Experimental and numerical study on dynamic mechanical behaviors of shale under true triaxial compression at high strain rate

High-energy gas fracturing of shale is a novel,high efficacy and eco-friendly mining technique,which is a typical dynamic perturbing behavior.To effectively extract shale gas,it is important to understand the dynamic mechanical properties of shale.Dynamic experiments on shale subjected to true triaxial compression at different strain rates are first conducted in this research.The dynamic stress-strain curves,peak strain,peak stress and failure modes of shale are investigated.The results of the study indicate that the intermediate principal stress and the minor principal stress have the significant influence on the dynamic mechanical behaviors,although this effect decreases as the strain rate increases.The characteristics of compression-shear failure primarily occur in shale subjected to triaxial compression at high strain rates,which distinguishes it from the fragmentation characteristics observed in shale under dynamic uniaxial compression.Additionally,a numerical three-dimensional Split Hopkinson Pressure Bar(3D-SHPB),which is established by coupling PFC3D and FLAC3D methods,is validated to replicate the laboratory characteristics of shale.The dynamic mechanical characteristics of shale subjected to different confining stresses are systematically investigated by the coupling PFC3D and FLAC3D method.The numerical results are in good agreement with the experimental data.

Two-dimensional plane strain consolidation of unsaturated soils considering the depth-dependent stress

In practical engineering,the total vertical stress in the soil layer is not constant due to stress diffusion,and varies with time and depth.Therefore,the purpose of this paper is to investigate the effect of stress diffusion on the two-dimensional(2D)plane strain consolidation properties of unsaturated soils when the stress varies with time and depth.A series of semi-analytical solutions in terms of excess pore air and water pressures and settlement for 2D plane strain consolidation of unsaturated soils can be derived with the joint use of Laplace transform and Fourier sine series expansion.Then,the inverse Laplace transform of the semi-analytical solution is given in the time domain using a self-programmed code based on Crump’s method.The reliability of the obtained solutions is proved by the degeneration.Finally,the 2D plots of excess pore pressures and the curves of settlement varying with time,considering different physical parameters of unsaturated soil stratum and depth-dependent stress,are depicted and analyzed to study the 2D plane strain consolidation properties of unsaturated soils subjected to the depthdependent stress.

Hot tearing behavior of AZ91D magnesium alloy

Hot tearing is a serious destructive solidification defect of magnesium alloys and other casting metals.Quantitative and controllable measurements on the thermal and the mechanical behavior of an alloy during its solidification process are crucial for the understanding of hot tearing formation.We developed a new experimental method and setup to characterize hot tearing behavior via controlled cooling and active loading to force hot hearing formation on cooling at selected fractions of solid.The experimental setup was fully instrumented so that stress,strain,strain rate,and temperature can be measured in-situ while hot tearing was developing.An AZ91D magnesium alloy,which is prone to hot tearing,was used in this study.Results indicate that when hot hearing occurred,the local temperature,critical stress,and cumulative strain were directly affected by strain rate.Depending on the applied strain rate,hot tearing of the AZ91D magnesium alloy could occur in two solidification stages:one in the dendrite solidification stage(fS∼0.81-0.82)and the other in the eutectic solidification stage(fS∼0.99).AZ91D alloy exhibited distinct mechanical behaviors in these two ranges of fraction solid.

鸡传染性支气管炎病毒D_(41) 株S1基因部分序列的测定

通过反转录及变退火温度ＰＣＲ方法扩增出含先导序列的ＩＢＶ广东地方分离株Ｄ４１的Ｓ１基因ｃＤＮＡ，长度约１．７ｋｂ．利用双脱氧链终止法对其５′端测序，准确读到３４２个碱基，并确定了翻译起始密码子ＡＴＧ的位置．

