures of the functionalized Cahn–Hilliard equation. In contrast to analysis based on single-layer interfaces, we show that the Stefan and Mullins–Sekerka problems derived for the evolution of single-layer interfaces for the Cahn–Hilliard equation are trivial in this context, and the sharp interface limit yields a quenched mean-curvature-driven normal velocity at O ( ε −1 ), whereas on the longer O ( ε −2 ) time scale, it leads to a total surface area preserving Willmore flow. In particular, for space dimension n =2, the constrained Willmore flow drives collections of spherically symmetric vesicles to a common radius, whereas for n =3, the radii are constant, and for n ≥4 the largest vesicle dominates.
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Pereira, Carlos Alvarez, and José M. Vega. "On the pulsating instability of two-dimensional flames." European Journal of Applied Mathematics 3, no. 1 (March 1992): 55–73. http://dx.doi.org/10.1017/s0956792500000681.
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We consider a well-known thermo-diffusive model for the propagation of a premixed, adiabatic flame front in the large-activation-energy limit. That model depends only on one nondimensional parameter β, the reduced Lewis number. Near the pulsating instability limit, as β↓β0= 32/3, we obtain an asymptotic model for the evolution of a quasi-planar flame front, via a multi-scale analysis. The asymptotic model consists of two complex Ginzburg–Landau equations and a real Burgers equation, coupled by non-local terms. The model is used to analyse the nonlinear stability of the flame front.
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Glazman, Roman E. "A simple theory of capillary–gravity wave turbulence." Journal of Fluid Mechanics 293 (June 25, 1995): 25–34. http://dx.doi.org/10.1017/s0022112095001613.
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Employing a recently proposed ‘multi-wave interaction’ theory (Glazman 1992), inertial spectra of capillary-gravity waves are derived. This case is characterized by a rather high degree of nonlinearity and a complicated dispersion law. The absence of scale invariance makes this and some other problems of wave turbulence (e.g. nonlinear inertia-gravity waves) intractable by small-perturbation techniques, even in the weak-turbulence limit. The analytical solution obtained in the present work for an arbitrary degree of nonlinearity is shown to be in reasonable agreement with experimental data. The theory explains the dependence of the wave spectrum on wind input and describes the accelerated roll-off of the spectral density function in the narrow sub-range separating scale-invariant regimes of purely gravity and capillary waves, while the appropriate (long- and short-wave) limits yield power laws corresponding to the Zakharov-Filonenko and Phillips spectra.
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Jeon, Suyeon, and Yong Seok Heo. "Efficient Multi-Scale Stereo-Matching Network Using Adaptive Cost Volume Filtering." Sensors 22, no. 15 (July 23, 2022): 5500. http://dx.doi.org/10.3390/s22155500.
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While recent deep learning-based stereo-matching networks have shown outstanding advances, there are still some unsolved challenges. First, most state-of-the-art stereo models employ 3D convolutions for 4D cost volume aggregation, which limit the deployment of networks for resource-limited mobile environments owing to heavy consumption of computation and memory. Although there are some efficient networks, most of them still require a heavy computational cost to incorporate them to mobile computing devices in real-time. Second, most stereo networks indirectly supervise cost volumes through disparity regression loss by using the softargmax function. This causes problems in ambiguous regions, such as the boundaries of objects, because there are many possibilities for unreasonable cost distributions which result in overfitting problem. A few works deal with this problem by generating artificial cost distribution using only the ground truth disparity value that is insufficient to fully regularize the cost volume. To address these problems, we first propose an efficient multi-scale sequential feature fusion network (MSFFNet). Specifically, we connect multi-scale SFF modules in parallel with a cross-scale fusion function to generate a set of cost volumes with different scales. These cost volumes are then effectively combined using the proposed interlaced concatenation method. Second, we propose an adaptive cost-volume-filtering (ACVF) loss function that directly supervises our estimated cost volume. The proposed ACVF loss directly adds constraints to the cost volume using the probability distribution generated from the ground truth disparity map and that estimated from the teacher network which achieves higher accuracy. Results of several experiments using representative datasets for stereo matching show that our proposed method is more efficient than previous methods. Our network architecture consumes fewer parameters and generates reasonable disparity maps with faster speed compared with the existing state-of-the art stereo models. Concretely, our network achieves 1.01 EPE with runtime of 42 ms, 2.92M parameters, and 97.96G FLOPs on the Scene Flow test set. Compared with PSMNet, our method is 89% faster and 7% more accurate with 45% fewer parameters.
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Xiong, Wei, Jianfeng Wang, and Zhuang Cheng. "A Novel Multi-Scale Particle Morphology Descriptor with the Application of SPHERICAL Harmonics." Materials 13, no. 15 (July 23, 2020): 3286. http://dx.doi.org/10.3390/ma13153286.
