bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of air in fatigue load interaction
Authors: SUNDER R. , PORTER W. J. , ASHBAUGH N. E. 
Published: March 2003

ABSTRACTNatural fatigue crack formation and growth were studied in notched Al–Cu alloy coupons through high‐resolution SEM fractography. The experiments were conducted under programmed loading conditions designed to induce microscopic marking of the crack formation and growth process under varying stress ratio and closure‐free crack tip conditions. Control experiments were performed by switching between an air and vacuum environment. In air, varying the stress ratio from 0.74 down to 0.64 retards crack growth by up to a factor of five. This ‘closure‐free’ stress ratio history effect totally disappears in vacuum, suggesting a significant environmental influence on stress ratio and its history. Crack‐tip stress state appears to moderate environmental action, revealing a potential mechanism sensitive to residual stress. Consequently, crack closure, residual stress and crack front and plane orientation are identified as major load interaction mechanisms whose synergistic action controls fatigue under variable amplitude loading. The study also appears to suggest that as a consequence of the crack seeking the path of least resistance, load‐sequence sensitive crack plane and front orientation may only induce retardation effects.
On the explicit evaluation of stress intensity factors in the hybrid boundary element method
Authors: DUMONT N. A. , LOPES A. A. O. 
Published: March 2003

ABSTRACTThe hybrid boundary element method, as based on the Hellinger‐Reissner potential for assumed singular stress fields, is suited for the explicit mathematical description of high gradients. In this paper, after an introductory overview of the method and an account of different attempts of application to fracture mechanics problems, one makes use of Westergaard complex functions for numerically handling general curved cracks, in which the exact gradient of the stress field at crack tip is considered, for any planar configurations. Modes I and II stress intensity factors are directly obtained as the primary unknowns of the problem, which eliminates the necessity of post‐processing results. Fairly good accuracy is achieved at low computational costs, as numerically assessed by means of several examples. The formulation seems to present no restrictions, for cases of both single and multiple internal cracks. At present, an extension to generally curved edge cracks as well as to kinked cracks is being investigated, as the method relies on the existence of analytical functions for the explicit description of local stress fields.
Analysis of cracked steel members reinforced by pre‐stress composite patch
Authors: COLOMBI P. , BASSETTI A. , NUSSBAUMER A. 
Published: March 2003

ABSTRACTPre‐stress bonded composite patch is a promising technique to reinforce steel member damaged by fatigue. The effectiveness of this technique was verified by fatigue tests on notched steel plates. Results showed that the application of carbon fibre reinforced plastic (CFRP) strips and, eventually, the introduction of a compressive stress by pretension of the CFRP strips prior to bonding produced a significant increment of the remaining fatigue life. In this paper, the stress intensity factor in the notched plates is computed by a two‐dimensional finite element model in connection with the three‐layer technique in order to reduce the computational effort. Due to high stress concentration at the plate crack tip, debond is assumed at the adhesive–plate interface. The goal is to illustrate the influence of some reinforcement parameters such as the composite strip stiffness, the pre‐stress level, the adhesive layer thickness and the size of the debonded region on the effectiveness of the composite patch reinforcement.
The functional implications of active and passive pollination in dioecious figs
Authors: Jousselin  , Kjellberg  
Published: March 2003

Fig‐pollinating wasps lay their eggs in fig flowers. Some species of fig‐pollinating wasps are active pollinators, while others passively transfer pollen. In dioecious fig species, the ovules of male figs produce wasps but no seeds. By observations and experiments on four dioecious Ficus species we show that (i) passive pollinators distribute pollen haphazardly within figs, but fertilization of female flowers in male figs is inhibited. Consequently, wasp larvae will develop in nonfertilized ovules: they cannot benefit from pollination; (ii) active pollinators efficiently fertilize flowers in which they oviposit. Lack of pollination increases larval mortality. Hence, fig pollinators are not obligate seed eaters but ovule gallers. Active pollination has probably evolved as a way to improve progeny nourishment.Comparison of pollination and oviposition process in male and female figs, suggests that stigma shape and function have coevolved with pollination behaviour, in relation to constraints linked with dioecy.
Marine reserves have rapid and lasting effects
Authors: Halpern Benjamin S. , Warner Robert R. 
Published: March 2003

