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Short Distances (short + distance)
Selected AbstractsOn the Magnet Effect of Price LimitsEUROPEAN FINANCIAL MANAGEMENT, Issue 5 2007David Abad G1; G14; D44 Abstract The ,magnet' or ,gravitational' effect hypothesis asserts that, when trading halts are rule-based, investors concerned with a likely impediment to trade advance trades in time. This behaviour actually pushes prices further towards the limit. Empirical studies about the magnet effect are scarce, most likely because of the unavailability of data on rule-based halts. In this paper, we use a large database from the Spanish Stock Exchange (SSE), which combines intraday stock specific price limits and short-lived rule-based call auctions to stabilise prices, to test this hypothesis. The SSE is particularly well suited to test the magnet effect hypothesis since trading halts are price-triggered and, therefore, predictable to some extent. Still, the SSE microstructure presents two particularities: (i) a limit-hit triggers an automatic switch to an alternative trading mechanism, a call auction, rather than a pure halt; (ii) the trading halt only lasts 5 minutes. We find that, even when prices are within a very short distance to the price limits, the probability of observing a limit-hit is unexpectedly low. Additionally, prices either initiate reversion (non limit-hit days) or slow down gradually (limit-hit days) as they come near the intraday limits. Finally, the most aggressive traders progressively become more patient as prices approach the limits. Therefore, both the price patterns and the trading behaviour reported near the limits do not agree with the price limits acting as magnetic fields. Consequently, we conclude that the switching mechanism implemented in the SSE does not induce traders to advance their trading programs in time. [source] Sampling and analytical plus subsampling variance components for five soil indicators observed at regional scaleEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2009B. G. Rawlins Summary When comparing soil baseline measurements with resampled values there are four main sources of error. These are: i) location (errors in relocating the sample site), ii) sampling errors (representing the site with a sample of material) iii) subsampling error (selecting material for analysis) and iv) analytical error (error in laboratory measurements). In general we cannot separate the subsampling and analytical sources of error (since we always analyse a different subsample of a specimen), so in this paper we combine these two sources into subsampling plus analytical error. More information is required on the relative magnitudes of location and sampling errors for the design of effective resampling strategies to monitor changes in soil indicators. Recently completed soil surveys of the UK with widely differing soils included a duplicate site and subsampling protocol to quantify ii), and the sum of iii) and iv) above. Sampling variances are estimated from measurements on duplicate samples , two samples collected on a support of side length 20 m separated by a short distance (21 m). Analytical and subsampling variances are estimated from analyses of two subsamples from each duplicate site. After accounting for variation caused by region, parent material class and land use, we undertook a nested analysis of data from 196 duplicate sites across three regions to estimate the relative magnitude of medium-scale (between sites), sampling and subsampling plus analytical variance components, for five topsoil indicators: total metal concentrations of copper (Cu), nickel (Ni) and zinc (Zn), soil pH and soil organic carbon (SOC) content. The variance components for each indicator diminish by about an order of magnitude from medium-scale, to sampling, to analytical plus subsampling. Each of the three fixed effects (parent material, land use and region) were statistically significant for each of the five indicators. The most effective way to minimise the overall uncertainty of our observations at sample sites is to reduce the sampling variance. [source] The effect of overload on the fatigue crack growth behaviour of 304 stainless steel in hydrogenFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2001M. H. Kelestemur Fatigue crack growth (FCG) behaviour and its characteristics following tensile overloads were investigated for AISI 304 stainless steel in three different atmospheres; namely dry argon, moist air and hydrogen. The FCG tests were performed by MTS 810 servohydraulic machine. CT specimens were used for the tests and crack closure measurements were made using an extensometer. FCG rates of 304 stainless steel at both dry argon and moist air atmospheres have shown almost the same behaviour. In other words, the effect of moisture on FCG of this material is very small. However, in a hydrogen atmosphere, the material showed considerably higher crack growth rate in all regimes. In general, for all environments, the initial effect of overloads was to accelerate the FCG rate for a short distance (less than a mm) after which retardation occurred for a considerable amount of time. The main causes for retardation were found as crack blunting and a long reinitiation period for the fatigue crack. Regarding the environmental effect, the overload retardation was lowest in a hydrogen atmosphere. This low degree of retardation was explained by a hydrogen embrittlement mechanism. In a general sense, hydrogen may cause a different crack closure mechanism and hydrogen induced crack closure has come in to the picture. Scanning electron microscope and light microscope examinations agreed well with the above results. [source] An eastern Tethyan (Tibetan) record of the Early Jurassic (Toarcian) mass extinction eventGEOBIOLOGY, Issue 3 2006P. B. WIGNALL ABSTRACT A record of the Early Jurassic mass extinction event is reported from eastern Tethyan (Tibetan) locations for the first time. In the Mount Everest region a thick Lower Jurassic carbonate formation, here named the Yungjia Formation, is developed within the predominantly clastic