bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of loading waveform and microstructure on the fatigue response of titanium aero‐engine compressor disk alloys
Authors: SHANIAVSKI A. A. , LOSEV A. I. 
Published: December 2004

ABSTRACTMicrostructural variations produced from manufacturing processes and their influence on fatigue crack growth in titanium disks were investigated. Charpy‐tests on titanium disk material were performed and materials with fracture energy values in the range of 3.8–19.1 J/cm2 were selected for tests under cyclic loads. Results of Charpy‐tests were compared with fractographic features related to fatigue crack growth in Ti−6Al−3Mo−0.4Si and Ti−6Al−3Mo−2Cr alloys with a two‐phase (α + β) lamellar structure under various cyclic waveforms using specimens made from compressor disks. The material sensitivity to cyclic load waveform can be seen for in‐service disks using a criteria based on fracture energy values determined in Charpy‐tests.A difference in fatigue crack growth periods of 2.5 times was discovered for specimens made from the disk with a filament type microstructure and the mainly globular two‐phase structure of the Ti−6Al−3Mo−0.4Si alloy. The shorter crack growth period correlated with the mainly facetted pattern formation with local zones of fatigue striations when fatigue crack growth is along the planes of the filaments. Fatigue striations are the major fracture surface relief when crack growth occurs in the perpendicular direction to the plane of the filaments. A quantitative fractographic method for estimating the crack growth period for in‐service failed disks was performed for the case of crack development along planes of such microstructural filaments created during the manufacturing process.Specimen tests involving a hold‐time in the cyclic loads are recommended for in‐service accepted titanium disks using a criteria based on the fracture energy value. Selection of disks based on these criteria can indicate a material sensitivity to cyclic load waveforms.
Colonization front of the understorey palmAstrocaryum sciophilumin a pristine rain forest of French Guiana
Authors: Charles‐dominique Pierre , Chave Jerome , Dubois MARC.‐A. , De Granville Jean‐Jacques , Riera Bernard , Vezzoli Cecile 
Published: December 2004

ABSTRACTAimsAstrocaryum sciophilum(Miq.) Pulle (Arecaceae) is an understorey palm, endemic to north‐eastern South America with a patchy distribution. We tested the hypothesis that the spatial distribution of this palm species is not in equilibrium but is slowly colonizing the forest understorey.LocationInventories and seed dispersal studies were conducted in the undisturbed tropical forest close to the Nouragues research station, French Guiana. Additional data were collected in the entire territory of French Guiana.MethodsWe studied the demography ofA. sciophilumon a 20‐ha plot located at the edge of its distribution. The age of the palms was estimated by postulating an exponentially decreasing abundance by age class. Direct seed dispersal experiments were also conducted, to estimate dispersal parameters. The seeds ofA. sciophilumwere dispersed only by rodents. This information was used to parameterize a forest growth simulator, to study the spatial spread of this species.ResultsWithin the sampling plot, the density ofA. sciophilumdropped sharply from about 500 individuals per hectare to zero. The maturation age was estimated to be 170 ± 70 years, and over 55 years with 95% confidence. Seed‐dispersal experiments yielded an average seed dispersal distance of 11 m and a maximum estimated dispersal distance of 125 m across a generational span of 55 years to maturity. Therefore, the maximal estimated colonization speed is 2.3 m/y.ConclusionsEmpirical results and numerical simulations suggest that the boundary of theA. sciophilumpopulation is a colonization front, and that the range of this species is slowly expanding. The implications of this result in respect of palaeoenvironmental changes in this region are discussed.
Climate‐driven changes in shoot density and shoot biomass in Leymus chinensis (Poaceae) on the North‐east China Transect (NECT)
Authors: Renzhong Wang , Qiong Gao 
Published: December 2004

