The catalytic activities are generally believed to be relevant to the electronic states of their active center, but understanding this relationship is usually difficult. Here, we design two types of catalysts for elec...The catalytic activities are generally believed to be relevant to the electronic states of their active center, but understanding this relationship is usually difficult. Here, we design two types of catalysts for electrocatalytic urea via a coordination strategy in a metal–organic frameworks: Cu^(Ⅲ)-HHTP and Cu^(Ⅱ)-HHTP. Cu^(Ⅲ)-HHTP exhibits an improved urea production rate of 7.78 mmol h^(−1)g^(−1) and an enhanced Faradaic efficiency of 23.09% at-0.6 V vs. reversible hydrogen electrode, in sharp contrast to Cu^(Ⅱ)-HHTP.Isolated CuⅢspecies with S = 0 spin ground state are demonstrated as the active center in Cu^(Ⅲ)-HHTP, different from Cu^(Ⅱ) with S = 1/2 in Cu^(Ⅱ)-HHTP. We further demonstrate that isolated Cu^(Ⅲ)with an empty dx2-y20orbital in Cu^(Ⅲ)-HHTP experiences a single-electron migration path with a lower energy barrier in the C–N coupling process, while Cu^(Ⅱ)with a single-spin state( d_(x2-y2)^(1)) in Cu^(Ⅱ)-HHTP undergoes a two-electron migration pathway.展开更多
The spherical oscillation of a gas bubble in liquids is important to growth in liquids during rectified diffusions( e. g., the onset of the sonoluminescence and the enhancement of sonochemical reactions). The present ...The spherical oscillation of a gas bubble in liquids is important to growth in liquids during rectified diffusions( e. g., the onset of the sonoluminescence and the enhancement of sonochemical reactions). The present paper numerically shows stability maps( divided into four zones),in which gas bubbles maintain the linearly spherical oscillation without nonlinear disturbance of rectified diffusions within a large range of bubble radius. The critical pressures of spherical and diffusional oscillations are two decisive indexes determining the stability status. Specifically,the stability boundaries and influential factors( including acoustic parameters and gas concentration in liquids) were discussed and analyzed. The results show that the variations of gas concentration and acoustic parameters dramatically changed the stable status of the gas bubbles. The gas bubble maintained stable status when external parameters and gas concentration were set between the two critical values properly. The cases of high-frequency and low-frequency limits were also introduced at the end of the whole paper.展开更多
In order to evaluate the emergency evacuation capacity of subway stations, the data collected were analyzed based on grounded theory, and an evaluation model of emergency evacuation capacity was constructed by combini...In order to evaluate the emergency evacuation capacity of subway stations, the data collected were analyzed based on grounded theory, and an evaluation model of emergency evacuation capacity was constructed by combining the analytic hierarchy process (AHP). Finally, 12 secondary indicators (categories) and 4 primary indicators (main categories) were obtained, among which the primary indicators were management factors, emergency response, construction factors and personnel factors. From the weight value calculated by analytic hierarchy process, we can see that management factors and emergency response have great influence on the emergency evacuation capacity of subway stations. Therefore, we should focus on management factors and emergency response to improve the emergency evacuation capacity of subway stations.展开更多
Power Shell has been widely deployed in fileless malware and advanced persistent threat(APT)attacks due to its high stealthiness and live-off-theland technique.However,existing works mainly focus on deobfuscation and ...Power Shell has been widely deployed in fileless malware and advanced persistent threat(APT)attacks due to its high stealthiness and live-off-theland technique.However,existing works mainly focus on deobfuscation and malicious detection,lacking the malicious Power Shell families classification and behavior analysis.Moreover,the state-of-the-art methods fail to capture fine-grained features and semantic relationships,resulting in low robustness and accuracy.To this end,we propose Power Detector,a novel malicious Power Shell script detector based on multimodal semantic fusion and deep learning.Specifically,we design four feature extraction methods to extract key features from character,token,abstract syntax tree(AST),and semantic knowledge graph.Then,we intelligently design four embeddings(i.e.,Char2Vec,Token2Vec,AST2Vec,and Rela2Vec) and construct a multi-modal fusion algorithm to concatenate feature vectors from different views.Finally,we propose a combined model based on transformer and CNN-Bi LSTM to implement Power Shell family detection.Our experiments with five types of Power Shell attacks show that PowerDetector can accurately detect various obfuscated and stealth PowerShell scripts,with a 0.9402 precision,a 0.9358 recall,and a 0.9374 F1-score.Furthermore,through singlemodal and multi-modal comparison experiments,we demonstrate that PowerDetector’s multi-modal embedding and deep learning model can achieve better accuracy and even identify more unknown attacks.展开更多
