Asymmetric Control Research Articles

All-dielectric metamirror for independent and asymmetric wave-front control

We report on the design and the numerical and experimental characterization of an all-dielectric reflecting focusing metasurface (metamirror) which does not have a back reflector, but effectively reflects incident waves with the desired reflection phase gradient. The profile of the reflection phase can be tuned independently for both sides of the single-layer subwavelength-thick metamirror by properly selecting dimensions of its dielectric inclusions. Such a feature stems from the bianisotropic omega properties of the inclusions. To demonstrate independent control of the reflection phase, we have designed a metamirror focusing normally incident plane waves at different focal distances being illuminated from the opposite sides. The proposed two-sided metamirror can find applications in antennas, diffraction gratings, and complex holograms. The absence of conducting elements makes it a perfect candidate for optical applications requiring asymmetric wave-front control.

Asymmetrical nonlinear impedance control for dual robotic machining of thin-walled workpieces

• An asymmetrical nonlinear impedance control (ANIC) is designed for a dual robotic machining system. • A comparison study between asymmetrical nonlinear impedance control and symmetrical linear impedance control is proposed. • The robots under the ANIC act as variable stiffness actuators to adapt the variation in thickness of workpieces. Impedance control is to provide stable tracking by regulating the impedance response of a robot. In this paper, an asymmetrical nonlinear impedance control (ANIC) is proposed for a dual robotic machining system. The symmetrical linear impedance control (SLIC) is also analyzed as a comparison study. We compared two controllers in terms of the stability and the sensitivity property of the grinding force, as well as the trajectory design. The main advantage of the ANIC is that the grinding force is robust to the environmental disturbances and the variation in thickness of workpieces. In contrast to the traditional control concept, which is devoted to compensate the nonlinear effect of the original system, our design philosophy is to increase the system robustness by introducing an artificial nonlinearity to the system. As a result, the dual robotic system acts as variable stiffness actors to adapt the variation in the thickness of workpieces. Grinding experiments are conducted in the dual robotic machining test rig for both workpieces with the uniform and varied thickness. The experimental results show that the dual robotic system with the ANIC can achieve better grinding quality.

A Dual-Split 6T SRAM-Based Computing-in-Memory Unit-Macro With Fully Parallel Product-Sum Operation for Binarized DNN Edge Processors

Computing-in-memory (CIM) is a promising approach to reduce the latency and improve the energy efficiency of deep neural network (DNN) artificial intelligence (AI) edge processors. However, SRAM-based CIM (SRAM-CIM) faces practical challenges in terms of area overhead, performance, energy efficiency, and yield against variations in data patterns and transistor performance. This paper employed a circuit-system co-design methodology to develop a SRAM-CIM unit-macro for a binary-based fully connected neural network (FCNN) layer of the DNN AI edge processors. The proposed SRAM-CIM unit-macro supports two binarized neural network models: an XNOR neural network (XNORNN) and a modified binary neural network (MBNN). To achieve compact area, fast access time, robust operations, and high energy-efficiency, our proposed SRAM-CIM uses a split-wordline compact-rule 6T SRAM and circuit techniques, including a dynamic input-aware reference generation (DIARG) scheme, an algorithm-dependent asymmetric control (ADAC) scheme, a write disturb-free (WDF) scheme, and a common-mode-insensitive small offset voltage-mode sensing amplifier (CMI-VSA). A fabricated 65-nm 4-Kb SRAM-CIM unit-macro achieved 2.4- and 2.3-ns product-sum access times for a FCNN layer using XNORNN and MBNN, respectively. The measured maximum energy efficiency reached 30.49 TOPS/W for XNORNN and 55.8 TOPS/W for the MBNN modes.

