In recent years,numerous textual studies have appeared.However,the majority of them concentrated on the study of cohesion and coherence of sentences.Van Dijk(1977,1980),Holland famous linguist,put forward"Macrost...In recent years,numerous textual studies have appeared.However,the majority of them concentrated on the study of cohesion and coherence of sentences.Van Dijk(1977,1980),Holland famous linguist,put forward"Macrostructures"which provide us with a theo retical basis to study macrostructure of texts.The paper aims to introduce it in very detail and make it known to all the English learners.展开更多
As structural materials, closed-cell aluminum foams possess obvious advantages in product dimension, strength and process economics compared with open cell aluminum foams. However, as a kind of structure-function inte...As structural materials, closed-cell aluminum foams possess obvious advantages in product dimension, strength and process economics compared with open cell aluminum foams. However, as a kind of structure-function integration materials, the application of closed-cell aluminum foams has been restricted greatly in acoustic fields due to the difficulty of sound wave penetration. It was reported that closed-cell foams with macrostructures have important effect on the propagation of sound waves. To date, the relationship between macrostructures and acoustic properties of commercially pure closedcell aluminum foams is ambiguous. In this work, different perforation and air gap types were designed for changing the macrostructures of the foam. Meanwhile, the effect of macrostructures on the sound absorption coefficient and sound reduction index were investigated. The results showed that the foams with half-hole exhibited excellent sound absorption and sound insulation behaviors in high frequency range（〉2500 Hz）. In addition, specimens with air gaps showed good sound absorption properties in low frequency compared with the foams without air gaps. Based on the experiment results, propagation structural models of sound waves in commercially pure closed-cell aluminum foams with different macrostructures were built and the influence of macrostructures on acoustic properties was discussed.展开更多
In friction stir welding of aluminum alloys, tunnel defect may occur due to insufficient plastic material flow caused by lower heat input in the weld region. The inadequacy in heat input is due to improper selection o...In friction stir welding of aluminum alloys, tunnel defect may occur due to insufficient plastic material flow caused by lower heat input in the weld region. The inadequacy in heat input is due to improper selection of friction stir welding tool and process parameters. Ultimately, such defects degrade the properties of weld and may pose serious concerns towards the integrity and safety of the weld component. In order to improve the properties of weld joints, an ultrasonic-assisted friction stir welding device has been configured where ultrasonic energy is transferred from an ultrasonic unit directly into one of the workpieces near the tool. Using this configuration, ultrassonic-assisted friction stir welding was conducted on 6 mm thick 2024- 73 aluminum alloy sheets. The macrostructure and mechanical properties of these welds were compared with the welds of this alloy prepared by conventional friction stir welding using identical process parameters. The results show that the welding speed can be increased while satisfactory weld quality is still ensured. The ultrasonic energy transferred in this configuration could enlarge the volume of weld nugget zone. Also, the influence of ultrasonic energy on the suppression or elimination of the tunnel defect is quite apparent. However, any beneficial effects of ultrasonic vibration on the tensile strength and the elongation of the joint were less obvious in this configuration.展开更多
1 Results Carbon nanotubes (CNTs) have fascinating properties.In order to use these novel one-dimensional structures for applications such as in nano-electronic,nano-mechanical and electrochemical energy storage devic...1 Results Carbon nanotubes (CNTs) have fascinating properties.In order to use these novel one-dimensional structures for applications such as in nano-electronic,nano-mechanical and electrochemical energy storage device and as structural elements in various composites,the structure of nanotubes needs to be tailored and various architectures and macroscale assembles have to be configured using nanotube building blocks.Nanotube macrostructures are macroscopically organized groups of CNTs,which are expecte...展开更多
Controlled synthesis of hierarchically assembled titanium dioxide （TiO2） nano- structures is important for practical applications in environmental purification and solar energy conversion. We present here the fabric...Controlled synthesis of hierarchically assembled titanium dioxide （TiO2） nano- structures is important for practical applications in environmental purification and solar energy conversion. We present here the fabrication of interconnected TiO2 nanotubes as a macroscopic bulk material by using a porous carbon nanotube （CNT） sponge as a template. The basic idea is to uniformly coat an amorphous titania layer onto the CNT surface by the infiltration of a TiO2 precursor into the sponge followed by a subsequent hydrolysis process. After calcination, the CNTs are completely removed and the titania is simultaneously crystallized, which results in a porous macrostructure composed of interconnected anatase TiO2 nanotubes. The TiO2 nanotube macrostructures show comparable photocatalytic activities to commercial products （AEROXIDE TiO2 P25） for the degradation of rhodamine B （RhB）. Moreover, the TiO2 nanotube macrostructures can be settled and separated from water within 12 h after photocatalysis, whereas P25 remains suspended in solution after weeks. Thus the TiO2 nanotube macrostructures offer the advantage of easy catalyst separation and recycle and can be a promising candidate for wastewater treatment.展开更多
