Selective laser melting(SLM) is an attractive rapid prototyping technology for the fabrication of metallic components with complex structure and high performance. Aluminum alloy, one of the most pervasive structural m...Selective laser melting(SLM) is an attractive rapid prototyping technology for the fabrication of metallic components with complex structure and high performance. Aluminum alloy, one of the most pervasive structural materials, is well known for high specific strength and good corrosion resistance. But the poor laser formability of aluminum alloy restricts its application. There are problems such as limited processable materials, immature process conditions and metallurgical defects on SLM processing aluminum alloys. Some efforts have been made to solve the above problems. This paper discusses the current research status both related to the scientific understanding and technology applications. The paper begins with a brief introduction of basic concepts of aluminum alloys and technology characterization of laser selective melting. In addition, solidification theory of SLM process and formation mechanism of metallurgical defects are discussed. Then, the current research status of microstructure, properties and heat treatment of SLM processing aluminum alloys is systematically reviewed respectively. Lastly, a future outlook is given at the end of this review paper.展开更多
Grouting is a major method used to prevent water and mud inrush in tunnels and underground engineering. In this paper, the current situation of control and prevention of water and mud inrush is summarized and recent a...Grouting is a major method used to prevent water and mud inrush in tunnels and underground engineering. In this paper, the current situation of control and prevention of water and mud inrush is summarized and recent advances in relevant theories, grout/equipment, and critical techniques are introduced. The time-variant equations of grout viscosity at different volumetric ratios were obtained based on the constitutive relation of typical fast curing grouts. A large-scale dynamic grouting model testing system （4000 mm × 2000 mm × 5 mm） was developed, and the diffusions of cement and fast curing grouts in dynamic water grouting were investigated. The results reveal that the diffusions of cement grouts and fast curing grouts are U-shaped and asymmetric elliptical, respectively. A multi-parameter real-time monitoring system （＆#981; = 1.5 m, h = 1.2 m） was developed for the grouting process to study the diffusion and reinforcement mechanism of grouting in water-rich faulted zone. A high early strength cream-type reinforcing/plugging grout, a high permeability nano-scale silica gel grout, and a high-expansion filling grout were proposed for the control of water hazards in weak water-rich faulted zone rocks, water inrush in karst passages, and micro-crack water inrush, respectively. Complement technologies and equipment for industrial applications were also proposed. Additionally, a novel full-life periodic dynamic water grouting with the critical grouting borehole as the core was proposed. The key techniques for the control of water inrush in water-rich faulted zone, jointed fissures and karst passages, and micro-crack water inrush were developed.展开更多
Donor shortages for organ transplantations are a major clinical challenge worldwide. Potential risks that are inevitably encountered with traditional methods include complications, secondary injuries, and limited sour...Donor shortages for organ transplantations are a major clinical challenge worldwide. Potential risks that are inevitably encountered with traditional methods include complications, secondary injuries, and limited source donors. Three-dimensional （3D） printing technology holds the potential to solve these limitations; it can he used to rapidly manufacture personalized tissue engineering scaffolds, repair tissue defects in situ with cells, and even directly print tissue and organs. Such printed implants and organs not only perfectly match the patient＇s damaged tissue, hut can also have engineered material microstructures and cell arrangements to promote cell growth and differentiation. Thus, such implants allow the desired tissue repair to he achieved, and could eventually solve the donor-shortage problem. This review summarizes relevant studies and recent progress on four levels, introduces different types of biomedical materials, and discusses existing problems and development issues with 3D printing that are related to materials and to the construction of extracellular matrix in vitro for medical applications.展开更多
Selective laser melting （SLM）, as one of the additive manufacturing technologies, is widely investigated to fabricate metal parts. In SLM, parts are manufactured directly from powders in a layer-by-layer fashion; SL...Selective laser melting （SLM）, as one of the additive manufacturing technologies, is widely investigated to fabricate metal parts. In SLM, parts are manufactured directly from powders in a layer-by-layer fashion; SLM also provides several advantages, such as production of complex parts with high three-dimensional accuracy, compared with other additive manufacturing technologies. Therefore, SLM can be applied in aeronautics, astronautics, medicine, and die and mould industry. However, this technique differs from traditional methods, such as casting and forging; for instance, the former greatly differs in terms of microstructure and properties of products. This paper summarizes relevant studies on metal material fabrication through SLM. Based on a work completed in Huazhong Univ. Sci Tech., Rapid Manuf. Center （HUST-RMC） and compared with characteristics described in other reported studies, microstructure, properties, dimensional accuracy, and application of SLM are presented.展开更多