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Particle morphology is of great significance to the grain- and macro-scale behaviors of granular soils. Most existing traditional morphology descriptors have three perennial limitations, i.e., dissensus of definition, inter-scale effect, and surface roughness heterogeneity, which limit the accurate representation of particle morphology. The inter-scale effect refers to the inaccurate representation of the morphological features at the target relative length scale (RLS, i.e., length scale with respective to particle size) caused by the inclusion of additional morphological details existing at other RLS. To effectively eliminate the inter-scale effect and reflect surface roughness heterogeneity, a novel spherical harmonic-based multi-scale morphology descriptor Rinc is proposed to depict the incremental morphology variation (IMV) at different RLS. The following conclusions were drawn: (1) the IMV at each RLS decreases with decreasing RLS while the corresponding particle surface is, in general, getting rougher; (2) artificial neural network (ANN)-based mean impact values (MIVs) of Rinc at different RLS are calculated and the results prove the effective elimination of inter-scale effects by using Rinc; (3) Rinc shows a positive correlation with the rate of increase of surface area RSA at all RLS; (4) Rinc can be utilized to quantify the irregularity and roughness; (5) the surface morphology of a given particle shows different morphology variation in different sections, as well as different variation trends at different RLS. With the capability of eliminating the existing limitations of traditional morphology descriptors, the novel multi-scale descriptor proposed in this paper is very suitable for acting as a morphological gene to represent the multi-scale feature of particle morphology.
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Liu, Changyuan, Yunfu Yin, Yuhan Sun, and Okan K. Ersoy. "Multi-scale ResNet and BiGRU automatic sleep staging based on attention mechanism." PLOS ONE 17, no. 6 (June 16, 2022): e0269500. http://dx.doi.org/10.1371/journal.pone.0269500.
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Sleep staging is the basis of sleep evaluation and a key step in the diagnosis of sleep-related diseases. Despite being useful, the existing sleep staging methods have several disadvantages, such as relying on artificial feature extraction, failing to recognize temporal sequence patterns in the long-term associated data, and reaching the accuracy upper limit of sleep staging. Hence, this paper proposes an automatic Electroencephalogram (EEG) sleep signal staging model, which based on Multi-scale Attention Residual Nets (MAResnet) and Bidirectional Gated Recurrent Unit (BiGRU). The proposed model is based on the residual neural network in deep learning. Compared with the traditional residual learning module, the proposed model additionally uses the improved channel and spatial feature attention units and convolution kernels of different sizes in parallel at the same position. Thus, multiscale feature extraction of the EEG sleep signals and residual learning of the neural networks is performed to avoid network degradation. Finally, BiGRU is used to determine the dependence between the sleep stages and to realize the automatic learning of sleep data staging features and sleep cycle extraction. According to the experiment, the classification accuracy and kappa coefficient of the proposed method on sleep-EDF data set are 84.24% and 0.78, which are respectively 0.24% and 0.21 higher than the traditional residual net. At the same time, this paper also verified the proposed method on UCD and SHHS data sets, and the figure of classification accuracy is 79.34% and 81.6%, respectively. Compared to related existing studies, the recognition accuracy is significantly improved, which validates the effectiveness and generalization performance of the proposed method.
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Shi, Jian, and Mingbo Tong. "Multi-Scale Nonlinear Progressive Damage and Failure Analysis for Open-Hole Composite Laminates." Aerospace 9, no. 2 (January 24, 2022): 59. http://dx.doi.org/10.3390/aerospace9020059.
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In order to study the nonlinear behaviors and interactions among the constituents for the composite material structure under the tensile load, multiscale damage model using generalized method of cells (GMC) and a lamina-level progressive damage model were established, respectively, for fiber reinforced composite laminates with a central hole, which were based on the thermodynamic Schapery Theory (ST) at either the micro-level or the lamina level. Once the nonlinear progressive degradation of the matrix material reached the lower limit value for the ST method, matrix failures naturally occurred, the failure of the fiber was determined by the maximum stress failure criterion. For the multiscale progressive damage model, the GMC model consisting of a fiber subcell and three matrix subcells was imposed at each integral point of FEM elements, and the three matrix subcells undergo independent damage evolution. The load versus displacement curves and failure modes of the open-hole laminates were predicted by using the two progressive failure models, and the results were compared with that obtained by the Hashin-Rotem progressive failure model and the experimental results. The results show that the ST based method can obtain the nonlinear progressive damage evolution states and failure states of the composite at both the lamina level and the multiscale level. Finally, the damage contours and failure paths obtained are also presented.
