bluuebunny/crossref_metadata_2025_split huggingface dataset:
Critical linkages of coalescing microcracks under stress loading
Authors: LI T. , YANG W. 
Published: March 2003

ABSTRACT The fracture process of brittle materials with randomly orientated microcracks critically depends on strong interactions among microcracks and the coalescence path that leads to a fatal crack. In this paper, a model based on the coalescence process for planar orientated microcracks is presented. An energy ratio is defined as the competition between the potential energy release and the new crack surface energy in each coalescence step, which is a token of the excessive driving force for microcrack propagation. A critical linkage dictates the coalescence of microcracks under stress loading. Probabilities of microcrack coalescence dominated by the first linkage and subsequent linkages are analysed for collinear and wavy microcrack arrays in detail.
On ‘multi‐stage’ fatigue life diagrams and the relevant life‐controlling mechanisms in ultrahigh‐cycle fatigue
Authors: MUGHRABI H. 
Published: March 2003

ABSTRACT In recent years, several fatigue studies on different metallic materials have indicated that fatigue failures can occur even at amplitudes below the conventional high‐cycle fatigue (HCF) fatigue limit in the gigacycle or ultrahigh‐cycle fatigue (UHCF) range (number of cycles to failure in excess of ca. 107−108). In the latter case, fatigue failures were observed to originate from internal defects (non‐metallic inclusions). The S–N curves displayed a multi‐stage shape, sometimes with a second lower fatigue limit in the UHCF range.The present paper specifies the conditions under which internal and/or surface fatigue failure can occur at low load levels below the conventional HCF fatigue limit. The relevant fatigue thresholds are discussed for two classes of materials, namely pure single‐phase metallic materials (type I) without internal defects and materials such as steels or cast materials (type II) with internal defects (inclusions or pores). In the case of type II materials, the probability of surface versus internal fatigue is discussed in terms of the volume density, size and location of the inclusions and the relevant cracking mechanisms. It is argued that, in both type I and type II materials, multi‐stage S–N curves or Manson–Coffin plots can be expected under certain conditions.
Durability assessment of automotive aluminium parts
Authors: HEULER P. , BIRK O. 
Published: March 2003

ABSTRACTAutomotive chassis components made from aluminium alloys are often used without any paint or corrosion protection system. Therefore, the fatigue performance under corrosive environments has to be assessed as part of the design process. Literature data reveal a diffuse picture with regard to the extent of fatigue strength reduction due to corrosive environments. On the other hand, there is no standard or well‐established guideline on relevant details of corrosion fatigue tests. Thus the definition of such tests has to be based on individual judgement. After a brief review of corrosion fatigue data and trends collected from the literature, test results are reported for components tested under simplified spectrum load cases in 3.5% NaCl including spectrum variations via omission and truncation. These data backed up by a numerical fatigue life prediction exercise have been used to support decisions on test conditions to be adopted for proof testing.
Fatigue design of structures under thermomechanical loadings
Authors: Charkaluk E. , Bignonnet A. , Constantinescu A. , Dang Van K. 
Published: March 2003

ABSTRACTThis paper presents a global approach to the design of structures that experience thermomechanical fatigue loading, which has been applied successfully in the case of cast‐iron exhaust manifolds. After a presentation of the design context in the automotive industry, the important hypotheses and choices of this approach, based on a thermal 3D computation, an elastoviscoplastic constitutive law and the dissipated energy per cycle as a damage indicator associated with a failure criterion, are first pointed out. Two particular aspects are described in more detail: the viscoplastic constitutive models, which permit a finite element analysis of complex structures and the fatigue criterion based on the dissipated energy per cycle. The FEM results associated with this damage indicator permit the construction of a design curve independent of temperature; an agreement is observed between the predicted durability and the results of isothermal as well as non isothermal tests on specimens and thermomechanical fatigue tests on real components on an engine bench. These results show that thermomechanical fatigue design of complex structures can be performed in an industrial context.
Evaluating the linear normalization technique for deriving J‐resistance curves
Authors: TARPANI J. R. , COLAFEMEA A. A. , BOSE FILHO W. W. , SPINELLI D. 
Published: March 2003

