bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fatigue of cemented hip replacements under torsional loads
Authors: McCormack B.A.O. , Prendergast P.J. , O’Dwyer B. 
Published: March 2003

ABSTRACTFatigue resistance of hip replacement prostheses is becoming ever more important as the operation is carried out on younger and more active patients. Torsional loading of the implant, which occurs especially during activities, such as rising from a chair or climbing stairs, is implicated in the failure process. To examine fatigue failure of the implant–bone fixation, which is made using polymethylmethacrylate cement, an experimental model was designed and 16 specimens tested at torsional moments of 50 Nm and 80 Nm to both 1 and 2 million cycles. The numbers and lengths of cracks initiated under cyclic loading were quantified using dye penetrant to highlight the cracks and a profile projector to magnify them. The majority of cracks initiated from the PMMA/metal and PMMA/bone interfaces, more often than from pores in the PMMA. A bimaterial fracture mechanics analysis confirmed that the interfaces are too weak to sustain in vivo levels of cyclic loading. It is proposed that, under torsional loading, fatigue failure of PMMA fixated implants originates from pores located on the interfaces.
Energy criteria of multiaxial fatigue failure
Authors: Macha  , Sonsino  
Published: March 2003

ABSTRACTThis paper contains a review of energy‐based criteria of multiaxial fatigue. The criteria have been divided into three groups, depending on the kind of strain energy density per cycle which is assumed as a damage parameter. They are: (i) criteria based on elastic strain energy for high‐cycle fatigue; (ii) criteria based on plastic strain energy for low‐cycle fatigue; and (iii) criteria based on the sum of plastic and elastic strain energies for both low‐ and high‐cycle fatigue. The criteria which take into account strain energy density in the critical plane seem to be the most promising. In the energy approach to multiaxial fatigue there is an important unsolved problem, i.e. the evaluation of energy, especially plastic strain energy density, from closed stress–strain hysteresis loops under random loadings.
Review of fatigue monitoring of agile military aircraft
Authors: Molent L. , Aktepe B. 
Published: March 2003

Fatigue monitoring of airframes has developed over the decades to the stage where it is now incumbent for all fighter type aircraft to be fitted with an airborne fatigue monitoring system. These systems typically collect operational data for the calculation of the safe‐life or the inspection interval of the airframe.This paper presents a state‐of‐the‐art review of fatigue monitoring systems of agile military aircraft. It reviews and comprehensively examines the techniques used in individual aircraft fatigue monitoring programs, and examines current systems and practises. Based on experience from Australian fatigue monitoring programs, it highlights some of the potential pitfalls in the systems and techniques. It also investigates the issues of strain gauge utilization and calibration, collection of flight parameter data, data integrity, comparisons with fatigue test results and fatigue damage models. Some of the problems with current systems are highlighted and requirements for future fatigue monitoring systems are suggested.This review has determined that there is little uniformity in the fatigue management practices of operators and that many aspects of the fatigue management process have been overlooked by some structural integrity managers. Also, very few of the papers reviewed specified the philosophy or aims of their monitoring systems.
The characteristics of fatigue under isothermal and thermo‐mechanical load in Cr–Ni–Mo cast hot work die steel
Authors: FANG J. R. , JIANG Q. C. , GUAN Q. F. , WANG S. Q. 
Published: March 2003

ABSTRACTHigh temperature isothermal fatigue (IF) and in‐phase thermo‐mechanical fatigue (TMF) tests in load control were carried out in cast hot work die steel. At the same load amplitude, the fatigue lives obtained in the in‐phase TMF tests are lower than those obtained in the isothermal tests. Observations of fracture surface and the response of stress–strain reveal that cyclic creep in the tensile direction occurs and the intergranular cracks dominate in TMF tests, whereas cyclic creep in the compressive direction occurs and the path of the crack growth is mainly transgranular in IF tests. A model of life prediction, based on the Chaboche law, was discussed. Damage coefficients that are functions of the maximum temperature and the variation of temperature are introduced in the model so as to evaluate TMF lives in load control. With this method, the lifetime prediction gives results corresponding well to experimental data.
Characteristics of microcrack initiation in CuNiAl shape memory alloy
Authors: LU Y. H. , QIAO L. J. , CHU W. Y. 
Published: March 2003

