[Background]Traveling-wave tubes(TWTs)are widely applied in radar,imaging,and military systems owing to their excellent amplification characteristics.Miniaturization and integration are critical to the future of TWTs,...[Background]Traveling-wave tubes(TWTs)are widely applied in radar,imaging,and military systems owing to their excellent amplification characteristics.Miniaturization and integration are critical to the future of TWTs,with multi-channel slow-wave structures(SWSs)forming the foundation for their realization in high-power vacuum electronic devices.[Purpose]To provide design insights for multi-channel TWTs and simultaneously enhance their output power,a W-band folded-waveguide TWT with dual electron beams and H-plane power combining was proposed.[Methods]Three-dimensional electromagnetic simulations in CST were conducted to verify the highfrequency characteristics,electric field distribution,and amplification performance of the proposed SWS,thereby confirming the validity of the design.[Results]Results indicate that the designed TWT achieves a transmission bandwidth of 10 GHz.With an electron beam voltage of 17.9 kV and a current of 0.35 A,the output power reaches 450 W at 94 GHz,corresponding to an efficiency of 7.18%and a gain of 23.5 dB.Moreover,under fixed beam voltage and current,the TWT delivers over 200 W output power across 91–99 GHz,with a 3 dB bandwidth of 91–98.5 GHz.The particle voltage distribution after modulation further validates the mode analysis.[Conclusions]These results demonstrate the feasibility of compact dual-beam power-combining structures and provide useful guidance for the design of future multi-channel TWTs.展开更多
This research investigates the bending response of folded multi-celled tubes(FMTs)fabricated by folded metal sheets.A three-point bending test for FMTs with circular and square sections is designed and introduced.The ...This research investigates the bending response of folded multi-celled tubes(FMTs)fabricated by folded metal sheets.A three-point bending test for FMTs with circular and square sections is designed and introduced.The base numerical models are correlated with physical experiments and a static crashworthiness analysis of six FMT configurations to assess their energy absorption characteristics.The influences of thickness,sectional shape,and load direction on the bending response are studied.Results indicate that increasing the thickness of the tube and radian of the inner tube enhances the crashworthiness performance of FMT,yielding a 20.50%increase in mean crushing force,a 55.53%increase in specific energy absorption,and an 18.05%decrease in peak crushing force compared to traditional multi-celled tubes(TMTs).A theoretical analysis of the specific energy absorption indicates that FMTs outperform TMTs,particularly when the peak crushing force is prominent.This study highlights the innovative and practical potential of FMTs to improve the crashworthiness of thin-walled structures.展开更多
Given a graph G and a non-negative integer h, the h-restricted connectivity κh（G） of G is the minimum cardinality of a set of vertices of G, in which at least h neighbors of any vertex is not included, if any, whos...Given a graph G and a non-negative integer h, the h-restricted connectivity κh（G） of G is the minimum cardinality of a set of vertices of G, in which at least h neighbors of any vertex is not included, if any, whose deletion disconnects G and every remaining component has the minimum degree of vertex at least h; and the h-extra connectivity κh（G） of G is the minimum cardinality of a set of vertices of G, if any, whose deletion disconnects G and every remaining component has order more than h. This paper shows that for the hypercube Qn and the folded hypercube FQn, κ1（Qn）=κ（1）（Qn）=2n-2 for n≥3, κ2（Qn）=3n-5 for n≥4, κ1（FQn）=κ（1）（FQn）=2n for n≥4 and κ（2）（FQn）=4n-4 for n≥8.展开更多
In this research,two novel folded lattice-core sandwich cylinders were designed,manufactured,and tested.The lattice core has periodic zigzag corrugations,whose ridges and valleys are directed axially or circumferentia...In this research,two novel folded lattice-core sandwich cylinders were designed,manufactured,and tested.The lattice core has periodic zigzag corrugations,whose ridges and valleys are directed axially or circumferentially.Free vibration and axial compression experiments were performed to reveal the fundamental frequency,free vibration modes,bearing capacity,and failure mode of the cylinder.A folded lattice core effectively restricts local buckling by reducing the dimension of the local skin periodic cell,and improves the global buckling resistance by enhancing the shear stiffness of the sandwich core.The cylinders fail at the mode of material failure and possess excellent load-carrying capacity.An axially directed folded sandwich cylinder has greater load-carrying capacity,while a circumferentially directed folded sandwich cylinder has higher fundamental frequencies.These two types of folded lattices provide a selection for engineers when designing a sandwich cylinder requiring strength or vibration.This research also presents a feasible way to fabricate a large-dimensional folded structure and promote its engineering application.展开更多
By using a mapping approach and a linear variable separation approach, a new family of solitary wave solutions with arbitrary functions for the （2＋1）-dimensional modified dispersive water-wave system （MDWW） is de...By using a mapping approach and a linear variable separation approach, a new family of solitary wave solutions with arbitrary functions for the （2＋1）-dimensional modified dispersive water-wave system （MDWW） is derived. Based on the derived solutions and using some multi-valued functions, we obtain some novel folded localized excitations of the system.展开更多
