46,453 research outputs found
Repetitive current control of two-level and interleaved three-phase PWM utility connected converters
No full textThis thesis is mainly concerned with investigations into digital repetitive current controlof two-level and interleaved utility connected PWM converters. The research ismotivated by the relatively poor performance of classical (PI) controllers when theutility voltage harmonic distortion is high. This is due to the low gain, and poordisturbance rejection of the PI controller at the utility harmonic frequencies. Repetitivefeedback controllers have the ability to track or reject periodic disturbances, such asutility harmonics, as they naturally have high gains at the utility voltage harmonicfrequencies, assuming that these frequencies do not change.Repetitive controllers (RC) are known for being sensitive to variations in systemparameters and disturbance frequency, which in practice renders them either ineffectiveor unstable. Another challenge arises from the memory requirements of RC in case ofthe absence of even harmonics, which can make its practical implementation difficultand expensive. In addition, another problem that has not been investigated extensivelyin the literature is that the effectiveness of RC is severely limited by the limitedbandwidth of the plant (the utility connected converter and its filter). Theoreticalanalysis and simulation results presented in this thesis show that RC could noteffectively reject disturbances at frequencies above the closed loop system bandwidth.The design of the converter's output filter bandwidth and the values of its componentsneed to be selected carefully, to enable RC to be used effectively.The research in this thesis focuses on investigating the practical implementation andperformance limits of two types of repetitive controllers (conventional and oddharmonics),used for current control of two-level utility connected converter with LCLoutput filter. The odd-harmonic repetitive controller halves the memory requirementand offers higher gains only at odd harmonic frequencies of interest. The overall controlscheme consists of the traditional classical tracking controller with a dual loop feedbacksystem and RC. The results indicate that the repetitive controller improves the steadystate error and the total harmonic distortion of the output current, provided that theplant's bandwidth is sufficiently large.Finally, a repetitive controller for an interleaved utility connected converter has beendesigned and investigated in this study. The interleaved converter system has higherbandwidth than the two-level converter, which improves the effectiveness of RC. Itprovides good disturbance rejection compared to classical controllers which results inlow output current THD. The RC was demonstrated to be robust despite uncertainty inutility impedance, while achieving a fast almost zero error convergence. The proposedRC has been experimentally implemented using a DSP and the results indicate that thequality of output current complies with international standards on harmonic limits andmatches simulation results obtained from the Matlab/Simulink model of the system
Black hole surrounded by a dark matter halo in the M87 galactic center and its identification with shadow images
No full textIn this paper we present a new black hole solution surrounded by dark matter (DM) halo in the galactic center using the mass model of M87 and that coming from the universal rotation curve (URC) dark matter profile representing family of spiral galaxies. In both cases the DM halo density is cored with a size r0 and a central density ρ0: ρ(r)=ρ0/(1+r/r0)(1+(r/r0)2). Since r0ρ0=120 M/pc2 [Mon. Not. R. Astron. Soc. 397, 1169 (2009)MNRAA40035-871110.1111/j.1365-2966.2009.15004.x], then by varying the central density one can reproduce the DM profile in any spiral. Using the Newman-Jains method we extend our solution to obtain a rotating black hole surrounded by dark matter halo. We find that the apparent shape of the shadow beside the black hole spin a, it also depends on the central density of the surrounded dark matter ρ0. As a specific example we consider the galaxy M87, with a central density ρ0=6.9×106 M/kpc3 and a core radius r0=91.2 kpc. In the case of M87, our analyses show that the effect of dark matter on the size of the black hole shadow is almost negligible compared to the shadow size of the Kerr vacuum solution hence the angular diameter 42 μas remains almost unaltered when the dark matter is considered. For a small totally dark matter dominated spiral such as UGC 7232, we find similar effect of dark matter on the shadow images compared to the M87. However, in specific conditions having a core radius comparable to the black hole mass and dark matter with very high density, we show that the shadow images decreases compared to the Kerr vacuum black hole. The effect of dark matter on the apparent shadow shape can shed some light in future observations as an indirect way to detect dark matter using the shadow images
Active control of vibrations of a tall structure excited by external forces
No full textThis paper is concerned with active control of vibrations of tall structures subjected to strong wind or earth quake shocks using an active mass damper (AMD). A linear black box model of the systems is obtained from an experimental scale model of the structure. Two alternative control systems, and associated observers are designed and their performance assessed theoretically and experimentally
Understanding t-Darpp's role in conferring drug resistance in Her2 positive breast cancer
No full textApproximately 25% of breast cancers overexpress human epidermal receptor 2 (HER2). Herceptin, a humanized antibody, targets these receptors but a year into treatment resistance to the drug arises. The truncated Darpp32 protein, t-Darpp, is implicated in this resistance as it is overexpressed in cell lines resistant to Herceptin. However, Darpp32 co-expression with t-Darpp, minimizes this resistance. One hypothesis that explains these observations is that there may be a dominant negative interaction between the two proteins which this project attempted to prove. We also analyzed potential interactions that t-Darpp or Darpp32 may have with PKA or PRXV. A faint interaction appears to occur between t-Darpp and Darpp32; however, this data remains inconclusive. We were unable to prove or disprove an interaction with PKA or PRXV. Further experimentation on these proteins is necessary as results may shed light on t-Darpp's role in Herceptin resistance and could potentially result in new therapy targets.Thesis (M.S.) California State University, Los Angeles, 2012Breast Cancer, Herceptin, Protein Interactions, Resistance, Signaling PathwayCommittee members: Jamil A Momand, Sandra B Sharp, Raymond Garcia, Xin Wen, Robert Vellanowet
Understanding t-Darpp's role in conferring drug resistance in Her2 positive breast cancer
No full textThesis (M.S.)
