Understanding the sedimentation and simultaneous consolidation behavior of xanthan gum(XG)-biopolymer-treated soils remains a significant research gap in developing environmentally friendly ground-improvement techniqu...Understanding the sedimentation and simultaneous consolidation behavior of xanthan gum(XG)-biopolymer-treated soils remains a significant research gap in developing environmentally friendly ground-improvement techniques for geotechnical applications.This study addresses this gap by conducting laboratory experiments on kaolinite suspensions with varying XG-to-kaolinite mass ratios(mb/ms).The results showed that the XG treatment modified the sedimentation patterns by promoting larger floc formation and accelerated settling.Additionally,the XG treatment enhanced the shear stiffness and shear strength,particularly at shallow depths.At mb/ms ratios less than 1%,the volume compression was reduced by the XG;the coefficient of compressibility decreased by 49%at 1%mb/ms,and the consolidation was accelerated,as indicated by a 387%increase in the hydraulic conductivity at 0.5%mb/ms under the vertical effective stress of 40 kPa.Contrastingly,at mb/ms ratios greater than 1%,viscous XG hydrogels clogged pores,resulting in a 45%reduction in the coefficient of consolidation at 2%mb/ms under a vertical effective stress of 15 kPa and a 35%decrease in the hydraulic conductivity at 2%mb/ms under a vertical effective stress of 40 kPa.These findings underscore the potential of XG treatment in improving the sedimentation and consolidation processes,highlighting its applicability in geotechnical projects,such as dredging,landfilling,and artificial island construction.展开更多
Adipose tissue is a major metabolic organ, and it has been traditionally classified as either white adipose tissue(WAT) or brown adipose tissue(BAT). WAT and BAT are characterized by different anatomical locations, mo...Adipose tissue is a major metabolic organ, and it has been traditionally classified as either white adipose tissue(WAT) or brown adipose tissue(BAT). WAT and BAT are characterized by different anatomical locations, morphological structures, functions, and regulations. WAT and BAT are both involved in energy balance. WAT is mainly involved in the storage and mobilization of energy in the form of triglycerides, whereas BAT specializes in dissipating energy as heat during cold- or diet-induced thermogenesis. Recently, brownlike adipocytes were discovered in WAT. These brownlike adipocytes that appear in WAT are called beige or brite adipocytes. Interestingly, these beige/brite cells resemble white fat cells in the basal state, but they respond to thermogenic stimuli with increased levels of thermogenic genes and increased respiration rates. In addition, beige/brite cells have a gene expressionpattern distinct from that of either white or brown fat cells. The current epidemic of obesity has increased the interest in studying adipocyte formation(adipogenesis), especially in beige/brite cells. This review summarizes the developmental process of adipose tissues that originate from the mesenchymal stem cells and the features of these three different types of adipocytes.展开更多
Cubic boron nitride particles coated by titanium nitride (TiN/cBN) as well as diamond particles coated by titanium carbide (TiC/diamond) were prepared by Ti molten salt deposition followed by heat-treatment process. c...Cubic boron nitride particles coated by titanium nitride (TiN/cBN) as well as diamond particles coated by titanium carbide (TiC/diamond) were prepared by Ti molten salt deposition followed by heat-treatment process. cBN or diamond particles were mixed separately with Ti powders and molten salts (KCl, NaCl and K<sub>2</sub>TiF<sub>6</sub>). The mixture was heated at 900 °C under argon atmosphere. The produced particles were heat-treated under hydrogen at 1000 °C. The morphologies and chemical compositions of the produced particles were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and focused ion beam (FIB). The results show that the cBN and the diamond particles are coated by nano-sized Ti layers. By heat-treatment of the Ti/cBN and TiC/diamond coated particles under hydrogen atmosphere, the deposited Ti layers were interacted by the in-situ transformation reaction with the surfaces of cBN and diamond particles and converted to titanium compounds (TiN and TiC), respectively.展开更多
Light and strong AlxCrNbVMo(x=0,0.5,and 1.0)refractory high-entropy alloys(RHEAs)were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BC...Light and strong AlxCrNbVMo(x=0,0.5,and 1.0)refractory high-entropy alloys(RHEAs)were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2-3μm,and small amounts(<4 vol.%)of fine oxide dispersoids.This homogeneous microstructure,without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering.The alloys exhibited superior mechanical properties at 25 and 1000℃compared to those of other RHEAs.Here,CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature.Surprisingly,the yield strength of the CrNbVMo alloy at 1000℃was 1513 MPa.The specific yield strength of the CrNbVMo alloy was increased by 27%and 87%at 25 and 1000℃,respectively,compared to the AlMo_(0.5) NbTa_(0.5)TiZr RHEA,which exhibited so far the highest specific yield strength among the cast RHEAs.The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm^(3),while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy.Quantitative analysis of the strengthening contributions,showed that the solid solution strengthening,arising from a large misfit effect due to the size and modulus,and the high shear modulus of matrix,was revealed to predominant strengthening mechanism,accounting for over 50%of the yield strength of the AlxCrNbVMo RHEAs.展开更多
This paper addresses mechanisms for active flapping and twisting of robotic wings and assesses flying effectiveness as a function of twist angle. Unlike the flapping motion of bird wings, insects generally make a twis...This paper addresses mechanisms for active flapping and twisting of robotic wings and assesses flying effectiveness as a function of twist angle. Unlike the flapping motion of bird wings, insects generally make a twisting motion at the root of their wings while flapping, which makes it possible for them to hover in midair. This work includes the development of a Voice Coil Motor （VCM） because a flapping-wing air vehicle should be assembled with a compact actuator to decrease size and weight. A linkage mechanism is proposed to transform the linear motion of the VCM into the flapping and twisting motions of wings. The assembled flapping-wing air vehicle, whose weight is 2.86 g, produces an average positive vertical force proportional to the twist angle. The force saturates because the twist angle is mechanically limited. This work demonstrates the possibility of developing a flapping-wing air vehicle that can hover in midair using a mechanism that actively twists the roots of wings during flapping.展开更多