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Luo, Tao, and Yan-Lin Wang. "Multi-scale nonlinear singular limit for thermal non-equilibrium gas flow with multiple non-equilibrium modes for analytic data in multi-dimensions with physical boundaries." Journal of Mathematical Physics 61, no. 10 (October 1, 2020): 101512. http://dx.doi.org/10.1063/5.0025752.
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CHALONS, C., and F. COQUEL. "THE RIEMANN PROBLEM FOR THE MULTI-PRESSURE EULER SYSTEM." Journal of Hyperbolic Differential Equations 02, no. 03 (September 2005): 745–82. http://dx.doi.org/10.1142/s0219891605000610.
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We prove the existence and uniqueness of the Riemann solutions to the Euler equations closed by N independent constitutive pressure laws. This model stands as a natural asymptotic system for the multi-pressure Navier–Stokes equations in the regime of infinite Reynolds number. Due to the inherent lack of conservation form in the viscous regularization, the limit system exhibits measure-valued source terms concentrated on shock discontinuities. These non-positive bounded measures, called kinetic relations, are known to provide a suitable tool to encode the small-scale sensitivity in the singular limit. Considering N independent polytropic pressure laws, we show that these kinetic relations can be derived by solving a simple algebraic problem which governs the endpoints of the underlying viscous shock profiles, for any given but prescribed ratio of viscosity coefficient in the viscous perturbation. The analysis based on traveling wave solutions allows us to introduce the asymptotic Euler system in the setting of piecewise Lipschitz continuous functions and to study the Riemann problem.
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Guillaumet, Alban, and Guillaume Leotard. "Annoying neighbors: Multi-scale distribution determinants of two sympatric sibling species of birds." Current Zoology 61, no. 1 (February 1, 2015): 10–22. http://dx.doi.org/10.1093/czoolo/61.1.10.
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Abstract We tested the role of interspecific competition in driving species distribution at multiple spatial scales using two sibling species of Galerida larks (G. cristata and G. theklae) in Morocco (sympatry), Balearic islands (G. theklae only) and Israel (G. cristata only). We first investigated regional-scale determinants by contrasting allopatric versus sympatric patterns in five distinct habitat types. We next focused on a single habitat used by both species, the coastal sand dunes. Dune quadrats were established along the Moroccan coast and completed by a quadrat in the nearest distinct landscape habitat. Poisson regressions were used to model Galerida counts together with ecological predictors as concerns the climate, topography, vegetation structure and soil gra-nulometry. At the local scale, both species preferred grey dunes over white sand dunes, and both were negatively affected by the abundance of the congeneric species in the dune. However, we found that G. theklae tended to replace G. cristata in more arid sand dunes, even if the transition was not strictly clinal. Instead, the transition occurred when the surrounding landscape changed from coastal wetlands to bathas (grasslands with shrubs), highlighting the importance of habitat composition at the landscape scale. The fact that G. cristata used bathas in allopatry, but not in sympatry, suggested that the competitive environment contributed to determine sand dune occupancy. We suggest that landscape-level effects may be pivotal in explaining species distribution not only at the local scale, by affecting the pool of potential immigrants, but also at the regional scale, by contributing to species’ range limit.
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Siorikis, Dimitris K., Christos V. Nastos, Dimitris A. Saravanos, and Esteban Martino Gonzalez. "A Strain-rate Dependant Micromechanical Finite Element Model for High-velocity Impacts on Laminated Composite Plates." MATEC Web of Conferences 304 (2019): 01009. http://dx.doi.org/10.1051/matecconf/201930401009.
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A novel multi-scale numerical model for the simulation of high-velocity impacts on laminated composite plates is developed, which encompasses a micromechanics module for the accurate assessment of damage initiation and growth in the individual composite micromechanical constituents and for the efficient inclusion of strain rate effects into the analysis. A series of woven carbon/epoxy plate specimens impacted by steel ball impactors of high velocities and energies reaching and exceeding the ballistic limit (m=110 g, v=60-100 m/s, E=200-500 J) are also investigated. Ultimately, key impact simulation results, such as the ballistic limit and induced impact damage, are correlated with representative experimental results, demonstrating the validity of the proposed impact model.
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Dimarco, Giacomo, Lorenzo Pareschi, and Vittorio Rispoli. "Implicit-Explicit Runge-Kutta Schemes for the Boltzmann-Poisson System for Semiconductors." Communications in Computational Physics 15, no. 5 (May 2014): 1291–319. http://dx.doi.org/10.4208/cicp.090513.151113a.
