In the present study, we constructed an “ap- plied core collection” for phosphorus (P) efficiency of soy- bean germplasm using a GIS-assisted approach. Systematic characterization and comparative analysis of root ar...In the present study, we constructed an “ap- plied core collection” for phosphorus (P) efficiency of soy- bean germplasm using a GIS-assisted approach. Systematic characterization and comparative analysis of root architec- ture were conducted to evaluate the relationship between root architecture and P efficiency and its possible evolution- ary pattern. Our results found that: i) root architecture was closely related to P efficiency in soybean. Shallow root archi- tecture had better spatial configuration in the P-rich culti- vated soil layer hence higher P efficiency and soybean yield; ii) there was a possible co-evolutionary pattern among shoot type, root architecture and P efficiency. The bush cultivated soybean had a shallow root architecture and high P efficiency, the climbing wild soybean had a deep root architecture and low P efficiency, while the root architecture and P efficiency of semi-wild soybean were intermediate between cultivated and wild soybean; iii) P availability regulated root architec- ture. Soybean roots became shallower with P addition to the topsoil, indicating that the co-evolutionary relationship be- tween root architecture and P efficiency might be attributed to the long-term effects of topsoil fertilization. Our results could provide important theoretical basis for improving soy- bean root traits and P efficiency.展开更多
High-quality reservoirs occur in the middle-shallow horizons of the northern Songliao Basin. The distribution and genesis of their anomalously high porosity zones were studied using measured porosities, examination of...High-quality reservoirs occur in the middle-shallow horizons of the northern Songliao Basin. The distribution and genesis of their anomalously high porosity zones were studied using measured porosities, examination of ordinary thin sections and blue epoxy resin-impregnated thin sections and by SEM. The results show that there are three anomalously high porosity zones at the depth of 450-900 m, 1,300-1,900 m, 2,050-2,350 m respectively, named zone i, zone ii and zone iii from top to bottom. Horizontally, zone i and zone ii are distributed all over the basin except in the Southeastern Uplift, while zone iii is only distributed in the Central Depression. Zone i was formed by meteoric water leaching as well as organic acid dissolution. Zones ii and iii were dominantly formed by organic acid dissolution. Additionally, clay mineral transformation generating H＋ and hydrocarbon emplacement retarding the cementation of sandstones are also important for the formation of zones ii and iii.展开更多
Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of th...Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of the two coaxial rotors both become worse because of the aerodynamic interaction between them, and the influence of the top rotor on the bottom rotor is greater than that of the bottom rotor on the top rotor. The downwash velocity at the bottom rotor plane is much larger than that at the top rotor plane, and the downwash velocity at the top rotor plane is a little larger than that at an individual rotor plane. The downwash velocity and thrust coefficient both become larger when the collective angle of blades is added. When the spacing between the two coaxial rotors increases, the thrust coefficient of the top rotor increases, but the total thrust coefficient reduces a little, because the decrease of the bottom rotor thrust coefficient is larger than the increase of the top rotor thrust coefficient.展开更多
Due to a lack of suitable minerals, the gas/oil emplacement ages have never been accurately obtained before. CH4-CO2-saline- bearing secondary inclusions are found in quartz from the volcanic rocks of the Yingcheng Fo...Due to a lack of suitable minerals, the gas/oil emplacement ages have never been accurately obtained before. CH4-CO2-saline- bearing secondary inclusions are found in quartz from the volcanic rocks of the Yingcheng Formation, the container rocks of the deep CO2 gas reservoir in the Songliao Basin. The inclusion fluid was trapped into microcracks in quartz during the gas em- placement and accumulation, providing an optimal target for the 40Ar-39Ar stepwise crushing technique to determine the CO2 gas emplacement age. 40Ar-39Ar dating results of a quartz sample by stepwise crushing yield a highly linear-regression isochron with an age of 78.4±1.3 Ma, indicating that the accumulation of the deep CO2 gas reservoir in the Songliao Basin occurred in the late Cretaceous. This is the first time to report an exact isotopic age for a CO2 gas reservoir, which indicates that the 40Ar-39Ar dating can serve as a new technique to date the oil/gas emplacement ages.展开更多
The 2015 Nobel Prize in Physiology or Medicine has been awarded to avermectins and artemisinin,respectively.Avermectins produced by Streptomyces avermitilis are excellent anthelmintic and potential antibiotic agents.B...The 2015 Nobel Prize in Physiology or Medicine has been awarded to avermectins and artemisinin,respectively.Avermectins produced by Streptomyces avermitilis are excellent anthelmintic and potential antibiotic agents.Because wild-type strains only produce low levels of avermectins,much research effort has focused on improvements in avermectin production to meet the ever increasing demand for such compounds.This review describes the strategies that have been widely employed and the future prospects of synthetic biology applications in avermectin yield improvement.With the help of genome sequencing of S.avermitilis and an understanding of the avermectin biosynthetic/regulatory pathways,synthetic and systems biotechnology approaches have been applied for precision engineering.We focus on the design and synthesis of biological chassis,parts,devices,and modules from diverse microbes to reconstruct and optimize their dynamic processes,as well as predict favorable effective overproduction of avermectins by a 4Ms strategy(Mine,Model,Manipulation,and Measurement).展开更多
