GH4169 joints manufactured by Linear Friction Welding(LFW)are subjected to tensile test and stair-case method to evaluate the High Cycle Fatigue(HCF)performance at 650℃.The yield and ultimate tensile strengths are 58...GH4169 joints manufactured by Linear Friction Welding(LFW)are subjected to tensile test and stair-case method to evaluate the High Cycle Fatigue(HCF)performance at 650℃.The yield and ultimate tensile strengths are 582 MPa and 820 MPa,respectively.The HCF strength of joint reaches 400 MPa,which is slightly lower than that of Base Metal(BM),indicating reliable quality of this type of joint.The microstructure observation results show that all cracks initiate at the inside of specimens and transfer into deeper region with decrease of external stress,and the crack initiation site is related with microhardness of matrix.The Electron Backscattered Diffraction(EBSD)results of the observed regions with different distances to fracture show that plastic deformation plays a key role in HCF,and the Schmid factor of most grains near fracture exceeds 0.4.In addition,the generation of twins plays a vital role in strain concentration release and coordinating plastic deformation among grains.展开更多
The pre-weld heat treatment was carried out to obtain different initial microstructures of the GH4169 superalloy,and then Linear Friction Welding(LFW)was performed.The effect of the pre-weld heat treatment on the micr...The pre-weld heat treatment was carried out to obtain different initial microstructures of the GH4169 superalloy,and then Linear Friction Welding(LFW)was performed.The effect of the pre-weld heat treatment on the microstructure evolution and mechanical properties of the joint was analyzed,and the joint electrochemical corrosion behavior as well as the hot corrosion behavior was studied.The results show that the joint hardness of Base Metal(BM)increases after pre-weld heat treatment,and the strengthening phasesγ′andγ″further precipitate.However,the precipitation phases dissolve significantly in the Weld Zone(WZ)due to the thermal process of LFW.The corrosion resistance in BM is reduced after the pre-weld heat treatment,while it is similar in WZ with a slight decrease.The surface morphology of the BM and WZ can be generally divided into a loose and porous matrix and a scattered oxide particle layer after hot corrosion.The joint cross section exhibits a Cr-depleted zone with the diffusion of Cr to form an oxide film.The corrosion product mainly consists of Fe_(2)O_(3)/Fe_(3)O_(4) as the outer layer and Cr_(2)O_(3) as the inner layer.展开更多
The hyperloop idea,which is one of the most ecofriendly,low-carbon emissions,and fossil fuel-efficient modes of transportation,has recently become quite popular.In this study,a double-sided linear induction motor(LIM)...The hyperloop idea,which is one of the most ecofriendly,low-carbon emissions,and fossil fuel-efficient modes of transportation,has recently become quite popular.In this study,a double-sided linear induction motor(LIM)with 500 W of output power,60 N of thrust force and 200 V/38.58 Hz of supply voltage was designed to be used in hyperloop development competition hosted by the scientific and technological research council of turkey(TüB?TAK)rail transportation technologies institute(RUTE).In contrast to the studies in the literature,concentrated winding is preferred instead of distributed winding due to mechanical constraints.The electromagnetic design of LIM,whose mechanical and electrical requirements were determined considering the hyperloop development competition,was carried out by following certain steps.Then,the designed model was simulated and analyzed by finite element method(FEM),and the necessary optimizations have been performed to improve the motor characteristics.By examining the final model,the applicability of the concentrated winding type LIM for hyperloop technology has been investigated.Besides,the effects of primary material,railway material,and mechanical air-gap length on LIM performance were also investigated.In the practical phase of the study,the designed LIM has been prototyped and tested.The validation of the experimental results was achieved through good agreement with the finite element analysis results.展开更多
Due to the heterogeneity of rock masses and the variability of in situ stress,the traditional linear inversion method is insufficiently accurate to achieve high accuracy of the in situ stress field.To address this cha...Due to the heterogeneity of rock masses and the variability of in situ stress,the traditional linear inversion method is insufficiently accurate to achieve high accuracy of the in situ stress field.To address this challenge,nonlinear stress boundaries for a numerical model are determined through regression analysis of a series of nonlinear coefficient matrices,which are derived from the bubbling method.Considering the randomness and flexibility of the bubbling method,a parametric study is conducted to determine recommended ranges for these parameters,including the standard deviation(σb)of bubble radii,the non-uniform coefficient matrix number(λ)for nonlinear stress boundaries,and the number(m)and positions of in situ stress measurement points.A model case study provides a reference for the selection of these parameters.Additionally,when the nonlinear in situ stress inversion method is employed,stress distortion inevitably occurs near model boundaries,aligning with the Saint Venant's principle.Two strategies are proposed accordingly:employing a systematic reduction of nonlinear coefficients to achieve high inversion accuracy while minimizing significant stress distortion,and excluding regions with severe stress distortion near the model edges while utilizing the central part of the model for subsequent simulations.These two strategies have been successfully implemented in the nonlinear in situ stress inversion of the Xincheng Gold Mine and have achieved higher inversion accuracy than the linear method.Specifically,the linear and nonlinear inversion methods yield root mean square errors(RMSE)of 4.15 and 3.2,and inversion relative errors(δAve)of 22.08%and 17.55%,respectively.Therefore,the nonlinear inversion method outperforms the traditional multiple linear regression method,even in the presence of a systematic reduction in the nonlinear stress boundaries.展开更多
Let a_(1),a_(2),a_(3)be nonzero integers with gcd(a_(1),a_(2),a_(3))=1,and let k be any positive integer,K=max[3,|a_(1)|,|a_(2)|,|a_(3)|,k].Suppose that l_(1),l_(2),l_(3)are integers each coprime to k.Suppose further ...Let a_(1),a_(2),a_(3)be nonzero integers with gcd(a_(1),a_(2),a_(3))=1,and let k be any positive integer,K=max[3,|a_(1)|,|a_(2)|,|a_(3)|,k].Suppose that l_(1),l_(2),l_(3)are integers each coprime to k.Suppose further that b is any integer satisfying some necessary congruent conditions.The solvability of linear equation a_(1)p_(1)+a_(2)p_(2)+a_(3)p_(3)=b(p_(j)=l_(j)(mod k),1≤j≤3)with prime variables pi,p_(2),ps is investigated.It is proved that if ai,a_(2),a_(3)are all positive,then the above equation is solvable whenever b≥K^(25);if a,a_(2),a_(3)are not all of the same sign,then the above equation has a solution p_(1),p_(2),p_(3)satisfying max(p_(1),p_(2),p_(3))≤3|b|+K^(25).展开更多
