Owing to the Fermi pinning effect arose in the metal electrodes deposition process, metal–semiconductor contact is always independent on the work function, which challenges the next‐generation ...optoelectronic devices. In this work, a metal‐assisted transfer approach is developed to transfer Bi2O2Se nanosheets onto the pre‐deposited metal electrodes, benefiting to the tunable metal–semiconductor contact. The success in Bi2O2Se nanosheets transfer is contributed to the stronger van der Waals adhesion of metal electrodes than that of growth substrates. With the pre‐deposited asymmetric electrodes, the self‐powered near‐infrared photodetectors are realized, demonstrating low dark current of 0.04 pA, high Ilight/Idark ratio of 380, fast rise and decay times of 4 and 6 ms, respectively, under the illumination of 1310 nm laser. By pre‐depositing the metal electrodes on polyimide and glass, high‐performance flexible and omnidirectional self‐powered near‐infrared photodetectors are achieved successfully. This study opens up new opportunities for low‐dimensional semiconductors in next‐generation high‐performance optoelectronic devices.
By adopting the metal‐assisted transfer approach, tunable metal–semiconductor contacts of Ohmic contact, Schottky contact, and asymmetric contact are achieved in Bi2O2Se nanosheet MSM photodetectors. With the asymmetric contact, the MSM photodetector displays the typical self‐powered NIR photodetection behaviors with a low dark current of 0.04 pA, and high Ilight/Idark ratio of 380.
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Trifluoromethyl cationic carbyne (CF3C+:) possessing dual carbene‐carbocation behavior emulated as trifluoromethyl metal‐carbynoid (CF3C+=M) has not been explored yet, and its reaction ...characteristics are unknown. Herein, a novel α‐diazotrifluoroethyl sulfonium salt was prepared and used in Rh‐catalyzed three‐component 2+1+2 cycloadditions for the first time with commercially available N‐fused heteroarenes and nitriles, yielding a series of imidazo1,5‐a N‐heterocycles that are of interest in medicinal chemistry, in which the insertion of trifluoromethyl Rh‐carbynoid (CF3C+=Rh) into C=N bonds of N‐fused heteroarenes was involved. This strategy demonstrates synthetic applications in late‐stage modification of pharmaceuticals, construction of CD3‐containing N‐heterocycles, gram‐scale experiments, and synthesis of phosphodiesterase 10A inhibitor analog. These highly valuable and modifiable imidazo1,5‐a N‐heterocycles exhibit good antitumor activity in vitro, thus demonstrating their potential applications in medicinal chemistry.
A novel α‐diazotrifluoroethyl sulfonium salt was prepared, and it was applied in Rh‐catalyzed three‐component 2+1+2 cycloadditions for the first time, affording various imidazo1,5‐a N‐heterocycles under mild conditions. This strategy involved a unique trifluoromethyl Rh‐carbynoid (CF3C+=Rh), wherein three new chemical bonds were forged at the α‐carbon of trifluoromethyl in a single step.
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The distributed patch dissemination strategies are a promising alternative to the conventional centralized patch dissemination strategies. This paper aims to establish a theoretical framework for ...evaluating the effectiveness of distributed patch dissemination mechanism. Assuming that the Internet offers P2P service for every pair of nodes on the network, a dynamic model capturing both the virus propagation mechanism and the distributed patch dissemination mechanism is proposed. This model takes into account the infected removable storage media and hence captures the interaction of patches with viruses better than the original SIPS model. Surprisingly, the proposed model exhibits much simpler dynamic properties than the original SIPS model. Specifically, our model admits only two potential (viral) equilibria and undergoes a fold bifurcation. The global stabilities of the two equilibria are determined. Consequently, the dynamical properties of the proposed model are fully understood. Furthermore, it is found that reducing the probability per unit time of disconnecting a node from the Internet benefits the containment of electronic viruses.
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Abstract
The galactic 511 keV gamma-ray line has been observed since 1970's, and was identified as the result of electron-positron annihilation, but the origin of such positrons is still not clear.
...Apart from the astrophysical explanations, the possibilities that such positrons come from dark matter (DM) annihilation are also widely studied.
