Observed Distribution (observed + distribution)

Distribution by Scientific Domains
Distribution within Life Sciences


Selected Abstracts


Modelling canopy CO2 fluxes: are ,big-leaf' simplifications justified?

GLOBAL ECOLOGY, Issue 6 2001
A. D. Friend
Abstract 1The ,big-leaf' approach to calculating the carbon balance of plant canopies is evaluated for inclusion in the ETEMA model framework. This approach assumes that canopy carbon fluxes have the same relative responses to the environment as any single leaf, and that the scaling from leaf to canopy is therefore linear. 2A series of model simulations was performed with two models of leaf photosynthesis, three distributions of canopy nitrogen, and two levels of canopy radiation detail. Leaf- and canopy-level responses to light and nitrogen, both as instantaneous rates and daily integrals, are presented. 3Observed leaf nitrogen contents of unshaded leaves are over 40% lower than the big-leaf approach requires. Scaling from these leaves to the canopy using the big-leaf approach may underestimate canopy photosynthesis by ~20%. A leaf photosynthesis model that treats within-leaf light extinction displays characteristics that contradict the big-leaf theory. Observed distributions of canopy nitrogen are closer to those required to optimize this model than the homogeneous model used in the big-leaf approach. 4It is theoretically consistent to use the big-leaf approach with the homogeneous photosynthesis model to estimate canopy carbon fluxes if canopy nitrogen and leaf area are known and if the distribution of nitrogen is assumed optimal. However, real nitrogen profiles are not optimal for this photosynthesis model, and caution is necessary in using the big-leaf approach to scale satellite estimates of leaf physiology to canopies. Accurate prediction of canopy carbon fluxes requires canopy nitrogen, leaf area, declining nitrogen with canopy depth, the heterogeneous model of leaf photosynthesis and the separation of sunlit and shaded leaves. The exact nitrogen profile is not critical, but realistic distributions can be predicted using a simple model of canopy nitrogen allocation. [source]


Spatial utilisation of fast-ice by Weddell seals Leptonychotes weddelli during winter

ECOGRAPHY, Issue 3 2005
Samantha Lake
This study describes the distribution of Weddell seals Leptonychotes weddelli in winter (May,September 1999) at the Vestfold Hills, in Prydz Bay, East Antarctica. Specifically, we describe the spatial extent of haul-out sites in shore,fast sea-ice, commonly referred to as fast-ice. As winter progressed, and the fast-ice grew thick (ca 2 m), most of the inshore holes closed over, and the seals' distribution became restricted to ocean areas beyond land and islands. Using observations from the end of winter only, we fitted Generalised Additive Models (GAMs) to generate resource selection functions, which are models that yield values proportional to the probability of use. The models showed that seal distribution was defined mainly by distance to ice-edge and distance to land. Distance to ice-bergs was also selected for models of some regions. We present the results as maps of the fitted probability of seal presence, predicted by the binomial GAM for offshore regions, both with and without autocorrelation terms. The maps illustrate the expected distribution encompassing most of the observed distribution. On this basis, we hypothesise that propensity for the fast-ice to crack is the major determinant of Weddell seal distribution in winter. Proximity to open water and pack-ice habitats could also influence the distribution of haul-out sites in fast-ice areas. This is the first quantitative study of Weddell seal distribution in winter. Potential for regional variation is discussed. [source]


