Flow simulation and investigating the effects of cutoff wall on the uplift pressure in earth dams

Since the construction of dam is significantly important both according to economic and safety aspects, it should be carefully assessed before construction. The use of available software is one of the evaluation and behavioral investigation methods. On this basis, we have investigated the effect of cutoff wall on the seepage flow, uplift pressure, etc, in the body of earth dam in Baft city through numerical modeling using the finite element method through GeoStudio software package. The results of this analysis indicate that the location and dimensions of cutoff wall significantly affects its performance on reducing the seepage flow. The soil type in terms of permeability is another important parameter and the results indicate that the one-time reduction of soil dam penetration reduces the seepage flow by 97%.Keywords: Earth dam, cutoff wall, soil permeability, GeoStudio software, uplift pressure

Electronic thermal conductivity measurements in intrinsic graphene

The electronic thermal conductivity of graphene and two-dimensional Dirac materials is of fundamental interest and can play an important role in the performance of nanoscale devices.We report the electronic thermal conductivity Ke in suspended graphene in the nearly intrinsic regime over a temperature range of 20–300 K. We present a method to extract Ke using two-point dc electron transport at low bias voltages, where the electron and lattice temperatures are decoupled. We find Ke ranging from 0.5 to 11 W/m K over the studied temperature range. The data are consistent with a model in which heat is carried by quasiparticles with the same mean free path and velocity as graphene’s charge carriers

Ultra-short suspended single-wall carbon nanotube transistors

We describe a method to fabricate clean suspended single-wall carbon nanotube (SWCNT) transistors hosting a single quantum dot ranging in length from a few 10 s of nm down to ≈3 nm. We first align narrow gold bow-tie junctions on top of individual SWCNTs and suspend the devices. We then use a feedback-controlled electromigration to break the gold junctions and expose nm-sized sections of SWCNTs. We measure electron transport in these devices at low temperature and show that they form clean and tunable single-electron transistors. These ultra-short suspended transistors offer the prospect of studying THz oscillators with strong electron-vibron coupling

Few-Hundred GHz Carbon Nanotube Nanoelectromechanical Systems (NEMS)

We study 23–30 nm long suspended single-wall carbon nanotube quantum dots and observe both their stretching and bending vibrational modes. We use low-temperature DC electron transport to excite and measure the tubes’ bending mode by making use of a positive feedback mechanism between their vibrations and the tunneling electrons. In these nanoelectromechanical systems (NEMS), we measure fundamental bending frequencies <i>f</i>_bend ≈ 75–280 GHz and extract quality factors <i>Q</i> ∼ 10⁶. The NEMS's frequencies can be tuned by a factor of 2 with tension induced by mechanical breakjunctions actuated by an electrostatic force or tension from bent suspended electrodes