ABSTRACTIn this paper, results from the linear normalization (LN) technique of Reese and Schwalbe for deriving J‐crack resistance (J–R) curves have been compared, related to J–Δa (J‐integral–ductile crack growth) data points, to those obtained from traditional elastic compliance technique. Research results regarding a nuclear grade steel exhibiting a wide range of elastic–plastic fracture resistance agree quite well for both techniques until a certain level of toughness of the material. Below this critical level, LN produces inconsistent results for the sub‐sized compact tension specimens (0.4T C[T]). The evidence suggests that the loss of applicability of the LN technique can be determined on the basis of the η plastic factor (ηpl) for the best linear correlation achieved for ΔPN–Δa (normalised load gradient–ductile crack growth) data.
Micromechanics modelling of ductile fracture in tensile specimens using computational cells
Authors: DOS SANTOS F. F. , RUGGIERI C. 
Published: March 2003

ABSTRACTThis study extends the computational cell framework to model ductile fracture behaviour in tensile specimens. In the computational cell model, ductile damage occurs through void growth and coalescence (by cell extinction) within a thin layer of material located well inside the fracture process zone for the ductile process. Laboratory testing of a high strength structural steel provides the experimental stress–strain data for round bar and circumferentially notched tensile specimens to calibrate the cell model parameters for the material. Numerical simulations employing the micromechanics model reproduce the essential features of the ductile behaviour for the tensile specimens, including the development of intense necking and void growth in the centre of the specimen cross section. The resulting methodology enables the detailed study of ductile failure in small‐scale tensile specimens.
A shakedown model for high‐cycle fatigue
Authors: CRUZ I. , ZOUAIN N. 
Published: March 2003

ABSTRACTThe phenomenological description of the elastic accommodation occurring in a representative volume is implemented in a high‐cycle fatigue criterion. A model for fatigue is directly formulated in the usual continuum mechanics elastic formulation; there, internal variables are introduced to represent the changes in the mesoscopic level of the material. These internal variables do not interact with the macroscopic elastic analysis. The condition for infinite life is the existence of internal variables, independent of time, and rendering admissible stress variations with respect to a fatigue admissibility criterion. The model is applied to experimental data and compared to other criteria.
On the relationship and the short fatigue crack threshold
Authors: McEVILY A. J. , ENDO M. , MURAKAMI Y. 
Published: March 2003

ABSTRACTMurakami and Endo have used the parameter to successfully predict the endurance limits and the threshold levels for components, which contain small defects or cracks. The present paper uses a modified linear–elastic fracture mechanics (LEFM) approach to examine the mechanistic basis for these correlations. The modifications include consideration of the endurance limit rather than the threshold level as a factor controlling fatigue crack growth in the very short crack growth range, consideration of elastic–plastic behaviour, and consideration of the role of crack closure in the wake of a newly formed crack. Predictions based upon the modified LEFM behaviour are found to be consistent with the earlier predictions of Murakami and Endo.
Spatial explicit demography: The effects habitat patch isolation have on vole matrilines
Authors: Johannesen E. , Andreassen H.P. , Ims R.A. 
Published: March 2003

Populations of many species are spatially structured in matrilines, and their dynamics may be determined by matriline specific demographic processes. We examined whether the isolation of habitat patches (i.e. interpatch distance) affected the demography of matrilines in 14 experimentally fragmented populations of the root vole. Matrilines inhabiting the most isolated patches decreased in size over the breeding season, while matrilines in less isolated patches increased. The survival rate of adult females was the main factor underlying the variation in growth rates among matrilines. Low survival when patches were isolated seemed to be due to long‐distance interpatch movements exposing females to increased predation rate.The differential success of matrilines in patchy populations with variable interpatch distances acted to decrease the matrilineal diversity at the population level. Furthermore, isolated patches may function as sinks. Thus spatially explicit landscape features may affect both population demography and genetics.
How large do reserve networks need to be?
Authors: Rodrigues Ana S. L. , Gaston Kevin J. 
Published: March 2003

