Pulse multiplication in autotransformer based AC-DC converters using a zigzag connection

This paper deals with pulse multiplication in zigzag connected autotransformer based 12-pulse AC-DC converters feeding vector controlled induction motor drives (VCIMD) for improving the power quality at the point of common coupling (PCC) without using a Zero-Sequence-Blocking-Transformer (ZSBT). The proposed 24-pulse AC-DC converter is based on the principle of DC ripple re-injection technique for pulse multiplication and harmonic mitigation. The design of the autotransformer is carried out for the proposed AC-DC converter and the effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed AC-DC converter. Test results from a laboratory developed prototype, along with simulated results, are presented to validate the design and model of the proposed 24-pulse AC-DC converter

Remote sensing object-oriented approaches coupled with ecological informatics to map invasive plant species

nvasive alien plants are considered one of the major threats to biodiversity conservation worldwide. Hence, understanding their distribution and abundance is important in order to assess the impact on native ecosystems. It is particularly important to be able to track the spread of invasive species across landscapes; a task best achieved using remotely sensed imagery. The availability of high resolution data, combined with efficient classification methods, can potentially improve early detection of invasive alien species thereby enhancing their management. This study aims to classify woody species with a focus on Melia azedarach (Meliaceae) trees in a moderately invaded coastal belt valley on the east coast of South Africa using WorldView-2 (WV-2) satellite imagery, and to compare the commonly used pixel-based classification with object-oriented approaches. The results show that object-oriented approaches are more suitable for classifying woody species, as well as other land cover classes when using high-resolution WV-2 imagery. The overall accuracy was 90% by object- oriented classification, while the pixel-based classification gave an overall accuracy of 78%. For Melia, a producer accuracy of 92% and user accuracy of 91% was obtained by object-oriented classification and a producer accuracy of 85% and user accuracy of 83% was obtained by pixel-based classification. Hence the combined use of new generation sensor imagery and the employment of object-oriented image classification techniques provided more accurate information on Melia invasion in the study area. This is an encouraging result given the high degree of intermingling of Melia with other plants at the study site. In particular, the vegetation maps produced from this study would aid in gathering accurate knowledge about the distribution and spreading status of Melia, a major invasivespecies over large areas of South Africa and elsewhere in the world

Effects of light, temperature, salinity, and maternal habitat on seed germination of aeluropus lagopoides (Poaceae): An economically important halophyte of arid Arabian deserts

In this study, salt tolerance during germination of Aeluropus lagopoides (L.) Trin. was tested using fresh seeds collected from three different maternal habitats under three thermoperiods and two light regimes. Additionally, we tested the ability of non-germinated seeds that had been exposed to different concentrations of NaCl to recover their germination in distilled water. The results showed a significant effect of seed source, temperature, and salinity, and some of their two-and three-way interactions on final germination and recovery percentage. The seeds from non-saline provenances had the highest percentages for germination (ca. 79%) under the 35/25 °C temperature regime, whereas the lowest percentages for germination (ca. 21%) was recorded for seeds from saline conditions under the 25/15 °C treatment. Additionally, percent germination was significantly lower for the seeds incubated in the saline solutions (100, 200, 400, and 600 mmol/L NaCl) and germinated under colder conditions (15/25 °C), compared with the seeds incubated in non-saline solutions (control group, 0 mmol/L NaCl) and germinated under warmer conditions (35/25 °C). The highest recovery percentage was recorded for seeds of the hyper-saline habitat incubated at 35/25 °C. Thus, seeds maintained their viability despite experiencing a range of saline conditions and were able to germinate upon the arrival of suitable conditions, which can be an adaptation to its saline arid desert habitat.Fil: Bhatt, Arvind. Botanical Garden; China. Kuwait Institute For Scientific Research; KuwaitFil: Gairola, Sanjay. Sharjah Research Academy; Emiratos Arabes UnidosFil: Carón, María Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Santo, Andrea. Università Degli Studi Di Cagliari.; ItaliaFil: Murru, Valentina. Università Degli Studi Di Cagliari.; ItaliaFil: El-Keblawy, Ali. University Of Sharjah; Emiratos Arabes UnidosFil: Mahmoud, Tamer. University Of Sharjah; Emiratos Arabes Unido