Polarization manipulation of light is of great importance because it could promote development of wireless communications,biosensing,and polarization imaging.In order to use natural light more efficiently,it is highly...Polarization manipulation of light is of great importance because it could promote development of wireless communications,biosensing,and polarization imaging.In order to use natural light more efficiently,it is highly demanded to design and fabricate high performance asymmetric polarization converters which could covert the natural light to one particular linearly polarized light with high efficiency.Traditionally,polarizers could be achieved by controllers with crystals and polymers exhibiting birefringence.However,the polarizers are bulky in size and the theoretical conversion efficiency of the polarizers is limited to 0.5 with unpolarized light incidence.In this paper,we propose a polarization converter which could preserve high transmission for one linearly polarized light and convert the orthogonal linearly polarized light to its cross-polarized with high transmittance based on a multi-layer chiral metasurface.Theoretical results show that normally incident y-polarized light preserves high transmittance for the wavelength range from 685 nm to 800 nm while the orthogonal normally incident x-polarized light is efficiently converted to the y-polarized light with high transmittance from 725 nm to 748 nm.Accordingly,for unpolarized light incidence,transmittance larger than 0.5 has been successfully achieved in a broadband wavelength range from 712 nm to 773 nm with a maximum transmittance of 0.58 at 732 nm.展开更多
Flexible sensors with high sensitivity and stability are essential components of electronic skin,applicable to detecting human movement,monitoring physiological health,preventing diseases,and other domains.In this stu...Flexible sensors with high sensitivity and stability are essential components of electronic skin,applicable to detecting human movement,monitoring physiological health,preventing diseases,and other domains.In this study,we utilized a straightforward and efficient femtosecond laser direct writing technique using phenolic resin(PR)as a carbon precursor to produce high-quality laser-induced graphene(LiG)characterized by high crystallinity and low defect density.The fabricated LIG underwent comprehensive characterization using SEM,Raman spectroscopy,XPS,and XRD.Subsequently,we developed strain sensors with a hexagonal honeycomb pattern and temperature sensors with a line pattern based on PR-derived LIG.The strain sensor exhibited an outstanding measurement factor of 4.16×104 with a rapid response time of 32 ms,which is applied to detect various movements like finger movements and human pulse.Meanwhile,the temperature sensor demonstrated a sensitivity of 1.49%/°C with a linear response range of 20-5o C.The PR-derived LIG shows promising potential for applications in human physiological health monitoring and other advanced wearable technologies.展开更多
Because iron is the richest transition-metal element in the earth’s crust,if iron complexes could be used as the emitters in organic light-emitting diodes(OLEDs),the cost of OLEDs would be reduced dramatically.Lumine...Because iron is the richest transition-metal element in the earth’s crust,if iron complexes could be used as the emitters in organic light-emitting diodes(OLEDs),the cost of OLEDs would be reduced dramatically.Luminescent iron(III)complexes with low-spin d5 electronic structure theoretically possess spin-allowed doublet metal-to-ligand charge transfer(^(2)MLCT)emission,but little attention has been paid to their application in OLEDs.展开更多
Designing and synthesizing cost-effective bifunctional catalysts for overall alkaline water/seawater splitting is still a huge challenge for hydrogen production.Herein,Co/Ni/Fe/Mn based-amorphous high-entropy phosphox...Designing and synthesizing cost-effective bifunctional catalysts for overall alkaline water/seawater splitting is still a huge challenge for hydrogen production.Herein,Co/Ni/Fe/Mn based-amorphous high-entropy phosphoxide self-standing electrode(CNFMPO)is synthesized by the facile and fast electrodeposition method.CNFMPO exhibits excellent bifunctional electrocatalytic performances on alkaline water/seawater electrolysis.The hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)overpotentials of CNFMPO in alkaline water/seawater are as low as 43/73 and 252/282 mV to reach a current density of 10 mA cm^(-2),respectively.Additionally,two-electrode electrolyzers with CNFMPO||CNFMPO successfully achieve the current density of 10 mA cm^(-2) at low voltages of 1.54 and 1.56 V for overall alkaline water/seawater splitting,respectively.CNFMPO exhibits satisfactory long-term stability on overall alkaline water/seawater splitting for the surface reconstruction into active metal hydroxide/(oxy)hydroxide,phosphite,and phosphate.Moreover,no hypochlorite is detected during seawater electrolysis for the beneficial chlorite oxidation inhibition of the reconstructed phosphite and phosphate.The excellent catalytic performances of CNFMPO are due to the unique amorphous structure,multi-component synergistic effect,beneficial electronic structure modulation,and surface reconstruction during the catalytic reaction process.Therefore,CNFMPO has shown potential promotion to the development of the water/seawater splitting industry as a promising substituent for noble-metal electrocatalysts.This work provides new insights into the design of efficient bifunctional catalysts for overall water/seawater splitting.展开更多
基金supported by“Key Program for International S&T Cooperation Projects of China”from the Ministry of Science and Technology of China(Grant No.2019YFE0123000)the National Natural Science Foundation of China(Grant Nos.91961125 and 21905019)+2 种基金Science and Technology Project of Guangdong Province(No.2020B0101370001)Chemistry and Chemical Engineering Guangdong Laboratory(No.1932004)the Project from China Petrochemical Corporation(No.S20L00151).
