Shape ratio effects on the mechanical characteristics of rectangular prism rocks and isolated pillars under uniaxial compression

Isolated pillars in underground mines are subjected to uniaxial stress,and the load bearing cross-section of pillars is commonly rectangularly shaped.In addition,the uniaxial compression test(UCT)is widely used for determining the basic mechanical properties of rocks and revealing the mechanism of isolated pillar disasters under unidimensional stress.The shape effects of rock mechanical properties under uniaxial compression are mainly quantitatively reflected in the specific shape ratios of rocks.Therefore,it is necessary to study the detailed shape ratio effects on the mechanical properties of rectangular prism rock specimens and isolated pillars under uniaxial compressive stress.In this study,granite,marble and sandstone rectangular prism specimens with various height to width ratios(r)and width to thickness ratios(u)were prepared and tested.The study results show that r and u have a great influence on the bearing ability of rocks,and thin or high rocks have lower uniaxial compressive strength.Reducing the level of r can enhance the u effect on the strength of rocks,and increasing the level of u can enhance the r effect on the strength of rocks.The lateral strain on the thickness side of the rock specimen is larger than that on the width side,which implies that crack growth occurs easily on the thickness side.Considering r and u,a novel strength prediction model of isolated pillars was proposed based on the testing results,and the prediction model was used for the safety assessment of 179 isolated pillars in the Xianglu Mountain Tungsten Mine.

Theoretical Insight into the Influence of Molecular Ratio on the Stability, Mechanical Property, Solvent Effect and Cooperativity Effect of HMX/DMI Cocrystal Explosive

Molecular dynamics method was employed to study the binding energies of the selected crystal planes of the 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane（HMX）/1,3-dimethyl-2-imidazolidinone（DMI） cocrystal in different molecular molar ratios. The mechanical properties were estimated in different molar ratios. Solvent effects were evaluated and the cooperativity effects were discussed in the HMX···HF···DMI ternary by using the M06-2x/6-311＋G（2df,2p） and MP2（full）/6-311＋G（2df,2p） methods. The results indicate that the substituted patterns（020） and（100） own the highest binding energies. The stabilities of cocrystals in the 1：1 and 2：1 ratios are the greatest, and thus the HMX/DMI cocrystals prefer cocrystallizing in the 1：1 and 2：1 molar ratios, which have good mechanical properties. The sensitivity change of cocrystal originates from not only the formation of intermolecular interaction but also the increment of bond dissociation energy of the N–NO2 bond. The cooperativity effect appears in the linear complex while the anti-cooperativity effect is found in the cyclic system. DMI binding to HMX is not energetically and structurally favored in the presence of HF. This is perhaps the reason that the solvent with large dielectric constant weakens the stability of the HMX/DMI cocrystals. Therefore, the solvents with low dielectric constants should be chosen in the preparation of HMX/DMI cocrystals.

Degradation of effective carrier-power-to-noise densityratio based on code trackingspectral sensitivitycoefficient for GNSS radio frequencycompatibilityin C band

The frequency band between 5 010 MHz and 5 030 MHz allocated as C band has been used as a candidate in the global navigation satellite systems （GNSS） along with more and more naviga- tion services in L band. The potential benefits and technical requirements of C band for satellite navi- gation have been analyzed before. However the degradation of effective carrier-power-to-noise densi- ty ratio（ A （C/No ）eu） based on code tracking spectral sensitivity coefficient（ CT_SSC ） as a compati- bility assessment methodology for potential GNSS radio frequency compatibility in C-Band has not been discussed clearly. So the compatibility of the signals in the C band between BeiDou （BD） B1 C and GPS L1C, L1C/A, Galileo E1Os as the interoperability or classical signals in L band is analyzed. Simulation results reveal the interference degree between BD III B1C and GPS L1C/A, L1C, Galileo E1OS. The results can also reveal that the multiplexed binary offset carrier （MBOC） and binary phase shift keying （BPSK） modulation is not appropriate for C band.

