نتایج جستجو برای: Coulomb’s friction
تعداد نتایج: 34144 فیلتر نتایج به سال:
The aim of this paper is to investigate the effect of cutting speed and uncut chip thickness on cutting performance. A Finite Element Method (FEM) based on the ABAQUS explicit software which involves Johnson-Cook material mode and Coulombs friction law was used to simulate of High Speed Machining (HSM) of AISI 1045 steel. In this simulation work, feed rate ranging from 0.05 mm/rev to 0.13 mm/re...
Current experimental physics programs at a number of electron accelerator laboratories worldwide require the delivery of high average current highly polarized electron beams for long periods of time. The polarized electrons are produced by near bandgap photoemission from certain semiconductor photocathodes. We observe the quantum efficiency of these cathodes to be inversely related to the total...
A highly precise coulometer is described which permits time integration of currents totaling 100 coulombs or more with a precision of about 1 part in 100,000. The current to be integrated oxidizes hydroquinone in an electrolysis cell, producing quinone and acid. The quinone is t hen reduced by constant-current coulometric titration, the end point being indicated by hydrogen-ion concentration me...
Lithium-ion batteries raise safety, environmental, and cost concerns, which mostly arise from their nonaqueous electrolytes. The use of aqueous alternatives is limited by their narrow electrochemical stability window (1.23 volts), which sets an intrinsic limit on the practical voltage and energy output. We report a highly concentrated aqueous electrolyte whose window was expanded to ~3.0 volts ...
چکیده به منظور درک بهتری از حرکت صفحات تکتونیکی، می توان از شبیه سازی عددی به عنوان یک ابزار مهم و نیرومند استفاده نمود. لذا بر اساس قوانین فیزیکی و ژئوفیزیکی و در نظر گرفتن نحوه ارتباط و شکل صفحات، می توان رفتارهای آنها را در شرایط متفاوت مدل سازی نمود. نواحی مختلف به دلیل شرایط متفاوت ساختاری، رفتار لرزه ای مشابه ای را نشان نمی دهند. هدف این تحقیق بررسی الگوهای رفتاری مواد با ویژگیها ی مت...
Recent research on friction in robot joints and transmission systems has considered meshing friction a position-dependent friction component. However, in this paper we show experimental evidence that meshing friction depends highly on joint speed. We identify the meshing friction in the gearboxes of a robotic leg, and we propose a new mathematical model that considers the rate dependency of mes...
Novel PMMA-STO-CNT matrices were created by opened-tip vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) with conformal coatings of strontium titanate (STO) and poly(methyl methacrylate) (PMMA). Emission threshold of 0.8 V/μm was demonstrated, about 5-fold lower than that of the as-grown VA-MWCNTs. This was obtained after considering the related band structures under the perspective o...
Microelectromechanical systems (MEMS) incorporating active piezoelectric layers offer integrated actuation, sensing, and transduction. The broad implementation of such active MEMS has long been constrained by the inability to integrate materials with giant piezoelectric response, such as Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PMN-PT). We synthesized high-quality PMN-PT epitaxial thin films on vicinal...
We present the design of a modular, robust, high-current switch for controlling discharge current in the large plasma device ~LAPD! at UCLA. As developed, 10 insulated gate bipolar transistor units are connected in parallel to provide 24 kA current-carrying capacity. Associated snubber and protection circuits are described in detail. The switch is typically operated at a 1 Hz repetition rate, w...
We quantify the effects of the duration of the charge-discharge cycling period on the irreversible loss of anode material in rechargeable lithium metal batteries. We have developed a unique quantification method for the amount of dead lithium crystals (DLCs) produced by sequences of galvanostatic charge-discharge periods of variable duration τ in a coin battery of novel design. We found that th...
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