Selective laser melting （SLM）, an additive manufacturing process, is capable of manufacturing metallic parts with complex shapes directly from computer-aided design （CAD） models. SLM parts are created on a layer-b...Selective laser melting （SLM）, an additive manufacturing process, is capable of manufacturing metallic parts with complex shapes directly from computer-aided design （CAD） models. SLM parts are created on a layer-by-layer manner, making it more flexible than traditional material processing techniques, in this paper, Inconel 625 alloy, a widely used material in the aerospace industry, were chosen as the build material. Scanning electron microscopy （SEM）, electron back scattering diffraction （EBSD） and X-ray diffraction （XRD） analysis techniques were employed to analyze its microstructure. It was observed that the molten pool was composed of elongated columnar crystal, Due to the rapid cooling speed, the primary dendrite arm space was approximately 0.5 μm and the hardness of SLM state was very high （343 HV）. The inverse pole figure （IPF） indicated that the growing orientation of the most grains was 〈001〉 due to the epitaxial growth and heat conduction. The XRD results revealed that the austenite structure with large lattice distortion was fully formed. No carbides or precipitated phases were found. After heat treatment the grains grew into two microstructures with distinct morphological characters, namely, rectangular grains and limited in the molten pool, and equiaxed grains along the molten boundaries. Upon experiencing the heat treatment, MC carbides with triangular shapes gradually precipitated. The results also identified that a large number of zigzag grain boundaries were formed. In this study, the grain formation and microstructure, and the laws of the molten pool evolution were also analyzed and discussed,展开更多
The complicated geological conditions and geological hazards are challenging problems during tunnel construction,which will cause great losses of life and property.Therefore,reliable prediction of geological defective...The complicated geological conditions and geological hazards are challenging problems during tunnel construction,which will cause great losses of life and property.Therefore,reliable prediction of geological defective features,such as faults,karst caves and groundwater,has important practical significances and theoretical values.In this paper,we presented the criteria for detecting typical geological anomalies using the tunnel seismic prediction（TSP） method.The ground penetrating radar（GPR） signal response to water-bearing structures was used for theoretical derivations.And the 3D tomography of the transient electromagnetic method（TEM） was used to develop an equivalent conductance method.Based on the improvement of a single prediction technique,we developed a technical system for reliable prediction of geological defective features by analyzing the advantages and disadvantages of all prediction methods.The procedure of the application of this system was introduced in detail.For prediction,the selection of prediction methods is an important and challenging work.The analytic hierarchy process（AHP） was developed for prediction optimization.We applied the newly developed prediction system to several important projects in China,including Hurongxi highway,Jinping II hydropower station,and Kiaochow Bay subsea tunnel.The case studies show that the geological defective features can be successfully detected with good precision and efficiency,and the prediction system is proved to be an effective means to minimize the risks of geological hazards during tunnel construction.展开更多
The high-affinity K＋ （HAK） transporter gene family is the largest family in plant that functions as potassium transporter and is important for various aspects of plant life. In the present study, we identified 27 m...The high-affinity K＋ （HAK） transporter gene family is the largest family in plant that functions as potassium transporter and is important for various aspects of plant life. In the present study, we identified 27 members of this family in rice genome. The phylogenetic tree divided the land plant HAK transporter proteins into 6 distinct groups. Although the main characteristic of this family was established before the origin of seed plants, they also showed some differences between the members of non-seed and seed plants. The HAK genes in rice were found to have expanded in lineage-specific manner after the split of monocots and dicots, and both segmental duplication events and tandem duplication events contributed to the expansion of this family. Functional divergence analysis for this family provided statistical evidence for shifted evolutionary rate after gene duplication. Further analysis indicated that both point mutant with positive selection and gene conversion events contributed to the evolution of this family in rice.展开更多
Using data from previous research on Quercus sect. Heterobalanus, the coexistence approach to Xix-abangma and Namling fossil sets, and altitudinal ranges of vegetation presented by fossil floras, a re-view and reevalu...Using data from previous research on Quercus sect. Heterobalanus, the coexistence approach to Xix-abangma and Namling fossil sets, and altitudinal ranges of vegetation presented by fossil floras, a re-view and reevaluation have been made of existing theories on the uplift of the Himalayas, especially the palaeoaltitudes of Xixabangma and Namling in Tibet. The Xixabangma fossil set has a palaeoaltitude range of 2500―3500 m, and has risen 2200―3400 m since the Pliocene. The lower and upper assem-blages of the Miocene Namling had palaeoaltitudes of 2500―3000 m and 2800―3000 m, respectively. Therefore, Namling has risen at least 1300 m since the Miocene, thereby challenging some existing theories that suggest Namling has been static since the Miocene.展开更多
This paper presents a comprehensive study conducted to optimize the selective laser melting(SLM)parameters and subsequent heat-treatment temperatures for near-α high-temperature titanium alloy Ti-6 Al-2 Zr-1 Mo-1 V(T...This paper presents a comprehensive study conducted to optimize the selective laser melting(SLM)parameters and subsequent heat-treatment temperatures for near-α high-temperature titanium alloy Ti-6 Al-2 Zr-1 Mo-1 V(TA15),which is widely used in the aerospace industry.Based on the surface morphology and relative density analysis,the optimized process parameters were:laser power from 230 W to 380 W,scan speed from 675 mm/s to 800 mm/s,scan spacing of 0.12 mm,and layer thickness of0.03 mm.The effects of the laser power and the layer thickness on the phase constitutions,microstructure features,as well as room-temperature and high-temperature(500℃) tensile properties,were then studied to obtain an in-depth understanding of SLM-built TA15.Six typical temperatures(650,750,850,950,1000 and 1100℃) covering three representative temperature ranges,i.e.,martensite partial decomposition temperature range,martensite complete decomposition temperature range and above βtransus temperature,were subsequently selected as heat-treatment temperatures.The heat treatmentmicrostructure-mechanical property relationships of SLM-built TA15 were elucidated in detail.These results provide valuable information on the development of SLM-built TA15 alloy for industrial applications,and these findings are also beneficial to additive manufacturing of other near-α Ti alloys with desirable high-temperature properties.展开更多
