WorldWideScience

Sample records for namib aridity gradient

  1. Advanced Photogrammetry to Assess Lichen Colonization in the Hyper-Arid Namib Desert.

    Science.gov (United States)

    Hinchliffe, Graham; Bollard-Breen, Barbara; Cowan, Don A; Doshi, Ashray; Gillman, Len N; Maggs-Kolling, Gillian; de Los Rios, Asuncion; Pointing, Stephen B

    2017-01-01

    The hyper-arid central region of the Namib Desert is characterized by quartz desert pavement terrain that is devoid of vascular plant covers. In this extreme habitat the only discernible surface covers are epilithic lichens that colonize exposed surfaces of quartz rocks. These lichens are highly susceptible to disturbance and so field surveys have been limited due to concerns about disturbing this unusual desert feature. Here we present findings that illustrate how non-destructive surveys based upon advanced photogrammetry techniques can yield meaningful and novel scientific data on these lichens. We combined 'structure from motion analysis,' computer vision and GIS to create 3-dimensional point clouds from two-dimensional imagery. The data were robust in its application to estimating absolute lichen cover. An orange Stellarangia spp. assemblage had coverage of 22.8% of available substrate, whilst for a black Xanthoparmelia spp. assemblage coverage was markedly lower at 0.6% of available substrate. Hyperspectral signatures for both lichens were distinct in the near-infra red range indicating that Xanthoparmelia spp. was likely under relatively more moisture stress than Stellarangia spp. at the time of sampling, and we postulate that albedo effects may have contributed to this in the black lichen. Further transformation of the data revealed a colonization preference for west-facing quartz surfaces and this coincides with prevailing winds for marine fog that is the major source of moisture in this system. Furthermore, a three-dimensional 'fly through' of the lichen habitat was created to illustrate how the application of computer vision in microbiology has further potential as a research and education tool. We discuss how advanced photogrammetry could be applied in astrobiology using autonomous rovers to add quantitative ecological data for visible surface colonization on the surface of Mars.

  2. Advanced Photogrammetry to Assess Lichen Colonization in the Hyper-Arid Namib Desert

    Directory of Open Access Journals (Sweden)

    Graham Hinchliffe

    2017-10-01

    Full Text Available The hyper-arid central region of the Namib Desert is characterized by quartz desert pavement terrain that is devoid of vascular plant covers. In this extreme habitat the only discernible surface covers are epilithic lichens that colonize exposed surfaces of quartz rocks. These lichens are highly susceptible to disturbance and so field surveys have been limited due to concerns about disturbing this unusual desert feature. Here we present findings that illustrate how non-destructive surveys based upon advanced photogrammetry techniques can yield meaningful and novel scientific data on these lichens. We combined ‘structure from motion analysis,’ computer vision and GIS to create 3-dimensional point clouds from two-dimensional imagery. The data were robust in its application to estimating absolute lichen cover. An orange Stellarangia spp. assemblage had coverage of 22.8% of available substrate, whilst for a black Xanthoparmelia spp. assemblage coverage was markedly lower at 0.6% of available substrate. Hyperspectral signatures for both lichens were distinct in the near-infra red range indicating that Xanthoparmelia spp. was likely under relatively more moisture stress than Stellarangia spp. at the time of sampling, and we postulate that albedo effects may have contributed to this in the black lichen. Further transformation of the data revealed a colonization preference for west-facing quartz surfaces and this coincides with prevailing winds for marine fog that is the major source of moisture in this system. Furthermore, a three-dimensional ‘fly through’ of the lichen habitat was created to illustrate how the application of computer vision in microbiology has further potential as a research and education tool. We discuss how advanced photogrammetry could be applied in astrobiology using autonomous rovers to add quantitative ecological data for visible surface colonization on the surface of Mars.

  3. Adaptation of metabolism and evaporative water loss along an aridity gradient.

    Science.gov (United States)

    Tieleman, B Irene; Williams, Joseph B; Bloomer, Paulette

    2003-01-22

    Broad-scale comparisons of birds indicate the possibility of adaptive modification of basal metabolic rate (BMR) and total evaporative water loss (TEWL) in species from desert environments, but these might be confounded by phylogeny or phenotypic plasticity. This study relates variation in avian BMR and TEWL to a continuously varying measure of environment, aridity. We test the hypotheses that BMR and TEWL are reduced along an aridity gradient within the lark family (Alaudidae), and investigate the role of phylogenetic inertia. For 12 species of lark, BMR and TEWL decreased along a gradient of increasing aridity, a finding consistent with our proposals. We constructed a phylogeny for 22 species of lark based on sequences of two mitochondrial genes, and investigated whether phylogenetic affinity played a part in the correlation of phenotype and environment. A test for serial independence of the data for mass-corrected TEWL and aridity showed no influence of phylogeny on our findings. However, we did discover a significant phylogenetic effect in mass-corrected data for BMR, a result attributable to common phylogenetic history or to common ecological factors. A test of the relationship between BMR and aridity using phylogenetic independent constrasts was consistent with our previous analysis: BMR decreased with increasing aridity.

  4. Climate change impacts on freshwater wetland hydrology and vegetation cover cycling along a regional aridity gradient

    Science.gov (United States)

    Global mean temperature may increase up to 6°C by the end of this century and together with precipitation change may steepen regional aridity gradients, impacting the hydrology, productivity, diversity, and ecosystem goods and services from freshwater wetlands, where the water balance is tightly cou...

  5. An examination of recharge mound decay and fossil gradients in arid regional sedimentary basins

    International Nuclear Information System (INIS)

    Lloyd, J.W.

    1980-01-01

    In many of the vast arid sedimentary basins of the world, groundwater gradients exist that appear to be anomalous in the context of the probable modern recharge potential. The possibility that such gradients are in fact remnant fossil conditions representing the decay of ancient recharge mounds is examined. An example of decay condition is represented using a resistor-network analogue model in which the time control is based on 14 C ages. The decay hypothesis is found to be plausible with realistic aquifer characteristics but a non-homogeneous flow is indicated from the 14 C data. (author)

  6. Changes of AM fungal abundance along environmental gradients in the arid and semi-arid grasslands of northern China.

    Directory of Open Access Journals (Sweden)

    Yajun Hu

    Full Text Available Arbuscular mycorrhizal (AM fungi are ubiquitous symbionts of higher plants in terrestrial ecosystems, while the occurrence of the AM symbiosis is influenced by a complex set of abiotic and biotic factors. To reveal the regional distribution pattern of AM fungi as driven by multiple environmental factors, and to understand the ecological importance of AM fungi in natural ecosystems, we conducted a field investigation on AM fungal abundance along environmental gradients in the arid and semi-arid grasslands of northern China. In addition to plant parameters recorded in situ, soil samples were collected, and soil chemo-physical and biological parameters were measured in the lab. Statistical analyses were performed to reveal the relative contribution of climatic, edaphic and vegetation factors to AM fungal abundance, especially for extraradical hyphal length density (HLD in the soil. The results indicated that HLD were positively correlated with mean annual temperature (MAT, soil clay content and soil pH, but negatively correlated with both soil organic carbon (SOC and soil available N. The multiple regressions and structural equation model showed that MAT was the key positive contributor and soil fertility was the key negative contributor to HLD. Furthermore, both the intraradical AM colonization (IMC and relative abundance of AM fungi, which was quantified by real-time PCR assay, tended to decrease along the increasing SOC content. With regard to the obvious negative correlation between MAT and SOC in the research area, the positive correlation between MAT and HLD implied that AM fungi could potentially mitigate soil carbon losses especially in infertile soils under global warming. However, direct evidence from long-term experiments is still expected to support the AM fungal contribution to soil carbon pools.

  7. Changes in semi-arid plant species associations along a livestock grazing gradient.

    Directory of Open Access Journals (Sweden)

    Hugo Saiz

    Full Text Available In semi-arid ecosystems, vegetation is heterogeneously distributed, with plant species often associating in patches. These associations between species are not constant, but depend on the particular response of each species to environmental factors. Here, we investigated how plant species associations change in response to livestock grazing in a semi-arid ecosystem, Cabo de Gata-Níjar Natural Park in South East Spain. We established linear point-intercept transects at four sites with different grazing intensity, and recorded all species at each point. We investigated plant associations by comparing the number of times that each pair of species occurred at the same spatial point (co-occurrences, with the expected number of times based on species abundances. We also assessed associations for each shrub and grass species by considering all their pairs of associations and for the whole plant community by considering all pairs of associations on each site. At all sites, the plant community had a negative pattern of association, with fewer co-occurrences than expected. Negative association in the plant community increased at maximum grazing intensity. Most species associated as expected, particularly grass species, and positive associations were most important at intermediate grazing intensities. No species changed its type of association along the grazing gradient. We conclude that in the present plant community, grazing-resistant species compete among themselves and segregate in space. Some shrub species act as refuges for grazing-sensitive species that benefit from being spatially associated with shrub species, particularly at intermediate grazing intensities where positive associations were highest. At high grazing intensity, these shrubs can no longer persist and positive associations decrease due to the disappearance of refuges. Spatial associations between plant species and their response to grazing help identify the factors that organize

  8. Alterations in flowering strategies and sexual allocation of Caragana stenophylla along a climatic aridity gradient

    OpenAIRE

    Lina Xie; Hongyu Guo; Chengcang Ma

    2016-01-01

    Plant can alter reproductive strategies for adaptation to different environments. However, alterations in flowering strategies and sexual allocation for the same species growing in different environments still remain unclear. We examined the sexual reproduction parameters of Caragana stenophylla across four climatic zones from semi-arid, arid, very arid, to intensively arid zones in the Inner Mongolia Steppe, China. Under the relatively favorable climatic conditions of semi-arid zone, C. sten...

  9. Arid landscape dynamics along a precipitation gradient: addressing vegetation - landscape structure - resource interactions at different time scales

    NARCIS (Netherlands)

    Buis, E.

    2008-01-01

    This research is entitled ‘Arid landscape dynamics along a precipitation gradient: addressing
    vegetation – landscape structure – resource interactions at different time scales’ with as subtitle
    ‘A case study for the Northern Negev Desert of Israel’. Landscape dynamics describes the

  10. Environmental gradients across wetland vegetation groups in the arid slopes of Western Alborz Mountains, N. Iran

    Directory of Open Access Journals (Sweden)

    Asghar Kamrani

    2011-01-01

    Full Text Available Mountain wetlands are unique ecosystems in the arid southern slopes of Alborz range, the second largest range in Iran. The spatial distribution characteristics of wetland vegetation in the arid region of the Alborz and the main factors affecting their distributional patterns were studied. A classification of vegetation and ecological characteristics were carried out using data extracted from 430 relevés in 90 wetland sites. The data were analyzed using Two Way Indicator Species Analysis (TWINSPAN and detrended correspondence analysis (DCA. The wetland vegetation of Alborz Mountain was classified into four large groups. The first vegetation group was calcareous rich vegetation, mainly distributed in the river banks and characterized by helophytes such as Bolboschoenus affinis as indicator species. The second group was saline transitional vegetation, distributed in the ecotone areas and dominated by Phragmites australis. The third vegetation group is wet meadow vegetation which mainly consists of geophytes, endemic and Irano-Turanian species, distributed in the higher altitudes. This vegetation is mainly characterized by indicator species such as Carex orbicularis, high level concentration of Fe2+ and percentage of organic matter in the soil. The fourth vegetation group is aquatic vegetation, distributed in the lakeshores. The aquatic group species are mainly hydrophytic such as Batrachium trichophyllum. The TWINSPAN vegetation groups could be also recognized in the DCA graphs and ecologically differentiated by ANOVA of studied variables. Four vegetation groups can be differentiated on two first axes of indirect ordination. There is a gradient of pH, EC and organic matter associated with altitude on the DCA diagram. Correlation analysis between the axes of DCA and environmental factors shows that altitude, soil texture and other dependant environmental variables (e.g. pH are the main environmental factors affecting the distribution of wetland

  11. Observing Semi-Arid Ecoclimates across Mountain Gradients in the Great Basin, USA

    Science.gov (United States)

    Strachan, Scotty

    Observation of climate and ecohydrological variables in mountain systems is a necessary (if challenging) endeavor for modern society. Water resources are often intimately tied to mountains, and high elevation environments are frequently home to unique landscapes and biota with limited geographical distributions. This is especially true in the temperate and semi-arid mountains of the western United States, and specifically the Great Basin. Stark contrasts in annual water balance and ecological populations are visible across steep elevational gradients in the region; and yet the bulk of our historical knowledge of climate and related processes comes from lowland observations. Interpolative models that strive to estimate conditions in mountains using existing datasets are often found to be inaccurate, making future projections of mountain climate and ecosystem response suspect. This study details the results of high-resolution topographically-diverse ecohydrological monitoring, and describes the character and seasonality of basic climatic variables such as temperature and precipitation as well as their impact on soil moisture and vegetation during the 2012-2015 drought sequence. Relationships of topography (elevation/aspect) to daily and seasonal temperatures are shown. Tests of the PRISM temperature model are performed at the large watershed scale, revealing magnitudes, modes, and potential sources of bias that could dramatically affect derivative scientific conclusions. A new method of precipitation phase partitioning to detect and quantify frozen precipitation on a sub-daily basis is described. Character of precipitation from sub-daily to annual scales is quantified across all major Great Basin vegetation/elevation zones, and the relationship of elevation to precipitation phase, intensity, and amount is explored. Water-stress responses of Great Basin conifers including Pinus flexilis, Pinus longaeva, and Pinus ponderosa are directly observed, showing potential

  12. Life Histories of Frogs in the Namib Desert | Channing | African ...

    African Journals Online (AJOL)

    Four anuran taxa inhabit the central Namib: Xenopus laevis, Tomopterna delalandei cryptotis, Phrynomerus annectens and Bufo vertebrate hoeschi. Xenopus is confined to permanent pools in the Kuiseb river canyon. Tomopterna extends further into the Namib, but is restricted to the Kuiseb river bed. The Kuiseb is normally ...

  13. Spatiotemporal soil and saprolite moisture dynamics across a semi-arid woody plant gradient

    Science.gov (United States)

    Woody plant cover has increased 10-fold over the last 140+ years in many parts of the semi-arid western USA. Woody plant cover can alter the timing and amount of plant available moisture in the soil and saprolite. To assess spatiotemporal subsurface moisture dynamics over two water years in a snow-d...

  14. Quantitative assessments of water-use efficiency in Temperate Eurasian Steppe along an aridity gradient.

    Directory of Open Access Journals (Sweden)

    Yizhao Chen

    Full Text Available Water-use efficiency (WUE, defined as the ratio of net primary productivity (NPP to evapotranspiration (ET, is an important indicator to represent the trade-off pattern between vegetation productivity and water consumption. Its dynamics under climate change are important to ecohydrology and ecosystem management, especially in the drylands. In this study, we modified and used a late version of Boreal Ecosystem Productivity Simulator (BEPS, to quantify the WUE in the typical dryland ecosystems, Temperate Eurasian Steppe (TES. The Aridity Index (AI was used to specify the terrestrial water availability condition. The regional results showed that during the period of 1999-2008, the WUE has a clear decreasing trend in the spatial distribution from arid to humid areas. The highest annual average WUE was in dry and semi-humid sub-region (DSH with 0.88 gC mm-1 and the lowest was in arid sub-region (AR with 0.22 gC mm-1. A two-stage pattern of WUE was found in TES. That is, WUE would enhance with lower aridity stress, but decline under the humid environment. Over 65% of the region exhibited increasing WUE. This enhancement, however, could not indicate that the grasslands were getting better because the NPP even slightly decreased. It was mainly attributed to the reduction of ET over 70% of the region, which is closely related to the rainfall decrease. The results also suggested a similar negative spatial correlation between the WUE and the mean annual precipitation (MAP at the driest and the most humid ends. This regional pattern reflected the different roles of water in regulating the terrestrial ecosystems under different aridity levels. This study could facilitate the understanding of the interactions between terrestrial carbon and water cycles, and thus contribute to a sustainable management of nature resources in the dryland ecosystems.

  15. Quantitative assessments of water-use efficiency in Temperate Eurasian Steppe along an aridity gradient.

    Science.gov (United States)

    Chen, Yizhao; Li, Jianlong; Ju, Weimin; Ruan, Honghua; Qin, Zhihao; Huang, Yiye; Jeelani, Nasreen; Padarian, José; Propastin, Pavel

    2017-01-01

    Water-use efficiency (WUE), defined as the ratio of net primary productivity (NPP) to evapotranspiration (ET), is an important indicator to represent the trade-off pattern between vegetation productivity and water consumption. Its dynamics under climate change are important to ecohydrology and ecosystem management, especially in the drylands. In this study, we modified and used a late version of Boreal Ecosystem Productivity Simulator (BEPS), to quantify the WUE in the typical dryland ecosystems, Temperate Eurasian Steppe (TES). The Aridity Index (AI) was used to specify the terrestrial water availability condition. The regional results showed that during the period of 1999-2008, the WUE has a clear decreasing trend in the spatial distribution from arid to humid areas. The highest annual average WUE was in dry and semi-humid sub-region (DSH) with 0.88 gC mm-1 and the lowest was in arid sub-region (AR) with 0.22 gC mm-1. A two-stage pattern of WUE was found in TES. That is, WUE would enhance with lower aridity stress, but decline under the humid environment. Over 65% of the region exhibited increasing WUE. This enhancement, however, could not indicate that the grasslands were getting better because the NPP even slightly decreased. It was mainly attributed to the reduction of ET over 70% of the region, which is closely related to the rainfall decrease. The results also suggested a similar negative spatial correlation between the WUE and the mean annual precipitation (MAP) at the driest and the most humid ends. This regional pattern reflected the different roles of water in regulating the terrestrial ecosystems under different aridity levels. This study could facilitate the understanding of the interactions between terrestrial carbon and water cycles, and thus contribute to a sustainable management of nature resources in the dryland ecosystems.

  16. Background aerosol composition in the Namib desert

    International Nuclear Information System (INIS)

    Annegarn, H.J.; Sellschop, J.P.F.; Van Grieken, R.E.; Winchester, J.W.

    The sulfur content of atmospheric particulate matter in non-urban areas is apparently rising above natural levels in the Northern Hemisphere. Sulfur emissions to the atmosphere are also increasing with increasing combustion of fossil fuels. Current research is being focussed not only on gaseous sulfur dioxide, but also on particulate forms, including sulfates and sulfuric acid. A global network of non urban studies using proton induced X-ray emission (PIXE) of which the sampling site at Gobabeb in the Namib desert is one, are developing a data base on which questions of natural levels of sulfur can be answered

  17. The effect of discontinuous gas exchange on respiratory water loss in grasshoppers (Orthoptera: Acrididae) varies across an aridity gradient.

    Science.gov (United States)

    Huang, Shu-Ping; Talal, Stav; Ayali, Amir; Gefen, Eran

    2015-08-01

    The significance of discontinuous gas-exchange cycles (DGC) in reducing respiratory water loss (RWL) in insects is contentious. Results from single-species studies are equivocal in their support of the classic 'hygric hypothesis' for the evolution of DGC, whereas comparative analyses generally support a link between DGC and water balance. In this study, we investigated DGC prevalence and characteristics and RWL in three grasshopper species (Acrididae, subfamily Pamphaginae) across an aridity gradient in Israel. In order to determine whether DGC contributes to a reduction in RWL, we compared the DGC characteristics and RWL associated with CO2 release (transpiration ratio, i.e. the molar ratio of RWL to CO2 emission rates) among these species. Transpiration ratios of DGC and continuous breathers were also compared intraspecifically. Our data show that DGC characteristics, DGC prevalence and the transpiration ratios correlate well with habitat aridity. The xeric-adapted Tmethis pulchripennis exhibited a significantly shorter burst period and lower transpiration ratio compared with the other two mesic species, Ocneropsis bethlemita and Ocneropsis lividipes. However, DGC resulted in significant water savings compared with continuous exchange in T. pulchripennis only. These unique DGC characteristics for T. pulchripennis were correlated with its significantly higher mass-specific tracheal volume. Our data suggest that the origin of DGC may not be adaptive, but rather that evolved modulation of cycle characteristics confers a fitness advantage under stressful conditions. This modulation may result from morphological and/or physiological modifications. © 2015. Published by The Company of Biologists Ltd.

  18. Aridity promotes bet hedging via delayed hatching: a case study with two temporary pond crustaceans along a latitudinal gradient.

    Science.gov (United States)

    Pinceel, Tom; Vanschoenwinkel, Bram; Hawinkel, Wouter; Tuytens, Karen; Brendonck, Luc

    2017-05-01

    Climate change does affect not only average rainfall and temperature but also their variation, which can reduce the predictability of suitable conditions for growth and reproduction. This situation is problematic for inhabitants of temporary waters whose reproductive success depends on rainfall and evaporation that determine the length of the aquatic phase. For organisms with long-lived dormant life stages, bet hedging models suggest that a fraction of these should stay dormant during each growing season to buffer against the probability of total reproductive failure in variable environments. Thus far, however, little empirical evidence supports this prediction in aquatic organisms. We study geographic variation in delayed hatching of dormant eggs in natural populations of two crustaceans, Branchinella longirostris and Paralimnadia badia, that occur in temporary rock pools along a 725 km latitudinal aridity gradient in Western Australia. Consistent with bet hedging theory, populations of both species were characterised by delayed hatching under common garden conditions and hatching fractions decreased towards the drier end of the gradient where the probability of reproductive success was shown to be lower. This decrease was most pronounced in the species with the longer maturation time, presumably because it is more sensitive to the higher prevalence of short inundations. Overall, these findings illustrate that regional variation in climate can be reflected in differential investment in bet hedging and hints at a higher importance of delayed hatching to persist when the climate becomes harsher. Such strategies could become exceedingly relevant as determinants of vulnerability under climate change.

  19. Bridging Thermal Infrared Sensing and Physically-Based Evapotranspiration Modeling: From Theoretical Implementation to Validation Across an Aridity Gradient in Australian Ecosystems

    DEFF Research Database (Denmark)

    Mallick, Kaniska; Toivonen, Erika; Trebs, Ivonne

    2018-01-01

    model, the Surface Temperature Initiated Closure (STIC1.2), that physically integrates TR observations into a combined Penman‐Monteith Shuttleworth‐Wallace (PM‐SW) framework for directly estimating E, and overcoming the uncertainties associated with T0 and gA determination. An evaluation of STIC1.......2 against high temporal frequency SEB flux measurements across an aridity gradient in Australia revealed a systematic error of 10% – 52% in E from mesic to arid ecosystem, and low systematic error in sensible heat fluxes (H) (12% – 25%) in all ecosystems. Uncertainty in TR versus moisture availability...

  20. Birds and conservation significance of the Namib Desert's least ...

    African Journals Online (AJOL)

    -long Namib Desert and it remains the least known coastal wetland on a desert coast rich in shorebirds. Two surveys of the Baia dos Tigres region in 1999 and 2001 indicated a rich wetland bird diversity consisting of 25 species, with a total of ...

  1. Biology of larks (Aves: Alaudidae) in the central Namib Desert ...

    African Journals Online (AJOL)

    The biology of six species of larks in the Namib Desert near Walvis Bay, South West Africa, was studied in 1964, 1965 and 1966. 2. All species reproduced following rainfall in summer and autumn months, with the appearance of green grass and abundant insects on which the birds fed. 3. The primarily insectivorous species ...

  2. Reproductive cycle of the Namib giant ground gecko ...

    African Journals Online (AJOL)

    The reproductive cycle of the Namib giant ground gecko, Chondrodactylus angulifer, from southern Africa was described from a histological examination of gonadal material from museum specimens. Males followed a seasonal testicular cycle in which (based on available specimens) the major period of spermiogenesis ...

  3. Modelling the topsoil carbon stock of agricultural lands with the Stochastic Gradient Treeboost in a semi-arid Mediterranean region

    KAUST Repository

    Schillaci, Calogero

    2016-10-29

    Efficient modelling methods to assess soil organic carbon (SOC) stocks have a pivotal importance as inputs for global carbon cycle studies and decision-making processes. However, laboratory analyses of SOC field samples are costly and time consuming. Global-scale estimates of SOC were recently made according to categorical variables, including land use and soil texture. Remote sensing (RS) data can contribute to the better modelling of the spatial distribution of SOC stock at a regional scale. In the present study, we used Stochastic Gradient Treeboost (SGT) to estimate the topsoil (0–30 cm) SOC stock of a Mediterranean semiarid area (Sicily, Italy, 25,286 km2). In particular, our study examined agricultural lands, which represent approximately 64% of the entire region. An extensive soil dataset (2202 samples, 1 profile/7.31 km2 on average) was acquired from the soil database of Sicily. The georeferenced field observations were intersected with remotely sensed environmental data and other spatial data, including climatic data from WORLDCLIM, land cover from CORINE, soil texture, topography and derived indices. Finally, the SGT was compared to published global estimates (GSOC) and data from the International Soil Reference and Information Centre (ISRIC) Soil Grids by comparing the pseudo-regressions of the SGT, GSOC and ISRIC with soil observations. The mean SOC stock across the entire region that was estimated by GSOC and ISRIC was 3.9% lower and 46.2% higher compared to the SGT. The SGT efficiently predicted SOC stocks that were < 70 t ha− 1 (corresponding to the 90th percentile of the observed values). On average, the coefficient of variation of the SGT model was 3.6% when computed on the whole dataset and remained lower than 23% when computed on a distribution basis. The SGT mean absolute error was 14.84 t ha− 1, 18.4% and 36.3% lower than GSOC and ISRIC, respectively. The mean annual rainfall, soil texture, land use, mean annual temperature and Landsat 7

  4. Modelling the topsoil carbon stock of agricultural lands with the Stochastic Gradient Treeboost in a semi-arid Mediterranean region

    KAUST Repository

    Schillaci, Calogero; Lombardo, Luigi; Saia, Sergio; Fantappiè , Maria; Mä rker, Michael; Acutis, Marco

    2016-01-01

    Efficient modelling methods to assess soil organic carbon (SOC) stocks have a pivotal importance as inputs for global carbon cycle studies and decision-making processes. However, laboratory analyses of SOC field samples are costly and time consuming. Global-scale estimates of SOC were recently made according to categorical variables, including land use and soil texture. Remote sensing (RS) data can contribute to the better modelling of the spatial distribution of SOC stock at a regional scale. In the present study, we used Stochastic Gradient Treeboost (SGT) to estimate the topsoil (0–30 cm) SOC stock of a Mediterranean semiarid area (Sicily, Italy, 25,286 km2). In particular, our study examined agricultural lands, which represent approximately 64% of the entire region. An extensive soil dataset (2202 samples, 1 profile/7.31 km2 on average) was acquired from the soil database of Sicily. The georeferenced field observations were intersected with remotely sensed environmental data and other spatial data, including climatic data from WORLDCLIM, land cover from CORINE, soil texture, topography and derived indices. Finally, the SGT was compared to published global estimates (GSOC) and data from the International Soil Reference and Information Centre (ISRIC) Soil Grids by comparing the pseudo-regressions of the SGT, GSOC and ISRIC with soil observations. The mean SOC stock across the entire region that was estimated by GSOC and ISRIC was 3.9% lower and 46.2% higher compared to the SGT. The SGT efficiently predicted SOC stocks that were < 70 t ha− 1 (corresponding to the 90th percentile of the observed values). On average, the coefficient of variation of the SGT model was 3.6% when computed on the whole dataset and remained lower than 23% when computed on a distribution basis. The SGT mean absolute error was 14.84 t ha− 1, 18.4% and 36.3% lower than GSOC and ISRIC, respectively. The mean annual rainfall, soil texture, land use, mean annual temperature and Landsat 7

  5. Tree water potentials supporting an explanation for the occurrence of Vachellia erioloba in the Namib Desert (Namibia

    Directory of Open Access Journals (Sweden)

    Joachim H. A. Krug

    2017-09-01

    Full Text Available Background Site-vegetation relations of Vachellia erioloba, Faidherbia albida, Euclea pseudebenus and Tamarix usneoides in two contrasting locations in the Namib Desert (Namibia were evaluated with the goal to relate soil water availability to the occurrence of trees under hyper-arid conditions. Methods Plant water potentials were measured using a pressure chamber in the field. Pre-dawn water potentials were assessed to reflect the soil water potential of the rhizosphere. Midday water potentials were measured to assess the strongest negative water potential applied by the sample trees. Results Pre-dawn water potentials and midday water potentials indicated access to soil water in the rhizosphere and by this, provide an explanation for an occurrence of V. erioloba within the extreme environmental conditions of sand dunes in the Namib Desert. Diurnal ranges seem to reflect more and less suitable stands, in terms of soil water availability, within the sampling sites. While the impact of the ephemeral Kuiseb river on soil water availability was assessed through the four species’ plant-internal water relations, comparable pre-dawn water potentials of V. erioloba at both sites indicate soil water availability also in the dunes of Namibrand. The extreme midday water potentials of the dune plants possibly show the upper limit of tolerance for V. erioloba. Conclusions The preliminary data provide an explanation of the occurrence and distribution of the investigated species in beds of ephemeral rivers and on dunes under the hyper-arid climatic conditions of the Namib Desert and qualify suitability within the assessed sites. Understanding the plant-physiological processes and assessing the plant-internal water potential provides a valuable tool to evaluate soil water availability within the rhizosphere and to describe an adaptation potential of investigated species. The comparability of pre-dawn water potentials at both sites indicates unexpected soil

  6. Dynamic responses of photosystem II in the Namib Desert shrub, Zygophyllum prismatocarpum, during and after foliar deposition of limestone dust

    International Nuclear Information System (INIS)

    Heerden, P.D.R. van; Krueger, G.H.J.; Kilbourn Louw, M.

    2007-01-01

    The effects of limestone dust deposition on vegetation in desert ecosystems have not yet been reported. We investigated these effects in a succulent shrub from the Namib Desert at a limestone quarry near Skorpion Zinc mine (Namibia). Effects of limestone dust were determined in Zygophyllum prismatocarpum (dollar bush) plants with heavy, moderate and no visible foliar dust cover by means of chlorophyll a fluorescence measurements. Limestone dust deposition decreased overall plant performance through loss of chlorophyll content, inhibition of CO 2 assimilation, uncoupling of the oxygen-evolving complex and decreased electron transport. Importantly, dynamic recovery occurred after termination of limestone extraction at the quarry. Recovery was accelerated by rainfall, mainly because of dust removal from leaves and stimulation of new growth. These results indicate that limestone dust has severe effects on photosynthesis in desert shrubs, but that recovery is possible and that, in arid environments, this process is modulated by rainfall. - Limestone dust deposition reduced photosynthetic capacity in the Namib Desert shrub, Zygophyllum prismatocarpum

  7. Fog water chemistry in the Namib desert, Namibia

    Science.gov (United States)

    Eckardt, Frank D.; Schemenauer, Robert S.

    This study documents the ion concentrations and ion enrichment relative to sea water, in Namib Desert fog water, with the purpose of establishing its suitability for future fogwater collection schemes, while also examining claims that Namib Desert fog water carries exceptionally high concentrations of sulphate, which may be responsible for the formation of gypsum deposits in the desert. The work suggests that Namibian fog water is at least as clean as has been reported from other coastal deserts in South America and Arabia, and provides a source of very clean water for the coastal desert region of south-western Africa. It does not appear that fog is an efficient sulphur source for the formation of the gypsum deposits, unless rare events with high concentrations of marine sulphur compounds occur.

  8. Water regime history drives responses of soil Namib Desert microbial communities to wetting events

    Science.gov (United States)

    Frossard, Aline; Ramond, Jean-Baptiste; Seely, Mary; Cowan, Don A.

    2015-07-01

    Despite the dominance of microorganisms in arid soils, the structures and functional dynamics of microbial communities in hot deserts remain largely unresolved. The effects of wetting event frequency and intensity on Namib Desert microbial communities from two soils with different water-regime histories were tested over 36 days. A total of 168 soil microcosms received wetting events mimicking fog, light rain and heavy rainfall, with a parallel “dry condition” control. T-RFLP data showed that the different wetting events affected desert microbial community structures, but these effects were attenuated by the effects related to the long-term adaptation of both fungal and bacterial communities to soil origins (i.e. soil water regime histories). The intensity of the water pulses (i.e. the amount of water added) rather than the frequency of wetting events had greatest effect in shaping bacterial and fungal community structures. In contrast to microbial diversity, microbial activities (enzyme activities) showed very little response to the wetting events and were mainly driven by soil origin. This experiment clearly demonstrates the complexity of microbial community responses to wetting events in hyperarid hot desert soil ecosystems and underlines the dynamism of their indigenous microbial communities.

  9. Infidelity in the outback: climate signal recorded in Δ18O of leaf but not branch cellulose of eucalypts across an Australian aridity gradient.

    Science.gov (United States)

    Cheesman, Alexander W; Cernusak, Lucas A

    2017-05-01

    The isotopic composition of leaf water in terrestrial plants is highly dependent upon a plant's environment. This isotopic signature can become integrated into organic molecules, allowing the isotopic composition of biomarkers such as cellulose to be used as sensitive paleo and climatic proxies. However, the mechanisms by which cellulose isotopic composition reflect environmental conditions are complex, and may vary between leaf and woody tissues. To date few empirical tests have been made on the relative roles of leaf-water enrichment and source water on the isotopic composition of leaf and wood cellulose within the same plant. Here, we study both leaf and branch wood cellulose, as well as xylem/source water of eucalypts across a 900 km aridity gradient in NE Australia. Across 11 sites, spanning average annual precipitation of 235-1400 mm and average relative humidity of 33-70%, we found a strong and consistent trend in leaf cellulose. However, once the effect of altered source water was considered we found wood cellulose to show no trend across this environmental gradient. We consider potential mechanisms that could explain the 'damping' of a climatic signal within wood cellulose and consider the implication and limitations on the use of tree-ring cellulose as a climate proxy. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  10. Orbital radar studies of paleodrainages in the central Namib Desert

    Science.gov (United States)

    Lancaster, N.; Schaber, G.G.; Teller, J.T.

    2000-01-01

    Orbital radar images of the central Namib Desert show clearly the extent of relict fluvial deposits associated with former courses of the Tsondab and Kuiseb rivers. South of the Kuiseb River, radar data show the existence of a drainage network developed in calcrete-cemented late Tertiary fluvial deposits. The sand-filled paleovalleys are imaged as radar-dark tones in contrast to the radar-bright interfluves where the calcreted gravels occur. The drainage network developed as a result of local runoff from indurated gravels and channeled surface and subsurface flow to the sites of the many interdune lacustrine deposits found in the area. (C) Elsevier Science Inc., 2000.Orbital radar images of the central Namib Desert show clearly the extent of relict fluvial deposits associated with former courses of the Tsondab and Kuiseb rivers. South of the Kuiseb River, radar data show the existence of a drainage network developed in calcrete-cemented late Tertiary fluvial deposits. The sand-filled paleovalleys are imaged as radar-dark tones in contrast to the radar-bright interfluves where the calcreted gravels occur. The drainage network developed as a result of local runoff from indurated gravels and channeled surface and subsurface flow to the sites of the many interdune lacustrine deposits found in the area.

  11. Differences in Water-use Strategies Along an Aridity Gradient Between Two Coexisting Desert Shrubs (Reaumuria soongorica and Nitraria sphaerocarpa): Isotopic Approaches with Physiological Evidence

    Science.gov (United States)

    Zhang, C.; Li, X.; Huawu, W.; Wang, P.; Wang, Y.; WU, X.; Li, W.; Huang, Y.

    2017-12-01

    Understanding of the responses of different plant species to changes in available water source is critical for accurately modeling and predicting species dynamic and the effect of expected climate change on plant distribution. Our study aimed to explore whether there were differences of water use strategies between the two coexisting shrubs (Reaumuria songarica Maxim and Nitraria.sphaerocarpa Maxim ) in response to different amounts of summer precipitation. We conducted a 3-year field observations at three sites along a gradient of precipitation from middle to lower reaches of Heihe River basin (HRB), northwestern China. Stable oxygen composition (δ18O) in plant xylem water, soil water, and groundwater were analyzed concurrently with ecophysiological measurement at monthly intervals during the growing seasons. The results showed that both R. soongorica and N. sphaerocarpa growing in regions with precipitation dominated water supply exhibited distinct seasonal pattern in water source utilization. In contrast, R. soongorica in the most arid site has the consistent water-use strategy relying primarily on groundwater sources regardless seasonality of precipitation. Water source for coexisting R. soongorica and N. sphaerocarpa did not differ at the sites where precipitation amount was high, but they were a significant different in more arid locations. N. sphaerocarpa is more sensitive to summer precipitation than R. soongorica in terms of predawn water potential (Ψpd), stomatal conductance and foliage δ13C. Our findings reveal that plant relying groundwater sources could maintain a consistent water use strategies, but did not for plants took up precipitation-derived water source. Our results demonstrated that N. sphaerocarpa with a shallower rooting system was more responsive for summer rainfall than did for R. soongorica. We also found that the difference in water source uptake between the coexisting species was more apparent in more arid locations. Results of this

  12. Comparable Monoterpene emission from pine forests across 500 mm precipitation gradient in the semi-arid transition zone

    Science.gov (United States)

    Seco, Roger; Karl, Thomas; Turnipseed, Andrew; Greenberg, Jim; Guenther, Alex; Llusia, Joan; Penuelas, Josep; Dicken, Uri; Rotenberg, Eyal; Rohatyn, Shani; Preisler, Yakir; Yakir, Dan

    2014-05-01

    Atmospheric volatile organic compounds (VOCs) have key environmental and biological roles, and can affect atmospheric chemistry, secondary aerosol formation, and as a consequence also climate. At the same time, global changes in climate arising from human activities can modify the VOC emissions of vegetation in the coming years. Monoterpene emission fluxes were measured during April 2013 at two forests in the semi-arid climate of Israel. Both forests were dominated by Pinus halepensis trees of similar age, but differed in the amount of annual average precipitation received (~276 and ~760 mm at the Yatir and Birya sites, respectively). Measurements performed included leaf-level sampling and gas exchange, as well as canopy-level flux calculations. Leaf level monoterpene emissions were sampled from leaf cuvettes with adsorbent cartridges and later analyzed by GC-MS. Canopy scale fluxes were calculated with the Disjunct Eddy Covariance technique by means of a Quadrupole PTRMS and eddy-covariance system. We report the differences observed between the two forests in terms of photosynthetic activity and monoterpene emissions, aiming to see the effect of the different climatic regimes at each location. Significantly higher emission rates of monoterpenes were observed in the wetter site during mid-day, in both the leaf scale and canopy scale measurements. Remarkably, however, normalized to 30C and corrected for tree density differences between the sites indicated comparable emission rates for both sites, with higher emission rated in the evening hours in the dry site at the edge of the Negev Desert. Modeling the monoterpene emission rates using MEGAN v2.1 indicated better agreement with observations in the wetter site then in the dry site, especially with respect to fluxes during the evening hours.

  13. Interannual variability of a precipitation gradient along the semi-arid catchment areas for the metropolitan region of Lima- Peru in relation to atmospheric circulation at the mesoscale

    Science.gov (United States)

    Otto, Marco; Seidel, Jochen; Trachte, Katja

    2013-04-01

    following questions. How is the interannual variability of the observed precipitation gradient related to atmospheric circulation east (Amazon basin) and west (south-east Pacific) of the study region? If those relations are quantifiable, are there any forecast potentials for the characteristics of the precipitation gradient during the raining season? The results of the study provide valuable information needed to understand the generation of rainfall in the frame of a case study for the largest metropolitan area that is located at the arid Pacific coast of Peru. This information may also be useful for local managers in order to optimise water resource management and land use strategies.

  14. Hybrid engineered materials with high water-collecting efficiency inspired by Namib Desert beetles.

    Science.gov (United States)

    Zhu, Hai; Guo, Zhiguang

    2016-05-21

    Inspired by Namib Desert beetles, a hybrid superhydrophobic surface was fabricated, showing highly efficient fog harvesting with a water collection rate (WCR) of 1309.9 mg h(-1) cm(-2). And, the surface possessed an excellent robustness and self-cleaning property.

  15. Fog inhibition, satellite fauna and unusual leaf structure in a Namib Desert dune plant Trianthema hereroensis

    International Nuclear Information System (INIS)

    Seely, M.K.; De Vos, M.P.; Louw, G.N.

    1977-01-01

    The plant Trianthema hereroensis, which is endemic to the Namib Desert, has been shown to absorb tritiated water rapidly through its leaves and translocate the labelled water to the root system. The unusual leaf structure and the associated satellite fauna have been described [af

  16. Radioactive waste isolation in arid zones

    International Nuclear Information System (INIS)

    Nativ, R.

    1991-01-01

    Arid zones are currently considered ideal sites for the isolation of radioactive and other hazardous wastes. Because arid zones have low precipitation, other hydrological features such as minimal surface water, low recharge rates, small hydraulic gradients, deep water table and lower water quality are also inferred. These premises have proved to be misleading in many circumstances, resulting in groundwater contamination by radionuclides. Case studies indicating surface water damages, occurrence of active recharge, groundwater flow and considerable discharge of potable water in arid and hyper-arid terrains, as well as the possibility of future climatic changes, require careful hydrological assessment of proposed sites in arid areas. (author)

  17. Fog-basking behaviour and water collection efficiency in Namib Desert Darkling beetles

    OpenAIRE

    Dacke Marie; Nørgaard Thomas

    2010-01-01

    Abstract Background In the Namib Desert fog represents an alternative water source. This is utilised by Darkling beetles (Tenebrionidae) that employ different strategies for obtaining the fog water. Some dig trenches in the sand, while others use their own bodies as fog collectors assuming a characteristic fog-basking stance. Two beetle species from the genus Onymacris have been observed to fog-bask on the ridges of the sand dunes. These beetles all have smooth elytra surfaces, while another ...

  18. Footprints in the sand: independent reduction of subdigital lamellae in the Namib-Kalahari burrowing geckos.

    Science.gov (United States)

    Lamb, Trip; Bauer, Aaron M

    2006-04-07

    Many desert organisms exhibit convergence, and certain physical factors such as windblown sands have generated remarkably similar ecomorphs across divergent lineages. The burrowing geckos Colopus, Chondrodactylus and Palmatogecko occupy dune ecosystems in the Namib and Kalahari deserts of southwest Africa. Considered closely related, they share several putative synapomorphies, including reduced subdigital pads (toe pads) and spinose digital scales. Though recognized as part of Africa's ecologically diverse Pachydactylus Group, the burrowing geckos' precise phylogenetic affinities remain elusive. Convergent pedal modification provides a tenable alternative explaining the geckos' derived terrestriality and adaptation to Namib and Kalahari sands. We generated a molecular phylogeny for the Pachydactylus Group to examine evolutionary relationships among the burrowing geckos and infer historical patterns of pedal character change. Bayesian and parsimony analyses revealed all three burrowing genera to be deeply nested within Pachydactylus, each genus belonging to a separate clade. Strong support for these distinct clades indicates ecomorphological adaptations for burrowing have evolved independently three times in the southern Pachydactylus Group. We argue that the physical properties of Namib and Kalahari sands played a principal role in selecting for pedal similarity.

  19. River sediment metal and nutrient variations along an urban-agriculture gradient in an arid austral landscape: implications for environmental health.

    Science.gov (United States)

    Dalu, Tatenda; Wasserman, Ryan J; Wu, Qihang; Froneman, William P; Weyl, Olaf L F

    2018-01-01

    The effect of metals on environmental health is well documented and monitoring these and other pollutants is considered an important part of environmental management. Developing countries are yet to fully appreciate the direct impacts of pollution on aquatic ecosystems and as such, information on pollution dynamics is scant. Here, we assessed the temporal and spatial dynamics of stream sediment metal and nutrient concentrations using contaminant indices (e.g. enrichment factors, pollution load and toxic risk indices) in an arid temperate environment over the wet and dry seasons. The mean sediment nutrient, organic matter and metal concentration were highest during the dry season, with high values being observed for the urban environment. Sediment contaminant assessment scores indicated that during the wet season, the sediment quality was acceptable, but not so during the dry season. The dry season had low to moderate levels of enrichment for metals B, Cu, Cr, Fe, Mg, K and Zn. Overall, applying the sediment pollution load index highlighted poor quality river sediment along the length of the river. Toxic risk index indicated that most sites posed no toxic risk. The results of this study highlighted that river discharge plays a major role in structuring temporal differences in sediment quality. It was also evident that infrastructure degradation was likely contributing to the observed state of the river quality. The study contributes to our understanding of pollution dynamics in arid temperate landscapes where vast temporal differences in base flow characterise the riverscape. Such information is further useful for contrasting sediment pollution dynamics in aquatic environments with other climatic regions.

  20. Concentrations and Fractionation of Carbon, Iron, Sulfur, Nitrogen and Phosphorus in Mangrove Sediments Along an Intertidal Gradient (Semi-Arid Climate, New Caledonia

    Directory of Open Access Journals (Sweden)

    Jonathan Deborde

    2015-02-01

    Full Text Available In mangrove ecosystems, strong reciprocal interactions exist between plant and substrate. Under semi-arid climate, Rhizophora spp. are usually predominant, colonizing the seashore, and Avicennia marina develops at the edge of salt-flats, which is the highest zone in the intertidal range. Along this zonation, distribution and speciation of C, Fe, S, N, and P in sediments and pore-waters were investigated. From the land-side to the sea-side of the mangrove, sediments were characterized by I/ increase in: (i water content; (ii TOC; (iii mangrove-derived OM; II/ and decrease in: (i salinity; (ii redox; (iii pH; (iv solid Fe and solid P. Beneath Avicennia and Rhizophora, TS accumulated at depth, probably as a result of reduction of iron oxides and sulfate. The loss of total Fe observed towards the sea-side may be related to sulfur oxidation and to more intense tidal flushing of dissolved components. Except the organic forms, dissolved N and P concentrations were very low beneath Avicennia and Rhizophora stands, probably as a result of their uptake by the root systems. However, in the unvegetated salt-flat, NH4+ can accumulate in organic rich and anoxic layers. This study shows: (i the evolution of mangrove sediment biogeochemistry along the intertidal zone as a result of the different duration of tidal inundation and organic enrichment; and (ii the strong links between the distribution and speciation of the different elements.

  1. Regional evapotranspiration from an image-based implementation of the Surface Temperature Initiated Closure (STIC1.2) model and its validation across an aridity gradient in the conterminous US

    Science.gov (United States)

    Bhattarai, Nishan; Mallick, Kaniska; Brunsell, Nathaniel A.; Sun, Ge; Jain, Meha

    2018-04-01

    Recent studies have highlighted the need for improved characterizations of aerodynamic conductance and temperature (gA and T0) in thermal remote-sensing-based surface energy balance (SEB) models to reduce uncertainties in regional-scale evapotranspiration (ET) mapping. By integrating radiometric surface temperature (TR) into the Penman-Monteith (PM) equation and finding analytical solutions of gA and T0, this need was recently addressed by the Surface Temperature Initiated Closure (STIC) model. However, previous implementations of STIC were confined to the ecosystem-scale using flux tower observations of infrared temperature. This study demonstrates the first regional-scale implementation of the most recent version of the STIC model (STIC1.2) that integrates the Moderate Resolution Imaging Spectroradiometer (MODIS) derived TR and ancillary land surface variables in conjunction with NLDAS (North American Land Data Assimilation System) atmospheric variables into a combined structure of the PM and Shuttleworth-Wallace (SW) framework for estimating ET at 1 km × 1 km spatial resolution. Evaluation of STIC1.2 at 13 core AmeriFlux sites covering a broad spectrum of climates and biomes across an aridity gradient in the conterminous US suggests that STIC1.2 can provide spatially explicit ET maps with reliable accuracies from dry to wet extremes. When observed ET from one wet, one dry, and one normal precipitation year from all sites were combined, STIC1.2 explained 66 % of the variability in observed 8-day cumulative ET with a root mean square error (RMSE) of 7.4 mm/8-day, mean absolute error (MAE) of 5 mm/8-day, and percent bias (PBIAS) of -4 %. These error statistics showed relatively better accuracies than a widely used but previous version of the SEB-based Surface Energy Balance System (SEBS) model, which utilized a simple NDVI-based parameterization of surface roughness (zOM), and the PM-based MOD16 ET. SEBS was found to overestimate (PBIAS = 28 %) and MOD16 was found

  2. Fog-basking behaviour and water collection efficiency in Namib Desert Darkling beetles.

    Science.gov (United States)

    Nørgaard, Thomas; Dacke, Marie

    2010-07-16

    In the Namib Desert fog represents an alternative water source. This is utilised by Darkling beetles (Tenebrionidae) that employ different strategies for obtaining the fog water. Some dig trenches in the sand, while others use their own bodies as fog collectors assuming a characteristic fog-basking stance. Two beetle species from the genus Onymacris have been observed to fog-bask on the ridges of the sand dunes. These beetles all have smooth elytra surfaces, while another species with elytra covered in bumps is reported to have specialised adaptations facilitating water capture by fog-basking. To resolve if these other beetles also fog-bask, and if an elytra covered in bumps is a more efficient fog water collector than a smooth one, we examined four Namib Desert beetles; the smooth Onymacris unguicularis and O. laeviceps and the bumpy Stenocara gracilipes and Physasterna cribripes. Here we describe the beetles' fog-basking behaviour, the details of their elytra structures, and determine how efficient their dorsal surface areas are at harvesting water from fog. The beetles differ greatly in size. The largest P. cribripes has a dorsal surface area that is 1.39, 1.56, and 2.52 times larger than O. unguicularis, O. laeviceps, and S. gracilipes, respectively. In accordance with earlier reports, we found that the second largest O. unguicularis is the only one of the four beetles that assumes the head standing fog-basking behaviour, and that fog is necessary to trigger this behaviour. No differences were seen in the absolute amounts of fog water collected on the dorsal surface areas of the different beetles. However, data corrected according to the sizes of the beetles revealed differences. The better fog water harvesters were S. gracilipes and O. unguicularis while the large P. cribripes was the poorest. Examination of the elytra microstructures showed clear structural differences, but the elytra of all beetles were found to be completely hydrophobic. The differences in

  3. Fog-basking behaviour and water collection efficiency in Namib Desert Darkling beetles

    Directory of Open Access Journals (Sweden)

    Dacke Marie

    2010-07-01

    Full Text Available Abstract Background In the Namib Desert fog represents an alternative water source. This is utilised by Darkling beetles (Tenebrionidae that employ different strategies for obtaining the fog water. Some dig trenches in the sand, while others use their own bodies as fog collectors assuming a characteristic fog-basking stance. Two beetle species from the genus Onymacris have been observed to fog-bask on the ridges of the sand dunes. These beetles all have smooth elytra surfaces, while another species with elytra covered in bumps is reported to have specialised adaptations facilitating water capture by fog-basking. To resolve if these other beetles also fog-bask, and if an elytra covered in bumps is a more efficient fog water collector than a smooth one, we examined four Namib Desert beetles; the smooth Onymacris unguicularis and O. laeviceps and the bumpy Stenocara gracilipes and Physasterna cribripes. Here we describe the beetles' fog-basking behaviour, the details of their elytra structures, and determine how efficient their dorsal surface areas are at harvesting water from fog. Results The beetles differ greatly in size. The largest P. cribripes has a dorsal surface area that is 1.39, 1.56, and 2.52 times larger than O. unguicularis, O. laeviceps, and S. gracilipes, respectively. In accordance with earlier reports, we found that the second largest O. unguicularis is the only one of the four beetles that assumes the head standing fog-basking behaviour, and that fog is necessary to trigger this behaviour. No differences were seen in the absolute amounts of fog water collected on the dorsal surface areas of the different beetles. However, data corrected according to the sizes of the beetles revealed differences. The better fog water harvesters were S. gracilipes and O. unguicularis while the large P. cribripes was the poorest. Examination of the elytra microstructures showed clear structural differences, but the elytra of all beetles were found to

  4. Arid Zone Hydrology

    Science.gov (United States)

    Arid zone hydrology encompasses a wide range of topics and hydro-meteorological and ecological characteristics. Although arid and semi-arid watersheds perform the same functions as those in humid environments, their hydrology and sediment transport characteristics cannot be readily predicted by inf...

  5. Landsat TM data processing for lithological discrimination in the Caraculo area (Namibe Province, SW Angola)

    Science.gov (United States)

    Alberti, A.; Alessandro, V.; Pieruccini, U.; Pranzini, E.

    1993-10-01

    Landsat TM data were used for lithological discrimination and mapping in the little-known, semiarid 900 km 2 area around Caraculo station and the middle course of the Rio Giraul (Namibe Province, SW Angola) following two main procedures. The first of these was based on visual evaluation of three-band composites, band-ratio composites and Principal Component Analysis. The second method relied on the extraction of spectral signatures, and their use to obtain automatic classifications. Satisfactory results were reached with the first procedure, thus allowing - with limited support of ground information — the draft of a lithological map, while the second method was not systematically efficient, even for confirmation of data acquired with the first procedure. Image interpretation suggests that an extensive but hithertoun differentiated metasedimentary complex consisting of a heterogeneous supracrustal sequence should be subdivided into at least two units. Field observations proved that one of these is marked by a notable frequency of marbles and the other is characterized by a widespread occurrence of amphibolitic bodies. Moreover, a belt of undetermined (thermally metamorphosed ?) metamorphic rocks is interposed between them. The distinction of so far unidentified units, though restricted to interpretation of processed Landsat TM data, has significant geological implications also in the regional context and will be helpful in guiding future work with conventional geological methods.

  6. The impact of fog on soil moisture dynamics in the Namib Desert

    Science.gov (United States)

    Li, Bonan; Wang, Lixin; Kaseke, Kudzai F.; Vogt, Roland; Li, Lin; Seely, Mary K.

    2018-03-01

    Soil moisture is a crucial component supporting vegetation dynamics in drylands. Despite increasing attention on fog in dryland ecosystems, the statistical characterization of fog distribution and how fog affects soil moisture dynamics have not been seen in literature. To this end, daily fog records over two years (Dec 1, 2014-Nov 1, 2016) from three sites within the Namib Desert were used to characterize fog distribution. Two sites were located within the Gobabeb Research and Training Center vicinity, the gravel plains and the sand dunes. The third site was located at the gravel plains, Kleinberg. A subset of the fog data during rainless period was used to investigate the effect of fog on soil moisture. A stochastic modeling framework was used to simulate the effect of fog on soil moisture dynamics. Our results showed that fog distribution can be characterized by a Poisson process with two parameters (arrival rate λ and average depth α (mm)). Fog and soil moisture observations from eighty (Aug 19, 2015-Nov 6, 2015) rainless days indicated a moderate positive relationship between soil moisture and fog in the Gobabeb gravel plains, a weaker relationship in the Gobabeb sand dunes while no relationship was observed at the Kleinberg site. The modeling results suggested that mean and major peaks of soil moisture dynamics can be captured by the fog modeling. Our field observations demonstrated the effects of fog on soil moisture dynamics during rainless periods at some locations, which has important implications on soil biogeochemical processes. The statistical characterization and modeling of fog distribution are of great value to predict fog distribution and investigate the effects of potential changes in fog distribution on soil moisture dynamics.

  7. A systemic and interdisciplinary perspective of environmental education. The case of the Higher Education School of Namibe, Angola

    Directory of Open Access Journals (Sweden)

    Adriana Mercedes Ortiz-Blanco

    2017-07-01

    Full Text Available One of the priorities of the Government of the Republic of Angola is the training of teachers and the eradication of illiteracy. The present work to make a proposal of study of environmental education with a systemic and interdisciplinary perspective making recommendations for the generalization of the aforementioned relationship in the context of the Pedagogical Higher School of Namibe. The analysis that is carried out around this in this work transits through fundamental moments: the first, characterized by a general theoretical treatment of the concepts of environmental education, systemic approach and interdisciplinarity and its dialectical interaction, the second focuses its attention on Proposal of some theoretical and methodological recommendations without neglecting the social plan and with the purpose of contributing to the professional improvement in the school object of our study.

  8. Energy and water budgets of larks in a life history perspective : Parental effort varies with aridity

    NARCIS (Netherlands)

    Tieleman, BI; Williams, JB; Visser, GH

    We compared physiological, demographic, and ecological variables of larks to gain insights into life history variation along an aridity gradient, incorporating phylogenetic relationships in analyses when appropriate. Quantifying field metabolic rate (FMR). and water influx rate (WIR) of parents

  9. Geological exploration of Angola from Sumbe to Namibe: A review at the frontier between geology, natural resources and the history of geology

    Science.gov (United States)

    Masse, Pierre; Laurent, Olivier

    2016-01-01

    This paper provides a review of the Geological exploration of the Angola Coast (from Sumbe to Namibe) from pioneer's first geological descriptions and mining inventory to the most recent publications supported by the oil industry. We focus our attention on the following periods: 1875-1890 (Paul Choffat's work, mainly), 1910-1949 (first maps at country scale), 1949-1974 (detailed mapping of the Kwanza-Namibe coastal series), 1975-2000, with the editing of the last version of the Angola geological map at 1:1 million scale and the progressive completion of previous works. Since 2000, there is a renewal in geological fieldwork publications on the area mainly due to the work of university teams. This review paper thus stands at the frontier between geology, natural resources and the history of geology. It shows how geological knowledge has progressed in time, fueled by economic and scientific reasons.

  10. Determining termite diversity in arid Namibian rangelands – a ...

    African Journals Online (AJOL)

    Three methods of sampling termite diversity in arid rangelands were tested in Namibia during the wet (March) and dry (October) seasons of 1998. Six sites were chosen: one pair on each of three farms representing a gradient of land use intensity. At each site, two adjacent plots of 1 ha each were sampled: one plot by a ...

  11. Aridity and decomposition processes in complex landscapes

    Science.gov (United States)

    Ossola, Alessandro; Nyman, Petter

    2015-04-01

    Decomposition of organic matter is a key biogeochemical process contributing to nutrient cycles, carbon fluxes and soil development. The activity of decomposers depends on microclimate, with temperature and rainfall being major drivers. In complex terrain the fine-scale variation in microclimate (and hence water availability) as a result of slope orientation is caused by differences in incoming radiation and surface temperature. Aridity, measured as the long-term balance between net radiation and rainfall, is a metric that can be used to represent variations in water availability within the landscape. Since aridity metrics can be obtained at fine spatial scales, they could theoretically be used to investigate how decomposition processes vary across complex landscapes. In this study, four research sites were selected in tall open sclerophyll forest along a aridity gradient (Budyko dryness index ranging from 1.56 -2.22) where microclimate, litter moisture and soil moisture were monitored continuously for one year. Litter bags were packed to estimate decomposition rates (k) using leaves of a tree species not present in the study area (Eucalyptus globulus) in order to avoid home-field advantage effects. Litter mass loss was measured to assess the activity of macro-decomposers (6mm litter bag mesh size), meso-decomposers (1 mm mesh), microbes above-ground (0.2 mm mesh) and microbes below-ground (2 cm depth, 0.2 mm mesh). Four replicates for each set of bags were installed at each site and bags were collected at 1, 2, 4, 7 and 12 months since installation. We first tested whether differences in microclimate due to slope orientation have significant effects on decomposition processes. Then the dryness index was related to decomposition rates to evaluate if small-scale variation in decomposition can be predicted using readily available information on rainfall and radiation. Decomposition rates (k), calculated fitting single pool negative exponential models, generally

  12. Leaf surface structures enable the endemic Namib desert grass Stipagrostis sabulicola to irrigate itself with fog water.

    Science.gov (United States)

    Roth-Nebelsick, A; Ebner, M; Miranda, T; Gottschalk, V; Voigt, D; Gorb, S; Stegmaier, T; Sarsour, J; Linke, M; Konrad, W

    2012-08-07

    The Namib grass Stipagrostis sabulicola relies, to a large degree, upon fog for its water supply and is able to guide collected water towards the plant base. This directed irrigation of the plant base allows an efficient and rapid uptake of the fog water by the shallow roots. In this contribution, the mechanisms for this directed water flow are analysed. Stipagrostis sabulicola has a highly irregular surface. Advancing contact angle is 98° ± 5° and the receding angle is 56° ± 9°, with a mean of both values of approximately 77°. The surface is thus not hydrophobic, shows a substantial contact angle hysteresis and therefore, allows the development of pinned drops of a substantial size. The key factor for the water conduction is the presence of grooves within the leaf surface that run parallel to the long axis of the plant. These grooves provide a guided downslide of drops that have exceeded the maximum size for attachment. It also leads to a minimum of inefficient drop scattering around the plant. The combination of these surface traits together with the tall and upright stature of S. sabulicola contributes to a highly efficient natural fog-collecting system that enables this species to thrive in a hyperarid environment.

  13. Leaf surface structures enable the endemic Namib desert grass Stipagrostis sabulicola to irrigate itself with fog water

    Science.gov (United States)

    Roth-Nebelsick, A.; Ebner, M.; Miranda, T.; Gottschalk, V.; Voigt, D.; Gorb, S.; Stegmaier, T.; Sarsour, J.; Linke, M.; Konrad, W.

    2012-01-01

    The Namib grass Stipagrostis sabulicola relies, to a large degree, upon fog for its water supply and is able to guide collected water towards the plant base. This directed irrigation of the plant base allows an efficient and rapid uptake of the fog water by the shallow roots. In this contribution, the mechanisms for this directed water flow are analysed. Stipagrostis sabulicola has a highly irregular surface. Advancing contact angle is 98° ± 5° and the receding angle is 56° ± 9°, with a mean of both values of approximately 77°. The surface is thus not hydrophobic, shows a substantial contact angle hysteresis and therefore, allows the development of pinned drops of a substantial size. The key factor for the water conduction is the presence of grooves within the leaf surface that run parallel to the long axis of the plant. These grooves provide a guided downslide of drops that have exceeded the maximum size for attachment. It also leads to a minimum of inefficient drop scattering around the plant. The combination of these surface traits together with the tall and upright stature of S. sabulicola contributes to a highly efficient natural fog-collecting system that enables this species to thrive in a hyperarid environment. PMID:22356817

  14. Effect of wettability and topological features of Namib beetle inspired bumps on dropwise condensation

    Science.gov (United States)

    Ahmad, Shakeel; Tang, Hui; Yao, Haimin

    2017-11-01

    The Stenocara beetle lives in arid desert environment where the only available source of water is fog droplets. The beetle contains many hydrophobic/hydrophilic bumps on its back. Water collection occurs on the hydrophilic patches. Once the droplet reaches the critical volume, it sheds down due to gravity. Although a number of studies on condensation and water collection on beetle inspired structures have been reported in literature, most of them were on micro/nano scale textures. However, in nature the beetle bumps are in millimeter scale. At this scale the role of topological features and gravity becomes crucial for early droplet shedding. Therefore, in this work we numerically investigated the effects of bump shape, wettability contrast, surface slope and hydrophilic patch to total area ratio on droplet shedding volume and time. A three-dimensional lattice Boltzmann method (LBM) based numerical framework was used for the simulations. Compared with bumps of other shapes such a cube or a circular cylinder, faster droplet shedding was obtained over a hemispherical bump. Furthermore, it was found that larger hydrophilic patch to total area ratio for the hemispherical bump significantly increased the droplet shedding time.

  15. Rainwater harvesting in arid and semi-arid zones

    NARCIS (Netherlands)

    Boers, T.M.

    1994-01-01

    In arid and semi-arid regions, the scarcity of water can be alleviated by rainwater harvesting, which is defined as a method of inducing, collecting, storing, and conserving local surface runoff for agriculture. Rainwater harvesting can be applied with different

  16. Water balance and osmoregulation in Stenocara gracilipes, a wax-blooming tenebrionid beetle from the Namib Desert.

    Science.gov (United States)

    Naidu, S G.

    2001-12-01

    Dehydration (10 days at 27 degrees C) of the Namib tenebrionid Stenocara gracilipes resulted in a rapid weight loss (17.5%), and a substantial decline in haemolymph volume (72%). Although the lipid content decreased significantly, metabolic water production was insufficient to maintain total body water (TBW). Rehydration (no food) resulted in increases in haemolymph volume, body weight (sub-normal), and TBW to normality. Haemolymph osmolality, sodium, potassium, chloride, amino acids, and sugars (trehalose and glucose), were all subject to osmoregulatory control during both dehydration and rehydration. Major osmolar effectors in this species are sodium, chloride, and amino acids, with most of the contribution to regulation of haemolymph osmolality coming from changes in the levels of these constituents. Changes in amino acid levels are not the result of interchange with soluble protein during dehydration (the possibility exists during extended rehydration, however). Despite faecal losses of sodium being low (8.2% of that removed from the haemolymph during dehydration), sodium concentrations do not return to normal during rehydration. Chloride concentrations increase supra-normally when access to water is allowed, and remain elevated throughout the rehydration period. Although faecal loss of potassium greatly exceeded the amount removed from the haemolymph (by approximately 1.8 times), haemolymph potassium levels were strongly regulated during rehydration. S. gracilipes demonstrates an exquisite capacity to regulate haemolymph osmolality under conditions of both acute water-shortage and -abundance. Together with an efficient water economy (drinking when fog-water is available, and a superb water conservation mechanism in the form of wax-bloom production), this must serve to contribute to long-term survival of this species in an otherwise harsh abode.

