Bending strength and fracture surface topography of natural fiber-reinforced shell for investment casting process

In order to improve the properties of silica sol shell for investment casting process, various contents of cattail fibers were added into the slurry to prepare a fiber-reinforced shell in the present study. The bending strength of fiber-reinforced shell was investigated and the fracture surfaces of shell specimens were observed using SEM. It is found that the bending strength increases with the increase of fiber content, and the bending strength of a green shell with 1.0 wt.% fiber addition increases by 44% compared to the fiber-free shell. The failure of specimens of the fiber-reinforced green shell results from fiber rupture and debonding between the interface of fibers and adhesive under the bending load. The micro-crack propagation in the matrix is inhibited by the micro-holes for ablation of f ibers in specimens of the f iber-reinforced shell during the stage of being fired. As a result, the bending strength of specimens of the fired shell had no significant drop. Particularly, the bending strength of specimens of the fired shell reinforced with 0.6wt.% fiber reached the maximum value of 4.6 MPa.

Mechanical behaviour of fiber-reinforced grout in rock bolt reinforcement

Grouted rock bolts subject to axial loading in the field exhibit various failure modes,among which the most predominant one is the bolt-grout interface failure.Thus,mechanical characterization of the grout is essential for understanding its performance in ground support.To date,few studies have been conducted to characterize the mechanical behaviour of fiber-reinforced grout(FRG)in rock bolt reinforcement.Here we experimentally studied the mechanical behaviour of FRG under uniaxial compression,indirect tension,and direct shear loading conditions.We also conducted a series of pullout tests of rebar bolt encapsulated with different grouts including conventional cementitious grout and FRG.FRG was developed using 15%silica fume(SF)replacement of cement(by weight)and steel fiber to achieve highstrength and crack-resistance to overcome drawbacks of the conventional grout.Two types of steel fibers including straight and wavy steel fibers were further added to enhance the grout quality.The effect of fiber shape and fiber volume proportion on the grout mechanical properties were examined.Our experimental results showed that the addition of SF and steel fiber by 1.5%fiber volume proportion could lead to the highest compressive,tensile,and shear strengths of the grout.The minimum volume of fiber that could improve the mechanical properties of grout was found at 0.5%.The scanning electron microscopy(SEM)analysis demonstrated that steel fibers act as an excellent bridge to prevent the cracks from propagating at the interfacial region and hence to aid in maintaining the integrity of the cementitious grout.Our laboratory pullout tests further confirmed that FRG could prevent the cylindrical grout annulus from radial crack and hence improve the rebar’s load carrying capacity.Therefore,FRG has a potential to be utilized in civil and mining applications where high-strength and crack-resistance support is required.

基于SHELL模型的航空货物运输安全问题研究

文章阐述了SHELL 模型的基本理论,分析了航空货物运输的基本流程及常见安全问题,应用SHELL模型重点探究航空货物运输中人与硬件(L-H)、人与软件(L-S)、人与环境(L-E)及人与人(L-L)的要素特征与关系界面,梳理引发安全问题导致不安全事件的原因,提出缩小关系界面空隙、提高关系匹配度的措施,保障航空货物运输安全,促进航空货运持续稳定发展。

基于邻域K-shell分布的关键节点识别方法

复杂网络中关键节点的精准识别对于网络结构稳定和信息传播起着至关重要的作用。传统K-shell方法仅通过节点在网络中所处位置对节点的重要性进行评估,导致区分度不高。基于此,综合考虑了节点的全局信息和局部信息对节点重要性的影响,提出一种基于邻域K-shell分布的关键节点识别方法。该方法通过节点邻域Ks值定义节点的熵,从而反映邻居节点的K-shell分布特征。通过11个网络数据集上的仿真实验,验证了所提方法能够更准确地识别并区分复杂网络中的关键节点。

基于Shell脚本的KVM虚拟化技术应用

虚拟化技术是当前计算机信息技术中一个新的变革,其中开源的虚拟化技术(Kernel-Based Virtual Machines,KVM)更是以稳定、高效、经济而著称,为科学研究、工程仿真等领域提供了强大的计算能力。文章以某高职院校虚拟化应用为实例,探讨在普通高职院校的虚拟化技术应用管理中使用Shell脚本进行智能化管理,并展示其技术用于云平台辅助管理的优势,为用户轻便智能管理KVM虚拟化技术应用提供参考。

