Accuracy allocation is crucial in the accuracy design of machining tools.Current accuracy allocation methods primarily focus on positional deviation,with little consideration for tool direction deviation.To address th...Accuracy allocation is crucial in the accuracy design of machining tools.Current accuracy allocation methods primarily focus on positional deviation,with little consideration for tool direction deviation.To address this issue,we propose a geometric error cost sensitivity-based accuracy allocation method for five-axis machine tools.A geometric error model consisting of 4l error components is constructed based on homogeneous transformation matrices.Volumetric points with positional and tool direction deviations are randomly sampled to evaluate the accuracy of the machine tool.The sensitivity of each error component at these sampling points is analyzed using the Sobol method.To balance the needs of geometric precision and manufacturing cost,a geometric error cost sensitivity function is developed to estimate the required cost.By allocating error components affecting tool direction deviation first and the remaining components second,this allocation scheme ensures that both deviations meet the requirements.We also perform numerical simulation of a BC-type(B-axis and C-axis type)five-axis machine tool to validate the method.The results show that the new allocation scheme reduces the total geometric error cost by 27.8%compared to a uniform allocation scheme,and yields the same positional and tool direction machining accuracies.展开更多
Porous ceramic composites with directional microchannels from micrometer to dozens of micrometer levels have attracted more and more attention in various fields including aerospace,biomedicines,and thermal insulation ...Porous ceramic composites with directional microchannels from micrometer to dozens of micrometer levels have attracted more and more attention in various fields including aerospace,biomedicines,and thermal insulation due to their excellent fluid permeability,mechanical properties,etc.In this article,we summarize the recent directional porous ceramics developments including their main processing routes and respective properties.Meanwhile,the properties get from different processing routes have been com-pared and analyzed in terms of microstructures,mechanical properties,and permeability.Emphasis has been given to the deeper understanding which can allow one to control the microstructural features of these porous ceramic composites to obtain the desired characteristics.This work can provide a useful reference for the development and application of porous ceramic composites with directional microchan-nels.展开更多
To improve the resolution and accuracy of Direct Position Determination(DPD),this paper investigates the problem of positioning multiple emitters directly with a single moving Rotating Linear Array(RLA).Firstly,the ge...To improve the resolution and accuracy of Direct Position Determination(DPD),this paper investigates the problem of positioning multiple emitters directly with a single moving Rotating Linear Array(RLA).Firstly,the geometry of the RLA is formulated and analysed.According to its geometry,the intercepted noncoherent signals in multiple interception intervals are modeled.Correspondingly,the Multiple SIgnal Classification(MUSIC)based noncoherent DPD approach is proposed.Secondly,the synchronous coherent pulse signals are individually considered and formulated.And the coherent DPD approach which aims for localizing this special type of signal is presented by stacking all array responses at different interception intervals.Besides,we also derive the constrained Cramer-Rao Lower Bound(CRLB)expression for both noncoherent and coherent DPD with RLA under the constraint that the altitudes of the emitters are known.At last,computer simulations are included to examine the performance of the proposed approach.The results demonstrate that the localization accuracy and resolution of DPD with single moving linear array can be significantly improved by the array rotation.In addition,coherent DPD with RLA further improves the resolution and increases the maximum emitter number that can be localized compared with the noncoherent DPD with RLA.展开更多
Able to precisely control and manipulate materials'states at micro/nano-scale level,femtosecond(fs)laser micro/nano processing technology has undergone tremendous development over the past three decades.Free-formi...Able to precisely control and manipulate materials'states at micro/nano-scale level,femtosecond(fs)laser micro/nano processing technology has undergone tremendous development over the past three decades.Free-forming three-dimensional(3D)microscale functional devices and inducing fascinating and unique physical or chemical phenomena have granted this technology powerful versatility that no other technology can match.As this technology advances rapidly in various fields of application,some key challenges have emerged and remain to be urgently addressed.This review firstly introduces the fundamental principles for understanding how fs laser pulses interact with materials and the associated unique phenomena in section 2.Then micro/nano-fabrication in transparent materials by fs laser processing is presented in section 3.Thereafter,several high efficiency/throughput fabrication methods as well as pulse-shaping techniques are listed in sections 4 and 5 reviews four-dimensional(4D)and nanoscale printing realized by fs laser processing technology.Special attention is paid to the heterogeneous integration(HI)of functional materials enabled by fs laser processing in section 6.Several intriguing examples of 3D functional micro-devices created by fs laser-based manufacturing methods such as microfluidics,lab-on-chip,micro-optics,micro-mechanics,micro-electronics,micro-bots and micro-biodevices are reviewed in section 7.Finally,a summary of the review and a perspective are proposed to explore the challenges and future opportunities for further betterment of fs laser micro/nano processing technology.展开更多
In non-homogeneous environment, traditional space-time adaptive processing doesn＇t effectively suppress interference and detect target, because the secondary data don＇ t exactly reflect the statistical characteristi...In non-homogeneous environment, traditional space-time adaptive processing doesn＇t effectively suppress interference and detect target, because the secondary data don＇ t exactly reflect the statistical characteristic of the range cell under test. A ravel methodology utilizing the direct data domain approach to space-time adaptive processing （ STAP ） in airbome radar non-homogeneous environments is presented. The deterministic least squares adaptive signal processing technique operates on a ＂snapshot-by-snapshot＂ basis to dethrone the adaptive adaptive weights for nulling interferences and estimating signal of interest （SOI）. Furthermore, this approach eliminates the requirement for estimating the covariance through the data of neighboring range cell, which eliminates calculating the inverse of covariance, and can be implemented to operate in real-time. Simulation results illustrate the efficiency of interference suppression in non-homogeneous environment.展开更多
