Existence of asymptotically almost periodic solutions and stability properties for functional difference equations

For functional difference equations with unbounded delay,we characterized the existence of totally stable and asymptotically almost periodic solution by using stability properties of a bounded solution in a certain limiting equation.

Influence of roll speed difference on microstructure, texture and mechanical properties of 7075 aluminum plates produced via combined continuous casting and rolling process

The influences of the dissimilarity in the roll speeds on the microstructure, texture and mechanical properties of 7075 aluminum plates produced via combined continuous casting and rolling(CCCR) process were investigated. Several experiments were conducted with three different upper/lower roll rotational speed ratios(ω/ω0, ω is the upper roll rotational speed and ω0 is the lower roll rotational speed), namely 1:1, 1:1.2 and 1:1.4. It was found that the greatest dissimilarity in the roll speed(ω/ω0=1:1.4) improved the yield strength and ultimate tensile strength of 7075 Al plate in the rolling direction by 41.5% and 21.9%, respectively. Moreover, at a roll speed ratio of ω/ω0=1:1.4, the average grain size was decreased by 36% whereas the mean hardness of the transverse cross-section of the finally rolled plate was increased by about 9.2%. Texture studies also revealed that the more the difference in the roll speeds was, the greater the isotropy and the hardness of the final product were. Nevertheless, conducting CCCR operation with different roll speeds resulted in about 6% reduction in the elongation of the deformed plate.

SOME GEOMETRIC PROPERTIES OF A NEW DIFFERENCE SEQUENCE SPACE INVOLVING LACUNARY SEQUENCES

In this paper, we define a new generalized difference sequence space involving lacunary sequence. Then, we examine k-NUC property and property （β） for this space and also show that it is not rotund where p = （pr） is a bounded sequence of positive real numbers with pr ≥ 1 for all r ∈ N.

The difference analysis of physical-mechanical properties of sediments in the central South Yellow Sea and Zhe-Min coastal area in China

The difference analysis of physical-mechanical properties of muddy sediments is made in the central South Yellow Sea and the Zhe-Min（Zhejiang Province to Fujian Province of China） coastal area. The results show that sediments in the two regions are both dominated by mud. There are perfect negative power function correlations between the water content and the density, the compression coefficient and the compression modulus; a good positive power function correlation between the liquid limit and the plastic limit, a perfect positive linear correlation between the water content and the void ratio, and a perfect polynomial function correlation between the miniature vane shear strength and the pocket penetration resistance. In general, compared with sediments in the Zhe-Min coastal area, sediments in the central South Yellow Sea possess high water content, high void ratio,low density, high plasticity, high compressibility, low shear strength. The causes of the differences between physical-mechanical properties of sediments are analyzed from the topographic features, material sources,hydrodynamic conditions, deposition rate, and material composition. Compared with the Zhe-Min coastal area,the central South Yellow Sea is far from the Mainland and low-lying; has poor hydrodynamic condition; the materials diffused to the area are less and dominated by fine clay, have the high content of smectite and organic matters. These factors lead to sediments of the central South Yellow Sea has the higher water content, the higher plasticity, the lower density, and the lower strength than sediments in the Zhe-Min coastal area.

DIFFERENCE DISCRETE SYSTEM OF EULER-BEAM WITH ARBITRARY SUPPORTS AND SIGN-OSCILLATORY PROPERTY OF STIFFNESS MATRICES

The difference discrete system of Euler-beam with arbitrary supports was constructed by using the two order central difference formulas. This system is equivalent to the spring-mass-rigidrod model. By using the theory of oscillatory matrix, the signoscillatory property of stiffness matrices of this system was proved, and the necessary and sufficient condition for the system to be positive was obtained completely.

Spatial and Temporal Differences of Urban Land Comprehensive Carrying Capacity in Guangxi

The comprehensive carrying capacity of urban land can reflect the re- source level, economic scale, social development and environmental pressure of ur- ban land carrying. The assessment indicator system of urban land comprehensive carrying capacity was constructed from the 4 aspects of resource, economy, society, environment, and principal component analysis and cluster analysis were used to evaluate the urban land comprehensive carrying capacity of Guangxi and the 14 cities in 2005-2014, and analyzed its spatial and temporal characteristics as well as the driving forces, with the aim to provide references for improving the urban land comprehensive carrying capacity. The results showed that, the overall urban land comprehensive carrying capacity in Guangxi increased in 2005-2014, and there were significant differences in the land comprehensive carrying capacities among the cities in Guangxi in 2005-2014, in which Liuzhou, Guilin, Nanning belonged to the regions with the highest carrying capacity, while Beihai, Yulin, Wutong belonged to the regions with high carrying capacity, and the carrying capacities of the other cities changed with the changes of time. The economic development degree was an important factor influencing urban land comprehensive carrying capacity, but could not directly represent the urban land comprehensive carrying capacity level.

