Mechanics criterion and factors affecting overburden stability in solid dense filling mining

The effect of controlling strata movement in solid filling mining depends on the filling rate of the goal. However, the mechanical property of the overburden in the backfill stope and the designed size of the backfill mining workface should also be considered. In this study, we established a main roof strata model with loads in accordance with the theory of key strata to investigate the stability of the overburden in solid dense filling mining. We analyzed the stress distribution law of the main roof strata based on elastic thin plate theory. The results show that the position of the long side midpoint of the main roof strata failed more easily because of tensile yield, indicating that this position is the area where failure is likely to occur more easily. We also deduced the stability mechanics criterion of the main roof strata based on tensile yield criterion. The factors affecting the stability of the overburden in solid dense filling mining were also analyzed, including the thickness and elasticity modulus of the main roof strata, overlying strata loads, advanced distance and length of workface, and elastic foundation coefficient of backfill body. The research achievements can provide an important theoretical basis for determining the designed size of the solid dense filling mining workface.

3D stability assessment of stepped slopes in inhomogeneous soils

Stability assessment of slopes has historically been performed assuming soils to be homogeneous in two-dimensional(2D) cases. In real cases, soils are usually inhomogeneous, and each slope collapse indicates a three-dimensional(3D) nature. Based on a 3D rotational failure mechanism, this work develops an approach to account for the impact of the vertical strength inhomogeneity on the 3D stability of stepped slopes. Seismic actions are taken into account by introducing the concept of a horizontal seismic coefficient. An upper-bound expression for stability factors is derived in the light of the kinematic approach, and the most critical solution is obtained from an optimization programming. In comparison with the previously published solutions, the validity of the proposed method is shown. A sensitivity analysis is carried out to discuss parametric effects on the stability of 3D stepped inhomogeneous slopes.

Analytical solution for slope instability assessment considering impact of confined aquifer

An analytical approach was presented for estimating the factor of safety(FS) for slope failure, with consideration of the impact of a confined aquifer. An upward-moving wetting front from the confined water was assumed and the pore water pressure distribution was then estimated and used to obtain the analytical expression of FS. Then, the validation of the theoretical analysis was applied based on an actual case in Hong Kong. It is shown that the presence of a confined aquifer leads to a lower FS value, and the impact rate of hydrostatic pressure on FS increases as the confined water pressure increases, approaching to a maximum value determined by the ratio of water density to saturated soil density. It is also presented that the contribution of hydrostatic pressure and hydrodynamic pressure to the slope stability vary with the confined aquifer pressure.

Relationships between Artemisia ordosica communities and environmental factors following sand-dune stabilization in the Mu Us desert,northwest China

Artemisia ordosica is an excellent sand-fixing shrub for sand stabilization in northwestern China. Sand dune stabilization, a critically important process, leads changes in abiotic factors, such as soil structure and nutrient contents. However, the effects of factors on an A. ordosica community following sand stabilization remain unclear. In this study, we used canonical correspondence analysis （CCA） to examine the relationships between A. ordosica communities and environmental factors at three habitats： semi-fixed dune （SF）, fixed dune with low-cov- erage biological soil crust （F）, and fixed dune with high- coverage biological soil crust （FC） in Mu Us desert. The mean height and coverage of plants increased with sand stabilization, while species diversity and richness increased initially and then reduced significantly. Correlation analysis and CCA revealed that slope, soil organic carbon, and nutrient contents, proportion of fine soil particles, soil moisture, and thickness of biological soil crust were all highly correlated with vegetation characteristics. These environmental factors could explain 40.42 % of the vege- tation-environment relationships at the three habitats. The distribution of plant species was positively related to soil moisture in the SF dune. Soil moisture, soil nutrient, and fine-particle contents mainly affected plants distribution in the F dune. In the FC dune, distribution of plant species was positively and negatively correlated with the thickness of biological soil crust and soil moisture at a depth 0-20 cm, respectively. The dominance value of typical steppe species increased significantly following sand-dune stabilization and relations between species and samples in CCA ordination bi-plots showed that perennial grasses could invade the A. ordosica community on FC, indicating A. ordosica communities had a tendency to change into typical steppe vegetation with the further fixation. We conclude that the significant differentiation not only occurred in community characteristics, but also in the relationships between vegetation and environmental factors among the three stages of dune fixation. So, restoration of degraded dune ecosystems should be based on habitat conditions and ecological needs.

Effects of intense rainfall on stability of infinite terraced slope

For fully understanding the hydrological dynamics of an infinite terraced slope, the infiltration process was studied by employing the Green and Ampt infiltration model. The limit equilibrium method and the Mohr-Coulomb failure criterion were adopted to derive a stability model for the infinite terraced slope subjected to an intense rainfall. Numerical simulation was performed for verifying its applicability. The results of numerical simulation indicate that a set of stepped wetting fronts are found during infiltration, and the infiltration of terraced slope covered by coarse-textured soils can be approximated as one-dimensional infiltration. The potential sliding surfaces from the numerical method are all parallel to the slope line, and the proposed model and framework can provide an approximate method of estimating how the infiltration affects the stability of an infinite terraced slope.