According to the stress-strain curves of single-phase martensite and single-phase ferrite steels,whose compositions are similar to those of martensite and ferrite in low Si-Mn-Nb dual-phase steel,the stress-strain cur...According to the stress-strain curves of single-phase martensite and single-phase ferrite steels,whose compositions are similar to those of martensite and ferrite in low Si-Mn-Nb dual-phase steel,the stress-strain curve of the low Si-Mn-Nb dual-phase steel was simulated using the finite element method（FEM）.The simulated result was compared with the measured one and they fit closely with each other, which proves that the FE model is correct.Based on the FE model,the microstress and microstrain of the dual-phase steel were analyzed. Meanwhile,the effective factors such as the volume fraction of martensite and the yield stress ratio between martensite and ferrite phases on the stress-strain curves of the dual-phase steel were simulated,too.The simulated results indicate that for the low Si-Mn-Nb dual-phase steel, the maximum stress occurs in the martensite region,while the maximum strain occurs in the ferrite one.The effect of the volume fraction of martensite（fm） and the yield stress ratio on the stress-strain curve of the dual-phase steel is small in the elastic part,while it is obvious in the plastic part.In the plastic part of this curve,the strain decreases with the increase of f_M,while it decreases with the decrease of the yield stress ratio.展开更多
Fe alloy composites reinforced with in-situ titanium carbide （TIC） particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8, 0.9, 1 and 1.1 to investigate the microstructure and me...Fe alloy composites reinforced with in-situ titanium carbide （TIC） particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8, 0.9, 1 and 1.1 to investigate the microstructure and mechanical properties ofin-situ TiC/Fe alloy composites. The microstructure showed that the in-situ syn- thesized TiC particles were spherical with a size of 1-3 }~m, irrespective of C/Ti ratio. The stoichiometry of in-situ TiC increased from 0.85 to 0.88 with increasing C/Ti ratio from 0.8 to 0.9, but remained almost unchanged for C/Ti ratios between 0.9 and 1.1 due to the same driving force for carbon diffusion in TiCx at the common sintering temperature. The in-situ TiC/Fe alloy composite with C[Ti ~ 0.9 showed improved mechanical properties compared with other C/Ti ratios because the presence of excess carbon （C/Ti = 1 and 1.1） resulted in unreacted carbon within the Fe alloy matrix, while insufficient carbon （C/Ti = 0.8） caused the depletion of carbon from the Fe alloy matrix, leading to a significant decrease in hardness. This study presents that the maximized hardness and superior strength of in-situ TiC/Fe alloy composites can be achieved by microstructure control and stoichiometric analysis of the in-situ synthesized TiC par- ticles, while maintaining the ductility of the composites, compared to those of the unreinforced Fe alloy. Therefore, we anticipate that the in-situ synthesized TiC/Fe alloy composites with enhanced mechanical properties have great potential in cutting tool, mold and roller material applications.展开更多
Fiber reinforced composite frame structure is an ideal lightweight and large-span structure in the fields of aerospace,satellite and wind turbine.Natural fundamental frequency is one of key indicators in the design re...Fiber reinforced composite frame structure is an ideal lightweight and large-span structure in the fields of aerospace,satellite and wind turbine.Natural fundamental frequency is one of key indicators in the design requirement of the composite frame since structural resonance can be effectively avoided with the increase of the fundamental frequency.Inspired by the concept of integrated design optmization of composite frame structures and materials,the design optimization for the maximum structural fundamental frequency of fiber reinforced frame structures is proposed.An optimization model oriented at the maximum structural fundamental frequency under a composite material volume constraint is established.Two kinds of independent design variables are optimized,in which one is variables represented structural topology,the other is variables of continuous fiber winding angles.Sensitivity analysis of the frequency with respect to the two kinds of independent design variables is implemented with the semi-analytical sensitivity method.Some representative examples in the manuscript demonstrate that the integrated design optimization of composite structures can effectively explore coupled effects between structural configurations and material properties to increase the structural fundamental frequency.The proposed integrated optimization model has great potential to improve composite frames structural dynamic performance in aerospace industries.展开更多
This paper provides a unified formulation of optimal guidance-to-collision law for a target with an arbitrary acceleration or deceleration.The collision course for general target acceleration or deceleration is first ...This paper provides a unified formulation of optimal guidance-to-collision law for a target with an arbitrary acceleration or deceleration.The collision course for general target acceleration or deceleration is first determined from the engagement geometry in conjunction with the nonlinear engagement kinematics in the proposed approach.The heading error defined in the collision course is then adopted as a variable to be nullified for accomplishing the intercept condition.The proposed guidance law is derived based on the heading error dynamics and the optimal error dynamics to ensure optimality and finite-time convergence.As illustrative examples,the proposed guidance command for a constant target acceleration and a target deceleration in the form of a quadratic function of speed are provided.Additionally,the time-to-go prediction method is suggested for implementing the proposed method.The characteristics of the proposed guidance command are analytically investigated to provide insight into the proposed method.The key benefits of the proposed method lie in not producing unnecessary guidance commands near a target compared to other methods and ensuring optimality in guidance command even in the nonlinear engagement kinematics.Finally,numerical simulations are performed to validate the proposed method and to show our findings.展开更多
All-polymer solar cells(all-PSCs)possess attractive merits including superior thermal stability and mechanical flexibility for large-area roll-to-roll processing.Introducing flexible conjugation-break spacers(FCBSs)in...All-polymer solar cells(all-PSCs)possess attractive merits including superior thermal stability and mechanical flexibility for large-area roll-to-roll processing.Introducing flexible conjugation-break spacers(FCBSs)into backbones of polymer donor(P_(D))or polymer acceptor(P_(A))has been demonstrated as an efficient approach to enhance both the photovoltaic(PV)and mechanical properties of the all-PSCs.However,length dependency of FCBS on certain all-PSC related properties has not been systematically explored.In this regard,we report a series of new non-conjugated P_(A)s by incorporating FCBS with various lengths(2,4,and 8 carbon atoms in thioalkyl segments).Unlike com-mon studies on so-called side-chain engineering,where longer side chains would lead to better solubility of those resulting polymers,in this work,we observe that the solubilities and the resulting photovoltaic/mechanical properties are optimized by a proper FCBS length(i.e.,C2)in P_(A) named PYTS-C2.Its all-PSC achieves a high efficiency of 11.37%,and excellent mechanical robustness with a crack onset strain of 12.39%,significantly superior to those of the other P_(A)s.These results firstly demonstrate the effects of FCBS lengths on the PV performance and mechanical properties of the all-PSCs,providing an effective strategy to fine-tune the structures of P_(A)s for highly efficient and mechanically robust PSCs.展开更多
