The Negative Thermal Expansion Property of NdMnO_(3) Based on Pores Effect and Phase Transition

A novel negative thermal expansion(NTE) material NdMnO_(3) was synthesized by solid-state method at 1 523 K. The crystal structure, phase transition, pores effect and negative expansion properties of NdMnO_(3) were investigated by variable temperature X-ray diffraction(XRD), scanning electron microscope(SEM) and variable temperature Raman spectra. The compound exhibits NTE properties in the orderly O' phase crystal structure. When the temperature is from 293 to 759 K, the ceramic NdMnO_(3) shows negative thermal expansion of-4.7×10^(-6)/K. As temperature increases, the ceramic NdMnO_(3) presents NTE property range from 759 to 1 007 K. The average linear expansion coefficient is-18.88×10^(-6)/K. The physical mechanism of NTE is discussed and clarified through experiments.

Semi-analytical solution for drained expansion analysis of a hollow cylinder of critical state soils

The expansion of a thick-walled hollow cylinder in soil is of non-self-similar nature that the stress/deformation paths are not the same for different soil material points.As a result,this problem cannot be solved by the common self-similar-based similarity techniques.This paper proposes a novel,exact solution for rigorous drained expansion analysis of a hollow cylinder of critical state soils.Considering stress-dependent elastic moduli of soils,new analytical stress and displacement solutions for the nonself-similar problem are developed taking the small strain assumption in the elastic zone.In the plastic zone,the cavity expansion response is formulated into a set of first-order partial differential equations(PDEs)with the combination use of Eulerian and Lagrangian descriptions,and a novel solution algorithm is developed to efficiently solve this complex boundary value problem.The solution is presented in a general form and thus can be useful for a wide range of soils.With the new solution,the non-self-similar nature induced by the finite outer boundary is clearly demonstrated and highlighted,which is found to be greatly different to the behaviour of cavity expansion in infinite soil mass.The present solution may serve as a benchmark for verifying the performance of advanced numerical techniques with critical state soil models and be used to capture the finite boundary effect for pressuremeter tests in small-sized calibration chambers.

Magneto-volume effect in Fe_(n)Ti_(13-n)clusters during thermal expansion

Ab initio molecular dynamics calculations have been carried out to search for the ground state structure of Fe_(n)Ti_(13-n)clusters and measure the thermal expansion of Fe_(n)Ti_(13-n).The volume of Fe_(n)Ti_(13-n)clusters during thermal expansion is jointly determined by anharmonic interaction and magneto-volume effect.It has been found that Fe_(6)Ti_(7),Fe_9Ti_(4),Fe_(11)Ti_(2),and Fe_(13)clusters can exhibit the remarkable magneto-volume effect with abnormal volume behaviors and magnetic moment behaviors during thermal expansion.A prerequisite for the magneto-volume effect of Fe_(n)Ti_(13-n)clusters during thermal expansion has been revealed and the magnitude of the magneto-volume is also approximately determined.Furthermore,the magneto-volume behaviors of Fe_(n)Ti_(13-n)clusters are qualitatively characterized by the energy contour map.Our results shed light on the mechanism of the magneto-volume effect in Fe_(n)Ti_(13-n)clusters during thermal expansion,which can guide the design of nanomaterials with zero expansion or even controllable expansion properties.

Fractional derivative statistical damage model of unsaturated expansive soil based on unified hydraulic effect

Unsaturated expansive soil is widely distributed in China and has complex engineering properties.This paper proposes the unified hydraulic effect shear strength theory of unsaturated expansive soil based on the effective stress principle,swelling force principle,and soil–water characteristics.Considering the viscoelasticity and structural damage of unsaturated expansive soil during loading,a fractional hardening–damage model of unsaturated expansive soil was established.The model parameters were established on the basis of the proposed calculation method of shear strength and the triaxial shear experiment on unsaturated expansive soil.The proposed model was verified by the experimental data and a traditional damage model.The proposed model can satisfactorily describe the entire process of the strain-hardening law of unsaturated expansive soil.Finally,by investigating the damage variables of the proposed model,it was found that:(a)when the values of confining pressure and matric suction are close,the coupling of confining pressure and matric suction contributes more to the shear strength;(b)there is a damage threshold for unsaturated expansive soil,and is mainly reflected by strength criterion of infinitesimal body;(c)the strain hardening law of unsaturated expansive soil is mainly reflected by fractional derivative operator.

