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In this paper, we find formulas of general solution for a kind of impulsive differential equations with Hadamard fractional derivative of order \(q \in(1, 2)\) by analysis of the limit case (as the impulse tends to zero) and provi...
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In this paper, we find formulas of general solution for a kind of impulsive differential equations with Hadamard fractional derivative of order \(q \in(1, 2)\) by analysis of the limit case (as the impulse tends to zero) and provide an example to illustrate the importance of our results.
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Coalbed methane (CBM), once a hazard to the undermining safety, is becoming an important addition to the global energy Supply. Injecting carbon dioxide (CO_2) into coal seams not only aids to enhance CBM production but also offers...
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Coalbed methane (CBM), once a hazard to the undermining safety, is becoming an important addition to the global energy Supply. Injecting carbon dioxide (CO_2) into coal seams not only aids to enhance CBM production but also offers an option of CO_2 sequestration helpful for the reduction of greenhouse gas release. Multiphase flow occurs in those cases as most coalbeds are initially saturated with water. Accurate determination of relative permeability of coal plays an important role in the prediction and evaluation of those operations because it is in effect the effective permeability (absolute permeability multiplied by relative permeability) to gas/water rather than absolute permeability that controls the flow in coal seams. To date, varying methods have been reported of obtaining relative permeability curves of coals through either laboratory tests or field data analysis, which are reviewed in this paper. Also, this paper includes a summary of the characteristics of relative permeability curves of coals, relative permeability models, effects of varying factors on curves and effects of the curves on CBM production. This paper concludes that despite the importance of relative permeability in CBM-related operation process, limited research efforts have been paid on improvements concerning this subject in the past two decades: the advance in the research of relative permeability-related subjects can barely keep up with the rate at which the developments of CBM and CO_2-ECBM projects are booming worldwide. More efforts are needed to conduct related investigations such that a reliable standard or workflow can be established that can as accurately determine coal relative permeability with repeatability.
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Single-molecule magnets (SMMs) have attracted much attention due to their potential applications in molecular spintronic devices. Rare earth SMMs are considered to be the most promising for application owing to their large magneti...
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Single-molecule magnets (SMMs) have attracted much attention due to their potential applications in molecular spintronic devices. Rare earth SMMs are considered to be the most promising for application owing to their large magnetic moment and strong magnetic anisotropy. In this review, the recent progress in rare earth SMMs represented by mononuclear and dinuclear complexes is highlighted, especially for the modulation of magnetic anisotropy, effective energy barrier (Ueff) and blocking temperature (TB). The terbium- and dysprosium-based SMMs have a Ueff of 1541 cm?1 and an increased TB of 80 K. They break the boiling point temperature of liquid nitrogen. The development of the preparation technology of rare earth element SMMs is also summarized in an overview. This review has important implications and insights for the design and research of Ln-SMMs.
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Microengineering/nanoengineering is an emerging field that enables engineering and scientific discoveries in the microworld. As an effective and powerful tool for automation and manipulation at small scales, precision motion measu...
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Microengineering/nanoengineering is an emerging field that enables engineering and scientific discoveries in the microworld. As an effective and powerful tool for automation and manipulation at small scales, precision motion measurement by computer microvision is now broadly accepted and widely used in microengineering/nanoengineering. Unlike other measurement methods, the vision-based techniques can intuitively visualize the measuring process with high interactivity, expansibility, and flexibility. This article aims to comprehensively present a survey of microvision-based motion measurement from the collective experience. Working principles of microvision systems are first introduced and described, where the hardware configuration, model calibration, and motion measurement algorithms are systematically summarized. The characteristics and performances of different microvision-based methods are then analyzed and discussed in terms of measurement resolution, range, degree of freedom, efficiency, and error sources. Recent advances of applications empowered by the developed computer microvision-based methods are also presented. The review can be helpful to researchers who engage in the development of microvision-based techniques and provide the recent state and tendency for the research community of vision-based measurement, manipulation, and automation at microscale/nanoscale.
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A new level set-based multi-objective optimization method is proposed for topological design of hinge-free compliant mechanisms. Firstly, the flexibility requirement of compliant mechanisms is formulated by using the mutual energy...
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A new level set-based multi-objective optimization method is proposed for topological design of hinge-free compliant mechanisms. Firstly, the flexibility requirement of compliant mechanisms is formulated by using the mutual energy. Two types of mean compliance are developed to meet the stiffness requirement. Secondly, several objective functions are developed for designing hinge-free compliant mechanisms based on the weighting method in which a new scheme for determining weighting factors is used. Thirdly, several numerical examples are performed to demonstrate the validity of the proposed method. It is shown that the resulting compliant mechanism configurations contain only strip-like members which are suitable for generating distributed compliance and decreasing stress concentration.
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In this paper, for packet transmission over flat fading channel in single-input-single-output system, we consider the power control problem in a cross-layer design where adaptive modulation is adopted at physical layer to improve ...
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In this paper, for packet transmission over flat fading channel in single-input-single-output system, we consider the power control problem in a cross-layer design where adaptive modulation is adopted at physical layer to improve spectral efficiency and the queues are modeled as of finite length at data link layer. The goal is to identify the optimal queuing-aware power allocation algorithm to minimize the overall system packet error rate under the constraint of long-term transmit power. One crucial step which we call `inner’ problem is to find the optimal power vector at a given target packet error rate at physical layer. Rather than attack the multi-dimensional optimization problem directly using conventional methods, we first observe that the `inner’ problem is closely related to an average reward Markov decision process problem, and relax the former to the latter so as to take advantage of its equivalence with linear program which allows efficient solution. Since randomness in the associated Markov decision process is only slight, at most mild, we propose an approximately deterministic policy as suboptimal solution to the `inner’ problem with insignificant performance degradation. We also propose two-parameter power allocation functions to achieve suboptimal results with low complexity. The impacts of system parameters on the overall system performance are also evaluated. The accuracy of the numerical result is verified by Monte Carlo simulations.
