7,999 research outputs found
Ballistic transport properties across nonuniform strain barriers in graphene
We study the effect of uniaxial strain on the transmission and the
conductivity across a strain-induced barrier in graphene. At variance with
conventional studies, which consider sharp barriers, we consider a more
realistic, smooth barrier, characterized by a nonuniform, continuous strain
profile. Our results are instrumental towards a better understanding of the
transport properties in corrugated graphene.Comment: High Press. Res., to appea
The Bohr radius of the -dimensional polydisk is equivalent to
We show that the Bohr radius of the polydisk behaves
asymptotically as . Our argument is based on a new
interpolative approach to the Bohnenblust--Hille inequalities which allows us
to prove that the polynomial Bohnenblust--Hille inequality is subexponential.Comment: The introduction was expanded and some misprints correcte
Position estimation delays in signal injection-based sensorless PMSM drives
The causes of position estimation delays and their effects on the sensorless control of permanent magnet synchronous motor drives are investigated. The position of a permanent magnet synchronous machine is estimated via the injection of high frequency voltage signals. The delays under investigation are due to the digital implementation of the control algorithm and to the digital filters adopted for decoupling the inspection signals from the fundamental components of the stator current measures. If not correctly modeled and compensated, such delays can reduce the performance of the control scheme. Experimental results are provided, proving the accuracy of the modeling approach and the effectiveness of the related compensation strateg
Accurate Inverter Error Compensation and Related Self-Commissioning Scheme in Sensorless Induction Motor Drives
This paper presents a technique for accurately identifying and compensating the inverter nonlinear voltage errors that deteriorate the performance of sensorless field-oriented controlled drives at low speed. The inverter model is more accurate than the standard signum-based models that are common in the literature, and the self-identification method is based on the feedback signal of the closed-loop flux observer in dc current steady-state conditions. The inverter model can be identified directly by the digital controller at the drive startup with no extra measures other than the motor phase currents and dc-link voltage. After the commissioning session, the compensation does not require to be tuned furthermore and is robust against temperature detuning. The experimental results, presented here for a rotor-flux-oriented SFOC IM drive for home appliances, demonstrate the feasibility of the proposed solution
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