We study the existence and stability of dark-gap solitons in linear lattice and nonlinear lattices.The results indicate that the combination of linear and nonlinear lattices gives dark-gap solitons unique properties.T...We study the existence and stability of dark-gap solitons in linear lattice and nonlinear lattices.The results indicate that the combination of linear and nonlinear lattices gives dark-gap solitons unique properties.The linear lattice can stabilize dark-gap solitons,while the nonlinear lattice reduces the stability of dark-gap solitons.On the basis of numerical analysis,we investigate the effects of lattice depth,chemical potential,nonlinear lattice amplitude,and nonlinear lattice period on the soliton in mixed lattices with the same and different periods.The stability of dark-gap soliton is studied carefully by means of real-time evolution and linear stability analysis.Dark-gap solitons can exist stably in the band gap,but the solitons formed by the mixed lattices are slightly different when the period is the same or different.展开更多
The hydroformylation of olefins,known as the"oxo reaction",involves the use of syngas(CO/H_(2))to produce aldehyde with an additional carbon atom.However,side reactions such as the isomerization or hydrogena...The hydroformylation of olefins,known as the"oxo reaction",involves the use of syngas(CO/H_(2))to produce aldehyde with an additional carbon atom.However,side reactions such as the isomerization or hydrogenation of olefins often result in unexpected products and other by-products.Recent efforts in developing efficient ligands represent the most effective approach to addressing these challenges.In this study,we described a Bis-OPNN phosphorus ligand facilitated Rh-catalyzed hydroformylation with a high degree of linear selectivity across various olefins.Under mild conditions,a broad range of olefins were efficiently converted into linear aldehydes with high yields and excellent regioselectivity.The protocol also showed impressive functional group tolerance and was successfully applied to modify drugs and natural products,including the total synthesis of(±)-crispine A.Preliminary mechanistic studies revealed that this Bis-OPNN phosphorus ligand anchoring the rhodium catalyst is crucial for controlling the linear selectivity.展开更多
We have designed,assembled,and tested a 4-MA,60-ns fast linear transformer driver(LTD),which is the first operating generator featuring multiple LTD modules connected in parallel.The LTD-based accelerator comprises si...We have designed,assembled,and tested a 4-MA,60-ns fast linear transformer driver(LTD),which is the first operating generator featuring multiple LTD modules connected in parallel.The LTD-based accelerator comprises six modules in parallel,each of which has ten-stage cavities stacked in series.The six LTD modules are connected to a water tank of diameter 6 m via a 3-m-long impedance-matched deionized waterinsulated coaxial transmission line.In the water tank,the electrical pulses are transmitted down by six horizontal tri-plate transmission lines.A 2.1-m-diameter two-level vacuum insulator stack is utilized to separate the deionized water region from the vacuum region.In the vacuum,the currents are further transported downstream by a two-level magnetically insulated transmission-line and then converged through four post-hole convolutes.Plasma radiation loads or bremsstrahlung electron beam diodes serve as loads that are expected to generate intense soft X rays or warm X rays.The machine is 3.2 m in height and 22 m in outer diameter,including support systems such as a high-voltage charge supply,magnetic core reset system,trigger system,and support platform for inner stalk installation and maintenance.A total of 1440 individual±100-kV multi-gap spark switches and 2880 individual 100-kV capacitors are employed in the accelerator.A total of 12 fiberoptic laser-controlled trigger generators combining photoconductive and traditional gas spark switch technologies are used to realize the synchronous discharge of the more than 1000 gas switches.At an LTD charge voltage of±85 kV,the accelerator stores an initial energy of about 300 kJ and is expected to deliver a current of 3–5 MA into various loads.To date,the LTD facility has shot into a thick-walled aluminum liner load and a reflex triode load.With a thick-walled aluminum liner of inductance 1.81 nH,a current with peak up to 4.1 MA and rise time(10%–90%)of about 60 ns has been achieved.The current transport efficiency from the insulator stack to the liner load approaches 100%during peak times.The LTD accelerator has been used to drive reflex triode loads generating warm X rays with high energy fluence and large radiation area.It has been demonstrated that this LTD is a promising and high-efficiency prime pulsed power source suitable for use in constructing the next generation of large-scale accelerators with currents of tens of megaamperes.展开更多
A family of neural networks is proposed to solve linear complementarity problems(LCP).The neural networks are constructed from the novel equivalent model of LCP,which is reformulated by utilizing the modulus and smoot...A family of neural networks is proposed to solve linear complementarity problems(LCP).The neural networks are constructed from the novel equivalent model of LCP,which is reformulated by utilizing the modulus and smoothing technologies.Some important properties of the proposed novel equivalent model are summarized.In addition,the stability properties of the proposed steepest descent-based neural networks for LCP are analyzed.In order to illustrate the theoretical results,we provide some numerical simulations and compare the proposed neural networks with existing neural networks based on the NCP-functions.Numerical results indicate that the performance of the proposed neural networks is effective and robust.展开更多
Dear Editor,This letter studies output consensus problem of heterogeneous linear multiagent systems over directed graphs. A novel adaptive dynamic event-triggered controller is presented based only on the feedback com...Dear Editor,This letter studies output consensus problem of heterogeneous linear multiagent systems over directed graphs. A novel adaptive dynamic event-triggered controller is presented based only on the feedback combination of the agent's own state and neighbors' output,which can achieve exponential output consensus through intermittent communication. The controller is obtained by solving two linear matrix equations, and Zeno behavior is excluded.展开更多