改进K-shell算法的城市道路网关键交叉口识别

交叉口重要性不仅与自身属性相关,还受相邻路段属性的影响,针对城市道路网中关键交叉口识别方法准确率不足的问题,提出一种考虑城市道路网特性的改进K-shell算法。即在传统K-shell算法基础上,综合考虑交叉口及其相邻路段的结构特性与交通特性,提出交叉口重要度的概念,利用CRITIC法确定交叉口重要度中相关指标的权重系数,对城市道路网中的交叉口进行重要性排序。以哈尔滨市二环内道路网为例,构建级联失效模型,分析随着失效交叉口比例的增加,不同排序方法下的网络效率、网络最大连通子图比率、故障节点比率的波动情况,结果表明,改进K-shell算法能够更加有效地识别城市道路网关键交叉口。

Experimental study of polyurea-coated fiber-reinforced cement boards under gas explosions

Five types of polyurea elastomers were synthesized by changing the isocyanate component and the mechanical properties of polyurea materials were measured. Fiber-reinforced cement boards(FRCB)strengthened by polyurea with different formulations were processed, and a series of experiments were carried out on the specimens with gas explosion devices. The results showed that the conventional mechanical properties of different types of polyureas had their own advantages. Based on the gas explosion overpressure criterion, the blast resistances of reinforced plates were quantitatively evaluated,and the best polyurea was selected to guide the formulation design. The three typical failure modes of polyurea-reinforced FRCBs were flexural, shear, and flexural-shear failure. Dynamic thermodynamics and shock wave spectral analysis revealed that the polyurea did not undergo a glass transition in the gas explosion tests but retained its elastic properties, allowing it to effectively wrap the fragments formed by the brittle substrates.

Mechanical Performance of Bio-inspired Bidirectional Corrugated Sandwich Pressure Shell Under External Hydrostatic Pressure

This paper aims to enhance the compression capacity of underwater cylindrical shells by adopting the corrugated sandwich structure of cuttlebone.The cuttlebone suffers uniaxial external compression,while underwater cylindrical shells are in a biaxial compressive stress state.To suit the biaxial compressive stress state,a novel bidirectional corrugated sandwich structure is proposed to improve the bearing capacity of cylindrical shells.The static and buckling analysis for the sandwich shell and the unstiffened cylindrical shell with the same volume-weight ratio are studied by numerical simulation.It is indicated that the proposed sandwich shell can effectively reduce the ratio between circumferential and axial stress from 2 to 1.25 and improve the critical buckling load by about 1.63 times.Numerical simulation shows that optimizing and adjusting the structural parameters could significantly improve the advantage of the sandwich shell.Then,the hydrostatic pressure tests for shell models fabricated by 3D printing are carried out.According to the experimental results,the overall failure position of the sandwich shell is at the center part of the sandwich shell.It has been found the average critical load of the proposed sandwich shell models exceeds two times that of the unstiffened shell models.Hence,the proposed bio-inspired bidirectional corrugated sandwich structure can significantly enhance the pressure resistance capability of cylindrical shells.

Snap-through behaviors and nonlinear vibrations of a bistable composite laminated cantilever shell:an experimental and numerical study

The snap-through behaviors and nonlinear vibrations are investigated for a bistable composite laminated cantilever shell subjected to transversal foundation excitation based on experimental and theoretical approaches.An improved experimental specimen is designed in order to satisfy the cantilever support boundary condition,which is composed of an asymmetric region and a symmetric region.The symmetric region of the experimental specimen is entirely clamped,which is rigidly connected to an electromagnetic shaker,while the asymmetric region remains free of constraint.Different motion paths are realized for the bistable cantilever shell by changing the input signal levels of the electromagnetic shaker,and the displacement responses of the shell are collected by the laser displacement sensors.The numerical simulation is conducted based on the established theoretical model of the bistable composite laminated cantilever shell,and an off-axis three-dimensional dynamic snap-through domain is obtained.The numerical solutions are in good agreement with the experimental results.The nonlinear stiffness characteristics,dynamic snap-through domain,and chaos and bifurcation behaviors of the shell are quantitatively analyzed.Due to the asymmetry of the boundary condition and the shell,the upper stable-state of the shell exhibits an obvious soft spring stiffness characteristic,and the lower stable-state shows a linear stiffness characteristic of the shell.

