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Distribution Changes (distribution + change)
Selected AbstractsDynamic distribution modelling: predicting the present from the pastECOGRAPHY, Issue 1 2009Stephen G. Willis Confidence in projections of the future distributions of species requires demonstration that recently-observed changes could have been predicted adequately. Here we use a dynamic model framework to demonstrate that recently-observed changes at the expanding northern boundaries of three British butterfly species can be predicted with good accuracy. Previous work established that the distributions of the study species currently lag behind climate change, and so we presumed that climate is not currently a major constraint at the northern range margins of our study species. We predicted 1970,2000 distribution changes using a colonisation model, MIGRATE, superimposed on a high-resolution map of habitat availability. Thirty-year rates and patterns of distribution change could be accurately predicted for each species (, goodness-of-fit of models >0.64 for all three species, corresponding to >83% of grid cells correctly assigned), using a combination of individual species traits, species-specific habitat associations and distance-dependent dispersal. Sensitivity analyses showed that population productivity was the most important determinant of the rate of distribution expansion (variation in dispersal rate was not studied because the species are thought to be similar in dispersal capacity), and that each species' distribution prior to expansion was critical in determining the spatial pattern of the current distribution. In future, modelling approaches that combine climate suitability and spatially-explicit population models, incorporating demographic variables and habitat availability, are likely to be valuable tools in projecting species' responses to climatic change and hence in anticipating management to facilitate species' dispersal and persistence. [source] Change in mean temperature as a predictor of extreme temperature change in the Asia,Pacific regionINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2005G. M. Griffiths Abstract Trends (1961,2003) in daily maximum and minimum temperatures, extremes and variance were found to be spatially coherent across the Asia,Pacific region. The majority of stations exhibited significant trends: increases in mean maximum and mean minimum temperature, decreases in cold nights and cool days, and increases in warm nights. No station showed a significant increase in cold days or cold nights, but a few sites showed significant decreases in hot days and warm nights. Significant decreases were observed in both maximum and minimum temperature standard deviation in China, Korea and some stations in Japan (probably reflecting urbanization effects), but also for some Thailand and coastal Australian sites. The South Pacific convergence zone (SPCZ) region between Fiji and the Solomon Islands showed a significant increase in maximum temperature variability. Correlations between mean temperature and the frequency of extreme temperatures were strongest in the tropical Pacific Ocean from French Polynesia to Papua New Guinea, Malaysia, the Philippines, Thailand and southern Japan. Correlations were weaker at continental or higher latitude locations, which may partly reflect urbanization. For non-urban stations, the dominant distribution change for both maximum and minimum temperature involved a change in the mean, impacting on one or both extremes, with no change in standard deviation. This occurred from French Polynesia to Papua New Guinea (except for maximum temperature changes near the SPCZ), in Malaysia, the Philippines, and several outlying Japanese islands. For urbanized stations the dominant change was a change in the mean and variance, impacting on one or both extremes. This result was particularly evident for minimum temperature. The results presented here, for non-urban tropical and maritime locations in the Asia,Pacific region, support the hypothesis that changes in mean temperature may be used to predict changes in extreme temperatures. At urbanized or higher latitude locations, changes in variance should be incorporated. Copyright © 2005 Royal Meteorological Society. [source] Tree species range shifts at a continental scale: new predictive insights from a process-based modelJOURNAL OF ECOLOGY, Issue 4 2008Xavier Morin Summary 1Climate change has already caused distribution shifts in many species, and climate predictions strongly suggest that these will accelerate in the future. Obtaining reliable predictions of species range shifts under climate change is thus currently one of the most crucial challenges for both ecologists and stakeholders. 2Here we simulate the distributions of 16 North American tree species at a continental scale for the 21st century according to two IPCC storylines, using a process-based species distribution model that for the first time allows identification of the possible causes of distribution change. 