Nerve guidance conduit （NGC） is a potential alternative to autologous nerve for peripheral nerve regeneration. A promising therapeutic strategy is to modify the nerve guidance conduit intraluminal microenvironment u...Nerve guidance conduit （NGC） is a potential alternative to autologous nerve for peripheral nerve regeneration. A promising therapeutic strategy is to modify the nerve guidance conduit intraluminal microenvironment using physical and/or chemical guidance cues. In this study, a neurotrophic peptide-functionalized self-assembling peptide nanofiber hydrogel that could promote PC12 cell adhesion, proliferation, and neuronal differentiation in vitro was prefilled in the lumen of a hollow chitosan tube （hCST） to accelerate axonal regeneration in a rat sciatic nerve defect model. The functionalized self-assembling peptide was developed by introducing a neurotrophic peptide （RGI, RGIDKRHWNSQ） derived from brain-derived neurotrophic factor （BDNF） to the C-terminus of the self-assembling peptide RADA16-I （Ac-（RADA）4-CONH2）. Morphological, histological, electrophysiological, and functional analyses demonstrated that the RGI-functionalized, self-assembling, peptide nanofiber hydrogel RAD/RGI could produce a neurotrophic microenvironment that markedly improved axonal regeneration with enhanced re-myelination and motor functional recovery.展开更多
This paper concerns problem of the delay-dependent robust stability and stabilizationfor uncertain neutral systems. Some new delay-dependent stability criteria are derived by takingthe relationship between the terms i...This paper concerns problem of the delay-dependent robust stability and stabilizationfor uncertain neutral systems. Some new delay-dependent stability criteria are derived by takingthe relationship between the terms in the Leibniz-Newton formula into account. Free weightingmatrices are given to express the relationship between the terms in the Leibniz-Newton formula andthe new criteria are based on linear matrix inequalities such that the free weighting matrices can beeasily obtained. Moreover, the stability criteria are also used to design the state-feedback controller.Numerical examples demonstrates that the proposed criteria are e?ective and are an improvementover the previous papers.展开更多
Nitrogen enrichment and land use are known to influence various ecosystems,but how these anthropogenic changes influence community and ecosystem responses to disturbance remains poorly understood.Here we investigated ...Nitrogen enrichment and land use are known to influence various ecosystems,but how these anthropogenic changes influence community and ecosystem responses to disturbance remains poorly understood.Here we investigated the effects of increased nitrogen input and mowing on the resistance and recovery of temperate semiarid grassland experiencing a three-year drought.Nitrogen addition increased grassland biomass recovery but decreased structural recovery after drought,whereas annual mowing increased grassland biomass recovery and structural recovery but reduced structural resistance to drought.The treatment effects on community biomass/structural resistance and recovery were largely modulated by the stability of the dominant species and asynchronous dynamics among species,and the community biomass resistance and recovery were also greatly driven by the stability of grasses.Community biomass resistance/recovery in response to drought was positively associated with its corresponding structural stability.Our study provides important experimental evidence that both nitrogen addition and mowing could substantially change grassland stability in both functional and structural aspects.Our findings emphasize the need to study changes across levels of ecological organization for a more complete understanding of ecosystem responses to disturbances under widespread environmental changes.展开更多
The problem of delay-dependent criteria for the robust stability of neutral systems with time-varying structured uncertainties and identi-cal neutral-delay and discrete-delay is concerned. A criterion for nominal syst...The problem of delay-dependent criteria for the robust stability of neutral systems with time-varying structured uncertainties and identi-cal neutral-delay and discrete-delay is concerned. A criterion for nominal systems is presented by taking the relationship between the terms in the Leibniz-Newton formula into account, which is described by some free-weighting matrices. In addition, this criterion is extended to robust stability of the systems with time-varying structured uncertainties. All of the criteria are based on linear matrix inequality such that it is easy to calculate the upper bound of the time-delay and the free-weighting matrices. Numerical examples illustrate the effectiveness and the improvement over the existing results.展开更多
In this paper, we consider Parallel Machines Scheduling with nonsimultaneous machine available time. We give the exact worst case performance bound of MLPT proposed by Lee. Furthermore, two other modified LPT algorith...In this paper, we consider Parallel Machines Scheduling with nonsimultaneous machine available time. We give the exact worst case performance bound of MLPT proposed by Lee. Furthermore, two other modified LPT algorithms are discussed. The paper is ended by numerical ex-periments of these algorithms.展开更多
Colloidal particles,heterogeneous mixture with various organic components and continuous molecular weight(MW)distribution,is omnipresent in lake sediments and substantially influence the retention,transportation,and f...Colloidal particles,heterogeneous mixture with various organic components and continuous molecular weight(MW)distribution,is omnipresent in lake sediments and substantially influence the retention,transportation,and fate of contaminants in lake ecosystem.We sampled and extracted sedimentary colloids from different ecology regions in Taihu Lake,Jiangsu,East China,in June 2020,and they were further separated into four different particle size ranges by tangent ultrafiltration,and the properties of colloids were studied in various methods,including zeta potential analysis,transmission electron micrograph images(TEM),Fourier transformation infrared(FTIR),and 3D fluorescence.Results show that the surface of the colloids is covered with organic macromolecular substances,such as humuslike substances and protein-like substances.There were significant differences in molecular weight and fraction content of colloids in the sediments from macrophyte-dominant(MD)area and algae-dominant(AD)area in the lake.Colloids from MD area are mainly composed of humic acid,protein,and fulvic acid;the content of fulvic acid is lower than that of humic acid and protein.The humic acid exists mainly in small molecular weight(10-100 kDa),protein exists in mainly large molecular weight colloids(0.45-1μm).Colloids from AD area are mainly composed of humic acid,and mainly distributed in the molecular weight(10 kDa-0.45μm).The presence of humic acid inhibits effectively the agglomeration of the colloids.Especially,the stability of colloids is closely related to the molecular weight,with low molecular weight from MD area show higher stability.The existence of humic acid in colloids increases the electrostatic repulsion between colloidal particles,which can effectively inhibit the agglomeration of colloids,thus enhancing the stability of colloids.Furthermore,both monovalent and divalent electrolytes enhance colloidal aggregation,and the low-molecular-weight(LMW)colloid fraction exhibits higher stability efficiency than the high-molecular-weight(HM展开更多