AbstractMarine reserves are becoming a popular tool for marine conservation and resource management worldwide. In the past, reserves have been created with little understanding of how they actually affect the areas they are intended to protect. A few recent reviews have evaluated how reserves in general affect the density and biomass of organisms within them, but little work has been done to assess temporal patterns of these impacts. Here we review 112 independent measurements of 80 reserves to show that the higher average values of density, biomass, average organism size, and diversity inside reserves (relative to controls) reach mean levels within a short (1–3 y) period of time and that the values are subsequently consistent across reserves of all ages (up to 40 y). Therefore, biological responses inside marine reserves appear to develop quickly and last through time. This result should facilitate their use in the management of marine resources.
Food web complexity and chaotic population dynamics
Authors: Fussmann Gregor F. , Heber Gerd 
Published: March 2003

AbstractIn mathematical models, very simple communities consisting of three or more species frequently display chaotic dynamics which implies that long‐term predictions of the population trajectories in time are impossible. Communities in the wild tend to be more complex, but evidence for chaotic dynamics from such communities is scarce. We used supercomputing power to test the hypothesis that chaotic dynamics become less frequent in model ecosystems when their complexity increases. We determined the dynamical stability of a universe of mathematical, nonlinear food web models with varying degrees of organizational complexity. We found that the frequency of unpredictable, chaotic dynamics increases with the number of trophic levels in a food web but decreases with the degree of complexity. Our results suggest that natural food webs possess architectural properties that may intrinsically lower the likelihood of chaotic community dynamics.
The Arctic Oscillation predicts effects of climate change in two trophic levels in a high‐arctic ecosystem
Authors: Aanes Ronny , Sæther Bernt‐Erik , Smith Fiona M. , Cooper Elisabeth J. , Wookey Philip A. , Øritsland Nils Are 
Published: March 2003

AbstractDuring recent decades there has been a change in the circulation of atmospheric pressure throughout the Northern Hemisphere. These variations are expressed in the recently described Arctic Oscillation (AO), which has shown an upward trend (associated with winter warming in the eastern Arctic) during the last three decades. We analysed a 12‐year time series on growth ofCassiope tetragona(Lapland Cassiope) and a 21‐year time series on abundance of a Svalbard reindeer population. High values of the AO index were associated with reduced plant growth and reindeer population growth rate. The North Atlantic Oscillation index was not able to explain a significant proportion of the variance in either plant growth or reindeer population fluctuations. Thus, the AO index may be a better predictor for ecosystem effects of climate change in certain high‐arctic areas compared to the NAO index.
Annual variation in nesting numbers of marine turtles: the effect of sea surface temperature on re‐migration intervals
Authors: Solow Andrew R , Bjorndal Karen A. , Bolten Alan B 
Published: March 2003

AbstractThe assessment of marine turtle populations is complicated by large inter‐annual variations in nesting numbers. This variability has been attributed to synchrony in the re‐migration intervals (i.e., intervals between successive nesting years) of individuals. It has been hypothesized that this synchrony arises from environmental variations that affect the feeding conditions at sea. This paper presents the first direct test of this hypothesis. The analysis identifies a significant effect of sea surface temperature on the re‐migration interval in the largest Atlantic population of green turtles.
Dissecting adaptive clinal variation: markers, inversions and size/stress associations in Drosophila melanogaster from a central field population
Authors: Weeks Andrew R. , McKechnie Stephen W. , Hoffmann Ary A. 
Published: March 2003

