Terahertz communication technology can provide abundant frequency resources,strong confidentiality,antijamming capability,communication tracking capability and the ability to achieve highspeed data transmissions and c...Terahertz communication technology can provide abundant frequency resources,strong confidentiality,antijamming capability,communication tracking capability and the ability to achieve highspeed data transmissions and can serve as an important technical method for high-speed communications in the future.Among these terahertz communication technologies,terahertz direct modulation technology is a key means to achieve low system complexity and power consumption.In this paper,a review and outlook of terahertz direct modulation technology are proposed from the aspects of high-electron-mobilitytransistor-based terahertz direct modulation,parallelswitch terahertz direct modulation,diode-based terahertz direct modulation,quantum cascade laser-based terahertz direct modulation and new-material-based terahertz direct modulation.We hope through this paper that more readers can gain knowledge about the development and challenges of terahertz direct modulation technology for high-speed communication systems,thus promoting the development of high-speed terahertz communication technology based on direct modulation.展开更多
Proton exchange membranes(PEMs),which are crucial fuel cell parts,play an important role in the field of energy science.However,the further development of conventional PEMs based on synthetic polymers is greatly limit...Proton exchange membranes(PEMs),which are crucial fuel cell parts,play an important role in the field of energy science.However,the further development of conventional PEMs based on synthetic polymers is greatly limited by high energy consumption and difficult degradation.In this work,we reported the fabrication of a novel viscose-based PEM via cationic modification and dyeing treatment with the reactive dyes KE-7B1.High-efficiency proton transmission channels can be constructed due to the for-mation of the complex internal three-dimensional network of the as-prepared viscose-based PEM.Hþconductivity(sHþ)and water uptake are intensively investigated by changing the cationic agents and KE-7B1,and the maximum sHþreaches 44.19 mS/cm at 80℃and 98%relative humidity(RH).Furthermore,the prepared membrane shows the lowest calculated activation energy value(12.25 kJ/mol),indicating that both Grotthuss and Vehicle mechanisms play an important role in ionic transport.The membrane chemical structure and micromorphology are analyzed and the proton transmission modes are explored in detail,supplemented with research on the hydrophilic/hydrophobic characteristics and crystallinity of the membranes.The application stability of the membranes is also evaluated analyzing the thermal,mechanical,and oxygen resistance properties,and the results show that all the prepared membranes can maintain good thermal stability within 200℃.The maximum tensile strength reaches 42.12 MPa,and the mass losses of the membranes soaked in 30%(in mass,same below)H_(2)O_(2)solution for 120 h can be restricted to 10%.Therefore,as a novel PEM,the obtained dye viscose-based membranes show great potential for application in fuel cells.展开更多
This paper presents a mechanical reliability study of 3-dB waveguide hybrid couplers in submillimeter and terahertz bands.To show the necessity of improving the mechanical properties of the coupler’s branch in submil...This paper presents a mechanical reliability study of 3-dB waveguide hybrid couplers in submillimeter and terahertz bands.To show the necessity of improving the mechanical properties of the coupler’s branch in submillimeter and terahertz bands,a comprehensive study regarding the displacement of hybrid branch variation with varying width-length ratio and height-length ratio has been completed.In addition,a modified 3-dB waveguide hybrid coupler is designed and presented.Compared with the traditional branch structure,the proposed hybrid consists of a modified middle branch with circular cutouts at the top and bottom on both sides instead of the traditional rectangle branch,which increases the branch size and improves its mechanical reliability while achieving the same performance.Simulation results show that the deformation of the modified hybrid branch is 22%less than those of other traditional structure designs under the same stress.In practice,a vibration experiment is set up to verify the mechanical reliability of hybrid couplers.Measurement results show that the experiment deteriorates the coupling performance.Experimental results verify that the performance of the novel structure coupler is better than that of a traditional structure branch hybrid coupler under the same electrical properties.展开更多