Vertical distribution of picoeukaryotic diversity in the Sargasso Sea

ENVIRONMENTAL MICROBIOLOGY, Issue 5 2007
Fabrice Not
Summary Eukaryotic molecular diversity within the picoplanktonic size-fraction has primarily been studied in marine surface waters. Here, the vertical distribution of picoeukaryotic diversity was investigated in the Sargasso Sea from euphotic to abyssal waters, using size-fractionated samples (< 2 ,m). 18S rRNA gene clone libraries were used to generate sequences from euphotic zone samples (deep chlorophyll maximum to the surface); the permanent thermocline (500 m); and the pelagic deep-sea (3000 m). Euphotic zone and deep-sea data contrasted strongly, the former displaying greater diversity at the first-rank taxon level, based on 232 nearly full-length sequences. Deep-sea sequences belonged almost exclusively to the Alveolata and Radiolaria, while surface samples also contained known and putative photosynthetic groups, such as unique Chlorarachniophyta and Chrysophyceae sequences. Phylogenetic analyses placed most Alveolata and Stramenopile sequences within previously reported ,environmental' clades, i.e. clades within the Novel Alveolate groups I and II (NAI and NAII), or the novel Marine Stramenopiles (MAST). However, some deep-sea NAII formed distinct, bootstrap supported clades. Stramenopiles were recovered from the euphotic zone only, although many MAST are reportedly heterotrophic, making the observed distribution a point for further investigation. An unexpectedly high proportion of radiolarian sequences were recovered. From these, five environmental radiolarian clades, RAD-I to RAD-V, were identified. RAD-IV and RAD-V were composed of Taxopodida-like sequences, with the former solely containing Sargasso Sea sequences, although from all depth zones sampled. Our findings highlight the vast diversity of these protists, most of which remain uncultured and of unknown ecological function. [source]


NATURAL SELECTION ALONG AN ENVIRONMENTAL GRADIENT: A CLASSIC CLINE IN MOUSE PIGMENTATION

EVOLUTION, Issue 7 2008
Lynne M. Mullen
We revisited a classic study of morphological variation in the oldfield mouse (Peromyscus polionotus) to estimate the strength of selection acting on pigmentation patterns and to identify the underlying genes. We measured 215 specimens collected by Francis Sumner in the 1920s from eight populations across a 155-km, environmentally variable transect from the white sands of Florida's Gulf coast to the dark, loamy soil of southeastern Alabama. Like Sumner, we found significant variation among populations: mice inhabiting coastal sand dunes had larger feet, longer tails, and lighter pigmentation than inland populations. Most striking, all seven pigmentation traits examined showed a sharp decrease in reflectance about 55 km from the coast, with most of the phenotypic change occurring over less than 10 km. The largest change in soil reflectance occurred just south of this break in pigmentation. Geographic analysis of microsatellite markers shows little interpopulation differentiation, so the abrupt change in pigmentation is not associated with recent secondary contact or reduced gene flow between adjacent populations. Using these genetic data, we estimated that the strength of selection needed to maintain the observed distribution of pigment traits ranged from 0.0004 to 21%, depending on the trait and model used. We also examined changes in allele frequency of SNPs in two pigmentation genes, Mc1r and Agouti, and show that mutations in the cis -regulatory region of Agouti may contribute to this cline in pigmentation. The concordance between environmental variation and pigmentation in the face of high levels of interpopulation gene flow strongly implies that natural selection is maintaining a steep cline in pigmentation and the genes underlying it. [source]


Probability modelling and statistical analysis of damage in the lower wing skins of two retired B-707 aircraft

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2001
D. G. Harlow
A plausible mechanistically based probability model for localized pitting corrosion and subsequent fatigue crack nucleation and growth is used to analyse tear-down inspection data from two retired B-707 aircraft that had been in commercial service for about 24 and 30 years. Sections of the left-hand lower wing skins from these aircraft had been previously disassembled and inspected optically at 20× magnification. The inspections were augmented by metallographic examinations for the lower time aircraft. The evolution of damage in the fastener holes is estimated by using reasonable values for the localized corrosion and fatigue crack growth rates, statistically estimated from laboratory data. The primary loading, assumed to be the mean design load, is considered to be from ground,air,ground wing bending cycles, augmented by ,average' gust loading, only. The encouraging agreement between the estimated probability of occurrence and the observed distribution of multiple hole,wall cracks attests to the efficacy of the approach and its relevancy to airworthiness assessment and fleet life management. [source]


Depth distribution of earthquakes in the Baikal rift system and its implications for the rheology of the lithosphere

