Home About us Contact
|
Home About us Contact | ||
|
|
||
Same Scale (same + scale)
Selected AbstractsTaxonomic diversity gradients through geological timeDIVERSITY AND DISTRIBUTIONS, Issue 4 2001J. Alistair Crame Abstract., There is evidence from the fossil record to suggest that latitudinal gradients in taxonomic diversity may be time-invariant features, although almost certainly not on the same scale as that seen at the present day. It is now apparent that both latitudinal and longitudinal gradients increased dramatically in strength through the Cenozoic era (i.e. the last 65 my) to become more pronounced today than at any time in the geological past. Present-day taxonomic diversity gradients, in both the marine and terrestrial realms, are underpinned by the tropical radiations of a comparatively small number of species-rich clades. Quite why these particular taxa proliferated through the Cenozoic is uncertain, but it could be that at least part of the explanation involves the phenomenon of evolutionary escalation. This is, in essence, a theory of biological diversification through evolutionary feedback mechanisms between predators and prey; first one develops an adaptive advantage, and then the other. However, there may also have been some form of extrinsic control on the process of tropical diversification, and this was most likely centred on the phenomenon of global climate change. This is especially so over the last 15 my Various Late Cenozoic (Neogene) vicariant events effectively partitioned the tropics into a series of high diversity centres, or foci. It has been suggested that, in the largest of these in the marine realm (the Indo-West Pacific or IWP centre), a critical patterns of islands acted as a template for rapid speciation during glacioeustatic sea level cycles. The same process occurred in the Atlantic, Caribbean and East Pacific (ACEP) centre, though on a lesser scale. Tropical terrestrial diversity may also have been promoted by rapid range expansions and contractions in concert with glacial cycles (a modified refugium hypothesis). We are beginning to appreciate that an integrated sequence of Neogene tectonic and climatic events greatly influenced the formation of contemporary taxonomic diversity patterns. [source] A comprehensive framework for global patterns in biodiversityECOLOGY LETTERS, Issue 1 2004Robert E. Ricklefs Abstract The present study proposes to reconcile the different spatial and temporal scales of regional species production and local constraint on species richness. Although interactions between populations rapidly achieve equilibrium and limit membership in ecological communities locally, these interactions occur over heterogeneous environments within large regions, where the populations of species are stably regulated through competition and habitat selection. Consequently, exclusion of species from a region depends on long-term regional-scale environmental change or evolutionary change among interacting populations, bringing species production and extinction onto the same scale and establishing a link between local and regional processes. [source] Multiscale estimation of GPS velocity fieldsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2009Carl Tape SUMMARY We present a spherical wavelet-based multiscale approach for estimating a spatial velocity field on the sphere from a set of irregularly spaced geodetic displacement observations. Because the adopted spherical wavelets are analytically differentiable, spatial gradient tensor quantities such as dilatation rate, strain rate and rotation rate can be directly computed using the same coefficients. In a series of synthetic and real examples, we illustrate the benefit of the multiscale approach, in particular, the inherent ability of the method to localize a given deformation field in space and scale as well as to detect outliers in the set of observations. This approach has the added benefit of being able to locally match the smallest resolved process to the local spatial density of observations, thereby both maximizing the amount of derived information while also allowing the comparison of derived quantities at the same scale but in different regions. We also consider the vertical component of the velocity field in our synthetic and real examples, showing that in some cases the spatial gradients of the vertical velocity field may constitute a significant part of the deformation. This formulation may be easily applied either regionally or globally and is ideally suited as the spatial parametrization used in any automatic time-dependent geodetic transient detector. [source] Dense Alumina,Zirconia Coatings Using the Solution Precursor Plasma Spray ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Dianying Chen For the first time, dense coatings have been made by the solution precursor plasma spray (SPPS) process. The conditions are described for the deposition of dense Al2O3,40 wt% 7YSZ (yttria-stabilized zirconia) coatings; the coatings are characterized and their thermal stability is evaluated. X-ray diffraction analysis shows that the as-sprayed coating is composed of ,-Al2O3 and tetragonal ZrO2 phases with grain sizes of 72 and 56 nm, respectively. The as-sprayed coating has a 95.6% density and consists of ultrafine splats (1,5 ,m) and unmelted spherical particles (<0.5 ,m). The lamellar structure, typical of conventional plasma-sprayed coatings, is absent at the same scale in the SPPS coating. The formation of a dense Al2O3,40 wt% 7YSZ coating is favored by the lower melting point of the eutectic composition, and resultant superheating of the molten particles. Phase and microstructural thermal stabilities