Spherical microfossils are present in the Hindeodus parvus zone of the Lower Triassic in Ziyun,Guizhou Province. They generally range from 0.15 to 0.30 mm across,with micritic wall and filled by micro-sparry calcites,...Spherical microfossils are present in the Hindeodus parvus zone of the Lower Triassic in Ziyun,Guizhou Province. They generally range from 0.15 to 0.30 mm across,with micritic wall and filled by micro-sparry calcites,and are evenly scattered in micritic matrix. Their abundance makes the rock as-signed to microbialites. The accompanied organisms include ostracods and algal mat,but no gastro-pods or bivalves. Presence of small (<7 μm) pyrite framboids indicates that this bed formed in anoxic conditions. In some sections,this bed is overlain and underlain by tidal-flat micritic limestone with microgastropods and small burrows. Occurrence only in deposits on reef top indicates that the micro-bial organism was benthic,and needed sunlight in life. The size of the microbial fossil exceeds that of any bacteria or cyanobacteria. Thus,it does not belong to these two phyla. It may belong to lower green algae,and is assigned to a new species in a new genus,Ziyunosphaeridium sinensis gen. et sp. nov. Up to now,the rocks described as microbialites from the Permian-Triassic transition include six types: (1) porous micritic limestone such as that descried from Japan by Sano and Nakashima (1997),(2) limestone with rich globular microfossils such as that described from the Nanpanjiang Basin in China by Lehrmann (1999),(3) dendroidal limestone such as that described from the vicinity of Chongqing by Kershaw et al. (1999),(4) spherical microbial limestone adapted to anoxic environments described from Ziyun,Guizhou reported in this paper,(5) limestone with cyanobacterial fossils such as that described by Wang et al. (2005),and (6) stromatolites. All these microbialites are not reefs in the proper sense,and the argument that Permian reef ecosystems extended into the Mesozoic is incorrect.展开更多
Studies of two Permian-Triassic boundary (PTB) sections on top of a Changhsingian reef in Ziyun, Guizhou Province, southwestern China indicate that the end-Permian mass extinction of reef ecosystems occurred in two st...Studies of two Permian-Triassic boundary (PTB) sections on top of a Changhsingian reef in Ziyun, Guizhou Province, southwestern China indicate that the end-Permian mass extinction of reef ecosystems occurred in two steps. The first step is the extinction of all stenotropic organisms such as calcisponges and fusulinids in the latest Permian (in the Clarkina yini conodont zone). The biota after the first extinction is simple, comprising eurytropic organisms including microgastropods, ostracods, and some small burrowing organisms, or only algal mats. At the beginning of the Early Triassic (i.e. the beginning of the Hindeodus parvus zone), the environments became anoxic, and the microgastropod dominated biota or algal mats disappeared, which constituted the second episode of the mass extinction. The biota after the second extinction comprises small spherical microproblematica, some kinds of specialized organisms tolerant of anoxic or oxygen-poor conditions. As the environments became oxygenated, the specialized biota was replaced by a microgastropod-dominated simple biota. When the environmental conditions improved further, the simple biota was replaced by a diverse biota with normal-sized ammonoids, bivalves, and gastropods, representing restoration of normal oceanic condi- tions. Comparison with PTB sections in Dolomites, Italy and Meishan, Zhejiang Province shows that non-reef ecosystems had a similar first episode of mass extinction in the latest Permian. In the case that oceanic anoxia happened, non-reef ecosystems had a second extinction episode similar to that of reef ecosystems.展开更多
Mg and its alloys evince strong candidature for biodegradable bone implants,cardiovascular stents,and wound closing devices.However,their rapid degradation rate causes premature implant failure,constraining clinical a...Mg and its alloys evince strong candidature for biodegradable bone implants,cardiovascular stents,and wound closing devices.However,their rapid degradation rate causes premature implant failure,constraining clinical applications.Bio-functional surface coatings have emerged as the most competent strategy to fulfill the diverse clinical requirements,besides yielding effective corrosion resistance.This article reviews the progress of biodegradable and advanced surface coatings on Mg alloys investigated in recent years,aiming to build up a comprehensive knowledge framework of coating techniques,processing parameters,performance measures in terms of corrosion resistance,adhesion strength,and biocompatibility.Recently developed conversion and deposition type surface coatings are thoroughly discussed by reporting their essential therapeutic responses like osteogenesis,angiogenesis,cytocompatibility,hemocompatibility,anti-bacterial,and controlled drug release towards in-vitro and in-vivo study models.The challenges associated with metallic,ceramic and polymeric coatings along with merits and demerits of various coatings have been illustrated.The use of multilayered hybrid coating comprising a unique combination of organic and inorganic components has been emphasized with future perspectives to obtain diverse bio-functionalities in a facile single coating system for orthopedic implant applications.展开更多