3Our projections show local extinctions in the south of species ranges (21% of the present distribution, on average), and colonizations of new habitats in the north, though these are limited by dispersal ability for most species. Areas undergoing local extinctions are slightly larger under climate scenario A2 (+3.2 C, +22% on average) than B2 (+1.0 C, +19% on average). This small difference is caused by nonlinear responses of processes (leaves and flowers phenological processes in particular) to temperature. We also show that local extinction may proceed at a slower rate than forecasted so far. 4Although predicted distribution shifts are very species-specific, we show that the loss of habitats southward will be mostly due to increased drought mortality and decreased reproductive success, while northward colonizations will be primarily promoted by increased probability of fruit ripening and flower frost survival. 5Synthesis. Our results show that different species will not face the same risks due to climate change, because their responses to climate differ as well as their dispersal rate. Focusing on processes, our study therefore tempers the alarming conclusions of widely used niche-based models about biodiversity loss, mainly because our predictions take into account the local adaptation and trait plasticity to climate of the species. [source] Manipulation of image intensity distribution at 7.0 T: Passive RF shimming and focusing with dielectric materials,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2006Qing X. Yang Abstract Purpose To investigate the effects of high dielectric material padding on RF field distribution in the human head at 7.0 T, and demonstrate the feasibility and effectiveness of RF passive shimming and focusing with such an approach. Materials and Methods The intensity distribution changes of gradient-recalled-echo (GRE) and spin-echo (SE) images of a human head acquired with water pads (dielectric constant = 78) placed in specified configurations around the head at 7.0 T were evaluated and compared with computer simulation results using the finite difference time domain (FDTD) method. The contributions to the B1 field distribution change from the displacement current and conductive current of a given configuration of dielectric padding were determined with computer simulations. Results MR image intensity distribution in the human head with an RF coil at 7.0 T can be changed drastically by placing water pads around the head. Computer simulations reveal that the high permittivity of water pads results in a strong displacement current that enhances image intensity in the nearby region and alters the intensity distribution of the entire brain. Conclusion The image intensity distribution in the human head at ultra-high field strengths can be effectively manipulated with high permittivity padding. Utilizing this effect, the B1 field inside the human head of a given RF coil can be adjusted to reduce the B1 field inhomogeneity artifact associated with the wave behavior (RF passive shimming) or to locally enhance the signal-to-noise ratio (SNR) in targeted regions of interest (ROIs; RF field focusing). J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Differential distribution of voltage-gated potassium channels Kv 1.1,Kv1.6 in the rat retina during developmentJOURNAL OF NEUROSCIENCE RESEARCH, Issue 1 2007M. Höltje Abstract The discharge behavior of neurons depends on a variable expression and sorting pattern of voltage-dependent potassium (Kv) channels that changes during development. The rodent retina represents a neuronal network whose main functions develop after birth. To obtain information about neuronal maturation we analyzed the expression of subunits of the Kv1 subfamily in the rat retina during postnatal development using immunocytochemistry and immunoelectron microscopy. At postnatal day 5 (P5) all the ,-subunits of Kv1.1,Kv1.6 channels were found to be expressed in the ganglion cell layer (GCL), most of them already at P1 or P3. Their expression upregulates postnatally and the pattern and distribution change in an isoform-specific manner. Additionally Kv1 channels are found in the outer and inner plexiform layer (OPL, IPL) and in the inner nuclear layer (INL) at different postnatal stages. In adult retina the Kv 1.3 channel localizes to the inner and outer segments of cones. In contrast, Kv1.4 is highly expressed in the outer retina at P8. In adult retina Kv1.4 occurs in rod inner segments (RIS) near the connecting cilium where it colocalizes with synapse associated protein SAP 97. By using confocal laser scanning microscopy we showed a differential localization of Kv1.1-1.6 to cholinergic amacrine and rod bipolar cells of the INL of the adult retina. © 2006 Wiley-Liss, Inc. [source] Exploring spatiotemporal patterns in early stages of primary succession on former lignite mining sitesJOURNAL OF VEGETATION SCIENCE, Issue 2 2008Birgit Felinks Abstract Questions: 1. Does random colonization predominate in early stages of primary succession? 