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001
Jacques Déverchère
Summary The correspondence between the predicted brittle,plastic transition within the crust and the maximum depth of earthquakes is examined in the case of the Baikal rift, Siberia. Although little accurate information on depths is available through large- and moderate-size earthquakes, there are frequent indications of foci at 20 km depth and more. We have relocated 632 events recorded at nearby stations that occurred between 1971 and 1997, with depth and epicentral uncertainties less than 5 km, over the eastern and southern parts of the Baikal rift. We have compared these results with other depth distributions obtained in previous studies from background seismicity in the NE rift (1365 events in the Kalar-Chara zone and 704 events in the Muya region). The relative abundance of earthquakes is generally low at depths between 0 and 10 km (7,15 per cent) and high between 15 and 25 km (,50 per cent). Earthquake activity is still significant between 25 and 30 km (9,15 per cent) and persists between 30 and 40 km (7,13 per cent). Very few earthquakes are below the Moho. We use empirical constitutive laws to obtain the yield-stress limits of several layers made of dominant lithologies and to examine whether the observed distribution of earthquakes at depth (519 events controlled by a close station and located within the extensional domain of the Baikal rift system) can match the predicted crustal strength proportion with depth and the deeper brittle,ductile transition in the crust. A good fit is obtained by using a quartz rheology at 0,10 km depth and a diabase rheology at 10,45 km depth with a moderate temperature field which corresponds to a ,100 Myr thermal lithosphere. No dioritic composition of the crust is found necessary. In any case, earthquakes occur at deep crustal levels, where the crust is supposed to be ductile, in a way very similar to what is found in the East African Rift System. From these results we conclude that the seismogenic thickness is ,35,40 km in the Baikal rift system and that the depth distribution of earthquakes is at first order proportional to the strength profile found in a rheologically layered crust dominated by a mafic composition in the ,10,45 km depth range. An upper mantle core with high strength, however, generally prevents it from reaching stress failure at greater depth. [source]


Impact of twenty-first century climate change on diadromous fish spread over Europe, North Africa and the Middle East

GLOBAL CHANGE BIOLOGY, Issue 5 2009
G. LASSALLE
Abstract Climate change is expected to drive species ranges towards the poles and to have a strong influence on species distributions. In this study, we focused on diadromous species that are of economical and ecological importance in the whole of Europe. We investigated the potential distribution of all diadromous fish regularly encountered in Europe, North Africa and the Middle East (28 species) under conditions predicted for twenty-first century climate change. To do so, we investigated the 1900 distribution of each species in 196 basins spread across all of Europe, North Africa and the Middle East. Four levels were used to semiquantitatively describe the abundance of species, that is missing, rare, common and abundant. We then selected five variables describing the prevailing climate in the basins, the physical nature of the basins and reflecting historical events known to have affected freshwater fish distribution. Logistic regressions with a four-level ordinal response variable were used to develop species-specific models. These predictive models related the observed distribution of these species in 1900 to the most explanatory combination of variables. Finally, we selected the A2 SRES scenario and the HadCM3 (Hadley Centre Coupled Model version 3) global climate model (GCM) to obtain climate variables (temperature and precipitation) at the end of this century. We used these 2100 variables in our models and obtained maps of climatically suitable and unsuitable basins, percentages of contraction or expansion for each species. Twenty-two models were successfully built, that is there were five species for which no model could be established because their distribution range was too narrow and the Acipenser sturio model failed during calibration. All the models selected temperature or/and precipitation as explanatory variables. Responses to climate change were species-specific but could be classified into three categories: little or no change in the distribution (five species), expansion of the distribution range (three species gaining suitable basins mainly northward) and contraction of the distribution (14 species losing suitable basins). Shifting ranges were in accordance with those found in other studies and underlined the high sensitivity of diadromous fish to modifications in their environment. [source]


Research Submission: Mixture Analysis of Age at Onset in Migraine Without Aura: Evidence for Three Subgroups