The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of tal...The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of talus deposits that widely exist in the hydro-power engineering in the southwest of China were first reconstructed by small particles according to the in-situ photographs based on the self-adaptive PCNN digital image processing,and then numerical direct shear tests were carried out for studying the mechanical properties of talus deposits.Results indicate that the reconstructed meso-structures of talus deposits are more consistent with the actual situation because the self-adaptive PCNN digital image processing has a higher discrimination in the details of soil-rock segmentation.The existence and random distribution of rock blocks make the initial shear stiffness,the peak strength and the residual strength higher than those of the "pure soil" with particle size less than 1.25 cm apparently,but reduce the displacements required for the talus deposits reaching its peak shear strength.The increase of rock proportion causes a significant improvement in the internal friction angle of talus deposit,which to a certain degree leads to the characteristics of shear stress-displacement curves having a changing trend from the plastic strain softening deformation to the nonlinear strain hardening deformation,while an unconspicuous increase in cohesion.The uncertainty and heterogeneity of rock distributions cause the differences of rock proportion within shear zone,leading to a relatively strong fluctuation in peak strengths during the shear process,while movement features of rock blocks,such as translation,rotation and crossing,expand the scope of shear zone,increase the required shear force,and also directly lead to the misjudgment that the lower shear strength is obtained from the samples with high rock proportion.That,however,just explains the reason why the shear strength gained from a small amount of indoor test data is not consistent with engineering practice.展开更多
Background Pain sensitivity is critical for preventing non-suicidal self-injury(NSSI)behaviours;however,individuals engaging in such behaviours often exhibit decreased pain sensitivity,which may undermine this natural...Background Pain sensitivity is critical for preventing non-suicidal self-injury(NSSI)behaviours;however,individuals engaging in such behaviours often exhibit decreased pain sensitivity,which may undermine this natural safeguard.The dorsolateral prefrontal cortex(DLPFC)is a key region involved in pain regulation,and recent approaches using transcranial direct current stimulation(tDCS)to target the DLPFC have shown potential for modulating pain processing and restoring normal pain perception for individuals engaging in NSSI behaviours.Aims This study aimed to explore the immediate and short-term effects of a single session of tDCS on pain sensitivity in individuals with NSSI,as well as its secondary effects on mood and NSSI-related factors.Methods In this randomised,double-blind,parallel,sham-controlled clinical trial,participants with a history of NSSI were randomly assigned to receive either active or sham tDCS.The intervention consisted of a single 20 min tDCS session targeting the left DLPFC.The primary outcome was pain sensitivity,measured by the pressure pain threshold(PPT)and heat pain score(HPS).Secondary and additional outcomes included NSSI urges,NSSI resistance,self-efficacy in resisting NSSI,mood-related variables and exploratory cognitive-affective processes such as rumination,self-criticism and self-perceived pain sensitivity,assessed at baseline,immediately post-intervention,and at 24 hours,1 week and 2 weeks follow-ups.Results For the primary outcomes,no significant differences between groups were observed for pain sensitivity(PPT,padj=0.812;HPS,padj=0.608).However,an exploratory sensitivity analysis treating each trial as an individual observation revealed a significant effect on HPS(padj=0.036).For the secondary and additional outcomes,although there were initial improvements in joyful feelings and reductions in negative affect at 2 weeks post-intervention,these effects did not remain significant after multiple comparison corrections.Notably,reductions in rumination were statistically significant at both 1-week and 2-week follow-ups(1 week,p_(adj)=0.040;2 weeks,p_(adj)=0.042).There were no significant effects on NSSI urges,NSSI resistance,self-efficacy in resisting NSSI or self-criticism.Conclusions A single session of tDCS over the left DLPFC did not produce significant changes in pain sensitivity in individuals with NSSI.A sensitivity analysis indicated an effect on heat pain sensitivity,possibly reflecting changes in brain activity,warranting confirmation through neuroimaging.These findings suggest that tDCS warrants further investigation for its potential to influence pain-related cognitive-affective processes in individuals with NSSI.展开更多
Laser processing technologies enable the precise fabrication of arbitrary structures and devices with broad applications in micro-optics,micro-mechanics,and biomedicine.However,its adoption is limited by the large siz...Laser processing technologies enable the precise fabrication of arbitrary structures and devices with broad applications in micro-optics,micro-mechanics,and biomedicine.However,its adoption is limited by the large size,complexity,high cost,and low flexibility of optical systems.Metasurfaces enable precise multidimensional control of light fields,aligning well with the development trend toward compact,high-performance optical systems.Here,we review several recent studies on the application of metasurfaces in laser processing technologies,including 3D nanolithography,direct laser writing,and laser cutting.Metasurfaces provide an integrated operational platform with exceptional performance,poised to disrupt conventional laser processing workflows.This combination presents significant cost efficiency and substantial development potential,with promising applications in areas such as imaging,optical storage,advanced sensing,and space on-orbit manufacturing.展开更多
Background:Research on therapeutic processes has explored the elements that enhance psychotherapy’s effectiveness,particularly the role of common factors across various models.The therapist’s use of directiveness an...Background:Research on therapeutic processes has explored the elements that enhance psychotherapy’s effectiveness,particularly the role of common factors across various models.The therapist’s use of directiveness and support,as common variables,is crucial for effective treatment.Effective therapists adapt their level of directiveness and support according to the treatment phase,the issue being addressed,and the patient’s characteristics.This study examines the importance therapists attribute to directiveness and support,as well as its relationship with theoretical orientation,access to research publications,and stance on the similar effectiveness of different psychotherapeutic models.It aims to determine whether therapists’attributions regarding this variable are in line with the importance it is given in process research.Methods:Responses from 69 psychotherapists to the Psychotherapeutic Effectiveness Attribution Questionnaire(PEAQ-12),which assesses the importance therapists place on key psychotherapeutic process variables,including the directiveness and support provided,were analyzed.Theoretical orientations,ages,and experience levels were considered.Non-parametric tests,contingency tables,χ^(2)tests,t-tests,and ANOVAs were used to assess the variation in responses.Results:Common factors were often identified as key contributors to therapeutic healing,though these differences were not statistically significant(χ^(2)(2,N=67)=3.701,p=0.157).For the“directiveness and support from the therapist”variable,significant differences were observed:Cognitive-behavioral therapists valued directiveness and support more than psychodynamic therapists(t(20)=−3.569,p=0.002;Cohen’s d=1.18).Therapists who view cognitive-behavioral therapies as most effective also rated this variable higher(t(38)=3.816,p<0.001;Cohen’s d=1.21).Those regularly accessing specialized psychotherapy research publications valued this variable less than those who do so occasionally(t(64)=−2.693,p=0.009;Cohen’s d=0.65).Therapists who support the similar effectiveness of different models tend to favor common factors,including directiveness and support(χ^(2)(2,N=66)=12.522,p=0.002).Conclusions:Therapists express doubts about the factors influencing psychotherapy’s effectiveness,reflecting the ongoing debate.They align their views on the importance of directiveness and support with their theoretical orientation and positioning on the similar effectiveness of psychotherapies.The importance of analyzing therapists’attributions about the factors responsible for therapeutic change is emphasized,which will impact clinical practice.Advocacy for therapist flexibility and adaptation of therapy to the patient’s needs,including the level of directiveness and support provided,has been shown to be essential for effective psychotherapy.展开更多
