bluuebunny/crossref_metadata_2025_split huggingface dataset:
REPRESENTATION OF CYCLIC PROPERTIES OF AUSTENITIC STEELS WITH PLASTICITY‐INDUCED MARTENSITIC TRANSFORMATION
Authors: Kaleta J , Zie G 
Published: March 2003

This study is part of a wider research project on the cyclic properties, energy cumulation and fatigue life of metastable austenitic steels undergoing a martensitic transformation induced by plastic straining.This paper considers the representation of the σ–ε hysteresis loop over a wide range of strain. A novel, power‐function model of cyclic elastic–plastic material behaviour was used. The model allows the occurrence of a cyclic yield point and the characteristic inflection point of the CSS curve, which separates the single‐phase (austenite) region from the two‐phase (austenite + martensite) one. The plastic strain corresponding to the inflection point is assumed to be a material constant and is termed the martensitic transformation cyclic limit ε1 . The generalization of the model made possible the representation of cyclic softening of the two‐phase material.In addition, the study chose a measurement technique that assisted the estimation of the cyclic plastic strain (ε1 ) inducing the martensitic transformation. The crossed magnetomechanical (Villari) effect was shown to be applicable in detecting the nucleation and estimating the increase of the α′‐martensite content.The identification was performed making use of experimental results obtained from an AISI 304 high nickel content steel. The tests were performed under both increasing and constant plastic strain amplitude. The measured quantities were: total strain εt elastic strain εe , plastic strain εp , stress σ and hysteresis loop area ΔW. The results justify the assumed model.
The crack‐modelling technique: optimization of parameters
Authors: Taylor D. , Carr A. K. 
Published: March 2003

ABSTRACTThe crack‐modelling technique is a method for prediction of fatigue in components using finite element (FE) analysis. The technique, which is based on the estimation of equivalent K factors for stress‐concentrators, has had some initial success in analysing components of complex shape, but this has raised a number of questions about the potential accuracy of the method and its sensitivity to the choice of operating parameters. The present paper reports on a systematic study using four different specimen types and one component geometry. Accurate estimates of equivalent K values are shown to be possible for both sharp notches and blunt notches, loaded in uniaxial tension or bending, using a very simple approach in which the stress distribution from the notch is compared to that from a standard cracked body. The method shows some sensitivity to the optimization routines used, and to some extent to the choice of the standard cracked body. It is relatively insensitive to mesh refinement and can be used with simple, elastic FE models.
Fracture modelling of WC‐Co hardmetals using crystal plasticity theory and the Gurson model
Authors: Connolly P. , McHugh P.E. 
Published: March 2003

ABSTRACTThe behaviour of edge cracks under Mode I loading in the WC–Co material system is studied using the finite element method (FEM). This work focuses on ductile failure mechanisms in the Co binder. A micromechanical approach is taken whereby Co layers are modelled explicitly. An embedding technique is employed. Crystal plasticity theory and J2 flow theory are used to represent plastic deformation in Co ligaments. Areas of high hydrostatic stress, triaxiality and accumulated slip or effective plastic strain are identified within the binder material. The Gurson model is used to model crack growth in the Co ligaments. Fracture resistance curves are obtained giving a relationship between macroscopic material behaviour and microscopic failure mechanisms. Factors effecting the crack growth in single and multiple ligaments are identified.
A microstructural approach to flaw size dependence of strength in engineering ceramics
Authors: Hoshide  , Hiramatsu  
Published: March 2003