Asymmetric Control of Coexisting Slow and Fast Rhythms in a Multifunctional Central Pattern Generator: A Model Study

Using a simulation approach, we propose a biophysically feasible mechanism describing how a multifunctional central pattern generator (CPG) can produce co-existing slow and fast rhythms of the patterned motor output. This mechanism suggests that the same core elemental CPG can produce either a locomotion or a paw shaking rhythm in mammals (cat). We built a Hodgkin–Huxley-style biophysical model that generates multistability of a locomotion-like regime and a paw shake-like regime. This model is constructed as a half-center oscillator (HCO), in which two inhibitory neurons (representing the respective neuronal populations in real CPGs) reciprocally inhibit each other. We propose that the locomotion rhythm and the paw shaking rhythm are controlled by two different slowly inactivating intrinsic ion currents. In our model, slowly inactivating low voltage-activated calcium current (ICaS) drives the locomotion-like regime, while slowly inactivating sodium current (INaS) drives the paw shakelike regime. We investigated whether asymmetric characteristics of these regimes could be reliably and separately controlled by asymmetric variation of the conductances of these two currents. We found that variation of the conductance of ICaS in only one neuron, while holding this conductance constant in the other neuron, produces asymmetric changes in bursting characteristics, including the burst duration and interburst interval of the locomotion-like regime without producing notable changes of the paw shake-like regime. We also found that similar variation of the conductance of INaS affects the bursting characteristics of both regimes, although the paw shake-like regime is affected more remarkably than the locomotion-like one.

Iterative and Complex Asymmetric Divisions Control Cell Volume Differences in Ciona Notochord Tapering.

The notochord of the invertebrate chordate Ciona forms a tapered rod at tailbud stages consisting of only 40 cylindrical cells in a single-file column. This tapered shape involves differences in notochord cell volume along the anterior-posterior axis. Here,we quantify sibling cell volume asymmetry throughout the developing notochord and find that there are distinctive patterns of unequal cleavage in all 4 bilateral pairs of A-line primary notochord founder cells and also in the B-line-derived secondary notochord founder cells. A quantitative model confirms that the observed patterns of unequal cleavage are sufficient to explain all the anterior-posterior variation in notochord cell volume. Many examples are known of cells that divide asymmetrically to give daughter cells of different size and fate. Here, by contrast, a series of subtle but iterative and finely patterned asymmetric divisions controls the shape of an entire organ. Quantitative 3D analysis of cell shape and spindle positioning allows us to infer multiple cellular mechanisms driving these unequal cleavages, including polarized displacements of the mitotic spindle, contributions from the shape of the mother cell, and late changes occurring between anaphase and abscission that potentially involve differential cortical contractility. We infer differential use of these mechanisms between different notochord blastomeres and also between different rounds of cell division. These results demonstrate a new role for asymmetric division in directly shaping a developing organ and point toward complex underlying mechanisms.

Milling chatter control based on asymmetric stiffness

Chatter is a kind of instability phenomenon occurred in the machining process. It not only reduces the quality of the workpieces, but also limits the improvement of productivity. In this work, an asymmetric stiffness (AS) control method is proposed for chatter control in the milling process. First of all, a two-degree-of-freedom dynamic model of the AS spindle-milling system is developed. Based on that, the milling stability of the AS spindle system is analyzed. It shows that only increasing the stiffness of the spindle system in the X direction can effectively improve the stability in up milling process. However, in down milling process, the result is opposite, which means the stability will be improved by increasing the stiffness of the spindle system only in the Y direction. The phenomena are then experimentally validated in both down milling and up milling processes by asymmetrically controlling the stiffness of the spindle in the X and Y directions. Finally, an asymmetric stiffness control based chatter control method is proposed and also verified through the milling experiments. The experiment results show that chatter is effectively controlled by the proposed asymmetric stiffness control method and the quality of the finished surface is significantly improved.

Recent Advances in First-Row Transition Metal/Chiral Phosphoric Acid Combined Catalysis.

Since the pioneering independent reports of Akiyama and Terada, the use of chiral phosphoric acids (CPAs) and derivatives as a versatile tool for asymmetric synthesis with good reactivity, regioselectivity, diastereoselectivity and enantioselectivity has emerged, forming an important part of the implementation of asymmetric counteranion-directed catalysis reported to date. In these achievements, the combination of metals with CPAs has enabled various catalytic modes beyond the scope of typical acid catalysis, such as relay catalysis, ion-pairing catalysis, and binary acid catalysis. The first-row transition metals (Sc-Zn) are considered to be sustainable transition metals and have received a great deal of attention. These naturally abundant metals display excellent Lewis acidity and function as powerful redox catalysts in synthesis involving both one and two-electron transfers. Hence, in this chapter, we summarize recent advances in the development of asymmetric reactions using a combination of first-row transition metals and CPAs. Furthermore, we provide a detailed discussion of the mechanisms involved in order to understand the interaction of the metal/phosphate and the origins of the asymmetric control of the transformations.