2. Do pioneer species facilitate the establishment of later arriving species? 3. Does an initially random distribution change to an aggregated pattern with ongoing succession? Location: Lignite mining region of Lower Lusatia, eastern Germany. Methods: Individual plants were mapped along a 2 m × 28 m transect during three successive years and classified into two groups (1) the pioneer Corynephorus canescens and (2),all other species'. Using the pair-correlation function, univariate point pattern analysis was carried out by applying a heterogeneous Poisson process as null model. Bivariate analysis and a toroidal shift null model were applied to test for independence between the spatial patterns of the two groups separately for each year, as well by exploring spatiotemporal patterns from different years. Results: In the first year Corynephorus and ,all other species' showed an aggregated pattern on a spatial scale > 40 cm and in the second and third years a significant attraction for distances between 4 and 12 cm, with an increasing radius in the third year. The analyses of interspecific spatiotemporal dynamics revealed a change from independence to attraction between distances of 4 cm and 16 cm when using Corynephorus as focal species. However, applying ,all other species' as focal points results in a significant attraction at distances up to 60 cm in the first year and a diminishing attraction in the second and third years with distances , 6 cm. Conclusions: Facilitative species-species interactions are present in early stages of primary succession, resulting mainly from pioneer species acting as physical barriers and their ability to capture diaspores being drifted by secondary dispersal along the substrate surface. However, due to gradual establishment of perennial species and their ability of lateral extension by vegetative dispersal, facilitation may influence spatial pattern formation predominantly on short temporal and fine spatial scales. [source] Distribution of mountain hares Lepus timidus in Scotland: results from a questionnaireMAMMAL REVIEW, Issue 4 2010Vikki PATTON ABSTRACT A questionnaire survey of land owners, managers and gamekeepers was conducted in order to assess the distribution of mountain hares in Scotland, assess their current management, collate numbers harvested in 2006,07 and estimate distribution change by comparing with similar data collected in 1995,96. The land area covered by returned questionnaires was 71098km2 (90% of Scotland). Mountain hares were reported as present on 34359km2 (48%) and absent from 36739km2 (52%). Mountain hare presence was strongly associated with heather moorland managed for red grouse shooting. Moorland managed for driven grouse shooting had the highest percentage area of mountain hare presence (median 64%) followed by moorland managed for walked-up grouse shooting (median 9%) and moorland with no grouse shooting (median 0%). Approximately 25000 mountain hares were harvested in 2006,07. Based on the estimated UK population in 1995 of 350000 (range ±50%), this represents around 7% of the population (range 5,14%). Reasons given by respondents for harvesting hares were tick control (50%), sport (40%) and forestry or crop protection (10%). Comparison of the estates surveyed in both 2006,07 and 1995,96 (a total area of 20462km2) indicated no net gain or loss in hare distribution. Furthermore, there was no evidence that levels of harvest had reduced the range of mountain hares in this area. It is not possible to comment on any distribution change outside this area (58737km2). Similarly, as no data were collected on abundance, it is not possible to draw conclusions on changes in density. Regular monitoring of mountain hare distribution within Scotland is required to identify any distribution changes. Measures of abundance throughout the range are necessary to estimate the population size, investigate the relationship between harvest intensity and changes in abundance and further assess the conservation status of this UK Biodiversity Action Plan species. [source] Semi-Automatic Time-Series Transfer Functions via Temporal Clustering and SequencingCOMPUTER GRAPHICS FORUM, Issue 3 2009Jonathan Woodring Abstract When creating transfer functions for time-varying data, it is not clear what range of values to use for classification, as data value ranges and distributions change over time. In order to generate time-varying transfer functions, we search the data for classes that have similar behavior over time, assuming that data points that behave similarly belong to the same feature. We utilize a method we call temporal clustering and sequencing to find dynamic features