The lattice dynamics of a high Al composition semiconductor alloy,Al_(0.86)Ga_(0.14)N,in comparison with intrinsic GaN and AlN are studied by Stokes/anti-Stokes Raman spectroscopy in the temperature range of 85–823 K...The lattice dynamics of a high Al composition semiconductor alloy,Al_(0.86)Ga_(0.14)N,in comparison with intrinsic GaN and AlN are studied by Stokes/anti-Stokes Raman spectroscopy in the temperature range of 85–823 K.The phonon anharmonic effect in Al_(0.86)Ga_(0.14)N is found to be stronger than that in GaN,revealing low thermal conductivity in the semiconductor alloy.Multi-phonon coupling behavior is analyzed by both Stokes Raman and anti-Stokes Raman spectroscopy.It is interesting to find that the anti-Stokes scattering exhibits stronger three-phonon coupling than the Stokes scattering,which may be due to the fact that the anti-stokes scattering process is generated from an excited state and the scattered photons have higher energies.The Stokes/anti-Stokes temperature correction factor β for Raman modes in Al_(0.86)Ga_(0.14)N alloy are all smaller than those of the corresponding intrinsic modes in GaN and AlN.The reasons for the difference in b can be attributed to three aspects,including the equipment setups,materials properties(the binding energy)and the coupling strength of Raman scattering and the sample.展开更多
The wear of work rolls significantly affects the production efficiency and product quality.However,existing methods for wear assessment fail to effectively quantify work roll surface wear conditions,thereby affecting ...The wear of work rolls significantly affects the production efficiency and product quality.However,existing methods for wear assessment fail to effectively quantify work roll surface wear conditions,thereby affecting the quality control of steel strips and maintenance strategies for rolls.To accurately assess the wear conditions of hot-rolling work rolls,this study initially established an apparatus for capturing high-precision roll surfaces images.Subsequently,a quantitative assessment of common surface wear morphologies was conducted,and a hot-rolling work roll surface wear dataset was constructed.The MobileNetV2 convolutional neural network(CNN),augmented by transfer learning,was employed to develop a MobileNetV2-wear detection and classification(WDC)surface wear grading model.A comparison with mainstream CNN models revealed that the MobileNetV2-WDC model achieved high-speed(21.92 ms)and accurate(96.86%)grading with minimal model parameters(2.27 M)and size(27 M),meeting the industrial efficiency and practicality requirements.A visual analysis of the model classification errors was conducted,outlining paths for further optimization.This study provides an efficient and accurate solution for detecting and grading surface wear on hot-rolling work rolls,enhancing product quality and extending the lifespan of rolls.展开更多
The worldwide large-scale commercial deployment of 5G has commenced in 2020 for supporting enhanced Mobile BroadBand(eMBB),ultra-Reliable and Low-Latency Communications(uRLLC),and massive Machine-Type Communications(m...The worldwide large-scale commercial deployment of 5G has commenced in 2020 for supporting enhanced Mobile BroadBand(eMBB),ultra-Reliable and Low-Latency Communications(uRLLC),and massive Machine-Type Communications(mMTC)services.Nevertheless,the upsurge of Artificial Intelligence(AI)-powered applications,the developmental law of one-decade-one-generation of wireless communications and the inherent limitations of 5G have also been spurring the industry and academia to dedicate their efforts to the research of future 6G wireless systems.6G will be a disruptive,pervasive,intelligent,and endogenous wireless system,which will revolutionize all walks of life and accelerate the transformation and innovation of the global society.In this paper,we present a forward-looking,comprehensive and in-depth analysis and technical identification of 6G.Specifically,we firstly introduce the fundamental theories of 6G in terms of potential requirements.Then,we focus our attention on the discussion of promising key technologies in terms of spectrum,air interface,delay,access,energy consumption,coverage,AI,electromagnetism,interaction,etc.展开更多
