Search

When a parallel-plate electrostatic actuator (ESA) is driven by a voltage source, pull-in instability limits the range of displacement to one-third of the gap between plates. In this paper, a nonlinear active disturbance rejection controller (NADRC) is originally developed on the ESA. Our control objectives are stabilizing and increasing the displacement of an ESA to 99.99% of its full gap. Most of the reported controllers in literature are based on linearized models of the ESAs and depend on detailed model information of them. However, the ESA is inherently nonlinear and has model uncertainties due to the imperfections of microfabrication and packaging. The NADRC consists of a nonlinear extended state observer (NESO) and a feedback controller. The NESO is used to estimate system states and unknown nonlinear dynamics for the ESA. Therefore, it does not require accurate model. We simulate the NADRC on a nonlinear ESA in the presences of external disturbance, system uncertainties, and noise. The simulation results verify the effectiveness of the controller by successfully extending the travel range of ESA beyond pull-in point. They also demonstrate that the controller is robust against both disturbance and parameter variations, and has low sensitivity to measurement noise. Furthermore, the stability for the control system with NADRC is theoretically proved.

The need for a low-cost, high reliability power flow control technology is becoming exceedingly clear in the face of increased renewable penetration and electrification of automobiles. This paper proposes a power routing technology called the compact dynamic phase angle regulator (CD-PAR) for dynamic control of active/reactive power. The proposed device is a hybrid solution realized by pairing a fractionally-rated low-frequency transformer with a fractionally-rated power converter for a solution that is of lower cost and of higher reliability compared to traditional power electronics technologies for grid applications. The paper provides discussion of the technology and its implementation, followed by simulation and experimental measurements at 13 kV / 1 MVA. Key design challenges and their potential resolutions are also discussed.

There has been an increasing interest in development of power routers to realize dynamically controllable grid. Previously the authors have proposed a power router based on fractionally-rated BTB (FR-BTB) converter, which was shown to have reduced semiconductor and magnetics requirement compared to traditional power routing solutions. This paper presents the development and functional demonstration of the FR-BTB based power router at 13 kV, 1 MVA while reflecting on the challenges associated with high voltage and high power applications. The paper also presents applications of the power router in distribution systems.

The increasing load, increasing level of penetration of renewable energy and limited investment in transmission infrastructure have significantly increased the need for a smart, dynamically controllable grid. This paper proposes a power flow control device to maximize asset utilization, improve reliability, and reduce congestion. To ensure low cost of implementation and high reliability, the technology is based on a system with fractionally-rated electronics paired with a line-frequency transformer built using standard materials and processes as utility-grade transformers. The proposed “power router” is realized by augmenting a three-phase utility-grade transformer with three fractionally-rated direct AC converters. The paper will address key design challenges associated with utility-grade equipment that include requirement for high reliability and availability, long life in excess of 20 years with limited or no maintenance schedule, rugged and often harsh operating environment, high BIL ratings and high fault-handling capabilities. The paper will discuss design and development of a 12.47 kV, 1 MVA three-phase system with these challenges taken into account and conclude with experimental results.

Late referral of patients with chronic kidney disease (CKD) by primary care physicians (PCPs) is associated with poor outcomes. We sought to assess factors influencing PCPs referral patterns in the general population and in geriatric patients, and compared their perceptions to the referral patterns.We retrospectively reviewed 268 patients with Stage 3 CKD (early referral) and 280 with Stage 4 CKD (appropriate referral) seen in renal clinic and compared them to 268 randomly selected non-referred Stage 4 CKD patients from primary care physicians office records. We also surveyed 400 regional PCPs on factors influencing their referral for CKD.Non-referred patients were significantly (p0.05) more likely to be over 65 years (OR: 3.5; 95% CI: 2.3 - 5.2), females (OR: 1.4; 95% CI: 1.0 - 2.0) and of non-white race (OR: 2.6; 95% CI: 1.5 - 4.5) after adjusting for relevant confounding variables. Charlson comorbidity index greater than 4 was associated with non-referral when the non-referral group was compared to the early referral group. Among geriatric patients, women and a higher comorbidity index were associated with non-referral. 25% of PCPs completed the survey and 62% PCPs were unfamiliar with K/DOQI referral guidelines. Age75 years, limited life expectancy, patient noncompliance or refusal to consider dialysis influenced PCPs decision to refer.Our study shows that elderly women, minorities and patients with multiple comorbidities are at risk for non-referral for CKD care. Educating PCPs on the appropriate referral of CKD patients, especially those at risk for late or non-referral to a nephrologist is warranted, as are trials assessing different educational strategies.

The characteristics of providing spatial and frequency information in the transform domain by wavelet transform, plays a crucial role in forming a significance map of coefficients that needs to be coded in the case of image compression. This paper presents a wavelet based image compression technique where transmission of spatial locations of wavelet decomposed lower subbands coefficients is eliminated. The spatial position information of significant coefficients of subbands of each level can be found by interpolation of higher level subbands to lower level at decoder side. This in turn, saves the data corresponding to positional information of significant coefficients, further giving an opportunity to enhance image quality at same compression level by including additional wavelet coefficients. The simulation results show that the combination of interpolation and vector quantization (VQ) using neural networks performs better than baseline JPEG.

Reduction of the image colors, which is also called color quantization (CQ), has been the focus of recent research interest. It is as an integral part of various digital image related areas such as compression, segmentation etc.. Neural networks play a significant role in either assisting conventional color quantization techniques or providing standalone solutions for color quantization. In the present work three new algorithms have been proposed using modified forward only counterpropogation network (MFOCPN). These algorithms introduce, 1) sub-clustering in Kohonen layer for enhancing the clustering process, 2) a new entropy metric based initialization of the Kohonen layer for efficient color-map design and faster convergence of network. Further, the two approaches are merged, to yield third algorithm to achieve better results. The proposed algorithms have been tested on standard test image.

Tc-99m MIBI and TI-201 uptake have been reported in benign and malignant lesions. However, concordant uptake of both radiotracers has been described infrequently. The authors report a patient with a case history of tuberculosis and breast cancer who underwent a TI-201 cardiac stress/planar study initially for complaints of angina pectoris, and 3 years later a follow-up Tc-99m MIBI cardiac study was completed for similar complaints. These studies incidentally revealed uptake of TI-201 and Tc-99m MIBI in a large left lung mass unchanged in size between the two studies. CT with intravenous contrast performed 2 months after the Tc-99m MIBI study revealed a 9 cm calcified soft-tissue mass in the left lung with adjacent pleural calcifications.