ABSTRACTIn this work, microstructural effects on the flaw size dependence of ceramic strength were investigated from aspects of stress analysis in the grain just ahead of the crack tip and also R‐curve behaviour. In the analysis, it was assumed that the stress averaged in one grain just ahead of the crack tip, in ceramics, might control the fracture from a flaw. A microstructurally modified fracture criterion using the averaged stress was established by introducing the R‐curve due to the grain bridging effect for longer cracks. A new R‐curve of an exponential type was proposed for the fracture criterion. The criterion could adequately express the central trend in the dispersal of experimental results in the strength versus flaw size relation. To explain the scatter of results, the size distribution and the crystallographic anisotropy of the grain ahead of the crack tip were examined as dominant factors. The lower bound of strength scatter was estimated from the largest grain size, and the strength dispersion was reduced by decreasing the range of grain size variation. In FEM simulations, each element was regarded as one grain with a different crystallographic orientation, which was randomly selected by using a series of quasi‐uniform random numbers. It was revealed that the scatter of strength due to crystallographic variations was smaller than the strength dispersion caused by a distributed grain size.
Standing contact fatigue testing of a ductile material: surface and subsurface cracks
Authors: Alfredsson  , Olsson  
Published: March 2003

During standing contact fatigue testing of case hardened steel plates, four different fatigue crack types are found: ring/cone; lateral; radial; and median cracks. Fatigue results are presented as load versus cycle number, with endurance limits and initiation laws for the ring/cone and lateral cracks. The behaviour of the radial surface strain outside the contact is altered by the presence of cracks. In particular this makes in situ crack detection possible for the lateral crack.The ductility of the tested material is found to be important for fatigue crack initiation. Numerical elastoplastic computations are used to derive the stress cycles responsible for each crack type. Stress cycles at different locations and in different directions are compared in order to explain why a particular crack type initiates. It is noted that cracks are produced normal to principal stresses of sufficient range, which are tensile sometime during the load cycle. Implications for spalling are discussed.
Combining virtual simulation and physical vehicle test data to optimize durability testing
Authors: FERRY W. B. , FRISE P. R. , ANDREWS G. T. , MALIK M. A. 
Published: March 2003

ABSTRACTThis paper describes an ongoing project to model a vehicle on a computer with a multibody dynamics simulation software package and to merge that work with physical proving ground and laboratory tests in order to shorten vehicle development time. The intention is to mirror as closely as possible the behaviour of a physical vehicle in order to assist in determining its durability characteristics under varying road conditions. This modelling work is important because, if done with sufficient fidelity, it can be used in order to assess vehicle responses by using different suspension components or payloads. Also, potential issues associated with vehicle structure, suspension components or payload positioning can be observed on a computer prior to performing physical tests. The process has the potential to reduce vehicle development cost and time. The virtual dynamic vehicle model has been created by using Automatic dynamic analysis of mechanical systems (ADAMS) software package. The calculated outputs from the model are being compared to force and displacement data collected from actual vehicle on‐road testing or a servo‐hydraulic road test simulator (RTS). The virtual model can be adjusted until the calculated responses are in close agreement with those of the physical vehicle, thus linking the virtual and real‐world results.
Material damping in 6061‐T6511 aluminium to assess fatigue damage
Authors: COLAKOGLU M. , JERINA K. L. 
Published: March 2003

ABSTRACTStudies in fatigue can be summarized into two stages, fatigue crack initiation and crack propagation. Fatigue damage may increase the risk of failure under cyclic load. Energy dissipation, termed damping, occurs in engineering metals and is a function of the cyclic loading history. Damping behaviour of materials has been estimated using many different experimental techniques, and parameters i.e. the loss factor vs. strain amplitude, frequency range, etc. However, micro‐structural changes in the form of fatigue damage are also contributors to damping in engineering materials. In order to measure energy dissipation, a damping monitoring method has been used. Under a constant cyclic load up to the point of fatigue crack initiation, the effects of fatigue on damping factor were studied for 6061‐T6511 aluminium alloy. In the experiments, the stress levels were below yield point, 50% and 70% of ultimate strength. Experimental results showed that the damping factor changes with the number of fatigue cycles. Percentage increase in damping energy was calculated using experimental data.
Isolation and characterization of a chromium‐reducing bacterium from a chromated copper arsenate‐contaminated site
Authors: McLean Jeff S. , Beveridge Terry J. , Phipps David 
Published: March 2003