The Milan Gobi area of the Golmud-Korla Railway in northwest China is located in the lower dispersal area of the mountain pass and has strong winds with evident double wind direction characteristics.This study introdu...The Milan Gobi area of the Golmud-Korla Railway in northwest China is located in the lower dispersal area of the mountain pass and has strong winds with evident double wind direction characteristics.This study introduced a novel sand fence deployment technique,termed‘folded linear deployment',designed to position the sand fence orthogonally to the two predominant wind directions for optimal protection.This study used wind tunnel and field tests to evaluate the wind and sand flow characteristics,as well as the windproof and sandresistant performance of folded linear HDPE(Highdensity polyethylene)board sand fences.The results suggest that the airflow around the fence creates clear zoning characteristics.The deceleration area on the BSF(backwind side of the sand fence)is much larger than that on the DSF(downwind side of the sand fence).Thus,sand particles are primarily deposited on the BSF.At different wind speeds,the airflow at 2 and 5 h on the DSF is not disturbed.The WSP(wind speed profile)presents a logarithmic distribution.The airflow is disturbed at 1-20 h on the BSF,and the WSP gradually deviates from the logarithmic law.However,as the airflow moves away from the fence,the WSP gradually approaches a logarithmic distribution.Meanwhile,the WPE(windproof efficiency)and SRE(sand-resistant efficiency)of the sand fence exceed 80%.In addition,the results of wind tunnel tests are compared with those of field tests.The overall dispersion is good,and the best dispersion is found at z/H=2.00,indicating good agreement between the two test results.This study provides a scientific basis for the design of sand hazard control measures,similar to the railway project in the Gobi Gale area.展开更多
The generalized conditional fault-tolerant embedding is investigated, in which the n-dimensional folded hypercube networks （denoted by FQn） acts as the host graph, and the longest fault-free cycle represents the gue...The generalized conditional fault-tolerant embedding is investigated, in which the n-dimensional folded hypercube networks （denoted by FQn） acts as the host graph, and the longest fault-free cycle represents the vip graph. Under the conditions looser than that of previous works, it is shown that FQn has a cycle with length at least 2n -21F, I when the number of faulty vertices and non-critical edges is at most 2n-4; where ｜Fv｜ is the number of faulty vertices. It provides further theoretical evidence for the fact that FQn has excellent node-fault-tolerance and edge-fault-tolerance when used as a topology of large scale computer networks.展开更多
Toughness and strength are important material parameters in practical structural applications.However,it remains a great challenge to achieve high toughness and high strength simultaneously for most materials.Here,we ...Toughness and strength are important material parameters in practical structural applications.However,it remains a great challenge to achieve high toughness and high strength simultaneously for most materials.Here,we report a folded graphene(FG)reinforced copper(Cu)nanocomposite that overcomes the long-standing conflicts between toughness and strength.Intensive molecular dynamics simulations show that the 10%pre-strain-induced four-wave-patterned FG(1.09 wt%)reinforced Cu nanocomposite exhibits simultaneous enhancement in toughness(~13.59 J/m^(2)),ductility(~32.38%),and strength(~9.52 GPa),corresponding to 38.53%,58.88%,and 2.26%increase,respectively when compared with its counterpart reinforced by pristine graphene(PG).More importantly,the mechanical properties of FG/Cu nanocomposites can be effectively tuned by changing the pre-compressive strain,wave number,and peak number of FG.The toughening and strengthening mechanisms are applicable to other metal materials reinforced by other 2 D nanomaterials,opening up a new avenue for developing tough and strong metal nanocomposites.展开更多
Wind and sand hazards are serious in the Milan Gobi area of the Xinjiang section of the Korla Railway. In order to ensure the safe operation of railroads, there is a need for wind and sand protection in heavily sandy ...Wind and sand hazards are serious in the Milan Gobi area of the Xinjiang section of the Korla Railway. In order to ensure the safe operation of railroads, there is a need for wind and sand protection in heavily sandy areas. The wind and sand flow in the region is notably bi-directional. To shield railroads from sand, a unique sand fence made of folded linear high-density polyethylene(HDPE) is used, aligning with the principle that the dominant wind direction is perpendicular to the fence. This study employed field observations and numerical simulations to investigate the effectiveness of these HDPE sand fences in altering flow field distribution and offering protection. It also explored how these fences affect the deposition and erosion of sand particles. Findings revealed a significant reduction in wind speed near the fence corner;the minimum horizontal wind speed on the leeward side of the first sand fence(LSF) decreased dramatically from 3 m/s to 0.64 m/s. The vortex area on the LSF markedly impacted horizontal wind speeds. Within the LSF, sand deposition was a primary occurrence. As wind speeds increased, the deposition zone shrank, whereas the positive erosion zone expanded. Close to the folded corners of the HDPE sand fence, there was a notable shift from the positive erosion zone to a deposition zone. Field tests and numerical simulations confirmed the high windproof efficiency(WE) and sand resistance efficiency(SE) in the HDPE sand fence. Folded linear HDPE sheet sand fence can effectively slow down the incoming flow and reduce the sand content, thus achieving good wind and sand protection. This study provides essential theoretical guidance for the design and improvement of wind and sand protection systems in railroad engineering.展开更多