The intensive development of micro-/nanotechnologies offers a new route to construct sophisticated architectures of emerging soft electronics.Among the many classes of stretchable materials,micro-/nanostructured poly(...The intensive development of micro-/nanotechnologies offers a new route to construct sophisticated architectures of emerging soft electronics.Among the many classes of stretchable materials,micro-/nanostructured poly(dimethylsiloxane)(PDMS)has emerged as a vital building block based on its merits of flexibility,stretchability,simple processing,and,more importantly,high degrees of freedom of incorporation with other functional materials,including metals and semiconductors.The artificially designed geometries play important roles in achieving the desired mechanical and electrical performances of devices and thus show great potential for applications in the fields of stretchable displays,sensors and actuators as well as in health-monitoring device platforms.Meanwhile,novel lithographic methods to produce stretchable platforms with superb reliability have recently attracted research interest.The aim of this review is to comprehensively summarize the progress regarding micro-/nanostructured PDMS and their promising soft electronic applications.This review is concluded with a brief outlook and further research directions.展开更多
Size control of BaTiO3 in solid-state reaction between BaCO3 and TiO2 was demonstrated by varying the size of TiO2 and milling conditions of BaCO3. The smaller TiO2 particles had higher surface area, resulting in fast...Size control of BaTiO3 in solid-state reaction between BaCO3 and TiO2 was demonstrated by varying the size of TiO2 and milling conditions of BaCO3. The smaller TiO2 particles had higher surface area, resulting in faster initial reaction. The mechanically milled BaCO3 particles accelerated the diffusion process and decreased the calcinations temperature. It can be deduced from the results that the size control is possible and nano-sized BaTiO3 particles with about 60 nm can be synthesized by using the conventional solid-state reaction between BaCO3 and TiO2.展开更多
With the increase in silver（Ag）-based products in our lives, it is essential to test the potential toxicity of silver nanoparticles（Ag NPs） and silver ions（Ag ions） on living organisms under various conditions. ...With the increase in silver（Ag）-based products in our lives, it is essential to test the potential toxicity of silver nanoparticles（Ag NPs） and silver ions（Ag ions） on living organisms under various conditions. Here, we investigated the toxicity of Ag NPs with Ag ions to Escherichia coli K-12 strain under various conditions. We observed that both Ag NPs and Ag ions display antibacterial activities, and that Ag ions had higher toxicity to E. coli K-12 strain than Ag NPs under the same concentrations. To understand the toxicity of Ag NPs at a cellular level, reactive oxygen species（ROS） enzymes were detected for use as antioxidant enzymatic biomarkers. We have also studied the toxicity of Ag NPs and Ag ions under various coexistence conditions including： fixed total concentration, with a varied the ratio of Ag NPs to Ag ions; fixed the Ag NPs concentration and then increased the Ag ions concentration; fixed Ag ions concentration and then increasing the Ag NPs concentration.Exposure to Ag NPs and Ag ions clearly had synergistic toxicity; however, decreased toxicity（for a fixed Ag NPs concentration of 5 mg/L, after increasing the Ag ions concentration） to E. coli K-12 strain. Ag NPs and Ag ions in the presence of L-cysteine accelerated the bacterial cell growth rate, thereby reducing the bioavailability of Ag ions released from Ag NPs under the single and coexistence conditions. Further works are needed to consider this potential for Ag NPs and Ag ions toxicity across a range of environmental conditions.Environmental Significance Statement： As silver nanoparticles（Ag NPs）-based products are being broadly used in commercial industries, an ecotoxicological understanding of the Ag NPs being released into the environment should be further considered. Here, we investigate the comparative toxicity of Ag NPs and silver ions（Ag ions） to Escherichia coli K-12 strain, a representative ecotoxicological bioreporter. This study showed that toxicities of Ag NPs and Ag ions to E. coli K-12 strain display different relationships when existing individually or when coexisting, and in the presence of L-cysteine materials. These findings suggest that the toxicology research of nanomaterials should consider conditions when NPs coexist with and without their bioavailable ions.展开更多
We report laser cladding of pure titanium on a CoCrMo alloy using directed energy deposition.Using electron microscopy,the microstructural evolution upon varying the process parameters,especially laser power and powde...We report laser cladding of pure titanium on a CoCrMo alloy using directed energy deposition.Using electron microscopy,the microstructural evolution upon varying the process parameters,especially laser power and powder feed rate,was investigated in relation to crack formation.Cladding layers showing dilution rates of more than 5%contained cracks due to the formation of the brittle Co_(2)Ti intermetallic phase.The observed cracks could be ascribed to a mismatch in thermal expansion and a resulting stress of more than 440 MPa acting on the Co_(2)Ti phase,as determined by density functional theory and nanoindentation.Furthermore,an excess laser energy caused chemical inhomogeneity and unmelted Ti powder particles,while a deficient laser energy resulted in a lack of fusion.Neither cracks nor partially melted powders were observed for a powder feed rate of 3 g/min and a laser power of 225–300 W,for which the dilution rate was minimized to less than 5%.For such samples,the cladding layers comprised pureα-Ti and a uniform CoT i interface with Co_(2)Ti islands.展开更多
It is difficult for polyethylene terephthalate （PET） to degrade,which caused severe pollution.In this work,polylactic acid （PLA） was introduced to improve the degradation of PET.PET/PLA was synthesized by extrusio...It is difficult for polyethylene terephthalate （PET） to degrade,which caused severe pollution.In this work,polylactic acid （PLA） was introduced to improve the degradation of PET.PET/PLA was synthesized by extrusion blending.The thermal,crystalline and mechanical properties of blends were investigated with TGA,DSC,WAXD and universal testing machine.The degradation of the blends in soil,acid and alkaline buffer solutions was assessed,respectively.It was found that the introduction of a little PLA promoted crystallization of PET during injection molding process.The starting decomposition temperature lowered from 412.1 ℃ of pure PET to 330.4 ℃ at 50% PLA content,tensile and bending strength of blends gradually decreased with the PLA content increasing,while the degradation rate improved.Alkaline environment was most beneficial for blends to degrade.The degradation mechanism was discussed.展开更多