Primordial black hole (PBH) is also an extensively studied candidate of DM.
If PBHs exist, the DM particles may be gravitationally bound to the PBHs and form halo around PBHs with density spikes.
DM annihilation in these density spikes can enhance the production rate of positrons from DM particles, but the signal morphology is similar to the decaying DM.
We consider such a mixed model consisting of DM particles and PBHs and obtain the upper limit from the data of 511 keV gamma-ray line from INTEGRAL/SPI on the decaying component of DM particles and the constraint on the PBH abundance.
These constraints are general and independent of particle DM models.
For the mixed model consisting of excited DM and PBHs, the constraints on the PBH abundance can be down to O(10
-17
) for DM particle with mass around 1, which is more stringent than that obtained from the extragalactic gamma-ray background.
Path planning plays an important role in navigation and motion planning for robotics and automated driving applications. Most existing methods use iterative frameworks to calculate and plan the ...optimal path from the starting point to the endpoint. Iterative planning algorithms can be slow on large maps or long paths. This work introduces an end-to-end path-planning algorithm based on a fully convolutional neural network (FCNN) for grid maps with the concept of the traversability cost, and this trains a general path-planning model for 10 × 10 to 80 × 80 square and rectangular maps. The algorithm outputs the lowest-cost path while considering the cost and the shortest path without considering the cost. The FCNN model analyzes the grid map information and outputs two probability maps, which show the probability of each point in the lowest-cost path and the shortest path. Based on the probability maps, the actual optimal path is reconstructed by using the highest probability method. The proposed method has superior speed advantages over traditional algorithms. On test maps of different sizes and shapes, for the lowest-cost path and the shortest path, the average optimal rates were 72.7% and 78.2%, the average success rates were 95.1% and 92.5%, and the average length rates were 1.04 and 1.03, respectively.
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The advanced persistent threat (APT) as a new kind of cyber attack has posed a severe threat to modern organizations. When the APT has been detected, the organization has to deal with the APT ...response problem, i.e., to allocate the available response resources to fix her insecure hosts so as to mitigate her potential loss. This paper addresses the APT response problem by using the risk management approach. First, we introduce a model characterizing the evolution of the organization's expected state. By analyzing this model, we find the organization's expected state approaches a common limit expected state. Then, we use the organization's expected loss per unit time to measure her potential loss, and we find this measure is determined by the organization's limit expected state. On this basis, we model the APT response problem as a game-theoretic problem (the APT response game) in which the organization seeks a Nash equilibrium. We present a greedy algorithm for solving the game. Comparative experiments show that the algorithm is effective. Therefore, we recommend the response strategy generated by performing the algorithm. These findings contribute to defending against the APT. To our knowledge, this is the first time the APT response problem is addressed.
The geomagnetically induced current (GIC) produced during extreme geomagnetic storms can easily lead to large‐scale blackouts in China due to the increase in the scale of its electric power grid. A ...power grid's resilience is its capability to resist various natural hazards, withstand primary failures, and quickly resume normal operation. To avoid power grid damages, this study developed a resilient power grid, incorporating failure, power flow calculation and recovery models under a uniform induced geoelectric field. We chose a system's performance loss as the resilience evaluation indicator, which intuitively reflected a system's loss under GIC. In addition, the recovery model was optimized using a genetic algorithm, and two resilience improvement measures were proposed. The IEEE‐RTS‐79 system, consisting of 10 generators, 24 buses and 5 transformers, was chosen as an example to verify the feasibility of this study. The results show that the genetic algorithm and optimization measures effectively enhanced the system's resilience indicator and provided a reference for preventing system damages under GIC and quick recovery after possible failures.
Plain Language Summary
Extreme space weather produces large geomagnetic field disturbances; these disturbances propagate down to Earth, inducing secondary geomagnetically induced currents (GICs) in earthed electric power grids. GICs increase transformers' reactive power loss and raise their temperatures; this affects a power system's normal operation, and in extreme cases causes major blackouts. Therefore, it is vital to study power grids' resilience under GIC events. In this study, we calculated the GIC level using a uniform geoelectrical conductivity model. Based on this, we proposed a resilient power grid model consisting of the failure model, power flow calculation model and recovery model, and evaluated optimization strategies. Our results show that the proposed model can improve a power system's recovery performance after possible failure due to GICs and effectively avoid GIC‐related large‐scale blackouts.