The main types of defect in the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys with the 'one-step' directional solidification process were investigated. The effect of the dendrite, grain boundaries, twin boundaries, and R...The main types of defect in the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys with the 'one-step' directional solidification process were investigated. The effect of the dendrite, grain boundaries, twin boundaries, and REFe_3 precipitates on the magnetostrictive response of the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys was analyzed respectively. The experiment results demonstrate that the dendrite, twin boundaries, and REFe_3 precipitates can be avoided by modifying alloying ingredient, solidification parameters and annealing technique. The dendritic growth front often leads to dendrite sheet, rare earth-rich phase, and twin boundaries. The lower proportion of rare earth, or slow solidification rate, results in the occurrence of REFe_3 precipitatates. It is vital for diminishing the defects to control the undercooling of solid-liquid interface at (2.4～5.1)×10~4 K·s·cm^(-2) so that the crystal grows in cellular growth front.展开更多
In several stress responsive gene loci of monocot cereal crops,we have previously identified an unusual posttranscriptional processing mediated by paired presence of short direct repeated （SDR） sequences at 5＇ and ...In several stress responsive gene loci of monocot cereal crops,we have previously identified an unusual posttranscriptional processing mediated by paired presence of short direct repeated （SDR） sequences at 5＇ and 3＇ splicing junctions that are distinct from conventional （U2/U12-type） splicing boundaries.By using the known SDR-containing sequences as probes,24 plant candidate genes involved in diverse functional pathways from both monocots and dicots that potentially possess SDR-mediated posttranscriptional processing were predicted in the GenBank database.The SDRs-mediated posttranscriptional processing events including cis-and trans-actions were experimentally detected in majority of the predicted candidates.Extensive sequence analysis demonstrates several types of SDR-associated splicing peculiarities including partial exon deletion,exon fragment repetition,exon fragment scrambling and trans-splicing that result in either loss of partial exon or unusual exonic sequence rearrangements within or between RNA molecules.In addition,we show that the paired presence of SDR is necessary but not sufficient in SDR-mediated splicing in transient expression and stable transformation systems.We also show prokaryote is incapable of SDR-mediated premRNA splicing.展开更多
A novel universal preprocessing method is proposed to estimate angles of arrival,which is applicable to one-or two-dimensional high resolution processing based on arbitrarycenter-symmetric arrays (such as uniform line...A novel universal preprocessing method is proposed to estimate angles of arrival,which is applicable to one-or two-dimensional high resolution processing based on arbitrarycenter-symmetric arrays (such as uniform linear arrays, equal-spaced rectangular planar arraysand symmetric circular arrays). By mapping the complex signal space into the real one, the newmethod can effectively reduce the computation needed by the signal subspace direction findingtechniques without any performance degradation. In addition, the new preprocessing scheme itselfcan decorrelate the coherent signals received on the array. For regular array geometry such asuniform linear arrays and equal-spaced rectangular planar arrays, the popular spatial smoothingpreprocessing technique can be combined with the novel approach to improve the decorrelatingability. Simulation results confirm the above conclusions.展开更多
In bistaic acoustic testing, there will be strong direct blast interference. An algorithm based on signal phase-matching array processing that rejects direct blast interference in bistatic acoustic testing has been st...In bistaic acoustic testing, there will be strong direct blast interference. An algorithm based on signal phase-matching array processing that rejects direct blast interference in bistatic acoustic testing has been studied, through which the object scattering signal is accurately extracted. Characteristics of bistatic acoustic testing and signal phase matching processing principle are fully integrated in this algorithm. Firstly, the direct blast interference is calculated from the receiving signal based on three subarrays signal phase matching processing. Secondly, the direct blast is rejected by subtraction from the receiving signal. In this way the limitations of the high signal to noise ratio that signal phase matching processing required for direct calculating the object scattering signal can be avoided. Simulation and sea trial results show that, when the ratio of signal to interference is greater than -20 dB, this algorithm of direct blast interference rejection based phase matching signal processing can accurately extract the object scattering signal.展开更多
By theoretical analysis of heat transfer during the "one-step" directional solidification process, the functional relation between the temperature in solid-liquid interface and its effect factor was studied....By theoretical analysis of heat transfer during the "one-step" directional solidification process, the functional relation between the temperature in solid-liquid interface and its effect factor was studied. The thermal gradient in solid liquid interface and heat transfer coefficient between the samples and surroundings were also calculated. On the basis of the above analysis, some suggestions for improving the thermal gradient in solid-liquid interface were put forward. It will provide a theoretical instruction for preparing high performance giant magnetostrictive materials (GMM).展开更多
The solute redistribution in directional melting process is theoretically studied. Based on quantitative evaluations, uniform.solute distribution in liquid and a quasi-steady solute distribution in solid are supposed....The solute redistribution in directional melting process is theoretically studied. Based on quantitative evaluations, uniform.solute distribution in liquid and a quasi-steady solute distribution in solid are supposed. The discussion on the solute balance comes to a simple model for the solute redistribution in directional melting process. As an example, the variation of liquid composition during melting process of carbon steel is quantitatively evaluated using the model. Results show that the melting of an alloy starts at solidus temperature, but approaches the liquidus temperature after a very short transient process.展开更多
