Structural design and mechanical responses of closely spaced super-span double tunnels in strongly weathered tuff strata

This paper presents a study of closely spaced double tunnels in Taizhou,China.One is Xiabei Mountain No.2 four-line super-span high-speed railway tunnel(HRT),and the other is Xiabei Mountain double-line large-span subway tunnel(ST).The excavation spans of HRT and ST are 26.3 and 14 m,respectively.The two tunnels are located at different levels,and their separating distance is 17.2 m.Due to the short construction period,the HRT excavation was completed earlier than ST.The structural design of the HRT,taking account of the disturbance by the ST construction,was analyzed by a numerical simulation.It was found that the“yielding principle”design was more feasible than the“resistance principle”design when considering the safety and durability of the HRT secondary lining.The mechanical responses of the HRT during ST construction were comprehensively monitored and analyzed,including the vault settlement,horizontal convergence,surrounding rock pressure,and the internal stress in shotcrete and steel arch.Results show that the longitudinal influence range of the ST construction on the HRT was approximately 0.6–1.1 times the ST outer diameter;the disturbance was mainly generated in the ST upper bench excavation;and the final axial force of the HRT shotcrete was approximately 9–16 times that of the steel arch,which indicated that the shotcrete was the main bearing structure.The safety status of the HRT was assessed based on the monitoring data,and the minimum safety factors of the HRT shotcrete and steel arch were 1.61 and 1.89,respectively.Parametric studies were performed to show how the lining stress of HRT was affected by the relative angle,pillar width,ST excavation method and excavation footage.Finally,the design and construction optimization were proposed according to the monitoring data and parameter analysis results.This study might provide practical reference for similar projects.

Low frequency noise in asymmetric double barrier magnetic tunnel junctions with a top thin MgO layer

Low frequency noise has been investigated at room temperature for asymmetric double barrier magnetic tunnel junctions（DBMTJs）, where the coupling between the top and middle CoFeB layers is antiferromagnetic with a 0.8-nm thin top Mg O barrier of the CoFeB/MgO/CoFe/CoFeB/MgO/CoFe B DBMTJ. At enough large bias, 1/f noise dominates the voltage noise power spectra in the low frequency region, and is conventionally characterized by the Hooge parameter αmag.With increasing external field, the top and bottom ferromagnetic layers are aligned by the field, and then the middle free layer rotates from antiparallel state（antiferromagnetic coupling between top and middle ferromagnetic layers） to parallel state. In this rotation process αmag and magnetoresistance-sensitivity-product show a linear dependence, consistent with the fluctuation dissipation relation. With the magnetic field applied at different angles（θ） to the easy axis of the free layer,the linear dependence persists while the intercept of the linear fit satisfies a cos（θ） dependence, similar to that for the magnetoresistance, suggesting intrinsic relation between magnetic losses and magnetoresistance.

Investigation and statistical modeling of InAs-based double gate tunnel FETs for RF performance enhancement

In this paper,RF performance analysis of In As-based double gate（DG）tunnel field effect transistors（TFETs）is investigated in both qualitative and quantitative fashion.This investigation is carried out by varying the geometrical and doping parameters of TFETs to extract various RF parameters,unity gain cut-off frequency（f_t）,maximum oscillation frequency（f_（max））,intrinsic gain and admittance（Y）parameters.An asymmetric gate oxide is introduced in the gate-drain overlap and compared with that of DG TFETs.Higher ON-current（ION）of about 0.2 mA and less leakage current（IOFF）of 29 f A is achieved for DG TFET with gate-drain overlap.Due to increase in transconductance（g_m）,higher ft and intrinsic gain is attained for DG TFET with gate-drain overlap.Higher f_（max） of 985 GHz is obtained for drain doping of 5×10^（17）cm^（-3） because of the reduced gate-drain capacitance（C_（gd））with DG TFET with gate-drain overlap.In terms of Y-parameters,gate oxide thickness variation offers better performance due to the reduced values of Cgd.A second order numerical polynomial model is generated for all the RF responses as a function of geometrical and doping parameters.The simulation results are compared with this numerical model where the predicted values match with the simulated values.