Investigation of hydroxyl-terminated polybutadiene propellant breaking characteristics and mechanism impacted by submerged cavitation water jet

A submerged cavitation water jet(SCWJ)is an effective method to recycle solid propellant from obsolete solid engines by the breaking method.Solid propellant's breaking modes and mechanical process under SCWJ impact are unclear.This study aims to understand those impact breaking mechanisms.The hydroxyl-terminated polybutadiene(HTPB)propellant was chosen as the research material,and a self-designed test system was used to conduct impact tests at four different working pressures.The high-speed camera characterized crack propagation,and the DIC method calculated strain change during the impact process.Besides,micro and macro fracture morphologies were characterized by scanning electron microscope(SEM)and computed tomography(CT)scanning.The results reveal that the compressive strain concentration region locates right below the nozzle,and the shear strain region distributes symmetrically with the jet axis,which increases to 4% at first 16th ms,the compressive strain rises to 2% and 6% in the axial and transverse direction,respectively.The two tensile cracks formed first at the compression strain concentrate region,and there generate many shear cracks around the tensile cracks,and those shear cracks that develop and aggregate cause the cracks to become wider and cut through the tensile cracks,forming the tensile-shear cracks and the impact parts eventually fail.The HTPB propellant forms a breaking hole shaped conical after impact 10 s.The mass loss increases by 17 times at maximum,with the working pressure increasing by three times.Meanwhile,the damage value of the breaking hole remaining on the surface increases by 7.8 times while 2.9 times in the depth of the breaking hole.The breaking efficiency is closely affected by working pressures.The failure modes of HTPB impacted by SCWJ are classified as tensile crack-dominated and tensile-shear crack-dominated damage mechanisms.

A spatiotemporal evolution model of a short-circuit arc to a secondary arc based on the improved charge simulation method

The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experimental analysis of the evolution process of the short-circuit arc to the secondary arc is critical.In this study,an improved charge simulation method was used to develop the internal-space electric-field model of the short-circuit arc.The intensity of the electric field was used as an independent variable to describe the initial shape of the secondary arc.A secondary arc evolution model was developed based on this model.Moreover,the accuracy of the model was evaluated by comparison with physical experimental results.When the secondary arc current increased,the arcing time and dispersion increased.There is an overall trend of increasing arc length with increasing arcing time.Nevertheless,there is a reduction in arc length during arc ignition due to short circuits between the arc columns.Furthermore,the arcing time decreased in the range of 0°-90°as the angle between the wind direction and the x-axis increased.This work investigated the method by which short-circuit arcs evolve into secondary arcs.The results can be used to develop the secondary arc evolution model and to provide both a technical and theoretical basis for secondary arc suppression.

Observation of Zero-Energy Modes with Possible Time-Reversal Symmetry Breaking on Step Edge of CaKFe_(4)As_(4)

Topologically nontrivial Fe-based superconductors attract extensive attentions due to their ability of hosting Majorana zero modes(MZMs)which could be used for topological quantum computation.Topological defects such as vortex lines are required to generate MZMs.Here,we observe the robust edge states along the surface steps of CaKFe_(4)As_(4).Remarkably,the tunneling spectra show a sharp zero-bias peak(ZBP)with multiple integerquantized states at the step edge under zero magnetic field.We propose that the increasing hole doping around step edges may drive the local superconductivity into a state with possible spontaneous time-reversal symmetry breaking.Consequently,the ZBP can be interpreted as an MZM in an effective vortex in the superconducting topological surface state by proximity to the center of a tri-junction with different superconducting order parameters.Our results provide new insights into the interplay between topology and unconventional superconductivity,and pave a new path to generate MZMs without magnetic field.

Optimization of short-circuit transition parameters of Q235B steel GMAW based on orthogonal gray relational analysis

In gas metal arc welding(GMAW)process,the short-circuit transition was the most typical transition observed in molten metal droplets.This paper used orthogonal tests to explore the coupling effect law of welding process parameters on the quality of weld forming under short-circuit transition,the design of 3 factors and 3 levels of a total of 9 groups of orthogonal tests,welding current,welding voltage,welding speed as input parameters:effective area ratio,humps,actual linear power density,aspect ratio,Vickers hardness as output paramet-ers(response targets).Using range analysis and trend charts,we can visually depict the relationship between input parameters and a single output parameter,ultimately determining the optimal process parameters that impact the single output index.Then combined with gray the-ory to transform the three response targets into a single gray relational grade(GRG)for analysis,the optimal combination of the weld mor-phology parameters as follows:welding current 100 A,welding voltage 25 V,welding speed 30 cm/min.Finally,validation experiments were conducted,and the results showed that the error between the gray relational grade and the predicted value was 2.74%.It was observed that the effective area ratio of the response target significantly improved,validating the reliability of the orthogonal gray relational method.