Rotating Single-Baseline Interferometer(RSBI)systems have attracted considerable attention for Direct Position Determination(DPD)due to their simplicity and high localization accuracy.Nevertheless,the growing complexi...Rotating Single-Baseline Interferometer(RSBI)systems have attracted considerable attention for Direct Position Determination(DPD)due to their simplicity and high localization accuracy.Nevertheless,the growing complexity of electromagnetic environments has led to scenarios with multiple time-frequency aliased sources,rendering conventional DPD methods for RSBI systems ineffective.Previous studies have predominantly concentrated on deploying antenna arrays and applying related signal-processing techniques for localization.Typically,these approaches necessitate that the number of physical antennas exceeds the number of sources.For RSBI systems already in practical operation,this would entail the installation of additional physical antennas,which implies equipment recycling and hardware upgrades.In numerous cases,such modifications are unfeasible.This paper proposes a novel Relative Offset-based Direct Position Determination(RO-DPD)method for RSBI systems that can handle multiple time-frequency aliased sources.The proposed method overcomes the challenge of simultaneous positioning without requiring hardware modifications by leveraging time accumulation and algorithmic enhancements.The implementation of the method involves three key steps.Firstly,the rotation of the interferometer is synthesized into a virtual Uniform Circular Array(UCA).Secondly,a novel estimation variable,termed relative offset,is introduced.The variable serves as an intermediate parameter to establish correlation equations between the positions of multiple time-frequency aliased sources and the intercepted signals.Thirdly,the relative offset model in the UCA is transformed into a virtual Uniform Linear Array(ULA)model,from which the cost function can be derived via the Spatial Smoothing(SS)MUSIC algorithm.Theoretical analysis and simulation results verify the effectiveness of the proposed method.Compared with traditional approaches,the RO-DPD method maintains the low complexity of RSBI systems while demonstrating robust performance in complex electromagnetic environments.展开更多
A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions in...A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions including iron oxide reductions, zinc oxide reduction and carbon gasification, and it was numerically solved by the tridiagonal matrix algorithm （TDMA）. In order to verify the model, an experiment was performed, in which the profiles of temperature and zinc removal rate were measured during the reduction process. Results calculated by the mathematical model were in fairly good agreement with experimental data. Finally, the effects of furnace temperature, pellet size, and carbon content were investigated by model calculations. It is found that the pellet temperature curve can be divided into four parts according to heating rate. Also, the zinc removal rate increases with the increase of furnace temperature and the decrease of pellet size, and carbon content in the pellet has little influence on the zinc removal rate.展开更多
Lotus-type porous Mg–xMn(x=0,1,2 and 3 wt.%)alloys were fabricated by metal/gas eutectic unidirectional solidification(the Gasar process).The effects of Mn addition and the fabrication process on the porosity,pore di...Lotus-type porous Mg–xMn(x=0,1,2 and 3 wt.%)alloys were fabricated by metal/gas eutectic unidirectional solidification(the Gasar process).The effects of Mn addition and the fabrication process on the porosity,pore diameter and microstructure of the porous Mg-Mn alloy were investigated.Mn addition improved the Mn precipitates and increased the porosity and pore diameter.With increasing hydrogen pressure from 0.1 to 0.6 MPa,the overall porosity of the Mg-2wt.%Mn ingot decreased from 55.3%to 38.4%,and the average pore diameter also decreased from 2465 to 312μm.Based on a theoretical model of the change in the porosity with the hydrogen pressure,the calculated results were in good agreement with the experimental results.It is shown that this technique is a promising method to fabricate Gasar Mg–Mn alloys with uniform and controllable pore structure.展开更多
Compared with the traditional non-cutting measurement,machining tests can more accurately reflect the kinematic errors of five-axis machine tools in the actual machining process for the users.However,measurement and c...Compared with the traditional non-cutting measurement,machining tests can more accurately reflect the kinematic errors of five-axis machine tools in the actual machining process for the users.However,measurement and calculation of the machining tests in the literature are quite difficult and time-consuming.A new method of the machining tests for the trunnion axis of five-axis machine tool is proposed.Firstly,a simple mathematical model of the cradle-type five-axis machine tool was established by optimizing the coordinate system settings based on robot kinematics.Then,the machining tests based on error-sensitive directions were proposed to identify the kinematic errors of the trunnion axis of cradle-type five-axis machine tool.By adopting the error-sensitive vectors in the matrix calculation,the functional relationship equations between the machining errors of the test piece in the error-sensitive directions and the kinematic errors of C-axis and A-axis of five-axis machine tool rotary table was established based on the model of the kinematic errors.According to our previous work,the kinematic errors of C-axis can be treated as the known quantities,and the kinematic errors of A-axis can be obtained from the equations.This method was tested in Mikron UCP600 vertical machining center.The machining errors in the error-sensitive directions can be obtained by CMM inspection from the finished test piece to identify the kinematic errors of five-axis machine tool trunnion axis.Experimental results demonstrated that the proposed method can reduce the complexity,cost,and the time consumed substantially,and has a wider applicability.This paper proposes a new method of the machining tests for the trunnion axis of five-axis machine tool.展开更多
Laser direct deposition （LDD） of metallic components is an advanced technology of combining CAD/CAM （computer aided design/computer aided manufacturing）, high power laser, and rapid prototyping. This technology us...Laser direct deposition （LDD） of metallic components is an advanced technology of combining CAD/CAM （computer aided design/computer aided manufacturing）, high power laser, and rapid prototyping. This technology uses laser beam to melt the powders fed coaxiaUy into the molten pool by the laser beam to fabricate fuUy dense metallic components. The present article mainly studies the LDD of Ti-6Al-4V alloy, which can be used to fabricate aircraft components. The mechanical properties of the Ti-6Al-4V alloy, fabricated by LDD, are obtained using the tension test, and the oxygen content of used powders and deposited specimens are measured. In the present article, it can be seen that the mechanical properties obtained using this method are higher than the ones obtained by casting, and equal to those got by wrought anneal. One aircraft part has been made using the LDD process. Because of this aircraft part, with sophisticated shape, the effect of the laser scanning track on the internal soundness of the deposited part was discussed.展开更多
基金supported by the Key R&D Program of Zhejiang Province(Nos.2023C01166 and 2024SJCZX0046)the Zhejiang Provincial Natural Science Foundation of China(Nos.LDT23E05013E05 and LD24E050009)the Natural Science Foundation of Ningbo(No.2021J150),China.