The disk resonator gyroscope is an attractive candidate for high-performance MEMS gyroscopes.This gyroscope consists of a sensor and readout electronics,and the characteristics of the sensor directly determine the per...The disk resonator gyroscope is an attractive candidate for high-performance MEMS gyroscopes.This gyroscope consists of a sensor and readout electronics,and the characteristics of the sensor directly determine the performance.For the sensor,a high-quality factor and long decaying time constant are the most important characteristics required to achieve high performance.We report a disk resonator gyroscope with a measured quality factor of 510 k and decaying time constant of 74.9 s,which is a record for MEMS silicon disk resonator gyroscopes,to the best of our knowledge.To improve the quality factor of the DRG,the quality factor improvement mechanism is first analyzed,and based on this mechanism two stiffness-mass decoupled methods,i.e.,spoke length distribution optimization and lumped mass configuration design,are proposed and demonstrated.A disk resonator gyroscope prototype is fabricated based on these design strategies,and the sensor itself shows an angle random walk as low as 0.001°/√h,demonstrating true potential to achieve navigation-grade performance.The gyroscope with readout electronics shows an angle random walk of 0.01°/√h and a bias instability of 0.04°/h at room temperature without compensation,revealing that the performance of the gyroscope is severely limited by the readout electronics,which should be further improved.We expect that the quality factor improvement methods can be used in the design of other MEMS gyroscopes and that the newly designed DRG can be further improved to achieve navigation-grade performances for high-end industrial,transportation,aerospace,and automotive applications.展开更多
The problem of task assignment for multiple cooperating unmanned aerial vehicle(UAV) teams is considered. Multiple UAVs forming several small teams are needed to perform attack tasks on a set of predetermined ground t...The problem of task assignment for multiple cooperating unmanned aerial vehicle(UAV) teams is considered. Multiple UAVs forming several small teams are needed to perform attack tasks on a set of predetermined ground targets. A hierarchical task assignment method is presented to address the problem. It breaks the original problem down to three levels of sub-problems: target clustering, cluster allocation and target assignment. The first two sub-problems are centrally solved by using clustering algorithms and integer linear programming, respectively, and the third sub-problem is solved in a distributed and parallel manner, using a mixed integer linear programming model and an improved ant colony algorithm. The proposed hierarchical method can reduce the computational complexity of the task assignment problem considerably, especially when the number of tasks or the number of UAVs is large. Experimental results show that this method is feasible and more efficient than non-hierarchical methods.展开更多
The Matuyama/Brunhes polarity boundary (MBPB) is recorded in Chinese loess L8, which is associated with the glacial period. It is proved that loess L8 is capable of recording earth’s secular variation, and the lock-i...The Matuyama/Brunhes polarity boundary (MBPB) is recorded in Chinese loess L8, which is associated with the glacial period. It is proved that loess L8 is capable of recording earth’s secular variation, and the lock-in depth in Chinese loess is no more than that of marine sediments. Comparison with the location of MBPB in Chinese loess and marine sediments, it is put forward that there is a recording phase lag between ocean and continent climate changes.展开更多
Flowering time and plant height are key agronomic traits that directly affect soybean(Glycine max)yield.APETALA1(AP1)functions as a class A gene in the ABCE model for floral organ development,helping to specify carpel...Flowering time and plant height are key agronomic traits that directly affect soybean(Glycine max)yield.APETALA1(AP1)functions as a class A gene in the ABCE model for floral organ development,helping to specify carpel,stamen,petal,and sepal identities.There are four AP1 homologs in soybean,all of which are mainly expressed in the shoot apex.Here,we used clustered regularly interspaced short palindromic repeats(CRISPR)–CRISPR-associated protein 9 technology to generate a homozygous quadruple mutant,gmap1,with loss-of-function mutations in all four GmAP1 genes.Under short-day(SD)conditions,the gmap1 quadruple mutant exhibited delayed flowering,changes in flower morphology,and increased node number and internode length,resulting in plants that were taller than the wild type.Conversely,overexpression of GmAP1a resulted in early flowering and reduced plant height compared to the wild type under SD conditions.The gmap1 mutant and the overexpression lines also exhibited altered expression of several genes related to flowering and gibberellic acid metabolism,thereby providing insight into the role of GmAP1 in the regulatory networks controlling flowering time and plant height in soybean.Increased node number is the trait with the most promise for enhancing soybean pod number and grain yield.Therefore,the mutant alleles of the four AP1 homologs described here will be invaluable for molecular breeding of improved soybean yield.展开更多
Due to the limitations in autogenous nerve grafting or Schwann cell transplantation,large gap peripheral nerve injuries require a bridging strategy supported by nerve conduit.Cell based therapies provide a novel treat...Due to the limitations in autogenous nerve grafting or Schwann cell transplantation,large gap peripheral nerve injuries require a bridging strategy supported by nerve conduit.Cell based therapies provide a novel treatment for peripheral nerve injuries.In this study,we first experimented an optimal scaffold material synthesis protocol,from where we selected the 10%GFD formula(10%GelMA hydrogel,recombinant human basic fibroblast growth factor and dental pulp stem cells(DPSCs))to fill a cellulose/soy protein isolate composite membrane(CSM)tube to construct a third generation of nerve regeneration conduit,CSM-GFD.Then this CSM-GFD conduit was applied to repair a 15-mm long defect of sciatic nerve in a rat model.After 12 week post implant surgery,at histologic level,we found CSM-GFD conduit could regenerate nerve tissue like neuron and Schwann like nerve cells and myelinated nerve fibers.At physical level,CSM-GFD achieved functional recovery assessed by a sciatic functional index study.In both levels,CSM-GFD performed like what gold standard,the nerve autograft,could do.Further,we unveiled that almost all newly formed nerve tissue at defect site was originated from the direct differentiation of exogeneous DPSCs in CSM-GFD.In conclusion,we claimed that this third-generation nerve regeneration conduit,CSM-GFD,could be a promising tissue engineering approach to replace the conventional nerve autograft to treat the large gap defect in peripheral nerve injuries.展开更多