ABSTRACTThe mechanism of microcrack initiation in CuNiAl shape memory alloy was investigated through in situ tensile tests under optical microscopy, scanning electron microscopy and transmission electron microscopy. The results indicated that various martensite phases appeared first around a notch tip upon loading, and then microcracks initiated along the martensite/parent interface. The small martensite regions could transform back to the parent phase not only upon unloading but also upon loading or during crack propagation. There was no dislocation emission and motion before martensite formation. The slip bands formed after the crack had propagated a definite distance, and the microcracks nucleated and the cracks propagated either along the slip bands or the martensite/parent interface.
A non‐local theory applied to high cycle multiaxial fatigue
Authors: Morel F. , Palin‐Luc T. 
Published: March 2003

ABSTRACT The stress gradient effect on the fatigue limit is an important factor which has to be taken into account for an efficient transfer of fatigue data from laboratory tests to design of industrial components. A short review of some multiaxial high cycle fatigue criteria considering this effect is presented. On the basis of the two local mesoscopic approaches of Papadopoulos, two new non‐local high cycle multiaxial fatigue criteria are developed. These proposals are based on the concept of volume influencing fatigue crack initiation. Their predictions are compared with experimental multiaxial fatigue data on four materials (a mild steel, two high strength steels and a spheroidal graphite cast iron). The accuracy of the two local Papadopoulos criteria and of the non‐local proposals are compared and discussed, together with the physical interpretation of the threshold defining the volume influencing fatigue crack initiation.
Variable amplitude fatigue of spot welds
Authors: HENRYSSON H.‐F. 
Published: March 2003

ABSTRACTA new method for fatigue life prediction of spot welds subjected to variable amplitude loads is proposed. The method is based on the concept of crack closure and is experimentally verified with three different specimens and four different load signals with variable amplitude. Experimental fatigue lives were found to be within a factor of three from the predicted lives. To start with, the stress intensity factor history at the spot weld is calculated with a finite element analysis. Then, crack closure is taken into account: the crack opening stress intensity factor, which is assumed to be constant, is determined from the maximum and minimum in the history. All stress intensities lower than the crack opening level are filtered from the calculated history. The filtered history is then analysed with rain flow count. Finally, fatigue life is predicted with the Palmgren–Miner cumulative damage rule together with an effective (closure‐free) curve for spot welds. In addition, single overload tests were carried out to investigate the assumption of a constant crack opening stress.
Material aspects and design methods for high‐pressure‐components of hard steels subject to cyclical loads
Authors: BACHER‐HÖCHST M. , LINKEWITZ T. , MÜHLEDER F. 
Published: March 2003

ABSTRACTThis paper deals with high cycle fatigue design methods for internal pressure loaded components of diesel injection systems. Intensive studies of material fatigue behaviour and the derivation of fatigue calculation methods in combination with adequate finite element calculations led to successful prediction methods. One interesting approach is the description of notch effects with volume integrals, which is outlined in more detail.
Spatio‐temporal variation in Markov chain models of subtidal community succession
Authors: Hill M. Forrest , Witman Jon D. , Caswell Hal 
Published: March 2003

AbstractIn this paper we ask whether succession in a rocky subtidal community varies in space and time, and if so how much affect that variation has on predictions of community dynamics and structure. We describe succession by Markov chain models based on observed frequencies of species replacements. We use loglinear analysis to detect and quantify spatio‐temporal variation in the transition matrices describing succession. The analysis shows that space and time, but not their interaction, have highly significant effects on transition probabilities. To explore the ecological importance of the spatio‐temporal variability detected in this analysis, we compare the equilibria and the transient dynamics among three Markov chain models: a time‐averaged model that includes the effects of space on succession, a spatially averaged model that include the effects of time, and a constant matrix that averages over the effects of space and time. All three models predicted similar equilibrium composition and similar rates of convergence to equilibrium, as measured by the damping ratio or the subdominant Lyapunov exponent. The predicted equilibria from all three models were very similar to the observed community structure. Thus, although spatial and temporal variation is statistically significant, at least in this system this variation does not prevent homogeneous models from predicting community structure.
Jasmonate‐deficient plants have reduced direct and indirect defences against herbivores
Authors: Thaler Jennifer S. , Farag Mohamed A. , Paré Paul W. , Dicke Marcel 
Published: March 2003