Partitioning Calculation Method of Short-Circuit Current for High Proportion DG Access to Distribution Network

Aiming at the problemthat the traditional short-circuit current calculationmethod is not applicable to Distributed Generation(DG)accessing the distribution network,the paper proposes a short-circuit current partitioning calculation method considering the degree of voltage drop at the grid-connected point of DG.Firstly,the output characteristics of DG in the process of low voltage ride through are analyzed,and the equivalent output model of DG in the fault state is obtained.Secondly,by studying the network voltage distribution law after fault in distribution networks under different DG penetration rates,the degree of voltage drop at the grid-connected point of DG is used as a partition index to partition the distribution network.Then,iterative computation is performed within each partition,and data are transferred between partitions through split nodes to realize the fast partition calculation of short-circuit current for high proportion DG access to distribution network,which solves the problems of long iteration time and large calculation error of traditional short-circuit current.Finally,a 62-node real distribution network model containing a high proportion of DG access is constructed onMATLAB/Simulink,and the simulation verifies the effectiveness of the short-circuit current partitioning calculation method proposed in the paper,and its calculation speed is improved by 48.35%compared with the global iteration method.

Across two phylogeographic breaks: Quaternary evolutionary history of a mountain aspen (Populus rotundifolia) in the Hengduan Mountains

Biogeographical barriers to gene flow are central to plant phylogeography.In East Asia,plant distribution is greatly influenced by two phylogeographic breaks,the Mekong-Salween Divide and Tanaka-Kaiyong Line,however,few studies have investigated how these barriers affect the genetic diversity of species that are distributed across both.Here we used 14 microsatellite loci and four chloroplast DNA fragments to examine genetic diversity and distribution patterns of 49 populations of Populus rotundifolia,a species that spans both the Mekong-Salween Divide and the Tanaka-Kaiyong Line in southwestern China.Demographic and migration hypotheses were tested using coalescent-based approaches.Limited historical gene flow was observed between the western and eastern groups of P.rotundifolia,but substantial flow occurred across both the Mekong-Salween Divide and Tanaka-Kaiyong Line,manifesting in clear admixture and high genetic diversity in the central group.Wind-borne pollen and seeds may have facilitated the dispersal of P.rotundifolia following prevalent northwest winds in the spring.We also found that the Hengduan Mountains,where multiple genetic barriers were detected,acted on the whole as a barrier between the western and eastern groups of P.rotundifolia.Ecological niche modeling suggested that P.rotundifolia has undergone range expansion since the last glacial maximum,and demographic reconstruction indicated an earlier population expansion around 600 Ka.The phylogeographic pattern of P.rotundifolia reflects the interplay of biological traits,wind patterns,barriers,niche differentiation,and Quaternary climate history.This study emphasizes the need for multiple lines of evidence in understanding the Quaternary evolution of plants in topographically complex areas.

Generating highly active oxide-phosphide heterostructure through interfacial engineering to break the energy scaling relation toward urea-assisted natural seawater electrolysis

Urea-assisted natural seawater electrolysis is an emerging technology that is effective for grid-scale carbon-neutral hydrogen mass production yet challenging.Circumventing scaling relations is an effective strategy to break through the bottleneck of natural seawater splitting.Herein,by DFT calculation,we demonstrated that the interface boundaries between Ni_(2)P and MoO_(2) play an essential role in the selfrelaxation of the Ni-O interfacial bond,effectively modulating a coordination number of intermediates to control independently their adsorption-free energy,thus circumventing the adsorption-energy scaling relation.Following this conceptual model,a well-defined 3D F-doped Ni_(2)P-MoO_(2) heterostructure microrod array was rationally designed via an interfacial engineering strategy toward urea-assisted natural seawater electrolysis.As a result,the F-Ni_(2)P-MoO_(2) exhibits eminently active and durable bifunctional catalysts for both HER and OER in acid,alkaline,and alkaline sea water-based electrolytes.By in-situ analysis,we found that a thin amorphous layer of NiOOH,which is evolved from the Ni_(2)P during anodic reaction,is real catalytic active sites for the OER and UOR processes.Remarkable,such electrode-assembled urea-assisted natural seawater electrolyzer requires low voltages of 1.29 and 1.75 V to drive 10 and600 mA cm^(-2)and demonstrates superior durability by operating continuously for 100 h at 100 mA cm^(-2),beyond commercial Pt/C||RuO_(2) and most previous reports.