HEADACHE, Issue 8 2010
Carlo Asuni MD
(Headache 2010;50:1313-1319) Objective. , To verify the presence of different age at onset (AAO) subgroups of patients in a sample of patients with migraine without aura (MWA) and compare clinical correlates among them. Background., MWA is a long-lasting disease whose prognosis has not yet been fully investigated. Patients may present complete remission, partial clinical remission, persistence and progression (migraine attack frequency and disability may increase over time leading to chronic migraine). Limited evidence exists regarding the identification of risk factors or predictors which might influence migraine prognosis. AAO has been proven a useful tool in the investigation of the clinical, biological, and genetic characteristics able to influence the prognosis of a number of neuropsychiatric disorders. AAO distribution was studied using mixture analysis, a statistical approach that breaks down the empirical AAO distribution observed into a mixture of normal components. Methods., A sample of 334 outpatients affected by MWA, recruited in a clinical genetic study at our Headache Center from 2004 to 2008, was enrolled for this study. Diagnosis was made according to International Headache Society criteria 2004. AAO distribution in patients was studied using mixture analysis. Chi-square test was used to compare clinical correlates among identified subgroups. Logistic regression was performed in order to correct for effect of possible confounders. Results., Mixture analysis broke up the observed distribution of AAO into 3 normal theoretical distributions. Informational criteria clearly showed a better 3-component model rather than the 2-component one. An early-onset (,7 years of age), an intermediate-onset (,8 and ,22), and a late-onset group (,23) were identified. Comparison of clinical correlates among subgroups by means of chi-square test showed a statistically significant result for migraine frequency (,2 = 7.41, P = .02). Considering the frequency of migraine attacks as a main outcome, the regression model showed a higher AAO is associated with low frequency (odds ratio = 0.95; P = .02). Conclusions., The significant association between AAO and attack frequency found in our study supports the hypothesis that AAO could act as a predictor factor able to influence prognosis. AAO could represent a phenotype suitable for identifying MWA susceptibility genes. [source]


Brain region binding of the D2/3 agonist [11C]-(+)-PHNO and the D2/3 antagonist [11C]raclopride in healthy humans

HUMAN BRAIN MAPPING, Issue 4 2008
Ariel Graff-Guerrero
Abstract The D2 receptors exist in either the high- or low-affinity state with respect to agonists, and while agonists bind preferentially to the high-affinity state, antagonists do not distinguish between the two states. [11C]-(+)-PHNO is a PET D2agonist radioligand and therefore provides a preferential measure of the D2high receptors. In contrast, [11C]raclopride is an antagonist radioligand and thus binds with equal affinity to the D2 high- and low-affinity states. The aim was to compare the brain uptake, distribution and binding characteristics between [11C]-(+)-PHNO and [11C]raclopride in volunteers using a within-subject design. Both radioligands accumulated in brain areas rich in D2/D3 -receptors. However, [11C]-(+)-PHNO showed preferential uptake in the ventral striatum and globus pallidus, while [11C]raclopride showed preferential uptake in the dorsal striatum. Mean binding potentials were higher in the putamen (4.3 vs. 2.8) and caudate (3.4 vs 2.1) for [11C]raclopride, equal in the ventral-striatum (3.4 vs. 3.3), and higher in the globus pallidus for [11C]-(+)-PHNO (1.8 vs. 3.3). Moreover [11C]-(+)-PHNO kinetics in the globus pallidus showed a slower washout than other regions. One explanation for the preferential binding of [11C]-(+)-PHNO in the globus pallidus and ventral-striatum could be the presence of a greater proportion of high- vs. low-affinity receptors in these areas. Alternatively, the observed distribution could also be explained by a preferential binding of D3 -over-D2 with [11C]-(+)-PHNO. This differential binding of agonist vs. antagonist radioligand, especially in the critically important region of the limbic striatum/pallidum, offers new avenues to investigate the role of the dopamine system in health and disease. Hum Brain Mapp 2008. © 2007 Wiley-Liss, Inc. [source]