文摘Accuracy allocation is crucial in the accuracy design of machining tools.Current accuracy allocation methods primarily focus on positional deviation,with little consideration for tool direction deviation.To address this issue,we propose a geometric error cost sensitivity-based accuracy allocation method for five-axis machine tools.A geometric error model consisting of 4l error components is constructed based on homogeneous transformation matrices.Volumetric points with positional and tool direction deviations are randomly sampled to evaluate the accuracy of the machine tool.The sensitivity of each error component at these sampling points is analyzed using the Sobol method.To balance the needs of geometric precision and manufacturing cost,a geometric error cost sensitivity function is developed to estimate the required cost.By allocating error components affecting tool direction deviation first and the remaining components second,this allocation scheme ensures that both deviations meet the requirements.We also perform numerical simulation of a BC-type(B-axis and C-axis type)five-axis machine tool to validate the method.The results show that the new allocation scheme reduces the total geometric error cost by 27.8%compared to a uniform allocation scheme,and yields the same positional and tool direction machining accuracies.
基金supported by the National Science and Technol-ogy Major Project(No.J2019-IV-0003-0070)the National Natural Science Foundation of China(Grant No.12202343)the China Postdoctoral Science Foundation(No.2021M702582).
文摘Porous ceramic composites with directional microchannels from micrometer to dozens of micrometer levels have attracted more and more attention in various fields including aerospace,biomedicines,and thermal insulation due to their excellent fluid permeability,mechanical properties,etc.In this article,we summarize the recent directional porous ceramics developments including their main processing routes and respective properties.Meanwhile,the properties get from different processing routes have been com-pared and analyzed in terms of microstructures,mechanical properties,and permeability.Emphasis has been given to the deeper understanding which can allow one to control the microstructural features of these porous ceramic composites to obtain the desired characteristics.This work can provide a useful reference for the development and application of porous ceramic composites with directional microchan-nels.
基金funded by the National Defence Science and Technology Project Fund of China(No.3101140)the Shanghai Aerospace Science and Technology Innovation Fund of China(No.SAST2015028)the Equipment Prophecy Fund of China(No.9140A21040115KG01001).
文摘To improve the resolution and accuracy of Direct Position Determination(DPD),this paper investigates the problem of positioning multiple emitters directly with a single moving Rotating Linear Array(RLA).Firstly,the geometry of the RLA is formulated and analysed.According to its geometry,the intercepted noncoherent signals in multiple interception intervals are modeled.Correspondingly,the Multiple SIgnal Classification(MUSIC)based noncoherent DPD approach is proposed.Secondly,the synchronous coherent pulse signals are individually considered and formulated.And the coherent DPD approach which aims for localizing this special type of signal is presented by stacking all array responses at different interception intervals.Besides,we also derive the constrained Cramer-Rao Lower Bound(CRLB)expression for both noncoherent and coherent DPD with RLA under the constraint that the altitudes of the emitters are known.At last,computer simulations are included to examine the performance of the proposed approach.The results demonstrate that the localization accuracy and resolution of DPD with single moving linear array can be significantly improved by the array rotation.In addition,coherent DPD with RLA further improves the resolution and increases the maximum emitter number that can be localized compared with the noncoherent DPD with RLA.
基金supported by National Key R&D Program of China(Grant Nos.2021YFB2802000 and 2022YFB2804300)Science and Technology Commission of Shanghai Municipality(Grant No.21DZ1100500)+3 种基金Shanghai Municipal Science and Technology Major Projectthe Shanghai Frontiers Science Center Program(2021-2025 No.20)National Natural Science Foundation of China(Grant No.61975123)Shanghai Scienceand Technology Innovation Action Plan(Grant No.23JC1403100)。
文摘Able to precisely control and manipulate materials'states at micro/nano-scale level,femtosecond(fs)laser micro/nano processing technology has undergone tremendous development over the past three decades.Free-forming three-dimensional(3D)microscale functional devices and inducing fascinating and unique physical or chemical phenomena have granted this technology powerful versatility that no other technology can match.As this technology advances rapidly in various fields of application,some key challenges have emerged and remain to be urgently addressed.This review firstly introduces the fundamental principles for understanding how fs laser pulses interact with materials and the associated unique phenomena in section 2.Then micro/nano-fabrication in transparent materials by fs laser processing is presented in section 3.Thereafter,several high efficiency/throughput fabrication methods as well as pulse-shaping techniques are listed in sections 4 and 5 reviews four-dimensional(4D)and nanoscale printing realized by fs laser processing technology.Special attention is paid to the heterogeneous integration(HI)of functional materials enabled by fs laser processing in section 6.Several intriguing examples of 3D functional micro-devices created by fs laser-based manufacturing methods such as microfluidics,lab-on-chip,micro-optics,micro-mechanics,micro-electronics,micro-bots and micro-biodevices are reviewed in section 7.Finally,a summary of the review and a perspective are proposed to explore the challenges and future opportunities for further betterment of fs laser micro/nano processing technology.
文摘In non-homogeneous environment, traditional space-time adaptive processing doesn＇t effectively suppress interference and detect target, because the secondary data don＇ t exactly reflect the statistical characteristic of the range cell under test. A ravel methodology utilizing the direct data domain approach to space-time adaptive processing （ STAP ） in airbome radar non-homogeneous environments is presented. The deterministic least squares adaptive signal processing technique operates on a ＂snapshot-by-snapshot＂ basis to dethrone the adaptive adaptive weights for nulling interferences and estimating signal of interest （SOI）. Furthermore, this approach eliminates the requirement for estimating the covariance through the data of neighboring range cell, which eliminates calculating the inverse of covariance, and can be implemented to operate in real-time. Simulation results illustrate the efficiency of interference suppression in non-homogeneous environment.