Machine learning(ML)techniques and algorithms have been successfully and widely used in various areas including software engineering tasks.Like other software projects,bugs are also common in ML projects and libraries...Machine learning(ML)techniques and algorithms have been successfully and widely used in various areas including software engineering tasks.Like other software projects,bugs are also common in ML projects and libraries.In order to more deeply understand the features related to bug fixing in ML projects,we conduct an empirical study with 939 bugs from five ML projects by manually examining the bug categories,fixing patterns,fixing scale,fixing duration,and types of maintenance.The results show that(1)there are commonly seven types of bugs in ML programs;(2)twelve fixing patterns are typically used to fix the bugs in ML programs;(3)68.80%of the patches belong to micro-scale-fix and small-scale-fix;(4)66.77%of the bugs in ML programs can be fixed within one month;(5)45.90%of the bug fixes belong to corrective activity from the perspective of software maintenance.Moreover,we perform a questionnaire survey and send them to developers or users of ML projects to validate the results in our empirical study.The results of our empirical study are basically consistent with the feedback from developers.The findings from the empirical study provide useful guidance and insights for developers and users to effectively detect and fix bugs in MLprojects.展开更多
Hydroxyl anion conducting membrane composed of poly(vinyl alcohol)(PVA),poly(diallyldimethylammonium chloride)(PDDA),and hydroxylated multiwalled carbon nanotubes(MWCNTs-OH)have been synthesized via a facile blending-...Hydroxyl anion conducting membrane composed of poly(vinyl alcohol)(PVA),poly(diallyldimethylammonium chloride)(PDDA),and hydroxylated multiwalled carbon nanotubes(MWCNTs-OH)have been synthesized via a facile blending-casting method assisted by a hot-chemical cross-linking process.Fourier-transform infrared spectroscopy(FTIR)and scanning electron microscopy(SEM)showed that PDDA and MWCNTs-OH were successfully introduced into the PVA matrix and MWCNTs-OH could effectively improve the network structure of the membrane.With the addition of MWCNTs-OH,many properties of the membranes such as thermal,chemical,mechanical stability and swelling property were improved significantly.Most prominent is the improvement of mechanical property,where the PVA/PDDA/MWCNTs-OH(1:0.5/3 wt.%)membrane showed high tensile strength of 40.3 MPa,tensile elongation of 12.3%and high Young's modulus of 782.8 MPa.Moreover,MWCNTs-OH bound the polymer chains in the membranes more compactly,resulting in decreased water uptake.By tuning the mass fraction of PVA,PDDA,and MWCNTs-OH in the membrane,the maximum OH-conductivity(0.030 S cm^(-1)at room temperature)was achieved for the composition of 0.5 wt.%MWCNTs-OH doped with the PVA:PDDA(1:0.5 by mass)blend.The membranes showed excellent oxidative stability when treated with both a solution of H_(2)O_(2)(30 wt.%)at room temperature and in a hot KOH solution(8 M)at 80℃.Based on the full aliphatic structure membrane(PVA/PDDA-OH/1 wt.%MWCNTs-OH),membrane electrode assemblies(MEAs)fabricated with Pt/C cathode catalyst can achieve power densities of 41.3 mW cm^(-2)and 66.4 mW cm^(-2)in a H_(2)/O_(2)system at room temperature and 40℃,respectively.Using CoPc as the Pt-free cathode catalyst,power densities of 9.1 mW cm^(-2)and 14.0 mW cm^(-2)at room temperature and 40℃ were obtained,respectively.展开更多
Achieving ultra-precise wide-range terahertz(THz)phase modulation has been a long-standing challenge due to the short wavelength and sensitive phase of THz waves.This paper proposes a new ultra-high precision phase co...Achieving ultra-precise wide-range terahertz(THz)phase modulation has been a long-standing challenge due to the short wavelength and sensitive phase of THz waves.This paper proposes a new ultra-high precision phase control method employing a digitally coding needle meta-chip embedded in a waveguide.The needle tips can effectively couple THz waves via the charge aggregation effect.By controlling the Schottky diodes with coding voltages,the charge on each meta-structure part can be tuned to form strong or weak resonances,producing phase shifts.Crucially,the massive charge accumulation and the sub-λ∕10 distance between needle tips lead to near-field coupling among multiple tips.Therefore,modulation of the charge at each tip by multichannel coding voltages enables combined resonance tuning of THz waves,yielding a nonlinear phase superposition.Here,a meta-chip containing 8 needle meta-structure units is demonstrated,which breaks through the precision limitation of independent units and realizes super-resolution precision phase modulation similar to super-resolution imaging.In the 213–227 GHz band,we achieve a phase shift exceeding 180°with 11.25°accuracy,and a phase shift of over 170°with an accuracy of 3°.This super-resolution phase modulation strategy provides a new idea for future highprecision applications of THz integrated systems.展开更多
基金the The National Key Research and Development Program of China under Contract No.2018YFB1801503National Natural Science Foundation of China under Contract Nos.61931006,61921002,61771327,61927813,61775229,61991430 and 62022022.