were investigated by heat treatment of the as-sprayed coating at temperatures of 1000°,1500°C. No phase transformation occurs, and the grain size is still in the nanometer range after the 1500°C exposure for 2 h. The coating hardness increases from 11.8 GPa in the as-coated condition to 15.8 GPa following 1500°C exposure due to a decrease in coating porosity. [source] Attitudes towards the doctor,patient relationship: a prospective study in an Asian medical schoolMEDICAL EDUCATION, Issue 11 2008Kheng Hock Lee Context, Patient-centredness is an accepted guiding principle for health system reform, patient care and medical education. Although these attitudes are strongly linked with cultural values, few studies have examined attitudes towards patient-centredness in a cross-cultural setting. Objectives, This prospective study evaluated attitudes towards patient-centredness in a cohort of Asian medical students and examined changes in these attitudes in the same students on completion of their junior clinical clerkships. Methods, The study was conducted in a cohort of 228 medical students entering Year 3 in medical school. The Patient,Practitioner Orientation Scale (PPOS), a validated instrument which scores an individual's level of patient-centredness, was used. Results, Being female and having personal experience of continuing care were significantly associated with higher scores. Students in the USA were previously reported to have similar ,caring' but higher ,sharing' scores on the same scale. At the end of the junior clinical clerkship, there were improvements in the ,caring' subscale, but no change or a reduction in ,sharing'. Students who did not have previous personal experience with continuing care experienced a greater increase in overall PPOS score. Conclusions, When compared with students in the USA, the students in our study appear to have a lower propensity to view the doctor,patient relationship as a partnership. This may be a reflection of differences in cultural norms and expectations of doctor,patient interaction in different societies. Our finding that attitudes towards patient-centredness did not decline over the course of the year, which contrasts with findings of other studies, may be attributed to various factors and warrants further study. [source] Evaluating planetesimal bow shocks as sites for chondrule formationMETEORITICS & PLANETARY SCIENCE, Issue 11 2004Fred J. CIESLA The formation of such shocks is modeled using a piecewise parabolic method (PPM) code under a variety of conditions. The results of this modeling are used as a guide to study chondrule formation in a one-dimensional, finite shock wave. This model considers a mixture of chondrule-sized particles and micron-sized dust and models the kinetic vaporization of the solids. We found that only planetesimals with a radius of ,1000 km and moving at least ,8 km/s with respect to the nebular gas can generate shocks that would allow chondrule-sized particles to have peak temperatures and cooling rates that are generally consistent with what has been inferred for chondrules. Planetesimals with smaller radii tend to produce lower peak temperatures and cooling rates that are too high. However, the peak temperatures of chondrules are only matched for low values of chondrule wavelength-averaged emissivity. Very slow cooling (<,100s of K/hr) can only be achieved if the nebular opacity is low, which may result after a significant amount of material has been accreted into objects that are chondrule-sized or larger, or if chondrules formed in regions of the nebula with small dust concentrations. Large shock waves of approximately the same scale as those formed by gravitational instabilities or tidal interactions between the nebula and a young Jupiter do not require this to match the inferred thermal histories of chondrules. [source] Multi-scale sampling and statistical linear estimators to assess land use status and changeAPPLIED VEGETATION SCIENCE, Issue 2 2009D. Rocchini Abstract Question: Multi-temporal analysis of remotely sensed imagery has proven to be a powerful tool for assessment and monitoring of landscape diversity. Here the feasibility of assessing land-use diversity and land-use change was tested at multiple scales and over time by means of statistical linear estimators based on a probabilistic sampling design. Location: The study area (the district of Asciano, Tuscany, Italy) is characterized by erosional forms typical of Pliocene claystone (i.e. calanchi and biancane) that have been subject to the phenomenon of biancane reworking over the past 50 years, mainly owing to the expansion of intensive agriculture. Methods: Cells at two different scales (50 m × 50 m and 10 m × 10 m) were classified by two operators according to a multilevel legend, using 1954 and 2000 aerial photographs. Inter-operator agreement and accuracy were tested by Cohen's K coefficient. Total land cover estimation for each class was carried out using a multistage estimator, while the variance was estimated by means of the Wolter estimator. Field-based information on plant species composition was recorded in order to test for a relationship between land use and plant community composition by anova and indicator species analysis. Results: Agreement between photointerpreters and accuracy were significantly higher than those expected by chance, proving that the approach proposed is reproducible, as long as proper quality assurance methods are used. Our data show that, at the two scales considered (50 m × 50 m and 10 m × 10 m), crops have increased against woodlands and semi-natural areas, the latter showing the highest and significantly different mean species