Team China’s Groundbreaking Success at Paris Olympics

China’s Olympic delegation at the Paris 2024,with 404 athletes competing in 232 events across 30 sports,clinched 40 gold,27 silver,and 24 bronze medals,marking their best performance at an Olympics held abroad.The success of these athletes across various disciplines demonstrates the country’s efforts to expand its athletic prowess while also marks a new chapter for Chinese sportsmanship on the international stage.

Enhancing textile production:Smartex exhibits groundbreaking solutions

Smartex,a trailblazing leader in textile industry innovation,was proud to announce its return to ITM 2024,showcasing unparalleled advancements in quality control and production efficiency.Building on the success of previous exhibitions at ITM 2022 and ITMA Milan 2023,Smartex emerges stronger than ever,presenting its complete Smartex System tailored to transform textile manufacturing.

Impacts of monsoon break events in the western North Pacific on the cross-equatorial flows over the Maritime Continent

本文利用ERA5逐日再分析资料,探讨了1979-2020年间西北太平洋季风中断事件对海洋性大陆越赤道气流的影响.合成结果表明,西北太平洋季风中断事件会造成高,低空越赤道气流减弱,即高层南风异常,低层北风异常,与此相关的环流异常表现为西北太平洋高层气旋,低层反气旋的斜压结构。特别的是,西北太平洋季风中断对高空越赤道气流的影响更为显著,92%的季风中断事件都导致高空越赤道气流减弱,而只有70%的事件造成低空越赤道气流减弱,这是由于低空越赤道气流同时还受到赤道中东太平洋海温异常的调控.

Numerical Simulation of Dam-Break Flows Using Radial Basis Functions: Application to Urban Flood Inundation

Dam-break flows pose significant threats to urban areas due to their potential for causing rapid and extensive flooding. Traditional numerical methods for simulating these events struggle with complex urban landscapes. This paper presents an alternative approach using Radial Basis Functions to simulate dam-break flows and their impact on urban flood inundation. The proposed method adapts a new strategy based on Particle Swarm Optimization for variable shape parameter selection on meshfree formulation to enhance the numerical stability and convergence of the simulation. The method’s accuracy and efficiency are demonstrated through numerical experiments, including well-known partial and circular dam-break problems and an idealized city with a single building, highlighting its potential as a valuable tool for urban flood risk management.

A record-breaking high efficiency facilitated by hierarchical morphology in all polymer solar cells

Organic solar cells(OSCs) especially non-fullerene OSCs(NF-OSCs) are promising to become the next-generation of commercial applications and have received great attention from many researchers due to their typical advantages of low cost,light weight,and flexibility [1,2].

Experimental research and energy analysis of a new type of dry ice powder pneumatic rock breaking technology

When the traditional drill and blast method is applied to rock crushing projects,it has strong vibration,loud noise and dust pollution,so it cannot be used in densely populated areas such as urban public works.We developed a supercritical CO_(2)true triaxial pneumatic rock-breaking experimental system,and conducted laboratory and field tests of dry ice powder pneumatic rock-breaking.The characteristics of the blast-induced vibration velocity waveform and the evolution of the vibration velocity and frequency with the focal distance were analyzed and discussed.The fracturing mechanism of dry ice powder pneumatic rock breaking is studied.The research results show that:(1)The vibration velocity induced by dry ice powder pneumatic rock breaking decays as a power function with the increase of the focal distance;(2)The vibration frequency caused by dry ice powder pneumatic rock breaking is mainly distributed in 1–120 Hz.Due to the dispersion effect,the dominant frequency of 10–30 Hz appears abnormally attenuated;(3)The traditional CO_(2)phase change fracturing energy calculation formula is also applicable to dry ice pneumatic rock breaking technology,and the trinitrotoluene(TNT)equivalent of fracturing energy is applicable to the Sadovsky formula;(4)Dry ice powder pneumatic rock breaking is shock wave and highenergy gas acting together to fracture rock,which can be divided into three stages,among which the gas wedge action of high-energy gas plays a dominant role in rock mass damage.