Effect of residual interface stress on effective thermal expansion coefficient of particle-filled thermoelastic nanocomposite

The surface/interface energy theory based on three configurations proposed by Huang et al. is used to study the effective properties of thermoelastic nanocomposites. The particular emphasis is placed on the discussion of the influence of the residual inter- face stress on the thermal expansion coefficient of a thermoelastic composite filled with nanoparticles. First, the thermo-elastic interface constitutive relations expressed in terms of the first Piola-Kirchhoff interface stress and the Lagrangian description of the gen- eralized Young-Laplace equation are presented. Second, the Hashin＇s composite sphere assemblage （CSA） is taken as the representative volume element （RVE）, and the residual elastic field induced by the residual interface stress in this CSA at reference configuration is determined. Elastic deformations in the CSA from the reference configuration to the current configuration are calculated. Prom the above calculations, analytical expressions of the effective bulk modulus and the effective thermal expansion coefficient of thermoelastic composite are derived. It is shown that the residual interface stress has a significant effect on the thermal expansion properties of thermoelastic nanocomposites.

Aerodynamic Optimization of the Expansion Section in a Hypersonic Quiet Nozzle Based on Favorable Pressure Effect

Maximum expansion angle is the primary parameter for the design of expansion section of hypersonic quiet nozzle. According to the quantity of maximum expansion angle, expansion section could be classified as fast expansion and slow expansion. In order to diminish the effect of instability of Görtler vortex, gradually, slow expansion was employed for quiet nozzle design. Based on the favorable pressure effect, the maximum expansion angle is optimized in this paper, and a considerable selective session of maximum expansion angle is obtained. The trend that slow expansion is employed instead of fast expansion is explained, and a new method is established for aerodynamic optimization of expansion section contour in a quiet nozzle.

A New Approach: About the Appearance of “Dark Matter” Effects in the Process of Expansion of the Universe*

The paper considers cosmological objects belonging to fundamentally different classes that do not intersect with each other. Firstly, these are objects that make up a pure Hubble stream. Secondly, these are objects that have constant proper distances. These include planets, stars, and galaxies in gravitationally coupled systems. They all do not participate in the Hubble stream as independent objects. It is shown that the commoving reference system and proper reference system standardly used in cosmology change places with each other when switching from considering Hubble objects to “planets”. The features of the evolution (more precisely, devolution, degradation, reverse development) of the latter were analyzed and it was found that the cosmological acceleration of all “planets”, in contrast to Hubble objects, coincides in order of magnitude with the fundamental value of H2R. As applied to the Pioneers anomaly, this approach allowed us to obtain the calculated value of cosmological acceleration, which coincides in order of magnitude with the observed value. It seems that this approach is applicable also to other local gravitationally coupled systems and allows us to explain the characteristic flattened shape of the orbital curves of stars and galaxies by the fact that the influence of the fundamental cosmological acceleration H2R is added to the system’s own gravitational field.

Economic Effects of China’s Import Expansion Strategy

Since 2018,China has enacted a string of policy initiatives to increase imports.To quantify this import expansion strategy’s economic effects,we created a large numerical general equilibrium model and quantitatively simulated the economic effects of the reductions of tariff and non-tariff barriers on China and other economies.Our simulation results show that overall,China’s import expansion strategy benefited both itself and others and contributed to employment,welfare,and trade growth in China and the rest of the world.In relative terms,however,China’s import expansion strategy benefited other countries more than it did itself and contributed more to the growth of the world economy.Additionally,the import expansion strategy may effectively promote China’s trade balance,and the trade equilibrium effect driven by the reduction of non-tariff barriers is more significant than that of tariff barriers.Furthermore,regarding the self-benefiting effects of import expansion,the effects of nontariff measures are significantly greater than those of tariff measures,and this result has policy implications for China’s import expansion strategy going forward.