Warhead power assessment of the anti-ship missile plays a vital role in determining the optimal design of missile, thus having important strategic research significance. However, in the assessment process, expert’s j...Warhead power assessment of the anti-ship missile plays a vital role in determining the optimal design of missile, thus having important strategic research significance. However, in the assessment process, expert’s judgement will directly affect the assessment accuracy. In addition,there are many criteria involved in the missile design alternatives. Some criteria with poor performance may be compensated by other criteria with excellent performance, and then it is impossible to find the truly optimal alternative. Aimed at solving these problems, this paper proposes a synthetical assessment process based on fuzzy hesitant linguistic term set and the Gained and Lost Dominance Score(GLDS) method. In order to improve the assessment accuracy of experts and solve the problem that experts generate different opinions, combined with the advantages of fuzzy hesitant sets and linguistic term sets, the double hierarchy hesitant fuzzy linguistic term sets are used in this paper to improve the accuracy of expert’s judgement. In order to effectively combine expert’s experience with the data of criteria, the evidence theory and entropy weight method are used to transfer the expert’s judgement to the weight. In order to avoid selecting defective alternative of missile design, the GLDS is used to fuse expert information and criteria information. Sensitivity analysis shows that the assessment process has sensitivity to some extent. However, when the fluctuation of expert’s assessment makes the fluctuation of θ in the range of-5% to 5%, the impact on the results is not quite conspicuous. The analysis of calculation result and comparative analysis show that the assessment process proposed in this paper is accurate enough, has great advantage in selecting the current and potential optimal alternative of missile design, and avoids the alternatives with low criteria performance that cannot be compensated by other criteria being selected.展开更多
In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2 Fe17 compounds and their paraffin composites. It is found that the introduction of S...In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2 Fe17 compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2 Fe17 compounds, making the R2 Fe17 exSix-paraffin composites excellent microwave absorption materials(MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε’ by about 40%e50%, which finally enhances the performance of the microwave absorption. The peak frequency(fRL) of the reflection loss(RL) curve moves toward high frequency domain and the qualified bandwidth(QB, RL≤-10 dB) increases remarkably. The maximum QB of 3.3 GHz(12.0 e15.3 GHz) is obtained for the Sm1.5 Y0.5 Fe15 Si2-paraffin composite(d = 1.0 mm) and the maximum RL of -53.6 dB is achieved for Nd2 Fe15 Si2-paraffin composite(d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites.展开更多
In order to assess effects of Summer Fishing Moratorium (SFM) in Daya Bay, variations in stock density, fish diversity, fish species composition, fish body length and weight, and bio-environments during the pre-SFM (M...In order to assess effects of Summer Fishing Moratorium (SFM) in Daya Bay, variations in stock density, fish diversity, fish species composition, fish body length and weight, and bio-environments during the pre-SFM (May in 2015) and post-SFM (August in 2015) in Daya Bay were analyzed, based on trawl survey data. Results showed that the average stock density in the post-SFM was 5.65 times of that in the pre-SFM, and the average species numbers in the post-SFM was 1.76 times of that in the pre-SFM. Analysis of fish body length and weight indicated that fish grew faster during the SFM, and body weight was more uniform in the post-SFM. In the post-SFM, the Shannon-Wiener diversity index and Pielou evenness index increased by 0.36 and 0.14, respectively, indicating that the fish biodiversity and community structure improved. SFM alleviated fishing intensity, recovered and conserved coastal fish resource. In order to improve efficiency and impacts of SFM and to promote sustainable development of coastal fish resource, prolonging the time of SFM, reducing the number of coastal fishing boats and enforcing the conservation of fish resources were suggested.展开更多
Dapeng Bay is a typical offshore fisheries area in the South China Sea (SCS). In order to understand the fishery resources, seasonal variations of species composition, dominant species composition, standardized catch ...Dapeng Bay is a typical offshore fisheries area in the South China Sea (SCS). In order to understand the fishery resources, seasonal variations of species composition, dominant species composition, standardized catch per unit effort (SCPUE) and community diversity of fishery resources in Dapeng Bay, China were analyzed based on trawl survey data in spring (March) and summer (May) of 2013 as well as autumn (August) and winter (December) of 2012. Results demonstrated that there are 113 fishery species, which belong to 78 categories, 50 families, 14 catalogues, 3 classes. There are the most species in summer (61 species) and about 56 species in other seasons. In all four seasons, fish and crustacea are dominant species, and there are