Polydopamine-based melanin-like materials have been widely used in the fields of ultraviolet(UV)shielding,solar desalination and anti-inflammatory treatment owing to their unique physical properties.The well-establish...Polydopamine-based melanin-like materials have been widely used in the fields of ultraviolet(UV)shielding,solar desalination and anti-inflammatory treatment owing to their unique physical properties.The well-established synthesis of polydopamine nanoparticles involves the oxidative polymerization of dopamine-derived monomers,resulting in cross-linked nanostructures with high complexity and heterogeneity.Therefore,the controlled synthesis of polydopamine-based melanin-like materials with well-defined structures and predictable properties remains challenging.Herein,we propose a mechanochemical Suzuki polymerization approach for the synthesis of linear melanin-like polymers with tunable physical properties.Compared with polydopamine nanoparticles,the mechanochemical approach offers a more flexible chain-like structure,thereby enhancing its antioxidant performance.Furthermore,this approach also enables the preparation of a melanin-like alternating copolymer that exhibits green fluorescence owing to itsπ-conjugated structure.This study not only offers opportunities for exploring novel synthetic melanin materials,but also provides new insights into the structure-function relationships of polydopamine-based materials.展开更多
Piecewise linear systems are prevalent in engineering practice,and can be categorized into symmetric and asymmetric piecewise linear systems.Considering that symmetry is a special case of asymmetry,it is essential to ...Piecewise linear systems are prevalent in engineering practice,and can be categorized into symmetric and asymmetric piecewise linear systems.Considering that symmetry is a special case of asymmetry,it is essential to investigate the broader model,namely the asymmetric piecewise linear system.The traditional averaging method is frequently used for studying nonlinear systems,particularly symmetric piecewise linear systems,with the harmonic response of the oscillator serving as a key prerequisite for calculating steady-state solutions.However,asymmetric systems inherently exhibit nonharmonic,asymmetric responses,rendering the traditional averaging method inapplicable.To overcome this limitation,this paper introduces an improved averaging method tailored for an oscillator characterized by asymmetric gaps and springs.Unlike the traditional method,which assumes a purely harmonic response,the improved averaging method redefines the system response as a superposition of a direct current(DC)term and a first harmonic component.Herein,the DC term can be regarded as the offset induced by model asymmetry.Furthermore,the DC term is treated as a slow variable function of time,with its time derivative assumed to be zero when calculating the steady-state solution,akin to the amplitude and phase in the traditional averaging method.Numerical validation demonstrates that the responses computed in both time and frequency domains with the improved averaging method exhibit greater accuracy compared with those derived from the traditional method.Leveraging these improved results,the study also examines the parameter effect,stability,and bifurcation phenomena within the amplitude-frequency responses.展开更多
In this paper,a linear optimization method(LOM)for the design of terahertz circuits is presented,aimed at enhancing the simulation efficacy and reducing the time of the circuit design workflow.This method enables the ...In this paper,a linear optimization method(LOM)for the design of terahertz circuits is presented,aimed at enhancing the simulation efficacy and reducing the time of the circuit design workflow.This method enables the rapid determination of optimal embedding impedance for diodes across a specific bandwidth to achieve maximum efficiency through harmonic balance simulations.By optimizing the linear matching circuit with the optimal embedding impedance,the method effectively segregates the simulation of the linear segments from the nonlinear segments in the frequency multiplier circuit,substantially improving the speed of simulations.The design of on-chip linear matching circuits adopts a modular circuit design strategy,incorporating fixed load resistors to simplify the matching challenge.Utilizing this approach,a 340 GHz frequency doubler was developed and measured.The results demonstrate that,across a bandwidth of 330 GHz to 342 GHz,the efficiency of the doubler remains above 10%,with an input power ranging from 98 mW to 141mW and an output power exceeding 13 mW.Notably,at an input power of 141 mW,a peak output power of 21.8 mW was achieved at 334 GHz,corresponding to an efficiency of 15.8%.展开更多
In this paper,we introduce TianXing,a transformer-based data-driven model designed with physical augmentation for skillful and efficient global weather forecasting.Previous data-driven transformer models such as Pangu...In this paper,we introduce TianXing,a transformer-based data-driven model designed with physical augmentation for skillful and efficient global weather forecasting.Previous data-driven transformer models such as Pangu-Weather,FengWu,and FuXi have emerged as promising alternatives for numerical weather prediction in weather forecasting.However,these models have been characterized by their substantial computational resource consumption during training and limited incorporation of explicit physical guidance in their modeling frameworks.In contrast,TianXing applies a linear complexity mechanism that ensures proportional scalability with input data size while significantly diminishing GPU resource demands,with only a marginal compromise in accuracy.Furthermore,TianXing proposes an explicit attention decay mechanism in the linear attention derived from physical insights to enhance its forecasting skill.The mechanism can reweight attention based on Earth's spherical distances and learned sparse multivariate coupling relationships,promptingTianXing to prioritize dynamically relevant neighboring features.Finally,to enhance its performance in mediumrange forecasting,TianXing employs a stacked autoregressive forecast algorithm.Validation of the model's architecture is conducted using ERA5 reanalysis data at a 5.625°latitude-longitude resolution,while a high-resolution dataset at 0.25°is utilized for training the actual forecasting model.Notably,the TianXing exhibits excellent performance,particularly in the Z500(geopotential height)and T850(temperature)fields,surpassing previous data-driven models and operational fullresolution models such as NCEP GFS and ECMWF IFS,as evidenced by latitude-weighted RMSE and ACC metrics.Moreover,the TianXing has demonstrated remarkable capabilities in predicting extreme weather events,such as typhoons.展开更多
Codebooks are widely applied in code division multiple access communication systems.Based on the subspaces of singular linear spaces over the finite fields,two classes of new codebooks are constructed.Firstly,a kind o...Codebooks are widely applied in code division multiple access communication systems.Based on the subspaces of singular linear spaces over the finite fields,two classes of new codebooks are constructed.Firstly,a kind of binary codebooks are constructed by using the subspace of the singular linear space over the finite fields.According to the anzahl theorem,the parameters and the maximum correlation amplitude I_(max)(C)of the codebooks are calculated,and then given the conditions that the I_(max)(C)asymptotically reaches the Welch bound.On this basis,by mixing with Hadamard matrices,the number of columns are increased and obtain another class of new code,which further relaxes the conditions that the I_(max)(C)asymptotically reaches the Welch bound.展开更多
