Cooperation Enforcement and Collusion Resistance in Repeated Public Goods Games

Enforcing cooperation among substantial agents is one of the main objectives for multi-agent systems. However, due to the existence of inherent social dilemmas in many scenarios, the free-rider problem may arise during agents' long-run interactions and things become even severer when self-interested agents work in collusion with each other to get extra benefits. It is commonly accepted that in such social dilemmas, there exists no simple strategy for an agent whereby she can simultaneously manipulate on the utility of each of her opponents and further promote mutual cooperation among all agents. Here, we show that such strategies do exist. Under the conventional repeated public goods game, we novelly identify them and find that, when confronted with such strategies, a single opponent can maximize his utility only via global cooperation and any colluding alliance cannot get the upper hand. Since a full cooperation is individually optimal for any single opponent, a stable cooperation among all players can be achieved. Moreover, we experimentally show that these strategies can still promote cooperation even when the opponents are both self-learning and collusive

How Much Time is Required for Phase Shift Delivery in RIS-Aided Wireless Systems?

Reconfigurable intelligent surface (RIS) has become a focal point of extensive research due to its remarkable "squared gain". However, achieving a substantial beamforming gain typically requires a significant number of elements, which leads to a non-negligible overhead that forwards the coherent phase shift to the RIS. Different from previous works, which primarily focus on the information transmission phase, we consider the phase delivery overhead during the phase-shift delivery phase to explore the trade-off between performance and overhead. To reduce the phase delivery overhead via the control link, we introduce a hybrid phase shift mechanism, encompassing both the coherent and fixed phase shifts. Specifically, a beamforming problem is formulated for maximizing the throughput. In light of the intractability of the problem, we develop an alternating optimization-based iterative algorithm by combining quadratic transformation and successive convex approximation. To gain more insights, we derive the closed-form expression of the number of elements adopting the coherent phase shift in the large signal-to-noise ratio region. This expression serves as a valuable guide for the practical implementation of the RIS technology. Our simulation results conclusively demonstrate the effectiveness of the proposed algorithm in achieving a favorable trade-off between throughput and overhead. Furthermore, the introduction of the hybrid phase shift approach significantly reduces phase delivery overhead while concurrently enhancing the system throughput

To Reflect or Not To Reflect: On-Off Control and Number Configuration for Reflecting Elements in RIS-Aided Wireless Systems

Reconfigurable intelligent surface (RIS) has been regarded as a promising technique due to its high array gain and low power. However, the traditional passive RIS suffers from the ``double fading'' effect, which has restricted the performance of passive RIS-aided communications. Fortunately, active RIS can alleviate this problem since it can adjust the phase shift and amplify the received signal simultaneously. Nevertheless, a high beamforming gain often requires a number of reflecting elements, which leads to non-negligible power consumption, especially for the active RIS. Thus, one challenge is how to improve the scalability of the RIS and the energy efficiency. Different from the existing works where all reflecting elements are activated, we propose a novel element on-off mechanism where reflecting elements can be flexibly activated and deactivated. Two different optimization problems for passive RIS and active RIS are formulated by maximizing the total energy efficiency. We develop two different alternating optimization-based iterative algorithms to obtain sub-optimal solutions. Furthermore, we consider special cases involving rate maximization problems for given the same total power budget, and respectively analyze the number configuration for passive RIS and active RIS. Simulation results verify that reflecting elements under the proposed algorithms can be flexibly activated and deactivated

A study of the effect of combination of acupuncture and Chinese medicine (Ban Xia Xie Xin Decoction) on patients with sepsis-induced gastrointestinal dysfunction

Purpose: To investigate the therapeutic effect of combination of acupuncture and Ban Xia Xie Xin Decoction (BXXXD) in patients with sepsis-induced gastrointestinal dysfunction.Methods: A total of 100 patients with sepsis and gastrointestinal dysfunction admitted to our hospitalfrom June 2019 to December 2020 were randomly assigned to a control group and a study group for a retrospective analysis. Both groups received acupuncture treatment, while BXXXD was given to the study group, in addition to acupuncture. Treatment effectiveness, incidence of adverse reactions, degree of recurrence at 1, 2 and 3 months after treatment, gastrointestinal dysfunction scores after 1week of treatment, quality of life index (QLI) scores, frequencies of flatulence and defecation within 48 h, number of bowel rumblings, as well as levels of gastrin and  cholecystokinin (CCK), were determined and compared between the two groups.Results: The group with BXXXD intervention demonstrated superior treatment effectiveness, QLI cores, frequencies of flatulence and defecation within 48 h, number of bowel rumblings, and level of gastrin than those who received only acupuncture treatment (p < 0.05). There was strong evidence of lower incidence of adverse reactions, recurrence at 1, 2, and 3 months after treatment; gastrointestinal dysfunction scores and CCK levels after 1 week of treatment was higher in the study group than in the control group (p < 0.05).Conclusion: The combination of acupuncture and BXXXD is superior to acupuncture alone in sepsis patients with gastrointestinal dysfunction. The combination therapy produces its effect by decreasing clinical symptoms, promoting recovery of the patients, and elevating their quality of life