Currently,the effective and clean suppression of lithium-ion battery(LIB)fires remains a challenge.The present work investigates the use of various inhibitor doses(Xin)of dodecafluoro-2-methylpentan-3-one(C_(6) F_(12)...Currently,the effective and clean suppression of lithium-ion battery(LIB)fires remains a challenge.The present work investigates the use of various inhibitor doses(Xin)of dodecafluoro-2-methylpentan-3-one(C_(6) F_(12)O)in 300 Ah LIBs,and systematically examines the thermal and toxic hazards of the extinguished batteries via real scale combustion and gas analysis.The inhibitor is shown to be completely effective.The inhibition mechanism involves a combination of chemical inhibition and physical cooling.While the chemical inhibition effect tends to saturate with increasing Xin,the physical cooling remains effective at higher inhibitor doses.However,extinguishing the battery fire with a high Xin of C_(6)F_(12)O is found to incur serious toxicity problems.These results are expected to provide a guideline for the design of inhibitor doses for the suppression of LIB fires.展开更多
Ionic Polymer-Metal Composite （IPMC） is a new electro-active polymer, which has the advantages of light weight, flexibility, and large stroke with low driving voltage. Because of these features, IPMC can be applied ...Ionic Polymer-Metal Composite （IPMC） is a new electro-active polymer, which has the advantages of light weight, flexibility, and large stroke with low driving voltage. Because of these features, IPMC can be applied to bionic robotic actuators, artificial muscles, as well as dynamic sensors. However, IPMC has the major drawback of low generative blocking force. In this paper, in order to enhance the blocking force, the Nation membranes with thickness of 0.22 mm, 0.32 mm, 0.42 mm, 0.64 mm and 0.8 mm were prepared by casting from liquid solution. By employing these Nation membranes, IPMCs with varying thickness were fabricated by electroless plating. The elastic modulus of the casted Nation membranes were obtained by a nano-indenter, and the current, the displacement and the blocking force were respectively measured by the apparatus for actuation test. Finally, the effects of the thickness on the performance of IPMC were analyzed with an electromechanical model. Experimental study and theory analysis indicate that as the thickness increases, the elastic modulus of Nation membrane and the blocking force of IPMC increase, however, the current and the displacement decrease.展开更多
As a study method of traffic flow, dynamics models were developed and applied in the last few decades. However, there exist some flaws in most existing models. In this note, a new dynamics model is proposed by using c...As a study method of traffic flow, dynamics models were developed and applied in the last few decades. However, there exist some flaws in most existing models. In this note, a new dynamics model is proposed by using car-following theory and the usual connection method of micro-macro variables, which can overcome some ubiquitous problems in the existing models. Numerical results show that the new model can very well simulate traffic flow conditions, such as congestion, evacuation of congestion, stop-and-go phenomena and phantom jam.展开更多
Nickel-based superalloys have been widely used in aerospace fields,especially for engine hot-end parts,because of their excellent high-temperature resistance.However,they are difficult to machine and process because o...Nickel-based superalloys have been widely used in aerospace fields,especially for engine hot-end parts,because of their excellent high-temperature resistance.However,they are difficult to machine and process because of their special properties.High-energy beam additive manufacturing(HEB-AM)of nickel-based superalloys has shown great application potential in aerospace and other fields.However,HEB-AM of nickel-based superalloys faces serious cracking problems because of the unique characteristics of superalloys,and this has become the most significant bottleneck restricting their application.In this review,the current research status related to the types,formation mechanisms,and suppression methods of cracks in nickel-based superalloys produced by HEB-AM is described.The initiation and propagation mechanisms of cracks and their multiple influencing factors are also analyzed and discussed.Then,several possible research directions to solve the cracking problems in nickel-based superalloys produced by HEB-AM are outlined.This review provides an in-depth and comprehensive understanding of the cracking problem in AM nickel-based superalloys.It also provides valuable references for AM crack-free nickel-based superalloy components.展开更多
基金sponsored by National Key Research and Development Program "Additive Manufacturing and Laser Manufacturing" (No. 2016YFB1100101)Natural and Science Foundation of China (Grant Nos. 51775208, 51505166)+4 种基金Hubei Science Fund for Distinguished Young Scholars (No. 0216110085)Wuhan Morning Light Plan of Youth Science and Technology (No. 0216110066)Graduates’ Innovation Fund, Huazhong University of Science and Technology (No. 5003110027)Fundamental Research Funds for the Central University (No. 2017JYCXJJ004)the Academic frontier youth team at Huazhong University of Science and Technology (HUST)
文摘Selective laser melting(SLM) is an attractive rapid prototyping technology for the fabrication of metallic components with complex structure and high performance. Aluminum alloy, one of the most pervasive structural materials, is well known for high specific strength and good corrosion resistance. But the poor laser formability of aluminum alloy restricts its application. There are problems such as limited processable materials, immature process conditions and metallurgical defects on SLM processing aluminum alloys. Some efforts have been made to solve the above problems. This paper discusses the current research status both related to the scientific understanding and technology applications. The paper begins with a brief introduction of basic concepts of aluminum alloys and technology characterization of laser selective melting. In addition, solidification theory of SLM process and formation mechanism of metallurgical defects are discussed. Then, the current research status of microstructure, properties and heat treatment of SLM processing aluminum alloys is systematically reviewed respectively. Lastly, a future outlook is given at the end of this review paper.