the fewest cephalopoda. High values of SCPUE occur in spring and autumn, reaching 5.65 and 5.33, respectively. SCPUE is generally low in summer, ranging between 0.52 - 0.96. Fish biodiversity is the highest in summer and the lowest in winter. Among biodiversity, Shannon-Wiener diversity index, Margalef diversity index and Pielou evenness index vary in the same trend. They are decreasing from summer, spring, autumn to winter successively. Therefore, there are violent seasonal variation of species composition, quantity and structure of fishery resources in Dapeng Bay. The community structure and function are highly stable in summer, but they have poor stability in autumn and winter. This research can provide scientific references for protection and sustainable use of fishery resources in typical offshore fisheries area in the SCS.展开更多
With the further development of service-oriented,performance-based contracting(PBC)has been widely adopted in industry and manufacturing.However,maintenance optimization problems under PBC have not received enough att...With the further development of service-oriented,performance-based contracting(PBC)has been widely adopted in industry and manufacturing.However,maintenance optimization problems under PBC have not received enough attention.To further extend the scope of PBC’s application in the field of maintenance optimization,we investigate the condition-based maintenance(CBM)optimization for gamma deteriorating systems under PBC.Considering the repairable single-component system subject to the gamma degradation process,this paper proposes a CBM optimization model to maximize the profit and improve system performance at a relatively low cost under PBC.In the proposed CBM model,the first inspection interval has been considered in order to reduce the inspection frequency and the cost rate.Then,a particle swarm algorithm(PSO)and related solution procedure are presented to solve the multiple decision variables in our proposed model.In the end,a numerical example is provided so as to demonstrate the superiority of the presented model.By comparing the proposed policy with the conventional ones,the superiority of our proposed policy is proved,which can bring more profits to providers and improve performance.Sensitivity analysis is conducted in order to research the effect of corrective maintenance cost and time required for corrective maintenance on optimization policy.A comparative study is given to illustrate the necessity of distinguishing the first inspection interval or not.展开更多
Seasonal variations and causes for these were elaborated for fishery resources in Shenzhen sea area,to provide scientific basis for sustainable utilization and management of fishery resources in typical fisheries of S...Seasonal variations and causes for these were elaborated for fishery resources in Shenzhen sea area,to provide scientific basis for sustainable utilization and management of fishery resources in typical fisheries of South China Sea coasts. Based on the data of fishery resources collected through trawl surveys in Egong Bay fisheries area,Shenzhen,from August( autumn) and December( winter) of 2012 to March(spring) and May(summer) of 2013,seasonal variation of nekton species composition,stock density,dominant species composition,size spectra and biodiversity were studied. Results showed that there were 113 species of nekton in Shenzhen sea area,which belonged to 78 genus,50 families,14 orders and 3 classes. The number of species was the largest in summer(61 species) and smallest in autumn(53 species). In spring and winter,there was 56 species. The stock density and individual density of nekton were the minimum in summer(5950. 20 kg/km2 and 356. 45 ind/km2,respectively),whereas the percentage of fish stock density and individual density were the highest in summer(51. 99%and 42. 19%). The seasonal variations of size spectra indicated that fishing intensity was the highest in autumn,and was the lowest in summer. Additionally,biodiversity index presented significant seasonal variations,including Shannon-Wiener diversity index( H '),Margalef richness index( D') and Pielou evenness index( J'),with the same trend as summer > spring > autumn > winter. In conclusion,there are clear seasonal variations in the nekton species,biomass and structure in Egong Bay fisheries area in Shenzhen. Due to the difference in fishing intensity in different seasons( low intensity in summer and high intensity in autumn),community structure and function in summer are more stable than that in autumn and winter. Particularly,with the increase in the fishing intensity in autumn,k selection species will be replaced by r selection species.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.12374013)the Fundamental Research Funds for the Central Universities(Grant No.2020SCUNL107).
