Macroscopic and microscopic mechanical behavior and seepage characteristics of coal under hydro-mechanical coupling

Understanding the physical,mechanical behavior,and seepage characteristics of coal under hydro-mechanical coupling holds significant importance for ensuring the stability of surrounding rock formations and preventing gas outbursts.Scanning electron microscopy,uniaxial tests,and triaxial tests were conducted to comprehensively analyze the macroscopic and microscopic physical and mechanical characteristics of coal under different soaking times.Moreover,by restoring the stress path and water injection conditions of the protective layer indoors,we explored the coal mining dynamic behavior and the evolution of permeability.The results show that water causes the micro-surface of coal to peel off and cracks to expand and develop.With the increase of soaking time,the uniaxial and triaxial strengths were gradually decreased with nonlinear trend,and decreased by 63.31%and 30.95%after soaking for 240 h,respectively.Under different water injection pressure conditions,coal permeability undergoes three stages during the mining loading process and ultimately increases to higher values.The peak stress of coal,the deviatoric stress and strain at the permeability surge point all decrease with increasing water injection pressure.The results of this research can help improve the understanding of the coal mechanical properties and seepage evolution law under hydro-mechanical coupling.

EXPERIMENTAL STUDY ON THE MACRO-AND MICRO- CHARACTERISTICS OF THE SPRAY FROM A PRESSURE SWIRL NOZZLE

The experimental study on the macro and micro characteristics of the spray from a pressure swirl nozzle embraces the growth of surface unstable wave,disintegration process,spray angle,breakup length and so on.The effects of injection pressure,nozzle geometry and liquid properties on these characteristics are also discussed.The results are helpful to understand the underlying physics of the pressure swirl nozzle and serve as the basis for the practical design,usage and improvement of the nozzle.

The Influence of Macro and Micro Contexts on Teaching and Learning in the Classroom

This paper is based on three observations and independent thinking of the classroom teaching of the author’s colleagues.It attempts to examine how macro and micro contexts affect teaching and learning in the classroom.The author focuses the discussion on three aspects:(i)the present EFL contextual setting in China;(ii)the influence of the evaluation system on both teachers and students;(iii)his own beliefs as a teacher.Finally,he comes to the implications that teachers should often reflect on their teaching by means of observing other teachers’teachings;In order to bring more effective teaching and learning to the class,Teachers should change their class from a teacher-centered one to a students-centered one.

An overview of laser-based multiple metallic material additive manufacturing: from macro- to micro-scales

Additive manufacturing(AM)is an emerging customized three-dimensional(3D)functional product fabrication technology.It provides a higher degree of design freedom,reduces manufacturing steps,cost and production cycles.However,existing metallic component 3D printing techniques are mainly for the manufacture of single material components.With the increasing commercial applications of AM technologies,the need for 3D printing of more than one type of dissimilar materials in a single component increases.Therefore,investigations on multi-material AM(MMAM)emerge over the past decade.Lasers are currently widely used for the AM of metallic components where high temperatures are involved.Here we report the progress and trend in laser-based macro-and micro-scale AM of multiple metallic components.The methods covered in this paper include laser powder bed fusion,laser powder directed energy deposition,and laser-induced forward transfer for MMAM applications.The principles and process/material characteristics are described.Potential applications and challenges are discussed.Finally,future research directions and prospects are proposed.

Macro-and Micro-Properties of Two Natural Marine Clays in China

In this paper,macro-and micro-properties of natural marine clay in two different and representative regions of China are investigated in detail.In addition to in-situ tests,soil samples are collected by use of Shelby tubes for laboratory examination in Shanghai and Zhuhai respectively,two coastal cities in China.In the laboratory tests,macro-properties such as consolidation characteristics and undrained shear strength are measured.Moreover,X-ray diffraction test,scanning electron microscope test,and mercury intrusion test are carried out for the investigation of their micro-properties including clay minerals and microstructure.The study shows that：（1）both clays are Holocene series formations,classified as either normal or underconsolidated soils.The initial gradient of the stress-strain curves shows their increase with increasing consolidation pressure;however,the Shanghai and the Zhuhai clays are both structural soils with the latter shown to be more structured than the former.As a result,the Zhuhai clay shows strain softening behavior at low confining pressures,but strain hardening at high pressures.In contrast,the Shanghai clay mainly manifests strain-hardening.（2）An activity ranges from 0.75 to 1.30 for the Shanghai marine clay and from 0.5 to 0.85 for the Zhuhai marine clay.The main clay mineral is illite in the Shanghai clay and kaolinite in the Zhuhai clay.The Zhuhai clay is mainly characterized by a flocculated structure,while the typical Shanghai clay shows a dispersed structure.The porous structure of the Shanghai clay is characterized mainly by large and medium-sized pores,while the Zhuhai clay porous structure is mainly featured by small and medium-sized pores.The differences in their macro-and micro-properties can be attributed to different sedimentation environments.

