MAXIMUM POWER TRACKING OF A GRID-CONNECTED WIND-DRIVEN BRUSHLESS DOUBLY-FED RELUCTANCE GENERATOR USING SCALAR CONTROL

This paper presents a scalar volt per hertz (v/f) control technique for maximum power tracking of a grid-connected wind-driven Brushless Doubly-Fed Reluctance Generator (BDFRG). The proposed generator has two stator windings namely; power winding, directly connected to the grid, and control winding, connected to the grid through a bi-directional converter. The presented control technique is based on the abc-axis and dq-axis dynamic model of BDFRG. A detailed abc-axis and dq-axis dynamic model, by which the dynamic behaviour of the BDFRG can be successfully predicted under different operating conditions, is presented. In addition, a soft starting method is suggested to avoid the over-current of the bi-directional converter. The presented simulation results ensure the effectiveness of the proposed control strategy for maximum wind-power extraction under wind-speed variations

Three-to-five-phase matrix converter using carrier-based PWM technique

<p><strong>Abstract</strong> - This paper proposes a simple Carrier-Based PWM (CBPWM) technique to control the three- to five-phase Direct Matrix Converter (3×5 DMC). The proposed technique uses the indirect modulation approach to control the 3×5 DMC such as a three-phase bidirectional rectifier followed by five-phase voltage source inverter (VSI). Based on this approach, it is possible to synthesize the desired five-phase output voltages with sinusoidal three-phase input currents and unity input power factor. A CBPWM method is suggested for each stage independently including both linear and overmodulation operating modes. By the proposed technique, in both operating modes, the maximum possible overall Voltage Transfer Ratio (VTR) are achieved. Moreover, this technique allows the input power factor to be controlled by controlling the input current displacement angle. The feasibility of the proposed technique has been verified by a series of simulation and experimental results based on Matlab/Simulink and dSPACE-DS1104 platform. The results show that, a sinusoidal output and input waveforms can be achieved with a maximum possible VTR in the linear region. However, in the overmodulation region, a maximum possible VTR is achieved at the cost of some distortion of output and input waveforms. Therefore, this technique can be used for the application where a higher VTR is essential.</p

SPACE VECTOR PWM TECHNIQUE FOR THREE- TO SEVEN-PHASE AC-TO-AC POWER CONVERTERS: ANALYSIS AND EXPERIMENTAL VERIFICATIONS

This paper presents Pulse Width Modulation (PWM) control technique for three to seven-phase ac-to-ac power converters. These proposed PWM techniques are based on Indirect Space Vector Modulation (ISVM), which model the converter as two independent stages perform rectification and inversion stages. Two schemes of ISVM are proposed. The first scheme maximizes the voltage transfer ratio (VTR) of the converter but it produces unwanted low order harmonics. The second scheme generates sinusoidal output voltage waveforms; the cost is a reduction in the VTR of this configuration in linear mode. The viability of the proposed technique is proved using experimental results

The Sloan Bright Arcs Survey : Six Strongly Lensed Galaxies at z=0.4-1.4

We present new results of our program to systematically search for strongly lensed galaxies in the Sloan Digital Sky Survey (SDSS) imaging data. In this study six strong lens systems are presented which we have confirmed with follow-up spectroscopy and imaging using the 3.5m telescope at the Apache Point Observatory. Preliminary mass models indicate that the lenses are group-scale systems with velocity dispersions ranging from 466-878 km s^{-1} at z=0.17-0.45 which are strongly lensing source galaxies at z=0.4-1.4. Galaxy groups are a relatively new mass scale just beginning to be probed with strong lensing. Our sample of lenses roughly doubles the confirmed number of group-scale lenses in the SDSS and complements ongoing strong lens searches in other imaging surveys such as the CFHTLS (Cabanac et al 2007). As our arcs were discovered in the SDSS imaging data they are all bright ($r\lesssim22$), making them ideally suited for detailed follow-up studies.Comment: 13 pages, 3 figures, submitted to ApJL, the Sloan Bright Arcs page is located here: http://home.fnal.gov/~kubo/brightarcs.htm

VisIVOWeb: A WWW Environment for Large-Scale Astrophysical Visualization

This article presents a newly developed Web portal called VisIVOWeb that aims to provide the astrophysical community with powerful visualization tools for large-scale data sets in the context of Web 2.0. VisIVOWeb can effectively handle modern numerical simulations and real-world observations. Our open-source software is based on established visualization toolkits offering high-quality rendering algorithms. The underlying data management is discussed with the supported visualization interfaces and movie-making functionality. We introduce VisIVOWeb Network, a robust network of customized Web portals for visual discovery, and VisIVOWeb Connect, a lightweight and efficient solution for seamlessly connecting to existing astrophysical archives. A significant effort has been devoted for ensuring interoperability with existing tools by adhering to IVOA standards. We conclude with a summary of our work and a discussion on future developments

Foreign body ingestion in children: unusual presentations and timely intervention