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AbstractIn this paper we develop a class of Implicit-Explicit Runge-Kutta schemes for solving the multi-scale semiconductor Boltzmann equation. The relevant scale which characterizes this kind of problems is the diffusive scaling. This means that, in the limit of zero mean free path, the system is governed by a drift-diffusion equation. Our aim is to develop a method which accurately works for the different regimes encountered in general semiconductor simulations: the kinetic, the intermediate and the diffusive one. Moreover, we want to overcome the restrictive time step conditions of standard time integration techniques when applied to the solution of this kind of phenomena without any deterioration in the accuracy. As a result, we obtain high order time and space discretization schemes which do not suffer from the usual parabolic stiffness in the diffusive limit. We show different numerical results which permit to appreciate the performances of the proposed schemes.
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Zhang, Rosa, Anamika Chowdhury, Justin C. Bui, Clayton J. Radke, and Adam Z. Weber. "Multi-Scale Modeling of Hydrogen Transport in a Porous Fuel Cell Anode." ECS Meeting Abstracts MA2022-01, no. 55 (July 7, 2022): 2313. http://dx.doi.org/10.1149/ma2022-01552313mtgabs.
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Proton-exchange-membrane fuel cells (PEMFC) are a clean energy conversion alternative to traditional fossil-fuel combustion; however, transport resistances in the electrode pose a lower-limit to catalyst loading and commercialization of PEMFCs. PEMFCs consist of simultaneous hydrogen (H2) oxidation and oxygen (O2) reduction at the anode and cathode, respectively. While oxygen transport resistances in PEMFCs have been widely studied both experimentally and analytically, hydrogen transport resistances are less understood. Herein, we present a physics-based model that encompasses multi-scale transport within the anode side of the PEMFC. The O2 in the cathode here is omitted and replaced with H2 to deconvolute O2 transport resistance contributions, similar to that of a hydrogen pump. Replication of the hydrogen pump setup allows for comparison of the model against experimental analysis of H2 gas-transport resistance in H2 limiting-current experiments, which can also inform gas transport (including oxygen) in general. Herein, we present a multi-scale analytical model of the porous anode catalyst layers and individual catalyst agglomerates that enables determination of the effects of electrode morphology such as agglomerate size, catalyst loading, etc. on H2 transport resistance through the porous electrode to complement and better understand H2 limiting current experiments and deconvolute local H2 transport resistances. Electrodes within PEMFCs are heterogeneous porous structures formed by agglomerates of carbon particles containing Pt nanoparticles, held together by an ion-conducting polymer (ionomer). The gas transport hence involves transport through multiple phases and length-scales: (i) gas-phase transport through electrode pores at the length scale of electrode thickness (micrometer) and (ii) diffusion into the agglomerate through an ionomer film at the length scale of agglomerate radius (nanometer). Based on previous modeling efforts of varying length-scales of the catalyst layer, our analytical model adequately and simultaneously captures reaction-diffusion at all of the aforementioned scales (i.e., the electrode thickness and agglomerate radius) to better describe porous anode performance. A sensitivity analysis is subsequently performed to compare current generated against transport parameters for both scales. This work ultimately provides insight that will guide the design and engineering of future porous anodes for applications in hydrogen pumping and PEMFCs.
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Yang, Junfang, Yi Ma, Yabin Hu, Zongchen Jiang, Jie Zhang, Jianhua Wan, and Zhongwei Li. "Decision Fusion of Deep Learning and Shallow Learning for Marine Oil Spill Detection." Remote Sensing 14, no. 3 (January 30, 2022): 666. http://dx.doi.org/10.3390/rs14030666.
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Marine oil spills are an emergency of great harm and have become a hot topic in marine environmental monitoring research. Optical remote sensing is an important means to monitor marine oil spills. Clouds, weather, and light control the amount of available data, which often limit feature characterization using a single classifier and therefore difficult to accurate monitoring of marine oil spills. In this paper, we develop a decision fusion algorithm to integrate deep learning methods and shallow learning methods based on multi-scale features for improving oil spill detection accuracy in the case of limited samples. Based on the multi-scale features after wavelet transform, two deep learning methods and two classical shallow learning algorithms are used to extract oil slick information from hyperspectral oil spill images. The decision fusion algorithm based on fuzzy membership degree is introduced to fuse multi-source oil spill information. The research shows that oil spill detection accuracy using the decision fusion algorithm is higher than that of the single detection algorithms. It is worth noting that oil spill detection accuracy is affected by different scale features. The decision fusion algorithm under the first-level scale features can further improve the accuracy of oil spill detection. The overall classification accuracy of the proposed method is 91.93%, which is 2.03%, 2.15%, 1.32%, and 0.43% higher than that of SVM, DBN, 1D-CNN, and MRF-CNN algorithms, respectively.
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Tang, Chao, Xiaofan Chen, Zhimin Du, Ping Yue, and Jiabao Wei. "Numerical Simulation Study on Seepage Theory of a Multi-Section Fractured Horizontal Well in Shale Gas Reservoirs Based on Multi-Scale Flow Mechanisms." Energies 11, no. 9 (September 4, 2018): 2329. http://dx.doi.org/10.3390/en11092329.