A method of unstructured dynamic overset grids is developed for the numerical simulation of helicopter unsteady rotorairframe aerodynamic interaction.For the effective treatment of the relative motion between the roto...A method of unstructured dynamic overset grids is developed for the numerical simulation of helicopter unsteady rotorairframe aerodynamic interaction.For the effective treatment of the relative motion between the rotor and the airframe,the domain of flowfield is divided into two overset subzones,namely,a rotational subzone containing the blades and a stationary subzone containing the airframe.The overset part of two subzones is used to convect the flow variables of the two zones.The Taylor series expansion is used to obtain a second-order spatial accuracy,and dual-time stepping is adopted to improve the solution accuracy.Mesh deformation from the blade motion in forward flight is treated by using a spring analogy.Validation is made by numerically simulating the flows around a wind tunnel configuration and comparing the predicted time-averaged and instantaneous inflow and airframe surface pressure distributions with the experimental data.It shows that the present method is efficient and robust for the prediction of complicated unsteady rotor-airframe aerodynamic interaction phenomena.展开更多
Nickel-based single crystal superalloys have become the main structural materials of the aero-engines due to excellent high-temperature strength.The micro defects evolution of nickel-based single crystal superalloys u...Nickel-based single crystal superalloys have become the main structural materials of the aero-engines due to excellent high-temperature strength.The micro defects evolution of nickel-based single crystal superalloys under shear deformation was investigated by molecular dynamics(MD)simulations in the present study.It is found that the interfacial dislocations decompose into Shockley dislocations under low shear stress,resulting in the plastic deformation of the Ni phase.The initial plastic deformation of the Ni3Al phase is caused by Shockley dislocations cutting into the Ni3Al phase.The following deformation from low temperature to medium temperature is controlled by dislocation slip,but the deformation at high temperature is changed.It is also found that the microvoid evolution can be divided into void growth and coalescence during shear deformation.The microvoid could prevent dislocation entanglement,accelerate dislocation decomposition,and promote earlier plastic deformation under relatively low temperatures.展开更多
Anatase TiO2 samples with different ratios of {101} to {001} facets were prepared with hydrothermal method and further treated under three specific calcination atmospheres (air,H2,N2).The characterization results indi...Anatase TiO2 samples with different ratios of {101} to {001} facets were prepared with hydrothermal method and further treated under three specific calcination atmospheres (air,H2,N2).The characterization results indicate that {001} facets may generate more oxygen vacancies and more Ti3+ species than {101} facets.展开更多
Gene therapy constitutes a promising strategy for the treatment of osteoarthritis (OA). We assessed the use of electroporation (EP) of non-viral gene vectors, and compared its efficacy with that of adeno-associated vi...Gene therapy constitutes a promising strategy for the treatment of osteoarthritis (OA). We assessed the use of electroporation (EP) of non-viral gene vectors, and compared its efficacy with that of adeno-associated virus (AAV) vectors. EP- and AAV-mediated delivery of human interleukin-1 receptor antagonist (hIL-1Ra) was localized performed in the joints of rats following induction of OA. mRNA levels for hIL-1Ra, IL-1β, TNF-α, MMP-13 and ADAMTS-4 in the cartilage and synovial tissues were analyzed. Structural analyses of the subchondral bone at the medial femoral condyle were performed by Micro-CT after treatment. Knee joint specimens were staining with hematoxylin and eosin and Saffron O. Induction of hIL-1Ra by both EP and AAV inhibited inflammatory-induced sub-chondral bone reconstruction, and effectively suppressed IL-1β activity, as evidenced by decreased expression of MMP-13 and ADAMTS-4. Histological analyses revealed significant protection of cartilage, proteoglycan by EP and AAV. hIL-1Ra expression was similar in both the EP and AAV groups. Notably, this gene is not easier degraded transduced by EP compared with AAV. Taken together, these results show that EP offers transfection efficiency comparable to that of AAV, with the potential for longer gene expression, making EP a promising candidate for efficient non-viral delivery of OA gene therapy.展开更多
Nickel-based superalloys have become the critical materials of micro-parts depending on outstanding mechanical properties.The effects of the grain size and precipitates on the mechanical properties at the mesoscopic s...Nickel-based superalloys have become the critical materials of micro-parts depending on outstanding mechanical properties.The effects of the grain size and precipitates on the mechanical properties at the mesoscopic scale are difficult to be revealed using conventional macroscopic material constitutive models.In the present study,the microstructure evolution of the γ" phase and the tensile mechanical properties of a nickel-based superalloy at the mesoscopic scale were investigated systematically.Three variants of γ" phases precipitated corresponding to [00],[00] and [001] orientations of the matrix y phase.The quantitative statistics results showed that as the aging time increases,the particle size and volume fraction of the γ~" phase increase.As the grain size increases,the flow stress decreases due to the dwindling of grain boundary strengthening.Furthermore,the precipitation strengthening of γ" and γ" phases induces the increase of flow stress.An important conclusion is drawn that the size effect at the mesoscopic scale depends not only on the sample size and grain size but also on the particle size and volume fraction of the precipitates.The established constitutive model which considers grain boundary strengthening,precipitation strengthening and solid solution strengthening can accurately describe the flow stress characteristics of nickel-based superalloys at the mesoscopic scale.展开更多