Laser frequency microcombs provide a series of equidistant,coherent frequency markers across a broad spectrum,enabling advancements in laser spectroscopy,dense optical communications,precision distance metrology,and a...Laser frequency microcombs provide a series of equidistant,coherent frequency markers across a broad spectrum,enabling advancements in laser spectroscopy,dense optical communications,precision distance metrology,and astronomy.Here,we design and fabricate silicon nitride,dispersion-managed microresonators that effectively suppress avoided-mode crossings and achieve close-to-zero averaged dispersion.Both the stochastic noise and mode-locking dynamics of the resonator are numerically and experimentally investigated.First,we experimentally demonstrate thermally stabilized microcomb formation in the microresonator across different mode-locked states,showing negligible center frequency shifts and a broad frequency bandwidth.Next,we characterize the femtosecond timing jitter of the microcombs,supported by precise metrology of the timing phase and relative intensity noise.For the single-soliton state,we report a relative intensity noise of−153.2 dB∕Hz,close to the shot-noise limit,and a quantum-noise–limited timing jitter power spectral density of 0.4 as 2∕Hz at a 100 kHz offset frequency,measured using a self-heterodyne linear interferometer.In addition,we achieve an integrated timing jitter of 1.7 fs±0.07 fs,measured from 10 kHz to 1 MHz.Measuring and understanding these fundamental noise parameters in high clock rate frequency microcombs is critical for advancing soliton physics and enabling new applications in precision metrology.展开更多
The arc-linear motor(ALM) is a new type of special motor derived from the linear motor, which has the merits of high torque, compact structure and fast dynamic response. This kind of motor does not need a complex inte...The arc-linear motor(ALM) is a new type of special motor derived from the linear motor, which has the merits of high torque, compact structure and fast dynamic response. This kind of motor does not need a complex intermediate transmission device, it is used in some direct-drive applications for continuous rotation or limited angle motion. However, there is no systematic summary and generalization of the ALMs so far.Therefore, this paper systematically overviews the recent advances in ALMs for direct-drive systems. First, the evolution process and basic structure of the ALM are introduced. And then, various ALMs are reviewed with particular reference to motor topologies, working principle, motor performance,optimization design and control techniques. To heel, a comprehensive comparison of several typical ALMs is carried out. Finally, the application areas, main challenges and development trends of the ALMs are highlighted.展开更多
The effect of a metal shell on the launch efficiency of an asynchronous coil launcher(coil AC pulse linear motor)remains insufficiently understood in terms of the underlying mechanisms and principles.To address this g...The effect of a metal shell on the launch efficiency of an asynchronous coil launcher(coil AC pulse linear motor)remains insufficiently understood in terms of the underlying mechanisms and principles.To address this gap,this study conducted extensive modelling simulations and calculations,varying the shell's conductivity,permeability,and dimensions.Through comparative analysis of these models,this paper identifies a unique‘tick-shaped efficiency curve’for the asynchronous coil launcher:the launch efficiency first decreases and then increases as the shell's electromagnetic parameters are enhanced.Enhancements that bolster the electromagnetic induction effect within the shell-such as increased conductivity,permeability and dimensions-are termed as the augmentation of electromagnetic parameters.This study delves into Lenz's law of electromagnetism to elucidate the observed phenomena,attributing them to the spatio-temporal force characteristics of the multipeak and multi-valley armature of the transmitting device,and the resulting‘tick-shaped efficiency curve’.A comprehensive summary of shell-related research in electromagnetic emission reveals that the driving current fundamentally dictates the shell's impact on launch efficiency.DC-driven launchers conform to the monotonic effect efficiency curve,whereas AC-driven launchers conform to the tick-shaped efficiency curve.展开更多
The long-term Mittag-Leffler stability of solutions to multi-term timefractional diffusion equations with constant coefficients was rigorously established,which demonstrated that the algebraic decay rate of the soluti...The long-term Mittag-Leffler stability of solutions to multi-term timefractional diffusion equations with constant coefficients was rigorously established,which demonstrated that the algebraic decay rate of the solution,characterized by||u_(n)||L^(2)(Ω)=O(t^(−αs)) as t→∞,is determined by the minimum order α_(s) of the time-fractional derivatives.Building on this foundational result,this article pursues two primary objectives.First,we introduce a strongly A-stable fractional linear multistep method and derive the numerical stability region for the governing equation.Second,we rigorously prove the long-term decay rate of the numerical solution through a detailed singularity analysis of its generating function.Notably,the numerical decay rate||u_(n)||L^(2)(Ω)=O(t_(n)^(−α_(s)) as t_(n)→∞aligns precisely with the continuous case.Theoretical findings are further validated through comprehensive numerical simulations,underscoring the robustness of our proposed method.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52074228,52305420,and 51875470)the China Postdoctoral Science Foundation(No.2023M742830)。
文摘GH4169 joints manufactured by Linear Friction Welding(LFW)are subjected to tensile test and stair-case method to evaluate the High Cycle Fatigue(HCF)performance at 650℃.The yield and ultimate tensile strengths are 582 MPa and 820 MPa,respectively.The HCF strength of joint reaches 400 MPa,which is slightly lower than that of Base Metal(BM),indicating reliable quality of this type of joint.The microstructure observation results show that all cracks initiate at the inside of specimens and transfer into deeper region with decrease of external stress,and the crack initiation site is related with microhardness of matrix.The Electron Backscattered Diffraction(EBSD)results of the observed regions with different distances to fracture show that plastic deformation plays a key role in HCF,and the Schmid factor of most grains near fracture exceeds 0.4.In addition,the generation of twins plays a vital role in strain concentration release and coordinating plastic deformation among grains.
