Model test of negative Poisson’s ratio cable for supporting super-largespan tunnel using excavation compensation method

In recent years,there is a scenario in urban tunnel constructions to build super-large-span tunnels for traffic diversion and route optimization purposes.However,the increased size makes tunnel support more difficult.Unfortunately,there are few studies on the failure and support mechanism of the surrounding rocks in the excavation of supported tunnel,while most model tests of super-large-span tunnels focus on the failure characteristics of surrounding rocks in tunnel excavation without supports.Based on excavation compensation method(ECM),model tests of a super-large-span tunnel excavation by different anchor cable support methods in the initial support stage were carried out.The results indicate that during excavation of super-large-span tunnel,the stress and displacement of the shallow surrounding rocks decrease,following a step-shape pattern,and the tunnel failure is mainly concentrated on the vault and spandrel areas.Compared with conventional anchor cable supports,the NPR(negative Poisson’s ratio)anchor cable support is more suitable for the initial support stage of the super-large-span tunnels.The tunnel support theory,model test materials,methods,and the results obtained in this study could provide references for study of similar super-large-span tunnels。

Tunneling Negative Magnetoresistance via δ Doping in a Graphene-Based Magnetic Tunnel Junction

We investigate the tunneling magnetoresistance via δ doping in a graphei2e-based magnetic tunnel junction in detail. It is found that the transmission probability and the conductance oscillates with the position and the aptitude of the 8 doping. Also, both the transmission probability and the conductance at the paxallel configuration are suppressed by the magnetic field more obviously than that at the antiparallel configuration, which implies a large negative magnetoresistance for this device. The results show that the negative magnetoresistance of over 300% at B = 1.0 T is observed by choosing suitable doped parameters, and the temperature plays an important role in the magnetoresistance. Thus it is possible to open a way to effectively manipulate the magnetoresistance devices, and to make a type of magnetoresistance device by controlling the structural parameter of the δ doping.

Impact of the Negative Resistance on the Characteristics of a Tunnel Diode-Inductive Circuit

The I-V diagram of a tunnel diode inherits a voltage range corresponding to a specific current domain with a negative slope. Within this range, the electric resistance is negatively impacting the characteristics of the electric circuits. One such circuit containing a tunnel diode in series with an inductor driven by a DC source is considered. The negative resistance significantly alters the characteristics of the circuit. In this research-oriented project, we unveil these characteristics comparing them to the classic inductive circuit with an ohmic resistor. This project stems from our previous work [1] and may be considered an application of the tunnel diode embodying unseen surprises. The circuit analysis is entirely based on utilizing a Computer Algebra System (CAS) specifically Mathematica. Without a CAS, the completion of the project wouldn’t have been possible otherwise.

Negative Poisson’s ratio cable compensation support for 32 m super-large-span highway tunnel:A case study

Although super-large-span tunnels ensure convenient transportation,they face many support challenges.The lack of normative construction guidance and the limited number of reference engineering cases pose a significant challenge to the stability control of superlarge-span tunnels.Based on the geological conditions of a super-large-span tunnel(span=32.17 m)at the bifurcation section of the Shenzhen interchange,this study determined support parameters via theoretical calculation,numerical simulation,and engineering analogy.The support effects of negative Poisson’s ratio(NPR)anchor cables and ordinary anchor cables on super-long-span tunnels were simulated and studied.Further,based on FLAC3D simulations,the surrounding rock stress field of NPR anchor cables was analyzed under different prestressing conditions,and the mechanism of a long-short combination,high-prestress compensation NPR anchor cable support was revealed.On the basis of numerical simulations,to our knowledge,the three-dimensional(3D)geomechanical model test of the NPR anchor cable and ordinary anchor cable support for super-large-span tunnel excavation is conducted for the first time,revealing the stress evolution law of super-large-span tunnels,deformation and failure characteristics of the surrounding rock,and the changing trend of the anchor cable’s axial force,and verifies that NPR anchor cables with high preloads are suitable for super-large-span tunnel support and have advantages over ordinary anchor cables.This study can provide a reliable theoretical reference for the support design and stability control of the surrounding rock of similar shallow-buried super-large-span tunnels.