基金Project(2013BAB06B00) supported by the National Key Technology R&D Programof ChinaProject(2011CB013504) supported by the National Basic Research Program of ChinaProject(50911130366) supported by the National Natural Science Foundation of China
文摘The macro mechanical properties of materials with characteristics of large scale and complicated structural composition can be analyzed through its reconstructed meso-structures.In this work,the meso-structures of talus deposits that widely exist in the hydro-power engineering in the southwest of China were first reconstructed by small particles according to the in-situ photographs based on the self-adaptive PCNN digital image processing,and then numerical direct shear tests were carried out for studying the mechanical properties of talus deposits.Results indicate that the reconstructed meso-structures of talus deposits are more consistent with the actual situation because the self-adaptive PCNN digital image processing has a higher discrimination in the details of soil-rock segmentation.The existence and random distribution of rock blocks make the initial shear stiffness,the peak strength and the residual strength higher than those of the "pure soil" with particle size less than 1.25 cm apparently,but reduce the displacements required for the talus deposits reaching its peak shear strength.The increase of rock proportion causes a significant improvement in the internal friction angle of talus deposit,which to a certain degree leads to the characteristics of shear stress-displacement curves having a changing trend from the plastic strain softening deformation to the nonlinear strain hardening deformation,while an unconspicuous increase in cohesion.The uncertainty and heterogeneity of rock distributions cause the differences of rock proportion within shear zone,leading to a relatively strong fluctuation in peak strengths during the shear process,while movement features of rock blocks,such as translation,rotation and crossing,expand the scope of shear zone,increase the required shear force,and also directly lead to the misjudgment that the lower shear strength is obtained from the samples with high rock proportion.That,however,just explains the reason why the shear strength gained from a small amount of indoor test data is not consistent with engineering practice.
基金supported by National Natural Science Foundation of China(82471564)YT is supported by National Natural Science Foundation of China(32322035,32171078).
文摘Background Pain sensitivity is critical for preventing non-suicidal self-injury(NSSI)behaviours;however,individuals engaging in such behaviours often exhibit decreased pain sensitivity,which may undermine this natural safeguard.The dorsolateral prefrontal cortex(DLPFC)is a key region involved in pain regulation,and recent approaches using transcranial direct current stimulation(tDCS)to target the DLPFC have shown potential for modulating pain processing and restoring normal pain perception for individuals engaging in NSSI behaviours.Aims This study aimed to explore the immediate and short-term effects of a single session of tDCS on pain sensitivity in individuals with NSSI,as well as its secondary effects on mood and NSSI-related factors.Methods In this randomised,double-blind,parallel,sham-controlled clinical trial,participants with a history of NSSI were randomly assigned to receive either active or sham tDCS.The intervention consisted of a single 20 min tDCS session targeting the left DLPFC.The primary outcome was pain sensitivity,measured by the pressure pain threshold(PPT)and heat pain score(HPS).Secondary and additional outcomes included NSSI urges,NSSI resistance,self-efficacy in resisting NSSI,mood-related variables and exploratory cognitive-affective processes such as rumination,self-criticism and self-perceived pain sensitivity,assessed at baseline,immediately post-intervention,and at 24 hours,1 week and 2 weeks follow-ups.Results For the primary outcomes,no significant differences between groups were observed for pain sensitivity(PPT,padj=0.812;HPS,padj=0.608).However,an exploratory sensitivity analysis treating each trial as an individual observation revealed a significant effect on HPS(padj=0.036).For the secondary and additional outcomes,although there were initial improvements in joyful feelings and reductions in negative affect at 2 weeks post-intervention,these effects did not remain significant after multiple comparison corrections.Notably,reductions in rumination were statistically significant at both 1-week and 2-week follow-ups(1 week,p_(adj)=0.040;2 weeks,p_(adj)=0.042).There were no significant effects on NSSI urges,NSSI resistance,self-efficacy in resisting NSSI or self-criticism.Conclusions A single session of tDCS over the left DLPFC did not produce significant changes in pain sensitivity in individuals with NSSI.A sensitivity analysis indicated an effect on heat pain sensitivity,possibly reflecting changes in brain activity,warranting confirmation through neuroimaging.These findings suggest that tDCS warrants further investigation for its potential to influence pain-related cognitive-affective processes in individuals with NSSI.
文摘Laser processing technologies enable the precise fabrication of arbitrary structures and devices with broad applications in micro-optics,micro-mechanics,and biomedicine.However,its adoption is limited by the large size,complexity,high cost,and low flexibility of optical systems.Metasurfaces enable precise multidimensional control of light fields,aligning well with the development trend toward compact,high-performance optical systems.Here,we review several recent studies on the application of metasurfaces in laser processing technologies,including 3D nanolithography,direct laser writing,and laser cutting.Metasurfaces provide an integrated operational platform with exceptional performance,poised to disrupt conventional laser processing workflows.This combination presents significant cost efficiency and substantial development potential,with promising applications in areas such as imaging,optical storage,advanced sensing,and space on-orbit manufacturing.