With the increasing capacity of wind farm, HVDC technology has become a promising transmission scheme for long distance transportation of large-scale wind power. However oscillation caused by this system will have a g...With the increasing capacity of wind farm, HVDC technology has become a promising transmission scheme for long distance transportation of large-scale wind power. However oscillation caused by this system will have a great influence on the security and stability of power system operation. In this paper, the oscillation of a doubly-fed induction generator(DFIG)-based wind farm interfaced with line commutated converter(LCC) based HVDC is discussed. Low-frequency oscillation and subsynchronous oscillation(SSO) are studied since these two oscillations are the particularly concerned oscillations in the stability study of power system in recent years. The model of a DFIG-based wind farm interconnected with LCC-HVDC is developed. The impact of drive train model's structure and parameters on the oscillation characteristics is analyzed. Eigenvalue and participation factor analysis are used to identify the three main modes, which include controller mode, electromechanical mode, and shaft mode. The effects of DFIG controller's parameters, wind speed and operating conditions of HVDC on those modes are studied. Electromagnetic transient simulations are performed to verify the results of the eigenvalue analysis.展开更多
High-performance nonlinear optical(NLO)crystals are crucial devices to convert wavelength of solid-state lasers.Chalcogenides play an indispensable role in the research of infrared NLO materials.In this work,ternary c...High-performance nonlinear optical(NLO)crystals are crucial devices to convert wavelength of solid-state lasers.Chalcogenides play an indispensable role in the research of infrared NLO materials.In this work,ternary chalcogenide ZnGa_(2)S_(4) with defect diamond-like structure was screened out and synthesized by chemical vapor transport method.展开更多
The multi-depot vehicle routing problem(MDVRP)is one of the most essential and useful variants of the traditional vehicle routing problem(VRP)in supply chain management(SCM)and logistics studies.Many supply chains(SC)...The multi-depot vehicle routing problem(MDVRP)is one of the most essential and useful variants of the traditional vehicle routing problem(VRP)in supply chain management(SCM)and logistics studies.Many supply chains(SC)choose the joint distribution of multiple depots to cut transportation costs and delivery times.However,the ability to deliver quality and fast solutions for MDVRP remains a challenging task.Traditional optimization approaches in operation research(OR)may not be practical to solve MDVRP in real-time.With the latest developments in artificial intelligence(AI),it becomes feasible to apply deep reinforcement learning(DRL)for solving combinatorial routing problems.This paper proposes a new multi-agent deep reinforcement learning(MADRL)model to solve MDVRP.Extensive experiments are conducted to evaluate the performance of the proposed approach.Results show that the developed MADRL model can rapidly capture relative information embedded in graphs and effectively produce quality solutions in real-time.展开更多
Aims Environmental heterogeneity is a primary mechanism explain-ing species coexistence and extant patterns of diversity.Despite strong theoretical support and ample observational evidence,few experimental studies in ...Aims Environmental heterogeneity is a primary mechanism explain-ing species coexistence and extant patterns of diversity.Despite strong theoretical support and ample observational evidence,few experimental studies in plant communities have been able to demonstrate a causal link between environmental heterogene-ity and plant diversity.This lack of experimental evidence sug-gests that either fine-scale heterogeneity has weak effects on plant diversity or previous experiments have been unable to effectively manipulate heterogeneity.Here,we utilize a unique soil manipu-lation to test whether