Triassic,Jurassic succession. Within the formation a sharp transition from peloidal packstones/grainstones to thin-bedded, pyritic micrite-shales interbeds records a sharp pulse of deepening and development of dysoxic bottom waters. Both the lithiotid bivalves and the lituolid foraminifera are important constituents of the lower Yungjia Formation but they disappear at this flooding surface or a short distance below it. This extinction event is comparable to that seen at the base of the Pliensbachian/Toarcian boundary in western Tethyan platform carbonates but the Tibetan events occurred late in the Toarcian Stage as indicated by nannofossil biostratigraphy and C isotope chemostratigraphy. The Early Jurassic extinction event (and the associated spread of oxygen-poor waters) was therefore not synchronous throughout the Tethyan region. [source] Homogeneity analysis of Turkish meteorological data setHYDROLOGICAL PROCESSES, Issue 8 2010Sinan Sahin Abstract The missing value interpolation and homogeneity analysis were performed on the meteorological data of Turkey. The data set has the observations of six variables: the maximum air temperature, the minimum air temperature, the mean air temperature, the total precipitation, the relative humidity and the local pressure of 232 stations for the period 1974,2002. The missing values on the monthly data set were estimated using two methods: the linear regression (LR) and the expectation maximization (EM) algorithm. Because of higher correlations between test and reference series, EM algorithm results were preferred. The homogeneity analysis was performed on the annual data using a relative test and four absolute homogeneity tests were used for the stations where non-testable series were found due to the low correlation coefficients between the test and the reference series. A comparison was accomplished by the graphics where relative and absolute tests provided different outcomes. Absolute tests failed to detect the inhomogeneities in the precipitation series at the significance level 1%. Interestingly, most of the inhomogeneities detected on the temperature variables existed in the Aegean region of Turkey. It is considered that theseinhomogeneities were mostly caused by non-natural effects such as relocation. Because of changes at topography at short distance in this region intensify non-random characteristics of the temperature series when relocation occurs even in small distances. The marine effect, which causes artifical cooling effect due to sea breezes has important impact on temperature series and the orograhpy allows this impact go through the inner parts in this region. Copyright © 2010 John Wiley & Sons, Ltd. [source] Use of experimenter-given directional cues by a young white-handed gibbon (Hylobates lar)1JAPANESE PSYCHOLOGICAL RESEARCH, Issue 3 2004YOICHI INOUE Abstract:, A three-year-old white-handed gibbon (Hylobates lar) was tested in terms of her ability to follow experimenter-given directional cues in an object-choice task. Four conditions were run: the experimenter baited one of two cups and then gave one of the following four directional cues: (a) pointing at the baited cup from a short distance (5 cm); (b) pointing at the target from a long distance (20 cm); (c) orienting body, head, and eyes toward the baited cup; and (d) orienting eyes only toward the baited cup. A young gibbon was able to use all of the experimenter-given cues to obtain hidden food rewards. Several possible reasons for the gibbon's superior performance in comparison to other primates reported in the existing literature were discussed. [source] Morphology of deltoid origin and end tendons , a generic modelJOURNAL OF ANATOMY, Issue 6 2008J. N. A. L. Leijnse Abstract This study provides a model of the complex deltoid origin and end tendons, as a basis for further anatomical, biomechanical and clinical research. Although the deltoid is used in transpositions with upper limb paralysis, its detailed morphology and segmentation has not been object of much study. Morphologically, the deltoid faces two distinct challenges. It closely envelops a ball joint, and it reduces its width over a short distance from a very wide origin along clavicle, acromion and spina scapula, to an insertion as narrow as the humerus. These challenges necessitate specific morphological tendon adaptations. A qualitative model for these tendons is developed by the stepwise transformation of a unipennate muscle model into a functional deltoid muscle. Each step is the solution to one of the mentioned morphological challenges. The final model is of an end tendon consisting of a continuous succession of bipennate end tendon blades centrally interspaced by unipennate tendon parts. The origin tendon consists of lamellae that interdigitate with the end tendon blades, creating a natural segmentation. The model is illustrated by qualitative dissection results. In addition, in view of a proliferation of terms found in the literature to describe deltoid tendons, tendon concepts are reviewed and the systematic use of the unique and simple terminology of ,origin and end tendons' is proposed. [source] The ghost of hybridization past: niche pre-emption is not the only explanation of apparent monophyly in island endemicsJOURNAL OF ECOLOGY, Issue 3 2005TOMÁ? Summary 1Published molecular phylogenies show that many plant groups in the Canary Islands are monophyletic despite the fact that the short distance between the islands and Africa should have led to many independent colonization events. 2Low establishment rates of later migrants owing to niche pre-emption by earlier, already established, colonists could explain these patterns. The apparent monophyly is, however, also compatible with multiple colonizations, with later colonizers making only limited contributions to the total gene pool (and therefore being undetected in the molecular phylogeny) or being wiped out by stochastic processes. 3Experimental evidence for niche pre-emption and species-specific interactions in plants is weak, with survival and establishment of a newly immigrant species depending on the overall composition of the community, rather than on the presence of a particular ,ecologically similar' species. 