Background:Soil microbial communities cope with an imbalanced supply of resources by adjusting their element acquisition and utilization strategies.Although soil pH has long been considered an essential driver of micr...Background:Soil microbial communities cope with an imbalanced supply of resources by adjusting their element acquisition and utilization strategies.Although soil pH has long been considered an essential driver of microbial growth and community composition,little is known about how soil acidification affects microbial acquisition and utilization of carbon(C)and nitrogen(N).To close the knowledge gap,we simulated soil acidification and created a pH gradient by adding eight levels of elemental sulfur(S)to the soil in a meadow steppe.Results:We found that S-induced soil acidification strongly enhanced the ratio of fungi to bacteria(F:B)and microbial biomass C to N(MBC:MBN)and subsequently decreased the C:N imbalance between microbial biomass and their resources.The linear decrease in the C:N imbalance with decreasing soil pH implied a conversion from N limitation to C limitation.To cope with enhanced C versus N limitation,soil microbial communities regulated the relative production of enzymes by increasing the ratio ofβ-glucosidase(BG,C-acquiring enzyme)to leucine aminopeptidase(LAP,N-acquiring enzyme),even though both enzymatic activities decreased with S addition.Structural equation modeling(SEM)suggested that higher C limitation and C:N-acquiring enzyme stimulated microbial carbon-use efficiency(CUE),which counteracted the negative effect of metal stress(i.e.,aluminum and manganese)under soil acidification.Conclusions:Overall,these results highlight the importance of stoichiometric controls in microbial adaption to soil acidification,which may help predict soil microbial responses to future acid deposition.展开更多
A series of mesoporous Nb and Nb-W oxides were employed as highly active solid acid catalysts for the con- version of glucose to 5-hydroxymethylfurfural （HMF）. The results of solid state 31p MAS NMR spectroscopy wit...A series of mesoporous Nb and Nb-W oxides were employed as highly active solid acid catalysts for the con- version of glucose to 5-hydroxymethylfurfural （HMF）. The results of solid state 31p MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Bronsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb-W oxides varied with the ratio of Bronsted to Lewis acid sites and high glucose conversion was observed over NbsW5 and NbTWs oxides with high ratios of Bronsted to Lewis acid sites. All Nb-W oxides show a relatively high selectivity of HMF, whereas no HMF forms over sulfuric acid due to its pure Bronsted acidity. The results indicate fast isom- erization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Bronsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2-butanol/H2O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over NbTW3 oxide. The 2-butanol/H2O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb5W5 oxide.展开更多
Group recommendations derive from a phenomenon in which people tend to participate in activities together regardless of whether they are online or in reality,which creates real scenarios and promotes the development o...Group recommendations derive from a phenomenon in which people tend to participate in activities together regardless of whether they are online or in reality,which creates real scenarios and promotes the development of group recommendation systems.Different from traditional personalized recommendation methods,which are concerned only with the accuracy of recommendations for individuals,group recommendation is expected to balance the needs of multiple users.Building a proper model for a group of users to improve the quality of a recommended list and to achieve a better recommendation has become a large challenge for group recommendation applications.Existing studies often focus on explicit user characteristics,such as gender,occupation,and social status,to analyze the importance of users for modeling group preferences.However,it is usually difficult to obtain extra user information,especially for ad hoc groups.To this end,we design a novel entropy-based method that extracts users’implicit characteristics from users’historical ratings to obtain the weights of group members.These weights represent user importance so that we can obtain group preferences according to user weights and then model the group decision process to make a recommendation.We evaluate our method for the two metrics of recommendation relevance and overall ratings of recommended items.We compare our method to baselines,and experimental results show that our method achieves a significant improvement in group recommendation performance.展开更多
文摘In the present study, we constructed an “ap- plied core collection” for phosphorus (P) efficiency of soy- bean germplasm using a GIS-assisted approach. Systematic characterization and comparative analysis of root architec- ture were conducted to evaluate the relationship between root architecture and P efficiency and its possible evolution- ary pattern. Our results found that: i) root architecture was closely related to P efficiency in soybean. Shallow root archi- tecture had better spatial configuration in the P-rich culti- vated soil layer hence higher P efficiency and soybean yield; ii) there was a possible co-evolutionary pattern among shoot type, root architecture and P efficiency. The bush cultivated soybean had a shallow root architecture and high P efficiency, the climbing wild soybean had a deep root architecture and low P efficiency, while the root architecture and P efficiency of semi-wild soybean were intermediate between cultivated and wild soybean; iii) P availability regulated root architec- ture. Soybean roots became shallower with P addition to the topsoil, indicating that the co-evolutionary relationship be- tween root architecture and P efficiency might be attributed to the long-term effects of topsoil fertilization. Our results could provide important theoretical basis for improving soy- bean root traits and P efficiency.
