ExaGridPF: A Parallel Power Flow Solver for Transmission and Unbalanced Distribution Systems

This paper investigates parallelization strategies for solving power flow problems in both transmission and unbalanced, three-phase distribution systems by developing a scalable power flow solver, ExaGridPF, which is compatible with existing high-performance computing platforms. Newton-Raphson (NR) and Newton-Krylov (NK) algorithms have been implemented to verify the performance improvement over both standard IEEE test cases and synthesized grid topologies. For three-phase, unbalanced system, we adapt the current injection method (CIM) to model the power flow and utilize SuperLU to parallelize the computing load across multiple threads. The experimental results indicate that more than 5 times speedup ratio can be achieved for synthesized large-scale transmission topologies, and significant efficiency improvements are observed over existing methods for the distribution networks

Images in clinical medicine. Meckel's diverticulum in action.

published_or_final_versio

Estimation of fast fading channel in impulse noise environment

This paper studies the estimation of fast fading channel in the present of impulse noise. Fast fading channel in wireless communications system is typically modeled as autoregressive (AR) process. Least-square algorithm and Kalman filter are previously proposed for estimating the AR parameters and the channel impulse response respectively using training sequence. The performance of these algorithms, however, is very sensitive to impulse noise. In this paper, a robust Kalman filter and a robust recursive least M-estimate algorithm are employed to jointly estimate the channel impulse response and the AR parameters of fast fading channel under impulse noise. Simulation showed that the proposed algorithms are much less sensitive to impulse noise than the conventional algorithms.published_or_final_versio

Estimating the commuting cost and commuting time property price gradients

In this paper, we estimate the property price gradients in Hong Kong. We distinguish our effort from previous studies on the subject by directly measuring the economic distance, i.e., the monetary commuting cost and commuting time, instead of merely the physical distance. Our results are generally supportive of the prediction of a negative property price gradient. In one specification, the estimated capitalization of the savings of commuting cost in property prices appears to be just right. The expected negative effect of commuting time on property values, however, can only be detected among observations with larger commuting times. Nevertheless, over the range where the effect of commuting time has the expected negative sign, the values of time implied by the estimates agree well with the results reported in the transportation economics literature. © 2003 Elsevier B.V. All rights reserved.preprin

A decentralized approach for operating reserve procurement

In power markets, operating reserve procurement is usually centrally handled according to certain reliability rules and aiming at minimization of total cost for reserve procurement. In this approach, there are no customers' choices, no incentives for ISO to minimize the total cost or for reserve suppliers to commit promised reserve capacity. It may leads to severe inefficiency. In this paper, we propose a decentralized approach for operating reserve procurement and in the meantime, to discover the market price for it. In the approach, each participant selects the optimal decision to maximize his or her own interests. Insurance theory is applied; which allows consumers to transfer their risk for financial loss of outage to the ISO, and induces incentive for the ISO to manage the entire amount of reserve capacity in an efficient manner. A penalty system is introduced, which improves the liability for the genco to provide operating reserve. Detailed math model and solution procedure are presented. It is also shown that with properly defined reserve market's structure, the decentralized approach can yield same optimal solution as its centralized counterpart. Numerical example results illustrate the effectiveness of the suggested approach.published_or_final_versio

Characteristics of nonmethane hydrocarbons (NMHCs) in industrial, industrial-urban, and industrial-suburban atmospheres of the Pearl River Delta (PRD) region of south China

In a study conducted in late summer 2000, a wide range of volatile organic compounds (VOCs) were measured throughout five target cities in the Pearl River Delta (PRD) region of south China. Twenty-eight nonmethane hydrocarbons (NMHCs; 13 saturated, 9 unsaturated, and 6 aromatic) are discussed. The effect of rapid industrialization was studied for three categories of landuse in the PRD: Industrial, industrial-urban, and industrial-suburban. The highest VOC mixing ratios were observed in industrial areas. Despite its relatively short atmospheric lifetime (2-3 days), toluene, which is largely emitted from industrial solvent use and vehicular emissions, was the most abundant NMHC quantified. Ethane, ethene, ethyne, propane, n-butane, i-pentane, benzene, and m-xylene were the next most abundant VOCs. Direct emissions from industrial activities were found to greatly impact the air quality in nearby neighborhoods. These emissions lead to large concentration variations for many VOCs in the five PRD study cities. Good correlations between isoprene and several short-lived combustion products were found in industrial areas, suggesting that in addition to biogenic sources, anthropogenic emissions may contribute to urban isoprene levels. This study provides a snapshot of industrial, industrial-urban, and industrial-suburban NMHCs in the five most industrially developed cities of the PRD. Increased impact of industrial activities on PRD air quality due to the rapid spread of industry from urban to suburban and rural areas, and the decrease of farmland, is expected to continue until effective emission standards are implemented. Copyright 2006 by the American Geophysical Union

Ambient halocarbon mixing ratios in 45 Chinese cities

During this study 158 whole air samples were collected in 45 Chinese cities in January and February 2001. The spatial distribution of different classes of halocarbons in the Chinese urban atmosphere, including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), Halon-1211, and other chlorinated compounds is presented and discussed. Most of these compounds were enhanced compared to background levels. However, the mean enhancement of CFCs was relatively small, with CFC-12 and CFC-11 increases of 6% (range 1-31%) and 10% (range 2-89%), respectively, with respect to the global background. On the contrary, strongly enhanced levels of CFC replacement compounds and halogenated compounds used as solvents were measured. The average Halon-1211 concentration exceeded the background of 4.3 pptv by 75% and was higher than 10 pptv in several cities. Methyl chloride mixing ratios were also strongly elevated (78% higher than background levels), which is likely related to the widespread use of coal and biofuel in China. © 2006 Elsevier Ltd. All rights reserved

A study of operating reserve procurance in power markets with application of insurance theory: contract-based vs pool-based approaches

In the power markets, the ancillary services are treated as special commodities. Operating reserve is an important commodity in the category of ancillary services, which supports the system reliability against unexpected generator outages. In this paper, we study the procurance of operating reserve via two approaches, i.e. contract-based model and pool-based model. In order to guarantee the availability of reserved capacity and reduce the loss of consumer at generator forced outages, insurance policy is applied. Decentralized optimal decision is adopted. After presenting the math models of the two approaches, it is proven that the pool-based approach is more cost-effective and should be adopted in the deregulated power markets.published_or_final_versio

The effect of carrier-induced change on the optical properties of AlGaAs-GaAs intermixed quantum wells

The carrier-induced effects in the change of absorption and refractive index on the AlGaAs-GaAs intermixing modified quantum wells (QW's) have been investigated theoretically. Band-filling, bandgap shrinkage, and free-carrier absorption have been included for various carrier concentrations. The Schrodinger and the Poisson equations have been considered self-consistently. The polarized absorption coefficients are calculated using the Kane k·p method for a four band model and followed by the Kramers-Kranig transformation to obtain the refractive index change. The results obtained show a more enhanced bandgap renormalization and change of absorption, but a reduced change in refractive index for the larger intermixing extents. It is important to know the carrier-induced optical parameter changes the intermixed QW's because of their recent interests in photonics.published_or_final_versio