Great experimental results and observations achieved by Astronomy in the last decades revealed new unexplainable phenomena. Astronomers have conclusive new evidence that a recently discovered “dark galaxy” is, in fa...Great experimental results and observations achieved by Astronomy in the last decades revealed new unexplainable phenomena. Astronomers have conclusive new evidence that a recently discovered “dark galaxy” is, in fact, an object the size of a galaxy, made entirely of dark matter. They found that the speed of the Earth’s rotation varies randomly each day. 115 years ago, the Tunguska Event was observed, and astronomers still do not have an explanation of It. Main results of the present article are: 1) Dark galaxies explained by the spinning of their Dark Matter Cores with the surface speed at equator less than the escape velocity. Their Rotational Fission is not happening. Extrasolar systems do not emerge;2) 21-cm Emission explained by the self-annihilation of Dark Matter particles XIONs (5.3 μeV);3) Sun-Earth-Moon Interaction explained by the influence of the Sun’s and the Moon’s magnetic field on the electrical currents of the charged Geomagma (the 660-km layer), and, as a result, the Earth’s daylength varies;4) Tunguska Event explained by a huge atmospheric explosion of the Superbolide, which was a stable Dark Matter Bubble before entering the Earth’s atmosphere.展开更多
Bio-inspired macrostructure array(MAA,size:submillimeter to millimeter scale)materials with special wettability(MAAMs-SW)have attracted significant research attention due to their outstanding performance in many appli...Bio-inspired macrostructure array(MAA,size:submillimeter to millimeter scale)materials with special wettability(MAAMs-SW)have attracted significant research attention due to their outstanding performance in many applications,including oil repellency,liquid/droplet manipulation,anti-icing,heat transfer,water collection,and oil–water separation.In this review,we focus on recent developments in the theory,design,fabrication,and application of bio-inspired MAAMs-SW.We first review the history of the basic theory of special wettability and discuss representative structures and corresponding functions of some biological surfaces,thus setting the stage for the design and fabrication of bio-inspired MAAMs-SW.We then summarize the fabrication methods of special wetting MAAs in terms of three categories:additive manufacturing,subtractive manufacturing,and formative manufacturing,as well as their diverse functional applications,providing insights into the development of these MAAMs-SW.Finally,the challenges and directions of future research on bio-inspired MAAMs-SW are briefy addressed.Worldwide efforts,progress,and breakthroughs from surface engineering to functional applications elaborated herein will promote the practical application of bio-inspired MAAMs-SW.展开更多
As a new solid state welding,pinless friction stir welding（PFSW） can be used to join thin-wall structures.In this study,four new pinless tools with different groove distributions were designed and manufactured in or...As a new solid state welding,pinless friction stir welding（PFSW） can be used to join thin-wall structures.In this study,four new pinless tools with different groove distributions were designed and manufactured in order to enrich technological storage of PFSW and obtain sound joint with high quality of alclad 2A12-T4 alloy.The results show that the small-obliquity tool is detrimental to the transfer of plasticized materials,resulting in the formation of kissing bond defect.For the through-groove tool or the large-curvature tool,bigger flashes form on the joint surface and alclad layer is observed in the nugget zone（NZ）,deteriorating mechanical properties.Compared with the above-mentioned three tools,using the six-groove tool with rational curvature and obliquity can not only yield sound joint with small flashes and thickness reduction,but also prevent alclad from flowing into NZ,which has potential to weld thin alclad aluminum alloys.Meanwhile,the tensile strength and elongation of joint using the six-groove tool reach the maximum values of 362 MPa and 8.3%,up to 85.1% and 64% of BM.展开更多
The results of measurements of the Hubble constant H<sub>0</sub>, which characterizes the expansion rate of the universe, show that the values of H<sub>0</sub> vary significantly depending on M...The results of measurements of the Hubble constant H<sub>0</sub>, which characterizes the expansion rate of the universe, show that the values of H<sub>0</sub> vary significantly depending on Methodology. The disagreement in the values of H<sub>0</sub> obtained by the various teams far exceeds the standard uncertainties provided with the values. This discrepancy is called the Hubble Tension. In this paper, we discuss Macrostructures of the World (Superclusters and Galaxies);explain their Origin and Evolution in frames of the developed Hypersphere World-Universe Model (WUM), which is an alternative to the prevailing Big Bang Model (BBM) [1];and provide the explanation of the Hubble Tension. The main difference between WUM and BBM is: Instead of the Infinite Homogeneous and Isotropic Universe around the Initial Singularity in BBM, in WUM, the 3D Finite Boundless World (a Hypersphere) presents a Patchwork Quilt of different Luminous Superclusters (10<sup>3</sup>), which emerged in various places of the World at different Cosmological times. In WUM, the Medium of the World is Homogeneous and Isotropic. The distribution of Macroobjects in the World is spatially Inhomogeneous and Anisotropic and temporally Non-simultaneous.展开更多
A complicated Cu-Ni based alloy was developed to fabricate wear-resisting bush for high temperature application.The concern focuses on the control of equiaxed grains in the developed alloy ingot prepared by centrifuga...A complicated Cu-Ni based alloy was developed to fabricate wear-resisting bush for high temperature application.The concern focuses on the control of equiaxed grains in the developed alloy ingot prepared by centrifugal casting.The results show that the equiaxed grains are determined by the pouring temperature of the melt,the cooling rate and the rotation speed of the mold.With the decrease in pouring temperature,the fraction of the equiaxed grains in the transverse section of the ingot increases and the average length of columnar grain decreases.When the pouring temperature is confined below 1,250℃,complete equiaxed grains can be obtained.Based on the optimal centrifugal casting processing,the tensile strength of the developed alloy ingot with complete equiaxed grains reaches to 810 MPa and 435 MPa at room temperature and 500℃,respectively,which is 14% and 110% higher than that of common commercial QAl10-4-4 alloy.The wear rate of the developed alloy is 7.0 × 10-8 and 3.8 × 10-7 mm3?N-1?mm-1 at room temperature and 500℃,respectively,which is 5 times and 39 times lower than that of QAl10-4-4 alloy.展开更多