基金supported by the National Natural ScienceFoundation (Grant No. 40872076)
文摘High-quality reservoirs occur in the middle-shallow horizons of the northern Songliao Basin. The distribution and genesis of their anomalously high porosity zones were studied using measured porosities, examination of ordinary thin sections and blue epoxy resin-impregnated thin sections and by SEM. The results show that there are three anomalously high porosity zones at the depth of 450-900 m, 1,300-1,900 m, 2,050-2,350 m respectively, named zone i, zone ii and zone iii from top to bottom. Horizontally, zone i and zone ii are distributed all over the basin except in the Southeastern Uplift, while zone iii is only distributed in the Central Depression. Zone i was formed by meteoric water leaching as well as organic acid dissolution. Zones ii and iii were dominantly formed by organic acid dissolution. Additionally, clay mineral transformation generating H＋ and hydrocarbon emplacement retarding the cementation of sandstones are also important for the formation of zones ii and iii.
基金China Postdoctoral Science Foundation (20100481368)National Key Laboratory Foundation of China
文摘Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of the two coaxial rotors both become worse because of the aerodynamic interaction between them, and the influence of the top rotor on the bottom rotor is greater than that of the bottom rotor on the top rotor. The downwash velocity at the bottom rotor plane is much larger than that at the top rotor plane, and the downwash velocity at the top rotor plane is a little larger than that at an individual rotor plane. The downwash velocity and thrust coefficient both become larger when the collective angle of blades is added. When the spacing between the two coaxial rotors increases, the thrust coefficient of the top rotor increases, but the total thrust coefficient reduces a little, because the decrease of the bottom rotor thrust coefficient is larger than the increase of the top rotor thrust coefficient.
基金supported by the National Natural Science Foundation of China (40772080)Daqing Oilfield Company Ltd (DQYT-1201002-2006-JS-11351)
文摘Due to a lack of suitable minerals, the gas/oil emplacement ages have never been accurately obtained before. CH4-CO2-saline- bearing secondary inclusions are found in quartz from the volcanic rocks of the Yingcheng Formation, the container rocks of the deep CO2 gas reservoir in the Songliao Basin. The inclusion fluid was trapped into microcracks in quartz during the gas em- placement and accumulation, providing an optimal target for the 40Ar-39Ar stepwise crushing technique to determine the CO2 gas emplacement age. 40Ar-39Ar dating results of a quartz sample by stepwise crushing yield a highly linear-regression isochron with an age of 78.4±1.3 Ma, indicating that the accumulation of the deep CO2 gas reservoir in the Songliao Basin occurred in the late Cretaceous. This is the first time to report an exact isotopic age for a CO2 gas reservoir, which indicates that the 40Ar-39Ar dating can serve as a new technique to date the oil/gas emplacement ages.
基金the National Program on Key Basic Research Project(973 program,2013CB734000 and 2012CB725203)the National Natural Science Foundation of China(31170095,31000057,and 31100075)+1 种基金the Ministry of Science and Technology of the People’s Republic of China(2011ZX11102-011-11 and 2013ZX10005004-005)China Ocean Mineral Resources R&D Association(DY125-15-T-07)。
文摘The 2015 Nobel Prize in Physiology or Medicine has been awarded to avermectins and artemisinin,respectively.Avermectins produced by Streptomyces avermitilis are excellent anthelmintic and potential antibiotic agents.Because wild-type strains only produce low levels of avermectins,much research effort has focused on improvements in avermectin production to meet the ever increasing demand for such compounds.This review describes the strategies that have been widely employed and the future prospects of synthetic biology applications in avermectin yield improvement.With the help of genome sequencing of S.avermitilis and an understanding of the avermectin biosynthetic/regulatory pathways,synthetic and systems biotechnology approaches have been applied for precision engineering.We focus on the design and synthesis of biological chassis,parts,devices,and modules from diverse microbes to reconstruct and optimize their dynamic processes,as well as predict favorable effective overproduction of avermectins by a 4Ms strategy(Mine,Model,Manipulation,and Measurement).