ABSTRACTAim Climate‐driven changes affecting ecosystem primary production have been well documented for many vegetation types, while the effects of climate on plant populations remains unclear. Herein, we address the relationships between climatic variables and shoot density, reproductive allocation and shoot biomass in Leymus chinensis on a large‐scale climatic gradient in 2000.Location Nine sites experiencing similar light regimes, but differing in longitude, precipitation and altitude were selected on the North‐east China Transect (NECT) from 115° to 124°E, around a latitude of 43.5°N.Methods Densities of total, vegetative and reproductive shoots and of shoot biomass were measured twice over the growing season in each site. Climatic data were taken from the climate database of the Laboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese Academy of Sciences and from the local weather stations throughout the NECT.Results Densities of total, vegetative and reproductive shoots increased significantly from the west to the east and from dry to moist along the NECT, and were strongly correlated with annual precipitation (r2 = 0.934, 0.943 and 0.863, respectively) and an aridity index (r2 = 0.809, 0.816 and 0.744, respectively). The average total shoot density at the east end (470/m2) was about three times that at the west (160/m2). Reproductive allocation and shoot biomass for both vegetative and reproductive shoots increased with precipitation and declined with the aridity index along the NECT. There were positive correlations between shoot biomass and annual precipitation for vegetative shoots (P < 0.05, R2 = 0.604) and March precipitation for reproductive shoots (P < 0.05, R2 = 0.533), respectively.Main conclusions These findings suggest that L. chinensis adjusts to decreasing precipitation/increasing aridity by alterations in shoot density, reproductive allocation and shoot biomass along the drought gradient of the NECT.
A retrospective analysis of land cover change using a polygon shape index
Authors: Comber A. J. , Birnie R. V. , Hodgson M. 
Published: December 2004

ABSTRACTAim This study tests the hypothesis that the propensity of land cover patches to change is related to their shape and geometric complexity.Location The analysis is based on a 1000‐km2 area of the Cairngorms in Scotland, incorporating part of Speyside and the high plateau area within the Grampian Mountains.Methods A combined dataset was created by intersecting 1964 land cover data (derived from archive aerial photography) and 1988 land cover data (from the Land Cover of Scotland dataset). A shape index was calculated for each land cover polygon inside a GIS. Information on land cover change was analysed with reference to land cover class and the polygon shape index using a regression analysis.Results For upland seminatural land cover classes, subject to low levels of management, change is related to polygon shape, such that the more complex patches were found to be more susceptible to change. This relationship breaks down where classes are more intensively managed or have been aggregated into mosaic classes.Conclusions Propensity to change was related to shape index for seminatural land cover classes. This implies that at least some landscape processes, such as anthropogenic disturbance of seminatural land covers, can be linked to ecological theory via measurements of spatial pattern. The study also highlighted some of the cartographic issues involved in estimating changes between land cover classes: there are advantages in replacing the ‘cartographic paradigm’ of comparing two derived datasets (in this case land cover maps) with direct comparison of the digital data — air photographs or satellite imagery. Such a direct approach avoids the compounding of errors introduced by the approximation of each successive air photo as a thematic map.
Near extinction of a highly fecund fish: the one that nearly got away
Authors: Sadovy Yvonne , Cheung Wai Lung 
Published: December 2004

AbstractIt is widely assumed that commercial fisheries of highly fecund species are particularly resilient to exploitation, and that, should populations become seriously diminished, economic constraints will force fishing to cease before biological extinction can occur. Indeed, among commercially exploited marine fishes there is not one confirmed global extinction. Here we document, using nonconventional means, a story that not only questions such assumptions but that should also alert us to how little we know about significant fisheries in some parts of the world. Our case study is that of the highly threatened Chinese bahaba, Bahaba taipingensis, a member of the Sciaenidae (the drums or croakers), and an example of a fecund and commercially important group of fishes that appears to be especially vulnerable to fishing. We also demonstrate that the careful use of informal, or traditional, information can provide a powerful, sometimes unique, means of identifying and assessing the status and history of species that might be quietly slipping away before we learn anything about them.
Extinction vulnerability in marine populations
Authors: Dulvy Nicholas K , Sadovy Yvonne , Reynolds John D 
Published: December 2004