An idea to develop a family of cellular cores for sandwich panels using a technology of prepreg folding is presented. Polar folded quadra structures are regarded as a geometric basis for these cores whose standard fra...An idea to develop a family of cellular cores for sandwich panels using a technology of prepreg folding is presented. Polar folded quadra structures are regarded as a geometric basis for these cores whose standard frag ment has lhe fourlh degree of axial symmelry. The classification of the polar strucluresaredeseribedanda method of various quadra slrueture synthesis is developed. A possibilily to provide high strength of lhe structure due m preservation of faces reinforcement pattern is presented. Arrangemen! of the plane core on a bi curvature surface is also introduced. Besides, provision of isotropyof the core in two or three directions are described. Finally, exam ples of cellular folded cores manufaclured from basalt reinforced plaslic are demonslrated.展开更多
With the help of an improved mapping approach and a linear-variable-separation approach, a new family of exact solutions with arbitrary functions of the （2＋1）-dimensional Nizhnik-Novikov-Veselov system （NNV） is d...With the help of an improved mapping approach and a linear-variable-separation approach, a new family of exact solutions with arbitrary functions of the （2＋1）-dimensional Nizhnik-Novikov-Veselov system （NNV） is derived. Based on the derived solutions and using some multi-valued functions, we find a few new folded solitary wave excitations for the （2＋1）-dimensional NNV system.展开更多
Mercury is a promising candidate for the optical lattice clock, due to its low sensitivity to the blackbody radiation. We develop a single folded beam magneto-optical trap for the neutral mercury optical lattice clock...Mercury is a promising candidate for the optical lattice clock, due to its low sensitivity to the blackbody radiation. We develop a single folded beam magneto-optical trap for the neutral mercury optical lattice clock, with a 253. 7nm frequency quadrupled laser. Up to 1.7 × 10^6 （202Hg） or 1.5 × 10^6 （199Hg） atoms can be captured, and the atom temperature is lowered to 170μK （202Hg） or 50μK （199Hg）. The cold atom signals of all six rich abundant isotopes are observed in this system.展开更多
The periodic nonuniform folded waveguides are special structures, the physical dimension of which is between the periodic folded waveguide and the tapering period folded waveguide. Therefore, the synchronization betwe...The periodic nonuniform folded waveguides are special structures, the physical dimension of which is between the periodic folded waveguide and the tapering period folded waveguide. Therefore, the synchronization between the microwave and the electron beam can be maintained in the whole interaction process and the periods are not tapered. In comparison with the tapering period folded waveguide, the theoretical analysis and the technological requirements for this structure are more convenient. In order to study this structure, the space harmonics are analysed, the conditions to make the rn-th space harmonic synchronizing with the electron beam in the whole interaction process are present, and the dispersion curve and the coupling impedance curve are obtained by the simulation software HFSS.展开更多
In this paper, the basic equations of beam-wave interaction for designing the 220 GHz folded waveguide （FW） backward wave oscillator （BWO） are described. On the whole, these equations are mainly classified into sm...In this paper, the basic equations of beam-wave interaction for designing the 220 GHz folded waveguide （FW） backward wave oscillator （BWO） are described. On the whole, these equations are mainly classified into small signal model （SSM）, large signal model （LSM）, and simplified small signal model （SSSM）. Using these linear and nonlinear one-dimensional （1D） models, the oscillation characteristics of the FW BWO of a given configuration of slow wave struc- ture （SWS） can be calculated by numerical iteration algorithm, which is more time efficient than three-dimensional （3D） particle-in-cell （PIC） simulation. The SSSM expressed by analytical formulas is innovatively derived for determining the initial values of the FW SWS conveniently. The dispersion characteristics of the FW are obtained by equivalent circuit analysis. The space charge effect, the end reflection effect, the lossy wall effect, and the relativistic effect are all considered in our models to offer more accurate results. The design process of the FW BWO tube with output power of watt scale in a frequency range between 215 GHz and 225 GHz based on these 1D models is demonstrated. The 3D PIC method is adopted to verify the theoretical design results, which shows that they are in good agreement with each other.展开更多
Ultra-violet(UV)curing is an efficient method for composite molding.Firstly,thermophysical properties of UV cured glass-fiber reinforced plastics are conducted.Material properties are studied for various kinds of post...Ultra-violet(UV)curing is an efficient method for composite molding.Firstly,thermophysical properties of UV cured glass-fiber reinforced plastics are conducted.Material properties are studied for various kinds of postcuring modes.Then the UV curing method is suggested in manufacturing V-crimp folded core for sandwich panels.Two kinds of processing schemes for V-crimp folded core manufacturing using UV curing are presented.Finally,the effect of post-curing on the mechanical properties of folded core sandwiches is experimentally studied,and optimum modes of post-curing are determined.The experimental results show that the ultimate compressive strength of the folded sandwiches is increased by 60% after post-curing with the optimum post-curing mode.展开更多