基于Python和Shell的《Linux实训项目自测平台》软件设计

近年来,Linux操作系统在各国不断地发展与推广,高等院校开设的Linux操作系统课程也越来越受到重视。通过对软件界面设计及在Linux操作系统中检测实训项目的几种常用方式进行分析和研究,给操作系统课程教学提供一种教学思路,同时对Linux教学辅助软件开发者提供一些借鉴和参考。

Enhancing electromagnetic wave absorption with core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres

Material composition and structural design are important factors influencing the electromagnetic wave(EMW)absorption performance of materials.To alleviate the impedance mismatch attributed to the high dielectric constant of Ti_(3)C_(2)T_(x)MXene,we have successfully synthesized core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres.This architecture,comprising SiO_(2)as the core,MXene as the intermediate layer,and MoS_(2)as the outer shell,is achieved through an electrostatic self‐assembly method combined with a hydrothermal process.This complex core‐shell structure not only provides a variety of loss mechanisms that effectively dissipate electromagnetic energy but also prevents self‐aggregation of MXene and MoS_(2)nanosheets.Notably,the synergistic combination of SiO_(2)and MoS_(2)with highly conductive MXene enables the suitable dielectric constant of the composites,ensuring optimal impedance matching.Therefore,the core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres exhibit excellent EMW absorption performance,featuring a remarkable minimum reflection loss(RL_(min))of−52.11 dB(2.4 mm).It is noteworthy that these nanospheres achieve an ultra‐wide effective absorption bandwidth(EAB)of 6.72 GHz.This work provides a novel approach for designing and synthesizing high‐performance EMW absorbers characterized by“wide bandwidth and strong reflection loss.”

Cl/S与Na相互作用对Shell气化炉合成气冷却器入口积灰机制的影响

Shell干粉煤加压气化是煤炭洁净高效利用的重要技术之一,由碱金属化合物引起的合成气冷却器入口积灰结垢是导致气化炉非正常停工检修的主要原因。以添加不同含量的Na、Cl和S的Shell气化炉飞灰为原料,利用自主设计的高温竖直炉中沉积探针模拟Shell气化炉合成气冷却器入口管路,通过对积灰进行内、外分层研究,探讨内外层积灰质量的变化,并结合ICP-MS、IC、SEM-EDS和XRD等表征手段对内外层积灰的理化性质进行比较分析,获得Na、Cl、S和Fe等不同元素之间的相互作用对积灰行为的影响。结果表明,内层积灰质量随时间延长而增大,含S化合物的添加会降低内外层积灰质量,且外层积灰质量会随着时间延长而减小。Na更多以铝硅酸盐形式在外层积灰中存在,促进积灰增长;Cl通常以碱金属氯化物的形式集中在初始黏性层;S的存在会减缓管路积灰;当Cl和S共同存在时,Fe易与灰中的Si、Al和Na形成多种低温共熔物促进内、外层积灰熔融。Shell气化炉合成气冷却器入口积灰形成机制为:飞灰颗粒组分在Na、Cl、Si和Al的共同作用下,于内层形成碱金属氯化物和铝硅酸盐共晶;同时Cl、S的存在促使Fe和Na迁移到这些共晶中,形成Fe-O-Si、Fe-O-S和Fe-Na-O-Al-S共熔体。进而,铝硅酸盐与多种低温共熔体相互熔融使灰颗粒尺寸增加,促进积灰的进一步生长。

Dynamics of a rotating ring-stiffened sandwich conical shell with an auxetic honeycomb core

The free vibration analysis of a rotating sandwich conical shell with a reentrant auxetic honeycomb core and homogenous isotropic face layers reinforced with a ring support is studied.The shell is modeled utilizing the first-order shear deformation theory(FSDT)incorporating the relative,centripetal,and Coriolis accelerations alongside the initial hoop tension created by the rotation.The governing equations,compatibility conditions,and boundary conditions are attained using Hamilton’s principle.Utilizing trigonometric functions,an analytical solution is derived in the circumferential direction,and a numerical one is presented in the meridional direction via the differential quadrature method(DQM).The effects of various factors on the critical rotational speeds and forward and backward frequencies of the shell are studied.The present work is the first theoretical work regarding the dynamic analysis of a rotating sandwich conical shell with an auxetic honeycomb core strengthened with a ring support.

