13 research outputs found
Superiority of the Stochastic Restricted Liu Estimator under misspecification
No full textThis paper deals with the use of correct prior infromation in the estimation of regression coefficients when the regression model is misspecified due to the exclusion of some relevant regressor variables. In particular, the attention is focused on the Stochastic Restricted Liu estimator introduced by Hubert and Wijekoon (2004), which outperforms Liu estimator with respect to the matrix mean squared error matrix criterion. Further the superiority of the Stochastic Restricted Liu predictor over the Liu predictor is also examined, and concluded that there are situations where the Stochastic Restricted Liu predictor outperforms the Liu predictor with respect to the mean squared error matrix criterion even the model is misspecified
Mean square error matrix superiority of the mixed regression estimator under misspecification
No full textConditions are derived under which the mixed regression estimator (MRE) is better then the ordinary least-squares estimator (OLSE) with respect to the mean square error (MSE) matrix criterion especially for the case that the regression model is misspecified. Some attention is paid to prediction, where it is shown that the MRE-predictor is potentially superior to the OLS-predictor under the same criterion
Design of a power electronic assisted series compensator for grid voltage regulation
No full textIn recent years, high penetration of distributed generation (DG) driven by PV panels and heavy load insertion in the distribution network has led to frequent voltage fluctuations in the form of undervoltage and overvoltage. Voltage control using traditional voltage regulators are unable to cope with this situation as frequent tap changes reduce the lifetime of the mechanical taps due to arcing. Further, the nature of European distribution network in general, makes voltage control through shunt compensation methods typically ineffective and expensive. Series compensation through centralized on-load tap changing (OLTC) distribution transformers or feeder-specific compensators is hence a suitable strategy for voltage regulation in Europe. The thesis work describes the design of a novel, power electronic assisted OLTC transformer that provides voltage regulation in the European distribution network through series compensation. The aim is to ensure that the tap changes occur in an arc free manner, thus providing for long lifetime of the OLTC. Different topologies for OLTC are examined in detail and shortlisted based on the steady state operation and power ratings of transformer and switches required. A novel design of a partially rated autotransformer is proposed which has taps developed through a combination of no-load switches and a single hybrid switch. The hybrid switch is composed of a mechanical switch and two semiconductor switches which are used for steady state and tap change operation respectively. The mechanical switch ensures low steady state losses and the semiconductor switches are used for arc-free tap changing. Back-back series connected IGBT with anti-parallel diodes are used for the two semiconductor switches and voltage polarity based 4-step commutation is used for commutation between the taps. The novel design of the OLTC autotransformer is cost effective, efficient and has long lifetime. The complete system is simulated in the PLECS and the steady state and transient operation of the system have been investigated. The OLTC has customized for application in both MV and LV three phase distribution network. Detailed study of the failure mechanisms owing to internal and external faults is performed and possible protection mechanisms are suggested. A low level control mechanism is also developed, thus providing a holistic design for building a prototype.Electrical Power ProcessingElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Design of a power-electronic-assisted OLTC for grid voltage regulation
No full textHigh penetration of distributed generation (DG) has led to frequent voltage fluctuations in the distribution network. This paper describes the design of a partially rated, power-electronic-assisted onload tap-changing (OLTC) autotransformer. Positive and negative compensation of the grid voltage can be achieved on feeders that have high distributed generation and/or loading. A novel design of taps comprised of several no-load switches and a single semiconductor-mechanical hybrid switch have been proposed, that requires reduced voltage rating and a number of switches. In steady state, the mechanical switch in the hybrid switch conducts the load current resulting in low steady-state losses. During the tap change process, the OLTC uses semiconductor switches, namely insulated-gate bipolar transistor /metal-oxide semiconductor field-effect transistor, thus achieving arc-free tap change and long lifetime of switches. The OLTC system has been customized for both low-voltage and medium-voltage three-phase distribution networks. An open-delta configuration for the medium-voltage application has been proposed that requires only two OLTC units to control all three line voltages. Simulations are carried out to verify the steady-state and transient operation of the proposed OLTC.Accepted Author ManuscriptOld - EWI-ESE-DC&S DC systems & Storag
Using Historical Data for Retrospective Prediction of Rainfall In the Midwest