The flexible product shape of additive manufacturing(AM)is attractive,but the process suffers from a lack of material property diversity due to a limited number of printable alloys and post-processing options.To overc...The flexible product shape of additive manufacturing(AM)is attractive,but the process suffers from a lack of material property diversity due to a limited number of printable alloys and post-processing options.To overcome this problem,the AM of metal matrix composites(MMCs)is a highly suitable solution because the properties of MMC can be tailored using various reinforcements.Therefore,extensive research has been conducted on the AM of MMCs;however,the major huddle for this process has been the difficulties in preparing feedstock powder and operating the AM process.This study introduces an easily synthesizable core-shell composite powder,which was fabricated by a recently developed process called the SMART process.The core-shell powder has a novel morphology,consisting of a metal core and composite shell,distinguishing it from the powders used in conventional AM approaches.Inconel 625/TiCp composites were fabricated using the core-shell composite powder,with various fractions of TiCp up to 10 vol.%.Compared to additive-manufactured Inconel 625,the additive-manufactured MMCs showed enhanced strength with significantly fewer defects.The results of this study may accelerate the application of MMC fabricated by AM,which offers superior properties and reliability compared to casting and powder metallurgy due to the higher degree of dislocation density and reinforcement dispersion.展开更多
Nanoscale zero-valent iron （NZVI） is considered to have potential to reduce nitrate in the concentrate generated by high pressure membrane processes aimed at water reuse. However, it is necessary to verify the effec...Nanoscale zero-valent iron （NZVI） is considered to have potential to reduce nitrate in the concentrate generated by high pressure membrane processes aimed at water reuse. However, it is necessary to verify the effect of the matrix components in the concentrates on NZVI reactivity. In this study, the influence of hardness, alkalinity, and organic matter on NZVI reactivity was evaluated by the response surface method （RSM）. Hardness （Ca/＋） had a positive effect on NZVI reactivity by accelerating iron corrosion. In contrast, alkalinity （bicarbonate; HCO3） and organic matter （humic acid; HA） had negative effects on NZVI reactivity due to morphological change to carbonate green rust, and to competitive adsorption of HA, respectively. The validity of the statistical prediction model derived from RSM was confirmed by an additional confirmation experiment, and the experimental result was within the 95% confidential interval. Therefore, it can be indicated that the RSM model produced results that were statistically significant.展开更多
SnSe is a promising thermoelectric material with a high figure of merit in single crystal form, which has stimulated continuous research on polycrystalline SnSe. In this study, we investigated a metallization techniqu...SnSe is a promising thermoelectric material with a high figure of merit in single crystal form, which has stimulated continuous research on polycrystalline SnSe. In this study, we investigated a metallization techniques for polycrystalline SnSe to achieve highly efficient and practical SnSe thermoelectric modules. The Ag/Ni metallization layers were formed on pristine polycrystalline SnSe using various deposition technique: sputter coating Ni, powder Niand foil Ni by spark plasma sintering. Structural analysis demonstrated that the microstructure and con tact resistance could be different according to the metallization process, despite using the same metals. The Ag/Ni metallization layer using foil Ni acted as an effective diffusion barrier and minimized electrical contact resistance (2.3×10^-4Ωcm^2). A power loss in the thermoelectric module of only 5% was demonstrated using finite element simulation.展开更多
In this study, we demonstrate a novel method for fabricating polythiophene patterns, i.e., cylindrical holes and cylinders, through blending of a thermally curable polythiophene carrying with tertiary ester groups(PT-...In this study, we demonstrate a novel method for fabricating polythiophene patterns, i.e., cylindrical holes and cylinders, through blending of a thermally curable polythiophene carrying with tertiary ester groups(PT-tert-ESTER) and poly(methyl methacrylate)(PMMA), followed by thermal conversion of the PT-tert-ESTER to an insoluble polythiophene via low-temperature cleavage of the tertiary ester groups and removal of the PMMA component via ultraviolet degradation. We show that the surface polarity of substrates, the mass ratio of PT-tert-ESTER to PMMA in the blend solutions as well as the concentration of the blend solutions strongly influence the formation of the polythiophene patterns. Cylindrical holes are more readily formed on less polar substrates when a PT-tert-ESTER dominated blend solution is used, while cylinders are more readily formed on more polar substrates when a PMMA dominated blend solution is used. Moreover, the diameters of both the cylindrical holes and the cylinders decrease as the PT-tert-ESTER concentration is increased in the respective ranges of the PT-tert-ESTER/PMMA ratios where the patterns are formed. Grazing incident X-ray diffraction data have indicated that the patterning of the PT-tert-ESTER component in the blend films improves the crystallinity of PT-tert-ESTER as well as the molecular packing of the insoluble polythiophene in the resultant patterned polythiophene films.展开更多
Switchable conductivity in elementary semiconducting materials has a high potential for the design of diodes,transistors and energy conversion technologies.However,the ability to utilize their physical properties is d...Switchable conductivity in elementary semiconducting materials has a high potential for the design of diodes,transistors and energy conversion technologies.However,the ability to utilize their physical properties is dependent on doping within the carrier density transition temperature.Single-crystal tellurium has a high Seebeck coefficient and intrinsic p-n-p conduction at room temperature and therefore,is not suitable for thermoelectric applications.We demonstrate that the addition of iso valent Se lowers the Fermi level to achieve a stable p-type conductivity with a high band degeneracy near the valence band.We observed shifts in the n-p transition temperature below the intrinsic conductivity at 470 K based on changes in stoichiometry and carrier concentration above 10^(17)cm^(-3).In addition,the high thermal conductivity is significantly reduced with the increase in Se alloying due to the mass and strain fluctuations.This results in a moderately high zT of 0.4 at 673 K.展开更多
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(Grant No.2022R1A2C2091517).
