The forced commutation of thyristors connected in series

Widespread high voltage application of forced commutation was then, and still is, some years ahead. The thesis puts foward methods which have been devised for ensuring satisfactory thyristor turn-off in this context and suggests Some possible future trends in application. Individual tbyristor turn-off characteristics are first studied together with the equivalent diode characteristics. The difficulties of using thyristors in series for high voltage working are described and the limitations of the conventional resistive-capacitive voltage sharing network discussed in relation to forced commutation. Three forms of improved voltage sharing network are presented together with developments which use these in suitable combination. All have been tested with series-connected thyristors operating in a high voltage force-commutated chopper circuit. The advantages and disadvantages, and a design procedure, are given for each form of network. The two most appropriate voltage sharing arrangements are applied to the series thyristors and diodes in a high voltage, variable frequency d.c. chopper, and their overall influence on chopper performance is considered in detail. Owing to the possibility of cascade failure when many semiconductor devices are connected in series, extensive component damage can result from circuit malfunction or incorrect component connection. Great care has therefore. been necessary in the design, construction and checking of the high voltage experimental equipment. It is concluded that the voltage sharing methods devised make possible forced commutation of thyristors at high voltages and do not, in themselves, provide the practical constraints on system performance. The methods are compared on a technical and economic basis. Possible future applications are reviewed, with particular emphasis placed on the transformation of d.c. at high voltages using chopping techniques. Other problems which must be solved before such applications become realisable outside the laboratory are outlined and suggestions made for future work

Regular expressions as violin bowing patterns

String players spend a significant amount of practice time creating and learning bowings. These may be indicated in the music using up-bow and down-bow symbols, but those traditional notations do not capture the complex bowing patterns that are latent within the music. Regular expressions, a mathematical notation for a simple class of formal languages, can describe precisely the bowing patterns that commonly arise in string music. A software tool based on regular expressions enables performers to search for passages that can be handled with similar bowings, and to edit them consistently. A computer-based music editor incorporating bowing patterns has been implemented, using Lilypond to typeset the music. Our approach has been evaluated by using the editor to study ten movements from six violin sonatas by W. A. Mozart. Our experience shows that the editor is successful at finding passages and inserting bowings; that relatively complex patterns occur a number of times; and that the bowings can be inserted automatically and consistently

Training for recovery:impact of sprint interval training on recovery dynamics and aerobic performance in kickboxing athletes

PurposeRecovery within and between rounds is crucial to combat sports performance. We sought to determine whether sprint interval training (SIT) improves recovery dynamics and aerobic performance.MethodsEleven male kickboxing athletes (26 ± 5 years; body mass index 25 ± 3 kg/m2) were recruited. Participants were tested three times for VO2peak/time to exhaustion and critical power; baseline, 3 weeks control, 3 weeks of SIT (8 × 10 s lower body sprints followed by a maximum of 10 min recovery before completing 8 × 10 s upper body sprints). During SIT session 1 and 9 continuous gas analysis was performed.ResultsThere was a significant reduction in recovery time between lower and upper body sprints with training (session 1: 441 ± 150 s; session 9: 268 ± 10 s; P < 0.01; d = 2.77) and change in oxygen off-kinetics amplitude (session1: 3.0 ± 0.7 L/min, session 9: 3.6 ± 1.0 L/min; P < 0.05; d = − 1.77), VO2 end (session 1: 0.59 ± 0.19 L/min, session 9: 0.81 ± 0.21 L/min; P < 0.05, d = − 0.90), time constant (session 1: 81 ± 21 s; session 9: 60 ± 11 s; P < 0.05; d = 1.03). Following training there was a significant improvement in critical power (P < 0.05; η2p = 0.72) time to exhaustion (P < 0.05; η2p = 0.30) but not VO2peak (P > 0.05).ConclusionSIT improves recovery time associated and aerobic performance associated with improved oxygen off-kinetics. Therefore, training needs to focus on improving oxygen off-kinetics to enhance combat performance

Winter Wheat Test Results for South Dakota, 2002

The winter wheat variety recommendations for 2003 are listed in table 1. Comments: The dominant issue facing South Dakota agriculture in the 2002 crop season was the lack of moisture in the fall of 2001 and the winter and spring of 2002. Limited moisture led to a large deficit in subsoil moisture in many cropping regions of the state. This in turn resulted in many acres of winter wheat and other small grains being harvested for hay. The average winter wheat yield in the South Dakota Crop Performance Testing (CPT) Program was 39 bu/A for year 2002 and 48 bu/A for the 3-year period (2000-2002). Compared to 2001, this was a drop of 7 bu/A in both the 1- and 3-year CPT yield averages

Morris Jesup Spur and Rise north of Greenland – exploring present seabed features, the history of sediment deposition, volcanism and tectonic deformation at a Late Cretaceous/early Cenozoic triple junction in the Arctic Ocean

