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[1] Convective sedimentation in a stably stratified saltwater is studied using the linear stability analysis. Convective sedimentation is known to occur due to the double-diffusive mechanism and the settling-driven mechanism. In t...
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[1] Convective sedimentation in a stably stratified saltwater is studied using the linear stability analysis. Convective sedimentation is known to occur due to the double-diffusive mechanism and the settling-driven mechanism. In this study, a semi-empirical closure of sediment diffusivity based on the long-range hydrodynamics effect is adopted. The sediment phase can act as either the slow-or fast-diffusing agent in the double-diffusive system for the given salt diffusivity. Moreover, the settling-driven effect is proportional to the square of the sediment diameter via Stoke settling law. We consider sediment concentration (grain size) in the upper freshwater layer to be in the range of 0.1 to 39.4 g/l (2 to 60 um), which is on top of a saltwater layer with salinity 35 ppt. Linear stability analysis allows us to identify the dominant mechanism that triggers the instability, the growth rate, and the resulting characteristic finger width. Model results suggest that for fine sediment with grain diameter smaller than 10 μm (settling velocity 0.09 mm/s), double-diffusive mechanism controls the instability and the resulting sediment finger size is of millimeter scale. For the given threshold of growth rate of O(0.01) s-1, the minimum sediment concentration is about 8-15 g/l. For grain size greater than or around 10 μm, the settling-driven mechanism dominates and instabilities occur at sediment concentration as low as O(0.1)g/l with centimeter-scale fingers. Our findings may contribute to a better understanding on the observed rapid sediment removal in the plume of small mountainous rivers.
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摘要 :
[1] Convective sedimentation in a stably stratified saltwater is studied using the linear stability analysis. Convective sedimentation is known to occur due to the double-diffusive mechanism and the settling-driven mechanism. In t...
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[1] Convective sedimentation in a stably stratified saltwater is studied using the linear stability analysis. Convective sedimentation is known to occur due to the double-diffusive mechanism and the settling-driven mechanism. In this study, a semi-empirical closure of sediment diffusivity based on the long-range hydrodynamics effect is adopted. The sediment phase can act as either the slow-or fast-diffusing agent in the double-diffusive system for the given salt diffusivity. Moreover, the settling-driven effect is proportional to the square of the sediment diameter via Stoke settling law. We consider sediment concentration (grain size) in the upper freshwater layer to be in the range of 0.1 to 39.4 g/l (2 to 60 um), which is on top of a saltwater layer with salinity 35 ppt. Linear stability analysis allows us to identify the dominant mechanism that triggers the instability, the growth rate, and the resulting characteristic finger width. Model results suggest that for fine sediment with grain diameter smaller than 10 μm (settling velocity 0.09 mm/s), double-diffusive mechanism controls the instability and the resulting sediment finger size is of millimeter scale. For the given threshold of growth rate of O(0.01) s-1, the minimum sediment concentration is about 8-15 g/l. For grain size greater than or around 10 μm, the settling-driven mechanism dominates and instabilities occur at sediment concentration as low as O(0.1)g/l with centimeter-scale fingers. Our findings may contribute to a better understanding on the observed rapid sediment removal in the plume of small mountainous rivers.
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We introduce a methodology for obtaining inventories of error results for families of numerical dense linear algebra algorithms. The approach for deriving the analyses is goal-oriented, systematic, and layered. The presentation pl...
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We introduce a methodology for obtaining inventories of error results for families of numerical dense linear algebra algorithms. The approach for deriving the analyses is goal-oriented, systematic, and layered. The presentation places the analysis side-by-side with the algorithm so that it is obvious where roundoff error is introduced. The approach supports the analysis of more complex algorithms, such as the blocked LU factorization. For this operation we derive a tighter error bound than has been previously reported in the literature.
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Developing predictive mathematical models for regulatory networks in biological systems would be useful for their analysis and design. This paper studies the parameter-dependent characteristics of a gene switching model that consi...
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Developing predictive mathematical models for regulatory networks in biological systems would be useful for their analysis and design. This paper studies the parameter-dependent characteristics of a gene switching model that consists of dual positive feedback loops. Deterministic and stochastic stability are studied for this model, as well as other important system behaviors such as convergence rate to a stable equilibrium point, hysteresis induced by two time scales of the system model, and noise sensitivity with respect to the system parameters. Sensitivity of system performance indices with respect to the system parameters are analyzed in terms of H_∞- and H_2-norms of the linearized system model with their closed-form solutions. The presented qualitative and quantitative studies of the system characteristics enable the synthesis of a robust gene regulatory network that achieves desired static and dynamic responses.
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Moving toward more-electric aircraft (MEA) architecture, future aircraft power system will consist of a large number of power converters and motor drive loads which behave as constant power load and may cause stability issues. It ...
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Moving toward more-electric aircraft (MEA) architecture, future aircraft power system will consist of a large number of power converters and motor drive loads which behave as constant power load and may cause stability issues. It is essential to ensure stable operation of the MEA power system, even though the complexity of the system hinders the comprehensive analysis of system stability. This paper presents a framework for stability analysis of a complex MEA power system. A module-based approach is proposed to provide a general and flexible solution for modeling and integrating complex systems, even under situations of system extension and reconfiguration. Using the proposed technique, a complex system model is conveniently formulated and overall system stability can be evaluated. Then, the critical stability points can be investigated. Impacts of parameters and their damping effects are identified by eigenvalue analysis and sensitivity analysis. The hybrid ac/dc MEA power system adopted by Boeing 787 is analyzed using the proposed technique. Simulations in MATLAB/Simulink are conducted to validate the effectiveness of the proposed modeling technique and the analytical results.