基金supported by the National Natural Science Foundation of China(Nos.52074228,52305420 and 51875470)the Practice and Innovation Funds for Graduate Students of Northwestern Polytechnical University,China(No.PF2024053)the Xi’an Beilin District Science and Technology Planning Project,China(No.GX2349).
文摘The pre-weld heat treatment was carried out to obtain different initial microstructures of the GH4169 superalloy,and then Linear Friction Welding(LFW)was performed.The effect of the pre-weld heat treatment on the microstructure evolution and mechanical properties of the joint was analyzed,and the joint electrochemical corrosion behavior as well as the hot corrosion behavior was studied.The results show that the joint hardness of Base Metal(BM)increases after pre-weld heat treatment,and the strengthening phasesγ′andγ″further precipitate.However,the precipitation phases dissolve significantly in the Weld Zone(WZ)due to the thermal process of LFW.The corrosion resistance in BM is reduced after the pre-weld heat treatment,while it is similar in WZ with a slight decrease.The surface morphology of the BM and WZ can be generally divided into a loose and porous matrix and a scattered oxide particle layer after hot corrosion.The joint cross section exhibits a Cr-depleted zone with the diffusion of Cr to form an oxide film.The corrosion product mainly consists of Fe_(2)O_(3)/Fe_(3)O_(4) as the outer layer and Cr_(2)O_(3) as the inner layer.
基金the Istanbul Technical University Scientific Research Projects Unit with grant number MGA-2022-43948。
文摘The hyperloop idea,which is one of the most ecofriendly,low-carbon emissions,and fossil fuel-efficient modes of transportation,has recently become quite popular.In this study,a double-sided linear induction motor(LIM)with 500 W of output power,60 N of thrust force and 200 V/38.58 Hz of supply voltage was designed to be used in hyperloop development competition hosted by the scientific and technological research council of turkey(TüB?TAK)rail transportation technologies institute(RUTE).In contrast to the studies in the literature,concentrated winding is preferred instead of distributed winding due to mechanical constraints.The electromagnetic design of LIM,whose mechanical and electrical requirements were determined considering the hyperloop development competition,was carried out by following certain steps.Then,the designed model was simulated and analyzed by finite element method(FEM),and the necessary optimizations have been performed to improve the motor characteristics.By examining the final model,the applicability of the concentrated winding type LIM for hyperloop technology has been investigated.Besides,the effects of primary material,railway material,and mechanical air-gap length on LIM performance were also investigated.In the practical phase of the study,the designed LIM has been prototyped and tested.The validation of the experimental results was achieved through good agreement with the finite element analysis results.
基金funded by the National Key R&D Program of China(Grant No.2022YFC2903904)the National Natural Science Foundation of China(Grant Nos.51904057 and U1906208).
文摘Due to the heterogeneity of rock masses and the variability of in situ stress,the traditional linear inversion method is insufficiently accurate to achieve high accuracy of the in situ stress field.To address this challenge,nonlinear stress boundaries for a numerical model are determined through regression analysis of a series of nonlinear coefficient matrices,which are derived from the bubbling method.Considering the randomness and flexibility of the bubbling method,a parametric study is conducted to determine recommended ranges for these parameters,including the standard deviation(σb)of bubble radii,the non-uniform coefficient matrix number(λ)for nonlinear stress boundaries,and the number(m)and positions of in situ stress measurement points.A model case study provides a reference for the selection of these parameters.Additionally,when the nonlinear in situ stress inversion method is employed,stress distortion inevitably occurs near model boundaries,aligning with the Saint Venant's principle.Two strategies are proposed accordingly:employing a systematic reduction of nonlinear coefficients to achieve high inversion accuracy while minimizing significant stress distortion,and excluding regions with severe stress distortion near the model edges while utilizing the central part of the model for subsequent simulations.These two strategies have been successfully implemented in the nonlinear in situ stress inversion of the Xincheng Gold Mine and have achieved higher inversion accuracy than the linear method.Specifically,the linear and nonlinear inversion methods yield root mean square errors(RMSE)of 4.15 and 3.2,and inversion relative errors(δAve)of 22.08%and 17.55%,respectively.Therefore,the nonlinear inversion method outperforms the traditional multiple linear regression method,even in the presence of a systematic reduction in the nonlinear stress boundaries.