AbstractHuman impacts on the world's oceans have been substantial, leading to concerns about the extinction of marine taxa. We have compiled 133 local, regional and global extinctions of marine populations. There is typically a 53‐year lag between the last sighting of an organism and the reported date of the extinction at whatever scale this has occurred. Most disappearances (80%) were detected using indirect historical comparative methods, which suggests that marine extinctions may have been underestimated because of low‐detection power. Exploitation caused most marine losses at various scales (55%), followed closely by habitat loss (37%), while the remainder were linked to invasive species, climate change, pollution and disease. Several perceptions concerning the vulnerability of marine organisms appear to be too general and insufficiently conservative. Marine species cannot be considered less vulnerable on the basis of biological attributes such as high fecundity or large‐scale dispersal characteristics. For commercially exploited species, it is often argued that economic extinction of exploited populations will occur before biological extinction, but this is not the case for non‐target species caught in multispecies fisheries or species with high commercial value, especially if this value increases as species become rare. The perceived high potential for recovery, high variability and low extinction vulnerability of fish populations have been invoked to avoid listing commercial species of fishes under international threat criteria. However, we need to learn more about recovery, which may be hampered by negative population growth at small population sizes (Allee effect or depensation) or ecosystem shifts, as well as about spatial dynamics and connectivity of subpopulations before we can truly understand the nature of responses to severe depletions. The evidence suggests that fish populations do not fluctuate more than those of mammals, birds and butterflies, and that fishes may exhibit vulnerability similar to mammals, birds and butterflies. There is an urgent need for improved methods of detecting marine extinctions at various spatial scales, and for predicting the vulnerability of species.
Transient fluid flow in and around a fault
Authors: Braun J. , M. Munroe S. , Cox S. F. 
Published: December 2004

AbstractWe present the results of simple numerical experiments in which we study the evolution with time of fluid flow around and within a permeable fault embedded in a less permeable porous medium. Fluid movement is driven by an imposed vertical pressure gradient. The results show that fluid flow is controlled by two timescales: τf = Sl2/κF and τF = Sl2/κM, where S is the specific storage of the porous material, l the length of the fault, and κM and κF are the hydraulic conductivities of the porous material and the fault, respectively. Fluid flow and the associated fluid pressure field evolve through three temporal stages: an early phase [t < τf] during which the initial fluid pressure gradient within the fault is relaxed; a second transient stage [τf < t < τF] when fluid is rapidly expelled at one end of the fault and extracted from the surrounding rocks at the other end leading to a reduction in the pressure gradient in the intact rock; a third phase [t < τF] characterized by a steady‐state flow. From the numerical experiments we derive an expression for the steady‐state maximum fluid velocity in the fault and the values of the two timescales, τf and τF. A comparison indicates excellent agreement of our results with existing asymptotic solutions. For km‐scale faults, the model results suggest that steady‐state is unlikely to be reached over geological timescales. Thus, the current use of parameters such as the focusing ratio defined under the assumption of steady‐state conditions should be reconsidered.
Reconstruction of palaeo‐burial history and pore fluid pressure in foothill areas: a sensitivity test in the Hammam Zriba (Tunisia) and Koh‐i‐Maran (Pakistan) ore deposits
Authors: Benchilla L. , Guilhaumou N. , Mougin P. , Jaswal T. , Roure F. 
Published: December 2004

AbstractThe burial and pore fluid pressure history of fluorite ore deposits is reconstructed: (i) at Hammam Zriba–Djebel Guebli along the eastern margin of the Tunisian Atlas; and (ii) at Koh‐i‐Maran within the northern part of the Kirthar Range in Pakistan. Both the deposits are hosted by Late Jurassic carbonate reservoirs, unconformably overlain by Late Cretaceous seals. Microthermometric analyses on aqueous and petroleum fluid inclusions with pressure–volume–temperature–composition (PVTX) modeling of hydrocarbon fluid isochores are integrated with kinematics and thermal 2D basin modeling in order to determine the age of mineralization. The results suggest a Cenozoic age for the fluorite mineralization and a dual fluid migration model for both ore deposits. The PVTX modeling indicates that the initial stage of fluorite cementation at Hammam Zriba occurred under fluid pressures of 115 ± 5 bars and at a temperature close to 130°C. At Koh‐i‐Maran, the F3 geodic fluorite mineralization developed under hydrostatic pressures of 200 ± 10 bars, and at temperatures of 125–130°C. The late increase in temperature recorded in the F3 fluorites can be accounted for by rapid rise of hotter fluids (up to 190°C) along open fractures, resulting from hydraulic fracturing of overpressured sedimentary layers.
The origin of overpressure in ‘old’ sedimentary basins: an example from the Cooper Basin, Australia
Authors: Van Ruth P. , Hillis R. , Tingate P. , Swarbrick R. 
Published: December 2004