A comprehensive mathematical model was established and used to simulate the macro and microstructure evolution during the production process of 5CrNiMo steel ingot by electroslag remelting （ESR） method. Along the in...A comprehensive mathematical model was established and used to simulate the macro and microstructure evolution during the production process of 5CrNiMo steel ingot by electroslag remelting （ESR） method. Along the ingot height, the macrostructure distribution characteristics changed from vertical, fine columnar grains to tilted, coarse columnar grains, and this transformation process occurred at the very beginning of ESR. In the cross section of the ingot, there were three grain morphology regions and two grain type transition regions from the outside to the center of the ingot. These regions were the fine columnar grain region, columnar competitive growth transition re gion, coarse columnar grain region, columnar to equiaxed grain transition （CET） region, and coarse equiaxed grain region. The influence of the remelting rate on the macrostructure and mlcrostructure was investigated using a series of experiments and simulations. The results showed that a low remelting rate could produce a small grain growth angle （GGA） ; the average secondary dendrite arm spacing （SDAS） firstly decreased and then increased as the remelting rate increased. An excessively high or low remelting rate can increase the GGA and average SDAS in ingots. Thus, the remelting rate should be controlled within a suitable range to reduce composition microsegregation and microshrinkage in the ingot to produce an ESR ingot with satisfactory hot forging performance.展开更多
In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium a...In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium alloy ingots during VAR process.The results show that the temperature fields obtained by the simulation are well validated through the experiment results.The temperature distribution is different during the whole VAR process and the steady-state molten pool forms at 329 s for d100 mm × 180 mm ingots.At the initial stage of remelting,the heat dissipation of crucible bottom plays an important role in the whole heat dissipation system.At the middle of remelting,the crucible wall becomes a major heat dissipation way.The effect of cooling velocity on the solidification structure of ingots was investigated based on the temperature fields and the results can well explain the macrostructure of titanium alloy ingots.展开更多
The simulation models of the thermal and macrostructural evolutions during directional solidification of Ni-base single crystal(SX) turbine blades under high rate solidification(HRS) and liquid metal cooling(LMC) have...The simulation models of the thermal and macrostructural evolutions during directional solidification of Ni-base single crystal(SX) turbine blades under high rate solidification(HRS) and liquid metal cooling(LMC) have been constructed using Pro CAST software, coupled with a 3D Cellular Automaton Finite Element(CAFE) model. The models were used to investigate the tendencies of stray grain(SG) formation in the platform region of turbine blades fabricated by HRS and LMC techniques. The results reveal that the LMC technique can prohibit SG formation by smoothing the concaved isotherm and in turn alleviating the undercooling in the platform ends to let the dendrites fill up the undercooled zone before SG nucleation. The simulation results agreed well with the experimental results, indicating that these models could be used to analyze the macrostructural evolution or to optimize process parameters to suppress SG formation. Using these models, the critical withdrawal rate for casting SX turbine blades without SG formation were determined to be around 75 μm·s^(-1) and 100 μm·s^(-1) for HRS and LMC respectively, suggesting that LMC can be used as an efficient technique in fabricating SX turbine blades without any SG defect formation.展开更多
Ion conductive membranes(ICMs)are frequently used as separators for energy conversion and storage technologies of fuel cells,flow battery,and hydrogen pump,because of their good ion-selective conduction and low electr...Ion conductive membranes(ICMs)are frequently used as separators for energy conversion and storage technologies of fuel cells,flow battery,and hydrogen pump,because of their good ion-selective conduction and low electronic conductivity.Firstly,this feature article reviews the recent studies on the development of new nonfluorinated ICMs with low cost and their macro/micro-structure control.In general,these new nonfluorinated ICMs have lower conductivity than commercial perfluorinated ones,due to their poor ion transport channels.Increasing ion exchange capacity(IEC)would create more continuous hydrophilic channels,thus enhancing the conductivity.However,high IEC also expands the overall hydrophilic domains,weakens the interaction between polymer chains,enhances the mobility of polymer chains,and eventually induces larger swelling.The micro-scale expansion and macro-scale swelling of the ICMs with high IEC could be controlled by limiting the mobility of polymer chains.Based on this strategy,some ef ficient techniques have been developed,including covalent crosslinking,semi-interpenatrating polymer network,and blending.Secondly,this review introduces the optimization of macro/microstructure of both perfluorinated and nonfluorinated ICMs to improve the performance.Macro-scale multilayer composite is an ef ficient way to enhance the mechanical strength and the dimensional stability of the ICMs,and could also decrease the content of per fluorosulfonic acid resin in the membrane,thereby reducing the cost of the perfluorinated ICMs.Long side chain,multiple functionalization,small molecule inducing micro-phase separation,electrospun nano fiber,and organic–inorganic hybrid could construct more ef ficient ion transport channels,improving the ion conductivity of ICMs.展开更多
This paper reviews the latest research progress in the additive manufacturing(AM)process of 18%nickel maraging steels,which involves laser-based powder bed fusion(L-PBF),laser-based directed energy deposition(L-DED),a...This paper reviews the latest research progress in the additive manufacturing(AM)process of 18%nickel maraging steels,which involves laser-based powder bed fusion(L-PBF),laser-based directed energy deposition(L-DED),and wire arc additive manufacturing(WAAM).The emphasis is on the defects,structure,and mechanical properties of the additive manufactured 18%nickel maraging steels.At first,this article outlines the influences of the processing parameters of AM techniques on the defects formed in the fabricated parts,in terms of the L-PBF and WAAM.The macrostructure and microstructure characteristics of as-built and heat-treated 18%nickel maraging steel are then described in detail.Later,the mechanical properties of as-built and heat-treated 18%nickel maraging steel are assessed,such as their tensile,hardness,impact toughness,and fatigue performances.Finally,future directions for work on the AM of 18%nickel maraging steel are provided.展开更多