The folded double-ridged waveguide structure is presented and its properties used for wide-band traveling-wave tube are investigated. Expressions of dispersion characteristics, normalized phase velocity and interactio...The folded double-ridged waveguide structure is presented and its properties used for wide-band traveling-wave tube are investigated. Expressions of dispersion characteristics, normalized phase velocity and interaction impedance of this structure are derived and numerically calculated. The calculated results using our theory agree well with those obtained by using the 3D electromagnetic simulation software HFSS. Influences of the ridge-loaded area and broad-wall dimensions on the high frequency characteristics of the novel slow-wave structure are discussed. It is shown that the folded double-ridged waveguide structure has a much wider relative passband than the folded waveguide slow-wave structure and a relative passband of 67% could be obtained, indicating that this structure can operate in broad-band frequency ranges of beam-wave interaction. The small signal gain property is investigated for ensuring the improvement of bandwidth. Meanwhile, with comparable dispersion characteristics, the transverse section dimension of this novel structure is much smaller than that of conventional one, which indicates an available way to reduce the weight of traveling-wave tube.展开更多
The central wavelength of the first Bragg scattering bandgap is approximately twice that of the lattice.Therefore,a low-frequency Bragg scattering bandgap with a small structural dimension for phononic crystals is dif...The central wavelength of the first Bragg scattering bandgap is approximately twice that of the lattice.Therefore,a low-frequency Bragg scattering bandgap with a small structural dimension for phononic crystals is difficult to obtain.In this study,a folded S-type periodic structure is developed to reduce the dimension in the direction of vibration suppression by folding unit cells.According to the foregoing,an improved folded S-type periodic structure with different unit cell arrangements is designed to widen the bandgap frequency range.Energy band diagrams and frequency responses are calculated based on the Bloch theory and using the finite element method.Furthermore,a prototype of the improved folded S-type periodic structure is fabricated using a three-dimensional printing technique,and a vibration experiment is conducted.To verify the vibration reduction performance of the structure,numerical simulation and experimental results are compared.This type of folded periodic structure can effectively reduce dimensions to satisfy the dimension requirements pertaining to the direction of vibration suppression.Hence,the foregoing can aid in promoting the use of elastic bandgap structures in engineering.展开更多
In this project, a Blumlein line with a folded parallel-plates configuration using Kapton film as dielectrics was investigated. The characteristic parameters of this Blumlein line were analysed theoretically. The elec...In this project, a Blumlein line with a folded parallel-plates configuration using Kapton film as dielectrics was investigated. The characteristic parameters of this Blumlein line were analysed theoretically. The electric field distributions under different inner radii of the folded part were simulated. The output waveforms on the match load were also simulated by means of an equivalent electric circuit. According to the results of the theoretecal analysis and simulation, a Blumlein line with the folded parallel-plates configuration with an output voltage of 500 kV, a pulse duration of 100 ns, and a characteristic impedance of 4.773Ω was designed and manufactured. The experimental results properly demonstrated the wave transmitting process in the Blumlein line, and provided the voltage waveform of 500 kV and the current waveform of 50 kA with a pulse duration of 150 ns. Some engineering problems such as the edge electric breakdown and measuring precision by a resistance divider were revealed, which must be solved in future work to produce a more compact transmission line.展开更多
A period-varying folded waveguide is formed by varying the period of a folded waveguide. It has the advantages of the space harmonic selectivity and the wide bandwidth. However, the regularities of the variety of thes...A period-varying folded waveguide is formed by varying the period of a folded waveguide. It has the advantages of the space harmonic selectivity and the wide bandwidth. However, the regularities of the variety of these period-varying folded waveguides are unavailable from the published papers. In order to solve this problem, the principle of the space harmonic selectivity of a period-varying folded waveguide is analysed, and the conditions to select the space harmonic for this slow wave system are obtained. In addition, the space harmonic selectivities for a linear period-varying folded waveguide and a hyperbolic sine-varying period folded waveguide are also analysed as examples.展开更多
Based on the first-order shear deformation theory,a 3-node co-rotational triangular finite element formulation is developed for large deformation modeling of non-smooth,folded and multi-shell laminated composite struc...Based on the first-order shear deformation theory,a 3-node co-rotational triangular finite element formulation is developed for large deformation modeling of non-smooth,folded and multi-shell laminated composite structures.The two smaller components of the mid-surface normal vector of shell at a node are defined as nodal rotational variables in the co-rotational local coordinate system.In the global coordinate system,two smaller components of one vector,together with the smallest or second smallest component of another vector,of an orthogonal triad at a node on a non-smooth intersection of plates and/or shells are defined as rotational variables,whereas the two smaller components of the mid-surface normal vector at a node on the smooth part of the plate or shell(away from non-smooth intersections)are defined as rotational variables.All these vectorial rotational variables can be updated in an additive manner during an incremental solution procedure,and thus improve the computational efficiency in the nonlinear solution of these composite shell structures.Due to the commutativity of all nodal variables in calculating of the second derivatives of the local nodal variables with respect to global nodal variables,and the second derivatives of the strain energy functional with respect to local nodal variables,symmetric tangent stiffness matrices in local and global coordinate systems are obtained.To overcome shear locking,the assumed transverse shear strains obtained from the line-integration approach are employed.The reliability and computational accuracy of the present 3-node triangular shell finite element are verified through modeling two patch tests,several smooth and non-smooth laminated composite shells undergoing large displacements and large rotations.展开更多