fine-scale soil heterogeneity will increase plant richness through species sorting among experimental patch types.Methods This experiment was conducted in the tallgrass prairie region of south-central Kansas,USA.We utilized the inherent variation found in the vertical soil profile,which varied in both biotic and abiotic characteristics,and redistributed these strata into either homoge-neous or heterogeneous spatial arrangements in 2.4×2.4 m plots.After the soil manipulation,34 native prairie species were sown into all plots.We conducted annual censuses at peak biomass to quantify species composition and plant density by species within the experimental communities.Important Findings After 2 years,species richness was significantly higher in heteroge-neous relative to homogeneous plots and this pattern was independ-ent of total plant density.In the heterogeneous plots,13 species had higher establishment in a specific patch type representing one of the three soil strata.Conversely,no species had greater estab-lishment in the mixed stratum,which comprised the homogene-ous plots,relative to the heterogeneous strata.These species sorting patterns suggest that fine-scale heterogeneity creates opportunities for plant establishment due to niche differences,which translates into increased plant diversity at the plot scale.Species richness was more strongly related to plant density among patches comprising homogenous plots-where fine-scale展开更多
Recycled polystyrene （PS） cups were chopped up and separately incorporated with multiwall carbon nanotubes （MWCNTs） and NiZn ferrite （Ni0.6Zn0.4Fe2O4） nanoparticles prior to electrospinning under different condi...Recycled polystyrene （PS） cups were chopped up and separately incorporated with multiwall carbon nanotubes （MWCNTs） and NiZn ferrite （Ni0.6Zn0.4Fe2O4） nanoparticles prior to electrospinning under different conditions. These nanoscale inclusions were initially dispersed well in dimethylformamide （DMF）, and then known amounts of the recycled PS pieces were added to the dispersions prior to 30 min of sonication followed by 4 h of high-speed agitation at 750 r/min. The thermal, dielectric, surface hydrophobic, and magnetic properties of the resultant nanocomposite fibers were determined by thermal comparative, capacitance bridge, vibrating sample magnetometer （VSM）, and goniometer techniques, respectively. Test results confirmed that the physical properties of recycled nanofibers were significantly increased as a function of the inclusion concentrations, which may be because of their excellent properties. The consumption of polymeric products as well as their waste materials has dramatically grown worldwide. Although plastic recycling, reprocessing, and reusing rates are growing, the physical properties and economic value of recycled plastics are significantly low. Consequently, this work provides a detailed explanation of how to improve recycled plastics, making them into highly valued new nanoproducts for various industrial applications, including filtration, textile, transportation, construction, and energy.展开更多
Surface coatings have been extensively used to control the degradation rate of Mg alloys for bioimplant applications.However,these coatings only act as passive barriers.In corrosive media,structural damage impairs the...Surface coatings have been extensively used to control the degradation rate of Mg alloys for bioimplant applications.However,these coatings only act as passive barriers.In corrosive media,structural damage impairs their barrier properties,resulting in rapid degradation of Mg alloys.The present study incorporates phytic acid(PA)as a healing agent in polycaprolactone(PCL)microcapsules with a unique honeycomb core matrix to obtain a self-healing PA-PCLcaps coating.The contact between simulated body fluid(SBF)and PA-PCLcaps coated ZM21 exhibited Cassie-Baxter interfacial states,resulting in significant hydrophobicity with a contact angle(CA)of 116.3.The corrosion potential(Ecorr)and current density(Icorr)were found to be-0.28 V and 1.1×10^(-9)A/cm^(2),respectively,for PA-PCLcaps coating,resulting in biosafe corrosion rate of 2.5×10^(-4)mm/year.After mechanical scratching,rapid HA mineralization at scratched regions recovered the hydrogen evolution rate(HER,0.36 mL/cm^(2)/day)and pH change(pH 7.10)of scratched PA-PCLcaps coated ZM21 samples to corresponding unscratched samples within one day of immersion.The coating’s self-healing ability could be attributed to PA released from punctured microcapsules,which facilitates HA chelation.The pH-triggered(pH 10)and Mg(II)-triggered(5 mM)conditions enhanced PA release from PA-PCLcaps coating by 2.5 and 3.1 times,respectively.As a result,dense HA mineralization occurred,which protects the coating from structural defects and ensures its durability in stimulating conditions.The findings of present study provide new insight for design of multiple stimuli-feedback based self-healing coatings on biodegradable Mg alloys.展开更多