Background/purpose: Foreign body (FB) ingestion in children is very common. Children can ingest a wide variety of FBs. Most of the ingested FBs pass spontaneously through the gastrointestinal tract. Other FBs, especially uncommonly ingested objects, can present with complications and need intervention to be extracted. The aim of this study was to highlight the importance of timely intervention to extract these FBs.Patients and methods: Between November 2012 and October 2017, patients who presented to our department with variously ingested FBs were retrospectively reviewed to detect those who needed intervention (surgical or endoscopic) to extract these FBs.Results: During the specified time period, 480 patients with FB ingestion presented to our department. Out of these children, 12 patients ingested uncommon FBs or presented with symptoms of complications of impaction and needed intervention to extract these FBs. Three patients ingested multiple magnets. Three patients ingested pins which were impacted in and penetrated the duodenum. One patient ingested a screw which was impacted in the appendix. One patient ingested a sticky rubber toy which was impacted in the pylorus. One patient ingested hair (bezoar), which was also impacted in the pylorus. One patient ingested a disk battery which was impacted in and penetrated the esophagus, and all were surgically extracted. One patient had a slipped stent of repaired choanal atresia which was impacted in the gastroesophageal junction and one patient with repaired tracheoesophageal fistula ingested a stone which was impacted at the site of esophageal anastomosis, and both were endoscopically retrieved.Conclusion: Children who ingested uncommon FBs or presented late with symptoms of complications of impaction needed intervention (surgically or endoscopically) to extract these FBs.Keywords: foreign bodies, foreign body extraction, ingestion, magnets ingestion, pin ingestio

The Sloan Bright Arcs Survey: Four Strongly Lensed Galaxies with Redshift >2

We report the discovery of four very bright, strongly-lensed galaxies found via systematic searches for arcs in Sloan Digital Sky Survey Data Release 5 and 6. These were followed-up with spectroscopy and imaging data from the Astrophysical Research Consortium 3.5m telescope at Apache Point Observatory and found to have redshift $z>2.0$. With isophotal magnitudes $r = 19.2 - 20.4$ and 3\arcsec-diameter magnitudes $r = 20.0 - 20.6$, these systems are some of the brightest and highest surface brightness lensed galaxies known in this redshift range. In addition to the magnitudes and redshifts, we present estimates of the Einstein radii, which range from 5.0 \arcsec to 12.7 \arcsec, and use those to derive the enclosed masses of the lensing galaxies

Large Scale Structure in the SDSS Galaxy Survey

The Large Scale Structure (LSS) in the galaxy distribution is investigated using the Sloan Digital Sky Survey Early Data Release (SDSS EDR). Using the Minimal Spanning Tree technique we have extracted sets of filaments, of wall-like structures, of galaxy groups, and of rich clusters from this unique sample. The physical properties of these structures were then measured and compared with the expectations from Zel'dovich' theory. The measured characteristics of galaxy walls were found to be consistent with those for a spatially flat $\Lambda$CDM cosmological model with $\Omega_m\approx$ 0.3 and $\Omega_\Lambda \approx$ 0.7, and for Gaussian initial perturbations with a Harrison -- Zel'dovich power spectrum. Furthermore, we found that the mass functions of groups and of unrelaxed structure elements generally fit well with the expectations from Zel'dovich' theory, although there was some discrepancy for lower mass groups which may be due to incompleteness in the selected sample of groups. We also note that both groups and rich clusters tend to prefer the environments of walls, which tend to be of higher density, rather than the environments of filaments, which tend to be of lower density. Finally, we note evidence of systematic differences in the properties of the LSS between the Northern Galactic Cap stripe and the Southern Galactic Cap stripe -- in particular, in the physical properties of the walls, their spatial distribution, and the relative numbers of clusters embedded in walls. Because the mean separation of walls is $\approx$ 60 -- 70$h^{-1}$ Mpc, each stripe only intersects a few tens of walls. Thus, small number statistics and cosmic variance are the likely drivers of these systematic differences.Comment: 13 pages, 11 figures, MNRAS submitte

Penggunaan jenis-jenis penilaian oleh pensyarah dalam pengajaran dan pembelajaran di Jabatan Kejuruteraan Awam, Politeknik Ungku Omar

Penilaian ialah satu sistem atau proses yang meliputi aktiviti-aktiviti mengumpul maklumat tentang st'artegi dan aktiviti pengajaran dan pembelajaran, untuk membuat analisis dan keputusan denagn tujuan mengambil tindakan yang sewajamya seperti merancang aktiviti pengajaran dan pembelajaran selanjutnya dengan cara yang lebih berkesan. Penilaian terdiri daripada empat iaitu pra penempatan, formatif, diognastik dan sumatif. Keempat-empat jenis penilaian ini mempunyai kelebihan dan kelemahan yang tersendiri. Melalui dapatan kajian menunjukkan bahawa pensyarah lelaki lebih banyak menggunakan jenis-jenis penilaian dalam bilik kuliah iaitu min 3.37 berbanding dengan pensyarah perempuan iaitu min 3.28. Selain daripada itu, dapatan kajian juga menunjukkan sebanyak 47 % responden mempunyai pengetahuan tentang penilaian pendidikan jenis objektif, 6 4 % responden mengaplikasikan jenis penilaian kaedah lisan dalam aktiviti pengajaran dan 84 % responden bersetuju bahawa penilaian pendidikan telah dapat meningkatkan mutu diri pensyarah dalam aktiviti pengajaran. Manakala 2.7 % responden tidak bersetuju bahawa pelajar diberi masa yang mencukupi sebelum sesuatu jenis penilaian dilakukan. Sehubungan dengan itu pengkaji mencadangkan supaya pensyarah-pensyarah didedahkan dengan penggunaan jenis-jenis penilaian untuk meningkatkan keupayaan dan kecekapan dalam usaha membina jenis-jenis ujian dengan lebih bermutu. Pensyarah juga digalakkan untuk melakukan jenis-jenis penilaian dalam bilik kuliah. Selain daripada itu, pensyarah juga perlu memastikan pelajar sentiasa bersedia untuk dibuat penilaian. Seterusnya pensyarah perlu mempelbagaikan jenis-jenis penilaian pendidikan dalam aktiviti pengajaran bagi mengesan peringkat penguasaan dan kemajuan pelajar dalam semua bidang yang berkaitan dengan pendidika