AbstractMany organisms show latitudinal variation for quantitative traits that is assumed to be due to climatic adaptation. These clines provide an opportunity to study the genetics of the adaptive process both at the phenotypic and the underlying molecular levels. Yet researchers rarely try to link variation in quantitative traits to their underlying molecular genetic basis. We describe a novel approach for exploring the genetic basis for clinal variation in size and stress traits in Drosophila melanogaster. We look for associations between genetic markers and traits that exhibit clinal patterns on the east coast of Australia using a single, geographically central population. There are strong associations between markers found within In(3R)Payne and variation in size, suggesting that this inversion explains much of the clinal variation in this trait. We also find that development time is associated with the Adh allozyme locus, cold resistance is negatively associated with the In(3L)Payne inversion and a genetic marker for Hsp70, a heat‐shock protein, is associated with heat resistance. Finally we discuss the importance of inversions in clinal variation for quantitative traits and for identifying quantitative trait loci.
Variation in butterfly egg adhesion: adaptation to local host plant senescence characteristics?
Authors: Fordyce James A. , Nice Chris C. 
Published: March 2003

AbstractMost butterflies that overwinter as diapausing eggs have evolved oviposition behaviours where egg placement is near or on perennating portions of their host plant. We describe an alternative strategy used by alpine populations of a Lycaenid butterfly species complex where eggs are not attached strongly to the leaf substrate and subsequently fall off the plant. Other populations occurring at lower elevations attach their eggs strongly to the plant. In the laboratory, we measured the amount of force required to detach eggs from the leaf substrate. Eggs of the non‐alpine populations required more than five times the force required to detach eggs of the alpine population. Field surveys of the host plant characteristics used by various populations suggest that easy detachment may be adaptive for alpine populations because, unlike the host plants used by other populations, nearly all of the preceding year's vegetative growth is blown away by strong winds during the winter months.
Ecological replacement of native red squirrels by invasive greys driven by disease
Authors: Tompkins D. M. , White A. R. , Boots M. 
Published: March 2003

AbstractAlthough a parapoxvirus harmful to red squirrels is present in UK squirrel populations it has not been considered a major cause of red squirrel decline, and replacement by the introduced grey squirrel, mainly because diseased individuals are rarely observed. By developing a generic model we show that parapoxvirus is likely to have played a crucial role in the red squirrel decline even though the prevalence of infection is low. Conservationists are quite rightly concerned with the invasion of exotic organisms such as the grey squirrel. Our work emphasizes that they, along with other ecologists, should pay particular attention to pathogens, even when they occur at low prevalence.
Novel forms of ring‐hydroxylating dioxygenases are widespread in pristine and contaminated soils
Authors: Yeates Christine , Holmes Andrew J. , Gillings Michael R. 
Published: March 2003

Ring‐hydroxylating dioxygenases (RHDs) are of central importance to bacterial recycling of aromatic hydrocarbons, including anthropogenic pollutants. The database of presently characterized RHDs is biased towards those from organisms readily isolated on anthropogenic substrates. To investigate the extent to which RHDs from extant organisms reflect the natural diversity of these enzymes, we developed a polymerase chain reaction (PCR) method for retrieval of RHD gene fragments from environmental samples. Gene libraries from two contaminated and two pristine soil samples were constructed. None of the inferred peptides from clones examined were identical to previously described RHDs; however, all showed significant sequence homology and contained key catalytic residues. On the basis of sequence identity, the environmental clones clustered into six distinct groups, only one of which included known RHDs. One of the new sequence groupings was particularly widespread, being recovered from all soil samples tested. Comparison of inferred peptide sequences of the environmental clones and known RHDs showed the former to have greater sequence variation at sites thought to influence accessibility of the active site than that seen between currently known RHDs. We conclude that presently characterized RHDs do not adequately represent the diversity of function found in in situ forms.
Following spread of fire blight in Western, Central and Southern Europe by molecular differentiation of Erwinia amylovora strains with PFGE analysis
Authors: Jock Susanne , Donat Victoria , López Maria M. , Bazzi Carlo , Geider Klaus 
Published: March 2003