文摘Grouting is a major method used to prevent water and mud inrush in tunnels and underground engineering. In this paper, the current situation of control and prevention of water and mud inrush is summarized and recent advances in relevant theories, grout/equipment, and critical techniques are introduced. The time-variant equations of grout viscosity at different volumetric ratios were obtained based on the constitutive relation of typical fast curing grouts. A large-scale dynamic grouting model testing system （4000 mm × 2000 mm × 5 mm） was developed, and the diffusions of cement and fast curing grouts in dynamic water grouting were investigated. The results reveal that the diffusions of cement grouts and fast curing grouts are U-shaped and asymmetric elliptical, respectively. A multi-parameter real-time monitoring system （＆#981; = 1.5 m, h = 1.2 m） was developed for the grouting process to study the diffusion and reinforcement mechanism of grouting in water-rich faulted zone. A high early strength cream-type reinforcing/plugging grout, a high permeability nano-scale silica gel grout, and a high-expansion filling grout were proposed for the control of water hazards in weak water-rich faulted zone rocks, water inrush in karst passages, and micro-crack water inrush, respectively. Complement technologies and equipment for industrial applications were also proposed. Additionally, a novel full-life periodic dynamic water grouting with the critical grouting borehole as the core was proposed. The key techniques for the control of water inrush in water-rich faulted zone, jointed fissures and karst passages, and micro-crack water inrush were developed.
文摘Donor shortages for organ transplantations are a major clinical challenge worldwide. Potential risks that are inevitably encountered with traditional methods include complications, secondary injuries, and limited source donors. Three-dimensional （3D） printing technology holds the potential to solve these limitations; it can he used to rapidly manufacture personalized tissue engineering scaffolds, repair tissue defects in situ with cells, and even directly print tissue and organs. Such printed implants and organs not only perfectly match the patient＇s damaged tissue, hut can also have engineered material microstructures and cell arrangements to promote cell growth and differentiation. Thus, such implants allow the desired tissue repair to he achieved, and could eventually solve the donor-shortage problem. This review summarizes relevant studies and recent progress on four levels, introduces different types of biomedical materials, and discusses existing problems and development issues with 3D printing that are related to materials and to the construction of extracellular matrix in vitro for medical applications.
文摘Selective laser melting （SLM）, as one of the additive manufacturing technologies, is widely investigated to fabricate metal parts. In SLM, parts are manufactured directly from powders in a layer-by-layer fashion; SLM also provides several advantages, such as production of complex parts with high three-dimensional accuracy, compared with other additive manufacturing technologies. Therefore, SLM can be applied in aeronautics, astronautics, medicine, and die and mould industry. However, this technique differs from traditional methods, such as casting and forging; for instance, the former greatly differs in terms of microstructure and properties of products. This paper summarizes relevant studies on metal material fabrication through SLM. Based on a work completed in Huazhong Univ. Sci Tech., Rapid Manuf. Center （HUST-RMC） and compared with characteristics described in other reported studies, microstructure, properties, dimensional accuracy, and application of SLM are presented.