in value space and create a corresponding transfer function. First, clustering finds groups of data points that have the same value space activity over time. Then, sequencing derives a progression of clusters over time, creating chains that follow value distribution changes. Finally, the cluster sequences are used to create transfer functions, as sequences describe the value range distributions over time in a data set. [source] Gastroesophageal reflux disease and non-small cell lung cancer.DISEASES OF THE ESOPHAGUS, Issue 5 2008Results of a pilot study SUMMARY., The sharp rise in the frequency of adenocarcinoma and relative decrease of squamous cell carcinoma of the respiratory and digestive systems, raises suspicion of a common element in their carcinogenetic cascade, which could result in similar trends in cell,type distribution changes of esophageal and lung cancers. The possible role of chemical irritation caused by gastroesophageal reflux disease (GERD) in non-small cell lung cancer (NSCLC) patients was investigated. There was no significant difference between the adenocarcinoma and the squamous cell carcinoma groups, neither in the composite DeMeester scores nor in any of the separate parameters of the complex score investigated. However, the ratio of detected gastroesophageal reflux cases was considerably higher than in the average population. This factor may be one element of a multifactorial cancer promotion. [source] Dynamic distribution modelling: predicting the present from the pastECOGRAPHY, Issue 1 2009Stephen G. Willis Confidence in projections of the future distributions of species requires demonstration that recently-observed changes could have been predicted adequately. Here we use a dynamic model framework to demonstrate that recently-observed changes at the expanding northern boundaries of three British butterfly species can be predicted with good accuracy. Previous work established that the distributions of the study species currently lag behind climate change, and so we presumed that climate is not currently a major constraint at the northern range margins of our study species. We predicted 1970,2000 distribution changes using a colonisation model, MIGRATE, superimposed on a high-resolution map of habitat availability. Thirty-year rates and patterns of distribution change could be accurately predicted for each species (, goodness-of-fit of models >0.64 for all three species, corresponding to >83% of grid cells correctly assigned), using a combination of individual species traits, species-specific habitat associations and distance-dependent dispersal. Sensitivity analyses showed that population productivity was the most important determinant of the rate of distribution expansion (variation in dispersal rate was not studied because the species are thought to be similar in dispersal capacity), and that each species' distribution prior to expansion was critical in determining the spatial pattern of the current distribution. In future, modelling approaches that combine climate suitability and spatially-explicit population models, incorporating demographic variables and habitat availability, are likely to be valuable tools in projecting species' responses to climatic change and hence in anticipating management to facilitate species' dispersal and persistence. [source] Measurement of the size distribution of water-filled pores at different matric potentials by stray field nuclear magnetic resonanceEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2005N. R. A. Bird Summary The water retention characteristic provides the traditional data set for the derivation of a soil's pore-size distribution. However, the technique employed to achieve this requires that assumptions be made about the way pores interconnect. We explore an alternative approach based on stray field nuclear magnetic resonance (STRAFI-NMR) to probe the water-filled pores of both saturated and unsaturated soils, which does not require information relating to pore connectivity. We report the relative size distributions of water-occupied pores in saturated and unsaturated samples of two sets of glass beads of known particle size, two sands, and three soils (a silty loam, a sandy loam and a loamy sand), using measurements of the NMR T1 proton relaxation time of water. The T1 values are linearly related to pore size and consequently measured T1 distributions provide a measure of the pore-size distribution. For both the sands and the glass beads at saturation the T1 distributions are unimodal, and the samples with small particle sizes show a shift to small T1 values indicating smaller voids relative to the samples with larger particles. Different matric potentials were used to reveal how the water-occupied pore-size distribution changes during drainage. These changes are inconsistent with, and demonstrate the inadequacies of, the commonly employed parallel-capillary tube model of