Atmospheric chemistry of isopropyl formate and tert -butyl formate

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2010
Andre Silva Pimentel
Formates are produced in the atmosphere as a result of the oxidation of a number of species, notably dialkyl ethers and vinyl ethers. This work describes experiments to define the oxidation mechanisms of isopropyl formate, HC(O)OCH(CH3)2, and tert -butyl formate, HC(O)OC(CH3)3. Product distributions are reported from both Cl- and OH-initiated oxidation, and reaction mechanisms are proposed to account for the observed products. The proposed mechanisms include examples of the ,-ester rearrangement reaction, novel isomerization pathways, and chemically activated intermediates. The atmospheric oxidation of isopropyl formate by OH radicals gives the following products (molar yields): acetic formic anhydride (43%), acetone (43%), and HCOOH (15,20%). The OH radical initiated oxidation of tert -butyl formate gives acetone, formaldehyde, and CO2 as major products. IR absorption cross sections were derived for two acylperoxy nitrates derived from the title compounds. Rate coefficients are derived for the kinetics of the reactions of isopropyl formate with OH (2.4 ± 0.6) × 10,12, and with Cl (1.75 ± 0.35) × 10,11, and for tert -butyl formate with Cl (1.45 ± 0.30) × 10,11 cm3 molecule,1 s,1. Simple group additivity rules fail to explain the observed distribution of sites of H-atom abstraction for simple formates. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 479,498, 2010 [source]


A structural model of US aggregate job flows

JOURNAL OF APPLIED ECONOMETRICS, Issue 3 2002
Fabrice Collard
This paper contributes to the analysis of jobs flows dynamics through the explicit modelling of job creations and job destructions. We propose a simple matching model extended for endogenous separation and tractable heterogeneity. The parameters of the model are estimated using a simulation-based estimation method. We then test the ability of trade externalities, generated by the matching process, to (i) propagate reallocation and aggregate disturbances in the whole labor market and (ii) generate the observed distribution of aggregate job flows. The results clearly indicate that the model is able to match the dynamics of US aggregate job flows. Copyright © 2002 John Wiley & Sons, Ltd. [source]


Do community-level models describe community variation effectively?

JOURNAL OF BIOGEOGRAPHY, Issue 10 2010
Andrés Baselga
Abstract Aim, The aim of community-level modelling is to improve the performance of species distributional models by taking patterns of co-occurrence among species into account. Here, we test this expectation by examining how well three community-level modelling strategies (,assemble first, predict later', ,predict first, assemble later', and ,assemble and predict together') spatially project the observed composition of species assemblages. Location, Europe. Methods, Variation in the composition of European tree assemblages and its spatial and environmental correlates were examined with cluster analysis and constrained analysis of principal coordinates. Results were used to benchmark spatial projections from three community-based strategies: (1) assemble first, predict later (cluster analysis first, then generalized linear models, GLMs); (2) predict first, assemble later (GLMs first, then cluster analysis); and (3) assemble and predict together (constrained quadratic ordination). Results, None of the community-level modelling strategies was able to accurately model the observed distribution of tree assemblages in Europe. Uncertainty was particularly high in southern Europe, where modelled assemblages were markedly different from observed ones. Assembling first and predicting later led to distribution models with the simultaneous occurrence of several types of assemblages in southern Europe that do not co-occur, and the remaining strategies yielded models with the presence of non-analogue assemblages that presently do not exist and that are much more strongly correlated with environmental gradients than with the real assemblages. Main conclusions, Community-level models were unable to characterize the distribution of European tree assemblages effectively. Models accounting for co-occurrence patterns along environmental gradients did not outperform methods that assume individual responses of species to climate. Unrealistic assemblages were generated because of the models' inability to capture fundamental processes causing patterns of covariation among species. The usefulness of these forms of community-based models thus remains uncertain and further research is required to demonstrate their utility. [source]