文摘The lattice dynamics of a high Al composition semiconductor alloy,Al_(0.86)Ga_(0.14)N,in comparison with intrinsic GaN and AlN are studied by Stokes/anti-Stokes Raman spectroscopy in the temperature range of 85–823 K.The phonon anharmonic effect in Al_(0.86)Ga_(0.14)N is found to be stronger than that in GaN,revealing low thermal conductivity in the semiconductor alloy.Multi-phonon coupling behavior is analyzed by both Stokes Raman and anti-Stokes Raman spectroscopy.It is interesting to find that the anti-Stokes scattering exhibits stronger three-phonon coupling than the Stokes scattering,which may be due to the fact that the anti-stokes scattering process is generated from an excited state and the scattered photons have higher energies.The Stokes/anti-Stokes temperature correction factor β for Raman modes in Al_(0.86)Ga_(0.14)N alloy are all smaller than those of the corresponding intrinsic modes in GaN and AlN.The reasons for the difference in b can be attributed to three aspects,including the equipment setups,materials properties(the binding energy)and the coupling strength of Raman scattering and the sample.
基金Supported by National Key Research and Development Program of China(Grant No.2018YFA0707300)Hebei Natural Science Foundation(Grant No.E2023203260)+1 种基金Scientific and Technological Research Projects of Hebei Higher Education Institutions(Grant No.CXY2024009)Central Government Guide Local Science and Technology Development Fund Project(Grant No.216Z1602G)。
文摘The wear of work rolls significantly affects the production efficiency and product quality.However,existing methods for wear assessment fail to effectively quantify work roll surface wear conditions,thereby affecting the quality control of steel strips and maintenance strategies for rolls.To accurately assess the wear conditions of hot-rolling work rolls,this study initially established an apparatus for capturing high-precision roll surfaces images.Subsequently,a quantitative assessment of common surface wear morphologies was conducted,and a hot-rolling work roll surface wear dataset was constructed.The MobileNetV2 convolutional neural network(CNN),augmented by transfer learning,was employed to develop a MobileNetV2-wear detection and classification(WDC)surface wear grading model.A comparison with mainstream CNN models revealed that the MobileNetV2-WDC model achieved high-speed(21.92 ms)and accurate(96.86%)grading with minimal model parameters(2.27 M)and size(27 M),meeting the industrial efficiency and practicality requirements.A visual analysis of the model classification errors was conducted,outlining paths for further optimization.This study provides an efficient and accurate solution for detecting and grading surface wear on hot-rolling work rolls,enhancing product quality and extending the lifespan of rolls.
文摘The worldwide large-scale commercial deployment of 5G has commenced in 2020 for supporting enhanced Mobile BroadBand(eMBB),ultra-Reliable and Low-Latency Communications(uRLLC),and massive Machine-Type Communications(mMTC)services.Nevertheless,the upsurge of Artificial Intelligence(AI)-powered applications,the developmental law of one-decade-one-generation of wireless communications and the inherent limitations of 5G have also been spurring the industry and academia to dedicate their efforts to the research of future 6G wireless systems.6G will be a disruptive,pervasive,intelligent,and endogenous wireless system,which will revolutionize all walks of life and accelerate the transformation and innovation of the global society.In this paper,we present a forward-looking,comprehensive and in-depth analysis and technical identification of 6G.Specifically,we firstly introduce the fundamental theories of 6G in terms of potential requirements.Then,we focus our attention on the discussion of promising key technologies in terms of spectrum,air interface,delay,access,energy consumption,coverage,AI,electromagnetism,interaction,etc.