A Gram‐negative bacterium (CRB5) was isolated from a chromium‐contaminated site that was capable of reducing hexavalent chromium to an insoluble precipitate, thereby removing this toxic chromium species from solution. Analysis of the 16S rRNA from the isolate revealed that it was a pseudomonad with high similarity to Pseudomaonas synxantha. CRB5 was tolerant to high concentrations of chromate (500 mg l−1) and can reduce Cr(VI) under aerobic and anaerobic conditions. It also exhibited a broad range of reduction efficiencies under minimal nutrient conditions at temperatures between 4°C and 37°C and at pH levels from 4 to 9. As reduction increased, so did total cellular protein, indicating that cell growth was a requirement for reduction. Under low nutrient conditions with CRB5 or when using non‐sterile contaminated groundwater from the site, reduction of Cr(VI) was followed by a increase in solution turbidity as a result of the formation of fine‐grained Cr(III) precipitates, most probably chromium hydroxide mineral phases such as Cr(OH)3. Chromium adsorption and precipitation, as observed by transmission electron microscopy coupled with energy dispersive X‐ray spectroscopy (TEM/EDS), revealed that the surfaces of the cells were uniformly stained with bound Cr(III) and amorphous precipitates (as determined by selected area electron diffraction; SAED). A mass balance of chromium in a batch bioreactor revealed that up to 30% of the total Cr was as settable precipitates or bound to cells.
Upstream‐independent ribosomal RNA amplification analysis (URA): a new approach to characterizing the diversity of natural microbial communities
Authors: Yakimov Michail M. , Giuliano Laura , Timmis Kenneth N. , Golyshin Peter N. 
Published: March 2003

Summary Here, we propose an advanced method for recently developed fingerprinting strategies to analyse microbial populations by direct detection of 16S rRNA sequences occurring in natural habitats. The differential display (DD) technique, which is widely used to analyse for eukaryotic gene expression, was optimized to assess bacterial rRNA diversity in environmental samples. Double‐stranded cDNAs of rRNAs were synthesized without a forward primer digested with endonuclease and ligated with a double‐stranded adapter. The fragments obtained were then amplified using an adapter‐specific extended primer and a 16S rDNA universal reverse primer pair displayed by electrophoresis on a polyacrylamide gel. We validated this approach by characterization of a microbial community colonizing a geothermal (48°C) vent system located close to the eruption zone of the south‐east crater of the Mount Etna volcano, Sicily. Analysis of the patterns of abundant 16S rRNA revealed a considerable diversity of metabolically active bacteria phylogenetically clustering within the Crenarchaeota, Cyanobacteria, Firmicutes, Planctomycetales and Thermus divisions. Two sequence phylotypes were affiliated with uncultivated representatives of the recently described candidate division OP10 from a Yellowstone hot spring.
A review of bacterial methyl halide degradation: biochemistry, genetics and molecular ecology
Authors: McDonald I. R. , Warner K. L. , McAnulla C. , Woodall C. A. , Oremland R. S. , Murrell J. C. 
Published: March 2003

SummaryMethyl halide‐degrading bacteria are a diverse group of organisms that are found in both terrestrial and marine environments. They potentially play an important role in mitigating ozone depletion resulting from methyl chloride and methyl bromide emissions. The first step in the pathway(s) of methyl halide degradation involves a methyltransferase and, recently, the presence of this pathway has been studied in a number of bacteria. This paper reviews the biochemistry and genetics of methyl halide utilization in the aerobic bacteria Methylobacterium chloromethanicum CM4T, Hyphomicrobium chloromethanicum CM2T, Aminobacter strain IMB‐1 and Aminobacter strain CC495. These bacteria are able to use methyl halides as a sole source of carbon and energy, are all members of the α‐Proteobacteria and were isolated from a variety of polluted and pristine terrestrial environments. An understanding of the genetics of these bacteria identified a unique gene (cmuA) involved in the degradation of methyl halides, which codes for a protein (CmuA) with unique methyltransferase and corrinoid functions. This unique functional gene, cmuA, is being used to develop molecular ecology techniques to examine the diversity and distribution of methyl halide‐utilizing bacteria in the environment and hopefully to understand their role in methyl halide degradation in different environments. These techniques will also enable the detection of potentially novel methyl halide‐degrading bacteria.
Molecular phylogenetic analyses of reverse‐transcribed bacterial rRNA obtained from deep‐sea cold seep sediments
Authors: Inagaki Fumio , Sakihama Yuri , Inoue Akira , Kato Chiaki , Horikoshi Koki 
Published: March 2003