Recent Advances in Computational Simulation of Macro-,Meso-,and Micro-Scale Biomimetics Related Fluid Flow Problems

Over the last decade, computational methods have been intensively applied to a variety of scientific researches and engineering designs. Although the computational fluid dynamics （CFD） method has played a dominant role in studying and simulating transport phenomena involving fluid flow and heat and mass transfers, in recent years, other numerical methods for the simulations at meso- and micro-scales have also been actively applied to solve the physics of complex flow and fluid-interface interactions. This paper presents a review of recent advances in multi-scale computational simulation of biomimetics related fluid flow problems. The state-of-the-art numerical techniques, such as lattice Boltzmann method （LBM）, molecular dynamics （MD）, and conventional CFD, applied to different problems such as fish flow, electro-osmosis effect of earthworm motion, and self-cleaning hydrophobic surface, and the numerical approaches are introduced. The new challenging of modelling biomimetics problems in developing the physical conditions of self-clean hydrophobic surfaces is discussed.

Numerical Simulation of Macro-and Micro-structures of Intense Convective Clouds with a Spectral Bin Microphysics Model

By use of a three-dimensional compressible non-hydrostatic convective cloud model with detailed microphysics featuring spectral bins of cloud condensation nuclei （CCN）, liquid droplets, ice crystals, snow and graupel particles, the spatial and temporal distributions of hydrometeors in a supercell observed by the （Severe Thunderstorm Electrification and Precipitation Study） STEPS triple-radar network are simulated and analyzed. The bin model is also employed to study the effect of CCN concentration on the evolution characteristics of the supercell. It is found that the CCN concentration not only affects the concentration and spectral distribution of water droplets, but also influences the characteristics of ice crystals and graupel particles. With a larger number of CCN, more water droplets and ice crystals are produced and the growth of graupel is restrained. With a small quantity of CCN the production of large size water droplets are promoted by initially small concentrations of water droplets and ice crystals, leading to earlier formation of small size graupel and restraining the recycling growth of graupel, and thus inhibiting the formation of large size graupel （or small size hail）. It can be concluded that both the macroscopic airflow and microphysical processes influence the formation and growth of large size graupel （or small size hail）. In regions with heavy pollution, a high concentration of CCN may restrain the formation of graupel and hail, and in extremely clean regions, excessively low concentrations of CCN may also limit the formation of large size graupel （hail）.

Sedimentary Micro-facies and Macro Heterogeneity of Reservoir Beds in the Third Member of the Qingshankou Formation,Qian'an Area,Songliao Basin

An analysis of drill cores and well logs shows that the main micro-facies of the third member sand bodies of the Qingshankou Formation in Qian＇an are subaqueous distributary channel facies, sheet sand facies and subaqueous fan facies （olistostrome）. Maps showing the distribution of these micro-facies together with inter-channel bay and prodelta mocro-facies are presented for different time-slices （lower, middle and upper parts of the Qingshankou Formation）. These maps reveal the instability and change of sediment transport in the Baokang sedimentary system during the depositional period. Sediment transport was from the west in the early stage, from the south in the middle stage and from the northwest in the late stage. Values of thickness, porosity and permeability of the sand bodies in the third member of the Qingshankou Formation show that they have low to medium porosity and low permeability, and are characterized by serious reservoir heterogeneity. The joints between micro-facies and subaqueous fan micro-facies are characterized by the highest heterogeneity, the sheet sand and distal sand bar subfacies come next, and the heterogeneity of the subaqueous distributary channel sand bodies is relatively weak.

A Fractional Micro-Macro Model for Crowds of Pedestrians Based on Fractional Mean Field Games

Modeling a crowd of pedestrians has been considered in this paper from different aspects. Based on fractional microscopic model that may be much more close to reality, a fractional macroscopic model has been proposed using conservation law of mass. Then in order to characterize the competitive and cooperative interactions among pedestrians, fractional mean field games are utilized in the modeling problem when the number of pedestrians goes to infinity and fractional dynamic model composed of fractional backward and fractional forward equations are constructed in macro scale. Fractional micromacro model for crowds of pedestrians are obtained in the end. Simulation results are also included to illustrate the proposed fractional microscopic model and fractional macroscopic model, respectively. © 2014 Chinese Association of Automation.