文摘Warhead power assessment of the anti-ship missile plays a vital role in determining the optimal design of missile, thus having important strategic research significance. However, in the assessment process, expert’s judgement will directly affect the assessment accuracy. In addition,there are many criteria involved in the missile design alternatives. Some criteria with poor performance may be compensated by other criteria with excellent performance, and then it is impossible to find the truly optimal alternative. Aimed at solving these problems, this paper proposes a synthetical assessment process based on fuzzy hesitant linguistic term set and the Gained and Lost Dominance Score(GLDS) method. In order to improve the assessment accuracy of experts and solve the problem that experts generate different opinions, combined with the advantages of fuzzy hesitant sets and linguistic term sets, the double hierarchy hesitant fuzzy linguistic term sets are used in this paper to improve the accuracy of expert’s judgement. In order to effectively combine expert’s experience with the data of criteria, the evidence theory and entropy weight method are used to transfer the expert’s judgement to the weight. In order to avoid selecting defective alternative of missile design, the GLDS is used to fuse expert information and criteria information. Sensitivity analysis shows that the assessment process has sensitivity to some extent. However, when the fluctuation of expert’s assessment makes the fluctuation of θ in the range of-5% to 5%, the impact on the results is not quite conspicuous. The analysis of calculation result and comparative analysis show that the assessment process proposed in this paper is accurate enough, has great advantage in selecting the current and potential optimal alternative of missile design, and avoids the alternatives with low criteria performance that cannot be compensated by other criteria being selected.
基金Project supported by the National Key Research and Development Program of China(2016YFB0700901,2017YFA0403701)National Natural Science Foundation of China(51731001,11675006,11805006)
文摘In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R2 Fe17 compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R2 Fe17 compounds, making the R2 Fe17 exSix-paraffin composites excellent microwave absorption materials(MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε’ by about 40%e50%, which finally enhances the performance of the microwave absorption. The peak frequency(fRL) of the reflection loss(RL) curve moves toward high frequency domain and the qualified bandwidth(QB, RL≤-10 dB) increases remarkably. The maximum QB of 3.3 GHz(12.0 e15.3 GHz) is obtained for the Sm1.5 Y0.5 Fe15 Si2-paraffin composite(d = 1.0 mm) and the maximum RL of -53.6 dB is achieved for Nd2 Fe15 Si2-paraffin composite(d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites.
文摘In order to assess effects of Summer Fishing Moratorium (SFM) in Daya Bay, variations in stock density, fish diversity, fish species composition, fish body length and weight, and bio-environments during the pre-SFM (May in 2015) and post-SFM (August in 2015) in Daya Bay were analyzed, based on trawl survey data. Results showed that the average stock density in the post-SFM was 5.65 times of that in the pre-SFM, and the average species numbers in the post-SFM was 1.76 times of that in the pre-SFM. Analysis of fish body length and weight indicated that fish grew faster during the SFM, and body weight was more uniform in the post-SFM. In the post-SFM, the Shannon-Wiener diversity index and Pielou evenness index increased by 0.36 and 0.14, respectively, indicating that the fish biodiversity and community structure improved. SFM alleviated fishing intensity, recovered and conserved coastal fish resource. In order to improve efficiency and impacts of SFM and to promote sustainable development of coastal fish resource, prolonging the time of SFM, reducing the number of coastal fishing boats and enforcing the conservation of fish resources were suggested.