基金National Key Research and Development Program of China(2022YFF0707602)National Natural Science Foundation of China(62471097,62471115,62471101)National Natural Science Foundation of Sichuan(2025ZNSFSC0537)。
文摘[Background]Traveling-wave tubes(TWTs)are widely applied in radar,imaging,and military systems owing to their excellent amplification characteristics.Miniaturization and integration are critical to the future of TWTs,with multi-channel slow-wave structures(SWSs)forming the foundation for their realization in high-power vacuum electronic devices.[Purpose]To provide design insights for multi-channel TWTs and simultaneously enhance their output power,a W-band folded-waveguide TWT with dual electron beams and H-plane power combining was proposed.[Methods]Three-dimensional electromagnetic simulations in CST were conducted to verify the highfrequency characteristics,electric field distribution,and amplification performance of the proposed SWS,thereby confirming the validity of the design.[Results]Results indicate that the designed TWT achieves a transmission bandwidth of 10 GHz.With an electron beam voltage of 17.9 kV and a current of 0.35 A,the output power reaches 450 W at 94 GHz,corresponding to an efficiency of 7.18%and a gain of 23.5 dB.Moreover,under fixed beam voltage and current,the TWT delivers over 200 W output power across 91–99 GHz,with a 3 dB bandwidth of 91–98.5 GHz.The particle voltage distribution after modulation further validates the mode analysis.[Conclusions]These results demonstrate the feasibility of compact dual-beam power-combining structures and provide useful guidance for the design of future multi-channel TWTs.
基金supported by the National Natural Science Foundation of China(Grant No.52475277)2022 Guangxi University Young and Middle-aged Teachers’Basic Research Ability Improvement Project(Grant No.2022KY0781)Scientific Research Funds of Guilin University of Aerospace Technology(Grant No.XJ22KT29).
文摘This research investigates the bending response of folded multi-celled tubes(FMTs)fabricated by folded metal sheets.A three-point bending test for FMTs with circular and square sections is designed and introduced.The base numerical models are correlated with physical experiments and a static crashworthiness analysis of six FMT configurations to assess their energy absorption characteristics.The influences of thickness,sectional shape,and load direction on the bending response are studied.Results indicate that increasing the thickness of the tube and radian of the inner tube enhances the crashworthiness performance of FMT,yielding a 20.50%increase in mean crushing force,a 55.53%increase in specific energy absorption,and an 18.05%decrease in peak crushing force compared to traditional multi-celled tubes(TMTs).A theoretical analysis of the specific energy absorption indicates that FMTs outperform TMTs,particularly when the peak crushing force is prominent.This study highlights the innovative and practical potential of FMTs to improve the crashworthiness of thin-walled structures.
文摘Given a graph G and a non-negative integer h, the h-restricted connectivity κh（G） of G is the minimum cardinality of a set of vertices of G, in which at least h neighbors of any vertex is not included, if any, whose deletion disconnects G and every remaining component has the minimum degree of vertex at least h; and the h-extra connectivity κh（G） of G is the minimum cardinality of a set of vertices of G, if any, whose deletion disconnects G and every remaining component has order more than h. This paper shows that for the hypercube Qn and the folded hypercube FQn, κ1（Qn）=κ（1）（Qn）=2n-2 for n≥3, κ2（Qn）=3n-5 for n≥4, κ1（FQn）=κ（1）（FQn）=2n for n≥4 and κ（2）（FQn）=4n-4 for n≥8.
基金Support from the National Natural Science Foundation of China(11672130 and 11972184)the State Key Laboratory of Mechanics and Control of Mechanical Structures(MCMS-0217G03)Aerospace System Engineering Shanghai are gratefully acknowledged.
文摘In this research,two novel folded lattice-core sandwich cylinders were designed,manufactured,and tested.The lattice core has periodic zigzag corrugations,whose ridges and valleys are directed axially or circumferentially.Free vibration and axial compression experiments were performed to reveal the fundamental frequency,free vibration modes,bearing capacity,and failure mode of the cylinder.A folded lattice core effectively restricts local buckling by reducing the dimension of the local skin periodic cell,and improves the global buckling resistance by enhancing the shear stiffness of the sandwich core.The cylinders fail at the mode of material failure and possess excellent load-carrying capacity.An axially directed folded sandwich cylinder has greater load-carrying capacity,while a circumferentially directed folded sandwich cylinder has higher fundamental frequencies.These two types of folded lattices provide a selection for engineers when designing a sandwich cylinder requiring strength or vibration.This research also presents a feasible way to fabricate a large-dimensional folded structure and promote its engineering application.
基金Project supported by the Natural Science Foundation of Zhejiang Province, China (Grant Nos. Y6100257 and Y6110140)
文摘By using a mapping approach and a linear variable separation approach, a new family of solitary wave solutions with arbitrary functions for the （2＋1）-dimensional modified dispersive water-wave system （MDWW） is derived. Based on the derived solutions and using some multi-valued functions, we obtain some novel folded localized excitations of the system.