This paper develops a high-order adaptive scheme for solving nonlinear Schrödinger equa-tions.The solutions to such equations often exhibit solitary wave and local structures,which make adaptivity essential in im...This paper develops a high-order adaptive scheme for solving nonlinear Schrödinger equa-tions.The solutions to such equations often exhibit solitary wave and local structures,which make adaptivity essential in improving the simulation efficiency.Our scheme uses the ultra-weak discontinuous Galerkin(DG)formulation and belongs to the framework of adaptive multiresolution schemes.Various numerical experiments are presented to demon-strate the excellent capability of capturing the soliton waves and the blow-up phenomenon.展开更多
This study is aimed at developing a methodology to assess and quantify the human limb motions and interactions with the exoskeleton in relation to alignment.Three different basic and common upper arm joint movements a...This study is aimed at developing a methodology to assess and quantify the human limb motions and interactions with the exoskeleton in relation to alignment.Three different basic and common upper arm joint movements and their interaction with a joint-based exoskeleton are considered:shoulder vertical and horizontal abduction-adduction,and elbow flexion-extension.The exoskeleton and the human model are aligned to the respective joints inside a Musculoskeletal Modeling software.Within the range of motion,the linear and angular displacement errors were analyzed,and the effect of those errors on the length of the associated tendons was studied.Results have shown a noticeable variation of the muscle-tendon lengths up to 65.7 mm and a change in the pattern on different muscle groups of the shoulder.Similarly,about 4 mm muscle-tendon length changes observed particularly at the elbow anconeus muscle-tendon.These changes of length could cause unwanted stresses at the joints,specially for people with disabilities due to stroke that might not have the flexibility to accommodate those extra pose variations imposed by the exoskeleton.展开更多
文摘在江西修水四都镇东岭村发现了一个连续的、出露完好的二叠纪-三叠纪界线地层剖面。在剖面中有一段厚约2.1m 的地层具有指示海平面下降的岩石组构。这段地层的底部为红色的碳酸盐颗粒岩。红色是颗粒表面的红色铁染,成分为褐铁矿,是出露地表风化形成的。这层红色颗粒岩之上有约2.0 m 的去白云石化灰岩,其中保留了原来粉晶白云石的晶形。去白云石化作用是白云岩受淡水影响而发生的,指示海平面下降事件。这段地层之上是厚1m 的颗粒岩和灰泥岩,代表浅水潮下环境。其上是二叠系-三叠系的界线。这段地层之下的地层中生物丰富多样,并且有复(蜒)、钙藻等大绝灭前的生物。这段地层及其以上的地层中生物种类很少,(蜓)、钙藻等已经消失,表明集群绝灭事件开始于这段地层之下,生物大绝灭的发生与海平面下降事件的发生是基本同时的。由此认为,可能是海平面下降有关的环境剧变事件引发了二叠纪末的集群绝灭事件。
基金Supported by the National Natural Science Foundation of China (Grant No. 40472015)the State Key Laboratory of Modern Paleontology and Stratigraphy (Grant No. 053102)as well as the Key Laboratory for Minerals and Resources, the Chinese Academy of Sciences
文摘Spherical microfossils are present in the Hindeodus parvus zone of the Lower Triassic in Ziyun,Guizhou Province. They generally range from 0.15 to 0.30 mm across,with micritic wall and filled by micro-sparry calcites,and are evenly scattered in micritic matrix. Their abundance makes the rock as-signed to microbialites. The accompanied organisms include ostracods and algal mat,but no gastro-pods or bivalves. Presence of small (<7 μm) pyrite framboids indicates that this bed formed in anoxic conditions. In some sections,this bed is overlain and underlain by tidal-flat micritic limestone with microgastropods and small burrows. Occurrence only in deposits on reef top indicates that the micro-bial organism was benthic,and needed sunlight in life. The size of the microbial fossil exceeds that of any bacteria or cyanobacteria. Thus,it does not belong to these two phyla. It may belong to lower green algae,and is assigned to a new species in a new genus,Ziyunosphaeridium sinensis gen. et sp. nov. Up to now,the rocks described as microbialites from the Permian-Triassic transition include six types: (1) porous micritic limestone such as that descried from Japan by Sano and Nakashima (1997),(2) limestone with rich globular microfossils such as that described from the Nanpanjiang Basin in China by Lehrmann (1999),(3) dendroidal limestone such as that described from the vicinity of Chongqing by Kershaw et al. (1999),(4) spherical microbial limestone adapted to anoxic environments described from Ziyun,Guizhou reported in this paper,(5) limestone with cyanobacterial fossils such as that described by Wang et al. (2005),and (6) stromatolites. All these microbialites are not reefs in the proper sense,and the argument that Permian reef ecosystems extended into the Mesozoic is incorrect.
