Completely positive and trace-preserving maps characterize physically implementable quantum operations. On the other hand, general linear maps, such as positive but not completely positive maps, which can not be physically implemented, are fundamental ingredients in quantum information, both in theoretical and practical perspectives. This raises the question of how well one can simulate or approximate the action of a general linear map by physically implementable operations. In this work, we introduce a systematic framework to resolve this task using the quasiprobability decomposition technique. We decompose a target linear map into a linear combination of physically implementable operations and introduce the physical implementability measure as the least amount of negative portion that the quasiprobability must pertain, which directly quantifies the cost of simulating a given map using physically implementable quantum operations. We show this measure is efficiently computable by semidefinite programs and prove several properties of this measure, such as faithfulness, additivity, and unitary invariance. We derive lower and upper bounds in terms of the Choi operator's trace norm and obtain analytic expressions for several linear maps of practical interests. Furthermore, we endow this measure with an operational meaning within the quantum error mitigation scenario: it establishes the lower bound of the sampling cost achievable via the quasiprobability decomposition technique. In particular, for parallel quantum noises, we show that global error mitigation has no advantage over local error mitigation.
Active power-assist exoskeletons are becoming more prospective than follow-up types, especially for elderly and handicapped motion auxiliary. The exoskeleton is required not only to withstand load but also to actively share the weight of a human body. Active power-assist lower limb is designed to meet this expectation. The definition of ''active powerassist'' was suggested in this article. A unique man-machine motion mapping was derived based on the configuration matching, wherein the exoskeleton obtains the wearer's motion data and parse out the corresponding intention. Manmachine coupling mechanisms were exquisitely configured, which rationalize the degrees of freedom of the manmachine system and facilitate force transmission for active assistant. The dynamic knees and hip joints with the integrated force servo unit were designed, which is the key to realize soft contact and cooperative movement. The prototype was developed, and three basic functions (human movement perception, force transmission, and movement cooperation) were preliminarily verified in a single leg swinging experiment. The effect of follow-up mode and active power-assist mode were quantitatively analyzed in marches-on-the-spot experiment. A 24.6% proportional reduction of the wearer foot force and smooth man-machine coordination in field experiments has demonstrated the feasibility of this structure design of active power-assist lower limb.
A novel balance assistance control strategy of a hip exoskeleton robot was proposed in this paper. The organic fusion of the human balance assessment and the exoskeleton balance assistance control strategy are the assurance of balance recovery. However, currently there are few human balance assessment methods that are suitable for detecting balance loss during standing and walking, and very little research has focused on exoskeleton balance recovery control. In this paper, a single step balance assessment method was proposed first, and then based on this method an "assist-as-needed" balance assistance control strategy was established. Finally, the exoskeleton balance assistance control experiment was carried out. The experiment results verified the effectiveness of the single balance assessment method and the active balance assistance control strategy.
Extensive deployment of LTE cellular networks can enhance network throughput via the shared spectrum utilization; however, the energy efficiency is largely ignored during the current spectral efficiency maximization, which is especially important in large-scale LTE networks. By now, we know that green communications and energy efficiency are important for the future sustainable 5G networks. Power control can improve both spectral efficiency and energy efficiency. In this paper, a distributed power control method is investigated for LTE uplink, which is based on the formulation and analysis of a defined cooperative game theoretic power control framework. A novel utility function is designed with the energy efficiency into consideration. Furthermore, the location-aware weighted bargaining game theory is formulated with a denoted balancing factor. Finally, simulation results show that the presented algorithm is with a fast convergence rate. Meanwhile, it can ensure the SINR of all users with reducing power consumption, therefore, improve energy efficiency.
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