文摘Terahertz communication technology can provide abundant frequency resources,strong confidentiality,antijamming capability,communication tracking capability and the ability to achieve highspeed data transmissions and can serve as an important technical method for high-speed communications in the future.Among these terahertz communication technologies,terahertz direct modulation technology is a key means to achieve low system complexity and power consumption.In this paper,a review and outlook of terahertz direct modulation technology are proposed from the aspects of high-electron-mobilitytransistor-based terahertz direct modulation,parallelswitch terahertz direct modulation,diode-based terahertz direct modulation,quantum cascade laser-based terahertz direct modulation and new-material-based terahertz direct modulation.We hope through this paper that more readers can gain knowledge about the development and challenges of terahertz direct modulation technology for high-speed communication systems,thus promoting the development of high-speed terahertz communication technology based on direct modulation.
基金supported by Natural Science Foun-dation of Jiangsu,China(Project Number:BK20201061)The Jiangsu Agricultural Science and Technology Innovation Fund(Project Number:CX(21)3086)+1 种基金Shanghai Engineering Research Center of Marine Renewable Energy(Grant No.19DZ2254800)The authors would like to thank to Guchuan Machinery Co.,LTD for offering some instruments.
文摘Proton exchange membranes(PEMs),which are crucial fuel cell parts,play an important role in the field of energy science.However,the further development of conventional PEMs based on synthetic polymers is greatly limited by high energy consumption and difficult degradation.In this work,we reported the fabrication of a novel viscose-based PEM via cationic modification and dyeing treatment with the reactive dyes KE-7B1.High-efficiency proton transmission channels can be constructed due to the for-mation of the complex internal three-dimensional network of the as-prepared viscose-based PEM.Hþconductivity(sHþ)and water uptake are intensively investigated by changing the cationic agents and KE-7B1,and the maximum sHþreaches 44.19 mS/cm at 80℃and 98%relative humidity(RH).Furthermore,the prepared membrane shows the lowest calculated activation energy value(12.25 kJ/mol),indicating that both Grotthuss and Vehicle mechanisms play an important role in ionic transport.The membrane chemical structure and micromorphology are analyzed and the proton transmission modes are explored in detail,supplemented with research on the hydrophilic/hydrophobic characteristics and crystallinity of the membranes.The application stability of the membranes is also evaluated analyzing the thermal,mechanical,and oxygen resistance properties,and the results show that all the prepared membranes can maintain good thermal stability within 200℃.The maximum tensile strength reaches 42.12 MPa,and the mass losses of the membranes soaked in 30%(in mass,same below)H_(2)O_(2)solution for 120 h can be restricted to 10%.Therefore,as a novel PEM,the obtained dye viscose-based membranes show great potential for application in fuel cells.
基金Project supported by the National Natural Science Foundation of China(Nos.61771116 and 62022022)the National Key R&D Program of China(No.2018YFB1801502)the China Postdoctoral Science Foundation(No.2021TQ0057)。
文摘This paper presents a mechanical reliability study of 3-dB waveguide hybrid couplers in submillimeter and terahertz bands.To show the necessity of improving the mechanical properties of the coupler’s branch in submillimeter and terahertz bands,a comprehensive study regarding the displacement of hybrid branch variation with varying width-length ratio and height-length ratio has been completed.In addition,a modified 3-dB waveguide hybrid coupler is designed and presented.Compared with the traditional branch structure,the proposed hybrid consists of a modified middle branch with circular cutouts at the top and bottom on both sides instead of the traditional rectangle branch,which increases the branch size and improves its mechanical reliability while achieving the same performance.Simulation results show that the deformation of the modified hybrid branch is 22%less than those of other traditional structure designs under the same stress.In practice,a vibration experiment is set up to verify the mechanical reliability of hybrid couplers.Measurement results show that the experiment deteriorates the coupling performance.Experimental results verify that the performance of the novel structure coupler is better than that of a traditional structure branch hybrid coupler under the same electrical properties.
基金This work was supported partially by the National Natural Science Foundation of China(Grant Nos.61872312,61972335,61472344,61611540347,61402396 and 61662021)partially by the Open Funds of State Key Laboratory for Novel Software Technology of Nanjing University(KFKT2020B15 and KFKT2020B16)+3 种基金partially by the Jiangsu“333”Project,partially by the Six Talent Peaks Project in Jiangsu Province(RJFW-053)partially by the Natural Science Foundation of Jiangsu(BK20181353)partially by the Yangzhou city-Yangzhou University Science and Technology Cooperation Fund Project(YZU201803),by the CERNET Innovation Project(NGII20180607)partially by the Yangzhou University Top-level Talents Support Program(2019).
