The radiation of electromagnetic and mechanical waves depends not only on the intrinsic properties of the emitter but also on the surrounding environment. This principle has laid the foundation for ...the development of lasers, quantum optics, sonar, musical instruments and other fields related to wave–matter interaction. In the conventional wisdom, the environment is defined exclusively by its eigenstates, and an emitter radiates into and interacts with these eigenstates. Here we show experimentally that this scenario breaks down at a non-Hermitian degeneracy known as an exceptional point. We find a chirality-reversal phenomenon in a ring cavity where the radiation field reveals the missing dimension of the Hilbert space, known as the Jordan vector. This phenomenon demonstrates that the radiation field of an emitter can become fully decoupled from the eigenstates of its environment. The generality of this striking phenomenon in wave–matter interaction is experimentally confirmed in both electromagnetic and acoustic systems. Our finding transforms the fundamental understanding of light–matter interaction and wave–matter interaction in general, and enriches the intriguing physics of exceptional points.The modes of the radiation field generated from an emitter are usually determined by the eigenstates of the surrounding environment. However, this scenario breaks down in a non-Hermitian system, at the spectral degeneracy known as an exceptional point.
Simultaneously harvesting, converting and storing solar energy in a single device represents an ideal technological approach for the next generation of power sources. Herein, we propose a device ...consisting of an integrated carbon-based perovskite solar cell module capable of harvesting solar energy (and converting it into electricity) and a rechargeable aqueous zinc metal cell. The electrochemical energy storage cell utilizes heterostructural Co
P-CoP-NiCoO
nanometric arrays and zinc metal as the cathode and anode, respectively, and shows a capacity retention of approximately 78% after 25000 cycles at 32 A/g. In particular, the battery cathode and perovskite material of the solar cell are combined in a sandwich joint electrode unit. As a result, the device delivers a specific power of 54 kW/kg and specific energy of 366 Wh/kg at 32 A/g and 2 A/g, respectively. Moreover, benefiting from its narrow voltage range (1.40-1.90 V), the device demonstrates an efficiency of approximately 6%, which is stable for 200 photocharge and discharge cycles.
As data have become an increasingly important asset of modern companies in the digital era, certain types of data, known as 'essential data', have become particularly crucial in market competition. ...The refusal to share 'essential data' may raise competition-relevant concerns, and the intervention by competition law to ensure its sharing is thus in demand. Yet, three dimensions should be carefully assessed before the legal interventions are deployed and applied. First, clear criteria should be crafted for identifying 'essential data'. Second, it is vital to assess the role of 'essential data' concerning potential abuses of market dominance and merger control by corporations. Finally, the reasonable conditions under which the sharing of 'essential data' is compelled should be specified.
Capacity-achieving polar codes have gained significant attention in recent years. In general, polar codes can be decoded by either successive cancellation (SC) or the belief propagation (BP) ...algorithm. However, unlike SC decoders, performance optimizations for BP decoders have not been fully explored yet. In this paper, we explore novel early stopping criteria for polar BP decoding to significantly reduce energy dissipation and decoding latency. First, we propose two detection-type novel early stopping criteria for detecting valid outputs. For polar (1024, 512) codes, these two stopping criteria can reduce the number of iterations by up to 42.5% at 3.5 dB. Then, we propose a novel channel condition estimation approach, which can help select different stopping criteria in different SNR regions. Furthermore, the hardware architectures of polar BP decoders with the proposed stopping criteria are presented and developed. Synthesis results show that with the use of the proposed stopping criteria, the energy dissipation, and average latency of polar (1024, 512) BP decoder can be reduced by 10% ~ 30% with 2% ~ 5% hardware overhead, and average throughput can be increased by 20% ~ 55%.