Negative Resistance and Its Impact on a RC-DC Driven Electric Circuit

It is a common misconception that electric “resistance” always is a positive defined electric element. i.e., the plot of the voltage across the resistor, V vs. its current, i is a slanted straight line with a positive slope. Esaki diode also known as tunnel diode is an exception to this character. For a certain voltage range, the current recedes resulting in a line with a negative slope;it is interpreted as negative resistance. In this research flavored report, we investigate the impact of the negative resistance in a typical classic electric circuit. E.g., a tunnel diode, D is inserted in a classic electric circuit that is composed of an ohmic resistor, R and a capacitor, C which are all in series with a DC power supply. The circuit equation for the RCD circuit is a nonlinear ordinary differential equation (NLODE). In line with the ever-growing popular Computer Algebra System (CAS), this is solved numerically utilizing two distinctly different CASs. The consistency of the solutions confidently leads to the understanding of the impact of the negative resistance. The circuit characteristics are compared to the classic analogous RC circuit. The report embodies an atlas of characteristics of the circuits making the analysis visually comprehensible.

开挖补偿法防控深部地下岩爆灾害——引汉济渭工程秦岭输水隧洞案例分析

Rockburst disasters occur frequently during deep underground excavation,yet traditional concepts and methods can hardly meet the requirements for support under high geo-stress conditions.Consequently,rockburst control remains challenging in the engineering field.In this study,the mechanism of excavation-induced rockburst was briefly described,and it was proposed to apply the excavation compensation method(ECM)to rockburst control.Moreover,a field test was carried out on the Qinling Water Conveyance Tunnel.The following beneficial findings were obtained:Excavation leads to changes in the engineering stress state of surrounding rock and results in the generation of excess energy DE,which is the fundamental cause of rockburst.The ECM,which aims to offset the deep excavation effect and lower the risk of rockburst,is an active support strategy based on high pre-stress compensation.The new negative Poisson’s ratio(NPR)bolt developed has the mechanical characteristics of high strength,high toughness,and impact resistance,serving as the material basis for the ECM.The field test results reveal that the ECM and the NPR bolt succeed in controlling rockburst disasters effectively.The research results are expected to provide guidance for rockburst support in deep underground projects such as Sichuan-Xizang Railway.

Preparation and Characteristics of Cu/Al_2O_3/MgF_2/Au Tunnel Junction

The fabrication process of Cu/Al2O3/MgF2/Au double-barrier metal/insulator/metal junction （DMIMJ） was introduced, and more stable light emission from this junction was successfully observed. The light emission physical mechanism of the junction was discussed. Results show that light emission spectrum of this structure locates at wavelength of 250-700 nm with two peaks at around 460 nm and 640 nm, which moves towards shorter wavelength region in comparison with that of the Al/Al2O3/Au junction. The light emission efficiency of this junction ranges from 0.7×10^-5-2.0×10^-5, which is 1 to 2 orders higher than that of the single-barrier Al/Al2O3/Au junction. The improved properties of this structure should be due to the electrons resonant tunneling effect in the double-barrier.

Comparison of resonant tunneling diodes grown on freestanding GaN substrates and sapphire substrates by plasma-assisted molecular-beam epitaxy

AlN/GaN resonant tunneling diodes(RTDs)were grown separately on freestanding Ga N(FS-GaN)substrates and sapphire substrates by plasma-assisted molecular-beam epitaxy(PA-MBE).Room temperature negative differential resistance(NDR)was obtained under forward bias for the RTDs grown on FS-GaN substrates,with the peak current densities(Jp)of 175-700 kA/cm^(2)and peak-to-valley current ratios(PVCRs)of 1.01-1.21.Two resonant peaks were also observed for some RTDs at room temperature.The effects of two types of substrates on epitaxy quality and device performance of GaN-based RTDs were firstly investigated systematically,showing that lower dislocation densities,flatter surface morphology,and steeper heterogeneous interfaces were the key factors to achieving NDR for RTDs.