4Although niche pre-emption might have contributed to the observed patterns of monophyly, we do not think that phylogeographical data from Macaronesia can be taken as evidence for its action in the geological past. [source] The ParB protein of Streptomyces coelicolor A3(2) recognizes a cluster of parS sequences within the origin-proximal region of the linear chromosomeMOLECULAR MICROBIOLOGY, Issue 5 2002Dagmara Jakimowicz Summary The mycelial prokaryote Streptomyces coelicolor A3(2) possesses a large linear chromosome (8.67 Mb) with a centrally located origin of replication (oriC). Recently, chromosome partitioning genes (parA and parB) and putative ParB binding sites (parS sequences) were identified in its genome. The S. coelicolor chromosome contains more parS sequences than any other bacterial chromosome characterized so far. Twenty of the 24 parS sequences are densely packed within a relatively short distance (, 200 kb) around oriC. A series of in vitro and in vivo experiments showed that S. coelicolor ParB protein interacts specifically with the parS sequences, albeit with a rather low affinity. Our results suggested that the binding of ParB is not only determined by the parS sequence, but also by the location of target DNA close to oriC. The unusually high number and close proximity to each other of the parS sites, together with in vivo and in vitro evidence that multiple ParB molecules may assemble along the DNA from an initial ParB,parS complex, suggest that a large DNA segment around the replication origin may form a massive nucleoprotein complex as part of the replication-partitioning cycle. [source] Finite element analysis of vent/hand hole designs for corrugated fibreboard boxesPACKAGING TECHNOLOGY AND SCIENCE, Issue 1 2007Jongkoo Han Abstract Corrugated fibreboard is an economical and efficient material for fabricating shipping containers that are widely used for the distribution, transportation and storage of goods. Corrugated fibreboard is usually considered to be an orthotropic material because the principal fibre directions, machine direction (MD) and cross-machine direction (CD), are identical to the fibres in paperboard, which has apparent directional property differences. The purpose of this study is to investigate the principal design parameters of ventilation holes and hand holes in the faces of the shipping container, (corrugated fibreboard boxes), using finite element analysis (FEA). Various designs of ventilation holes were studied with respect to stress distribution and stress level. It was found that the appropriate pattern and location of the ventilation holes were vertical oblong-shaped and symmetrically positioned within a certain extent of distance to the right and left from the centre of the front and rear faces of the boxes. On the other hand, the appropriate location and pattern of the hand holes were a short distance from the centre to the top of the boxes on both side faces. The appropriate pattern was a modified shape, such as the radius of curvature of both sides in horizontal oblong. The pattern and location of both the ventilation holes and the hand holes determined by the FEA simulation generally agreed well with laboratory experimental results. The decrease in compression strength of the box could be minimized with identical area of the ventilation holes if the length of the major axis of the ventilation hole is less than 1/4 of the depth of the box and the ratio of the minor axis to the major axis is 1/3.5,1/2.5, provided that even-numbered holes are located symmetrically. Copyright © 2006 John Wiley & son, Ltd. [source] Formation of luminescence centres under excitation with electron beams in PbWO4 and ZnWO4 crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005S. Chernov Abstract The leading edge of intrinsic luminescence pulse in PbWO4 and ZnWO4 single crystals is studied. The rise of luminescence intensity is observed after excitation with electron beam pulse. The luminescence rise is shown to be a result of luminescence center formation via electron-hole recombination within spatially correlated pairs. An electron of a geminate electron-hole pair of PbWO4 crystal self-traps and stimulates self-trapping of a hole at a close distance. In the ZnWO4 crystal a hole of a geminate electron-hole pair self-traps and stimulates self-trapping of the electron producing a W5+ center at a short distance. The rise-time of luminescence depends on spatial separation of recombining components. It is short even at 80 K (100 ns in PbWO4 and 10 ns in ZnWO4). The reasons for different rise time and different spatial distribution of electron and hole self-trapped centers are discussed. [source] Attenuating PP/PET bicomponent melt blown microfibersPOLYMER ENGINEERING & SCIENCE, Issue 2 2003Rongguo Zhao This research investigated the attenuation of polypropylene (PP)/poly(ethylene terephthalate) (PET) bicomponent (bico) filaments during the melt blowing (MB) process. It was found that both mono- and bi-component filaments attenuated from several hundred micrometers to a few micrometers in the first 5 centimeters from the die. However, fiber diameter distributions were found to be broad in these regions. The filaments were attenuated much slower but exhibited narrower diameter distributions as they moved further from the die. The diameters of bico MB filaments were between those of 100% PP and 100% PET filaments. The PET component in a bico filament controls the final fiber diameter. During melt blowing, filaments were aligned orderly with the airflow direction in a short distance near the die. Filament entanglements started at about 2.5 cm from the die and became more and more randomly oriented as the distance-from-the-die (DFD) increased. The fiber diameter distribution of bico filaments was broader than that of 100% PP filaments. A higher airflow rate led to a narrower fiber size distribution for bico filaments. [source] Design Considerations for Plate and Frame Ultrafiltration Modules by Computational Fluid Dynamics