Suitable layout of gate roads related to slice mining in an ultra-thick unstable coal seam

We determi：ned a suitable gate road layout in slice mining in an ultra-thick unstable coal seam, using theoretical anallysis and numerical calculations. Based on plasticity theory in terms of limiting equilibrium, the width of chain pillar in the upper slice was calculated to be 18 m. The stress distribution in the chain pillar after the upper slice was mined out was described with numerical simulation. The extent of the effect of stress on the upper chain pillar on the lower solid coal was obtained on the basis of an elastic solution of a distributed force loaded on a half-plane. Three layout designs for lower gate roads were pro- posed and a stability factor was introduced to analyze the stability of the lower pillar with numerical calculation. Gate road translation was determined as the most suitable layout method, which maximizes the extraction rate on the basis of the pillar stability.

Geotechnical methods of reinforcement of slopes near railroads

In order to generate well-based design decisions on reinforcement of landslide slopes and road embankment slopes, a system of combined geotechnical analysis of geological conditions is suggested which includes topographic and geo- physical survey, and laboratory studies of soils using infra-red spectroscopy methods. Calculations of slopes＇ deflected modes are carried out with taking into account elastic and elasto-plastic behavior of soil, and the presence of supporting man-made constructions. Results of the application of the system suggested may be used as criteria for the classification of landslide slopes along permanent ways according to the degree of danger when used for transportation.

Underground storage tank blowout analysis:Stability prediction using an artificial neural network

Most geotechnical stability research is linked to“active”failures,in which soil instability occurs due to soil self-weight and external surcharge applications.In contrast,research on passive failure is not common,as it is predominately caused by external loads that act against the soil self-weight.An earlier active trapdoor stability investigation using the Terzaghi’s three stability factor approach was shown to be a feasible method for evaluating cohesive-frictional soil stability.Therefore,this technical note aims to expand“active”trapdoor research to assess drained circular trapdoor passive stability(blowout condition)in cohesive-frictional soil under axisymmetric conditions.Using numerical finite element limit analysis(FELA)simulations,soil cohesion,surcharge,and soil unit weight effects are considered using three stability factors(Fc,Fs,and Fγ),which are all associated with the cover-depth ratio and soil internal friction angle.Both upper-bound(UB)and lower-bound(LB)results are presented in design charts and tables,and the large dataset is further studied using an artificial neural network(ANN)as a predictive model to produce accurate design equations.The proposed passive trapdoor problem under axisymmetric conditions is significant when considering soil blowout stability owing to faulty underground storage tanks or pipelines with high internal pressures.

Optimum Design for a Low Noise Amplifier in S-Band

An optimum design of a low noise amplifier （LNA） in S-band working at 2-4 GHz is described. Choosing FHC40LG high electronic mobility transistor （HEMT）, the noise figure of the designed amplifier simulated by Microwave Office is no more than 1.5 dB, meanwhile the gain is no less than 20 dB in the given bandwidth. The simulated results agree with the performance of the transistor itself well in consideration of its own minimum noise figure （0.3 dB） and associated gain （15.5 dB）. Simultaneously, the stability factor of the designed amplifier is no less than 1 in the given bandwidth.

Radar emitter signal recognition based on multi-scale wavelet entropy and feature weighting

In modern electromagnetic environment, radar emitter signal recognition is an important research topic. On the basis of multi-resolution wavelet analysis, an adaptive radar emitter signal recognition method based on multi-scale wavelet entropy feature extraction and feature weighting was proposed. With the only priori knowledge of signal to noise ratio(SNR), the method of extracting multi-scale wavelet entropy features of wavelet coefficients from different received signals were combined with calculating uneven weight factor and stability weight factor of the extracted multi-dimensional characteristics. Radar emitter signals of different modulation types and different parameters modulated were recognized through feature weighting and feature fusion. Theoretical analysis and simulation results show that the presented algorithm has a high recognition rate. Additionally, when the SNR is greater than-4 d B, the correct recognition rate is higher than 93%. Hence, the proposed algorithm has great application value.

Improved formulations of the CR and KR methods for structural dynamics

Although the Chen-Ricles（CR）method and the Kolay-Ricles（KR）method have been applied to conduct pseudodynamic tests,they have both been found to have some adverse numerical properties,such as conditional stability for stiffness hardening systems and an unusual overshoot in the steady-state response of a high-frequency mode.An improved formulation for each method can be achieved by using a stability amplification factor to boost the unconditional stability range for stiffness hardening systems and a loading correction term to eliminate the unusual overshoot in the steady-state response of a high-frequency mode.The details for developing improved formulations for each method are shown in this work.

Reinforcement strength reduction in FEM for mechanically stabilized earth structures

The factor of safety of mechanically stabilized earth(MSE) structures can be analyzed either using limit equilibrium method(LEM) or strength reduction method(SRM) in finite element/difference method. In LEM, the strengths of the reinforcement members and soils are reduced with the same factor. While using the SRM, only soil strength is reduced during the calculation of the factor of safety. This causes inconsistence in calculating the factor of safety of the MSE structures. To overcome this, an iteration method is proposed to consider the strength reduction of the reinforcements in SRM. The method is demonstrated by using PLAXIS, a finite element software. The results show that the factor of safety converges after a few iterations. The reduction of strength has different effects on the factor of safety depending on the properties of the reinforcements and the soil, and failure modes.