  17. Asynchronous glaciations in arid continental climate

    Science.gov (United States)

    Batbaatar, Jigjidsurengiin; Gillespie, Alan R.; Fink, David; Matmon, Ari; Fujioka, Toshiyuki

    2018-02-01

    Mountain glaciers at ∼26-19 ka, during the global Last Glacial Maximum near the end of the last 105 yr glacial cycle, are commonly considered on the basis of dating and field mapping in several well-studied areas to have been the largest of the late Quaternary and to have advanced synchronously from region to region. However, a numerical sensitivity model (Rupper and Roe, 2008) predicts that the fraction of ablation due to melting varies across Central Asia in proportion to the annual precipitation. The equilibrium-line altitude of glaciers across this region likely varies accordingly: in high altitude, cold and arid regions sublimation can ablate most of the ice, whereas glaciers fed by high precipitation cannot ablate completely due to sublimation alone, but extend downhill until higher temperatures there cause them to melt. We have conducted field studies and 10Be dating at five glaciated sites along a precipitation gradient in Mongolia to test the Rupper/Roe model. The sites are located in nearby 1.875 × 1.875° cells of the Rupper/Roe model, each with a different melt fraction, in this little-studied region. The modern environment of the sites ranges from dry subhumid in the north (47.7° N) to arid in the south (45° N). Our findings show that the maximum local advances in the dry subhumid conditions predated the global Last Glacial Maximum and were likely from MIS 3. However, we also found that at ∼8-7 ka a cirque glacier in one mountain range of the arid Gobi desert grew to a magnitude comparable to that of the local maximum extent. This Holocene maximum occurred during a regional pluvial period thousands of years after the retreat of the Pleistocene glaciers globally. This asynchronous behavior is not predicted by the prevailing and generally correct presumption that glacier advances are dominantly driven by temperature, although precipitation also plays a role. Our findings are consistent with and support the Rupper/Roe model, which calls for

  18. Origin and diagenetic evolution of gypsum and microbialitic carbonates in the Late Sag of the Namibe Basin (SW Angola)

    Science.gov (United States)

    Laurent, Gindre-Chanu; Edoardo, Perri; Ian, Sharp R.; Peacock, D. C. P.; Roger, Swart; Ragnar, Poulsen; Hercinda, Ferreira; Vladimir, Machado

    2016-08-01

    Ephemeral evaporitic conditions developed within the uppermost part of the transgressive Late Sag sequence in the Namibe Basin (SW Angola), leading to the formation of extensive centimetre- to metre-thick sulphate-bearing deposits and correlative microbialitic carbonates rich in pseudomorphs after evaporite crystals. The onshore pre-salt beds examined in this study are located up to 25 m underneath the major mid-Aptian evaporitic succession, which is typified at the outcrop by gypsiferous Bambata Formation and in the subsurface by the halite-dominated Loeme Formation. Carbonate-evaporite cycles mostly occur at the top of metre-thick regressive parasequences, which progressively onlap and overstep landward the former faulted (rift) topography, or fill major pre-salt palaeo-valleys. The sulphate beds are made up of alabastrine gypsum associated with embedded botryoidal nodules, dissolution-related gypsum breccia, and are cross-cut by thin satin-spar gypsum veins. Nodular and fine-grained fabrics are interpreted as being diagenetic gypsum deposits resulting from the dissolution and recrystallisation of former depositional subaqueous sulphates, whereas gypsum veins and breccia result from telogenetic processes. The carbonates display a broader diversity of facies, characterised by rapid lateral variations along strike. Thin dolomitic and calcitic bacterial-mediated filamentous microbialitic boundstones enclose a broad variety of evaporite pseudomorphs and can pass laterally over a few metres into sulphate beds. Dissolution-related depositional breccias are also common and indicate early dissolution of former evaporite layers embedded within the microbialites. Sulphate and carbonate units are interpreted as being concomitantly deposited along a tide-dominated coastal supra- to intertidal- sabkha and constitute high-frequency hypersaline precursor events, prior to the accumulation of the giant saline mid-Aptian Bambata and Loeme Formations. Petrographic and geochemical

  19. The potential vulnerability of the Namib and Nama Aquifers due to low recharge levels in the area surrounding the Naukluft Mountains, SW Namibia

    Science.gov (United States)

    Kambinda, Winnie N.; Mapani, Benjamin

    2017-12-01

    The Naukluft Mountains in the Namib Desert are a high rainfall-high discharge area. It sees increased stream-, spring-flow as well as waterfalls during the rainy season. The mountains are a major resource for additional recharge to the Namib and Nama aquifers that are adjacent to the mountains. This paper aimed to highlight the potential vulnerability of the aquifers that surround the Naukluft Mountain area; if the strategic importance of the Naukluft Karst Aquifer (NKA) for bulk water supply becomes necessary. Chloride Mass Balance Method (CMBM) was applied to estimate rainfall available for recharge as well as actual recharge thereof. This was applied using chloride concentration in precipitation, borehole and spring samples collected from the study area. Groundwater flow patterns were mapped from hydraulic head values. A 2D digital elevation model was developed using Arc-GIS. Results highlighted the influence of the NKA on regional groundwater flow. This paper found that groundwater flow was controlled by structural dip and elevation. Groundwater was observed to flow predominantly from the NKA to the south west towards the Namib Aquifer in two distinct flow patterns that separate at the center of the NKA. A distinct groundwater divide was defined between the two flow patterns. A minor flow pattern from the northern parts of the NKA to the north east towards the Nama Aquifer was validated. Due to the substantial water losses, the NKA is not a typical karst aquifer. While the project area receives an average rainfall of 170.36 mm/a, it was estimated that 1-14.24% (maximum 24.43 mm/a) rainfall was available for recharge to the NKA. Actual recharge to the NKA was estimated to be less than 1-18.21% (maximum 4.45 mm/a) reflecting the vast losses incurred by the NKA via discharge. This paper concluded that groundwater resources of the NKA were potentially finite. The possibility of developing the aquifer for bulk water supply would therefore drastically lower recharge

  20. Gut morpbology of tbe Otomyine rodents: an arid-mesic comparison

    African Journals Online (AJOL)

    1998-06-15

    Jun 15, 1998 ... Despite the broad similarity in the gross gastro-intestinal anatomy between the speCies ... Present address: Department of Physiology, University of the Western ..... on growth and renal performance of juvenile Namib rodents.

  1. Causes of early Holocene desertification in arid central Asia

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Liya [Lanzhou University, Key Laboratory of Western China' s Environmental System, Lanzhou, Gansu (China); University of Kiel, Institute of Geosciences, Kiel (Germany); Chen, Fahu [Lanzhou University, Key Laboratory of Western China' s Environmental System, Lanzhou, Gansu (China); Morrill, Carrie [University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, CO (United States); NOAA' s National Climatic Data Center, Paleoclimatology Branch, Boulder, CO (United States); Otto-Bliesner, Bette L.; Rosenbloom, Nan [National Center for Atmospheric Research, Climate and Global Dynamics Division, Boulder, CO (United States)

    2012-04-15

    Paleoclimate records of effective moisture (precipitation minus evaporation, or P-E) show a dry (low effective moisture) period in mid-latitude arid/semi-arid central Asia during the early Holocene (11,000-8,000 years ago) relative to the middle and late Holocene, in contrast to evidence for greater-than-present precipitation at the same time in the south and east Asian monsoonal areas. To investigate the spatial differences in climate response over mid-latitude central Asia and monsoonal Asia we conducted a series of simulations with the Community Climate System Model version 3 coupled climate model for the early, middle and late Holocene. The simulations test the climatic impact of all important forcings for the early Holocene, including changes in orbital parameters, the presence of the remnant Laurentide ice sheet and deglacial freshening of the North Atlantic. Model results clearly show the early Holocene patterns indicated by proxy records, including both the decreased effective moisture in arid central Asia, which occurs in the model primarily during the winter months, and the increase in summer monsoon precipitation in south and east Asia. The model results suggest that dry conditions in the early Holocene in central Asia are closely related to decreased water vapor advection due to reduced westerly wind speed and less evaporation upstream from the Mediterranean, Black, and Caspian Seas in boreal winter. As an extra forcing to the early Holocene climate system, the Laurentide ice sheet and meltwater fluxes have a substantial cooling effect over high latitudes, especially just over and downstream of the ice sheets, but contribute only to a small degree to the early Holocene aridity in central Asia. Instead, most of the effective moisture signal can be explained by orbital forcing decreasing the early Holocene latitudinal temperature gradient and wintertime surface temperature. We find little evidence for regional subsidence related to a stronger summer Asian

  2. Gardens on the Arid Climate

    Science.gov (United States)

    Eka Saputra, Weldy

    2017-12-01

    Bahrain is located in the climate of the arid zone which rainfall is low and irregular. This paper discusses the approaches which response to the local context that has been implemented by the government of Bahrain to sustain the quality of the public garden in the arid climate, turning to green. Generally, the approach is an improvement in the central treatment of waste water system plant that used to irrigate the landscaping, agriculture as well as for industry use. These approaches are not the only technologically, but also involves the participation of community to achieve sustainable garden in this country.

  3. Irradiance gradients

    International Nuclear Information System (INIS)

    Ward, G.J.; Heckbert, P.S.; Technische Hogeschool Delft

    1992-04-01

    A new method for improving the accuracy of a diffuse interreflection calculation is introduced in a ray tracing context. The information from a hemispherical sampling of the luminous environment is interpreted in a new way to predict the change in irradiance as a function of position and surface orientation. The additional computation involved is modest and the benefit is substantial. An improved interpolation of irradiance resulting from the gradient calculation produces smoother, more accurate renderings. This result is achieved through better utilization of ray samples rather than additional samples or alternate sampling strategies. Thus, the technique is applicable to a variety of global illumination algorithms that use hemicubes or Monte Carlo sampling techniques

  4. ARID1B is a specific vulnerability in ARID1A-mutant cancers.

    Science.gov (United States)

    Helming, Katherine C; Wang, Xiaofeng; Wilson, Boris G; Vazquez, Francisca; Haswell, Jeffrey R; Manchester, Haley E; Kim, Youngha; Kryukov, Gregory V; Ghandi, Mahmoud; Aguirre, Andrew J; Jagani, Zainab; Wang, Zhong; Garraway, Levi A; Hahn, William C; Roberts, Charles W M

    2014-03-01

    Recent studies have revealed that ARID1A, encoding AT-rich interactive domain 1A (SWI-like), is frequently mutated across a variety of human cancers and also has bona fide tumor suppressor properties. Consequently, identification of vulnerabilities conferred by ARID1A mutation would have major relevance for human cancer. Here, using a broad screening approach, we identify ARID1B, an ARID1A homolog whose gene product is mutually exclusive with ARID1A in SWI/SNF complexes, as the number 1 gene preferentially required for the survival of ARID1A-mutant cancer cell lines. We show that loss of ARID1B in ARID1A-deficient backgrounds destabilizes SWI/SNF and impairs proliferation in both cancer cells and primary cells. We also find that ARID1A and ARID1B are frequently co-mutated in cancer but that ARID1A-deficient cancers retain at least one functional ARID1B allele. These results suggest that loss of ARID1A and ARID1B alleles cooperatively promotes cancer formation but also results in a unique functional dependence. The results further identify ARID1B as a potential therapeutic target for ARID1A-mutant cancers.

  5. Controls on plant functional surface cover types along a precipitation gradient in the Negev Desert of Israel

    NARCIS (Netherlands)

    Buis, E.; Veldkamp, A.; Boeken, B.; Breemen, van N.

    2009-01-01

    We studied the controls on functional surface cover types in four catchments along a semi-arid to arid precipitation gradient in the northern Negev Desert of Israel. First, we selected four functional types, based on their unique water use and redistribution functionality: shrubs, Asphodelus

  6. Stability measures in arid ecosystems

    Science.gov (United States)

    Nosshi, M. I.; Brunsell, N. A.; Koerner, S.

    2015-12-01

    Stability, the capacity of ecosystems to persist in the face of change, has proven its relevance as a fundamental component of ecological theory. Here, we would like to explore meaningful and quantifiable metrics to define stability, with a focus on highly variable arid and semi-arid savanna ecosystems. Recognizing the importance of a characteristic timescale to any definition of stability, our metrics will be focused scales from annual to multi-annual, capturing different aspects of stability. Our three measures of stability, in increasing order of temporal scale, are: (1) Ecosystem resistance, quantified as the degree to which the system maintains its mean state in response to a perturbation (drought), based on inter-annual variability in Normalized Difference Vegetation Index (NDVI). (2) An optimization approach, relevant to arid systems with pulse dynamics, that models vegetation structure and function based on a trade off between the ability to respond to resource availability and avoid stress. (3) Community resilience, measured as species turnover rate (β diversity). Understanding the nature of stability in structurally-diverse arid ecosystems, which are highly variable, yields theoretical insight which has practical implications.

  7. Aridity influences the recovery of vegetation and shrubland birds after wildfire

    OpenAIRE

    Puig Gironès, Roger; Brotons, Lluís; Pons Ferran, Pere

    2017-01-01

    Wildfires play a determining role in the composition and structure of many plant and animal communities. On the other hand, climate change is considered to be a major driver of current and future fire regime changes. Despite increases in drought in many areas of the world, the effects of aridity on post-fire colonization by animals have been rarely addressed. This study aims to analyse how a regional aridity gradient affects post-fire recovery of vegetation, bird species richness and the numb...

  8. Aridity influences the recovery of vegetation and shrubland birds after wildfire.

    Science.gov (United States)

    Puig-Gironès, Roger; Brotons, Lluís; Pons, Pere

    2017-01-01

    Wildfires play a determining role in the composition and structure of many plant and animal communities. On the other hand, climate change is considered to be a major driver of current and future fire regime changes. Despite increases in drought in many areas of the world, the effects of aridity on post-fire colonization by animals have been rarely addressed. This study aims to analyse how a regional aridity gradient affects post-fire recovery of vegetation, bird species richness and the numbers of four early to middle-successional warbler species associated with the shrub cover. The database contains bird relative abundance and environmental variables from 3072 censuses in 695 transects located in 70 recently burnt areas (1 to 11 years after wildfire) in Catalonia (Spain), which were sampled between 2006 and 2013. Generalized linear mixed models (GLMMs) showed that plant cover was affected by time since fire, aridity and forest management. However, only the highest vegetation height layer (>100 cm) recovered slower in arid areas after fire. Time since fire positively influenced bird species richness and the relative abundance of the four focal species. The post-fire recovery of Melodious (Hippolais polyglotta) and Subalpine warblers (Sylvia cantillans) was hampered by aridity. Although this was not demonstrated for Dartford (S. undata) and Sardinian warblers (S. melanocephala), their occurrence was low in the driest areas during the first three years after fire. Overall, this study suggests that future increases in aridity can affect plant regeneration after fire and slow down the recovery of animal populations that depend on understorey and shrublands. Given the recently highlighted increases in aridity and fire frequency in Mediterranean-climate regions, improved knowledge on how aridity affects ecological succession is especially necessary.

  9. Testing the stress-gradient hypothesis during the restoration of tropical degraded land using the shrub Rhodomyrtus tomentosa as a nurse plant

    Science.gov (United States)

    Nan Liu; Hai Ren; Sufen Yuan; Qinfeng Guo; Long Yang

    2013-01-01

    The relative importance of facilitation and competition between pairwise plants across abiotic stress gradients as predicted by the stress-gradient hypothesis has been confirmed in arid and temperate ecosystems, but the hypothesis has rarely been tested in tropical systems, particularly across nutrient gradients. The current research examines the interactions between a...

  10. Apparent over-investment in leaf venation relaxes leaf morphological constraints on photosynthesis in arid habitats

    Science.gov (United States)

    de Boer, Hugo; Drake, Paul; Veneklaas, Erik

    2017-04-01

    The close relationship between leaf water status and stomatal conductance implies that the hydraulic architecture of leaves poses an important constraint on transpiration, specifically in arid environments with high evaporative demands. However, it remains uncertain how morphological, hydraulic and photosynthetic traits are coordinated to achieve optimal leaf functioning in arid environments. Critical is that leaf veins supply the mesophyll with water that evaporates when stomata are open to allow CO2 uptake for photosynthesis. Theoretical analyses suggest that water is optimally distributed in the mesophyll when the lateral distance between veins (dx) is equal to the distance from these veins to the epidermis (dy), expressed as dx:dy≈1. Although this theory is supported by observations on many derived angiosperms, we hypothesize that plants in arid environments may reduce dx:dy below unity owing to climate-specific functional adaptations of increased leaf thickness and increased vein density. To test our hypothesis we assembled leaf hydraulic, morphological and photosynthetic traits of 68 species from the Eucalyptus and Corymbia genera (termed eucalypts) along an aridity gradient in southwestern Australia. We inferred the potential gas exchange advantage of reducing dx beyond dy using a model that links leaf morphology and hydraulics to photosynthesis. Our observations reveal that eucalypts in arid environments have thick amphistomatous leaves with high vein densities, resulting in dx:dy ratios that range from 1.6 to 0.15 along the aridity gradient. Our model suggests that as leaves become thicker, the effect of reducing dx beyond dy is to offset the reduction in leaf gas exchange that would result from maintaining dx:dy at unity. This apparent over-investment in leaf venation may be explained from the selective pressure of aridity, under which traits associated with long leaf lifespan, high hydraulic and thermal capacitances, and high potential rates of leaf

  11. Distribution of greenhouse gases in hyper-arid and arid areas of northern Chile and the contribution of the high altitude wetland microbiome (Salar de Huasco, Chile).

    Science.gov (United States)

    Molina, Verónica; Eissler, Yoanna; Cornejo, Marcela; Galand, Pierre E; Dorador, Cristina; Hengst, Martha; Fernandez, Camila; Francois, Jean Pierre

    2018-04-06

    Northern Chile harbors different bioclimatic zones including hyper-arid and arid ecosystems and hotspots of microbial life, such as high altitude wetlands, which may contribute differentially to greenhouse gases (GHG) such as carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O). In this study, we explored ground level GHG distribution and the potential role of a wetland situated at 3800 m.a.s.l, and characterized by high solar radiation arid to hyper-arid zones. The microbiome from the water and sediments was described by high-throughput sequencing 16S rRNA and rDNA genes. The results indicate that GHG at ground level were variable along the elevation gradient potentially associated with different bioclimatic zones, reaching high values at the high Andean steppe and variable but lower values in the Atacama Desert and at the wetland. The water areas of the wetland presented high concentrations of CH 4 and CO 2 , particularly at the spring areas and in air bubbles below microbial mats. The microbial community was rich (> 40 phyla), including archaea and bacteria potentially active in the different matrices studied (water, sediments and mats). Functional microbial groups associated with GHG recycling were detected at low frequency, i.e., arid and arid areas of northern Chile are sites of GHG exchange associated with various bioclimatic zones and particularly in aquatic areas of the wetland where this ecosystem could represent a net sink of N 2 O and a source for CH 4 and CO 2 .

  12. Meaningful traits for grouping plant species across arid ecosystems.

    Science.gov (United States)

    Bär Lamas, Marlene Ivonne; Carrera, A L; Bertiller, M B

    2016-05-01

    Grouping species may provide some degree of simplification to understand the ecological function of plants on key ecosystem processes. We asked whether groups of plant species based on morpho-chemical traits associated with plant persistence and stress/disturbance resistance reflect dominant plant growth forms in arid ecosystems. We selected twelve sites across an aridity gradient in northern Patagonia. At each site, we identified modal size plants of each dominant species and assessed specific leaf area (SLA), plant height, seed mass, N and soluble phenol concentration in green and senesced leaves at each plant. Plant species were grouped according with plant growth forms (perennial grasses, evergreen shrubs and deciduous shrubs) and plant morphological and/or chemical traits using cluster analysis. We calculated mean values of each plant trait for each species group and plant growth form. Plant growth forms significantly differed among them in most of the morpho-chemical traits. Evergreen shrubs were tall plants with the highest seed mass and soluble phenols in leaves, deciduous shrubs were also tall plants with high SLA and the highest N in leaves, and perennial grasses were short plants with high SLA and low concentration of N and soluble phenols in leaves. Grouping species by the combination of morpho-chemical traits yielded 4 groups in which species from one growth form prevailed. These species groups differed in soluble phenol concentration in senesced leaves and plant height. These traits were highly correlated. We concluded that (1) plant height is a relevant synthetic variable, (2) growth forms adequately summarize ecological strategies of species in arid ecosystems, and (3) the inclusion of plant morphological and chemical traits related to defenses against environmental stresses and herbivory enhanced the potential of species grouping, particularly within shrubby growth forms.

  13. Changes in spatial patterns of Caragana stenophylla along a climatic drought gradient on the Inner Mongolian Plateau.

    Science.gov (United States)

    Xie, Li-Na; Guo, Hong-Yu; Gabler, Christopher A; Li, Qing-Fang; Ma, Cheng-Cang

    2015-01-01

    Few studies have investigated the influence of water availability on plant population spatial patterns. We studied changes in the spatial patterns of Caragana stenophylla along a climatic drought gradient within the Inner Mongolian Plateau, China. We examined spatial patterns, seed density, "nurse effects" of shrubs on seedlings, transpiration rates and water use efficiency (WUE) of C. stenophylla across semi-arid, arid, and intensively arid zones. Our results showed that patches of C. stenophylla populations shifted from a random to a clumped spatial pattern towards drier environments. Seed density and seedling survival rate of C. stenophylla decreased from the semi-arid zone to the intensively arid zone. Across the three zones, there were more C. stenophylla seeds and seedlings underneath shrub canopies than outside shrub canopies; and in the intensively arid zone, there were almost no seeds or seedlings outside shrub canopies. Transpiration rates of outer-canopy leaves and WUE of both outer-canopy and inner-canopy leaves increased from the semi-arid zone to the intensively arid zone. In the intensively arid zone, transpiration rates and WUE of inner-canopy leaves were significantly lower and higher, respectively, than those of outer-canopy leaves. We conclude that, as drought stress increased, seed density decreased, seed proportions inside shrubs increased, and "nurse effects" of shrubs on seedlings became more important. These factors, combined with water-saving characteristics associated with clumped spatial patterns, are likely driving the changes in C. stenophylla spatial patterns.

  14. Apparent Overinvestment in Leaf Venation Relaxes Leaf Morphological Constraints on Photosynthesis in Arid Habitats1[OPEN

    Science.gov (United States)

    de Boer, Hugo J.; Drake, Paul L.; Wendt, Erin; Price, Charles A.; Schulze, Ernst-Detlef; Turner, Neil C.; Nicolle, Dean

    2016-01-01

    Leaf veins supply the mesophyll with water that evaporates when stomata are open to allow CO2 uptake for photosynthesis. Theoretical analyses suggest that water is optimally distributed in the mesophyll when the lateral distance between veins (dx) is equal to the distance from these veins to the epidermis (dy), expressed as dx:dy ≈ 1. Although this theory is supported by observations of many derived angiosperms, we hypothesize that plants in arid environments may reduce dx:dy below unity owing to climate-specific functional adaptations of increased leaf thickness and increased vein density. To test our hypothesis, we assembled leaf hydraulic, morphological, and photosynthetic traits of 68 species from the Eucalyptus and Corymbia genera (termed eucalypts) along an aridity gradient in southwestern Australia. We inferred the potential gas-exchange advantage of reducing dx beyond dy using a model that links leaf morphology and hydraulics to photosynthesis. Our observations reveal that eucalypts in arid environments have thick amphistomatous leaves with high vein densities, resulting in dx:dy ratios that range from 1.6 to 0.15 along the aridity gradient. Our model suggests that, as leaves become thicker, the effect of reducing dx beyond dy is to offset the reduction in leaf gas exchange that would result from maintaining dx:dy at unity. This apparent overinvestment in leaf venation may be explained from the selective pressure of aridity, under which traits associated with long leaf life span, high hydraulic and thermal capacitances, and high potential rates of leaf water transport confer a competitive advantage. PMID:27784769

  15. Water conservation for semi-arid rangelands

    International Nuclear Information System (INIS)

    Willis, W.O.

    1983-01-01

    Water deficiency is most often the cause for low forage production on rangelands in semi-arid and arid regions. Water conservation methods have been developed but additional research is needed to develop the best management practices for various climatic regions. Poor management is another major cause of low rangeland production. Better management, including the application of research findings, depends on attitudes, policies, adaptability of findings, resources for implementation and a good understanding of the governing biotic and abiotic factors. (author)

  16. Greening reclamation of arid region

    Energy Technology Data Exchange (ETDEWEB)

    Kamichika, Makio [Tottori Univ. (Japan)

    1989-01-20

    Arid regions occupy a third of the whole land in the world, and desertification in the rimland makes a problem become more acute. It is also a problem that the large part of such areas is distributed in developing countries. Desertification is defined as a phenomenon, by which the ecological system is degenerated by the change of weather conditions and the pressure of human beings and livestock, and productivity of land is markedly deteriorated. In order to prevent desertification and to promote greening reclamation and agricultural development, it is necessary to analyze desertification mechanism in detail. Artificial factors are overpopulation, too much pasturage, and conversion of grassland into farmland. Natural environmental factors are weather conditions, water resources, soil conditions, etc. It is also important for greening reclamation and development of farm land to evaluate the amount of meteorological resources (such as water resources, energy resources, etc.) and to search for the possibility of their utilization. Because of major condition to grow plants is water environment, investigation and development of water resources are important. If a project ignores the cycle of the ecological system, it might be in danger of retrogradation toward desertification. 8 refs., 10 figs., 4 tabs.

  17. Shrubland primary production and soil respiration diverge along European climate gradient

    DEFF Research Database (Denmark)

    Reinsch, Sabine; Koller, Eva; Sowerby, Alwyn

    2017-01-01

    uncertain. Here we show the responses of ecosystem C to 8-12 years of experimental drought and night-time warming across an aridity gradient spanning seven European shrublands using indices of C assimilation (aboveground net primary production: aNPP) and soil C efflux (soil respiration: Rs). The changes...

  18. Nitrogen mineralization across an atmospheric nitrogen deposition gradient in Southern California deserts

    Science.gov (United States)

    L.E. Rao; D.R. Parker; Andrzej Bytnerowicz; E.B. Allen

    2009-01-01

    Dry nitrogen deposition is common in arid ecosystems near urban and agricultural centers, yet its impacts on natural environments are relatively understudied. We examined the effects of N deposition on soil N mineralization across a depositional gradient at Joshua Tree National Park. We hypothesized that N deposition affects N mineralization by promoting...

  19. Evaluating rainwater harvesting systems in arid and semi-arid regions

    NARCIS (Netherlands)

    Ammar, Adham Ali

    2017-01-01

    Rainwater harvesting (RWH) is an ancient traditional technology practised in many parts of the world, especially in arid and semi-arid regions (ASARs). ASARs represent 40% of the earth’s land surface and are characterised by low average annual rainfall and uneven temporal and spatial

  20. Development of hardy sorghum cultivars for the arid and semi arid ...

    African Journals Online (AJOL)

    Development of hardy sorghum cultivars for the arid and semi arid regions. MN Makobe, EM Kahangi, AK Misra, MO Imbuga. Abstract. No Abstract. Full Text: EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT · DOWNLOAD FULL TEXT DOWNLOAD FULL TEXT · AJOL African Journals Online. HOW TO USE AJOL.

  1. Is annual recharge coefficient a valid concept in arid and semi-arid regions?

    Directory of Open Access Journals (Sweden)

    Y. Cheng

    2017-10-01

    Full Text Available Deep soil recharge (DSR (at depth greater than 200 cm is an important part of water circulation in arid and semi-arid regions. Quantitative monitoring of DSR is of great importance to assess water resources and to study water balance in arid and semi-arid regions. This study used a typical bare land on the eastern margin of Mu Us Sandy Land in the Ordos Basin of China as an example to illustrate a new lysimeter method of measuring DSR to examine if the annual recharge coefficient is valid or not in the study site, where the annual recharge efficient is the ratio of annual DSR over annual total precipitation. Positioning monitoring was done on precipitation and DSR measurements underneath mobile sand dunes from 2013 to 2015 in the study area. Results showed that use of an annual recharge coefficient for estimating DSR in bare sand land in arid and semi-arid regions is questionable and could lead to considerable errors. It appeared that DSR in those regions was influenced by precipitation pattern and was closely correlated with spontaneous strong precipitation events (with precipitation greater than 10 mm other than the total precipitation. This study showed that as much as 42 % of precipitation in a single strong precipitation event can be transformed into DSR. During the observation period, the maximum annual DSR could make up 24.33 % of the annual precipitation. This study provided a reliable method of estimating DSR in sandy areas of arid and semi-arid regions, which is valuable for managing groundwater resources and ecological restoration in those regions. It also provided strong evidence that the annual recharge coefficient was invalid for calculating DSR in arid and semi-arid regions. This study shows that DSR is closely related to the strong precipitation events, rather than to the average annual precipitation, as well as the precipitation patterns.

  2. $L_{0}$ Gradient Projection.

    Science.gov (United States)

    Ono, Shunsuke

    2017-04-01

    Minimizing L 0 gradient, the number of the non-zero gradients of an image, together with a quadratic data-fidelity to an input image has been recognized as a powerful edge-preserving filtering method. However, the L 0 gradient minimization has an inherent difficulty: a user-given parameter controlling the degree of flatness does not have a physical meaning since the parameter just balances the relative importance of the L 0 gradient term to the quadratic data-fidelity term. As a result, the setting of the parameter is a troublesome work in the L 0 gradient minimization. To circumvent the difficulty, we propose a new edge-preserving filtering method with a novel use of the L 0 gradient. Our method is formulated as the minimization of the quadratic data-fidelity subject to the hard constraint that the L 0 gradient is less than a user-given parameter α . This strategy is much more intuitive than the L 0 gradient minimization because the parameter α has a clear meaning: the L 0 gradient value of the output image itself, so that one can directly impose a desired degree of flatness by α . We also provide an efficient algorithm based on the so-called alternating direction method of multipliers for computing an approximate solution of the nonconvex problem, where we decompose it into two subproblems and derive closed-form solutions to them. The advantages of our method are demonstrated through extensive experiments.

  3. Attribute Analysis of Aridity Variability in North Xinjiang, China

    Directory of Open Access Journals (Sweden)

    Yanfeng Wu

    2016-01-01

    Full Text Available Identifying the dominant meteorological factors affecting aridity variability can improve our understanding of climate change and its future trend in arid and semiarid regions. This study investigated the spatiotemporal aridity variability in North Xinjiang, China, from 1961 to 2013, based on the UNESCO aridity index (precipitation/potential evapotranspiration, and analyzed its association with meteorological factors. The results suggest that North Xinjiang is becoming more humid with an increasing trend in aridity index. Precipitation, temperature, and relative humidity have positive correlation with aridity, and evapotranspiration, sunshine hours, and wind speed have negative correlation with aridity. Wind speed and sunshine hours have a higher sensitivity and more contribution to aridity. This study provides an understanding of the effect of recent climate change on drought in northwest China.

  4. Co-evolution and thresholds in arid floodplain wetland ecosystems.

    Science.gov (United States)

    Sandi, Steven; Rodriguez, Jose; Riccardi, Gerardo; Wen, Li; Saintilan, Neil

    2017-04-01

    Vegetation in arid floodplain wetlands consist of water dependent and flood tolerant species that rely on periodical floods in order to maintain healthy conditions. The floodplain often consist of a complex system of marshes, swamps and lagoons interconnected by a network of streams and poorly defined rills. Over time, feedbacks develop between vegetation and flow paths producing areas of flow obstruction and flow concentration, which combined with depositional and erosional process lead to a continuous change on the position and characteristics of inundation areas. This coevolution of flow paths and vegetation can reach a threshold that triggers major channel transformations and abandonment of wetland areas, in a process that is irreversible. The Macquarie Marshes is a floodplain wetland complex in the semi-arid region of north western NSW, Australia. The site is characterised by a low-gradient topography that leads to channel breakdown processes where the river network becomes practically non-existent and the flow extends over large areas of wetland that later re-join and reform channels exiting the system. Due to a combination of climatic and anthropogenic pressures, the wetland ecosystem in the Macquarie Marshes has deteriorated over the past few decades. This has been linked to decreasing inundation frequencies and extent, with whole areas of flood dependent species such as Water Couch and Common Reed undergoing complete succession to terrestrial species and dryland. In this presentation we provide an overview of an ecogeomorphological model that we have developed in order to simulate the complex dynamics of the marshes. The model combines hydrodynamic, vegetation and channel evolution modules. We focus on the vegetation component of the model and the transitional rules to predict wetland invasion by terrestrial vegetation.

  5. Isotope techniques in water resource investigations in arid and semi-arid regions

    International Nuclear Information System (INIS)

    2001-03-01

    The Co-ordinated Research Project (CRP) on the Use of Isotope Techniques in Water Resources Investigations in Arid and Semi-arid Regions was initiated with the aim od contributing to the assessment of groundwater resources in arid areas through the use of environmental isotope techniques, and thereby to help in better management of these valuable fresh groundwater resources. The main emphases identified were in three key areas: (i) the evaluation of water balance components such as recharge rate estimation and recharge and discharge cycles at different spatial scales, (ii) paleohydrology and hydroclimatic change and, (iii) anthropogenic impacts and the assessment of the vulnerability of arid zone ground waters to salinisation and pollution impacts. This publication presents individual projects carried out within the frameworks of the CRP. Each paper has been indexed separately

  6. Arid and semiarid land stewardship: A 10-year review of accomplishments and contributions of the lnternational Arid Lands Consortium

    Science.gov (United States)

    Peter F. Ffolliott; Jeffrey O. Dawson; James T. Fisher; Itshack Moshe; Darrell W. DeBoers; Timothy. E. Fulbright; John Tracy; Abdullah Al Musa; Carter Johnson; Jim P. M. Chamie

    2001-01-01

    The International Arid Lands Consortium (IALC) was established in 1990 to promote research, education, and training activities related to the development, management, and restoration or reclamation of arid and semiarid lands worldwide. The IALC, a leading international organization, supports ecological sustainability and development of arid and semiarid lands. Building...

  7. CHARACTERISTICS OF ARIDITY CONDITIONS IN SOUTH DOBRUDJA

    Directory of Open Access Journals (Sweden)

    A. TISCOVSCHI

    2013-04-01

    Full Text Available Characteristics of Aridity Conditions in South Dobrudja. For most people, the arid and semi-arid lands are those where precipitation is low (less than 200 mm per year, and yet enough for supplying streams capable of temporarily carrying the debris resulted from weathering, but insufficient for encouraging the development of a vegetal cover meant to protect the soil blanket against eroding agents. The drought is a major and permanent climatic risk for the Dobrudja territory as a whole and for South Dobrudja in particular, a territory where hydrographic network is underdeveloped, streams are ephemeral, and semi-endorheic areas are well developed. When the period of moisture deficiency lasts longer, it can bring about a significant water imbalance, which results in crop losses or restrictions in water consumption, thus leading to a number of economic problems. Under the circumstances, the risk of aridity expansion is significant, this being the reason why a better water management system in Romania is urgently needed. In the last decades, the numerous specialty studies undertaken in the area have emphasized an intensification of the process of dryness, because atmospheric and pedological droughts have become more and more serious. Romania is a member of the United Nations Convention to Combat Desertification (UNCCD and the World Meteorological Organization (WMO. It actively participates within the drought management network and the Drought Management Center for Southeastern Europe, which comprises 11 countries. The scope is to work together and exchange experience with the neighboring countries that have recorded positive results and acquired a rich experience in terms of drought management. The employment of appropriate pluvial indices in identifying the areas prone to aridity may prove to be convenient tool for finding practical solutions meant to mitigate the impact of this phenomenon on the local communities living in South Dobrudja.

  8. Aridity under conditions of increased CO2

    Science.gov (United States)

    Greve, Peter; Roderick, Micheal L.; Seneviratne, Sonia I.

    2016-04-01

    A string of recent of studies led to the wide-held assumption that aridity will increase under conditions of increasing atmospheric CO2 concentrations and associated global warming. Such results generally build upon analyses of changes in the 'aridity index' (the ratio of potential evaporation to precipitation) and can be described as a direct thermodynamic effect on atmospheric water demand due to increasing temperatures. However, there is widespread evidence that contradicts the 'warmer is more arid' interpretation, leading to the 'global aridity paradox' (Roderick et al. 2015, WRR). Here we provide a comprehensive assessment of modeled changes in a broad set of dryness metrics (primarily based on a range of measures of water availability) over a large range of realistic atmospheric CO2 concentrations. We use an ensemble of simulations from of state-of-the-art climate models to analyse both equilibrium climate experiments and transient historical simulations and future projections. Our results show that dryness is, under conditions of increasing atmospheric CO2 concentrations and related global warming, generally decreasing at global scales. At regional scales we do, however, identify areas that undergo changes towards drier conditions, located primarily in subtropical climate regions and the Amazon Basin. Nonetheless, the majority of regions, especially in tropical and mid- to northern high latitudes areas, display wetting conditions in a warming world. Our results contradict previous findings and highlight the need to comprehensively assess all aspects of changes in hydroclimatological conditions at the land surface. Roderick, M. L., P. Greve, and G. D. Farquhar (2015), On the assessment of aridity with changes in atmospheric CO2, Water Resour. Res., 51, 5450-5463

  9. Travelling gradient thermocouple calibration

    International Nuclear Information System (INIS)

    Broomfield, G.H.

    1975-01-01

    A short discussion of the origins of the thermocouple EMF is used to re-introduce the idea that the Peltier and Thompson effects are indistinguishable from one another. Thermocouples may be viewed as devices which generate an EMF at junctions or as integrators of EMF's developed in thermal gradients. The thermal gradient view is considered the more appropriate, because of its better accord with theory and behaviour, the correct approach to calibration, and investigation of service effects is immediately obvious. Inhomogeneities arise in thermocouples during manufacture and in service. The results of travelling gradient measurements are used to show that such effects are revealed with a resolution which depends on the length of the gradient although they may be masked during simple immersion calibration. Proposed tests on thermocouples irradiated in a nuclear reactor are discussed

  10. Quaternion Gradient and Hessian

    OpenAIRE

    Xu, Dongpo; Mandic, Danilo P.

    2014-01-01

    The optimization of real scalar functions of quaternion variables, such as the mean square error or array output power, underpins many practical applications. Solutions typically require the calculation of the gradient and Hessian. However, real functions of quaternion variables are essentially nonanalytic, which are prohibitive to the development of quaternion-valued learning systems. To address this issue, we propose new definitions of quaternion gradient and Hessian, based on the novel gen...

  11. Aeolian dust nutrient contributions increase with substrate age in semi-arid ecosystems

    Science.gov (United States)

    Coble, A. A.; Hart, S. C.; Ketterer, M. E.; Newman, G. S.

    2013-12-01

    Rock-derived nutrients supplied by mineral weathering become depleted over time, and without an additional nutrient source the ecosystem may eventually regress or reach a terminal steady state. Previous studies have demonstrated that aeolian dust act as parent materials of soils and important nutrients to plants in arid regions, but the relative importance of these exogenous nutrients to the function of dry ecosystems during soil development is uncertain. Here, using strontium isotopes as a tracer and a well-constrained, three million year old substrate age gradient, we show that aeolian-derived nutrients become increasingly important to plant-available soil pools and tree (Pinus edulis) growth during the latter stages of soil development in a semi-arid climate. Furthermore, the depth of nutrient uptake increased on older substrates, suggesting that trees in arid regions acquire nutrients from greater depths as ecosystem development progresses presumably in response to nutrient depletion in the more weathered surface soils. Our results contribute to the unification of biogeochemical theory by demonstrating the similarity in roles of atmospheric nutrient inputs during ecosystem development across contrasting climates.

  12. CONTROLLING FACTORS OF POTENTIAL EVAPOTRANSPIRATION ABOVE GRASSLAND IN HUMID AND ARID AREA

    Directory of Open Access Journals (Sweden)

    . Yanto

    2013-05-01

    Full Text Available Potential evapotranspiration (PET is an importance process in water balance studies controlled by a number of meteorological factors such as temperature, wind speed, atmospheric pressure, solar radiation, vapor pressure gradient, relative humidity and biological factors such as vegetation type, canopy height and plant density that varied in time-scale and in spatial scale. Of all those variables, determining the most controlling factors of evapotranspiration in humid and arid area is of interest of this paper. Two sites representing humid and arid area i.e. Fermi Prairie site in Illinois and Audubon Research Ranch in Arizona respectively were investigated in this study.  The flux data employed in this study was acquired from Ameriflux Netwotk. Penmann-Monteith formula is employed in to estimate evapotranspiration rate in both sites. The result shows that the PET is in dependence on the considered meteorological factor such as shortwave radiation, vapor pressure, air temperature, wind speed, net radiation and vapor pressure deficit. It is also can be inferred from the analysis that PET is also strongly controlled by vegetation factors represented as stomatal resistance. Keywords: Potential evapotranspiration, Penmann-Monteith, humid, arid.

  13. Gradient Alloy for Optical Packaging

    Data.gov (United States)

    National Aeronautics and Space Administration — Advances in additive manufacturing, such as Laser Engineered Net Shaping (LENS), enables the fabrication of compositionally gradient microstructures, i.e. gradient...

  14. Lower fecundity in parthenogenetic geckos than sexual relatives in the Australian arid zone.

    Science.gov (United States)

    Kearney, M; Shine, R

    2005-05-01

    Theoretical models of the advantage of sexual reproduction typically assume that reproductive output is equal in sexual and parthenogenetic females. We tested this assumption by comparing fecundity between parthenogenetic and sexual races of gekkonid lizards in the Heteronotia binoei complex, collected across a 1200 km latitudinal gradient through the Australian arid zone. Under laboratory conditions, parthenogenetic geckos had approximately 30% lower fecundity when compared with their sexual progenitors, irrespective of body size. Reflecting clutch-size constraints in gekkonids, this fecundity difference was mainly because of fewer clutches over a shorter period. When parthenogens were compared more broadly with all coexisting sexual races across the latitudinal gradient, parthenogens had lower fecundity than sexuals only when corrected for body size. Differences in fecundity between parthenogens and coexisting sexual races depended on which sexual race was considered. There was no significant relationship between fecundity and parasite (mite) load, despite significantly higher mite loads in parthenogens than in sexual races.

  15. In situ fragmentation and rock particle sorting on arid hills

    Science.gov (United States)

    McGrath, Gavan S.; Nie, Zhengyao; Dyskin, Arcady; Byrd, Tia; Jenner, Rowan; Holbeche, Georgina; Hinz, Christoph

    2013-03-01

    Transport processes are often proposed to explain the sorting of rock particles on arid hillslopes, where mean rock particle size often decreases in the downslope direction. Here we show that in situ fragmentation of rock particles can also produce similar patterns. A total of 93,414 rock particles were digitized from 880 photographs of the surface of three mesa hills in the Great Sandy Desert, Australia. Rock particles were characterized by the projected Feret's diameter and circularity. Distance from the duricrust cap was found to be a more robust explanatory variable for diameter than the local hillslope gradient. Mean diameter decreased exponentially downslope, while the fractional area covered by rock particles decreased linearly. Rock particle diameters were distributed lognormally, with both the location and scale parameters decreasing approximately linearly downslope. Rock particle circularity distributions showed little change; only a slight shift in the mode to more circular particles was noted to occur downslope. A dynamic fragmentation model was used to assess whether in situ weathering alone could reproduce the observed downslope fining of diameters. Modeled and observed size distributions agreed well and both displayed a preferential loss of relatively large rock particles and an apparent approach to a terminal size distribution of the rocks downslope. We show this is consistent with a size effect in material strength, where large rocks are more susceptible to fatigue failure under stress than smaller rocks. In situ fragmentation therefore produces qualitatively similar patterns to those that would be expected to arise from selective transport.

  16. VOCs in Arid soils: Technology summary

    International Nuclear Information System (INIS)

    1994-02-01

    The Volatile Organic Compounds In Arid Soils Integrated Demonstration (VOC-Arid ID) focuses on technologies to clean up volatile organic compounds and associated contaminants in soil and groundwater at arid sites. The initial host site is the 200 West Area at DOE's Hanford site in southeastern Washington state. The primary VOC contaminant is carbon tetrachloride, in association with heavy metals and radionuclides. An estimated 580--920 metric tons of carbon tetrachloride were disposed of between 1955 and 1973, resulting in extensive soil and groundwater contamination. The VOC-Arid ID schedule has been divided into three phases of implementation. The phased approach provides for: rapid transfer of technologies to the Environmental Restoration (EM-40) programs once demonstrated; logical progression in the complexity of demonstrations based on improved understanding of the VOC problem; and leveraging of the host site EM-40 activities to reduce the overall cost of the demonstrations. During FY92 and FY93, the primary technology demonstrations within the ID were leveraged with an ongoing expedited response action at the Hanford 200 West Area, which is directed at vapor extraction of VOCs from the vadose (unsaturated) zone. Demonstration efforts are underway in the areas of subsurface characterization including: drilling and access improvements, off-gas and borehole monitoring of vadose zone VOC concentrations to aid in soil vapor extraction performance evaluation, and treatment of VOC-contaminated off-gas. These current demonstration efforts constitute Phase 1 of the ID and, because of the ongoing vadose zone ERA, can result in immediate transfer of successful technologies to EM-40

  17. High Gradient Accelerator Research

    International Nuclear Information System (INIS)

    Temkin, Richard

    2016-01-01

    The goal of the MIT program of research on high gradient acceleration is the development of advanced acceleration concepts that lead to a practical and affordable next generation linear collider at the TeV energy level. Other applications, which are more near-term, include accelerators for materials processing; medicine; defense; mining; security; and inspection. The specific goals of the MIT program are: • Pioneering theoretical research on advanced structures for high gradient acceleration, including photonic structures and metamaterial structures; evaluation of the wakefields in these advanced structures • Experimental research to demonstrate the properties of advanced structures both in low-power microwave cold test and high-power, high-gradient test at megawatt power levels • Experimental research on microwave breakdown at high gradient including studies of breakdown phenomena induced by RF electric fields and RF magnetic fields; development of new diagnostics of the breakdown process • Theoretical research on the physics and engineering features of RF vacuum breakdown • Maintaining and improving the Haimson / MIT 17 GHz accelerator, the highest frequency operational accelerator in the world, a unique facility for accelerator research • Providing the Haimson / MIT 17 GHz accelerator facility as a facility for outside users • Active participation in the US DOE program of High Gradient Collaboration, including joint work with SLAC and with Los Alamos National Laboratory; participation of MIT students in research at the national laboratories • Training the next generation of Ph. D. students in the field of accelerator physics.

  18. Cereals for the semi-arid tropics

    International Nuclear Information System (INIS)

    De Wet, J.M.J.

    1989-01-01

    The region of semi-arid tropics is the most famine prone area of the world. This region with nearly one billion people extends across some 20 million square kilometres. Major domesticated cereals adapted to semi-arid regions are sorghum (Sorghum bicolor (L.) Moench), foxtail millet (Setaria italica (L.) P. Beauv.) and pearl millet (Pennisetum glaucum (L.) R. Br.). Several minor cereals are grown as speciality crops, or harvested in the wild in times of severe drought and scarcity. Important in the African Sahel are the fonios Digitaria iburua Stapf, D. exilis (Kapist) Stapf and Brachiaria deflexa (Schumach). C.E. Hubbard. These species are aggressive colonizers and are commonly encouraged as weeds in cultivated fields. Sown genotypes differ from their close wild relatives primarily in the lack of efficient natural seed dispersal. The fonios lend themselves to rapid domestication. Several wild cereals extend well beyond the limits of agriculture into the Sahara. Commonly harvested are the perennial Stipagrostis pungens and Panicum turgidum, and the annual Cenchrus biflorus (kram-kram). Kram-kram yields well under extreme heat and drought stress, and holds promise as a domesticated cereal. Sauwi millet (Panicum sonorum) is promising cereal in arid northwestern Mexico. (author). 31 refs

  19. Fluvial signatures of modern and paleo orographic rainfall gradients

    Science.gov (United States)

    Schildgen, Taylor; Strecker, Manfred

    2016-04-01

    The morphology of river profiles is intimately linked to both climate and tectonic forcing. While much interest recently has focused on how river profiles can be inverted to derive uplift histories, here we show how in regions of strong orographic rainfall gradients, rivers may primarily record spatial patterns of precipitation. As a case study, we examine the eastern margin of the Andean plateau in NW Argentina, where the outward (eastward) growth of a broken foreland has led to a eastward shift in the main orographic rainfall gradient over the last several million years. Rivers influenced by the modern rainfall gradient are characterized by normalized river steepness values in tributary valleys that closely track spatial variations in rainfall, with higher steepness values in drier areas and lower steepness values in wetter areas. The same river steepness pattern has been predicted in landscape evolution models that apply a spatial gradient in rainfall to a region of uniform erosivity and uplift rate (e.g., Han et al., 2015). Also, chi plots from river networks on individual ranges affected by the modern orographic rainfall reveal patterns consistent with assymmetric precipitation across the range: the largest channels on the windward slopes are characterized by capture, while the longest channels on the leeward slopes are dominated by beheadings. Because basins on the windward side both lengthen and widen, tributary channels in the lengthening basins are characterized by capture, while tributary channels from neighboring basins on the windward side are dominated by beheadings. These patterns from the rivers influenced by the modern orographic rainfall gradient provide a guide for identifying river morphometric signatures of paleo orographic rainfall gradients. Mountain ranges to the west of the modern orographic rainfall have been interpreted to mark the location of orographic rainfall in the past, but these ranges are now in spatially near-uniform semi-arid to

  20. Uniform gradient expansions

    CERN Document Server

    Giovannini, Massimo

    2015-01-01

    Cosmological singularities are often discussed by means of a gradient expansion that can also describe, during a quasi-de Sitter phase, the progressive suppression of curvature inhomogeneities. While the inflationary event horizon is being formed the two mentioned regimes coexist and a uniform expansion can be conceived and applied to the evolution of spatial gradients across the protoinflationary boundary. It is argued that conventional arguments addressing the preinflationary initial conditions are necessary but generally not sufficient to guarantee a homogeneous onset of the conventional inflationary stage.

  1. High gradient superconducting quadrupoles

    International Nuclear Information System (INIS)

    Lundy, R.A.; Brown, B.C.; Carson, J.A.; Fisk, H.E.; Hanft, R.H.; Mantsch, P.M.; McInturff, A.D.; Remsbottom, R.H.

    1987-07-01

    Prototype superconducting quadrupoles with a 5 cm aperture and gradient of 16 kG/cm have been built and tested as candidate magnets for the final focus at SLC. The magnets are made from NbTi Tevatron style cable with 10 inner and 14 outer turns per quadrant. Quench performance and multipole data are presented. Design and data for a low current, high gradient quadrupole, similar in cross section but wound with a cable consisting of five insulated conductors are also discussed

  2. Spatial heterogeneity of physicochemical properties explains differences in microbial composition in arid soils from Cuatro Cienegas, Mexico

    Directory of Open Access Journals (Sweden)

    Silvia Pajares

    2016-09-01

    Full Text Available Arid ecosystems are characterized by high spatial heterogeneity, and the variation among vegetation patches is a clear example. Soil biotic and abiotic factors associated with these patches have also been well documented as highly heterogeneous in space. Given the low vegetation cover and little precipitation in arid ecosystems, soil microorganisms are the main drivers of nutrient cycling. Nonetheless, little is known about the spatial distribution of microorganisms and the relationship that their diversity holds with nutrients and other physicochemical gradients in arid soils. In this study, we evaluated the spatial variability of soil microbial diversity and chemical parameters (nutrients and ion content at local scale (meters occurring in a gypsum-based desert soil, to gain knowledge on what soil abiotic factors control the distribution of microbes in arid ecosystems. We analyzed 32 soil samples within a 64 m2 plot and: (a characterized microbial diversity using T-RFLPs of the bacterial 16S rRNA gene, (b determined soil chemical parameters, and (c identified relationships between microbial diversity and chemical properties. Overall, we found a strong correlation between microbial composition heterogeneity and spatial variation of cations (Ca2, K+ and anions (HCO ${}_{3}^{-}$ 3 − , Cl−, SO ${}_{4}^{2-}$ 4 2 − content in this small plot. Our results could be attributable to spatial differences of soil saline content, favoring the patchy emergence of salt and soil microbial communities.

  3. Independent Transitions between Monsoonal and Arid Biomes Revealed by Systematic Revison of a Complex of Australian Geckos (Diplodactylus; Diplodactylidae.

    Directory of Open Access Journals (Sweden)

    Paul M Oliver

    Full Text Available How the widespread expansion and intensification of aridity through the Neogene has shaped the Austral biota is a major question in Antipodean biogeography. Lineages distributed across wide aridity gradients provide opportunities to examine the timing, frequency, and direction of transitions between arid and mesic regions. Here, we use molecular genetics and morphological data to investigate the systematics and biogeography of a nominal Australian gecko species (Diplodactylus conspicillatus sensu lato with a wide distribution spanning most of the Australian Arid Zone (AAZ and Monsoonal Tropics (AMT. Our data support a minimum of seven genetically distinct and morphologically diagnosable taxa; we thus redefine the type species, ressurrect three names from synonymy, and describe three new species. Our inferred phylogeny suggests the history and diversification of lineages in the AAZ and AMT are intimately linked, with evidence of multiple independent interchanges since the late Miocene. However, despite this shared history, related lineages in these two regions also show evidence of broadly contrasting intra-regional responses to aridification; vicarance and speciation in older and increasingly attenuated mesic regions, versus a more dynamic history including independent colonisations and recent range expansions in the younger AAZ.

  4. Correction: Independent transitions between monsoonal and arid biomes revealed by systematic revison of a complex of Australian geckos (Diplodactylus; Diplodactylidae.

    Directory of Open Access Journals (Sweden)

    Paul M Oliver

    Full Text Available How the widespread expansion and intensification of aridity through the Neogene has shaped the Austral biota is a major question in Antipodean biogeography.Lineages distributed across wide aridity gradients provide opportunities to examine the timing, frequency, and direction of transitions between arid and mesic regions.Here, we use molecular genetics and morphological data to investigate the systematics and biogeography of a nominal Australian gecko species(Diplodactylus conspicillatus sensu lato with a wide distribution spanning most of the Australian Arid Zone (AAZ and Monsoonal Tropics (AMT. Our data support a minimum of seven genetically distinct and morphologically diagnosable taxa; we thus redefine the type species, ressurrect three names from synonymy, and describe three new species. Our inferred phylogeny suggests the history and diversification of lineages in the AAZ and AMT are intimately linked, with evidence of multiple independent interchanges since the late Miocene. However, despite this shared history, related lineages in these two regions also show evidence of broadly contrasting intra-regional responses to aridification; vicarance and speciation in older and increasingly attenuated mesic regions, versus a more dynamic history including independent colonisations and recent range expansions in the younger AAZ.

  5. Independent Transitions between Monsoonal and Arid Biomes Revealed by Systematic Revison of a Complex of Australian Geckos (Diplodactylus; Diplodactylidae).

    Science.gov (United States)

    Oliver, Paul M; Couper, Patrick J; Pepper, Mitzy

    2014-01-01

    How the widespread expansion and intensification of aridity through the Neogene has shaped the Austral biota is a major question in Antipodean biogeography. Lineages distributed across wide aridity gradients provide opportunities to examine the timing, frequency, and direction of transitions between arid and mesic regions. Here, we use molecular genetics and morphological data to investigate the systematics and biogeography of a nominal Australian gecko species (Diplodactylus conspicillatus sensu lato) with a wide distribution spanning most of the Australian Arid Zone (AAZ) and Monsoonal Tropics (AMT). Our data support a minimum of seven genetically distinct and morphologically diagnosable taxa; we thus redefine the type species, ressurrect three names from synonymy, and describe three new species. Our inferred phylogeny suggests the history and diversification of lineages in the AAZ and AMT are intimately linked, with evidence of multiple independent interchanges since the late Miocene. However, despite this shared history, related lineages in these two regions also show evidence of broadly contrasting intra-regional responses to aridification; vicarance and speciation in older and increasingly attenuated mesic regions, versus a more dynamic history including independent colonisations and recent range expansions in the younger AAZ.

  6. Correction: Independent transitions between monsoonal and arid biomes revealed by systematic revison of a complex of Australian geckos (Diplodactylus; Diplodactylidae).

    Science.gov (United States)

    Oliver, Paul M; Couper, Patrick J; Pepper, Mitzy

    2015-01-01

    How the widespread expansion and intensification of aridity through the Neogene has shaped the Austral biota is a major question in Antipodean biogeography.Lineages distributed across wide aridity gradients provide opportunities to examine the timing, frequency, and direction of transitions between arid and mesic regions.Here, we use molecular genetics and morphological data to investigate the systematics and biogeography of a nominal Australian gecko species(Diplodactylus conspicillatus sensu lato) with a wide distribution spanning most of the Australian Arid Zone (AAZ) and Monsoonal Tropics (AMT). Our data support a minimum of seven genetically distinct and morphologically diagnosable taxa; we thus redefine the type species, ressurrect three names from synonymy, and describe three new species. Our inferred phylogeny suggests the history and diversification of lineages in the AAZ and AMT are intimately linked, with evidence of multiple independent interchanges since the late Miocene. However, despite this shared history, related lineages in these two regions also show evidence of broadly contrasting intra-regional responses to aridification; vicarance and speciation in older and increasingly attenuated mesic regions, versus a more dynamic history including independent colonisations and recent range expansions in the younger AAZ.

  7. Analysis list: ARID3A [Chip-atlas[Archive

    Lifescience Database Archive (English)

    Full Text Available ARID3A Blood,Liver + hg19 http://dbarchive.biosciencedbc.jp/kyushu-u/hg19/target/ARID3A.1.tsv http:...//dbarchive.biosciencedbc.jp/kyushu-u/hg19/target/ARID3A.5.tsv http://dbarchive.biosciencedb...c.jp/kyushu-u/hg19/target/ARID3A.10.tsv http://dbarchive.biosciencedbc.jp/kyushu-u/hg19/colo/ARID3A.Blood.tsv,http:...//dbarchive.biosciencedbc.jp/kyushu-u/hg19/colo/ARID3A.Liver.tsv http://db...archive.biosciencedbc.jp/kyushu-u/hg19/colo/Blood.gml,http://dbarchive.biosciencedbc.jp/kyushu-u/hg19/colo/Liver.gml ...

  8. Microbial functional diversity associated with plant litter decomposition along a climatic gradient.

    Science.gov (United States)

    Sherman, Chen; Steinberger, Yosef

    2012-08-01

    Predicted changes in climate associated with increased greenhouse gas emissions can cause increases in global mean temperature and changes in precipitation regimes. These changes may affect key soil processes, e.g., microbial CO(2) evolution and biomass, mineralization rates, primary productivity, biodiversity, and litter decomposition, which play an important role in carbon and nutrient cycling in terrestrial ecosystems. Our study examined the changes in litter microbial communities and decomposition along a climatic gradient, ranging from arid desert to humid Mediterranean regions in Israel. Wheat straw litter bags were placed in arid, semi-arid, Mediterranean, and humid Mediterranean sites. Samples were collected seasonally over a 2-year period in order to evaluate mass loss, litter moisture, C/N ratio, bacterial colony-forming units (CFUs), microbial CO(2) evolution and biomass, microbial functional diversity, and catabolic profile. Decomposition rate was the highest during the first year of the study at the Mediterranean and arid sites. Community-level physiological profile and microbial biomass were the highest in summer, while bacterial CFUs were the highest in winter. Microbial functional diversity was found to be highest at the humid Mediterranean site, whereas substrate utilization increased at the arid site. Our results support the assumption that climatic factors control litter degradation and regulate microbial activity.

  9. Hydraulic integration and shrub growth form linked across continental aridity gradients.

    Science.gov (United States)

    H. Jochen Schenk; Susana Espino; Christine M. Goedhart; Marisa Nordenstahl; Hugo I. Martinez Cabrera; Cynthia S. Jones

    2009-01-01

    Both engineered hydraulic systems and plant hydraulic systems are protected against failure by resistance, reparability, and redundancy. A basic rule of reliability engineering is that the level of...

  10. Female fecundity traits in wild populations of African annual fish: the role of the aridity gradient

    Czech Academy of Sciences Publication Activity Database

    Vrtílek, Milan; Reichard, Martin

    2016-01-01

    Roč. 6, č. 16 (2016), s. 5921-5931 ISSN 2045-7758 R&D Projects: GA ČR GBP505/12/G112; GA ČR(CZ) GAP506/11/0112 Institutional support: RVO:68081766 Keywords : annual killifish * egg size * interpopulation variation * intrapopulation variability * life expectancy * reproductive allocation Subject RIV: EH - Ecology, Behaviour Impact factor: 2.440, year: 2016

  11. Phenotypic variation of larks along an aridity gradient : Are desert birds more flexible?

    NARCIS (Netherlands)

    Tieleman, BI; Williams, JB; Buschur, ME; Brown, CR

    We investigated interindividual variation and intra-individual phenotypic flexibility in basal metabolic rate (BMR), total evaporative water loss (TEWL), body temperature (T-b), the minimum dry heat transfer coefficient (h), and organ and muscle size of five species of larks geographically

  12. Lipid composition of the stratum corneum and cutaneous water loss in birds along an aridity gradient.

    Science.gov (United States)

    Champagne, Alex M; Muñoz-Garcia, Agustí; Shtayyeh, Tamer; Tieleman, B Irene; Hegemann, Arne; Clement, Michelle E; Williams, Joseph B

    2012-12-15

    Intercellular and covalently bound lipids within the stratum corneum (SC), the outermost layer of the epidermis, are the primary barrier to cutaneous water loss (CWL) in birds. We compared CWL and intercellular SC lipid composition in 20 species of birds from desert and mesic environments. Furthermore, we compared covalently bound lipids with CWL and intercellular lipids in the lark family (Alaudidae). We found that CWL increases in birds from more mesic environments, and this increase was related to changes in intercellular SC lipid composition. The most consistent pattern that emerged was a decrease in the relative amount of cerebrosides as CWL increased, a pattern that is counterintuitive based on studies of mammals with Gaucher disease. Although covalently bound lipids in larks did not correlate with CWL, we found that covalently bound cerebrosides correlated positively with intercellular cerebrosides and intercellular cholesterol ester, and intercellular cerebrosides correlated positively with covalently bound free fatty acids. Our results led us to propose a new model for the organization of lipids in the avian SC, in which the sugar moieties of cerebrosides lie outside of intercellular lipid layers, where they may interdigitate with adjacent intercellular cerebrosides or with covalently bound cerebrosides.

  13. Adaptation of metabolism and evaporative water loss along an aridity gradient

    NARCIS (Netherlands)

    Tieleman, BI; Williams, JB; Bloomer, P

    2003-01-01

    Broad-scale comparisons of birds indicate the possibility of adaptive modification of basal metabolic rate (BMR) and total evaporative water loss (TEWL) in species from desert environments, but these might be confounded by phylogeny or phenotypic plasticity. This study relates variation in avian BMR

  14. Lipid composition of the stratum corneum and cutaneous water loss in birds along an aridity gradient

    NARCIS (Netherlands)

    Champagne, Alex M.; Munoz-Garcia, Agusti; Shtayyeh, Tamer; Tieleman, B. Irene; Hegemann, Arne; Clement, Michelle E.; Williams, Joseph B.

    2012-01-01

    Intercellular and covalently bound lipids within the stratum corneum (SC), the outermost layer of the epidermis, are the primary barrier to cutaneous water loss (CWL) in birds. We compared CWL and intercellular SC lipid composition in 20 species of birds from desert and mesic environments.

  15. Repeated intraspecific divergence in life span and aging of African annual fishes along an aridity gradient

    Czech Academy of Sciences Publication Activity Database

    Blažek, Radim; Polačik, Matej; Kačer, P.; Cellerino, A.; Řežucha, Radomil; Methling, Caroline; Tomášek, Oldřich; Syslová, K.; Terzibasi Tozzini, E.; Albrecht, Tomáš; Vrtílek, Milan; Reichard, Martin

    2017-01-01

    Roč. 71, č. 2 (2017), s. 386-402 ISSN 0014-3820 R&D Projects: GA ČR GA13-05872S; GA ČR(CZ) GA16-00291S Institutional support: RVO:68081766 Keywords : Intraspecific variation * life span * neoplasia * pace-of-life syndrome * parallel evolution * reproductive senescence Subject RIV: EG - Zoology OBOR OECD: Ecology Impact factor: 4.201, year: 2016

  16. Trends in savanna structure and composition along an aridity gradient in the Kalahari

    CSIR Research Space (South Africa)

    Scholes, RJ

    2002-06-01

    Full Text Available Rooyen 1998). Sa- line areas such as the vast Makgadigadi pan support halophytic shrubs and grasses or are bare. Non-saline pans, for example at Nxai pan, support sedge- and grasslands, sometimes with tree clumps on slightly more elevated ground... being larger than about 20 mm (major axis); fine-leafed is smaller than 20 mm, and usually less than 2 mm. Deciduous means that > 90% of all tree and shrub leaves are lost for at least three months, evergreen means that > 80% of tree leaf is retained...

  17. Community structure of soil phototrophs along environmental gradients in arid Himalaya

    Czech Academy of Sciences Publication Activity Database

    Janatková, Kateřina; Řeháková, Klára; Doležal, Jiří; Šimek, Miloslav; Chlumská, Zuzana; Dvorský, Miroslav; Kopecký, Martin

    2013-01-01

    Roč. 15, č. 9 (2013), s. 2505-2516 ISSN 1462-2912 R&D Projects: GA ČR GA13-13368S Institutional research plan: CEZ:AV0Z60050516 Institutional support: RVO:67985939 ; RVO:60077344 Keywords : Cyanobacteria * nitrogen fixation * Tibetan Platea Subject RIV: EH - Ecology, Behaviour; EE - Microbiology, Virology (BC-A) Impact factor: 6.240, year: 2013

  18. Manipulating the Gradient

    Science.gov (United States)

    Gaze, Eric C.

    2005-01-01

    We introduce a cooperative learning, group lab for a Calculus III course to facilitate comprehension of the gradient vector and directional derivative concepts. The lab is a hands-on experience allowing students to manipulate a tangent plane and empirically measure the effect of partial derivatives on the direction of optimal ascent. (Contains 7…

  19. Improving large-scale groundwater models by considering fossil gradients

    Science.gov (United States)

    Schulz, Stephan; Walther, Marc; Michelsen, Nils; Rausch, Randolf; Dirks, Heiko; Al-Saud, Mohammed; Merz, Ralf; Kolditz, Olaf; Schüth, Christoph

    2017-05-01

    Due to limited availability of surface water, many arid to semi-arid countries rely on their groundwater resources. Despite the quasi-absence of present day replenishment, some of these groundwater bodies contain large amounts of water, which was recharged during pluvial periods of the Late Pleistocene to Early Holocene. These mostly fossil, non-renewable resources require different management schemes compared to those which are usually applied in renewable systems. Fossil groundwater is a finite resource and its withdrawal implies mining of aquifer storage reserves. Although they receive almost no recharge, some of them show notable hydraulic gradients and a flow towards their discharge areas, even without pumping. As a result, these systems have more discharge than recharge and hence are not in steady state, which makes their modelling, in particular the calibration, very challenging. In this study, we introduce a new calibration approach, composed of four steps: (i) estimating the fossil discharge component, (ii) determining the origin of fossil discharge, (iii) fitting the hydraulic conductivity with a pseudo steady-state model, and (iv) fitting the storage capacity with a transient model by reconstructing head drawdown induced by pumping activities. Finally, we test the relevance of our approach and evaluated the effect of considering or ignoring fossil gradients on aquifer parameterization for the Upper Mega Aquifer (UMA) on the Arabian Peninsula.

  20. Use of environmental isotopes in arid zone hydrology

    International Nuclear Information System (INIS)

    Dincer, T.

    1980-01-01

    After aridity is defined some physical and hydrologic features common in arid lands are described. An attempt has been made to identify various groundwater recharge mechanisms in arid countries and to assess their relative importance. The influence of the arid climates on the isotopic composition of the precipitation is discussed. The use of environmental isotopes in run-off and precipitation infiltration and recharge is evaluated, and the importance of isotopic studies in investigating interrelations between aquifers is stressed. Finally, some examples of isotope applications in surface water and its relation to groundwater are given. (author)

  1. A review of Cordylus machadoi (Squamata: Cordylidae) in southwestern Angola, with the description of a new species from the Pro-Namib desert.

    Science.gov (United States)

    Stanley, Edward L; Ceríaco, Luis M P; Bandeira, Suzana; Valerio, Hilaria; Bates, Michael F; Branch, William R

    2016-01-07

    The girdled lizard genus Cordylus is represented in Angola by two species, Cordylus angolensis and C. machadoi, separated from their nearest congeners by over 700 km. Here we describe a new species, Cordylus namakuiyus sp. nov., endemic to the arid lowlands west of the southern Angolan escarpment. Phylogenetic analysis using three mitochondrial and eight nuclear genes shows that the low-elevation forms and the proximate, high-elevation species C. machadoi are genetically divergent and reciprocally monophyletic, and together form the earliest diverging lineage of the northern Cordylus clade. Morphological data, collected using computed tomography and traditional techniques (scalation and morphology), identify consistent phenotypic differences between these high- and low-elevation species and allows for a detailed description of the osteology and osteodermal arrangements of the new species. A series of 50 specimens, collected during the 1925 Vernay expedition to southwestern Angola and housed at the American Museum of Natural History, are assigned to the new species, although the identity of Cordylus from northern Namibia remains ambiguous and requires further investigation.

  2. Predicting the future impact of droughts on ungulate populations in arid and semi-arid environments.

    Directory of Open Access Journals (Sweden)

    Clare Duncan

    Full Text Available Droughts can have a severe impact on the dynamics of animal populations, particularly in semi-arid and arid environments where herbivore populations are strongly limited by resource availability. Increased drought intensity under projected climate change scenarios can be expected to reduce the viability of such populations, yet this impact has seldom been quantified. In this study, we aim to fill this gap and assess how the predicted worsening of droughts over the 21(st century is likely to impact the population dynamics of twelve ungulate species occurring in arid and semi-arid habitats. Our results provide support to the hypotheses that more sedentary, grazing and mixed feeding species will be put at high risk from future increases in drought intensity, suggesting that management intervention under these conditions should be targeted towards species possessing these traits. Predictive population models for all sedentary, grazing or mixed feeding species in our study show that their probability of extinction dramatically increases under future emissions scenarios, and that this extinction risk is greater for smaller populations than larger ones. Our study highlights the importance of quantifying the current and future impacts of increasing extreme natural events on populations and species in order to improve our ability to mitigate predicted biodiversity loss under climate change.