文摘Understanding the sedimentation and simultaneous consolidation behavior of xanthan gum(XG)-biopolymer-treated soils remains a significant research gap in developing environmentally friendly ground-improvement techniques for geotechnical applications.This study addresses this gap by conducting laboratory experiments on kaolinite suspensions with varying XG-to-kaolinite mass ratios(mb/ms).The results showed that the XG treatment modified the sedimentation patterns by promoting larger floc formation and accelerated settling.Additionally,the XG treatment enhanced the shear stiffness and shear strength,particularly at shallow depths.At mb/ms ratios less than 1%,the volume compression was reduced by the XG;the coefficient of compressibility decreased by 49%at 1%mb/ms,and the consolidation was accelerated,as indicated by a 387%increase in the hydraulic conductivity at 0.5%mb/ms under the vertical effective stress of 40 kPa.Contrastingly,at mb/ms ratios greater than 1%,viscous XG hydrogels clogged pores,resulting in a 45%reduction in the coefficient of consolidation at 2%mb/ms under a vertical effective stress of 15 kPa and a 35%decrease in the hydraulic conductivity at 2%mb/ms under a vertical effective stress of 40 kPa.These findings underscore the potential of XG treatment in improving the sedimentation and consolidation processes,highlighting its applicability in geotechnical projects,such as dredging,landfilling,and artificial island construction.
基金Supported by Grants from the National Research of Foundation of the South Korea,No.2012M3A9C7050101,No.2011-0030028 and No.2006-2004112
文摘Adipose tissue is a major metabolic organ, and it has been traditionally classified as either white adipose tissue(WAT) or brown adipose tissue(BAT). WAT and BAT are characterized by different anatomical locations, morphological structures, functions, and regulations. WAT and BAT are both involved in energy balance. WAT is mainly involved in the storage and mobilization of energy in the form of triglycerides, whereas BAT specializes in dissipating energy as heat during cold- or diet-induced thermogenesis. Recently, brownlike adipocytes were discovered in WAT. These brownlike adipocytes that appear in WAT are called beige or brite adipocytes. Interestingly, these beige/brite cells resemble white fat cells in the basal state, but they respond to thermogenic stimuli with increased levels of thermogenic genes and increased respiration rates. In addition, beige/brite cells have a gene expressionpattern distinct from that of either white or brown fat cells. The current epidemic of obesity has increased the interest in studying adipocyte formation(adipogenesis), especially in beige/brite cells. This review summarizes the developmental process of adipose tissues that originate from the mesenchymal stem cells and the features of these three different types of adipocytes.
文摘Cubic boron nitride particles coated by titanium nitride (TiN/cBN) as well as diamond particles coated by titanium carbide (TiC/diamond) were prepared by Ti molten salt deposition followed by heat-treatment process. cBN or diamond particles were mixed separately with Ti powders and molten salts (KCl, NaCl and K<sub>2</sub>TiF<sub>6</sub>). The mixture was heated at 900 °C under argon atmosphere. The produced particles were heat-treated under hydrogen at 1000 °C. The morphologies and chemical compositions of the produced particles were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and focused ion beam (FIB). The results show that the cBN and the diamond particles are coated by nano-sized Ti layers. By heat-treatment of the Ti/cBN and TiC/diamond coated particles under hydrogen atmosphere, the deposited Ti layers were interacted by the in-situ transformation reaction with the surfaces of cBN and diamond particles and converted to titanium compounds (TiN and TiC), respectively.
基金the National Research Foundation(NRF)grant funded by the Ministry of Science and ICT of Korea through contracts NRF-2018K2A9A1A06069970,NRF2020R1A5A6017701the Asian Office of Aerospace Research and Development(AOARD)grant funded by the Air Force Office of Scientific Research(AFOSR)through a grant FA2386-19-1-4009。
文摘Light and strong AlxCrNbVMo(x=0,0.5,and 1.0)refractory high-entropy alloys(RHEAs)were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2-3μm,and small amounts(<4 vol.%)of fine oxide dispersoids.This homogeneous microstructure,without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering.The alloys exhibited superior mechanical properties at 25 and 1000℃compared to those of other RHEAs.Here,CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature.Surprisingly,the yield strength of the CrNbVMo alloy at 1000℃was 1513 MPa.The specific yield strength of the CrNbVMo alloy was increased by 27%and 87%at 25 and 1000℃,respectively,compared to the AlMo_(0.5) NbTa_(0.5)TiZr RHEA,which exhibited so far the highest specific yield strength among the cast RHEAs.The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm^(3),while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy.Quantitative analysis of the strengthening contributions,showed that the solid solution strengthening,arising from a large misfit effect due to the size and modulus,and the high shear modulus of matrix,was revealed to predominant strengthening mechanism,accounting for over 50%of the yield strength of the AlxCrNbVMo RHEAs.
文摘This paper addresses mechanisms for active flapping and twisting of robotic wings and assesses flying effectiveness as a function of twist angle. Unlike the flapping motion of bird wings, insects generally make a twisting motion at the root of their wings while flapping, which makes it possible for them to hover in midair. This work includes the development of a Voice Coil Motor （VCM） because a flapping-wing air vehicle should be assembled with a compact actuator to decrease size and weight. A linkage mechanism is proposed to transform the linear motion of the VCM into the flapping and twisting motions of wings. The assembled flapping-wing air vehicle, whose weight is 2.86 g, produces an average positive vertical force proportional to the twist angle. The force saturates because the twist angle is mechanically limited. This work demonstrates the possibility of developing a flapping-wing air vehicle that can hover in midair using a mechanism that actively twists the roots of wings during flapping.
基金supported by the Natural Science Foundation of Hebei Province(No.E2008000822) the Program for One Hundred Excellent Talents of Hebei Province,China.