文摘Nerve guidance conduit （NGC） is a potential alternative to autologous nerve for peripheral nerve regeneration. A promising therapeutic strategy is to modify the nerve guidance conduit intraluminal microenvironment using physical and/or chemical guidance cues. In this study, a neurotrophic peptide-functionalized self-assembling peptide nanofiber hydrogel that could promote PC12 cell adhesion, proliferation, and neuronal differentiation in vitro was prefilled in the lumen of a hollow chitosan tube （hCST） to accelerate axonal regeneration in a rat sciatic nerve defect model. The functionalized self-assembling peptide was developed by introducing a neurotrophic peptide （RGI, RGIDKRHWNSQ） derived from brain-derived neurotrophic factor （BDNF） to the C-terminus of the self-assembling peptide RADA16-I （Ac-（RADA）4-CONH2）. Morphological, histological, electrophysiological, and functional analyses demonstrated that the RGI-functionalized, self-assembling, peptide nanofiber hydrogel RAD/RGI could produce a neurotrophic microenvironment that markedly improved axonal regeneration with enhanced re-myelination and motor functional recovery.
文摘This paper concerns problem of the delay-dependent robust stability and stabilizationfor uncertain neutral systems. Some new delay-dependent stability criteria are derived by takingthe relationship between the terms in the Leibniz-Newton formula into account. Free weightingmatrices are given to express the relationship between the terms in the Leibniz-Newton formula andthe new criteria are based on linear matrix inequalities such that the free weighting matrices can beeasily obtained. Moreover, the stability criteria are also used to design the state-feedback controller.Numerical examples demonstrates that the proposed criteria are e?ective and are an improvementover the previous papers.
基金supported by the National Natural Science Foundation of China(32060284,31870441)the Natural Science Foundation of Inner Mongolia,China(2019JQ04)+2 种基金the Central Government Guides the Local Science and Technology Development Foundation(2020ZY0027)the National Science Foundation of the United States(DEB-1856318,CBET-1833988)the Natural Science Foundation of Hebei Province(C2022201042)。
文摘Nitrogen enrichment and land use are known to influence various ecosystems,but how these anthropogenic changes influence community and ecosystem responses to disturbance remains poorly understood.Here we investigated the effects of increased nitrogen input and mowing on the resistance and recovery of temperate semiarid grassland experiencing a three-year drought.Nitrogen addition increased grassland biomass recovery but decreased structural recovery after drought,whereas annual mowing increased grassland biomass recovery and structural recovery but reduced structural resistance to drought.The treatment effects on community biomass/structural resistance and recovery were largely modulated by the stability of the dominant species and asynchronous dynamics among species,and the community biomass resistance and recovery were also greatly driven by the stability of grasses.Community biomass resistance/recovery in response to drought was positively associated with its corresponding structural stability.Our study provides important experimental evidence that both nitrogen addition and mowing could substantially change grassland stability in both functional and structural aspects.Our findings emphasize the need to study changes across levels of ecological organization for a more complete understanding of ecosystem responses to disturbances under widespread environmental changes.
文摘The problem of delay-dependent criteria for the robust stability of neutral systems with time-varying structured uncertainties and identi-cal neutral-delay and discrete-delay is concerned. A criterion for nominal systems is presented by taking the relationship between the terms in the Leibniz-Newton formula into account, which is described by some free-weighting matrices. In addition, this criterion is extended to robust stability of the systems with time-varying structured uncertainties. All of the criteria are based on linear matrix inequality such that it is easy to calculate the upper bound of the time-delay and the free-weighting matrices. Numerical examples illustrate the effectiveness and the improvement over the existing results.
文摘In this paper, we consider Parallel Machines Scheduling with nonsimultaneous machine available time. We give the exact worst case performance bound of MLPT proposed by Lee. Furthermore, two other modified LPT algorithms are discussed. The paper is ended by numerical ex-periments of these algorithms.