175 Toward an Optical Biogeography of the Oceans

JOURNAL OF PHYCOLOGY, Issue 2003
A. M. Wood
Remote sensing of ocean color has revolutionized our ability to understand the processes leading to the observed distribution of different taxa in marine waters. Many scientists in the remote sensing and optics community are working toward retrieval of species distributions using ocean color measurements to derive the concentration of recognized chemotaxonomic markers. In this talk, I work toward an optical biogeography of the ocean by viewing the optical environment as a selection regime that creates biogeographic boundaries or "optical fences" defining the distribution of taxa with different light harvesting systems and/or different physiologies. Working primarily with data from a wide range of tropical, sub-tropical, and warm temperate coastal margins, I show that there is a close association between the distribution of different spectral forms of PE-containing picocyanobacteria and the optical properties of the water masses in which they are found. This pattern also appears to be reflected in the distribution some dinoflagellate taxa, indicating that the optical environment encompasses a range of key niche parameters that, in turn, determine the biogeographic distribution of species. [source]


Modelling the distributions of Culicoides bluetongue virus vectors in Sicily in relation to satellite-derived climate variables

MEDICAL AND VETERINARY ENTOMOLOGY, Issue 2 2004
B. V. Purse
Abstract., Surveillance data from 268 sites in Sicily are used to develop climatic models for prediction of the distribution of the main European bluetongue virus (BTV) vector Culicoides imicola Kieffer (Diptera: Ceratopogonidae) and of potential novel vectors, Culicoides pulicaris Linnaeus, Culicoides obsoletus group Meigen and Culicoides newsteadi Austen. The models containing the ,best' climatic predictors of distribution for each species, were selected from combinations of 40 temporally Fourier-processed remotely sensed variables and altitude at a 1 km spatial resolution using discriminant analysis. Kappa values of around 0.6 for all species models indicated substantial levels of agreement between model predictions and observed data. Whilst the distributions of C. obsoletus group and C. newsteadi were predicted by temperature variables, those of C. pulicaris and C. imicola were determined mainly by normalized difference vegetation index (NDVI), a variable correlated with soil moisture and vegetation biomass and productivity. These models were used to predict species presence in unsampled pixels across Italy and for C. imicola across Europe and North Africa. The predicted continuous presence of C. pulicaris along the appenine mountains, from north to south Italy, suggests BTV transmission may be possible in a large proportion of this region and that seasonal transhumance (seasonal movement of livestock between upland and lowland pastures) even in C. imicola -free areas should not generally be considered safe. The predicted distribution of C. imicola distribution shows substantial agreement with observed surveillance data from Greece and Iberia (including the Balearics) and parts of mainland Italy (Lazio, Tuscany and areas of the Ionian coast) but is generally much more restricted than the observed distribution (in Sardinia, Corsica and Morocco). The low number of presence sites for C. imicola in Sicily meant that only a restricted range of potential C. imicola habitats were included in the training set and that predictions could only be made within this range. Future modelling exercises will use abundance data collected according to a standardized protocol across the Mediterranean and, for Sicily in particular, should include non-climatic environmental variables that may influence breeding site suitability such as soil type. [source]


Estimation of the seed dispersal kernel from exact identification of source plants

MOLECULAR ECOLOGY, Issue 23 2007
JUAN J. ROBLEDO-ARNUNCIO
Abstract The exact identification of individual seed sources through genetic analysis of seed tissue of maternal origin has recently brought the full analytical potential of parentage analysis to the study of seed dispersal. No specific statistical methodology has been described so far, however, for estimation of the dispersal kernel function from categorical maternity assignment. In this study, we introduce a maximum-likelihood procedure to estimate the seed dispersal kernel from exact identification of seed sources. Using numerical simulations, we show that the proposed method, unlike other approaches, is independent of seed fecundity variation, yielding accurate estimates of the shape and range of the seed dispersal kernel under varied sampling and dispersal conditions. We also demonstrate how an obvious estimator of the dispersal kernel, the maximum-likelihood fit of the observed distribution of dispersal distances to seed traps, can be strongly biased due to the spatial arrangement of seed traps relative to source plants. Finally, we illustrate the use of the proposed method with a previously published empirical example for the animal-dispersed tree species Prunus mahaleb. [source]


identix, a software to test for relatedness in a population using permutation methods