Comparative Transcriptome Analysis of Shell-Matrix-Protein Genes and Observation of the Shell Microstructure in the Deep-Sea Clam Calyptogena marissinica

The deep-sea clam Calyptogena marissinica is widely distributed in the Haima cold seep ecosystem on the northwes-tern slope of the South China Sea with low pH values,low temperature and high pressure.Limited information is available on the biomineralization of this species.In this research,we generated a comprehensive transcript dataset of C.marissinica’s mantle tissue,and a total of 19821 unigenes were assembled.Fourteen shell matrix proteins(SMP)-related genes were identified.The qPCR results showed that four out of six prismatic matrix genes(MSP2,MSP5,prisilkin-39,and shematrin),four out of the six nacreous matrix genes(perlucin,pif,pif97,and papilin),and two extrapallial fluid proteins(SPARC and calmodulin)were significantly expressed in the mantle.Both the nacreous and the prismatic layers are chrysanthemum-shaped,which are stacked on the top of each other to form a laminated nacreous structure.The alignment and phylogenetic analysis of MSP-5,Prisilkin-39,Perlucin,and Pif homologues showed that some amino acids of C.marissinica that differed from those detected in other molluscs may cause the different shape of the nacreous and prismatic layers,but do not lead to a change in the species’evolutionary status.These results indicated the conservation of the functions of SMP-related genes in C.marissinica,and the specific shape of the prismatic and nacreous layers of this deep-sea mollusc,which will contribute to the research on the molecular regulation mechanisms of biomineralization in C.marissinica and provide a new perspective to investigate biomineralization in deep-sea clams in general.

Identification of Shell Color-Associated Genes Using Mantle Branch-Specific RNA Sequencing of Yellow-Colored Line of Pearl Oyster Pinctada fucata martensii

The yellow-colored line of pearl oyster Pinctada fucata martensii displays a yellow prismatic layer and a white nacreous layer that can be used as an ideal model for research on shell color formation.Micro-Raman spectroscopy and transcriptome analyses were performed to explore the potential molecular mechanism underlying the phenotype differentiation.The micro-Raman spectroscopy results indicate that the prismatic layer exhibits distinct characteristic peaks of carotenoids,while these peaks are not prominent in the nacreous layer.In the transcriptome comparison of the central zone of mantle and mantle edge tissue,which function in nacreous and prismatic layer formation,respectively,935 significantly differentially expressed genes(DEGs)were identified,with 385 genes upregulated and 227 genes downregulated(|log_(2)(Fold change)|>1 and false discovery rate<0.05)in the mantle edge tissue.Among these genes,some were associated with melanoma/melanogenesis,such as tyrosinase,zinc metalloprotease,glutathione S-transferase,and ATP-binding cassette sub-family;some were associated with the carotenoid-related pathway,including scavenger receptors,cytochrome P450 and lipoprotein receptor.Genes associated with porphyrin metabolism,including porphobilinogen deaminase,and copper/zinc superoxide dismutase,and genes associated with shell matrix protein,including amorphous calcium carbonate binding protein,shematrin,PIF,and collagen,also exhibited significantly different expressions.It is speculated that the different colours between prismatic layer and nacreous layer in the yellow-colored line of P.f.martensii might be resulted from melanin,carotenoids and porphyrin metabolism,while genes related to shell structure and biomineralization might also affect coloration.Our results provide new insights to understand the mechanism of shell color formation in mollusca.

Dynamic response of honeycomb-FGS shells subjected to the dynamic loading using non-polynomial higher-order IGA

The main goal of this study is to use higher-order isogeometric analysis(IGA)to study the dynamic response of sandwich shells with an auxetic honeycomb core and two different functionally graded materials(FGM)skin layers(namely honeycomb-FGS shells)subjected to dynamic loading.Touratier's non-polynomial higher-order shear deformation theory(HSDT)is used due to its simplicity and performance.The governing equation is derived from Hamilton's principle.After verifying the present approach,the effect of input parameters on the dynamic response of honeycomb-FGS shells is carried out in detail.

Control and vibration analyses of a sandwich doubly curved micro-composite shell with honeycomb,truss,and corrugated cores based on the fourth-order shear deformation theory

Curved shells are increasingly utilized in applied engineering due to their shared characteristics with other sandwich structures,flexibility,and attractive appearance.However,the inability of controlling and regulating vibrations and destroying them afterward is a challenge to scientists.In this paper,the curve shell equations and a linear quadratic regulator are adopted for the state feedback design to manage the structure vibrations in state space forms.A five-layer sandwich doubly curved micro-composite shell,comprising two piezoelectric layers for the sensor and actuator,is modeled by the fourth-order shear deformation theory.The core(honeycomb,truss,and corrugated)is analyzed for the bearing of transverse shear forces.The results show that the honeycomb core has a greater effect on the vibrations.When the parameters related to the core and the weight percentage of graphene increase,the frequency increases.The uniform distribution of graphene platelets results in the lowest natural frequency while the natural frequency increases.Furthermore,without taking into account the piezoelectric layers,the third-order shear deformation theory(TSDT)and fourth-order shear deformation theory(FOSDT)align closely.However,when the piezoelectric layers are incorporated,these two theories diverge significantly,with the frequencies in the FOSDT being lower than those in the TSDT.