AbstractOverpressure in ‘old’ sedimentary basins that have not undergone rapid, recent sedimentation cannot be easily explained using traditional burial‐driven mechanisms. The last significant burial event in the Cooper Basin, Australia, was the Late Cretaceous deposition of the Winton Formation (98.5–90 Ma). Maximum temperature in the basin was attained during the Late Cretaceous, with cooling beginning prior to 75 Ma. Hence, overpressure related to rapid burial or palaeomaximum temperatures (e.g. hydrocarbon generation) must have developed prior to 75 Ma. Retaining overpressure for 75 Ma in ‘old’ basins such as the Cooper Basin requires extremely low seal permeabilities. An alternative explanation is that overpressure in the Cooper Basin has been generated because of an increase in mean stress associated with an increase in horizontal compressive stress since Late Cretaceous times. Structural observations and contemporary stress data indicate that there has been an increase in mean stress of approximately 50 MPa between Late Cretaceous times to that presently measured at 3780 m. The largest measured overpressure in the Cooper Basin is 14.5 MPa at 3780 m in the Kirby 1 well. Hence, disequilibrium compaction driven by increasing mean stress can explain the magnitude of the observed overpressure in the Cooper Basin. Increases in mean stress (tectonic loading) may be a feasible mechanism for overpressure generation in other ‘old’ basins that have undergone a recent increase in horizontal stress (e.g. Anadarko Basin).
Patterns and costs of printed and online journal usage
Authors: Obst Oliver 
Published: December 2004

AbstractThis study in an academic medical sciences library setting examines the correlation of usage of a matched set of print and online titles, the validity of e‐journals usage statistics and the impact of online journals on print journal usage. The print and online usage was determined for 270 journals, both versions of which were available. Print usage was determined annually since 1997 using the reshelving and the error‐copies method. Online usage statistics were delivered by five publishers and corrected for redundant multiple accesses. Print journal usage decreased by 22.3 and 30.2% respectively over each of 2 years after the introduction of online journals. Journals published both in print and online lost 30.4% of their print usage within 2 years. The total loss of usage of print‐only titles in the same period was somewhat higher, at 45.8%. The average correlation between online and print usage is 0.60 and 0.67 respectively. For the examined titles, users accessed the online versions ten times as often as the print version. Two clearly distinguishable groupings emerged: while with Academic Press and Elsevier, e‐journal usage exceeded print usage by a factor of 3 or 4, the e‐journals of Blackwell, HighWire and Springer were used on average 14.6 times as frequently as the corresponding print journals. Each usage of a print article cost 2.79–50.82 €, each usage of an online article 0.31–15.10 €, depending on the publisher. On average, the usage of an online article was 5.4 times cheaper. Within 2–3 years the usage of online journals has outstripped that of print titles by a factor of ten, but the specific spectrum of usage remains much the same as when only print journals alone existed. Print titles not available online suffer a greater decline in usage compared with print/online journals. This confirms that what is read or purchased is determined primarily by ease of access and that there is a steady tendency to reduce the multiplicity of access modes to a manageable few. The availability of journals online seems to have created a new clientele, at least in the case of the German‐language Springer journals. The connection between supplier and supply is much less clear with e‐journals than it is with print titles. Therefore it is very important to stress and encourage the role of the library as the supplier of this sort of information in the university environment. Collection building issues are discussed in the light of the results.
Sulphate‐reducing bacteria induce low‐temperature Ca‐dolomite and high Mg‐calcite formation
Authors: Van Lith Yvonne , Warthmann Rolf , Vasconcelos Crisogono , Mckenzie Judith A. 
Published: December 2004