文摘The catalytic activities are generally believed to be relevant to the electronic states of their active center, but understanding this relationship is usually difficult. Here, we design two types of catalysts for electrocatalytic urea via a coordination strategy in a metal–organic frameworks: Cu^(Ⅲ)-HHTP and Cu^(Ⅱ)-HHTP. Cu^(Ⅲ)-HHTP exhibits an improved urea production rate of 7.78 mmol h^(−1)g^(−1) and an enhanced Faradaic efficiency of 23.09% at-0.6 V vs. reversible hydrogen electrode, in sharp contrast to Cu^(Ⅱ)-HHTP.Isolated CuⅢspecies with S = 0 spin ground state are demonstrated as the active center in Cu^(Ⅲ)-HHTP, different from Cu^(Ⅱ) with S = 1/2 in Cu^(Ⅱ)-HHTP. We further demonstrate that isolated Cu^(Ⅲ)with an empty dx2-y20orbital in Cu^(Ⅲ)-HHTP experiences a single-electron migration path with a lower energy barrier in the C–N coupling process, while Cu^(Ⅱ)with a single-spin state( d_(x2-y2)^(1)) in Cu^(Ⅱ)-HHTP undergoes a two-electron migration pathway.
基金Sponsored by the Fundamental Research Fund for Central Universities(Grant No.2017XS063)
文摘The spherical oscillation of a gas bubble in liquids is important to growth in liquids during rectified diffusions( e. g., the onset of the sonoluminescence and the enhancement of sonochemical reactions). The present paper numerically shows stability maps( divided into four zones),in which gas bubbles maintain the linearly spherical oscillation without nonlinear disturbance of rectified diffusions within a large range of bubble radius. The critical pressures of spherical and diffusional oscillations are two decisive indexes determining the stability status. Specifically,the stability boundaries and influential factors( including acoustic parameters and gas concentration in liquids) were discussed and analyzed. The results show that the variations of gas concentration and acoustic parameters dramatically changed the stable status of the gas bubbles. The gas bubble maintained stable status when external parameters and gas concentration were set between the two critical values properly. The cases of high-frequency and low-frequency limits were also introduced at the end of the whole paper.
文摘In order to evaluate the emergency evacuation capacity of subway stations, the data collected were analyzed based on grounded theory, and an evaluation model of emergency evacuation capacity was constructed by combining the analytic hierarchy process (AHP). Finally, 12 secondary indicators (categories) and 4 primary indicators (main categories) were obtained, among which the primary indicators were management factors, emergency response, construction factors and personnel factors. From the weight value calculated by analytic hierarchy process, we can see that management factors and emergency response have great influence on the emergency evacuation capacity of subway stations. Therefore, we should focus on management factors and emergency response to improve the emergency evacuation capacity of subway stations.
基金This work was supported by National Natural Science Foundation of China(No.62172308,No.U1626107,No.61972297,No.62172144,and No.62062019).
文摘Power Shell has been widely deployed in fileless malware and advanced persistent threat(APT)attacks due to its high stealthiness and live-off-theland technique.However,existing works mainly focus on deobfuscation and malicious detection,lacking the malicious Power Shell families classification and behavior analysis.Moreover,the state-of-the-art methods fail to capture fine-grained features and semantic relationships,resulting in low robustness and accuracy.To this end,we propose Power Detector,a novel malicious Power Shell script detector based on multimodal semantic fusion and deep learning.Specifically,we design four feature extraction methods to extract key features from character,token,abstract syntax tree(AST),and semantic knowledge graph.Then,we intelligently design four embeddings(i.e.,Char2Vec,Token2Vec,AST2Vec,and Rela2Vec) and construct a multi-modal fusion algorithm to concatenate feature vectors from different views.Finally,we propose a combined model based on transformer and CNN-Bi LSTM to implement Power Shell family detection.Our experiments with five types of Power Shell attacks show that PowerDetector can accurately detect various obfuscated and stealth PowerShell scripts,with a 0.9402 precision,a 0.9358 recall,and a 0.9374 F1-score.Furthermore,through singlemodal and multi-modal comparison experiments,we demonstrate that PowerDetector’s multi-modal embedding and deep learning model can achieve better accuracy and even identify more unknown attacks.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.62075173 and 12274478)the National Key Research and Development Program of China(Grant Nos.2021YFB2800302 and 2021YFB2800604).
