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Search Results: 1 - 10 of 439 matches for " SABBE KOEN "
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Paleolimnological studies of Laguna Chica of San Pedro (VIII Region): Diatoms, hydrocarbons and fatty acid records Estudio Paleolimnológico de Laguna Chica de San Pedro (VIII Región): Diatomeas, hidrocarburos y ácidos grasos
ROBERTO URRUTIA,SABBE KOEN,FABIOLA CRUCES,KARLA POZO
Revista chilena de historia natural , 2000,
Abstract: Diatom, hydrocarbons and fatty acid sedimentary records were used for reconstructing the recent (last 150 years) palaeolimnological history of Laguna Chica of San Pedro (Concepción, VIII Región, Chile). Cluster analyses (Constrained Incremental Sum of Squares) on the diatom data revealed three distinct periods. The first period (1883-1940's) showed a pronounced increase in sedimentation rate and a slight increase in organic matter accumulation. In this period, eutrophic species (Aulacoseira granulata and Staurosira construens) became increasingly dominant. From the 1940s until the 1970s the diatom signal is more equivocal: after the initial decrease in the relative abundance of A. granulata and S. construens their numbers fluctuate without a clear pattern. Sedimentation rates strongly fluctuate in this period. From 1978 onwards eutrophic species are in decline while indicators of oligotrophic conditions, such as Cyclotella stelligera and Aulacoseira distans, become more abundant. This shift in the lake trophic status could not be attributed to a reduction in the nutrient load from the catchment and we hypothesize that the invasion of the lake by the submersed macrophyte Egeria densa has altered nutrient availability to the plankton communities. This is in agreement with the hydrocarbons and fatty acid analyses which demonstrate a shift in carbon number distributions from short chain alkanes and alkanoic acids (typical for microalgae) to long chain molecules (characteristic for higher plants) in the upper layers of the lake sediment Se realizó la reconstrucción histórica de los últimos 150 a os de Laguna Chica de San Pedro (Concepción, VIII Región, Chile), a través de la utilización de los restos de diatomeas, hidrocarburos y ácidos grasos contenidos en la columna de sedimento. El análisis estratigráfico de las diatomeas reveló la presencia de tres períodos diferentes. El primer período (1883-1940's), mostró un marcado aumento de las tasas de sedimentación y un leve aumento en la acumulación de materia orgánica; en este período se registra un incremento de las especies eutróficas (Aulacoseira granulata y Staurosira construens). Desde los a os cuarenta hasta la década del setenta el cambio en la comunidad de diatomeas fue más evidente y las tasas de sedimentación variaron fuertemente. A partir de 1978 disminuyen las especies eutróficas y aumentan las indicadoras de condiciones oligotróficas (Cyclotella stelligera y Aulacoseira distans). El cambio en el estado trófico del lago, no se atribuye a una reducción de los aportes de nutrientes desde la cuenca, si
Linkage Mapping Identifies the Sex Determining Region as a Single Locus in the Pennate Diatom Seminavis robusta
Ives Vanstechelman, Koen Sabbe, Wim Vyverman, Pieter Vanormelingen, Marnik Vuylsteke
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0060132
Abstract: The pennate diatom Seminavis robusta, characterized by an archetypical diatom life cycle including a heterothallic mating system, is emerging as a model system for studying the molecular regulation of the diatom cell and life cycle. One of its main advantages compared with other diatom model systems is that sexual crosses can be made routinely, offering unprecedented possibilities for forward genetics. To date, nothing is known about the genetic basis of sex determination in diatoms. Here, we report on the construction of mating type-specific linkage maps for S. robusta, and use them to identify a single locus sex determination system in this diatom. We identified 13 mating type plus and 15 mating type minus linkage groups obtained from the analysis of 463 AFLP markers segregating in a full-sib family, covering 963.7 and 972.2 cM, respectively. Five linkage group pairs could be identified as putative homologues. The mating type phenotype mapped as a monogenic trait, disclosing the mating type plus as the heterogametic sex. This study provides the first evidence for a genetic sex determining mechanism in a diatom.