richness. Meanwhile, an increase in the coverage of trees and shrubs was found within the semi-natural areas, probably as a result of secondary succession occurring on typical landscape elements such as biancane. Conclusions: Inferential statistics made it possible to acquire quantitative information on the abundance of land cover classes, allowing formal multi-temporal and multi-scale analysis. Sampling design-based statistical linear estimators were found to be a powerful tool for assessing landscape trends considering both time expenditure and other costs. They make it possible to maintain the same scale of analysis over time series data and to detect both coarse- and fine-grained changes in spatial patterns. [source] Decadal changes (1996,2006) in coastal ecosystems of the Chagos archipelago determined from rapid assessmentAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2009Andrew R.G. Price Abstract 1.The atolls and islands comprising Chagos are a biodiversity hotspot of global conservation significance in a remote part of the central Indian Ocean. 2.This study examines the condition of the archipelago's coastal ecosystems by rapid environmental assessment at 21 sites/islands, which were also investigated a decade earlier using the same methodology. Major changes in ecosystem structure and environmental disturbance were determined. 3.Coral fish abundance was significantly lower in 2006 than 1996. Decrease in the physical structural complexity of the reefs, as a result of coral bleaching and mortality induced by the 1998 warming event, may have been a contributing factor. 4.Evidence of collecting/fishing was significantly greater in 2006 than 1996. This is attributed mainly to an illegal fishery for holothurians (sea cucumbers), which has expanded over recent years and now exerts substantial pressure on the resource. The significant decline observed in beach wood, a readily accessible fuel for fishing camps, is consistent with this. 5.Solid waste on islands was high (median 2 to 20 items m,1 beach) in both 1996 and 2006. Potentially harmful biological impacts, determined from other studies, include entanglement, toxic effects and provision of transport for invasives or other ,hitchhiker' species. 6.Significantly higher bird abundances were recorded in protected areas than ,unprotected' areas, attributed mainly to absence of predation by rats. 7.Rapid assessment augments more comprehensive ecosystem investigations. It provides a valuable snapshot of environmental conditions based upon a broad suite of features (ecosystems and disturbances) determined, concurrently, within the same site inspection quadrats and using the same scale of assessment. Copyright © 2009 John Wiley & Sons, Ltd. [source] Refinement of protein crystal structures using energy restraints derived from linear-scaling quantum mechanicsACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2005Ning Yu A novel method is proposed in which combined restraints derived from linear-scaling semiempirical quantum-mechanical (QM) calculations and X-ray diffraction data are combined to refine crystal structures of proteins. Its performance has been tested on a small protein molecule, bovine pancreatic trypsin inhibitor (BPTI). The refinement involves minimization of the sum of a geometric energy function and an X-ray target function based on either the least-squares residual or the maximum-likelihood formalism. For comparison, similar refinement runs have also been performed using energy restraints derived from the force field available in the Crystallography & NMR System (CNS) program. The QM refinements were carried out with weights that were varied by several orders of magnitude and the optimal weights were identified by observing the trend in the final free R values, QM heats of formation and coordinate root-mean-square deviations (r.m.s.d.s) from the crystal structure. It is found that the QM weights are typically smaller but generally on the same scale as the molecular-mechanics (MM) weights for the respective X-ray target functions. The crystallographic R, free R, real-space R values and correlation coefficients based on the structures refined with the energy restraints derived from our QM calculations and Engh and Huber parameters are comparable, suggesting that the QM restraints are capable of maintaining reasonable stereochemistry to a similar degree as the force-field parameters. A detailed inspection of the structures refined with the QM and MM energy restraints reveals that one of the common differences between them and the crystal structure is that the strained bond angles in the crystal structure are corrected after energetically restrained refinements. Systematic differences in certain bond lengths between the QM-refined structures and the statistical averages of experimental structures have also been observed and discussed. [source] Visible and invisible effects of hurricanes on forest ecosystems: an international reviewAUSTRAL ECOLOGY, Issue 4 2008A. E. LUGO Abstract Hurricanes have visible and invisible effects on forests. The visible effects are dramatic, noticeable over the short-term and relatively well documented in the literature. Invisible effects are less understood as they require well-focused research both in the short- and long-term time scales. This review of the literature on hurricane effects focuses on the Neotropics and the temperate zone of North America. The material is organized according to a heuristic model that distinguishes between immediate effects (0 to 3 years), immediate responses (0 to 20 years), trajectories of responses (0 to 100 years) and long-term legacies (>100 years). It is suggested that the