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Few Decades (few + decade)
Selected AbstractsPopulation genetics of the European trout (Salmo trutta L.) migration system in the river Rhine: recolonisation by sea troutECOLOGY OF FRESHWATER FISH, Issue 1 2005A. Schreiber Abstract , Allozyme genetics (34 loci) is studied in up to 1010 European trout (Salmo trutta) from the Rhine, Meuse, Weser, Elbe and Danube river systems in Central Europe. Population samples from single collection sites, chiefly small streams (GCG = 0.2126), rather than the divergence of the trout from Atlantic and Danubian drainages (GSG = 0.0711), contributed to the overall gene diversity of GST = 0.2824. Sea trout (n = 164) and brown trout (n = 767) in Atlantic rivers adhere to the same biogeographical stock, but anadromous trout from the Rhine and the Elbe display more genetic cohesion than resident brown trout from the Rhine system alone. Strayers from the Elbe could have founded the recently re-established sea trout population of the Rhine, after a few decades of absence or precarious rarity. Migrants may even connect the Rhine and Elbe stocks by ongoing gene flow. A release,recapture study confirms that all trout in the Rhine belong to one partly migratory population network: Six of 2400 juvenile sea trout released into a tributary of the Rhine were later recorded as emigrants to the Rhine delta, against three of 1600 released brown trout. One migrant had entered the open North Sea, but the other dispersers were recorded in fresh waters of the Rhine delta (Ijsselmeer, Amstelmeer). Stocking presumably elevated both heterozygosity and fixation indices of brown trout, but this effect is subtle within the range of the Atlantic population group. Improved sea trout management in the Rhine, and modifications to brown trout stocking in the upper Danubian area are recommended. [source] Advances and Applications of Biodegradable Elastomers in Regenerative MedicineADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Maria Concepcion Serrano Abstract When elastomers were first proposed as useful materials for regenerative medicine a few decades ago, their high versatility and suitability for a diverse and wide range of in vivo applications could not have been predicted. Due to their ability to recover after deformation, these materials were first introduced in tissue engineering in an attempt to mimic the mechanical properties of the extracellular matrix. Furthermore, elastomeric characteristics have been described as important criteria for cell interaction by modulating cellular behavior. From soft to hard tissues, elastomers have demonstrated degradation, mechanical, and biocompatibility requirements in accordance with the target tissue. In this feature article, biodegradable synthetic polyester elastomers that have been reported in the literature are discussed, with special focus on those that show promise for in vivo tissue replacement. Their satisfactory performance in vivo shows the promise of elastomers for use in regenerative medicine. However, further investigation is required to demonstrate the prospect of elastomer-based therapies in clinical trials. [source] Sequestration and turnover of plant- and microbially derived sugars in a temperate grassland soil during 7 years exposed to elevated atmospheric pCO2GLOBAL CHANGE BIOLOGY, Issue 2 2007MICHAEL BOCK Abstract Temperate grasslands contribute about 20% to the global terrestrial carbon (C) budget with sugars contributing 10,50% to this soil C pool. Whether the observed increase of the atmospheric CO2 concentration (pCO2) leads to additional C sequestration into these ecosystems or enhanced mineralization of soil organic matter (SOM) is still unclear. Therefore, the aim of the presented study was to investigate the impact of elevated atmospheric pCO2 on C sequestration and turnover of plant- (arabinose and xylose) and microbially derived (fucose, rhamnose, galactose, mannose) sugars in soil, representing a labile SOM pool. The study was carried out at the Swiss Free Air Carbon Dioxide Enrichment (FACE) experiment near Zurich. For 7 years, Lolium perenne swards were exposed to ambient and elevated pCO2 (36 and 60 Pa, respectively). The additional CO2 in the FACE plots was depleted in 13C compared with ambient plots, so that ,new' (<7 years) C inputs could be determined by means of compound-specific stable isotope analysis (13C : 12C). Samples were fractionated into clay, silt, fine sand and coarse sand, which yielded relatively stable and labile SOM pools with different turnover rates. Total sugar sequestration into bulk soil after 7 years of exposure to elevated pCO2 was about 28% compared with the control plots. In both ambient and elevated plots, total sugar concentrations in particle size fractions increased in the order sand Natural gradient algorithm for neural networks applied to non-linear high power amplifiers,INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 8 2002H. Abdulkader Abstract This paper investigates the processing techniques for non-linear high power amplifiers (HPA) using neural networks (NNs). Several applications are presented: Identification and Predistortion of the HPA. Various Neural Network structures are proposed