文摘Machine learning(ML)techniques and algorithms have been successfully and widely used in various areas including software engineering tasks.Like other software projects,bugs are also common in ML projects and libraries.In order to more deeply understand the features related to bug fixing in ML projects,we conduct an empirical study with 939 bugs from five ML projects by manually examining the bug categories,fixing patterns,fixing scale,fixing duration,and types of maintenance.The results show that(1)there are commonly seven types of bugs in ML programs;(2)twelve fixing patterns are typically used to fix the bugs in ML programs;(3)68.80%of the patches belong to micro-scale-fix and small-scale-fix;(4)66.77%of the bugs in ML programs can be fixed within one month;(5)45.90%of the bug fixes belong to corrective activity from the perspective of software maintenance.Moreover,we perform a questionnaire survey and send them to developers or users of ML projects to validate the results in our empirical study.The results of our empirical study are basically consistent with the feedback from developers.The findings from the empirical study provide useful guidance and insights for developers and users to effectively detect and fix bugs in MLprojects.
基金This work was financially supported by Chinese National Natural Science Foundation(grant no.51803175)。
文摘Hydroxyl anion conducting membrane composed of poly(vinyl alcohol)(PVA),poly(diallyldimethylammonium chloride)(PDDA),and hydroxylated multiwalled carbon nanotubes(MWCNTs-OH)have been synthesized via a facile blending-casting method assisted by a hot-chemical cross-linking process.Fourier-transform infrared spectroscopy(FTIR)and scanning electron microscopy(SEM)showed that PDDA and MWCNTs-OH were successfully introduced into the PVA matrix and MWCNTs-OH could effectively improve the network structure of the membrane.With the addition of MWCNTs-OH,many properties of the membranes such as thermal,chemical,mechanical stability and swelling property were improved significantly.Most prominent is the improvement of mechanical property,where the PVA/PDDA/MWCNTs-OH(1:0.5/3 wt.%)membrane showed high tensile strength of 40.3 MPa,tensile elongation of 12.3%and high Young's modulus of 782.8 MPa.Moreover,MWCNTs-OH bound the polymer chains in the membranes more compactly,resulting in decreased water uptake.By tuning the mass fraction of PVA,PDDA,and MWCNTs-OH in the membrane,the maximum OH-conductivity(0.030 S cm^(-1)at room temperature)was achieved for the composition of 0.5 wt.%MWCNTs-OH doped with the PVA:PDDA(1:0.5 by mass)blend.The membranes showed excellent oxidative stability when treated with both a solution of H_(2)O_(2)(30 wt.%)at room temperature and in a hot KOH solution(8 M)at 80℃.Based on the full aliphatic structure membrane(PVA/PDDA-OH/1 wt.%MWCNTs-OH),membrane electrode assemblies(MEAs)fabricated with Pt/C cathode catalyst can achieve power densities of 41.3 mW cm^(-2)and 66.4 mW cm^(-2)in a H_(2)/O_(2)system at room temperature and 40℃,respectively.Using CoPc as the Pt-free cathode catalyst,power densities of 9.1 mW cm^(-2)and 14.0 mW cm^(-2)at room temperature and 40℃ were obtained,respectively.
基金National Natural Science Foundation of China(62301112,61921002,61931006,62101111,62131007,U20A20212)National Key Research and Development Program of China(2021YFA1401000)+2 种基金Sichuan Province Science and Technology Support Program(2020JDRc0028)Fundamental Research Funds for the Central Universities(ZYGX2020ZB011)“Pioneer”and“Leading Goose”R&D Program of Zhejiang(2023C01139).
文摘Achieving ultra-precise wide-range terahertz(THz)phase modulation has been a long-standing challenge due to the short wavelength and sensitive phase of THz waves.This paper proposes a new ultra-high precision phase control method employing a digitally coding needle meta-chip embedded in a waveguide.The needle tips can effectively couple THz waves via the charge aggregation effect.By controlling the Schottky diodes with coding voltages,the charge on each meta-structure part can be tuned to form strong or weak resonances,producing phase shifts.Crucially,the massive charge accumulation and the sub-λ∕10 distance between needle tips lead to near-field coupling among multiple tips.Therefore,modulation of the charge at each tip by multichannel coding voltages enables combined resonance tuning of THz waves,yielding a nonlinear phase superposition.Here,a meta-chip containing 8 needle meta-structure units is demonstrated,which breaks through the precision limitation of independent units and realizes super-resolution precision phase modulation similar to super-resolution imaging.In the 213–227 GHz band,we achieve a phase shift exceeding 180°with 11.25°accuracy,and a phase shift of over 170°with an accuracy of 3°.This super-resolution phase modulation strategy provides a new idea for future highprecision applications of THz integrated systems.