Nutrient resorption and its influencing factors of typical desert plants in different habitats on the northern margin of the Tarim Basin, China

The resorption of nutrients from senescent leaves allows plants to conserve and recycle nutrients. To explore the adaptation strategies of desert plants to nutrient-limited environments, we selected four typical desert plants(Populus euphratica Oliv., Tamarix ramosissima Ledeb., Glycyrrhiza inflata Batal., and Alhagi camelorum Fisch.) growing in the desert area of the northern margin of the Tarim Basin,China. The contents of nitrogen(N), phosphorus(P), potassium(K), calcium(Ca), magnesium(Mg), and Ferrum(Fe) in the leaves of these four typical desert plants and their resorption characteristics were analyzed. The relationship of nutrient resorption efficiency with leaf functional traits and soil physical-chemical properties in two different habitats(saline-alkali land and sandy land) was discussed.The results showed that the four plants resorbed most of the elements. Ca was enriched in the leaves of P.euphratica, G. inflate, and A. camelorum;Mg was enriched in the leaves of G. inflata;and Fe was enriched in the leaves of the four plants. The results of the redundancy analysis showed that leaf thickness, soil electrical conductivity, and soil P content were the major factors affecting the nutrient resorption efficiency of the four plants. Leaf thickness was negatively correlated with N resorption efficiency(NRE),P resorption efficiency, and Fe resorption efficiency;soil electrical conductivity was positively correlated with the resorption efficiency of most elements;and soil P content was negatively correlated with the resorption efficiency of most elements in the plant leaves. The results showed that soil physical-chemical properties and soil nutrient contents had an important impact on the nutrient resorption of plant leaves.The same species growing in different habitats also differed in their resorption of different elements. The soil environment of plants and the biological characteristics of plant leaves affected the resorption of nutrient elements in different plants. The purpose of this study is to provide small-scale data support for the protection of ecosystems in nutrient-deficient areas by studying leaf functional strategies and nutrient conservation mechanisms of several typical desert plants.

Analysis of regular and chaotic dynamics of the Euler-Bernoulli beams using finite difference and finite element methods

Chaotic vibrations of flexible non-linear Euler-Bernoulli beams subjected to harmonic load and with various boundary conditions（symmetric and non-symmetric）are studied in this work.Reliability of the obtained results is verified by the finite difference method（FDM）and the finite element method（FEM）with the Bubnov-Galerkin approximation for various boundary conditions and various dynamic regimes（regular and non-regular）.The influence of boundary conditions on the Euler-Bernoulli beams dynamics is studied mainly,dynamic behavior vs.control parameters { ωp,q0 } is reported,and scenarios of the system transition into chaos are illustrated.

Techniques for improving computational speed in numerical simulation of casting thermal stress based on finite difference method

Finite difference method (FDM) was applied to simulate thermal stress recently, which normally needs a long computational time and big computer storage. This study presents two techniques for improving computational speed in numerical simulation of casting thermal stress based on FDM, one for handling of nonconstant material properties and the other for dealing with the various coefficients in discretization equations. The use of the two techniques has been discussed and an application in wave-guide casting is given. The results show that the computational speed is almost tripled and the computer storage needed is reduced nearly half compared with those of the original method without the new technologies. The stress results for the casting domain obtained by both methods that set the temperature steps to 0.1 ℃ and 10 ℃, respectively are nearly the same and in good agreement with actual casting situation. It can be concluded that both handling the material properties as an assumption of stepwise profile and eliminating the repeated calculation are reliable and effective to improve computational speed, and applicable in heat transfer and fluid flow simulation.

Physicochemical difference of coffee beans with different species,production areas and roasting degrees

In recent decades,the demand for coffee has seen a continuous increase,and the aroma and flavor of coffee has been widely studied.The current research chose coffee beans of two species(Coffea arabica and C.canephora)from five production areas(Brazil,India,Indonesia,Uganda and Vietnam)with four different roasting degrees(medium light,medium,medium dark and dark),to investigate the difference on physicochemical properties.The results showed that Arabica coffee beans had higher concentrations of fat and organic acids,and total amount of volatile compounds,whereas Robusta beans had higher concentrations of protein.With the increase of roasting degree,the concentrations of protein,fat,organic acids,and the total amount of volatile compounds of coffee beans increased,while the concentrations of chlorogenic acid compounds decreased.The discriminant analysis indicated that the tested coffee beans could be clearly discriminated by species and roasting degrees,but not by production area.The results of this research conclude the physicochemical difference of Arabica and Robusta beans with different roasting degrees.The results can provide a theoretical basis for coffee bean selection for the relevant industries.