MOLECULAR ECOLOGY RESOURCES, Issue 4 2002
Khalid Belkhir
Abstract The computer program identix estimates relatedness in natural populations using multilocus genotypic data. Queller & Goodnight's (1989) and Lynch & Ritland's (1999) estimators of pairwise relatedness are implemented, as well as the identity index of Mathieu et al. (1990). Estimates of the confidence intervals around these pairwise values are also provided. The null hypothesis of no relatedness (multilocus genotypes are independent draws from a panmictic population) is tested using a permutation method that compares the observed distribution of the moments of pairwise relatedness coefficients to that expected in unstructured population. [source]


Probing the existence of the Epeak,Eiso correlation in long gamma ray bursts

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2005
Giancarlo Ghirlanda
ABSTRACT We probe the existence of the Epeak,Eiso correlation in long gamma-ray bursts (GRBs) using a sample of 442 BATSE bursts with known Epeak and with redshift estimated through the lag,luminosity correlation. This sample confirms that the rest-frame peak energy is correlated with the isotropic equivalent energy. The distribution of the scatter of the points around the best-fitting line is similar to that obtained with the 27 bursts with spectroscopic redshifts. We interpret the scatter in the Epeak,Eiso plane as due to the opening angle distribution of GRB jets. By assuming that the collimation corrected energy correlates with Epeak we can derive the observed distribution of the jet opening angles, which turns out to be lognormal with a peak value of . [source]


A simple two-stage model predicts response time distributions

THE JOURNAL OF PHYSIOLOGY, Issue 16 2009
R. H. S. Carpenter
The neural mechanisms underlying reaction times have previously been modelled in two distinct ways. When stimuli are hard to detect, response time tends to follow a random-walk model that integrates noisy sensory signals. But studies investigating the influence of higher-level factors such as prior probability and response urgency typically use highly detectable targets, and response times then usually correspond to a linear rise-to-threshold mechanism. Here we show that a model incorporating both types of element in series , a detector integrating noisy afferent signals, followed by a linear rise-to-threshold performing decision , successfully predicts not only mean response times but, much more stringently, the observed distribution of these times and the rate of decision errors over a wide range of stimulus detectability. By reconciling what previously may have seemed to be conflicting theories, we are now closer to having a complete description of reaction time and the decision processes that underlie it. [source]


Application of QuickBird and aerial imagery to detect Pinus radiata in remnant vegetation

AUSTRAL ECOLOGY, Issue 6 2010
NERISSA HABY
Abstract The invasion of Pinus radiata from long-term established plantations is contributing to the degradation of fragmented and isolated remnants of native vegetation. Within the south-east of South Australia, the 20 vegetation communities that occur within 500 m of a plantation edge are at risk, including nine state threatened communities. To plan effective mitigation strategies, the current extent and distribution of P. radiata needs to be ascertained. High spatial resolution, multispectral QuickBird imagery and aerial photography were used to classify P. radiata within eucalypt and acacia woodlands, melaleuca shrubland, modified pasture and an Eucalyptus globulus plantation. Unsupervised classification of aerial photography gave the best result showing reasonable conformity with the observed distribution of P. radiata at the site scale. However, the 9.4 ± 13.5 (SD) cover classified in the quadrats sampled for the accuracy assessment exceeded the 1.4 ± 2.4 (SD) P. radiata cover determined from an independent dataset. Only 30.1 ± 37.9% (SD) of trees within the quadrats and 9.40 ± 13.49% (SD) of their foliage cover were classified. Trees detected by partial classification of canopy were positively correlated with both tree height and canopy diameter. Overall, the low detection rates were attributed to insufficient spectral resolution. Using higher resolution imagery, together with an object-based image analysis or combination of multispectral and airborne digital image classification, restricted to large emergent adult trees using LiDAR analysis, is likely to improve adult P. radiata detection accuracy. [source]


Transport and environmental temperature variability of eggs and larvae of the Japanese anchovy (Engraulis japonicus) and Japanese sardine (Sardinops melanostictus) in the western North Pacific estimated via numerical particle-tracking experiments