Stability analysis of CO_(2)gas shielded welding short-circuit transition process based on GMAW dynamic model

Base on the arc phase and short-circuit phase and their relationship, the paper considers the changes of the extension of wire, the arc length, liquid bridge resistance and mass of liquid bridge, combines the improved “mass-spring” model with the loop model of welding power system, puts forward the critical judgment condition of droplet transition, and establishes a more accurate dynamic model for describing the short-circuit transition process. The dynamic changes of short-circuit transfer frequency, welding current and voltage, contact droplet and residual droplet equivalent radius and droplet equivalent radius at different wire feeding speeds were calculated and analyzed, and compared with the experimental results. It shows that the fluctuation of droplet displacement, velocity and wire extension length at the optimal arc starting point is the smallest. The smaller the initial liquid bridge curvature radius is, the better the stability of short-circuit transfer is.

Monsoon Break over the South China Sea during Summer: Statistical Features and Associated Atmospheric Anomalies

This study identifies break events of the South China Sea(SCS)summer monsoon(SCSSM)based on 42 years of data from 1979 to 2020,and investigates their statistical characteristics and associated atmospheric anomalies.A total of 214 break events are identified by examining the convection evolution during each monsoon season.It is found that most events occur between June and September and show a roughly even distribution.Short-lived events(3–7 days)are more frequent,accounting for about two thirds of total events,with the residual one third for long-lived events(8–24 days).The SCSSM break is featured by drastic variations in various atmospheric variables.Particularly,the convection and precipitation change from anomalous enhancement in adjoining periods to a substantial suppression during the break,with the differences being more than 60 W m−2 for outgoing longwave radiation(OLR)and 10 mm d−1 for precipitation.This convection/precipitation suppression is accompanied by an anomalous anticyclone in the lower troposphere,corresponding to a remarkable westward retreat of the monsoon trough from the Philippine Sea to the Indochina Peninsula,which reduces the transportation of water vapor into the SCS.Besides,the pseudo-equivalent potential temperature()declines sharply,mainly attributable to the local specific humidity reduction caused by downward dry advection.Furthermore,it is found that the suppressed convection and anomalous anticyclone responsible for the monsoon break form near the equatorial western Pacific and then propagate northwestward to the SCS.

Comparative Study of the Rock-breaking Mechanism of a Disc Cutter and Wedge Tooth Cutter by Discrete Element Modelling

The operation of a shield tunnel boring machine(TBM)in a high-strength hard rock stratum results in significant cutter damage,adversely affecting the thrust and torque of the cutter head.Therefore,it is very important to carry out the research on the stress characteristics and optimize the cutter parameters of cutters break high-strength hard rock.In this paper,the rock-breaking performance of cutters in an andesite stratum in the tunnel of Qingdao Metro Line No.8 was investigated using the discrete element method and theoretical analysis.The rock-breaking processes of a disc cutter and wedge tooth cutter were simulated by software particle flow code PFC^(3D),and the rock-breaking degree,stress of the cutter,and rock-breaking specific energy were analyzed.The rock damage caused by the cutter in a specific section was divided into three stages:the advanced influence,crushing,and stabilizing stages.The rock-breaking degree and the tangential and normal forces of the wedge tooth cutter are larger than that of the disc cutter under the same conditions.The disc cutter(wedge tooth cutter)has the highest rock-breaking efficiency at a cutter spacing of 100 mm(110 mm)and a penetration depth of 8 mm(10 mm),and the rock-breaking specific energy is 11.48 MJ/m^(3)(12.05 MJ/m^(3)).Therefore,two types of cutters with different penetration depths or cutter spacing should be considered.The number of teeth of wedge tooth cutters can be increased in hard strata to improve the rock-breaking efficiency of the shield.The research results provide a reference for shield cutterhead selection and cutter layout in similar projects.

多间隔信息融合的母线保护电流互感器断线再开放策略

对于电流互感器(CT)断线后发生金属性故障的情景,现有母线保护采取的闭锁差动保护动作方式将会引发多个变电站停电。此外,当母线区内发生高阻接地故障时,现有母线保护判据可能会将其误判为CT断线故障,不利于电力系统的安全稳定运行。针对这一问题,提出了一种母线保护CT断线再开放策略,该策略基于断线间隔与非断线间隔的零序电流变化量对负荷波动和故障进行区分,并基于非断线间隔的差流有效值和间隔失灵保护信息对区内外故障进行判别。实时数字仿真系统仿真结果验证了所提CT断线识别判据和再开放策略的正确性。

Rock breaking performance of the newly proposed unsubmerged cavitating abrasive waterjet