Effects of cooling rate on microstructure and mechanical properties of A357 alloy during differential pressure casting process

The microstructure and mechanical properties of A357 alloy under differential pressure casting process with different casting mould materials were studied. The results show that by using SiO2 resin sand the grain size is biggest and the tensile and elongation are the lowest, while the grain size is the smallest and the tensile strength and elongation are the highest when the chill is used, and the grain size, tensile strength and elongation of A357 alloy with SiC resin sand mould are in the middle. Furthermore, the results also demonstrate that for thin wall castings during differential pressure casting processes the grain size, tensile strength and elongation are different at different positions corresponding to the same casting mould material, while at the position of gating the grain size is the smallest and the tensile strength and elongation have the highest values. At the position of edge the grain size, the tensile strength and elongation take the second place. However, in the middle of the thin wall castings the grain size is coarsest and the tensile strength and elongation are the lowest.

Relationship Between Soil Properties and Different Fractions of Soil Hg

Correlation and path analysis methods were used to study the relationship between soil properties and the distribution of different soil Hg fractions with nine representative soils from Chongqing, China. Results showed that clay (< 2 m) could increase water-soluble Hg (r = 0.700*). Soil organic matter (OM) could enhance the increase of elemental Hg (r = 0.674*). The higher the base saturation percentage (BSP), the more the residual Hg (T = 0.684*). Organic Hg, the sum of acid-soluble organic Hg and alkali-soluble Hg, was positively affected by silt (2-20 μm) but negatively affected by pH, with the direct path coefficients amounting to 1.0487 and 0.5121, respectively. The positive effect of OM and negative effect of BSP on organic Hg were the most significant, with the direct path coefficients being 0.7614 and -0.8527, respectively. The indirect effect of clay (< 2 μm) via BSP (path coefficient = 0.4186) was the highest, showing that the real influencing factor in the effect of clay (< 2 μm) on acid-soluble organic Hg was BSP. Since the available Hg fraction, water-soluble Hg, was positively affected by soil clay content, and the quite immobile and not bioavailable residual Hg by soil BSP, suitable reduction of clay content and increase of BSP would be of much help to reduce the Hg availability and Hg activity in Hg-contaminated soils.

Microstructure and mechanical properties of laser beam welding 6061 aluminum alloy with different states

With the diversification of manufacture methods, joining the same materials with different states becomes indispensable in practical application. In present work, 6061 aluminum alloys with different states were welded by laser beam welding （LBW）. The microstructures of welded joint, before and after heat treating, were investigated. The mechanical properties, such as the tensile properties and microhardness , were tested. And the fracture characteristic was observed by means of scanning electron microscope （SEM）. The results show that the 6061 aluminum alloys have superior weldability and the microstructures are different significantly in different states. Besides, the grain boundaries of the joint microstructures become unclear after the heat treating. The strength and the elongations of welded joints could reach to those of the base metal. The tensile fracture occurs in the fusion zone and near 6061-0 alloy. And the fracture presents ductile rupture. Therefore, the LBW is an effective method for 6061 aluminum alloy.

Preparation of patterned boron nanowire films with different widths of unit-cell and their field emission properties

Large-area patterned films of boron nanowires（BNWs） are fabricated at various densities by chemical vapor deposition（CVD）. Different widths of unit-cell of Mo masks are used as templates. The widths of unit-cell of Mo masks are100 μm, 150 μm, and 200 μm, respectively. The distance between unit cells is 50 μm. The BNWs have an average diameter of about 20 nm and lengths of 10 μm–20 μm. High-resolution transmission electron microscopy analysis shows that each nanowire has a β-tetragonal structure with good crystallization. Field emission measurements of the BNW films show that their turn-on electric fields decrease with width of unit-cell increasing.