Anomalous thermal expansion and enhanced magnetocaloric effect in<001>-textured Mn_(x)Fe_(5-x)Si_(3) alloys

The development of zero and negative therma expansion(i.e.,ZTE and NTE)materials is of crucial importance to the control of undesirable thermal expansion for high-precision devices.In the present work,ZTE and NTE were obtained in directionally-solidified Mn_(x)Fe_(5-x)Si_(3)alloys with a strong<001>texture,in striking contrast to positive thermal expansion in their isotropic counterparts Magnetometry and in-situ X-ray diffraction(XRD)measurements were performed to uncover the origin of the anomalous thermal expansion.Magnetic measurements indicate a strong easy-plane magnetocrystalline anisotropy in the textured samples,where the magnetic moments are aligned within the ab plane of the hexagonal structure Temperature-dependent XRD on the x=1 sample reveals a ZTE character in the ab plane that is coupled to a ferromagnetic transition.As a result,the macroscopic ZTE(~0.22×10^(-6)K^(-1))in the x=1 sample can be attributed to the microscopic magneto volume effect within the ab plane,which is realized by the introduction of the<001>-textured microstructure.Besides,the competition between antiferromagnetic and ferromagnetic exchange coupling leads to NTE in textured x=1.5 and 2 samples.Additionally,textured x=1 sample displays enhanced magnetocaloric properties as compared to the conventional counterparts with randomly-oriented grains.Consequently this work demonstrates a new strategy toward the exploration of anomalous thermal expansion properties as well as the enhancement of magnetocaloric properties for materials with a strong magnetocrystalline anisotropy.

EQUIVALENT MODEL OF EXPANSION OF CEMENT MORTAR UNDER SULPHATE EROSION

The expansion property of cement mortar under the attack of sulfate ions is studied by experimental and theoretical methods. First, cement mortars are fabricated with the ratio of water to cement of 0.4, 0.6, and 0.8. Secondly, the expansion of specimen immerged in sulphate solution is measured at different times. Thirdly, a theoretical model of expansion of cement mortar under sulphate erosion is suggested by virtue of represent volume element method. In this model, the damage evolution due to the interaction between delayed ettringite and cement mortar is taken into account. Finally, the numerical calculation is results indicate that the model perfectly describes performed. The numerical and experimental the expansion of the cement mortar.

Inhibition effect of swelling characteristics of expansive soil using cohesive non-swelling soil layer under unidirectional seepage

Cohesive non-swelling soil(CNS)cushion technology is widely used to solve swelling deformation problems in expansive soil areas.However,the swelling inhibition mechanism is still not fully understood.In this study,the inhibition effect on expansive soil using a CNS layer was studied by performing five types of laboratory model tests under unidirectional seepage.The results showed that CNS cushion technology produced a sound inhibition effect on the swelling characteristics of expansive soil.It was shown that the cations in the CNS layer moved downward and accumulated on the surface of solids and produced an electrical environment inside the expansive soil.In this process,the adsorbed hydrated cations participated in ion exchange with the expansive soil,leading to the modification effect on its swelling potential.Meanwhile,the adsorbed water membrane surrounding the expansive soil aggregates formed by the hydrated cations obstructed further adsorption of water molecules,which inhibited the swelling development of expansive soil.Therefore,the swelling inhibition mechanism can be attributed to three factors:(i)modification effect,(ii)electrical environment,and(iii)deadweight of the CNS layer.The combined contribution of modification effect and electrical environment can be considered as an electric charge effect,which mainly controls the swelling characteristics of expansive soil.