Marine Ostracod Provinciality in the Late Ordovician of Palaeocontinental Laurentia and Its Environmental and Geographical Expression
Mohibullah Mohibullah, Mark Williams, Thijs R. A. Vandenbroucke, Koen Sabbe, Jan A. Zalasiewicz
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0041682
Abstract: Background We examine the environmental, climatic and geographical controls on tropical ostracod distribution in the marine Ordovician of North America. Methodology/Principal Findings Analysis of the inter-regional distribution patterns of Ordovician Laurentian ostracods, focussing particularly on the diverse Late Ordovician Sandbian (ca 461 to 456 Ma) faunas, demonstrates strong endemicity at the species-level. Local endemism is very pronounced, ranging from 25% (e.g. Foxe basin) to 75% (e.g. Michigan basin) in each basin, a pattern that is also reflected in other benthic faunas such as brachiopods. Multivariate (ordination) analyses of the ostracod faunas allow demarcation of a Midcontinent Province and a southern Marginal Province in Laurentia. While these are most clearly differentiated at the stratigraphical level of the bicornis graptolite biozone, analyses of the entire dataset suggest that these provinces remain distinct throughout the Sandbian interval. Differences in species composition between the provinces appear to have been controlled by changes in physical parameters (e.g. temperature and salinity) related to water depth and latitude and a possible regional geographic barrier, and these differences persist into the Katian and possibly the Hirnantian. Local environmental parameters, perhaps operating at the microhabitat scale, may have been significant in driving local speciation events from ancestor species in each region. Conclusions/Significance Our work establishes a refined methodology for assessing marine benthic arthropod micro-benthos provinciality for the Early Palaeozoic.
Gain and loss of elongation factor genes in green algae
Ellen Cocquyt, Heroen Verbruggen, Frederik Leliaert, Frederick W Zechman, Koen Sabbe, Olivier De Clerck
BMC Evolutionary Biology , 2009, DOI: 10.1186/1471-2148-9-39
Abstract: Within the Chlorophyta, EF-1α is shown to be present in three ulvophycean orders (i.e., Dasycladales, Bryopsidales, Siphonocladales) and the genus Ignatius. Models describing gene gain-loss dynamics revealed that the presence of EF-1α, EFL or both genes along the backbone of the green plant phylogeny is highly uncertain due to sensitivity to branch lengths and lack of prior knowledge about ancestral states or rates of gene gain and loss. Model refinements based on insights gained from the EF-1α phylogeny reduce uncertainty but still imply several equally likely possibilities: a primitive EF-1α state with multiple independent EFL gains or coexistence of both genes in the ancestor of the Viridiplantae or Chlorophyta followed by differential loss of one or the other gene in the various lineages.EF-1α is much more common among green algae than previously thought. The mutually exclusive distribution of EF-1α and EFL is confirmed in a large sample of green plants. Hypotheses about the gain-loss dynamics of elongation factor genes are hard to test analytically due to a relatively flat likelihood surface, even if prior knowledge is incorporated. Phylogenetic analysis of EFL genes indicates misinterpretations in the recent literature due to uncertainty regarding the root position.Elongation factor-1 alpha (EF-1α) is a core element of the translation apparatus and member of the GTPase protein family. The gene has been widely used as a phylogenetic marker in eukaryotes; either to resolve their early evolution [e.g., [1,2]] or more recent phylogenetic patterns [e.g., [3-7]]. The evolutionary history of genes used for such inferences should closely match that of the organisms and not be affected by ancient paralogy or lateral gene transfer [8]. A gene related to but clearly distinguishable from EF-1α, called elongation factor-like (EFL), appears to substitute EF-1α in a scattered pattern: several unrelated eukaryote lineages have representatives that encode EFL and others that p
Paleolimnological studies of Laguna Chica of San Pedro (VIII Region): Diatoms, hydrocarbons and fatty acid records
URRUTIA,ROBERTO; KOEN,SABBE; CRUCES,FABIOLA; POZO,KARLA; BECERRA,JOSE; ARANEDA,ALBERTO; VYVERMAN,WIM; PARRA,OSCAR;
Revista chilena de historia natural , 2000, DOI: 10.4067/S0716-078X2000000400014