Synthesis of Different TiO2 Nanostructures and Their Physical Properties

Titanium dioxide （TiO2） nanosheet, nanorod and nanotubes are synthesized using chemical vapor deposition （CVD） and anodizing processes. TiO2 nanosheets are grown on Ti foil which is coated with Au catalyst in CVD, TiO2 nanorods are synthesized on treated Ti foil with HCl by CVD, and TiO2 nanotubes are prepared by the three-step anodization method. Scanning electron microscopy shows the final TiO2 structures prepared using three processes with three different morphologies of nanosheet, nanorod and nanotube. X-ray diffraction verifies the presence of TiO2. TiO2 sheets and rods are crystalized in rutile phase, and TiO2 tubes after annealing turn into the anatase crystal phase. The optical investigations carried out by diffuse reflection spectroscopy reveal that the morphology of TiO2 nanostructures influencing their optical response and band gap energy of TiO2 is changed for different TiO2 nanostructures.

Study on Vegetation Characteristics & Soil Properties of Secondary Grassland in Farmland Areas Abandoned for Different Years in Minqin Oasis

[Objectives]This study was conducted to investigate the vegetation community characteristics and soil properties of secondary grassland in abandoned farmland areas of different years in Minqin Oasis. [Methods] By the method of space-for-time substitution, the changes of vegetation community characteristics(species composition, structural characteristics and important values) and soil microbial and enzyme activity were determined, and the correlation between various soil factors was analyzed. [Results](1) There were 39 species belonging to 32 genera of 15 families in the research area, including 8 shrub plants, 15 perennial herbs and 16 annual herbs.(2) Soil microbial biomass carbon, nitrogen and phosphorus contents were higher in the upper layer than in the lower layer, and the phenomenon of “surface aggregation” was obvious. The differences were different with the change of abandoned years.(3) Soil catalase content was the highest among different plots, and soil phosphatase, sucrase and urease all showed a trend of fluctuating decline with the increase in abandoned years. Soil enzyme changes were different in different soil layers. [Conclusions] This study can provide a theoretical basis for the restoration, reconstruction and rational protection and utilization of secondary grassland in abandoned farmland.

Various Chemical Properties of Carbon Isotopes in Natural Synthesis of Different Compounds

The previously unknown different chemical properties of carbon isotopes in natural processes of synthesis-formation of different carbon-containing compounds,in particular of the more difficult(13C)carbon isotope in the processes of synthesis of solid carbon-containing compounds:carbonates,diamonds and,respectively,lighter(12C)synthetic isotopes,including methane have been established.

“一带一路”倡议与全球价值链升级——基于沿线国家的实证数据

基于2007—2020年“一带一路”沿线国家的样本数据,利用多期双重差分模型实证检验了“一带一路”倡议对沿线国家的价值链升级作用。研究结果证实:“一带一路”倡议对于沿线国家全球价值链发展具有显著正向影响。机制分析表明:“一带一路”倡议对沿线国家存在“虹吸效应”,有利于沿线国家的发展。此外,政策沟通对于倡议的推行具有积极的促进作用。研究结果不仅证实了倡议对于沿线国家价值链升级的正向影响,也论证了其中存在的影响机制,为未来进一步的研究提供了理论支撑和有益探索。

农牧交错区不同撂荒年限对农田土壤的影响

为研究撂荒年限对农田土壤的影响,本试验于8月植物生长旺季进行,选取未撂荒农田(CK)、撂荒7年(7a)、15年(15a)和30年(30a)的农田采集土壤样品,室内计算分析土壤理化特征的变化规律,结果表明,撂荒显著提高了土壤容重,降低了土壤孔隙度和土壤pH。与未撂荒地对比,撂荒显著提高了土壤有机碳(Soil organic carbon,SOC)、全氮(Soil total nitrogen,TN)和全磷(Soil total phosphorus,TP)的含量。因此,长期撂荒对土壤养分状况具有显著改善作用。不同撂荒年限土壤含水量与土壤养分指标均呈显著正相关,长期撂荒下更少的蒸散耗水量减少了土壤水分的损失,使土壤养分得到了积累。本研究可为坝上农牧交错带撂荒地的合理规划提供理论支撑。

知识产权政策对制造业市场竞争力的影响

基于知识产权示范城市政策的准实验,利用2009—2020年中国沪深A股上市制造业企业的数据,结合三重差分模型考察知识产权保护政策对制造行业的企业市场竞争力的作用。研究发现:知识产权示范城市设立对不同制造行业的企业竞争力的影响具有差异性,高技术行业的竞争力相较于传统行业得到进一步提升;对于低股权集中度、国有性质以及大规模等特征的制造业企业,其影响存在差异。进一步分析发现,知识产权示范城市政策能够通过缓解融资约束、影响运营成本以及提高关键技术创新能力推动不同制造行业市场竞争力出现差异性变化。据此提出强化知识产权保护制度建设、完善知识产权服务体系、扶持关键核心技术创新联盟等政策建议。