文摘According to the stress-strain curves of single-phase martensite and single-phase ferrite steels,whose compositions are similar to those of martensite and ferrite in low Si-Mn-Nb dual-phase steel,the stress-strain curve of the low Si-Mn-Nb dual-phase steel was simulated using the finite element method（FEM）.The simulated result was compared with the measured one and they fit closely with each other, which proves that the FE model is correct.Based on the FE model,the microstress and microstrain of the dual-phase steel were analyzed. Meanwhile,the effective factors such as the volume fraction of martensite and the yield stress ratio between martensite and ferrite phases on the stress-strain curves of the dual-phase steel were simulated,too.The simulated results indicate that for the low Si-Mn-Nb dual-phase steel, the maximum stress occurs in the martensite region,while the maximum strain occurs in the ferrite one.The effect of the volume fraction of martensite（fm） and the yield stress ratio on the stress-strain curve of the dual-phase steel is small in the elastic part,while it is obvious in the plastic part.In the plastic part of this curve,the strain decreases with the increase of f_M,while it decreases with the decrease of the yield stress ratio.
基金supported by the Ministry of Trade,Industry&Energy(MOTIE,Korea)under Industrial Technology Innovation Program.No.10046591,‘Development of TiC reinforced metal matrix composite fabricated by in-situ liquid forming for tool steel’
文摘Fe alloy composites reinforced with in-situ titanium carbide （TIC） particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8, 0.9, 1 and 1.1 to investigate the microstructure and mechanical properties ofin-situ TiC/Fe alloy composites. The microstructure showed that the in-situ syn- thesized TiC particles were spherical with a size of 1-3 }~m, irrespective of C/Ti ratio. The stoichiometry of in-situ TiC increased from 0.85 to 0.88 with increasing C/Ti ratio from 0.8 to 0.9, but remained almost unchanged for C/Ti ratios between 0.9 and 1.1 due to the same driving force for carbon diffusion in TiCx at the common sintering temperature. The in-situ TiC/Fe alloy composite with C[Ti ~ 0.9 showed improved mechanical properties compared with other C/Ti ratios because the presence of excess carbon （C/Ti = 1 and 1.1） resulted in unreacted carbon within the Fe alloy matrix, while insufficient carbon （C/Ti = 0.8） caused the depletion of carbon from the Fe alloy matrix, leading to a significant decrease in hardness. This study presents that the maximized hardness and superior strength of in-situ TiC/Fe alloy composites can be achieved by microstructure control and stoichiometric analysis of the in-situ synthesized TiC par- ticles, while maintaining the ductility of the composites, compared to those of the unreinforced Fe alloy. Therefore, we anticipate that the in-situ synthesized TiC/Fe alloy composites with enhanced mechanical properties have great potential in cutting tool, mold and roller material applications.
基金Financial supports for this research were provided by the National Natural Science Foundation of China(Grants 11372060,11672057 and 11711530018)the 111 Project(Grant B14013)the Program of BK21 Plus.These supports are gratefully acknowledged.
文摘Fiber reinforced composite frame structure is an ideal lightweight and large-span structure in the fields of aerospace,satellite and wind turbine.Natural fundamental frequency is one of key indicators in the design requirement of the composite frame since structural resonance can be effectively avoided with the increase of the fundamental frequency.Inspired by the concept of integrated design optmization of composite frame structures and materials,the design optimization for the maximum structural fundamental frequency of fiber reinforced frame structures is proposed.An optimization model oriented at the maximum structural fundamental frequency under a composite material volume constraint is established.Two kinds of independent design variables are optimized,in which one is variables represented structural topology,the other is variables of continuous fiber winding angles.Sensitivity analysis of the frequency with respect to the two kinds of independent design variables is implemented with the semi-analytical sensitivity method.Some representative examples in the manuscript demonstrate that the integrated design optimization of composite structures can effectively explore coupled effects between structural configurations and material properties to increase the structural fundamental frequency.The proposed integrated optimization model has great potential to improve composite frames structural dynamic performance in aerospace industries.
文摘This paper provides a unified formulation of optimal guidance-to-collision law for a target with an arbitrary acceleration or deceleration.The collision course for general target acceleration or deceleration is first determined from the engagement geometry in conjunction with the nonlinear engagement kinematics in the proposed approach.The heading error defined in the collision course is then adopted as a variable to be nullified for accomplishing the intercept condition.The proposed guidance law is derived based on the heading error dynamics and the optimal error dynamics to ensure optimality and finite-time convergence.As illustrative examples,the proposed guidance command for a constant target acceleration and a target deceleration in the form of a quadratic function of speed are provided.Additionally,the time-to-go prediction method is suggested for implementing the proposed method.The characteristics of the proposed guidance command are analytically investigated to provide insight into the proposed method.The key benefits of the proposed method lie in not producing unnecessary guidance commands near a target compared to other methods and ensuring optimality in guidance command even in the nonlinear engagement kinematics.Finally,numerical simulations are performed to validate the proposed method and to show our findings.
基金the Swedish Research Council (2016-06146,2019-02345)Swedish Research Council (grant no.2020-05223)+7 种基金the Swedish Research Council Formas,the Swedish Energy Agency (52473-1)the Wallenberg Foundation (2017.0186 and 2016.0059) for financial supportsupported by the National Research Foundation of Korea (NRF-2017M3A7B8065584 and 2020R1A4A1018516)Support from the National Natural Science Foundation of China (61774077)the Key Projects of Joint Fund of Basic and Applied Basic Research Fund of Guangdong Province (2019B1515120073)the Research Fund of Guangdong-Hong Kong-Macao Joint Laboratory for Intelligent Micro-Nano Optoelectronic Technology (No.2020B1212030010)Support from Sino-Danish Center for Education and ResearchSwedish Energy Agency (grant no.45420-1)
文摘All-polymer solar cells(all-PSCs)possess attractive merits including superior thermal stability and mechanical flexibility for large-area roll-to-roll processing.Introducing flexible conjugation-break spacers(FCBSs)into backbones of polymer donor(P_(D))or polymer acceptor(P_(A))has been demonstrated as an efficient approach to enhance both the photovoltaic(PV)and mechanical properties of the all-PSCs.However,length dependency of FCBS on certain all-PSC related properties has not been systematically explored.In this regard,we report a series of new non-conjugated P_(A)s by incorporating FCBS with various lengths(2,4,and 8 carbon atoms in thioalkyl segments).Unlike com-mon studies on so-called side-chain engineering,where longer side chains would lead to better solubility of those resulting polymers,in this work,we observe that the solubilities and the resulting photovoltaic/mechanical properties are optimized by a proper FCBS length(i.e.,C2)in P_(A) named PYTS-C2.Its all-PSC achieves a high efficiency of 11.37%,and excellent mechanical robustness with a crack onset strain of 12.39%,significantly superior to those of the other P_(A)s.These results firstly demonstrate the effects of FCBS lengths on the PV performance and mechanical properties of the all-PSCs,providing an effective strategy to fine-tune the structures of P_(A)s for highly efficient and mechanically robust PSCs.