文摘Background:Research on therapeutic processes has explored the elements that enhance psychotherapy’s effectiveness,particularly the role of common factors across various models.The therapist’s use of directiveness and support,as common variables,is crucial for effective treatment.Effective therapists adapt their level of directiveness and support according to the treatment phase,the issue being addressed,and the patient’s characteristics.This study examines the importance therapists attribute to directiveness and support,as well as its relationship with theoretical orientation,access to research publications,and stance on the similar effectiveness of different psychotherapeutic models.It aims to determine whether therapists’attributions regarding this variable are in line with the importance it is given in process research.Methods:Responses from 69 psychotherapists to the Psychotherapeutic Effectiveness Attribution Questionnaire(PEAQ-12),which assesses the importance therapists place on key psychotherapeutic process variables,including the directiveness and support provided,were analyzed.Theoretical orientations,ages,and experience levels were considered.Non-parametric tests,contingency tables,χ^(2)tests,t-tests,and ANOVAs were used to assess the variation in responses.Results:Common factors were often identified as key contributors to therapeutic healing,though these differences were not statistically significant(χ^(2)(2,N=67)=3.701,p=0.157).For the“directiveness and support from the therapist”variable,significant differences were observed:Cognitive-behavioral therapists valued directiveness and support more than psychodynamic therapists(t(20)=−3.569,p=0.002;Cohen’s d=1.18).Therapists who view cognitive-behavioral therapies as most effective also rated this variable higher(t(38)=3.816,p<0.001;Cohen’s d=1.21).Those regularly accessing specialized psychotherapy research publications valued this variable less than those who do so occasionally(t(64)=−2.693,p=0.009;Cohen’s d=0.65).Therapists who support the similar effectiveness of different models tend to favor common factors,including directiveness and support(χ^(2)(2,N=66)=12.522,p=0.002).Conclusions:Therapists express doubts about the factors influencing psychotherapy’s effectiveness,reflecting the ongoing debate.They align their views on the importance of directiveness and support with their theoretical orientation and positioning on the similar effectiveness of psychotherapies.The importance of analyzing therapists’attributions about the factors responsible for therapeutic change is emphasized,which will impact clinical practice.Advocacy for therapist flexibility and adaptation of therapy to the patient’s needs,including the level of directiveness and support provided,has been shown to be essential for effective psychotherapy.
文摘The main types of defect in the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys with the 'one-step' directional solidification process were investigated. The effect of the dendrite, grain boundaries, twin boundaries, and REFe_3 precipitates on the magnetostrictive response of the (Tb_(0.3)Dy_(0.7))Fe_(1.95) alloys was analyzed respectively. The experiment results demonstrate that the dendrite, twin boundaries, and REFe_3 precipitates can be avoided by modifying alloying ingredient, solidification parameters and annealing technique. The dendritic growth front often leads to dendrite sheet, rare earth-rich phase, and twin boundaries. The lower proportion of rare earth, or slow solidification rate, results in the occurrence of REFe_3 precipitatates. It is vital for diminishing the defects to control the undercooling of solid-liquid interface at (2.4～5.1)×10~4 K·s·cm^(-2) so that the crystal grows in cellular growth front.
基金supported by the National Key Basic Research Program (973 program) (No. 2006CB100205)the National Science Fund for Distinguished Young Scholars (No. 30825030)+2 种基金the National Natural Science Foundation of China (No. 30770466, 90717110, 30970260 and 30971752)the Earmarked Fund for Modern Agro-industry Technology Research System (No. nycytx-01)the National High Technology Research and Development Program of China (863 Program) (No. 2007AA10Z100)
文摘In several stress responsive gene loci of monocot cereal crops,we have previously identified an unusual posttranscriptional processing mediated by paired presence of short direct repeated （SDR） sequences at 5＇ and 3＇ splicing junctions that are distinct from conventional （U2/U12-type） splicing boundaries.By using the known SDR-containing sequences as probes,24 plant candidate genes involved in diverse functional pathways from both monocots and dicots that potentially possess SDR-mediated posttranscriptional processing were predicted in the GenBank database.The SDRs-mediated posttranscriptional processing events including cis-and trans-actions were experimentally detected in majority of the predicted candidates.Extensive sequence analysis demonstrates several types of SDR-associated splicing peculiarities including partial exon deletion,exon fragment repetition,exon fragment scrambling and trans-splicing that result in either loss of partial exon or unusual exonic sequence rearrangements within or between RNA molecules.In addition,we show that the paired presence of SDR is necessary but not sufficient in SDR-mediated splicing in transient expression and stable transformation systems.We also show prokaryote is incapable of SDR-mediated premRNA splicing.
文摘A novel universal preprocessing method is proposed to estimate angles of arrival,which is applicable to one-or two-dimensional high resolution processing based on arbitrarycenter-symmetric arrays (such as uniform linear arrays, equal-spaced rectangular planar arraysand symmetric circular arrays). By mapping the complex signal space into the real one, the newmethod can effectively reduce the computation needed by the signal subspace direction findingtechniques without any performance degradation. In addition, the new preprocessing scheme itselfcan decorrelate the coherent signals received on the array. For regular array geometry such asuniform linear arrays and equal-spaced rectangular planar arrays, the popular spatial smoothingpreprocessing technique can be combined with the novel approach to improve the decorrelatingability. Simulation results confirm the above conclusions.
基金supported by the Foundation of Key Laboratory for Underwater Test & Control Technology under Grant No.9140C260201110C26
文摘In bistaic acoustic testing, there will be strong direct blast interference. An algorithm based on signal phase-matching array processing that rejects direct blast interference in bistatic acoustic testing has been studied, through which the object scattering signal is accurately extracted. Characteristics of bistatic acoustic testing and signal phase matching processing principle are fully integrated in this algorithm. Firstly, the direct blast interference is calculated from the receiving signal based on three subarrays signal phase matching processing. Secondly, the direct blast is rejected by subtraction from the receiving signal. In this way the limitations of the high signal to noise ratio that signal phase matching processing required for direct calculating the object scattering signal can be avoided. Simulation and sea trial results show that, when the ratio of signal to interference is greater than -20 dB, this algorithm of direct blast interference rejection based phase matching signal processing can accurately extract the object scattering signal.
基金This project was supported by the Natural Science Foundation of Beijing (2042012)
文摘By theoretical analysis of heat transfer during the "one-step" directional solidification process, the functional relation between the temperature in solid-liquid interface and its effect factor was studied. The thermal gradient in solid liquid interface and heat transfer coefficient between the samples and surroundings were also calculated. On the basis of the above analysis, some suggestions for improving the thermal gradient in solid-liquid interface were put forward. It will provide a theoretical instruction for preparing high performance giant magnetostrictive materials (GMM).
基金The research is funded by the National Natural Science FOundation of China! (No.59931030)
文摘The solute redistribution in directional melting process is theoretically studied. Based on quantitative evaluations, uniform.solute distribution in liquid and a quasi-steady solute distribution in solid are supposed. The discussion on the solute balance comes to a simple model for the solute redistribution in directional melting process. As an example, the variation of liquid composition during melting process of carbon steel is quantitatively evaluated using the model. Results show that the melting of an alloy starts at solidus temperature, but approaches the liquidus temperature after a very short transient process.