ABSTRACTIn this study, we demonstrate that sulphate‐reducing bacteria induce anoxic low‐temperature Ca‐dolomite formation both in situ in Lagoa Vermelha and Brejo do Espinho, two neighbouring, dolomite‐precipitating hypersaline lagoons in Brazil, and in laboratory culture experiments. The metabolic activity of sulphate‐reducing bacteria facilitates dolomite formation under anoxic conditions, as demonstrated with experiments using dialysis bags. Overall changes in the chemical conditions of the medium exclusively, without the presence of bacteria, did not result in carbonate precipitation. Only pure cultures of metabolizing sulphate‐reducing bacteria induced Ca‐dolomite and high Mg‐calcite precipitates, indicating that the carbonate nucleation takes place in the locally changed microenvironment around the sulphate‐reducing bacterial cells. Not all pure strains, however, produced Ca‐dolomite under similar conditions, suggesting that the bacterial metabolism, activity and the rate of mineral precipitation have an influence on the type of carbonate formed.
A critical stage in the formation of acid mine drainage: Colonization of pyrite by Acidithiobacillus ferrooxidans under pH‐neutral conditions
Authors: Mielke Randall E. , Pace Danielle L. , Porter Tim , Southam Gordon 
Published: December 2004

ABSTRACTA dominant Acidithiobacillus ferrooxidans ssp. was isolated from the supergene copper deposit in Morenci, Arizona, USA. Washed bacterial suspensions (108 MPN per treatment), in pH‐neutral buffer, were inoculated onto pyrite cubes for 24 h. Heterogeneous bacterial absorption onto the pyrite removed approximately 90% of the viable bacteria from the inoculum. At T = 0, the bacteria were observed primarily in regions enriched in phosphorus. Over 30 days, the bacterial population on the pyrite cubes increased from 1.3 × 107 to 2.9 × 108 bacteria cm−2. During this growth stage, low levels of thiobacilli (228 ± 167 MPN mL−1) were also recovered from the fluid phase; however, this population decreased to zero within 30 days. Growth on pyrite occurred as micrometre‐scale planar microcolonies, a biofilm, coating the mineral surfaces. These microcolonies possessed viable thiobacilli, even after 4 months at ‘circumneutral pH’. Imaging the pyrite cubes using SEM‐EDS and scanning force microscopy demonstrated that the thiobacilli grew as iron oxy‐hydroxide‐cemented cells, leading to the formation of mineralized microcolonies. Removing the iron oxy‐hydroxides with oxalic acid did not dislodge the bacteria, demonstrating that the secondary minerals were not responsible for ‘gluing’ the bacteria to the pyrite surface. Removing organic material, i.e. the cells, by an oxygen plasma treatment revealed the presence of corrosion pits the size and shape of bacteria. Because of the inherent geochemical constraints on pyrite oxidation at neutral pH, the colonization of pyrite under circumneutral pH conditions must be facilitated by the development of an acidic nanoenvironment between the bacteria and the pyrite mineral surface.
Problems in prescribing malaria chemoprophylaxis for travelers
Authors: Dupouy‐Camet Jean , Yera Hélène , Tourte‐Schaeffer Claudine 
Published: December 2004

AbstractTo offer effective malaria chemoprophylaxis for travelers in a country, the physician must know the precise status of malaria there (frequency, resistance), determine the degree of exposure to mosquito bites, evaluate the precise clinical condition of the traveler, and improve the traveler's compliance with treatment by providing good information on potential side‐effects. These side‐effects, sometimes overemphasized in the media, lead to poor compliance, particularly after returning home, and, consequently, increase the risk of acquiring malaria. The recently approved Malarone® could overcome these drawbacks. But its cost is high and its wide use could also lead to the emergence of resistant strains. Therefore, training professionals in travel medicine is important in malaria prevention and decrease the prescription of abusive or inaccurate prophylaxis (e.g., most tourists traveling in organized tours in Asia, with no stay in remote malaria endemic areas, do not need any prophylaxis). In addition, prevention of mosquito bites with repellents, impregnated bed nets, and indoor insecticide‐dispensing devices is still an important tool for controlling malaria in travelers.