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The conventional switching strategy for solving the inverted pendulum control problem is based on two steps: swinging-up and stabilization. In this note, first, a new strategy for swinging the Furuta pendulum up towards the desire...
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The conventional switching strategy for solving the inverted pendulum control problem is based on two steps: swinging-up and stabilization. In this note, first, a new strategy for swinging the Furuta pendulum up towards the desired upright position is designed using the Speed-Gradient method, which uses only directly measured coordinates. Then, a nonlinear controller, based on the Forwarding approach, stabilizes the upright position. As a new contribution the latter leads to a nonlinear stabilizer around the upright position, whose Lyapunov function yields a larger size estimation of the domain of attraction than the one obtained with the traditional linear approach. This estimation allows us to use it in a global switching strategy in the practical implementation and guarantees almost-global asymptotic stability of the equilibrium. Successful experimental results are reported with the available laboratory Furuta pendulum.
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Blind source separation (BSS) consists of recovering signals from different physical sources from several observed combinations independently of the propagation medium. BSS is also a promising tool for non-destructive machine cond...
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Blind source separation (BSS) consists of recovering signals from different physical sources from several observed combinations independently of the propagation medium. BSS is also a promising tool for non-destructive machine condition monitoring by vibration analysis, as it is intended to retrieve the signature of a single rotating machine from combinations of several working machines. In this way, BSS can be seen as a pre-processing step that improves the diagnosis.BSS methods generally assume observations that are either noise-free or corrupted with spatially distinct white noises. In the latter case, principal component analysis (PCA) is applied as a first step to filter out the noise and whiten the observations. Obviously, the efficiency of the whole separation procedure depends on the accuracy of the first step (PCA).However, in the real world, signals of rotating machine vibration may be severely corrupted with spatially correlated noises and therefore the signal subspace will not be correctly estimated with PCA. The purpose of this paper is to propose a 'robust-to-noise' technique for the separation of rotating machine signals. The Sources are assumed here to be periodic and so can be modelled as the sum of sinusoids of harmonic frequencies. A new estimator of the signal subspace and the whitening matrix is introduced which exploits the model of sinusoidal sources and uses spectral matrices of delayed observations to eliminate the influence of the noise. After whitening, the second step of source separation remains unchanged. Finally, performance of the algorithm is investigated with artificial data and experimental rotating machine vibration data. (C) 2003 Elsevier Ltd. All rights reserved.
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In the above-titled paper by Lu and Kumar (ibid., vol.36. no.12, pp.1406-1416, Dec 91), the issue of stability of a scheduling policy for a system with reentrant structure is studied. It has been shown that whenever the arrival ra...
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In the above-titled paper by Lu and Kumar (ibid., vol.36. no.12, pp.1406-1416, Dec 91), the issue of stability of a scheduling policy for a system with reentrant structure is studied. It has been shown that whenever the arrival rate, allowing for some burstiness, is less than the system capacity, the following four scheduling policies are stable: first buffer first serve, last buffer first serve, earliest due date, and least slack policies. To verify that the problem is not trivial, a counterexample of instability, yet satisfying the usual stability condition, is provided. However, the counter-example calls for zero processing times. It is shown that counter-examples with nonzero processing times do exist, and understanding of the stability issue of general discrete-event dynamic systems is promoted.
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Man-made factors take an important place in the formation of landslides besides the natural events. Road constructions, establishing new residential areas and interfering natural drainage systems are some of the common reasons tha...
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Man-made factors take an important place in the formation of landslides besides the natural events. Road constructions, establishing new residential areas and interfering natural drainage systems are some of the common reasons that cause landslides. A slope on an intercity road construction site in the western Black Sea region, Turkey, is selected for this study due to the presence of small-scale soil movements, rock falls, tension cracks and occurrence of landslides in the neighborhood. The study area is investigated at three different profiles based on the topography. Slope stability analyses are carried out on these profiles by three-dimensional finite element analyses. As the results of analysis critic levels of the factor of safety and the high soil movements are estimated for one of the profiles. There are a couple of methods developed to prevent potential landslides, ceasing soil movements and securing the construction zones. Stabilizing slopes with piles are widely being used to enhance slope stability of landslide-prone areas. In this study, the behavior of stabilizing piles with and without lateral support is investigated. The bending moments and shear forces of piles and the maximum soil displacements are estimated to evaluate the performance of pile-stabilized slopes. Slope angle reduction is being performed as a remediation option, and an optimal solution is proposed after comparing the result of the analyses.
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The robust H infinity dynamic output feedback (DOF) control for a class of nonlinear time-varying delay rectangular descriptor Markov jump systems (DMJSs) is discussed in this paper, there are no restrictions on the rows and colum...
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The robust H infinity dynamic output feedback (DOF) control for a class of nonlinear time-varying delay rectangular descriptor Markov jump systems (DMJSs) is discussed in this paper, there are no restrictions on the rows and columns of the differential matrix E. The rectangular DOF controller is designed to make the closed-loop system as square DMJSs. Firstly, by utilizing a mode-dependent and delaydependent Lyapunov-Krasovskii (L-K) functional and implicit function theorem, sufficient conditions are given to guarantee that the augmented closed-loop systems are robust stochastically admissible with an H infinity performance and have unique solution simultaneously. Then based on certain matrix decoupling techniques, a new strict linear matrix inequality (LMI) sufficient condition for the existence of a rectangular DOF controller is obtained, and the controller is given. Finally, numerical examples are presented to verify the validity of the results. (c) 2023 The Franklin Institute. Published by Elsevier Inc. All rights reserved.
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