Asymmetric arms control and strategic stability: Scenarios for limiting hypersonic glide vehicles

ABSTRACTCan arms control incorporate emerging technology? Other articles in this special issue identify potential risks emerging technologies pose to stability and how they are intertwined with international politics. Is there a future for multilateral strategic arms control? This article looks ahead to explore how arms control might reduce those risks but in order to do so we must update concepts of both arms control and strategic stability. Building on Thomas Schelling and Morton Halperin’s seminal study into the relationship between strategic stability and arms control, this article offers an original framework – asymmetric arms control – for incorporating new technologies, which is then used to identify six scenarios for arms control of hypersonic glide vehicles (HGVs). It concludes that arms control can potentially reduce the risks to strategic stability associated with emerging technologies by incorporating dynamism into arms control design. Ultimately, asymmetric arms control can best contribute to strategic stability by crossing domains and reflecting the cross-domain nature of international conflict, and the framework has potential application to emerging technologies beyond HGVs.

Online estimate and compensation of the gear machining error based on electronic gearbox cross-coupling controller

A novel method for online estimate and compensation of the gear machining error based on the flexible electronic gearbox (EGB) is introduced. EGB is a multi-axis controller, which is used to realize the gear generation process. Gear processing quality is directly dependent on the control precision of EGB. The present work focuses on the estimation, analysis, and compensation of the gear machining error during the gear hobbing process. First, an efficient method for the online evaluation of the helical gear tooth profile deviation, pitch error, and helix deviation is presented, from the perspective of the combination of the multi-axis linkage control structure model and the gear processing technology. Second, the online compensation architecture for the five-axis gear hobbing linkage is proposed, which is composed of an asymmetric cross-coupling controller and a master-slave EGB controller. Simulation results show that the proposed online compensation architecture has better control precision, in comparison to the conventional EGB. Finally, experiments are performed on a six-axis gear hobbing machine, where higher accuracies are obtained for the helical gear, processed by the proposed method.

Research on an Asymmetric Fault Control Strategy for an AC/AC System Based on a Modular Multilevel Matrix Converter

This paper studies control strategies for an AC/AC system based on a modular multilevel matrix converter (M3C) when an asymmetric fault occurs in the secondary side ac system. Firstly, the operating principle of M3C is briefly introduced and verified by simulation. Then, based on its mathematical model by double αβ0 transformation, the decoupled control strategies for the primary side and secondary side systems are designed. In view of the asymmetric fault condition of the secondary side system, the positive sequence and negative sequence components of voltages and currents are separated and extracted, and then a proportional resonant controller (PR) is used to regulate the positive and negative sequence currents at the same time to realize decoupled current control in the αβ reference frames. The capacitor voltage balancing control, which consists of an inter-subconverter balancing control and an inner-subconverter balancing control, is realized by adjusting four circulating currents. Finally, the proposed control strategy is validated by simulation in the PSCAD/EMTDC software (Manitoba HVDC Research Center, Canada). The result shows that during the period of the BC-phase short-circuit fault occurring in the secondary side system, the whole system can still operate stably and transmit a certain amount of active power, according to their set values. Furthermore, the capacitor voltages are balanced, with a slight increase during the fault period. The simulation results verify the effectiveness of the proposed control strategy.

Remote Functionalization through Symmetric or Asymmetric Substitutions Control the Pathway of Intermolecular Singlet Fission.

Singlet fission (SF) produces two coupled triplet excitons from a high energy singlet excitation. The mechanism of SF in a variety of phenyl (-Ph) substituted pentacene is systematically studied through both ab initio and density functional theory calculations. Two classes of substitution to pentacene are considered, namely, symmetric configuration with four Ph groups (TPP) and an asymmetric configuration with two Ph groups (DPP). The positions of the singlet and triplet states are determined by calibrating the active space through state averaged complete active space self-consistent field (SA-CASSCF) calculations. The SF rates are computed based on restricted active space with single and double spin flip wave functions (RAS-SF and RAS-2SF), which are analyzed based on different intermolecular π-stacking patterns of TPP and DPP. The contribution of charge transfer (CT) state near the multiexciton (ME) state plays a significant role for SF efficiency. The role of excimer formation is supportive for ME generation [J. Am. Chem. Soc. 2016, 138, 617], and hence it is critically studied. The ME generation in TPP is a slower process and occurs through an excimer-mediated path with a large coupling between the first singlet excited state and ME state. On the other hand, DPP exhibits a relatively faster SF rate through the formation of a ME state via low-lying CT state, especially the slip-stacked dimers. The present computation elegantly demonstrates the crucial role of functional group substitution in the structure of SF active molecules in determining the efficiency of fission dynamics.