基金Supported by the National Natural Science Foundation of China(Nos.42007332,51979137)the Natural Science Foundation of Jiangsu Province(No.20KJB610001)。
文摘Colloidal particles,heterogeneous mixture with various organic components and continuous molecular weight(MW)distribution,is omnipresent in lake sediments and substantially influence the retention,transportation,and fate of contaminants in lake ecosystem.We sampled and extracted sedimentary colloids from different ecology regions in Taihu Lake,Jiangsu,East China,in June 2020,and they were further separated into four different particle size ranges by tangent ultrafiltration,and the properties of colloids were studied in various methods,including zeta potential analysis,transmission electron micrograph images(TEM),Fourier transformation infrared(FTIR),and 3D fluorescence.Results show that the surface of the colloids is covered with organic macromolecular substances,such as humuslike substances and protein-like substances.There were significant differences in molecular weight and fraction content of colloids in the sediments from macrophyte-dominant(MD)area and algae-dominant(AD)area in the lake.Colloids from MD area are mainly composed of humic acid,protein,and fulvic acid;the content of fulvic acid is lower than that of humic acid and protein.The humic acid exists mainly in small molecular weight(10-100 kDa),protein exists in mainly large molecular weight colloids(0.45-1μm).Colloids from AD area are mainly composed of humic acid,and mainly distributed in the molecular weight(10 kDa-0.45μm).The presence of humic acid inhibits effectively the agglomeration of the colloids.Especially,the stability of colloids is closely related to the molecular weight,with low molecular weight from MD area show higher stability.The existence of humic acid in colloids increases the electrostatic repulsion between colloidal particles,which can effectively inhibit the agglomeration of colloids,thus enhancing the stability of colloids.Furthermore,both monovalent and divalent electrolytes enhance colloidal aggregation,and the low-molecular-weight(LMW)colloid fraction exhibits higher stability efficiency than the high-molecular-weight(HM
基金supported by the Basic Research Program of Northwestern Polytechnical University (Grant No. JC201219)the Postdoctoral Science Foundation of China (Grant No. 20100481368)
文摘A method of unstructured dynamic overset grids is developed for the numerical simulation of helicopter unsteady rotorairframe aerodynamic interaction.For the effective treatment of the relative motion between the rotor and the airframe,the domain of flowfield is divided into two overset subzones,namely,a rotational subzone containing the blades and a stationary subzone containing the airframe.The overset part of two subzones is used to convect the flow variables of the two zones.The Taylor series expansion is used to obtain a second-order spatial accuracy,and dual-time stepping is adopted to improve the solution accuracy.Mesh deformation from the blade motion in forward flight is treated by using a spring analogy.Validation is made by numerically simulating the flows around a wind tunnel configuration and comparing the predicted time-averaged and instantaneous inflow and airframe surface pressure distributions with the experimental data.It shows that the present method is efficient and robust for the prediction of complicated unsteady rotor-airframe aerodynamic interaction phenomena.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52175306,52205347)the Natural Science Foundation of Shandong Province(Grant No.ZR2021QE181)the China Postdoctoral Science Foundation(Grant No.2022M712432)。
文摘Nickel-based single crystal superalloys have become the main structural materials of the aero-engines due to excellent high-temperature strength.The micro defects evolution of nickel-based single crystal superalloys under shear deformation was investigated by molecular dynamics(MD)simulations in the present study.It is found that the interfacial dislocations decompose into Shockley dislocations under low shear stress,resulting in the plastic deformation of the Ni phase.The initial plastic deformation of the Ni3Al phase is caused by Shockley dislocations cutting into the Ni3Al phase.The following deformation from low temperature to medium temperature is controlled by dislocation slip,but the deformation at high temperature is changed.It is also found that the microvoid evolution can be divided into void growth and coalescence during shear deformation.The microvoid could prevent dislocation entanglement,accelerate dislocation decomposition,and promote earlier plastic deformation under relatively low temperatures.
基金This work was supported by the National Natural Science Foundation of China (Nos. 21673046, 91645201)the National Key R&D Program of China (No. 2017YFB0602204).
文摘Anatase TiO2 samples with different ratios of {101} to {001} facets were prepared with hydrothermal method and further treated under three specific calcination atmospheres (air,H2,N2).The characterization results indicate that {001} facets may generate more oxygen vacancies and more Ti3+ species than {101} facets.
文摘Gene therapy constitutes a promising strategy for the treatment of osteoarthritis (OA). We assessed the use of electroporation (EP) of non-viral gene vectors, and compared its efficacy with that of adeno-associated virus (AAV) vectors. EP- and AAV-mediated delivery of human interleukin-1 receptor antagonist (hIL-1Ra) was localized performed in the joints of rats following induction of OA. mRNA levels for hIL-1Ra, IL-1β, TNF-α, MMP-13 and ADAMTS-4 in the cartilage and synovial tissues were analyzed. Structural analyses of the subchondral bone at the medial femoral condyle were performed by Micro-CT after treatment. Knee joint specimens were staining with hematoxylin and eosin and Saffron O. Induction of hIL-1Ra by both EP and AAV inhibited inflammatory-induced sub-chondral bone reconstruction, and effectively suppressed IL-1β activity, as evidenced by decreased expression of MMP-13 and ADAMTS-4. Histological analyses revealed significant protection of cartilage, proteoglycan by EP and AAV. hIL-1Ra expression was similar in both the EP and AAV groups. Notably, this gene is not easier degraded transduced by EP compared with AAV. Taken together, these results show that EP offers transfection efficiency comparable to that of AAV, with the potential for longer gene expression, making EP a promising candidate for efficient non-viral delivery of OA gene therapy.