  3. Problems and Prospects of SWAT Model Application on an Arid/Semi-arid Watershed in Arizona

    Science.gov (United States)

    Hydrological characteristics in the semi-arid southwest create unique challenges to watershed modelers. Streamflow in these regions is largely dependent on seasonal, short term, and high intensity rainfall events. The objectives of this study are: 1) to analyze the unique hydrolo...

  4. Hazard Analysis of Arid and Semi-Arid (ASAL) Regions of Kenya ...

    African Journals Online (AJOL)

    Objectives: The overall objective of this study was to prioritize hazards in the ASAL region. ... Health, local Government, and Provincial Administration, Environment and NGO. ... and country level to inform interventions and other developmental activities. Women ... Keywords: hazard, natural disaster, disaster risk, arid, Kenya ...

  5. Hydropedological interpretation of arid soilscapes, South Africa

    Science.gov (United States)

    Tinnefeld, Martin; Van Tol, Jacobus; Le Roux, Pieter

    2017-04-01

    Hydropedological investigations in arid regions are scarce due to the low the low contribution of these areas to water resources. Infrequent rainfall and few flow events also complicates measurements hydrological studies. Hydropedological studies, relating soil morphological properties and their spatial distribution to hydrological response, have been studied in detail in semi-arid, temperate, and sub-humid regions. In this paper, we investigated the relation between soil morphological properties and selected hydrological properties of soils in an arid landscape. We also studied the spatial distribution of the morphological properties to conceptualise the hydrological behaviour of different soilscapes in the area. A total of 806 soil profiles, covering an area of 4836 ha in the Northern Cape Province of South Africa were described and classified. The geology is dominated by Dwyka tillite overlain by aeolian sands with scattered Dolerite buttes. Thirteen modal profiles, representing the dominant soils types were selected, sampled at horizon level, and analysed for pH, CEC, iron, manganese, carbonate content. In situ measurements of saturated and near saturated (tension) hydraulic conductivity (Ks) were conducted to determine the water conducting macroporosity (WCM). Undisturbed cores were collected on which water retention characteristics were determined under laboratory conditions. Results indicate that dry soil colour, degree of structure development and the presence, absence, and abundance of carbonates as well as the degree of precipitation, are important indicators of hydrological response. For example; grey soils typically have lower Ks with higher storage capacity than soils dominated by red colours, whereas abundant carbonate precipitations in the soil matrix have lower WCM due to clogging of macropores. The dominant soil distribution pattern indicates that rapid vertical flow, through and out of the pedon, might contribute to recharge of an accumulative

  6. Aridity of Central Asia through the Holocene

    Science.gov (United States)

    Aizen, E. M.; Aizen, V. B.; Mayewski, P. A.; Zhou, H.; Rodda, C.; Joswiak, D.; Takeuchi, N.; Fujita, K.; Kurbatov, A.; Grigholm, B. O.

    2017-12-01

    The dynamics of aridity in Central Asia for over the past 12,000 years has been analyzed using deep ice core records recovered from the Siberian Altai, Tien Shan and Pamir glaciers. An analysis of aridity in the 20-21 centuries based on the long-term meteorological observations complements the paleo- climate reconstruction. The goal of our research is to examine an aridity (at low and high temperatures) in Central Asia as a complex of characteristics including air temperature-precipitation relationship (Koppen, 1918, Geiger, 1961, Mezencev, 1973), intensity of dust loading and biomass burning. The stable isotope ratio, soluble ionic and insoluble particulate geochemical components and oxalate preserved in ice were considered in relation to climatic and environmental changes; and to determine the main aerosol sources using ground- and upper-level meteorological data. Multivariate statistical methods were employed for examination of the main geo-chemical components responsible for the preserved aridity variability. Insoluble particle concentrations preserved in the ice core were affected mainly by precipitation regimes and wind speed. Concentration of all size particles was found to be negatively correlated with monthly temperatures indicating low temperatures during the dry particle deposition. Two abrupt depletions in stable isotope records, i.e., Younger Dryas and Centurial Sever Drought (CSD), occurred during cold, dry, windy periods of intensified dust storms in large desert areas. When climate became colder and drier, the Central Asian deserts extended, wind speeds increased loading mineral dust to atmosphere, which formed inversion while the convection processes and precipitation occurrence were limited. Warmer and wetter conditions are associated with less dust loading that occurred during the Holocene climate optimum, medieval warm and modern warm periods. The sudden climate transitions are accompanied by the most intensifying mineral dust loading. From the

  7. Future aridity under conditions of global climate change

    Science.gov (United States)

    Asadi Zarch, Mohammad Amin; Sivakumar, Bellie; Malekinezhad, Hossein; Sharma, Ashish

    2017-11-01

    Global climate change is anticipated to cause some major changes in hydroclimatic conditions around the world. As aridity is a reliable indicator of potential available water, assessment of its changes under future climatic conditions is important for proper management of water. This study employs the UNESCO aridity/humidity index, which is a derivative of precipitation (P) and potential evapotranspiration (PET), for assessment of aridity. Historical (1901-2005) simulations and future (2006-2100) projections of 22 global climate models (GCMs) from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) are studied. The Nested Bias Correction (NBC) approach is used to correct possible biases of precipitation (simulated directly by the GCMs) and PET (estimated by applying FAO56-Penman-Monteith model on simulated parameters of the GCMs). To detect future aridity changes, the areal extents of the aridity zones in the past and future periods as well as through four sub-periods (2006-2025, 2026-2050, 2051-2075, and 2076-2100) of the future are compared. The results indicate that changes in climate will alter the areal extents of aridity zones in the future. In general, from the first sub-period towards the last one, the area covered by hyper-arid, arid, semi-arid, and sub-humid zones will increase (by 7.46%, 7.01%, 5.80%, and 2.78%, respectively), while the area of the humid regions will decrease (by 4.76%), suggesting that there will be less water over the global land area in the future. To understand the cause of these changes, precipitation and PET are also separately assumed to be stationary throughout the four future sub-periods and the resulting aridity changes are then analyzed. The results reveal that the aridity changes are mostly caused by the positive PET trends, even though the slight precipitation increase lessens the magnitude of the changes.

  8. Aridity and grazing as convergent selective forces: an experiment with an Arid Chaco bunchgrass.

    Science.gov (United States)

    Quiroga, R Emiliano; Golluscio, Rodolfo A; Blanco, Lisandro J; Fernández, Roberto J

    2010-10-01

    It has been proposed that aridity and grazing are convergent selective forces: each one selects for traits conferring resistance to both. However, this conceptual model has not yet been experimentally validated. The aim of this work was to experimentally evaluate the effect of aridity and grazing, as selective forces, on drought and grazing resistance of populations of Trichloris crinita, a native perennial forage grass of the Argentinean Arid Chaco region. We collected seeds in sites with four different combinations of aridity and grazing history (semiarid/ subhumid x heavily grazed/lightly grazed), established them in pots in a common garden, and subjected the resulting plants to different combinations of drought and defoliation. Our results agreed with the convergence model. Aridity has selected T. crinita genotypes that respond better to drought and defoliation in terms of sexual reproduction and leaf growth, and that can evade grazing due to a lower shoot: root ratio and a higher resource allocation to reserves (starch) in stem bases. Similarly, grazing has selected genotypes that respond better to drought and defoliation in terms of sexual reproduction and that can evade grazing due to a lower digestibility of leaf blades. These results allow us to extend concepts of previous models in plant adaptation to herbivory to models on plant adaptation to drought. The only variable in which we obtained a result opposite to predictions was plant height, as plants from semiarid sites were taller (and with more erect tillers) than plants from subhumid sites; we hypothesize that this result might have been a consequence of the selection exerted by the high solar radiation and soil temperatures of semiarid sites. In addition, our work allows for the prediction of the effects of dry or wet growing seasons on the performance of T. crinita plants. Our results suggest that we can rely on dry environments for selecting grazing-resistant genotypes and on high grazing pressure

  9. Bigravity from gradient expansion

    International Nuclear Information System (INIS)

    Yamashita, Yasuho; Tanaka, Takahiro

    2016-01-01

    We discuss how the ghost-free bigravity coupled with a single scalar field can be derived from a braneworld setup. We consider DGP two-brane model without radion stabilization. The bulk configuration is solved for given boundary metrics, and it is substituted back into the action to obtain the effective four-dimensional action. In order to obtain the ghost-free bigravity, we consider the gradient expansion in which the brane separation is supposed to be sufficiently small so that two boundary metrics are almost identical. The obtained effective theory is shown to be ghost free as expected, however, the interaction between two gravitons takes the Fierz-Pauli form at the leading order of the gradient expansion, even though we do not use the approximation of linear perturbation. We also find that the radion remains as a scalar field in the four-dimensional effective theory, but its coupling to the metrics is non-trivial.

  10. Gradient-Index Optics

    Science.gov (United States)

    2010-03-31

    nonimaging design capabilities to incorporate 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 12-04-2011 13. SUPPLEMENTARY NOTES The views, opinions...Box 12211 Research Triangle Park, NC 27709-2211 15. SUBJECT TERMS Imaging Optics, Nonimaging Optics, Gradient Index Optics, Camera, Concentrator...imaging and nonimaging design capabilities to incorporate manufacturable GRIN lenses can provide imaging lens systems that are compact and

  11. Surficial weathering of iron sulfide mine tailings under semi-arid climate.

    Science.gov (United States)

    Hayes, Sarah M; Root, Robert A; Perdrial, Nicolas; Maier, Raina; Chorover, Jon

    2014-09-15

    Mine wastes introduce anthropogenic weathering profiles to the critical zone that often remain unvegetated for decades after mining cessation. As such, they are vulnerable to wind and water dispersion of particulate matter to adjacent ecosystems and residential communities. In sulfide-rich ore tailings, propagation to depth of the oxidative weathering front controls the depth-variation in speciation of major and trace elements. Despite the prevalence of surficial mine waste deposits in arid regions of the globe, few prior studies have been conducted to resolve the near-surface profile of sulfide ore tailings weathered under semi-arid climate. We investigated relations between gossan oxidative reaction-front propagation and the molecular speciation of iron and sulfur in tailings subjected to weathering under semi-arid climate at an EPA Superfund Site in semi-arid central Arizona (USA). Here we report a multi-method data set combining wet chemical and synchrotron-based X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES) methods to resolve the tight coupling of iron (Fe) and sulfur (S) geochemical changes in the top 2 m of tailings. Despite nearly invariant Fe and S concentration with depth (130-140 and 100-120 g kg -1 , respectively), a sharp redox gradient and distinct morphological change was observed within the top 0.5 m, associated with a progressive oxidative alteration of ferrous sulfides to (oxyhydr)oxides and (hydroxy)sulfates. Transformation is nearly complete in surficial samples. Trends in molecular-scale alteration were co-located with a decrease in pH from 7.3 to 2.3, and shifts in Fe and S lability as measured via chemical extraction. Initial weathering products, ferrihydrite and gypsum, transform to schwertmannite, then jarosite-group minerals with an accompanying decrease in pH. Interestingly, thermodynamically stable phases such as goethite and hematite were not detected in any samples, but ferrihydrite was observed even in

  12. Understanding Flash Flood Generation in the Arid Region of the Dead Sea

    Science.gov (United States)

    Merz, R.; Hennig, H.; Rödiger, T.; Laronne, J. B.

    2017-12-01

    The arid region of the Dead Sea is prone by flash floods. Such flash floods in (semi-) arid regions are impressive. Generated within minutes, the peak unit discharge can be as high as 25 m³/s km². Floods are the main mechanism supplying water to alluvial aquifers, forming fluvial landscapes including canyons and often causing damage to humans, infrastructure, industry and tourism. Existing hydrological models in this region focus on peak discharges. However, these models are often based on simplified concepts and/or on concepts which were developed for humid regions. To more closely relate such models to local conditions, processes within catchments where floods occur require consideration. Therefore, a measurement network of rain gauges and level loggers to monitor runoff was installed in the beginning of the 2015/16 hydrological season in the tributaries of Wadi Arugot. The Arugot catchment is one of the largest ephemeral Wadis draining to the western shoreline of the Dead Sea at 450 m bsl. Due to the high gradient in elevation, the climate within the basin ranges from semiarid in the Judean Mountains, to hyper-arid near the Dead Sea with respective mean annual rainfall of 650 and 50 mm. The installed rain gauge network in the mountains is more dense compared to the Dead Sea area. Arid to semiarid catchments have different runoff generation processes compared to humid regions due local storm rainfall, low density of vegetation cover as well as patchy and shallow soil. These characteristics limit the contribution of groundwater flow, saturated overland flow and shallow subsurface flow, and therefore Hortonian overland flow is the most important contributor to overland flow. First analyses of the runoff data have shown that the storage capacity in the mountain area is lower compared to the more arid region. This is an evidence of high transmission losses in the coarse gravel wadi bed, therefore having a high permeability. The rain event duration and the amount of

  13. Herbivore-plant interactions and desertification in arid lands

    Science.gov (United States)

    Arid lands around the world have experienced or are currently experiencing degradation that is known as desertification. Animal-plant interactions that have an effect on desertification are among the most important function of animals in arid ecosystems. Desertification has been defined as land de...

  14. Arid Green Infrastructure for Water Control and Conservation ...

    Science.gov (United States)

    Green infrastructure is an approach to managing wet weather flows using systems and practices that mimic natural processes. It is designed to manage stormwater as close to its source as possible and protect the quality of receiving waters. Although most green infrastructure practices were first developed in temperate climates, green infrastructure also can be a cost-effective approach to stormwater management and water conservation in arid and semi-arid regions, such as those found in the western and southwestern United States. Green infrastructure practices can be applied at the site, neighborhood and watershed scales. In addition to water management and conservation, implementing green infrastructure confers many social and economic benefits and can address issues of environmental justice. The U.S. Environmental Protection Agency (EPA) commissioned a literature review to identify the state-of-the science practices dealing with water control and conservation in arid and semi-arid regions, with emphasis on these regions in the United States. The search focused on stormwater control measures or practices that slow, capture, treat, infiltrate and/or store runoff at its source (i.e., green infrastructure). The material in Chapters 1 through 3 provides background to EPA’s current activities related to the application of green infrastructure practices in arid and semi-arid regions. An introduction to the topic of green infrastructure in arid and semi-arid regions i

  15. Performance evaluation of constructed wetlands: A review of arid ...

    African Journals Online (AJOL)

    Aiming at environmental pollution control through the use of constructed wetlands systems (CWs) in arid and semi arid climatic region, a detailed review of CWs was undertaken. Given the practical application and simplicity of the technology, principles for building phytotechnology-ecohydrology environment used for ...

  16. Emerging crops in the USDA arid lands germplasm collection

    Science.gov (United States)

    The USDA National Plant Germplasm System maintains collections of several emerging crops for arid lands at the National Arid Land Plant Genetic Resources Unit in Parlier, CA (NALPGRU). The guayule, jojoba, and prickly pear collections are most active in terms of current research and crop development...

  17. Watershed Management in Arid Zones: A Prototype Short Course.

    Science.gov (United States)

    Thames, John L., Ed.; Fischer, John N., Ed.

    Presented is information recommended for inclusion in a short course to help extend knowledge of water resource development and research techniques in arid and semi-arid regions. Information is particularly intended for applicability in developing nations. Included are considerations of livestock grazing, use of hydrologic data, vegetation…

  18. Pathways to Resilience in Semi-Arid Economies (PRISE)

    International Development Research Centre (IDRC) Digital Library (Canada)

    rlarbey

    PRISE Goal. This research will support the emergence of equitable, climate resilient economic development in semi-arid lands through research excellence and ... change in semi-arid areas, and how is the private sector adapting? 4. How do ... Role. Individual. Contact email. Lead Principal Investigator. Dr Tom Mitchell.

  19. Uses of tree legumes in semi-arid regions

    Energy Technology Data Exchange (ETDEWEB)

    Felker, P.

    1980-01-01

    Uses of tree legumes in semi-arid and arid regions are reviewed. This review is divided into sections according to the following general use categories: fuels; human food; livestock food; to increase yields of crops grown beneath their canopies;and control of desertification. (MHR)

  20. Optimizing cooling systems in Egyptian arid urbans

    International Nuclear Information System (INIS)

    Medhat, Ahmed A.; Khalil, Essam E.

    2006-01-01

    Present study is devoted to climatic and site oriented investigations that were carried out in a new rural development in the Upper-Egypt. Bioclimatic classifications considered Upper Egypt region, near Sudan border, as a Hot and Dry climatic region. [1]. that is affected by solar heat intensities that can reach 900 W/m2 for a period ranged from 5-to-7 hours per day with the presence of study storms. Cooling season extends up to eight months per year having Upper-day-bulb temperature ranged from 400 degree centigrade - to - 470 degree centigrade while Lower-dry-bulb-temperature ranged from 280 degree centigrade - to - 320 degree centigrade with the relative humidity ranged from 10%-to-37% RH. [2]. Site surveys and field experimental and analyses of the commonly used cooling systems were investigated, evaluated and optimized for optimum indoor comfort conditions at efficient energy efficiency. [3]. Extensive analyses were performed based on Psychrometric formulae to evaluate the impact of energy consumptions related to different cooling systems such as direct expansion, chilled water, and evaporative systems. the present study enables the critical investigations of the influence of arid outdoor conditions and the required indoor thermal parameters on the energy efficiencies of HVAC-system. This work; focuses on the suggestion of suitable system that should be implemented by local energy codes in these arid urban.(Author)

  1. The current bioenergy production potential of semi-arid and arid regions in sub-Saharan Africa

    NARCIS (Netherlands)

    Wicke, B.; Smeets, E.M.W.; Watson, H.; Faaij, A.P.C.

    2011-01-01

    This article assesses the current technical and economic potential of three bioenergy production systems (cassava ethanol, jatropha oil and fuelwood) in semi-arid and arid regions of eight sub-Saharan African countries. The results indicate that the availability of land for energy production ranges

  2. Application of Isotope techniques in the arid and semi-arid zone hydrology

    International Nuclear Information System (INIS)

    Gonfiantini, R.; Louvat, D.; Aranyossy, J.F.

    1993-01-01

    The paper presents a brief introduction on the scientific background of isotope hydrology,and after, explains the applications of environment isotope techniques in groundwater hydrology of the arid and semi-arid zones. It includes the study of aquifer recharge and discharge, identification of palaeorecharge, groundwater movement and age in unconfined and confined aquifers, and interconnections between aquifers. The contribution of isotopes is highlighted with many examples of field case studies, with emphasis on studies carried out with IAEA support. Finally, a short description of IAEA program on isotope hydrology is given, with a list of regional projects supported through the IAEA Technical Cooperation program, and of Coordinated Research Programs. The latter give the modern research trends in isotope application to hydrology and hydrosphere environmental studies. (author). 2 tabs., 25 figs., 69 refs

  3. Wetting of flat gradient surfaces.

    Science.gov (United States)

    Bormashenko, Edward

    2018-04-01

    Gradient, chemically modified, flat surfaces enable directed transport of droplets. Calculation of apparent contact angles inherent for gradient surfaces is challenging even for atomically flat ones. Wetting of gradient, flat solid surfaces is treated within the variational approach, under which the contact line is free to move along the substrate. Transversality conditions of the variational problem give rise to the generalized Young equation valid for gradient solid surfaces. The apparent (equilibrium) contact angle of a droplet, placed on a gradient surface depends on the radius of the contact line and the values of derivatives of interfacial tensions. The linear approximation of the problem is considered. It is demonstrated that the contact angle hysteresis is inevitable on gradient surfaces. Electrowetting of gradient surfaces is discussed. Copyright © 2018 Elsevier Inc. All rights reserved.

  4. Determine the optimum spectral reflectance of juniper and pistachio in arid and semi-arid region

    Science.gov (United States)

    Fadaei, Hadi; Suzuki, Rikie

    2012-11-01

    Arid and semi-arid areas of northeast Iran cover about 3.4 million ha are populated by two main tree species, the broadleaf Pistacia vera. L (pistachio) and the conifer Juniperus excelsa ssp. polycarpos (Persian juniper). Natural stands of pistachio in Iran are not only environmentally important but genetically essential as seed sources for pistachio production in orchards. In this study, we estimated the optimum spectral reflectance of juniper forests and natural pistachio stands using remote sensing to help in the sustainable management and production of pistachio in Iran. In this research spectral reflectance are able to specify of multispectral from Advanced Land Observing Satellite (ALOS) that provided by JAXA. These data included PRISM is a panchromatic radiometer with a 2.5 m spatial resolution at nadir, has one band with a wavelength of 0.52-0.77 μm and AVNIR-2 is a visible and near infrared radiometer for observing land and coastal zones with a 10 m spatial resolution at nadir, has four multispectral bands: blue (0.42-0.50 μm), green (0.52-0.60 μm), red (0.61-0.69 μm), and near infrared (0.76-0.89 μm). Total ratio vegetation index (TRVI) of optimum spectral reflectance of juniper and pistachio have been evaluated. The result of TRVI for Pistachio and juniper were (R2= 0.71 and 0.55). I hope this research can provide decision of managers to helping sustainable management for arid and semi-arid regions in Iran.

  5. Analysis of Water Use and Water Scarcity in Arid and Semi-arid Regions

    Science.gov (United States)

    Samayoa, S. D.

    2017-12-01

    Analysis of Water Use and Water Scarcity in Arid and Semi-arid Regions Susana Samayoa , Muhammed A. G. Chowdhury, Tushar Sinha Department of Environmental Engineering, Texas A & M University - Kingsville Freshwater sustainability in arid and semi-arid regions is highly uncertain under increasing demands due to population growth and urban development as well as limited water supply. In particular, six largest cities by population among the top twenty U.S. cities are located in Texas (TX), which also experience high variability in water availability due to frequent droughts and floods. Similarly, several regions in Arizona (AZ) are rapidly growing (e.g. Phoenix and Tucson) despite receiving scanty rainfall. Thus, the goal of this study is to analyze water use and water scarcity in watersheds within TX and AZ between 1985 and 2010. The water use data from U.S. Geological Survey (USGS) is analyzed by Hydrological Unit Code (HUC) - 8 within TX and AZ. Total freshwater use by county during 1985 and 2010 were converted into water use by HUC-8 using geospatial analysis. Water availability will be estimated by using a large scale Variable Infiltration Capacity (VIC) hydrologic model. The VIC model will be calibrated and validated for multiple basins located in Texas and Arizona. The VIC model simulated total streamflow will be aggregated across the 1/8 degree grids that are within each HUC-8 to estimate water supply. The excess water for upstream HUC-8s (= local supply minus demands) will be routed, in addition to locally generated streamflow, to estimate water availability in downstream HUC-8s. Water Scarcity Index, defined as the ratio of total freshwater demand to supply, will be estimated during 1985 and 2010 to evaluate the effects of water availability and demands on scarcity. Finally, water scarcity and use will be analyzed by HUC-8s within TX and AZ. Such information could be useful in water resources management and planning. Keywords: Water scarcity, water use

  6. Development of an arid site closure plan

    International Nuclear Information System (INIS)

    Nyhan, J.W.; Barnes, F.J.

    1987-01-01

    This document describes the development of a prototype plan for the effective closure and stabilization of an arid low-level waste disposal site. This plan will provide demonstrated closure techniques for a trench in a disposal site at Los Alamos. The accuracy of modeling soil water storage by two hydrologic models, CREAMS and HELP, was tested by comparing simulation results with field measurements of soil moisture in eight experimental landfill cover systems having a range of well-defined soil profiles and vegetative covers. Regression analysis showed that CREAMS generally represented soil moisture more accurately than HELP simulations. Precautions for determining parameter values for model input and for interpreting simulation results are discussed. A specific example is presented showing how the field-validated hydrologic models can be used to develop a final prototype closure plan. 15 refs., 13 figs., 3 tabs

  7. Use of composts in revegetating arid lands

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, C.A.; Hendrickson, P.L.

    1991-09-01

    Compost has been suggested as a soil amendment for arid lands at the US Department of Energy's Hanford Site in southeastern Washington State. The operating contractor of the site, Westinghouse Hanford Company, requested that the Pacific Northwest Laboratory conduct a literature review to compile additional information on the use of compost amendments and their benefits. This report provides background information on the factors needed for plant growth and the consequences of severe soil disturbance. This report also discussed the characteristics of composts relative to other amendments and how they each affect plant growth. Finally,regulatory requirements that could affect land application of sludge-based compost on the Hanford Site are reviewed.

  8. Salinity shapes food webs in shallow lakes: implications for increasing aridity with climate change

    DEFF Research Database (Denmark)

    Vidal, Nicolas; Yu, Jinlei; Gutierrez, Maria Florencia

    2015-01-01

    on community and food web structure in 24 lakes along a wide salinity gradient, from freshwater (0.5 g L-1) to hypersaline lakes (115 g L-1), in a semiarid region in North West China. Fish, zooplankton and macroinvertebrate communities were sampled during July 2014 for determination of taxonomy and size......A reduction in runoff and higher evaporation rates are expected to occur towards 2050 in arid and semiarid regions of the world, resulting in a reduction of water level and salinization of inland waters. Besides the natural process of catchment erosion, human activities such as irrigation of crops...... may also increase salinization. Reduced biodiversity in freshwater systems is the most commonly reported effect of salinization, which may have implications for food web structure and likely for ecosystem functioning as well. The objective of the study was to analyze the effects of salinity...

  9. Impact of multiple soil nutrients on distribution patterns of shrubs in an arid valley, in southwest china

    International Nuclear Information System (INIS)

    Song, C.J.; Yishui, T.; Zao, L.X.

    2014-01-01

    Shrubs play key roles in arid regions and multiple interacting resources limit their distribution patterns. Identifying limiting resources and their coupling effects on shrubs is essential for developing restoration theory and practice. A survey of shrub composition, soil properties and topography was conducted in fifty-seven 15-m * 15-m plots in an arid valley of the upper Minjiang River, Southwest China. With quantitative classification method and ordination technique, 48 shrubs species were classified into four clusters and two categories along soil gradient. Cluster I and II composed Category I and had a significantly higher percentage of dominant legume shrubs than in Cluster III and Cluster IV, which made up Category II. Correlation analysis indicated that both multi-resource limitation and single resource limitation were coexisting simultaneously in this arid area, the extent of which was functional cluster-specific and also quantified hierarchical structure of multiple resource limitation: soil water played a primary limitation role, available nitrogen the next, and available phosphorus the third at community scale. Moreover, this study affirmed that both soil pH and soil texture could effectively regulate retention of soil moisture and available nutrients, respectively. Distinguishing critical limiting resources and their regulators is very meaningful to clarify couplings and controlling mechanisms in restoration practices. Therefore, decreasing soil pH and increasing soil clay content should be conducted thoroughly in plantation sites to remain abundant soil moisture and available nutrients in native restoration projects. (author)

  10. Trends and homogeneity of monthly, seasonal, and annual rainfall over arid region of Rajasthan, India

    Science.gov (United States)

    Meena, Hari Mohan; Machiwal, Deepesh; Santra, Priyabrata; Moharana, Pratap Chandra; Singh, D. V.

    2018-05-01

    Knowledge of rainfall variability is important for regional-scale planning and management of water resources in agriculture. This study explores spatio-temporal variations, trends, and homogeneity in monthly, seasonal, and annual rainfall series of 62 stations located in arid region of Rajasthan, India using 55 year (1957-2011) data. Box-whisker plots indicate presence of outliers and extremes in annual rainfall, which made the distribution of annual rainfall right-skewed. Mean and coefficient of variation (CV) of rainfall reveals a high inter-annual variability (CV > 200%) in the western portion where the mean annual rainfall is very low. A general gradient of the mean monthly, seasonal, and annual rainfall is visible from northwest to southeast direction, which is orthogonal to the gradient of CV. The Sen's innovative trend test is found over-sensitive in evaluating statistical significance of the rainfall trends, while the Mann-Kendall test identifies significantly increasing rainfall trends in June and September. Rainfall in July shows prominently decreasing trends although none of them are found statistically significant. Monsoon and annual rainfall show significantly increasing trends at only four stations. The magnitude of trends indicates that the rainfall is increasing at a mean rate of 1.11, 2.85, and 2.89 mm year-1 in August, monsoon season, and annual series. The rainfall is found homogeneous over most of the area except for few stations situated in the eastern and northwest portions where significantly increasing trends are observed. Findings of this study indicate that there are few increasing trends in rainfall of this Indian arid region.

  11. Isolation of microalgae species from arid environments and ...

    African Journals Online (AJOL)

    Isolation of microalgae species from arid environments and evaluation of their potentials for biodiesel production. ... African Journal of Biotechnology. Journal Home · ABOUT THIS JOURNAL · Advanced Search · Current Issue · Archives.

  12. Evaporation as the transport mechanism of metals in arid regions

    KAUST Repository

    Lima, Ana T.; Safar, Zeinab; Loch, J.P. Gustav

    2014-01-01

    in soils. Due to the low rainfall and high evaporation rates in arid regions, groundwater quality is not threatened and all soil contamination issues tend to be overlooked. But if soil contamination happens, where do contaminants go? This study tests

  13. Introducing Pathways to Resilience in Semi-Arid Economies (PRISE ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    rlarbey

    Equitable, climate resilient economic development in semi-arid .... manufacturing or services (apart from health, insurance and tourism). Further research ... evaluated, particularly economic impact assessments of adaptation both on existing.

  14. Patchiness in semi-arid dwarf shrublands: evidence from satellite ...

    African Journals Online (AJOL)

    ... Plants; Remote sensing; Rhigozum obovatum Burch; Satellite-derived vegetation indices; Woody species; patchiness; semi-arid; dwarf shrubland; shrublands; co2; assimilation; karoo; south africa; ndvi; satellite imagery; geochemical mound; rhigozum obovatum; eriocephalus ericoides; pentzia incana; vegetation; botany

  15. Gradient Boosting Machines, A Tutorial

    Directory of Open Access Journals (Sweden)

    Alexey eNatekin

    2013-12-01

    Full Text Available Gradient boosting machines are a family of powerful machine-learning techniques that have shown considerable success in a wide range of practical applications. They are highly customizable to the particular needs of the application, like being learned with respect to different loss functions. This article gives a tutorial introduction into the methodology of gradient boosting methods. A theoretical information is complemented with many descriptive examples and illustrations which cover all the stages of the gradient boosting model design. Considerations on handling the model complexity are discussed. A set of practical examples of gradient boosting applications are presented and comprehensively analyzed.

  16. Distinctive channel geometry and riparian vegetation: A geomorphic classification for arid ephemeral streams

    Science.gov (United States)

    Sutfin, N.; Shaw, J. R.; Wohl, E. E.; Cooper, D.

    2012-12-01

    Interactions between hydrology, channel form, and riparian vegetation along arid ephemeral streams are not thoroughly understood and current stream classifications do not adequately represent variability in channel geometry and associated riparian communities. Relatively infrequent hydrologic disturbances in dryland environments are responsible for creation and maintenance of channel form that supports riparian communities. To investigate the influence of channel characteristics on riparian vegetation in the arid southwestern United States, we develop a geomorphic classification for arid ephemeral streams based on the degree of confinement and the composition of confining material that provide constraints on available moisture. Our conceptual model includes five stream types: 1) bedrock channels entirely confined by exposed bedrock and devoid of persistent alluvium; 2) bedrock with alluvium channels at least partially confined by bedrock but containing enough alluvium to create bedforms that persist through time; 3) incised alluvium channels bound only by unconsolidated alluvial material into which they are incised; 4) braided washes that exhibit multi-thread, braided characteristics regardless of the composition of confining material; and 5) piedmont headwater 0-2nd order streams (Strahler) confined only by unconsolidated alluvium and which initiate as secondary channels on piedmont surfaces. Eighty-six study reaches representing the five stream types were surveyed on the U.S. Army Yuma Proving Ground in the Sonoran Desert of southwestern Arizona. Non-parametric multivariate analysis of variance (PERMANOVA) indicates significant differences between the five stream types with regards to channel geometry (i.e., stream gradient, width-to-depth ratio, the ratio between valley width and channel width (Wv/Wc), shear stress, and unit stream power) and riparian vegetation (i.e., presence and canopy coverage by species, canopy stratum, and life form). Discriminant analysis

  17. Aridity changes in the Tibetan Plateau in a warming climate

    International Nuclear Information System (INIS)

    Gao, Yanhong; Li, Xia; Xu, Jianwei; Ruby Leung, L.; Chen, Deliang

    2015-01-01

    Desertification in the Tibetan Plateau (TP) has drawn increasing attention in the recent decades. It has been postulated as a consequence of increasing climate aridity due to the observed warming. This study quantifies the aridity changes in the TP and attributes the changes to different climatic factors. Using the ratio of precipitation to potential evapotranspiration (P/PET) as an aridity index, we used observed meteorological records at 83 stations in the TP to calculate PET using the Penman–Monteith algorithm and the ratio. Spatial and temporal changes of P/PET in 1979–2011 were analyzed. Results show that stations located in the arid and semi-arid northwestern TP are becoming significantly wetter, and half of the stations in the semi-humid eastern TP are becoming drier, though not significantly, in the recent three decades. The aridity change patterns are significantly correlated with the change patterns of precipitation, sunshine duration and diurnal temperature range. Temporal correlations between the annual P/PET ratio and other meteorological variables confirm the significant correlation between aridity and the three variables, with precipitation being the dominant driver of P/PET changes at the interannual time scale. Annual PET are insignificantly but negatively correlated with P/PET in the cold season. In the warm season, however, the correlation between PET and P/PET is significant at the confidence level of 99.9% when the cryosphere near the surface melts. Significant correlation between annual wind speed and aridity occurs in limited locations and months. Consistency in the climatology pattern and linear trends in surface air temperature and precipitation calculated using station data, gridded data, and nearest grid-to-stations for the TP average and across sub-basins indicate the robustness of the trends despite the large spatial heterogeneity in the TP that challenge climate monitoring. (letter)

  18. Gradient waveform synthesis for magnetic propulsion using MRI gradient coils

    International Nuclear Information System (INIS)

    Han, B H; Lee, S Y; Park, S

    2008-01-01

    Navigating an untethered micro device in a living subject is of great interest for both diagnostic and therapeutic applications. Magnetic propulsion of an untethered device carrying a magnetic core in it is one of the promising methods to navigate the device. MRI gradients coils are thought to be suitable for navigating the device since they are capable of magnetic propulsion in any direction while providing magnetic resonance images. For precise navigation of the device, especially in the peripheral region of the gradient coils, the concomitant gradient fields, as well as the linear gradient fields in the main magnetic field direction, should be considered in driving the gradient coils. For simple gradient coil configurations, the Maxwell coil in the z-direction and the Golay coil in the x- and y-directions, we have calculated the magnetic force fields, which are not necessarily the same as the conventional linear gradient fields of MRI. Using the calculated magnetic force fields, we have synthesized gradient waveforms to navigate the device along a desired path

  19. ARID1B alterations identify aggressive tumors in neuroblastoma.

    Science.gov (United States)

    Lee, Soo Hyun; Kim, Jung-Sun; Zheng, Siyuan; Huse, Jason T; Bae, Joon Seol; Lee, Ji Won; Yoo, Keon Hee; Koo, Hong Hoe; Kyung, Sungkyu; Park, Woong-Yang; Sung, Ki W

    2017-07-11

    Targeted panel sequencing was performed to determine molecular targets and biomarkers in 72 children with neuroblastoma. Frequent genetic alterations were detected in ALK (16.7%), BRCA1 (13.9%), ATM (12.5%), and PTCH1 (11.1%) in an 83-gene panel. Molecular targets for targeted therapy were identified in 16 of 72 patients (22.2%). Two-thirds of ALK mutations were known to increase sensitivity to ALK inhibitors. Sequence alterations in ARID1B were identified in 5 of 72 patients (6.9%). Four of five ARID1B alterations were detected in tumors of high-risk patients. Two of five patients with ARID1B alterations died of disease progression. Relapse-free survival was lower in patients with ARID1B alterations than in those without (p = 0.01). In analysis confined to high-risk patients, 3-year overall survival was lower in patients with an ARID1B alteration (33.3 ± 27.2%) or MYCN amplification (30.0 ± 23.9%) than in those with neither ARID1B alteration nor MYCN amplification (90.5 ± 6.4%, p = 0.05). These results provide possibilities for targeted therapy and a new biomarker identifying a subgroup of neuroblastoma patients with poor prognosis.

  20. Spatiotemporal trends in mean temperatures and aridity index over Rwanda

    Science.gov (United States)

    Muhire, I.; Ahmed, F.

    2016-01-01

    This study aims at quantifying the trends in mean temperatures and aridity index over Rwanda for the period of 1961-1992, based on analysis of climatic data (temperatures, precipitations, and potential evapotranspiration). The analysis of magnitude and significance of trends in temperatures and aridity index show the degree of climate change and mark the level of vulnerability to extreme events (e.g., droughts) in different areas of the country. The study reveals that mean temperatures increased in most parts of the country, with a significant increase observed in the eastern lowlands and in the southwestern parts. The highlands located in the northwest and the Congo-Nile crest showed a nonsignificant increase in mean temperatures. Aridity index increased only in March, April, October, and November, corresponding with the rainy seasons. The remaining months of the year showed a decreasing trend. At an annual resolution, the highlands and the western region showed a rise in aridity index with a decreasing pattern over the eastern lowlands and the central plateau. Generally, the highlands presented a nonsignificant increase in mean temperatures and aridity index especially during the rainy seasons. The eastern lowlands showed a significant increase in mean temperatures and decreasing trends in aridity index. Therefore, these areas are bound to experience more droughts, leading to reduced water and consequent decline in agricultural production. On the other hand, the north highlands and southwest region will continue to be more productive.

  1. Surficial weathering of iron sulfide mine tailings under semi-arid climate

    Science.gov (United States)

    Hayes, Sarah M.; Root, Robert A.; Perdrial, Nicolas; Maier, Raina M.; Chorover, Jon

    2014-09-01

    Mine wastes introduce anthropogenic weathering profiles to the critical zone that often remain unvegetated for decades after mining cessation. As such, they are vulnerable to wind and water dispersion of particulate matter to adjacent ecosystems and residential communities. In sulfide-rich ore tailings, propagation to depth of the oxidative weathering front controls the depth-variation in speciation of major and trace elements. Despite the prevalence of surficial mine waste deposits in arid regions of the globe, few prior studies have been conducted to resolve the near-surface profile of sulfide ore tailings weathered under semi-arid climate. We investigated relations between gossan oxidative reaction-front propagation and the molecular speciation of iron and sulfur in tailings subjected to weathering in a semi-arid climate at an EPA Superfund Site in central Arizona (USA). Here we report a multi-method data set combining wet chemical and synchrotron-based X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES) methods to resolve the tight coupling of iron (Fe) and sulfur (S) geochemical changes in the top 2 m of tailings. Despite nearly invariant Fe and S concentration with depth (130-140 and 100-120 g kg-1, respectively), a sharp redox gradient and distinct morphological change was observed within the top 0.5 m, associated with a progressive oxidative alteration of ferrous sulfides to (oxyhydr)oxides and (hydroxy)sulfates. Transformation is nearly complete in surficial samples. Trends in molecular-scale alteration were co-located with a decrease in pH from 7.3 to 2.3, and shifts in Fe and S lability as measured via chemical extraction. Initial weathering products, ferrihydrite and gypsum, transform to schwertmannite, then jarosite-group minerals with an accompanying decrease in pH. Interestingly, thermodynamically stable phases such as goethite and hematite were not detected in any samples, but ferrihydrite was observed even in samples with

  2. Hierarchy of responses to resource pulses in arid and semi-arid ecosystems.

    Science.gov (United States)

    Schwinning, Susanne; Sala, Osvaldo E

    2004-10-01

    In arid/semi-arid ecosystems, biological resources, such as water, soil nutrients, and plant biomass, typically go through periods of high and low abundance. Short periods of high resource abundance are usually triggered by rainfall events, which, despite of the overall scarcity of rain, can saturate the resource demand of some biological processes for a time. This review develops the idea that there exists a hierarchy of soil moisture pulse events with a corresponding hierarchy of ecological responses, such that small pulses only trigger a small number of relatively minor ecological events, and larger pulses trigger a more inclusive set and some larger ecological events. This framework hinges on the observation that many biological state changes, where organisms transition from a state of lower to higher physiological activity, require a minimal triggering event size. Response thresholds are often determined by the ability of organisms to utilize soil moisture pulses of different infiltration depth or duration. For example, brief, shallow pulses can only affect surface dwelling organisms with fast response times and high tolerance for low resource levels, such as some species of the soil micro-fauna and -flora, while it takes more water and deeper infiltration to affect the physiology, growth or reproduction of higher plants. This review first discusses how precipitation, climate and site factors translate into soil moisture pulses of varying magnitude and duration. Next, the idea of the response hierarchy for ecosystem processes is developed, followed by an exploration of the possible evolutionary background for the existence of response thresholds to resource pulses. The review concludes with an outlook on global change: does the hierarchical view of precipitation effects in ecosystems provide new perspectives on the future of arid/semiarid lands?

  3. Denaturing gradient gel electrophoresis

    International Nuclear Information System (INIS)

    Kocherginskaya, S.A.; Cann, I.K.O.; Mackie, R.I.

    2005-01-01

    It is worthwhile considering that only some 30 species make up the bulk of the bacterial population in human faeces at any one time based on the classical cultivation-based approach. The situation in the rumen is similar. Thus, it is practical to focus on specific groups of interest within the complex community. These may be the predominant or the most active species, specific physiological groups or readily identifiable (genetic) clusters of phylogenetically related organisms. Several 16S rDNA fingerprinting techniques can be invaluable for selecting and monitoring sequences or phylogenetic groups of interest and are described below. Over the past few decades, considerable attention was focussed on the identification of pure cultures of microbes on the basis of genetic polymorphisms of DNA encoding rRNA such as ribotyping, amplified fragment length polymorphism and randomly amplified polymorphic DNA. However, many of these methods require prior cultivation and are less suitable for use in analysis of complex mixed populations although important in describing cultivated microbial diversity in molecular terms. Much less attention was given to molecular characterization of complex communities. In particular, research into diversity and community structure over time has been revolutionized by the advent of molecular fingerprinting techniques for complex communities. Denaturing or temperature gradient gel electrophoresis (DGGE/TGGE) methods have been successfully applied to the analysis of human, pig, cattle, dog and rodent intestinal populations

  4. Ion temperature gradient instability

    International Nuclear Information System (INIS)

    1989-01-01

    Anomalous ion thermal conductivity remains an open physics issue for the present generation of high temperature Tokamaks. It is generally believed to be due to Ion Temperature Gradient Instability (η i mode). However, it has been difficult, if not impossible to identify this instability and study the anomalous transport due to it, directly. Therefore the production and identification of the mode is pursued in the simpler and experimentally convenient configuration of the Columbia Linear Machine (CLM). CLM is a steady state machine which already has all the appropriate parameters, except η i . This parameter is being increased to the appropriate value of the order of 1 by 'feathering' a tungsten screen located between the plasma source and the experimental cell to flatten the density profile and appropriate redesign of heating antennas to steepen the ion temperature profile. Once the instability is produced and identified, a thorough study of the characteristics of the mode can be done via a wide range of variation of all the critical parameters: η i , parallel wavelength, etc

  5. Summary: special waste form lysimeters - arid program

    International Nuclear Information System (INIS)

    Skaggs, R.L.; Walter, M.B.

    1987-01-01

    The purpose of the Special Waste Form Lysimeters - Arid Program is to determine the performance of solidified commercial low-level waste forms using a field-scale lysimeter facility constructed for measuring the release and migration of radionuclides from the waste forms. The performance of these waste forms, as measured by radionuclide concentrations in lysimeter effluent, will be compared to that predicted by laboratory characterization of the waste forms. Waste forms being tested include nuclear power reactor waste streams that have been solidified in cement, Dow polymer, and bitumen. To conduct the field leaching experiments a lysimeter facility was built to measure leachate under actual environmental conditions. Field-scale samples of waste were buried in lysimeters equipped to measure water balance components, effluent radionuclide concentrations, and to a limited extent, radionuclide concentrations in lysimeter soil samples. The waste forms are being characterized by standard laboratory leach tests to obtain estimates of radionuclide release. These estimates will be compared to leach rates observed in the field. Adsorption studies are being conducted to determine the amount of contaminant available for transport after the release. Theoretical solubility calculations will also be performed to investigate whether common solid phases could be controlling radionuclide release. 4 references, 8 figures, 1 table

  6. Salinization mechanisms in semi-arid regions

    International Nuclear Information System (INIS)

    Santiago, M.M.F.

    1984-01-01

    During a period of three years the basins of the Pereira de Miranda and Caxitore dams, located in the crystalline rock area of Ceara, Brazil, were studied in order to determine the mechanisms of salinization of their waters. Isotope methods ( 18 O/ 16 O) and hidrochemistry (determination of the of the maior ions) were applied to surface, underground and rain water in this study. An isotope model was designed and applied to the determination of evaporation and percolation of dams in semi-arid zones during the dry season. The results are compared to those from a conventional chemical model. As causes of salinization of the water in the dams, the contributions of the rain itself and the lixiviation of the soil are quantified. An interaction between the dams and the underground water is imperceptible. The salinization of the underground water is attributed to recharge of the aquifer with rain water from the surface runoff followed by evaporation of the water rising, due to capilarity, in a one-directional flow to the surface. (Author) [pt

  7. Growth and Nutrient Status of Introduced Black Locust (Robinia pseudoacacia L.) Afforestation in Arid and Semi Arid Areas of Iran

    OpenAIRE

    Moshki, A.; Lamersdorf, N. P.

    2011-01-01

    Under global climate change it is expected that many arid regions in the world will experience enhanced desertification in the next decades. Black locust (Robinia pseudoacacia L.) is a one commonly used species for afforestation projects in arid regions of Iran due to its soil rehabilitation capabilities. This study aims to characterize how Robinia growth parameters and nutrient status interacted and were influenced soil properties. The experiment was conducted at three Robinia plantations in...

  8. Characterization of gradient control systems

    NARCIS (Netherlands)

    Cortés, Jorge; van der Schaft, Arjan; Crouch, Peter E.

    2005-01-01

    Given a general nonlinear affine control system with outputs and a torsion-free affine connection defined on its state space, we investigate the gradient realization problem: we give necessary and sufficient conditions under which the control system can be written as a gradient control system

  9. Characterization of Gradient Control Systems

    NARCIS (Netherlands)

    Cortés, Jorge; Schaft, Arjan van der; Crouch, Peter E.

    2005-01-01

    Given a general nonlinear affine control system with outputs and a torsion-free affine connection defined on its state space, we investigate the gradient realization problem: we give necessary and sufficient conditions under which the control system can be written as a gradient control system

  10. Sobolev gradients and differential equations

    CERN Document Server

    Neuberger, J W

    2010-01-01

    A Sobolev gradient of a real-valued functional on a Hilbert space is a gradient of that functional taken relative to an underlying Sobolev norm. This book shows how descent methods using such gradients allow a unified treatment of a wide variety of problems in differential equations. For discrete versions of partial differential equations, corresponding Sobolev gradients are seen to be vastly more efficient than ordinary gradients. In fact, descent methods with these gradients generally scale linearly with the number of grid points, in sharp contrast with the use of ordinary gradients. Aside from the first edition of this work, this is the only known account of Sobolev gradients in book form. Most of the applications in this book have emerged since the first edition was published some twelve years ago. What remains of the first edition has been extensively revised. There are a number of plots of results from calculations and a sample MatLab code is included for a simple problem. Those working through a fair p...

  11. Electric field gradients in metals

    International Nuclear Information System (INIS)

    Schatz, G.

    1979-01-01

    A review of the recent works on electric field gradient in metals is given. The main emphasis is put on the temperature dependence of the electric field gradient in nonmagnetic metals. Some methods of investigation of this effect using nuclear probes are described. One of them is nuclear accoustic resonance method. (S.B.)

  12. The geomagnetic field gradient tensor

    DEFF Research Database (Denmark)

    Kotsiaros, Stavros; Olsen, Nils

    2012-01-01

    We develop the general mathematical basis for space magnetic gradiometry in spherical coordinates. The magnetic gradient tensor is a second rank tensor consisting of 3 × 3 = 9 spatial derivatives. Since the geomagnetic field vector B is always solenoidal (∇ · B = 0) there are only eight independent...... tensor elements. Furthermore, in current free regions the magnetic gradient tensor becomes symmetric, further reducing the number of independent elements to five. In that case B is a Laplacian potential field and the gradient tensor can be expressed in series of spherical harmonics. We present properties...... of the magnetic gradient tensor and provide explicit expressions of its elements in terms of spherical harmonics. Finally we discuss the benefit of using gradient measurements for exploring the Earth’s magnetic field from space, in particular the advantage of the various tensor elements for a better determination...

  13. Non-parametric trend analysis of the aridity index for three large arid and semi-arid basins in Iran

    Science.gov (United States)

    Ahani, Hossien; Kherad, Mehrzad; Kousari, Mohammad Reza; van Roosmalen, Lieke; Aryanfar, Ramin; Hosseini, Seyyed Mashaallah

    2013-05-01

    Currently, an important scientific challenge that researchers are facing is to gain a better understanding of climate change at the regional scale, which can be especially challenging in an area with low and highly variable precipitation amounts such as Iran. Trend analysis of the medium-term change using ground station observations of meteorological variables can enhance our knowledge of the dominant processes in an area and contribute to the analysis of future climate projections. Generally, studies focus on the long-term variability of temperature and precipitation and to a lesser extent on other important parameters such as moisture indices. In this study the recent 50-year trends (1955-2005) of precipitation (P), potential evapotranspiration (PET), and aridity index (AI) in monthly time scale were studied over 14 synoptic stations in three large Iran basins using the Mann-Kendall non-parametric test. Additionally, an analysis of the monthly, seasonal and annual trend of each parameter was performed. Results showed no significant trends in the monthly time series. However, PET showed significant, mostly decreasing trends, for the seasonal values, which resulted in a significant negative trend in annual PET at five stations. Significant negative trends in seasonal P values were only found at a number of stations in spring and summer and no station showed significant negative trends in annual P. Due to the varied positive and negative trends in annual P and to a lesser extent PET, almost as many stations with negative as positive trends in annual AI were found, indicating that both drying and wetting trends occurred in Iran. Overall, the northern part of the study area showed an increasing trend in annual AI which meant that the region became wetter, while the south showed decreasing trends in AI.

  14. Aquaculture and mangrove ecosys of temproductivity in arid and semi-arid Balochistan coastal environments

    International Nuclear Information System (INIS)

    Khattak, M.I.

    2005-01-01

    A survey of coastal shrimp-pond operations, and the structure and functioning of coastal mangrove forest ecosystems with particular reference to Ecuador, indicates that certain physical parameters may be good predictors of key biological processes. The most important factors are those associated with the regional water balance, tidal and surface water circulation patterns, and the physicochemical properties of the underlying soils. One important conclusion to emerge from the analyses is that at both regional and local levels, well-developed and productive mangrove forest areas often represent the least desirable sites for the construction and operation of commercial shrimp ponds. In certain regards semi-arid and arid coastal environments where mangroves are poorly developed, shrimp ponds that are constructed on barren mud flats and inland salt pans appear to have the potential to produce higher yields of shrimp with fewer management problems and at a relatively lower production cost. The data and research results from coast of Baluchistan and elsewhere are briefly summarized to suggest why productive mangrove ecosystems to not make the best areas in which to obtain maximum shrimp-pond yields. (author)

  15. Excessive reliance on afforestation in China's arid and semi-arid regions: Lessons in ecological restoration

    Science.gov (United States)

    Cao, Shixiong; Chen, Li; Shankman, David; Wang, Chunmei; Wang, Xiongbin; Zhang, Hong

    2011-02-01

    Afforestation is a primary tool for controlling desertification and soil erosion in China. Large-scale afforestation, however, has complex and poorly understood consequences for the structure and composition of future ecosystems. Here, we discuss the potential links between China's historical large-scale afforestation practices and the program's effects on environmental restoration in arid and semi-arid regions in northern China based on a review of data from published papers, and offer recommendations to overcome the shortcomings of current environmental policy. Although afforestation is potentially an important approach for environmental restoration, current Chinese policy has not been tailored to local environmental conditions, leading to the use of inappropriate species and an overemphasis on tree and shrub planting, thereby compromising the ability to achieve environmental policy goals. China's huge investment to increase forest cover seems likely to exacerbate environmental degradation in environmentally fragile areas because it has ignored climate, pedological, hydrological, and landscape factors that would make a site unsuitable for afforestation. This has, in many cases, led to the deterioration of soil ecosystems and decreased vegetation cover, and has exacerbated water shortages. Large-scale and long-term research is urgently needed to provide information that supports a more effective and flexible environmental restoration policy.

  16. Identification and functional characterization of a novel bipartite nuclear localization sequence in ARID1A

    Energy Technology Data Exchange (ETDEWEB)

    Bateman, Nicholas W. [Women' s Health Integrated Research Center at Inova Health System, Gynecologic Cancer Center of Excellence, Annandale 22003, VA (United States); The John P. Murtha Cancer Center, Walter Reed National Military Medical Center, 8901 Wisconsin Avenue, Bethesda 20889, MD (United States); Shoji, Yutaka [Department of Obstetrics, Gynecology and Reproductive Biology, Michigan State University, Grand Rapids 49503, MI (United States); Conrads, Kelly A.; Stroop, Kevin D. [Women' s Health Integrated Research Center at Inova Health System, Gynecologic Cancer Center of Excellence, Annandale 22003, VA (United States); Hamilton, Chad A. [Women' s Health Integrated Research Center at Inova Health System, Gynecologic Cancer Center of Excellence, Annandale 22003, VA (United States); The John P. Murtha Cancer Center, Walter Reed National Military Medical Center, 8901 Wisconsin Avenue, Bethesda 20889, MD (United States); Gynecologic Oncology Service, Department of Obstetrics and Gynecology, Walter Reed National Military Medical Center, 8901 Wisconsin Ave, MD, Bethesda, 20889 (United States); Department of Obstetrics and Gynecology, Uniformed Services University of the Health Sciences, Bethesda 20814, MD (United States); Darcy, Kathleen M. [Women' s Health Integrated Research Center at Inova Health System, Gynecologic Cancer Center of Excellence, Annandale 22003, VA (United States); The John P. Murtha Cancer Center, Walter Reed National Military Medical Center, 8901 Wisconsin Avenue, Bethesda 20889, MD (United States); Maxwell, George L. [Department of Obstetrics and Gynecology, Inova Fairfax Hospital, Falls Church, VA 22042 (United States); Risinger, John I. [Department of Obstetrics, Gynecology and Reproductive Biology, Michigan State University, Grand Rapids 49503, MI (United States); and others

    2016-01-01

    AT-rich interactive domain-containing protein 1A (ARID1A) is a recently identified nuclear tumor suppressor frequently altered in solid tumor malignancies. We have identified a bipartite-like nuclear localization sequence (NLS) that contributes to nuclear import of ARID1A not previously described. We functionally confirm activity using GFP constructs fused with wild-type or mutant NLS sequences. We further show that cyto-nuclear localized, bipartite NLS mutant ARID1A exhibits greater stability than nuclear-localized, wild-type ARID1A. Identification of this undescribed functional NLS within ARID1A contributes vital insights to rationalize the impact of ARID1A missense mutations observed in patient tumors. - Highlights: • We have identified a bipartite nuclear localization sequence (NLS) in ARID1A. • Confirmation of the NLS was performed using GFP constructs. • NLS mutant ARID1A exhibits greater stability than wild-type ARID1A.

  17. Shallow Horizontal GCHP Effectiveness in Arid Climate Soils

    Science.gov (United States)

    North, Timothy James

    Ground coupled heat pumps (GCHPs) have been used successfully in many environments to improve the heating and cooling efficiency of both small and large scale buildings. In arid climate regions, such as the Phoenix, Arizona metropolitan area, where the air condi-tioning load is dominated by cooling in the summer, GCHPs are difficult to install and operate. This is because the nature of soils in arid climate regions, in that they are both dry and hot, renders them particularly ineffective at dissipating heat. The first part of this thesis addresses applying the SVHeat finite element modeling soft-ware to create a model of a GCHP system. Using real-world data from a prototype solar-water heating system coupled with a ground-source heat exchanger installed in Menlo Park, California, a relatively accurate model was created to represent a novel GCHP panel system installed in a shallow vertical trench. A sensitivity analysis was performed to evaluate the accuracy of the calibrated model. The second part of the thesis involved adapting the calibrated model to represent an ap-proximation of soil conditions in arid climate regions, using a range of thermal properties for dry soils. The effectiveness of the GCHP in the arid climate region model was then evaluated by comparing the thermal flux from the panel into the subsurface profile to that of the prototype GCHP. It was shown that soils in arid climate regions are particularly inefficient at heat dissipation, but that it is highly dependent on the thermal conductivity inputted into the model. This demonstrates the importance of proper site characterization in arid climate regions. Finally, several soil improvement methods were researched to evaluate their potential for use in improving the effectiveness of shallow horizontal GCHP systems in arid climate regions.

  18. Loess and floods: High-resolution multi-proxy data of Last Glacial Maximum (LGM) slackwater deposition in the Flinders Ranges, semi-arid South Australia

    Czech Academy of Sciences Publication Activity Database

    Haberlah, D.; Williams, M. A. J.; Halverson, G.; McTainsh, G. H.; Hill, S. M.; Hrstka, Tomáš; Jaime, P.; Butcher, A. R.; Glasby, P.

    2010-01-01

    Roč. 29, 19/20 (2010), s. 2673-2693 ISSN 0277-3791 Institutional research plan: CEZ:AV0Z30130516 Keywords : Namib desert * paleoclimatic implications * C-4 photosynthesis * climatic controls * atmospheric CO2 * Yellow-River * Kuiseb River * Lake Frome * sediments Subject RIV: DB - Geology ; Mineralogy Impact factor: 4.657, year: 2010

  19. MODIFIED ARMIJO RULE ON GRADIENT DESCENT AND CONJUGATE GRADIENT

    Directory of Open Access Journals (Sweden)

    ZURAIDAH FITRIAH

    2017-10-01

    Full Text Available Armijo rule is an inexact line search method to determine step size in some descent method to solve unconstrained local optimization. Modified Armijo was introduced to increase the numerical performance of several descent algorithms that applying this method. The basic difference of Armijo and its modified are in existence of a parameter and estimating the parameter that is updated in every iteration. This article is comparing numerical solution and time of computation of gradient descent and conjugate gradient hybrid Gilbert-Nocedal (CGHGN that applying modified Armijo rule. From program implementation in Matlab 6, it's known that gradient descent was applying modified Armijo more effectively than CGHGN from one side: iteration needed to reach some norm of the gradient  (input by the user. The amount of iteration was representing how long the step size of each algorithm in each iteration. In another side, time of computation has the same conclusion.

  20. Influence of Microclimate on Semi-Arid Montane Conifer Forest Sapflux Velocity in Complex Terrain

    Science.gov (United States)

    Thirouin, K. R.; Barnard, D. M.; Barnard, H. R.

    2016-12-01

    Microclimate variation in complex terrain is key to our understanding of large-scale climate change effects on montane ecosystems. Modern climate models forecast that semi-arid montane ecosystems in the western United States are to experience increases in temperature, number of extreme drought events, and decreases in annual snowpack, all of which will potentially influence ecosystem water, carbon, and energy balances. In this study, we developed response curves that describe the relationships between stem sapflux velocity, air temperature (Tair), incoming solar radiation (SWin), soil temperature (Tsoil), and soil moisture content (VWC) in sites of Pinus contorta and Pinus ponderosa distributed along an elevation and aspect gradient in the montane zone of the Central Rocky Mountains, Colorado, USA. Among sites we found sapflux velocity to be significantly correlated with all four environmental factors (p physiological differences, the highest elevation south-facing P. contorta site behaved similarly to the south-facing P. ponderosa, suggesting that environmental drivers may dominate the response. In response to Tair, peak sapflux velocity occurred at 12-13 degrees C at all sites except the mid-slope north-facing P. contorta site, which also had the lowest Tsoil. The responses of stem sapflux velocity to climate drivers indicate that forest transpiration is regulated by microclimate gradients across small spatial scales in complex terrain, which need to be characterized in order to understand broader ecosystem dynamics and the role that large-scale climate change will play in these systems.

  1. Ecosystem services provided by agricultural terraces in semi-arid climates.

    Science.gov (United States)

    Romero-Díaz, Asunción; Díaz-Pereira, Elvira; Boix-Fayos, Carolina; de Vente, Joris

    2016-04-01

    Since ancient times, agricultural terraces are common features throughout the world, especially on steep slope gradients. Nowadays many terraces have been abandoned or removed and few new terraces are build due to increased mechanisation and intensification of agriculture. However, terraces are amongst the most effective soil conservation practices, reducing the slope gradient and slope length, as well as runoff rate and soil erosion, and without terraces, it would be impossible to cultivate on many hillslopes. Moreover, their scenic interest is undeniable, as in some cases, terraced slopes have even become part of UNESCO World Heritage. In order to highlight the potential benefits, requirements and limitations of terraces, we reviewed different types of sustainable land management practices related to terraces and characterised their implications for provisioning, regulating, supporting, and cultural ecosystem services. We centred our review on terraces in semi-arid environments worldwide, as were documented in the WOCAT (World Overview of Conservation Approaches and Technologies) database. Our results show that the most important ecosystem services provided by terraces relate to regulation of the on-site and off-site effects of runoff and erosion, and maintenance of soil fertility and vegetation cover. The presence of terraces also favours the provision of food, fiber, and clean water. In short, our results stress the crucial environmental, geomorphological and hydrological functions of terraces that directly relate to improving the quality of life of the people that use them. These results highlight the need for renewed recognition of the value of terraces for society, their preservation and maintenance.

  2. Combining Step Gradients and Linear Gradients in Density.

    Science.gov (United States)

    Kumar, Ashok A; Walz, Jenna A; Gonidec, Mathieu; Mace, Charles R; Whitesides, George M

    2015-06-16

    Combining aqueous multiphase systems (AMPS) and magnetic levitation (MagLev) provides a method to produce hybrid gradients in apparent density. AMPS—solutions of different polymers, salts, or surfactants that spontaneously separate into immiscible but predominantly aqueous phases—offer thermodynamically stable steps in density that can be tuned by the concentration of solutes. MagLev—the levitation of diamagnetic objects in a paramagnetic fluid within a magnetic field gradient—can be arranged to provide a near-linear gradient in effective density where the height of a levitating object above the surface of the magnet corresponds to its density; the strength of the gradient in effective density can be tuned by the choice of paramagnetic salt and its concentrations and by the strength and gradient in the magnetic field. Including paramagnetic salts (e.g., MnSO4 or MnCl2) in AMPS, and placing them in a magnetic field gradient, enables their use as media for MagLev. The potential to create large steps in density with AMPS allows separations of objects across a range of densities. The gradients produced by MagLev provide resolution over a continuous range of densities. By combining these approaches, mixtures of objects with large differences in density can be separated and analyzed simultaneously. Using MagLev to add an effective gradient in density also enables tuning the range of densities captured at an interface of an AMPS by simply changing the position of the container in the magnetic field. Further, by creating AMPS in which phases have different concentrations of paramagnetic ions, the phases can provide different resolutions in density. These results suggest that combining steps in density with gradients in density can enable new classes of separations based on density.

  3. Block-conjugate-gradient method

    International Nuclear Information System (INIS)

    McCarthy, J.F.

    1989-01-01

    It is shown that by using the block-conjugate-gradient method several, say s, columns of the inverse Kogut-Susskind fermion matrix can be found simultaneously, in less time than it would take to run the standard conjugate-gradient algorithm s times. The method improves in efficiency relative to the standard conjugate-gradient algorithm as the fermion mass is decreased and as the value of the coupling is pushed to its limit before the finite-size effects become important. Thus it is potentially useful for measuring propagators in large lattice-gauge-theory calculations of the particle spectrum

  4. Spatial gradient tuning in metamaterials

    Science.gov (United States)

    Driscoll, Tom; Goldflam, Michael; Jokerst, Nan; Basov, Dimitri; Smith, David

    2011-03-01

    Gradient Index (GRIN) metamaterials have been used to create devices inspired by, but often surpassing the potential of, conventional GRIN optics. The unit-cell nature of metamaterials presents the opportunity to exert much greater control over spatial gradients than is possible in natural materials. This is true not only during the design phase but also offers the potential for real-time reconfiguration of the metamaterial gradient. This ability fits nicely into the picture of transformation-optics, in which spatial gradients can enable an impressive suite of innovative devices. We discuss methods to exert control over metamaterial response, focusing on our recent demonstrations using Vanadium Dioxide. We give special attention to role of memristance and mem-capacitance observed in Vanadium Dioxide, which simplify the demands of stimuli and addressing, as well as intersecting metamaterials with the field of memory-materials.

  5. Low-gradient aortic stenosis.

    Science.gov (United States)

    Clavel, Marie-Annick; Magne, Julien; Pibarot, Philippe

    2016-09-07

    An important proportion of patients with aortic stenosis (AS) have a 'low-gradient' AS, i.e. a small aortic valve area (AVA gradient (gradient discrepancy raises uncertainty about the actual stenosis severity and thus about the indication for aortic valve replacement (AVR) if the patient has symptoms and/or left ventricular (LV) systolic dysfunction. The most frequent cause of low-gradient (LG) AS is the presence of a low LV outflow state, which may occur with reduced left ventricular ejection fraction (LVEF), i.e. classical low-flow, low-gradient (LF-LG), or preserved LVEF, i.e. paradoxical LF-LG. Furthermore, a substantial proportion of patients with AS may have a normal-flow, low-gradient (NF-LG) AS: i.e. a small AVA-low-gradient combination but with a normal flow. One of the most important clinical challenges in these three categories of patients with LG AS (classical LF-LG, paradoxical LF-LG, and NF-LG) is to differentiate a true-severe AS that generally benefits from AVR vs. a pseudo-severe AS that should be managed conservatively. A low-dose dobutamine stress echocardiography may be used for this purpose in patients with classical LF-LG AS, whereas aortic valve calcium scoring by multi-detector computed tomography is the preferred modality in those with paradoxical LF-LG or NF-LG AS. Although patients with LF-LG severe AS have worse outcomes than those with high-gradient AS following AVR, they nonetheless display an important survival benefit with this intervention. Some studies suggest that transcatheter AVR may be superior to surgical AVR in patients with LF-LG AS. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2016. For permissions please email: journals.permissions@oup.com.

  6. Graded/Gradient Porous Biomaterials

    Directory of Open Access Journals (Sweden)

    Xigeng Miao

    2009-12-01

    Full Text Available Biomaterials include bioceramics, biometals, biopolymers and biocomposites and they play important roles in the replacement and regeneration of human tissues. However, dense bioceramics and dense biometals pose the problem of stress shielding due to their high Young’s moduli compared to those of bones. On the other hand, porous biomaterials exhibit the potential of bone ingrowth, which will depend on porous parameters such as pore size, pore interconnectivity, and porosity. Unfortunately, a highly porous biomaterial results in poor mechanical properties. To optimise the mechanical and the biological properties, porous biomaterials with graded/gradient porosity, pores size, and/or composition have been developed. Graded/gradient porous biomaterials have many advantages over graded/gradient dense biomaterials and uniform or homogenous porous biomaterials. The internal pore surfaces of graded/gradient porous biomaterials can be modified with organic, inorganic, or biological coatings and the internal pores themselves can also be filled with biocompatible and biodegradable materials or living cells. However, graded/gradient porous biomaterials are generally more difficult to fabricate than uniform or homogenous porous biomaterials. With the development of cost-effective processing techniques, graded/gradient porous biomaterials can find wide applications in bone defect filling, implant fixation, bone replacement, drug delivery, and tissue engineering.

