A total of 128 Simao pine trees （Pinus kesiya var. langbianensis） from three regions of Pu＇er City, Yunnan Province, People＇s Republic of China, were destructively sampled to obtain tree aboveground biomass （AGB...A total of 128 Simao pine trees （Pinus kesiya var. langbianensis） from three regions of Pu＇er City, Yunnan Province, People＇s Republic of China, were destructively sampled to obtain tree aboveground biomass （AGB）. Tree variables such as diameter at breast height and total height, and topographical factors such as altitude, aspect of slope, and degree of slope were recorded. We considered the region and site quality classes as the ran- dom-effects, and the topographic variables as the fixed- effects. We fitted a total of eight models as follows： least- squares nonlinear models （BM）, least-squares nonlinear models with the topographic factors （BMT）, nonlinear mixed-effects models with region as single random-effects （NLME-RE）, nonlinear mixed-effects models with site as single random-effects （NLME-SE）, nonlinear mixed-ef- fects models with the two-level nested region and site random-effects （TLNLME）, NLME-RE with the fixed-ef- fects of topographic factors （NLMET-RE）, NLME-SE with the fixed-effects of topographic factors （NLMET-SE）, and TLNLME with the fixed-effects of topographic factors （TLNLMET）. The eight models were compared by modelfitting and prediction statistics. The results showed： model fitting was improved by considering random-effects of region or site, or both. The models with the fixed-effects of topographic factors had better model fitting. According to AIC and BIC, the model fitting was ranked as TLNLME 〉 NLMET-RE 〉 NLME-RE.〉 NLMET-SE 〉 TLNLMET 〉 NLME-SE 〉 BMT 〉 BM. The differences among these models for model prediction were small. The model pre- diction was ranked as TLNLME 〉 NLME-RE 〉 NLME- SE 〉 NLMET-RE 〉 NLMET-SE 〉 TLNLMET 〉 BMT 〉 BM. However, all eight models had relatively high prediction precision （〉90 %）. Thus, the best model should be chosen based on the available data when using the model to predict individual tree AGB.展开更多
Characteristics of the precipitate α″-Fe16N2 phase have been investigated by X-ray diffraction and TEM analysis. VSM measurements give the saturation magnetization of the α″ phase.
Oriented attachment of nanocrystals is an important route to constructing epitaxially-connected nanocrystal superlattices for various applications.During oriented attach me nt of semic on ductor nano crystals,neck can...Oriented attachment of nanocrystals is an important route to constructing epitaxially-connected nanocrystal superlattices for various applications.During oriented attach me nt of semic on ductor nano crystals,neck can be formed betwee n nan ocrystals and it strongly influe nces the properties of the resulting superlattice.However,the neck formation mechanism is poorly understood.Here,we use in situ liquid cell transmission electro n microscopy(TEM)to directly observe the initiatio n and growth of homoepitaxial n ecks betwee n PbSe nano crystals with atomic details.We find that neck initiatio n occurs slowly(~10 s)whe n two nano crystals approach to each other within an edge-to-edge dista nee of 0.6 nm.During neck initiation,Pb and Se atoms defuse from other facets into the gap,forming"dynamic reversible"filaments.Once the filament(n eck)width is larger than a critical size of 0.9 nm,it gradually(15 s)widens into a 3-nm-wide n eck.The atomic structure of the neck is further obtained using ex situ aberration-corrected seanning TEM imaging.Neck initiation and growth mechanisms are elucidated with density functional theory calculati ons.Our direct unveiling of the atomic pathways of neck formatio n duri ng oriented attach me nt shed light into the fabrication of nanocrystal superlattices with improved structural order and electronic properties.展开更多
Thermoelectric materials, which can convert waste heat into electricity, have received increasing research interest in recent years. This paper describes the recent progress in thermoelectric nanocomposites based on s...Thermoelectric materials, which can convert waste heat into electricity, have received increasing research interest in recent years. This paper describes the recent progress in thermoelectric nanocomposites based on solution-synthesized nanoheterostructures. We start our discussion with the strategies of improving the power factor of a given material by using nanoheterostructures. Then we discuss the methods of decreasing thermal conductivity. Finally, we highlight a way of decoupling power factor and thermal conductivity, namely, incorporating phase-transition materials into a nanowire heterostructure. We have explored the lead telluride-copper telluride thermoelectric nanowire heterostructure in this work. Future possible ways to improve the figure of merit are discussed at the end of this paper.展开更多
The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of view.Spherulite structures with radial fibrillar branches hav...The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of view.Spherulite structures with radial fibrillar branches have been found in various solids;however,their growth mechanisms remain poorly understood.Here,we report real time imaging of the formation of two-dimensional(2D)iron oxide spherulite nanostructures in a liquid cell using transmission electron microscopy(TEM).By tracking the growth trajectories,we show the characteristics of the reaction front and growth kinetics.Our observations reveal that the tip of a growing branch splits as the width exceeds certain sizes(5.5–8.5 nm).The radius of a spherulite nanostructure increases linearly with time at the early stage,transitioning to nonlinear growth at the later stage.Furthermore,a thin layer of solid is accumulated at the tip and nanoparticles from secondary nucleation also appear at the growing front which later develop into fibrillar branches.The spherulite nanostructure is polycrystalline with the co-existence of ferrihydrite and Fe3O4 through-out the growth.A growth model is further established,which provides rational explanations on the linear growth at the early stage and the nonlinearity at the later stage of growth.展开更多
基金supported by National Natural Science Foundation of China(Grant No.3116015731560209)Application Fundamental Research Plan Project of Yunnan Province,China(Grant No.2012FD027)
