341 research outputs found
Monitoring of liquid flow through microtubes using a micropressure sensor
No full textThe pressure-driven liquid flow through microtubes was studied in a range of very low Reynolds numbers (<0.15) by monitoring the pressure change in situ. Cylindrical microtubes with diameters ranging from 50 ?m to 500 ?m were examined and two types of tube material, namely PEEK polymer and fused silica were compared. A good linear relation for the pressure drop versus flow rate was obtained. Apparent deviations between the measured slopes with those calculated using conventional theory were attributed to uncertainties in the calculated values which are dominated by the uncertainties in the microtube diameters. It was found that a period of stabilisation time was required for reaching a steady flow after the syringe pump was switched on/off or to a different flow rate. The stabilisation time was likely due to the compressibility of the fluid. Insignificant difference between PEEK polymer and fused silica microtubes in terms of flow resistance was observed. The in-situ measurement of pressure drops provides a convenient approach for monitoring fluid flow through microtubes and detecting dimensional changes within microchannels in Lab-on-a-Chip and microreactor systems
Virtual resistance based active damping solution for constant power instability in AC microgrids
No full textWith ever-increasing share of power electronic loads constant power instability is becoming a significant issue in microgrids, especially when they operate in the islanding mode. Transient conditions like resistive load-shedding or sudden increase of constant power loads (CPL) might destabilize the whole system. Modeling and stability analysis of AC microgrids with CPLs have already been discussed in literature. However, no effective solutions are provided to stabilize this kind of system. Therefore, this paper proposes a virtual resistance based active damping method to eliminate constant power instability in AC microgrids. Advantages and limitations of the proposed method are also discussed in detail. Simulation results are presented to validate the proposed active damping solution
Ordinary And Extraordinary Giant Hall Effects In Co-sio2 Granular Films
No full textMagnetization, resistance and Hall effect are studied in granular magnetic Co-SiO2 nanocomposites in the temperature range 5-300 K and fields up to 6 T. Relative contributions from spin-independent and spin-dependent processes to the giant Hall effect near the metal-insulator transition are analysed. © 2001 Published by Elsevier Science B.V.226-230PART I680682Hurd, C.M., (1972) The Hall Effect in Metals and Alloys, , Plenum Press, New YorkPakhomov, A.B., Yan, X., Zhao, B., (1995) Appl. Phys. Lett., 67, p. 3497Jing, X.N., Wang, N., Pakhomov, A.B., Fung, K.K., Yan, X., (1996) Phys. Rev. B, 53, p. 14032Zhao, B., Yan, X., (1997) J. Appl. Phys., 81, p. 4290Aronzon, B.A., Kovalev, D.Y., Lagar'Kov, A.N., Meilikhov, E.Z., Ryl'Kov, V.V., Sedova, M.A., Negre, N., Leotin, J., (1999) JETP Lett., 70, p. 90Xu, Q.Y., Ni, G., Sang, H., Du, Y.W., (2000) J. Appl. Phys., 87, p. 6998Gang, N., Lu, J., Xu, Q.Y., Sang, H., Du, Y.W., (1999) Acta Phys. Sinica, 48, pp. S47Chiriac, H., Lozovan, M., Urse, M., (2000) J. Magn. Magn. Mater., 215, p. 535Zhang, X.X., Liu, H., Pakhomov, A.B., (2000) Physica B, 279, p. 81Aronzon, B.A., Meilikhov, E.Z., Rylkov, V.V., Lagarkov, A.N., Sedova, M.A., Evstushina, I.A., Kovalev, D.Y., Leotin, J., (2000) Physica. B, 284, p. 1980Luo, E.Z., Pakhomov, A.B., Zhang, Z.Q., Chan, M.C., Wilson, I.H., Xu, J.B., Yan, X., (2000) Physica. B, 279, p. 98Chan, M.C., Pakhomov, A.B., Zhang, Z.Q., (2000) J. Appl. Phys., 87, p. 1584Denardin, J.C., Pakhomov, A.B., Knobel, M., Liu, H., Zhang, X.X., (2000) J. Phys.: Condens. Matter, 12, p. 3397Holstein, T., (1961) Phys. Rev., 124, p. 1329Vedyaev, A.V., Kotel'Nikova, O.A., Pugach, N.G., Ryzhanova, N.V., (2000) JETP, 90, p. 103
A loop cancellation based active damping solution for constant power instability in vehicular power systems
No full textIn recent years, electric propulsion systems have increasingly been used in land, sea and air vehicles. The vehicular power systems are usually loaded with tightly regulated power electronic converters which tend to draw constant power. Since the constant power loads (CPLs) impose negative incremental resistance characteristics on the feeder system, they pose a potential threat to the stability of vehicular power systems. This effect becomes more significant in the presence of distribution lines between source and load in large vehicular power systems such as electric ships and more electric aircrafts. System transients such as sudden drop of converter side loads or increase of constant power requirement can cause complete system instability. Most of the existing research work focuses on the modeling and stabilization of DC vehicular power systems with CPLs. Only a few solutions are proposed to stabilize AC vehicular power systems with non-negligible distribution lines and CPLs. Therefore, this paper proposes a novel loop cancellation technique to eliminate constant power instability in AC vehicular power systems with a theoretically unbounded system stability region. Analysis is carried out on system stability with the proposed method and simulation results are presented to validate its effectiveness
- …