  7. Dose gradient curve: A new tool for evaluating dose gradient.

    Science.gov (United States)

    Sung, KiHoon; Choi, Young Eun

    2018-01-01

    Stereotactic radiotherapy, which delivers an ablative high radiation dose to a target volume for maximum local tumor control, requires a rapid dose fall-off outside the target volume to prevent extensive damage to nearby normal tissue. Currently, there is no tool to comprehensively evaluate the dose gradient near the target volume. We propose the dose gradient curve (DGC) as a new tool to evaluate the quality of a treatment plan with respect to the dose fall-off characteristics. The average distance between two isodose surfaces was represented by the dose gradient index (DGI) estimated by a simple equation using the volume and surface area of isodose levels. The surface area was calculated by mesh generation and surface triangulation. The DGC was defined as a plot of the DGI of each dose interval as a function of the dose. Two types of DGCs, differential and cumulative, were generated. The performance of the DGC was evaluated using stereotactic radiosurgery plans for virtual targets. Over the range of dose distributions, the dose gradient of each dose interval was well-characterized by the DGC in an easily understandable graph format. Significant changes in the DGC were observed reflecting the differences in planning situations and various prescription doses. The DGC is a rational method for visualizing the dose gradient as the average distance between two isodose surfaces; the shorter the distance, the steeper the dose gradient. By combining the DGC with the dose-volume histogram (DVH) in a single plot, the DGC can be utilized to evaluate not only the dose gradient but also the target coverage in routine clinical practice.

  8. Interpretation of environmental isotopic groundwater data. Arid and semi-arid zones

    International Nuclear Information System (INIS)

    Geyh, M.A.

    1980-01-01

    Various hydrodynamic aspects are discussed in order to show their implication for the hydrogeological interpretation of environmental isotope and hydrochemical groundwater data. Special attention is drawn to radiocarbon and tritium studies carried out in arid and semi-arid zones. An exponential model has been utilized to determine the mean residence time of the long-term water from springs in karst and crystalline regions. Hydrogeological parameters such as the porosity can be checked by this result. In addition, the exponential model offers the possibility of determining the initial 14 C content of spring water, which is sensitively dependent on the soil of the recharge area. A base-flow model has been introduced to interpret the 14 C and 3 H data of groundwater samples from older karst regions. Differences between pumped and drawn samples exist with respect to the groundwater budget. Owing to pumping, the old base flow is accelerated and becomes enriched in pumped groundwater in comparison to the short-term water. Radiocarbon ages of groundwater in alluvium may be dubious because of isotope exchange with the CO 2 in the root zone along the river bank. Under confined conditions 14 C groundwater ages are diminished if the hydraulic head of the confined aquifer is lower than that of the shallow one. This is due to the radiocarbon downwards transport by convection of shallow groundwater. The same effect occurs, though much faster, if the groundwater table is depleted by groundwater withdrawal. The decrease of the radiocarbon groundwater ages in time can be used to determine the hydraulic transmissibility coefficient of the aquitarde. According to the practical and theoretic results obtained the hydrodynamic aspects require at least the same attention for the interpretation of environmental isotope and hydrochemical data of groundwater as do hydrochemical and isotope fractionation processes. (author)

  9. Biological soil crusts in Chile along the precipitation gradient

    Science.gov (United States)

    Samolov, Elena; Glaser, Karin; Baumann, Karen; Leinweber, Peter; Jung, Patrick; Büdel, Burkhard; Mikhailyuk, Tatiana; Karsten, Ulf

    2017-04-01

    Biological soil crusts in Chile along a precipitation gradient Elena Samolov* (1), Karin Glaser (1), Karen Baumann (2), Peter Leinweber (2), Patrick Jung (3), Burkhard Büdel (3), Tatiana Mikhailyuk (4) and Ulf Karsten (1) (1) Institute of Biological Sciences - Applied Ecology and Phycology, University of Rostock, Rostock, Germany, (2) Faculty of Agricultural and Environmental Sciences - Soil Sciences, University of Rostock, Rostock, Germany (3) University of Kaiserslautern, Kaiserslautern, Germany (4) M.H. Kholodny Institute of Botany, National Academy of Science of Ukraine, Kyiv, Ukraine * elena.samolov@uni-rostock.de Biological soil crusts (BSCs) are an association of different microorganisms and soil particles in the top millimeters of the soil. They are formed by algae, cyanobacteria, microfungi, bacteria, bryophytes and lichens in various compositions; together with their by-products they create a micro-ecosystem that performs important ecological functions, e.g. primary production, nitrogen fixation, mineralization and stabilization of soils. These top-soil assemblages are almost unstudied in South America (Büdel et al. 2016). Therefore, our aim is to investigate for the first time biodiversity of the key photosynthetic organisms, green algae and cyanobacteria following a precipitation gradient along the west coast of Chile. We are applying polyphasic approach - a combination of microscopy, culture dependent (16S and 18S rRNA, ITS) and culture independent molecular techniques (NGS). First results, based on culturing and light microscopy, showed high diversity of eukaryotic algae in biocrusts from humid regions, followed by semi-arid regions. Lichen dominated biocrusts from arid regions were characterized by a high diversity of green algae, while cyanobacteria were scarcely present. The functional role of the BSCs in the biogeochemical cycle of phosphorous (P) was evaluated using state of the art analytical methods including 31P-NMR (nuclear magnetic

  10. Actinobacteria from arid and desert habitats: diversity and biological activity

    Directory of Open Access Journals (Sweden)

    Joachim eWink

    2016-01-01

    Full Text Available Abstract The lack of new antibiotics in the pharmaceutical pipeline guides more and more researchers to leave the classical isolation procedures and to look in special niches and ecosystems. Bioprospecting of extremophilic Actinobacteria through mining untapped strains and avoiding resiolation of known biomolecules is among the most promising strategies for this purpose. With this approach, members of acidtolerant, alkalitolerant, psychrotolerant, thermotolerant, halotolerant and xerotolerant Actinobacteria have been obtained from respective habitats. Among these, little survey exists on the diversity of Actinobacteria in arid areas, which are often adapted to relatively high temperatures, salt concentrations, and radiation. Therefore, arid and desert habitats are special ecosystems which can be recruited for the isolation of uncommon Actinobacteria with new metabolic capability.At the time of this writing, members of Streptomyces, Micromonospora, Saccharothrix, Streptosporangium, Cellulomonas, Amycolatopsis, Geodermatophilus, Lechevalieria, Nocardia and Actinomadura are reported from arid habitats. However, metagenomic data present dominant members of the communities in desiccating condition of areas with limited water availability that are not yet isolated. Furthermore, significant diverse types of polyketide synthase (PKS and nonribosomal peptide synthetase (NRPS genes are detected in xerophilic and xerotolerant Actinobacteria and some bioactive compounds are reported from them. Rather than pharmaceutically active metabolites, molecules with protection activity against drying such as Ectoin and Hydroxyectoin with potential application in industry and agriculture have also been identified from xerophilic Actinobacteria. In addition, numerous biologically active small molecules are expected to be discovered from arid adapted Actinobacteria in the future. In the current survey, the diversity and biotechnological potential of Actinobacteria

  11. Actinobacteria from Arid and Desert Habitats: Diversity and Biological Activity.

    Science.gov (United States)

    Mohammadipanah, Fatemeh; Wink, Joachim

    2015-01-01

    The lack of new antibiotics in the pharmaceutical pipeline guides more and more researchers to leave the classical isolation procedures and to look in special niches and ecosystems. Bioprospecting of extremophilic Actinobacteria through mining untapped strains and avoiding resiolation of known biomolecules is among the most promising strategies for this purpose. With this approach, members of acidtolerant, alkalitolerant, psychrotolerant, thermotolerant, halotolerant and xerotolerant Actinobacteria have been obtained from respective habitats. Among these, little survey exists on the diversity of Actinobacteria in arid areas, which are often adapted to relatively high temperatures, salt concentrations, and radiation. Therefore, arid and desert habitats are special ecosystems which can be recruited for the isolation of uncommon Actinobacteria with new metabolic capability. At the time of this writing, members of Streptomyces, Micromonospora, Saccharothrix, Streptosporangium, Cellulomonas, Amycolatopsis, Geodermatophilus, Lechevalieria, Nocardia, and Actinomadura are reported from arid habitats. However, metagenomic data present dominant members of the communities in desiccating condition of areas with limited water availability that are not yet isolated. Furthermore, significant diverse types of polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) genes are detected in xerophilic and xerotolerant Actinobacteria and some bioactive compounds are reported from them. Rather than pharmaceutically active metabolites, molecules with protection activity against drying such as Ectoin and Hydroxyectoin with potential application in industry and agriculture have also been identified from xerophilic Actinobacteria. In addition, numerous biologically active small molecules are expected to be discovered from arid adapted Actinobacteria in the future. In the current survey, the diversity and biotechnological potential of Actinobacteria obtained from arid ecosystems

  12. Actinobacteria from Arid and Desert Habitats: Diversity and Biological Activity

    Science.gov (United States)

    Mohammadipanah, Fatemeh; Wink, Joachim

    2016-01-01

    The lack of new antibiotics in the pharmaceutical pipeline guides more and more researchers to leave the classical isolation procedures and to look in special niches and ecosystems. Bioprospecting of extremophilic Actinobacteria through mining untapped strains and avoiding resiolation of known biomolecules is among the most promising strategies for this purpose. With this approach, members of acidtolerant, alkalitolerant, psychrotolerant, thermotolerant, halotolerant and xerotolerant Actinobacteria have been obtained from respective habitats. Among these, little survey exists on the diversity of Actinobacteria in arid areas, which are often adapted to relatively high temperatures, salt concentrations, and radiation. Therefore, arid and desert habitats are special ecosystems which can be recruited for the isolation of uncommon Actinobacteria with new metabolic capability. At the time of this writing, members of Streptomyces, Micromonospora, Saccharothrix, Streptosporangium, Cellulomonas, Amycolatopsis, Geodermatophilus, Lechevalieria, Nocardia, and Actinomadura are reported from arid habitats. However, metagenomic data present dominant members of the communities in desiccating condition of areas with limited water availability that are not yet isolated. Furthermore, significant diverse types of polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) genes are detected in xerophilic and xerotolerant Actinobacteria and some bioactive compounds are reported from them. Rather than pharmaceutically active metabolites, molecules with protection activity against drying such as Ectoin and Hydroxyectoin with potential application in industry and agriculture have also been identified from xerophilic Actinobacteria. In addition, numerous biologically active small molecules are expected to be discovered from arid adapted Actinobacteria in the future. In the current survey, the diversity and biotechnological potential of Actinobacteria obtained from arid ecosystems

  13. An Overview of Biodegradation of LNAPLs in Coastal (Semi)-arid Environment.

    KAUST Repository

    Yadav, Brijesh Kumar; Hassanizadeh, S Majid

    2011-01-01

    environmental variables, and their remediation favoring customization requires a sound understanding of their integrated behavior on fate and transport of LNAPLs under site-specific conditions. The arid and semi-arid coastal sites are characterized by specific

  14. Potential of arid zone vegetation as a source of substrates

    Energy Technology Data Exchange (ETDEWEB)

    Bassham, J.A.

    1977-11-01

    Three aspects of the potential of vegetation in arid zones as a source of substrates are discussed. The first includes the limitations on efficiency of conversion of solar energy to the stored chemical energy of biomass in green plants, and the subsequent biochemical pathways of carbon dioxide fixation and biosynthesis. Second is the potential of plants endogenous to arid zones. Finally, the use of covered agriculture or controlled environmental agriculture (CEA) is considered both in its present form and in terms of possible extenion to the large scale production of stable crops. (JGB)

  15. Observations of cloud and rainfall enhancement over irrigated agriculture in an arid environment

    Science.gov (United States)

    Garcia-Carreras, Luis; Marsham, John H.; Spracklen, Dominick V.

    2017-04-01

    The impact of irrigated agriculture on clouds and rainfall remains uncertain, particularly in less studied arid regions. Irrigated crops account for 20% of global cropland area, and non-renewable groundwater accounts for 20% of global irrigation water demand. Quantifying the feedbacks between agriculture and the atmosphere are therefore not only necessary to better understand the climate impacts of land-use change, but are also crucial for predicting long-term water use in water-scarce regions. Here we use high spatial-resolution satellite data to show the impact of irrigated crops in the arid environment of northern Saudi Arabia on cloud cover and rainfall patterns. Land surface temperatures over the crops are 5-10 K lower than their surroundings, linked to evapotranspiration rates of up to 20 mm/ month. Daytime cloud cover is up to 30% higher over the cropland compared to its immediate surroundings, and this enhancement is highly correlated with the seasonal variability in leaf area index. The cloud enhancement is associated with a much more rapid cloud cloud development during the morning. Afternoon rainfall is 85% higher over, and just downwind, of the cropland during the growing season, although rainfall remains very low in absolute terms. The feedback sign we find is the opposite to what has been observed in tropical and semiarid regions, where temperature gradients promote convergence and clouds on the warmer side of land-surface type discontinuities. This suggests that different processes are responsible for the land-atmosphere feedback in very dry environments, where lack of moisture may be a stronger constraint. Increased cloud and rainfall, and associated increases in diffuse radiation and reductions in temperature, can affect vegetation growth thus producing an internal feedback. These effects will therefore need to be taken into account to properly assess the impact of climate change on crop productivity and water use, as well as how global land

  16. Impact and consequences of evapotranspiration changes on water resources availability in the arid Zhangye Basin, China

    NARCIS (Netherlands)

    Jin, X.; Schaepman, M.E.; Clevers, J.G.P.W.; Su, Z.

    2009-01-01

    Evapotranspiration (ET) plays an important role in the hydrological cycle and it is essential to estimate ET accurately for the evaluation of available water resources. This is most important in arid and semi-arid regions. In this paper, the long-term changes in daily ET in the semi-arid Zhangye

  17. Effects of environmental conditions on soil salinity and arid region in Tunisia

    International Nuclear Information System (INIS)

    Ben Ahmed, C.; Ben Rouina, B.; Boukhris, M.

    2009-01-01

    The shortage of water resources of good water quality is becoming an issue in the arid and semi arid regions. for this reason, the use of water resources of marginal quality such as treated wastewater and saline groundwater has become and important consideration, particularly in arid region in Tunisia, where large quantities of saline water are used for irrigation. (Author)

  18. International Arid Lands Consortium: Better land stewardship in water and watershed management

    Science.gov (United States)

    Peter F. Ffolliott; James T. Fisher; Menachem Sachs; Darrell W. DeBoer; Jeffrey O. Dawson; Timothy E. Fulbright; John Tracy

    2000-01-01

    The International Arid Lands Consortium (IALC) was established in 1990 to promote research, education, and training for the development, management, and restoration of arid and semi-arid lands throughout the world. One activity of IALC members and cooperators is to support research and development and demonstration projects that enhance management of these fragile...

  19. Rapid Gradient-Echo Imaging

    Science.gov (United States)

    Hargreaves, Brian

    2012-01-01

    Gradient echo sequences are widely used in magnetic resonance imaging (MRI) for numerous applications ranging from angiography to perfusion to functional MRI. Compared with spin-echo techniques, the very short repetition times of gradient-echo methods enable very rapid 2D and 3D imaging, but also lead to complicated “steady states.” Signal and contrast behavior can be described graphically and mathematically, and depends strongly on the type of spoiling: fully balanced (no spoiling), gradient spoiling, or RF-spoiling. These spoiling options trade off between high signal and pure T1 contrast while the flip angle also affects image contrast in all cases, both of which can be demonstrated theoretically and in image examples. As with spin-echo sequences, magnetization preparation can be added to gradient-echo sequences to alter image contrast. Gradient echo sequences are widely used for numerous applications such as 3D perfusion imaging, functional MRI, cardiac imaging and MR angiography. PMID:23097185

  20. The influence of ALN-Al gradient material gradient index on ballistic performance

    International Nuclear Information System (INIS)

    Wang Youcong; Liu Qiwen; Li Yao; Shen Qiang

    2013-01-01

    Ballistic performance of the gradient material is superior to laminated material, and gradient materials have different gradient types. Using ls-dyna to simulate the ballistic performance of ALN-AL gradient target plates which contain three gradient index (b = 1, b = 0.5, b = 2). Through Hopkinson bar numerical simulation to the target plate materials, we obtained the reflection stress wave and transmission stress wave state of gradient material to get the best gradient index. The internal stress state of gradient material is simulated by amplification processing of the target plate model. When the gradient index b is equal to 1, the gradient target plate is best of all.

  1. Cyanobacterial Diversity in Biological Soil Crusts along a Precipitation Gradient, Northwest Negev Desert, Israel.

    Science.gov (United States)

    Hagemann, Martin; Henneberg, Manja; Felde, Vincent J M N L; Drahorad, Sylvie L; Berkowicz, Simon M; Felix-Henningsen, Peter; Kaplan, Aaron

    2015-07-01

    Cyanobacteria occur worldwide but play an important role in the formation and primary activity of biological soil crusts (BSCs) in arid and semi-arid ecosystems. The cyanobacterial diversity in BSCs of the northwest Negev desert of Israel was surveyed at three fixed sampling stations situated along a precipitation gradient in the years 2010 to 2012. The three stations also are characterized by marked differences in soil features such as soil carbon, nitrogen, or electrical conductivity. The cyanobacterial biodiversity was analyzed by sequencing inserts of clone libraries harboring partial 16S rRNA gene sequences obtained with cyanobacteria-specific primers. Filamentous, non-diazotrophic strains (subsection III), particularly Microcoleus-like, dominated the cyanobacterial community (30% proportion) in all years. Specific cyanobacterial groups showed increased (e.g., Chroococcidiopsis, Leptolyngbya, and Nostoc strains) or decreased (e.g., unicellular strains belonging to the subsection I and Scytonema strains) abundances with declining water availability at the most arid, southern station, whereas many cyanobacterial strains were frequently found in the soils of all three stations. The cyanobacterial diversity at the three sampling stations appears dependent on the available precipitation, whereas the differences in soil chemistry were of lower importance.

  2. Effect of water stress in soil-water-vegetation relationships, along a rainfall gradient in southern Spain; Incidencia del stress hidrico en las relaciones suelo-agua-planta a lo largo de un gradiente pluviometrico en el sur de Espana

    Energy Technology Data Exchange (ETDEWEB)

    Ruiz-Sinoga, J. D.; Ferre Bueno, E.; Martinez-Murillo, J. F.; Gabarron-Galeote, M. A.

    2009-07-01

    The Andalusian Mediterranean Watershed, in the South of the Iberian Peninsula, shows a climatic gradient from the Straits of Gibraltar (1,600 mm year{sup -1}) to the Cabo de Gata (150 mm year{sup -1}). Climate conditions differences are translating into variations in the elements of the eco-geomorphologic system at hillslope scale. In this study has been analysed the immediate consequences of a period of two years drought (2004-06) on several elements of the Mediterranean eco-geomorphologic system at three hillslopes (sub-humid, dry Mediterranean and semi-arid). the soil water content, the pattern of vegetation and some soil properties (organic matter content, aggregate stability and permeability) were analysed before (Nov-2003) and during (Nov-2005) the drought period. Final results have shown: i) reduction in soil water content which reached in the wet seasons values below wilting point, affecting negatively to the water available for vegetation and especially in the wettest sites; ii) reduction in vegetation cover and in the number of plants, especially at semi-arid field site; iii) changes in the organic matter content which aggravates the loss of stability of soil aggregates, a process seen more clearly under more arid conditions; and iv) reduction of soil permeability in all situations in the climate gradient studied, which supposes a priori an increase in erosive processes due to surface runoff. These results indicate increased vulnerability of the eco-geomorphologic system because of the rainfall drought situation. (Author) 14 refs.

  3. Modelling annual evapotranspiration in a semi-arid, African savanna ...

    African Journals Online (AJOL)

    Accurately measuring evapotranspiration (ET) is essential if we are to derive reasonable estimates of production and water use for semi-arid savannas. Estimates of ET are also important in defining the health of an ecosystem and the quantity of water used by the vegetation when preparing a catchment-scale water balance.

  4. On dew and micrometeorology in an arid coastal ecosystem

    NARCIS (Netherlands)

    Heusinkveld, B.G.

    2008-01-01

    This study investigated intriguing aspects of dew within a sandy arid ecosystem situated in the NW Negev desert, Israel. The goal was to quantify dew formation and evaporation processes through sensor design, field measurements and modelling. To do this, two new sensors were developed. The first

  5. Improved climate risk simulations for rice in arid environments

    NARCIS (Netherlands)

    Oort, van P.A.J.; Vries, de M.; Yoshida, H.; Saito, K.

    2015-01-01

    We integrated recent research on cardinal temperatures for phenology and early leaf growth, spikelet formation, early morning flowering, transpirational cooling, and heat- and cold-induced sterility into an existing to crop growth model ORYZA2000. We compared for an arid environment observed

  6. Hypogeous fungi from Southern Spanish semi-arid lands

    NARCIS (Netherlands)

    Honrubia, M.; Cano, A.; Molina-Niñirola, C.

    1992-01-01

    Six hypogeous fungi of Ascomycotina and Basidiomycotina have been studied from semiarid zones in Southern Spain. Melanogaster variegatus (Vitt.) Tul. is recorded for the first time from Spain. Picoa juniperi Vitt. and Terfezia claveryi Chat. are revealed as the most frequent species in semi-arid

  7. Determining Dry Matter Degradability of Some Semi-Arid Browse ...

    African Journals Online (AJOL)

    acer

    ABSTRACT: The in vitro gas production of some semi-arid browse species were evaluated. The relationship between in ... between in vitro gas measured on incubation of browse leaves and that calculated from SCFA allows the prediction of SCFA from ... with concentrate feed (40% corn, 10% wheat offal, 10% palm kernel ...

  8. Evaporation as the transport mechanism of metals in arid regions

    NARCIS (Netherlands)

    Lima, A.T.; Safar, Z.; Loch, J.P.G.

    Soils of arid regions are exposed to drought and drastic temperature oscillations throughout the year. Transport mechanisms in these soils are therefore very different from the ones in temperate regions, where rain dictates the fate of most elements in soils. Due to the low rainfall and high

  9. Adaptation at Scale in Semi-Arid Regions | IDRC - International ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    People living in Africa and South Asia's semi-arid regions face challenges that hinder their economic growth and development. This project seeks to find proactive, longer-term approaches to climate change adaptation in these vulnerable regions, while helping locals manage existing risks. Short-term focus must shift. So far ...

  10. THE SURFACE WATER STORAGE PROBLEM IN ARID REGIONS:

    African Journals Online (AJOL)

    H. Benfetta

    2017-09-01

    Sep 1, 2017 ... This dam is located in an arid zone where water resources are becoming increasingly scarce. It is situated 5 km ... Leakage leads to considerable losses of valuable, scarce water. ...... Detection of water leaks in the restraints ...

  11. Evaporation as the transport mechanism of metals in arid regions

    KAUST Repository

    Lima, Ana T.

    2014-09-01

    Soils of arid regions are exposed to drought and drastic temperature oscillations throughout the year. Transport mechanisms in these soils are therefore very different from the ones in temperate regions, where rain dictates the fate of most elements in soils. Due to the low rainfall and high evaporation rates in arid regions, groundwater quality is not threatened and all soil contamination issues tend to be overlooked. But if soil contamination happens, where do contaminants go? This study tests the hypothesis of upward metal movement in soils when evaporation is the main transport mechanism. Laboratory evaporation tests were carried out with heavy metal spiked Saudi soil, using circulation of air as the driving force (Fig. 1). Main results show that loamy soil retains heavy metals quite well while evaporation drives heavy metals to the surface of a sandy soil. Evaporation transports heavy metals upward in sandy soils of arid regions, making them accumulate at the soil surface. Sand being the dominating type of soil in arid regions, soils can then be a potential source of contaminated aerosols and atmospheric pollution - a transboundary problem. Some other repercussions for this problem are foreseen, such as the public ingestion or inhalation of dust. © 2014 Elsevier Ltd.

  12. Characterization of lactic acid bacteria isolated from Algerian arid ...

    African Journals Online (AJOL)

    Diversity and density of lactic acid bacteria isolated from Algerian raw goats\\' milk in arid zones were studied by determination of morphological, cultural, physiological and biochemical characteristics. 206 lactic acid bacterial strains were isolated, with 115 of them belonging to lactic acid cocci and others to the genus, ...

  13. Simulation of water use and herbage growth in arid regions

    NARCIS (Netherlands)

    Keulen, van H.

    1975-01-01

    The and and semi-arid regions of the world, totalling about 30% of the land surface of the earth, are predominantly used for extensive grazing, as low and erratic rainfall presents too high a risk for arable farming. The population that can be sustained by the animal products -meat, milk or

  14. Paclobutrazol biodegradation in unsaturated soil in the Semi-Arid ...

    African Journals Online (AJOL)

    Paclobutrazol (PBZ) is a plant growth regulator, increasing flowe ring and yield that is widely used in mango cultivation in the semi-arid northeastern Brazil. PBZ remains active in the soil for several years. However, it can severely affect the growth and development of subsequent crops, mainly by reducing vegetative vigor.

  15. Rates of wood and dung disintegration in arid South African ...

    African Journals Online (AJOL)

    Dead shrubs lying on the soil surface in an arid shrubland in the southern Karoo have half-lives of 9 to 18 years depending on wood density which varies among species. Dung pellets of sheep and springbok can remain intact on the soil surface in Karoo shrubland and desert grassland for five years or more. Highlights the ...

  16. Interstitial meiofauna of Namib sandy beaches

    African Journals Online (AJOL)

    1988-03-16

    Mar 16, 1988 ... Zoology Department, Institute for Coastal Research, University of Port Elizabeth, P.O. Box ... Oliff, Gardner, Turner & Sharp (1970) and later Dye, ... Wooldridge, Dye & ...... potential sources of food for interstitial organisms,.

  17. Effect of water stress in soil-water-vegetation relationships, along a rainfall gradient in southern Spain

    International Nuclear Information System (INIS)

    Ruiz-Sinoga, J. D.; Ferre Bueno, E.; Martinez-Murillo, J. F.; Gabarron-Galeote, M. A.

    2009-01-01

    The Andalusian Mediterranean Watershed, in the South of the Iberian Peninsula, shows a climatic gradient from the Straits of Gibraltar (1,600 mm year - 1) to the Cabo de Gata (150 mm year 1 ). Climate conditions differences are translating into variations in the elements of the eco-geomorphologic system at hillslope scale. In this study has been analysed the immediate consequences of a period of two years drought (2004-06) on several elements of the Mediterranean eco-geomorphologic system at three hillslopes (sub-humid, dry Mediterranean and semi-arid). the soil water content, the pattern of vegetation and some soil properties (organic matter content, aggregate stability and permeability) were analysed before (Nov-2003) and during (Nov-2005) the drought period. Final results have shown: i) reduction in soil water content which reached in the wet seasons values below wilting point, affecting negatively to the water available for vegetation and especially in the wettest sites; ii) reduction in vegetation cover and in the number of plants, especially at semi-arid field site; iii) changes in the organic matter content which aggravates the loss of stability of soil aggregates, a process seen more clearly under more arid conditions; and iv) reduction of soil permeability in all situations in the climate gradient studied, which supposes a priori an increase in erosive processes due to surface runoff. These results indicate increased vulnerability of the eco-geomorphologic system because of the rainfall drought situation. (Author) 14 refs.

  18. An Investigation into the Effects of Temperature Gradient on the Soil Water–Salt Transfer with Evaporation

    Directory of Open Access Journals (Sweden)

    Rong Ren

    2017-06-01

    Full Text Available Temperature gradients exist in the field under brackish water irrigation conditions, especially in northern semi–arid areas of China. Although there are many investigators dedicated to studying the mechanism of brackish water irrigation and the effect of brackish water irrigation on crops, there are fewer investigations of the effects of temperature gradient on the water–salt transport. Based on the combination of a physical experiment and a mathematical model, this study was conducted to: (a build a physical model and observe the redistribution of soil water–heat–salt transfer; (b develop a mathematical model focused on the influence of a temperature gradient on soil water and salt redistribution based on the physical model and validate the proposed model using the measured data; and (c analyze the effects of the temperature gradient on the soil water–salt transport by comparing the proposed model with the traditional water–salt model in which the effects of temperature gradient on the soil water–salt transfer are neglected. Results show that the soil temperature gradient has a definite influence on the soil water–salt migration. Moreover, the effect of temperature gradient on salt migration was greater than that of water movement.

  19. Chemical and Physical Weathering of Granites in a Semi-Arid Savanna

    Science.gov (United States)

    Khomo, L.; Hartshorn, A.; Chadwick, O.; Kurtz, A.; Heimsath, A.; Rogers, K.

    2005-12-01

    The catena concept describes soil properties on hillslopes and implies a hydrological mass redistribution process that has been applied differently in different parts of the Earth. In tectonically active regions, it is mostly used to describe the redistribution of mass by overland flow leading to thickening soil mantles downslope. This application is somewhat different from its initial and still popular usage in tectonically inactive areas of Africa, where it defines long-term soil property differentiation along hillslopes as controlled by internal soil hydrology as opposed to overland flow. Many ecologists have found the "African" catena concept to be useful as an organizing principal for savanna studies, but there has been little recent research on catenas per se in Africa. Elsewhere however, there is a growing body of research that places the concept ever more strongly into a landscape evolution context. Here, we apply these new approaches to catenas in a South African savanna underlain by a heterogeneous suite of Basement granites straddling a gradient in effective precipitation. We constrain the weathering extent of hilly terrains formed on these oldrocks by calculating element losses with solid-phase mass-balance calculations augmented by cosmogenic (26Al/10Be) derived rates of landscape denudation. We test the efficacy of Ti, Zr and Nb as immobile elements to benchmark chemical losses and gains in these semi-arid weathering environments. We also trace and quantify the abundance of the host minerals for these elements (Ti = rutile and ilmenite, Nb = columbite and Zr = zircon and baddleyite) in a variety of rocks in the basement complex. This analysis provides the boundary conditions for assigning immobile elements to parent materials required for the mass balance calculations. We calculate total denudation using the cosmogenic isotopes and then partition it into chemical and physical loss vectors using the mass balance calculations for representative

  20. Soil bacterial and fungal community responses to nitrogen addition across soil depth and microhabitat in an arid shrubland

    Science.gov (United States)

    Mueller, Rebecca C.; Belnap, Jayne; Kuske, Cheryl R.

    2015-01-01

    Arid shrublands are stressful environments, typified by alkaline soils low in organic matter, with biologically-limiting extremes in water availability, temperature, and UV radiation. The widely-spaced plants and interspace biological soil crusts in these regions provide soil nutrients in a localized fashion, creating a mosaic pattern of plant- or crust-associated microhabitats with distinct nutrient composition. With sporadic and limited rainfall, nutrients are primarily retained in the shallow surface soil, patterning biological activity. We examined soil bacterial and fungal community responses to simulated nitrogen (N) deposition in an arid Larrea tridentata-Ambrosia dumosa field experiment in southern Nevada, USA, using high-throughput sequencing of ribosomal RNA genes. To examine potential interactions among the N application, microhabitat and soil depth, we sampled soils associated with shrub canopies and interspace biological crusts at two soil depths (0–0.5 or 0–10 cm) across the N-amendment gradient (0, 7, and 15 kg ha−1 yr−1). We hypothesized that localized compositional differences in soil microbiota would constrain the impacts of N addition to a microhabitat distribution that would reflect highly localized geochemical conditions and microbial community composition. The richness and community composition of both bacterial and fungal communities differed significantly by microhabitat and with soil depth in each microhabitat. Only bacterial communities exhibited significant responses to the N addition. Community composition correlated with microhabitat and depth differences in soil geochemical features. Given the distinct roles of soil bacteria and fungi in major nutrient cycles, the resilience of fungi and sensitivity of bacteria to N amendments suggests that increased N input predicted for many arid ecosystems could shift nutrient cycling toward pathways driven primarily by fungal communities.

  1. Soil bacterial and fungal community responses to nitrogen addition across soil depths and microhabitat in an arid shrubland

    Directory of Open Access Journals (Sweden)

    Rebecca C Mueller

    2015-09-01

    Full Text Available Arid shrublands are stressful environments, typified by alkaline soils low in organic matter, with biologically-limiting extremes in water availability, temperature and UV radiation. The widely-spaced plants and interspace biological soil crusts in these regions provide soil nutrients in a localized fashion, creating a mosaic pattern of plant- or crust-associated microhabitats with distinct nutrient composition. With sporadic and limited rainfall, nutrients are primarily retained in the shallow surface soil, patterning biological activity. We examined soil bacterial and fungal community responses to simulated nitrogen (N deposition in an arid Larrea tridentata-Ambrosia dumosa field experiment in southern Nevada, USA, using high-throughput sequencing of ribosomal RNA genes. To examine potential interactions among the N application, microhabitat and soil depth, we sampled soils associated with shrub canopies and interspace biological crusts at two soil depths (0-0.5 cm or 0-10 cm across the N-amendment gradient (0, 7 and 15 kg ha-1 yr-1. We hypothesized that localized compositional differences in soil microbiota would constrain the impacts of N addition to a microhabitat distribution that would reflect highly localized geochemical conditions and microbial community composition. The richness and community composition of both bacterial and fungal communities differed significantly by microhabitat and with soil depth in each microhabitat. Only bacterial communities exhibited significant responses to the N addition. Community composition correlated with microhabitat and depth differences in soil geochemical features. Given the distinct roles of soil bacteria and fungi in major nutrient cycles, the resilience of fungi and sensitivity of bacteria to N amendments suggests that increased N input predicted for many arid ecosystems could shift nutrient cycling toward pathways driven primarily by fungal communities.

  2. SGH: stress or strain gradient hypothesis? Insights from an elevation gradient on the roof of the world.

    Science.gov (United States)

    Liancourt, Pierre; Le Bagousse-Pinguet, Yoann; Rixen, Christian; Dolezal, Jiri

    2017-07-01

    The stress gradient hypothesis (SGH), the view that competition prevails in undisturbed and productive environments, and shifts to facilitation in disturbed or stressful environments, has become a central paradigm in ecology. However, an alternative view proposes that the relationship between biotic interactions and environmental severity should be unimodal instead of monotonic. Possible causes of discrepancies between these two views were examined in the high elevation desert of the arid Trans-Himalayas. A putative nurse species and its associated plant community was surveyed over its entire elevation range, spanning from alpine to desert vegetation belts. The results were analysed at the community level (vegetation cover and species richness), considering the distinction between the intensity and the importance of biotic interactions. Interactions at the species level (pairwise interactions) were also considered, i.e. the variation of biotic interactions within the niche of a species, for which the abundance (species cover) and probability of occurrence (presence/absence) for the most widespread species along the gradient were distinguished. Overall, facilitation was infrequent in our study system; however, it was observed for the two most widespread species. At the community level, the intensity and importance of biotic interactions showed a unimodal pattern. The departure from the prediction of the SGH happened abruptly where the nurse species entered the desert vegetation belt at the lowest elevation. This abrupt shift was attributed to the turnover of species with contrasting tolerances. At the species level, however, facilitation increased consistently as the level of stress increases and individuals deviate from their optimum (increasing strain). While the stress gradient hypothesis was not supported along our elevation gradient at the community level, the strain gradient hypothesis, considering how species perceive the ambient level of stress and deviate

  3. A Tool for the Evaluation of Irrigation Water Quality in the Arid and Semi-Arid Regions

    Directory of Open Access Journals (Sweden)

    Lucia Bortolini

    2018-02-01

    Full Text Available In the Mediterranean arid and semi-arid regions, large amounts of low quality waters could be used for crop irrigation, but the adoption of articulated classifications with too rigid quality limits can often reduce the recoverable quantities of water and make the monitoring of water quality too much expensive. Therefore, an evaluation of irrigation water quality based on only a few crucial parameters, which consider the crop species to be irrigated and the type of irrigation system and management adopted, can be an easy and flexible method for maximizing the reuse of wastewater and low-quality water for agricultural purposes. In this view, an irrigation water quality tool (IWQT was developed to support farmers of arid and semi-arid regions on evaluating the use of low quality water for crop irrigation. The most significant and cheapest parameters of irrigation water quality were identified and clustered in three quality classes according to their effects on crop yield and soil fertility (agronomic quality indicators, human health (hygiene and health quality indicators, and irrigation systems (management quality indicators. According to IWQT parameters, a tool reporting a series of recommendations, including water treatment types, was implemented to guide farmers on the use of low quality irrigation water.

  4. Management of nutrients and water in rainfed arid and semi-arid areas. Proceedings of a consultants meeting

    International Nuclear Information System (INIS)

    1998-07-01

    Sustainable food security is needed for the arid and semi-arid regions of the tropical, subtropical and warm-temperate climatic zones. In these regions the supply of locally grown food is unreliable because much of it is produced in conditions of highly variable rainfall. Even in favourable seasons, these regions re becoming increasingly dependent on imported food. The IAEA's involvement in field studies on soil-water use dates back several years. A five year Co-ordinated Research Project on ''The Use of Nuclear and Related Techniques in Assessment of Irrigation Schedules of Field Crops to Increase Effective Use of Water in Irrigation Projects''. That project, completed in 1995, laid a solid foundation for future research. Because of a scarcity of water in many developing countries and increasing needs for sustainable food security in the face of increasing populations and lack of funds for irrigation schemes of significant dimension, research must focus on improved management of (i) the modest quantities of fertilizers that are available to farmers, (ii) the natural resources that are available to farmers for increasing soil organic matter content, and (iii) rain water. The Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture held a Consultants Meeting on Management of Nutrients and Water in Rainfed Arid and Semi-Arid Areas for Increasing Crop Production, 26-29 May 1997

  5. Agave: a biofuel feedstock for arid and semi-arid environments

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Stephen; Martin, Jeffrey; Simpson, June; Wang, Zhong; Visel, Axel

    2011-05-31

    Efficient production of plant-based, lignocellulosic biofuels relies upon continued improvement of existing biofuel feedstock species, as well as the introduction of newfeedstocks capable of growing on marginal lands to avoid conflicts with existing food production and minimize use of water and nitrogen resources. To this end, specieswithin the plant genus Agave have recently been proposed as new biofuel feedstocks. Many Agave species are adapted to hot and arid environments generally unsuitable forfood production, yet have biomass productivity rates comparable to other second-generation biofuel feedstocks such as switchgrass and Miscanthus. Agavesachieve remarkable heat tolerance and water use efficiency in part through a Crassulacean Acid Metabolism (CAM) mode of photosynthesis, but the genes andregulatory pathways enabling CAM and thermotolerance in agaves remain poorly understood. We seek to accelerate the development of agave as a new biofuelfeedstock through genomic approaches using massively-parallel sequencing technologies. First, we plan to sequence the transcriptome of A. tequilana to provide adatabase of protein-coding genes to the agave research community. Second, we will compare transcriptome-wide gene expression of agaves under different environmentalconditions in order to understand genetic pathways controlling CAM, water use efficiency, and thermotolerance. Finally, we aim to compare the transcriptome of A.tequilana with that of other Agave species to gain further insight into molecular mechanisms underlying traits desirable for biofuel feedstocks. These genomicapproaches will provide sequence and gene expression information critical to the breeding and domestication of Agave species suitable for biofuel production.

  6. Global patterns and environmental controls of perchlorate and nitrate co-occurrence in arid and semi-arid environments

    Science.gov (United States)

    Jackson, W Andrew; Böhlke, John Karl; Andraski, Brian J.; Fahlquist, Lynne S.; Bexfield, Laura M.; Eckardt, Frank D.; Gates, John B.; Davila, Alfonso F.; McKay, Christopher P.; Rao, Balaji; Sevanthi, Ritesh; Rajagopalan, Srinath; Estrada, Nubia; Sturchio, Neil C.; Hatzinger, Paul B.; Anderson, Todd A.; Orris, Greta J.; Betancourt, Julio L.; Stonestrom, David A.; Latorre, Claudio; Li, Yanhe; Harvey, Gregory J.

    2015-01-01

    Natural perchlorate (ClO4−) is of increasing interest due to its wide-spread occurrence on Earth and Mars, yet little information exists on the relative abundance of ClO4− compared to other major anions, its stability, or long-term variations in production that may impact the observed distributions. Our objectives were to evaluate the occurrence and fate of ClO4− in groundwater and soils/caliche in arid and semi-arid environments (southwestern United States, southern Africa, United Arab Emirates, China, Antarctica, and Chile) and the relationship of ClO4− to the more well-studied atmospherically deposited anions NO3−and Cl− as a means to understand the prevalent processes that affect the accumulation of these species over various time scales. ClO4− is globally distributed in soil and groundwater in arid and semi-arid regions on Earth at concentrations ranging from 10−1to 106 μg/kg. Generally, the ClO4− concentration in these regions increases with aridity index, but also depends on the duration of arid conditions. In many arid and semi-arid areas, NO3− and ClO4− co-occur at molar ratios (NO3−/ClO4−) that vary between ∼104and 105. We hypothesize that atmospheric deposition ratios are largely preserved in hyper-arid areas that support little or no biological activity (e.g. plants or bacteria), but can be altered in areas with more active biological processes including N2 fixation, N mineralization, nitrification, denitrification, and microbial ClO4− reduction, as indicated in part by NO3− isotope data. In contrast, much larger ranges of Cl−/ClO4− and Cl−/NO3−ratios indicate Cl− varies independently from both ClO4− and NO3−. The general lack of correlation between Cl− and ClO4− or NO3− implies that Cl− is not a good indicator of co-deposition and should be used with care when interpreting oxyanion cycling in arid systems. The Atacama Desert appears to be unique compared to all other terrestrial locations having a

  7. Global patterns and environmental controls of perchlorate and nitrate co-occurrence in arid and semi-arid environments

    Science.gov (United States)

    Jackson, W. Andrew; Böhlke, J. K.; Andraski, Brian J.; Fahlquist, Lynne; Bexfield, Laura; Eckardt, Frank D.; Gates, John B.; Davila, Alfonso F.; McKay, Christopher P.; Rao, Balaji; Sevanthi, Ritesh; Rajagopalan, Srinath; Estrada, Nubia; Sturchio, Neil; Hatzinger, Paul B.; Anderson, Todd A.; Orris, Greta; Betancourt, Julio; Stonestrom, David; Latorre, Claudio; Li, Yanhe; Harvey, Gregory J.

    2015-09-01

    Natural perchlorate (ClO4-) is of increasing interest due to its wide-spread occurrence on Earth and Mars, yet little information exists on the relative abundance of ClO4- compared to other major anions, its stability, or long-term variations in production that may impact the observed distributions. Our objectives were to evaluate the occurrence and fate of ClO4- in groundwater and soils/caliche in arid and semi-arid environments (southwestern United States, southern Africa, United Arab Emirates, China, Antarctica, and Chile) and the relationship of ClO4- to the more well-studied atmospherically deposited anions NO3- and Cl- as a means to understand the prevalent processes that affect the accumulation of these species over various time scales. ClO4- is globally distributed in soil and groundwater in arid and semi-arid regions on Earth at concentrations ranging from 10-1 to 106 μg/kg. Generally, the ClO4- concentration in these regions increases with aridity index, but also depends on the duration of arid conditions. In many arid and semi-arid areas, NO3- and ClO4- co-occur at molar ratios (NO3-/ClO4-) that vary between ∼104 and 105. We hypothesize that atmospheric deposition ratios are largely preserved in hyper-arid areas that support little or no biological activity (e.g. plants or bacteria), but can be altered in areas with more active biological processes including N2 fixation, N mineralization, nitrification, denitrification, and microbial ClO4- reduction, as indicated in part by NO3- isotope data. In contrast, much larger ranges of Cl-/ClO4- and Cl-/NO3- ratios indicate Cl- varies independently from both ClO4- and NO3-. The general lack of correlation between Cl- and ClO4- or NO3- implies that Cl- is not a good indicator of co-deposition and should be used with care when interpreting oxyanion cycling in arid systems. The Atacama Desert appears to be unique compared to all other terrestrial locations having a NO3-/ClO4- molar ratio ∼103. The relative

  8. Genomic and proteomic characterization of ARID1A chromatin remodeller in ampullary tumors.

    Science.gov (United States)

    Nastase, Anca; Teo, Jin Yao; Heng, Hong Lee; Ng, Cedric Chuan Young; Myint, Swe Swe; Rajasegaran, Vikneswari; Loh, Jia Liang; Lee, Ser Yee; Ooi, London Lucien; Chung, Alexander Yaw Fui; Chow, Pierce Kah Hoe; Cheow, Peng Chung; Wan, Wei Keat; Azhar, Rafy; Khoo, Avery; Xiu, Sam Xin; Alkaff, Syed Muhammad Fahmy; Cutcutache, Ioana; Lim, Jing Quan; Ong, Choon Kiat; Herlea, Vlad; Dima, Simona; Duda, Dan G; Teh, Bin Tean; Popescu, Irinel; Lim, Tony Kiat Hon

    2017-01-01

    AT rich interactive domain 1A (ARID1A) is one of the most commonly mutated genes in a broad variety of tumors. The mechanisms that involve ARID1A in ampullary cancer progression remains elusive. Here, we evaluated the frequency of ARID1A and KRAS mutations in ampullary adenomas and adenocarcinomas and in duodenal adenocarcinomas from two cohorts of patients from Singapore and Romania, correlated with clinical and pathological tumor features, and assessed the functional role of ARID1A . In the ampullary adenocarcinomas, the frequency of KRAS and ARID1A mutations was 34.7% and 8.2% respectively, with a loss or reduction of ARID1A protein in 17.2% of the cases. ARID1A mutational status was significantly correlated with ARID1A protein expression level (P=0.023). There was a significant difference in frequency of ARID1A mutation between Romania and Singapore (2.7% versus 25%, P=0.04), suggestive of different etiologies. One somatic mutation was detected in the ampullary adenoma group. In vitro studies indicated the tumor suppressive role of ARID1A . Our results warrant further investigation of this chromatin remodeller as a potential early biomarker of the disease, as well as identification of therapeutic targets in ARID1A mutated ampullary cancers.

  9. Hydraulic gradients in rock aquifers

    International Nuclear Information System (INIS)

    Dahlblom, P.

    1992-05-01

    This report deals with fractured rock as a host for deposits of hazardous waste. In this context the rock, with its fractures containing moving groundwater, is called the geological barrier. The desired properties of the geological barrier are low permeability to water, low hydraulic gradients and ability to retain matter dissolved in the water. The hydraulic gradient together with the permeability and the porosity determines the migration velocity. Mathematical modelling of the migration involves calculation of the water flow and the hydrodynamic dispersion of the contaminant. The porous medium approach can be used to calculate mean flow velocities and hydrodynamic dispersion of a large number of fractures are connected, which means that a large volume have to be considered. It is assumed that the porous medium approach can be applied, and a number of idealized examples are shown. It is assumed that the groundwater table is replenished by percolation at a constant rate. One-dimensional analytical calculations show that zero hydraulic gradients may exist at relatively large distance from the coast. Two-dimensional numerical calculations show that it may be possible to find areas with low hydraulic gradients and flow velocities within blocks surrounded by areas with high hydraulic conductivity. (au)

  10. A theory of gradient analysis

    NARCIS (Netherlands)

    Braak, ter C.J.F.

    1988-01-01

    The theory of gradient analysis is presented in this chapter, in which the heuristic techniques are integrated with regression, calibration, ordination and constrained ordination as distinct, well-defined statistical problems. The various techniques used for each type of problem are classified into

  11. Compositional gradients in Gramineae genes

    DEFF Research Database (Denmark)

    Wong, Gane Ka-Shu; Wang, Jun; Tao, Lin

    2002-01-01

    In this study, we describe a property of Gramineae genes, and perhaps all monocot genes, that is not observed in eudicot genes. Along the direction of transcription, beginning at the junction of the 5'-UTR and the coding region, there are gradients in GC content, codon usage, and amino-acid usage...

  12. Orderings for conjugate gradient preconditionings

    Science.gov (United States)

    Ortega, James M.

    1991-01-01

    The effect of orderings on the rate of convergence of the conjugate gradient method with SSOR or incomplete Cholesky preconditioning is examined. Some results also are presented that help to explain why red/black ordering gives an inferior rate of convergence.

  13. Color gradients in elliptical galaxies

    International Nuclear Information System (INIS)

    Franx, M.; Illingworth, G.

    1990-01-01

    The relationship of the color gradients within ellipticals and the color differences between them are studied. It is found that the local color appears to be strongly related to the escape velocity. This suggests that the local escape velocity is the primary factor that determines the metallicity of the stellar population. Models with and without dark halos give comparable results. 27 refs

  14. Changes of soil bacterial diversity as a consequence of agricultural land use in a semi-arid ecosystem.

    Directory of Open Access Journals (Sweden)

    Guo-Chun Ding

    Full Text Available Natural scrublands in semi-arid deserts are increasingly being converted into fields. This results in losses of characteristic flora and fauna, and may also affect microbial diversity. In the present study, the long-term effect (50 years of such a transition on soil bacterial communities was explored at two sites typical of semi-arid deserts. Comparisons were made between soil samples from alfalfa fields and the adjacent scrublands by two complementary methods based on 16S rRNA gene fragments amplified from total community DNA. Denaturing gradient gel electrophoresis (DGGE analyses revealed significant effects of the transition on community composition of Bacteria, Actinobacteria, Alpha- and Betaproteobacteria at both sites. PhyloChip hybridization analysis uncovered that the transition negatively affected taxa such as Acidobacteria, Chloroflexi, Acidimicrobiales, Rubrobacterales, Deltaproteobacteria and Clostridia, while Alpha-, Beta- and Gammaproteobacteria, Bacteroidetes and Actinobacteria increased in abundance. Redundancy analysis suggested that the community composition of phyla responding to agricultural use (except for Spirochaetes correlated with soil parameters that were significantly different between the agricultural and scrubland soil. The arable soils were lower in organic matter and phosphate concentration, and higher in salinity. The variation in the bacterial community composition was higher in soils from scrubland than from agriculture, as revealed by DGGE and PhyloChip analyses, suggesting reduced beta diversity due to agricultural practices. The long-term use for agriculture resulted in profound changes in the bacterial community and physicochemical characteristics of former scrublands, which may irreversibly affect the natural soil ecosystem.

  15. Experimental Measurement of Diffusive Extinction Depth and Soil Moisture Gradients in Southwestern Saudi Arabian Dune Sand

    KAUST Repository

    Mughal, Iqra

    2013-05-01

    In arid lands, a major contribution to water loss is by soil water evaporation. Desert sand dunes in arid regions are devoid of runoff and have high rates of infiltration. Rainwater is commonly stored within them because of the low permeability soils in the underlying desert pavement. In such cases, moisture is confined in the sand dune below a depth, termed as the “extinction depth”, where it is protected from evaporation during long dry periods. Moreover, desert sand dunes have sparse vegetation, which results in low transpiration losses from the stored water. The water accumulated below the extinction depth of the sand dunes can be utilized for various purposes such as in irrigation to support desert agriculture. In this study, field experiments were conducted in Western Saudi Arabia to monitor the soil moisture gradients and determine the diffusive extinction depth of dune sand. The dune sand was saturated with water and was exposed to natural conditions (evaporation and precipitation). The decline of the water level in the sand column was continuously recorded using transducers and sensors installed at different depths monitored the temporal variation of temperature and moisture content within the sand. The hydrological simulator HYDRUS-1D was used to construct the vertical profiles of soil water content and temperature and the results obtained from HYDRUS-1D were compared to the gradients monitored by the sensors.

  16. Essential Roles for ARID1B in Dendritic Arborization and Spine Morphology of Developing Pyramidal Neurons

    Science.gov (United States)

    Ka, Minhan; Chopra, Divyan A.; Dravid, Shashank M.

    2016-01-01

    De novo truncating mutations in ARID1B, a chromatin-remodeling gene, cause Coffin–Siris syndrome, a developmental disorder characterized by intellectual disability and speech impairment; however, how the genetic elimination leads to cognitive dysfunction remains unknown. Thus, we investigated the neural functions of ARID1B during brain development. Here, we show that ARID1B regulates dendritic differentiation in the developing mouse brain. We knocked down ARID1B expression in mouse pyramidal neurons using in utero gene delivery methodologies. ARID1B knockdown suppressed dendritic arborization of cortical and hippocampal pyramidal neurons in mice. The abnormal development of dendrites accompanied a decrease in dendritic outgrowth into layer I. Furthermore, knockdown of ARID1B resulted in aberrant dendritic spines and synaptic transmission. Finally, ARID1B deficiency led to altered expression of c-Fos and Arc, and overexpression of these factors rescued abnormal differentiation induced by ARID1B knockdown. Our results demonstrate a novel role for ARID1B in neuronal differentiation and provide new insights into the origin of cognitive dysfunction associated with developmental intellectual disability. SIGNIFICANCE STATEMENT Haploinsufficiency of ARID1B, a component of chromatin remodeling complex, causes intellectual disability. However, the role of ARID1B in brain development is unknown. Here, we demonstrate that ARID1B is required for neuronal differentiation in the developing brain, such as in dendritic arborization and synapse formation. Our findings suggest that ARID1B plays a critical role in the establishment of cognitive circuitry by regulating dendritic complexity. Thus, ARID1B deficiency may cause intellectual disability via abnormal brain wiring induced by the defective differentiation of cortical neurons. PMID:26937011

  17. Assessment of Plant Functional Types in Tropical Arid and Semi-Arid Ecosystems of India Using Remote Sensing Data and GIS

    Science.gov (United States)

    Sudhakar Reddy, C.; Krishna, P. Hari; Murthy, M. S. R.

    2011-09-01

    vegetation systems were studied along arid, semi-arid and sub-humid regions of Indian Desert and Aravallis of Rajasthan, India, with a distance of 600 km. The annual precipitation decreases from as high as 1600 mm in the south to 700 mm in the north-east and 100 mm in the west. The study is based on the integrated approach of remote sensing, GIS, and phytosociology. In the step 1, vegetation type map was prepared using multi-season IRS P6 LISS III data. Screening of plant traits was done based on field observations and literature. Phytosociological data pertains to 500 sample plots was used to identify plant functional traits of 900 species at morphological level. The vegetation classification scheme at regional level identified thorn forest, dry deciduous forest, broad leaved forest, woodland, shrubland and grasslands. Five plant traits selected in the study were significant for tropical environments. Attributes such as leaf size, leaf texture, spinescence, stem diameter and bark consistency were categorized systematically. Ordination analysis was carried out across the environmental gradient. Plant functional traits were measured on 20 individuals per species at each site. Environmental information was integrated to identify plant trait response. The spatial trends in PFTs were analysed and compared across the vegetation types, along the gradient of land surface temperature, climate, elevation and time integrated NDVI. Results established the occurrence of recurrent patterns of association among selected plant traits. Functional response groups were identified by summarizing results and relating them to individual species. Finally phytoclimatic map was prepared to represent spatial distribution of PFTs. The species with of functional traits of representing microphylls, sclerophyll, rough bark, spinescence and therophyte are demarcated as drought tolerant traits. Drought Intolerant PFTs are represented by macrophyll, malacophyll, smooth Bark, non spinescent stems and leaves

  18. Elemental gradients in macrophytes from a reactor effluent gradient

    International Nuclear Information System (INIS)

    Grace, J.B.; Tilly, L.J.

    1978-01-01

    The tissues of submersed macrophtes from along the thermal gradient were analyzed for phosphorus to determine whether any pattern correspondent to standing crop distributions could be detected. Although water concentrations of phosphorus showed no detectable relationship to the thermal effluent, tissue concentrations of this element in submersed macrophytes declined with distance from the effluent entry point. The occurrence of this concentration pattern suggests that phosphorus availability is greater near the discharge. Because phosphorus is the element most often determined to limit aquatic productivity, its greater availability may partially account for the apparent enhancement of macrophte growth near the thermal discharge. A patter of macrophyte abundance which indicated enchancement related to the discharge gradient in the reactor-cooling reservoir, Par Pond is reported. Correlative data tended to implicate light and temperature as important in influencing the differential abundance pattern

  19. Two-dimensional microclimate distribution within and above a crop canopy in an arid environment: Modeling and observational studies

    Science.gov (United States)

    Naot, O.; Mahrer, Y.

    1991-08-01

    A numerical two-dimensional model based on higher-order closure assumptions is developed to simulate the horizontal microclimate distribution over an irrigated field in arid surroundings. The model considers heat, mass, momentum, and radiative fluxes in the soil-plant-atmosphere system. Its vertical domain extends through the whole planetary boundary layer. The model requires temporal solar and atmospheric radiation data, as well as temporal boundary conditions for wind-speed, air temperature, and humidity. These boundary conditions are specified by an auxiliary mesoscale model and are incorporated in the microscale model by a nudging method. Vegetation parameters (canopy height, leaf-angle orientation distribution, leaf-area index, photometric properties, root-density distribution), soil texture, and soil-hydraulic and photometric properties are considered. The model is tested using meteorological data obtained in a drip-irrigated cotton field located in an extremely arid area, where strong fetch effects are expected. Four masts located 50 m before the leading edge of the field and 10, 30, and 100 m inward from the leading edge are used to measure various meteorological parameters and their horizontal and vertical gradients. Calculated values of air and soil temperatures, wind-speed, net radiation and soil, latent, and sensible heat fluxes agreed well with measurements. Large horizontal gradients of air temperature are both observed and measured within the canopy in the first 40 m of the leading edge. Rate of evapotranspiration at both the upwind and the downwind edges of the field are higher by more than 15% of the midfield value. Model calculations show that a stable thermal stratification is maintained above the whole field for 24 h. The aerodynamic and thermal internal boundary layer (IBL) growth is proportional to the square root of the fetch. This is also the observed rate of growth of the thermal IBL over a cool sea surface.

  20. Do Quercus ilex woodlands undergo abrupt non-linear functional changes in response to human disturbance along a climatic gradient?

    Science.gov (United States)

    Bochet, Esther; García-Fayos, Patricio; José Molina, Maria; Moreno de las Heras, Mariano; Espigares, Tíscar; Nicolau, Jose Manuel; Monleon, Vicente

    2017-04-01

    Theoretical models predict that drylands are particularly prone to suffer critical transitions with abrupt non-linear changes in their structure and functions as a result of the existing complex interactions between climatic fluctuations and human disturbances. However, so far, few studies provide empirical data to validate these models. We aim at determining how holm oak (Quercus ilex) woodlands undergo changes in their functions in response to human disturbance along an aridity gradient (from semi-arid to sub-humid conditions), in eastern Spain. For that purpose, we used (a) remote-sensing estimations of precipitation-use-efficiency (PUE) from enhanced vegetation index (EVI) observations performed in 231x231 m plots of the Moderate Resolution Imaging Spectroradiometer (MODIS); (b) biological and chemical soil parameter determinations (extracellular soil enzyme activity, soil respiration, nutrient cycling processes) from soil sampled in the same plots; (c) vegetation parameter determinations (ratio of functional groups) from vegetation surveys performed in the same plots. We analyzed and compared the shape of the functional change (in terms of PUE and soil and vegetation parameters) in response to human disturbance intensity for our holm oak sites along the aridity gradient. Overall, our results evidenced important differences in the shape of the functional change in response to human disturbance between climatic conditions. Semi-arid areas experienced a more accelerated non-linear decrease with an increasing disturbance intensity than sub-humid ones. The proportion of functional groups (herbaceous vs. woody cover) played a relevant role in the shape of the functional response of the holm oak sites to human disturbance.

  1. Soil moisture and its role in growth-climate relationships across an aridity gradient in semiarid Pinus halepensis forests.

    Science.gov (United States)

    Manrique-Alba, Àngela; Ruiz-Yanetti, Samantha; Moutahir, Hassane; Novak, Klemen; De Luis, Martin; Bellot, Juan

    2017-01-01

    In Mediterranean areas with limited availability of water, an accurate knowledge of growth response to hydrological variables could contribute to improving management and stability of forest resources. The main goal of this study is to assess the temporal dynamic of soil moisture to better understand the water-growth relationship of Pinus halepensis forests in semiarid areas. The estimates of modelled soil moisture and measured tree growth were used at four sites dominated by afforested Pinus halepensis Mill. in south-eastern Spain with 300 to 609mm mean annual precipitation. Firstly, dendrochronological samples were extracted and the widths of annual tree rings were measured to compute basal area increments (BAI). Secondly, soil moisture was estimated over 20 hydrological years (1992-2012) by means of the HYDROBAL ecohydrological model. Finally, the tree growth was linked, to mean monthly and seasonal temperature, precipitation and soil moisture. Results depict the effect of soil moisture on growth (BAI) and explain 69-73% of the variance in semiarid forests, but only 51% in the subhumid forests. This highlights the fact that that soil moisture is a suitable and promising variable to explain growth variations of afforested Pinus halepensis in semiarid conditions and useful for guiding adaptation plans to respond pro-actively to water-related global challenges. Copyright © 2016 Elsevier B.V. All rights reserved.

  2. Plasticity in vulnerability to cavitation of Pinus canariensis occurs only at the driest end of an aridity gradient

    Directory of Open Access Journals (Sweden)

    Rosana eLópez

    2016-06-01

    Full Text Available Water availability has been considered one of the crucial drivers of species distribution. However, the increasing of temperatures and more frequent water shortages could overcome the ability of long-lived species to cope with rapidly changing conditions. Growth and survival of natural populations adapted to a given site, transferred and tested in other environments as part of provenance trials, can be interpreted as a simulation of ambient changes at the original location. We compare the intraspecific variation and the relative contribution of plasticity to adaptation of key functional traits related to drought resistance: vulnerability to cavitation, efficiency of the xylem to conduct water and biomass allocation. We use six populations of Canary Island pine growing in three provenance trials (wet, dry and xeric. We found that the variability for hydraulic traits was largely due to phenotypic plasticity, whereas genetic variation was limited and almost restricted to hydraulic safety traits and survival. Trees responded to an increase in climate dryness by lowering growth, and increasing leaf-specific hydraulic conductivity by means of increasing the Huber value. Vulnerability to cavitation only showed a plastic response in the driest provenance trial located in the ecological limit of the species. This trait was more tightly correlated with annual precipitation, drought length and temperature oscillation at the origin of the populations than hydraulic efficiency or the Huber value. Vulnerability to cavitation was directly related to survival in the dry and the xeric provenance trials, illustrating its importance in determining drought resistance. In a new climatic scenario where more frequent and intense droughts are predicted, the magnitude of extreme events together with the fact that plasticity of cavitation resistance is only shown in the very dry limit of the species could hamper the capacity to adapt and buffer against environmental changes of some populations growing in dry locations.

  3. Repeated intra-specific divergence in lifespan and ageing of African annual fishes along an aridity gradient

    DEFF Research Database (Denmark)

    Blažek, Radim; Polačik, Matej; Kačer, Petr

    2017-01-01

    intrinsic lifespans and a greater increase in mortality with age, more pronounced cellular and physiological deterioration (oxidative damage, tumor load), and a faster decline in fertility than populations from wetter regions. This parallel intra-specific divergence in lifespan and ageing was not associated......Lifespan and ageing are substantially modified by natural selection. Across species, higher extrinsic (environmentally-related) mortality (and hence shorter life expectancy) selects for the evolution of more rapid ageing. However, among populations within species, high extrinsic mortality can lead...... to extended lifespan and slower ageing as a consequence of condition-dependent survival. Using within-species contrasts of eight natural populations of Nothobranchius fishes in common garden experiments, we demonstrate that populations originating from dry regions (with short life expectancy) had shorter...

  4. Intraspecific variation in stomatal traits, leaf traits and physiology reflects adaptation along aridity gradients in a South African shrub.

    Science.gov (United States)

    Carlson, Jane E; Adams, Christopher A; Holsinger, Kent E

    2016-01-01

    Trait-environment relationships are commonly interpreted as evidence for local adaptation in plants. However, even when selection analyses support this interpretation, the mechanisms underlying differential benefits are often unknown. This study addresses this gap in knowledge using the broadly distributed South African shrub Protea repens. Specifically, the study examines whether broad-scale patterns of trait variation are consistent with spatial differences in selection and ecophysiology in the wild. In a common garden study of plants sourced from 19 populations, associations were measured between five morphological traits and three axes describing source climates. Trait-trait and trait-environment associations were analysed in a multi-response model. Within two focal populations in the wild, selection and path analyses were used to test associations between traits, fecundity and physiological performance. Across 19 populations in a common garden, stomatal density increased with the source population's mean annual temperature and decreased with its average amount of rainfall in midsummer. Concordantly, selection analysis in two natural populations revealed positive selection on stomatal density at the hotter, drier site, while failing to detect selection at the cooler, moister site. Dry-site plants with high stomatal density also had higher stomatal conductances, cooler leaf temperatures and higher light-saturated photosynthetic rates than those with low stomatal density, but no such relationships were present among wet-site plants. Leaf area, stomatal pore index and specific leaf area in the garden also co-varied with climate, but within-population differences were not associated with fitness in either wild population. The parallel patterns of broad-scale variation, differences in selection and differences in trait-ecophysiology relationships suggest a mechanism for adaptive differentiation in stomatal density. Densely packed stomata may improve performance by increasing transpiration and cooling, but predominately in drier, hotter climates. This study uniquely shows context-dependent benefits of stomatal density--a trait rarely linked to local adaptation in plants. © The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  5. Modeling of hydrological processes in arid agricultural regions

    Directory of Open Access Journals (Sweden)

    Jiang LI,Xiaomin MAO,Shaozhong KANG,David A. BARRY

    2015-12-01

    Full Text Available Understanding of hydrological processes, including consideration of interactions between vegetation growth and water transfer in the root zone, underpins efficient use of water resources in arid-zone agriculture. Water transfers take place in the soil-plant-atmosphere continuum, and include groundwater dynamics, unsaturated zone flow, evaporation/transpiration from vegetated/bare soil and surface water, agricultural canal/surface water flow and seepage, and well pumping. Models can be categorized into three classes: (1 regional distributed hydrological models with various land uses, (2 groundwater-soil-plant-atmosphere continuum models that neglect lateral water fluxes, and (3 coupled models with groundwater flow and unsaturated zone water dynamics. This review highlights, in addition, future research challenges in modeling arid-zone agricultural systems, e.g., to effectively assimilate data from remote sensing, and to fully reflect climate change effects at various model scales.

  6. Domesticated proboscidea parviflora: a potential oilseed crop for arid lands

    Energy Technology Data Exchange (ETDEWEB)

    Berry, J.; Bretting, P.K.; Nabhan, G.P.; Weber, C.

    1981-01-01

    Wild and domesticated Proboscidea parviflora were evaluated as oilseed crops for arid lands through chemical and biological analyses. Domesticated plants grown in the Sonoran desert bore seed containing 35-40 per cent oil and 23-27 per cent protein. Yield per hectare was estimated at 1000 kg of oil and 675 kg of protein, quantities which compare favourably with other crops. An ephemeral life cycle and certain characteristics of the fruit and seed allow this plant to grow in xeric habitats unsuitable for many other plants. Several Proboscidea species hybridize with P. parviflora and could be used in future crop breeding. Rapid germination and higher oil and protein content of seed make the domesticated P. parviflora superior to the wild form as a crop. Domesticated P. parviflora thus shows promise as an oilseed crop for the Sonoran Desert and possibly for other arid regions. (Refs. 22).

  7. How Sustainable are Engineered Rivers in Arid Lands?

    Directory of Open Access Journals (Sweden)

    Jurgen Schmandt

    2013-06-01

    Full Text Available Engineered rivers in arid lands play an important role in feeding the world’s growing population. Each continent has rivers that carry water from distant mountain sources to fertile soil downstream where rainfall is scarce. Over the course of the last century most rivers in arid lands have been equipped with large engineering structures that generate electric power and store water for agriculture and cities. This has changed the hydrology of the rivers. In this paper we discuss how climate variation, climate change, reservoir siltation, changes in land use and population growth will challenge the sustainability of engineered river systems over the course of the next few decades. We use the Rio Grande in North America, where we have worked with Mexican and American colleagues, to describe our methodology and results. Similar work is needed to study future water supply and demand in engineered rivers around the world.