基金funded by the National Science & Technology Pillar Program of China (Granted No. 2012BAF08B00)the National Natural Science Foundation of China (Granted Nos. 51375189 and 51375188)+2 种基金the independent R&D subjects of Huazhong University of Science and Technologythe State Key Laboratory of Materials Processing and Die & Mold Technologyco-funded by China Scholarship Council (CSC)
文摘Selective laser melting （SLM）, an additive manufacturing process, is capable of manufacturing metallic parts with complex shapes directly from computer-aided design （CAD） models. SLM parts are created on a layer-by-layer manner, making it more flexible than traditional material processing techniques, in this paper, Inconel 625 alloy, a widely used material in the aerospace industry, were chosen as the build material. Scanning electron microscopy （SEM）, electron back scattering diffraction （EBSD） and X-ray diffraction （XRD） analysis techniques were employed to analyze its microstructure. It was observed that the molten pool was composed of elongated columnar crystal, Due to the rapid cooling speed, the primary dendrite arm space was approximately 0.5 μm and the hardness of SLM state was very high （343 HV）. The inverse pole figure （IPF） indicated that the growing orientation of the most grains was 〈001〉 due to the epitaxial growth and heat conduction. The XRD results revealed that the austenite structure with large lattice distortion was fully formed. No carbides or precipitated phases were found. After heat treatment the grains grew into two microstructures with distinct morphological characters, namely, rectangular grains and limited in the molten pool, and equiaxed grains along the molten boundaries. Upon experiencing the heat treatment, MC carbides with triangular shapes gradually precipitated. The results also identified that a large number of zigzag grain boundaries were formed. In this study, the grain formation and microstructure, and the laws of the molten pool evolution were also analyzed and discussed,
基金Supported by National Natural Science Foundation of China (50625927,50727904)the National Basic Research Program (973) of China (2007CB209407)Ministry of Communications’Scientific and Technological Program of Transportation Development in Western China(2009318000008)
文摘The complicated geological conditions and geological hazards are challenging problems during tunnel construction,which will cause great losses of life and property.Therefore,reliable prediction of geological defective features,such as faults,karst caves and groundwater,has important practical significances and theoretical values.In this paper,we presented the criteria for detecting typical geological anomalies using the tunnel seismic prediction（TSP） method.The ground penetrating radar（GPR） signal response to water-bearing structures was used for theoretical derivations.And the 3D tomography of the transient electromagnetic method（TEM） was used to develop an equivalent conductance method.Based on the improvement of a single prediction technique,we developed a technical system for reliable prediction of geological defective features by analyzing the advantages and disadvantages of all prediction methods.The procedure of the application of this system was introduced in detail.For prediction,the selection of prediction methods is an important and challenging work.The analytic hierarchy process（AHP） was developed for prediction optimization.We applied the newly developed prediction system to several important projects in China,including Hurongxi highway,Jinping II hydropower station,and Kiaochow Bay subsea tunnel.The case studies show that the geological defective features can be successfully detected with good precision and efficiency,and the prediction system is proved to be an effective means to minimize the risks of geological hazards during tunnel construction.
基金supported by the National Basic Research Program of China (No. 2006CB101700)the National High- tech Research and Development Program (No. 2006AA10Z165)the Program for New Century Excellent Talents in Uni-versity of China (No. NCET2005-05- 0502).
文摘The high-affinity K＋ （HAK） transporter gene family is the largest family in plant that functions as potassium transporter and is important for various aspects of plant life. In the present study, we identified 27 members of this family in rice genome. The phylogenetic tree divided the land plant HAK transporter proteins into 6 distinct groups. Although the main characteristic of this family was established before the origin of seed plants, they also showed some differences between the members of non-seed and seed plants. The HAK genes in rice were found to have expanded in lineage-specific manner after the split of monocots and dicots, and both segmental duplication events and tandem duplication events contributed to the expansion of this family. Functional divergence analysis for this family provided statistical evidence for shifted evolutionary rate after gene duplication. Further analysis indicated that both point mutant with positive selection and gene conversion events contributed to the evolution of this family in rice.
基金the National Natural Science Foundation of China (Grant Nos. 40332021, 30670159)Wu Zhengyi's Splendidly Contributing Award of Yunnan Province (Grant No. KIB-WU-2001-01)
文摘Using data from previous research on Quercus sect. Heterobalanus, the coexistence approach to Xix-abangma and Namling fossil sets, and altitudinal ranges of vegetation presented by fossil floras, a re-view and reevaluation have been made of existing theories on the uplift of the Himalayas, especially the palaeoaltitudes of Xixabangma and Namling in Tibet. The Xixabangma fossil set has a palaeoaltitude range of 2500―3500 m, and has risen 2200―3400 m since the Pliocene. The lower and upper assem-blages of the Miocene Namling had palaeoaltitudes of 2500―3000 m and 2800―3000 m, respectively. Therefore, Namling has risen at least 1300 m since the Miocene, thereby challenging some existing theories that suggest Namling has been static since the Miocene.
基金financially supported by the National Key Research and Development Program of China “the Clinical Application of Personalized Implant Prosthesis Additive Manufacturing Process Research” (No. 2016YFB1101303)the National Natural Science Foundation of China (Nos. 51705170 and 51905192)the China Postdoctoral Science Foundation (Nos. 2017M620312 and 2018T110756)。
文摘This paper presents a comprehensive study conducted to optimize the selective laser melting(SLM)parameters and subsequent heat-treatment temperatures for near-α high-temperature titanium alloy Ti-6 Al-2 Zr-1 Mo-1 V(TA15),which is widely used in the aerospace industry.Based on the surface morphology and relative density analysis,the optimized process parameters were:laser power from 230 W to 380 W,scan speed from 675 mm/s to 800 mm/s,scan spacing of 0.12 mm,and layer thickness of0.03 mm.The effects of the laser power and the layer thickness on the phase constitutions,microstructure features,as well as room-temperature and high-temperature(500℃) tensile properties,were then studied to obtain an in-depth understanding of SLM-built TA15.Six typical temperatures(650,750,850,950,1000 and 1100℃) covering three representative temperature ranges,i.e.,martensite partial decomposition temperature range,martensite complete decomposition temperature range and above βtransus temperature,were subsequently selected as heat-treatment temperatures.The heat treatmentmicrostructure-mechanical property relationships of SLM-built TA15 were elucidated in detail.These results provide valuable information on the development of SLM-built TA15 alloy for industrial applications,and these findings are also beneficial to additive manufacturing of other near-α Ti alloys with desirable high-temperature properties.