Stability analysis of the pillars between bedded salt cavern gas storages by cusp catastrophe model

The failure of pillars between bedded salt cavern gas storages can be seen as processes that the deformations of pillars convert from continuous gradual change system to catastrophe state,which are typical nonlinear catastrophe problems.In the paper,the cusp catastrophe model is proposed to obtain the stability factors of pillars.It can overcome the shortages of traditional strength reduction finite element method(SR FEM) and greatly improve the accuracy of stability factors obtained by numerical simulations.The influences of cavern depth,gas pressure,pillar width,and time on the stability factors are studied.Y-1 and Y-2 salt cavern gas storages,located at Jiangsu province of China,were simulated as examples.The stability factors of pillars between Y-1 and Y-2 were evaluated,and the running parameters were recommended to ensure the pillars stability.The results showed that the cusp catastrophe model has high practicability and can precisely predict the stability factors.The stability factors are equidirectional with the increase of gas pressure and pillar width,but reverse to the increase of cavern depth and time.The stability factors of pillars between Y-1 and Y-2 are small for narrow widths,which are influenced greatly by gas pressure,time,pressure difference,and gas production rate.In order to ensure the safety of pillars,the lowest gas pressure,safe running time,max.pressure difference and max.gas production rate of Y-1 and Y-2 were recommended as 7 MPa,5 years,3 MPa,and 0.50 MPa/d,respectively.

Impact of parameter fluctuations on RF stability performance of DG tunnel FET

This paper presents the impact of parameter fluctuation due to process variation on radio frequency （RF） stability performance of double gate tunnel FET （DG TFET）. The influence of parameter fluctuation due to process variation leads to DG TFET performance degradation. The RF figures of merit （FoM） such as cut-off frequency （ft）, maximum oscillation frequency （fmax） along with stability factor for different silicon body thickness, gate oxide thickness and gate contact alignment are obtained from extracted device parameters through numerical simulation. The impact of parameter fluctuation of silicon body thickness, gate oxide thickness and gate contact alignment was found significant and the result provides design guidelines ofDG TFET for RF applications.

Stability performance of optimized symmetric DG-MOSFET

This article presents the bias and geometry optimization procedure for the radio frequency （RF） stability performance of nanoscale symmetric double-gate metal-oxide semiconductor field-effect transistors （DG- MOSFETs）. The stability model can provide hints for optimizing the DG-MOSFET under an RF range. The device parameters are extracted for different bias and geometry conditions through numerical simulation, and the RF figures of merit such as cut-off frequency （ft） and maximum oscillation frequency （fmax）, along with stability factor, are calculated for an optimized structure. The proposed structure exhibits good RF stability performance.

Intrinsic stability of an HBT based on a small signal equivalent circuit model

Intrinsic stability ofthe heterojunction bipolar transistor （HBT） was analyzed and discussed based on a small signal equivalent circuit model. The stability factor of the HBT device was derived based on a compact T-type small signal equivalent circuit model of the HBT. The effect of the mainly small signal model parameters of the HBT on the stability of the HBT was thoroughly examined. The discipline of parameter optimum to improve the intrinsic stability of the HBT was achieved. The theoretic analysis results of the stability were also used to explain the experimental results of the stability of the HBT and they were verified by the experimental results.

Frequency stability of InP HBT over 0.2 to 220 GHz

The frequency stabilities of lnP DHBTs in a broadband over 1 to 220 GHz are investigated. A hybrid π-topology small-signal model is used to accurately capture the parasitics of devices. The model parameters are extracted from measurements analytically. The investigation results show that the excellent agreement between the measured and simulated data is obtained in the frequency range 200 MHz to 220 GHz. The dominant parameters of the π-topology model, bias conditions and emitter area have significant effects on the stability factor K. The HBT model can be unconditionally stable by reasonable selection of the proper bias condition and the physical layout of the device.

DNA End Resection:Facts and Mechanisms

DNA double-strand breaks（DSBs）,which arise following exposure to a number of endogenous and exogenous agents,can be repaired by either the homologous recombination（HR）or non-homologous end-joining（NHEJ） pathways in eukaryotic cells.A vital step in HR repair is DNA end resection,which generates a long 30single-stranded DNA（ss DNA） tail that can invade the homologous DNA strand.The generation of 30 ss DNA is not only essential for HR repair,but also promotes activation of the ataxia telangiectasia and Rad3-related protein（ATR）.Multiple factors,including the MRN/X complex,C-terminal-binding protein interacting protein（Ct IP）/Sae2,exonuclease 1（EXO1）,Bloom syndrome protein（BLM）/Sgs1,DNA2 nuclease/helicase,and several chromatin remodelers,cooperate to complete the process of end resection.Here we review the basic machinery involved in DNA end resection in eukaryotic cells.