文摘Polarization manipulation of light is of great importance because it could promote development of wireless communications,biosensing,and polarization imaging.In order to use natural light more efficiently,it is highly demanded to design and fabricate high performance asymmetric polarization converters which could covert the natural light to one particular linearly polarized light with high efficiency.Traditionally,polarizers could be achieved by controllers with crystals and polymers exhibiting birefringence.However,the polarizers are bulky in size and the theoretical conversion efficiency of the polarizers is limited to 0.5 with unpolarized light incidence.In this paper,we propose a polarization converter which could preserve high transmission for one linearly polarized light and convert the orthogonal linearly polarized light to its cross-polarized with high transmittance based on a multi-layer chiral metasurface.Theoretical results show that normally incident y-polarized light preserves high transmittance for the wavelength range from 685 nm to 800 nm while the orthogonal normally incident x-polarized light is efficiently converted to the y-polarized light with high transmittance from 725 nm to 748 nm.Accordingly,for unpolarized light incidence,transmittance larger than 0.5 has been successfully achieved in a broadband wavelength range from 712 nm to 773 nm with a maximum transmittance of 0.58 at 732 nm.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFB4600400)the National Natural Science Foundation of China(Grant No.52275401).
文摘Flexible sensors with high sensitivity and stability are essential components of electronic skin,applicable to detecting human movement,monitoring physiological health,preventing diseases,and other domains.In this study,we utilized a straightforward and efficient femtosecond laser direct writing technique using phenolic resin(PR)as a carbon precursor to produce high-quality laser-induced graphene(LiG)characterized by high crystallinity and low defect density.The fabricated LIG underwent comprehensive characterization using SEM,Raman spectroscopy,XPS,and XRD.Subsequently,we developed strain sensors with a hexagonal honeycomb pattern and temperature sensors with a line pattern based on PR-derived LIG.The strain sensor exhibited an outstanding measurement factor of 4.16×104 with a rapid response time of 32 ms,which is applied to detect various movements like finger movements and human pulse.Meanwhile,the temperature sensor demonstrated a sensitivity of 1.49%/°C with a linear response range of 20-5o C.The PR-derived LIG shows promising potential for applications in human physiological health monitoring and other advanced wearable technologies.
基金from the National Natural Science Foundation of China(grant nos.51925303 and 91833304)the Program for JLU Science and Technology Innovative Research Team of China(JLUSTIRTgrant no.2019TD-33).
文摘Because iron is the richest transition-metal element in the earth’s crust,if iron complexes could be used as the emitters in organic light-emitting diodes(OLEDs),the cost of OLEDs would be reduced dramatically.Luminescent iron(III)complexes with low-spin d5 electronic structure theoretically possess spin-allowed doublet metal-to-ligand charge transfer(^(2)MLCT)emission,but little attention has been paid to their application in OLEDs.
基金supported by the Natural Science Foundation of Hebei Province(No.B2021208030)the College Students Innovation Training Program(Nos.202206224 and S2021113409001).
文摘Designing and synthesizing cost-effective bifunctional catalysts for overall alkaline water/seawater splitting is still a huge challenge for hydrogen production.Herein,Co/Ni/Fe/Mn based-amorphous high-entropy phosphoxide self-standing electrode(CNFMPO)is synthesized by the facile and fast electrodeposition method.CNFMPO exhibits excellent bifunctional electrocatalytic performances on alkaline water/seawater electrolysis.The hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)overpotentials of CNFMPO in alkaline water/seawater are as low as 43/73 and 252/282 mV to reach a current density of 10 mA cm^(-2),respectively.Additionally,two-electrode electrolyzers with CNFMPO||CNFMPO successfully achieve the current density of 10 mA cm^(-2) at low voltages of 1.54 and 1.56 V for overall alkaline water/seawater splitting,respectively.CNFMPO exhibits satisfactory long-term stability on overall alkaline water/seawater splitting for the surface reconstruction into active metal hydroxide/(oxy)hydroxide,phosphite,and phosphate.Moreover,no hypochlorite is detected during seawater electrolysis for the beneficial chlorite oxidation inhibition of the reconstructed phosphite and phosphate.The excellent catalytic performances of CNFMPO are due to the unique amorphous structure,multi-component synergistic effect,beneficial electronic structure modulation,and surface reconstruction during the catalytic reaction process.Therefore,CNFMPO has shown potential promotion to the development of the water/seawater splitting industry as a promising substituent for noble-metal electrocatalysts.This work provides new insights into the design of efficient bifunctional catalysts for overall water/seawater splitting.