No full textThe Missouri River Basin (MRB) is an important food-producing region in the United States and Canada. Climate variability and water availability affect crops production in this region. Past climate data have been recorded at various locations in the basin over a period of ten years. We use the data for a retrospective prediction of rainfall. As the dimension of the data is relatively large, a sufficient dimension reduction approach is used to reduce the dimensionality of the data while preserving the regression information pertinent to rainfall. We use the nascent dimension reduction methodology called Minimum Average Deviance Estimation or MADE to reduce the dimensionality of the climate data. Since MADE is still a tool in development, we explored two of its intrinsic prediction methods and compared them to the Nadaraya-Watson prediction approach by a cross-validation. A parallel implementation of MADE and its prediction methods on a high performance computer were carried out. A performance study was
performed along with the application of the best prediction method to the MRB climate data.These results were obtained as part of the REU Site: Interdisciplinary Program in High Performance Computing (hpcreu.umbc.edu) in the Department of Mathematics and Statistics at the University of Maryland, Baltimore County (UMBC) in Summer 2016. This program is funded by the National Science Foundation (NSF), the National Security Agency (NSA), and the Department of Defense (DoD), with additional support from UMBC, the Depart- ment of Mathematics and Statistics, the Center for Interdisciplinary Research and Consulting (CIRC), and the UMBC High Performance Computing Facility (HPCF). HPCF is supported by the U.S. National Science Foundation through the MRI program (grant nos. CNS{0821258 and CNS{1228778) and the SCREMS program (grant no. DMS{0821311), with additional substantial support from UMBC. Co-author Ephraim Alfa was supported, in part, by the UMBC National Security Agency (NSA) Scholars Program through a contract with the NSA. Graduate assistants Sai Popuri and Nadeesri Wijekoon were supported by UMBC.https://userpages.umbc.edu/~gobbert/papers/REU2016Team1.pd
Quantification of Variabilities of Baseflow of Watersheds
No full textThe U.S. Geological Survey National Water-Quality Assessment Project conducted a study of 225 sites in the Chesapeake Bay watershed to estimate base flow. Baseflow is the estimated volumetric discharge of water, primarily from groundwater sources,
that is relayed to the measurement sites. The study is necessary in order to address the nation’s water supply for changes in the environment. Baseflow is estimated using a recursive digital filter. Calculating the variability of baseflow water discharge is
important to make informed decisions about water regulation. We explored the estimation of variability of baseflow using two methods: the bootstrap method and the Delta method. Each method has its own limitations and requirements. Ultimately,
bootstrapping was shown to be a reasonable recommendation for estimating baseflow variability. The bootstrapping algorithm was parallelized in order to compute numerous iterations on multiple processors for big data analysis. The derivation of the
variability of a non-constant streamflow was also considered for further study, but not implemented.These results were obtained as part of the REU Site: Interdisciplinary Program in High Performance Computing
(hpcreu.umbc.edu) in the Department of Mathematics and Statistics at the University of Maryland, Baltimore County (UMBC) in Summer 2017. This program is funded by the National Science Foundation (NSF), the National Security Agency (NSA), and the Department of Defense (DOD), with additional support from UMBC, the Department of Mathematics and Statistics, the Center for Interdisciplinary Research and Consulting (CIRC), and the UMBC High Performance Computing Facility (HPCF). HPCF is supported by the U.S. National Science Foundation through the MRI program (grant nos. CNS-0821258 and CNS-1228778) and the SCREMS program (grant no. DMS-0821311), with additional substantial support from UMBC. Author Christian Dixon was supported, in part, by the UMBC National Security Agency (NSA) Scholars Program through a contract with the NSA. Graduate assistants Nadeesri Wijekoon and Sai Popuri were supported by UMBC.https://userpages.umbc.edu/~gobbert/papers/REU2017Team2.pd
An Overview on Medium Voltage Grid Integration of Ultra-fast Charging Stations: Current Status and Future Trends
No full textThe emphasis on clean and green technologies to curtail greenhouse gas emissions due to fossil fuel-based economies has originated the shift towards electric mobility. As on-road electric vehicles (EVs) have shown exponential growth over the last decade, so have the charging demands. The provision of charging facilities from the low-voltage network will not only increase the distribution system's complexity and dynamics but will also challenge its operational capabilities, and large-scale upgrades will be required to meet the inevitably increasing charging demands. An ultra-fast (UF) charging infrastructure that replicates the gasoline refueling network is urgently needed to facilitate a seamless transition to EVs and ensure smooth operation. This paper presents a review of state-of-the-art DC fast chargers, the charging infrastructure's current status, motivation, and challenges for medium-voltage (MV) UF charging stations (UFCS). Furthermore, we consider the possible UFCS architectures and suitable power electronics topologies for UF charging applications. To address the peak formation issues in the daily load profile and high operational expenses of UFCSs, integration of renewable energy sources and energy storage systems due to their technological and economic benefits is being considered. The benefits of line frequency transformer (LFT) replacement with a solid-state transformer (SST), SST models, SST-based UF chargers, and MV SST-based UFCS architectures, as well as related MV active front-end and back-end power electronics topologies, are presented. Finally, the application of microgrids' hierarchical control architecture is considered for chargers and system-level control and management of UFCSs.DC systems, Energy conversion & Storag