Reserve networks are essential for the long‐term persistence of biodiversity. To fulfil this goal, they need not only to represent all species to be conserved but also to be sufficiently large to ensure species’ persistence over time. An extensive literature exists on the required size of individual reserves, but to date there has been little investigation regarding the appropriate size of entire networks. The IUCN’s proposal that 10% of each nation be reserved is often presented as a desirable target, but concerns have been raised that this is insufficient and is dictated primarily by considerations of feasibility and politics.We found that the minimum percentage of area needed to represent all species within a region increases with the number of targeted species, the size of selection units, and the level of species’ endemism. This has important implications for conservation planning. First, no single universal target is appropriate, as ecosystems or nations with higher diversity and/or higher levels of endemism require substantially larger fractions of their areas to be protected. Second, a minimum conservation network sufficient to capture the diversity of vertebrates is not expected to be effective for biodiversity in general. Third, the 10% target proposed by the IUCN is likely to be wholly insufficient, and much larger fractions of area are estimated to be needed, especially in tropical regions.
Tropical pasture carbon cycling: relationships between C source/sink strength, above‐ground biomass and grazing
Authors: Wilsey Brian J. , Parent Gabrielle , Roulet Nigel T. , Moore Tim R. , Potvin Catherine 
Published: March 2003

AbstractWe measured net ecosystem CO2 exchange (NEE) in Panamá over C4 pasture plots that varied in grazing intensity. After adjusting for variation in light, there were noticeable effects of grazing‐related variables on CO2 exchange that were largely dependent on the developmental stage of the plant canopy. Above‐ground productivity was positively related to grazing intensity (r2=0.30). Two experimentally grazed fields had significantly lower standing crop biomass but no significant difference in CO2 uptake (24.2 μmol/m2/s) compared with two ungrazed fields (20.3 μmol/m2/s). Grazed fields had significantly lower ecosystem respiration rates (10.3 μmol/m2/s) than did ungrazed fields (17.6 μmol/m2/s). These results suggest that, although these pastures were possible sources of CO2 during the time intervals sampled, the size of the sources tended to be dampened by cattle grazing through reductions in ecosystem respiration. Thus, it appears that disturbance caused by cattle grazing will not always result in an increase in CO2 release from tropical pastures to the atmosphere.
The alpha–beta–regional relationship: providing new insights into local–regional patterns of species richness and scale dependence of diversity components
Authors: Gering Jon C. , Crist Thomas O. 
Published: March 2003

AbstractEcologists frequently regress local species richness on regional species richness to draw inferences about the processes that structure local communities. A more promising approach is to quantify the contributions of alpha and beta diversity to regional diversity (the ABR approach) using additive partitioning. We applied this approach to four local–regional relationships based on data from 583 arboreal beetle species collected in a hierarchically nested sampling design. All four local–regional relationships exhibited proportional sampling, yet the ABR approach indicated that each was produced by a different combination of alpha and beta richness. Using the results of the ABR analysis, we also analysed the scale dependence of alpha and beta using a hierarchical linear model. Alpha diversity contributed less than expected to regional diversity at the finest spatial scale and more than expected at the broadest spatial scale. A switch in relative dominance from beta to alpha diversity with increasing spatial scale suggested scale transitions in ecological processes. Analysing the scale dependence of diversity components using the ABR approach furthers our understanding about the additivity of species diversity in biological communities.
The 2002 European seal plague: epidemiology and population consequences
Authors: C. Harding Karin , Härkönen Tero , Caswell Hal 
Published: March 2003