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Aimed at the multi-scale fractures for stimulated reservoir volume (SRV)-fractured horizontal wells in shale gas reservoirs, a mathematical model of unsteady seepage is established, which considers the characteristics of a dual media of matrix and natural fractures as well as flow in the large-scale hydraulic fractures, based on a discrete-fracture model. Multi-scale flow mechanisms, such as gas desorption, the Klinkenberg effect, and gas diffusion are taken into consideration. A three-dimensional numerical model based on the finite volume method is established, which includes the construction of spatial discretization, calculation of average pressure gradient, and variable at interface, etc. Some related processing techniques, such as boundedness processing upstream and downstream of grid flow, was used to limit non-physical oscillation at large-scale hydraulic fracture interfaces. The sequential solution is performed to solve the pressure equations of matrix, natural, and large-scale hydraulic fractures. The production dynamics and pressure distribution of a multi-section fractured horizontal well in a shale gas reservoir are calculated. Results indicate that, with the increase of the Langmuir volume, the average formation pressure decreases at a slow rate. Simultaneously, the initial gas production and the contribution ratio of the desorbed gas increase. With the decrease of the pore size of the matrix, gas diffusion and the Klinkenberg effect have a greater impact on shale gas production. By changing the fracture half-length and the number of fractured sections, we observe that the production process can not only pursue the long fractures or increase the number of fractured sections, but also should optimize the parameters such as the perforation position, cluster spacing, and fracturing sequence. The stimulated reservoir volume can effectively control the shale reservoir.
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Jiang, Wei, Xianglian Meng, and Ji Xi. "Multilevel Attention and Multiscale Feature Fusion Network for Author Classification of Chinese Ink-Wash Paintings." Discrete Dynamics in Nature and Society 2022 (March 10, 2022): 1–10. http://dx.doi.org/10.1155/2022/9188356.
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How to effectively extract features with high representation ability has always been a research topic and a challenge for classification tasks. Most of the existing methods mainly solve the problem by using deep convolutional neural networks as feature extractors. Although a series of excellent network structures have been successful in the field of Chinese ink-wash painting classification, but most of them adopted the methods of only simple augmentation of the network structures and direct fusion of different scale features, which limit the network to further extract semantically rich and scale-invariant feature information, thus hindering the improvement of classification performance. In this paper, a novel model based on multi-level attention and multi-scale feature fusion is proposed. The model extracts three types of feature maps from the low-level, middle-level and high-level layers of the pretrained deep neural network firstly. Then, the low-level and middle-level feature maps are processed by the spatial attention module, nevertheless the high-level feature maps are processed by the scale invariance module to increase the scale-invariance properties. Moreover, the conditional random field module is adopted to fuse the optimized three-scale feature maps, and the channel attention module is followed to refine the features. Finally, the multi-level deep supervision strategy is utilized to optimize the model for better performance. To verify the effectiveness of the model, extensive experimental results on the Chinese ink-wash painting dataset created in this work show that the classification performance of the model is better than other mainstream research methods.
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Ximenes, Arimatéa, Leandro Ponsoni, Catarina Lira, Nico Koedam, and Farid Dahdouh-Guebas. "Does Sea Surface Temperature Contribute to Determining Range Limits and Expansion of Mangroves in Eastern South America (Brazil)?" Remote Sensing 10, no. 11 (November 11, 2018): 1787. http://dx.doi.org/10.3390/rs10111787.
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Low Sea Surface Temperature (SST) is a climate barrier because it may inhibit and reduce seedling growth of mangrove propagules upon dispersal through seawater. Our objective is to analyze the spatio-temporal series of daily SST data from the Multi-scale Ultra-high Resolution (MUR)-SST in order to identify the occurrence of chilling events for mangrove plants at the Eastern South America mangrove limit and beyond. We focus our study on three key sites: (i) the Rhizophora mangle L. distribution limit (Praia do Sonho: 27°53′S), (ii) the Eastern South America mangrove limit (Laguna: 28°30′S) and (iii) one beyond mangrove areas, in Araranguá (28°55′S). Our results show that, in Araranguá, chilling events are more intense and occur more frequently than in the other two sites that have a mangrove cover. We conclude that, the chilling events of SST may play a role in restricting mangroves within their actual limits. In this sense, higher occurrences of chilling events of SST could be an explanation for the absence of R. mangle in Laguna. However, Laguncularia racemosa (L.) C.F. Gaertn. was reported to be tolerant to low temperatures, and yet it is absent from the southernmost study site. This may be an indication of the role of other factors than SST in determining a mangrove range expansion, such as dispersal constraints.