  8. Computational Strain Gradient Crystal Plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Kysar, Jeffrey W.

    2011-01-01

    A model for strain gradient crystal visco-plasticity is formulated along the lines proposed by Fleck andWillis (2009) for isotropic plasticity. Size-effects are included in the model due to the addition of gradient terms in both the free energy as well as through a dissipation potential. A finite...... element solution method is presented, which delivers the slip-rate field and the velocity-field based on two minimum principles. Some plane deformation problems relevant for certain specific orientations of a face centered cubic crystal under plane loading conditions are studied, and effective in......-plane parameters are developed based on the crystallographic properties of the material. The problem of cyclic shear of a single crystal between rigid platens is studied as well as void growth of a cylindrical void....

  9. Computational strain gradient crystal plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Kysar, Jeffrey W.

    2014-01-01

    A numerical method for viscous strain gradient crystal plasticity theory is presented, which incorporates both energetic and dissipative gradient effects. The underlying minimum principles are discussed as well as convergence properties of the proposed finite element procedure. Three problems...... of plane crystal plasticity are studied: pure shear of a single crystal between rigid platens as well as plastic deformation around cylindrical voids in hexagonal close packed and face centered cubic crystals. Effective in-plane constitutive slip parameters for plane strain deformation of specifically...... oriented face centered cubic crystals are developed in terms of the crystallographic slip parameters. The effect on geometrically necessary dislocation structures introduced by plastic deformation is investigated as a function of the ratio of void radius to plasticity length scale....

  10. Vertebrate pressure-gradient receivers

    DEFF Research Database (Denmark)

    Christensen-Dalsgaard, Jakob

    2011-01-01

    The eardrums of all terrestrial vertebrates (tetrapods) are connected through Eustachian tubes or interaural canals. In some of the animals, these connections create pressure-gradient directionality, an enhanced directionality by interaction of sound arriving at both sides of the eardrum and stro......The eardrums of all terrestrial vertebrates (tetrapods) are connected through Eustachian tubes or interaural canals. In some of the animals, these connections create pressure-gradient directionality, an enhanced directionality by interaction of sound arriving at both sides of the eardrum....... Recent vertebrates form a continuum from perfect interaural transmission (0 dB in a certain frequency band) and pronounced eardrum directionality (30-40 dB) in the lizards, over somewhat attenuated transmission and limited directionality in birds and frogs, to the strongly attenuated interaural...

  11. Karoo-fynbos biomass along an elevational gradient in the western Cape.

    Directory of Open Access Journals (Sweden)

    M. C. Rutherford

    1978-12-01

    Full Text Available A short characterization of the vegetational gradient from two basic physiognomic forms of fynbos, through Renosterbosveld to arid Karoo vegetation of the south-western Cape, is given with reference to possible vegetational analogues within similar gradients in winter-rainfall areas elsewhere. Description is limited to some aspects affecting biomass and its measurement, as well as to consideration of community stability needed for valid comparison of community biomass. Live individuals, including single dominant species, all other shrubs, graminoids and other herbaceous species as well as dead individuals were harvested separately in each major community type within an elevational gradient corresponding to the vegetational gradient described. Greatest biomass (14311 kg ha-1 was found in a summit restionaceous community, while lowest biomass (7564 kg ha-1 was found in a low-lying succulent Karoo community. There was an inverse relationship between elevation and percentage dead material mass and a strongly positive relationship between elevation and percentage biomass of the graminoid group. Total biomass values appear to be in keeping with available data for analogue communities in different Mediterranean climate areas, although distinct differences sometimes occur in the relative biomass contributions of component groups.

  12. Semi-arid development: competitiveness factors in biodiesel productive chain

    OpenAIRE

    Breno Barros Telles do Carmo; Dmontier Pinheiro Aragão; Heráclito Lopes Jaguaribe Pontes; Bruno Magalhães Ribeiro; Marcos Ronaldo Albertin

    2009-01-01

    The new global market competitiveness considerer the competition between productive chains (PC) or supply chains, not just between enterprises. In this case, it can be observed collaboration and cooperation enterprises that dispute with others productives chain. The PC competitiveness can be impaired if is subject by inhibitors factors, that can impairer the performance. This paper analyses these competitiveness factors inhibitors in biodiesel productive chain (CPB) in semi-arid area: exporte...

  13. Wind power variations under humid and arid meteorological conditions

    International Nuclear Information System (INIS)

    Şen, Zekâi

    2013-01-01

    Highlights: • It indicates the role of weather parameters’ roles in the wind energy calculation. • Meteorological variables are more significant in arid regions for wind power. • It provides opportunity to take into consideration air density variability. • Wind power is presented in terms of the wind speed, temperature and pressure. - Abstract: The classical wind power per rotor area per time is given as the half product of the air density by third power of the wind velocity. This approach adopts the standard air density as constant (1.23 g/cm 3 ), which ignores the density dependence on air temperature and pressure. Weather conditions are not taken into consideration except the variations in wind velocity. In general, increase in pressure and decrease in temperature cause increase in the wind power generation. The rate of increase in the pressure has less effect on the wind power as compared with the temperature rate. This paper provides the wind power formulation based on three meteorological variables as the wind velocity, air temperature and air pressure. Furthermore, from the meteorology point of view any change in the wind power is expressed as a function of partial changes in these meteorological variables. Additionally, weather conditions in humid and arid regions differ from each other, and it is interesting to see possible differences between the two regions. The application of the methodology is presented for two meteorology stations in Istanbul, Turkey, as representative of the humid regions and Al-Madinah Al-Monawwarah, Kingdom of Saudi Arabia, for arid region, both on daily record bases for 2010. It is found that consideration of air temperature and pressure in the average wind power calculation gives about 1.3% decrease in Istanbul, whereas it is about 13.7% in Al-Madinah Al-Monawwarah. Hence, consideration of meteorological variables in wind power calculations becomes more significant in arid regions

  14. Primordial vorticity and gradient expansion

    CERN Document Server

    Giovannini, Massimo

    2012-01-01

    The evolution equations of the vorticities of the electrons, ions and photons in a pre-decoupling plasma are derived, in a fully inhomogeneous geometry, by combining the general relativistic gradient expansion and the drift approximation within the Adler-Misner-Deser decomposition. The vorticity transfer between the different species is discussed in this novel framework and a set of general conservation laws, connecting the vorticities of the three-component plasma with the magnetic field intensity, is derived. After demonstrating that a source of large-scale vorticity resides in the spatial gradients of the geometry and of the electromagnetic sources, the total vorticity is estimated to lowest order in the spatial gradients and by enforcing the validity of the momentum constraint. By acknowledging the current bounds on the tensor to scalar ratio in the (minimal) tensor extension of the $\\Lambda$CDM paradigm the maximal comoving magnetic field induced by the total vorticity turns out to be, at most, of the or...

  15. Human-environment interactions in arid Australia: a geoarchaeological approach

    Science.gov (United States)

    Fanning, Patricia C.; Holdaway, Simon J.; Rhodes, Edward J.

    2010-05-01

    The conventional approach to assessing the archaeological record in semi-arid regions of many parts of the world involves extensive survey of surface deposits thought to indicate the use of space by past peoples. However, such interpretations require a detailed understanding not only of how these deposits formed but also why they have survived. In summarizing more than a decade of research in western New South Wales, Australia, we argue that over much of semi-arid and arid Australia, archaeological ‘sites' are, in fact, accretion phenomena (or ‘palimpsests') that are not easily interpreted as the outcome of short-term behavioural events. Moreover, while the desert landscapes may appear to be unchanging, there is considerable variability in landsurface age, and hence the ‘availability' of archaeological surfaces. It cannot be assumed that stone artefact deposits, for example, from a similar location are of a similar age. To make behavioural inferences from these records, an approach is needed based on a geoarchaeological assessment of landscape potential, analyses able to detect human responses to environmental change, and analyses of artefacts that emphasise mobility rather than static settlement patterns. Landscape, paleoenvironmental and artifact assemblage data from our field area will be presented that demonstrates episodic occupation by highly mobile groups of people, most likely reacting to environmental changes and resource availability.

  16. SC-HTGR Performance Impact for Arid Sites

    International Nuclear Information System (INIS)

    Lommers, L.; Geschwindt, J.; Southworth, F.; Shahrokhi, F.

    2014-01-01

    The SC-HTGR provides high temperature steam which can support industrial process heat applications as well as high efficiency electricity generation. The increased generating efficiency resulting from using high steam temperature provides greater plant output than lower temperature concepts, and it also reduces the fraction of waste heat which must be rejected. This capability is particularly attractive for sites with little or no water for heat rejection. This high temperature capability provides greater flexibility for these sites, and it results in a smaller performance penalty than for lower temperature systems when dry cooling must be used. The performance of the SC-HTGR for a conventional site with wet cooling is discussed first. Then the performance for arid sites is evaluated. Dry cooling performance is evaluated for both moderately arid sites and very hot sites. Offdesign performance of the dry cooling system under extreme conditions is also considered. Finally, operating strategies are explored for sites where some cooling water may be available but only in very limited quantities. Results of these assessments confirm that the higher operating temperatures of the SC-HTGR are very beneficial for arid sites, providing significant advantages for both gross and net power generation. (author)

  17. Protocol for VOC-Arid ID remediation performance characterization

    International Nuclear Information System (INIS)

    Tegner, B.J.; Hassig, N.L.; Last, G.V.

    1994-09-01

    The Volatile Organic Compound-Arid Integrated Demonstration (VOC-Arid ID) is a technology development program sponsored by the US Department of Energy's Office of Technology Development that is targeted to acquire, develop, demonstrate, and deploy new technologies for the remediation of VOC contaminants in the soils and groundwaters of arid DOE sites. Technologies cannot be adequately evaluated unless sufficient site characterization and technology performance data have been collection and analyzed. The responsibility for identifying these data needs has been placed largely on the Principal Investigators (PIs) developing the remediation technology, who usually are not experts in site characterization or in identification of appropriate sampling, analysis, and monitoring techniques to support the field testing. This document provides a protocol for planning the collection of data before, during, and after a test of a new technology. This generic protocol provides the PIs and project managers with a set of steps to follow. The protocol is based on a data collection planning process called the Data Quality Objectives (DQO) process, which was originally developed by the US Environmental Protection Agency and has been expanded by DOE to support site cleanup decisions. The DQO process focuses on the quality and quantity of data required to make decision. Stakeholders to the decisions must negotiate such key inputs to the process as the decision rules that will be used and the acceptable probabilities of making decision errors

  18. Characteristics of the volatile organic compounds -- Arid Integrated Demonstration Site

    International Nuclear Information System (INIS)

    Last, G.V.; Lenhard, R.J.; Bjornstad, B.N.; Evans, J.C.; Roberson, K.R.; Spane, F.A.; Amonette, J.E.; Rockhold, M.L.

    1991-10-01

    The Volatile Organic Compounds -- Arid Integrated Demonstration Program (VOC-Arid ID) is targeted at demonstration and testing of technologies for the evaluation and cleanup of volatile organic compounds and associated contaminants at arid DOE sites. The initial demonstration site is an area of carbon tetrachloride (CCl 4 ) contamination located near the center of the Hanford Site. The movement of CCl 4 and other volatile organic contaminants in the subsurface is very complex. The problem at the Hanford Site is further complicated by the concurrent discharge of other waste constituents including acids, lard oil, organic phosphates, and transuranic radionuclides. In addition, the subsurface environment is very complex, with large spatial variabilities in hydraulic properties. A thorough understanding of the problem is essential to the selection of appropriate containment, retrieval, and/or in situ remedial technologies. The effectiveness of remedial technologies depends on knowing where the contaminants are, how they are held up in a given physical and chemical subsurface environment; and knowing the physical, chemical, and microbiological changes that are induced by the various remedial technologies

  19. Gradient computation for VTI acoustic wavefield tomography

    KAUST Repository

    Li, Vladimir; Wang, Hui; Tsvankin, Ilya; Diaz, Esteban; Alkhalifah, Tariq Ali

    2016-01-01

    -power objective functions. We also obtain the gradient expressions for the data-domain objective function, which can incorporate borehole information necessary for stable VTI velocity analysis. These gradients are compared to the ones obtained with a space

  20. Jojoba, Simmondsia chinensis: an alternative for the economic development of the arid and semi arid zones of Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Sepulveda Betancourt, J I; Parra Hake, H

    1976-01-01

    Simmondsia chinensis is, in spite of its name, a species indigenous to SE California and Arizona (US) and to the states of Sonora, Baja California Norte and Baja California Sur in Mexico. It is a shrubby forage plant that reaches a height of 1.5 m and can grow under conditions of extreme drought and high salinity provided that frost does not occur; it is thus suitable for many arid and semi-arid parts of Mexico as well as other similar regions of the world. The seed, traditionally associated with medicinal properties, was found in 1933 to produce a liquid wax with properties similar to those of sperm-whale oil, an increasingly scarce product used for the lubrication of machinery run at high temperatures and speeds. Some other uses for S. chinensis wax are listed, and silvicultural research on the species in progress in Baja California Sur and elsewhere is briefly described.

  1. Jojoba, Simmondsia chinensis. An alternative for the economic development of the arid and semi arid zones of Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Sepulveda Betancourt, J I; Parra Hake, H

    1976-01-01

    S. chinensis is, in spite of its name, a species indigenous to SE California and Arizona (US) and to the states of Sonora, Baja California Norte and Baja California Sur in Mexico. It is a shrubby forage plant that reaches a height of 1.5 m and can grow under conditions of extreme drought and high salinity provided that frost does not occur; it is thus suitable for many arid and semi-arid parts of Mexico as well as other similar regions of the world. The seed, traditionally associated with medicinal properties, was found in 1933 to produce a liquid wax with properties similar to those of sperm-whale oil, an increasingly scarce product used for the lubrication of machinery run at high temperatures and speeds. Some other uses for S. chinensis wax are listed, and silvicultural research on the species in progress in Baja California Sur and elsewhere is briefly described.

  2. Radiating despite a Lack of Character: Ecological Divergence among Closely Related, Morphologically Similar Honeyeaters (Aves: Meliphagidae) Co-occurring in Arid Australian Environments.

    Science.gov (United States)

    Miller, Eliot T; Wagner, Sarah K; Harmon, Luke J; Ricklefs, Robert E

    2017-02-01

    Quantifying the relationship between form and function can inform use of morphology as a surrogate for ecology. How the strength of this relationship varies continentally can inform understanding of evolutionary radiations; for example, does the relationship break down when certain lineages invade and diversify in novel habitats? The 75 species of Australian honeyeaters (Meliphagidae) are morphologically and ecologically diverse, with species feeding on nectar, insects, fruit, and other resources. We investigated Meliphagidae ecomorphology and community structure by (1) quantifying the concordance between morphology and ecology (foraging behavior), (2) estimating rates of trait evolution in relation to the packing of ecological space, and (3) comparing phylogenetic and trait community structure across the broad environmental gradients of the continent. We found that morphology explained 37% of the variance in ecology (and 62% vice versa), and we uncovered well-known bivariate relationships among the multivariate ecomorphological data. Ecological trait diversity declined less rapidly than phylogenetic diversity along a gradient of decreasing precipitation. We employ a new method (trait fields) and extend another (phylogenetic fields) to show that while species in phylogenetically clustered, arid-environment assemblages are similar morphologically, they are as varied in foraging behavior as those from more diverse assemblages. Thus, although closely related and similar morphologically, these arid-adapted species have diverged in ecological space to a similar degree as their mesic counterparts.

  3. Instabilities in power law gradient hardening materials

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Tvergaard, Viggo

    2005-01-01

    Tension and compression instabilities are investigated for specimens with dimensions in the micron range. A finite strain generalization of a higher order strain gradient plasticity theory is implemented in a finite element scheme capable of modeling power law hardening materials. Effects...... of gradient hardening are found to delay the onset of localization under plane strain tension, and significantly reduce strain gradients in the localized zone. For plane strain compression gradient hardening is found to increase the load-carrying capacity significantly....

  4. Quantifying the effects of ecological constraints on trait expression using novel trait-gradient analysis parameters.

    Science.gov (United States)

    Ottaviani, Gianluigi; Tsakalos, James L; Keppel, Gunnar; Mucina, Ladislav

    2018-01-01

    Complex processes related to biotic and abiotic forces can impose limitations to assembly and composition of plant communities. Quantifying the effects of these constraints on plant functional traits across environmental gradients, and among communities, remains challenging. We define ecological constraint ( C i ) as the combined, limiting effect of biotic interactions and environmental filtering on trait expression (i.e., the mean value and range of functional traits). Here, we propose a set of novel parameters to quantify this constraint by extending the trait-gradient analysis (TGA) methodology. The key parameter is ecological constraint, which is dimensionless and can be measured at various scales, for example, on population and community levels. It facilitates comparing the effects of ecological constraints on trait expressions across environmental gradients, as well as within and among communities. We illustrate the implementation of the proposed parameters using the bark thickness of 14 woody species along an aridity gradient on granite outcrops in southwestern Australia. We found a positive correlation between increasing environmental stress and strength of ecological constraint on bark thickness expression. Also, plants from more stressful habitats (shrublands on shallow soils and in sun-exposed locations) displayed higher ecological constraint for bark thickness than plants in more benign habitats (woodlands on deep soils and in sheltered locations). The relative ease of calculation and dimensionless nature of C i allow it to be readily implemented at various scales and make it widely applicable. It therefore has the potential to advance the mechanistic understanding of the ecological processes shaping trait expression. Some future applications of the new parameters could be investigating the patterns of ecological constraints (1) among communities from different regions, (2) on different traits across similar environmental gradients, and (3) for the same

  5. Plan and Some Results of "Advanced Study on Precipitation Enhancement in Arid and Semi-Arid Regions"

    Science.gov (United States)

    Murakami, M.

    2016-12-01

    There are several technologies to secure water resources, including the desalination of seawater, recycling of industrial water and reuse of wastewater. However precipitation enhancement is the only way we can create a large amount of water for industrial use, for example, water for irrigation, provided we find clouds suitable for cloud seeding and apply appropriate and effective methods to increase precipitation. Therefore, rain enhancement research is critical in the quest for new water security options and innovative solutions in the UAE and other arid and semi-arid regions. The main objective of our project is to better evaluate, and ultimately improve, the effectiveness of rain enhancement in the UAE and other arid and semi-arid regions using hygroscopic and glaciogenic seeding techniques. One of the major questions regarding rain enhancement today is the effectiveness of hygroscopic seeding for warm and supercooled convective clouds. Our research will investigate the microphysical processes in seeded and unseeded clouds using a combination of laboratory experiments, numerical simulations and in-situ aircraft measurements in order to decipher the mechanism responsible for precipitation augmentation due to hygroscopic seeding. In our research, major elements of cloud seeding, e.g., assessment of seedability, development of optimal seeding methods and evaluation of seeding effects, will be investigated in the most efficient and realistic way, within three years, using mainly the numerical models with the sophisticated seeding scheme, which is developed on a basis of laboratory experiments and then validated against in-situ and remote sensing observations. In addition to the research plan, the outcomes of the research projects, which will be made available to the public at the end of the project and benefit the broader society, is discussed.

  6. An education gradient in health, a health gradient in education, or a confounded gradient in both?

    Science.gov (United States)

    Lynch, Jamie L; von Hippel, Paul T

    2016-04-01

    There is a positive gradient associating educational attainment with health, yet the explanation for this gradient is not clear. Does higher education improve health (causation)? Do the healthy become highly educated (selection)? Or do good health and high educational attainment both result from advantages established early in the life course (confounding)? This study evaluates these competing explanations by tracking changes in educational attainment and Self-rated Health (SRH) from age 15 to age 31 in the National Longitudinal Study of Youth, 1997 cohort. Ordinal logistic regression confirms that high-SRH adolescents are more likely to become highly educated. This is partly because adolescent SRH is associated with early advantages including adolescents' academic performance, college plans, and family background (confounding); however, net of these confounders adolescent SRH still predicts adult educational attainment (selection). Fixed-effects longitudinal regression shows that educational attainment has little causal effect on SRH at age 31. Completion of a high school diploma or associate's degree has no effect on SRH, while completion of a bachelor's or graduate degree have effects that, though significant, are quite small (less than 0.1 points on a 5-point scale). While it is possible that educational attainment would have greater effect on health at older ages, at age 31 what we see is a health gradient in education, shaped primarily by selection and confounding rather than by a causal effect of education on health. Copyright © 2016 Elsevier Ltd. All rights reserved.

  7. Eco-geomorphology of banded vegetation patterns in arid and semi-arid regions

    Directory of Open Access Journals (Sweden)

    P. M. Saco

    2007-11-01

    Full Text Available The interaction between vegetation and hydrologic processes is particularly tight in water-limited environments where a positive-feedback links soil moisture and vegetation. The vegetation of these systems is commonly patterned, that is, arranged in a two phase mosaic composed of patches with high biomass cover interspersed within a low-cover or bare soil component. These patterns are strongly linked to the redistribution of runoff and resources from source areas (bare patches to sink areas (vegetation patches and play an important role in controlling erosion.

    In this paper, the dynamics of these systems is investigated using a new modeling framework that couples landform and vegetation evolution, explicitly accounting for the dynamics of runon-runoff areas. The objective of this study is to analyze water-limited systems on hillslopes with mild slopes, in which overland flow occurs predominantly in only one direction and vegetation displays a banded pattern. Our simulations reproduce bands that can be either stationary or upstream migrating depending on the magnitude of the runoff-induced seed dispersal. We also found that stationary banded systems redistribute sediment so that a stepped microtopography is developed. The modelling results are the first to incorporate the effects of runoff redistribution and variable infiltration rates on the development of both the vegetation patterns and microtopography. The microtopography for stationary bands is characterized by bare soil on the lower gradient areas and vegetation on steeper gradients areas. For the case of migrating vegetation bands the model generates hillslope profiles with planar topography. The success at generating not only the observed patterns of vegetation, but also patterns of runoff and sediment redistribution suggests that the hydrologic and erosion mechanisms represented in the model are correctly capturing some of the key processes driving these ecosystems.

  8. Strain gradient effects in surface roughening

    DEFF Research Database (Denmark)

    Borg, Ulrik; Fleck, N.A.

    2007-01-01

    evidence for strain gradient effects. Numerical analyses of a bicrystal undergoing in-plane tensile deformation are also studied using a strain gradient crystal plasticity theory and also by using a strain gradient plasticity theory for an isotropic solid. Both theories include an internal material length...

  9. Gradient remediability in linear distributed parabolic systems ...

    African Journals Online (AJOL)

    The aim of this paper is the introduction of a new concept that concerned the analysis of a large class of distributed parabolic systems. It is the general concept of gradient remediability. More precisely, we study with respect to the gradient observation, the existence of an input operator (gradient efficient actuators) ensuring ...

  10. Deep Soil Recharge in Arid and Semi-Arid Regions: New Evidences in MU-US Sandy Land of China

    Science.gov (United States)

    Cheng, Y.; Yang, W.; Zhan, H.

    2017-12-01

    Precipitation induced recharge is an important source of groundwater budget but it is very difficult to quantify in arid and semiarid regions. In this study, a newly invented lysimeter was used to monitor deep soil recharge (DSR) under 200 cm depth in MU-US sandy land in western China under three kinds of landforms (mobile dune, semi-fixed dune, and fixed dune). We found that the annual DSRs in such three different kinds of landforms varied significantly. Specifically, the annual DSRs were 224.1 mm (50.5% of the annual precipitation), 71.1 mm (50.5% of the annual precipitation), and 1.3 mm (0.3% of the annual precipitation) in mobile dune, semi-fixed dune, and fixed dune, respectively. We also found that vegetation coverage and precipitation pattern significantly affected DSR. A 24-hr precipitation event with the precipitation amount greater than 8 mm was able to infiltrate soil deeper than 200 cm and contributed to ground water recharge directly. Vegetation was a dominant factor influencing infiltration in the fixed sand dune. Our research revealed that precipitation induced DSR in arid and semi-arid regions was a complex process that required long-term monitoring and innovative system analysis of interrelated factors such as precipitation strength and pattern, meteorological parameters, and dynamic soil moisture. Key words: Precipitation pattern, sand dune groundwater, deep soil recharge, infiltration.

  11. Temperate grassland songbird species accumulate incrementally along a gradient of primary productivity.

    Directory of Open Access Journals (Sweden)

    William L Harrower

    Full Text Available Global analyses of bird communities along elevation gradients suggest that bird diversity on arid mountains is primarily limited by water availability, not temperature or altitude. However, the mechanism by which water availability, and subsequently primary productivity, increases bird diversity is still unclear. Here we evaluate two possible mechanisms from species-energy theory. The more individuals hypothesis proposes that a higher availability of resources increases the total number of individuals that can be supported, and therefore the greater number of species that will be sampled. By contrast, the more specialization hypothesis proposes that increasing resource availability will permit specialists to exploit otherwise rare resources, thus increasing total diversity. We used 5 years of surveys of grassland songbird communities along an elevational gradient in British Columbia, Canada, to distinguish between these hypotheses. Vegetation changed markedly in composition along the gradient and contrary to the expectations of the more specialization hypothesis, bird community composition was remarkably constant. However, both total abundance and species richness of birds increased with increasing water availability to plants. When we used rarefaction to correct species richness for differences in total abundance, much of the increase in bird diversity was lost, consistent with the expectations of the more individuals hypothesis. Furthermore, high species richness was associated with reductions in territory size of common bird species, rather than the fine-scale spatial partitioning of the landscape. This suggests that bird diversity increases when greater resource availability allows higher densities rather than greater habitat specialization. These results help explain a pervasive global pattern in bird diversity on arid mountains, and suggest that in such landscapes conservation of grassland birds is strongly linked to climate and hydrology.

  12. VOC-Arid Integrated Demonstration guide to preparation of demonstration documents

    International Nuclear Information System (INIS)

    Jensen, E.J.; Brouns, T.M.; Koegler, K.J.; McCabe, G.H.; Morris, F.A.

    1994-06-01

    This guide has been prepared by Demonstration Operations of the Volatile Organic Compound-Arid Integrated Demonstration (VOC-Arid ID). Its purpose is to describe demonstration documents, designate responsibilities for these documents, and guide the Principal Investigator (PI) and others in their preparation. The main emphasis of this guide is to describe the documentation required of the PI. However, it does cover some of the responsibilities of other members of the VOC-Arid ID team. The VOC-Arid ID is one of several US Department of Energy (DOE) integrated demonstrations designed to support the demonstration of emerging environmental management and restoration technologies. The principal objective of the VOC-Arid ID is to identify, develop, and demonstrate new and innovative technologies for environmental restoration at arid or semiarid sites containing volatile organic compounds with or without associated contamination (e.g., radionuclides and metals)

  13. Microhabitat amelioration and reduced competition among understorey plants as drivers of facilitation across environmental gradients: towards a unifying framework

    Science.gov (United States)

    Soliveres, Santiago; Eldridge, David J.; Maestre, Fernando T.; Bowker, Matthew A.; Tighe, Matthew; Escudero, Adrián

    2015-01-01

    Studies of facilitative interactions as drivers of plant richness along environmental gradients often assume the existence of an overarching stress gradient equally affecting the performance of all the species in a given community. However, co-existing species differ in their ecophysiological adaptations, and do not experience the same stress level under particular environmental conditions. Moreover, these studies assume a unimodal richness-biomass curve, which is not as general as previously thought. We ignored these assumptions to assess changes in plant-plant interactions, and their effect on local species richness, across environmental gradients in semi-arid areas of Spain and Australia. We aimed to understand the relative importance of direct (microhabitat amelioration) and indirect (changes in the competitive relationships among the understorey species: niche segregation, competitive exclusion or intransitivity) mechanisms that might underlie the effects of nurse plants on local species richness. By jointly studying these direct and indirect mechanisms using a unifying framework, we were able to see how our nurse plants (trees, shrubs and tussock grasses) not only increased local richness by expanding the niche of neighbouring species, but also by increasing niche segregation among them, though the latter was not important in all cases. The outcome of the competition-facilitation continuum changed depending on the study area, likely because the different types of stress gradient considered. When driven by both rainfall and temperature, or rainfall alone, the community-wide importance of nurse plants remained constant (Spanish sites), or showed a unimodal relationship along the gradient (Australian sites). This study expands our understanding of the relative roles of plant-plant interactions and environmental conditions as drivers of local species richness in semi-arid environments. These results can also be used to refine predictions about the response of

  14. Microhabitat amelioration and reduced competition among understorey plants as drivers of facilitation across environmental gradients: towards a unifying framework.

    Science.gov (United States)

    Soliveres, Santiago; Eldridge, David J; Maestre, Fernando T; Bowker, Matthew A; Tighe, Matthew; Escudero, Adrián

    2011-11-20

    Studies of facilitative interactions as drivers of plant richness along environmental gradients often assume the existence of an overarching stress gradient equally affecting the performance of all the species in a given community. However, co-existing species differ in their ecophysiological adaptations, and do not experience the same stress level under particular environmental conditions. Moreover, these studies assume a unimodal richness-biomass curve, which is not as general as previously thought. We ignored these assumptions to assess changes in plant-plant interactions, and their effect on local species richness, across environmental gradients in semi-arid areas of Spain and Australia. We aimed to understand the relative importance of direct (microhabitat amelioration) and indirect (changes in the competitive relationships among the understorey species: niche segregation, competitive exclusion or intransitivity) mechanisms that might underlie the effects of nurse plants on local species richness. By jointly studying these direct and indirect mechanisms using a unifying framework, we were able to see how our nurse plants (trees, shrubs and tussock grasses) not only increased local richness by expanding the niche of neighbouring species, but also by increasing niche segregation among them, though the latter was not important in all cases. The outcome of the competition-facilitation continuum changed depending on the study area, likely because the different types of stress gradient considered. When driven by both rainfall and temperature, or rainfall alone, the community-wide importance of nurse plants remained constant (Spanish sites), or showed a unimodal relationship along the gradient (Australian sites). This study expands our understanding of the relative roles of plant-plant interactions and environmental conditions as drivers of local species richness in semi-arid environments. These results can also be used to refine predictions about the response of

  15. Role of Aeolian Dust in Shaping Landscapes and Soils of Arid and Semi-Arid South Africa

    Directory of Open Access Journals (Sweden)

    Joseph R. McAuliffe

    2018-05-01

    Full Text Available The deposition of fine aeolian sediment profoundly influences the morphology of several different landscapes of the arid and semi-arid western portion of South Africa. Such landscapes and features include: (1 regularly-spaced mounds known as heuweltjies of the succulent Karoo region, (2 barren stone pavements in the more arid regions, and (3 hillslopes with smooth, curvilinear slope profiles that are mantled with coarse, stony colluvium. Investigations of each of these are presented, together with comparisons of similar features found within arid and semi-arid portions of Western North America. Recent findings suggest that the formation of the distinct, regularly-spaced heuweltjies involves a linked set of biological and physical processes. These include nutrient accumulation by termites and the production of dense vegetation patches, which, in turn, serve as a trap for aeolian sediments. Dust deposition is also responsible for the formation of stone pavements as demonstrated by research conducted principally in the Mojave Desert region of the United States. Mineralogical and geochronological studies have demonstrated that the stone clasts remain on the surface as fine aeolian sediments are translocated downward beneath the clasts resulting in a silt-rich soil horizon directly beneath the clasts. Pavements examined in South Africa have the same morphological features that can only be explained by the same process. The formation of soils on hillslopes mantled with stony colluvium are commonly viewed as having formed through the in-situ weathering of the stony colluvium. However, like pavements, mantles of coarse, stony colluvium are effective dust traps that provide the long-term stability required for advanced development of thick, fine-grained soils. This process contributes to the evolution of smooth, vegetated, curvilinear slope profiles. In each of these examples, the accumulation of dust has a profound influence, not only in soil formation

  16. Temperature Gradient in Hall Thrusters

    International Nuclear Information System (INIS)

    Staack, D.; Raitses, Y.; Fisch, N.J.

    2003-01-01

    Plasma potentials and electron temperatures were deduced from emissive and cold floating probe measurements in a 2 kW Hall thruster, operated in the discharge voltage range of 200-400 V. An almost linear dependence of the electron temperature on the plasma potential was observed in the acceleration region of the thruster both inside and outside the thruster. This result calls into question whether secondary electron emission from the ceramic channel walls plays a significant role in electron energy balance. The proportionality factor between the axial electron temperature gradient and the electric field is significantly smaller than might be expected by models employing Ohmic heating of electrons

  17. Generalized Gradient Approximation Made Simple

    International Nuclear Information System (INIS)

    Perdew, J.P.; Burke, K.; Ernzerhof, M.

    1996-01-01

    Generalized gradient approximations (GGA close-quote s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. copyright 1996 The American Physical Society

  18. Dai-Kou type conjugate gradient methods with a line search only using gradient.

    Science.gov (United States)

    Huang, Yuanyuan; Liu, Changhe

    2017-01-01

    In this paper, the Dai-Kou type conjugate gradient methods are developed to solve the optimality condition of an unconstrained optimization, they only utilize gradient information and have broader application scope. Under suitable conditions, the developed methods are globally convergent. Numerical tests and comparisons with the PRP+ conjugate gradient method only using gradient show that the methods are efficient.

  19. Ternary gradient metal-organic frameworks.

    Science.gov (United States)

    Liu, Chong; Rosi, Nathaniel L

    2017-09-08

    Gradient MOFs contain directional gradients of either structure or functionality. We have successfully prepared two ternary gradient MOFs based on bMOF-100 analogues, namely bMOF-100/102/106 and bMOF-110/100/102, via cascade ligand exchange reactions. The cubic unit cell parameter discrepancy within an individual ternary gradient MOF crystal is as large as ∼1 nm, demonstrating the impressive compatibility and flexibility of the component MOF materials. Because of the presence of a continuum of unit cells, the pore diameters within individual crystals also change in a gradient fashion from ∼2.5 nm to ∼3.0 nm for bMOF-100/102/106, and from ∼2.2 nm to ∼2.7 nm for bMOF-110/100/102, indicating significant porosity gradients. Like previously reported binary gradient MOFs, the composition of the ternary gradient MOFs can be easily controlled by adjusting the reaction conditions. Finally, X-ray diffraction and microspectrophotometry were used to analyse fractured gradient MOF crystals by comparing unit cell parameters and absorbance spectra at different locations, thus revealing the profile of heterogeneity (i.e. gradient distribution of properties) and further confirming the formation of ternary gradient MOFs.

  20. Strain gradient effects on cyclic plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Legarth, Brian Nyvang

    2010-01-01

    Size effects on the cyclic shear response are studied numerically using a recent higher order strain gradient visco-plasticity theory accounting for both dissipative and energetic gradient hardening. Numerical investigations of the response under cyclic pure shear and shear of a finite slab between...... rigid platens have been carried out, using the finite element method. It is shown for elastic–perfectly plastic solids how dissipative gradient effects lead to increased yield strength, whereas energetic gradient contributions lead to increased hardening as well as a Bauschinger effect. For linearly...... hardening materials it is quantified how dissipative and energetic gradient effects promote hardening above that of conventional predictions. Usually, increased hardening is attributed to energetic gradient effects, but here it is found that also dissipative gradient effects lead to additional hardening...

  1. Subsurface thermal regime to delineate the paleo-groundwater flow system in an arid area, Al Kufra, Libya

    Directory of Open Access Journals (Sweden)

    Zenhom El-Said Salem

    2016-12-01

    Full Text Available The purpose of this study was to understand the groundwater flow system in Al Kufra basin, Libya, as a case study of arid areas using subsurface temperature. The temperature-depth profiles and water levels were measured in eight boreholes in the area. Well 6 is considered a recharge type profile with low geothermal gradient (0.0068 °C/m and an estimated paleo-temperature around 19.5 °C. The other profiles are of discharge type with higher geothermal gradient (0.0133 to 0.0166 °C/m. The constructed horizontal 2D distribution maps of the hydraulic heads and the subsurface temperature measurements reveal that the main recharge area is located to the south with low temperature while the main discharge area is located to the north with higher temperature. Vertical 2D distribution maps show that location of well 4 has low hydraulic heads and higher temperature indicating that the fault defined in the area may have affected the groundwater flow system. The estimated groundwater flux ranges from 0.001 to 0.1 mm/day for the recharge area and from −0.3 to −0.7 mm/day in average in the discharge area.

  2. High gradient RF breakdown study

    International Nuclear Information System (INIS)

    Laurent, L.; Luhmann, N.C. Jr.; Scheitrum, G.; Hanna, S.; Pearson, C.; Phillips, R.

    1998-01-01

    Stanford Linear Accelerator Center and UC Davis have been investigating high gradient RF breakdown and its effects on pulse shortening in high energy microwave devices. RF breakdown is a critical issue in the development of high power microwave sources and next generation linear accelerators since it limits the output power of microwave sources and the accelerating gradient of linacs. The motivation of this research is to find methods to increase the breakdown threshold level in X-band structures by reducing dark current. Emphasis is focused on improved materials, surface finish, and cleanliness. The test platform for this research is a traveling wave resonant ring. A 30 MW klystron is employed to provide up to 300 MW of traveling wave power in the ring to trigger breakdown in the cavity. Five TM 01 cavities have previously been tested, each with a different combination of surface polish and/or coating. The onset of breakdown was extended up to 250 MV/m with a TiN surface finish, as compared to 210 MV/m for uncoated OFE copper. Although the TiN coating was helpful in depressing the field emission, the lowest dark current was obtained with a 1 microinch surface finish, single-point diamond-turned cavity

  3. NIF optics phase gradient specfication

    International Nuclear Information System (INIS)

    Williams, W.; Auerbach, J.; Hunt, J.; Lawson, L.; Manes, K.; Orth, C.; Sacks, R.; Trenholme, J.; Wegner, P.

    1997-01-01

    A root-mean-square (rms) phase gradient specification seems to allow a good connection between the NIP optics quality and focal spot requirements. Measurements on Beamlet optics individually, and as a chain, indicate they meet the assumptions necessary to use this specification, and that they have a typical rms phase gradient of ∼80 angstrom/cm. This may be sufficient for NIP to meet the proposed Stockpile Stewardship Management Program (SSMP) requirements of 80% of a high- power beam within a 200-250 micron diameter spot. Uncertainties include, especially, the scale length of the optics phase noise, the ability of the adaptive optic to correct against pump-induced distortions and optics noise, and the possibility of finding mitigation techniques against whole-beam self-focusing (e.g. a pre- correction optic). Further work is needed in these areas to better determine the NIF specifications. This memo is a written summary of a presentation on this topic given by W. Williams 24 April 1997 to NIP and LS ampersand T personnel

  4. Refining surface net radiation estimates in arid and semi-arid climates of Iran

    Science.gov (United States)

    Golkar, Foroogh; Rossow, William B.; Sabziparvar, Ali Akbar

    2018-06-01

    Although the downwelling fluxes exhibit space-time scales of dependency on characteristic of atmospheric variations, especially clouds, the upward fluxes and, hence the net radiation, depends on the variation of surface properties, particularly surface skin temperature and albedo. Evapotranspiration at the land surface depends on the properties of that surface and is determined primarily by the net surface radiation, mostly absorbed solar radiation. Thus, relatively high spatial resolution net radiation data are needed for evapotranspiration studies. Moreover, in more arid environments, the diurnal variations of surface (air and skin) temperature can be large so relatively high (sub-daily) time resolution net radiation is also needed. There are a variety of radiation and surface property products available but they differ in accuracy, space-time resolution and information content. This situation motivated the current study to evaluate multiple sources of information to obtain the best net radiation estimate with the highest space-time resolution from ISCCP FD dataset. This study investigates the accuracy of the ISCCP FD and AIRS surface air and skin temperatures, as well as the ISCCP FD and MODIS surface albedos and aerosol optical depths as the leading source of uncertainty in ISCCP FD dataset. The surface air temperatures, 10-cm soil temperatures and surface solar insolation from a number of surface sites are used to judge the best combinations of data products, especially on clear days. The corresponding surface skin temperatures in ISCCP FD, although they are known to be biased somewhat high, disagreed more with AIRS measurements because of the mismatch of spatial resolutions. The effect of spatial resolution on the comparisons was confirmed using the even higher resolution MODIS surface skin temperature values. The agreement of ISCCP FD surface solar insolation with surface measurements is good (within 2.4-9.1%), but the use of MODIS aerosol optical depths as

  5. Mitigating Climate Change in the Arid Lands of Namibia

    Science.gov (United States)

    Schneider, Martin B.; Sorensen, Marten

    2014-05-01

    Mitigating Climate Change in the Arid Lands of Namibia Namibia is the most arid country south of the Sahara, with scarce rainfall and perennial rivers only at its borders, > 80% of the area relies solely on groundwater. This has had devastating economic effects limiting opportunities for sustainable rural livelihoods that keep the population majority living below the World Bank poverty line (IFAD, 2013). A primary example of climatic variability which affects agrarian productivity is increased bush encroachment of Namibia's arid grazing land. The result has been a severe biodiversity loss, increased desertification and diminished water-use efficiency and underground water tables. Given these factors, Namibia's arid lands provide a unique opportunity to assess and test innovative / appropriate adaptation and mitigation strategies. Working toward sustainable management, restoration, and maintenance of balanced, resilient arid ecosystems in Namibia will also be a means to support and expand economic sectors incl. opportunities for job creation and potentially provide a model for similar arid regions. Main vegetation zones are: desert (46%), savannah (37%), and dry woodlands and forests (17%), i.e. management strategies currently used by rural communities. 2. Capture and assess cultural and gender dimensions of management strategies within stakeholder groups using participatory approaches. 3. Determine science-based alternatives for adaptive land management strategies and test their acceptability to local communities and within the current policy framework. 4. Integrate identified indigenous knowledge with appropriate science and new emerging technologies to develop a training toolkit of effective strategies relevant to all stakeholders. 5. Utilize training sessions, education workshops, curriculum revisions, and appropriate information and communication technologies (ICTs) including social media outlets to disseminate the toolkit strategies. 6. Apply a modified logic

  6. Improved climate risk simulations for rice in arid environments.

    Directory of Open Access Journals (Sweden)

    Pepijn A J van Oort

    Full Text Available We integrated recent research on cardinal temperatures for phenology and early leaf growth, spikelet formation, early morning flowering, transpirational cooling, and heat- and cold-induced sterility into an existing to crop growth model ORYZA2000. We compared for an arid environment observed potential yields with yields simulated with default ORYZA2000, with modified subversions of ORYZA2000 and with ORYZA_S, a model developed for the region of interest in the 1990s. Rice variety 'IR64' was sown monthly 15-times in a row in two locations in Senegal. The Senegal River Valley is located in the Sahel, near the Sahara desert with extreme temperatures during day and night. The existing subroutines underestimated cold stress and overestimated heat stress. Forcing the model to use observed spikelet number and phenology and replacing the existing heat and cold subroutines improved accuracy of yield simulation from EF = -0.32 to EF =0.70 (EF is modelling efficiency. The main causes of improved accuracy were that the new model subversions take into account transpirational cooling (which is high in arid environments and early morning flowering for heat sterility, and minimum rather than average temperature for cold sterility. Simulations were less accurate when also spikelet number and phenology were simulated. Model efficiency was 0.14 with new heat and cold routines and improved to 0.48 when using new cardinal temperatures for phenology and early leaf growth. The new adapted subversion of ORYZA2000 offers a powerful analytic tool for climate change impact assessment and cropping calendar optimisation in arid regions.

  7. Arid site water balance: evapotranspiration modeling and measurements

    International Nuclear Information System (INIS)

    Gee, G.W.; Kirkham, R.R.

    1984-09-01

    In order to evaluate the magnitude of radionuclide transport at an aird site, a field and modeling study was conducted to measure and predict water movement under vegetated and bare soil conditions. Significant quantities of water were found to move below the roo of a shallow-rooted grass-covered area during wet years at the Hanford site. The unsaturated water flow model, UNSAT-1D, was resonably successful in simulating the transient behavior of the water balance at this site. The effects of layered soils on water balance were demonstrated using the model. Models used to evaluate water balance in arid regions should not rely on annual averages and assume that all precipitation is removed by evapotranspiration. The potential for drainage at arid sites exists under conditions where shallow rooted plants grow on coarse textured soils. This condition was observed at our study site at Hanford. Neutron probe data collected on a cheatgrass community at the Hanford site during a wet year indicated that over 5 cm of water drained below the 3.5-m depth. The unsaturated water flow model, UNSAT-1D, predicted water drainage of about 5 cm (single layer, 10 months) and 3.5 cm (two layers, 12 months) for the same time period. Additional field measurements of hydraulic conductivity will likely improve the drainage estimate made by UNSAT-1D. Additional information describing cheatgrass growth and water use at the grass site could improve model predictions of sink terms and subsequent calculations of water storage within the rooting zone. In arid areas where the major part of the annual precipitation occurs during months with low average potential evapotranspiration and where soils are vegetated but are coarse textured and well drained, significant drainage can occur. 31 references, 18 figures, 1 table

  8. Strength gradient enhances fatigue resistance of steels

    Science.gov (United States)

    Ma, Zhiwei; Liu, Jiabin; Wang, Gang; Wang, Hongtao; Wei, Yujie; Gao, Huajian

    2016-02-01

    Steels are heavily used in infrastructure and the transportation industry, and enhancing their fatigue resistance is a major challenge in materials engineering. In this study, by introducing a gradient microstructure into 304 austenitic steel, which is one of the most widely used types of stainless steel, we show that a strength gradient substantially enhances the fatigue life of the material. Pre-notched samples with negative strength gradients in front of the notch’s tip endure many more fatigue cycles than do samples with positive strength gradients during the crack initiation stage, and samples with either type of gradient perform better than do gradient-free samples with the same average yield strength. However, as a crack grows, samples with positive strength gradients exhibit better resistance to fatigue crack propagation than do samples with negative gradients or no gradient. This study demonstrates a simple and promising strategy for using gradient structures to enhance the fatigue resistance of materials and complements related studies of strength and ductility.

  9. Disturbance by an endemic rodent in an arid shrubland is a habitat filter: effects on plant invasion and taxonomical, functional and phylogenetic community structure.

    Science.gov (United States)

    Escobedo, Víctor M; Rios, Rodrigo S; Salgado-Luarte, Cristian; Stotz, Gisela C; Gianoli, Ernesto

    2017-03-01

    Disturbance often drives plant invasion and may modify community assembly. However, little is known about how these modifications of community patterns occur in terms of taxonomic, functional and phylogenetic structure. This study evaluated in an arid shrubland the influence of disturbance by an endemic rodent on community functional divergence and phylogenetic structure as well as on plant invasion. It was expected that disturbance would operate as a habitat filter favouring exotic species with short life cycles. Sixteen plots were sampled along a disturbance gradient caused by the endemic fossorial rodent Spalacopus cyanus , measuring community parameters and estimating functional divergence for life history traits (functional dispersion index) and the relative contribution to functional divergence of exotic and native species. The phylogenetic signal (Pagel's lambda) and phylogenetic community structure (mean phylogenetic distance and mean nearest taxon phylogenetic distance) were also estimated. The use of a continuous approach to the disturbance gradient allowed the identification of non-linear relationships between disturbance and community parameters. The relationship between disturbance and both species richness and abundance was positive for exotic species and negative for native species. Disturbance modified community composition, and exotic species were associated with more disturbed sites. Disturbance increased trait convergence, which resulted in phylogenetic clustering because traits showed a significant phylogenetic signal. The relative contribution of exotic species to functional divergence increased, while that of natives decreased, with disturbance. Exotic and native species were not phylogenetically distinct. Disturbance by rodents in this arid shrubland constitutes a habitat filter over phylogeny-dependent life history traits, leading to phylogenetic clustering, and drives invasion by favouring species with short life cycles. Results can be

  10. Functionally relevant climate variables for arid lands: Aclimatic water deficit approach for modelling desert shrub distributions

    Science.gov (United States)

    Thomas E. Dilts; Peter J. Weisberg; Camie M. Dencker; Jeanne C. Chambers

    2015-01-01

    We have three goals. (1) To develop a suite of functionally relevant climate variables for modelling vegetation distribution on arid and semi-arid landscapes of the Great Basin, USA. (2) To compare the predictive power of vegetation distribution models based on mechanistically proximate factors (water deficit variables) and factors that are more mechanistically removed...

  11. Coupled flow and salinity transport modelling in semi-arid environments

    DEFF Research Database (Denmark)

    Bauer-Gottwein, Peter; Held, R.J.; Zimmermann, S.

    2006-01-01

    Numerical groundwater modelling is used as the base for sound aquifer system analysis and water resources assessment. In many cases, particularly in semi-arid and arid regions, groundwater flow is intricately linked to salinity transport. A case in point is the Shashe River Valley in Botswana. A ...

  12. Pathways to Resilience in Semi-Arid Economies | CRDI - Centre de ...

    International Development Research Centre (IDRC) Digital Library (Canada)

    Pathways to Resilience in Semi-Arid Economies. How can populations become resilient to climate change while pursuing economic growth? This question is at the heart of a research project designed to support climate-resilient economic development in semi-arid lands. It will do so by addressing the conditions for ...

  13. Survival and long-term growth of eucalypts on semi-arid sites in a ...

    African Journals Online (AJOL)

    1, which is comparable to volume obtained at more favourable aridity indices in the summer rainfall zone of South Africa and exceeds the growth rates obtained in several other arid zone studies globally. The E. grandis × E. camaldulensis ...

  14. Impact of grazing on range plant community components under arid Mediterranean climate in northern Syria

    NARCIS (Netherlands)

    Niane, A.A.

    2013-01-01

    Keywords: Rotational grazing, full protection, continuous grazing species richness,

    species diversity, soil seed bank, Bayesian methods, Salsola vermiculata, seed

    longevity, rangeland management, Syria.

    Rangelands represent 70% of the semi-arid and arid

  15. The ARID1B phenotype: what we have learned so far.

    Science.gov (United States)

    Santen, Gijs W E; Clayton-Smith, Jill

    2014-09-01

    Evidence is now accumulating from a number of sequencing studies that ARID1B not only appears to be one of the most frequently mutated intellectual disability (ID) genes, but that the range of phenotypes caused by ARID1B mutations seems to be extremely wide. Thus, it is one of the most interesting ID genes identified so far in the exome sequencing era. In this article, we review the literature surrounding ARID1B and attempt to delineate the ARID1B phenotype. The vast majority of published ARID1B patients have been ascertained through studies of Coffin-Siris syndrome (CSS), which leads to bias when documenting the frequencies of phenotypic features. Additional observations of those individuals ascertained through exome sequencing studies helps in delineation of the broader clinical phenotype. We are currently establishing an ARID1B consortium, aimed at collecting ARID1B patients identified through genome-wide sequencing strategies. We hope that this endeavor will eventually lead to a more comprehensive view of the ARID1B phenotype. © 2014 Wiley Periodicals, Inc.

  16. Special waste form lysimeters-arid. Annual report, 1985

    International Nuclear Information System (INIS)

    Walter, M.B.; Graham, M.J.

    1985-09-01

    The Special Waste Form Lysimeters-Arid program was initiated to determine typical source terms generated by commercial solidified low-level nuclear waste in an arid climate. Waste-form leaching tests are being conducted at a field facility at the Hanford site near Richland, Washington. A similar program is being conducted at a humid site. The field facility consists of 10 lysimeters placed around a central instrument caisson. The waste samples from boiling water and pressurized water reactors were emplaced in 1984, and the lysimeters are being monitored for movement of contaminants and water. Solidifying agents being tested include vinyl ester-styrene, bitumen, and cement. Laboratory leaching and geochemical modeling studies are being conducted to predict expected leach rates at the field site and to aid field-data interpretation. Small samples of the solidified waste forms were made for use in the laboratory leaching studies that include standard leach tests and leaching of solidified waste forms in soil columns. Complete chemical and radionuclide analyses are being conducted on the solid and liquid portions of the wastes. 2 refs

  17. Feasibility of groundwater recharge dam projects in arid environments

    Science.gov (United States)

    Jaafar, H. H.

    2014-05-01

    A new method for determining feasibility and prioritizing investments for agricultural and domestic recharge dams in arid regions is developed and presented. The method is based on identifying the factors affecting the decision making process and evaluating these factors, followed by determining the indices in a GIS-aided environment. Evaluated parameters include results from field surveys and site visits, land cover and soils data, precipitation data, runoff data and modeling, number of beneficiaries, domestic irrigation demand, reservoir objectives, demography, reservoirs yield and reliability, dam structures, construction costs, and operation and maintenance costs. Results of a case study on more than eighty proposed dams indicate that assessment of reliability, annualized cost/demand satisfied and yield is crucial prior to investment decision making in arid areas. Irrigation demand is the major influencing parameter on yield and reliability of recharge dams, even when only 3 months of the demand were included. Reliability of the proposed reservoirs as related to their standardized size and net inflow was found to increase with increasing yield. High priority dams were less than 4% of the total, and less priority dams amounted to 23%, with the remaining found to be not feasible. The results of this methodology and its application has proved effective in guiding stakeholders for defining most favorable sites for preliminary and detailed design studies and commissioning.

  18. Uranium isotopes in carbonate aquifers of arid region setting

    International Nuclear Information System (INIS)

    Alshamsi, D.M.; Murad, A.A.

    2013-01-01

    Groundwater in arid and semiarid regions is vital resource for many uses and therefore information about concentrations of uranium isotopes among other chemical parameters are necessary. In the study presented here, distribution of 238 U and 235 U in groundwater of four selected locations in the southern Arabian peninsula, namely at two locations within the United Arab Emirates (UAE) and two locations in Oman are discussed. The analyses of the uranium isotopes were performed using ICP-MS and the results indicated a range of concentrations for 235 U and 238 U at 3-39 ng L -1 (average: 18 ng L -1 ) and 429-5,293 ng L -1 (average: 2,508 ng L -1 ) respectively. These uranium concentrations are below the higher permissible WHO limit for drinking water and also comparable to averages found in groundwater from similar aquifers in Florida and Tunisia. Negative correlation between rainfall and uranium concentrations suggests that in lithologically comparable aquifers, climate may influence the concentration of uranium in subtropical to arid regions. (author)

  19. Soil microbial responses to nitrogen addition in arid ecosystems

    Directory of Open Access Journals (Sweden)

    Robert L Sinsabaugh

    2015-08-01

    Full Text Available The N cycle of arid ecosystems is influenced by low soil organic matter, high soil pH and extremes in water potential and temperature that lead to open canopies and development of biological soil crusts (biocrusts. We investigated the effects of N amendment on soil microbial dynamics in a Larrea tridentata-Ambrosia dumosa shrubland site in southern Nevada USA. Sites were fertilized with a NO3-NH4 mix at 0, 7, and 15 kg ha-1 yr-1 from March 2012 to March 2013. In March 2013, biocrust (0-0.5 cm and bulk soils (0-10 cm were collected beneath Ambrosia canopies and in the interspaces between plants. Biomass responses were assessed as bacterial and fungal SSU rRNA gene copy number and chlorophyll a concentration. Metabolic responses were measured by five ecoenzyme activities (EEA and rates of N transformation. By most measures, nutrient availability, microbial biomass and process rates were greater in soils beneath the shrub canopy compared to the interspace between plants, and greater in the surface biocrust horizon compared to the deeper 10 cm soil profile. Most measures responded positively to experimental N addition. Effect sizes were generally greater for bulk soil than biocrust. Results were incorporated into a meta-analysis of arid ecosystem responses to N.

  20. Diversity of avian haemosporidians in arid zones of northern Venezuela.

    Science.gov (United States)

    Belo, Nayara O; Rodríguez-Ferraro, Adriana; Braga, Erika M; Ricklefs, Robert E

    2012-07-01

    Arid zones of northern Venezuela are represented by isolated areas, important from an ornithological and ecological perspective due to the occurrence of restricted-range species of birds. We analysed the prevalence and molecular diversity of haemosporidian parasites of wild birds in this region by screening 527 individuals (11 families and 20 species) for parasite mitochondrial DNA. The overall prevalence of parasites was 41%, representing 17 mitochondrial lineages: 7 of Plasmodium and 10 of Haemoproteus. Two parasite lineages occurred in both the eastern and western regions infecting a single host species, Mimus gilvus. These lineages are also present throughout northern and central Venezuela in a variety of arid and mesic habitats. Some lineages found in this study in northern Venezuela have also been observed in different localities in the Americas, including the West Indies. In spite of the widespread distributions of some of the parasite lineages found in northern Venezuela, several, including some that are relatively common (e.g. Ven05 and Ven06), have not been reported from elsewhere. Additional studies are needed to characterize the host and geographical distribution of avian malaria parasite lineages, which will provide a better understanding of the influence of landscape, vector abundance and diversity, and host identity on haemosporidian parasite diversity and prevalence.

  1. Temporal variations of isotopes in arid rain storms

    International Nuclear Information System (INIS)

    Adar, E.M.; Dodi, A.; Geyh, M.A.; Yair, A.

    1999-01-01

    The distribution of isotopes in rainfall has long been used to elaborate on hydrological systems. Both isotopic composition of stable isotopes (oxygen-18 and deuterium) and tritium content are used to illuminate on sources of groundwater recharge and as tracers upon which groundwater fluxes are assessed. As runoff is concerned, stable isotopes have been used to identify flow paths and the precise location of the rain storm which produced the floods. Analyses of stable isotopes in arid storms in the Negev desert revealed clear discrepancy between the spatial isotopic composition in floods versus the spatial and temporal isotopic composition in rainfall. In addition, simple water balance revealed that the entire flood volume is equivalent to a very small portion of the rain storm, suggesting that a specific flood is produced by a very short and intensive portion of the rainfall. Therefore, knowledge of the weighted isotopic average of a rainfall can not serve as an adequate input function for modeling of desert floods. Since in arid environment, floods are considered as major source of groundwater recharge it also can not be used as input function for modeling of groundwater systems. This paper summarizes detailed isotopic study of short segments (∼2 mm each) of desert rainstorms as sampled in the Negev desert, Israel

  2. Aridity, desalination plants and tourism in the eastern Canary Islands

    Directory of Open Access Journals (Sweden)

    José-León García-Rodríguez

    2016-05-01

    Full Text Available The islands of Lanzarote and Fuerteventura are the easternmost of the Canary Islands, and are located on the southern edge of the temperate zone, in the subtropical anticyclone belt. With less than 150 mm of rainfall a year, they are classified as an arid zone. Their inhabitants have devised original agricultural systems to combat the aridity, although low yields have historically limited socio-economic development and population growth. These systems were used until the introduction of seawater desalination plants and the arrival of tourism in the last third of the twentieth century, which improved living standards for the local population but also led to a cultural transition. Nevertheless, these farming systems have left behind an important regional heritage, with an environmental and scenic value that has played an integral role in the latest phase of development. The systems have become a tourist attraction and have been central to the two islands being designated biosphere reserves by UNESCO. This article aims to analyse the main socioeconomic and land-use changes that have come about as a result of desalination technology.

  3. Isotope hydrology applied to evaluation of groundwater in arid areas

    International Nuclear Information System (INIS)

    Froehlich, K.; Geyh, M.A.; Verhagen, B.T.; Wirth, K.

    1987-01-01

    Capture of underground water in arid or semi-arid areas in developing countries is essential to safeguarding life. In order to realize in time, or to prevent, endangerment of exploitable groundwater resources due to pollution or excess exploitation, isotope hydrology offers low-cost methods that are applied along with other methods. Their results contribute to determine the origin, mixing, residence time (or age), and pollution of endangered groundwater resources. The research report in hand uses the results of hydrochemical analyses and isotope hydrological data from hydrogeological studies made over some years by the Bundesanstalt fuer Geowissenschaften und Rohstoffe in six selected countries: Jordan, Cyprus, Brazil, Sudan, Djibouti, Senegal. It also uses data of recent analyses of the years 1985 and 1986. Data evaluation is done applying modern, qualitative and quantitative methods of interpretation. The available long-term series of isotopic data are scanned for any early information on water quality deterioration that is not otherwise detected. The information thus obtained is a prerequisite of urgently needed measures for protecting the groundwater reserves. (orig./HP) [de

  4. Special Waste Form Lysimeters-Arid: annual report 1985

    International Nuclear Information System (INIS)

    Walter, M.B.; Graham, M.J.

    1986-01-01

    The Special Waste Form Lysimeters-Arid program was initiated to determine typical source terms generated by commercial solidified low-level nuclear waste in an arid climate. Waste-form leaching tests are being conducted at a field facility at the Hanford site near Richland, Washington. A similar program is being conducted at a humid site. The field facility consists of 10 lysimeters placed around a central instrument caisson. The waste samples from boiling water and pressurized water reactors were emplaced in 1984, and the lysimeters are being monitored for movement of contaminants and water. Solidifying agents being tested include vinyl ester-styrene, bitumen, and cement. Laboratory leaching and geochemical modeling studies are being conducted to predict expected leach rates at the field site and to aid field-data interpretation. Small samples of the solidified waste forms were made for use in the laboratory leaching studies that include standard leach tests and leaching of solidified waste forms in soil columns. Complete chemical and radionuclide analyses are being conducted on the solid and liquid portions of the wastes

  5. Study on Applicability of Conceptual Hydrological Models for Flood Forecasting in Humid, Semi-Humid Semi-Arid and Arid Basins in China

    Directory of Open Access Journals (Sweden)

    Guangyuan Kan

    2017-09-01

    Full Text Available Flood simulation and forecasting in various types of watersheds is a hot issue in hydrology. Conceptual hydrological models have been widely applied to flood forecasting for decades. With the development of economy, modern China faces with severe flood disasters in all types of watersheds include humid, semi-humid semi-arid and arid watersheds. However, conceptual model-based flood forecasting in semi-humid semi-arid and arid regions is still challenging. To investigate the applicability of conceptual hydrological models for flood forecasting in the above mentioned regions, three typical conceptual models, include Xinanjiang (XAJ, mix runoff generation (MIX and northern Shannxi (NS, are applied to 3 humid, 3 semi-humid semi-arid, and 3 arid watersheds. The rainfall-runoff data of the 9 watersheds are analyzed based on statistical analysis and information theory, and the model performances are compared and analyzed based on boxplots and scatter plots. It is observed the complexity of drier watershed data is higher than that of the wetter watersheds. This indicates the flood forecasting is harder in drier watersheds. Simulation results indicate all models perform satisfactorily in humid watersheds and only NS model is applicable in arid watersheds. Model with consideration of saturation excess runoff generation (XAJ and MIX perform better than the infiltration excess-based NS model in semi-humid semi-arid watersheds. It is concluded more accurate mix runoff generation theory, more stable and efficient numerical solution of infiltration equation and rainfall data with higher spatial-temporal resolution are main obstacles for conceptual model-based flood simulation and forecasting.

  6. Expanding the phenotypic spectrum of ARID1B-mediated disorders and identification of altered cell-cycle dynamics due to ARID1B haploinsufficiency

    DEFF Research Database (Denmark)

    Sim, J. C. H.; White, S. M.; Fitzpatrick, E.

    2014-01-01

    Background: Mutations in genes encoding components of the Brahma-associated factor (BAF) chromatin remodeling complex have recently been shown to contribute to multiple syndromes characterised by developmental delay and intellectual disability. ARID1B mutations have been identified as the predomi......Background: Mutations in genes encoding components of the Brahma-associated factor (BAF) chromatin remodeling complex have recently been shown to contribute to multiple syndromes characterised by developmental delay and intellectual disability. ARID1B mutations have been identified...

  7. Thermal conduction down steep temperature gradients

    International Nuclear Information System (INIS)

    Bell, A.R.; Evans, R.G.; Nicholas, D.J.

    1980-08-01

    The Fokker-Planck equation has been solved numerically in one spatial and two velocity dimensions in order to study thermal conduction in large temperature gradients. An initially cold plasma is heated at one end of the spatial grid producing temperature gradients with scale lengths of a few times the electron mean free path. The heat flow is an order of magnitude smaller than that predicted by the classical theory which is valid in the limit of small temperature gradients. (author)

  8. Testing the limits of gradient sensing.

    Directory of Open Access Journals (Sweden)

    Vinal Lakhani

    2017-02-01

    Full Text Available The ability to detect a chemical gradient is fundamental to many cellular processes. In multicellular organisms gradient sensing plays an important role in many physiological processes such as wound healing and development. Unicellular organisms use gradient sensing to move (chemotaxis or grow (chemotropism towards a favorable environment. Some cells are capable of detecting extremely shallow gradients, even in the presence of significant molecular-level noise. For example, yeast have been reported to detect pheromone gradients as shallow as 0.1 nM/μm. Noise reduction mechanisms, such as time-averaging and the internalization of pheromone molecules, have been proposed to explain how yeast cells filter fluctuations and detect shallow gradients. Here, we use a Particle-Based Reaction-Diffusion model of ligand-receptor dynamics to test the effectiveness of these mechanisms and to determine the limits of gradient sensing. In particular, we develop novel simulation methods for establishing chemical gradients that not only allow us to study gradient sensing under steady-state conditions, but also take into account transient effects as the gradient forms. Based on reported measurements of reaction rates, our results indicate neither time-averaging nor receptor endocytosis significantly improves the cell's accuracy in detecting gradients over time scales associated with the initiation of polarized growth. Additionally, our results demonstrate the physical barrier of the cell membrane sharpens chemical gradients across the cell. While our studies are motivated by the mating response of yeast, we believe our results and simulation methods will find applications in many different contexts.

  9. Competition amplifies drought stress in forests across broad climatic and compositional gradients

    Science.gov (United States)

    Gleason, Kelly; Bradford, John B.; Bottero, Alessandra; D'Amato, Tony; Fraver, Shawn; Palik, Brian J.; Battaglia, Michael; Iverson, Louis R.; Kenefic, Laura; Kern, Christel C.

    2017-01-01

    Forests around the world are experiencing increasingly severe droughts and elevated competitive intensity due to increased tree density. However, the influence of interactions between drought and competition on forest growth remains poorly understood. Using a unique dataset of stand-scale dendrochronology sampled from 6405 trees, we quantified how annual growth of entire tree populations responds to drought and competition in eight, long-term (multi-decadal), experiments with replicated levels of density (e.g., competitive intensity) arrayed across a broad climatic and compositional gradient. Forest growth (cumulative individual tree growth within a stand) declined during drought, especially during more severe drought in drier climates. Forest growth declines were exacerbated by high density at all sites but one, particularly during periods of more severe drought. Surprisingly, the influence of forest density was persistent overall, but these density impacts were greater in the humid sites than in more arid sites. Significant density impacts occurred during periods of more extreme drought, and during warmer temperatures in the semi-arid sites but during periods of cooler temperatures in the humid sites. Because competition has a consistent influence over growth response to drought, maintaining forests at lower density may enhance resilience to drought in all climates.

  10. Tree Growth Response to Drought Along a Depth to Groundwater Gradient in Northern Wisconsin

    Science.gov (United States)

    Ciruzzi, D. M.; Loheide, S. P., II

    2017-12-01

    Understanding complex spatial and temporal patterns of drought-induced forest stress requires knowledge of the physiological drivers and ecosystem attributes that lead to or inhibit tree mortality. Prevailing meteorological conditions leading to drought may have lesser effect on vegetation that has evolved to avoid drought by accessing deeper soil moisture reserves or shallow groundwater to meet evapotranspiration demand. This is especially true in arid and semi-arid regions, yet groundwater use by trees is rarely explored in temperate systems and the extent to which groundwater use reduces drought vulnerability in these climates and regions is unknown. We explored responses of radial growth in temperate tress to wet and dry years across a depth to groundwater gradient from 1 to 9 meters in sandy forests in northern Wisconsin. The spatial patterns of tree growth in this watershed show areas where tree growth is influenced by depth to groundwater. Preliminary results showed trees in areas of shallower groundwater with low variability in tree growth and indicated that tree growth remains consistent during both wet and dry years. Conversely, trees in areas of deeper groundwater showed higher variability in tree growth during wet and dry years. We hypothesize that even in this humid region, the sandy soils do not retain sufficient moisture leading to potentially frequent water stress in trees and reductions in productivity. However, where and when accessible, we suspect trees use shallow groundwater to sustain evapotranspiration and maintain consistent growth during dry periods.

