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Search Results: 1 - 10 of 53217 matches for " David Wessel "
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Seamount Discovery Tool Aids Navigation to Uncharted Seafloor Features
David T. Sandwell,Paul Wessel
Oceanography , 2010,
Abstract: Wessel et al. (2010) highlight the need for a systematic mapping of seamounts in ocean basins. They estimate that 100,000 or 90% of the seamounts greater than 1-km tall are unobserved by either ship soundings or satellite gravity. There are two reasons why most of these relatively large, predicted seamounts remain uncharted. First, satellite-derived gravity is only able to reliably measure seamounts that are more than 2-km tall, although smaller seamounts can be detected (Wessel, 2001). Second, the freely available ship sounding data collected during the past 50 years only covers 10% of the seafloor at the 1-minute resolution needed to detect these 1-km and taller seamounts (Becker et al., 2009). Based on current trends in seafloor mapping, the rate of seamount discoveries is not likely to change significantly because modern research surveys are focused on particular areas of high scientific interest such as mid-ocean ridges, continental margins, and subduction zones. This exploration strategy has resulted in gaps in remote areas of up to 600 km by 300 km. As Figure 1 shows, more than 50% of the seafloor lies more than 9.5 km from the nearest ship sounding. This sparse coverage, combined with a relatively random spatial distribution of seamounts, results in the situation today where there are even 3-km and 4-km tall seamounts that have not been surveyed by ships.
The Global Seamount Census
Paul Wessel,David T. Sandwell,Seung-Sep Kim
Oceanography , 2010,
Abstract: Seamounts are active or extinct undersea volcanoes with heights exceeding ~ 100 m. They represent a small but significant fraction of the volcanic extrusive budget for oceanic seafloor and their distribution gives information about spatial and temporal variations in intraplate volcanic activity. In addition, they sustain important ecological communities, determine habitats for fish, and act as obstacles to currents, thus enhancing tidal energy dissipation and ocean mixing. Mapping the complete global distribution will help constrain models of seamount formation as well as aid in understanding marine habitats and deep ocean circulation. Two approaches have been used to map the global seamount distribution. Depth soundings from single- and multibeam echo sounders can provide the most detailed maps with up to 200-m horizontal resolution. However, soundings from the > 5000 publicly available cruises sample only a small fraction of the ocean floor. Satellite altimetry can detect seamounts taller than ~ 1.5 km and studies using altimetry have produced seamount catalogues holding almost 13,000 seamounts. Based on the size-frequency relationship for larger seamounts, we predict over 100,000 seamounts > 1 km in height remain uncharted, and speculatively 25 million > 100 m in height. Future altimetry missions could improve on resolution and significantly decrease noise levels, allowing for an even larger number of intermediate (1–1.5 km height) seamounts to be detected. Recent retracking of the radar altimeter waveforms to improve the accuracy of the gravity field has resulted in a twofold increase in resolution. Thus, improved analyses of existing altimetry with better calibration from multibeam bathymetry could also increase census estimates.
Control Improvisation
Daniel J. Fremont,Alexandre Donzé,Sanjit A. Seshia,David Wessel
Computer Science , 2014,
Abstract: We formalize and analyze a new automata-theoretic problem termed control improvisation. Given an automaton, the problem is to produce an improviser, a probabilistic algorithm that randomly generates words in its language, subject to two additional constraints: the satisfaction of an admissibility predicate, and the exhibition of a specified amount of randomness. Control improvisation has multiple applications, including, for example, generating musical improvisations that satisfy rhythmic and melodic constraints, where admissibility is determined by some bounded divergence from a reference melody. We analyze the complexity of the control improvisation problem, giving cases where it is efficiently solvable and cases where it is #P-hard or undecidable. We also show how symbolic techniques based on Boolean satisfiability (SAT) solvers can be used to approximately solve some of the intractable cases.
