Design and verification of an improved experimental platform for stray current in urban rail transit

With the rapid development of urban rail transit,there have been an urgent problem of excessive stray current.Because the stray current distribution is random and difficult to verify in the field,we designed an improved stray current experimental platform by replacing the simulated aqueous solution with a real soil environment and by calculating the transition resistance by measuring the soil resistivity,which makes up for the defects in the previous references.Firstly,the mathematical models of rail-drainage net and rail-drainage netground were established,and the analytical expressions of current and voltage of rail,drainage net and other structures were derived.In addition,the simulation model was built,and the mathematical analysis results were compared with the simulation results.Secondly,the accuracy of the improved stray current experimental platform was verified by comparing the measured and simulation results.Finally,based on the experimental results,the influence factors of stray current were analyzed.The relevant conclusions provide experimental data and theoretical reference for the study of stray current in urban rail transit.

Temperature-induced resistance transition behaviors of melamine sponge composites wrapped with different graphene oxide derivatives

Temperature-re s ponsive resistance transition behaviors of the melamine sponges wrapped with different graphene oxide derivatives(i.e.nanoribbon,wide-ribbon and sheet)were investigated.Melamine sponge composites coated by three types of GO derivatives were prepared by a simple dip-coating approach.All these composites show good mechanical flexibility and reliability(almost unchanged compressive stress at 70%strain after 100 cycles),high hydrophobicity(water contact angle>120°),excellent flame resistance(self-extinguishing)and structural stability even after burning,which was used to construct the resistance-based fire alarm/warning sensor.Notably,the different resistance response behaviors of such sensors are strongly dependent on the GO size and network formed on the MF skeleton surface.Typically,at a fixed high temperature of~350℃,the three fire alarm sensors show different response time(to trigger the alarm light)of 6.3,8.4 and 11.1 s for nanoribbon,wide-ribbon and sheet at the same concentration,respectively.The structural observation and chemical analysis demonstrated that the discrepancy of temperature-responsive resistance transition behaviors of various GO derivatives was strongly determined by their different thermal reduction degrees during the high-tempe rature or flame treating process.This work offers a design and development for construction of smart fire alarm device for potential fire prevention and safety applications.

Superconductivity in self-flux-synthesized single crystalline R2Pt3Ge5(R=La,Ce,Pr)

In order to study the basic superconductivity properties of R2Pt3Ge5, we synthesized the single crystalline samples by the Pt–Ge self-flux method. R2Pt3Ge5（R = La, Ce） were also grown for a systematic study. Zero-resistivity was observed in both the La-and Pr-based samples below the reported superconducting transition temperatures. However, magnetic susceptibility measurements showed low superconductivity volume fractions in both La2Pt3Ge5 and R2Pt3Ge5（less than2%）. Ce2Pt3Ge5 did not show any signature of superconductivity. From the specific heat measurements, we did not observe a superconducting transition peak in R2Pt3Ge5, suggesting that it is not a bulk superconductor. The magnetic susceptibility and heat capacity measurements revealed two antiferromagnetic（AFM） orders in R2Pt3Ge5 at T（N1）= 4.2 K and T（N2）= 3.5K, as well as a single AFM transition at TN= 3.8 K in Ce2Pt3Ge5.