The narrow Morris Jesup Spur and an adjacent broader western rise extend 220 km into the Eurasia Basin from the shelf edge north of Greenland. We have used a hovercraft platform drifting with the sea to collect the first seismic reflection transect across an area postulated to be a former triple junction between the Greenland, Eurasian and North American plates. The narrow, flat-topped Morris Jesup Spur is a succession of west-dipping (? 3°) sediments overlying a basal volcanic unit truncated at the top by an unconformity. The Morris Jesup Rise is formed by intensely deformed sediments and volcanic rocks with a deformation front to the northwest. The basin between theMorris Jesup Rise and the Lomonosov Ridge has a sediment thickness of >3 km with a large submarine channel/levee complex in the upper part and repeated volcanic units present in the deeper stratigraphy below 1.0 sec. sub-bottom. Volcanism on the Morris Jesup Spur is considered to be Late Cretaceous–early Cenozoic in age, and continued into the late Miocene on the Morris Jesup Rise and possibly into early Oligocene in the SW Amundsen Basin. The western slope of the Morris Jesup Spur represented the continental slope north of Svalbard in the Late Cretaceous. A block which included the Morris Jesup Spur and Yermak Plateau rifted off during the initial opening of the Eurasia Basin and moved as part of Greenland until about Chron 22. The architecture of the Morris Jesup Rise is a result of plate convergence possibly including a former extensional plate boundary segment which connected the Gakkel spreading centre to the Hornsund Fault between Chron 22 and Chron 13. The Morris Jesup Rise may be a northern tectonic outlier of a more extensive Eurekan tectonic domain hidden below the Lincoln Sea continental shelf. The Morris Jesup Spur remained subaerial until latest Miocene and submergence of the spur most likely intensified the East Greenland Current.publishedVersio

Sediment deformation atop the Lomonosov Ridge, central Arctic Ocean: Evidence for gas-charged sediment mobilization

We have used a hovercraft platform drifting with the sea ice to acquire the first digitally recorded seismic reflection data transects across the Canada/Greenland (89°N-85°N) section of the Lomonosov Ridge, central Arctic Ocean. The flat-lying, laterally uniform Cenozoic sediment package on top of the ridge at 87°N, 60° W shows at least four sites with local seismic amplitude anomalies. The common feature is a column (<600 m wide) of partly discontinuous or chaotic bright reflection events at the center of a <1.5 km wide dome (amplitude <25 m) terminating at the seabed in a 8–12 m deep depression. The amplitude anomalies are interpreted as gas-charged fluid escape pipes marked by a pockmark at the seabed. Gas and fluids introduced from below have mobilized the overlying high porosity, low density Eocene bio-siliceous ooze causing the doming. The gas and fluids appear to originate from the top of rotated fault blocks and sub-basalt sediments of Mesozoic or older age deposited when the Lomonosov Ridge was part of the pre-Late Cretaceous continental margin north of Franz Josef Land.publishedVersio

Variation in Seedling Density, Herbivory and Disease Incidence among Seedling Stages and Mother Prunus Africana Trees Growing on Varying Microsites in a Transitional Rainforest in Kenya

The study was carried out at Kakamega Forest   which is generally considered to be the easternmost limit in today’s climate of the lowland Guineo Congolean rainforest of central Africa. Faunally and florally, Kakamega is dominated by central African lowland species, but due to its elevation (1,400-2,300 meters (4,000-7,000 ft.) and proximity to the formerly contiguous Nandi Forests it also contains well-represented highland elements and is thus unique, thus, it is a significant island of biodiversity that has developed along its own unique evolutionary course for thousands of years and which shows a high level of endemism.  The objective of the study was to determine how herbivory and disease incidence vary among seedling stages and trees growing in varying micro sites. The study began at the end of the fruiting season and start of germination of seeds. A natural stand was identified where Prunus africana was abundant because the species density. The results indicated that seedling abundance, disease incidence and herbivory varied among trees and microsites. Keywords: Herbivory, Disease incidence, Regeneration, Prunu

The Crystal Structure of the Extracellular 11-heme Cytochrome UndA Reveals a Conserved 10-heme Motif and Defined Binding Site for Soluble Iron Chelates

Members of the genus Shewanella translocate deca- or undeca-heme cytochromes to the external cell surface thus enabling respiration using extracellular minerals and polynuclear Fe(III) chelates. The high resolution structure of the first undeca-heme outer membrane cytochrome, UndA, reveals a crossed heme chain with four potential electron ingress/egress sites arranged within four domains. Sequence and structural alignment of UndA and the deca-heme MtrF reveals the extra heme of UndA is inserted between MtrF hemes 6 and 7. The remaining UndA hemes can be superposed over the heme chain of the decaheme MtrF, suggesting that a ten heme core is conserved between outer membrane cytochromes. The UndA structure has also been crystallographically resolved in complex with substrates, an Fe(III)-nitrilotriacetate dimer or an Fe(III)-citrate trimer. The structural resolution of these UndA-Fe(III)-chelate complexes provides a rationale for previous kinetic measurements on UndA and other outer membrane cytochromes

Rural-Urban Disparities in Emergency Department Intimate Partner Violence Resources

Objective: Little is known about availability of resources for managing intimate partner violence (IPV) at rural hospitals. We assessed differences in availability of resources for IPV screening and management between rural and urban emergency departments (EDs) in Oregon. Methods: We conducted a standardized telephone interview of Oregon ED directors and nurse managers on six IPV-related resources: official screening policies, standardized screening tools, public displays regarding IPV, on-site advocacy, intervention checklists and regular clinician education. We used chi-square analysis to test differences in reported resource availability between urban and rural EDs. Results: Of 57 Oregon EDs, 55 (96%) completed the survey. A smaller proportion of rural EDs, compared to urban EDs, reported official screening policies (74% vs. 100%, p=0.01), standardized screening instruments (21% vs. 55%, p=0.01), clinician education (38% vs. 70%, p=0.02) or on-site violence advocacy (44% vs. 95%, p<0.001). Twenty-seven percent of rural EDs had none or one of the studied resources, 50% had two or three, and 24% had four or more (vs. 0%, 35%, and 65% in urban EDs, p=0.003). Small, remote rural hospitals had fewer resources than larger, less remote rural hospitals or urban hospitals. Conclusion: Rural EDs have fewer resources for addressing IPV. Further work is needed to identify specific barriers to obtaining resources for IPV management that can be used in all hospital settings. [West J Emerg Med. 2011;12(2):178-183.