Power Supply of Macro-Micro Driven Linear Piezoelectric Motor

To investigate a novel macro and micro driven linear piezoelectric motor composed of an ultrasonic motor with macro movement and a piezoelectric actuator with micro movement,a digital signal processing(DSP)based macro and micro power supply is designed,which fits the new linear piezoelectric motor.The power supply comprises a control circuit,a voltage conversion circuit,an amplifier circuit,a half-bridge module,an optical isolatorsdrive circuit,etc,where the DSP of TMS320F28335 is used as the controller.When the linear piezoelectric motor working in a macro driven state,the power supply outputs alternating currents with high frequency and high voltage,which drives the linear piezoelectric motor dynamically at an ultrasonic frequency;while working in the micro driven state,the power supply outputs direct currents with high voltage,which drives the linear piezoelectric motor in micro driven statically.Here a prototype of the macro-micro power supply is designed.After a series of experiments on the power supply with and without loads,the results show that the power supply can drive and control the macro micro driven linear piezoelectric motor,and realizes quick and seamless switch between macro and micro drive.In addition,the power supply can drive and control the ultrasonic motor or piezoelectric ceramic micro actuator individually.The power supply achieves the multiple parameters of output signals adjustable simultaneously and exhibits good control characteristics.

Macro-Micro-Anatomy of the Lingual Artery

The macro-micro-anatomy of the lingual artery of 25 adult cadavers wasstudied.The origin of the artery is rather concentrated and the greater cornu of thehyoid bone can be used as the indicator.The entrance of the artery into the hyoglossusmuscle is almost constantly along the posterior border of the muscle,where the artery issuperficially located and easily to be exposed,and has a constant relationship with thevein and hypoglossal nerve.Thus the lingual artery can be used as the artery of a recipientarea in case of tongue reconstruction.The deep lingual artery has two types ofbranches;the short ones mainly supply the muscles of tongue while the long ones mainlysupply the mucosa by forming a submucosal network.In the muscles of tongue,minutearterioles run tortuously along the muscular fibers with abundant anastomoses betweeneach other,but no anastomosis is found to cross over the rnidline of the tongue.Be-neath the mucosa,there is an arterial network spreading all over the whole tongue notlimited to one side.The relationship of the arterial architecture to the structure and thefunctions of the tongue and its clinical significance were discussed.

Effect of dry-wet cycles on dynamic properties and microstructures of sandstone:Experiments and modelling

Underground pumped storage power plant(UPSP)is an innovative concept for space recycling of abandoned mines.Its realization requires better understanding of the dynamic performance and durability of reservoir rock.This paper conducted ultrasonic detection,split Hopkinson pressure bar(SHPB)impact,mercury intrusion porosimetry(MIP),and backscatter electron observation(BSE)tests to investigate the dynamical behaviour and microstructure of sandstone with cyclical dry-wet damage.A coupling FEM-DEM model was constructed for reappearing mesoscopic structure damage.The results show that dry-wet cycles decrease the dynamic compressive strength(DCS)with a maximum reduction of 39.40%,the elastic limit strength is reduced from 41.75 to 25.62 MPa.The sieved fragments obtain the highest crack growth rate during the 23rd dry-wet cycle with a predictable life of 25 cycles for each rock particle.The pore fractal features of the macropores and micro-meso pores show great differences between the early and late cycles,which verifies the computational statistics analysis of particle deterioration.The numerical results show that the failure patterns are governed by the strain in pre-peak stage and the shear cracks are dominant.The dry-wet cycles reduce the energy transfer efficiency and lead to the discretization of force chain and crack fields.

Design of a control system for a macro-micro dual-drive high acceleration high precision positioning stage for IC packaging

A macro-micro dual-drive positioning system showing good potential for high acceleration and high precision positioning required in IC packaging applications is devised in this paper. The dual-drive positioning stage uses a VCM (voice coil motor) driven macro positioning stage and a PZT piezo-electric driven micro positioning stage. The coupling characteristics of the system are analyzed to produce a control structure with a micro positioning stage that can dynamically compensate for the positioning error produced by the macro positioning stage. Models of the two positioning stages are described. The models cover both the mechanism and the actuator. For the macro positioning stage, friction characteristics are taken into account, and a controller with an LQG (linear-quadratic-Gaussian) control algorithm combining a feed-forward compensation algorithm is derived. A PID controller is used to control the micro positioning stage. Detailed designs are derived for the proposed approach, and the performance is validated by simulation.