D汕A(B)、丛广41A(B)原种提纯总结

总结了三系杂交稻亲本D汕A(B)和丛广 4 1A(B)的原种提纯工作。 1989～ 1993年 ,采用“一选三圃”法提纯D汕A(B) ,D汕A(B)纯度分别从 99.8%和 99.98%提高到 99.98%和 99.997% ;1994年至今 ,采用“一选二圃法”对丛广 4 1A(B)提纯 ,其纯度分别由 96 .5 4 %和 99.9%提高到 99.9%和 99.99% ;

MCM-41分子筛催化D-葡萄糖酸制备D-葡萄糖酸-δ-内酯的研究

以MCM-41分子筛为催化剂,由D-葡萄糖酸制备D-葡萄糖酸-δ-内酯。考察了反应温度、反应时间、催化剂用量以及催化剂循环使用次数对D-葡萄糖酸-δ-内酯产率的影响。实验结果表明,MCM-41是制备D-葡萄糖酸-δ-内酯较好的催化剂。最佳工艺条件为:催化剂用量为30%,反应温度80℃,反应时间2 h,D-葡萄糖酸-δ-内酯产率达到90.39%。

IBVD41株主要结构基因及3′端非编码区序列分析

采用反转录及聚合酶链式反应 ( RT-PCR) ,成功地扩增出鸡传染性支气管炎病毒 ( IBV)人工致弱毒D41株 S1基因、M基因、N基因和基因组 3′端非编码区 ( U TR)的 c DNA。序列测定结果表明 :D41株的 S1基因全长 1611bp(从 ATG到 S前体蛋白裂解位点 ) ,编码一条由 53 7个氨基酸组成的多肽 ;M基因全长 678bp,编码一条由 2 2 6个氨基酸组成的多肽 ;N基因全长 12 3 0 bp,编码一条由 410个氨基酸残基组成的多肽 ,3′端 UTR长度为52 5bp,其中高变区 ( HVR)长度为 2 2 5bp。与国内外已报道的一些 IBV标准毒株的相应基因序列进行核苷酸序列同源性分析后发现 :D41株与麻省血清型的毒株同源性最高 ,尤其与国际常用的标准疫苗株 H52和 H12 0的亲缘关系最接近。但它与国内“腺胃型”毒株

应变式弹性成像联合D-二聚体对下肢深静脉血栓分期的诊断价值

目的 探讨应变式弹性成像(SE)联合D-二聚体对下肢深静脉血栓(DVT)分期的诊断价值。方法 回顾性选取2020年10月至2022年10月在聊城市人民医院经下肢深静脉彩色多普勒超声确诊为下肢DVT的患者86例。根据下肢DVT临床分期标准分为急性期(发病14 d内)28例、亚急性期(发病15 d~6个月)31例、慢性期(发病6个月以上)27例。行SE检查与D-D检测。比较不同分期患者SE参数[SE弹性评分、血栓应变率比值(SR)]和D-D水平差异,应用受试者工作特征(ROC)曲线分析SE联合D-二聚体对下肢DVT分期的诊断价值。结果 不同分期患者SE参数和D-二聚体比较,差异均有统计学意义(P<0.05);急性期患者SE弹性评分及SR分别为(1.96±0.48)分、0.97±0.29,均低于亚急性期[(3.01±0.63)分、1.69±0.56]和慢性期患者[(4.14±0.59)分、3.07±0.73],D-二聚体水平为(0.96±0.09) mg/L,高于亚急性期[(0.75±0.09) mg/L]和慢性期患者[(0.59±0.08) mg/L],亚急性期患者SE弹性评分及SR均低于慢性期患者,D-二聚体水平高于慢性期患者,差异均有统计学意义(P<0.05)。ROC曲线分析显示,SE联合D-二聚体诊断下肢DVT分期(急性期、亚急性期)的曲线下面积为0.989,敏感度为93.55%,特异度为96.55%,95%CI:0.919~1.000,预测价值较好(P<0.001);SE联合D-二聚体诊断下肢DVT分期(亚急性期、慢性期)的曲线下面积为0.978,敏感度为92.59%,特异度为96.77%,95%CI:0.901~0.999,预测价值较好(P<0.001)。结论 SE对下肢DVT分期有诊断作用,且联合D-二聚体能够提高诊断效能。