The Promise of Molecular and Genomic Techniques for Biodiversity Research and DNA Barcoding of the Arabian Peninsula Flora

The Arabian Peninsula is known to have a comprehensive and rich endowment of unique and genetically diverse plant genetic resources. Analysis and conservation of biological diversity is a crucial issue to the whole Arabian Peninsula. The rapid and accurate delimitation and identification of a species is crucial to genetic diversity analysis and the first critical step in the assessment of distribution, population abundance and threats related to a particular target species. During the last two decades, classical strategies of evaluating genetic variability, such as morphology and physiology, have been greatly complemented by phylogenetic, taxonomic, genetic diversity and breeding research molecular studies. At present, initiatives are taking place around the world to generate DNA barcode libraries for vascular plant flora and to make these data available in order to better understand, conserve and utilize biodiversity. The number of herbarium collection-based plant evolutionary genetics and genomics studies being conducted has been increasing worldwide. The herbaria provide a rich resource of already preserved and identified material, and these as well as freshly collected samples from the wild can be used for creating a reference DNA barcode library for the vascular plant flora of a region. This review discusses the main molecular and genomic techniques used in plant identification and biodiversity analysis. Hence, we highlight studies emphasizing various molecular techniques undertaken during the last 10 years to study the plant biodiversity of the Arabian Peninsula. Special emphasis on the role of DNA barcoding as a powerful tool for plant biodiversity analysis is provided, along with the crucial role of herbaria in creating a DNA barcode library

An autotransformer-based 36-pulse controlled AC-DC converter

This paper proposes a non-isolated 36-pulse controlled AC–DC converter for medium power rating drives. It involves pulse multiplication in a 12-pulse AC–DC converter. The approach employs a polygon autotransformer arrangement, which results in a near equal leakage reactance in series with each thyristor bridge. The volt–ampere rating of the autotransformer is observed to be small and the converter meets IEEE-519 standard power–quality requirements over a wide range of firing angle

A 40-pulse AC-DC converter fed vector-controlled induction motor drive

In this paper, a novel autotransformer for a 40-pulse ac-dc converter configuration is designed, modeled, simulated, and implemented to feed vector-controlled induction motor drive (VCIMD). The proposed converter consists of two paralleled ten-pulse ac-dc converters along with pulse doubling circuit at dc bus. Each ten-pulse ac-dc converter involves five-phase diode bridge rectifiers. It improves power quality at ac mains, and it meets IEEE-519 standard requirements at varying loads. A set of power quality indexes on input ac mains and dc bus for a VCIMD fed from 20-pulse and 6-pulse converters is also given to compare their performance. It is observed that input current total harmonic distortion (THD) of much less than 5% is possible with the proposed topology at varying loads

A novel harmonic mitigation converter for variable frequency drives

In this paper, a novel autotransformer for 56-pulse AC-DC converter configuration is designed, modeled and simulated to feed vector controlled induction motor drive (VCIMD). The proposed autotransformer configuration consists of two paralleled 14-pulse AC-DC converters involving seven-phase shifted uncontrolled diode bridges with pulse doubling circuit. It improves power quality at AC mains and it meets IEEE-519 standard requirements at varying loads

A 36-pulse AC-DC converter for line current harmonic reduction

In this paper, a novel transformer for 36-pulse AC-DC conversion is designed, modeled and developed to feed isolated varying DC loads. The proposed transformer is normally used for large current rating rectifiers such as electric-aircraft power supply, electrowinning, electrochemical processes, induction heating, drives, plasma torches, etc., where isolation is required mainly for stepping down the supply voltage. It consists of two paralleled 18-pulse AC-DC converters involving nine-phase shifted diode bridges. It improves power quality at AC mains and it meets IEEE-519 standard requirements at varying loads

A fork connected transformer based 24-pulse AC-DC converter

In this paper, a 24-pulse AC-DC converter is designed, modeled and simulated to feed isolated industrial loads. The proposed configuration consists of an isolation transformer based fork connection. It improves power quality at AC mains and it meets IEEE-519 standard requirements at varying loads. A set of power quality indices on input AC mains and on DC bus for load fed from 6-pulse and 12-pulse AC-DC converters is also given to compare their performance. It is observed that input current total harmonic distortion (THD) of less than 5% is possible with the proposed topology of AC-DC converter at varying loads