to identify and predistort the HPA. Since a few decades, NNs have shown excellent performance in solving complex problems (like classification, recognition, etc.) but usually they suffer from slow convergence speed. Here, we propose to use the natural gradient instead of the classical ordinary gradient in order to enhance the convergence properties. Results are presented concerning identification and predistortion using classical and natural gradient. Practical implementations issues are given at the end of the paper. Copyright © 2002 John Wiley & Sons, Ltd. [source] Explaining Migration: A Critical ViewINTERNATIONAL SOCIAL SCIENCE JOURNAL, Issue 165 2000Joaquín Arango The article surveys the major contemporary explanations of migration, starting with the neo-classical theory, and then the array of theories and conceptual frameworks that have flourished in the last quarter of the century. The survey highlights the fact that in its relatively short history, theorising about migration has taken the form of a string of separate, generally unconnected theories, models, conceptual frameworks and empirical generalisations, rather than a cumulative sequence of contributions. As awhole, existing theories of migration can be faulted for focusing almost exclusively on the explanation of the causes of migration, to the detriment of other dimensions; for making ,grand claims' out of proportion with effective explanatory power; and for providing explanations ex-post rather than guiding empirical research and providing testable hypotheses. In addition to the difficulties that all the social sciences experience when trying to explainhuman behaviour, migration theories face special ones: its subject matter is hard to define, difficult to measure, extremely multifaceted and multiform, and thus resistant to theory-building. Whilst the reservoir of theories, and especially of conceptual frameworks, available nowadays represents a clear improvement over the situation a few decades ago, their contribution toour knowledge of migration is still limited. [source] Opportunities for the stratospheric collection of dust from short-period cometsMETEORITICS & PLANETARY SCIENCE, Issue 11 2002Scott MESSENGER These comets have had the rare characteristics of low eccentricity, low inclination orbits with nodes very close to 1 AU. Dust from these comets is directly injected into Earth-crossing orbits by radiation pressure, unlike the great majority of interplanetary dust particles collected in the stratosphere which spend millennia in space prior to Earth-encounter. Complete dust streams from these comets form within a few decades, and appreciable amounts of dust are accreted by the Earth each year regardless of the positions of the parent comets. Dust from these comets could be collected in the stratosphere and identified by its short space exposure age, as indicated by low abundances of implanted solar-wind noble gases and/or lack of solar flare tracks. Dust from Grigg-Skjellerup probably has the highest concentration at Earth orbit. We estimate that the proportion of dust from this comet will reach at least several percent of the background interplanetary dust flux in the >40 ,m size range during April 23,24 of 2003. [source] Are cattle, sheep, and goats endangered species?MOLECULAR ECOLOGY, Issue 1 2008P. TABERLET Abstract For about 10 000 years, farmers have been managing cattle, sheep, and goats in a sustainable way, leading to animals that are well adapted to the local conditions. About 200 years ago, the situation started to change dramatically, with the rise of the concept of breed. All animals from the same breed began to be selected for the same phenotypic characteristics, and reproduction among breeds was seriously reduced. This corresponded to a strong fragmentation of the initial populations. A few decades ago, the selection pressures were increased again in order to further improve productivity, without enough emphasis on the preservation of the overall genetic diversity. The efficiency of modern selection methods successfully increased the production, but with a dramatic loss of genetic variability. Many industrial breeds now suffer from inbreeding, with effective population sizes falling below 50. With the development of these industrial breeds came economic pressure on farmers to abandon their traditional breeds, and many of these have recently become extinct as a result. This means that genetic resources in cattle, sheep, and goats are highly endangered, particularly in developed countries. It is therefore important to take measures that promote a sustainable management of these genetic resources; first, by in situ preservation of endangered breeds; second, by using selection programmes to restore the genetic diversity of industrial breeds; and finally, by protecting the wild relatives that might provide useful genetic resources. [source] Degradation of nitroaromatic compounds: a model to study evolution of metabolic pathwaysMOLECULAR MICROBIOLOGY, Issue 4 2009Maia Kivisaar Summary Although many nitroaromatic compounds have been in nature for only a few decades, bacteria have already evolved the ability to metabolize them. Both horizontal transfer of genes and mutagenesis induced under