Estimating the site effects in Luoyang basin using horizontal-to-vertical spectral ratio method from a short-period dense array

The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins can help to reduce the earthquake hazard. Site effects of Luoyang basin are estimated by the horizontal-to-vertical spectral ratio(HVSR) method using ambient noise records from a short-period dense array. The sites in Luoyang basin are sorted into three types according to the pattern of the HVSR curves. There are cases with a single clear peak, two clear peaks, and an unclear low frequency peak or multiple peaks, which correspond to there being one large impedance contrast interface, two large interfaces, and a moderate one beneath the sites, respectively. The site effects characterized by fundamental frequency from HVSR curves are affected by underlying sedimentary layers and depth of sedimentary basement. According to our results, the existence of thick sediment layer obviously lowers the fundamental frequency to the period range from 2 to 4 s in the downtown area of Luoyang city. The ground motion will amplify when through the sites and the buildings with height of 20–50 floors can resonate at the similar frequency domain. Site effects estimation using HVSR method from a short-period dense array is an effective technique in areas of moderate seismic risk where strong motion recordings are lacking, such as the Luoyang basin.

THE EFFECTS OF VELOCITY RATIO ON THE LARGE SCALE COHERENT STRUCTURES IN FREE SHEAR LAYERS

The velocity ratio of a free shear layer has an important influence on the spatial development of the large scale coherent structures in the layer. In this study, numerical simulations are performed to get an insight into this problem. The obtained numerical results agree quite well with those of a linear inviscid stability theory and the available experimental data.

Pile-soil stress ratio in bidirectionally reinforced composite ground by considering soil arching effect

To discuss the soil arching effect on the load transferring model and sharing ratios by the piles and inter-pile subsoil in the bidirectionally reinforced composite ground, the forming mechanism, mechanical behavior and its effect factors were discussed in detail. Then, the unified strength theory was introduced to set up the elastoplastic equilibrium differential equation of the subsoil under the limit equilibrium state. And from the equation, the solutions were derived with the corresponding formulas presented to calculate the earth pressure over and beneath the horizontal reinforced cushion or pillow, the stress of inter-pile subsoil and the pile-soil stress ratio. Based on the obtained solutions and measured data from an engineering project, the influence rules by the soil property parameters (i.e., the cohesion c and internal friction angle φ) and pile spacing on the pile-soil stress ratio n were discussed respectively. The results show that to improve the load sharing ratio by the piles, the more effective means for filling materials with a larger value of φ is to increase the ratio of pile cap size to spacing, while to reduce the pile spacing properly and increase the value of cohesion c is advisable for those filling materials with a smaller value of φ.

The Effect of Mass Ratio and Air Damper Characteristics on the Resonant Response of an Air Damped Dynamic Vibration Absorber

In this paper, it is shown that, a road vehicle 2DOF air damped quartercar suspension system can conveniently be transformed into a 2DOF air damped vibrating system representing an air damped dynamic vibration absorber (DVA) with an appropriate change in the ratio μ of the main mass and the absorber mass i.e. when mass ratio μ >> 1. Also the effect of variation of the mass ratio, air damping ratio and air spring rate ratio, on the motion transmissibility at the resonant frequency of the main mass of the DVA has been dis- cussed. It is shown that, as the air damping ratio in the absorber system increases, there is a substantial decrease in the motion transmissibility of the main mass system where the air damper has been modeled as a Maxwell type. Optimal value of the air damping ratio for the minimum motion transmissibility of the main mass of the system has been determined. An experimental setup has been designed and developed with a control system to vary air pressure in the damper in the absorber system. The motion transmissibility characteristics of the main mass system have been obtained, and the optimal value of the air damping ratio has been determined for minimum motion transmissibility of the main mass of the

Experimental Study on the Effect of Sediment Composition Ratio on Shallow Water Delta

1 Introduction Shallow water delta in the middle-newborn Stratum Widely developed with huge oil and gas in China(Hu Shengwu et al.,2013).The control factors on the deltadevelopment like Climate,sea level,tectonic subsidence,sediment supply(flow,type),the geometric characteristics of the upstream river,the energy(wave,

Chemical Effect on K Shell X-ray Fluorescence Parameters and Radiative Auger Ratios of Co, Ni, Cu, and Zn Complexes

The production cross-sections, intensity ratios, and radiative Auger intensity ratios of Co, Ni, Cu, and Zn elements in different complexes were measured. The chemical effects on the K shell fluorescence parameters and the radiative Auger intensity ratios of these elements were investigated and the changes in these parameters were interpreted according to the charge transfer process. The samples were excited by 59.5 keV γ-rays from a ^241Am annular radioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV.