AbstractPlants employ a variety of defence mechanisms, some of which act directly by having a negative effect on herbivores and others that act indirectly by attracting natural enemies of herbivores. In this study we asked if a common jasmonate‐signalling pathway links the regulation of direct and indirect defences in plants. We examined the performance of herbivores (direct defence) and the attraction of natural enemies of herbivores (indirect defence) to wild‐type tomato plants and mutant plants that are deficient in the production of the signalling hormone jasmonic acid. Wild‐type plants supported lower survivorship of caterpillars compared with jasmonic acid‐deficient plants. Damaged wild‐type plants were more attractive to predaceous mites compared with undamaged wild‐type plants, whereas damaged jasmonate‐deficient plants were not more attractive to predators. Damaged wild‐type plants induced a greater production of volatile compounds (primarily the sesquiterpene β‐caryophyllene and the monoterpenes α‐pinene, β‐pinene, 2‐carene and β‐phellandrene) compared with damaged jasmonate‐deficient plants. Treating jasmonate‐deficient plants with exogenous jasmonic acid restored both the direct and indirect defence capabilities, demonstrating that jasmonic acid is an essential regulatory component for the expression of direct and indirect plant defence.
Genetically engineered Pseudomonas: a factory of new bioplastics with broad applications
Authors: Olivera Elías R. , Carnicero David , Jodra Ruth , Miñambres Baltasar , García Belén , Abraham Gustavo A. , Gallardo Alberto , Román Julio San , García José L. , Naharro Germán , Luengo José M. 
Published: March 2003

SummaryNew bioplastics containing aromatic or mixtures of aliphatic and aromatic monomers have been obtained using genetically engineered strains of Pseudomonas putida. The mutation (–) or deletion (Δ) of some of the genes involved in the β‐oxidation pathway (fadA−, fadB−ΔfadA or Δfad BA mutants) elicits a strong intracellular accumulation of unusual homo‐ or co‐polymers that dramatically alter the morphology of these bacteria, as more than 90% of the cytoplasm is occupied by these macromolecules. The introduction of a blockade in the β‐oxidation pathway, or in other related catabolic routes, has allowed the synthesis of polymers other than those accumulated in the wild type (with regard to both monomer size and relative percentage), the accumulation of certain intermediates that are rapidly catabolized in the wild type and the accumulation in the culture broths of end catabolites that, as in the case of phenylacetic acid, phenylbutyric acid, trans‐cinnamic acid or their derivatives, have important medical or pharmaceutical applications (antitumoral, analgesic, radiopotentiators, chemopreventive or antihelmintic). Furthermore, using one of these polyesters (poly 3‐hydroxy‐6‐phenylhexanoate), we obtained polymeric microspheres that could be used as drug vehicles.
Reduction of Fe(III) oxide by methanogens in the presence and absence of extracellular quinones
Authors: Bond Daniel R. , Lovley Derek R. 
Published: March 2003

SummaryFive methanogens (Methanosarcina barkeri MS, Methanosphaera cuniculi 1R7, Methanobacterium palustre F, Methanococcus voltaei A3 and Methanolobus vulcani PL‐12/M) were investigated for their ability to reduce Fe(III) oxide and the soluble quinone anthraquinone‐2,6‐disulphonate (AQDS). Two species (M. barkeri and M. voltaei) reduced significant amounts of Fe(III) oxide using hydrogen as the electron donor, and 0.1 mM AQDS greatly accelerated Fe(III) reduction by these organisms. Although Fe(III) appeared to inhibit growth and methanogenesis of some strains, hydrogen partial pressures under donor‐limited conditions were much lower (<0.5 Pa) in the presence of Fe(III) than in normal media (1–10 Pa) for all species except for M. vulcani. These results demonstrate that electrons were transferred to Fe(III) by hydrogen‐utilizing methanogens even when growth and methanogenesis were inhibited. All species except the obligate methylotroph M. vulcani were able to reduce AQDS when their growth substrates were present as electron donors, and rates were highest when organisms used hydrogen as the electron donor. Purified soil humic acids could also be reduced by the AQDS‐reducing methanogens. The ability of methanogens to interact with extracellular quinones, humic acids and Fe(III) oxides raises the possibility that this functional group of organ‐isms contributes to Fe(III) and humic acid reduction under certain conditions in the environment and provides an alternative explanation for the inhibition of methanogenesis in some Fe(III)‐containing ecosystems.
Isolation of small‐subunit rRNA for stable isotopic characterization
Authors: MacGregor Barbara J. , Brüchert Volker , Fleischer Swantje , Amann Rudolf 
Published: March 2003