Silicon is the most extensively studied semiconductor mainly owing to its wide applicability in the photovoltaic solar cell industry.However the qualily of Si photovoltaic cells depends on the purity of the material a...Silicon is the most extensively studied semiconductor mainly owing to its wide applicability in the photovoltaic solar cell industry.However the qualily of Si photovoltaic cells depends on the purity of the material and on the grain structure of the ingot from which the wafers are cutting.The electrical performance of such materials,i.e. mainly their minority carrier lifetime,is closely related to metal impurities present in the feedstock or introduced during crystal growth.These impurities strongly interact with existing crystal defects to form complexes,accumulate at dislocations or grain boundaries in different forms,or even form silieide precipitates,which simultaneously contain several metal impurities.In such a context,it is necessary to control the segregation of impurities especially metallic in the grown ingot in order to optimize the cell properties as a function of the raw material purity.A new Bridgman set-up is developed in order to study the crystallization of photovoltaic Si under independently controlled solidification parameters growth rate,thermal gradient,purity and convection.Convection,either natural or forced,plays a very important role during the crystallization.Its intensity and flow pattern affect heat and mass transfer and,consequently,macrostructure and segregation in a solidified ingot.Here the convection can be controlled by a travelling magnetic field in order to homogenize or segregate the rejected impurities such as metallic elements.The effects of the magnetic field intensity and frequency on the segregation and crystalline structure will be presented.展开更多
The development of a numerical model for the melting process of Al--Ti alloy targetmaterial in vacuum induction furnace with cold crucible (VIFCC)was described. It isa two--dimensional computational methodology to cal...The development of a numerical model for the melting process of Al--Ti alloy targetmaterial in vacuum induction furnace with cold crucible (VIFCC)was described. It isa two--dimensional computational methodology to calculate electromagnetic field, heattransfer field and fluid flow field. Based on the aid of the finite element method withthe commercial software--ANSYS, a superimposition method of a layer of copper anda slit to simulate the VIFCC melting process was used. The method was effectiveto save large quantity of memory and computing time. Meanwhile, a temperaturedistribution profile during the melting process was obtained. Validity of the model wasconfirmed by comparison between the result from calculation and those from directmeasurement by optical pyrometer and indirect investigation by ingot macrostructure.A relatively good agreement was found. Further, a nearly directional solidificationstrvcture was obtained under properly controlling the cooling rate and heating power.Therefore, such model developed in this article is feasible.展开更多
The macrostructure and properties of the thin walled copper tube prepared by the downward continuous unidirectional solidification （DCUS） method were studied. The result shows that the macrostructure is closely rela...The macrostructure and properties of the thin walled copper tube prepared by the downward continuous unidirectional solidification （DCUS） method were studied. The result shows that the macrostructure is closely related to the solid-liquid interface profile, which is influenced by the distance between the cooling water location and the solidification front. The mechanical properties of the thin walled copper tube prepared by the DCUS method are near those of the normal cast copper, and it has good relative density, electrical conductivity, and elongation, which are not greatly affected by casting speed. The thin walled copper tube prepared by the DCUS method also has good processing properties that can be taken to further drawing procedures directly without an intermediate process, and obtains good mechanical properties with the total processing rate of 89.8%.展开更多
To improve the quality of high carbon wire rods,combined electromagnetic stirring was introduced in the continuous casting of round billets with a diameter of 250mm at Tianjin Rockcheck Steel Group Co.In this paper,th...To improve the quality of high carbon wire rods,combined electromagnetic stirring was introduced in the continuous casting of round billets with a diameter of 250mm at Tianjin Rockcheck Steel Group Co.In this paper,the positioning of final electromagnetic stirring(F-EMS)was determined by nail-shooting method.Furthermore,the effect of mold electromagnetic stirring(M-EMS)on the macrostructure and internal defects in the round billets was investigated to find out the optimal operating parameters for continuous casting of SWRH 82B round billets.The results show the desirable positioning of F-EMS locates 9.7m below the mold level where the molten steel can be effectively driven by electromagnetic force and disperse central composition segregation.The shrinkage cavity is totally eliminated with the rotational M-EMS.The ratio and index of central composition segregation and center porosity can be reduced significantly. Furthermore,the equiaxed crystal ratio is considerably increased to 64%under 480A/3Hz M-EMS and 500A/10Hz F-EMS. Fine microstructure and mechanical property of wire rod are presented after optimization of combined electromagnetic stirring.Accordingly,the probability of occurrence of cup-cone fracture of wire rod is reduced dramatically.展开更多
Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructura...Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.展开更多
文摘In recent years,numerous textual studies have appeared.However,the majority of them concentrated on the study of cohesion and coherence of sentences.Van Dijk(1977,1980),Holland famous linguist,put forward"Macrostructures"which provide us with a theo retical basis to study macrostructure of texts.The paper aims to introduce it in very detail and make it known to all the English learners.