SummaryA depth profile of naturally occurring bacterial community structures associated with the deep‐sea cold seep push‐core sediment in the Japan Trench at a depth of 5343 m were evaluated using molecular phylogenetic analyses of RNA reverse transcription‐PCR (RT‐PCR) amplified 16S crDNA fragments. A total of 137 clones of bacterial crDNA (complimentary rDNA) phylotypes (phylogenetic types) obtained at three different depths (2–4, 8–10 and 14–16 cm) were identified in partial crDNA sequencings. crDNA phylotypes from the cold seep sediment were dominantly composed of δ‐ and ɛ‐Proteobacteria (36% and 42% respectively). Phylotype analysis of crDNA clone libraries and terminal restriction fragment length polymorphism (T‐RFLP) analysis revealed that the majority of bacterial components shifted from δ‐ Proteobacteria to ɛ‐Proteobacteria with increasing depth. Among the δ‐proteobacterial crDNA clones, the sequences related to the genus Desulfosarcina were dominant. Almost all sequences of crDNA belonging to ɛ‐Proteobacteria were affiliated with the same cluster (ɛ‐CSG: ɛ‐proteobacterial cold seep group), and were closely related with rDNA sequences from deep‐sea hydrothermal vent environments.
The influence of host dynamics on the clonal composition of Escherichia coli populations
Authors: Davis Stephen A. , Gordon David M. 
Published: March 2003

SummarySpecies, be they plant or animal, vary in their capacity for population growth or decline. Populations of the same species may also differ in their capacity for population change. A series of mathematical models were developed with the aim of determining if host population dynamics could influence the clonal composition of the Escherichia coli community in that host population. The biological assumptions
underlying the models are described in some detail. Analytical and numerical approaches
were used to investigate the behaviour of these models. The results demonstrate that
host dynamics can have a profound influence on the E. coli clonal composition of the host population. This outcome is largely independent of the nature of the assumptions underlying the models. The ways in which the predictions of these models may be tested empirically are discussed, as are the implications of these models for understanding the nature of host–bacterial pathogen dynamics.
First insight into the genome of an uncultivated crenarchaeote from soil
Authors: Quaiser Achim , Ochsenreiter Torsten , Klenk Hans‐Peter , Kletzin Arnulf , Treusch Alexander H. , Meurer Guido , Eck Jürgen , Sensen Christoph W. , Schleper Christa 
Published: March 2003

SummaryMolecular phylogenetic surveys based on the characterization of 16S rRNA genes have revealed that soil is an environment particularly rich in microbial diversity. A clade of crenarchaeota (archaea) has frequently been detected among many other novel lineages of uncultivated bacteria. In this study we have initiated a genomic approach for the characterization of uncultivated microorganisms from soil. We have developed a procedure based on a two‐phase electrophoresis technique that allows the fast and reliable purification of concentrated and clonable, high molecular weight DNA. From this DNA we have constructed complex large‐insert genomic libraries. Using archaea‐specific 16S rRNA probes we have isolated a 34 kbp fragment from a 900 Mbp fosmid library of soil DNA. The clone contained a complete 16S/23S rRNA operon and 17 genes encoding putative proteins. Phylogenetic analyses of the rRNA genes and of several protein encoding genes (e.g. DNA polymerase, FixAB, glycosyl transferase) confirmed the specific affiliation of the genomic fragment with the non‐thermophilic clade of the crenarchaeota. Content and structure of the genomic fragment indicated that the archaea from soil differ significantly from their previously studied uncultivated marine relatives. The protein encoding genes gave the first insights into the physiological potential of these organisms and can serve as a basis for future genomic and functional genomic studies.
High bacterial diversity of a waste gas‐degrading community in an industrial biofilter as shown by a 16S rDNA clone library
Authors: Friedrich Udo , Prior Karola , Altendorf Karlheinz , Lipski André 
Published: March 2003