SummaryFire blight has been detected recently in several areas of northern Spain and north‐eastern Italy. To follow spread of the disease within Europe, more than 120 Erwinia amylovora strains isolated from 1957–1900 in England, France, Germany, The Netherlands, Belgium, Poland, Italy and Spain were assayed using pulsed‐field gel electrophoresis (PFGE) analysis of genomic DNA after XbaI digestion. Pattern types Pt1 and Pt4 were found for strains from England. Pt1 was also found in central Europe and eastern France, Pt4 in western France. Pt2 appeared first in Egypt, from where strains with this pattern disseminated northwards as far as into the Balkans. Pt3 was typical for northern France and Belgium. Strains from Spain displayed the pattern types Pt3 and Pt4. In Italy, Pt2 was found in the south‐eastern areas, Pt3 in the north‐eastern areas, and Pt1 was found very recently in orchards adjacent to the Austrian border, together with Pt3. Despite barely controlled trade with fire blight host plants and associated plant products within Europe, the PFGE patterns of the E. amylovora isolates were ordered indicating sequential spread. On the other hand, the appearance of Pt3 in northern Italy and central Spain can be explained by the import of contaminated plants by nurseries.
Occurrence and activity of Archaea in aerated activated sludge wastewater treatment plants
Authors: Gray Neil D. , Miskin Ian P. , Kornilova Oksana , Curtis Thomas P. , Head Ian M. 
Published: March 2003

SummaryThe occurrence, distribution and activity of archaeal populations within two aerated, activated sludge wastewater treatment systems, one treating domestic waste and the second treating mixed domestic and industrial wastewater, were investigated by denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction (PCR)‐amplified ribosomal RNA gene fragments and process measurements. In the plant receiving mixed industrial and domestic waste the archaeal populations found in the mixed liquor were very similar to those in the influent sewage, though a small number of DGGE bands specific to the mixed liquor were identified. In contrast, the activated sludge treating principally domestic waste harboured distinct archaeal populations associated with the mixed liquor that were not prevalent in the influent sewage. We deduce that the Archaea in the plant treating mixed wastewater were derived principally
from the influent, whereas those in the plant treating solely domestic waste were
actively growing in the treatment plant. Archaeal 16S rRNA gene sequences related
to the Methanosarcinales, Methanomicrobiales and the Methanobacteriales were detected. Methanogenesis was measured in activated sludge samples incubated under oxic and anoxic conditions, demonstrating that the methanogens present in both activated sludge plants were active only in anoxic incubations. The relatively low rates of methanogenesis measured indicated that, although active, the methanogens play a minor role in carbon turnover in activated sludge.
A chlorophyll a fluorescence‐based Lemna minor bioassay to monitor microbial degradation of nanomolar to micromolar concentrations of linuron
Authors: Hulsen Kris , Minne Veerle , Lootens Peter , Vandecasteele Paul , Höfte Monica 
Published: March 2003

SummaryA plant–microbial bioassay, based on the aquatic macrophyte Lemna minor L. (duckweed), was used to monitor biodegradation of nano‐ and micromolar concentrations of the phenylurea herbicide linuron. After 7 days of exposure to linuron, log‐logistic‐based dose–response analysis revealed significant growth inhibition on the total frond area of L. minor when linuron concentrations ≥ 80 nM were added to the bioassay. A plant‐protective effect was obtained for all concentrations > 80 nM by inoculation with either a bacterial consortium or Variovorax paradoxus WDL1, which is probably the main actor in this consortium. The outcome of the plant–microbe–toxicant interaction was also assessed using pulse amplitude‐modulated chlorophyll a fluorescence and chlorophyll a fluorescence imaging. Linuron toxicity to L. minor became apparent as a significant decrease in the effective quantum yield (ΔF/Fm′) within 90 min after exposure of the plants to linuron concentrations ≥ 160 nM. Inoculation of the bioassay with the linuron‐degrading bacteria neutralized the effect on the effective quantum yield at concentrations ≥ 160 nM, indicating microbial degradation of these concentrations. The chlorophyll a fluorescence‐based Lemna bioassay described here offers a sensitive, fast and cost‐effective approach to study the potential of biodegrading microorganisms to break down minute concentrations of photosynthesis‐inhibiting xenobiotics.
The genome structure of Pseudomonas putida: high‐resolution mapping and microarray analysis
Authors: Stjepandic´ Diana , Weinel Christian , Hilbert Helmut , Koo Hean L. , Diehl Frank , Nelson Karen E. , Tümmler Burkhard , Hoheisel Jörg D. 
Published: March 2003

