Nonlinear Impact Damage Evolution of Charpy Type and Analysis of Its Key Influencing Factors

The current research of Charpy impact mainly focuses on obtaining the ductile brittle transition temperature of materials by experiments.Compared with experiments,numerical simulation can study many problems with harsh conditions.However,there are still few studies on the influence of geometric factors such as side grooves.In this paper,the geometry of standard Charpy impact test is designed.Specimens with different widths and side grooves are tested.The finite element model of Charpy impact was established by ABAQUS software.Use test results and simulation results to verify each other.The effects of sample width,side groove depth and side groove bottom fillet on the impact fracture resistance of the sample were studied.The results show that the specimen width is positively correlated with the impact toughness of the specimen.The side groove greatly reduces the impact toughness of the material;the toughness of side groove decreases with the increase of depth;the fracture toughness of side groove decreases with the increase of fillet at the bottom of side groove.The proportion of toughness energy to impact energy of samples was analyzed.The results show that the toughness energy accounts for about 70%of the impact energy of the sample,which has little to do with the geometric characteristics of the sample.This study presents a reliable method for studying Charpy impact tests.The influence of geometric parameters is obtained,which provides a reference method for the study of impact toughness of high toughness materials.

Germination and early seedling growth of Pinus densata Mast.provenances

We studied seed germination and early seedling growth of Pinus densata to explore the range of variability within the species and to inform afforestation practices. Phenotypes were evaluated at a forest tree nursery under conditions that support Pinus yunnanensis, one of the presumed parental species of P. densata. Seeds were col- lected from 20 open-pollinated trees within each of eight autochthonous populations representing the natural distri- bution of P. densata in China to assess variation in ger- mination traits and early seedling growth, and to examine the relationships among these traits. Results showed that seeds from all populations germinated and seedlings established successfully. There were significant differences among populations in 13 of 14 traits evaluated. Seed germination and early seedling growth were strongly related to seed size and seed weight. Bigger seeds germi- nated earlier and faster than small seeds, and seedling size was positively correlated with seed size. Some germination traits were strongly and significantly correlated with cli- matic variables associated with the provenance of the studied populations. Based on these observations, we conclude there were large, significant, and biologically important differences among P. densata populations in seed germination and seedling growth traits. The observed variability probably reflects a high degree of adaptive dif- ferentiation among populations that is likely to be relevant for future afforestation.

The critical role of carbon in marrying silicon and graphite anodes for high-energy lithium-ion batteries

Increasing the energy density of conventional lithium-ion batteries(LIBs)is important for satisfying the demands of electric vehicles and advanced electronics.Silicon is considered as one of the most-promising anodes to replace the traditional graphite anode for the realization of high-energy LIBs due to its extremely high theoretical capacity,although its severe volume changes during lithiation/delithiation have led to a big challenge for practical application.In contrast,the co-utilization of Si and graphite has been well recognized as one of the preferred strategies for commercialization in the near future.In this review,we focus on different carbonaceous additives,such as carbon nanotubes,reduced graphene oxide,and pyrolyzed carbon derived from precursors such as pitch,sugars,heteroatom polymers,and so forth,which play an important role in constructing micrometersized hierarchical structures of silicon/graphite/carbon(Si/G/C)composites and tailoring the morphology and surface with good structural stability,good adhesion,high electrical conductivity,high tap density,and good interface chemistry to achieve high capacity and long cycling stability simultaneously.We first discuss the importance and challenge of the co-utilization of Si and graphite.Then,we carefully review and compare the improved effects of various types of carbonaceous materials and their associated structures on the electrochemical performance of Si/G/C composites.We also review the diverse synthesis techniques and treatment methods,which are also significant factors for optimizing Si/G/C composites.Finally,we provide a pertinent evaluation of these forms of carbon according to their suitability for commercialization.We also make far-ranging suggestions with regard to the selection of proper carbonaceous materials and the design of Si/G/C composites for further development.