O. Wessel,O. Wessel
South African Journal of Industrial Engineering , 2012,
Abstract: ENGLISH ABSTRACT: The final car assembly lines at Volkswagen’s production sites in Germany and South Africa are analysed to determine the best automation level based on cost, productivity, quality, and flexibility for a plant location. The methodology used is proposed by the Fraunhofer Institute. The final assembly processes are analysed and classified according to the automation level. The operations are evaluated at every level of automation based on information from existing factories. If the best levels of automation for all the parameters correspond, the optimal level of automation for a plant is reached. Otherwise, improvements and/or additional considerations are required to optimise the automation level. The result of the analysis indicates that the highest automation level is not necessarily the best in terms of cost and quality, and some de-automation is required. The analysis also shows that a low automation level can result in poor product quality and low productivity. The best automation strategy should be based on the analysis of all the aspects of the process in the local context. AFRIKAANSE OPSOMMING: Die finale monteerlyne by Volkswagen se aanlegte in Duitsland en Suid-Afrika is ontleed om die beste outomatisasievlak te bepaal gebaseer op koste, produktiwiteit, gehalte en aanpasbaarheid gegee die ligging. Die metodologie wat gevolg is, word voorgestel deur die Fraunhofer Instituut. Die finale monteerprosesse is ontleed volgens outomatisasievlak. Die aktiwiteite is ontleed teen elke vlak van outomatisasie gebaseer op inligting van bestaande vervaardigingsaanlegte. Indien die beste outomatisasievlakke vir alle parameters ooreenstem, dan is die optimale vlak van outomatisasie bereik. Indien nie, is verbeterings en/of addisionele oorwegings nodig om die outomatisasievlak te optimiseer. Die resultaat van die ontleding toon dat die grootste mate van outomatisasie nie noodwendig die beste is in terme van koste en gehalte nie, en dat ‘n mate van ‘de-outomatisasie’ benodig word. Die ontleding toon verder dat lae vlakke van outomatisasie kan lei tot swak produkgehalte en lae produktiwiteit. Die beste outomatisasiestrategie moet dus gebaseer word op ‘n ontleding van al die prosesaspekte in ‘n plaaslike konteks.
God, Master of Arts
Stoker, Wessel
Ars Disputandi : the Online Journal for Philosophy of Religion , 2007,
Abstract: What does theology have to do with art in this (post)modern period? To make clear why art and religion can be related in a positive way, the question of why art is of value will be posed (1). Subsequently some examples will be critically discussed of how art and religion have been related in theological aesthetics (2). Finally, in dialogue with the positions discussed, I will develop my own approach to theological aesthetics (3).
Ekonomiese aspekte van pypleidingvervoer: 'n Suid-Afrikaanse perspektief
Wessel Pienaar
Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie , 2009, DOI: 10.4102/satnt.v28i2.53
Abstract: Daar bestaan ’n sterk moontlikheid dat daar binne die volgende dekade drie pypleidings vir die kommersi le vervoer van brandstofprodukte van Suider-Afrikaanse hawens na Gautengprovinsie aangelê gaan word. Omdat pypleidingvervoer (1) die energiedoelmatigste vervoermodus is, (2) aansienlik goedkoper is as pad- en spoorvervoer, (3) heelwat veiliger is as spoorvervoer en veral padvervoer, (4) pad- en spoorvervoer- en infrastruktuurkapasiteit vir ander verkeer beskikbaar stel, en (5) minder onverhaalde eksterne koste (soos lugbesoedeling, geraas en verkeersophopings) as ander vervoermodusse tot gevolg het, behoort pypleidingvervoer (onderhewig aan grondige ekonomiese evaluering) as ’n bykomende vervoermodus tussen tenkwerwe in Suid-Afrika oorweeg te word. In die lig van die besondere uitdagings wat die beplanning, aanlê en doeltreffende bedryf van groot pypleidings verg, word in hierdie artikel ’n oorsig gebied van die resultate van ’n ondersoek na die ekonomiese aspekte van die kommersi le vervoer van petroleumkommoditeite per pypleiding. Die potensi le waarde van die navorsing lê hoofsaaklik in (1) die voorgestelde raamwerk vir die ekonomiese evaluering en beplanning van nuwe pypleidings, en (2) die riglyne vir die beprysing van die kommersi le vervoer van petroleumkommoditeite per pypleiding. Daar word in die besonder aan die volgende aspekte van die kommersi le pypleidingvervoer van petroleumkommoditeite aandag gegee: relatiewe doelmatigheid, ekonomiese beplanning, markstruktuur en eienaarskapspatrone, kostestruktuur, en die doeltreffende beprysing van die dienslewering. Economic aspects of pipeline transport: a South African perspective Pipeline transport is unique among modes of transport in that the pipe, which facilitates freight movement, is both the way and the vehicle, and it is permanently connected to terminals, which facilitate freight storage. This feature makes it the only mode of transport that does not require any materials or goods handling. In view of the facts that pipeline infrastructure is extremely capital intensive and that it has an unprecedented longevity, pipeline transport enjoys the highest level of economies of scale of all modes of transport. This economy is subject to steady and enduring high levels of demand. It is also the only mode of freight transport of which the operations do not require a return journey, whereby joint cost due to empty running is avoided. The commercial transport of crude oil and petroleum products by pipeline and the envisaged new investment in this mode of transport are receiving increased attention
Logistieke aspekte van pypleidingvervoer in die voorsiening van petroleumprodukte
Wessel Pienaar
Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie , 2008, DOI: 10.4102/satnt.v27i2.85
Abstract: Die kommersi le vervoer van ruolie en brandstofprodukte per pypleiding en die beoogde verdereinvestering in hierdie vervoermodus kry in Suid-Afrika toenemend aandag. Pypleidingvervoer is’n grootmaat-, nie-behoueringsmetode van vervoer van geskikte vloeistowwe (byvoorbeeldpetroleumkommoditeite wat ruolie, brandstofprodukte en vloeibare petrochemikalie insluit), aardgasen geflodderiseerde grondstowwe. In Suid-Afrika verteenwoordig brandstofprodukte die grootstedeel van kommersi le pypleidingverkeer, gevolg deur ruolie en aardgas.Daar is drie basiese soorte petroleumpypleidingvervoerstelsels. Insamelingspypleidingstelsels Ruolie-hoofaarpypleidingstelsels Pypleidingstelsels vir geraffineerde produkte Saam verskaf hierdie stelsels ’n aaneenlopende verbinding tussen ontginning, verwerking,verspreiding en groothandeldepots in verbruiksgebiede.Aangesien daar koste verbonde aan goederehantering by eindpunte en opbergingsfasiliteiteis sonder dat dit waarde toevoeg tot die goedere, is dit ’n primêre oogmerk om hantering sovermoontlik uit te skakel. Met die vervoer van ruolie en brandstofprodukte per pypleiding wordvolkome aan hierdie oogmerk voldoen. Net die kommoditeit beweeg – die pypleiding verskaf dienodige omhulsel en beskerming van die kommoditeit. Indien nodig kan ’n volgehoue diens gelewerword sonder die noodsaaklikheid van ’n terugrit of ’n terugpomp-proses. Die uitskakeling vanhantering, verpakking en terugwaartse logistieke aktiwiteite dra aansienlik by tot die skaalvoordelewat pypleidingvervoer geniet.Doeltreffende logistieke diens is ’n voorvereiste om te help verseker dat kli nte die verlangdegoedere op die aangewese tyd by die bestemde plek in die vereiste toestand en hoeveelheidontvang. Die vernaamste logistieke diensmaatstawwe is geskiktheid, toeganklikheid, goederesekuriteit, deurvoertyd, betroubaarheid, en buigsaamheid. Die artikel bied ’nuiteensetting van die mate waartoe pypleidingvervoer aan hierdie doeltreffendheidsmaatstawwevoldoen. Logistics aspects of pipeline transport in the supply of petroleum products The commercial transportation of crude oil and petroleum products by pipeline is receiving increased attention in South Africa. Transnet Pipeline Transport has recently obtained permission from the National Energy Regulator of South Africa (Nersa) to construct and operate a new petroleum products pipeline of 60 cm diameter from Durban to Gauteng. At an operating speed of 10 km/h the proposed 60 cm Transnet pipeline would be able to deliver 3,54 million litres of petroleum product per hour. This is equivalent to 89 deliveries per hour u
’n Voorgestelde reguleringsraamwerk vir pad- en spoorvragvervoer in Suid-Afrika
Wessel Pienaar
Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie , 2007, DOI: 10.4102/satnt.v26i4.140
Abstract: Die toenemende aantal swaar goederevoertuie op Suid-Afrika se buitestedelike padnetwerk ontlok aansienlike aandag. Aantygings kom steeds hardnekkig voor dat langafstand-padvragvervoer van ongure ekonomiese aard is en dat streng ekonomiese herregulering van die bedryf nodig is. Gedurende die jare 1970 het padvervoer in Suid-Afrika spoorvervoer vervang as die oorheersende vorm van vragvervoer oor lang afstande (minerale en erts uitgesluit). Op langafstand- deurskofte vervoer padvragkarweiers sekere primêre goedere van ’n organiese aard (soos bosbou- , vissery- en landbouprodukte), sommige halfklaar goedere, heelwat klaar goedere en die meeste verbruikersware. Padvragkarweiers wen voortdurend markaandeel op langafstandroets waar spoorvervoer die koste-doelmatigste