基金financially supported by the Chang Jiang Scholar and Innovation Team Development Plan of China(IRT_15R29)the Basic Research Innovation Group Project of Gansu Province,China(21JR7RA347)the Natural Science Foundation of Gansu Province,China(20JR10RA231)。
文摘The Milan Gobi area of the Golmud-Korla Railway in northwest China is located in the lower dispersal area of the mountain pass and has strong winds with evident double wind direction characteristics.This study introduced a novel sand fence deployment technique,termed‘folded linear deployment',designed to position the sand fence orthogonally to the two predominant wind directions for optimal protection.This study used wind tunnel and field tests to evaluate the wind and sand flow characteristics,as well as the windproof and sandresistant performance of folded linear HDPE(Highdensity polyethylene)board sand fences.The results suggest that the airflow around the fence creates clear zoning characteristics.The deceleration area on the BSF(backwind side of the sand fence)is much larger than that on the DSF(downwind side of the sand fence).Thus,sand particles are primarily deposited on the BSF.At different wind speeds,the airflow at 2 and 5 h on the DSF is not disturbed.The WSP(wind speed profile)presents a logarithmic distribution.The airflow is disturbed at 1-20 h on the BSF,and the WSP gradually deviates from the logarithmic law.However,as the airflow moves away from the fence,the WSP gradually approaches a logarithmic distribution.Meanwhile,the WPE(windproof efficiency)and SRE(sand-resistant efficiency)of the sand fence exceed 80%.In addition,the results of wind tunnel tests are compared with those of field tests.The overall dispersion is good,and the best dispersion is found at z/H=2.00,indicating good agreement between the two test results.This study provides a scientific basis for the design of sand hazard control measures,similar to the railway project in the Gobi Gale area.
基金Supported by the National Natural Science Foundation of China(11071022)the Key Project of Hubei Department of Education(D20092207)
文摘The generalized conditional fault-tolerant embedding is investigated, in which the n-dimensional folded hypercube networks （denoted by FQn） acts as the host graph, and the longest fault-free cycle represents the vip graph. Under the conditions looser than that of previous works, it is shown that FQn has a cycle with length at least 2n -21F, I when the number of faulty vertices and non-critical edges is at most 2n-4; where ｜Fv｜ is the number of faulty vertices. It provides further theoretical evidence for the fact that FQn has excellent node-fault-tolerance and edge-fault-tolerance when used as a topology of large scale computer networks.
基金supported by the Australian Research Council grant under the Discovery Project scheme(No.DP210103656)。
文摘Toughness and strength are important material parameters in practical structural applications.However,it remains a great challenge to achieve high toughness and high strength simultaneously for most materials.Here,we report a folded graphene(FG)reinforced copper(Cu)nanocomposite that overcomes the long-standing conflicts between toughness and strength.Intensive molecular dynamics simulations show that the 10%pre-strain-induced four-wave-patterned FG(1.09 wt%)reinforced Cu nanocomposite exhibits simultaneous enhancement in toughness(~13.59 J/m^(2)),ductility(~32.38%),and strength(~9.52 GPa),corresponding to 38.53%,58.88%,and 2.26%increase,respectively when compared with its counterpart reinforced by pristine graphene(PG).More importantly,the mechanical properties of FG/Cu nanocomposites can be effectively tuned by changing the pre-compressive strain,wave number,and peak number of FG.The toughening and strengthening mechanisms are applicable to other metal materials reinforced by other 2 D nanomaterials,opening up a new avenue for developing tough and strong metal nanocomposites.
基金financially supported by the Chang Jiang Scholar and Innovation Team Development Plan of China (IRT_15R29)the Basic Research Innovation Group Project of Gansu Province, China (21JR7RA347)the Natural Science Foundation of Gansu Province, China (20JR10RA231)。
文摘Wind and sand hazards are serious in the Milan Gobi area of the Xinjiang section of the Korla Railway. In order to ensure the safe operation of railroads, there is a need for wind and sand protection in heavily sandy areas. The wind and sand flow in the region is notably bi-directional. To shield railroads from sand, a unique sand fence made of folded linear high-density polyethylene(HDPE) is used, aligning with the principle that the dominant wind direction is perpendicular to the fence. This study employed field observations and numerical simulations to investigate the effectiveness of these HDPE sand fences in altering flow field distribution and offering protection. It also explored how these fences affect the deposition and erosion of sand particles. Findings revealed a significant reduction in wind speed near the fence corner;the minimum horizontal wind speed on the leeward side of the first sand fence(LSF) decreased dramatically from 3 m/s to 0.64 m/s. The vortex area on the LSF markedly impacted horizontal wind speeds. Within the LSF, sand deposition was a primary occurrence. As wind speeds increased, the deposition zone shrank, whereas the positive erosion zone expanded. Close to the folded corners of the HDPE sand fence, there was a notable shift from the positive erosion zone to a deposition zone. Field tests and numerical simulations confirmed the high windproof efficiency(WE) and sand resistance efficiency(SE) in the HDPE sand fence. Folded linear HDPE sheet sand fence can effectively slow down the incoming flow and reduce the sand content, thus achieving good wind and sand protection. This study provides essential theoretical guidance for the design and improvement of wind and sand protection systems in railroad engineering.