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In this paper, for packet transmission over flat fading channel in single-input-single-output system, we consider the power control problem in a cross-layer design where adaptive modulation is adopted at physical layer to improve ...
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In this paper, for packet transmission over flat fading channel in single-input-single-output system, we consider the power control problem in a cross-layer design where adaptive modulation is adopted at physical layer to improve spectral efficiency and the queues are modeled as of finite length at data link layer. The goal is to identify the optimal queuing-aware power allocation algorithm to minimize the overall system packet error rate under the constraint of long-term transmit power. One crucial step which we call 'inner' problem is to find the optimal power vector at a given target packet error rate at physical layer. Rather than attack the multi-dimensional optimization problem directly using conventional methods, we first observe that the 'inner' problem is closely related to an average reward Markov decision process problem, and relax the former to the latter so as to take advantage of its equivalence with linear program which allows efficient solution. Since randomness in the associated Markov decision process is only slight, at most mild, we propose an approximately deterministic policy as suboptimal solution to the 'inner' problem with insignificant performance degradation. We also propose two-parameter power allocation functions to achieve suboptimal results with low complexity. The impacts of system parameters on the overall system performance are also evaluated. The accuracy of the numerical result is verified by Monte Carlo simulations.
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Compliant constant-force mechanisms are compliant mechanisms that provide a nearly constant force over a prescribed deflection range. Topology optimization is an effective method for compliant constant-force mechanism design. Howe...
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Compliant constant-force mechanisms are compliant mechanisms that provide a nearly constant force over a prescribed deflection range. Topology optimization is an effective method for compliant constant-force mechanism design. However, instabilities caused by buckling often cause the optimization algorithm to fail to converge. This study analyzes the causes of buckling-induced instability and proposes methods to avoid this instability. A mechanism with three torsional springs is proposed, and its three force-displacement curves are analyzed. These bifurcated force-displacement curves cause the optimization algorithm to be unstable. Several topology optimization models with buckling constraints are proposed for designing compliant constant-force mechanisms. Their effects are tested and analyzed in numerical examples with different target constant forces and constant-force strokes. Almost all optimization results have three hinges, corresponding to a proposed mechanism with three torsion springs. A slight change in their initial design causes a large change in the force-displacement curve, which eventually leads to buckling-induced instability. This instability can be avoided by constraining the buckling load calculated at the configuration near the start of the constant-force stroke.
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Compliant mechanisms with intermediate-deformation ranges are increasingly applied in large-stroke precision manipulators and other actuators. The nonlinearities of axially-loaded stiffening and kinematics-arching effects (P-Δ ef...
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Compliant mechanisms with intermediate-deformation ranges are increasingly applied in large-stroke precision manipulators and other actuators. The nonlinearities of axially-loaded stiffening and kinematics-arching effects (P-Δ effects) have a pronounced influence on the kineto-static and dynamic behaviors of such a class of compliant mechanisms. A dynamic beam constraint model (DBCM) with the pseudo-static characteristic is reported for the nonlinear kinetostatics and large-amplitude vibration analyses of intermediate-deformation compliant mechanisms. Firstly, the DBCM of flexure beams is derived in a closed-form equation on the frequency domain, including the P-Δ effects. A matrix-based modeling methodology with a step-by- step iteration procedure is then introduced to calculate the nonlinear performance of general planar compliant mechanisms with serial-parallel configurations avoiding inner force analysis and kinematics calculation. Except for the static constraint behaviors in the BCM, the amplitude-dependent resonance frequency is captured with the DBCM. Theoretical, numerical and experimental comparisons for a double parallel guiding flexure pivot and Scott-Russell compliant amplifying mechanism verify the feasibility of the DBCM. In summary, the DBCM enables both the nonlinear kinetostatics and large-amplitude vibration analyses of moderately large-stroke compliant mechanisms in a straightforward way.
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In this paper, we propose a novel numerical approach and algorithm to compute and visualize the workspace of a multifingered hand manipulating an object. Based on feasibility analysis of grasps, the proposed approach uses an optim...
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In this paper, we propose a novel numerical approach and algorithm to compute and visualize the workspace of a multifingered hand manipulating an object. Based on feasibility analysis of grasps, the proposed approach uses an optimization technique to first compute discretely the position boundary of the grasped object and then calculate the rotation ranges of the object at specified positions within the boundary. In other words, workspace generation with the approach is fulfilled by obtaining reachable boundaries of the grasped object in the sense of both position and orientation, and the discrete boundary points are computed by a series of optimization models. Unlike in workspace generation of other robotic systems where only geometric and kinematic parameters of the robots are considered, all factors including geometric, kinematic and force-related factors that affect the workspace of a hand-object system can be taken into account in our approach to generate the workspace of multifingered manipulation. Since various constraints can be integrated into the optimization models, our method is general and complete, with adaptability to various grasps and manipulations. Workspace generation with the approach in both planar and spatial cases are illustrated with examples. The approach provides an effective and general solution to the long-term open and challenging problem of workspace generation of multifingered manipulation. Part of the work has been published in the Proceedings of IEEE/RSJ IROS2008 and IEEE/ASME AIM2008.
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