基金This work was supported by the National Natural Science Foundation of China under Grant 51575521the 2017 Huxiang Provincial Scholar Program.
文摘The disk resonator gyroscope is an attractive candidate for high-performance MEMS gyroscopes.This gyroscope consists of a sensor and readout electronics,and the characteristics of the sensor directly determine the performance.For the sensor,a high-quality factor and long decaying time constant are the most important characteristics required to achieve high performance.We report a disk resonator gyroscope with a measured quality factor of 510 k and decaying time constant of 74.9 s,which is a record for MEMS silicon disk resonator gyroscopes,to the best of our knowledge.To improve the quality factor of the DRG,the quality factor improvement mechanism is first analyzed,and based on this mechanism two stiffness-mass decoupled methods,i.e.,spoke length distribution optimization and lumped mass configuration design,are proposed and demonstrated.A disk resonator gyroscope prototype is fabricated based on these design strategies,and the sensor itself shows an angle random walk as low as 0.001°/√h,demonstrating true potential to achieve navigation-grade performance.The gyroscope with readout electronics shows an angle random walk of 0.01°/√h and a bias instability of 0.04°/h at room temperature without compensation,revealing that the performance of the gyroscope is severely limited by the readout electronics,which should be further improved.We expect that the quality factor improvement methods can be used in the design of other MEMS gyroscopes and that the newly designed DRG can be further improved to achieve navigation-grade performances for high-end industrial,transportation,aerospace,and automotive applications.
基金supported by the National Natural Science Foundation of China(7147205871401048)the Fundamental Research Funds for the Central Universities(2012HGZY0009)
文摘The problem of task assignment for multiple cooperating unmanned aerial vehicle(UAV) teams is considered. Multiple UAVs forming several small teams are needed to perform attack tasks on a set of predetermined ground targets. A hierarchical task assignment method is presented to address the problem. It breaks the original problem down to three levels of sub-problems: target clustering, cluster allocation and target assignment. The first two sub-problems are centrally solved by using clustering algorithms and integer linear programming, respectively, and the third sub-problem is solved in a distributed and parallel manner, using a mixed integer linear programming model and an improved ant colony algorithm. The proposed hierarchical method can reduce the computational complexity of the task assignment problem considerably, especially when the number of tasks or the number of UAVs is large. Experimental results show that this method is feasible and more efficient than non-hierarchical methods.
文摘The Matuyama/Brunhes polarity boundary (MBPB) is recorded in Chinese loess L8, which is associated with the glacial period. It is proved that loess L8 is capable of recording earth’s secular variation, and the lock-in depth in Chinese loess is no more than that of marine sediments. Comparison with the location of MBPB in Chinese loess and marine sediments, it is put forward that there is a recording phase lag between ocean and continent climate changes.
基金The authors would like to thank Professor YaoguangLiu at the South China Agricultural University forproviding the vector pYLCRISPR/Cas9P35SThiswork was supported by the National Naturalscience Foundation of China(31901499,31725021,31930083,31801384)This work was also funded bythe Major Program of Guangdong Basic and AppliedResearch(2019B030302006).
文摘Flowering time and plant height are key agronomic traits that directly affect soybean(Glycine max)yield.APETALA1(AP1)functions as a class A gene in the ABCE model for floral organ development,helping to specify carpel,stamen,petal,and sepal identities.There are four AP1 homologs in soybean,all of which are mainly expressed in the shoot apex.Here,we used clustered regularly interspaced short palindromic repeats(CRISPR)–CRISPR-associated protein 9 technology to generate a homozygous quadruple mutant,gmap1,with loss-of-function mutations in all four GmAP1 genes.Under short-day(SD)conditions,the gmap1 quadruple mutant exhibited delayed flowering,changes in flower morphology,and increased node number and internode length,resulting in plants that were taller than the wild type.Conversely,overexpression of GmAP1a resulted in early flowering and reduced plant height compared to the wild type under SD conditions.The gmap1 mutant and the overexpression lines also exhibited altered expression of several genes related to flowering and gibberellic acid metabolism,thereby providing insight into the role of GmAP1 in the regulatory networks controlling flowering time and plant height in soybean.Increased node number is the trait with the most promise for enhancing soybean pod number and grain yield.Therefore,the mutant alleles of the four AP1 homologs described here will be invaluable for molecular breeding of improved soybean yield.
基金supported by the National Natural Science Funding of China(81701032,81871503)the Wenzhou Science and Technology Association Project,the Wenzhou Major Scientific and Technological Innovation Key Medical and Health Project(ZY2019010)+4 种基金the Wenzhou Medical University grant(QTJ16026)Wenzhou Science and Technology Association Project,Wenzhou Basic Research Project(Y20180131)Zhejiang Province Program of the Medical and Health Science and Technology(2018KY537)Zhejiang Natural Science Foundation(LGF18C100002)Zhejiang Xinmiao Talents Program(2018R413186).