基金supported by the Ministry of Education and Science of Russian Federation (No.RFMEFI57414X0078)
文摘An idea to develop a family of cellular cores for sandwich panels using a technology of prepreg folding is presented. Polar folded quadra structures are regarded as a geometric basis for these cores whose standard frag ment has lhe fourlh degree of axial symmelry. The classification of the polar strucluresaredeseribedanda method of various quadra slrueture synthesis is developed. A possibilily to provide high strength of lhe structure due m preservation of faces reinforcement pattern is presented. Arrangemen! of the plane core on a bi curvature surface is also introduced. Besides, provision of isotropyof the core in two or three directions are described. Finally, exam ples of cellular folded cores manufaclured from basalt reinforced plaslic are demonslrated.
基金supported by the Natural Science Foundation of Zhejiang Province under Grant No.Y604106the Scientific Research Foundation of Zhejiang Provincial Education Department under Grant No.20070568the Natural Science Foundation of Zhejiang Lishui University under Grant No.KZ08001
文摘With the help of an improved mapping approach and a linear-variable-separation approach, a new family of exact solutions with arbitrary functions of the （2＋1）-dimensional Nizhnik-Novikov-Veselov system （NNV） is derived. Based on the derived solutions and using some multi-valued functions, we find a few new folded solitary wave excitations for the （2＋1）-dimensional NNV system.
基金Supported by the National Natural Science Foundation of China under Grant No 91436105the National Basic Research Program of China under Grant No 2011CB921504the Research Project of Shanghai Science and Technology Commission under Grant No 09DJ1400700
文摘Mercury is a promising candidate for the optical lattice clock, due to its low sensitivity to the blackbody radiation. We develop a single folded beam magneto-optical trap for the neutral mercury optical lattice clock, with a 253. 7nm frequency quadrupled laser. Up to 1.7 × 10^6 （202Hg） or 1.5 × 10^6 （199Hg） atoms can be captured, and the atom temperature is lowered to 170μK （202Hg） or 50μK （199Hg）. The cold atom signals of all six rich abundant isotopes are observed in this system.
基金supported by the National Natural Science Foundation of China (Grant Nos 60532010 and 60401005)
文摘The periodic nonuniform folded waveguides are special structures, the physical dimension of which is between the periodic folded waveguide and the tapering period folded waveguide. Therefore, the synchronization between the microwave and the electron beam can be maintained in the whole interaction process and the periods are not tapered. In comparison with the tapering period folded waveguide, the theoretical analysis and the technological requirements for this structure are more convenient. In order to study this structure, the space harmonics are analysed, the conditions to make the rn-th space harmonic synchronizing with the electron beam in the whole interaction process are present, and the dispersion curve and the coupling impedance curve are obtained by the simulation software HFSS.
基金Project supported by the Innovative Research Foundation of China Academy of Engineering Physics(Grant No.426050502-2)
文摘In this paper, the basic equations of beam-wave interaction for designing the 220 GHz folded waveguide （FW） backward wave oscillator （BWO） are described. On the whole, these equations are mainly classified into small signal model （SSM）, large signal model （LSM）, and simplified small signal model （SSSM）. Using these linear and nonlinear one-dimensional （1D） models, the oscillation characteristics of the FW BWO of a given configuration of slow wave struc- ture （SWS） can be calculated by numerical iteration algorithm, which is more time efficient than three-dimensional （3D） particle-in-cell （PIC） simulation. The SSSM expressed by analytical formulas is innovatively derived for determining the initial values of the FW SWS conveniently. The dispersion characteristics of the FW are obtained by equivalent circuit analysis. The space charge effect, the end reflection effect, the lossy wall effect, and the relativistic effect are all considered in our models to offer more accurate results. The design process of the FW BWO tube with output power of watt scale in a frequency range between 215 GHz and 225 GHz based on these 1D models is demonstrated. The 3D PIC method is adopted to verify the theoretical design results, which shows that they are in good agreement with each other.
基金supported by the Ministry of Education and Science of Russian Federation (No.RFMEFI57414X0078)
文摘Ultra-violet(UV)curing is an efficient method for composite molding.Firstly,thermophysical properties of UV cured glass-fiber reinforced plastics are conducted.Material properties are studied for various kinds of postcuring modes.Then the UV curing method is suggested in manufacturing V-crimp folded core for sandwich panels.Two kinds of processing schemes for V-crimp folded core manufacturing using UV curing are presented.Finally,the effect of post-curing on the mechanical properties of folded core sandwiches is experimentally studied,and optimum modes of post-curing are determined.The experimental results show that the ultimate compressive strength of the folded sandwiches is increased by 60% after post-curing with the optimum post-curing mode.