Analysis,THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2006Mauro M. Dal-Cin Abstract Pressure and flow maldistributions were studied in a full-scale industrial plate and frame ultrafiltration module, operating in a Z flow pattern, for the recovery of used motor oils. Solutions were obtained using (1) a three-dimensional solution of the Navier-Stokes equation using computational fluid dynamics and (2) Bernoulli's equation and a momentum balance in one dimension. Fluid decelerations and accelerations generated pressure increases and decreases in the distributor and collector, respectively, biasing the flow distribution to the last channel. Several modifications to the original design were evaluated; the most effective was larger distributor and collector diameters, which greatly improved the uniformity of the flow distribution and transmembrane pressure, and reduced the overall pressure drop in a bank. A variable diameter distributor and collector module was designed using the 1-D model. Flow distribution was significantly improved but also yielded an undesirable overall higher pressure drop and a pressure maldistribution in the bank. The maldistribution of the main inlet manifold to the distributors in the first bank was strongly dependent on the module design. The flow distribution across the width of a channel became uniform within a short distance, essentially eliminating the need to consider this design aspect any further. Flows at the bank outlets, and hence inlets of the following bank, showed uniform lateral distribution in all cases, suggesting that future modelling work can be limited to a fraction of the module width, based on symmetry, in order to gain computational efficiency. On a étudié les mauvaises distributions de pression et d'écoulement dans un module d'ultrafiltration à plateaux et à cadres à l'échelle industrielle, fonctionnant dans un schéma d'écoulement en Z, pour la récupération des huiles de moteurs usées. Des solutions ont été obtenues avec (1) une solution tridimensionnelle de l'équation de Navier-Stokes utilisant la mécanique des fluides par ordinateur, et (2) l'équation de Bernoulli et un bilan de quantité de mouvement unidimensionnel. Les décélérations et accélérations de fluide entraînent des augmentations et diminutions de pression dans le distributeur et le collecteur, respectivement, ce qui fausse la distribution d'écoulement dans le dernier canal. On a évalué plusieurs modifications du concept original; la plus efficace sont des diamètres de distributeur et de collecteur plus larges, qui permettent d'améliorer grandement l'uniformité de la distribution d'écoulement et la pression transmembranaire, et qui réduisent la perte de charge globale dans une batterie. Un module de distributeur et de collecteur de diamètres variables a été conçu au moyen du modèle 1D. La distribution d'écoulement est significativement améliorée mais cause une perte de charge globale plus grande indésirable et une mauvaise distribution de pression dans la batterie. La mauvaise distribution du manifold d'entrée principal vers les distributeurs dans la première batterie est fortement dépendante de la conception du module. La distribution d'écoulement dans toute la largeur d'un canal devient uniforme sur une courte distance, éliminant essentiellement le besoin d'approfondir cet aspect de la conception. L'écoulement en sortie de batteries et donc à l'entrée des batteries suivantes montre une distribution latérale uniforme dans tous les cas, ce qui suggère que le travail de modélisation futur peut se limiter à une fraction de la largeur du module, pour des raisons de symétrie, pour gagner de l'efficacité numérique. [source] Large, larger, largest , a family of cluster-based tantalum copper aluminides with giant unit cells.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2009This is the second of two papers, where we discuss the cluster structures of a novel family of cluster-based intermetallic phases of unprecedented complexity: cF444-Al63.6Ta36.4 (AT-19), a = 19.1663,(1),Å, V = 7040,Å3, cF(5928,,,x)-Al56.6Cu3.9Ta39.5, x = 20 (ACT-45), a = 45.376,(1),Å, V = 93,428,Å3 and cF(23,,256,,,x)-Al55.4Cu5.4Ta39.1, x = 122 (ACT-71), a = 71.490,(4),Å, V = 365,372,Å3. The space group is in all three cases. The structures can be described as packings of clusters such as fullerenes, dodecahedra, pentagonal bifrusta and Friauf polyhedra. A characteristic feature of the two larger structures are nets of hexagonal bipyramidal Ta clusters (h.b.p.). The extremely short distance of 2.536,2.562,Å between their apical Ta atoms indicates unusually strong bonding. The large h.b.p. nets are sandwiched between slabs of Friauf polyhedra resembling the structure of the , phase. [source] Vaginal Ring and Round Ligament of the Uterus in the Female CatANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 4 2009A. Watson Summary The peritoneum was examined for the existence of a vaginal ring and the round ligament of the uterus was dissected through the inguinal region in eleven embalmed adult female cats. In all cats, there was no evidence of a peritoneal evagination into the inguinal canal. There was no vaginal ring and no vaginal process. The round ligament of the uterus passed through the inguinal canal and disintegrated in the fascia a short distance beyond the superficial inguinal ring. [source] Radiofrequency exposure on fast patrol boats in the Royal Norwegian Navy,an approach to a dose assessmentBIOELECTROMAGNETICS, Issue 5 2010Valborg Baste Abstract Epidemiological studies related to radiofrequency (RF) electromagnetic fields (EMF) have mainly used crude proxies for exposure, such as job titles, distance to, or use of different equipment emitting RF EMF. The Royal Norwegian Navy (RNoN) has measured RF field emitted from high-frequency antennas and radars on several spots where the crew would most likely be located aboard fast patrol boats (FPB). These boats are small, with short distance between the crew and the equipment emitting RF field. We have described the measured RF exposure aboard FPB and suggested different methods for calculations of total exposure