基金supported financially by the Training Program of the Major Research Plan of the National Natural Science Foundation of China(No.91860129)the National Natural Science Foundation of China(No.51575129)+1 种基金the Key Research and Development Program of Shandong Province(No.2016GGX102026)the Fundamental Research Funds for the Central Universities(No.HIT.NSRIF.2017064)。
文摘Nickel-based superalloys have become the critical materials of micro-parts depending on outstanding mechanical properties.The effects of the grain size and precipitates on the mechanical properties at the mesoscopic scale are difficult to be revealed using conventional macroscopic material constitutive models.In the present study,the microstructure evolution of the γ" phase and the tensile mechanical properties of a nickel-based superalloy at the mesoscopic scale were investigated systematically.Three variants of γ" phases precipitated corresponding to [00],[00] and [001] orientations of the matrix y phase.The quantitative statistics results showed that as the aging time increases,the particle size and volume fraction of the γ~" phase increase.As the grain size increases,the flow stress decreases due to the dwindling of grain boundary strengthening.Furthermore,the precipitation strengthening of γ" and γ" phases induces the increase of flow stress.An important conclusion is drawn that the size effect at the mesoscopic scale depends not only on the sample size and grain size but also on the particle size and volume fraction of the precipitates.The established constitutive model which considers grain boundary strengthening,precipitation strengthening and solid solution strengthening can accurately describe the flow stress characteristics of nickel-based superalloys at the mesoscopic scale.
基金supported by the National Natural Science Foundation of China(31870441,32071563,and 31800398)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA23080400)the Key State Research&Development Program of China(2016YFC0500601).
文摘Background:Soil microbial communities cope with an imbalanced supply of resources by adjusting their element acquisition and utilization strategies.Although soil pH has long been considered an essential driver of microbial growth and community composition,little is known about how soil acidification affects microbial acquisition and utilization of carbon(C)and nitrogen(N).To close the knowledge gap,we simulated soil acidification and created a pH gradient by adding eight levels of elemental sulfur(S)to the soil in a meadow steppe.Results:We found that S-induced soil acidification strongly enhanced the ratio of fungi to bacteria(F:B)and microbial biomass C to N(MBC:MBN)and subsequently decreased the C:N imbalance between microbial biomass and their resources.The linear decrease in the C:N imbalance with decreasing soil pH implied a conversion from N limitation to C limitation.To cope with enhanced C versus N limitation,soil microbial communities regulated the relative production of enzymes by increasing the ratio ofβ-glucosidase(BG,C-acquiring enzyme)to leucine aminopeptidase(LAP,N-acquiring enzyme),even though both enzymatic activities decreased with S addition.Structural equation modeling(SEM)suggested that higher C limitation and C:N-acquiring enzyme stimulated microbial carbon-use efficiency(CUE),which counteracted the negative effect of metal stress(i.e.,aluminum and manganese)under soil acidification.Conclusions:Overall,these results highlight the importance of stoichiometric controls in microbial adaption to soil acidification,which may help predict soil microbial responses to future acid deposition.
文摘A series of mesoporous Nb and Nb-W oxides were employed as highly active solid acid catalysts for the con- version of glucose to 5-hydroxymethylfurfural （HMF）. The results of solid state 31p MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Bronsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb-W oxides varied with the ratio of Bronsted to Lewis acid sites and high glucose conversion was observed over NbsW5 and NbTWs oxides with high ratios of Bronsted to Lewis acid sites. All Nb-W oxides show a relatively high selectivity of HMF, whereas no HMF forms over sulfuric acid due to its pure Bronsted acidity. The results indicate fast isom- erization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Bronsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2-butanol/H2O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over NbTW3 oxide. The 2-butanol/H2O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb5W5 oxide.
基金This study is funded by the National Natural Science Foundation of China(Nos.61862013,61662015,U1811264,and U1711263)Guangxi Natural Science Foundation of China(Nos.2018GXNSFAA281199 and 2017GXNSFAA198035)+1 种基金Guangxi Key Laboratory of Automatic Measurement Technology and Instrument(No.YQ19109)Guangxi Key Laboratory of Trusted Software(No.kx201915).
文摘Group recommendations derive from a phenomenon in which people tend to participate in activities together regardless of whether they are online or in reality,which creates real scenarios and promotes the development of group recommendation systems.Different from traditional personalized recommendation methods,which are concerned only with the accuracy of recommendations for individuals,group recommendation is expected to balance the needs of multiple users.Building a proper model for a group of users to improve the quality of a recommended list and to achieve a better recommendation has become a large challenge for group recommendation applications.Existing studies often focus on explicit user characteristics,such as gender,occupation,and social status,to analyze the importance of users for modeling group preferences.However,it is usually difficult to obtain extra user information,especially for ad hoc groups.To this end,we design a novel entropy-based method that extracts users’implicit characteristics from users’historical ratings to obtain the weights of group members.These weights represent user importance so that we can obtain group preferences according to user weights and then model the group decision process to make a recommendation.We evaluate our method for the two metrics of recommendation relevance and overall ratings of recommended items.We compare our method to baselines,and experimental results show that our method achieves a significant improvement in group recommendation performance.
