324,132 research outputs found
Multi-Carrier and Spread Spectrum Systems
No full textTable of Contents Multi-Carrier and Spread Spectrum Systems describes and analyses the basic concepts of the combination of multi-carrier transmission with spread spectrum (MC-SS). The various architectures and the different detection strategies are examined in some depth. Techniques for capacity and flexibility enhancement of multi-carrier systems such as diversity techniques and space-time/frequency coding (STC, STFC) are also analysed. Since 1993 different multiple access concepts based on the MC-SS combination for mobile and wireless indoor communications called OFDM/CDMA or MC-CDMA and MC-DS-CDMA, have been proposed. The main differences between these schemes are in the spreading, frequency mapping, and detection strategies. Meanwhile, other alternative hybrid schemes such as OFDM/OFDMA, MC-TDMA, etc. have been deeply studied that benefit from the advantages of multi-carrier transmission. This book: · Covers multi-carrier and spread spectrum and all derivatives of spread spectrum and OFDM systems. · Describes not only HIPERLAN but also wireless multi-user systems dealing with OFDM or spread spectrum techniques: 2G IS-95, 3G UMTS, and 4th Generation mobile communications. · Provides significant analysis on multi-carrier transmission, from theory to practical implementations and is therefore invaluable for systems designers. · Examines the essentials of all wireless standards based on multi-carrier/spread spectrum technique. Written in a highly accessible manner this book will provide a unique reference on the topic of multi-carrier spread spectrum, assisting 4G engineers for their implementation
Five crisp and fuzzy models for supply chain of an automotive manufacturing system
No full textSupply Chain Management (SCM) is a new approach to production planning. It integrates the components
of supply chain in a holistic manner. Modeling this large-scale system, which contains all effective
enterprises in production such as raw material suppliers, part manufacturers, assembly plants, distribution
organizations, and the like, is challenging for managers, engineers and researchers. This paper concentrates
on supply chain system modeling with fuzzy linear programming, and fuzzy expert system for an automobile
plant. First, a linear programming model is developed in such a way that while the input data is fuzzy, the
constraints are crisp. In the second linear model, the coefficients of the model are crisp while the constraints
are fuzzy. In the third model, we aggregate the first and the second models into one fuzzy linear programming
where all constraints and coefficients are fuzzy. In each case, we compare the results with those of classical
SC models. Finally, a rule based fuzzy expert system for SC is developed and the results are compared with
those of the classical and fuzzy LP models. The results of the fuzzy expert system show its superiority over
the former crisp and fuzzy linear programming models
Response to 'The Use of Meta-Analysis to Compare and Select Offender Risk Instruments'
No full textA complex meta-analysis often addresses more than one principal question, which may be published in two or three separate papers. The Singh 2011 review compares risk assessment instruments and asks the question whether there are differences in their predictive accuracy using multiple performance statistics (Singh, Grann, and Fazel, 2011). It relies on how the research literature has used these instruments, which likely reflects the intended population and practical considerations. However, there were two other key questions that we tried to address when we reviewed risk assessment tools, which required separate publications. In a 2012 publication, using mostly the same data but with updated information, we stratified the performance of these instruments according to whether they focused on violent, sexual, and general criminal offending separately (Fazel, Singh, Doll, and Grann, 2012). So a key criticism of the current paper – that stratification by type of offender was not done - has been addressed to a large extent in the 2012 review. Furthermore, the current paper conflates the aims of the 2011 and 2012 reviews. The 2011 review was not primarily intended to examine the overall accuracy of risk assessment tools. Rather that was the main question of the 2012 review according to whether the particular instrument was focused on the assessment of violent, sexual, and criminal recidivism. </p
A comprehensive study on performance of YD transformer in ac electrified railway systems
No full textThe selection of appropriate traction transformers decreases power quality problems and critical impacts of Electrified Railway System (ERS) on the power grid. Using the Yd transformer in ERSs is not common and popular like the power systems. In this paper, the performance of Yd transformer in a Traction Power Substation (TPS) is investigated and its superiority against single-phase, V/V and Scott transformer is ascertained. The evaluation and analysis is based on electrical performance, power quality parameters and economics issues. The analysis is studied under unbalanced and balanced conditions considering Railway Power Quality Compensator (RPQC) as the auxiliary compensator is TPS. The simulation results validate correctness of theoretical analysis
Regenerative Braking Energy and Power Quality Analysis in 2x2 kV High-Speed Railway Lines Operating with 4QC Locomotives
No full textThe AC 2× 25 kV feeding system is considered as a wide applicated existing power supply system for high speed and high capacity railway lines all around the world. Multiconductor overhead catenary system (OCS), high-power four-quadrant converter (4QC) based trains and a large number of elements have made the power flow and power quality (PQ) analysis complex in such a system. In this paper, an accurate simulation of 4QCs along with traction motors and eight-conductor based OCS have been implemented for the 114 km double-track railway line with realistic information. The PQ analysis together with regenerative braking energy (RBE) assessment are carried out based on extracted voltage and currents waveforms. The proposed methodology is executed in MATLAB software taking into account train movement equations, speed profile and various modes of operation
Power quality indicators in electric railway systems: A comprehensive classification
No full textElectric railway systems (ERSs) have been challenged with power quality (PQ) problems since they were operated. Over the years, numerous researches have been presented investigating various aspects of PQs related to the different developmental structures of railway power supply systems (RPSS). However, this diversity and progress have led to face with a significant variety of two-way interactive interfaces as well as reliability and PQ issues. The essential purpose of this paper is to classify and explain these distortions and PQ indices in the field of operating RPSS. It can provide a perfect perspective on the status of PQ issues of ERS to researchers and engineers
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