  11. Gradient Flow Convolutive Blind Source Separation

    DEFF Research Database (Denmark)

    Pedersen, Michael Syskind; Nielsen, Chinton Møller

    2004-01-01

    Experiments have shown that the performance of instantaneous gradient flow beamforming by Cauwenberghs et al. is reduced significantly in reverberant conditions. By expanding the gradient flow principle to convolutive mixtures, separation in a reverberant environment is possible. By use...... of a circular four microphone array with a radius of 5 mm, and applying convolutive gradient flow instead of just applying instantaneous gradient flow, experimental results show an improvement of up to around 14 dB can be achieved for simulated impulse responses and up to around 10 dB for a hearing aid...

  12. On lower order strain gradient plasticity theories

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Hutchinson, J. W.

    2003-01-01

    By way of numerical examples, this paper explores the nature of solutions to a class of strain gradient plasticity theories that employ conventional stresses, equilibrium equations and boundary conditions. Strain gradients come into play in these modified conventional theories only to alter...... the tangent moduli governing increments of stress and strain. It is shown that the modification is far from benign from a mathematical standpoint, changing the qualitative character of solutions and leading to a new type of localization that is at odds with what is expected from a strain gradient theory....... The findings raise questions about the physical acceptability of this class of strain gradient theories....

  13. Community and ecosystem responses to elevational gradients

    DEFF Research Database (Denmark)

    Sundqvist, Maja K.; Sanders, Nate; Wardle, David A.

    2013-01-01

    Community structure and ecosystem processes often vary along elevational gradients. Their responses to elevation are commonly driven by changes in temperature, and many community- and ecosystem-level variables therefore frequently respond similarly to elevation across contrasting gradients...... elevational gradients for understanding community and ecosystem responses to global climate change at much larger spatial and temporal scales than is possible through conventional ecological experiments. However, future studies that integrate elevational gradient approaches with experimental manipulations...... will provide powerful information that can improve predictions of climate change impacts within and across ecosystems....

  14. STOCHASTIC GRADIENT METHODS FOR UNCONSTRAINED OPTIMIZATION

    Directory of Open Access Journals (Sweden)

    Nataša Krejić

    2014-12-01

    Full Text Available This papers presents an overview of gradient based methods for minimization of noisy functions. It is assumed that the objective functions is either given with error terms of stochastic nature or given as the mathematical expectation. Such problems arise in the context of simulation based optimization. The focus of this presentation is on the gradient based Stochastic Approximation and Sample Average Approximation methods. The concept of stochastic gradient approximation of the true gradient can be successfully extended to deterministic problems. Methods of this kind are presented for the data fitting and machine learning problems.

  15. Primary productivity as a control over soil microbial diversity along environmental gradients in a polar desert ecosystem

    Directory of Open Access Journals (Sweden)

    Kevin M. Geyer

    2017-07-01

    Full Text Available Primary production is the fundamental source of energy to foodwebs and ecosystems, and is thus an important constraint on soil communities. This coupling is particularly evident in polar terrestrial ecosystems where biological diversity and activity is tightly constrained by edaphic gradients of productivity (e.g., soil moisture, organic carbon availability and geochemical severity (e.g., pH, electrical conductivity. In the McMurdo Dry Valleys of Antarctica, environmental gradients determine numerous properties of soil communities and yet relatively few estimates of gross or net primary productivity (GPP, NPP exist for this region. Here we describe a survey utilizing pulse amplitude modulation (PAM fluorometry to estimate rates of GPP across a broad environmental gradient along with belowground microbial diversity and decomposition. PAM estimates of GPP ranged from an average of 0.27 μmol O2/m2/s in the most arid soils to an average of 6.97 μmol O2/m2/s in the most productive soils, the latter equivalent to 217 g C/m2/y in annual NPP assuming a 60 day growing season. A diversity index of four carbon-acquiring enzyme activities also increased with soil productivity, suggesting that the diversity of organic substrates in mesic environments may be an additional driver of microbial diversity. Overall, soil productivity was a stronger predictor of microbial diversity and enzymatic activity than any estimate of geochemical severity. These results highlight the fundamental role of environmental gradients to control community diversity and the dynamics of ecosystem-scale carbon pools in arid systems.

  16. Consistency between Sweat Rate and Wet Bulb Globe Temperature for the Assessment of Heat Stress of People Working Outdoor in Arid and Semi-arid Regions

    Directory of Open Access Journals (Sweden)

    Hamidreza Heidari

    2018-01-01

    Full Text Available Background: Heat stress is common among workers in arid and semi-arid areas. In order to take every preventive measure to protect exposed workers against heat-related disorders, it is crucial to choose an appropriate index that accurately relates environmental parameters to physiological responses. Objective: To investigate the consistency between 2 heat stress and strain indices, ie, sweat rate and wet bulb globe temperature (WBGT, for the assessment of heat stress of people working outdoor in arid and semi-arid regions in Iran. Methods: During spring and summer, 136 randomly selected outdoor workers were enrolled in this study. Using a defined protocol, the sweat rate of these workers was measured 3 times a day. Simultaneously, the environmental parameters including WBGT index were recorded for each working station. Results: The level of agreement between sweat rate and WBGT was poor (κ<0.2. Based on sweat rate, no case exceeding the reference value was observed during the study. WBGT overestimated the heat stress in outdoor workers compared to sweat rate. Conclusion: It seems that the sweat rate standards may need some modifications related to real condition of work in arid and semi-arid regions in Iran. Moreover, it seems that judging workers solely based on monitoring their sweat rate in such regions, can probably result in underestimation of heat stress.

  17. Evidence for micronutrient limitation of biological soil crusts: Importance to arid-lands restoration

    Science.gov (United States)

    Bowker, M.A.; Belnap, J.; Davidson, D.W.; Phillips, S.L.

    2005-01-01

    Desertification is a global problem, costly to national economies and human societies. Restoration of biological soil crusts (BSCs) may have an important role to play in the reversal of desertification due to their ability to decrease erosion and enhance soil fertility. To determine if there is evidence that lower fertility may hinder BSC recolonization, we investigated the hypothesis that BSC abundance is driven by soil nutrient concentrations. At a regional scale (north and central Colorado Plateau, USA), moss and lichen cover and richness are correlated with a complex water-nutrient availability gradient and have approximately six-fold higher cover and approximately two-fold higher species richness on sandy soils than on shale-derived soils. At a microscale, mosses and lichens are overrepresented in microhabitats under the north sides of shrub canopies, where water and nutrients are more available. At two spatial scales, and at the individual species and community levels, our data are consistent with the hypothesis that distributions of BSC organisms are determined largely by soil fertility. The micronutrients Mn and Zn figured prominently and consistently in the various analyses, strongly suggesting that these elements are previously unstudied limiting factors in BSC development. Structural-equation modeling of our data is most consistent with the hypothesis of causal relationships between the availability of micronutrients and the abundance of the two major nitrogen (N) fixers of BSCs. Specifically, higher Mn availability may determine greater Collema tenax abundance, and both Mn and Zn may limit Collema coccophorum; alternative causal hypotheses were less consistent with the data. We propose experimental trials of micronutrient addition to promote the restoration of BSC function on disturbed lands. Arid lands, where BSCs are most prevalent, cover ???40% of the terrestrial surface of the earth; thus the information gathered in this study is potentially useful

  18. Testing the assumptions of the pyrodiversity begets biodiversity hypothesis for termites in semi-arid Australia.

    Science.gov (United States)

    Davis, Hayley; Ritchie, Euan G; Avitabile, Sarah; Doherty, Tim; Nimmo, Dale G

    2018-04-01

    Fire shapes the composition and functioning of ecosystems globally. In many regions, fire is actively managed to create diverse patch mosaics of fire-ages under the assumption that a diversity of post-fire-age classes will provide a greater variety of habitats, thereby enabling species with differing habitat requirements to coexist, and enhancing species diversity (the pyrodiversity begets biodiversity hypothesis). However, studies provide mixed support for this hypothesis. Here, using termite communities in a semi-arid region of southeast Australia, we test four key assumptions of the pyrodiversity begets biodiversity hypothesis (i) that fire shapes vegetation structure over sufficient time frames to influence species' occurrence, (ii) that animal species are linked to resources that are themselves shaped by fire and that peak at different times since fire, (iii) that species' probability of occurrence or abundance peaks at varying times since fire and (iv) that providing a diversity of fire-ages increases species diversity at the landscape scale. Termite species and habitat elements were sampled in 100 sites across a range of fire-ages, nested within 20 landscapes chosen to represent a gradient of low to high pyrodiversity. We used regression modelling to explore relationships between termites, habitat and fire. Fire affected two habitat elements (coarse woody debris and the cover of woody vegetation) that were associated with the probability of occurrence of three termite species and overall species richness, thus supporting the first two assumptions of the pyrodiversity hypothesis. However, this did not result in those species or species richness being affected by fire history per se. Consequently, landscapes with a low diversity of fire histories had similar numbers of termite species as landscapes with high pyrodiversity. Our work suggests that encouraging a diversity of fire-ages for enhancing termite species richness in this study region is not necessary.

  19. Influence of Acacia trees on soil nutrient levels in arid lands

    Science.gov (United States)

    De Boever, Maarten; Gabriels, Donald; Ouessar, Mohamed; Cornelis, Wim

    2014-05-01

    The potential of scattered trees as keystone structures in restoring degraded environments is gaining importance. Scattered trees have strong influence on their abiotic environment, mainly causing changes in microclimate, water budget and soil properties. They often function as 'nursing trees', facilitating the recruitment of other plants. Acacia raddiana is such a keystone species which persists on the edge of the Sahara desert. The study was conducted in a forest-steppe ecosystem in central Tunisia where several reforestation campaigns with Acacia took place. To indentify the impact of those trees on soil nutrients, changes in nutrient levels under scattered trees of three age stages were examined for the upper soil layer (0-10 cm) at five microsites with increasing distance from the trunk. In addition, changes in soil nutrient levels with depth underneath and outside the canopy were determined for the 0-30 cm soil layer. Higher concentrations of organic matter (OM) were found along the gradient from underneath to outside the canopy for large trees compared to medium and small trees, especially at microsites close to the trunk. Levels of soluble K, electrical conductivity (EC), available P, OM, total C and N decreased whereas pH and levels of soluble Mg increased with increasing distance from tree. Levels of soluble Ca and Na remained unchanged along the gradient. At the microsite closest to the trunk a significant decrease in levels of soluble K, EC, OM, available P, total C and N, while a significant increase in pH was found with increasing depth. The concentration of other nutrients remained unchanged or declined not differently underneath compared to outside the canopy with increasing depth. Differences in nutrient levels were largely driven by greater inputs of organic matter under trees. Hence, Acacia trees can affect the productivity and reproduction of understory species with the latter in term an important source of organic matter. This positive feedback

  20. Identification of suitable sites for rainwater harvesting structures in arid and semi-arid regions: A review

    Directory of Open Access Journals (Sweden)

    Ammar Adham

    2016-06-01

    Full Text Available Harvested rainwater is an alternative source of water in arid and semi-arid regions (ASARs around the world. Many researchers have developed and applied various methodologies and criteria to identify suitable sites and techniques for rainwater harvesting (RWH. Determining the best method or guidelines for site selection, however, is difficult. The main objective of this study was to define a general method for selecting suitable RWH sites in ASARs by assembling an inventory of the main methods and criteria developed during the last three decades. We categorised and compared four main methodologies of site selection from 48 studies published in scientific journals, reports of international organisations, or sources of information obtained from practitioners. We then identified three main sets of criteria for selecting RWH locations and the main characteristics of the most common RWH techniques used in ASARs. The methods were diverse, ranging from those based only on biophysical criteria to more integrated approaches including socio-economic criteria, especially after 2000. The most important criteria for the selection of suitable sites for RWH were slope, land use/cover, soil type, rainfall, distance to settlements/streams, and cost. The success rate of RWH projects tended to increase when these criteria were considered, but an objective evaluation of these selection methods is still lacking. Most studies now select RHW sites using geographic information systems in combination with hydrological models and multi-criteria analysis.

  1. Do invasive riparian Tamarix alter hydrology of riparian areas of arid and semi-arid regions under climate change scenarios?

    Science.gov (United States)

    Bhattarai, M. P.; Acharya, K.; Chen, L.

    2012-12-01

    Competitiveness of riparian invasive species, Tamarix, in arid and semi-arid riparian areas of the southwestern United States under climate change scenario (SRES A2) was investigated. Tamarix has been replacing native vegetation along the riparian corridors of these areas for the past several decades and is thought to alter water balance. Changes in depth to groundwater, soil moisture distribution and flood frequency are critical in survival and growth of a facultative phreatophyte such as Tamarix. In this study, a fully coupled 2d surface flow and 3d subsurface flow hydrologic model, HydroGeoSphere, was used to simulate surface-subsurface hydrology of the lower Virgin River basin (4500 sq. km), located in Nevada, Utah and Arizona. The hydrologic model results, depth to groundwater and soil saturation, were then applied to the species distribution model, Maxent, along with other bioclimatic parameters to asses future Tamarix distribution probability. Simulations were made for the climate scenarios of the end of 21st centry conditions. Depth to groundwater is found to be the most important predictor variable to the Maxent model. Future Tamarix distribution range is not uniform across the basin. It is likely to decrease at lower elevations and increase in some higher elevation areas.

  2. Lake Area Changes and Their Influence on Factors in Arid and Semi-Arid Regions along the Silk Road

    Directory of Open Access Journals (Sweden)

    Chao Tan

    2018-04-01

    Full Text Available In the context of global warming, the changes in major lakes and their responses to the influence factors in arid and semi-arid regions along the Silk Road are especially important for the sustainable development of local water resources. In this study, the areas of 24 lakes were extracted using MODIS NDVI data, and their spatial-temporal characteristics were analyzed. In addition, the relationship between lake areas and the influence factors, including air temperature, precipitation, evapotranspiration, land use and land cover change (LULCC and population density in the watersheds, were investigated. The results indicated that the areas of most lakes shrank, and the total area decreased by 22,189.7 km2 from 2001 to 2016, except for those of the lakes located on the Qinghai-Tibetan Plateau. The air temperature was the most important factor for all the lakes and increased at a rate of 0.113 °C/a during the past 16 years. LULCC and the increasing population density markedly influenced the lakes located in the middle to western parts of this study area. Therefore, our results connecting lake area changes in the study region highlight the great challenge of water resources and the urgency of implementation of the green policy in the One Belt and One Road Initiative through international collaboration.

  3. Vegetation index anomaly response to varying lengths of drought across vegetation and climatic gradients in Hawaii

    Science.gov (United States)

    Lucas, M.; Miura, T.; Trauernicht, C.; Frazier, A. G.

    2017-12-01

    A drought which results in prolonged and extended deficit in naturally available water supply and creates multiple stresses across ecosystems is classified as an ecological drought. Detecting and understanding the dynamics and response of such droughts in tropical systems, specifically across various vegetation and climatic gradients is fairly undetermined, yet increasingly important for better understandings of the ecological effects of drought. To understanding the link between what lengths and intensities of known meteorological drought triggers detectable ecological vegetation responses, a landscape scale regression analysis evaluating the response (slope) and relationship strength (R-squared) of several cumulative SPI (standard precipitation index) lengths(1, 3, 6, 12, 18, 24, 36, 48, and 60 month), to various satellite derived monthly vegetation indices anomalies (NDVI, EVI, EVI2, and LSWI) was performed across a matrix of dominant vegetation covers (grassland, shrubland, and forest) and climatic moisture zones (arid, dry, mesic, and wet). The nine different SPI lags across these climactic and vegetation gradients was suggest that stronger relationships and steeper slopes were found in dryer climates (across all vegetation covers) and finer vegetation types (across all moisture zones). Overall NDVI, EVI and EVI2 showed the best utility in these dryer climatic zones across all vegetation types. Within arid and dry areas "best" fits showed increasing lengths of cumulative SPI were with increasing vegetation coarseness respectively. Overall these findings suggest that rainfall driven drought may have a stronger impact on the ecological condition of vegetation in water limited systems with finer vegetation types ecologically responding more rapidly to meteorological drought events than coarser woody vegetation systems. These results suggest that previously and newly documented trends of decreasing rainfall and increasing drought in Hawaiian drylands may have

  4. Gravity gradient preprocessing at the GOCE HPF

    Science.gov (United States)

    Bouman, J.; Rispens, S.; Gruber, T.; Schrama, E.; Visser, P.; Tscherning, C. C.; Veicherts, M.

    2009-04-01

    One of the products derived from the GOCE observations are the gravity gradients. These gravity gradients are provided in the Gradiometer Reference Frame (GRF) and are calibrated in-flight using satellite shaking and star sensor data. In order to use these gravity gradients for application in Earth sciences and gravity field analysis, additional pre-processing needs to be done, including corrections for temporal gravity field signals to isolate the static gravity field part, screening for outliers, calibration by comparison with existing external gravity field information and error assessment. The temporal gravity gradient corrections consist of tidal and non-tidal corrections. These are all generally below the gravity gradient error level, which is predicted to show a 1/f behaviour for low frequencies. In the outlier detection the 1/f error is compensated for by subtracting a local median from the data, while the data error is assessed using the median absolute deviation. The local median acts as a high-pass filter and it is robust as is the median absolute deviation. Three different methods have been implemented for the calibration of the gravity gradients. All three methods use a high-pass filter to compensate for the 1/f gravity gradient error. The baseline method uses state-of-the-art global gravity field models and the most accurate results are obtained if star sensor misalignments are estimated along with the calibration parameters. A second calibration method uses GOCE GPS data to estimate a low degree gravity field model as well as gravity gradient scale factors. Both methods allow to estimate gravity gradient scale factors down to the 10-3 level. The third calibration method uses high accurate terrestrial gravity data in selected regions to validate the gravity gradient scale factors, focussing on the measurement band. Gravity gradient scale factors may be estimated down to the 10-2 level with this method.

  5. Canonical trivialization of gravitational gradients

    International Nuclear Information System (INIS)

    Niedermaier, Max

    2017-01-01

    A one-parameter family of canonical transformations is constructed that reduces the Hamiltonian form of the Einstein–Hilbert action to its strong coupling limit where dynamical spatial gradients are absent. The parameter can alternatively be viewed as the overall scale of the spatial metric or as a fractional inverse power of Newton’s constant. The generating function of the canonical transformation is constructed iteratively as a powerseries in the parameter to all orders. The algorithm draws on Lie–Deprit transformation theory and defines a ‘trivialization map’ with several bonus properties: (i) Trivialization of the Hamiltonian constraint implies that of the action while the diffeomorphism constraint is automatically co-transformed. (ii) Only a set of ordinary differential equations needs to be solved to drive the iteration via a homological equation where no gauge fixing is required. (iii) In contrast to (the classical limit of) a Lagrangian trivialization map the algorithm also produces series solutions of the field equations. (iv) In the strong coupling theory temporal gauge variations are abelian, nevertheless the map intertwines with the respective gauge symmetries on the action, the field equations, and their solutions. (paper)

  6. Canonical trivialization of gravitational gradients

    Science.gov (United States)

    Niedermaier, Max

    2017-06-01

    A one-parameter family of canonical transformations is constructed that reduces the Hamiltonian form of the Einstein-Hilbert action to its strong coupling limit where dynamical spatial gradients are absent. The parameter can alternatively be viewed as the overall scale of the spatial metric or as a fractional inverse power of Newton’s constant. The generating function of the canonical transformation is constructed iteratively as a powerseries in the parameter to all orders. The algorithm draws on Lie-Deprit transformation theory and defines a ‘trivialization map’ with several bonus properties: (i) Trivialization of the Hamiltonian constraint implies that of the action while the diffeomorphism constraint is automatically co-transformed. (ii) Only a set of ordinary differential equations needs to be solved to drive the iteration via a homological equation where no gauge fixing is required. (iii) In contrast to (the classical limit of) a Lagrangian trivialization map the algorithm also produces series solutions of the field equations. (iv) In the strong coupling theory temporal gauge variations are abelian, nevertheless the map intertwines with the respective gauge symmetries on the action, the field equations, and their solutions.

  7. Rank gradient and p-gradient of amalgamated free products and HNN extensions

    OpenAIRE

    Pappas, Nathaniel

    2013-01-01

    We calculate the rank gradient and p-gradient of free products, free products with amalgamation over an amenable subgroup, and HNN extensions with an amenable associated subgroup. The notion of cost is used to compute the rank gradient of amalgamated free products and HNN extensions. For the p-gradient the Kurosh subgroup theorems for amalgamated free products and HNN extensions will be used.

  8. Preconditioning the modified conjugate gradient method ...

    African Journals Online (AJOL)

    In this paper, the convergence analysis of the conventional conjugate Gradient method was reviewed. And the convergence analysis of the modified conjugate Gradient method was analysed with our extension on preconditioning the algorithm. Convergence of the algorithm is a function of the condition number of M-1A.

  9. Structures and Strength of Gradient Nanostructures

    DEFF Research Database (Denmark)

    Hansen, Niels; Zhang, Xiaodan; Huang, Xiaoxu

    distance from the surface forming a gradient structure. In this study [2], by shot peening of a low carbon steel a gradient structure has been produced extending to about 1 mm below the surface. A number of strengthening mechanisms have been analyzed as a basis for a calculation of the stress and strain...

  10. On lower order strain gradient plasticity theories

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Hutchinson, J. W.

    2002-01-01

    By way of numerical examples, this paper explores the nature of solutions to a class of strain gradient plasticity theories that employ conventional stresses, equilibrium equations and boundary conditions. Strain gradients come into play in these modified conventional theories only to alter...

  11. Ultra-high gradient compact accelerator developments

    NARCIS (Netherlands)

    Brussaard, G.J.H.; Wiel, van der M.J.

    2004-01-01

    Continued development of relatively compact, although not quite 'table-top', lasers with peak powers in the range up to 100 TW has enabled laser-plasma-based acceleration experiments with amazing gradients of up to 1 TV/m. In order to usefully apply such gradients to 'controlled' acceleration,

  12. An Inexpensive Digital Gradient Controller for HPLC.

    Science.gov (United States)

    Brady, James E.; Carr, Peter W.

    1983-01-01

    Use of gradient elution techniques in high performance liquid chromatography (HPLC) is often essential for direct separation of complex mixtures. Since most commercial controllers have features that are of marginal value for instructional purposes, a low-cost controller capable of illustrating essential features of gradient elution was developed.…

  13. 40 CFR 230.25 - Salinity gradients.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 24 2010-07-01 2010-07-01 false Salinity gradients. 230.25 Section 230.25 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) OCEAN DUMPING SECTION 404(b... Physical and Chemical Characteristics of the Aquatic Ecosystem § 230.25 Salinity gradients. (a) Salinity...

  14. Microinstabilities in weak density gradient tokamak systems

    International Nuclear Information System (INIS)

    Tang, W.M.; Rewoldt, G.; Chen, L.

    1986-04-01

    A prominent characteristic of auxiliary-heated tokamak discharges which exhibit improved (''H-mode type'') confinement properties is that their density profiles tend to be much flatter over most of the plasma radius. Depsite this favorable trend, it is emphasized here that, even in the limit of zero density gradient, low-frequency microinstabilities can persist due to the nonzero temperature gradient

  15. Patterns of macromycete community assemblage along an elevation gradient: options for fungal gradient and metacommunity analyse

    Science.gov (United States)

    Marko Gómez-Hernández; Guadalupe Williams-Linera; Roger Guevara; D. Jean Lodge

    2012-01-01

    Gradient analysis is rarely used in studies of fungal communities. Data on macromycetes from eight sites along an elevation gradient in central Veracruz, Mexico, were used to demonstrate methods for gradient analysis that can be applied to studies of communities of fungi. Selected sites from 100 to 3,500 m altitude represent tropical dry forest, tropical montane cloud...

  16. Density Gradient Stabilization of Electron Temperature Gradient Driven Turbulence in a Spherical Tokamak

    International Nuclear Information System (INIS)

    Ren, Y.; Kaye, S.M.; Mazzucato, E.; Guttenfelder, W.; Bell, R.E.; Domier, C.W.; LeBlanc, B.P.; Lee, K.C.; Luhmann, N.C. Jr.; Smith, D.R.; Yuh, H.

    2011-01-01

    In this letter we report the first clear experimental observation of density gradient stabilization of electron temperature gradient driven turbulence in a fusion plasma. It is observed that longer wavelength modes, k (perpendicular) ρ s ∼< 10, are most stabilized by density gradient, and the stabilization is accompanied by about a factor of two decrease in the plasma effective thermal diffusivity.

  17. Dual fuel gradients in uranium silicide plates

    Energy Technology Data Exchange (ETDEWEB)

    Pace, B.W. [Babock and Wilcox, Lynchburg, VA (United States)

    1997-08-01

    Babcock & Wilcox has been able to achieve dual gradient plates with good repeatability in small lots of U{sub 3}Si{sub 2} plates. Improvements in homogeneity and other processing parameters and techniques have allowed the development of contoured fuel within the cladding. The most difficult obstacles to overcome have been the ability to evaluate the bidirectional fuel loadings in comparison to the perfect loading model and the different methods of instilling the gradients in the early compact stage. The overriding conclusion is that to control the contour of the fuel, a known relationship between the compact, the frames and final core gradient must exist. Therefore, further development in the creation and control of dual gradients in fuel plates will involve arriving at a plausible gradient requirement and building the correct model between the compact configuration and the final contoured loading requirements.

  18. Approximate error conjugation gradient minimization methods

    Science.gov (United States)

    Kallman, Jeffrey S

    2013-05-21

    In one embodiment, a method includes selecting a subset of rays from a set of all rays to use in an error calculation for a constrained conjugate gradient minimization problem, calculating an approximate error using the subset of rays, and calculating a minimum in a conjugate gradient direction based on the approximate error. In another embodiment, a system includes a processor for executing logic, logic for selecting a subset of rays from a set of all rays to use in an error calculation for a constrained conjugate gradient minimization problem, logic for calculating an approximate error using the subset of rays, and logic for calculating a minimum in a conjugate gradient direction based on the approximate error. In other embodiments, computer program products, methods, and systems are described capable of using approximate error in constrained conjugate gradient minimization problems.

  19. Protein gradient films of fibroin and gelatine.

    Science.gov (United States)

    Claussen, Kai U; Lintz, Eileen S; Giesa, Reiner; Schmidt, Hans-Werner; Scheibel, Thomas

    2013-10-01

    Gradients are a natural design principle in biological systems that are used to diminish stress concentration where materials of differing mechanical properties connect. An interesting example of a natural gradient material is byssus, which anchors mussels to rocks and other hard substrata. Building upon previous work with synthetic polymers and inspired by byssal threads, protein gradient films are cast using glycerine-plasticized gelatine and fibroin exhibiting a highly reproducible and smooth mechanical gradient, which encompasses a large range of modulus from 160 to 550 MPa. The reproducible production of biocompatible gradient films represents a first step towards medical applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Algae from the arid southwestern United States: an annotated bibliography

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, W.H.; Gaines, S.R.

    1983-06-01

    Desert algae are attractive biomass producers for capturing solar energy through photosynthesis of organic matter. They are probably capable of higher yields and efficiencies of light utilization than higher plants, and are already adapted to extremes of sunlight intensity, salinity and temperature such as are found in the desert. This report consists of an annotated bibliography of the literature on algae from the arid southwestern United States. It was prepared in anticipation of efforts to isolate desert algae and study their yields in the laboratory. These steps are necessary prior to setting up outdoor algal culture ponds. Desert areas are attractive for such applications because land, sunlight, and, to some extent, water resources are abundant there. References are sorted by state.

  1. Pipeline monitoring with interferometry in non-arid regions

    Energy Technology Data Exchange (ETDEWEB)

    McCardle, Adrian; Rabus, Bernhard; Ghuman, Parwant [MacDonald Dettwiler, Richmond, BC (Canada); Freymueller, Jeff T. [University of Alaska, Fairbanks (United States)

    2005-07-01

    Interferometry has become a proven technique for accurately measuring ground movements caused by subsidence, landslides, earthquakes and volcanoes. Using space borne sensors such as the ERS, ENVISAT and RADARSAT satellites, ground deformation can be monitored on a millimeter level. Traditionally interferometry has been limited to arid areas however new technology has allowed for successful monitoring in vegetated regions and areas of changing land-cover. Analysis of ground movement of the Trans-Alaskan pipeline demonstrates how these techniques can offer pipeline engineers a new tool for observing potential dangers to pipeline integrity. Results from Interferometric Point Target Analysis were compared with GPS measurements and speckle tracking interferometry was demonstrated to measure a major earthquake. (author)

  2. In situ bioventing in deep soils at arid sites

    International Nuclear Information System (INIS)

    Frishmuth, R.A.; Ratz, J.W.; Blicker, B.R.; Hall, J.F.; Downey, D.C.

    1995-01-01

    In situ bioventing has been shown to be a cost-effective remedial alternative for vadose zone soils. The success of the technology relies on the ability of indigenous soil microorganisms to utilize petroleum hydrocarbon contaminants as a primary metabolic substrate. Soil microbial populations are typically elevated in shallow soils due to an abundance of naturally occurring substrates and nutrients, but may be limited at greater depths due to a lack of these constituents. Therefore, the effectiveness of in situ bioventing is questionable in contaminated soil zones that extend far below the ground surface. Also, because the soil microbial population relies on soil moisture to sustain hydrocarbon degradation, the viability of bioventing is questionable in arid climates, where the soil moisture content is suspected to be minimal

  3. Analysing the mechanisms of soil water and vapour transport in the desert vadose zone of the extremely arid region of northern China

    Science.gov (United States)

    Du, Chaoyang; Yu, Jingjie; Wang, Ping; Zhang, Yichi

    2018-03-01

    The transport of water and vapour in the desert vadose zone plays a critical role in the overall water and energy balances of near-surface environments in arid regions. However, field measurements in extremely dry environments face many difficulties and challenges, so few studies have examined water and vapour transport processes in the desert vadose zone. The main objective of this study is to analyse the mechanisms of soil water and vapour transport in the desert vadose zone (depth of ∼350 cm) by using measured and modelled data in an extremely arid environment. The field experiments are implemented in an area of the Gobi desert in northwestern China to measure the soil properties, daily soil moisture and temperature, daily water-table depth and temperature, and daily meteorological records from DOYs (Days of Year) 114-212 in 2014 (growing season). The Hydrus-1D model, which simulates the coupled transport of water, vapour and heat in the vadose zone, is employed to simulate the layered soil moisture and temperature regimes and analyse the transport processes of soil water and vapour. The measured results show that the soil water and temperatures near the land surface have visible daily fluctuations across the entire soil profile. Thermal vapour movement is the most important component of the total water flux and the soil temperature gradient is the major driving factor that affects vapour transport in the desert vadose zone. The most active water and heat exchange occurs in the upper soil layer (depths of 0-25 cm). The matric potential change from the precipitation mainly re-draws the spatio-temporal distribution of the isothermal liquid water in the soil near the land surface. The matric potential has little effect on the isothermal vapour and thermal liquid water flux. These findings offer new insights into the liquid water and vapour movement processes in the extremely arid environment.

  4. Expanding the phenotypic spectrum of ARID1B-mediated disorders and identification of altered cell-cycle dynamics due to ARID1B haploinsufficiency.

    Science.gov (United States)

    Sim, Joe C H; White, Susan M; Fitzpatrick, Elizabeth; Wilson, Gabrielle R; Gillies, Greta; Pope, Kate; Mountford, Hayley S; Torring, Pernille M; McKee, Shane; Vulto-van Silfhout, Anneke T; Jhangiani, Shalini N; Muzny, Donna M; Leventer, Richard J; Delatycki, Martin B; Amor, David J; Lockhart, Paul J

    2014-03-27

    Mutations in genes encoding components of the Brahma-associated factor (BAF) chromatin remodeling complex have recently been shown to contribute to multiple syndromes characterised by developmental delay and intellectual disability. ARID1B mutations have been identified as the predominant cause of Coffin-Siris syndrome and have also been shown to be a frequent cause of nonsyndromic intellectual disability. Here, we investigate the molecular basis of a patient with an overlapping but distinctive phenotype of intellectual disability, plantar fat pads and facial dysmorphism. High density microarray analysis of the patient demonstrated a heterozygous deletion at 6q25.3, which resulted in the loss of four genes including AT Rich Interactive Domain 1B (ARID1B). Subsequent quantitative real-time PCR analysis revealed ARID1B haploinsufficiency in the patient. Analysis of both patient-derived and ARID1B knockdown fibroblasts after serum starvation demonstrated delayed cell cycle re-entry associated with reduced cell number in the S1 phase. Based on the patient's distinctive phenotype, we ascertained four additional patients and identified heterozygous de novo ARID1B frameshift or nonsense mutations in all of them. This study broadens the spectrum of ARID1B associated phenotypes by describing a distinctive phenotype including plantar fat pads but lacking the hypertrichosis or fifth nail hypoplasia associated with Coffin-Siris syndrome. We present the first direct evidence in patient-derived cells that alterations in cell cycle contribute to the underlying pathogenesis of syndromes associated with ARID1B haploinsufficiency.

  5. Diversity and activity of denitrifiers of Chilean arid soil ecosystems

    Directory of Open Access Journals (Sweden)

    Julieta eOrlando

    2012-04-01

    Full Text Available The Chilean sclerophyllous matorral is a Mediterranean semiarid ecosystem affected by erosion, with low soil fertility and limited by nitrogen. However, limitation of resources is even more severe for desert soils such as from the Atacama Desert, one of the most extreme arid deserts on Earth. Topsoil organic matter, nitrogen and moisture content were significantly higher in the semiarid soil compared to the desert soil. Although the most significant loss of biologically preferred nitrogen from terrestrial ecosystems occurs via denitrification, virtually nothing is known on the activity and composition of denitrifier communities thriving in arid soils. In this study, we explored denitrifier communities from two soils with profoundly distinct edaphic factors. While denitrification activity in the desert soil was below detection limit, the semiarid soil sustained denitrification activity. To elucidate the genetic potential of the soils to sustain denitrification processes we performed community analysis of denitrifiers based on nitrite reductase (nirK and nirS genes as functional marker genes for this physiological group. Presence of nirK-type denitrifiers in both soils was demonstrated but failure to amplify nirS from the desert soil suggests very low abundance of nirS-type denitrifiers shedding light on the lack of denitrification activity. Phylogenetic analysis showed a very low diversity of nirK with only three distinct genotypes in the desert soil which conditions presumably exert a high selection pressure. While nirK diversity was also limited to only few, albeit distinct genotypes, the semiarid matorral soil showed a surprisingly broad genetic variability of the nirS gene. The Chilean matorral is a shrub land plant community which form vegetational patches stabilizing the soil and increasing its nitrogen and carbon content. These islands of fertility may sustain the development and activity of the overall microbial community and of

  6. Designing of zero energy office buildings in hot arid climate

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Gwad, Mohamed

    2011-07-01

    The designing of office buildings by using large glass areas to have a transparent building is an attractive approach in the modern office building architecture. This attitude increases the energy demand for cooling specially in the hot arid region which has long sun duration time, while the use of small glazing areas increases the energy demand for lighting. The use of uncontrolled natural ventilation increases the rate of hot ambient air flow which increases the building energy demand for cooling. At the same time, the use of mechanical ventilation to control the air change rate may increase the energy demand for fans. Some ideas such as low energy design concept are introduced for improving the building energy performance and different rating systems have been developed such as LEED, BREEAM and DGNB for evaluating building energy performance system. One of the new ideas for decreasing the dependence on fossil fuels and improving the use of renewable energy is the net zero-energy building concept in which the building generates enough renewable energy on site to equal or exceed its annual energy use. This work depends on using the potentials of mixing different energy strategies such as hybrid ventilation strategy, passive night cooling, passive chilled ceiling side by side with the integrating of photovoltaic modules into the building facade to produce energy and enrich the architectural aesthetics and finally reaching the Net Zero Energy Building. There are different definitions for zero energy buildings, however in this work the use of building-integrated Photovoltaic (BIPV) to provide the building with its annual energy needs is adopted, in order to reach to a Grid-Connected Net-Zero Energy Office Building in the hot arid desert zone represented by Cairo, Egypt. (orig.)

  7. Ecotoxicology for risk assessment in arid zones: some key issues.

    Science.gov (United States)

    Everts, J W

    1997-01-01

    In the hot arid zones of the world, ecotoxicological research is in statu nascendi. In these zones, the major sources of contamination by toxicants are: (1) plant protection and vector control in wet zones; (2) large-scale crop protection campaigns in dry and ephemeral wet zones; (3) refuse and obsolete pesticides in dry zones; and (4) mining. Economic development in many of these zones requires an adequate knowledge of certain basic principles, i.e., where extrapolating existing knowledge does not apply. The vulnerability of ecosystems to contaminants is closely related to water flow. In dry areas, species are susceptible to factors that interfere with the ecophysiological properties regulating water loss. Most hot arid areas are found at low latitudes where temperatures show striking extremes both in time and space. Living organisms are physiologically resistant and/or show adaptive behavior to these temperature extremes. Very little is known about the effects of toxicants on these key resistant and adaptive functions, although by extrapolation a few assumptions can be made. The effects of hyperthermia, for instance, can be aggravated by GSH depleting substances, and the temporary disabling effects characteristic of many pesticides may prove fatal under these circumstances. Most wet areas show a spatial concentration of both human activity and wildlife. In mesic zones, the contamination of water represents a health risk to both humans and other living organisms. The vast majority of aquatic communities are those inhabiting temporary pools and streams. Their populations are characterized by short reproductive cycles and/or long dormant stages. Toxicants affecting growth in these areas have been shown to have a deleterious effect. In a synthesis of existing knowledge the most prominent gaps are identified and priorities for further research are made.

  8. Intermediate depth burial of classified transuranic wastes in arid alluvium

    International Nuclear Information System (INIS)

    Cochran, J.R.; Crowe, B.M.; Di Sanza, F.

    1999-01-01

    Intermediate depth disposal operations were conducted by the US Department of Energy (DOE) at the DOE's Nevada Test Site (NTS) from 1984 through 1989. These operations emplaced high-specific activity low-level wastes (LLW) and limited quantities of classified transuranic (TRU) wastes in 37 m (120-ft) deep, Greater Confinement Disposal (GCD) boreholes. The GCD boreholes are 3 m (10 ft) in diameter and founded in a thick sequence of arid alluvium. The bottom 15 m (50 ft) of each borehole was used for waste emplacement and the upper 21 m (70 ft) was backfilled with native alluvium. The bottom of each GCD borehole is almost 200 m (650 ft) above the water table. The GCD boreholes are located in one of the most arid portions of the US, with an average precipitation of 13 cm (5 inches) per year. The limited precipitation, coupled with generally warm temperatures and low humidities results in a hydrologic system dominated by evapotranspiration. The US Environmental Protection Agency's (EPA's) 40 CFR 191 defines the requirements for protection of human health from disposed TRU wastes. This EPA standard sets a number of requirements, including probabilistic limits on the cumulative releases of radionuclides to the accessible environment for 10,000 years. The DOE Nevada Operations Office (DOE/NV) has contracted with Sandia National Laboratories (Sandia) to conduct a performance assessment (PA) to determine if the TRU wastes emplaced in the GCD boreholes complies with the EPA's 40 CFR 191 requirements. This paper describes DOE's actions undertaken to evaluate whether the TRU wastes in the GCD boreholes will, or will not, endanger human health. Based on preliminary modeling, the TRU wastes in the GCD boreholes meet the EPA's requirements, and are, therefore, protective of human health

  9. Diversity and activity of denitrifiers of chilean arid soil ecosystems.

    Science.gov (United States)

    Orlando, Julieta; Carú, Margarita; Pommerenke, Bianca; Braker, Gesche

    2012-01-01

    The Chilean sclerophyllous matorral is a Mediterranean semiarid ecosystem affected by erosion, with low soil fertility, and limited by nitrogen. However, limitation of resources is even more severe for desert soils such as from the Atacama Desert, one of the most extreme arid deserts on Earth. Topsoil organic matter, nitrogen and moisture content were significantly higher in the semiarid soil compared to the desert soil. Although the most significant loss of biologically preferred nitrogen from terrestrial ecosystems occurs via denitrification, virtually nothing is known on the activity and composition of denitrifier communities thriving in arid soils. In this study we explored denitrifier communities from two soils with profoundly distinct edaphic factors. While denitrification activity in the desert soil was below detection limit, the semiarid soil sustained denitrification activity. To elucidate the genetic potential of the soils to sustain denitrification processes we performed community analysis of denitrifiers based on nitrite reductase (nirK and nirS) genes as functional marker genes for this physiological group. Presence of nirK-type denitrifiers in both soils was demonstrated but failure to amplify nirS from the desert soil suggests very low abundance of nirS-type denitrifiers shedding light on the lack of denitrification activity. Phylogenetic analysis showed a very low diversity of nirK with only three distinct genotypes in the desert soil which conditions presumably exert a high selection pressure. While nirK diversity was also limited to only few, albeit distinct genotypes, the semiarid matorral soil showed a surprisingly broad genetic variability of the nirS gene. The Chilean matorral is a shrub land plant community which form vegetational patches stabilizing the soil and increasing its nitrogen and carbon content. These islands of fertility may sustain the development and activity of the overall microbial community and of denitrifiers in particular.

  10. A novel microduplication of ARID1B: Clinical, genetic, and proteomic findings.

    Science.gov (United States)

    Seabra, Catarina M; Szoko, Nicholas; Erdin, Serkan; Ragavendran, Ashok; Stortchevoi, Alexei; Maciel, Patrícia; Lundberg, Kathleen; Schlatzer, Daniela; Smith, Janice; Talkowski, Michael E; Gusella, James F; Natowicz, Marvin R

    2017-09-01

    Genetic alterations of ARID1B have been recently recognized as one of the most common mendelian causes of intellectual disability and are associated with both syndromic and non-syndromic phenotypes. The ARID1B protein, a subunit of the chromatin remodeling complex SWI/SNF-A, is involved in the regulation of transcription and multiple downstream cellular processes. We report here the clinical, genetic, and proteomic phenotypes of an individual with a unique apparent de novo mutation of ARID1B due to an intragenic duplication. His neurodevelopmental phenotype includes a severe speech/language disorder with full scale IQ scores 78-98 and scattered academic skill levels, expanding the phenotypic spectrum of ARID1B mutations. Haploinsufficiency of ARID1B was determined both by RNA sequencing and quantitative RT-PCR. Fluorescence in situ hybridization analysis supported an intragenic localization of the ARID1B copy number gain. Principal component analysis revealed marked differentiation of the subject's lymphoblast proteome from that of controls. Of 3426 proteins quantified, 1014 were significantly up- or down-regulated compared to controls (q constitutional haploinsufficiency of ARID1B causes syndromic and non-syndromic developmental disabilities. © 2017 Wiley Periodicals, Inc.

  11. Evolution of Asian Interior Arid-Zone Biota: Evidence from the Diversification of Asian Zygophyllum (Zygophyllaceae)

    Science.gov (United States)

    Li, Hong-Lei; Yu, Sheng-Xiang; Zhang, Lin-Jing; Wang, Wei

    2015-01-01

    The Asian interior arid zone is the largest desert landform system in the Northern Hemisphere, and has high biodiversity. Little is currently known about the evolutionary history of its biota. In this study, we used Zygophyllum, an important and characteristic component of the Asian interior arid zone, to provide new insights into the evolution of this biota. By greatly enlarged taxon sampling, we present the phylogenetic analysis of Asian Zygophyllum based on two plastid and one nuclear markers. Our phylogenetic analyses indicate that Asian Zygophyllum and Sarcozygium form a clade and Sarcozygium is further embedded within the shrub subclade. An integration of phylogenetic, biogeographic, and molecular dating methods indicates that Zygophyllum successfully colonized the Asian interior from Africa in the early Oligocene, and Asian Zygophyllum became differentiated in the early Miocene and underwent a burst of diversification in the late Miocene associated with the expansion of Asian interior arid lands due to orogenetic and climatic changes. Combining diversification patterns of other important components of the Asian interior arid zone, we propose a multi-stage evolution model for this biota: the late Eocene–early Oligocene origin, the early Miocene expansion, and the middle-late Miocene rapid expansion to the whole Asian interior arid zone. This study also demonstrates that, for Zygophyllum and perhaps other arid-adapted organisms, arid biomes are evolutionary cradles of diversity. PMID:26393796

  12. Tropical Warm Semi-Arid Regions Expanding Over Temperate Latitudes In The Projected 21st Century

    Science.gov (United States)

    Rajaud, A.; de Noblet, N. I.

    2015-12-01

    Two billion people today live in drylands, where extreme climatic conditions prevail, and natural resources are limited. Drylands are expected to expand under several scenarios of climatic change. However, relevant adaptation strategies need to account for the aridity level: it conditions the equilibrium tree-cover density, ranging from deserts (hyper-arid) to dense savannas (sub-humid). Here we focus on the evolution of climatically defined warm semi-arid areas, where low-tree density covers can be maintained. We study the global repartition of these regions in the future and the bioclimatic shifts involved. We adopted a bioclimatological approach based on the Köppen climate classification. The warm semi-arid class is characterized by mean annual temperatures over 18°C and a rainfall-limitation criterion. A multi-model ensemble of CMIP5 projections for three representative concentration pathways was selected to analyze future conditions. The classification was first applied to the start, middle and end of the 20th and 21st centuries, in order to localize past and future warm semi-arid regions. Then, time-series for the classification were built to characterize trends and variability in the evolution of those regions. According to the CRU datasets, global expansion of the warm semi-arid area has already started (~+13%), following the global warming trend since the 1900s. This will continue according to all projections, most significantly so outside the tropical belt. Under the "business as usual" scenario, the global warm semi-arid area will increase by 30% and expand 12° poleward in the Northern Hemisphere, according to the multi-model mean. Drying drives the conversion from equatorial sub-humid conditions. Beyond 30° of latitude, cold semi-arid conditions become warm semi-arid through warming, and temperate conditions through combined warming and drying processes. Those various transitions may have drastic but also very distinct ecological and sociological

  13. Changes in the forest ecosystems in areas impacted by aridization in south-western Romania.

    Science.gov (United States)

    Pravalie, Remus; Sîrodoev, Igor; Peptenatu, Daniel

    2014-01-06

    In the past few decades, global climate change has accentuated the intensification of aridization in South-Western Romania, with direct and indirect consequences on the quality of forest ecosystems. In addition to qualitative deterioration, the quantitative changes brought about by intensive anthropic deforestation have created the conditions for a decline in the size of forest areas on vast tracts of land. The paper aims to analyze the qualitative and quantitative changes in the forest ecosystems in South-Western Romania, changes due to the synergic context of the global climate changes and the anthropic pressures of the past three decades. In order to capture the evolution of aridization in the study area, specific aridization indexes have been calculated, such as the De Martonne index and the UNEP aridity index. 1990 and 2011 satellite images have been used in order to quantify the qualitative changes. The results obtained indicated that, in the past two decades, the quality of the biomass declined as a result of the increase in the climatic aridity conditions (De Martonne si UNEP aridity index, indicating in the last decades, annual values under 15 mm/°C, and under 0.5 mm/mm, that means that the values situated under these thresholds, describe arid and semi-arid climate conditions). Also, the uncontrolled logging across vast surfaces caused the loss of forest ecosystems by 7% in the overall study area, during the last three decades. The severe effects of aridization meant, first of all, a significant decline in the quality of the ecosystem services supplied by forests. In the absence of viable actions to correct the present situation, the extremely undesirable consequences of an ecological and social nature will arise in the near future.

  14. Foliar δ13C Showed No Altitudinal Trend in an Arid Region and Atmospheric Pressure Exerted a Negative Effect on Plant δ13C

    Directory of Open Access Journals (Sweden)

    Zixun Chen

    2017-07-01

    Full Text Available Previous studies have suggested foliar δ13C generally increases with altitude. However, some observations reported no changes or even decreased trends in foliar δ13C. We noted that all the studies in which δ13C increased with elevation were conducted in the human regions, whereas those investigations in which δ13C did not vary or decreased were conducted in areas with water stress. Thus, we proposed that the pattern of increasing δ13C with elevation is not a general one, and that δ13C may remain unchanged or decrease in plants grown in arid environments. To test the hypothesis, we sampled plants along altitude gradients on the shady and sunny slopes of Mount Tianshan characterized by arid and semiarid climates. The measurements of foliar δ13C showed no altitudinal trends for the plants grown on either of the slopes. Therefore, this study supported our hypothesis. In addition, the present study addressed the effect of atmospheric pressure on plant δ13C by accounting for the effects of temperature and precipitation on δ13C. This study found that the residual foliar δ13C increased with increasing altitude, suggesting that atmospheric pressure played a negative role in foliar δ13C.

  15. Gradient pre-emphasis to counteract first-order concomitant fields on asymmetric MRI gradient systems.

    Science.gov (United States)

    Tao, Shengzhen; Weavers, Paul T; Trzasko, Joshua D; Shu, Yunhong; Huston, John; Lee, Seung-Kyun; Frigo, Louis M; Bernstein, Matt A

    2017-06-01

    To develop a gradient pre-emphasis scheme that prospectively counteracts the effects of the first-order concomitant fields for any arbitrary gradient waveform played on asymmetric gradient systems, and to demonstrate the effectiveness of this approach using a real-time implementation on a compact gradient system. After reviewing the first-order concomitant fields that are present on asymmetric gradients, we developed a generalized gradient pre-emphasis model assuming arbitrary gradient waveforms to counteract their effects. A numerically straightforward, easily implemented approximate solution to this pre-emphasis problem was derived that was compatible with the current hardware infrastructure of conventional MRI scanners for eddy current compensation. The proposed method was implemented on the gradient driver subsystem, and its real-time use was tested using a series of phantom and in vivo data acquired from two-dimensional Cartesian phase-difference, echo-planar imaging, and spiral acquisitions. The phantom and in vivo results demonstrated that unless accounted for, first-order concomitant fields introduce considerable phase estimation error into the measured data and result in images with spatially dependent blurring/distortion. The resulting artifacts were effectively prevented using the proposed gradient pre-emphasis. We have developed an efficient and effective gradient pre-emphasis framework to counteract the effects of first-order concomitant fields of asymmetric gradient systems. Magn Reson Med 77:2250-2262, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  16. Intracellular chemical gradients: morphing principle in bacteria

    Directory of Open Access Journals (Sweden)

    Endres Robert G

    2012-09-01

    Full Text Available Abstract Advances in computational biology allow systematic investigations to ascertain whether internal chemical gradients can be maintained in bacteria – an open question at the resolution limit of fluorescence microscopy. While it was previously believed that the small bacterial cell size and fast diffusion in the cytoplasm effectively remove any such gradient, a new computational study published in BMC Biophysics supports the emerging view that gradients can exist. The study arose from the recent observation that phosphorylated CtrA forms a gradient prior to cell division in Caulobacter crescentus, a bacterium known for its complicated cell cycle. Tropini et al. (2012 postulate that such gradients can provide an internal chemical compass, directing protein localization, cell division and cell development. More specifically, they describe biochemical and physical constraints on the formation of such gradients and explore a number of existing bacterial cell morphologies. These chemical gradients may limit in vitro analyses, and may ensure timing control and robustness to fluctuations during critical stages in cell development.

  17. Ecotoxicology of organisms adapted to life in temporary freshwater ponds in arid and semi-arid regions.

    Science.gov (United States)

    Lahr, J

    1997-01-01

    Hot arid and semi-arid zones are characterized by an abundance of temporary ponds. Most of these depend on rain for their existence. These habitats are distinguished by fluctuating and unpredictable changes in their hydrological regime and of physical and chemical conditions.They contain a uniquely-adapted fauna that copes in different ways with changing and often extreme temperatures, oxygen levels, pH, salinity and turbidity. A classification is presented of the most distinctive adaptations,the various tactics that organisms apply to survive dry periods. The main strategies are dormancy (escape in time) and dispersal (escape in space). These adaptations may affect the impact of toxicants on individuals, populations and communities of temporary ponds. The physiological adaptations of species found in temporary ponds are likely to alter the sensitivity to pollutants of characteristic species. Results from laboratory experiments,for example, suggest that fairy shrimp (Branchiopoda, Anostraca) may react differently to heavy metals and pesticides as the standard test species Daphnia. Life history strategies influence recovery rates of populations after exposure to acutely toxic substances such as pesticides. It is also suggested that slow growth and decreased reproductive capacity of organisms caused by toxicants may, in ephemeral ponds, result in the failure of annual recruitment. Whether assemblages of organisms in temporary ponds are generally more vulnerable or more resilient than those in permanent waters or temperate regions could not be determined conclusively with the limited data available. Ecological concepts for studying the habitat and the development of risk assessment methods for temporary ponds are briefly discussed.

  18. Sound beam manipulation based on temperature gradients

    Energy Technology Data Exchange (ETDEWEB)

    Qian, Feng [Key Laboratory of Modern Acoustics, Institute of Acoustics and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China); School of Physics & Electronic Engineering, Changshu Institute of Technology, Changshu 215500 (China); Quan, Li; Liu, Xiaozhou, E-mail: xzliu@nju.edu.cn; Gong, Xiufen [Key Laboratory of Modern Acoustics, Institute of Acoustics and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China)

    2015-10-28

    Previous research with temperature gradients has shown the feasibility of controlling airborne sound propagation. Here, we present a temperature gradients based airborne sound manipulation schemes: a cylindrical acoustic omnidirectional absorber (AOA). The proposed AOA has high absorption performance which can almost completely absorb the incident wave. Geometric acoustics is used to obtain the refractive index distributions with different radii, which is then utilized to deduce the desired temperature gradients. Since resonant units are not applied in the scheme, its working bandwidth is expected to be broadband. The scheme is temperature-tuned and easy to realize, which is of potential interest to fields such as noise control or acoustic cloaking.

  19. Modelling hydrological connectivity in semi-arid flat areas: effect of the flow accumulation algorithm on the spatial pattern

    Science.gov (United States)

    López-Vicente, Manuel; Álvarez, Sara

    2017-04-01

    Much of the water and sediment fluxes in semi-arid landscapes are found to be concentrated in localized pathways. Identifying the location of these pathways is important for management and restoration. This task becomes more complicated in flat areas, such as alluvial terraces, where geomorphic features of concentrated overland flow (rills and ephemeral gullies) are scarce or inexistent. Field identification of sediment delivery pathways as well as depositional areas is also difficult and challenged. The concept of hydrological connectivity (HC) helps us to express the complexity of landscape non-linear responses to rainfall inputs. One of the unsolved issues in overland flow modelling studies is the choice of the right flow accumulation algorithm (FAA). There is an abundant literature on runoff generation under semi-arid conditions, and relating HC and land use management and changes. However, we found a scientific gap in the literature focussed on modelling of HC in flat areas under semi-arid conditions. This study aims to fill in this gap by modelling HC in alluvial terraces (28 ha) in NE Spain under semi-arid conditions (342 mm / year), mainly devoted to rain-fed cereal fields, by using eight FAA. For this purpose, we applied a modified version of the Borselli's index of runoff and sediment connectivity (IC). The study area includes seven fields on flat alluvial terraces, three fields on a gentle slope, small patches of scrubland, and twelve grass buffer strips that are located between each set of fields. Gentle and flat areas (S drone (model eBee by senseFly Ltd.). In order to minimize the effect of the vegetation on the photogrammetry restitution technique, pictures were taken in early spring, before the growth of the cereals. Then, several DEMs were generated independently. For this study, we chose the DEM at 0.5 x 0.5 m of spatial resolution. Before running the IC model, the continuity of the flow path lines throughout the landscape was ensured by removing

  20. Applying an Avian Index of Biological Integrity to Assess and Monitor Arid and Semi-arid Riparian Ecosystems

    Science.gov (United States)

    2009-01-01

    e.g., foraging or reproduction behavior). Measurement of the IHD. The purpose of the IHD is to establish a gradient of human disturbance that may...sparverius Resident Insectivore Ground Hawk PIF 2A Non-Dependent Native Cavity Domestic Peacock Pavo cristatus Resident Granivore Ground Captive

  1. Observations of the atmospheric boundary layer height over Abu Dhabi, United Arab Emirates: Investigating boundary layer climatology in arid regions

    Science.gov (United States)

    Marzooqi, Mohamed Al; Basha, Ghouse; Ouarda, Taha B. M. J.; Armstrong, Peter; Molini, Annalisa

    2014-05-01

    Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature in the boundary layer over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main features however, desert ABLs present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as the transport of dust and pollutants, and turbulent fluxes of momentum, heat and water vapor in hyper-arid regions. In this study, we analyze a continuous record of observations of the atmospheric boundary layer (ABL) height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4oN, 54.6o E, Abu Dhabi, United Arab Emirates), starting March 2013. We compare different methods for the estimation of the ABL height from Ceilometer data such as, classic variance-, gradient-, log gradient- and second derivation-methods as well as recently developed techniques such as the Bayesian Method and Wavelet covariance transform. Our goal is to select the most suited technique for describing the climatology of the ABL in desert environments. Comparison of our results with radiosonde observations collected at the nearby airport of Abu Dhabi indicate that the WCT and the Bayesian method are the most suitable tools to accurately identify the ABL height in all weather conditions. These two methods are used for the definition of diurnal and seasonal climatologies of the boundary layer conditional to different atmospheric stability classes.

  2. Unimodal and crossmodal gradients of spatial attention

    DEFF Research Database (Denmark)

    Föcker, J.; Hötting, K.; Gondan, Matthias

    2010-01-01

    Behavioral and event-related potential (ERP) studies have shown that spatial attention is gradually distributed around the center of the attentional focus. The present study compared uni- and crossmodal gradients of spatial attention to investigate whether the orienting of auditory and visual...... spatial attention is based on modality specific or supramodal representations of space. Auditory and visual stimuli were presented from five speaker locations positioned in the right hemifield. Participants had to attend to the innermost or outmost right position in order to detect either visual...... or auditory deviant stimuli. Detection rates and event-related potentials (ERPs) indicated that spatial attention is distributed as a gradient. Unimodal spatial ERP gradients correlated with the spatial resolution of the modality. Crossmodal spatial gradients were always broader than the corresponding...

  3. Full Gradient Solution to Adaptive Hybrid Control

    Science.gov (United States)

    Bean, Jacob; Schiller, Noah H.; Fuller, Chris

    2017-01-01

    This paper focuses on the adaptation mechanisms in adaptive hybrid controllers. Most adaptive hybrid controllers update two filters individually according to the filtered reference least mean squares (FxLMS) algorithm. Because this algorithm was derived for feedforward control, it does not take into account the presence of a feedback loop in the gradient calculation. This paper provides a derivation of the proper weight vector gradient for hybrid (or feedback) controllers that takes into account the presence of feedback. In this formulation, a single weight vector is updated rather than two individually. An internal model structure is assumed for the feedback part of the controller. The full gradient is equivalent to that used in the standard FxLMS algorithm with the addition of a recursive term that is a function of the modeling error. Some simulations are provided to highlight the advantages of using the full gradient in the weight vector update rather than the approximation.

  4. Continuous spray forming of functionally gradient materials

    International Nuclear Information System (INIS)

    McKechnie, T.N.; Richardson, E.H.

    1995-01-01

    Researchers at Plasma Processes Inc. have produced a Functional Gradient Material (FGM) through advanced vacuum plasma spray processing for high heat flux applications. Outlined in this paper are the manufacturing methods used to develop a four component functional gradient material of copper, tungsten, boron, and boron nitride. The FGM was formed with continuous gradients and integral cooling channels eliminating bondlines and providing direct heat transfer from the high temperature exposed surface to a cooling medium. Metallurgical and x-ray diffraction analyses of the materials formed through innovative VPS (vacuum plasma spray) processing are also presented. Applications for this functional gradient structural material range from fusion reactor plasma facing components to missile nose cones to boilers

  5. Vegetation patterns and environmental gradients in Benin

    NARCIS (Netherlands)

    Adomou, A.

    2005-01-01

    Key words: West Africa, Benin, vegetation patterns, floristic areas, phytogeography, chorology, floristic gradients, climatic factors, water availability, Dahomey Gap, threatened plants, biodiversity, conservation.Understanding plant species distribution patterns and the underlying factors is a

  6. Coreless Concept for High Gradient Induction Cell

    International Nuclear Information System (INIS)

    Krasnykh, Anatoly

    2008-01-01

    An induction linac cell for a high gradient is discussed. The proposed solid state coreless approach for the induction linac topology (SLIM(reg s ign)) is based on nanosecond mode operation. This mode may have an acceleration gradient comparable with gradients of rf- accelerator structures. The discussed induction system has the high electric efficiency. The key elements are a solid state semiconductor switch and a high electric density dielectric with a thin section length. The energy in the induction system is storied in the magnetic field. The nanosecond current break-up produces the high voltage. The induced voltage is used for acceleration. This manner of an operation allows the use of low voltage elements in the booster part and achieves a high accelerating gradient. The proposed topology was tested in POP (proof of principle) experiments

  7. Flexoelectricity: strain gradient effects in ferroelectrics

    Energy Technology Data Exchange (ETDEWEB)

    Ma Wenhui [Department of Physics, Shantou Unversity, Shantou, Guangdong 515063 (China)

    2007-12-15

    Mechanical strain gradient induced polarization effect or flexoelectricity in perovskite-type ferroelectric and relaxor ferroelectric ceramics was investigated. The flexoelectric coefficients measured at room temperature ranged from about 1 {mu} C m{sup -1} for lead zirconate titanate to 100 {mu} C m{sup -1} for barium strontium titanate. Flexoelectric effects were discovered to be sensitive to chemical makeup, phase symmetry, and domain structures. Based on phenomenological discussion and experimental data on flexoelectricity, the present study proposed that mechanical strain gradient field could influence polarization responses in a way analogous to electric field. Flexoelectric coefficients were found to be nonlinearly enhanced by dielectric permittivity and strain gradient. Interfacial mismatch in epitaxial thin films can give rise to high strain gradients, enabling flexoelectric effects to make a significant impact in properly engineered ferroelectric heterostructure systems.

  8. On fracture in finite strain gradient plasticity

    DEFF Research Database (Denmark)

    Martínez Pañeda, Emilio; Niordson, Christian Frithiof

    2016-01-01

    In this work a general framework for damage and fracture assessment including the effect of strain gradients is provided. Both mechanism-based and phenomenological strain gradient plasticity (SGP) theories are implemented numerically using finite deformation theory and crack tip fields are invest......In this work a general framework for damage and fracture assessment including the effect of strain gradients is provided. Both mechanism-based and phenomenological strain gradient plasticity (SGP) theories are implemented numerically using finite deformation theory and crack tip fields...... are investigated. Differences and similarities between the two approaches within continuum SGP modeling are highlighted and discussed. Local strain hardening promoted by geometrically necessary dislocations (GNDs) in the vicinity of the crack leads to much higher stresses, relative to classical plasticity...... in the multiple parameter version of the phenomenological SGP theory. Since this also dominates the mechanics of indentation testing, results suggest that length parameters characteristic of mode I fracture should be inferred from nanoindentation....

  9. TEK twisted gradient flow running coupling

    CERN Document Server

    Pérez, Margarita García; Keegan, Liam; Okawa, Masanori

    2014-01-01

    We measure the running of the twisted gradient flow coupling in the Twisted Eguchi-Kawai (TEK) model, the SU(N) gauge theory on a single site lattice with twisted boundary conditions in the large N limit.

  10. Integral Field Spectroscopy Surveys: Oxygen Abundance Gradients

    Science.gov (United States)

    Sánchez, S. F.; Sánchez-Menguiano, L.

    2017-07-01

    We present here the recent results on our understanding of oxygen abundance gradients derived using Integral Field Spectroscopic surveys. In particular we analyzed more than 2124 datacubes corresponding to individual objects observed by the CALIFA (˜ 734 objects) and the public data by MaNGA (˜ 1390 objects), deriving the oxygen abundance gradient for each galaxy. We confirm previous results that indicate that the shape of this gradient is very similar for all galaxies with masses above 109.5M⊙, presenting in average a very similar slope of ˜ -0.04 dex within 0.5-2.0 re, with a possible drop in the inner regions (r109.5M⊙) the gradient seems to be flatter than for more massive ones. All these results agree with an inside-out growth of massive galaxies and indicate that low mass ones may still be growing in an outside in phase.

  11. Stability of gradient semigroups under perturbations

    Science.gov (United States)

    Aragão-Costa, E. R.; Caraballo, T.; Carvalho, A. N.; Langa, J. A.

    2011-07-01

    In this paper we prove that gradient-like semigroups (in the sense of Carvalho and Langa (2009 J. Diff. Eqns 246 2646-68)) are gradient semigroups (possess a Lyapunov function). This is primarily done to provide conditions under which gradient semigroups, in a general metric space, are stable under perturbation exploiting the known fact (see Carvalho and Langa (2009 J. Diff. Eqns 246 2646-68)) that gradient-like semigroups are stable under perturbation. The results presented here were motivated by the work carried out in Conley (1978 Isolated Invariant Sets and the Morse Index (CBMS Regional Conference Series in Mathematics vol 38) (RI: American Mathematical Society Providence)) for groups in compact metric spaces (see also Rybakowski (1987 The Homotopy Index and Partial Differential Equations (Universitext) (Berlin: Springer)) for the Morse decomposition of an invariant set for a semigroup on a compact metric space).

  12. Stability of gradient semigroups under perturbations

    International Nuclear Information System (INIS)

    Aragão-Costa, E R; Carvalho, A N; Caraballo, T; Langa, J A

    2011-01-01

    In this paper we prove that gradient-like semigroups (in the sense of Carvalho and Langa (2009 J. Diff. Eqns 246 2646–68)) are gradient semigroups (possess a Lyapunov function). This is primarily done to provide conditions under which gradient semigroups, in a general metric space, are stable under perturbation exploiting the known fact (see Carvalho and Langa (2009 J. Diff. Eqns 246 2646–68)) that gradient-like semigroups are stable under perturbation. The results presented here were motivated by the work carried out in Conley (1978 Isolated Invariant Sets and the Morse Index (CBMS Regional Conference Series in Mathematics vol 38) (RI: American Mathematical Society Providence)) for groups in compact metric spaces (see also Rybakowski (1987 The Homotopy Index and Partial Differential Equations (Universitext) (Berlin: Springer)) for the Morse decomposition of an invariant set for a semigroup on a compact metric space)

  13. Gradient High Performance Liquid Chromatography Method ...

    African Journals Online (AJOL)

    Purpose: To develop a gradient high performance liquid chromatography (HPLC) method for the simultaneous determination of phenylephrine (PHE) and ibuprofen (IBU) in solid ..... nimesulide, phenylephrine. Hydrochloride, chlorpheniramine maleate and caffeine anhydrous in pharmaceutical dosage form. Acta Pol.

  14. Evaluation of mulched drip irrigation for cotton in arid Northwest China

    NARCIS (Netherlands)

    Wang, Z.; Jin, M.; Simunek, J.; van Genuchten, M.T.

    2014-01-01

    Field experiments were conducted in arid Southern Xinjiang, Northwest China, for 3 years to evaluate sustainable irrigation regimes for cotton. The experiments involved mulched drip irrigation during the growing season and flood irrigation afterward. The drip irrigation experiments included control

  15. Effects of tillage on runoff from a bare clayey soil on a semi-arid ...

    African Journals Online (AJOL)

    arid areas. However, by adopting appropriate soil management practices, the runoff can be harnessed for improving crop yields. The main objective of this study was to quantify rainfall-runoff relationships under in-field rainwater harvesting ...

  16. Karst characterization in a semi-arid region using gravity, seismic, and resistivity geophysical techniques.

    Energy Technology Data Exchange (ETDEWEB)

    Barnhart, Kevin Scott

    2013-10-01

    We proposed to customize emerging in situ geophysical monitoring technology to generate time-series data during sporadic rain events in a semi-arid region. Electrodes were to be connected to wireless \

  17. Energy exploration in the Australian arid zone: constraints and environmental consequences

    Energy Technology Data Exchange (ETDEWEB)

    Buckley, R C

    1982-03-01

    The main constraints on energy exploration in the Australian arid zone are logistic, with limited additional constraints from Aboriginal reserves. The main consequence is increased access, with possible introduction of weeds and expansion of tourism and cattle grazing in consequence.