a soil pore space. We find that not all pores of the same size drain at the same matric potential. Further, we observe that the T1 distribution is shifted to smaller values beyond the distribution at saturation. This shift is explained by a change in the weighted average of the relaxation rates as the proportion of water in the centre of water-filled pores decreases. This is evidence for the presence of pendular structures resulting from incomplete drainage of pores. For the soils the results are similar except that at saturation the T1 distributions are bimodal or asymmetrical, indicative of inter-aggregate and intra-aggregate pore spaces. We conclude that the NMR method provides a characterization of the water-filled pore space which complements that derived from the water retention characteristic and which can provide insight into the way pore connectivity impacts on drainage. [source] Predicting the impacts of climate change on the distribution of species: are bioclimate envelope models useful?GLOBAL ECOLOGY, Issue 5 2003Richard G. Pearson ABSTRACT Modelling strategies for predicting the potential impacts of climate change on the natural distribution of species have often focused on the characterization of a species' bioclimate envelope. A number of recent critiques have questioned the validity of this approach by pointing to the many factors other than climate that play an important part in determining species distributions and the dynamics of distribution changes. Such factors include biotic interactions, evolutionary change and dispersal ability. This paper reviews and evaluates criticisms of bioclimate envelope models and discusses the implications of these criticisms for the different modelling strategies employed. It is proposed that, although the complexity of the natural system presents fundamental limits to predictive modelling, the bioclimate envelope approach can provide a useful first approximation as to the potentially dramatic impact of climate change on biodiversity. However, it is stressed that the spatial scale at which these models are applied is of fundamental importance, and that model results should not be interpreted without due consideration of the limitations involved. A hierarchical modelling framework is proposed through which some of these limitations can be addressed within a broader, scale-dependent context. [source] Predicting the effects of marine climate change on the invertebrate prey of the birds of rocky shoresIBIS, Issue 2004Michael A. Kendall By the end of the 21st century models of climate change predict that the air temperature over most of the British Isles will increase by between 2 and 3 °C and sea-level will rise by 40,50 cm. Over that period it will become windier and mean wave height will increase, as will the frequency of storms. These changes in climate and weather will impact the intertidal zone of the UK and will cause distribution changes in many of the common invertebrate species that live there. Where these changes are severe they may well impact on patterns of distribution of ducks and wading birds. In the British Isles a number of organisms live close to their geographical limits of distribution. Some of these species might be expected to extend their range as climatic restraints are relaxed. Species currently limited by cool summers or winter cold will move northwards. In most cases the effects on the distribution of waterbirds will be small. For example, the replacement of the Northern Limpet Patella vulgata by the Southern Limpet P. depressa is unlikely to adversely affect Eurasian Oystercatchers Haematopus ostralegus. Of wider concern is the possibility that as climate warms the abundance and productivity of brown algae will decrease. This is likely to have two significant effects for waders. First, it would represent a loss of potentially rich feeding grounds for species such as Ruddy Turnstone Arenaria interpres that feed on small easily desiccated invertebrates living on or below the seaweed. Secondly, as algae die or are broken away the resulting debris is exported to sediment habitats where it considerably boosts the in situ production of bacteria at the base of the food web. An increase in sea-level will only have a major impact on the extent of rocky shore invertebrate communities where shore topography prevents the upward migration of the biota. Where a seawall limits shores, for example, biological production will be curtailed as the area available for colonization decreases. Increases in the size of waves and the frequency of storms will mimic increasing exposure and there will be a significant reduction in algal production in areas that are affected. [source] Combined effects of climate and biotic interactions on the elevational range of a phytophagous insectJOURNAL OF ANIMAL ECOLOGY, Issue 1 2008Richard M. Merrill Summary 1The ranges of many species have expanded in cool regions but contracted at warm margins in response to recent climate warming, but the mechanisms behind such changes remain unclear. Particular debate concerns the roles of direct climatic limitation vs. the effects of interacting species in explaining the location of low latitude or low elevation range margins. 