Scaling of the chiral magnetic effect in quantum diffusive Weyl semimetals

We investigate the effect of short-range spin-independent disorder on the chiral magnetic effect (CME) in Weyl semimetals. Based on a minimum two-band model, the disorder effect is examined in the quantum diffusion limit by including the Drude correction and the correction due to the Cooperon channel. It is shown that the Drude correction renormalizes the CME coefficient by a factor to a finite value that is independent of the system size. Furthemore, due to an additional momentum expansion involved in deriving the CME coefficient, the contribution of Cooperon to the CME coefficient is governed by the quartic momentum term. As a result, in contrast to the weak localization and weak anti-localization effects observed in the measurement of conductivity of Dirac fermions, we find that in the limit of zero magnetic field, the CME coefficients of finite systems manifest the same scaling of localization even in three dimension. Our results indicate that while the chiral magnetic current due to slowly oscillating magnetic fields can exist in clean systems, its observability will be limited by suppression due to short-range disorder in condensed matters.Comment: 13 pages, 4 figure, to appear in Phys. Rev.

Surface micromachined electrostatically actuated micro peristaltic pump

An electrostatically actuated micro peristaltic pump is reported. The micro pump is entirely surface micromachined using a multilayer parylene technology. Taking advantage of the multilayer technology, the micro pump design enables the pumped fluid to be isolated from the electric field. Electrostatic actuation of the parylene membrane using both DC and AC voltages was demonstrated and applied to fluid pumping based on a 3-phase peristaltic sequence. A maximum flow rate of 1.7 nL min^–1 and an estimated pumping pressure of 1.6 kPa were achieved at 20 Hz phase frequency. A dynamic analysis was also performed with a lumped-parameter model for the peristaltic pump. The analysis results allow a quantitative understanding of the peristaltic pumping operation, and correctly predict the trends exhibited by the experimental data. The small footprint of the micro pump is well suited for large-scale integration of microfluidics. Moreover, because the same platform technology has also been used to fabricate other devices (e.g. valves, electrospray ionization nozzles, filters and flow sensors), the integration of these different devices can potentially lead to versatile and functional micro total analysis systems (µTAS)

Dynamic simulation of a peristaltic micropump considering coupled fluid flow and structural motion

This paper presents lumped-parameter simulation of dynamic characteristics of peristaltic micropumps. The pump consists of three pumping cells connected in series, each of which is equipped with a compliant diaphragm that is electrostatically actuated in a peristaltic sequence to mobilize the fluid. Diaphragm motion in each pumping cell is first represented by an effective spring subjected to hydrodynamic and electrostatic forces. These cell representations are then used to construct a system-level model for the entire pump, which accounts for both cell- and pump-level interactions of fluid flow and diaphragm vibration. As the model is based on first principles, it can be evaluated directly from the device's geometry, material properties and operating parameters without using any experimentally identified parameters. Applied to an existing pump, the model correctly predicts trends observed in experiments. The model is then used to perform a systematic analysis of the impact of geometry, materials and pump loading on device performance, demonstrating its utility as an efficient tool for peristaltic micropump design