文摘Let a_(1),a_(2),a_(3)be nonzero integers with gcd(a_(1),a_(2),a_(3))=1,and let k be any positive integer,K=max[3,|a_(1)|,|a_(2)|,|a_(3)|,k].Suppose that l_(1),l_(2),l_(3)are integers each coprime to k.Suppose further that b is any integer satisfying some necessary congruent conditions.The solvability of linear equation a_(1)p_(1)+a_(2)p_(2)+a_(3)p_(3)=b(p_(j)=l_(j)(mod k),1≤j≤3)with prime variables pi,p_(2),ps is investigated.It is proved that if ai,a_(2),a_(3)are all positive,then the above equation is solvable whenever b≥K^(25);if a,a_(2),a_(3)are not all of the same sign,then the above equation has a solution p_(1),p_(2),p_(3)satisfying max(p_(1),p_(2),p_(3))≤3|b|+K^(25).
基金supported by the Innovation Capability Improvement Project of Hebei Province,China(Grant No.22567605H).
文摘We study the existence and stability of dark-gap solitons in linear lattice and nonlinear lattices.The results indicate that the combination of linear and nonlinear lattices gives dark-gap solitons unique properties.The linear lattice can stabilize dark-gap solitons,while the nonlinear lattice reduces the stability of dark-gap solitons.On the basis of numerical analysis,we investigate the effects of lattice depth,chemical potential,nonlinear lattice amplitude,and nonlinear lattice period on the soliton in mixed lattices with the same and different periods.The stability of dark-gap soliton is studied carefully by means of real-time evolution and linear stability analysis.Dark-gap solitons can exist stably in the band gap,but the solitons formed by the mixed lattices are slightly different when the period is the same or different.
基金financial support from the National Key Research and Development Program of China(No.2021YFF0600704).
文摘The hydroformylation of olefins,known as the"oxo reaction",involves the use of syngas(CO/H_(2))to produce aldehyde with an additional carbon atom.However,side reactions such as the isomerization or hydrogenation of olefins often result in unexpected products and other by-products.Recent efforts in developing efficient ligands represent the most effective approach to addressing these challenges.In this study,we described a Bis-OPNN phosphorus ligand facilitated Rh-catalyzed hydroformylation with a high degree of linear selectivity across various olefins.Under mild conditions,a broad range of olefins were efficiently converted into linear aldehydes with high yields and excellent regioselectivity.The protocol also showed impressive functional group tolerance and was successfully applied to modify drugs and natural products,including the total synthesis of(±)-crispine A.Preliminary mechanistic studies revealed that this Bis-OPNN phosphorus ligand anchoring the rhodium catalyst is crucial for controlling the linear selectivity.
基金supported by the National Natural Science Foundation of China(Grant Nos.12027811 and 51790524).
文摘We have designed,assembled,and tested a 4-MA,60-ns fast linear transformer driver(LTD),which is the first operating generator featuring multiple LTD modules connected in parallel.The LTD-based accelerator comprises six modules in parallel,each of which has ten-stage cavities stacked in series.The six LTD modules are connected to a water tank of diameter 6 m via a 3-m-long impedance-matched deionized waterinsulated coaxial transmission line.In the water tank,the electrical pulses are transmitted down by six horizontal tri-plate transmission lines.A 2.1-m-diameter two-level vacuum insulator stack is utilized to separate the deionized water region from the vacuum region.In the vacuum,the currents are further transported downstream by a two-level magnetically insulated transmission-line and then converged through four post-hole convolutes.Plasma radiation loads or bremsstrahlung electron beam diodes serve as loads that are expected to generate intense soft X rays or warm X rays.The machine is 3.2 m in height and 22 m in outer diameter,including support systems such as a high-voltage charge supply,magnetic core reset system,trigger system,and support platform for inner stalk installation and maintenance.A total of 1440 individual±100-kV multi-gap spark switches and 2880 individual 100-kV capacitors are employed in the accelerator.A total of 12 fiberoptic laser-controlled trigger generators combining photoconductive and traditional gas spark switch technologies are used to realize the synchronous discharge of the more than 1000 gas switches.At an LTD charge voltage of±85 kV,the accelerator stores an initial energy of about 300 kJ and is expected to deliver a current of 3–5 MA into various loads.To date,the LTD facility has shot into a thick-walled aluminum liner load and a reflex triode load.With a thick-walled aluminum liner of inductance 1.81 nH,a current with peak up to 4.1 MA and rise time(10%–90%)of about 60 ns has been achieved.The current transport efficiency from the insulator stack to the liner load approaches 100%during peak times.The LTD accelerator has been used to drive reflex triode loads generating warm X rays with high energy fluence and large radiation area.It has been demonstrated that this LTD is a promising and high-efficiency prime pulsed power source suitable for use in constructing the next generation of large-scale accelerators with currents of tens of megaamperes.
基金Supported by the National Natural Science Foundation of China(12371378,41725017,11901098).
文摘A family of neural networks is proposed to solve linear complementarity problems(LCP).The neural networks are constructed from the novel equivalent model of LCP,which is reformulated by utilizing the modulus and smoothing technologies.Some important properties of the proposed novel equivalent model are summarized.In addition,the stability properties of the proposed steepest descent-based neural networks for LCP are analyzed.In order to illustrate the theoretical results,we provide some numerical simulations and compare the proposed neural networks with existing neural networks based on the NCP-functions.Numerical results indicate that the performance of the proposed neural networks is effective and robust.
基金supported by the National Science and Technology Innovation 2030-Major Program(2022ZD 0115403)the National Natural Science Foundation of China(61991414)+1 种基金Chongqing Natural Science Foundation(CSTB2023NSCQJQX0018)Beijing Natural Science Foundation(L221005)
文摘Dear Editor,This letter studies output consensus problem of heterogeneous linear multiagent systems over directed graphs. A novel adaptive dynamic event-triggered controller is presented based only on the feedback combination of the agent's own state and neighbors' output,which can achieve exponential output consensus through intermittent communication. The controller is obtained by solving two linear matrix equations, and Zeno behavior is excluded.