ecological role of hurricanes involves six principal effects: 1. they change the ecological space available to organisms; 2. they set organisms in motion; 3. they increase the heterogeneity of the landscape and the variability in ecosystem processes; 4. they rejuvenate the landscape and its ecosystems and redirect succession; 5. they shape forest structure, influence their species composition and diversity and regulate their function; and 6. they induce evolutionary change through natural selection and ecological creativity through self-organization. A new approach to hurricane research will study hurricanes at the same scale at which they operate (i.e., across latitudes and longitudes and over disturbed and undisturbed landscapes). This research will require networks of observation platforms located along expected hurricane paths to facilitate forest structure and functioning observations across gradients of hurricane frequency and intensity. This research will also require use of remote sensing and automated wireless technology, hardened to survive hurricane-strength winds and floods to assure real time measurements of the characteristics of hurricanes and ecosystem responses. No progress will be forthcoming in the understanding of hurricane effects if we do not learn to quantify objectively the energy dissipation of hurricanes on the full grid of affected forests as the hurricane passes over a landscape. [source] Comparative analysis of efficiency, environmental impact, and process economics for mature biomass refining scenariosBIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 2 2009Mark Laser Abstract Fourteen mature technology biomass refining scenarios , involving both biological and thermochemical processing with production of fuels, power, and/or animal feed protein , are compared with respect to process efficiency, environmental impact , including petroleum use, greenhouse gas (GHG) emissions, and water use,and economic profitability. The emissions analysis does not account for carbon sinks (e.g., soil carbon sequestration) or sources (e.g., forest conversion) resulting from land-use considerations. Sensitivity of the scenarios to fuel and electricity price, feedstock cost, and capital structure is also evaluated. The thermochemical scenario producing only power achieves a process efficiency of 49% (energy out as power as a percentage of feedstock energy in), 1359 kg CO2 equivalent avoided GHG emissions per Mg feedstock (current power mix basis) and a cost of $0.0575/kWh ($16/GJ), at a scale of 4535 dry Mg feedstock/day, 12% internal rate of return, 35% debt fraction, and 7% loan rate. Thermochemical scenarios producing fuels and power realize efficiencies between 55 and 64%, avoided GHG emissions between 1000 and 1179 kg/dry Mg, and costs between $0.36 and $0.57 per liter gasoline equivalent ($1.37 , $2.16 per gallon) at the same scale and financial structure. Scenarios involving biological production of ethanol with thermochemical production of fuels and/or power result in efficiencies ranging from 61 to 80%, avoided GHG emissions from 965 to 1,258 kg/dry Mg, and costs from $0.25 to $0.33 per liter gasoline equivalent ($0.96 to $1.24/gallon). Most of the biofuel scenarios offer comparable, if not lower, costs and much reduced GHG emissions (>90%) compared to petroleum-derived fuels. Scenarios producing biofuels result in GHG displacements that are comparable to those dedicated to power production (e.g., >825 kg CO2 equivalent/dry Mg biomass), especially when a future power mix less dependent upon fossil fuel is assumed. Scenarios integrating biological and thermochemical processing enable waste heat from the thermochemical process to power the biological process, resulting in higher overall process efficiencies than would otherwise be realized , efficiencies on par with petroleum-based fuels in several cases. © 2009 Society of Chemical Industry and John Wiley & Sons, Ltd [source] A microhistological survey on the trees of a relict subtropical laurel forest from the Macaronesian Islands as a base for assessing vertebrate plant dietBOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2005PATRICIA MARRERO A microhistological collection and its respective key on the leaves and fleshy fruits produced by the mostly endemic trees that integrate the relict laurel forest in the Macaronesian Islands are presented. Epidermal tissues from the adaxial and abaxial surfaces of leaves and fruits of 23 species were extracted by scraping and prepared on individual microscope slides. An optical microscope with a camera lucida fixed at magnifications of ×400 was used to analyse and to draw the morphological traits of epidermal tissues to the same scale. Furthermore, quantitative data for those congeneric species were also obtained by using an image analysis program system. The results indicate that this microhistological method permits the differentiation of practically all species of trees present in the Macaronesian laurel forest. Furthermore, most species belonging to the same taxa (genus or family) show a general common pattern in the morphology of the different epidermal traits. Lastly, despite the effort that constitutes the preparation of plant microhistological collections of a determined ecosystem, it is of basic importance because it makes possible the performance of feeding ecological studies of several herbivorous and frugivorous vertebrate species. These results provide crucial information that elucidates the functioning of the food web and energetic flux dynamics of the Macaronesian laurel forest ecosystem. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 148, 409,426. [source] | ||||||||||||||||