Genetic structure of needle morphological and anatomical traits of Pinus yunnanensis

Pinus yunnanensis Franch. is an particular conifer tree species in Yunnan-Guizhou plateau in south- west China. The morphological and anatomical traits of needles are important to evaluate geographic variation and population dynamics of conifer species. Seedlings from seven populations of P. yunnanensis were analyzed, look- ing at 22 morphological and anatomical needle traits. The results showed that variations among and within popula- tions were significantly different for all traits and the variance components within populations were generally higher than that among populations in the most tested needle traits. The proportions of three-needle fascicle were significantly different among populations. The traits related to needle size in both morphology and anatomy were positive with latitude and negative with annual temperature and precipitation. Ratio indices, including mesophyllarea/vascular bundle area, mesophyll area/resin canals area, vascular bundle area/resin canals area and mesophyU area/（resin canals area and vascular bundle area）, were negatively correlated with elevation and positively corre- lated with the annual mean temperature, showing some fitness feature for the populations. Needle traits were more significantly correlated with longitude than with other four environmental factors. Needle length was significantly correlated with almost all environmental factors. First four principal components accounted for 81.596 % of the variation with eigenvalues 〉1; the differences among populations were mainly dependent on needle width, stomatal density, section areas of vascular bundle, total resin canals, and mesophyll, as well as area ratio traits. Seven populations were divided into three categories by Euclidean distance. Variations in needle traits among the populations have shown systematic microevolution in terms of geographic impact on P. yunnanensis. This study would provide empirical data to characterize adaptation and genetic variation of P. yunnanensis, which would be helpful for management of genetic resources and reason- able utilization of them in future.

Carbon‐based metal‐free catalysts for electrochemical CO2 reduction: Activity, selectivity, and stability

Zero or negative emissions of carbon dioxide(CO2)is the need of the times,as inexorable rising and alarming levels of CO2 in the atmosphere lead to global warming and severe climate change.The electrochemical CO2 reduction(eCO2R)to value‐added fuels and chemicals by using renewable electricity provides a cleaner and more sustainable route with economic benefits,in which the key is to develop clean and economical electrocatalysts.Carbon‐based catalyst materials possess desirable properties such as high offset potential for H2 evolution and chemical stability at the negative applied potential.Although it is still challenging to achieve highly efficient carbon‐based catalysts,considerable efforts have been devoted to overcoming the low selectivity,activity,and stability.Here,we summarize and discuss the recent progress in carbon‐based metal‐free catalysts including carbon nanotubes,carbon nanofibers,carbon nanoribbons,graphene,carbon nitride,and diamonds with an emphasis on their activity,product selectivity,and stability.In addition,the key challenges and future potential approaches for efficient eCO2R to low carbon‐based fuels are highlighted.For a good understanding of the whole history of the development of eCO2R,the CO2 reduction reactions,principles,and techniques including the role of electrolytes,electrochemical cell design and evaluation,product selectivity,and structural composition are also discussed.The metal/metal oxides decorated with carbon‐based electrocatalysts are also summarized.We aim to provide insights for further development of carbon‐based metal‐free electrocatalysts for CO2 reduction from the perspective of both fundamental understanding and technological applications in the future.

Quasi-Reversibility Regularization Method for Solving a Backward Heat Conduction Problem

Non-standard backward heat conduction problem is ill-posed in the sense that the solution(if it exists) does not depend continuously on the data. In this paper, we propose a regularization strategy-quasi-reversibility method to analysis the stability of the problem. Meanwhile, we investigate the roles of regularization parameter in this method. Numerical result show that our algorithm is effective and stable.

Fourier Truncation Method for Fractional Numerical Differentiation

We consider a ill-posed problem-fractional numerical differentiation with a new method. We propose Fourier truncation method to compute fractional numerical derivatives. A Holder-type stability estimate is obtained. A numerical implementation is described. Numerical examples show that the proposed method is effective and stable.