SummarySmall‐subunit ribosomal RNA (SSU rRNA) has several characteristics making it a good candidate biomarker compound: it is found in bacteria, archaea and eukaryotes; it is quickly degraded extracellularly, hence SSU rRNA extracted from a sample probably derives from the currently active population; it includes both conserved and variable regions, allowing the design of capture probes at various levels of phylogenetic discrimination; and rRNA sequences from uncultured species can be classified by comparison with the large and growing public database. Here we present a method for isolation of specific classes of rRNAs from mixtures of total RNA, employing biotin‐labelled oligonucleotide probes and streptavidin‐coated paramagnetic beads. We also show that the stable carbon isotope composition of Escherichia coli total RNA and SSU rRNA reflects that of the growth substrate for cells grown on LB, M9 glucose and M9 acetate media. SSU rRNA is therefore a promising biomarker for following the flow of carbon, and potentially nitrogen, in natural microbial populations. Some possible applications are discussed.
Analysis of the microbial community structure and function of a laboratory scale enhanced biological phosphorus removal reactor
Authors: Levantesi Caterina , Serafim Luísa S. , Crocetti Gregory R. , Lemos Paulo C. , Rossetti Simona , Blackall Linda L. , Reis Maria A. M. , Tandoi Valter 
Published: March 2003

SummaryA laboratory scale sequencing batch reactor (SBR) operating for enhanced biological phosphorus removal (EBPR) and fed with a mixture of volatile fatty acids (VFAs) showed stable and efficient EBPR capacity over a four‐year‐period. Phosphorus (P), poly–β–hydroxyalkanoate (PHA) and glycogen cycling consistent with classical anaerobic/aerobic EBPR were demonstrated with the order of anaerobic VFA uptake being propionate, acetate then butyrate. The SBR was operated without pH control and 63.67 ± 13.86 mg P l−1 was released anaerobically. The P% of the sludge fluctuated between 6% and 10% over the operating period (average of 8.04 ± 1.31%). Four main morphological types of floc‐forming bacteria were observed in the sludge during one year of in‐tensive microscopic observation. Two of them were mainly responsible for anaerobic/aerobic P and PHA transformations. Fluorescence in situ hybridization (FISH) and post‐FISH chemical staining for intracellular polyphosphate and PHA were used to determine that ‘Candidatus Accumulibacter phosphatis’ was the most abundant polyphosphate accumulating organism (PAO), forming large clusters of coccobacilli (1.0–1.5 µm) and comprising 53% of the sludge bacteria. Also by these methods, large coccobacillus‐shaped gammaproteobacteria (2.5–3.5 µm) from a recently described novel cluster were glycogen‐accumulating organisms (GAOs) comprising 13% of the bacteria. Tetrad‐forming organisms (TFOs) consistent with the ‘G bacterium’ morphotype were alphaproteobacteria, but not Amaricoccus spp., and comprised 25% of all bacteria. According to chemical staining, TFOs were occasionally able to store PHA anaerobically and utilize it aerobically.
Metabolic shifts in hypersaline microbial mats upon addition of organic substrates
Authors: Grötzschel Stefan , Abed Raeid M. M. , De Beer Dirk 
Published: March 2003