  18. Can behaviour buffer the impacts of climate change on an arid-zone ...

    African Journals Online (AJOL)

    Can behaviour buffer the impacts of climate change on an arid-zone bird? ... These could include reduced opportunity for foraging, breeding or territorial defence, each ... We investigated patterns of microclimate use and foraging behaviour by ...

  19. Birth of a biome: insights into the assembly and maintenance of the Australian arid zone biota.

    Science.gov (United States)

    Byrne, M; Yeates, D K; Joseph, L; Kearney, M; Bowler, J; Williams, M A J; Cooper, S; Donnellan, S C; Keogh, J S; Leys, R; Melville, J; Murphy, D J; Porch, N; Wyrwoll, K-H

    2008-10-01

    The integration of phylogenetics, phylogeography and palaeoenvironmental studies is providing major insights into the historical forces that have shaped the Earth's biomes. Yet our present view is biased towards arctic and temperate/tropical forest regions, with very little focus on the extensive arid regions of the planet. The Australian arid zone is one of the largest desert landform systems in the world, with a unique, diverse and relatively well-studied biota. With foci on palaeoenvironmental and molecular data, we here review what is known about the assembly and maintenance of this biome in the context of its physical history, and in comparison with other mesic biomes. Aridification of Australia began in the Mid-Miocene, around 15 million years, but fully arid landforms in central Australia appeared much later, around 1-4 million years. Dated molecular phylogenies of diverse taxa show the deepest divergences of arid-adapted taxa from the Mid-Miocene, consistent with the onset of desiccation. There is evidence of arid-adapted taxa evolving from mesic-adapted ancestors, and also of speciation within the arid zone. There is no evidence for an increase in speciation rate during the Pleistocene, and most arid-zone species lineages date to the Pliocene or earlier. The last 0.8 million years have seen major fluctuations of the arid zone, with large areas covered by mobile sand dunes during glacial maxima. Some large, vagile taxa show patterns of recent expansion and migration throughout the arid zone, in parallel with the ice sheet-imposed range shifts in Northern Hemisphere taxa. Yet other taxa show high lineage diversity and strong phylogeographical structure, indicating persistence in multiple localised refugia over several glacial maxima. Similar to the Northern Hemisphere, Pleistocene range shifts have produced suture zones, creating the opportunity for diversification and speciation through hybridisation, polyploidy and parthenogenesis. This review highlights

  20. Ultimate gradient in solid-state accelerators

    International Nuclear Information System (INIS)

    Whittum, D.H.

    1998-08-01

    The authors recall the motivation for research in high-gradient acceleration and the problems posed by a compact collider. They summarize the phenomena known to appear in operation of a solid-state structure with large fields, and research relevant to the question of the ultimate gradient. They take note of new concepts, and examine one in detail, a miniature particle accelerator based on an active millimeter-wave circuit and parallel particle beams

  1. Quasistatic nonlinear viscoelasticity and gradient flows

    OpenAIRE

    Ball, John M.; Şengül, Yasemin

    2014-01-01

    We consider the equation of motion for one-dimensional nonlinear viscoelasticity of strain-rate type under the assumption that the stored-energy function is λ-convex, which allows for solid phase transformations. We formulate this problem as a gradient flow, leading to existence and uniqueness of solutions. By approximating general initial data by those in which the deformation gradient takes only finitely many values, we show that under suitable hypotheses on the stored-energy function the d...

  2. Tolman temperature gradients in a gravitational field

    OpenAIRE

    Santiago, Jessica; Visser, Matt

    2018-01-01

    Tolman's relation for the temperature gradient in an equilibrium self-gravitating general relativistic fluid is broadly accepted within the general relativity community. However, the concept of temperature gradients in thermal equilibrium continues to cause confusion in other branches of physics, since it contradicts naive versions of the laws of classical thermodynamics. In this paper we discuss the crucial role of the universality of free fall, and how thermodynamics emphasises the great di...

  3. Water and vapor transfer in vadose zone of Gobi desert and riparian in the hyper arid environment of Ejina, China

    Science.gov (United States)

    Du, C.; Yu, J.; Sun, F.; Liu, X.

    2015-12-01

    To reveal how water and vapor transfer in vadose zone affect evapotranspiration in Gobi desert and riparian in hyper arid region is important for understanding eco-hydrological process. Field studies and numerical simulations were imported to evaluate the water and vapor movement processes under non isothermal and lower water content conditions. The soil profiles (12 layers) in Gobi desert and riparian sites of Ejina were installed with sensors to monitor soil moisture and temperature for 1 year. The meteorological conditions and water table were measured by micro weather stations and mini-Divers respectively in the two sites. Soil properties, including particles composition, moisture, bulk density, water retention curve, and saturated hydraulic conductivity of two site soil profiles, was measured. The observations showed that soil temperatures for the two sites displayed large diurnal and seasonal fluctuations. Temperature gradients with depth resulted in a downward in summer and upward in winter and became driving force for thermal vapor movement. Soil moistures in Gobi desert site were very low and varied slowly with time. While the soil moistures in riparian site were complicated due to root distribution but water potentials remained uniform with time. The hydrus-1D was employed to simulate evapotranspiration processes. The simulation results showed the significant difference of evaporation rate in the Gobi desert and riparian sites.

  4. Tearing modes with pressure gradient effect in pair plasmas

    International Nuclear Information System (INIS)

    Cai Huishan; Li Ding; Zheng Jian

    2009-01-01

    The general dispersion relation of tearing mode with pressure gradient effect in pair plasmas is derived analytically. If the pressure gradients of positron and electron are not identical in pair plasmas, the pressure gradient has significant influence at tearing mode in both collisionless and collisional regimes. In collisionless regime, the effects of pressure gradient depend on its magnitude. For small pressure gradient, the growth rate of tearing mode is enhanced by pressure gradient. For large pressure gradient, the growth rate is reduced by pressure gradient. The tearing mode can even be stabilized if pressure gradient is large enough. In collisional regime, the growth rate of tearing mode is reduced by the pressure gradient. While the positron and electron have equal pressure gradient, tearing mode is not affected by pressure gradient in pair plasmas.

  5. Synthetic Lethal Therapeutic Approaches for ARID1A-Mutated Ovarian Cancer

    Science.gov (United States)

    2017-10-01

    Award Number: W81XWH-16-1-0496 TITLE: Synthetic lethal therapeutic approaches for ARID1A-mutated ovarian cancer PRINCIPAL INVESTIGATOR: Rugang...AND SUBTITLE Synthetic lethal therapeutic approaches for ARID1A-mutated ovarian cancer 5a. CONTRACT NUMBER 5b. GRANT NUMBER W81XWH-16-1-0496 5c...Release; Distribution Unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT Epithelial ovarian cancer (EOC) is the leading cause of death among gynecological

  6. Observational characteristics of cloud radiative effects over three arid regions in the Northern Hemisphere

    Science.gov (United States)

    Li, Jiandong; Wang, Tianhe; Habib, Ammara

    2017-08-01

    Cloud-radiation processes play an important role in regional energy budgets and surface temperature changes over arid regions. Cloud radiative effects (CREs) are used to quantitatively measure the aforementioned climatic role. This study investigates the characteristics of CREs and their temporal variations over three arid regions in central Asia (CA), East Asia (EA), and North America (NA), based on recent satellite datasets. Our results show that the annual mean shortwave (SW) and net CREs (SWCRE and NCRE) over the three arid regions are weaker than those in the same latitudinal zone of the Northern Hemisphere. In most cold months (November-March), the longwave (LW) CRE is stronger than the SWCRE over the three arid regions, leading to a positive NCRE and radiative warming in the regional atmosphere-land surface system. The cold-season mean NCRE at the top of the atmosphere (TOA) averaged over EA is 4.1 W m-2, with a positive NCRE from November to March, and the intensity and duration of the positive NCRE is larger than that over CA and NA. The CREs over the arid regions of EA exhibit remarkable annual cycles due to the influence of the monsoon in the south. The TOA LWCRE over arid regions is closely related to the high-cloud fraction, and the SWCRE relates well to the total cloud fraction. In addition, the relationship between the SWCRE and the low-cloud fraction is good over NA because of the considerable occurrence of low cloud. Further results show that the interannual variation of TOA CREs is small over the arid regions of CA and EA, but their surface LWCREs show certain decreasing trends that correspond well to their decreasing total cloud fraction. It is suggested that combined studies of more observational cloud properties and meteorological elements are needed for indepth understanding of cloud-radiation processes over arid regions of the Northern Hemisphere.

  7. More than ten million years of hyper-aridity recorded in the Atacama Gravels

    Science.gov (United States)

    Sun, Tao; Bao, Huiming; Reich, Martin; Hemming, Sidney R.

    2018-04-01

    The Atacama Desert's hyper-aridity is closely linked to the development of world-class copper and nitrate/iodine ores and to regional tectonics and global paleoclimate changes in the Cenozoic era. The timing when the hyper-aridity commenced remains controversial, with proposed ages ranging from Late Oligocene to Pleistocene. In this study, we provide an independent constraint on the initiation of Atacama hyper-aridity utilizing a 100-m deep profile within the Atacama Gravels and underneath porphyry copper deposit in Spence, northern Chile. The overall high concentration of sulfate (up to 10 wt%) and a multimodal distribution of water soluble salt (sulfates, chlorides and nitrates) indicate multiple generations of sedimentation and salt accumulation events under semi-arid to hyper-arid climate conditions. The multiple sulfate isotope compositions (Δ17O, δ18O, δ34S) of the upper section (-15.0 to -34.5 m) are close to those of modern hyperarid surface sulfates, while the lower section (-34.5 to -65 m) displays a depth dependent isotope trend that is best interpreted as marking a period of climate change from semi-arid to hyper-arid. When these data are combined with new chronological 40Ar/39Ar dates obtained from a volcanic ash layer at depth of -28.0 m, our results show that hyper-arid condition in the Atacama Desert was prevailing at least prior to 9.47 Ma and may go back as old as the middle Miocene.

  8. Lake Evaporation in a Hyper-Arid Environment, Northwest of China—Measurement and Estimation

    OpenAIRE

    Xiao Liu; Jingjie Yu; Ping Wang; Yichi Zhang; Chaoyang Du

    2016-01-01

    Lake evaporation is a critical component of the hydrological cycle. Quantifying lake evaporation in hyper-arid regions by measurement and estimation can both provide reliable potential evaporation (ET0) reference and promote a deeper understanding of the regional hydrological process and its response towards changing climate. We placed a floating E601 evaporation pan on East Juyan Lake, which is representative of arid regions’ terminal lakes, to measure daily evaporation and conducted simulta...

  9. Spatial and temporal variability of the Aridity Index in Greece

    Science.gov (United States)

    Nastos, Panagiotis T.; Politi, Nadia; Kapsomenakis, John

    2013-01-01

    The objective of this paper is to study the spatial and temporal variability of the Aridity Index (AI) in Greece, per decade, during the 50-year period (1951-2000). Besides, the projected changes in ensemble mean AI between the period 1961-1990 (reference period) and the periods 2021-2050 (near future) and 2071-2100 (far future) along with the inter-model standard deviations were presented, based on the simulation results, derived from a number of Regional Climatic Models (RCMs), within the ENSEMBLE European Project. The projection of the future climate was done under SRES A1B. The climatic data used, concern monthly precipitation totals and air temperature from 28 meteorological stations (22 stations from the Hellenic National Meteorological Service and 6 stations from neighboring countries, taken from the Monthly Climatic Data for the World). The estimation of the AI was carried out based on the potential evapotranspiration (PET) defined by Thornthwaite (1948). The data processing was done by the application of the statistical package R-project and the Geographical Information Systems (GIS). The results of the analysis showed that, within the examined period (1951-2000), a progressive shift from the "humid" class, which characterized the wider area of Greece, towards the "sub-humid" and "semi-arid" classes appeared in the eastern Crete Island, the Cyclades complex, the Evia and Attica, that is mainly the eastern Greece. The most significant change appears during the period 1991-2000. The future projections at the end of twentieth century, using ensemble mean simulations from 8 RCMs, show that drier conditions are expected to establish in regions of Greece (Attica, eastern continental Greece, Cyclades, Dodecanese, eastern Crete Island and northern Aegean). The inter-model standard deviation over these regions ranges from 0.02 to 0.05 against high values (0.09-0.15) illustrated in western mountainous continental Greece, during 2021-2050. Higher values of inter

  10. Limits on carbon sequestration in arid blue carbon ecosystems.

    Science.gov (United States)

    Schile, Lisa M; Kauffman, J Boone; Crooks, Stephen; Fourqurean, James W; Glavan, Jane; Megonigal, J Patrick

    2017-04-01

    Coastal ecosystems produce and sequester significant amounts of carbon ("blue carbon"), which has been well documented in humid and semi-humid regions of temperate and tropical climates but less so in arid regions where mangroves, marshes, and seagrasses exist near the limit of their tolerance for extreme temperature and salinity. To better understand these unique systems, we measured whole-ecosystem carbon stocks in 58 sites across the United Arab Emirates (UAE) in natural and planted mangroves, salt marshes, seagrass beds, microbial mats, and coastal sabkha (inter- and supratidal unvegetated salt flats). Natural mangroves held significantly more carbon in above- and belowground biomass than other vegetated ecosystems. Planted mangrove carbon stocks increased with age, but there were large differences for sites of similar age. Soil carbon varied widely across sites (2-367 Mg C/ha), with ecosystem averages that ranged from 49 to 156 Mg C/ha. For the first time, microbial mats were documented to contain soil carbon pools comparable to vascular plant-dominated ecosystems, and could arguably be recognized as a unique blue carbon ecosystem. Total ecosystem carbon stocks ranged widely from 2 to 515 Mg C/ha (seagrass bed and mangrove, respectively). Seagrass beds had the lowest carbon stock per unit area, but the largest stock per total area due to their large spatial coverage. Compared to similar ecosystems globally, mangroves and marshes in the UAE have lower plant and soil carbon stocks; however, the difference in soil stocks is far larger than with plant stocks. This incongruent difference between stocks is likely due to poor carbon preservation under conditions of weakly reduced soils (200-350 mV), coarse-grained sediments, and active shoreline migration. This work represents the first attempt to produce a country-wide coastal ecosystem carbon accounting using a uniform sampling protocol, and was motivated by specific policy goals identified by the Abu Dhabi Global

  11. Final Technical Report: The effects of climate, forest age, and disturbance history on carbon and water processes at AmeriFlux sites across gradients in Pacific Northwest forests

    Energy Technology Data Exchange (ETDEWEB)

    Law, Beverly E. [Oregon State Univ., Corvallis, OR (United States)

    2016-12-03

    Investigate the effects of disturbance and climate variables on processes controlling carbon and water processes at AmeriFlux cluster sites in semi-arid and mesic forests in Oregon. The observations were made at three existing and productive AmeriFlux research sites that represent climate and disturbance gradients as a natural experiment of the influence of climatic and hydrologic variability on carbon sequestration and resulting atmospheric CO2 feedback that includes anomalies during the warm/ dry phase of the Pacific Decadal Oscillation.

  12. Rapid warming accelerates tree growth decline in semi-arid forests of Inner Asia.

    Science.gov (United States)

    Liu, Hongyan; Park Williams, A; Allen, Craig D; Guo, Dali; Wu, Xiuchen; Anenkhonov, Oleg A; Liang, Eryuan; Sandanov, Denis V; Yin, Yi; Qi, Zhaohuan; Badmaeva, Natalya K

    2013-08-01

    Forests around the world are subject to risk of high rates of tree growth decline and increased tree mortality from combinations of climate warming and drought, notably in semi-arid settings. Here, we assess how climate warming has affected tree growth in one of the world's most extensive zones of semi-arid forests, in Inner Asia, a region where lack of data limits our understanding of how climate change may impact forests. We show that pervasive tree growth declines since 1994 in Inner Asia have been confined to semi-arid forests, where growing season water stress has been rising due to warming-induced increases in atmospheric moisture demand. A causal link between increasing drought and declining growth at semi-arid sites is corroborated by correlation analyses comparing annual climate data to records of tree-ring widths. These ring-width records tend to be substantially more sensitive to drought variability at semi-arid sites than at semi-humid sites. Fire occurrence and insect/pathogen attacks have increased in tandem with the most recent (2007-2009) documented episode of tree mortality. If warming in Inner Asia continues, further increases in forest stress and tree mortality could be expected, potentially driving the eventual regional loss of current semi-arid forests. © 2013 John Wiley & Sons Ltd.

  13. Hydrological Response of Semi-arid Degraded Catchments in Tigray, Northern Ethiopia

    Science.gov (United States)

    Teka, Daniel; Van Wesemael, Bas; Vanacker, Veerle; Hallet, Vincent

    2013-04-01

    To address water scarcity in the arid and semi-arid part of developing countries, accurate estimation of surface runoff is an essential task. In semi-arid catchments runoff data are scarce and therefore runoff estimation using hydrological models becomes an alternative. This research was initiated in order to characterize runoff response of semi-arid catchments in Tigray, North Ethiopia to evaluate SCS-CN for various catchments. Ten sub-catchments were selected in different river basins and rainfall and runoff were measured with automatic hydro-monitoring equipments for 2-3 years. The Curve Number was estimated for each Hydrological Response Unit (HRU) in the sub-catchments and runoff was modeled using the SCS-CN method at λ = 0.05 and λ = 0.20. The result showed a significant difference between the two abstraction ratios (P =0.05, df = 1, n= 132) and reasonable good result was obtained for predicted runoff at λ = 0.05 (NSE = -0.69; PBIAS = 18.1%). When using the CN values from literature runoff was overestimated compared to the measured value (e= -11.53). This research showed the importance of using measured runoff data to characterize semi-arid catchments and accurately estimate the scarce water resource. Key words: Hydrological response, rainfall-runoff, degraded environments, semi-arid, Ethiopia, Tigray

  14. Changes in precipitation recycling over arid regions in the Northern Hemisphere

    Science.gov (United States)

    Li, Ruolin; Wang, Chenghai; Wu, Di

    2018-01-01

    Changes of precipitation recycling (PR) in Northern Hemisphere from 1981 to 2010 are investigated using a water recycling model. The temporal and spatial characteristics of recycling in arid regions are analyzed. The results show that the regional precipitation recycling ratio (PRR) in arid regions is larger than in wet regions. PRR in arid regions has obvious seasonal variation, ranging from more than 25 % to less than 1 %. Furthermore, in arid regions, PRR is significantly negatively correlated with precipitation (correlation coefficient r = -0.5, exceeding the 99 % significance level). Moreover, the trend of PRR is related to changes in precipitation in two ways. PRR decreases with increasing precipitation in North Africa, which implies that less locally evaporated vapor converts into actual precipitation. However, in Asian arid regions, the PRR increases as precipitation reduces, which implies that more locally evaporated vapor converts into rainfall. Further, as PRR mainly depends on evapotranspiration, the PRR trend in Asian arid regions develops as temperature increases and more evaporated vapor enters the atmosphere to offset the reduced rainfall.

  15. Arid1b haploinsufficient mice reveal neuropsychiatric phenotypes and reversible causes of growth impairment.

    Science.gov (United States)

    Celen, Cemre; Chuang, Jen-Chieh; Luo, Xin; Nijem, Nadine; Walker, Angela K; Chen, Fei; Zhang, Shuyuan; Chung, Andrew S; Nguyen, Liem H; Nassour, Ibrahim; Budhipramono, Albert; Sun, Xuxu; Bok, Levinus A; McEntagart, Meriel; Gevers, Evelien F; Birnbaum, Shari G; Eisch, Amelia J; Powell, Craig M; Ge, Woo-Ping; Santen, Gijs We; Chahrour, Maria; Zhu, Hao

    2017-07-11

    Sequencing studies have implicated haploinsufficiency of ARID1B , a SWI/SNF chromatin-remodeling subunit, in short stature (Yu et al., 2015), autism spectrum disorder (O'Roak et al., 2012), intellectual disability (Deciphering Developmental Disorders Study, 2015), and corpus callosum agenesis (Halgren et al., 2012). In addition, ARID1B is the most common cause of Coffin-Siris syndrome, a developmental delay syndrome characterized by some of the above abnormalities (Santen et al., 2012; Tsurusaki et al., 2012; Wieczorek et al., 2013). We generated Arid1b heterozygous mice, which showed social behavior impairment, altered vocalization, anxiety-like behavior, neuroanatomical abnormalities, and growth impairment. In the brain, Arid1b haploinsufficiency resulted in changes in the expression of SWI/SNF-regulated genes implicated in neuropsychiatric disorders. A focus on reversible mechanisms identified Insulin-like growth factor (IGF1) deficiency with inadequate compensation by Growth hormone-releasing hormone (GHRH) and Growth hormone (GH), underappreciated findings in ARID1B patients. Therapeutically, GH supplementation was able to correct growth retardation and muscle weakness. This model functionally validates the involvement of ARID1B in human disorders, and allows mechanistic dissection of neurodevelopmental diseases linked to chromatin-remodeling.

  16. Functional Analysis of In-frame Indel ARID1A Mutations Reveals New Regulatory Mechanisms of Its Tumor Suppressor Functions

    Directory of Open Access Journals (Sweden)

    Bin Guan

    2012-10-01

    Full Text Available AT-rich interactive domain 1A (ARID1A has emerged as a new tumor suppressor in which frequent somatic mutations have been identified in several types of human cancers. Although most ARID1A somatic mutations are frame-shift or nonsense mutations that contribute to mRNA decay and loss of protein expression, 5% of ARID1A mutations are in-frame insertions or deletions (indels that involve only a small stretch of peptides. Naturally occurring in-frame indel mutations provide unique and useful models to explore the biology and regulatory role of ARID1A. In this study, we analyzed indel mutations identified in gynecological cancers to determine how these mutations affect the tumor suppressor function of ARID1A. Our results demonstrate that all in-frame mutants analyzed lost their ability to inhibit cellular proliferation or activate transcription of CDKN1A, which encodes p21, a downstream effector of ARID1A. We also showed that ARID1A is a nucleocytoplasmic protein whose stability depends on its subcellular localization. Nuclear ARID1A is less stable than cytoplasmic ARID1A because ARID1A is rapidly degraded by the ubiquitin-proteasome system in the nucleus. In-frame deletions affecting the consensus nuclear export signal reduce steady-state protein levels of ARID1A. This defect in nuclear exportation leads to nuclear retention and subsequent degradation. Our findings delineate a mechanism underlying the regulation of ARID1A subcellular distribution and protein stability and suggest that targeting the nuclear ubiquitin-proteasome system can increase the amount of the ARID1A protein in the nucleus and restore its tumor suppressor functions.

  17. Determining the resilience of carbon dynamics in semi-arid biomes of the Southwestern US to severe drought and altered rainfall patterns

    Science.gov (United States)

    Litvak, M. E.; Krofcheck, D. J.; Hilton, T. W.; Fox, A. M.; Osuna, J. L.

    2011-12-01

    Water is critically important for biotic processes in semi-arid ecosystems and 2011 is developing as one of the most severe drought years on record for many parts of the Southwestern US. To quantify the impact of this severe drought on regional carbon and energy balance, we need a more detailed understanding of how water limitation alters ecosystem processes across a range of semi-arid biomes. We quantified the impact of severe drought and changes in both the quantity and distribution of precipitation on ecosystem biotic structure and function across the range of biomes represented in the NM elevation gradient network (desert grassland, creosote shrubland, juniper savanna, piñon-juniper woodland, ponderosa pine forest and subalpine mixed conifer forest). We compared how daily, seasonal and annual carbon and energy balance and their components in each of these biomes respond to changes in rainfall patterns using continuous measurements of carbon, water and energy exchange and associated measurements in each of these biomes during a 5 year period (2006-2011) that included a severe drought, and large variability in both winter precipitation and the timing and intensity of the monsoon. To understand the underlying mechanisms, we used time series of radiation absorbed by vegetation, surface albedo, soil moisture storage, phenology, gross primary productivity (GPP), ecosystem respiration (Re), and WorldView-2 images acquired pre- and post-monsoon in each of these biomes. In all of the biomes except the desert grassland site, the strength and timing of both winter and monsoon precipitation are important controls over carbon and energy dynamics in this region, though we see site-specific sensitivities across the elevation gradient. Over the past 5 years, carbon dynamics in the desert grassland site appears to be decoupled from winter precipitation. In addition, carbon dynamics in disturbed grassland and pinon-juniper ecosystems were more sensitive to severe drought than

  18. Magnetoelectric Transverse Gradient Sensor with High Detection Sensitivity and Low Gradient Noise

    OpenAIRE

    Zhang, Mingji; Or, Siu Wing

    2017-01-01

    We report, theoretically and experimentally, the realization of a high detection performance in a novel magnetoelectric (ME) transverse gradient sensor based on the large ME effect and the magnetic field gradient (MFG) technique in a pair of magnetically-biased, electrically-shielded, and mechanically-enclosed ME composites having a transverse orientation and an axial separation. The output voltage of the gradient sensor is directly obtained from the transverse MFG-induced difference in ME vo...

  19. Full magnetic gradient tensor from triaxial aeromagnetic gradient measurements: Calculation and application

    Science.gov (United States)

    Luo, Yao; Wu, Mei-Ping; Wang, Ping; Duan, Shu-Ling; Liu, Hao-Jun; Wang, Jin-Long; An, Zhan-Feng

    2015-09-01

    The full magnetic gradient tensor (MGT) refers to the spatial change rate of the three field components of the geomagnetic field vector along three mutually orthogonal axes. The tensor is of use to geological mapping, resources exploration, magnetic navigation, and others. However, it is very difficult to measure the full magnetic tensor gradient using existing engineering technology. We present a method to use triaxial aeromagnetic gradient measurements for deriving the full MGT. The method uses the triaxial gradient data and makes full use of the variation of the magnetic anomaly modulus in three dimensions to obtain a self-consistent magnetic tensor gradient. Numerical simulations show that the full MGT data obtained with the proposed method are of high precision and satisfy the requirements of data processing. We selected triaxial aeromagnetic gradient data from the Hebei Province for calculating the full MGT. Data processing shows that using triaxial tensor gradient data allows to take advantage of the spatial rate of change of the total field in three dimensions and suppresses part of the independent noise in the aeromagnetic gradient. The calculated tensor components have improved resolution, and the transformed full tensor gradient satisfies the requirement of geological mapping and interpretation.

  20. Reintroduction of locally extinct vertebrates impacts arid soil fungal communities.

    Science.gov (United States)

    Clarke, Laurence J; Weyrich, Laura S; Cooper, Alan

    2015-06-01

    Introduced species have contributed to extinction of native vertebrates in many parts of the world. Changes to vertebrate assemblages are also likely to alter microbial communities through coextinction of some taxa and the introduction of others. Many attempts to restore degraded habitats involve removal of exotic vertebrates (livestock and feral animals) and reintroduction of locally extinct species, but the impact of such reintroductions on microbial communities is largely unknown. We used high-throughput DNA sequencing of the fungal internal transcribed spacer I (ITS1) region to examine whether replacing exotic vertebrates with reintroduced native vertebrates led to changes in soil fungal communities at a reserve in arid central Australia. Soil fungal diversity was significantly different between dune and swale (interdune) habitats. Fungal communities also differed significantly between sites with exotic or reintroduced native vertebrates after controlling for the effect of habitat. Several fungal operational taxonomic units (OTUs) found exclusively inside the reserve were present in scats from reintroduced native vertebrates, providing a direct link between the vertebrate assemblage and soil microbial communities. Our results show that changes to vertebrate assemblages through local extinctions and the invasion of exotic species can alter soil fungal communities. If local extinction of one or several species results in the coextinction of microbial taxa, the full complement of ecological interactions may never be restored. © 2015 John Wiley & Sons Ltd.

  1. Synthetic socioeconomic based domestic wastewater hydrographs for small arid communities

    KAUST Repository

    Elnakar, H.

    2012-06-04

    A model was developed to predict synthetic socioeconomic based domestic wastewater hydrographs for the small arid communities. The model predicts the flow hydrograph for random weekdays and weekends based on the specific socioeconomic characteristics of the community. The main socioeconomic characteristics are the composition of the community, the different user behaviours in using water appliances, and the unit discharges of such appliances. Use patterns of water appliances are assumed to vary for the various members of the community and the type of day. Each community is composed of several social categories such as the employee, working woman, stay home woman, stay home child, students etc. The use patterns account for the stochastic nature of use in terms of number of uses, duration of the use and times of use in the day. Randomly generated hydrographs are generated for weekdays and weekends along with synthetic hydrographs of non-exceedance. The model was verified for a small residential compound in Sharm El Shiekh - Egypt using 11 days of flow measurements performed in summer. The synthetic hydrographs based on assumed water use patterns of the various members of the community compared reasonably with the measured hydrographs. Synthetic hydrographs can be derived for a community under consideration to reflect its socioeconomic conditions and thus can be used to generate probability based peaking factors to be used in the design of sewerage systems pumping facilities, and treatment plants. © 201 WIT Press.

  2. Mining the Agave Microbiome for adaptions to arid environments

    Energy Technology Data Exchange (ETDEWEB)

    Coleman-Derr, Devin; Wojke, Tanja; North, Gretchen; Partida-Martinez, Laila; DeAngeli, Kristen; Clingenpeel, Scott; Gross, Stephen; Tringe, Susannah; Visel, Axel

    2013-03-25

    A major challenge facing the biofuels industry is the identification of high-yield plant feedstocks that can be cultivated with minimal resource inputs without competing for land and water supplies with existing food crops. Recent research has demonstrated that the Agave plant, cultivated in Mexico and Southwestern United States for the production of fiber and alcohol, meets these criteria1. Agaves grow on non-arable rocky soils in regions characterized by prolonged drought and extreme temperatures, due in part to physiological adaptions that prevent excess water-loss in arid environments2. Plant-microbial symbioses can play a role in helping plants adapt to heat and drought stress, increasing the accessibility of soil nutrients, or compete with plant pathogens3. Whether agaves have similar beneficial microbe interactions in their native environment is unknown. We aim to provide a comprehensive characterization of the Agave microbiome, with the goal of identifying specific community members that may contribute to Agave biotic and abiotic stress tolerance

  3. Synthetic socioeconomic based domestic wastewater hydrographs for small arid communities

    KAUST Repository

    Elnakar, H.; Imam, E.; Nassar, K.

    2012-01-01

    A model was developed to predict synthetic socioeconomic based domestic wastewater hydrographs for the small arid communities. The model predicts the flow hydrograph for random weekdays and weekends based on the specific socioeconomic characteristics of the community. The main socioeconomic characteristics are the composition of the community, the different user behaviours in using water appliances, and the unit discharges of such appliances. Use patterns of water appliances are assumed to vary for the various members of the community and the type of day. Each community is composed of several social categories such as the employee, working woman, stay home woman, stay home child, students etc. The use patterns account for the stochastic nature of use in terms of number of uses, duration of the use and times of use in the day. Randomly generated hydrographs are generated for weekdays and weekends along with synthetic hydrographs of non-exceedance. The model was verified for a small residential compound in Sharm El Shiekh - Egypt using 11 days of flow measurements performed in summer. The synthetic hydrographs based on assumed water use patterns of the various members of the community compared reasonably with the measured hydrographs. Synthetic hydrographs can be derived for a community under consideration to reflect its socioeconomic conditions and thus can be used to generate probability based peaking factors to be used in the design of sewerage systems pumping facilities, and treatment plants. © 201 WIT Press.

  4. Soil-moisture transport in arid site vadose zones

    International Nuclear Information System (INIS)

    Isaacson, R.E.; Brownell, L.E.; Nelson, R.W.; Roetman, E.L.

    1974-01-01

    Soil-moisture transport processes in the arid soils of the United States Atomic Energy Commission's Hanford site are being evaluated. The depth of penetration of meteoric precipitation has been determined by profiling fall-out tritium at two locations where the water table is about 90 m below ground surface. In situ temperatures and water potentials were measured with temperature transducers and thermocouple psychrometers at the same location to obtain thermodynamic data for identifying the factors influencing soil-moisture transport. Neutron probes are being used to monitor soil-moisture changes in two lysimeters, three metres in diameter by 20 metres deep. The lysimeters are also equipped to measure pressure, temperature and relative humidity as a function of depth and time. Theoretical models based on conservation of momentum expressions are being developed to analyse non-isothermal soil-moisture transport processes. Future work will be concerned with combining the theoretical and experimental work and determining the amount of rainfall required to cause migration of soil-moisture to the water table. (author)

  5. Using NDVI to measure precipitation in semi-arid landscapes

    Science.gov (United States)

    Birtwhistle, Amy N.; Laituri, Melinda; Bledsoe, Brian; Friedman, Jonathan M.

    2016-01-01

    Measuring precipitation in semi-arid landscapes is important for understanding the processes related to rainfall and run-off; however, measuring precipitation accurately can often be challenging especially within remote regions where precipitation instruments are scarce. Typically, rain-gauges are sparsely distributed and research comparing rain-gauge and RADAR precipitation estimates reveal that RADAR data are often misleading, especially for monsoon season convective storms. This study investigates an alternative way to map the spatial and temporal variation of precipitation inputs along ephemeral stream channels using Normalized Difference Vegetation Index (NDVI) derived from Landsat Thematic Mapper imagery. NDVI values from 26 years of pre- and post-monsoon season Landsat imagery were derived across Yuma Proving Ground (YPG), a region covering 3,367 km2 of semiarid landscapes in southwestern Arizona, USA. The change in NDVI from a pre-to post-monsoon season image along ephemeral stream channels explained 73% of the variance in annual monsoonal precipitation totals from a nearby rain-gauge. In addition, large seasonal changes in NDVI along channels were useful in determining when and where flow events have occurred.

  6. Agricultural sustainability in the semi-arid Near East

    Directory of Open Access Journals (Sweden)

    F. Hole

    2007-05-01

    Full Text Available Agriculture began in the eastern Mediterranean Levantine Corridor about 11000 years ago toward the end of the Younger Dryas when aridity had diminished wild food resources. During the subsequent Climatic Optimum, agricultural villages spread rapidly but subsequent climatic changes on centennial to millennial scales resulted in striking oscillations in settlement, especially in marginal areas. Natural climate change thus alternately enhanced and diminished the agricultural potential of the land. Growing populations and more intensive land us, both for agriculture and livestock, have led to changes in the structure of vegetation, hydrology, and land quality. Over the millennia, political and economic interventions, warfare and incursions by nomadic herding tribes all impacted sustainability of agriculture and the ability of the land to supports its populations. In much of the region today, agricultural land use is not sustainable given existing technology and national priorities. The Near Eastern case is instructive because of the quality of information, the length of the record, and the pace of modern change.

  7. Root zone effects on tracer migration in arid zones

    International Nuclear Information System (INIS)

    Tyler, S.W.; Walker, G.R.

    1994-01-01

    The study of groundwater recharge and soil water movement in arid regions has received increased attention in the search for safe disposal sites for hazardous wastes. In passing through the upper 1 to 2 m of most soil profiles, tracers indicative of recharge such as Cl, 2 H, 18 O, Br, 3 H, and 56 Cl are subjected to a wide range of processes not encountered deeper in the profile. This transition zone, where water enters as precipitation and leaves as recharge, is often ignored when environmental tracers are used to estimate deep soil water flux and recharge, yet its effect may be profound. In this work, we reexamine the processes of root extraction and its effect on the velocity and distribution of tracers. Examples are presented for idealized conditions, which show clearly the relation between the root zone processes and the deep drainage or recharge. The results indicate that, when recharge is small and root zone processes are not accounted for, tracer techniques can significantly overestimate recharge until the tracer has moved well below the root zone. By incorporating simple models of root zone processes, a clearer understanding of tracer distributions and a more accurate estimate of recharge can then be made. 11 refs., 9 figs

  8. Evolutionary speed limited by water in arid Australia.

    Science.gov (United States)

    Goldie, Xavier; Gillman, Len; Crisp, Mike; Wright, Shane

    2010-09-07

    The covariation of biodiversity with climate is a fundamental pattern in nature. However, despite the ubiquity of this relationship, a consensus on the ultimate cause remains elusive. The evolutionary speed hypothesis posits direct mechanistic links between ambient temperature, the tempo of micro-evolution and, ultimately, species richness. Previous research has demonstrated faster rates of molecular evolution in warmer climates for a broad range of poikilothermic and homeothermic organisms, in both terrestrial and aquatic environments. In terrestrial systems, species richness increases with both temperature and water availability and the interaction of those terms: productivity. However, the influence of water availability as an independent variable on micro-evolutionary processes has not been examined previously. Here, using methodology that limits the potentially confounding role of cladogenetic and demographic processes, we report, to our knowledge, the first evidence that woody plants living in the arid Australian Outback are evolving more slowly than related species growing at similar latitudes in moist habitats on the mesic continental margins. These results support a modified evolutionary speed explanation for the relationship between the water-energy balance and plant diversity patterns.

  9. Simulating the Dependence of Sagebrush Steppe Vegetation on Redistributed Snow in a Semi-Arid Watershed.

    Science.gov (United States)

    Soderquist, B.; Kavanagh, K.; Link, T. E.; Strand, E. K.; Seyfried, M. S.

    2014-12-01

    In mountainous regions across the western USA, the composition of aspen (Populus tremuloides) and sagebrush steppe plant communities is often closely related to heterogeneous soil moisture subsidies resulting from redistributed snow. With decades of climate and precipitation data across elevational and precipitation gradients, the Reynolds Creek Experimental Watershed (RCEW) and critical zone observatory (CZO) in southwest Idaho provides a unique opportunity to study the relationship between vegetation types and redistributed snow. Within the RCEW, the total amount of precipitation has remained unchanged over the past 50 years, however the percentage of the precipitation falling as snow has declined by approximately 4% per decade at mid-elevation sites. As shifts in precipitation phase continue, future trends in vegetation composition and net primary productivity (NPP) of different plant functional types remains a critical question. We hypothesize that redistribution of snow may supplement drought sensitive species like aspen more so than drought tolerant species like mountain big sagebrush (Artemisia tridentata spp. vaseyana). To assess the importance of snowdrift subsidies on sagebrush steppe vegetation, NPP of aspen, shrub, and grass species was simulated at three sites using the biogeochemical process model BIOME-BGC. Each site is located directly downslope from snowdrifts providing soil moisture inputs to aspen stands and neighboring vegetation. Drifts vary in size with the largest containing up to four times the snow water equivalent (SWE) of a uniform precipitation layer. Precipitation inputs used by BIOME-BGC were modified to represent the redistribution of snow and simulations were run using daily climate data from 1985-2013. Simulated NPP of annual grasses at each site was not responsive to subsidies from drifting snow. However, at the driest site, aspen and shrub annual NPP was increased by as much as 44 and 30%, respectively, with the redistribution of

  10. Groundwater Modeling in Coastal Arid Regions Under the Influence of Marine Saltwater Intrusion

    Science.gov (United States)

    Walther, Marc; Kolditz, Olaf; Grundmann, Jens; Liedl, Rudolf

    2010-05-01

    The optimization of an aquifer's "safe yield", especially within agriculturally used regions, is one of the fundamental tasks for nowaday's groundwater management. Due to the limited water ressources in arid regions, conflict of interests arise that need to be evaluated using scenario analysis and multicriterial optimization approaches. In the context of the government-financed research project "International Water Research Alliance Saxony" (IWAS), the groundwater quality for near-coastal, agriculturally used areas is investigated under the influence of marine saltwater intrusion. Within the near-coastal areas of the study region, i.e. the Batinah plains of Northern Oman, an increasing agricultural development could be observed during the recent decades. Simultaneously, a constant lowering of the groundwater table was registered, which is primarily due to the uncontrolled and unsupervised mining of the aquifers for the local agricultural irrigation. Intensively decreased groundwater levels, however, cause an inversion of the hydraulic gradient which is naturally aligned towards the coast. This, in turn,leads to an intrusion of marine saltwater flowing inland, endangering the productivity of farms near the coast. Utilizing the modeling software package OpenGeoSys, which has been developed and constantly enhanced by the Department of Environmental Informatics at the Helmholtz Centre for Environmental Research Leipzig (UFZ; Kolditz et al., 2008), a three-dimensional, density-dependent model including groundwater flow and mass transport is currently being built up. The model, comprehending three selected coastal wadis of interest, shall be used to investigate different management scenarios. The main focus of the groundwater modelling are the optimization of well positions and pumping schemes as well as the coupling with a surface runoff model, which is also used for the determination of the groundwater recharge due to wadi runoff downstream of retention dams. Based on

  11. Effects of Urbanization on the Flow Regimes of Semi-Arid Southern California Streams

    Science.gov (United States)

    Hawley, R. J.; Bledsoe, B. P.; Stein, E. D.

    2010-12-01

    Stream channel erosion and associated habitat degradation are pervasive in streams draining urban areas in the southwestern US. The prevalence of these impacts results from the inherent sensitivity of streams in semi-arid climates to changes in flow and sediment regimes, and past inattention to management of geomorphically effective flows. Addressing this issue is difficult due to the lack of data linking ranges of flow (from small to large runoff events) to geomorphic channel response. Forty-three U. S. Geological Survey gages with record lengths greater than ~15 yrs and watershed areas less than ~250 square kilometers were used to empirically model the effects of urbanization on streams in southern California. The watersheds spanned a gradient of urban development and ranged from 0 to 23% total impervious area in 2001. With little flow control at the subdivision scale to date, most impervious area in the region is relatively well-connected to surface-drainage networks. Consequently, total impervious area was an effective surrogate for urbanization, and emerged as a significant (p approach expands on previous scaling procedures to produce histogram-style cumulative flow duration graphs for ungaged sites based on urbanization extent and other watershed descriptors. Urbanization resulted in proportionally-longer durations of all geomorphically-effective flows, with a more pronounced effect on the durations of moderate flows. For example, an average watershed from the study domain with ~20% imperviousness could experience five times as many days of mean daily flows on the order of 100 cfs (3 cubic meters per second) and approximately three times as many days on the order of 1,000 cfs (30 cubic meters per second) relative to the undeveloped setting. Increased duration of sediment-transporting flows is a primary driver of accelerated changes in channel form that are often concurrent with urbanization throughout southern California, particularly in unconfined, fine

  12. Decreased expression of the ARID1A gene is associated with poor prognosis in primary gastric cancer.

    Directory of Open Access Journals (Sweden)

    Dan-dan Wang

    Full Text Available BACKGROUND: The ARID1A gene encodes adenine-thymine (AT-rich interactive domain-containing protein 1A, which participates in chromatin remodeling. ARID1A has been showed to function as a tumor suppressor in various cancer types. In the current study, we investigated the expression and prognosis value of ARID1A in primary gastric cancer. Meanwhile, the biological role of ARID1A was further investigated using cell model in vitro. METHODOLOGY/PRINCIPAL FINDINGS: To investigate the role of ARID1A gene in primary gastric cancer pathogenesis, real-time quantitative PCR and western blotting were used to examine the ARID1A expression in paired cancerous and noncancerous tissues. Results revealed decreased ARID1A mRNA (P = 0.0029 and protein (P = 0.0015 expression in most tumor-bearing tissues compared with the matched adjacent non-tumor tissues, and in gastric cancer cell lines. To further investigate the clinicopathological and prognostic roles of ARID1A expression, we performed immunohistochemical analyses of the 224 paraffin-embedded gastric cancer tissue blocks. Data revealed that the loss of ARID1A expression was significantly correlated with T stage (P = 0.001 and grade (P = 0.006. Consistent with these results, we found that loss of ARID1A expression was significantly correlated with poor survival in gastric cancer patients (P = 0.003. Cox regression analyses showed that ARID1A expression was an independent predictor of overall survival (P = 0.029. Furthermore, the functions of ARID1A in the proliferation and colony formation of gastric cell lines were analyzed by transfecting cells with full-length ARID1A expression vector or siRNA targeting ARID1A. Restoring ARID1A expression in gastric cancer cells significantly inhibited cell proliferation and colony formation. Silencing ARID1A expression in gastric epithelial cell line significantly enhanced cell growth rate. CONCLUSIONS/SIGNIFICANCE: Our data suggest that ARID1A may play an important role

  13. Income inequality and socioeconomic gradients in mortality.

    Science.gov (United States)

    Wilkinson, Richard G; Pickett, Kate E

    2008-04-01

    We investigated whether the processes underlying the association between income inequality and population health are related to those responsible for the socioeconomic gradient in health and whether health disparities are smaller when income differences are narrower. We used multilevel models in a regression analysis of 10 age- and cause-specific US county mortality rates on county median household incomes and on state income inequality. We assessed whether mortality rates more closely related to county income were also more closely related to state income inequality. We also compared mortality gradients in more- and less-equal states. Mortality rates more strongly associated with county income were more strongly associated with state income inequality: across all mortality rates, r= -0.81; P=.004. The effect of state income inequality on the socioeconomic gradient in health varied by cause of death, but greater equality usually benefited both wealthier and poorer counties. Although mortality rates with steep socioeconomic gradients were more sensitive to income distribution than were rates with flatter gradients, narrower income differences benefit people in both wealthy and poor areas and may, paradoxically, do little to reduce health disparities.

  14. Jupiter's evolution with primordial composition gradients

    Science.gov (United States)

    Vazan, Allona; Helled, Ravit; Guillot, Tristan

    2018-02-01

    Recent formation and structure models of Jupiter suggest that the planet can have composition gradients and not be fully convective (adiabatic). This possibility directly affects our understanding of Jupiter's bulk composition and origin. In this Letter we present Jupiter's evolution with a primordial structure consisting of a relatively steep heavy-element gradient of 40 M⊕. We show that for a primordial structure with composition gradients, most of the mixing occurs in the outer part of the gradient during the early evolution (several 107 yr), leading to an adiabatic outer envelope (60% of Jupiter's mass). We find that the composition gradient in the deep interior persists, suggesting that 40% of Jupiter's mass can be non-adiabatic with a higher temperature than the one derived from Jupiter's atmospheric properties. The region that can potentially develop layered convection in Jupiter today is estimated to be limited to 10% of the mass. Movies associated to Figs. 1-3 are available at http://https://www.aanda.org

  15. Gradient dissimilation in Mongolian: Implications for diachrony

    DEFF Research Database (Denmark)

    Jatteau, Adèle; Hejná, Michaela

    2018-01-01

    This paper explores the implications of ‘gradient dissimilation’ (Jatteau & Hejná 2016) for the diachronic implementation of dissimilation. Since this sound change is usually considered as typically sporadic, lexically regular cases should result from lexical diffusion. In contrast with this ass......This paper explores the implications of ‘gradient dissimilation’ (Jatteau & Hejná 2016) for the diachronic implementation of dissimilation. Since this sound change is usually considered as typically sporadic, lexically regular cases should result from lexical diffusion. In contrast...... with this assumption, we explore the hypothesis that gradient dissimilation may represent the phonetic precursor of completed, regular dissimilatory processes. Such cases of dissimilation might then be reanalysed as Neogrammarian types of change. To assess this question, we gather and analyse new data from Halh...... Mongolian, a language reported to show gradient dissimilation (Svantesson et al. 2005), and compare it to two completed patterns of dissimilation reconstructed within the Mongolic family: Mongolian Chahar and Monguor. The results suggest that the gradient dissimilation in Halh may represent the phonetic...

  16. Gradient algorithm applied to laboratory quantum control

    International Nuclear Information System (INIS)

    Roslund, Jonathan; Rabitz, Herschel

    2009-01-01

    The exploration of a quantum control landscape, which is the physical observable as a function of the control variables, is fundamental for understanding the ability to perform observable optimization in the laboratory. For high control variable dimensions, trajectory-based methods provide a means for performing such systematic explorations by exploiting the measured gradient of the observable with respect to the control variables. This paper presents a practical, robust, easily implemented statistical method for obtaining the gradient on a general quantum control landscape in the presence of noise. In order to demonstrate the method's utility, the experimentally measured gradient is utilized as input in steepest-ascent trajectories on the landscapes of three model quantum control problems: spectrally filtered and integrated second harmonic generation as well as excitation of atomic rubidium. The gradient algorithm achieves efficiency gains of up to approximately three times that of the standard genetic algorithm and, as such, is a promising tool for meeting quantum control optimization goals as well as landscape analyses. The landscape trajectories directed by the gradient should aid in the continued investigation and understanding of controlled quantum phenomena.

  17. Book title: Exotic brome grasses in arid and semi-arid ecosystems of the western US: causes, consequences, and management implications

    Science.gov (United States)

    Exotic invasive annual grass research and management in arid and semiarid ecosystems of the western US have historically focused on the outcome of efforts to reduce weed abundance. Given the current impact of invasive annual grasses and their continued spread in this region, we assessed components ...

  18. A Review of Applicability and Effectiveness of Low Impact Development/Green Infrastructure Practices in Arid/Semi-Arid United States

    Directory of Open Access Journals (Sweden)

    Yan Jiang

    2015-06-01

    Full Text Available Urbanized areas of the southwestern/western United States are among the fastest growing in the nation and face multiple water resource challenges. Low impact development (LID/green infrastructure (GI practices are increasingly popular technologies for managing stormwater; however, LID is often not as common in the southwest/west due to the lack of regulatory and/or economic drivers. There is also a lack of performance evaluation of these practices, particularly at the field scale. This study focused on investigating the hydrologic and pollutant removal performance of field-scale LID/GI systems in arid/semi-arid climates. Nine typical practices were reviewed: rainwater harvest system, detention pond, retention pond, bioretention, media filter, porous pavement, vegetated swale/buffer/strip, green roof, and infiltration trench, as well as integrated LIDs. We evaluate these practices by a cost-effectiveness analysis and also recommend best practices for the arid/semi-arid area. The analysis provides data support and insights for future implementation of LID/GI in the southwest/west.

  19. Date palm (Phoenix dactylifera L.) leaves as biomonitors of atmospheric metal pollution in arid and semi-arid environments

    Energy Technology Data Exchange (ETDEWEB)

    Al-Khashman, Omar Ali, E-mail: omarkhashman@yahoo.com [Department of Environmental Engineering, Faculty of Engineering, Al-Hussein Bin Talal University, P.O. Box (20), Ma' an-Jordan (Jordan); Al-Muhtaseb, Ala' a H.; Ibrahim, Khalid A. [Department of Chemical Engineering, Faculty of Engineering, Al-Hussein Bin Talal University, P.O. Box (20), Ma' an-Jordan (Jordan)

    2011-06-15

    The leaves of date palms were evaluated as a possible biomonitor of heavy metal contamination in Ma'an city, Jordan. Concentrations of (Fe), (Pb), (Zn), (Cu), (Ni), and (Cr) were determined in washed and unwashed leaves and soil samples collected from different sites with different degrees of metal contamination (urban, suburban, industrial, highway and rural sites); separate leaves were taken from outside the city to be used as a control sample. Samples collected from industrial sites were found to have high concentrations of all metals except those of Cu, Ni and Pb, which were found at high levels in the highway site samples which is associated with the road traffic. The difference between unwashed and washed samples showed that metal pollutants exist as contaminants, particularly Pb, Zn and Ni, which varied in concentration, depending on the source of the metal. - Highlights: > High metal concentration in plant samples and roadside soil was due to the heavy traffic. > The mean concentrations (C) were in the order: C{sub Fe} > C{sub Pb} > C{sub Zn} > C{sub Ni} > C{sub Cu} > C{sub Cr}. > Difference between unwashed and washed samples showed that pollutants exist as contaminants. - Date palm (Phoenix dactylifera L.) leaves can be used as an inexpensive biomonitor of the deposition, accumulation and distribution of heavy metal contamination in arid environments.

  20. Date palm (Phoenix dactylifera L.) leaves as biomonitors of atmospheric metal pollution in arid and semi-arid environments

    International Nuclear Information System (INIS)

    Al-Khashman, Omar Ali; Al-Muhtaseb, Ala'a H.; Ibrahim, Khalid A.

    2011-01-01

    The leaves of date palms were evaluated as a possible biomonitor of heavy metal contamination in Ma'an city, Jordan. Concentrations of (Fe), (Pb), (Zn), (Cu), (Ni), and (Cr) were determined in washed and unwashed leaves and soil samples collected from different sites with different degrees of metal contamination (urban, suburban, industrial, highway and rural sites); separate leaves were taken from outside the city to be used as a control sample. Samples collected from industrial sites were found to have high concentrations of all metals except those of Cu, Ni and Pb, which were found at high levels in the highway site samples which is associated with the road traffic. The difference between unwashed and washed samples showed that metal pollutants exist as contaminants, particularly Pb, Zn and Ni, which varied in concentration, depending on the source of the metal. - Highlights: → High metal concentration in plant samples and roadside soil was due to the heavy traffic. → The mean concentrations (C) were in the order: C Fe > C Pb > C Zn > C Ni > C Cu > C Cr . → Difference between unwashed and washed samples showed that pollutants exist as contaminants. - Date palm (Phoenix dactylifera L.) leaves can be used as an inexpensive biomonitor of the deposition, accumulation and distribution of heavy metal contamination in arid environments.

  1. Some cirad activities and perspectives in water and nutrient management in arid and semi-arid regions using nuclear techniques

    International Nuclear Information System (INIS)

    Maraux, F.; Affholder, F.; Forest, F.; Ganry, F.; N'diaye, M.; Oliver, R.; Scopel, E.

    1998-01-01

    The Centre de Cooperation Internationale en Recherche Agronomique pour le Developpement has conducted collaborative research with national agricultural research services in several semi-arid regions that has led to a general understanding of the relationship between water consumption and growth, and crop responses to fertilizers. However, farmers' adoption of practices arising from the research has been minimal. Current effort is directed at overcoming limits to adoption, firstly by understanding the interaction of fertilizer response and water supply, especially through modelling, in order to quantify risk criteria from the farmer's point of view. Secondly, research now takes account of the whole cropping system, including labour availability, access to credit, livestock management, etc., with a multidisciplinary approach. Approaches that offer sustainability are improved intercropping systems, retention of crop residues, increased plant cover, and agroforestry. There are important technical gaps in understanding of how these systems should operate. The allocation of nutrients and water among the components of intercropped or agroforestry systems is not understood and solutions could lead to improved spatial arrangements. The integrated effects of residues on runoff, soil evaporation, crop transpiration and N mineralization are not quantified. In these and other problems, the full range of risks as well as benefits need to be evaluated. (author)

  2. An implicit tensorial gradient plasticity model - formulation and comparison with a scalar gradient model

    NARCIS (Netherlands)

    Poh, L.H.; Peerlings, R.H.J.; Geers, M.G.D.; Swaddiwudhipong, S.

    2011-01-01

    Many rate-independent models for metals utilize the gradient of effective plastic strain to capture size-dependent behavior. This enhancement, sometimes termed as "explicit" gradient formulation, requires higher-order tractions to be imposed on the evolving elasto-plastic boundary and the resulting

  3. Evidence of counter-gradient growth in western pond turtles (Actinemys marmorata) across thermal gradients

    Science.gov (United States)

    Snover, Melissa; Adams, Michael J.; Ashton, Donald T.; Bettaso, Jamie B.; Welsh, Hartwell H.

    2015-01-01

    Counter-gradient growth, where growth per unit temperature increases as temperature decreases, can reduce the variation in ectothermic growth rates across environmental gradients. Understanding how ectothermic species respond to changing temperatures is essential to their conservation and management due to human-altered habitats and changing climates.

  4. Momentum-weighted conjugate gradient descent algorithm for gradient coil optimization.

    Science.gov (United States)

    Lu, Hanbing; Jesmanowicz, Andrzej; Li, Shi-Jiang; Hyde, James S

    2004-01-01

    MRI gradient coil design is a type of nonlinear constrained optimization. A practical problem in transverse gradient coil design using the conjugate gradient descent (CGD) method is that wire elements move at different rates along orthogonal directions (r, phi, z), and tend to cross, breaking the constraints. A momentum-weighted conjugate gradient descent (MW-CGD) method is presented to overcome this problem. This method takes advantage of the efficiency of the CGD method combined with momentum weighting, which is also an intrinsic property of the Levenberg-Marquardt algorithm, to adjust step sizes along the three orthogonal directions. A water-cooled, 12.8 cm inner diameter, three axis torque-balanced gradient coil for rat imaging was developed based on this method, with an efficiency of 2.13, 2.08, and 4.12 mT.m(-1).A(-1) along X, Y, and Z, respectively. Experimental data demonstrate that this method can improve efficiency by 40% and field uniformity by 27%. This method has also been applied to the design of a gradient coil for the human brain, employing remote current return paths. The benefits of this design include improved gradient field uniformity and efficiency, with a shorter length than gradient coil designs using coaxial return paths. Copyright 2003 Wiley-Liss, Inc.

  5. Energy Productivity of the High Velocity Algae Raceway Integrated Design (ARID-HV)

    Energy Technology Data Exchange (ETDEWEB)

    Attalah, Said; Waller, Peter M.; Khawam, George; Ryan, Randy D.; Huesemann, Michael H.

    2015-06-03

    The original Algae Raceway Integrated Design (ARID) raceway was an effective method to increase algae culture temperature in open raceways. However, the energy input was high and flow mixing was poor. Thus, the High Velocity Algae Raceway Integrated Design (ARID-HV) raceway was developed to reduce energy input requirements and improve flow mixing in a serpentine flow path. A prototype ARID-HV system was installed in Tucson, Arizona. Based on algae growth simulation and hydraulic analysis, an optimal ARID-HV raceway was designed, and the electrical energy input requirement (kWh ha-1 d-1) was calculated. An algae growth model was used to compare the productivity of ARIDHV and conventional raceways. The model uses a pond surface energy balance to calculate water temperature as a function of environmental parameters. Algae growth and biomass loss are calculated based on rate constants during day and night, respectively. A 10 year simulation of DOE strain 1412 (Chlorella sorokiniana) showed that the ARID-HV raceway had significantly higher production than a conventional raceway for all months of the year in Tucson, Arizona. It should be noted that this difference is species and climate specific and is not observed in other climates and with other algae species. The algae growth model results and electrical energy input evaluation were used to compare the energy productivity (algae production rate/energy input) of the ARID-HV and conventional raceways for Chlorella sorokiniana in Tucson, Arizona. The energy productivity of the ARID-HV raceway was significantly greater than the energy productivity of a conventional raceway for all months of the year.

  6. Progress and prospects of climate change impacts on hydrology in the arid region of northwest China.

    Science.gov (United States)

    Chen, Yaning; Li, Zhi; Fan, Yuting; Wang, Huaijun; Deng, Haijun

    2015-05-01

    The arid region of Northwest China, located in the central Asia, responds sensitively to global climate change. Based on the newest research results, this paper analyzes the impacts of climate change on hydrology and the water cycle in the arid region of Northwest China. The analysis results show that: (1) In the northwest arid region, temperature and precipitation experienced "sharply" increasing in the past 50 years. The precipitation trend changed in 1987, and since then has been in a state of high volatility, during the 21st century, the increasing rate of precipitation was diminished. Temperature experienced a "sharply" increase in 1997; however, this sharp increasing trend has turned to an apparent hiatus since the 21st century. The dramatic rise in winter temperatures in the northwest arid region is an important reason for the rise in the average annual temperature, and substantial increases in extreme winter minimum temperature play an important role in the rising average winter temperature; (2) There was a significant turning point in the change of pan evaporation in the northwest arid area in 1993, i.e., in which a significant decline reversed to a significant upward trend. In the 21st century, the negative effects of global warming and increasing levels of evaporation on the ecology of the northwest arid region have been highlighted; (3) Glacier change has a significant impact on hydrology in the northwest arid area, and glacier inflection points have appeared in some rivers. The melting water supply of the Tarim River Basin possesses a large portion of water supplies (about 50%). In the future, the amount of surface water will probably remain at a high state of fluctuation. Copyright © 2015 Elsevier Inc. All rights reserved.

  7. Cuticular waxes in alpine meadow plants: climate effect inferred from latitude gradient in Qinghai-Tibetan Plateau.

    Science.gov (United States)

    Guo, Yanjun; Guo, Na; He, Yuji; Gao, Jianhua

    2015-09-01

    Alpine meadow ecosystems are susceptible to climate changes. Still, climate impact on cuticular wax in alpine meadow plants is poorly understood. Assessing the variations of cuticular wax in alpine meadow plants across different latitudes might be useful for predicting how they may respond to climate change. We studied nine alpine meadows in a climate gradient in the east side of Qinghai-Tibetan Plateau, with mean annual temperature ranging from -7.7 to 3.2°C. In total, 42 plant species were analyzed for cuticular wax, averaged 16 plant species in each meadow. Only four plant species could be observed in all sampling meadows, including Kobresia humilis,Potentilla nivea,Anaphalis lacteal, and Leontopodium nanum. The amounts of wax compositions and total cuticular wax in the four plant species varied among sampling meadows, but no significant correlation could be observed between them and temperature, precipitation, and aridity index based on plant species level. To analyze the variations of cuticular wax on community level, we averaged the amounts of n-alkanes, aliphatic acids, primary alcohols, and total cuticular wax across all investigated plant species in each sampling site. The mean annual temperature, mean temperature in July, and aridity index were significantly correlated with the averaged amounts of wax compositions and total cuticular wax. The average chain length of n-alkanes in both plant and soil linearly increased with increased temperature, whereas reduced with increased aridity index. No significant correlation could be observed between mean annual precipitation and mean precipitation from June to August and the cuticular wax amounts and average chain length. Our results suggest that the survival of some alpine plants in specific environments might be depended on their abilities in adjusting wax deposition on plant leaves, and the alpine meadow plants as a whole respond to climate change, benefiting the stability of alpine meadow ecosystem.

  8. Bacterial community of cushion plant Thylacospermum ceaspitosum on elevational gradient in the Himalayan cold desert.

    Science.gov (United States)

    Řeháková, Klára; Chroňáková, Alica; Krištůfek, Václav; Kuchtová, Barbora; Čapková, Kateřina; Scharfen, Josef; Čapek, Petr; Doležal, Jiří

    2015-01-01

    Although bacterial assemblages are important components of soils in arid ecosystems, the knowledge about composition, life-strategies, and environmental drivers is still fragmentary, especially in remote high-elevation mountains. We compared the quality and quantity of heterotrophic bacterial assemblages between the rhizosphere of the dominant cushion-forming plant Thylacospermum ceaspitosum and its surrounding bulk soil in two mountain ranges (East Karakoram: 4850-5250 m and Little Tibet: 5350-5850 m), in communities from cold steppes to the subnival zone in Ladakh, arid Trans-Himalaya, northwest India. Bacterial communities were characterized by molecular fingerprinting in combination with culture-dependent methods. The effects of environmental factors (elevation, mountain range, and soil physico-chemical parameters) on the bacterial community composition and structure were tested by multivariate redundancy analysis and conditional inference trees. Actinobacteria dominate the cultivable part of community and represent a major bacterial lineage of cold desert soils. The most abundant genera were Streptomyces, Arthrobacter, and Paenibacillus, representing both r- and K-strategists. The soil texture is the most important factor for the community structure and the total bacteria counts. Less abundant and diverse assemblages are found in East Karakoram with coarser soils derived from leucogranite bedrock, while more diverse assemblages in Little Tibet are associated with finer soils derived from easily weathering gneisses. Cushion rhizosphere is in general less diverse than bulk soil, and contains more r-strategists. K-strategists are more associated with the extremes of the gradient, with drought at lowest elevations (4850-5000 m) and frost at the highest elevations (5750-5850 m). The present study illuminates the composition of soil bacterial assemblages in relation to the cushion plant T. ceaspitosum in a xeric environment and brings important information about

  9. Hydraulic properties and fine root mass of Larix sibirica along forest edge-interior gradients

    Science.gov (United States)

    Chenlemuge, Tselmeg; Dulamsuren, Choimaa; Hertel, Dietrich; Schuldt, Bernhard; Leuschner, Christoph; Hauck, Markus

    2015-02-01

    At its southernmost distribution limit in Inner Asia, the boreal forest disintegrates into forest fragments on moist sites (e.g. north-facing slopes), which are embedded in grasslands. This landscape mosaic is characterized by a much higher forest edge-to-interior ratio than in closed boreal forests. Earlier work in the forest-steppe ecotone of Mongolia has shown that Larix sibirica trees at forest edges grow faster than in the forest interior, as the more xeric environment at the edge promotes self-thinning and edges are preferentially targeted by selective logging and livestock grazing. Lowered stand density reduces competition for water in these semi-arid forests, where productivity is usually limited by summer drought. We studied how branch and coarse root hydraulic architecture and xylem conductivity, fine root biomass and necromass, and fine root morphology of L. sibirica respond to sites differing in water availability. Studying forest edge-interior gradients in two regions of western Mongolia, we found a significant reduction of branch theoretical (Kp) and empirical conductivity (Ks) in the putatively more drought-affected forest interior in the Mongolian Altai (mean precipitation: 120 mm yr-1), while no branch xylem modification occurred in the moister Khangai Mountains (215 mm yr-1). Kp and Ks were several times larger in roots than in branches, but root hydraulics were not influenced by stand density or mean annual precipitation. Very low fine root biomass: necromass ratios at all sites, and in the forest interior in particular, suggest that L. sibirica seeks to maintain a relatively high root conductivity by producing large conduits, which results in high root mortality due to embolism during drought. Our results suggest that L. sibirica is adapted to the semi-arid climate at its southernmost distribution limit by considerable plasticity of the branch hydraulic system and a small but apparently dynamic fine root system.

  10. Assessing Freshwater Ecosystem Service Risk over Ecological, Socioeconomic, and Cultural Gradients: Problem Space Characterization and Methodology

    Science.gov (United States)

    Harmon, T. C.; Villamizar, S. R.; Conde, D.; Rusak, J.; Reid, B.; Astorga, A.; Perillo, G. M.; Piccolo, M. C.; Zilio, M.; London, S.; Velez, M.; Hoyos, N.; Escobar, J.

    2014-12-01

    Freshwater ecosystems and the services they provide are under increasing anthropogenic pressure at local (e.g., irrigation diversions, wastewater discharge) and global scales (e.g., climate change, global trading). The impact depends on an ecosystem's sensitivity, which is determined by its geophysical and ecological settings, and the population and activities in its surrounding watershed. Given the importance of ecosystem services, it is critical that we improve our ability to identify and understand changes in aquatic ecosystems, and translate them to risk of service loss. Furthermore, to inspire changes in human behavior, it is equally critical that we learn to communicate risk, and pose risk mitigation strategies, in a manner acceptable to a broad spectrum of stakeholders. Quantifying the nature and timing of the risk is difficult because (1) we often fail to understand the connection between anthropogenic pressures and the timing and extent of ecosystem changes; and (2) the concept of risk is inherently coupled to human perception, which generally differs with cultural and socio-economic conditions. In this study, we endeavor to assess aquatic ecosystem risks across an international array of six study sites. The challenge is to construct a methodology capable of capturing the marked biogeographical, socioeconomic, and cultural differences among the sites, which include: (1) Muskoka River watershed in humid continental Ontario, Canada; (2) Lower San Joaquin River, an impounded snow-fed river in semi-arid Central California; (3) Ciénaga Grande de Santa Marta, a tropical coastal lagoon in Colombia; (4) Senguer River basin in the semi-arid part of Argentina; (5) Laguna de Rocha watershed in humid subtropical Uruguay; and (6) Palomas Lake complex in oceanic Chilean Patagonia. Results will include a characterization of the experimental gradient over the six sites, an overview of the risk assessment methodology, and preliminary findings for several of the sites.