AbstractWe present the first epidemiological data on the 2002 outbreak of phocine distemper virus (PDV) in European harbour seals (Phoca vitulina). The epizootic curve to date supports a mortality rate and probability of infection identical to that of the 1988 outbreak, which killed 58% of the population. Thus immunity is playing no significant role in the dynamics of the current outbreak. Because the timing of the outbreak is important in determining local mortality rates, we predict higher mortality rates on the European continent than in Great Britain or Ireland. A stochastic model is used to quantify how recurrent epizootics affect the long‐term growth, fluctuation, and persistence of the population. Recurrent PDV epizootics with the observed frequency and severity would reduce the long‐term stochastic growth rate of the harbour seal population by half, and significantly increase the risk of quasi‐extinction.
When leaves act like flowers: how dwarf palms attract their pollinators
Authors: Dufaÿ Mathilde , Hossaert‐McKey Martine , Anstett Marie Charlotte 
Published: March 2003

AbstractIn pollination mutualisms, floral odours are signals advertising the presence and location of rewards. However, in the case of the dwarf palm (Chamaerops humilis) and its species‐specific pollinating weevil (Derelomus chamaeropsis), rewards and advertisements are spatially separated. Flowers provide their specific pollinators with food and sites for both egg laying and larval development, but do not advertise them with floral odours or visually conspicuous petals. Insect behavioural bioassays revealed that pollinators are attracted by scents emitted by the leaves, which provide no rewards. These scents are released by large structures located at the sinuses of the palmate leaf. Such scent‐releasing structures have not been previously reported on palm leaves, and we suggest that they may represent an ‘exaptation’ (pre‐existing trait that acquired new functions). We also propose that such functional crossovers between vegetative and reproductive domains may be more frequent in plants than is currently documented.
Predation‐dependent oviposition habitat selection by the mosquitoCuliseta longiareolata: a test of competing hypotheses
Authors: Kiflawi Moshe , Blaustein Leon , Mangel Marc 
Published: March 2003

AbstractWe investigated the mechanism underlying oviposition habitat selection (OHS) in the mosquitoCuliseta longiareolata. The putative outcome of a trade‐off between the risk of predation and detrimental density dependence, OHS in this species presents an opportunity to test two competing alternatives: (1) a polymorphic scenario, in which a fixed proportion of females constantly avoid ‘predator pools’, while the remainder oviposits at random; and (2) a monomorphic scenario, in which all females oviposit in predator pools with a certain probability. We present a conceptual framework that demonstrates how a simple experimental design – whereby predator incidence in artificial pools is alternated between 0.25 and 0.75 – can distinguish between, or refute, the two scenarios. Given the proportional use, by ovipositing females, of predator‐free pools observed under each treatment, and a bootstrap estimate of the ratio of daily oviposition rates, we find the monomorphic scenario twice as likely as the polymorphic.
Evidence for collective medication in ants
Authors: Christe Philippe , Oppliger Anne , Bancalà Francesco , Castella Grégoire , Chapuisat Michel 
Published: March 2003

AbstractSocial organisms are exposed to many pathogens, and have evolved various defence mechanisms to limit the cost of parasitism. Here we report the first evidence that ants use plant compounds as a collective mean of defence against microorganisms. The wood ants Formica paralugubris often incorporate large quantities of solidified conifer resin into their nests. By creating resin‐free and resin‐rich experimental nests, we demonstrate that this resin inhibits the growth of microorganisms in a context mimicking natural conditions. Such a collective medication probably confers major ecological advantages, and may be an unrecognized yet common feature of large, complex and successful societies.
Temperature‐based population segregation in birch
Authors: Kelly Colleen K. , Chase Mark W. , De Bruijn Anette , Fay Michael F. , Woodward F. Ian 
Published: March 2003