SummaryThe responses of hypersaline microbial mats to the addition of acetate, glycolate or glucose were investigated using oxygen, pH and sulphide microsensors. Changes in community structure were investigated with molecular techniques. Acetate addition inhibited respiration in the photic zone, stimulated respiration in the aphotic zone and had no effect on gross photosynthesis. Glycolate addition strongly increased both respiration and gross photosynthesis in the photic zone. Thus, glycolate and acetate were probably consumed in those regions of the mat where these substrates are usually formed. Moreover, photosynthesis was only stimulated by increased respiration and concomitant CO2 production in the photic zone which indicates that the photosynthetic and respiratory populations must be present in close proximity to each other. Glucose addition had an unexpected negative effect on the microbial population, strongly inhibiting both respiration and gross photosynthesis within hours. After four days, oxygen profiles in the light were equal to those measured in the dark. After replacing the water phase with unamended water, photosynthesis and respiration recovered within a week. None of the physiological changes were accompanied by detectable shifts in the cyanobacterial or the overall microbial community. The mechanism of inhibition of photosynthesis by glucose requires further investigation.
Non‐invasive determination of plant‐associated bacteria in the phyllosphere of plants
Authors: Gau Achim E. , Dietrich Christof , Kloppstech Klaus 
Published: March 2003

SummaryEpiphytic living Pseudomonas strains isolated from different Malus domestica cultivars were transformed with two reporter genes [green fluorescent protein (gfp) and luciferase (luxAB)]. The establishment and distribution of these bacteria on sterile, in vitro‐propagated, and thus genetically identical, Malus domestica plants were continuously analysed with a cooled, back‐illuminated, charge‐coupled‐device (CCD) camera system. The combination of the assessment of bioluminescence and the use of a CCD camera offer an intriguing method to study, non‐invasively and in real time, plant–microbe interactions as well as the colonization of the phyllosphere by microorganisms. Here we report on the applicability and sensitivity of the method with the goal to investigate quantitatively the interaction of symbiotic and pathogenic microorganisms with the corresponding host plant. It will be shown that the three bacterial isolates of the genus Pseudomonas studied, differ considerably with respect to their establishment on the host plants. It will also be shown that the chosen host apple variety has an impact on the activity of the bacterial cultivars. Analysis by a laser scanning fluorescence microscope provides the first evidence for the mode by which the epiphytic microorganisms interact with the plant.
Diversity of siderophore‐mediated iron uptake systems in fluorescent pseudomonads: not only pyoverdines
Authors: Cornelis Pierre , Matthijs Sandra 
Published: March 2003

SummaryFluorescent pseudomonads are γ‐proteobacteria known for their capacity to colonize various ecological niches. This adaptability is reflected by their sophisticated and diverse iron uptake systems. The majority of fluorescent pseudomonads produce complex peptidic siderophores called pyoverdines or pseudobactins, which are very efficient iron scavengers. A tremendous variety of pyoverdines has been observed, each species producing a different pyoverdine. This variety can be used as an interesting tool to study the diversity and taxonomy of fluorescent pseudomonads. Other siderophores, including newly described ones, are also produced by pseudomonads, sometimes endowed with interesting properties in addition to iron scavenging, such as formation of complexes with other metals or antimicrobial activity. Factors other than iron limitation, and different regulatory proteins also seem to influence the production of siderophores in pseudomonads and are reviewed here as well. Another peculiarity of pseudomonads is their ability to use a large number of heterologous siderophores via different TonB‐dependent receptors. A first genomic analysis of receptors in four different fluorescent pseudomonads suggests that their siderophore ligand repertoire is likely to overlap, and that not all receptors recognize siderophores as ligands.
Monitoring the colonization of monuments by bacteria: cultivation versus molecular methods
Authors: Laiz Leonila , Piñar Guadalupe , Lubitz Werner , Saiz‐Jimenez Cesareo 
Published: March 2003

SummaryBuilding materials commonly used in wall paintings and monuments (mortar, limestone and sandstone) were inoculated with an artificial consortium composed of 14 microorganisms and incubated for 6 months at 28°C. The colonization of the different materials by the consortium was investigated. Culture‐independent techniques revealed the presence of a diversity of bacteria, whereas culture‐dependent techniques yielded mainly spore‐forming bacteria. The data suggest that plating leads to an overestimation of the number of spore‐forming bacteria with respect to quiescent vegetative forms; the latter are less easily cultured, but are readily detected by culture‐independent techniques.