and annual dose. Linear and spatial average in addition to percentage of ICNIRP and squared deviation of ICNIRP has been used. The methods will form the basis of a job exposure matrix where relative differences in exposure between groups of crew members can be used in further epidemiological studies of reproductive health. Bioelectromagnetics 31:350,360, 2010. © 2010 Wiley-Liss, Inc. [source] Comparative floral structure and systematics of Pelagodoxa and Sommieria (Arecaceae)BOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2004FRED W. STAUFFER Floral structure is compared in Pelagodoxa and Sommieria (Arecaceae, Arecoideae). Male flowers have three free, imbricate sepals, three basally congenitally united and apically valvate petals, and six stamens. Anthers are dorsifixed and dehiscence introrse. The sterile gynoecium is tricarpellate. Female flowers have three free, imbricate sepals and three free, imbricate petals, which are slightly fused with the sepals at the base. Four to six staminodes are congenitally united at the base and fused with the ovary for a short distance. The gynoecium is syncarpous. Carpels are almost equal in early development; later the gynoecium becomes pseudomonomerous. The three stigmatic branches are equally developed, apical and sessile. The carpels are (syn-)ascidiate up to the level of the placenta and (sym-)plicate above. Each carpel has one ovule, in the sterile carpels it is aborted at anthesis. The fertile ovule is erect up to anthesis and pendant afterwards because of the bulging out of the ovary. Pollen tube transmitting tracts (PTTT) encompass the secretory epidermis of the ventral slits of each carpel. Floral structure in Pelagodoxa and Sommieria supports the sister group relationship between the two genera suggested in recent molecular phylogenies and reflects their close relationships to a major clade of pseudomonomerous arecoid palms from the Indo-Pacific region. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 146, 27,39. [source] 3144: Cataract formation after incorporation of radioactive iodineACTA OPHTHALMOLOGICA, Issue 2010C DALKE Purpose The ocular lens is one of the most radiosensitive organs in mammals and a pathological sign after exposure to ionising radiation is the formation of cataracts. We generated a mouse model to mimic the situation after the accident in the Chernobyl power plant. Methods Pregnant and nursing FBV-mice were treated with iodine131 for diaplacentar and galactogen transfer to the litter. The offspring which incorporated the radioiodine were examined for lens opacities at the age of 6 and 12 months. Iodine131 is a beta radiation emitting nuclide with a short half live of 8 days. Mothers were injected twice with 100 kBq I-131, on day 14 post conception and day 6 post natal. Cataracts were investigated at 6 and 12 months of age using a slit lamp. Results Depending on the litter size and weight, a single progeny incorporates between 8 to 14 % of entire activity. More than 50% of the injected activity is transmitted from the mother to the entire offspring. Iodine is accumulated in the thyroid and an average thyroid dose of 3.7 Gy was calculated. Because of the short distance between the thyroid and the eye, a lens dose of 0.5 Gy was estimated. In the FBV mice, we observed at the age of 6 months two cataracts among 15 irradiated lenses (13%), but none among 7 unirradiated controls. At the age of 12 months, almost all lenses showed cortical cataracts in both groups. However, there were 17 nuclear cataracts among 66 irradiated lenses (25%), but only 1 among 16 controls (6%). Conclusion These preliminary data indicate that this method is sensitive enough to detect the cataract-causing potential of low-dose ionizing radiation in the mouse. However, for detailed analysis larger cohorts and quantification of the data are necessary. [source] Effects of Habitat Fragmentation on Effective Dispersal of Florida Scrub-JaysCONSERVATION BIOLOGY, Issue 4 2010AURÉLIE COULON Aphelocoma c,rulescens; dispersión; flujo génico; fragmentación Abstract:,Studies comparing dispersal in fragmented versus unfragmented landscapes show that habitat fragmentation alters the dispersal behavior of many species. We used two complementary approaches to explore Florida Scrub-Jay (Aphelocoma c,rulescens) dispersal in relation to landscape fragmentation. First, we compared dispersal distances of color-marked individuals in intensively monitored continuous and fragmented landscapes. Second, we estimated effective dispersal relative to the degree of fragmentation (as inferred from two landscape indexes: proportion of study site covered with Florida Scrub-Jay habitat and mean distance to nearest habitat patch within each study site) by comparing genetic isolation-by-distance regressions among 13 study sites having a range of landscape structures. Among color-banded individuals, dispersal distances were greater in fragmented versus continuous landscapes, a result consistent with other studies. Nevertheless, genetic analyses revealed that effective dispersal decreases as the proportion of habitat in the landscape decreases. These results suggest that although individual Florida Scrub-Jays may disperse farther as fragmentation increases, those that do so are less successful as breeders than those that disperse short distances. Our study highlights the importance of combining observational data with genetic inferences when evaluating the complex biological and life-history implications of dispersal. Resumen:,Estudios que comparan la dispersión en paisajes fragmentados versus no fragmentados muestran que la fragmentación del hábitat altera la conducta de dispersión de muchas especies. Utilizamos dos métodos complementarios para explorar la dispersión de Aphelocoma c,rulescens en relación con la fragmentación del paisaje. Primero, comparamos las distancias de dispersión de individuos marcados con color en paisajes continuos y fragmentados monitoreados intensivamente. Segundo, estimamos la dispersión efectiva en relación con el grado de fragmentación (inferida a partir de dos índices del paisaje: proporción del sitio de