Autoresonance in a Dissipative System

We study the autoresonant solution of Duffing's equation in the presence of dissipation. This solution is proved to be an attracting set. We evaluate the maximal amplitude of the autoresonant solution and the time of transition from autoresonant growth of the amplitude to the mode of fast oscillations. Analytical results are illustrated by numerical simulations.Comment: 22 pages, 3 figure

Adjustment methods of measuring channels for ac electric drive with high quality variables control

Базовым условием обеспечения высокого качества регулирования переменных электропривода является высокая точность каналов измерения/вычисления токов, напряжений, скорости. Предложена методика настройки измерительных каналов, позволяющая достичь погрешности менее 1% во всем диапазоне изменения фазных токов, напряжения в звене постоянного тока, а также погрешности измерения скорости менее 0,01 номинального скольжения при небольшом (120-180) количестве меток датчика. Разработан алгоритм и методика настройки пофазной компенсации «мёртвого» времени, обеспечивающая высокую точность формирования напряжения статора, в том числе на уровне в 0,01 его номинального значения. Применение указанной методики в тяговых электроприводах позволило достичь погрешности вычисления электромагнитного момента не более 5% во всех рабочих режимах электропривода, включая глубокую 2-ю и 3-ю зоны регулирования скорости.High accuracy of measuring/calculating channels of current, voltage, speed is base condition of high quality electric drive variables control. The methods of measuring channels adjustment, allowing to reach an measuring error less than 1% in all range of phase current, dc link voltage change, is offered. Speed measuring error less than 1% of rated slip at small number (120-180) of encoder labels is reached. The algorithm and adjustment technique of segregated-phase dead time compensation, providing high accuracy of stator voltage formation, including at level of 0,01 its nominal value, is developed. Application of the methods in traction electric drives has allowed to reach errors of electromagnetic moment calculation no more than 5 % in all operating modes of electric drive, including deep 2-nd and 3-d speed control ranges

Measurements of Ion Stopping Around the Bragg Peak in High-Energy-Density Plasmas

For the first time, quantitative measurements of ion stopping at energies around the Bragg peak (or peak ion stopping, which occurs at an ion velocity comparable to the average thermal electron velocity), and its dependence on electron temperature (T[subcontract e]) and electron number density (n[subcontract e]) in the range of 0.5–4.0 keV and 3 × 10[superscript 22] to 3 × 10[superscript 23]  cm[superscript −3] have been conducted, respectively. It is experimentally demonstrated that the position and amplitude of the Bragg peak varies strongly with T[subscript e] with n[subscript e]. The importance of including quantum diffraction is also demonstrated in the stopping-power modeling of high-energy-density plasmas.United States. Dept. of Energy (Grant DE-FG03-03SF22691)Lawrence Livermore National Laboratory (Subcontract Grant B504974)University of Rochester. Laboratory for Laser Energetics (Subcontract Grant 412160-001G

Morphology of supported polymer electrolyte ultra-thin films: a numerical study

Morphology of polymer electrolytes membranes (PEM), e.g., Nafion, inside PEM fuel cell catalyst layers has significant impact on the electrochemical activity and transport phenomena that determine cell performance. In those regions, Nafion can be found as an ultra-thin film, coating the catalyst and the catalyst support surfaces. The impact of the hydrophilic/hydrophobic character of these surfaces on the structural formation of the films has not been sufficiently explored yet. Here, we report about Molecular Dynamics simulation investigation of the substrate effects on the ionomer ultra-thin film morphology at different hydration levels. We use a mean-field-like model we introduced in previous publications for the interaction of the hydrated Nafion ionomer with a substrate, characterized by a tunable degree of hydrophilicity. We show that the affinity of the substrate with water plays a crucial role in the molecular rearrangement of the ionomer film, resulting in completely different morphologies. Detailed structural description in different regions of the film shows evidences of strongly heterogeneous behavior. A qualitative discussion of the implications of our observations on the PEMFC catalyst layer performance is finally proposed