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Cai, Zhi, Tao Wang, Qing Mi, Xing Su, Limin Guo, and Zhiming Ding. "Dynamic Weighted Road Network Based Multi-Vehicles Navigation and Evacuation." ISPRS International Journal of Geo-Information 12, no. 3 (March 16, 2023): 127. http://dx.doi.org/10.3390/ijgi12030127.
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Many events such as large-scale activities and traffic accidents could cause an increase in vehicle density in an area, which makes the evacuation of vehicles important. However, the existing evacuation methods are not efficient limit to multi-vehicles sequences or destinations. In this paper, we introduce a novel dynamic weighted road network model for route planning. Based on the model, the route planning algorithm can obtain higher search efficiency while avoiding congested roads. For multi-vehicles evacuation, we propose a spatial diversity theory to evaluate the overlaps of routes between vehicles to be evacuated and those already evacuated. To verify the efficiency and effectiveness of our model, we conducted experiments on real road network. The results showed that our methods and algorithms can provide more reasonable paths and manage the process more efficiently.
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Neronov, A., D. Semikoz, and Ie Vovk. "New limit on high Galactic latitude PeV γ-ray flux from Tibet ASγ data." Astronomy & Astrophysics 653 (September 2021): L4. http://dx.doi.org/10.1051/0004-6361/202141800.
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The Tibet ASγ collaboration has recently reported the detection of γ-rays with energies up to Peta-electronvolt from parts of the Galactic plane. We note that the analysis of γ-ray flux by the Tibet-ASγ experiment also implies an upper bound on the diffuse γ-ray flux from high Galactic latitudes (|b|> 20°) in the energy range between 100 TeV and 1 PeV. This bound is up to an order of magnitude stronger than previously derived bounds from GRAPES3, KASCADE, and CASA-MIA experiments. We discuss the new Tibet-ASγ limit on the high Galactic latitude γ-ray flux in the context of possible mechanisms of multi-messenger (γ-ray and neutrino) emission from nearby cosmic ray sources, dark matter decays, and the large-scale cosmic ray halo of the Milky Way.
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Dieker, A. B., and T. Suk. "Randomized longest-queue-first scheduling for large-scale buffered systems." Advances in Applied Probability 47, no. 4 (December 2015): 1015–38. http://dx.doi.org/10.1239/aap/1449859798.
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We develop diffusion approximations for parallel-queueing systems with the randomized longest-queue-first scheduling (LQF) algorithm by establishing new mean-field limit theorems as the number of buffers n → ∞. We achieve this by allowing the number of sampled buffers d = d(n) to depend on the number of buffers n, which yields an asymptotic 'decoupling' of the queue length processes. We show through simulation experiments that the resulting approximation is accurate even for moderate values of n and d(n). To the best of the authors' knowledge, this is the first derivation of diffusion approximations for a queueing system in the large-buffer mean-field regime. Another noteworthy feature of our scaling idea is that the randomized LQF algorithm emulates the LQF algorithm, yet is computationally more attractive. The analysis of the system performance as a function of d(n) is facilitated by the multi-scale nature in our limit theorems: the various processes we study have different space scalings. This allows us to show the trade-off between performance and complexity of the randomized LQF scheduling algorithm.
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Dieker, A. B., and T. Suk. "Randomized longest-queue-first scheduling for large-scale buffered systems." Advances in Applied Probability 47, no. 04 (December 2015): 1015–38. http://dx.doi.org/10.1017/s0001867800048990.
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We develop diffusion approximations for parallel-queueing systems with the randomized longest-queue-first scheduling (LQF) algorithm by establishing new mean-field limit theorems as the number of buffers n → ∞. We achieve this by allowing the number of sampled buffers d = d(n) to depend on the number of buffers n, which yields an asymptotic 'decoupling' of the queue length processes. We show through simulation experiments that the resulting approximation is accurate even for moderate values of n and d(n). To the best of the authors' knowledge, this is the first derivation of diffusion approximations for a queueing system in the large-buffer mean-field regime. Another noteworthy feature of our scaling idea is that the randomized LQF algorithm emulates the LQF algorithm, yet is computationally more attractive. The analysis of the system performance as a function of d(n) is facilitated by the multi-scale nature in our limit theorems: the various processes we study have different space scalings. This allows us to show the trade-off between performance and complexity of the randomized LQF scheduling algorithm.
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HE, DONGXIAO, JIE LIU, BO YANG, YUXIAO HUANG, DAYOU LIU, and DI JIN. "AN ANT-BASED ALGORITHM WITH LOCAL OPTIMIZATION FOR COMMUNITY DETECTION IN LARGE-SCALE NETWORKS." Advances in Complex Systems 15, no. 08 (November 8, 2012): 1250036. http://dx.doi.org/10.1142/s0219525912500361.