estudio cubierta con hábitat para A. c,rulescens y la distancia promedio al parche más cercano en cada sitio de estudio) mediante la comparación de regresiones de aislamiento genético por distancia entre 13 sitios de estudio con una gama de estructuras de paisaje. Entre los individuos marcados con color, las distancias de dispersión fueron mayores en los paisajes fragmentados versus los continuos, un resultado consistente con otros estudios. Sin embargo, los análisis genéticos revelaron que la dispersión efectiva decrece a medida que decrece la proporción de hábitat en el paisaje. Estos resultados sugieren que aunque individuos de A. c,rulescens pueden dispersarse más lejos a medida que incrementa la fragmentación, aquellos que lo hacen son reproductores menos exitosos que los que se dispersan a corta distancia. Nuestro estudio resalta la importancia de combinar datos observacionales con inferencias genéticas cuando se evalúan las complejas implicaciones de la dispersión sobre la biología y la historia natural. [source] The influence of parent material on topsoil geochemistry in eastern EnglandEARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2003B. G. Rawlins Abstract The topsoil of around 10 000 km2 in eastern England has recently been sampled intensely at 4609 sites to characterize its geochemistry. The parent materials, which include both solid geology and Quaternary sediments, range in age from Permian to Holocene. The distributions of the concentrations of major and trace elements have been characterized geostatistically, and the role of parent material on their spatial structure (anisotropy) and their spatial relationships (coregionalization) have been investigated. Analysis of variance with the sites grouped by major parent material type showed that this classi,cation accounted for 14 to 48 per cent of the variance for the various elements. Global variograms of 13 elements (Al, As, Ca, Cr, Cu, Fe, Mg, Mo, Ni, P, Pb, Ti, and U) have been computed and modelled. Eleven of the variograms seem to comprise two structures, both of which we modelled with spherical functions, one of short range, 3·5 to 9 km, and the other with a range of 15 to 23 km. The models included a nugget variance, which varied from 27 per cent (for As, Fe, and Mg) to 63 per cent (for P) of the total. The long-range structures are related to the separations of the major parent materials. The variograms of several elements showed appreciable anisotropy, most notably that of Mg. Anisotropy is evident at short ranges of less than 5 km. This accords with the geological structure of the beds which dip from west to east so that their outcrops are elongated from north to south. A linear model of coregionalization ,tted to the data emphasized several important geochemical associations, which we interpret. Elements commonly associated with clay minerals (Mg, Al) and the clay size fraction (Ti) are dominated by the long-range structure of the coregionalization, whilst several trace elements (As, Cr, Ni and U) are spatially correlated with Fe over short distances, through adsorption of the former on the surfaces of Fe oxyhydroxides. The topsoil around large urban areas is enriched in lead, but it is not clear whether anthropogenic sources are responsible for this metal's anomalous spatial relationships with other elements. Crown copyright © 2003. Reproduced with the permission of Her Majesty's Stationery Of,ce. Published by John Wiley & Sons, Ltd. [source] Air pollution impedes plant-to-plant communication by volatilesECOLOGY LETTERS, Issue 9 2010James D. Blande Ecology Letters (2010) 13: 1172,1181 Abstract Volatile organic compounds (VOCs) emitted by damaged plants convey information to undamaged neighbouring plants, and previous research has shown that these signals are effective over short distances in nature. Many herbivore-induced VOCs react with ozone, which is the most important tropospheric air pollutant in rural areas. We used extrafloral nectar (EFN) secretion as a phenotypic indicator of between-plant communication in Phaseolus lunatus L. (Lima bean) and show that an ozone-rich (80 ppb) atmosphere reduces the distance over which signalling occurs. We found that ozone degrades several herbivore-induced VOCs, a likely mechanism reducing communication distances. Direct exposure to 80-ppb ozone did not affect the VOC emissions from P. lunatus. In addition, we demonstrated that high ozone concentrations, 120 and 160 ppb, induced EFN secretion in exposed plants, whereas more moderate concentrations, 80 and 100 ppb, did not. This suggests that ozone can play a complex role in the indirect defence of P. lunatus. [source] When do localized natural enemies increase species richness?ECOLOGY LETTERS, Issue 4 2005Frederick R. Adler Abstract The Janzen,Connell hypothesis states that local species-specific density dependence, mediated through specialist enemies of offspring such as fungal pathogens and insect seed predators, can facilitate coexistence of species by preventing recruitment near conspecific adults. We use spatially explicit simulation models and analytical approximations to evaluate how spatial scales of offspring and enemy dispersal affect species richness. In comparison with model communities in which both offspring and enemies disperse long distances, species richness is substantially decreased when offspring disperse long distances and enemies disperse short distances. In contrast, when both offspring and enemies disperse short distances species richness more than doubles and adults of each species are highly spatially clumped. For the range of conditions typical of tropical forests, locally dispersing specialist enemies may decrease species richness relative to enemies that disperse long distances. In communities where dispersal distances of both offspring and enemies are short, local effects may enhance species richness. [source] Epidemiology of sharka disease in FranceEPPO BULLETIN, Issue 2 2006G. Labonne Plum pox virus was first detected in France in the 1960s. Both PPV-D and PPV-M strains are present but epidemics related to the PPV-M strain detected in the late 