To improve the rock breaking ability, cavitating waterjet and abrasive waterjet are combined by using a coaxial low-speed waterjet generated around the periphery of a high-speed abrasive waterjet, and a new type of waterjet called unsubmerged cavitating abrasive waterjet(UCAWJ) is thus produced. The rock breaking performance of UCAWJ was compared with submerged cavitating abrasive waterjet(SCAWJ)and unsubmerged abrasive waterjet(UAWJ) by impinging sandstone specimens. Moreover, the effects of jet pressure, standoff distance, abrasive flow rate and concentration were studied by evaluating the specific energy consumption, and the area, depth, and mass loss of the eroded specimen. The results show that the artificially generated submerged environment in UCAWJ is able to enhance the rock breaking performance under the same operating parameters. Furthermore, the rock breaking performance of UCAWJ is much better at higher jet pressures and smaller standoff distances when compared with UAWJ. The greatest rock breaking ability of UCAWJ appears at jet pressure of 50 MPa and standoff distance of 32 mm, with the mass loss of sandstone increased by 370.6% and the energy dissipation decreased by 75.8%. In addition, under the experimental conditions the optimal abrasive flow rate and concentration are 76.5 m L/min and 3%, respectively.

Comprehensive evaluation of chemical breakers for multistage network ultra-high strength gel

Polymer gels have been accepted as a useful tool to address many sealing operations such as drilling and completion,well stimulation,wellbore integrity,water and gas shutoff,etc.Previously,we developed an ultra-high strength gel(USGel)for medium to ultra-low temperature reservoirs.However,the removal of USGel is a difficult problem for most temporary plugging operations.This paper first provides new insights into the mechanism of USGel,where multistage network structure and physical entanglement are the main reasons for USGel possessing ultra-high strength.Then the effects of acid breakers,encapsulated breakers,and oxidation breakers(including H_(2)O_(2),Na_(2)S_(2)O_(8),Ca(ClO)_(2),H_(2)O_(2)+NaOH,Na_(2)S_(2)O_(8)+NaOH,and Ca(ClO)_(2)+NaOH)were evaluated.The effects of component concentration and temperature on the breaking solution were studied,and the corrosion performance,physical simulation and formation damage tests of the breaking solution were carried out.The final formulation of 2%-4%NaOH+4.5%-6%H_(2)O_(2) breaking solution was determined,which can make USGel completely turn into water at 35e105C.The combinations of“acid t breaking solution”,“acid+encapsulated breaker”and“encapsulated breaker+breaking solution”were evaluated for breaking effect.The acid gradually reduced the volume of USGel,which increased the contact area between breaking solution and USGel,and the effect of“4%acid+breaking solution”was 23 times higher than that of breaking solution alone at 35C.However,the acid significantly reduced the strength of USGel.This paper provides new insights into the breaking of high-strength gels with complex network structures.

非刀具破岩理论与技术研究进展与趋势

随着我国深地战略的逐步实施,深部资源开采和地下空间建设迎来新的机遇,但也面临诸多挑战,高地应力、高地温和坚硬岩体等极端地质条件层出不穷。岩石破碎技术是所有资源开采和地下空间建设的主要工程活动,是决定施工工艺和工程效率的主要因素。在极端地质条件下,以刀具为基础的岩石破碎技术由于刀具磨损快、岩石破碎效率低,已成为遏制深地战略顺利实施的关键技术瓶颈,为解决深地岩石高效破碎难题,保障深地战略的顺利实施,迫切需求革命性的岩石破碎技术。无刀具破岩技术作为刀具破岩技术的重要补充,是突破刀具破岩技术瓶颈的可行性思路。为此,将无刀具破岩技术归纳为冲击破岩、热应力破岩和冲蚀磨损破岩3类技术体系,系统分析了水射流、激光和磨料空气射流等16种岩石破碎技术,总结了每种技术的发展历史和技术原理,分析了其破岩优势和技术瓶颈。得出,目前非刀具破岩技术没有在资源开采和地下空间建设中广泛应用的主要原因为破岩能耗高、适用较差和技术装备复杂等。相比刀具破岩,非刀具破岩技术破岩能量利用率较低,水射流破岩比能耗为刀具的40~70倍。微波、激光和等离子体等技术对施工环境要求较高,无法适用于钻井、隧道掘进等受限和恶劣环境。为解决极端地质条件岩石破碎难题,提出多种非刀具破岩技术协同破岩的思路,充分发挥每一种非刀具破岩的技术优势,构建了以射流切缝卸除高地应力、粒子冲击体积破碎坚硬岩体的破岩理念,最大限度降低岩石破碎能耗,简化系统装备,为岩石破碎技术向非刀具化发展提供理论支撑。