FISHERIES OCEANOGRAPHY, Issue 2 2009
SACHIHIKO ITOH
Abstract Numerical particle-tracking experiments were performed to investigate the transport and variability in environmental temperature experienced by eggs and larvae of Pacific stocks of the Japanese anchovy (Engraulis japonicus) and Japanese sardine (Sardinops melanostictus) using high-resolution outputs of the Ocean General Circulation Model for the Earth Simulator (OFES) and the observed distributions of eggs collected from 1978 to 2004. The modeled anchovy individuals tend to be trapped in coastal waters or transported to the Kuroshio,Oyashio transition region. In contrast, a large proportion of the sardines are transported to the Kuroshio Extension. The egg density-weighted mean environmental temperature until day 30 of the experiment was 20,24°C for the anchovy and 17,20°C for the sardine, which can be explained by spawning areas and seasons, and interannual oceanic variability. Regression analyses revealed that the contribution of environmental temperature to the logarithm of recruitment per spawning (expected to have a negative relationship with the mean mortality coefficient) was significant for both the anchovy and sardine, especially until day 30, which can be regarded as the initial stages of their life cycles. The relationship was quadratic for the anchovy, with an optimal temperature of 21,22°C, and linear for the sardine, with a negative coefficient. Differences in habitat areas and temperature responses between the sardine and anchovy are suggested to be important factors in controlling the dramatic out-of-phase fluctuations of these species. [source]


An evaluation of the potential influence of SST and currents on the oceanic migration of juvenile and immature chum salmon (Oncorhynchus keta) by a simulation model

FISHERIES OCEANOGRAPHY, Issue 1 2004
Tomonori Azumaya
Abstract Using a salmon migration model based on the assumption that swimming orientation is temperature dependent, we investigated the determining factors of the migration of juvenile and immature chum salmon (Oncorhynchus keta) in the North Pacific. We compared the predictions of the model with catch data of immature and juvenile chum salmon collected by Japanese research vessels from 1972 to 1999. The salmon migration model reproduced the observed distributions of immature chum salmon and indicates that passive transport by wind-driven and geostrophic currents plays an important role in the eastward migration of Asian salmon. These factors result in a non-symmetric distribution of Asian and North American chum salmon in the open ocean. The directional swimming component contributes to the northward migration in summer. The model results indicate that during the first winter Asian chum salmon swim northward against the southward wind-driven currents to stay in the western North Pacific. This suggests that Asian chum salmon require more energy to migrate than other stocks during the first winter of their ocean life. [source]


History in the interpretation of the pattern of p49a,f TaqI RFLP Y-chromosome variation in Egypt: A consideration of multiple lines of evidence

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2005
S.O.Y. Keita
The possible factors involved in the generation of p49a,f TaqI Y-chromosome spatial diversity in Egypt were explored. The object was to consider explanations beyond those that emphasize gene flow mediated via military campaigns within the Nile corridor during the dynastic period. Current patterns of the most common variants (V, XI, and IV) have been suggested to be primarily related to Middle Kingdom and New Kingdom political actions in Nubia, including occasional settler colonization, and the conquest of Egypt by Kush (in upper Nubia, northern Sudan), thus initiating the Twenty-Fifth Dynasty. However, a synthesis of evidence from archaeology, historical linguistics, texts, distribution of haplotypes outside Egypt, and some demographic considerations lends greater support to the establishment, before the Middle Kingdom, of the observed distributions of the most prevalent haplotypes V, XI, and IV. It is suggested that the pattern of diversity for these variants in the Egyptian Nile Valley was largely the product of population events that occurred in the late Pleistocene to mid-Holocene through the First Dynasty, and was sustained by continuous smaller-scale bidirectional migrations/interactions. The higher frequency of V in Ethiopia than in Nubia or upper (southern) Egypt has to be taken into account in any discussion of variation in the Nile Valley. Am. J. Hum. Biol. 17: 559,567, 2005. © 2005 Wiley-Liss, Inc. [source]