Time-Lag Effect of Dietary Fiber and Fat Intake Ratio on Japanese Colon Cancer Mortality

The daily intake of total dietary fiber (TDF) was evaluated from data of the National Nutrition Survey (NNS) in Japan for 41 years since 1947. An interrelationship between the nutrient intake, including TDF, and the mortality from colon cancer in Japanese people was calculated by a simple correlation coefficient and time-series correlation coeffcient.TDF intake per capita decreased rapidly from 27.4 g in 1947 to 15.8 g in 1963, and subsequently decreased by a lesser rate to 15.3 g in 1987. Fat intake increased rapidly from 18.0 g in 1950 to 56.6 g in 1987.The age-adjusted mortality from colon cancer shows a significant positive correlation with both the intakes of animal protein and of total fat, and the fat energy ratio. A time-series analysis indicates that the mortality from colon cancer was negatively correlated with TDF with a 15-27 year delay, the maximum correlation existing with a 23-year lag (r = -0.947). The TDF intake was less than 17.9 g in 1965. At the same time, the mortality from colon cancer increased rapidly. A fat/TDF ratio above 3.0 resulted in a rapid increase in colon cancer mortality.The non-adjusted mortality from colon cancer has much the same interrelationship with TDF and fat intake as the adjusted figures. It is suggested that the cause of the increased mortality from colon cancer in Japan is positively related to the increased intake of fat and protein. In addition, the decrease in TDF intake has accelerated the mortality of colon cancer after a delay of 23-24 years. The importance of fat/TDF as a nutritional criterion for the incidence of colon cancer needs to be better recognized

地震作用下调谐黏滞质量阻尼器阻尼比增效效应与优化设计研究

调谐黏滞质量阻尼器(Tuned Viscous Mass Damper,TVMD)是一种有效的被动惯容减震装置,本文针对地震作用下建筑结构TVMD阻尼比增效效应与优化设计展开研究。将TVMD对结构自身阻尼耗能功率的控制效果归纳为TVMD等效附加阻尼比,并基于随机振动理论推导了等效附加阻尼比的理论表达式。为了使TVMD更具实际应用价值,TVMD理论上应取得比同阻尼系数的黏滞阻尼器(VD)更大的等效附加阻尼比,这一现象定义为TVMD阻尼比增效效应,并定义了阻尼比增效系数来量化评估阻尼比增效效应。将等效附加阻尼比和阻尼比增效系数均作为优化目标,提出了TVMD最优设计参数理论解。参数分析结果表明,本文解具有良好的稳定性和适用性,为了更高效地发挥阻尼比增效效应,推荐TVMD质量比不超过0.3或阻尼比不超过0.1。以某七层标准钢框架结构作为工程算例展示了TVMD设计流程,并验证了本文解的有效性和优越性。算例分析结果表明,使用本文解设计TVMD能显著放大其阻尼元件变形,表现出了理想的阻尼比增效效应。与传统解相比,本文解还具有另一个明显优势,即保证TVMD的减震效果优于同阻尼系数的VD,不存在减震效率问题。

基于能量转化机制的岩石强度的演化机理研究

针对岩石强度的演化机理是提高强度准则计算精度与适用性的前提,基于能量转化是物质物理过程的本质属性,弹性应变能是材料破坏的内在机理,通过试验与理论研究,探究了围压、中间主应力及泊松比对岩石强度演化规律的影响.结果表明:岩石破坏与应力状态及岩石变形特性有关,忽略泊松比的影响是中间主应力效应提出的理论依据,并指出围压效应与中间主应力效应忽略变形影响,既与试验结果不一致,又是据此建立的强度理论精度较差的内在原因.岩石强度的演化是围压、中间主应力及泊松比共同作用的结果,并据此研究了静水应力状态下材料破坏特性、围压区间性及三轴拉伸强度恒大于三轴压缩强度条件.理论及试验表明,体现了围压、中间主应力及泊松比影响的强度理论具有较高计算精度与适用性.研究成果对于精准地描述岩石破坏特性,建立普遍适用的强度理论具有重要意义.