Chemical analysis,antimicrobial and anti-oxidative properties of Daucus gracilis essential oil and its mechanism of action

Objective:To evaluate the essential oils(EO) composition,antimicrobial and antioxidant power of a local plant,Daucus gracilis(D.gracilis).Methods:The aerial parts of D.gracilis were subjected to hydro distillation by a Clevenger apparatus type to obtain the EO which had been analyzed by gas chromatography and gas chromatography coupled with mass spectrometry,and screened for antimicrobial activity against five bacteria and three fungi by agar diffusion method.The mechanism of action of the EO was determined on the susceptible strains by both of time kill assay and lysis experience.The minimal inhibitory concentrations were determined by agar macrodilution and micro-dilution methods.Anti-oxidative properties of the EO were also studied by free diphenyl-2-picrylhydrazyl radical scavenging and reducing power techniques.Results:The EO yielded 0.68(v/w).The chemical analysis presented two dominant constituents which were the elemicin(35.3%) and the geranyl acetate(26.8%).D.gracilis EO inhibited the growth of Bacillus cereus and Proteus mirabilis significantly with minimal inhibitory concentrations of 17.15 μg/mL by the agar dilution method and57.05 μg/mL and 114.1 μg/mL,respectively by liquid micro-dilution.A remarkable decrease in a survival rate as well as in the absorbance in 260 nm was recorded,which suggested that the cytoplasm membrane was one of the targets of the EO.The EO showed,also,important anti-oxidative effects with an IC50 of 0.002 mg/mL and a dosedependent reducing power.Conclusions:D.gracilis EO showed potent antimicrobial and anti-oxidative activities and had acted on the cytoplasm membrane.These activities could be exploited in the food industry for food preservation.

A micromechanical damage model for rocks and concretes under triaxial compression

Based on analysis of deformation in an infinite isotropic elastic matrix containing an embedded elliptic crack, subject to far field triaxial compressive stress, the energy release rate and a mixed fracture criterion are obtained by using an energy balance approach. The additional compliance tensor induced by a single closed elliptic microcrack in a representative volume element and its in-plane growth is derived. The additional compliance tensor induced by the kinked growth of the elliptic microcrack is also obtained. The effect of the microcracks, randomly distributed both in geometric characteristics and orientations, is analyzed with the Taylor＇s scheme by introducing an appropriate probability density function. A micromechanical damage model for rocks and concretes under triaxial compression is obtained and experimentally verified.

论新质生产力研究的经济学思维

“新质生产力”思维概念,基于历史唯物主义发展观的理论范式,将马克思主义的“生产力-生产关系”理论范式,运用于对新时代新现象的观察和研究。在新质生产力的经济学理论范式中,对于“人”的概化具有特别重要的认识论和逻辑自洽性意义。“人”的概化,不仅包含人与自然的关系,也包含人与人的关系,即马克思所说的人的本质是“社会关系的总和”。新质生产力经济学思维所概化的“人”,从“经济人”“组织人”演化产生了“智能机器人”。当新质生产力研究接受数字化人工智能的经济学思维时,主流经济学将发生颠覆性的范式变革。对生产力的“质态”关切,超越对生产力的“量态”关切,是新质生产力重要的经济学属性。经济学的范式变革,须将长期性、未来性、存量性、多元性等因素也纳入观察研究体系,这是域观经济学与新质生产力相契合的逻辑基础,可以引导现代经济学的“微观-宏观”范式体系,更科学地研究新时代、新世界所产生的新现象。

Proximate composition and antimicrobial activity of three wild edible mushrooms consumed by ethnic inhabitants of Tripura in northeast India

The study was focused on edible mushrooms consumed by the ethnic inhabitants of Tripura,northeast India.Three mushrooms namely Lentinus squarrosulus,Lentinus tuber-regium and Macrocybe gigantea were evaluated quantitatively for proximate composition and mineral nutrients.In addition,the efficacy of the mycelial extract was tested for antimicrobial activity against the bacteria.The results of this study indicated that mushrooms were rich in protein and carbohydrate with low fat content.Macrocybe gigantea proved to the best source of protein and carbohydrate among the three mushrooms.There were varied amount of micronutrients recorded in all the three mushrooms.The antimicrobial activity of mycelial extract of M.gigantea was found against all the tested strains of bacteria.The study suggested that these mushrooms are rich in nutrients particularly M.gigantea which could be used as an alternative source of vegetarian food to the ethnic people of Tripura.The antimicrobial activity exhibited by these mushrooms indicated their medicinal properties.