1980s are the most problematic. The two PPV strains have unequal distributions in peach and apricot orchards and different prevalences. More than 20 different aphid species have been identified as vectors of PPV but most of them do not colonize Prunus species. Thus, aphids involved in the spread of PPV in orchards are essentially visiting aphids. The main sources of inoculum for the vectors are leaves and fruits of infected stone-fruit trees. Spontaneous, wild and ornamental Prunus species such as Prunus dulcis, P. spinosa or P. pissardii are susceptible to PPV isolates found in France but their role as a reservoir in sharka epidemics is probably negligible. The disease spreads rapidly in orchards but the rate of progression may vary according to the identity of the PPV strain and the Prunus species. Analysis of spatial patterns of disease has shown that secondary spread by aphids frequently occurs over short distances in the orchards (aggregated patterns) but also that dissemination at longer distances (of several hundred metres) is a common event. [source] Fruit Colour Preferences of Redwings (Turdus iliacus): Experiments with Hand-Raised Juveniles and Wild-Caught AdultsETHOLOGY, Issue 6 2004Johanna Honkavaara Certain fruit colours and their contrast with the background coloration are suggested to attract frugivorous birds. To test the attractiveness of different colours, we performed three experiments in laboratory with controlled light conditions. In the first two experiments, we studied the fruit colour preferences of naive juvenile redwings. In the third experiment, we continued to investigate whether the contrast of the fruit colour with the background coloration affects the preference of both naive juveniles and experienced adult redwings. In the first experiment, juvenile birds preferred black, UV-blue and red berries, to white ones. In pairwise trials, a new set of juveniles still preferred red berries to white ones. When testing the effect of contrasts on their choice, juveniles preferred UV-blue berries to red ones on a UV-blue background. However, no preference was found, when the background was either red or green. Adult redwings preferred UV-blue berries to red ones on all backgrounds. According to these results, juveniles seem to have an innate avoidance of white berries. Furthermore, the foraging decisions of fruit-eating birds are affected more by fruit colour than its contrast with background coloration, at least when contrasting displays are encountered from relatively short distances. Differences in preferences of adult and juvenile birds also indicate that learning seems to play a role in fruit choices. [source] Natal Dispersal Patterns of a Subsocial Spider Anelosimus cf. jucundus (Theridiidae)ETHOLOGY, Issue 9 2003Kimberly S. Powers Species that alternate periods of solitary and social living may provide clues to the conditions that favor sociality. Social spiders probably originated from subsocial-like ancestors, species in which siblings remain together for part of their life cycle but disperse prior to mating. Exploring the factors that lead to dispersal in subsocial species, but allow the development of large multigenerational colonies in social species, may provide insight into this transition. We studied the natal dispersal patterns of a subsocial spider, Anelosimus cf. jucundus, in Southeastern Arizona. In this population, spiders disperse from their natal nests in their penultimate and antepenultimate instars over a 3-mo period. We tracked the natal dispersal of marked spiders at sites with clustered vs. isolated nests. We found that most spiders initially dispersed less than 5 m from their natal nests. Males and females, and spiders in patches with different densities of nests, dispersed similar distances. The fact that both sexes in a group dispersed, the lack of a sex difference in dispersal distance, and the relatively short distances dispersed are consistent with the hypothesis that natal dispersal results from resource competition within the natal nest, rather than inbreeding avoidance in competition for mates. Additionally, an increase in the average distance dispersed with time and with the number of spiders leaving a nest suggests that competition for nest sites in the vicinity of the natal nest may affect dispersal distances. The similar distances dispersed in patches with isolated vs. clustered nests, in contrast, suggest that competition among dispersers from different nests may not affect dispersal distances. [source] Eight-Coordinate Endohedral Rhenium, Osmium and Iridium Atoms in Rare-Earth Halide Cluster ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2010Sina Zimmermann Abstract Endohedral (interstitial) atoms are essential for almost all of the rare-earth halide cluster complexes. Most of these contain octahedral clusters, some are isolated, but the majority exhibits condensation by common edges to structures of higher dimensionality. Higher coordination numbers of the endohedral atoms are rare. Four examples of extended cluster complexes with eight-coordinate endohedral atoms of sixth-period elements (Re, Os, Ir) are presented. In the quasi-isostructural, non-isotypic halides {ReGd4}Br4 and {OsSc4}Cl4, square antiprisms of gadolinium and scandium atoms, respectively, are connected by two common faces to chains, surrounded and loosely connected by halogenido ligands. The Re and Os atoms build a slightly bent chain with only little bonding interactions. Chemical bonding is dominated by endohedral atom,cluster atom and cluster atom,halide interactions. The same is true for the two scandium bromides {Ir3Sc12}Br16 and {Os3Sc12}Br16Sc, which contain chains of face-sharing square antiprisms and cubes in a ratio of 2:1. Metal,metal bonding is attested by short distances between those endohedral Ir and Os atoms, respectively, which center the square antiprisms (283 pm and 290 pm, respectively). Magnetic and conductivity measurements on {Ir3Sc12}Br16 reveal paramagnetism and a small-band-gap semiconductor. This is in accord with electronic structure calculations. [source] Migration of rheophilic fish