Effects of Film Thickness and Ar/O2 Ratio on Resistive Switching Characteristics of HfOx-Based Resistive-Switching Random Access Memories

Cu/HfOx/n^＋Si devices are fabricated to investigate the influence of technological parameters including film thickness and Ar/02 ratio on the resistive switching （RS） characteristics of HfOx films, in terms of switch ratio, endurance properties, retention time and multilevel storage. It is revealed that the RS characteristics show strong dependence on technological parameters mainly by altering the defects （oxygen vacancies） in the film. The sample with thickness of 2Onto and Ar/O2 ratio of 12：3 exhibits the best RS behavior with the potential of multilevel storage. The conduction mechanism of all the films is interpreted based on the filamentary model.

扩底桩竖向承载特性及群桩效应研究

为探明扩底群桩竖向承载特性,采用扩底桩筏结构,开展单桩(扩径比分别为1.5、2.0、2.5、3.0)和桩筏(扩径比为2)基础静载模型试验,分析其荷载传递规律,并建立桩间距为3.75、4.00、4.50、5.00倍桩直径时扩底桩筏基础有限元模型,研究桩间距对群桩效应影响。结果表明:扩底单桩和扩底桩筏结构荷载沉降曲线均为缓变型;扩底桩极限承载力随扩径比增大而逐渐增大,扩径比2.5~3.0时极限承载力增幅变缓,建议扩底桩扩径比取2.5~3.0;由于桩土共同沉降,桩间土压缩,桩土作用更充分,扩底桩筏基础中心桩侧摩阻力荷载分担比比扩底单桩增大了17.71%;群桩效应系数随桩间距增大而逐渐增大,桩间距为4.5~5.0倍桩直径时群桩效应系数增幅较小,群桩效应较弱,建议扩底桩筏基础桩间距取值不小于4.5倍桩直径。

P-Δ effect on inelastic displacement ratio spectra for inelastic structures

For the evaluation of structures with known ductility demands,the constant-ductility displacement ratio spectra(CDDRS) are particularly useful for providing inelastic displacement ratios to estimate maximum lateral inelastic displacement demands from maximum elastic displacement demands.The CDDRS are computed for single-degree-of-freedom systems(SDOF) by considering or ignoring P-Δ effect for different ductility levels when subjected to 344 earthquake ground motions recorded in four site classes.The modified expressions of CDDRS for P-Δ effect are proposed.It is concluded that the P-Δ effect on CDDRS is significant,and the effect increases with the increase of ductility level.In the long-period region,the CDDRS ignoring P-Δ effect almost conforms to the equal-displacement rule.But in the case of higher ductility level,the CDDRS considering P-Δ effect are much higher than 1.0,which do not conform to the equal-displacement rule.

不同冲击气压下煤样动态剪切强度的长径比效应

采用Φ50mm分离式霍普金森压杆(SHPB)试验系统,开展了不同冲击气压下直径75mm,长径比分别为0.20,0.27,0.33,0.40和0.47的5组煤样的动态剪切试验,划分了煤动态剪应力时程曲线的阶段,探讨了冲击气压对煤样动态剪切强度的影响,分析了煤样动态剪切强度和加载率的长径比效应,并建立了长径比效应理论模型。研究结果表明:①煤样动态剪应力时程曲线可分为应力初始上升、应力线性增长、应力缓慢上升和应力下降4个阶段;②煤样动态剪切强度与冲击气压呈正线性相关,但不同长径比下增加幅度存在差异,具体表现为:相同冲击气压增量下,煤样长径比越小,动态剪切强度的增加幅度越大;③煤样动态剪切强度和加载率均与长径比有关,在0.25,0.35 MPa较低冲击气压与0.45,0.55 MPa较高冲击气压下分别呈现出正、负长径比效应,并通过方差分析确定了长径比对其影响最小的冲击气压为0.376MPa;④建立了不同冲击气压下煤样动态剪切强度长径比效应理论模型,通过加载率效应推导出加载率长径比效应理论模型,并验证了模型的合理性和准确性。

