Water Alternating Gas (WAG) is a consolidated enhanced oil recovery method that outperforms secondary recovery methods such as waterflooding or gas injection. Optimization of the WAG parameters can increase the cost f...
详细信息
Domain walls, topological defects that define the frontier between regions of different stacking order in multilayer graphene, have proved to host exciting physics. The ability to tune these topological defects in sit...
详细信息
Domain walls, topological defects that define the frontier between regions of different stacking order in multilayer graphene, have proved to host exciting physics. The ability to tune these topological defects in situ in an electronic transport experiment brings a wealth of possibilities in terms of fundamental understanding of domain walls as well as for electronic applications. Here, we demonstrate, through a MEMS (microelectromechanical system) actuator and magnetoresistance measurements, the effect of domain walls in multilayer graphene quantum Hall effect. Reversible and controlled uniaxial strain triggers the topological defects, manifested as addtional quantum Hall effect plateaus as well as a discrete and reversible modulation of the current across the device. Our findings are supported by theoretical calculations and constitute indication of the in situ tuning of topological defects in multilayer graphene probed through electronic transport, opening the way for the use of reversible topological defects in electronic applications.
This paper presents the design and analysis of a 2-DOF monolithic parallel mechanism for micro- and nano-manipulations. Two sets of statically indeterminate leaf parallelograms are employed to provide the decoupling e...
详细信息
ISBN:
(纸本)9781467353199
This paper presents the design and analysis of a 2-DOF monolithic parallel mechanism for micro- and nano-manipulations. Two sets of statically indeterminate leaf parallelograms are employed to provide the decoupling effect, and the displacement of the piezoelectric actuator (PEA) is amplified with a statically indeterminate lever mechanism. Due to the static indeterminacy, the load-deflection relationship of the mechanism is nonlinear. Computational analysis is utilized to investigate the nonlinearity. Computational results reveal that the structural nonlinearities of the mechanism is negligible within the maximum driving force of the PEA. The influence of the contact interface and the load mass is also investigated through computational analyses. Ultimately, a prototype is fabricated and a laser interferometer measurement system is established to obtain the position and velocity of the prototype. A number of experiments are performed to investigate the performance of the prototype. Experimental results show that the developed prototype has achieved a workspace of 82×82 μm 2 , a first natural frequency of 423 Hz (with a 53.4 g load mass), and a cross-axis coupling ratio below 1%.
The effects of varying interfacial conditions between two contacting hollow cylinders on the propagation of helical Lamb waves are studied. Experiments were carried out on two aluminum hollow cylinders (114 mm in oute...
The effects of varying interfacial conditions between two contacting hollow cylinders on the propagation of helical Lamb waves are studied. Experiments were carried out on two aluminum hollow cylinders (114 mm in outer-diameter and 6 mm of wall thickness) axially loaded by a horizontal press to control contact interfacial stiffness. An ultrasonic measurement setup using broadband transducers, with semispherical contact probes coupled to the cylinders surface, in a pitchcatch configuration is presented. Time-frequency representation (TFR) is employed to accurately perform mode identification of ultrasonic captured signals. The effect of different interfacial contact conditions in mechanically joined cylinders into propagation parameters of helical Lamb waves is studied. Finally, a comparison of sensitivity, between Lamb waves in straight and helical propagating paths, under different interfacial conditions is presented.
The present study was undertaken to investigate the effect of metallurgical parameters on the hardness and microstructural characterisations of as-cast and heat-treated 356 and 319 alloys, with the aim of adjusting th...
详细信息
The present study was undertaken to investigate the effect of metallurgical parameters on the hardness and microstructural characterisations of as-cast and heat-treated 356 and 319 alloys, with the aim of adjusting these parameters to produce castings of suitable hardness and Feintermetallic volume fractions for subsequent use in studies relating to the machinability of these alloys. Hardness measurements were carried out on specimens prepared from 356 and 319 alloys in the as-cast and heat-treated conditions, using different combinations of grain refining, Srmodification, and alloying additions. Aging treatments were carried out at 155?C, 180?C, 200?C, and 220?C for 4 h, followed by air cooling, as well as at 180?C and 220?C for 2, 4, 6, and 8 h. Peak hardness was observed in 356 alloys when aging was carried out at 180oC/4h. In the case of unmodified or modified 356 alloys containing mostly α-Fe intermetallics, aging at 180?C up to 8h produced a sharp rise in hardness during the first two hours of aging, followed by a broad peak or plateau over the 2-8 h aging period. Aging at 220?C revealed a hardness peak at 2h aging time for both 356 and 319 alloys.
A collision-free coordinated control scheme is discussed for multi-operator-multi-robot (MOMR) teleoperation through a network with communication time delay. Collaboration tasks have rapidly emerged in many possible a...
详细信息
ISBN:
(纸本)0780358414
A collision-free coordinated control scheme is discussed for multi-operator-multi-robot (MOMR) teleoperation through a network with communication time delay. Collaboration tasks have rapidly emerged in many possible applications such as the plant maintenance, construction, and surgery, because multi-robot collaboration would have a significant advantage over a single robot in such cases. However, the effect of time-delay would pose a more difficult problem to MOMR teleoperation systems and seriously affect their performance. In this work, the virtual impedance based coordinated control method is proposed to cope with collision arising from the communication delay in the MOMR teleoperation system. We impose a variable impedance on the master hand and change the impedance according to the distance between two slave arms in the local predictor simulator. When a possible collision is expected during the task, a high impedance is set to master hand and signals the operator to stop or to change her master command. This adjustable impedance of the master hand safely guides an operator through unexpected collisions in time-delayed MOMR teleoperation. To verify the validity of the proposed scheme, an experimental setup is built and a block arrangement task is performed by two slave arms based on simulation models.
The modeling of joints on human limbs involves complexities due to the presence of articular cartilage at the synovial joint interface between mating bones, and the geometries involved. In this work, a simple yet inno...
详细信息
The modeling of joints on human limbs involves complexities due to the presence of articular cartilage at the synovial joint interface between mating bones, and the geometries involved. In this work, a simple yet innovative model for such a joint which can still capture most of the behavior of the bone joint system is presented. The model is applied to a ball and socket joint system with soft cartilage. The functional role of the soft cartilage material is replaced by a nonlinear stiffness field, whose properties are defined with relation to the ball position with respect to any fixed reference point within the socket. Bond graph modeling and simulation are used to study the system dynamics. Simulations indicate that this simple but significant model holds promise for applications in simulation, control of biomechanical, robotic and virtual reality based devices
This paper presents a numerical analysis for kinematics of robot fish. The fish model in this paper is assumed to act as carangiform motion. The carangiform motion can be modeled as several serial links, and generally...
详细信息
This paper presents a numerical analysis for kinematics of robot fish. The fish model in this paper is assumed to act as carangiform motion. The carangiform motion can be modeled as several serial links, and generally robot fish is composed of motors and links. In this research, some analysis has been performed for calculation of kinematics of robot fish. To do this, a geometrical numerical method has been used and a code is made for N-link robot fish kinematics.
One major obstacle hindering the advancement of modeling and simulation capabilities of two-phase flows is the lack of high-quality, high-resolution experimental data for model development and model/code validation. T...
详细信息
暂无评论