2The mountains of the Sierra de Guadarrama (central Spain) include both cool and warm range margins for the black-veined white butterfly, Aporia crataegi, which has disappeared from low elevations since the 1970s without colonizing the highest elevations. 3We found that the current upper elevation limit to A. crataegi's distribution coincided closely with that of its host plants, but that the species was absent from elevations below 900 m, even where host plants were present. The density of A. crataegi per host plant increased with elevation, but overall abundance of the species declined at high elevations where host plants were rare. 4The flight period of A. crataegi was later at higher elevations, meaning that butterflies in higher populations flew at hotter times of year; nevertheless, daytime temperatures for the month of peak flight decreased by 6·2 °C per 1 km increase in elevation. 5At higher elevations A. crataegi eggs were laid on the south side of host plants (expected to correspond to hotter microclimates), whereas at lower sites the (cooler) north side of plants was selected. Field transplant experiments showed that egg survival increased with elevation. 6Climatic limitation is the most likely explanation for the low elevation range margin of A. crataegi, whereas the absence of host plants from high elevations sets the upper limit. This contrasts with the frequent assumption that biotic interactions typically determine warm range margins, and thermal limitation cool margins. 7Studies that have modelled distribution changes in response to climate change may have underestimated declines for many specialist species, because range contractions will be exacerbated by mismatch between the future distribution of suitable climate space and the availability of resources such as host plants. [source] Wildfires and the expansion of threatened farmland birds: the ortolan bunting Emberiza hortulana in Mediterranean landscapesJOURNAL OF APPLIED ECOLOGY, Issue 4 2008Lluís Brotons Summary 1It has been argued that wildfires are one of the major agents involved in landscape transformation in many European regions and their impact is expected to increase in the near future. Despite the recognized impact of fire on wildlife at a local scale, we lack information on the species responses to fire at larger spatial scales. 2In this study, we used the ortolan bunting Emberiza hortulana to evaluate the potential effects of wildfires on open-habitat species distribution. In contrast to most European countries, this farmland species has experienced a consistent range expansion during the last decades in Catalonia (northeast Iberian peninsula). Distribution data of the species collected at different time periods allowed us to test the role of fires in determining range expansions at a regional scale, and to evaluate the importance of dispersal constraints on distribution changes. 3Analyses of distribution data from 1975,1983 and 1999,2002 showed a consistent expansion of the ortolan bunting in Catalonia. After correcting for differences in sampling effort, changes in distribution showed a strong spatial pattern with colonization and stability, but not local extinction, being clumped in space. Patterns of change were also strongly and significantly associated with the amount of shrubland burnt between the two time periods, since areas that experienced a larger impact of fires in terms of burnt area showed a much higher probability of maintaining species presence or of being colonized. Colonization events appeared to be more likely in areas affected by fire especially when surrounding areas had already been colonized by the species. 4Synthesis and applications. Overall, our results support the hypothesis that wildfires, especially those affecting open woodlands or shrubby areas, play a critical role in the ecology of the ortolan bunting and have contributed to the recent expansion of the species in Catalonia. Furthermore, we have shown that colonization appears to be limited, not only by the availability of new burnt habitat but also by specific dispersal constraints. We suggest that, for several European threatened species associated with open habitats, burnt areas may partially compensate for the widespread loss and deterioration of farmland habitat, opening new management opportunities for their conservation. [source] Distribution of mountain hares Lepus timidus in Scotland: results from a questionnaireMAMMAL REVIEW, Issue 4 2010Vikki PATTON ABSTRACT A questionnaire survey of land owners, managers and gamekeepers was conducted in order to assess the distribution of mountain