基金supported financially by the National Natural Science Foundation of China (Nos. 51501053, 51325401 and U1660201)the National Magnetic Confinement Fusion Energy Research Program (No. 2014GB125006)Science and Technology Plan Projects of Hebei Province (No. 15211026)
文摘As structural materials, closed-cell aluminum foams possess obvious advantages in product dimension, strength and process economics compared with open cell aluminum foams. However, as a kind of structure-function integration materials, the application of closed-cell aluminum foams has been restricted greatly in acoustic fields due to the difficulty of sound wave penetration. It was reported that closed-cell foams with macrostructures have important effect on the propagation of sound waves. To date, the relationship between macrostructures and acoustic properties of commercially pure closedcell aluminum foams is ambiguous. In this work, different perforation and air gap types were designed for changing the macrostructures of the foam. Meanwhile, the effect of macrostructures on the sound absorption coefficient and sound reduction index were investigated. The results showed that the foams with half-hole exhibited excellent sound absorption and sound insulation behaviors in high frequency range（〉2500 Hz）. In addition, specimens with air gaps showed good sound absorption properties in low frequency compared with the foams without air gaps. Based on the experiment results, propagation structural models of sound waves in commercially pure closed-cell aluminum foams with different macrostructures were built and the influence of macrostructures on acoustic properties was discussed.
基金Acknowledgement The authors are grateful to the financial support for this research from the National Natural Science Foundation of China （Grant No. 51475272）.
文摘In friction stir welding of aluminum alloys, tunnel defect may occur due to insufficient plastic material flow caused by lower heat input in the weld region. The inadequacy in heat input is due to improper selection of friction stir welding tool and process parameters. Ultimately, such defects degrade the properties of weld and may pose serious concerns towards the integrity and safety of the weld component. In order to improve the properties of weld joints, an ultrasonic-assisted friction stir welding device has been configured where ultrasonic energy is transferred from an ultrasonic unit directly into one of the workpieces near the tool. Using this configuration, ultrassonic-assisted friction stir welding was conducted on 6 mm thick 2024- 73 aluminum alloy sheets. The macrostructure and mechanical properties of these welds were compared with the welds of this alloy prepared by conventional friction stir welding using identical process parameters. The results show that the welding speed can be increased while satisfactory weld quality is still ensured. The ultrasonic energy transferred in this configuration could enlarge the volume of weld nugget zone. Also, the influence of ultrasonic energy on the suppression or elimination of the tunnel defect is quite apparent. However, any beneficial effects of ultrasonic vibration on the tensile strength and the elongation of the joint were less obvious in this configuration.
文摘1 Results Carbon nanotubes (CNTs) have fascinating properties.In order to use these novel one-dimensional structures for applications such as in nano-electronic,nano-mechanical and electrochemical energy storage device and as structural elements in various composites,the structure of nanotubes needs to be tailored and various architectures and macroscale assembles have to be configured using nanotube building blocks.Nanotube macrostructures are macroscopically organized groups of CNTs,which are expecte...
文摘Controlled synthesis of hierarchically assembled titanium dioxide （TiO2） nano- structures is important for practical applications in environmental purification and solar energy conversion. We present here the fabrication of interconnected TiO2 nanotubes as a macroscopic bulk material by using a porous carbon nanotube （CNT） sponge as a template. The basic idea is to uniformly coat an amorphous titania layer onto the CNT surface by the infiltration of a TiO2 precursor into the sponge followed by a subsequent hydrolysis process. After calcination, the CNTs are completely removed and the titania is simultaneously crystallized, which results in a porous macrostructure composed of interconnected anatase TiO2 nanotubes. The TiO2 nanotube macrostructures show comparable photocatalytic activities to commercial products （AEROXIDE TiO2 P25） for the degradation of rhodamine B （RhB）. Moreover, the TiO2 nanotube macrostructures can be settled and separated from water within 12 h after photocatalysis, whereas P25 remains suspended in solution after weeks. Thus the TiO2 nanotube macrostructures offer the advantage of easy catalyst separation and recycle and can be a promising candidate for wastewater treatment.