  11. Toxic metal(loid) speciation during weathering of iron sulfide mine tailings under semi-arid climate

    Science.gov (United States)

    Root, Robert A.; Hayes, Sarah M.; Hammond, Corin M.; Maier, Raina M.; Chorover, Jon

    2015-01-01

    Toxic metalliferous mine-tailings pose a significant health risk to ecosystems and neighboring communities from wind and water dispersion of particulates containing high concentrations of toxic metal(loid)s (e.g., Pb, As, Zn). Tailings are particularly vulnerable to erosion before vegetative cover can be reestablished, i.e., decades or longer in semi-arid environments without intervention. Metal(loid) speciation, linked directly to bioaccessibility and lability, is controlled by mineral weathering and is a key consideration when assessing human and environmental health risks associated with mine sites. At the semi-arid Iron King Mine and Humboldt Smelter Superfund site in central Arizona, the mineral assemblage of the top 2 m of tailings has been previously characterized. A distinct redox gradient was observed in the top 0.5 m of the tailings and the mineral assemblage indicates progressive transformation of ferrous iron sulfides to ferrihydrite and gypsum, which, in turn weather to form schwertmannite and then jarosite accompanied by a progressive decrease in pH (7.3 to 2.3). Within the geochemical context of this reaction front, we examined enriched toxic metal(loid)s As, Pb, and Zn with surficial concentrations 41.1, 10.7, 39.3 mM kg-1 (3080, 2200, and 2570 mg kg-1), respectively. The highest bulk concentrations of As and Zn occur at the redox boundary representing a 1.7 and 4.2 fold enrichment relative to surficial concentrations, respectively, indicating the translocation of toxic elements from the gossan zone to either the underlying redox boundary or the surface crust. Metal speciation was also examined as a function of depth using X-ray absorption spectroscopy (XAS). The deepest sample (180 cm) contains sulfides (e.g., pyrite, arsenopyrite, galena, and sphalerite). Samples from the redox transition zone (25-54 cm) contain a mixture of sulfides, carbonates (siderite, ankerite, cerrusite, and smithsonite) and metal(loid)s sorbed to neoformed secondary Fe

  12. Inversion gradients for acoustic VTI wavefield tomography

    KAUST Repository

    Li, Vladimir; Wang, Hui; Tsvankin, Ilya; Dí az, Esteban; Alkhalifah, Tariq Ali

    2017-01-01

    Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a generalized pseudospectral operator based on a separable approximation for the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified image-power objective functions. We also obtain the gradient expressions for a data-domain objective function that can more easily incorporate borehole information necessary for stable VTI velocity analysis. These gradients are similar to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations but the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show the potential advantages of the modified image-power objective function in estimating the anellipticity parameter η.

  13. Gradient pattern analysis applied to galaxy morphology

    Science.gov (United States)

    Rosa, R. R.; de Carvalho, R. R.; Sautter, R. A.; Barchi, P. H.; Stalder, D. H.; Moura, T. C.; Rembold, S. B.; Morell, D. R. F.; Ferreira, N. C.

    2018-06-01

    Gradient pattern analysis (GPA) is a well-established technique for measuring gradient bilateral asymmetries of a square numerical lattice. This paper introduces an improved version of GPA designed for galaxy morphometry. We show the performance of the new method on a selected sample of 54 896 objects from the SDSS-DR7 in common with Galaxy Zoo 1 catalogue. The results suggest that the second gradient moment, G2, has the potential to dramatically improve over more conventional morphometric parameters. It separates early- from late-type galaxies better (˜ 90 per cent) than the CAS system (C˜ 79 per cent, A˜ 50 per cent, S˜ 43 per cent) and a benchmark test shows that it is applicable to hundreds of thousands of galaxies using typical processing systems.

  14. Dynamics of gradient formation by intracellular shuttling

    Energy Technology Data Exchange (ETDEWEB)

    Berezhkovskii, Alexander M. [Mathematical and Statistical Computing Laboratory, Division of Computational Bioscience, Center for Information Technology, National Institutes of Health, Bethesda, Maryland 20892 (United States); Shvartsman, Stanislav Y. [Department of Chemical and Biological Engineering and Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey 08544 (United States)

    2015-08-21

    A number of important cellular functions rely on the formation of intracellular protein concentration gradients. Experimental studies discovered a number of mechanisms for the formation of such gradients. One of the mechanisms relies on the intracellular shuttling of a protein that interconverts between the two states with different diffusivities, under the action of two enzymes, one of which is localized to the plasma membrane, whereas the second is uniformly distributed in the cytoplasm. Recent work reported an analytical solution for the steady state gradient in this mechanism, obtained in the framework of a one-dimensional reaction-diffusion model. Here, we study the dynamics in this model and derive analytical expressions for the Laplace transforms of the time-dependent concentration profiles in terms of elementary transcendental functions. Inverting these transforms numerically, one can obtain time-dependent concentration profiles of the two forms of the protein.

  15. Relativistic klystrons for high-gradient accelerators

    International Nuclear Information System (INIS)

    Westenskow, G.A.; Aalberts, D.P.; Boyd, J.K.; Deis, G.A.; Houck, T.L.; Orzechowski, T.J.; Ryne, R.D.; Yu, S.S.; Allen, M.A.; Callin, R.S.; Deruyter, H.; Eppley, K.R.; Fant, K.S.; Fowkes, W.R.; Hoag, H.A.; Koontz, R.F.; Lavine, T.L.; Loew, G.A.; Miller, R.H.; Ruth, R.D.; Vlieks, A.E.; Wang, J.W.; Hopkins, D.B.; Sessler, A.M.; Haimson, J.; Mecklenburg, B.

    1991-01-01

    Experimental work is being performed by collaborators at LLNL, SLAC, and LBL to investigate relativistic klystrons as a possible rf power source for future high-gradient accelerators. The authors have learned how to overcome their previously reported problem of high power rf pulse shortening and have achieved peak rf power levels of 330 MW using an 11.4-GHz high-gain tube with multiple output structures. In these experiments the rf pulse is of the same duration as the beam current pulse. In addition, experiments have been performed on two short sections of a high-gradient accelerator using the rf power from a relativistic klystron. An average accelerating gradient of 84 MV/m has been achieved with 80-MW of rf power

  16. Substrate curvature gradient drives rapid droplet motion.

    Science.gov (United States)

    Lv, Cunjing; Chen, Chao; Chuang, Yin-Chuan; Tseng, Fan-Gang; Yin, Yajun; Grey, Francois; Zheng, Quanshui

    2014-07-11

    Making small liquid droplets move spontaneously on solid surfaces is a key challenge in lab-on-chip and heat exchanger technologies. Here, we report that a substrate curvature gradient can accelerate micro- and nanodroplets to high speeds on both hydrophilic and hydrophobic substrates. Experiments for microscale water droplets on tapered surfaces show a maximum speed of 0.42  m/s, 2 orders of magnitude higher than with a wettability gradient. We show that the total free energy and driving force exerted on a droplet are determined by the substrate curvature and substrate curvature gradient, respectively. Using molecular dynamics simulations, we predict nanoscale droplets moving spontaneously at over 100  m/s on tapered surfaces.

  17. Nonlinear conjugate gradient methods in micromagnetics

    Directory of Open Access Journals (Sweden)

    J. Fischbacher

    2017-04-01

    Full Text Available Conjugate gradient methods for energy minimization in micromagnetics are compared. The comparison of analytic results with numerical simulation shows that standard conjugate gradient method may fail to produce correct results. A method that restricts the step length in the line search is introduced, in order to avoid this problem. When the step length in the line search is controlled, conjugate gradient techniques are a fast and reliable way to compute the hysteresis properties of permanent magnets. The method is applied to investigate demagnetizing effects in NdFe12 based permanent magnets. The reduction of the coercive field by demagnetizing effects is μ0ΔH = 1.4 T at 450 K.

  18. Inversion gradients for acoustic VTI wavefield tomography

    KAUST Repository

    Li, Vladimir

    2017-03-21

    Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a generalized pseudospectral operator based on a separable approximation for the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified image-power objective functions. We also obtain the gradient expressions for a data-domain objective function that can more easily incorporate borehole information necessary for stable VTI velocity analysis. These gradients are similar to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations but the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show the potential advantages of the modified image-power objective function in estimating the anellipticity parameter η.

  19. Vertical gradients of sunspot magnetic fields

    Science.gov (United States)

    Hagyard, M. J.; Teuber, D.; West, E. A.; Tandberg-Hanssen, E.; Henze, W., Jr.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; Woodgate, B. E.

    1983-01-01

    The results of a Solar Maximum Mission (SMM) guest investigation to determine the vertical gradients of sunspot magnetic fields for the first time from coordinated observations of photospheric and transition-region fields are described. Descriptions are given of both the photospheric vector field of a sunspot, derived from observations using the NASA Marshall Space Flight Center vector magnetograph, and of the line-of-sight component in the transition region, obtained from the SMM Ultraviolet Spectrometer and Polarimeter instrument. On the basis of these data, vertical gradients of the line-of-sight magnetic field component are calculated using three methods. It is found that the vertical gradient of Bz is lower than values from previous studies and that the transition-region field occurs at a height of approximately 4000-6000 km above the photosphere.

  20. Conjugate gradient algorithms using multiple recursions

    Energy Technology Data Exchange (ETDEWEB)

    Barth, T.; Manteuffel, T.

    1996-12-31

    Much is already known about when a conjugate gradient method can be implemented with short recursions for the direction vectors. The work done in 1984 by Faber and Manteuffel gave necessary and sufficient conditions on the iteration matrix A, in order for a conjugate gradient method to be implemented with a single recursion of a certain form. However, this form does not take into account all possible recursions. This became evident when Jagels and Reichel used an algorithm of Gragg for unitary matrices to demonstrate that the class of matrices for which a practical conjugate gradient algorithm exists can be extended to include unitary and shifted unitary matrices. The implementation uses short double recursions for the direction vectors. This motivates the study of multiple recursion algorithms.

  1. Bird migration patterns in the arid southwest-Final report

    Science.gov (United States)

    Ruth, Janet M.; Felix, Rodney K.; Dieh, Robert H.

    2010-01-01

    To ensure full life-cycle conservation, we need to understand migrant behavior en route and how migrating species use stopover and migration aerohabitats. In the Southwest, birds traverse arid and mountainous landscapes in migration. Migrants are known to use riparian stopover habitats; we know less about how migrant density varies across the Southwest seasonally and annually, and how migrants use other habitat types during migratory stopover. Furthermore, we lack information about migrant flight altitudes, speeds, and directions of travel, and how these patterns vary seasonally and annually across the Southwest. Using weather surveillance radar data, we identified targets likely dominated by nocturnally migrating birds and determined their flight altitudes, speeds, directions over ground, and variations in abundance. Migrating or foraging bats likely are present across the region in some of these data, particularly in central Texas. We found that migrants flew at significantly lower altitudes and significantly higher speeds in spring than in fall. In all seasons migrants maintained seasonally appropriate directions of movement. We detected significant differences in vertical structure of migrant densities that varied both geographically within seasons and seasonally within sites. We also found that in fall there was a greater and more variable passage of migrants through the central part of the borderlands (New Mexico and west Texas); in spring there was some suggestion of greater and more variable passage of migrants in the eastern borderlands (central and south Texas). Such patterns are consistent with the existence of at least two migration systems through western North America and the use of different migration routes in spring and fall for at least some species. Using radar data and satellite land cover data, we determined the habitats with which migrants are associated during migration stopover. There were significant differences in bird densities among

  2. let-7 Modulates Chromatin Configuration and Target Gene Repression through Regulation of the ARID3B Complex

    Directory of Open Access Journals (Sweden)

    Tsai-Tsen Liao

    2016-01-01

    Full Text Available Let-7 is crucial for both stem cell differentiation and tumor suppression. Here, we demonstrate a chromatin-dependent mechanism of let-7 in regulating target gene expression in cancer cells. Let-7 directly represses the expression of AT-rich interacting domain 3B (ARID3B, ARID3A, and importin-9. In the absence of let-7, importin-9 facilitates the nuclear import of ARID3A, which then forms a complex with ARID3B. The nuclear ARID3B complex recruits histone demethylase 4C to reduce histone 3 lysine 9 trimethylation and promotes the transcription of stemness factors. Functionally, expression of ARID3B is critical for the tumor initiation in let-7-depleted cancer cells. An inverse association between let-7 and ARID3A/ARID3B and prognostic significance is demonstrated in head and neck cancer patients. These results highlight a chromatin-dependent mechanism where let-7 regulates cancer stemness through ARID3B.

  3. METALLICITY GRADIENTS OF THICK DISK DWARF STARS

    Energy Technology Data Exchange (ETDEWEB)

    Carrell, Kenneth; Chen Yuqin; Zhao Gang, E-mail: carrell@nao.cas.cn [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

    2012-12-01

    We examine the metallicity distribution of the Galactic thick disk using F, G, and K dwarf stars selected from the Sloan Digital Sky Survey, Data Release 8. Using the large sample of dwarf stars with proper motions and spectroscopically determined stellar parameters, metallicity gradients in the radial direction for various heights above the Galactic plane and in the vertical direction for various radial distances from the Galaxy center have been found. In particular, we find a vertical metallicity gradient of -0.113 {+-} 0.010 (-0.125 {+-} 0.008) dex kpc{sup -1} using an isochrone (photometric) distance determination in the range 1 kpc <|Z| < 3 kpc, which is the vertical height range most consistent with the thick disk of our Galaxy. In the radial direction, we find metallicity gradients between +0.02 and +0.03 dex kpc{sup -1} for bins in the vertical direction between 1 kpc <|Z| < 3 kpc. Both of these results agree with similar values determined from other populations of stars, but this is the first time a radial metallicity gradient for the thick disk has been found at these vertical heights. We are also able to separate thin and thick disk stars based on kinematic and spatial probabilities in the vertical height range where there is significant overlap of these two populations. This should aid further studies of the metallicity gradients of the disk for vertical heights lower than those studied here but above the solar neighborhood. Metallicity gradients in the thin and thick disks are important probes into possible formation scenarios for our Galaxy and a consistent picture is beginning to emerge from results using large spectroscopic surveys, such as the ones presented here.

  4. Review of new shapes for higher gradients

    International Nuclear Information System (INIS)

    Geng, R.L.

    2006-01-01

    High-gradient superconducting RF (SRF) cavities are needed for energy frontier superconducting accelerators. Progress has been made over the past decades and the accelerating gradient E acc has been increased from a few MV/m to ∼42 MV/m in SRF niobium cavities. The corresponding peak RF magnetic field H pk on the niobium cavity surface is approaching the intrinsic RF critical magnetic field H crit,RF , a hard physical limit at which superconductivity breaks down. Pushing the gradient envelope further by adopting new cavity shapes with a lower ratio of H pk /E acc has been recently proposed. For a reduced H pk /E acc , a higher ultimate E acc is sustained when H pk finally strikes H crit,RF . The new cavity geometry include the re-entrant shape conceived at Cornell University and the so-called 'Low-loss' shape proposed by a DESY/JLAB/KEK collaboration. Experimental work is being pursued at Cornell, KEK and JLAB. Results of single-cell cavities are encouraging. A record gradient of 47 MV/m was first demonstrated in a 1.3 GHz re-entrant niobium cavity at Cornell University. At the time of writing, a new record of 52 MV/m has been realized with another 1.3 GHz re-entrant cavity, designed and built at Cornell and processed and tested at KEK. Single-cell low-loss cavities have reached equally high gradients in the range of 45-51 MV/m at KEK and JLAB. Owing to their higher gradient potential and the encouraging single-cell cavity results, the new cavity shapes are becoming attractive for their possible use in the international linear collider (ILC). Experimental work on multi-cell niobium cavities of new shapes is currently under active exploration

  5. Review of new shapes for higher gradients

    Science.gov (United States)

    Geng, R. L.

    2006-07-01

    High-gradient superconducting RF (SRF) cavities are needed for energy frontier superconducting accelerators. Progress has been made over the past decades and the accelerating gradient Eacc has been increased from a few MV/m to ∼42 MV/m in SRF niobium cavities. The corresponding peak RF magnetic field Hpk on the niobium cavity surface is approaching the intrinsic RF critical magnetic field Hcrit,RF, a hard physical limit at which superconductivity breaks down. Pushing the gradient envelope further by adopting new cavity shapes with a lower ratio of Hpk/ Eacc has been recently proposed. For a reduced Hpk/ Eacc, a higher ultimate Eacc is sustained when Hpk finally strikes Hcrit,RF. The new cavity geometry include the re-entrant shape conceived at Cornell University and the so-called “Low-loss” shape proposed by a DESY/JLAB/KEK collaboration. Experimental work is being pursued at Cornell, KEK and JLAB. Results of single-cell cavities are encouraging. A record gradient of 47 MV/m was first demonstrated in a 1.3 GHz re-entrant niobium cavity at Cornell University. At the time of writing, a new record of 52 MV/m has been realized with another 1.3 GHz re-entrant cavity, designed and built at Cornell and processed and tested at KEK. Single-cell low-loss cavities have reached equally high gradients in the range of 45-51 MV/m at KEK and JLAB. Owing to their higher gradient potential and the encouraging single-cell cavity results, the new cavity shapes are becoming attractive for their possible use in the international linear collider (ILC). Experimental work on multi-cell niobium cavities of new shapes is currently under active exploration.

  6. Adaptive wetland management in an uncertain and changing arid environment

    Directory of Open Access Journals (Sweden)

    Rebekah Downard

    2014-06-01

    Full Text Available Wetlands in the arid western United States provide rare and critical migratory bird habitat and constitute a critical nexus within larger social-ecological systems (SES where multiple changing land-use and water-use patterns meet. The Bear River Migratory Bird Refuge in Utah, USA, presents a case study of the ways that wetland managers have created adaptive management strategies that are responsive to the social and hydrological conditions of the agriculture-dominated SES within which they are located. Managers have acquired water rights and constructed infrastructure while cultivating collaborative relationships with other water users to increase the adaptive capacity of the region and decrease conflict. Historically, water management involved diversion and impoundment of water within wetland units timed around patterns of agricultural water needs. In the last 20 years, managers have learned from flood and drought events and developed a long-term adaptive management plan that specifies alternative management actions managers can choose each year based on habitat needs and projected water supply. Each alternative includes habitat goals and target wetland water depth. However, wetland management adapted to agricultural return-flow availability may prove insufficient as population growth and climate change alter patterns of land and water use. Future management will likely depend more on negotiation, collaboration, and learning from social developments within the SES than strictly focusing on water management within refuge boundaries. To face this problem, managers have worked to be included in negotiations with regional water users, a strategy that may prove instructive for other wetland managers in agriculture-dominated watersheds.

  7. VOCs in Non-Arid Soils Integrated Demonstration: Technology summary

    International Nuclear Information System (INIS)

    1994-02-01

    The Volatile Organic Compounds (VOCs) in Non-Arid Soils Integrated Demonstration (ID) was initiated in 1989. Objectives for the ID were to test the integrated demonstration concept, demonstrate and evaluate innovative technologies/systems for the remediation of VOC contamination in soils and groundwater, and to transfer technologies and systems to internal and external customers for use in fullscale remediation programs. The demonstration brought together technologies from DOE laboratories, other government agencies, and industry for demonstration at a single test bed. The Savannah River Site was chosen as the location for this ID as the result of having soil and groundwater contaminated with VOCS. The primary contaminants, trichlorethylene and tetrachloroethylene, originated from an underground process sewer line servicing a metal fabrication facility at the M-Area. Some of the major technical accomplishments for the ID include the successful demonstration of the following: In situ air stripping coupled with horizontal wells to remediate sites through air injection and vacuum extraction; Crosshole geophysical tomography for mapping moisture content and lithologic properties of the contaminated media; In situ radio frequency and ohmic heating to increase mobility, of the contaminants, thereby speeding recovery and the remedial process; High-energy corona destruction of VOCs in the off-gas of vapor recovery wells; Application of a Brayton cycle heat pump to regenerate carbon adsorption media used to trap VOCs from the offgas of recovery wells; In situ permeable flow sensors and the colloidal borescope to determine groundwater flow; Chemical sensors to rapidly quantify chlorinated solvent contamination in the subsurface; In situ bioremediation through methane/nutrient injection to enhance degradation of contaminants by methanotrophic bateria

  8. Two thousand wind pumps in the arid region of Brazil

    International Nuclear Information System (INIS)

    Feitosa, E.A.N.; Sampaio, G.M.P.

    1991-01-01

    The North-East part of Brazil is an arid region where water pumping is of vital importance. The main strategy of the Wind Energy Group (Eolica) at the University of Pernambuco is to act as a 'catalyst' between the Brazilian government and the companies involved in wind energy. The company CONESP is a drilling company that is also responsible for choosing the appropriate pumping system and providing maintenance. CONESP already has drilled about 6,000 wells and installed 2,000 conventional windmills with piston pumps. Most of the wells have a very low capacity; thus wind pumps, having a relatively low water pumping capacity, are a suitable solution. However, one of the problems with the installed conventional wind pumps is that the drilled tube wells are not perfectly vertical, resulting in wear of the pump rod. Besides, the maintenance or replacement of the piston pump is time consuming and consequently costly. To reduce operation and maintenance costs, windmills coupled to pneumatic pumps have been developed. Examples are given of air-lift pumps and barc pumps, both using commercially available compressors. The main advantage is that there are no moving parts situated below ground level. Moreover, the windmill does not necessarily have to be placed above the well. Well and windmill can be situated up to 100 metres from each other. The starting torque of this system is also lower than the conventional wind pump. It is concluded that windmills with pneumatic pumps have a relatively low efficiency and higher investment costs compared with windmills coupled to piston pumps. However, CONESP's effort is to optimize the total performance of the pumping system. Due to the lower maintenance costs, pneumatic pumps seem to be a viable alternative to piston pumps. 7 figs., 3 refs

  9. Characterization of magnetically enhanced buried soil layer in arid environment

    Science.gov (United States)

    Petrovsky, E.; Grison, H.; Kapicka, A.; Silva, P. F.; Font, E.

    2011-12-01

    Magnetic susceptibility (MS) of soils, reflecting the presence of magnetite/maghemite, can be used in several environmental applications. Magnetic topsoil mapping is often used to outline areas polluted by atmospherically deposited dust. However, in these studies, the magnetically enhanced layer is usually shallow, some 5-6 cm under the surface. In our contribution, we present the case when the magnetic susceptibility is enhanced in deeper soil layers. Investigated soils are mostly sandy soils, from several localities in Portugal, in a zone with arid climate. Sample profiles were collected always in forests or forest stands with pines, cork oaks or eucalyptus trees in two areas: around the city of Sines (on the coast south of Lisbon) and around the city of Abrantes (inland, north-east of Lisbon). Both areas are presumably affected by one major source of pollution - power plant. Surface magnetic susceptibility measurements were performed by Bartington MS2D loop; values vary from 10 to 300 x 10-5 SI units. Vertical distribution of magnetic susceptibility was measured already in situ using the SM400 (ZHInstruments) on profiles about 40cm in length. Mass-specific MS was determined using Bartington MS2B dual frequency meter and Agico MFK1. Nine vertical profiles were selected for detailed analyses including the ARM, IRM and hysteresis measurements. Distinctly enhanced magnetic layers were detected in deeper horizons. This enhancement can be ascribed to several mechanisms. Migration of magnetic particles seems to be probable, as observed in our model experiments with sand columns. In coastal areas, the enhanced layer could be due to tsunami deposits, as described in other areas. Finally, in particular at sites close to power plants, the construction works followed by surface remediation have to be also considered as one of the possible mechanisms.

  10. Managing soil moisture on waste burial sites in arid regions

    International Nuclear Information System (INIS)

    Anderson, J.E.; Ratzlaff, T.D.; Nowak, R.S.; Markham, O.D.

    1993-01-01

    In semiarid regions, where potential evapotranspiration greatly exceeds precipitation, it is theoretically possible to preclude water form reaching interred wastes by (i) providing a sufficient cap of soil to store precipitation that falls while plants are dormant and (ii) establishing sufficient plant cover to deplete soil moisture during the growing season, thereby emptying the water storage reservoir of the soil. Here the authors discuss the theory and rationale for such an approach and then present the results of a field study to test its efficacy at the Idaho National Engineering Laboratory (INEL). They examined the capacity of four species of perennial plants to deplete soil moisture on simulated waste trenches and determined the effective water storage capacity of the soil. Those data enabled them to estimate the minimum depth of fill soil required to prevent deep drainage. Any of the species studied can use all of the plant-available soil water, even during a very wet growing season. The water storage capacity of the soil studied is 17% by volume, so a trench cap of 1.6 m of soil should be adequate to store precipitation received at the INEL while plants are dormant. They recommend a fill soil depth of 2 m to provide a margin of safety in case water accumulates in local areas as a result of heavy snow accumulation, subsidence, or runoff. Fill soil requirements and choice of plant species will vary, but the concepts and general approach are applicable to other shallow land burial sites in arid or semiarid regions. 23 refs., 5 figs

  11. Frequency Analysis of Gradient Estimators in Volume Rendering

    NARCIS (Netherlands)

    Bentum, Marinus Jan; Lichtenbelt, Barthold B.A.; Malzbender, Tom

    1996-01-01

    Gradient information is used in volume rendering to classify and color samples along a ray. In this paper, we present an analysis of the theoretically ideal gradient estimator and compare it to some commonly used gradient estimators. A new method is presented to calculate the gradient at arbitrary

  12. Lactate uptake against a concentration gradient

    DEFF Research Database (Denmark)

    Nordström, Carl-Henrik; Nielsen, Troels Halfeld; Nielsen, Hans Boye

    2014-01-01

    The recently published article by Jalloh et al (Jalloh I, Helmy A, Shannon RJ, Gallagher CN, Menon D, Carpenter K, Hutchinson P. Lactate uptake by the injured human brain - evidence from an arterio-venous gradient and cerebral microdialysis study. J Neurotrauma. 2013 Aug 22. [Epub ahead of print......]) concludes that lactate may be transported across the blood brain barrier into the brain against a concentration gradient. Unfortunately the authors have misinterpreted the concept of analytical imprecision and their conclusion is based on analytical artifact. As the topic of lactate transport into the brain...

  13. Measurement of gradient magnetic field temporal characteristics

    International Nuclear Information System (INIS)

    Bartusek, K.; Jflek, B.

    1994-01-01

    We describe a technique of measuring the time dependence and field distortions of magnetic fields due to eddy currents (EC) produced by time-dependent magnetic field gradients. The EC measuring technique makes use of a large volume sample and selective RF excitation pulses and free induction decay (FID) (or a spin or gradient echo) to measure the out-of-phase component of the FID, which is proportional to γδB, i.e. the amount the signal is off resonance. The measuring technique is sensitive, easy to implement and interpret, and used for determining pre-emphasis compensation parameters

  14. Magnetic field of longitudinal gradient bend

    Science.gov (United States)

    Aiba, Masamitsu; Böge, Michael; Ehrlichman, Michael; Streun, Andreas

    2018-06-01

    The longitudinal gradient bend is an effective method for reducing the natural emittance in light sources. It is, however, not a common element. We have analyzed its magnetic field and derived a set of formulae. Based on the derivation, we discuss how to model the longitudinal gradient bend in accelerator codes that are used for designing electron storage rings. Strengths of multipole components can also be evaluated from the formulae, and we investigate the impact of higher order multipole components in a very low emittance lattice.

  15. CFRMF neutron flux gradient and spectral determinations

    International Nuclear Information System (INIS)

    Rogers, J.W.; Turk, E.H.; Hogg, C.H.

    1976-01-01

    Recently more accurate and complete measurements of the flux gradient have been measured by the activation of 235 U and Au samples. Neutron spectrum characteristics were studied by making activation measurements with and without the ends of the CFRMF test region plugged with 10 B. These measurements define the flux gradient to +-1 to 2% and indicate there is no detectable streaming of thermal or resonance neutrons from the ends in the central 30 cm of the CFRMF test region. Measurements of the Cd ratio of Au foil activations were conducted and these results also indicate there is no streaming of thermal and resonance neutrons into the CFRMF test region

  16. The effect of density gradients on hydrometers

    Science.gov (United States)

    Heinonen, Martti; Sillanpää, Sampo

    2003-05-01

    Hydrometers are simple but effective instruments for measuring the density of liquids. In this work, we studied the effect of non-uniform density of liquid on a hydrometer reading. The effect induced by vertical temperature gradients was investigated theoretically and experimentally. A method for compensating for the effect mathematically was developed and tested with experimental data obtained with the MIKES hydrometer calibration system. In the tests, the method was found reliable. However, the reliability depends on the available information on the hydrometer dimensions and density gradients.

  17. Relativistic klystron research for high gradient accelerators

    International Nuclear Information System (INIS)

    Allen, M.A.; Callin, R.S.; Deruyter, H.

    1988-06-01

    Relativistic klystrons are being developed as a power source for high gradient accelerator applications which include large linear electron--positron colliders, compact accelerators, and FEL sources. We have attained 200MW peak power at 11.4 GHz from a relativistic klystron, and 140 MV/m longitudinal gradient in a short 11.4 GHz accelerator section. We report here on the design of our first klystrons, the results of our experiments so far, and some of our plans for the near future. 5 refs., 7 figs

  18. Gradient Learning Algorithms for Ontology Computing

    Science.gov (United States)

    Gao, Wei; Zhu, Linli

    2014-01-01

    The gradient learning model has been raising great attention in view of its promising perspectives for applications in statistics, data dimensionality reducing, and other specific fields. In this paper, we raise a new gradient learning model for ontology similarity measuring and ontology mapping in multidividing setting. The sample error in this setting is given by virtue of the hypothesis space and the trick of ontology dividing operator. Finally, two experiments presented on plant and humanoid robotics field verify the efficiency of the new computation model for ontology similarity measure and ontology mapping applications in multidividing setting. PMID:25530752

  19. Gradient Learning Algorithms for Ontology Computing

    Directory of Open Access Journals (Sweden)

    Wei Gao

    2014-01-01

    Full Text Available The gradient learning model has been raising great attention in view of its promising perspectives for applications in statistics, data dimensionality reducing, and other specific fields. In this paper, we raise a new gradient learning model for ontology similarity measuring and ontology mapping in multidividing setting. The sample error in this setting is given by virtue of the hypothesis space and the trick of ontology dividing operator. Finally, two experiments presented on plant and humanoid robotics field verify the efficiency of the new computation model for ontology similarity measure and ontology mapping applications in multidividing setting.

  20. Redfield Ratios in Inland Waters: Higher Biological Control of C:N:P Ratios in Tropical Semi-arid High Water Residence Time Lakes

    Directory of Open Access Journals (Sweden)

    Ng H. They

    2017-08-01

    Full Text Available The canonical Redfield C:N:P ratio for algal biomass is often not achieved in inland waters due to higher C and N content and more variability when compared to the oceans. This has been attributed to much lower residence times and higher contributions of the watershed to the total organic matter pool of continental ecosystems. In this study we examined the effect of water residence times in low latitude lakes (in a gradient from humid to a semi-arid region on seston elemental ratios in different size fractions. We used lake water specific conductivity as a proxy for residence time in a region of Eastern Brazil where there is a strong precipitation gradient. The C:P ratios decreased in the seston and bacterial size-fractions and increased in the dissolved fraction with increasing water retention time, suggesting uptake of N and P from the dissolved pool. Bacterial abundance, production and respiration increased in response to increased residence time and intracellular nutrient availability in agreement with the growth rate hypothesis. Our results reinforce the role of microorganisms in shaping the chemical environment in aquatic systems particularly at long water residence times and highlights the importance of this factor in influencing ecological stoichiometry in all aquatic ecosystems.

  1. Testing the Stress-Gradient Hypothesis at the Roof of the World: Effects of the Cushion Plant Thylacospermum caespitosum on Species Assemblages

    Science.gov (United States)

    Dvorský, Miroslav; Doležal, Jiří; Kopecký, Martin; Chlumská, Zuzana; Janatková, Kateřina; Altman, Jan; de Bello, Francesco; Řeháková, Klára

    2013-01-01

    Many cushion plants ameliorate the harsh environment they inhabit in alpine ecosystems and act as nurse plants, with significantly more species growing within their canopy than outside. These facilitative interactions seem to increase with the abiotic stress, thus supporting the stress-gradient hypothesis. We tested this prediction by exploring the association pattern of vascular plants with the dominant cushion plant Thylacospermum caespitosum (Caryophyllaceae) in the arid Trans-Himalaya, where vascular plants occur at one of the highest worldwide elevational limits. We compared plant composition between 1112 pair-plots placed both inside cushions and in surrounding open areas, in communities from cold steppes to subnival zones along two elevational gradients (East Karakoram: 4850–5250 m and Little Tibet: 5350–5850 m). We used PERMANOVA to assess differences in species composition, Friedman-based permutation tests to determine individual species habitat preferences, species-area curves to assess whether interactions are size-dependent and competitive intensity and importance indices to evaluate plant-plant interactions. No indications for net facilitation were found along the elevation gradients. The open areas were not only richer in species, but not a single species preferred to grow exclusively inside cushions, while 39–60% of 56 species detected had a significant preference for the habitat outside cushions. Across the entire elevation range of T. caespitosum, the number and abundance of species were greater outside cushions, suggesting that competitive rather than facilitative interactions prevail. This was supported by lower soil nutrient contents inside cushions, indicating a resource preemption, and little thermal amelioration at the extreme end of the elevational gradient. We attribute the negative associations to competition for limited resources, a strong environmental filter in arid high-mountain environment selecting the stress-tolerant species

  2. Testing the stress-gradient hypothesis at the roof of the world: effects of the cushion plant Thylacospermum caespitosum on species assemblages.

    Directory of Open Access Journals (Sweden)

    Miroslav Dvorský

    Full Text Available Many cushion plants ameliorate the harsh environment they inhabit in alpine ecosystems and act as nurse plants, with significantly more species growing within their canopy than outside. These facilitative interactions seem to increase with the abiotic stress, thus supporting the stress-gradient hypothesis. We tested this prediction by exploring the association pattern of vascular plants with the dominant cushion plant Thylacospermum caespitosum (Caryophyllaceae in the arid Trans-Himalaya, where vascular plants occur at one of the highest worldwide elevational limits. We compared plant composition between 1112 pair-plots placed both inside cushions and in surrounding open areas, in communities from cold steppes to subnival zones along two elevational gradients (East Karakoram: 4850-5250 m and Little Tibet: 5350-5850 m. We used PERMANOVA to assess differences in species composition, Friedman-based permutation tests to determine individual species habitat preferences, species-area curves to assess whether interactions are size-dependent and competitive intensity and importance indices to evaluate plant-plant interactions. No indications for net facilitation were found along the elevation gradients. The open areas were not only richer in species, but not a single species preferred to grow exclusively inside cushions, while 39-60% of 56 species detected had a significant preference for the habitat outside cushions. Across the entire elevation range of T. caespitosum, the number and abundance of species were greater outside cushions, suggesting that competitive rather than facilitative interactions prevail. This was supported by lower soil nutrient contents inside cushions, indicating a resource preemption, and little thermal amelioration at the extreme end of the elevational gradient. We attribute the negative associations to competition for limited resources, a strong environmental filter in arid high-mountain environment selecting the stress

  3. On the Role of Hyper-arid Regions within the Virtual Water Trade Network

    Science.gov (United States)

    Aggrey, James; Alshamsi, Aamena; Molini, Annalisa

    2016-04-01

    Climate change, economic development, and population growth are bound to increasingly impact global water resources, posing a significant threat to the sustainable development of arid regions, where water consumption highly exceeds the natural carrying capacity, population growth rate is high, and climate variability is going to impact both water consumption and availability. Virtual Water Trade (VWT) - i.e. the international trade network of water-intensive products - has been proposed as a possible solution to optimize the allocation of water resources on the global scale. By increasing food availability and lowering food prices it may in fact help the rapid development of water-scarce regions. The structure of the VWT network has been analyzed by a number of authors both in connection with trade policies, socioeconomic constrains and agricultural efficiency. However a systematic analysis of the structure and the dynamics of the VWT network conditional to aridity, climatic forcing and energy availability, is still missing. Our goal is hence to analyze the role of arid and hyper-arid regions within the VWN under diverse climatic, demographic, and energy constraints with an aim to contribute to the ongoing Energy-Water-Food nexus discussion. In particular, we focus on the hyper-arid lands of the Arabian Peninsula, the role they play in the global network and the assessment of their specific criticalities, as reflected in the VWN resilience.

  4. Land–atmosphere feedbacks amplify aridity increase over land under global warming

    Science.gov (United States)

    Berg, Alexis; Findell, Kirsten; Lintner, Benjamin; Giannini, Alessandra; Seneviratne, Sonia I.; van den Hurk, Bart; Lorenz, Ruth; Pitman, Andy; Hagemann, Stefan; Meier, Arndt; Cheruy, Frédérique; Ducharne, Agnès; Malyshev, Sergey; Milly, Paul C. D.

    2016-01-01

    The response of the terrestrial water cycle to global warming is central to issues including water resources, agriculture and ecosystem health. Recent studies indicate that aridity, defined in terms of atmospheric supply (precipitation, P) and demand (potential evapotranspiration, Ep) of water at the land surface, will increase globally in a warmer world. Recently proposed mechanisms for this response emphasize the driving role of oceanic warming and associated atmospheric processes. Here we show that the aridity response is substantially amplified by land–atmosphere feedbacks associated with the land surface’s response to climate and CO2 change. Using simulations from the Global Land Atmosphere Coupling Experiment (GLACE)-CMIP5 experiment, we show that global aridity is enhanced by the feedbacks of projected soil moisture decrease on land surface temperature, relative humidity and precipitation. The physiological impact of increasing atmospheric CO2 on vegetation exerts a qualitatively similar control on aridity. We reconcile these findings with previously proposed mechanisms by showing that the moist enthalpy change over land is unaffected by the land hydrological response. Thus, although oceanic warming constrains the combined moisture and temperature changes over land, land hydrology modulates the partitioning of this enthalpy increase towards increased aridity.

  5. Australia's arid-adapted butcherbirds experienced range expansions during Pleistocene glacial maxima.

    Science.gov (United States)

    Kearns, Anna M; Joseph, Leo; Toon, Alicia; Cook, Lyn G

    2014-05-30

    A model of range expansions during glacial maxima (GM) for cold-adapted species is generally accepted for the Northern Hemisphere. Given that GM in Australia largely resulted in the expansion of arid zones, rather than glaciation, it could be expected that arid-adapted species might have had expanded ranges at GM, as cold-adapted species did in the Northern Hemisphere. For Australian biota, however, it remains paradigmatic that arid-adapted species contracted to refugia at GM. Here we use multilocus data and ecological niche models (ENMs) to test alternative GM models for butcherbirds. ENMs, mtDNA and estimates of nuclear introgression and past population sizes support a model of GM expansion in the arid-tolerant Grey Butcherbird that resulted in secondary contact with its close relative--the savanna-inhabiting Silver-backed Butcherbird--whose contemporary distribution is widely separated. Together, these data reject the universal use of a GM contraction model for Australia's dry woodland and arid biota.

  6. A simple formula for estimating global solar radiation in central arid deserts of Iran

    International Nuclear Information System (INIS)

    Sabziparvar, Ali A.

    2008-01-01

    Over the last two decades, using simple radiation models has been an interesting task to estimate daily solar radiation in arid and semi-arid deserts such as those in Iran, where the number of solar observation sites is poor. In Iran, most of the models used so far, have been validated for a few specific locations based on short-term solar observations. In this work, three different radiation models (Sabbagh, Paltridge, Daneshyar) have been revised to predict the climatology of monthly average daily solar radiation on horizontal surfaces in various cities in central arid deserts of Iran. The modifications are made by the inclusion of altitude, monthly total number of dusty days and seasonal variation of Sun-Earth distance. A new height-dependent formula is proposed based on MBE, MABE, MPE and RMSE statistical analysis. It is shown that the revised Sabbagh method can be a good estimator for the prediction of global solar radiation in arid and semi-arid deserts with an average error of less than 2%, that performs a more accurate prediction than those in the previous studies. The required data for the suggested method are usually available in most meteorological sites. For the locations, where some of the input data are not reported, an alternative approach is presented. (author)

  7. Up-gradient transport in a probabilistic transport model

    DEFF Research Database (Denmark)

    Gavnholt, J.; Juul Rasmussen, J.; Garcia, O.E.

    2005-01-01

    The transport of particles or heat against the driving gradient is studied by employing a probabilistic transport model with a characteristic particle step length that depends on the local concentration or heat gradient. When this gradient is larger than a prescribed critical value, the standard....... These results supplement recent works by van Milligen [Phys. Plasmas 11, 3787 (2004)], which applied Levy distributed step sizes in the case of supercritical gradients to obtain the up-gradient transport. (c) 2005 American Institute of Physics....

  8. Variation in White Stork ( Ciconia ciconia) diet along a climatic gradient and across rural-to-urban landscapes in North Africa

    Science.gov (United States)

    Chenchouni, Haroun

    2017-03-01

    Assessing diet composition of White Storks ( Ciconia ciconia) breeding under North African conditions provides key information to understanding its trophic niche for conservation purpose. Since, climate controls productivities of foraging habitats and thus food availability for predators, this study examines how Storks' diet parameters varied following a climate gradient along with rural-to-urban landscapes in north-eastern Algeria. Feeding strategies to cope with severe conditions were discussed in light of climate aridity and urbanization and how these influence reproduction, population dynamics and distribution. While invertebrate prey accounted for 94 % of ingested individuals, the biomass intake was dominated by chicken remains scavenged from rubbish dumps (67 %) and small mammals (14 %). Generalized linear models revealed that prey numbers varied significantly between climatic regions and landscapes types, but no significant differences were observed for other dietary parameters, including prey biomass. The study showed high dietary similarity between study climates and landscapes, mainly among rural and urban colonies located in semi-arid and sub-humid areas, which differed from those in suburban and arid climate. Rarefaction and extrapolation curves indicated that prey species richness in White Stork diets was expected to be higher in urban colonies located in sub-humid climate. Despite low prey species diversity in arid regions, the White Stork demonstrates a broad trophic niche, which could be due to supplementary feeding from human refuse. This study suggests that regardless of the climate or landscape, White Storks ensure a constant food intake, despite prey biomass fluctuations, by adapting their diet. Foraging in diverse habitats, including trash dumps, ensures a sufficiently balanced diet to meet nutritional requirements.

  9. Magnetoelectric Transverse Gradient Sensor with High Detection Sensitivity and Low Gradient Noise.

    Science.gov (United States)

    Zhang, Mingji; Or, Siu Wing

    2017-10-25

    We report, theoretically and experimentally, the realization of a high detection performance in a novel magnetoelectric (ME) transverse gradient sensor based on the large ME effect and the magnetic field gradient (MFG) technique in a pair of magnetically-biased, electrically-shielded, and mechanically-enclosed ME composites having a transverse orientation and an axial separation. The output voltage of the gradient sensor is directly obtained from the transverse MFG-induced difference in ME voltage between the two ME composites and is calibrated against transverse MFGs to give a high detection sensitivity of 0.4-30.6 V/(T/m), a strong common-mode magnetic field noise rejection rate of gradient noise of 0.16-620 nT/m/ Hz in a broad frequency range of 1 Hz-170 kHz under a small baseline of 35 mm. An analysis of experimental gradient noise spectra obtained in a magnetically-unshielded laboratory environment reveals the domination of the pink (1/ f ) noise, dielectric loss noise, and power-frequency noise below 3 kHz, in addition to the circuit noise above 3 kHz, in the gradient sensor. The high detection performance, together with the added merit of passive and direct ME conversion by the large ME effect in the ME composites, makes the gradient sensor suitable for the passive, direct, and broadband detection of transverse MFGs.

  10. Large Airborne Full Tensor Gradient Data Inversion Based on a Non-Monotone Gradient Method

    Science.gov (United States)

    Sun, Yong; Meng, Zhaohai; Li, Fengting

    2018-03-01

    Following the development of gravity gradiometer instrument technology, the full tensor gravity (FTG) data can be acquired on airborne and marine platforms. Large-scale geophysical data can be obtained using these methods, making such data sets a number of the "big data" category. Therefore, a fast and effective inversion method is developed to solve the large-scale FTG data inversion problem. Many algorithms are available to accelerate the FTG data inversion, such as conjugate gradient method. However, the conventional conjugate gradient method takes a long time to complete data processing. Thus, a fast and effective iterative algorithm is necessary to improve the utilization of FTG data. Generally, inversion processing is formulated by incorporating regularizing constraints, followed by the introduction of a non-monotone gradient-descent method to accelerate the convergence rate of FTG data inversion. Compared with the conventional gradient method, the steepest descent gradient algorithm, and the conjugate gradient algorithm, there are clear advantages of the non-monotone iterative gradient-descent algorithm. Simulated and field FTG data were applied to show the application value of this new fast inversion method.

  11. Energy Transfer Using Gradient Index Metamaterial

    Directory of Open Access Journals (Sweden)

    Boopalan Ganapathy

    2018-01-01

    Full Text Available The gradient refractive index structure in this paper is used to increase the quantum of energy transfer. This is done by improving the directive gain of the pyramidal horn antenna at a frequency of 10 GHz. A three-dimensional array of closed square rings is placed in front of the horn antenna aperture to form a gradient refractive index structure. This structure increases the directive gain by 1.6 dB as compared to that of the conventional horn antenna. The structure nearly doubles the wireless power transfer quantum between the transmitter and the receiver when placed at both ends. The increase in the directivity is achieved by converting the spherical wave emanating from the horn to a plane wave once it passes through the structure. This transformation is realized by the gradient refractive index structure being placed perpendicular to the direction of propagation. The gradient refractive index is constructed by changing the dimensions of a closed square ring placed in the unit cell of the array. The change in the refractive index gives rise to an improvement of the half power beam width and side lobe level compared to that of the normal horn. The design and simulation were done using CST Studio software.

  12. Crack Tip Mechanics in Distortion Gradient Plasticity

    DEFF Research Database (Denmark)

    Fuentes-Alonso, Sandra; Martínez Pañeda, Emilio

    2017-01-01

    Gradient Plasticity (DGP), the influence on crack tip mechanics of DGP's distinguishing features that entail superior modelling capabilities has not been investigated yet. In this work crack tip fields are thoroughly examined by implementing the higher order theory of DGP in an implicit finite element...

  13. Discrete gradients in discrete classical mechanics

    International Nuclear Information System (INIS)

    Renna, L.

    1987-01-01

    A simple model of discrete classical mechanics is given where, starting from the continuous Hamilton equations, discrete equations of motion are established together with a proper discrete gradient definition. The conservation laws of the total discrete momentum, angular momentum, and energy are demonstrated

  14. Gradient based filtering of digital elevation models

    DEFF Research Database (Denmark)

    Knudsen, Thomas; Andersen, Rune Carbuhn

    We present a filtering method for digital terrain models (DTMs). The method is based on mathematical morphological filtering within gradient (slope) defined domains. The intention with the filtering procedure is to improbé the cartographic quality of height contours generated from a DTM based...

  15. Gradient Space under Orthography and Perspective

    Science.gov (United States)

    1982-05-24

    surfaceorientation to image geometry [8, 9, 10, 13, 15]. The descriptions of important gradient space properties, however, have been scattered throughout...Kanade, T. A Theory of Origami World. Artificial Intelligence 13:279-311, 1980. *[8] Kanade, T. and Kender, J. Mapping Image Properies into Shape

  16. Joining of Tungsten Armor Using Functional Gradients

    International Nuclear Information System (INIS)

    John Scott O'Dell

    2006-01-01

    The joining of low thermal expansion armor materials such as tungsten to high thermal expansion heat sink materials has been a major problem in plasma facing component (PFC) development. Conventional planar bonding techniques have been unable to withstand the high thermal induced stresses resulting from fabrication and high heat flux testing. During this investigation, innovative functional gradient joints produced using vacuum plasma spray forming techniques have been developed for joining tungsten armor to copper alloy heat sinks. A model was developed to select the optimum gradient architecture. Based on the modeling effort, a 2mm copper rich gradient was selected. Vacuum plasma pray parameters and procedures were then developed to produce the functional gradient joint. Using these techniques, dual cooling channel, medium scale mockups (32mm wide x 400mm length) were produced with vacuum plasma spray formed tungsten armor. The thickness of the tungsten armor was up to 5mm thick. No evidence of debonding at the interface between the heat sink and the vacuum plasma sprayed material was observed.

  17. Mass balance gradients and climatic change

    NARCIS (Netherlands)

    Oerlemans, J.; Hoogendoorn, N.C.

    1989-01-01

    It is generally assumed that the mass-balance gradient on glaciers is more or less conserved under climatic change. In studies of the dynamic response of glaciers to climatic change, one of the following assumptions is normally made: (i) the mass-balance perturbation is independent of altitude

  18. Considerations of ion temperature gradient driven turbulence

    International Nuclear Information System (INIS)

    Cowley, S.C.; Kulsrud, R.M.

    1991-02-01

    The ion temperature gradient driven instability is considered in this paper. Physical pictures are presented to clarify the nature of the instability. The saturation of a single eddy is modeled by a simple nonlinear equation. We show that eddies which are elongated in the direction of the temperature gradient are the most unstable and have the highest saturation amplitudes. In a sheared magnetic field, such elongated eddies twist with the field lines. This structure is shown to be alternative to the usual Fourier mode picture in which the mode is localized around the surface where k parallel = 0. We show how these elongated twisting eddies, which are an integral part of the ''ballooning mode'' structure, could survive in a torus. The elongated eddies are shown to be unstable to secondary instabilities that are driven by the large gradients in the long eddy. We argue that this mechanism isotropizes ion temperature gradient turbulence. We further argue that the ''mixing length'' is set by this nonlinear process, not by a linear eigenmode width. 17 refs., 6 figs

  19. Analysis of magnetic gradients to study gravitropism.

    Science.gov (United States)

    Hasenstein, Karl H; John, Susan; Scherp, Peter; Povinelli, Daniel; Mopper, Susan

    2013-01-01

    Gravitropism typically is generated by dense particles that respond to gravity. Experimental stimulation by high-gradient magnetic fields provides a new approach to selectively manipulate the gravisensing system. The movement of corn, wheat, and potato starch grains in suspension was examined with videomicroscopy during parabolic flights that generated 20 to 25 s of weightlessness. During weightlessness, a magnetic gradient was generated by inserting a wedge into a uniform, external magnetic field that caused repulsion of starch grains. The resultant velocity of movement was compared with the velocity of sedimentation under 1 g conditions. The high-gradient magnetic fields repelled the starch grains and generated a force of at least 0.6 g. Different wedge shapes significantly affected starch velocity and directionality of movement. Magnetic gradients are able to move diamagnetic compounds under weightless or microgravity conditions and serve as directional stimulus during seed germination in low-gravity environments. Further work can determine whether gravity sensing is based on force or contact between amyloplasts and statocyte membrane system.

  20. Gradient computation for VTI acoustic wavefield tomography

    KAUST Repository

    Li, Vladimir

    2016-09-06

    Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a pseudospectral operator that employes a separable approximation of the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified stack-power objective functions. We also obtain the gradient expressions for the data-domain objective function, which can incorporate borehole information necessary for stable VTI velocity analysis. These gradients are compared to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations. Whereas the kernels computed with the two wave-equation operators are similar, the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show that the modified stack-power objective function produces cleaner gradients than the more conventional DSO operator.

  1. Conjugate Gradient Algorithms For Manipulator Simulation

    Science.gov (United States)

    Fijany, Amir; Scheid, Robert E.

    1991-01-01

    Report discusses applicability of conjugate-gradient algorithms to computation of forward dynamics of robotic manipulators. Rapid computation of forward dynamics essential to teleoperation and other advanced robotic applications. Part of continuing effort to find algorithms meeting requirements for increased computational efficiency and speed. Method used for iterative solution of systems of linear equations.

  2. Examining the Education Gradient in Chronic Illness

    Science.gov (United States)

    Chatterji, Pinka; Joo, Heesoo; Lahiri, Kajal

    2015-01-01

    We examine the education gradient in diabetes, hypertension, and high cholesterol. We take into account diagnosed as well as undiagnosed cases and use methods accounting for the possibility of unmeasured factors that are correlated with education and drive both the likelihood of having illness and the propensity to be diagnosed. Data come from the…

  3. Subspace learning from image gradient orientations

    NARCIS (Netherlands)

    Tzimiropoulos, Georgios; Zafeiriou, Stefanos; Pantic, Maja

    2012-01-01

    We introduce the notion of subspace learning from image gradient orientations for appearance-based object recognition. As image data is typically noisy and noise is substantially different from Gaussian, traditional subspace learning from pixel intensities fails very often to estimate reliably the

  4. Ecological Diversity in South American Mammals: Their Geographical Distribution Shows Variable Associations with Phylogenetic Diversity and Does Not Follow the Latitudinal Richness Gradient.

    Directory of Open Access Journals (Sweden)

    Paula Nilda Fergnani

    Full Text Available The extent to which the latitudinal gradient in species richness may be paralleled by a similar gradient of increasing functional or phylogenetic diversity is a matter of controversy. We evaluated whether taxonomic richness (TR is informative in terms of ecological diversity (ED, an approximation to functional diversity and phylogenetic diversity (AvPD using data on 531 mammal species representing South American old autochthonous (marsupials, xenarthrans, mid-Cenozoic immigrants (hystricognaths, primates and newcomers (carnivorans, artiodactyls. If closely related species are ecologically more similar than distantly related species, AvPD will be a strong predictor of ED; however, lower ED than predicted from AvPD may be due to species retaining most of their ancestral characters, suggesting niche conservatism. This pattern could occur in tropical rainforests for taxa of tropical affinity (old autochthonous and mid-Cenozoic immigrants and in open and arid habitats for newcomers. In contrast, higher ED than expected from AvPD could occur, possibly in association with niche evolution, in arid and open habitats for taxa of tropical affinity and in forested habitats for newcomers. We found that TR was a poor predictor of ED and AvPD. After controlling for TR, there was considerable variability in the extent to which AvPD accounted for ED. Taxa of tropical affinity did not support the prediction of ED deficit within tropical rainforests, rather, they showed a mosaic of regions with an excess of ED interspersed with zones of ED deficit within the tropics; newcomers showed ED deficit in arid and open regions. Some taxa of tropical affinity showed excess of ED in tropical desert areas (hystricognaths or temperate semideserts (xenarthrans; newcomers showed excess of ED at cold-temperate latitudes in the Northern Hemisphere. This result suggests that extreme climatic conditions at both temperate and tropical latitudes may have promoted niche evolution in

  5. A review of research on ecosystem of arid area using RS-GIS in China

    Science.gov (United States)

    Han, Hongling

    2007-06-01

    Arid area is classical mountain-oasis-desert ecosystem in North-west China. As the ecosystem has its nature geography character obviously, it has superior to research with remote-sensing and geography information system. The study on arid ecosystem in RS-GIS' way is focused on that the landscape spatial pattern of complex MODS ecosystem, the dynamic development of Land use/land cover, the security of ecological environment of eco-tone and so on. At the same time, the research on the single system is more and more, which has provided more ways and deeper fields of arid area using RS-GIS. Through the use of RS-GIS, desertification, oasis' development, urbanization etc. can be known, which would provide precaution for human-being and suitable ways to adjust the problems.

  6. Large-scale hydrological modelling in the semi-arid north-east of Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Guentner, A

    2002-09-01

    Semi-arid areas are characterized by small water resources. An increasing water demand due to population growth and economic development as well as a possible decreasing water availability in the course of climate change may aggravate water scarcity in future in these areas. The quantitative assessment of the water resources is a prerequisite for the development of sustainable measures of water management. For this task, hydrological models within a dynamic integrated framework are indispensable tools. The main objective of this study is to develop a hydrological model for the quantification of water availability over a large geographic domain of semi-arid environments. The study area is the Federal State of Ceara in the semi-arid north-east of Brazil. Surface water from reservoirs provides the largest part of water supply. The area has recurrently been affected by droughts which caused serious economic losses and social impacts like migration from the rural regions. (orig.)

  7. Water balance of two earthen landfill caps in a semi-arid climate

    International Nuclear Information System (INIS)

    Khire, M.V.; Benson, C.H.; Bosscher, P.J.

    1997-01-01

    Water balance data are presented that were obtained from two earthen cap test sections located in a semi-arid region. The test sections were constructed on a municipal solid waste landfill in East Wenatchee, Washington, USA. One test section represents a traditional resistive barrier, and is constructed with a compacted silty clay barrier 60 cm thick and a vegetated silty clay surface layer 15 cm thick. The other test section represents a capillary barrier and has a sand layer 75 cm thick overlain by a 15-cm-thick vegetated surface layer of silt. Extensive hydrological and meteorological data have been collected since November 1992. Unsaturated hydraulic properties of soils, hydrologic parameters, and vegetation have been extensively characterized. Results of the study show that capillary barriers can be effective caps in semi-arid and arid regions. They are also cheaper to construct and can perform better than traditional resistive barriers

  8. REUSE OF TREATED WASTEWATER IN AGRICULTURE: SOLVING WATER DEFICIT PROBLEMS IN ARID AREAS (REVIEW

    Directory of Open Access Journals (Sweden)

    Faissal AZIZ

    2014-12-01

    Full Text Available In the arid and semiarid areas, the availability and the management of irrigation water have become priorities of great importance. The successive years of drought, induced by climate change and population growth, increasingly reduced the amount of water reserved for agriculture. Consequently, many countries have included wastewater reuse as an important dimension of water resources planning. In the more arid areas wastewater is used in agriculture, releasing high resource of water supplies. In this context, the present work is a review focusing the reuse of treated wastewater in agriculture as an important strategy for solving water deficit problems in arid areas. Much information concerning the wastewater reuse in different regions of the world and in Morocco, the different wastewater treatment technologies existing in Morocco were discussed. The review focused also the fertilizing potential of wastewater in agriculture, the role of nutrients and their concentrations in wastewater and their advantages effects on plant growth and yield.

  9. Are acid volatile sulfides (AVS) important trace metals sinks in semi-arid mangroves?

    Science.gov (United States)

    Queiroz, Hermano Melo; Nóbrega, Gabriel Nuto; Otero, Xose L; Ferreira, Tiago Osório

    2018-01-01

    Acid-volatile sulfides (AVS) formation and its role on trace metals bioavailability were studied in semi-arid mangroves. The semi-arid climatic conditions at the studied sites, marked by low rainfall and high evapotranspiration rates, clearly limited the AVS formation (AVS contents varied from 0.10 to 2.34μmolg -1 ) by favoring oxic conditions (Eh>+350mV). The AVS contents were strongly correlated with reactive iron and organic carbon (r=0.84; r=0.83 respectively), evidencing their dominant role for AVS formation under semi-arid conditions. On the other hand, the recorded ΣSEM/AVS values remained >1 evidencing a little control of AVS over the bioavailability of trace metals and, thus, its minor role as a sink for toxic metals. Copyright © 2017 Elsevier Ltd. All rights reserved.

  10. Plant Communities Suitable for Green Roofs in Arid Regions

    Directory of Open Access Journals (Sweden)

    Rachel Gioannini

    2018-05-01

    , and root-to-shoot dry weight ratio (0.45 than native Euphorbia. At the end of year 2, the relative growth rate (RGR of native Euphorbia of 0.15 g·g−1·d−1 was greater than that of Sedum. While the native succulent had a smaller root biomass, its greater RWC and RGR would indicate it had better plant water status and grew faster than the non-native. The lack of differences in plant performance regardless of assignment to monoculture or community would imply that communities and monocultures are equally suitable for arid region green roofs.

  11. Spatial and temporal variability of Aridity Index in Greece

    Science.gov (United States)

    Nastos, Panagiotis; Politi, Nadia; Douvis, Kostas

    2010-05-01

    Drought events have deteriorated in most European regions during the last decades in frequency, duration, or intensity. Besides, increased drying associated with higher temperatures and decreased precipitation have contributed to changes in drought. Drought-affected areas are projected to increase in extent, with the potential for adverse impacts on multiple sectors, e.g. agriculture, water supply, energy production and health, according to IPCC. The objective of this study is the spatial and temporal variability of the Aridity Index (AI) per decade, in Greece during the period 1951-2000, as far as the projections of AI for the period 2051-2100, based on simulations of ensemble regional climate models (RCMs), for A1B SRES scenario. The climatic data used for the analysis concern monthly values of precipitation and air temperature from 28 meteorological stations; 22 stations from the National Hellenic Meteorological Service and 6 stations from neighboring countries. According to the United Nations Environment Programme (UNEP), AI is defined as P/PET, where P is the average annual precipitation and PET is the potential evapotranspiration, estimated by the Thornthwaite method; PET and P must be expressed in same units, e.g., in milimetres. All the meteorological data processing was carried out by the application of Geographical Information System (GIS). The results of the analysis showed that within the examined period a clear shift from "humid" class that characterized the greater area of Greece in 1950's to "sub-humid" and "semi-dry" classes appeared in mainly the eastern regions of Greece, such as eastern Crete Island, Cyclades Islands, Evia and Attica in 1990's. The future projections derived by the simulations of ensemble RCMs indicated that drier conditions are very likely to appear in Greece associated with significant socio-economic consequences. The decreasing precipitation along with the high rates of evapotranspiration, because of increase in the air

  12. Arid urban ecosystem not a hotspot for N deposition

    Science.gov (United States)

    Grimm, N. B.; Cook, E. M.; Hall, S. J.; Wheeler, M.

    2017-12-01

    Urban areas are omitted in most long-term data collection for nitrogen deposition in the United States. Nitrogen sources in and surrounding cities are notoriously variable in space and time. In the desert Southwest, cities are distinct and isolated from one another, deposition is dominated by dryfall, and rainfall is spatially and temporally heterogeneous. These conditions present a challenge for understanding the overall rate, spatial pattern, and fate of nitrogen deposition in urbanized aridlands. We quantified long-term spatial and temporal patterns of inorganic nitrogen deposition in protected aridland ecosystems across an extensive urban-rural gradient in central Arizona, using multiple sampling methods. Furthermore, we assessed the impact of nitrogen deposition along the same gradient on winter annual plant growth and community structure, as an integrative indicator of the fate and impact of nitrogen deposition. Best estimates of nitrogen deposition, based on ion-exchange resin collectors, wet-dry bucket collectors, and inferential estimates of dryfall using passive samplers, were 7.2 ± 0.4 kg N ha-1 y-1 within city boundaries and 6.1 ± 0.3 kg N ha-1 y-1 in nearby desert lands. Although the data indicate the city may not be a hotspot of nitrogen deposition, species diversity of annual plants in urban desert remnant parks is reduced in a manner similar to diversity losses associated with experimental nitrogen fertilization. Thus, reduced species diversity is a possible consequence of locally elevated nitrogen deposition within the city. The long-term mean urban deposition rate estimated with mixed methods is substantially lower than that predicted by regional models and by estimated inorganic nitrogen fixation from automobile and other combustion sources. This discrepancy raises a question about the fate of this excess nitrogen in the larger aridland region.

  13. An Overview of Biodegradation of LNAPLs in Coastal (Semi)-arid Environment.

    KAUST Repository

    Yadav, Brijesh Kumar

    2011-02-22

    Contamination of soil and water due to the release of light non-aqueous phase liquids (LNAPLs) is a ubiquitous problem. The problem is more severe in arid and semi-arid coastal regions where most of the petroleum production and related refinery industries are located. Biological treatment of these organic contaminated resources is receiving increasing interests and where applicable, can serve as a cost-effective remediation alternative. The success of bioremediation greatly depends on the prevailing environmental variables, and their remediation favoring customization requires a sound understanding of their integrated behavior on fate and transport of LNAPLs under site-specific conditions. The arid and semi-arid coastal sites are characterized by specific environmental extremes; primarily, varying low and high temperatures, high salinity, water table dynamics, and fluctuating soil moisture content. An understanding of the behavior of these environmental variables on biological interactions with LNAPLs would be helpful in customizing the bioremediation for restoring problematic sites in these regions. Therefore, this paper reviews the microbial degradation of LNAPLs in soil-water, considering the influences of prevailing environmental parameters of arid and semi-arid coastal regions. First, the mechanism of biodegradation of LNAPLs is discussed briefly, followed by a summary of popular kinetic models used by researchers for describing the degradation rate of these hydrocarbons. Next, the impact of soil moisture content, water table dynamics, and soil-water temperature on the fate and transport of LNAPLs are discussed, including an overview of the studies conducted so far. Finally, based on the reviewed information, a general conclusion is presented with recommendations for future research subjects on optimizing the bioremediation technique in the field under the aforesaid environmental conditions. The present review will be useful to better understand the

  14. Can biochar be used as a seed coating to improve native plant germination and growth in arid conditions?

    Science.gov (United States)

    Mary I. Williams; R. Kasten Dumroese; Deborah S. Page-Dumroese; Stuart P. Hardegree

    2016-01-01

    Direct seeding is a common large-scale restoration practice for revegetating arid and semi-arid lands, but success can be limited by moisture and temperature. Seed coating technologies that use biochar may have the potential to overcome moisture and temperature limitations on native plant germination and growth. Biochar is a popular agronomic tool for improving soil...

  15. Comments on: The moisture from the air as water resource in arid region: hopes, doubt and facts

    NARCIS (Netherlands)

    Beysens, D.; Milimouk, I.; Nikolayev, V.; Berkowicz, S.M.; Muselli, M.; Heusinkveld, B.G.; Jacobs, A.F.G.

    2006-01-01

    Kogan and Trahtman [2003. The moisture from the air as water resource in arid region: hopes, doubts and facts. Journal of Arid Environments 53, 231¿240] analysed the functioning of a passive dew condenser built by F.I. Zibold in 1912 in Feodosia, and proposed a model to explain how thousands of

  16. Exploring the strategies for households to adapt to climate-change in arid and semiarid East Africa

    NARCIS (Netherlands)

    Ng'ang'a, Stanley K.

    2018-01-01

    In this thesis I set out to investigate how households cope and adapt to climate change in the context of arid and semi-arid areas of East Africa. This research fits well in the wider literature on the relationship between climate change and variability and household responses in term of coping

  17. Retreating or standing: Responses of forest species and steppe species to climate change in arid eastern central Asia

    Science.gov (United States)

    Hong-Xiang Zhang; Ming-Li Zhang; Stewart C. Sanderson

    2013-01-01

    The temperature in arid Eastern Central Asia is projected to increase in the future, accompanied by increased variability of precipitation. To investigate the impacts of climate change on plant species in this area, we selected two widespread species as candidates, Clematis sibirica and C. songorica, from montane coniferous forest and arid steppe habitats respectively...

  18. Climate-smart crop production in semi-arid areas through increased knowledge of varieties, environment and management factors

    NARCIS (Netherlands)

    Murungweni, C.; Wijk, van M.T.; Smaling, E.M.A.; Giller, K.E.

    2016-01-01

    In large regions of sub-Saharan Africa, semi-arid conditions are likely to increase with climate change, yet these regions are becoming more important to feed production zones due to increasing population pressure. A production system in the semi-arid south eastern Zimbabwe was studied to assess

  19. Mutations in SWI/SNF chromatin remodeling complex gene ARID1B cause Coffin-Siris syndrome

    NARCIS (Netherlands)

    Santen, G.W.; Aten, E.; Sun, Y; Almomani, R.; Gilissen, C.F.; Nielsen, M.; Kant, S.G.; Snoeck, I.N.; Peeters, E.A.; Hilhorst-Hofstee, Y.; Wessels, M.W.; Hollander, N.S. den; Ruivenkamp, C.A.; van Ommen, G.J.; Breuning, M.H.; den Dunnen, J.T.; van Haeringen, A.; Kriek, M.

    2012-01-01

    We identified de novo truncating mutations in ARID1B in three individuals with Coffin-Siris syndrome (CSS) by exome sequencing. Array-based copy-number variation (CNV) analysis in 2,000 individuals with intellectual disability revealed deletions encompassing ARID1B in 3 subjects with phenotypes

  20. Analysis and evaluation of tillage on an alfisol in a semi-arid tropical region of India

    NARCIS (Netherlands)

    Klaij, M.C.

    1983-01-01

    Tillage field experiments were conducted on Alfisols in a semi-arid tropical environment in India. The research was conducted within the framework of the Farming Systems Research Program of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).

    To put the