基金Supported by the National Natural Science Foundation of China (Grant No. 40472015)the State Key Laboratory of Modern Paleontology and Stratigraphy (Grant No. 053102)Key Laboratory for Minerals and Resources, Chinese Academy of Sciences.
文摘Studies of two Permian-Triassic boundary (PTB) sections on top of a Changhsingian reef in Ziyun, Guizhou Province, southwestern China indicate that the end-Permian mass extinction of reef ecosystems occurred in two steps. The first step is the extinction of all stenotropic organisms such as calcisponges and fusulinids in the latest Permian (in the Clarkina yini conodont zone). The biota after the first extinction is simple, comprising eurytropic organisms including microgastropods, ostracods, and some small burrowing organisms, or only algal mats. At the beginning of the Early Triassic (i.e. the beginning of the Hindeodus parvus zone), the environments became anoxic, and the microgastropod dominated biota or algal mats disappeared, which constituted the second episode of the mass extinction. The biota after the second extinction comprises small spherical microproblematica, some kinds of specialized organisms tolerant of anoxic or oxygen-poor conditions. As the environments became oxygenated, the specialized biota was replaced by a microgastropod-dominated simple biota. When the environmental conditions improved further, the simple biota was replaced by a diverse biota with normal-sized ammonoids, bivalves, and gastropods, representing restoration of normal oceanic condi- tions. Comparison with PTB sections in Dolomites, Italy and Meishan, Zhejiang Province shows that non-reef ecosystems had a similar first episode of mass extinction in the latest Permian. In the case that oceanic anoxia happened, non-reef ecosystems had a second extinction episode similar to that of reef ecosystems.
文摘Mg and its alloys evince strong candidature for biodegradable bone implants,cardiovascular stents,and wound closing devices.However,their rapid degradation rate causes premature implant failure,constraining clinical applications.Bio-functional surface coatings have emerged as the most competent strategy to fulfill the diverse clinical requirements,besides yielding effective corrosion resistance.This article reviews the progress of biodegradable and advanced surface coatings on Mg alloys investigated in recent years,aiming to build up a comprehensive knowledge framework of coating techniques,processing parameters,performance measures in terms of corrosion resistance,adhesion strength,and biocompatibility.Recently developed conversion and deposition type surface coatings are thoroughly discussed by reporting their essential therapeutic responses like osteogenesis,angiogenesis,cytocompatibility,hemocompatibility,anti-bacterial,and controlled drug release towards in-vitro and in-vivo study models.The challenges associated with metallic,ceramic and polymeric coatings along with merits and demerits of various coatings have been illustrated.The use of multilayered hybrid coating comprising a unique combination of organic and inorganic components has been emphasized with future perspectives to obtain diverse bio-functionalities in a facile single coating system for orthopedic implant applications.