SummaryThe bacterial diversity of an industrial biofilter used for waste gas abatement in an animal‐rendering plant was investigated. A 16S rDNA clone library was generated and 444 clones were screened using computer‐aided amplified ribosomal DNA restriction analysis (ARDRA). Of the screened clones, 60.8% showed unique ARDRA patterns and the remaining 174 clones were clustered into 65 groups. Almost full‐length 16S rDNA sequences of 106 clones were determined and 90.5% of the clones were affiliated with the two phyla Proteobacteria and Bacteroidetes. Alpha‐, Beta‐, and Gammaproteobacteria accounted for 22.1, 17.6 and 18.6% respectively. Minor portions were affiliated with the Actinobacteria (2.0%), Firmicutes and Verrucomicrobia (both 1.0%), and the Deltaproteobacteria and Thermomicrobia (each 0.5%). Only six out of the 106 16S rDNA sequences exhibited similarities of more than 97% to classified bacterial species indicating that a substantial fraction of the clone sequences were derived from unknown taxa. It was also evaluated whether a database containing 281 computer‐simulated bacterial rDNA fragment patterns generated from published reference sequences can be used for identification purposes. The data analysis demonstrated that this was possible only for a small number of clones, which were closely related to described bacterial strains. Rarefaction analysis of ARDRA clusters demonstrated that the 444 clones screened are insufficient to describe the entire diversity of the clone library.
`Canoe closure' of loop ileostomy gives improved cosmesis compared with conventional closure
Authors: Patel  , Frost  , Bearn  , Allan  
Published: March 2003

ObjectiveThe cosmetic appearance of the abdominal scar following closure of loop ileostomy can result in puckering and tethering of the skin, together with a shallow depression. A technique to improve the cosmetic result which also facilitates an easier and more secure closure is described.Patients and methodsA measured elliptical incision, five times greater in length than the ileostomy diameter, is marked. The skin ellipse, subcutaneous fat and ileo‐ stomy are mobilized together. The skin is removed and the ileostomy is closed with a stapler. This technique is compared with conventional techniques with regard to operative stay, complications and cosmetic appearance over an 18‐month period.ResultsThe median operating time has been 50 min and post‐operative stay 5 days. There have been no major complications.ConclusionThis technique allows better access, improves on cosmesis and has a low complication rate.
Restorative proctocolectomy for distal proctocolitis
Authors: Connolly  , Tan  , Morton  , Keighley  
Published: March 2003

BackgroundRestorative proctocolectomy (RP) is usually the surgical treatment of choice for severe ulcerative colitis, but patients with distal disease (rectosigmoid only) are frequently denied operation on the grounds that they are not systemically ill. Nevertheless, they may continue to have high frequency, low volume diarrhoea with severe urgency and bleeding, despite medical therapy.ObjectiveTo report the outcome of RP in `distal disease' compared with `more extensive' disease.Patients and methodsThe results of all patients having RP for ulcerative colitis between February 1983 and February 1997 were reviewed. We excluded patients later found to have Crohn's disease.ResultsRP was used for 34 with `distal' disease compared with 134 with `more extensive' disease. Pre‐operative steroids were used in 9% of the `distal' group compared with 34% in the `more extensive' group. Anastomotic leaks and pelvic sepsis occurred in 3% and 9%, respectively, in the `distal' group compared with 13% and 17% in the `more extensive' group, but these differences were not statistically significant. Pre‐operative steroids significantly influenced anastomotic leaks 22% vs 5% (P = 0.006). Pouch‐related fistulas occurred in 12% of the `distal' group compared with 15% in the remainder. Pouchitis occurred in 44% of the `distal' group: 44% compared with 33% in the remainder. Pouch failure occurred in 3% in `distal' compared with 15% in those with `more extensive' disease.ConclusionThese results imply that RP has a role in the treatment of intractable `distal' colitis, that morbidity is low and urgency is usually eliminated.