hares in Scotland, assess their current management, collate numbers harvested in 2006,07 and estimate distribution change by comparing with similar data collected in 1995,96. The land area covered by returned questionnaires was 71098km2 (90% of Scotland). Mountain hares were reported as present on 34359km2 (48%) and absent from 36739km2 (52%). Mountain hare presence was strongly associated with heather moorland managed for red grouse shooting. Moorland managed for driven grouse shooting had the highest percentage area of mountain hare presence (median 64%) followed by moorland managed for walked-up grouse shooting (median 9%) and moorland with no grouse shooting (median 0%). Approximately 25000 mountain hares were harvested in 2006,07. Based on the estimated UK population in 1995 of 350000 (range ±50%), this represents around 7% of the population (range 5,14%). Reasons given by respondents for harvesting hares were tick control (50%), sport (40%) and forestry or crop protection (10%). Comparison of the estates surveyed in both 2006,07 and 1995,96 (a total area of 20462km2) indicated no net gain or loss in hare distribution. Furthermore, there was no evidence that levels of harvest had reduced the range of mountain hares in this area. It is not possible to comment on any distribution change outside this area (58737km2). Similarly, as no data were collected on abundance, it is not possible to draw conclusions on changes in density. Regular monitoring of mountain hare distribution within Scotland is required to identify any distribution changes. Measures of abundance throughout the range are necessary to estimate the population size, investigate the relationship between harvest intensity and changes in abundance and further assess the conservation status of this UK Biodiversity Action Plan species. [source] The effect of whole-body sunbed ultraviolet A exposure on the pharmacokinetics of the photolabile drug nifedipinePHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 3 2000H. S. Al-Ajmi The calcium antagonist nifedipine absorbs ultraviolet A (UVA) radiation and readily photodegrades in vitro to a toxic nitroso-pyridine photoproduct. We examined whether whole body exposure of normal subjects to sunbed UVA radiation would affect the pharmacokinetics of nifedipine. Eight healthy, male, Caucasian volunteers (phototypes I,III) participated in this ethically approved, randomised, cross-over study. Each subject attended on 2 occasions, one week apart, and on each occasion was given a single oral dose (10 mg) of nifedipine following which blood samples were collected at 0, 0.5, 1. 1.5, 2, 2.5, 3, 3.5, 4, 5, 6 and 7 h. During one of the visits, 15 min after nifedipine ingestion, a whole-body UVA (sunbed comprising Philips R-UVA lamps) dose of 70% of the individual's predetermined minimal phototoxic dose was delivered over a period of 17,36 min. Plasma nifedipine levels were measured using a standard reverse-phase high-performance liquid chromatography method. The area under the plasma concentration-time curve (AUC) of nifedipine during the UVA irradiation session (median 206 ng,·,ml,1,·,h,1) was significantly higher than during the non-irradiation control session (median 174.5 ng,·,ml,1,·,h,1) (P=0.03; 95% C.I. for difference in medians 9.9 to 55.9 ng,·,ml,1,·,h,1). UVA irradiation did not significantly affect any of the other measured pharmacokinetic parameters (Cmax, t1/2, tmax). We demonstrate that sunbed UVA irradiation does not lead to in vivo photodegradation of nifedipine in healthy humans after a single dose. The apparent increase in AUC during UVA irradiation may be due to slightly slower metabolism of nifedipine in the presence of toxic photoproduct(s) or due to blood distribution changes affecting liver blood flow. [source] Distribution sensitivity in a highway flow modelAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 6 2009Andrew M. Ross, Article first published online: 13 FEB 200 Abstract We examine a model of traffic flow on a highway segment, where traffic can be impaired by random incidents (usually, collisions). Using analytical and numerical methods, we show the degree of sensitivity that the model exhibits to the distributions of service times (in the queueing model) and incident clearance times. Its sensitivity to the distribution of time until an incident is much less pronounced. Our analytical methods include an M/Gt/, analysis (Gt denotes a service process whose distribution changes with time) and a fluid approximation for an M/M/c queue with general distributions for the incident clearance times. Our numerical methods include M/PH2/c/K models with many servers and with phase-type distributions for the time until an incident occurs or is cleared. We also investigate different time scalings for the rate of incident occurrence and clearance. Copyright © 2009 John Wiley & Sons, Ltd. 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