文摘Due to the limitations in autogenous nerve grafting or Schwann cell transplantation,large gap peripheral nerve injuries require a bridging strategy supported by nerve conduit.Cell based therapies provide a novel treatment for peripheral nerve injuries.In this study,we first experimented an optimal scaffold material synthesis protocol,from where we selected the 10%GFD formula(10%GelMA hydrogel,recombinant human basic fibroblast growth factor and dental pulp stem cells(DPSCs))to fill a cellulose/soy protein isolate composite membrane(CSM)tube to construct a third generation of nerve regeneration conduit,CSM-GFD.Then this CSM-GFD conduit was applied to repair a 15-mm long defect of sciatic nerve in a rat model.After 12 week post implant surgery,at histologic level,we found CSM-GFD conduit could regenerate nerve tissue like neuron and Schwann like nerve cells and myelinated nerve fibers.At physical level,CSM-GFD achieved functional recovery assessed by a sciatic functional index study.In both levels,CSM-GFD performed like what gold standard,the nerve autograft,could do.Further,we unveiled that almost all newly formed nerve tissue at defect site was originated from the direct differentiation of exogeneous DPSCs in CSM-GFD.In conclusion,we claimed that this third-generation nerve regeneration conduit,CSM-GFD,could be a promising tissue engineering approach to replace the conventional nerve autograft to treat the large gap defect in peripheral nerve injuries.
基金funded by the Science and Technology Project of the State Grid Corporation of China (Exploration study on Fire Extinguishing Technology of Lithium Ion Energy Storage Battery DG71-18-002)。
文摘Currently,the effective and clean suppression of lithium-ion battery(LIB)fires remains a challenge.The present work investigates the use of various inhibitor doses(Xin)of dodecafluoro-2-methylpentan-3-one(C_(6) F_(12)O)in 300 Ah LIBs,and systematically examines the thermal and toxic hazards of the extinguished batteries via real scale combustion and gas analysis.The inhibitor is shown to be completely effective.The inhibition mechanism involves a combination of chemical inhibition and physical cooling.While the chemical inhibition effect tends to saturate with increasing Xin,the physical cooling remains effective at higher inhibitor doses.However,extinguishing the battery fire with a high Xin of C_(6)F_(12)O is found to incur serious toxicity problems.These results are expected to provide a guideline for the design of inhibitor doses for the suppression of LIB fires.
基金Acknowledgement The authors thank the financial support from the National Natural Science Foundation of China （Grant No. 50705043, 60535020 and 60910007）.
文摘Ionic Polymer-Metal Composite （IPMC） is a new electro-active polymer, which has the advantages of light weight, flexibility, and large stroke with low driving voltage. Because of these features, IPMC can be applied to bionic robotic actuators, artificial muscles, as well as dynamic sensors. However, IPMC has the major drawback of low generative blocking force. In this paper, in order to enhance the blocking force, the Nation membranes with thickness of 0.22 mm, 0.32 mm, 0.42 mm, 0.64 mm and 0.8 mm were prepared by casting from liquid solution. By employing these Nation membranes, IPMCs with varying thickness were fabricated by electroless plating. The elastic modulus of the casted Nation membranes were obtained by a nano-indenter, and the current, the displacement and the blocking force were respectively measured by the apparatus for actuation test. Finally, the effects of the thickness on the performance of IPMC were analyzed with an electromechanical model. Experimental study and theory analysis indicate that as the thickness increases, the elastic modulus of Nation membrane and the blocking force of IPMC increase, however, the current and the displacement decrease.
基金the National Natural Science Foundation of China (Grant No. 19872062).
文摘As a study method of traffic flow, dynamics models were developed and applied in the last few decades. However, there exist some flaws in most existing models. In this note, a new dynamics model is proposed by using car-following theory and the usual connection method of micro-macro variables, which can overcome some ubiquitous problems in the existing models. Numerical results show that the new model can very well simulate traffic flow conditions, such as congestion, evacuation of congestion, stop-and-go phenomena and phantom jam.
基金National Natural Science Foundation of China(Grant Nos.52201040,52275333)China Postdoctoral Science Foundation(Grant No.2021M701291)+2 种基金AVIC Manufacturing Technology Institute of China(Grant No.KZ571801)Hubei Provincial Department of Science and Technology 2020 Provincial Key R&D Plan of China(Grant No.2020BAB049)Wuhan Science and Technology Project of China(Grant No.2020010602012037).
文摘Nickel-based superalloys have been widely used in aerospace fields,especially for engine hot-end parts,because of their excellent high-temperature resistance.However,they are difficult to machine and process because of their special properties.High-energy beam additive manufacturing(HEB-AM)of nickel-based superalloys has shown great application potential in aerospace and other fields.However,HEB-AM of nickel-based superalloys faces serious cracking problems because of the unique characteristics of superalloys,and this has become the most significant bottleneck restricting their application.In this review,the current research status related to the types,formation mechanisms,and suppression methods of cracks in nickel-based superalloys produced by HEB-AM is described.The initiation and propagation mechanisms of cracks and their multiple influencing factors are also analyzed and discussed.Then,several possible research directions to solve the cracking problems in nickel-based superalloys produced by HEB-AM are outlined.This review provides an in-depth and comprehensive understanding of the cracking problem in AM nickel-based superalloys.It also provides valuable references for AM crack-free nickel-based superalloy components.