“Yolk-shell”结构中高效双酶级联催化体系的构筑

合成了一种生物-无机杂化材料ZIF-8@GOx-CPO@ZIF-8,该材料以具有“蛋黄-壳(Yolk-shell)”结构的金属有机框架(MOF)为载体,将葡萄糖氧化酶(GOx)和氯过氧化物酶(CPO)封装在不同隔离空间中构建了双酶纳米反应器.“Yolk-shell”结构可为封装的酶提供纳米邻近效应,GOx催化底物原位生成的H_(2)O_(2)可启动相邻的CPO催化反应,有效减少了反应物的扩散阻力和H_(2)O_(2)的分解和逃逸,同时避免了两种酶催化反应的相互影响.与均相缓冲液中的游离酶相比,ZIF-8@GOx-CPO@ZIF-8的级联催化效率更高.由于MOF的屏蔽效应,酶的热稳定性和有机溶剂耐受性显著提高.“Yolk-shell”结构还可有效抑制材料重复使用过程中酶分子的泄漏,经过20次重复使用后,ZIF-8@GOx-CPO@ZIF-8仍可保持初始级联催化效率的72%.将ZIF-8@GOx-CPO@ZIF-8双酶级联反应生成的HClO应用于偶氮染料的高效脱色和水果保鲜.在1 mg/mL ZIF-8@GOx-CPO@ZIF-8水溶液中,橙黄G(0.3 mmol/L)在15 min内可完成脱色(脱色率>98%).在新鲜草莓的杀菌保鲜实验中,ZIF-8@GOx-CPO@ZIF-8也显示出良好效果.ZIF-8@GOx-CPO@ZIF-8双酶级联催化体系具有高效、稳定、温和及绿色的特点,极具应用潜力.

Kentish Plover(Charadrius alexandrinus) and Little Tern(Sternula albifrons) prefer shells for nesting:A field experiment

Shorebird populations are declining worldwide,mainly due to human disturbances and loss of coastal wetlands.However,supratidal habitats as saltpans could play a role in buffering human impact.Saltpans have shown to be important as feeding or breeding sites of some shorebird species.A potential conservation strategy to increase shorebird populations in saltpans is to manipulate the cues that birds use to select optimal breeding habitat.Here it is hypothesized that shorebirds are attracted to bivalve shells due to the advantages they offer.Following this hypothesis,we supplemented a restored saltpan in 2019 and 2021 with bivalve shells,expecting an increase in the number of breeding birds’ nests.More than 75% of Kentish Plover(Charadrius alexandrinus) and Little Tern(Sternula albifrons) nests were found in patches with shells in both years.The best model for both species indicates that the presence of shells is the factor that most correlates with the location of nests.The probability of choosing one place over another to settle their nest increases in areas with an abundance of shells,double in the case of the Kentish Plover and triple in the case of the Little Tern.The result of this study may constitute a valuable tool for attracting birds to restored saltpans and could contribute to the success of expensive restoration projects where time is usually a constraint.

Simple and High-Yield Synthesis of a Thinner Layer of Graphenic Carbon from Coconut Shells

Biomass has become of recent interest as a raw material for‘green’graphenic carbon(GC)since it promotes an environmentally friendly approach.Here,we investigate a single pyrolysis route to synthesize GC from coconut shells which provides a simple method and can produce a high yield,thus being convenient for large-scale pro-duction.The pyrolysis involves a stepped holding process at 350℃ for 1 h and at 650℃ or 900℃ for 3 h.The GC sample resulted at the 900℃ pyrolysis has a thinner sheet,a less porous structure,a higher C/O ratio,and an enhanced electrical conductivity than those pyrolyzed at 650℃.The addition of Na3PO4 catalyst has no signifi-cant effects on the GC structures obtained by this route.The single pyrolysis route generates thinner GC sheets compared to the two-step heat treatment followed by the liquid phase exfoliation(LPE)procedure.Nevertheless,the latter method offers a formation of clean samples with a porous or holey feature which has potential for advanced energy-storage applications.