Current Reference Generation Based on Next-Generation Grid Code Requirements of Grid-Tied Converters During Asymmetrical Faults

Increased penetration of converter-based power generation has enforced system operators to require ancillary services from distributed generation in order to support the grid and improve the power system stability and reliability. Recent and next-generation grid codes require asymmetrical current provision during unbalanced faults for optimal voltage support. To address this, based on the highly used flexible positive- and negative-sequence control method for current reference generation, this paper presents a general current reference strategy for asymmetrical fault control, where a direct and explicit method is proposed to calculate power references and controller gains while simultaneously complying with converter current limitation and fulfilling the next-generation grid code requirements. The proposed method is tested for three distinct asymmetrical grid faults considering the requirements for dynamic voltage support of the recently revised German grid code as well as the next-generation grid codes. It is shown that the proposed method can improve the fault ride-through performance during asymmetrical faults compared with conventional solutions and comply with modern grid code requirements in a general and flexible manner.

Design and Simulation of Broadband Beam Splitter on a Silicon Nitride Platform for Optical Coherence Tomography

ABSTRACTIntegrated photonics enables the miniaturization of bulk optical components for biosensing applications such as optical coherence tomography (OCT) and is therefore promising for future lab-on-chip solutions. Here, we report the design and simulation of a compact low loss broadband beam splitter with arbitrary coupling ratios on silicon nitride platform for OCT systems. The reported coupler uses asymmetric waveguide-based phase control section for 10:90, 20:80, 30:70, 40:60, and 50:50 splitting ratios and is broadband over 100 nm with the central wavelength of 850 nm. The couplers are realized for transverse electric, transverse magnetic, and fully vectorial modes, and maximum excess loss for all mode types is reported to be less than 0.19 dB. The design tolerance of waveguide width and thickness of the designed coupler is further calculated and is within fabrication limit.

Asymmetric scattering of flexural waves in a parity-time symmetric metamaterial beam.

Non-Hermitian parity-time (PT) symmetric systems that possess real eigenvalues have been intensively investigated in quantum mechanics and rapidly extended to optics and acoustics demonstrating a lot of unconventional wave phenomena. Here, a PT symmetric metamaterial beam is designed based on shunted piezoelectric patches and asymmetric wave scattering in the form of flexural waves is demonstrated through analytical and numerical approaches. The gain and loss components in the PT symmetric beam are realized by the introduction of negative and positive resistances into the external shunting circuits, respectively. Effective medium theory and transfer matrix method are employed to determine the effective material parameters and scattering properties of the PT symmetric metamaterial beam. Unidirectional reflectionlessness has been demonstrated analytically and numerically, together with illustrations of the PT phase transition and exceptional points. The tunability of exceptional points is studied by changing the spacing between piezoelectric patches and shunting circuit parameters. The design explores complex material parameters of the beam structure, and could open unique ways to asymmetric wave control, enhanced sensing, amplification, and localization of flexural waves.

Comparative Analysis of Fault-Tolerant Dual-Channel BLDC and SR Motors

This article presents the results of a comparative analysis of two electronically commutated brushless direct current machines intended for fault-tolerant drives. Two machines designed by the authors were compared: a 12/14 dual-channel brushless direct current motor (DCBLDCM) with permanent magnets and a 12/8 dual-channel switched reluctance motor (DCSRM). Information is provided here on the winding configuration, the parameters, and the power converters of both machines. We developed mathematical models of the DCBLDCM and DCSRM which accounted for the nonlinearity of their magnetization characteristics in dual-channel operation (DCO) and single-channel operation (SCO) modes. The static torque characteristics and flux characteristics of both machines were compared for operation in DCO and SCO modes. The waveforms of the current and the electromagnetic torque are presented for DCO and SCO operating conditions. For DCO mode, an analysis of the behavior of both machines under fault conditions (i.e., asymmetrical control, shorted coil, and open phase) was performed. The two designs were compared, and their strengths and weaknesses were indicated.

