Influences of clean fracturing fluid viscosity and horizontal in-situ stress difference on hydraulic fracture propagation and morphology in coal seam

The viscosity of fracturing fluid and in-situ stress difference are the two important factors that affect the hydraulic fracturing pressure and propagation morphology. In this study, raw coal was used to prepare coal samples for experiments, and clean fracturing fluid samples were prepared using CTAB surfactant. A series of hydraulic fracturing tests were conducted with an in-house developed triaxial hydraulic fracturing simulator and the fracturing process was monitored with an acoustic emission instrument to analyze the influences of fracturing fluid viscosity and horizontal in-situ stress difference on coal fracture propagation. The results show that the number of branched fractures decreased, the fracture pattern became simpler, the fractures width increased obviously, and the distribution of AE event points was concentrated with the increase of the fracturing fluid viscosity or the horizontal in-situ stress difference. The acoustic emission energy decreases with the increase of fracturing fluid viscosity and increases with the increase of horizontal in situ stress difference. The low viscosity clean fracturing fluid has strong elasticity and is easy to be compressed into the tip of fractures, resulting in complex fractures. The high viscosity clean fracturing fluids are the opposite. Our experimental results provide a reference and scientific basis for the design and optimization of field hydraulic fracturing parameters.

What does Bourdieu Mean by the‘Habitus’and What Implications does This Idea Have for English Language Teaching in China?:Using Bourdieu:Introducing Habitus,Field and Capital

Habitus remains an ambiguous and cryptic concept,triggering drastic debate not only in sociology and anthropology but also in culture studies and literary criticism.The topic has been cited by a range of writers,notably Mauss,Husserl and Bourdieu.Even Bourdieu did not provide a clear,authoritative or coherent definition of the term in his work.Due to the fact that habitus plays an indispensable part of social constructionism,which defines our understanding of the world.It is necessary for parents,schools and the government to learn about this concept,and utilize it to guide their education practice and policy enactment.This essay will explore the theoretical concept of“habitus”and its interrelationship with“field”and“capital”.Then discuss the wide disparity in different social groups,in terms of habitus and capital in China.Followed by an analysis of the imbalances in Chinese rural and urban schools respectively,in the field of English language teaching.It aims to help readers better understand the poor performance of students who come from less advantageous social groups in language learning,rather than attributing their failure to their individual defects.The essay will also introduce the 2003 English curriculum reform,illustrate the current status of its implementation in various family upbringing and school locations and put forward some feasible proposals for parents,teachers,students and government to promote social equity in English language teaching in China.

Modifed Pre-stretching Assembly Method for Cable-Driven Systems

Soft cable-driven systems have been employed in many assembled mechanisms, such as industrial robots, parallel kinematic mechanism machines, medical devices, and humaniform hands. A pre-stretching process is necessary to guarantee the quality of cable-driven systems during the assembly process. However, the stress relaxation of cables becomes a critical concern during long-term operation. This study investigates the effects of non-uniform deformation and long-term stress relaxation of the driven cables owing to moving parts in the system. A simple closed-loop cable-driven system is built and an alternating load is applied to it to replicate the operation of transmission cables. Under different experimental conditions, the cable tension is recorded and the boundary data are selected to be curve-fitted. Based on the fitted results, a formula is presented to estimate the stress relaxation of cables to evaluate the assembly performance. Further experimental results show that the stress relaxation is mainly caused by cable creep and the assembly procedure. To remove the influence of the assembly procedure, a modified pre-stretching assembly method based on the stress relaxation theory is proposed and verification experiments are performed. Finally, the assembly performance is optimized using a cable-driven surgical robot as an example. This paper proposes a dual stretching method instead of the pre-stretching method to assemble the cable-driven system to improve its performance and prolong its service life.

Method for Latency Measurement of Visual Feedback-Based Master–Slave Minimally Invasive Surgical Robot

To measure the latency between human motion stimulation and stereo image display response in a visual feedback-based minimally invasive surgical(MIS) robotic system,a method was proposed by comparing the orientations of input and output events through image-processing technology. This method used a black bar to keep pace with the measured joint rotating at a number of speeds. During tests,an external camera was placed in front of the apparatus with a proper visual field,so that it can simultaneously view orientations of both bars fixed on the corresponding joints. After quantitatively analyzing the accuracy of the proposed measurement method,the method was applied to a visual feedback-based master–slave robotic system with two-degrees-of-freedom. Experimental results show that the latency of the overall system was approximately 250 ms,and the opposite clearance of the measured joint was in the range of 1.7°–1.9°.