Evaluation of Gallium Arsenide Thermal Expansion Coefficient by Extended X-Ray Absorption Fine Structure

Negative thermal expansion of gallium arsenide has been investigated through temperature dependent Extended X-ray Absorption Fine Structure (EXAFS) measurements. The bond thermal expansion coefficient αbond has been evaluated and compared to negative expansion coefficient αtens due to tension effects. The overall thermal expansion coefficient is the sum?of?αbond?and αtens. Below 60 K, αtens is greater than αbond? yielding to a negative expansion in this temperature region. Tension effects are progressively overcome by the stretching effects in the region 60 - 300 K. The asymmetry of nearest neighbors distribution is not negligible since the gaussian approximation underestimates the bond expansion by about 0.00426 &#197;. This error decreases when the temperature is lowered. The accuracy in the thermal expansion evaluation and the connection between third cumulant and thermal expansion are discussed.

Relativistic Quantum Mechanical Condition for Expansion of the Universe

In this manuscript, we will discuss about the quantum mechanical system for the movement of non-intractable particle, non-intractable particle which attends every mass state in the universe, the form of a non-intractable particle is n = -m, this manuscript defines the stable cross system for the movement of n-i particles and elementary particles with a perfect black body at centre with proofs of picture of super massive black hole, the linear hamiltonian of the cross quantum mechanical system and with this, it’s co-related matrixes, then by the use of cross system of Non-Intractable Particles defining a new right angel theorem. Then the new black body relation free from plank constant depends on non interactive mechanics and m, which has already mentioned in non-interactive mechanics and it’s relation with galaxies. The unique property of cross system is that it is surrounded by the energy of 10e + e always, and at last the relation between zero point energy and dark energy.

数字化情境中的流通效率实现机制——基于匹配与扩张视角的案例研究

当前,快速发展的数字技术深刻影响了流通效率的实现。在数字化情境中探讨流通效率的微观实现机制,需要从流通的时空双重维度出发,将宏观层面的商品流通效率对应为企业在“匹配”和“扩张”的微观流通活动中的效率。采用追踪访谈的一手数据,基于韩都衣舍、酒仙网的案例,探讨了企业在数字化情境中的流通效率实现问题。研究发现:在“去中间化”路径中,数字化驱动了基于供应链整合的匹配效率实现和基于消费社群拓展的扩张效率实现,交叉网络效应与数据网络效应动态放大了这一作用;在“再中间化”路径中,数字化辅助了基于渠道纵向协作的匹配效率实现和基于店面连锁的扩张效率实现,用户网络效应与数据网络效应动态放大了这一作用。因此,承担流通活动的企业需结合自身对于流通渠道演化的路径选择,采取适配的数字化战略,以促进流通效率实现。

团聚体级配对固废改良膨胀土耐久性的影响

通过工业固废改良膨胀土团聚体的搅拌破碎试验以及破碎土的耐久性试验,揭示了团聚体尺寸效应对改良效果的影响,并分析了其影响机理.结果表明:掺入铁尾矿砂和电石渣能加速土团聚体在搅拌过程中的破碎;大粒径团聚体内部膨胀土的改良效果较差,容易产生裂隙;粒径大于15 mm的团聚体含量越高,试样的耐久性越差;相对于电石渣改良土,复合改良土的耐久性更好;对于应用于底基层的电石渣改良土和复合改良土,建议控制粒径大于15 mm土团聚体的含量分别小于2.5%和21.8%.

扩底桩竖向承载特性及群桩效应研究

为探明扩底群桩竖向承载特性,采用扩底桩筏结构,开展单桩(扩径比分别为1.5、2.0、2.5、3.0)和桩筏(扩径比为2)基础静载模型试验,分析其荷载传递规律,并建立桩间距为3.75、4.00、4.50、5.00倍桩直径时扩底桩筏基础有限元模型,研究桩间距对群桩效应影响。结果表明:扩底单桩和扩底桩筏结构荷载沉降曲线均为缓变型;扩底桩极限承载力随扩径比增大而逐渐增大,扩径比2.5~3.0时极限承载力增幅变缓,建议扩底桩扩径比取2.5~3.0;由于桩土共同沉降,桩间土压缩,桩土作用更充分,扩底桩筏基础中心桩侧摩阻力荷载分担比比扩底单桩增大了17.71%;群桩效应系数随桩间距增大而逐渐增大,桩间距为4.5~5.0倍桩直径时群桩效应系数增幅较小,群桩效应较弱,建议扩底桩筏基础桩间距取值不小于4.5倍桩直径。

