The Experts below are selected from a list of 26799 Experts worldwide ranked by ideXlab platform
Peter C Hauser - One of the best experts on this subject based on the ideXlab platform.
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fundamental aspects of contactless conductivity detection for capillary electrophoresis part ii signal to noise ratio and stray capacitance
Electrophoresis, 2004Co-Authors: Pavel Kubaň, Peter C HauserAbstract:The signal-to-noise ratio of a contactless conductivity detector for capillary electrophoresis was examined for different cell arrangements and operating parameters. The best signal-to-noise ratios, and hence the best detection limits, are obtained for frequencies which give highest sensitivity. Comparative experiments for three different Excitation Voltages (20, 100, and 200 V p p ) showed that the best signal-to-noise ratios were achieved for the highest Excitation Voltage of 200 V p p . Low conductivity of the background electrolyte solution is mandatory to obtain lowest noise levels, and also the improvement on applying high Excitation Voltages was best for the electrolyte solution with lowest conductivity. The diameter of the electrodes was found to have only a negligible effect, so that a tight fitting of the electrodes to the external diameter of the capillary is not necessary. A cell without shielding between the two electrodes showed significant direct coupling (stray capacitance) and lower signal-to-noise ratios for all experimental conditions used. A serious distortion of the peak shapes was also observed for this cell arrangement.
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high Voltage capacitively coupled contactless conductivity detection for microchip capillary electrophoresis
Analytical Chemistry, 2002Co-Authors: Jatisai Tanyanyiwa, Peter C HauserAbstract:Contactless conductivity detection was carried out on a planar electrophoresis device by capacitive coupling using an ac Excitation Voltage of 500 V(p-p) and a frequency of 100 kHz. It was possible to carry out detection in this way through a cover plate of 1 mm thickness. Better sensitivity is obtained, however, by placing the electrodes into troughs that allow tighter coupling to the separation channel. The 3 x S/N detection limits are 0.49, 0.41, and 0.35 microM for the small inorganic ions K+, Na+, and Mg2+. The detection of heavy metals is demonstrated with the example of Mn2+, Zn2+, and Cr3+ with detection limits of 2.1, 2.8, and 6.8 microM, respectively. The universal nature of the method is further illustrated by the detection of citric and lactic acids, which are of interest in food and beverage analysis, and detection of three antiinflammatory nonsteroid drugs, 4-acetamidophenol, ibuprofen, and salicylic acid, as examples of species of pharmaceutical interest.
Xuan F Zha - One of the best experts on this subject based on the ideXlab platform.
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study on a piezoelectric micropump for the controlled drug delivery system
Microfluidics and Nanofluidics, 2007Co-Authors: Qifeng Cui, Chengliang Liu, Xuan F ZhaAbstract:We present the design of a new controlled drug delivery system potential for in vitro injection of diabetics. The system incorporates some integrated circuit units and microelectromechanical system devices, such as micropump, microneedle array and microsensor. Its goal is to achieve safer and more effective drug delivery. Moreover, a valveless micropump excited by the piezoelectric actuator is designed for the drug delivery system, and a simple fabrication process is proposed. A dynamic model is developed for the valveless micropump based upon the mass conservation. To characterize the micropump, a complete electro-solid-fluid coupling model, including the diffuser/nozzle element and the piezoelectric actuator, is built using the ANSYS software. The simulation results show that the performance of micropump is in direct proportion to the stroke volume of the pump membrane and there is an optimal thickness of the piezoelectric membrane under the 500 V/mm electric field. Based on this simulation model, the effects of several important parameters such as Excitation Voltage, Excitation frequency, pump membrane dimension, piezoelectric membrane dimension and mechanical properties on the characteristics of valveless micropump have been investigated.
K Latha - One of the best experts on this subject based on the ideXlab platform.
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identification of resonance in hybrid stepper motor through measured current dynamics in online for accurate position estimation and control
IEEE Transactions on Industrial Informatics, 2013Co-Authors: K Balakrishnan, B Umamaheswari, K LathaAbstract:Stepper motors suffer with skipped steps due to the occurrence of resonance and instability, under certain load conditions. Unlike in other machines, variation of torque is not reflected in the current. Hence the current measurement based position estimation techniques fail. Experimental investigations reveal that high frequency ripples are present in the current dynamics during the resonating periods. This paper proposes an identification technique which works based on ripple content during the transient period of the current rise. It is shown that resonance can be identified and compensated well before the motor misses the step through the Excitation Voltage. With such compensation, current measurement based estimation techniques provide accurate speed & position estimation. The paper also matches experimental results with the simulation.
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estimation of rotor position and speed for hybrid stepper motor under various phase Excitation schemes and compensated resonance
International Conference on Power Engineering Energy and Electrical Drives, 2011Co-Authors: K Balakrishnan, B Umamaheswari, K LathaAbstract:Estimation of rotor position and speed plays an important role to avoid skipped step and reduced resonance in Hybrid Stepper Motor (HSM). In this paper, the effect of various phase Excitation schemes on estimation of rotor position and speed in the presence of resonance is studied. A method has been proposed to identify the resonance from the frequency content of measured phase currents well before it is exhibited in the mechanical measurement. It is compensated through Excitation Voltage. The microstepping Excitation is found to provide fastest and smooth tracking of rotor position and speed. The results are validated through experimentation.
Yuan-yih Hsu - One of the best experts on this subject based on the ideXlab platform.
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Effect of Rotor Excitation Voltage on Steady-State Stability and Maximum Output Power of a Doubly Fed Induction Generator
IEEE Transactions on Industrial Electronics, 2011Co-Authors: Chien-hung Liu, Yuan-yih HsuAbstract:The effect of rotor Excitation Voltage on steady-state stability and output power of a doubly fed induction generator (DFIG) is investigated. Wind turbine mechanical torque-speed characteristics, as well as generator electromagnetic torque-speed characteristics, are considered in the derivation of the steady-state stability region for the magnitude and phase angle of the rotor Excitation Voltage. To evaluate the maximum output power of a DFIG, detailed expressions for stator power, rotor power, stator loss, rotor loss, and electrical power are derived as functions of the generator speed and the magnitude and phase angle of the rotor Excitation Voltage. The effect of stator resistance on the magnitude and phase angle of the resultant optimal rotor Excitation Voltage, which gives maximum output power and minimum loss, is examined. Experimental results are given to demonstrate the effectiveness of the theoretical analysis.
Lj Z Petrovic - One of the best experts on this subject based on the ideXlab platform.
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time resolved optical emission imaging of an atmospheric plasma jet for different electrode positions with a constant electrode gap
Plasma Sources Science and Technology, 2015Co-Authors: Dejan Maletic, Nenad Selakovic, Gordana Malović, Lj Z Petrovic, Antonije đorđevic, Nevena Puač, Saša LazovićAbstract:The aim of this paper is to determine the influence of the position of the electrodes on the range of a plasma jet, for specific experimental conditions, by using time-resolved optical emission spectroscopy. The optimal position of the electrodes is determined for a fixed gas flow rate and applied Excitation Voltage. We characterize the helium plasma jet for different distances from the end of the glass tube, showing detailed results for four different electrode positions from the jet nozzle (7, 15, 30 and 50mm). It was found that at the distance of 15mm, the length of the plasma jet is at its maximum. The highest speeds of the plasma package travelling outside the glass tube of the atmospheric plasma jet are obtained for the same electrode configuration (15mm from the jet nozzle). With the electrodes positioned at smaller distances from the nozzle, the plasma plume was much shorter, and at the larger distances the plasma did not even leave the glass tube.