烫漂预处理对苹果干燥过程中微观结构及质构品质的影响

为提高烫漂预处理后苹果片的热风干燥效率和品质,本研究系统评估了热水烫漂与真空蒸汽脉动烫漂两种预处理方法对苹果片的宏观干燥效果。研究结果表明,在真空度0.07 MPa、烫漂2次和烫漂时间3 min条件下真空蒸汽脉动烫漂预处理提升了苹果片的复水比和质构品质,同时缩短了干燥时间。通过石蜡切片、显微观测、图像处理等技术对两种预处理方法干燥的苹果片微观结构进行研究,对比分析在不同烫漂条件(热水烫漂:温度和时间;真空蒸汽脉动烫漂:真空度、次数和时间)下苹果片的细胞横截面面积、周长、当量直径、细胞圆度、壁面粗糙度因子和孔隙率的变化规律。结果显示,随着漂烫温度的升高、时间的延长和烫漂次数的增加,苹果片的细胞会产生使后续干燥过程中水分加速蒸发的变化,从而缩短干燥时间。此外,通过多项式拟合建立了微观结构参数与复水比之间的关系方程。研究结果可为揭示真空蒸汽脉动烫漂预处理对苹果微观结构和宏观品质影响的机理提供理论依据。

基于SBFEM的剪切型裂纹动态开裂模拟

剪切型断裂是岩土工程中常见的破坏模式,了解剪切破坏机理并准确预测剪切型裂纹的萌生、扩展过程对保障工程结构的安全性与稳定性具有重要意义.文章建立了基于比例边界有限元法(scaled boundary finite element methods,SBFEM)和非局部宏-微观损伤模型的剪切型裂纹动态开裂模拟方法,定义了基于偏应变概念的物质点对的正伸长量,可作为预测剪切型裂纹扩展行为的动态开裂准则,一点的损伤定义为该点影响域范围内连接的物质键损伤的加权平均值,而物质键的损伤则与基于偏应变概念的物质点对的正伸长量相关联,并引入能量退化函数建立结构域几何拓扑损伤与能量损失之间的关系,将拓扑损伤与应力应变联系起来,通过能量退化函数修正了SBFEM的刚度系数矩阵,得到了子域在损伤状态下的刚度矩阵,推导了考虑结构损伤的SBFEM动力控制方程,采用Newmark隐式算法对控制方程进行时间离散.最后,通过3个典型算例验证了建议的模型可较好地模拟剪切型断裂问题,能够很好地捕捉剪切型裂纹的扩展路径,并得到较为准确的载荷-位移曲线.

中国典型集体离职案例的思考与启示——基于事件理论分析改革开放40余年来的典型案例

企业员工集体离职对相关组织和员工群体影响深远。研究以1978年至2021年中国改革开放的43年为时间背景,从中国知网(CNKI)的5个子数据库中甄选出我国集体离职案例102个和典型集体离职案例16个。基于编码分析、事件分析等案例研究方法,主要发现:典型集体离职案例的事件强度在新颖度、中断度、重要度中占据其一,即具有代表性;事件空间主要受所在企业规模、行业地位、社会影响力等因素影响;事件时间主要受集体离职人员的层级、重要性、不可替代性等因素影响。分析典型集体离职案例既要考虑时代背景、法律变迁、文化冲突等宏观因素——这些因素可能诱发集体离职;更要考虑外部诱惑、股东更替、高管套现等微观因素——这些因素可能直接导致集体离职。集体离职的发生受到中国改革开放进程的影响:发生地呈现由沿海向内陆变迁的趋势;所涉行业多集中在制造业,这一点尤其在中国加入世贸组织后更加明显;离职人员所涉层级由高层向中层和基层扩展,同时涉及高层、中层和基层的连带离职对企业影响更大。研究还提炼出影响集体离职的宏观因素和微观因素的作用与特征模型,并有针对性地提出预防集体离职事件发生的意见建议。