文摘Dapeng Bay is a typical offshore fisheries area in the South China Sea (SCS). In order to understand the fishery resources, seasonal variations of species composition, dominant species composition, standardized catch per unit effort (SCPUE) and community diversity of fishery resources in Dapeng Bay, China were analyzed based on trawl survey data in spring (March) and summer (May) of 2013 as well as autumn (August) and winter (December) of 2012. Results demonstrated that there are 113 fishery species, which belong to 78 categories, 50 families, 14 catalogues, 3 classes. There are the most species in summer (61 species) and about 56 species in other seasons. In all four seasons, fish and crustacea are dominant species, and there are the fewest cephalopoda. High values of SCPUE occur in spring and autumn, reaching 5.65 and 5.33, respectively. SCPUE is generally low in summer, ranging between 0.52 - 0.96. Fish biodiversity is the highest in summer and the lowest in winter. Among biodiversity, Shannon-Wiener diversity index, Margalef diversity index and Pielou evenness index vary in the same trend. They are decreasing from summer, spring, autumn to winter successively. Therefore, there are violent seasonal variation of species composition, quantity and structure of fishery resources in Dapeng Bay. The community structure and function are highly stable in summer, but they have poor stability in autumn and winter. This research can provide scientific references for protection and sustainable use of fishery resources in typical offshore fisheries area in the SCS.
文摘With the further development of service-oriented,performance-based contracting(PBC)has been widely adopted in industry and manufacturing.However,maintenance optimization problems under PBC have not received enough attention.To further extend the scope of PBC’s application in the field of maintenance optimization,we investigate the condition-based maintenance(CBM)optimization for gamma deteriorating systems under PBC.Considering the repairable single-component system subject to the gamma degradation process,this paper proposes a CBM optimization model to maximize the profit and improve system performance at a relatively low cost under PBC.In the proposed CBM model,the first inspection interval has been considered in order to reduce the inspection frequency and the cost rate.Then,a particle swarm algorithm(PSO)and related solution procedure are presented to solve the multiple decision variables in our proposed model.In the end,a numerical example is provided so as to demonstrate the superiority of the presented model.By comparing the proposed policy with the conventional ones,the superiority of our proposed policy is proved,which can bring more profits to providers and improve performance.Sensitivity analysis is conducted in order to research the effect of corrective maintenance cost and time required for corrective maintenance on optimization policy.A comparative study is given to illustrate the necessity of distinguishing the first inspection interval or not.
基金Supported by National Key Technology Research and Development Program of the Ministry of Science and Technology of China(2012BAD18B01&2012BAD18B02)Science and Technology Planning Project of Shenzhen(JSGG20141015154342147&JCYJ20160331141759795)
文摘Seasonal variations and causes for these were elaborated for fishery resources in Shenzhen sea area,to provide scientific basis for sustainable utilization and management of fishery resources in typical fisheries of South China Sea coasts. Based on the data of fishery resources collected through trawl surveys in Egong Bay fisheries area,Shenzhen,from August( autumn) and December( winter) of 2012 to March(spring) and May(summer) of 2013,seasonal variation of nekton species composition,stock density,dominant species composition,size spectra and biodiversity were studied. Results showed that there were 113 species of nekton in Shenzhen sea area,which belonged to 78 genus,50 families,14 orders and 3 classes. The number of species was the largest in summer(61 species) and smallest in autumn(53 species). In spring and winter,there was 56 species. The stock density and individual density of nekton were the minimum in summer(5950. 20 kg/km2 and 356. 45 ind/km2,respectively),whereas the percentage of fish stock density and individual density were the highest in summer(51. 99%and 42. 19%). The seasonal variations of size spectra indicated that fishing intensity was the highest in autumn,and was the lowest in summer. Additionally,biodiversity index presented significant seasonal variations,including Shannon-Wiener diversity index( H '),Margalef richness index( D') and Pielou evenness index( J'),with the same trend as summer > spring > autumn > winter. In conclusion,there are clear seasonal variations in the nekton species,biomass and structure in Egong Bay fisheries area in Shenzhen. Due to the difference in fishing intensity in different seasons( low intensity in summer and high intensity in autumn),community structure and function in summer are more stable than that in autumn and winter. Particularly,with the increase in the fishing intensity in autumn,k selection species will be replaced by r selection species.