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In this paper, we propose a multi-layer ant-based algorithm (MABA), which detects communities from networks by means of locally optimizing modularity using individual ants. The basic version of MABA, namely SABA, combines a self-avoiding label propagation technique with a simulated annealing strategy for ant diffusion in networks. Once the communities are found by SABA, this method can be reapplied to a higher level network where each obtained community is regarded as a new vertex. The aforementioned process is repeated iteratively, and this corresponds to MABA. Thanks to the intrinsic multi-level nature of our algorithm, it possesses the potential ability to unfold multi-scale hierarchical structures. Furthermore, MABA has the ability that mitigates the resolution limit of modularity. The proposed MABA has been evaluated on both computer-generated benchmarks and widely used real-world networks, and has been compared with a set of competitive algorithms. Experimental results demonstrate that MABA is both effective and efficient (in near linear time with respect to the size of network) for discovering communities.
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Yang, Chao-Tung, Wen-Jen Hu, and Kuan-Chou Lai. "On Construction of a Multi-Grid Resource Selection Strategy on Grids." International Journal of Grid and High Performance Computing 6, no. 1 (January 2014): 38–62. http://dx.doi.org/10.4018/ijghpc.2014010103.
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Grid computing is now in widespread use, integrating geographical computing resources across multiple virtual organizations to achieve high performance computing. A single grid does not often provide a vast resource because virtual organizations have inadequate computing resource restrictions for management on an organizational scale. This paper presents a new grid architecture named Multi-Grid, which integrates multiple computational grids from different virtual organizations. This study builds a resource broker on multiple grid environments, integrating a number of single grids from different virtual organizations without the limit of organizations. The purpose of the multiple-grid resource is to avoid wasting resources. In addition, this study proposes a Multi-Grid Resource Selection Strategy (MRGSS) for the resource broker to better allocate resources before submitting jobs, to avoid network congestion that consequently causes a decrease in performance.
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Liu, Chunyue, Hongxing Jiang, Shuqing Zhang, Chunrong Li, Yunqiu Hou, and Fawen Qian. "Multi-scale analysis to uncover habitat use of red-crowned cranes: Implications for conservation." Current Zoology 59, no. 5 (October 1, 2013): 604–17. http://dx.doi.org/10.1093/czoolo/59.5.604.
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Abstract A multi-scale approach is essential to assess the factors that limit avian habitat use. Numerous studies have examined habitat use by the red-crowned crane, but integrated multi-scale habitat use information is lacking. We evaluated the effects of several habitat variables quantified across many spatial scales on crane use and abundance in two periods (2000 and 2009) at Yancheng National Nature Reserve, China. The natural wetlands decreased in area by 30,601 ha (-6.9%) from 2000 to 2009, predominantly as a result of conversion to aquaculture ponds and farmland, and the remaining was under degradation due to expansion of the exotic smooth cordgrass. The cranes are focusing in on either larger patches or those that are in close proximity to each other in both years, but occupied patches had smaller size, less proximity and more regular boundaries in 2009. At landscape scales, the area percentage of common seepweed, reed ponds and paddy fields had a greater positive impact on crane presence than the area percentage of aquaculture ponds. The cranes were more abundant in patches that had a greater percent area of common seepweed and reed ponds, while the percent area of paddy fields was inversely related to crane abundance in 2009 due to changing agricultural practices. In 2009, cranes tended to use less fragmented plots in natural wetlands and more fragmented plots in anthropogenic paddy fields, which were largely associated with the huge loss and degradation of natural habitats between the two years. Management should focus on restoration of large patches of natural wetlands, and formation of a relatively stable area of large paddy field and reed pond to mitigate the loss of natural wetlands.
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Yang, F., D. La Civita, M. Vannoni, and H. Sinn. "Damage simulation due to heat load from X-ray FEL beam at European XFEL." Journal of Physics: Conference Series 2380, no. 1 (December 1, 2022): 012067. http://dx.doi.org/10.1088/1742-6596/2380/1/012067.
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Abstract In the X-ray FEL beam transport system, the optic components which have direct contact with the beam, e.g. mirror, absorber and beam shutter, etc., could exceed 10 kW peak heat load on a sub-mm spot. Therefore, the thermo-mechanical performance of these components under the extreme high heat load will limit the maximum allowed pulses for the safety operation of the facility. In this contribution, a selection of multi-scale and multi-physics numerical models using finite element tools is introduced to describe the interaction of X-ray laser beam with different materials, taking into consideration of the multi-coupling of heat transfer, solid mechanics, fluid dynamics and phase transitions. The verified and validated models can be referred to define damage threshold of the optic components, and to virtually reproduce the damage mechanism of the materials.