Environmental reporting and firm profitability: Evidence from Sri Lanka
No full textBackground of study
Literature review: gaps
Research questions
1 Do disclosures on materials, energy, and water impact firms’ profitability?
2. Do bio-diversity disclosures impact firms’ profitability?
3. Do disclosures on emissions, effluents, and waste impact firms’ profitability?
4. Do disclosures on products & services, compliance, transport, overall supplier assessment, and environment grievance mechanisms impact firms’ profitability?
Contribution
Research context
Methodology
Conceptual framework
Measurement of variables
Model development
Data analysis
Findings
Conclusions, limitations and suggestions
NOTE:
Initial author = Lakshan Attanayake on Unitec staff directory; and A.M.I. Lakshan on paper
Corporate characteristics and integrated reporting disclosure level before and during the COVID-19 pandemic: Evidence from a developing country
No full textPURPOSE
The purpose of the study is to examine the level of Integrated Reporting (IR) disclosure, investigate the impact of corporate characteristics (Profitability, Company Size, Foreign Trading, Foreign Ownership, Sustainability Reporting, External Assurance) on the IR disclosure level, and identify whether there is a significant difference exists in the IR disclosure level before and during COVID-19 in the Sri Lankan context.
DESIGN/METHODOLOGY/APPROACH
Based on the adoption of International Integrated Reporting Framework (IIRF) guidelines, integrated annual reports of 37 companies for the four years (2017/18 to 2020/21) representing financial, consumer staples, and industrial sectors were analyzed. A quantitative approach was adopted. Mean testing, regression analysis, and paired sample t-tests were used to test the hypotheses.
FINDINGS
Results revealed a moderate level of disclosure with content elements described in the IIRF in the Sri Lankan context. Results of the regression analysis revealed that company size and sustainability reporting have a significant positive impact on the IR disclosure level of Sri Lankan listed companies. Moreover, the study's findings revealed a significant increase in the IR disclosure level during COVID-19 compared to before the pandemic.
PRACTICAL IMPLICATIONS
The study's empirical findings may provide implications for current and potential IR adopters, policymakers, assurance providers, and many other stakeholders who refer to integrated annual reports. Moreover, the findings of the study may provide useful insights to the corporate management in facilitating the IR process and adopting IR practices in Sri Lanka in line with the guidelines prescribed in the International Integrated Reporting Framework.
ORIGINALITY/VALUE
The empirical findings of the study contribute to the existing literature by enhancing the understanding of IR adapters on the aspects of IR where it needs improvement in the Sri Lankan context. Further, the study addresses the methodological gap in the literature by undertaking a longitudinal analysis and using a weighted IR disclosure index.
Author note: Lakshan Attanayake on Unitec staff directory; and A.M.I. Lakshan on pape
The Influence of Chemical Risk Communication on Consumer Behavior in Purchasing Foods: A Psychological Study
No full textConsumers prefer a nutritious and delicious diet which is natural. Hence, they pay attention to research which focuses on chemical added food and risks involved in such consumption. Communication media plays a major role in deciding consumer willingness. Therefore, it is necessary to identify the influence of chemical risk communication on consumer behavior in purchasing foods. A qualitative and quantitative research method has been followed by the author to collect data, and questionnaires and in-depth interviews have been used to collect data. Data obtained are analyzed using SPSS for quantitative data whereas; the qualitative data is analyzed thematically. The data were collected from 100 Householders in the Badulla district. This study analyses the problem of how the messages on health risk influence consumer psychological behavior in purchasing food. The main objective of this research is to identify how the messages on health risk due to chemical additives in food influence the psychological behavior of consumers in purchasing food. The findings of the study reveal that consumers are not clear about the term, organic. The major factor that inhibited people from buying organic food was the high price. A majority of respondents had expressed interest in healthy and nutritionally rich food as well as environmental concerns and sustainability. Ultimately this study indicated that consumer awareness effectively advances the demand for organic products. It could be concluded that adoption of proper awareness programs would help in promoting the organic product consumption.DOI: http://doi.org/10.31357/fhss/vjhss.v05i01.0