California State University, Los Angeles, 2012Committee members: Jamil A Momand, Sandra B Sharp, Raymond Garcia, Xin Wen, Robert VellanowethBreast Cancer, Herceptin, Protein Interactions, Resistance, Signaling PathwayApproximately 25% of breast cancers overexpress human epidermal receptor 2 (HER2). Herceptin, a humanized antibody, targets these receptors but a year into treatment resistance to the drug arises. The truncated Darpp32 protein, t-Darpp, is implicated in this resistance as it is overexpressed in cell lines resistant to Herceptin. However, Darpp32 co-expression with t-Darpp, minimizes this resistance. One hypothesis that explains these observations is that there may be a dominant negative interaction between the two proteins which this project attempted to prove. We also analyzed potential interactions that t-Darpp or Darpp32 may have with PKA or PRXV. A faint interaction appears to occur between t-Darpp and Darpp32; however, this data remains inconclusive. We were unable to prove or disprove an interaction with PKA or PRXV. Further experimentation on these proteins is necessary as results may shed light on t-Darpp's role in Herceptin resistance and could potentially result in new therapy targets
Supplemental Material - From Supportive to Strained: A Mixed Methods Exploration of Emerging Adults’ Characterizations of Past and Present Grandparent-Grandchild Roles and Relationships
No full textSupplemental Material for From Supportive to Strained: A Mixed Methods Exploration of Emerging Adults’ Characterizations of Past and Present Grandparent-Grandchild Roles and Relationships by Abigail T. Stephan, Nora D. Hochstetter, Virginia E. Clark, and Faiza M. Jamil in Journal of Social and Personal Relationships.</p
Robust repetitive feedback control of a three-phase grid connected inverter
No full textThis paper discusses the design of a repetitive feedback
controller for a grid-connected two-level three-phase voltagesource inverter connected between a DC source and the grid through an LCL filter. The controller incorporates a classical
two loop feedback of the output current and the capacitor
current in addition to a repetitive feedback loop. The results
show that the proposed technique improves the steady state
error and the total harmonic distortion of output current in
presence of utility harmonics
Settling of finite-size particles in isotropically forced, homogeneous turbulence: interface-resolved simulations
No full textWe have simulated the gravity-induced settling of finite-size particles in a turbulent background flow which is forced in a statistically-stationary fashion. The simulations are accurately resolving the solid-fluid interface with the aid of an immersed boundary technique [1]. The parameters of the simulation are (apart from background turbulence) identical to those of reference [2], where particle clustering was observed at a Galileo number of 178 and a solid volume fraction of 0.005. In the present case, it is found that a relative turbulence intensity of 0.24 leads to the disappearance of the clusters; as a consequence, the increase in average particle settling velocity found in [2] also vanishes. [1] M. Uhlmann. An immersed boundary method with direct forcing for the simulation of particulate flows. J. Comput. Phys., 209(2):448–476, 2005. [2] M. Uhlmann and T. Doychev. Sedimentation of a dilute suspension of rigid spheres at intermediate Galileo numbers: the effect of clustering upon the particle motion. J. Fluid Mech., 752:310–348, 2014
Mesophilic-hydrothermal-thermophilic (M-H-T) digestion of green corn straw
No full textMesophilic-hydrothermal (80-160 degrees C, 30 min)-thermophilic (M-H-T) digestion and control tests of mesophilic (M), thermophilic (T), hydrothermal-mesophilic (H-M), and mesophilic-thermophilic digestion (M-T) of green corn straw were conducted for a 20-day fermentation period. The results indicate that M-H-T is an efficient method to improve methane production. A maximum methane yield of 371.74 mL/g volatile solid was obtained by the M (3 days)-H (140 degrees C)-T (17 days) process, which was 20.44%, 16.55%, 31.44%, and 14.31% higher than the yields of the M, T, 140-M, and M-T processes. The enhanced methane production was attributed to (1) the improved hemicellulose degradation and lignin disorganization; (2) prevention of the degradation of soluble sugar, easily hydrolyzed hemicellulose and cellulose into furfural and methylfurfural; and (3) lack of formation of Maillard reaction products during initial hydrothermal treatment. (C) 2015 Elsevier Ltd. All rights reserved
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
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