文摘A total of 128 Simao pine trees （Pinus kesiya var. langbianensis） from three regions of Pu＇er City, Yunnan Province, People＇s Republic of China, were destructively sampled to obtain tree aboveground biomass （AGB）. Tree variables such as diameter at breast height and total height, and topographical factors such as altitude, aspect of slope, and degree of slope were recorded. We considered the region and site quality classes as the ran- dom-effects, and the topographic variables as the fixed- effects. We fitted a total of eight models as follows： least- squares nonlinear models （BM）, least-squares nonlinear models with the topographic factors （BMT）, nonlinear mixed-effects models with region as single random-effects （NLME-RE）, nonlinear mixed-effects models with site as single random-effects （NLME-SE）, nonlinear mixed-ef- fects models with the two-level nested region and site random-effects （TLNLME）, NLME-RE with the fixed-ef- fects of topographic factors （NLMET-RE）, NLME-SE with the fixed-effects of topographic factors （NLMET-SE）, and TLNLME with the fixed-effects of topographic factors （TLNLMET）. The eight models were compared by modelfitting and prediction statistics. The results showed： model fitting was improved by considering random-effects of region or site, or both. The models with the fixed-effects of topographic factors had better model fitting. According to AIC and BIC, the model fitting was ranked as TLNLME 〉 NLMET-RE 〉 NLME-RE.〉 NLMET-SE 〉 TLNLMET 〉 NLME-SE 〉 BMT 〉 BM. The differences among these models for model prediction were small. The model pre- diction was ranked as TLNLME 〉 NLME-RE 〉 NLME- SE 〉 NLMET-RE 〉 NLMET-SE 〉 TLNLMET 〉 BMT 〉 BM. However, all eight models had relatively high prediction precision （〉90 %）. Thus, the best model should be chosen based on the available data when using the model to predict individual tree AGB.
文摘Characteristics of the precipitate α″-Fe16N2 phase have been investigated by X-ray diffraction and TEM analysis. VSM measurements give the saturation magnetization of the α″ phase.
文摘Oriented attachment of nanocrystals is an important route to constructing epitaxially-connected nanocrystal superlattices for various applications.During oriented attach me nt of semic on ductor nano crystals,neck can be formed betwee n nan ocrystals and it strongly influe nces the properties of the resulting superlattice.However,the neck formation mechanism is poorly understood.Here,we use in situ liquid cell transmission electro n microscopy(TEM)to directly observe the initiatio n and growth of homoepitaxial n ecks betwee n PbSe nano crystals with atomic details.We find that neck initiatio n occurs slowly(~10 s)whe n two nano crystals approach to each other within an edge-to-edge dista nee of 0.6 nm.During neck initiation,Pb and Se atoms defuse from other facets into the gap,forming"dynamic reversible"filaments.Once the filament(n eck)width is larger than a critical size of 0.9 nm,it gradually(15 s)widens into a 3-nm-wide n eck.The atomic structure of the neck is further obtained using ex situ aberration-corrected seanning TEM imaging.Neck initiation and growth mechanisms are elucidated with density functional theory calculati ons.Our direct unveiling of the atomic pathways of neck formatio n duri ng oriented attach me nt shed light into the fabrication of nanocrystal superlattices with improved structural order and electronic properties.
文摘Thermoelectric materials, which can convert waste heat into electricity, have received increasing research interest in recent years. This paper describes the recent progress in thermoelectric nanocomposites based on solution-synthesized nanoheterostructures. We start our discussion with the strategies of improving the power factor of a given material by using nanoheterostructures. Then we discuss the methods of decreasing thermal conductivity. Finally, we highlight a way of decoupling power factor and thermal conductivity, namely, incorporating phase-transition materials into a nanowire heterostructure. We have explored the lead telluride-copper telluride thermoelectric nanowire heterostructure in this work. Future possible ways to improve the figure of merit are discussed at the end of this paper.
基金supported by the National Natural Science Foundation of China(51420105003,11327901,61601116 and 61974021)the National Science Fund for Distinguished Young Scholars(11525415)China Scholarship Council(201806090114)。
基金This project was supported by the U.S.Department of Energy(DOE),Office of Science,Office of Basic Energy Sciences(BES),Materials Sciences and Engineering Division under Contract No.DE-AC02-05-CH11231 within the in-situ TEM(KC22ZH)program.Work at the Molecular Foundry was supported by the Office of Science,Office of Basic Energy Sciences,of the U.S.Department of Energy under Contract No.DE-AC02-05CH11231.We acknowledge Gatan Inc.for the advanced K2 IS camera and Dr.Ming Pan and Dr.Cory Czarnik for their help with part of experimental set up in this work.W.J.Z.acknowledges the support from Tianjin University Graduate School International Academic Exchange Fund.M.R.H.was funded by KAUST project under H.M.Z.at UC Berkeley.
文摘The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of view.Spherulite structures with radial fibrillar branches have been found in various solids;however,their growth mechanisms remain poorly understood.Here,we report real time imaging of the formation of two-dimensional(2D)iron oxide spherulite nanostructures in a liquid cell using transmission electron microscopy(TEM).By tracking the growth trajectories,we show the characteristics of the reaction front and growth kinetics.Our observations reveal that the tip of a growing branch splits as the width exceeds certain sizes(5.5–8.5 nm).The radius of a spherulite nanostructure increases linearly with time at the early stage,transitioning to nonlinear growth at the later stage.Furthermore,a thin layer of solid is accumulated at the tip and nanoparticles from secondary nucleation also appear at the growing front which later develop into fibrillar branches.The spherulite nanostructure is polycrystalline with the co-existence of ferrihydrite and Fe3O4 through-out the growth.A growth model is further established,which provides rational explanations on the linear growth at the early stage and the nonlinearity at the later stage of growth.