Abstract: diatom, hydrocarbons and fatty acid sedimentary records were used for reconstructing the recent (last 150 years) palaeolimnological history of laguna chica of san pedro (concepción, viii región, chile). cluster analyses (constrained incremental sum of squares) on the diatom data revealed three distinct periods. the first period (1883-1940's) showed a pronounced increase in sedimentation rate and a slight increase in organic matter accumulation. in this period, eutrophic species (aulacoseira granulata and staurosira construens) became increasingly dominant. from the 1940s until the 1970s the diatom signal is more equivocal: after the initial decrease in the relative abundance of a. granulata and s. construens their numbers fluctuate without a clear pattern. sedimentation rates strongly fluctuate in this period. from 1978 onwards eutrophic species are in decline while indicators of oligotrophic conditions, such as cyclotella stelligera and aulacoseira distans, become more abundant. this shift in the lake trophic status could not be attributed to a reduction in the nutrient load from the catchment and we hypothesize that the invasion of the lake by the submersed macrophyte egeria densa has altered nutrient availability to the plankton communities. this is in agreement with the hydrocarbons and fatty acid analyses which demonstrate a shift in carbon number distributions from short chain alkanes and alkanoic acids (typical for microalgae) to long chain molecules (characteristic for higher plants) in the upper layers of the lake sediment
Philosophie der neuesten Musik-ein Versuch zur Extrapolation von Adornos 'Philosophie der neuen Musik'
H. Sabbe
Philosophica , 1971,
Abstract:
Isometric coactions of compact quantum groups on compact quantum metric spaces
Johan Quaegebeur,Marie Sabbe
Mathematics , 2010,
Abstract: We propose a notion of isometric coaction of a compact quantum group on a compact quantum metric space in the framework of Rieffel where the metric structure is given by a Lipnorm. We prove the existence of a quantum isometry group for finite metric quantum spaces, preserving a given state.
Practical Considerations for Wireless Sensor Network Algorithms  [PDF]
Gertjan Halkes, Koen Langendoen
Wireless Sensor Network (WSN) , 2010, DOI: 10.4236/wsn.2010.26055
Abstract: Many researchers from different backgrounds have found interesting research challenges that arise from the physical constraints and envisaged applications in Wireless Sensor Networks (WSNs). The WSN community that has formed over the years is divided into two sub-communities: the systems sub-community and the theory sub-community. However, there seems to be no connection between the two. Algorithms developed from a theoretic perspective are rarely implemented on real hardwares. In this paper we identify the most important reasons why these algorithms are disregarded by the systems sub-community, and provide pointers to remedy the lack of connection.
Resensie: "Die arkvaarders"
D Koen
Tydskrif vir letterkunde , 2012,
Abstract: Die arkvaarders. Anne Provoost (vertaal deur Daniel Hugo). Pretoria: Protea Boekhuis, 2012. 311 pp. ISBN: 978-1-86919-461-1.
In Defence of Pashukanism
R Koen
Potchefstroom Electronic Law Journal/Potchefstroomse Elektroniese Regsblad , 2011,
Abstract: This essay presents an extended defence of the general theory of law formulated by the Bolshevik jurist, Evgeny Pashukanis, and published in his Law and Marxism: A General Theory in 1924. The general theory is a theory of the legal form. Although Pashukanis did not name his theory, it has become known as the commodity form theory of law because of its theorising the legal form as a homologue of the commodity form. However, despite having weighty Marxist and revolutionary Bolshevik credentials, the general theory has been subjected to sustained attack, especially from new left and neo-Marxist circles. This essay identifies and explicates six major objections to Pashukanism from its left critics. These are that the general theory is too abstract to comprehend the reality of legal relations; that it is infused with economic reductionism; that it derives the legal form wrongly from commodity exchange; that it classifies the legal form incorrectly as an attribute of capitalism only; that it lacks the generality required of a general theory of law; and that it is imbricated in the growth of anarchism and Stalinism. Following a brief exegetical exercise, the bulk of the essay is devoted to demonstrating in detail that each of the six objections to the general theory is without merit, and that none makes any serious incursion into its integrity as a theory of the legal form. The central submission of the essay is that the Pashukanist general theory of law is rooted in the first principles of classical Marxism and hence may lay claim legitimately to being the Marxist theory of law. KEYWORDS: Capitalism; Commodity form; Homologue; Legal form; Legal subject; Marxism; Mode of production; Principle of equivalence; Relations of exchange and Relations of production http://dx.doi.org/10.4314/pelj.v14i4.5
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