modus is. Die groter waarde wat padvragkarweiers deur beter diensdoel- treffendheid in vergelyking met spoorvervoer bied, oorskry dikwels die kostepremie wat betaal word vir vragvervoerdiens per pad eerder as per spoor. Deur die geskiedenis heen was owerhede betrokke by vervoer. ’n Uiteenlopende reeks argumente is met die verloop van tyd voorgehou vir hierdie betrokkenheid by vervoer, wat die onderstaande insluit: Beheer van oormatige mededinging, ko rdinasie van vervoer, integrasie van vervoer met ekonomiese beleid, behoud van veiligheid, sekuriteit, en orde voorsiening van duursame infrastruktuur, voorsiening van openbare goedere, verhaling van die werklike hulpbronkoste van vervoerinsette, regulering van skadelike optrede en eksternaliteite, inkorting van monopoliemag, maatskaplike ondersteuning. ’n Stel van nege beleidsinstrumente kan ge dentifiseer word wat owerhede aanwend om die werkverrigting van die vervoerbedryf te be nvloed: Wetgewing, regstreekse voorsiening, fiskale maatre ls, monetêre maatre ls, morele oorreding, beleid rakende strategiese kommoditeite, verkrygingsbeleid, voorsiening van inligting navorsing en ontwikkeling. ’n Ekonomies vrye mark bied die beste vooruitsig vir die bevordering van sowel pad- as spoorvragaktiwiteite. A proposed regulatory framework for road and rail freight transport in South Africa The increase in the number of freight vehicles on South Africa’s rural road network has received substantial attention. Insinuations persist that long-distance road freight haulage is of a somewhat unsavoury economic nature, and that strict economic re-regulation of the land freight transport is necessary. During the 1970s road transport replaced rail carriage as the dominant form of long-distance freight transport (excluding minerals and ore) in South Africa. On long ha
Karl Barth’s definition of church in politics and culture: Growth points for the church in South Africa
Wessel Bentley
HTS Theological Studies/Teologiese Studies , 2009, DOI: 10.4102/hts.v63i4.263
Abstract: The article describes briefly Karl Barth’s views on church, its role in politics and how it relates to culture. This is done by identifying the way in which the church participates in the social realm through its relationship with the State. The historic religious question asks whether there is a natural mutual-determining relationship between church and State. The church may ask whether faith and politics should mix, while a secular state may question the authority which the church claims to speak from. To a large extent culture determ-ines the bias in this relationship. History has shown that church-State dynamics is not an either/or relationship, whereby either the authority of the church or the authority of the State should function as the ruling norm. Karl Barth describes the dynamics of this relationship very well, within the context of culture, in the way his faith engages with the political status quo. Once the relationship is better understood, Barth’s definition of the church will prove to be more effective in its evangelical voice, speaking to those who guide its citizens through political power. “Fürchtet Gott, ehret den K nig!” (1 Pt 2:17)
Exploring the Ends of the Earth
Paul Wessel
Oceanography , 2010,
Abstract: With low-tech equipment, variable levels of planning, and plenty of courage, late nineteenth and early twentieth century explorers mesmerized the world with daring attempts to reach Earth’s geographic poles. The one hundredth anniversary of Robert Peary’s controversial North Pole claim was in April 2009, and the centennial of Roald Amundsen’s undisputed dash to the South Pole is coming up in December 2011. Much less known are the “poles of inaccessibility” (PIA), which are distinguished by their great distances from any coast (Stefansson, 1920). As 50% of humanity lives within 200 km of the coast, such remote points are particularly difficult to reach. In addition to numerous local maxima, there are two global maxima of particular interest: the Eurasian PIA, representing the land-locked point farthest from the ocean, and the South Pacific PIA, being the most remote oceanic point. The Eurasian PIA has been called the “Center of the Earth” (CE), and it was “conquered” in 1985 by Richard and Nicholas Crane during a bike journey across the Himalayas (Crane and Crane, 1987). However, recent calculations have placed the CE considerably further south (Garcia-Castellanos and Lombardo, 2007). The oceanic PIA is more elusive and was only recently named “Point Nemo” (Lukatela, 2005) after the globetrotting captain in Jules Verne’s classic 20,000 Leagues Under the Sea.
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