Characteristics and mechanisms of strain waves generated in rock by cylindrical explosive charges

A superposing principle, by suitably adding the strain waves from a number of concentrated explosive charges to approximate the waves generated by a cylindrical charge based on the strain wave of a point or small spherical explosive charge generated in rock, is used to further study the triggering time of strain gauges installed in radial direction at same distances but different positions surrounding a cylindrical explosive charge in rock. The duration of the first compression phase and peak value of strain wave, and furthermore, their differences are analyzed and some explanations are given. Besides that, the gauge orientation in which the maximum peak value occurs is also discussed. At last, the effect of velocity of detonation(V.O.D.) of a cylindrical explosive charge on the strain waves generated in the surrounding rock is taken as key research and the pattern of peak amplitude of a strain wave varies with the V.O.D. is likely to have been found.

Crack initiation stress and strain of jointed rock containing multi-cracks under uniaxial compressive loading: A particle flow code approach

The ratio of crack initiation stress to the uniaxial compressive strength(SCI,B/SUC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength(B,UCB,CI,A,A/SSSS) were studied by performing numerical stress analysis on blocks having multi flaws at close spacing's under uniaxial loading using PFC3 D. The following findings are obtained: SCI,B/SUC,B has an average value of about 0.5 with a variability of ± 0.1. This range agrees quite well with the values obtained by former research. For joint inclination angle, β=90°,B,UCB,CI,A,A/SSSS is found to be around 0.48 irrespective of the value of joint continuity factor, k. No particular relation is found betweenB,UCB,CI,A,A/SSSS and β; however, the average B,UCB,CI,A,A/SSSS seems to slightly decrease with increasing k. The variability ofB,UCB,CI,A,A/SSSS is found to increase with k.Based on the cases studied in this work,B,UCB,CI,A,A/SSSS ranges between 0.3 and 0.5. This range is quite close to the range of 0.4to 0.6 obtained for SCI,B/SUC,B. The highest variability of ± 0.12 forB,UCB,CI,A,A/SSSS is obtained for k=0.8. For the remaining k values the variability ofB,UCB,CI,A,A/SSSS can be expressed within ± 0.05. This finding is very similar to the finding obtained for the variability of SCI,B/SUC,B.

Recent Advances in Strain-Induced Piezoelectric and Piezoresistive Effect-Engineered 2D Semiconductors for Adaptive Electronics and Optoelectronics

The development of two-dimensional(2D)semiconductors has attracted widespread attentions in the scientific community and industry due to their ultra-thin thickness,unique structure,excellent optoelectronic properties and novel physics.The excellent flexibility and outstanding mechanical strength of 2D semiconductors provide opportunities for fabricated strain-sensitive devices and utilized strain tuning their electronic and optic–electric performance.The strain-engineered one-dimensional materials have been well investigated,while there is a long way to go for 2D semiconductors.In this review,starting with the fundamental theories of piezoelectric and piezoresistive effect resulted by strain,following we reviewed the recent simulation works of strain engineering in novel 2D semiconductors,such as Janus 2D and 2D-Xene structures.Moreover,recent advances in experimental observation of strain tuning PL spectra and transport behavior of 2D semiconductors are summarized.Furthermore,the applications of strain-engineered 2D semiconductors in sensors,photodetectors and nanogenerators are also highlighted.At last,we in-depth discussed future research directions of strain-engineered 2D semiconductor and related electronics and optoelectronics device applications.