基于相依网络的无人机集群通信系统鲁棒性分析

作为地震灾害救援和侦察战场等的主力设备,无人机集群通信系统的鲁棒性是抗毁性的重要指标,本文借助复杂相依网络理论建模无人机集群通信系统,引入相对网络效能比作为通信系统网络整体鲁棒性的指标,准确地反映节点之间的相互依赖关系,为评估通信系统在目标攻击下的鲁棒性提供了一种全新的视角。基于经典M-L模型和动态信息的负载重分配策略,建立相依同构ER-ER和异构ER-BA网络模型,考虑两层网络中相依节点度数的特性进行目标攻击,分析其在攻击下的级联失效动态过程,以及任意两节点的连边概率、平均度数和容量系数等特征参数,对通信网络整体鲁棒性的影响。研究表明,网络鲁棒性和网络相依强度负相关,在级联失效过程中可考虑降低52.09%~72.9%相依强度,以抵抗更严重的通信网络崩塌;对同构网络来说,相依模式的不同,RL、AL较DL整体鲁棒性分别降低了9.25%和15.95%。

长江漫滩相超固结软土最大动剪切模量试验研究

为探究长江漫滩相超固结软土最大动剪切模量G_(max)变化特征,利用弯曲元对原状长江漫滩相软土开展了系列试验研究,探讨了不同超固结比H_(OCR)、初始有效固结围压σ'_(3c)及孔隙比e对漫滩相软土G_(max)的影响规律。试验结果表明,当σ'_(3c)和H_(OCR)均相同时,G_(max)随e的增大而减小;H_(OCR)的增大会导致G_(max)随e的衰减速度逐渐降低,而σ'_(3c)的增大不会引起G_(max)衰减速度的变化。孔隙归准化最大剪切模量G_(max)/F(e)随归准化初始有效围压σ'_(c0)/Pa的增大而增加,但其增长速率逐渐降低,G_(max)/F(e)与σ'_(3c)/Pa呈幂函数关系。基于回归分析,提出了合理表征具有不同超固结状态、初始应力条件及密实程度的长江漫滩相软土G_(max)预测方法,并通过独立试验验证了该方法的有效性。

广东省污水资源化利用经济可行性评价方法研究

污水资源化利用是我国贯彻“节水优先”治水方针的一项重要战略性举措,是集水资源开源—节流—提质—增效于一体的系统治水措施。针对目前地方政府和社会资本对污水资源化利用的价值认识偏差问题,文章通过构建污水资源化利用项目的费用与效益量化计算模型,建立了适合污水资源化利用项目的费效比经济可行性评价方法。以广东省为例,定量计算了广东省实施污水资源化项目费效比,从经济角度评价了广东省推行污水资源化利用项目的可行性,结果表明,广东省实施污水资源化利用项目的费效比为0.67,产出效益明显高于投入费用,具备较强的经济可行性。相关研究方法与研究成果可以为推动我国污水资源化利用发展提供参考。

复掺海水海砂混凝土配合比优化及抗渗性能研究

通过正交试验研究海砂、粉煤灰及矿渣替代率对海水海砂混凝土力学性能的影响,得到混凝土最优配合比,并对其抗渗性能进行研究。结果表明:各因素对海水海砂混凝土抗压强度的影响大小为:海砂替代率>矿渣替代率>粉煤灰替代率。最优配合比为:海砂替代率70%,粉煤灰替代率15%,矿渣替代率5%。海水海砂混凝土早期抗压强度的增长速度大于普通混凝土,但后期抗压强度的增长速度低于普通混凝土。最优配合比的海水海砂混凝土抗渗等级、抗渗压力均高于普通混凝土。复掺矿物掺合料可以填充水泥水化和硬化过程中残留的孔隙,改善水泥浆体的孔结构,提高其抗压强度及抗渗性能。