stressful conditions might facilitate evolution of new catabolic pathways. Nitrotoluene degradation pathways are supposedly derived from an ancestral naphthalene degradation pathway. The 2-nitrotoluene degradation genes in Acidovorax sp. strain JS42 are controlled by the transcriptional activator NtdR, which differs from NagR, the activator of the naphthalene degradation operon in Ralstonia sp. strain U2, by only five amino acids. Both regulators respond to salicylate, an intermediate of naphthalene degradation, but NtdR also recognizes a wide range of nitroaromatic compounds. In this issue of Molecular Microbiology, Ju et al. present results of site-directed mutagenesis of NtdR and NagR and show how the nitrotoluene-responsive regulator NtdR can be generated from a NagR-like ancestor by only a few mutations. The reconstructed hypothetical pathway for the evolution of NtdR from NagR demonstrates stepwise broadening of the effector range of the evolving protein without loss of the original activity. These results provide strong evidence for the idea that promiscuity of proteins is an important step in the evolution of new functions. [source] The Struggle between Security and Democracy: An Alternative Explanation of the Democratization of South KoreaPACIFIC FOCUS, Issue 1 2010Dongsoo Kim South Korea experienced democratic reform relatively recently. Before its significant democratic reform in 1987, South Korea had been dominated by a series of authoritarian regimes over a few decades since its liberation from Japanese colonial rule. This study aims to uncover a set of variables that helped the democratic development of South Korea. For that purpose, I will demonstrate that prior to democratization the politics of South Korea were characterized by the struggle between democracy and security, and that the authoritarian leaders were successful in utilizing the unstable international security environment to strengthen their power during those years. I will also show that the favorably changing security environment played a significant role in the process of democratic transition. In so doing, I will argue that consideration of the external security environment is essential in the discussion of democratization. [source] NOTES: past, present and futureASIAN JOURNAL OF ENDOSCOPIC SURGERY, Issue 3 2010B Dallemagne MD Abstract Once in a few decades in science or medicine, an idea emerges that is so powerful that it changes forever how we think about that field. Natural Orifices Translumenal Endoscopic Surgery (NOTES) has the potential to break the physical barrier between bodily trauma and surgery. At the dawn of surgery, excellence was associated with big incisions: "big scar - big surgeon". In the 80s, minimally invasive surgery was born representing one of the greatest surgical evolutions of the 20th century. After Kalloo's first report in 2004 on transgastric peritoneoscopy in a porcine model, the interest in natural orifice transluminal endoscopic surgery (NOTES) has blossomed. Theoretically the same operation performed laparoscopically could be carried out through natural orifices without any abdominal incision avoiding pain and scarring. The lesson learned from the advent of laparoscopic surgery, thought us that we could be witnessing the birth of another surgical revolution. Since 2004 many abdominal procedures that use a NOTES approach have been successfully performed in animal models. However, the initial excitement for NOTES has been somewhat tempered by the reality that a NOTES procedure in human without laparoscopic assistance has not been performed by most groups. Indeed, a major issue is the lack of stable operative platform and flexible instruments that allow retraction and exposure of the organs, such as appendix or gallbladder. Will this issue change the future of NOTES? [source] Recombinant bacteria for environmental release: what went wrong and what we have learnt from itCLINICAL MICROBIOLOGY AND INFECTION, Issue 2009V. De Lorenzo Abstract From a biotechnological point of view, bacteria can be seen as either pathogens to target with new drugs or as biocatalysts for large-scale processes in industry, agriculture or the environment. The last includes the exploitation of bacterial activities for bioremediation of toxic waste either in situ or ex situ. The onset of genetic engineering in the late 70s opened the possibility of tailoring recombinant bacteria for environmental release, aimed at biodegradation of otherwise recalcitrant chemicals. However, a few decades later the outcome of this prospect has been quite meager. The literature counts very few cases where the use of genetically engineered bacteria has been proven to be more efficient than natural microorganisms in elimination of recalcitrant compounds under natural (not laboratory) conditions. Fortunately, the emergence of Systems and Synthetic Biology in the last few years is helping to identify what were the caveats of the former approaches and how to correct them. In addition, robust design concepts imported from process engineering provides fresh approaches to the challenge of designing microorganisms á la carte for environmental applications. [source]
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