基金Project supported in part by the National Natural Science Foundation of China (Grant No. 60971038)in part by the Fundamental Research Funds for Central Universities,China (Grant No. ZYGX2009Z003)
文摘The folded double-ridged waveguide structure is presented and its properties used for wide-band traveling-wave tube are investigated. Expressions of dispersion characteristics, normalized phase velocity and interaction impedance of this structure are derived and numerically calculated. The calculated results using our theory agree well with those obtained by using the 3D electromagnetic simulation software HFSS. Influences of the ridge-loaded area and broad-wall dimensions on the high frequency characteristics of the novel slow-wave structure are discussed. It is shown that the folded double-ridged waveguide structure has a much wider relative passband than the folded waveguide slow-wave structure and a relative passband of 67% could be obtained, indicating that this structure can operate in broad-band frequency ranges of beam-wave interaction. The small signal gain property is investigated for ensuring the improvement of bandwidth. Meanwhile, with comparable dispersion characteristics, the transverse section dimension of this novel structure is much smaller than that of conventional one, which indicates an available way to reduce the weight of traveling-wave tube.
基金supported by the National Natural Science Foundation of China(Nos.12072086,12211540384 and 11761131006)the Fundamental Research Funds for the Central Universities(No.3072022CF0203).
文摘The central wavelength of the first Bragg scattering bandgap is approximately twice that of the lattice.Therefore,a low-frequency Bragg scattering bandgap with a small structural dimension for phononic crystals is difficult to obtain.In this study,a folded S-type periodic structure is developed to reduce the dimension in the direction of vibration suppression by folding unit cells.According to the foregoing,an improved folded S-type periodic structure with different unit cell arrangements is designed to widen the bandgap frequency range.Energy band diagrams and frequency responses are calculated based on the Bloch theory and using the finite element method.Furthermore,a prototype of the improved folded S-type periodic structure is fabricated using a three-dimensional printing technique,and a vibration experiment is conducted.To verify the vibration reduction performance of the structure,numerical simulation and experimental results are compared.This type of folded periodic structure can effectively reduce dimensions to satisfy the dimension requirements pertaining to the direction of vibration suppression.Hence,the foregoing can aid in promoting the use of elastic bandgap structures in engineering.
基金National Natural Science Foundation of China(No.10675168)
文摘In this project, a Blumlein line with a folded parallel-plates configuration using Kapton film as dielectrics was investigated. The characteristic parameters of this Blumlein line were analysed theoretically. The electric field distributions under different inner radii of the folded part were simulated. The output waveforms on the match load were also simulated by means of an equivalent electric circuit. According to the results of the theoretecal analysis and simulation, a Blumlein line with the folded parallel-plates configuration with an output voltage of 500 kV, a pulse duration of 100 ns, and a characteristic impedance of 4.773Ω was designed and manufactured. The experimental results properly demonstrated the wave transmitting process in the Blumlein line, and provided the voltage waveform of 500 kV and the current waveform of 50 kA with a pulse duration of 150 ns. Some engineering problems such as the edge electric breakdown and measuring precision by a resistance divider were revealed, which must be solved in future work to produce a more compact transmission line.
基金supported by the National Natural Science Foundation of China (Grant Nos 60532010 and 60401005)
文摘A period-varying folded waveguide is formed by varying the period of a folded waveguide. It has the advantages of the space harmonic selectivity and the wide bandwidth. However, the regularities of the variety of these period-varying folded waveguides are unavailable from the published papers. In order to solve this problem, the principle of the space harmonic selectivity of a period-varying folded waveguide is analysed, and the conditions to select the space harmonic for this slow wave system are obtained. In addition, the space harmonic selectivities for a linear period-varying folded waveguide and a hyperbolic sine-varying period folded waveguide are also analysed as examples.
基金This work was supported by National Natural Science Foundation of China under Grant 11672266.
文摘Based on the first-order shear deformation theory,a 3-node co-rotational triangular finite element formulation is developed for large deformation modeling of non-smooth,folded and multi-shell laminated composite structures.The two smaller components of the mid-surface normal vector of shell at a node are defined as nodal rotational variables in the co-rotational local coordinate system.In the global coordinate system,two smaller components of one vector,together with the smallest or second smallest component of another vector,of an orthogonal triad at a node on a non-smooth intersection of plates and/or shells are defined as rotational variables,whereas the two smaller components of the mid-surface normal vector at a node on the smooth part of the plate or shell(away from non-smooth intersections)are defined as rotational variables.All these vectorial rotational variables can be updated in an additive manner during an incremental solution procedure,and thus improve the computational efficiency in the nonlinear solution of these composite shell structures.Due to the commutativity of all nodal variables in calculating of the second derivatives of the local nodal variables with respect to global nodal variables,and the second derivatives of the strain energy functional with respect to local nodal variables,symmetric tangent stiffness matrices in local and global coordinate systems are obtained.To overcome shear locking,the assumed transverse shear strains obtained from the line-integration approach are employed.The reliability and computational accuracy of the present 3-node triangular shell finite element are verified through modeling two patch tests,several smooth and non-smooth laminated composite shells undergoing large displacements and large rotations.