Three-Level DC-DC Controlled-Source Circuit of Marine Electromagnetic Detection Transmitter

Nowadays, marine electromagnetic method is a geophysical method which can effectively explore natural gas hydrate (NGH) resources. This method acquires seafloor structure and distribution laws of mineral resources by transmitting high-power electromagnetic waves to the seafloor, and its detection depth relies on the intensity of transmitted electromagnetic waves. At present, marine electromagnetic transmitter is not proper for transmission of high-power electromagnetic waves, and therefore, a novel controlled-source circuit of soft switching three-level marine electromagnetic transmitter is proposed in this paper, one step-down winding is added at the secondary side of high-frequency transformer in series connection with a linear inductor, asymmetric phase-shift PWM control is used, and soft switching of controlled-source circuit within the overall power range is realized. A detailed analysis of the operation process and circuit characteristics is given, and finally, a prototype is designed. Experimental results indicate that this circuit is of wide ZVS range and high efficiency, and it meets requirements for deep-sea detection of high-voltage power supply transmitter.

Effect of Asymmetric Control Constraints on Fixed-Wing UAV Trajectories

Reference trajectories, for the longitudinal states of a fixed-wing unmanned aerial vehicle subjected to asymmetric control constraints, are distinguished using the characteristics of regions of asymptotic stability calculated as ellipsoidal domains by solving linear matrix inequalities. These domains are used to determine the maximum allowable deviations from the reference, for which stable closed-loop tracking can be ensured. Constraints are imposed on a linear state feedback controller with the saturation modeled as a sector nonlinearity.

초전도 에너지 저장 장치용 3상 사이리스터 브리지의 비대칭 제어에 관한 연구

초전도 에너지 저장 장치용 3상 사이리스터 브리지의 비대칭 제어에 관한 연구

Microstructure and ratcheting behavior of 6061 aluminum alloy laser-MIG hybrid welding joint

In this paper, 6061-T6 aluminum alloy was welded by laser-MIG hybrid welding. The microstructures of the upper part of the weld center, the lower part and the edge of the weld near the fusion line in the welded joint were analyzed. The hardness and mechanical properties of welded joints were analyzed in detail. The ratchet strain of 6061 aluminum alloy welded joints was tested, and the asymmetric stress control method was used to test the ratchet strain of 6061 aluminum alloy welded joints. The results show that ratcheting strain increases with the increase of average stress and stress amplitude, and has the characteristics of cyclic softening first and then hardening. The degree of hardening increases with the increase of the maximum cyclic stress. Cyclic hardening is mainly caused by the uninterrupted dislocations in the process of cycling. The accumulation of ratchet strain results in plastic damage of materials. Pre-ratcheting can improve the tensile properties of welded joints by 6.49% and 97.7% yield strength, which is mainly attributed to cyclic hardening caused by ratcheting strain.

Sex-allocation conflict and sexual selection throughout the lifespan of eusocial colonies.

Models of sex‐allocation conflict are central to evolutionary biology but have mostly assumed static decisions, where resource allocation strategies are constant over colony lifespan. Here, we develop a model to study how the evolution of dynamic resource allocation strategies is affected by the queen‐worker conflict in annual eusocial insects. We demonstrate that the time of dispersal of sexuals affects the sex‐allocation ratio through sexual selection on males. Furthermore, our model provides three predictions that depart from established results of classic static allocation models. First, we find that the queen wins the sex‐allocation conflict, while the workers determine the maximum colony size and colony productivity. Second, male‐biased sex allocation and protandry evolve if sexuals disperse directly after eclosion. Third, when workers are more related to new queens, then the proportional investment into queens is expected to be lower, which results from the interacting effect of sexual selection (selecting for protandry) and sex‐allocation conflict (selecting for earlier switch to producing sexuals). Overall, we find that colony ontogeny crucially affects the outcome of sex‐allocation conflict because of the evolution of distinct colony growth phases, which decouples how queens and workers affect allocation decisions and can result in asymmetric control.