基金supported by the National Hi-Tech Research and Development Program of China("863"Project)(Grant No.2011AA05A301)"111"Project of China(Grant No.B08013)
文摘With the increasing capacity of wind farm, HVDC technology has become a promising transmission scheme for long distance transportation of large-scale wind power. However oscillation caused by this system will have a great influence on the security and stability of power system operation. In this paper, the oscillation of a doubly-fed induction generator(DFIG)-based wind farm interfaced with line commutated converter(LCC) based HVDC is discussed. Low-frequency oscillation and subsynchronous oscillation(SSO) are studied since these two oscillations are the particularly concerned oscillations in the stability study of power system in recent years. The model of a DFIG-based wind farm interconnected with LCC-HVDC is developed. The impact of drive train model's structure and parameters on the oscillation characteristics is analyzed. Eigenvalue and participation factor analysis are used to identify the three main modes, which include controller mode, electromechanical mode, and shaft mode. The effects of DFIG controller's parameters, wind speed and operating conditions of HVDC on those modes are studied. Electromagnetic transient simulations are performed to verify the results of the eigenvalue analysis.
基金financially supported by the National Natural Science Foundation of China(Nos.52072109,21975062 and 22101069)the Science and Technology Project of Hebei Education Department(Nos.BJK2023029 and QN2023234)。
文摘High-performance nonlinear optical(NLO)crystals are crucial devices to convert wavelength of solid-state lasers.Chalcogenides play an indispensable role in the research of infrared NLO materials.In this work,ternary chalcogenide ZnGa_(2)S_(4) with defect diamond-like structure was screened out and synthesized by chemical vapor transport method.
文摘The multi-depot vehicle routing problem(MDVRP)is one of the most essential and useful variants of the traditional vehicle routing problem(VRP)in supply chain management(SCM)and logistics studies.Many supply chains(SC)choose the joint distribution of multiple depots to cut transportation costs and delivery times.However,the ability to deliver quality and fast solutions for MDVRP remains a challenging task.Traditional optimization approaches in operation research(OR)may not be practical to solve MDVRP in real-time.With the latest developments in artificial intelligence(AI),it becomes feasible to apply deep reinforcement learning(DRL)for solving combinatorial routing problems.This paper proposes a new multi-agent deep reinforcement learning(MADRL)model to solve MDVRP.Extensive experiments are conducted to evaluate the performance of the proposed approach.Results show that the developed MADRL model can rapidly capture relative information embedded in graphs and effectively produce quality solutions in real-time.
文摘Aims Environmental heterogeneity is a primary mechanism explain-ing species coexistence and extant patterns of diversity.Despite strong theoretical support and ample observational evidence,few experimental studies in plant communities have been able to demonstrate a causal link between environmental heterogene-ity and plant diversity.This lack of experimental evidence sug-gests that either fine-scale heterogeneity has weak effects on plant diversity or previous experiments have been unable to effectively manipulate heterogeneity.Here,we utilize a unique soil manipu-lation to test whether fine-scale soil heterogeneity will increase plant richness through species sorting among experimental patch types.Methods This experiment was conducted in the tallgrass prairie region of south-central Kansas,USA.We utilized the inherent variation found in the vertical soil profile,which varied in both biotic and abiotic characteristics,and redistributed these strata into either homoge-neous or heterogeneous spatial arrangements in 2.4×2.4 m plots.After the soil manipulation,34 native prairie species were sown into all plots.We conducted annual censuses at peak biomass to quantify species composition and plant density by species within the experimental communities.Important Findings After 2 years,species richness was significantly higher in heteroge-neous relative to homogeneous plots and this pattern was independ-ent of total plant density.In the heterogeneous plots,13 species had higher establishment in a specific patch type representing one of the three soil strata.Conversely,no species had greater estab-lishment in the mixed stratum,which comprised the homogene-ous plots,relative to the heterogeneous strata.These species sorting patterns suggest that fine-scale heterogeneity creates opportunities for plant establishment due to niche differences,which translates into increased plant diversity at the plot scale.Species richness was more strongly related to plant density among patches comprising homogenous plots-where fine-scale
基金the Department of Energy(DE-EE0004167)the Wichita State University for financial and technical support to the present work
文摘Recycled polystyrene （PS） cups were chopped up and separately incorporated with multiwall carbon nanotubes （MWCNTs） and NiZn ferrite （Ni0.6Zn0.4Fe2O4） nanoparticles prior to electrospinning under different conditions. These nanoscale inclusions were initially dispersed well in dimethylformamide （DMF）, and then known amounts of the recycled PS pieces were added to the dispersions prior to 30 min of sonication followed by 4 h of high-speed agitation at 750 r/min. The thermal, dielectric, surface hydrophobic, and magnetic properties of the resultant nanocomposite fibers were determined by thermal comparative, capacitance bridge, vibrating sample magnetometer （VSM）, and goniometer techniques, respectively. Test results confirmed that the physical properties of recycled nanofibers were significantly increased as a function of the inclusion concentrations, which may be because of their excellent properties. The consumption of polymeric products as well as their waste materials has dramatically grown worldwide. Although plastic recycling, reprocessing, and reusing rates are growing, the physical properties and economic value of recycled plastics are significantly low. Consequently, this work provides a detailed explanation of how to improve recycled plastics, making them into highly valued new nanoproducts for various industrial applications, including filtration, textile, transportation, construction, and energy.