基金supported by the National Natural Science Foundation of China(Nos.22471185 and 52225311)Science and Technology Program of Suzhou(No.ZXL2022480)+1 种基金Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)Program of Innovative Research Team of Soochow University。
文摘Polydopamine-based melanin-like materials have been widely used in the fields of ultraviolet(UV)shielding,solar desalination and anti-inflammatory treatment owing to their unique physical properties.The well-established synthesis of polydopamine nanoparticles involves the oxidative polymerization of dopamine-derived monomers,resulting in cross-linked nanostructures with high complexity and heterogeneity.Therefore,the controlled synthesis of polydopamine-based melanin-like materials with well-defined structures and predictable properties remains challenging.Herein,we propose a mechanochemical Suzuki polymerization approach for the synthesis of linear melanin-like polymers with tunable physical properties.Compared with polydopamine nanoparticles,the mechanochemical approach offers a more flexible chain-like structure,thereby enhancing its antioxidant performance.Furthermore,this approach also enables the preparation of a melanin-like alternating copolymer that exhibits green fluorescence owing to itsπ-conjugated structure.This study not only offers opportunities for exploring novel synthetic melanin materials,but also provides new insights into the structure-function relationships of polydopamine-based materials.
基金Project supported by the National Natural Science Foundation of China(Nos.12272242 and U1934201)。
文摘Piecewise linear systems are prevalent in engineering practice,and can be categorized into symmetric and asymmetric piecewise linear systems.Considering that symmetry is a special case of asymmetry,it is essential to investigate the broader model,namely the asymmetric piecewise linear system.The traditional averaging method is frequently used for studying nonlinear systems,particularly symmetric piecewise linear systems,with the harmonic response of the oscillator serving as a key prerequisite for calculating steady-state solutions.However,asymmetric systems inherently exhibit nonharmonic,asymmetric responses,rendering the traditional averaging method inapplicable.To overcome this limitation,this paper introduces an improved averaging method tailored for an oscillator characterized by asymmetric gaps and springs.Unlike the traditional method,which assumes a purely harmonic response,the improved averaging method redefines the system response as a superposition of a direct current(DC)term and a first harmonic component.Herein,the DC term can be regarded as the offset induced by model asymmetry.Furthermore,the DC term is treated as a slow variable function of time,with its time derivative assumed to be zero when calculating the steady-state solution,akin to the amplitude and phase in the traditional averaging method.Numerical validation demonstrates that the responses computed in both time and frequency domains with the improved averaging method exhibit greater accuracy compared with those derived from the traditional method.Leveraging these improved results,the study also examines the parameter effect,stability,and bifurcation phenomena within the amplitude-frequency responses.
基金Supported by the Beijing Municipal Science&Technology Commission(Z211100004421012),the Key Reaserch and Development Pro⁃gram of China(2022YFF0605902)。
文摘In this paper,a linear optimization method(LOM)for the design of terahertz circuits is presented,aimed at enhancing the simulation efficacy and reducing the time of the circuit design workflow.This method enables the rapid determination of optimal embedding impedance for diodes across a specific bandwidth to achieve maximum efficiency through harmonic balance simulations.By optimizing the linear matching circuit with the optimal embedding impedance,the method effectively segregates the simulation of the linear segments from the nonlinear segments in the frequency multiplier circuit,substantially improving the speed of simulations.The design of on-chip linear matching circuits adopts a modular circuit design strategy,incorporating fixed load resistors to simplify the matching challenge.Utilizing this approach,a 340 GHz frequency doubler was developed and measured.The results demonstrate that,across a bandwidth of 330 GHz to 342 GHz,the efficiency of the doubler remains above 10%,with an input power ranging from 98 mW to 141mW and an output power exceeding 13 mW.Notably,at an input power of 141 mW,a peak output power of 21.8 mW was achieved at 334 GHz,corresponding to an efficiency of 15.8%.
基金supported in part by the Meteorological Joint Funds of the National Natural Science Foundation of China under Grant U2142211in part by the National Natural Science Foundation of China under Grant 42075141,42341202+2 种基金in part by the National Key Research and Development Program of China under Grant 2020YFA0608000in part by the Shanghai Municipal Science and Technology Major Project(2021SHZDZX0100)the Fundamental Research Funds for the Central Universities。
文摘In this paper,we introduce TianXing,a transformer-based data-driven model designed with physical augmentation for skillful and efficient global weather forecasting.Previous data-driven transformer models such as Pangu-Weather,FengWu,and FuXi have emerged as promising alternatives for numerical weather prediction in weather forecasting.However,these models have been characterized by their substantial computational resource consumption during training and limited incorporation of explicit physical guidance in their modeling frameworks.In contrast,TianXing applies a linear complexity mechanism that ensures proportional scalability with input data size while significantly diminishing GPU resource demands,with only a marginal compromise in accuracy.Furthermore,TianXing proposes an explicit attention decay mechanism in the linear attention derived from physical insights to enhance its forecasting skill.The mechanism can reweight attention based on Earth's spherical distances and learned sparse multivariate coupling relationships,promptingTianXing to prioritize dynamically relevant neighboring features.Finally,to enhance its performance in mediumrange forecasting,TianXing employs a stacked autoregressive forecast algorithm.Validation of the model's architecture is conducted using ERA5 reanalysis data at a 5.625°latitude-longitude resolution,while a high-resolution dataset at 0.25°is utilized for training the actual forecasting model.Notably,the TianXing exhibits excellent performance,particularly in the Z500(geopotential height)and T850(temperature)fields,surpassing previous data-driven models and operational fullresolution models such as NCEP GFS and ECMWF IFS,as evidenced by latitude-weighted RMSE and ACC metrics.Moreover,the TianXing has demonstrated remarkable capabilities in predicting extreme weather events,such as typhoons.