文摘Great experimental results and observations achieved by Astronomy in the last decades revealed new unexplainable phenomena. Astronomers have conclusive new evidence that a recently discovered “dark galaxy” is, in fact, an object the size of a galaxy, made entirely of dark matter. They found that the speed of the Earth’s rotation varies randomly each day. 115 years ago, the Tunguska Event was observed, and astronomers still do not have an explanation of It. Main results of the present article are: 1) Dark galaxies explained by the spinning of their Dark Matter Cores with the surface speed at equator less than the escape velocity. Their Rotational Fission is not happening. Extrasolar systems do not emerge;2) 21-cm Emission explained by the self-annihilation of Dark Matter particles XIONs (5.3 μeV);3) Sun-Earth-Moon Interaction explained by the influence of the Sun’s and the Moon’s magnetic field on the electrical currents of the charged Geomagma (the 660-km layer), and, as a result, the Earth’s daylength varies;4) Tunguska Event explained by a huge atmospheric explosion of the Superbolide, which was a stable Dark Matter Bubble before entering the Earth’s atmosphere.
基金supported by the National Defense Basic Scientific Research Project(No.JCKY2020210B001)the National Natural Science Foundation of China(No.U19A20103),the China Postdoctoral Science Foundation(No.2019M661184)+2 种基金the Jilin Province Scientific and Technological Development Program(No.YDZJ202101ZYTS025)the Jilin Province Young Science and Technology Talent Lift Project(No.QT202030)the Science and Technology Innovation Fund of CUST(No.XJJLG-2019-05)。
文摘Bio-inspired macrostructure array(MAA,size:submillimeter to millimeter scale)materials with special wettability(MAAMs-SW)have attracted significant research attention due to their outstanding performance in many applications,including oil repellency,liquid/droplet manipulation,anti-icing,heat transfer,water collection,and oil–water separation.In this review,we focus on recent developments in the theory,design,fabrication,and application of bio-inspired MAAMs-SW.We first review the history of the basic theory of special wettability and discuss representative structures and corresponding functions of some biological surfaces,thus setting the stage for the design and fabrication of bio-inspired MAAMs-SW.We then summarize the fabrication methods of special wetting MAAs in terms of three categories:additive manufacturing,subtractive manufacturing,and formative manufacturing,as well as their diverse functional applications,providing insights into the development of these MAAMs-SW.Finally,the challenges and directions of future research on bio-inspired MAAMs-SW are briefy addressed.Worldwide efforts,progress,and breakthroughs from surface engineering to functional applications elaborated herein will promote the practical application of bio-inspired MAAMs-SW.
基金supported by the National Natural Science Foundation of China(No.51204111)the Natural Science Foundation of Liaoning Province(No.2014024008)the Aeronautical Science Foundation of China(No.2014ZE54021)
文摘As a new solid state welding,pinless friction stir welding（PFSW） can be used to join thin-wall structures.In this study,four new pinless tools with different groove distributions were designed and manufactured in order to enrich technological storage of PFSW and obtain sound joint with high quality of alclad 2A12-T4 alloy.The results show that the small-obliquity tool is detrimental to the transfer of plasticized materials,resulting in the formation of kissing bond defect.For the through-groove tool or the large-curvature tool,bigger flashes form on the joint surface and alclad layer is observed in the nugget zone（NZ）,deteriorating mechanical properties.Compared with the above-mentioned three tools,using the six-groove tool with rational curvature and obliquity can not only yield sound joint with small flashes and thickness reduction,but also prevent alclad from flowing into NZ,which has potential to weld thin alclad aluminum alloys.Meanwhile,the tensile strength and elongation of joint using the six-groove tool reach the maximum values of 362 MPa and 8.3%,up to 85.1% and 64% of BM.
文摘The results of measurements of the Hubble constant H<sub>0</sub>, which characterizes the expansion rate of the universe, show that the values of H<sub>0</sub> vary significantly depending on Methodology. The disagreement in the values of H<sub>0</sub> obtained by the various teams far exceeds the standard uncertainties provided with the values. This discrepancy is called the Hubble Tension. In this paper, we discuss Macrostructures of the World (Superclusters and Galaxies);explain their Origin and Evolution in frames of the developed Hypersphere World-Universe Model (WUM), which is an alternative to the prevailing Big Bang Model (BBM) [1];and provide the explanation of the Hubble Tension. The main difference between WUM and BBM is: Instead of the Infinite Homogeneous and Isotropic Universe around the Initial Singularity in BBM, in WUM, the 3D Finite Boundless World (a Hypersphere) presents a Patchwork Quilt of different Luminous Superclusters (10<sup>3</sup>), which emerged in various places of the World at different Cosmological times. In WUM, the Medium of the World is Homogeneous and Isotropic. The distribution of Macroobjects in the World is spatially Inhomogeneous and Anisotropic and temporally Non-simultaneous.
文摘A complicated Cu-Ni based alloy was developed to fabricate wear-resisting bush for high temperature application.The concern focuses on the control of equiaxed grains in the developed alloy ingot prepared by centrifugal casting.The results show that the equiaxed grains are determined by the pouring temperature of the melt,the cooling rate and the rotation speed of the mold.With the decrease in pouring temperature,the fraction of the equiaxed grains in the transverse section of the ingot increases and the average length of columnar grain decreases.When the pouring temperature is confined below 1,250℃,complete equiaxed grains can be obtained.Based on the optimal centrifugal casting processing,the tensile strength of the developed alloy ingot with complete equiaxed grains reaches to 810 MPa and 435 MPa at room temperature and 500℃,respectively,which is 14% and 110% higher than that of common commercial QAl10-4-4 alloy.The wear rate of the developed alloy is 7.0 × 10-8 and 3.8 × 10-7 mm3?N-1?mm-1 at room temperature and 500℃,respectively,which is 5 times and 39 times lower than that of QAl10-4-4 alloy.