基金supported by the National Research Foundation (NRF) of Korea funded by the Ministry of Science and ICT and Future Planning (MSIP) (2016R1E1A1A01943131)
文摘The intensive development of micro-/nanotechnologies offers a new route to construct sophisticated architectures of emerging soft electronics.Among the many classes of stretchable materials,micro-/nanostructured poly(dimethylsiloxane)(PDMS)has emerged as a vital building block based on its merits of flexibility,stretchability,simple processing,and,more importantly,high degrees of freedom of incorporation with other functional materials,including metals and semiconductors.The artificially designed geometries play important roles in achieving the desired mechanical and electrical performances of devices and thus show great potential for applications in the fields of stretchable displays,sensors and actuators as well as in health-monitoring device platforms.Meanwhile,novel lithographic methods to produce stretchable platforms with superb reliability have recently attracted research interest.The aim of this review is to comprehensively summarize the progress regarding micro-/nanostructured PDMS and their promising soft electronic applications.This review is concluded with a brief outlook and further research directions.
文摘Size control of BaTiO3 in solid-state reaction between BaCO3 and TiO2 was demonstrated by varying the size of TiO2 and milling conditions of BaCO3. The smaller TiO2 particles had higher surface area, resulting in faster initial reaction. The mechanically milled BaCO3 particles accelerated the diffusion process and decreased the calcinations temperature. It can be deduced from the results that the size control is possible and nano-sized BaTiO3 particles with about 60 nm can be synthesized by using the conventional solid-state reaction between BaCO3 and TiO2.
基金supported through the National Research Foundation of Korea (No. 2013R1A1A1007708)
文摘With the increase in silver（Ag）-based products in our lives, it is essential to test the potential toxicity of silver nanoparticles（Ag NPs） and silver ions（Ag ions） on living organisms under various conditions. Here, we investigated the toxicity of Ag NPs with Ag ions to Escherichia coli K-12 strain under various conditions. We observed that both Ag NPs and Ag ions display antibacterial activities, and that Ag ions had higher toxicity to E. coli K-12 strain than Ag NPs under the same concentrations. To understand the toxicity of Ag NPs at a cellular level, reactive oxygen species（ROS） enzymes were detected for use as antioxidant enzymatic biomarkers. We have also studied the toxicity of Ag NPs and Ag ions under various coexistence conditions including： fixed total concentration, with a varied the ratio of Ag NPs to Ag ions; fixed the Ag NPs concentration and then increased the Ag ions concentration; fixed Ag ions concentration and then increasing the Ag NPs concentration.Exposure to Ag NPs and Ag ions clearly had synergistic toxicity; however, decreased toxicity（for a fixed Ag NPs concentration of 5 mg/L, after increasing the Ag ions concentration） to E. coli K-12 strain. Ag NPs and Ag ions in the presence of L-cysteine accelerated the bacterial cell growth rate, thereby reducing the bioavailability of Ag ions released from Ag NPs under the single and coexistence conditions. Further works are needed to consider this potential for Ag NPs and Ag ions toxicity across a range of environmental conditions.Environmental Significance Statement： As silver nanoparticles（Ag NPs）-based products are being broadly used in commercial industries, an ecotoxicological understanding of the Ag NPs being released into the environment should be further considered. Here, we investigate the comparative toxicity of Ag NPs and silver ions（Ag ions） to Escherichia coli K-12 strain, a representative ecotoxicological bioreporter. This study showed that toxicities of Ag NPs and Ag ions to E. coli K-12 strain display different relationships when existing individually or when coexisting, and in the presence of L-cysteine materials. These findings suggest that the toxicology research of nanomaterials should consider conditions when NPs coexist with and without their bioavailable ions.
基金the support of the KAIST GCO_(2) RE(Global Center for Open Research with Enterprise)grant funded by the Ministry of Science and ICT(N11200010)National Research Foundation of Korea(NRF)[grant number NRF-2019R1A2C1002165]。
文摘We report laser cladding of pure titanium on a CoCrMo alloy using directed energy deposition.Using electron microscopy,the microstructural evolution upon varying the process parameters,especially laser power and powder feed rate,was investigated in relation to crack formation.Cladding layers showing dilution rates of more than 5%contained cracks due to the formation of the brittle Co_(2)Ti intermetallic phase.The observed cracks could be ascribed to a mismatch in thermal expansion and a resulting stress of more than 440 MPa acting on the Co_(2)Ti phase,as determined by density functional theory and nanoindentation.Furthermore,an excess laser energy caused chemical inhomogeneity and unmelted Ti powder particles,while a deficient laser energy resulted in a lack of fusion.Neither cracks nor partially melted powders were observed for a powder feed rate of 3 g/min and a laser power of 225–300 W,for which the dilution rate was minimized to less than 5%.For such samples,the cladding layers comprised pureα-Ti and a uniform CoT i interface with Co_(2)Ti islands.
文摘It is difficult for polyethylene terephthalate （PET） to degrade,which caused severe pollution.In this work,polylactic acid （PLA） was introduced to improve the degradation of PET.PET/PLA was synthesized by extrusion blending.The thermal,crystalline and mechanical properties of blends were investigated with TGA,DSC,WAXD and universal testing machine.The degradation of the blends in soil,acid and alkaline buffer solutions was assessed,respectively.It was found that the introduction of a little PLA promoted crystallization of PET during injection molding process.The starting decomposition temperature lowered from 412.1 ℃ of pure PET to 330.4 ℃ at 50% PLA content,tensile and bending strength of blends gradually decreased with the PLA content increasing,while the degradation rate improved.Alkaline environment was most beneficial for blends to degrade.The degradation mechanism was discussed.