AbstractMean temperature of establishment years for warm‐ and cold‐year subpopulations of a naturally occurring stand of Betula pendula (birch) shows a difference equivalent to that between current temperatures and temperatures projected for 35–55 years hence, given ‘business as usual.’ The existence of ‘pre‐adapted’ individuals in standing tree populations would reduce temperature‐based advantages for invading species and, if general, bring into question assumptions currently used in models of global climate change. Our results demonstrate a methodology useful for investigating the important ecological issue of adaptation vs. range shifts as a means of response to climate change.
Molecular analyses of methyl‐coenzyme M reductase α‐subunit (mcrA) genes in rice field soil and enrichment cultures reveal the methanogenic phenotype of a novel archaeal lineage
Authors: Lueders Tillmann , Chin Kuk‐Jeong , Conrad Ralf , Friedrich Michael 
Published: March 2003

The diversity of methanogen‐specific methyl‐coenzyme M reductase α‐subunit (mcrA/mrtA) genes in Italian rice field soil was analysed using a combination of molecular techniques and enrichment cultures. From 75 mcrA/mrtA clones retrieved from rice field soil, 52 were related to members of the Methanosarcinaceae, Methanosaetaceae and Methanobacteriaceae. However, 19 and four clones formed two novel clusters of deeply branching mcrA sequences, respectively, which could not be affiliated to known methanogens. A new methanogen‐specific fingerprinting assay based on terminal restriction fragment length polymorphism (T‐RFLP) analysis of fluorescently labelled polymerase chain reaction (PCR) products allowed us to distinguish all environmental mcrA/mrtA sequences via group‐specific Sau96I restriction sites. Even genes for the isoenzyme methyl‐coenzyme M reductase two (mrtA) of Methanobacteriaceae present in rice field soil were represented by a unique 470 bp terminal restriction fragment (T‐RF). Both cloning and T‐RFLP analysis indicated a significant representation of novel environmental mcrA sequences in rice field soil (238 bp T‐RF). To identify these mcrA sequences, methanogenic enrichment cultures with rice field soil as inoculum were established with H2/CO2 as substrates at a temperature of 50°C, and these were monitored using molecular tools. In subsequent transfers of these enrichment cultures, cloning and T‐RFLP analysis detected predominantly SSU rRNA genes of rice cluster I (RC‐I), an uncultivated euryarchaeotal lineage discovered previously in anoxic rice field soil. In parallel, both mcrA cloning and T‐RFLP analyses of the enrichment culture identified the more frequent cluster of novel environmental mcrA sequences as belonging to members of RC‐I. Thus, we could demonstrate the genotype and phenotype of RC‐I Archaea by the presence of a catabolic gene in a methanogenic enrichment culture before the isolation of pure cultures.
Molecular detection of marine bacterial populations on beaches contaminated by the Nakhodka tanker oil‐spill accident
Authors: Kasai Yuki , Kishira Hideo , Syutsubo Kazuaki , Harayama Shigeaki 
Published: March 2003

In January 1997, the tanker Nakhodka sank in the Japan Sea, and more than 5000 tons of heavy oil leaked. The released oil contaminated more than 500 km of the coastline, and some still remained even by June 1999. To investigate the long‐term influence of the Nakhodka oil spill on marine bacterial populations, sea water and residual oil were sampled from the oil‐contaminated zones 10, 18, 22 and 29 months after the accident, and the bacterial populations in these samples were analysed by denaturing gradient gel electrophoresis (DGGE) of PCR‐amplified 16S rDNA fragments. The dominant DGGE bands were sequenced, and the sequences were compared with those in DNA sequence libraries. Most of the bacteria in the sea water samples were classified as the Cytophaga–Flavobacterium–Bacteroides phylum, α‐Proteobacteria or cyanobacteria. The bacteria detected in the oil paste samples were different from those detected in the sea water samples; they were types related to hydrocarbon degraders, exemplified by strains closely related to Sphingomonas subarctica and Alcanivorax borkumensis. The sizes of the major bacterial populations in the oil paste samples ranged from 3.4 × 105 to 1.6 × 106 bacteria per gram of oil paste, these low numbers explaining the slow rate of natural attenuation.