中国降碳-减污-扩绿-增长协同发展空间关联网络特征及影响因素研究

协同推进降碳-减污-扩绿-增长已成为我国经济社会发展全面绿色转型的必然选择。基于我国30个省份面板数据(不包含港澳台地区以及西藏自治区数据),运用熵值法、耦合协调度模型和社会网络分析方法,分析各省份间降碳-减污-扩绿-增长协同演变趋势及空间关联网络特征。结果表明:①各省份降碳-减污-扩绿-增长协同效应的变化趋势基本一致,但在空间上呈现东部>东北>西部>中部的区域不均衡特征。②降碳-减污-扩绿-增长协同效应呈现以东部地区为核心的复杂空间网络结构,省际间空间关联性呈上升态势,但网络结构稳定性还有待提高。③北京市、天津市和上海市等地区凭借优越区位,在关联网络中处于主导地位,而宁夏回族自治区、黑龙江省和新疆维吾尔自治区等地区对其他地区的影响较小。④北京市、天津市和上海市等地区属于“主受益”板块,浙江省、广东省等地区属于“经纪人板块”,安徽省、江西省和湖北省等地区属于“净溢出”板块。⑤降碳-减污-扩绿-增长协同效应的空间关联网络受多种因素共同影响,人力资本水平、科技投入、市场化水平和数字经济发展均有利于空间关联关系的建立。研究显示,中国降碳-减污-扩绿-增长协同效应存在空间关联性,需进一步加强省份间的绿色合作与交流,共同推动降碳-减污-扩绿-增长协同发展。

压裂缝高度对致密砂岩气储层水平井产能的影响

越来越多的开发实践显示,对于多隔夹层型致密砂岩气藏,并不是有效储层钻遇率越高,产能越高。为搞清鄂尔多斯盆地苏里格气田盒8段储层部分低钻遇率水平井(钻遇率小于60%,最低仅31%)压裂改造效果好、产能较高(初期产能最高可达7.5×10^(4) m^(3)/d)的原因,文中综合储层发育特征、岩石力学参数并结合数值模拟方法,讨论了压裂缝高度对隔夹层发育的致密砂岩气储层水平井产能的影响。结果表明:对于隔夹层发育的致密砂岩气储层,隔夹层被压穿,使得纵向多套气层通过压裂缝与井筒连通投产,是低钻遇率水平井高产的主要原因,压裂缝高度对水平井产能有重要影响;对于隔夹层不发育的单一厚层致密砂岩气储层,随压裂缝高度增加,水平井产能并无明显变化。因此,对于长水平段(大于100 m)连续钻遇薄隔夹层的水平井,可根据致密砂岩气储层纵向砂体及气层发育情况,考虑在非有效储层段射孔压裂,并尽可能压穿纵向多套隔夹层,以明显提高气井产能。这对鄂尔多斯盆地内外类似致密砂岩气储层水平井压裂优化设计和水平井单井产能提高具有重要指导意义。

考虑粉土温度效应与排水状态的CPTu计算模型

温度变化对土体性质和行为的潜在影响已成为许多岩土工程设计和应用的重要组成部分。针对粉土中孔压静力触探试验(piezocone penetration test,简称CPTu)的温度效应及部分排水状态,提出了基于小孔扩张理论的计算模型和分析方法。采用一种能够表征粉土强度温度效应的本构模型,给出了完全不排水和排水条件下的解析解;以Bourke粉土为例,分析了温度对扩张压力的影响,揭示了扩张压力随温度升高而减小的规律。采用一种线性映射方法给出了部分排水条件下的小孔扩张半解析解,并基于物理模型试验的结果得出了排水状态与温度的相关关系,建立了考虑粉土温度效应与排水状态的CPTu计算模型。研究了不同贯入速率下温度对CPTu测试结果的影响,结果表明,温度升高导致锥尖阻力与锥肩孔压减小,且变化幅度随超固结比的增加而增大,通过试验结果与计算模型预测结果的对比验证了模型的可靠性。