Practical assessment of the energy density of potassium-ion batteries

1 Introduction The evolution of modern human society closely depends on affordable,efficient,and safe energy storage systems.Today,lithium-ion batteries(LIBs)are the dominant energy storage systems to power portable electronics and a global push toward electric transportation and smart grids.

Recent progress in electrolyte design for advanced lithium metal batteries

Lithium metal batteries(LMBs)have attracted considerable interest for use in electric vehicles and as next-generation energy storage devices because of their high energy density.However,a significant practical drawback with LMBs is the instability of the Li metal/electrolyte interface,with concurrent parasitic reactions and dendrite growth,that leads to low Coulombic efficiency and poor cycle life.Owing to the significant role of electrolytes in batteries,rationally designed electrolytes can improve the electrochemical performance of LMBs and possibly achieve fast charge and a wide range of working temperatures to meet various requirements of the market in the future.Although there are some review papers about electrolytes for LMBs,the focus has been on a single parameter or single performance separately and,therefore,not sufficient for the design of electrolytes for advanced LMBs for a wide range of working environments.This review presents a systematic summary of recent progress made in terms of electrolytes,covering the fundamental understanding of the mechanism,scientific challenges,and strategies to address drawbacks of electrolytes for high-performance LMBs.The advantages and disadvantages of various electrolyte strategies are also analyzed,yielding suggestions for optimum properties of electrolytes for advanced LMBs applications.Finally,the most promising research directions for electrolytes are discussed briefly.

Synthesis and enhanced piezoelectric response of CVD-grown SnSe layered nanosheets for flexible nanogenerators

Piezoelectricity is the electric charge which accumulates in certain materials in response to mechanical stimuli,while piezoelectric nanogenerators(PENGs)converting mechanical energy into electricity can be widely used for energy harvesting and self-powered systems.The group IV-VI monochalcogenides may exhibit strong piezoelectricity because of their puckered C_(2v)symmetry and electronic structure,making them promising for flexible PENG.Herein,we investigated the synthesis and piezoelectric properties of multilayer SnSe nanosheets grown by chemical vapor deposition(CVD).The SnSe nanosheets exhibited high single-crystallinity,large area,and good stability.The strong layer-dependent in-plane piezoelectric coefficient of SnSe nanosheets showed a saturated trend to be~110 pm/V,which overcomes the weak piezoelectric response or odd-even effects in other layered nanosheets.A high energy conversion efficiency of 9.3%and a maximum power density of 538 mW/cm^(2)at 1.03%strain have been demonstrated in a SnSe-based PENG.Based on the enhanced piezoelectricity of SnSe and attractive output performance of the nanogenerator,a self-powered sensor for human motion monitoring is further developed.These results demonstrate the strong piezoelectricity in high quality CVD-grown SnSe nanosheets,allowing for application in flexible smart piezoelectric sensors and advanced microelectromechanical devices.

Challenges and prospects of lithium-CO_(2) batteries

The key role played by carbon dioxide in global temperature cycles has stimulated constant research attention on carbon capture and storage.Among the various options,lithium-carbon dioxide batteries are intriguing,not only for the transformation of waste carbon dioxide to value-added products,but also for the storage of electricity from renewable power resources and balancing the carbon cycle.The development of this system is still in its early stages and faces tremendous hurdles caused by the introduction of carbon dioxide.In this review,detailed discussion on the critical problems faced by the electrode,the interface,and the electrolyte is provided,along with the rational strategies required to address these problematic issues for efficient carbon dioxide fixation and conversion.We hope that this review will provide a resource for a comprehensive understanding of lithium-carbon dioxide batteries and will serve as guidance for exploring reversible and rechargeable alkali metal-based carbon dioxide battery systems in the future.

Improved algebraic method for linear continuous-time model identification

Recently a novel algebraic method was proposed for linear continuous-time model identification,which has attracted extensive attention in the literature.This work reveals its connection to classic identification methods,discusses a limitation and presents a useful modification of the method.The discussions are supported by analysis and numerical experiments.