Tunneling field effect transistors based on in-plane and vertical layered phosphorus heterostructures

Tunneling field effect transistors（TFETs） based on two-dimensional materials are promising contenders to the traditional metal oxide semiconductor field effect transistor, mainly due to potential applications in low power devices. Here,we investigate the TFETs based on two different integration types： in-plane and vertical heterostructures composed of two kinds of layered phosphorous（β-P and δ-P） by ab initio quantum transport simulations. NDR effects have been observed in both in-plane and vertical heterostructures, and the effects become significant with the highest peak-to-valley ratio（PVR）when the intrinsic region length is near zero. Compared with the in-plane TFET based on β-P and δ-P, better performance with a higher on/off current ratio of - 10-6 and a steeper subthreshold swing（SS） of - 23 mV/dec is achieved in the vertical TFET. Such differences in the NDR effects, on/off current ratio and SS are attributed to the distinct interaction nature of theβ-P and δ-P layers in the in-plane and vertical heterostructures.

Silicon cross-coupled gated tunneling diodes

Tunneling-based static random-access memory(SRAM)devices have been developed to fulfill the demands of high density and low power,and the performance of SRAMs has also been greatly promoted.However,for a long time,there has not been a silicon based tunneling device with both high peak valley current ratio(PVCR)and practicality,which remains a gap to be filled.Based on the existing work,the current manuscript proposed the concept of a new silicon-based tunneling device,i.e.,the silicon crosscoupled gated tunneling diode(Si XTD),which is quite simple in structure and almost completely compatible with mainstream technology.With technology computer aided design(TCAD)simulations,it has been validated that this type of device not only exhibits significant negative-differential-resistance(NDR)behavior with PVCRs up to 10^(6),but also possesses reasonable process margins.Moreover,SPICE simulation showed the great potential of such devices to achieve ultralow-power tunneling-based SRAMs with standby power down to 10^(−12)W.

基于FLUENT的导流隧洞水力特性模拟

针对传统的二维导流隧洞水力学计算,采用CFD方法对导流隧洞的水力特性进行了三维数值模拟,通过导流隧洞各典型断面总水头与传统公式、模型试验计算结果的比较,验证了三维数值模拟的准确性,进而可通过数值模拟对导流隧洞的三维流场进行分析研究。文中对导流隧洞各典型断面及整体进行了流态分析和出口负压分析,结果显示导流隧洞满足设计要求。可见,流体力学计算方法能够有效地模拟导流隧洞水流的流态,可应用于导流隧洞的设计与优化工作。

Impact and explosion resistance of NPR anchor cable:Field test and numerical simulation

With the reduction of shallow resources,the degree of damage and the frequency of dynamic hazards,such as deep rock bursts and impact ground pressure,are increasing dramatically.However,the existing support materials are incapable of meeting the safety require-ments of the refuges and roadways under a strong impact force.To effectively solve these problems,a novel negative Poisson’s ratio(NPR)anchor cable with excellent properties,such as impact resistance and the ability to withstand large deformation,is proposed.In the present study,a series of field tests and numerical simulations are conducted to investigate the mechanical and support charac-teristics of NPR anchor cables under blast impact.Laboratory mechanical tests show that NPR anchor cables can maintain constant resistance and produce large deformation under the action of multiple drop hammer impacts.According to the results of field tests,the roadway supported by conventional anchor cables was unable to endure the blast impact,while the roadway supported by NPR anchor cables was able to withstand the severe impact equivalent to a Class 3 mine earthquake.The dynamic response of the NPR anchor cable that supports the roadway under explosion is investigated using the innovative coupled modeling approach that combines the finite element method and the discrete element method,and the support effect of the NPR anchor cable is verified.The study shows that the NPR anchor cable has a superior impact and blast resistance performance,and a broad application prospect in the support of chambers and roadways that are at high risk of rock bursts and impact ground pressure.