Scaling law of hydrogen evolution reaction for InSe monolayer with 3d transition metals doping and strain engineering

Recently, two dimensional In Se attracts great attentions as potential hydrogen production photocatalysts.Here, comprehensive investigations on the hydrogen evolution reaction activity of In Se monolayer with3 d transition metal doping and biaxial strain were performed based on the density functional theory.Transition metal dopants significantly increase the bonding strength between H and Se, and then adjust the hydrogen adsorption free energy to 0.02 e V by Zn doping. The enhanced hydrogen evolution reaction activity results from less electron occupying H 1 s-Se 4 pzanti-bonding states, which is well correlated with the pzband center level. Importantly, the universal scalling law was proposed to descript the evolution of hydrogen adsorption free energy including both doping and strain effects. Moreover, with appropriate band alignment, optical absorption, and carriers separation ability, Zn doped In Se monolayer is considered as a promising candidate of visible-light photocatalyst for hydrogen production.

Isogeometric nonlocal strain gradient quasi-three-dimensional plate model for thermal postbuckling of porous functionally graded microplates with central cutout with different shapes

This study presents the size-dependent nonlinear thermal postbuckling characteristics of a porous functionally graded material(PFGM) microplate with a central cutout with various shapes using isogeometric numerical technique incorporating nonuniform rational B-splines. To construct the proposed non-classical plate model, the nonlocal strain gradient continuum elasticity is adopted on the basis of a hybrid quasithree-dimensional(3D) plate theory under through-thickness deformation conditions by only four variables. By taking a refined power-law function into account in conjunction with the Touloukian scheme, the temperature-porosity-dependent material properties are extracted. With the aid of the assembled isogeometric-based finite element formulations,nonlocal strain gradient thermal postbuckling curves are acquired for various boundary conditions as well as geometrical and material parameters. It is portrayed that for both size dependency types, by going deeper in the thermal postbuckling domain, gaps among equilibrium curves associated with various small scale parameter values get lower, which indicates that the pronounce of size effects reduces by going deeper in the thermal postbuckling regime. Moreover, we observe that the central cutout effect on the temperature rise associated with the thermal postbuckling behavior in the presence of the effect of strain gradient size and absence of nonlocality is stronger compared with the case including nonlocality in absence of the strain gradient small scale effect.

Correction of hypovitaminosis D improved global longitudinal strain earlier than left ventricular ejection fraction in cardiovascular older adults after orthopaedic surgery

Background Cardiovascular diseases and insufficient levels of vitamin D are risk factors for adverse surgical outcomes, and they are both commonly present among older adults undergoing orthopaedic surgery. Giving the cardiovascular effects of vitamin D, pre-operative diagnosis of hypovitaminosis D would be a valuable step for the implementation of supplementation protocols. We investigated if the nor- malization of serum 25 [OH] D could ameliorate cardiac performance of older adults suffering from cardiovascular diseases. Methods We enrolled 47 older adults scheduled for major orthopaedic surgery and suffering from hypovitaminosis D. Patients underwent 6-months cal- cifediol supplementation with a starting dose at first post-operative day of 50 ~tg/die in liquid preparation. Down-titration to 20 Ixg/die at 3-months assessment was planned. Cardiac performance was evaluated by measuring left ventricular ejection fraction （LVEF） and global longitudinal strain （GLS） during pre-operative assessments and at 1-month, 3-months, 6-months follow-ups. Results Six months of cal- cifediol supplementation were associated with a significant improvement of both LVEF （＋ 3.94%; 95% CI： -4.0789 to -0.8232; P 〈 0.01） and GLS （＋ 18.56%; Z = -5.895; P 〈 0.0001）. Conclusions Calcifediol supplementation normalized serum 25 [OH] D concentration after 1-month treatment. GLS offered better insights into myocardial contractile amelioration than LVEF, thus being useful for detecting earlier subclinical changes that may anticipate hemodynamic modifications.