Key Points
We proposed a resilience assessment method for transmission systems under extreme space weather
We calculated a resilience indicator and identified multiple effective methods to improve a system’s resilience
We chose the IEEE‐RTS‐79 system as an example to verify the effectiveness of a genetic algorithm and optimization measures
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(1)Objective: In this study, a quantitative analysis of chemical groups (the triterpenoids, water-soluble polysaccharides, and acidic polysaccharides) and quantitative high liquid performance ...chromatography (HPLC) fingerprint of Poria cocos (Schw.) Wolf (PC) for quality control was developed. (2) Methodology: First, three main chemical groups, including triterpenoids, water-soluble polysaccharides, and acidic polysaccharides, in 16 batches of PC were evaluated by ultraviolet spectrophotometry. Afterward, the quantitative fingerprint of PC was established, and the alcohol extract of PC was further evaluated. The method involves establishing 16 batches of PC fingerprints by HPLC, evaluating the similarity of different batches of PC, and identifying eight bioactive components, including poricoic acid B (PAB), dehydrotumulosic acid (DTA), poricoic acid A (PAA), polyporenic acid C (PAC), 3-epidehydrotumulosic acid (EA), dehydropachymic acid (DPA), dehydrotrametenolic acid (DTA-1), and dehydroeburicoic acid (DEA), in PC by comparison with the reference substance. Combined with the quantitative analysis of multi-components by a single marker (QAMS), six bioactive ingredients, including PAB, DTA, PAC, EA, DPA, and DEA, in PC from different places were established. In addition, the multivariate statistical analyses, such as principal component analysis and heatmap hierarchical clustering analysis are more intuitive, and the visual analysis strategy was used to evaluate the content of bioactive components in 16 batches of PC. Finally, the analysis strategy of three main chemical groups in PC was combined with the quantitative fingerprint strategy, which reduced the error caused by the single method. (3) Results: The establishment of a method for the quantification of chemical groups and quantitative HPLC fingerprint of PC was achieved as demonstrated through the quantification of six triterpenes in PC by a single marker. (4) Conclusions: Through qualitative and quantitative chemical characterization, a multi-directional, simple and efficient routine evaluation method of PC quality was established. The results reveal that this strategy can provide an analytical method for the quality evaluation of PC and other Chinese medicinal materials.
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1D III–V semiconductor nanowires (NWs) attract significant interests in fundamental physics and promising applications of high‐performance room‐temperature infrared (IR) detectors. Here, a ...comprehensive overview of recent advances in the study of III–V NW‐based IR detectors is presented, starting from the rationale of III–V NWs for IR detectors, the controllable synthesis of III–V NWs to the precise manipulation of III–V NW‐based IR detector performances. With a bandgap covering the whole IR wavelength range and a high carrier mobility, III–V NWs are considered as the most optimal channel materials for high‐performance IR detectors. The synthesis methods and growth mechanisms of high quality III–V NWs are discussed, emphasizing the low‐cost solid source chemical vapor deposition (CVD) technique, which is developed as the two‐step and surfactant‐assisted CVD methods in the growth of various III–V NWs. Next, the representative types of III–V NW IR detectors are discussed and typical strategies to resolve main challenges limiting the performance of III–V NW‐based IR detectors are reviewed, including high density of surface trap states, large dark current, etc. Finally, the possible challenges and opportunities in the future development of III–V NW‐based IR detectors are discussed.
Group III–V nanowires (NWs) are attractive candidates for high‐performance room‐temperature infrared (IR) detectors. This review presents recent advances in the study of III–V NW‐based IR detectors, starting from the cost‐effective synthesis of III–V NWs to the precise manipulation of their optoelectronic properties in IR detectors. The possible challenges and opportunities in the future development are also discussed.
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