Polar codes, as the first provable capacity-achieving error-correcting codes, have received much attention in recent years. However, the decoding performance of polar codes with traditional ...successive-cancellation (SC) algorithm cannot match that of the low-density parity-check or Turbo codes. Because SC list (SCL) decoding algorithm can significantly improve the error-correcting performance of polar codes, design of SCL decoders is important for polar codes to be deployed in practical applications. However, because the prior latency reduction approaches for SC decoders are not applicable for SCL decoders, these list decoders suffer from the long-latency bottleneck. In this paper, we propose a multibit-decision approach that can significantly reduce latency of SCL decoders. First, we present a reformulated SCL algorithm that can perform intermediate decoding of 2 b together. The proposed approach, referred as 2-bit reformulated SCL (2b-rSCL) algorithm, can reduce the latency of SCL decoder from (3n-2) to (2n-2) clock cycles without any performance loss. Then, we extend the idea of 2-b-decision to general case, and propose a general decoding scheme that can perform intermediate decoding of any 2 K bits simultaneously. This general approach, referred as 2 K -bit reformulated SCL (2 K b-rSCL) algorithm, can reduce the overall decoding latency to as short as n/2 K-2 -2 cycles. Furthermore, on the basis of the proposed algorithms, very large-scale integration architectures for 2b-rSCL and 4b-rSCL decoders are synthesized. Compared with a prior SCL decoder, the proposed (1024, 512) 2b-rSCL and 4b-rSCL decoders can achieve 21% and 60% reduction in latency, 1.66 and 2.77 times increase in coded throughput with list size 2, and 2.11 and 3.23 times increase in coded throughput with list size 4, respectively.
Flexible AC transmission system (FACTS) has become the main development direction of power system in the future, so scientific configuration method of FACTS device is very important. At present, the ...configuration method of FACTS device has been explored to some extent, but there is still a lack of comprehensive summary of FACTS device configuration method and scientific configuration methods of FACTS device adapting to various application scenes in power system. To this end, this paper summarizes research progress and research prospects of configuration methods of FACTS device. Firstly, starting from the single device configuration within three types of FACTS devices and the multiple device configuration of several types of FACTS devices, research progress of the configuration methods is summarized. Then, from four perspectives which are multiple targets, multiple types, power-supply planning and power grid planning, realization ideas of configuration methods with multiple targets or with multiple types, and the configuration methods considering power-supply planning or considering power grid planning are all are proposed in this paper, which can meet the development needs of power system in the future. The summary of research progress and the four proposed adaptive configuration methods done in this paper aims to provide a reference for the subsequent research on configuration method of FACTS devices.
Nonnegative matrix factorization (NMF) is a powerful matrix decomposition technique that approximates a nonnegative matrix by the product of two low-rank nonnegative matrix factors. It has been ...widely applied to signal processing, computer vision, and data mining. Traditional NMF solvers include the multiplicative update rule (MUR), the projected gradient method (PG), the projected nonnegative least squares (PNLS), and the active set method (AS). However, they suffer from one or some of the following three problems: slow convergence rate, numerical instability and nonconvergence. In this paper, we present a new efficient NeNMF solver to simultaneously overcome the aforementioned problems. It applies Nesterov's optimal gradient method to alternatively optimize one factor with another fixed. In particular, at each iteration round, the matrix factor is updated by using the PG method performed on a smartly chosen search point, where the step size is determined by the Lipschitz constant. Since NeNMF does not use the time consuming line search and converges optimally at rate in optimizing each matrix factor, it is superior to MUR and PG in terms of efficiency as well as approximation accuracy. Compared to PNLS and AS that suffer from numerical instability problem in the worst case, NeNMF overcomes this deficiency. In addition, NeNMF can be used to solve -norm, -norm and manifold regularized NMF with the optimal convergence rate. Numerical experiments on both synthetic and real-world datasets show the efficiency of NeNMF for NMF and its variants comparing to representative NMF solvers. Extensive experiments on document clustering suggest the effectiveness of NeNMF.
In-situ formation of appropriate interfacial carbides by matrix-alloying with carbide-forming elements offers an efficient approach to improve the interfacial bonding of graphene/CuX composites. ...However, the carbide formation commonly occurs at graphene edge/matrix interface, which is not enough to achieve the sufficient interfacial bonding because the vast majority of graphene/matrix interface is basal-plane/matrix interface rather than edge/matrix interface. To alleviate this limitation, we reported a new design of creating defects on graphene basal-plane (CDGB) to optimize the interface and mechanical properties of graphene/CuCr composites. Plasma treatment was employed to create the structural defects (∼7 nm nanopores) on graphene basal-plane. When incorporating the plasma-treated graphene into the CuCr matrix, the Cr7C3 carbides were found to be in-situ formed at both basal-plane/matrix and edge/matrix interfaces. Ex-situ and in-situ tensile tests both demonstrated that the plasma-treated graphene led to the composite that showed a larger strength enhancement and a higher load transfer capability than untreated counterpart, which was ascribed to the largely improved interfacial bonding contributed by the Cr7C3 formed at basal-plane/matrix interface. This study suggests that the CDBG via plasma treatment affords a feasible solution for the interface optimization of graphene/CuX composites with enhanced mechanical properties.
Display omitted
PDF