The 4-D integrated geodesy and strain analysis

Research of the practical 4-D integrated geodesy(IG) and strain analysis is presented in this paper.The practical model and basic observation equation are established by using IG and dynamic adjustment.Furthermore,the observation equations about gravity vector,zenith distance,azimuth angle,difference are derived and determination of local gravity field covariance solved.The 3-D strain formular is derived and the strain parameters calculated from it.The improvement of the OPERA software of Landan and Hem etc,FRG has been done to get a new software in Fortran Language which implements in MASSCOMP computer.Using the software,the integrated adjustment of two term observation data of triangle chain, triangle net,gravity,level,astronomic observation and strain analysis are established.The result is satisfactory.

Modulation Effects of the 3D Strain Microenvironment on Characteristics of Mesenchymal Stem Cell-Derived Exosomes

It is necessary to investigate the characteristics of Mesenchymal stem cells(MSCs)derived exosomes,and especially their application in tissue regeneration.Previous studies have shown that inflammatory stimulation enhanced the secretion of MSC-derived exosomes with stronger anti-inflammatory protein,cytokine profiles,and functional RNA via altering COX2/PGE2 pathway.Recently,accumulating evidence has also revealed that biophysical cues(especially biomechanical cues)in cell microenvironment have significant effects not only on cells but also on their exosomes.It has been reported that applying bi-axial strain to MSCs induces formation of a stiffer cytoskeleton through mTORC2 signaling,which biases against adipogenic differentiation and toward osteoblastogenesis.At the same time,For example,dimensionality,composition and stiffness of the extracellular matrix(ECM)has been proved to affect the size and composition of exosomes secreted by cancer cells.However,the effects of biomechanical cues in the three-dimensional(3D)microenvironment on stem cell-derived exosomes remains to be unveiled.Therefore,it is important to understand the roles of 3D cell mechanical microenvironment in regulating the characteristics of stem cell-derived exosomes and develop more efficient approaches to enhance their functions.This study aimed to explore the changes in characteristics of exosomes secreted by MSCs in periodontium in response to the matrix strain in 3D.Periodontal ligament stem cells(PDLSCs)were cultured in a 3D strain microenvironment engineered with microscale magnetically stretched collagen hydrogels.The morphology,particle distribution,marker protein expression of PDLSC-derived exosomes were analyzed.Then the pro-osteogenic property of exosomes was evaluated by assessing cell viability,proliferation,migration and osteogenic differentiation of target cells,for instance human bone marrow mesenchymal stem cells(hBMSCs).Detailed characterizations revealed that PDLSC-derived exosomes in the 3D strain mi-croenvironment were with similar morphology,particle distribution and surface markers.Notably,Exosomes secreted by PDLSCs in strain microenvironment were more endocytosed by hBMSCs and were more potent in improving proliferation and migration of hBMSCs,comparing with PDLSCs in non-strain environment.Alizarin red staining and molecular biology experiments confirmed that treatment of exosomes secreted by PDLSCs under mechanical stimulation led to a significant increase in osteogenic differentiation of hBMSCs in vitro.Meanwhile,in vivo study also indicated that PDLSC-derived exosomes obtained from the 3D strain microenvironment could obviously promote new bone formation.Our findings revealed that mechanical cues profoundly affected the characteristics of PDLSC-derived exosomes,especially for their bio-activity,providing a foundation for using the 3D mechanical microenvironment to enhance the osteo-inductive functions of stem cell-derived exosomes in cell-free therapy for bone regeneration.

A novel two-dimensional SiO sheet with high-stability,strain tunable electronic structure,and excellent mechanical properties

Using the structure search of particle swarm optimization(PSO)algorithm combined with density functional theory(DFT),we conduct a systematic two-dimensional(2D)material research on the SiO and discover a P2 monolayer structure.The phonon spectrum shows that the 2D P2 is dynamic-stable under ambient pressure.Molecular dynamics simulations show that 2D P2 can still exist stably at a high temperature of 1000 K,indicating that 2D P2 has application potential in high-temperature environments.The intrinsic 2D P2 structure has a quasi-direct band gap of 3.2 e V.The 2D P2 structure can be transformed into a direct band gap semiconductor by appropriate strain,and the band gap can be adjusted to the ideal band gap of 1.2 e V–1.6 e V for photovoltaic materials.These unique properties of the 2D P2 structure make it expected to have potential applications in nanomechanics and nanoelectronics.