高效蓝光钙钛矿发光二极管的埋底界面修饰和光耦合策略

Perovskite light-emitting diodes(PeLEDs)exhibit remarkable potential in the field of displays and solidstate lighting.However,blue PeLEDs,a key element for practical applications,still lag behind their green and red counterparts,due to a combination of strong nonradiative recombination losses and unoptimized device structures.In this report,we propose a buried interface modification strategy to address these challenges by focusing on the bottom-hole transport layer(HTL)of the PeLEDs.On the one hand,a multifunctional molecule,aminoacetic acid hydrochloride(AACl),is introduced to modify the HTL/perovskite interface to regulate the perovskite crystallization.Experimental investigations and theoretical calculations demonstrate that AACl can effectively reduce the nonradiative recombination losses in bulk perovskites by suppressing the growth of low-n perovskite phases and also the losses at the bottom interface by passivating interfacial defects.On the other hand,a self-assembly nanomesh structure is ingeniously developed within the HTLs.This nanomesh structure is meticulously crafted through the blending of poly-(9,9-dioctyl-fluorene-co-N-(4-butyl phenyl)diphenylamine)and poly(n-vinyl carbazole),significantly enhancing the light outcoupling efficiency in PeLEDs.As a result,our blue PeLEDs achieve remarkable external quantum efficiencies,20.4%at 487 nm and 12.5%at 470 nm,which are among the highest reported values.Our results offer valuable insights and effective methods for achieving high-performance blue PeLEDs.

Symmetry breaking of highly symmetrical nanoclusters for triggering highly optical activity

Developing new approaches to fulfill the enantioseparation of nanocluster racemates and construct cluster-based nanomaterials with optical activity remains highly desired in cluster science,because it is an essential prerequisite for fundamental research and extensive applications of these nanomaterials.We herein propose a strategy termed“active-site exposing and partly re-protecting”to trigger the symmetry breaking of highly symmetrical nanoclusters and to render cluster crystals optically active.The vertex PPh_(3)of the symmetrical Ag_(29)(SSR)_(12)(PPh_(3))_(4)(SSR=1,3-benzenedithiol)nanocluster was firstly dissociated in the presence of counterions with large steric hindrance,and then the exposed Ag active sites of the obtained Ag_(29)(SSR)_(12)nanocluster were partly re-protected by Ag^(+),yielding an Ag_(29)(SSR)_(12)-Ag_(2)nanocluster with a symmetry-breaking construction.Ag_(29)(SSR)_(12)-Ag_(2)followed a chiral crystallization mode,and its crystal displayed strong optical activity,derived from CD and CPL characterizations.Overall,this work presents a new approach(i.e.,active-site exposing and partly re-protecting)for the symmetry breaking of highly symmetrical nanoclusters,the enantioseparation of nanocluster racemates,and the achievement of highly optical activity.

Climate warming shifts the time interval between flowering and leaf unfolding depending on the warming period

The timing of flowering(FL)and leaf unfolding(LU)determine plants’reproduction and vegetative growth.Global warming has substantially advanced FL and LU of temperate and boreal plants,but their responses to warming differ,which may influence the time interval between FL and LU(ΔLU-FL),thereby impacting plant fitness and intraspecific physiological processes.Based on twigs collected from two flowering-first tree species,Populus tomentosa and Amygdalus triloba,we conducted a manipulative experiment to investigate the effects of winter chilling,spring warming and photoperiod on theΔLU-FL.We found that photoperiod did not affect theΔLU-FL of Amygdalus triloba,but shortenedΔLU-FL by 5.1 d of Populus tomentosa.Interestingly,spring warming and winter chilling oppositely affected theΔLU-FL of both species.Specifically,low chilling accumulation extended theΔLU-FL by 3.8 and 9.4 d for Populus tomentosa and Amygdalus triloba,but spring warming shortened theΔLU-FL by 4.1 and 0.2 d℃^(-1).Our results indicate that climate warming will decrease or increase theΔLU-FL depending on the warming periods,i.e.,spring or winter.The shifted time interval between flowering and leaf unfolding may have ecological effects including affecting pollen transfer efficiency and alter the structure and functioning of terrestrial ecosystem.

镧掺杂的普适性策略提升铅卤钙钛矿多晶薄膜光致发光性能用以背光显示

金属卤化物钙钛矿多晶薄膜因其低廉的成本以及可大面积制备的优势受到研究者的广泛关注.然而,钙钛矿多晶薄膜的光致发光量子效率和稳定性仍然无法媲美钙钛矿量子点,也无法满足显示技术要求.本文采用镧离子掺杂策略,提高钙钛矿多晶薄膜的发光性能,进一步提升了钙钛矿材料商业化的可能性.镧离子进入晶格可大大改善晶体质量,过量的镧离子和钙钛矿前驱液自组装形成了(FA,Cs)2LaBr5这种多能级物质,因此构建了新型能量漏斗,增强了钙钛矿主体发光性能.最终,镧掺杂FA0.7Cs0.3PbBr3钙钛矿薄膜实现了99.5%的光致发光量子效率.得益于镧掺杂带来的离子迁移活化能和可迁移离子形成能的提升,优化后的钙钛矿多晶薄膜也实现了近1000天的储存半衰期(T50)和400小时的持续光照稳定性(T90).此外,得益于多能级物质的自组装形成,镧掺杂的方式对于全可见光波段钙钛矿材料发光都具有明显的增强作用.由此得到的高纯高效三基色钙钛矿发光覆盖了Rec.2020色域标准的98.9%,这项工作大大推进了钙钛矿多晶薄膜在液晶显示技术背光板中的应用.