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Butler, CL, VL Lucieer, SJ Wotherspoon, and CR Johnson. "Multi-decadal decline in cover of giant kelp Macrocystis pyrifera at the southern limit of its Australian range." Marine Ecology Progress Series 653 (October 29, 2020): 1–18. http://dx.doi.org/10.3354/meps13510.
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Knowledge of long-term and multi-scale trends in ecological systems is a vital component in understanding their dynamics. We used Landsat satellite imagery to develop the first long-term (1986-2015) data set describing the cover of dense surface canopies of giant kelp Macrocystis pyrifera around the entire coastline of Tasmania, Australia, and assessed the extent to which potential environmental drivers explain the dynamics of surface canopies at multiple spatial and temporal scales. Broad-scale temporal patterns in canopy cover are correlated with El Niño-Southern Oscillation events, while regional patterns are related to sea surface temperature and nutrient regimes are associated with the East Australian Current. Regression models developed to predict the presence or absence of giant kelp canopy emphasise the importance of sea surface temperature in these systems. Long-term decline in canopy cover is clearly evident in most regions, and in light of increasing thermal stress associated with a changing ocean climate, this raises concern for the future of this species as a major habitat-forming kelp in Australia and some other regions worldwide. Given that Tasmania represents the stronghold of the range of this species in Australia, but is a geographic trap in that there is no suitable habitat for M. pyrifera to the south, our findings support the Federal listing of giant kelp communities in Australia as an endangered marine community type.
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Blank, Lior, and Leon Blaustein. "A multi-scale analysis of breeding site characteristics of the endangered fire salamander (Salamandra infraimmaculata) at its extreme southern range limit." Hydrobiologia 726, no. 1 (December 7, 2013): 229–44. http://dx.doi.org/10.1007/s10750-013-1770-8.
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Angioni, R., E. Ros, M. Kadler, R. Ojha, C. Müller, P. G. Edwards, P. R. Burd, et al. "Gamma-ray emission in radio galaxies under the VLBI scope." Astronomy & Astrophysics 627 (July 2019): A148. http://dx.doi.org/10.1051/0004-6361/201935697.
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Aims. In the framework of the multi-wavelength and very long baseline interferometry (VLBI) monitoring program TANAMI (Tracking Active Nuclei with Austral Milliarcsecond Interferometry), we study the evolution of the parsec-scale radio emission in radio galaxies in the southern hemisphere and their relationship to the γ-ray properties of the sources. Our study investigates systematically, for the first time, the relationship between the two energy regimes in radio galaxies. In this first paper, we focus on Fermi-LAT-detected sources. Methods. The TANAMI program monitors a large sample of radio-loud AGN at 8.4 GHz and 22.3 GHz with the Australian long baseline array (LBA) and associated telescopes in Antarctica, Chile, New Zealand and South Africa. We performed a kinematic analysis for five γ-ray detected radio galaxies using multi-epoch 8.4 GHz VLBI images, deriving limits on intrinsic jet parameters such as speed and viewing angle. We analyzed 103 months of Fermi-LAT data in order to study possible connections between the γ-ray properties and the pc-scale jets of Fermi-LAT-detected radio galaxies, both in terms of variability and average properties. We discuss the individual source results and draw preliminary conclusions on sample properties including published VLBI results from the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) survey, with a total of fifteen sources. Results. We find that the first γ-ray detection of Pictor A might be associated with the passage of a new VLBI component through the radio core, which appears to be a defining feature of high-energy emitting Fanaroff-Riley type II radio galaxies. We detect subluminal parsec-scale jet motions in the peculiar AGN PKS 0521−36, and we confirm the presence of fast γ-ray variability in the source down to timescales of six hours, which is not accompanied by variations in the VLBI jet. We robustly confirm the presence of significant superluminal motion, up to βapp ∼ 3, in the jet of the TeV radio galaxy PKS 0625−35. Our VLBI results constrain the jet viewing angle to be θ < 53°, allowing for the possibility of a closely aligned jet. Finally, by analyzing the first pc-scale multi-epoch images of the prototypical compact symmetric object (CSO) PKS 1718−649, we place an upper limit on the separation speed between the two mini-lobes. This in turn allows us to derive a lower limit on the age of the source. Conclusions. We can draw some preliminary conclusions on the relationship between pc-scale jets and γ-ray emission in radio galaxies, based on Fermi-LAT-detected sources with available multi-epoch VLBI measurements. We find that the VLBI core flux density correlates with the γ-ray flux, as seen in blazars. On the other hand, the γ-ray luminosity does not show any dependence on the core brightness temperature and core dominance, which are two common indicators of jet Doppler boosting. This seems to indicate that γ-ray emission in radio galaxies is not driven by orientation-dependent effects, as in blazars, in accordance with the unified model of jetted AGN.