基金supported by the National Research Foundation of Korea(NRF,Nos.NRF-2021R1A2C2014025,NRF-2022R1A5A1030054,and NRF-2022M3H4A1A02076759)grants funded by the Ministry of Science and ICT.
文摘The flexible product shape of additive manufacturing(AM)is attractive,but the process suffers from a lack of material property diversity due to a limited number of printable alloys and post-processing options.To overcome this problem,the AM of metal matrix composites(MMCs)is a highly suitable solution because the properties of MMC can be tailored using various reinforcements.Therefore,extensive research has been conducted on the AM of MMCs;however,the major huddle for this process has been the difficulties in preparing feedstock powder and operating the AM process.This study introduces an easily synthesizable core-shell composite powder,which was fabricated by a recently developed process called the SMART process.The core-shell powder has a novel morphology,consisting of a metal core and composite shell,distinguishing it from the powders used in conventional AM approaches.Inconel 625/TiCp composites were fabricated using the core-shell composite powder,with various fractions of TiCp up to 10 vol.%.Compared to additive-manufactured Inconel 625,the additive-manufactured MMCs showed enhanced strength with significantly fewer defects.The results of this study may accelerate the application of MMC fabricated by AM,which offers superior properties and reliability compared to casting and powder metallurgy due to the higher degree of dislocation density and reinforcement dispersion.
基金supported by the Program for the Construction of Eco Industrial Park, which was conducted by the Korea Industrial Complex Corporation and the Ministry of Knowledge Economyfinancially supported by the National Research Foundation of Korea grant funded by the Korea government Ministry of Education, Science and Technology (NRF2012M1A2A2026587)
文摘Nanoscale zero-valent iron （NZVI） is considered to have potential to reduce nitrate in the concentrate generated by high pressure membrane processes aimed at water reuse. However, it is necessary to verify the effect of the matrix components in the concentrates on NZVI reactivity. In this study, the influence of hardness, alkalinity, and organic matter on NZVI reactivity was evaluated by the response surface method （RSM）. Hardness （Ca/＋） had a positive effect on NZVI reactivity by accelerating iron corrosion. In contrast, alkalinity （bicarbonate; HCO3） and organic matter （humic acid; HA） had negative effects on NZVI reactivity due to morphological change to carbonate green rust, and to competitive adsorption of HA, respectively. The validity of the statistical prediction model derived from RSM was confirmed by an additional confirmation experiment, and the experimental result was within the 95% confidential interval. Therefore, it can be indicated that the RSM model produced results that were statistically significant.
基金supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP)the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20172010000830)supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MSIP) (NRF-2015R1A5A1036133)
文摘SnSe is a promising thermoelectric material with a high figure of merit in single crystal form, which has stimulated continuous research on polycrystalline SnSe. In this study, we investigated a metallization techniques for polycrystalline SnSe to achieve highly efficient and practical SnSe thermoelectric modules. The Ag/Ni metallization layers were formed on pristine polycrystalline SnSe using various deposition technique: sputter coating Ni, powder Niand foil Ni by spark plasma sintering. Structural analysis demonstrated that the microstructure and con tact resistance could be different according to the metallization process, despite using the same metals. The Ag/Ni metallization layer using foil Ni acted as an effective diffusion barrier and minimized electrical contact resistance (2.3×10^-4Ωcm^2). A power loss in the thermoelectric module of only 5% was demonstrated using finite element simulation.
基金financially supported by the National Natural Science Foundation of China(Nos.21274158 and 91333114)the National Research Laboratory Program of the Korea Science and Engineering Foundation(KOSEF)+1 种基金the World Class University Program(No.R32-2008-000-10142-0)the Center for Nanoscale Mechatronics&Manufacturing(08K140100414,CNMM)
文摘In this study, we demonstrate a novel method for fabricating polythiophene patterns, i.e., cylindrical holes and cylinders, through blending of a thermally curable polythiophene carrying with tertiary ester groups(PT-tert-ESTER) and poly(methyl methacrylate)(PMMA), followed by thermal conversion of the PT-tert-ESTER to an insoluble polythiophene via low-temperature cleavage of the tertiary ester groups and removal of the PMMA component via ultraviolet degradation. We show that the surface polarity of substrates, the mass ratio of PT-tert-ESTER to PMMA in the blend solutions as well as the concentration of the blend solutions strongly influence the formation of the polythiophene patterns. Cylindrical holes are more readily formed on less polar substrates when a PT-tert-ESTER dominated blend solution is used, while cylinders are more readily formed on more polar substrates when a PMMA dominated blend solution is used. Moreover, the diameters of both the cylindrical holes and the cylinders decrease as the PT-tert-ESTER concentration is increased in the respective ranges of the PT-tert-ESTER/PMMA ratios where the patterns are formed. Grazing incident X-ray diffraction data have indicated that the patterning of the PT-tert-ESTER component in the blend films improves the crystallinity of PT-tert-ESTER as well as the molecular packing of the insoluble polythiophene in the resultant patterned polythiophene films.
基金financially supported by the National Research Foundation of the Republic of Korea funded by the Ministry of Science and ICT(Nos.2020M3D1A1110501 and 2021M2D1A1039966)。
文摘Switchable conductivity in elementary semiconducting materials has a high potential for the design of diodes,transistors and energy conversion technologies.However,the ability to utilize their physical properties is dependent on doping within the carrier density transition temperature.Single-crystal tellurium has a high Seebeck coefficient and intrinsic p-n-p conduction at room temperature and therefore,is not suitable for thermoelectric applications.We demonstrate that the addition of iso valent Se lowers the Fermi level to achieve a stable p-type conductivity with a high band degeneracy near the valence band.We observed shifts in the n-p transition temperature below the intrinsic conductivity at 470 K based on changes in stoichiometry and carrier concentration above 10^(17)cm^(-3).In addition,the high thermal conductivity is significantly reduced with the increase in Se alloying due to the mass and strain fluctuations.This results in a moderately high zT of 0.4 at 673 K.