文摘Codebooks are widely applied in code division multiple access communication systems.Based on the subspaces of singular linear spaces over the finite fields,two classes of new codebooks are constructed.Firstly,a kind of binary codebooks are constructed by using the subspace of the singular linear space over the finite fields.According to the anzahl theorem,the parameters and the maximum correlation amplitude I_(max)(C)of the codebooks are calculated,and then given the conditions that the I_(max)(C)asymptotically reaches the Welch bound.On this basis,by mixing with Hadamard matrices,the number of columns are increased and obtain another class of new code,which further relaxes the conditions that the I_(max)(C)asymptotically reaches the Welch bound.
基金support from the Lawrence Livermore National Laboratory(Grant No.B622827)the National Science Foundation(Grant Nos.1824568,1810506,1741707,and 1829071)the Office of Naval Research(Grant No.N00014-16-1-2094).
文摘Laser frequency microcombs provide a series of equidistant,coherent frequency markers across a broad spectrum,enabling advancements in laser spectroscopy,dense optical communications,precision distance metrology,and astronomy.Here,we design and fabricate silicon nitride,dispersion-managed microresonators that effectively suppress avoided-mode crossings and achieve close-to-zero averaged dispersion.Both the stochastic noise and mode-locking dynamics of the resonator are numerically and experimentally investigated.First,we experimentally demonstrate thermally stabilized microcomb formation in the microresonator across different mode-locked states,showing negligible center frequency shifts and a broad frequency bandwidth.Next,we characterize the femtosecond timing jitter of the microcombs,supported by precise metrology of the timing phase and relative intensity noise.For the single-soliton state,we report a relative intensity noise of−153.2 dB∕Hz,close to the shot-noise limit,and a quantum-noise–limited timing jitter power spectral density of 0.4 as 2∕Hz at a 100 kHz offset frequency,measured using a self-heterodyne linear interferometer.In addition,we achieve an integrated timing jitter of 1.7 fs±0.07 fs,measured from 10 kHz to 1 MHz.Measuring and understanding these fundamental noise parameters in high clock rate frequency microcombs is critical for advancing soliton physics and enabling new applications in precision metrology.
基金supported in part by the National Natural Science Foundation of China under Grants 52307049 and U23A20644in part by the Fundamental Research Funds for the Central Universities under Grant JZ2023HGTB0243+1 种基金in part by the Key Laboratory of Electric Drive and Control of Anhui Province under Grant DQKJ202403in part by the China Postdoctoral Science Foundation under Grant 2024M751073。
文摘The arc-linear motor(ALM) is a new type of special motor derived from the linear motor, which has the merits of high torque, compact structure and fast dynamic response. This kind of motor does not need a complex intermediate transmission device, it is used in some direct-drive applications for continuous rotation or limited angle motion. However, there is no systematic summary and generalization of the ALMs so far.Therefore, this paper systematically overviews the recent advances in ALMs for direct-drive systems. First, the evolution process and basic structure of the ALM are introduced. And then, various ALMs are reviewed with particular reference to motor topologies, working principle, motor performance,optimization design and control techniques. To heel, a comprehensive comparison of several typical ALMs is carried out. Finally, the application areas, main challenges and development trends of the ALMs are highlighted.
基金supported by Scientific Instrument Developing Project of Chinese Academy of Sciences(Grant/Award YJKYYQ20200011)Chinese Academy of Sciences‘Light of West China’Program(Grant/Award xbzg-zdsys-202317).
文摘The effect of a metal shell on the launch efficiency of an asynchronous coil launcher(coil AC pulse linear motor)remains insufficiently understood in terms of the underlying mechanisms and principles.To address this gap,this study conducted extensive modelling simulations and calculations,varying the shell's conductivity,permeability,and dimensions.Through comparative analysis of these models,this paper identifies a unique‘tick-shaped efficiency curve’for the asynchronous coil launcher:the launch efficiency first decreases and then increases as the shell's electromagnetic parameters are enhanced.Enhancements that bolster the electromagnetic induction effect within the shell-such as increased conductivity,permeability and dimensions-are termed as the augmentation of electromagnetic parameters.This study delves into Lenz's law of electromagnetism to elucidate the observed phenomena,attributing them to the spatio-temporal force characteristics of the multipeak and multi-valley armature of the transmitting device,and the resulting‘tick-shaped efficiency curve’.A comprehensive summary of shell-related research in electromagnetic emission reveals that the driving current fundamentally dictates the shell's impact on launch efficiency.DC-driven launchers conform to the monotonic effect efficiency curve,whereas AC-driven launchers conform to the tick-shaped efficiency curve.
文摘The long-term Mittag-Leffler stability of solutions to multi-term timefractional diffusion equations with constant coefficients was rigorously established,which demonstrated that the algebraic decay rate of the solution,characterized by||u_(n)||L^(2)(Ω)=O(t^(−αs)) as t→∞,is determined by the minimum order α_(s) of the time-fractional derivatives.Building on this foundational result,this article pursues two primary objectives.First,we introduce a strongly A-stable fractional linear multistep method and derive the numerical stability region for the governing equation.Second,we rigorously prove the long-term decay rate of the numerical solution through a detailed singularity analysis of its generating function.Notably,the numerical decay rate||u_(n)||L^(2)(Ω)=O(t_(n)^(−α_(s)) as t_(n)→∞aligns precisely with the continuous case.Theoretical findings are further validated through comprehensive numerical simulations,underscoring the robustness of our proposed method.