in the large lowland rivers Meuse and Rhine, the NetherlandsFISHERIES MANAGEMENT & ECOLOGY, Issue 5-6 2008J. J. DE LEEUW Abstract, Large-scale migratory patterns of adult rheophilic fish [barbel, Barbus barbus (L.), chub, Leuciscus cephalus (L.), ide, Leuciscus idus (L.), nase, Chondrostoma nasus (L.)] were studied in relation to habitat quality and possible migration barriers in the lower rivers Meuse and Rhine, the Netherlands, using a telemetry system with transponders and detection stations based on inductive coupling. Most fish moved over short distances (<10 km), especially those residing in river stretches with high habitat diversity year-round. About 16% of fish used river stretches over 50 km and two ide moved more than 200 km along free-flowing river stretches. One-third of barbel, chub and nase from a Weir-regulated river stretch moved upstream during the spawning season to spawning habitats. Some fish resided in the areas immediately downstream of weirs and fishways during the spawning season, although it was unclear to what extent these observations reflected habitat choice or barriers to migration. [source] Spatial correlation patterns in coastal environmental variables and survival rates of salmon in the north-east Pacific OceanFISHERIES OCEANOGRAPHY, Issue 4 2002Franz J. Mueter We examined spatial correlations for three coastal variables [upwelling index, sea surface temperature (SST), and sea surface salinity (SSS)] that might affect juvenile salmon (Oncorhynchus spp.) during their early marine life. Observed correlation patterns in environmental variables were compared with those in survival rates of pink (O. gorbuscha), chum (O. keta), and sockeye (O. nerka) salmon stocks to help identify appropriate variables to include in models of salmon productivity. Both the upwelling index and coastal SST were characterized by strong positive correlations at short distances, which declined slowly with distance in the winter months, but much more rapidly in the summer. The SSS had much weaker and more variable correlations at all distances throughout the year. The distance at which stations were no longer correlated (spatial decorrelation scale) was largest for the upwelling index (> 1000 km), intermediate for SST (400,800 km in summer), and shortest for SSS (< 400 km). Survival rate indices of salmon showed moderate positive correlations among adjacent stocks that decreased to zero at larger distances. Spatial decorrelation scales ranged from approximately 500 km for sockeye salmon to approximately 1000 km for chum salmon. We conclude that variability in the coastal marine environment during summer, as well as variability in salmon survival rates, are dominated by regional scale variability of several hundred to 1000 km. The correlation scale for SST in the summer most closely matched the observed correlation scales for survival rates of salmon, suggesting that regional-scale variations in coastal SST can help explain the observed regional-scale covariation in survival rates among salmon stocks. [source] Extrafloral nectar from cotton (Gossypium hirsutum) as a food source for parasitic waspsFUNCTIONAL ECOLOGY, Issue 1 2006U. S. R. RÖSE Summary 1For many adult nectar-feeding parasitoids food and moisture are essential for survival in the field. Early in the season, when floral nectar is not yet available in cotton, extrafloral nectar (EFN) is already present on young cotton plants. 2The parasitoid Microplitis croceipes (Cresson) can use EFN cotton plants as an only food source. The longevity and reproduction of EFN-fed female wasps was comparable to wasps fed with honey and water provided on nectariless (NL) cotton plants, and was significantly higher compared with wasps kept on NL plants with no additional food source. 3Wasps that were given preflight experiences on EFN cotton plants choose EFN cotton over NL cotton plants in two choice experiments in the flight tunnel. The parasitoids are more willing to search on an EFN plant at their second and third encounter with a plant previously visited, compared with an NL cotton plant. 4Wasps can locate EFN from short distances by its odour alone, and find it almost as fast as honey, but much faster than odourless sucrose, which is only found randomly. Experience with EFN increased the retention ability of parasitoids on a flower model. [source] The surface archaeological record in arid Australia: Geomorphic controls on preservation, exposure, and visibilityGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 2 2009Patricia C. Fanning The conventional approach to assessing the archaeological record in most parts of the world involves a combination of excavation of stratified deposits and extensive survey of surface deposits. Although widely applied in Australia, in both research-based and management archaeology, the method does not conform well to the nature of the surface archaeological record here. Over much of semi-arid and arid Australia, archaeological "sites" are, in fact, accretion phenomena that are not easily interpreted as the outcome of short-term behavioral events. Using results from twelve years of geoarchaeological research in western New South Wales, we demonstrate that there is considerable variability in landsurface age, and hence the "availability" of archaeological surfaces, over relatively short distances. Therefore, it cannot be assumed that stone artifact deposits, for example, that appear to be similar in character are of similar age. Data are also presented that demonstrate that the presence of artifacts on the surface, their apparent absence in sediments buried beneath the surface, and the apparent recent ubiquity of the archaeological record are all a function of geomorphic processes that, at the same time, expose some artifact deposits at the surface and erode and bury others amid large volumes of sediment. Interpreting the surface artifact record within a spatial and temporal geomorphic framework is crucial to understanding the past human behavior that the artifact deposits represent. © 2009 Wiley Periodicals, Inc. 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