SummaryAs part of a collaborative project aimed at sequencing and functionally analysing the entire genome of Pseudomonas putida strain KT2440, a physical clone map was produced as an initial resource. To this end, a high‐coverage cosmid library was arrayed and ordered by clone hybridizations. Restriction fragments generated by rare‐cutting enzymes and plasmids containing the rrn operon and 23S rDNA of Pseudomonas aeruginosa were used as probes and, parts of the cosmids were end‐sequenced. This provided the information necessary for merging and comparing the macro‐restriction map, cosmid clone order and sequence information, thereby assuring co‐linearity of the eventual sequence assembly with the actual genome. A tiling path of clones was selected, from the shotgun clones used for sequencing, for the production of DNA microarrays that represent the entire genome including its non‐coding portions.
Pseudomonas aeruginosa biofilms react with and precipitate toxic soluble gold
Authors: Karthikeyan S. , Beveridge T. J. 
Published: March 2003

SummaryThe interaction between biofilms of Pseudomonas aeruginosa PAO1 and 0.01–5 mM gold chloride was investigated using flow‐cells. Scanning confocal laser microscopy (SCLM) of these biofilms revealed the formation of two distinct structural features: (i) confluent areas of uniform thickness and (ii) cell clusters which often emerged as 30–40 µm, tall narrow pillars (or pedestals) of cells and exopolymeric substance (EPS). When 5‐day‐old, quasi‐steady state biofilms (as indicated by the stability of film thickness and overall structure) were exposed to relatively high AuCl3 (i.e. 0.5–5 mM) for 30 min at 20°C, reduction of the auric ion resulted in the formation of both extracellular and intracellular metallic gold colloids, as revealed by transmission electron microscopy (TEM). Most mineralization occurred on cell surfaces with lesser amounts within cells and little throughout the EPS. Little to no mineralization of gold was seen at 0.01–0.1 mM concentrations. As initial AuCl3 concentrations approached 0.5 mM or greater, more gold particles were seen and cell viability, as determined by a BacLight® live/dead viability probe, approached zero. At an intermediate concentration of 0.1 mM, the live:dead ratio increased to 4:1. However, when planktonic cells were exposed to this same 0.1 mM concentration, it resulted in a 4‐log reduction in viable counts as determined by plating. The higher resistance of biofilm cells to 0.1 mM gold can be attributed to its binding to the EPS and cell surfaces of the biofilm which ensured a (presumably) low effective cytoplasmic concentration of gold (i.e. no gold crystals were seen in cells by TEM). In addition, SCLM revealed the formation of larger extracellular gold crystals at the substratum (coverslip) level of the biofilms, with a higher proportion of crystals detected beneath pillars (cell cluster structures), suggesting the possibility of unique cell types, more reduced microenvironments at the base of each cluster, or a combination of both. These results suggest that the biomineralization of gold is impacted by biofilm structure.
A fluorimetric method for the estimation of G+C mol% content in microorganisms by thermal denaturation temperature
Authors: Gonzalez J. M. , Saiz‐Jimenez C. 
Published: March 2003

SummaryG+C mol% content in microorganisms is one of the recommended characteristics for the standard description of bacterial species. In this study we present a novel fluorimetric method to estimate the G+C mol% content in microorganisms. Double‐stranded DNA was specifically stained with SYBR Green I, and its thermal denaturalization was followed by measuring a decrease in fluorescence using a real‐time PCR thermocycler. Unlike most previous determinations of G+C mol%, in this study only DNA from microorganisms with an available completely sequenced genome were used to prepare the calibration curves. Calibration curves showed a linear relationship between G+C mol% content and melting temperature and they were performed both in the absence and presence of 30% formamide. This protocol proves to be a rapid and inexpensive method to estimate DNA base ratios of novel microorganisms.