基金partially supported by the National Natural Science Foundation of China(Nos.61901494,62101563)。
文摘Rotating Single-Baseline Interferometer(RSBI)systems have attracted considerable attention for Direct Position Determination(DPD)due to their simplicity and high localization accuracy.Nevertheless,the growing complexity of electromagnetic environments has led to scenarios with multiple time-frequency aliased sources,rendering conventional DPD methods for RSBI systems ineffective.Previous studies have predominantly concentrated on deploying antenna arrays and applying related signal-processing techniques for localization.Typically,these approaches necessitate that the number of physical antennas exceeds the number of sources.For RSBI systems already in practical operation,this would entail the installation of additional physical antennas,which implies equipment recycling and hardware upgrades.In numerous cases,such modifications are unfeasible.This paper proposes a novel Relative Offset-based Direct Position Determination(RO-DPD)method for RSBI systems that can handle multiple time-frequency aliased sources.The proposed method overcomes the challenge of simultaneous positioning without requiring hardware modifications by leveraging time accumulation and algorithmic enhancements.The implementation of the method involves three key steps.Firstly,the rotation of the interferometer is synthesized into a virtual Uniform Circular Array(UCA).Secondly,a novel estimation variable,termed relative offset,is introduced.The variable serves as an intermediate parameter to establish correlation equations between the positions of multiple time-frequency aliased sources and the intercepted signals.Thirdly,the relative offset model in the UCA is transformed into a virtual Uniform Linear Array(ULA)model,from which the cost function can be derived via the Spatial Smoothing(SS)MUSIC algorithm.Theoretical analysis and simulation results verify the effectiveness of the proposed method.Compared with traditional approaches,the RO-DPD method maintains the low complexity of RSBI systems while demonstrating robust performance in complex electromagnetic environments.
基金the Fundamen-tal Research Funds for Central Universities(No.FRF-SD-12-013A)the State Key Laboratory of Advanced Metallurgy,China
文摘A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions including iron oxide reductions, zinc oxide reduction and carbon gasification, and it was numerically solved by the tridiagonal matrix algorithm （TDMA）. In order to verify the model, an experiment was performed, in which the profiles of temperature and zinc removal rate were measured during the reduction process. Results calculated by the mathematical model were in fairly good agreement with experimental data. Finally, the effects of furnace temperature, pellet size, and carbon content were investigated by model calculations. It is found that the pellet temperature curve can be divided into four parts according to heating rate. Also, the zinc removal rate increases with the increase of furnace temperature and the decrease of pellet size, and carbon content in the pellet has little influence on the zinc removal rate.
基金Project(51771101)supported by the National Natural Science Foundation of China。
文摘Lotus-type porous Mg–xMn(x=0,1,2 and 3 wt.%)alloys were fabricated by metal/gas eutectic unidirectional solidification(the Gasar process).The effects of Mn addition and the fabrication process on the porosity,pore diameter and microstructure of the porous Mg-Mn alloy were investigated.Mn addition improved the Mn precipitates and increased the porosity and pore diameter.With increasing hydrogen pressure from 0.1 to 0.6 MPa,the overall porosity of the Mg-2wt.%Mn ingot decreased from 55.3%to 38.4%,and the average pore diameter also decreased from 2465 to 312μm.Based on a theoretical model of the change in the porosity with the hydrogen pressure,the calculated results were in good agreement with the experimental results.It is shown that this technique is a promising method to fabricate Gasar Mg–Mn alloys with uniform and controllable pore structure.
基金Supported by National Nature Science Foundation of China(Grant No.51175461)Science Fund for Creative Research Groups of National Natural Science Foundation of China(Grant No.51221004)Program for Zhejiang Leading Team of S&T Innovation of China(Grant No.2009R50008)
文摘Compared with the traditional non-cutting measurement,machining tests can more accurately reflect the kinematic errors of five-axis machine tools in the actual machining process for the users.However,measurement and calculation of the machining tests in the literature are quite difficult and time-consuming.A new method of the machining tests for the trunnion axis of five-axis machine tool is proposed.Firstly,a simple mathematical model of the cradle-type five-axis machine tool was established by optimizing the coordinate system settings based on robot kinematics.Then,the machining tests based on error-sensitive directions were proposed to identify the kinematic errors of the trunnion axis of cradle-type five-axis machine tool.By adopting the error-sensitive vectors in the matrix calculation,the functional relationship equations between the machining errors of the test piece in the error-sensitive directions and the kinematic errors of C-axis and A-axis of five-axis machine tool rotary table was established based on the model of the kinematic errors.According to our previous work,the kinematic errors of C-axis can be treated as the known quantities,and the kinematic errors of A-axis can be obtained from the equations.This method was tested in Mikron UCP600 vertical machining center.The machining errors in the error-sensitive directions can be obtained by CMM inspection from the finished test piece to identify the kinematic errors of five-axis machine tool trunnion axis.Experimental results demonstrated that the proposed method can reduce the complexity,cost,and the time consumed substantially,and has a wider applicability.This paper proposes a new method of the machining tests for the trunnion axis of five-axis machine tool.
基金This work was supported by the National Natural Science Foundation of China （No. 50331010）
文摘Laser direct deposition （LDD） of metallic components is an advanced technology of combining CAD/CAM （computer aided design/computer aided manufacturing）, high power laser, and rapid prototyping. This technology uses laser beam to melt the powders fed coaxiaUy into the molten pool by the laser beam to fabricate fuUy dense metallic components. The present article mainly studies the LDD of Ti-6Al-4V alloy, which can be used to fabricate aircraft components. The mechanical properties of the Ti-6Al-4V alloy, fabricated by LDD, are obtained using the tension test, and the oxygen content of used powders and deposited specimens are measured. In the present article, it can be seen that the mechanical properties obtained using this method are higher than the ones obtained by casting, and equal to those got by wrought anneal. One aircraft part has been made using the LDD process. Because of this aircraft part, with sophisticated shape, the effect of the laser scanning track on the internal soundness of the deposited part was discussed.