Versatile GaInO_3-sheet with strain-tunable electronic structure,excellent mechanical flexibility,and an ideal gap for photovoltaics

Due to many remarkable physical and chemical properties, two-dimensional(2D) nanomaterials have become a hot spot in the field of condensed matter physics. In this paper, we have studied the structural, mechanical, and electronic properties of the 2D GaInO_3 system by first-principles method. We find that 2D Ga InO_3 can exist stably at ambient condition. Molecular dynamic simulations show that GaInO_3-sheet has excellent thermal stability and is stable up to1100 K. Electronic structural calculations show that GaInO_3-sheet has a band gap of 1.56 eV, which is close to the ideal band gap of solar cell materials, demonstrating great potential in future photovoltaic application. In addition, strain effect studies show that the GaInO_3-sheet structure always exhibits a direct band gap under biaxial compressive strain, and as the biaxial compressive strain increases, the band gap gradually decreases until it is converted into metal. While biaxial tensile strain can cause the 2D material to transform from a direct band gap semiconductor into an indirect band gap semiconductor,and even to metal. Our research expands the application of the Ga InO_3 system, which may have potential application value in electronic devices and solar energy.

Strain tunable band structure of a new 2D carbon allotrope C568

Recently,C568 has emerged as a new carbon allotrope,which shows semiconducting properties with a band gap around 1 eV and has attracted much attention.In this work,the external strain effects on the electronic properties of C568 have been studied theoretically through first-principle calculations.The numerical results show that while in-plane uniaxial and biaxial strains both reduces the band gap of C568 in case of tensile strain,their effects are quite different in the case of compressive strain.With increasing compressive uniaxial strain,the band gap of C568 first increases,and then dramatically decreases.In contrast,the application of compressive biaxial strain up to -10% only leads to a slight increase of band gap.Moreover,an indirect-todirect gap transition can be realized under both types of compressive strain.The results also show that the optical anisotropy of C568 can be induced under uniaxial strain,while biaxial strain does not cause such an effect.These results indicate good strain tunability of the band structure of C568,which could be helpful for the design and optimization of C568-based nanodevices.

Static and dynamic stability responses of multilayer functionally graded carbon nanotubes reinforced composite nanoplates via quasi 3D nonlocal strain gradient theory

This manuscript presents the comprehensive study of thickness stretching effects on the free vibration,static stability and bending of multilayer functionally graded(FG)carbon nanotubes reinforced composite(CNTRC)nanoplates.The nanoscale and microstructure influences are considered through a modified nonlocal strain gradient continuum model.Based on power-law functions,four different patterns of CNTs distribution are considered in this analysis,a uniform distribution UD,FG-V CNTRC,FG-X CNTRC,and FG-O CNTRC.A 3D kinematic shear deformation theory is proposed to include the stretching influence,which is neglected in classical theories.Hamilton's principle is applied to derive the governing equations of motion and associated boundary conditions.Analytical solutions are developed based on Galerkin method to solve the governing equilibrium equations based on the generalized higher-order shear deformation theory and the nonlocal strain gradient theory and get the static bending,buckling loads,and natural frequencies of nanoplates.Verification with previous works is presented.A detailed parametric analysis is carried out to highlight the impact of thickness stretching,length scale parameter(nonlocal),material scale parameter(gradient),CNTs distribution pattern,geometry of the plate,various boundary conditions and the total number of layers on the stresses,deformation,critical buckling loads and vibration frequencies.Many new results are also reported in the current study,which will serve as a benchmark for future research.