Noble and valuable: atomically precise gold nanoclusters

Atomically precise gold nanoclusters have recently attracted intensive attention due to their significance in catalysis,chemical sensing,and bio-application.These nanoclusters often possess unique optical,chemical or physical properties originated from the quantum size effect（i.e.size andshapemorphology）.

Selecting nitride host for Yb^(3+) toward near-infrared emission with low-energy charge transfer band

Yb^(3+)-doped phosphors have characteristic near-infrared(NIR)emissions,but their applications in phosphor-converted light-emitting-diodes(pc-LEDs)and Si solar cells are limited due to their mismatching excitation spectra.Here,we selected nitride La3 Si6 N11(LSN)as host material to achieve Yb^(3+)NIR emission upon low-energy charge transfer(CT)excitation.The obtained phosphor LSN:Yb^(3+)has a broad CT excitation band ranging from 250 to 500 nm and narrowband NIR emissions ranging from 950 to 1100 nm centered at 983 nm.On the basis of spectral data,the vacuum referred binding energies(VRBE)schemes are constructed to locate energy levels of all lanthanide ions in LSN.We also fabricated NIR pc-LED device using 395 nm LED chip to demonstrate the potential applications of LSN:Yb^(3+)phosphors.

A Bionic Flexible-bodied Underwater Glider with Neutral Buoyancy

The buoyancy of traditional Underwater Glider(UG)with a rigid hull is aff ected by the changing marine parameters,making it difficult for the vehicle to dive deeper with good motion characteristics.In the present work,the development of a novel UG for neutral buoyancy,which is equipped with a Flexible-Liquid-Rigid(FLR)composite hull,is presented.The innovative hull that imitates the buoyancy regulation mechanism of marine organisms is easily adaptable to the changing marine environment.The rigid part of the composite hull withstands hydrostatic pressure for inner function modules of the vehicle.The liquid of the composite hull mainly serves as a buoyancy compensation to mitigate the eff ect of buoyancy variation caused by the changing marine parameters.The flexible covering provides a good hydrodynamic shape for the vehicle under the internal liquid pressure.The buoyancy variation due to the composite hull compression as well as changes of seawater density and temperature was comprehensively considered in the design process and integrated to the dynamic model.In addition,sea trials were performed to verify the motion characteristics of the proposed vehicle.The results reveal that the Flexible-bodied Underwater Glider(FUG)has a better gliding performance in practice.

Aggregation of Surface Structure Induced Photoluminescence Enhancement in Atomically Precise Nanoclusters

Although intermolecular aggregation-induced emission(AIE)has been extensively studied in nanocluster science,it remains challenging to activate AIE via intracluster aggregation(i.e.,the aggregation at the single-molecular level).Here,an intracluster AIE system based on the Pt_(1)Ag_(24)(SR)18 nanocluster has been established.Specifically,triggered by the addition of free thiol ligands,the Ag_(2)(SR)_(3)surface motif structures of Pt_(1)Ag_(24)(SR)18 are aggregated to nanocluster poles.

Polystyrene microplastics and di-2-ethylhexyl phthalate co-exposure: Implications for female reproductive health

Microplastics and phthalates are prevalent and emerging pollutants that pose a potential impact on human health.Previous studies suggest that both microplastics and phthalates can adversely affect the reproductive systems of humans and mammals.However,the combined impact of these pollutants on the female reproductive system remains unclear.Here we show the impacts of exposure to polystyrene microplastics(PS-MPs)and di-2-ethylhexyl phthalate(DEHP)on female Sprague-Dawley rats’reproductive systems.We find that co-exposure to PS-MPs and DEHP results in a marked increase in cystic and atretic follicles,oxidative stress,fibrosis,and dysregulation of serum sex hormone homeostasis in the ovaries of the rats.Proteomic analysis identified differentially expressed proteins that were predominantly enriched in signaling pathways related to fatty acid metabolism and tight junctions,regulated by transforming growth factorβ1(TGF-β1).We further confirm that co-exposure to DEHP and PS-MPs activates the TGF-β1/Smad3 signaling pathway,and inhibiting this pathway alleviates oxidative stress,hormonal dysregulation,and ovarian fibrosis.These results indicate that exposure to the combination of microplastics and phthalates leads to a significant increase in atretic follicles and may increase the risk of polycystic ovary syndrome(PCOS).Our study provides new insights into the reproductive toxicity effects of microplastics and DEHP exposure on female mammals,highlighting the potential link between environmental pollutants and the occurrence of PCOS.These findings highlight the need for comprehensive assessments of the reproductive health risks posed by microplastic pollution to women and contribute to the scientific basis for evaluating such risks.