文摘Surface coatings have been extensively used to control the degradation rate of Mg alloys for bioimplant applications.However,these coatings only act as passive barriers.In corrosive media,structural damage impairs their barrier properties,resulting in rapid degradation of Mg alloys.The present study incorporates phytic acid(PA)as a healing agent in polycaprolactone(PCL)microcapsules with a unique honeycomb core matrix to obtain a self-healing PA-PCLcaps coating.The contact between simulated body fluid(SBF)and PA-PCLcaps coated ZM21 exhibited Cassie-Baxter interfacial states,resulting in significant hydrophobicity with a contact angle(CA)of 116.3.The corrosion potential(Ecorr)and current density(Icorr)were found to be-0.28 V and 1.1×10^(-9)A/cm^(2),respectively,for PA-PCLcaps coating,resulting in biosafe corrosion rate of 2.5×10^(-4)mm/year.After mechanical scratching,rapid HA mineralization at scratched regions recovered the hydrogen evolution rate(HER,0.36 mL/cm^(2)/day)and pH change(pH 7.10)of scratched PA-PCLcaps coated ZM21 samples to corresponding unscratched samples within one day of immersion.The coating’s self-healing ability could be attributed to PA released from punctured microcapsules,which facilitates HA chelation.The pH-triggered(pH 10)and Mg(II)-triggered(5 mM)conditions enhanced PA release from PA-PCLcaps coating by 2.5 and 3.1 times,respectively.As a result,dense HA mineralization occurred,which protects the coating from structural defects and ensures its durability in stimulating conditions.The findings of present study provide new insight for design of multiple stimuli-feedback based self-healing coatings on biodegradable Mg alloys.
基金Funding Y.Liu:Research supported in part by a grant from the Simons Foundation(426993,Yuan Liu)W.Guo:Research is supported by NSF grant DMS-1830838+1 种基金Y.Cheng:Research is supported by NSF grants DMS-1453661 and DMS-1720023Z.Tao:Research is supported by NSFC Grant 12001231.
文摘This paper develops a high-order adaptive scheme for solving nonlinear Schrödinger equa-tions.The solutions to such equations often exhibit solitary wave and local structures,which make adaptivity essential in improving the simulation efficiency.Our scheme uses the ultra-weak discontinuous Galerkin(DG)formulation and belongs to the framework of adaptive multiresolution schemes.Various numerical experiments are presented to demon-strate the excellent capability of capturing the soliton waves and the blow-up phenomenon.
文摘This study is aimed at developing a methodology to assess and quantify the human limb motions and interactions with the exoskeleton in relation to alignment.Three different basic and common upper arm joint movements and their interaction with a joint-based exoskeleton are considered:shoulder vertical and horizontal abduction-adduction,and elbow flexion-extension.The exoskeleton and the human model are aligned to the respective joints inside a Musculoskeletal Modeling software.Within the range of motion,the linear and angular displacement errors were analyzed,and the effect of those errors on the length of the associated tendons was studied.Results have shown a noticeable variation of the muscle-tendon lengths up to 65.7 mm and a change in the pattern on different muscle groups of the shoulder.Similarly,about 4 mm muscle-tendon length changes observed particularly at the elbow anconeus muscle-tendon.These changes of length could cause unwanted stresses at the joints,specially for people with disabilities due to stroke that might not have the flexibility to accommodate those extra pose variations imposed by the exoskeleton.