基金Item Sponsored by National Natural Science Foundation of China(51165030)
文摘A comprehensive mathematical model was established and used to simulate the macro and microstructure evolution during the production process of 5CrNiMo steel ingot by electroslag remelting （ESR） method. Along the ingot height, the macrostructure distribution characteristics changed from vertical, fine columnar grains to tilted, coarse columnar grains, and this transformation process occurred at the very beginning of ESR. In the cross section of the ingot, there were three grain morphology regions and two grain type transition regions from the outside to the center of the ingot. These regions were the fine columnar grain region, columnar competitive growth transition re gion, coarse columnar grain region, columnar to equiaxed grain transition （CET） region, and coarse equiaxed grain region. The influence of the remelting rate on the macrostructure and mlcrostructure was investigated using a series of experiments and simulations. The results showed that a low remelting rate could produce a small grain growth angle （GGA） ; the average secondary dendrite arm spacing （SDAS） firstly decreased and then increased as the remelting rate increased. An excessively high or low remelting rate can increase the GGA and average SDAS in ingots. Thus, the remelting rate should be controlled within a suitable range to reduce composition microsegregation and microshrinkage in the ingot to produce an ESR ingot with satisfactory hot forging performance.
基金Project(2007CB613802) supported by the National Basic Research Program of China
文摘In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium alloy ingots during VAR process.The results show that the temperature fields obtained by the simulation are well validated through the experiment results.The temperature distribution is different during the whole VAR process and the steady-state molten pool forms at 329 s for d100 mm × 180 mm ingots.At the initial stage of remelting,the heat dissipation of crucible bottom plays an important role in the whole heat dissipation system.At the middle of remelting,the crucible wall becomes a major heat dissipation way.The effect of cooling velocity on the solidification structure of ingots was investigated based on the temperature fields and the results can well explain the macrostructure of titanium alloy ingots.
基金financially supported by the National Key Research and Development Program(2016YFB0701405)the National 973 Program(2011CB610406)+4 种基金National 863 Project(2012AA03A511)the National Natural Science Foundation of China(51171151,51331005,51501151,51631008)the Natural Science Foundation of Shaanxi Province(2014JM6227)the Aeronautical Science Foundation of China(2015ZE53059)the Fund of the State Key Laboratory of Solidification Processing in NWPU(SKLSP201411)
文摘The simulation models of the thermal and macrostructural evolutions during directional solidification of Ni-base single crystal(SX) turbine blades under high rate solidification(HRS) and liquid metal cooling(LMC) have been constructed using Pro CAST software, coupled with a 3D Cellular Automaton Finite Element(CAFE) model. The models were used to investigate the tendencies of stray grain(SG) formation in the platform region of turbine blades fabricated by HRS and LMC techniques. The results reveal that the LMC technique can prohibit SG formation by smoothing the concaved isotherm and in turn alleviating the undercooling in the platform ends to let the dendrites fill up the undercooled zone before SG nucleation. The simulation results agreed well with the experimental results, indicating that these models could be used to analyze the macrostructural evolution or to optimize process parameters to suppress SG formation. Using these models, the critical withdrawal rate for casting SX turbine blades without SG formation were determined to be around 75 μm·s^(-1) and 100 μm·s^(-1) for HRS and LMC respectively, suggesting that LMC can be used as an efficient technique in fabricating SX turbine blades without any SG defect formation.
基金Supported by the National Science Fund for Distinguished Young Scholars of China(Grant No.21125628)the Major National Scienti fic Instrument Development Project(Grant No.21527812)+3 种基金the National Natural Science Foundation of China(Grant Nos.21406031 and 21476044)the State Key Laboratory of Fine Chemicals(KF1507)the Fundamental Research Funds for the Central Universities(Grant Nos.DUTPJ14RC(3)003)State Key Laboratory of fine chemicals(Panjin)project(Grant No.JH2014009)
文摘Ion conductive membranes(ICMs)are frequently used as separators for energy conversion and storage technologies of fuel cells,flow battery,and hydrogen pump,because of their good ion-selective conduction and low electronic conductivity.Firstly,this feature article reviews the recent studies on the development of new nonfluorinated ICMs with low cost and their macro/micro-structure control.In general,these new nonfluorinated ICMs have lower conductivity than commercial perfluorinated ones,due to their poor ion transport channels.Increasing ion exchange capacity(IEC)would create more continuous hydrophilic channels,thus enhancing the conductivity.However,high IEC also expands the overall hydrophilic domains,weakens the interaction between polymer chains,enhances the mobility of polymer chains,and eventually induces larger swelling.The micro-scale expansion and macro-scale swelling of the ICMs with high IEC could be controlled by limiting the mobility of polymer chains.Based on this strategy,some ef ficient techniques have been developed,including covalent crosslinking,semi-interpenatrating polymer network,and blending.Secondly,this review introduces the optimization of macro/microstructure of both perfluorinated and nonfluorinated ICMs to improve the performance.Macro-scale multilayer composite is an ef ficient way to enhance the mechanical strength and the dimensional stability of the ICMs,and could also decrease the content of per fluorosulfonic acid resin in the membrane,thereby reducing the cost of the perfluorinated ICMs.Long side chain,multiple functionalization,small molecule inducing micro-phase separation,electrospun nano fiber,and organic–inorganic hybrid could construct more ef ficient ion transport channels,improving the ion conductivity of ICMs.
基金supported by the Natural Sciences and Engineering Research Council(NSERC)of Canada。
文摘This paper reviews the latest research progress in the additive manufacturing(AM)process of 18%nickel maraging steels,which involves laser-based powder bed fusion(L-PBF),laser-based directed energy deposition(L-DED),and wire arc additive manufacturing(WAAM).The emphasis is on the defects,structure,and mechanical properties of the additive manufactured 18%nickel maraging steels.At first,this article outlines the influences of the processing parameters of AM techniques on the defects formed in the fabricated parts,in terms of the L-PBF and WAAM.The macrostructure and microstructure characteristics of as-built and heat-treated 18%nickel maraging steel are then described in detail.Later,the mechanical properties of as-built and heat-treated 18%nickel maraging steel are assessed,such as their tensile,hardness,impact toughness,and fatigue performances.Finally,future directions for work on the AM of 18%nickel maraging steel are provided.
文摘Silicon is the most extensively studied semiconductor mainly owing to its wide applicability in the photovoltaic solar cell industry.However the qualily of Si photovoltaic cells depends on the purity of the material and on the grain structure of the ingot from which the wafers are cutting.The electrical performance of such materials,i.e. mainly their minority carrier lifetime,is closely related to metal impurities present in the feedstock or introduced during crystal growth.These impurities strongly interact with existing crystal defects to form complexes,accumulate at dislocations or grain boundaries in different forms,or even form silieide precipitates,which simultaneously contain several metal impurities.In such a context,it is necessary to control the segregation of impurities especially metallic in the grown ingot in order to optimize the cell properties as a function of the raw material purity.A new Bridgman set-up is developed in order to study the crystallization of photovoltaic Si under independently controlled solidification parameters growth rate,thermal gradient,purity and convection.Convection,either natural or forced,plays a very important role during the crystallization.Its intensity and flow pattern affect heat and mass transfer and,consequently,macrostructure and segregation in a solidified ingot.Here the convection can be controlled by a travelling magnetic field in order to homogenize or segregate the rejected impurities such as metallic elements.The effects of the magnetic field intensity and frequency on the segregation and crystalline structure will be presented.
文摘The development of a numerical model for the melting process of Al--Ti alloy targetmaterial in vacuum induction furnace with cold crucible (VIFCC)was described. It isa two--dimensional computational methodology to calculate electromagnetic field, heattransfer field and fluid flow field. Based on the aid of the finite element method withthe commercial software--ANSYS, a superimposition method of a layer of copper anda slit to simulate the VIFCC melting process was used. The method was effectiveto save large quantity of memory and computing time. Meanwhile, a temperaturedistribution profile during the melting process was obtained. Validity of the model wasconfirmed by comparison between the result from calculation and those from directmeasurement by optical pyrometer and indirect investigation by ingot macrostructure.A relatively good agreement was found. Further, a nearly directional solidificationstrvcture was obtained under properly controlling the cooling rate and heating power.Therefore, such model developed in this article is feasible.
文摘The macrostructure and properties of the thin walled copper tube prepared by the downward continuous unidirectional solidification （DCUS） method were studied. The result shows that the macrostructure is closely related to the solid-liquid interface profile, which is influenced by the distance between the cooling water location and the solidification front. The mechanical properties of the thin walled copper tube prepared by the DCUS method are near those of the normal cast copper, and it has good relative density, electrical conductivity, and elongation, which are not greatly affected by casting speed. The thin walled copper tube prepared by the DCUS method also has good processing properties that can be taken to further drawing procedures directly without an intermediate process, and obtains good mechanical properties with the total processing rate of 89.8%.
基金Item Sponsored by National Natural Science Foundation of China[No.50834009]the National Natural Science Foundation of China[No.51004038]+1 种基金Key Grant Project of China Ministry of Education(No.311014)the 111 Project of China(No.B07015)
文摘To improve the quality of high carbon wire rods,combined electromagnetic stirring was introduced in the continuous casting of round billets with a diameter of 250mm at Tianjin Rockcheck Steel Group Co.In this paper,the positioning of final electromagnetic stirring(F-EMS)was determined by nail-shooting method.Furthermore,the effect of mold electromagnetic stirring(M-EMS)on the macrostructure and internal defects in the round billets was investigated to find out the optimal operating parameters for continuous casting of SWRH 82B round billets.The results show the desirable positioning of F-EMS locates 9.7m below the mold level where the molten steel can be effectively driven by electromagnetic force and disperse central composition segregation.The shrinkage cavity is totally eliminated with the rotational M-EMS.The ratio and index of central composition segregation and center porosity can be reduced significantly. Furthermore,the equiaxed crystal ratio is considerably increased to 64%under 480A/3Hz M-EMS and 500A/10Hz F-EMS. Fine microstructure and mechanical property of wire rod are presented after optimization of combined electromagnetic stirring.Accordingly,the probability of occurrence of cup-cone fracture of wire rod is reduced dramatically.
文摘Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.
